Abstract:
A system includes a first bus coupler element, a second bus coupler element, and a visual element associated with the second bus coupler element and including a transparent media enabling the second coupler element to be visually aligned with the first coupler element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional application (and claims the benefit of priority under 35 U.S.C. § 120) of U.S. patent application Ser. No. 10/334,663, filed Dec. 30, 2002 now U.S. Pat. No. 6,887,095. The disclosure of the prior application is considered part of (and is incorporated by reference in) the disclosure of this application. 

   BACKGROUND 
   A typical multi-drop signal distribution system includes a device at one end of a bus and multiple devices electrically coupled to the bus by respective couplings requiring direct metal to metal contact. Coupling the devices to the bus typically requires mechanical fixtures such as pins, card guides, latches, and other similar types of fixtures for registration and mating. Registration generally refers to lining up couplers on the device side and the bus side within alignment tolerances, while mating generally refers to providing adequate electronic connection between each device and the bus so that a signal can flow between them. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  shows an example multi-drop signal distribution system including a device electromagnetically coupled to other devices by respective electromagnetic couplers. 
       FIG. 2  shows an example electrical model of the electromagnetic couplers of  FIG. 1 . 
       FIG. 3  shows an example of a device electromagnetically coupled to a circuit board. 
       FIGS. 4 and 5  show examples of coupler alignment with transparent coupler media. 
       FIG. 6  shows an example of coupler alignment using fiducial marks. 
       FIG. 7  shows a partial cross-sectional view of an example electromagnetic coupler formed by the device and circuit board of  FIG. 3 . 
       FIG. 8  illustrates an example flex circuit. 
       FIG. 9  illustrates an exploded perspective view of the example device of  FIG. 3 . 
       FIG. 10  illustrates an example exploded perspective view of the top and one side of a clamp to clamp a flex circuit to a circuit board. 
       FIG. 11  shows an exploded perspective view of the top and another side of the example clamp of  FIG. 10 . 
       FIG. 12  shows an exploded perspective view of the bottom and one side of the example clamp of  FIG. 10 . 
       FIG. 13  shows a perspective view of the example clamp of  FIG. 10 . 
       FIG. 14  shows an example electrical coupling of a flex circuit to a circuit board. 
       FIG. 15  shows an example partial cross-sectional view of a device electromagnetically coupled to a circuit board. 
       FIGS. 16 and 17  show example partial cross-sectional views of a device electromagnetically coupled to a board. 
       FIG. 18  shows an example perspective view of a device positioned for insertion into a socket. 
       FIG. 19  shows a perspective view of the example socket of  FIG. 18  securing the device relative to the circuit board. 
       FIG. 20  shows a perspective view of a top and one side of the example socket of  FIG. 18 . 
       FIG. 21  shows a perspective view of a bottom and one side of the example socket of  FIG. 18 . 
       FIG. 22  shows an elevational view of one side of the example socket of  FIG. 18 . 
       FIG. 23  shows a plan view of a top of the example socket of  FIG. 18 . 
       FIG. 24  shows a plan view of a bottom of the example socket of  FIG. 18 . 
       FIG. 25  shows an exploded perspective view of a top and one side of the example socket of  FIG. 18 . 
       FIG. 26  shows an example of a plurality of devices electromagnetically coupled to a flex circuit of a circuit board. 
   

   DESCRIPTION 
   Coupler registration and mating may be performed using various techniques using non-mechanical fixtures. Performing registration can include using transparent coupler elements to aid registration of couplers to lines or signal traces. The coupler elements may be transparent to human vision, machine vision, or both. Having a transparent coupling element on one or both sides of the coupler (e.g., transparent media on one or both side of the coupler that includes an electrically conductive line) allows the human or machine performing the registration to see through the elements and properly align the coupler using conductive lines of the coupler or fiducial marks such as tick marks, printed symbols, or the like on the coupler elements. Performing coupler mating can include introducing an adhesive material between the coupler elements to hold the coupler together enough to ensure proper mating. 
   Performing registration and mating without solely using alternatives to mechanical fixtures may be beneficial in applications having narrow or serial buses, applications having a small number of bus slots, applications where coupler mating is performed by hand such as with test probes, applications having test points and signals that cannot easily be anticipated, applications having modest bandwidth requirements that are accommodating to poor coupling control, and/or applications having other similar types of configurations. Examples of such applications include signaling to peripheral computer subsystems or optional connectors. Furthermore, performing registration and mating with alternatives to mechanical fixtures may be less expensive than with mechanical fixtures. 
   Before further discussing registration and mating techniques, an example system is described that includes couplers that may use alternative registration and mating techniques. 
     FIG. 1  illustrates a multi-drop signal distribution system  100  in which a device is electromagnetically coupled to other devices by respective electromagnetic couplers. The system  100  includes a device  110  and other devices  120 ,  130 , and  140 . Device  110  is coupled to a bus  112 . Devices  120 ,  130 , and  140  each include a bus  122 ,  132 , and  142 , respectively, and a component  124 ,  134 , and  144 , respectively. Buses  122 ,  132 , and  142  are coupled to components  124 ,  134 , and  144 , respectively. 
   Devices  120 ,  130 , and  140  are each electromagnetically coupled to bus  112  by an electromagnetic coupler  160 ,  170 , and  180 , respectively. Electromagnetic couplers  160 ,  170 , and  180  electromagnetically couple buses  122 ,  132 , and  142 , respectively, to bus  112 , allowing components  124 ,  134 , and  144 , respectively, to communicate with device  110 . Electromagnetically coupling each device  120 ,  130 , and  140  to bus  112  forms a data channel having substantially uniform electrical properties for transferring signals among devices  110 ,  120 ,  130 , and  140  and allows use of relatively high frequency signaling without significantly increasing noise attributable to transmission line effects. 
   Although illustrated with three devices  120 ,  130 , and  140  electromagnetically coupled to bus  112 , bus  112  may have any length and may accommodate any number of devices. For example, bus  112  may be approximately fifty centimeters (cm) in length, allowing up to sixteen devices each to be electromagnetically coupled along approximately one cm of the length of bus  112  with each device spaced on a pitch of approximately 1.5 cm. 
   Each device  120 ,  130 , and  140  may be fixedly or removably coupled to bus  112 . As devices  120 ,  130 , and  140  are electromagnetically coupled to bus  112 , each device  120 ,  130 , and  140  may be added to or removed from bus  112  with minimized effect on the communication bandwidth of bus  112 . 
