A fast and accurate method for measuring the dielectric constant of printed wiring board materials

A new time-domain-reflectometry measurement method is described that provides accurate measurements of the average high-frequency (0.1 GHz to 5 GHz) dielectric constant of printed wiring board (PWB) materials and that is suitable for "factory-floor" usage. A parallel-plate transmission line is used for the sample geometry. A model is developed that describes the electrical behavior of the transmission line thereby allowing the dielectric constant to be extracted from the observed signal. The data analysis and the sample preparation are both simple to accomplish.