Posts Tagged ‘PCB Soldering’

What is flux in soldering? PCB assembly and soldering

星期五, 14 2 月, 2025

What is flux in soldering? Soldering is a vital process in electronics manufacturing. It ensures secure connections between components, creating a stable and efficient circuit.

One crucial element in soldering is flux. This chemical agent plays an essential role in improving solder adhesion, preventing oxidation, and ensuring a clean joint.

Without flux, achieving strong and long-lasting soldered connections would be difficult. It eliminates contaminants and promotes smooth solder flow.

What is flux in soldering?

Flux is a chemical substance used in soldering to remove oxidation from metal surfaces and improve solderability. It helps solder flow smoothly, creating strong and conductive joints. Without flux, metal surfaces would oxidize, making it difficult for solder to bond properly.

In PCB assembly, flux ensures that solder adheres well to components and circuit traces. It plays a critical role in maintaining the reliability of electronic devices.

Whether working with through-hole or surface-mount technology (SMT), using flux improves the overall soldering process.

What is the purpose of flux in soldering?

Flux serves multiple purposes in the soldering process:

Removes oxidation – Eliminates surface oxides that hinder solder adhesion.

Prevents re-oxidation – Forms a protective layer to keep metal surfaces clean.

Improves solder wetting – Helps solder spread evenly, ensuring a strong bond.

Enhances conductivity – Ensures a clean and stable electrical connection.

By using flux, soldering becomes more efficient and produces high-quality, durable joints. It is an essential component in both manual and automated soldering processes.

Is flux necessary for soldering?

Yes, flux is essential for effective soldering. Without it, solder may not properly bond to metal surfaces, leading to weak joints and poor conductivity.

The oxidation that forms on metal surfaces prevents proper adhesion, making flux a necessary step in the process.

For PCB assembly, flux is particularly important. It ensures that tiny solder joints remain clean and reliable. Some solder wires contain flux within their core, but additional flux may be required for complex soldering tasks.

What is flux made of?

Flux is composed of various chemical agents designed to clean metal surfaces and improve solder flow. The primary ingredients include:

Rosin or synthetic resin – Helps remove oxidation and enhances solder adhesion.

Activators – Chemically break down oxides and contaminants.

Solvents – Keep the flux in liquid or paste form for easy application.

Different formulations exist depending on the type of soldering process. Selecting the right flux ensures optimal results and long-term solder joint reliability.

How to use solder flux?

Using solder flux correctly ensures clean and strong joints. Follow these steps for proper application:

Apply flux – Use a brush, pen, or syringe to apply a thin layer to the joint.

Heat the joint – Use a soldering iron to warm the metal surfaces.

Add solder – Introduce solder to the heated joint, allowing it to flow evenly.

Let it cool – Allow the joint to solidify naturally for a strong bond.

Clean excess flux – Remove residue to prevent corrosion or contamination.

Following these steps ensures better soldering results and long-lasting electrical connections.

What are the types of flux?

Flux comes in different forms, each designed for specific soldering applications:

Rosin flux – Commonly used in electronics; provides strong cleaning properties.

Water-soluble flux – Easy to clean; ideal for high-precision soldering.

No-clean flux – Leaves minimal residue, eliminating the need for post-cleaning.

Acid flux – Used for plumbing and metalwork; not suitable for electronics.

Selecting the right flux depends on the soldering environment and the type of components being assembled.

What is the difference between solder flux and solder paste?

Although both are used in soldering, they serve different purposes:

Solder flux – A cleaning agent that removes oxidation and improves solder flow.

Solder paste – A mixture of flux and solder particles used in SMT assembly.

Flux is often applied separately in manual and wave soldering, while solder paste is essential in automated PCB manufacturing. Both materials play a critical role in ensuring high-quality solder joints.

Conclusion：

Flux is a fundamental component in soldering, playing a key role in achieving strong, clean, and conductive connections.Choosing the right flux and applying it correctly ensures reliable performance in electronic assemblies.

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How do you melt stubborn solder?

Methods for melting stubborn solder include using appropriate solvents, heating methods and special solvents or cleaning agents.

How to melt strong solder joints? Types of soldering joints

Use solvent: According to the composition of the solder, choose a suitable solvent for dissolving. Common solvents include acetone, alcohol, acetic acid, toluene, etc. Pour the solvent on the solder, let it soak for a while, and then gently wipe it with a soft cloth to dissolve the solder.

Heating method: For hot-melt solder, heating can be used to dissolve it. Use a hot air gun or a special hot melt device to heat the solder to a molten state.

Use special solvents or cleaners: You can try to use special solvents or cleaners. Some solvents or cleaners have strong dissolving power and are suitable for specific types of solder.

How do you remove excess solder from PCB?

During the production or repair process, some solder residues left by solder will easily remain on the PCB. If you want to avoid affecting the normal use of the circuit board, you must remove these solder residues. The following are common cleaning methods:

The first method:

1. Soak the circuit board in acetone solution for about 10 minutes;

2. Clean with more than 95% alcohol. If it is difficult to remove, you can use a soft brush to gently sweep;

3. After cleaning, use cotton and other absorbent items to dry;

4. Use a tin sucker, a needle for the welding hole, insert and rotate after the soldering iron is heated. Or you can quickly shake the printed plate after heating to shake off the tin residue. Be careful not to move too much to avoid damaging the circuit board.

