Patent Publication Number: US-10312615-B2

Title: Electrical interconnection system and electrical connectors for the same

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to an electrical interconnection system, and in particular, to an electrical interconnection system and electrical connectors for the same capable of being used for signal transmission. 
     BACKGROUND OF THE INVENTION 
     In conventional electrical communication equipment, a Printed Circuit Board (PCB) is usually used as the backpanel in an electrical communication system, and, interconnections and signal transmissions among independent electrical modules are achieved by connecting these independent electrical modules to the backpanel. Due to more and more requirements on intensity and velocity of signal transmissions in the electrical communication field, there are more attentions on developments of the backpanel. However, the existing high speed backpanel faces some challenges on its signal transmission capabilities like long distance transmission deficiency and loss of the signal. Particularly, signal transmission capabilities of the printed circuit board, as the existing backpanel, are constrained e.g. by its insulation materials and electric circuits thereon. For example, in the PCB application, epoxy resin, which is usually used as insulation materials of the PCB, has high loss factor of about 0.01; further, the electric circuit&#39;s size may be restricted due to the high density layout on the board. Especially, when the conventional PCB backpanel is used for a transmission distance of about 100 cm or more and/or a transmission speed of more than about 15 Gbps, signal loss/attenuations and transmission speed restrictions can happen. 
     On the other hand, electrical cables play an important role in the electrical communications and signal transmissions. Compared with PCBs, electrical cables usually have more advantages on the long distance transmission, due to its structure, material, and so on. Furthermore, insulation material in electrical cables usually have a lower loss factor, for example, less than 0.002. Also, electrical cables have cost and manufacturing advantages. Accordingly, electrical cable assemblies, other than PCB backpanels, become a trend in the electrical communications and signal transmissions. 
     Some efforts have been in place in the industry. For example, Chinese Patent CN102160239 discloses a high density cable assembly for printed circuit board connection. In this reference, a pin header connector is mounted on the printed circuit board, and a plurality of electrical cable assemblies are compactly arranged by a carrier and configured to mate with the header. Each electrical cable assembly includes an electrical cable termination and an electrical cable coupled to the electrical cable termination. The pin header and electrical cable terminations are configured such that each of the electrical cable terminations makes electrical contact with at least one of the contact pins. Accordingly, a number of (for example, hundreds of) cable terminations are needed for high density transmission. Further, it is costly because the cable terminations should be mounted at each of these electrical cables. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to overcome or alleviate at least one aspect of the above mentioned disadvantages existing in the conventional technical solutions. 
     Accordingly, it is at least one object of the present invention to provide an electrical interconnection system suitable for long distance and high density electrical communications and signal transmissions. 
     Accordingly, it is another object of the present invention to provide an electrical receptacle connector suitable for long distance and high density electrical communications and signal transmissions. 
     Accordingly, it is yet another object of the present invention to provide an electrical plug connector suitable for long distance and high density electrical communications and signal transmissions. 
     Accordingly, it is still yet another object of the present invention to provide an electrical signal transmission system suitable for long distance and high density of electrical communications and signal transmissions. 
     According to one aspect of the present invention, an electrical interconnection system comprises: 
     a paddle card in a plate shape and having a first surface and a back to back second surface, comprising a plurality of first contact pads positioned on the first surface of the paddle card and a plurality of second contact pads positioned on the second surface of the paddle card; 
     a first wafer comprising a plurality of first conductors each having a first contact portion; and 
     a second wafer comprising a plurality of second conductors each having a second contact portion; 
     wherein each wafer comprises a housing enclosing at least part of the plurality of first conductors and the plurality of second conductors, and each said housing comprises a mounting edge at which the wafer can be mounted onto a printed circuit board, and a mating edge at which the first and second contact portions are located; 
     wherein the first wafer and the second wafer are assembled together to have the first contact portion and the second contact portion face each other and be able to form a gap therebetween for accommodating at least part of the paddle card; 
     wherein each first contact portion is adapted to be in electrical contact with a corresponding first contact pad and each second contact portion is adapted to be in electrical contact with a corresponding second contact pad when the paddle card is at least partly accommodated in the gap. 
     Particularly, the electrical interconnection system may comprise more than one first wafer and more than one second wafer, wherein each of the first wafer and second wafer is in a sheet shape, and configured to be alternately arranged side by side one another, and one first wafer and one second wafer constitute a wafer unit to match with one paddle card. Preferably, each wafer is configured to be erectly mounted on a printed circuit board. 
     In at least one embodiment, each first conductor and each second conductor may further comprise a mounting portion, and the mounting portion is located on the mounting edge and configured to be in electrical connection with a printed circuit board. For example, at least one of the first conductors and at least one of the second conductors are signal conductors for signal transmission, and at least one of the first conductors and at least one of the second conductors are ground conductors for grounding, and each of the signal conductors and the ground conductors comprises a connecting portion fixed within a housing and alternately arranged with one another along a transverse direction of the housing, and the connecting portions of each pair of signal conductors in one wafer facing the connecting portion of a ground conductor in the other wafer when viewed from a side of the wafer. At least one of the first conductors and at least one of the second conductors are signal conductors for signal transmission, and at least one of the first conductors and at least one of the second conductors are ground conductors for grounding. The first contact portion of the signal conductor of the first wafer is configured to face the second contact portion of the ground conductor of the second wafer while the first contact portion of the ground conductor of the first wafer is configured to face the second contact portion of the signal conductor of the second wafer when viewed from a side of the wafer. The signal conductor and the ground conductor of each of the first wafer and the second wafer are alternately arranged. 
     Specifically, the paddle card may further comprise a plurality of electrical bonding pads configured for electrical connection with at least one electrical cable and positioned on at least one of the first surface and the second surface of the paddle card and each being electrically connected to at least one of the first contact pads and the second contact pads. 
     More specifically, the electrical interconnection system may further comprise at least one electrical cable (e.g. an electrical ribbon cable) in electrical connection with the first electrical bonding pads, respectively. Also, the electrical interconnection system may further comprise a printed circuit board, wherein the first wafer and the second wafer are erectly mounted on and electrically contacted with the printed circuit board. 
     According to another aspect of the present invention, an electrical receptacle connector comprises: at least one first wafer comprising a plurality of first conductors each having a first contact portion; and at least one second wafer comprising a plurality of second conductors each having a second contact portion; wherein each wafer ( 11   a ,  11   b ) comprises a housing enclosing at least part of the plurality of first conductors and the plurality of second conductors, and each said housing comprises a mounting edge at which the wafer can be mounted onto a printed circuit board, and a mating edge at which the first and second contact portions are located; wherein the first and second wafers are alternately arranged side by side one another such that each first contact portion and each second contact portion are assembled together to have the first contact portion and the corresponding second contact portion face each other and be able to form a gap therebetween and constitute a wafer unit configured to have the gap receive a paddle card to be coupled to the electrical receptacle connector. 
