Title:
MOUNTING ARRANGEMENT FOR FERRITE CORES
United States Patent 3582910


Abstract:
In a mounting arrangement for multiapertured ferrite core devices either single cores or groups of cores are mounted in the cavities of framework members. Core windings are suitably interconnected or terminated on similar framework members that also interconnect the core mounting frameworks. A group of framework members is held together by a superimposed tape or nonconducting mesh and the assembly is then folded in accordion fashion to form a compact unitary module.



Inventors:
DRAGER JOHN A
Application Number:
04/694330
Publication Date:
06/01/1971
Filing Date:
12/28/1967
Assignee:
BELL TELEPHONE LABORATORIES INC.
Primary Class:
Other Classes:
29/604, 365/55, 365/70, 365/140
International Classes:
G11C5/05; G11C5/08; G11C5/12; (IPC1-7): G11C5/04; G11C5/08; G11C5/12
Field of Search:
340/174MA,174M,3A
View Patent Images:
US Patent References:
3435435SOLID STACK MEMORY1969-03-25Bergman et al.
3139610Magnetic-core memory construction1964-06-30Crown et al.



Primary Examiner:
Konick, Bernard
Assistant Examiner:
Pokotllow, Steven B.
Claims:
What I claim is

1. A module assembly for magnetic cores comprising, in combination,

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the mounting and packaging of electronic circuit elements and more specifically to mounting arrangements for ferrite core devices.

2. Description of the Prior Art

Multiaperture ferrite core elements are widely employed in digital computer circuitry, and in similar environments that require exceptionally reliable, high speed, low cost memory systems. These devices are built in various forms depending upon the particular function to be served. In one common form, for example, the device is a rather thin rectangular strip of ferrite material with a single row of round apertures along each side thereof and a rectangular aperture at each end. Fine insulated wire is typically threaded or looped through one or more of these apertures, depending again upon the particular memory function to be served.

One very limiting disadvantage inherent in ferrite elements of the type indicated is the difficulty of providing suitable mounting means that afford protection against shock, inasmuch as ferrite materials are typically extremely brittle and hence readily subject to shock damage. Another disadvantage relates to the difficulty of mounting the ferrite elements in an array of sufficient density to permit convenient interconnection and common mounting with miniaturized circuit boards which may include integrated circuit subassemblies and the like. High density mounting, of and in itself, fails to provide an ideal solution to the problems indicated in that efficient wiring of the ferrite cores, as by an automated wiring machine for example, requires that the cores be spread out in a low density array rather than being superimposed in any way. Affixing the ferrite elements to circuit boards by adhesives and similar prior art attempts to solve the problems indicated have thus far been ineffective.

SUMMARY OF THE INVENTION

The problems indicated above are solved in accordance with the principles of the invention by mounting either single ferrite cores or each group of a plurality of groups of cores within a respective frame member. A complete core array includes a plurality of individual frame members. A strip of easily penetrable tape material which may be formed from nylon mesh, paper or plastic, for example, is employed as a common backing strip for all of the frame members and as a common supporting surface for all of the ferrite cores. With this arrangement a suitably programmed automatic wiring machine, of a known type that is similar to a sewing machine, may advantageously be employed in threading the cores. The cores are amply protected against damage by shock as they are effectively insulated from any shock force against the relatively rigid frame members owing to the low shock transmission properties of the backing strip.

A ferrite core array formed in accordance with the invention in the manner described has an additional significant advantage in that the frame members may be folded together in accordion fashion to form a compact, high density module that may readily be mounted on a circuit board. In some applications it may be desirable to plasticize or "pot" the entire modular combination prior to its actual connection to a circuit board.

In accordance with a particular feature of the invention, interconnecting frame members or modules similar in construction to the core supporting frames (also termed core containing modules) are interspaced with the core containing modules to provide connecting and terminal points for the core connecting loops. A third frame member type, a terminal or base module, similar in size and shape to the other two module types, may advantageously be employed as a mounting base for the array of terminals which is used to connect the combination module grouping to external control or utilization circuitry.

