Study On Influence Of Dispersant On The Sintering Quality Of Nanoscale Silver Paste

With development of lead-free interconnect materials, low-temperature sinterednanoscale silver paste which acts as a new kind of interconnect material begins toreceive widely attention. Theoretically，low-temperature sintered nanoscale silver pastehas high electrical conductivity and thermal conductivity, so it is a kind of idealinterconnect material for power electronic devices. Actually, the dispersants in the silverpaste can not decompose completely at low temperature, and the residual dispersantsprevent sintering process proceeding. Therefore, the main purposes of this thesis are toresolve the problem of incomplete sintering of nanoscale silver paste at low temperatureand improve sintering quality.In this thesis, the preparation of silver nanoparticles is based on Carey-Lea method.The influence of dispersants on dispersibility and sintering property of silvernanoparticles is investigated by adjusting the concentration and types of the dispersants.The dispersants absorbed on silver nanoparticles can be effectively reduced by purifyingthe nanoscale silver paste with water, so that sintering quality were improved.Furthermore test the properties of low-temperature sintered nanoscale silver paste.It is shown that both too high and too low concentration of dispersants make thedispersibility of silver nanoparticles worse. Especially, too low concentration causes thedispersibility worse dramatically, which leads to a bad sintering property. Differentkinds of dispersants have significant influence on dispersibility and sintering property ofnanoparticles either. When mercapto-propanoic acid which has a worse dispersingproperty than sodium citrate is added, the dispersibility of nanoparticles becomesworse dramatically, which leads to a bad sintering quality. When potassiumpyrophosphate which has a better dispersing property than sodium citrate is added, thedispersibility is improved. But potassium pyrophosphate can strongly absorb on thesilver nanoparticles, which prevents sintering proceeding. At the same time, it is foundin the research that directly washing nanoscale silver paste can reduce the quantity ofdispersants absorbed on particles, and the silver paste washed one time has the bestproperty. Compared to Carey-Lea, the electrical conductivity, hardness and density ofsintered silver paste and the strength of sintered joint after reducing the quantity ofdispersants are improved significantly.