     Specifically, at least one of the first conductors and at least one of the second conductors are signal conductors for signal transmission, and at least one of the first conductors and at least one of the second conductors are ground conductors for grounding, and each of the signal conductors and the ground conductors comprises a connecting portion fixed within a housing and alternately arranged with one another along a transverse direction of the housing, and the connecting portions of each pair of signal conductors in one wafer facing the connecting portion of a ground conductor in the other wafer when viewed from a side of the wafer. More specifically, at least one of the first conductors and at least one of the second conductors are signal conductors for signal transmission, and at least one of the first conductors and at least one of the second conductors are ground conductors for grounding, the first contact portion of the signal conductor of the first wafer is configured to face the second contact portion of the ground conductor of the second wafer while the first contact portion of the ground conductor of the first wafer is configured to face the second contact portion of the signal conductor of the second wafer when viewed from a side of the wafer. Still more specifically, the gap is configured to accommodate at least part of a paddle card in a plate shape and having a first surface and a back to back second surface and comprising a plurality of first contact pads positioned on a first surface of the paddle card and a plurality of second contact pads positioned on an opposite second surface of the paddle card; each first contact portion is adapted to be in electrical contact with a corresponding first contact pad and each second contact portion is adapted to be in electrical contact with a corresponding second contact pad when the paddle card is at least partly accommodated in the gap. Preferably, each of the first wafer and second wafer is in a sheet shape and configured to be alternately arranged side by side one another. Preferably, each wafer is configured to be erectly mounted on a printed circuit board. 
     More specifically, each wafer comprises a housing enclosing at least part of the plurality of first conductors and the second conductors respectively, and the housing comprises a mounting edge configured to be ready for be mounted onto a printed circuit board, and a mating edge on which the first and second contact portions are located respectively. Preferably, the mating edge is orthogonal or parallel to the mounting edge. 
     Further, each first conductor and each second conductor further comprises a mounting portion, and the mounting portion is located on the mounting edge and configured to be in electrical connection with a printed circuit board. 
     The electrical receptacle connector may further comprise a receptacle housing configured to accommodate at least part of the first and second wafers, wherein the receptacle housing comprises a top wall or/and a bottom wall orthogonal to the extending direction of the gap and having an engagement mechanism to have the first and second wafers arranged together. Alternatively, the receptacle housing may be configured to accommodate the first and second contact portion, wherein the receptacle housing comprises at least one receptacle ports disposed at a first receiving end thereof and at least two rows of contact receiving apertures disposed at an opposing second receiving end thereof; and each contact portion of one wafer is configured to pass through one contact receiving aperture and the contact portions of every pair of first and second wafers are accommodated within one receptacle port. Further, the receptacle housing may comprise a plurality of guide grooves disposed on the inner surface of the top wall or/and the bottom wall and configured to position the first and second wafers in the receptacle housing. Furthermore, the electrical receptacle connector may also comprises a plurality of latch mechanisms provided for latching these first and second wafers in the receptacle housing, wherein each latch mechanism comprises a projection provided on each wafer and a corresponding locking groove disposed on the receptacle housing and engaged with the projection. In addition, the electrical receptacle connector may further comprise an alignment cover configured to at least partly enclose the first and second wafers at an end opposing to the first and second contact portion, wherein a plurality of latch mechanisms provided to latch all of the first and second wafers to the alignment cover. 
     According to yet another aspect of the present invention, an electrical plug connector comprises: at least one paddle cards being in a plate shape having a first surface and a back to back second surface and comprising a plurality of first contact pads positioned on the first surface of the paddle card and a plurality of second contact pads positioned on the second surface of the paddle card; and a plug housing comprising at least one opening each configured to accommodate part or whole of one paddle card therein; wherein the plug housing comprises a top wall or/and a bottom wall having a mechanical engagement part configured to engage with an external electronic device so as to have the paddle card be in electrical connection with the external electronic device, and each paddle card is orthogonal to the top wall or/and the bottom wall. For example, the mechanical engagement part comprises at least one rib or groove respectively positioned on inner surface of the top wall or/and the bottom wall. 
     Specifically, the paddle card comprises a plurality of electrical bonding pads configured for electrical connection with at least one electrical cable and positioned on at least one of the first surface and the second surface of the paddle card and each being electrically connected to at least one of the first electrical contact pads and the second contact pads. 
     Further, the electrical plug connector may comprise a cable shell removably attached to the plug housing and configured to receive at least one electrical cable to be coupled to the paddle cards. Specifically, the cable shell comprises a front end adjacent the front wall, an opposing rear end, a channel extending from the opposing rear end to the front end and configured to receive end portions of an electrical cable coupled to the plurality of paddle cards, and a pair of retaining members positioned at the front end and configured to retain the plurality of paddle cards in the plug housing. More specifically, the cable shell comprises a lower shell part and an upper shell part removably engaged with the lower shell part, wherein the channel is disposed in the lower shell part. 
     According to an alternative aspect of the present invention, an electrical signal transmission system comprises an electrical receptacle connector according to an aspect of the present invention; an electrical plug connector according to an aspect of the present invention; at least one electrical cable; and a printed circuit board, wherein the electrical cable is in electrical connection with the electrical plug connector, and the electrical plug connector is in electrical connection with the electrical receptacle connector, and the electrical receptacle connector is mounted on and electrically contacted with the printed circuit board. 
     According to still another aspect of the present invention, an electrical plug connector housing includes: a plug housing including a front wall having a plurality of openings therethrough and configured for retaining a plurality of paddle cards therein; and a cable shell removably attached to the plug housing and including a front end adjacent the front wall, an rear end, a channel extending from the rear end to the front end and configured to receive end portions of an electrical cable electrically connected to the plurality of paddle cards, and a pair of retaining members positioned at the front end and configured to retain the plurality of paddle cards in the plug housing. 
     According to still another aspect of the present invention, a connector is disclosed and includes first and second wafers. Each wafer includes a housing, a plurality of pairs of signal conductors and a plurality of ground conductors. The housing includes a mating edge configured to face a mating connector and orthogonal to a mounting edge configured to mount onto a board. The plurality of pairs of signal conductors and a plurality of ground conductors are fixed at least partly within the housing and alternately arranged with one another along a transverse direction of the housing, Each signal conductor and each ground conductor includes a contact portion outside and at the mating edge of the housing for contacting a corresponding contact of a mating connector, a mounting portion outside and at the mounting edge of the housing for contacting a corresponding conductive trace on a board; and a connecting portion disposed within the housing and connecting the contact portion and the mounting portion. The connecting portion has opposing longitudinal edges extending from the mating edge to the mounting edge. The contact portions of each pair of signal conductors in one wafer face the contact portion of a different corresponding ground conductor in the other wafer. And when viewed from a side of the connector, the longitudinal edges of the contact portions of the pair of signal conductors are disposed between the longitudinal edges of the contact portion of the different corresponding ground conductor. 
