Effects of Zn and Sb additions on micro-structure, creep behavior and thermal properties of binary eutectic Sn-0.7%Cu lead-free solder

Abstract

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 Cu 5 Zn 8 intermetallic compound (IMC) and reduction of Cu 6 Sn 5 phase in β-Sn matrix. Conversely, the Sbaddition 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 Cu 6 Sn 5 phase through the β-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.