Reliability of Au bump flip chip packages with adhesive materials using four-point bending test

In this study, the bending fatigue reliability of Au bump flip chip packages with anisotropic conductive film (ACF) and non-conductive film (NCF) as adhesive materials was evaluated using a four-point bending test. Differential bending between the substrate and the Si chip was the dominant failure driver for the Au bump flip chip packages subjected to the bending test. The bending fatigue life of the NCF joint was longer than that of the ACF joint, regardless of the bending frequency. The main reason for the increased electrical resistance of the packages with ACF and NCF was the delamination between the adhesive material and the electroless Ni-immersion Au (ENIG) pad and between the Au bump and ENIG pad, respectively. For the ACF package, the bending stress was concentrated at the conductive particles between the Au bump and the ENIG pad during the bending fatigue test, resulting in a low bending fatigue strength. The delamination in the packages propagated with increasing bending fatigue cycles and frequency. The Au bump flip chip package with NCF was mechanically robust due to the higher initial strength and the larger bonding area between the Au bump and the ENIG pad.