The microstructure and shear behavior of Zn–25Sn–xTi solder joints with Ni substrate

The effect of Ti addition on the shear behavior of a Zn–25Sn–xTi solder bonding with Ni substrate at 25 °C and 100 °C was investigated. The microstructures of the solder joints had three different phases, which are the Zn-rich phase, laminar Sn-Zn eutectic phase, and the intermetallic compound with some pores. The average atomic composition of the intermetallic compound was 16.38 at.% Zn and 81.46 at.% Ni corresponding to a ratio of Ni to Zn of 1:4.63. The Ni₅Zn₂₁ intermetallic compounds were confirmed by Wavelength dispersive spectroscopy and X-ray diffraction analysis. The addition of Ti refined the Zn-rich phase. Moreover, compared with Pb–5Sn/Ni, the Zn–25Sn–xTi/Ni solder joints exhibited superior shear strength at 25 °C and 100 °C. The mechanical properties of the solder joints were further investigated with nanoindentation tests. The Ni₅Zn₂₁ intermetallic layer exhibited the lowest value of plasticity parameter compared with the solder matrix and substrate. Accordingly, shear fracture tended to occur in the IMC layer at room temperature.