Abstract:
A high speed, high density electrical connector for use with printed circuit boards. The connector is in two pieces with one piece having pins and shield plates and the other having socket type signal contacts and shield plates. The shields have a grounding arrangement which is adapted to control the electromagnetic fields, for various system architectures, simultaneous switching configurations and signal speeds, allowing all of the socket type signal contacts to be used for signal transmission. Additionally, at least one piece of the connector is manufactured from wafers, with each ground plane and signal column injection molded into components which, when combined, form a wafer. This construction allows very close spacing between adjacent columns of signal contacts as well as tightly controlled spacing between the signal contacts and the shields. It also allows for easy and flexible manufacture, such as a connector that has wafers intermixed in a configuration to accommodate single ended, point to point and differential applications.

Description:
This application is a divisional of application Ser. No. 08/797,540, filed on Feb. 7, 1997 now U.S. Pat. No. 5,980,321. 
    
    
     This invention relates generally to electrical connectors used to interconnect printed circuit boards and more specifically to a method of simplifying the manufacture of 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 which are then 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, are connected through the backplane. 
     A traditional backplane is a printed circuit board with many connectors. Conducting traces in the printed circuit board connect to signal pins in the connectors so that signals may be routed between the connectors. Other printed circuit boards, called “daughter boards” also contain connectors that are plugged into the connectors on the backplane. In this way, signals are routed among the daughter boards through the backplane. The daughter cards often plug into the backplane at a right angle. The connectors used for these applications contain a right angle bend and are often called “right angle connectors.” 
     Connectors are also used in other configurations for interconnecting printed circuit boards, and even for connecting cables to printed circuit boards. Sometimes, one or more small printed circuit boards are connected to another larger printed circuit board. The larger printed circuit board is called a “mother board” and the printed circuit boards plugged into it are called daughter boards. Also, boards of the same size are sometimes aligned in parallel. Connectors used in these applications are sometimes called “stacking connectors” or “mezzanine connectors.” 
     Regardless of the exact application, electrical connector designs have generally needed to mirror trends in the electronics industry. Electronic systems generally have gotten smaller and faster. They also handle much more data than systems built just a few years ago. To meet the changing needs of these electronic systems, some electrical connectors include shield members. Depending on their configuration, the shields might control impedance or reduce cross talk so that the signal contacts can be placed closer together. 
     An early use of shielding is shown in Japanese patent disclosure 49-6543 by Fujitsu, Ltd. dated Feb. 15, 1974. U.S. Pat. Nos. 4,632,476 and 4,806,107—both assigned to AT&amp;T Bell Laboratories—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 and the backplane connectors. 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—all assigned to Framatome Connectors International—show a similar arrangement. The electrical connection between the backplane and shield is, however, made with a spring type contact. 
     Other connectors have the shield plate within only the daughter card connector. Examples of such connector designs can be found in U.S. Pat. Nos. 4,846,727; 4,975,084; 5,496,183; 5,066,236—all assigned to AMP, Inc. An other connector with shields only within the daughter board connector is shown in U.S. Pat. No. 5,484,310, assigned to Teradyne, Inc. 
     Another modification made to connectors to accomodate changing requirements is that connectors must be much larger. In general, increasing the size of a connector means that manufacturing tolerances must be much tighter. The permissible mismatch between the pins in one half of the connector and the receptacles in the other is constant, regardless of the size of the connector. However, this constant mismatch, or tolerance, becomes a decreasing percentage of the connector&#39;s overall length as the connector gets larger. Therefore, manufacturing tolerances must be tighter for larger connectors, which can 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+®, with the modules organized on a stiffener. Each module had multiple columns of signal contacts, such as 15 or 20 columns. The modules were held together on a metal stiffener. 
     An other modular connector system is shown in U.S. Pat. Nos. 5,066,236 and 5,496,183. Those patents describe “module terminals” with 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 could be placed between the module terminals as well. 
     It would be highly desirable if a modular connector could be made with an improved shielding configuration. It would also be desirable if the manufacturing operation were simplified. It would be further desirable if a design could be developed that allowed easy intermixing of single ended and differential signal contacts. 
     SUMMARY OF THE INVENTION 
     With the foregoing background in mind, it is an object of the invention to provide a high speed, high density connector. 
