The effects of fluxes with different activators (sebacic acid and diethylamine hydrochlcoride) on the wetting behavior of Sn-Zn lead-free solders were investigated. The wettability tests showed that fluxes with the addition of single sebacic acid or diethylamine hydrochlcoride significantly improved wettability of Sn-Zn solder on Cu substrate. However, fluxes with combined additions of above activators promoted wetting performance of the solder further. Thermal analysis (thermal-gravimetry analyzer and differential scanning calorimeter) results demonstrated that the effective temperature range of diethylamine hydrochlcoride is higher than that of sebacic acid. So diethylamine hydrochlcoride could react with oxides on the solder and substrate surfaces at a wider temperature range which resulted in an enhanced spreading of solders. Scanning electron microscopy (SEM) image showed that two kinds of diffusion layers were formed between Sn-Zn solder and Cu substrate, indicating fluxes with binary activators markedly improved welding quality of Sn-Zn solder.