Flip chip interfacial behavior under thermal testing

In this study, the interfacial behavior of a flip chip structure under thermal testing was investigated using high sensitivity moire interferometry. The real-time moire interferometry was used to monitor and measure the deformation of the specimen during the test. Two kinds of specimen were prepared: (1) specimen without a crack and (2) specimen with horizontal crack at the silicon-epoxy interface. The results show that the maximum shear strain occurs at the silicon-epoxy interface. The shear strain variation increases significantly along the interface, with the maximum shear concentration occurring at the edge of the specimen. The creep effect is more dominant in the FR4-epoxy interface. In order to characterize the behavior of the interfacial crack, stress intensity factors K_I and K_II, and the strain energy release rate in the vicinity of the crack tip were used to conduct a qualitative study. It was observed that a sharp strain gradient occurred at the crack tip. The stress intensity factors K_I and K_II were dependent on temperature. The strain energy release rate with respect to temperature was dominated by K_I for the interfacial crack in the specimen.