Evaluation of ultrasonic vibration energy for copper-to-copper bonding by flip-chip bonding technology

The ultrasonic vibration energy for Cu-Cu bonding by flip-chip bonding technology was evaluated in ambient air. Transmissibility of ultrasonic vibration is assumed to be different in bump structure with height or low stiffness. Therefore, we investigated the bonding strength of Cu bump with the different aspect ratio (bump height: 5 µm, 20 µm, and 40 µm). As a result, the Cu bumps with 20 µm height were properly bonded with sufficient bonding strength, compared with the others. In addition, there were no significant voids at Cu-Cu interface of well-bonded Cu bump.