Patent Publication Number: US-2023137227-A1

Title: Plug connector assembly, receptacle connector assembly and connector assembly with improved data transmission speed

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application claims priority of a Chinese Patent Application No. 202111281307.X, filed on Nov. 1, 2021 and titled “PLUG CONNECTOR ASSEMBLY, RECEPTACLE CONNECTOR ASSEMBLY AND CONNECTOR ASSEMBLY”, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a plug connector assembly, a receptacle connector assembly and a connector assembly, which belongs to a technical field of connectors. 
     BACKGROUND 
     An existing SFP (Small Form Factor Pluggable) connector assembly usually includes an SFP receptacle connector assembly and an SFP plug connector assembly. The SFP receptacle connector assembly usually includes a metal cage and an SFP receptacle connector located in the metal cage. The SFP receptacle connector includes an insulating body and a plurality of conductive terminal modules which are assembled to the insulating body and arranged at intervals. Each conductive terminal module includes an insulating bracket and a plurality of conductive terminals insert-molded with the insulating bracket. Among the plurality of conductive terminal modules, some conductive terminal modules are signal terminal modules, and some conductive terminal modules are ground terminal modules. After assembling, the plurality of conductive terminal modules are disposed next to each other. Two adjacent signal terminal modules form a differential pair. It should be noted that two signal terminals of the differential pair are located on different terminal modules. 
     The SFP plug connector assembly usually includes a built-in circuit board, a cable connected to the built-in circuit board, and a shell enclosing the built-in circuit board. The built-in circuit board includes a tongue plate portion and a plurality of gold fingers provided on a surface of the tongue plate portion. 
     When the SFP plug connector assembly is inserted into the SFP receptacle connector assembly and plugged in place, the gold fingers on the tongue plate portion contact the conductive terminals of the SFP receptacle connector so as to transmit data. 
     However, with the continuous improvement of the data transmission requirements of the connector assembly, there is still room for improvement of the existing connector assembly. 
     SUMMARY 
     An object of the present disclosure is to provide a plug connector assembly, a receptacle connector assembly, and a connector assembly which are compact in layout and easy to realize high-speed data transmission. 
     In order to achieve the above object, the present disclosure adopts the following technical solution: a plug connector assembly, including: a metal shell, the metal shell including a first end surface and an installation space extending through the first end surface; and a plug connector, the plug connector being at least partially received in the installation space, the plug connector including a plug housing and a plurality of plug terminal modules, the plurality of plug terminal modules being arranged side by side and assembled to the plug housing; wherein at least one plug terminal module includes a plurality of plug conductive terminals, the plurality of plug conductive terminals include a first differential signal terminal, a first ground terminal and a second ground terminal, and the first differential signal terminal is located between the first ground terminal and the second ground terminal. 
     In order to achieve the above object, the present disclosure adopts the following technical solution: a receptacle connector assembly, including: a metal cage, the metal cage including a second end surface and a mating space extending through the second end surface; and a receptacle connector, the receptacle connector being located at a rear end of the mating space and communicating with the mating space, the receptacle connector including a receptacle housing and a plurality of receptacle terminal modules assembled to the receptacle housing; wherein at least one receptacle terminal module includes a second differential signal terminal, a grounding element, and a receptacle cable electrically connected to the second differential signal terminal. 
     In order to achieve the above object, the present disclosure adopts the following technical solution: a connector assembly, including a plug connector assembly and a receptacle connector assembly which are matched with each other, the plug connector assembly including: a metal shell, the metal shell including an installation space; and a plug connector, the plug connector being at least partially received in the installation space, the plug connector including a plug housing and a plurality of plug terminal modules, the plurality of plug terminal modules being arranged side by side and assembled to the plug housing; wherein at least one plug terminal module includes an insulating bracket and a plurality of plug conductive terminals fixed to the insulating bracket, and the plurality of plug conductive terminals include a first differential signal terminal; the receptacle connector assembly including: a metal cage, the metal cage including a mating space; and a receptacle connector, the receptacle connector being located at a rear end of the mating space and communicating with the mating space, the receptacle connector including a receptacle housing and a plurality of receptacle terminal modules assembled to the receptacle housing; wherein at least one receptacle terminal module includes a second differential signal terminal and a receptacle cable electrically connected to the second differential signal terminal; and wherein the plug connector assembly is at least partially inserted into the mating space, so that the first differential signal terminal and the second differential signal terminal are in contact with each other. 
     Compared with the prior art, at least one plug terminal module of the plug connector assembly of the present disclosure includes a first differential signal terminal, a first ground terminal, and a second ground terminal; and the first differential signal terminal is located between the first ground terminal and the second ground terminal. By arranging the first differential signal terminal, the first ground terminal, and the second ground terminal on a single plug terminal module, the arrangement of the first differential signal terminal, the first ground terminal and the second ground terminal becomes more compact, and it is beneficial to increase the speed of data transmission. Besides, at least one receptacle terminal module of the receptacle connector assembly of the present disclosure includes a second differential signal terminal, a metal shield surrounding member surrounding a periphery of the second differential signal terminal, and a receptacle cable electrically connected to the second differential signal terminal. By arranging the second differential signal terminal on the receptacle terminal module, the arrangement of the second differential signal terminal becomes more compact, and it is beneficial to increase the data transmission speed. In addition, by matching the plug connector assembly with the receptacle connector assembly, the data transmission speed is improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective schematic view of a connector assembly in accordance with an embodiment of the present disclosure, in which a plug connector assembly is inserted into a receptacle connector assembly; 
         FIG.  2    is a right side view of  FIG.  1   ; 
         FIG.  3    is a partially exploded perspective view of  FIG.  1   ; 
         FIG.  4    is a front view of the plug connector assembly in  FIG.  3   ; 
         FIG.  5    is a rear view of  FIG.  4   ; 
         FIG.  6    is a right side view of the plug connector assembly in  FIG.  3   ; 
         FIG.  7    is a partial perspective exploded view of  FIG.  6   , in which a plug connector and a built-in circuit board are separated; 
         FIG.  8    is a partial perspective exploded view of  FIG.  7    from another angle; 
         FIG.  9    is a perspective exploded view of the plug connector assembly in  FIG.  3   ; 
         FIG.  10    is a perspective exploded view of  FIG.  9    from another angle; 
         FIG.  11    is a partial perspective exploded view of the plug connector in  FIG.  10   ; 
         FIG.  12    is a partially exploded perspective view of  FIG.  11    from another angle; 
         FIG.  13    is a partial perspective exploded view of the plug connector of the present disclosure, in which one plug terminal module is separated; 
         FIG.  14    is a partial perspective exploded view of the plug terminal module in  FIG.  13   ; 
         FIG.  15    is a partial perspective exploded view of  FIG.  14    from another angle; 
         FIG.  16    is a side view of an insulating bracket and plug conductive terminals separated from the insulating bracket; 
         FIG.  17    is a perspective schematic view of the plug connector in  FIG.  3    from another angle; 
         FIG.  18    is a partially exploded perspective view of  FIG.  17   ; 
         FIG.  19    is a partially exploded perspective view of  FIG.  18    from another angle; 
         FIG.  20    is a schematic cross-sectional view taken along line A-A in  FIG.  17   ; 
         FIG.  21    is a partial enlarged view of a frame part B in  FIG.  20   ; 
         FIG.  22    is a schematic cross-sectional view taken along line C-C in  FIG.  17   ; 
         FIG.  23    is a partial enlarged view of a frame part D in  FIG.  22   ; 
         FIG.  24    is a side view of a first metal shield of the plug connector; 
         FIG.  25    is a side view of a second metal shield of the plug connector; 
         FIG.  26    is a front view of the plug terminal module in  FIG.  11   ; 
         FIG.  27    is a partial enlarged view of a frame part E in  FIG.  26   ; 
         FIG.  28    is a top view of the plug terminal module in  FIG.  11   ; 
         FIG.  29    is a partial enlarged view of a frame part F in  FIG.  28   ; 
         FIG.  30    is a front view of the receptacle connector assembly in  FIG.  3   ; 
         FIG.  31    is a rear view of  FIG.  30   ; 
         FIG.  32    is a right side view of the receptacle connector assembly in  FIG.  3   ; 
         FIG.  33    is a partially exploded perspective view of the receptacle connector assembly in  FIG.  3   ; 
         FIG.  34    is a perspective exploded view of a metal cage in  FIG.  33   ; 
         FIG.  35    is a perspective exploded view of  FIG.  34    from another angle; 
         FIG.  36    is a partially exploded perspective view of a receptacle connector in  FIG.  33   ; 
         FIG.  37    is a partially exploded perspective view of  FIG.  36    from another angle; 
         FIG.  38    is a partial perspective exploded view of a receptacle terminal module in  FIG.  36   ; and 
         FIG.  39    is a schematic cross-sectional view taken along H-H in  FIG.  3   . 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments will be described in detail here, examples of which are shown in drawings. When referring to the drawings below, unless otherwise indicated, same numerals in different drawings represent the same or similar elements. The examples described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of devices and methods consistent with some aspects of the application as detailed in the appended claims. 