     According to still another aspect of the present invention, a plug connector housing is disclosed and including a front housing portion, a top housing portion, a bottom housing portion. The front housing portion includes: a top wall, a bottom wall, a pair of opposing side walls extending between the top and bottom walls, and a vertical front mating wall. The vertical front mating wall extends between the top, bottom and side walls and defines a plurality of spaced apart vertical slots extending therethrough. Each vertical slot is configured to receive a circuit board. The front housing portion further includes: a top flange coplanar with the top wall and extending forwardly from the mating wall, and a bottom flange coplanar with the bottom wall and extending forwardly from the mating wall. At least one first engaging member is disposed on a top side of one of the side walls behind the top wall. At least one second engaging member is disposed on a bottom side of one of the side walls behind the bottom wall. A third engaging member is disposed on an inside surface of one of the top and bottom walls. The top housing portion includes: a top wall, a pair of opposing side walls extending downwardly from the top wall. The top and side wall defines a cavity for receiving a plurality of circuit boards. A first divider extends downwardly from the top wall and is disposed between the sidewalls. At least one first engaging member is disposed on an inside surface and front of the top wall. A second engaging member is disposed on an inside surface of the top wall. A first position hole is located on a bottom of the divider. The bottom housing portion includes: a bottom wall, a pair of opposing side walls extending upwardly from the bottom wall, and a second divider extending upwardly from the top wall and disposed between the sidewalls. The bottom housing portion further includes at least one first engaging member on a top side and front of the bottom wall, and a first position hole on a top of the divider. The front, top and bottom housing portions are reversibly assembled such that the at least one first engaging member of the front housing portion engages the at least one first engaging member of the top housing portion, and the at least one second engaging member of the front housing portion engages the at least one first engaging member of the bottom housing portion. A fastener is provided to engage the first position hole of the top housing portion with the first position hole of the bottom housing portion. The plug connector housing is configured to receive at least one circuit board. The circuit board has first and second engaging members along an edge of the circuit board and an edge connector at a front of the circuit board. Each circuit board is disposed within a corresponding vertical slot with the edge connector of the circuit board extending forwardly from the mating wall between the top and bottom flanges. When the circuit board is well located, the third engaging member of the front housing portion engages the first engaging member of the circuit board, and the second engaging member of the top housing portion engages the second engaging member of the circuit board. 
     Concerning the above, in at least one aspect, the present invention provides an electrical interconnection system which may be used in a high speed and high density of electrical communication system. The electrical plug cable assembly according to embodiments of the present invention may substitute a conventional backpanel printed circuit board which brings signal loss/attenuations in the signal transmission adopted in the conventional electrical communication system. Accordingly, applications of the electrical interconnection system and cable assembly according to aspects of the present invention in the high speed and high density of electrical communication system may achieve long distance signal transmission with lower signal loss/attenuations than a conventional backpanel PCB, which is suitable for high density electrical communications and signal transmissions. Further, in at least one aspect, the present invention provides an electrical receptacle connector and an electrical plug cable assembly for the electrical interconnection system. Furthermore, in at least one aspect, the present invention provides an electrical signal transmission system suitable for long distance and high density of electrical communications and signal transmissions. In addition, in at least one aspect, the present invention provides an electrical plug connector housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments of the present invention, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic perspective view of an electrical interconnection system according to one embodiment of the present invention; 
         FIG. 2 a , 2 b , 2 c    are schematic side views of the electrical interconnection system according to one embodiment of the present invention; 
         FIG. 3  is a schematic perspective view of an electrical receptacle connector, with a PCB to be connected thereto, according to one embodiment of the present invention; 
         FIG. 4  is an exploded schematic perspective view of the electrical receptacle connector according to one embodiment of the present invention; 
         FIG. 5  is a schematic perspective view of an electrical plug connector, with an electrical cable to be connected thereto, according to one embodiment of the present invention; 
         FIG. 6  is an exploded schematic perspective view of the electrical plug connector according to one embodiment of the present invention; 
         FIG. 7  is a schematic perspective view of an application of an electrical signal transmission system according to one embodiment of the present invention; and 
         FIG. 8  is a schematic perspective view of another application of an electrical signal transmission system according to one embodiment of the present invention; 
         FIG. 9  is a schematic perspective view of an electrical connector, according to one embodiment of the present invention; 
         FIG. 10  is a schematic view of some conductors contained in the wafer of the connector shown in  FIG. 9 ; 
         FIG. 11  is a schematic perspective view of a plug connector housing, according to one embodiment of the present invention; and 
         FIG. 12  is a slightly angled front view of the front housing portion of the plug connector housing shown in  FIG. 11 . 
     
    
    
     The scope of the present invention will in no way be limited to the simply schematic views of the drawings, the number of constituting components, the materials thereof, the shapes thereof, the relative arrangement thereof, etc., and are disclosed simply as an example of an embodiment. 
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Exemplary embodiments of the present disclosure will be described hereinafter in detail with reference to the attached drawings, wherein the like reference numerals refer to the like elements. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein; rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the concept of the disclosure to those skilled in the art. 
     One aspect of the present invention provides an electrical interconnection system capable of being used in long distance electrical communications and signal transmissions. Referring to  FIGS. 1-7 , an electrical interconnection system according to one embodiment of the present invention is provided. 
     Referring to  FIG. 1  and  FIGS. 2 a -2 c   , an electrical interconnection system according to one embodiment of the present invention comprises a paddle card  30 , a first wafer  11   a , and a second wafer  11   b . The paddle card  30  is in a plate shape and comprises a plurality of first contact pads  33  positioned on a first surface  31  of the paddle card  30  and a plurality of second contact pads  34  positioned on a second surface  32  back to back to the first surface  31 . The first surface  31  can be also referred to as the front surface of the paddle card  30 , and the second surface  32  can be also referred to as the back surface of the paddle card  30 . The first wafer  11   a  comprises a plurality of first conductors  13   a  each having a first contact portion  131   a ; and the second wafer  11   b  comprises a plurality of second conductors  13   b  each having a second contact portion  131   b . The first wafer  11   a  and the second wafer  11   b  are assembled together (e.g. assembled to form an integral or adjacently positioned) to have the first contact portion  131   a  and the second contact portion  131   b  face each other and be able to form a gap  1310  therebetween for accommodating at least part of the paddle card  30 . Each first contact portion  131   a  is adapted to be in electrical contact with a corresponding first contact pad  33  and each second contact portion  131   b  is adapted to be in electrical contact with a corresponding second contact pad  34  when the paddle card  30  is at least partly accommodated in the gap  1310 . 
