The authors demonstrate that the ultrasonic vibration in flip chip FC bonding results in the generation of dislocations, and the atomic diffusion can be activated more easily along the dislocation lines which perform the fast diffusion channels, thus the dislocation diffusion is probably more prominent than the body diffusion during ultrasonic bonding. To minimize the intermetallic compound layer, the effectiveness of a different bonding approach is confirmed. Furthermore, an experiment-based mode of ultrasonic energy conversion was found that the ratio of up interface to down interface in ultrasonic FC bonding was about 2.3:1.