Feasibility of Copper-Base Leadframe Preplated with a Cu-Sn Alloy instead of Ni

Abstract

A preplated frame (PPF) consisting of Au/Pd/Cu-Sn/Cu substrate, i.e., preplated with a Cu-Sn alloy instead of Ni commercially used, was fabricated by electroplating and then the feasibility of the frame as an alternative PPF was investigated. The wettability of the Cu-Sn alloy was better than that of Ni, resulting in excellent contact with the substrate and smoother surface on the upper Au/Pd protective layer. By XPS analyses, it was confirmed that Cu atoms in the Cu-Sn alloy layer did not diffuse through the thin protective layer to the surface at temperatures used in IC assembly. The wire pull-strength and solderability of the Cu-Sn alloy PPF were almost equivalent to those of the Ni PPF. However, the former showed much better corrosion resistance than the latter.