The Synthesis Of Conductive Copper Paste And The Study Of Its Pattern Printing Sintering Properties

With the development of printing electronic technology,printable conductive paste has attracted a wide attention.At present,silver is used in conductive because of its great conductity and sintering.However,the high price and poor electromigration resistance of silver limit its application in industry and key components.Cu is the best choice to substitute for silver beacuse of its high conductivity,good electromigration,and low price,only 1/16 of silver.This project is to develop a conductive Cu paste with high conductivity and adhesion for the metallization of ceramic substrates to replace expensive metal conductive paste.The project is mainly about the synthesis of conductive Cu paste and the study of its pattern printing sintering properties.The preparation of the Cu paste includes the preparation of glass frit,the formic acid treatment of Cu particles,and the preparation of organic carrier.The glass frit was prepared by a conventional melt-quenching method with glass transition temperature of 360°C and a crystallization temperature of531°C detected by DSC.In order to further study the sintering properties of the glass frit,glass paste was printed on Al₂O₃ ceramic substrate by a steel mesh and sintered at different temperatures.It can be found that Bi₂B₄O₉ is crystallization from glass and ZnAl₂O₄ is reaction product of glass and Al₂O₃,which helps to improve the bonding strength with the substrate.At the same time,it was found that Cu reduced the Bi element in the glass to form Bi when the glass paste was sintered on the Cu bulk.In this paper,the micron copper powder was treated with formic acid,and the affect of the formic acid treatment on Cu microparticles was characterized by XPS and TEM.It was confirmed that the oxide on the surface of the Cu particles was cleaned and a layer of Cu（COOH）₂ was formed on the surface.The organic vehicle is selected from the terpineol-ethyl cellulose system,and other components are added to adjust the properties.Through the observation of the microstructure of sintered conductive film,resistivity and shear strength,to analyse the effect of glass frit content and the sintering process to sintering of the Cu paste.It has been found that glass frit in Cu paste can promote the sintering of Cu microparticles,and the density and shear strength of sintered conductive thick films increase with the increase of glass content.At the same time,the resistivity of the sintered conductive thick film decreases as the density increases,but the excess frit reduces its conductivity.When the sintering temperature is lower than 650°C,the comprehensive performance of the sintered conductive thick film increases with the temperature increase.The sintering temperature continues to rise,shrinkage pores are formed in the thick film and the oxidation is aggravated resulting in a decrease in electrical conductivity.At the same time,the degree of crystallization of the glass is greater,the mechanical properties of the glass are decreased,and the content of Bi formed during the sintering process is increased,resulting in a decrease in the mechanical properties of the sintered conductive thick film.The glass boils at the sintering temperaturethe in vacuum,leading a bad wettability thereby affecting the densification process,resulting in a poor conductity and mechanical properties of the sintered conductive thick film compared with the thick film obtained in the Ar atmosphere.The Cu film has excellent comprehensive performance,with the resistivity of 3.38μΩ·cm,and the shear strength of 35.24 MPa formed by Cu paste with 10 wt.%glass sintered at 650°C for 20 min under Ar atmosphere.