Understanding the Effect of Process Changes and Flux Chemistry on Mid-Chip Solder Balling

Mid-chip solder balling is a defect typically associated with solder paste exhibiting poor hot slump and/or insufficient wetting during the reflow soldering process. If a solder paste exhibits excessive hot slump, there is an increased possibility that a proportion of the solder will become detached from the bulk deposit and flow under the component. In parallel, a paste exhibiting slow or insufficient wetting (low activity) will have a weak interaction with the solderable surface of both the PCB and component metallisation; this will increase the possibility of solder flowing onto the solder resist.