Chelating resin for removal of nickel impurities from gold electroplating solutions

Nickel impurities in pure gold deposits, because of the presence of nickel(II) ions in gold electroplating solutions, can cause adverse effects on the bonding of semiconductor chips. In order to remove the nickel impurities in gold electroplating solutions, the chelating resin, which is composed of styrene divinylbenzene copolymer as a backbone and also contains aminophosphonate ligands, has been studied for its nickel adsorption properties from gold electroplating solutions. Batch shaking adsorption experiments were performed, and the results showed that the resin could successfully purge gold electroplating solutions of nickel contamination, without a great influence on the concentration of gold in the form of Au(CN)2-. Approximately 98% of the nickel and a few percent of gold were adsorbed by the resin. The Ni adsorption percentage does not vary with the operational gold concentration. A small increment in the Ni adsorption percentage was observed when the pH of the gold electroplating solutions was increased from 6 to 8, since more active groups in the resin were deprotonated at higher pH. Because of the independence of Ni adsorption from operational gold concentrations and the independence of gold adsorption from pH, active sites for Ni adsorption differing from those for Au adsorption was proposed. The XPS data revealed that -PO32- in the aminophosphonate ligands in the resin participated into the chelation of Ni; however, -NH- in the aminophosphonate ligands in the resin could be protonated. The Ni adsorption on the resin in a gold electroplating solution obeys pseudo-second-order kinetics rather than pseudo-first-order kinetics. Supporting by the kinetics results, the Sips (Langmuir-Freundlich) isotherm is suggested for a more adequate description of the Ni adsorption on the resin in a gold electroplating solution, although the experimental data could also satisfactorily fit to the Langmuir isotherm and the Freundlich isotherm.