Method And Apparatus For Terminating Electrical Ribbon Cable

Abstract

A new termination, with which a miniature ribbon cable can be connected readily to other electrical devices, has adjacent cable conductors connected without fan-out to a connector plate having contacts on opposite sides of a board-like insulator. The cable insulation is removed from the conductors, prior to assembly of the cable with the connector plate, preferably along the entire conductor length that overlies the insulator.

Parent Case Text

This application is a division of pending application Ser. No. 750,291, filed Aug. 5, 1968, now U.S. Pat. No. 3,605,060, owned by the assignee hereof.

Description

BACKGROUND

This invention relates to the connection of a miniature electrical ribbon cable to other electrical elements. More particularly the invention provides a ribbon cable with a new termination to which other electrical devices can readily be connected. The invention also provides a new method for terminating a miniature ribbon cable. The termination and the method of preparing it provide a new degree of cost saving and compactness for terminations for ribbon cable having miniature fragile conductors in such close proximity to each other that separate connection to each conductor has heretofore been relatively impractical.

A ribbon cable is terminated, within the context of this invention, by electrically and mechanically attaching the cable conductors to an assemblage of contacts to which further connection can readily be made. The further connection can be by plug-in or other readily effected, removable connection and, alternatively, can be more permanent as by soldering or welding.

Ribbon cable is electrical cable in which many conductors are embedded in a flat ribbon-like insulator. The conductors are generally arranged sideby-side in a single layer. Recently ribbon cable of miniature dimensions, and further, miniature cable dimensioned to operate as open wire transmission line, have been desired for electrical equipment, such as for interconnecting elements of a computer. However, use of such cables has been severely restricted by difficulty in terminating the cable at reasonable cost with a compact structure to which further connection can be effected with ease A further problem is to terminate transmission line ribbon cable without introducing excessive impedance discontinuities.

One reason miniature ribbon cable is difficult to terminate is that there is little space between adjacent conductors, typically there are 30 conductors in a cable 3/4 inch wide. Further, the small size (typically less than 10 mil diameter) and hence fragility of each conductor introduces mechanical problems, particularly problems in positioning and supporting the individual conductors during automatic machine or manual manipulation. This latter problem has generally been skirted in the prior art by leaving the conductor ends embedded in the cable insulation until the final steps in the termination process, or by requiring that extensions of the conductors - beyond the point of termination - remain on the cable until the terminating connections are secure. These and other prior techniques such as are disclosed in U.S. Pat. Nos. 3,004,237, 3,355,669, 3,221,286, 3,149,897, 3,189,864 and 3,017,602 are not satisfactory, especially with miniature cables of rod-like transmission-line conductors, as distinguished from older, cables having relatively widely-spaced ribbon-like conductors.

Accordingly, it is an object of this invention to provide a new cable termination suited for economical use with miniature ribbon cables, with ribbon cables operated as transmission lines, and with ribbon cables of rod-like conductors.

Another object is to provide a termination for cable of the foregoing types which is compact, and, further, which can be attached with relatively simple and low cost equipment by relatively unskilled labor.

Another object is to provide a cable termination of the above character to which further connection can be made readily, including by plug-in connector, by soldering, and by welding.

A further object is to provide such a cable termination that does not require conductor fan-out, that is compact, and that introduces relatively small impedance discontinuities into transmission line cables.

It is also an object of the invention to provide an economically practical method for terminating miniature ribbon cable, transmission line ribbon cable, and ribbon cable having rod-like conductors.

A particular further object is to provide such a method in which surplus conductor insulation, or surplus conductor length, is not required during fabrication of the termination.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

SUMMARY OF INVENTION

In general, the cable termination of this invention is formed by removing the ribbon insulation from the end of the ribbon cable to expose, uninsulated, the ends of the cable conductors. Alternate ones of the uninsulated conductor ends are displaced relative to each other in opposite directions in the direction of the cable thickness. This forms the uninsulated conductor ends into two rows spaced apart in the direction of the cable thickness with the ends of adjacent conductors being in different rows.

A connector plate, illustratively in the form of a small printed circuit board, is fitted on the cable end with the edge of the plate seated between the two rows of preformed conductor ends. The connector plate has contacts on both plate surfaces, with a contact under each conductor end. The conductor ends are then soldered or otherwise secured to the contacts. The termination can be encapsulated or otherwise packaged as desired.

Connection to the cable is now easily effected by the use of conventional connector structure contacting the contacts on the connector plate.

The resultant termination is characterized, particularly when compared to the ribbon cable termination of the above-noted Cole et al U.S. Pat. No. 3,004,237, by having the cable insulation terminate sufficiently short of the cable end so that the conductors extend without insulation to, and along, the connector board. Further, the termination is easily used on cables having conductors so close together, or so otherwise arranged, that one cannot readily "weave" the connector plate between the cable conductors, whether insulated or not; such weaving is disclosed in the Cole patent.

The present cable termination is well suited for use with ribbon cable having cylindrical or other rod-like conductors, as used in recently introduced ribbon cable constructed to operate as open wire transmission line. The invention generally requires that the uninsulated conductor ends be self-supporting in the sense that the uninsulated conductor ends maintain the position of being preformed into two rows as described above.

