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How to prevent false soldering and solder joint defects common to PCBs in SMT surface mounting

2019-07-25 18:11:37 476

1. Moisture-proof storage of components

If the components are placed in the air for too long, the components will absorb moisture and the components will oxidize, which will result in the components in the soldering process not being able to fully remove the oxides, resulting in defects of soldering and false soldering. Therefore, during the soldering process, the components with moisture are baked and the oxidized components are replaced. Generally, the SMT placement processing factory on the PCB surface is equipped with an oven to bake components with moisture.


2, select the famous brand of solder paste

The solder joints and false solder joints that appear in the SMT placement soldering process on the PCB surface have a great relationship with the quality of the solder paste. The metal component and the flux composition in the solder paste composition are unreasonable, which tends to cause the flux activation ability to be weak during the soldering process, and the solder paste cannot sufficiently wet the pad, thereby causing a false soldering or a false soldering defect. Therefore, you can choose solder pastes from well-known brands such as Qianju, Alpha, and Victaulic.


3, adjust the printing parameters

The problem of virtual soldering and false soldering is largely due to the fact that Shaoxi needs to adjust the pressure of the scraper during the printing process. The steel mesh should not be too small to avoid too little tin.


4, adjust the reflow soldering temperature curve

When performing the reflow process, it is necessary to control the welding time, the time in the preheating zone is not enough, the flux can not be fully activated, the surface oxide of the weld is removed, and the time in the weld zone is too long or too short, which will cause the virtual Welding and false welding.


5, try to use reflow soldering to reduce manual soldering

Generally, when using a soldering iron for manual soldering, the technical requirements of the soldering personnel are relatively high, the temperature of the soldering iron tip is too high or too low, or the soldered components are loosened during soldering, and it is easy to cause soldering and false soldering. Welding can reduce the external factors of man-made and improve the quality of welding.


6, to avoid the temperature of the soldering iron is too high or low

Soldering iron is required for manual soldering during post-weld processing and repair of SMT mount solder on the PCB surface. When using the soldering iron, the irregular operation causes the temperature of the soldering iron to be too high or too low, which is very likely to cause soldering and false soldering. Therefore, when soldering, keep the soldering iron head clean, select the soldering iron of different power types according to different components and solder joint size and device shape, and control the soldering temperature between 300 °C and 360 °C.


The virtual welding and false welding caused by the SMT placement and soldering process on the PCB surface are caused by many factors. The above are just some of the more common reasons. Through these precautions, combined with the actual situation, it can be effective. Reduced defects in solder joints and false solder joints.

label: PCB Assembly