   Buses  112 ,  122 ,  132 , and  142  may each include any number of lines of any conductive material. Devices  110 ,  120 ,  130 , and  140  may each include any circuitry to perform any function. As one example, device  110  may include a memory controller and devices  120 ,  130 , and  140  may each include a memory module. Devices  110 ,  120 ,  130 , and  140  may communicate over buses  112 ,  122 ,  132 , and  142  using any signaling scheme. Each device  110 ,  120 ,  130 , and  140  may communicate using differential signal pairs to help reduce power and electromagnetic interference (EMI) and to help increase noise immunity. 
   Each component  122 ,  132 , and  142  may include any circuitry. Each component  122 ,  132 , and  142  may serve as an interface for each device  120 ,  130 , and  140  to communicate with device  110 . 
   Although illustrated in multi-drop signal distribution system  100 , each device  120 ,  130 , and  140  in other examples may communicate with device  110  in a point-to-point manner by electromagnetically coupling each device  120 ,  130 , and  140  to a respective bus coupled to device  110 . 
   In the example in  FIG. 1 , electromagnetic coupler  160  is formed by a portion  162  of the length of bus  112 , a portion  164  of the length of bus  122 , and a dielectric  166  between portions  162  and  164 . Electromagnetic coupler  170  is formed by a portion  172  of the length of bus  112 , a portion  174  of the length of bus  132 , and a dielectric  176  between portions  172  and  174 . Electromagnetic coupler  180  is formed by a portion  182  of the length of bus  112 , a portion  184  of the length of bus  142 , and a dielectric  186  between portions  182  and  184 . Each of the dielectrics  166 ,  176 , and  186  may include any dielectric material such as air, various polyimides, various epoxies, various polymeric materials, various plastics, various ceramics, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) such as Teflon® by E. I. du Pont de Nemours and Company of Wilmington, Del., RT/Duroid® by World Properties, Inc. of Lincolnwood, Ill., alumina, and/or other similar types of materials. Each of the electromagnetic couplers  160 ,  170 , and  180  may be formed to have any coupling coefficient, such as, e.g., in the range of approximately 0.15 to approximately 0.45. 
     FIG. 2  illustrates an example of an electrical model  200  for electromagnetic coupler  160  coupling a single conductive line  212  of bus  112  and a single conductive line  222  of bus  122 , for electromagnetic coupler  170  coupling line  212  of bus  112  and a single conductive line  232  of bus  132 , and for electromagnetic coupler  180  coupling line  212  of bus  112  and a single conductive line  242  of bus  142  (see also  FIG. 1 ). 
   Lines  212 ,  222 ,  232 , and  242  are each terminated with a parallel resistor  216 ,  226 ,  236  and  246 , respectively, coupled between the end of its respective line  212 ,  222 ,  232 , and  242  distant from device  110  and a voltage reference, such as ground. Resistors  216 ,  226 ,  236 , and  246  may each have a resistance approximately equal to the characteristic impedance of their respective lines  212 ,  222 ,  232 , and  242 . Lines  212 ,  222 ,  232 , and  242  are each terminated with a matched impedance for transmitting relatively high frequency signals. 
   As device  110  transmits a signal on line  212 , a corresponding signal is induced on lines  22 , 2 ,  232 , and  242  through electromagnetic couplers  160 ,  170 , and  180 , respectively, due to the electromagnetic fields generated by driving the signal on line  212 . Similarly, as component  124 ,  134 , or  144  transmits a signal on line  222 ,  232 , or  242 , respectively, a corresponding signal is induced on line  212 . 
   Lines  222 ,  232 , and  242  each absorb only a fraction of the power of a corresponding signal driven on line  212 . Each line  222 ,  232 , and  242  terminates the received power using resistor  226 ,  236 , and  246 , respectively. Similarly, line  212  absorbs only a fraction of the power of a corresponding signal driven on line  222 ,  232 , and  242 . Line  212  terminates the received power using resistor  216 . Each electromagnetic coupler  160 ,  170 , and  180  may absorb any amount of power depending, for example, on the amount of driven power and the coupling coefficient of the electromagnetic coupler. Each electromagnetic coupler  160 ,  170 , and  180  may absorb less than approximately one percent of the power of a signal driven on any line coupled to the electromagnetic coupler. Because any capacitive load of devices  120 ,  130 , and  140  and their respective lines  222 ,  232 , and  242  are isolated from one another and from line  212 , a generally constant impedance environment may be maintained on line  212  and any disturbance or impact of communication system parasitics on lines  212 ,  222 ,  232 , and  242  is minimized or avoided. 
   Bus  112  may be mounted on or integrated in a circuit board, and device  110  may be mounted to or otherwise coupled to the circuit board such that device  110  is electrically coupled to bus  112 . Each electromagnetic coupler  160 ,  170 , and  180  may be formed by positioning bus portions  164 ,  174 , and  184 , respectively, relative to bus portions  162 ,  172 , and  182  with dielectric  166 ,  176 , and  186  between the electromagnetically coupled portions. 
   Each device  120 ,  130 , and  140  may be implemented in any manner, such as that of device  350  of  FIG. 3  for example, to form electromagnetic couplers  160 ,  170 , and  180 , respectively. As illustrated in  FIG. 3 , device  350  is electromagnetically coupled to a circuit board  300  and includes a circuit board  352 , a flex circuit  354 , and a clamp  356  to secure flex circuit  354  to circuit board  352 . Circuit board  300  and circuit board  352  may each include any circuitry, such as a motherboard for circuit board  300  and a daughter board for circuit board  352 . 
   Circuit board  300  includes conductive lines for a bus, such as conductive lines  311  and  312  for bus  112 . (Conductive lines  311  and  312  are two illustrative conductive lines included on circuit board  300 .) Flex circuit  354  includes conductive lines, such as conductive lines  361  and  362 , for example, which form at least a portion of bus  122 , for example. 
