Title: Thermally Stabilized RF Hybrids for Improved Power Handling and Reliability
Primary Author: Hoffman, James
Organization: Jet Propulsion Laboratory
Co-Author(s): Linda Del Castillo, Gajanana Birur, Jennifer Miller
Active antenna arrays are composed of tens, hundreds or even thousands of densely packed TR (transmit/receive) modules. Thermal handling, especially for spaceborne platforms, is critical to instrument performance and reliability. New concepts for civilian spaceborne radar, such as DESDynI, employ active feeds with large passive reflectors. These concepts require even higher RF power densities for the active feed. This work investigates designing thermal management at the beginning of TR module design, and integrating existing and novel technologies to significantly improve thermal management. This is accomplished through the use of advanced materials with reduced thermal resistance and low coefficients of thermal expansion (CTEs) that are matched with those of the electronics as well as novel heat storage methods for power cycled electronics. To reduce the thermal resistance of the electronic module, we are investigating the implementation of Stablcor (carbon core laminate) high thermal conductivity, low thermal sensitivity composite layers with RF materials. Our goal is to build printed circuit boards (PCBs) that can move heat out quickly, while maintaining their shape and RF properties to improve both reliability and performance. The electrical, mechanical, and thermal performance of these carbon composite boards are being compared with that of the baseline thick Cu core RF printed circuit boards. In addition, we are evaluating spray deposited Si-Al alloys for use within the electronic chassis. Some of the benefits of this family of materials are CTEs that are closely matched with those of Si and GaAs devices, which reduce the stresses generated within the die attachment during thermal cycling, as well as high thermal conductivity and low density. We will discuss the results of mechanical behavior analyses and application specific die attach studies.
We are also investigating PCM (Phase Change Material), which is a reservoir of carbon fiber impregnated paraffin encapsulated in an aluminum carrier. Properly designed PCM absorbs heat through phase change of the paraffin during periods of peak power, and can substantially mitigate thermal cycling, which improves reliability and improves stability.