Rate-dependent behavior of Sn3.8Ag0.7Cu solder over strain rates of 10−6 to 102 s−1

Solder joints are subjected to different loading conditions depending on the application environment. Desktop and server applications for example, involve thermomechanical fatigue loads at low-strain rates and the dominant mode of failure is creep fatigue. Mobile electronics applications on the other hand, are subject to dynamic stresses on the solder joint during impact. In our previous work, we developed a constitutive model based on mechanical test data at low strain rates. Experiments were carried out using double-lap shear test specimens of specially prepared solder assemblies over strain rate regimes of 10^-6 to 10^-3 s^-1 [D. Bhate et al.]. In this work, the previous experimental results are augmented with tests performed at higher strain rates (10^-3 to 10² s^-1) at room temperature. These experiments were performed using two different experimental setups: a MTS 810 uniaxial compression tester and a Split Hopkinson Pressure Bar (SHPB). The experimental results demonstrate a remarkably consistent relationship between the yield stress and the strain rate over eight decades of strain rate! We also fit the data to viscoplastic constitutive models popularly available in commercial finite element programs. Although the constitutive models are built using data at low strain rate regimes, the model is shown to be a reasonable fit to the experimental data over the entire strain rate regime under consideration (10^-6 to 10² s^-1). The differences in observed behavior under compression and tension are discussed, along with a microstructural study of the samples used in the tests.