ASSEMBLY FOR SPLICING MULTIPLE SCREENED CABLES

Abstract: A method for terminating a cable having a central conductor which is overlaid by a concentric insulation layer which is overlaid by a concentric braid which is overlaid by a concentric braid which is overlaid by a concentric jacket to a metal shell and circuit board combination. The metal shell and circuit board will have at least one aperture extending through said metal shell and circuit board. First at least part of the jacket is stripped from the cable. The stripped cable is then inserted through the aperture in the shell and circuit board. The braid is compressed adjacent the aperture and the braid is fixed to the circuit board. The invention also encompasses the product of this method.

Description: ASSEMBLY FOR SPLICING MULTIPLE SCREENED CABLES Background of the Invention The present invention concerns a means of splicing multiple screened cables, as one would need to undertake, e.g. to connect or replace cables in, for example, conduits. Such an interconnection is in most cases factory manufactured, but field installed. The increase in the clock speed and the increase of digital signal transmission has resulted in the use of specialized screened cables. A whole range of screened cables e.g. from single conductor, twin-axial to multi-conductor cables with braid or tape shield with drain wire are in use. Other key specifications associated with such cables are the overall diameter, jacket and primary insulating material and size, the attenuation loss at specified frequency, and the like. The primary objective of various applications are to attain an efficient connecting means, i.e. manufacturable solution, of such screened cable types. The interconnect is manufactured and tested in the factory, while an interconnect with the two joined cables (each side may have multiple screened cables) may be installed in the field. Additional constraints for such connecting means are: the outer contour of this interconnect needs to be adequately profiled to facilitate being pulled through densely populated cable conduits; this connection needs to withstand severe pull forces equivalent to the rupture force of such cables; cost and case in installation are important criteria for users. The most important requirements, however are, the inter-connect needs to have a low loss, should not introduce skew or cross-talk to impair the signal integrity at the interface. Summary of the Invention The present invention is a method for terminating a cable having a central conductor which is overlaid by a concentric insulation layer which is overlaid by a concentric braid which is overlaid by a concentric braid which is overlaid by a concentric jacket to a metal shell and circuit board combination. The metal shell and circuit board will have at least one aperture extending through said metal shell and circuit board. First at least part of the jacket is stripped from the cable. The stripped cable is then inserted through the aperture in the shell and circuit board. The braid is compressed adjacent the aperture and the braid is fixed to the circuit board. The invention also encompasses the product of this method. Brief Description of the Drawings The invention is further described with reference to the accompanying drawings in which: Fig. 1 is an exploded perspective view showing the components of the present invention; Fig. 2 is a perspective view of the components shown in Fig. 1 which are partially assembled; Fig. 3 is a perspective view of the components in Fig. 1 which are further assembled; Fig. 4 is a perspective view of the assembled components shown in Fig. 3 and a pair of stripline circuit boards; Fig. 4A - 4D are respectively alternative board splice terminations showing (a) two slotted boards back to back (b) one double sided unslotted board, (c) one double sided board with slots and ground sides and (d) one angle mounted double sided boards with slots and ground side; Fig. 4E - 4H are schematic drawings showing various possible interconnect alternatives; Fig. 5 is a perspective view of the assembled cable conductors as terminated on the stripline circuit board shown in Fig. 4; Fig. 6 is a perspective view of the disassembled stripline circuit boards shown in Figs. 4 and 5; Fig. 7 is a perspective view of a cable connector which makes up the front part of the cable interconnect of the present invention; Fig. 8 is a perspective view of the cable connector of Fig. 7 and the board and cable assembly of claim 6; Fig. 9 is a perspective view of the assembled cables and boards shown in Fig. 8; Fig. 10 is a perspective view of a further assembled cables and boards shown in Fig. 9; Fig. 1 1 is a perspective view of an overmolded assembly shown in Fig. 10; Fig. 12 is a perspective view showing an alternate application for connecting wires to a board; Detailed Description of the Preferred Embodiments Fig. 1 shows the initial steps (for one cable side, assumed to be and referred to as the rear side of the interconnect) which consists of pre- stripping the screened cable assembly 1 with outer jacket 2 and braid 3 over the insulator 4 contain within thereof the copper