The effects of zincation process on aluminum bond pad surfaces for electroless nickel immersion gold (ENIG) deposition

This paper reports the number of experiments that were designed to study the effects of aluminum bond pad surfaces prior to electroless nickel immersion gold (ENIG). During this process, called as zincation, an oxide layer of aluminum will be replaced with a thin layer of zinc metal through the reduction and oxidation process. Zincation process is very important process to provide trustworthy interconnection of under bump metallurgy in advanced packaging. The study was carried out to determine the best conditions, through the various zincation exposure times and multiple zincation process to the surface topographic and morphology. In addition, for further understanding the effect of zincation process, the study includes of investigating aluminum dissolution rate and ball shear strength between eutectic Pb/Sn solder ball and under bump metallurgy (UBM) interfaces. Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), Focus Ion Beam (FIB) and Intellectest STORM series FA1500 were used as analytical tools in this study. The result suggests, the triple zincation process consistently produces a smooth surface of ENIG UBM and consequently a better shear strength with only minimum aluminum dissolved.