Effects of Reducing Agents on the Electrical Properties of Electrically Conductive Adhesives

Electrically conductive adhesives (ECAs) are a promising alternative for lead-containing solders in electronic packaging. However, the conductivity of ECA is lower than that of solders due to the physical contact between conductive fillers and insulative organic lubricants on Ag flakes. In this study, a group of reducing agents were introduced into a typical ECA formulation. During the curing process, the reducing agents can reduce metal oxide within ECAs. At the same time, the consumption of oxygen with the reducing agents prevents further oxidation of the metal fillers in the ECA. The oxidation product, carboxylic acids, could partially replace or remove the long chain steric acid (C-18) surfactant on the Ag flakes, improve the electrons tunneling between the Ag flakes, and act as a fluxing agents in the ECAs. As such, the multiple effects of reducing agents in ECAs improved the conductivity significantly. Dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) studies indicated the improved electrical performance was achieved without sacrificing the mechanical and physical properties of ECAs.