Preparation and characterization of cordierite filled PTFE laminates for microwave substrate applications

Abstract

Phase pure cordierite (2MgO center dot A 2Al(2)O(3) center dot A 5SiO(2)) powder was prepared through solid state ceramic route. Silane coated cordierite powder was filled in the PTFE matrix through SMECH process comprising of sigma mixing, extrusion, calendering, followed by hot pressing, to fabricate flexible microwave substrates. Filling fraction of cordierite in the PTFE matrix was varied from 10 to 70 wt% and its effects on density, dielectric properties, coefficient of thermal expansion and water absorption were investigated. The morphology and filler distribution of the filled composite were studied by SEM. Waveguide cavity perturbation technique was employed to measure the dielectric properties of the composites at X-band (8.2-12.4 GHz). Dielectric constant and loss tangent were found increasing with filler loading from 10 wt% (epsilon (r)' = 2.17, tan delta = 0.0007) to 60 wt% (epsilon (r)' = 3.17, tan delta = 0.0034).