US3710355A

US3710355A - Unitized plate wire memory plane

Info

Publication number: US3710355A
Application number: US00135286A
Authority: US
Inventors: Pherson G Mc
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1971-04-19
Filing date: 1971-04-19
Publication date: 1973-01-09
Anticipated expiration: 1990-01-09

Abstract

Plated wires are incorporated as an integral part of a dielectric support medium, thereby forming a plated wire memory plane. The tensile strengths or thermal coefficients of expansion of the plated wires and the dielectric support medium are so related that over a desired operating temperature range the plated wires are maintained in a relatively stress-free condition.

Description

United States Patent 1 McPherson [54] UNITIZED PLATE WIRE MEMORY PLANE [75] Inventor: Gary C. McPherson, Excelsior,

Minn. 1

[73] Assignee: Honeywell Inc., Minneapolis, Minn.

[22] Filed: April 19, 1971 [21] Appl.No.: 135,286

[52] US. CI..340/I74 PW, 340/174 TF, 340/174 JA,

511 1111. c1 ..Gllc5/04,Gl1c 11/14 58 Field of Search....340/l74 TF, 174 PW; 29/604; 156/52, 179, 275, 309

[56] References Cited UNITED STATES PATENTS 3,083,353 3/1963 Bobeck ..340/174 TW 3,553,648 1/1971 Gorman et al ..340/l74 PW OTHER PUBLICATIONS The Western Electric Engineer-Vol. 6, No. 3, July 1962 pg 35-39. V 7

Primary Examiner-James W. Moffitt Att0mey-Lamont B. Koontz and Omund R. Dahle [57] ABSTRACT 18 Claims, 4 Drawing Figures ",l f/////////////7i /-///l EXTERNAL BIAS, 1 h 1 2.. Q- TENSION PATENTEDJM 9 I973 3,710,355

SHEET 1 [1F 2 "-E//////////////$ U//////fl EXTERNAL ems TENSION LZ///////// /l/////////// I INVENTOR. GARY c. McPHERSON Y B 0mg 00%.

A TTOfP/VE X PAIENTEDJAH 91975 3.710.355

IN VEN TOR.

Fla 4 T 1/ BY GARY c. McPHERSON A TTOR/VEX UNITIZED PLATE WIRE MEMORY PLANE B ACKGROUND (IF THE INVENTION This invention relates, in general, to a memory device and in particular to a plated wire memory of unitized construction. As used in this specification, the term plated wire refers to small diameter wires having a magnetic coating.

The conventional plated wire memory plane consists of a dielectric support medium having a plurality of parallel spaced holes, or tunnels. A plated wire having a diameter smaller than that of the tunnel is positioned in each tunnel. A grid of substantially parallel conductors is attached to the opposing surfaces of the dielectric support medium. The substantially parallel conductors are positioned orthogonal to the plated wires so as to form word straps.

The most widely used method of forming a tunnel structure has been to embed a plurality of parallel wires between two sheets of dielectric material which are bonded together. The wires are then removed to form parallel holes within the laminate. The plated wires are threaded into the tunnels after the structure is fabricated, and are free to slide within the tunnel in order to avoid subjecting the wires to physical stress. The wires must be held in a stress-free condition because the magnetic properties of plated wires are strain sensitive.

As can be seen, it has not been possible to fabricate a plated wire memory device which is uniformly reproducible using low cost mass production processes. Fabrication of a dielectric support medium having a large number of small parallel tunnels has added to manufacturing costs. The largest difficulty of the conventional plated wire memory plane has been the requirement that each plated wire, which has a diameter of 5 mils or less, must be individually inserted by hand into the tunnel structure. This difficult and expensive process greatly increases the cost of plated wire memory planes.

SUMMARY OF THE INVENTION The present invention provides a plated wire memory plane in which the plated wires are incor porated as an integral part of the dielectric support medium. The thermal coefficients of expansion of the plated wires and the dielectric support medium are so related that over a desired operating temperature range the plated wires are maintained in a relatively stressfree condition. In this manner, a plated wire memory plane is provided which is simple and economical to manufacture using low cost mass production processes. The expensive tunnel structure type dielectric support medium is avoided and the difficult and expensive process of inserting the plated wires in the tunnel structure is eliminated.

