Microstructural modifications and properties of low-Ag-content Sn-Ag-Cu solder joints induced by Zn alloying

[摘要] The effects of Zn addition on microstructure development and tensile properties of Sn-2.0Ag-0.7Cu (SAC207) lead-free solders were investigated. Microstructural analysis reveal that 1.5 wt.% Zn addition not only refined the Ag3Sn and Cu6Sn5 particles, but also increased the eutectic area and promoted the formation of small gamma-(Cu, Ag)(5)Zn-8 intermetallic compound (IMC), which in turn increased the yield strength (YS), ultimate tensile strength (UTS) and Young's modulus, but the ductility decreased. With increasing Zn content up to 3.0 wt.%, the reaction phase grain, gamma-(Cu, Ag)(5)Zn-8, becomes larger and its morphology changes from a strip-like shape into flower-like or dendritic shape. Moreover, the Ag3Sn and Cu6Sn5 particles are significantly diminished. The observed decrease of Ag3Sn and Cu6Sn5 particles appears to cause a slight increase in Young's modulus, YS and UTS of Zn modified solder. Detailed mechanisms of Ag3Sn and Cu6Sn5 suppression and gamma-(Cu, Ag)(5)Zn-8 formation were discussed and proposed. (C) 2015 Elsevier B.V. All rights reserved.

[发布日期] 2015-12-25

[关键词] Lead-free solders;Microstructure;Mechanical properties