   Conductive lines of circuit board  300  each include a respective conductive area to be positioned relative to a corresponding conductive area of a respective conductive line of flex circuit  354  with dielectric  166 , for example, between such corresponding conductive areas to form an electromagnetic coupler such as electromagnetic coupler  160 , for example. Corresponding conductive areas, such as those for conductive lines  311  and  361  for example, may be positioned by positioning a surface  355  of flex circuit  354  relative to a surface  301  of circuit board  300 . For example, conductive lines of flex circuit  354  may each positioned relative to a respective corresponding conductive line of circuit board  300  with dielectric  166  between each pair of corresponding conductive lines along at least a portion of the length of each conductive line in each pair to form electromagnetic coupler  160 . Electromagnetic coupler  160  may be formed with approximately one centimeter (cm) in length of each conductive line in each pair. 
   Dielectric  166  between each conductive area may include any dielectric material of any thickness. Dielectric  166  for one example may include one or more layers each including a dielectric material. Circuit board. 300  and/or flex circuit  354  may each include at least a portion of dielectric  166 . Circuit board  300  or flex circuit  354  may include dielectric  166 . Circuit board  300  and flex circuit  354  for one example may each include a portion of dielectric  166 . 
     FIG. 4  illustrates an example of a coupler  400  included within a transparent media  402  that may help conductive areas to be visually positioned to form an electromagnetic coupler. A coupler trace  404  and a conductive line  406  (e.g., a test trace or conductive line on a circuit board or other similar media) are both visible through transparent media  402 . This visibility allows the user (human or mechanical) to properly align coupler  400 . Transparent media  402  may include fiducial marks at the end of the coupler that can be visually aligned with the conductive line  406  to help aid visual registration. 
   The transparency of transparent media  402  may be aided by making a voltage reference plane of a coupler perforated instead of solid. Voltage reference plane perforations may also be beneficial for electrical reasons such as impedance matching with particular choices of coupler to voltage reference plane dielectric thickness. 
   As an example of a device using couplers similar to coupler  400 , flex circuit  354  of  FIG. 3  may be a transparent media similar to transparent media  402 . The conductive lines of flex circuit  354  such as conductive lines  361  and  362  would thus be visible through the transparent flex circuit and could be visually aligned with conductive lines of circuit board  300  such as conductive lines  311  and  312  to form electromagnetic couplers such as electromagnetic couplers  160 ,  170 , and  180 . 
   In another example, electromagnetic couplers  160 ,  170 , and  180  may be implemented as differential coupler  408  as illustrated in  FIG. 5 . A differential coupler  408  included within a transparent media  408  includes visible differential coupler traces  412   a  and  412   b  and visible differential conductive lines  414   a  and  414   b . Differential coupler  408  may be visually registered similar to the registration described for coupler  400  of  FIG. 4 . 
   In another example illustrated in  FIG. 6 , electromagnetic couplers  160 ,  170 , and  180  may each be implemented as a coupler  416  included in a non-transparent media  418 . Coupler  416  may be visually aligned using media-side fiducial marks  420   a - b  and board-side fiducial marks  422   a - b . Even though coupler trace  424  and conductive line  426  are obscured from view when non-transparent media  416  is positioned over the media including conductive line  426 , fiducial marks  420   a - b  and  422   a - b  may be aligned by a user (human or mechanical) to properly align coupler trace  424  and conductive line  426  to form a coupler. 
   Only two sets of media-side and board-side fiducial marks are shown in  FIG. 6 , but more fiducial marks may be used in any location to aid alignment. Furthermore, the fiducial marks are all shown as triangles, but the fiducial marks may be any combination of shapes (e.g., triangles, diamonds, rectangles, etc.) and/or lines. 
     FIG. 7  illustrates an example of a partial cross-sectional view of circuit board  300  including a conductive layer including conductive lines  311 ,  312 ,  313 ,  314 ,  315 , and  316  for bus  112 , for example, and of flex circuit  354  including a conductive layer including conductive lines  361 ,  362 ,  363 ,  364 ,  365 , and  366  for bus  122 , for example. Each conductive line  361 - 366  is positioned relative to each conductive line  311 - 316  with dielectric  166  between each pair of corresponding conductive lines  311  and  361 ,  312  and  362 ,  313  and  363 ,  314  and  364 ,  315  and  365 , and  316  and  366  to form electromagnetic coupler  160 . 
   As illustrated in an example in  FIG. 7 , circuit board  300  includes a dielectric layer  320 , a voltage reference layer  330 , and a dielectric layer  340 . Dielectric layer  320  is between voltage reference layer  330  and the conductive layer including conductive lines  311 - 316 . Voltage reference layer  330  can help reduce electromagnetic interference (EMI) that may be generated by signals propagating through conductive lines  311 - 316 . Dielectric layer  320  electrically insulates conductive lines  311 - 316  from voltage reference layer  330 . The conductive layer including conductive lines  311 - 316  is between at least a portion of dielectric layer  320  and at least a portion of dielectric layer  340 . Dielectric layer  340  lies adjacent to the conductive layer including conductive lines  311 - 316  opposite dielectric layer  320 . Dielectric layer  340  forms at least a portion of dielectric  166  for electromagnetic coupler  160 . 
   Dielectric layer  320  may include any dielectric or electrically insulating material and may include one or more layers of a dielectric material. Dielectric layer  320  may include a material that is also relatively rigid, such as a fiberglass epoxy material for example. One material is known as Flame Retardant  4  (FR 4 ). Dielectric layer  320  may have any thickness. If dielectric layer  320  includes FR 4 , dielectric layer  320  may have a thickness of approximately five mils, for example. 
   Each conductive line  311 - 316  is positioned on a surface of dielectric layer  320 . Conductive lines  311 - 316  may each include any conductive material, such as copper (Cu), a conductive plastic, or a printed conductive ink for example. Conductive lines  311 - 316  may each include one or more layers of a conductive material. Each conductive line  311 - 316  may have any thickness. If each conductive line  311 - 316  includes copper (Cu), each conductive line  311 - 316  may have a thickness of approximately two mils, for example. 
   Voltage reference layer  330  is positioned on a surface of dielectric layer  320  opposite conductive lines  311 - 316 . Voltage reference layer  330  may include any conductive material, such as copper (Cu) or a conductive plastic for example, and may include one or more layers of a conductive material. Voltage reference layer  330  may have any thickness. If voltage reference layer  330  includes copper (Cu), voltage reference layer  330  may have a thickness of approximately 1.4 mils, for example. 
