UBM structures for lead free solder bumping using C4NP

This paper analyzes electroless Ni/immersion Au (ENIG), with and without Pd, as an alternative Under Bump Metallurgy (UBM) structure in combination with lead free solders. Wafers were fabricated with these UBM structures, lead-free solders applied with Controlled Collapse Chip Connection - New Process (C4NP), and chip level stressing performed to determine the robustness of this alternative stack-up. Shear strength of these structures following multiple reflows and thermal cycling is presented. The data in this paper is provided by the analytical laboratory at Fraunhofer Institute, IZM, Berlin, Germany. UBM formation was done at Fraunhofer IZM. Wafer bumping was done using the C4NP process at IBM Hudson Valley Research Park, NY.