Influence of nitrogen and forming gas towards palladium coated copper wire

Copper (Cu) wire development started in the early 1980's as the cost for semiconductor manufacturing has become competitive and challenging with the increase of gold price. The lessons learned along the research and studies carried out, helped the industry to understand the subtleties and facts about Cu wire bonding process. The most common and important facts about Cu wire bonding is its sensitivity towards oxidation. Studies showed that oxidized copper ball can contribute towards bond pad damages and further induced quality issues. In addition, bond pad galvanic corrosion with ball bond and CuAl diffusion is also the contributor towards the degradation of Cu wire quality. Kaimori et. al.[1] did research by electroplating different material over the Cu wire. The studies showed that Pd-plated Cu wire doesn't give problems when forming the free air ball. This type of wire is named as “hybrid Bonding Wire”. The discovery of this new metallurgy can prevent the oxidation as well as slowing down the intermetallic diffusion during reliability stress test, to improve 2nd bond process during wire bonding and enhance stitch strength. This paper will focus on the fundamental study of the free air ball (FAB) formation of Pd coated Cu wire under the atmosphere of N2 versus forming gas. FAB impact is measured via ball size with different spark current and time. CuPd processibility under different gas environment will be accessed and assembly level reliability will be checked.