Thermal compression bonding for power IC attachment using pure Zn

Abstract

This study developed a low temperature solid-state direct bonding process for dissimilar metals. Experimental results show that Cu/Zn can be bonded successfully at 200°C under the loading of 10MPa for 30 minutes. The joints thus formed exhibited a shear strength up to 20MPa. If the thermal compression was performed at 300°C, the shear strength of bonded Cu/Zn and Cu/Ni/Zn joints exceeded 50MPa, especially for Cu/Zn joint, the strength even reached 70MPa. With respect to high temperature mechanical properties, due to the softening of Zn, the shear strength of all the joints decreased with a higher testing temperature. During aging at 250°C, the shear strength of Cu/Zn degraded drastically up to 500hr and after that the joint strength remained almost constant. The strength of Cu/Ni/Zn joints decreased gradually and maintained 30MPa for 500hr. The shear strength of both of the joints tended to be identical subjected to aging for 800hr. The deterioration of the joint strength during aging can be ascribed to the competitive growth between CuZn5 and Cu5Zn8 resulting in collapse and oxidation of CuZn5. The electroplated Ni and Ni5Zn21 thus formed can retard the excessive growth of Cu5Zn8 to some extent.