中国有色金属学报(英文版)
Transactions of Nonferrous Metals Society of China
Vol. 31 No. 5 May 2021 |
(1. Department of Industrial Engineering, Faculty of Engineering, Rajamangala University of Technology Srivijaya, 90000 Songkhla, Thailand;
2. Division of Physical Science, Faculty of Science, Prince of Songkla University, 90112 Hat Yai, Thailand;
3. Center of Excellence in Metal and Materials Engineering, Faculty of Engineering, Prince of Songkla University, 90112 Hat Yai, Thailand)
Abstract:This research sought to improve the properties of SAC305 solder joints by the addition of 1 and 2 wt.% Bi. The effects of bismuth doping on the microstructure, thermal properties, and mechanical performance of the SAC305-xBi/Cu solder joints were investigated. Bi-doping modified the microstructure of the solder joints by refining the primary β-Sn and eutectic phases. Bi-doping below 2 wt.% dissolved in the β-Sn matrix and formed a solid solution, whereas Bi additions equal to or greater than 2 wt.% formed Bi precipitates in the β-Sn matrix. Solid solution strengthening and precipitation strengthening mechanisms in the β-Sn matrix increased the ultimate tensile strength and microhardness of the alloy from 35.7 MPa and 12.6 HV to 55.3 MPa and 20.8 HV, respectively, but elongation decreased from 24.6% to 16.1%. The fracture surface of a solder joint containing 2 wt.% Bi was typical of a brittle failure rather than a ductile failure. The interfacial layer of all solder joints comprised two parallel IMC layers: a layer of Cu6Sn5 and a layer of Cu3Sn. The interfacial layer was thinner and the shear strength was greater in SAC305-xBi/Cu joints than in SAC305/Cu solder joints. Therefore, small addition of Bi refined microstructure, reduced melting temperature and improved the mechanical performance of SAC305/Cu solder joints.
Key words: Sn-3.0Ag-0.5Cu solder alloy; interfacial behavior; mechanical performance; strengthening effect; thermal properties