GB784673A - A method of producing printed circuit master drawings - Google Patents

Abstract

784,673. Etching. STANDARD TELEPHONES & CABLES, Ltd. Feb. 28, 1956, No. 6114/56. Class 100(2) [Also in Groups XV, XX and XXXVI] A method of producing a printed circuit master drawing from a scraper board, consisting of a base board covered with a white layer which is in turn covered with a black layer, comprising removal of portions of the black layer corresponding to a required circuit or its complement. As shown the circuit pattern is engraved on the scraper board which consists of a soft pulp-board backing on which is coated a layer of pure white china clay and chalk to a thickness of 0.02-0.04 inches which is covered with a 'very thin layer of black ink. The printed circuit may be produced from the master drawing by photo-engraving. Firstly an actual size reverse pattern photographic transparency is produced and secondly a transparent negative is obtained which is used to make a contact print on a copper-clad laminate coated with a photographic emulsion. The negative is placed in contact with the coated surface and atter exposure to light the laminate is developed whereby the unexposed unprinted portion of the emulsion is dissolved to leave the light-hardened emulsion as an acid resistant pattern. The laminate is then placed in an etching solution which removes all the copper that is not protected by the emulsion. If the printed circuit is produced by a screen printing method, a reverse pattern photographic transparency of the master drawing is produced as before and is used to make a stencil which is placed on to a silk or metal screen. The screen and stencil are placed on a copper-clad laminate and an acid-resistant liquid is spread over the stencil, and after being forced through, forms a pattern corresponding to the required circuit pattern. The laminate is then etched as before. The above methods in which larger areas of copper are etched away may be replaced by a method in which only thin lines are etched.