Patent Publication Number: US-2016248210-A1

Title: Interconnect architecture with stacked flex cable

Description:
BACKGROUND 
     There are a number of ways to interconnect signals from one electronic device to another. One method routes the signals through a package substrate of one device to a socket, onto a printed circuit board (PCB), and to another device, which may also be mounted on a package substrate and electrically coupled to the PCB through a socket. However, signals along such a path are susceptible to signal degradation and losses due to various parasitic mechanisms, transmission and return losses, and cross talk. The signal degradation and losses may be especially pronounced for high speed signals. Transmission losses may be reduced, for example, by constructing the PCB with materials having improved dielectric characteristics. However, significant degradation and losses may still be occur for longer interconnect paths and at higher signaling rates. Another way to interconnect signals uses flex cable that is electrically coupled to substrate packages and avoids routing the signals through the PCB. The flex cable may include a dielectric (insulating) material and an electrically conductive material, and conventionally includes a row of traces separated from a ground plane (or ground traces) by a dielectric layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-sectional view of an assembly including a flex cable structure, in accordance with certain embodiments. 
         FIG. 2  illustrates a top down view of a connector used in accordance with certain embodiments. 
         FIG. 3  illustrates a top down view of an assembly including a flex cable extending between two devices, in accordance with certain embodiments. 
         FIGS. 4A-4I  illustrate operations for forming an assembly, in accordance with certain embodiments. 
         FIGS. 5A-5H  illustrate operations for forming an assembly, in accordance with certain embodiments. 
         FIGS. 6A-6C  illustrate operations for forming an assembly, in accordance with certain embodiments. 
         FIG. 7  illustrates a flow chart including operations for forming an assembly, in accordance with certain embodiments. 
         FIG. 8  illustrates a flow chart including operations for forming an assembly, in accordance with certain embodiments. 
         FIG. 9  illustrates a flow chart including operations for forming an assembly, in accordance with certain embodiments. 
         FIG. 10  illustrates a side elevated view of an assembly, in accordance with certain embodiments. 
         FIG. 11  illustrates an electronic system arrangement in which embodiments may find application. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings which form a part hereof and which illustrate several embodiments of the present disclosure. It is understood that other embodiments may be utilized and structural and operational changes may be made without departing from the scope of the present description. 
     It has been found that the use of flex cable to form interconnections between electronic devices can enable high speed signaling while minimizing signal degradation and losses. However, to achieve enhanced speed with suitable loss characteristics for high performance applications using conventional flex cable, the width of the flex cable may become relatively large, for example, in a range of 70 to 150 mm. Such widths may interfere with other components in the system and also block air flow, which may be vital for cooling various components. Examples of high speed signaling systems may include Many Integrated Core (MIC) Exascale systems (400 GB/s Bandwidth per CPU, with 128 differential pairs) and HPC (high performance computing) systems, to achieve 25 Gb/s signal speed within an insertion loss budget of 25 dB and cross-talk-insertion loss margin of about 25 dB for about 15 inches of interconnect length from a device such as a CPU, to a device such as a router or switch. To achieve this signaling capability, one needs to minimize conductor loss, die electric loss, and cross-talk. These requirements lead to trace width/spacing for differential signals to values in the range of 100 μm to 125 μm and differential pairs pitch to the range of 500 μm (for stripline routing or microstrip routing with guard traces between differential pairs) to 1200 μm (for microstrip routing without guard traces between the differential pairs) in the flex cable. These flex design rules drive the conventional flex cable width to the range of 70-150 mm for the above bandwidth/signal density requirements. However, such a large flex cable width can interfere with other components in the system and also block air flow in. Certain embodiments as described herein provide for the formation of stacked flex cable assemblies having suitable properties and a smaller width such as, for example, approximately 35 mm. 
     Certain embodiments provide a more narrow flex cable configuration utilizing a stacked flex cable structure in which, for example, 50% of the signals are routed through a first flex cable, and 50% of the signals are routed through a second flex cable that is stacked on the first flex cable. Such a structure enables the flex cables to have a width that is reduced by 50%, because only half the number of signals are carried along the length of each flex cable. 