     The terminology used in this application is only for the purpose of describing particular embodiments, and is not intended to limit this application. The singular forms “a”, “said”, and “the” used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. 
     It should be understood that the terms “first”, “second” and similar words used in the specification and claims of this application do not represent any order, quantity or importance, but are only used to distinguish different components. Similarly, “an” or “a” and other similar words do not mean a quantity limit, but mean that there is at least one; “multiple” or “a plurality of” means two or more than two. Unless otherwise noted, “front”, “rear”, “lower” and/or “upper” and similar words are for ease of description only and are not limited to one location or one spatial orientation. Similar words such as “include” or “comprise” mean that elements or objects appear before “include” or “comprise” cover elements or objects listed after “include” or “comprise” and their equivalents, and do not exclude other elements or objects. The term “a plurality of” mentioned in the present disclosure includes two or more. 
     Hereinafter, some embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the case of no conflict, the following embodiments and features in the embodiments can be combined with each other. 
     Referring to  FIGS.  1  to  3   , the present disclosure discloses a connector assembly  500  including a plug connector assembly  300  and a receptacle connector assembly  400 . The plug connector assembly  300  is adapted to be inserted into the receptacle connector assembly  400  so as to realize transmission of high-speed signals, control signals, and power, etc. 
     Referring to  FIGS.  4  to  10   , the plug connector assembly  300  includes a metal shell  5  and a plug connector  100  at least partially installed in the metal shell  5 . In the illustrated embodiment of the present disclosure, the plug connector  100  is a backplane connector. The plug connector  100  is located at a front end of the metal shell  5 . It is understandable to those skilled in the art that the backplane connector generally includes a plurality of terminal modules. Each terminal module includes multiple groups of differential signal terminals. By providing the differential signal terminals, the data transmission speed of the plug connector assembly  300 , the receptacle connector assembly  400  and the connector assembly  500  can be improved, and the miniaturization of the connector assemblies can be achieved. 
     The metal shell  5  includes a first end surface  50  and an installation space  501  extending through the first end surface  50 . The plug connector  100  is at least partially received in the installation space  501 . In the illustrated embodiment of the present disclosure, the metal shell  5  includes a first top wall  51 , a first bottom wall  52 , a first side wall  53  and a second side wall  54 . The installation space  501  is at least jointly enclosed by the first top wall  51 , the first bottom wall  52 , the first side wall  53  and the second side wall  54 . Specifically, the metal shell  5  includes a first metal shell  55  and a second metal shell  56  assembled together. The first metal shell  55  includes the first top wall  51 , a first side wall portion  531  extending downwardly from one side of the first top wall  51 , and a second side wall portion  541  extending downwardly from the other side of the first top wall  51 . The second metal shell  56  includes the first bottom wall  52 , a third side wall portion  532  extending upwardly from one side of the first bottom wall  52 , and a fourth side wall portion  542  extending upwardly from the other side of the first bottom wall  52 . The first side wall portion  531  and the third side wall portion  532  are located on a same side of the metal shell  5 . The first side wall  53  includes the first side wall portion  531  and the third side wall portion  532 . Similarly, the second side wall portion  541  and the fourth side wall portion  542  are located on a same side of the metal shell  5 . The second side wall  54  includes the second side wall portion  541  and the fourth side wall portion  542 . In the illustrated embodiment of the present disclosure, a length of the metal shell  5  extending in a mating direction (i.e., a front-to-rear direction) is much longer than a length of the plug connector  100  after a plug cable  302  is removed, which is beneficial to improve the shielding effect of the plug connector  100 . When the plug connector assembly  300  is just inserted into the receptacle connector assembly  400 , static electricity can be discharged through the metal shell  5 , thereby avoiding adverse effects on the connection between plug conductive terminals and receptacle conductive terminals. 
     In an embodiment of the present disclosure, both the first metal shell  55  and the second metal shell  56  are casted from metal materials, so as to facilitate manufacturing and improve the shielding performance of the first metal shell  55  and the second metal shell  56 . The first metal shell  55  and the second metal shell  56  are fixed together by bolts  57 . 
     In addition, the first metal shell  55  includes an opening  551  located between the first side wall portion  531  and the second side wall portion  541 . The metal shell  5  includes a plug heat sink  59  installed in the opening  551 . The plug heat sink  59  includes a plurality of heat dissipation channels  591  arranged at intervals. 
     In the illustrated embodiment of the present disclosure, the plug connector assembly  300  further includes a built-in circuit board  301 , a plug cable  302 , an unlocking assembly  303  mounted on the metal shell  5 , and a pull strap  304  connected to the unlocking assembly  303 . The plug connector  100  is mounted on the built-in circuit board  301 . The plug cable  302  is electrically connected to the plug connector  100  through the built-in circuit board  301 . Of course, in other embodiments, the plug cable  302  can also be directly electrically connected to the plug connector  100 . 
     The unlocking assembly  303  is substantially U-shaped, and includes a first locking side wall  3031 , a second locking side wall  3032 , and a connection bottom wall  3033  connecting the first locking side wall  3031  and the second locking side wall  3032 . The first locking side wall  3031  includes a first protrusion  3031   a  protruding backwardly from the connection bottom wall  3033 . The second locking side wall  3032  includes a second protrusion  3032   a  protruding backwardly from the connection bottom wall  3033 . 
     The third side wall portion  532  of the second metal shell  56  is provided with a first slot  5321  for receiving the first locking side wall  3031 . The fourth side wall  542  of the second metal shell  56  is provided with a second slot  5421  for receiving the second locking side wall  3032 . In addition, the plug connector  100  further includes compression springs  58  received in the third side wall portion  532  and the fourth side wall portion  542 , and abutting against the first locking side wall  3031  and the second locking side wall  3032 . 
     The pull strap  304  includes a first coupling portion  3041  fixed to the first protrusion  3031   a,  a second coupling portion  3042  fixed to the second protrusion  3032   a,  and a force applying portion  3043  connecting the first coupling portion  3041  and the second coupling portion  3042 . In an embodiment of the present disclosure, the first protrusion  3031   a  is insert-molded with the first coupling portion  3041 , and the second protrusion  3032   a  is insert-molded with the second coupling portion  3042 . 
     The unlocking assembly  303  is slidable back and forth under the action of the pull strap  304 . When unlocking is required, a backward force is applied to the force applying portion  3043  of the pull strap  304 , the unlocking assembly  303  overcomes the elastic force of the compression springs  58 , so that the first locking side wall  3031  and the second locking side wall  3032  move backwardly so as to realize unlocking. When the force disappears, the compression springs  58  release part of the elastic force, so that the unlocking assembly  303  moves forwardly and resets. 
