Characterisation of insoluble anodes for acid copper electrodeposition

With the advent of horizontal electroplating equipment for PCB manufacture, the use of insoluble anodes in acid copper electrolytes has become critical to the viability of such machines. The impact of using insoluble anodes has been under-appreciated and the aim of this study was to characterise some of those that were commercially available. It was found that the chemical composition of the insoluble anodes could clearly be related to their morphology, electrochemical behaviour and their effect on brightener consumption. The brightener oxidation rates for insoluble anodes were always significantly higher than for traditional soluble copper anodes since they operate at higher potentials and therefore electrochemical reactions that cannot take place on copper can now happen. For example, not only is the direct oxidation of brightener at the anode possible but also the generation of highly oxidising species can occur. Reducing the anode area decreases brightener oxidation on certain anodes. Titanium coated with tridium dioxide was considered to be the best choice for an insoluble anode in an acid copper electrolyte. Platinum and ruthenium dioxide coated electrodes gave high brightener consumption rates with lead dioxide the greatest rate of all.