       FIG. 1  illustrates a cross-sectional view of an assembly in accordance with certain embodiments, including s substrate  12  on which a connector  14  and a stacked flex cable  16  positioned thereon. As seen in  FIG. 1 , the stacked flex cable  16  includes flex cable  16 A and flex cable  16 B. The stacked flex cables  16 A and  16 B may each include a connection region where electrical connections are made to the connector  14 , a transmission region extending towards another structure, and a break-out region between the connection region and the transmission region. The break-out region is the region where the electrical pathways transition from the connection region to the transmission region. These portions are described below in connection with  FIG. 3 . If desired, the assembly may include a stiffener  28  positioned, for example, on the flex cable  16 B. The stiffener  28  is formed from a rigid material. 
     The substrate  12  may in certain embodiments comprise a variety of electronic devices such as, for example, a semiconductor die, a package including a semiconductor die such as a CPU (central processing unit) package, or a structure such as, for example, a dongle. A dongle may in certain embodiments act as a package extender so that the electrical connections to a device such as a CPU can be positioned to clear a structure such as, for example, a heat sink. The substrate  12  may in turn be coupled to another structure such as, for example, a PCB (printed circuit board). The connector  14  may in certain embodiments comprise a LIF (low insertion force) connector that includes a pin carrier and a plug. In other embodiments the connector  14  may be, for example, a ZIF (zero insertion force) connector. Any suitable connector may be used, including, for example, connectors that are solder bonded to another structure and that are solder bonded to the flex cable. As illustrated in  FIG. 1 , the connector  14  may be coupled to the substrate  12  using a suitable connection such as, for example, solder connections  18 . 
     The flex cable  16 A may be coupled to the connector  14  using a suitable connection, such as solder connections  20  positioned between flex cable  16 A and connector  14 . The flex cable  16 A may also include electrical pathways  22  that extend from a bottom surface to a top surface thereof. The flex cable  16 B may be coupled to the flex cable  16 A using a suitable connection, such as solder connections  24 . As noted above, the use of the stacked flex cable  16  including flex cables  16 A and  16 B permit each cable to route some of the signals instead of one flex cable routing all of the signals. As illustrated in  FIG. 1 , every other contact position on flex cable  16 B is electrically coupled to the flex cable  16 A through a solder connection  24 , and every contact position on flex cable  16 A is coupled to the array of contacts on the connector  14  through the solder connection  20 . The electrical connections to the upper flex cable  16 B may be made through the electrically conductive vias  22  extending thorough the flex cable  16 A. As illustrated, all the signals passing through the connector  14  will be directed to the flex cable  16 A. In certain embodiments, half of the signals directed to flex cable  16 A will be sent through pathways in flex cable  16 A and half of the signals will be sent through pathways in flex cable  16 B. If desired, a capillary underfill using a suitable polymeric material  51 ,  53 ,  55  may be used to protect the various solder connections between the connector  14  and substrate  12 , between the flex cable  16 A and the connector  14 , and between the flex cable  16 A and the flex cable  16 B. 
       FIG. 2  illustrates a view of the top surface of a portion of the connector  14 , showing an array of contact locations  30 ,  32  that may be electrically coupled to one or more of flex cables  16 A and  16 B. In accordance with certain embodiments, all of the contact locations  30 ,  32  are electrically coupled to the lower flex cable  16 A. Every other contact location  32  will also be electrically coupled through a via  22  and into electrical contact with the upper flex cable  16 B. 
       FIG. 3  illustrates a top view of an embodiment in which two devices are electrically coupled to one another through a stacked flex cable structure including first and second stacked flex cables. The embodiment of  FIG. 3  includes a PCB  102  such as a motherboard, on which substrate bodies  112 ,  113  are positioned. The substrate bodies  112 ,  113  may be structures such as package substrates that include one or more electronic devices  104 ,  105  (including, for example, a semiconductor die) thereon. Signals may be passed between the electronic devices  104 ,  105  through a stacked flex cable structure. The stacked flex cable structure may include an upper flex cable  116 B and a lower flex cable that is hidden from view by the upper flex cable  116 B in  FIG. 3 . 
