Analysis of test coupon structures for the extraction of high frequency PCB material properties

The driving forces behind low cost RF/Microwave components and the ever increasing data rates of the digital world have resulted in a proliferation of printed circuit board (PCB) materials and manufacturing techniques to provide cost effective solutions for modern day applications. This has resulted in the need for practical ways of identifying the frequency dependent loss properties of the after fabrication or “as-fabricated” PCB designs for accurate pre- and postlayout simulation. Variations in key parameters such as dielectric constant, loss tangent, dielectric height, etched trace width, surface roughness, glass weave, moisture content, etc. can easily reduce the effectiveness of simulations to predict the final design performance. Few companies have the time, money, or equipment to fully dissect a fabricated PCB and determine all of these key dimensions and material loss properties for a design. There is a strong need for simpler techniques, such as measurable test structures, that can enable extraction of material properties for improved accuracy of simulations. Recent papers using two transmission line lengths do demonstrate measurements of dielectric constant and complex loss tangent [1,2,3,4], but this method makes it difficult to predict the as-fabricated PCB trace width and dielectric height. The intent of this paper is to explore the addition of Beatty series resonant impedance structures [5] to improve the accuracy of extracting the as-fabricated PCB material properties for the purpose of constructing 3D-EM simulations.