| Recently,lead-free solders are replacing Sn-Pb solders because of human health and the environmental protection and legal regulation worldwide. Sn-9Zn eutectic solder alloy is a promising candidate for new lead-free solders, however its wettability is poor. The present work focused on developing a new flux for Sn-9Zn by modifying rosin based fluxes.We studied the behavior Sn-9Zn solder joint in the process of reflow by adding SnCl2 and inhibitor to ethanal-rosin as a flux. The spreading area and wetting force are measured. We examine the corrosiveness of the fluxes to copper and flux, and the effect of an inhibitor. The results show that the wettability Sn-9Zn to copper can be greatly improved by addition of such to ethanal-rosin as a flux. However, the SnCl2-containing flux is found corrosive to the solder alloys. An inhibitor with high activity was chosen. Addition of this inhibitor to the SnCl2-containing flux can diminish its most corrosiveness, while further enhancing the wettability of Sn-9Zn alloy to copper.Furthermore, we consider structure in the surface, shear stress and creep strength of solder joints by different fluxes. Joint samples and experimental facility were made by ourselves. The results show that the fluxes have no influence on structure in the surface. They can significant improve the shear stress in solder joints compared to rosin flux, but shear stress of solder joints in the exceed 5 wt% SnCl2 to ethanal-rosin as a flux will decrease, meanwhile creep strength in solder joints deteriorate quickly, which indicate that addition of SnCl2 can improve the wettability to Sn-9Zn, but lower the adhesion of solder to the base. The effect of content of rosin on mechanical properties is complicated, and the results of shear stress and creep stress measurements are inconsistent. In this paper above questions are discussed, and a suitable ingredient range of new flux are suggested. |
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