Patent ID: 12205732

In the figures, like reference numerals designate like elements.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized, as structural and operational changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined by the appended claims.

A growing number of applications require high speed (e.g., >1 Gb/s) high signal integrity connections. These applications may include enterprise computing, network communication, factory automation, medical, test and instrumentation, etc. These applications may use twin axial (“twinax”) transmission lines that include parallel pairs of differentially-driven conductors. Each pair of conductors may be dedicated to a data transmission channel. The construction of choice for these purposes is often a jacketed loose bundle of shielded paired conductors. The jacket is often formed from shielding and/or insulating wrapped in a helical pattern around the conductor bundle.

Applications are demanding more speed from these channels and more channels per assembly. As a result, there will be a need for cables with improved termination signal integrity, termination cost, impedance/skew control, and cable cost over current twinax transmission lines. The present disclosure is generally directed to a shielded electrical ribbon cable that is suitable for, among other things, differentially driven conductor sets. Due to the ribbon construction, the cable can readily be terminated to a printed circuit board connector of similar pitch. Such a termination can provide very high termination signal integrity. The construction of this type of cable may generally include parallel insulated wires that are bonded to a substrate on one or both sides with specific placement of gaps between conductors. The substrates may or may not contain a ground plane. Such a cable may be used as an alternative to conventional bundled, e.g., differential pair, twin-axial (twinax) constructions and is expected to have lower cable cost, termination cost, skew, and termination parasitics.

Shielded cables currently used in high performance and high speed applications are generally not sharply bent because this may cause impedance discontinuities at the bend location. Such discontinuities can produce unwanted reflections and poor overall electrical performance. For example, a conventional parallel pair twinax cable for gigabit data applications may be constructed with an overlapped shield (helical wrap) and an outer layer of polymer film to maintain the wrapped shield in place while bending. The wrapped layers add significant stiffness to the cable for bending, and also can cause pinching and local geometry changes within the cable at the bend locations. This results in significant changes in cable characteristics (e.g., impedance) at and proximate to the bend.

Compared to conventional, wrapped, parallel-pair, twinax cables, the ribbon cable structures described in the present disclosure may exhibit improved performance in applications that require sharp bending of the cable. These shield structures and cable constructions can maintain high cable electrical performance even after sharp bending. For example, such ribbon cables may be used with connectors that require the cable be sharply bent within the connector. The constructions can also provide much lower stiffness (e.g., up to one half) on bending than conventional wrapped constructions with similar materials. The lower stiffness and minimal impact on electrical performance under bending allows such cables to be bent more sharply than conventional cables, thereby saving space and providing enhanced routability in a given application.

It is noted that the various sections and section headings are provided for improved organization and convenience, and are not to be construed in a limiting way. For example, the sections and section headings are not to be construed to mean that techniques, methods, features, or components of one section cannot be used with techniques, methods, features, or components of a different section. On the contrary, we intend for any information from any given section or sections to also be applicable to information in any other section or sections, unless otherwise clearly indicated to the contrary.

Section 1: Shielded Electrical Cable Constructions and Features

As the number and speed of interconnected devices increases, electrical cables that carry signals between such devices need to be smaller and capable of carrying higher speed signals without unacceptable interference or crosstalk. Shielding is used in some electrical cables to reduce interactions between signals carried by neighboring conductors. Many of the cables described herein have a generally flat configuration, and include conductor sets that extend along a length of the cable, as well as electrical shielding films disposed on opposite sides of the cable. Pinched portions of the shielding films between adjacent conductor sets help to electrically isolate the conductor sets from each other. Many of the cables also include drain wires that electrically connect to the shields, and extend along the length of the cable. The cable configurations described herein can help to simplify connections to the conductor sets and drain wires, reduce the size of the cable connection sites, and/or provide opportunities for mass termination of the cable.

InFIG.1an exemplary shielded electrical cable2is shown that includes a plurality of conductor sets4spaced apart from each other along all or a portion of a width, w, of the cable2and extend along a length, L, of the cable2. The cable2may be arranged generally in a planar configuration as illustrated inFIG.1or may be folded at one or more places along its length into a folded configuration. In some implementations, some parts of cable2may be arranged in a planar configuration and other parts of the cable may be folded. In some configurations, at least one of the conductor sets4of the cable2includes two insulated conductors6extending along a length, L, of cable2. The two insulated conductors6of the conductor sets4may be arranged substantially parallel along all or a portion of the length, L, of the cable2. Insulated conductors6may include insulated signal wires, insulated power wires, or insulated ground wires. Two shielding films8are disposed on opposite sides of the cable2.

The first and second shielding films8are arranged so that, in transverse cross section, cable2includes cover regions14and pinched regions18. In the cover regions14of the cable2, cover portions7of the first and second shielding films8in transverse cross section substantially surround each conductor set4. For example, cover portions of the shielding films may collectively encompass at least 75%, or at least 80, 85, or 90% of the perimeter of any given conductor set. Pinched portions9of the first and second shielding films form the pinched regions18of cable2on each side of each conductor set4. In the pinched regions18of the cable2, one or both of the shielding films8are deflected, bringing the pinched portions9of the shielding films8into closer proximity. In some configurations, as illustrated inFIG.1, both of the shielding films8are deflected in the pinched regions18to bring the pinched portions9into closer proximity. In some configurations, one of the shielding films may remain relatively flat in the pinched regions18when the cable is in a planar or unfolded configuration, and the other shielding film on the opposite side of the cable may be deflected to bring the pinched portions of the shielding film into closer proximity.

The cable2may also include an adhesive layer10disposed between shielding films8at least between the pinched portions9. The adhesive layer10bonds the pinched portions9of the shielding films8to each other in the pinched regions18of the cable2. The adhesive layer10may or may not be present in the cover region14of the cable2.

In some cases, conductor sets4have a substantially curvilinearly-shaped envelope or perimeter in transverse cross-section, and shielding films8are disposed around conductor sets4such as to substantially conform to and maintain the cross-sectional shape along at least part of, and preferably along substantially all of, the length L of the cable6. Maintaining the cross-sectional shape maintains the electrical characteristics of conductor sets4as intended in the design of conductor sets4. This is an advantage over some conventional shielded electrical cables where disposing a conductive shield around a conductor set changes the cross-sectional shape of the conductor set.

Although in the embodiment illustrated inFIG.1, each conductor set4has exactly two insulated conductors6, in other embodiments, some or all of the conductor sets may include only one insulated conductor, or may include more than two insulated conductors6. For example, an alternative shielded electrical cable similar in design to that ofFIG.1may include one conductor set that has eight insulated conductors6, or eight conductor sets each having only one insulated conductor6. This flexibility in arrangements of conductor sets and insulated conductors allows the disclosed shielded electrical cables to be configured in ways that are suitable for a wide variety of intended applications. For example, the conductor sets and insulated conductors may be configured to form: a multiple twinaxial cable, i.e., multiple conductor sets each having two insulated conductors; a multiple coaxial cable, i.e., multiple conductor sets each having only one insulated conductor; or combinations thereof. In some embodiments, a conductor set may further include a conductive shield (not shown) disposed around the one or more insulated conductors, and an insulative jacket (not shown) disposed around the conductive shield.

In the embodiment illustrated inFIG.1, shielded electrical cable2further includes optional ground conductors12. Ground conductors12may include ground wires or drain wires. Ground conductors12can be spaced apart from and extend in substantially the same direction as insulated conductors6. Shielding films8can be disposed around ground conductors12. The adhesive layer10may bond shielding films8to each other in the pinched portions9on both sides of ground conductors12. Ground conductors12may electrically contact at least one of the shielding films8.

The cross-sectional views ofFIGS.2a-2gmay represent various shielded electrical cables, or portions of cables. InFIG.2a, shielded electrical cable102aincludes a single conductor set104. Conductor set104extends along the length of the cable and has only a single insulated conductor106. If desired, the cable102amay be made to include multiple conductor sets104spaced apart from each other across a width of the cable102aand extending along a length of the cable. Two shielding films108are disposed on opposite sides of the cable. The cable102aincludes a cover region114and pinched regions118. In the cover region114of the cable102a, the shielding films108include cover portions107that cover the conductor set104. In transverse cross section, the cover portions107, in combination, substantially surround the conductor set104. In the pinched regions118of the cable102a, the shielding films108include pinched portions109on each side of the conductor set104.

An optional adhesive layer110may be disposed between shielding films108. Shielded electrical cable102afurther includes optional ground conductors112. Ground conductors112are spaced apart from and extend in substantially the same direction as insulated conductor106. Conductor set104and ground conductors112can be arranged so that they lie generally in a plane as illustrated inFIG.2a.

Second cover portions113of shielding films108are disposed around, and cover, the ground conductors112. The adhesive layer110may bond the shielding films108to each other on both sides of ground conductors112. Ground conductors112may electrically contact at least one of shielding films108. InFIG.2a, insulated conductor106and shielding films108are effectively arranged in a coaxial cable configuration. The coaxial cable configuration ofFIG.2acan be used in a single ended circuit arrangement.

As illustrated in the transverse cross sectional view ofFIG.2a, there is a maximum separation, D, between the cover portions107of the shielding films108, and there is a minimum separation, d1, between the pinched portions109of the shielding films108.

InFIG.2a, adhesive layer110is shown disposed between the pinched portions109of the shielding films108in the pinched regions118of the cable102and disposed between the cover portions107of the shielding films108and the insulated conductor106in the cover region114of the cable102a. In this arrangement, the adhesive layer110bonds the pinched portions109of the shielding films108together in the pinched regions118of the cable, and bonds the cover portions107of the shielding films108to the insulated conductor106in the cover region114of the cable102a.

Shielded cable102bofFIG.2bis similar to cable102aofFIG.2a, with similar elements identified by similar reference numerals, except that inFIG.2b, the optional adhesive layer110bis not present between the cover portions107of the shielding films108and the insulated conductor106in the cover region114of the cable102. In this arrangement, the adhesive layer110bbonds the pinched portions109of the shielding films108together in the pinched regions118of the cable, but the adhesive layer110does not bond cover portions107of the shielding films108to the insulated conductor106in the cover regions114of the cable102.

Referring toFIG.2c, shielded electrical cable102cis similar to shielded electrical cable102aofFIG.2a, except that cable102chas a single conductor set104cwhich has two insulated conductors106c. If desired, the cable102cmay be made to include multiple conductor sets104cspaced part across a width of the cable102cand extending along a length of the cable. Insulated conductors106care arranged generally in a single plane and effectively in a twinaxial configuration. The twin axial cable configuration ofFIG.2ccan be used in a differential pair circuit arrangement or in a single ended circuit arrangement.

Two shielding films108care disposed on opposite sides of conductor set104c. The cable102cincludes a cover region114cand pinched regions118c. In the cover region114cof the cable102c, the shielding films108cinclude cover portions107cthat cover the conductor set104c. In transverse cross section, the cover portions107c, in combination, substantially surround the conductor set104c. In the pinched regions118cof the cable102c, the shielding films108cinclude pinched portions109con each side of the conductor set104c.

An optional adhesive layer110cmay be disposed between shielding films108c. Shielded electrical cable102cfurther includes optional ground conductors112csimilar to ground conductors112discussed previously. Ground conductors112care spaced apart from, and extend in substantially the same direction as, insulated conductors106c. Conductor set104cand ground conductors112ccan be arranged so that they lie generally in a plane as illustrated inFIG.2c.