   Dielectric layer  340  lies adjacent to the conductive layer including conductive lines  311 - 316  and portions of the surface of dielectric layer  320  exposed by conductive lines  311 - 316 . Dielectric layer  340  may include any dielectric material, such as an epoxy dielectric soldermask for example, and may include one or more layers of a dielectric material. Dielectric layer  340  may have any thickness. If dielectric layer  340  includes an epoxy dielectric soldermask, dielectric layer  340  may have a thickness of approximately one mil, for example, to approximately 1.5 mils, for example. Although illustrated as having a relatively flat surface  301 , surface  301  may be contoured due to conductive lines  311 - 316 . 
   Circuit board  300  may be manufactured in any manner using any techniques. 
   Flex circuit  354 , as illustrated in the example in  FIG. 7 , includes a dielectric layer  370 , a voltage reference layer  380 , and a dielectric layer  390 . Dielectric layer  370  is between voltage reference layer  380  and the conductive layer including conductive lines  361 - 366 . Voltage reference layer  380  helps reduce electromagnetic interference (EMI) that may be generated by signals propagating through conductive lines  361 - 366 . Dielectric layer  370  electrically insulates conductive lines  361 - 366  from voltage reference layer  380 . The conductive layer including conductive lines  361 - 366  is between at least a portion of dielectric layer  370  and at least a portion of dielectric layer  390 . Dielectric layer  390  lies adjacent to the conductive layer including conductive lines  361 - 366  opposite dielectric layer  370 . Dielectric layer  390  forms at least a portion of dielectric  166  for electromagnetic coupler  160 . 
   Dielectric layer  370  may include any dielectric or electrically insulating material and may include one or more layers of a dielectric material. Dielectric layer  370  may include a material that is also relatively flexible and/or resilient, such as an epoxy dielectric material or a polyimide for example. One polyimide is known as Kapton® by E.I. du Pont de Nemours and Company of Wilmington, Del. Another material may be polyethylene terephthalate (PET). Dielectric layer  370  may have any thickness. If dielectric layer  370  includes Kapton®, dielectric layer  370  may have a thickness of approximately four mils, for example. 
   Each conductive line  361 - 366  is positioned on a surface of dielectric layer  370 . Conductive lines  361 - 366  may each include any conductive material, such as copper (Cu), a conductive plastic, or a printed conductive ink for example. Conductive lines  361 - 366  may each include one or more layers of a conductive material. Each conductive line  361 - 366  may have any thickness. If each conductive line  361 - 366  includes copper (Cu), each conductive line  361 - 366  may have a thickness of approximately 0.65 mils, for example. 
   Voltage reference layer  380  is positioned on a surface of dielectric layer  370  opposite conductive lines  361 - 366 . Voltage reference layer  380  may include any conductive material, such as copper (Cu) or a conductive plastic for example, and may include one or more layers of a conductive material. Voltage reference layer  380  may have any thickness. If voltage reference layer  380  includes copper (Cu), voltage reference layer  380  may have a thickness of approximately 0.65 mils, for example. 
   Dielectric layer  390  lies adjacent to the conductive layer including conductive lines  361 - 366  and portions of the surface of dielectric layer  370  exposed by conductive lines  361 - 366 . Dielectric layer  390  may include any dielectric material. Dielectric layer  390  may include a material that is also relatively flexible and/or resilient, such as an epoxy dielectric material or a polyimide for example. One polyimide is Kapton®. Another material may be a polymeric material or polyethylene terephthalate (PET). Dielectric layer  390  may have any thickness. Although illustrated as having a relatively flat surface  355 , surface  355  may be contoured due to conductive lines  361 - 366 . 
   Dielectric layer  390 , as illustrated in the example in  FIG. 7 , includes a layer  391  including a acrylic or epoxy adhesive dielectric material and another layer  392  including a polyimide, such as Kapton® for example. Layer  391  lies adjacent to the conductive layer including conductive lines  361 - 366  and portions of the surface of dielectric layer  370  exposed by conductive lines  361 - 366 . Layer  392  lies adjacent to layer  391 . Layers  391  and  392  may each have any thickness. Layer  391  may have a thickness of approximately 0.5 mils, for example. If layer  392  includes Kapton®, layer  392  may have a thickness of approximately 0.5 mils, for example. 
   Flex circuit  354  may be manufactured in any manner using any techniques. 
   Positioning flex circuit  354  relative to circuit board  300  as illustrated in  FIG. 7  forms electromagnetic coupler  160  with dielectric  166  between conductive lines  311 - 316  and  361 - 366 , respectively, formed by the combination of dielectric layer  340  of circuit board  300 , any ambient material such as air between flex circuit  354  and circuit board  300 , and dielectric layer  390  of flex circuit  354 . 
   Circuit board  300  may be manufactured without dielectric layer  340 . Dielectric  166  may then be formed by the combination of dielectric layer  390  and any ambient material between flex circuit  354  and circuit board  300 . Flex circuit  354  in another example may be manufactured without dielectric layer  390 . Dielectric  166  may then be formed by the combination of dielectric layer  340  and any ambient material between flex circuit  354  and circuit board  300 . Where circuit board  300  does not include dielectric layer  340  and where flex circuit  354  does not include dielectric layer  390 , dielectric  166  may be formed by ambient material between flex circuit  354  and circuit board  300 . 
   For example, a compliant liquid or gel dielectric material, such as a glycerine for example, may be used between flex circuit  354  and circuit board  300  to form at least a portion of dielectric  166 . Such material may help fill any ambient space between flex circuit  354  and circuit board  300  and help provide dielectric consistency. If flex circuit  354  is to be fixed to circuit board  300 , a adhesive dielectric material, such as an acrylic or epoxy for example, may be used to couple flex circuit  354  to circuit board  300  and form at least a portion of dielectric  166 . 
   Circuit board  300  and flex circuit  354  may have conductive lines with any shape, dimensions, and spacings. 
   Conductive lines for flex circuit  354  in one example are relatively straight. For another example, as illustrated in  FIG. 8 , flex circuit  354  has lattice shaped conductive lines, such as conductive lines  361  and  362  for example, that are each formed from multiple connected segments generally lying in a plane with adjacent segments arranged with an alternating angular displacement about the longitudinal axis of the conductive line. Such lines for one example each has a width of approximately 0.01 inches and segments approximately 0.0492 inches in length along the longitudinal axis of the conductive line and angled at an approximately thirty-five degree angle relative to the longitudinal axis of the conductive line. 