     Referring to  FIGS.  11  and  12   , the plug connector  100  includes a plug housing  1 , a plurality of plug terminal modules  2  at least partially assembled to the plug housing  1 , a spacer  3  held on the plurality of plug terminal modules  2 , and a mounting block  4  held at the bottom of the plurality of plug terminal modules  2 . The plurality of plug terminal modules  2  are disposed side by side along a left-right direction. 
     The plug housing  1  includes a first base  11 , a first extension wall  12  extending rearwardly from a top end of the first base  11 , and a second extension wall  13  extending rearwardly from a bottom end of the first base  11 . The first base  11  includes a mating surface  111  and a plurality of terminal mating grooves  112  extending through the mating surface  111 . The terminal mating grooves  112  are arranged in multiple rows along a first direction (i.e., a left-right direction). Two adjacent rows of terminal mating grooves  112  are staggered and arranged in a second direction (i.e., a top-bottom direction) perpendicular to the first direction. That is, the terminal mating grooves  112  at corresponding positions in the two adjacent rows of terminal mating grooves  112  are not aligned in the left-right direction. This arrangement is beneficial to reduce the signal crosstalk between two adjacent plug terminal modules  2 . The first extension wall  12  and the second extension wall  13  are provided with a plurality of first installation slots  14  for receiving the plurality of plug terminal modules  2 . The first extension wall  12  and the second extension wall  13  are respectively provided with positioning protrusions  15  protruding beyond the mating surface  111 . The first extension wall  12  is provided with a plurality of first locking grooves  121  extending upwardly through the first extension wall  12 . 
     The second extension wall  13  is provided with a plurality of second locking grooves  131  extending downwardly through the second extension wall  13 . The first locking grooves  121  and the second locking grooves  131  are used to lock the plug terminal module  2  so as to prevent the plug terminal modules  2  from escaping from the plug housing  1 . 
     Referring to  FIGS.  13  to  16   , each plug terminal module  2  includes an insulating bracket  21  inserted into the first installation slot  14 , a plurality of plug conductive terminals  22  fixed to the insulating bracket  21 , and a metal shield located at least on one side of the insulating bracket  21 . In the illustrated embodiment of the present disclosure, the metal shield includes a first metal shield  23  fixed on one side (i.e., a left side) of the insulating bracket  21  and a second metal shield  24  fixed on the other side (i.e., a right side) of the insulating bracket  21 . 
     Referring to  FIG.  16   , the insulating bracket  21  is roughly frame-shaped. The insulating bracket  21  includes a rear wall  211 , a front wall  212  opposite to the rear wall  211 , a top wall  213  connecting one side of the rear wall  211  and one side of the front wall  212 , a bottom wall  214  connecting the other side of the rear wall  211  and the other side of the front wall  212 , and a plurality of connecting walls  215 . The connecting wall  215  is capable of enhancing the structural strength of the frame. The rear walls  211  of the insulating brackets  21  include a plurality of first protrusions  2111  protruding backwardly and spaced apart from each other in the left-right direction. The top walls  213  of the insulating brackets  21  includes a plurality of second protrusions  2130  protruding upwardly and spaced apart from each other in the left-right direction. Referring to  FIG.  13   , in the illustrated embodiment of the present disclosure, each plug terminal module  2  includes two second protrusions  2130  which are spaced apart from each other along the front-rear direction. The second protrusions  2130  of two adjacent plug terminal modules  2  are staggered in the front-rear direction. That is, the second protrusions  2130  at the corresponding positions of two adjacent plug terminal modules  2  are not in alignment with each other in the left-right direction. An extending direction (i.e., the top-bottom direction) of the first protrusion  2111  is perpendicular to an extending direction (i.e., the front-rear direction) of the second protrusion  2130 . 
     Besides, the insulating bracket  21  further includes a plurality of third protrusions  2112  disposed at intervals from the first protrusions  2111 . The first protrusions  2111  and the corresponding third protrusions  2112  are in alignment with each other along the top-bottom direction. The first protrusion  2111  includes a first constriction portion  2113 , and the third protrusion  2112  includes a second constriction portion  2114 . In the illustrated embodiment of the present disclosure, the insulating bracket  21  has a hollow portion  210 . The connecting walls  215  include a first connecting wall  2151  connecting the top wall  213  and the bottom wall  214 , and a second connecting wall  2152  connecting the rear wall  211  and the bottom wall  214 . The first connecting wall  2151  and the second connecting wall  2152  are disposed obliquely. One ends of the first connecting wall  2151  and the second connecting wall  2152  are adjacent to each other, and the other ends are spread out so as to form a radial shape. The connecting walls  215  further include a first reinforcing wall  2153  connecting the top wall  213  and the bottom wall  214 . The first reinforcing wall  2153  is parallel to the first front wall  212 . Referring to  FIG.  16   , a width of the first reinforcing wall  2153  is smaller than a width of the first front wall  212 . The first connecting wall  2151  and the second connecting wall  2152  are exposed in the hollow portion  210 . The top wall  213  includes a first locking protrusion  2131  for being locked in the first locking groove  121 . The bottom wall  214  includes a second locking protrusion  2141  for being locked in the second locking groove  131 . 
     Referring to  FIGS.  14  to  16   , the insulating bracket  21  further includes a plurality of posts  216  for fixing the first metal shield  23  and the second metal shield  24 . In the illustrated embodiment of the present disclosure, the posts  216  are substantially cylindrical. In the illustrated embodiment of the present disclosure, the posts  216  are disposed on the bottom wall  214 , the first connecting wall  2151 , the second connecting wall  2152 , the first reinforcing wall  2153  and the front wall  212 . The first metal shield  23  and the second metal shield  24  are respectively located on opposite sides of the insulating bracket  21 . The posts  216  include a plurality of first posts  2161  and a plurality of second posts  2162 . The first posts  2161  and the second posts  2162  are respectively disposed on opposite sides of the insulating bracket  21  so as to be fixed and positioned with the first metal shield  23  and the second metal shield  24 , respectively. 
     Referring to  FIG.  16   , each group of plug conductive terminals  22  includes a mating portion  221 , a tail portion  222  and a first connection portion  223  connecting the mating portion  221  and the tail portion  222 . The mating portions  221  extend beyond the insulating bracket  21 . Some of the mating portions  221  are adapted to electrically connect with the receptacle connector assembly  400 . The tail portions  222  are used for being mounted to the circuit board  301 . In the illustrated embodiment of the present disclosure, the mating portion  221  is substantially perpendicular to the tail portion  222 . The first connection portion  223  is curved. Specifically, the first connection portion  223  includes a first section  223   a  parallel to the mating portion  221 , a second section  223   b  parallel to the tail portion  222 , and a third section  223   c  connecting the first section  223   a  and the second section  223   b.  Referring to  FIG.  16   , the first section  223   a  extends horizontally, the second section  223   b  extends vertically, and the third section  223   c  extends obliquely. 
     Each group of plug conductive terminals  22  include a plurality of first ground terminals G 1 , a plurality of second ground terminals G 2 , and a plurality of first signal terminals S 1 . In the illustrated embodiment of the present disclosure, two adjacent first signal terminals S 1  form a pair of first differential signal terminals. Each pair of first differential signal terminals are located between one first ground terminal G 1  and one second ground terminal G 2 . That is, each group of plug conductive terminals  22  are disposed in a manner of G 1 -S 1 -S 1 -G 2 , which is beneficial to improve the quality of signal transmission. The first differential signal terminals are narrow-side coupling or wide-side coupling. A width of the first ground terminal G 1  and a width the second ground terminal G 2  are greater than a width of each first signal terminal S 1  which is located between the first ground terminal G 1  and the second ground terminal G 2 . Therefore, it is beneficial to increase the shielding area and improve the shielding effect. The mating portion  221  of the first differential signal terminal is exposed in the corresponding terminal mating groove  112 . In some embodiments of the present disclosure, the plug cable  302  may also be directly electrically connected to the first differential signal terminal. Compared with a circuit board, by having the first differential signal terminal directly transmit data through the plug cable  302 , it is beneficial to improve the speed and quality of data transmission. 
