Zincate treatment of aluminum bond pads on silicon wafers is a critical process step in electroless nickel bumping. Zincating activates the pads for the subsequent electroless nickel (EN) deposition and gives rise to good adhesion between the pad and the bump. It is recognized that the resultant zincate morphology has a direct impact on the quality of EN bumping. This work was aimed at understanding the role zincate solution chemistry plays in achieving good zincate morphologies. Influence of the zincating bath's basic ingredients and their concentrations on zincate morphology has been experimentally studied and the bath subsequently optimized with the Design of Experiment (DOE) approach. The information presented may serve as a reference to the zincating chemistry design and zincate process control for flip chip EN wafer bumping.