EP1042168A2

EP1042168A2 - Assembly for splicing multiple screened cables

Info

Publication number: EP1042168A2
Application number: EP98951059A
Authority: EP
Inventors: Anthony M. Leeson
Original assignee: Berg Technology Inc
Current assignee: FCI Americas Technology LLC
Priority date: 1997-10-14
Filing date: 1998-10-14
Publication date: 2000-10-11
Also published as: WO1999019213A2; WO1999019213A3; EP1042168A4

Abstract

A method for terminating a cable (1) having a central conductor (5) which is overlaid by a concentric insulation layer (4) which is overlaid by a concentric braid (3) which is overlaid by a concentric jacket (2) to a metal shell (8) and circuit board (6) combination. The metal shell (8) and circuit board (6) will have at least one aperture (7) extending through the metal shell (8) and circuit board (6). First at least part of the jacket (2) is stripped from the cable (1). The stripped cable (1) is then inserted through the aperture (7) in the shell (8) and circuit board (6). The braid (3) is compressed adjacent the aperture (7) and the braid (3) is fixed to the circuit board (6). 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

CLAIMSWHAT 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.