Patent Publication Number: US-9407045-B2

Title: Electrical connector with joined ground shields

Description:
BACKGROUND OF THE INVENTION 
     The subject matter herein relates generally to electrical connectors that have ground shields and signal contacts. 
     Some known electrical connectors are mezzanine connectors that mechanically and electrically interconnect a pair of circuit boards in a parallel arrangement. In some connector arrangements, a single mezzanine connector will engage both circuit boards to interconnect the circuit boards. For example, the mezzanine connector will be mounted to one of the circuit boards and will engage the other circuit board at a separable mating interface. At least some known mezzanine connector systems utilize two mezzanine connectors, each mounted to a different circuit board and then mated together. Such systems can be complex and difficult to manufacture. For example, such mezzanine connectors have many contacts individually loaded into a housing, which may be difficult and time consuming to assemble. Furthermore, the contacts may be deflectable spring beams that require long beam lengths to achieve the required spring force and deformation range at the mating interface between the two connectors. The mezzanine connectors have ground shields that are designed to shield individual contacts or contact pairs along the beam length. But, known mezzanine connectors suffer from signal performance limits because the ground shields are not electrically commoned with each other along the length of the connectors. For example, the ground shields may be electrically commoned at the circuit boards, but a lack of commoning along the beam lengths and at the mating interface results in electrical interference that is detrimental to the signal integrity of the mezzanine connectors. 
     Thus, a need exists for an electrical connector having an array of signal contacts and enhanced ground shielding that improves electrical performance. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, an electrical connector is provided that includes a housing, signal contacts, and ground shields. The housing extends between a front end and an opposite, rear end. The housing defines a cavity at the front end. The signal contacts are held by the housing. The signal contacts are arranged in pairs carrying differential signals. The signal contacts have mating ends in the cavity for mating with a mating connector. The ground shields are held by the housing. The ground shields extend along the signal contacts in the cavity. The ground shields have center walls and side walls surrounding associated pairs of the signal contacts on at least two sides thereof. 
     The ground shields each have a commoning feature extending outward from a corresponding side wall. The commoning feature mechanically engages another ground shield in a group of ground shields to electrically join the ground shields of the group within the cavity. 
     In another embodiment, an electrical connector is provided that includes a housing, signal contacts, and ground shields. The housing extends between a front end and an opposite, rear end. The housing defines a cavity at the front end. The signal contacts are held by the housing. The signal contacts have mating ends in the cavity for mating with a mating connector. The ground shields are held by the housing. The ground shields extend along the signal contacts in the cavity and are arranged in an array of rows and columns. The ground shields each have one center wall and two side walls. The side walls extend from opposing ends of the center wall. At least one of the side walls of each ground shield has a commoning feature extending outward from the respective side wall. The commoning feature of a first ground shield of the ground shields mechanically engages a second ground shield of the ground shields such that the first and second ground shields are electrically joined with each other. The first and second ground shields are within a first row of the rows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an electrical assembly formed in accordance with an embodiment. 
         FIG. 2  is a perspective view of a header connector of the electrical assembly in accordance with an embodiment. 
         FIG. 3  is a cross-section of a portion of the header connector according to an embodiment. 
         FIG. 4  is a perspective view of a ground shield of the header connector according to another embodiment. 
         FIG. 5  is a cross-sectional bottom view of a portion of the header connector having the ground shield of  FIG. 4 . 
         FIG. 6  is a perspective view of a ground shield of the header connector according to another embodiment. 
         FIG. 7  is a perspective front view of a portion of the header connector having the ground shield of  FIG. 6 . 
         FIG. 8  is a perspective view of a ground shield of the header connector according to another embodiment. 
         FIG. 9  is a perspective front view of a portion of the header connector having the ground shield of  FIG. 8 . 
         FIG. 10  is a perspective view of a portion of a ground shield of the header connector according to another embodiment. 
         FIG. 11  is a perspective front view of a portion of the header connector having the ground shield of  FIG. 10 . 
         FIG. 12  is a perspective view of a portion of a ground shield of the header connector according to another embodiment. 
