High Performance Conductive Adhesives for Lead-Free Interconnects

Abstract

Tin-lead solder alloys are widely used in the electronic industry. With the recognition of toxicity of lead, however, electrically conductive adhesives (ECAs) have been considered as one of the most promising alternatives of tin-lead solder. While silver is the most widely used conductive fillers for ECA, silver migration has been the major concern for the high power and fine pitch applications. In this paper, a novel approach of using self-assembled monolayers (SAMs) passivation has been introduced to control the silver migration in nano-Ag ECAs. The protection of silver nano particles with SAMs 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. Unlike other migration control approaches which sacrifice electrical performance, the SAM passivated nano Ag fillers also enhanced the electrical conductivity and current carrying capability of adhesive joints significantly due to the improved interfacial properties and high current density of those molecular monolayers. 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 ×100 µm 2 ) and the maximum allowable current was higher than 3500 mA. 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.