Abstract: The electromigration behavior of eutectic SnAg solder reaction couples was studied at various temperature (25 and 120℃ when the current density was held constant at 104 A/cm² or 5×10³ A/cm². Under the current density of 104 A/cm², scallop type Cu₆Sn₅ spalls and migrates towards the direction of electron flow at room ambient temperature (25℃), but transforms to layer type Cu₃Sn and leaves Kirkendall voids in it at high ambient temperature (120℃). Under the current density of 5×10³ A/cm² plus room ambient temperature, no obvious directional migration of metal atoms/ions is found. Instead, the thermal stress induced by mismatch of dissimilar materials causes the formation of superficial valley at both interfaces. However, when the ambient temperature increases to 120℃, the mobility of metal atoms/ions is enhanced, and then the grains rotate due to the anisotropic property of β-Sn.