Dielectric Behavior of an Electrically Conductive Metal-Particle Thick Film

Electrically conductive metal-particle thick films made from paints upon volatile component evaporation are widely used for electrical contacts and interconnections. Prior work on the electrical behavior of these films addressed the electrical conduction behavior only. This work provides the first report of the dielectric behavior, which impedes conduction. The metal is silver flake amounting to 37.5 vol.% of the film, which is obtained from the paint by room-temperature drying. The paint contains 8.5 vol.% silver, 13.8 vol.% acrylic resin and 77.3 vol.% volatile solvent. Along the length of the thick-film conduction line (76.21-mm-long, 1.73-mm-wide and 19-µm-thick), the relative permittivity is 1.2 × 10⁶ (10 kHz) and the DC resistivity is 1.7 × 10⁻⁴ Ω cm. The fraction f of carriers that participate in the AC polarization through carrier-atom interaction decreases with increasing inter-electrode distance l. For silver, the carriers are the valence electrons. For the silver thick film and l = 50 mm, f is 2.5 × 10^-12, which is lower than 2 × 10^-9 for graphite-flake thick film (made from paint) and 2 × 10⁻¹¹ for monolithic graphite, due to the higher carrier concentration in silver than graphite (semi-metal); for the silver thick film f is higher than 4 × 10^-14 for monolithic Sn-4Ag alloy, due to the thick-film inter-particle interfaces promoting carrier-atom interaction.