   Conductive lines for circuit board  300  for one example are relatively straight. For another example, circuit board  300  has lattice shaped conductive lines that are each formed from multiple connected segments generally lying in a plane with adjacent segments arranged with an alternating angular displacement about the longitudinal axis of the conductive line. For one example where flex circuit  354  has lattice shaped conductive lines, conductive line segments for circuit board  300  are arranged with an alternating angular displacement in an opposite sense from corresponding conductive line segments of flex circuit  354 . Such lines for one example each has a width of approximately 0.008 inches and segments approximately 0.0492 inches in length along the longitudinal axis of the conductive line and angled at an approximately thirty-five degree angle relative to the longitudinal axis of the conductive line. 
   Using lattice shaped conductive lines for flex circuit  354  and circuit board  300  helps allow conductive lines of flex circuit  354  to be positioned relative to corresponding conductive lines of circuit board  300  with a relatively uniform coupling area at overlap locations and helps minimize any impact on the desired coupling coefficient for electromagnetic coupler  160  despite some misalignment. If conductive lines for flex circuit  354  and circuit board  300  are relatively straight, corresponding conductive lines in each pair to be electromagnetically coupled may each have a different width to help compensate for any misalignment. 
   Although described as including flex circuit  354  to form electromagnetic couplers  160 ,  170 , and  180  with circuit board  300 , each device  120 ,  130 , and  140  may include any carrier to help support bus  122 ,  132 , and  142 , respectively, for positioning relative to any carrier supporting bus  112 . As examples, each device  120 ,  130 , and  140  may support bus  122 ,  132 , and  142  with a relatively rigid circuit board to position relative to a relatively rigid circuit board supporting bus  112  or to a flex circuit supporting bus  112 . Each device  120 ,  130 , and  140  may also support bus  122 ,  132 , and  142  with a flex circuit to position relative to a flex circuit supporting bus  112 . 
   Flex circuit  354  for one example is conductively coupled to circuit board  352  such that one end of each conductive line for flex circuit  354  is conductively coupled to communication circuitry on circuit board  352  to transmit and receive signals and such that the other end of each such conductive line is terminated on circuit board  352 . If flex circuit  354  includes voltage reference layer  380 , voltage reference layer  380  may be conductively coupled to a reference voltage on circuit board  352 . Flex circuit  354  may be mechanically and conductively coupled to circuit board  352  in any manner. 
   As illustrated in the example in  FIGS. 3 and 9 , flex circuit  354  is mechanically secured to circuit board  352  using clamp  356 . Clamp  356  engages a bottom edge of circuit board  352  and mechanically secures opposite ends  510  and  520  of flex circuit  354  to opposite surfaces of circuit board  352 . In securing flex circuit  354  to circuit board  352 , clamp  356  helps support flex circuit  354  for stress relief for conductive coupling to circuit board  352  and helps align circuit board  352  relative to circuit board  300  in electromagnetically coupling device  350  to circuit board  300 . 
   Clamp  356 , as illustrated in  FIGS. 9 ,  10 ,  11 ,  12 , and  13 , includes two elongated pieces  600  and  650 . Piece  600  defines a wall  610  along one side of piece  600 , a raised edge  620  along the other side of piece  600 , and a bottom wall  630 . Wall  610 , raised edge  620 , and bottom wall  630  define a channel  640 . The bottom of piece  650  mates with the top of raised edge  620 , as illustrated in  FIG. 13 , to form a body for clamp  356 . When mated with piece  600 , piece  650  forms a wall opposite wall  610  from channel  640 . A bottom edge of circuit board  352  may be inserted into channel  640 , as illustrated in  FIG. 9 , such that wall  610  and the wall defined by piece  650  face opposite surfaces of circuit board  352 . 
   Piece  600  defines along wall  610  slots  611 ,  612 , and  613  each extending through wall  610  near the bottom of wall  610  and openings  614 ,  615 ,  616 ,  617 , and  618  each extending through wall  610  near the top of wall  610 . Piece  650  similarly defines slots  661 ,  662 , and  663  and openings  664 ,  665 ,  666 ,  667 , and  668 . 
   Pieces  600  and  650  may each include any material, such as an injection molded plastic for example, and may have any dimensions. For one example, piece  600  is approximately 2.844 inches in length, approximately 0.228 inches in width, and approximately 0.254 inches in height. Piece  650  for one example is approximately 2.844 inches in length, approximately 0.112 inches in width, and approximately 0.228 inches in height. Mated pieces  600  and  650  may optionally be bound together using, for example, an epoxy adhesive. Clamp  356  for another example may have one integral body shaped as mated pieces  600  and  650 . 
   As illustrated in  FIG. 8 , flex circuit  354  in one example defines tabs  511 ,  512 , and  513  and openings  515 ,  516 , and  517  along one end  510  of flex circuit  354 . Flex circuit  354  defines tabs  521 ,  522 , and  523  and openings  525 ,  526 , and  527  along an opposite end  520  of flex circuit  354 . Flex circuit  354  may have any dimensions. In one example, flex circuit  354  is approximately 2.586 inches in length and approximately 1.828 in width. 
   To secure flex circuit  354  to circuit board  352 , flex circuit  354  is rolled such that ends  510  and  520  are folded in toward the center of flex circuit  354  and away from the resulting curled surface of flex circuit  354 , as illustrated in  FIG. 9 , such that dielectric layer  390  of flex circuit  354  defines an outer curled surface  355 . Tabs  511 ,  512 , and  513  are inserted through slots  611 ,  612 , and  613 , respectively, such that each tab  511 ,  512 , and  513  extends from the exterior of wall  610  through slot  611 ,  612 , and  613 , respectively, to lie against the interior face of wall  610  and such that each opening  515 ,  516 , and  517  of flex circuit  354  aligns with each opening  615 ,  616 , and  617  of wall  610 . Tabs  521 ,  522 , and  523  are similarly inserted through slots  661 ,  662 , and  663 , respectively, such that each tab  521 ,  522 , and  523  extends from the exterior of the wall defined by piece  650  through slot  661 ,  662 , and  663 , respectively, to lie against the interior face of the wall defined by piece  650  and such that each opening  525 ,  526 , and  527  of flex circuit  354  aligns with each opening  665 ,  666 , and  667  of the wall defined by piece.  650 . 
   Circuit board  352  defines openings  534 ,  535 ,  536 ,  537 , and  538  that align with openings  614 - 618 , respectively, and with openings  664 - 668 , respectively, when circuit board  352  is inserted into clamp  536 . Openings  534 - 538  each extend through circuit board  352  between opposite surfaces of circuit board  352 . 
