Patent Publication Number: US-11658376-B2

Title: Signal transmission line including a flexible resin laminate having interior hollow portions overlapping the signal transmission line with the hollow portions having a vent hole

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2016-012945 filed on Jan. 27, 2016 and is a Continuation Application of U.S. application Ser. No. 16/843,979 filed on Apr. 9, 2020, now U.S. Pat. No. 11,251,511 issued on Feb. 15, 2022, which is a Continuation Application of U.S. application Ser. No. 16/022,761 filed on Jun. 29, 2018, now U.S. Pat. No. 10,673,114 issued on Jun. 2, 2020, which is a Continuation Application of PCT Application No. PCT/JP2017/000960 filed on Jan. 13, 2017. The entire contents of each application are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a signal transmission line that transmits a high-frequency signal. 
     2. Description of the Related Art 
     At present, a large number of signal transmission lines to be used for transmission of a high frequency signal are obtained by forming a signal conductor on a dielectric substrate. In such a signal transmission line, it is preferred that a transmission loss should be low. Therefore, for example, a printed circuit board for high-speed transmission disclosed in Japanese Unexamined Patent Application Publication No. 2003-133661 includes an air layer in a dielectric substrate, and a signal conductor arranged so as to be in contact with the air layer. 
     However, the printed circuit board for high-speed transmission disclosed in Japanese Unexamined Patent Application Publication No. 2003-133661 is not easily subjected to shape deformation, such as bending or twisting. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide signal transmission lines having reduced transmission loss and being easily deformed. 
     A signal transmission line according to a preferred embodiment of the present invention includes a laminate, a signal conductor, a hollow portion, and a reinforcing conductor. The laminate includes a plurality of resin layers each of which has flexibility and are laminated on one another, and the laminate has flexibility. The signal conductor extends in a signal transmission direction of the laminate and is disposed in an intermediate position in a laminating direction in which the plurality of resin layers in the laminate are laminated on each other. The hollow portion is provided in the laminate and defined by an opening provided at a portion of the plurality of resin layers. The reinforcing conductor is provided in the laminate. 
     The hollow portion is disposed at a position that overlaps with the signal conductor, in a plan view of the laminate from a surface perpendicular or substantially perpendicular to the laminating direction. The reinforcing conductor is disposed at a position different from the position of the hollow portion in a plan view. 
     With this configuration, the transmission loss of a high frequency signal that the signal conductor transmits is able to be significantly reduced or prevented by the hollow portion provided in the laminate. In addition, since the laminate has flexibility, the signal transmission line is able to be easily deformed. Further, due to the hollow portion provided in the laminate, the signal transmission line is able to be more easily deformed. On the other hand, the strength of a holding portion that does not include the hollow portion is increased by the reinforcing conductor, so that crushing of the hollow portion due to deformation of the laminate is able to be significantly reduced or prevented. 
     In addition, a signal transmission line according to a preferred embodiment of the present invention includes a ground conductor that faces the signal conductor across the hollow portion in the laminating direction. 
     With this configuration, a microstrip line or a stripline is able to be obtained as a signal transmission line. Then, the hollow portion is provided between the signal conductor and the ground conductor, so that a transmission loss is significantly reduced or prevented. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the reinforcing conductor preferably includes a plurality of reinforcing conductors, and the plurality of reinforcing conductors are preferably disposed in the laminating direction. 
     With this configuration, the strength of the holding portion that does not include the hollow portion is further increased, so that crushing of the hollow portion is able to be further significantly reduced or prevented. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the reinforcing conductor preferably includes a plurality of reinforcing conductors, and the plurality of reinforcing conductors are preferably disposed at intervals in the signal transmission direction. 
     With this configuration, the difference in strength of the holding portion is able to be provided in the signal transmission direction. As a result, the laminate is more easily deformed while crushing of the hollow portion is significantly reduced or prevented. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the plurality of reinforcing conductors arranged in the laminating direction are preferably connected to each other through an interlayer connection conductor in the laminating direction. 
     With this configuration, the strength of the holding portion that does not include the hollow portion is further increased, so that crushing of the hollow portion is able to be further significantly reduced or prevented. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the hollow portion preferably includes an insulating member disposed at the position that overlaps with the signal conductor in a plan view, the insulating member having a height in the laminating direction. 
     With this configuration, crushing of the hollow portion is able to be further significantly reduced or prevented. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the thickness of a portion that does not overlap with the hollow portion in a resin layer on which the signal conductor is provided is preferably smaller than the thickness of a portion that overlaps with the hollow portion. 
     With this configuration, when the plurality of resin layers are laminated to obtain the laminate, stress that acts on the resin layer on which the signal conductor is provided is able to be significantly reduced or prevented. As a result, the signal conductor is arranged in a desired shape at a desired position in the laminate. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the hollow portion is filled with an inert gas. 
     With this configuration, crushing of the hollow portion is able to be significantly reduced or prevented when the pressure in the hollow portion becomes lower. Further, in a case in which the signal conductor is exposed to the hollow portion, the oxidation of the signal conductor is significantly reduced or prevented. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the hollow portion is exposed to outside of the signal transmission line through a vent hole provided in the laminate. 
     With this configuration, the pressure in the hollow portion is the same as the pressure outside of the signal transmission line, which significantly reduces or prevents the hollow portion from being crushed. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the signal conductor is exposed to the hollow portion, and, on the surface of the signal conductor, the surface being exposed to the hollow portion, the signal conductor includes a protective film that significantly reduces or prevents oxidation of the signal conductor. 
     With this configuration, the oxidation of the signal conductor is significantly reduced or prevented. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the laminate preferably includes a portion that includes the hollow portion and a portion that does not include the hollow portion in the signal transmission direction; and the portion that does not include the hollow portion is preferably a bent portion. 
