Patent Publication Number: US-9419360-B2

Title: Mating interfaces for high speed high density electrical connectors

Description:
RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Application Ser. No. 61/800,900, filed Mar. 15, 2013, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This invention relates generally to electrical connectors used to interconnect printed circuit boards and more specifically to improved mating interfaces for such connectors. 
     Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system on several printed circuit boards (“PCBs”) which may be joined together with electrical connectors. A traditional arrangement for joining several printed circuit boards is to have one printed circuit board serve as a backplane. Other printed circuit boards, called “daughter boards” or “daughter cards,” may be connected through the backplane. 
     A traditional backplane is a printed circuit board onto which many connectors may be mounted. Conducting traces in the backplane may be electrically connected to signal conductors in the connectors so that signals may be routed between the connectors. Daughter cards may also have connectors mounted thereon. The connectors mounted on a daughter card may be plugged into the connectors mounted on the backplane. In this way, signals may be routed among the daughter cards through the backplane. The daughter cards may plug into the backplane at a right angle. The connectors used for these applications may therefore include a right angle bend and are often called “right angle connectors.” 
     Connectors may also be used in other configurations for interconnecting printed circuit boards and for interconnecting other types of devices such as cables to printed circuit boards. Sometimes, one or more smaller printed circuit boards may be connected to another larger printed circuit board. In such a configuration, the larger printed circuit board may be called a “mother board” and the printed circuit boards connected to it may be called daughter boards. Also, boards of the same size or similar sizes may sometimes be aligned in parallel. Connectors used in these applications are often called “stacking connectors” or “mezzanine connectors.” 
     Regardless of the exact application, electrical connector designs have been adapted to mirror trends in the electronics industry. Electronic systems generally have gotten smaller, faster, and functionally more complex. Because of these changes, the number of circuits in a given area of an electronic system, along with the frequencies at which the circuits operate, have increased significantly in recent years. Current systems pass more data between printed circuit boards and require electrical connectors that are electrically capable of handling more data at higher speeds than connectors of even a few years ago. 
     In a high density, high speed connector, electrical conductors may be so close to each other that there may be electrical interference between adjacent signal conductors. To reduce interference, and to otherwise provide desirable electrical properties, shield members are often placed between or around adjacent signal conductors. The shields may prevent signals carried on one conductor from creating “crosstalk” on another conductor. The shield may also impact the impedance of each conductor, which may further contribute to desirable electrical properties. 
     Examples of shielding can be found in U.S. Pat. Nos. 4,632,476 and 4,806,107, which show connector designs in which shields are used between columns of signal contacts. These patents describe connectors in which the shields run parallel to the signal contacts through both the daughter board connector and the backplane connector. Cantilevered beams are used to make electrical contact between the shield and the backplane connectors. U.S. Pat. Nos. 5,433,617, 5,429,521, 5,429,520, and 5,433,618 show a similar arrangement, although the electrical connection between the backplane and shield is made with a spring type contact. Shields with torsional beam contacts are used in the connectors described in U.S. Pat. No. 6,299,438. 
     Other connectors have the shield plate within only the daughter board connector. Examples of such connector designs can be found in U.S. Pat. Nos. 4,846,727, 4,975,084, 5,496,183, and 5,066,236. Another connector with shields only within the daughter board connector is shown in U.S. Pat. No. 5,484,310. 
     Another modification made to connectors to accommodate changing requirements is that connectors have become much larger in some applications. Increasing the size of a connector may lead to manufacturing tolerances that are much tighter. For instance, the permissible mismatch between the conductors in one half of a connector and the receptacles in the other half may be constant, regardless of the size of the connector. However, this constant mismatch, or tolerance, may become a decreasing percentage of the connector&#39;s overall length as the connector gets larger. Therefore, manufacturing tolerances may be tighter for larger connectors, which may increase manufacturing costs. One way to avoid this problem is to use modular connectors. Teradyne Connection Systems of Nashua, N.H., USA pioneered a modular connector system called HD+®. This system has multiple modules, each having multiple columns of signal contacts, such as 15 or 20 columns. The modules are held together on a metal stiffener. 
     Another modular connector system is shown in U.S. Pat. Nos. 5,066,236 and 5,496,183. Those patents describe “module terminals” each having a single column of signal contacts. The module terminals are held in place in a plastic housing module. The plastic housing modules are held together with a one-piece metal shield member. Shields may be placed between the module terminals as well. 
     Other techniques may be used to control the performance of a connector. For instance, transmitting signals differentially may also reduce crosstalk. Differential signals are carried on a pair of conducting paths, called a “differential pair.” The voltage difference between the conductive paths represents the signal. In general, a differential pair is designed with preferential coupling between the conducting paths of the pair. For example, the two conducting paths of a differential pair may be arranged to run closer to each other than to adjacent signal paths in the connector. No shielding is desired between the conducting paths of the pair, but shielding may be used between differential pairs. Electrical connectors can be designed for differential signals as well as for single-ended signals. Examples of differential electrical connectors are shown in U.S. Pat. Nos. 6,293,827, 6,503,103, 6,776,659, 7,163,421, and 7,794,278. 
     SUMMARY 
     In accordance with some embodiments, a mating interface of an electrical connector is provided, the mating interface comprising: a plurality of conductive elements positioned in a plurality of columns, each of the plurality of conductive elements comprising: a sheet of conductive material formed into a three dimensional structure such that the conductive material is disposed on at least two sides of an opening adapted to receive a mating conductive element; and at least one tab cut in the sheet, the at least one tab comprising a mating contact surface facing the opening and adapted to make contact to the mating conductive element. 
     In accordance with some embodiments, a mating interface of an electrical connector is provided, the mating interface comprising: a plurality of conductive elements positioned in a plurality of columns, each of the plurality of conductive elements comprising: a distal portion and a proximal portion; a first member extending between the distal portion and the proximal portion, the first member comprising a first mating contact facing a first side of an opening adapted to receive a mating conductive element; a second member extending between the distal portion and the proximal portion, the second member comprising a second mating contact facing a second side of the opening adapted to receive a mating conductive element, wherein the first member and second member are joined at the distal portion and the proximal portion. 
     In accordance with some embodiments, a method of operating an electrical connector is provided, the method comprising: inserting a second contact through an opening of a first contact into an open space at least partially surrounded by an elongated member of the first contact, wherein: the elongated member is elongated in a mating direction, the elongated member comprises one or more walls that are elongated in the mating direction and are adjacent to at least two sides of the second contact, the opening is bounded, at least in part, by one or more edges of the one or more walls, and the open space is also elongated in the mating direction; moving the second contact in the mating direction into contact with at least one tab extending from at least one wall of the elongated member. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In the drawings: 
         FIG. 1A  is an isometric view of an illustrative electrical interconnection system, in accordance with some embodiments; 
         FIG. 1B  is an exploded view of the illustrative electrical interconnection system shown in  FIG. 1A , in accordance with some embodiments; 
         FIGS. 2A-B  show opposing side views of an illustrative wafer, in accordance with some embodiments; 
         FIG. 3A  shows an illustrative blank that can be used to make a shield member, in accordance with some embodiments; 
         FIG. 3B  shows traces on an illustrative printed circuit board routed between holes used to mount a connector, in accordance with some embodiments; 
         FIG. 3C  shows an alternative routing of traces on an illustrative printed circuit board, in accordance with some embodiments; 
         FIG. 3D  shows the shield plate of  FIG. 3A  after it has been insert molded into a housing, in accordance with some embodiments; 
         FIG. 4A  shows, schematically, an illustrative signal path in an electrical interconnection system, in accordance with some embodiments; 
         FIG. 4B  shows, schematically, an illustrative torsional beam contact suitable for use in a shield plate, in accordance with some embodiments; 
         FIG. 4C  shows the illustrative shield plates of  FIG. 4B  in a mated configuration, in accordance with some embodiments. 
