Evolution of Ag3Sn compounds and microhardness of Sn3.5Ag0.5Cu nano-composite solders during different cooling rate and aging

This paper presents the microstructure and Vickers microhardness of Sn3.5Ag0.5Cu solder doped with trace amounts of TiO2 nanopowders, obtained with different cooling rate and aging conditions. The experiment results that the coupling effect by cooling rate and TiO2 nanopowders additions significantly affected primary β-Sn phase, Ag3Sn grain size and spacing of the Ag3Sn phase, as well as the morphology of Ag3Sn. Ag3Sn was relatively spherical at the water-cooling rate and had a needle-like morphology at the air-cooling rate. However, the Ag3Sn IMC not obviously roughed after aging time at 125 °C for 7 days. Due to both nano-Ag3Sn IMC and uniform microstructure of the nano-composite solders, the Vickers microhardness improved, in good agreement with the prediction of the classic theory of dispersion strengthening. It appears that adding trace TiO2 nanopowders are an efficient way to develop novel high-performance solders.