PCB propagation delay is the one-way time a signal takes to travel along a trace. For an initial estimate, multiply each trace segmentâs length by its delay per unit length. Do not use one FR-4 constant for every layer: an outer-layer microstrip and an inner-layer stripline can have different delay rates even when their physical lengths match.
Suppose two signals must reach a receiver within a tight timing window. Equal lengths can look good in the PCB editor while the actual paths have different electrical delays. The useful comparison is in picoseconds at agreed reference planes, not just millimeters.
Each routing structure needs its own delay estimate. AI-generated illustration; not a coupon design.
pcb propagation delay formula
For a uniform, low-dispersion transmission line, estimate the one-way delay as t â LâΔeff/c. Here L is trace length, Δeff is dimensionless effective relative permittivity, and c is about 299.792 mm/ns. The formula returns nanoseconds when length is in millimeters. For a route with several uniform structures, estimate each segment separately and sum the delays.
Input
Unit
Use
L
mm
Length of each segment
Δeff
None
Line model
Speed of light
mm/ns
299.792
Delay rate
ps/mm
Rate Ă L
Texas Instrumentsâ high-speed layout guide uses effective permittivity when comparing microstrip and stripline. Its example is a specific stackup, not an FR-4 rule. The approximation here also does not include connectors, package delay or a separate delay contribution from a via or launch.
pcb propagation delay per mm
In the simple model, the delay rate is about 3.336âΔeff ps/mm. Multiply a ps/mm value by 25.4 to express it in ps/in. Compare the rates using the same units and without rounding too early, especially when converting a short timing budget into allowable length mismatch.
Model
ps/mm
ps/in
Microstrip (3.0)
5.78
146.75
Stripline (4.0)
6.67
169.45
At 80 mm, those two example lines take approximately 462.2 ps and 533.7 ps. Equal lengths leave about 71.5 ps difference before package and transition contributions. These are modeled values, not universal measurements or recommended limits. In a real board, use the stackup and trace model agreed for the applicable layer, not the exampleâs assumed values.
Define the measurement reference planes before comparing delay. AI-generated illustration; no measured results are shown.
fr4 pcb propagation delay
FR-4 is a material designation, not a single line velocity. A microstripâs fields extend into more than one medium; laminate Dk, solder mask, trace width and height above the reference plane can all matter to the effective value. A homogeneous stripline approximation can use the surrounding dielectric value as a starting point, but mixed or asymmetric constructions still require a suitable model.
Microstrip vs. stripline for timing
When possible, route signals that must track each other through equivalent structures. If a layer change is unavoidable, ask for the relevant pressed thicknesses, material data and geometry so the solver can estimate delay by layer. Do not change to a different material solely to match the estimated velocity without also checking impedance, loss and manufacturing constraints.
pcb propagation delay calculator
Use a calculator only after choosing the units, reference planes and delay model. List every trace segment with its own delay rate; add a modeled or measured transition and package contribution if the timing budget includes those structures. Compare the complete path delays, not just their track-length totals.
Decide whether the budget is for the bare board or the complete path to the device pins.
Check the routing layers and divide mixed paths into uniform segments.
Calculate with full precision, sum, then round the result for reporting.
If the margin is small, confirm the model against a suitable coupon or measurement with agreed reference planes.
For a 50 mm outer segment at 5.7775 ps/mm and a 30 mm inner segment at 6.6713 ps/mm, the estimated trace-only delay is about 489.0 ps. Compare that with 462.2 ps for the 80 mm all-outer route: the same total length still leaves about 26.8 ps of difference. Add transition effects separately if the budget includes them.
A reflection on a TDR time axis includes travel out and back; that interval is not the one-way flight time used here. The TDR fault distance guide covers the separate round-trip conversion. Keep its time convention out of an end-to-end timing budget.
FAQ
Is propagation delay the same thing as impedance?
No. Impedance describes the voltage-to-current relationship of a traveling wave in the line; propagation delay describes travel time. A routing change can affect both, but matching nominal impedance alone does not guarantee equal delay. Evaluate each against its own requirement using the actual routing structure.
Should I use 150 ps/in for every FR-4 trace?
Use a rule of thumb for a quick feasibility screen, not as a final budget for every layer. A mask-covered outer trace and an inner trace can have different delay rates. Ask for a stackup-specific model when the difference matters to receiver timing or routing decisions.
Does equal PCB length guarantee that two signals arrive together?
Only if the paths have comparable delay per unit length and comparable contributions from transitions and packages. A board editor can report equal trace lengths for electrically different structures. Compare estimated time from the relevant launch to the relevant receiver plane before declaring the paths matched.
Do I include the device package delay in length tuning?
Include it when the timing requirement is defined at internal device reference points or when the component vendor specifies a package compensation model. If the budget is only for board connections, report package delay separately. Define the endpoint convention before adding package length or time to PCB results.
How does a via enter a propagation-delay budget?
Its effect is not always captured by adding the board thickness to the planar length. The transition includes a three-dimensional field and may add phase, loss and reflections. Use a suitable via model or measurement when the margin is small, and state whether the estimate includes that contribution.
Can a faster rise time change which delay estimate I should use?
A faster edge contains more high-frequency content. If the channel is dispersive, a single low-frequency delay may not describe the edge shape or timing of interest. Use an appropriate bandwidth and measurement definition rather than treating the simple low-dispersion model as exact at every frequency.
Should I measure a connector and trace together?
Measure them together if the requirement is for the complete interconnect. If you are trying to isolate the trace, use reference structures or agreed fixture removal to define the trace endpoints. Document which launch, cable or adapter contributions remain so another engineer can compare the results fairly.
How should I convert a skew budget into a length tolerance?
For two comparable uniform paths, divide the allowed time difference by the relevant delay per unit length. Do not use that shortcut across dissimilar structures without segment modeling. Apply package and transition allowances first if those contributions belong to the systemâs budget.
Discuss Your Project
Send Best Technology the proposed stackup, routing layers, length or delay targets and timing reference points. Flag any planned layer changes or connector launches that need to be considered in the board review. Contact sales@bestpcbs.com.
The PCB CCL shortage in 2026 is raising costs and complicating production schedules as AI server demand puts pressure on high-performance laminates. A November supply-chain report shows procurement lead times of 8â10 weeks for several CCL families and 24â32 weeks for selected high-performance materials. Panasonic has announced three rounds of price increases this year, while Kingboard raised prices for certain thin-glass laminates by 15% in October.
Does this mean AI server PCB production will face further delays? Which materials are hardest to source, and how much of the increase will reach finished PCB prices? Recent manufacturer announcements and supplier reports reveal where shortages are occurring, why costs continue to rise, and what engineers and buyers should check before their next production run.
What Is the Latest PCB CCL Shortage Update in November 2026?
As of November 9, 2026, supply shortages remain concentrated in certain CCL grades and fiberglass constructions rather than the entire laminate market. Availability has become less predictable, particularly for PCB designs requiring specific high-performance materials or thin-glass prepregs.
The clearest evidence comes from a November 4 supply-chain update by VersaLogic. Based on information from one of its PCB suppliers, the company reported CCL procurement periods of approximately 8â10 weeks for several material families, rising to 24â32 weeks for selected higher-performance grades. The supplier also identified shortages of 106, 1080, and 2116 glass fabrics, with multiple CCL manufacturers operating under allocation.
Recent capacity announcements point to the same market pressure. On October 30, Panasonic Industry unveiled a major investment in MEGTRON production, followed by Doosan's November 6 announcement of a new CCL expansion project in China. Both companies are increasing production capacity to support demand from AI infrastructure, although much of the additional output will not become available immediately.
The scale of demand is significant. In May, the Taiwan Printed Circuit Association (TPCA) forecast a US$21.5 billion global CCL market in 2026, up 34.2% year over year. This reflects projected market growth in value, not a measured shortage percentage.
For PCB buyers, the distinction matters. A project may remain on schedule if its approved materials are already available, while another could face delays because a single required laminate or prepreg construction cannot be sourced.
Why Is AI Server Demand Tightening High-Speed CCL Supply?
AI servers require complex multilayer PCBs that consume substantial amounts of specialized materials. As data center investment expands, demand for certain high-performance laminates is growing faster than qualified manufacturing capacity can respond.
Advanced AI server and networking boards can exceed 40 layers and use large PCB formats. These designs require multiple laminate cores and prepreg layers, often with tightly controlled thickness and electrical specifications. More layers and larger board areas generally increase material consumption, although the actual amount depends on the stackup and panel layout.
High-speed signal requirements further restrict sourcing options. Long electrical channels may require low dielectric loss, controlled dielectric properties, and specific copper foil characteristics. Once a material has been approved for signal integrity and reliability, changing to another grade may require additional engineering evaluation and customer approval.
Upstream manufacturing capacity is another constraint. Certain thin or specialty fiberglass fabrics require dedicated equipment and tightly controlled production processes. Adding CCL production lines cannot immediately increase output if the required glass fabric remains unavailable.
This explains why the shortage extends beyond premium AI server laminates. AI-related demand is not responsible for every supply problem, but competition for upstream fiberglass and other materials can affect conventional multilayer PCBs as well.
Which CCL Materials Are Most Affected by the 2026 Shortage?
The strongest reported supply constraints involve selected high-performance laminate grades and specific fiberglass constructions. There is no evidence that every low-loss laminate or standard FR-4 product is experiencing the same shortage.
For engineers reviewing PCB stackups, the following distinctions are important.
Material
Reported Supply Situation
What Buyers Should Verify
Selected high-performance CCL
Procurement periods of 24â32 weeks reported by one supplier
Exact grade, inventory, allocation
Several other CCL families
Procurement periods of 8â10 weeks reported
Manufacturer, thickness, delivery date
106, 1080, 2116 glass fabrics
Shortages reported within one PCB supplier network
Approved prepreg construction
M8/M9-class materials
Strong demand; availability differs by grade
Specific product and qualification
Conventional FR-4
Selected constructions exposed to glass supply and cost pressure
Core and prepreg specifications
The difference between glass fabric and finished laminate is particularly important. The numbers 106, 1080, and 2116 identify glass fabric styles, not complete CCL products. Different resin systems and laminate grades may use these fabrics, so a shortage of one construction does not establish that every related laminate is unavailable.
The same caution applies to M8/M9 terminology. These names are commonly used for high-performance material categories, but actual availability must be checked against a manufacturer's specific product. One approved grade may be available while another faces an extended procurement period.
When checking material availability, provide the manufacturer, laminate grade, core thickness, prepreg construction, copper foil requirements, and order quantity. A general inquiry about high-speed CCL rarely provides enough information for a reliable delivery commitment.
What Are Major CCL Manufacturers Reporting About Supply and Capacity?
Panasonic and Doosan have announced substantial investments in high-performance CCL production, but much of the new capacity will enter operation over the next several years. Their expansion plans suggest continued demand from AI infrastructure while highlighting the time required to increase qualified supply.
Panasonic Industry announced a JPY 92 billion AI-related investment program on October 30, including approximately JPY 67 billion for expanding MEGTRON production in Suzhou, China, and Ayutthaya, Thailand.
The company's Suzhou Phase I facility is scheduled to begin mass production in December 2026, followed by Ayutthaya Phase I in November 2027. Additional expansion phases are planned for August 2028 in Suzhou and April 2029 in Ayutthaya.
Doosan is pursuing a similar expansion strategy. Its KRW 970 billion CCL investment plan, announced in September, includes new production capacity in South Korea and China.
On November 6, Doosan confirmed a KRW 550 billion investment agreement for a new production facility near its existing Changshu plant. The project will be developed in stages, with operations expected to begin progressively in the second half of 2028.
Both manufacturers are targeting materials used in AI accelerators, network switches, optical communication equipment, and other high-performance applications.
These investments may improve supply over time, but new facilities must still complete production ramp-up and any required customer qualification. For buyers planning PCB production in the coming months, confirmed material inventory and supplier allocation remain more important than future capacity announcements.
Why Are CCL Prices Rising in 2026, and What Is the Price Trend?
CCL prices have risen repeatedly in 2026 as manufacturers face higher input costs while demand for selected laminates remains strong. Fiberglass shortages are an important factor, but resin, energy, logistics, and other manufacturing expenses are also contributing.
Kingboard's October price notice illustrates the fiberglass supply problem. The company cited strong demand for thin glass cloth, tight supplies of glass fabric and yarn, and rising upstream costs when announcing a 15% price increase for laminates and prepregs manufactured using 2116 or thinner glass fabrics.
