Thermally Robust Polymer Dielectric Systems for Air Force Wide- Temperature Power Electronics Applications

摘要

Thermally stable, mechanically robust, compact capacitors are the technology driver for high performance power systems. The proximity of power electronics to heat sources demands that the thermal load for electronic system cooling be reduced or eliminated in the new generation aircraft power systems. While aerospace power conditioning capacitors typically use polycarbonate (PC) films in wound capacitors for operation in the -55 deg C to 125 deg C range, there is a current need for high temperature polymer film dielectrics with dielectric stability up to 350-deg C. As part of our program toward meeting the objective of dielectric stability and reliability in capacitor devices at temperatures as high as 350-deg C, we designed and evaluated high strength polymer films with high glass transition temperatures (375-450 deg C) as well as high thermal stabilities (470-520 deg C). Variable temperature dielectric properties of metallized thin films in the RT-350 deg C range are reported for high temperature polymer systems such as fluorinated polybenzoxazoles (6F-PBO) and a fluorenyl polyester incorporating a diamond-like hydrocarbon unit, known as FDAPE. A comparative dielectric evaluation of the state-of-the-art fluorenyl polyester film FPE, with a glass transition temperature of 330 deg C, has also been performed. The focus of the study is on wide temperature dielectric measurements of film capacitance, and dissipation factor as well as insulation resistance and the effects of thermal cycling on polymer dielectric stability. Possible correlations between the thermo-mechanical properties of the polymer films and their high temperature dielectric properties are examined, from the viewpoint of their electro-mechanical stability for long-term operation in wide- temperature power electronics applications.