IL34531A - Construction of plated-wire memory planes - Google Patents

Description

IMPROVEMENTS IN OR RELATING TO THE CONSTRUCTION OF PLATED-VIRE MEMORY PLANES ^IDn *10Ώ TVDT 'ΠΟΕΒ *75 7_Π33 □''^T^DC The invention relates to a method of constructing a carrier or so-called "tunnel" structure for a plated-wire memory plane. In a typical prior art memory plane the carrier or tunnel structure is a lamina body having, within its thickness, a plurality of parallel tunnels each housing a wire that has been plated with a magnetizable material. Each of the two opposite sides of the lamina body has a printed circuit wafer applied to it so that parallel conductors or word straps on each wafer are directed normally to the axes of the plated-wires thereby constituting a memory device.

Hitherto, the carrier or tunnel structure has been constructed by placing dummy wires in parallel relation to one another on a first sheet of plastics material and then dverlaying a second sheet of plastics material and applying pressure and heat so as to laminate the two sheets together and encapsulate the dummy wires therebetween. Subsequent removal of the dummy wires leaves tunnels into which plated wires can be inserted.

Two significant disadvantages accompany the prior method of constructing a carrier or tunnel structure. The first is that considerable difficulty is experienced in arranging the dummy wires on the first sheet in the precise parallel relationship that is required to obtain optimum performance from a memory plane Incorporating the carrier. Even if such an arrangement is achieved, it is liable to be disturbed upon overlaying the second sheet or in the initial stages of laminating the two sheets together. The second disadvantage is that, in the laminating process, such is the pressure and temperature required to encapsulate the dummy wires between the two sheets, that ripples tend to form at the opposite sides of the lamina structure corresponding to the positions of the dummy wires. This is caused by the plastics material of the two sheets filling the spaces between the dummy wires. The ripples render the opposite surfaces of the carrier structure unsuitable for the direct application of conductors such as word straps and other circuitory by conventional printed circuit techniques, thus necessitating the application of separate printed circuit wafers already clad with electrically conductive material.

The invention is concerned with avoiding the first mentioned disadvantage and with providing for the direct application of printed conductors to each side of a carrier or tunnel structure for a plated-wire memory plane.

According to the invention, an improved method of constructing a carrier or tunnel structure for a plated-wire memory plane, comprises the steps of forming from plastics material a lamina support with a series of uniform parallel channels in one side of the support , placing a dummy wire lengthwise within each channel, filling with further plastics material the spaces not occupied by the dummy wires in the channels so as to encapsulate the said wires and form a flush surface at said one side of the support and, once the further plastics material is hardened, withdrawing the dummy wires so as to leave parallel tunnels into which plated wires, each having a slightly less transverse dimension than the corresponding dummy wire, can be inserted.

The step of forming the lamina support can comprise moulding the support in one piece to form the channels in said one side and a flush surface at the opposite side of the support.

In such a case, the method according to the invention preferably includes the step of applying a thin layer of electrically conductive material directly onto the flush surface at each side of the lamina support. Preferably, the two layers are laminated to the two flush surfaces, respectively, while the dummy wires remain in their encapsulated positions.

Alternatively, the step of forming the lamina support can comprise placing a first sheet of plastics material, having a layer of electrically conductive material applied to one side of it, in a mould having a set of parallel1 lands so that the tops of the lands are immediately adjacent to the opposite side of the sheet, and extruding plastics material into the mould between the landed surface thereof and the said opposite side of the sheet thereby forming an integral support structure. The alternative method preferably includes the further step of placing a second sheet of plastics material, having a layer of electrically conductive material applied to one side of it, with its opposite side on the flush surface defined at said one side of the support by the plastics material that fills the spaces in the channels, and applying heat and pressure to the laminate thus formed, with the dummy wires still in their encapsulated positions.

It will be appreciated that the invention further resides in a method of constructing a plated-wire memory plane by constructing a carrier or tunnel structure according to the invention and then etching each layer of electrically conductive material on the structure to form conductors that run in a direction transverse to the axes of the tunnels, and inserting a wire plated with a magnetizable material into each tunnel from which a corresponding dummy wire has been withdrawn.

A preferred method of constructing a carrier or tunnel structure for a plated-wire memory plane, and the articles produced thereby, will now be described, by way of example, with reference to the accompanying drawings in which s- Figure 1 is a plan view from above of the grooved section of a mould base plate; Figure 2 is a cross-section of the mould base plate and a mould cover plate viewed in the direction of the grooves; Figure 3 is an enlarged cross-section detail of part of the grooved section of the mould base plate; Figure k is an enlarged view, in cross-section of a carrier or tunnel structure housing plated wires; and Figure 5 is a plan view of a plated-wire memory plane according to the invention.

