Effect of Cu and PdCu wire bonding on bond pad splash

Abstract

Cu wire bonding research has exploded exponentially in the past few years. Many studies have been carried out to understand the different behaviours of Cu wire and Au wire. One of the observations on Cu wire bonding is the excessive formation of aluminium (Al) splash on the bond pad due to a higher bond force. This leads to pad peeling and bond failure resulting in poor reliability performance of Cu and PdCu wire semiconductor devices. It is known that the Al splash is influenced by the front-end pad metal process and back-end wire bond process. Reported is the design of an experiment carried out to study a few factors that could influence the Al splash. The characterisation work is implemented to understand the bond pad structure using the focused ion beam (FIB) followed by a hardness test of bond pad metallisation. Then the mechanical cross-section is taken to measure the Al splash in three different directions. The results show that Al splash can be controlled by optimising the bond pad thickness, hardness and additive for reliable Cu and PdCu wire bonding.