Patent Publication Number: US-2021184404-A1

Title: High-frequency electrical connector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 16/689,993, filed on Nov. 20, 2019, entitled “HIGH-FREQUENCY ELECTRICAL CONNECTOR,” which claims priority to and the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 62/770,462, filed on Nov. 21, 2018, entitled “HIGH-FREQUENCY ELECTRICAL CONNECTOR.” The entire contents of these applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     This disclosure relates generally to electrical interconnection systems and more specifically to improved signal integrity in interconnection systems, particularly in high speed electrical connectors. 
     Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system as separate electronic assemblies, such as printed circuit boards (“PCBs”), which may be joined together with electrical connectors. A known 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 known backplane has the form of a printed circuit board onto which many connectors may be mounted. Conductive 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.” Other known connectors include, but are not limited to, orthogonal midplane connectors and midplaneless direct attachment orthogonal 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 affect 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. Further shields are shown in U.S. Publication No. 2013/0109232. 
     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. U.S. Pat. No. 7,985,097 is a further example of a shielded connector. 
     Other techniques may be used to control the performance of a connector. For example, transmitting signals differentially may reduce crosstalk. Differential signals are carried on a pair of conductive 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 conductive paths of the pair. For example, the two conductive 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 conductive 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 signal 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. 
     In an interconnection system, such connectors are attached to printed circuit boards, one of which may serve as a backplanes for routing signals between the electrical connectors and for providing reference planes to which reference conductors in the connectors may be grounded. Typically the backplane is formed as a multi-layer assembly manufactured from stacks of dielectric sheets, sometimes called “prepreg”. Some or all of the dielectric sheets may have a conductive film on one or both surfaces. Some of the conductive films may be patterned, using lithographic or laser printing techniques, to form conductive traces that are used to make interconnections between circuit boards, circuits and/or circuit elements. Others of the conductive films may be left substantially intact and may act as ground planes or power planes that supply the reference potentials. The dielectric sheets may be formed into an integral board structure such as by pressing the stacked dielectric sheets together under pressure. 
     To make electrical connections to the conductive traces or ground/power planes, holes may be drilled through the printed circuit board. These holes, or “vias”, are filled or plated with metal such that a via is electrically connected to one or more of the conductive traces or planes through which it passes. 
     To attach connectors to the printed circuit board, contact pins or contact “tails” from the connectors may be inserted into the vias, with or without using solder. The vias are sized to accept the contact tails of the connector. 
     As in the case of the connectors that attach to the printed circuit boards, the electrical performance of printed circuit boards is at least partially dependent on the structures of the conductive traces, ground planes and vias formed in the printed circuit boards. Further, electrical performance issues become more acute as the density of signal conductors and the operating frequencies of the connectors increase. Such electrical performance issues may include, but are not limited to, crosstalk between closely-spaced signal conductors. 
     SUMMARY 
     In accordance with embodiments, an electrical connector comprises an insulative shell having a floor; a first plurality of contacts extending through the floor, wherein the first plurality of contacts are disposed in a plurality of columns; a second plurality of contacts extending through the floor, wherein the second plurality of contacts are interspersed with the first plurality of contacts within the plurality of columns; and a conductive member adjacent the floor. The conductive member comprises a first plurality of openings, wherein the first plurality of contacts extend through the openings of the first plurality of openings; a second plurality of openings, wherein the second plurality of contacts extend through the openings of the second plurality of openings; and a first plurality of tabs, extending into openings in the insulative shell. 
     In some embodiments, the first plurality of tabs are slidable in the openings in the insulative shell relative to the columns of contacts. 
     In some embodiments, each of the openings in the insulative shell has a pair of opposed slots; and each of the first plurality of tabs is inserted into the pair of opposed slots. 
     In some embodiments, the first plurality of contacts are disposed in a plurality of pairs; within each column of the plurality of columns, each pair of the plurality of pairs is disposed between two adjacent contacts of the second plurality of contacts. 
     In some embodiments, the conductive member reduces near end crosstalk between a first pair and a second pair diagonally adjacent to the first pair by at least 2 dB over the frequency range from 5 to 28 GHz. 
     In some embodiments, each of the second plurality of contacts comprises a mating contact portion and two contact tails, the mating contact portion comprises a contact surface, and each of the second plurality of contacts comprises a twisted region such that a line between the two contact tails is transverse to the contact surface. 
     In some embodiments, the line between the two contact tails is at an angle to the contact surface between 35 and 55 degrees. 
