Lead-Free Diffusion Bonding for High Temperature Using ZnAl Eutectic Alloy

Diffusion bonding with ZnAl represents a lead-free method suitable for power devices that must operate at high temperatures. However, traditional approaches require high pressure that could potentially damage semiconductor chips. In this study, we have developed a diffusion bonding process that achieves adequate bonding strength under lower pressure. This was accomplished by heat-treating ZnAl solder to obtain a fine crystalline structure after processing it into thinner plates. Additionally, we discovered that decreasing the pressing rate reduces the yield stress of ZnAl, facilitating perfect contact between the ZnAl solder and the adherends at room temperature with lower pressure. This results in enhanced bonding strength between ZnAl and Cu plates. Moreover, mechanical fatigue tests conducted on micro fatigue specimens three times revealed that the ZnAl solder did not develop cracks after 10,000 cycles.