The causes of bridging are primarily due to excessive solder or severe edge collapse after solder printing. Additionally, issues such as the PCB substrate solder area being out of tolerance and SMD placement offset can also contribute to bridging. As SOP and QFP circuits continue to miniaturize, bridging can lead to electrical short circuits that impact the product’s functionality.
2. Poor Wetting
Poor wetting refers to the phenomenon in which the solder and PCB substrate fail to create a metal-to-metal reaction during the soldering process, leading to insufficient or unsuccessful solder joints. This issue is often caused by contamination on the surface of the soldering area, solder resist, or the presence of a metal compound layer on the joined object’s surface.
For instance, poor wetting can occur if there are sulfides on silver surfaces or oxides on tin surfaces. Additionally, an excess of residual aluminum, zinc, cadmium, etc. in the solder (exceeding 0.005%) can reduce its activity due to moisture absorption from the flux, resulting in poor wetting. Gas on the PCB substrate’s surface can also contribute to this problem, especially in wave soldering processes.
To prevent poor wetting, it is essential to not only follow proper soldering procedures but also implement anti-fouling measures on the PCB substrate and component surfaces. Selecting the appropriate solder and establishing suitable soldering temperatures and times are also crucial steps in addressing this issue.
