Solder fatigue of Wafer Level package assemblies. Comparison with flip chip BGA’S

In this paper the solder fatigue of WLCSP (wafer level chip scale packages) assemblies is studied and a comparison with flip chip BGA is made. Previous works have already shown that for BGA, the most critical parameters are size, thickness, and underfill. We have evaluated both by thermal cycling and by simulations the effect of thickness and underfill in the WLCSP's case. WLCSP devices with a size of 13mm2 were stressed up to 1500 cycles to emphasize the BGA like failures and evaluate the behavior of this new technology. We have demonstrated that the same failure mechanisms occur in BGA and in WLCSP. We also highlight the criticality of the WLCSP regarding industrial assembly process on board.