     It is a further object to provide a modular connector that is easy to manufacture. 
     It is a further object to provide a low insertion force connector. 
     It is also an object to provide a connector that can be easily assmebled to include signal contacts configured for single end or differential signals. 
     The foregoing and other objects are achieved in an electrical connector manufactured from a plurality of wafers. Each wafer is made with a ground plane insert molded into a housing. The housing has cavities into which signal contacts are inserted. 
     In a preferred embodiment, the signal contacts are also insert molded into a second housing piece. The two housing pieces snap together to form one wafer. The wafers are held together on a metal stiffener. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood by reference to the following more detailed description and accompanying drawings in which 
     FIG. 1 is an exploded view of a connector made in accordance with the invention; 
     FIG. 2 is a shield plate blank used in the connector of FIG. 1; 
     FIG. 3 is a view of the shield plate blank of FIG. 2 after it is insert molded into a housing element; 
     FIG. 4 is a signal contact blank used in the connector of FIG. 1; 
     FIG. 5 is a view of the signal contact blank of FIG. 4 after it is insert molded into a housing element; 
     FIG. 6 is an alternative embodiment of the signal contact blank of FIG. 4 suitable for use in making a differential module; 
     FIGS. 7A-7C are operational views a prior art connector; 
     FIGS. 8A-8C are similar operational views of the connector of FIG. 1; 
     FIGS. 9A and 9B are backplane hole and signal trace patterns for single ended and differential embodiments of the invention, respectively; and 
     FIG. 10 is a view of an alternative embodiment of the invention. 
     FIG. 11A is a an alternative embodiment for the plate  128  in FIG. 1; 
     FIG. 11B is a cross sectional view taken through the line B—B of FIG. 11A; 
     FIG. 12 is an isometric view of a connector according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an exploded view of backplane assembly  100 . Backplane  110  has pin header  114  attached to it. Daughter card  112  has daughter card connector  116  attached to it. Daughter card connector  116  can be mated to pin header  114  to form a connector. Backplane assembly likely has many other pin headers attached to it so that multiple daughter cards can be connected to it. Additionally, multiple pin headers might be aligned end to end so that multiple pin headers are used to connect to one daughter card. However, for clarity, only a portion of backplane assembly and a single daughter card  112  are shown. 
     Pin header  114  is formed from shroud  120 . Shroud  120  is preferably injection molded from a plastic, polyester or other suitable insulative material. Shroud  120  serves as the base for pin header  114 . 
     The floor (not numbered) of shroud  120  contains columns of holes  126 . Pins  122  are inserted into holes  126  with their tails  124  extending through the lower surface of shroud  120 . Tails  124  are pressed into signal holes  136 . Holes  136  are plated through-holes in backplane  110  and serve to electrically connect pins  122  to traces (not shown) on backplane  110 . For clarity of illustration, only a single pin  122  is shown. However, pin header  114  contains many parallel columns of pins. In a preferred embodiment, there are eight rows of pins in each column. 
     The spacing between each column of pins is not critical. However, it is one object of the invention to allow the pins to be placed close together so that a high density connector can be formed. By way of example, the pins within each column can be spaced apart by 2.25 mm and the columns of pins can be spaced apart by 2 mm. Pins  122  could be stamped from 0.4 mm thick copper alloy. 
     Shroud  120  contains a groove  132  formed in its floor that runs parallel to the column of holes  126 . Shroud  120  also has grooves  134  formed in its sidewalls. Shield plate  128  fits into grooves  132  and  134 . Tails  130  protrude through holes (not visible) in the bottom of groove  132 . Tails  130  engage ground holes  138  in backplane  110 . Ground holes  138  are plated through-holes that connect to ground traces on backplane  110 . 
     In the illustrated embodiment, plate  128  has seven tails  130 . Each tail  130  falls between two adjacent pins  122 . It would be desirable for shield  128  to have a tail  130  as close as possible to each pin  122 . However, centering the tails  130  between adjacent signal pins  122  allows the spacing between shield  128  and a column of signal pins  122  to be reduced. 
