| Now no-pollution production, energy saving and emission reduction have become an objective trend for socio-economic development. Conductive ink, which develops with this trend, will become the key material of the printed electronics technology in electronic industry. A major challenge in manufacturing conductive ink is the preparation of the metal or non-metallic conductive fillers. To meet the application needs of cooperative enterprises, the conductive ink using epoxy resin as matrix has been researched. The preparation of ultra-fine copper powder, silver-plated copper powder and ultra-fine silver powder was studied. Then conductive ink can be filled by these powders. The effects of filler content, diluent and additives on the conductivity were investigated. Conductive inks that appropriately meet the needs of printed electronics technology have been produced.The reducing agents and reduction methods are analyzed by means of comparison Then the methods of preparation of ultra-fine metal powders have been obtained. Ultra-fine copper powder was prepared in polyol as the dispersant and protecting agent. Ultra-fine silver powder and silver-plated copper powder were prepared by ball milling reaction. The properties of obtained powders were characterized by XRD, SEM, EDS, and TG. Silver powder and copper powder with about 200nm in diameter were obtained. The prepared copper powder was plated with silver, and the silver-plated copper particles were observed with average diameter about 500nm. The XRD patterns and EDS analysis show the high purity of the samples. Thermostability of resultants were inspected by thermogravimetry with a temperature range of 20~800℃, and the heating rate was 20℃/min. TG analysis shows that the silver powder has the best thermostability and oxidation reaction was not found at the test conditions. The use of ultrasonic is more beneficial to the dispersion of the copper powder in liquid phase reaction. Copper powder with better thermal stability and finer particle size can be prepared. The results also show that, for the dispersion and thermal stability of particles, the use of glycerol was better than ethylene glycol in this reaction. While in the ball milling reaction, ethylene glycol was more suitable for milling because of its lower viscosity.To investigate the effects of the type and amount of fillers, solvent and additives, graphite powder, the self-made ultra-fine copper powder, plated-silver copper powder and ultra-fine silver powder were used as conductive fillers respectively, and epoxy resin was used as the matrix. The resistance of conductive lines was measured and the conducting mechanism was discussed. The optimum formulation was sought by the use of coordinate measuring machine and low/high temperature tests. The inks were prepared as follows: 2.0g epoxy resin was dissolved in 15~20mL butanone, 1.8g filler powder and ethylene glycol or malonic acid of 0.1~0.2g were added and then mixed thoroughly. Curing agent of 0.4g was added into the ink before being used and then after cured at room temperature or in the water bath of 20~40℃. The prepared graphite-epoxy resin ink had the electric resistivity of 4.00~4.25?·cm and an outstanding stability to heat, While the electric resistivity of plated-silver copper-epoxy resin ink was about 1.25?·cm. Such inks are suitable for the applications that require low conductivity. The electric resistivity of copper-epoxy resin ink was about 0.4?·cm. This ink can be applied very extensively because of the copper's cheapness. However, the ultra-fine copper particles are chemically active and very apt to be oxidized in humid atmospheres; hence the ink should be conditioned by the temperature as well as humidity. Silver-epoxy resin had the lowest electric resistivity and an excellent thermal stability. Yet because of the higher cost of this kind of ink, it is better to use it on the required applications such as fine circuit. |
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