     The upper flex cable  116 B includes connection regions positioned over the substrate bodies  112 ,  113  where electrical connections  130 ,  131  are made, a transmission region including traces  155  extending between the substrate bodies  112 ,  113 , and break-out regions between the connection regions and the transmission region. The lengths of these regions are indicated by the brackets positioned just below the PCB  102  at a lower portion of  FIG. 3 , with the connection region having a length  150 ,  151 , the transmission region having a length  154 , and the break-out regions having a length  152 ,  153 . The transmission region in  FIG. 3  is substantially longer than the connection and break-out regions. 
       FIG. 3  also includes dotted lines extending between portions of the stacked flex cable  116 B that corresponds to a width if instead of a stacked flex cable, only a single flex cable layer was used. In such a case, all traces between the substrate bodies would go through a one trace layer flex cable and the one layer flex cable would have to be relatively wide (e.g., the width of the dotted lines) in the transmission region to ensure that the spacing between the adjacent traces would provide adequate signal integrity, power, and loss properties. In contrast, when multiple stacked flex cables are used, the width of each flex cable may be more narrow because each flex cable layer only needs to accommodate some of the signals and as a result there can be less traces in each flex cable layer. In general, if two stacked flex cables are used, then the width of each may be decreased, for example, by about 50%. Certain embodiments may also use more than two stacked flex cables, which may permit even greater decreases in width. 
       FIGS. 4A-4I  illustrate processing operations for forming a stacked flex cable assembly such as that illustrated in  FIG. 1 , in accordance with certain embodiments. As illustrated in  FIG. 4A , a first flex cable  16 A may be positioned in a suitable pallet  11  for supporting the flex cable  16 A during various processing operations, such as, for example, solder paste printing, placing other components onto the flex cable, and reflow. The pallet may also include a tension mechanism for holding the flex cable. The pallet may also include holes for heat transfer and include fiducial marks for alignment. The flex cable  16 A may include a plurality of electrically conductive vias  22  therein. Solder paste  17  may be printed on the flex cable  16 A in electrical contact with the vias  22 , as illustrated in  FIG. 4B . 
     A connector  14  such as a LIF connector may be aligned with the flex cable  16 A using a pick and place device  21  so that solder bumps  19  on the connector are aligned with the solder paste  17  on the flex cable  16 A, as illustrated in  FIG. 4C . Heat is applied to reflow the solder and join the connector  14  to the flex cable  16 A through solder connections  20 , as illustrated in  FIGS. 4D-4E . As illustrated in  FIG. 4F , the assembly may be removed from the pallet  11  and positioned in a suitable pick and place tray  23 . 
     A second flex cable  16 B may be positioned in a pallet  11  and processed in a similar manner as the first flex cable  16 A to form solder paste  37  on the flex cable  16 B. The solder paste  37  may be positioned on every other possible site, as illustrated in  FIG. 4G . The assembly including the first flex cable  16 A and the connector  14  may then be aligned with the flex cable  16 B and heat applied to reflow and join the flex cable  16 A to the flex cable  16 B through solder connections  24 , as illustrated in  FIGS. 4H-4I . A spacer structure  40  may be positioned between the flex cables  16 A and  16 B, if desired, in order to assist in providing a uniform distance between the flex cables  16 A and  16 B. The spacer structure  40  may act to inhibit the assembly from bending due to, for example, the weight of the flex cable  16 A adjacent to the solder connections. Certain embodiments may not require the use of such a spacer. The spacer structure  40  may take a variety of forms including, but not limited to, a block of solid material, one or more pins, or a material that hardens into a rigid spacer such as, for example, a glue or epoxy. The spacer  40  may be removed after the flex cables  16 A and  16 B are coupled to one another. 
     As described above in connection with  FIGS. 4A-4I , for example, in accordance with certain embodiments, a connector may be coupled to a flex cable to form an assembly, and then the assembly may be coupled to another flex cable to form a stacked flex cable assembly. Other embodiments may couple together a plurality of flex cables, then couple a connector to the stacked flex cables. 