     In some embodiments, a first of the two adjacent second contacts is twisted in a first direction relative to the contact surface; and a second of the two adjacent second contacts is twisted in a second direction, opposite to the first direction, relative to the contact surface. 
     In some embodiments, the floor comprises a plurality of surface portions and a recessed portion, recessed relative to the surface portions; the plurality of surface portions extend through the first plurality of openings; and the conductive member is disposed within the recessed portion. 
     In some embodiments, the first plurality of contacts are disposed in a plurality of pairs; each of the plurality of pairs extends through a surface portion of the plurality of surface portions. 
     In some embodiments, the second plurality of contacts extend through the recessed portion. 
     In some embodiments, the first plurality of contacts and the second plurality of contacts comprise mating contact portions and contact tails; the floor comprises a first surface and an opposed second surface; the mating contact portions of the first plurality of contacts and the second plurality of contacts extend from the first surface; the contact tails of the first plurality of contacts and the second plurality of contacts extend from the second surface; and the recessed portion comprises a recess in the first surface. 
     In some embodiments, the conductive member also comprises a second plurality of tabs; and the second plurality of tabs press against the second plurality of contacts. 
     In some embodiments, the second plurality of contacts comprise first surfaces, facing a first direction, and opposing second surfaces; the second plurality of tabs press against the second plurality of contacts at the second surfaces. 
     In some embodiments, the second plurality of contacts comprise dimples that are concave in the second surfaces; the second plurality of tabs comprise tips; and the tips of the second plurality of tabs contact the second surfaces at the dimples. 
     In some embodiments, the tips of the second plurality of tabs are rounded such that the tips contact the dimples at at least two points. 
     In some embodiments, the second plurality of tabs are compliant beams and exert a spring force against the second surfaces, biasing the conductive member in a second direction normal to the second surfaces; the floor comprises a plurality of surface portions and a recessed portion, recessed relative to the surface portions; the plurality of surface portions extend through the first plurality of openings such that edges of the conductive member abut the surface portions so as to counter spring forces biasing the conductive member in the second direction. 
     In some embodiments, the first surfaces of the second plurality of contacts comprise a selective plating of gold. 
     In some embodiments, the second plurality of contacts comprises at least 16 contacts; and the conductive member electrically connects the at least 16 contacts. 
     In some embodiments, the first plurality of contacts comprise differential signal contacts; and the second plurality of contacts comprise ground contacts. 
     In some embodiments, the conductive member comprises a metal member. 
     In some embodiments, the metal member comprises a metal sheet with the openings of the first plurality of openings and the second plurality of openings and the tabs formed therein. 
     In accordance with further embodiments, a printed circuit board comprises a plurality of signal traces; a plurality of ground layers; and the electrical connector as mentioned above mounted to the printed circuit board, wherein the first plurality of contacts are connected to the signal traces; and the second plurality of contacts are connected to the ground layers. 
     In accordance with further embodiments, a conductive member comprises a conductive sheet with a first plurality of openings and a second plurality of openings, wherein the first plurality of openings are disposed in a plurality of columns, and the second plurality of openings are interspersed with the first plurality of openings within the plurality of columns; and a first plurality of tabs, disposed at edge of the conductive sheet and bendable at an angle relative to the conductive sheet. 
     In some embodiments, the conductive member also comprises a second plurality of tabs; and each of the second plurality of tabs is disposed in each of the second plurality of openings. 
     In some embodiments, each of the second plurality of tabs is a compliant beam. 
     In some embodiments, the second plurality of tabs comprise tips; and the tips of the second plurality of tabs are rounded. 
     In some embodiments, each column of the plurality of columns is offset in the column direction with respect to adjacent columns. 
     In accordance with further embodiments, a method of forming an electrical connector, the method comprises placing a conductive member adjacent to a floor of a shell of the electrical connector; inserting a first plurality of contacts through a first plurality of openings in the conductive member such that the first plurality of contacts are positioned in columns on the floor; and inserting a second plurality of contacts through a second plurality of openings in the conductive member such that the second plurality of contacts are positioned in the columns, wherein a first plurality of tabs of the conductive member extend into openings in the shell such that the conductive member are attached to the shell. 
     In some embodiments, a second plurality of tabs on the conductive member press against the second plurality of contacts such that the second plurality of contacts are electrically connected through the conductive member. 
     In some embodiments, forming the conductive member by stamping in a metal sheet the openings of the first plurality of openings and the second plurality of openings and the first plurality of tabs and the second plurality of tabs. 
