The use of insoluble anodes in acid sulphate copper electrodeposition solutions

The use of insoluble anodes in horizontal acid copper electroplating machines is becoming the industry standard. Despite this fact there appears to be little published work on the optimisation of the anode material for this application. Although titanium coated with iridium dioxide is widely used for its long lifetime under oxygen evolution conditions, it appears that no consideration has been given to the effect of this oxide on other electroplating parameters, for example the oxidation of additives, pulse plating etc. This paper reviews the materials that have been employed as insoluble anodes in acid sulphate electrolytes including those used for electrodeposition, electrowinning operations, and other electrochemical processes. It considers the factors that affect the materials performance under oxygen evolving conditions and collates values from the literature for the oxygen evolution potential and Tafel slopes for this reaction that have been obtained for various metal oxides. From these data, a set of criteria is established which an insoluble anode material should meet if it is to be successfully employed in an acid copper horizontal electroplating machine.