As illustrated in the cross section ofFIG.2c, there is a maximum separation, D, between the cover portions107cof the shielding films108c; there is a minimum separation, d1, between the pinched portions109cof the shielding films108c; and there is a minimum separation, d2, between the shielding films108cbetween the insulated conductors106c.

FIG.2cshows the adhesive layer110cdisposed between the pinched portions109cof the shielding films108cin the pinched regions118cof the cable102cand disposed between the cover portions107cof the shielding films108cand the insulated conductors106cin the cover region114cof the cable102c. In this arrangement, the adhesive layer110cbonds the pinched portions109cof the shielding films108ctogether in the pinched regions118cof the cable102c, and also bonds the cover portions107cof the shielding films108cto the insulated conductors106cin the cover region114cof the cable102c.

Shielded cable102dofFIG.2dis similar to cable102cofFIG.2c, with similar elements identified by similar reference numerals, except that in cable102dthe optional adhesive layer110dis not present between the cover portions107cof the shielding films108cand the insulated conductors106cin the cover region114cof the cable. In this arrangement, the adhesive layer110dbonds the pinched portions109cof the shielding films108ctogether in the pinched regions118cof the cable, but does not bond the cover portions107cof the shielding films108cto the insulated conductors106cin the cover region114cof the cable102d.

Referring now toFIG.2e, we see there a transverse cross-sectional view of a shielded electrical cable102esimilar in many respects to the shielded electrical cable102aofFIG.2a. However, where cable102aincludes a single conductor set104having only a single insulated conductor106, cable102eincludes a single conductor set104ethat has two insulated conductors106eextending along a length of the cable102e. Cable102emay be made to have multiple conductor sets104espaced apart from each other across a width of the cable102eand extending along a length of the cable102e. Insulated conductors106eare arranged effectively in a twisted pair cable arrangement, whereby insulated conductors106etwist around each other and extend along a length of the cable102e.

InFIG.2fanother shielded electrical cable102fis shown that is also similar in many respects to the shielded electrical cable102aofFIG.2a. However, where cable102aincludes a single conductor set104having only a single insulated conductor106, cable102fincludes a single conductor set104fthat has four insulated conductors106fextending along a length of the cable102f. The cable102fmay be made to have multiple conductor sets104fspaced apart from each other across a width of the cable102fand extending along a length of the cable102f.

Insulated conductors106fare arranged effectively in a quad cable arrangement, whereby insulated conductors106fmay or may not twist around each other as insulated conductors106fextend along a length of the cable102f.

Referring back toFIGS.2a-2f, further embodiments of shielded electrical cables may include a plurality of spaced apart conductor sets104,104c,104e, or104f, or combinations thereof, arranged generally in a single plane. Optionally, the shielded electrical cables may include a plurality of ground conductors112spaced apart from, and extending generally in the same direction as, the insulated conductors of the conductor sets. In some configurations, the conductor sets and ground conductors can be arranged generally in a single plane.FIG.2gillustrates an exemplary embodiment of such a shielded electrical cable.

Referring toFIG.2g, shielded electrical cable102gincludes a plurality of spaced apart conductor sets104,104carranged generally in plane. Shielded electrical cable102gfurther includes optional ground conductors112disposed between conductor sets104,104cand at both sides or edges of shielded electrical cable102g.

First and second shielding films208are disposed on opposite sides of the cable102gand are arranged so that, in transverse cross section, the cable102gincludes cover regions224and pinched regions228. In the cover regions224of the cable, cover portions217of the first and second shielding films208in transverse cross section substantially surround each conductor set104,104c. Pinched portions219of the first and second shielding films208form the pinched regions218on two sides of each conductor set104,104c.

The shielding films208are disposed around ground conductors112. An optional adhesive layer210is disposed between shielding films208and bonds the pinched portions219of the shielding films208to each other in the pinched regions228on both sides of each conductor set104,104c. Shielded electrical cable102gincludes a combination of coaxial cable arrangements (conductor sets104) and a twinaxial cable arrangement (conductor set104c) and may therefore be referred to as a hybrid cable arrangement.

One, two, or more of the shielded electrical cables may be terminated to a termination component such as a printed circuit board, paddle card, or the like. Because the insulated conductors and ground conductors can be arranged generally in a single plane, the disclosed shielded electrical cables are well suited for mass-stripping, i.e., the simultaneous stripping of the shielding films and insulation from the insulated conductors, and mass-termination, i.e., the simultaneous terminating of the stripped ends of the insulated conductors and ground conductors, which allows a more automated cable assembly process. This is an advantage of at least some of the disclosed shielded electrical cables. The stripped ends of insulated conductors and ground conductors may, for example, be terminated to contact conductive paths or other elements on a printed circuit board, for example. In other cases, the stripped ends of insulated conductors and ground conductors may be terminated to any suitable individual contact elements of any suitable termination device, such as, e.g., electrical contacts of an electrical connector.

InFIGS.3a-3dan exemplary termination process of shielded electrical cable302to a printed circuit board or other termination component314is illustrated. This termination process can be a mass-termination process and includes the steps of stripping (illustrated inFIGS.3a-3b), aligning (illustrated inFIG.3c), and terminating (illustrated inFIG.3d). When forming shielded electrical cable302, which may in general take the form of any of the cables shown and/or described herein, the arrangement of conductor sets304, insulated conductors306, and ground conductors312of shielded electrical cable302may be matched to the arrangement of contact elements316on printed circuit board314, which would eliminate any significant manipulation of the end portions of shielded electrical cable302during alignment or termination.

In the step illustrated inFIG.3a, an end portion308aof shielding films308is removed. Any suitable method may be used, such as, e.g., mechanical stripping or laser stripping. This step exposes an end portion of insulated conductors306and ground conductors312. In one aspect, mass-stripping of end portion308aof shielding films308is possible because they form an integrally connected layer that is separate from the insulation of insulated conductors306. Removing shielding films308from insulated conductors306allows protection against electrical shorting at these locations and also provides independent movement of the exposed end portions of insulated conductors306and ground conductors312. In the step illustrated inFIG.3b, an end portion306aof the insulation of insulated conductors306is removed. Any suitable method may be used, such as, e.g., mechanical stripping or laser stripping. This step exposes an end portion of the conductor of insulated conductors306. In the step illustrated inFIG.3c, shielded electrical cable302is aligned with printed circuit board314such that the end portions of the conductors of insulated conductors306and the end portions of ground conductors312of shielded electrical cable302are aligned with contact elements316on printed circuit board314. In the step illustrated inFIG.3d, the end portions of the conductors of insulated conductors306and the end portions of ground conductors312of shielded electrical cable302are terminated to contact elements316on printed circuit board314. Examples of suitable termination methods that may be used include soldering, welding, crimping, mechanical clamping, and adhesively bonding, to name a few.

In some cases, the disclosed shielded cables can be made to include one or more longitudinal slits or other splits disposed between conductor sets. The splits may be used to separate individual conductor sets at least along a portion of the length of shielded cable, thereby increasing at least the lateral flexibility of the cable. This may allow, for example, the shielded cable to be placed more easily into a curvilinear outer jacket. In other embodiments, splits may be placed so as to separate individual or multiple conductor sets and ground conductors. To maintain the spacing of conductor sets and ground conductors, splits may be discontinuous along the length of shielded electrical cable. To maintain the spacing of conductor sets and ground conductors in at least one end portion of a shielded electrical cable so as to maintain mass-termination capability, the splits may not extend into one or both end portions of the cable. The splits may be formed in the shielded electrical cable using any suitable method, such as, e.g., laser cutting or punching. Instead of or in combination with longitudinal splits, other suitable shapes of openings may be formed in the disclosed shielded electrical cables, such as, e.g., holes, e.g., to increase at least the lateral flexibility of the cable.

The shielding films used in the disclosed shielded cables can have a variety of configurations and be made in a variety of ways. In some cases, one or more shielding films may include a conductive layer and a non-conductive polymeric layer. The conductive layer may include any suitable conductive material, including but not limited to copper, silver, aluminum, gold, and alloys thereof. The non-conductive polymeric layer may include any suitable polymeric material, including but not limited to polyester, polyimide, polyamide-imide, polytetrafluoroethylene, polypropylene, polyethylene, polyphenylene sulfide, polyethylene naphthalate, polycarbonate, silicone rubber, ethylene propylene diene rubber, polyurethane, acrylates, silicones, natural rubber, epoxies, and synthetic rubber adhesive. The non-conductive polymeric layer may include one or more additives and/or fillers to provide properties suitable for the intended application. In some cases, at least one of the shielding films may include a laminating adhesive layer disposed between the conductive layer and the non-conductive polymeric layer. For shielding films that have a conductive layer disposed on a non-conductive layer, or that otherwise have one major exterior surface that is electrically conductive and an opposite major exterior surface that is substantially non-conductive, the shielding film may be incorporated into the shielded cable in several different orientations as desired. In some cases, for example, the conductive surface may face the conductor sets of insulated wires and ground wires, and in some cases the non-conductive surface may face those components. In cases where two shielding films are used on opposite sides of the cable, the films may be oriented such that their conductive surfaces face each other and each face the conductor sets and ground wires, or they may be oriented such that their non-conductive surfaces face each other and each face the conductor sets and ground wires, or they may be oriented such that the conductive surface of one shielding film faces the conductor sets and ground wires, while the non-conductive surface of the other shielding film faces conductor sets and ground wires from the other side of the cable.

In some cases, at least one of the shielding films may be or include a stand-alone conductive film, such as a compliant or flexible metal foil. The construction of the shielding films may be selected based on a number of design parameters suitable for the intended application, such as, e.g., flexibility, electrical performance, and configuration of the shielded electrical cable (such as, e.g., presence and location of ground conductors). In some cases, the shielding films may have an integrally formed construction. In some cases, the shielding films may have a thickness in the range of 0.01 mm to 0.05 mm. The shielding films desirably provide isolation, shielding, and precise spacing between the conductor sets, and allow for a more automated and lower cost cable manufacturing process. In addition, the shielding films prevent a phenomenon known as “signal suck-out” or resonance, whereby high signal attenuation occurs at a particular frequency range. This phenomenon typically occurs in conventional shielded electrical cables where a conductive shield is wrapped around a conductor set.

As discussed elsewhere herein, adhesive material may be used in the cable construction to bond one or two shielding films to one, some, or all of the conductor sets at cover regions of the cable, and/or adhesive material may be used to bond two shielding films together at pinched regions of the cable. A layer of adhesive material may be disposed on at least one shielding film, and in cases where two shielding films are used on opposite sides of the cable, a layer of adhesive material may be disposed on both shielding films. In the latter cases, the adhesive used on one shielding film is preferably the same as, but may if desired be different from, the adhesive used on the other shielding film. A given adhesive layer may include an electrically insulative adhesive, and may provide an insulative bond between two shielding films. Furthermore, a given adhesive layer may provide an insulative bond between at least one of shielding films and insulated conductors of one, some, or all of the conductor sets, and between at least one of shielding films and one, some, or all of the ground conductors (if any). Alternatively, a given adhesive layer may include an electrically conductive adhesive, and may provide a conductive bond between two shielding films. Furthermore, a given adhesive layer may provide a conductive bond between at least one of shielding films and one, some, or all of the ground conductors (if any). Suitable conductive adhesives include conductive particles to provide the flow of electrical current. The conductive particles can be any of the types of particles currently used, such as spheres, flakes, rods, cubes, amorphous, or other particle shapes. They may be solid or substantially solid particles such as carbon black, carbon fibers, nickel spheres, nickel coated copper spheres, metal-coated oxides, metal-coated polymer fibers, or other similar conductive particles. These conductive particles can be made from electrically insulating materials that are plated or coated with a conductive material such as silver, aluminum, nickel, or indium tin-oxide. The metal-coated insulating material can be substantially hollow particles such as hollow glass spheres, or may comprise solid materials such as glass beads or metal oxides. The conductive particles may be on the order of several tens of microns to nanometer sized materials such as carbon nanotubes. Suitable conductive adhesives may also include a conductive polymeric matrix.

