Development of the Damage State Variable for a Unified Creep Plasticity Damage Constitutive Model of the 95.5Sn–3.9Ag–0.6Cu Lead-Free Solder

Abstract

A unified creep plasticity damage (UCPD) constitutive model was developed to predict the fatigue of 95.5Sn–3.9Ag–0.6Cu solder joints. Compression, stress-strain and creep properties were generated in previous studies of this solder. Crack damage was reflected in a single state variable, Dω, in the model. Isothermal fatigue tests were performed at 25°C, 100°C, and 160°C using a double-lap shear test specimen. A new approach to fitting the revised damage model is proposed based on finite element analysis (FEA) simulation of the load decay of the fatigued solder material. Accurate predictions required that those parameters be temperature dependent. The UCPD constitutive model was successfully implemented as a subroutine in the commercial finite element code ANSYS ®. Consistent predictions were obtained as demonstrated by a comparison of results generated from FEA simulation of the test assembly against analogous experimental results.