Patent Publication Number: US-2022225525-A1

Title: Electronic device

Description:
TECHNICAL FIELD 
     The present disclosure relates to an electronic device and particularly to an electronic device in which a pair of wiring substrates disposed to face each other is accommodated in a housing. 
     BACKGROUND ART 
     For example, Japanese Patent Laying-Open No. 2014-160378 (PTL 1) is one of literatures disclosing an electronic device in which a pair of wiring substrates disposed to face each other is accommodated in a housing. The literature discloses a programmable logic controller (PLC) that is a building block-type electronic device system constituted of component units including a power supply unit, a CPU unit, and I/O units. In each of these units (and only some of the I/O units), a pair of wiring substrates disposed to face each other is accommodated in a housing. 
     In the electronic device disclosed in the above-mentioned literature, a female connector is provided on a main surface of one of the paired wiring substrates and a male connector is provided on a main surface of the other of the paired wiring substrates. The paired wiring substrates are accommodated in the housing in the state where the paired wiring substrates are disposed to face each other such that the male connector is fitted to the female connector. 
     Further, the electronic device disclosed in the above-mentioned literature is configured as follows. Specifically, an external connection terminal enabling transmission of a reference potential is provided on a rear wall of the housing and a connection fitting pressed into contact with the external connection terminal is provided on a portion in a main surface that is close to a rear end of one of the paired wiring substrates. This allows transmission of a reference potential from outside to one of the paired wiring substrates. 
     On the other hand, the other of the paired wiring substrates is not directly connected to the external connection terminal. Although not clearly described, it is conceivable that a reference potential can be transmitted through the above-mentioned male connector and female connector from one to the other of the paired wiring substrates. 
     CITATION LIST Patent Literature 
     PTL 1: Japanese Patent Laying-Open No. 2014-160378 
     SUMMARY OF INVENTION 
     Technical Problem 
     In an electronic device in which a pair of wiring substrates is accommodated in a housing, this electronic device adopts one of the two following configurations including: a configuration in which the paired wiring substrates are separately fixed to the housing; and a configuration in which one of the paired wiring substrates is fixed to the other of the paired wiring substrates that is then fixed to the housing. 
     In particular, when a configuration in which a connector provided on one wiring substrate is fitted to a connector provided on the other wiring substrate is adopted in order to electrically connect a pair of these wiring substrates to each other as in the electronic device disclosed in the above-mentioned literature, the latter configuration of the above-described two configurations is often adopted from the viewpoint of allowing easy assembly operation. As a method of fixing the pair of wiring substrates to each other in this case, a stud (a pillar-shaped or cylindrical metal fitting having screw holes at both ends) is generally interposed between the paired wiring substrates and fixed with screws to each of the paired wiring substrates. 
     Thus, when the fixing method using the stud and the screws is adopted as a method of fixing the pair of wiring substrates in the electronic device disclosed in the above-mentioned literature, a space for installing the stud and the screws is further required in addition to the space for providing the above-mentioned connection fitting through which the reference potential is transmitted. This causes a problem that the mounting area of electronic components on each wiring substrate is reduced. This naturally requires upsizing of the electronic device in order to ensure a sufficient mounting area for electronic components. 
     On the other hand, when a configuration in which the paired wiring substrates are separately fixed to the housing (that is, the former configuration of the above-described two configurations) is adopted in the electronic device disclosed in the above-mentioned literature, the paired wiring substrates need to be separately fixed to the housing while the connector provided in one wiring substrate is fitted to the connector provided in the other wiring substrate. This also causes a problem that the assembly operation becomes significantly complicated. 
     Therefore, the present disclosure has been made in view of the above-described problems, and an object of the present disclosure is to allow both size reduction of and easy assembly operation for an electronic device in which a pair of wiring substrates disposed to face each other is accommodated in a housing. 