         FIG. 5A  is a plan view of an illustrative lead frame used in the manufacture of a connector, in accordance with some embodiments; 
         FIG. 5B  is an enlarged detail view of the area encircled by arrow  5 B- 5 B in  FIG. 4A , in accordance with some embodiments; 
         FIG. 6  is a cross-sectional view of an illustrative backplane connector, in accordance with some embodiments; 
         FIG. 7A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 7B  is a side view of the illustrative contacts in the example of  FIG. 7A , in accordance with some embodiments; 
         FIG. 7C  is a front view of the illustrative contacts in the example of  FIG. 7A , in accordance with some embodiments; 
         FIG. 8A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 8B  is a bottom view of the illustrative contacts in the example of  FIG. 8A , in accordance with some embodiments; 
         FIG. 8C  is a front view of the illustrative contacts in the example of  FIG. 8A , in accordance with some embodiments; 
         FIG. 8D  is a side view of the illustrative contacts in the example of  FIG. 8A , in accordance with some embodiments; 
         FIG. 9A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 9B  is a bottom view of the illustrative contacts in the example of  FIG. 9A , in accordance with some embodiments; 
         FIG. 9C  is a front view of the illustrative contacts in the example of  FIG. 9A , in accordance with some embodiments; 
         FIG. 10A  shows an illustrative contact mated another illustrative contact, in accordance with some embodiments; 
         FIG. 10B  is a front view of the illustrative contacts in the example of  FIG. 10A , in accordance with some embodiments; 
         FIG. 10C  is a bottom view of the illustrative contacts in the example of  FIG. 10A , in accordance with some embodiments; 
         FIG. 11A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 11B  is a front view of the illustrative contacts in the example of  FIG. 11A , in accordance with some embodiments; 
         FIG. 11C  is a bottom view of the illustrative contacts in the example of  FIG. 11A , in accordance with some embodiments; 
         FIG. 12A  shows an illustrative contact mated another illustrative contact, in accordance with some embodiments; 
         FIG. 12B  is a front view of the illustrative contacts in the example of  FIG. 12A , in accordance with some embodiments; 
         FIG. 12C  is a side view of the illustrative contacts in the example of  FIG. 12A , in accordance with some embodiments; 
         FIG. 12D  is a bottom view of the illustrative contacts in the example of  FIG. 12A , in accordance with some embodiments; 
         FIG. 13A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 13B  is a front view of the illustrative contacts in the example of  FIG. 13A , in accordance with some embodiments; 
         FIG. 13C  is a side view of the illustrative contacts in the example of  FIG. 13A , in accordance with some embodiments; 
         FIG. 13D  is a bottom view of the illustrative contacts in the example of  FIG. 13A , in accordance with some embodiments; 
         FIG. 14A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 14B  is a front view of the illustrative contacts in the example of  FIG. 14A , in accordance with some embodiments; 
         FIG. 14C  is a side view of the illustrative contacts in the example of  FIG. 14A , in accordance with some embodiments; 
         FIG. 14D  is a bottom view of the illustrative contacts in the example of  FIG. 14A , in accordance with some embodiments; 
         FIG. 15A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 15B  is a front view of the illustrative contacts in the example of  FIG. 15A , in accordance with some embodiments; 
         FIG. 15C  is a bottom view of the illustrative contacts in the example of  FIG. 15A , in accordance with some embodiments; 
         FIG. 16A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 16B  is a back view of the illustrative contacts in the example of  FIG. 16A , in accordance with some embodiments; 
         FIG. 16C  is a bottom view of the illustrative contacts in the example of  FIG. 16A , in accordance with some embodiments; 
         FIG. 17A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 17B  is a front view of the illustrative contacts in the example of  FIG. 17A , in accordance with some embodiments; 
         FIG. 18A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 18B  is a front view of the illustrative contacts in the example of  FIG. 18A , in accordance with some embodiments; 
         FIG. 18C  is a side view of the illustrative contacts in the example of  FIG. 18A , in accordance with some embodiments; 
         FIG. 18D  is a bottom view of the illustrative contacts in the example of  FIG. 18A , in accordance with some embodiments; 
         FIG. 19A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 19B  is a front view of the illustrative contacts in the example of  FIG. 19A , in accordance with some embodiments; 
         FIG. 19C  is a side view of the illustrative contacts in the example of  FIG. 19A , in accordance with some embodiments; 
         FIG. 20A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 20B  is a front view of the illustrative contacts in the example of  FIG. 20A , in accordance with some embodiments; 
         FIG. 20C  is a side view of the illustrative contacts in the example of  FIG. 20A , in accordance with some embodiments; 
         FIG. 21A  shows a pair of illustrative contacts mated respectively with another pair of illustrative contacts, in accordance with some embodiments; 
         FIG. 21B  is a front view of the illustrative contacts in the example of  FIG. 21A , in accordance with some embodiments; and 
         FIG. 21C  is a side view of the illustrative contacts in the example of  FIG. 21A , in accordance with some embodiments. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The inventors have recognized and appreciated designs of mating contact portions of an electrical connector that improve signal integrity for high frequency signals, such as at frequencies in the GHz range, including up to about 25 GHz or up to about 40 GHz or higher, while maintaining high density, such as with a spacing between adjacent mating contacts on the order of 2 mm or less, including center-to-center spacing between adjacent contacts in a column of between 0.75 mm and 1.8 mm or between 1 mm and 1.75 mm, for example. Spacing between columns of mating contact portions may be similar, although there is no requirement that the spacing between all mating contacts in a connector be the same. 
     The present disclosure is not limited to the details of construction or the arrangements of components set forth in the following description and/or the drawings. Various embodiments are provided solely for purposes of illustration, and the concepts described herein are capable of being practiced or carried out in other ways. Also, the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof herein, is meant to encompass the items listed thereafter (or equivalents thereof) and/or as additional items. 
       FIG. 1A  is an isometric view of an illustrative electrical interconnection system  100 , in accordance with some embodiments. In this example, the electrical interconnection system  100  includes a backplane connector  114  and a daughter card connector  116  adapted to mate with each other. 
       FIG. 1B  shows an exploded view of the illustrative electrical interconnection system  100  shown in  FIG. 1B , in accordance with some embodiments. As shown in  FIG. 1A , the backplane connector  114  may be adapted to plug into a backplane  110 , and the daughter card connector  116  may be adapted to plug into a daughter card  112 . When the backplane connector  114  and the daughter card connector  116  mate with each other, conductors in these two connectors become electrically connected, thereby completing conductive paths between corresponding conductive elements in the backplane  110  and the daughter card  112 . 
     Although not shown, the backplane  110  may, in some embodiments, have many other backplane connectors attached to it so that multiple daughter cards can be connected to the backplane  110 . Additionally, multiple backplane connectors may be aligned end to end so that they may be used to connect to one daughter card. However, for clarity, only a portion of the backplane  110  and a single daughter card  112  are shown in  FIG. 1B . 
     In the example of  FIG. 1B , the backplane connector  114  may include a shroud  120 , which may serve as a base for the backplane connector  114 . In various embodiments, the shroud  120  may be molded from a dielectric material such as plastic or nylon. Examples of suitable materials include, but are not limited to, liquid crystal polymer (LCP), polyphenyline sulfide (PPS), high temperature nylon or polypropylene (PPO). Other suitable materials may be employed, as aspects of the present disclosure are not limited in this regard. 
     All of the above-described materials are suitable for use as binder material in manufacturing connectors. In accordance some embodiments, one or more fillers may be included in some or all of the binder material used to form the backplane shroud  120  to control the electrical and/or mechanical properties of the backplane shroud  120 . As a non-limiting example, thermoplastic PPS filled to 30% by volume with glass fiber may be used. 
     In some embodiments, the floor of the shroud  120  may have columns of openings  126 , and conductors  122  may be inserted into the openings  126  with tails  124  extending through the lower surface of the shroud  120 . The tails  124  may be adapted to be attached to the backplane  110 . For example, in some embodiments, the tails  124  may be adapted to be inserted into respective signal holes  136  on the backplane  110 . The signal holes  136  may be plated with some suitable conductive material and may serve to electrically connect the conductors  122  to signal traces (not shown) in the backplane  110 . 
     In some embodiments, the tails  124  may be press fit “eye of the needle” compliant sections that fit within the signal holes  136 . However, other configurations may also be used, such as surface mount elements, spring contacts, solderable pins, etc., as aspects of the present disclosure are not limited to the use of any particular mechanism for attaching the backplane connector  114  to the backplane  110 . 
     For clarity of illustration, only one of the conductors  122  is shown in  FIG. 1B . However, in various embodiments, the backplane connector may include any suitable number of parallel columns of conductors and each column may include any suitable number of conductors. For example, in one embodiment, there are eight conductors in each column. 
     The spacing between adjacent columns of conductors is not critical. However, a higher density may be achieved by placing the conductors closes together. As a non-limiting example, the conductors  122  may be stamped from 0.4 mm thick copper alloy, and the conductors within each column may be spaced apart by 2.25 mm and the columns of conductors may be spaced apart by 2 mm. However, in other embodiments, smaller dimensions may be used to provide higher density. 
     In the example shown in  FIG. 1B , a groove  132  is formed in the floor of the shroud  120 . The groove  132  runs parallel to the column of openings  126 . The shroud  120  also has grooves  134  formed in its inner sidewalls. In some embodiments, a shield plate  128  is adapted fit into the grooves  132  and  134 . The shield plate  128  may have tails  130  adapted to extend through openings (not visible) in the bottom of the groove  132  and to engage ground holes  138  in the backplane  110 . Like the signal holes  136 , the ground holes  138  may be plated with any suitable conductive material, but the ground holes  138  may connect to ground traces (not shown) on the backplane  110 , as opposed to signal traces. 
     In the example shown in  FIG. 1B , the shield plate  128  has seven tails  130 , with each tail falling between two adjacent conductors  122 . It may be desirable for a tail of the shield plate  128  to be as close as possible to a corresponding one of the conductors  122 . However, centering a tail between two adjacent signal conductors may allow the spacing between the shield plate  128  and a column of signal conductors  122  to be reduced. 
     In the example shown in  FIG. 1B , the shield plate  128  has several torsional beam contacts  142  formed therein. In some embodiments, each contact may be formed by stamping arms  144  and  146  in the shield plate  128 . Arms  144  and  146  may then be bent out of the plane of the shield plate  128 , and may be long enough that they may flex when pressed back into the plane of the shield plate  128 . Additionally, the arms  144  and  146  may be sufficiently resilient to provide a spring force when pressed back into the plane of the shield plate  128 . The spring force generated by each arm  144  or  146  may create a point of contact between the arm and a shield plate  150  of the daughter card connector  116  when the backplane connector  114  is mated with the daughter card connector  116 . The generated spring force may be sufficient to ensure this contact even after the daughter card connector  116  has been repeatedly mated and unmated from the backplane connector  114 . 
     In some embodiments, the arms  144  and  146  may be coined during manufacture. Coining may reduce the thickness of the material and increase the compliancy of the beams without weakening the shield plate  128 . For enhanced electrical performance, it may also be desirable that the arms  144  and  146  be short and straight. Therefore, in some embodiments, the arms  114  and  146  are made only as long as needed to provide sufficient spring force. 
     In addition, for electrical performance, it may be desirable to have at least one arm of the shield plate  128  close to each one of the signal conductors  122 . For example, in some embodiments, there may be one pair of arms  144  and  146  for each of the signal conductors  122 . For the example, if there are eight signal conductors  122  in each column, there may be eight arms, forming four balanced torsional beam contacts  142  (i.e., a pair of arms  144  and  146  forming one torsional beam contact). However, other configurations are also possible. For instance, in the example shown in  FIG. 1B , there are only three balanced torsional beam contacts  142  for each column of conductors. This configuration may represent a compromise between desired electrical properties and a desired amount of spring force generated by each torsional beam contact. 
     In the example shown in  FIG. 1B , grooves  140  are formed on the inner sidewalls of the shroud  120 . These grooves may be used to align the daughter card connector  116  with the backplane connector  114  during mating. For example, in some embodiments, tabs  152  of the daughter card connector  116  may be adapted to fit into corresponding grooves  140  for alignment and/or to prevent side-to-side motion of the daughter card connector  116  relative to the backplane connector  114 . 
     In some embodiments, the daughter card connector  116  may include one or more wafers. In the example of  FIG. 1B , only one wafer  154  is shown for clarity, but the daughter card connector  116  may have several wafers stacked side to side. In some embodiments, the wafer  154  may include a column of one or more receptacles  158 , where each receptacle  158  may be adapted to engage a respective one of the conductors  122  of the backplane connector  114  when the backplane connector  114  and the daughter card connector  116  are mated. Thus, in such an embodiment, the daughter card connector  116  may have as many wafers as there are columns of conductors in the backplane connector  114 . 