     In some embodiments, the method further comprises plating a first surface of the second plurality of contacts with a noble metal; and inserting the second plurality of contacts comprises sliding each of the second plurality of tabs over a second surface of the second plurality of contacts. 
     In some embodiments, placing the conductive member adjacent to the floor of the shell comprises receiving portions of the shell within the first plurality of openings, wherein the portions of the shell electrically insulate the first plurality of contacts from the conductive member. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       For a better understanding of the disclosed technology, reference is made to the accompanying drawings, which are incorporated herein by reference and in which: 
         FIG. 1  is an exploded view of a high speed, high density electrical connector, a backplane and a daughter board; 
         FIG. 2  is a perspective view of a backplane connector in accordance with a first embodiment of a high speed, high density electrical connector; 
         FIG. 2A  is an enlarged view of region A in  FIG. 2 ; 
         FIG. 3  is an exploded view of the backplane connector of  FIG. 2 ; 
         FIG. 3A  is an enlarged view of region B in  FIG. 3 ; 
         FIG. 4  an another exploded view of the backplane connector of  FIG. 2 , wherein a conductive member is attached to an insulative shell; 
         FIG. 4A  is an enlarged view of region C in  FIG. 4 ; 
         FIG. 5  is a top view of an insulative shell with a conductive member attached in accordance with second embodiment of a high speed, high density electrical connector; 
         FIG. 5A  is an enlarged view of region D in  FIG. 5 ; 
         FIG. 5B  is a sectional view taken along line E-E in  FIG. 5 ; 
         FIG. 6  is a perspective view of second contacts in accordance with a third embodiment of a high speed, high density electrical connector; and 
         FIG. 7  is a partial top view of a connector footprint on a printed circuit board. 
     
    
    
     DETAILED DESCRIPTION 
     The inventors have recognized and appreciated that the operating speed of an electrical connector may be improved with a conductive member adapted to be mounted adjacent a floor in a connector housing. In one implementation, such a conductive member may be made by forming one or more cutouts in a sheet of conductive material. The cutouts may be arranged such that, when the conductive member is disposed across a mating interface of the connector, the conductive member is in electrical contact with at least some of the ground conductors in the connector, but not with any conductive elements adapted to be signal conductors. For example, the cutouts may be aligned with the signal conductors at the mating interface so that each signal conductor extends through a corresponding cutout without making electrical contact with the conductive member. Though, alternatively or additionally, such a conductive member may be integrated into the connector near the contact tails. 
     Such techniques may be used alone or in any suitable combination, examples of which are provided in the exemplary embodiments described below. 
     Referring to  FIG. 1 , an electrical interconnection system  100  with two connectors is shown. The electrical interconnection system  100  includes a daughter card connector  120  and a backplane connector  150 . 
     Daughter card connector  120  is designed to mate with backplane connector  150 , creating electronically conducting paths between a backplane  160  and a daughter card  140 . Though not expressly shown, interconnection system  100  may interconnect multiple daughter cards having similar daughter card connectors that mate to similar backplane connections on backplane  160 . Accordingly, the number and type of subassemblies connected through an interconnection system is not a limitation. 
       FIG. 1  shows an interconnection system using a right-angle, separable mating interface connector. It should be appreciated that in other embodiments, the electrical interconnection system  100  may include other types and combinations of connectors, as the invention may be broadly applied in many types of electrical connectors, such as right-angle, separable mating interface connectors, mezzanine connectors and chip sockets. 
     Backplane connector  150  and daughter card connector  120  each contains conductive elements. The conductive elements of daughter card connector  120  are coupled to traces, of which trace  142  is numbered, ground planes or other conductive elements within daughter card  140 . The traces carry electrical signals and the ground planes provide reference levels for components on daughter card  140 . Ground planes may have voltages that are at earth ground or positive or negative with respect to earth ground, as any voltage level may act as a reference level. 
     Daughter card connector  120  includes a plurality of wafers  122   1  . . .  122   6  coupled together, with each of the plurality of wafers  122   1  . . .  122   6  having a housing and a column of conductive elements. In the illustrated embodiment, each column has a plurality of signal conductors and a plurality of ground conductors. The ground conductors may be employed within each wafer  122   1  . . .  122   6  to minimize crosstalk between signal conductors or to otherwise control the electrical properties of the connector. 
     In the illustrated embodiment, daughter card connector  120  is a right angle connector and has conductive elements that traverse a right angle. As a result, opposing ends of the conductive elements extend from perpendicular edges of the wafers  122   1  . . .  122   6 . 
