Workpieces, such as semiconductor wafers, are electroplated with improved thickness uniformity by providing a diffuser member intermediate the cathode and anode of a fountain-type electroplating apparatus. The diffuser or member has a pattern of openings specifically designed to prevent channeling and/or selective directing of electrolyte towards the workpiece. In one embodiment, the diffuser member comprises a spiral-shaped pattern of openings originating at the center of the diffuser member and extending to the periphery thereof.