In flip chip (FC), thermosonic FC method had shown more advantages in term of bonding temperature, time and force than mass reflow and thermocompression FC. In this paper, the child die was fused with the mother die (with Cu stud bumps) by using thermosonic FC bonding. Ultrasonic power and bonding time have been studied to evaluate the die strength together with cross section and Hisomet images. Chip to chip interconnection managed to form good joints and die shear strength is 864.9 gf under optimized thermosonic FC. Medium ultrasonic power and high bonding time are beneficial for increased the die shear strength. Therefore, thermosonic FC bonding method with Cu stud bump are suitable for low count input/output (I/O) device.
