Assessment of Constitutive Properties of Solder Materials Used in Surface-Mount Devices for Harsh Environment Applications

To perform a thermomechanical simulation of surface-mount devices (SMD), relevant solder constitutive properties are needed. This paper reviews some promising Pb and Pb-free solders that are candidates to harsh environment applications. It presents the discrepancy in their common mechanical properties reported in the literature. The mechanical test systems, solder microstructure under test, and the test conditions (temperature and strain rate) are among the major causes for the discrepancy. The use of such variations in the solder thermomechanical properties as input data for simulation studies may cause reliability prediction less meaningful. A novel and reliable test methodology to extract relevant solder properties for surface mount applications is presented in this paper. To fulfill the methodology requirements, lap shear tests with accurate control of the reflow profile and dimensionally accurate solder joint thickness need to be conducted to reproduce the SMD solder joint microstructures for determining solder joint properties for elastic, plastic, and creep model simulations. Two case studies with high-Pb and Pb-free solders are presented. Time-independent yield strength and ultimate tensile strength data obtained from our studies were found to be higher than the reported literature data. This methodology can be extended for other solder material systems with any surface finish plating materials.