Microelectronics Packaging Line Sintering Of Nano-silver Conductive Adhesive Preparation And Research

Recently,nano-materials are attracting more and more researchers'interests due to their specific electrical,mechanical,optical,magnetic and chemical properties and the nano-conductive adhesives with nano-fillers have been extensively studied. The unique property that the nano-size metal melts at a temperature well below the melting point of the bulk metal,has been utilized to prepare sintered electrically conductive adhesives (ECAs) in microelectronic packaging with the development of nano science and technology. One-dimensional nanostructures such as nanowires have been the focus of many recent studies for their many outstanding physical and chemical performances.The different surface treatments of silver flakes for ECAs can affect the conductive property of ECAs and the results showed that the dicarboxylic acids, especially pentanedioic acid and hexanedioic acid,can increase the conductivity of ECAs significantly. About 1.4 wt% pentanedioic acid on the silver suface can protects the silver from oxidation and can be desorbed at temperature higher than 150℃to leave a fresh silver surface.The silver nanowires with a slenderness ratio of 50-60 were synthesized through a polyol process and modified on the surface by pentanedioic acids.The sintering of modified silver nanowires at different temperatures was analyzed by SEM and the modified silver nanowires began to sinter at 200℃and formed large chunks at a higher temperature.The sintering of silver nanowires dispersed in epoxy composite was also observed by SEM when ECAs were cured at high temperature. ECAs filled with silver flakes and low temperature sintered silver nanowires were formulated and a conductive adhesives filled with 75 wt% of silver flakes and nanowires cured at 300℃reached a resistivity of 5.8×10-6Ω·cm,which is very close to the ultimate value of the resistivity of ECAs-4.3×10-6Ω·cm. The mainly reason for this is that the sintered silver nanowires can form a conductive network throughout the cured ECAs and dramatically reduce the resistivity of ECAs.Although the high temperature curing condition is not suitable for most epoxy adhesives,the results suggest the several ways to improve the conductivity of ECAs. The sintering temperature of silver nanoparticles depends on the size of the particles, smaller nanowires or particles are required for preparing low temperature cured epoxy based EC As.For larger size silver nanowires,polymer binders with high thermal stability,such as polyimides and cyanates,may meet the requirement. In addition, the partial evaporation of polymer components during the curing process can increase the silver content and promote sintering of nanowires,and thus reduce the resistivity of ECAs.