Effect of Ni content on microstructure and shearing property of 304/Sn-8Sb-4Cu-xNi/304 solder joints

Effect of Ni content on melting point and microstructure of Sn-8Sb-4Cu-xNi (x=0, 0.5, 1 and 2, mass fraction) solders were investigated. 304 stainless steel were joined by Sn-8Sb-4Cu-xNi solders, and interfacial microstructure and shearing property of the solder joints were analyzed. The results showed that all of the Sn-8Sb-4Cu-xNi with different Ni content are near eutectic solders, with a melting point of 245 ℃. The microstructure of Sn-8Sb-4Cu solder was consisted of α phase, Sb₂Sn₃ + Cu₆Sn₅+Sn composite phase and Cu₆(Sn,Sb)₅ phase. After the addition of Ni, the bulk Cu₆(Sn,Sb)₅ transformed into fine and uniformly distributed (Cu,Ni)₆(Sn,Sb)₅. When Ni content was less than 1%, the amount of composite phase and (Cu,Ni)₆(Sn,Sb)₅ phase increased with the increasing of Ni content. When Ni content increased to 2%, the amount of composite phase and (Cu,Ni)₆(Sn,Sb)₅ phase decreased with the increasing of Ni content, however, Ni content in the (Cu,Ni)₆(Sn,Sb)₅ phase increases to be comparable to Cu. A diffusion layer with a thickness of about 1.5 μm formed at the Sn-8Sb-4Cu-xNi/304 interface, which was identified to be Fe₂Sn by EDS. Only Cu₆Sn₅ type intermetallic compounds formed in the solders of 304/Sn-8Sb-4Cu-xNi/304 joints. The addition of Ni element improved the shear strength of 304/Sn-8Sb-4Cu-xNi/304 brazed joints, and the maximum shear strength of 67 MPa was achieved when the Ni content was 0.5%, which was 60% higher compared to the Ni-free brazing material. The shear fracture locations of all joints were located in the soldering seam.