conductor 5. This pre-stripped cable is introduced through apertures 7 in an insulating block 6 located in a metal shell 8, such that the stripped portion of each cable receives a ferrule 9 in between the braid 3 and insulator 4. The aforementioned method is further outlined by inventor, as shown in Fig. 2, keeping in mind that his definition of circuit and circuit hole is equivalent respectively to insulating block 6 and aperture 7 shown in Fig. 1. The circuit is soldered to the metal end shell, then: 1. Pre-stripped coax cables are inserted through the circuit hole. 2. Ferrules are located on each conductor (under the braids) until the braid is compressed against the inside of a through plated hole. 3. The junction of each braid to circuit is then soldered. The ferrules can be solderable metal or heat insulating material if cable conductor insulations are to be used which cannot withstand soldering temperatures. The circuit has at least one surface with a conducting shielding layer. Screened terminations to a circuit board may be done in applications with no metal end shell. Further, this insulating block 6 can be a PCB, ceramic or other circuit material having the apertures 7 being plated through with some metal land to contact the ferrule head 10; all the surfaces of this insulating block 6 is full or selectively metallized, but in particular along the area of contact periphery which is touching the metal shell 8. This initial mutual contact of these two parts permits solder fixation of the insulating block with the metal shell in an earlier assembly operation to form an integral unit. Such a connection provides, in essence, a 360 degree shielding possibility for the multi-strip cable. The cross-sectional dimensions of the interconnect are defined by the shape and size of the insulating block 6; it is further defined by the number of cables, the diameter of the screened cables, and the connection pattern. The assembly of one side of this interconnect can be visualized in Fig. 3 showing a "blown-up" section of ferrule to cable braid attachment for different options, i.e. "punched" solderable metal sleeves instead of a circuit boards, or a heat insulating sleeve, for those cables without heat resisting (such as PTFE) insulators. This initial part of connector assembly with protruding pre-stripped conductors having all the braids properly terminated to metal shell, a configuration depicted in Fig. 3, is now ready for termination with a two stripline boards 11 and 11 located above each other and having slot openings respectively 12 and 12 at the rear side, as shown in Fig. 4. The front side of these stripline boards 1 1 and 11 has other slots respectively 13 and 13 * . In the particular configuration of Fig. 4, the slot openings 12 and 12 * are directly in line with each other, while the front slots 13 and 13 ' are staggered with respect to each other. The circuit fingers are placed through holes in the metal end shells circuit board, where it is soldered. From Figs. 8 and 9 the front cable pre-assembly is located in the front side in slot opening 13, which being somewhat smaller in dimension than the cable insulator 4 and cable insulator (as in Fig. 4B), allowing the latter to be captured and held prior to soldering. In fact, such a wire management means is equally applicable to the rear side of stripline board. In doing so, these slot openings have an important manufacturing function. This permits to ensure that the conductor 5 can be (SMT) laid over associated track 15, ready for the soldering operation. Interposed between adjacent tracks, are ground lines 15, for signal integrity reasons. Although not evident in this figure, each stripline board rear side opposite to the tracks, can be covered by a metallized copper plane, two such boards can be located in this assembly with their ground planes in contact to each other. Also at the rear end of this stripline board 11 and 11 ' are figures 16 and 16 ' which may fit in appropriately dimensioned and spaced receiving apertures 17 and 17 ' (or one common hole for both boards, depending on design), as can be seen in Fig. 4A - 4D. This type of fixation is useful to maintain the assembly in position, during the manufacturing process (e.g. overmolding) of this interconnect, and can provide a means of grounding both stripline boards. The latter figure shows different connection options of the mutual location of the two stripline boards, the intermediary space and the mutual angle. Method of terminating and positioning discreet conductors is as follows. The discreet cables are each located over the slot and solder pad where it is intended it to be placed. Then it is pressed down into its slot until fully located. When all the required discreet cables have been pressed into their respective slots, the cable conductors can then be soldered to their own surface mount solder pads provided. Additional through grounding of the multiple conductor cables screens (other than through the overall metal shield) can be accomplished by soldering the braids down to both circuits ground planes. The advantages of this arrangement are as follows. The slots grip the cables