Effect of Zn and in to the microstructure and mechanical properties of SAC305-Cu joints
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Date
2016-06
Authors
Aili Zuriatie Norizan
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Abstract
In this project, Sn-3.0Ag-0.5Cu (SAC305) solder alloyed with Indium and Zinc with a variety percent were developed. The effects of In and Zn addition on bulk microstructure and intermetallic compound (IMC) formed at solder joint, wetting behavior, strength of solder joint, hardness and IMC growth upon aging were evaluated. Five group of samples were prepared via casting process ; SAC305, SAC/1In, SAC/1In-0.5Zn, SAC/1In-1Zn and SAC/1In-1.5Zn. Solders were characterized in terms of their elemental composition via XRF, thermal behavior using DSC, bulk microstructure analysis via SEM equipped with EDX, wettability which includes spreading and wetting angle, and the wetting force and time from wettability test. Reflowed solder joints on Cu substrate were also tested in terms of their strength. In was added to reduce melting temperature and improved wettability. Results showed that wettability reduced with increasing amount of Zn but the solder joint strength and hardness were increased. Among the various percentages evaluated, microstructural analysis revealed that addition of 1.0% Zn not only refined the Ag3Sn and Cu6Sn5 particles, but also increased the eutectic area and promoted the formation of small (Cu,Ag)5Zn8 intermetallic compound (IMC). This 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 1.0 wt.%, the reaction phase grain, g-(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 seems to have significantly reduced. The observed decrease of Ag3Sn and Cu6Sn5 particles appears to cause a slight increase in Young's modulus and UTS of Zn modified solder.