     In the embodiments of this disclosure, the gap between the first contact portion  131   a  and the second contact portion  131   b  may be formed when the paddle card  30  is inserted by force, and before the paddle card  30  is accommodated there the first contact portion  131   a  and the second contact portion  131   b  may be in contact with each other. For example, the first contact portion  131   a  and the second contact portion  131   b  may have an angled lead-in portion to allow insertion of the paddle card and other portion of the contact portion ( 131   a , 131   b ) may be straight and in touch with each other. Or, the first wafer  11   a  and the second wafer  11   b  are assembled in a way that there is a slit with certain width between the first contact portion  131   a  and the second contact portion  131   b  before the paddle card  30  is accommodated there. 
     In the electrical interconnection system according to other embodiment of the present invention, there are many paddle cards  30  and many corresponding units of the first and second wafers  11   a ,  11   b  provided for high density electrical communications and signal transmissions among different modules (such as the PCBs  60 ) by electrical cables (such as an assembly of electrical cables  50 ). 
     According to one embodiment of the present invention, as shown in  FIG. 1  and  FIGS. 2 a -2 c   , one first wafer  11   a  and one second wafer  11   b  constitute a wafer unit which is for being electrically connected with one paddle card  30  in the electrical interconnection system. Referring to  FIG. 1  and  FIGS. 2 a -2 c   , the first wafer  11   a  and the second wafer  11   b  each is generally in a rectangular plate shape and is configured to be erectly mounted on a printed circuit board  60  for being electrically connected to the printed circuit board  60 . The first wafer  11   a  and the second wafer  11   b  each comprises at least one pair of signal conductors for signal transmission and at least one ground conductor for grounding. In the wafer unit, the first wafer  11   a  and the second wafer  11   b  are arranged such that a signal conductor of the first wafer  11   a  faces a ground conductor of the second wafer  11   b  while a ground conductor of the first wafer  11   a  faces a signal conductor of the second wafer  11   b . Correspondingly, in the case where a number of wafer units are provided side by side one another, a signal conductor of the first wafer  11   a  in one wafer unit face a ground conductor of the second wafer  11   b  in an adjacent wafer unit while a ground conductor of the first wafer  11   a  in the one wafer unit faces a signal conductor of the second wafer  11   b  in another adjacent wafer unit. 
     Referring to  FIG. 1  and  FIGS. 2 a -2 c   , in a wafer unit, each of the first wafer  11   a  and the second wafer  11   b  comprises a plurality of signal conductors for signal transmission and a plurality of ground conductors for grounding alternately arranged with the signal conductors. Alternatively, in the wafer unit, signal conductors of the first wafer  11   a  face corresponding ground conductors of the second wafer  11   b , while ground conductors of the first wafer  11   a  face corresponding signal conductors of the second wafer  11   b . For example, in the embodiment shown in  FIG. 1  and FIGS.  2   a - 2   c , there are eight conductors, i.e., four signal conductors and four ground conductors arranged in an alternate manner, in one wafer  11   a  or  11   b . Of course, in another embodiment according to the present invention, number of these conductors may be vary, such as, twelve or sixteen. 
     In at least one aspect, the ground conductors in one wafer serve as isolator and return path for adjacent signal conductors in same wafer. In at least one aspect, the ground conductors in one wafer serve as reference plane and shield to form a stripline structure for signal conductors in adjacent alternate wafers. For specific signal conductors, the effect of ground conductors in same wafer and adjacent alternate wafer contributes to providing desired characteristic impedance and crosstalk isolation. 
     Every conductor  13 ,  13   a ,  13   b  of the signal conductors and the ground conductors in the wafer  11   a  or  11   b  of a wafer unit comprises a contact portion  131   a  or  131   b . That is, as mentioned in the above, the first wafer  11   a  comprises the plurality of first conductors  13   a  each having a first contact portion  131   a ; and the second wafer  11   b  comprises the plurality of second conductors  13   b  each having a second contact portion  131   b . And, the first wafer  11   a  and the second wafer  11   b  in one wafer unit are assembled together to have the first contact portion  131   a  and the second contact portion  131   b  face each other and be able to form a gap  1310  therebetween for accommodating at least part of the paddle card  30 . 
     In this description, although in some embodiment, in one wafer unit, the first contact portion  131   a  of the first wafer  11   a  and the second contact portion  131   b  of the second wafer  11   b  may be configured in an opposite deformation direction (in order to form the gap  1310 ) at the end while the respective signal conductors (paths) and the respective ground conductors (paths) in the first wafers  11   a  are arranged to face the respective ground conductors (paths) and the respective signal conductors (paths) in the second wafer  11   b , the first wafers  11   a  and the second wafers  11   b  are generally the same outline and have a similar (opposed) conductor arrangement. Accordingly, in the following description and its accompanying drawings, a wafer signed by number “ 11 ” denotes either the first wafer  11   a  or the second wafer  11   b ; similarly, a plurality of conductors (including the signal conductors and the ground conductors) signed by number “ 13 ” denotes either the plurality of first conductors  13   a  or the plurality of second conductors  13   b ; and, contact portions signed by number “ 131 ” denotes either the first contact portion  131   a  or the second contact portion  131   b , etc., for clarity and concision purposes. 
     Since there is such a wafer unit (including one first wafer  11   a  and one second wafer  11   b ) provided in the electrical interconnection system as shown in  FIG. 1  and  FIGS. 2 a -2 c    and configured to be erectly mounted on a printed circuit board  60 , in at least one embodiment, many wafer units may be arranged side by side on the printed circuit board  60 , to realize a high density arrangement. 
     According to one embodiment of the present invention, each wafer  11  ( 11   a ,  11   b ) has a housing  12  enclosing at least part of the plurality of conductors  13  (i.e., the plurality of first conductors  13   a  and the plurality of second conductors  13   b ) respectively therein. Each housing  12  comprises a mounting edge  122  where the wafer is to be mounted onto a printed circuit board  60  and a mating edge  121  where the contact portions  131  (i.e., the first contact portions  131   a  and the second contact portions  131   b ) are located. In at least one embodiment, the mating edge  121  is orthogonal or parallel to the mounting edge  122 . For example, in the embodiment shown in  FIGS. 2 a -2 c   , the housing  12  of the wafer  11  is in a substantially rectangular shape and the mating edge  121  is orthogonal to the mounting edge  122 . Nevertheless, the mating edge  121  of the housing  12  may be at any angle relative to the mounting edge  122  in other embodiments of the present invention. 
