Patent Publication Number: US-2018045903-A1

Title: Optical-electric circuit board

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of PCT/JP2015/060827 filed on Apr. 7, 2015, the entire contents of which are incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical-electric circuit board which includes a polymer-type optical waveguide substrate provided with a reflective surface which optically couples a first optical path and a second optical path to each other. 
     2. Description of the Related Art 
     An optical waveguide substrate having an optical waveguide allows an optical circuit to be miniaturized. To drive an optical element such as a light emitting element which optically couples to an optical path of the optical waveguide and to transmit a signal of the optical element, it is necessary to provide electrical wiring. Accordingly, an optical-electric circuit board has been developed where an optical waveguide substrate having an optical circuit and a wiring board having an electric circuit are formed into an integral body. 
     Japanese Patent Application Laid-Open Publication No. 2013-68650 discloses an optical-electric circuit board where an optical element is arranged on an upper surface of the optical-electric circuit board. An optical waveguide substrate is arranged on a center portion of the optical-electric circuit board. Conducting members are arranged on an outer peripheral portion of the optical-electric circuit board, and each conducting member has through wiring which extends from the upper surface to a lower surface of the optical-electric circuit board. That is, in the optical-electric circuit board, the optical waveguide substrate forming an optical circuit board and the conducting member forming an electric circuit board are disposed individually and separately. 
     SUMMARY OF THE INVENTION 
     An optical-electric circuit board according to an embodiment of the present invention is an optical-electric circuit board which includes: a polymer-type optical waveguide substrate provided with a reflective surface which optically couples a first optical path and a second optical path to each other; and electrical wiring, wherein at least a portion of a member which configures the reflective surface is formed of a conductive member, the electrical wiring is formed of first wiring disposed on a side of a first principal surface of the optical waveguide substrate and second wiring disposed on a side of a second principal surface of the optical waveguide substrate, and the conductive member electrically connects the first wiring and the second wiring with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an optical-electric circuit board according to a first embodiment; 
         FIG. 2  is an exposed view of the optical-electric circuit board according to the first embodiment; 
         FIG. 3  is a cross-sectional view of an optical-electric circuit board according to a modification of the first embodiment; 
         FIG. 4A  is a top plan view of an optical-electric circuit board according to a second embodiment; 
         FIG. 4B  is a cross-sectional view of the optical-electric circuit board according to the second embodiment; 
         FIG. 5A  is a perspective view of a micro pin of the optical-electric circuit board according to the second embodiment; 
         FIG. 5B  is a perspective view of a micro pin of an optical-electric circuit board according to a modification of the second embodiment; 
         FIG. 5C  is a perspective view of a micro pin of the optical-electric circuit board according to a modification of the second embodiment; 
         FIG. 5D  is a perspective view of a micro pin of the optical-electric circuit board according to a modification of the second embodiment; 
         FIG. 5E  is a perspective view of a micro pin of the optical-electric circuit board according to a modification of the second embodiment; 
         FIG. 5F  is a perspective view of a micro pin of the optical-electric circuit board according to a modification of the second embodiment; 
         FIG. 5G  is a perspective view of a micro pin of the optical-electric circuit board according to a modification of the second embodiment; 
         FIG. 6  is an exposed view of an optical-electric circuit board according to a third embodiment; and 
         FIG. 7  is an exposed view of an optical-electric circuit board according to a modification of the third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     First Embodiment 
     As shown in  FIG. 1  and  FIG. 2 , an optical-electric circuit board  1  according to a first embodiment of the present invention includes a polymer-type optical waveguide substrate  20  as a main constitutional element, and also includes a first wiring board  10  and a second wiring board  40 . 
     Here, in the description made hereinafter, drawings referenced in respective embodiments are schematic. Note that a relationship between a thickness and a width of respective parts, and a thickness ratio, a relative angle and the like of each part differ from those of an actual optical-electric circuit board. Some parts may have a different size relationship or a different size ratio between drawings. 
