Electrochemical gold deposition from non-toxic electrolytes

An additive free electrolyte containing aurochloric acid, sodium sulphite and sodium thiosulphate has been used to electrodeposit gold. The electrolyte is stable at near-neutral conditions and was stable on storage after formulation. Laboratory scale experiments showed that the electrolyte was compatible with positive resists. UV-Vis spectroscopy and cyclic voltammetry indicate that gold is discharged from a thiosulphate ligand. Industrial scale piloting experiments showed that high quality gold could be deposited from the electrolyte and the deposition process was stable up to a few weeks. Gold precipitation was observed when the used electrolyte was stored for a long period; this suggests that a product formed during the deposition process, was responsible for gold precipitation.