Another feature relates to the employment of a construction jig in the assembly of a multimodule combination in accordance with the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a conventional ferrite core device;

FIG. 2 is a perspective view of an assembled array of ferrite core modules arranged in accordance with the invention to facilitate wiring by machine;

FIG. 3 is a perspective view of the array shown in FIG. 2 in partially folded form;

FIG. 4 is a sketch of the array shown in FIG. 3 in fully folded accordion form;

FIG. 5 is a sketch of a supporting tool or jig employed in accordance with the principles of the invention in the assembly of modules of the type shown in FIG. 1;

FIG. 6 is a perspective, partially broken away view of a portion of an interconnection module in accordance with the invention;

FIG. 7 is a perspective, partially broken away view of a portion of a base module in accordance with the invention; and

FIG. 8 is a perspective, partially broken away view of the underside of a base module of the type shown in FIG. 7.

DETAILED DESCRIPTION

The ferrite core packaging apparatus and techniques which are employed in accordance with the principles of the invention are not restricted in their application to any particular type of ferrite core device, but instead may be employed for the functions indicated with a wide variety of different types of core devices. One typical ferrite core device to which the principles of the invention are applicable is shown in FIG. 1. The core 101 is basically a thin framework structure 102 generally rectangular in configuration with rectangular holes 103 and 104 in the opposite ends. The sides of the framework 102 are completed by two contiguous groups of six toroidal contiguous cores 105 through 110 and 105A--110A. Typical dimensions for a core device of this type are: length, three-quarter inch; width, one-quarter inch; and thickness, one-sixteenth inch.

The combination of the type of material from which such cores are constructed (typically pressed ferrite powder) and the somewhat delicate structural configuration renders these cores easily subject to damage from physical shock. If for example they are dropped from heights as low as a few inches onto a hard surface, they are prone to break, cracking generally occurring along one of the lower legs, as illustrated by the fractures 111. Additionally, these core structures have low resistance to bending loads, which is to be expected because of the ceramic nature of the material. Under bending stress, failures are also more likely to occur across one of the longer legs. These failures have in most instances been of the type shown in FIG. 1, wherein the plane of the fracture is perpendicular to the fractured leg and the face of the fracture has the typically jagged characteristics of a brittle failure.

Protection of magnetic core structures from fractures of the type described as provided in accordance with the invention involves two major aspects. The first has to do with strengthening or reinforcing the core material, and the second concerns protecting the material from being subjected to fracturing stresses. In strengthening the cores, the technique of prestressing the structure in compression has been employed with results broadly analogous to those achieved in the prestressing of concrete beams. Specifically, a surface coating of fluidized epoxy is applied and the shrinkage of the coating as it cools on the core effects the desired prestressing. Electrical properties of the core, however, remain uneffected by this technique.

Physical protection for magnetic core structures is provided in accordance with the invention by the assembly arrangement illustrated in FIG. 2. This assembly includes the core containing modules 203, 204, 205, 206, 207 and 208, a pair of interconnecting modules 209 and 210, and a base connection module 202. Each of the core containing modules, such as the module 203, is simply a framework designed to form a protective border around one or more of the ferrite cores 212. The module 203 includes two cavities 203A and 203B, but it may also be constructed to include only a single cavity or a number of cavities in line, depending upon the particular needs of the system. For more complex circuits, the module could contain, for example, two rows of cavities side-by-side. Core containing modules may be formed from any suitable nonconducting material, such as plastic for example, in which event injection molding may be utilized for the fabricating process.

The interconnection modules 209 and 210 provide a means for interconnecting the core containing modules among themselves and with the base module 202. An interconnecting module ideally has the same outside dimensions as the framework of a core containing module, although the construction inside the framework is quite different. As shown, in the interconnecting modules 209 and 210 a center strip portion includes a double row of holes 213. These holes are provided in pairs so that the interconnections and fan-out--fan-in of the wiring 214 may be accomplished by a wiring machine, looping the wires through the pairs in the manner shown in FIG. 6. As indicated above, more than one row of hole pairs may be provided. The material used for producing this module must be resistant to thermal shock since it is desirable to complete the interconnections by wave soldering as described hereinbelow. One method found to be effective for producing interconnection modules is to form them from phenolic paper by machine punching.

The slots 220 of the interconnection modules have the sole function of helping to ensure a ready flow of potting compound if the modules are to be potted. As indicated above, the double row of holes 213 provides a means for looping and anchoring the various wires 214 which are threaded through the cores 212. A continuous wire which loops a number of cores may thus be formed by starting and ending the loop on one of the modules.

