Patent Publication Number: US-7588463-B2

Title: Connector and method of producing the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present invention is related to and claims priority of the following co-pending applications, namely, Japanese Patent Applications Nos. 2007-117407 filed on Apr. 26, 2007 and 2007-323626 filed on Dec. 14, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a type of connector including a plurality of contact modules, and further relates to a method of producing this type of connector. 
     2. Description of the Prior Art 
     In recent years, information and communication apparatuses, broadcast and video apparatuses, control devices for factory automation systems, medical equipment, semi-conductor manufacturing equipment, semi-conductor testers, etc., have been required to process enormous volumes of data at a high speed with a high degree of precision. Therefore, connectors for these apparatuses or devices are required to have a high shielding capability. 
     The connector (the plug connector  3 ) disclosed in Japanese unexamined patent publication 2005-197163 is provided with a front housing  5  and a plurality of contact modules  6  which are fixed to the front housing  5  to be arranged in layers in a specific direction. 
     Each contact module  6  includes an insulator  28 , a plurality of signal contacts  16  fixed to the insulator  28 , and a plurality of shielding members (the first ground plates  14  and the second ground plates  15 ) which are made of metal by insert molding and embedded in the insulator  28 . One end of each signal contact  16  is connected to a board (electrical circuit board), while the other end of each signal contact  16  is connectable with contact pins of another connector (the receptacle connector  4 ), respectively. 
     Each of the first and second ground plates  14  and  15  includes a plurality of substantially L-shaped portions  18  and a plurality of protrusion-shaped ribs  22 . The substantially L-shaped portions  18  and the protrusion-shaped ribs  22  partly surround the signal contacts  16  in the insulator  28  to shield each signal contact  16  electromagnetically. 
     However, in the connector disclosed in the aforementioned patent publication, the connector needs to be provided with shielding members (the first ground plates  14  and the second ground plates  15 ) and also needs to be formed in a complicated shape in order to exhibit a shielding effect. Therefore, the number of elements of the connector increases; moreover, it is difficult to increase productivity, and accordingly, the cost of production tends to increase. 
     In addition, although the metal-made shielding members are provided for the purpose of surrounding the signal contacts  16 , the internal area and the external surface area of an integrally-molded product  27  (i.e., the portion of the contact module  6  excluding the signal contacts  16 ) in which no shielding member exits are large, and accordingly, it is hard to obtain a sufficient shielding effect. 
     Additionally, since the plurality of shielding members are embedded in the insulator  28 , it is difficult to miniaturize the integrally-molded product  27  (it is difficult for the integrally-molded product  27  to have a high a space-saving efficiency). Accordingly, each contact module  6  becomes large in size, thus increasing the dimensions of the connector. 
     Additionally, since the plurality of shielding members are embedded in the insulator  28 , it is difficult to achieve a higher density in each contact module  6  (i.e., increase the number of the signal contacts  16  in each contact module  6  with no increase in size of each contact module  6 ). 
     SUMMARY OF THE INVENTION 
     The present invention provides a simple and easy-to-produce connector (receptacle/plug) having a small number of elements, wherein a high-shielding capability is obtained even if each contact module is miniaturized. 
     According to an aspect of the present invention, a receptacle is provided, including a plurality of contact modules, each of which includes a plurality of contacts, one of common ends of the contacts being connected to a corresponding plurality of contact pins of a plug, respectively, when the receptacle and the plug are connected to each other, and the other of the common ends of the contacts being connected to a circuit board. Each of the plurality of contact modules includes a plurality of holding plates arranged in a direction of thickness of the each contact module. At least one conductive layer and at least one insulating portion are formed on each of opposed surfaces of adjacent holding plates of the plurality of holding plates, and at least one of the plurality of contacts is held between the insulating portions that are formed on the opposed surfaces of the adjacent holding plates, respectively. 
     In an embodiment, a plug is provided, including a plurality of contact modules, each of which includes a plurality of contact pins, one of common ends of the contact pins being inserted into a receptacle to be connected to a corresponding plurality of contacts included in the receptacle, respectively, when the plug and the receptacle are connected to each other, and the other of the commons ends of the plurality of contact pins being connected to a circuit board. Each of the contact modules includes a plurality of holding plates arranged in a direction of thickness of the each contact module. At least one conductive layer and at least one insulating portion are formed on each of opposed surfaces of adjacent holding plates of the holding plates. At least one of the contact pins is held between the insulating portions that are formed on the opposed surfaces of the adjacent holding plates, respectively. It is desirable for each of the plurality of contact modules to include two adjacent holding plates of the plurality of holding plates. 
     It is desirable for each of the plurality of contact modules to include at least three holding plates of the plurality of holding plates. 
     Accordingly, the receptacle and the plug achieve a smaller number of elements and are simpler in structure than those of conventional connectors using one or more metal-made shielding members in either case where the contact or contact pins of the receptacle and the plug are constituted by the same type of contacts or contact pins (this case also includes both the case of single-ended signaling and the case of differential signaling, as described above, and where the contact or contact pins of the receptacle and the plug are constituted by two types of contacts or contact pins. 
     Moreover, since no metal shielding member becomes no longer necessary, each contact module can be made smaller than before and the contacts or contact pins in each contact module can be further densified in the case where each contact module is provided therein with the same number of contacts or contact pins as a conventional contact module. 
     Furthermore, the shielding effect of the connector (receptacle/plug) can be enhanced because the surface area of each conductive layer can be increased. Accordingly, the connector (receptacle/plug) according to the present invention makes high-speed signal transmission possible. 
     It is desirable for the opposed surfaces of the adjacent holding plates to include first opening recesses and second opening recesses, respectively, the first opening recesses and second opening recesses being open at common end surfaces of the adjacent holding plates, respectively. Engaging holes, through which an outside and an inside of the each contact module are communicatively connected to each other, is formed by the first opening recesses and the second opening recesses upon the adjacent holding plates being joined to each other. Electrical continuity is established between the contacts of the each contact module and the contact pins of the plug upon the contact pins of the plug being inserted into the each contact module through the engaging holes, respectively. 
     It is desirable for the opposed surfaces of the adjacent holding plates to include first opening recesses and second opening recesses, respectively, the first opening recesses and the second opening recesses being open at common end surfaces of the adjacent holding plates, respectively. Engaging holes through which outside and inside of the each contact module are communicatively connected to each other are formed by the first opening recesses and the second opening recesses upon the adjacent holding plates being joined to each other. The contact pins project to the outside of the each contact module through the engaging holes. 
     Accordingly, the connector (receptacle/plug) does not have to be provided with a housing that is an indispensable element of a convention connector, which achieves a further reduction in the number of elements of the connector. 
     It is desirable for at least one of the adjacent holding plates to include a plurality of contact holding grooves formed on the insulating portion, the contacts being engaged in the contact holding grooves to be held thereby, respectively. 
     It is desirable for some of the contacts to be held between the insulating portions formed on the adjacent holding plates, and for the remainder of the plurality of contacts to be held between the conductive layers formed on the adjacent holding plates. 
     It is desirable for a plurality of the insulating portions to be formed on each of the opposed surfaces of the adjacent holding plates with the conductive layer on the each of the opposed surfaces of the adjacent holding plates being provided on opposite sides of each of the plurality of insulating portions. Only one of the contacts is held between each of the insulating portions that are formed on the opposed surfaces of the adjacent holding plates, respectively. 
     Accordingly, each contact or contact pin can be securely held by the adjacent holding plates. 
     It is desirable for the conductive layer to be formed entirely over each of the opposed surfaces of the adjacent holding plates of the plurality of holding plates, and for the insulating portion to be formed partly on the conductive layer. 
     Accordingly, since the range of shielding by the conductive layer with respect to the contacts or contact pins that are held by the associated insulating portions widens, a far superior shielding effect is achieved. 
     It is desirable for the conductive layer to cover a pair of side edges of each of the insulating portions positioned on both sides of the plurality of contacts. 
     Accordingly, if each contact or contact pin is held between the insulating portions formed on the opposed surfaces of the adjacent holding plates, the perimeter of each contact or contact pin is perfectly shielded since each contact or contact pin is totally surrounded by the conductive layers of a pair of holding plates. Accordingly, an extremely superior shielding effect is obtained. 
     It is desirable for a continuous conductive layer to be formed on all surfaces of the adjacent holding plates other than the opposed surfaces of the adjacent holding plates. 
     If the conductive layer portion is formed entirely over the surface of each holding plate in such a manner, the surface area of each conductive layer becomes extremely large, so that a far superior shielding effect is achieved. 
     It is desirable for each of the plurality of holding plates to include a conductive layer portion including a resin-made substrate on which the conductive layer is plated, and at least one insulation recess formed on a surface which faces the other of the adjacent holding plates; and for the insulating portion to be made of a resin material and be provided in the insulation recesses so as to occupy the insulation recesses. 
     Accordingly, the holding plates can be easily produced. 
     It is desirable for the receptacle to include a retainer which is attached to a contact module group formed by the plurality of contact modules arranged in layers to combine the plurality of contact modules into one integral module. 
     Accordingly, the contact module group can be easily combined into one integral body. 
     In an embodiment, a method is provided for making a receptacle with a plurality of contact modules, each of which includes a plurality of contacts, one of common ends of the contacts being connected to a corresponding plurality of contact pins of a plug, respectively, when the receptacle and the plug are connected to each other, and the other of the common ends of the contacts being connected to a circuit board. The method includes forming a plurality of conductive layer portions which each include a resin-made substrate which has been plated; forming a plurality of holding plates by putting a resin-made insulating portion on each of the conductive layer portions so as to occupy a part of a surface thereof; forming the contact modules by arranging the holding plates in a direction of thickness of the each contact module and by joining opposed surfaces of adjacent holding plates thereof, on which the insulating resin-made insulating portion is placed, to each other so that at least one of the contacts is held between the insulating portions that are formed on the opposed surfaces of the adjacent holding plates; and connecting the contact modules into one integral module. 
     Accordingly, a receptacle which includes contact modules which are simple in structure with a small number of elements and which can achieve a high shielding capability even if the size of each contact module is reduced, can be easily produced. 
     In an embodiment, a method is provided for making a plug with a plurality of contact modules each of which includes a plurality of contact pins, one of common ends of the contact pins being inserted into a receptacle to be connected to a corresponding plurality of contacts included in the receptacle, respectively, when the plug and the receptacle are connected to each other, and the other of the common ends of the plurality of contact pins being connected to a circuit board. The method includes forming a plurality of conductive layer portions which each include a resin-made substrate which has been plated, respectively; forming a plurality of holding plates by putting a resin-made insulating portion on each of the conductive layer portions so as to occupy a part of a surface thereof; forming the contact modules by arranging the holding plates in a direction of thickness of the each contact module and by joining opposed surfaces of adjacent holding plates thereof, on which the insulating resin-made insulating portion is placed, to each other so that at least one of the contact pins is held between the insulating portions that are formed on the opposed surfaces of the adjacent holding plates; and connecting the contact modules into one integral module. 
     Similarly, a plug which includes contact modules which are simple in structure with a small number of elements and which can achieve a high shielding capability even if the size of each contact module is reduced, can be easily produced. 
