Sustained immersion tin (Sn) deposition onto a copper (Cu) surface was achieved from choline chloride aqueous (ChCl-H2O) solution free of reducing agents. The electrode potentials of Cu and Sn were investigated by open-circuit potential (OCP) to reveal the driving force of Sn deposition process in ChCl-H2O solution. Thiourea reversed the electrode potentials of Cu and Sn, causing the replacement reaction between Sn2+ and Cu occurring. The replacement reaction is significantly influenced by the concentration of ChCl, SnCl2, and thiourea. The phenomenon of sustained Sn deposition was mainly facilitated by diffusing of Cu into the Sn coating and the reaction between Sn2+ and Cu+. Furthermore, Sn coating got in ChCl-H2O solution had fairly good performance such as solderability. (C) 2013 The Electrochemical Society. All rights reserved.