Transient Liquid Phase Die Attach for High-Temperature Silicon Carbide Power Devices

Recently, silicon carbide power devices have been receiving attention for applications above 300 °C. For high-temperature applications, the die attached for these devices has to withstand the maximum operating temperature. In this paper, a transient liquid phase (TLP) die attach technique was demonstrated for two binary alloy systems, Ag-In and Au-In, on Si₃N₄ substrates. A nearly void-free joint was developed using the Ag-In alloy. Two inter-metallic phases of Agln₂ and Ag₂ln, along with pure Ag were identified. After annealing at 400 °C, the silver appears to be more evenly spread to form a silver-rich Ag-In alloy with a Ag composition of 70-75 wt.%, even though a nearly pure silver phase is still found in the region where the silver was initially deposited on the Si₃N₄ substrate. For the Au-In system, there was no indication of bonding degradation at the interface after annealing at 400 °C for 100 h in air. Two inter-metallic phases, Auln and Auln₂, along with pure gold, were identified in the Au-In TLP joint. After annealing, the bonding interface became a more Au-rich Au-In alloy. The die attach pull strength, after thermal annealing, increased to approximately twice the minimum strength. The uniformity of the bonds improves and they become more homogeneous because the formation of intermetallic phases continues during thermal annealing.