Novel conductive adhesives for surface mount applications

Electrically conductive adhesives (ECAs) have been explored as a SnPb solder alternative for attaching encapsulated surface mount components on rigid and flexible printed circuits. However, limited practical use of conductive adhesives in surface mount applications is found because of the limitations and concerns over current commercial ECAs. One critical limitation is the significant increase of joint resistance with SnPb finished components under 85°C/85% relative humidity (RH) aging. Conductive adhesives with stable joint resistance are especially desirable. In this study, a novel conductive adhesive system based on epoxy resins has been developed. Conductive adhesives from this system show very stable joint resistance with SnPb finished components during 85°C/85% RH aging. One ECA selected from this system has been tested here and compared with two popular commercial surface mount conductive adhesives. ECA properties studied included: cure profile, glass transition temperature (T_g), bulk resistivity, moisture absorption, die shear adhesion strength, and shift of joint resistance with SnPb metallization under 85°C/85%RH aging. It was found that, compared to the commercial conductive adhesives, our in-house conductive adhesive had higher T_g, comparable bulk resistivity, lower moisture absorption, comparable adhesion strength and, most importantly, much more stable joint resistance. Therefore, this conductive adhesive system should have better performance for surface mount applications than current commercial surface mount conductive adhesives