Study on evaluation techniques of effective conductivity for copper-clad dielectric substrates

Copper-clad dielectric substrates are commonly used to construct a planar circuit such as microstrip line and coplanar waveguide etc. Generally, an adhesive surface of a copper film is roughened to increase peel strength from a substrate. A measurement method of the interface conductivity for copper-clad dielectric substrates has been presented, which is based on the dielectric rod resonator method. In this method, it has been reported that can be measured the interface conductivity when a substrate thickness is 10% or less than a length of a dielectric rod. However, there has been no detailed study on the effect of the substrate thickness. In this report, the interface conductivities of substrates with different thickness are evaluated using this method. And the effect of the thickness for the measured results is studied. In addition, we investigate the relationships between the effective conductivity and the roughness of the interface.