| For environmental regulations and the development of highly integrated microelectronics requirements, the new lead-free solder electronic research and development has become one of the hot topics in recent years. The eutectic Sn-Zn based lead-free solder as Sn-8.8Zn, its melting point is 198 ℃, and is close to the temperature of eutectic SnPb solder, while Zn reserves on earth is rich, low prices, and the mechanical properties is well, Sn-Zn based solders are one of the most promising lead-free solder. But the wettability of Sn-Zn based lead-free solder is poor and easily oxidized, these shortcomings hinder its development and application.This paper summarizes a lot of basic research on Sn-Zn alloy system, taking the most promising Sn-8Zn-3Bi alloy for the study,using the micro-alloying elements Cu and other methods to improve the oxidation resistance of Sn-8Zn-3Bi alloy, and further improve the wetting properties and plastic of the alloy. Tn addition, the paper also studied the interfacial intermetallic compound growth behavior of Sn-8Zn-3Bi-xCu after aging, and explored the effect of Cu on the reliability of Sn-8Zn-3Bi alloy.Studies have shown that:when the content of Cu is 0.3% to 0.8%, little change in the melting point, but with the increasing of the Cu content, the solder melting point increase sharply, and alloy melting range upward trend; adding Cu elements can significantly improve the oxidation resistance, thereby reducing the surface tension of the solder alloy. So the solder wettability has been improved. Sn-8Zn-3Bi-0.5Cu alloy has the best wetting properties.Adding Cu element can reduces the intermetallic compound phase CuZn phase.Then the the shear strength of Sn-8Zn-3Bi alloy will improve, Sn-8Zn-3Bi-1.5Cu alloy has the best shear mechanical properties, shear strength at room temperature of the alloy reaches to 44MPa. Before aging, there are many dimples at the the fracture of Sn-8Zn-3Bi-xCu joints, the fracture mode is ductile fracture; After aging, IMC layer at the interface grow thick, with the IMC phase is brittle, the strength of welded joints decreased, and the fracture mode changes to brittle fracture.Sn-8Zn-3Bi-xCu solder alloys during aging at 120 ℃, the thickness of interfacial intermetallic compound (IMC) increases with the aging time, in the case of the same aging time, IMC thickness of SnZnBiCu solder alloy is less than Sn-8Zn-3Bi joints. It means that Cu inhibits the growth of IMC, because Cu depletion the free Zn, controls the diffusion of Zn to the interface, thereby indirectly inhibit the interfacial IMC grew up.After adding Cu element, the average corrosion rate showed a decreasing trend, and the corrosion potential of solders gradually increases with the increasing of Cu content, it indicates that the corrosion resistance improve. The corrosion products of Sn-8Zn-3Bi solder in 3.5% NaCl solution include ZnO, SnO, ZnCl2 and Zn5 (OH) 8Cl2H2O. However, with the increase of copper content Zn5(OH)8Cl2 H2O gradually disappear, CuO and CuCl2 appear in corrosion area. The new product makes corrosion corrosion zone intact and dense, served to protect the alloy being further corrosion. |
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