     Each of the conductors  13  comprises a mounting portion  133 , and the mounting portion  133  is located at the mounting edge  122  of the housing  12  and configured to be in electrical connection with the printed circuit board  60 . Each of the conductors  13  further comprises a connecting portion  132  disposed within the housing  12  and connecting the contact portion  131  and the mounting portion  133 . In at least one embodiment, each of the signal conductors and the ground conductors have the connecting portion  132  fixed within the housing  12  and alternately arranged with one another along a transverse direction of the housing  12 , and the connecting portion  132  of the signal conductor in one wafer  11   a  or  11   b  faces the connecting portion  132  of the ground conductor in the other wafer  11   b  or  11   a  when viewed from a side of the wafer. And, in one wafer unit, the signal conductor and the ground conductor of each of the first wafer  11   a  and the second wafer  11   b  are alternately arranged. 
     Referring to  FIG. 1  and  FIGS. 2 a -2 c   , as mentioned above, the paddle card  30  comprises a plurality of first contact pads  33  positioned on the first surface  31  and a plurality of second contact pads  34  positioned on an opposite second surface  32 . Further, the paddle card  30  may comprise a plurality of electrical bonding pads  35  configured for electrical connection with at least one electrical cable  50 . As shown in  FIG. 1  and  FIG. 2 a -2 c   , these electrical bonding pads  35  are positioned on at least one of the first surface  31  and the second surface  32  of the paddle card  30  and each being electrically connected to at least one of the first contact pads  33  and the second contact pads  34 . For example, in the embodiment shown in  FIGS. 2 a -2 c   , these electrical bonding pads  35  are positioned on the first surface  31  of the paddle card  30  while being electrically connected to the respective first contact pads  33  on the first surface  31  of the paddle card  30  and the respective second contact pads  34  on the second surface  32  of the paddle card  30 . The paddle card  30  may further comprise a pair of electrical ground pads  36  provided for example at both outer ends of the plurality of electrical bonding pads  35  and configured for grounding. 
     According to one embodiment of the present invention, referring to  FIG. 1  and  FIG. 2 a -2 c   , the electrical interconnection system may further comprise at least one electrical cable  50  in electrical connection with the first electrical bonding pads  35 , respectively. In at least one embodiment, the at least one electrical cable  50  may be embodied as a ribbon cable The at least one electrical cable  50  may have any suitable cable configuration, including but not limited to a coaxial cable, a twinaxial cable, a shielded cable, and an unshielded cable. 
     According to one embodiment of the present invention, referring to  FIG. 1 , the electrical interconnection system may comprise one or more printed circuit board  60 . The first wafers  11   a  and the second wafers  11   b  are erectly mounted on and electrically contacted with the printed circuit board  60 , such that one or more units of the first and second wafers  11   a ,  11   b  may be arranged side by side on the printed circuit board  60 . This mounting and arranging allows for expanding the wafer units so as to achieve high density signal transmission. 
     Then, referring to  FIGS. 2 a -2 c   ,  3  and  4 , an electrical receptacle connector  10  according to one embodiment of the present invention is provided. The electrical receptacle connector  10  comprises at least one first wafer  11   a  and at least one second wafer  11   b . Each first wafer  11   a  comprises a plurality of first conductors  13   a  each having a first contact portion  131   a . Each second wafer  11   b  comprises a plurality of second conductors  13   b  each having a second contact portion  131   b . One first wafer  11   a  and one second wafer  11   b  are assembled together (including adjacently positioned) to have the first contact portions  131   a  and the corresponding second contact portions  131   b  face each other and be able to form a gap  1310  therebetween. Alternatively, the first and second wafers  11   a ,  11   b  are alternately arranged side by side one another and one first wafer and one second wafer constitute a wafer unit configured to have the gap  1310  receive a paddle card  30  to be coupled to the electrical receptacle connector  10 . Alternatively, the gap  1310  is configured to accommodate at least part of a paddle card  30 . 
     The paddle card  30  comprises a plurality of first contact pads  33  positioned on a first surface  31  of the paddle card  30  and a plurality of second contact pads  34  positioned on an opposite second surface  32  of the paddle card  30 . Each first contact portion  131   a  is adapted to be in electrical contact with a corresponding first contact pad  33  and each second contact portion  131   b  is adapted to be in electrical contact with a corresponding second contact pad  34  when the paddle card  30  is at least partly accommodated in the gap  1310 . 
     According to one embodiment of the present invention, each of the first wafer  11   a  and second wafer  11   b  is in a plate shape and configured to be alternately arranged side by side one another. In at least one aspect, each wafer  11  is configured to be mounted on a printed circuit board  60 . In at least one aspect, each wafer  11  comprises a housing  12  enclosing at least part of the plurality of conductors  13  respectively, and the housing  12  comprises a mounting edge  122  where the wafer is to be mounted onto a printed circuit board  60 , and a mating edge  121  at which the first and second contact portions  131   a ,  131   b  are located respectively. In at least one aspect, the mating edge  121  is orthogonal or parallel to the mounting edge  122 . For example, in the embodiment shown in  FIGS. 2 a -2 c   , the housing  12  of the wafer  11  is in a substantially rectangular shape and the mating edge  121  is orthogonal to the mounting edge  122 . 
     Each of the conductors  13  comprise a mounting portion  133 , and the mounting portion  133  is located at the mounting edge  122  and configured to be in electrical connection with the printed circuit board  60 . Also, each of the conductors  13  also comprises a connecting portion  132  disposed within the housing  12  and connecting the contact portion  131  and the mounting portion  133 . Specifically, the contact portions  131  of the conductors  13  are provided outside and at the mating edge  121  of the housing  12 , the mounting portions  133  are outside and at the mounting edge  122  of the housing  12  for contacting a corresponding conductive trace  61  on a printed circuit board  60 ; and the connecting portions  132  are disposed within the housing  12  and connecting the contact portion  131  and the mounting portion  133 . In other words, the electrical receptacle connector  10  may be an assembly of several above-mentioned wafer units. 
