Under bump metallization development for high Sn solders

摘要

Several under bump metallisation (UBM) schemes using Ni or CuNi alloys as the solderable layer were investigated. Cr or Ti was used as the adhesion layer. The UBM pads of diferent compositions were sputter deposited on silicon wafers and patterned using standard photolithographic processes. Eutectic Sn-Pb solder balls were reflowed on top of the pads. The resulting interfacial microstructures were examined by SEM/EDX analysis of cross-sectioned samples. The integrity of the UBM/solder interface was characterized by micromechanical shear testing of flip chip test samples. Growth of intermetallic layers was found to be significantly slower in Ni and CuNi schemes compared to pure Cu. The joints on Ni and CuNi had also a better adhesion at the UBM/ solder interface, and in the shear tests the fracture occurred through the solder.