Miniature Lacquer Film Capacitors

Abstract

Miniaturization of capacitors for low voltage applications has been restricted by lack of availability of thin dielectric films which can be handled mechanically. This restriction is not relieved by ceramics with dielectric constants of one or two thousand, because of the relatively thick films which must be used, because of the poor performance of such ceramics at elevated temperature, and because ceramics do not lend themselves to construction of wound capacitors to provide high capacitance values. Lacquer film capacitors represent an attempt to overcome the restriction on dielectric thickness. Although these capacitors are still in the development stage they show considerable promise for use in transistor circuits. One type of lacquer film capacitor is made by casting a thin dielectric film on a supporting base and carrying it through the process of metallizing and slitting while supported. After stripping the film, the only mechanical process which it has to endure as a self-supporting sheet is that of being wound into capacitor units. Metallized films 0.1 mil thick have been made in appreciable quantity, and resulting capacitors are about one-seventh the size of the smallest metallized paper capacitors. For fragile dielectrics, the supporting film may be wound into the capacitor unit. This type suffers in compactness when compared with the stripped lacquer film type, but its use may be justified when it is desired to use fragile dielectrics of exceptional electrical properties.