       FIGS. 5A-5H  illustrate processing operations for forming a stacked flex cable assembly, in accordance with certain embodiments, in which a plurality of flex cables are coupled together, then a connection is coupled thereto. As illustrated in  FIG. 5A , a flex cable  16 B may be positioned in a suitable pallet  11 . The flex cable  16 B may include a plurality of electrically conductive vias  26  therein. Solder paste  37  may be printed on the flex cable  16 B in electrical contact with every other via  26 , as illustrated in  FIG. 5B . A flex cable  16 A may be positioned in another pallet  11  and may include a plurality of electrically conductive vias  22  therein, as illustrated in  FIG. 5C . Solder paste  17  may be printed on the flex cable  16 A in electrical contact with the vias  22 , as illustrated in  FIG. 5D . 
     The flex cable  16 A may be removed from the pallet and placed on the flex cable  16 B, as illustrated in  FIG. 5E . A connector  14  such as a LIF connector may be aligned with the flex cable  16 A so that solder bumps  19  on the connector are aligned with the solder paste  17  on the flex cable  16 A, as illustrated in  FIG. 5F . Heat is applied to reflow the solder and join the connector  14  to the flex cable  16 A through solder connections  20 , as illustrated in  FIGS. 5G-5H . If desired, a spacer such as the spacer  40  described above in connection with  FIGS. 4G-4I  may be utilized. 
       FIGS. 6A-6C  illustrate the formation of a stacked flex cable assembly in accordance with certain embodiments, in which a portion of a flex cable is bent around a body to form the stacked assembly. As illustrated in  FIG. 6A , a flex cable  216  may be electrically coupled to a connector  214  such as a LIF connector using solder connections  220 . A body  244  such as a stiffener is also coupled to the flex cable  216 . The flex cable  216  is positioned between the connector  214  and the body  244 . If desired, an adhesive may be positioned between the body  244  and the flex cable  216 , on one or both sides of the body  244 . The connector  214  is electrically coupled to the flex cable  216  so that a first group of signals will travel in one direction (as indicated by arrows A) along the flex cable  216  and a second group of the signals (as indicated by arrows B) will travel in an opposite direction along the flex cable  216 . 
     The flex cable  216  may be bent around the body  244  so that part of the flex cable folds back over itself as illustrated in  FIG. 6C . The flex cable  216  will then be configured to have a stacked structure, with a first flex cable portion  216 A and a second flex cable portion  216 B. Signals traveling in the direction indicated by the arrows A ( FIG. 6B ) will travel along flex cable portion  216 A ( FIG. 6C ). Signals traveling in the direction indicated by arrows B ( FIG. 6B ) will travel around the curved portion of flex cable  216 , and then along the flex cable portion  216 B. Such a structure permits the flex cable  216  to be made more narrow because the stacked structure enables, for example, half of the signals to be transmitted along direction A and along flex cable portion  216 A and half of the signals to be transmitted along direction B and along flex cable portion  216 B. 
       FIG. 7  illustrates a flowchart of operations for forming an assembly in accordance with certain embodiments. Box  300  is positioning a first flex cable in a first pallet or other holding mechanism for processing. Box  302  is placing solder on the first flex cable in desired locations for electrically coupling the first flex cable to a connector. The solder may be in the form of a solder paste that is printed on the first flex cable. Box  304  is positioning the connector on the first flex cable on the solder paste. The connector may be any suitable connector for coupling a flex cable to a substrate, including, but not limited to, a LIF connector or a ZIF connector. The connector may have solder positioned thereon that is aligned with the solder on the first flex cable. Box  306  is heating the assembly to reflow the solder and couple the first flex cable to the connector. 
     Box  308  is positioning a second flex cable in a pallet or other holding mechanism for processing. Box  310  is placing solder on the second flex cable in desired locations for electrically coupling the second flex cable to the first flex cable. The solder may be in the form of a solder paste that is printed on the first flex cable. Box  312  is positioning the first flex cable that has the connector coupled thereto on the second flex cable. Box  314  is heating the assembly to reflow the solder and join the second flex cable to the first flex cable. Box  316  is positioning a stiffener on the second flex cable. Adhesive may be positioned if desired between the stiffener and the second flex cable. The stiffener may be positioned so that the second flex cable is between the stiffener and the first flex cable. It should be appreciated that various of the operations in the flowchart may be modified or are optional, and additional operations may be added. For example, an operation of inserting a spacer on the first flex cable may be included between boxes  310  and  312  to inhibit bending. 