     In the illustrated embodiment of the present disclosure, the first connection portions  223  of the plug conductive terminals  22  are insert-molded with the insulating bracket  21 . The first connection portions  223  of the differential signal terminals, the first connection portion  223  of the first ground terminal G 1  and the first connection portion  223  of the second ground terminal G 2  are all exposed in the same hollow portion  210 . Each first connection portion  223  of the first signal terminals S 1  includes a narrowed portion  2230  insert-molded with the insulating bracket  21  so as to adjust the impedance of the first signal terminals S 1  for achieving impedance matching. In the illustrated embodiment of the present disclosure, the mating portions  221  of the first signal terminals S 1  are substantially needle-shaped. The mating portions  221  of the first ground terminal G 1  and the second ground terminal G 2  are substantially rectangular-shaped. The mating portions  221  of the first signal terminals S 1  and the first connection portions  223  of the plug conductive terminals  22  are coplanar, which means they are located in a first plane (i.e., a horizontal plane). It should be noted that the technical term “coplanar” used in the present disclosure is intended to indicate that related components are substantially flush, which includes situations of incomplete coplanarity caused by manufacturing tolerances. However, in the illustrated embodiment of the present disclosure, the first ground terminal G 1  includes a first torsion portion  2241  connected between its mating portion  221  and its first section  223   a,  so that the mating portion  221  of the first ground terminal G 1  is located in a second plane (i.e., a vertical plane) perpendicular to the first plane. The second ground terminal G 2  includes a second torsion portion  2242  connected between its mating portion  221  and its first section  223   a,  so that the mating portion  221  of the second ground terminal G 2  is also located in the second plane (i.e., the vertical plane) perpendicular to the first plane. The mating portion  221  of the first ground terminal G 1  and the mating portion  221  of the second ground terminal G 2  are parallel to each other. 
     As shown in  FIG.  16   , each plug terminal module  2  includes multiple pairs of first differential signal terminals in order to increase the speed of signal transmission. Among the first differential signal terminals in different pairs, an average length of the first differential signal terminals located on an outer side is greater than an average length of the first differential signal terminals located on an inner side. Among the first differential signal terminals in a same pair, a length of the first signal terminal S 1  located on an outer side is greater than a length of the first signal terminal S 1  located on an inner side. 
     Referring to  FIGS.  12  to  16   , in the illustrated embodiment of the present disclosure, each plug terminal module  2  is located in a vertical plane as a whole. The first ground terminals G 1 , the first differential signal terminals, and the second ground terminals G 2  are stacked and separated by a certain distance in the vertical plane. The first differential signal terminals are divided into least three pairs. Each pair of the first differential signal terminals is located between one first ground terminal G 1  and one second ground terminal G 2 . In the illustrated embodiment of the present disclosure, the number of the plug terminal modules  2  is at least five and they are arranged side by side. Any two adjacent plug terminal modules  2  are arranged next to each other. That is, a front end (a mating end) of each plug terminal module  2  is close to the adjacent plug terminal module  2 . 
     Referring to  FIGS.  17  to  19   , in the illustrated embodiment of the present disclosure, the spacer  3  is made of a metal material or an insulating material. The spacer  3  is used to assemble the plurality of plug terminal modules  2  together. The spacer  3  includes a first body portion  31 , a second body portion  32 , a bending portion  33  connecting the first body portion  31  and the second body portion  32 , and a protruding piece  34  extending downwardly from the first body portion  31 . The first body portion  31  is perpendicular to the second body portion  32 . The first body portion  31  includes a plurality of first slots  311  for holding the first protrusions  2111 . The second body portion  32  includes a plurality of second slots  321  for holding the second protrusions  2130 . The protrusion piece  34  is provided with a plurality of slits  341  corresponding to the third protrusions  2112 , so that the protrusion piece  34  is substantially comb-shaped. Each first slot  311  is a closed slot, which means a periphery of the first slot  311  is surrounded by the first body portion  31 . Each slit  341  is a non-closed slit, which means one end (i.e., a bottom end) of the slit  341  is opened. The slits  341  and the corresponding first slots  311  are spaced apart and aligned along the top-bottom direction. The first slot  311  includes a first slit  3111  and a second slit  3112  having a width larger than the first slit  3111 . The first slit  3111  is located above the second slit  3112  and communicates with the second slit  3112 . The slit  341  is located below the second slit  3112 . The bending portion  33  includes with a plurality of openings  331  spaced apart along the left-right direction, so as to facilitate bending and control bending accuracy. 
     When assembling the spacer  3  to the plurality of plug terminal modules  2 , firstly, the second slits  3112  of the spacer  3  correspond to the first protrusions  2111  along an extending direction of the mating portions  221 , and the first protrusions  2111  pass through the second slits  3112 . At this time, the second slots  321  are located above the second protrusions  2130 . The second slots  321  and the second protrusions  2130  are in alignment with each other in a vertical direction. Then, the spacer  3  is moved downwardly along an extending direction of the tail portions  222 , so that the first constriction portions  2113  are tightly clamped in the first slits  3111 . At the same time, the second protrusions  2130  are positioned in the second slots  321 . The second constriction portions  2114  of the third protrusions  2112  are tightly clamped in the slits  341  so as to achieve multiple fixation and improve reliability. With this arrangement, all the plug terminal modules  2  can be combined into a whole by the spacer  3  in order to prevent loosening. In addition, the plug terminal modules  2  can be prevented from being separated from the spacer  3  along the extending direction of the mating portions  221 . At the same time, distances between the plug terminal modules  2  can be effectively controlled. Through the mating of the second protrusions  2130  and the second slots  321 , the retaining piece  3  can be prevented from falling off by an external force in a horizontal direction, thereby the structural reliability of the plug connector  100  is improved. 
     Referring to  FIGS.  18  and  19   , the mounting block  4  includes a plurality of through holes  41  for allowing the tail portions  222  of the plug conductive terminals  22  to pass through. Preferably, the mounting block  4  is made of electroplated plastic in order to further improve the shielding effect. 
     Referring to  FIGS.  20  and  23   , in the illustrated embodiment of the present disclosure, the mating portion  221  and the first connection portion  223  of the first ground terminal G 1  have a first wide surface  221   a  and a first narrow surface  221   b  perpendicular to the first wide surface  221   a.  The mating portion  221  and the first connection portion  223  of the second ground terminal G 2  have a second wide surface  221   c  and a second narrow surface  221   d  perpendicular to the second wide surface  221   c.  The first connection portions  223  of each pair of first differential signal terminals are located between the first narrow surface  221   b  of the first ground terminal G 1  and the second narrow surface  221   d  of the second ground terminal G 2  which are located on opposite sides of the first connection portions  223  of each pair of first differential signal terminals. The mating portions  221  of each pair of first differential signal terminals are located between the first wide surface  221   a  of the first ground terminal G 1  and the second wide surface  221   c  of the second ground terminal G 2  which are located on opposite sides of the mating portions  221  of each pair of first differential signal terminals. In the illustrated embodiment of the present disclosure, a width of the first wide surface  221   a  and a width of the second wide surface  221   c  are greater than a width of each mating portion  221  of the first signal terminals S 1 , thereby better shielding can be provided for the mating portions  221  of the first signal terminals S 1 . 
