Electromigration (EM) is a major reliability issue in VLSI. Many physical processes are involved simultaneously in an EM process, namely atom migration due to electron wind force, thermal migration due to temperature gradient, stress migration due to stress gradient, and surface migration (just when free surface is available) due to surface tension. In this work, the intrinsic EM damages of Al and Cu, that is without the effect from the surrounding materials, was investigated and compared based on the finite element analysis (FEA). The FEA results show that, in the intrinsic Al EM damage, electron wind force induced flux divergence is always the main cause of void growth; however, in the intrinsic Cu EM damage, dominant flux divergence varies with time, with the final dominant flux divergence due to electron wind force. It is also found that current density and temperature gradient are the most important factors affecting flux divergence. These simulation predictions agree with experimental observation and theoretical analysis.