Patent Publication Number: US-2023163505-A1

Title: Electric connector and board assembly

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2021-188483, filed on Nov. 19, 2021, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The present disclosure relates to an electric connector and a board assembly. 
     As shown in  FIG.  19    of the present application, Patent Literature 1 (Japanese Patent No. 6901603) discloses a board-to-board connector  101  in which a plurality of contacts  100  are arranged in a row. 
     SUMMARY 
     As the current path length of a contact is shorter, the resistance value in this current path is smaller. However, reducing the current path length of a contact directly causes the contact to harden, which degrades the connection reliability. 
     One of the objects of the present disclosure is to provide a technique of reducing the current path length without degrading the connection reliability of a contact. 
     According to an aspect of the present disclosure, there is provided an electric connector including a housing and a plurality of contacts held by the housing. The plurality of contacts electrically connect a plurality of first conductors provided on an object and a plurality of second conductors provided on a board, respectively. At least one contact of the plurality of contacts includes a fixed part to be fixed to the housing, a soldering part to be soldered to a corresponding second conductor and an elastic deformation part being a cantilever extending from the fixed part. The elastic deformation part includes a first contact part configured to come into contact with a corresponding first conductor; and a second contact part configured to come into contact with a third conductor provided on the board, the third conductor being at the same potential as the second conductor. When the first contact part is not in contact with the first conductor, the second contact part is not in contact with the third conductor, and when the first contact part comes into contact with the first conductor and the elastic deformation part is elastically deformed, the second contact part comes into contact with the third conductor. A current path length from the first contact part to the second contact part is shorter than a current path length from the first contact part to the soldering part. 
     According to the present disclosure, the current path length is reduced without degrading the connection reliability of a contact. 
     The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an exploded perspective view of an information processing device (first embodiment); 
         FIG.  2    is a perspective view of a CPU board when viewed from another angle (first embodiment); 
         FIG.  3    is a perspective view of a connector (first embodiment); 
         FIG.  4    is an exploded perspective view of the connector (first embodiment); 
         FIG.  5    is a perspective view of a housing (first embodiment); 
         FIG.  6    is a partially cutout perspective view of the connector (first embodiment); 
         FIG.  7    is a partially cutout perspective view of the connector (first embodiment); 
         FIG.  8    is a partially cutout perspective view of the connector (first embodiment); 
         FIG.  9    is a cross-sectional view of the connector corresponding to  FIG.  6    (first embodiment); 
         FIG.  10    is a perspective view of a contact (first embodiment); 
         FIG.  11    is a perspective view of the contact when viewed from another angle (first embodiment); 
         FIG.  12    is a plan view of the contact (first embodiment); 
         FIG.  13    is a view illustrating the movement of the contact (first embodiment); 
         FIG.  14    is a view illustrating the movement of the contact (second embodiment); 
         FIG.  15    is a perspective view of the contact (third embodiment); 
         FIG.  16    is a view illustrating the movement of the contact (third embodiment); 
         FIG.  17    is a perspective view of the contact (fourth embodiment); 
         FIG.  18    is a view illustrating the movement of the contact (fourth embodiment); and 
         FIG.  19    is a simplified drawing of  FIG.  3    of Patent Literature 1. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present disclosure will be described hereinafter with reference to  FIGS.  1  to  13   .  FIG.  1    is an exploded perspective view of an information processing device  1  (electronic device). As shown in  FIG.  1   , the information processing device  1  includes a CPU board  2  (first board; object), a connector  3 , an input-output board  4  (second board; board), and a support board  5 . The CPU board  2 , the connector  3 , the input-output board  4 , and the support board  5  are placed on top of one another in this recited order. Specifically, the connector  3  is disposed between the CPU board  2  and the input-output board  4 . 
     The CPU board  2  and the input-output board  4  are rigid boards such as a paper phenolic board or a glass epoxy board, for example. 
       FIG.  2    is a perspective view of the CPU board  2  when viewed from another angle. As shown in  FIGS.  1  and  2   , the CPU board  2  includes a connector opposed surface  2 A to be opposed to the connector  3 . As shown in  FIG.  2   , a plurality of signal pad rows  6  are formed on the connector opposed surface  2 A. Further, the CPU board  2  has a plurality of bolt fastening holes  8 . 
     The plurality of signal pad rows  6  extend parallel to one another. Each of the signal pad rows  6  includes a plurality of signal pads  10  (first conductor). The longitudinal direction of each signal pad row  6  is referred to as a pitch direction. Further, the direction orthogonal to the pitch direction is defined as a width direction. The plurality of signal pad rows  6  are arranged in the width direction. The thickness direction of the CPU board  2  is orthogonal to the pitch direction and the width direction, and it is referred to hereinafter as a vertical direction. The vertical direction includes downward which the connector opposed surface  2 A faces, and upward opposite to downward. Note that the vertical direction, the upward direction, and the downward direction are directions used by way of illustration only and should not be interpreted as limiting the position of the information processing device  1  and the connector  3  when they are actually used. 
     The plurality of bolt fastening holes  8  are disposed separately from each other in the pitch direction. The plurality of bolt fastening holes  8  include a first bolt fastening hole  8 A, a second bolt fastening hole  8 B, and a third bolt fastening hole  8 C. The first bolt fastening hole  8 A, the second bolt fastening hole  8 B, and the third bolt fastening hole  8 C are arranged in this recited order. 
     Referring back to  FIG.  1   , the input-output board  4  includes a connector opposed surface  4 A to be opposed to the connector  3 . A plurality of signal pad rows  11  and a plurality of hold-down pads  12  are formed on the connector opposed surface  4 A. Further, the input-output board  4  has a plurality of bolt fastening holes  13 . 
     The plurality of signal pad rows  11  extend parallel to one another. The plurality of signal pad rows  11  are arranged in the width direction. Each of the signal pad rows  11  includes a plurality of signal pads  15  (second conductor). 
