Effects of Package Level Structure and Material Properties on Solder Joint Reliability Under Impact Loading

In this paper, the effects of package level structures and material properties on solder joint reliability subjected to impact loading are investigated by the integrated experimental testing, failure analysis, and finite element modeling. Three different package structures: ball on I/O wafer level package (WLP), copper post WLP, and chip-scale (CS) ball grid array (BGA) package, are studied. Experimental testing based on JESD22-B111 is conducted to obtain the components' failure mode, rate, location, and the corresponding board strains and accelerations. Finite element models are developed and validated against the experimental results. For a CS BGA package, the compliance of the plastic substrate/mold compound provides a "stress buffer mechanism" at corner joints in BGA to relieve stresses. For a copper post (or pillar) WLP, wafer level epoxy, which encapsulates copper pillars, serves as a compliant layer for solder joint stress reduction under dynamic loading. Comprehensive data from simulation and experimental results show that package structure and material properties play a significant role on the dynamic responses of solder joints. The actual solder joint reliability performance of a CS BGA or WLP package depends on the resultant effects of package structure, material properties, package body size, and the component locations.