Patent Publication Number: US-6712646-B2

Title: High-speed transmission connector with a ground structure having an improved shielding function

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a high-speed transmission connector and, in particular, to a ground structure of the high-speed transmission connector. 
     An electrical connector is used to connect two electrical apparatuses. Particularly when a signal is transmitted at a high speed, shielding is required for preventing leakage of the signal and entrance of noise. In case of a connector for connecting two circuit boards to each other, a simple ground structure as a shield is important. 
     Referring to FIGS. 1A through 1F, description will be made of an assembling process of an existing high-speed transmission connector having a shielding ground structure. In the illustrated example, the high-speed transmission connector is a plug connector having socket contacts for transmitting signals therethrough, which will be referred to as signal socket contacts. 
     At first referring to FIG. 1A, a plurality of sets of four signal socket contacts  42 A through  42 D for use in the plug connector ( 41  in FIG. 1F) are connected to a plurality of arms  43 A protruding from a carrier  43 , respectively. Each of the signal socket contacts  42 A through  42 D has a substantially L shape. Such a plurality of sets of the signal socket contacts  42 A through  42 D connected to the carrier  43  are prepared by pressing a single metal plate. 
     Next referring to FIG. 1B, the signal socket contacts  42 A through  42 D in each set are subjected to insert-molding by the use of an insulating resin material to form a contact module  44 . 
     Subsequently, the signal socket contacts  42 A through  42 D in each contact module  44  are separated from the arm  43 A of the carrier  43 . As illustrated in FIG. 1C, four ground plates  45 A through  45 D are incorporated into the contact module  44  on opposite sides thereof, two on one side and two on the other side. Specifically, the ground plates  45 A through  45 D are press-fitted into grooves formed in the contact module  44 . The ground plates  45 A through  45 D correspond to the signal socket contacts  42 A through  42 D, respectively. The ground plates  45 A through  45 D are alternately arranged on the opposite sides of the contact module  44 . Specifically, the ground plates  45 A and  45 C corresponding to the signal socket contacts  42 A and  42 C are arranged on one side of the contact module  44  while the ground plates  45 B and  45 D corresponding to the signal socket contacts  42 B and  42 D are arranged on the other side of the contact module  44 . 
     Turning to FIG. 1D, a shield plate  46  bent into a generally L shape is prepared. Into the shield plate  46 , the contact modules  44  with the ground plates  45 A through  45 D incorporated therein are provisionally inserted one by one. After the contact modules  44 , six in total, are inserted, they are collectively press fitted. Then, an assembly illustrated on a left-hand side in FIG. 1E is obtained. 
     Finally, the assembly including the six contact modules  44  and the shield plate  46  are press fitted into a housing  47  to complete the socket connector  41  as illustrated in FIG.  1 F. 
     Thus, the socket connector  41  includes the six sets of the signal socket contacts  42 A through  42 D as the six contact modules  44 . Among the six sets of the signal socket contacts  42 A through  42 D, the four sets located inside are shielded by the ground plates on both of the left and the right sides. However, the signal socket contacts  42 B and  42 D of the leftmost set are not shielded on the left side by the ground plates. Likewise, the signal socket contacts  42 A and  42 C of the rightmost set are not shielded on the right side by the ground plates. Therefore, the leftmost and the rightmost sets are not practically used. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of this invention to provide a high-speed transmission connector in which all of signaling contacts including outermost ones are shielded by grounding plates so as to reliably transmit a high-speed signal. 
     According to this invention, the following structures are provided: 
     1. A high-speed transmission connector comprising an insulating connector housing, a plurality of contacts fixed to the connector housing at positions forming a plurality of rows and a plurality of columns in a matrix arrangement, and a shield attached to the connector housing, wherein: 
     the shield comprises a plurality of first ground plates extending in parallel to the columns of the contacts and a plurality of second ground plates extending in parallel to the rows of the contacts; 
     at least either one ground plates of the first ground plates and the second ground plates being provided with contacting portions to be connected to the other ground plates, one of each of the first ground plates and each of the second ground plates having at least one ground terminal to be connected to an external circuit; 
     the first ground plates being arranged at an outside of opposite outermost ones of and between every two adjacent ones of the columns of the contacts, the second ground plates being arranged at an outside of opposite outermost ones of and between every two adjacent one of the rows of the contacts, the first and the second ground plates surrounding the contacts and forming a grid structure. 