     The plurality of bolt fastening holes  13  are disposed separately from each other in the pitch direction. The plurality of bolt fastening holes  13  include a first bolt fastening hole  13 A, a second bolt fastening hole  13 B, and a third bolt fastening hole  13 C. The first bolt fastening hole  13 A, the second bolt fastening hole  13 B, and the third bolt fastening hole  13 C are arranged in this recited order. 
     The support board  5  is typically a part of a casing that accommodates the CPU board  2 , the connector  3 , and the input-output board  4 , and it is made of aluminum or aluminum alloy, for example. The support board  5  includes a flat-plate board main body  20 , and a plurality of nuts  21 . The plurality of nuts  21  project upward from the board main body  20 . 
     The plurality of nuts  21  include a first nut  21 A, a second nut  21 B, and a third nut  21 C. The first nut  21 A, the second nut  21 B, and the third nut  21 C are disposed to correspond to the first bolt fastening hole  13 A, the second bolt fastening hole  13 B, and the third bolt fastening hole  13 C of the input-output board  4 , respectively. 
     The connector  3  is mountable on the connector opposed surface  4 A of the input-output board  4 .  FIG.  3    is a perspective view of the connector  3 .  FIG.  4    is an exploded perspective view of the connector  3 . As shown in  FIGS.  3  and  4   , the connector  3  includes a rectangular flat-plate housing  30  made of insulating resin, a plurality of contact rows  31 , and a plurality of hold-downs  32 . The plurality of contact rows  31  and the plurality of hold-downs  32  are held on the housing  30 . 
     The plurality of contact rows  31  extend parallel to one another. The plurality of contact rows  31  are arranged in the width direction. Each contact row  31  extends linearly in the pitch direction. Each contact row  31  includes a plurality of contacts  33 . Each contact  33  is conductive and formed by punching and bending a metal plate formed by plating copper or copper alloy, for example. The plurality of contacts  33  include signal contacts for differential transmission and ground contacts. The signal contact for differential transmission means a signal contact to be used for differential transmission. 
     As shown in  FIG.  1   , the plurality of hold-downs  32  are disposed to correspond to the plurality of hold-down pads  12  of the input-output board  4 , respectively. Each hold-down  32  is formed by punching and bending a metal plate such as a stainless steel plate, for example. 
       FIG.  5    is a perspective view of the housing  30 . As shown in  FIG.  5   , the housing  30  includes a CPU board opposed surface  30 A serving as a housing upper surface that can be opposed to the CPU board  2  by facing upward, and an input-output board opposed surface  30 B serving as a housing lower surface that can be opposed to the input-output board  4  by facing downward. The CPU board opposed surface  30 A is the uppermost surface of the housing  30 . The input-output board opposed surface  30 B is the lowermost surface of the housing  30 . 
     Referring back to  FIG.  1   , the overview of the assembly procedure of the information processing device  1  is described. 
     First, the connector  3  is mounted on the input-output board  4 . To be specific, the plurality of contact rows  31  are respectively soldered to the plurality of signal pad rows  11 , and further the plurality of hold-downs  32  are respectively soldered to the plurality of hold-down pads  12 . 
     Next, the input-output board  4  on which the connector  3  is mounted is placed on the support board  5 . At this time, the first nut  21 A, the second nut  21 B, and the third nut  21 C of the support board  5  penetrate the first bolt fastening hole  13 A, the second bolt fastening hole  13 B, and the third bolt fastening hole  13 C of the input-output board  4 , respectively. 
     Then, the CPU board  2  is attached to the support board  5  in such a way that the CPU board  2  overlaps the connector  3 . To be specific, a first bolt  40 A is fastened to the first nut  21 A through the first bolt fastening hole  8 A and the first bolt fastening hole  13 A, a second bolt  40 B is fastened to the second nut  21 B through the second bolt fastening hole  8 B and the second bolt fastening hole  13 B, and a third bolt  40 C is fastened to the third nut  21 C through the third bolt fastening hole  8 C and the third bolt fastening hole  13 C. In this manner, the connector  3  is interposed between the CPU board  2  and the input-output board  4 , and thereby the plurality of signal pads  15  of the input-output board  4  and the plurality of signal pads  10  of the CPU board  2  shown in  FIG.  2    are respectively electrically connected to each other through the plurality of contacts  33  of the connector  3 . 
     The connector  3  according to this embodiment is designed for high-speed transmission, and the assumed frequency of a signal flowing through each contact  33  is from 10 GHz to 25 GHz. In one example, the connector  3  may be a connector for differential transmission. 
     The connector  3  is described hereinafter in further detail. 
     As shown in  FIG.  5   , the housing  30  is formed in a rectangular flat-plate shape. A plurality of contact accommodation rows  62  are formed in the housing  30 . The plurality of contact accommodation rows  62  extend parallel to one another. Each contact accommodation row  62  extends linearly in the pitch direction. The plurality of contact accommodation rows  62  are arranged in the width direction. Each contact accommodation row  62  includes a plurality of contact accommodation parts  63 . 
       FIG.  6    is a partially cutout perspective view of the connector  3  where the housing  30  is cut along a plane orthogonal to the pitch direction.  FIG.  7    is a partially cutout perspective view of the connector  3  where the housing  30  is cut along a plane orthogonal to the pitch direction and a plane orthogonal to the width direction.  FIG.  8    is a partially cutout perspective view of the connector  3  where the housing  30  is cut along a plane orthogonal to the pitch direction.  FIG.  9    is a cross-sectional view of the connector  3  where the housing  30  is cut along a plane orthogonal to the pitch direction. 