     Each conductive element of wafers  122   1  . . .  122   6  has at least one contact tail, shown collectively as contact tails  126  that can be connected to daughter card  140 . Each conductive element in daughter card connector  120  also has a mating contact portion, shown collectively as mating contact portions  124 , which can be connected to a corresponding contact in backplane connector  150 . Each conductive element also has an intermediate portion between the mating contact portion and the contact tail, which may be enclosed by or embedded within a wafer housing. 
     The contact tails  126  electrically connect the contacts within daughter card and connector  120  to conductive elements, such as traces  142  in daughter card  140 . In the embodiment illustrated, contact tails  126  are press fit “eye of the needle” contacts that make an electrical connection through via holes in daughter card  140 . However, any suitable attachment mechanism may be used instead of or in addition to via holes and press fit contact tails. 
     In the illustrated embodiment, each of the mating contact portions  124  has a dual beam structure configured to mate to a corresponding mating contact portion  154  of backplane connector  150 . The conductive elements acting as signal conductors may be grouped in pairs, separated by ground conductors in a configuration suitable for use as a differential electrical connector. However, other embodiments are possible for single-ended use in which the conductive elements are evenly spaced with or without designated ground conductors separating signal conductors or with a ground conductor between signal conductors. 
     In the embodiments illustrated, some conductive elements are designated as forming a differential pair of conductors and some conductive elements are designated as ground conductors. These designations refer to the intended use of the conductive elements in an interconnection system as they would be understood by one skilled in the art. For example, though other uses of the conductive elements may be possible, differential pairs may be identified based on preferential coupling between the conductive elements that make up the pair. Electrical characteristics of the pair, such as its impedance, that make it suitable for carrying a differential signal may provide an alternative or additional method of identifying a differential pair. As another example, in a connector with differential pairs, ground conductors may be identified by their positioning relative to the differential pairs. In other instances, ground conductors may be identified by their shape or electrical characteristics. For example, ground conductors may be relatively wide to provide low inductance, which is desirable for providing a stable reference potential, but provides an impedance that is undesirable for carrying a high speed signal. 
     For exemplary purposes only, daughter card connector  120  is illustrated with six wafers  122   1  . . .  122   6 , with each wafer having a plurality of pairs of signal conductors and adjacent ground conductors. As pictured, each of the wafers  122   1  . . .  122   6  includes one column of conductive elements. However, the disclosed technology is not limited in this regard, as the number of wafers and the number of signal conductors and ground conductors in each wafer may be varied as desired. 
     As shown, each wafer  122   1  . . .  122   6  is inserted into front housing  130  such that mating contact portions  124  are inserted into and held within openings in front housing  130 . The openings in front housing  130  are positioned so as to allow mating contact portions  154  of the backplane connector  150  to enter the openings in front housing  130  and allow electrical connection with mating contact portions  124  when daughter card connector  120  is mated to backplane connector  150 . 
     Daughter card connector  120  may include a support member instead of or in addition to front housing  130  to hold wafers  122   1  . . .  122   6 . In the pictured embodiment, stiffener  128  supports the plurality of wafers  122   1  . . .  122   6 . Stiffener  128  is, in the embodiment illustrated, a stamped metal member. However, stiffener  128  may be formed from any suitable material. Stiffener  128  may be stamped with slots, holes, grooves or other features that can engage a wafer. 
     Similarly, contacts in backplane connector  150  are coupled to traces, of which trace  162  is numbered, ground planes or other conductive elements within backplane  160 . When daughter card connector  120  and backplane connector  150  mate, contacts in the backplane connector and conductive elements in the daughter card connector mate to complete electrically conductive paths between the conductive elements within backplane  160  and daughter card  140 . 
     Backplane connector  150  includes a backplane shell  158  and a plurality of contacts. The contacts of backplane connector  150  are held within the shell  158 , which may be formed of an insulative material. In some embodiments, the contacts extend through floor  514  of the backplane shell  158  with portions both above and below floor  514 . Here, the portions of the contacts that extend above floor  514  form mating contact portions, shown collectively as mating contact portions  154 , which are adapted to mate to corresponding conductive elements of daughter card connector  120 . In the illustrated embodiment, mating contact portions  154  are in the form of blades, although other suitable contact configurations may be employed, as the disclosed technology is not limited in this regard. 