sufficiently to hold them in place for soldering and also then provide some individual cable strain relief. The slots position the cables equidistantly apart which in conjunction with the grounded circuit construction; helps to minimize crosstalk and control signal impedances over the axis of the cable conductors. This control is extended over the length of the circuit boards by the accompanying grounding areas. This is a method of providing electrically controlled signal paths in a cable termination system. Fig. 4B shows the simplified cross-section of the rear end of this interconnect. The various options and the method discreet cable fixation in the slots, are depicted in this Fig. 4B. The cables prior to solder assembly step can be visualized in Fig. 5. The soldering step when completed results in a sound electrical (gradual) connection with tracks having a minimum of discontinuities, as desired for signal integrity reasons. In this context, this SMT termination of the conductor gives lesser discontinuity problems than for say, if this conductor were to be terminated in a plated through hole in the stripline board. Fig. 6 shows the one of these stripline boards 11 , showing below the rear face of this board, in some detail. Key features include the use of the slot openings as at opening 26 to capture the cable, while permitting the use of two identical boards (with slot 13 being asymmetric with respect to stripline board centreline) which are turned upside-down back-to-back (as in Fig. 5), resulting in that the signal track on front end on 11 is opposing ground track on 11 ' . This condition has similarities with a stripline condition to ensure proper signal integrity conditions prevail. These provisions ultimately results in a controlled impedance interconnect. Other features of the circuit boards include signal tracks as at track 28, slots as at slot 30, ground plane areas as at area 32 and circuit fingers as at finger 34 The advantages of this arrangement are the following. Double sided copper boards, where all copper areas that are not signal tracking are part of the circuit ground planes. At the circuits wider end, the circuit is made into fingers, suitable for soldering into any compatible mating substrate plated through hole of appropriate diameters. Optional cable slots are provided for room for cable insulations when straddling in line cable terminations at that end. At the circuits other 'front' end, the circuit is made with 'slots', which are grooves made in the circuit boards to a width just less than the required cable diameters to be terminated. Per each circuit the sets of signals and slots are made asymmetrically with the circuits centre lines. Then when an identical circuit is turned upside down and placed under the first (top) circuit, each circuits signals and 'slots' are enclosed by the second circuit. In addition, the signals are provided additional grounding coverage by the other circuits grounding layers since a stripline has then been formed when the two circuits are brought together. Fig. 8 shows the initial assembly of the (pre-assigned) cable configuration, for the front part of the cable interconnect. As evident from Fig. 7, prior to jacket strip-off, a metallic crimp ferrule 17 and a specially shaped rectangular metal cap 18, are firstly located on the cable 20; in this case 19 is the assembly of conductor and cable insulator which needs to be terminated on the stripline boards 11 and 11 ' . Fig. 8 shows some details relevant for this termination step. The discreet cables are located in the slots 13 and 13 ' at the front side of the stripline boards (see Fig. 4 and 9). These equi-spaced slots position the discreet cables in conjunction with a grounded circuit construction while maintaining a impedance uniformity over the length of the stripline board, for signal integrity reasons. As evident from Fig. 9, additional through grounding of multiple conductor cable screens (other than through the overall metal shield) can be accomplished by soldering "pig-tailed" braids down to the circuit ground planes. After this soldering step is completed the crimp ferrule and rectangular metal cap are located forward so that its front portion encloses and fixes on metal shell 8 on the rear side of this interconnect to form one integral unit as shown in Fig. 10. The crimp ferrule 17 is crimped simultaneously to the metal shell 18 and to the cable 20 (Fig. 7) ensuring a 360 degrees shielding termination is achieved. Finally in Fig. 11 , the total interconnect is formed by overmolding the prior assembly with a polymer form 22. The specific shape and size is one that facilitates cable through densely populated conduits. This molding step imparts the desired strength and rigidity of the interconnect. Fig. 12, shows yet another embodiment of this design whereby discreet cables may be connected to a PCB or a solderable substrate by cover housing 24 to provide additional strain relief. Pre-prepared terminated wires into a circuit assembly with cover housing enables easier final installation of one single assembly to a solderable substrate. While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.