       FIG. 8  illustrates a flowchart of operations for forming an assembly in accordance with certain embodiments. Box  400  is positioning a second flex cable in a second pallet or other holding mechanism for processing. Box  402  is placing solder on the second flex cable in desired locations for electrically coupling the second flex cable to a first flex cable. The solder may be in the form of a solder paste that is printed on the second cable. Box  404  is positioning a first flex cable in a first pallet or other holding mechanism for processing. Box  406  is placing solder on the first flex cable in desired locations for electrically coupling the first flex cable to a connector in a subsequent operation. The solder may be in the form of a solder paste that is printed on the second cable. Box  408  is removing the first flex cable from its holding mechanism and positioning the first flex cable on the second flex cable. 
     Box  410  is positioning a connector on the solder on the first flex cable to form a stack with the connector, the first flex cable, and the second flex cable. The connector may be any suitable connector for coupling a flex cable to a substrate, including, but not limited to, a LIF connector or a ZIF connector. The connector may have solder positioned thereon that is aligned with the solder on the first flex cable. Box  412  is heating the assembly to reflow the solder between the connector and the first flex cable and between the first flex cable and the second flex cable, for form solder joints coupling the stack together. Box  414  is positioning a stiffener on the second flex cable. Adhesive may be positioned if desired between the stiffener and the second flex cable. The stiffener may be positioned so that the second flex cable is between the stiffener and the first flex cable. It should be appreciated that various of the operations in the flowchart may be modified or are optional, and additional operations may be added. For example, the order of operations may be modified so that Box  400  and Box  402  are switched with Box  404  and  406 . 
     The process set forth in  FIG. 8  differs from that set forth in  FIG. 7  is several aspects. One difference is that the operations described in  FIG. 8  include a single reflow operation for coupling the connector to the first flex cable and for coupling the first and second flex cables together, whereas the operations described in  FIG. 7  include a reflow operation for coupling the connector and the first flex cable, and then another reflow operation for coupling the first and second flex cables. 
       FIG. 9  illustrates operations for forming an assembly in accordance with certain embodiments. Box  500  is coupling a connector to a flex cable. The connector may be any suitable connector for coupling a flex cable to a substrate, including, but not limited to, a LIF connector or a ZIF connector. A solder joint connection may be used to couple the connector to the flex cable. Box  502  is attaching a body to the flex cable. The body may take the form of a stiffener that is coupled to an opposite surface than the connector is coupled to. An adhesive may be used if desired to obtain a good bond between the stiffener and the flex cable. Box  504  is bending the flex cable around the body so that the flex cable extends in approximately a 180 degree path, resulting in a stacked flex cable having a first flex cable portion on one side of the body and a second flex cable portion on a second side of the body. An adhesive may be positioned between the second flex cable portion and the second side of the body, if desired. 
     The first flex cable portion and the second flex cable portion will in certain embodiments be substantially parallel to one another in regions beyond the curved region that extends around part of the body. The connector and flex cable are configured so that a first group of signals passing from the connector to the flex cable may travel along the first flex cable portion and a second group of signals may travel around the curved region and along the second flex cable portion. Such a structure formed using an embodiment such as described in connection with  FIG. 9  enables a stacked flex cable configuration while using a single flex cable. It should be appreciated that a variety of modifications, deletions, and additions may be made to the operations described in  FIG. 9 . For example, the order of coupling the connector and the body to the flex cable may be reversed so that the body is first coupled and then the connector is coupled. In addition, the flex cable may in certain embodiments be bent around the body prior to the connector being coupled thereto. 
     Embodiments are applicable to a variety of configurations of electronic devices.  FIG. 10  illustrates a side elevation view including a plurality of substrates  611 ,  612 ,  613  positioned on a PCB  602 , in accordance with certain embodiments. Each of the substrates  611 ,  612 ,  613  includes a semiconductor device  603 ,  604 ,  605  such as, for example, a CPU. A plurality of stacked flex cable assemblies and are used to electrically couple the semiconductor devices  603 ,  604 ,  605  together. A first stacked flex cable assembly as illustrated in  FIG. 10  includes first stacked flex cables  616 A and  616 B, which are electrically coupled to connector  614 A on substrate  611  and to connector  614 B on substrate  612 . A second stacked flex cable assembly as illustrated in  FIG. 10  includes stacked flex cables  636 A and  636 B, which are electrically coupled to connector  615 A on substrate  612  and to connector  615 B on substrate  613 . As seen in  FIG. 10 , the stacked flex cables  616 A,  616 B and  636 A,  636 B have a width dimension W that is more narrow in the transmission region of the flex cables than in the connection regions over the connectors  614 A,  614 B,  615 A,  615 B. As a result, other components such as, for example, a portion of a heat sink, may be positioned in these more narrow regions. Alternatively, these more narrow regions may be maintained so that enhanced air flow can be achieved in the assembly. 
