Study On Properties Of Sn-based Lead-free Solders For Soldering Al And Cu

It has important engineering application value to achieve soldering aluminum and copper dissimilar metal connections at low temperature,especially in the refrigerator and other industries.This paper based on the theory of "[cluster](glue atom)",combined with phase diagram,mixed enthalpy and interaction principle to design and optimize lead-free solder alloy used in low temperature soldering of aluminum and copper.In this paper,four groups of 12 kinds of brazing elements were designed,and their microstructure,melting and wetting properties,microstructure and shear strength were investigated.The main conclusions were as follows:1.By analyzing the quaternary solder composition designed by Sn-Zn eutectic and Sn-Bi eutectic clusters,the addition of the fourth element(A)in the solders can refine the matrix structure of the brazing alloy obviously,especially the Zn phase,and the degree of refinement is proportional to the content of A element.By analyzing the Sn-Bi-Ag ternary solder designed by Sn-Bi eutectic clusters,the matrix of solder was basically composed of Sn-Bi eutectic structure and a small amount of Ag3 Sn phase.The addition of Ag element serves to refine the matrix structure.2.According to the melting performance of solder,there was no precipitation of the primary Zn phase in the six solders of the quaternary designed by Sn-Zn and Sn-Bi eutectic clusters,and the addition of appropriate A element can effectively improve the oxidation resistance of solder.The melting performance of solder with Sn-Bi eutectic clusters has the advantages of low melting point,small melting range.3.Through the study of the wetting properties of the twelve kinds of solders,it is found that the wetting ability of solders designed by Sn-Zn and Sn-Ag clusters was better on the Al substrate.Maximum wetting area of the the solder alloy on the Al substrate was about 36 mm2(diameter 1.5 mm solder ball).4.Ag element and Zn element in the solders all react with the Al substrate,but the mechanism of reaction is different.The quaternary solders designed by Sn-Zn and Sn-Bi eutectic clusters combined with Al substrate by forming the solid solution of Al and Zn.The solders designed by Sn-Ag eutectic cluster connected with Al substrate reliably by forming intermetallic compound layer(IMC).The solders designed by Sn-Bi eutectic cluster connected with Al based material reliably by forming solid solution of Al-rich(Ag).The combination between the four groups of solders and Cu substrate was the formation of Al4.2Cu3.2Zn0.7 or Cu6Sn5 type IMC layer.5.The solders designed by Sn-Zn eutectic cluster had greater shear strength,and the maximum shear strength was about 37.5 MPa.