     The optical-electric circuit board  1  includes: a light emitting element  50  forming a first optical element; a light receiving element  60  forming a second optical element; the optical waveguide substrate  20 ; an optical fiber  70 ; and signal cables  75 ,  76 . The second board (the second wiring board)  40  on which the light emitting element  50  and the light receiving element  60  are mounted is disposed on an upper surface  20 SA forming a first principal surface of the optical waveguide substrate  20 . 
     The first board (the first wiring board)  10  is disposed on a lower surface  20 SB forming a second principal surface of the optical waveguide substrate  20 . 
     In the optical-electric circuit board  1 , the light emitting element  50  transmits a first optical signal with first wavelength λ 1  the light receiving element  60  receives a second optical signal with second wavelength λ 2  which differs from the first wavelength λ 1 , and a third optical signal which is formed by multiplexing the first optical signal and the second optical signal is guided by the optical fiber  70 . For example, the first wavelength λ 1  is 850 nm, and the second wavelength λ 2  is 650 nm. 
     The light emitting element  50  is formed of a vertical cavity surface emitting laser (VCSEL). The light emitting element  50  emits light of an optical signal to a light emitting surface (XY plane) in the vertical direction (Z axis direction) in response to a drive electrical signal inputted to the light emitting element  50 . For example, the highly miniaturized light emitting element  50  with a size of 250 μm×300 μm as viewed in a plan view has, on the light emitting surface thereof: a light emitting portion  51  having a diameter of 20 μm; and connection terminals  52  which are electrically connected to the light emitting portion  51  so as to supply an electrical signal. 
     The light receiving element  60  is formed of a photodiode (PD) or the like. The light receiving element  60  converts an optical signal which is incident on a light receiving surface from the vertical direction (Z axis direction) into an electrical signal, and the light receiving element  60  outputs the electrical signal. For example, the highly miniaturized light receiving element  60  with a size of 250 μm×300 μm as viewed in a plan view has, on the light receiving surface thereof: a light receiving portion  61  having a diameter of 50 μm; and connection terminals  62  which are electrically connected with the light receiving portion  61  so as to output the received electrical signal. 
     The optical waveguide substrate  20  is a polymer-type optical waveguide substrate where the longitudinal direction of a core  23  extends in the X axis direction, and a periphery of the core  23  is surrounded by a cladding  25 . The core  23  which guides an optical signal configures an optical path LP 23 . The polymer-type optical waveguide substrate  20  where the core  23  and the cladding  25  are made of a resin can be easily processed and has sufficiently high plasticity compared to an optical waveguide substrate made of an inorganic material such as quartz. Further, the optical-electric circuit board  1  is formed by sandwiching the optical waveguide substrate  20  having flexibility between the two flexible first board  10  and second board  40  so that the optical-electric circuit board  1  has flexibility and hence, the optical-electric circuit board  1  can be easily disposed in a narrow space. That is, it is preferable that the first board  40  and the second board  10  have flexibility. 
     The core  23  forming the optical waveguide is made of a first resin, and the cladding  25  is made of a second resin having a smaller refractive index than the first resin. As described later, the cladding  25  is formed of a lower cladding  25 A disposed below the core  23  and an upper cladding  25 B surrounding side surfaces and an upper surface of the core  23 . 
     To efficiently transmit light, a difference in refractive index between the core  23  and the cladding  25  is preferably set to 0.01 or more. The core  23  configures the optical waveguide which is an optical path for guiding an optical signal. 
     For example, the core  23  and the cladding  25  are made of a fluorinated polyimide resin. The fluorinated polyimide resin has sufficiently high heat resistance, transparency and isotropy, and a refractive index of the fluorinated polyimide resin is 1.50 to 1.60. 
     The light emitting element  50  and the light receiving element  60  are electrically connected to electrode pads  43  and electrode pads  44  on the wiring board  40  respectively. The wiring board  40  has a through hole  41  forming an optical path LP 50  for a first optical signal and a through hole  42  forming an optical path LP 60  for a second optical signal. 