     Shield plate  128  has several torsional beams contacts  142  formed therein. Each contact  142  is formed by stamping arms  144  and  146  in plate  128 . Arms  144  and  146  are then bent out of the plane plate  128 . Arms  144  and  146  are long enough that they will flex when pressed back into the plane of plate  128 . Arms  144  and  148  are sufficiently resilient to provide a spring force when pressed back into the plane of plate  128 . The spring force generated by arms  144  and  146  creates a point of contact between each arm  144  or  146  and plate  150 . The generated spring force must be sufficient to ensure this contact even after the daughter card connector  116  has been repeatedly mated and unmated from pin header  114 . 
     During manufacture, arms  144  and  146  are coined. Coining reduces the thickness of the material and increases the compliancy of the beams without weakening of plate  128 . 
     For enhanced electrical performance, it is desirable that arms  144  and  146  be as short and straight as possible. Therefore, they are made only as long as needed to provide the required spring force. In addition, for electrical performance, it is desirable that there be one arm  144  or  146  as close as possible to each signal pin  122 . Ideally, there would be one arm  144  and  146  for each signal pin  122 . For the illustrated embodiment with eight signal pins  122  per column, there would ideally be eight arms  144  or  146 , making a total of four balanced torsional beam contacts  142 . However, only three balanced torsional beam contacts  142  are shown. This configuration represents a compromise between the required spring force and desired electrical properties. 
     Grooves  140  on shroud  120  are for aligning daughter card connector  116  with pin header  114 . Tabs  152  fit into grooves  140  for alignment and to prevent side to side motion of daughter card connector  116  relative to pin header  114 . 
     Daughter card connector  116  is made of wafers  154 . Only one wafer  154  is shown for clarity, but daughter card connector  116  has, in a preferred embodiment, several wafers stacked side to side. Each wafer  154  contains one column of receptacles  158 . Each receptacle  158  engages one pin  122  when the pin header  114  and daughter card connector  116  are mated. Thus, daughter card connector  116  is made from as many wafers as there are columns of pins in pin header  114 . 
     Wafers  154  are supported in stiffener  156 . Stiffener  156  is preferably stamped and formed from a metal strip. It is stamped with features to hold wafer  154  in a required position without rotation and therefore preferably includes three attachment points. Stiffener  156  has slot  160 A formed along its front edge. Tab  160 B fits into slot  160 A. Stiffener  156  also includes holes  162 A and  164 A. Hubs  162 B and  164 B fit into holes  162 A and  164 A. The hubs  162 B and  164 B are sized to provide an interference fit in holes  162 A and  164 A. 
     FIG. 1 shows only a few of the slots  160 A and holes  162 A and  164 A for clarity. The pattern of slots and holes is repeated along the length of stiffener  156  at each point where a wafer  156  is to be attached. 
     In the illustrated embodiment, wafer  154  is made in two pieces, shield piece  166  and signal piece  168 . Shield piece  166  is formed by insert molding housing  170  around the front portion of shield  150 . Signal piece  168  is made by insert molding housing  172  around contacts  410 A . . .  410 H (FIG.  4 ). 
     Signal piece  168  and shield piece  166  have features which hold the two pieces together. Signal piece  168  has hubs  512  (FIG. 5) formed on one surface. The hubs align with and are inserted into clips  174  cut into shield  150 . Clips  174  engage hubs  512  and hold plate  150  firmly against signal piece  168 . 
     Housing  170  has cavities  176  formed in it. Each cavity  176  is shaped to receive one of the receptacles  158 . Each cavity  176  has platform  178  at its bottom. Platform  178  has a hole  180  formed through it. Hole  180  receives a pin  122  when daughter card connector  116  mates with pin header  114 . Thus, pins  122  mate with receptacles  158 , providing a signal path through the connector. 
     Receptacles  158  are formed with two legs  182 . Legs  182  fit on opposite sides of platform  178  when receptacles  158  are inserted into cavities  176 . Receptacles  158  are formed such that the spacing between legs  182  is smaller than the width of platform  178 . To insert receptacles  158  into cavity  176 , it is therefore necessary to use a tool to spread legs  182 . 
     The receptacles form what is known as a preloaded contact. Preloaded contacts have traditionally been formed by pressing the receptacle against a pyramid shaped platform. The apex of the platform spreads the legs as the receptacle is pushed down on it. Such a contact has a lower insertion force and is less likely to stub on the pin when the two connectors are mated. The receptacles of the invention provide the same advantages, but are achieved by inserting the receptacles from the side rather than by pressing them against a pyramid. 
