| For the silver powder has the best conductivity, it is widly used in the electronics industry as a basic functional materials in the electronic paste. In the past30years, with the rapid development of the electronics industry, market demand for silver powder greatly increases, while it’s performance requirements have become more sophiscated. Now many countries in the world research on this subject and have made great progress. Our country start this subject later and the technology is relatively backward, coupled with the confidentiability of foreign high-tech, so our country has a big gap on the research of silver powder compared with foreign countries. Especially with the rapid developement of photovoltaic industry, the application of silver powder has expanded significantly, the technical requirements of silver powder is also getting higher and higher. Silver powder as a conductive phase in the the electronic paste can’t be replaced by other metals,coupled with the foreign silver embargo on China, so how to develop high-performance ultra-fine silver powder has great practical significance. This paper mainly research on ultra-fina silver powder and we have prepared low temperature curing silver paste with epoxy resin,curing agent, additives and the silver powders obtained by experiment. With the help of scanning electron microscope, laser scattering particle analyzer, PF-100B vibration solid density spectrometer, Netzsch DTA449PC DSCmeter and D/Max2500XRD, we observed and analysed the morphologies, mean grain sizes, tap density of silver powder, and the crystallinity. By using four-probe meter measured the conductivity of low-temperature curing silver paste.The results are as follows:(1) Selecting polyacrilic acid as the dispersant, ascorbic acid as the reducing agent, we had prepared highly dispersed ultrafine silver powders from silver nitrate by chemical reduction method. The effects of different addition style of the solution, pH value, temperature, dispersant dosage, Concentration of silver nitrate and ascorbic acid on the mean partical size and morphology of the ultrafine silver powders were mainly researched.When adding silver nitrate solution to polyacrilic acid solution, the dispersion of silver powder is better. The acidity-basicity of the reaction solution has a big effect on the morphology of the ultrafine silver powders. The dosage of the dispersant has a remarkable influence on the particle size of the ultrafine silver powders. And finally we got the optimization process of the experiments. The ultrafine silver powders have the best dispersion in the condition that the silver nitrate solution is30g/L, the concentration of ascorbic acid solution is70g/L, the pH value is8, temperature is50℃, the mass ratio of polyacrylic acid and silver nitrate is0.005,and the mean particle size can reach1.41μm.(2) In order to improve the dispersion and tap density of silver powders, we do the experiment by mixing the two different dispersant.The influence of ratio of dispersant, pH value,temperature on the mean partical size, morphology and tap density of the ultrafine silver powders were mainly researched.The silver powders has the best dispersion and crystallinity, the tap density can reach4.6g/cm3in the condition that the mass ratio of polyacrylic acid and silver nitrate is0.005, the dosage of TEOA is5.0ml/L, pH is1,temperature is45℃.(3) Following the temperature increases,the curing effect of the paste is getting better and better and the resistance is getting much lower,the best curing temperature can be selected for150℃. Extending curing time can make the paste completely cured, but may cause oversintering.So the best curing time can be selected for30min.While the ratio of the epoxy resin and curing agent is70%, the paste has the best electrical propeties and the viscosity and adhesion is also fit for screen printing. |
PDF Full Text Request