     Tail portions, shown collectively as contact tails  156 , of the contacts extend below the shell floor  514  and are adapted to be attached to backplane  160 . Here, the tail portions are in the form of a press fit, “eye of the needle” compliant sections that fit within via holes, shown collectively as via holes  164 , on backplane  160 . However, other configurations are also suitable, such as surface mount elements, spring contacts, solderable pins, etc., as the disclosed technology is not limited in this regard. 
       FIG. 2  shows a perspective view of a backplane connector  200  suitable for use with a daughter card connector (e.g., the daughter card connector  120  shown in  FIG. 1 ), in accordance with some embodiments. In this example, the contacts in backplane connector  200  generally include a first plurality of contacts  210  and a second plurality of contacts  220 , which are accommodated in an insulative shell  230 . In some embodiments, the first contacts may be adapted to be signal conductors, while the second contacts may be adapted to be ground conductors. The first contacts  210  are disposed in a plurality of columns. For example, first contacts  2101 ,  2102  and  2103  are disposed in a column. The second contacts  220  are interspersed with the first contacts  210  within each column. In the illustrated embodiment, the first contacts  210  are disposed in a plurality of pairs, for example, for transmitting signals differentially. The adjacent pairs of the first contacts  210  within a column are separated by at least a second contact  220 . For instance, within each column, each pair of the first contacts is disposed between and adjacent two second contacts. The pair of the first contacts  2101 , the pair of the first contacts  2102  and the pair of the first contacts  2103  are disposed between and adjacent two second contacts  220  respectively. The ground conductors may be employed to reduce crosstalk between signal conductors or to otherwise control one or more electrical properties of the connector. The ground conductors may perform these functions based on their shape and/or position within the column of contacts within a wafer or position within an array of contacts formed when multiple wafers are arranged side-by-side. 
     While a connector with differential pairs is shown in figures for purposes of illustration, it should be appreciated that embodiments are possible for single-ended use in which contacts are evenly spaced without designated ground conductors separating designated differential pairs, or with designated ground conductors between adjacent designated signal conductors for some or all of the columns. 
     The backplane connector  200  further includes a conductive member  300 , which is visible in the exploded view of  FIG. 3 . The conductive member  300  is disposed adjacent the floor  232  of the insulative shell  230 , as shown in  FIG. 4 . The conductive member  300  comprises a first plurality of openings  310  and a second plurality of openings  320 . For instance, the conductive member  300  may be a conductive sheet  302  with the first openings  310  and the second openings  320 . In an assembled connector, the first contacts  210  extend through the first openings  310 , and the second contacts  220  extend through the second openings  320 . The mating contact portions of the first and second contacts  210  and  220  extend above the conductive member  300 . The first openings  310  are arranged in a plurality of columns. The second openings  320  are interspersed with the first openings  310  within each column. For instance, the first and second openings  310  and  320  may be adapted to receive the mating contact portions of the first and second contacts  210  and  220  shown in  FIG. 2 , respectively. On the other hand, each of the first openings  310  may be adapted to receive two mating contact portions of two first contacts shown in  FIG. 2 , but without making electrical connection with either of the mating contact portions. In the illustrated embodiment, two first contacts  210  pass through each of first openings  310 . Between any two adjacent first openings  310 , there is a second opening  320 . One second contact  220  passes through each of second openings  320 . The second openings  320  may be adapted to make electrical connection between conductive member  300  and the mating contact portions of the second contacts. The connections, in some embodiments, may be made by sizing openings adapted to receive second contacts to be approximately the same size as the second contacts in one or more dimensions. However, it should be appreciated that aspects of the present disclosure are not limited to this. 
     Moreover, the second openings  320  may be shaped and positioned so that the conductive member  300  is in electrical contact with mating contact portions of second contacts  220 , but not with mating contact portions of first contacts  210 . In this manner, the second contacts  220  may be electrically connected to each other via the conductive member  300 . 
     In some embodiments, each column of the first and second contacts  210  and  220  is offset in the column direction with respect to adjacent columns of the first and second contacts  210  and  220 . Thus, the pairs of first contacts in a column are diagonally adjacent to the corresponding pairs of first contacts in adjacent columns. In the cases that the first contacts serve as signal conductors, even with diagonal pairs of signal conductors, the conductive member  300  can reduce crosstalk between them. Near End Crosstalk (NEXT), for example, may be reduced in this way. The conductive member  300  has an important benefit in reducing cross-talk at higher frequencies. The conductive member  300  can reduce crosstalk between diagonal pairs of signal conductors by at least 2 dB over the frequency range from 5 to 28 GHz. 