     As shown in  FIGS.  6  and  7   , the plurality of contact accommodation rows  62  accommodate the plurality of contact rows  31 , respectively. In other words, the plurality of contact accommodation parts  63  accommodate the plurality of contacts  33 , respectively. Each contact accommodation part  63  is formed to attach each contact  33  to the housing  30 . As shown in  FIG.  8   , each contact accommodation part  63  is formed to penetrate the housing  30  in the vertical direction. 
     As shown in  FIGS.  8  and  9   , each contact accommodation part  63  includes a contact accommodation part main body  70  and a solder connection checking hole  71 . The contact accommodation part main body  70  and the solder connection checking hole  71  are formed apart from each other in the width direction. Each of the contact accommodation part main body  70  and the solder connection checking hole  71  is a penetrating hole that penetrates the housing  30  in the vertical direction. 
     The housing  30  includes a width separating wall  72  that defines, in the width direction, the contact accommodation part main body  70  and the solder connection checking hole  71  of the contact accommodation part  63 . A notch  73  is formed at the lower end of the width separating wall  72 . 
     The housing  30  includes a pitch separating wall  74  that defines, in the pitch direction, the contact accommodation part main bodies  70  of the two contact accommodation parts  63  adjacent to each other in the pitch direction. A restriction wall  75  that projects in the pitch direction is formed at the upper end of the pitch separating wall  74 . 
     Each contact  33  is described hereinafter in detail with reference to  FIGS.  10  to  12   . In this embodiment, all of the contacts  33  have the same shape. Alternatively, some of the contacts  33  may have different shapes. 
       FIGS.  10  and  11    are perspective views of each contact  33 .  FIG.  12    is a plan view of each contact  33 . 
     As shown in  FIGS.  10  to  12   , each contact  33  includes a fixed part  80 , a soldering part  81 , and an elastic deformation part  82 . 
     The fixed part  80  is a part to be press-fit into the contact accommodation part main body  70  shown in  FIG.  8   . Specifically, the fixed part  80  is press-fit into the contact accommodation part main body  70 , and thereby each contact  33  is held by the housing  30 . The fixed part  80  is a plate body whose thickness direction is parallel to the width direction. The fixed part  80  includes a fixed part main body  80 A and two press-fit lances  80 B. The two press-fit lances  80 B are formed to project in the pitch direction respectively from the both ends of the fixed part main body  80 A in the pitch direction. 
     The soldering part  81  and the elastic deformation part  82  are disposed on the opposite sides to each other with the fixed part  80  interposed therebetween. The direction of viewing the elastic deformation part  82  from the soldering part  81  is referred to as frontward, and the direction of viewing the soldering part  81  from the elastic deformation part  82  is referred to as backward. Thus, the elastic deformation part  82  is disposed on the frontward side of the fixed part  80 , and the soldering part  81  is disposed on the backward side of the fixed part  80 . 
     The soldering part  81  includes a soldering part main body  81 A and a position stabilization spring piece  81 B. The soldering part main body  81 A is a part to be soldered to the corresponding signal pad  15  of the input-output board  4  shown in  FIG.  1   . As shown in  FIG.  10   , the soldering part main body  81 A extends backward from the lower end of the fixed part  80 . The position stabilization spring piece  81 B projects upward from the backward end of the soldering part main body  81 A. 
     The elastic deformation part  82  is a part that functions as an electrical contact point with the corresponding signal pad  10  of the CPU board  2  shown in  FIG.  2   . As shown in  FIG.  10   , the elastic deformation part  82  includes a curve joining part  83 , a U-shaped curve part  84 , an upper contact part  85  (first contact part), a displacement restriction part  86 , and a lower contact part  87  (second contact part). The curve joining part  83 , the U-shaped curve part  84 , the upper contact part  85 , and the displacement restriction part  86  link together in this recited order. 
     The curve joining part  83  includes a joining part main body  83 A and a vertical part  83 B. The joining part main body  83 A projects frontward from the upper end of the fixed part  80  and curves in a U-shape so as to be convex upward and open downward. The vertical part  83 B projects downward from the distal end of the joining part main body  83 A. 
     When the U-shaped curve part  84  is observed along the line of sight in the pitch direction, the U-shaped curve part  84  includes a lower straight part  84 A, a curve part  84 B, and an upper straight part  84 C. The lower straight part  84 A, the curve part  84 B, and the upper straight part  84 C link together in this recited order. 
     The lower straight part  84 A extends frontward from the lower end of the vertical part  83 B of the curve joining part  83  so as to be parallel to the width direction. The curve part  84 B projects upward from the frontward end of the lower straight part  84 A, and curves to be convex frontward and open backward. The upper straight part  84 C projects backward from the upper end of the curve part  84 B and is slightly inclined upward. Thus, when the U-shaped curve part  84  is observed along the line of sight in the pitch direction, the U-shaped curve part  84  is in a substantially U-shape that opens backward. 
     As shown in  FIG.  11   , the U-shaped curve part  84  has two spring pieces connected at both ends. Specifically, the U-shaped curve part  84  includes two spring pieces  90  that extend along the U-shaped curve part  84 , a fixed part-side joining part  91  that join the two spring pieces  90  on the fixed part  80  side, and an upper contact part-side joining part  92  that join the two spring pieces  90  on the upper contact part  85  side. The two spring pieces  90  are opposed to each other in the pitch direction and separated from each other in the pitch direction. The two spring pieces  90  extend parallel to each other. The fixed part-side joining part  91  is located in the vertical part  83 B of the curve joining part  83 . The upper contact part-side joining part  92  is located in the upper straight part  84 C. Thus, the two spring pieces  90  are formed along the lower straight part  84 A and the upper straight part  84 C. In other words, a slit  93  that is surrounded by the two spring pieces  90 , the fixed part-side joining part  91 , and the upper contact part-side joining part  92  extends along the lower straight part  84 A and the upper straight part  84 C. 
