Development of high temperature polyimide dielectric film for leaded and surface mount capacitor application

The authors discuss work on the development of thin solution-cast high-temperature polyimide (PI) film, made from commercially available soluable thermoplastic polyimide resin. The detailed thermal, structural, and electrical characteristics are considered. Dielectric constant data as a function of temperature indicate that PI contains absorbed species such as water, which are removed during heating. Dissipation factor data show that at temperatures below the glass transition temperature, flexible chain motion related to local reorientation processes occurs. AC and DC electrical breakdown strengths exceed values previously reported by industry, which may be due to differences in morphology and film preparation processes. X-ray diffraction spectra and thermomechanical analysis data indicate that the PI film is amorphous and isotropic, capable of retaining its dimensional stability under load up to 300°C. Overall, PI appears to be an acceptable dielectric for surface mount multilayer film capacitors and also for high temperature leaded DC filter capacitors