When used in a given cable construction, an adhesive layer is preferably substantially conformable in shape relative to other elements of the cable, and conformable with regard to bending motions of the cable. In some cases, a given adhesive layer may be substantially continuous, e.g., extending along substantially the entire length and width of a given major surface of a given shielding film. In some cases, the adhesive layer may include be substantially discontinuous. For example, the adhesive layer may be present only in some portions along the length or width of a given shielding film. A discontinuous adhesive layer may for example include a plurality of longitudinal adhesive stripes that are disposed, e.g., between the pinched portions of the shielding films on both sides of each conductor set and between the shielding films beside the ground conductors (if any). A given adhesive material may be or include at least one of a pressure sensitive adhesive, a hot melt adhesive, a thermoset adhesive, and a curable adhesive. An adhesive layer may be configured to provide a bond between shielding films that is substantially stronger than a bond between one or more insulated conductor and the shielding films. This may be achieved, e.g., by appropriate selection of the adhesive formulation. An advantage of this adhesive configuration is to allow the shielding films to be readily strippable from the insulation of insulated conductors. In other cases, an adhesive layer may be configured to provide a bond between shielding films and a bond between one or more insulated conductor and the shielding films that are substantially equally strong. An advantage of this adhesive configuration is that the insulated conductors are anchored between the shielding films. When a shielded electrical cable having this construction is bent, this allows for little relative movement and therefore reduces the likelihood of buckling of the shielding films. Suitable bond strengths may be chosen based on the intended application. In some cases, a conformable adhesive layer may be used that has a thickness of less than about 0.13 mm. In exemplary embodiments, the adhesive layer has a thickness of less than about 0.05 mm.

A given adhesive layer may conform to achieve desired mechanical and electrical performance characteristics of the shielded electrical cable. For example, the adhesive layer may conform to be thinner between the shielding films in areas between conductor sets, which increases at least the lateral flexibility of the shielded cable. This may allow the shielded cable to be placed more easily into a curvilinear outer jacket. In some cases, an adhesive layer may conform to be thicker in areas immediately adjacent the conductor sets and substantially conform to the conductor sets. This may increase the mechanical strength and enable forming a curvilinear shape of shielding films in these areas, which may increase the durability of the shielded cable, for example, during flexing of the cable. In addition, this may help to maintain the position and spacing of the insulated conductors relative to the shielding films along the length of the shielded cable, which may result in more uniform impedance and superior signal integrity of the shielded cable.

A given adhesive layer may conform to effectively be partially or completely removed between the shielding films in areas between conductor sets, e.g., in pinched regions of the cable. As a result, the shielding films may electrically contact each other in these areas, which may increase the electrical performance of the cable. In some cases, an adhesive layer may conform to effectively be partially or completely removed between at least one of the shielding films and the ground conductors. As a result, the ground conductors may electrically contact at least one of shielding films in these areas, which may increase the electrical performance of the cable. Even in cases where a thin layer of adhesive remains between at least one of shielding films and a given ground conductor, asperities on the ground conductor may break through the thin adhesive layer to establish electrical contact as intended.

InFIGS.4a-4c, cross sectional views are shown of three exemplary shielded electrical cables, which illustrate examples of the placement of ground conductors in the shielded electrical cables. An aspect of a shielded electrical cable is proper grounding of the shield, and such grounding can be accomplished in a number of ways. In some cases, a given ground conductor can electrically contact at least one of the shielding films such that grounding the given ground conductor also grounds the shielding film or films. Such a ground conductor may also be referred to as a “drain wire”. Electrical contact between the shielding film and the ground conductor may be characterized by a relatively low DC resistance, e.g., a DC resistance of less than 10 ohms, or less than 2 ohms, or of substantially 0 ohms. In some cases, a given ground conductor may not electrically contact the shielding films, but may be an individual element in the cable construction that is independently terminated to any suitable individual contact element of any suitable termination component, such as, e.g., a conductive path or other contact element on a printed circuit board, paddle board, or other device. Such a ground conductor may also be referred to as a “ground wire”.FIG.4aillustrates an exemplary shielded electrical cable in which ground conductors are positioned external to the shielding films.FIGS.4band4cillustrate embodiments in which the ground conductors are positioned between the shielding films, and may be included in the conductor set. One or more ground conductors may be placed in any suitable position external to the shielding films, between the shielding films, or a combination of both.

Referring toFIG.4a, a shielded electrical cable402aincludes a single conductor set404athat extends along a length of the cable402a. Conductor set404ahas two insulated conductors406, i.e., one pair of insulated conductors. Cable402amay be made to have multiple conductor sets404aspaced apart from each other across a width of the cable and extending along a length of the cable. Two shielding films408adisposed on opposite sides of the cable include cover portions407a. In transverse cross section, the cover portions407a, in combination, substantially surround conductor set404a. An optional adhesive layer410ais disposed between pinched portions409aof the shielding films408a, and bonds shielding films408ato each other on both sides of conductor set404a. Insulated conductors406are arranged generally in a single plane and effectively in a twinaxial cable configuration that can be used in a single ended circuit arrangement or a differential pair circuit arrangement. The shielded electrical cable402afurther includes a plurality of ground conductors412positioned external to shielding films408a. Ground conductors412are placed over, under, and on both sides of conductor set404a. Optionally, the cable402aincludes protective films420surrounding the shielding films408aand ground conductors412. Protective films420include a protective layer421and an adhesive layer422bonding protective layer421to shielding films408aand ground conductors412. Alternatively, shielding films408aand ground conductors412may be surrounded by an outer conductive shield, such as, e.g., a conductive braid, and an outer insulative jacket (not shown).

Referring toFIG.4b, a shielded electrical cable402bincludes a single conductor set404bthat extends along a length of cable402b. Conductor set404bhas two insulated conductors406, i.e., one pair of insulated conductors. Cable402bmay be made to have multiple conductor sets404bspaced apart from each other across a width of the cable and extending along the length of the cable. Two shielding films408bare disposed on opposite sides of the cable402band include cover portions407b. In transverse cross section, the cover portions407b, in combination, substantially surround conductor set404b. An optional adhesive layer410bis disposed between pinched portions409bof the shielding films408band bonds the shielding films to each other on both sides of the conductor set. Insulated conductors406are arranged generally in a single plane and effectively in a twinaxial or differential pair cable arrangement. Shielded electrical cable402bfurther includes a plurality of ground conductors412positioned between shielding films408b. Two of the ground conductors412are included in conductor set404b, and two of the ground conductors412are spaced apart from conductor set404b.

Referring toFIG.4c, a shielded electrical cable402cincludes a single conductor set404cthat extends along a length of cable402c. Conductor set404chas two insulated conductors406, i.e., one pair of insulated conductors. Cable402cmay be made to have multiple conductor sets404cspaced apart from each other across a width of the cable and extending along the length of the cable. Two shielding films408care disposed on opposite sides of the cable402cand include cover portions407c. In transverse cross section, the cover portions407c, in combination, substantially surround the conductor set404c. An optional adhesive layer410cis disposed between pinched portions409cof the shielding films408cand bonds shielding films408cto each other on both sides of conductor set404c. Insulated conductors406are arranged generally in a single plane and effectively in a twinaxial or differential pair cable arrangement. Shielded electrical cable402cfurther includes a plurality of ground conductors412positioned between shielding films408c. All of the ground conductors412are included in the conductor set404c. Two of the ground conductors412and insulated conductors406are arranged generally in a single plane.

The disclosed shielded cables can, if desired, be connected to a circuit board or other termination component using one or more electrically conductive cable clips. For example, a shielded electrical cable may include a plurality of spaced apart conductor sets arranged generally in a single plane, and each conductor set may include two insulated conductors that extend along a length of the cable. Two shielding films may be disposed on opposite sides of the cable and, in transverse cross section, substantially surround each of the conductor sets. A cable clip may be clamped or otherwise attached to an end portion of the shielded electrical cable such that at least one of shielding films electrically contacts the cable clip. The cable clip may be configured for termination to a ground reference, such as, e.g., a conductive trace or other contact element on a printed circuit board, to establish a ground connection between shielded electrical cable and the ground reference. The cable clip may be terminated to the ground reference using any suitable method, including soldering, welding, crimping, mechanical clamping, and adhesively bonding, to name a few. When terminated, the cable clip may facilitate termination of end portions of the conductors of the insulated conductors of the shielded electrical cable to contact elements of a termination point, such as, e.g., contact elements on printed circuit board. The shielded electrical cable may include one or more ground conductors as described herein that may electrically contact the cable clip in addition to or instead of at least one of the shielding films.

InFIGS.5a-5can exemplary method of making a shielded electrical cable is illustrated. Specifically, these figures illustrate an exemplary method of making a shielded electrical cable that may be substantially the same as that shown inFIG.1. In the step illustrated inFIG.5a, insulated conductors506are formed using any suitable method, such as, e.g., extrusion, or are otherwise provided. Insulated conductors506may be formed of any suitable length. Insulated conductors506may then be provided as such or cut to a desired length. Ground conductors512(seeFIG.5c) may be formed and provided in a similar fashion.

In the step illustrated inFIG.5b, shielding films508are formed. A single layer or multilayer web may be formed using any suitable method, such as, e.g., continuous wide web processing. Shielding films508may be formed of any suitable length. Shielding films508may then be provided as such or cut to a desired length and/or width. Shielding films508may be pre-formed to have transverse partial folds to increase flexibility in the longitudinal direction. One or both of the shielding films may include a conformable adhesive layer510, which may be formed on the shielding films508using any suitable method, such as, e.g., laminating or sputtering.

In the step illustrated inFIG.5c, a plurality of insulated conductors506, ground conductors512, and shielding films508are provided. A forming tool524is provided. Forming tool524includes a pair of forming rolls526a,526bhaving a shape corresponding to a desired cross-sectional shape of the finished shielded electrical cable, the forming tool also including a bite528. Insulated conductors506, ground conductors512, and shielding films508are arranged according to the configuration of the desired shielded cable, such as any of the cables shown and/or described herein, and positioned in proximity to forming rolls526a,526b, after which they are concurrently fed into bite528of forming rolls526a,526band disposed between forming rolls526a,526b. The forming tool524forms shielding films508around conductor sets504and ground conductor512and bonds shielding films508to each other on both sides of each conductor set504and ground conductors512. Heat may be applied to facilitate bonding. Although in this embodiment, forming shielding films508around conductor sets504and ground conductor512and bonding shielding films508to each other on both sides of each conductor set504and ground conductors512occur in a single operation, in other embodiments, these steps may occur in separate operations.