     Various embodiments as described herein may provide one or more advantages over conventional flex cable configurations that have one layer of signal traces for transmitting signals. By providing a plurality of stacked flex cable portions, each of the stacked flex cable portions may be made more narrow because it does not need to house all the signal traces for transmitting the signals. As a result, additional open spaces within an electronic assembly or system may be provided that enable other components to be fit within the open space and/or which permit improved airflow through the system. A variety of processing schemes may be utilized for forming stacked flex cable structures, including those with separate flex cables that are coupled together and those with a single flex cable that is bent to form a layered configuration. 
     Assemblies including components formed as described in embodiments above may find application in a variety of electronic components.  FIG. 11  schematically illustrates one example of an electronic system environment in which aspects of described embodiments may be embodied. Other embodiments need not include all of the features specified in  FIG. 11 , and may include alternative features not specified in  FIG. 11 . 
     The system  701  of  FIG. 11  may include at least one central processing unit (CPU)  703 . The CPU  703 , also referred to as a microprocessor, may be a die which is attached to an integrated circuit package substrate  705 , which is then coupled to a PCB  707 , which in this embodiment, may be a motherboard. A variety of other system components, including, but not limited to memory and other components discussed below, may also include structures formed in accordance with the embodiments described above. 
     The system  701  may further include memory  709  and one or more controllers  711   a ,  711   b  . . .  711   n , which are also disposed on the PCB  707 . The CPU  703  and memory  709  are examples of components that may be electrically connected to one another in accordance with embodiments such as described above, using a stacked flex cable  716 . The PCB  707  may be a single layer or multi-layered board which has a plurality of conductive lines that may provide communication between the circuits various components mounted to the board  707 . Alternatively, one or more of the CPU  703 , memory  709  and controllers  711   a ,  711   b  . . .  711   n  may be disposed on other cards such as daughter cards or expansion cards. At least some of the components may alternatively be seated in individual sockets or may be connected directly to a printed circuit board. A display  715  may also be included. The display  715  may in certain embodiments be an interactive touch screen. 
     Any suitable operating system and various applications execute on the CPU  703  and reside in the memory  709 . The content residing in memory  709  may be cached in accordance with known caching techniques. Programs and data in memory  709  may be swapped into storage  713  as part of memory management operations. The system  701  may comprise any suitable computing device, including, but not limited to, a mainframe, server, personal computer, workstation, laptop, handheld computer, handheld gaming device, handheld entertainment device (for example, MP3 (moving picture experts group layer—3 audio) player), PDA (personal digital assistant) telephony device (wireless or wired), network appliance, virtualization device, storage controller, network controller, router, etc. 
     The controllers  711   a ,  711   b  . . .  711   n  may include one or more of a system controller, peripheral controller, memory controller, hub controller, I/O (input/output) bus controller, video controller, network controller, storage controller, communications controller, etc. For example, a storage controller can control the reading of data from and the writing of data to the storage  713  in accordance with a storage protocol layer. The storage protocol of the layer may be any of a number of known storage protocols. Data being written to or read from the storage  713  may be cached in accordance with known caching techniques. A network controller can include one or more protocol layers to send and receive network packets to and from remote devices over a network  717 . The network  717  may comprise, for example, a Local Area Network (LAN), the Internet, a Wide Area Network (WAN), Storage Area Network (SAN), etc. Embodiments may be configured to transmit and receive data over a wireless network or connection. In certain embodiments, the network controller and various protocol layers may employ the Ethernet protocol over unshielded twisted pair cable, token ring protocol, Fibre Channel protocol, etc., or any other suitable network communication protocol. 