     It is desirable for the connecting of the contact modules into one integral module to include arranging the plurality of contact modules in layers to form a contact module group, and attaching a retainer to the contact module group. 
     Accordingly, a connector (receptacle/plug) can be easily produced since the contact module group can be easily combined into one integral body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The present invention will be discussed below in detail with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a first embodiment of a connector according to the present invention which includes a receptacle and a plug, showing a state where the receptacle and the plug are connected to each other; 
         FIG. 2  is a perspective view of the receptacle and the plug, showing a state where the receptacle and the plug are disengaged from each other; 
         FIG. 3  is an exploded perspective view of the receptacle, which is disassembled into three pieces: a contact module group, a retainer and a connecting rod; 
         FIG. 4  is a front elevational view of the plug and the receptacle which are connected to each other; 
         FIG. 5  is a cross sectional view taken along the V-V line shown in  FIG. 4 , viewed in the direction of the appended arrows; 
         FIG. 6  is a perspective view of each contact module of the receptacle; 
         FIG. 7  is an exploded perspective view of the contact module shown in  FIG. 6 ; 
         FIG. 8  is an exploded perspective view of the contact module shown in  FIG. 6 , viewed from a different angle; 
         FIG. 9  is a side elevational view of the contact module shown in  FIG. 6 ; 
         FIG. 10  is a cross sectional view taken along the X-X line shown in  FIG. 9 , viewed in the direction of the appended arrows; 
         FIG. 11  is a cross sectional view taken along the XI-XI line shown in  FIG. 9 , viewed in the direction of the appended arrows; 
         FIG. 12  is a perspective view of one of the two holding plates of each contact module; 
         FIG. 13  is a side elevational view of the holding plate shown in  FIG. 12 ; 
         FIG. 14  is a cross sectional view taken along the XIV-XIV line shown in  FIG. 13 , viewed in the direction of the appended arrows; 
         FIG. 15  is a perspective view of the holding plate shown in  FIG. 12  before an insulating portion is molded integrally with the holding plate; 
         FIG. 16  is a side elevational view of the holding plate shown in  FIG. 15 ; 
         FIG. 17  is a cross sectional view taken along the XVII-XVII line shown in  FIG. 16 , viewed in the direction of the appended arrows; 
         FIG. 18  is a perspective view of the other of the two holding plates of each contact module; 
         FIG. 19  is a side elevational view of the holding plate shown in  FIG. 18 ; 
         FIG. 20  is a cross sectional view taken along the XX-XX line shown in  FIG. 19 , viewed in the direction of the appended arrows; 
         FIG. 21  is a perspective view of the holding plate shown in  FIG. 18  before an insulating portion is molded integrally with the holding plate; 
         FIG. 22  is a side elevational view of the holding plate shown in  FIG. 21 ; 
         FIG. 23  is a cross sectional view taken along the XXIII-XXIII line shown in  FIG. 22 , viewed in the direction of the appended arrows; 
         FIG. 24  is a rear perspective view of the plug shown in  FIGS. 1 and 2 ; 
         FIG. 25  is a plan view of the plug; 
         FIG. 26  is a cross sectional view taken along the XXVI-XXVI line shown in  FIG. 25 , viewed in the direction of the appended arrows; 
         FIG. 27  is a perspective view of a second embodiment of the connector according to the present invention which includes a receptacle and a plug, showing a state where the receptacle and the plug are disengaged from each other; 
         FIG. 28  is a perspective view of the receptacle and the plug of the second embodiment of the connector, showing a state where the receptacle and the plug are connected to each other; 
         FIG. 29  is an exploded front perspective view of the receptacle of the second embodiment of the connector, which is disassembled into three pieces: a contact module group, a retainer and a connecting rod, viewed obliquely from above; 
         FIG. 30  is an exploded rear perspective view of the contact module group, the retainer and the connecting rod that are shown in  FIG. 29 , viewed obliquely from above; 
         FIG. 31  is a front perspective view of the receptacle of the second embodiment of the connector, viewed obliquely from above; 
         FIG. 32  is a rear perspective view of the receptacle of the second embodiment of the connector, viewed obliquely from below; 
         FIG. 33  is an exploded front perspective view of the receptacle of the second embodiment of the connector, which is disassembled into five pieces: two side contact modules, a center contact module, a retainer and a connecting rod, viewed obliquely from above; 
         FIG. 34  is an exploded perspective view of each side contact module shown in  FIG. 33 ; 
         FIG. 35  is an exploded perspective view of each side contact module shown in  FIG. 33 ; 
         FIG. 36  is a perspective view of the conductive layer portion of the center holding plate of the side contact module shown in  FIG. 35  in a state before an insulating portion is molded integrally with the conductive layer portion, viewed obliquely from below; 
         FIG. 37  is a perspective view of the conductive layer portion of the right-side holding plate of the side contact module shown in  FIG. 35  in a state before an insulating portion is molded integrally with the conductive layer portion, viewed obliquely from the upper left side; 
         FIG. 38  is a perspective view of the conductive layer portion shown in  FIG. 36 , viewed obliquely from the upper right side; 
         FIG. 39  is a perspective view of the conductive layer portion shown in  FIG. 36 , viewed obliquely from the upper left side; 
         FIG. 40  is an enlarged front perspective view of an insulating portion shown in  FIG. 35 , viewed obliquely from the upper left side thereof; 
         FIG. 41  is an enlarged front perspective view of the insulating portion shown in  FIG. 40 , viewed obliquely from the upper right side thereof; 
         FIG. 42  is an enlarged perspective view of a contact (signal contact) of the second embodiment of the connector, viewed obliquely from the upper left side; 
         FIG. 43  is a front elevational view of the receptacle of the second embodiment of the connector; 
         FIG. 44  is a cross sectional view of the receptacle of the second embodiment of the connector taken along the XLIV-XLIV line shown in  FIG. 43 , viewed in the direction of the appended arrows; 
         FIG. 45  is a bottom view of the receptacle of the second embodiment of the connector; 
         FIG. 46  is a side elevational view of the receptacle of the second embodiment of the connector; 
         FIG. 47  is a cross sectional view taken along the XLVII-XLVII line shown in  FIG. 46 , viewed in the direction of the appended arrows; 
         FIG. 48  is a cross sectional view taken along the XLVIII-XLVIII line shown in  FIG. 46 , viewed in the direction of the appended arrows; 
         FIG. 49  is a cross sectional view taken along the XLIX-XLIX line shown in  FIG. 46 , viewed in the direction of the appended arrows; 
         FIG. 50  is an exploded perspective view of the plug of the second embodiment of the connector, which is disassembled into three pieces: a contact module group, a retainer and a connecting rod, viewed obliquely from above; 
         FIG. 51  is an exploded perspective view of each side contact module shown in  FIG. 50 ; 
         FIG. 52  is a side elevational view of the plug shown in  FIG. 51 ; 
         FIG. 53  is a cross sectional view taken along the LIII-LIII line shown in  FIG. 52 , viewed in the direction of the appended arrows; 
         FIG. 54  is a cross sectional view taken along the LIV-LIV line shown in  FIG. 52 , viewed in the direction of the appended arrows; 
         FIG. 55  is a rear elevational view of the plug of the second embodiment of the connector; 
         FIG. 56  is a cross sectional view taken along the LVI-LVI line shown in  FIG. 55 , viewed in the direction of the appended arrows; 
         FIG. 57  is a perspective view of a contact module group in a modified embodiment of the receptacle, viewed obliquely from the upper left side; 
         FIG. 58  is an exploded perspective view of the contact module group shown in  FIG. 57 , showing a state where the contact module group is partly disassembled; 
         FIG. 59  is a view similar to that of  FIG. 10 , showing a modified embodiment of each contact module of the receptacle in the first embodiment of the connector; 
         FIG. 60  is a view similar to that of  FIG. 10 , showing another modified embodiment of each contact module of the receptacle in the first embodiment of the connector; and 
         FIG. 61  is a view similar to that of  FIG. 12 , showing one of the two holding plates of another modified embodiment of each contact module of the receptacle in the first embodiment of the connector. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of a connector according to the present invention will be discussed below with reference to  FIGS. 1 through 26 . Note that forward, rearward, leftward and rightward directions of the connector (receptacle/plug) in the following descriptions are determined with reference to the double-headed arrows shown in  FIGS. 1 ,  2 ,  6 , etc. 
     As shown in  FIGS. 1 and 2 , the first embodiment of the connector  10  is for use in differential signaling and includes ground contacts and signal contacts. For instance, the connector  10  is applicable to information and communication apparatuses, broadcast and video apparatuses, control devices for factory automation systems, medical equipment, semi-conductor manufacturing equipment, semi-conductor testers, etc. The connector  10  is provided with a plug  20  and a receptacle  30  which are engageable with each other. The plug  20  and the receptacle  30  are electrically connected to each other when connected to each other as shown in  FIG. 1 . 
     As shown in  FIGS. 2 ,  24  through  26 , etc., the plug  20  is provided with an insulator  21  having a substantially U-shaped cross section, a large number of ground contact pins  25 A and  25 D, and a large number of signal contact pins  25 B,  25 C,  25 E and  25 F. The insulator  21  is made of a heat-resistant insulating synthetic resin by injection molding. The insulator  21  is provided in a bottom plate portion  22  thereof with a large number of through holes into which the ground contact pins  25 A and  25 D and the signal contact pins  25 B,  25 C,  25 E and  25 F are press-fitted. The ground contact pins  25 A and  25 D and the signal contact pins  25 B,  25 C,  25 E and  25 F are all identical in shape and arranged in a 10 by 6 matrix of contact pins, i.e., there are ten columns of contact pins arranged in the left-right direction. The ground contact pins  25 A and  25 D and the signal contact pins  25 B,  25 C,  25 E and  25 F are all stamp molded out of metal. More specifically, in order to manufacture each contact pin  25 A through  25 F of the receptacle  30 , a base material (e.g., phosphor bronze, beryllium copper, titanium copper, stainless steel, or Corson-copper alloy) is first coated with a base plating (e.g., nickel (Ni) plating) and subsequently with a finish plating (e.g., gold(Au) plating, tin(Sn)-copper(Cu) plating, or tin(Sn)-lead(Pb) plating). The rear ends of the ground contact pins  25 A and  25 D and the signal contact pins  25 B,  25 C,  25 E and  25 F are formed as contact ends connectable with the front ends of ground contacts  65 A and  65 D and signal contacts  65 B,  65 C,  65 E and  65 F of the plug  20 , respectively. The front ends of the ground contact pins  25 A and  25 D and the signal contact pins  25 B,  25 C,  25 E and  25 F are formed as press-fit terminals  27  which are driven (press-fitted) into through holes formed in a circuit board (not shown), respectively. The press-fit terminals  27  of the ground contact pins  25 A and  25 D are electrically connected to a ground pattern on the circuit board, and the press-fit terminals  27  of the signal contact pins  25 B,  25 C,  25 E and  25 F are electrically connected to a circuit pattern on the same circuit board. 
     The receptacle  30  will be discussed with reference mainly to  FIGS. 5 through 23 . The receptacle  30  is provided with ten contact modules  31  and a retainer  75  as relatively large elements of the receptacle  30 . 
     Each contact module  31  is provided with a pair of holding plates  33  and  34 , two of the ground contacts  65 A and  65 D and four of the signal contacts  65 B,  65 C,  65 E and  65 F. 
