Understanding the Complexities of Solder Ball Pull Testing on BGAs

摘要

One of today's needs is obtaining reliable, meaningful data about the adhesion of solder balls to the substrate of a ball grid array (BGA) package. Should we approach it as we do wire bonds, and perform a combination of shear and pull testing? Or should we perform shear testing alone? The answer to these questions lies in understanding why adhesion testing of solder balls on BGAs is more difficult than testing gold wire bonds. Initial reasoning suggests that we use shear testing, which is easy to set up and quick to perform. Shear testing is a straightforward approach that applies a load to a ball with a flat tool until it breaks away at the bond interface. The first concern when shearing BGA solder balls, however, is that errors can result if the passivation layer around the solder ball joint is too high. A high passivation layer can prevent the shear tool from applying the shear force in the plane of the bond intermetallics.