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How to prevent pseudo soldering or cold soldering defects in PCBA manufacturing?

PCBA manufacturing processing mainly refers to the soldering the PCB circuit board and the components through the soldering process. Soldering defects such as pseudo soldering or cold soldering are prone to occur during the soldering process. And pseudo soldering or cold soldering will seriously affect the reliability of the product and greatly increase the maintenance cost of the product.

The problem of pseudo soldering and cold soldering defects in PCBA soldering processing is caused by many reasons, mainly because the solder can not fully wet the pads and components pins, and the components and circuit board pads cannot be fully soldered. In the PCBA production process, specific prevention can be done in the following ways.

1. Moisture-proof storage of components
If the components are exposed in the air for too long, which will cause the components to absorb moisture and oxidize the components, as a result, the oxide cannot be fully removed from the components during the soldering process, resulting in the defects of pseudo soldering. Therefore, during the soldering process, the components with moisture should be baked, and the oxidized components should be replaced. Generally, the PCBA processing plant will be equipped with an oven to bake the components absorbed moisture.

2. Choose solder paste from well-known brands
The pseudo soldering and cold soldering defects that appear in the PCBA soldering process have a great relationship with the quality of the solder paste. The unreasonable configuration of the tin alloy composition and flux composition can easily lead to weak flux activating during the soldering process, and the solder paste cannot fully wet the pad, resulting in pseudo soldering and cold soldering defects. Therefore, you can choose solder paste from well-known brands such as SMIC, Alpha, and Vital.

3. Adjust printing parameters
The problem of pseudo soldering and cold soldering is largely due to the lack of tin. In the printing process, adjust the pressure of squeegee, select the appropriate stencil can reduce such defects, and the stencil opening should not be too small to avoid too little tin.

4. Adjust the reflow soldering temperature curve
During the reflow soldering process, it is necessary to control the soldering time. If the time in the preheating zone is not enough to fully activate the flux and remove the surface oxides on the soldering area or the time in the soldering zone is too long or too short, it will cause pseudo soldering and cold soldering.

5. Try to use as many as reflow soldering and reduce manual soldering
Generally, when using an electric soldering iron for manual soldering, the technical requirements of the soldering personnel are relatively high. If the temperature of the soldering iron tip is too high or too low, or the soldered components become loose during soldering, which can easily cause pseudo soldering and cold soldering. Use reflow soldering can reduce external factors caused by human and improve the quality of soldering.

6. Avoid too high or low temperature of the electric soldering iron
In the manual soldering processing and repair soldering of PCBA, improper operation will lead to the temperature of the soldering iron tip to be too high or too low when using an electric soldering iron, which will easily result in pseudo soldering and cold soldering. Therefore, when soldering, keep the soldering iron tip clean, select different output power electric soldering irons according to the size of different parts and solder joints, and components shapes, and control the soldering temperature between 300°C and 360°C.

The pseudo soldering and cold soldering caused in the PCBA soldering process are caused by many factors. The above is just a list of some relatively common reasons. Through the above preventive measures, combined with the actual situation, the pseudo soldering and cold soldering defects can be effectively reduced.