Abstract
This research investigated the effect of different shapes of solder on the microstructure and cracks evolution under the fast thermal shock. The experimental results firstly indicated that as the fast thermal shock cycles increased, the surface crack of three shape solders was generated, and then the surface crack widened and deepened. The number of surface cracks was more than other shapes for solder preform as the fast thermal shock cycles increased. the surface crack on the solder ball gradually expanded to the inside of the solder ball and the surface crack exhibited an insignificant change in length during the whole thermal shock test. As the increase of the fast thermal shock cycles, internal cracks of the solder ball and remelted solder preform gradually expanded and the microstructure of the three shapes of solders gradually refined. The expanded track of the internal crack was along the recrystallized grain boundaries and β-Sn grain boundaries. Meanwhile, the formation of cracks was relevant to the grain orientation and solder shape.
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