     As discussed below, the holding plate  33  shown in  FIGS. 12 through 14  is made of two resin members integrated into one piece. 
     A conductive layer portion (conductive layer)  35  serving as a base of the holding plate  33  is made by firstly being molded from an insulating synthetic resin into the shape shown in  FIGS. 15 through 17  with the use of molding dies (not shown), and subsequently being entirely plated so as to constitute a continuous conductive layer. 
     The method of applying such plating can be a so-called resin plating method or thin-film forming method (evaporation method, spattering, etc.). In the case of the resin plating method, firstly a molded member (molding) as a base of the conductive layer portion  35  is subjected to a grease removing process to remove grease from the outer surface of the molded member, a cleaning process to cleanse the outer surface of the molded member and thereafter a surface activating process to activate the outer surface of the molded member by catalysis. Thereafter, the molded member is given electroless plating, nickel strike plating, electric copper plating, nickel plating, and finish plating in that order. Alternatively, the conductive layer portion  35  can be molded by MID (molded interconnect device). 
     As shown in the drawings, the conductive layer portion  35  is provided on the inner surface thereof with two insulation recesses  36  and  37  which are open to both the front end surface and the bottom end surface of the conductive layer portion  35 . The conductive layer portion  35  is further provided, on two ribs formed on the inner surface of the conductive layer portion  35  which are respectively adjacent to the two insulation recesses  36  and  37 , with two opening recesses  39  and two end accommodation grooves (ground-contact holding grooves)  40  positioned immediately behind the two opening recesses  39 , respectively. The two opening recesses  39  are elongated rearward from the front end surface of the conductive layer portion  35 , and the two end accommodation grooves  40  are communicatively connected with the rear ends of the two opening recesses  39  and are greater in width than the two opening recesses  39 , respectively. The conductive layer portion  35  is further provided, on the inner surface thereof in the vicinity of the upper rear corner of the conductive layer portion  35 , with a circular-columnar-shaped engaging recess (bottomed hole)  41  and an elongated insertion hole (through-hole)  42 . 
     An insulating portion  43  made of an insulating synthetic resin is molded with the use of molding dies (not shown) to be integral with the inner surface of the conductive layer portion  35 , which is molded in the above described manner, so that the two insulation recesses  36  and  37  are provided (occupied) with the insulating portion  43  as shown in  FIGS. 12 through 14 . In addition, at the time of molding the insulating portion  43 , four opening recesses  44  which are identical in shape to the two opening recesses  39 , and associated four end accommodation grooves (contact holding grooves)  45  which are identical in shape to the two end accommodation grooves  40  and are communicatively connected with the rear ends of the four opening recesses  44  are formed in the insulating portion  43  in the two insulation recesses  36  and  37 , and a circular-columnar-shaped engaging recess  46  is formed in the insulating portion  43  in the vicinity of the bottom front corner of the conductive layer portion  35 . 
     The two holding plates  33  and  34  of each contact module  31  are substantially bilaterally symmetrical in shape; however, the holding plate  34  is partly different in shape from the holding plate  33 . 
     A conductive layer portion (conductive layer)  48  of the holding plate  34 , which is shown in  FIGS. 21 through 23 , is an element corresponding to the conductive layer portion  35  of the holding plate  33  (the material of the conductive layer portion  48  (including the plating material) is the same as that of the conductive layer portion  35 ). The conductive layer portion  48  is molded with the use of molding dies (not shown) in the same manner as the conductive layer portion  35 , and is provided with two insulation recesses  49  and  50 , two opening recesses  51  and two end accommodation grooves (ground-contact holding grooves)  52  which correspond to the two insulation recesses  36  and  37 , the two opening recesses  39  and the two end accommodation grooves  40  of the conductive layer portion  35  of the holding plate  33 , respectively. The two insulation recesses  49  and  50 , two opening recesses  51  and two end accommodation grooves  52 , and the two insulation recesses  36  and  37 , the two opening recesses  39  and the two end accommodation grooves  40  are bilaterally symmetrical to each other (mirror images to each other), respectively. Unlike the conductive layer portion  35 , the conductive layer portion  48  is further provided, on two ribs formed on the inner surface of the conductive layer portion  48  which are respectively adjacent to the two insulation recesses  49  and  50 , with two communication grooves (ground-contact holding grooves)  53 . One end (front ends) of each of the two communication grooves  53  is communicatively connected to each of the two end accommodation grooves  52 , respectively, and the other end of each of the two communication grooves  53  is open to the bottom end surface of the conductive layer portion  48 . Each communication groove  53  is narrower than each end accommodation groove  52 . Additionally, the conductive layer portion  48  is provided, in the vicinity of the upper rear corner of the conductive layer portion  48 , with an elongated insertion hole (through-hole)  42  which corresponds to the elongated insertion hole  42  of the conductive layer portion  35 , and is further provided, on the inner surface thereof in the vicinity of the upper rear corner of the conductive layer portion  48 , with an engaging projection  54  which is shaped to correspond to the circular-columnar-shaped engaging recess  41  of the conductive layer portion  35  to be engageable therein. An insulating portion  55  which corresponds to the insulating portion  43  of the holding plate  33  is molded with the use of molding dies (not shown) to be integral with the inner surface of the conductive layer portion  48  after the conductive layer portion  48  has been molded (the material of the insulating portion  55  and the method of molding thereof are the same as those of the insulating portion  43 ). Four opening recesses  56  and four end accommodation grooves (contact holding grooves)  57  which correspond to the four opening recesses  44  and the four end accommodation grooves  45 , respectively, are formed on the inner surface of the insulating portion  55 . In addition, the conductive layer portion  48  is further provided on the inner surface of the insulating portion  55  with four communication grooves (contact holding grooves)  58  which respectively extend from the four end accommodation grooves  57  to the bottom end of the insulating portion  55 . Each communication groove  58  is narrower than each end accommodation groove  57 . Additionally, an engaging projection  59  which is shaped to correspond to the engaging recess  46  of the insulating portion  43  of the holding plate  33  to be engageable therein is formed in the insulating portion  55  in the vicinity of the bottom front corner of the conductive layer portion  48 . 
     The side edges (upper and lower side edges) of each insulating portion  43  and  55  in each associated insulation recess ( 36 ,  37 ,  49  and  50 ) are covered by the associated conductive layer. 
     The two ground contacts  65 A and  65 D and the four signal contacts  65 B,  65 C,  65 E and  65 F, which are held between the two holding plates  33  and  34 , are stamp molded out of metal. More specifically, to make each contact  65 A through  65 F, a base material (e.g., phosphor bronze, beryllium copper, titanium copper, stainless steel, or Corson-copper alloy) is coated firstly with a base plating (e.g., nickel (Ni) plating), and subsequently with a finish plating (e.g., gold(Au) plating, tin(Sn)-copper(Cu) plating, or tin(Sn)-lead(Pb) plating). The side shapes of the ground contacts  65 A and  65 D and the signal contacts  65 B,  65 C,  65 E and  65 F are all in the shape of a substantially letter L and mutually different in length. The front ends and the lower ends of all the ground contacts  65 A and  65 D and the signal contacts  65 B,  65 C,  65 E and  65 F are formed as bifurcated resilient (spring) portions  66  and press-fit terminals  67 , respectively. 
     The ground contacts  65 A and  65 D, the signal contacts  65 B,  65 C,  65 E and  65 F and the two holding plates  33  and  34  are combined into one integral component in the following manner. 
     First of all, the bifurcated resilient portions  66  of the ground contacts  65 A and  65 D are respectively accommodated in the two end accommodation grooves  52 , and middle portions (conductive positions) of the ground contacts  65 A and  65 D between the bifurcated resilient portions  66  and the press-fit terminals  67  thereof are respectively held by the two communication grooves  53  (with projections (not shown) which are formed on the aforementioned conductive portions of the ground contacts  65 A and  65 D pressing against side surfaces of the two communication grooves  53 , respectively ) so that the press-fit terminals  67  of the ground contacts  65 A and  65 D project downward from the bottom end of the holding plate  34 . At the same time, the bifurcated resilient portions  66  of the signal contacts  65 B,  65 C,  65 E and  65 F are respectively accommodated in the four end accommodation grooves  57 , and middle portions (conductive positions) of the signal contacts  65 B,  65 C,  65 E and  65 F between the bifurcated resilient portions  66  and the press-fit terminals  67  thereof are respectively held by the four communication grooves  58  (with projections (not shown) which are formed on the aforementioned conductive portions of the signal contacts  65 B,  65 C,  65 E and  65 F pressing against side surfaces of the four communication grooves  58 , respectively ) so that the press-fit terminals  67  of the signal contacts  65 B,  65 C,  65 E and  65 F project downward from the bottom end of the holding plate  34 . 
     Subsequently, the inner surface of the holding plate  33  is combined with the inner surface of the holding plate  34  to which the ground contacts  65 A and  65 D and the signal contacts  65 B,  65 C,  65 E and  65 F have been installed while the engaging projections  54  and  59  of the holding plate  34  are fitted into the engaging recesses  41  and  46 , respectively. Thereupon, the bifurcated resilient portions  66  of the ground contacts  65 A and  65 D are accommodated in the two end accommodation grooves  40  of the conductive layer portion  35  of the holding plate  33 , respectively, the bifurcated resilient portions  66  of the signal contacts  65 B,  65 C,  65 E and  65 F are accommodated in the four end accommodation grooves  45  of the conductive layer portion  35  of the holding plate  33 , respectively, the inner surfaces of the conductive layer portions  35  and  48  come in intimate contact with each other, and the inner surfaces of the insulating portions  43  and  55  come in intimate contact with each other. In addition, the two opening recesses  39  of the holding plate  33  and the two opening recesses  51  of the holding plate  34 , which face each other, form two engaging holes  69  at the front end of the contact module  31 , and the two opening recesses  44  of the holding plate  33  and the two opening recesses  56  of the holding plate  34 , which face each other, form two engaging holes  70  at the front end of the contact module  31  (see  FIGS. 2 ,  3  and  6 ). 
     Ten of the contact modules  31 , each of which is assembled in the above described manner, are arranged in layers in the left-right direction as shown in  FIG. 3  to constitute a contact module group  72 . Thereupon, the elongated insertion holes  42  of the ten contact modules  31  are aligned, so that a connecting rod  73  (see  FIG. 3 ) made of synthetic resin and having the same cross sectional shape as each elongated insertion hole  42  is inserted into each elongated insertion hole  42 . Additionally, the retainer  75  that is shaped as a rectangular frame is fitted on the outer peripheral surface of the front end of the contact module group  72 . Thereupon, the inner peripheral surface of the retainer  75  comes into intimate contact with the outer peripheral surface of the front end of the contact module group  72 , which makes each contact module  31  and the retainer  75  integral with each other. 
     After the receptacle  30  is assembled in the above described manner, the press-fit terminals  67  of the ground contacts  65 A and  65 D and the signal contacts  65 B,  65 C,  65 E and  65 F are driven (press-fitted) into the through holes formed in the aforementioned circuit board (not shown), respectively. Thereupon, the press-fit terminals  67  of the ground contacts  65 A and  65 D are connected to a ground pattern on this circuit board, and the press-fit terminals  67  of the signal contacts  65 B,  65 C,  65 E and  65 F are connected to a circuit pattern on this circuit board. 
