Dielectric behavior discovered in electrically conductive thick film

摘要

Electrically conductive thick films are used for electrical interconnections in electronic packaging. They also serve as functional coatings for materials and structures. Although the conduction behavior has long been addressed, the dielectric behavior of these films has not been previously reported. The dielectric behavior impedes conduction. This work reports the dielectric behavior of a conductive thick film made from a paint comprising 7.9 vol.% graphite flakes, 89 vol.% volatile solvent (comprising mainly acetone and iso-butyl acetate) and 1.7 vol.% acrylic resin binder. After evaporation of the volatile solvent upon drying, the flakes substantially touch one another without being sintered and form a conductive thick film in solid form. The film thickness is approximately 25 μm and contains graphite flakes at volume fraction approximately 37.5%. The relative permittivity at 10 kHz is 5 × 10~5 and the DC resistivity is 0.38 Ω.cm along the length of the film. The permittivity is much greater than that previously reported for monolithic polycrystalline graphite, partly due to the much higher resistivity. The low degree of electrical connectivity in the film compared to the monolithic graphite hinders conduction, but it promotes polarization, due to the carrier-atom interaction that is responsible for the polarization occurring at the sites of low electrical connectivity, i.e., the interface between the graphite flakes in the film. The permittivity is also much higher than that of previously reported graphite flake film in the direction perpendicular to the film, due to the long excursion distance along the length of the film of this work.