Claims: CLAIMS WHAT IS CLAIMED IS: 1. A method for terminating a cable having a central conductor which is overlaid by a concentric insulation layer which is overlaid by a concentric braid which is overlaid by a concentric braid which is overlaid by a concentric jacket and a metal shell and circuit board combination having at least one aperture extending through said metal shell and circuit board, comprising the steps of: (a) stripping at least part of the jacket from the cable and inserting the cable through the aperture in the shell and circuit board; (b) compressing the braid adjacent the aperture; and (c) fixing the braid to the circuit board. 2. The method of claim 1 wherein the braid is compressed by means of a ferrule. 3. The method of claim 1 wherein the braid is welded to the circuit board. 4. The method of claim 1 wherein there is at least one other cable having a conductor extends through another aperture in the metal shell and circuit board and at least one additional circuit board is positioned between the cables and at least one of the cables is connected to the additional circuit board. 5. The method of claim 4 wherein there are two additional circuit boards mounted back to back and each of the cables is connected to one of said additional circuit boards. 6. The method of claim 5 wherein the additional circuit boards have slots and the conductors of the cables are positioned in said slots. 7. The method of claim 6 wherein the conductors in the cables join other conducts in the slot. 8. The method of claim 7 wherein a cap is superimposed over the additional circuit boards. 9. The method of claim 7 wherein the additional circuit boards are overmolded. 10. The method of claim 7 wherein the additional circuit boards are surrounded by a housing to provide strain relief. 1 1. The product of the method for terminating a cable having a central conductor which is overlaid by a concentric insulation layer which is overlaid by a concentric braid which is overlaid by a concentric braid which is overlaid by a concentric jacket and a metal shell and circuit board combination having at least one aperture extending through said metal shell and circuit board, comprising the steps of: (a) stripping at least part of the jacket from the cable and inserting the cable through the aperture in the shell and circuit board; (b) compressing the braid adjacent the aperture; and (c) fixing the braid to the circuit board. 12. The product of claim 1 1 wherein the braid is compressed by means of a ferrule. 13. The product of claim 11 wherein the braid is welded to the circuit board. 14. The product of claim 11 wherein there is at least one other cable having a conductor extends through another aperture in the metal shell and circuit board and at least one additional circuit board is positioned between the cables and at least one of the cables is connected to the additional circuit board. 15. The product of claim 14 wherein there are two additional circuit boards mounted back to back and each of the cables is connected to one of said additional circuit boards. 16. The product of the method of claim 15 wherein the additional circuit boards have slots and the conductors of the cables are positioned in said slots. 17. The product of the method of claim 16 wherein the conductors in the cables join other conducts in the slot. 18. The product of the method of claim 17 wherein a cap is superimposed over the additional circuit boards. 19. The product of the method of claim 17 wherein the additional circuit boards are overmolded. 20. The product of the method of claim 17 wherein the additional circuit boards are surrounded by a housing to provide strain relief.

Inventors: LEESON ANTHONY M, LEESON, ANTHONY, M.
Applicants: BERG TECH INC, LEESON ANTHONY M, BERG TECHNOLOGY, INC., LEESON, ANTHONY, M.
Application year: 1998
Main classification: B65B
IPC codes: H01R9