In subsequent fabrication operations, longitudinal splits may if desired be formed between the conductor sets. Such splits may be formed in the shielded cable using any suitable method, such as, e.g., laser cutting or punching. In another optional fabrication operation, the shielded electrical cable may be folded lengthwise along the pinched regions multiple times into a bundle, and an outer conductive shield may be provided around the folded bundle using any suitable method. An outer jacket may also be provided around the outer conductive shield using any suitable method, such as, e.g., extrusion. In other embodiments, the outer conductive shield may be omitted and the outer jacket may be provided by itself around the folded shielded cable.

InFIGS.6a-6ca detail of an exemplary method of making a shielded electrical cable is illustrated. In particular, these figures illustrate how one or more adhesive layers may be conformably shaped during the forming and bonding of the shielding films. In the step illustrated inFIG.6a, an insulated conductor606, a ground conductor612spaced apart from the insulated conductor606, and two shielding films608are provided. Shielding films608each include a conformable adhesive layer610. In the steps illustrated inFIGS.6b-6c, shielding films608are formed around insulated conductor606and ground conductor612and bonded to each other. Initially, as illustrated inFIG.6b, the adhesive layers610still have their original thickness. As the forming and bonding of shielding films608proceeds, the adhesive layers610conform to achieve desired mechanical and electrical performance characteristics of finished shielded electrical cable602(FIG.6c).

As illustrated inFIG.11c, adhesive layers610conform to be thinner between shielding films608on both sides of insulated conductor606and ground conductor612; a portion of adhesive layers610displaces away from these areas. Further, adhesive layers610conform to be thicker in areas immediately adjacent insulated conductor606and ground conductor612, and substantially conform to insulated conductor606and ground conductor612; a portion of adhesive layers610displaces into these areas. Further, adhesive layers610conform to effectively be removed between shielding films608and ground conductor612; the adhesive layers610displace away from these areas such that ground conductor612electrically contacts shielding films608.

Shown inFIGS.7aand7bare details pertaining to a pinched region during the manufacture of an exemplary shielded electrical cable. Shielded electrical cable702(seeFIG.7b) is made using two shielding films708and includes a pinched region718(seeFIG.7b) wherein shielding films708may be substantially parallel. Shielding films708include a non-conductive polymeric layer708b, a conductive layer708adisposed on non-conductive polymeric layer708b, and a stop layer708ddisposed on the conductive layer708a. A conformable adhesive layer710is disposed on stop layer708d. Pinched region718includes a longitudinal ground conductor712disposed between shielding films708. After the shielding films are forced together around the ground conductor, the ground conductor712makes indirect electrical contact with the conductive layers708aof shielding films708. This indirect electrical contact is enabled by a controlled separation of conductive layer708aand ground conductor712provided by stop layer708d. In some cases, the stop layer708dmay be or include a non-conductive polymeric layer. As shown in the figures, an external pressure (seeFIG.17a) is used to press conductive layers708atogether and force the adhesive layers710to conform around the ground conductor712(FIG.17b). Because the stop layer708ddoes not conform at least under the same processing conditions, it prevents direct electrical contact between the ground conductor712and conductive layer708aof the shielding films708, but achieves indirect electrical contact. The thickness and dielectric properties of stop layer708dmay be selected to achieve a low target DC resistance, i.e., electrical contact of an indirect type. In some embodiments, the characteristic DC resistance between the ground conductor and the shielding film may be less than 10 ohms, or less than 5 ohms, for example, but greater than 0 ohms, to achieve the desired indirect electrical contact. In some cases, it is desirable to make direct electrical contact between a given ground conductor and one or two shielding films, whereupon the DC resistance between such ground conductor and such shielding film(s) may be substantially 0 ohms.

In exemplary embodiments, the cover regions of the shielded electrical cable include concentric regions and transition regions positioned on one or both sides of a given conductor set. Portions of a given shielding film in the concentric regions are referred to as concentric portions of the shielding film, and portions of the shielding film in the transition regions are referred to as transition portions of the shielding film. The transition regions can be configured to provide high manufacturability and strain and stress relief of the shielded electrical cable. Maintaining the transition regions at a substantially constant configuration (including aspects such as, e.g., size, shape, content, and radius of curvature) along the length of the shielded electrical cable may help the shielded electrical cable to have substantially uniform electrical properties, such as, e.g., high frequency isolation, impedance, skew, insertion loss, reflection, mode conversion, eye opening, and jitter.

Additionally, in certain embodiments, such as, e.g., embodiments wherein the conductor set includes two insulated conductors that extend along a length of the cable that are arranged generally in a single and effectively as a twinaxial cable that can be connected in a differential pair circuit arrangement, maintaining the transition portion at a substantially constant configuration along the length of the shielded electrical cable can beneficially provide substantially the same electromagnetic field deviation from an ideal concentric case for both conductors in the conductor set. Thus, careful control of the configuration of this transition portion along the length of the shielded electrical cable can contribute to the advantageous electrical performance and characteristics of the cable.FIGS.8athrough10illustrate various exemplary embodiments of a shielded electrical cable that include transition regions of the shielding films disposed on one or both sides of the conductor set.

The shielded electrical cable802, which is shown in cross section inFIGS.8aand8b, includes a single conductor set804that extends along a length of the cable. The cable802may be made to have multiple conductor sets804spaced apart from each other along a width of the cable and extending along a length of the cable. Although only one insulated conductor806is shown inFIG.8a, multiple insulated conductors may be included in the conductor set804if desired.

The insulated conductor of a conductor set that is positioned nearest to a pinched region of the cable is considered to be an end conductor of the conductor set. The conductor set804, as shown, has a single insulated conductor806, and it is also an end conductor since it is positioned nearest to the pinched region818of the shielded electrical cable802.

First and second shielding films808are disposed on opposite sides of the cable and include cover portions807. In transverse cross section, the cover portions807substantially surround conductor set804. An optional adhesive layer810is disposed between the pinched portions809of the shielding films808, and bonds shielding films808to each other in the pinched regions818of the cable802on both sides of conductor set804. The optional adhesive layer810may extend partially or fully across the cover portion807of the shielding films808, e.g., from the pinched portion809of the shielding film808on one side of the conductor set804to the pinched portion809of the shielding film808on the other side of the conductor set804.

Insulated conductor806is effectively arranged as a coaxial cable which may be used in a single ended circuit arrangement. Shielding films808may include a conductive layer808aand a non-conductive polymeric layer808b. In some embodiments, as illustrated byFIGS.8aand8b, the conductive layer808aof both shielding films faces the insulated conductors. Alternatively, the orientation of the conductive layers of one or both of shielding films808may be reversed, as discussed elsewhere herein.

Shielding films808include a concentric portion that is substantially concentric with the end conductor806of the conductor set804. The shielded electrical cable802includes transition regions836. Portions of the shielding film808in the transition region836of the cable802are transition portions834of the shielding films808. In some embodiments, shielded electrical cable802includes a transition region836positioned on both sides of the conductor set804, and in some embodiments a transition region836may be positioned on only one side of conductor set804.

Transition regions836are defined by shielding films808and conductor set804. The transition portions834of the shielding films808in the transition regions836provide a gradual transition between concentric portions811and pinched portions809of the shielding films808. As opposed to a sharp transition, such as, e.g., a right-angle transition or a transition point (as opposed to a transition portion), a gradual or smooth transition, such as, e.g., a substantially sigmoidal transition, provides strain and stress relief for shielding films808in transition regions836and prevents damage to shielding films808when shielded electrical cable802is in use, e.g., when laterally or axially bending shielded electrical cable802. This damage may include, e.g., fractures in conductive layer808aand/or debonding between conductive layer808aand non-conductive polymeric layer808b. In addition, a gradual transition prevents damage to shielding films808in manufacturing of shielded electrical cable802, which may include, e.g., cracking or shearing of conductive layer808aand/or non-conductive polymeric layer808b. Use of the disclosed transition regions on one or both sides of one, some, or all of the conductor sets in a shielded electrical ribbon cable represents a departure from conventional cable configurations, such as, e.g., a typical coaxial cable, wherein a shield is generally continuously disposed around a single insulated conductor, or a typical conventional twinaxial cable in which a shield is continuously disposed around a pair of insulated conductors. Although these conventional shielding configurations may provide model electromagnetic profiles, such profiles may not be necessary to achieve acceptable electrical properties in a given application.

According to one aspect of at least some of the disclosed shielded electrical cables, acceptable electrical properties can be achieved by reducing the electrical impact of the transition region, e.g., by reducing the size of the transition region and/or carefully controlling the configuration of the transition region along the length of the shielded electrical cable. Reducing the size of the transition region reduces the capacitance deviation and reduces the required space between multiple conductor sets, thereby reducing the conductor set pitch and/or increasing the electrical isolation between conductor sets. Careful control of the configuration of the transition region along the length of the shielded electrical cable contributes to obtaining predictable electrical behavior and consistency, which provides for high speed transmission lines so that electrical data can be more reliably transmitted. Careful control of the configuration of the transition region along the length of the shielded electrical cable is a factor as the size of the transition portion approaches a lower size limit.

An electrical characteristic that is often considered is the characteristic impedance of the transmission line. Any impedance changes along the length of a transmission line may cause power to be reflected back to the source instead of being transmitted to the target. Ideally, the transmission line will have no impedance variation along its length, but, depending on the intended application, variations up to 5-10% may be acceptable. Another electrical characteristic that is often considered in twinaxial cables (differentially driven) is skew or unequal transmission speeds of two transmission lines of a pair along at least a portion of their length. Skew produces conversion of the differential signal to a common mode signal that can be reflected back to the source, reduces the transmitted signal strength, creates electromagnetic radiation, and can dramatically increase the bit error rate, in particular jitter. Ideally, a pair of transmission lines will have no skew, but, depending on the intended application, a differential S-parameter SCD21 or SCD12 value (representing the differential-to common mode conversion from one end of the transmission line to the other) of less than −25 to −30 dB up to a frequency of interest, such as, e.g., 6 GHz, may be acceptable. Alternatively, skew can be measured in the time domain and compared to a required specification. Depending on the intended application, values of less than about 20 picoseconds/meter (ps/m) and preferably less than about 10 ps/m may be acceptable.

Referring again toFIGS.8aand8b, in part to help achieve acceptable electrical properties, transition regions836of shielded electrical cable802may each include a cross-sectional transition area836a. The transition area836ais preferably smaller than a cross-sectional area806aof conductor806. As best shown inFIG.8b, cross-sectional transition area836aof transition region836is defined by transition points834′ and834″.

The transition points834′ occur where the shielding films deviate from being substantially concentric with the end insulated conductor806of the conductor set804. The transition points834′ are the points of inflection of the shielding films808at which the curvature of the shielding films808changes sign. For example, with reference toFIG.8b, the curvature of the upper shielding film808transitions from concave downward to concave upward at the inflection point which is the upper transition point834′ in the figure. The curvature of the lower shielding film808transitions from concave upward to concave downward at the inflection point which is the lower transition point834′ in the figure. The other transition points834″ occur where a separation between the pinched portions809of the shielding films808exceeds the minimum separation d1of the pinched portions809by a predetermined factor, e.g., 1.2 or 1.5.

In addition, each transition area836amay include a void area836b. Void areas836bon either side of the conductor set804may be substantially the same. Further, adhesive layer810may have a thickness Tac at the concentric portion811of the shielding film808, and a thickness at the transition portion834of the shielding film808that is greater than thickness Tac. Similarly, adhesive layer810may have a thickness Tap between the pinched portions809of the shielding films808, and a thickness at the transition portion834of the shielding film808that is greater than thickness Tap. Adhesive layer810may represent at least 25% of cross-sectional transition area836a. The presence of adhesive layer810in transition area836a, in particular at a thickness that is greater than thickness Tac or thickness Tap, contributes to the strength of the cable802in the transition region836.