     When the receptacle  30  and the plug  20 , each of which having the above described structure, are connected to each other as shown in  FIG. 1  from an disengaged state shown in  FIG. 2 , terminal contacts  26  of the ground contact pins  25 A and  25 D are inserted into the associated engaging holes  69 , respectively, that are formed on the front surface of the receptacle  30 , so that the terminal contacts  26  of the ground contact pins  25 A and  25 D enter the spaces formed between the associated end accommodation grooves  52  of the holding plate  34  and the associated end accommodation grooves  40  of the holding plate  33 , respectively, through the engaging holes  69  as shown in  FIG. 5 , while the terminal contacts  26  of the signal contact pins  25 B,  25 C,  25 E and  25 F are inserted into the associated engaging holes  70 , respectively, that are formed on the front surface of the receptacle  30 , so that the terminal contacts  26  of the signal contact pins  25 B,  25 C,  25 E and  25 F enter the spaces formed between the associated end accommodation grooves  57  of the holding plate  34  and the associated end accommodation grooves  45  of the holding plate  33 , respectively, through the engaging holes  70  as shown in  FIG. 5 . Thereupon, the terminal contacts  26  of the ground contact pins  25 A and  25 D enter the bifurcated resilient portions  66  of the ground contacts  65 A and  65 D while resiliently deforming the same bifurcated resilient portions  66  to establish connections therewith, respectively, while the terminal contacts  26  of the signal contact pins  25 B,  25 C,  25 E and  25 F enter the bifurcated resilient portions  66  of the signal contacts  65 B,  65 C,  65 E and  65 F while resiliently deforming the same bifurcated resilient portions  66  to establish connections therewith, respectively. 
     Therefore, the ground contact pins  25 A and  25 D of the plug  20  are electrically connected to a ground pattern formed on a circuit board on the receptacle  30  side, and the ground contacts  65 A and  65 D of the receptacle  30  are electrically connected to a ground pattern formed on a circuit board on the plug  20  side. Similarly, the signal contact pins  25 B,  25 C,  25 E and  25 F of the plug  20  are electrically connected to a circuit pattern formed on the circuit board on the receptacle  30  side, and the signal contacts  65 B,  65 C,  65 E and  65 F of the receptacle  30  are electrically connected to a circuit pattern formed on the circuit board on the plug  20  side. 
     In the above illustrated first embodiment of the connector, the peripheries of the signal contacts  65 B,  65 C,  65 E and  65 F are totally covered by the insulating portions  43  and  55 ; moreover, the peripheries of the insulating portions  43  and  55  are totally covered by the insulation recesses  36  and  37  and the insulation recesses  49  and  50  that are formed on the conductive layer portions  35  and  48 , respectively. Due to this structure, the signal contacts  65 B,  65 C,  65 E and  65 F are securely shielded by the inner surfaces of the insulation recesses  36 ,  37 ,  49  and  50  (which makes it possible to prevent the signal contacts  65 B,  65 C,  65 E and  65 F from both picking up noise from the outside and leaking noise caused by themselves during signal transmission in an extremely effective manner). Accordingly, the connector  10  which has superior shielding characteristics and makes a high-speed signal transmission possible is achieved. 
     Moreover, the surface areas of the conductive layer portions  35  and  48  are large because the conductive layer portions  35  and  48  are formed over the entire surface of the holding plates  33  and  34  and because a surface (inner surface) of the conductive layer portion  35  of the holding plate  33  which faces the other holding plate  34  is provided with recesses (the insulation recesses  36  and  37 ) and a surface (inner surface) of the conductive layer portion  48  of the holding plate  34  which faces the other holding plate  33  is also provided with recesses (the insulation recesses  49  and  50 ). 
     Furthermore, the connector can be easily produced with no decrease in productivity even if the holding plates  33  and  34  (conductive layer portions and insulating portions) that are elements of each contact module  31  include complicated shapes such as the insulation recesses and the contact holding grooves because each holding plate  33  and  34  is a molded member made of synthetic resin. 
     Furthermore, since no shielding member made of metal is embedded in each contact module  31 , the number of elements of the connector can be reduced as compared with conventional contacts; moreover, each contact module  31  can be miniaturized in the case where the present embodiment of the connector is provided therein with the same number of contacts as a conventional contact. 
     Furthermore, since the contact modules  31  are joined together by the retainer  75  to be made as an integral member instead of using a housing that was an indispensable element of a conventional connector, in this respect also it can be said that the present embodiment of the connector is easy to produce (assemble). 
     In addition, since the ground contacts  65 A and  65 D and the signal contacts signal contacts  65 B,  65 C,  65 E and  65 F are held between the end accommodation grooves  40  and  45 , which are recessed in the holding plate  33 , and the end accommodation grooves  52 , the communication grooves  53 , the end accommodation grooves  57  and the communication grooves  58 , which are recessed in the holding plate  34 , the ground contacts  65 A and  65 D and the signal contacts signal contacts  65 B,  65 C,  65 E and  65 F can be firmly held and retained by the holding plates  33  and  34  and easily produced with a high degree of productivity. 
     A second embodiment of the connector according to the present invention will be discussed below with reference to  FIGS. 27 through 56 . Note that forward, rearward, leftward and rightward directions of the connector (receptacle/plug) in the following descriptions are determined with reference to the double-headed arrows shown in  FIGS. 27 ,  28 ,  30 , etc. 
     As shown in  FIGS. 27 and 28 , the second embodiment of the connector  100  is for use in differential signaling and includes ground contacts and signal contacts. For instance, the connector  100  is applicable to information and communication apparatuses, broadcast and video apparatuses, control devices for factory automation systems, medical equipment, semi-conductor manufacturing equipment, semi-conductor testers, etc., similar to the above-described first embodiment of the connector  10 . The connector  100  is provided with a plug  120  and a receptacle  130  which are engageable with each other. The plug  120  and the receptacle  130  are electrically connected to each other when connected to each other as shown in  FIG. 28 . 
     Firstly, the receptacle  130  will be discussed with reference mainly to  FIGS. 29 through 49 . 
     The receptacle  130  is provided with three contact modules (two contact modules  131  and a contact module  132 ), a connecting bar  173  and a retainer  175  as relatively large elements of the receptacle  130 . 
     First of all, the structures of the two contact modules  131  will be discussed hereinafter. 
     Among the three contact modules  131  and  132 , each of the two contact modules  131  that are positioned on the laterally opposite sides of the contact module  132  is provided with two holding plates (side holding plates)  133  and  134 , a holding plate (center holding plate)  138  positioned between the two holding plates  133  and  134 , four ground contacts  165 A and  165 D and eight signal contacts  165 B,  165 C,  165 E and  165 F. 
     As shown in  FIGS. 34 through 41 , each of the holding plates  133 ,  134  and  138  is made of two resin members integrated into one member. 
     A conductive layer portion (conductive layer)  135  serving as a base of the holding plate  133  in each contact module  131  is made by firstly being molded of an insulating synthetic resin into the shape shown in  FIG. 37  with the use of molding dies (not shown) and subsequently being entirely plated so as to constitute a continuous conductive layer. The method of applying such plating can be a so-called resin plating method or a thin-film forming method (evaporation method, spattering, etc.). In the case of the resin plating method, firstly a molded member (molding) serving as a substrate of the conductive layer portion  135  is subjected to firstly a grease removing process to remove grease from the outer surface of the molded member, a cleaning process to cleanse the outer surface of the molded member and thereafter a surface activating process to activate the outer surface of the molded member by catalysis. Thereafter, electroless plating, nickel strike plating, electric copper plating, nickel plating, and finish plating are applied to the molded member, in that order. Alternatively, the conductive layer portion  135  can be molded by a MID (molded interconnect device). 
     As shown in the drawings, the conductive layer portion  135  is provided on the left side thereof with two insulation recesses  136  and  137  which are open to both the front end surface and the bottom end surface of the conductive layer portion  135 . The conductive layer portion  135  is further provided, on two ribs formed on the left side of the conductive layer portion  135  which are respectively adjacent to the two insulation recesses  136  and  137 , with two opening recesses  139 , two end accommodation grooves (ground-contact holding grooves)  140  and two communication grooves (ground-contact holding grooves)  141 , respectively. The two opening recesses  139  are elongated rearward from the front end surface of the conductive layer portion  135 , the two end accommodation grooves  140  are communicatively connected to the rear ends of the two opening recesses  139  and are greater in width than the two opening recesses  139 , respectively. The two communication grooves  141  extend from the two end accommodation grooves  140  to the rear ends of the aforementioned two ribs, respectively. Additionally, the conductive layer portion  135  is further provided on the left side thereof with four substantially circular-columnar-shaped engaging recesses  135 A and two circular-columnar-shaped engaging pins  135 B. The conductive layer portion  135  is further provided, at the upper front end and the upper rear end of the conductive layer portion  135 , with a front engaging groove  135 C and a rear engaging groove  135 D, respectively. The conductive layer portion  135  is further provided, on the right side thereof in the vicinity of the bottom front corner of the conductive layer portion  135 , with a key groove  135 E having a rectangular shape as viewed from the right side of the conductive layer portion  135 . As shown in  FIGS. 47 and 48 , the depth of each key groove  135 E gradually increases in the direction from the bottom upwards. Namely, the bottom surface of the key groove  135 E (a portion of the right side of the conductive layer portion  135  in the key groove  125 E) is formed as a beveled surface. An upper edge  135 F and a lower edge  135 G of the front half of the right side of the conductive layer portion  135  are chamfered as shown in  FIGS. 48 and 49 . 
     An insulating portion  143  made of an insulating synthetic resin is fitted into the left side of the conductive layer portion  135 , which is molded in the above described manner as shown in  FIG. 34 , etc. The insulating portion  143  is molded with the use of molding dies (not shown) separately from the conductive layer portion  135 . As shown in  FIG. 40 , the insulating portion  143  is provided on the left side thereof with four opening recesses  144 , associated four end accommodation grooves (contact holding grooves)  145 , four communication grooves (contact holding grooves)  142  and two communication grooves (contact holding grooves)  146 . The four opening recesses  144  are identical in shape to the two opening recesses  139 . The four end accommodation grooves  145  are identical in shape to the two end accommodation grooves  140  and communicatively connected to the rear ends of the four opening recesses  144 . The four communication grooves  142  extend from the rear ends of the of the four end accommodation grooves  145  to the bottom end of the insulating portion  143 , respectively. The insulating portion  143  is provided, on surfaces of on the right side thereof which face the associated conductive layer portion  135 , with two engaging recesses  143 A (see  FIG. 41 ) in which the engaging pins  135 B of the associated conductive layer portion  135  can be engaged, respectively. The insulating portion  143  that has the above described structure becomes integral with the conductive layer portion  135  by fitting a substantially upper half portion of the insulating portion  143  into the two insulation recesses  136  and  137  of the conductive layer portion  135  while fitting the two engaging pins  135 B into the two engaging recesses  143 A, respectively. 
     The two holding plates  133  and  134  of each contact module  131  are substantially bilaterally symmetrical in shape; however, the holding plate  134  is partly different in shape from the holding plate  133 . 
