High Speed Gold Plating: Anodic Bath Degradation and Search for Stable Low Polarization Anodes

Abstract

Two kinds of anodic bath degradation occur in high speed gold plating: the oxidation of cyanoaurate(I) to cyanoaurate(III) ion resulting in a decrease in plating current efficiency, and the oxidation of citrate ion causing a loss of buffer capacity. These oxidation reactions can be minimized by replacing the conventional platinum or platinum‐coated anode with a low polarization anode such as the so‐called “dimensionally stable anode (DSA®).” However, the ordinary DSA with a coating consisting of and is not sufficiently stable under the conditions of this application. This paper describes results of three studies: (i) analysis of laboratory data for the rate of Au(III) accumulation to develop a method for predicting the concentration of Au(III) and plating current efficiency under scaled‐up production conditions; (ii) analysis of the rate of degradation of citrate buffer capacity as a function of bath operating conditions; and (iii) an extensive search for a more stable low polarization anode, which led to the development of a coating consisting of and with barium as the additive.