     According to one embodiment of the present invention, referring to  FIGS. 3 and 4 , the electrical receptacle connector  10  may further comprise a receptacle housing  14  configured to accommodate at least part of the first and second wafers therein. Alternatively, the receptacle housing  14  is configured to accommodate the first and second contact portions  131   a ,  131   b  of the first and second wafers  11   a ,  11   b . The receptacle housing  14  comprises at least one receptacle port  141  disposed at a first receiving end  148  thereof and at least two rows of contact receiving apertures  142  disposed at an opposing second receiving end  149  thereof. Each contact portion  131  of one wafer  11  is configured to pass through one contact receiving aperture  142 , and the contact portions  131  of every pair of first and second wafers  11   a ,  11   b  are accommodated within one receptacle port  141 . For example, accordingly, in the embodiment shown in  FIGS. 2 and 3 , there are four wafer units (i.e., four first wafers  11   a  and four second wafers  11   b ) arranged with one another in the electrical receptacle connector  10 , and correspondingly, four receptacle ports  141  and eight rows of contact receiving apertures  142  are disposed in the receptacle housing  14 . Every two rows of contact receiving apertures  142  are intercommunicated with one corresponding receptacle port  141 . In at least one embodiment, guide edges  144  (shown in  FIG. 3 ) are disposed on these receptacle ports  141 , for smooth connection of the electrical receptacle connector  10  with a mating connector, e.g. the paddle card  30  as disclosed above. 
     The receptacle housing  14  comprises top and bottom walls  143  orthogonal to the extending direction of the gap  1310  and having an engagement mechanism to have the first and second wafers  11   a ,  11   b  arranged together. The engagement mechanism may comprise a plurality of first guide grooves  145  disposed on the inner surfaces of one or both top and bottom walls  143  of the receptacle housing  14  and configured to position the first and second wafers  11  in the receptacle housing  14 , in order to guide and position the contact portions  131  in the corresponding rows of contact receiving apertures  142 . Alternatively, a plurality of secondary guide grooves  146  may be disposed on outside surfaces of both top and bottom walls  143 . The secondary guide grooves serve to help the receptacle housing  14  mated with corresponding mating connector, for instance, serve to guide the electrical receptacle connector  10  during mating to a mating connector. Provision of the guide structure helps smooth connection between the receptacle housing  14  and these wafer units. 
     Alternatively, referring to  FIGS. 3 and 4 , in order for retention of these wafers  11  in the receptacle housing  14 , a plurality of latch mechanisms are provided for latching these first and second wafers  11  in the receptacle housing  14 . Each latch mechanism may comprise a projection  111  provided on each wafer  11  and a corresponding locking groove  147  may be disposed on the receptacle housing  14  and engaged with the projection  111 . Alternatively, the projection  111  can be provided at the mounting edge  122  and/or an edge  124  opposing to the mounting edge  122  of the housing  12  of a wafer  11  and the corresponding locking groove (through hole)  147  can be disposed on the corresponding first guide grooves  145  of the receptacle housing  14  and engaged with the projection  111 . 
     According to one embodiment of the present invention, the electrical receptacle connector  10  may further comprise an alignment cover  15  configured to at least partly enclose the first and second wafers  11   a ,  11   b  at an edge opposite the first and second contact portions, for helping to protect and position these wafers  11 . As shown in  FIGS. 3 and 4 , the alignment cover  15  is provided to cover at least an edge  123  opposite the mating edge  121  and an edge  124  opposite the mounting edge  122  of the housing  12  of one wafer  11 . A plurality of latch mechanisms may be provided to latch all of the first and second wafers  11  to the alignment cover  15 . Referring to  FIG. 4 , for example, the latch mechanism may comprise a plurality of first projections  112  each provided at the edge  124  opposite the mounting edge  122  of the housing  12  of each wafer  11  and a plurality of first corresponding locking through holes  151  each disposed on the alignment cover  15  for engagement with the corresponding first projection  112 . The latch mechanisms may further comprise a plurality of second projections  113  each provided on a corner between the edge  124  opposite the mounting edge  122  and the edge  123  opposite the mating edge  121  of the housing  12  of each wafer  11 , and a plurality of corresponding second locking through holes  152  each disposed on a corresponding location of the alignment cover  15  for engagement with the corresponding second projection  113 . The latch mechanisms may further comprise a plurality of third bar projections  114  each provided on the edge  123  opposite the mating edge  121  of the housing  12  of each wafer  11  and a plurality of corresponding third locking slots  153  each disposed on a corresponding location of the alignment cover  15  for engagement with the corresponding third bar projection  114 . 
     Referring to  FIGS. 5 and 6 , an electrical plug connector  20  according to one embodiment of the present invention, matable with the above electrical receptacle connector  10 , is provided. The electrical plug connector  20  comprises: at least one paddle card  30  and a plug housing  22 . As shown in  FIGS. 2 a -2 c   , each paddle card  30  comprises a plurality of first contact pads  33  positioned on a first surface  31  of the paddle card  30  and a plurality of second contact pads  34  positioned on an opposite second surface  32  of the paddle card  30 . Back to  FIGS. 5 and 6 , the plug housing  22  comprises at least one opening  220  configured to accommodate part or whole of a paddle card  30  therein. The plug housing  22  further comprises opposing top and bottom walls  222  having a mechanical engagement part configured to engage with an external electronic device so as to have the paddle card  30  be in electrical connection with the external electronic device (such as the electrical cable  50  for example). Each paddle card  30  is orthogonally arranged to the top and bottom walls  222 . 
     The paddle card  30  can be electrically coupled to an electrical cable  50  and electrically contacted with the electrical receptacle connector  10 . As shown in  FIGS. 2 a -2 c   , the paddle card  30  includes a plurality of first electrical contact pads  33  positioned on a first surface  31  of the paddle card  30  and a plurality of second electrical contact pads  34  positioned on an opposing second surface  32  of the paddle card  30 . Each of these electrical contact pads  33 ,  34  are configured to make electrical contact with one contact portion  131  of each conductor  13  in the electrical receptacle connector  10 . The paddle card  30  further comprises a plurality of electrical bonding pads  35  configured for electrical connection with at least one electrical cable  50  and positioned on at least one of the first surface  31  and the second surface  32  of the paddle card  30  and each being electrically connected to one of the first electrical contact pads  33  and the second contact pads  34  of the paddle card  30 . These electrical bonding pads  35  are configured to receive end portions  51  of an electrical cable  50  coupled to the paddle card  30 . Alternatively, the paddle card  30  may comprise a plurality of first electrical bonding pads  35  positioned on a first surface  31  of the paddle card  30  and each being electrically connected to the first electrical contact pad  33  and a plurality of second electrical bonding pads (not shown) positioned on an opposing second surface  32  of the paddle card  30  and each being electrically connected to the second electrical contact pad  34 . The first and/or second electrical contact pads  33 ,  34  are configured to receive end portions  51  of an electrical cable  50  coupled to the paddle card  30 . In addition, the paddle card  30  may further comprise a pair of electrical ground pads  36  provided at both outer lateral of the plurality of electrical cable pads  35  and configured for grounding. 
     Referring to  FIG. 6 , the plug housing  22  may include a front wall  221  having a plurality of openings  220  therethrough, each opening being configured to receive one paddle card  30  in the plug housing  22 . 
