Electrodeposition of tin coatings from ethylene glycol and propylene glycol electrolytes

Stable nonaqueous EG or PG electrolytes containing SnCl4·5H2O and boric acid have been developed for electrochemical plating of tin coatings at the rate of ~ 14 μm·h− 1 and current yield 91-93%. Owing to the absence of hydrogen evolution and whisker formation typical to aqueous-electrolytes tin deposition the current yield is increased. The tin coatings obtained from glycolic electrolytes consist of compactly packed grains connected in a dense network. IR spectroscopy showed that the dissolution of SnCl4·5H2O in glycol proceeds with the formation of bidentate complex ions SnCl2G(H2O)22 + (G = EG or PG) and weakening of the intermolecular interaction in the solvent. Cyclic voltammetry demonstrated that Sn(IV) reduction is a single cathodic process in EG and PG electrolytes and anodic tin oxidation proceeds in two stages via Sn(II) compounds formation and their further oxidation to Sn(IV). When adding boric acid to EG and PG electrolytes the formation of whiskers is completely inhibited providing 2-7 fold increase in the rate of coatings growth. It also neutralizes the differences in the maximal values of the deposition rate in both electrolytes and promotes the current yield increase.