GB784516A - Electric circuits and methods of making same - Google Patents

Abstract

784,516. Printed circuits. BECK'S, Inc. July 2, 1954, No. 19436/54. Class 37. A printed circuit is made by bonding a conductive metal sheet to a sheet of resinous insulating material, etching away part of the metal sheet to produce conductive areas on the surface of the insulating sheet, embedding the conductive areas in the insulating sheet in such manner that they interlock leaving at least part of the areas exposed at the surface, and finally curing the resinous insulating material. According to one embodiment, a metal foil is secured to an uncured or partially cured thermosetting sheet 10 by adhesive 30, and the assembly heated to partially cure the adhesive. The design of the circuit to be produced is applied to the metal foil, using a lacquer or paint which acts as a resist 34, and the assembly immersed in an etching bath which removes the exposed parts of the metal foil, leaving only the part 15 after which the assembly is pressed between heated platens to force the remaining metal parts such as 15 into the surface of the sheet 10 and to cure the sheet 10 and adhesive 30. The sides 35, 36 of the metal parts slope outwards to interlock with the plastic material and may be rough. Where the conductive areas are to form terminals holes 55 may be punched or drilled therethrough for the reception of wires 51 from a circuit component 50, which are secured in place by dip-soldering. In a second embodiment, after securing the metal foil to the insulating base 110, areas which are to form connection points 136 are marked thereon in a resist and the exposed metal partially etched away. The areas 127 which are to form conductors are then covered with resist and the remaining exposed areas completely etched away. An uncured thermosetting sheet 111 having apertures 136A therein corresponding to the connection points 136 is placed over the assembly and the whole is then pressed between heated platens to cure and bond the insulating layers together and embed the conductors 127 therein, leaving the upper surfaces of connection points 136 exposed. Holes for the reception of connecting wires may be formed through points 136 as described above. The etching is carried out in such manner that the sides of the remaining metal parts such as 136 are rough and slope or are curved to interlock with the plastic. In a third embodiment an insulating sheet 210 provided with apertures, corresponding to the connection points required, has a metal sheet 213 temporarily bonded thereto. The assembly is then pressed between heated platens to deform the metal sheet (Fig. 23). A resist is then applied to the depressed portions of the metal sheet and elsewhere where a conductive pattern is to be formed and the assembly etched to completely remove exposed portions of the metal. After removing the resist the metallized surface of the assembly is coated with thermosetting adhesive, the recesses being filled therewith, and a further plastic sheet applied thereover. Heat and pressure are applied to bond together and cure the layers. As before, holes may be punched through the connection points for the reception of connecting wires, a terminal 215 (Fig. 28) with integral lead 216 remaining from the original sheet 213. Specifications 602,492 and 639,178 are referred to.