     A groove  22  is formed on the optical waveguide substrate  20 . A long axis direction of the groove  22  is parallel to a long axis direction of the core  23 , and has a rectangular shape in cross section orthogonal to a long axis of the groove  22 . An upper surface of the groove  22  is open, and a bottom surface of the groove  22  is formed of an upper surface  25 AS 1  of the lower cladding  25 A. Here, by bounding the wiring board  40  to an upper surface of the groove  22 , the groove  22  forms a hole with one end thereof open. 
     Further, a first reflective surface  21 M with an inclination angle of 45 degrees is formed on the core  23 . The first reflective surface  21 M is an inclined surface of a recessed portion  21  formed from a lower surface side by excimer laser processing, for example. The first reflective surface  21 M reflects light which is incident on the core  23  from the vertical direction (Z axis direction) by 90 degrees thus guiding the light to the optical path LP 23  extending in the longitudinal direction (X axis direction) of the core  23 . Here, the recessed portion  21  may be a groove formed by a dicing blade. 
     Further, at the time of manufacture, the core  23  further extends from a vertical surface  21 T of the recessed portion  21 . After the recessed portion  21  is formed, however, a portion of the core  23  disposed further on the outer side than the first reflective surface  21 M does not function as an optical waveguide so that the first reflective surface  21 M forms an end surface of the core  23  forming the optical waveguide. 
     On the other hand, a prism  30  and the optical fiber  70  are disposed in the groove  22 . The prism  30  is an approximately rectangular parallelepiped body having a rectangular shape as viewed in a plan view, and has a second reflective surface  30 M with an inclination angle of 45 degrees. The second reflective surface  30 M allows an optical signal with first wavelength to pass therethrough, but reflects an optical path of a second optical signal with second wavelength thereon. That is, the prism  30  is a right-angle dichroic prism having the reflective surface  30 M with characteristics that allow light of wavelength λ 1  to pass therethrough and that reflect light of wavelength λ 2  thereon. 
     As shown in  FIG. 1 , the light emitting element  50  and the light receiving element  60  are mounted on the first board (wiring board)  40 , and the first board  40  is disposed on the upper surface of the optical waveguide substrate  20 . Further, the first board  40  and the optical waveguide substrate  20  are positioned so that the light emitting element  50  and the light receiving element  60  are right above the core  23 . 
     The light emitting element  50  emits (transmits) a first optical signal to the optical path LP 50  perpendicular to the X axis. The first optical signal is reflected on the first reflective surface  21 M in the direction parallel to an X axis thus being guided to the optical path LP 23 . In other words, the first reflective surface  21 M optically couples the optical path LP 50  to the optical path LP 23 . The first optical signal guided through the optical path LP 23  passes through the second reflective surface  30 M, and is incident on the optical fiber  70 . 
     Here, an optical waveguide is not disposed in the optical waveguide substrate  20  for the optical path LP 50 . This is because the optical path LP 50  is an optical path extending in the thickness direction (Z direction) of the optical waveguide substrate  20 , and is extremely short in length and hence, a remarkable effect cannot be acquired by forming the optical waveguide for the optical path LP 50 . However, the optical waveguide may be disposed in the optical waveguide substrate  20  for the optical path LP 50  using the same resin as the core  23 . 
     On the other hand, the optical fiber  70  guides a second optical signal through an optical path LP 70  extending parallel to the X axis. The second optical signal is reflected on the second reflective surface  30 M toward the direction perpendicular to the X axis, and is guided to the optical path LP 60 . Further, the second optical signal is incident on and received by the light receiving portion  61  of the light receiving element  60 . In other words, the second reflective surface  30 M optically couples the optical path LP 60  and the optical path LP 70  to each other. 
     In the optical-electric circuit board  1 , a reflective film  26  made of a conductive material such as gold is formed on a wall surface of the recessed portion  21 , particularly, on the first reflective surface  21 M. In other words, the first reflective surface  21 M is configured of a conductive member made of gold. Further, the reflective film  26  has a function of through wiring which electrically connects wiring  46  of the first board  40  and wiring  16  of the second board  10  with each other. 
