Conductive Adhesives From Low-VOC Silver Inks for Advanced Microelectronics Applications

A low-volatile organic compound, screen-printable silver ink system capable of also performing as a conductive adhesive was developed for use in advanced microelectronics. Silver flake and micron-sized spherical silver powder were used as the conductive fillers with the binder system consisting of monofunctional liquid acrylate monomers. Because of the thermoplastic nature of the cured binder system, the ink can be softened at elevated temperature even after solidification by polymerization and thus can serve as a conductive adhesive. The ink system was characterized by differential scanning calorimetry, thermogravimetric analysis, thermomechanical analysis, and scanning electron microscopy. Screen printing was carried out on both rigid FR4 substrates as well as flexible polysulfone sheets. Efficacy of this conductive adhesive was demonstrated by bonding the Ag ink to a copper radio-frequency identification antenna using an Ohashi bonder (T = 140°, P = 40 psi, t = 2 min) where resistance values <; 1 Ω were measured through the adhesive bond and shear tests showed yield strengths on the order of 10 N.