Patent Publication Number: US-11038313-B1

Title: Orthogonal cross-connecting of printed circuit boards without a midplane board

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 14/840,149 now U.S. Pat. No. 10,135,214, entitled, “Orthogonal Cross-Connecting of Printed Circuit Boards Without a Midplane Board,” filed Aug. 31, 2015, which is a divisional of U.S. patent application Ser. No. 13/852,183, now U.S. Pat. No. 9,136,624, entitled, “Orthogonal Cross-Connecting of Printed Circuit Boards without a Midplane Board,” filed Mar. 28, 2013, the disclosure of each of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Embodiments described herein relate generally to orthogonal cross connects, and more particularly, to methods of improved placement of switch fabric cards in a chassis with orthogonal cross-connects. 
     Some known high bandwidth systems include a set of line cards or the like that are arranged in an orthogonal many-to-many connectivity configuration as part of a cross-connect system or a switch-fabric. In such systems, a set of connectors of a line card are operatively coupled to corresponding connectors of a switch-fabric card that is orthogonal to the line card. Such systems allow for high speed transmission and high speed switching of data units. In some instances, however, the orthogonal configuration results in relatively large line cards and/or switch-fabric cards (or a similar electronic device having a printed circuit board (PCB)) because of the square matrix formed by the array of connectors. In some instances, in an effort to reduce the size of the line cards and/or switch-fabric cards, the connectors of each line card and/or switch-fabric cards included in the cross-connect system are arranged with a relatively tight spacing. Such arrangements can lead to challenges in cooling the line cards and/or switch-fabric cards of the cross-connect system as well as providing sufficient ventilation for the removal of heated air (e.g., heated by the electronics of the line cards). 
     In some instances, scaling (e.g., building chassis using a different number of similar line cards and/or switch-fabric cards) of such known systems can result in compute components on each line card and/or switch-fabric cards being underutilized. For example, in some instances, the line cards and/or switch-fabric cards of a cross-connect system each can include a number of application specific integrated circuits (ASICs) that can correspond to a number of connectors included on the line card and/or switch-fabric cards. In such instances, the reduced number of connectors, as a result of the scaling, results in the ASICs of each line card and/or switch-fabric card being underutilized. 
     Thus, a need exists for apparatus and methods for improved placement of line cards and/or switch-fabric cards in a chassis with orthogonal cross-connects. 
     SUMMARY 
     Apparatus and methods for improved placement of cross-connect system cards in a chassis with an orthogonal cross-connect are described herein. In some embodiments, a line card of a set of line cards is configured to be coupled to a set of switch-fabric cards to collectively define at least a portion of an orthogonal cross fabric without a midplane board. The line card has an edge portion, a first side and a second side, opposite the first side. The line card includes a set of first set of connectors and a second set of connectors. The first set of connectors is disposed along the edge portion on the first side of the line card and the second set of connectors is disposed along the edge portion on the second side of the line card. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic block diagram of a cross-connect system according to an embodiment. 
         FIG. 2  is a schematic illustration of a portion of a cross-connect system according to an embodiment. 
         FIG. 3  is a schematic illustration of a line card included in the portion of the cross-connect system of  FIG. 2 . 
         FIG. 4  is a cross-sectional illustration of the line card taken along the line  4 - 4  in  FIG. 3 , showing a ground contact and a signal contact for simplicity. 
         FIG. 5  is a schematic illustration of a switch-fabric card included in the cross-connect system of  FIG. 2 . 
         FIG. 6  is a schematic illustration of a portion of a cross-connect system in a first arrangement, according to an embodiment. 
         FIG. 7  is a schematic illustration of a portion of the cross-connect system of  FIG. 6  in a second arrangement. 
         FIG. 8  is a schematic front perspective view of a portion of a cross-connect system according to an embodiment. 
         FIG. 9  is a schematic rear perspective view of the portion of the cross-connect system of  FIG. 8 . 
         FIG. 10  is a flowchart illustrating a method of forming a portion of a printed circuit board assembly according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments for improved placement of cross-connect system cards in a chassis with an orthogonal cross-connect are described herein. In some embodiments, a line card of a set of line cards is configured to be coupled to a set of switch-fabric cards to collectively define at least a portion of an orthogonal cross fabric (e.g., an orthogonal cross-connect system) without a midplane board. The line card has an edge portion, a first side and a second side, opposite the first side. The line card includes a set of first set of connectors and a second set of connectors. The first set of connectors is disposed along the edge portion on the first side of the line card, and the second set of connectors is disposed along the edge portion on the second side of the line card. 
     In some embodiments, a printed circuit board (PCB) is coupled to a set of line cards, having an orientation, and a set of switch-fabric cards, having the orientation, to define a midplane for a cross-connect system. The PCB has a first side with a first set of connectors. The PCB has a second side that is opposite the first side with a second set of connectors. 
     In some embodiments, a method includes forming a set of connector-receiving portions in a PCB. Each connector-receiving portion from the set of connector-receiving portions has a via and a semi-blind via. A first set of connectors is coupled to a first side of the PCB. Each connector from the set of connectors includes a ground contact and a signal contact. A second set of connectors is coupled to a second side of the PCB. Each connector from the set of connectors includes a ground contact and a signal contact. The ground contact for each connector from the first set of connectors is electrically coupled to the corresponding connector from the second set of connectors through the via of the corresponding connector-receiving portion of the PCB. The signal contact for each connector from the first set of connectors is not electrically coupled to the corresponding connector from the second set of connectors through the semi-blind via of the corresponding connector-receiving portion of the PCB. 