         FIG. 13  is a cross-sectional view of a portion of two ground shields mechanically engaged to each other according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a connector assembly  100  formed in accordance with an embodiment. The connector assembly  100  includes a first electrical connector  102  and a second electrical connector  104  that are mated together to electrically connect first and second circuit boards  106 ,  108 . The first electrical connector  102  and the second electrical connector  104  are arranged to interconnect the first and second circuit boards  106 ,  108 . The first connector  102  and the second connector  104  may be mezzanine connectors that connect the circuit boards  106 ,  108  in a parallel arrangement. However, it is realized that the subject matter herein may be used in other types of electrical connectors as well, such as right angle connectors, cable connectors (being terminated to an end of one of more cables), or other types of electrical connectors. In an embodiment, the first electrical connector  102  is a header connector  102  and the second electrical connector  104  is a receptacle connector  104 . The terms “header connector  102 ” and “receptacle connector  104 ” are used herein to identify the first electrical connector  102  and the second electrical connector  104 , respectively. The header connector  102  and the receptacle connector  104  may also be referred to herein as “mezzanine header connector  102 ” and “mezzanine receptacle connector  104 ,” respectively. 
     The circuit boards  106 ,  108  are interconnected by the header and receptacle connectors  102 ,  104  so that the circuit boards  106 ,  108  are substantially parallel to one another. The first and second circuit boards  106 ,  108  include conductors that communicate data signals and/or electric power between the header and receptacle connectors  102 ,  104  and one or more electrical components (not shown) that are electrically connected to the circuit boards  106 ,  108 . The conductors may be embodied in conductive pads or traces deposited on one or more layers of the circuit boards  106 ,  108 , in plated vias, or in other conductive pathways, contacts, and the like. 
     The header connector  102  includes a mating interface  110  and a mounting interface  112 . The mating interface  110  is configured to mate with the receptacle connector  104 . The mounting interface  112  is configured to mount to the first circuit board  106 . For example, the header connector  102  includes plural conductive tails  114  that extend along the mounting interface  112  and are configured to be electrically terminated to the conductors on the circuit board  106 . The conductive tails  114  may be compliant pins configured to be received in plated vias of the circuit board  106 . Although the mating interface  110  is shown as being on an opposite end of the header connector  102  relative to the mounting interface  112 , in other embodiments the mating interface  110  may be adjacent to the mounting interface  112 , such as for a right angle connector. The receptacle connector  104  also includes a mating interface  116  that mates to the header connector  102  and a mounting interface  118  that mounts to the second circuit board  108 . The receptacle connector  104  includes conductive tails  120  extending from the mounting interface  118  that are configured to electrically terminate to the conductors on the circuit board  108 . 
       FIG. 2  is a perspective view of the mezzanine header connector  102  in accordance with an embodiment. The mezzanine header connector  102  includes a housing  122  that holds signal contacts  128  and ground shields  130 . The housing  122  extends between a front end  124  and an opposite, rear end  126 . As used herein, relative or spatial terms such as “top,” “bottom,” “left,” “right,” “front,” and “rear” are only used to distinguish the referenced elements and do not necessarily require particular positions or orientations in the mezzanine connector assembly  100  (shown in  FIG. 1 ), in the mezzanine header connector  102  specifically, or in the surrounding environment. The front end  124  includes the mating interface  110 . The housing  122  defines a cavity  132  at the front end  124 . The cavity  132  is configured to receive at least a portion of the mating interface  116  (shown in  FIG. 1 ) of the receptacle connector  104  ( FIG. 1 ) when the connectors  102 ,  104  are mated. The housing  122  includes sides  134  that define a perimeter of the housing  122  between the front end  124  and the rear end  126 . Optionally, the housing  122  may be generally box shaped, although the housing  122  may have other shapes in alternative embodiments. The housing  122  is formed of a dielectric material, such as a plastic. 
     The signal contacts  128  are held by the housing  122  and extend into the cavity  132  from a rear wall  136  (shown in  FIG. 3 ) of the housing  122 . For example, the signal contacts  128  have mating ends  138  in the cavity  132 . The signal contacts  128  are conductive and are configured to mechanically engage corresponding receptacle contacts (not shown) of the mezzanine receptacle connector  104  (shown in  FIG. 1 ). Optionally, the signal contacts  128  are arranged in pairs carrying differential signals. In the illustrated embodiment, the mating ends  138  of the signal contacts  128  are arranged in an array of rows  140  and columns  142  within the cavity  132  of the housing  122 . The rows  140  and columns  142  are both parallel to a mounting surface  144  of the first circuit board  106 . In the illustrated embodiment, the rows  140  are oriented horizontally and the columns  142  are oriented vertically. 