In one embodiment of the present invention the tensile strength of the material forming the sheet-like dielectric support medium is much less than the tensile strength of the material forming the plated wires. The plated wires are arranged in a substantially parallel grid. The dielectric support medium embeds each of the plated wires of the grid. The ratio of the cross-sectional areas of the dielectric support medium and the grid is such that the total tensile strength of the crosssection of the dielectric support medium is less than the total tensile strength of the grid. Therefore, the dielectric support medium applies a negligible amount of stress to the plated wires over a desired operating temperature range.

In another embodiment of the present invention, a reinforced dielectric support medium having a tensile strength comparable to that of the plated wires is utilized. As in the first embodiment, the plated wires are arranged in a substantially parallel grid. Each wire has a residual bias tension applied to it. The dielectric support medium has a thermal coefficient of expansion which is different from the thermal coefficient of expansion of the plated wires. The dielectric support medium embeds and adheres to each of the plated wires and applies a compressive force to the wires over a desired operating temperature range due to the difference between the thermal coefficients of the plated wires and the dielectric support medium. The compressive force effectively cancels the residual bias tension on the wires over the desired operating temperature range such that the plated wires are maintained in a relatively stress-free condition.

BRIEF DESCRIPTION OF THE DRAWING FIG. 4 shows a memory plane in which a portion of v the dielectric support medium has been removed to expose the plated wire ends for electrical connection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a method of fabrication of a unitized plated wire memory plane is shown. A plurality of plated wires 10 are arranged in a substantially parallel grid. To each wire is applied a constant external bias tension, illustrated by arrows in FIG. 1. The number of plated wires used is dependent upon the storage capacity desired for the memory device. The plated wires are positioned between a first and a second sheet of dielectric material 11 and 12, respectively. The dielectric material has a tensile strength which is much less than the tensile strength of plated wires 10. At the extreme top and bottom of the assembly are first and second sheets of

metal foil

13 and 14. Polished metal platens l5 apply a pressure to the assembly sufficient to cause bonding. The result is a unitary laminated structure.

FlG2 shows a section of the completed laminate and illustrates how the first and second sheets 11 and 12 have bonded together to permanently embed plated wires 10 in a unitary body of dielectric material hereafter referred to as dielectric support medium 20. The dielectric material of dielectric support'medium 20 adheres to the plated wires 10. After lamination, the external bias tension applied to plated wires 10 is removed. Plated wires 10 immediately contract to attain a stress-free condition in which no residual bias tension remains on the wires. Since dielectric support medium 20 adheres to the plated wires but has a tensile strength much less than that of plated wires 10, it similarly contracts. Although the thermal coefficient of expansion of dielectric support medium 20 in this embodiment is ordinarily much larger than that of plated wires 10, the ratio of the cross-sectional areas of dielectric support medium 20 and the grid of plated wires 10 is such that the total tensile strength of the grid of plated wires 10 is greater than that of dielectric support medium 20. Therefore plated wires 10 are held in a relatively stress-free condition over a desired temperature range.

In the next step of the method, selected portions of the thin metal top and

bottom layers

13 and 14 are removed by photo-chemical techniques well known in the art. As a result, an array of parallel conductors 22 is formed on the top and bottom surfaces of dielectric support medium 20. FIG. 3 shows an array of conductors aligned orthogonal to plates wires 10. To form word strap conductors, circuit connection must be made between a conductor on the top surface and a conductor on the bottom surface. Although several techniques are available for making the circuit connections, one particularly successful method consists of forming holes through the dielectric material and plating the holes with an electrically conductive material to make circuit connections between the conductors on the opposite surfaces. The plated-through hole 23 illustrates the result of this technique.

FIG. 4 illustrates the final step of the method in which dielectric material is selectively removed from the ends of the plated wires to allow electrical connec tions to be made to the plated wires. In a preferred embodiment of the present invention the dielectric material is removed from the plated wire ends by heat stripping.

Heat sealable thermoplastic materials have been found to be suitable for use as the dielectric support medium in the present invention. Examples of such heat sealable thermoplastic materials include polyethylene, vinyl, polypropolene, nylon, polycarbonate, polyester, polystyrene, fluorocarbons and polyvinylchloride. In addition, adhesive thermosetting materials may also be used in the present invention as a dielectric support medium. Suitable adhesive thermosetting materials include phenolic and epoxy resins.