     The upper contact part  85  is a part that is configured to come into electrical contact with the corresponding signal pad  10  of the CPU board  2  shown in  FIG.  2   . As shown in  FIG.  11   , the upper contact part  85  is placed at the distal end of the upper straight part  84 C of the U-shaped curve part  84 , and it curves in a U-shape that is convex upward and opens downward. 
     As shown in  FIG.  10   , the displacement restriction part  86  includes two restriction pieces  86 A that project oppositely from each other in the pitch direction from the distal end of the upper contact part  85 . 
     Referring to  FIGS.  10  and  11   , the lower contact part  87  is disposed between the two spring pieces  90  in the pitch direction when viewed from above. As shown in  FIG.  11   , the lower contact part  87  is a cantilever that extends frontward from the vertical part  83 B of the curve joining part  83 , and it is inclined downward. Thus, the lower contact part  87  is a cantilever extending in a direction away from the fixed part  80 . 
     As shown in  FIG.  12   , each contact  33  is formed symmetrically with respect to a bisecting line  33 D that divides each contact  33  in half in the pitch direction. 
       FIG.  9    shows the state where each contact  33  is attached to each contact accommodation part  63 . To attach each contact  33  to each contact accommodation part  63 , each contact  33  is press-fit into the contact accommodation part main body  70  of each contact accommodation part  63  from below. Specifically, the two press-fit lances  80 B of the fixed part  80  respectively bite into wall surfaces of the two pitch separating walls  74  that define the contact accommodation part main body  70  in the pitch direction. The elastic deformation part  82  is thereby accommodated into the contact accommodation part main body  70 , the position stabilization spring piece  81 B of the soldering part  81  is accommodated into the solder connection checking hole  71 , and the soldering part main body  81 A of the soldering part  81  is accommodated into the notch  73 . 
     When press-fitting each contact  33 , the two restriction pieces  86 A of the displacement restriction part  86  come into contact with the lower surfaces of the corresponding restriction walls  75 , and thereby the U-shaped curve part  84  is slightly elastically deformed in such a way that the U-shaped curve part  84  is compressed in the vertically direction. Thus, the elastic deformation part  82  is accommodated in the contact accommodation part main body  70  in the state where the U-shaped curve part  84  is slightly elastically deformed. This improves the coplanarity between the upper contact parts  85  of the plurality of contacts  33 . 
     Further, when press-fitting each contact  33 , since the width separating wall  72  is inserted between the fixed part  80  and the position stabilization spring piece  81 B of the soldering part  81 , the soldering part  81  is elastically deformed so that the position stabilization spring piece  81 B moves away from the fixed part  80  in the width direction. Then, in the state where each contact  33  is press-fit, the position stabilization spring piece  81 B is pressed against the width separating wall  72  by the elastic restoring force of the soldering part  81 . In other words, the fixed part  80  and the soldering part  81  elastically sandwich the width separating wall  72  in the width direction. The position of each contact  33  after press-fitting is thereby stabilized. 
       FIG.  13    shows the state where the connector  3  is mounted on the connector opposed surface  4 A of the input-output board  4 . As shown in  FIG.  13   , on the connector opposed surface  4 A of the input-output board  4 , a short-circuiting pad  16  (third conductor) is formed in close proximity to the signal pad  15  (second conductor). The signal pad  15  and the short-circuiting pad  16  are coupled by a coupling pattern  17 . The signal pad  15  and the short-circuiting pad  16  are thereby at the same potential. Alternatively, the signal pad  15  and the short-circuiting pad  16  may be coupled to each other to form a single pad without through the connection pattern  17 . 
     The signal pad  15  and the short-circuiting pad  16  have the same thickness and are disposed on the connector opposed surface  4 A of the input-output board  4 . The signal pad  15  is disposed below the soldering part main body  81 A of the soldering part  81 , and the short-circuiting pad  16  is disposed below the lower contact part  87 . As described above, in the state where the connector  3  is mounted on the connector opposed surface  4 A of the input-output board  4 , a distal end  87 A of the lower contact part  87  is opposed to the short-circuiting pad  16  in the vertical direction without being in contact with the short-circuiting pad  16 . 
     Referring further to  FIG.  13   , when the soldering part main body  81 A of the soldering part  81  is soldered to the corresponding signal pad  15 , a solder fillet F is formed between the soldering part main body  81 A of the soldering part  81  and the signal pad  15 . In this embodiment, the presence of the solder fillet F is checkable from above through the solder connection checking hole  71 . This enables determining whether the soldering of each contact  33  is successfully made or not after mounting the connector  3  onto the input-output board  4 . 
     Referring back to  FIG.  1   , when the CPU board  2  is fixed to the support board  5 , the upper contact part  85  comes into contact with the corresponding signal pad  10  (refer also to  FIG.  2   ) of the CPU board  2  and is also pressed downward as indicated by the chain double-dashed line in  FIG.  13   . When the upper contact part  85  is pressed downward, the uppermost part of the upper contact part  85  coincides with the CPU board opposed surface  30 A of the housing  30  in the vertical direction. The amount of displacement of the upper contact part  85  in the vertical direction at this time is the same in all of the contacts  33 . 
     As described above, when the upper contact part  85  is elastically displaced downward, in the early stage of displacement, the distal end  87 A of the lower contact part  87  comes closer to the corresponding short-circuiting pad  16  but the distal end  87 A of the lower contact part  87  does not come into contact with the short-circuiting pad  16 . In the middle stage of displacement, the distal end  87 A of the lower contact part  87  comes into contact with the short-circuiting pad  16 . In the late stage of displacement, with the distal end  87 A of the lower contact part  87  being in contact with the short-circuiting pad  16 , the upper contact part  85  is further elastically displaced downward as the elastic deformation part  82  is elastically deformed. Then, when the upper contact part  85  is displaced to the position indicated by the chain double-dashed line, the upper contact part  85  comes to rest without being further displaced downward. 