     The ground shields  130  are held by the housing  122  and extend along the signal contacts  128  within the cavity  132 . For example, each ground shield  130  may peripherally surround an associated signal contact  128  or pair of signal contacts  128  on at least two sides thereof along a length between the rear wall  136  (shown in  FIG. 3 ) and the mating end  138  of the associated signal contact(s)  128 . The ground shields  130  are conductive and provide electrical shielding between the associated signal contact(s)  128  and other signal contacts  128  in the cavity  132 . The ground shields  130  are arranged in the rows  140  and columns  142  of the signal contacts  128 . As will be described below, at least some of the ground shields  130  are electrically joined or commoned with each other within the cavity  132  of the housing  122 . As used herein, “electrically join” and “electrically common” are used synonymously to mean connection via a continuous conductive electrical pathway. Electrically commoning at least some of the ground shields  130  within the housing  122  may improve electrical performance of the connector assembly  100  (shown in  FIG. 1 ) by canceling and/or reducing signal noise (for example, cross-talk), improving inter-pair signal skew, providing a pre-determined impedance, raising resonant frequencies to a range outside of operating frequency levels, and/or the like. The ground shields  130  may be electrically joined via mechanical engagement of the ground shields  130  so as to provide a continuous electrical pathway from any one ground shield  130  of a group of connected ground shields  130  to all other ground shields  130  in the group. The group of connected ground shields  130  may include multiple ground shields  130  in the same row  140 , multiple ground shields  130  in the same column  142 , or both. 
       FIG. 3  is a cross-section of a portion of the mezzanine header connector  102  according to an embodiment. The cross-section extends through the rear wall  136  of the housing  122 . In the illustrated embodiment, the signal contacts  128  are arranged in pairs that carry differential signals. In alternative embodiments, the signal contacts  128  may carry single-ended signals rather than differential signals. In other alternative embodiments, the signal contacts  128  may carry power rather than data signals. The signal contacts  128  in the illustrated embodiment are held on dielectric rails  146 . Optionally, the rails  146  may each be part of a single dielectric holder that is overmolded over and/or around a leadframe that includes the signal contacts  128 . In alternative embodiments, the signal contacts  128  may be coupled to the rails  146  by methods other than overmolding, such as via fasteners and/or adhesives. 
     The rails  146 , with the signal contacts  128  thereon, extend through openings  148  in the rear wall  136 . Optionally, the rails  146  may be loaded into the cavity  132  through the openings  148  from behind the rear wall  136  of the housing  122 . The rails  146  extend along generally linear paths. The rails  146  define front support beams  150  that are cantilevered forward of the rear wall  136  in the cavity  132 . The front support beams  150  support portions of the signal contacts  128 . The front support beams  150  have ramped lead-ins  152  that lead to the signal contacts  128 . The lead-ins  152  prevent stubbing when the header connector  102  is mated with the mezzanine receptacle connector  104  (shown in  FIG. 1 ). In an embodiment, the signal contacts  128  are exposed along an outer side  154  of each corresponding rail  146 . For example, the dielectric rail  146  is overmolded around the signal contacts  128  such that side surfaces  156  of the signal contacts  128  are flush with and exposed at the outer side  154 . In the illustrated embodiment, the two signal contacts  128  of each pair are arranged side-by-side along the same outer side  154  of the corresponding rail  146 . In an alternative embodiment, one signal contact  128  is disposed along the outer side  154 , and the other signal contact  128  of the pair is disposed along an opposite outer side (not shown) of the rail  146 . 
     Each of the ground shields  130  peripherally surrounds an associated pair of the signal contacts  128  in the illustrated embodiment. For example, the ground shields  130  have center walls  158  and side walls  160  that surround the pairs of signal contacts  128  on at least two sides. In the illustrated embodiment, each of the ground shields  130  is C-shaped, covering three sides of the associated pair of signal contacts  128 . The ground shields  130  each include one center wall  158  and two side walls  160 . The two side walls  160  extend from opposite ends  162  of the center wall  158 . 
     Optionally, the side walls  160  may extend parallel to each other and perpendicular to the center wall  158 . Since the ground shield  130  is C-shaped, one side of the ground shield  130  is open. In the illustrated embodiment, each of the ground shields  130  has an open bottom, and an adjacent ground shield  130  below the open bottom provides shielding across the open bottom. For example, the adjacent ground shield  130  that provides shielding across the open bottom may be in the same column  142  but a different row  140  from the associated ground shield  130 . Each pair of signal contacts  128  is therefore surrounded on all four sides thereof by the associated C-shaped ground shield  130  and the adjacent ground shield  130  below the pair of signal contacts  128 . As such, the ground shields  130  cooperate to provide circumferential electrical shielding for each pair of signal contacts  128 . The ground shields  130  electrically shield each pair of signal contacts  128  from every other pair of signal contacts  128 . For example, the ground shields  130  may span all direct line paths from any one pair of the signal contacts  128  to any other pair of the signal contacts  128  to provide electrical shielding across all of the direct line paths. 
