Patent GB-995177-A (GB)
Title: Multi-layer capacitor
IPC: H01G4/255
Filed: 1963-05-24
Abstract: 995,177. Capacitors. AEROVOX CORPORATION. May 24, 1963 [Sept. 6, 1962], No. 20766/63. Heading H1M. A miniature ceramic capacitor is constructed by forming and drying thin coherent green ceramic sheets containing a plastic binder, out of an air-free slip which is cast on a non- absorbent surface, by imposing electrodes on such sheets composed of a refractory metal non- oxident at the firing temperature; by die punching out the electroded elements of the sheets into a stack which is consolidated under high pressure, and firing to burn off the binder and mature the ceramic; conducting metal being present along the respective exposed electrode edges of the sheets to give parallel connections to opposed electrodes. A ceramic slip of titanate, zirconate or stannate of alkali earth metals e.g. calcium, barium, strontium; of titanium dioxide; or of alumina or steatite; admixed with water, polyvinyl alcohol or other binder, and a lignate, alginate, or other defloculant; is freed from air by dispersal in vacuo and cast on a smooth impervious surface; after which it is dehydrated or oven dried into a coherent flexible sheet. Electrodes are applied to opposite sides of the sheet by offset printing, spraying, painting, or screening using a suspension of platinum, palladium, or other refractory noble metal in a high boiling point organic solvent such as butyl cellosolve or carbital acetate with a binder. Sheet 16 (Figs. 1, 2) has electrodes 10, 11 imposed alternately on opposite faces with connection tabs 12, 13 extending outwardly in opposite senses, and after drying the sheet is placed over a die 18 (Fig. 3) from which punch 19 punches out successive elements defined by outlines 14 to leave margins 28, into a stack 20 retained by lower punch 21 in the die recess 22; the tabs 12, 13 being cut off flush with the sides of the stack. Pressure of 10 to 20 tons p.s.i. is applied to the punches, and the pack is fired at 2100‹ to 2600‹ F. into a solid block with the tab ends of alternate electrodes exposed on opposite sides (Figs. 4, 5, not shown) which may be metallized with e.g. silver at 25 for soldering at 28 of axial leads 27 (Fig. 6) and the block may be protected with insulating material. Metallizing may be applied before firing. Alternatively a ceramic strip 35 may be electrode coated on each side at 36, 38 with opposed uncoated margins, and sections are punched therefrom so that margins 40, 41 alternate on opposite sides (Fig. 8). The sections are compressed into a pack (Fig. 9) with alternate electrodes exposed on opposite sides 44 of the block, to which metallizing is applied at 45 and axial leads 46 are soldered at 47; the block being enclosed in a layer of porcelain glaze or an epoxy, silicone, or phenoline resin. Plural capacitors may be assembled in a single block by applying single electrodes with tabs to the tops of even sheets and bottoms of odd sheets, and triple parallel tabbed electrodes to the tops of odd sheets and bottoms of even sheets in a pack, compressing, and firing; the tabs of the single electrodes and those of the triple electrodes emerging respectively on adjacent sides of the block and being appropriately interconnected by metallizing for soldering to connecting leads (Figs. 11, 12, 13, 14, 15, 16, not shown). The dielectric sheets may be metallized with alternate circular and annular electrodes on top and bottom faces and the elements may be punched out leaving alternate circumferential and central margins. After compression, the pack is jig drilled centrally to clear and to intersect alternate electrodes and fired, after which the periphery and the inside of the drilling are metallized for respective connection to alternate electrodes (Figs. 20 to 23, not shown). The drilled and fired block may be soldered to a central conductor 115 and also soldered into a cylindrical steel case 119 (Figs. 24, 25). The capacitors may be calibrated by edge grinding and the electrode elements may be metallized and punched to irregular shapes.