     Thus, the current path from the upper contact part  85  to the signal pad  15  in the early stage of displacement is a path that runs through the upper contact part  85  of the elastic deformation part  82 , the U-shaped curve part  84  of the elastic deformation part  82 , the curve joining part  83  of the elastic deformation part  82 , the fixed part  80 , the soldering part main body  81 A of the soldering part  81 , and the signal pad  15  in sequence. Since the distal end  87 A of the lower contact part  87  is not in contact with the short-circuiting pad  16  in the early stage of displacement, the elasticity of the elastic deformation part  82  does not harden. Therefore, the connection reliability between the contact  33  and the corresponding signal pad  10  (refer also to  FIG.  2   ) is not degraded. 
     On the other hand, the current path from the upper contact part  85  to the signal pad  15  in the middle and late stages of displacement is a path that runs through the upper contact part  85  of the elastic deformation part  82 , the U-shaped curve part  84  of the elastic deformation part  82 , the lower contact part  87  of the elastic deformation part  82 , the short-circuiting pad  16 , and the signal pad  15  in sequence. In this manner, since the current path length in the contact  33  is substantially reduced in the middle and late stages of displacement, the resistance value in the contact  33  in the middle and late stages of displacement is reduced. 
     When the CPU board  2  is detached from the support board  5 , the upper contact part  85  is elastically displaced upward by the elastic restoring force of the elastic deformation part  82 . Then, when the two restriction pieces  86 A of the displacement restriction part  86  reach the lower surface of the restriction walls  75 , further displacement is restricted, and it returns to the state indicated by the solid line in  FIG.  13   . 
     The first embodiment is described above. The above-described embodiment has the following features. 
     As shown in  FIGS.  1 ,  2 ,  9  and  13   , the connector  3  (electric connector) includes the housing  30  and the plurality of contacts  33  held by the housing  30 . The plurality of contacts  33  electrically connect the plurality of signal pads  10  (first conductors) provided on the CPU board  2  (object) and the plurality of signal pads  15  (second conductors) provided on the input-output board  4  (board), respectively. At least one or several of the plurality of contacts  33  included in the connector  3  have the following feature. 
     Specifically, the contact  33  includes the fixed part  80  to be fixed to the housing  30 , the soldering part  81  to be soldered to the corresponding signal pad  15 , and the elastic deformation part  82  being a cantilever extending from the fixed part  80 . The elastic deformation part  82  includes the upper contact part  85  (first contact part) configured to come into contact with a corresponding signal pad  10 , and the lower contact part  87  (second contact part) configured to come into contact with the short-circuiting pad  16  (third conductor) provided on the input-output board  4  and at the same potential as the signal pad  15 . When the upper contact part  85  is not in contact with the signal pad  10 , the lower contact part  87  is not in contact with the short-circuiting pad  16 , and when the upper contact part  85  comes into contact with the signal pad  10  and the elastic deformation part  82  is elastically deformed, the lower contact part  87  comes into contact with the short-circuiting pad  16 . The current path length from the upper contact part  85  to the lower contact part  87  is shorter than the current path length from the upper contact part  85  to the soldering part  81 . Thus, the current path from the upper contact part  85  to the signal pad  15  is reduced by running through the lower contact part  87 . In this structure, the current path length is reduced without degrading the connection reliability of the contact  33 . 
     Further, in this embodiment, when the upper contact part  85  is not in contact with the signal pad  10 , the lower contact part  87  is not in contact with the short-circuiting pad  16 . This achieves sufficient coplanarity of the soldering parts  81  of all of the contacts  33  and thereby allows the soldering parts  81  of all of the contacts  33  to come into contact with all of the signal pads  15 , respectively, without any problem during reflow, and therefore the presence of the lower contact part  87  does not affect the success or failure of reflow. 
     Further, as shown in  FIGS.  10  and  11   , the elastic deformation part  82  has the two spring pieces  90  interposed between the upper contact part  85  and the fixed part  80 . The two spring pieces  90  extend separately from each other in the pitch direction and parallel to each other. The two spring pieces  90  are connected at both ends. The lower contact part  87  is disposed between the two spring pieces  90  in the pitch direction. In this structure, the lower contact part  87  is not easily touchable, which avoids damaging the lower contact part  87  when handling the contact  33 . 
     The lower contact part  87  is a cantilever extending in a direction away from the fixed part  80 . In this structure, the beam length of the lower contact part  87  increases, which allows the lower contact part  87  to have sufficient elasticity. This contributes to high connection reliability between the lower contact part  87  and the short-circuiting pad  16 . 
     The insertion loss of transmission signals in a connector for differential transmission generally has frequency characteristics that increase as the frequency of transmission signals increases. A local increase in insertion loss, which is called spiking phenomenon, can occur in the waveform representing such frequency characteristics. When the spike occurs at a relatively low frequency, product requirements related to the frequency characteristics of the insertion loss are not met. Note that product requirements related to the frequency characteristics of the insertion loss are specified in a predetermined frequency range, and no problem arises as long as the spiking phenomenon occurs at higher frequencies than this frequency range. One known way to shift the spiking phenomenon to the high frequency side is to reduce the current path length in ground contacts. However, reducing the current path lengths of a contact causes the elasticity of the contact to harden, which degrades the connection reliability. Thus, there is a problem that compatibility between the high-frequency transmission characteristics and the connection reliability is not achievable in a connector for differential transmission. 
     On the other hand, as described above, the contact  33  according to this embodiment has a feature that enables reducing the current path length while retaining a certain degree of elasticity. Thus, by using this contact  33  as a ground contact, the high-frequency transmission characteristics and the connection reliability are both achievable in a connector for differential transmission. 
     The plurality of contacts  33  include signal contacts for differential transmission and ground contacts. The contact  33  having the lower contact part  87  is applied at least to the ground contacts. 
