In order to study the electromigration characteristics of the butting solder joint in microelectronic packaging devices, this paper designs a Cu/Solder/Cu electromigration experiment to observe the change of the microstructure of the interface by scanning electron microscopy (SEM). It is found that the evolvement of the IMC at anode follows a parabolic growth rule under the condition of electric current density for 1.0×104A/cm2, and test temperature at 25°C. It is interesting to note that the circular void is gradually expanded into a strip crack, resulting in the failure of the interface. The growth mechanism of Cu3Sn diffusion flux is analyzed at the cathode and the anode before the full-IMC joint. Surprisingly, nucleation and condensation of small vacancies was found in the Cu3Sn/Cu6Sn5 interlayer at the anode. Finally, the experimental phenomena was explained by employing there-dimensional simulation with the distribution of current density and Joule heating in the solder joint.