Surface Treatment Of Insulation Polyimide Film By Low-temperature Plasma

With the development of the electrical and electronic technologies towards high-tension and integration, insulation with higher dielectric properties are required, so new technology are proposed to modify existing material or new materials are developed. Insulation breakdown voltage increased significantly by low-temperature plasma surface modification, because of plasma's wonderful chemistry properties. Much work has been done domestic and abroad, but the mechanism of enhanced breakdown voltage by plasma surface modification has uniformed, that is the tenet of this dissertation. Polyimide (PI) film with a superior competitive electrical property was chose as the treatment insulation, and was prepared by two-step polymerization in this thesis. The breakdown voltage was increased after exposing to Oxygen plasma. Main researches of thesis are included as follow:(1) The property of low-temperature plasma was introduced, the routine plasma source and its diagnostic principle was discussed. The application of low-temperature plasma in insulation production and modification was summarized. The main content of this thesis has been given out.(2) By comparing several plasma sources, source suitable for insulation material surface modification has been selected. Introduced the forming process of surface wave and outlined sketch map of antenna and the whole SWP (surface-wave plasma).(3) Langmuir probe has been were designed for diagnosing RF plasma, but the satisfying results were not obtained. The problems have been discussed and methods have been given out. Compared with Langmuir probe, microwave interferometry diagnostic can be adopted because it is impervious to RF signals.(4) Oxygen plasma was excited by CCP source and was used to treat polyimides (PI) films surface. The ac breakdown voltage of PI films which was surface modified by oxygen plasma with different treatment time were measured. The ac breakdown voltage increased 12% when treatment time is 30 seconds.(5) The dielectric breakdown theory was studied, which is the base of increasing breakdown voltage. The process of plasma treatment can produce free radicals, polarity groups and form cross linkage lays. These chemical reactions may change the structures of the film surface, and bring about the reduction of initial charge injection and decrease of charge conductivity in the bulk. Decreased the charge injection and charge conductivity in the bulk should prevent dielectric breakdown from taking place, thus can lead to increase of the breakdown voltage of the film.