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.