     Note that, only ground contacts among the plurality of contacts  33  of the connector  3  may be the contacts  33  having the lower contact part  87  as shown in  FIG.  10   , or all of the contacts  33  of the connector  3  may be the contacts  33  having the lower contact part  87  as shown in  FIG.  10   . 
     Further, a board assembly E shown in  FIG.  13    includes the input-output board  4  and the connector  3  mounted on the input-output board  4 . In the board assembly E, the connector  3  is mounted on the input-output board  4 . In this structure, the board assembly E in which the current path length is reduced without degrading the connection reliability of the contact  33  is achieved. 
     Second Embodiment 
     A second embodiment will be described hereinafter with reference to  FIG.  14   . Differences of this embodiment from the above-described first embodiment will be mainly described below, and redundant description thereof is omitted.  FIG.  14    shows the state where the connector  3  is mounted on the connector opposed surface  4 A of the input-output board  4 . 
     Referring back to  FIG.  13   , in the above-described first embodiment, the contact  33  includes the lower contact part  87  that is configured to come into contact with the short-circuiting pad  16 . 
     On the other hand, as shown in  FIG.  14   , the contact  33  in this embodiment has a structure in which the lower straight part  84 A of the U-shaped curve part  84  of the elastic deformation part  82  of the contact  33  is inclined downward as it goes frontward, rather than including the lower contact part  87 . 
     As shown in  FIG.  14   , the short-circuiting pad  16  is disposed below the curve part  84 B. As described above, in the state where the connector  3  is mounted on the connector opposed surface  4 A of the input-output board  4 , the curve part  84 B is opposed to the short-circuiting pad  16  in the vertical direction without being in contact with the short-circuiting pad  16 . 
     Referring back to  FIG.  1   , when the CPU board  2  is fixed to the support board  5 , the upper contact part  85  comes into contact with the corresponding signal pad  10  (refer also to  FIG.  2   ) of the CPU board  2  and is also pressed downward as indicated by the chain double-dashed line in  FIG.  14   . When the upper contact part  85  is pressed downward, the uppermost part of the upper contact part  85  coincides with the CPU board opposed surface  30 A of the housing  30  in the vertical direction. The amount of displacement of the upper contact part  85  in the vertical direction at this time is the same in all of the contacts  33 . 
     As described above, when the upper contact part  85  is elastically displaced downward, in the early stage of displacement, the curve part  84 B of the U-shaped curve part  84  comes closer to the corresponding short-circuiting pad  16  but does not come into contact with the short-circuiting pad  16 . In the middle stage of displacement, the curve part  84 B of the U-shaped curve part  84  comes into contact with the short-circuiting pad  16 . In the late stage of displacement, with the curve part  84 B of the U-shaped curve part  84  being in contact with the short-circuiting pad  16 , the upper contact part  85  is further elastically displaced downward as the elastic deformation part  82  is elastically deformed. Then, when the upper contact part  85  is displaced to the position indicated by the chain double-dashed line, the upper contact part  85  comes to rest without being further displaced downward. 
     Thus, the current path from the upper contact part  85  to the signal pad  15  in the early stage of displacement is a path that runs through the upper contact part  85  of the elastic deformation part  82 , the U-shaped curve part  84  of the elastic deformation part  82 , the curve joining part  83  of the elastic deformation part  82 , the fixed part  80 , the soldering part main body  81 A of the soldering part  81 , and the signal pad  15  in sequence. Since the curve part  84 B of the U-shaped curve part  84  is not in contact with the short-circuiting pad  16  in the early stage of displacement, the elasticity of the elastic deformation part  82  does not harden. Therefore, the connection reliability between the contact  33  and the corresponding signal pad  10  (refer also to  FIG.  2   ) is not degraded. 
     On the other hand, the current path from the upper contact part  85  to the signal pad  15  in the middle and late stages of displacement is a path that runs through the upper contact part  85  of the elastic deformation part  82 , the curve part  84 B of the U-shaped curve part  84  of the elastic deformation part  82 , the short-circuiting pad  16 , and the signal pad  15  in sequence. In this manner, since the current path length in the contact  33  is substantially reduced in the middle and late stages of displacement, the resistance value in the contact  33  in the middle and late stages of displacement is reduced. 
     The second embodiment is described above, and the above-described embodiment has the following features. 
     As shown in  FIG.  14   , the elastic deformation part  82  has the U-shaped curve part  84  interposed between the upper contact part  85  (first contact part) and the fixed part  80 . The curve part  84 B serving as a second contact part is a part of the U-shaped curve part  84 . In this structure, the current path length is reduced in a simple structure without degrading the connection reliability of the contact  33 . 
     Further, the U-shaped curve part  84  includes the lower straight part  84 A (first straight part), the curve part  84 B, and the upper straight part  84 C (second straight part) in this recited order from the fixed part  80  toward the upper contact part  85 . The curve part  84 B functions as the second contact part. In this structure, the curve part  84 B serves as a contact point with the short-circuiting pad  16 . 
     Third Embodiment 
     A third embodiment will be described hereinafter with reference to  FIGS.  15  and  16   . Differences of this embodiment from the above-described first embodiment will be mainly described below, and redundant description thereof is omitted.  FIG.  15    is a perspective view of the contact  33 .  FIG.  16    shows the state where the connector  3  is mounted on the connector opposed surface  4 A of the input-output board  4 . 
     Referring back to  FIG.  13   , in the above-described first embodiment, the contact  33  includes the lower contact part  87  that is configured to come into contact with the short-circuiting pad  16 . 
     On the other hand, as shown in  FIGS.  15  and  16   , the contact  33  in this embodiment includes a downward extending spring piece  88  (second contact part), rather than including the lower contact part  87 . The downward extending part spring piece  88  is a part of the elastic deformation part  82 . 