Panasonic's announcements reflect broader cost pressure. Its June notice identified higher costs for petrochemical-derived materials, including resins and solvents, along with international logistics disruptions. Its August notice again pointed to elevated raw material, energy, auxiliary material, and transportation costs.
AI server demand has increased pressure on advanced CCL products, but it would be inaccurate to attribute every material price increase solely to AI infrastructure.
How Have CCL Prices Changed in 2026?
Panasonic announced three separate price adjustments for circuit board materials, taking effect in May, August, and September. Kingboard followed with another adjustment in October.
Effective Date
Manufacturer
General Multilayer CCL
Low-Loss / Other CCL
May 1, 2026
Panasonic
+30%
MEGTRON/XPEDION +20%
August 1, 2026
Panasonic
+20%
MEGTRON/XPEDION +10%
September 1, 2026
Panasonic
+30%
MEGTRON/XPEDION +15%
October 13, 2026
Kingboard
+15% for specified thin-glass laminates and prepregs
Depends on covered product
These figures represent the manufacturers' announced adjustments for specific materials and pricing periods. They cannot simply be added together to calculate a universal annual CCL price increase. Actual transaction prices depend on the applicable commercial terms.
The announcements nevertheless show that material cost pressure persisted through several pricing rounds during 2026.
How Much Will This Add to Finished PCB Costs?
A 20% increase in a laminate grade does not automatically mean a 20% increase in the finished PCB quotation.
CCL is only one part of total fabrication cost. Drilling, plating, imaging, lamination, inspection, testing, and other manufacturing operations also contribute to the final price.
A high-layer-count AI server PCB containing a large amount of specialized low-loss material may be more exposed to certain price increases than a simpler industrial board. Even two PCBs with the same layer count can be affected differently if their dimensions, material specifications, and panel utilization differ.
When a new quotation is higher, ask which laminate has increased in price, whether the same approved grade is still being quoted, and whether the change reflects current purchasing costs or an existing supply agreement.
That provides a more useful basis for evaluating PCB cost changes than the headline material price increase alone.
How Is the CCL Shortage Affecting AI Server PCB Manufacturing?
The main manufacturing risk is that one unavailable material can delay an otherwise production-ready multilayer PCB order. This is especially relevant to complex stackups using several different core thicknesses and prepreg constructions.
Consider a high-layer-count server PCB requiring multiple approved core and prepreg materials. The manufacturer may have sufficient inventory of most materials, but if one specified prepreg cannot be obtained, the approved layup cannot be completed. Production may be delayed before the board reaches the lamination stage.
Order quantity creates another challenge. A PCB manufacturer may have enough approved material to produce 20 prototype boards but insufficient inventory for a follow-on order of 1,000 units.
Successful prototype fabrication therefore does not guarantee that the same material will be available for mass production.
A proposed material replacement may introduce further delays. A different dielectric system can affect finished thickness, impedance, signal loss, lamination behavior, or reliability assumptions. Any necessary engineering review or qualification work must be completed before the revised construction is approved.
This is why PCB delivery schedules should account for both material readiness and available fabrication capacity. A factory may have an open production slot without having every material required to use it.
Can Engineers Replace Short-Supply CCL Materials Without Compromising PCB Performance?
An alternative CCL may be acceptable, but matching the material category or nominal Dk is not enough to establish interchangeability. High-speed PCB performance depends on the complete dielectric and conductor construction.
At 14 GHz, the manufacturer's published typical values for R-579Y(U) are Dk 3.08 and Df 0.0012, compared with Dk 3.13 and Df 0.0016 for R-579Y(N).
These values are typical test results, not guaranteed limits. Although the materials belong to the same family, their electrical properties differ. Whether those differences matter depends on channel length, operating frequency, and the available signal-loss budget.
Before approving a substitute, the engineering review should cover:
Electrical properties: Compare Dk and Df at relevant frequencies, then evaluate controlled impedance and channel loss.
Thermal and mechanical properties: Review Tg, Td, CTE, dimensional stability, and compatibility with the required assembly cycles.
Qualification requirements: Determine whether updated simulation, prototype testing, reliability testing, or formal customer approval is required.
The review should use comparable material data and the actual finished stackup. Similar datasheet values alone do not guarantee equivalent PCB performance.
For a design already released to manufacturing, retaining the approved material and adjusting the delivery schedule may sometimes present less risk than introducing an unqualified substitute.
The decision should be based on electrical performance, manufacturing compatibility, and qualification requirements, rather than material availability alone.
What Is the Current Lead Time for High-Speed CCL Materials?
The latest supplier report published on November 4 indicates procurement periods of 8â10 weeks for several CCL families and 24â32 weeks for selected higher-performance materials.
These figures came from one PCB supplier's October update, so they should not be treated as standard lead times for every material or manufacturer.
Actual availability can differ significantly between PCB factories. One manufacturer may already hold enough approved laminate to start production, while another must wait for new material deliveries or allocation confirmation.
Material procurement must also be distinguished from PCB fabrication.
If an approved laminate is already in stock, the normal PCB manufacturing schedule may still be achievable. If the material has not been allocated, even a factory offering quick-turn PCB services cannot guarantee the original shipment date.
When reviewing a quotation, ask for three confirmed dates: material availability, planned production start, and finished PCB shipment.
A single quoted lead time is less useful when material procurement and fabrication depend on different suppliers or unresolved allocations.
How Can PCB Buyers Reduce CCL Supply and Delivery Risks?
The best time to address material shortages is before the PCB order is released, while purchasing requirements and the manufacturing schedule can still be reviewed together.
For AI server and high-speed multilayer PCB projects, buyers should focus on the following checks:
Confirm the approved material specification: Identify the exact laminate, core, prepreg, and copper foil requirements. Record any alternatives already approved by engineering.
Verify material availability: Ask whether the required quantity is physically in stock, reserved for the order, or awaiting supplier allocation.
Check prototype-to-production continuity: If prototypes are being built first, confirm how the same approved material will be secured for volume production.
Review purchasing terms: Check quotation validity, material pricing assumptions, order quantities, and conditions governing delivery changes.
Control material substitutions: Any proposed replacement should be evaluated against the released PCB specification before manufacturing proceeds.
Confirm delivery milestones: Separate material arrival, fabrication, inspection, and shipment dates rather than relying on a generic total lead time.
For repeat orders, sharing a realistic production forecast can help the PCB manufacturer coordinate purchasing arrangements with its material suppliers. However, a forecast does not reserve inventory unless a specific commitment has been agreed.
These checks reduce the risk of discovering a material shortage after a delivery date has already been promised to the end customer.
Will the PCB CCL Shortage Continue Into 2027?
Some CCL supply constraints may continue through 2027, particularly for specialized high-performance grades and fiberglass constructions. However, the market does not have one confirmed recovery date.
VersaLogic's November report included a supplier expectation that tight conditions could persist into 2027 or 2028 while manufacturers expand capacity, introduce new glass-cloth equipment, and complete material qualifications.
That is one supplier's outlook rather than a guaranteed forecast for the entire industry.
The expansion schedules announced by Panasonic and Doosan suggest that additional high-performance CCL production capacity will become available gradually.
Panasonic expects new production milestones in late 2026 and 2027, while significant additional capacity from both companies is scheduled for 2028 and beyond.
The pace of recovery will depend on how quickly new lines reach stable production, whether specialty fiberglass supplies improve, and how much of the additional output is absorbed by AI infrastructure demand.
Standard laminates and advanced low-loss products may recover at different rates.
Buyers planning PCB production in 2027 should therefore monitor approved material grades and actual supplier commitments, rather than assume that broader CCL capacity expansion will resolve every sourcing problem.
FAQs About the 2026 PCB CCL Shortage
Q1: What Is the Difference Between Copper-Clad Laminate and Prepreg?
A1:Copper-clad laminate (CCL) consists of a cured insulating substrate bonded to copper foil, while prepreg is resin-impregnated reinforcement that is not yet fully cured. During multilayer PCB lamination, prepreg bonds cores and copper layers together. Both materials are essential to the stackup, but they have different storage, processing, and handling requirements.
Q2: Does FR-4 Refer to a Specific CCL Material Grade?
A2: No. FR-4 is a broad flame-retardant glass-reinforced epoxy material designation, not a single manufacturer's product. Different FR-4 laminates can have different thermal, electrical, and mechanical characteristics. A purchasing specification should identify the appropriate material properties, grade, and applicable standards rather than relying on the FR-4 designation alone.
Q3: Does a 40-Layer PCB Require 40 Separate CCL Sheets?
A3: No. Forty layers generally refers to 40 conductive copper layers, not 40 separate laminate cores. A multilayer PCB is constructed using a combination of copper-clad cores, prepregs, and sometimes copper foils. The number of cores depends on the stackup and fabrication method, so material consumption cannot be determined from layer count alone.
Q4: What Is Fiber-Weave Skew in High-Speed PCBs?
A4:Fiber-weave skew occurs when signals experience different propagation delays because of variations in the glass and resin distribution within the dielectric. It can affect timing relationships in high-speed differential pairs. The significance depends on routing geometry, material construction, and data rate. Material selection and routing strategies can help manage the risk.
Q5: Can CCL and Prepreg Be Stored Indefinitely Before PCB Manufacturing?
A5: No. Prepreg generally has manufacturer-defined storage conditions and a recommended shelf life, while cured CCL has different handling and storage requirements. Temperature, humidity, packaging condition, and material age can affect suitability for processing. Manufacturers should follow the relevant material supplier's instructions and evaluate any material outside its recommended storage conditions before use.
Q6: What Does a CCL Certificate of Conformity Confirm?
A6: A Certificate of Conformity (CoC) generally confirms that supplied material meets the specifications or requirements identified by the issuer. It does not necessarily provide individual measured test results for every material property. Buyers should check the certificate's scope and request additional test or traceability documentation when required by the project.
Q7: Does RoHS Compliance Mean a CCL Material Is Halogen-Free?
A7: No. RoHS compliance and halogen-free requirements are different. RoHS restricts specified hazardous substances in electrical and electronic equipment, while halogen-free material requirements commonly address chlorine and bromine content under applicable specifications. A RoHS-compliant laminate is not automatically halogen-free. Both claims should be verified against the relevant requirements and supporting documentation.
Q8: Are ABF Package Substrates and AI Server PCB Laminates the Same Material?
A8: No. ABF (Ajinomoto Build-up Film) is a dielectric material used in advanced semiconductor packaging substrates, while conventional PCB CCL is typically a copper-clad reinforced laminate. The materials serve different manufacturing and performance requirements. Although both supply chains can be influenced by AI hardware demand, their production capacities and shortage conditions should be evaluated separately.
The PCB CCL shortage in 2026 is being shaped by strong AI server demand, tight supplies of certain fiberglass constructions, and repeated increases in material and manufacturing costs. For PCB engineers, the priority is protecting the approved stackup and electrical performance; for buyers, it is securing material quantities and delivery commitments before production begins.
If you are planning a high-speed, multilayer, or AI server PCB project, EBest Circuit offers PCB fabrication, assembly, and a free DFM check. Send your Gerber files, approved stackup, material specifications, order quantity, required delivery date, and delivery location to sales@bestpcbs.com for a manufacturing review and quotation.
TDR spatial resolution describes whether two nearby impedance changes can be distinguished, not simply whether a reflection can be detected. Compare their echo separation with the effective step response at the device. A sharp instrument specification or a fine cursor readout does not guarantee two usable peaks on a real PCB.
Consider a coupon with two small discontinuities a few millimeters apart. The practical question is whether the setup can report two locations, one combined event, or only a difference from a known reference.
The launch belongs to the measurement path. AI-generated illustration, not a tested coupon.
Separate detection from resolution
A time-domain reflectometer sends a step and observes reflections from impedance changes. One visible bump can indicate that something changed without showing how many features contributed. Resolving two features is the stronger claim: the trace must contain enough evidence to distinguish the two responses under the actual measurement conditions.
Record the parameters that set the test
Record time intervals, edge definition, velocity and reference plane before comparing plots. Distinguish the instrumentâs specified step from the response available through the cable and launch. The resolution section of Tektronixâs TDR application note explains how step rise time, settling and ringing can cause nearby events to merge.
