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Electromigration and thermomigration behaviors of eutectic tin-lead solder joints were studied above 100 degC with the currents ranging from 1.6 A to 2.0 A. The local temperature of the chip was deducted according to temperature coefficient of resistance. Also, this temperature was inspected by a thermal infrared mapping technique. It is suggested that the heat accumulation within first-level solder interconnections was highly related to the current density. During the electromigration process, Pb migration was apparently visible because of its faster diffusivity. Meanwhile, voids were initiated at the entry location of the electron flow due to the current crowding effect. Numerical simulation also predicted a local current density of above 105 A/cm2 within the solder joint In the thermomigration process, the transport of Pb was detected owing to the thermal gradient across the solder joint. Voids also occurred at the contact window due to accelerated atomic diffusion. In addition, the effect of electromigration and thermomigration on the mechanical behavior of the solder joint was examined through shearing tests.