Dielectric and Underfill Characterization Using Cavity Resonators for Millimeter-Wave Applications

Having an accurate dielectric constant and loss tangent when creating radiofrequency (RF) models in full-wave simulation is essential. With the introduction of new low-loss dielectrics and with the variability of dielectrics due to the manufacturing process, there is a need for a quick and simple method to characterize the permittivity of these materials. Dielectric characterization has become even more critical with the rollout of 5G cellular communications. At the higher frequency bands of 5G, around 28 GHz and 39 GHz, the dielectric losses can be significant, and the package design can be sensitive to dielectric constant variations. In this letter, two dielectrics are characterized; a flip-chip underfill material and a low-loss dielectric. Cavity resonators are used to extract the dielectric constant and loss tangent of flip-chip underfill, while substrate integrated waveguide (SIW) resonators are used to characterize packaging substrates. Simulations and extractions of the dielectric constant and loss tangent are completed at several frequencies using an in-house tool called Kappa Extractor, based on a rapid plane solver. The results are verified with a commercial full-wave simulator.