Patent GB-1025016-A (GB)
Title: Method of making printed circuit patterns
IPC: H05K3/00
Filed: 1963-10-29
Abstract: 1,025,016. Maps, charts and diagrams- PHOTOCIRCUITS CORPORATION. Oct. 29, 1963 [Nov. 30, 1962 (2)], No. 42512/63. Heading G5G. A method of making accurate printed circuit patterns from original inaccurate drawings of such circuits comprises the steps of projecting to a translucent screen 14, Fig. 1, through a lens 13 of an accurate reference pattern of grid markings on a developed glass photographic plate 23, Fig. 3, having superimposed thereon a translucent driving, which drawing has a similar grid and a rough outline 24, Fig. 4, of the desired printed circuit, applying to the screen opaque adhesive tape 74a accurately positioned with respect to the reference pattern to depict the printed circuit accurately, and replacing the plate 23 and drawing 24 by a photographic plate, whereby the accurately depicted circuit (Fig. 5, not shown) on the screen 14 may be projected through the same lens 13 by means of projection lights 15 to expose the photographic plate and provide said accurate printed circuit patterns. When constructing patterns for boards having printed circuits on both sides or for multilayer boards having through-connections extending to several circuit layers, it is necessary to provide accurate registry between patterns of through-connections on two or more surfaces. For this purpose the method comprises the steps of projecting to the screen 14 of the accurate reference pattern on the plate 23 together with an outline drawing of the throughconnections, whereupon circular opaque pads 14a may be applied to the screen 14 to provide an accurate representation of the throughconnection with respect to the projected accurate reference pattern. A photographic plate or film is then substituted for the reference pattern and drawing in the camera and the accurate representation on the screen 14 projected through the lens to provide a negative of the through-connections only. The reference pattern and drawing of the printed circuit on the first side are then repositioned in the camera and projected to the screen whereby adhesive tape 14a representing the conductors may be applied to the screen. The drawing of the first side together with the reference pattern is then replaced by a photographic plate and the accurate printed circuit representation of the first side projected through the lens and the plate exposed. A developed positive film or photographic plate transparency of the through-connections only is then placed in the camera and projected with a superimposed outline drawing of the conductors of the second side. The tapes representing the conductors of the first side are removed from the screen and the tapes representing the conductors of the second side are then applied to the screen. The drawing is then replaced by a photographic plate and the conductors of the printed circuit is then projected through the lens 13, whereby the through-connections are contact printed on the same plate. The exposed plate may then be developed to provide a printed circuit pattern of the second side which has through-connections in registry with the through-connections of the first side.