     Solution to Problem 
     An electronic device according to an aspect of the present disclosure includes a first wiring substrate, a second wiring substrate, a housing, a fixing member, and an external connection terminal. The first wiring substrate and the second wiring substrate each have a first main surface and a second main surface that are located on a front surface and a rear surface, respectively, as a pair of main surfaces. The first wiring substrate and the second wiring substrate are spaced apart from each other in a facing direction in which the first main surface of the first wiring substrate faces the first main surface of the second wiring substrate. The housing accommodates the first wiring substrate and the second wiring substrate. The fixing member includes a first fixing portion fixed to the first wiring substrate and a second fixing portion fixed to the second wiring substrate. The fixing member is interposed between the first wiring substrate and the second wiring substrate to fix the first wiring substrate and the second wiring substrate to each other. The external connection terminal is provided in the housing. The fixing member is formed of an electrically conductive member. The first wiring substrate is provided with a first electrically conductive portion. The second wiring substrate is provided with a second electrically conductive portion. The fixing member is electrically conductive to the first electrically conductive portion by fixing the first fixing portion to the first wiring substrate. The fixing member is electrically conductive to the second electrically conductive portion by fixing the second fixing portion to the second wiring substrate. The external connection terminal is electrically conductive to the fixing member by electrically connecting the fixing member to the external connection terminal. 
     By the configuration as described above, the first wiring substrate and the second wiring substrate can be firmly fixed with the fixing member while the external connection terminals can be electrically connected to the first wiring substrate and the second wiring substrate with the fixing member interposed therebetween. In other words, the fixing member can allow both: the physical fixation between the first wiring substrate and the second wiring substrate; and the electrical connection between the external connection terminal and each of the first wiring substrate and the second wiring substrate. This eliminates the need to fix one of the first wiring substrate and the second wiring substrate to the housing, and also eliminates the need to separately provide a space for the physical fixation and a space for the electrical connection as mentioned above. Therefore, adopting the above-described configuration can achieve both size reduction of and easy assembly operation for the electronic device. 
     In the electronic device according to the above-described one aspect of the present disclosure, it is preferable that the fixing member is formed of a metal plate-shaped member having a bent shape and including at least a plate-shaped base portion extending in the facing direction. 
     By the configuration as described above, the fixing member can be formed of, what is called, a press-molded product, so that the cost for components can be significantly reduced. In this case, since the fixing member has a plate-shaped base portion extending in the above-mentioned facing direction, the mechanical strength of the fixing member can be increased while reducing the material cost. 
     In the electronic device according to the above-described one aspect of the present disclosure, it is preferable that the first fixing portion is formed of a tongue-shaped portion standing upright from one end portion of the plate-shaped base portion to extend along the first main surface of the first wiring substrate, the one end portion of the plate-shaped base portion being located close to the first wiring substrate, and the second fixing portion is formed of a tongue-shaped portion standing upright from the other end portion of the plate-shaped base portion to extend along the first main surface of the second wiring substrate, the other end portion of the plate-shaped base portion being located close to the second wiring substrate. 
     By the configuration as described above, the tongue-shaped first fixing portion can be disposed to face the first main surface of the first wiring substrate, and the tongue-shaped second fixing portion can be disposed to face the first main surface of the second wiring substrate. Thus, the first fixing portion and the first wiring substrate can be fixed in a wide area in the in-plane direction of the first main surface of the first wiring substrate, and also, the second fixing portion and the second wiring substrate can be fixed in a wide area in the in-plane direction of the first main surface of the second wiring substrate. Therefore, the strength of attachment of the fixing member to the first wiring substrate and the second wiring substrate can be increased, and thus, the strength of fixation of the first wiring substrate and the second wiring substrate can be increased. 
     In the electronic device according to the above-described one aspect of the present disclosure, the fixing member may have a reinforcement portion having a tongue shape standing upright from an end portion of the plate-shaped base portion in a direction orthogonal to the facing direction and extending in the facing direction. 
     By the configuration as described above, the mechanical strength of the fixing member can be further increased in a simple configuration. 
     In the electronic device according to the above-described one aspect of the present disclosure, the fixing member may include a first positioning protrusion protruding in the facing direction with respect to the first fixing portion toward the first wiring substrate, and a second positioning protrusion protruding in the facing direction with respect to the second fixing portion toward the second wiring substrate. In this case, it is preferable that the first positioning protrusion is inserted into a cut-out portion or a recessed portion provided in the first wiring substrate to position the fixing member with respect to the first wiring substrate, and the second positioning protrusion is inserted into a cut-out portion or a recessed portion provided in the second wiring substrate to position the fixing member with respect to the second wiring substrate. 
     By the configuration as described above, the fixing member can be readily positioned with respect to the first wiring substrate and the second wiring substrate during assembly, thereby allowing further easy assembly operation. 