     In some embodiments, such a conductive member  300  may be formed by stamping a preform with appropriate patterns of openings and tabs (if any). Though, other materials may be used instead of or in addition to such a preform. A sheet of metal material, for example, may be used. 
     In some embodiments, the conductive member  300  further includes a first plurality of tabs  330 , extending into openings  238  in the insulative shell  230 , as shown in  FIGS. 3-3A . In this way, the conductive member  300  is attached to the insulative shell  230 . In example embodiments, the openings  238  are disposed in the floor  232  of the insulative shell  230 , particularly, at the edge of the floor  232 . The first tabs  330  may be disposed at an edge of the conductive sheet  302  and bendable at an angle relative to the conductive sheet  302 . 
     In the embodiment illustrated in  FIGS. 3 and 3A , the first tabs  330  are bent at an angle, such as about 90 degrees, relative to the conductive sheet  302 . Each of the openings in the insulative shell  230  has a pair of opposed slots  2382 . The first tabs  330  are inserted into the slots  2382  of corresponding opening  238 . This both holds the conductive member  300  against the insulative shell  230  and sets the position of the conductive member  300  relative to the columns of contacts. In different embodiments, the angle of slots  2382  relative to horizontal direction may be different to accommodate first tabs  330  bent angle(s) other than 90 degrees. 
     In other embodiments illustrated in  FIGS. 5 and 5A-5B , the first tabs  510  of the conductive member  500  are slidable in the openings  520  in the insulative shell  500 . The openings  520  may have a configuration that is similar to or different from the opening  238  shown as  FIGS. 3 and 3A . In the case that the opening  520  is similar to the opening  238 , the first tabs  510  may be bent at less than 90 degrees. The first tab  510  are not inserted into the slots of the openings  520 , instead, the sides of the first tabs  510  press against walls of larger openings  520 , as shown in  FIG. 5A . In this way, the first tab  510  is slidable in the opening  520 . A benefit of this slidable connection is that the conductive member  500  is positioned relative to the columns of contacts based on the shape of the insulative shell  500  around the contacts. This avoids misalignment of the conductive member  500  relative to the contacts. It is found that misalignment of the conductive member  500  and contacts resulted in the conductive member  500  scraping along the edges of the contacts during assembly. This scraping caused metal to be scraped off the contact, which could interfere with operation of the connector. 
     In some embodiments, the conductive member  300  further includes a second plurality of tabs  340 , as shown in  FIGS. 3 and 2A . Each of the second tabs  340  is disposed in each of the second openings  320 . Each of the second tabs  340  presses against a corresponding second contact  220 . The second contacts  220  may comprise first surfaces, facing a first direction, and opposing second surfaces  2202 . In the embodiment illustrated, the second contacts  220  are shaped as blades with the first and second surfaces forming broadsides of the blades and edges joining the surfaces. 
     The second tabs  340  press against the second contacts  220  at the second surfaces  2202 . In some embodiments, the second tabs  340  are compliant beams. The compliant beams exert a spring force against the second surfaces  2202 , biasing the conductive member  300  in a second direction  240  normal to the second surfaces  2202 . The first surfaces of the second contacts  220  may include mating surfaces of the second contacts  220  and may be selectively plated with a noble metal, such as gold. When daughter card connector  120  and backplane connector  150  mate, contacts in the backplane connector and conductive elements in the daughter card connector mate to complete electrically conductive paths at the first surfaces. 
     In some embodiments, the second tabs  340  may comprise tips, and the tips of the second tabs  340  are rounded. There are dimples  2204  that are concave in the second surfaces of the second contacts  220 . The tips of the second tabs  340  can contact the second surfaces of the second contacts  220  at the dimples  2204 . In this way, pressing the rounded tip of the second tab  340  into the dimple  2204  makes two or more points of contact between the second tab  340  and the second contact  220 , such that the second tabs  340  can make good electrical contact with the second contacts  220 . However, any suitable contacting mechanism may be used instead of or in addition to dimples  2204  and the rounded tip of the second tab  340 . Thus, the above description is not a limitation. 
     As mentioned above, the second tabs  340  bias the conductive member  300  in the second direction  240 . In order to counter this biasing force, the floor  232  of the insulative shell  230  comprises a plurality of surface portions  234  and a recessed portion  236 , as shown in  FIGS. 3-3A . The recessed portion  236  is recessed relative to the surface portions  234 . The surface portions  234  extend through the first openings  310 , as shown in  FIG. 4A , and the conductive member  300  is disposed within the recessed portion  236 . Accordingly, edges of the openings of the conductive member  300  abut the surface portions  234  so as to counter spring forces biasing the conductive member  300  in the second direction  240 . In the embodiments in which the first contacts  210  are disposed in pairs, each pair of the first contacts  210  extends through a surface portion  234 . The second contacts  220  extend through the recessed portion  236 . 
