Analyze the Causes and Solutions of Poor PCB Surface Mount Soldering

1. Bridging

The causes of bridging are mostly caused by excessive solder or severe edge collapse after solder printing, or the size of PCB substrate solder area is out of tolerance, SMD placement offset, etc., when SOP and QFP circuits tend to be miniaturized, bridging will cause an electrical short circuit and affect the use of the product.

2. Poor Wetting

Poor wetting refers to the fact that the solder and PCB substrate welding area during the soldering process does not generate metal-to-metal reaction after wetting, which results in missing soldering or fewer soldering failures. The reason is mostly caused by contamination of the surface of the soldering zone, or solder resist, or a metal compound layer formed on the surface of the joined object. For example, if there are sulfides on the surface of silver and oxides on the surface of tin, poor wetting will occur. In addition, when the residual aluminum, zinc, cadmium, etc. in the solder exceeds 0.005%, the degree of activity is reduced due to the moisture absorption of the flux, and poor wetting may also occur. In wave soldering, if there is gas on the surface of the PCB substrate, this failure is also prone to occur. Therefore, in addition to performing a proper soldering process, anti-fouling measures must be taken for the surface of the PCB substrate and the surface of the components, selecting the appropriate solder, and setting a reasonable soldering temperature and time.