     In the electronic device according to the above-described one aspect of the present disclosure, the plate-shaped base portion may be provided with a bent portion such that the plate-shaped base portion has a stepped surface extending in a direction intersecting with the facing direction. 
     By the configuration as described above, the position at which the fixing member is fixed to the first wiring substrate and the position at which the fixing member is fixed to the second wiring substrate can be displaced from each other in the direction orthogonal to the facing direction in a simple configuration. Thus, these fixing positions are not necessarily located to face each other, so that the degree of freedom in designing the first wiring substrate and the second wiring substrate can be significantly increased. 
     In the electronic device according to the above-described one aspect of the present disclosure, the first fixing portion and the first wiring substrate may be fastened with a first fastening member to fix the first fixing portion to the first wiring substrate, and the second fixing portion and the second wiring substrate may be fastened with a second fastening member to fix the second fixing portion to the second wiring substrate. 
     By the configuration as described above, the fixing member can be readily attached to the first wiring substrate and the second wiring substrate with a fastening member such as a screw or a rivet, to thereby allow further easy assembly operation. 
     In the electronic device according to the above-described one aspect of the present disclosure, the housing may be provided with a guide groove that receives the first wiring substrate to be inserted into the housing in a direction orthogonal to the facing direction. In this case, the external connection terminal may be provided at a position on a deepest side in an insertion direction in which the first wiring substrate is inserted into the housing. In this case, it is preferable that the first wiring substrate is inserted into the housing in the insertion direction to press the fixing member into contact with the external connection terminal. 
     By the configuration as described above, in a simple operation of introducing the first wiring substrate into the guide groove provided in the housing and inserting the first wiring substrate into the housing, the assembly formed of the first wiring substrate, the second wiring substrate, and the fixing member can be fixed to the housing. Further, the fixing member is pressed into contact with the external connection terminal during the insertion, to thereby establish the electrical connection between the external connection terminal and each of the first wiring substrate and the second wiring substrate, so that the assembly operation can be dramatically improved. 
     In the electronic device according to the above-described one aspect of the present disclosure, it is preferable that a portion of the external connection terminal that is pressed into contact with the fixing member has a plate spring shape. 
     By the configuration as described above, the external connection terminal can be reliably pressed into contact with the fixing member during the above-mentioned insertion of the assembly into the housing. Thus, unintended contact failure can be prevented from occurring in these portions of connection. 
     Advantageous Effects of Invention 
     The present disclosure can achieve both size reduction of and easy assembly operation for an electronic device in which a pair of wiring substrates disposed to face each other is accommodated in a housing. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic perspective view of an electronic device according to an embodiment. 
         FIG. 2  is a schematic perspective view of the electronic device shown in  FIG. 1  as viewed in a different direction. 
         FIG. 3  is a schematic cross-sectional view of the electronic device shown in  FIG. 1 . 
         FIG. 4  is a partially exploded perspective view showing an assembly structure of the electronic device shown in  FIG. 1 . 
         FIG. 5  is a front view showing a structure for fixing a first wiring substrate and a second wiring substrate in the electronic device shown in  FIG. 1 . 
         FIG. 6  is a plan view showing the structure for fixing the first wiring substrate and the second wiring substrate in the electronic device shown in  FIG. 1 . 
         FIG. 7  is an exploded perspective view showing the structure for fixing the first wiring substrate and the second wiring substrate in the electronic device shown in  FIG. 1 . 
         FIG. 8  is a schematic perspective view showing a structure of connection between a fixing member and an external connection terminal in the electronic device shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, embodiment will be described in detail with reference to the accompanying drawings. In the embodiments described below, the same or common portions are denoted by the same reference characters, and the description thereof will not be repeated. 
     &lt;A. Schematic Configuration of Electronic Device&gt; 
       FIG. 1  is a schematic perspective view of an electronic device according to an embodiment viewed from diagonally upper right on the front side.  FIG. 2  is a schematic perspective view of the electronic device as viewed from diagonally lower left on the rear side.  FIG. 3  is a schematic cross-sectional view of the electronic device taken along a line III-III shown in  FIG. 1 .  FIG. 4  is a partially exploded perspective view showing an assembly structure of the electronic device. First, a schematic configuration of an electronic device  1  according to the present embodiment will be described with reference to  FIGS. 1 to 4 . Note that  FIGS. 3 and 4  fail to show some components (mainly electronic components and the like) for the sake of easy understanding. 
