Determination of the 450℃ Isothermal Section of the Ag-Cu-Sn Ternary System in the Ag-Cu-Rich Region

Keywords: Ag-Cu-Sn ternary diffusion couple phase diagram, electron probe. Ag-Cu-Sn mid-temperature solder alloys, with their excellent resistance to temperature, creep, and corrosion, are widely used in the field of electronic packaging. However, due to their inherent brittleness, these alloys are difficult to fabricate, resulting in low yield rates. Therefore, establishing the Ag-Cu-Sn phase diagram is of great significance for guiding the design and preparation of Ag-Cu-Sn solder alloys. In this study, we utilized the principle of local equilibrium in ternary diffusion couples and employed scanning electron microscopy and electron probe microanalysis to determine the phase equilibrium relationships and compositions of the Ag-Cu-Sn ternary diffusion couple at 450℃, thereby constructing the phase diagram.

　　Keywords: Ag-Cu-Sn ternary diffusion couple phase diagram, electron probe

　　Ag-Cu-Sn medium-temperature solder, owing to its excellent resistance to temperature, creep, and corrosion, is widely used in the field of electronic packaging. However, due to its inherent brittleness, it is difficult to fabricate, resulting in a low yield rate. Therefore, establishing the Ag-Cu-Sn phase diagram plays a crucial role in guiding the design and fabrication of Ag-Cu-Sn solder.

　　This paper utilizes the principle of local equilibrium in ternary diffusion couples and employs scanning electron microscopy and electron probe microanalysis to determine the phase equilibrium relationships and compositions of Ag-Cu-Sn ternary diffusion couples at 450℃. Based on these findings, a ternary isothermal section diagram for the Ag-Cu-rich region of the Ag-Cu-Sn system at 450℃ has been established.

　　The research results indicate that the Ag-Cu-Sn ternary diffusion couple contains four binary compounds: Cu41Sn11, Cu3Sn, Ag5Sn, and Ag3Sn. No ternary compounds were detected. Moreover, the solid solubility of Cu in Ag5Sn and of Ag in Cu41Sn11 and Cu3Sn are 4.89 at%, 4.63 at%, and 7.89 at%, respectively. The study also found that, at 450℃, the Ag-Cu-Sn ternary system exhibits three triphasic regions within the Ag-Cu-rich region: Ag + Cu41Sn11 + Cu, Ag + Cu41Sn11 + Cu3Sn, and Ag5Sn + Ag + Cu3Sn.

　　The determination of the ternary isothermal section for the Ag-Cu-Sn system using the diffusion couple technique helps to assess the reliability of existing results and to incorporate new data into the Ag-Cu-Sn phase equilibrium.

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