Relationship of tensile interfacial strength to lead-free BGA impact performance

With the increased use of Lead-free alloys in BGA packages and assemblies, new reliability issues have become critical. A common mode of failure during impact conditions for BGA assemblies is brittle failure at the interface between the BGA substrate pad and the bulk solder joint. However, the strength characteristics of these interfaces, which include an intermetallic compound (IMC) layer, are not well understood as most existing tests focus on the strain of the entire joint at failure (or number of drops to failure). The present study uses high-speed tensile tests to isolate and characterize the interfacial strength of BGA assemblies. These results are compared to the impact performance of the BGA assemblies as measured by a four-point dynamic bend test and the relative merit of the test methods are assessed. In addition, the interfacial mi era structure of the different assemblies is characterized and related to test results