     A conductive layer portion (conductive layer)  148  of the holding plate  134  is an element corresponding to the conductive layer portion  135  of the holding plate  133  (the material of the conductive layer portion  148  (including the material of plating) is the same as that of the conductive layer portion  135 ). The conductive layer portion  148  is molded with the use of molding dies (not shown) in the same manner as the conductive layer portion  135 . The conductive layer portion  148  is provided, on the right side thereof at positions thereon which correspond to the positions of the two insulation recesses  136  and  137 , with two insulation recesses  149  and  150 . The two insulation recesses  149  and  150  and the two insulation recesses  136  and  137  are bilaterally symmetrical to each other (are mirror images to each other), respectively. The conductive layer portion  148  is further provided, on the right side thereof at positions thereon which correspond to the positions of the two opening recesses  139 , the two end accommodation grooves  140  and the two communication grooves  141 , with two opening-forming projecting portions  151 , intermediate recessed portions  152  and two pressure ribs  153 , respectively. One of the two pressure ribs  153  projects from the surface of a rib on the right side of the conductive layer portion  148  between the two insulation recesses  149  and  150 , while the other of the two pressure ribs  153  projects from a portion on the right side of the conductive layer portion  148  directly below the insulation recess  150 . Although none of the accompanying drawings shows the right side of the conductive layer portion  148 , the two insulation recesses  149  and  150 , the two opening-forming projecting portions  151 , the intermediate recessed portions  152  and the two pressure ribs  153 , which are formed on the right side of the conductive layer portion  148 , are identical in shape and size to those formed on the right side of a conductive layer portion (conductive layer)  160  serving as a base of the holding plate  138  in each contact module  131 . Accordingly,  FIGS. 36 and 38  can be alternatively referred to with regard to the elements formed on the right side of the conductive layer portion  148 , which show the right side of the conductive layer portion  160 . 
     The conductive layer portion  148  is provided with a front engaging groove  148 C and a rear engaging groove  148 D which correspond to the engaging groove  135 C and the rear engaging groove  135 D of the conductive layer portion  135 , respectively. The conductive layer portion  148  is provided, on the right side at positions thereon which correspond to the positions of the four engaging recesses  135 A, with four engaging projections  148 A (see  FIGS. 34 and 35 ), respectively, and is further provided, on the right side of the conductive layer portion  148  at positions thereon which correspond to the positions of the two engaging pins  135 B, with two engaging pins  148 B having the same shapes as the two engaging pins  135 B, respectively (see  FIG. 35 ). The conductive layer portion  148  is provided, on the left side thereof in the vicinity of the bottom front corner of the conductive layer portion  148 , with a key groove  148 E which is bilaterally symmetrical shaped with respect to the key groove  135 E. An upper edge  148 F and a lower edge  148 G of the front half of the left side of the conductive layer portion  148  are chamfered as shown in  FIGS. 33 ,  48  and  49 . 
     An insulating portion  155  made of an insulating synthetic resin is fitted into the right side of the conductive layer portion  148 . The insulating portion  155  is molded with the use of molding dies (not shown) separately from the conductive layer portion  148  (the material of the insulating portion  155  and the method of molding thereof are the same as those of the insulating portion  143 ). 
     The insulating portion  155  is provided on the right side thereof with four opening recesses  156  (see  FIGS. 34 and 35 ) which correspond to the four opening recesses  144 , respectively, that are formed on the insulating portion  143  of the holding plate  133 . The insulating portion  155  is further provided on the right side thereof with associated four end accommodation grooves (not shown) which correspond to the four end accommodation grooves  145 , respectively. On the other hand, although no communication grooves corresponding to the communication grooves  142  of the insulating portion  143  are formed on the insulating portion  155 , the insulating portion  155  is provided, on portions thereof which face the four communication grooves  142 , with four pressure ribs  154  which are substantially identical in side shape to the four communication grooves  142 , respectively (see  FIG. 35 ). The insulating portion  155  is further provided on the left side thereof with two engaging recesses  155 A which correspond to the two engaging recesses  143 A of the insulating portion  143 , respectively (see  FIG. 35 ). 
     The shape of the conductive layer portion  160  of the holding plate  138 , which is held between the holding plates  133  and  134 , is shown in  FIGS. 36 ,  38  and  39 . The material of the conductive layer portion  160  (including the material of plating) is the same as those of the conductive layer portions  135  and  148 . The conductive layer portion  160  is molded with the use of molding dies (not shown) in the same manner as the conductive layer portion  135  and  148 . 
     As shown in  FIG. 38 , the conductive layer portion  160  is provided on the right side thereof with two insulation recesses  149  and  150 , two opening-forming projecting portions  151 , intermediate recessed portions  152  and two pressure ribs  153 , which are identical in shape and size to those formed on the conductive layer portion  148 . One of the two pressure ribs  153  projects from the surface of a rib on the right side of the conductive layer portion  160  between the two insulation recesses  149  and  150 , while the other of the two pressure ribs  153  projects from a portion on the right side of the conductive layer portion  160  directly below the insulation recess  150  (a portion on the right side of the conductive layer portion  160  in the vicinity of one of four engaging projections  160 A 1  that project from the right side of the conductive layer portion  160 ). The conductive layer portion  160  is further provided, at positions on the right side thereon which face the positions of the four engaging recesses  135 A, with four engaging projections  160 A 1  engageable in the four engaging recesses  135 A, respectively, and is further provided, at positions on the right side thereon which face the positions of the two engaging pins  135 B, with two engaging pins  160 B having the same shapes as the two engaging pins  135 B, respectively. As shown in  FIG. 39 , the conductive layer portion  160  is provided on the left side thereof with two insulation recesses  136  and  137 , two opening recesses  139 , two end accommodation grooves  140  and two communication grooves  141 . Additionally, the conductive layer portion  160  is provided, at positions on the left side thereof which correspond to the positions of the four engaging projections  160 A 1 , with four engaging recesses  160 A 2 , respectively, and is further provided, at positions on the left side of the conductive layer portion  160  which correspond to the positions of the two engaging pins  143 A, with two engaging pins  160 B, respectively. The conductive layer portion  160  is provided, on the left side thereof at the upper front end of the conductive layer portion  160 , with a front engaging groove  160 C, and is provided, at the upper rear end of the conductive layer portion  160 , with a rear engaging groove  160 D. As shown in  FIG. 36 , the conductive layer portion  160  is provided on the bottom surface thereof with a locking lug  160 H. 
     After the conductive layer portion  160  is molded, the insulating portions  155  and  143 , which are molded separately from the conductive layer portion  160 , are fitted into the right and left sides of the conductive layer portion  160  to become integral therewith, which completes the holding plate  138 . 
     Note that the side edges (upper and lower side edges) of each insulating portion  143  and  155  in each associated insulation recess ( 136 ,  137 ,  149  and  150 ) are covered by the associated conductive layer. 
     A set of six contacts are held between the insulating portion  143  of the holding plate  133  and the insulating portion  155  of the holding plate  138 , and another set of six contacts are held between the insulating portion  155  of the holding plate  134  and the insulating portion  143  of the holding plate  138 . Each of these two sets of contacts is composed of two ground contacts  165 A and  165 D and four signal contacts  165 B,  165 C,  165 E and  165 F. The two ground contacts  165 A and  165 D and the four signal contacts  165 B,  165 C,  165 E and  165 F are stamp molded out of metal. More specifically, to make each contact  165 A through  165 F, a base material (e.g., phosphor bronze, beryllium copper, titanium copper, stainless steel, or Corson-copper alloy) is coated firstly with a base plating (e.g., nickel (Ni) plating) and subsequently with a finish plating (e.g., gold(Au) plating, tin(Sn)-copper(Cu) plating, or tin(Sn)-lead(Pb) plating). The side shapes of the ground contacts  165 A and  165 D and the signal contacts  165 B,  165 C,  165 E and  165 F are all in the shape of a substantially letter L and mutually different in length. The front ends and the lower ends of all the ground contacts  165 A and  165 D and the signal contacts  165 B,  165 C,  165 E and  165 F are formed as bifurcated resilient (spring) portions  166  and press-fit terminals  167 , respectively. 
     One set of six contacts (the ground contacts  165 A and  165 D, and the signal contacts  165 B,  165 C,  165 E and  165 F) (hereinafter referred to as a first set of contacts), another set of six contacts (the ground contacts  165 A and  165 D, and the signal contacts  165 B,  165 C,  165 E and  165 F) (hereinafter referred to as a second set of contacts) and the two of the holding plates  133 ,  134  and  138  are combined into one with these two sets of six contacts being held between the two holding plates  133  and  138  and between the two holding plates  134  and  138 , respectively, in the following manner. 
     Firstly, the bifurcated resilient portions  166  of the ground contacts  165 A and  165 D of the first set of contacts are accommodated in the two end accommodation grooves  140  of the conductive layer portion  135  of the holding plate  133 , respectively, and middle portions (conductive positions) of the ground contacts  165 A and  165 D of the first set of contacts between the bifurcated resilient portions  166  and the press-fit terminals  167  thereof are respectively held by the two communication grooves  141  of the conductive layer portion  135  of the holding plate  133  and the communication grooves  146  of the insulating portion  143  so that the press-fit terminals  167  of the ground contacts  165 A and  165 D of the first set of contacts project downward from the bottom end of the holding plate  133 . On the other hand, the bifurcated resilient portions  166  of the ground contacts  165 A and  165 D of the second set of contacts are accommodated in the two end accommodation grooves  140  of the conductive layer portion  160  of the holding plate  138 , respectively, and middle portions (conductive positions) of the ground contacts  165 A and  165 D of the second set of contacts between the bifurcated resilient portions  166  and the press-fit terminals  167  thereof are respectively held by the two communication grooves  141  of the conductive layer portion  160  of the holding plate  138  so that the press-fit terminals  167  of the ground contacts  165 A and  165 D of the second set of contacts project downward from the bottom end of the holding plate  138 . At the same time, the bifurcated resilient portions  166  of the signal contacts  165 B,  165 C,  165 E and  165 F of the first set of contacts are accommodated in the four end accommodation grooves  145  of the insulating portion  143  of the holding plate  133 , respectively, and middle portions (conductive positions) of the signal contacts  165 B,  165 C,  165 E and  165 F of the first set of contacts between the bifurcated resilient portions  166  and the press-fit terminals  167  thereof are respectively held by the two communication grooves  142  of the insulating portion  143  of the holding plate  133  so that the press-fit terminals  167  of the signal contacts  165 B,  165 C,  165 E and  165 F of the first set of contacts project downward from the bottom end of the holding plate  133 . On the other hand, the bifurcated resilient portions  166  of the signal contacts  165 B,  165 C,  165 E and  165 F of the second set of contacts are accommodated in the four end accommodation grooves  145  of the insulating portion  143  of the holding plate  138 , respectively, and middle portions (conductive positions) of the signal contacts  165 B,  165 C,  165 E and  165 F of the second set of contacts between the bifurcated resilient portions  166  and the press-fit terminals  167  thereof are respectively held by the two communication grooves  142  of the insulating portion  143  of the holding plate  138  so that the press-fit terminals  167  of the signal contacts  165 B,  165 C,  165 E and  165 F of the second set of contacts project downward from the bottom end of the holding plate  138 . 