Parameter
Record
Effective edge
Rise time and threshold convention
Echo gap
Interval on the reflection time axis
Velocity
Measured or modeled path basis
Reference
Calibration or fixture plane
Signal quality
Noise, ringing and repeatability
Compare three different measurement claims
Choose the strongest conclusion supported by the data, not by the instrumentâs display precision. A one-feature reference and a controlled two-feature coupon can help separate a real resolution result from a convenient interpretation of a broad trace.
Claim
Evidence needed
An event exists
Repeatable difference from reference
Two events resolve
Distinct responses on matched setup
Feature sizes are known
Suitable model and validation
Convert spacing to an echo interval
For two features on the same uniform line with one-way spacing d and propagation velocity v, their first-return spacing is approximately Ît = 2d Ă· v. Use d in mm and v in mm/ns to obtain ns. The formula describes expected timing, not a resolution specification. For absolute location or an instrument distance display, see the TDR fault distance guide.
Test the two-feature teaching example
Assume 3.2 mm spacing and 160 mm/ns velocity. The calculated echo gap is 0.040 ns, or 40 ps. A hypothetical effective 100 ps edge makes overlap a serious concern; a 30 ps edge is a better candidate for separation. Neither example is a pass criterion: amplitudes, polarity, ringing, fixture quality and noise still affect the result.
Treat rise-time rules as screening only
Published heuristics describe when small, similar discontinuities may be separated. Check whether a ruleâs timing refers to one-way electrical separation, displayed reflection interval or a specific instrument convention before converting it to length. A known two-feature reference tested with the actual setup is a better basis for making a product-specific resolution claim.
Account for the path before the device
Cables, adapters and a launch can broaden the incident edge or add their own reflections. Document where the test plane is and what fixture treatment was used. If the suspected features are near a strong launch response, compare a reference with the same launch before treating a second shoulder as a separate defect.
Check the effect of polarity and magnitude
Similar reflections can merge into a broader feature, and opposite-polarity contributions can partially cancel. A small event next to a large one can disappear into its tail even when the spacing looks promising. Compare changes relative to an approved reference rather than counting visible peaks as a complete map of the underlying structures.
Use a documented reference before interpreting nearby echoes. AI-generated illustration, not a calibration result.
Avoid confusing oversampling with bandwidth
A small sample interval can produce a smooth plot without recovering detail removed by a slow edge or bandwidth limit. Record acquisition settings, averaging and any filtering. Look for a stable conclusion when settings change within a controlled comparison; do not treat a software zoom or extra digits as a physical improvement.
Use an edge sweep as a diagnostic comparison
If the equipment supports controlled changes in effective edge, compare the same reference plane and coupon at two settings. A shoulder that becomes reproducible as the response improves deserves investigation. Changing the edge also changes how strongly some features appear, so use a reference and do not label the outcome as a universal acceptance threshold.
Validate a coupon against the intended question
For a fabrication test, confirm whether the deliverable is nominal impedance, a controlled discontinuity comparison or a resolution study. A routine coupon designed to measure a long uniform line may not answer the last question. Agree on feature spacing, construction, reference data and criteria before ordering a special verification coupon.
Report uncertainty instead of inventing a second location
State the feature geometry, timing basis, observed edge and what the trace supports. If two returns cannot be distinguished reliably, report a combined or unresolved event and identify the next check. The test can still narrow an investigation without claiming a defect count or location precision beyond the evidence.
FAQ
Does seeing one bump mean there is one defect?
No. A broad response can include multiple nearby discontinuities or a fixture contribution. Compare the expected physical features and a known reference before deciding what the event represents. If the setup cannot reliably distinguish candidates, report the observation as unresolved rather than assigning an exact count.
Can a TDR see a feature smaller than its quoted resolution?
A small feature may change the measured response relative to a suitable reference even when its two boundaries are not separately identifiable. Detection, separation and dimension extraction are different claims. State which one is supported by the evidence and avoid treating a visible difference as a calibrated feature size.
Does averaging make two reflections easier to separate?
Averaging can help with repeatability when noise is the limiting factor. It does not restore bandwidth or remove systematic ringing. Compare the same setup and keep the acquisition settings with the result. If two responses are still inseparable after noise improves, changing the edge or reference may be more useful.
Should I test at the fastest available edge?
Use an edge suited to the question. A fast setting can help identify nearby features, while a slower setting can help assess the response under a different relevant excitation. Record which setting supports each conclusion, and do not use one trace to imply performance at every system edge rate.
Can a VNA time-domain plot answer the same question?
It can support a related investigation if the frequency span, window, calibration and transform are appropriate. Its effective time response is not automatically identical to a direct-step TDR. Compare validated reference structures and report the settings and observable result rather than assuming the two displays are interchangeable.
Is a launch artifact always removed by calibration?
Not if the launch is outside the calibrated plane and remains part of the measured network. A suitable fixture treatment or a matched comparison may be needed. Record the physical plane and which structures remain included, then verify that a changed feature is not simply a different launch response.
Can the impedance coupon prove an assembled channel will pass?
No. The coupon can document behavior of its defined geometry under the measured conditions. An assembled channel includes connectors, components and other transitions, and can have different acceptance criteria. Use coupon evidence for the property it represents and perform appropriate channel verification separately.
What should a report say when separation is borderline?
Include the expected echo gap, effective response, test reference and comparison result. State whether the trace supports detection only or separation under specific conditions. If a decision depends on distinguishing the features, define the next controlled measurement instead of rounding the reported distance to imply greater certainty.
References and Question Research
Controlled-impedance inspection discussion informed the coupon and reference-plane questions; instrument guidance and the stated model support the technical explanation.
Discuss Your Project
For a fabrication or coupon review, send Best Technology the stackup, relevant geometry, test purpose and required evidence at sales@bestpcbs.com. Specify whether the request concerns nominal impedance or a separate two-feature measurement study.
Ceramic substrate mounting needs a defined load path, suitable support and a controlled thermal interface. Do not pull a bare ceramic circuit flat with screws or copy a packaged power module’s mounting torque onto an unqualified ceramic plate. A module housing or pressure system can distribute load in ways that a bare substrate does not.
Consider a hypothetical copper-patterned ceramic circuit intended to sit on an aluminum heat spreader. Its underside must make useful thermal contact without being forced to bridge an unsupported gap. This guide shows how to review that mechanical interface; it does not provide a universal torque, clamping pressure or installation recipe.
AI-generated physical illustration; not an approved mounting arrangement or a tested Best Technology product.
Identify the Product Being Mounted
A bare ceramic circuit, a ceramic-based power module and a baseplate-equipped package are different mechanical objects. Start with the exact part drawing and assembly construction. The word ceramic alone does not identify the surface to clamp or the component designed to carry fastening load.
A bare substrate exposes the circuit carrier directly. A packaged module may include a housing, spring elements, terminals and specified fastening points. A metal baseplate adds another structural and thermal interface. Treat these as different designs rather than three versions of the same screw-mounting problem.
Collect Detailed Mounting Parameters
The review needs dimensions and limits for the actual assembly. Record where each requirement comes from and what surface it applies to. Missing force, support or flatness limits should remain engineering questions, not numbers copied from an unrelated module.
Input
Identify
Substrate
Material, thickness, outline, copper pattern
Support
Contact region and unsupported span
Mating surface
Flatness, roughness, steps, cleanliness
Retention
Load points and approved force basis
Thermal interface
Material, coverage and thickness basis
Environment
Temperature range, cycling, vibration
For a product-specific numerical example, SEMIKRON’s SKiM4/5 mounting instruction, revision 4.0, May 2017 specifies heatsink unevenness no greater than 50 ”m per 100 mm and Rz no greater than 6.3 ”m. Those are source-specific examples, not universal bare-ceramic limits.
Compare Bare Ceramic, Baseplate-Less and Baseplate Designs
The structure determines how fastening force reaches the thermal interface. Do not assume that a screw visible on a module presses directly on its ceramic in a way that can be copied safely.
The load path is the route through which fastening force reaches the support. Sketch the screw or clamp, load-spreading features, substrate, interface and supporting plate. Include terminals or cables that could apply unintended leverage.
In the hypothetical circuit, ask whether a clamp force reaches a supported region or pushes the ceramic across a gap. If the design cannot explain where force enters and leaves the assembly, stop before selecting a torque. A clearer drawing is more valuable than a precise tightening number with no mechanical basis.
Separate Flatness from Surface Roughness
Flatness describes shape over a region; roughness describes smaller-scale surface texture under a defined measurement. A surface can have low roughness and still be bowed. Cleaning it does not remove a geometric step or correct a distorted mating plate.
Specify the measurement area, reference and method before comparing reports. For the aluminum spreader, inspect burrs, steps and particles as well as the overall shape. Do not treat a single finish designation as evidence that the complete contact region meets the assembly drawing.
Do Not Force a Gap Closed
A visible gap is a reason to investigate the interface, not automatically a reason to tighten harder. Determine whether its cause is substrate shape, mating-surface geometry, contamination or the specified interface material. Use the approved inspection and disposition process.
For example, a particle beneath one corner can create a local support problem. A small apparent contact area can then carry a concentrated load. Remove the cause through an authorized process and recheck the assembly; do not deliberately bend the ceramic as a substitute for establishing the correct support.
Treat the Thermal Interface as a Controlled Layer
The interface must suit both the thermal objective and mechanical construction. A thermal grease, pad, phase-change layer or adhesive is not interchangeable merely because each is described as thermally conductive. Their behavior under load and temperature differs.
The SKiM instruction provides a named-paste and application-specific example; use the actual product’s current instructions rather than generalizing its thickness. An unqualified thick layer should not be used to compensate for an unexplained mechanical mismatch. Agree the material, coverage, application control and inspection basis together.
AI-generated interface-review scene, not a verified package design or an interchangeable thermal-material recommendation.
Understand Why Torque Is Not Clamping Pressure
Torque is a turning moment applied to a fastener; clamping pressure is force divided by the relevant contact area. The relationship depends on the joint, friction, fastener and load path. A torque number cannot be converted into ceramic stress without that information.
For a simple teaching example, a uniformly distributed 100 N force over 100 mmÂČ would give 1 N/mmÂČ, or 1 MPa. Real contact need not be uniform, and this arithmetic is not an allowable load. It illustrates why effective area and local stress matter as well as total force.
Review Thermal Expansion and External Constraints
The substrate, copper, support and attached hardware can change dimensions differently with temperature. The mounting design must account for the resulting constraints, rather than treating room-temperature fit as the entire requirement.
Identify the operating range and cycling conditions, then review how the assembly accommodates movement. Avoid letting a rigid cable or busbar become an unintended structural brace. The related ceramic substrate CTE discussion explains why material interactions need their own assessment.
Inspect Edges Before and After Assembly
Keep an inspection baseline so that new damage can be distinguished from incoming condition. Record chipped edges, cracks and disputed surface features with the part identity and drawing requirements. Do not invent an allowable defect size from a photograph.
If damage is found after mounting, preserve the assembly state and process history before disassembly where safe and appropriate. Compare the evidence with the approved criteria and seek engineering disposition. See the ceramic edge-chipping guide for the distinction between observation and acceptance.
Validate the Assembly, Not Only the Fastener Setting
A correctly recorded fastener setting does not establish every thermal, electrical or mechanical requirement. The validation plan must address the actual construction and intended environment. Include the properties that matter to the product rather than relying on a single installation record.
For the hypothetical circuit, appropriate engineering review would define contact inspection, temperature assessment and relevant environmental or insulation validation. Do not energize a cracked or uncertain power assembly as an informal test. High-energy work requires trained personnel, safe isolation and an approved plan.
Use a Mounting Release Checklist
Identify the exact substrate or module construction.
Obtain the applicable drawing and mounting instructions.
Draw support regions and the complete load path.
Verify the mating surface and interface material.
Confirm retention requirements without borrowing unrelated limits.
Review thermal movement and external loads.
Record inspection, validation and engineering approval.
The release should explain why the ceramic is supported and why the applied loads are acceptable. If those explanations are missing, more tightening precision cannot fill the gap.
FAQ
Can I use a power-module torque on a bare ceramic circuit?
No generic transfer is justified. A module may distribute force through a housing or engineered pressure system that the bare ceramic lacks. Obtain a mounting design and approved limits for the actual substrate. Matching the material name or overall dimensions does not make the mechanical load paths equivalent.
Will a softer thermal pad automatically protect the ceramic?
Not automatically. The result depends on the pad’s properties, thickness, compression behavior, contact area and the complete mounting design. A compliant layer can also change the support condition. Review it as part of the assembly rather than assuming that softness alone establishes a safe load or good thermal contact.