Careful control of the manufacturing process and the material characteristics of the various elements of shielded electrical cable802may reduce variations in void area836band the thickness of conformable adhesive layer810in transition region836, which may in turn reduce variations in the capacitance of cross-sectional transition area836a. Shielded electrical cable802may include transition region836positioned on one or both sides of conductor set804that includes a cross-sectional transition area836athat is substantially equal to or smaller than a cross-sectional area806aof conductor806. Shielded electrical cable802may include a transition region836positioned on one or both sides of conductor set804that includes a cross-sectional transition area836athat is substantially the same along the length of conductor806. For example, cross-sectional transition area836amay vary less than 50% over a length of 1 meter. Shielded electrical cable802may include transition regions836positioned on both sides of conductor set804that each include a cross-sectional transition area, wherein the sum of cross-sectional areas834ais substantially the same along the length of conductor806. For example, the sum of cross-sectional areas834amay vary less than 50% over a length of 1 m. Shielded electrical cable802may include transition regions836positioned on both sides of conductor set804that each include a cross-sectional transition area836a, wherein the cross-sectional transition areas836aare substantially the same. Shielded electrical cable802may include transition regions836positioned on both sides of conductor set804, wherein the transition regions836are substantially identical. Insulated conductor806has an insulation thickness Ti, and transition region836may have a lateral length Lt that is less than insulation thickness Ti. The central conductor of insulated conductor806has a diameter Dc, and transition region836may have a lateral length Lt that is less than the diameter Dc. The various configurations described above may provide a characteristic impedance that remains within a desired range, such as, e.g., within 5-10% of a target impedance value, such as, e.g., 50 ohms, over a given length, such as, e.g., 1 meter.

Factors that can influence the configuration of transition region836along the length of shielded electrical cable802include the manufacturing process, the thickness of conductive layers808aand non-conductive polymeric layers808b, adhesive layer810, and the bond strength between insulated conductor806and shielding films808, to name a few.

In one aspect, conductor set804, shielding films808, and transition region836may be cooperatively configured in an impedance controlling relationship. An impedance controlling relationship means that conductor set804, shielding films808, and transition region836are cooperatively configured to control the characteristic impedance of the shielded electrical cable.

InFIG.9an exemplary shielded electrical cable902is shown, in transverse cross section, that includes two insulated conductors in a connector set904, the individually insulated conductors906each extending along a length of the cable902. Two shielding films908are disposed on opposite sides of the cable902and in combination substantially surround conductor set904. An optional adhesive layer910is disposed between pinched portions909of the shielding films908and bonds shielding films908to each other on both sides of conductor set904in the pinched regions918of the cable. Insulated conductors906can be arranged generally in a single plane and effectively in a twinaxial cable configuration. The twinaxial cable configuration can be used in a differential pair circuit arrangement or in a single ended circuit arrangement. Shielding films908may include a conductive layer908aand a non-conductive polymeric layer908b, or may include the conductive layer908awithout the non-conductive polymeric layer908b. In the figure, the conductive layer908aof each shielding film is shown facing insulated conductors906, but in alternative embodiments, one or both of the shielding films may have a reversed orientation.

The cover portion907of at least one of the shielding films908includes concentric portions911that are substantially concentric with corresponding end conductors906of the conductor set904. In the transition regions of the cable902, transition portion934of the shielding films908are between the concentric portions911and the pinched portions909of the shielding films908. Transition portions934are positioned on both sides of conductor set904, and each such portion includes a cross-sectional transition area934a. The sum of cross-sectional transition areas934ais preferably substantially the same along the length of conductors906. For example, the sum of cross-sectional areas934amay vary less than 50% over a length of 1 m.

In addition, the two cross-sectional transition areas934amay be substantially the same and/or substantially identical. This configuration of transition regions contributes to a characteristic impedance for each conductor906(single-ended) and a differential impedance that both remain within a desired range, such as, e.g., within 5-10% of a target impedance value over a given length, such as, e.g., 1 m. In addition, this configuration of the transition regions may minimize skew of the two conductors906along at least a portion of their length.

When the cable is in an unfolded, planar configuration, each of the shielding films may be characterizable in transverse cross section by a radius of curvature that changes across a width of the cable902. The maximum radius of curvature of the shielding film908may occur, for example, at the pinched portion909of the cable902, or near the center point of the cover portion907of the multi-conductor cable set904illustrated inFIG.9. At these positions, the film may be substantially flat and the radius of curvature may be substantially infinite. The minimum radius of curvature of the shielding film908may occur, for example, at the transition portion934of the shielding film908. In some embodiments, the radius of curvature of the shielding film across the width of the cable is at least about 50 micrometers, i.e., the radius of curvature does not have a magnitude smaller than 50 micrometers at any point along the width of the cable, between the edges of the cable. In some embodiments, for shielding films that include a transition portion, the radius of curvature of the transition portion of the shielding film is similarly at least about 50 micrometers.

In an unfolded, planar configuration, shielding films that include a concentric portion and a transition portion are characterizable by a radius of curvature of the concentric portion, R1, and/or a radius of curvature of the transition portion r1. These parameters are illustrated inFIG.9for the cable902. In exemplary embodiments, R1/r1is in a range of 2 to 15.

InFIG.10another exemplary shielded electrical cable1002is illustrated which includes a conductor set having two insulated conductors1006. In this embodiment, the shielding films1008have an asymmetric configuration, which changes the position of the transition portions relative to a more symmetric embodiment such as that ofFIG.9. InFIG.10, shielded electrical cable1002has pinched portions1009of shielding films1008that lie in a plane that is slightly offset from the plane of symmetry of the insulated conductors1006. Despite the slight offset, the cable ofFIG.10and its various elements can still be considered to extend generally along a given plane and to be substantially planar. The transition regions1036have a somewhat offset position and configuration relative to other depicted embodiments. However, by ensuring that the two transition regions1036are positioned substantially symmetrically with respect to corresponding insulated conductors1006(e.g. with respect to a vertical plane between the conductors1006), and that the configuration of transition regions1036is carefully controlled along the length of shielded electrical cable1002, the shielded electrical cable1002can be configured to still provide acceptable electrical properties.

InFIGS.11aand11badditional exemplary shielded electrical cables are illustrated. These figures are used to further explain how a pinched portion of the cable is configured to electrically isolate a conductor set of the shielded electrical cable. The conductor set may be electrically isolated from an adjacent conductor set (e.g., to minimize crosstalk between adjacent conductor sets) or from the external environment of the shielded electrical cable (e.g., to minimize electromagnetic radiation escape from the shielded electrical cable and minimize electromagnetic interference from external sources). In both cases, the pinched portion may include various mechanical structures to realize the electrical isolation. Examples include close proximity of the shielding films, high dielectric constant material between the shielding films, ground conductors that make direct or indirect electrical contact with at least one of the shielding films, extended distance between adjacent conductor sets, physical breaks between adjacent conductor sets, intermittent contact of the shielding films to each other directly either longitudinally, transversely, or both, and conductive adhesive, to name a few.

Shown inFIG.11a, in cross section, is a shielded electrical cable1102that includes two conductor sets1104a,104bspaced apart across a width of the cable102and extending longitudinally along a length of the cable. Each conductor set1104a,1104bhas two insulated conductors1106a,1106b. Two shielding films1108are disposed on opposite sides of the cable1102. In transverse cross section, cover portions1107of the shielding films1108substantially surround conductor sets1104a,1104bin cover regions1114of the cable1102. In pinched regions1118of the cable, on both sides of the conductor sets1104a,1104b, the shielding films1108include pinched portions1109. In shielded electrical cable1102, the pinched portions1109of shielding films1108and insulated conductors1106are arranged generally in a single plane when the cable1102is in a planar and/or unfolded arrangement. Pinched portions1109positioned in between conductor sets1104a,1104bare configured to electrically isolate conductor sets1104a,1104bfrom each other. When arranged in a generally planar, unfolded arrangement, as illustrated inFIG.11a, the high frequency electrical isolation of the first insulated conductor1106ain the conductor set1104arelative to the second insulated conductor1106bin the conductor set1104ais substantially less than the high frequency electrical isolation of the first conductor set1104arelative to the second conductor set1104b.

As illustrated in the cross section ofFIG.11a, the cable1102can be characterized by a maximum separation, D, between the cover portions1107of the shielding films1108, a minimum separation, d2, between the cover portions1107of the shielding films1108, and a minimum separation, d1, between the pinched portions1109of the shielding films1108. In some embodiments, d1/D is less than 0.25, or less than 0.1. In some embodiments, d2/D is greater than 0.33.

An optional adhesive layer may be included as shown between the pinched portions1109of the shielding films1108. The adhesive layer may be continuous or discontinuous. In some embodiments, the adhesive layer may extend fully or partially in the cover region1114of the cable1102, e.g., between the cover portion1107of the shielding films1108and the insulated conductors1106a,1106b. The adhesive layer may be disposed on the cover portion1107of the shielding film1108and may extend fully or partially from the pinched portion1109of the shielding film1108on one side of a conductor set1104a,1104bto the pinched portion1109of the shielding film1108on the other side of the conductor set1104a,1104b.

The shielding films1108can be characterized by a radius of curvature, R, across a width of the cable1102and/or by a radius of curvature, r1, of the transition portion1112of the shielding film and/or by a radius of curvature, r2, of the concentric portion1111of the shielding film.

In the transition region1136, the transition portion1112of the shielding film1108can be arranged to provide a gradual transition between the concentric portion1111of the shielding film1108and the pinched portion1109of the shielding film1108. The transition portion1112of the shielding film1108extends from a first transition point1121, which is the inflection point of the shielding film1108and marks the end of the concentric portion1111, to a second transition point1122where the separation between the shielding films exceeds the minimum separation, d1, of the pinched portions1109by a predetermined factor.

In some embodiments, the cable1102includes at least one shielding film that has a radius of curvature, R, across the width of the cable that is at least about 50 micrometers and/or the minimum radius of curvature, r1, of the transition portion1112of the shielding film1102is at least about 50 micrometers. In some embodiments, the ratio of the minimum radius of curvature of the concentric portion to the minimum radius of curvature of the transition portion, r2/r1is in a range of 2 to 15.

InFIG.11bis a cross sectional view of a shielded electrical cable1202that includes two conductor sets1204spaced apart from each other across a width of the cable and extending longitudinally along a length of the cable. Each conductor set1204has only one insulated conductor1206, and two shielding films1208are disposed on opposite sides of the cable1202. In transverse cross section, the cover portions1207of the shielding films1208in combination substantially surround the insulated conductor1206of conductor sets1204in a cover region1214of the cable. In pinched regions1218of the cable, on both sides of the conductor sets1204, the shielding films1208include pinched portions1209. In shielded electrical cable1202, pinched portions1209of shielding films1208and insulated conductors1206can be arranged generally in a single plane when the cable1202is in a planar and/or unfolded arrangement. The cover portions1207of the shielding films1208and/or the pinched regions1218of the cable1202are configured to electrically isolate the conductor sets1204from each other.

As shown in the figure, the cable1202can be characterized by a maximum separation, D, between the cover portions1207of the shielding films1208, and a minimum separation, d1, between the pinched portions1209of the shielding films1208. In exemplary embodiments, d1/D is less than 0.25, or less than 0.1.

