Research On Process And Mechanism Of Brazing YIG And Copper

Yttrium iron garnet ferrite（YIG）,a typical kind of microwave ferrite,is widely used in radar,microwave communications,missiles and many other fields,where YIG usually needs to be connected with copper.In this paper,a metal lization method was proposed to metalize YIG first.Then,metalized YIG was brazed to copper.The effects of CuO content,temperature and holding time on wetting ability of Ag-CuO solder on YIG surface were studied.The effect of YIG content in Ag-CuO/YIG composite solder on the microstructure of metallization layer was studied.The effects of YIG content,brazing temperature and holding time on the microstructure and mechanical properties of the Cu/metallized YIG joint were analyzed then.Finally,the mechanism of YIG surface metallization and the formation mechanism of the Cu/metallized YIG joint was studied.The wetting ability of Ag-CuO solder on YIG surface improved as CuO content increasing,brazing temperature increasing or holding time prolonging.CuO was found to react with b YIG to produce CuFe₂O₄,which improved the wetting ability of the solder.The typical interfacial structure of the metallization layer obtained by Ag-CuO solder was: Ag+CuO+CuFe₂O₄/YIG.Considering the effect of all factors,the solder was determined to be Ag-7.5CuO,and the metallization parameters were as follows: the brazing temperature was 1040℃ and the holding time was 20 min.Adding YIG particles into Ag-CuO solder greatly improved the wetting ability of the solder and increased the yield of CuFe₂O₄,thus forming flat metallization layer that can be used in indirect brazing.The composition of the typical metallization layer obtained by Ag-CuO/YIG composite solder was: Ag+Y₃Fe₅O₁₂+CuO+ CuFe₂O₄/ YIG.The increase of YIG content in the solder caused the increase of YIG and CuFe₂O₄ in the metallization layer,and the flatness of the metallization layer surface decreased correspondingly.More CuFe₂O₄ was observed and found to enrich near the interface of the metallization layer and YIG when 1% TiO₂ was added to Ag7.5CuO/5YIG composite solder.Well performed joint of metallized YIG and copper was obt ained using Sn-3.5Ag-0.75 Cu solder,and the typical microstructure of the brazed joint was: Cu/Cu₃Sn/Cu6Sn5/Sn+Ag3Sn+Cu6Sn5/Ag3Sn/Ag+Y₃Fe₅O₁₂+CuO+CuFe₂O₄/YIG.Experiment results showed that with the increase of YIG content,the YIG and CuFe₂O₄ in the joint increased,and the shear strength decreased correspondingly.The increase of brazing temperature and the prolongation of the holding time will thicken the reaction layer on both sides of the Sn-based solid solution.Test results showed that shear strength of the joints increased firstly then decreased as the brazing temperature increased,and decreased as the extension of holding time.The maximum joint shear strength was 28.7MPa when the content of YIG in the composite solder was 5%,the brazing parameter was: the brazing temperature was 270℃,and the holding time was 1min.The addition of a small amount of TiO₂ can improve the mechanical properties of the joint by changing the distribution of YIG ceramic particles in the joint.