A model for efficient and improved measurements of the complex permittivity of thin organic packaging materials using open-ended coaxial line technique

In this paper, the open-ended coaxial line is analyzed and an improved lumped equivalent model proposed. The interaction between the probe, material under test (MUT) and the backing of the MUT is studied and the sample backing was found to have a strong effect over the results, especially over high frequencies. Consequently, an optimum dielectric backing was used for accurate extraction of the complex permittivity of thin packaging materials. The validity of the model was verified through numerical modeling and high frequency measurements, with a good correlation obtained. In particular, the implications of probe polishing on achieving measurement repeatability using the open-ended coaxial line technique were also extensively investigated. Furthermore, the effects of imposing different testing conditions on the dielectric properties of FR4 and Teflon-based laminates were investigated over broadband using the improved model, with the results compared and reported in this paper.