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

• Published in: Journal of alloys and compounds Vol. 653; pp. 402 - 410
• Main Authors: El-Daly, A.A., El-Hosainy, H., Elmosalami, T.A., Desoky, W.M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.12.2015
• Subjects: ALLOYING; Alloys; ELASTICITY; Formations; Intermetallic compounds; Lead-free solders; Mechanical properties; Microstructure; MICROSTRUCTURES; Modulus of elasticity; SOLDERING ALLOYS; Solders; TENSILE STRENGTH; Tin; Ultimate tensile strength; YIELD STRENGTH; Mechanical properties; Microstructure; Lead-free solders
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2015.09.033

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 γ-(Cu, Ag)5Zn8 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, γ-(Cu, Ag)5Zn8, 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 γ-(Cu,Ag)5Zn8 formation were discussed and proposed. The addition of small amounts of Zn into Sn–2.0Ag–0.7Cu solder leads to formation of new types of flower-like or coarse dendrite γ-(Cu, Ag)5Zn8 intermetallic compounds, which controls the overall properties. The optimum percentage of Zn to enhance the inclusive properties was 1.5% Zn. [Display omitted] •Small amounts of Zn have been added into Sn–2.0Ag–0.7Cu (SAC207) solder.•Zn refined the Ag3Sn and Cu6Sn5 IMC particles of SAC207 solder.•Addition of Zn leads to formation of new (Cu,Ag)5Zn8 IMC particles.•The optimum amount of Zn to enhance the mechanical properties is 1.5 wt.%.