Patent Publication Number: US-8110744-B2

Title: Flexible shielded cable

Description:
TECHNICAL FIELD 
     The present invention relates generally to electrical conductors, and more particularly to a shielded cable with improved flexibility. 
     BACKGROUND 
     Electronic devices are ubiquitous in society and can be found in everything from computers to cellular telephones. These electronic devices often have many electrical signals that are communicated among various subsystems of the electrical device. The electrical signals are often conveyed through some type of physical media that include cable-type conductors capable of routing the electrical signals. Cable conductors often communicate a plurality of signals within a single cable by including multiple strands of electrical conductors within the single cable. For example, a cable may include multiple strands of copper conductors, one for each signal being conveyed. 
     One problem with conventional conductors is electromagnetic interference (EMI). EMI may be generated by any conductor carrying an electrical signal. In cables containing multiple strands of conductors, the EMI generated in one conductor may interfere with the signal being communicated in other adjacent conductors or electrical devices. Emitting EMI in this manner may cause the electronic device not to function as expected and/or may cause the electronic device to exceed EMI emission levels established by governmental regulations. EMI likewise poses at least two issues for a conductor in an electronic device. First, the conductor may emit EMI, thereby interfering with the operations of other components of the electronic device or other nearby devices. Second, EMI from an external source may corrupt a signal or data carried on the conductor. 
     To reduce EMI interference and/or emission, conductors are often insulated with shielding materials. Unfortunately, shielding the conductors in this manner may introduce additional problems. For example, shielding the conductors may change their electrical impedance and affect their ability to convey electrical signals. Also, shielding the conductors may result in the cabling becoming thick and/or rigid thereby making it difficult to properly route the cable between various sub-portions of the electrical device. Accordingly, there is a need for a shielded cable that provides protection against EMI while minimizing changing the electrical characteristics and/or the flexibility of the cable. 
     SUMMARY 
     One or more embodiments may include a flexible shielded cable and methods for manufacturing the same. In one embodiment, the cable may include a plurality of conductors formed on a common base, a dielectric material disposed about the plurality of conductors, and a shielding material disposed adjacent the dielectric material. At least one of the plurality of conductors may include an unshielded portion not overlaid by the shielding material and at least one of the plurality of conductors may include a shielded portion overlaid by the shielding material. 
     Another embodiment may include a method of making a flexible cable, the method comprising the operations of determining the signal content of a first conductor determining the signal content of a second conductor adjacent to the first conductor, and selectively shielding the first conductor based upon the signal content of at least one of the first and second conductors. 
     In one embodiment, a flexible cable may be implemented in an electronic system. The electronic system comprising a first operating component, a second operating component, the cable coupling at least the first operating component to the second operating component. The cable comprising a plurality of conductors formed on a common base, a dielectric material disposed about the plurality of conductors, and a shielding material disposed adjacent the dielectric material. At least one of the plurality of conductors includes an unshielded portion not overlaid by the shielding material and at least one of the plurality of conductors includes a shielded portion overlaid by the shielding material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary cable. 
         FIG. 2  illustrates an exemplary cross section of a cable. 
         FIG. 3  illustrates another exemplary cross section of a cable. 
         FIG. 4  illustrates an exemplary cable implementing the shielding configurations of  FIGS. 2 and 3 . 
         FIG. 5  illustrates exemplary removable portions of a cable. 
         FIG. 6  illustrates an exemplary process for shielding the conductors. 
         FIG. 7  illustrates an exemplary electronic system. 
     
    
    
     The use of the same reference numerals in different drawings indicates similar or identical items. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following discussion describes various embodiments including a flexible shielded cable. Although one or more of these embodiments may be described in detail, the embodiments disclosed should not be interpreted or otherwise used as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application. For example, the use of the term “cable” is intended to have broad application and include all cable types and electrical connectors in general. Accordingly, the discussion of any embodiment is meant only to be exemplary and is not intended to intimate that the scope of the disclosure, including the claims, is limited to these embodiments. 
     Generally, certain embodiments described herein may take the form of a cable that interconnects two electrical systems, components or subsystems. For example, the cable may be used in a computer to connect an input/output port to a storage device, a motherboard to a power supply, and so forth. Likewise, the cable may be used in a mobile or portable telephone, a stereo receiver, television and so forth. Accordingly, any sample operating embodiments that may be described herein should be regarded as illustrative and not limiting. 
     One sample embodiment may be a cable having an electrically conductive signal path formed thereon or therein. The signal path may be formed by traces of an electrically conductive material deposited on, formed on, or otherwise placed on a nonconductive layer. Further, a nonconductive layer may be placed over these signal traces in whole or in part. That is, the nonconductive layer may not extend across an entire width or along an entire length of the cable depending on the electrical characteristics of the signal trace. Signal traces are referred to herein as “conductors.” 
