Research Of Rosin-based Fluxes For Zn20Sn Lead-free Solder

With the development of highly integrated package technology and the increaseof demands for electronic components under high temperature, the demand ofhigh-temperature lead-free soft solders is increasing. Zinc-based alloys are a promisingcandidate for high-temperature lead-free soft solders, which have high strength andhardness, satisfactory damping property, cheap in materials and manufacturing cost.But the disadvantage of Zn-based solders is poor wetting property. It impedes thedevelopment of Zn-based solders. So researching a new kind of flux for Zn-basedsolders to improve its wetting property will be very meaningful.Tradition-based activated rosin flux, a set of various activated rosin flux wereprepared by the accession of organic acid active agents, surface active agent, combinedsolvent and inhibitor. Studied and threshed the mechanism of constituents ofrosin-based fluxes for Zn20Sn lead-free solder By orthogonal testing method andunivariate analysis and the optimum doses of constituents in the flux could be found.The results of the studies in the dissertation as bellow:When the content of organic acid active agents, surface active agent andinhibitor are fixed, the accession of suitable contents of the rosin has certain effect onon the spreadability of Zn20Sn solder alloys on Cu substrate. When the content ofrosin is about55wt.%, the spreading area and spreading ratio of the Zn20Sn solderreach to the maximum value, are70.3mm~2and87%respectively. And the solder jointis brighted; formability of the solder joint is very good; intermetalic layer is relativelyflat; no crack and cavity appear and the satisfying results could be given. When thecontent of rosin, surface active agent and inhibitor are fixed, the addition ofappropriate amount of organic acid active agent, the spreading area and spreading ratioof the Zn20Sn solder on Cu substrate have increased. When the content of organic acidactive agent is5wt.%, the spreading area and spreading ratio of the Zn20Sn solderreach to the maximum value, are72.9mm~2and88%respectively. When the content of organic acid active agent is3wt.%and5wt.%, the solder surfaces have less pits, fulllight and smooth relatively. When the content of organic acid active agents, rosin andinhibitor are fixed, the spreading area and spreading ratio of the Zn20Sn solder areincreased as the content of surface active agent is increased. The increasing value ofthe spreading area is very small when the content of surface active agent is over1wt.%.The overdose of the surface active agent has little influence on the spreadability ofZn20Sn solder alloy. Moreover, it is not beneficial to weld material. BTA is a kind ofefficient corrosion for Cu and has little influence on the spreadability of Zn20Sn solderalloy. When the content of organic acid active agents, rosin and surface active are fixedand the percent content of BTA is between0.1wt.%-0.3wt.%, the spreadability ofZn20Sn solder alloy has not changes obviously. But the spreading area and spreadingratio of Zn20Sn solder alloy decline when the content of BTA is over0.3wt.%.To sum up, the best content of various components of rosin-based flux forZn20Sn solder is:55wt.%rosin,5wt.%organic acid active agents,1wt.%surfaceactive,0.1wt.%-0.3wt.%BTA, solvent residual.