     In the example shown in  FIG. 1B , wafers of the daughter card connector  116  are supported in a stiffener  156 . In some embodiments, the stiffener  156  may be stamped and formed from a metal strip. However, it should be appreciated that other materials and/or manufacturing techniques may also be suitable, as aspects of the present disclosure are not limited to the use of any particular type of stiffeners, or any stiffener at all. Furthermore, other structures, including a housing portion to which individual wafers may be attached may alternatively or additionally be used to support the wafers. In some embodiments, if the housing portion is insulative, it may have cavities that receive mating contact portions of the wafers to electrically isolate the mating contact portions. Alternatively or additionally, a housing portion may incorporate materials that impact electrical properties of the connector. For example, the housing may include shielding and/or electrically lossy material. 
     In embodiments with a stiffener, the stiffener  156  may be stamped with features (e.g., one or more attachment points) to hold the wafer  154  in a desired position. As a non-limiting example, the stiffener  156  may have a slot  160 A formed along its front edge. The slot  160 A may be adapted to engage a tab  160 B of the wafer  154 . The stiffener  156  may further include holes  162 A and  164 A, which may be adapted to engage, respectively, hubs  162 B and  164 B of the wafer  154 . In some embodiments, the hubs  162 B and  164 B are sized to provide an interference fit in the holes  162 A and  164 A, respectively. However, it should be appreciated that other types of attachment mechanism may also be suitable, such as by using adhesives. 
     While specific combination and arrangement of slots and holes on the stiffener  156  are shown in  FIG. 1B , it should be appreciated that aspects of the present disclosure are not limited to any particular way of attaching wafers to the stiffener  156 . For example, the stiffener  156  may have a set of slots and/or holes for each wafer supported by the stiffener  156 , so that a pattern of slots and/or holes is repeated along the length of stiffener  156  at each point where a wafer is to be attached. Alternatively, the stiffener  156  may have different combinations of slots and/or holes, or may have different attachment mechanisms for different wafers. 
     In the example shown in  FIG. 1B , the wafer  154  includes two pieces, a shield piece  166  and a signal piece  168 . In some embodiments, the shield piece  166  may be formed by insert molding a housing  170  around a front portion of the shield plate  150 , and the signal piece  168  may be formed by insert molding a housing  172  around one or more conductive elements. Examples of such conductive elements are described in greater detail below in connection with  FIG. 5A . 
     In some embodiments, the signal piece  168  and the shield piece  166  may have features that hold them together. For example, the signal piece  168  may have hubs (not visible) formed on one surface. The hubs may be positioned and adapted to engage clips  174  formed in the shield plate  150  when the shield piece  166  and the signal piece  168  are assembled into the wafer  154 . An interference fit between the clips  174  and the corresponding hubs may hold the shield plate  150  firmly against the signal piece  168 . However, it should be appreciated that other attachment mechanisms may be used to hold the signal piece  168  and the shield piece  166  together. Furthermore, in alternative embodiments, there may be no attachment mechanism, and the signal piece  168  and the shield piece  166  may simply be disposed next to each other in the daughter card connector  116 . Furthermore, it should be appreciated that in some embodiments, a wafer may be manufactured without any shield plate and may include attachment features such that a shield plate may be attached. Further still, it should be appreciated that a shield plate, though pictured as stamped from a sheet of metal, need not be continuous or planar. In some embodiments, the shield plate may have one or more openings and may have any suitable contour, for example, to position shielding material between conductive elements that may be susceptible to crosstalk. 
     In the example shown in  FIG. 1B , the housing  170  has cavities  176  formed in it, where each cavity is shaped to receive a respective one of the receptacles  158 . In some embodiments, a cavity may have a platform  178  at its bottom, and the platform  178  may have an opening  180  formed through it. The opening  180  may be adapted to receive a corresponding one of the conductors  122  of the daughter card connector  116  when the daughter card connector  116  mates with the backplane connector  114 . Thus, when a corresponding one of the receptacles  158  is received in the cavity and a corresponding one of the conductors  122  is received in the opening  180 , the receptacle makes electrical contact with the conductor, thereby providing a signal path through the electrical interconnection system  100 . 
     In some embodiments, a receptacle may be formed with two legs, such as legs  182  in the example of  FIG. 1B . The legs  182  may be adapted to fit on opposite sides of the platform  178  when the receptacle is inserted into the corresponding one of the cavities  176 . In some embodiments, the receptacle may be formed such that the spacing between the two legs  182  is smaller than the width of platform  178 . Thus, to insert the receptacle into the corresponding one of the cavities  176 , a tool may be used to spread the legs  182 . 
     A receptacle formed in this manner is sometimes called a “preloaded” contact. Because the legs  182  are spread by the platform  178 , such a contact has a lower insertion force and is less likely to stub on the corresponding conductor of the daughter card connector  116  when the daughter card connector  116  mates with the backplane connector  114 . 
     In the example shown in  FIG. 1B , the housing  172  has grooves  184  formed in it. As described above, in some embodiments, hubs formed on one side of the signal piece  168  project through the shield plate  150 . The grooves  184  on the housing  172  may be positioned and adapted to receive similar hubs of the signal piece of another wafer disposed adjacent to the wafer  154 . Such hubs and the grooves  184  may help hold adjacent wafers together and prevent the rotation of one wafer with respect to an adjacent wafer. These features, in conjunction with the stiffener  156 , may be used in some embodiments to replace a separate box or housing that holds the wafers together, thereby simplifying the electrical interconnection system  100 . However, it should be appreciated that aspects of the present disclosure are not limited to the use of any particular fastening features. 
     In the example shown in  FIG. 1B , the housings  170  and  172  are shown with numerous holes (not numbered) in them. These are “pinch holes” used to hold the shield plate  150  or conductive elements during injection molding. Aspects of the present disclosure are not limited to the presence or any particular arrangement of such pinch holes. 
       FIGS. 2A-B  show opposing side views of an illustrative wafer  220 A, in accordance with some embodiments. The wafer  220 A may be formed in whole or in part by injection molding of material to form a housing  260  around a wafer strip assembly. Examples of wafer strip assemblies are described in greater detail below in connection with  FIGS. 4A-B . In the example shown in  FIGS. 2A-B , the wafer  220 A is formed with a two shot molding operation, allowing the housing  260  to be formed of two types of materials having different properties. The insulative portion  240  is formed in a first shot and a lossy portion  250  is formed in a second shot. However, any suitable number and types of materials may be used in the housing  260 . For example, in some embodiments, the housing  260  is formed around a column of conductive elements by injection molding plastic. 
     In some embodiments, the housing  260  may be provided with openings, such as windows or slots  264   1  . . .  264   6 , and holes, of which hole  262  is numbered, adjacent signal conductors enclosed in the housing  260 . These openings may serve multiple purposes, including: (i) to ensure during an injection molding process that the conductive elements are properly positioned, and/or (ii) to facilitate insertion of materials that have different electrical properties, if so desired. 
     In some embodiments, regions of different dielectric constants may be selectively located adjacent signal conductors of a wafer to obtain desired performance characteristics. (The dielectric constant of a material is sometimes also referred to as the “relative permittivity” of the material.) 
     In the example shown in  FIGS. 2A-B , the slots  264   1  . . .  264   6  in the housing  260  may position air adjacent selected signal conductors enclosed in the housing  260 . The ability to place air, or other material that has a dielectric constant lower than the dielectric constant of material used to form other portions of the housing  260 , in close proximity to a signal conductor in a differential pair provides a way to “de-skew” the differential pair of signal conductors, as discussed below. 
     The time it takes an electrical signal to propagate from one end of a signal conductor to the other end is known as the “propagation delay.” In some embodiments, it may be desirable that the signals within a pair have the same propagation delay, which is commonly referred to as having “zero skew” within the pair. The propagation delay within a conductor may be influenced by the dielectric constant of material near the conductor, where a lower dielectric constant may lead to a lower propagation delay. A vacuum has the lowest possible dielectric constant with a value of 1. Air has a similarly low dielectric constant, whereas dielectric materials have higher dielectric constants. For example, LCP has a dielectric constant of between about 2.5 and about 4.5. 
     In some embodiments, the signal conductors of a differential pair may have different physical lengths. This may be the case, for example, in a right-angle connector. To equalize the propagation delay in the signal conductors of a differential pair even though they have physically different lengths, the relative proportion of materials of different dielectric constants around the conductors may be adjusted. For instance, in some embodiments, more air may be positioned in close proximity to the physically longer signal conductor of the pair than to the shorter signal conductor of the pair, thereby lowering the effective dielectric constant around the longer signal conductor and decreasing its propagation delay. 
     However, as the dielectric constant around a signal conductor is lowered, the impedance of the signal conductor may rise. To maintain balanced impedance within the pair, the size of the signal conductor in close proximity to more air may in some embodiments be increased in thickness and/or width. This may result in two signal conductors with different physical geometries, but better matched propagation delays and impedance profiles. 
       FIG. 3A  shows an illustrative blank  300  that can be used to make a shield member, in accordance with some embodiments. For instance, the blank  300  may be used to make the shield plate  150  in the example shown in  FIG. 1 . In some embodiments, the shield plate  150  may be stamped from a roll of metal, and may be retained on a carrier strip  210  for ease of handling. After the shield plate  150  is injection molded to form a shield piece (e.g., the shield piece  166  in the example shown in  FIG. 1 ), the carrier strip  210  may be cut off. 
     In the example shown in  FIG. 3A , the shield plate  150  includes holes  212 , which may be filled with plastic when a housing (e.g., the housing  170  in the example shown in  FIG. 1 ) is molded onto the shield plate  150 , thereby locking the shield plate  150  in the housing. 
     In some embodiments, the shield plate  150  may also include slots  214 , which may be positioned to fall between receptacles (e.g., the receptacles  158  in the example shown in  FIG. 1 ) when the shield plate is disposed against a signal piece (e.g., the signal piece  168  in the example shown in  FIG. 1 ). The slots  214  may be adapted to control the capacitance of the shield plate  150 , which may raise or lower the overall impedance of an electrical inter connection system. The slots  214  may also channel current flow in the shield plate  150  near the receptacles of the signal piece, which form signal paths in the electrical inter connection system. Higher return current flow near the signal paths may reduce crosstalk. 
     In the example shown in  FIG. 3A , a slot  218  may be provided in the blank  300  to allow a tail region  222  to be bent out of the plane of the shield plate  150 , if desired. In some embodiments, the tail region  222  may be bent or not depending on whether the electrical interconnection system is carrying single-ended or differential signals. For example, the tail region  222  may be bent for single-ended signals, but not bent for differential signals, or vice versa. 
     It should be appreciated that a shield plate on a backplane connector (e.g., the shield plate  128  in the example of  FIG. 1 ) may similarly be bent in its tail region, if desired. For example, the shield plate  128  may be bent whenever the shield plate  150  is bent, or vice versa. 