Because the tensile strength of the dielectric support medium is much less than tensile strength of the plated wires, the dielectric support medium provides very little mechanical strength to the plated wire memory plane.

In one successful embodiment of the present invention, nickel-iron coated beryllium-copper wires were used as the plated wire memory element. The wires had a diameter of 2% mils and a tensile strength of about 160 X 10 lbs./in. An external bias tension of approximately to grams was applied to the plated wires for alignment purposes. The center-to-center spacing of the plated wires was about 0.0l0 inches. The plated wires were positioned between two 0.002 inch thick sheets of type 2 or type 3 polyethylene. The two sheets of polyethylene were bonded together at approximately l20C, thereby permanently embedding the plated wires. The finished thickness of the plated wire memory plane was approximately 4 mils.

In this embodiment, thin metal sheets as described in FIG. 1 were not utilized. Instead, a separate word strap envelope containing a plurality of word strap conductors was positioned around the dielectric support medium having the plated wires embedded.

In some applications it is desirable to provide additional mechanical strength to the plated wire memory plane. One well known method of providing this additional mechanical strength is to utilize a reinforced dielectric material. In this case, however, the reinforced dielectric material no longer has a tensile strength which is much less that the tensile strength of the plated wires. With another embodiment of the present invention, it is possible to utilize a reinforced dielectric support medium and still incorporate the plated wires as an integral part of the dielectric support medium.

The fabrication of the reinforced unitized plated wire memory plane is quite similar to the method described previously. A plurality of plated wires are aligned in a parallel array. The plated wires have a first thermal coefficient of expansion. An external bias tension is applied to the plated wires. The external bias tension is less than the elastic limit of the wire and the plating. For example, in 2% mil diameter beryllium-copper wire having a nickel-iron coating the maximum bias tension is approximately grams. Although 50 grams is not the elastic limit of the beryllium-copper wire, bias tensions greater than 50 grams permanently damage the magnetic characteristics of the nickel-iron coating. As previously described, the plated wires are positioned between a first and a second sheet of dielectric material. The dielectric material has a second thermal coefficient of expansion which is slightly greater than the first coefficient. The first and second sheets are then bonded together to permanently embed the plated wires in a unitary body of dielectric material hereafter referred to as the dielectric support medium. The bonding occurs at a temperature greater than the desired operating temperature range. When bonding takes place, the dielectric support medium adheres to each of the plated wires. Since the tensile strength of the dielectric support medium is comparable to that of the plated wires, a residual bias tension remains on the plated wires although the external bias tension has been removed. If the thermal coefficient of expansion of the dielectric material is slightly greater than that of the plated wires, the dielectric material will apply a compressive force to the plated wires as the-plated wire memory plane is cooled to temperatures within the desired operating temperature range. In the present invention the thermal coefficient of the dielectric support medium is so selected that the compressive force applied to the plated wire due to the difference between the first and second thermal coefficients effectively cancels the residual bias tension on the plated wires over the desired operating temperature range.

Although a large variety of reinforced thermoplastic and thermosetting materials are available, one particularly successful dielectric support medium is formed by epoxy resin filled with glass fibers. The glass fibers increase the structural strength of the dielectric support medium and also provide for an adjustable thermal coefficient of expansion. The epoxy resin molded has a thermal coefficient of expansion which is approximately 25.2 X 10 in/in/C while the glass fiber has a thermal coefficient of 4.5 X in/in/C. The relative amounts of epoxy resin and glass fiber in the dielectric support medium determines the thermal coefficient. The tensile strength of the epoxy resin glass fiber composite is comparable to that of the plated wires, between about 50 and 160 X 10 lbs/in depending upon the relative amounts of resin and fibers.

One successful embodiment of the reinforced unitized plated wire memory plane utilized 2% mil diameter nickel-iron coated beryllium-copper wires. The plated wires have a thermal coefficient of expansion of about 16.7 X 10' in/in/C. A 25 gram external bias tension was applied to the plated wires. The plated wires were positioned between two sheet-like layers of partially cured epoxy resin which were filled with glass fibers. Each sheet was approximately three mils in thickness. The relative amount of epoxy resin and glass fiber was such that the thermal coefficient of the sheets was approximately 18 X 10 in/in/C. The materials were positioned between polished metal platens and bonded at a pressure of approximately 200 pounds per square inch at a temperature of approximately 140C. After bonding, the thickness of the plated wire memory plane was about 6 to 7 mils.

