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Local Melting and Formation Steps of Solder Bumps via Induction Heating Reflow

This work focuses on the nonuniform melting process and its theoretical explanation. After induction heating for 0.8 s, 1.0 s, 1.4 s and 2.0 s, different welding state can be obtained, which gives a proof of the melting process. The experiment results demonstrate that the skin effect of induction heating forms the great temperature gradient in the solder bump. The computation results give a theoretical support of the local melting phenomena. The surface melting of solder ball can affect the height and shape of the solder bumps, which is an important factor of the thermal reliability for BGA.