A novel non-migration nano-Ag conductive adhesive with enhanced electrical and thermal properties via self-assembled monolayers modification

Silver migration has long been one of the most critical issues in semiconductor electronic industry, while no effective approaches have been developed to control silver migration and maintain its excellent electrical and thermal properties. In this paper, we report a novel approach of using molecular self-assembled monolayers (SAMs) to dramatically reduce silver migration in the nano-Ag conductive adhesives. The protection of silver nano particles with molecular monolayers reduced the silver migration dramatically and no migration was observed upon application of high voltages (up to 500 V) due to the formation of surface chelating compounds between the SAM and nano silver fillers. The migration behavior of SAM passivated nano-Ag conductive adhesives was investigated by analyzing the results with DiGiacomo´s model. In addition to a controlled migration, the SAM passivated nano Ag fillers also enhanced the electrical conductivity and current carrying capability of ACA joints significantly due to the improved interfacial properties and high current density of those molecular monolayers. Unlike typical anisotropic conductive adhesive (ACA) joints which showed high joint resistance and limited current carrying capability, the joint resistance of the SAM incorporated nano-Ag conductive adhesive could be achieved as low as 10^-5 Ohm (the contact area is 100 times 100 mum ) and the maximum allowable current was higher than 3500 mA. Furthermore, the improved electrical performance of SAM treated nano Ag ACAs was also achieved with the increased thermal conductivity. As such, a fine pitch, high performance, non-migration and high reliability adhesives are developed for potential solder replacement in high voltage, high power device applications. The novel approach for silver migration control and electrical properties enhancement can also be applied in next generation high performance semiconductor devices to replace aluminum and copper metallization with the bett- - er performance silver