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Electronic manufacturing industry
post welding in the PCBA process

In PCBA processing, there are both SMD processing and plug-in cases. Plug-in generally speaking is the use of wave soldering for welding to improve the welding efficiency to achieve mass production. In the DIP production workshop, wave soldering is the most commonly used welding method, the machine inside the flow of solder liquid, so that the PCB board through the uniform tin, complete the welding, can greatly improve the welding efficiency.

But in addition to wave soldering, there is a welding method – post welding, that is, the operator is required to directly use the soldering iron for welding processing.What is the post-soldering process? What is the need for its existence?

Table of Contents

What is post welding?

Post-welding processing refers to the manual soldering of some components that are not suitable for wave soldering by using a soldering iron after wave soldering is performed on the circuit board.

Why is post welding needed?

Why is post welding needed?

1、Components are not resistant to high temperature

Today, lead-free technology is becoming more and more popular. When soldering by wave soldering, the temperature in the furnace is higher than the temperature of lead. Therefore, some components that are not resistant to high temperature cannot be soldered by wave soldering.

2.Components of excessive height

Wave soldering has height requirements for components. General components can enter the wave soldering inside smoothly, but there are components that are too high or too long, the height of which exceeds the standard height of the wave soldering, and need to be post-soldered.

3, Components are rare

If there are only a few components on the wave-soldered side of a board, post-soldering can be used to increase efficiency.

4, Components are close to the edge of the board

After wave soldering, some components near the edge of the board may collide with the machine or not touch the liquid tin, which will affect the soldering effect, and then need to be post-soldered.

5、Special components

For customers with special requirements of high sensitivity components, also can not over wave soldering.

What tools are needed for the post welding?

Welding of circuit boards, especially in the context of electronics assembly and repair, requires specialized tools and equipment to ensure precise and reliable connections. When performing post welding (also known as through-hole soldering) on circuit boards, the following tools are commonly used:

Soldering Iron: A soldering iron is the primary tool used to heat the solder and make electrical connections between components and circuit board pads. It consists of a heated metal tip that melts solder when it comes into contact with it. For rear welding, a soldering iron with a fine tip is typically preferred to access tight spaces and make precise solder joints.

Solder: Solder is a metal alloy with a low melting point that is used to create electrical connections between components and circuit board pads. Typically, solder consists of a combination of tin and lead (or other materials for lead-free solder).

Flux: Flux is a chemical compound used to clean and prepare the surfaces being soldered. It helps remove oxidation and contaminants, improves the wetting of solder, and enhances the overall quality of solder joints. Flux is often applied to the soldering area before soldering, either in the form of a liquid flux or flux-core solder wire.

Desoldering Tool: In case of mistakes or rework, a desoldering tool is used to remove excess solder or unsolder components from circuit boards. Desoldering tools can include desoldering pumps, desoldering wicks, or desoldering irons with built-in vacuum suction.

Soldering Station: A soldering station provides a stable and controlled environment for soldering operations. It typically includes a soldering iron holder, temperature control unit, and sometimes a sponge or brass wire tip cleaner.

Magnifying Lamp or Microscope: Given the small size of components and solder joints on circuit boards, a magnifying lamp or microscope is often used to provide better visibility and precision during soldering and inspection.

Fume Extractor: Soldering generates fumes that may contain harmful substances, so a fume extractor or soldering fume absorber is used to remove and filter out these fumes, ensuring a safe working environment.

ESD Protection Equipment: Electrostatic discharge (ESD) can damage sensitive electronic components, so ESD protection equipment such as anti-static wrist straps, mats, and containers should be used to prevent ESD-related damage during soldering.

How to use the soldering iron welding?

How to use the soldering iron welding?

1.Before using the new soldering iron, polish the soldering iron tip with fine sandpaper, heat it up by powering it on, dip it in rosin, and then use the soldering iron tip to contact the solder wire to evenly coat the soldering iron tip with tin.

2.Pre-treat the soldering area of component pins or circuit boards, remove the oxide layer from the soldering area, and tin the components.

3.Hold the soldering iron with your right hand. Hold the component or wire with pointed nose pliers or tweezers in your left hand. Before soldering, the soldering iron should be fully preheated. The soldering iron tip should be tinned, i.e., coated with a certain amount of solder.

4.The flux (rosin and soldering oil) is crucial during soldering. Fresh rosin and non-corrosive soldering oil can help achieve good soldering, making the surface clean and beautiful. It’s advisable to use more flux during operation.

5.After soldering, it is necessary to check for any missed solder joints, cold solder joints, or component short circuits caused by solder flow. Cold solder joints are difficult to detect. You can gently tug on the component pins with tweezers. If there is any movement, immediately add more solder.

Operating Methods and Precautions

After inserting the components, turn the circuit board with the back facing up. Proceed to solder each pin of the components one by one. When soldering, the soldering iron and thin solder wire should simultaneously contact the component pin and the solder pad. Ideally, the solder should quickly and evenly melt into the pin hole and around the pin. For components that have been soldered, use diagonal pliers or scissors to trim off excess pins. If the solder joint loosens during the pin trimming process, it indicates poor soldering quality and requires re-soldering.

During the soldering operation, pay attention to the following points:

(1) Soldering actions should be quick, meaning the soldering iron should stay on the circuit board for as short a time as possible to avoid damaging the copper traces or components. If the solder pad is difficult to wet with solder, it indicates poor quality or oxidation on the surface. Clean it with a blade before soldering, and avoid prolonged contact with the pad.

(2) Ensure the solder joint size is moderate, and when soldering two closely spaced pads, avoid them touching each other. Also, when soldering one pad, if another nearby pad does not have a component inserted, make sure the solder does not block the pin hole to prevent difficulty in inserting the next component pin.

(3) Since both the solder pad and pins are relatively large, insufficient power in the soldering iron can easily lead to false soldering or cold solder joints, especially in winter. Consider using a higher-power soldering iron to avoid these issues.

(4) Take care not to damage the insulation coating on the copper traces of the circuit board during soldering. The areas outside the solder pad are coated with insulation, which serves as insulation.

(5) If soldering causes a break in the copper trace, there are various methods to fix it. If it’s just a crack, carefully scrape off the insulation coating at both ends of the crack with a blade, then solder it back together.

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