Ag–(In–Bi) solid-state bonding

Abstract

Solid-state diffusion bonding is a metallurgical technique to bond interfaces. We identify Ag–(In–Bi) as a material system that can be bonded at 65 °C. This work aims to demonstrate low-temperature bonding and to determine if Bi precipitates form through a solid-state diffusion mechanism. Bonds were formed at 65 °C utilizing a 78.5-at% In–Bi eutectic foil and a 95-at% In–Bi foil, with bonding times 1, 2, 4, and 8 days. These foils were sandwiched between two pieces of Ag, forming an Ag/In–Bi foil/Ag bonding stack. Thanks to bridging of AgIn2, a temperature stability of ~166 °C is possible. Using a bonding material with higher In content (in our case 95 at% In) than the eutectic did not reduce the growth rate of AgIn2. The BiIn2 left over from the reaction was surrounded by the growth of AgIn2. The solid-state bonding results presented in this paper indicate that dissolution is a necessary condition for the unique Bi precipitates previously seen in the Ag–(In–Bi) solid–liquid system.