     2. A board connector to be mounted on a circuit board, the connector being a high-speed transmission connector for use in connecting a signal circuit of a differential signal transmission system in which a single differential signal is transmitted through each air of two adjacent ones of a plurality of contacts, the connector comprising: 
     an insulating connector housing provided with a plurality of contact holding holes arranged in a matrix fashion to form a plurality of columns and a plurality of rows including two upper rows and two lower rows, a plurality of first slits formed between every two adjacent ones of and at the outside of opposite outermost ones of the columns of the holding holes and extending in parallel to the columns, and a second slit formed between the two upper rows and the two lower rows of the holding holes and extending in parallel to the rows; 
     a plurality of contacts fixed to the contact holding holes, respectively; 
     a plurality of ground plates inserted into the first slits, respectively; and 
     a second ground plate inserted into the second slit and brought into contact with the first ground plates. 
     Each of the contacts has a contact lead terminal to be connected to a circuit pattern on the circuit board. Each of the first ground plates has first, second, and third ground terminals which are to be connected to a ground pattern of the circuit board. The contact lead terminals are arranged to form a plurality of columns and plurality of rows in a matrix arrangement. The first, the second, and the third ground terminals are arranged at the outside of opposite outermost ones of and between every two adjacent ones of the columns of the contact lead terminals in a direction parallel to the columns. The first ground terminals of the first ground plates are arranged at the outside of the first row of the contact lead terminals in parallel to the first row. The second ground terminals are arranged between the second and the third rows of the contact lead terminals in parallel to the second and the third rows. The third ground terminals are arranged at the outside of the fourth row of the contact lead terminals in parallel to the fourth row. 
     3. A high-speed transmission connector for use in connecting a signal circuit of a differential signal transmission system in which a single differential signal is transmitted through each pair of two adjacent ones of a plurality of contacts. The connector comprises: 
     an insulating connector housing having a plurality of contact holding holes arranged in a matrix fashion to form a plurality of columns and a plurality of rows including two upper rows and two lower rows. A plurality of first slits are formed between every two adjacent ones of and at the outside of opposite outermost ones of the columns of the holding holes and extending in parallel to the columns. A second slit is formed between the two upper rows and the two lower rows of the holding holes and extending in parallel to the rows. 
     A plurality of contacts are fixed to the contact holding holes, respectively. 
     A plurality of first ground plates are inserted into the first slits, respectively. 
     A second ground plate is inserted into the second slit and brought into contact with the first ground plates. 