     In alternative embodiments, other types of ground shields  130  may be provided. For example, L-shaped ground shields may be used that provide shielding on two sides of the associated pair of signal contacts  128 . Cooperation with other ground shields  130  provides electrical shielding on all sides (for example, above, below, and on both sides of the pair). In some other embodiments, the ground shields  130  may be associated with individual signal contacts  128  as opposed to pairs of signal contacts  128 . 
     The ground shields  130  are loaded into the cavity  132  from the front end  124  (shown in  FIG. 2 ) of the housing  122 . The housing  122  defines slots  164  in the rear wall  136  that receive rear portions  166  of the ground shields  130 . Optionally, some of the slots  164  are sized to accommodate one side wall  160  from each of two adjacent ground shields  130  in the same row  140 . The ground shields  130  are held in the slots  164  by an interference fit. The ground shields  130  may be loaded into the cavity  132  one at a time. 
     In an exemplary embodiment, the ground shields  130  have at least one commoning feature  168  extending outward from a corresponding side wall  160 . Each commoning feature  168  mechanically engages another ground shield  130  in a same group of ground shields  130  to electrically join or common the ground shields  130  of the group. The commoning feature  168  engages the other ground shield  130  in the cavity  132  of the housing  122 . As a result, the ground shields  130  of the group are electrically commoned proximate to the separable mating interface between the header connector  102  and the receptacle connector  104  (shown in  FIG. 1 ). 
     In an embodiment, the commoning feature  168  extends from the corresponding side wall  160  of a first ground shield  130 A and engages, directly or indirectly, one of the side walls  160  of a second ground shield  130 B. The commoning feature  168  engages the side wall  160  of the second ground shield  130 B directly when the commoning feature  168  physically contacts a planar surface of the side wall  160 . The commoning feature  168  engages the side wall  160  of the second ground shield  130 B indirectly when the commoning feature  168  physically contacts a component on or extending from the side wall  160 , such as another commoning feature  168 . The first and second ground shields  130 A,  130 B that engage each other are in the same row  140  within the cavity  132 . For example, the commoning feature  168  of the first ground shield  130 A extends at least partially across a gap  170  between adjacent ground shields  130  in the same row  140  to engage the side wall  160  of the second shield  130 B. Thus, the group of ground shields  130  that are electrically commoned may be the ground shields  130  in each row  140 . For example, the commoning feature  168  of the first ground shield  130 A mechanically engages the second ground shield  130 B, which is adjacent to the first ground shield  130 A on one side of the first ground shield  130 A. Furthermore, a different side wall  160  of the first ground shield  130 A may be mechanically engaged by the commoning feature  168  of a third ground shield  130 C that is adjacent to the first ground shield  130 A on a second side of the first ground shield  130 A. As such, the first ground shield  130 A is disposed between the third ground shield  130 C and the second ground shield  130 B in the same row  140 , and all three ground shields  130 A- 130 C are electrically commoned via the commoning features  168 . 
     In an embodiment, the side walls  160  of each ground shield  130  include a left side wall  160 A and a right side wall  160 B. One or both of the left and right side walls  160 A,  160 B may include the commoning feature  168  thereon. The commoning feature  168  on the right side wall  160 B is configured to mechanically engage the left side wall  160 A (or a commoning feature  168  on the left side wall  160 A) of an adjacent ground shield  130  in the row  140  to the right. Conversely, the commoning feature  168  on the left side wall  160 A is configured to mechanically engage the right side wall  160 B (or a commoning feature  168  on the right side wall  160 B) of an adjacent ground shield  130  in the row  140  to the left. 
     In the illustrated embodiment, the commoning feature  168  is a convexity  172  that protrudes outwards from the corresponding side wall  160 . For example, the convexity  172  may be a bulge, a boss, or a protuberance that extends out of plane of the corresponding side wall  160 . The convexity  172  may deflect at least partially inwards (for example, towards an interior of the ground shield  130 ) upon mechanically engaging the adjacent ground shield  130  in the group. The convexity  172  applies a biasing force on the adjacent ground shield  130  to retain mechanical engagement therewith. In the illustrated embodiment, the ground shields  130  include one commoning feature  168  on each of the side walls  160 A,  160 B. In addition, the commoning feature  168  on both side walls  160 A,  160 B optionally is an identical convexity  172 . For example, the convexity  172  on the right side wall  160 B engages the ground shield  130  to the right within the row  140 , and the convexity  172  on the left side wall  160 A engages the ground shield  130  to the left within the row  140 . As a result, the convexity  172  on the right side wall  160 B engages a different ground shield in the group than the convexity  172  on the left side wall  60 A. Optionally, the convexities  172  are all disposed a same distance from the rear wall  136 , and the convexity  172  on the right side wall  160 B of the first ground shield  130 A engages the convexity  172  on the left side wall  160 A of the adjacent second ground shield  130 B. Thus, the contacting convexities  172  each extend half of the full width of the gap  170  separating the ground shields  130 A,  130 B and engage each other in the gap  170 . 
