Capacitor Film Surface Assessment Studies

Three prominent biaxially oriented capacitor films were investigated for surface defect occurrence and thickness variation. The three films, polypropylene, polyester, and polyvinylidene fluoride, were chosen because of their widely different permittivities and loss behavior. polypropylene has a very low dissipation factor because of the propylene repeating group which results in a stereoregular polymer chain that is helical in nature. The propylene repeating group is also responsible for the low dielectric constant of 2.2. Polyester film shows an intermediate electrical behavior with a dissipation factor of 0.001 and a dielectric constant of 3.2 due to the bulky polyester repeating group which hinders chain movement. Polyvinylidene fluoride is very polar with a dielectric constant of ~10. However, the polar repeating vinylidene fluoride group results in an unusually high dissipation factor. An optical surface assessment system was applied to these three films to determine surface defect prevalence. Types of film surface defects and occurrence were related to film polymer structure, chemical groups and fabrication processing. Film thickness variation was low and varied for each film type. dc breakdown voltages were determined and related to film surface defects and morphology.