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Ternary mixture of choline chloride, ethylene glycol and urea (molar ratio 1 : 1 : 1) has been proposed as non-aqueous media for the electrochemical plating in galvanostatic mode of tinsilver alloy coatings. The conditions for the deposition of an alloy with a composition and melting temperature close to the eutectic, which is in demand for microassembly in the electronic industry, have been determined. The significant features on the simultaneous tin(II) and silver(I) reduction and the alloy formation are revealed. It has been determined that silver(I) is reduced from the solution both electrochemically and by the galvanic displacement with freshly deposited tin. The presence of silver on the surface of the coatings initiates underpotential tin(II) reduction. The interactions of components in the non-aqueous electrolyte have been studied for the first time by IR spectroscopy, and the formation of coordination compounds between tin(II) and silver(I) ions and solvent molecules has been revealed.

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The optimal conditions for the electrochemical synthesis in the sulfate electrolyte of low-melting Sn–Ag alloy coatings used in the assembly of electronic equipment containing 7.1–8.3 at. % of silver and with total current yield of metals equal to 88.8–87.0 % are determined. It is established that electrochemical reduction of Sn(II) and Ag(I) on the surface of the alloy is accompanied by the process of contact displacement of Ag(I) with tin included into the coating. The process of contact displacement is intensified with the electrolyte temperature growth and leads to the increase in silver content in the alloy, to the appearance of dendrites on the surface of the coating due to its passivation.