     With this configuration, in any bent shape, the hollow portion is not crushed. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the bent portion is preferably thinner than the portion that includes the hollow portion in the laminate. 
     With this configuration, the laminate is more easily bent. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the following configuration may also be provided. A plurality of signal conductors are disposed in the width direction perpendicular or substantially perpendicular to the laminating direction in the laminate. The laminate includes an intermediate holding portion that does not include the hollow portion between the plurality of signal conductors, in the width direction. The intermediate holding portion includes the reinforcing conductor. 
     With this configuration, in a multicore signal transmission line, the reduction of transmission loss and the ease of deformation are able to be achieved. 
     In addition, in a signal transmission line according to a preferred embodiment of the present invention, the reinforcing conductor provided in the intermediate holding portion is preferably grounded. 
     With this configuration, coupling between adjacent signal conductors is significantly reduced or prevented. 
     According to various preferred embodiments of the present invention, signal transmission lines having a low transmission loss and being easily deformed are provided. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings, where the same or similar features in the drawings are labeled by the same reference labels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an external perspective view of a signal transmission line according to a first preferred embodiment of the present invention. 
         FIG.  2    is an exploded perspective view of the signal transmission line according to the first preferred embodiment of the present invention. 
         FIGS.  3 A to  3 C  are cross-sectional views of the signal transmission line according to the first preferred embodiment of the present invention. 
         FIG.  4    is a cross-sectional view of a signal transmission line according to a second preferred embodiment of the present invention. 
         FIG.  5    is a cross-sectional view of a signal transmission line according to a third preferred embodiment of the present invention. 
         FIG.  6    is an exploded perspective view of a signal transmission portion of a signal transmission line according to a fourth preferred embodiment of the present invention. 
         FIG.  7    is a cross-sectional view of the signal transmission portion of the signal transmission line according to the fourth preferred embodiment of the present invention. 
         FIG.  8    is an exploded perspective view of a signal transmission portion of a signal transmission line according to a fifth preferred embodiment of the present invention. 
         FIGS.  9 A and  9 B  are cross-sectional views of the signal transmission portion of the signal transmission line according to the fifth preferred embodiment of the present invention. 
         FIG.  10    is a cross-sectional view of a signal transmission portion of a signal transmission line according to a sixth preferred embodiment of the present invention. 
         FIG.  11    is a cross-sectional view of a signal transmission portion of a signal transmission line according to a seventh preferred embodiment of the present invention. 
         FIG.  12    is an exploded perspective view of a signal transmission portion of a signal transmission line according to an eighth preferred embodiment of the present invention. 
         FIG.  13    is an exploded perspective view of a signal transmission portion of a signal transmission line according to a ninth preferred embodiment of the present invention. 
         FIG.  14    is a cross-sectional view of the signal transmission portion of the signal transmission line according to the ninth preferred embodiment of the present invention. 
         FIG.  15    is an external perspective view of a signal transmission line according to a tenth preferred embodiment of the present invention. 
         FIG.  16    is a side cross-sectional view of a structure of a signal transmission line according to an eleventh preferred embodiment of the present invention. 
         FIG.  17    is a side cross-sectional view of a structure of a signal transmission line according to a twelfth preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A signal transmission line according to a first preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  1    is an external perspective view of a signal transmission line according to the first preferred embodiment of the present invention.  FIG.  2    is an exploded perspective view of a signal transmission portion of the signal transmission line according to the first preferred embodiment of the present invention.  FIG.  3 A  is an A-A cross-sectional view of the signal transmission line as shown in  FIG.  1    according to the first preferred embodiment of the present invention,  FIG.  3 B  is a B-B cross-sectional view of the signal transmission line as shown in  FIG.  1    according to the first preferred embodiment of the present invention, and  FIG.  3 C  is a C-C cross-sectional view of the signal transmission line as shown in  FIG.  1    according to the first preferred embodiment of the present invention. Features of the signal transmission line according to the first preferred embodiment shown in each of  FIGS.  1 ,  2 ,  3 A,  3 B, and  3 C  that are the same as or similar to one another are denoted by the same reference characters. 
     As illustrated in  FIG.  1   , a signal transmission line  10  includes a laminate  20 . The laminate  20  includes a signal transmission portion  21  and external connection portions  22  and  23 . The signal transmission portion  21  and the external connection portions  22  and  23  are integrally provided. The external connecting portion  22  is provided at one end in a direction in which the signal transmission portion  21  extends. The external connecting portion  23  is provided at the other end in a direction in which the signal transmission portion  21  extends. The external connection conductor  22  includes a first surface and external connection conductors  61  and  71  provided on the first surface. The external connection conductor  23  includes a first surface and external connection conductors  62  and  72  provided on the first surface. 
     As illustrated in  FIG.  2   , the laminate  20  has flexibility and is formed by stacking and thermally pressing resin layers  211 ,  212 ,  213 , and  214 , the resin layers having thermoplasticity. The resin layer  214  defines a first surface of the laminate  20 , and the resin layer  211  defines a second surface of the laminate  20 . The resin layers  211 ,  212 ,  213 , and  214  are preferably made of a material primarily including liquid crystal polymer, for example. Since the resin layers  211 ,  212 ,  213 , and  214  have flexibility, the laminate  20  also has flexibility. 
