Application of Viscoplastic-Creep Separate Constitutive Model to Lead-Free Solder Alloy

Abstract

When we estimate the fatigue life of lead-free solder joints, we have to conduct FE analysis using a constitutive model which can exhibit mechanical properties of lead-free solder. In FE analysis of solder joints under cyclic temperature load, a constitutive model has to express stress strain curves, stress strain hysteresis loops and stress relaxation curves accurately, containing these temperature dependencies and these rate dependencies. In this study, we proposed a separate type viscoplastic-creep constitutive model which can describe stress strain curves, stress strain hysteresis loops and stress relaxation curves, with these temperature dependencies and these rate dependencies. We implemented the proposed model into finite element analysis code ABAQUS. We conducted tensile tests, tension-compression tests and tension-stress relaxation tests of Sn3.5Ag0.5Cu0.07Ni0.01Ge solder and determined material parameters of the proposed model from tensile test data and tension-compression test data. Then, we analyzed the conducted material tests using the proposed model and compared FE analysis results with experimental test data to examine the validity of the proposed model. It was confirmed that analytical results were in good agreements with the experimental ones.