Abstract:
A terminal structure of coaxial cable includes a substrate, a coaxial cable, and a conductive shield member. The substrate includes a ground potential layer therein and a ground electrode thereon which is electrically connected to the ground potential layer through a via. The coaxial cable includes a conductor core, a dielectric body surrounding the conductor core, an external conductor layer surrounding the dielectric body, and an outer coat layer surrounding the external conductor layer. The dielectric body has a first protrusion portion configured to protrude from an end of the external conductor layer. The conductor core has a second protrusion portion configured to protrude from an end of the dielectric body. The second protrusion portion is electrically connected to the substrate. The conductive shield member covers the first protrusion portion and the second protrusion portion, and is connected to the ground electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2010-205530, filed on Sep. 14, 2010, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein relate to a terminal structure of coaxial cable, a connector, and a substrate unit. 
       BACKGROUND 
       [0003]    For example, when a high frequency signal of 1 GHz or more is transmitted using a coaxial cable, the high frequency signal is transmitted from the coaxial cable to a signal line on a circuit board via a connector connecting the coaxial cable with the circuit board. If impedances are not matched in a transmission path of the high frequency signal, such as input/output of driver/receiver, a pattern of circuit board, a connector, a cable, and a terminal processing portion of the cable, the transmission signal is reflected in a portion where impedances are not matched, and waveform distortion occurs. Therefore, it is preferred that the impedances are matched in the transmission path of the high frequency signal. 
         [0004]    Generally, a coaxial cable includes a conductor core, a dielectric body surrounding the conductor core, a conductor layer surrounding the dielectric body, and a protective layer surrounding the conductor layer. To electrically connect the conductor core of the coaxial cable with a pattern of the circuit board, at the end portion of the coaxial cable, an outer coat (sheath) is removed and an external conductor layer is exposed. Further, the external conductor layer is removed, and the dielectric body is exposed. Furthermore, the dielectric body is removed, and the conductor core is exposed (protrudes from an end of the dielectric body). 
         [0005]    The impedance of the coaxial cable is determined by the inductance and the capacitance per unit length of the cable. Therefore, the impedances are different between a portion in which the conductor core and the dielectric are exposed and a portion in which the conductor core and the dielectric are covered by the external conductor layer (shield layer). 
         [0006]    JP-A-2007-19232 discloses a terminal structure of coaxial cable in which a shield member is arranged to cover the dielectric exposed by removing the conductor layer. 
         [0007]    However, the conductor core is exposed in a portion in which the dielectric body is removed, so the impedances are not matched between a portion in which the conductor core is exposed and a portion in which the conductor core is covered by the external conductor layer (shield layer). 
       SUMMARY 
       [0008]    According to an embodiment of the invention, a terminal structure of coaxial cable includes a substrate, a coaxial cable, and a conductive shield member. The substrate includes a ground potential layer therein and a ground electrode thereon which is electrically connected to the ground potential layer through a via. The coaxial cable includes a conductor core, a dielectric body surrounding the conductor core, an external conductor layer surrounding the dielectric body, and an outer coat layer surrounding the external conductor layer. The dielectric body has a first protrusion portion configured to protrude from an end of the external conductor layer. The conductor core has a second protrusion portion configured to protrude from an end of the dielectric body. The second protrusion portion is electrically connected to the substrate. The conductive shield member covers the first protrusion portion and the second protrusion portion, and is connected to the ground electrode 
         [0009]    The objects and advantages of embodiments of the invention will be realized and attained at least by the elements, features, and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are not restrictive of the invention. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a perspective view showing an example of a substrate unit according to a first embodiment. 
           [0011]      FIG. 2  is a plan view showing an example of a coaxial cable according to the first embodiment. 
           [0012]      FIG. 3A  is a cross-sectional view taken along line IIIA-IIIA in  FIG. 2 .  FIG. 3B  is a cross-sectional view taken along line IIIB-IIIB in  FIG. 2 .  FIG. 3C  is a cross-sectional view taken along line IIIC-IIIC in  FIG. 2 . 
           [0013]      FIG. 4  is a plan view showing an example of a substrate according to the first embodiment. 
           [0014]      FIG. 5  is a cross-sectional view taken along line V-V in  FIG. 4 . 
           [0015]      FIG. 6  is a perspective view showing an example of a shield member according to the first embodiment. 
           [0016]      FIG. 7  is a cross-sectional view taken along a direction in which a conductor core extends in  FIG. 1  according to the first embodiment. 
