Co-deposition of gold-tin alloys from a non-cyanide solution

Gold-30 at. % tin eutectic solder is used in optoelectronic applications, particularly to join InP devices to submounts. The solder can be applied using solder preforms, paste, electron-beam evaporation or electrodeposition. Co-deposition of the solder by electroplating offers advantages over the other methods, as a simple, cost-effective technique. In this study, pulsed current electrodeposits were formed using a solution based on ammonium citrate, KAuCl 4 , SnCl 2 .2H 2 O, sodium sulfite, L-ascorbic acid and ethylenediamine. The effects of changing the ethylenediamine and SnCl 2 .2H 2 O concentrations on the structure of the deposits were observed using scanning electron microscopy and X-ray diffraction. Increasing the ethylenediamine concentration in the Au/Sn plating solution results in increased solution stability, an increased deposition rate and a coarser grain structure. Decreasing the Sn content in the solution leads to a lower Sn content in the resulting deposit and a coarser structure. Increasing the average current density during plating affects the homogeneity of the structure in the electroplated deposit.