     Furthermore, the right side of the holding plate  138  (which includes the conductive layer portion  160  and the insulating portion  155 ) is combined with the left side of the holding plate  133  (which includes the conductive layer portion  135  and the insulating portion  143 ) to which the ground contacts  165 A and  165 D and the signal contacts  165 B,  165 C,  165 E and  165 F have been installed, and the right side of the holding plate  134  (which includes the conductive layer portion  148  and the insulating portion  155 ) is combined with the left side of the holding plate  138  (which includes the conductive layer portion  160  and the insulating portion  143 ). At this time, the four engaging projections  160 A 1  of the conductive layer portion  160  are fitted into the four engaging recesses  135 A of the conductive layer portion  135 , respectively, and the four engaging projections  148 A of the conductive layer portion  148  are fitted into the four engaging recesses  160 A 2  of the conductive layer portion  160 , respectively. Thereupon, the right side of the insulating portion  155  of the holding plate  134  comes into intimate contact with the left side of the insulating portion  143  of the holding plate  138 , the right side of the insulating portion  155  of the holding plate  138  comes into intimate contact with the left side of the insulating portion  143  of the holding plate  133 , the right side of the conductive layer portion  148  comes into intimate contact with the left side of the conductive layer portion  160 , and the right side of the conductive layer portion  160  comes into intimate contact with the left side of the conductive layer portion  135 . Additionally, the four opening recesses  144  of each insulating portion  143  and the four opening recesses  156  of the associated insulating portion  155 , which face each other, form four engaging holes  169  at the front ends of the insulating portions  143  and  155  (see  FIGS. 29 and 33 ). Likewise, the two opening recesses  139  of the conductive layer portion  135  and the two opening-forming projecting portions  151  of the conductive layer portion  160  (with the two opening-forming projecting portions  151  blocking the left-side openings of the two opening recesses  139 ) form two engaging holes  170  at the front end of the contact module  131  (specifically at the front ends of the conductive layer portions  135  and  160 ), and the two opening recesses  139  of the conductive layer portion  160  and the two opening-forming projecting portions  151  of the conductive layer portion  148  form two engaging holes  170  at the front end of the contact module  131  (specifically at the front ends of the conductive layer portions  148  and  160 ) (see  FIGS. 29 and 33 ). Additionally, as shown in  FIG. 44 , the bifurcated resilient portions  166  of the signal contacts  165 B,  165 C,  165 E and  165 F of the first set of contacts are respectively accommodated in the spaces formed between the four end accommodation grooves  145  on the insulating portion  143  of the holding plate  133  and the aforementioned four end accommodation grooves (not shown) on the insulating portion  155  of the holding plate  138 , respectively. Likewise, the bifurcated resilient portions  166  of the signal contacts  165 B,  165 C,  165 E and  165 F of the second set of contacts are respectively accommodated in the spaces formed between the four end accommodation grooves  145  on the insulating portion  143  of the holding plate  138  and the aforementioned four end accommodation grooves (not shown) on the insulating portion  155  of the holding plate  134 , respectively. Additionally, the upper pressure rib  153  (narrower in width than the grand contact  165 D) on the right side of the conductive layer portion  160  of each contact module  131  is in press contact with the left side of the ground contact  165 D of the first set of contacts while the right side of this ground contact  165 D is in press contact with the bottom surface (left side) of the associated communication recess (contact holding recess)  141  of the conductive layer portion  135 . Likewise, the lower pressure rib  153  on the right side of the conductive layer portion  160  of each contact module  131  is in press contact with the left side of the ground contact  165 A of the first set of contacts while the right side of the same ground contact  165 A is in press contact with the bottom surface of the associated communication recess  141  of the conductive layer portion  135 . Similarly, the upper pressure rib  153  on the right side of the conductive layer portion  148  of each contact module  131  is in press contact with the left side of the ground contact  165 D of the second set of contacts while the right side of the same ground contact  165 D is in press contact with the bottom surface of the associated communication recess (contact holding recess)  141  of the conductive layer portion  160 . Likewise, the lower pressure rib  153  on the right side of the conductive layer portion  148  of each contact module  131  is in press contact with the left side of the ground contact  165 A of the second set of contacts while the right side of the same ground contact  165 A is in press contact with the bottom surface of the associated communication recess  141  of the conductive layer portion  160 . Accordingly, electrical continuity is securely established between the ground contacts  165 A and  165 D of the first set of contacts and the conductive layer portions  135  and  160  while electrical continuity is securely established between the ground contacts  165 A and  165 D of the second set of contacts and the conductive layer portions  148  and  160 , respectively. Moreover, the signal contacts  165 B,  165 C,  165 E and  165 F of the first set of contacts are held between the bottom surfaces (left sides) of the communication grooves (contact holding grooves)  142  of the insulating portion  143  of the holding plate  133  and the four pressure ribs  154  on the right side of the insulating portion  155  of the holding plate  138 , respectively, to be in contact with both the bottom surfaces (left sides) of the same communication grooves (contact holding grooves)  142  and the same four pressure ribs  154 , and the signal contacts  165 B,  165 C,  165 E and  165 F of the second set of contacts are held between the bottom surfaces (left sides) of the communication grooves (contact holding grooves)  142  of the insulating portion  143  of the holding plate  138  and the four pressure ribs  154  on the right side of the insulating portion  155  of the holding plate  134 , respectively, to be in contact with both the bottom surfaces (left sides) of the same communication grooves (contact holding grooves)  142  and the same four pressure ribs  154 . 
     Hence, each of the two contact modules  131  (the right contact module  131  and the left contact module  131 ) are assembled in the above described manner. 
     The structures of the contact module  132 , which is held between the two contact modules  131 , will be discussed hereinafter. 
     The contact module  132  is assembled by joining the left side of the holding plate  133  (which includes the conductive layer portion  135  and the insulating portion  143 ) and the right side of the holding plate  134  (which includes the conductive layer portion  148  and the insulating portion  155 ) to each other with a set of six contacts (the two grand contacts  165 A and  165 D and the four signal contacts  165 B,  165 C,  165 E and  165 F) being held between the holding plates  133  and  134 . Upon the contact module  132  being assembled in this manner, the four engaging holes  169  and the two engaging holes  170  are formed at the front end of the contact module  132  (see  FIGS. 29 and 33 ). 
     The manner of assembling the contact module  132  is similar to the manner of assembling each contact module  131 . Namely, in the first place, the bifurcated resilient portions  166  of the ground contacts  165 A and  165 D are accommodated in the two end accommodation grooves  140  of the conductive layer portion  135  of the holding plate  133 , respectively, and middle portions (conductive positions) of the ground contacts  165 A and  165 D between the bifurcated resilient portions  166  and the press-fit terminals  167  thereof are respectively held by the two communication grooves  141  of the conductive layer portion  135  of the holding plate  133  and the communication grooves  146  of the insulating portion  143  so that the press-fit terminals  167  of the ground contacts  165 A and  165 D project downward from the bottom end of the conductive layer portion  135  of the holding plate  133 . Additionally, the bifurcated resilient portions  166  of the signal contacts  165 B,  165 C,  165 E and  165 F are accommodated in the four end accommodation grooves  145  of the insulating portion  143  of the holding plate  133 , respectively, and middle portions (conductive positions) of the signal contacts  165 B,  165 C,  165 E and  165 F between the bifurcated resilient portions  166  and the press-fit terminals  167  thereof are respectively held by the two communication grooves  142  of the insulating portion  143  of the holding plate  133  so that the press-fit terminals  167  of the signal contacts  165 B,  165 C,  165 E and  165 F project downward from the bottom end of the conductive layer portion  135  of the holding plate  133 . Furthermore, the right side of the holding plate  134  (which includes the conductive layer portion  148  and the insulating portion  155 ) is combined with the left side of the holding plate  133  (which includes the conductive layer portion  135  and the insulating portion  143 ) to which the ground contacts  165 A and  165 D and the signal contacts  165 B,  165 C,  165 E and  165 F have been installed, and the four engaging projections  148 A of the conductive layer portion  148  are fitted into the four engaging recesses  135 A of the conductive layer portion  135 , respectively. Thereupon, the upper pressure rib  153  on the right side of the conductive layer portion  148  of the contact module  132  is in press contact with the left side of the ground contact  165 D while the right side of the same ground contact  165 D is in press contact with the bottom surface of the associated communication recess (contact holding recess)  141  of the conductive layer portion  135 . Likewise, the lower pressure rib  153  on the right side of the conductive layer portion  148  of the contact module  132  is in press contact with the left side of the ground contact  165 A while the right side of the same ground contact  165 A is in press contact with the bottom surface of the associated communication recess  141  of the conductive layer portion  135 . Moreover, the signal contacts  165 B,  165 C,  165 E and  165 F are held between the bottom surfaces (left sides) of the communication grooves (contact holding grooves)  142  of the insulating portion  143  of the holding plate  133  and the four pressure ribs  154  on the right side of the insulating portion  155  of the holding plate  134 , respectively. 
     Two contact modules  131  and one contact module  132 , each of which is assembled in the above described manner, are arranged in layers in the left-right direction as shown in  FIGS. 29 and 30  to constitute a contact module group  172 . The connecting bar  173  and the retainer  175  are the elements which prevent the two contact modules  131  and the contact module  132  from separating from each other. 
     The connecting bar  173  is an element with a substantially L-shaped cross section which is substantially identical in length (in the left-right direction) to the contact module group  172 , and is provided with an insertion jutting portion  174 A and a contacting portion  174 B. 
     The retainer  175  is an element having a substantially U-shaped cross section. The retainer  175  is provided with a vertical side  176 , an upper side  177  and a lower side  178 . The upper side  177  and the lower side  178  extend rearward from the upper and lower ends of the vertical side  176 , respectively. 
     The vertical side  176  is provided with five columns of through holes  179  arranged in the left-right direction, wherein each column includes six through holes  179 . Namely, a total of thirty through holes  179  are formed in the vertical side  176 . 
     The lower side  178  is provided, in a central part on the top surface thereof, with a pair of guide keys (right and left guide keys)  180  which extend in the forward-rearward direction. The lower side  178  is provided, on the top surface thereof at the right and left ends thereof with a pair of guide keys  182  which extend in the forward-rearward direction. As shown in  FIG. 30 , the lower side  178  is provided at the front ends of the pair of guide keys  180  with two engaging keys  183  which project upward. As shown in  FIGS. 47 and 48 , each of the two engaging keys  183  increases in width (dimensions in the left-right direction) in the direction from down to up and also increases in width in the direction from rear to front. In other words, the right and left sides of each engaging key  183  are formed as tapered surfaces. The lower side  178  is provided at the front ends of the pair of guide keys  180  with two engaging keys  184  which project upward. The inner surfaces of the engaging keys  184  are formed as beveled surfaces which approach each other in the direction from rear to front and approach each other in the bottom thereof in upward direction (toward the right on the left engaging key  184  and toward the left on the right engaging key  184 ). In addition, the lower side  178  is provided on the top surface thereof with a pair of lock holes (right and left lock holes)  185  in which the locking lugs  160 H of the conductive layer portions  160  of the two contact modules  131  engage upon the retainer  175  being attached to the contact module group  172 , which is composed of the two contact modules  131  and the contact module  132 . 