     Housing  172  has grooves  184  formed in it. As described above, hubs  512  (FIG. 5) project through plate  150 . When two wafers are stacked side by side, hubs  512  from one wafer  154  will project into grooves  184  of an adjacent wafer. Hubs  512  and grooves  184  help hold adjacent wafers together and prevent rotation of one wafer with respect to the next. These features, in conjunction with stiffener  156  obviate the need for a separate box or housing to hold the wafers, thereby simplifying the connector. 
     Housings  170  and  172  are shown with numerous holes (not numbered) in them. These holes are not critical to the invention. They are “pinch holes” used to hold plates  150  or receptacle contacts  410  during injection molding. It is desirable to hold these pieces during injection molding to maintain uniform spacing between the plates and receptacle contacts in the finished product. 
     FIG. 2 shows in greater detail the blank used to make plate  150 . In a preferred embodiment, plates  150  are stamped from a roll of metal. The plates are retained on carrier strip  210  for ease of handling. After plate  150  is injection molded into a shield piece  166 , the carrier strip can be cut off. 
     Plates  150  include holes  212 . Holes  212  are filled with plastic from housing  170 , thereby locking plate  150  in housing  170 . 
     Plates  150  also include slots  214 . Slots  214  are positioned to fall between receptacles  158 . Slots  214  serve to control the capacitance of plate  150 , which can overall raise or lower the impedance of the connector. They also channel current flow in the plate near receptacles  158 , which are the signal paths. Higher return current flow near the signal paths reduces cross talk. 
     Slot  216  is similar to the slots  214 , but is larger to allow a finger  316  (FIG. 3) to pass through plate  150  when plate  150  is molded into a housing  170 . Finger  316  is a small finger of insulating material that could aid in holding a plate  128  against plate  150 . Finger  316  is optional and could be omitted. Note in FIG. 1 that the central two cavities  176  have their intermediate wall partially removed. Finger  316  from an adjacent wafer  154  (not shown) would fit into this space to complete the wall between the two central cavities. Finger  316  would extend beyond housing  170  and would fit into a slot  184 B of an adjacent wafer (not shown). 
     Slot  218  allows tail region  222  to be bent out of the plane of plate  150 , if desired. FIG. 9A shows traces  910  and  912  on a printed circuit board routed between holes used to mount a connector according to the invention. FIG. 9A shows portions of a column of signal holes  186  and portions of a column of ground contacts  188 . When the connector is used to carry single ended signals, it is desirable that the traces  910  and  912  be separated by ground to the greatest extent possible. Thus, it is desirable that the ground holes  188  be centered between the column of signal holes  186  so that the signal traces  910  and  912  can be routed between the signal holes  186  and ground holes  188 . On the other hand, FIG. 9B shows the preferred routing for differential pair signals. For differential pair signals, it is desirable that the traces be routed as close together as possible. To allow the traces  914  and  916  to be close together, the ground holes  188  are not centered between columns of signal holes  186 . Rather, they are offset to be as close to one row of signal contacts. That placement allows both signal traces  914  and  916  to be routed between the ground holes  188  and a column of signal holes  186 . In the single ended configuration, tail region  222  is bent out of the plane of plate  150 . For the differential configuration, it is not bent. 
     It should also be noted that plate  128  (FIG. 1) can be similarly bent in its tail region, if desired. In the preferred embodiment, though, plate  128  is not bent for single ended signals and is bent for differential signals. 
     Tabs  220  are bent out of the plane of plate  150  prior to injection molding of the housing  170 . Tabs  220  will wind up between holes  180  (FIG.  1 ). Tabs  220  aid in assuring that plate  150  adheres to housing  170 . They also reinforce housing  170  across its face, i.e. that surface facing pin header  114 . 
     FIG. 3 shows shield  150  after it has been insert molded into housing  170  to form ground portion  166 . FIG. 3 shows that housing  170  includes pyramid shaped projections  310  on the face of shield piece  166 . Matching recesses (not shown) are included in the floor of pin header  114 . Projections  310  and the matching recesses serve to prevent the spring force of torsional beam contacts  142  from spreading adjacent wafers  154  when daughter card connector  116  is inserted into pin header  114 . 
