The compact and high-performance Lead-free BGA device has become the modern highly integrated device which is required in electronics assembly. In the course of service, they experience thermal cycling and become invalid. The failure mode of BGA device, which has undergone the thermal cycling, is investigated by scanning electronic microscope, electron back scattered diffraction and micro Vickers hardness tester. It concludes that the mismatch of the coefficient of thermal expansion between materials provides the driving force for the initiation and propagation of cracks which are along the grain boundaries of the local recrystallization weakened in the solder ball, and eventually the fracture of solder joint occurs.

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