An optional adhesive layer may be disposed as shown between the pinched portions1209of the shielding films1208. The adhesive layer may be continuous or discontinuous. In some embodiments, the adhesive layer may extend fully or partially in the cover region1214of the cable, e.g., between the cover portions1207of the shielding films1208and the insulated conductors1206. The adhesive layer may be disposed on the cover portions1207of the shielding films1208and may extend fully or partially from the pinched portions1209of the shielding films1208on one side of a conductor set1204to the pinched portions1209of the shielding films1208on the other side of the conductor set1204.

The shielding films1208can be characterized by a radius of curvature, R, across a width of the cable1202and/or by a minimum radius of curvature, r1, in the transition portion1212of the shielding film1208and/or by a minimum radius of curvature, r2, of the concentric portion1211of the shielding film1208. In the transition regions1236of the cable1202, transition portions1212of the shielding films1202can be configured to provide a gradual transition between the concentric portions1211of the shielding films1208and the pinched portions1209of the shielding films1208. The transition portion1212of the shielding film1208extends from a first transition point1221, which is the inflection point of the shielding film1208and marks the end of the concentric portion1211, to a second transition point1222where the separation between the shielding films exceeds the minimum separation, d1, of the pinched portions1209by a predetermined factor.

In some embodiments, the radius of curvature, R, of the shielding film across the width of the cable is at least about 50 micrometers and/or the minimum radius of curvature in the transition portion of the shielding film is at least 50 micrometers.

In some cases, the pinched regions of any of the described shielded cables can be configured to be laterally bent at an angle α of at least 30°, for example. This lateral flexibility of the pinched regions can enable the shielded cable to be folded in any suitable configuration, such as, e.g., a configuration that can be used in a round cable. In some cases, the lateral flexibility of the pinched regions is enabled by shielding films that include two or more relatively thin individual layers. To warrant the integrity of these individual layers in particular under bending conditions, it is preferred that the bonds between them remain intact. The pinched regions may for example have a minimum thickness of less than about 0.13 mm, and the bond strength between individual layers may be at least 17.86 g/mm (1 lbs/inch) after thermal exposures during processing or use.

It may be beneficial to the electrical performance of any of the disclosed shielded electrical cables for the pinched regions of the cable to have approximately the same size and shape on both sides of a given conductor set. Any dimensional changes or imbalances may produce imbalances in capacitance and inductance along the length of the pinched region. This in turn may cause impedance differences along the length of the pinched region and impedance imbalances between adjacent conductor sets. At least for these reasons, control of the spacing between the shielding films may be desired. In some cases, the pinched portions of the shielding films in the pinched regions of the cable (on each side of a conductor set) may be separated from each other by no more than about 0.05 mm.

InFIG.12, the far end crosstalk (FEXT) isolation is shown between two adjacent conductor sets of a conventional electrical cable wherein the conductor sets are completely isolated, i.e., have no common ground (Sample 1), and between two adjacent conductor sets of the shielded electrical cable1102illustrated inFIG.11awherein the shielding films1108are spaced apart by about 0.025 mm (Sample 2), both having a cable length of about 3 meters. The test method for creating this data is well known in the art. The data was generated using an Agilent 8720ES 50 MHz-20 GHz S-Parameter Network Analyzer. It can be seen by comparing the far end crosstalk plots that the conventional electrical cable and the shielded electrical cable1102provide a similar far end crosstalk performance. Specifically, it is generally accepted that a far end crosstalk of less than about −35 dB is suitable for most applications. It can be easily seen fromFIG.12that for the configuration tested, both the conventional electrical cable and shielded electrical cable1102provide satisfactory electrical isolation performance. The satisfactory electrical isolation performance in combination with the increased strength of the pinched portion due to the ability to space apart the shielding films is an advantage of at least some of the disclosed shielded electrical cables over conventional electrical cables.

In exemplary embodiments described above, the shielded electrical cable includes two shielding films disposed on opposite sides of the cable such that, in transverse cross section, cover portions of the shielding films in combination substantially surround a given conductor set, and surround each of the spaced apart conductor sets individually. In some embodiments, however, the shielded electrical cable may contain only one shielding film, which is disposed on only one side of the cable. Advantages of including only a single shielding film in the shielded cable, compared to shielded cables having two shielding films, include a decrease in material cost and an increase in mechanical flexibility, manufacturability, and ease of stripping and termination. A single shielding film may provide an acceptable level of electromagnetic interference (EMI) isolation for a given application, and may reduce the proximity effect thereby decreasing signal attenuation.FIG.13illustrates one example of such a shielded electrical cable that includes only one shielding film.

InFIG.13a shielded electrical cable1302having only one shielding film1308is illustrated. Insulated conductors1306are arranged into two conductor sets1304, each having only one pair of insulated conductors, although conductor sets having other numbers of insulated conductors as discussed herein are also contemplated. Shielded electrical cable1302is shown to include ground conductors1312in various exemplary locations, but any or all of them may be omitted if desired, or additional ground conductors can be included. The ground conductors1312extend in substantially the same direction as insulated conductors1306of conductor sets1304and are positioned between shielding film1308and a carrier film1346which does not function as a shielding film. One ground conductor1312is included in a pinched portion1309of shielding film1308, and three ground conductors1312are included in one of the conductor sets1304. One of these three ground conductors1312is positioned between insulated conductors1306and shielding film1308, and two of the three ground conductors1312are arranged to be generally co-planar with the insulated conductors1306of the conductor set.

In addition to signal wires, drain wires, and ground wires, any of the disclosed cables can also include one or more individual wires, which are typically insulated, for any purpose defined by a user. These additional wires, which may for example be adequate for power transmission or low speed communications (e.g. less than 1 or 0.5 Gbps, or less than 1 or 0.5 GHz, or in some cases less than 1 MHz) but not for high speed communications (e.g. greater than 1 Gpbs or 1 GHz), can be referred to collectively as a sideband. Sideband wires may be used to transmit power signals, reference signals or any other signal of interest. The wires in a sideband are typically not in direct or indirect electrical contact with each other, but in at least some cases they may not be shielded from each other. A sideband can include any number of wires such as 2 or more, or 3 or more, or 5 or more.

Section 2: Bending Characteristics of Shielded Electrical Cable

In the above described cable configurations, the shield is not a wrapped structure but is arranged in two layers around the insulated wires. This shield structure may eliminate the resonance that afflicts helically wrapped constructions, and may also exhibit bend behavior that is less stiff than a wrapped construction and has superior retention of electrical performance after a sharp bend. These properties are enabled by, among other things, the use of a single ply thin shielding film rather than an overlapped and an additional overwrapped film. One advantage of this construction is that the cable can be bent sharply to more effectively route the cable within a constrained space such as within a server, router, or other enclosed computer system.

In reference now toFIG.14, a perspective view shows an application of a shielded, high-speed, electrical ribbon cable1402according to example embodiments. The cable1402may include any combination of the features shown inFIGS.1,2a-f, and4a-c,8a-b,9,10,11a-b, and13, but at least includes features shown inFIG.2b. The ribbon cable1402is used to carry signals within a chassis1404or other object. In many situations, it is desirable to route the cable1402along sides of the chassis1404. For example, such routing may allow cooling air to more freely flow within the chassis1404, ease access for maintenance, allow tighter spacing of components, improve appearance, etc. Accordingly, the cable1402may need to make sharp bends, such as corner bends1406and1408, e.g., to conform to structural features of the chassis1404and/or components contained therein. These bends1406,1408are shown as right angle (90 degree) bends, although the cable may be bent at sharper or broader angles in some applications.

In another application, an approximately 180 degree fold1410may be used to allow the cable1402to make a turn in a substantially planar space. In such a case, the cable1402is folded across a fold line that is at a particular angle relative to a longitudinal edge of the cable. In the illustrated fold1410, the fold line is approximately 45 degrees relative to such an edge, causing the cable1402to turn 90 degrees. Other fold angles may be used to form other turning angles as needed. Generally, the cable1402can configured to a given turn angle in response to proximate regions1412,1414before and after the fold1410being attached flat to a planar surface, e.g., a side of the chassis1404, or formed equivalently relative to a plane without being attached to a surface.

In order for cable1402to be shaped as shown, the inner radii of bends1406,1408and folds1410may need to be relatively small. InFIGS.15and16, a side view shows cable1402bent/folded according to example embodiments. InFIG.15, a 90 degree bend is shown, and inFIG.16, a 180-degree bend is shown. In both cases, an inner bend radius1502may be a limiting factor when determining how flexible the cable is and how such bending may affect performance. The bend radius1502may be measured relative to a centerline1504, which is parallel to and offset from a fold line1506on the cable1402. Both lines1504and1506project orthogonally out of the page in this example, although may project at other angles for fold line angles different than 90 degrees.

For cables of constructions described here with conductors of wire diameter 24 American wire gauge (AWG) or less, the inner radius1502may range from 5 mm to 1 mm (or lower in some cases) without significant impact to electrical performance (e.g., characteristic impedance, skew, attenuation loss, insertion loss, etc.). It is noted, that unless otherwise stated, diameters of insulated conductors that are expressed in terms of AWG are intended to refer to a wire portion of the insulated conductor, and not a diameter of the covering insulation.

Table 1 below illustrates expected maximum variations of some of these characteristics for production cables having wire diameters of 24 AWG or less. These characteristics are measured for differential pairs of conductors. While the cables may be capable of performance better than illustrated in Table 1, these values may represent at least a conservative baseline usable for a system designer for estimating performance in production and/or deployment environments, and may still represent a significant improvement over wrapped twinax cables commonly used in similar environments.

TABLE 1Variance of electrical characteristics for ribbon cable,24 AWG or smaller, bend angle 180 degrees or lessInner bendLocal differentialInsertion lossradiusimpedance variancevariance5 mm1 ohm0.1 dB4 mm2 ohms0.2 dB3 mm3 ohms0.3 dB2 mm4 ohms0.4 dB1 mm5 ohms0.5 dB

Generally, ribbon cables according to the embodiments discussed herein may be more flexible than conventional (e.g., wrapped) twinax cables designed for high speed data transfer. This flexibility may be measured in a number of ways, including defining a minimum bend radius1502for a given conductor/wire diameter, definition of an amount of force needed to deflect the cable, and/or impact on electrical characteristics for a given set of bending parameters. These and other characteristics will be discussed in greater detail below.

In reference now toFIG.17, a block diagram illustrates a test setup1700for measuring force versus deflection of a cable1402according to an example embodiment. In this setup, the cable1402is initially laid flat across roller-type supports1702as indicated by dashed lines. The supports1702prevent downward motion, but otherwise allow free movement of the cable in a side-to-side direction. This may be analogous to the constraint of a simply supported beam, e.g., a beam that has hinged connection at one end and roller connection in other end, although in the case of the cable there need be no side-to-side restraint such as a hinge might provide.

The supports1702in this test setup include 2.0 inch diameter cylinders separated by a constant distance1704of 5.0 inches between the top sides of the cylinders (e.g., 12 o'clock position when viewed from the side as seen inFIG.17). A force1706is applied to the cable1402via a force actuator1710at a point equidistant between supports1704, and deflection1708is measured. The force actuator1710is a 0.375 inch diameter cylinder, driven at a 5.0 inches per minute crosshead speed.