     The top and bottom walls  222 , which correspond to the top and bottom walls  143  of the receptacle housing  14 , extend from both ends of plug housing  22 . The mechanical engagement part comprises a plurality of ribs  223  disposed on inside surfaces  2220  of both top and bottom walls  222 , respectively. The ribs  223  of the plug housing  22  is configured for engagement with corresponding secondary guide grooves  146  of the receptacle housing  14  such that the plug housing  22  and the receptacle housing  14  are smoothly connected with each other. 
     Referring to  FIG. 6 , the electrical plug connector  20  may further comprise a cable shell  40  removably attached to the plug housing  22  and configured to receive at least one electrical cable  50  to be coupled to the paddle cards  30 . 
     The cable shell  40  comprises a front end  41  adjacent the front wall  221 , an opposing rear end  42 , a channel  43  extending from the rear end  42  to the front end  41  and configured to receive end portions  51  of an electrical cable  50  coupled to the plurality of paddle cards  30 , and a pair of retaining members  44  positioned at the front end  41  and configured to retain the plurality of paddle cards  30  in the plug housing  22 . The pair of retaining members  44  comprises several top wall retaining members  44   a  disposed on the inside surface  4410  of the top wall  441  of the cable shell  40  and several corresponding bottom wall retaining members  44   b  disposed on the inside surface  4420  of the bottom wall  442  of the cable shell  40 . Preferably, one pair of top wall and bottom wall retaining members  44  is provided to engage with corresponding retaining grooves disposed at both outer lateral ends of one paddle card  30 , respectively, so as to retain one paddle card  30  in the plug housing  22 . For example, in the embodiment shown in  FIG. 6 , four pairs of top wall and bottom wall retaining members  44  are provided for retaining four paddle cards  30  in the plug housing  22 , respectively. 
     A retaining mechanical arrangement may be provided for latching the plug housing  22  to the cable shell  40 . For example, the retaining mechanical arrangement may comprise a pair of retaining grooves  224  disposed at a rear end of the plug housing  22  (i.e., at both outer lateral ends of the rear end of plug housing  22  shown in  FIG. 6 ), and two retaining members  44  (i.e., the outermost pair of the retaining members  44 ) of the cable shell  40 . The pair of retaining grooves  224  and the outmost pair of retaining members  44  are engaged with respect to each other so as to mount the plug housing  22  and the cable shell  40  together. The retaining mechanical arrangement may further comprise a pair of retaining pins  49  disposed respectively on the inside surfaces of the top wall and the bottom wall of the cable shell  40 , to provide additional security in mounting the plug housing  22  and the cable shell  40  together. 
     As shown in  FIG. 6 , the cable shell  40  includes a lower shell part  45  and an upper shell part  46  removably engaged with the lower shell part  45 . The channel  43  is disposed in the lower shell part  45 . Further, a plurality of locking members  47  (for example, one at the front end  41  while two at the opposing rear end  42 ) is disposed in the channel  43  of the lower shell part  45 . A plurality of corresponding locking holes  48  (for example, one at the front end  41  while two at the opposing rear end  42 , correspondingly) is disposed in the upper shell part  46 . The lower shell part  45  and the upper shell part  46  are detachably fixed together when fasteners are provided extending through locking holes  48  and into corresponding locking members  47 . 
     In accordance with principles and spirits of the present invention, an embodiment of the present invention also provides an electrical signal transmission system for high-speed signal transmission. 
       FIG. 7  shows an application of an electrical signal transmission system according to one embodiment of the present invention. Referring to  FIG. 7 , the electrical signal transmission system mainly comprises two electrically receptacle connectors  10 , two electrical plug connectors  20  each having a plurality of paddle cards  30  therein and connectable with the corresponding electrical receptacle connector  10 , assembly of electrical cables  50 , and two printed circuit board  60 . Each electrical receptacle connector  10  includes four wafer units arranged side by side while each wafer in the wafer unit is mounted on and electrically contacted with the corresponding printed circuit board  60 . The assembly of electrical cables is provided for being in electrical connection between the two electrical plug connectors  20 . And, each of the two electrical plug connectors  20  is in electrical connection with corresponding electrical receptacle connector  10  by electrical connections among these wafer units and these corresponding paddle cards  30 . In this way, these printed circuit boards (PCB)  60  are electrically connected by assembly of the electrical cables  50  through electrical connections between the electrical receptacle connectors  10  and the corresponding electrical plug connectors  20 . Accordingly, in at least one aspect, this electrical signal transmission system can provide long distance signal transmission with lower signal loss/attenuations than a conventional backpanel PCB. 
       FIG. 8  shows another application of an electrical signal transmission system according to an embodiment of the present invention. The electrical signal transmission system mainly comprises three electrical receptacle connectors  10 A,  10 B,  10 C (especially, two connectors having four wafer units while one connector has eight wafer units, as shown in  FIG. 8 ) respectively being mounted on and being electrically connected with three individual printed circuit boards  60 A,  60 B,  60 C, and three electrical plug connectors  20 A,  20 B, and  20 C in which a plurality of corresponding paddle cards  30  are provided. The three electrical plug connectors  20 A,  20 B, and  20 C, each covered by the respective cable shells  40 , are electrically connected by two electrical cables  50 A and  50 B. In the illustrated embodiment, electrical plug connectors  20 A and  20 C are electrically connected by electrical cable  50 A, and electrical plug connector  20 B and  20 C are electrically connected by electrical cable  50 B. In the electrical signal transmission system shown in  FIG. 8 , the three electrical plug connectors  20 A,  20 B, and  20 C are connectable with the corresponding electrical receptacle connectors  10 A,  10 B, and  10 C, respectively, to achieve the electrical signal transmission system. 
     Consequently, the electrical signal transmission system according to embodiments of the present invention is suitable for high density electrical communications and signal transmissions. Further, applications of the electrical connector and cable assembly according to aspects of the present invention in high speed and high density electrical communication systems may achieve long distance signal transmission with lower signal loss/attenuations than a conventional backpanel PCB. 
     According to an alternative aspect of the present invention, an electrical plug connector housing is provided. The electrical plug connector housing includes: a plug housing  22  including a front wall  221  having a plurality of openings  220  therethrough and configured for retaining a plurality of paddle cards  30  therein; and a cable shell  40  removably attached to the plug housing  22  and including a front end  41  adjacent the front wall, an rear end  42 , a channel  43  extending from the rear end to the front end and configured to receive end portions of an electrical cable  50  electrical connected to the plurality of paddle cards, and a pair of retaining members  44  positioned at the front end and configured to retain the plurality of paddle cards in the plug housing. 
