Pressure dependent conduction behaviour of various particles for conductive adhesive applications

The efficiency of electric conduction in particle filled conductive adhesives largely depends on the interparticle conduction. In order to gain insight into the pressure dependent conduction behavior with particles of different size, shape and type, the effects of external pressure on the filler resistance were measured by the four-point probe method using different conductive fillers. The following types of particles were used: Ni powder, Ni flake, Ag powder, Ni filament, magnetite (Fe₃O₄) spindles, and Cu particles. Nonfilament particle size was in the 0.7-44 μm range. The filaments were 20 μm in diameter, and 160 or 260 μm in length. Particle treatment procedures assessed included silver coating using different methods, and the use of acid solutions including H₃PO₄, HF, and HCl to remove the surface oxide layer. Resistivity levels were measured using a nonconductive hollow cylinder plunger device developed in the authors´ laboratories