   When circuit board  352  and flex circuit  354  are inserted into clamp  356 , clamp  356  and flex circuit  354  may be secured to circuit board  352  by inserting screws or rivets  544 ,  545 ,  546 ,  547 , and  548  through the aligned openings of clamp  356 , flex circuit  354 , and circuit board  352 . For another example, piece  600  and/or piece  650  may be molded with screws or rivets to insert through aligned openings in flex circuit  354 , circuit board  352 , and opposite piece  600  or  650 . 
   Although described as using three slots to receive three tabs at each end of flex circuit  354  and as using five openings to secure flex circuit  354  to circuit board  352  with five screws or rivets, any number of slots, tabs, and openings may be used. 
   As illustrated in  FIG. 9 , flex circuit  354  for one example includes exposed leads, such as leads  551  and  552  for example, for each conductive line at each end  510  and  520  of flex circuit  354 . Circuit board  352  for one example, as illustrated in  FIG. 14 , defines contact areas, such as contact areas  561  and  562  for example, that align with such leads when flex circuit  354  is secured to circuit board  352 . Such contact areas on one surface of circuit board  352  are conductively coupled to electronic circuitry on circuit board  352 , and such contact areas on the other surface of circuit board  352  are conductively coupled to terminate a respective conductive line of flex circuit  354  on circuit board  352 . Leads of flex circuit  354  may each be conductively coupled to a respective contact area in any manner, such as using a hot bar soldering technique or using an epoxy adhesive for example. 
   As ends  510  and  520  of rolled flex circuit  354  may tend to pull away from circuit board  352  due to the resiliency of flex circuit  354 , clamp  356  helps secure at least a portion of flex circuit  354  against circuit board  352 . In this manner, any tendency of flex circuit  354  to move the secured portion away from circuit board  352  and pull leads of flex circuit  354  from contact areas of circuit board  352  is minimized or avoided. 
   As illustrated in the examples in  FIGS. 10-13 , clamp  356  defines an optional alignment pin or post  633  extending outward from bottom wall  630 . As flex circuit  354  is positioned against circuit board  300 , as illustrated in  FIG. 15 , alignment post  633  may be inserted through an opening  571  in flex circuit  354 , as illustrated in  FIG. 8 , and into an opening  575  in circuit board  300  to help align conductive lines of flex circuit  354  relative to conductive lines of circuit board  300 . In another example, clamp  356  may define two or more alignment pins or posts to engage corresponding openings in flex circuit  354  and circuit board  300 . 
   Flex circuit  354  for other examples may be secured to circuit board  352  in other manners. As examples, flex circuit  352  may be epoxied, screwed, riveted, or stapled directly to circuit board  352 . Leads of flex circuit  354  may then be conductively coupled to a respective contact area of circuit board  352 , for example, with an adhesive material such as solder, adhesive tape, epoxy, or similar adhesive materials. In other example, flex circuit  354  may be integrally formed with circuit board  352  or a chip on flex arrangement having a relatively rigid stiffener board may be used. 
     FIG. 16  illustrates an example mating scheme using an adhesive material  430  that can assist proper mating between flex circuit  354  and circuit board  300 . As flex circuit  354  is positioned against circuit board  300 , adhesive material  430  may aid connection between the conductive lines on flex circuit  354  and circuit board  300 . Adhesive material  430  may also serve as a dielectric separator or be an add on. Adhesive material  430  is shown in this example on the flex circuit side, but adhesive material may be on either side of the coupler or on both sides. 
   Adhesive material  430  may be disposable and be replaced after each use, which may be beneficial in temporary coupler connection situations such as in test trace scenarios. For more permanent attachments, after adhesive material  430  is used to fix coupler position, an epoxy blanket (or similar mechanism) over the coupler and at least part of the circuit board  300  may be used to fix and mechanically bolster the coupler in place. 
   In another example illustrated in  FIG. 17 , a compliant material  432  and a lever  434  may assist proper mating between flex circuit  354  and circuit board  300 . Examples of compliant materials include air bladders, diaphragms, and similar materials. As flex circuit  354  is positioned against circuit board  300 , compliant material  432  and lever  434  may aid connection between the conductive lines on flex circuit  354  and circuit board  300 . When circuit board  352  is placed against flex circuit  354 , raising lever  434  expands the volume of compliant material  432  and the surrounding air pressure can exert downward force on the coupler to assist in proper mating. 
   In another example, flex circuit  354  may be attached onto a rigid card and that rigid card may be used as part of a C-clamp. The downward force could then be exerted by squeezing circuit board  300  between jaws of the clamp, compressing flex circuit  354  against the proper lines. 
   Circuit board  352  and flex circuit  354  may be positioned relative to circuit board  300  and coupled to circuit board  300  in any manner using any mechanism to form an electromagnetic coupler. As illustrated in the examples in  FIGS. 18 and 19 , a socket  700  may be used to mount circuit board  352  and flex circuit  354  relative to circuit board  300  to form an electromagnetic coupler. While circuit board  352  and flex circuit  354  are mounted by socket  700 , the resilience of flex circuit  354  helps hold flex circuit  354  against circuit board  300  and therefore helps maintain a relatively stable coupling coefficient for the resulting electromagnetic coupler. In mounting circuit board  352  and flex circuit  354  to circuit board  300 , socket  700  helps align circuit board  352  relative to circuit board  300  and helps align flex circuit  354  relative to circuit board  300 . Socket  700  may also electrically couples circuit board  352  to circuit board  300 . 
   As illustrated in  FIGS. 18 ,  19 ,  20 ,  21 ,  22 ,  23 ,  24 , and  25 , socket  700  includes a base  710  near the bottom of sicket  700  and arms  730  and  740  extending from base  710  toward the top of socket  700  at opposite ends of base  710 . 
   Base  710  includes a body  711  defining walls  712  and  713  on opposite sides of base  710  and adjacent to a coupler region  715  between walls  712  and  713 . Base  710  also includes connectors  750  and  760  supported on opposite ends of coupler region  715  at opposite ends of base  710 . Connectors  750  and  760  mount circuit board  352  to base  710  such that flex circuit  354  is inserted into coupler region  715 . Connectors  750  and  760  also mount base  710  to circuit board  300  such that flex circuit  354  is mounted relative to circuit board  300  to form an electromagnetic coupler. Connectors  750  and  760  for one example also electrically couple circuit board  352  to circuit board  300 . 