     A portion corresponding to the signal transmission portion  21  as illustrated in  FIG.  1    in the resin layer  212  includes resin layers  2121  and  2122 . The resin layers  2121  and  2122  are provided at both ends in the width direction that is perpendicular or substantially perpendicular to a direction in which the laminate  20  extends, as a signal transmission direction, and that is also perpendicular or substantially perpendicular to the laminating direction. The resin layer  2121  and the resin layer  2122  are disposed at intervals. In this configuration, in the laminate  20 , a hollow portion  81  surrounded by the resin layers  211 ,  2121 ,  2122 , and  213  is provided. It is to be noted that, at both ends of the hollow portion  81  in a direction in which the laminate  20  extends, the resin layer  212  that defines the external connection portions  22  and  23  ( FIG.  1   ) provides a wall surface. As a result, the hollow portion  81  is an enclosed space. 
     As illustrated in  FIGS.  2  and  3 C , a conductor  41  is provided on a surface of the resin layer  211  opposite to the resin layers  2121  and  2122  ( FIG.  2   ) so as to cover the entire or substantially the entire surface of the resin layer  211 . In other words, the conductor  41  is provided on the entire or substantially the entire area of the second surface of the laminate  20 . The conductor  41  is connected to the external connection conductor  71  ( FIG.  1   ) through an interlayer connection conductor, and is connected to the external connection conductor  72  through an interlayer connection conductor  702 . 
     As illustrated in  FIG.  2   , on the surfaces of the resin layers  2121  and  2122  on the side of the resin layer  211 , reinforcing conductors  51  and  52  are respectively provided. The reinforcing conductors  51  and  52  extend in a direction in which the laminate  20  extends, as the signal transmission direction. The reinforcing conductors  51  and  52  are disposed at a portion that corresponds to at least the signal transmission portion  21 . The width of the reinforcing conductors  51  and  52  is preferably smaller than the width of the resin layers  2121  and  2122 . The reinforcing conductor  51  is disposed in the center or substantially the center of the width direction of the resin layer  2121 , and the reinforcing conductor  52  is disposed in the center or substantially the center of the width direction of the resin layer  2122 . 
     On the surface of the resin layer  213  on the side of the resin layer  212 , the signal conductor  31  and the reinforcing conductors  51  and  52  are provided. The signal conductor  31  and the reinforcing conductors  51  and  52  extend in a direction in which the laminate  20  extends, as the signal transmission direction. The signal conductor  31  extends to the external connection portions  22  and  23  in addition to the signal transmission portion  21 . The reinforcing conductors  51  and  52  are provided in the signal transmission portion  21 . The signal conductor  31  is disposed in the center or substantially the center of the width direction of the resin layer  213 . In other words, the signal conductor  31  is disposed at a portion that is not in contact with the resin layers  2121  and  2122  in the resin layer  213 . As a result, the signal conductor  31  overlaps with the hollow portion  81  in a plan view from a surface (the first surface and the second surface) perpendicular or substantially perpendicular to the laminate  20  in the laminating direction. In addition, the signal conductor  31  is exposed to the hollow portion  81 . One end in a direction in which the signal conductor  31  extends is connected to the external connection conductor  61  ( FIG.  1   ) through an interlayer connection conductor. Another end in a direction in which the signal conductor  31  extends is connected to the external connection conductor  62  through an interlayer connection conductor  602  as illustrated in  FIG.  3 B . 
     The reinforcing conductor  51  of the resin layer  213 , in the above plan view, is disposed at a position that overlaps with the reinforcing conductor  51  of the resin layer  2121 . The reinforcing conductor  52  of the resin layer  213 , in the above plan view, is disposed at a position that overlaps with the reinforcing conductor  52  of the resin layer  2122 . 
     With such a configuration in which the conductor  41  ( FIGS.  3 B and  3 C ) is a ground conductor, a microstrip line in which the signal conductor  31  faces the conductor  41  through the hollow portion  81  is provided as illustrated in  FIG.  3 A . Then, the signal conductor  31  is exposed to the hollow portion  81  preferably being a gas layer, such as an air layer, for example, so that the occurrence of dielectric loss is significantly reduced or prevented, and a microstrip line in which transmission loss is significantly reduced or prevented is obtained. In addition, since the signal conductor  31  is provided in the laminate  20 , the signal conductor  31  is not exposed to an external environment, so that deterioration of characteristics, such as an increase in transmission loss due to oxidation of the signal conductor  31 , is significantly reduced or prevented. 
     With the above-described configuration, the reinforcing conductors  51  and  52  are positioned so as not to overlap with the hollow portion  81 , so that the shape of the hollow portion  81  is able to be maintained while the laminate  20  has flexibility. 
     It is to be noted that, while the present preferred embodiment illustrates a mode in which the reinforcing conductors  51  and  52  are preferably provided in two layers, for example, the reinforcing conductors  51  and  52  may be provided in one layer or may be formed in three or more layers. For example, a pair of the reinforcing conductors  51  and  52  of any of the resin layers  212  and  213  may not be provided. 
     Subsequently, a signal transmission line according to a second preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  4    is a cross-sectional view of a signal transmission line according to the second preferred embodiment of the present invention. 
     A signal transmission line  10 A according to the second preferred embodiment of the present invention is a stripline while the signal transmission line  10  according to the first preferred embodiment of the present invention is a microstrip line. It is to be noted that the material and other characteristics of a resin layer are preferably the same or substantially the same as the material and other characteristics of the signal transmission line according to the first preferred embodiment of the present invention, and overlapping description will be omitted. Features of the signal transmission line according to the second preferred embodiment shown in  FIG.  4    that are the same as or similar to the features shown in the signal transmission line according to the first preferred embodiment shown in  FIGS.  1 ,  2 , and  3 A- 3 C  are denoted by the same reference characters. In addition, although the following preferred embodiments including the present preferred embodiment specifically illustrate the shape of the signal transmission portion, an external connection portion is able to be provided by the same or substantially the same layer structure as the signal transmission portion and the structure with which a hollow portion and a reinforcing conductor are not provided, and the illustration and description will be omitted. 