Results of a first test using setup1700for cables according to embodiments are shown in graph1800ofFIG.18. Curve1802represents force-deflection results for a ribbon cable (e.g., similar to configuration102cinFIG.2c) with two solid 30 AWG conductors, solid polyolefin insulation, and two 32 AWG drain wires. The maximum force is approximately 0.025 lbf, and occurs at approximately 1.2 inches of deflection. By way of a rough comparison, curve1804was measured for a wrapped twinax cable having two 30 AWG wires, and two 30 AWG drain wires. This curve has maximum force of around 0.048 lbs at a deflection of 1.2 inches. All things being equal, it would be expected that the twinax cable would be slightly stiffer due to the thicker (30 AWG vs. 32 AWG) drain wires used, however this would not fully explain the significant difference between curves1802and1804. Generally, it is expected that the application of the force of 0.03 lbf on the cable represented by curve1802midpoint between the supporting points causes the deflection in the direction of the force of at least 1 inch. It should be apparent that the cable represented by curve1804would deflect about half that much in response to the same 0.03 lbf force.

InFIG.19, a graph1900shows results of a subsequent test of cables according to example embodiments using the force deflection setup ofFIG.17. For each of four wire gauges (24, 26, 30, and 32 AWG), four cables were tested, each having two solid wire conductors of the respective gauges. The cables included polypropylene insulation on the conductors, shielding films on both sides of the cables, and no drain wires. The force was measured for every 0.2 inches of deflection. Table 2 below summarizes the results at the maximum force points1902,1904,1906,1908, which correspond to the results for the sets of cables with respective wire gauge sizes of 24, 26, 30, and 32 AWG. The fifth and sixth columns of Table 2 correspond to the respective highest and lowest maximum forces of the four cables tested within each gauge group.

TABLE 2Force-deflection results for shielded ribboncables with one conductor pair.ConductorDeflectionAverageStandardHighestLowestwireatmaximumdeviationmaxmaxgaugemaximumforce, Fmaxofforceforce(AWG)force (in.)(lbf)Fmax(lbf)(lbf)(lbf)241.20.2070.0050.2140.202261.20.1110.0030.1140.108301.40.02610.0020.02840.0241321.40.01400.00060.01490.0137

For the data in Table 2, it is possible to perform a linear regression of the form y=mx+b on the logarithms of wire diameters versus the logarithms of maximum deflection force. The natural logarithms (1n) of the forces in the third column of Table 2 are plotted versus natural logarithms of the respective diameters in graph2000ofFIG.20. The diameters of 24, 26, 30, and 32 AWG wires are 0.0201, 0.0159, 0.010, and 0.008, respectively. A least squares linear regression of the curve in graph2000results in the following fit: ln(Fmax)=2.96*ln(dia)+10.0. By solving for Fmax and rounding to two significant figures, the following empirical result is obtained:
Fmax=M*dia3, whereM=22,000 lbf/in3[1]

Equation [1] predicts that a similar cable made using two 28 AWG conductors (diameter=0.0126) would bend at a maximum force of 22,000*0.01263=0.044 lbf. Such a result is reasonable in view of the results for other gauges shown inFIG.19. Further, Equation [1] may be modified to express the individual maximum force (Fmax-single) for each single insulated conductor as follows:
Fmax-single=M*dia3, whereM=11,000 lbf/in3[2]

The individual forces calculated from [2] for each insulated conductor (and drain wires or other non-insulated conductors) may be combined to obtain a collective maximum bending force for a give cable. For example, a combination of two 30 AWG and two 32 AWG wires would be expected to have a maximum bending resistance force of 0.0261+0.014=0.0301 lbf. This is higher than the 0.025 lbf value seen in curve1802ofFIG.18for the tested cable that had a combination of 30 AWG insulated wires and 32 AWG drain wires. However, such a difference may be expected. The drain wires in the tested cable are not insulated, thereby making the tested cable more flexible than the theoretical case. Generally, the results of Equations [1] and [2] are expected to return a high-end limit of bending forces, which would still be more flexible than a conventional wrapped cable. By way of comparison, using Equation [2] for four 30 AWG wires, the maximum force would be 4*11,000*0.01=0.044 lbf, which is below what is seen with the conventional wrapped cable test curve1804inFIG.18. If the drain wires in the wrapped cable were insulated (which was not the case) the curve1804would be expected exhibit an even higher maximum force.

A number of other factors could alter the results predicted by Equations [1] and [2], including the type of wire insulation (polyethylene and foamed insulation would likely be less stiff, and fluoropolymer insulation more stiff), the type of wire (stranded wires would be less stiff), etc. Nonetheless, Equations [1] and [2] may provide a reasonable estimate of maximum bending forces for a given cable assembly, and present ribbon cable constructions exhibiting such properties should be measurably more flexible than equivalent wrapped constructions.

Also of interest in these cables is the minimum size of the radius1506over which the cable1402may be bent/folded (seeFIGS.15and16) without significantly affecting electrical characteristics of the cable (e.g., impedance, crosstalk). These characteristics may be measured locally and/or over the entire cable. In reference now toFIG.21, a graph2100illustrates bending performance of a cable according to an example embodiment. Graph2100represents characteristic impedance measurements of a representative cable measured using a time domain reflectometer (TDR) with a rise time of 35 ps. Area2102represents an envelope of differential impedance readings for a 100-ohm, solid conductor, differential pair, 30 AWG ribbon cable with a construction similar to that of cable construction102cshown inFIG.2c. The impedance of the cable was measured in an initial, unbent state, and again when the cable was bent once at 180-degree angle over a 1.0 mm bend radius. The bent-cable impedance measurement was made again after the cable was bent ten times over the same angle and radius. The time region2104indicated by the vertical dashed lines corresponds to a location generally proximate to this bending.

The envelope2102represents an outline of the extremum of the measured impedance curves under all of the above described tests. This envelope2102includes an impedance variance/discontinuity2106due to the bending. The variance2106is estimated to be approximately 0.5 ohms (peak impedance 95.9 ohms versus nominal 96.4 ohms in an unbent configuration at this location2104). This variance2106was seen after the first bend, but not after the tenth, where no significant deviation from the envelope2102was seen. By way of comparison, a similar test, represented by envelope2108, was performed on a conventional, helically-wrapped, 30 AWG, twinax cable. This measurement2108shows a local impedance variance2110of approximately 1.6 ohms. The variance2110not only is of greater magnitude than variance2106, but is wider in the time scale, thereby affecting a larger region of the cable. This deviation2110was also seen both in the first and tenth bend measurement of the conventional cable.

A similar set of impedance measurements was made for solid 26 AWG and 24 AWG 100 ohm cables of similar construction to that of cable construction102cshown inFIG.2c, except without drain wires112c. The 26 and 24 AWG cables were bent 180 degrees over a 1.0 mm bend radius. The resulting average variance was 0.71 ohms for the 26 AWG cable and 2.4 ohms for the 24 AWG cable. Further, the 24 AWG was bent 180 degrees over a 2.0 mm radius, and the average variance was 1.7 ohms. Therefore a cable of this construction should exhibit a variance of characteristic impedance of no more than 2 ohms (or 2% of 100 ohm nominal impedance) proximate a 2.0 mm bend for conductor wire diameters of 24 AWG or less. Further, a cable of this construction should exhibit a variance of characteristic impedance of no more than 1 ohms (or 2% of 100 ohm nominal impedance) proximate a 1.0 mm bend for conductor wire diameters of 26 AWG or less.

Although the measurements shown in graph2100are differential impedance measurements for cables with nominal 100 ohm characteristic impedance, the deviation/discontinuity2106is expected to scale linearly for other cable impedances and measurement techniques. For example, a 50 ohm single-ended impedance measurement (e.g., measuring just one wire of a differential pair) would be expected to vary no more than 2% (1 ohm) proximate the bending for conductor wire diameters of 24 AWG or less, and 1% (0.5 ohm) for conductor wire diameters of 26 AWG or less. Similar scaling may be seen with different nominal values, e.g., 75 ohm characteristic differential impedance versus 100 ohms.

One possible reason for the improvement in impedance characteristics2102of the representative ribbon cable compared to characteristics2108of the wrapped cable is because of how the outer layers are formed on the wrapped cable. Having a wrapped construction (e.g., individual layers being overlapped, leading to more layers of covering) tends to increase the stiffness of the wrap. This can pinch or “choke” the cable in the local area of a bend more than a ribbon cable with a single layer. Thus, all things being equal, a ribbon cable can be bent more sharply than a conventional cable with less effect on impedance. The effect of these impedance discontinuities is cumulative in the same cable, and so the ribbon cable can contain a greater number bends and still function acceptably relative to a conventional wrapped cable. This improved bend performance may be present whether the conductor set is alone (discrete), or in a ribbon cable with other conductor sets.

Among the benefits of a ribbon cable type construction are reduced labor and cost associated with terminating the cable. One connector of choice for high speed connections is a printed circuit board (PCB) style “paddle-card” that connects to stamped contacts on the one or both sides of the board. To facilitate this type of termination, the ground planes of the ribbon cable may be made easily strippable from the core and the core can be made readily strippable from the wires. Lasers, fixtures, and mechanical cutting can be employed to make the process repeatable and fast.

Connection of the PCB to the cable ground planes can be accomplished by any number of methods such as conductive adhesives, conductive tapes, soldering, welding, ultrasound, mechanical clamping, etc. Likewise, connection of the conductors to the PCB can be accomplished using solder, welding, ultrasound, and other processes and is most efficiently done all at once (gang bonding). In many of these configurations, the PCB has wire connections on both sides, therefore one or two such ribbon cables can be used (one for each side) and can be stacked on top of one another in the cable.

In addition to the time savings that may be seen using ribbon cable to paddle card termination, the magnitude and length of any impedance discontinuities or skew may be reduced at the termination site. One approach used in terminating the cables is to limit the length of conductor at the termination that is not impedance-controlled. This may accomplished by presenting the wire to the connection in roughly the same format as the connector, which may include a linear array of traces with pads on a PCB. The pitch of the cable may be able to be matched with the pitch of the PCB, thereby eliminating unequal and long exposed wire lengths needed when the cables do not have a matching pitch. Also, since the pitch can be made to match the board pitch, a length of uncontrolled wire extending from the cable to the connector can be minimized.

Another benefit the cables described herein may exhibit with regards to termination is that folded portions of such cables can be encapsulated in connectors. This may readily facilitate the formation of inexpensive angled connectors. Various examples of connectors according to example embodiments are shown inFIGS.22-27. InFIG.22, connector assembly2200terminates two layers of cable of previously described shielded ribbon cable configuration1402. Some or all conductors of cables1402are electrically coupled to the paddle card at top and bottom termination areas2204,2206. The cables1402include bends at region2208that facilitate routing the cables1402at a right angle relative to the paddle card. An overmold2210encompasses at least the bend region2208, and may encompass at least part of the paddle card2202(e.g., near termination areas2204,2206).

InFIG.23, a connector assembly2300may include components similar to2200, except that a single shielded ribbon cable1402is used. The assembly2300may include a similar overmold2210, which in this example encompasses bend region2302and termination area2204.FIGS.24and25include connector assemblies2400and2500similar to2300and1400, respectively, except that respective overmolds2402encompass bend regions2404,2502with approximate 45 degree bends.