     The downward extending spring piece  88  is a cantilever extending downward from the distal end of the upper contact part  85 . Specifically, the downward extending spring piece  88  is a cantilever extending from the distal end of the upper contact part  85  toward the input-output board  4 . As shown in  FIG.  16   , the downward extending spring piece  88  includes a first extending part  88 A, a bent part  88 B, and a second extending part  88 C. The first extending part  88 A, the bent part  88 B, and the second extending part  88 C link together in this recited order. 
     The first extending part  88 A extends downward in a straight manner from the distal end of the upper contact part  85 . To be specific, the first extending part  88 A extends downward from the distal end of the upper contact part  85  and is inclined frontward. 
     The bent part  88 B is provided at the lower end of the distal end of the upper contact part  85  and is bent in a V-shape to be convex downward. 
     The second extending part  88 C extends upward in a straight manner from the distal end of the bent part  88 B. To be specific, the second extending part  88 C extends upward from the distal end of the bent part  88 B and is inclined frontward. 
     Thus, the downward extending spring piece  88  is formed in a substantially V-shape when viewed in the pitch direction. 
     As shown in  FIG.  16   , the short-circuiting pad  16  is disposed below the bent part  88 B. As described above, in the state where the connector  3  is mounted on the connector opposed surface  4 A of the input-output board  4 , the bent part  88 B of the downward extending spring piece  88  is opposed to the short-circuiting pad  16  in the vertical direction without being in contact with the short-circuiting pad  16 . 
     Referring back to  FIG.  1   , when the CPU board  2  is fixed to the support board  5 , the upper contact part  85  comes into contact with the corresponding signal pad  10  (refer also to  FIG.  2   ) of the CPU board  2  and is also pressed downward as indicated by the chain double-dashed line in  FIG.  16   . When the upper contact part  85  is pressed downward, the uppermost part of the upper contact part  85  coincides with the CPU board opposed surface  30 A of the housing  30  in the vertical direction. The amount of displacement of the upper contact part  85  in the vertical direction at this time is the same in all of the contacts  33 . 
     As described above, when the upper contact part  85  is elastically displaced downward, in the early stage of displacement, the bent part  88 B of the downward extending spring piece  88  comes closer to the corresponding short-circuiting pad  16  but does not come into contact with the short-circuiting pad  16 . In the middle stage of displacement, the bent part  88 B of the downward extending spring piece  88  comes into contact with the short-circuiting pad  16 . In the late stage of displacement, with the bent part  88 B of the downward extending spring piece  88  being in contact with the short-circuiting pad  16 , the upper contact part  85  is further elastically displaced downward as the elastic deformation part  82  is elastically deformed. Then, when the upper contact part  85  is displaced to the position indicated by the chain double-dashed line, the upper contact part  85  comes to rest without being further displaced downward. 
     Thus, the current path from the upper contact part  85  to the signal pad  15  in the early stage of displacement is a path that runs through the upper contact part  85  of the elastic deformation part  82 , the U-shaped curve part  84  of the elastic deformation part  82 , the curve joining part  83  of the elastic deformation part  82 , the fixed part  80 , the soldering part main body  81 A of the soldering part  81 , and the signal pad  15  in sequence. Since the bent part  88 B of the downward extending spring piece  88  is not in contact with the short-circuiting pad  16  in the early stage of displacement, the elasticity of the elastic deformation part  82  does not harden. Therefore, the connection reliability between the contact  33  and the corresponding signal pad  10  (refer also to  FIG.  2   ) is not degraded. 
     On the other hand, the current path from the upper contact part  85  to the signal pad  15  in the middle and late stages of displacement is a path that runs through the upper contact part  85  of the elastic deformation part  82 , the first extending part  88 A of the downward extending spring piece  88 , the bent part  88 B of the downward extending spring piece  88 , the short-circuiting pad  16 , and the signal pad  15  in sequence. In this manner, since the current path length in the contact  33  is substantially reduced in the middle and late stages of displacement, the resistance value in the contact  33  in the middle and late stages of displacement is reduced. 
     Note that, in the late stage of displacement, the bent part  88 B of the downward extending spring piece  88  slides frontward on the short-circuiting pad  16 . Therefore, contact resistance between the bent part  88 B of the downward extending spring piece  88  and the short-circuiting pad  16  is improved by wiping. 
     The third embodiment is described above, and the above-described embodiment has the following features. 
     As shown in  FIG.  16   , the elastic deformation part  82  has the U-shaped curve part  84  interposed between the upper contact part  85  (first contact part) and the fixed part  80 . The downward extending spring piece  88  (second contact part) is a cantilever extending from the upper contact part  85  toward the input-output board  4  (board). In this structure, since the U-shaped curve part  84  is not included in the current path from the upper contact part  85  to the signal pad  15  in the state where the bent part  88 B of the downward extending spring piece  88  is in contact with the short-circuiting pad  16 , the length of this current path is significantly reduced. 
     Note that, as shown in  FIG.  16   , the U-shaped curve part  84 , the upper contact part  85 , and the downward extended spring piece  88  link together in this recited order. 
     Fourth Embodiment 
     A fourth embodiment will be described hereinafter with reference to  FIGS.  17  and  18   . Differences of this embodiment from the above-described first embodiment will be mainly described below, and redundant description thereof is omitted.  FIG.  17    is a perspective view of the contact  33 .  FIG.  18    shows the state where the connector  3  is mounted on the connector opposed surface  4 A of the input-output board  4 . 
     Referring back to  FIG.  13   , in the above-described first embodiment, the contact  33  includes the lower contact part  87  that is configured to come into contact with the short-circuiting pad  16 . 
     On the other hand, as shown in  FIGS.  17  and  18   , the contact  33  in this embodiment includes a downward projecting part  95  (second contact part) and a horizontal projecting part  96  (third contact part), rather than including the lower contact part  87 . Each of the downward projecting part  95  and the horizontal projecting part  96  is a part of the elastic deformation part  82 . 