           [0017]      FIG. 8  is a cross-sectional view taken along a direction in which a conductor core extends in  FIG. 1  according to a second embodiment. 
           [0018]      FIG. 9  is a cross-sectional view taken along a direction in which a conductor core extends in  FIG. 1  according to a third embodiment. 
           [0019]      FIG. 10  is a perspective view showing an example of a connector according to a fourth embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    A substrate unit  100  of a first embodiment will be described with reference to  FIG. 1 .  FIG. 1  is a perspective view showing an example of the substrate unit  100  of the present embodiment. As shown in  FIG. 1 , the substrate unit  100  of the present embodiment can include a coaxial cable  110 , a substrate  140 , and a shield member  160 . Hereinafter, the configuration of each component will be described in detail. 
         [0021]    First, the coaxial cable  110  of the present embodiment will be described with reference to  FIGS. 2 and 3 .  FIG. 2  is a plan view showing an example of the coaxial cable  110  of the present embodiment. The coaxial cable  110  of the present embodiment can be a two-core coaxial cable. FIG.  3 A is a cross-sectional view taken along line IIIA-IIIA in  FIG. 2 .  FIG. 3B  is a cross-sectional view taken along line IIIB-IIIB in  FIG. 2 .  FIG. 3C  is a cross-sectional view taken along line IIIC-IIIC in  FIG. 2 . 
         [0022]    As shown in  FIG. 2 , the coaxial cable  110  includes conductor cores  112 , dielectrics  114 , an external conductor layer (shield layer)  116 , an outer coat layer (sheath)  118 , and a grounding wire (drain wire)  120 . In this example, as shown in  FIG. 3A , the dielectric  114  surrounds the conductor core  112 . The external conductor layer (shield layer)  116  surrounds the dielectrics  114 . The outer coat layer (sheath)  118  surrounds the external conductor layer (shield layer)  116 . 
         [0023]    The conductor core  112  and the grounding wire (drain wire)  120  are formed of a conductive material such as, for example, copper. The external conductor layer (shield layer)  116  can be formed by wrapping metal foil (Al, Cu, or the like) around the dielectric  114 . The dielectric  114  is formed of an insulating material such as, for example, a polyethylene system resin and a fluorine system resin. The outer coat layer (sheath)  118  is formed of an insulating material such as, for example, a polyvinyl chloride series resin, a polyethylene system resin, or a fluorine system resin. 
         [0024]    As shown in  FIG. 2 , the coaxial cable  110  can include a first protrusion portion  122  and a second protrusion portion  124  at the end of the coaxial cable  110 . In the first protrusion portion  122 , the dielectric  114  protrudes from the external conductor layer (shield layer)  116 . In the second protrusion portion  124 , the conductor core  112  protrudes from the dielectric  114 . 
         [0025]    As described above, the impedance of the coaxial cable  110  is determined by the inductance and the capacitance per unit length of the cable. As shown in  FIG. 3B , in the first protrusion portion  122 , the dielectric  114  protrudes from the external conductor layer (shield layer)  116 , and the dielectric  114  is covered by air. As shown in  FIG. 3C , in the second protrusion portion  124 , the conductor core  112  protrudes from the dielectric  114 , and the conductor core  112  is covered by air. Therefore, the impedances in the first protrusion portion  122  and the second protrusion portion  124  are different from the impedance of the coaxial cable  110  in a portion in which the circumference of the dielectric  114  is covered by the external conductor layer (shield layer)  116  and the outer coat layer (sheath)  118  as shown in  FIG. 3A . 
         [0026]    In the substrate unit  100  of the present embodiment, by using the substrate  140  and the shield member  160  described below, it is possible to match impedances more effectively than conventionally known. 
         [0027]    Although in the present embodiment an example of two-core coaxial cable is described, a single-core coaxial cable can also be used. 
         [0028]    Next, the substrate  140  of the present embodiment will be described with reference to  FIGS. 4 and 5 .  FIG. 4  is a plan view showing an example of the substrate  140  of the present embodiment.  FIG. 5  is a cross-sectional view taken along line V-V in  FIG. 4 . As shown in  FIG. 4 , the substrate  140  of the present embodiment can include ground electrodes  142 , a ground potential layer  144 , vias  146 , electrodes  148 , and signal patterns  150 . 
         [0029]    The ground electrode  142  is provided on the surface of the substrate  140 . The substrate  140  in the example shown in  FIG. 4  includes two ground electrodes  142 . As described below, the ground electrode  142  is connected to the shield member  160 . 