     In alternative embodiments, the commoning features  168  on the left side walls  160 A may be different than the commoning features  168  on the right side walls  160 B. The commoning features  168  in one or more alternative embodiments are disposed on only one of the side walls  160  of each ground shield  130  instead of on both. Furthermore, the commoning features  168  in other embodiments have shapes and orientations different from the convexities  172 , as shown and described in the embodiments below. 
       FIG. 4  is a perspective view of a ground shield  130  of the mezzanine header connector  102  (shown in  FIG. 1 ) according to another embodiment. 
       FIG. 5  is a cross-sectional bottom view of a portion of the mezzanine header connector  102  having the ground shield  130  shown in  FIG. 4 . The ground shield  130  has a center wall  158  and two side walls  160  like the ground shield  130  shown in  FIG. 3 . The ground shield  130  extends between a front end  176  and a rear end  178 . The front end  176  is configured to mechanically engage and electrically connect to a receptacle ground shield (not shown) of the mezzanine receptacle connector  104  (shown in  FIG. 1 ). Sections near the front end  176  may be plated for enhanced durability at mating interfaces that engage the receptacle connector  104 . The rear portion  166  of the ground shield  130  that is received in the slot  164  of the housing  122  includes the rear end  178 . The ground shield  130  defines an interior region  182  that is between the two side walls  160 . In an exemplary embodiment, the ground shield  130  is stamped and formed from a panel of metal or another conductive material. For example, the side walls  160  are bent out of plane of the center wall  158  to define the side walls  160 . In addition, the commoning feature  168  is integral with the corresponding side wall  160  from which the commoning feature extends. Thus, the commoning feature  168  is bent or otherwise formed out of the corresponding side wall  160 . 
     In the illustrated embodiment, the commoning feature  168  is a spring arm  180 . The spring arm  180  is cut and bent out of plane of the corresponding side wall  160 . In the illustrated embodiment, both the left side wall  160 A and the right side wall  160 B include a spring arm  180 . As shown in  FIG. 5 , the spring arm  180  on the right side wall  160 B of a first ground shield  130 A extends partially across the gap  170  between the first ground shield  130 A and a second ground shield  130 B to engage the spring arm  180  on the left side wall  160 A of the second ground shield  130 B. In an alternative embodiment, the spring arm  180  on the right side wall  160 B of the first ground shield  130 A extends fully across the gap  170  and engages the left side wall  160 A of the second ground shield  130 B. In the alternative embodiment, the left side wall  160 A either does not have a spring arm  180  or the spring arm  180  of the left side wall  160 A is at a different location along the side wall  160 A such that the spring arm  180  does not engage the spring arm  180  of the right side wall  160 B of the adjacent ground shield  130 A. 
     In the illustrated embodiment, each spring arm  180  extends outward from the corresponding side wall  160 . The spring arms  180  each extend outward to an end  184  having an engagement surface  186 . The spring arm  180  is configured to physically contact the adjacent ground shield at the engagement surface  186 . The end  184  of each spring arm  180  is resiliently deflectable along an arc  188  in a direction  190  from the natural resting position of the spring arm  180  shown in  FIG. 4 . The resilience of the spring arm  180  (i.e., the bias of the end  184  of the spring arm  180  to the natural resting position thereof) generates an engagement force between the engagement surface  186  and the adjacent ground shield  130  within the same row  140  to provide a reliable engagement and thus electrical connection between the two ground shields  130 . 