     Electronic device  1  shown in  FIGS. 1 to 4  forms a component unit of a programmable multi-axis motion controller as a building block-type electronic device system. The programmable multi-axis motion controller is a control device for performing multi-axis synchronous control at high speed and with high accuracy in the industrial field and suitably utilized, for example, in precision linear motor drive control requiring ultra-high speed response performance, nano-order positioning control, and the like. 
     In this case, the building block-type electronic device system is an electronic device system constituted of a plurality of electronic devices (each corresponding to the above-mentioned component unit) electrically connected to each other in the state where these electronic devices are assembled to be positioned side by side in a prescribed direction (in a Y-axis direction shown in the figure in electronic device  1  according to the present embodiment). This configuration is adopted in the above-mentioned PLC and the like in addition to the programmable multi-axis motion controller. 
     As shown in  FIGS. 1 to 4 , electronic device  1  has a substantially rectangular parallelepiped shape in which the length in the width direction (in the Y-axis direction shown in the figure) is shorter than the length in the height direction (in a Z-axis direction shown in the figure) and shorter than the length in the depth direction (in an X-axis direction shown in the figure), and mainly includes a housing  10 , a first wiring substrate  20  and a second wiring substrate  30  that are accommodated in housing  10 . 
     Housing  10  includes a front-side housing  11  and a rear-side housing  12 , and has a box shape as a result of combination of front-side housing  11  and rear-side housing  12 . Front-side housing  11  mainly constitutes parts of housing  10  that include a front wall  10   a,  a part of an upper wall  10   c,  a part of a lower wall  10   d,  a part of a right-side wall  10   e,  and a part of a left-side wall  10   f.  Rear-side housing  12  mainly constitutes parts of housing  10  that include a rear wall  10   b,  a part of upper wall  10   c,  a part of lower wall  10   d,  a part of right-side wall  10   e,  and a part of left-side wall  10   f.    
     Front wall  10   a  of housing  10  is provided with a connection portion through which electronic device  1  is electrically connected to an external device (for example, a linear motor and the like). Rear wall  10   b  of housing  10  is provided with a rail attachment groove portion  13  along which rear wall  10   b  is detachably fixed to a DIN (German Industry Standard) rail, for example. Further, right-side wall  10   e  and left-side wall  10   f  of housing  10  are provided with connectors  51  and  52 , respectively, for electrical connection to their respective adjacently installed component units. 
     Further, rear wall  10   b  of housing  10  is provided with an external connection terminal  60 . External connection terminal  60  has a substantially C shape so as to cover a portion near the upper end of rear wall  10   b  of housing  10  and a portion near the upper end of each of right-side wall  10   e  and left-side wall  10   f  of housing  10 . External connection terminal  60  allows transmission of a reference potential and is electrically connected to first wiring substrate  20  and second wiring substrate  30 , as will be described later. 
     The portions of external connection terminal  60  that cover the above-mentioned respective portions near the upper ends of right-side wall  10   e  and left-side wall  10   f  serve to electrically connect external connection terminal  60  to the adjacently installed component units. Further, a portion of rear wall  10   b  of housing  10  that is covered by external connection terminal  60  is provided with an opening not shown in the figure. A prescribed portion of external connection terminal  60  faces the space inside housing  10  through the opening. 
     As shown in  FIGS. 3 and 4 , first wiring substrate  20  and second wiring substrate  30  each have a flat plate shape. First wiring substrate  20  has a first main surface  20   a  and a second main surface  20   b  as a pair of main surfaces located on the front surface and the rear surface of first wiring substrate  20 . Second wiring substrate  30  has a first main surface  30   a  and a second main surface  30   b  as a pair of main surfaces located on the front surface and the rear surface of second wiring substrate  30 . 
     First wiring substrate  20  and second wiring substrate  30  are accommodated in housing  10  as described above. First wiring substrate  20  and second wiring substrate  30  are spaced apart from each other such that first main surfaces  20   a  and  30   a  face each other, and thus, first wiring substrate  20  and second wiring substrate  30  are positioned to face each other inside housing  10 . In this case, the facing direction in which first wiring substrate  20  and second wiring substrate  30  are disposed to face each other corresponds to the width direction of electronic device  1  (the Y-axis direction shown in the figure). 
