Determination of Parameters in Mixed-Mode Cohesive Zone Models for Modified Button Shear Tests by Particle Swarm Optimization

Delamination is a common failure mode and widely concerned in microelectronic package. In this paper, we focus on the underfill/Si interface in flip-chip package. To predict the risk of delamination, a modified button shear test with pre-delamination varying shearing height is taken. In finite element analysis, virtual crack closure technique is applied to calculate the critical strain energy release rate and phase angle. In addition, BK law is fitted to specify the mode-mix criterion of the interface. Finally, a corresponding cohesive zone model is built to fully define the initiation and propagation of interfacial delamination. The model parameters are determined by particle swarm optimization, a heuristic algorithm, that can automatically find the optimal solution and reduce repeated manual attempts.