Change in electrical conductivity of electrically conductive adhesives during curing process

摘要

In principle, the conductivity mechanism of electrically conductive adhesives (ECAs) is described by percolation theory. However, no universal conclusion has been reached regarding this matter because these adhesives vary depending on the materials present between metal particles and the intimacy of metal-to-metal contact. In this work, the change in electrical resistivity during curing of silver particle-dispersed epoxy resin adhesives, which are commonly used as ECAs, was measured in situ to evaluate the effect of each component material of the adhesives on its electrical properties. The ECAs containing silver particles coated with different fatty acids exhibited different electrical resistivity changes during curing. Before curing, most of ECAs were not electrically conductive. The ECAs containing silver particles coated with hexanoic acid demonstrated an electrical resistivity of 4.0 x 10(-3) Omega m before curing, exhibited a rapid decrease in electrical resistivity at low temperatures (100-140 degrees C), and achieved an electrical resistivity of 5.5 x 10(-7) Omega m after curing. In addition, dipropylene glycol monomethyl ether acetate, the solvent contained in the conductive adhesive, reduced the contact resistance between silver particles. A high amount of the solvent in the ECAs resulted in a low electrical resistivity after curing. Furthermore, in this curing system, cure shrinkage was a minor factor affecting the electrical conductivity. Our study revealed that the thin fatty acid layer provided insulating properties to the silver surface. During curing, the fatty acids were removed from the particle surface via evaporation, and the electrical resistivity of the conductive adhesives decreased considerably. GRAPHICS .