Iron-42 wt pct nickel lead frame with palladium electroplated multi-layer for semiconductor packages

摘要

There has been considerable interest in the use of palladium for lead frame plating material for its various advantages in the semiconductor assembly process. Its usage has been confined, however, to the copper alloy lead frame as a two-layerstructure: palladium over a nickel layer over copper alloy, because of severe corrosion in wet atmospheres. In this study, various layer structures with copper, nickel and palladium were electroplated on an iron-42 wt pct nickel lead frame, then packagedin the assembly line. The corrosion behavior of each layer structure was studied by using the salt atmosphere test and the electrochemical impedance method. The lead frame was plasticmolded to an SOJ-type package; the surface states after trimming andforming of the lead were investigated by optical microscope. The experimental results indicated that the additional layer formation of palladium and copper between the lead frame and the nickel intermediate layer greatly increased the corrosionresistance, and was well accounted for in terms of electrode kinetics of a metal-metal couple composite system. Additionally, it was found that the higher corrosion resistance supported good assembly properties solderability and wire bondability.