       FIG. 1  illustrates an exemplary cable  100  that may include multiple conductors  105 A-H. The cable  100  may couple together two electronic components  110  and  115 . In some embodiments, this coupling may be electrical in nature and the conductors  105 A-H may be made from electrically conductive materials such as copper, aluminum, and/or tin to name but a few. 
     During operation, the cable  100  generally establishes a signal path between two electrical components and thus may permit a first electrical component  110  to send and receive signals to and/or from a second electrical component  115  via the conductors  105 A-H. Although  FIG. 1  shows only two electronic components  110  and  115 , it should be appreciated that any number of electronic components may be coupled together using a suitably configured cable  100 . As will be described in more detail below, in some embodiments, the electronic components  110  and  115  may be sub-portions of a common electrical device and located within a common housing. In other embodiments, the electronic components  110  and  115  may be located in physically separate locations. The term “component,” as used herein, is intended to refer both to subsystems of a larger electrical or electronic device (such as the hard drive, input/output connectors, motherboard, and processor of a computer) and stand-alone devices (such as the computer taken as a whole). By contrast, the term “device” generally refers to an overall apparatus or system into which a component may be integrated or which may include one or more components. 
     Depending upon the particular implementation, the electrical signals being conveyed over the conductors  105 A-H may have different EMI parameters. For example, some conductors may convey electrical signals that change with respect to time, such as clock or data signals, while other conductors may include electrical signals that are relatively constant with respect to time, such as power supply signals. Signals that change with respect to time are more likely to emanate EMI (i.e., are more noisy) than those that are constant with respect to time. Also, some of the signals being conveyed over the conductors  105 A-H may be more susceptible to EMI than others. For example, if the electronic components  110  and  115  are two routers within a data communication system, then the signals conveyed between the components  110  and  115  may high speed data signals that leave little room for signal error due to EMI. Because the electrical signals being conveyed over the conductors  105 A-H may have different EMI parameters, in some embodiments, the content of the signal being conveyed via the conductors  105 A-H may be used to determine selective shielding for the conductors  105 A-H. 
     For example, if the conductor  105 A includes a signal that emanates relatively high EMI levels it may be shielded. On the other hand, if the conductor  105 H includes a signal with relatively low EMI levels it may be unshielded. Likewise, if the conductor  105 A conveys a signal that is particularly susceptible to EMI it may be shielded, whereas if the signal in conductor  105 H is relatively insensitive to EMI it may be unshielded. The actual EMI levels sufficient to consider a signal particularly susceptible to EMI or particularly insensitive to EMI may vary between embodiments and may be related to levels imposed by governmental regulation. Notably, shielded cables may be more rigid and less flexible than unshielded cables. Thus, by determining selective shielding patterns for the cable  100 , a more flexible and less rigid cable  100  may be implemented and while providing desired levels of EMI protection. Accordingly, the environment in which the cable is placed, as well as its operating requirements, may also be a factor in determining how many or how few conductors are shielded. For example, a cable that is routed between components  110 ,  115  in such a manner that it must bend at relatively sharp angles in a relatively short distance may be less shielded than a straight-run cable. 
     In practice, the cable  100  may take a variety of physical forms. Some embodiments may implement the cable  100  as a flat ribbon-type cable where the conductors  105 A-H are made of metallic conductive material such as copper, aluminum, and/or tin to name but a few. Other embodiments may implement the cable  100  using printed circuit board (PCB) technology such as microstrip and/or stripline technology. 
       FIG. 2  illustrates a cross section of the cable  100  (taken along the line A-A′ of  FIG. 1 ), showing the cable  100  formed of a combination of both stripline and microstrip technology. “Microstrip” refers to a type of transmission line that may be fabricated using PCB technology wherein the conductors may be separated from a ground plane using a substrate made of dielectric material. Section  205  illustrates an exemplary microstrip implementation where the conductors  105 C-E may be separated from a ground plane  207  by a dielectric layer  208 . By contrast, “stripline” refers to a type of transmission line that may be fabricated using PCB technology with the conductors sandwiched between two parallel ground planes using a substrate made of dielectric material. Sections  210 A-B illustrate an exemplary stripline implementation where the conductors  105 A-B and  105 F-H may be separated from the ground planes  207 ,  215 , and  220  by dielectric layers  225  and  230  respectively. In some embodiments, one or more the dielectric layers  208 ,  225 , and/or  230  may include first and second portions. For example, dielectric  208  may include  208 A and  208 B (not specifically shown in  FIG. 2 ) above and below a dielectric boundary line  226 . In these embodiments, each dielectric may be deposited in layers above and beneath the conductors. 