     The wiring  46  is connected to the connection terminals  52  of the light emitting element  50  through the electrode pads  43 . On the other hand, the wiring  16  is connected to one of two signal cables  76 . That is, a drive signal supplied from one signal cable  76  is transmitted to the light emitting element  50  through the reflective film  26 . 
     Here, after the reflective film  26  is disposed, the inside of the recessed portion  21  may be filled with a resin material or other material. 
     In the optical-electric circuit board  1 , the reflective film  26  which is a component of an optical circuit has a function as wiring which is a component of an electric circuit. With such a configuration, in the optical-electric circuit board  1 , it is not necessary to dispose a wiring board or the like having through wiring on the periphery of the optical waveguide substrate  20  and hence, it is possible to provide the miniaturized optical-electric circuit board  1 . Further, the through wiring can be formed simultaneously with the formation of the optical waveguide substrate  20  and hence, the optical-electric circuit board  1  can be easily manufactured. 
     Here, it is sufficient for the reflective film  26  to be electrically connected with either one of the wiring  46  of the first board  40  or the wiring  16  of the second board  10 . That is, it is not always necessary for the reflective film  26  to form through wiring, and it is sufficient for the reflective film  26  to have a function as wiring connected to either one of electrical wirings. 
     Modification of First Embodiment 
       FIG. 3  shows an optical-electric circuit board  1 A according to a modification of the first embodiment. The optical-electric circuit board  1 A is similar to the optical-electric circuit board  1 , and has substantially the same advantageous effects as the optical-electric circuit board  1 . Accordingly, constitutional elements of the optical-electric circuit board  1 A having substantially the same function as the corresponding constitutional elements of the optical-electric circuit board  1  are given the same symbols, and the description of such constitutional elements is omitted. 
     In the optical-electric circuit board  1 A, the inside of the recessed portion  21  is filled with a conductive member  26 A made of a silver paste, for example. In other words, the first reflective surface  21 M is configured of the conductive member  26 A. Further, the conductive member  26 A electrically connects the wiring  46  of the first board  40  and the wiring  16  of the second board  10  with each other. 
     It is not necessary that the inside of the recessed portion  21  is completely filled with a conductive material with no gap. It is sufficient for the conductive material to cover at least a wall surface forming a reflective surface, a connecting portion with the wiring  46  of the first board  40  and a connecting portion with the wiring  16  of the second board  10 . 
     As the conductive material, a conductive resin or other resin may be used in place of a conductive paste or the like made of a conductive powder and a resin. 
     The optical-electric circuit board  1 A can be manufactured more easily than the optical-electric circuit board  1 . 
     Second Embodiment 
       FIG. 4A  and  FIG. 4B  show an optical-electric circuit board  1 B of a second embodiment. The optical-electric circuit board  1 B is similar to the optical-electric circuit board  1 , and has substantially the same advantageous effects as the optical-electric circuit board  1 . Accordingly, constitutional elements of the optical-electric circuit board  1 B having substantially the same function as the corresponding constitutional elements of the optical-electric circuit board  1  are given the same symbols, and the description of such constitutional elements is omitted. 
     In the optical-electric circuit board  1 B, both of two optical paths LP 23 A, LP 23 B are arranged in the optical waveguide substrate  20  such that the optical paths LP 23 A, LP 23 B are orthogonal to each other in an XY plane. Further, a micro pin  80  with a side surface forming a reflective surface  80 M is inserted into a guide hole (not shown in the drawing) formed in the optical waveguide substrate  20  from the upper surface  20 SA. 
     Light generated by the light emitting element  50  is reflected on an inclined surface of a V groove  21 V, and is guided to the optical path LP 23 A of a first waveguide  23 A. The light guided through the optical path LP 23 A is reflected on the reflective surface  80 M of the micro pin  80 , and is guided to the optical path LP 23 B of a second waveguide  23 B. That is, the reflective surface  80 M optically couples the optical path LP 23 A and the optical path LP 23 B to each other. 
