Fabrication of low thermal expansion and low dielectric ceramic substrates by control of microstructure

An alumina platelet-filled, cordierite matrix was studied as a ceramic substrate having a low thermal expansion coefficient and low dielectric constant. Alumina platelet powders, 3-5 μm, 5-10 μm, 10-15 μm and 15-25 μm in size, were mixed with amorphous-type cordierite powders, which were fabricated by a soft solution process employing PVA polymer, with various compositions. Slip cast, green bodies were sintered at 1300°C for 2 hours. The microstructures of the sintered bodies were dependant on the mixing content and particle size of the alumina-platelets. In the densified cordierite containing 10 vol% alumina platelets of 5-10 μm in size, a flexural strength of about 90 MPa, a low dielectric constant of 5.0 at 1 MHz and a low thermal expansion coefficient of 3.5 × 10^-6 K^-1 were obtained. Isolated micropores were formed in the alumina platelet-filled, cordierite matrix, and the micropores reduced the increased dielectric constant which accompanied the alumina platelet filler.