     In some embodiments, the tail region  222  of the shield plate  150  may be bent to match the placement of ground holes on a printed circuit board. For example, the tail region  222  may be bent to allow contact tails in the tail region (e.g., contact tail  220 ) to be inserted into corresponding ground holes, depending on the configuration of the ground holes. Illustrative configurations of ground holes are discussed below in connection with  FIGS. 3B-C . 
       FIG. 3B  shows traces  910  and  912  on an illustrative printed circuit board routed between holes used to mount a connector, in accordance with some embodiments. In some embodiments, the printed circuit board may have one or more signal holes  186  and one or more ground holes  188 . When the connector is used to carry single ended signals, it may be desirable that the signal traces  910  and  912  be separated by ground to the greatest extent possible. Thus, it may be desirable that the ground holes  188  be centered between the signal holes  186  so that the signal traces  910  and  912  can be routed between the signal holes  186  and the ground holes  188 , as shown in  FIG. 3B . 
       FIG. 3C  shows an alternative routing of traces on an illustrative printed circuit board, in accordance with some embodiments. This alternative routing pattern may be suitable for traces carrying differential signals, as it may be desirable to route such traces as close together as possible. In the example shown in  FIG. 3C , to allow signal traces  914  and  916  to be close together, the ground holes  188  are not centered between the signal holes  186 . Rather, the ground holes  188  are offset to be close to some of the signal holes  186 . This placement allows both the signal traces  914  and  916  to be routed on the same side relative to the ground holes  188 . 
       FIG. 3D  shows the shield plate  150  of  FIG. 3A  after it has been insert molded into a housing (e.g., the housing  170  in the example shown in  FIG. 1B ) to form a ground portion (e.g., the shield piece  166  in the example shown in  FIG. 1B ), in accordance with some embodiments. In the example of  FIG. 3D , the housing  170  includes pyramid shaped projections  310  on a bottom face of the shield piece  166 . In some embodiments, recesses (not shown) may be included in the floor of a backplane connector (e.g., the backplane connector  114  in the example of  FIG. 1B ) and may be adapted to receive respective ones of the projections  310 . The projections  310  and the corresponding recesses may prevent the spring forces generated by the torsional beam contacts  142  from spreading adjacent wafers when the daughter card connector  116  is inserted into the backplane connector  114 . 
       FIG. 4A  shows, schematically, an illustrative signal path  310  in an electrical interconnection system (e.g., the system  100  in the example of  FIG. 1B ), in accordance with some embodiments. For example, the signal path  310  may pass through one of the signal conductors  122  of the backplane connector  114  of the example shown in  FIG. 1B , return through the shield plate  150  of the daughter card connector  116  to a point of contact X between the shield plate  150  and the arm  146  of the shield plate  128  of the backplane connector  114 , and then through the arm  146 , the shield plate  128 , and the tail  130 . Finally, the signal path  310  may be completed through the backplane  110  shown in  FIG. 1B . In this manner, the signal path  310  may not cut through any adjacent one of the signal conductors  122 , so that crosstalk may be reduced. 
       FIG. 4B  shows, schematically, an illustrative torsional beam contact suitable for use in a shield plate, in accordance with some embodiments. For example, such a torsional beam contact may be used in the shield plate  128  of the backplane connector  114  of the example shown in  FIG. 1B . 
     In the example shown in  FIG. 4B , the arm  146  of the shield plate  128  is bent out of the plane of the shield plate  128 . The shield plate  128  may be positioned and adapted to slide along the shield plate  150  of the daughter card connector  116  when the backplane connector  114  is mated with the daughter card connector  116 . As the shield plates  150  and  128  slide along one another, the arm  146  may be pressed back into the plane of the shield plate  128 . 
       FIG. 4C  shows the illustrative shield plates  128  and  150  of  FIG. 4B  in a mated configuration, in accordance with some embodiments. In the example shown in  FIG. 4C , the arm  146  is pressed back into the plane of the shield plate  128  of the backplane connector  114  by the shield plate  150  of the daughter card connector  116 . In some embodiments, a dimple  320  formed on the arm  146  may be positioned and adapted to be in contact with the shield plate  150  in this mated configuration. The torsional spring force generated by pressing the arm  146  back into the plane of the shield plate  128  may facilitate a good electrical contact between the dimple  320  and the shield plate  150 . However, it should be appreciated that other types of contacts between the shield plates  128  and  150  are also possible, such as cantilevered beam contacts, as aspects of the present disclosure are not limited to any particular contact interface between two shield members. 
     Wafers with various configurations may be formed in any suitable way, as aspects of the present disclosure are not limited to any particular manufacturing method.  FIG. 5A  shows illustrative wafer strip assemblies  410 A and  410 B suitable for use in making a wafer, in accordance with some embodiments. For example, the wafer strip assemblies  410 A-B may be used in making the wafer  154  in the example of  FIG. 1B . Moreover, it should be appreciated that mating contract structures disclosed herein may be incorporated into electrical connectors whether or not manufactured using wafers. 
     In the example of  FIG. 5A , the wafer strip assemblies  410 A-B each includes conductive elements in a configuration suitable for use as one column of conductors in a daughter card connector (e.g., the daughter card connector  116  in the example of  FIG. 1B ). A housing may then be molded around the conductive elements in each wafer strip assembly in an insert molding operation to form a wafer. 
     To facilitate the manufacture of wafers, signal conductors (e.g., signal conductor  420 ) and ground conductors (e.g., ground conductor  430 ) may be held together on a lead frame, such as the illustrative lead frame  400  in the example of FIG.  5 A. For example, the signal conductors and the ground conductors may be attached to one or more carrier strips, such as the illustrative carrier stripes  402  shown in  FIG. 5A . 
     In some embodiments, conductive elements (e.g., in single-ended or differential configuration) may be stamped for many wafers from a single sheet of conductive material. The sheet may be made of metal or any other material that is conductive and provides suitable mechanical properties for conductive elements in an electrical connector. Phosphor-bronze, beryllium copper and other copper alloys are non-limiting example of materials that may be used. 
       FIG. 5A  illustrates a portion of a sheet of conductive material in which the wafer strip assemblies  410 A-B have been stamped. Conductive elements in the wafer strip assemblies  410 A-B may be held in a desired position by one or more retaining features (e.g., tie bars  452 ,  454  and  456  in the example of  FIG. 5A ) to facilitate easy handling during the manufacture of wafers. Once material is molded around the conductive elements to form housings, the retaining features may be disengaged. For example, the tie bars  452 ,  454  and  456  may be severed, thereby providing electronically separate conductive elements and/or separating the wafer strip assemblies  410 A-B from the carrier strips  402 . The resulting individual wafers may then be assembled into daughter board connectors. 
     In the example of  FIG. 5A , ground conductors (e.g., the ground conductor  430 ) are wider compared to signal conductors (e.g., the signal conductor  420 ). Such a configuration may be suitable for carrying differential signals, where it may be desirable to have the two signal conductors within a differential pair disposed close to each other to facilitate preferential coupling. However, it should be appreciated that aspects of the present disclosure are not limited to the use of differential signals. Various concepts disclosed herein may alternatively be used in connectors adapted to carry single-ended signals. 
     Although the illustrative lead frame  400  in the example of  FIG. 5A  has both ground conductors and signal conductors, such a construction is not required. In alternative embodiments, ground and signal conductors may be formed in two separate lead frames, respectively. In yet some embodiments, no lead frame may be used, and individual conductive elements may instead be employed during manufacture. Additionally, in some embodiments, no insulative material may be molded over a lead frame or individual conductive elements, as a wafer may be assembled by inserting the conductive elements into one or more preformed housing portions. If there are multiple housing portions, they may be secured together with any suitable one or more attachment features, such as snap fit features. 
     The wafer strip assemblies shown in  FIG. 5A  provide just one illustrative example of a component that may be used in the manufacture of wafers. Other types and/or configurations of components may also be suitable. For example, a sheet of conductive material may be stamped to include one or more additional carrier strips and/or bridging members between conductive elements for positioning and/or support of the conductive elements during manufacture. Accordingly, the details shown in  FIG. 5A  are merely illustrative and are non-limiting. 
       FIG. 5B  is a detailed view of a group of mating contacts of the illustrative wafer strip assembly  410 B at the region circled by the arrow  5 B- 5 B shown in  FIG. 5A , in accordance with some embodiments. In this example, the group of mating contacts include a pair of mating contacts  424   1  positioned between two other mating contacts  434   1  and  434   2 . The mating contact pair  424   1  may be mating contacts of two conductors adapted to carry a differential signal, whereas the mating contacts  434   1  and  434   2  may be those of ground conductors. However, it should be appreciated that aspects of the present disclosure are not limited to the use of differential signals. Various concepts disclosed herein may alternatively be used in connectors adapted to carry single-ended signals. 
     In the example of  FIG. 5B , the ground conductors may have mating contacts of different sizes. For example, the mating contact  434   2  may be wider than the mating contact  434   1 . To reduce the size of a wafer, smaller mating contacts such as the mating contact  434   1  may be positioned on one or both ends of the wafer. However, it should be appreciated that aspects of the present disclosure are not limited to mating contacts of any particular size. 
     In some embodiments, one or more of the mating contacts of conductive elements in a daughter card connector may have a dual beam structure. For example, the illustrative mating contact  434   1  in the example of  FIG. 5B  includes beams  460   1  and  460   2 , and the illustrative mating contact  434   2  includes two beams  460   7  and  460   8 . Likewise, the illustrative mating contact pair  424   1  in the example of  FIG. 5B  includes four beams, two for each of the signal conductors of the differential pair. In particular, in this example, beams  460   3  and  460   4  are associated with one signal conductor of the pair and beams  460   5  and  460   6  are associated with the other signal conductor of the pair. 
     In the example of  FIG. 5B , each of the contact beams includes a mating surface, of which mating surface  462  on the beam  460   1  is numbered. To form a reliable electrical connection between a conductive element in the daughter card connector  116  and a corresponding conductive element in the backplane connector  114 , each of the beams  460   1  . . .  460   8  may be shaped to press against a corresponding mating contact in the backplane connector  114  with sufficient mechanical force. Having two beams per contact increases the likelihood that an electrical connection will be formed even if one beam is damaged, contaminated or otherwise precluded from making an effective connection. However, aspect of the present disclosure are not limited to the use of dual-beam contacts, as other types of contacts may also be suitable. Examples of suitable contact designs are discussed in greater detail below. 
