Dielectric Characterization of Stacked Packaging Substrates Using a Coaxial Transmission Line Technique

In this paper, the dielectric characterization of RT/duroid® 5880 is presented from 100 MHz to 8.50 GHz, using a coaxial transmission line technique, by stacking the material under test (MUT) inside a 3.50 mm airline. We stacked 3.10 mm thick toroidal pieces to increase the total length of the MUT for better accuracy of the method. The extraction method is wideband and reference-plane-invariant (RPI) which combines Nicolson-Ross-Weir (NRW) and Baker-Jarvis methods. The data analysis reveals that the dielectric properties approach the datasheet value over a wideband for thick MUT. The measured mean dielectric constant for three stacked pieces of 9.30 mm thick (0.39λ) MUT is 2.32 below 1 GHz and 2.22 above 1 GHz, compared to the datasheet value of 2.20±0.02. The extracted loss tangent of simulated and measured data is 0.002 from 1-8.5 GHz compared to the datasheet value of 0.0009.