     Terms such as “first”, “second”, and the like may be used herein and do not necessarily denote any particular order, quantity, or importance, but are used to distinguish one element from another. Terms such as “upper”, “lower”, “top”, “bottom”, and the like may be used for descriptive purposes only and are intended to denote the relative position of certain features. Embodiments may be manufactured, used, and contained in a variety of positions and orientations. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive, and that embodiments are not restricted to the specific constructions and arrangements shown and described since modifications may occur to those having ordinary skill in the art. Various features are grouped together for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the claims reflect, inventive subject matter may lie in less than all features of a single disclosed embodiment. 
     EXAMPLES 
     The following examples pertain to further embodiments. 
     Example 1 is a stacked flex cable comprising: a first flex cable; a second flex cable electrically coupled to the first flex cable; and a connector electrically coupled to the first flex cable; wherein the first flex cable is positioned between the connector and the second flex cable. 
     In Example 2, the subject matter of Example 1 may optionally include wherein the first flex cable and the second flex cable are electrically coupled to each other through a solder connection. 
     In Example 3, the subject matter of any of Examples 1-2 may optionally include wherein the second flex cable is positioned over the first flex cable. 
     In Example 4, the subject matter of any of Examples 1-3 may optionally include a stiffener coupled to the second flex cable, wherein the stiffener is positioned over the second flex cable. 
     In Example 5, the subject matter of any of Examples 1-4 may optionally include wherein the connector is coupled to a substrate. 
     In Example 6, the subject matter of any of Examples 1-5 may optionally include a semiconductor die coupled to the substrate, wherein the connector is electrically coupled to the semiconductor die. 
     Example 7 is a stacked flex cable assembly comprising: a first flex cable portion; a second flex cable portion positioned over the first flex cable portion; and a connector electrically coupled to the first flex cable portion; wherein the first flex cable portion is positioned between the connector and the second flex cable portion. 
     In Example 8, the subject matter of Example 7 may optionally include wherein the first flex cable portion and the second flex cable portion are part of a common flex cable. 
     In Example 9, the subject matter of Example 8 may optionally include wherein the common flex cable includes a curved region positioned between the first flex cable portion and the second flex cable portion. 
     In example 10, the subject matter of any of Examples 7-9 may optionally include wherein the second flex cable portion is positioned directly over the first flex cable portion. 
     In example 11, the subject matter of any of Examples 7-10 may optionally include a body positioned between the first flex cable portion and the second flex cable portion. 
     In Example 12, the subject matter of any of Examples 7-11 may optionally include a stiffener positioned between the first flex cable portion and the second flex cable portion, the stiffener being positioned over the connector. 
     In Example 13, the subject matter of any of Examples 7-12 may optionally include wherein the connector is coupled to a substrate, the assembly further comprising a semiconductor die coupled to the substrate, wherein the connector is electrically coupled to the semiconductor die. 
     In Example 14, the subject matter of any of Examples 7-13 may optionally include wherein the first flex cable portion and the second flex cable portion are separate flex cables. 
     Example 15 is a method for forming a stacked flex cable assembly, comprising: coupling a first flex cable to a second flex cable; and coupling a connector to the first flex cable; wherein the first flex cable is positioned between the connector and the second flex cable. 
     In Example 16, the subject matter of Example 15 may optionally include wherein the coupling the connector to the first flex cable comprises forming a solder connection between the connector and the first flex cable, and wherein the coupling the first flex cable to the second flex cable comprises forming a solder connection between the first flex cable and the second flex cable. 
     In Example 17, the subject matter of any of Examples 15-16 may optionally include wherein the coupling the connector to the first flex cable is carried out prior to the coupling the first flex cable to the second flex cable. 
     In Example 18, the subject matter of any of Examples 15-16 may optionally include wherein the forming a solder connection between the connector and the first flex cable and the forming a solder connection between the first flex cable and the second flex cable are carried out during a single heating operation. 
     In Example 19, the subject matter of any of Examples 15-18 may optionally include positioning the connector on a substrate in electrical contact with a semiconductor die. 
