Low Cost UBM for Lead Free Solder Bumping with C4NP

This paper analyzes electroless Ni/immersion Au (ENIG), with and without Pd, as an alternative UBM structure. Wafers were fabricated with these UBM structures, solder applied with C4NP, and chip level stressing performed to determine the robustness of these alternative stack-ups. Analysis of these structures following multiple reflows and thermal cycling is presented. In addition, the paper also reviews production cost analysis for various UBM stackups and solder bump processes, based on a specifically developed cost model. The ENIG UBM structures in combination with C4NP solder bumping provide a significant cost reduction over alternative structures.