Effects of hydroquinone and gelatin on the electrodeposition of SnBi low temperature Pb-free solder

The effects of an antioxidant, hydroquinone (HQ) and a grain refining additive, gelatin, on the electroplating characteristics of SnBi alloys were investigated. Methane sulfonic acid (MSA) based plating baths with varying contents of additives are prepared and the electrochemical behavior of each bath was investigated. Cathodic polarization studies showed that the presence of HQ possesses insignificant effect on the deposition behavior. The combination of HQ and gelatin successfully reduces the deposition potential gap of both elements hence allows co-deposition of SnBi in this plating bath. The adhesion of deposits and the formation of spongy deposits are respectively improved and eliminated by the synergistic effects of these two additives. The electroplated SnBi deposits showed a decrease in Bi content and with increasing current density. Near eutectic Sn-60.75 wt.%Bi alloy was successfully deposited from the bath with both HQ and gelatin at a current density of 18 mA cm^-2.