Patent GB-1451127-A (GB)
Title: Printed circuit board
IPC: H05K1/09
Filed: 1974-05-17
Abstract: 1451127 Printed circuits MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 17 May 1974 22170/74 Heading H1R A printed circuit board formed with conductors wholly or in part of silver on an insulant substrate, e.g. alumina or other ceramic, glass, phenolic resin, imprengated paper, epoxy impregnated glass cloth; is provided with an underlayer of insulant resin between conductors and substrate and an overlayer of resin over the conductors; the resin being doped with an organic inhibitor discouraging migration of silver. The substrate may have conductively coated through holes and be planar, spherical, cylindrical or rod-shaped. A flat printed circuit board 1 has silver electrodes 3 on the surface 2 thereof over an underlayer 4, and an overlayer 5 is applied thereto (Fig. 3) the underlayer being formed by screen printing with epoxy resin and heat curing, after which the electrodes 3 are screen printed with resin based silver paint and heat cured. The overlayer is formed by screen printing with epoxy resin to cover the electrodes and heat cured. The organic inhibitant admixed with the resin may be one or more of a number of aliphatic or aromatic amines or azoles, while the resin may be unsaturated polyester resin, polybutadiene resin, melamine resin, alkyd resin, phenol resin, polyurethane resin, and the like. The silver layers may be formed superincumbently on the same surface separated by the overlayor (Fig. 4, not shown) or underlayers of resin 4 are formed on both sides of the substrate to receive silver conductors 3 overcoated with resin over layers 5 (Fig. 5). The electrodes may be replaced by an etched copper layer on the underside of the substrate board (Fig. 6, not shown) and through holes of the board; may be coated with inhibited resin to prevent silver migration, and if required with silver and over coating resin (Figs. 7a, 7b, not shown). Silver conductors may be formed on the surface and edges of the substrate to interconnect the two surfaces with an underlayer and overlayer extending over such edges (Fig. 8, not shown) and a resistor may be embedded in the resin underlayer between two electrodes (Fig. 9, not shown) and the underlayer may be omitted under the resistor (Fig. 10, not shown). A silver conductive layer may overlay part of the resistor for adjusting its value (Fig. 11, not shown). The resin coatings may be omitted from certain conductors (Fig. 12, not shown) or from the walls of the through holes when the conductors therein are not silver (Figs. 13, 14, not shown). A conductive layer of another material may be printed round the coated silver conductors to prevent silver migration over the board edges (Fig. 15, not shown). In a multilayer printed circuit board copper conductors 3c may be printed directly on the substrate overlain by resin 5, and superimposed silver layers may similarly be overlain by resin 5<SP>1</SP> (Fig. 16). A resin underlayer may be provided when the conductors nearest the substrate are silver (Fig. 17, not shown) and a further resin layer 42 may be applied after the initial layer 41 has been applied and heat cured; to reduce pinholing. Thereafter electrodes and successive overlayers 51, 52 are applied (Fig. 18). Capacitors may be formed on underlayers by applying a lower silver electrode, a dielectric, and an upper silver electrode with thereupon a resin overlayer.