     Each of third ground terminals of the second ground plate has a pair of wing portions formed at its base to protrude towards adjacent columns of the contact lead terminals on opposite sides. Each of the contact lead terminals of the contacts and the ground terminals of the first ground plates is formed into a press-fit portion. Each of the first ground plates is integrally coupled with an insulator by press-fitting or insert-molding to form a ground plate module. The ground plate modules are inserted into the connector housing at the outside of the opposite outermost ones of and between every two adjacent ones of the columns of the contacts. The connector is attached to the circuit board by incorporating the ground plate modules into the connector housing in a state when lower ends of the insulators of the ground plate modules are brought into contact with upper ends of the wing portions and then pressing the ground plate modules to the circuit board. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIGS. 1A through 1F are perspective views showing an assembling process of a socket connector as an existing high-speed transmission connector; 
     FIGS. 2A and 2B are perspective views of a receptacle connector and a plug connector as high-speed transmission connectors according to a first embodiment of this invention, respectively; 
     FIG. 2C is a perspective view showing contacts and a ground plate when the receptacle connector in FIG.  2 A and the plug connector in FIG. 2B are fitted to each other; 
     FIG. 3 is an exploded perspective view of the receptacle connector illustrated in FIG. 2A; 
     FIGS. 4A and 4B are exploded perspective views of the plug connector illustrated in FIG. 2B; 
     FIGS. 5A and 5B are a plan view and a front view of a receptacle connector and a plug connector as high-speed transmission connectors according to a second embodiment of this invention, respectively, when they are fitted to each other; 
     FIG. 5C is a sectional view taken along a line  5 C— 5 C in FIG. 5B; 
     FIG. 5D is a perspective view showing contacts and a ground plate in FIG. 5C; 
     FIG. 6A is a partially-cutaway perspective view of the plug connector illustrated in FIGS. 5A through 5C; 
     FIGS. 6B and 6C are exploded perspective views of the plug connector illustrated in FIG. 6A; 
     FIGS. 7A and 7B are a perspective view and an exploded perspective view of the receptacle connector illustrated in FIGS. 5A through 5C, respectively; 
     FIGS. 8A and 8B are perspective views of a receptacle connector and a plug connector as high-speed transmission connectors according to a third embodiment of this invention, respectively, when they are not fitted to each other; 
     FIG. 9A is a sectional view of the receptacle connector and the plug connector illustrated in FIGS. 8A and 8B when they are fitted to each other; 
     FIG. 9B is a partially-cutaway perspective view of a part of the receptacle connector and the plug connector in FIG. 9A; 
     FIG. 10 is a perspective view of a second ground plate module of the plug connector illustrated in FIG. 8B; 
     FIGS. 11A and 11B are perspective views of a receptacle connector and a plug connector as high-speed transmission connectors according to a fourth embodiment of this invention, respectively, when they are not fitted to each other; 
     FIG. 12A is a sectional view of the receptacle connector and the plug connector illustrated in FIGS. 11A and 11B when they are fitted to each other; 
     FIG. 12B is a partially-cutaway perspective view of a part of the receptacle connector and the plug connector illustrated in FIG. 12A; and 
     FIG. 13 is a partially cutaway perspective view for describing an internal structure of the plug connector illustrated in FIGS.  11 B. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, description will be made of a high-speed transmission connector according to this invention in conjunction with several preferred embodiments of this invention with reference to the drawing. 
     At first referring to FIGS. 2A to  2 C,  3 , and  4 A to  4 C, description will be made of a receptacle connector  1  and a plug connector  11  as high-speed transmission connectors to be fitted or connected to each other. 
     Referring to FIGS. 2A-2C and  3 , the receptacle connector  1  comprises an insulating receptacle housing  2  having a generally U-shaped section, a plurality of signal pin contacts  3  for transmitting signals held by the receptacle housing  2  and arranged in a matrix fashion, a plurality of first ground plates  4  extending in a first direction or a column direction, and a plurality of second ground plates  5  extending in a second direction or a row direction perpendicular to the column direction. More in detail, the pin contacts  3 , twenty in number, are arranged in five columns and four rows. In other words, four pin contacts are arranged in each of the columns while five pin contacts are arranged in each of the rows. The first ground plates  4 , six in number, are arranged between every two adjacent ones of and at the outside of opposite outermost ones of the columns of the pin contacts  3 . The second ground plates  5 , five in number, are arranged between every two adjacent ones of and at the outside of opposite outermost ones of the rows of the pin contacts  3 . 
     Each of the first ground plates  4  has two terminal portions  4 A which are connected to a carrier  6  depicted by a two-dot-and-dash line in FIG.  3 . The four pin contacts  3  in each column have terminal portions as contact lead terminals  3 A, respectively, which are connected to a carrier  7  depicted by a two-dot-and-dash line in FIG.  3 . 
     The carriers  6  and  7  are cut off after the first ground plate  4  and the contacts  3  are incorporated into the receptacle housing  2 . 
     Each of the second ground plates  5  is provided with six contacting portions  5 A formed on one side and three terminal portions (butt leads)  5 B formed on the other side. The first ground plates  4  intersect with the second ground plates  5  to be perpendicular thereto and are electrically connected to the second ground plates  5  through the contacting portions  5 A and the terminal portions  5 B. 
