Fabrication of 0.95Sn-0.05Au solder micro-bumps for flip-chip bonding

This letter describes the successful fabrication of a 0.95Sn-0.05Au solder micro-bump on a compound semiconductor wafer by reflowing of multi-layer me tal film. Since the inherent interdiffusion in Au-Sn phases results in the alloying of multi-layer films, the composition of mirco-bump is wt ll contr olled by the thickness of constituent metal films. The micro-bumps melt at about 220 degreesC, which is close to the lowest eutectic temperature in a Au-Sn system. Solder bonding using 0.95Sn-0.05Au micro-bump is a very usefu l technique for the flip-chip bonding of compound semiconductor devices.