Improving tensile strength of SnAgCu/Cu solder joint through multi-elements alloying

In this study, different content combinations of the Sb, Bi, Ni, In and Ce elements were added into the SnAgCu (SAC) solder, then the composite alloying effects of these elements on microstructure and properties of the SAC solder, and the interfacial reaction and tensile strength of the SAC/Cu solder joints were investigated. The results reveal that the melting ranges of the multi-alloyed solders are larger, and their wetting areas increase by different degree. More intermetallic compounds (IMCs) and some Bi particles are formed in the multi-alloyed solders and the solder grains are refined, which significantly increase the microhardness. The interfacial IMC layer change from single layered scallop-type Cu6Sn5 grains at the SAC/Cu interface to an agglomeration of fine (Cu, Ni)6Sn5 particles by the multi-element alloying, while the residual stress in the interfacial IMC layers can be released due to the decrease in the IMC grain size. Through solid solution strengthening, precipitation strengthening and fine grain strengthening of the solder and release of residual stress in the interfacial IMCs, tensile strength of the multi-alloyed SAC/Cu solder joints was significantly improved to 100–160 MPa, and the fracture location transfer from inside the solders close to the joint interface to inside the interfacial IMCs layer.