Electrical properties and practical applications of Liquid Crystal Polymer flex

Abstract

We present the electrical characterization of our Liquid Crystal Polymer (LCP) at microwave and millimeter frequencies and the applications of LCP to circuit components. We use several methodologies to determine the electrical characteristics of LCP for microwave and millimeter wave frequencies. Cavity resonators [1], microstrip T-resonators [2], and microstrip ring resonators [1, 3] are measured in order to characterize both the dielectric constant and loss tangent up to 40GHz. The measured dielectric constant is shown to be steady near 3.0, and the loss tangent stays below 0.002, which is better than conventional FR-4, BT, and polyimide materials. Furthermore, microstrip lines are designed and fabricated on both LCP substrate and other conventional materials in order to compare loss characteristics. The measured insertion loss at 40GHz of microstrip lines on a LCP substrate (25μm) and a polyimide substrate (25μm) is 0.11dB/mm and 0.18 dB/mm, respectively. These results show that LCP has excellent and stable dielectric properties at high frequencies and the data suggests that this material can be used for applications extending through millimeter wave frequencies. LCP's inherent properties such as multi-layer capabilities, excellent electrical properties, flexibility, and near hermetic nature suit it to a wide range of applications such as passive devices, packages, and RF cables. Finally, we demonstrate the development of a banpass filter on LCP flex to achieve an insertion loss less than 1 dB at 6GHz in the passband, which is comparable to that of LTCC. The microwave characteristics of LCP have provided the feasibility of this material for low cost and high performance substrates for microwave and millimeter wave applications.