Solder joint voids are vacant round holes in the solder joints of the board. The voids that produce pcb solder joints are mainly due to the following reasons:
The surface of the PCB is plated. The effect of the surface coating of the PCB on the void is mainly related to the wettability, and the better the wettability, the less the void. Generally, the general tendency of the coating to create voids is OSP (maximum) > non-precious metal > precious metal (minimum). Reducing voids by improving wettability is more effective than increasing the fluxing ability of the flux. Another special case is the Im-Ag coating, which is a precious metal, but is also prone to voids, which is related to the organic content of the coating. Typically, Im-Ag coatings may contain 30% organic impurities, as shown in Figure 7-15. When the coating is as thin as 0.2um (0.8mil), the silver dissolves into the solder in a fraction of a second, and there is almost no organic residue in the solder joint. However, if the plating layer is relatively thick, the solder will not be completely dissolved, and the organic impurities remaining in the silver plating layer during the reflow soldering will decompose and discharge the gas, forming a dense interface void phenomenon, that is, a champagne cavity.
Pcb solder mask: Typically, the solder mask defines the void caused by the pad and the micro blind via. Enclosed air or residual organic magazine volatilization can cause voids.
Solder joint area: The larger the pin width, the more voids there are.