     The downward projecting part  95  is a cantilever extending downward in a straight manner from the distal end of the upper contact part  85 . Specifically, the downward projecting part  95  is a cantilever extending from the distal end of the upper contact part  85  toward the input-output board  4 . In other words, the downward projecting part  95  projects downward from the distal end of the upper contact part  85 . 
     The horizontal projecting part  96  is a cantilever projecting in the width direction from the vertical part  83 B of the curve joining part  83 . Specifically, the horizontal projecting part  96  projects frontward from the vertical part  83 B of the curve joining part  83 . The horizontal projecting part  96  is disposed between the two spring pieces  90  in the pitch direction when viewed from above. The horizontal projecting part  96  is disposed above the lower straight part  84 A of the U-shaped curve part  84  in lateral view. As shown in  FIG.  18   , the downward projecting part  95  and the horizontal projecting part  96  are opposed to each other in the vertical direction. Specifically, the horizontal projecting part  96  is disposed below the downward projecting part  95 . As described above, in the state where the connector  3  is mounted on the connector opposed surface  4 A of the input-output board  4 , the downward projecting part  95  is opposed to the horizontal projecting part  96  in the vertical direction without being in contact with the horizontal projecting part  96 . 
     Referring back to  FIG.  1   , when the CPU board  2  is fixed to the support board  5 , the upper contact part  85  comes into contact with the corresponding signal pad  10  (refer also to  FIG.  2   ) of the CPU board  2  and is also pressed downward as indicated by the chain double-dashed line in  FIG.  18   . When the upper contact part  85  is pressed downward, the uppermost part of the upper contact part  85  coincides with the CPU board opposed surface  30 A of the housing  30  in the vertical direction. The amount of displacement of the upper contact part  85  in the vertical direction at this time is the same in all of the contacts  33 . 
     As described above, when the upper contact part  85  is elastically displaced downward, in the early stage of displacement, the downward projecting part  95  comes closer to the horizontal projecting part  96  but does not come into contact with the horizontal projecting part  96 . In the middle stage of displacement, the downward projecting part  95  comes into contact with the horizontal projecting part  96 . In the late stage of displacement, with the downward projecting part  95  being in contact with the horizontal projecting part  96 , the upper contact part  85  is further elastically displaced downward as the curve joining part  83  and the horizontal projecting part  96  are elastically deformed. Then, when the upper contact part  85  is displaced to the position indicated by the chain double-dashed line, the upper contact part  85  comes to rest without being further displaced downward. 
     Thus, the current path from the upper contact part  85  to the signal pad  15  in the early stage of displacement is a path that runs through the upper contact part  85  of the elastic deformation part  82 , the U-shaped curve part  84  of the elastic deformation part  82 , the curve joining part  83  of the elastic deformation part  82 , the fixed part  80 , the soldering part main body  81 A of the soldering part  81 , and the signal pad  15  in sequence. Since the downward projecting part  95  is not in contact with the horizontal projecting part  96  in the early stage of displacement, the elasticity of the elastic deformation part  82  does not harden. Therefore, the connection reliability between the contact  33  and the corresponding signal pad  10  (refer also to  FIG.  2   ) is not degraded. 
     On the other hand, the current path from the upper contact part  85  to the signal pad  15  in the middle and late stages of displacement is a path that runs through the upper contact part  85  of the elastic deformation part  82 , the downward projecting part  95 , the horizontal projecting part  96 , the curve joining part  83 , the fixed part  80 , the soldering part  81 , and the signal pad  15  in sequence. In this manner, since the current path length in the contact  33  is substantially reduced in the middle and late stages of displacement, the resistance value in the contact  33  in the middle and late stages of displacement is reduced. 
     The fourth embodiment is described above, and the above-described embodiment has the following features. 
     The elastic deformation part  82  has the U-shaped curve part  84  interposed between the upper contact part  85  (first contact part) and the fixed part  80 . The downward projecting part  95  (second contact part) is a cantilever extending from the upper contact part  85  toward the input-output board  4  (board). The elastic deformation part  82  further includes the horizontal projecting part  96  (third contact part). The downward projecting part  95  is configured to come into contact with the horizontal projecting part  96  instead of coming into contact with the short-circuiting pad  16  as shown in  FIG.  16   . When the upper contact part  85  is not in contact with the signal pad  10  (first conductor), the downward projecting part  95  is not in contact with the horizontal projecting part  96 , and when the upper contact part  85  comes into contact with the signal pad  10  and the elastic deformation part  82  is elastically deformed, the downward projecting part  95  comes into contact with the horizontal projecting part  96 . The current path length from the upper contact part  85  to the soldering part  81  through the downward projecting part  95  and the horizontal projecting part  96  is shorter than the current path length from the upper contact part  85  to the soldering part  81  through the U-shaped curve part  84 . In this structure, the current path length is reduced without degrading the connection reliability of the contact  33 . 
     Further, as shown in  FIG.  17   , the U-shaped curve part  84  includes the two spring pieces  90  that extend separately from each other in the pitch direction and parallel to each other. The two spring pieces  90  are connected at both ends. The horizontal projecting part  96  is a cantilever disposed between the two spring pieces  90  in the pitch direction when viewed from above. In this structure, the horizontal projecting part  96  is not easily touchable, which avoids damaging the horizontal projecting part  96  when handling the contact  33 . 
     The first to fourth embodiments of the present disclosure are described above. Each of the embodiments may be varied as follows, for example. 
     Although, as shown in  FIG.  1   , the connector  3  is a board-to-board connector that connects the CPU board  2  and the input-output board  4  in the above-described embodiments, the present disclosure is not limited thereto. The connector  3  may be a cable-to-board connector or a cable-to-cable connector. 
     The first and forth embodiments can be combined as desirable by one of ordinary skill in the art. From the disclosure thus described, it will be obvious that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.