Solder joint reliability modeling of 96.5Sn/3.5Ag flip chip bumps under temperature cycling condition

In this paper, the thermo-mechanical analysis of eutectic 96.5Sn/3.5Ag flip chip solder joints subjected to temperature cycling was investigated using finite element analysis (FEA). The elastic-plastic-creep constitutive model for the 96.5Sn/3.5Ag solder alloy was implemented in the FEA model to describe the deformation behavior of flip chip solder joints in 3D-slice and 3D-octant models. Experimental solder joint fatigue data was obtained by subjecting flip chip on board (FCOB) assemblies to -40°C/+125°C temperature cycling test. A two-parameter Weibull analysis was used to determine the mean time to failure (MTTF) of FCOB assemblies. Scanning electron microscopy (SEM) examination was performed on the solder joints to determine the crack path and failure mode. From the predicted N_f, the 3D-slice model was preferred to the 3D-octant model due to better computational efficiency. It was found that the predicted fatigue life in the 3D-slice model using volume averaging method has a better agreement with the experimental results as compared to the fatigue life generated by nodal point solution.