The invention accordingly comprises an article of manufacture possessing features, properties and the relation of elements exemplified in the article hereinafter described and further comprises the several steps for making the article and the relation of one or more of such steps with respect to each of the others thereof, all as exemplified in the method hereinafter disclosed, and the scope of the invention is indicated in the claims.

BRIEF DESCRIPTION OF DRAWINGS

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which

FIG. 1 is a perspective view, partly broken away, of a cable termination embodying features of the invention;

FIG. 2 is a plan view of a ribbon cable illustrative of those with which the invention can be practiced;

FIG. 3 is a plan view of the cable of FIG. 2 with the insulation removed from an end thereof and, further, of a connector plate for use in making the termination of FIG. 1;

FIG. 4 is a side elevation view of the cable end and connector plate of FIG. 3 with the uninsulated conductor ends formed into two rows illustrative of the practice of the invention; and

FIGS. 5 and 6 show respectively side elevation and end views of processing equipment for forming the conductor ends into two rows as shown in FIG. 4.

DESCRIPTION OF ILLUSTRATED EMBODIMENT

In FIG. 1, the termination 10 on ribbon cable 12 has the cable conductors 14 soldered to contacts 16 carried on a connector plate 18. An insulating encapsulation 20 is molded over the adjacent ends of cable 12 and plate 18 to secure these elements together mechanically and thereby minimize stress applied to the conductor ends 14a that interconnect the plate and cable. The encapsulation also facilitates attaching a conventional connector to the connector plate 18 to effect further connection to the cable 12.

The cable 12 has a substantial number of conductors 14 disposed side-by-side embedded in a ribbon of insulation 22. It is the general practice that this is a unitary insulation formed over all the conductors simultaneously; the individual conductors normally do not have, in addition, individual insulating jackets. On the other hand, the conductors alternatively could be individually insulated and bonded side-by-side to provide the cable configuration. The illustrated conductors 14 are cylindrical and the illustrated cable is designed so that adjacent conductors operate as open wire transmission line. The illustrated cable also has miniature dimensions. For example, in one embodiment, the conductors have 8 mil diameters, are spaced apart on 25 mil centers, and are embedded in insulation 33 mils thick. The insulation 22 is typically a synthetic resin of high loss and low electric permitivity; trichlorofluorethylene (commercially available under the trademark Teflon) is a preferred insulator although it has such a high melting point that it cannot be melted away with conventional soldering equipment.

As shown in FIGS. 2 and 3, the first step in fabricating the FIG. 1 termination 10 with a trimmed cable 12 as shown in FIG. 2 is to remove the insulation 22 from the conductor ends 14a, as shown in FIG. 3. This can be done with conventional skills, as by thermally softening the insulation to be removed and then removing it from the end of the cable 12. The technique selected often depends on the nature of the insulation 22.

In the event the conductor ends 14a are bent or otherwise misaligned after having the insulation stripped terefrom, they are next straightened by pulling them through a comblike structure or with equivalent techniques so that the conductor ends are straight and aligned as in FIG. 3.

The conductor ends are next formed into two rows 24 and 26 as shown in FIG. 4 with adjacent conductor ends being in different rows, as shown also in FIG. 1. The two rows 24 and 26 are spaced apart, in the direction of the thickness of the cable 12, sufficiently to receive between them the connector plate 18 shown in FIGS. 1, 3 and 4 and described further below. As indicated, the rows 24 and 26 are essentially parallel to the side-by-side arrangement of the conductors 14 in the cable 12. It should be noted that the illustrated conductors are not fanned apart in the plane of FIG. 3; on the contrary, in this plane and in the plane parallel to the cabled conductors and transverse to the plane of the ribbon cable, the conductor ends remain in-line with the cabled conductors.

The cable ends can be staggered to form the two rows 24 and 26 by laying the cable on a flat support bed 28 shown in FIG. 5. The conductor ends 14 lie in slots 30 and 32 of a stamping form 34. The slots 30 and 32 are aligned parallel to each other in-line with the cabled conductors 14 but, as shown in FIG. 6, the alternate slots 32 are shallower than the intervening alternate slots 30 by the amount of offset desired between the conductor rows 24 and 26 (FIG. 4). The bases of the slots 30 are substantially in the same plane as the support bed 28, and the bases of slots 32 are above this level.

As also shown in FIGS. 5 and 6, with the cable thus disposed, a stamping die 36 having alternate long and short forming teeth 38 and 40, respectively, is pressed against the stamping form 34 with the teeth 38 and 40 respectively meshing into the slots 30 and 32 to press alternate ones of the conductor ends 14a into the slots 30 and the other alternate conductor ends into the slots 32. The teeth 38 on stamping die 36 are dimensioned to position the conductor ends at the bases of the deep slots 30 on the stamping form 34, and similarly, the stamping die teeth 40 are dimensioned to press the conductor ends lying in slots 32 to the bases of these slots.