     In the illustrated embodiment of the present disclosure, the first metal shield  23  and the second metal shield  24  are symmetrically disposed on opposite sides of the first insulating bracket  21 . Referring to  FIG.  24   , the first metal shield  23  includes a first main body portion  231  and a first extension portion  232  extending from the first main body portion  231 . The first main body portion  231  is located on one side of the first connection portions  223  of the first plug conductive terminals  22 . The first extension portion  232  is located on one side of the mating portions  221  of the first plug conductive terminals  22 . In the illustrated embodiment of the present disclosure, the first extension portion  232  and the first main body portion  231  are located in different planes, in which the first extension portion  232  is farther away from the second metal shield  24  than the first main body portion  231 . The first main body portion  231  includes a plurality of first mounting holes  2311  for mating with the plurality of first posts  2161 . The first posts  2161  are fixed and positioned in the first mounting holes  2311  by soldering, thereby the fixing and positioning of the first metal shield  23  and the first insulating bracket  21  are realized. The first main body portion  231  includes a plurality of ribs  233 . The ribs  233  include a plurality of first ribs  2331  protruding toward the first ground terminals G 1  and a plurality of second ribs  2332  protruding toward the second ground terminals G 2 . The first ribs  2331  corresponding to the first ground terminal G 1  are disposed along an extending direction of the first connection portion  223  of the first ground terminal G 1 . The second ribs  2332  corresponding to the second ground terminal G 2  are disposed along an extending direction of the first connection portion  223  of the second ground terminal G 2 . In the illustrated embodiment of the present disclosure, the first ribs  2331  and the second ribs  2332  are formed by stamping the first main body portion  231 . The first ribs  2331  and the second ribs  2332  protrude toward the second metal shield  24 . The first ribs  2331  and the second ribs  2332  are discontinuously disposed along the extending direction of the first connection portion  223  of the first ground terminal G 1  and the extending direction of the first connection portion  223  of the second ground terminal G 2 , respectively, so as to achieve multi-position contact. In order to improve the reliability of the contact between the first metal shield  23  and the first ground terminals G 1  and the second ground terminals G 2 , in the illustrated embodiment of the present disclosure, referring to  FIG.  21   , a wall thickness of the first rib  2331 , a wall thickness of the second rib  2332 , and a wall thickness of a portion of the first main body portion  231  located between the first rib  2331  and the second rib  2332  are the same. Specifically, each of the first ribs  2331  and the second ribs  2332  includes a first rib section  233   a  parallel to the mating portion  221 , a second rib section  233   b  parallel to the tail portion  222 , and a third rib section  233   c  connecting the first rib section  233   a  and the second rib section  233   b.  Referring to  FIG.  20   , the first rib section  233   a  extends horizontally, the second rib section  233   b  extends vertically, and the third rib section  233   c  extends obliquely. The first rib section  233   a,  the second rib section  233   b  and the third rib section  233   c  are in contact with the first section  223   a,  the second section  223   b  and the third section  223   c  of the first ground terminal G 1  and the second ground terminal G 2 , respectively. 
     The first extension portion  232  includes a plurality of first bulges  2321  protruding toward the corresponding mating portions  221  of the first ground terminals G 1 , a plurality of second bulges  2322  protruding toward the corresponding mating portions  221  of the second ground terminals G 2 , and a plurality of first elastic pieces  2323  each of which is located between adjacent first bulge  2321  and second bulge  2322 . The first elastic pieces  2323  extend along directions toward the first main body portion  231 . Each first elastic piece  2323  has an arc-shaped contact portion  2324 . In the illustrated embodiment of the present disclosure, the first extension portion  232  further includes two first protruding tabs  2325  located at opposite sides of each first elastic piece  2323 . The first protruding tabs  2325  and the first elastic pieces  2323  extend along opposite directions. The first protruding tabs  2325  protrude sidewardly to contact the second metal shield  24  of the adjacent plug terminal module  2  so as to improve the shielding effect. In the illustrated embodiment of the present disclosure, referring to  FIG.  23   , a wall thickness of the first bulge  2321 , a wall thickness of the second bulge  2322  and a wall thickness of a portion of the first extension portion  232  located between the first bulge  2321  and the second bulge  2322  are the same. 
     Similarly, referring to  FIG.  25   , the second metal shield  24  includes a second main body portion  241  and a second extension portion  242  extending from the second main body portion  241 . The second main body portion  241  is located on the other side of the first connection portions  223  of the plug conductive terminals  22 . The second extension portion  242  is located on the other side of the mating portions  221  of the plug conductive terminals  22 . In the illustrated embodiment of the present disclosure, the second extension portion  242  and the second main body portion  241  are located in different planes, in which the second extension portion  242  is farther away from the first metal shield  23  than the second main body portion  241 . The second main body portion  241  includes a plurality of second mounting holes  2411  for mating with the plurality of second posts  2162 . The second posts  2162  are fixed and positioned in the second mounting holes  2411  by soldering, so as to realize the fixing and positioning of the second metal shield  24  and the first insulating bracket  21 . The second main body portion  241  includes a plurality of ribs  243 . The ribs  243  include a plurality of third ribs  2431  protruding toward the first ground terminals G 1  and a plurality of fourth ribs  2432  protruding toward the second ground terminals G 2 . The third ribs  2431  are disposed along the extending direction of the first connection portion  223  of the first ground terminal G 1 . The fourth ribs  2432  are disposed along the extending direction of the first connection portion  223  of the second ground terminal G 2 . In the illustrated embodiment of the present disclosure, the third ribs  2431  and the fourth ribs  2432  are formed by stamping the second main body portion  241 . The third ribs  2431  and the fourth ribs  2432  protrude toward the first metal shield  23 . The third ribs  2431  and the fourth ribs  2432  are discontinuously disposed along the extending direction of the first connection portion  223  of the first ground terminal G 1  and the extending direction of the first connection portion  223  of the second ground terminal G 2 , respectively, so as to achieve multi-position contact. As a result, the reliability of the contact between the second metal shield  24  and the first ground terminals G 1  and the second ground terminals G 2  is improved. In the illustrated embodiment of the present disclosure, a wall thickness of the third rib  2431 , a wall thickness of the fourth rib  2432  and a wall thickness of a portion of the second main body portion  241  located between the third rib  2431  and the fourth rib  2432  are the same. Specifically, each of the third rib  2431  and the fourth rib  2432  includes a first rib section  243   a  parallel to the mating portion  221 , a second rib section  243   b  parallel to the tail portion  222 , a third rib section  243   c  connecting the first rib section  243   a  and the second rib section  243   b.  Referring to  FIG.  25   , the first rib section  243   a  extends horizontally, the second rib section  243   b  extends vertically, and the third rib section  243   c  extends obliquely. The first rib section  243   a,  the second rib section  243   b  and the third rib section  243   c  are in contact with the first section  223   a,  the second section  223   b  and the third section  223   c  of the first ground terminal G 1  and the second ground terminal G 2 , respectively. In an embodiment of the present disclosure, soldering is performed on the surfaces of the ribs  233  and the ribs  243  to solder the ribs  233  and the ribs  243  to the first ground terminals G 1  and the second ground terminals G 2 . I.e., soldering is performed on the surfaces of the first ribs  2331 , the second ribs  2332 , the third ribs  2431  and the fourth ribs  2432  in order to solder the first ribs  2331 , the second ribs  2332 , the third ribs  2431  and the fourth rib  2432  to the first ground terminals G 1  and the second ground terminals G 2 . The soldering method is at least one of spot soldering, laser soldering and ultrasonic soldering. Preferably, the first rib  2331 , the second rib  2332 , the third rib  2431  and the fourth rib  2432  include through holes to expose the corresponding first ground terminal G 1  and the corresponding second ground terminal G 2 , thereby facilitating soldering. 
