Composition control of co-electroplating Au–Sn deposits using experimental strategies

Abstract

The optimal electroplating parameters for a pulse-current co-electroplating system of Au–Sn deposits in a non-cyanide electrolyte were investigated using experimental strategies, including fractional factorial design (FFD) and central composite design (CCD) coupled with the response surface methodology. pH value, ethylene diamine tetraacetic acid (EDTA) concentration, catechol concentration and metallic ions molar ratio (i.e., [Au]/[Sn]) were identified as the key factors affecting the composition of Au–Sn deposits in the FFD study. A reliable model between the response variable and the key factors of pH value, EDTA concentration and catechol concentration was established for the composition control of Au–Sn alloys in the CCD study. The standard deviation of the response variable (tin content) was set at the minimum level to determine the optimal co-electroplating parameters for the predicted composition value of Au–Sn deposits. Pair T test was conducted to validate both predicted and observed composition values under the optimal electroplating parameters, and the composition of Au–Sn deposits can be precisely controlled based on the established model. Scanning electron microscope observation and X-ray diffractometer analysis revealed that the morphology and crystalline of the Au–Sn deposits were composition-dependent.