A liquid displacement test method for determining the anisotropic dielectric properties of printed wiring boards

The increasing use of precision printed wiring circuits at very high and microwave frequencies has created a growing need for insulating materials having isotropic dielectric constant and dissipation factor since the electric field of printed wiring boards is active in both the perpendicular and parallel directions. It is recognized that the dielectric properties of laminated sheet insulating materials are not the same in both the perpendicular and parallel directions and that these properties are frequency, temperature, and moisture sensitive. Therefore, the present practice of controlling the properties of such materials by measuring only the dielectric properties perpendicular to laminations has proven inadequate from a functional standpoint in critical electronic applications.