Due to a significant change in electro-migration behavior of eutectic SnPb at different temperatures, it is critical to understand it at the device temperature, i.e., 100°C. In the present study, the electromigration behavior of e-SnPb is investigated at 100°C and at different current densities, varying within the range of 5 × 10 3-5 × 10 4 A/cm 2. The test samples are prepared by reflowing solder into V grooves etched on (001) Si wafers. The electromigration is observed at the current densities higher than 1 × 10 4 A/cm 2. The dominant diffusing species at 100°C is found to be Pb. The threshold current density for electromigration to occur in e-SnPb comes out to be 5 × 10 3 A/cm 2. We also notice Pb rich phase coarsening, which becomes significant at high current densities. The results are compared to that in preannealed samples. The effects of the changes in microstructure on the electrical reliability are also discussed. The interface diffusion is dominant when the grain size is small. Subsequently, as the grain size increases, it is reduced to the order of the lattice diffusion, and therefore the electromigration is impeded. The critical product for e-SnPb solder is estimated to be 150 experimentally, and is also compared to the theoretically calculated value of 8. The reason for the discrepancy is discussed.