     In some embodiments, a PCB has a first side, a second side, and a set of connector-receiving portions. Each connector-receiving portion has a via and a semi-blind via. The PCB includes a first set of connectors disposed on the first side of the PCB with each connector having a ground contact and a signal contact. The PCB includes a second set of connectors disposed on the second side of the PCB with each connector having a ground contact and a signal contact. Each connector from the first set of connectors is disposed opposite a unique connector from the second set of connectors. The ground contact for each connector from the first set of connectors is electrically coupled to the corresponding connector from the second set of connectors through the via of the corresponding connector-receiving portion of the PCB. The signal contact for each connector from the first set of connectors is not electrically coupled to the corresponding connector from the second set of connectors through the semi-blind via of the corresponding connector-receiving portion of the PCB. 
     As used in this specification, the term “parallel” generally describes a relationship between two geometric constructions (e.g., two lines, two planes, a line and a plane or the like) in which the two geometric constructions are substantially non-intersecting as they extend substantially to infinity. For example, a line is said to be parallel to another line when the lines do not intersect as they extend to infinity. Similarly, when a planar surface (i.e., a two-dimensional surface) is said to be parallel to a line, every point along the line is spaced apart from the nearest portion of the surface by a substantially equal distance. Two geometric constructions are described herein as being “parallel” or “substantially parallel” to each other when they are nominally parallel to each other, such as for example, when they are parallel to each other within a tolerance. Such tolerances can include, for example, manufacturing tolerances, measurement tolerances, or the like. 
     As used herein, the terms “perpendicular” and “orthogonal” generally described a relationship between two geometric constructions (e.g., two lines, two planes, a line and a plane, or the like) in which the two geometric constructions are disposed at substantially 90°. For example, a line is said to be perpendicular to another line when the lines intersect at an angle substantially equal to 90°. Similarly, when a planar surface (e.g., a two dimensional surface) is said to be orthogonal to another planar surface, the planar surfaces are disposed at substantially 90° as the planar surfaces extend to infinity. 
     As used herein, the term “via” refers to an electrical interconnect included in, for example, a printed circuit board (PCB). For example, in some embodiments, a first conductive layer can be placed in electrical communication with a second conductive layer by one or more vias. A via can be a through hole defined by the PCB that has a conductive portion such as an annulus or the like. The term “semi-blind via” refers to a via that doesn&#39;t extend through the thickness of the PCB. For example, a semi-blind via can be configured to extend through a first set of layers of a PCB but not a second set of layers. Moreover, a semi-blind via is differentiated from a “blind via” or a “buried via” (not discussed herein) that generally refer to a via that extends through a set of inner layers but not the outer layers of a PCB. Thus, a semi-blind via refers to a via that extends through an outer layer (e.g., a single outer layer of a PCB) and a subset of inner layers (e.g., not all the inner layers of the PCB). 
     As used herein, the term “data processing unit” refers to any computer, cross-connect component, electronic switch, switch-fabric, portion of a switch-fabric, router, host device, data storage device, line card or the like used to process, transmit and/or convey electrical and/or optical signals. A data processing unit can include, for example, a component included within an electronic communications network. In some embodiments, for example, a data processing unit can be a component included within or forming a portion of a core cross-connect system (e.g., a core switch-fabric) of a data center. In other embodiments, a data processing unit can be an access switch located at an edge of a data center, or a host device (e.g., a server) coupled to the access device. For example, an access switch can be located on top of a chassis containing several host devices. 
     As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, the term “a line card” is intended to mean a single line card or multiple line cards, “a connector” is intended to mean one or more connectors, or a combination thereof. 
       FIG. 1  is a schematic block diagram of a cross-connect system  100  according to an embodiment. The cross-connect system  100  can include a set of devices and/or data processing units that are interconnected to route data (e.g., a data unit, a data packet, a data frame, a string of bit values and/or a payload of data) between various devices (not shown in  FIG. 1 ). For example, the cross-connect system  100  can include any number and/or any combination of the data processing units described above. The cross-connect system  100  can be included in, for example, a data center network or the like. In such embodiments, any suitable number of data processing units (e.g., line cards or the like) can be operably coupled via any suitable set of connectors or interfaces to form the cross-connect system  100 . 
     The cross-connect system  100  can be a cell-based fabric where one or more portions of data (e.g., data packets) are transmitted via the cross-connect system  100  in one or more cells (e.g., variable size cells, fixed size cells). In other words, an edge data processing device can provide a device, which can be configured to communicate via one protocol, with access to the cross-connect system  100 , which can be configured to communicate via another protocol. The cross-connect system  100 , which can be a multi-stage switch-fabric (e.g., 3-stage switch-fabric, 5-stage switch-fabric), can include multiple switch-fabrics. For example, the cross-connect system  100  can include an ingress stage, a middle stage, and an egress stage. In some embodiments, the cross-connect system  100  can be a reconfigurable (e.g., a rearrangeable) switch-fabric and/or a time-division multiplexed switch-fabric. In some embodiments, the cross-connect system  100  can be a cell-based switch-fabric configured to transmit one or more cells (e.g., fixed-size cells, variable-size cells) that can include various types of data such as portions of one or more data packets. In some embodiments, the cross-connect system  100  can be a lossless or substantially lossless switch-fabric (e.g., not based on lossy best-effort transmission protocol). In some embodiments, cross-connect system  100  can be defined based on a Clos network architecture (e.g., a strict sense non-blocking Clos network, a Benes network) and the cross-connect system  100  can include a data plane and a control plane. In this manner, the functionality of the cross-connect system  100  can be substantially related to routing and management of a data center network (not shown in  FIG. 1 ). 