Can grease fill a large gap caused by a bent support?
Do not use an unqualified interface layer to hide a geometry problem. Establish whether the support and substrate meet their drawings first, then select the approved interface process. Thermal contact, retention and stress must be evaluated together. A filled-looking gap is not proof that the resulting assembly is acceptable.
Does a smooth-looking heat spreader prove it is flat enough?
No. Appearance and surface texture do not establish shape over the required region. Use the specified measurement basis and inspect the actual contact area. A surface may look polished while still containing a step, bow or local feature that matters to the mounting design. Keep flatness and roughness records separate.
Can washers alone prevent mounting damage?
A washer may change how a load is distributed, but it does not validate the entire joint or eliminate bending. The substrate support, hole geometry, fastener and interface still require review. Do not add hardware by analogy to an FR-4 board and assume it creates an approved ceramic mounting arrangement.
Is an edge chip automatically harmless if the circuit conducts?
No. Continuity does not determine the structural or insulation significance of the damage. Record the feature and assess it against the drawing and product requirements. Obtain engineering disposition when the effect is uncertain. Do not enlarge, grind or cover the defect merely to make the part look acceptable.
Can a used module be remounted with the old interface layer?
Follow the actual product and interface-material instructions for reuse, cleaning and reapplication. Do not assume that a previously compressed layer will reproduce its original condition. Preserve evidence if the unit is under investigation, and use an approved remounting process rather than treating the first installation record as continuing qualification.
What information should accompany a ceramic mounting drawing?
Include the exact substrate or module identity, support and contact regions, mating-surface requirements, retention basis, interface material and relevant operating conditions. Identify the controlling instructions and validation requirements. This gives the reviewer a complete assembly question rather than an isolated request for a generic screw size or torque.
Send Best Technology the substrate drawing, copper pattern, support concept, thermal interface and operating conditions at sales@bestpcbs.com. Ask for clarification of the fabrication requirements. Final mounting loads and product qualification require approval for the actual assembly.
For a PCB conductor modeled as a constant resistance, average resistive heating follows IRMSÂČRânot IaverageÂČR. A repeating rectangular current that switches between zero and a positive peak has Iaverage = IpeakD and IRMS = IpeakâD, where D is the duty cycle expressed as a fraction.
That difference matters in switched loads, motor-drive paths and pulsed actuators. It does not mean RMS alone determines a safe trace width. Peak current, pulse duration, repetition, copper geometry, connections and temperature still need review. Start with the actual current waveform in the specific conductorânot the controller’s PWM setting.
AI-generated power-board illustration; not a validated current rating or a tested circuit design.
Understand Peak, Average and RMS Current
Peak current is the largest instantaneous current magnitude of interest. Average current is the signed mean over the chosen observation interval. RMS means root mean square: square each current value, average those squares, then take the square root. Squaring makes both current directions contribute positively to resistive heating.
For an ideal resistor, a waveform’s RMS value corresponds to the direct current that produces the same average heating. Fluke explains the heating-value basis of RMS measurement. Average current remains useful for other questions, but it is not interchangeable with RMS when evaluating copper loss.
Record the Detailed Waveform Parameters
Duty cycle is on-time divided by period. A 25% duty cycle is D = 0.25, not 25, in the formulas. The off-state current must actually be zero for the simple zero-to-peak equations below; freewheeling and ripple can make that assumption wrong.
Parameter
Record
Why it matters
Peak current
Magnitude and polarity
Instantaneous stress
On-time
Seconds or subunits
Pulse energy
Period
Full repeating interval
Repetition and RMS
Off current
Zero or measured value
Formula validity
Burst pattern
Active and idle intervals
Thermal history
Path resistance
Temperature and geometry
Loss and voltage drop
Also record ambient temperature, enclosure airflow, copper construction and the allowable temperature rise. These are project inputs, not fixed universal values or a Best Technology capability table.
Calculate a Zero-to-Peak Rectangular Pulse
Consider a hypothetical conductor carrying 8 A for one quarter of each period and zero for the rest. Its average current is 8 Ă 0.25 = 2 A. Its RMS current is 8 Ă â0.25 = 4 A.
Why are the results different? The average calculation weights current directly, whereas heating weights its square. The on-state contributes 8ÂČ Ă 0.25 = 16 AÂČ to the mean square. Taking the square root gives 4 A. The example assumes ideal rectangular pulses and constant resistance; it is not a qualified operating point for any particular PCB.
Compare Equal-Average Waveforms
Three waveforms can deliver the same average current but produce different conductor losses. The following teaching comparison assumes identical constant resistance and sufficient repetition to discuss average electrical loss. It does not predict a temperature rise or approve a peak current.
Waveform
Mean
RMS
Loss vs 2 A DC
2 A DC
2 A
2 A
1Ă
4 A, 50% on
2 A
2.83 A
2Ă
8 A, 25% on
2 A
4 A
4Ă
The practical lesson is simple: reducing duty cycle does not make peak current harmless. Compare the full waveform and resulting loss, then investigate transient temperature and the weakest part of the path.
Temperature rise depends on heat spreading and cooling, and resistance changes as copper heats. At higher frequencies, current distribution can also make a simple DC-resistance model incomplete. Treat IRMSÂČR as the defined model here, not as a substitute for the actual electrical and thermal assessment.
Distinguish Repeating Heating from Single-Pulse Stress
A repeating low-duty waveform and one isolated pulse are not the same thermal problem. A long pulse can create a significant local temperature excursion even if an average over a very long idle interval looks small. A short repeating pulse train can accumulate heat if cooling between pulses is limited.
State pulse width, repetition and burst duration together. For an isolated event, evaluate energy and transient response as appropriate. Do not choose a long averaging interval merely to make the reported RMS lower. The observation interval must represent the operating question being answered.
Measure the Current in the Correct Branch
A PWM control signal describes switching commands, not necessarily the current in every copper path. An inductive load can continue carrying current during a switch’s off interval through another route. Capacitors may supply a pulse locally while the input connector sees a smoother waveform.
Draw the current loop for each switching state and identify the exact trace, via or connector under review. Measure or calculate that branch current. Applying the controller’s duty cycle to the input current, load current and switch current indiscriminately can give three plausible-looking but incorrect heating estimates.
Handle Nonzero Off-State Current and Ripple
For a two-level waveform, use IRMS = â[D IonÂČ + (1 â D) IoffÂČ]. The simple peak-times-square-root formula is its special case when the off current is zero. Average current is D Ion + (1 â D) Ioff.
For arbitrary measured samples, square the current samples, average over a representative interval and take the square root, with appropriate sampling and time weighting. A waveform with ramps or spikes needs its actual shape represented. Do not force it into a rectangular model solely because the switching command is rectangular.
AI-generated bench illustration; not a verified probe connection, live measurement or safety procedure.
Check Meter Coupling, Bandwidth and Crest Factor
A true-RMS label alone does not guarantee that a meter captures the desired waveform. Determine whether the selected function measures the AC component only or total AC-plus-DC RMS. For a unipolar pulse train, removing the DC component changes the reported result.
Check bandwidth, crest-factor limits, range, probe saturation and sampling interval. Consult the actual instrument manual; the Fluke 287/289 manual, for example, separates functions and frequency-dependent specifications. Use suitable low-voltage test arrangements and qualified personnel. Never put a current-mode meter directly across a voltage source.
Review Neckdowns, Vias and Connections
A wide copper pour can feed through a narrow neck, small thermal-relief spokes, a via group or a connector pin. Those local features can govern loss and temperature. Parallel conductors do not necessarily share current equally if their electrical and thermal paths differ.
Review the complete route rather than calculating only its widest section. Record copper thickness, minimum finished width, path length and connection details. The high-current PCB overview provides related construction context; no generic article replaces validation of the actual board and operating cycle.
Do Not Borrow a MOSFET Pulse Rating for a PCB Trace
A component’s pulsed-current rating belongs to that component and its stated conditions. It does not qualify the board, connector or solder joint around it. TI’s discussion of MOSFET pulse-current ratings emphasizes pulse-duration and duty-cycle conditions.
Check each element independently, including component operating limits and the complete current path. A trace that survives a few demonstrations has not thereby established its production margin, lifetime or fault behavior. Separate normal repeated operation, startup surge and fault events in the design review.
Validate the Board with a Repeatable Checklist
Identify the branch and actual waveform.
Record peak, RMS, mean, timing and burst conditions.
Check the formula’s zero-current and constant-resistance assumptions.
Review every neckdown, via and connection.
Measure temperature at representative worst-case operation.
Include enclosure, ambient and startup conditions.
Record limits, uncertainty and the approved configuration.
Use controlled measurements to connect electrical loss to real temperature. If using infrared inspection, account for surface measurement limitations; see the PCB infrared temperature guide. RMS is a powerful starting point because it addresses the right heating quantityânot because it removes the need for validation.
FAQ
Can I size a pulsed-current trace from average current?
Not as a general heating calculation. For a constant-resistance conductor, average loss depends on mean-square current. Use the actual waveform’s RMS value, then check transient and peak limits separately. Average current can describe charge delivery, but it can substantially understate heating when substituted into the squared-current loss equation.
Does a 25% duty cycle mean one quarter of the heating?
Only under clearly stated comparisons. With the same peak current and constant resistance, a zero-to-peak rectangular waveform has one quarter of the continuous-peak average loss at 25% duty. It does not have the same loss as DC at one quarter of that peak current. Keep the reference case explicit.
Can RMS current alone prove a PCB trace is safe?
No. It estimates resistive heating within a defined model but does not establish allowable temperature, transient stress, connection ratings or failure margin. Evaluate the real geometry, copper construction, cooling and operating history. Peak events and fault conditions need their own review even when the normal RMS value looks modest.
Why does my current meter disagree with the calculation?
Check whether the meter measures mean DC, AC-only RMS or total AC-plus-DC RMS. Also check bandwidth, crest factor, range and probe behavior. Then verify the waveform and measurement interval. A meter and calculation can both be internally correct while describing different components or time windows of the same signal.
Does the PWM duty cycle equal the load-current duty cycle?
Not necessarily. Inductance, freewheeling paths and local capacitors can keep current flowing or move pulse current between branches. Determine the waveform in the actual conductor under review. A controller’s on-time is not sufficient evidence that the trace current switches instantly between zero and a fixed peak.
What if current continues during the off interval?
Include that current instead of using the zero-off shortcut. For two constant levels, average their squared values with their time fractions and take the square root. If the current ramps or rings, integrate or sample the real waveform appropriately. The model should follow the current, not only the switch command.
Can I use a component’s pulse rating as the board limit?
No. The rating applies to that component under its documented conditions. Copper, vias, terminals, solder joints and other parts have separate constraints. Review the entire path and verify the actual pulse timing and thermal environment. One part’s large pulsed-current headline does not qualify the surrounding assembly.
How should I validate a burst that occurs only occasionally?
Record the pulse shape inside the burst, burst duration, repetition interval and initial temperature. Evaluate both local temperature excursion and longer-term heating under the real operating sequence. Do not dilute the event with an arbitrary idle interval. Include plausible repeated commands and startup conditions in the approved validation plan.
References and Question Research
Technical references are the instrument-manufacturer and semiconductor-manufacturer sources linked above. Community discovery included questions about pulsed trace width and pulse current and trace limits. Their anecdotes are not current ratings; the FAQ answers use the stated electrical model and source limitations.
Discuss a High-Current Fabrication Requirement
Send Best Technology the stackup, copper geometry, current waveform, temperature limits and validation requirements at sales@bestpcbs.com. Request a project-specific fabrication review. Any current or thermal performance commitment must be supported by the actual design, agreed construction and validation evidence.
PCB infrared temperature measurement needs a defined surface and measurement setup, not just a thermal camera pointed at the board. Shiny copper can emit little infrared radiation while reflecting its surroundings. A cool-looking copper path may therefore be hotter than it appears, and a bright patch may be a reflection rather than a local heat source.
Consider a hypothetical high-current prototype with exposed copper beside green solder mask. An engineer wants to check its conductor temperature under the approved load. This guide follows the measurement review before any layout decision; it does not provide permission to energize, probe or modify an unsafe circuit.
AI-generated measurement-context illustration. No camera display or image here is a measured temperature result.
What the Camera Measures at a Copper Surface
The camera detects radiation reaching its sensor and uses a model to estimate surface temperature. For an opaque surface, emitted and reflected contributions both matter; the reading is not a direct electrical measurement of the copper.
