Effects of curing agents on the properties of conductive adhesives

Electrically conductive adhesives (ECAs) are an environmentally friendly alternative for traditional tin/lead (Sn/Pb) solders. As a new technology, conductive adhesive technology still has many concerns and limitations. In order that conductive adhesive technology achieves universal acceptance, ECAs with better properties must be developed. ECAs consist of a polymeric matrix and a conductive filler. Formulations of the polymeric matrix play a very important role in determining the overall properties of ECAs. The objective of this study is to investigate the effects of different curing agents on the properties, especially contact resistance of conductive adhesives. Five polymeric matrix formulations are prepared by mixing five different curing agents, selected from different categories, with an epoxy resin. Using these polymeric matrix formulations, five ECAs are formulated. The properties of these ECAs studied include: curing profile, glass transition temperature (Tg), coefficient of thermal expansion (CTE), moisture absorption, adhesion strength, and shifts (of contact resistance of these ECAs) on non-noble metals such as tin, tin/lead, and copper, during elevated temperature and humidity aging. Also, a corrosion inhibitor is used to stabilize contact resistance of these ECAs on Sn/Pb. It is found that (1) the curing agents do affect the properties including contact resistance of ECAs and (2) the corrosion inhibitor is effective to stabilize contact resistance on Sn/Pb in all of the five ECA formulations.