Study Of Organic Activated Flux For Sn-9Zn Lead-free Solder

Recently, Sn-Pb solders are substituted by lead-free solders are replacing because of human health and the environmental protection and legislations 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.It was found that, adding 0.5 wt% DMA to ethanol-rosin could remarkably raise its activity and improve the wettabilty of Sn-9Zn to copper when used as a flux. Addition of minor amount of ethylenediamine to the flux can further improve the wettability, and greatly reduce the corrosivity of the flux to Sn-9Zn alloy and substrate. The content of activator in flux has an optimum value: 0.5 wt% DMA & 1 wt% ethylenediamine.Furthermore, we studied the interfacial structure, shear strength and creep strength of solder joints using different fluxes. Joint samples and experimental facility were made by ourselves. The results show that:(1) In the case of using the flux containing two activators, DMA and ethylenediamine, the tensile strength of Sn-9Zn/Cu solder joint is the best, which also indicates the effect of this flux is the best.(2) It was confirmed that the self-made bend-creep tester is simple and reliable.Comparing with using the other fluxes, the bend-creep strength of Sn-9Zn/Cu solder joint is the best by using the flux including two activators, DMA and ethylenediamine.(3) The characters of the interfacial structure are the same when using differentfluxes, expect the thickness of IMC layers have some difference. We can ensure that the fluxes have no influence on interfacial structure, and are impossible to lead to new reliable problems.