Effects of Zn and Sb Additions on Microstructure, Creep Behavior and Thermal Properties of Binary Eutectic Sn-0.7% Cu Lead-Free Solder

The effects of Zn and Sb additions on microstructure, creep behavior and thermal properties of binary eutectic Sn-0.7% Cu lead-free solder were investigated. Results show that Zn-addition reduced the melting temperature of Sn-0.7Cu and enhanced the creep resistance due to the formation of Cu5Zn8 intermetallic compound (IMC) and reduction of Cu6Sn5 phase in beta-Sn matrix. Conversely, the Sb-addition showed a negative effect on both the creep resistance and melting temperature compared to the plain Sn-0.7 Cu and Sn-0.7 Cu-2.0 Zn alloys due to the formation of SnSb IMC particles and coarse Cu6Sn5 phase through the beta-Sn rich phase. The average stress exponents of 4.9-6.0 and activation energies of 50-60 KJ/mol were obtained for three solders; suggesting that the dislocation climb controlled by lattice diffusion is the dominant creep mechanism. X-ray diffraction (XRD) analysis revealed that the lattice parameters (a), (c), the axial rate (c/a) and the peak height intensities (hkl) of some crystallographic planes are changed with alloying additions and the crystallite size is decreased.