Preparation Of Bi₂O₃-B₂O₃-ZnO Low Melting Glass Solder And Its Application In Optical Fiber Sealing

Glass solder has been widely used in vacuum electronics and semiconductors fields because of its high insulation and good chemical stability.However,the glass solder currently used has the problems of high sealing temperature and lead content.In this paper,a promising lead-free glass of Bi₂O₃-B₂O₃-ZnO system is selected,and the effects of Bi₂O₃,B₂O₃,ZnO and GeO₂ on the structure and properties of the glass are studied.The formula is optimized to conform to the development trend of lead-free,low temperature and microcrystallization.The glass is applied to weld optical fiber,and the microstructure of interconnection interface is studied through experiments.The thermal stress of the"optical fiber-glass-Kovar"interconnection structure is simulated by ANSYS Workbench,and both the material parameters and geometric size of the structure are optimized.The main research results are as follows:(1)Bi₂O₃-B₂O₃-ZnO glasses are prepared by melt quenching method and characterized by X-Ray Diffraction(XRD),Fourier Transform Infrared Spectroscopy(FTIR),and Differential Scanning Calorimeter(DSC).The results show that ternary glass has a wide virtrification range.With the increase of B₂O₃content,[BiO₆]decreases;the network becomes dense;and both the transition temperature(T_g)and the onset crystallization temperature(T_x)of the glass increase.As the content of Bi₂O₃increases,[BiO₆]increase;the glass network becomes loose;meanwhile,both T_g and T_x decrease.The addition of GeO₂has no effect on T_g,but promotes glass devitrifing.A large number of Bi₂₄B₂O₃₉ crystals are detected at 460?.(2)Glass with T_g,softening temperature(T_f)and linear expansion coefficient(CTE)of344.3?,365.6?and 11.17×10^-6/?,respectively,is optimized as solder for optical fiber sealing.The interconnection interface of“optical fiber-glass solder-Kovar alloy”sealed at420?480?has no obvious defects,and square crystals(Bi₂₄B₂O₃₉)and dendritic crystals(Bi₄B₂O₉)are precipitated in the solder area.The increase of sealing temperature would increase the number of crystals and the ratio of the dendritic crystals.Moreover,the gas leakage rate of“optical fiber-glass solder-Kovar tube”structure is 1.8×10^-10 Pa·m³/s.(3)The thermal stress-strain field of optical fiber interconnect is simulated by finite element method,and it is found that using glass solder as the sealing material can cause less damage to optical fiber than Au Sn solder.With the glass's CTE increasing,the stress and deformation of optical fiber become larger.Besides,the inner diameter of Kovar tube(D₂)and the depth of solder filling(H)also influence the stress and deformation of the optical fiber.The optimized parameters of the structure included:CTE=3×10^-6/?,d₂=640?m and H=300?m.