Development Of Special Flux Matching Sn-Zn Lead-free Solder For Electronic Packaging

Due to the advantages of low melting point close to that of Sn-37Pb, low cost and greatmechanical properties, Sn-Zn alloys was considered as one of the most potential lead-free solders.However, the existence of element Zn caused poor performances in wettability and oxidationresistance, thus, hindered its application. In order to solve these problems, one way is to improve theproperties of solder by alloying, the other way is to develop a kind of flux which can greatly help thewettability of Sn-Zn.In this paper, Effects of addition of succinic acid, two ethanol amine, stannous sulfonate, TX-10,catechol and polyethylene glycol, two glycol, ethanol contents on wettability of Sn-Zn lead-freesolders were studied. The optimum formula of Sn-Zn solder flux based on the designed orthogonalexperiments was investigated and found that the flux can be helpful for the wettability. Then, theeffects of maching this flux on the wettability, mechanical properties and reliability of the solderedjoints were studid. In addition, the mechanism of flux was also analyzed.The results indicate that the G8optimum contents of succinic acid, two ethanolamine,stannousmethane sulfonate, TX-10, adjacent benzene two Fen and polyethylene glycol, ethanol, two DEG inthe flux is10wt.%,8wt.%,0.8wt.%,20wt.%,1.2wt.%,30wt.%,20wt.%and10wt.%, respectively.When matched self-made G8special flux of Sn-Zn in the optimum formula can greatly improved thewettability of Sn-Zn lead-free solder compared to commercially available flux, achieving full brightspot solder, with no corrosion residue.The Sn-Zn solder exhibited excellent wettability when matching self-made special flux of Sn-Znin the optimum formula without halogen which the largest spreading area was116.8mm², the largestwetting force was116.8mm², the shortes wetting time was0.8second, achieving full bright spot solder,with no corrosion residue. In addition, the wettability of Sn-Cu-Ni and Sn-Ag-Cu lead free solderscan be slightly less improved than Sn-Zn.Basic properties of self-made special flux of Sn-Zn were measured compared to thecommercially available resin flux, the water-solubility flux and the flux of ZnCl2NH4Cl.The resultshowed that this flux was a white paste at room temperature, stability, corrosion resistance, insulationresistance, viscosity, the non-volatile matter content all reached established soldering standards.Besides, good thixotropy, mixing into uniform texture, good fluidity thin paste liquid. The pH value ofthe flux was equal to6.5closed to neutral. Compared with resin flux, water-solubility flux andZnCl2NH4Cl flux, matching self-made fluxcould significantly reduced the tendency of Sn, Zn oxidation, effectively removed the oil andimpurities between substrate and the liquid melt solder.In addition matching this flux could refine thegrains of microstructure and suppress the increase of intermetallic layer thickness and the formationof interfacial porosity. Further more, the mechanical properties of joint was greatly improved whichthe largest shear strength was39.06MPa, the largest tensile strength was25.65MPa. The shearstrength will increased by99.69%,76.18%,9.26%, the tensile strength will increased by111.11%,77.91%,27.49%, when compared with the NH₄Cl-ZnCl₂, resin and water-solubility fluxes.During the process of aging treatment, the mechanical properties of soldered joints decreasedwith the time of aging treatment extended. The solder joint mechanical properties matched self-madespecial flux of Sn-Zn declined less than matched other fluxes, exhibited the best mechanicalproperties.