The recent advances in surface mount conductive adhesives

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 SnPb 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 electronic applications. Unstable electrical conductivity or contact resistance under elevated temperature and humidity, and the impact resistance of the adhesive interconnections are two areas that need immediate improvement. A structure-property-performance 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 oxidation of the metal surface may be the principal cause of unstable conductivity. This study also identified energy dissipation as the key factor governing SMCA impact resistance, which is characterized by the drop test performance. Accordingly, reduced modulus and increased loss factor were found to be the material properties of importance. This study not only led to a thorough understanding of the property-performance relationships of the SMCA material, but also yielded a series of novel adhesive materials with superior performance.