     A signal transmission portion  21 A of the laminate includes resin layers  211 A,  2121 A,  2122 A,  213 A,  2141 A,  2142 A, and  215 A. 
     The resin layers  2121 A and  2122 A are provided between the resin layer  211 A and the resin layer  213 A. The resin layer  2121 A is provided at one end in the width direction of the resin layers  211 A and  213 A. The resin layer  2122 A is provided at another end in the width direction of the resin layers  211 A and  213 A. The resin layer  2121 A and the resin layer  2122 A are disposed at intervals in the width direction of the signal transmission portion  21 A of the laminate. The resin layers  211 A,  2121 A,  2122 A, and  213 A define a hollow portion  81 . 
     The resin layers  2141 A and  2142 A are provided between the resin layer  213 A and the resin layer  215 A. The resin layer  2141 A is provided at one end in the width direction of the resin layers  213 A and  215 A. The resin layer  2142 A is provided at another end in the width direction of the resin layers  213 A and  215 A. The resin layer  2141 A and the resin layer  2142 A are disposed at intervals in the width direction of the signal transmission portion  21 A of the laminate. The resin layers  213 A,  2141 A,  2142 A, and  215 A define a hollow portion  82 . The hollow portion  81  and the hollow portion  82  overlap with each other in a plan view. 
     The signal conductor  31  is provided on the side of the hollow portion  81  in the resin layer  213 A, and is exposed to the hollow portion  81 . 
     The conductor  41  is provided on a surface opposite to the side of the resin layers  2121 A and  2122 A in the resin layer  211 A. The conductor  42  is provided on a surface opposite to the side of the resin layers  2141 A and  2142 A in the resin layer  215 A. With such a configuration that the conductors  41  and  42  are a ground conductor, a stripline in which the signal conductor  31  is provided between the conductors  41  and  42  is obtained. In such a case, the hollow portion  81  is provided between the signal conductor  31  and the conductor  41 , and the hollow portion  82  is provided between the signal conductor  31  and the conductor  42 , so that dielectric loss is significantly reduced or prevented and transmission loss is able to be significantly reduced or prevented. In addition, similarly to the first preferred embodiment, the signal conductor  31  is able to be protected from the external environment. 
     The reinforcing conductor  51 , in a plan view, is disposed at a portion with which the resin layers  211 A,  2121 A,  213 A,  2141 A, and  215 A overlap. The reinforcing conductor  52 , in a plan view, is disposed at a portion with which the resin layers  211 A,  2122 A,  213 A,  2142 A, and  215 A overlap. In other words, the reinforcing conductors  51  and  52 , in a plan view, are disposed at portions (hollow-shaped holding portions) that do not overlap with the hollow portions  81  and  82 . With such a configuration, as is similar to the first preferred embodiment, the shape of the hollow portions  81  and  82  is able to be maintained while the flexibility as a laminate is maintained. 
     Subsequently, a signal transmission line according to a third preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  5    is a cross-sectional view of a signal transmission line according to the third preferred embodiment of the present invention. 
     A signal transmission line  10 B according to the third preferred embodiment of the present invention does not include the conductors  41  and  42  that are included in the signal transmission line  10 A according to the second preferred embodiment of the present invention. In other words, the signal transmission line  10 B is a single-line signal transmission line. Features of the signal transmission line according to the third preferred embodiment shown in  FIG.  5    that are the same as or similar to the features shown in the signal transmission line according to the second preferred embodiment shown in  FIG.  4    are denoted by the same reference characters. 
     A signal transmission portion  21 B of the laminate includes resin layers  211 B,  2121 B,  2122 B,  213 B,  2141 B,  2142 B, and  215 B. The layered structure of the resin layers  211 B,  2121 B,  2122 B,  213 B,  2141 B,  2142 B, and  215 B is preferably the same or substantially the same as the layered structure of the resin layers  211 A,  2121 A,  2122 A,  213 A,  2141 A,  2142 A, and  215 A in the signal transmission portion  21 A according to the second preferred embodiment of the present invention. 
     The signal conductor  31  is exposed to the hollow portion  81 . The reinforcing conductors  51  and  52  include four layers at portions that do not overlap with the hollow portions  81  and  82  in a plan view. 
     Even with such a configuration, the transmission loss of the signal conductor  31  is able to be significantly reduced or prevented, and the signal transmission line  10 B that has flexibility is obtained. 
     It is to be noted that it is also possible to omit the resin layers  2141 B,  2142 B, and  215 B in the present preferred embodiment. 
     Subsequently, a signal transmission line according to a fourth preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  6    is an exploded perspective view of a signal transmission portion of a signal transmission line according to the fourth preferred embodiment of the present invention.  FIG.  7    is a cross-sectional view of the signal transmission portion of the signal transmission line according to the fourth preferred embodiment of the present invention.  FIG.  7    illustrates a portion at which an interlayer connection conductor is arranged. 
     A signal transmission line  10 C according to the fourth preferred embodiment of the present invention is obtained by adding interlayer connection conductors  510  and  520  to the signal transmission line  10 B according to the third preferred embodiment of the present invention. Other configurations are preferably the same or substantially the same as the configurations of the signal transmission line  10 B according to the third preferred embodiment of the present invention, and overlapping description will be omitted. Features of the signal transmission line according to the fourth preferred embodiment shown in  FIGS.  6  and  7    that are the same as or similar to the features of the signal transmission line according to the third preferred embodiment shown in  FIG.  5    are denoted by the same reference characters. 
