Effect of microstructure evolution on Pb-free solder joint reliability in thermomechanical fatigue

The performance of solder joints in an accelerated thermal cycling (ATC) test depends on the accumulation of fatigue damage, which is affected by various simultaneously evolving microstructure features. A mechanistic understanding of microstructure evolution and damage accumulation in Pb-free solder joints will help us better interpret thermal cycling test results. In this study various components, including Ball Grid array (BGA), Land Grid Array (LGA), Thin Small-Outline Package (TSOP), Quad Flat No-Lead (QFN) and surface mount resistors, were compared for their failure mechanisms. The focus was on the evolution of microstructure, particularly recrystallization, and its correlation to fatigue crack propagation. A general understanding of damage accumulation was proposed, based upon the observed recrystallization behavior and the fatigue life dependence on ATC parameters.