   As illustrated in the examples in  FIGS. 18 ,  20 ,  23 , and  25 , connectors  750  and  760  each include an edge connector facing the top of socket  700 . Circuit board  352  may be removably mounted to base  710  by inserting a bottom edge of circuit board  352  into the edge connector of connectors  750  and  760 . 
   Circuit board  352  for one example has contact areas, such as contact areas  581 ,  582 ,  583 , and  584  of  FIG. 18  for example, conductively coupled to circuitry on circuit board  352  and positioned along the bottom edge of circuit board  352  on opposite sides of clamp  356  such that each such contact area is electrically coupled to connector  750  or connector  760  when circuit board  352  is mounted to connectors  750  and  760 . 
   Connectors  750  and  760  for one example, as illustrated in  FIGS. 21 ,  22 ,  24 , and  25 , each include contact pins, such as contact pins  751 ,  752 ,  761 , and  762  of  FIG. 21  for example, extending outward from the bottom of base  710 . Base  710 , and therefore socket  700 , may be removably mounted to circuit board  300  by inserting the contact pins of connectors  750  and  760  into respective female connectors positioned on circuit board  300  such that conductive lines of flex circuit  354 , when mounted in coupler region  715 , are positioned relative to conductive lines on circuit board  300  to form an electromagnetic coupler. 
   Socket  700 , as illustrated in the examples in  FIGS. 20 ,  21 ,  22 ,  24 , and  25 , also includes optional locating and hold-down pins  781  and  782  each extending from the bottom of body  711  for insertion into corresponding openings of circuit board  300  to help align base  710  relative to circuit board  300  and to help secure base  710  to circuit board  300 . 
   Circuit board  300  for one example includes circuitry conductively coupled to such female connectors. As connectors  750  and  760  for one example electrically couple the bottom edge contact areas of circuit board  352  to the contact pins of connectors  750  and  760 , connectors  750  and  760  electrically couple circuit board  352  to circuit board  300  when base  710  is mounted to circuit board  300 . In this manner, power signals, voltage reference signals, any other direct current (DC) signals, and/or any other signals may be supplied between circuit board  352  and circuit board  300 . 
   Although described as including connectors  750  and  760  as having edge connectors and contact pins, other connectors may be used for mechanically mounting circuit board  352  to base  710  and base  710  to circuit board  300  and for electrically coupling circuit board  352  to circuit board  300 . As one example, banana jack connectors may be used instead of edge connectors. In another example, high current mated pair connectors or impedance controlled mated pair connectors may be used. 
   Socket  700  in another example may not provide for any electrical coupling of circuit board  352  to circuit board  300 . Connectors  750  and  760  may then include any mechanical connectors without concern for electrical coupling through connectors  750  and  760 . In addition to or in lieu of any electrical coupling of circuit board  352  to circuit board  300  provided through connectors  750  and  760 , circuit board  352  may be electrically coupled to circuit board  300  through flex circuit  354 , for example, by coupling exposed conductive contact areas on flex circuit  354  and circuit board  300  in securing flex circuit  354  against circuit board  300 . 
   Arms  730  and  740  secure circuit board  352  and flex circuit  354  relative to circuit board  300 . As illustrated in  FIGS. 20-25 , arms  730  and  740  each include an upright guide  732  and  742 , respectively, and a latch  734  and  744 , respectively. 
   Upright guides  732  and  742  each engage circuit board  352  to help support circuit board  352  relative to circuit board  300  and to help minimize any angular displacement of circuit board  352  relative to circuit board  300 . Upright guides  732  and  742  may extend from base  710  toward the top of socket  700  at opposite ends of base  710  and define slots  733  and  743 , respectively, facing inward toward coupler region  715 . In mounting circuit board  352  to base  710 , opposite side edges of circuit board  352  are inserted into slots  733  and  743 . In another example, upright guides  732  and  734  may engage circuit board  352  in any other manner. Although illustrated as being integrally formed with body  711 , upright guides  732  and  742  in another example may each be a separate component connected to base  710  in any manner. In another example, socket  700  may not have upright guides  732  and  734 . 
   Latches  734  and  744  each engage circuit board  352  to help secure flex circuit  354 .against circuit board  300 . Because of the shape and resiliency of flex circuit  354 , flex circuit  354  exerts a force against latches  734  and  744  as well as against circuit board  300  when circuit board  352  and flex circuit  354  are mounted to circuit board  300  with socket  700 . Latches  734  and  744  therefore help maintain a relatively stable coupling coefficient for the resulting electromagnetic coupler. Latches  734  and  744  may exert any amount of force against flex circuit  354 , such as approximately ten to approximately twenty pounds of normal force for example. 
   Latches  734  and  744  in one example are pivotably mounted at opposite ends of base  710  such that each latch  734  and  744  may be pivoted inward toward coupler region  715  to engage circuit board  352  and outward from coupler region  715  to disengage circuit board  352 . In one example, as illustrated in  FIG. 25 , latches  734  and  744  are pivotably mounted to base  710  and connectors  750  and  760 , respectively, by pins  771  and  772 , respectively, and to pivoting guides  752  and  762 , respectively, of connectors  750  and  760 , respectively, with pins  773  and  774 , respectively, to help align latches  734  and  744  relative to connectors  750  and  760 , respectively, and to circuit board  352 . 
   Pivoting guides  752  and  762  each engage circuit board  352  when latching circuit board  352  with latches  734  and  744  to help support circuit board  352  relative to circuit board  300  and to help align circuit board  352 , when mounted in base  710 , with latches  734  and  744 . Pivoting guides  752  and  762  in one example extend toward the top of socket  700  at opposite ends of base  710  and define slots  753  and  763 , respectively, facing inward toward coupler region  715 . Pivoting guides  752  and  762  pivot with latches  734  and  744 , respectively. Slots  753  and  763  engage opposite side edges of circuit board  352  when circuit board  352  is mounted in base  710  and when latches  734  and  744  are pivoted inward to latch circuit board  352 . In another example, pivoting guides  752  and  762  may engage circuit board  352  in any other manner. Although illustrated as a portion of each connector  750  and  760 , pivoting guides  752  and  762  in another example may each form a portion of latches  734  and  744 , respectively, or may each be a separate component connected to socket  700  in any manner. 