     The micro pin  80  made of a gold alloy also has a function as through wiring which electrically connects wiring  27 A disposed on the upper surface  20 SA of the optical waveguide substrate  20 B and wiring  27 B disposed on the lower surface  20 SB of the optical waveguide substrate  20 B with each other. 
     Here, the wiring  27 B is a ground potential film which is electrically connected with ground potential wiring of the signal cable  76  not shown in the drawing. That is, wiring to which the micro pin  80  is connected is not limited to wiring through which an electrical signal is transmitted, and may be ground potential wiring. A ground potential film is disposed on the upper surface (first principal surface)  20 SA or the lower surface (second principal surface)  20 SB of the optical waveguide substrate  20 B so that the optical waveguide substrate  20 B has sufficiently high noise resistance. 
     It is also not limited that the reflective surface  80 M is configured of one surface of the micro pin  80 . For example, as described with reference to  FIG. 1 , it may be possible to adopt the configuration where a recessed portion forming a through hole is formed in a region which corresponds to an arrangement position of the micro pin  80  by dry etching such as RIE or other etching, and a metal film is formed on an inner wall of the recessed portion by electroless plating or the like thus forming the reflective surface  80 M. 
     As shown in  FIG. 5A , the micro pin  80  has a quadrangular prism shape, and the side surface of the micro pin  80  has a function as the reflective surface  80 M. A proximal end portion of the micro pin  80  forms a holding portion  82 . Here, although the holding portion  82  is not an indispensable constitutional element, the holding portion  82  is disposed so as to facilitate handling of the micro pin  80 . For example, the micro pin  80  with the holding portion  82  including a ferromagnetic body can be held by a jig having a magnet thus having sufficiently high operability. The micro pin  80  and the holding portion  82  may be made of the same material so as to be configured into an inseparable integral body. 
     Although the micro pin  80  is preferably made of a conductor such as a metal, it is sufficient for the micro pin  80  that at least an outer surface of the micro pin  80  be made of a conductor. For example, assume a micro pin where an insulator such as glass is used as a base material, and a conductive film made of gold or the like is disposed on a surface of the micro pin. Such a micro pin may be used in the same manner as a micro pin made of a conductor. 
     The guide hole into which the micro pin  80  is inserted preferably has a size slightly smaller than an outer size of the micro pin  80 . For example, in the case where the outer size of the micro pin  80  is L 2 , when a dimension L 1  of the guide hole is set to a value which satisfies an expression of (L 2 ×0.9) (L 2 ×0.95), no space nor other materials such as an adhesive agent exist between the micro pin  80  and the optical waveguide substrate  20 . In other words, a reflective surface  50 M and the optical waveguide substrate  20  are brought into close contact with each other. With such a configuration, a coupling efficiency between the first optical waveguide  23 A and the second optical waveguide  23 B which are optically coupled to each other by the reflective surface  50 M is extremely high. 
     Here, assume a case where a micro pin has a small cross-sectional area. For example, in the case of the micro pin  80  having a square cross section, when a side length of the micro pin  80  is 50 μm or less, in other words, when the cross-sectional area of the micro pin  80  is 250 μm 2  or less, the micro pin can be pierced into the optical waveguide substrate  20  without forming the guide hole in advance. In the embodiment, “pierce” means that the micro pin  80  enters the optical waveguide substrate  20  while the micro pin  80  per se forms an insertion path by cutting. 
     Here, also in the case where a board is bonded to at least either one of the upper surface or the lower surface of the optical waveguide substrate  20 , the micro pin can be pierced into the optical waveguide substrate  20  when the board is formed of a flexible board made of a resin. 
     &lt;Micro Pins According to Modifications&gt; 
     As has been described heretofore, the micro pin is not limited to the micro pin  80  described in the second embodiment. Next, micro pins according to modifications are described. 