     According to an alternative aspect of the present invention, in one embodiment, a connector is disclosed. As shown in  FIGS. 9 and 10 , the connector  100  includes at least one first wafer  11   a  and at least one second wafer  11   b . Each wafer  11   a ,  11   b  includes a housing  12 , a plurality of pairs of signal conductors  13   c ,  13   d  and a plurality of ground conductors  14 . The housing  12  includes a mating edge  121  configured to face a mating connector (e.g. a paddle card) and orthogonal to a mounting edge  122  configured to mount onto a board (e.g. printed circuit board). The plurality of pairs of signal conductors  13   c ,  13   d  and the plurality of ground conductors  14  are fixed at least partly within the housing  12  and alternately arranged with one another along a transverse direction of the housing  12 . 
     Each signal conductor  13   c ,  13   d  and each ground conductor  14  includes a contact portion  138 ,  139 ,  149 , a mounting portion  136 ,  137 ,  148  and a connecting portion  134 , 135 ,  147 . The contact portion  138 ,  139 ,  149  is outside and at the mating edge  121  of the housing  12  for contacting a corresponding contact of a mating connector. The mating connector can be the electrical plug connector as mentioned above. The mounting portion  136 ,  137 ,  148  is outside and at the mounting edge  122  of the housing for contacting a corresponding conductive trace on a board. The connecting portion  134 ,  135 ,  147  is disposed within the housing  12  and connecting the contact portion  138 ,  139 ,  149  and the mounting portion  136 ,  137 ,  148 . 
     The connecting portion  134 ,  135 ,  147  has opposing longitudinal edges  134   a ,  1134   b ;  135   a ,  135   b ;  147   a ,  147   b  extending from the mating edge  121  to the mounting edge  122 . The contact portions  138 ,  139  of each pair of signal conductors  13   c ,  13   d  in one wafer face the contact portion  149  of a different corresponding ground conductor  14  in the other wafer. And when viewed from a side of the connector, the longitudinal edges  138   a ,  139   b  of the contact portions  138 ,  139  of the pair of signal conductors  13   c ,  13   d  are disposed between the longitudinal edges  149   a ,  149   b  of the contact portion  149  of the different corresponding ground conductor  14 . 
     According to an alternative aspect of the present invention, in one embodiment, a plug connector housing  500  is disclosed. As shown in  FIGS. 11 and 12 , the plug connector housing  500  includes a front housing portion  600 , a top housing portion  700 , a bottom housing portion  800 . 
     The front housing portion  600  includes: a top wall  610 , a bottom wall  620 , a pair of opposing side walls  630  extending between the top and bottom walls, and a vertical front mating wall  640 . The vertical front mating wall  640  extends between the top, bottom and side walls and defines a plurality of spaced apart vertical slots  650  extending therethrough. Each vertical slot  650  is configured to receive a circuit board  400 . 
     The front housing portion  600  further includes: a top flange  660  coplanar with the top wall and extending forwardly from the mating wall, and a bottom flange  665  coplanar with the bottom wall and extending forwardly from the mating wall. At least one first engaging member  670  (e.g. a notch) is disposed on a top side of one of the side walls behind the top wall. At least one second engaging member  680  (e.g. a notch) is disposed on a bottom side of one of the side walls behind the bottom wall. A third engaging member  690  is disposed on an inside surface of one of the top and bottom walls. 
     The top housing portion  700  includes: a top wall  710 , a pair of opposing side walls  720  extending downwardly from the top wall. The top and side wall defines a cavity  730  for receiving a plurality of circuit boards  400 . A first divider  740  extends downwardly from the top wall  710  and is disposed between the sidewalls  720 . At least one first engaging member  750  (e.g a bump) is disposed on an inside surface and front of the top wall  710 . A second engaging member  760  (e.g a bump) is disposed on an inside surface of the top wall  710 . A first position hole  770  is located on a bottom of the divider. 
     The bottom housing portion  800  includes: a bottom wall  810 , a pair of opposing side walls  820  extending upwardly from the bottom wall, and a second divider  830  extending upwardly from the top wall  810  and disposed between the sidewalls  820 . The bottom housing portion  800  further includes at least one first engaging member (e.g a bump)  840  on a top side and front of the bottom wall  810 , and a first position hole  850  on a top of the divider. 
     The front, top and bottom housing portions are reversibly assembled such that the at least one first engaging member  670  of the front housing portion engages the at least one first engaging member  750  of the top housing portion, and the at least one second engaging member  680  of the front housing portion engages the at least one first engaging member  840  of the bottom housing portion. A fastener is provided to engage the first position hole  770  of the top housing portion with the first position hole  850  of the bottom housing portion. 
     The plug connector housing is configured to receive at least one circuit board  400 . The circuit board  400  has first  410  and second  420  engaging members along an edge of the circuit board and an edge connector  430  at a front of the circuit board. Each circuit board is disposed within a corresponding vertical slot  650  with the edge connector  430  of the circuit board extending forwardly from the mating wall  640  between the top  660  and bottom  665  flanges. As an example shown in the  FIG. 11 , the plug connector housing has four vertical slots  650  and configured to receive four circuit boards  400  at the most. Three of such circuit boards  400  have been exemplarily located in the slots  650 . When the circuit board  400  is well located, the third engaging member  690  of the front housing portion engages the first engaging member  410  of the circuit board, and the second engaging member  760  of the top housing portion engages the second engaging member  420  of the circuit board. 
     As an example, the paddle card  30  mentioned above can be selected as the circuit board  400 . 
     Concerning the above, an embodiment of the present invention provides an electrical interconnection system and electrical connectors (i.e., electrical receptacle connector and electrical plug cable assembly) for such electrical interconnection system, which may be used in a high speed and high density electrical communication system. The electrical plug cable assembly according to the present invention may substitute a conventional backpanel printed circuit board that brings signal loss/attenuations in the signal transmission adopted in the conventional electrical communication system. Accordingly, applications of the electrical connector assembly according to aspects of the present invention in high speed and high density electrical communication systems may achieve low signal loss/attenuations and long distance signal transmission, which is suitable for high density electrical communications and signal transmissions. Furthermore, in at least one aspect, the present invention provides an electrical signal transmission system suitable for long distance and high density electrical communications and signal transmissions. In at least one aspect, the present invention may further provide an electrical plug connector housing adopted in the electrical connector in such electrical interconnection system. 
     In some embodiments as described above, the face to face arrangement of the signal conductor and ground conductor in two wafers and the alternation arrangement of the signal conductor and ground conductor in one wafer can help shield at least part of the electromagnetic interference from adjacent signal conductors, and consequently reduce the EMI and improve the signal transmission quality. 
     Although several exemplary embodiments have been shown and described, it would be appreciated by those skilled in the art that various changes or modifications may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.