   Latches  734  and  744  in one example each define a finger  735  and  745 , respectively, extending inward toward coupler region  715 . Fingers  735  and  745  each define a knob  736  and  746 , respectively, at their respective ends to engage respective notches or indentations  591  and  592  at a top edge of circuit board  352 , as illustrated in  FIG. 18 , when circuit board  352  is mounted in base  710  and when latches  734  and  744  are pivoted inward. Fingers  735  and  745  therefore secure circuit board  352  and flex circuit  354  against circuit board  300 . In another example, latches  734  and  744  may engage circuit board  352  in any other manner. As one example, fingers  735  and  745  may each engage a notch or indentation in opposite side edges of circuit board  352 . 
   While circuit board  352  and flex circuit  354  are mounted to circuit board  300  by socket  700 , walls  712  and/or  713  may help support flex circuit  354  relative to circuit board  300  despite any tendency by flex circuit  354  to roll to one side due to its shape and the force exerted on flex circuit  354  against circuit board  300  by latches  734  and  744 . Walls  712  and/or  713  may therefore help align conductive lines of flex circuit  354  relative to conductive lines of circuit board  300 . In another example, each interior face of wall  712  and/or  713  may be contoured in a relatively concave manner, for example, to help support the rolled shape of flex circuit  354  and help align flex circuit  354  relative to circuit board  300 . Although illustrated as walls  712  and  713 , socket  700  in another example may include one or more guide rails of any other shape, such as rods for example, to help support flex circuit  354 . Socket  700  for another example may include only one or no guide rail adjacent to coupler region  715 . 
   In addition to or in lieu of the use of walls  712  and/or  713  and/or alignment post  633 , as illustrated in  FIG. 15 , to help align flex circuit  354  relative to circuit board  300 , one or more other alignment techniques may be used. As one example, flex circuit  354  may be defined with one or more notches or indentations along one or each side of flex circuit  354  to engage corresponding guide pins or tabs at one or both opposite ends of coupler region  715 . Such guide pins or tabs may extend from socket  700  inward toward coupler region  715  or from circuit board  300  into coupler region  715  when base  710  is mounted to circuit board  300 . As another example, one or more guide pins or posts may extend from circuit board  300  into coupler region  715 , when base  710  is mounted to circuit board  300 , to engage corresponding openings in flex circuit  354 . As another example, one or more guide pins or posts may extend from flex circuit  354  into corresponding openings in circuit board  300  when circuit board  352  and flex circuit  354  are mounted to circuit board  300 . 
   To help maintain outer surface  355  of flex circuit  354  against circuit board  300  when circuit board  352  and flex circuit  354  are mounted to circuit board  300 , relatively flexible or semi-rigid supports may be placed between the bottom of clamp  356  and the bottom interior surface of flex circuit  354 . Such supports may include any material, such as foam, rubber, injection molded plastic, and/or an elastomeric material for example, and may be shaped in any manner, such as a brick, as a spring, or as springy fingers for example. In addition to or in lieu of such supports, a relatively springy material may be formed along the interior surface of flex circuit  354  to help maintain outer surface  355  of flex circuit  354  against circuit board  300 . As one example, beryllium copper may be laminated along the interior surface of flex circuit  354 . 
   To remove circuit board  352  and flex circuit  354  from socket  700 , latches  734  and  744  may be pivoted outward from circuit board  352  to disengage latches  734  and  744  from circuit board  352 . Circuit board  352  and flex circuit  354  may then be lifted from socket  700 . 
   Each component of socket  700  may include any material and may have any dimensions. Body  711 , upright guides  732  and  734 , and latches  734  and  744  for one example may each include an injection molded plastic, for example. Base  710  for one example is approximately 5.55 inches in length, approximately 0.55 inches in width, and approximately 0.425 inches in height and defines coupler region  715  to be approximately 3.041 inches in length. Upright guides  732  and  742  for one example are each approximately 1.576 inches in height. 
   Although illustrated as mounted to circuit board  300  with socket  700 , circuit board  352  and flex circuit  354  may be mounted to circuit board  300  using other mechanisms. As one example, a single connector and arm, similar to the combination of connector  750  and arm  730  for example, may be used. For another example, a clam shell clamp arrangement may be used to hold a flattened flex circuit  354  against circuit board  300 . 
   As illustrated in  FIG. 26 , a circuit board  2152  for another example may be positioned relative to a flex circuit  2154  of a circuit board  2100  to form an electromagnetic coupler. Flex circuit  2154  includes one or more conductive lines for bus  112 , for example, and may be similarly formed as flex circuit  354 . Circuit board  2152  includes one or more conductive lines for bus  122 , for example, that may be similarly formed on circuit board  2152  as conductive lines for circuit board  300 , for example. 
   Conductive lines of flex circuit  2154  are conductively coupled to communication circuitry on circuit board  2100  and may be terminated in flex circuit  2154  or on circuit board  2100 . Flex circuit  2154  may be conductively coupled to circuit board  2100  in any manner, such as through surface mount solder pads or a connector for example. 
   As illustrated in  FIG. 26 , flex circuit  2154  for one example is folded to form a coupler region  2157 . Conductive lines of circuit board  2152  may be positioned relative to coupler region  2157  to form an electromagnetic coupler by positioning a surface of circuit board  2152  relative to coupler region  2157 . Circuit board  2152  for another example may include other conductive lines for another bus such that positioning an opposite surface of circuit board  2152  relative to a coupler region  2158  of folded flex circuit  2152  forms another electromagnetic coupler. Flex circuit  2154  may be folded to form an electromagnetic coupler with any number of circuit boards, such as six, for example, as illustrated in  FIG. 26 . Although illustrated as being folded to form an electromagnetic coupler with circuit board  2152  positioned generally perpendicularly relative to circuit board  2100 , flex circuit  2154  may be positioned in other manners to form an electromagnetic coupler with circuit board  2152  positioned in other manners. 
   In one example, flex circuit supports, such as supports  2105  and  2106  for example, may be used to support flex circuit  2154  in a folded position. Such supports may include any material. In one example, such supports include a resilient material to help hold circuit board  2152  against flex circuit  2154 . Also, a circuit board guide  2108  may be used to help support and align one or more circuit boards relative to flex circuit  2154 . 
   Other embodiments are within the scope of the following claims.