     The floor  232  comprises a first surface, from which the mating contact portions of the first and second contacts  210  and  220  extend, and an opposed second surface, from which the contact tails of the first and second contacts  210  and  220  extend. In the example illustrated in the figures, the first surface corresponds to the upper surface of the floor  232 , and the second surface corresponds to the lower surface of the floor  232 . The recessed portion  236  comprises a recess in the first surface. In some embodiments, the conductive member  300  is recessed below the floor  232  of the shell. This positions the conductive member  300  by counters the forces exerted by the second tabs  340  against the second contacts  220 . All second tabs  340  press the same direction, because the second tabs  340  should press on backs (second surfaces) of the second contacts  220 . Fronts (first surfaces) of the second contacts  220  have the contact surface and are plated with gold. Gold would be scraped off if the second tabs  340  were to slide along the front as the second contacts  220  are inserted through the conductive member  300 . 
     In some embodiments, each of the second contacts  600  comprises a mating contact portion  610  and two contact tails  620 , as shown in  FIG. 6 . The dual beam contact tails are used to provide multiple points of contact between the second contacts and the backplane  160 . Again, it should be appreciated that other numbers of contact tails and other types of mating contact portion structures may also be suitable for the second contacts  600 . The second contact  600  has a first (front) surface  601  and an opposed second (back) surface  602 , as mentioned above. The first surface  601  has the contact surface and is plated with gold, and the second surface  602  has a dimple. A second tab of the conductive member presses against the dimple. 
     In some embodiments, the second contacts  600  comprise twisted regions  630 , which are connected between the mating contact portions  610  and contact tails  620 . Because of the twisted region  630 , a line between the two contact tails  620  is transverse to the contact surface. In some embodiments, the line between the two contact tails is at an angle to the contact surface between 35 and 55 degrees. This results in a via hole pattern in the backplane to which the connector is attached that reduces crosstalk. It especially reduces crosstalk between two pairs of vias carrying signals that are close to each other in a column. 
     In some embodiments, one of two adjacent second contacts is twisted in a first direction relative to the contact surface, and the other of the two adjacent contacts is twisted in a second direction, opposite to the first direction, relative to the contact surface. As shown in  FIG. 6 , take two adjacent second contacts  610 A and  610 B for example, the contact tails of the second contact  610 A are twisted in counterclockwise direction relative to the contact surface, while the contact tails of the second contact  610 B are twisted in clockwise direction relative to the contact surface. Accordingly, it seems that the contact tails of the second contacts  610 A and  610 B face to each other. This feature is provided to further reduce crosstalk between two pairs of signal conductors close to each other in a column. 
     Preferably, the connector comprises at least 16 second contacts, and the conductive member  300  electrically connects the at least 16 contacts as a common conductive member. 
     Any backplane connector mentioned above may be mounted to a printed circuit board. The printed circuit board further comprises a plurality of signal traces and a plurality of ground layers. The first contacts of backplane connector are connected to the signal traces, and the second contacts are connected to the ground layer. 
     The assembling of the electrical connector is described by reference to the embodiment as shown in  FIGS. 4-4A . Firstly, the conductive member  300  is placed adjacent to the floor of the shell  230 . The first tabs  350  of the conductive member  300  extend into openings  238  in the shell such that the conductive member  300  is attached to the shell  230 . Then, the first contacts  210  are inserted through the first openings in the conductive member  300  and the floor  232  of first contacts  210 , and the second contacts  220  are inserted through the second openings in the conductive member  300  and the floor  232  of first contacts  210 . In this manner, the first and second contacts  210  and  220  are positioned in columns on the floor. 
     In this embodiment, the first tabs are bent down to engage the slots of shell. However, the manner by which the conductive member  300  is attached to the shell  230  is not limited to this. Alternatively or additionally, the conductive member  300  may be attached to the shell by an interference fit, and/or smaller first tabs  510  and larger openings  520  as shown in  FIGS. 5-5A .The step of placing the conductive member adjacent to the floor of the shell comprises receiving portions of the shell within the first openings. For instance, a plurality of projecting surface portions  234  may extend into first openings  310 , as shown in  FIG. 3 . The portions of the shell electrically insulate the first contacts from the conductive member. The second tabs may press against the second contacts such that the second contacts are electrically connected through the conductive member. 