The connectors2200,2300,2400,2500are all illustrated as terminating connectors, e.g., located at the end of a cable assembly. In some situations, a connector may be desired at a middle portion of the cable assembly, which may include any non-terminal part of one or more cables1402that make up the assembly. Examples of middle portion connectors2600and2700are shown inFIGS.26and27. InFIG.26, a portion of respective cables1402may be broken off from the ribbon, bent at bend area2602and terminated at termination areas2204,2206. An overmold2604encompasses at least the bend area2602, and also include an exit region2606(e.g., strain relief) where unbent portions of ribbon cables1402continue on. Cable2700is similar to cable2600, except that one of the ribbon cables1402is bent at region2702and terminated entirely at area2204. The other of the cables1402is not bent or terminated, but exits region2606.

Those of ordinary skill in the art will appreciate that the features shown inFIGS.22-27are provided for purposes of illustration and not of limitation. It will be appreciated that many variations may exist that combine various disclosed features inFIGS.22-27. For example, the bends in regions2208,2302,2404, and2502may take on any angle and bend radius described herein for cable1402and equivalents. In another example, while the illustrated connectors2200,2300,2400,2500,2600, and2700are all shown using paddle cards2206, other termination structures (e.g., crimped pins/sockets, insulation displacement connections, solder cups, etc.) may be used for similar purposes without departing from the inventive scope of these embodiments. In yet another example, the connectors2200,2300,2400,2500,2600, and2700may use alternate casings/covers instead of overmolds, such as multi-piece, mechanically-attached housings, shrink wrap structures, bonded/adhesive attached coverings, etc.

The foregoing description of the example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not with this detailed description, but rather determined by the claims appended hereto.

The following items are exemplary embodiments of a shielded electrical cable according to aspects of the present invention.Item 1 is a shielded electrical cable, comprising: a plurality of conductor sets extending along a length of the cable and being spaced apart from each other along a width of the cable, each conductor set including one or more insulated conductors; first and second shielding films disposed on opposite sides of the cable, the first and second films including cover portions and pinched portions arranged such that, in transverse cross section, the cover portions of the first and second films in combination substantially surround each conductor set, and the pinched portions of the first and second films in combination form pinched portions of the cable on each side of each conductor set; and a first adhesive layer bonding the first shielding film to the second shielding film in the pinched portions of the cable; wherein: the plurality of conductor sets comprises a first conductor set that comprises neighboring first and second insulated conductors and has corresponding first cover portions of the first and second shielding films and corresponding first pinched portions of the first and second shielding films forming a first pinched cable portion on one side of the first conductor set; a selected one of the insulated conductors has a wire diameter no greater than 24 American wire gauge (AWG); and wherein a transverse bending of the cable at a cable location of no more than 180 degrees over an inner radius of at most 2 mm causes a cable impedance of the selected insulated conductor proximate the cable location to vary by no more than 2 percent from an initial cable impedance measured at the cable location in an unbent configuration.Item 2 is a cable according to item 1, wherein the wire diameter of the selected insulated conductor is no greater than 26 AWG, and wherein a transverse bending of a cable location of no more than 180 degrees over an inner radius of at most 1 mm causes the cable impedance of the selected insulated conductor proximate the cable location to vary by no more than 1 percent from the initial cable impedance.Item 3 is a cable according to item 1, wherein the selected insulated conductor is part of a selected one of the conductor sets that includes at least two insulated conductors each having a wire diameter no greater than 24 AWG and a nominal differential impedance of 100 ohms, and wherein the transverse bending of the cable causes a differential cable impedance of the selected conductor set proximate the cable location to vary by no more than 2 ohms from an initial differential cable impedance measured at the cable location in the unbent configuration.Item 4 is a cable according to item 3, wherein the wire diameter of the at least two insulated conductors is no greater than 26 AWG, and wherein the transverse bending of a cable location of no more than 180 degrees over a second inner radius of at most 1 mm causes the differential cable impedance of the selected conductor set proximate the cable location to vary by no more than 1 ohm from the initial differential impedance.Item 5 is a cable according to items 1 or 2, wherein the selected insulated conductor has a nominal cable impedance of 50 ohms, and wherein the cable impedance of the selected insulated conductor proximate the cable location varies by no more than 1 ohm from the initial cable impedance.Item 6 is a cable according to any of items 1-5, wherein the cable further comprises a bend of at least 45 degrees around a fold line that extends across a width of the cable, wherein the bend has an inner radius of at most 5 mm.Item 7 is a cable according to item 6, wherein the bend is at least 90 degrees and conforms to geometry of a structure that encloses the cable.Item 8 is a cable according to item 6 or 7, wherein the bend is at least 180 degrees and the fold line is at a fold angle relative to a longitudinal edge of the cable such that the cable turns at a turn angle in response to flattening of proximate regions before and after the bend to a plane.Item 9 is a cable according to item 8, wherein the fold angle is 45 degrees, and the turn angle is 90 degrees.Item 10 is a shielded electrical cable, comprising: a plurality of conductor sets extending along a length of the cable and being spaced apart from each other along a width of the cable, each conductor set including one or more insulated conductors; first and second shielding films disposed on opposite sides of the cable, the first and second films including cover portions and pinched portions arranged such that, in transverse cross section, the cover portions of the first and second films in combination substantially surround each conductor set, and the pinched portions of the first and second films in combination form pinched portions of the cable on each side of each conductor set; and a first adhesive layer bonding the first shielding film to the second shielding film in the pinched portions of the cable; wherein: the plurality of conductor sets comprises a first conductor set that comprises neighboring first and second insulated conductors and has corresponding first cover portions of the first and second shielding films and corresponding first pinched portions of the first and second shielding films forming a first pinched cable portion on one side of the first conductor set; a selected one of the insulated conductors has a wire diameter no greater than 24 American wire gauge (AWG); and wherein a transverse bending of the cable at a cable location of no more than 180 degrees over an inner radius of at most 5 mm causes an insertion loss of the selected insulated conductor proximate the cable location to vary by no more than 0.5 dB from an initial insertion loss measured at the cable location in an unbent configuration.Item 11 is a cable according to item 10, wherein the cable further comprises a bend of at least 45 degrees around a fold line that extends across a width of the cable, wherein the bend has an inner radius of at most 5 mm.Item 12 is a cable according to item 11, wherein the bend is at least 90 degrees and conforms to geometry of a structure that encloses the cable.Item 13 is a cable according to item 11, wherein the bend is at least 180 degrees and the fold line is at a fold angle relative to a longitudinal edge of the cable such that the cable turns at a turn angle in response to flattening of proximate regions before and after the bend to a plane.Item 14 is a cable according to item 13, wherein the fold angle is 45 degrees, and the turn angle is 90 degrees.Item 15 is a shielded electrical cable, comprising: a plurality of conductor sets extending along a length of the cable and being spaced apart from each other along a width of the cable, each conductor set including one or more insulated conductors; first and second shielding films disposed on opposite sides of the cable, the first and second films including cover portions and pinched portions arranged such that, in transverse cross section, the cover portions of the first and second films in combination substantially surround each conductor set, and the pinched portions of the first and second films in combination form pinched portions of the cable on each side of each conductor set; and a first adhesive layer bonding the first shielding film to the second shielding film in the pinched portions of the cable; wherein: the plurality of conductor sets comprises a first conductor set that comprises neighboring first and second insulated conductors and has corresponding first cover portions of the first and second shielding films and corresponding first pinched portions of the first and second shielding films forming a first pinched cable portion on one side of the first conductor set; and an application of a force on the cable, the cable being simply supported between two supporting points that are 3.0 inches apart and the force being applied midpoint between the supporting points, results in a deflection in the direction of the force of at least one inch, and wherein the force, measured in pounds-force, does not exceed the sum of individual forces for each of the insulated conductors, the individual forces being equal to 11000 times a wire diameter cubed of the respective insulated conductor, the wire diameter being expressed in inches.Item 16 is a cable according to item 15, wherein the wire diameter is no greater than 24 American wire gauge (AWG).Item 17 is a cable according to item 15 or 16, wherein the maximum force occurs when the deflection is between 1 inch and 1.5 inches.Item 18 is a cable according to any of items 15-17, wherein the cable further comprises a bend of at least 45 degrees around a fold line that extends across a width of the cable, wherein the bend has an inner radius of at most 5 mm.Item 19 is a cable according to item 18, wherein the bend is at least 90 degrees and conforms to geometry of a structure that encloses the cable.Item 20 is a cable according to item 18, wherein the bend is at least 180 degrees and the fold line is at a fold angle relative to a longitudinal edge of the cable such that the cable turns at a turn angle in response to flattening of proximate regions before and after the bend to a plane.Item 21 is a cable according to item 20, wherein the fold angle is 45 degrees, and the turn angle is 90 degrees.Item 22 is a cable assembly, comprising: a shielded electrical cable comprising: a plurality of conductor sets extending along a length of the cable and being spaced apart from each other along a width of the cable, each conductor set including one or more insulated conductors; first and second shielding films disposed on opposite sides of the cable, the first and second films including cover portions and pinched portions arranged such that, in transverse cross section, the cover portions of the first and second films in combination substantially surround each conductor set, and the pinched portions of the first and second films in combination form pinched portions of the cable on each side of each conductor set; a first adhesive layer bonding the first shielding film to the second shielding film in the pinched portions of the cable; and a bend in the cable of at least 45 degrees around a fold line that extends across a width of the cable, wherein the bend has an inner radius of at most 5 mm; wherein: the plurality of conductor sets comprises a first conductor set that comprises neighboring first and second insulated conductors and has corresponding first cover portions of the first and second shielding films and corresponding first pinched portions of the first and second shielding films forming a first pinched cable portion on one side of the first conductor set; and an electrical connector encompassing at least the bend in the cable, wherein at least one of the insulated conductors is electrically coupled to at least one contact of the electrical connector.Item 23 is a cable assembly according to item 22, wherein the electrical connector comprises an overmold formed onto the cable.Item 24 is a cable assembly according to items 22-23, wherein the electrical connector comprises a multi-piece housing.Item 25 is a cable assembly according to any of items 22-24, wherein the connector comprises a paddle card connector.Item 26 is a cable assembly according to any of items 22-24, wherein the bend is at least 90 degrees around the fold line.Item 27 is a cable assembly according to item 26, wherein the inner radius of the bend is at most 1 mm.Item 28 is a cable assembly according to any of items 22-25, wherein the inner radius of the bend is at most 1 mm.Item 29 is a cable assembly according to any of items 22-28, wherein the connector is disposed on an end of the cable.Item 30 is a cable assembly according to any of items 22-28, wherein the connector is disposed on a middle portion of the cable.Item 31 is a cable assembly according to any of items 22-30, wherein the insulated conductors have a wire diameter of no more than 24 American wire gauge (AWG).Item 32 is a cable assembly according to any of items 22-31, wherein the cable further comprises a second bend not encompassed by the electrical connector, the second bend being of at least 45 degrees around a second fold line that extends across a width of the cable, wherein the second bend has an inner radius of at most 5 mm.Item 33 is a cable assembly according to item 32, wherein the second bend is at least 90 degrees and conforms to geometry of a structure that encloses the cable assembly.Item 34 is a cable assembly according to item 32, wherein the second bend is at least 180 degrees and the second fold line is at a fold angle relative to a longitudinal edge of the cable such that the cable turns at a turn angle in response to flattening of proximate regions before and after the second bend to a plane.Item 35 is a cable assembly according to item 34, wherein the second fold angle is degrees, and the turn angle is 90 degrees.Item 36 is the cable assembly according to any of items 22-35, wherein the at least one conductor set is adapted for maximum data transmission rates of at least 1 Gb/s.

Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Those with skill in the mechanical, electro-mechanical, and electrical arts will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the preferred embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.