     The upper side  177  is provided at the rear end thereof with a pair of engaging projections (right and left engaging projections)  186 . The upper side  177  is provided, at the rear end thereof between the pair of engaging projections  186 , with an engaging projection  187  which is greater in width than each engaging projection  186 . As shown in  FIG. 48 , the upper side  177  is provided in a central part on the lower surface thereof with a pair of guide keys  188  which extend from the front end to the rear end of the lower surface of the upper side  177 , and is further provided at the right and left ends of the lower surface of the upper side  177  with a pair of guide keys (right and left guide keys)  189  which extend from the front end to the rear end of the lower surface of the upper side  177 . 
     The manner of combining the contact module group  172 , the connecting bar  173  and the retainer  175  into one will be discussed hereinafter. 
     Firstly, the manner of combining the contact module group  172  and the retainer  175  will be discussed hereinafter. 
     In this case, firstly the retainer  175  is brought to approach the contact module group  172  as shown in  FIGS. 29 and 30 . Subsequently, as shown in  FIG. 49 , the pair of guide keys  180  of the lower side  178  are brought to be engaged in two grooves each having a substantially V-shaped cross section, respectively, wherein one of the two grooves (left groove) is formed between a lower-left chamfered edge  148 G of the conductive layer portion  148  of the contact module  132  and a lower-right chamfered edge  135 G of the conductive layer portion  135  of the left contact module  131 , and the other groove (right groove) is formed between a lower-right chamfered edge  135 G of the conductive layer portion  135  of the contact module  132  and a lower-left chamfered edge  148 G of the conductive layer portion  148  of the right contact module  131 . At the same time, the right and left guide keys  182  of the lower side  178  are brought to be engaged with a lower-left chamfered edge  148 G of the conductive layer portion  148  of the left contact module  131  and a lower-right chamfered edge  135 G of the conductive layer portion  135  of the right contact module  131 , respectively. In addition, as shown in  FIG. 49 , the pair of guide keys  188  of the upper side  177  are brought to be engaged in two grooves each having a substantially V-shaped cross section, respectively, wherein one of the two grooves (left groove) is formed between an upper-left chamfered edge  148 F of the conductive layer portion  148  of the contact module  132  and an upper-right chamfered edge  135 F of the conductive layer portion  135  of the left contact module  131 , and further wherein the other groove (right groove) is formed between an upper-right chamfered edge  135 F of the conductive layer portion  135  of the contact module  132  and an upper-left chamfered edge  148 F of the conductive layer portion  148  of the right contact module  131 . At the same time, the right and left guide keys  189  of the upper side  177  are brought to be engaged with an upper-left chamfered edge  148 F of the conductive layer portion  148  of the left contact module  131  and an upper-right chamfered edge  135 F of the conductive layer portion  135  of the right contact module  131 , respectively. Thereafter, the retainer  175  is slidingly moved rearward on the contact module group  172  along the guide keys  180 ,  182 ,  188  and  189 . Upon the retainer  175  being fully moved rearward relative to the contact module group  189 , the rear surface (inner surface) of the vertical side  176  comes in contact with the front surface of the contact module group  172 , and thereupon, the upper side  177  covers a front half of the top surface of the contact module group  172  while the lower side  178  covers a front half of the bottom surface of the contact module group  172 . Moreover, the left engaging projection  186  engages in both the front engaging groove  148 C and the front engaging groove  160 C of the left contact module  131 , the right engaging projection  186  engages in the front engaging groove  135 C of the right contact module  131 , the engaging projection  187  engages a laterally-elongated groove which is formed on top of the contact module group  172  by the front engaging groove  135 C of the left contact module  131 , the front engaging groove  148 C and the front engaging groove  135 C of the contact module  132 , and the front engaging groove  148 C and the front engaging groove  160 C of the right contact module  131 . Furthermore, as shown in  FIG. 48 , the pair of engaging keys  183  of the lower side  178  are engaged in a groove formed between the key groove  148 E of the contact module  132  and the key groove  135 E of the left contact module  131  and a groove formed between the key groove  135 E of the contact module  132  and the key groove  148 E of the right contact module  131 , respectively. Furthermore, as shown in  FIG. 48 , the pair of engaging keys  184  are engaged in the key groove  148 E of the left contact module  131  and the key groove  135 E of the right contact module  131 , respectively. Accordingly, each contact module  131  and  132  is held between the adjacent engaging keys  183  and  184 . Furthermore, the locking lugs  160 H of the conductive layer portions  160  of the two contact modules  131  engage in the pair of lock holes  185  of the lower side  178 , respectively (this state of engagement between the locking lugs  160 H and the pair of lock holes  185  is not shown in the drawings). 
     The contact module group  172  and the retainer  175  are combined into one integral module in the above described manner. 
     Next the manner of combining the contact module group  172  and the connecting bar  173  will be discussed hereinafter. 
     Upon completion of the contact module group  172 , the rear engaging groove  135 D of each conductive layer portion  135 , the rear engaging groove  148 D of each conductive layer portion  148 D and the rear engaging groove  160 D of each conductive layer portion  160  are aligned in the left-right direction to form a laterally-elongated engaging groove (see  FIGS. 30 , etc.). The connecting bar  173  is fixed to the contact module  172  to be integral therewith by fitting the insertion jutting portion  174 A into this laterally-elongated engaging groove while making the front surface of the contacting portion  174 B contact with the rear end surface of the top end of the contact module group  172  (see  FIG. 44 ). 
     After the completion of the receptacle  130  by combining the contact module group  172 , the connecting bar  173  and the retainer  175  into one integral module in the above described manner, the press-fit terminals  167  of the ground contacts  165 A and  165 D and the signal contacts  165 B,  165 C,  165 E and  165 F, which project downward from a bottom surface of the receptacle  130 , are driven (press-fitted) into through holes (not shown) formed in a circuit board CB 1 , respectively (see  FIGS. 27 and 28 ). Thereupon, the press-fit terminals  167  of the ground contacts  165 A and  165 D are electrically connected to a ground pattern on the circuit board CB 1  while the press-fit terminals  167  of the signal contacts  165 B,  165 C,  165 E and  165 F are electrically connected to a circuit pattern on the circuit board CB 1 . 
     Next, the plug  120  will be discussed with reference mainly to  FIGS. 50 through 56 . 
     The plug  120  is provided with two contact modules  121 , a contact module  122 , a connecting bar  173  and a retainer  110  as relatively large elements of the plug  120 . 
     Each contact module  121  is identical in structure to each contact module  131  except that each contact module  121  is provided with four ground contact pins  125 A and  125 D and eight signal contact pins  125 B,  125 C,  125 E and  125 F, whereas each contact module  131  is provided with the four ground contacts  165 A and  165 D and the eight signal contacts  165 B,  165 C,  165 E and  165 F. 
     As shown in  FIG. 51 , etc., the ground contact pins  125 A and  125 D and the signal contact pins  125 B,  125 C,  125 E and  125 F of each contact module  121  are each provided with a terminal contact  126  and a press-fit terminal  127  and greater in length in the forward-rearward direction than the ground contacts  165 A and  165 D and the signal contacts  165 B,  165 C,  165 E and  165 F, respectively. The terminal contacts  126  of the ground contact pins  125 A and  125 D and the signal contact pins  125 B,  125 C,  125 E and  125 F of each contact module  121  are connected with the bifurcated resilient portions  166  of the ground contacts  165 A and  165 D and the signal contacts  165 B,  165 C,  165 E and  165 F of the associated contact module  131 , respectively, when the plug  120  and the receptacle  130  are connected to each other. The ground contact pins  125 A and  125 D and the signal contact pins  125 B,  125 C,  125 E and  125 F are stamp molded out of metal. More specifically, to make each contact  125 A through  125 F, a base material (e.g., phosphor bronze, beryllium copper, titanium copper, stainless steel, or Corson-copper alloy) is coated firstly with base plating (e.g., nickel (Ni) plating) and subsequently with finish plating (e.g., gold(Au) plating, tin(Sn)-copper(Cu) plating, or tin(Sn)-lead(Pb) plating). 
     The manner of assembling each contact module  121  is the same as the manner of assembling each contact module  131 . 
     The contact module  122  is identical in structure to the contact module  132  except that the contact module  122  is provided with four ground contact pins  125 A and  125 D and eight signal contact pins  125 B,  125 C,  125 E and  125 F, whereas the contact module  132  is provided with four ground contacts  165 A and  165 D and eight signal contacts  165 B,  165 C,  165 E and  165 F. 
     The contact module  122  is assembled in the same manner as the contact module  132 . 
     The retainer  110  is an element having a substantially H-shaped cross section. The retainer  110  is provided with a vertical side  111 , an upper side  112  and a lower side  113 . The upper side  112  extends both forward and rearward from the upper end of the vertical side  111 . Likewise, the lower side  113  extends both forward and rearward from the lower end of the vertical side  111 . The upper side  112  is provided with a contact-module retaining portion  112 A and a receptacle retaining portion  112 B which extend forward and rearward, respectively. Likewise, the lower side  113  is provided with a contact-module retaining portion  113 A and a receptacle retaining portion  113 B which extend forward and rearward, respectively. 
     The vertical side  111  is provided with five columns of through holes  114  arranged in the left-right direction, wherein each column includes six through holes  114 . Namely, a total of thirty through holes  114  are formed in the vertical side  111 . The contact-module retaining portion  113 A is provided with a pair of guide keys  180 , a pair of guide keys  182 , two engaging keys  183 , two engaging keys  184  and a pair of lock holes  185  which are all formed in the same manner as those of the retainer  175  (see  FIG. 50 ). 
     The plug  120  that has the above described structure is completed by mounting the retainer  110  and the connecting bar  173  to the contact module group  116  in the same manner as the receptacle  131  after the completion of the contact module group  116  by combining the two contact module  121  and the contact module  122  into one. Upon the vertical side  111  being mounted to the contact module group  116 , the terminal contacts  126  of the ground contact pins  125 A and  125 D and the signal contact pins  125 B,  125 C,  125 E and  125 F project rearward from the vertical side  111  through the corresponding through holes  114  of the vertical side  111 , respectively, as shown in  FIG. 56 . 
     Upon the press-fit terminals  127  of the ground contact pins  125 A and  125 D being driven (press-fitted) into through holes (not shown) formed in a circuit board CB 2  (see  FIGS. 27 and 28 ), the press-fit terminals  127  of the ground contact pins  125 A and  125 D are electrically connected to a ground pattern on the circuit board CB 2  while the press-fit terminals  127  of the signal contact pins  125 B,  125 C,  125 E and  125 F are electrically connected to a circuit pattern on the circuit board CB 2 . 
     When the receptacle  130  and the plug  120  that have the above described structures are connected to each other so that the receptacle retaining portion  112 B of the retainer  110  covers the upper surface of the upper side  177  of the retainer  175  and so that the receptacle retaining portion  113 B of the retainer  110  covers the bottom surface of the lower side  178  of the retainer  175  as shown in  FIG. 28 , the terminal contacts  126  of the ground contact pins  125 A and  125 D and the signal contact pins  125 B,  125 C,  125 E and  125 F of each contact module  121  firstly pass through the corresponding through holes  179  and subsequently engage in the corresponding engaging holes  169  and  170 , respectively, thus entering inside of the receptacle  130  (specifically, entering the inside of the associated contact module  131  or  132 ). Thereupon, each terminal contact  126  enters the bifurcated resilient portion  166  of the associated ground or signal contact  165 A,  165 B,  165 C,  165 D,  165 E or  165 F while resiliently deforming the same bifurcated resilient portion  166  to establish connection therewith, respectively. 
