GB1005943A - Multilayer electrical circuit assemblies and processes for producing such assemblies - Google Patents

Abstract

1,005,943. Printed circuits. INTELLUX Inc. Oct. 18, 1962, No. 39424/62. Heading H1R. In the production of a multilayer electrical circuit a first circuit 24, Fig. 4, is applied by an etched foil process, or by painting or screening &c., on to a base 25 of ceramic or plastic or of metal having an insulating coating on its surface. An insulating coating 26, e.g. of epoxy resin, is applied by spraying or screening except at points where intercircuit connections are desired; then a thin layer 28 of Cu or other metal is applied by vapour deposition or, preferably, chemical reduction, over the entire surface. A second circuit 31 is then applied, as by electroplating Cu through a mask 32, which is subsequently removed, after which unplated parts of coating 28 are removed as by chemical etching. Alternatively, the whole coating 28 may be electroplated, the second circuit pattern being formed thereon in photoresist material, and the remainder of the electroplated coating being etched away. The process may be repeated until all circuits have been formed; Fig. 7 shows an assembly of three circuits, the connection between them being by means of an electrodeposited plug 44, keyed to insulating layers 26, 41. The plug 44 may be drilled to receive a component lead. The insulating coating 26 may be formed of a porous sheet, e.g. glass cloth or perforated polyester resin, coated on one or both sides by resin, applied in liquid or sheet form. The porous sheet may itself carry a conductive pattern; e.g. a thin sheet of Cu, laminated to a porous glass or resin sheet, may be etched to form the said pattern. An inlaid circuit is made by forming the first circuit pattern on a temporary support 51, Fig. 13; an insulating layer 52, a thin conductive coating, and the second circuit pattern are then applied, as described above. A permanent base 54, preferably a sheet of uncured thermoplastic material, is then bonded to the structure by heat and pressure, after which the temporary support 51 is removed. In the Fig. 4 embodiment, after the insulating coating 26 has been applied, the exposed portions of the first circuit may be built up to the level of the insulating coating 26 by electrodeposition. This is shown in Fig. 16, in which, moreover, the thin conductive coating 76 only partly covers the electrodeposited portion, so that the second circuit 77 is partly formed directly on to said portion.