In-situ observation of electromigration in thin film pattern of 63Sn-37Pb solder was performed using a scanning electron microscope system. The 63Sn-37Pb solder had the incubation stage of electromigration for edge movement when the current density of $6.0{ imes}10^{4}A/cm^2$ was applied the temperature between $90^{circ}C;and;110^{circ}C$. The major diffusion elements due to electromigration were Pb and Sn at temperatures of $90-110^{circ}C;and;25-50^{circ}C$, respectively, while no major diffusion of any element due to electromigration was detected when the test temperature was $70^{circ}C$. The reason was that both the elements of Sn and Pb were migrated simultaneously under such a stress condition. The existence of the incubation stage was observed due to Pb migration before Sn migration at $90-110^{circ}C$. Electromigration behavior of 63Sn-37Pb solder had an incubation time in common for edge drift and void nucleation, which seemed to be related the lifetime of flip chip solder bump. Diffusivity with $Z^*$(effective charges number) of Pb and Sn were strongly affect the electromigration-induced major diffusion element in SnPb solder by temperature, respectively.