A Viscoplasticity Model for Solder Alloys

Demand for long-term reliability of electronic packaging has lead to a large number of studies on visco-plastic behavior of solder alloys. Various creep models for solder alloys have been proposed. They range from purely empirical to mechanism based models where dislocation motion and diffusion processes are taken into account. In this study, most commonly used creep models are compared with the test data and implemented in ABAQUS to compare their performance in cycling loading. Finally, a new creep model is proposed that combines best features of many models. It is also shown that, while two viscoplasticity models may describe the same material stress-strain rate curves equally well, however they may yield very different results when utilized for cycling loading. One interesting observation of this study is that the stress exponent, n, also depends on the grain size.