Referring to Figures 1 to 3» a mould consists of a mould base plate 10, formed on one side with parallel longitudinal ridges or lands V', and a mould cover plate 12. Although a particular number of lands is illustrated, the number of lands will be dictated by the number of plated wires it is desired to place in one memory plane β In Figure 2, the cover plate 12 is shown secured onto the base plate 10 by any suitable fastening means, such as screws (not illustrated) with a sealing gasket 21 between the plates 10 and 12.

In Figure 3» four lands 13» l^ » 15» and 16 each having a generally trapezoidal cross-section, are shown on base plate 10, defining grooves between them. The corners of the lands will ordinarily be slightly rounded. As will become evident with reference to the following description of the moulding process, the formation of trapezoidal channels in the support of the carrier structure facilitates placing the wires in the channels, since the wires and channels are both very small. The specific cross-section of lands 13-16 is not, however, critical and the tops of the lands may, for example, be rounded.

The first step in the process of moulding the carrier or tunnel structure is to place a sheet 17 (Figure k) of plastics or epoxy resin material on cover 12 of the mould. A suitable plastics material that may be used is polyimide. In a preferred construction sheet 17 is a 0.001 inch (one mil) thick sheet of polimide material. A thin layer 20 of copper or other etchable electrically conductive material is laminated to one side of the polyimide sheet 17, the purpose of the copper layer 20 being to provide suitable conductors, when etched, such as word straps and other printed circuitry. The portion of the copper layer 20 which does not overlie the wire field (Figure 5) can be etched to form printed circuitry.

The polyimide layer 17 is dried prior to insertion into the mould by placing sheet 17 provided with layer 20, in a suitable oven and heating it for approximately 30 minutes at an oven temperature setting of approximately 200°F.

A suitable mould release is applied both to the mould cover plate 12 and to the mould base plate 10 prior to the moulding operations so that the mould support structure may be removed easily from the mould. Prior to attaching the mould cover plate 12 to the mould base plate 10, the sealing gasket 21 is placed around the periphery of the copper clad polyimide sheet 17» 20 as shown in Figure 3· Once the mould is assembled with the sheet 17» 20 therein, softened plastics material 22 (Figure 4), for example, epoxy resin, is extruded into the mould to fill the spaces, in particular the grooves in grooved area 11, between the copper clad polyimide sheet 17s 20 and the mould base plate 10. Cover plate 12 has suitable vent holes (not shown) to permit air to escape from the mould so as to inhibit the formation of bubbles in the extruded plastics material. Prior to filling the mould, the mould may be preheated, if necessary, for ease of filling and to keep the extruded plastics material softened. Once the mould is filled, it is placed into a heated press and pressure between 5Ο psi and 500 psi is applied to the mould at a temperature setting of approximately 200°FS for a period of about thirty minutes. Subsequently, the mould is cooled and the moulded support structure is removed. The support thus includes the copper layer 20, the polyimide layer 17 , and the plastics material 22 which were formed by the lands of the mould base plate 10 during moulding.

The dummy wires are slightly larger than the plated wires which are to be ultimately used so that the plated wires will fit loosely into the tunnels to be formed. The plated wires should be allowed to move slightly relative to the carrier or tunnel structure so that they do not bind and mechanical stresses in the plated wires are avoided. Mechanical stresses may damage the plating and so cause the plated wire to become inoperative. Before the forming or dummy wires are inserted into the channels, they are coated with a suitable mould release so that they can be removed easily after encapsulation which will now be described.

After the dummy wires are inserted into the channels in the moulded support, additional plastics material, such as epoxy resin, is spread over the dummy wires completely to fill the spaces unoccupied by the dummy wires within the moulded support. The dummy wires are thus completely encapsulated. A second sheet 2k of plastics material is then placed on the flush surface as seen in Figure k. Sheet 2k may be similar or identical to sheet 17 , and also includes a copper layer 25 laminated thereto. The lamina assembly is then placed in a further mould, which simply comprises two metallic plates, and the further mould is then placed in a heated press, and the assembly laminated together.

The pressure used in the press may be, for example, from 250 psi to 500 psi and the temperature of the press may be 200°F. The pressure and heat applied ensures that the extruded plastics material 22 (Figure k) completely surrounds the dummy wires to the exclusion of any air bubbles. After approximately thirty minutes, the laminated assembly is removed from the press. The laminate is sufficiently thin so that the copper layers 20 and 25 on sheets 17 and 2k, respectively, are as close as possible to the dummy wires. This provides good magnetic coupling between the word straps, when formed, and the plated wires when inserted in the tunnels.

Figure 5 shows a completed memory plane designated generally by the number 26. After the moulded tunnel structure is formed, the next step in forming a completed memory plane is to etch the copper layers 20 and 25 (Figure 4).

