Study of galvanized Sn-finished Ag surface

Typically, Sn cannot be finished on Ni and Ag surfaces via the immersion process. In this work, through galvanic reaction, immersion Sn finish was processed on an immersion Ag finish coexisting with a Ni surface. Herein, the detailed mechanism of the reduction of Sn²⁺ ions on the immersion Ag surface through galvanic reaction is reported. Through transmission electron microscopy and X-ray diffraction analysis, the uncommon Ag₄Sn phase, instead of the common Ag₃Sn phase, was confirmed to form during the Sn immersion of the Ag immersion layer. The Ag₄Sn phase was found to form between the Ag grains in the immersion Sn layer. The mixed Ag/Ag₄Sn structure in the immersion Sn layer can be explained by the galvanic reaction. The preferred formation of the Ag₄Sn during the Sn immersion of the Ag immersion layer is discussed from the viewpoint of thermodynamics. The changes in the Gibbs free energy of the formation of the Ag₃Sn and Ag₄Sn phases were calculated as − 3.67 and − 8.89 kJ/mol, respectively. This confirms that the Ag₄Sn phase is the favorable phase formed in the immersion Sn over the immersion Ag layer.