     In a micro pin  80 A according to the modification shown in  FIG. 5B , an inclined surface with an inclination angle of 45 degrees and a vertical surface intersect with each other at a distal end of the micro pin  80 A so that the distal end of the micro pin  80 A is pointed. Further, the inclined surface on a side surface of the micro pin  80 A forms a reflective surface  80 MA. 
     That is, to further facilitate the piercing of the micro pin, it is preferable for the micro pin to have a pointed distal end, that is, to have an apex angle of 90 degrees or less. 
     In the modification, the polymer-type optical waveguide substrate  20 , that is, the core  23  and the cladding  25  are made of plastic having a Vickers hardness Hv of 0.5 GP, for example. On the other hand, the micro pin  80 A is made of a gold alloy having a Vickers hardness Hv of 20 GPa to piece into the optical wave guide substrate  20 . To facilitate the piercing of the micro pin  80 A, it is preferable that hardness of the micro pin be 10 or more times as large as hardness of the optical waveguide substrate  20 . 
     A micro pin  80 B according to a modification shown in  FIG. 5C  has a shape where a lower portion of the micro pin  80 B has a quadrangular pyramid shape having an apex angle of 90 degrees and an upper portion of the micro pin  80 B has an elongated rectangular parallelepiped shape. The micro pin  80 B does not have the holding portion. In the micro pin  80 B, a side surface, that is, a surface of the quadrangular pyramid body forms a reflective surface  80 MB. 
     In the modification, in the case of a micro pin having a plurality of side surfaces such as the micro pin  80 B, only any one reflective surface may be used for changing an optical path of an optical signal, or the plurality of side surfaces may optically couple respective optical paths to each other. That is, one micro pin may optically couple different optical paths to each other. 
     Here, in the micro pin  80 B, a side surface of the upper portion having an elongated rectangular parallelepiped shape may be used as a reflective surface. Further, the surface of the quadrangular pyramid body and the side surface of the rectangular parallelepiped body may be respectively used as the reflective surface. 
     A micro pin  80 C shown in  FIG. 5D  is formed such that a cutout surface formed on a lower side of a circular column body forms a reflective surface  80 MC. 
     A micro pin  80 D shown in  FIG. 5E  is formed of a flat plate having knife-shaped edges, and both principal surfaces of the micro pin  80 D can be used as a reflective surface  80 MD. A plate thickness of the micro pin  80 D is set to approximately 10 μm to 500 μm. 
     A micro pin  80 E shown in  FIG. 5F  has a flat plate shape where a cutout surface  80 ME 1  is formed on a lower side of the micro pin  80 E. Not only the cutout surface  80 ME 1  but also an upper surface  80 ME 2  and a back surface  80 ME 3  can be used as a reflective surface. 
     A micro pin  80 F shown in  FIG. 5G  has a triangular prism shape, and a side surface  80 MF forms a reflective surface. 
     Here, the micro pin may be a flat plate body made of a transparent material, for example, glass. The reflective surface  50 M may be formed of a half mirror. Further, a predetermined function may be imparted to the reflective surface by disposing a bandpass filter, a polarizing filter or the like on the reflective surface of the micro pin. 
     It is not necessary for the reflective surface of the micro pin to have conductivity, and it is sufficient that at least one surface of the micro pin have conductivity. For example, in the case of a micro pin made of glass, it may be configured such that one side surface of the micro pin forms the reflective surface, and three side surfaces of the micro pin are covered by a conductive film That is, it is sufficient that at least a portion of a member which configures the reflective surface be formed of a conductive member. 
     As has been described above, in the optical-electric circuit board of the embodiment, various micro pins may be used according to a specification. A plurality of micro pins may be pierced into one optical-electric circuit board, and may be pierced into the optical-electric circuit board not only from an upper surface but also from a lower surface or a side surface of the optical-electric circuit board. Here, in the optical-electric circuit board having the plurality of micro pins, not all micro pins are required to have a function as a conductive member. 