Figure 5 shows a top view of the etched copper layer 25 with only the word straps 27 shown in detail. The word straps overlie the plated wire field 30, so that they can co-act with the plated wires to form a memory device. Similar word straps are etched in the copper layer 20 on the opposite side of memory plane 26. Magnetic keepers may be placed over the word straps if desired and necessary. The purpose of such magnetic keepers is to contain the magnetic field around the word straps so that less drive power is required.

Blocks 31 and 32, designated by dashed lines, include etched copper conductors and connections. These connections connect word straps 27 into a memory system and also provide a means for mounting circuit components on the tunnel structure .

The last step is to remove the forming or dummy wires thereby leaving tunnels running longitudinally through the tunnel structure. A plated wire is then inserted into each tunnel. The plated wires are designated 33» 3^» 35» and 36 in Figure h. The diameter of each plated wire is preferably the order of 5 mils and the diameter of each forming or dummy wire in the order of 7 mils. However, plated wires of much smaller diameters can be used. While it is preferred that sheets 17 and 2k of copper clad plastics material be used in making this invention, the copper cladding can be applied directly to the carrier or tunnel structure subsequent to forming the structure. In such cases it is not necessary to use sheets of plastics material such as sheets 17 and 24. In such cases the tunnel structure is conveniently entirely moulded .

A carrier or tunnel structure constructed in accordance with the method described with reference to the accompanying drawings, preferably has a total thickness less than 15 mils comprised by the plastics material 17» 22, 23» and 2k (Figure ¾). The transverse dimension of each tunnel is preferably just less than the thickness of the intermediate or sandwich plastics material 22 and 23 (Figure 4), say less than 10 mils.

Claims (3)

1. WHAT WE CLAIM IS : - 1. A method of constructing a carrier or tunnel structure for a plated-wire memory plane comprising the steps of forming from plastics material a lamina support with a series of uniform parallel channels in one side of the suppor placing a dummy wire lengthwise within each channel, filling with further plastics material the spaces not occupied by the dummy wires in the channels so as to encapsulate the said wires and form a flush surface at said one side of the support and, once the further plastics material is hardened, withdrawing the dummy wires so as to leave parallel tunnels into which plated wires, each having a slightly less transverse dimension than the corresponding dummy wire, can be inserted.

2. A method according to claim 1, in which the step of forming the lamina support comprises moulding the support in one piece to form the channels in said one side and a flush surface at the opposite side of the support.

3. A method according to claim 2, including the step of applying a thin layer of electrically conductive material directly onto the flush surface at each side of the lamina support . , A method according to claim 3» in which the two layers are laminated to the two flush surfaces, respectively, while the dummy wires remain in their encapsulated positions. 5β A method according to claim 1, in which the step of forming the lamina support comprises placing a first sheet of plastics material, having a layer of electrically conductive material applied to one side of it, in a mould having a set of parallel lands so that the tops of the lands are immediately adjacent to the opposite side of the sheet, and extruding plastics material into the mould between the landed surface thereof and the said opposite side of the sheet thereby forming an integral support structure. 6. A method according to claim 5, including the further step of placing a second sheet of plastics material, having a layer of electrically conductive material applied to one side of it, with its opposite side on the flush surface defined at said one side of the support by the plastics material that fills the spaces in the channels, and applying heat and pressure to the laminate thus formed, with the dummy wires still in their encapsulated positions. 7. A tunnel structure for a plated-wire memory plane, constructed in accordance with the method claimed in any one of claims 1 to 6. 8. A tunnel structure according to claim 7» insofar as claim 7 is appendent to claim 6, in which the total thickness of the said first and second sheets of plastics material is less than the thickness of the intermediate plastics material sandwiched between them, and the transverse dimension of each tunnel is almost as large as the thickness of the said intermediate plastics material. 9. A tunnel structure according to claim 8, in which each tunnel has a transverse dimension less than 10 mils and the total thickness of the first and second sheets and the intermediate plastics material is less than 15 mils. 10. A method of constructing a plated-wire memory plane comprising the steps of constructing a carrier or tunnel structure in accordance with the method claimed in any one of claims 3 to 5i etching each layer of electrically conductive material on the structure to form conductors that run in a direction transverse to the axes of the tunnels, and inserting a wire plated with a magnetizable material into each tunnel from which a corresponding dummy wire has been withdrawn. 11. A plated-wire memory plane constructed in accordance with the method claimed in claim 7· 12. A tunnel structure for a plated-wire memory plane, constructed substantially as hereinbefore described with reference to and as illustrated in cross-section in, Figure k of the accompanying drawings. 13. A plated-wire memory plane constructed substantially a hereinbefore described with reference to and as illustrated in Figure 5 of the accompanying drawings. For the Applicants -C-tiS3oamQ3Bd B¾ytcg w1r Ag-e -