     Various electronic components (not shown) are mounted on each of first main surface  20   a  and second main surface  20   b  of first wiring substrate  20 . These electronic components are connected to electrically conductive patterns (not shown) provided on first wiring substrate  20 , and are electrically connected to each other via the electrically conductive patterns. In this case, the above-mentioned connector  52  is provided on first main surface  20   a  of first wiring substrate  20  while the above-mentioned connector  51  is provided on second main surface  20   b  of first wiring substrate  20 . 
     Various electronic components (not shown) are mounted on each of first main surface  30   a  and second main surface  30   b  of second wiring substrate  30 . The electronic components are connected to electrically conductive patterns (not shown) provided on second wiring substrate  30  and are electrically connected to each other via the electrically conductive patterns. A portion of second wiring substrate  30  that faces connector  52  provided on first main surface  20   a  of first wiring substrate  20  is provided with a cut-out portion (not shown in the figure), and thereby, connector  52  is to be provided on left-side wall  10   f  of housing  10 . 
     In this case, a connector  53  formed as a male connector is provided on first main surface  20   a  of first wiring substrate  20 , and a connector  54  formed as a female connector is provided on first main surface  30   a  of second wiring substrate  30  (see  FIG. 3 ). Connectors  53  and  54  are positioned so as to face each other, and are fitted to each other to thereby implement electrical connection between first wiring substrate  20  and second wiring substrate  30 . 
     Thus, first wiring substrate  20 , second wiring substrate  30 , and various electronic components mounted thereon form a prescribed circuit to thereby achieve the electrical function as electronic device  1 . 
     In electronic device  1  according to the present embodiment, second wiring substrate  30  is fixed to first wiring substrate  20  by using fixing member  40  while first wiring substrate  20  to which second wiring substrate  30  is fixed is fixed to housing  10 . In other words, second wiring substrate  30  is firmly fixed to first wiring substrate  20  and lightly held by housing  10  in order to prevent its positional deviation with respect to housing  10  but is not firmly fixed to housing  10 . 
     More specifically, as shown in  FIGS. 3 and 4 , guide grooves  14  provided as one pair extending in the depth direction (in the X-axis direction shown in the figure) of electronic device  1  are provided on the respective inner surfaces of upper wall  10   c  and lower wall  10   d  of housing  10 . The upper and lower peripheral edges of first wiring substrate  20  are introduced into the paired guide grooves  14  and first wiring substrate  20  is held by holding portions formed of protruding portions (not shown in the figure) provided on rear wall  10   b  of housing  10 , so that first wiring substrate  20  is firmly fixed to housing  10 . 
     On the other hand, second wiring substrate  30  is lightly held by a locking portion  15  formed as a protruding portion or a recessed portion locally provided on each of rear wall  10   b,  upper wall  10   c,  lower wall  10   d,  and the like of housing  10  so as to prevent positional deviation of second wiring substrate  30 . However, second wiring substrate  30  is not firmly fixed to housing  10  while it is firmly fixed to first wiring substrate  20  with fixing member  40  as described above. 
     Thereby, as shown in  FIG. 4 , first wiring substrate  20  and second wiring substrate  30  are fixed to each other by using fixing member  40  in advance and thereby formed as an assembly. Then, the assembly formed of first wiring substrate  20 , second wiring substrate  30 , fixing member  40 , and the like is accommodated in rear-side housing  12  to which front-side housing  11  is subsequently attached to thereby form an assembly of electronic device  1 . In such a very simple operation, electronic device  1  can be manufactured. 
     &lt;B. Structure for Fixing First Wiring Substrate and Second Wiring Substrate&gt; 
       FIG. 5  is a front view showing a structure for fixing the first wiring substrate and the second wiring substrate in the electronic device according to the present embodiment and  FIG. 6  is a plan view thereof  FIG. 7  is an exploded perspective view showing the structure for fixing. The following specifically describes the structure for fixing first wiring substrate  20  and second wiring substrate  30  in electronic device  1  according to the present embodiment with reference to  FIGS. 5 to 7  and the above-mentioned  FIGS. 3 and 4 . Note that  FIGS. 5 to 7  each fail to show some components (mainly electronic components and the like) for the sake of easy understanding. 
