Influence Of Sintering Process On The Microstructure Of Nanosilver Paste

Nanosilver paste is a promising lead-free die-attach material suitable for high temperature and high power electronic packaging because of its good mechanical performance, high thermal and electrical conductivity. Nanosilver is now attracting many scientists' and engineers' attention in the electronic packaging industry. However, most of the studies on nanosilver paste were focused on sintering process that was studied with macroscopic experimental parameter as the criterion and on reliability of sintered silver joints. There are few researches on the evolution of microstructure and sintering mechanism. In view of limited studies reported previously, the variation of porosity and particle size under different sintering conditions were analyzed quantitatively, and the influence of sintering process on the microstructure was studied.In this paper, on the basic of traditional sintering theory, a low-temperature sintering technology was employed in the preparation for sintered nanosilver film. High-quality TEM sample was successfully prepared by ion thinning method.The physical mechanism in volatilization of organic components, added in nanosilver paste, was analyzed using thermogravimetric analyzer(TGA-DSC) to obtain a reasonable sintering parameter. The microstructure of nanosilver paste under different sintering conditions were observed by scanning electron microscope(SEM). Combining with image software, the variation of porosity and particle size was studied quantitatively. The results showed that elevated sintering temperature, accelerated the heating rate and extended the holding time of temperature can effectively increase the densification of nanosilver paste. However, on the one hand, too high temperature and too long holding time of temperature leaded to particle coarsening; on the other hand, rapid sintering could lead to the production of initial airway,cracks and other defects.The effect of sintering process on the characteristics of crystalline organization of nanosilver paste was studied using transmission electron microscope(TEM). A large number of ?growth twin? were generated during sintering process, which is related to the properties of the material itself and the sintering technology. The results showed that elevated sintering temperature and extended the holding time of temperature can increase the density and thickness of the twin. However, organic components can not completely volatile in the process of rapid sintering.