The influence of filler particle shapes on adhesive joints in microwave applications

Electrical conduction of adhesive joint is provided by the metal content. High conductivity requires high metallic content. Isotropic electrically conductive adhesives are usually manufactured with filler concentration sufficiently greater than percolation threshold to guarantee low resistance with allowance for manufacturing tolerances. But we have found that it is not sufficient in a case of microwave applications. In this work we have measured the quality factor of resonant circuit at the frequency of 3.5 GHz, which was made as stripline circuit including the measured joints. Adhesives were formulated on the base of two kinds of resin with four type of silver filler. Filler materials differ from each other as regards the shape of particles and their dimensions. It was stated that kind of silver filler, the interaction of filler/type of resin as well as the state of the surface of adhesive layer plays important role in the case of solder replacement with electrically conductive adhesives in microwave electronics.