GB926963A - Process for making a printed circuit - Google Patents

Abstract

926,963. Switch contacts. VACTRIC (CONTROL EQUIPMENT) Ltd. Aug. 16, 1960 [Aug 25, 1959], No. 29048/59. Class 38 (5). [Also in Group XXXVI] A printed circuit, for example a switch plate having the conductors embedded in an insulating base such that the switch plate has flush-bonded conducting and insulating parts, is made by positioning the integrally connected conducting parts against a working surface, the conducting parts being spaced from each other in a predetermined manner, forcing insulating material between the conducting parts into contact with the working surface, and finally removing the conducting material between the conducting parts. In its final form the printed circuit comprises segmental conducting areas 11 spaced from each other by segmental insulating areas 12, the areas 11, 12 being arranged in the form of an annulus 13. Internally and externally of the annulus 13 are insulating areas 14, 15 respectively. A rectangular sheet of copper 10 is covered with a layer of resist material except for the segmental insulating areas 12, the latter areas then being etched away so as to form holes 18 in the copper. The areas 14, 15 are then covered with a layer of resist material before plating the areas 11 with a layer 21 of conducting material, e.g. rhodium, gold or silver, the resist layer subsequently being removed. At this stage one or more conductors may be arranged on the unplated side 22 of the sheet 10 ; these conductors may be constituted by strips of copper foil which are soldered to the unplated side 22 and insulated from the parts of the copper sheet which they cross. The unplated side 22 is coated with an adhesive layer and the printed circuit 24 with this surface uppermost is placed between steel plates 25, 26 covered with a suitable release agent and between which is resin impregnated material 27. This assembly is then placed between the upper and lower heating plates 28, 29, sheets of paper 30 being interposed between the plates 26, 28 and 25, 29 respectively. After a heated press cycle, the printed circuit assumes the form shown in Fig. 7A. As a result of the pressing operation the impregnated material 27 flows into the holes 18 and gaps 21<SP>1</SP> to form the insulating areas 12 and is also formed into an insulating layer 31 on the unplated side 22 of the sheet 10. The copper in the areas 14, 15 is then completely etched away, the annulus 13 being covered by resist layer 32 during this operation.