         [0030]    The ground potential layer  144  is provided in an inner layer of the substrate  140 . Therefore, the ground potential layer  144  is shown by a dashed line in  FIG. 4 . The ground potential layer  144  is designed as the ground (0 V) of the circuit. The ground potential layer  144  is provided in an area including at least the first protrusion portion  122  and the second protrusion portion  124  of the coaxial cable  110  in a plan view. The ground potential layer  144  is provided so that the ground potential layer  144  overlaps the ground electrodes  142  in a plan view. 
         [0031]    The vias  146  are formed in areas where the ground potential layer  144  overlaps the ground electrodes  142  in a plan view. As shown in  FIG. 5 , the vias  146  electrically connect the ground electrodes  142  with the ground potential layer  144 . Therefore, the ground electrodes  142  have a ground potential via the vias  146 . 
         [0032]    The two conductor cores  112  of the coaxial cable  110  are connected to the electrodes  148 . Therefore, the substrate  140  in the example shown in  FIG. 4  includes two electrodes  148 . 
         [0033]    The signal pattern  150  is connected to the electrode  148 . In the example shown in  FIG. 4 , the signal pattern  150  has a shape circumventing the ground electrodes  142  so that the signal pattern  150  is not in contact with the ground electrodes  142 . The shape of the signal pattern  150  is not particularly limited, but may be any shape that is not in contact with the ground electrodes  142 . 
         [0034]    Next, the shield member  160  of the present embodiment will be described with reference to  FIG. 6 . The shield member  160  includes a housing  162 , solder terminals  164 , and an opening  166 . The housing  162  is formed of a conductive material such as, for example, a tinned brass plate. As shown in  FIG. 6 , the housing  162  has a rectangular solid shape. As shown in  FIG. 1 , the shield member  160  is provided to cover the coaxial cable  110  and the substrate  140 , so no surface structure is formed at the bottom and the rear of the shield member  160  in  FIG. 6 . 
         [0035]    The solder terminals  164  are provided on the front surface and the side surfaces of the housing  162 . In the example shown in  FIG. 6 , two solder terminals  164  are provided to each of the front surface, the right side surface, and the left side surface of the housing  162 . As shown in  FIG. 1 , the solder terminals  164  are provided to be positioned on the ground electrodes  142 . By soldering the solder terminals  164  to the ground electrodes  142 , the ground electrodes  142  and the shield member  160  are electrically connected to each other. 
         [0036]    The opening  166  is formed in the top surface of the housing  162 . As shown in  FIG. 1 , the opening  166  is an opening for pulling out the grounding wire (drain wire)  120  onto the top surface of the housing  162 . The grounding wire (drain wire)  120  pulled out onto the top surface of the housing  162  through the opening  166  is soldered on the top surface of the housing  162 . 
         [0037]    By arranging the coaxial cable  110 , the substrate  140 , the shield member  160  described above into the form shown  FIG. 1 , the substrate unit  100  of the present embodiment is formed. Here, the connection relationship between the components included in the substrate unit  100  of the present embodiment will be described with reference to  FIG. 7 .  FIG. 7  is a cross-sectional view taken along a direction in which the conductor core extends in  FIG. 1 . 
         [0038]    As shown in  FIG. 7 , the shield member  160  is arranged to cover at least the first protrusion portion  122  and the second protrusion portion  124 . The grounding wire (drain wire)  120  is connected to the top surface of the shield member  160 . The bottom end of the shield member  160  is connected to the ground electrodes  142 . The ground electrodes  142  and the ground potential layer  144  are electrically connected to each other via the vias  146  (not shown in  FIG. 7 ). Therefore, the ground potential of the ground potential layer  144 , and the potentials of the vias  146 , the ground electrodes  142 , the shield member  160 , the grounding wire (drain wire)  120 , and the external conductor layer (shield layer)  116  become the same ground potential. As a result, the space around the first protrusion portion  122  and the second protrusion portion  124  of the coaxial cable  110  is covered with the ground potential, so the impedances of the coaxial cable  110  can be matched better than before. 
         [0039]    In addition, the shield member  160  can cover the first protrusion portion  122  and the second protrusion portion  124 , so that it is possible to suppress cross-talk and radio noise. 
         [0040]    Next, the substrate unit  100  according to a second embodiment will be described. The substrate unit  100  of the second embodiment is different from that of the first embodiment in a point that a conductive material is provided between the first protrusion portion  122  and an inner wall of the shield member  160 . The other basic configuration of the substrate unit  100  of the second embodiment is the same as that of the first embodiment described above. Therefore, the description of the same configuration as that of the first embodiment will be omitted. Hereinafter, portions different from the first embodiment will be described with reference to  FIG. 8 . 