     Each of the first ground plates  4  is press-fitted or insert-molded into the receptacle housing  2 . Each of the second ground plates  5  is press-fitted into the receptacle housing  2 . Then, the first and the second ground plates  4  and  5  are connected to each other. 
     Specifically, the first ground plates  4 , six in number, and the second ground plates  5 , five in number, are combined with each other to form a grid structure. Each pin contact  3  is located in each grid cell and surrounded by the first and the second ground plates  4  and  5 . 
     Referring to FIGS. 2A-2C and  4 , the plug connector  11  comprises an insulating plug housing  12 , a plurality of signal socket contacts  13  held by the plug housing  12  and arranged in a matrix fashion, a plurality of ground modules  14  each of which has a first ground plate  16  extending in the column direction, and a plurality of second ground plates  17 A through  17 E extending in the row direction. More in detail, the socket contacts  13 , twenty in number, are arranged in five columns and four rows. In other words, four socket contacts are arranged in each of the columns while five socket contacts are arranged in each of the rows. The ground modules  14 , six in number, are arranged between every two adjacent ones of and at the outside of opposite outermost ones of the columns of the socket contacts  13 . The second ground plates  17 A through  17 E, five in number, are arranged between every two adjacent ones of and at the outside of opposite outermost ones of the rows of the socket contacts  13 . 
     Each of the ground modules  14  comprises an insulator  15  and the first ground plate  16  insert-molded into the insulator  15 . The first ground plate  16  is provided with a plurality of contacting portions  16 A through  16 H formed at its forward end to be connected to the second ground plates  17 A through  17 E. The first ground plate  16  is provided with three terminals  16 I formed at its lower end. 
     The second ground plate  17 A has a plurality of slits (four of six slits are shown)  17 A 1  into which first ground plates  16  are inserted to be combined with the second ground plate  17 A, while the second ground plates  17 A is fitted and connected to the contacting portion  16 A of each of the first ground plates  16 . Similarly, the second ground plate  17 B has a plurality of slits  17 B 1  into which the first ground plates  16  are fitted, and the second ground plate  17 B is fitted between the contacting portions  16 B and  16 C to be connected thereto. The second ground plate  17 C has a plurality of slits  17 C 1  into which the first ground plates  16  are also fitted, and the second ground plate  17 C is fitted between the contacting portions  16 D and  16 E to be connected thereto. The second ground plate  17 D has a plurality of slits  17 D 1  into which the first ground plates  16  are fitted, and the second ground plates  17 D is fitted between the contacting portions  16 F and  16 G to be connected thereto. The second ground plate  17 E has a plurality of slits  17 E 1  into which the first ground plates  16  are fitted, and the second ground plate  17 E is fitted and connected to the contacting portion  16 H. 
     Each of the second ground plates  17 A through  17 E is press-fitted into the plug housing  12 . Each of the ground modules  14  is press-fitted into the plug housing  12 . Then, the second ground plates  17 A through  17 E and the first ground plates  6  of the ground modules  14  are connected to each other. 
     Thus, the first ground plates  16 , six in number, and the second ground plates  17 A through  17 E, five in number, are combined with each other to form a grid structure. Each socket contact  13  is located in each grid cell and surrounded by the first and the second ground plates  16  and  17 . 
     Each of the terminal portions  16 I is driven or press-fitted into a through hole formed in a circuit board (not shown) to be connected and fixed to a ground pattern on the circuit board. 
     When the plug connector  11  is fitted to the receptacle connector  1 , the signal pin contacts  3 , twenty in number, and the signal socket contacts  13 , twenty in number, are connected to each other. Simultaneously, the second ground plates  17 A through  17 E of the plug connector  11  and the first ground plates  4  of the receptacle connector  1  are connected to each other. 