     As shown in  FIG. 1 , the cross-connect system  100  can include and/or be formed of a number of line cards  130  (collectively referred to herein as a set of line cards  110 ) and a number of switch-fabric cards  150  (collectively referred to herein as a set of switch-fabric cards  120 ). While the set of line cards  110  and the set of switch-fabric cards  120  of the cross-connect system  100  are shown in  FIG. 1  as including three line cards  130  and three switch-fabric cards  150 , respectively, in other embodiments, a cross-connect system can include a set of line cards having any suitable number of line cards and a set of switch-fabric cards having a corresponding number of switch-fabric cards. 
     Each line card  130  of the set of line cards  110  can be, for example, a printed circuit board (PCB) that can include a number of compute components (not shown in  FIG. 1 ). For example, each line card  130  can include at least a memory and a processor to enable each line card  130  to process, transmit, route, direct, and/or otherwise convey an electrical or optical signal. In some embodiments, each line card  130  included in the set of line cards  110  can include a hardware module such as an application-specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA) and/or a software-based module (e.g., a module of computer code stored in memory and/or executed at the processor). In some embodiments, one or more of the functions associated with the line card  130  can be included in different modules and/or combined into one or more modules. In some embodiments, each line card  130  can include an external connector (not shown) that can operatively couple the cross-connect system to an external electronic device(s) (e.g., a portion of a data center or the like). Each switch-fabric card  150  of the set of switch-fabric cards  120  can be a PCB that can include a number of compute components, as described with reference to the line cards  130 . 
     Each line card  130  of the set of line cards  110  includes an edge portion  131 , a first side  132 , and a second side  133 . Furthermore, each line card  130  of the set of line cards  110  includes a first set of connectors  140 A disposed on the first side  132  of each line card  130  and a second set of connectors  140 B disposed on the second side  133  of each line card  130 . Similarly each switch-fabric  150  of the set of switch-fabric cards  120  includes an edge portion  151 , a first side  152 , and a second side  153 . Each switch-fabric card  150  of the set of switch-fabric cards  120  includes a first set of connectors  160 A and a second set of connectors  160 B. While the set of connectors  140 A,  140 B,  160 A,  160 B are represented in  FIG. 1  by a single entity (e.g., a single box), the set of connectors  140 A can include any number of connectors and the connectors  140 B,  160 A, and  160 B can each include a corresponding number of connectors. The arrangement of the sets of connectors  140 A,  140 B,  160 A, and  160 B are described herein with respect to specific embodiments. 
     As shown in  FIG. 1 , the set of line cards  110  and the set of switch-fabric cards  120  are arranged in a substantially orthogonal configuration. In other words, each line card  130  is arranged perpendicularly to each corresponding switch-fabric card  150 . For example, in some embodiments, the set of line cards  110  can be arranged in a substantially vertical direction (e.g., the edge portion  131  of each line card  130  is substantially parallel to a vertical axis) and the set of switch-fabric cards  120  can be arranged in a substantially horizontal direction (e.g., the edge portion  151  of each switch-fabric card  150  is substantially parallel to a horizontal axis). In this manner, each connector in the first set of connectors  140 A of each line card  130  can align with and couple to a corresponding connector in the first set of connectors  160 A of each switch-fabric card  150 . Similarly, each connector in the second set of connectors  140 B of each line card  130  can align with and couple to a corresponding connector in the second of connectors  160 B of each switch-fabric card  150 . 
       FIGS. 2-5  illustrate a cross-connect system  200  according to an embodiment. As shown in  FIG. 2 , a line card  230  can be disposed in a first configuration and can be coupled to one or more switch-fabric cards  250  in a second configuration. More specifically, the line card  230  and the switch-fabric card  250  can be arranged in an orthogonal configuration to form the cross-connect system  200 . For example, the line card  230  can be arranged in a substantially horizontal orientation (e.g., the first configuration) and the switch-fabric card  250  can be arranged in a substantially vertical orientation (e.g., the second configuration) such that the line card  230  and the switch-fabric card  250  are substantially perpendicular. In other embodiments, a cross-connect system can include line cards and switch-fabric cards in an opposite orientation (e.g., the line card  230  is arranged in a substantially vertical orientation and the switch-fabric card  250  is arranged in a substantially horizontal orientation). Although the cross-connect system  200  is shown for simplicity in  FIG. 2  as including a single line card  230  in the first configuration, the cross-connect system  200  can include a number of line cards  230  in the first configuration and a corresponding number of switch-fabric cards  250  in the second configuration (e.g., switch-fabric cards  250 ′ and  250 ″). Moreover, the switch-fabric cards  250 ′ and  250 ″ are substantially similar to or the same as the switch-fabric card  250 . Thus, a discussion of the switch-fabric card  250  applies to the switch-fabric cards  250 ′ and  250 ″ unless explicitly expressed otherwise. 