     It should be appreciated that some or all of the concepts discussed above in connection with daughter card connectors for providing desirable characteristics may also be employed in the backplane connectors. For example, in some embodiments, signal conductors in a backplane connector (e.g., the backplane connector  114  in the example of  FIG. 1B ) may be arranged in columns, each containing differential pairs interspersed with ground conductors. The ground conductors may be wider relative to the signal conductors. Also, adjacent columns may have different configurations. For example, in some embodiments, some of the columns may have narrow ground conductors at one end or both ends to save space, while providing a desired ground configuration around signal conductors. Additionally, ground conductors in one column may be positioned adjacent to corresponding differential pairs in an adjacent column, which may reduce crosstalk from one column to the next. Furthermore, lossy material may be selectively placed within the shroud of a backplane connector (e.g., the illustrative shroud  120  in the example of  FIG. 1B ) to reduce crosstalk, without causing an undesirable level of attenuation for signals. For example, lossy material may be selectively placed in strips or portions of any suitable size adjacent a mating contact portion of a connector. Further still, adjacent signal conductors and ground conductors may have conforming portions so that in locations where the profile of either a signal conductor or a ground conductor changes, the signal-to-ground spacing may be maintained. 
       FIG. 6  shows a cross section of an illustrative backplane connector  600 , in accordance with some embodiments. For instance, the backplane connector  600  may be the backplane connector  114  in the example shown in  FIG. 1B . 
     In the example shown in  FIG. 6 , the backplane connector  600  includes a shroud  510  with walls  512  and a floor  514 . In some embodiments, conductive elements may be inserted into the shroud  510  and may have portions extending above the floor  514 , such as portions  530   1  . . .  530   5  and  540   1  . . .  540   4 . In some embodiments, these portions may be adapted to form electrical connections with corresponding mating contacts (e.g., the mating contacts  424   1 ,  434   1 , and  434   2  in the example of  FIG. 5B ) in a daughter card connector when the daughter card connector is mated with (e.g., inserted into) the backplane connector  600 . The conductive elements may also have portions extending below the floor  514 . These portions may form contact tails adapted to be inserted into via holes in a backplane (e.g., the signal holes  136  and/or ground holes  138  in the example shown in  FIG. 1B ) to make electrical connections with traces in the backplane. 
     In the example shown in  FIG. 6 , conductive elements in the backplane connector  600  are arranged in multiple parallel columns. The conductive elements in each column may be positioned and adapted to mate with corresponding conductive elements in a wafer of a daughter card connector when the daughter card connector is inserted into the backplane connector  600 . For example, in some embodiments, some of the conductive elements in the backplane connector  600  may form pairs adapted to carry differential signals (e.g., the pairs  540   1  . . .  540   4 ), while others may be adapted to be grounds (e.g.,  530   1  . . .  530   5 ). Again, it should be appreciated that aspects of the present disclosure are not limited to the use of differential signals. Various concepts disclosed herein may alternatively be used in connectors adapted to carry single-ended signals. 
       FIG. 7A  shows a pair of illustrative contacts  702 A and  702 B mated respectively with a like pair of contacts  704 A and  704 B, in accordance with some embodiments. For example, the contacts  702 A-B may be mating contacts of conductive elements in a daughter card connector (e.g., the daughter card connector  116  in the example of  FIG. 1B ), and the contacts  704 A-B may be mating contacts of conductive elements in a backplane connector (e.g., the backplane connector  114  in the example of  FIG. 1B ), or vice versa. 
     The illustrative contacts shown in  FIG. 7A  may be used as mating contacts for any suitable type of conductive elements. For example, in some embodiments, the contacts  702 A-B and  704 A-B may be mating contacts of conductors adapted to carry a differential signal (e.g., two conductors disposed close to each other to facilitate preferential coupling). However, in alternative embodiments, the contacts  702 A-B and  704 A-B may be mating contacts of two conductors adapted to carry single ended signals. In yet some embodiments, one or both of the contacts  702 A-B may be a mating contact of a ground conductor and correspondingly for the contacts  704 A-B. 
     In the example of  FIG. 7A , the contact  702 A includes a base region  706 A. In some embodiments, the contact  702 A may be a mating contact of a conductive element extending from an insulative housing (not shown), and the base region  706 A may be adjacent the insulative housing. The contact  702 A may further include two elongated members  708 A and  710 A extending from the base region  706 A. In this example, the elongated member  708 A is configured as a blade having a planar member  712 A at the distal end, while the elongated member  710 A is configured as a beam having an arced segment  714 A at the distal end. 
     Similarly, in the example of  FIG. 7A , the contact  704 A may include a base region  716 A and two elongated members  718 A and  720 A. The elongated member  718 A may be configured as a blade having a planar member  722 A at the distal end, while the elongated member  720 A may be configured as a beam having an arced segment  724 A at the distal end. 
     In some embodiments, the contacts  702 A and  704 A may be mated with each other by sliding one of the contacts relative to the other along a direction that is parallel to the elongated members of the contacts  702 A and  704 A. For instance, in the example shown in  FIG. 7A , the contacts  702 A and  704 A may be mated with each other by sliding the contact  702 A along a direction D, while the contact  704 A is held fixed. Alternatively, the contacts  702 A and  704 A may be mated with each other by sliding the contact  704 A opposite the direction D, while the contact  702 A is held fixed. Yet another alternative is to slide the contacts  702 A and  704 A towards each other so that both contacts move relative to some other fixed reference point. 
     In some embodiments, the elongated member  708 A of the contact  702 A may be relatively rigid, while the elongated member  710 A may be relatively compliant. Likewise, the elongated member  718 A of the contact  704 A may be relatively rigid, while the elongated member  720 A may be relatively compliant. Furthermore, the contact  702 A may be aligned with respect to the contact  704 A such that when these two contacts slide against each other in opposite directions into a mated position (e.g., as shown in the example of  FIG. 7A ), a contact surface located on a convex region of the arced segment  714 A of the elongated member  710 A forms an electrical connection with the elongated member  718 A of the contact  704 A, and a contact surface located on a convex region of the arced segment  724 A of the elongated member  720 A forms an electrical connection with the elongated member  708 A of the contact  702 A. As a result, the elongated member  710 A may be deflected and may generate a spring force that presses the arced segment  714 A against the elongated member  718 A, thereby facilitation good electrical connection between the elongated member  710 A and the elongated member  718 A. Similarly, the elongated member  720 A may be deflected and may generate a spring force that presses the arced segment  724 A against the elongated member  708 A, thereby facilitation good electrical connection between the elongated member  720 A and the elongated member  708 A. 
     In some embodiments, the contact  702 A may additionally include a strap  726 A coupling the distal end of the elongated member  708 A and the distal end of the elongated member  710 A. The strap  726 A may be compliant, so that the distal end of the elongated member  710 A may move independently of the distal end of the elongated member  708 A, for example, when the elongated member  710 A is deflected during mating of the contacts  702 A and  704 A. Additionally, the strap  726 A may be conductive and therefore may make an electrical connection between the distal end of the elongated member  708 A and the distal end of the elongated member  710 A. 
     The strap  702 A may be formed in any suitable way, as aspects of the present disclosure are not limited to any particular manufacturing method. For example, in some embodiments, the strap  726 A may be a separate piece welded or otherwise attached onto the elongated members  708 A and  710 A. Similarly, either or both of the elongated members  708 A and  710 A may be welded or otherwise attached to the base region  706 A. In alternative embodiments, the strap  726 A and the elongated members  708 A and  710 A may all be stamped from a same sheet of material (e.g., some suitable metal alloy) and may be bent, stretched, or otherwise worked into desired configurations. 
       FIG. 7B  is a side view of the illustrative contacts  702 A and  704 A in the example of  FIG. 7A , in accordance with some embodiments. In this view, the elongated member  720 A of the contact  704 A is visible and the arced segment  724 A of the elongated member  720 A is shown in electrical contact with the elongated member  708 A of the contact  702 A at a contact region  730 A. Thus, the distal end of the elongated member  708 A is a distance S1 away from the contact region  730 A. 
     The portion of the elongated member  708 A between the distal end and the contact region  730 A is sometimes referred to as a “wipe” region. Providing sufficient wipe may help to ensure that adequate electrical connection is made between the contacts  702 A and  704 A even if the arced segment  724 A of the elongated member  720 A does not reach an intended contact region of the elongated member  708 A due to manufacturing and/or assembly variances. However, the inventors have also recognized and appreciated that a wipe region may form an unterminated stub when electrical currents flow between mated contacts of two connectors. The presence of such an unterminated stub may lead to unwanted resonances, which may lower the quality of the signals carried through the mated connectors. 
     In some embodiments, the strap  726 A coupling the distal end of the elongated member  708 A and the distal end of the elongated member  710 A may provide a structure to reduce an unterminated stub on the elongated member  708 A while still providing sufficient wipe to ensure adequate electrical connection. In the example shown in  FIG. 7B , the arced segment  714 A of the elongated member  710 A is in electrical contact with the elongated member  718 A of the contact  704 A at a contact region  732 A. As a result, when the contacts  702 A and  704 A are mated together, electrical current may flow through the portion of the elongated member  710 A that is above the contact region  732 A. By connecting the distal end of the elongated member  708 A with the portion of the elongated member  710 A that is above the contact region  732 A, the strap  726 A may allow electrical current to flow through a portion of the elongated member  708 A between the strap  726 A and the contact region  730 A, thereby reducing the unterminated stub length from S1 to S2. 
       FIG. 7C  is a front view of the illustrative contacts  702 A-B and  704 A-B in the example of  FIG. 7A , in accordance with some embodiments. As seen in this view, the contact  702 B may be a mirror image of the contact  702 A, and the contact  704 B may be a mirror image of the contact  704 A. However, it should be appreciated that adjacent contacts need not be mirror images of each other, as other configurations may also be suitable. For example, a pair of identical contacts may be used, or contacts that are neither identical, nor mirror images of each other. 
       FIG. 8A  shows an pair of illustrative contacts  802 A and  802 B mated respectively with another pair of illustrative contacts  804 A and  804 B, in accordance with some embodiments. In this example, the contact  802 A includes two elongated members  808 A and  810 A, which may be similar to the elongated members  708 A and  710 A of the contact  702 A in the example of  FIG. 7A . However, unlike the elongated members  708 A and  710 A which are generally parallel, the elongated members  808 A and  810 A may lie in different planes that intersect each other. For instance, in the example shown in  FIG. 8A , the elongated members  808 A and  810 A lie in orthogonal planes. However, it should be appreciated that a right angle between the elongated members  808 A and  810 A is not required, as other angles may also be suitable. 
