Effects of germanium on the microstructural, mechanical and thermal properties of Sn-0.7Cu solder alloy

Abstract

In this paper, we investigated the influences of germanium (Ge) addition into Sn-0.7Cu (SC) solder alloy on the microstructure, thermal and mechanical properties by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), universal testing machine and Vickers hardness instrument, respectively. The experiment results showed that the addition of Ge into SC alloy could increase slightly the melting temperature and decrease the undercooling. The pasty range of SC-0.01Ge alloy was reduced by 0.1 °C, compared to that of SC alloy. However, the pasty range of alloy increased obviously when the Ge content in solder alloys was 0.05 or 0.10 wt%. The microstructure of SC-xGe solder alloys were consisted of β-Sn phase and Cu6Sn5 particle. No other intermetallic compounds (IMCs) with Ge content were observed in the solder matrix for SC solder alloys with various Ge content. The tensile properties of the SC-xGe solder alloys, including ultimate tensile strength and elongation, were enhanced gradually with the Ge content increased from 0 to 0.10 pct. This may be due to the presences of Ge and its role in refining microstructure and solid solution strengthening. After aging for 168 h, the ultimate tensile strengths of four solder alloys decreased, which was attributed to the coarsening of Cu6Sn5 particles. But the ductility increased remarkably. This phenomenon could be due to the formation of Sn-rich areas. A comparison of all solder alloys microhardness indicated that the microhardness increased with increasing Ge content. And after aging for 168 h, the microhardness values of four solder alloys decreased by 19%–26%.