     The line card  230  and the switch-fabric card  250  can be substantially similar in function to any of those described herein. In this manner, the line card  230  and switch-fabric card  250  can include any number of compute components (e.g., a memory and/or a processor not shown in  FIGS. 2-5 ) that can receive, send, process, transmit, switch, route, direct, and/or otherwise convey an electrical or optical signal between the line card  230  and the switch-fabric card  250 . The line card  230  includes a printed circuit board (PCB)  236  ( FIG. 3 ) and a set of connectors  240  ( FIGS. 2-4 ) that are physically and electrically coupled to a set of connectors  260  of the switch-fabric card  250  ( FIGS. 2 and 5 ). As shown in  FIG. 3 , the PCB  236  of the line card  230  includes an edge portion  231 , a first side  232 , and a second side  233  that is opposite the first side  232 . The line card  230  includes a first set of connectors  240 A disposed along the edge portion  231  on the first side  232  of the PCB  236  and a second set of connectors  240 B disposed along the edge portion  231  on the second side  233  of the PCB  236 . 
     The connectors  240 A and  240 B can be disposed in any suitable arrangement relative to the PCB  236 . For example, as shown in  FIG. 3 , the connectors  240 A and  240 B can extend substantially perpendicularly from the first side  232  and the second side  233 , respectively, such that a connector  240 A disposed on the first side  232  of the line card  230  is substantially opposite a corresponding connector  240 B disposed on the second side  233  of the line card  230 . Said another way, the connectors  240 A and  240 B can be aligned along the edge portion such that an axis C 1  is substantially coaxial with a longitudinal centerline (not shown in  FIG. 3 ) of a pair of opposing connectors  240 A and  240 B (e.g., of the connectors  240 A and  240 B disposed on the top of the line card  230  in  FIG. 3 ). Furthermore, the connectors  240 A and  240 B extend from the first side  232  and the second side  233 , respectively, of the line card  230  such that an edge associated with a length L 1  of the connectors  240 A and  240 B is substantially perpendicular to the edge portion  231  associated with a length L 2  of the PCB  236 . The connectors  240 A and  240 B are symmetrically disposed along a length of the edge portion  231 . More specifically, the first set of connectors  240 A can be arranged in a pair  245 A such that a first distance D 1  is defined between the connectors  240 A of the pair  245 A, and a second distance D 2  is defined between adjacent pairs  245 A. The second set of connectors  240 B can be similarly arranged in pairs  240 B. 
     The connectors  240 A and  240 B can be any suitable configuration. For example, as shown in  FIG. 4 , the connector  240 A includes at least one ground contact  241 A having a first end portion  242 A and a second end portion  243 A, and at least one signal contact  246 A having a first end portion  247 A and a second end portion  248 A. The connector  240 B includes at least one ground contact  241 B having a first end portion  242 B and a second end portion  243 B, and at least one signal contact  246 B having a first end portion  247 B and a second end portion  248 B. As shown in  FIG. 4 , the first end portion  242 A of the ground contact  241 A included in the connector  240 A and the first end portion  242 B of the ground contact  241 B included in the connector  240 B are disposed within a via  234  included in or defined by the PCB  236  of the line card  230 . The via  234  included in the line card  230  extends through the first side  232  of the PCB  236  and the second side  233  of the PCB  236  such that the ground contact  241 A of the connector  240 A and the ground contact  241 B of the connectors  240 B are electrically coupled (e.g., by the conductive portion of the via  234 ) when disposed therein. More specifically, the first end portion  242 A of the ground contact  241 A and the first end portion  242 B of the ground contact  241 B can each include a press fit connector that is configured to engage the conductive portion of the via  234 . In this manner, the connector  240 A and the connector  240 B can share a common ground. 
     The second end portion  243 A of the ground contact  241 A included in the connector  240 A and the second end portion  243 B of the ground contact  241 B included in the connector  240 B can each be arranged, for example, as a female pin connector. For example, the second end portion  243 A of the ground contact  241 A can be configured to receive a second end portion of a ground contact that is arranged in a male configuration. In other embodiments, the second end portion of the ground contact can be, for example, a male pin connector. 
     The first end portion  247 A of the signal contact  246 A included in the connector  240 A and the first end portion  247 B of the signal contact  241 B included in the connector  240 B are each disposed within a semi-blind via  235 A and  235 B, respectively. For example, as shown in  FIG. 4 , the semi-blind via  235 A extends through the first side  232  of the PCB 236  and has a depth that is less than half of a thickness T 1  of the PCB 236 . Similarly, the semi-blind  235 B extends through the second side  233  of the PCB  236  and has a depth that is less than half of the thickness T 1 . Thus, the first end portion  247 A of the signal contact  246 A disposed within the semi-blind via  235 A is electrically isolated from the first end portion  247 B of the signal contact  246 B disposed within the semi-blind via  235 B. In this manner, the signal contact  246 A of the connector  240 A can be associated with a first signal and the signal contact  246 B of the connector  240 B can be associated with a second signal that is independent of the first signal. The second end portion  248 A of the signal contact  246 A included in the connector  240 A and the second end portion  248 B of the signal contact  246 B included in the connector  240 B can be arranged in a similar manner as the second end portion  243 A of the ground contact  241 A and, thus, are not described in further detail herein. Although the connectors  240 A and  240 B are shown, for simplicity, in  FIG. 4  as each including a single ground contact and a single signal contact, it should be understood that the connectors  240 A and  240 B can include any number of ground contacts and any number of signal contacts that can be arranged in a similar manner as described above. 