     Having the elongated members  808 A and  810 A disposed at an angle from each other may have one or more benefits. For example, an overall width of the contact  802 A may be reduced, so that more contacts like the contact  802 A may fit into a column of contacts having a fixed width. This may allow higher signal density in a connector, even though an overall thickness of the contact  802 A may be increased at the same time. As another example, having the elongated members  808 A and  810 A disposed at an angle from each other may allow the elongated members  808 A and  810 A to be made smaller and/or disposed further away from each other, so as to increase the ratio between air and conductive material at the mating interface between a backplane connector and a daughter card connector. This may lead to a decrease in impedance and as a result improved signal quality (e.g., when the connectors operate at a high data rate, such as 1.25, 6.25, 10, 20, 25, 30, 35, 40, or 45 Gbits/second, and/or a high frequency, such as 4, 7.5, 18, 25, 30, 40, 50, GHz). 
     Additionally, reducing the size of mating contacts may allow more space in which one or more shield members may be placed around one or more of the mating contacts, which may also improve signal quality. However, as noted above, the presence more metal and/or less air at the mating interface may increase impedance. Accordingly, a tradeoff may be made between providing more shielding and reducing the amount of metal at the mating interface. 
     In some embodiments, the amount of metal used at the mating interface may be reduced by using composite shield members. For example, a composite shield may be made by plating metal over electrically conductive plastic. The metal plating may provide shielding, while the conductive plastic may dampen unwanted resonances from the metal plating. Because the metal plating can be made very thin, the use of such composite shields may provide space savings over alternative designs with plastic molded over metal shields. Additionally, the metal plating on a composite shield may be coupled to ground, so that no separate ground conductor may be used, which may provide further space savings. However, it should be appreciated that aspects of the present disclosure are not limited to the use of composite shield members with metal plating, nor to the use of shields at all. 
     In some embodiments, the positioning of metal shields may be controlled using selective plating techniques. For example, precise areas on a piece of conductive plastic at which shielding is desired may be activated in some suitable fashion (e.g., using a laser), so that metal plating attaches only to the activated areas. Examples of selective plating techniques can be found in United States Patent Application Publication No. 2010/0323109, which is incorporated herein by reference in its entirety. However, it should be appreciated that aspects of the present disclosure are not limited to the use of those techniques, nor to the use of selective plating at all. 
     In the example shown in  FIG. 8A , the contact  804 A also includes two elongated members  818 A and  820 A, which may be similar to the elongated members  718 A and  720 A of the contact  704 A in the example of  FIG. 7A . As the elongated members  808 A and  810 A of the contact  802 A lie in orthogonal planes, the elongated members  820 A and  818 A may have a similar configuration so as to be aligned respectively with the elongated members  808 A and  810 A. 
       FIG. 8B  is a bottom view of the illustrative contacts  802 A-B and  804 A-B in the example of  FIG. 8A , in accordance with some embodiments. As seen in this view, the contact  804 A may be sized and/or shaped to fit inside a corner or nook formed by the elongated members of the contact  802 A. A strap  834 A connecting the elongated members of the contact  804 A may therefore be shorter than a strap  826 A connecting the elongated members of the contact  802 A. 
       FIG. 8C  is a front view of the illustrative contacts  802 A-B and  804 A-B in the example of  FIG. 8A , in accordance with some embodiments. As seen in this view, the contact  802 B may be a mirror image of the contact  802 A, and the contact  804 B may be a mirror image of the contact  804 A. Again, it should be appreciated that adjacent contacts need not be mirror images of each other, as other configurations may also be suitable, such as identical contacts, or contacts that are neither identical, nor mirror images of each other. 
       FIG. 8D  is a side view of the illustrative contacts  802 A and  804 A in the example of  FIG. 8A , in accordance with some embodiments. 
       FIG. 9A  shows an pair of illustrative contacts  902 A and  902 B mated respectively with another pair of illustrative contacts  904 A and  904 B, in accordance with some embodiments. In this example, the contact  902 A includes two elongated members  908 A and  910 A, which may be similar to the elongated members  808 A and  810 A of the contact  802 A in the example of  FIG. 8A . However, a strap  926 A may connect the elongated members  908 A and  910 A at locations different from where the strap  826 A connects the elongated members  808 A and  810 A in the example of  FIG. 8A . For instance, in the example of  FIG. 9A , the strap  926 A may be coupled to the elongated member  908 A at the distal end so as to completely or almost completely eliminate any unterminated stub on the elongated member  908 A. In addition, the strap  926 A may be coupled to the elongated member  910 A at the proximal end, near a base region  906 A of the contact  902 A. 
       FIG. 9B  is a bottom view of the illustrative contacts  902 A-B and  904 A-B in the example of  FIG. 9A , in accordance with some embodiments. As seen in this view, the contact  904 A may be sized and/or shaped to fit inside a corner or nook formed by the elongated members of the contact  902 A. 
       FIG. 9C  is a front view of the illustrative contacts  902 A-B and  904 A-B in the example of  FIG. 9A , in accordance with some embodiments. As seen in this view, the contact  902 B may be a mirror image of the contact  902 A, and the contact  904 B may be a mirror image of the contact  904 A. Again, it should be appreciated that adjacent contacts need not be mirror images of each other, as other configurations may also be suitable, such as identical contacts, or contacts that are neither identical, nor mirror images of each other. 
       FIG. 10A  shows an illustrative contact  1002  mated with another contact  1004 , in accordance with some embodiments. For example, the contact  1002  may be a mating contact for a conductive element in a daughter card connector (e.g., the daughter card connector  116  in the example of  FIG. 1B ), and the contact  1004  may be a mating contact of a conductive element in a backplane connector (e.g., the backplane connector  114  in the example of  FIG. 1B ), or vice versa. 
     The illustrative contacts shown in  FIG. 10A  may be used as mating contacts for any suitable type of conductive elements. For example, in some embodiments, the contacts  1002  and  1004  may be mating contacts of conductors adapted to carry a differential signal. However, in alternative embodiments, the contacts  1002  and  1004  may be mating contacts of conductors adapted to carry single ended signals. In yet some embodiments, the contacts  1002  and  1004  may be mating contacts of ground conductors. 
     In the example of  FIG. 10A , the contact  1002  includes a bridge region  1006 . In some embodiments, the contact  1006  may be a mating contact of a conductive element extending from an insulative housing (not shown), and the bridge region  1006  may be adjacent the insulative housing. The contact  1002  may further include two elongated members  1008  and  1010  extending from the bridge region  1006 . In this example, each of the elongated members  1008  and  1010  is configured as a tube having one or more tabs formed thereon. For example, the elongated member  1008  has a tab  1012  formed on one side, and may have another tab  1011  (not visible in  FIG. 10A  but shown in  FIG. 10B ) formed on the opposite side. Likewise, the elongated member  1010  has a tab  1014  formed on one side, and may have another tab  1013  (not visible in  FIG. 10A  but shown in  FIG. 10B ) formed on the opposite side. 
     The elongated members  1008  and  1010  may be formed in any suitable way, as aspects of the present disclosure are not limited to any particular method of manufacturing. For example, in some embodiments, the elongated members  1008  and  1010  may be formed by rolling pliable sheets of conductive material (e.g., a suitable metal alloy) into tubes. In alternative embodiments, the elongated members  1008  and  1010  may be made from drawn tubes of conductive material, and one or more other pieces (e.g., the bridge region  1006 ) may be welded or otherwise attached onto either or both of the elongated members  1008  and  1010 . 
     The tabs  1012  and  1014  may also be formed in any suitable fashion. For example, in some embodiments, the tab  1014  may be stamped from the same sheet of conductive material as the elongated member  1010  and may remain attached to the elongated member  1010  at a base region  1015 . In alternative embodiments, the tab  1014  may be a separate piece welded or otherwise attached to the elongated member  1010 . 
     In the example show in  FIG. 10A , the tabs  1012  and  1014  may be configured to respectively engage elongated members  1018  and  1020  of the contact  1004  to form electrical connections. In this example, the elongated members  1018  and  1020  are configured as pins, which may be relatively rigid. As the elongated members  1018  and  1020  are inserted respectively into the elongated members  1008  and  1010 , the elongated members  1018  and  1020  may deflect the tabs  1012  and  1014 , thereby generating spring forces that press the tabs  1012  and  1014  against the elongated members  1018  and  1020 , respectively, to form reliable electrical connections. 
     In the example of  FIG. 10A , the tab  1014  has an arced segment  1016  at a distal end, and a convex region of the arced segment  1016  may be in electrical contact with the elongated member  1020  when the elongated members  1010  and  1020  are mated. In some embodiments, the surface of the convex region of the arced segment  1016  may be coated with a suitable material, for example, to improve electrical properties. Any suitable material may be used, such as gold, silver, etc., or some suitable alloy. Additionally, the coated material may be ductile. In some embodiments, a region on the inner surface the elongated member  1020  that comes into contact with the tab  1014  may be coated with the same or a different material in addition to, or instead of, the coating on the tab  1014 . 
       FIG. 10B  is a side view of the illustrative contacts  1002  and  1004  in the example of  FIG. 10A , in accordance with some embodiments. In this view, the arced segment  1016  of the elongated member  1010  is shown in electrical contact with the elongated member  1020  at a contact region  1017 . Thus, if the elongated member  1020  extends towards the top of the elongated member  1010  (e.g., near the bridge region  1006 ), an unterminated stub of length S3 may result. However, resonances from the unterminated stub may be shielded completely or almost completely by the elongated member  1010 , because the elongated member  1020  is enclosed by the elongated member  1010 . 
       FIG. 10C  is a bottom view of the illustrative contacts  1002  and  1004  in the example of  FIG. 10A , in accordance with some embodiments. In this view, the elongated member  1018  is seen being enclosed by the elongated member  1008 , and the elongated member  1020  is seen being enclosed by the elongated member  1010 . Additionally, the arced segment  1016  of the tab  1014  of the elongated member  1010  is seen being in contact with the elongated member  1020 . 
       FIG. 11A  shows a pair of illustrative contacts  1102 A and  1102 B mated respectively with another pair of illustrative contacts  1104 B and  1104 A, in accordance with some embodiments. In this example, each of the contacts  1102 A and  1102 B is configured as an elongated tube, which may be similar to the elongated member  1008  in the example shown in  FIG. 10A  and described above. However, the contacts  1102 A and  1102 B may have a cross section that is not round. Rather, in some embodiments, the cross section may be roughly rectangular. For instance, in the example shown in  FIG. 11A , the contacts  1102 A and  1102 B may have a cross section that is square with rounded corners. 