     In the foregoing embodiment, the contacts, twenty in number, are arranged in a 5×4 matrix arrangement. However, as will readily be understood for those skilled in the art, the numbers of the rows and the columns in the matrix arrangement may be increased or decreased as desired. In this event, the number of the ground plates will be increased or decreased correspondingly. 
     Next referring to FIGS. 5A to  5 D,  6 A to  6 C, and  7 A and  7 B, description will be made of a second embodiment of this invention. 
     In this embodiment, high-speed transmission connectors are used to connect a signal circuit of a differential signal transmission system in which one information signal is transmitted as a differential signal by the use of a pair of two signal lines. 
     Referring to FIGS. 5A to  5 D and FIGS. 6A to  6 C, a plug connector  31  as one of the high-speed transmission connectors comprises a plug housing  32  made of an insulating plastic material, a plurality of signal socket contacts  33  held by the plug housing  32 , a plurality of ground modules  34  each of which has a first ground plate  36  extending in a first direction or a column direction, and a second ground plate  37  extending in a second direction or a row direction perpendicular to the column direction. More in detail, the socket contacts  33 , twenty in number, are arranged in five columns and four rows. In other words, four socket contacts are arranged in each of the columns while five socket contacts are arranged in each of the rows. The ground modules  34 , six in number, are arranged between every two adjacent ones of and at the outside of opposite outermost ones of the columns of the socket contacts  33 . The second ground plate  37  is arranged between two upper rows and two lower rows of the socket contacts  33 . The plug connector  31  further comprises a plurality of insulator blocks  38 , five in number, each of which covers two lower ones of the socket contacts  33  in each column to support the two lower socket contacts  33 . The insulator blocks  38  also support the second ground plate  37  placed thereon. 
     In each column, the two upper socket contacts  33  are paired into an upper contact pair while the lower two socket contacts  33  are paired into a lower contact pair. The upper and the lower contact pairs are adapted to transmit differential signals different and independent from each other. The second ground plate  37  serves to shield the upper and the lower contact pairs from each other. Thus, the second ground plate  37  is combined with the first ground plates  36 , six in number, to intersect therewith so that the upper and the lower contact pairs in the respective columns are individually partitioned by the first and the second ground plates  36  and  37 . As a consequence, the contact pairs for differential signal transmission are shielded from one another. 
     Each of the ground modules  34  comprises an insulator  35  and the first ground plate  36  insert-molded or press-fitted into the insulator  35 . The first ground plate  36  is provided with a pair of contacting portions  36 A formed at its forward end to be inserted into each of a plurality of slits  37 A of the second ground plate  37  to be connected thereto. The first ground plate  36  is provided with three ground terminal portions  36 B formed at its lower end. Each of the ground terminal portions  36 B is press-fitted into a through hole of a circuit board or a daughter board  39  to connect and fix the first ground plate  36  to a ground pattern on the daughter board  39 . 
     The second ground plate  37  is bent into a generally L shape and has the slits  37 A formed on one side and a plurality of contacting portions  37 B formed on the other side to be connected to a plurality of first ground plates  24  of a receptacle connector  21  which will later be described, respectively. 
     Upon assembling, the second ground plate  37  is press-fitted into the plug housing  32 . Each of the ground modules  34  is press-fitted into the plug housing  32 . Then, the first ground plates  36  in the ground modules  34  and the second ground plate  37  are connected to each other. 
     As illustrated in FIG. 5C, each of the insulator blocks  38  holds the two lower socket contacts  33 . Furthermore, the insulator blocks  38  support a lower surface of the second ground plate  37  and opposite side surfaces of the first ground plates  36 . 
     Referring to FIGS. 7A and 7B, the receptacle connector  21  as the other of the high-speed transmission connectors comprises a generally U-shaped receptacle housing  22 , a plurality of signal pin contacts  23  held by the receptacle housing  22 , a plurality of the first ground plates  24  extending in the column direction, and a second ground plate  25  extending in the row direction. More in detail, the pin contacts  23 , twenty in number, are arranged in five columns and four rows. In other words, four pin contacts are arranged in each of the columns while five pin contacts are arranged in each of the rows. The first ground plates  24 , six in number, are arranged between every two adjacent ones of and at the outside of opposite outermost ones of columns of the pin contacts  23 . The second ground plate  25  is arranged between two upper rows and two lower rows of the pin contacts  23 . 