     As shown in  FIG. 5 , the switch-fabric card  250  includes a PCB  256  having an edge portion  251 , a first side  252 , and a second side  253 . The switch-fabric card  250  includes a first set of connectors  260 A disposed along the edge portion  251  on the first side of the PCB  256  and a second set of connectors  260 B disposed along the edge portion  251  on the second side of the PCB 256 . The connectors  260 A and  260 B can be, for example, substantially similar in form and function as the connectors  240 A and  240 B described above. Therefore, portions of the connectors  260 A and  260 B are not described in further detail herein. The connectors  260 A and  260 B can differ, however, by including a ground contact (not shown in  FIG. 5 ) and a signal contact (not shown in  FIG. 5 ) that are arranged to matingly couple to the connectors  240 A and  240 B. For example, in some embodiments, the second end portions  243 A and  243 B of the ground contacts  241 A and  241 B, respectively, and the second end portion  248 A and  248 B of the signal contacts  246 A and  246 B, respectively, can be arranged with a female connector (as described above) while the second end portions of the ground contacts and the signal contacts (not shown) of the connectors  260 A and  260 B, respectively, can be arranged with a male connector (or vice versa). 
     As shown in  FIG. 5 , the connectors  260 A and  260 B can extend substantially perpendicularly from the first side  252  of the PCB  256  and the second side  253  of the PCB  256 , respectively, such that a connector  260 A disposed on the first side  252  is substantially opposite a corresponding connector  260 B disposed on the second side  253  (as described above with reference to the connectors  240 A and  240 B). The connectors  260 A and  260 B extend from the first side  252  and the second side  253 , respectively, of the switch-fabric card  250  such that an edge associated with the length L 1  of the connectors  260 A and  260 B (i.e., the connectors  260 A and  260 B are substantially the same length L 1  of the connectors  240 A and  240 B) is substantially parallel to the edge portion  251  associated with the length L 2  of the PCB  256  (i.e., the PCB  256  of the switch-fabric card  250  is substantially the same length of the PCB  236  of the line card  230 ). The connectors  260 A and  260 B are symmetrically disposed along a length of the edge portion  251  of the PCB  256  of the switch-fabric card  250 . More particularly, each connector  260 A in the first set of connectors can be spaced at a substantially equal distance from adjacent connectors  260 A. Similarly, each connector  260 B in the second set of connectors can be spaced the substantially equal distance from adjacent connectors  260 B. 
     In some embodiments, disposing the connectors  260 A on the first side  252  of the switch-fabric card  250  and the connectors  260 B on the second side  253  of the switch-fabric card  250  increases the number of connectors that would otherwise be included in or on the switch-fabric card  250  (e.g., some known switch-fabric cards and/or line cards include connectors on a single side). Moreover, by disposing the connectors  260 A and  260 B on each side (e.g., the first side  252  of the PCB  256  and the second side  250 B of the PCB  256 , respectively) of the switch-fabric card  250 , the density of connectors for a given portion of the length L 2  of the PCB  256  is increased. In this manner, more connectors  260 A and  260 B can be disposed on the switch-fabric card  250  without increasing the length L 2  of the PCB  256 , as described in further detail herein. 
     Referring back to  FIGS. 3 and 5 , the line card  230  in the first configuration can be coupled to the switch-fabric card  250  (and the switch-fabric cards  250 ′ and  250 ″) in the second configuration. The arrangement of the connectors  240 A and  240 B of the switch-fabric card  250  is such that a first connector  240 A and a second connector  240 A of a pair  245 A (e.g., shown on the far left in  FIG. 3 ) are physically and electrically coupled to a corresponding connectors  260 A and  260 B, respectively, of the switch-fabric card  250 . Moreover, the distance D 1  defined between the connectors  240 A included in the pair  245 A can substantially correspond to a thickness T 2  ( FIG. 5 ) of the PCB  256  of the switch-fabric card  250 . Thus, the connectors  260 A and  260 B of the switch-fabric card  250  in the second configuration are substantially aligned with the connectors  240 A and  240 B of the line card  230 A in the first configuration to define at least a portion of the cross-connect system  200 . 
     As described above, disposing connectors  260 A and  260 B on each side on the switch-fabric card  250  increases the number of connectors per a unit of the length L 2  of the PCB  256 . In some instances, the increase in the number of connectors  260 A and  260 B can be associated with a greater utilization of the compute components (e.g., ASICs) disposed on the switch-fabric card  250 . For example, in some embodiments, a switch-fabric card (e.g., the switch-fabric card  250  shown in  FIG. 5 ) can include an ASIC with a switching capacity to support a number of line cards equal to a number of rows of connectors multiplied by a number of connectors per row. In other words, by disposing the connectors  260 A and  260 B on both sides of the switch-fabric card  250 , the switching capacity of the AISC can be maximized (e.g., with or near 100% utilization) with a switching capacity to support a number of line cards equal to a number of rows of connectors multiplied by a number of connectors per row. In some known cross-connect systems including the same number of rows of connectors, however, an ASIC of a switch-fabric card included in the known cross-connect system results in an underutilization of the ASIC (e.g., a 50% utilization). In other known cross-connect systems, the length of the switch-fabric card is increased to include more rows of connectors to achieve a similar utilization as the cross-connect system  200 ; such a longer switch-fabric card, however, may not be possible at higher operation frequencies. 
