Conductive adhesives with stable contact resistance and superior impact performance

Abstract

Surface mount conductive adhesives (SMCAs) provide an environmentally friendly solution for interconnections in electronic applications. In addition, SMCAs offer other attractive technical advantages over conventional Sn/Pb metal solders including low temperature processing and fine pitch capability. However, there have been major obstacles preventing SMCAs from becoming a general replacement for metal solders in the electronics industry. Unstable electrical conductivity, (contact resistance), under elevated temperature and humidity conditions, and the inferior impact resistance of the adhesive interconnections are the two fatal flaws for current commercial SMCA products. A systematic study was undertaken to identify the fundamental mechanisms contributing to unstable contact resistance and poor impact resistance of current SMCAs. This study demonstrated that contact resistance stability depends strongly on the metals involved and suggested that electrochemical corrosion of the metal surface is the principal cause of unstable contact resistance. This study also identified energy dissipation as the key factor governing the impact resistance, or the drop test performance, of the SMCA interconnects. Based on the above fundamental understandings, novel approaches were taken to develop next generation SMCAs. These exploratory materials demonstrated significantly improved contact resistance stability and superior impact performance.