     A signal transmission portion  21 C of the laminate includes resin layers  211 C,  2121 C,  2122 C,  213 C,  2141 C,  2142 C, and  215 C. The resin layers  211 C,  2121 C,  2122 C,  213 C,  2141 C,  2142 C, and  215 C correspond to the resin layers  211 B,  2121 B,  2122 B,  213 B,  2141 B,  2142 B, and  215 B, respectively. 
     The reinforcing conductor  51  includes plural reinforcing conductors  51  and the reinforcing conductors  51  of each layer are connected by the interlayer connection conductor  510 . The reinforcing conductor  52  includes plural reinforcing conductors  52  and the reinforcing conductors  52  of each layer are connected by the interlayer connection conductor  520 . A plurality of interlayer connection conductors  510  and  520  are provided at intervals in a direction in which the signal transmission portion  21 C extends. 
     With such a configuration, the strength of the holding portion that supports the hollow portions  81  and  82  ( FIG.  7   ) is able to be further increased, so that it is possible to make the hollow portions  81  and  82  more difficult to be crushed. In such a case, the balance between the strength of the holding portion and the flexibility is able to be properly adjusted by properly adjusting the intervals of the plurality of the interlayer connection conductors  510  and  520 . 
     It is to be noted that the configuration of the present preferred embodiment is applicable to the structure of the microstrip line and the structure of the stripline according to the first and second preferred embodiments of the present invention. At this time, the reinforcing conductors  51  and  52  may be connected or may not be connected to the conductor  41  and the conductor  42  being ground conductors. 
     Subsequently, a signal transmission line according to a fifth preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  8    is an exploded perspective view of a signal transmission portion of a signal transmission line according to the fifth preferred embodiment of the present invention.  FIGS.  9 A and  9 B  are cross-sectional views of the signal transmission portion of the signal transmission line according to the fifth preferred embodiment of the present invention.  FIG.  9 A  illustrates a portion at which a reinforcing conductor and an interlayer connection conductor are provided.  FIG.  9 B  illustrates a portion at which a reinforcing conductor and an interlayer connection conductor are not provided. 
     A signal transmission line  10 D according to the fifth preferred embodiment of the present invention differs with respect to reinforcing conductors  511  and  521  ( FIGS.  8  and  9 A ) as compared to the signal transmission line  10 C according to the fourth preferred embodiment of the present invention. Other configurations are preferably the same or substantially the same as the configurations of the signal transmission line  10 C according to the fourth preferred embodiment of the present invention, and overlapping description will be omitted. Features of the signal transmission line according to the fifth preferred embodiment shown in  FIGS.  8 ,  9 A, and  9 B  that are the same as or similar to the features of the signal transmission line according to the fourth preferred embodiment shown in  FIGS.  6  and  7    are denoted by the same reference characters. 
     A signal transmission portion  21 D of the laminate includes resin layers  211 D,  2121 D,  2122 D,  213 D,  2141 D,  2142 D, and  215 D. The resin layers  211 D,  2121 D,  2122 D,  213 D,  2141 D,  2142 D, and  215 D correspond to the resin layers  211 C,  2121 C,  2122 C,  213 C,  2141 C,  2142 C, and  215 C, of the fourth preferred embodiment, respectively. 
     The reinforcing conductors  511  and  521  of each layer are a plurality of conductor patterns provided at intervals in a direction in which the signal transmission line  10 D extends. The reinforcing conductor  511  includes plural reinforcing conductors  511 , and the reinforcing conductors  511  of each layer that overlap with each other in a plan view are connected by the interlayer connection conductor  510  ( FIGS.  8  and  9 A ). The reinforcing conductor  521  includes plural reinforcing conductors  521 , and the reinforcing conductors  521  of each layer that overlap with each other in a plan view are connected by the interlayer connection conductor  520  ( FIGS.  8  and  9 A ). 
     According to such a configuration, a portion of which the strength is high since the reinforcing conductors  511  and  521  and the interlayer connection conductors  510  and  520  are provided as illustrated in  FIG.  9 A  and a portion of which the strength is low since the reinforcing conductors  511  and  521  and the interlayer connection conductors  510  and  520  are not provided as illustrated in  FIG.  9 B  are alternatively provided in the direction in which the signal transmission line  10 D extends. 
     As a result, the portion in which the reinforcing conductors  511  and  521  and the interlayer connection conductors  510  and  520  are not provided is flexible, and the portion in which the reinforcing conductors  511  and  521  and the interlayer connection conductors  510  and  520  are provided maintains the strength of the hollow portions  81  and  82 . 
     The configuration of the present preferred embodiment is also applicable to the structure of the microstrip line and the structure of the stripline according to the first and second preferred embodiments of the present invention. The reinforcing conductors  511  and  521  may be connected or may not be connected to the conductor  41  and the conductor  42  being ground conductors. 
     Subsequently, a signal transmission line according to a sixth preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  10    is a cross-sectional view of a signal transmission portion of a signal transmission line according to the sixth preferred embodiment of the present invention. 
     A signal transmission line  10 E according to the sixth preferred embodiment of the present invention is obtained by adding reinforcing insulating members  810  and  820  to the signal transmission line  10 B according to the third preferred embodiment of the present invention. Other configurations are preferably the same or substantially the same as the configurations of the signal transmission line  10 B according to the third preferred embodiment of the present invention, and overlapping description will be omitted. Features of the signal transmission line according to the sixth preferred embodiment shown in  FIG.  10    that are the same as or similar to the features of the signal transmission line according to the third preferred embodiment shown in  FIG.  5    are denoted by the same reference characters. 
     A signal transmission portion  21 E of the laminate includes resin layers  211 E,  2121 E,  2122 E,  213 E,  2141 E,  2142 E, and  215 E. The resin layers  211 E,  2121 E,  2122 E,  213 E,  2141 E,  2142 E, and  215 E correspond to the resin layers  211 B,  2121 B,  2122 B,  213 B,  2141 B,  2142 B, and  215 B of the third preferred embodiment, respectively. 