     FIG. 4 shows receptacle contact blank  400 . Receptacle contact blank is preferably stamped from a sheet of metal. Numerous such blanks are stamped in a roll. In the preferred embodiment, there are eight receptacle contacts  410 A. . .  410 H. The receptacle contacts  410  are held together on carrier strips  412 ,  414 ,  416 ,  418  and  422 . These carrier strips are severed to separate contacts  410 A . . .  410 H after housing  172  has been molded around the contacts. The carrier strips can be retained during much of the manufacturing operation for easy handling of receptacle portions  168 . 
     Each of the receptacle contacts  410 A . . .  410 H includes two legs  182 . The legs  182  are folded and bent to form the receptacle  158 . 
     Each receptacle contact  410 A . . .  410 H also includes a transmission region  424  and a tail region  426 . FIG. 4 shows that the transmission regions  424  are equally spaced. This arrangement is preferred for single ended signals as it results in maximum spacing between the contacts. 
     FIG. 4 shows that the tail regions are suitable for being press fit into plated through-holes. Other types of tail regions might be used. For example, solder tails might be used instead. 
     FIG. 5 shows receptacle contact blank  400  after housing  172  has been molded around it. 
     FIG. 6 shows a receptacle contact blank  600  suitable for use in an alternative embodiment of the invention. Receptacle contacts  610 A . . .  610 H are grouped in pairs: ( 610 A and  610 B), ( 610 C and  610 D), ( 610 E and  610 F) and ( 610 G and  610 H). Transmission regions  624  of each pair are as close together as possible while maintaining differential impedance. This increases the spacing between adjacent pairs. This configuration improves the signal integrity for differential signals. 
     The tail region  626  and the receptacles of receptacle contact blank  400  and  600  are identical. These are the only portions of receptacle contacts  410  and  610  extending from housing  172 . Thus, externally, signal portion  168  is the same for either single ended or differential signals. This allows single ended and differential signal wafers to be mixed in a single daughter card connector. 
     FIG. 7A illustrates a prior art connector as an aid in explaining the improved performance of the invention. FIG. 7A shows a shield plate  710  with a cantilevered beam  712  formed in it. The cantilevered beam  712  engages a blade  714  from the pin header. The point of contact is labeled X. Blade  714  is connected to a backplane (not shown) at point  722 . 
     Signals are transmitted through signal pins  716  and  718  running adjacent to the shield plate. Plate  710  and blade  714  act as the signal return. The signal path  720  through these elements is shown as a loop. It should be noted that signal path  720  cuts through pin  718 . As is well known, a signal traveling in a loop passing through a conductor will inductively couple to the conductor. Thus, the arrangement of FIG. 7A will have relatively high coupling or cross talk from pin  716  to  718 . 
     FIG. 7B shows a side view of the arrangement of FIG.  7 A. As the cantilevered beam  712  is above the blade  714  its distance from pin  716  is dl. In contrast, blade  714  has a spacing of d 2 , which is larger. In the transmission of high frequency signals, the distance between the signal path and the ground dictates the impedance of the signal path. Changes in distance mean changes in impedance. Changes in impedance cause signal reflections, which is undesirable. 
     FIG. 7C shows the same arrangement upon mating. The blade  714  must slide under cantilevered beam  712 . If not inserted correctly, blade  714  can but up against the end of cantilevered beam  712 . This phenomenon is called “stubbing.” It is highly undesirable in a connector because it can break the connector. 
     In contrast, FIG. 8 shows in a schematic sense the components of a connector manufactured according to the invention. Shield plates  128  and  150  overlap. Contact is made at the point marked X on torsional beam  146 . Signal path  820  is shown to pass through a signal pin  122 , return through plate  150  to point of contact X, pass through arm  146 , through plate  128  and through tail  130 . Signal path  820  is then completed through the backplane (not shown in FIG.  8 ). Significantly, signal path  820  does not cut through any adjacent signal pin  122 . In this way, cross talk is significantly reduced over the prior art. 
     FIG. 8B illustrates schematically plates  128  and  150  prior to mating of daughter card connector  116  to pin header  114 . In the perspective of FIG. 8B, arm  146  is shown bent out of the plane of plate  128 . As plates  150  and  128  slide along one another during mating, arm  146  is pressed back into the plane of plate  128 . 
