Application of Electroless Fe−42Ni(P) Film for Under-bump Metallization on Solder Joint

Because Fe has a more negative standard reduction potential than Ni, the simultaneous electroless deposition of Fe and Ni is difficult. In this study, Fe–42Ni(P) electroless deposit was prepared by using disodium ethylene diamine tetraacetate (ETDA-2Na) as complexing agent to reduce the difference in the electrode potential between Ni2+ and Fe2+. The solderability and the interfacial reaction between Fe−42Ni(P) alloy and Sn were investigated. It was found that the electroless Fe−42Ni(P) alloy has excellent wettability with Sn. Moreover, the interfacial reaction rate between Fe−42Ni(P) and Sn is very slow. These results suggest that Fe–42Ni(P) alloy may become an attractive under-bump metallization (UBM).