     The step of inserting the second plurality of contacts comprises sliding each of the second tabs over a second surface of the second plurality of contacts, to avoid the noble metal on the opposed first surface to be scraped off. 
     An example of a printed circuit board is described with reference to  FIG. 7 . A partial top view of backplane  160  showing a portion of a connector footprint  700  for mating with the contact tails of backplane connector  150  is shown in  FIG. 7 . The backplane  160  may be implemented as a printed circuit board as described below. As shown, the connector footprint  700  includes a plurality of columns of repeating via patterns.  FIG. 7  only schematically shows two via patterns  710  and  720 , and they are in different columns. In the illustrated embodiment, each via pattern includes two pairs of signal vias for forming two differential pair of signal conductors, and two pairs of ground vias for forming associated reference conductors. The via patterns  710  and  720  in adjacent columns may be offset by a distance D in a direction  730  of the columns such that Near End Crosstalk (NEXT) between adjacent pairs of signal vias, such as  712  and  722 , in different columns can be reduced. 
     Take the via pattern  710  for example, it includes a first pair of signal vias  712  and a second pair of signal vias  714 , as well as a first pair of ground vias  716  and a second pair of ground vias  718 . Within each column, the pairs of ground vias are positioned between adjacent pairs of signal vias. The first pair of ground vias  716  is positioned between the first pair of signal vias  712  and the second pair of signal vias  714 , and the second pair of ground vias  718  is positioned between the second pair of signal vias  714  and a first pair of signal vias in adjacent via pattern (not shown). Within each column, each pair of signal vias is positioned between a first pair of ground vias and a second pair of ground vias. The first pair of signal vias  712  is positioned between the first pair of ground vias  716  and a second pair of signal vias in adjacent via pattern (not shown), and the second pair of signal vias  714  is positioned between the second pair of ground vias  718  and the first pair of ground vias  716 . 
     In some embodiments, the centers of the signal vias  712  and  714  are aligned on a first line A-A in the column direction  730 . For each pair of ground vias, the centers of the ground vias have different offsets from the first line A-A in a direction perpendicular to the first line A-A. For instance, for the pair of first and second ground vias  7162  and  7164 , the first and second ground vias  7162  and  7164  are offset from the first line in a direction perpendicular to the first line. Furthermore, the first and second ground vias  7162  and  7164  are offset from the first line in opposite directions. The first ground via  7162  is offset from the first line A-A upwards, and the second ground vias  7164  is offset from the first line A-A downwards, in  FIG. 7 . 
     The centers of the first pair of ground vias  716  are aligned on a second line B-B, and the centers of the second pair of ground vias  718  are aligned on a second line C-C. In some embodiments, the second line B-B makes an angle a with the first line A-A, and the second line C-C makes an angle β with the first line A-A. In some embodiments, the angles α and β are in the opposite directions. The absolute values of angles α and β may be different or the same. These features are provided to reduce crosstalk between adjacent pairs of signal conductors in a column. 
     It will be understood that each of the via patterns  710  and  720  matches a pattern of contact tails of backplane connector  150 , as shown in  FIG. 1  and described above. In particular, each column of via patterns corresponds to one of the columns of contact tails of backplane connector  150 . It will be understood that the parameters of the connector footprint may vary, including the number and arrangement of via patterns and the configuration of each via pattern, provided that the connector footprint matches the pattern of contact tails in backplane connector. 
     The disclosed technology is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The disclosed technology is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is 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 and equivalents thereof as well as additional items. 
     Having thus described at least one illustrative embodiment of the invention, various alterations, modifications and improvements will readily occur to those skilled in the art. 
     For example, layers may be described as upper layers, or “above” or “below” other layers. It should be appreciated these terms are for ease of illustration and not a limitation on the orientation of layers. In the embodiment illustrated, “upper” refers to a surface of a printed circuit board to which components are attached or a normal to such a surface. In some embodiments, components may be attached to two sides of a printed circuit board, such that upper and lower may depend on which vias are being considered. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. 
     Further, it was described that each column of signal conductors within a connector may comprise pairs of signal conductors with one or more ground conductors between each pair. In some embodiments, the signal conductors and ground conductors may be arranged such that two ground conductors are between each pair of signal conductors. Such connectors may have a footprint with pairs of signal vias  712 ,  714  with multiple ground vias between each pair of signal vias, and, in some embodiments, with two pairs of ground vias  716 ,  718  between each pair of signal vias  714 . 
     Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.