     As shown in  FIGS. 3 to 7 , in electronic device  1 , first wiring substrate  20  and second wiring substrate  30  are fixed to each other with fixing member  40  at a portion closer to the upper end and the rear end of each of first wiring substrate  20  and second wiring substrate  30 . In this case, fixing member  40  is positioned to face external connection terminal  60  provided on rear wall  10   b  of housing  10 . 
     Fixing member  40  is made of an electrically conductive member. In the present embodiment, fixing member  40  is formed of a press-molded product formed by pressing a metal plate member so as to have a bent shape. More specifically, in the present embodiment, fixing member  40  is formed of a cold-rolled steel sheet (SPCC) plated with nickel. Fixing member  40  is interposed between first wiring substrate  20  and second wiring substrate  30  to thereby fix first wiring substrate  20  and second wiring substrate  30  to each other. 
     As shown in  FIGS. 5 to 7 , fixing member  40  mainly includes: a plate-shaped base portion  41  extending in the facing direction in which first wiring substrate  20  and second wiring substrate  30  face each other (in the Y-axis direction shown in  FIG. 7 ); a first fixing portion  42   a  formed of a tongue-shaped portion standing upright from one end portion of plate-shaped base portion  41  that is located close to first wiring substrate  20 ; and a second fixing portion  42   b  formed of a tongue-shaped portion standing upright from the other end portion of plate-shaped base portion  41  that is located close to second wiring substrate  30 . 
     Plate-shaped base portion  41  has a bent portion  41   a  at its intermediate position so as to have a stepped surface extending in a direction intersecting with the above-mentioned facing direction. Bent portion  41   a  is provided for causing displacement between the position of first fixing portion  42   a  and the position of second fixing portion  42   b  from each other in the direction orthogonal to the facing direction. 
     First fixing portion  42   a  formed of a tongue-shaped portion is positioned to face first main surface  20   a  of first wiring substrate  20  and provided with a first screw hole  42   a   1  (see  FIG. 7 ) at its prescribed position. First screw hole  42   a   1  has an inner circumferential surface provided with a female thread portion. 
     Second fixing portion  42   b  formed of a tongue-shaped portion is positioned to face first main surface  30   a  of second wiring substrate  30  and provided with a second screw hole  42   b   1  (see  FIG. 7 ) at its prescribed position. Second screw hole  42   b   1  has an inner circumferential surface provided with a female thread portion. 
     Further, fixing member  40  is provided with a plurality of reinforcement portions  43  so as to stand upright from both end portions of plate-shaped base portion  41  in the direction orthogonal to the facing direction. The plurality of reinforcement portions  43  each are formed in a tongue shape so as to extend in the above-mentioned facing direction, to thereby reinforce plate-shaped base portion  41 . By bending a part of fixing member  40  so as to provide reinforcement portion  43  in this way, the mechanical strength of fixing member  40  can be enhanced in a simple configuration. 
     Further, fixing member  40  has a pair of first positioning protrusions  44   a  protruding with respect to first fixing portion  42   a  toward first wiring substrate  20  in the facing direction, and a pair of second positioning protrusions  44   b  protruding with respect to second fixing portion  42   b  toward second wiring substrate  30  in the facing direction. The pair of first positioning protrusions  44   a  and the pair of second positioning protrusions  44   b  are provided so as to extend from the above-mentioned respective reinforcement portions  43 . 
     The pair of first positioning protrusions  44   a  is used for positioning fixing member  40  with respect to first wiring substrate  20  and the pair of second positioning protrusions  44   b  is used for positioning fixing member  40  with respect to second wiring substrate  30 . The details thereof will be described later. 
     As shown in  FIG. 7 , a first through portion  21  formed in a hole shape is provided at a prescribed position of first wiring substrate  20  so as to reach first main surface  20   a  and second main surface  20   b.  First through portion  21  is provided at a position corresponding to the above-mentioned first screw hole  42   a   1  provided in first fixing portion  42   a  of fixing member  40 . 
     In this case, a first electrically conductive portion  22  is provided on a portion around first through portion  21  in each of first main surface  20   a  and second main surface  20   b.  First electrically conductive portion  22  is formed, for example, of an electrically conductive pattern and serves to transmit a reference potential. Note that first electrically conductive portion  22  is not necessarily provided on both first main surface  20   a  and second main surface  20   b  but may be provided on only one of first main surface  20   a  and second main surface  20   b.    