     FIG. 8C show plates  128  and  150  in the mated configuration. Dimple  810  pressed into arm  146  is shown touching plate  150 . The torsional spring force generated by pressing arm  146  back into the plane of plate  128  ensures a good electrical contact. It should be noted that the spacing between the plates  128  or  150  and an adjacent signal contact do not have as large a discontinuity as shown in FIG.  7 B. This improvement should improve the electrical performance of the connector. 
     It should also be noted that in moving from the configuration of FIG. 8B to FIG. 8C, there is not an abrupt surface that could lead to stubbing. Thus, with torsional contacts, the mechanical robustness of the connector should be improved in comparison to the prior art. 
     FIG. 10 shows an alternative embodiment of a wafer  154  (FIG.  1 ). In the embodiment of FIG. 10, a shield blank on carrier strip  1010  is encapsulated in an insulative housing  1070  through injection molding. Shield tails  1030  are shown extending from housing  1070 . Housing  1070  includes cavities  1016 ,  1017 ,  1018  and  1019 . The shield blank is cut and bent to make contacts  1020  within cavities  1016 ,  1017 ,  1018  and  1019 . 
     Cavities  1016 ,  1017 ,  1018  and  1019  have holes  1022  formed in their floors. Pins from the pin header are inserted through the holes during mating and engage, through the springiness of the pin as well as of contacts  1020  ensure electrical connection to the shield. 
     In the embodiment of FIG. 10, the signal contacts are stamped separately. The transmission line section of the contacts are laid into cavities  1026 . The receptacle portions of the signal contacts are inserted into cavities  1024 . 
     A wafer as in FIG. 10 illustrates that any number of signal contacts might be used per column. In FIG. 10, four signal contacts per column are shown. That figure also illustrates that pins might be used in place of a plate  128 . However, there might be differences in electrical performance. A plate could be used in conjunction with the configuration of FIG.  10 . In that case, instead of a series of separate holes  1022  in cavities  1016 ,  1017 ,  1018  and  1019 , a slot would be cut through the cavities. 
     FIG. 11A shows an alternative embodiment for contacts  142  on plate  128 . Plate  1128  includes a series of torsional contacts  142 . Each contact is made by stamping an arm  1146  from plate  1128 . Here the arms have a generally serpentine shape. As described above, it is desirable for the arms  146  to be long enough to provide good flexibility. However, it is also desirable for the current to flow through the contacts  1142  in an area that is as narrow as possible in a direction perpendicular to the flow of current through signal pins  122 . To achieve both of these goals, arms  1146  are stamped in a serpentine shape. 
     FIG. 11B shows plate  1128  in cross section through the line indicated as B—B in FIG.  1 A. As shown, arms  1146  are bent out of the plane of plate  1128 . During mating of the connector half, they are pressed back into the plane of plate  1128 , thereby generating a torsional force. 
     FIG. 12 shows an additional view of connector  100 . FIG. 12 shows face  1210  of daughter card connector  116 . The lower surface of pin header  114  is also visible. In this view, it can be seen that the press fit tails  124  of plate  128  have an orientation that is at right angles to the orientation of press fit tails  130  of signal pins  122 . 
     EXAMPLE 
     A connector made according to the invention was made and tested. The test was made with the single ended configuration and measurements were made on one signal line with the ten closest lines driven. For signal rise times of 500 ps, the backward crosstalk was 4.9%. The forward cross talk was 3.2%. The reflection was too small to measure. The connector provided a real signal density of 101 per linear inch. 
     Having described one embodiment, numerous alternative embodiments or variations might be made. For example, the size of the connector could be increased or decreased from what is shown. Also, it is possible that materials other than those expressly mentioned could be used to construct the connector. 
     Various changes might be made to the specific structures. For example, clips  174  are shown generally to be radially symmetrical. It might improve the effectiveness of the shield plate  150  if clips  174  were elongated with a major axis running parallel with the signal contacts in signal pieces  168  and a perpendicular minor axis which is as short as possible. 
     Also, manufacturing techniques might be varied. For example, it is described that daughter card connector  116  is formed by organizing a plurality of wafers onto a stiffener. It might be possible that an equivalent structure might be formed by inserting a plurality of shield pieces and signal receptacles into a molded housing. 
     Therefore, the invention should be limited only by the spirit and scope of the appended claims.