Electrodeposition of Au-Sn Alloy from a Sulfite-Pyrophosphate Bath

Abstract

Au-Sn alloys ranging in Sn content from 15 to 46 atom% were electrodeposited from a newly developed sulfite-pyrophosphate bath (1 M sodium sulfite +0.2 M potassium pyrophosphate +0.05 M sodium tetrachloroaurate (III) +0.02 M stannous pyrophosphate (II) that did not contain cyanide. Codeposition behavior was investigated electrochemically. Electrodeposition was conducted under both galvanostatic and potentiostatic conditions. The composition, surface morphology, and phase structure of the electrodeposits were studied. Codeposition of gold and tin occurred at a potential between the potentials of gold and tin deposition. Tin content in the deposits increased with increasing current density. Au-Sn alloys with a composition near the eutectic composition (Au-29 atom%Sn) were obtained under both galvanostatic and potentiostatic conditions. The electrodeposited Au-Sn alloys consisted of single phase of ζ' phase (Au₅Sn phase) or of ζ' and δ phases (AuSn phase).