     Example 20 is a method for forming a stacked flex cable assembly, comprising: providing a flex cable including a first flex cable portion and a second flex cable portion; coupling a connector to the flex cable; coupling a body to the flex cable, wherein the body is positioned on an opposite side of the flex cable than the connector; and bending the flex cable around the body so that the resultant flex cable comprises a first flex cable portion positioned on a first side of the body, a second flex cable portion positioned on a second side of the body opposite the first side, and a curved flex cable portion connecting the first flex cable portion and the second flex cable portion. 
     In Example 21, the subject matter of Example 20 may optionally include wherein the coupling the connector to the flex cable is carried out prior to the coupling the body to the flex cable. 
     In Example 22, the subject matter of any of Examples 20-21 may optionally include wherein the coupling the connector to the flex cable is carried out prior to the coupling the body to the flex cable. 
     In Example 23, the subject matter of any of Examples 20-22 may optionally include coupling the connector to the flex cable so that: a first group of electrical signals may travel from the connector away from the curved region and along the first flex cable region; and a second group of electrical signals passed through the connector may travel from the connector towards and around the curved flex cable portion and along the second flex cable portion. 
     In Example 24, the subject matter of any of Examples 15-23 may optionally include wherein the second flex cable portion extends in a direction parallel to that of the first flex cable portion. 
     In Example 25, the subject matter of any of Examples 20-24 may optionally include positioning the connector on a substrate in electrical contact with a semiconductor die. 
     Example 26 is a stacked flex cable assembly comprising a connector means for making an electrical connection between two structures; a first flex cable means coupled to the connector means, for conducting electrical signals; a second flex cable means for conducting electrical signals; and coupling means for electrically coupling the first flex cable means to the second flex cable means so that the first flex cable means is positioned between the connector and the second flex cable means. 
     In Example 27, the subject matter of Example 26 may optionally include wherein the coupling means includes a solder connection. 
     In Example 28, the subject matter of Examples 26-27 may optionally include means for positioning the second flex cable means over the first flex cable means. 
     In Example 29, the subject matter of Examples 26-28 may optionally include stiffener means coupled to the second flex cable means and positioned over the second flex cable means for providing rigidity to the assembly. 
     In Example 30, the subject matter of Examples 26-29 may optionally include a substrate, wherein the connector means is coupled to the substrate. 
     In Example 31, the subject matter of Example 30 may optionally include a semiconductor die coupled to the substrate, and means for electrically coupling the connector means to the semiconductor die. 
     Example 32 is a stacked flex cable assembly comprising: a connector means for making an electrical connection between two structures; first flex cable portion means for conducting electrical signals, second flex cable portion means for conducting electrical signals; coupling means for electrically coupling the first flex cable portion means to the connector means and for positioning the first flex cable portion means between the connector means and the second flex cable portion means. 
     In Example 33, the subject matter of Example 32 may optionally include wherein the first flex cable portion means and the second flex cable portion means are part of a common flex cable means. 
     In Example 34, the subject matter of Examples 32-33 may optionally include wherein the common flex cable means includes a curved region positioned between the first flex cable portion means and the second flex cable portion means. 
     In Example 35, the subject matter of Examples 32-34 may optionally include wherein the second flex cable portion means is positioned directly over the first flex cable portion means. 
     In Example 36, the subject matter of Examples 32-35 may optionally include body means for separating the first flex cable portion means and the second flex cable portion means. 
     In Example 37, the subject matter of Examples 32-35 may optionally include stiffener means to stiffen the assembly, and coupling means for positioned the stiffener means between the first flex cable portion means and the second flex cable portion means, the stiffener means being positioned over the connector means. 
     In Example 38, the subject matter of Examples 32-37 may optionally include coupling means for coupling the connector means to a substrate, the assembly further comprising a semiconductor die coupled to the substrate, wherein the connector means is electrically coupled to the semiconductor die. 
     In Example 39, the subject matter of Examples 32-38 may optionally include wherein the first flex cable portion means and the second flex cable portion means comprise separate flex cables. 
     Example 40 is a computer program product, comprising a computer readable storage medium having computer readable program code embodied therein executable by a processor to perform the method of any one of Examples 15-25. 
     Example 41 is a computer program product, comprising a computer readable storage medium having computer readable program code embodied therein executable by a processor to implement a method or realize the apparatus of any one of the above Examples 1-40.