     Furthermore, in the example shown in  FIG. 11A , the contacts  1102 A and  1102 B each have only three sides, so that the elongated tubes are open towards each other. In an embodiment in which the contacts  1102 A and  1102 B are electrically connected, respectively, to a pair of conductors carrying a differential signal, this configuration may allow better coupling of the signals carried by the pair. However, it should be appreciated that aspects of the present disclosure are not limited to the use of differential signals, and the contacts  1102 A and  1102 B may also be used with conductors adapted to carry single-ended signals, or with ground conductors. 
     In some embodiments, the contacts  1102 A and  1102 B may have one or more tabs formed thereon. For instance, in the example shown in  FIG. 11A , the contact  1102 A has tabs  1114 A and  1116 A formed on one side. Likewise, the contact  1102 B has two tabs (not labeled) formed on one side. However, it should be appreciated that any suitable number of tabs may be used, as aspects of the present disclosure are not limited in this regard. 
     Additionally, in embodiments in which multiple tabs are used, such tabs may be configured in any suitable manner. For instance, in the example shown in  FIG. 11A , the tabs  1114 A and  1116 A may be in opposite orientations, so that they may share a base region  1115 A and their distal ends point away from each other. In alternative embodiments, the tabs may instead have the same orientation. Also, in various embodiments, the tabs may be disposed closer or farther away from each other. 
     In the example shown in  FIG. 11A , the tabs  1114 A and  1116 A may be configured to engage the contact  1104 A to form an electrical connection. In this example, the contacts  1104 A and  1104 B are configured as pins, which may be relatively rigid. As the contact  1104 A is inserted into the contact  1102 A, the contact  1104 A may deflect the tabs  1114 A and  1116 A, thereby generating spring forces that press the tabs  1114 A and  1116 A against the contact  1104 A. Having multiple points of contact (e.g., one at the tab  1114 A and another at the tab  1116 A) may facilitate forming a reliable electrical connection. 
       FIG. 11B  is a front view of the illustrative contacts in the example of  FIG. 11A , in accordance with some embodiments. 
       FIG. 11C  is a bottom view of the illustrative contacts in the example of  FIG. 11A , in accordance with some embodiments. In this view, the contact  1104 A is seen being partially enclosed by the contact  1102 A, and the contact  1104 B is seen being partially enclosed by the contact  1102 B, so that only air is between the contacts  1104 A and  1104 B. Additionally, the tab  1114 A of the contact  1102 A is seen being in contact with the contact  1104 A. 
       FIG. 12A  shows an illustrative contact  1202  mated with another contact  1204 , in accordance with some embodiments. In this example, the contact  1202  includes an elongated planar portion  1206  connect to a base portion  1215 . The base portion  1215  may be perpendicular to the planar portion  1206  and may have an opening  1216  formed therein and configured to receive the contact  1204 , so that when the contact  1204  is inserted into the opening  1216 , the contact  1204  is generally parallel to the planar portion and may extend along any portion of the length of the planar portion  1206 . 
     In the example of  FIG. 12A , the base portion  1216  has attached thereto two beams  1212  and  1214 , which may be configured to engage the contact  1204  when the contact  1204  is inserted into the opening  1216 . For instance, in some embodiments, the beams  1212  and  1214  may be disposed opposite to each other, so that they engage the contact  1204  at opposite sides when the contact  1204  is inserted into the opening  1216 . However, it should be appreciated that aspects of the present disclosure are not limited to any particular configuration of the beams  1212  and  1214 . 
     The contact  1202  may be formed in any suitable manner. For example, any one or more of the planar portion  1206 , the base  1216 , and the beams  1212  and  1214  may be welded or otherwise attached to another piece. Alternatively, all of these pieces may be stamped from a single sheet of conductive material. 
       FIG. 12B  is a front view of the illustrative contacts in the example of  FIG. 12A , in accordance with some embodiments. 
       FIG. 12C  is a side view of the illustrative contacts in the example of  FIG. 12A , in accordance with some embodiments. 
       FIG. 12D  is a bottom view of the illustrative contacts in the example of  FIG. 12A , in accordance with some embodiments. 
       FIG. 13A  shows a pair of illustrative contacts  1302 A and  1302 B mated respectively with another pair of illustrative contacts  1304 A and  1304 B, in accordance with some embodiments. In this example, the contact  1302 A includes two elongated members  1308 A and  1310 A configured as beams, which may be relatively compliant, and the contact  1304 A is configured as a blade, which may be relatively rigid. 
     In some embodiments, the elongated members  1308 A and  1310 A may be configured to engage the contact  1304 A in a mated configuration (e.g., as shown in  FIG. 13A ) to provide two points of contact  1316 A and  1318 A (e.g., as shown in  FIG. 13C ). The contact points  1316 A and  1318 A may be offset from each other along the length of the contact  1304 A. In some embodiments, an intended contact region on the contact  1304 A for the elongated member  1310 A may be close to the distal end of the contact  1304 A to reduce an unterminated stub length. 
     In some embodiments, the elongated members  1308 A and  1310 A may be formed by stamping two elongated portions from a single sheet of material and thereafter “folding” them over each other. For instance, in the example shown in  FIG. 13A , the “fold” may be at a region  1326 A connecting the elongated members  1308 A and  1310 A. Thus, the elongated members  1308 A and  1310 A may overlap or cross each other at one or more locations, for example, at a region  1312 A shown in  FIG. 13A  and a region  1314 A shown in  FIG. 13C . This may allow the elongated members  1308 A and  1310 A to make electrical connections with the contact  1304 A at two points that are vertically aligned with each other (e.g., at  1320 A and  1322 A in the example of  FIG. 13B ). However, it should be appreciated that an folding operation is not required, as the elongated members  1308 A and  1310 A may alternatively be separate pieces that are attached to each other, for example, by welding. 
       FIG. 13B  is a front view of the illustrative contacts in the example of  FIG. 13A , in accordance with some embodiments; 
       FIG. 13C  is a side view of the illustrative contacts in the example of  FIG. 13A , in accordance with some embodiments. 
       FIG. 13D  is a bottom view of the illustrative contacts in the example of  FIG. 13A , in accordance with some embodiments. 
       FIG. 14A  shows a pair of illustrative contacts  1402 A and  1402 B mated respectively with another pair of illustrative contacts  1404 A and  1404 B, in accordance with some embodiments. In this example, the contact  1402 A includes two elongated members  1408 A and  1410 A configured as beams, which may be similar to the elongated members  1308 A and  1310 A in the example of  FIG. 13A . However, in the example of  FIG. 14A , the elongated members  1408 A and  1410 A do not cross or overlap each other. 
     In some embodiments, the elongated members  1408 A and  1410 A may be configured to engage the contact  1404 A in a mated configuration (e.g., as shown in  FIG. 14A ) to provide two points of contact  1416 A and  1418 A (e.g., as shown in  FIG. 14C ). The contact points  1416 A and  1418 A may be offset from each other along the length of the contact  1404 A. In some embodiments, the two points of contact may be offset from each other both vertically and horizontally. For instance, in the example of  FIG. 14A , the contact  1404 A includes a widened planar portion  1412 A at its distal end to engage the elongated member  1408 A. 
     In the example of  FIG. 14A , the elongated member  1410 A is longer than the elongated member  1408 A and is disposed further away from the contact  1404 A. This may allow more air around the elongated members  1408 A and  1410 A and the contact  1404 A, which may reduce impedance and thereby improve signal quality. 
       FIG. 14B  is a front view of the illustrative contacts in the example of  FIG. 14A , in accordance with some embodiments. 
       FIG. 14C  is a side view of the illustrative contacts in the example of  FIG. 14A , in accordance with some embodiments. 
       FIG. 14D  is a bottom view of the illustrative contacts in the example of  FIG. 14A , in accordance with some embodiments. 
       FIG. 15A  shows a pair of illustrative contacts  1502 A and  1502 B mated respectively with another pair of illustrative contacts  1504 A and  1504 B, in accordance with some embodiments. In the example of  FIG. 15A , the contact  1502 A includes a base region  1506 A and two elongated members  1508 A and  1510 A extending from the base region  1506 A. In some embodiments, the elongated members  1508 A and  1510 A may be configured as beams each having at least one arced segment at any suitable location (e.g., the arced segments  1514 A and  1516 A in the example of  FIG. 15A ). 
     In the example shown in  FIG. 15A , the contact  1502 A further includes a strap  1526 A connecting the distal ends of the elongated members  1508 A and  1510 A, so that the base region  1506 A, the elongated members  1508 A and  1510 A, and the strap  1526 A together form a closed lope, thereby eliminating any unterminated stub. 
     In some embodiments, the contact  1504 A may be configured as a blade having an “L” shaped cross section and two orthogonal faces  1518 A and  1520 A. The base region  1506 A and the strap  1526 A of the contact  1502 A may each include a bend to conform to the “L” shape of the contact  1504 A, so that the elongated members  1508 A and  1510 A are disposed adjacent to the faces  1518 A and  1520 A, respectively. As a result, the arced segments  1514 A and  1516 A engage the contact  1504 A at the faces  1518 A and  1520 A, respectively, when the contact  1502 A is mated with the contact  1504 A. 
       FIG. 15B  is a front view of the illustrative contacts in the example of  FIG. 15A , in accordance with some embodiments. 
       FIG. 15C  is a bottom view of the illustrative contacts in the example of  FIG. 15A , in accordance with some embodiments. 
       FIG. 16A  shows a pair of illustrative contacts  1602 A and  1602 B mated respectively with another pair of illustrative contacts  1604 A and  1604 B, in accordance with some embodiments. The contacts  1602 A-B and  1604 A-B may be similar to the contacts  1502 A-B and  1504 A-B in the example of  FIG. 15A . For example, like the contacts  1502 A-B, the contacts  1602 A-B may each have a closed-lope structure. Also, like the contacts  1504 A-B, the contacts  1604 A-B may each have an “L” shaped cross section. However, unlike the contacts  1502 A-B, the contacts  1602 A-B may be disposed inside the “L” shape of the contacts  1604 A-B, rather than being on the outside. Thus, the contacts  1602 A-B may make electrical connections with the contacts  1604 A-B at their inner surfaces. Furthermore, the contacts  1602 A-B may be partially enclosed by the contacts  1604 A-B. 
       FIG. 16B  is a back view of the illustrative contacts in the example of  FIG. 16A , in accordance with some embodiments. 