     In addition, the increase in the number of connectors  260 A and  260 B of the switch-fabric card  250  (e.g., compared to some known switch-fabric cards) is such that a fewer number of switch-fabric cards  250 ,  250 ′ and  250 ″ are included in the cross-connect system  200  to achieve a desired switch capacity. In this manner, the distance D 2  defined between the pairs  245 A and  245 B of the connectors  240 A and  240 B, respectively, increases the distances between the switch-fabric cards  250 ,  250 ′, and/or  250 ″ that would otherwise be defined therebetween. Thus, the increase in the distance between the switch-fabric cards  250 ,  250 ′, and  250 ″ can facilitate in a cooling of the compute components disposed on the line card  230  and/or the switch-fabric cards  250 ,  250 ′ and/or  250 ″ (e.g., via front to back cooling or the like) because a greater volume of air can pass between the line cards  230  and/or the switch-fabric cards  250 ,  250 ′, and/or  250 ″. 
     While the line card  230  in the first configuration is shown as being physically and electrically coupled to the switch-fabric card  250  having the connectors  260 A and  260 B disposed on the first side  252  of the PCB  256  and the second side  253  of the PCB  256 , respectively, in other embodiments, the arrangement of a line card in the first configuration can provide, for example, backwards compatibility with switch-fabric cards having connectors disposed on a single side of a PCB. For example, as shown in  FIG. 6 , a cross-connect system  300  can include a line card  330  in the first configuration and a first switch-fabric card  350  and a second switch-fabric card  350 ′ in a second configuration. The line card  330  can be substantially similar to or the same as the line card  230  described above with reference to  FIGS. 2-4 . In this manner, the line card  330  has a PCB  336  and a set of connectors  340  that can be arranged in the same arrangement as the connectors  240 A and  240 B of the line card  230  (see e.g.,  FIG. 3 ). For example, the set of connectors  340  can be arranged in pairs  345  in a similar manner as described above. Therefore, portions of the line card  330  are not described in further detail herein. 
     The switch-fabric cards  350  and  350 ′ each have a PCB  356  and  356 ′, respectively, that include an edge portion  351  and  351 ′, respectively, and a side portion  352  and  352 ′, respectively. As shown, the switch-fabric card  350  includes a set of connectors  360  that are disposed along the edge portion  351  on the side portion  352  of the PCB  356 . Similarly, the switch-fabric card  350 ′ includes a set of connectors  360 ′ that are disposed along the edge portion  351 ′ on the side portion  352 ′ of the PCB  356 ′. In some embodiments, the arrangement of the switch-fabric card  350  and the switch-fabric card  350 ′ can be substantially the same. In some embodiments, the switch-fabric card  350  and/or the switch-fabric card  350 ′ can be substantially similar to known switch-fabric cards having a set of connectors disposed on a single side of the switch-fabric card and forming a portion of a cross-connect system. 
     As shown in  FIG. 6 , the switch-fabric card  350  and the switch-fabric card  350 ′ can be disposed adjacent to one another a mirrored orientation. More specifically, the arrangement of the switch-fabric cards  350  and  350 ′ in the cross-connect system  300  is such that both of the sets of connectors  360  and  360 ′ are disposed between the side portions  352  of the PCB  356  and side portion  352 ′ of the PCB  356 ′. The switch-fabric card  350  can be arranged, relative to the line card  330 , such that one of the connectors from the set of connectors  360  is disposed opposite a first connector  340  of the pair of connectors  345 . Similarly, the switch-fabric card  350 ′ can be arranged, relative to the line card  330 , such that one of the connectors from the set of connectors  360 ′ is disposed opposite a second connector  340  of the pair of connectors  345 . Although the line card  330  is shown with three pairs of connectors  345 , in other embodiments, a line card in the first configuration can include any number of pairs. In this manner, a corresponding number of switch-fabric cards in the second configuration (e.g., the switch-fabric cards  350  and  350 ′) can be physically and electrically coupled to the line card in the first configuration to for a cross-connect system. 
     While the switch-fabric cards  350  and  350 ′ in the second configuration are shown in a mirrored arrangement to form at least a portion of the cross-connect system  300 , in other embodiments, a cross-connect system can include switch-fabric cards in the second configuration in any suitable arrangement within the cross-connect system. For example,  FIG. 7  is an illustration of a cross-connect system  400  according to an embodiment. The cross-connect system  400  includes a line card  430  in a first configuration and a first switch-fabric card  450  and a second switch-fabric card  450 ′ in a second configuration. The line card  430  can be substantially similar in form and function as the line card  230  described above with reference to  FIGS. 2-4 . In this manner, the line card  430  includes a set of connectors  440  that can be arranged in pairs  445 , as described in detail above with reference to  FIG. 3 . The switch-fabric cards  450  and  450 ′ can each be substantially similar in form and function to the switch-fabric cards  350  and  350 ′, respectively. In this manner, the switch-fabric cards  450  and  450 ′ each include a set of connectors  460  and  460 ′, respectively, that are arranged in a similar manner as the connectors  360  and  360 ′ of the switch-fabric cards  350  and  350 ′. 
