Experimental study of workpiece-level variability in blind-via electroplating

The acid copper electroplating process for the manufacture of printed wire boards was studied by statistical techniques. The objectives of this study were to investigate the effects of process and product parameters on the workpiece-level uniformity during the acid copper plating of blind vias and to explore the minimization of the deposit thickness variation. The parameters studied were the concentrations of copper sulphate, sulphuric acid and additive, average current density (ACD), electrode separation (ES), the aspect ratio and the depth ratio of the via holes. Multifactor two-level factorial and the central composite rotatable five-level experiments were designed and conducted sequentially to generate statistical process models. Only the average current density and the electrode separation were found to be significant. A second-order model was then developed for the process in the proximity of the optimum region and verified experimentally to locate the optimum combinations of ACD and ES with respect to minimum thickness variability across the whole workpiece. Post-optimal analysis showed that the optimum solution was more sensitive to the electrode separation than the average current density