The second method:

1. First shake off the solder on the soldering iron and melt the solder joint again. Repeat several times.

2. Find a small section of multi-strand wire, dip it in rosin, melt it together with the solder joint, and remove the wire while it is hot to remove the excess solder.

3. If the solder is on a large area, a special hot air gun or tin furnace can be used.

The third method:

Ultrasonic cleaning method, also soak the circuit board in acetone solution for about 10 minutes, then take out the PCB circuit board and immerse it in a container filled with anhydrous ethanol, and then put the container into the ultrasonic cleaning tank, and continue to clean for about 5 minutes. After completion, take it out and dry it.

What temperature does PCB solder melt?

The melting temperature of PCB solder depends on its composition. The melting temperatures of common solders such as tin-lead alloys (such as 60/40 and 63/37) are as follows:

60/40 solder: melting temperature is about 188°C (370°F).

63/37 solder: melting temperature is about 183°C (361°F).

Temperature requirements for different welding methods

1. Manual welding:

Temperature range: generally between 300°C and 350°C. This temperature range can make the solder wire melt quickly and ensure good wettability.

Time requirement: The welding time for small components is about 2 to 3 seconds, and large components may take 3 to 5 seconds.

2. Wave soldering:

Temperature range: usually between 245°C and 265°C. This temperature can ensure that the solder fully wets the pads and component pins on the PCB board under the push of the wave crest.

Time requirement: depends on the speed of the conveyor belt and the height of the wave crest, generally around 3 to 5 seconds.

3. Reflow soldering:

Temperature curve: divided into preheating zone (100°C to 150°C), insulation zone (150°C to 180°C), reflow zone (210°C to 240°C) and cooling zone.

Time requirement: The entire reflow soldering process is generally between 3 and 6 minutes.

What are the types of PCB solder joints?

The types of PCB solder joints mainly include the following:

Surface mount solder joints (SMT): This type of solder joint is suitable for surface mount components. The solder paste is melted by hot air furnace and other equipment to fix the components on the PCB surface.

Plug-in solder joints: Suitable for plug-in components. The component pins need to be soldered on the PCB by wave soldering or manual soldering.

Through-hole solder joints: Used for component soldering on double-sided or multi-layer PCB boards. The component pins need to be passed through the PCB board and fixed by wave soldering or other technologies.

What temperature is needed to Desolder a PCB?

The optimal temperature range for desoldering a PCB is 250℃-350℃. This temperature range is adjusted according to factors such as component packaging form, volume, and board thickness. Too high a temperature can easily damage the circuit board, while too low a temperature can make it impossible to remove the components or easily cause component damage.

Specific temperature setting suggestions

Preheating table desoldering temperature: When desoldering on the preheating table, the preset temperature is 400 degrees. In actual operation, the temperature under the circuit board is about 170-200 degrees Celsius, and the temperature above the circuit board is about 130-140 degrees Celsius, which can effectively desolder without overheating the PCB.

Large component welding temperature: When handling large-size components, the soldering iron temperature should be set at 350 to 370 degrees Celsius, and the maximum temperature should not exceed 390 degrees Celsius. The welding time should be kept within a few seconds to prevent damage to the pads of the PCB board.

What happens if you overheat a solder joint?

Impact on PCB performance

Degradation of performance: Electronic components on PCBs are sensitive to temperature, and overheating may cause degradation of component performance.

Shortened lifespan: High temperatures accelerate the aging process of electronic components, resulting in a shortened lifespan of components.

Thermal expansion and thermal stress: PCBs and components on them will experience thermal expansion when the temperature changes, and overheating may cause deformation, cracking, or solder joints to fall off.

What temperature will damage a PCB?

When melting solder, the maximum temperature a PCB can withstand is 280 degrees Celsius. At this temperature, the solder will melt but will not cause permanent damage to the PCB. However, if the temperature exceeds this range, it may cause damage to the PCB.

Temperature control of PCBs during soldering

Preheating temperature: Before soldering, the preheating temperature of the PCB is generally controlled between 80°C and 120°C to reduce the impact of thermal stress on components.

Soldering temperature: During soldering, the temperature of the solder needs to reach above its melting point to ensure that the solder can fully melt and wet the soldering surface.

Peak temperature: During the soldering process, some hot spots on the PCB may reach a peak temperature higher than the soldering temperature.

Does flux help melt solder?

Flux helps melt solder during the soldering process, mainly through the following aspects:

Reduce surface tension: Flux can reduce the surface tension of solder, allowing the molten solder to spread better on the soldering surface, and prevent the solder from forming a ball due to surface tension and not being able to fully contact the soldering part.

Remove oxides: Flux has reducing properties and can react with oxides to remove oxide film, so that the solder can be melted smoothly and form a reliable solder joint, and it is also conducive to heat transfer.

Promote heat transfer: Flux can make the soldering iron tip contact with the soldering surface more closely. As a heat conduction medium, it accelerates the solder to absorb heat, thereby melting faster, improving soldering efficiency and solder joint quality.

In short, melting a solid solder joint requires attention in many aspects. Traditional tools such as electric soldering irons and hot air guns should select parameters and operate accurately according to the characteristics of the solder joint and PCB; materials such as flux and tin-absorbing tape should be used skillfully as needed. As a professional PCB manufacturer, BTST Technology has rich experience in the field of PCB welding and is very skilled in the use of tools such as soldering irons and heat guns. Whether it is delicate motherboard solder joints or connection points of large industrial PCBs, they can accurately control and ensure impeccable solder joint quality.