On the teaching board, exposed copper and adjacent solder mask can have different radiative behavior even where their actual temperatures are close. First identify exactly which visible surface the measurement region covers. A number taken across copper, mask and a component body is not automatically the temperature of any one of those objects.
Record the Parameters Behind a Temperature Reading
A credible result preserves the camera, surface, optical setup and operating condition together. A cropped color screenshot without these inputs is incomplete.
Parameter
Unit or record
Why it matters
Emissivity
Dimensionless, 0â1 model scale
Relates radiation to the surface
Reflected apparent temperature
°C, method stated
Accounts for reflected surroundings
Camera and lens
Model, calibration, spectral band
Defines measurement capability
Geometry
Distance, angle, target size
Defines what is resolved
Operating state
A, V, duration and airflow
Defines the heat-producing condition
Target
Surface, location and board revision
Prevents comparing different objects
The table specifies reporting fields, not universal settings. Use the actual cameraâs instructions and a qualified test plan to establish values. Do not insert a guessed emissivity simply because another board had the same color.
Compare Bare Copper, Solder Mask and a Reference Patch
These surfaces cannot be compared as if one camera setting makes all of them equally reliable. Their finish, optical properties and thermal relationship to the conductor differ.
Surface
Main concern
Useful check
Shiny copper
Low emission, strong reflection
Validate the surface method
Solder mask
Different surface from copper
Identify coating and target
Known reference patch
Compatibility and equilibration
Verify material and thermal contact
Component package
Surface is not the junction
Use component-specific limits
FLIRâs emissivity explanation notes that highly polished copper or aluminum commonly has emissivity below 0.10. That is a warning about reflective surfaces, not a calibrated value for this prototype. Plating, oxidation, roughness and wavelength can change the appropriate value.
Distinguish Emissivity from Thermal Conductivity
Emissivity concerns radiation from a surface; thermal conductivity concerns heat transfer through a material. Copper can conduct heat well while remaining difficult to measure by infrared imaging.
For the high-current path, do not conclude that a cool-colored area has low electrical loss or strong cooling simply because it is copper. Conversely, a dark high-emissivity patch does not make the underlying material a better heat conductor. Keep the thermal model, electrical loss estimate and radiometric measurement as related but separate pieces of evidence.
Check Reflections Before Calling a Bright Patch a Hotspot
A reflective surface can redirect radiation from nearby people, equipment or other warm objects into the camera. Its apparent temperature can then differ from its actual surface temperature.
Record the surroundings and viewing geometry. A feature that changes strongly with the viewing arrangement warrants investigation before it is labeled a fault; changing the view alone does not quantify the correct temperature. In the teaching review, keep people and movable heat sources from changing the scene during the comparison. Do not reach into an energized assembly to test a reflection hypothesis.
Use a Reference Patch Only Under an Approved Method
A known high-emissivity patch can make a difficult surface easier to observe, but only when its optical behavior, temperature suitability and thermal relationship are understood. Any preparation must occur under the appropriate safe, de-energized procedure.
FLIRâs reference-material guidance warns that tape can transmit infrared radiation and that emissivity depends on wavelength and surface condition. Not every black tape is a characterized reference. Do not apply coatings indiscriminately to live conductors, fine-pitch contacts, optical parts or contamination-sensitive areas.
AI-generated preparation illustration. Actual patch selection, placement and electrical safety require an approved procedure.
Verify the Patch Follows the Target Temperature
The patch must be in adequate thermal contact and allowed to reach the relevant condition; otherwise the camera is accurately reading the wrong surface temperature. A patch also changes the surface being tested.
FLIRâs Extech infrared-measurement FAQ instructs users to let the reference material adjust to the surface temperature. For the prototype, consider whether a large or thick patch changes local heat transfer, bridges distinct areas or lags a short pulse. Keep any modified test specimen identifiable and avoid presenting it as an untouched production assembly.
Check Focus and the Smallest Target Size
A visible feature is not necessarily large enough for a trustworthy temperature measurement. The lens, working distance and optical blur determine how much surrounding material contributes to the reported point.
FLIRâs electronics macro-imaging discussion illustrates why a measurement target needs adequate pixel coverage and suitable optics. Use the actual cameraâs measurement specification rather than assuming one illuminated pixel is sufficient. On our board, a narrow copper neck can be blended with cooler surroundings even when its location is apparent on screen.
Keep Load, Airflow and Timing Comparable
Temperature comparisons need the same defined operating condition. Different current, elapsed time, enclosure state or airflow can change the result independently of the copper geometry.
For the hypothetical prototype, record the approved load and whether the objective is a steady condition or a transient event. Opening an enclosure for the camera can alter cooling; document that boundary instead of treating the exposed bench result as a closed-product result. Do not improvise overload tests or infer a safe current rating from a single cool-looking frame.
Use Contact Measurements as an Independent Check
An appropriate contact sensor can help investigate a disputed infrared reading, but it has its own attachment, heat-flow and electrical-safety limitations. It is a cross-check, not an automatic truth source regardless of installation.
The two methods must address the same physical location and comparable time state. A sensor on a package top cannot validate a camera reading on a distant copper region, and neither directly measures an inaccessible semiconductor junction. If the methods disagree, review both setups before averaging the values or choosing the more convenient result.
Do Not Confuse Palette Contrast with Thermal Severity
Color maps depend on the selected range and palette; the brightest spot is not necessarily an unacceptable temperature. A different scale can make the same dataset look more or less dramatic.
Compare actual validated values, uncertainty and applicable limits, not color alone. Save the original radiometric data where the instrument supports it, together with the settings and visible-light context. A compressed screenshot may preserve the appearance while losing the ability to inspect measurement regions or revise justified analysis parameters.
Make a Layout Decision Only After the Measurement Is Defensible
A thermal image can direct the investigation, but it does not by itself identify electrical resistance, current distribution or the failure cause. Link the observation to the circuit and independent evidence.
Identify the surface and the exact test point.
Confirm optics, focus and target coverage.
Establish emissivity and reflection treatment.
Record load, airflow and timing.
Cross-check critical temperatures with a suitable method.
Compare against the correct component or conductor requirement.
The related high-current PCB neck-down guide explains one possible electrical heating mechanism. Investigate it when the geometry and loss evidence support that explanation, not merely because a thermal palette highlights the area.
FAQ
Can I use 0.95 for every part on a PCB?
No. A single convenient setting does not characterize shiny metal, coatings and package materials equally. Use a verified surface method and the cameraâs relevant instructions. A general material table can help identify a concern, but it is not calibration evidence for every finish, wavelength band, temperature and observation angle on the board.
Does a higher-resolution camera eliminate emissivity error?
No. More pixels can improve spatial detail, but they do not identify how the surface emits and reflects radiation. Focus, optics and target size still matter as well. Treat spatial resolution and radiometric interpretation as separate requirements; an exceptionally sharp picture of reflective copper can still carry a misleading temperature estimate.
Can the camera see a hot inner-layer trace through the board?
Ordinary PCB thermal imaging shows the observed surface response, not a direct view through an opaque stackup to each internal conductor. Internal heating can influence surface temperature, but that does not uniquely identify its source. Use construction information, electrical evidence and an appropriate thermal model before attributing the surface pattern to one hidden trace.
Can digital zoom make a narrow conductor measurable?
Digital enlargement does not add optical information that the sensor never resolved. It can make an image easier to view while leaving the original target coverage unchanged. Check the camera and lens measurement capability, focus and working distance. Do not mistake a large on-screen pixel block for a newly resolved physical temperature feature.
Will a visible-light photo tell me the infrared emissivity?
No. Appearance in visible light does not establish optical behavior in the cameraâs infrared band. A finish that looks dark or matte may still need characterization, and surface condition can vary. Use the appropriate material evidence or validated method rather than choosing a setting solely from a color photograph of the board.
Does a cool connector prove its contact resistance is acceptable?
No. The observed surface may be reflective, unresolved or thermally separated from the critical contact. Load and elapsed time also affect the result. Validate the temperature measurement and apply the relevant electrical and mechanical acceptance checks. A cool-looking connector image cannot replace contact-resistance evidence or establish the condition of a hidden joint.
Can I compare before-and-after boards using different automatic palettes?
Not by color intensity alone. Record comparable operating conditions and measurement settings, then compare validated temperatures at defined locations. An automatically rescaled image can exaggerate or conceal a difference. Preserve the underlying data and scale information so the comparison remains meaningful even if a presentation palette is later changed.
Does a checked surface temperature establish a semiconductor junction temperature?
Not automatically. The junction is inside the device, and the relationship to a measured surface depends on the package, heat paths and operating condition. Use the manufacturerâs appropriate characterization or validated thermal model. Do not compare a copper-surface reading directly with a junction-temperature limit and call the device qualified.
For a Best Technology high-current PCB enquiry, send the conductor construction, operating condition and defined temperature-validation scope to sales@bestpcbs.com. Distinguish calculated loss, observed surface temperature and verified assembly performance in the review package.
A Touchstone file stores frequency-dependent network parameters in text form. An .s2p file normally describes a two-port network, with four complex S-parameters at each frequency. Before importing it into a PCB simulation, check the units, data representation, port map and reference impedance; a file that loads successfully can still describe a different setup from the one you intended.
This guide follows a hypothetical passive RF PCB coupon between two connectors. Numerical examples are teaching values, not measured performance. The reference specification is Touchstone 2.1, ratified January 26, 2024; importing software may support a narrower subset.
AI-generated RF measurement-context illustration, not a measured S-parameter result or factory test record.
What an S2P File Tells Youâand What It Does Not
The data describes a network response at specified frequencies and reference conditions, not the complete physical design. For the coupon, S21 describes transmission toward port 2 from excitation at port 1, while S11 describes reflection at port 1 under the parameter definition.
The file may originate from a measurement or a simulation. That origin, the physical port locations and included fixtures need accompanying documentation. The filename alone does not establish temperature, calibration, geometry, manufacturing revision or validation quality. It also does not make a small-signal device model valid for every bias or large-signal operating condition.
Read the Option Line Before the Numbers
The option line explains how to interpret the data. For the example # GHz S MA R 50, read the fields separately rather than assuming a familiar instrumentâs export defaults.
Version-specific keywords can affect the interpretation, including reference values and port ordering. Read the complete header and the applicable specification instead of treating this one example as a universal template.
Compare MA, DB and RI Using the Same Complex Value
All three formats can describe the same complex S-parameter, but the two stored numbers mean different things. Keysightâs S-parameter table documentation identifies these supported representations.
Format
Pair means
Teaching example
MA
Magnitude, angle
0.5, â90°
DB
dB value, angle
â6.0206, â90°
RI
Real, imaginary
0, â0.5
The example value is âj0.5. Its magnitude in dB is 20 log10(0.5) â â6.0206 dB. These are calculated representations, not three measurement results. Simply changing MA to DB in the header without converting the data changes the meaning of the file.
Check the Special Two-Port Data Order
Do not assume every two-port row is stored in the intuitive S11, S12, S21, S22 sequence. The legacy two-port convention is frequency followed by the S11, S21, S12 and S22 pairs. Versions 2.0 and 2.1 use the applicable [Two-Port Data Order] declaration to identify the permitted order.
For the teaching coupon, manually identify one frequency and its transmission pair, then compare that point with the imported plot. This spot check can catch an ordering mistake before the wrong column becomes a design conclusion. Preserve any original header instead of rearranging columns by visual intuition.
Map File Ports to Physical Connector Locations
A correct numeric matrix still needs a physical port map. Label the coupon ends in the review record, identify signal and reference conductors, and confirm the direction represented by S21. Do not assume the left side of a photograph is always port 1.
For a reciprocal uniform coupon, forward and reverse transmission can look similar, so a reversed connection may not be obvious from one magnitude plot. Connector launches or other asymmetric features can matter when the model is connected to the next network. Keep a simple physical connection sketch with the data, separate from the fileâs numeric indexing.
Separate Reference Impedance from the Connected Load
When changing the S-parameter reference, use a valid renormalization operation rather than editing the R value alone. The scikit-rf renormalization example shows that the same physical load has a different reflection coefficient under a changed reference. More advanced complex-reference cases also require attention to wave definitions; do not improvise them from a simple real-resistance example.
Understand Why S4P Does Not Automatically Mean Differential Data
Four ports can represent two single-ended conductors at each end, but that physical arrangement must be established. A four-port file can also describe another network entirely. Even for a differential pair, single-ended data and mixed-mode data require the correct interpretation and pairing.
