Preparation And Performance Of Bi-B-Zn Low-temperature Glass Impregnated Silver Paste

In electronic packaging,the connection technology of replacing copper with aluminum is getting more and more attention.The commonly used method of partial melting and welding of aluminum and aluminum alloys will cause welding defects such as pores and cracks,which will reduce the performance of the joint.As a method with low temperature and simple process,brazing is widely used in the field of electronic packaging.In order to solve the problem of difficult brazing on the surface of aluminum alloy,this article uses the dip-pull method to coat a layer of solderable conductive silver paste on the surface of the aluminum alloy.After sintering,the silver paste forms a firm bond with the aluminum alloy substrate,thereby achieving soldering connection of aluminum alloy.In this paper,Bi₂O₃-B₂O₃-Zn O glass powder was prepared by the melting quenching method,the glass transition temperature was 360?,and the particle size after ball milling was about 4?m.Increase the solid content of the silver paste,the viscosity of the silver paste increases,the film thickness increases,and the wettability on the surface of the aluminum substrate decreases.In this paper,the viscosity of the70 wt.%solid content silver paste is 126.5 MPa·s,the wetting angle on the surface of the aluminum substrate is 21.9°,and the film thickness is about 40?m.Reducing the glass content,increasing the sintering temperature,controlling the reasonable holding time and the flake silver powder content are beneficial to improve the solderability of the silver film.In this paper,the 70 wt.%solid content silver film can be kept at 400?for 30 min before sintering at 500?,which can make the solder spreading rate reach the maximum 95.5%.The conductivity of the silver film is related to the glass content in the silver paste and also related to the density of the silver film structure.When sintered at 530?for 10 min,the spherical silver film with a glass content of 10 wt.%has the lowest resistivity of 2.23??·cm.The shear fracture position of the silver film after copper soldering depends on the bonding strength of the silver film and the substrate.When the glass content in the silver film is greater than 5 wt.%and the sintering temperature is greater than470?,the bonding strength of the silver film and the substrate exceeds that of the tin solder itself.Shear strength(54.1 MPa),the location of the shear fracture occurs at the interface between the silver film and the aluminum plate and the tin solder.The high bonding strength between the silver film and the aluminum substrate is due to the fact that the Mg and Al elements in the aluminum substrate diffuse into the glass during the sintering process of the silver film,and undergo oxidation-reduction reactions with Bi₂O₃ in the glass to form Bi element.A good metallurgical bond is formed between the phase and the aluminum plate.After 1000 thermal cycles in the temperature range of-55?to 125?,the shear strength of the silver film and the aluminum plate and the resistivity of the silver film remained stable.The tensile strength of the aluminum alloy substrate after sintering in the range of 440?to 530?was both More than 210 MPa,indicating that the sintered silver film on the aluminum alloy surface has good reliability.In summary,the sintered silver paste on the surface of aluminum alloy has good solderability,conductivity,bonding strength and reliability,and can effectively realize aluminum alloy soft soldering.