Investigation of various pad structure influence for copper wire bondability

As an alternative bonding interconnect material to gold wire, copper wire technology is getting more attention in assembly processes for its excellent electrical and thermal performance. Copper wire bonding meets lots of challenges because of its free air ball hardness, such as Al extrusion, pad crack/damage, reliability and low yield issue. General speaking, there are two ways to improve the issue for copper wire bonding, one is wire properties improvement, such as softer and high reliability wire research; another one is copper friendly pad design and make bond pads suits to copper wire very well. In order to design the bond pad for copper, we should figure out which are important factors in pad to copper first. The purpose of this paper is to study the effects of various bond pad structures on copper wire bonding. In our study, not only the pad total thickness but also the pad structure was considered. As a result, pad total thickness, final Al thickness and VIA design play an important role in bonding. Theoretical analysis and theoretical prediction of a state-of-art pad structures for copper wire bonding application was presented.