Fatigue Cracking Growth of SAC305 Solder Ball under Rapid Thermal Shock

Abstract This research investigated the effects of rapid thermal shock cycle on the internal cracks, microstructure and internal cracks of SAC305 ball by applying non-destructive high energy-X-ray diffraction measurements. The experimental results firstly indicated that the surface cracks of the solder ball widen and deepen as the increase of the rapid thermal shock cycles. Secondly, the microstructure of SAC305 ball was observed that the grain orientation of the solder ball tends to be consistent, and the grains are gradually refined due to the recrystallization of the solder ball after rapid thermal shock. From the perspective of internal cracks, the total volume and surface area of internal cracks in the solder ball increase at first and then decrease as the growth of thermal shock cycles, as well as the volume and surface area of the largest internal crack. But the internal cracks are repaired by the atomic diffusion and recrystallization after 4500 cycles. Another important factor observed is that the occurrence of internal cracks is related to the grain orientation inside the solder ball. The spreading of internal cracks of the solder ball is confirmed along the grain boundary.