     As shown, the first and second upper ground planes  215  and  220  may connect to the lower ground plane  207  through one or more vertically connecting vias  221 - 224 . In this manner the vias  221 - 224 , in combination with the upper and lower ground planes  207 ,  215 ,  220 , may effectively define the cable  100  as incorporating different microstrip sections  205  and stripline sections  210 A-B. It should be noted that the division between the microstrip and stripline sections shown is an example only. Alternative embodiments may include more or fewer of each type of section. 
     For both stripline and microstrip transmission lines, the width of the conductor, the thickness of the dielectric, and the relative permittivity of the dielectric may determine the characteristic impedance of the conductor. In some embodiments, such as the sections shown in sections  210 A-B, the stripline conductors  105 A-B and  105 F-H may be equally spaced between the ground planes. However, in other embodiments, the striplines may be spaced asymmetrically with respect to the ground planes of the stripline sections in which or on which they are formed. 
     Depending upon the particular implementation, the dielectric used may vary to suit the particular implementation. For example, in some embodiments, dielectric layers  208 ,  225  and  230  may be built using FR4 type dielectric. However, in other embodiments, substances that have better high frequency performance, such as alumina, may be used to build the dielectric layers  208 ,  225  and  230 . 
     Generally, the stripline sections  210 A-B may provide better electrical isolation (e.g., isolation from EMI and/or prevention of EMI emission) for the conductors  105 A-B and  105 F-H than the microstrip section  205  may provide for that section&#39;s respective conductors  105 C-E. By contrast, the microstrip section  205  may be less rigid and more flexible than the stripline sections  210 A-B. Thus, in some embodiments, the cable  100  may be configured such that the microstrip sections are implemented over conductors that typically carry a signal which is relatively constant with respect to time and the stripline sections are implemented over conductors that carry a signal typically changing relatively frequently with respect to time. Exemplary signals that are relatively constant with respect to time may include power supply signals and/or real time clock signals (i.e., 32 kHz). Exemplary signals that change relatively frequently with respect to time may include high speed serial communication signals. 
     In other embodiments, signals that are more susceptible to EMI (or that emit EMI above a certain threshold) may be shielded by implementing stripline sections over conductors carrying these signals. For example, conductors  105 A-B may convey differential signals, where the conductor  105 A may convey the positive version of the differential signals and the conductor  105 B may convey the negative version of the differential signal. Differential signals often are used to reduce the amount of noise induced in the signal by representing the signal of interest as the difference between the positive and negative versions of the differential signal, the notion being that EMI introduced in the conductor  105 A will likewise be introduced in the conductor  105 B so that the difference between them will cancel out this noise. By implementing stripline sections over the conductors carrying differential signals and microstrip sections over conductors carrying non-differential signals, the signal-to-noise ratio of the differential signals may be increased. As a result of increasing the signal-to-noise ratio of these differential signals, their power level may be decreased. 
       FIG. 3  depicts another exemplary cross section of the cable  100  taken along line B-B′ of  FIG. 1 . The cross section taken along B-B′ may be located in a different portion of the cable  100  than the cross section taken along the line A-A′. As can be appreciated from comparing  FIGS. 2 and 3 , the upper ground plane  220  may be removed along with vias  221  and  222  to form a microstrip section  305  along at least this portion of the cable  100 . In this manner, the cross sections shown in  FIGS. 2 and 3  may be part of the same cable  100  despite having different stripline-microstrip configurations over the length of the cable  100 . Thus, it may be appreciated that certain conductors may be shielded for a portion or the entirety of the cable&#39;s length. By configuring the shielding of the cable  100  such that certain conductors are shielded and others are not, the cable  100  may be fabricated so as to optimize the flexibility and the EMI shielding based upon the specific signals being conveyed on the various conductors. 
       FIG. 4  illustrates a cable  100  implementing the exemplary shielding configurations shown in  FIGS. 2 and 3 . The microstrip portions  205  and  305  from  FIGS. 2 and 3  are indicated using a hashed pattern to represent that the ground planes are not present over these portions of cable  100  in this embodiment. 
     In some embodiments, the particular shielding configurations may be determined after the cable  100  is coupled between the electrical components  110  and  115 . This may provide more options for designers of the electronic components in that a single type of cable may be purchased and custom configured based on the particular needs of the electronic components and/or physical flexibility requirements of the cable. For example, in some embodiments, the shielding may be configured to be selectively removable based upon the content of the signals in the conductors.  FIG. 5  illustrates exemplary removable shield portions  505  and  510  that may be selectively removed from the cable  100  and provide additional flexibility to the cable  100 . Thus, based on the flexibility and EMI needs of the signals conveyed in the cable  100 , one or more of these removable portions may be selectively removed. That is, certain segments of the shield portions (e.g., EMI shield or ground planes) may be peeled away or otherwise removed if unnecessary. The shield portions may be perforated or otherwise weakened at certain areas, lines and/or segments to facilitate their selective removal. 