       FIG. 16C  is a bottom view of the illustrative contacts in the example of  FIG. 16A , in accordance with some embodiments. 
       FIG. 17A  shows a pair of illustrative contacts  1702 A and  1702 B mated respectively with another pair of illustrative contacts  1704 A and  1704 B, in accordance with some embodiments. In this example, the contact  1702 A includes a base region  1715 A having attached thereto two beams  1712 A and  1714 A, which may be configured to engage the contact  1704 A. In some embodiments, the beams  1712 A and  1714 A may be disposed opposite to each other, so that they engage the contact  1704 A at opposite sides when the contact  1704 A is mated with the contact  1702 A. However, it should be appreciated that aspects of the present disclosure are not limited to any particular configuration of the beams  1712 A and  1714 A. 
       FIG. 17B  is a front view of the illustrative contacts in the example of  FIG. 17A , in accordance with some embodiments. 
       FIG. 18A  shows a pair of illustrative contacts  1802 A and  1802 B mated respectively with another pair of illustrative contacts  1804 A and  1804 B, in accordance with some embodiments. In this example, the contact  1802 A includes two opposing beams  1812 A and  1814 A, which may be similar to the beams  1712 A and  1714 A in the example of  FIG. 17A . However, the contact  1802 A may include an additional beam  1816 A which may be shorter than the beams  1812 A and  1814 A. Thus, when the contact  1802 A is mated with the contact  1804 A, the beam  1816 A makes an electrical connection with the contact  1804 A at a contact region that is closer to the distal end of the contact  1804 A than the contact regions for the beams  1812 A and  1814 A. This may reduce an unterminated stub length of the contact  1804 A. Additionally, any remaining unterminated stub of the contact  1804 A may be enclosed on three sides by the beams  1812 A,  1814 A, and  1816 A, which may reduce unwanted resonances. 
       FIG. 18B  is a front view of the illustrative contacts in the example of  FIG. 18A , in accordance with some embodiments. 
       FIG. 18C  is a side view of the illustrative contacts in the example of  FIG. 18A , in accordance with some embodiments. 
       FIG. 18D  is a bottom view of the illustrative contacts in the example of  FIG. 18A , in accordance with some embodiments. 
       FIG. 19A  shows a pair of illustrative contacts  1902 A and  1902 B mated respectively with another pair of illustrative contacts  1904 A and  1904 B, in accordance with some embodiments. In this example, the contact  1902 A has a “Y” shaped structure. 
       FIG. 19B  is a front view of the illustrative contacts in the example of  FIG. 19A , in accordance with some embodiments. 
       FIG. 19C  is a side view of the illustrative contacts in the example of  FIG. 19A , in accordance with some embodiments. 
       FIG. 20A  shows a pair of illustrative contacts  2002 A and  2002 B mated respectively with another pair of illustrative contacts  2004 A and  2004 B, in accordance with some embodiments. In this example, the contact  2002 A has a “Y” shaped structure with a strap  2026 A connecting the two upper legs of the “Y.” 
       FIG. 20B  is a front view of the illustrative contacts in the example of  FIG. 20A , in accordance with some embodiments; 
       FIG. 20C  is a side view of the illustrative contacts in the example of  FIG. 20A , in accordance with some embodiments; 
       FIG. 21A  shows a pair of illustrative contacts  2102 A and  2102 B mated respectively with another pair of illustrative contacts  2104 A and  2104 B, in accordance with some embodiments. In this example, the contact  2102 A has a “Y” shaped structure with an additional leg  2126 A connecting the two upper legs of the “Y.” 
       FIG. 21B  is a front view of the illustrative contacts in the example of  FIG. 21A , in accordance with some embodiments. 
       FIG. 21C  is a side view of the illustrative contacts in the example of  FIG. 21A , in accordance with some embodiments. 
     As discussed above, lossy material may be placed at one or more locations in a connector in some embodiments, for example, to reduce crosstalk. Any suitable lossy material may be used. Materials that conduct, but with some loss, over the frequency range of interest are referred to herein generally as “lossy” materials. Electrically lossy materials can be formed from lossy dielectric and/or lossy conductive materials. The frequency range of interest depends on the operating parameters of the system in which such a connector is used, but will generally have an upper limit between about 1 GHz and 25 GHz, although higher frequencies or lower frequencies may be of interest in some applications. Some connector designs may have frequency ranges of interest that span only a portion of this range, such as 1 to 10 GHz or 3 to 15 GHz or 3 to 6 GHz. 
     Electrically lossy material can be formed from material traditionally regarded as dielectric materials, such as those that have an electric loss tangent greater than approximately 0.003 in the frequency range of interest. The “electric loss tangent” is the ratio of the imaginary part to the real part of the complex electrical permittivity of the material. Electrically lossy materials can also be formed from materials that are generally thought of as conductors, but are either relatively poor conductors over the frequency range of interest, contain particles or regions that are sufficiently dispersed that they do not provide high conductivity or otherwise are prepared with properties that lead to a relatively weak bulk conductivity over the frequency range of interest. Electrically lossy materials typically have a conductivity of about 1 siemens/meter to about 6.1×10 7  siemens/meter, preferably about 1 siemens/meter to about 1×10 7  siemens/meter and most preferably about 1 siemens/meter to about 30,000 siemens/meter. In some embodiments material with a bulk conductivity of between about 10 siemens/meter and about 100 siemens/meter may be used. As a specific example, material with a conductivity of about 50 siemens/meter may be used. However, it should be appreciated that the conductivity of the material may be selected empirically or through electrical simulation using known simulation tools to determine a suitable conductivity that provides both a suitably low crosstalk with a suitably low insertion loss. 
     Electrically lossy materials may be partially conductive materials, such as those that have a surface resistivity between 1 Ω/square and 106 Ω/square. In some embodiments, the electrically lossy material has a surface resistivity between 1 Ω/square and 103 Ω/square. In some embodiments, the electrically lossy material has a surface resistivity between 10 Ω/square and 100 Ω/square. As a specific example, the material may have a surface resistivity of between about 20 Ω/square and 40 Ω/square. 
     In some embodiments, electrically lossy material is formed by adding to a binder a filler that contains conductive particles. In such an embodiment, a lossy member may be formed by molding or otherwise shaping the binder into a desired form. Examples of conductive particles that may be used as a filler to form an electrically lossy material include carbon or graphite formed as fibers, flakes or other particles. Metal in the form of powder, flakes, fibers or other particles may also be used to provide suitable electrically lossy properties. Alternatively, combinations of fillers may be used. For example, metal plated carbon particles may be used. Silver and nickel are suitable metal plating for fibers. Coated particles may be used alone or in combination with other fillers, such as carbon flake. The binder or matrix may be any material that will set, cure or can otherwise be used to position the filler material. In some embodiments, the binder may be a thermoplastic material such as is traditionally used in the manufacture of electrical connectors to facilitate the molding of the electrically lossy material into the desired shapes and locations as part of the manufacture of the electrical connector. Examples of such materials include LCP and nylon. However, many alternative forms of binder materials may be used. Curable materials, such as epoxies, may serve as a binder. Alternatively, materials such as thermosetting resins or adhesives may be used. 
     Also, while the above described binder materials may be used to create an electrically lossy material by forming a binder around conducting particle fillers, the invention is not so limited. For example, conducting particles may be impregnated into a formed matrix material or may be coated onto a formed matrix material, such as by applying a conductive coating to a plastic component or a metal component. As used herein, the term “binder” encompasses a material that encapsulates the filler, is impregnated with the filler or otherwise serves as a substrate to hold the filler. 
     Preferably, the fillers will be present in a sufficient volume percentage to allow conducting paths to be created from particle to particle. For example, when metal fiber is used, the fiber may be present in about 3% to 40% by volume. The amount of filler may impact the conducting properties of the material. 
     Filled materials may be purchased commercially, such as materials sold under the trade name Celestran® by Ticona. A lossy material, such as lossy conductive carbon filled adhesive preform, such as those sold by Techfilm of Billerica, Mass., US may also be used. This preform can include an epoxy binder filled with carbon particles. The binder surrounds carbon particles, which acts as a reinforcement for the preform. Such a preform may be inserted in a wafer to form all or part of the housing. In some embodiments, the preform may adhere through the adhesive in the preform, which may be cured in a heat treating process. In some embodiments, the adhesive in the preform alternatively or additionally may be used to secure one or more conductive elements, such as foil strips, to the lossy material. 
     Various forms of reinforcing fiber, in woven or non-woven form, coated or non-coated may be used. Non-woven carbon fiber is one suitable material. Other suitable materials, such as custom blends as sold by RTP Company, can be employed, as the present invention is not limited in this respect. 
     In some embodiments, a lossy member may be manufactured by stamping a preform or sheet of lossy material. For example, an insert may be formed by stamping a preform as described above with an appropriate patterns of openings. However, other materials may be used instead of or in addition to such a preform. A sheet of ferromagnetic material, for example, may be used. 
     However, lossy members also may be formed in other ways. In some embodiments, a lossy member may be formed by interleaving layers of lossy and conductive material, such as metal foil. These layers may be rigidly attached to one another, such as through the use of epoxy or other adhesive, or may be held together in any other suitable way. The layers may be of the desired shape before being secured to one another or may be stamped or otherwise shaped after they are held together. 
     Having thus described several embodiments, it is to be appreciated various alterations, modifications, and improvements may readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only. 
     Various changes may be made to the illustrative structures shown and described herein. For example, examples of techniques are described for improving signal quality at the mating interface of an electrical interconnection system. These techniques may be used alone or in any suitable combination. Furthermore, the size of a connector may be increased or decreased from what is shown. Also, it is possible that materials other than those expressly mentioned may be used to construct the connector. As another example, connectors with four differential signal pairs in a column are used for illustrative purposes only. Any desired number of signal conductors may be used in a connector. 
     Manufacturing techniques may also be varied. For example, embodiments are described in which the daughter card connector  116  is formed by organizing a plurality of wafers onto a stiffener. It may be possible that an equivalent structure may be formed by inserting a plurality of shield pieces and signal receptacles into a molded housing. 
     Furthermore, although many inventive aspects are shown and described with reference to a daughter board connector having a right angle configuration, it should be appreciated that aspects of the present disclosure is not limited in this regard, as any of the inventive concepts, whether alone or in combination with one or more other inventive concepts, may be used in other types of electrical connectors, such as backplane connectors, cable connectors, stacking connectors, mezzanine connectors, I/O connectors, chip sockets, etc.