     Therefore, the ground contact pins  125 A and  125 D of the plug  120  are electrically connected to a ground pattern formed on the circuit board CB 1  on the receptacle  130  side and the ground contacts  165 A and  165 D of the receptacle  130  are electrically connected to a ground pattern formed on the circuit board CB 2  on the plug  120  side, while the signal contact pins  125 B,  125 C,  125 E and  125 F of the plug  120  are electrically connected to a circuit pattern formed on the circuit board CB 1  on the receptacle  130  side and the signal contacts  165 B,  165 C,  165 E and  165 F of the receptacle  130  are electrically connected to a circuit pattern formed on the circuit board CB 2  on the plug  120  side. 
     The above illustrated second embodiment of the connector  100  can obtain effects similar to those obtained in the first embodiment of the connector  10  because the basic structure of the second embodiment of the connector  100  is the same as the basic structure of the first embodiment of the connector  10 . 
     In addition, since two sets of contacts  165 A through  165 F are sandwiched between three holding plates ( 133 ,  134  and  138 ) while two sets of contact pins  125 A through  125 F are sandwiched between three holding plates ( 133 ,  134  and  138 ) in each of the contact modules  121  and  131  of the second embodiment of the connector  100 , each of the contact modules  121  and  131  of the second embodiment of the connector  100  have the following advantages with respect to each contact module  31  of the first embodiment of the connector  10 , in which a set of contacts ( 65 A through  65 F) are sandwiched between two holding plates ( 33  and  34 ). 
     First of all, for instance, a total of four holding plates are required to sandwich two sets of contacts in the first embodiment of the connector, whereas a total of three holding plates can do the same in the second embodiment of the connector. Namely, according to the second embodiment of the connector, since the number of components, the number of assembly procedures, and the time required for the plating process performed on each component can be reduced, it is possible to achieve an improvement in productivity and a reduction in production cost. 
     Furthermore, since each of the contact modules  121  and  131  is composed of the two holding plates  133  and  134  and the holding plate  138  that is mechanically stronger and greater in thickness than either of the two holding plates  133  and  134 , the mechanical strength of each contact module and the contact module group itself in the second embodiment of the connector can be made higher than that in the first embodiment of the contact module  31 . 
     Moreover, more than one plug connector  120  or more than one receptacle  130  can be arranged in the left-right direction with all the contacts ( 125 A through  125 F and  165 A through  165 F) being positioned at regular intervals in the left-right direction because neither of the retainers  110  and  175  has side walls (either a left side wall or a right side wall) and because, among the three holding plates  133 ,  134  and  138  of the two contact modules  121  of the plug  120  that respectively include the left side portion and the right side portion of the plug  120 , the two conductive layer portions  135  and  148  of each contact module  121  that respectively include the left side portion and the right side portion of each contact module  121  are each designed to be smaller in wall thickness than a half the wall thickness of the conductive layer portion  160 , and further because, among the three holding plates  133 ,  134  and  138  of the two contact modules  131  of the receptacle  130  that respectively include the left side portion and the right side portion of the receptacle  130 , the two conductive layer portions  135  and  148  of each contact module  131  that respectively comprise the left side portion and the right side portion of each contact module  131  are each designed to be smaller in wall thickness than a half the wall thickness of the conductive layer portion  160 . 
     Furthermore, each contact pin ( 125 A through  125 F) of the plug  120  can be easily held at a predetermined position (i.e., all the contact pins  125 A through  125 F of the plug  120  can be placed in proper alignment) since the through holes  114  are formed in the vertical plate portion  111  of the retainer  110 . Likewise, since the through holes  179  are formed in the vertical side  176  of the retainer  175 , each contact pin ( 165 A through  165 F) of the receptacle  130  can be easily lead into the associated contact module  131  or  132  of the receptacle  130  (i.e., the ground contact pins  165 A and  165 D and the signal contact pins  165 B,  165 C,  15 E and  165 F of the receptacle  130  can be easily made contact with the ground contacts  125 A and  125 D and the signal contacts  125 B,  125 C,  125 E and  125 F of the plug  120 , respectively). 
     Although the present invention has been described based on the above illustrated first and second embodiments of the connectors, the present invention is not limited solely to these embodiments; making various modifications to these embodiments is possible. 
     For instance, although each contact module  31  includes the two holding plates (a pair of holding plates)  33  and  34  in the first embodiment of the connector and each of the contact modules  121  and  131  includes the three holding plates  133 ,  134  and  138  in the second embodiment of the connector, it is possible that each contact module include more than three holding plates so that contacts or contact pins are held between adjacent holding plates.  FIGS. 57 and 58  show an example of this modified embodiment of the receptacle. A contact module group  191  of this modified embodiment of a receptacle  190  is composed of six holding plates (four holding plates  138 , a left holding plate  133  and a right holding plate  134 ) and five sets of contacts  165 A through  165 F, and each set of contacts  165 A through  165 F is held between the adjacent holding plates. 
     Additionally, all the contacts (or contact pins) of each of the receptacle  30 , the plug  120  and the receptacle  130  can consist of only signal contacts (or signal contact pins) as shown in  FIGS. 59 and 60  though the contacts of each of the receptacle  30 , the plug  120  and the receptacle  130  consist of two types of contacts (the ground contacts  65 A and  65  and the signal contacts  65 B,  65 C,  65 E and  65 F, or the ground contact pins  125 A and  125 D and the signal contact pins  125 B,  125 C,  125 E and  125 F, or the ground contacts  165 A and  165 D and the signal contacts  165 B,  165 C,  165 E and  165 F). 
       FIG. 59  shows a modified embodiment of each contact module  31  of the receptacle  30  of the first embodiment of the connector, wherein each contact module  31  is modified for use in single-ended signaling. In this modified embodiment, the conductive layer portions  35  and  48  are provided on the laterally-opposed surfaces thereof with a total of six insulation recesses  68  and corresponding six insulation recesses  68 , respectively. In addition, the conductive layer portion  35  is provided in the six insulation recesses  68  thereof with six insulating portions  43  which are fitted into the six insulation recesses  68  so as to occupy the six insulation recesses  68 , respectively, and the conductive layer portion  48  is provided in the six insulation recesses  68  thereof with six insulating portions  55  which are fitted into the six insulation recesses  68  so as to occupy the six insulation recesses  68 , respectively. A signal contact  65  is held between each insulating portion  43  and the associated insulating portion  55 . 
       FIG. 60  shows another modified embodiment of each contact module  31  of the receptacle  30  of the first embodiment of the connector, wherein each contact module  31  is modified for use in differential signaling. In this modified embodiment, the conductive layer portions  35  and  48  are provided on the laterally-opposed surfaces thereof with a total of three insulation recesses  71  and corresponding three insulation recesses  71 , respectively. In addition, the conductive layer portion  35  is provided in the three insulation recesses  71  thereof with three insulating portions  43  which are fitted into the three insulation recesses  71  so as to occupy the three insulation recesses  71 , respectively, and the conductive layer portion  48  is provided in the three insulation recesses  71  thereof with three insulating portions  55  which are fitted into the three insulation recesses  71  so as to occupy the three insulation recesses  71 , respectively. Two signal contacts  65  are held between each insulating portion  43  and the associated insulating portion  55 . 
     Although not shown in the drawings, the number of contacts or contact pins held between the conductive layer portion and the conductive layer portion of the adjacent holding plates  33  and  34  can be any number so long as the number is at least one. In addition, it is possible that contact holding grooves and corresponding contact holding grooves be formed on two conductive layer portions which face each other, respectively. Additionally, it is also possible that contact holding grooves and no contact holding grooves be formed on two conductive layer portions which face each other, respectively. 
     In addition, in the first embodiment of the connector, it is possible to combine all the ten contact modules  31  into one integral module by a retainer similar to the retainer  175  of the second embodiment of the connector instead of combining all the ten contact modules  31  into one integral by the retainer  75 . 
     In addition, although the side edges (upper and lower side edges in the illustrated first embodiment of the connector) of each insulation recess ( 36 ,  37 ,  49  and  50 ) in either of the two holding plates  33  and  34 , which extend parallel to the associated signal contact  65 B,  65 C,  65 E or  65 F, are covered by the associated conductive layer portion  35  or  48  and also the side edges (upper and lower side edges in the illustrated second embodiment of the connector) of each insulation recess ( 136 ,  137 ,  149  and  150 ) in each of the three holding plates  133 ,  134  and  138 , which extend parallel to the associated signal contact  165 B,  165 C,  165 E or  165 F, are covered by the associated conductive layer portion  135 ,  148  or  160 , the side edges of each insulation recess ( 36 ,  37 ,  49  and  50 ) in either of the two holding plates  33  and  34  can be shaped so as only to be partly covered by the associated conductive layer portion  35  or  48 , and also the side edges of each insulation recess ( 136 ,  137 ,  149  and  150 ) in each of the three holding plates  133 ,  134  and  138  can be shaped so as only to be partly covered by the associated conductive layer portion  135 ,  148  or  160 .  FIG. 61  shows an example of this modified embodiment (one of the two holding plates of a modified embodiment of each contact module of the receptacle in the first embodiment of the connector). In this embodiment, the conductive layer portion  35  of the holding plate  33  is provided on the inner surface thereof with two insulation recesses  77  and  37  which correspond to the two insulation recesses  36  and  37  of the holding plate  33  shown in  FIGS. 12 and 13 , respectively, and the insulation recess  77  (the upper portion thereof) is not partly covered by the conductive layer portion  35 . 
     In addition, in the first embodiment of the connector, it is possible that the holding plate  33  be made by forming the conductive layer portion  35  on a synthetic-resin-made member, subsequently making the insulating portion  43  as a member separated from the conductive layer portion  35  (as a member independent of the conductive layer portion  35 ), and subsequently fitting the insulating portion  43  into the conductive layer portion  35 , and that the holding plate  34  be made by forming the conductive layer portion  48  on a synthetic-resin-made member, subsequently making the insulating portion  55  as a member separated from the conductive layer portion  48  (as a member independent of the conductive layer portion  48 ), and subsequently fitting the insulating portion  55  into the conductive layer portion  48 . Additionally, in the second embodiment of the connector, it is possible that each conductive layer portion ( 135 ,  148  and  160 ) be formed on a synthetic-resin-made member, and then the associated insulating portion ( 143  or  155 ) be molded integrally with this conductive layer portion with the use of molding dies (by so-called two-color forming). 
     In addition, it is possible that firstly the conductive layer portion ( 35 ,  48 ,  135 ,  148  or  160 ) be formed over the surface of a synthetic-resin-made member, subsequently a portion of this conductive layer portion (plating) on which the insulating portion ( 43 ,  55 ,  143  or  155 ) is to be formed be removed, and subsequently the insulating portion ( 43 ,  55 ,  143  or  155 ) be formed on this removed portion. 
     Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.