Research On Gold Cofireable Conductor For Ca-B-Si Green Tape

Multi-chip module(MCM)of low-temperature co-fired ceramic(LTCC)technology has the advantages of high packing density,small size,light weight,which is one of the effective ways to achieve the high-performance and miniaturization of electronic devices,and it is widely used in military,aerospace and wireless communications.The key to restrict the application of LTCC technology is LTCC materials,which includes substrates,conductive paste and buried components.The conductive pastes co-firing with the substrate has become one of the key materials to be developed urgently.Base on military MCM application requirements,the Au conductive paste co-firing with Ca-B-Si green tape was studied in the paper.The influence of functional phase,glass binder and organic vehicle of conductive paste on the property of screen printing and co-firing matching was studied systematically.The main work is as follows:(1)With the help of rheometer,the effect of different molecular weight and content of resin,different type and content of thixotropic agent,different volume fraction(φ=13%,20%,46%)and particle size(D50=0.9μm,1.8μm,3.1μm)of functional phase on rheological properties of paste was researched.The results show that increasing the molecular weight of resin or the content of thixotropic agent which will help to increase the shear viscosity in the low shear rate,and remain the low shear viscosity in high shear rate.The shear viscosity of paste increases with the increase of volume fraction of solid phase.When the volume fraction of the solid phase is 13%,the influence of the particle size and morphology of functional phase on the rheological properties of the paste can be neglected,so the regulation of the rheological property of silver paste can be used in the gold paste,and the gold paste with fine line printability(as small as 80μm)was obtained.(2)With the help of surface profile and thermomechanical analyzer,the effect of the particle size of functional phase,the composition and content of glass binder on the warp deformation of substrate was studied,and the microstructure of interface between thick film and substrate was analysed using scanning electron microscope.The results show the thick film densified earlier during co-firing for the silver paste with the minimum silver particle size,there were many pores at the interface between the thick film and the substrate.The thick film was not dense after co-firing for the silver paste with the maxium silver particle size.The substrate which was co-fired with the silver paste with the silver particle size 1.8μm showed the minimum warpage.During co-firing,the glass binder with the lower viscosity can promote the densification of thick film,the glass binders flowed in the thick film which will low the inner stress and reduce the warpage of substrate,but the thick film densified earlier which will make the pores existing in the interface between the thick film and substrate.On the contrary,the glass binder with higher viscosity can hinder the densification of the thick film,though it can provide more time for the gas emission during the process of the densification of the substrate,but it can’t reduce the co-firing warpage deformation due to the poor mobility in thick film.(3)The influence of particle size of functional phase,the component and content of glass binder on the surface microstructure and roughness of the thick film was studied.The effect of particle size of fucntional phase on the distribution of glass binder in the surface of thick film was not obvious,but with the decrease of the particle size of functional phase,the surface roughness of thick film decreased.When the glass binder with the lower viscosity was used,the thick film has a dense surface structure with a lot of lamina shape glass binder distributed in the surface,which increased the surface roughness of the thick film.And with the content of glass binder increased,the more glass binder was distributed in the surface of the thick film.(4)Based on the results of silver paste,the gold paste with better co-firing matching and wire bond performance was prepared by using the optimum particle size of gold powder,the recipe of organic vehicle and the component and content of glass binder.