Effects of rare earth additions on the microstructural evolution and microhardness of Sn30Bi0.5Cu and Sn35BilAg solder alloys

摘要

The effects of trace amounts of rare earth (RE) additions on the melting property, microstructural evolution and microhardness of SnBiCu and SnBiAg solder alloys were studied by differential scanning calorimetric tester, Vickers hardness tester and microstructural observation. The results indicated that with the additions of RE, the melting property of the SnBiCu-xRE and SnBi Ag-xRE (x = 0, 0.25 and 0.5) solder alloys changed slightly. The microstructures of the β-Sn phase, Cu_6Sn_5 and Ag_3Sn intermetallic compounds (IMCs) in the solder matrices were refined due to the surface adsorption effect of RE. In addition, the microhardness of the solder alloys increased remarkably with the additions of RE because of the refined microstructures. Moreover, the formed Cu_6Sn_5 IMC layers in SnBiCu-xRE/Cu and SnBiAg-xRE/Cu solder joints were much thinner than those in the undoped-RE SnBiCu/ Cu and SnBiAg/Cu solder joints after reflowing and aging tests. This is because the RE decreased the interfacial energy of Cu_6Sn_5 IMC layer and then suppressed the Cu atoms to react with Sn atoms to form Cu_6Sn_5 IMC layer.