Analysis of Causes of SMT Soldering Wetting Failure!

Wetting failure is a common defect in the PCB assembly process. The main manifestation of wetting failure is that the PCB pads and solder cannot be fully fused during the SMT soldering process. Therefore, wetting failure is also known as non-wetting or non-immersion. If not detected and dealt with in a timely manner, wetting failure can lead to soldering defects such as solder bridging or insufficient soldering, resulting in additional costs for repair and rework. If the problem is not effectively resolved, wetting failure can also directly cause poor contact between the PCBA board, resulting in electrical connectivity issues. Therefore, understanding the main causes of wetting failure is crucial to ensuring the quality of PCBA soldering.

During the PCBA soldering process, contaminants and oxide layers are the main causes of wetting failure. If there are contaminants such as foreign matter, fingerprints, or residual flux on the PCB pads or component pins, non-wetting will occur. Similarly, if the PCB pads or component pins are oxidized, wetting failure will also occur.

In addition, abnormal soldering temperature is also one of the causes of wetting failure. If the solder paste is not heated to the appropriate temperature, the tin powder inside the solder paste cannot be fully fused, resulting in a rough surface of the solder joint. If the surface of the solder joint is not smooth, wetting failure can also occur. If the soldering time is insufficient, the PCB pads and solder cannot be fully wetted, resulting in wetting failure.

Apart from the above two points, problems with flux or solder paste can also cause wetting failure. For example, insufficient activity of the flux or poor fluidity of the solder paste can cause the pads and solder to be unable to wet or fully wet. From the analysis of previous PCBA defects such as solder balls or tombstoning, it is not difficult to see that problems with solder paste can cause most of the PCBA soldering defects. Therefore, when selecting and using solder paste, caution should be exercised to avoid the occurrence of PCBA soldering defects.