The influence of Ag on the microstructure, thermal properties and mechanical behavior of Sn–25Sb-xAg high temperature lead-free solder

Abstract Adding Ag to Sn–25Sb solder to prepare Sn–25Sb-xAg (x = 0, 2.5, 3.0 and 3.5, x is the mass percentage) solder alloys. Using optical microscope, JSM-5610LV field emission scanning electron microscope, X-ray diffraction (XRD), differential scanning calorimetry (DSC), Vickers hardness tester and tensile testing machine to test the microstructure of the solder alloy, thermal performance and mechanical performance. The microstructure test results of the solder alloys show that Ag3 (Sn, Sb) intermetallic compounds (IMCs) are formed in the Sn–25Sb-xAg (x = 2.5, 3.0 and 3.5) alloys after Ag is added, and they are dispersed in β-Sn phase. Ag3 (Sn, Sb) IMCs are pinned at the grain boundary of β-Sn and SbSn phases. Moreover, it is also found that the addition of Ag makes the β-Sn and SbSn phases in the Sn–25Sb-xAg (x = 2.5, 3.0 and 3.5) solder alloy refined. DSC analysis results show that the melting point of Sn–25Sb-xAg (x = 0, 2.5, 3.0 and 3.5) solder alloy decreases slightly after adding Ag. Among them, the pasty range of Sn–25Sb-2.5Ag solder alloy is the smallest at 12.84 °C, followed by Sn–25Sb-3.5Ag at 14.81 °C. In the mechanical performance test of the solder alloy, it is found that the ultimate tensile strength (UTS) and elongation of the Sn–25Sb-xAg solder alloy increase with the increase of Ag addition. Sn–25Sb-3.5Ag solder alloy has the highest UTS and elongation, which are 69.25 MPa and 8.02% respectively. The increase is mainly through fine-grain strengthening and dispersion strengthening mechanisms.