The numerical analysis of strain behavior at the solder joint and interface in a flip chip package

The aim of this study was to investigate the strain behaviors at the joint interface of a flip chip package during thermal cycling testing using a numerical method. Because the underfill and solder bump material properties exhibit a large non-linearity in the higher temperature range, the linear elastic assumption may lose accuracy during numerical analysis. This study compared the differences in interfacial stress or strain between the linear and non-linear material property assumptions. The viscoplasticity of the solder bump and temperature-dependent underfill properties were assumed in the non-linear analysis. The numerical results showed that the solder bump failure mechanism was a combination of fatigue and creep actions dominated by plastic shear strain. The tensile stress due to shrinkage and hardening in the solder joints in the low thermal cycle temperature dwell period could result in ablation at the joint interface.