Upon bonding, the dielectric support medium embeds and adheres to eachof the plated wires thereby causing a residual bias tension to remain on the plated wires even after the external biasrtension is removed. As the structure cools to temperatures within the desired operating temperature range, the dielectric support medium applies a compressive force to the wires because the thermal coefficient of the dielectric support medium is slightly greater than that of plated wires. In the above example, the difference in thermal coefficients is such that the compressive force applied by the dielectric support medium cancels the residual bias tension and yields a zero stress condition upon the wires at approximately 25C. No significant performance change was noted over a 50C temperature range (:1: 25C) and operation with a reduced output was possible over a 150C temperature range 25C to 125C). Therefore, it can be stated that over these operating temperature ranges the compressive force applied to the wires by the dielectric support medium effectively cancels the residual bias tension. It can be seen that other operating temperature ranges can be obtained by adjusting the composition of the epoxy resin glass fiber composite and/or the external bias tension applied to the plated wire.

The word strap conductors may be formed by a method similar to that discussed previously with respect to the unreinforced unitized plated wire memory plane. Another method of forming the word strap conductors which has proved effective has been to utilize two epoxy resin glass fiber sheets each having a copper layer attached to one surface. After the dielectric support medium is formed by bonding the two sheets together, the copper layers, which are now on the outer surfaces of the dielectric support medium, are photochemically fabricated into an array of parallel word strap conductors. As described previously, the necessary circuit connections between conductors on opposite surfaces of the memory plane are accomplished with plated through holes.

In order to make electrical connections to the ends of the plated wires, it is usually necessary to remove portions of the dielectric support medium. In the case of the reinforced epoxy resin glass fiber dielectric support medium, amixture of four parts sulphuric acid and one part hydrofluoric acid is particularly useful in selectively removing the dielectric material from the ends of the plated wires by etching.

In another embodiment of the present invention the bonding of the first and second reinforced dielectric sheets together to permanently embed the plated wires is accomplished at a temperature within the desired operating temperature range. For instance, bonding may occur at room temperature, which is a temperature within the desired operating temperature range. Examples of dielectric materials used in room temperature bonding include pressure-sensitive adhesive materials and room temperature curing wet epoxy resins. These dielectric materials include a reinforcing material which contributes structural strength and adjusts the coefficient of thermal expansion of the dielectric support medium. The fabrication of the unitized plated wire memory plane is essentially identical to the process described previously for a reinforced dielectric support medium. However, when bonding occurs at a temperature within the desired operating temperature range, the external bias tension applied to the plated wires is the minimum amount of tension required for alignment of the wires and is less than the amount of tension which degrades the magnetic properties of the plated wires. In this manner the residual bias tension is minimized. Furthermore, the composition of the dielectric support medium is adjusted such that the thermal coefficient of expansion of the dielectric support medium is essentially identical to that of the plated wires. Therefore, over the desired operating temperature range the only stress applied to the plated wires is that of the residual bias tension. By minimizing the external bias tension utilized, the residual bias tension on the plated wires is small and does not significantly degrade the performance of the plated wire memory plane. Fabrication of the word strap conductors is accomplished by one of the methods described previously.

While this invention has been particularly shown and described with reference to the preferred embodiments thereof, it will beunderstood by those skilled in the art that changes in form and details may be made without departing from the spirit or scope of the invention.

The embodiments of the invention in which an exclusive property or right is claimed aredefined as follows:

1. A unitized plated wire memory plane in which plated wires are incorporated as an integral part of a dielectric support medium, the memory plane comprising:

a first grid of substantially parallel plated wires, each 7 wire having a first thermal coefficient of expansion and having a residual bias tension thereon,

a sheet-like dielectric support medium having a first and a second surface and a second thermal coeffcient of expansion different from the first coefficient, said dielectric support medium embedding and adhering to each of the plated wires of the first grid and applying a compressive force to the wires over a desired operating temperature range due to the difference between the first and second coefficients such thatv the compressive force effectively cancels the residual bias tension on the wires over the desired operating temperature range.

