Experimental investigation and numerical modelling of the high cycle fatigue behaviour of a SnAgCu-solder alloy including temperature and mean stress effects

In automotive electronic applications, solder joints are subjected to various loading conditions such as thermomechanical and vibrational loads. Local ther-momechanical passive loads acting on the solder often take place within the time scale of minutes to hours leading to low strain rate creep deformation. In contrast, under vibrational loads, high strain rate elastic and plastic deformations within a much shorter time scale are expected to govern the cyclic aging of the solder joint. The present work is focused on the investigation of the deformation and degradation behavior of the SnAgCu solder alloy in the high strain rate regime. This is achieved by performing tensile tests under varying strain rates and temperatures. Additionally, High Cycle Fatigue (HCF) experiments are performed using a frequency of 40 Hz at different stress amplitudes, mean stress and temperature levels. The experimental data reveals the high cycle fatigue behavior and, in particular, the impact of temperature and mean stress effects on the specimens lifetime. In order to describe the high cycle fatigue of SnAgCu in Finite Elements (FE) simulations we employ a viscoplasticity material model. We discuss the model parameter and propose a gradual calibration procedure using the HCF test results for the description of the complex viscoplastic deformation behavior in heigh cycle fatigue regime. Finally, the proposed finite element approach is applied for numerical modelling of the observed Woehler lifetime curves. The simulation results show the capability of the current modelling to map the mean stress and temperature effects on the high cycle fatigue failure of SnAgCu.