         [0041]      FIG. 8  is a cross-sectional view taken along a direction in which the conductor core extends in  FIG. 1  according to the second embodiment. As shown in  FIG. 8 , the substrate unit  100  of the second embodiment includes a conductive material  168  between the first protrusion portion  122  and the inner wall of the shield member  160  in addition to the configuration described in the first embodiment. The conductive material  168  is, for example, a conductive sponge. It is preferred that the conductive material  168  is formed of the same material as that of the external conductor layer (shield layer)  116 . 
         [0042]    In the substrate unit  100  of the present second embodiment, the dielectric  114  exposed from the external conductor layer (shield layer)  116  in the first protrusion portion  122  is covered with the conductive material  168  instead of air. Therefore, the impedance in the first protrusion portion  122  can be close to the impedance of the portion in which the dielectric  114  is covered with the external conductor layer (shield layer)  116 . As a result, it is possible to effectively match the impedances of the coaxial cable  110 . 
         [0043]    Next, the substrate unit  100  according to a third embodiment will be described. The substrate unit  100  of the third embodiment is different from that of the first embodiment in a point that an insulating material is provided between the second protrusion portion  124  and the inner wall of the shield member  160 . The other basic configuration of the substrate unit  100  of the third embodiment is the same as that of the first embodiment described above. Therefore, the description of the same configuration as that of the first embodiment will be omitted. Hereinafter, portions different from the first embodiment will be described with reference to  FIG. 9 . 
         [0044]      FIG. 9  is a cross-sectional view taken along a direction in which the conductor core extends in  FIG. 1  according to the third embodiment. As shown in  FIG. 9 , the substrate unit  100  of the third embodiment includes an insulating material  170  between the second protrusion portion  124  and the inner wall of the shield member  160  in addition to the configuration described in the first embodiment. It is preferred that the insulating material  170  is formed of the same material as that of the dielectric  114 . 
         [0045]    In the substrate unit  100  of the third embodiment, the conductor core  112  exposed from the dielectric  114  in the second protrusion portion  124  is covered with the insulating material  170  instead of air. Therefore, the impedance in the second protrusion portion  124  can be close to the impedance of the portion in which the conductor core  112  is covered with the dielectric  114 . As a result, it is possible to effectively match the impedances of the coaxial cable  110 . 
         [0046]    In the example shown in  FIG. 9 , the dielectric  114  exposed from the external conductor layer (shield layer)  116  in the first protrusion portion  122  is covered by air. However, as described in the second embodiment, the dielectric  114  exposed from the external conductor layer (shield layer)  116  in the first protrusion portion  122  may be covered with the conductive material  168 . By providing the insulating material  170  between the second protrusion portion  124  and the inner wall of the shield member  160  as well as providing the conductive material  168  between the first protrusion portion  122  and the inner wall of the shield member  160 , it is possible to further match the impedances of the coaxial cable  110 . 
         [0047]    Next, a connector  180  of a fourth embodiment will be described with reference to  FIG. 10 .  FIG. 10  is a perspective view showing an example of the connector of the present embodiment. As shown in  FIG. 10 , the connector  180  of the fourth embodiment includes the substrate  140 , the shield members  160 , and contacts  182 . The coaxial cables  110  are connected to the connector  180 . 
         [0048]    The coaxial cable  110 , the substrate  140 , and the shield member  160  of the fourth embodiment are the same as the coaxial cable  110 , the substrate  140 , and the shield member  160  described in the first embodiment, so the descriptions thereof will be omitted. As shown in  FIG. 10 , the contacts  182  are connected to the substrate  140 . Although the contact  182  shown in  FIG. 10  is a plug type contact, a receptacle type contact may be used. 
         [0049]    In the connector  180  of the fourth embodiment, the shield members  160  are arranged to cover at least the first protrusion portion  122  and the second protrusion portion  124 . The space around the first protrusion portion  122  and the second protrusion portion  124  of the coaxial cable  110  is covered with the ground potential. Therefore, in the same manner as in the first embodiment, it is possible to effectively match the impedances of the coaxial cable  110 . 
         [0050]    In the fourth embodiment, in the same manner as in the second embodiment, the conductive material  168  may be provided between the first protrusion portion  122  and the inner wall of the shield member  160 . In the fourth embodiment, in the same manner as in the third embodiment, the insulating material  170  may be provided between the second protrusion portion  124  and the inner wall of the shield member  160 . 
         [0051]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventors to further the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.