     The material of the reinforcing insulating members  810  and  820  may be the same as or may be different from the material of the resin layers  211 E,  2121 E,  2122 E,  213 E,  2141 E,  2142 E, and  215 E. In a case of the same material, the reinforcing insulating members  810  and  820  are preferably made of the same material as the resin layers  2121 E and  2122 E and the resin layers  2141 E and  2142 E. As a result, the resin layers  2121 E,  2122 E,  2141 E, and  2142 E and the reinforcing insulating members  810  and  820  are able to be integrally provided. In addition, the material of the reinforcing insulating members  810  and  820  is also preferably the same as the material of the resin layers  211 E and  215 E, so that it is possible to reduce or prevent delamination due to bending stress when the reinforcing insulating members  810  and  820  are bent. On the other hand, in a case of different materials, a material of which the elasticity is higher than the elasticity of the material of the resin layers  211 E,  2121 E,  2122 E,  213 E,  2141 E,  2142 E, and  215 E is preferably used. 
     The reinforcing insulating member  810  is disposed in the hollow portion  81 , and overlaps with the signal conductor  31  in a plan view. The reinforcing insulating member  810  is in contact with the signal conductor  31  and the resin layer  211 E. As a result, the shape of the hollow portion  81  is maintained by the reinforcing insulating member  810 . 
     The reinforcing insulating member  820  is disposed in the hollow portion  82 , and overlaps with the signal conductor  31  in a plan view. The reinforcing insulating member  820  is in contact with the resin layers  213 E and  215 E. As a result, the shape of the hollow portion  82  is maintained by the reinforcing insulating member  820 . 
     It is to be noted that the reinforcing insulating members  810  and  820  may be continuously provided in the direction in which the signal transmission portion  21 E extends or may be intermittently provided at intervals. It is also to be noted that the reinforcing insulating members  810  and  820  are able to reduce transmission loss by preventing contact with an end portion in the width direction of the signal conductor  31  on which charge concentrates. 
     In this manner, with the configuration according to the present preferred embodiment, the signal transmission line  10 E in which a hollow portion is even more difficult to be crushed is able to be obtained. 
     The configuration of the present preferred embodiment is also applicable to the structure of the microstrip line and the structure of the stripline according to the first and second preferred embodiments of the present invention. 
     Subsequently, a signal transmission line according to a seventh preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  11    is a cross-sectional view of a signal transmission portion of a signal transmission line according to the seventh preferred embodiment of the present invention. 
     A signal transmission line  10 F according to the seventh preferred embodiment includes a plurality of signal conductors  31  and  32 , and the basic structure of each of the signal conductors  31  and  32  is obtained by combining the signal transmission line  10 A according to the second preferred embodiment and the signal transmission line  10 C according to the fourth preferred embodiment. 
     A signal transmission portion  21 F of the laminate includes resin layers  211 F,  2121 F,  2122 F,  2123 F,  213 F,  2141 F,  2142 F,  2143 F, and  215 F. 
     The resin layers  2121 F,  2122 F, and  2123 F are provided between the resin layers  211 F and  213 F. The resin layer  2121 F is provided at one end in the width direction of the resin layers  211 F and  213 F. The resin layer  2122 F is provided at another end in the width direction of the resin layers  211 F and  213 F. The resin layer  2123 F is provided at an intermediate position (a center or substantially at a center position in  FIG.  11   ) in the width direction of the resin layers  211 F and  213 F. The resin layers  2121 F,  2122 F, and  2123 F are spaced apart from each other. This configuration provides the hollow portions  811  and  812 . The hollow portion  811  is defined by the resin layers  211 F,  2121 F,  2123 F, and  213 F. The hollow portion  812  is defined by the resin layers  211 F,  2122 F,  2123 F, and  213 F. 
     The resin layers  2141 F,  2142 F, and  2143 F are provided between the resin layers  213 F and  215 F. The resin layer  2141 F is provided at one end in the width direction of the resin layers  213 F and  215 F. The resin layer  2142 F is provided at another end in the width direction of the resin layers  213 F and  215 F. The resin layer  2143 F is provided at an intermediate position (a center or substantially at a center position in  FIG.  11   ) in the width direction of the resin layers  213 F and  215 F. The resin layers  2141 F,  2142 F, and  2143 F are spaced apart from each other. This configuration provides the hollow portions  821  and  822 . The hollow portion  821  is defined by the resin layers  213 F,  2141 F,  2143 F, and  215 F. The hollow portion  822  is defined by the resin layers  213 F,  2142 F,  2143 F, and  215 F. 
     The signal conductor  31  is exposed to the hollow portion  811 . The signal conductor  32  is exposed to the hollow portion  812 . The conductor  41  defining a ground conductor is provided on a surface opposite to the side of the resin layers  2121 F,  2122 F, and  2123 F in the resin layer  211 F. The conductor  42  defining a ground conductor is provided on a surface opposite to the side of the resin layers  2141 F,  2142 F, and  2143 F in the resin layer  215 F. 
     The reinforcing conductor  51  is disposed in three layers at a portion with which the resin layers  211 F,  2121 F,  213 F,  2141 F, and  215 F overlap. The reinforcing conductor  51  of three layers is connected by a plurality of interlayer connection conductors  510  provided at intervals in the direction in which the signal transmission portion  21 F extends. The interlayer connection conductor  510  is also connected to the conductors  41  and  42 . 
     The reinforcing conductor  52  is disposed in three layers at a portion with which the resin layers  211 F,  2122 F,  213 F,  2142 F, and  215 F overlap. The reinforcing conductor  52  of three layers is connected by the interlayer connection conductor  520 . The interlayer connection conductor  520  is also connected to the conductors  41  and  42 . 