     Thus, the second ground plate  25  is combined with the first ground plates  24 , six in number, to intersect therewith so that upper and lower pairs of the pin contacts  23  in the respective columns are individually partitioned by the first and the second ground plates  24  and  25 . As a consequence, the contact pairs for differential signal transmission are shielded from one another. 
     The receptacle connector  21  is mounted to a mother board  28  as a circuit board. 
     Each of the first ground plates  24  has two terminal portions  24 A to be connected to a ground pattern on the mother board  28 . The terminal portions  24 A are connected to a carrier  26  depicted by a two-dot-and-dash line in FIG.  7 B. 
     The four pin contacts  23  in each column have terminal portions  23 A, respectively, to be connected to a circuit pattern on the mother board  28 . The terminal portions  23 A are connected to a carrier  27  depicted by a two-dot-and-dash line in FIG.  7 B. 
     The second ground plate  25  is provided with six contacting portions  25 A formed on its one side and three terminal portions  25 B formed on the other side. The first ground plates  24  are connected through the contacting portions  25 A to the second ground plate  25 . The terminal portions  25 B are to be brought into press contact with the ground pattern on the mother board  28 . The terminal portions  25 B may be omitted. 
     Each of the first ground plates  24  is press-fitted or insert-molded into the receptacle housing  22 . The second ground plate  25  is press-fitted into the receptacle housing  22 . Then, the first and the second ground plates  24  and  25  are connected to each other. 
     When the receptacle connector  21  and the plug connector  31  are fitted to each other as illustrated in FIGS. 5A through 5D, the signal pin contacts  23 , twenty in number, and the signal socket contacts  33 , twenty in number, are connected to each other. Simultaneously, the first ground plates  24 , six in number, of the receptacle connector  21  are connected to the second ground plate  37  of the plug connector  31  through the contacting portions  37 B. 
     In the embodiment illustrated in FIGS. 5A-5D to FIGS. 7A and 7B, the second ground plate is not arranged at the outside of the opposite outermost ones of the rows of the contacts. Since the differential signal is transmitted, signal currents flowing through the contacts are cancelled by each other so that little influence is given to the outside. Therefore, the second ground plate is arranged only between the adjacent contact pairs in order to avoid occurrence of cross talk therebetween. Thus, the connector is simplified in structure and reduced in size. If desired, however, the second ground plates may be arranged at the outside of the opposite outermost ones of the rows of the contacts. 
     In the foregoing embodiment, two contact pairs for differential signals are arranged in each single column. However, as will readily be understood for those skilled in the art, the number of the contact pairs may be increased as desired. In this event, the second ground plate will be added correspondingly. Furthermore, the number of columns may be increased or decreased as desired. 
     Next referring to FIGS. 8A-8B to  10 , description will be made of high-speed transmission connectors according to a third embodiment of this invention as a modification of the second embodiment for the differential signal transmission system. 
     The high-speed signal transmission connectors according to the third embodiment are similar in basic structure to that of the second embodiment except that a receptacle connector does not have a second ground plate extending in a row direction and that, in a plug connector, a second ground plate extending in the row direction is integrally coupled with insulator blocks by insert-molding. Similar parts are designated by like reference numerals and description thereof will be omitted. 
     Referring to FIGS. 8A and 8B, the receptacle connector  21  and the plug connector  31  are similar in external appearance to those of the second embodiment, respectively. 
     A plug housing  32  of the plug connector  31  has a plurality of contact holding holes  32   a  arranged in a matrix fashion to form a plurality of columns and a plurality of rows including two upper rows and two lower rows, a plurality of first slits  32   b  formed between every two adjacent ones of and at the outside of opposite outermost ones of the columns of the contact holes  32   a  and extending in parallel to the columns, and a second slit  32   c  formed between the two upper rows and the two lower rows and extending in parallel to the rows. 
