Testing of techniques for improvement of conductivity of electrically conductive adhesives

The paper presents methods, which have been used for improvement of electrical conductivity of electrically conductive adhesives with isotropical electrical conductivity. Conductivity level depends, among other things, on level of aggregation of filler particles. The research has been focused on improvement of electrical properties by better aggregation of filler particles in adhesive. Following methods have been tested with the goal to support aggregation: ultrasound mixing for 60s, rotary mixing for 60 s, and addition of a small amount of AgNO3. The goal of addition of this salt has been to decrease Coulomb forces between particles of filler. Four types of formulations have been used for experiments. One-component formulations: adhesives bisphenol epoxy resin with 75 % (wt.) silver flakes, bisphenol epoxy resin with 75 % (wt.) silver flakes + 10 % (wt.) silver nanoparticles, bisphenol epoxy resin with 65 % (wt.) silver flakes + 20 % (wt.) silver nanoparticles. Two component formulation: bisphenol epoxy resin with 55 % (wt.) silver flakes. It has been found that ultrasound mixing has low influence only to the value of the electrical conductivity of adhesive, rotary mixing before application of the adhesive improves electrical conductivity significantly; addition of AgNO3 into the adhesive has improved electrical conductivity of two formulations and has had almost no effect for two other formulations. As a part of this work the course of electrical conductivity of adhesives during the curing time has also been investigated.