Patent GB-1075094-A (GB)
Title: Improvements in or relating to capacitors
IPC: H01G4/14
Filed: 1963-12-20
Abstract: A method of making capacitors, comprises vapour-depositing a reactive p-xylylene diradical on to a substrate surface cooled to a temperature below the condensation temperature of the p-xylylene diradical thus forming a film of linear poly (p-xylylene) thereon, continuing until said film has a thickness of at least 100A, and there-after applying at least one conductive metal layer, e.g. chromium, aluminium, lead, zinc, silver, gold, silenium, cadmium, copper, tin, nickel or iron, to the exposed surface of the film, said metal layer being applied either as a self-supporting foil or by vacuum deposition, in which latter case the layer may have a thickness of from 100 to 5000 A.  The substrate may be a self-supporting metallic foil or wire, or a plastics or other insulative material surfaced by vacuum deposition with a thin metallic coating.  Further alternate layers of the diradical and metal may be applied, and the final product may be used either as a planar capacitor or it may be wound up into a coil or roll.ALSO:Capacitors are encapsulated in poly(p-xylylene), wax, epoxy resins or other materials.  The capacitor, particularly those for use in micro-miniaturized circuitry, may be made by vapour depositing a reactive p-xylylene diradical on to a metal substrate surface cooled to a temperature below the condensation temperature of the p-xylylene diradical thus forming a film of linear poly (p-xylylene) thereon, continuing until said film has a thickness of at least 100 , and thereafter applying at least one conductive metal layer, e.g. chromium, aluminium, lead, zinc, silver, gold, selenium, cadmium, copper, tin nickel or iron, to the exposed surface of the film said metal layer being applied either as a self-supporting foil or by vacuum deposition, in which latter case the layer may have a thickness of from 100 to 5000 . The substrate may be a self-supporting metallic foil or wire, or a plastics or other insulative material surfaced by vacuum deposition with a thin metallic coating.  Further alternate layers of the diradical and metal may be applied, and the final product may be used either as a planar capacitor or it may be wound up into a coil or roll.  In a preferred embodiment, a single element rolled capacitor comprises a complete envelopment of poly (p-xylylene) about a metal foil which is then vacuum metallised on both sides except for a narrow margin along one edge.  After rolling, the end of the cylindrical unit presenting only polymer coated foil is cut to bare the foil and the electrode surfaces are connected to wire leads by spray soldering or conductive glues, paints or resins.  Optionally, the complete capacitor may then be encapsulated in poly (p-xylylene), wax, epoxy resins or other materials.  The term "p-xylylene diradical" comprises those compounds having one free radical site on each of two x-atoms attached in para-position to an aromatic nucleus, i.e. those represented by the formula:  <FORM:1075094/B1-B2/1> where y represents any inert monovalent group, preferably hydrogen.  They may be made by the pyrolysis of an aryl bis sulphane, a diaryl sulphane or, preferably, at least one cyclic dimer, and they may be substituted or unsubstituted, suitable substituent groups being any organic or inorganic group which can normally be substituted on an aromatic nucleous or on the aliphatic x carbon atoms of such a diradical, e.g. the halogens or alkyl or other groups.  When several different diradicals exist in the pyrolised mixture they will each have different condensation characteristics and consequently by selecting the appropriate temperature and pressure either homopolymerisation or copolymerisation can be achieved.  Examples are included which describe apparatus and detailed techniques for carrying out the method of the invention, and tables are included which list typical properties of the products and compare these properties with those of conventional capacitors.