A fluxless bonding technology using indium-silver multilayer composites

A fluxless bonding process has been developed using indium-silver multilayer composites deposited on silicon and GaAs wafers in one high vacuum cycle to inhibit the oxidation of the bonding media. The in situ formation of AgIn₂ intermetallic outer layer protects the inner media from oxidation when exposed to atmosphere. The bonding process is performed at 180°C temperature in inert environment to prevent oxygen from getting into the specimens. High quality joints are produced as confirmed by a scanning acoustic microscope. The joints are very uniform with a thickness of 4 μm. Scanning electron microscopy (SEM) evaluations reveal that the joint is composed of indium matrix with embedded intermetallic grains. Neither flux nor scrubbing motion is used in the bonding process. The process should be valuable in manufacturing applications where the use of flux cannot be tolerated