2. The unitized plated wire memory plane of claim 1 and further comprising:

a-second grid of substantially parallel conductors attached to the first and second surfaces, the substantially parallel conductors being orthogonal to the plated wires.

3. The unitized plated wire memory plane of claim 1 wherein the plated wires comprise nickel-iron coated beryllium-copper wires.

4. The unitized plated wire memory plane of claim 1 wherein the dielectric support medium comprises a reinforced thermosetting material.

5. The unitized plated wire memory plane of claim 4 wherein the reinforced thermosetting material comprises a composite of epoxy resin and glass fiber.

6. The unitized plated wire memory plane of claim 5 wherein the plated wire is comprised of nickel-iron coated beryllium-copper wires.

7. The unitized plated wire memory plane of claim 6 wherein the first thermal coefficient of expansion is about 16.7 X in/in/C and the second thermal coefficient of expansion is about 18 X 10 in/in/C.

8. A method of making a unitized plated wire memory plane in which plated wires are incorporated as an integral part of a dielectric support medium, the method comprising:

positioning plated wires having a first thermal coefficient of expansion in a parallel array,

applying an external bias tension to the plated wires, the external bias tension being less than the elastic limit of the plated wires,

positioning the plated wires between a first and a second sheet of dielectric material, the dielectric material having a second thermal coefficient of expansion different than the the first coefficient, and bonding the first and second sheets together at a temperature greater than a desired operating temperature range to permanently embed the plated wires in a unitary body of dielectric material formed by the first and second sheets, such that the unitary body of dielectric material adheres to the plated wires and applies a compressive force over the desired operating temperature range due to the difference between the first and the second coefficients which effectively cancels a residual bias tension on the plated wires over the desired operating temperature range.

'9. The method of claim 8 wherein the plated wires comprise nickel-iron coated beryllium-copper wires having a first thermal coefficient of expansion of about 16.7 X 10' in/in/C and the first and second sheets are epoxy resin glass fiber composite material having a second thermal coefficient of expansion of about 18 X 10 in/in/C, the step of bonding comprising:

heating the first and second sheets and the plated wires to a temperature of about 140C, and applying a pressure of about 200 pounds per square inch to cause bonding together of the first and second sheets. 10. The method of claim 9 wherein the external bias tension is about 25 grams. I

11. The method of claim 8 and further comprising selectively removing the dielectric material from the ends of the plated wires.

12. The method of claim 11 wherein the dielectric materialis an epoxy resin glass fiber composite and wherein selectively removing the dielectric material from the ends of the plated wires comprises etching away the epoxy resin glass fiber composite with a mixture of four parts sulphuric acid and one part hydrofluoric acid.

13. The method of claim 8 and further comprising:

fabricating a grid of substantially parallel conductors adjacent to the unitary sheet and orthogonal to the plated wires.

14. The method of claim 13 wherein the step of fabricating comprises:

bonding a first and a second sheet of metal foil to 0pposite surfaces of the unitary body of dielectric material, and

selectively etching portions of the first and second sheets of metal foil to form identical grids of substantially parallel conductors on the opposite surfaces of the unitary body, and

selectively making circuit connections between conductors on the opposite surfaces.

15. The method of claim 14 wherein selectively making circuit connections comprises:

forming holes through the dielectric material, and I plating the holes with an electrically conductive material to make circuit connections between conductors on the opposite surfaces.

16. A method of making a unitized plated wire memory plane in which plated wires are incorporated as an integral part of a dielectric support medium, the method comprising:

positioning plated wires having a first thermalcoefficient of expansion in a parallel array,

applying an external bias tension to the plated wires sufficient to align the plated wires, the external bias tension being insufficient to degrade the magnetic properties of the plated wires,

positioning the plated wires between a first and a second sheet of dielectric material, the dielectric material having a second thermal coefficient of expansion essentially identical to the first coefficient, and

bonding the first and second sheets together at a temperature within a desired operating temperature range to permanently embed the plated wires in a unitary body of dielectric material formed by the first and second sheets, such that the unitary body of dielectric material maintains the plated wires in an essentially stress free condition.