       FIG. 6  is a perspective view of a ground shield  130  of the mezzanine header connector  102  (shown in  FIG. 1 ) according to another embodiment.  FIG. 7  is a perspective front view of a portion of the mezzanine header connector  102  having the ground shield  130  shown in  FIG. 6 . The ground shield  130  has a center wall  158  and two side walls  160  like the ground shield  130  shown in  FIG. 3 . In the illustrated embodiment, both the left side wall  160 A and the right side wall  160 B include the commoning feature  168 . The commoning features  168  are each a ledge  192  that extends outward from the respective side wall  160 A,  160 B. Optionally, the ledge  192  extends perpendicular to the plane of the corresponding side wall  160 . The ledge  192  may extend parallel to the center wall  158 . The ledge  192  includes two opposite sides, referred to as a top side  194  and a bottom side  196 . The ledge  192  extending from the left side wall  160 A is referred to as a left ledge  192 A, and the ledge  192  extending from the right side wall  160 B is referred to as a right ledge  192 B. The right ledge  192 B of the ground shield  130  shown in  FIG. 6  is configured to engage a left ledge  192 A of an adjacent ground shield  130  to the right, and the left ledge  192 A of the ground shield  130  is configured to engage a right ledge  192 B of a different adjacent ground shield  130  to the left. As shown in  FIG. 7 , the bottom side  196  of the left ledge  192 A abuts against the top side  194  of the adjacent ledge  192  to the left of the ground shield  130 , and the top side  194  of the right ledge  192 B abuts against the bottom side  196  of the adjacent left ledge  192 A to the right. Alternatively, the side of each ledge  192  that engages the adjacent ledge  192  may be switched from the embodiment shown in  FIG. 7 . 
     As shown in  FIG. 6 , the side walls  160  of the ground shield  130  each have a proximal end  198  and a distal end  200 . The proximal end  198  is at the center wall  158 , while the distal end  200  is located away from the center wall  158 . Optionally, the ledge  192  extends outward from the distal end  200  of the corresponding side wall  160 . For example, the ledge  192  may be bent out of plane of the side wall  160  at the distal end  200  in a direction towards an adjacent ledge  192  of an adjacent ground shield  130 . In other embodiments, the ledge  192  extends from the proximal end  198  or from a location between the proximal and distal ends  198 ,  200 . 
     The ledge  192  of the ground shield  130  applies a biasing force on the adjacent ledge  192  to retain the mechanical engagement between the ground shields  130 . Optionally, the ledge  192  includes a spring arm  202  that is bent out of plane of the ledge  192  towards the adjacent ledge  192 . The spring arm  202  deflects along a plane parallel to the side wall  160 . For example, the spring arm  202  is resiliently deflectable along an arc  204  in a direction  206  from the natural resting position of the spring arm  202  shown in  FIG. 6 . The resilience of the spring arm  202  generates a biasing or engagement force between the ledge  192  and the adjacent ledge  192 . In the illustrated embodiment, both the left ledge  192 A and the right ledge  192 B of the ground shield  130  include a spring arm  202 . Optionally, the spring arm  202  of the left ledge  192 A is proximate to the front end  176  of the ground shield  130 , while the spring arm  202  of the right ledge  192 B is proximate to the rear end  178  of the ground shield  130 , so the spring arms  202  do not directly engage spring arms  202  of adjacent ground shields  130 . Rather, and as shown in  FIG. 7 , the spring arm  202  of the left ledge  192 A of a first ground shield  130 A in the group engages a planar surface of the right ledge  192 B of a second ground shield  130 B in the group. 
     In an embodiment, the groups of ground shields  130  that are mechanically engaged and electrically commoned are each ground shields  130  in the same row  140 . The rows  140  extend parallel to a lateral axis  208 . The columns  142  extend perpendicular to the rows  140 . In an embodiment, the biasing forces between the ledges  192  (for example, the left ledge  192 A of the first ground shield  130 A and the right ledge  192 B of the adjacent second ground shield  130 B) are oriented in a direction parallel to the columns  142 . Thus, in the embodiment shown in  FIGS. 6 and 7 , lateral biasing forces across the rows  140  are avoided. 
       FIGS. 8-13  show multiple embodiments of the ground shield  130  of the mezzanine header connector  102  (shown in  FIG. 1 ) in which the commoning feature  168  at least partially defines a slot  210 . The slot  210  is configured to receive a side wall  160  of an adjacent ground shield  130  or a tab extending from the side wall  160  of the adjacent ground shield  130 . The side wall  160  or the tab is held within the slot  210  by an interference fit to retain mechanical engagement between the contacting ground shields  130  and, therefore, electrically common the ground shields  130  together. 
       FIG. 8  is a perspective view of a ground shield  130  of the mezzanine header connector  102  (shown in  FIG. 1 ) according to another embodiment.  FIG. 9  is a perspective front view of a portion of the mezzanine header connector  102  having the ground shield  130  shown in  FIG. 8 . The ground shield  130  has a center wall  158  and two side walls  160  like the ground shield  130  shown in  FIG. 3 . The commoning feature  168  is a ledge  212  that extends outward from the distal end  200  of the respective side wall  160 , like the ledges  192  shown in  FIG. 6 . In addition, the ledge  212  also has a first or top side  194  and a second or bottom side  196 . However, the ground shield  130  in  FIGS. 8 and 9  only includes one ledge  212 , which optionally extends from the right side wall  160 B. The left side wall  160 A does not include a ledge. The ledge  212  includes a front edge  214  proximate to the front end  176  of the ground shield  130  and a rear edge  216  between the front edge  214  and the rear end  178  of the ground shield  130 . 