     As shown in  FIG. 7 , the switch-fabric card  450  and the switch-fabric card  450 ′ can be disposed adjacent to one another with each having the same orientation. The switch-fabric card  450  can be arranged, relative to the line card  430 , such that one of the connectors from the set of connectors  460  is disposed opposite a first connector  440  of a first pair of connectors  445  (e.g., the right side connector  440  included in the pair of connectors  445  that are disposed on the far left of the line card  430  in  FIG. 7 ). The switch-fabric card  450 ′ can be arranged, relative to the line card  430 , such that one of the connectors from the set of connectors  460 ′ is disposed opposite a first connector  440  of a second pair of connectors  445 . Similarly stated, the arrangement of the switch-fabric cards  450  and  450 ′ relative to the line card  430  is such that one of the connectors of the switch-fabric card  450  is physically and electrically coupled to one of the connectors  440  of a first pair  445  and the switch-fabric card  450 ′ is physically and electrically coupled to an adjacent connector  440  included in an adjacent pair of connectors  445 , as shown in  FIG. 7 . Although the line card  430  is shown with three pairs of connectors  445 , in other embodiments, a line card in the first configuration can include any number of pairs. In this manner, a corresponding number of switch-fabric cards in the second configuration (e.g., the switch-fabric cards  450  and  450 ′) can be physically and electrically coupled to the line card in the first configuration to form a cross-connect system. 
     Although not shown in  FIGS. 2-7 , in some embodiments, a line card in the first configuration (e.g., the line card  230 , the line card  330 , and/or the line card  430 ) can be physically and electrically coupled to a set of switch-fabric cards in various configurations. For example, in some embodiments, a cross-connect system can be formed from one or more line cards in the first configuration that are physically and electrically coupled to one or more switch-fabric cards including connectors on a single side (e.g., the switch-fabric cards  350 ,  350 ′,  450  and/or  450 ′) and one or more switch-fabric cards including connectors on both sides (e.g., the switch-fabric card  250 ). 
     Although the cross-connect systems  200 ,  300 , and  400  have been shown and described above as being without a midplane, in some embodiments, a cross-connect system can include a midplane disposed between one or more line cards in a first configuration and one or more switch-fabric cards in a second configuration. For example,  FIGS. 8 and 9  are a front perspective view and a rear perspective view, respectively, of a cross-connect system  500  according to an embodiment. The cross-connect system  500  includes a line card  530  in the first configuration, a switch-fabric card  550  in a second configuration, and a midplane  570  disposed therebetween. The line card  530  includes a set of connectors  540 . The line card  530  can be substantially similar to the line card  230  described above with reference to  FIGS. 2-4 . The switch-fabric card  550  includes a set of connectors  560  disposed on each side of the switch-fabric card  550 . The switch-fabric card  550  can be substantially similar to the switch-fabric card  250  described above with reference to  FIGS. 2 and 5 . Therefore, portions of the line card  530  and the switch-fabric card  550  are not described in further detail herein. 
     The midplane  570  has a first side  571  and a second side  572 . The first side  571  of the midplane  570  includes a set of connectors  575 A. The second side  572  of the midplane  570  includes a set of connectors  575 B, each of which is disposed opposite a connector  575 A on the first side  571 . As shown in  FIGS. 8 and 9 , the connectors  575 A and  575 B can be arranged on the midplane  570  in pairs as described above with reference to the line card  230 . In this manner, the midplane  570  can include an array of connectors  575 A and  575 B that can be substantially symmetric. Said another way, the pairs of the connectors  575 A and  575 B can be arranged in a matrix on the midplane  570 . In some embodiments, the matrix of the pair of connectors  575 A and  575 B can be square (e.g., the matrix can include a set of rows formed from a number of connector pairs and a set of columns formed from the number of connector pairs). 
     As shown in  FIGS. 8 and 9 , the arrangement of the connectors  575 A is such that the line card  530  in the first configuration can be physically and electrically coupled to a portion of the connectors  575 A disposed on the first side  571  of the midplane  570 . More specifically, the line card  530  can include a set of connectors  540  disposed on each side of the line card  530  such that when the line card  530  is coupled to the midplane  570 , the connectors  540  of the line card  530  are physically and electrically coupled to a first row of connectors  575 A and a second row of connectors  575 B. In a similar manner, the arrangement of the connectors  575 B disposed on the second side  572  of the midplane  570  is such that the switch-fabric card  550  in the second configuration can be physically and electrically coupled to a portion of the connectors  575 B. As described above, the switch-fabric card  550  can include a set of connectors  560  disposed on each side of the switch-fabric card  550  such that when the switch-fabric card  550  is coupled to the midplane  570 , the connectors  560  of the switch-fabric card  550  are physically and electrically coupled to a first column of connectors pairs (described above). With the line card  530  coupled to the first side  571  of the midplane  570  and with the switch-fabric card  550  coupled to the second side  572  of the midplane  570 , the midplane  570  can be configured to place the line card  530  in the first configuration in electrical communication with the switch-fabric card  550  in the second configuration, via the connectors  575 A and  575 B such that a data unit (e.g., a data cell, data frame, data packet, string of bits, and/or data payload) can be conveyed therebetween. As described above with reference to the cross-connect system  200  of  FIGS. 2-5 , the arrangement of the line card  530 , the midplane  570 , and the switch-fabric card  550  can increase the density of the connectors  540 ,  575 , and/or  560 , respectively, disposed thereon. Thus, the line card  530  and the switch-fabric card  550  can have an overall length that can be less than an overall length that would otherwise be associated with a line card without a midplane between the line cards and the switch-fabric cards. Moreover, because of the symmetry of the cross-connect system  500 , a connector surface of the midplane  570  (e.g., the surface of the midplane  570  on which the connectors  575 A or  575 B are disposed) can have an area that can be less than an area that would otherwise be associated with a connector surface of a midplane. In this manner, the cross-connect system  500  can accommodate, for example, components having a higher operating frequency that would otherwise be incompatible with longer switch-fabric cards and/or larger midplanes. 
