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| Effects of Trace Element on Properties of Sn–3.5Ag–0.7Cu Lead-Free Solder |
| KOU Lulu, QU Wenqing, ZHUANG Hongshou |
| ( School of Mechanical Engineering and Automation, Beihang University, Beijing 100191, China ) |
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Abstract By adding the trace elements such as In, Ge and Ce to the Sn–3.5Ag–0.7Cu solder, the effects on the melting point, oxidation resistance, interfacial compound thickness and joint properties of the solder were investigated. The results show that the addition of trace In can effectively reduce the melting point of the solder (5–7℃), but it is not conducive to the oxidation resistance of the solder. The addition of trace Ge and Ce to SnAgCuIn can effectively improve the oxidation resistance of the solder. The addition of trace elements of In, Ge and Ce reduces the probability of the solder producing compounds at the Cu matrix interface and has little effect on the joint strength. The Sn–3.5Ag–0.7Cu–1In– 0.05Ge–0.03Ce solder has the best overall performance, with a solidus line reduction of 5.9℃ and a liquidus reduction of 3.9℃, meanwhile has good oxidation resistance. The interfacial compound thickness was reduced by 36.6% compared to the SnAgCu solder, and the compound thickness was reduced by 23.0% after 20 days of aging.
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2020, 
