GB1276527A - Thermal dissipating metal core printed circuit board - Google Patents

Abstract

1276527 Printed circuits INTERNATIONAL ELECTRONIC RESEARCH CORP 30 Oct 1969 [1 Nov 1968 19 Sept 1969 13 Oct 1969] 53327/69 Heading H1R [Also in Division C7] A metal core printed circuit board has a circuit pattern on one or both sides, 'and possibly passing through holes in the core, formed on a layer 15 of synthetic plastics resin such as polyurethane coating the metal core, the layer 15 having keying-depressions 16 produced by mechanical and chemical etching to support the circuit pattern. The circuit pattern is made up of metal layers, the base layer of nickel 25 being keyed to the resin by means of the depressions and seeds of a pure metal, e.g. palladium (20, Fig. 5), deposited in the depressions. The other layers comprising the circuit pattern are a further layer of nickel 27, two layers of copper, 28, 29, the former being thinner than the latter, and possibly an overplating 35 of tin, solder or nickel. In an alternative embodiment (Fig. 16, not shown), the base layer of nickel (25<SP>1</SP>, Fig. 16) has layers of copper (26<SP>1</SP>), nickel (27<SP>1</SP>), copper (28<SP>1</SP>), copper (29<SP>1</SP>), and an overplating of tin-lead, gold or rhodium. In a further embodiment only the two layers of nickel 25, 27, and the copper layer 28 with an overplating metal form the circuit pattern. The metal sheet 10 is preferably aluminium but may be copper, a copper alloy, titanium, steel, magnesium or lithium-magnesium alloy, which is etched, anodized, treated with a primer, and coated with from three to ten coats of synthetic resin, heat cured, and sandblasted to produce cavities (17<SP>1</SP>, 18<SP>1</SP>, Fig. 6) for the seed metal (20, Fig. 5). The outer resin layer may contain nickel oxide or other metallic salt which is reduced to the metal to enhance adhesion of layer 25. Palladium metal is deposited from palladium chloride into the cavities (17<SP>1</SP>, 18<SP>1</SP>, Fig. 6), and electroless nickel layer 27 is deposited from given nickel salts on to the resin layer 15, followed by electrodeposition of the other metal layers. To form the circuit pattern the metallic layers are etched away, except where a wet or dry resist material protects them, or alternatively a resist material which may be applied using photographic techniques is applied to regions away from the circuit pattern which is thickened by electrodeposition of copper which receives an overplating metal of, for example, tin-lead, gold or rhodium. The resist material is then removed and the overplating itself protects the circuit pattern from the etchant which removes the metal layers elsewhere. In a modified process, nickel is grown on the palladium seeds from a nickel salt with boron reduction (Figs. 14, 15), followed by an electroless nickel deposit as before. Examples of etchants and other chemicals used are given, as well as examples of resist materials which can be used, and appropriate thicknesses of the various metal layers are given.