GB921017A - Process for making a printed circuit - Google Patents

Abstract

921,017. Switch contacts. VACTRIC (CONTROL EQUIPMENT) Ltd. Aug. 16, 1960 [Aug. 25, 1959], No. 29049/59. Class 38 (5). [Also in Group XXXVI] A method of making a printed circuit, e.g. a switch plate having flush-bonded contacts, comprises the steps of forming the conducting parts by applying a first layer of resist material to a conductive base member in regions which are to remain unplated and plating the base member, applying a second layer of resist material on to the first layer of resist material so as to overlap the latter, plating with a layer of metal to a thickness substantially greater than that of the second layer of resist so as to provide the plating layer with re-entrant portions, causing insulating material to enter the re-entrant portions such that the conducting portions and the insulating portions are keyed together, and removing the base member. A rigid steel baseplate 10 is plated with a layer 12 of copper or nickel and the whole of the upper surface apart from the areas forming the final switch contacts, is covered by a layer of resist material so that a layer 16 of rhodium, gold or silver can be plated only on the exposed areas. In order to obtain re-entrant portions a further layer 17 of resist material is applied to the upper surfaces of the resist regions 15 so as to overlap the latter, and conducting layers 19 are formed by plating copper or nickel on to the layers 16, the re-entrant upper portions 20 formed overlapping the resist areas 17. The resist material is then removed and the upper surfaces of areas 19 coated with adhesive, the printed circuit 22 then being placed with resin impregnated material 25 between steel plates 23, 24. This assembly is placed between the upper and lower plates 26, 27 of a heated platen, sheets of paper 28 being interposed between the plates 24, 26 and 23, 27 respectively. Thus on completion of the heated press cycle the printed circuit takes the form shown in Fig. 8A. Finally the rigid base-plate 10 may be stripped away and the layer 12 removed by etching. Instead of using the heated platen a casting process may be used. The portions 19 may be electrically interconnected by soldering preformed conductors between these areas prior to placing the conductive base between the heated platens, appropriate precautions being taken to ensure that they are not broken during the following pressing operation.