The Co-fired Behavior Of Silver Electrode Paste And LTCC Substrate Material

Low temperature co-fired ceramic（LTCC）technology,as a passive integration and high-density packaging technology,is an effective way to realize miniaturization,integration and high reliability of electronic components.silver electrode paste has the advantages of excellent conductivity,good process compatibility and moderate cost,and is an ideal material for preparing thick film conductors.However,how to realize the low-temperature co-firing of silver electrode paste and LTCC substrate material is the key problem restricting the application of LTCC technology.Based on the sintering characteristics of lead borosilicate glass/alumina LTCC substrate materials,the effects of silver particle size,morphology,glass powder content,softening temperature and particle size on the sintering behavior of silver/glass composite system were analyzed.The effects of glass phase composition and characteristics on the co-fired behavior of silver paste and LTCC substrate materials were systematically studied,and the regulation of co-fired behavior was realized.The difference in sintering shrinkage behavior between silver electrode paste and LTCC substrate was analyzed in this paper.The results showed that the initial sintering shrinkage temperature of micron-size silver powder used in silver paste was lower than500°C,and the rate of sintering process was slow.The initial sintering shrinkage temperature of LTCC ceramic substrate material was higher than 700°C,and the rate of sintering process was rapid,shrinkage reached 14.7%.Mismatch is inevitable in co-firing process of silver paste and LTCC substrate.The effects of silver powder characteristics and glass powder characteristics added in silver paste on the sintering shrinkage behavior of silver/glass composite system were studied.It was found that the change of particle size and morphology of silver powder had relatively small effect on sintering shrinkage behavior.The change of glass composition and content affected the softening flow characteristics of the glass phase in sintering process.Glass frits could change the initial sintering shrinkage temperature and the maximum sintering shrinkage rate of the silver/glass composite system,so that the sintering behavior of composite system could be modified to be close to the ceramic substrate material.The effect of glass composition and characteristics on Ag/LTCC co-firing behavior was studied.The results showed that the co-firing behavior and sintering mismatch of Ag/LTCC can be effectively adjusted by changing the composition of glass additive in silver paste.As the Pb content in Pb-B-Si-O glass increased,the softening temperature and viscosity of glass in sintering temperature decreased.The glass had good wettability with the silver layer and the ceramic substrate layer,which can promote the sintering densification of the silver film and improve the interface bonding strength of the silver film and ceramic substrate.However,when the Pb content was too high,the surface of the silver electrode layer was densified too early,and the gas discharged from the densification of the substrate rushed out of the surface,forming pin-hole structure,accompanied by the overflow of the glass phase.With the increase of Bi content in Bi-B-Si-O glass,the softening temperature and viscosity of glass in sintering temperature decreased,which showed similar behavior of the Pb-B-Si-O glass on Ag/LTCC co-firing process.However,the viscosity of Bi-based glass at the same temperature is lower than that of Pb-based glass.The warpage of silver paste prepared by Bi-based glass increased after co-firing with ceramics.The softening temperature and viscosity of Ca-B-Si-O glass-ceramics were high.Ca B₂O₄ phase and Ca Si O₃ phase could be precipitated at the co-firing temperature,resulting in poor fluidity and wettability of the glass.There were many pores and residual glass phase on the surface and in the internal of the prepared silver electrode layer,which could degrade the electrical performance of the electrode.But it alleviated the sintering warpage of the layer.The effect of co-firing behavior on the performance of silver electrode was analyzed.The results showed that the increase of fluidity and improvement of surface wettability of Pb-based glass were conducive to the densification of silver electrode film and the decrease of square resistance.However,when the relative content of glass additive is more than 2.0 wt%,the glass phase gathered on the surface,the square resistance of silver electrode increased,and the weldability became worse.The silver electrode with better comprehensive performance was fabricated by using Pb-3 glass with the addition amount of 1.0 wt%,of which the square resistance was 1.21 mΩ·sq^-1,silver diffusion was not shown,and the interface bonding between Ag electrode and LTCC was good.