     The second extension portion  242  includes a plurality of third bulges  2421  protruding toward the mating portions  221  of the first ground terminals G 1 , a plurality of fourth bulges  2422  protruding toward the mating portions  221  of the second ground terminals G 2 , and a plurality of second elastic pieces  2423  each of which is located between adjacent third bulge  2421  and fourth bulge  2422 . The second elastic pieces  2423  extend along directions toward the second main body portion  241 . Each second elastic piece  2423  has an arc-shaped contact portion  2424 . In the illustrated embodiment of the present disclosure, the second extension portion  242  further includes two second protruding tabs  2425  located at opposite sides of each second elastic piece  2423 . The second protruding tabs  2425  and the second elastic pieces  2423  extend along opposite directions. The second protruding tabs  2425  protrude sidewardly to contact the first metal shield  23  of the adjacent plug terminal module  2  so as to improve the shielding effect. In the illustrated embodiment of the present disclosure, a wall thickness of the third bulge  2421 , a wall thickness of the fourth bulge  2422 , and a wall thickness of a portion of the second extension portion  242  located between the third bulge  2421  and the fourth bulge  2422  are the same. 
     Referring to  FIG.  21   , along a length of the first connection portion  223  of the plug conductive terminal  22 , the first rib  2331  of the first metal shield  23  and the third rib  2431  of the second metal shield  24  respectively contact two opposite sides of the first connection portion  223  of the first ground terminal G 1 , and the second rib  2332  of the first metal shield  23  and the fourth rib  2432  of the second metal shield  24  respectively contact two opposite sides of the first connection portion  223  of the second ground terminal G 2 , thereby forming the shielding cavity  26  surrounding the outer periphery of the first connection portions  223  of each pair of first differential signal terminals. In the illustrated embodiment of the present disclosure, the first rib  2331  and the third rib  2431  respectively contact the first wide surface  221   a  of the first connection portion  223  of the first ground terminal G 1 . The second rib  2332  and the fourth rib  2432  respectively contact the second wide surface  221   c  of the first connection portion  223  of the second ground terminal G 2 . In the illustrated embodiment of the present disclosure, the shielding cavity  26  is jointly formed by the first main body portion  231 , the second main body portion  241 , the first ground terminal G 1  and the second ground terminal G 2 . The first connection portion  223  of the first ground terminal G 1  includes a first tab portion  2234  protruding into the shielding cavity  26 . The first connection portion  223  of the second ground terminal G 2  includes a second tab portion  2235  protruding into the shielding cavity  26 . The first connection portions  223  of the first differential signal terminals are located between the first tab portion  2234  and the second tab portion  2235 . In the illustrated embodiment of the present disclosure, there are a plurality of the shielding cavities  26  which are disposed along an arrangement direction of each group of the plug conductive terminals  22 . Two adjacent shielding cavities  26  share a single first ground terminal G 1  or a single second ground terminal G 2 . In addition, a part of the shared first ground terminal G 1  protrudes into one shielding cavity  26 , and another part of the shared first ground terminal G 1  protrudes into another shielding cavity  26 . 
     Referring to  FIG.  23   , in the length of the mating portion  221  of the plug conductive terminal  22 , the first bulge  2321  of the first metal shield  23  and the third bulge  2421  of the second metal shield  24  respectively contact two opposite side surfaces of the mating portion  221  of the first ground terminal G 1 , and the second bulge  2322  of the first metal shield  23  and the fourth bulge  2422  of the second metal shield  24  respectively contact two opposite side surfaces of the mating portion  221  of the second ground terminal G 2 . In the illustrated embodiment of the present disclosure, the first bulge  2321  of the first metal shield  23  and the third bulge  2421  of the second metal shield  24  respectively contact the first narrow surfaces  221   b  of the mating portion  221  of the first ground terminal G 1 . The second bulge  2322  of the first metal shield  23  and the fourth bulge  2422  of the second metal shield  24  respectively contact the second narrow surfaces  221   d  of the mating portion  221  of the second ground terminal G 2 . The first extension portion  232 , the second extension portion  242 , the first ground terminal G 1  and the second ground terminal G 2  jointly form a shielding space  27  for accommodating the corresponding mating portions  221  of the first differential signal terminals. The first elastic piece  2323  and the second elastic piece  2423  extend into the shielding space  27 . In the illustrated embodiment of the present disclosure, there are multiple shielding spaces  27  which are disposed along a stacking direction of each group of the plug conductive terminals  22 . Two adjacent shielding spaces  27  share a single first ground terminal G 1  or a single second ground terminal G 2 . One first wide surface  221   a  of the mating portion  221  of the shared first ground terminal G 1  is exposed to the shielding space  27 , and the other first wide surface  221   a  of the mating portion  221  of the shared first ground terminal G 1  is exposed to an adjacent shielding space  27 . Similarly, a first wide surface  221   c  of the mating portion  221  of the shared second ground terminal G 2  is exposed to the adjacent shielding space  27 , and the other wide surface  221   c  of the mating portion  221  of the shared second ground terminal G 2  is exposed to another adjacent shielding space  27 . The first protruding tabs  2325  and the second protruding tabs  2425  are inclined in a direction away from the shielding space  27  to facilitate contact with the adjacent plug terminal modules  2 . 
     In the illustrated embodiment of the present disclosure, there are multiple first plug terminal modules  2  of the plug connector  100 , and the terminal arrangement of two adjacent plug terminal modules  2  are staggered. Correspondingly, the shielding cavities  26  at the same position of two adjacent plug terminal modules  2  are staggered (referring to  FIG.  20   ), and the shielding spaces  27  at the same position of two adjacent plug terminal modules  2  are staggered (referring to  FIG.  22   ). 
     The first extension portion  232  and/or the second extension portion  242  include limiting structures which restrict the mating portions  221  of the first ground terminal G 1  and/or the mating portions  221  of the second ground terminal G 2  in the front-rear direction and/or the top-bottom direction. 
     Specifically, as shown in  FIGS.  14 ,  15 , and  26  to  29   , the mating portion  221  of the first ground terminal G 1  includes a first limiting slot  2211  and a third limiting slot  2213  opposite to the first limiting slot  2211 . The first limiting slot  2211  and the third limiting slot  2213  are symmetrically disposed on opposite sides of the mating portion  221  of the first ground terminal G 1 . The first limiting slot  2211  and the third limiting slot  2213  extend through the first narrow surfaces  221   b  of the first ground terminal G 1 , respectively. In the illustrated embodiment of the present disclosure, an angle between the first limiting slot  2211  and the front-rear direction, and an angle between the third limiting slot  2213  and the front-rear direction are approximately 45 degrees. Similarly, the mating portion  221  of the second ground terminal G 2  includes a second limiting slot  2212  and a fourth limiting slot  2214  opposite to the second limiting slot  2212 . The second limiting slot  2212  and the fourth limiting slot  2214  are symmetrically disposed on opposite sides of the mating portion  221  of the second ground terminal G 2 . The second limiting slot  2212  and the fourth limiting slot  2214  extend through the second narrow surfaces  221   d  of the second ground terminal G 2 , respectively. In the illustrated embodiment of the present disclosure, an angle between the second limiting slot  2212  and the front-rear direction, and an angle between the fourth limiting slot  2214  and the front-rear direction are approximately 45 degrees. 
     The first extension portion  232  includes a first limiting protrusion  2326  locked in the first limiting slot  2211  and a second limiting protrusion  2327  locked in the second limiting slot  2212 . Each of the first limiting protrusion  2326  and the second limiting protrusion  2327  forms an angle of 45 degrees with respect to a vertical plane. Similarly, the second extension portion  242  includes a third limiting protrusion  2426  locked in the third limiting slot  2213  and a fourth limiting protrusion  2427  locked in the fourth limiting slot  2214 . Each of the third limiting protrusion  2426  and the fourth limiting protrusion  2427  forms an angle of 45 degrees with respect to the vertical plane. The first limiting protrusion  2326  and the third limiting protrusion  2426  are symmetrically disposed on opposite sides of the mating portion  221  of the first ground terminal G 1 . The first limiting protrusion  2326  and the third limiting protrusion  2426  are adapted to restrict the mating portion  221  of the first ground terminal G 1  in the front-rear direction to prevent it from moving backwardly. The second limiting protrusion  2327  and the fourth limiting protrusion  2427  are symmetrically disposed on opposite sides of the mating portion  221  of the second ground terminal G 2 . The second limiting protrusion  2327  and the fourth limiting protrusion  2427  are adapted to restrict the mating portion  221  of the second ground terminal G 2  in the front-rear direction. 