The base module 202 is employed to connect the ferrite core array to an external circuit, which may be in the form of a printed wiring board for example. Certain details of the base module 202 are shown in FIG. 7. The base module also must be resistant to wave soldering and may be formed from Polysulphone by means of an insert molding process. The connecting terminals or pins 211 are ideally L-shaped and each includes an upright leg 211A extending through the bottom side of the module. The bottom leg 211B of each of the L-shaped pins 211, as shown in FIG. 8, is made to lie flat along the under surface of the base module 202 and each extends between a pair of the adjacent holes 212A. When the wiring machine terminates on the base module by looping these holes, each of the bottom legs 211B is enclosed by a respective one of the wire loops and the board.

In the assembly of an array of modules of the type shown in FIG. 2, the core containing modules 203--208, the interconnecting modules 209--210, and the base module 202 are first positioned on a backing strip 215 which may be formed from nylon mesh (as shown), clot tape, plastic tape or other similar flexible and easily penetrable material. Each of the cores 212 is then positioned within its individual frame on a respective one of the core containing modules. The connecting wires 214 are then threaded through the cores 212, through the holes 213 of the interconnecting modules and through the holes 212A of the base module, as described above, in accordance with the wiring scheme dictated by the function to be performed by the magnetic core assembly. As the wires 214 are being threaded, they are also looped through the tape or mesh 215 so that upon the completion of the wiring process the various modules, the cores and the tape 215 are all held together in a unitary assembly. It is evident that in such an assembly each of the cores 212 is well insulated against any possible mechanical shock and is also protected against the application of bending stresses.

In the next step of the assembly process the structure is folded at selected points so that the interconnecting modules 209 and 210 and the base module 202 remain in the plane shown in FIG. 2, while the core containing modules 203--208 are positioned in a plane perpendicular thereto. The interconnecting modules 209--210 and the base module 202 are then in a position to be wave soldered, while the core containing modules 203--208 are folded up out of the way. The solder thus adheres only to the wires on the bottom side of the interconnecting modules 209--210 and the base module 202, and in that manner only the required connections are made.

After soldering, the final assembly is formed by bending as shown in FIG. 3 and by folding all of the modules together in accordion fashion as shown in FIG. 4. The accordion assembly shown in FIG. 4 gives additional protection to the ferrite cores against possible damage from shock or bending. Moreover, owing to its compactness, the accordion assembly lends itself to convenient interconnection with a "mother" circuit board which may include integrated circuitry or other miniaturized circuit forms. The core density of the accordion assembly is greater by at least a factor of five than the density achieved by a conventional flat array.

In order to facilitate mass production of ferrite core assemblies in accordance with the invention, it is desirable to employ programmed automatic wiring machines which operate in sewing-machine fashion to loop the conductors in a preselected pattern around the cores and through the accommodating holes of the interconnection and base modules in a preselected pattern. To facilitate such wiring it is useful in accordance with the invention to employ an assembly tool or jig 500 in the form of a positioning base member or rack of the type shown in FIG. 5. An accommodating depression 501 is provided for placing each of the modules on the jig 500, and each of the ferrite cores is positioned and supported by respective opposite pairs of the supporting tabs 502. A core containing module 203, an interconnecting module 209 and a base module 202 are shown in place of the jig 500. The core structure may also be held onto the jig by a thin piece of tape or with a drop of silastic. The jig is then aligned on the wiring table of the wiring machine, not shown. The cores and modules are wired as required and finally terminations are made by the machine on the base module.

In the next step of the assembly process in which a jig is employed, the jig is removed from the wiring machine and a heat resistant tape is placed across all of the modules. The tape must be attached to the base module but need not be pushed down over the protruding terminal pins. One desirable arrangement, for example, is to start the tape on the edge of the base module and lay it over the other modules. The tape should be sufficiently wide, however, to cover all of the ferrite core structures. One tape found to perform satisfactorily for this purpose is Fluorglas M-281-3 produced by the Dodge Fibers Corporation of Hoosdick Falls, N.Y. As the tape is removed from the jig, the cores and modules remain stuck to it, owing to its high adhesive strength. Soldering is accomplished next in the manner described above, and after soldering, the assembly is folded in accordion fashion as illustrated in FIGS. 3 and 4. The accordion package may be canned or otherwise held together as by connecting pins placed through accommodating holes in the modules.

It is to be understood that the embodiment described herein is merely illustrative of the principles of the invention. Various modifications thereto may be effected by persons skilled in the art without departing from the spirit and scope of the invention.