       FIG. 6  illustrates an exemplary process  600  for forming a cable including one or more selectively shielded conductors. In operation  605 , the plurality of conductors may be formed. For example, one or more metal conductors may be deposited on a common substrate material, such as by using metal deposition techniques. A dielectric material may be disposed about the conductors per operation  610 . Akin to operation  605 , the dielectric material deposition in operation  610  may be disposed using deposition techniques. In some embodiments, the conductors and dielectric of operations  605  and  610  may formed using a series of deposition and etching techniques. The shielding layers and/or ground planes may be selectively disposed about the conductors such that some portions of the conductors have shielding while other portions of the conductors do not. This selective disposing of the shielding may be based upon a variety of cable specific factors such as, the signals being carried in the various conductors of the cable, the spacing of the conductors, and/or physical routing considerations of the cable in the electrical system to name but a few. In some embodiments, when designing the cable, the cable may be tested in an electrical system (such as the computer system described below with regard to  FIG. 7 ) per operation  620 . In this manner, if the cable does not meet desired flexibility requirements, then shielding may be removed as shown in  FIG. 5 . 
     The cable  100  may be implemented in a variety of different electronic devices.  FIG. 7  shows an exemplary computer system  700 , where the cable  100  may be used to couple together two or more of the computer system&#39;s subcomponents. The cable  100  also may be used to couple the computer system  700  to other computer systems. For example, in some embodiments, the computer system  700  may be an implementation of an enterprise level computer such as a blade-type server, and the cable  100  may be used to couple it to one or more additional blade-type servers within an enterprise. In other embodiments, the computer system  700  may be a personal computer and/or a handheld electronic device and the cable  100  may couple together various sub-components of the electronic device. 
     A keyboard  710  and mouse  711  may be coupled to the computer system  700  via a system bus  718 . The keyboard  710  and mouse  711 , in one example, may introduce user input to computer system  700  and communicate that user input to a processor  713 . Other suitable input devices may be used in addition to, or in place of, mouse  711  and keyboard  710 . An input/output unit  719  (I/O) coupled to system bus  718  represents such I/O elements as a printer, audio/video (A/V) I/O, etc. 
     Computer  700  also may include a video memory  714 , a main memory  715  and a mass storage  712 , all coupled to system bus  718  along with keyboard  710 , mouse  711  and processor  713 . Mass storage  712  may include both fixed and removable media, such as magnetic, optical or magnetic optical storage systems and any other available mass storage technology. Bus  718  may contain, for example, address lines for addressing video memory  714  or main memory  715 . System bus  718  also includes, for example, a data bus for transferring data between and among the components, such as processor  713 , main memory  715 , video memory  714  and mass storage  712 . Video memory  714  may be a dual-ported video random access memory. One port of video memory  714 , in one example, is coupled to video amplifier  716 , which is used to drive a monitor  717 . Monitor  717  may be any type of monitor suitable for displaying graphic images, such as a cathode ray tube monitor (CRT), flat panel, or liquid crystal display (LCD) monitor or any other suitable data presentation device. 
     In some embodiments, processor  713  is a SPARC® microprocessor from Sun Microsystems, Inc., or a microprocessor manufactured by Motorola, such as the 680XX0 processor, or a microprocessor manufactured by INTEL, such as the 80X86, PENTIUM or other suitable processor. Any other suitable microprocessor or microcomputer may be utilized, however. 
     Computer  700  also may include a communication interface  720  coupled to bus  718 . Communication interface  720  provides a two-way data communication coupling via a network link. For example, communication interface  720  may be an integrated services digital network (ISDN) card or a modem, a local area network (LAN) card, or a cable modem or wireless interface. In any such implementation, communication interface  720  sends and receives electrical, electromagnetic or optical signals which carry digital data streams representing various types of information. 
     Code received by computer  700  may be executed by processor  713  as it is received, and/or stored in mass storage  712 , or other non-volatile storage for later execution. In this manner, computer  700  may obtain application code in a variety of forms. Application code may be embodied in any form of computer program product such as a medium configured to store or transport computer readable code or data, or in which computer readable code or data may be embedded. Examples of computer program products include CD-ROM discs, ROM cards, floppy disks, magnetic tapes, computer hard drives, servers on a network, and solid state memory devices. 
     Although the present invention has been described with reference to preferred embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, in some embodiments, the cable  100  may couple electronic devices together optically, and the conductors  105 A-H may be made from an optically conductive material, such as glass, plastic, and/or quartz to name but a few.