     In the illustrated embodiment of the present disclosure, the first limiting protrusion  2326  is located at a front free end of the first bulge  2321  and is integrally stamped from the first bulge  2321 . The second limiting protrusion  2327  is located at a front free end of the second bulge  2322  and is integrally stamped from the second bulge  2322 . The third limiting protrusion  2426  is located at a front free end of the third bulge  2421  and is integrally stamped from the third bulge  2421 . The fourth limiting protrusion  2427  is located at a front free end of the fourth bulge  2422  and is integrally stamped from the fourth bulge  2422 . 
     In addition, the first extension portion  232  further includes two first clamping blocks  2326   a  and two second clamping blocks  2327   a.  The two first clamping blocks  2326   a  include a first clamping groove  2326   b  for restricting the mating portion  221  of the first ground terminal G 1  in the vertical direction. The two second clamping blocks  2327   a  include a second clamping groove  2327   b  for restricting the mating portion  221  of the second ground terminal G 2  in the vertical direction. Similarly, the second extension portion  242  further includes two third clamping blocks  2426   a  and two fourth clamping blocks  2427   a.  The two third clamping blocks  2426   a  include a third clamping groove  2426   b  for restricting the mating portion  221  of the first ground terminal G 1  in the vertical direction. The two fourth clamping blocks  2427   a  include a fourth clamping groove  2427   b  for restricting the mating portion  221  of the second ground terminal G 2  in the vertical direction. 
     Of course, in other embodiments, the first clamping block  2326   a,  the second clamping block  2327   a,  the third clamping block  2426   a  and the fourth clamping block  2427   a  can also be provided as one which is used to abut against the corresponding mating portions  221  of the first ground terminal G 1  and the second ground terminal G 2  in the vertical direction so as to achieve position restriction. In the illustrated embodiment of the present disclosure, the first clamping block  2326   a  is located at a front end of the first limiting protrusion  2326 . The second clamping block  2327   a  is located at a front end of the second limiting protrusion  2327 . The third clamping block  2426   a  is located at a front end of the third limiting protrusion  2426 . The fourth clamping block  2427   a  is located at a front end of the fourth limiting protrusion  2427 . 
     Referring to  FIGS.  30  to  35   , the receptacle connector assembly  400  includes a metal cage  8  and a receptacle connector  200  at least partially located in the metal cage  8 . The metal cage  8  includes a second end surface  80  and a mating space  801  extending through the second end surface  80 . The receptacle connector  200  is located at a rear end of the mating space  801  and communicates with the mating space  801 . In an embodiment of the present disclosure, the receptacle connector  200  is a backplane connector. 
     The metal cage  8  includes a second top wall  81 , a second bottom wall  82 , a third side wall  83 , a fourth side wall  84  and a rear wall  87 . The mating space  801  is enclosed by the second top wall  81 , the second bottom wall  82 , the third side wall  83  and the fourth side wall  84 . The third side wall  83  and the fourth side wall  84  are provided with abutting elastic arms  88  protruding into the mating space  801  to abut against the metal shell  5  of the plug connector  100 . The receptacle connector assembly  400  also includes grounding elastic arms  85  fixed to the second top wall  81 , the second bottom wall  82 , the third side wall  83 , and the fourth side wall  84 , respectively. The grounding elastic arms  85  are disposed adjacent to the second end surface  80 . 
     The receptacle connector assembly  400  further includes a receptacle heat sink  86  fixed to the second top wall  81  and/or the second bottom wall  82  to improve the heat dissipation effect. 
     Referring to  FIGS.  36  to  38   , the receptacle electrical connector  200  includes a receptacle housing  7  and a plurality of receptacle terminal modules  6  mounted to the receptacle housing  7 . The reason why the plug connector  100  is such called is because it is a component of the plug connector assembly  300 . The reason why the receptacle connector  200  is such called is because it is a component of the receptacle connector assembly  400 . So, it does not necessarily mean that the plug connector  100  must have some unique features to be a plug connector, and it does not necessarily mean that the receptacle connector  200  must have some unique features to be a receptacle connector. It is understandable to those of ordinary skill in the art that the plug connector  100  and the receptacle electrical connector  200  are exchangeable. For example, when the receptacle connector  200  is applied in the plug connector assembly  300 , it is then called a plug connector; and when the plug connector  100  is applied in the receptacle connector assembly  400 , it is then called a receptacle connector. 
     The receptacle housing  7  is made of insulating material, and includes a body portion  71 , a first extension wall  72  extending from the body portion  71  to one end, and a second extension wall  73  extending from the body portion  71  to the other end. The body portion  71  includes a plurality of terminal receiving grooves  711  extending along a front-rear direction. In the illustrated embodiment of the present disclosure, the terminal receiving grooves  711  are disposed in multiple rows along a left-right direction. Two adjacent rows of terminal receiving grooves  711  are staggered in a vertical direction. That is, the terminal receiving grooves  711  at corresponding positions in the two adjacent rows of terminal receiving grooves  711  are not aligned in the left-right direction. The first extension wall  72  includes a first extension wall portion  74  and a second extension wall portion  75  opposite to each other. The second extension wall  73  includes a receiving space  735  which is used for at least partially receiving the plug electrical connector  100 . The first extension wall portion  74  and the second extension wall portion  75  are provided with a plurality of second installation slots  76  for installing the receptacle terminal modules  6 . The first extension wall portion  74  and the second extension wall portion  75  further include positioning slots  77  for positioning the positioning protrusions  15 . 
     Referring to  FIG.  38   , each receptacle terminal module  6  includes a plurality of insulating blocks  65 , a plurality of terminal modules  60  mounted to the insulating blocks  65 , a grounding element, a metal shielding plate  67  for cooperating with the grounding element, a plurality of receptacle cables  68  electrically connected to the terminal modules  60 , and an outer covering portion  69  partially covering the terminal modules  60 , the grounding element, the metal shielding plate  67  and the receptacle cables  68 . In the illustrated embodiment of the present disclosure, the grounding element includes a plurality of metal shield surrounding members  66  sleeved on the insulating blocks  65  and the terminal modules  60 . The receptacle cables  68  extend through the rear wall  87  of the metal cage  8 . In some other embodiments, the receptacle terminal module  6  may not include receptacle cables  68 . Under such condition, the receptacle electrical connector  200  is located at the rear of the mating space  801 , but in front of the rear wall  87 . It is understandable to those of ordinary skill in the art that the mating space  801  is configured to receive the plug connector  100  before the plug conductive terminals  22  of the plug connector  100  are electrically connected with receptacle conductive terminals  62  of the receptacle electrical connector  200 . 
     The terminal module  60  includes an insulating member  61  and a plurality of receptacle conductive terminals  62  fixed to the insulating member  61 . In an embodiment of the present disclosure, the receptacle conductive terminals  62  are insert-molded with the insulating member  61 . Of course, in other embodiments, the receptacle conductive terminals  62  may also be fixed to the insulating member  61  by assembly. In a preferred embodiment of the present disclosure, each receptacle conductive terminal  62  is connected with a corresponding receptacle cable  68 . In other words, none of the receptacle conductive terminals  62  is directly connected to a circuit board. Compared to transmit signals through the circuit board, by transmitting signals, especially differential signals, through cables, it is more beneficial to reduce signal distortion and improve signal transmitting quality. 
