Reliability of Au/Al Bonds and its Governing Factors

In order to clarify the reliability of Au wire bonds to Al pads, failure causes such as void formation and corrosion behavior of Au-Al intermetallics were investigated in accelerated tests. The effects of annealing environments, temperatures and bonding conditions on bond reliability were also examined. The molding resin has a great influence on the corrosion behavior, GC-MASS (gas chromatography) analyses of outgasses produced from the resin revealed that a major Br-containing species was methyl bromide (CH3, Br). The corrosion reaction between the intermetallics and bromides produced minute Au precipitates and amorphous Al oxides. This corrosion behavior caused significant fluctuations in electrical resistivity. Non-uniform formation of intermetallics at the bonds accelerated the corrosion behavior. It was confirmed that initial conditions at the bond interface affected bond failure. Activation processes of void-induced and corrosion-induced failures were compared in the respect of bond lifetime. The void formation was controlled by an interdiffusion process, whereas the corrosion behavior was controlled by a decomposition process of the resin. Au/Al bond failure could be governed by the intermetallic corrosion at higher temperatures and by void formation at lower temperatures.