For a differential version of our coupon, identify the positive and negative conductors at both ends and check the fileâs declared mode/order information. A mistaken pairing can produce misleading differential transmission or mode-conversion results. Do not rename .s4p to .s2p to make an import dialog accept it.
AI-generated connection-planning illustration. Actual port numbering and differential pairing must come from the data provider.
Check the Frequency Band and Low-Frequency Treatment
The dataset supports its stated frequency range; behavior outside that range depends on the importing toolâs modeling assumptions. Record the first and last frequencies, point spacing and whether the intended analysis requires extrapolation or a DC estimate.
For the coupon, compare the planned simulation band with the data before running a time-domain analysis. Ask how the tool handles missing low-frequency data, interpolation and high-frequency truncation. A smooth-looking extrapolated curve is not an additional measurement. Keep any fitted or extended dataset distinguishable from the original supplied file.
Identify What the Measurement Reference Planes Include
The model boundary determines which physical effects are already in the data. A coupon file measured at coaxial reference planes may include launches that a trace-only electromagnetic model excludes. Cascading both without checking their boundaries can count the same transition twice.
Ask for the calibration or de-embedding description and a physical definition of each reference plane. For the teaching network, decide whether the connector bodies, launch pads and uniform line are included. This is different from the numerical impedance reference: both need to be correct, but they answer different questions.
Check Physical Plausibility for the Intended Network
Passing a syntax check does not demonstrate passivity, causality, reciprocity or measurement accuracy. A passive coupon and a biased amplifier are different model classes, so the applicable checks must match the object.
Use the simulatorâs documented validation tools and investigate suspicious behavior against the original data and measurement setup. Do not judge full multiport passivity solely by looking at one S21 magnitude. Likewise, do not ârepairâ a model automatically without understanding how the correction changes its response. Save the original and document any authorized fitted or corrected version.
Diagnose an Import Failure Without Corrupting the File
Identify the readerâs supported version and the exact reported problem before altering the data. Common review areas include the option line, frequency units, port count, pair format and required version-specific keywords.
Keep an unchanged original, test the file with a suitable independent reader, and compare at least one known point. If a format conversion is required, use a tool that actually converts the data and preserves the intended network meaning. Deleting unfamiliar header lines until the error disappears can remove information the importer needed to interpret the file correctly.
Release the Dataset with a Short Model Record
A usable handoff includes enough context to connect the network correctly and understand its limits.
File identity, revision and measured or simulated origin.
Format version, parameter type and pair representation.
Frequency range and any fitting or extrapolation.
Physical port map, reference planes and impedance convention.
Relevant bias, temperature and construction conditions.
Import spot check and applicable model validation results.
For interpretation of reflected signals, see the related PCB return loss and S11 guide. Reading the file correctly is the starting point for that interpretation, not proof that the manufactured channel meets its requirement.
FAQ
Can a CSV export be renamed to .s2p?
No. The content must follow the supported Touchstone syntax and contain the required complex network data. A spreadsheet of frequency and one magnitude curve is not a complete two-port network. Use an appropriate export or conversion method, then verify units, ordering and a known data point in the receiving tool.
Why does a file open in one tool but not another?
The tools may support different versions or subsets of the format, or may handle nonconforming input differently. Compare their documented capabilities with the actual header and data. A tolerant reader accepting the file does not prove full conformance, and a rejected file should not be fixed by removing required information blindly.
Can the file contain Y or Z parameters instead of S parameters?
Yes, the declared parameter type matters. Do not interpret every pair in a file as an S-parameter just because the workflow uses the word Touchstone. Check the option line and the receiving toolâs support for that parameter type. A conversion to scattering parameters must use the appropriate definitions and reference conventions.
Does a negative S21 dB value mean negative power?
No. It is a logarithmic representation of the magnitude of a complex transmission parameter under the stated reference definition. In the teaching example, magnitude 0.5 corresponds to about â6.02 dB. Interpreting delivered power additionally requires the relevant network and termination conditions; the sign alone is not a power measurement.
Can I recover phase from a magnitude-only screenshot?
Not as a complete replacement for the original complex dataset. A plot of magnitude omits phase information and usually lacks the full numeric precision and context needed for a network model. Ask for the original file rather than reconstructing a production simulation from a screenshot and assuming the missing phase is zero.
Does an S2P file fully describe an operational amplifier?
Not across every operating condition. Device data depends on how the part was biased, connected and characterized, and a small-signal network description does not replace all nonlinear, stability or supply behavior. Check the manufacturerâs intended model use and conditions before applying a two-port representation to an amplifier circuit.
Should I delete comment lines to improve compatibility?
Only if a documented conversion or troubleshooting step justifies it and the original is preserved. Comments may carry essential human-readable context such as port names or measurement conditions, even when they do not alter numeric parsing. Keep that context in the handoff record rather than stripping it simply to make the file smaller.
Is a supplierâs simulated file equivalent to a measured production coupon?
No. Both can be useful, but they answer different evidence questions. A simulated file depends on the model assumptions; a measurement depends on the specimen and test setup. Label the origin clearly and compare the construction and conditions with the intended PCB. Do not present simulation output as a manufacturing test certificate.
For a Best Technology RF PCB enquiry, send the stackup, conductor requirements, model boundary and intended validation scope to sales@bestpcbs.com. Keep the supplied network file paired with its physical port map and construction revision.
The Huray roughness model represents copper surface texture using an idealized nodule geometry to modify conductor surface impedance. In Ansys HFSS 3D Layout, its inputs include a nodule radius and a dimensionless Hall-Huray surface ratio. They are not interchangeable with a foil datasheetâs Rz roughness height.
This guide follows a hypothetical RF microstrip coupon from material selection to simulation review. Its useful output is a traceable input record: which copper face each value describes, where that value came from, which solver convention was used, and how the model was checked. It does not supply universal roughness settings for an unspecified PCB.
AI-generated physical-material illustration. Visible sheen does not measure micron-scale roughness or identify Huray parameters.
What the Huray Model Does to a PCB Simulation
The model accounts for electrical consequences of surface texture without requiring the mesh to reproduce every microscopic feature. A smooth-copper calculation and a roughness-enabled calculation can therefore differ even though the drawn trace geometry is unchanged.
Ansys documents a causal modification that also handles phase effects, rather than only a real-valued loss increase. See its Huray Surface Roughness Model documentation, 2025 R2. Record the actual implementation and version; the name âHurayâ alone is not a complete description of a simulation setup.
Why Copper Texture Matters More as Frequency Rises
At increasing frequency, skin effect concentrates current nearer conductor surfaces, making the condition of those surfaces relevant to loss. Skin depth is the characteristic penetration distance, not the physical foil thickness. That is why a thick copper layer can still need a surface model.
For the RF coupon, first define the operating frequency range and acceptable channel behavior. Do not ask whether roughness matters in isolation from frequency, geometry and field distribution. The current in both the signal conductor and its return path matters. A visual inspection of a shiny top surface does not characterize the less visible copper-dielectric interface.
Key Huray Parameters and Their Units
Keep physical dimensions, dimensionless factors and software defaults in separate fields. This avoids a numerically plausible entry acquiring an unsupported physical meaning.
Input
Unit
Interpretation
Nodule radius
Length, e.g. ”m
Radius in the idealized surface model
Hall-Huray ratio
None
Surface-area relationship under the model convention
Rz or Rq
Length
Measured profile statistic, not automatically either input above
Conductivity
S/m
Conductor property, separate from roughness
Frequency
Hz and stated sweep
Range over which the response is evaluated
The current PyEDB StackupLayer API reference shows default Huray inputs of 0.5 ”m and 2.9. These are API defaults, not measured values for your copper. Explicitly supply reviewed inputs and record their source rather than accepting a default because the solver runs.
Why Rz Cannot Simply Be Pasted into Nodule Radius
Rz describes a surface-profile measurement, while nodule radius describes the geometry assumed by the model. A numerical conversion requires an identified method and assumptions; equal units do not make two quantities equivalent.
A Cannonball-Huray derivation is one published route for estimating model inputs from foil roughness information. It introduces a close-packed-sphere assumption rather than proving that a real copper surface consists of identical spheres. Use the method as a documented estimate within its limits, not as an exact measurement. Keep the original roughness metric, measurement convention and derived parameters together so another engineer can reproduce the choice.
Huray vs Groiss and a Smooth-Copper Baseline
Compare models as modeling choices, not as three interchangeable fields accepting the same number.
Choice
Role
Review caution
Smooth copper
Diagnostic baseline
Not a claim that the physical copper is smooth
Groiss in Ansys 2025 R2
Legacy roughness correction
Frequency-domain limitation documented by Ansys
Huray in Ansys 2025 R2
Causal roughness model
Requires radius and surface-ratio convention
Cannonball-derived inputs
Parameter-estimation approach
Not a separate measurement of the finished interface
These statements refer to the named Ansys implementation. The layer roughness settings documentation explains its available choices. Other solvers may use different names, conventions or corrections, so do not translate settings solely by matching menu labels.
Map Model Values to the Correct Copper Faces
Assign values by physical interface, not merely by a layer name such as âtop copper.â A microstrip trace has a face toward the dielectric, a face away from it and etched sidewalls. Its reference plane also participates in the electromagnetic problem.
Draw a simple face map for the hypothetical coupon and identify which supplied value belongs to each interface. Ansys permits separate top, bottom and side settings. âSet allâ is a convenience command, not evidence that the three physical surfaces are identical. If only one face is characterized, record the uncertainty rather than quietly copying it everywhere.
Ask for Data That Matches the Manufactured Interface
Request foil identity, side identity, roughness metric and processing context together. The laminate name alone may not identify the exact copper supplied or the state of the surface after subsequent fabrication.
For the coupon, distinguish incoming foil data from information representing the finished stackup. Ask what treatment or processing stage the value describes and whether the modeled face corresponds to it. Keep an input marked âsupplier dataâ separate from one derived by an engineer or fitted to a coupon. Our related microstrip PCB guide provides the wider geometry and reference-plane context.
Build a Sensitivity Study Before Claiming a Prediction
A sensitivity study asks how much the result depends on uncertain inputs; it does not establish which input is true. For the hypothetical RF coupon, hold the verified trace geometry, dielectric model and ports fixed while comparing a smooth baseline with separately documented candidate roughness sets.
Save the baseline model and complete input record.
Change only the selected roughness parameters for each comparison.
Review insertion loss and phase across the same frequency sweep.
Mark which candidates are measured, supplied, derived or hypothetical.
Investigate whether the resulting spread changes the design decision.
No numerical outcome is implied here. If the acceptable design depends on one unverified roughness setting, the next action is better characterization, not a more confident caption on the plot.
AI-generated coupon illustration, not a measured comparison or evidence of factory test capability.
Use Coupon Measurements Without Hiding Other Errors
Measurement comparison must use a defined reference plane and a controlled geometry before it can usefully constrain a material model. A connector transition, calibration issue or incorrect trace width can otherwise be mistaken for roughness loss.
Two line lengths can support a suitable extraction method, but subtracting two arbitrary S21 magnitudes is not automatically a rigorous de-embedding procedure. Check the chosen methodâs assumptions, matching, fixture repeatability and frequency behavior. Use independent geometry and dielectric information where possible. Save the measured data, extraction steps and model version so the apparent agreement can be reproduced.
Do Not Fit Roughness and Dielectric Loss Blindly
A good-looking total-loss fit does not prove that the separate loss mechanisms were identified correctly. If both dielectric loss and roughness are freely adjusted, different parameter combinations may explain similar attenuation over a limited band.
Constrain one mechanism with independent evidence before interpreting the other. Review phase as well as loss, and test against a different length or suitable validation structure not used for fitting. If changing geometry or reference-plane assumptions destroys the fit, investigate those assumptions first. Describe a fitted parameter set as a model effective for its validation conditions, not as a universal copper material certificate.
Check Plating, Vias and Return Surfaces Separately
Do not use a roughness factor as a catch-all correction for every conductor-related effect. Surface finishes, plated conductors, etched geometry, vias and reference planes need their own modeling decisions and appropriate evidence.
For the RF coupon, write down which metal stack and interfaces the solver actually represents. If a later design adds a different finish or via transition, revisit the model instead of copying the couponâs fit unchanged. Applying a trace-surface setting to every conductor is not automatically conservative: it may misrepresent where the fields and currents are concentrated.
