Shielded ribbon cable

An improved shielded ribbon cable arranged to expedite termination of the shield for grounding the shield. There is an isolator strip placed during fabrication of the cable between the conductor array and the shield; the isolator strip prevents flow of plasticized insulating material between the cover sheet and the conductor array, which usually occurs through the interstices in the shield, so that the shield can be readily separated from the conductor array to permit termination of the shield without jeopardizing the integrity of the insulation on the conductor array.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to shielded ribbon cables such as are widely 
employed for interconnecting computer and like electronic circuit 
elements, and more particularly to a cable in which termination and 
connection of the shield can be effected rapidly and easily. 
2. Description of the Prior Art 
Shielded ribbon cable is widely used, particularly in environments where 
radio frequency interference and the like is present. In order to achieve 
good shielding of the conductors from such interference, it is imperative 
that the shield be connected to the ground at one or more points along the 
cable run. Connection of the shield to the ground necessitates access to 
the shield without impairing the conductors or the insulation thereon. 
Such access is difficult in presently known shielded ribbon cables because 
the shield is typically of woven or foraminous construction and during 
fabrication of the cable, portions of the plastic insulative cover are 
extruded through the foramina of the shield. Such renders removal of 
insulation from the shield a long and tedious job and requires great care 
in order to avoid severing the fine gauge conductors of which the shield 
is formed. 
SUMMARY OF THE INVENTION 
A shielded cable according to the present invention includes four layers, 
three of which are conventional; namely, at least one row of insulated 
conductors bonded together in a substantially flat array, a foraminous 
conductive flat shield substantially coextensive with the array and an 
insulative cover sheet for insulating the shield and retaining it in 
juxtaposition to the array. According to the present invention there is an 
isolator strip interposed between the conductor array and the shield, at 
least at the central portion thereof, which isolator strip is formed of a 
material to which the cover sheet and conductor insulation will not adhere 
or cohere. Consequently, one wishing to terminate the shield can very 
easily obtain access thereto without jeopardizing the conductors or the 
insulation thereon. 
The isolator strip is formed of a material having characteristics different 
from the material of which the conductor insulation and the cover sheet is 
formed. For example, many shield ribbon cables are fabricated by 
transporting the array, the shield and the cover sheet to a bonding 
station at which at least the confronting surfaces of the array and the 
cover sheet are plasticized, by heat or radiant energy, after which they 
are bonded together by compression. In adapting the invention to such 
fabrication procedure the isolator strip is formed of a material that will 
not be plasticized or otherwise affected by the energy levels employed to 
plasticize the conductor insulation and the cover sheet. 
An object of the invention is to provide a shielded ribbon cable which 
permits rapid and secure electrical connection into the shield. This 
object is achieved because the presence of the above mentioned isolator 
strip permits manipulation and cutting of the cover sheet and the shield 
without jeopardizing the conductors or the insulation surrounding the 
conductors. 
The foregoing together with other objects, features and advantages will be 
more apparent after referring to the following specification and the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring more particularly to the drawing, reference numeral 12 indicates 
a ribbon cable having a plurality of conductors 14 encased by insulative 
material 16 to form a flat array of conductors that are insulated from one 
another and from the exterior. The array has side margins 17 formed of the 
same material as insulative material 16. Such ribbon cable is a staple 
article of commerce and is constructed so that conductors 14 are typically 
of copper, insulative material 16 is typically of polyvinyl chloride (PVC) 
and is formed so that conductors 14 are uniformly spaced from one another 
throughout the length of the cable. 
An isolator strip 18 has a length coextensive with ribbon cable 12 and a 
width somewhat less than the width of the ribbon cable. The material of 
which isolator strip 18 is formed is chosen so that the material is 
non-adhesive and non-cohesive with respect to insulative material 16 that 
constitutes a part of ribbon cable 12. In typical practice isolator strip 
18 is formed of Mylar or the like and is positioned midway between the 
lateral extremities of the ribbon cable. 
There is a layer 20 formed of conductive shielding material which is 
foraminous. Typically employed for shield 20 is a layer of flexible 
material woven from fine copper conductors. Woven material is employed 
because it is flexible, light in weight and because it defines interstices 
or foramina 21 between which insulative material 16 can be extruded. 
Finally there is a cover sheet 22 which is typically formed of the same 
material as insulation 16. The cover sheet functions to protect and 
insulate shield 20 and to retain the shield into intimate juxtaposition to 
ribbon cable 12 so as to assure good shielding against radio frequency 
interference and like noise. Cover sheet 22 is typically substantially 
coextensive both in length and width with ribbon cable 12. 
Before an explanation of the salutary advantages arising from the use of 
the shielded cable embodying the present invention, a description of the 
manner of fabricating the flat shielded cable will be described in 
reference to FIG. 5. There is a bonding station 24 having an inlet at the 
lefthand side thereof as viewed in the drawing. Transported to the inlet 
end are insulated conductor array 12, isolator strip 18, conductive 
foraminous shield 20 and cover sheet 22. At bonding station 24 at least 
the confronting surfaces of conductor array 12 and cover sheet 22 are 
treated so as to bond to one another when compressed. The treatment of the 
confronting surfaces can be accomplished by subjecting the confronting 
surfaces to heat energy or by radiating the surfaces with microwave energy 
of a suitable wavelength to plasticize the material of which insulation 16 
and cover sheet 22 are formed. Alternatively an adhesive or solvent can be 
applied to the confronting surfaces to plasticize them. When such 
confronting surfaces have been plasticized, compressive forces are applied 
to the four layers within bonding station 24 so that the plasticized 
material on the confronting surfaces of conductor array 12 and cover sheet 
22 will adhere or cohere to one another. At the margins, i.e., exterior of 
the lateral edges of isolator strip 18, the plasticized material is 
extruded or forced through the foramina in foraminous shield 20 to form 
bonds 25 which retain the layers in a unitary assembly in which conductive 
shield 20 is in intimate juxtaposition to conductor array 12. Such unitary 
assembly constitutes the improved shielded ribbon cable 26 of the 
invention which upon solidification of the plasticized confronting 
surfaces is coiled or otherwise prepared for entry into commerce. 
