Patent GB-1491627-A (GB)
Title: Electrical assemblies
IPC: H01L23/36
Filed: 1975-05-23
Abstract: 1491627 Printed circuit assemblies INTERNATIONAL BUSINESS MACHINES CORP 23 May 1975 [6 Sept 1974] 22923/75 Heading H1R A printed circuit board 10 (Fig. 1A) has openings admitting plural printed circuit cards 12, 14, 16 as parts of a data processing system, e.g. card 12 for logic, card 14 for storage, and card 16 as power supply and regulation; the printed circuitry 17 of board 10 interconnecting the cards. The boards and cards (Fig. 1B) comprise insulant laminates 18 of, e.g. epoxy paper, polyamide, or glass epoxy superimposed with separating metal, e.g. copper planes 20. The cards may alternatively be of multi-layer ceramic. Openings 11 of board 10 receive the respective cards and insulant laminae 24, 26 of similar material to those of the cards and boards are disposed on the upper and lower surfaces overlain with conductive layers 28, 30; the whole forming a unitary assembly. The conductive layers are formed into circuit patterns 17; and via holes 29 are drilled and plated through cards to interconnect the internal and surface conductor patterns. In a modification (Figs. 2a, 2b, not shown) a stamped metallic, e.g. aluminium web or grid has openings which receive the printed circuit cards, and insulant laminates with surface conductor layers formed into circuit patterns are applied to the surfaces. Plated via holes receive terminals of an integrated circuit module, while a connector assembly also engaged by via holes provides input and output signals to the component units. The metal grid thermally conducts internally generated heat to a sink attached thereto by drilling and tapping through the surface insulating laminates. The surface of the grid is pre-etched prior to lamination to improve bonding, and its temperature coefficient of expansion is selected to be # that of the component cards to discourage delamination (Fig. 2c, not shown). In a further modification (Figs. 3A, 3B) an integrated circuit element 37 is directly connected, e.g. by soldering or wire bonding to surface conductors 28<SP>1</SP> overlying a member 50 of ceramic (e.g. alumina) or alternatively of an alloy having a low T.C.E. This is edge scored for firm glass epoxy bonding to a card or metallic grid member 12<SP>1</SP> during lamination with insulant layers 24<SP>1</SP>, 26<SP>1</SP>, and surface conductor layers 281, 30<SP>1</SP> under heat and pressure. Element 37 is attached without thermal expansion mismatch to member 12<SP>1</SP> by mounting on pads 53. Member 50 may have thereon a printed circuit pattern 56 and is also covered with insulant laminates 24<SP>1</SP>, 24<SP>11</SP> separated by conductor layer 28<SP>1</SP>. Apertures of the laminate permit connection between pads 53 and circuit pattern 56, which is connected over plated through holes 58 to circuits 17<SP>1</SP> formed in conductor layer 28<SP>1</SP>. An enclosure 60 mounted on epoxy sealing ring 62 protects element 37.  A card (Fig. 4, not shown) for insertion into an opening of board 20 (Figs. 1A, 1B) or metal grid (Figs. 2A, 2B, not shown) may carry an integrated circuit element similarly to that shown in Figs. 3A, 3B, but the laminations include a thermally conductive layer, e.g. of Ni-Fe alloy clad with surface copper layers having a similar T.C.E. to that of the integrated circuit element which serves as a heat path to a sink. Additional insulant and conductor overlaps may be added to provide additional circuits and isolated by a cast insulator ring surrounding the enclosure of the integrated circuit element. The completed assemblies may be passivated by coating with, e.g. urethane or epoxy varnish. In fabrication (Fig. 5, not shown) plural insulant layers of, e.g. glass epoxy, paper epoxy, polyimide are stacked with metal, e.g. copper interleaving or metal surface deposits to provide the necessary circuit planes, and thermally laminated under pressure. The cards are trimmed and the necessary openings are punched in the board, after which the card edges are scored for better engagement with the apertures of the board on insertion. A stamped metal grid may be used instead of a board to receive the cards, and surface etched for adhesion of the laminates. Openings are formed in the cards to receive inserted thermally conductive members, and the edge scored for retention. Metal alloy thermally conductive laminates may also be included in the laminated board. Additional insulant and metal laminates are externally applicable and thermally laminated under pressure. Via holes are drilled in the cards at required locations and electrolytically or electrolessly plated, while the conductor planes are additively plated or subtractively etched to form the required surface conductors. Thereafter components are soldered or wire bonded to the appropriately exposed surface conductors of the cards, after which the array is tested and an enclosure is fitted.