GB1042331A - Improvements relating to printed electric circuits and to the manufacture of such circuits - Google Patents

Abstract

1,042,331. Printed circuit assemblies. ELECTRIC & MUSICAL INDUSTRIES Ltd. Sept. 26, 1962 [Sept. 29, 1961; Oct. 26, 1961; March 10, 1962], Nos. 35059/61, 38290/61 and 9328/62. Heading H1R. In a printed circuit, a plurality of conductors adhering to insulating material bridge a gap between two portions of the insulating material to form " ladders " to whose " rungs," which are wholly exposed at the gap, electrical connections can be made. The invention is described with reference to a multi-plane word organized thin film magnetic store comprising printed digit and sense windings and coordinate address windings, the windings in different planes being connected by " ladders " which may be single or multiple, i.e. comprising a number of sets of " rungs " between parallel strips of insulation. As shown, Figs. 1, 3, a thin film magnetic store comprises four planes each carrying a plurality of rows of magnetic elements of Ni-Fe (80-20) alloy deposited on a glass substrate by evaporation, plating, sputtering &c., under the influence of an aligning magnetic field, the elements comprising discrete rectangular dots; alternatively a continuous film may be deposited. Each plane comprises a pair of glass plates 1a, 1b . . . 4a, 4b, upon the inner surfaces and front and rear edges of which are printed address windings 6. Digit input and sense output windings 5 are printed normal to the address windings on insulating plates 7 of, e.g. resin-impregnated fibreglass, in triads, Fig. 1A (not shown), each sense wire 5s lying between two digit wires 5d. Over the side edges of plates 1a . . . 4b are printed conductors 12 in groups of six, one group being allocated to each triad of digit and sense wires. The digit and sense wires are connected by two quadruple " ladders " 13 on one side of the store and by a single quadruple " ladder " 25 on the other side. The " rungs " of the ladders, or the conductors 12, are pre-tinned, and connection is effected by rolling a heated roller bit along the gaps between the insulating strips. The output from the sense windings and the connection of the digit windings are provided by a ladder 14, the insulating strips of which are folded back after connection of the rungs to conductors 12; a second ladder 24, also folded, provides for input to the digit windings and the shorting of the sense windings. The address wires 6 are connected at the rear edge of the store by double ladders 16. Since the address wires form 2-turn windings, the wires 6 at the front edge of the store are displaced by one place as between plates 1a, 1b &c., alternate wires on the plates of each plane being connected together by ladders 32. The remaining wires on the upper plate of each plane are contacted by a riser 18, and the remaining wires on the lower plate of each plane by a riser 26, the risers being formed by ladders folded so that the insulation is at right angles to the rungs. Conductors in register on risers 18, 26 are connected by ladders 8 which form vertical address bus-bars, the remaining conductors on the risers being connected in pairs by ladders 23 through diodes 10 to upper and lower horizontal bus-bars 9a, 9b (9a only shown in Fig. 1). A resistance (not shown) is also connected across each address winding. The risers which are mutually insulated pass through gaps in a copper screen 11, thr gap being broken periodically by lugs 20 to reduce the loss of screening effect. Fig. 20 (not shown) depicts how input and output conductors 133, 134, printed on flexible plastic sheets 136, 137, which are bonded together, pass across holes 139, 140 in the sheets to form tabs which are soldered to the pins of sockets 135 in a support 138 which is mounted on the frame of the store to permit the latter being inserted in a case comprising mating plugs. Modifications.-To avoid printing wires on the edges of the plates, plates 51a, 51b, Fig. 12 (not shown), of glass fibre reinforced synthetic resin are provided with slots 52a, 52b. Address conductors are printed on the plates, crossing slots 52a; a sheet of thin insulating material which does not cover the slots is placed over the address conductors and the digit wires 53d and sense wires 53s printed thereupon to cross slots 52b. Flexible sheets of glass fibre reinforced resin 54a, 54b and 55a, 55b are provided with conductors 56, 57, 58 and 59, 60, 61 which bridge gaps between pairs of sheets to form ladders as shown. Plates 54b, 55b are inserted between plates 51a, 51b, as far as the inner edges of slots 52b and digit and sense wires are soldered to registering conductors 56, 57, 60, 61 by a heated roller in slots 52b. Registering conductors in the ladders are next soldered together, after which sheets 54a, 55a may be folded as required. In Fig. 13 (not shown), digit wires 73d and sense wires 73s in two planes formed by plates 71a, 71b and 72a, 72b, are interconnected by conductors 78 . . . 85 printed in ladder form on insulating plates 74a, 74c ... 77a, 77c. Pairs of adjacent ladders, bonded together if required, are inserted between the plates of each plane and connection is effected between registering conductors through slots (not shown) in the plane plates, the shorting conductor between pairs of digit wires 73d being insulated from the ladder conductors. Registering rungs of the ladders are then connected, after which insulating strips 74c . . . 77c may be removed. Figures 18, 19A, 19B (not shown) depict methods of reducing inductive coupling between digit and sense windings. The copper screens 11 (Fig. 1) may be replaced by a conductive foil 91, Fig. 14 (not shown), adhered to an insulating bar 90 and having lugs 92 projecting upwards and downwards therefrom. An insulating film 93 insulates foil 91 from vertical conductors 94 which are soldered into holes 100 in address conductors 98 to form vertical address bus-bars; address conductors 97, 99 are connected by a ladder through diodes to horizontal bus-bars (not shown), and lugs 92 pass through slots 101 in plates 96. In a further modification, vertical bus-bars are passed through holes in the plane plates adjacent relevant tinned address wires and a current passed through bus-bars sufficient to cause fusion between bus-bars and address wires. The diodes may be connected in the centre of the address loops, a damping resistor in the form of a resistive paste being provided for each half loop. Printed circuit production.-The ladders may be formed by securing copper foil to two portions of insulating material so that it bridges a gap between the two portions, and etching away unwanted portions of copper; the remaining conductors may be thickened by electrodeposition. The foil bridging the gap may be supported by a temporary insulating support coated with a release agent. To produce printed plane plates 1a ... 4b, Fig. 1, a thin conducting, e.g. Cu, sheet 42, Fig. 10 (not shown), comprising skirts 43 is adhered to an insulating substrate 41. The whole of sheet 42 is painted with photo-resist and the assembly rotated about a vertical axis in a warm atmosphere; the edges 44 are thus uniformly coated, excess resist being collected on the skirts 43. The sheet 42 is then photo-etched in known manner, the resultant conductors being electroplated with, e.g. silver. Fig. 16 (not shown) depicts a jig for the production of pairs of plates with accurately registering conductors, comprising a transparent base 114 and three pillars 115 which define the position of two transparent sheets 116, 117. The upper plate negative is firmly bonded to sheet 116; the lower plate negative is releasably adhered to the upper plate negative after their emulsion layers have been optically aligned under a microscope; then sheet 117 is firmly bonded to the lower plate negative. The plates with their attached negatives are broken apart, and prepared laminate plates are aligned between the plates in the jig and exposed from the top and bottom. Fig. 17 (not shown) depicts an evaporation mask of annealed metal having windows, etched from both sides to avoid undercutting, through which the magnetic elements are evaporated; the elements are then given a protective coating of SiO.