Precipitation processes and phase interface structure of Ag3Sn during solidification of SnAg3Cu0.5/Cu solder joint

Abstract

Ag-containing solder alloys are widely used in high-end electronic soldering processes to improve the reliability of electronic components. This study investigates the precipitation process of Ag3Sn during solidification. The precipitation of β-Sn, Ag3Sn, and η′-Cu6Sn5 in SnAg3Cu0.5/Cu solder joints during solidification was examined using Thermo-Calc (2020a). Furthermore, the crystallographic structure of Ag3Sn/β-Sn and Ag3Sn/η′-Cu6Sn5 was analyzed by transmission electron microscopy. The results showed that, below 217.1 °C, the η-Cu6Sn5 phase begins to precipitate: β-Sn + Ag3Sn+η-Cu6Sn5. At the Ag3Sn/β-Sn interface, the angle between (1‾21‾)Ag3Sn and (101‾)β−Sn planes was measured to be 176.4°, with a mismatch of 26.47 %. The Ag3Sn/Cu6Sn5 interface exhibited a specific crystallographic relationship of [223]Ag3Sn// [1‾12]Cu6Sn5, with an angle between (212‾)Ag3Sn and [402]Cu6Sn5 planes of 101.5°. The growth patterns of β-Sn, Ag3Sn, and Cu6Sn5 phases during isothermal aging were further investigated according to their interface orientation relationship, providing a basis for improving the stability of the soldering process.