17. The method of claim 16 wherein the dielectric material is a reinforced pressure sensitive adhesive material.

18. The method of claim 16 wherein the dielectric material is a reinforced room temperature curing wet epoxy resin.

Claims

1. A unitized plated wire memory plane in which plated wires are incorporated as an integral part of a dielectric support medium, the memory plane comprising: a first grid of substantially parallel plated wires, each wire having a first thermal coefficient of expansion and having a residual bias tension thereon, a sheet-like dielectric support medium having a first and a second surface and a second thermal coefficient of expansion different from the first coefficient, said dielectric support medium embedding and adhering to each of the plated wires of the first grid and applying a compressive force to the wires over a desired operating temperature range due to the difference between the first and second coefficients such that the compressive force effectively cancels the residual bias tension on the wires over the desired operating temperature range.

2. The unitized plated wire memory plane of claim 1 and further comprising: a second grid of substantially parallel conductors attached to the first and second surfaces, the substantially parallel conductors being orthogonal to the plated wires.

7. The unitized plated wire memory plane of claim 6 wherein the first thermal coefficient of expansion is about 16.7 X 10 6 in/in/*C and the second thermal coefficient of expansion is about 18 X 10 6 in/in/*C.

8. A method of making a unitized plated wire memory plane in which plated wires are incorporated as an integral part of a dielectric support medium, the method comprising: positioning plated wires having a first thermal coefficient of expansion in a parallel array, applying an external bias tension to the plated wires, the external bias tension being less than the elastic limit of the plated wires, positioning the plated wires between a first and a second sheet of dielectric material, the dielectric material having a second thermal coefficient of expansion different than the the first coefficient, and bonding the first and second sheets together at a temperature greater than a desired operating temperature range to permanently embed the plated wires in a unitary body of dielectric material formed by the first and second sheets, such that the unitary body of dielectric material adheres to the plated wires and applies a compressive force over the desired operating temperature range due to the difference between the first and the second coefficients which effectively cancels a residual bias tension on the plated wires over the desired operating temperature range.

9. The method of claim 8 wherein the plated wires comprise nickel-iron coated beryllium-copper wires having a first thermal coefficient of expansion of about 16.7 X 10 6 in/in/*C and the first and second sheets are epoxy resin - gLass fiber composite material having a second thermal coefficient of expansion of about 18 X 10 6 in/in/*C, the step of bonding comprising: heating the first and second sheets and the plated wires to a temperature of about 140*C, and applying a pressure of about 200 pounds per square inch to cause bonding together of the first and second sheets.

10. The method of claim 9 wherein the external bias tension is about 25 grams.

12. The method of claim 11 wherein the dielectric material is an epoxy resin - glass fiber composite and wherein selectively removing the dielectric material from the ends of the plated wires comprises etching away the epoxy resin - glass fiber composite with a mixture of four parts sulphuric acid and one part hydrofluoric acid.

13. The method of claim 8 and further comprising: fabricating a grid of substantially parallel conductors adjacent to the unitary sheet and orthogonal to the plated wires.

14. The method of claim 13 wherein the step of fabricating comprises: bonding a first and a second sheet of metal foil to opposite surfaces of the unitary body of dielectric material, and selectively etching portions of the first and second sheets of metal foil to form identical grids of substantially parallel conductors on the opposite surfaces of the unitary body, and selectively making circuit connections between conductors on the opposite surfaces.

15. The method of claim 14 wherein selectively making circuit connections comprises: forming holes through the dielectric material, and plating the holes with an electrically conductive material to make circuit connections between conductors on the opposite surfaces.

16. A method of making a unitized plated wire memory plane in which plated wires are incorporated as an integral part of a dielectric support medium, the method comprising: positioning plated wires having a first thermal coefficient of expansion in a parallel array, applying an external bias tension to the plated wires sufficient to align the plated wires, the external bias tension being insufficient to degrade the magnetic properties of the plated wires, positioning the plated wires between a first and a second sheet of dielectric material, the dielectric material having a second thermal coefficient of expansion essentially identical to the first coefficient, and bonding the first and second sheets together at a temperature within a desired operating temperature range to permanently embed the plated wires in a unitary body of dielectric material formed by the first and second sheets, such that the unitary body of dielectric material maintains the plated wires in an essentially stress free condition.