Fatigue Crack Growth on the Interface of Copper and Epoxy Molding Compound under Mixed-Mode Loading

The fatigue growth of a crack on the interface of Cu and liquid epoxy molding compound (EMC) was investigated by using a novel mixed-mode bending test setup. In this setup, the mixed-mode loading is achieved by using two voice-coil motors for applying unequal end-loads on a split-beam specimen. The specimen consists of two oxygen-free Cu strips bonded by using EMC. By using an analytical formula based on the beam-on-elastic-foundation theory and compliance method, the crack length and the strain energy release rate are calculated from the crack-mouth opening displacement and the applied end forces. A real-time OS controller CompactRIO is used for the system control and data analysis. The control program calculates the crack length and phase angle for adjusting the applied force to maintain the prescribed mode mixity throughout the fatigue experiment. By post-processing the experiment results, the subcritical fatigue growth responses of the Cu-EMC interface were obtained. It was found that the steady-state cyclic fatigue delamination growth rate displays a power-law dependence on the applied strain energy release rate range. The measured fatigue growth characteristics may be further incorporate with the fracture mechanics analysis to predict the delamination growth on the interface of interest in a realistic structure.