     Third Embodiment 
       FIG. 6  and  FIG. 7  show an optical-electric circuit board  1 C of a third embodiment. The optical-electric circuit board  1 C is similar to the optical-electric circuit board  1 , and has substantially the same advantageous effects as the optical-electric circuit board  1 . Accordingly, constitutional elements of the optical-electric circuit board  1 C having substantially the same function as the corresponding constitutional elements of the optical-electric circuit board  1  are given the same symbols, and the description of such constitutional elements is omitted. Here, the description is made hereinafter only with respect to an electrical connection relationship between one connection terminal  52 A of the light emitting element  50  and one signal cable  76 . 
     In the optical-electric circuit board  1 C, the optical waveguide substrate  20 A and an optical waveguide substrate  20 AX are stacked with each other. Further, the optical-electric circuit board  1 C has two optical waveguides  23 ,  23 X which are orthogonal to each other in a plane. Here, differently to the optical-electric circuit board  1  and other optical-electric circuit boards, the light emitting element  50  and the light receiving element  60  are not arranged on the same straight line. 
     The conductive member  26 A filled in the recessed portion  21  of the optical waveguide substrate  20 A configures a reflective surface  26 M. A conductive member  26 AX is formed on an inclined surface of a recessed portion  21 X of the optical waveguide substrate  20 AX, and the conductive member  26 AX configures a reflective surface  26 MX. 
     Light generated by the light emitting element  50  is reflected on the reflective surface  26 M through the optical path LP 50  of the optical waveguide  23 , and is guided to the optical path LP 23 . On the other hand, light guided through an optical path LP 23 X of the optical waveguide  23 X is reflected on the reflective surface  26 MX, and is guided to the optical path LP 60  and, then, is incident on the light receiving element  60 . 
     That is, the direction of the optical path LP 23  and the direction of the optical path LP 23 X are orthogonal to each other. Light generated by the light emitting element  50  is guided through the optical paths LP 50 , LP 23  in the optical waveguide substrate  20 A. The light receiving element  60  receives light which is guided through the optical path LP 23 X in the optical waveguide substrate  20 AX, and is reflected on the reflective surface  26 MX of the optical waveguide substrate  20 AX. 
     The connection terminal  52 A of the light emitting element  50  is electrically connected to the wiring  46  through wiring  40 TH. The wiring  46  is electrically connected to the conductive member  26 A which configures the reflective surface  26 M of the optical waveguide substrate  20 A. The conductive member  26 A is electrically connected to the reflective film  26 AX formed of a conductive member which configures the reflective surface  26 MX of the optical waveguide substrate  20 AX. The conductive member  26 AX is electrically connected to the wiring  16  of the wiring board  10 . The wiring  16  is electrically connected to the signal cable  76  through wiring  10 TH. 
     That is, in the optical-electric circuit board  1 C, the light emitting element  50  mounted on the second wiring board  40  is connected to the signal cable  76  through the through wiring  40 TH, the wiring  46 , the conductive member  26 A, the reflective film  26 AX, the wiring  16  and the through wiring  10 TH. 
     As has been described above, in the optical-electric circuit board  1 C, two optical waveguide substrates  20 A,  20 AX are stacked with each other, and each of the optical waveguide substrates  20 A,  20 AX has a basic configuration where a reflective surface of an optical circuit has a function as wiring of an electric circuit. That is, a more-complicated optical circuit may be configured by stacking the optical waveguide substrates with each other. Also in such a case, a reflective surface of each optical waveguide substrate is made of a conductive material and hence, it is possible to impart a function as wiring of an electric circuit to the reflective surfaces. 
     It is needless to say that, even in the case of an optical-electric circuit board where three or more optical waveguide substrates are stacked with each other, such an optical-electric circuit board has substantially the same advantageous effect as the optical-electric circuit board  1 C. 
     The present invention is not limited to the above-mentioned embodiments, modifications and the like, and various changes, combinations and variations are conceivable without departing from the gist of the invention.