Abstract:

The effects of Ni content on the microstructure and the wetting behavior of Sn-9Zn-xNi solders on Al and Cu substrates, as well as the mechanical properties and electrochemical corrosion behavior of Al/Sn-9Zn-xNi/Cu solder joints, were investigated. The microstructure of Sn-9Zn-xNi revealed that tiny Zn and coarsened Ni₅Zn₂₁ phases dispersed in the β-Sn matrix. The wettability of Sn-9Zn-xNi solders on Al substrate was much better than that on Cu substrate. With increasing Ni content, the wettability on Cu substrate was slightly improved but became worse on Al substrate. In the Al/Sn-9Zn-xNi/Cu joints, an Al_4.2 Cu_3.2Zn_0.7 intermetallic compound (IMC) layer formed at the Sn-9Zn-xNi/Cu interfaces, while an Al{Zn{Sn solid solution layer formed at the Sn-9Zn-xNi/Al interface. The mixed compounds of Ni₃Sn₄ and Al₃Ni dispersed in the solder matrix and coarsened with increasing Ni content, thus leading to a reduction in shear strength of the Al/Sn-9Zn-xNi/Cu joints. Al particles were segregated at both interfaces in the solder joints. The corrosion potentials of
Sn-9Zn-xNi solders continuously increased with increasing Ni content. The Al/Sn-9Zn-0.25Ni/Cu joint was found to have the best electrochemical corrosion resistance in 5% NaCl solution.

Key words: Al-Cu dissimilar-metal solder joint, Sn-9Zn-xNi, Microstructure, Mechanical properties, Electrochemical corrosion, Corrosion potential