Release a Traceable Roughness Model, Not Just a Screenshot
The release record should let another engineer rebuild the same assumptions and identify what remains uncertain.
Solver, version, roughness model and unit convention.
Material and foil identity with source document revision.
Face-by-face assignment and treatment state.
Radius and ratio, labeled supplied, measured, derived or fitted.
Geometry, frequency range, dielectric model and port setup.
Validation data, limits and triggers for rechecking substitutions.
The practical decision is whether that evidence supports the design margin. A completed simulation proves that a model was solved, not that the finished PCB has been validated.
FAQ
Can I use the same Huray values in two different solvers?
Only after checking each solverâs parameter definitions, units, causal treatment and surface assignments. Similar field names do not establish equivalent implementations. Reproduce a simple controlled structure and compare the expected behavior before transferring a production model. Keep the original source and conversion assumptions with both projects rather than copying two unexplained numbers.
Does a lower foil Rz guarantee lower finished channel loss?
No. It is one potentially relevant input, not a channel-level guarantee. Dielectric loss, geometry, copper processing, finishes and transitions can also affect the measured response. Compare matched constructions and methods before attributing the difference to foil texture. Do not replace a complete channel requirement with one roughness statistic on a purchase order.
Should I increase mesh density until the microscopic texture appears?
Not as a substitute for understanding the selected surface model. A model-based correction represents effects that are not explicitly drawn as physical nodules. Follow the solverâs meshing and boundary guidance for the actual structure, then demonstrate convergence. Increasing computational effort does not repair unsupported material parameters or an incorrect face assignment.
Is a fitted roughness value valid for a different surface finish?
Not automatically. The fit may include effects that were not separately identified in the original coupon. A changed finish or metal stack can invalidate that interpretation. Review what the original model represented and repeat the relevant validation rather than treating the fitted value as an intrinsic property independent of manufacturing conditions.
Why can a model match loss but miss resonance frequency?
A loss match does not prove that phase delay and stored-energy behavior were modeled correctly. Geometry, dielectric dispersion, roughness implementation and transitions may need review. Use suitable phase or resonant measurements as additional constraints. Do not change dielectric constant solely to hide a mismatch before checking the physical construction and reference planes.
Can I use a single model for all fabrication lots?
Use it only within the construction and variation envelope that your evidence supports. A material substitution, changed foil treatment or altered fabrication process should trigger review. Define that envelope in the release record and ask how the relevant material identity is controlled. One successful coupon does not establish unlimited lot-to-lot equivalence.
Does the model predict DC resistance accurately from roughness alone?
No. DC resistance still depends on conductor dimensions, conductivity, temperature and the actual current path. A high-frequency surface correction is not a replacement for those inputs. Check the solverâs low-frequency treatment and compare against an appropriate baseline rather than interpreting a Huray radius as a standalone resistance specification.
What should I do when the supplier provides only Rz?
Ask which face and measurement method the value describes, then request a supported model parameter set if available. If you use a published derivation, record its assumptions and label the result as estimated. Carry the uncertainty into sensitivity and validation work; do not relabel the original Rz value as a measured sphere radius.
For a Best Technology RF PCB enquiry, send the stackup, foil requirements, simulation assumptions and intended validation scope to sales@bestpcbs.com. Confirm the proposed construction before treating the analysis as representative of the manufactured board.
For an ordinary passive PCB interconnect, S11 displayed as log magnitude is usually negative, while return loss is conventionally reported as the corresponding positive number. S11 of â20 dB means 20 dB return loss and 1% reflected power at that frequency and reference plane. It does not mean 20 dB of forward signal loss.
This guide follows a hypothetical RF coupon between two coaxial launches. An engineer receives a plot and needs to determine whether it meets a specified reflection limit. The task is to read the quantity, sign, frequency range, and measurement boundary correctlyânot to judge a PCB from one attractive marker value.
AI-generated physical-product illustration. No measured impedance or RF performance is represented.
What Does S11 Describe on a PCB?
S11 describes the reflected wave at port 1 relative to the incident wave at port 1 under the defined network conditions. It is a complex quantity, carrying magnitude and phase. The familiar negative-dB curve shows a transformation of its magnitude, not the complete complex result.
Keysight’s measurement-parameter documentation distinguishes reflection parameters S11 and S22 from transmission parameters S21 and S12. The port labels matter: a curve cannot be interpreted reliably without knowing where excitation and measurement occur and how the other ports are terminated.
Detailed S11 and Return-Loss Parameters
Write down the parameter definition before comparing a plot with a requirement. For equal real reference impedances in the usual passive interconnect context, use the following relationships. Here Î denotes the input reflection coefficient and log means base 10.
S11 log magnitude: 20 log(|Î|), in dB.
Return loss: â20 log(|Î|), in dB.
Reflected power fraction: |Î|ÂČ = 10âRL/10.
Record the reference impedance, frequency, calibration plane and termination conditions with every result.
S11 (dB)
RL (dB)
|Î|
Power back
â6 dB
6 dB
0.5012
25.12%
â10 dB
10 dB
0.3162
10%
â20 dB
20 dB
0.1000
1%
â30 dB
30 dB
0.03162
0.1%
These are calculated conversions, not PCB acceptance limits or measured results. The Teledyne LeCroy explanation of S-parameter terminology discusses the sign convention and the distinction between reflection and transmission.
Why More Negative S11 Means Less Reflection
A smaller reflected-to-incident wave ratio has a more negative logarithm. Therefore â30 dB S11 indicates less reflected power than â10 dB S11 at the same measurement conditions. Under the positive return-loss convention, the same comparison becomes 30 dB versus 10 dB.
Avoid saying only âlower return loss is betterâ or âhigher S11 is better.â Name the plotted quantity. For our coupon, a specification of RL â„20 dB corresponds to S11 log magnitude â€â20 dB. These are the same reflection requirement written in two conventions, not competing performance targets.
Return Loss vs Insertion Loss
Return loss concerns reflected signal; insertion loss concerns reduction in forward transmission under the stated reference conditions. Their desirable directions differ. A positive return-loss value should usually be large, while a positive insertion-loss value should usually be small for a transparent interconnect.
Quantity
Usual passive log-magnitude view
What a transparent path aims for
S11
Negative dB reflection trace
Small reflection magnitude
Return loss
Positive counterpart of S11 log magnitude
Larger positive value
S21
Forward transmission, often negative dB
Near 0 dB within the intended band
Insertion loss
Positive loss derived under stated conditions
Smaller positive value
For the broader forward-loss question, see the RF PCB insertion-loss guide. Do not substitute that quantity for the reflection criterion.
A Worked Power Example for an RF Coupon
Suppose a hypothetical passive two-port coupon has S11 = â20 dB and S21 = â3 dB at one frequency, with equal real reference impedances and a matched output. The calculated reflected fraction is 10â20/10 = 0.01, or 1%. The forward transmitted fraction is 10â3/10 â0.5012, or 50.12%.
About 48.88% remains outside those reflected and transmitted terms in this example. Do not automatically call all of it dielectric heating: losses, radiation, unmodelled paths and measurement limitations need consideration. The lesson is that little reflection does not guarantee nearly complete forward transmission. This is a teaching calculation, not a test report.
Judge the Whole Required Frequency Band
A reflection limit applies over the specified band unless the requirement says otherwise. One deep S11 minimum can coexist with poor matching elsewhere. A marker placed at the best point cannot demonstrate compliance across an operating range.
For the coupon, record the band endpoints and the worst result within that interval. Under the positive return-loss convention, the weakest point is the smallest RL. Under the negative S11 log-magnitude convention, it is the point closest to 0 dB. Check the same band when comparing two revisions or suppliers.
Keep the Reference Impedance Attached to the Result
S11 is referenced to a defined port impedance. A result normalized to one reference cannot be compared casually with a different reference. The relevant value should come from the measurement setup, model, or supplied network data rather than an assumption based on connector appearance.
A nominally 50-ohm test system does not prove that every part of the physical coupon is 50 ohms. It defines a reference for evaluating the structure. If data are renormalized, record that transformation and its basis. Do not describe a changed reference as a physical improvement to the board.
Know Whether the Launches Are Inside the Measurement
The calibration and de-embedding boundary determines which structures the reported network includes. A measurement can contain cable adapters, connectors, launches and PCB traces, or represent a narrower region after an appropriate correction.
In our example, decide whether the requirement applies to the entire connectorized coupon or the trace region alone. Do not blame laminate properties from a launch-inclusive reflection result without further evidence. The related PCB fixture de-embedding guide explains the separate boundary question. A correction must be validated; it is not merely a cosmetic plot adjustment.
AI-generated laboratory illustration, not an actual calibration or measurement record.
Why S11 and S22 Can Tell Different Stories
S11 looks into port 1; S22 looks into port 2. A structure with different launches or asymmetric discontinuities can present different reflection behavior from its two ends. Label the physical ports clearly before comparing curves.
Do not assume that similar forward and reverse transmission establishes identical input and output matching. In the controller’s RF path, the installed orientation can make the relevant end especially important. Record both reflection parameters when the test plan requires them and use the specified termination conditions rather than an undocumented open connector.
Single-Ended S11 Is Not Differential Return Loss
A differential interconnect needs the appropriate mixed-mode parameter and port definition. An individual single-ended S11 trace does not by itself describe the differential pair’s reflection behavior. Confirm the pairing, polarity and normalization used in the model or measurement.
Do not relabel a single-ended curve as SDD11 to match a requirement. Request the correct data or a documented conversion from a complete suitable multiport dataset. Keep the scope of this guide clear: the earlier numeric example is an ordinary single-ended two-port example, not a differential-channel qualification.
Investigate a Poor Result Without Guessing the Cause
Check the measurement configuration and repeatability before assigning a PCB defect. Verify connections, calibration applicability, port labels, data format, band and reference plane. Then compare the structure with its released design and any validated model.
A reflection feature can be associated with launches, geometry changes, vias, termination or other discontinuities. The S11 magnitude alone does not uniquely identify which one is responsible. Use additional evidenceâsuch as a controlled comparison or an appropriate time-domain analysisârather than announcing a root cause from the curve’s shape.
Report a Reflection Requirement Without Sign Ambiguity
A useful report names the quantity, inequality, band, reference impedance and measurement boundary. For example: âCalculated teaching requirement: return loss â„20 dB across the stated band; equivalent S11 log magnitude â€â20 dB.â Replace the example threshold with the actual approved requirement.
Include the dataset, setup notes and relevant uncertainty or validation limitations. For our coupon, release requires the agreed evidence across the band, not a universal âgood S11â number. Keep forward transmission and other channel requirements in their own acceptance checks so one passing metric cannot conceal another failing one.
FAQ
Is â10 dB S11 better or worse than â20 dB?
For the ordinary passive reflection comparison at the same frequency and conditions, â20 dB indicates less reflection. It corresponds to 1% reflected power, versus 10% at â10 dB. Whether either result is acceptable depends on the actual requirement and operating band. Do not turn these conversion examples into universal PCB pass limits.
Why does a report call a negative trace return loss?
People sometimes use return loss informally to refer to an S11 log-magnitude plot. Read the axis, instrument format and stated formula before applying an inequality. If the report is ambiguous, ask the author to name the quantity explicitly. Changing a label without clarifying its definition can reverse an acceptance decision.
Does a 20 dB return loss mean 99% reaches the output?
No. It means 1% is reflected under the stated conditions. The remaining power is not necessarily all delivered through the intended output; dissipation, radiation or other paths may matter. Check the relevant transmission measurement separately. A well-matched attenuating structure is a useful reminder that input matching and forward transmission are different properties.
Can I add return-loss dB values along a channel?
Not as a general channel calculation. Reflections interact with phase and multiple discontinuities, so scalar return-loss numbers do not preserve enough information to predict the cascade. Use suitable complete network data and a validated connection model. Keep reference impedances, port orientation and measurement boundaries consistent when evaluating the combined structure.
Is dB the same as dBm on an RF plot?
No. A ratio expressed in dB is not an absolute power level in dBm. S11 log magnitude describes a wave ratio, while a receiver power readout can be an absolute quantity. Check the selected measurement and units before converting numbers or comparing them with a reflection specification. Similar-looking axes can represent different physical questions.
What if S11 appears above 0 dB?
First establish the device and measurement context. An active network is not covered by the simple passive assumptions used here. For an expected passive interconnect, examine calibration, processing, reference definitions and uncertainty before drawing conclusions. Do not merely flip the sign or delete inconvenient points to make the curve resemble a typical passive result.