     The ledge  212  defines the slot  210  which extends fully through the ledge  212  between the top side  194  and the bottom side  196  (such that the slot  210  is open at both sides  194 ,  196 ). The slot  210  includes a reception portion  218  and a retention portion  220  that is narrower than the reception portion  218 . The slot  210  initially receives the side wall  160  or a tab extending from the side wall  160  of an adjacent ground shield  130  within the reception portion  218 , and the side wall  160  or tab is retained in the slot  210  along the retention portion  220 . Optionally, edges  222  of the slot  210  may define protrusions  224  that extend into the slot  210  at the retention portion  220 . The protrusions  224  narrow the slot  210  and are configured to engage both sides of the side wall  160  or tab received within the slot  210  to provide an interference fit. Optionally, the reception portion  218  is defined along the rear edge  216  of the ledge  212 , and the retention portion  220  is frontward of the reception portion  218 . Thus, as the ground shield  130  is moved rearward into the cavity  132  (shown in  FIG. 2 ) of the housing  122  to load the ground shield  130  in the housing  122 , the slot  210  receives either the side wall  160  or the tab of an adjacent ground shield  130  that is already loaded in the housing  122 . In an alternative embodiment, the reception portion  218  is defined along the front edge  214 , and the slot  210  receives the side wall  160  or the tab of an adjacent ground shield  130  as the adjacent ground shield  130  is being loaded into the housing  122 . 
     In the illustrated embodiment, the left side wall  160 A defines a cut-out or notch portion  226  at the distal end  200  of the side wall  160 A. The notch portion  226  extends to a front edge  228  of the side wall  160 A. A step  230  defines a rear end of the notch portion  226 . In an exemplary embodiment, the notch portion  226  is configured to accommodate the ledge  212  of an adjacent ground shield  130  as the adjacent ground shield  130  is being loaded into the housing  122 . As shown in  FIG. 9 , as an adjacent second ground shield  130 B moves further rearward into the housing  122 , the slot  210  of the ledge  212  moves over the step  230  of the left side wall  160 A of a first ground shield  130 A that is already loaded into the housing  122 . The protrusions  224  of the slot  210  engage both sides of the step  230  of the left side wall  160 A to electrically common the first and second ground shields  130 A,  130 B together. In other embodiments, the left side wall  160 A may define a tab extending outward from the side wall  160 A that is configured to be received in the slot  210  of an adjacent ground shield  130 , such as in the embodiments shown below. 
       FIG. 10  is a perspective view of a portion of a ground shield  130  of the mezzanine header connector  102  (shown in  FIG. 1 ) according to another embodiment.  FIG. 11  is a perspective front view of a portion of the mezzanine header connector  102  having the ground shield  130  shown in  FIG. 10 . The ground shield  130  has a center wall  158  and two side walls  160  like the ground shield  130  shown in  FIG. 3 . In the illustrated embodiment, the left side wall  160 A has a commoning feature  168  that is two parallel spring beams  234  that define the slot  210  therebetween. The spring beams  234  are bent outwards from a plane of the side wall  160 A at a crease  236  that extends parallel to the front edge  228  of the side wall  160 A. The slot  210  extends towards the crease  236  from distal ends  238  of the spring beams  234 . Although the distal ends  238  of the two spring beams  234  are not integral with each other in the illustrated embodiment (thus forming two separate spring beams  234 ), in an alternative embodiment the slot  210  may be defined within a single spring beam. The reception portion  218  of the slot  210  is more proximate to the crease  236  than the retention portion  220 , which is defined between a respective protrusion  224  on each of the spring beams  234 . As a result, the slot  210  resembles a keyhole. 
