GB1116299A - Method of preparing printed circuits - Google Patents

Abstract

1,116,299. Method of preparing printed circuits. UNITED-CARR Inc. 5 April, 1967, No. 15566/67. Heading H1R. In a method of preparing printed circuits a transfer plate 1, Figs. 4, 5, which is to form a temporary base for the circuit, is coated with a separable thin film or so-called parting layer 2 comprising an admixture of powdered electrically conductive material with an organic solvent, soluble resin or wax. A negative resist pattern (3), Fig. 2 (not shown) is laid on the layer 2, e.g. photographically, and a copper circuit pattern is then formed preferably electrolytically, the conductive layer 2 acting as a common cathode during plating. The resist is then removed by a solvent which will not attack the parting layer, leaving the arrangement shown in Fig. 4. A permanent insulating base 5 is now molded against the exposed surface of the circuit and parting layer, and finally the transfer plate 1 and layer 2 are removed leaving a conductive pattern flush with its insulating base, the assembly having a smooth surface which conforms to the surface of the transfer plate on which it was formed. The assembly may be used as a commutator or as the fixed contacts of a slider switch. The transfer plate 1 may be of glass, stainless steel or synthetic plastics, and the "parting" layer 2 may be a homogeneous dispersion of graphite or powdered metallic conductor in beeswax, silicone wax, synthetic hydrocarbon, carnauba, or in organic solvent soluble synthetic resins or waxes such as polystyrene, polyvinyl acetate etc. The permanent base may be any suitable curable insulating substance such as Bakelite (R.T.M.) and other phenolic resins, alkyd resins, polyesters, nylon, ureaformaldehyde resins, epoxy resins, melamine plastics or ceramics. The base material is cured in situ by the application of heat and pressure. The " printed " deposit may be metal or a semiconductor such as selenium, germanium, copper sulphide, cadmium sulphide; or integrated circuits of combined semi-conductive and conductive materials may be formed.