     The reinforcing conductor  53  is disposed in three layers at a portion with which the resin layers  211 F,  2123 F,  213 F,  2143 F, and  215 F overlap. The reinforcing conductor  53  of three layers is connected by the interlayer connection conductor  530 . The interlayer connection conductor  530  is also connected to the conductors  41  and  42 . 
     With such a configuration, the signal transmission line  10 F being a multicore, and having low transmission loss while having flexibility is obtained. In addition, in the configuration, the reinforcing conductor  53  and the interlayer connection conductor  530  that are connected to the conductors  41  and  42  defining ground conductors are provided between the signal conductors  31  and  32 . Accordingly, coupling between the signal conductors  31  and  32  is significantly reduced or prevented, and high isolation between the signal conductors  31  and  32  is obtained. 
     The configuration of the present preferred embodiment is applicable to the structure of the microstrip line according to the first preferred embodiment of the present invention. 
     Subsequently, a signal transmission line according to an eighth preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  12    is an exploded perspective view of a signal transmission portion of a signal transmission line according to the eighth preferred embodiment of the present invention. 
     A signal transmission line  10 G according to the eighth preferred embodiment of the present invention differs in structure with respect to the resin layer  213 G on which the signal conductor  31  is provided as compared to the signal transmission line  10 B according to the third preferred embodiment of the present invention. Other configurations are preferably the same or substantially the same as the configurations of the signal transmission line  10 B according to the third preferred embodiment of the present invention, and overlapping description will be omitted. Features of the signal transmission line according to the eighth preferred embodiment shown in  FIGS.  11  and  12    that are the same as or similar to the features of the signal transmission line according to the third preferred embodiment shown in  FIG.  5    are denoted by the same reference characters. 
     A signal transmission portion  21 G of the laminate includes resin layers  211 G,  212 G,  213 G,  214 G, and  215 G. The resin layers  211 G,  212 G,  213 G,  214 G, and  215 G correspond to the resin layers  211 B,  212 B (the portion defined by the resin layers  2121 B and  2122 B),  213 B,  214 B, and  215 B of the third preferred embodiment, respectively. 
     In the resin layer  213 G, in a plan view, the thickness of a portion that does not overlap with the hollow portions  81  and  82 , that is, portions  2131  and  2132  defining holding portions is preferably smaller than the thickness of a portion  2130  that overlaps with the hollow portions  81  and  82 . 
     With such a configuration, when the resin layers  211 G,  212 G,  213 G,  214 G, and  215 G are stacked and thermally pressed, resin is able to be significantly reduced or prevented from pushing out from the holding portion including a large number of resin layers to the side of the hollow portions  81  and  82 , and the portion  2130  that overlaps with the hollow portions  81  and  82  at which the signal conductor  31  is provided is able to be significantly reduced or prevented from deforming. As a result, the signal conductor  31  is able to be structured and configured in a desired shape and reliably provided at a desired position, and reliably obtains desired transmission characteristics. 
     The configuration of the present preferred embodiment is also applicable to the structure of the microstrip line and the structure of the stripline according to the first and second preferred embodiments of the present invention. 
     Subsequently, a signal transmission line according to a ninth preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  13    is an exploded perspective view of a signal transmission portion of a signal transmission line according to the ninth preferred embodiment of the present invention.  FIG.  14    is a cross-sectional view of the signal transmission portion of the signal transmission line according to the ninth preferred embodiment of the present invention. It is to be noted that the protective film of the signal conductor is omitted in  FIG.  13   . 
     A signal transmission line  10 H according to the ninth preferred embodiment of the present invention is obtained by adding a vent hole  29  and a protective film  310  ( FIG.  14   ) to the signal transmission line  10 B according to the third preferred embodiment of the present invention. Other configurations are preferably the same or substantially the same as the configurations of the signal transmission line  10 B according to the third preferred embodiment of the present invention, and overlapping description will be omitted. Features of the signal transmission line according to the ninth preferred embodiment shown in  FIGS.  13  and  14    that are the same as or similar to the features of the signal transmission line according to the third preferred embodiment shown in  FIG.  5    are denoted by the same reference characters. 
     A signal transmission portion  21 H of the laminate includes resin layers  211 H,  2121 H,  2122 H,  213 H,  2141 H,  2142 H, and  215 H. The resin layers  211 H,  2121 H,  2122 H,  213 H,  2141 H,  2142 H, and  215 H correspond to the resin layers  211 B,  2121 B,  2122 B,  213 B,  2141 B,  2142 B, and  215 B of the third preferred embodiment, respectively. 
     The resin layers  211 H and  215 H each include a vent hole  29  penetrating in the thickness direction, respectively. As a result, the hollow portions  81  and  82  ( FIG.  14   ) are exposed to the outside through the vent hole  29 , respectively. With such a vent hole  29 , the shape of the hollow portions  81  and  82  ( FIG.  14   ) is able to be significantly reduced or prevented from changing due to a pressure difference at a time of temperature change, such as when the signal transmission line  10 H is mounted on an external circuit board. 
     The protective film  310  is provided on the surface of the signal conductor  31  on the side of the hollow portion  81 . The protective film  310  may preferably be provided by plating with a stable metal, such as precious metals, for example. As a result, even when the hollow portion  81  is connected to the outside, deterioration of characteristics due to oxidation of the signal conductor  31  or other factors is able to be significantly reduced or prevented. 
     The configuration of the present preferred embodiment is also applicable to the structure of the microstrip line and the structure of the stripline according to the first and second preferred embodiments of the present invention. 