Does a Smith chart contradict the negative-dB trace?
Not necessarily. A Smith chart displays complex reflection information in a different representation. A log-magnitude plot discards phase and shows only a magnitude transformation. Verify that both use the same frequency, port, reference impedance and dataset before comparing them. One view may reveal information that the other deliberately does not display.
What should a supplier send with a return-loss plot?
Request the measured structure identity and revision, port map, frequency range, reference impedance, calibration or de-embedding boundary, and the underlying data where available. Ask how the reported quantity and limit are defined. This makes the plot reviewable and prevents confusion between a connectorized coupon, a corrected trace model and a complete installed channel.
References and RF Enquiries
The linked Keysight and Teledyne LeCroy documentation supports the parameter definitions and sign conventions; the numerical examples are calculated and explicitly hypothetical. For a Best Technology RF PCB enquiry, send the stackup, geometry and measurement requirement to sales@bestpcbs.com. Specific fabrication and verification scope require confirmation.
Aluminum nitride, or AlN, should not be treated as a ceramic that tolerates every water-based cleaner. Cleaning compatibility depends on the material grade, exposed surface, chemistry, temperature, contact time, and the other materials in the assembly. Obtain supplier guidance and qualify the complete process before using a new cleaner on production substrates.
This guide is a planning tool, not a chemical recipe. It follows a hypothetical power-electronics substrate with residue near copper metallization. The objective is to remove the residue without damaging the ceramic, metal, joints, or later bonding surface. A clean-looking part is not automatically an undamaged or electrically acceptable part.
AI-generated physical-product illustration, not a photograph of a tested or certified AlN product.
1. Why AlN Cleaning Needs a Compatibility Check
AlN is used where heat transfer and electrical insulation must coexist. Its value does not make its exposed surface chemically inert. Research on aqueous treatment and guidance from cleaning manufacturers both show why the specific exposure matters.
For example, Alconox’s AlN cleaning guidance warns about alkaline attack and prolonged or repeated exposure. Its product-specific recommendations should not be copied into a universal recipe for a metallized or assembled substrate. Compatibility must cover every exposed material, not only the ceramic named in the article.
2. Identify Which Form of AlN You Have
Powder, dense sintered ceramic, a coated substrate, and a single-crystal research sample are different test subjects. Their surface area, structure, additives, and exposed interfaces can differ. A cleaning method described for one form is not automatically suitable for another.
Start with the purchased substrate’s exact designation and supplier documentation. Identify whether the cleaning step reaches bare ceramic, a protective layer, metallization, or all three. If the grade or coating is unknown, that is a missing input to resolveânot a reason to use a familiar cleaner and hope for the best.
3. Detailed Cleaning Parameters to Record
A compatibility study needs a reproducible exposure description. Record the following parameters before comparing trial results. This table specifies what to document; it does not prescribe safe numerical limits.
Parameter
What to record
Why it matters
Material and surface
Grade, supplier, finish, coating, metallization
Defines the actual test subject
Chemistry
Product, concentration, water quality, measured pH
Names the real exposure, not a broad cleaner category
Temperature
Controlled range and measurement point
Prevents an unrecorded process change
Contact
Time, immersion or spray, agitation
Distinguishes different exposure conditions
Rinse and dry
Method, sequence, limits, delay
Extends the process beyond the wash bath
Repeat exposure
Normal and permitted rework cycles
Checks cumulative processing
Write the actual pH measurement conditions rather than relying only on a bottle label. A controlled process should also identify how solution condition and concentration are maintained under the approved procedure.
4. What Water-Exposure Research Does and Does Not Prove
A 2026 study of AlN under prolonged pool boiling observed surface degradation under its specific heated-water conditions. That supports taking water compatibility seriously even for bulk material. It does not establish a universal room-temperature cleaning lifetime.
Do not convert a severe laboratory exposure into a rule that a short rinse always failsâor that it is always safe. Use research to identify mechanisms and questions, then test the proposed substrate and process. Temperature, duration, surface preparation, and the exact material form must remain attached to any reported result.
5. Why pH Alone Cannot Select a Cleaner
pH describes one aspect of an aqueous solution. It does not fully describe its ingredients, residue-removal ability, interaction with metals, or effect on coatings. Two products with similar pH can still have different compatibility and rinsing behavior.
Likewise, âneutralâ is not a qualification certificate, and âacidicâ does not mean safe for every assembly. Compare candidate processes using the complete exposure record in the parameter table. If a proposed cleaner changes both chemistry and operating temperature, evaluate that combined change rather than approving it from a pH comparison alone.
6. AlN vs Alumina: Do Not Transfer a Cleaning Approval
Alumina and aluminum nitride are different materials. Their shared use as insulating substrates does not establish shared chemical behavior. A process approved for an alumina part therefore needs review before being applied to an AlN part.
Comparison
What may look similar
What still needs verification
AlN vs alumina
Ceramic substrate function
Grade-specific chemical and surface response
Bare vs metallized AlN
Underlying ceramic designation
Metal, interfaces, coatings and exposed edges
Powder vs dense AlN
Chemical name
Material form and relevance of the study
Unassembled vs assembled substrate
Same starting substrate
Joints, components, adhesives and trapped solution
For the hypothetical power substrate, changing only the ceramic while keeping the old wash program is a process change to evaluate, not a clerical substitution.
7. Check Metallization and Assembly Materials Too
A cleaner reaches whatever is exposed. Copper, surface finishes, bonding layers, solder joints, adhesives, markings, and component packages may impose limits different from those of the ceramic. A process that leaves bare AlN unchanged can still be unsuitable for an assembled product.
List all affected materials and obtain the relevant compatibility guidance. Pay particular attention to crevices and interfaces that may retain solution. Do not infer that a clean coupon proves compatibility with a complete power module. Test articles should represent the production surfaces and geometry that create the risk.
8. Start with the Residue You Need to Remove
Identify the contamination before choosing a process. Handling contamination, machining debris, flux residue, and an unknown white surface deposit are not interchangeable problems. Their removal and verification may require different approaches.
In our example, first establish whether the deposit is assembly residue or a change to the substrate itself. Repeatedly increasing wash strength can make the evidence harder to interpret. Preserve an uncleaned reference and document the starting condition so that the trial can distinguish removal of contamination from creation of new surface damage.
AI-generated laboratory illustration. No cleaning chemistry, procedure, or successful test result is implied.
9. Design a Small, Controlled Compatibility Trial
Use representative material and retain untreated controls. Define the wash, rinse, drying, and permitted repeat-cycle conditions. Decide in advance what measurements will demonstrate residue removal and what observations would indicate damage. Include appropriate handling and chemical safety controls under the organization’s approved procedures.
A staged trial makes discrepancies easier to interpret. If several variables change at once, a failure may not identify its cause. Do not assign production limits from one attractive photograph. Record the sample identity, process settings, inspection method, and acceptance criteria so the result is reviewable and repeatable.
10. Inspect More Than Cosmetic Appearance
Visual inspection can reveal discoloration, deposits, or obvious damage, but it cannot answer every surface or electrical question. Select verification methods according to the product’s risk: surface condition, dimensions, cleanliness, adhesion or bonding behavior, and relevant electrical performance may need separate checks.
Do not impose an arbitrary universal threshold for roughness, residue, or insulation. Use the product’s specifications and a suitable measurement method. Where qualification requires specialist analysis, involve the responsible laboratory or materials engineer before interpreting a change as harmless or assigning a chemical cause.
11. Common Failures in Cleaning Qualification
Common reasoning failures include testing the wrong ceramic grade, omitting a rinse from the trial, ignoring repeat cleaning, and checking only an unassembled coupon. Another is declaring that no visible change means no relevant change. Each can leave the actual production exposure untested.
Also avoid presenting a solvent as universally safe because it is not water-based. Solvents can introduce their own material compatibility, residue, fire, and handling constraints. This guide deliberately does not prescribe acids, alkalis, solvent mixtures, or temperatures for unknown assemblies. Supplier guidance and controlled qualification must come first.
12. Release the Process with Clear Boundaries
An approved cleaning instruction should identify the permitted material and assembly state, controlled chemistry, operating window, rinse and dry sequence, repeat-cycle allowance, inspection criteria, and change triggers. Define who reviews deviations and what to do when the starting contamination is outside the qualified scope.
For the power-substrate example, the useful result is a bounded process supported by representative evidenceânot a general claim that AlN can or cannot be washed. For broader material background, see the AlN PCB substrate guide; use this cleaning checklist for the separate compatibility decision.
FAQ
Can I rinse AlN with deionized water?
Do not assume that deionization alone establishes compatibility. Confirm the substrate supplier’s guidance and assess the proposed temperature, duration, exposed materials, and drying sequence. A brief approved rinse and prolonged immersion are different exposures. Qualification should cover the actual process, including repeated cycles where those can occur in production or rework.
Is a neutral-pH cleaner automatically safe?
No. pH does not identify every ingredient or interaction with ceramic, metallization, coatings, and assembly materials. A neutral label is one input, not a complete compatibility assessment. Obtain product-specific guidance and verify cleaning effectiveness and absence of unacceptable damage under the intended conditions before releasing the process for production use.
Can an alumina cleaning instruction be reused?
It can be considered as a candidate process, but it should not be treated as already approved for AlN. Confirm the new material and all exposed surfaces, review supplier guidance, and qualify the proposed process. Similar appearance or a shared role as an insulating substrate does not establish equivalent chemical behavior.
Does a white deposit prove hydrolysis?
No. Appearance alone cannot reliably identify a deposit’s composition or origin. Contamination, dried cleaner, process residue, and material changes may need different investigation methods. Preserve a reference sample, document the exposure history, and use appropriate analysis before declaring a mechanism or trying a more aggressive wash that could alter the evidence.
Can ultrasonic cleaning be added to an approved wash?
Not without reviewing the change. Ultrasonic exposure changes the process and may interact with part geometry, surfaces, joints, and components. Ask the relevant suppliers for limitations and evaluate representative samples under controlled conditions. An approved chemistry does not automatically approve every agitation method, exposure duration, or assembled configuration using that chemistry.
Does an AlN powder study apply to my dense substrate?
It may highlight a mechanism worth investigating, but it does not automatically establish a rate or safe exposure window for a dense substrate. Material form, surface area, grade, and test conditions matter. Use the study within its stated scope and obtain evidence relevant to the actual purchased substrate and proposed cleaning process.
Is alcohol a universal alternative to water?
No. A nonaqueous route still needs compatibility, cleanliness, drying, and safety review. It may not remove the target contamination and may affect other materials or leave unacceptable residue. Follow the chemical supplier’s safety information and the assembly’s approved process requirements rather than selecting a solvent solely because it avoids an aqueous label.
When should a qualified cleaning process be reviewed again?
Review it when the substrate grade, supplier, coating, metallization, assembly materials, cleaner, concentration, equipment, exposure window, or rework allowance changes. New residue types or unexplained inspection failures are also reasons to reassess. Keep change control linked to the qualification’s boundaries so that an old approval is not silently extended to a different process.
Sources and Technical Support
The linked cleaning-manufacturer guidance and original surface-reaction studies support the compatibility cautions; they do not establish a universal production recipe. Send the substrate identification, assembly materials, residue description, and proposed process to sales@bestpcbs.com for a Best Technology technical enquiry. Specific review and manufacturing scope require confirmation.
This website uses cookies to enhance your experience, remember your preferences, and help us understand how visitors use our site. You can accept all cookies, reject non-essential cookies, or manage your settings.
This website uses cookies to improve your experience while you navigate through the website. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may have an effect on your browsing experience.
Necessary cookies are absolutely essential for the website to function properly. These cookies ensure basic functionalities and security features of the website, anonymously.
Cookie
Duration
Description
cookielawinfo-checkbox-analytics
11 months
This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Analytics".
cookielawinfo-checkbox-functional
11 months
The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional".
cookielawinfo-checkbox-necessary
11 months
This cookie is set by GDPR Cookie Consent plugin. The cookies is used to store the user consent for the cookies in the category "Necessary".
cookielawinfo-checkbox-others
11 months
This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other.
cookielawinfo-checkbox-performance
11 months
This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Performance".
viewed_cookie_policy
11 months
The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. It does not store any personal data.
Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features.
Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.
Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. These cookies track visitors across websites and collect information to provide customized ads.