     A plurality of socket contacts  33  are held in the contact holding holes  32   a , respectively, to be arranged in a matrix fashion. 
     A plurality of first ground plates  36  are press-fitted into the first slits  32   b  while a second ground plate  37  is press-fitted into the second slit  32   c . Thus, the first and the second ground plates  36  and  37  are attached and fixed to the plug housing  32 . 
     The above-mentioned structure may be applied to the plug connector in the second embodiment. 
     Referring to FIG. 10, a plurality of insulator blocks  38  are integrally coupled to the second ground plate  37  by insert-molding. 
     The first ground plate  36  has a plurality of ground terminals  36 B extending in a plane same as the ground plate  36 . 
     In the plug connector  31  having the above-mentioned structure, terminals (contact lead terminals)  33 A of the contacts  33  and the ground terminals  36 B of the first ground plates  36  are arranged in correspondence to through holes formed in a daughter board  39  illustrated in FIG. 8B to receive these terminals. In the figure, the through holes are depicted by same reference numerals as these terminals. 
     Specifically, the three ground terminals  36 B of each of the first ground plates  36  are referred to as first, second, and third ground terminals in the order from the outermost one. The contact lead terminals  33 A are arranged to form a plurality of columns and a plurality of rows in a matrix arrangement. The first through the third ground terminals  36 B are arranged between every two adjacent ones of and at the outside of opposite outermost ones of the columns of the contact lead terminals  33 A. The first ground terminals  36 B of the first ground plates  36  are arranged at the outside of the first row of the contact lead terminals  33 A to be aligned in parallel to the first row. The second ground terminals  36 B are arranged between the second and the third rows of the contact lead terminals  33 A to be aligned in parallel to the second and the third rows. The third ground terminals  36 B are arranged outside the fourth row of the contact lead terminals  33 A to be aligned in parallel to the fourth row. 
     As seen from FIG. 9A, the receptacle connector  21  has no second ground plate. Each of a plurality of first ground plates  24  has three ground terminals  24 A extending in a plane of the first ground plate  24 . 
     In the receptacle connector  21 , terminals (contact lead terminals)  23 A of a plurality of pin contacts  23  and the ground terminals  24 A of the first ground plates  24  are arranged in correspondence to the through holes formed in a mother board  28  illustrated in FIG. 8A to receive these terminals. In the figure, the through holes are depicted by same reference numerals as these terminals. 
     Specifically, the three ground terminals  24 A of each of the first ground plates  24  are referred to as first, second, and third ground terminals in the order from the uppermost one. The contact lead terminals  23 A are arranged to form a plurality of columns and a plurality of rows in a matrix arrangement. The first through the third ground terminals  24 A are arranged between every two adjacent ones of and at the outside of opposite outermost ones of the columns of the contact lead terminals  23 A. The first ground terminals  24 A of the first ground plates  24  are arranged at the outside the first row of the contact lead terminals  23 A to be aligned in parallel to the first row. The second ground terminals  24 A are arranged between the second and the third rows of the contact lead terminals  23 A to be aligned in parallel to the second and the third rows. The third ground terminals  24 A are arranged at the outside of the fourth row of the contact lead terminals  23 A to be aligned in parallel to the fourth row. 
     Next referring to FIGS. 11A to  11 B and  12 A to  12 B, description will be made of high-speed transmission connectors according to a fourth embodiment of this invention as a further modification of the third embodiment. 
     The fourth embodiment is substantially similar in structure to the third embodiment except a lead-out structure of the ground terminals. Similar parts are designated by like reference numerals and detailed description thereof will be omitted. 
     Referring to FIG. 11A, each of three ground terminals  24 A of each of a plurality of first ground plates  24  of a receptacle connector  21  is connected to a bent portion formed by perpendicularly bending a part of the first ground plate  24  and extends in parallel to a plane of the bent portion and a plane of the first ground plate  24 . The ground terminals  24 A are arranged to be aligned in the columns of contact terminals  23 A of a plurality of pin contacts  23 . 