       FIG. 10  is a flowchart illustrating a method  690  for forming a printed circuit board assembly according to an embodiment. The method  690  includes forming a set of connector-receiving portions in a printed circuit board (PCB) with each set of the connector-receiving portions having a via and a semi-blind via, at  691 . The connector-receiving portions can be, for example, a region of the PCB configured to be coupled to a connector. In some embodiments, each connector-receiving portion can include a number of vias and the number of semi-blind vias. For example, connector-receiving portions can include one via and one semi-blind via. In some embodiments, the connector-receiving portion can include one via and more than one semi-blind via (e.g., two, three, four, five, six, seven, eight, nine, ten, fifteen, twenty, thirty, fifty, and/or any other suitable number). In some embodiments, the via can be a through via that extends through all of the layers of the PCB. In some embodiments, the semi-blind via can extend through a portion of the layers of the PCB (e.g., less than half the layers of the PCB). The via of the receiving portion can be associated with, for example, a ground contact and the semi-blind via of the receiving portion can be associated with, for example, a signal contact. In some embodiments, the PCB can include a connector-receiving portion disposed on a first side of the PCB and a corresponding connector-receiving portion disposed on a second side of the PCB. More specifically, a connector-receiving portion of the second side of the PCB can be opposite a corresponding connector-receiving portion of the first side of the PCB. In such embodiments, the connector-receiving portion on the first side and the connector-receiving portion of the second side can include the same via. Said another way, the via of the connector-receiving portion of the first side can be the via of the corresponding connector-receiving portion of the second side (as shown, for example, in  FIG. 4 ). 
     A first set of connectors are coupled to the first side of the PCB that is opposite a second side of the PCB, at  692 . Each connector from the first set of connectors includes a ground contact and a signal contact. The coupling of a connector to the first side of the PCB can include disposing a portion of the ground contact of the connector within the via. More specifically, the portion of the ground contact can be electrically coupled to the via (e.g., placed in electrical communication) when the portion of the ground contact is physically disposed within the via. For example, as shown in  FIG. 4 , a portion of the ground contact can be placed in contact with a surface of the via to place the ground contact in electrical communication with the via. Similarly, the coupling of the connector to the first side of the PCB can include disposing a portion of the signal contact of the connector within the semi-blind via. Thus, the signal contact can be physically and electrically coupled to the semi-blind via (as described above). In this manner, the signal contact and the ground contact of each connector included in the set of connectors can be placed in electrical communication with a conductive trace on the PCB. 
     A second set of connectors are coupled to the second side of the PCB such that each connector included in the first set of connectors is located opposite a unique connector form the second set of connectors, at  693 . Each connector from the second set of connectors includes a ground contact and a signal contact. The coupling of a connector of the second set of connectors to the second side of the PCB can include disposing a portion of the ground contact of the connector within the via. More specifically, with each connector of the second set of connectors being disposed opposite a corresponding connector of the first set of connectors, the portion of the ground contact of the connector included in the second set and the portion of the ground contact of the connector included in the first set each occupy the same via. Said another way, the ground contact for each connector from the first set of connectors is electrically coupled to the corresponding ground contact for each connector from the second set of connectors through the via. For example, as shown in  FIG. 4 , the ground contact  241 A of the first connector  240 A is electrically coupled to the ground contact  241 B of the second connectors  240 B through the via  234  of the line card  230 . 
     The coupling of each connector to the second side of the PCB can include disposing a portion of the signal contact of each connector within the corresponding semi-blind via of the connector-receiving portion. Thus, the signal contact can be physically and electrically coupled to the semi-blind via (as described above). In this manner, the ground contacts of each connector disposed on the first side of the PCB are in electrical communication with the ground contacts of the corresponding connector disposed on the second side of the PCB though the via while the signal contact of each connector disposed on the first side of the PCB is electrically isolated from the signal contact of the corresponding connector disposed on the second side of the PCB through the semi-blind vias. 
     While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Where methods and/or schematics described above indicate certain events and/or flow patterns occurring in certain order, the ordering of certain events and/or flow patterns may be modified. While the embodiments have been particularly shown and described, it will be understood that various changes in form and details may be made. For example, although the midplane  570  is shown in  FIG. 8  as having the line card  530  in the first configuration coupled to the first side  571  of the midplane  570  and the switch-fabric card  550  in the second configuration coupled to the second side  572  of the midplane  570 , in other embodiments, the switch-fabric card in the second configuration can be coupled to the first side of the midplane and the line card in the first configuration can be coupled to the second side of the midplane. 
     Although various embodiments have been described as having particular features and/or combinations of components, other embodiments are possible having a combination of any features and/or components from any of embodiments as discussed above.