     In addition, the structure including the protective film  310  of the present preferred embodiment is also applicable to the signal transmission line according to other preferred embodiments of the present invention. 
     Subsequently, a signal transmission line according to a tenth preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  15    is an external perspective view of a signal transmission line according to the tenth preferred embodiment of the present invention. 
     A signal transmission line  10 J according to the tenth preferred embodiment of the present invention is obtained by adding connectors  610  and  620  to the signal transmission line  10  according to the first preferred embodiment of the present invention. Other configurations are preferably the same or substantially the same as the configurations of the signal transmission line  10  according to the first preferred embodiment of the present invention, and overlapping description will be omitted. Features of the signal transmission line according to the tenth preferred embodiment shown in  FIG.  15    that are the same as or similar to the features of the signal transmission line according to the first preferred embodiment shown in  FIGS.  1 ,  2 , and  3 A- 3 C  are denoted by the same reference characters. 
     The connector  610  is provided at a first surface of the external connection portion  22  of the laminate  20 . While not illustrated, the center conductor of the connector  610  is connected to the external connection conductor  61  ( FIG.  1   ), and the outer peripheral conductor of the connector  610  is connected to the external connection conductor  71  ( FIG.  1   ). In addition, while not illustrated, the center conductor of the connector  620  is connected to the external connection conductor  62 , and the outer peripheral conductor of the connector  620  is connected to the external connection conductor  72  as illustrated in  FIG.  1   . 
     Even with such a configuration, the same operational effects and advantages as the operational effects and advantages of the above-described preferred embodiments are able to be obtained. In addition, the signal transmission line  10 J is able to be easily connected to the connector of an external circuit board by the connectors  610  and  620 . 
     It is to be noted that the structure of the present preferred embodiment is also applicable to the signal transmission line of each of the second and subsequent preferred embodiments. 
     Subsequently, a signal transmission line according to an eleventh preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  16    is a side cross-sectional view of a structure of a signal transmission line according to the eleventh preferred embodiment of the present invention. 
     A signal transmission line  10 K according to the eleventh preferred embodiment of the present invention is obtained by adding connectors  610  and  620  to the signal transmission line  10 B according to the third preferred embodiment of the present invention, and differs in the arrangement of the hollow portion from the signal transmission line  10 B. It is to be noted that the connectors  610  and  620  are also able to be omitted. Features of the signal transmission line according to the eleventh preferred embodiment shown in  FIG.  16    that are the same as or similar to the features of the signal transmission line according to the third preferred embodiment shown in  FIG.  5    are denoted by the same reference characters. 
     In a signal transmission portion  21 K of the signal transmission line  10 K, hollow portions  813 ,  814 ,  823 , and  824  are provided in a laminate  20 K. The hollow portions  813  and  823  overlap with each other in a plan view. The signal conductor  31  is disposed between the hollow portions  813  and  823 . The hollow portions  814  and  824  overlap with each other in a plan view. The signal conductor  31  is disposed between the hollow portions  814  and  824 . The hollow portions  813  and  823  and the hollow portions  814  and  824  are disposed with a space between each other in a direction in which the laminate  20 K extends. 
     As a result, the signal transmission portion  21 K of the laminate  20 K is provided with a portion that includes the hollow portions  813  and  823 , a portion that includes the hollow portions  814  and  824 , and a portion that includes no hollow portion. The portion that includes no hollow portion, in the direction in which the signal transmission portion  21 K of the laminate  20 K extends, is provided between the portion that includes the hollow portions  813  and  823  and the portion that includes the hollow portions  814  and  824 . 
     According to such a configuration, as illustrated in  FIG.  16   , the laminate  20 K is mounted on a circuit board BP that has a difference in level by using the portion that includes no hollow portion in the signal transmission portion  21 K as a bent portion, attaching the connector  610  to a connector B 610 , and attaching the connector  620  to a connector B 620 . In this manner, by using the portion that includes no hollow portion as the bent portion of the signal transmission portion  20 K, the hollow portion is able to be prevented from deforming due to the bending. As a result, transmission loss is able to be further reliably reduced. 
     The configuration of the present preferred embodiment is also applicable to the structure of the microstrip line and the structure of the stripline according to the first and second preferred embodiments of the present invention. 
     Subsequently, a signal transmission line according to a twelfth preferred embodiment of the present invention will be described with reference to the drawings.  FIG.  17    is a side cross-sectional view of a structure of a signal transmission line according to the twelfth preferred embodiment of the present invention. 
     A signal transmission line  10 L according to the twelfth preferred embodiment of the present invention differs from the signal transmission line  10 K according to the eleventh preferred embodiment of the present invention in that the thickness of a laminate  20 L at the bending portion is thin. Features of the signal transmission line according to the twelfth preferred embodiment shown in  FIG.  17    that are the same as or similar to the features of the signal transmission line according to the eleventh preferred embodiment shown in  FIG.  16    are denoted by the same reference characters. 
     A signal transmission portion  21 L of the laminate  20 L includes a portion that includes the hollow portions  813  and  823 , a portion that includes the hollow portions  814  and  824 , and a portion that includes no hollow portion. The thickness of the portion that includes no hollow portion is thinner than the thickness of the portion that includes a hollow portion. The thin portion is a bent portion. 
     With such a configuration, similarly to the eleventh preferred embodiment, the hollow portion is able to be prevented from deforming and bending is further easier. 
     The configuration of the present preferred embodiment, except the bent portion, is also applicable to the structure of the microstrip line and the structure of the stripline according to the first and second preferred embodiments of the present invention. Although it is also possible to apply the structure of the microstrip line and the structure of the stripline to the bending portion, in such a case, the thickness, and the line width of the signal conductor  31  may be set in consideration of characteristic impedance. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.