     In the receptacle connector  21 , the terminals (contact lead terminals)  23 A of the pin contacts  23  and the ground terminals  24 A of the first ground plates  24  are arranged in correspondence to the through holes formed in a mother board  28  illustrated in FIG. 11A to receive these terminals. In the figure, the through holes are depicted by same reference numerals as these terminals. 
     Specifically, the three ground terminals  24 A of each of the first ground plates  24  are referred to as first, second, and third ground terminals in the order from the uppermost one. The contact lead terminals  23 A and the first and the second ground terminals  24 A are arranged to form a plurality of columns and a plurality of rows in a matrix arrangement. The first ground terminals  24 A of the first ground plates  24  are arranged at the outside of the first row of the contact lead terminals  23 A to be aligned in parallel to the first row. The second ground terminals  24 A are arranged between the second and the third rows of the contact lead terminals  23 A to be aligned in parallel to the second and the third rows. The third ground terminals  24 A are arranged at the outside the fourth row of the contact lead terminals  23 A to be aligned in parallel to the fourth row. 
     The three ground terminals  24 A of the outermost one of the first ground plates  24  are aligned in a single column which does not contain any contact lead terminal. 
     Referring to FIG. 12B and 13, each of a plurality of first ground plates  36  of a plug connector  31  has two ground terminals  36 B as first and second ground terminals in the order from the outermost one. A middle one of three ground terminals of each of first ground plates in the foregoing embodiments is omitted in the present embodiment. Instead of the middle one, a ground contact is provided, as a third ground terminal, to a second ground plate  37 . Thus, the second ground plate  37  is provided with a plurality of third ground terminals  37 C corresponding to the first ground plates, respectively. 
     The first or outermost ground terminal  36 B of the first ground plate  36  is connected to a bent portion formed by perpendicularly bending a part of the first ground plate  36  and extends in parallel to a plane of the bent portion and a plane of the first ground plate  36 . As a consequence, the first ground terminal  36 B is aligned with one of adjacent columns of the contact terminals  33 A and one of the third ground terminal  37 C of the second ground plate  37 . 
     In the plug connector  31 , the first and the second ground terminals  36 B, the third ground terminals  37 C, and contact lead terminals  33 A are arranged in correspondence to through holes formed in a daughter board  39  illustrated in FIG.  11 B. In the figure, the through holes are depicted by same reference numerals as these terminals. 
     Specifically, the contact lead terminals  33 A, the first ground terminals  36 B, and the third ground terminals  37 C are arranged to form a plurality of columns and a plurality of rows in a matrix arrangement. The first ground terminals  36 B of the first ground plates  36  are arranged at the outside of the first row of the contact lead terminals  33 A to be aligned in parallel to the first row. The third ground terminals  37 C of the second ground plate  37  are arranged between the second and the third rows of the contact lead terminals  33 A to be aligned in parallel to the second and the third rows. The second ground terminals  36 B of the first ground plates  36  are arranged at the outside of the fourth row of the contact lead terminals  33 A to be aligned in parallel to the fourth row and at positions shifted from the respective columns of the contact lead terminals  33 A. 
     As is obvious from FIG. 13, each of the third ground terminals  37 C is provided with a pair of wing portions  37 D formed at its base to protrude on opposite sides. On the wing portions  37 D, the insulator  35  of an adjacent one of a plurality of ground modules  34  is placed. As a consequence, by pressing the ground module  34  upon mounting the plug connector  31  to the daughter board  39 , the third ground terminals  37 C as well as the first and the second ground terminals  36 B are press-fitted into the through holes corresponding thereto. 
     As is obvious from the foregoing description, this invention is advantageous in the following respects. 
     The ground plates are arranged in the grid structure to surround each individual contact or each individual contact pair. Therefore, it is possible to provide a high-speed transmission connector capable of transmitting a high-speed signal and having excellent cross talk characteristics. 
     The connector is simple in structure, small in number of parts, and easy in assembling and disassembling.