Reflow soldering defect solving skills in smt patch processing
When we carry out reflow soldering, we often encounter defects in soldering. In response to this problem, Shenzhen SMT SMD Xiaobian has compiled and found that there are 13 reasons for this kind of thing happening. Today, Xiaobian will list it in detail.
1, poor wetting
2, the amount of solder is insufficient and the virtual welding is broken
3, suspension bridge and shift
4, solder joint bridging or short circuit
5. Walking the solder ball near the solder joint
6. Air holes and pinholes distributed on the surface or inside of the solder joint
7. The solder joint is in contact with or exceeds the component body (suction phenomenon)
8. Fine tin wire between the soldered ends of the components, between the leads, between the soldered ends or between the leads and the through holes
9. The plating layer of the component tip peels off to different extents to expose the component body material.
10, the component surface is reversed
11. There are different degrees of crack defect in the component body or end.
12, cold welding, also known as solder joints
13. There are also some defects that are invisible to the naked eye, such as the size of the solder joints, the internal stress of the solder joints, the internal cracks of the solder joints, etc., which can be detected by X-ray, solder joint fatigue test and other means. These defects are mainly related to the temperature profile. For example, if the cooling rate is too slow, large crystal particles will be formed, resulting in poor fatigue resistance of the solder joints, but the cooling rate is too fast, and the component body and solder joint cracks are easily generated. For example, when the peak temperature is too low or the reflow time is too short, solder is generated. Insufficient melting and cold welding, but too high peak temperature or too long reflow time will increase the production of co-boundary metal compounds, making the solder joints brittle, affecting the solder joint strength, such as more than 235 degrees Celsius, it will also cause itching in the PCB. Carbonization of the resin affects PCB performance and life.
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