Because isolator strip 18 neither coheres or adheres to conductor array 12 
nor to the portion of cover sheet 22 that may be extruded through the 
foramina of shield 20 during fabrication of the shielded cable, 
installation of a conventional crimp terminal 28 can be achieved very 
quickly. If connection to the shield at a site spaced from the ends of the 
shielded ribbon cable is desired, an opening 30 in cover sheet 22 and an 
opening 32 in shield 20 can be formed with a sharp knife or like 
instrument. In cutting openings 30 and 32 the presence of isolator strip 
18 facilitates formation of the openings without cutting or otherwise 
injuring insulation 16 in conductor array 12. Moreover, when the openings 
are formed, the crimp terminal can easily be slid beneath shield 20 
because there is no significant cohesion or adhesion between shield 20 and 
the isolator strip. 
Installation of crimp terminal 28 at the end of the cable is likewise 
facilitated on a cable constructed according to the invention. Having 
reference to FIG. 3, a space between the upper surface of isolator strip 
18 and the lower surface of shield 20 can be formed by separating those 
layers at the end of the shielded ribbon cable. The crimp terminal can be 
slipped in so as to embrace shield 20 and cover sheet 22 and can be 
crimped to effect mechanical and electrical connection to the shield. 
In FIG. 4 there is a modified form of isolator strip generally indicated at 
18'. The width of the strip is approximately that of conductor array 12 
and cover sheet 22. Adjacent the lateral margins of isolator strip 18' are 
relatively large perforations 34 which permit bonding between the 
plasticized confronting surfaces of conductor array 12 and cover sheet 22 
during formation of the cable in bonding station 24. The inner or central 
regions of isolator strip 18' can be formed with minute perforations 36 
which are sized in reference to the strength of the material of which 
insulation 16 and cover sheet 22 are constructed so as to permit very 
thin, relatively weak bonds through the perforations and the foramina in 
shield 20. Because such bonds are of extremely small cross-sectional area 
as compared with the bonds present through relatively large perforations 
34, the bonds are readily frangible so that shield 20 can be easily 
separated from isolator strip 18' to afford installation of crimp terminal 
28. 
For the purpose of affording a clearer understanding of the invention and 
not for the purpose of limiting the invention, a specific exemplary 
shielded cable formed according to the invention will be described. 
Conductor array 12 in such exemplary shielded ribbon cable has fifty 
conductors 14 spaced on 0.050 inch centers, an overall width of 
approximately 2.75 inches and insulation 16 which is formed of PVC. 
Isolator strip 18 is formed of such material as Teflon, Mylar or Kapton. 
The width of the strip is approximately one inch and the strip is 
positioned midway between the lateral edges of the cable. Shield 20 has a 
width slightly less than the width of conductor array 12 and cover sheet 
22 has a width substantially equal to that of the conductor array. The 
cover sheet is formed of the same material as insulation 16; namely, PVC. 
In manufacturing such shielded ribbon cable the four layers are 
transported to bonding station 24 as described above in connection with 
FIG. 5. Within the bonding station the temperature of the confronting 
surfaces of conductor array 12 and cover sheet 22 are raised to a 
temperature in the range of about 310.degree. F.-348.degree. F. at which 
temperature the PVC becomes plasticized; i.e., becomes partially melted 
and sticky. The temperature required to plasticize the material of which 
isolator strip 18 is formed is substantially higher, for example, 
700.degree. F. in the case of Mylar. Accordingly, at the temperature 
established within bonding station 24 to plasticize the confronting 
surfaces of conductor array 12 and cover sheet 22, the isolator strip is 
virtually unaffected. When the confronting surfaces have been plasticized, 
the four layers are conducted through compression rolls (not shown) or the 
like so that bonding of the layers is accomplished. Except at the edges of 
the cable, the plasticized material is extruded through the foramina of 
shield 20 to effect the bond. Of course the presence of isolator strip 18 
prevents any such bonding throughout an area coextensive with the isolator 
strip. 
In the case of manufacture of a shielded ribbon cable employing the 
modified isolator strip 18' shown in FIG. 4, the presence of relatively 
large perforations 34 permits firm bonding at the edges of the shielded 
ribbon cable but the presence of relatively minute perforations 36 at the 
center portion of the modified isolator strip permits a minor degree of 
bonding which is readily frangible and can be easily broken for insertion 
of a crimp terminal such as crimp terminal 28 shown in the drawing. 
Thus it will be seen that the present invention provides a shielded ribbon 
cable in which the shield can be electrically terminated with great speed 
and facility and without jeopardizing the integrity of the conductors or 
the insulation surrounding the conductors. The improved shielded ribbon 
cable can be fabricated by existing manufacturing processes and equipment 
without significant modification thereof. Although several embodiments of 
the invention have been shown and described it will be obvious that other 
adaptations and modifications can be made without departing from the true 
spirit and scope of the invention.