The stamping die 36 also has a platen 47 that overlies the support bed 28 and presses the cable 12 to the bed 28 as the teeth 38 push conductor ends down into slots 30. Further, the illustrated die 36 has a cutting edge 46 that moves down closely spaced from the forward face 48 of the stamping form to trim off excess conductor lengths extending forward, out of the slots 30, 32 beyond the face 48.

With further reference to FIGS. 3 and 4, which show the alignment of the connector plate 18 relative to staggered conductor ends 14a prior to assembly of the plate with the cable, the illustrated connector plate is a dielectric board 42 having contacts 16 secured to the opposite "plate" surfaces thereof The board 42 and contacts 16 are conveniently of conventional printed circuit construction and the board 42 generally can have the same width as the cable 12. The contacts extend across the length of the board 42 from its forward end 42a to the back end 42b that is adjacent to the cable insulator 22 in the assembled termination. Further, the contacts 16 are so spaced apart on each side of the board 42 that each contact is aligned under a different conductor end when the connector plate is assembled with the cable, as shown in FIG. 1.

The connector plate 18 and cable 12 are assembled simply by inserting the back end 42b of the board between the two rows of conductor ends so that the end 42b is closely spaced from the edge of the cable insulation 22, FIG. 1. This assembly is conveniently carried out by placing the cable on a support plate in order to fix the position of the rows 24 and 26 of conductor ends. The connector plate is slid, toward the cable and between the rows of conductor ends, guided on rails that position the plate with respect to the width and thickness dimensions of the cable and hence relative to the rows of conductor ends.

With the connector plate 18 thus assembled with the cable 12, one row 24 of conductor ends overlays the contacts 16 on one side of the board 42 and the other row 26 of conductor ends overlays the contacts on the other side of the board 42. Further, each conductor end is disposed substantially above the center of a contact.

The conductor ends are then attached and electrically connected to the contacts as by reflow soldering. A preferred technique is to heat the assemblage with infrared energy to cause a solder pretinned on the contacts 16 to flow and bond to the overlying conductor ends 14a, which can also be pretinned. Because the contacts 16 on each side of the plate 14 are on center-line spacings twice as large as the conductor-to-conductor center-line spacing in the cable, sufficient space can be provided between adjacent contacts so that solder does not "bridge" between two adjacent contacts causing an undesired short circuit.

The final step in the assembly of the termination 10 is to mold or otherwise form the encapsulation 20 (FIG. 1) bridging the adjacent ends of the cable 12 and the connector plate 18. The forward portion of plate 18 extends beyond the encapsulation 20 (toward the board forward edge 42a) so that the contacts thereon can be engaged for connecting the cable 12 to other devices. A thermosetting synthetic resin material is preferred for the encapsulation 20. The encapsulation serves to join the conductor plate and cable insulation mechanically, thereby relieving the conductors that extend between the connector plate and the cable insulation from being stressed by manipulation and use of the terminated cable. The encapsulation also provides mechanical and electrical protection for the termination, and as previously noted, facilitates plugging the end of the connector plate protruding from the encapsulation into a mating conventional connector.

It will thus be seen that the object set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method, in the described article, and in the construction set forth, without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which is a matter of language, might be said to fall therebetween.

Claims

Having described the invention, what is claimed as new and secured by Letters Patent is:

1. A method for terminating an electrical ribbon cable having insulated electrical conductors disposed side-by-side, said method comprising the successive steps of

A. removing the insulation from the ends of said conductors at a first end of said cable,

B. forming said uninsulated conductor ends into first and second rows spaced apart in the direction of the thickness of said cable,

C. disposing the ends of a first array of electrical contacts along said uninsulated conductor ends in said first row thereof, with said first array of contacts being supported on an insulated board fitted between said rows of conductor ends, and

D. disposing the ends of a second array of electrical contacts under said uninsulated conductor ends in said second row thereof where said second array of contacts are supported on an insulated board having an edge fitted between said rows of conductor ends so that said first and second arrays of contacts are disposed back-to-back, and

E. electrically connecting said conductor ends in said first and second rows thereof to said contacts in said first and second arrays thereof, respectively.

2. A method as defined in claim 1 further characterized in that said cable connectors are substantially cylindrical.

3. A method as defined in claim 1 further comprising the step of encapsulating the adjoining ends of said cable and said board-supported contact arrays with an insulating material.

4. A method as defined in claim 1 further characterized in that said forming step disposes the ends of adjacent cable conductors in different ones of said first and second rows.

5. A method as defined in claim 1 including the step of maintaining the spacing between said conductor ends not substantially greater than the spacing between the corresponding cabled conductors.

6. A method as defined in claim 1 wherein said step of forming includes the steps of:

A. forming said first row of conductor ends in the same plane as said cable; and

B. forming said second row of conductor ends in a plane parallel to said plane of said first row of conductor ends.

7. A method as defined in claim 1 wherein said step of forming includes the steps of:

A. providing said uninsulated conductor ends in said first row in substantially the same plane as their corresponding insulated conductors which are in a first plane; and

B. forming said uninsulated conductor ends in said second row in a second plane substantially parallel to said first plane.

8. A method as defined in claim 7 wherein the distance between said first and second planes is slightly greater than the thickness of said insulated board.