     The right side wall  160 B includes a tab  240  that extends outward from the side wall  160 B. The tab  240  is configured to be received in the slot  210  and to engage the spring beams  234  of an adjacent ground shield  130  to electrically common the ground shields  130 . Thus, the tab  240  is also a commoning feature  168 . The tab  240  is a commoning feature  168  on the right side wall  160 B that is complementary to the commoning feature  168 —the spring beams  234 —on the left side wall  160 A. In another embodiment, the tab  240  extends from the left side wall  160 A, and the spring beams  234  defining the slot  210  extend from the right side wall  160 B. As shown in  FIG. 11 , a second ground shield  130 B is located to the right of a first ground shield  130 A in the same row  140 . The second ground shield  130 B is loaded into the housing  122  prior to the first ground shield  130 A. As the first ground shield  130 A is loaded into the housing  122  in the rearward direction, the tab  240  extending from the right side wall  160 B of the first ground shield  130 A is received in the keyhole reception portion  218  of the slot  210  of the second ground shield  130 B. Further rearward movement of the first ground shield  130 A relative to the second ground shield  130 B causes the tab  240  to be received in the retention portion  220  of the slot  210  between the protrusions  224  of the spring beams  234 , which retain the tab  240  by an interference fit. 
       FIG. 12  is a perspective view of a portion of a ground shield  130  of the mezzanine header connector  102  (shown in  FIG. 1 ) according to another embodiment.  FIG. 12  shows a commoning feature  168  extending from the right side wall  160 B of the ground shield  130 . The commoning feature  168  extends outward and rearward from a front edge  228  of the side wall  160 B. Like the slot  210  shown in  FIG. 10 , the reception portion  218  of the slot  210  resembles a keyhole opening and is disposed more proximate to the front edge  228  of the side wall  160 B than the retention portion  220 , resembling a keyhole opening. The commoning feature  168  is configured to receive a tab extending from a left side wall  160 A (shown in  FIG. 4 ) of an adjacent ground shield  130 . The tab may be the tab  240  shown in  FIG. 10 . For example, the ground shield  130  shown in  FIG. 12  may be loaded into the housing  122  (shown in  FIG. 2 ) prior to the adjacent ground shield  130 . As the adjacent ground shield  130  is loaded, the tab of the adjacent ground shield  130  is received in the reception portion  218  and then in the retention portion  220  of the slot  210  to retain and electrically common the ground shields  130  together. 
       FIG. 13  is a cross-sectional view of a portion of two ground shields  130  mechanically engaged to each other according to another embodiment. A left ground shield  130 A includes a commoning feature  168  that is a clip  250 , and a right ground shield  130 B engaged to the left ground shield  130 A includes a commoning feature  168  that is a tab  252 . Like the commoning feature  168  shown in  FIG. 12 , the clip  250  extends outward and rearward from the front edge  228  of the right side wall  160 B. However, unlike the commoning feature  168  shown in  FIG. 12 , the clip  250  does not define a slot  210  extending through the clip  250 . Instead, the edges of the slot  210  are defined by an interior surface  254  of the clip  250  and an exterior surface  256  of the right side wall  160 B. The clip  250  may resemble an R-clip or a hairpin cotter pin. Optionally, the right side wall  160 B includes a jogged section  258  that is jogged outward from a planar surface of the side wall  160 B, and the exterior surface  256  of the jogged section  258  defines an edge of the slot  210 . 
     The tab  252  extends outward from the left side wall  160 A of the right ground shield  130 B. The tab  252  has an S-shaped curve. A distal end  260  of the tab  252  extends forward generally parallel to the left side wall  160 A. The right ground shield  130 B is loaded in the housing  122  (shown in  FIG. 2 ) prior to the left ground shield  130 A. As the left ground shield  130 A is moved rearward to load the ground shield  130 A in the housing  122 , the distal end  260  of the tab  252  is received in the slot  210 . For example, the slot  210  may have a width that is narrower than a thickness of the tab  252  such that the clip  250  is deflected outward and/or the jogged section  258  of the right side wall  160 B is deflected inward relative to the left ground shield  130 A as the tab  252  is received in the slot  210 . The tab  252  is retained in the slot  210  between the clip  250  and the right side wall  160 B to mechanically couple and electrically common the left and right ground shields  130 A,  130 B. 
     Although the embodiments described herein primarily describe the ground shields  130  (shown in  FIG. 2 ) as being associated with the header connector  102  (shown in  FIG. 1 ), it is recognized that the embodiments of the ground shields  130  may additionally or alternatively be used in association with the receptacle connector  104  ( FIG. 1 ). In addition, the ground shields  130  and other components of the connectors described herein are not limited to use in mezzanine style connectors, although mezzanine connectors constitute one exemplary use of such components. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Dimensions, types of materials, orientations of the various components, and the number and positions of the various components described herein are intended to define parameters of certain embodiments, and are by no means limiting and are merely exemplary embodiments. Many other embodiments and modifications within the spirit and scope of the claims will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112(1), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.