     From a structural point of view, each receptacle conductive terminal  62  includes a contact arm  621 , an end portion  622 , and a second connection portion  623  connecting the contact arm  621  and the end portion  622 . The second connection portion  623  is fixed to the insulating member  61 . The contact arm  621  extends forwardly and protrudes beyond the insulating member  61  so as to be electrically connected to the first signal terminal Si of the plug connector  100 . The end portion  622  extends backwardly and protrudes beyond the insulating member  61  to be electrically connected to the receptacle cable  68 . In the illustrated embodiment of the present disclosure, each receptacle conductive terminal  62  is substantially in a shape of a straight bar and extends in the front-to-rear direction. 
     In an embodiment of the present disclosure, the receptacle conductive terminals  62  in each terminal module  60  form a pair of second differential signal terminals to increase the signal transmission rate. In other words, the plurality of receptacle conductive terminals  62  of each terminal module  60  include a first signal terminal and a second signal terminal. The first signal terminal and the second signal terminal form a differential pair and are fixed to the insulating member  61 . 
     Each insulating block  65  is provided with two through holes  651  into which the contact arms  621  of the receptacle conductive terminals  62  are inserted, and a mating surface  652  at an end of the insulating block  65 . The through holes  651  extend through the mating surface  652 . In the illustrated embodiment of the present disclosure, the insulating block  65  has a substantially cuboid shape. Correspondingly, the metal shield surrounding member  66  has a substantially cuboid shape. In an embodiment of the present disclosure, the insulating block  65  is fixed in the metal shield surrounding member  66  by soldering. Of course, in other embodiments, the insulating block  65  may also be fixed in the metal shield surrounding member  66  in other ways, i.e., by mechanical fixation. 
     Referring to  FIG.  38   , the metal shield surrounding member  66  includes a cylindrical portion  661 , an extended portion  662  connected to the cylindrical portion  661 , and an abutting portion  663  connected to the extended portion  662 . The cylindrical portion  661  is provided with a shielding cavity  6610  for accommodating the insulating block  65  and the terminal module  60  in order to improve the shielding effect. A cross section of the extended portion  662  is substantially U-shaped. 
     The metal shielding plate  67  is arranged opposite to the extended portion  662 , and the metal shielding plate  67  is in contact with the metal shield surrounding member  66  so as to improve the grounding shielding effect. 
     Referring to  FIG.  38   , each receptacle cable  68  includes a core  681  electrically connected to the end portion  622  of the second differential signal terminal, an insulating layer  682  wrapped on the core  681 , a shielding layer  683  wrapped on the insulating layer  682 , an insulating outer layer  684  wrapped on part of the shielding layer  683 , and a grounding wire  685  located between the shielding layer  683  and the insulating outer layer  684 . In an embodiment of the present disclosure, the core  681  and the end portion  622  of the second differential signal terminal are fixed by soldering. In the illustrated embodiment of the present disclosure, the grounding wire  685  is bent and extends out of the insulating outer layer  684 . 
     The metal shield surrounding member  66  surrounds a periphery of the second differential signal terminal to provide a better shielding effect on signal transmission. The metal shield surrounding member  66  is similar to the function of the first ground terminal G 1  and the second ground terminal G 2 . The metal shield surrounding member  66  is equivalent to connect the first ground terminal G 1  and the second ground terminal G 2  and forms a cylindrical shape wrapped around the periphery of the second differential signal terminal to further improve the ground shielding effect. The receptacle terminal module  6  further includes a connecting piece  64  connecting the grounding wire  685  and the metal shield surrounding member  66  so as to improve the ground shielding effect. 
     In the illustrated embodiment of the present disclosure, there are a plurality of receptacle terminal modules  6  of the receptacle connector  200 , and an arrangement of each two adjacent receptacle terminal modules  6  is staggered. When the receptacle terminal modules  6  are assembled to the receptacle housing  7 , each metal shield surrounding member  66  of the receptacle terminal modules  6  passes through the corresponding terminal receiving groove  711  to extend into the receiving space  735 . 
     Referring to  FIG.  37   , in the illustrated embodiment of the present disclosure, the plurality of receptacle terminal modules  6  include a first receptacle terminal module  601 , a second receptacle terminal module  602 , and at least one non-differential signal terminal (not shown) located between the first receptacle terminal module  601  and the second receptacle terminal module  602 . The plurality of receptacle terminal modules  6  include a cable  686  electrically connected to the non-differential signal terminal. The at least one non-differential signal terminal is adapted to transmit control signals and/or power supplies. 
     In the illustrated embodiment of the present disclosure, each of the first receptacle terminal modules  601  and each of the second receptacle terminal modules  602  are respectively located in a vertical plane as a whole. For each of the first receptacle terminal modules  601  and each of the second receptacle terminal modules  602 , a plurality of the metal shield surrounding members  66  and a plurality of pairs of the second differential signal terminals are stacked and separated by a certain distance in the vertical plane. The second differential signal terminals are divided into at least three pairs. Each pair of the second differential signal terminals is wrapped in the corresponding metal shield surrounding member  66 . The number of the first receptacle terminal modules  601  and the second receptacle terminal modules  602  is at least five and they are arranged side by side. Any two adjacent first receptacle terminal modules  601  are arranged next to each other. That is, a mating end of each first receptacle terminal module  601  is close to the adjacent first receptacle terminal module  601 . Any two adjacent second receptacle terminal modules  602  are arranged next to each other. That is, a mating end of each second receptacle terminal module  602  is close to the adjacent second receptacle terminal module  602 . The first receptacle terminal modules  601  are spaced a certain distance with respect to the second receptacle terminal modules  602  along a left-right direction as a whole in order to install the non-differential signal terminal. 
     Referring to  FIGS.  15 ,  38  and  39   , when the plug connector assembly  300  is mated with the receptacle connector assembly  400 , the plug connector assembly  300  is at least partially inserted into the mating space  801 . The length of the metal cage  8  extending in the mating direction (i.e., the front-to-rear direction) is much greater than the length of the receptacle connector  200  after the receptacle cable  68  is removed. In this way, a relatively deep mating space  801  is formed at the front end of the receptacle connector  200 , which is beneficial to improve the shielding effect. In addition, the length of the metal shell  5  extending in the mating direction (i.e., the front-to-rear direction) is much greater than the length of the plug connector  100  after the plug cable  302  is removed. In this way, it is beneficial to improve the shielding effect of the plug connector  100 . By providing the metal cage  8  and the metal shell  5 , the shielding effect of the connector assembly  500  of the present disclosure is improved, which is beneficial to improve the quality of signal transmission. When the plug connector assembly  300  is inserted in place, the plug housing  1  of the plug connector  100  is inserted into the receiving space  735  of the receptacle housing  7  of the receptacle connector  200 . Moreover, at a rear end (a deep end) of the receiving space  735 , the mating portion  221  of the plug terminal module  2  is inserted into the corresponding contact arm  621  of the receptacle terminal module  6  so as to achieve contact. By mating the plug connector  100  and the receptacle connector  200  at the rear end (the deep end) of the receiving space  735 , the shielding effect of the metal shell  5  and the metal cage  8  at the front end can be fully utilized, thereby improving the quality of signal transmission. In addition, the present disclosure increases the speed of signal transmission by arranging multiple pairs of differential signal terminals. 
     The above embodiments are only used to illustrate the present disclosure and not to limit the technical solutions described in the present disclosure. The understanding of this specification should be based on those skilled in the art. Descriptions of directions, such as “front”, “back”, “left”, “right”, “top” and “bottom”, although they have been described in detail in the above-mentioned embodiments of the present disclosure, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the application, and all technical solutions and improvements that do not depart from the spirit and scope of the application should be covered by the claims of the application.