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.
|Number of pages||11|
|Journal||Journal of Materials Science: Materials in Electronics|
|State||Published - Jul 2021|