     Further, a pair of first positioning hole portions  23  each having a cut-out shape (a hole shape in this case) is provided at prescribed positions of first wiring substrate  20  so as to reach first main surface  20   a  and second main surface  20   b.  Such paired first positioning hole portions  23  are provided at respective positions corresponding to the above-mentioned paired first positioning protrusions  44   a  provided in fixing member  40 . 
     On the other hand, a second through portion  31  having a cut-out shape is provided at a prescribed position of second wiring substrate  30  so as to reach first main surface  30   a  and second main surface  30   b.  Second through portion  31  is provided at a position corresponding to the above-mentioned second screw hole  42   b   1  provided in second fixing portion  42   b  of fixing member  40 . 
     In this case, a second electrically conductive portion  32  is provided on a portion around second through portion  31  in each of first main surface  30   a  and second main surface  30   b.  Second electrically conductive portion  32  is formed, for example, of an electrically conductive pattern and serves to transmit a reference potential. Note that second electrically conductive portion  32  is not necessarily provided on both first main surface  30   a  and second main surface  30   b  but may be provided on only one of first main surface  30   a  and second main surface  30   b.    
     Further, a pair of second positioning hole portions  33  each having a cut-out shape (a hole shape in this case) is provided at prescribed positions of second wiring substrate  30  so as to reach first main surface  30   a  and second main surface  30   b.  Such paired second positioning hole portions  33  are provided at respective positions corresponding to the above-mentioned paired second positioning protrusions  44   b  provided in fixing member  40 . 
     In this case, as shown in  FIGS. 3 to 7 , fixing member  40  is fixed to first wiring substrate  20  by fastening first fixing portion  42   a  to first wiring substrate  20  with a first screw  45   a  as the first fastening member. More specifically, fixing member  40  is positioned with respect to first wiring substrate  20  such that first screw hole  42   a   1  provided in first fixing portion  42   a  of fixing member  40  faces first through portion  21  of first wiring substrate  20 . In this state, first screw  45   a  is screwed into first screw hole  42   a   1  from the second main surface  20   b  side of first wiring substrate  20 , and thereby, fixing member  40  is fixed to first wiring substrate  20 . 
     At this time, the paired first positioning protrusions  44   a  provided in advance in fixing member  40  are inserted into the paired respective first positioning hole portions  23  provided in first wiring substrate  20 , to thereby allow positioning between first screw hole  42   a   1  and first through portion  21 . Thereby, fixing member  40  can be readily positioned with respect to first wiring substrate  20 . Note that first positioning hole portion  23  may be formed to have a recessed portion in place of a cut-out shape. 
     Further, fixing member  40  is fixed to second wiring substrate  30  by fastening second fixing portion  42   b  to second wiring substrate  30  with a second screw  45   b  as the second fastening member. More specifically, fixing member  40  is positioned with respect to second wiring substrate  30  such that second screw hole  42   b   1  provided in second fixing portion  42   b  of fixing member  40  faces second through portion  31  of second wiring substrate  30 . In this state, second screw  45   b  is screwed into second screw hole  42   b   1  from the second main surface  30   b  side of second wiring substrate  30 , and thereby, fixing member  40  is fixed to second wiring substrate  30 . 
     At this time, the paired second positioning protrusions  44   b  provided in advance in fixing member  40  are inserted into the paired respective second positioning hole portions  33  provided in second wiring substrate  30 , to thereby allow positioning between second screw hole  42   b   1  and second through portion  31 . Thereby, fixing member  40  can be readily positioned with respect to second wiring substrate  30 . Note that second positioning hole portion  33  may be formed to have a recessed portion in place of a cut-out shape. 
     As described above, first wiring substrate  20  and second wiring substrate  30  are fixed to each other with fixing member  40 , and thereby, first wiring substrate  20  and second wiring substrate  30  are physically fixed to each other. 
     &lt;C. Structure of Connection between Fixing Member and External Connection Terminal&gt; 
       FIG. 8  is a schematic perspective view showing a structure of connection between the fixing member and the external connection terminal in the electronic device according to the present embodiment. The following specifically describes a structure of connection between fixing member  40  and external connection terminal  60  in electronic device  1  according to the present embodiment with reference to  FIG. 8 .  FIG. 8  fails to show some components (mainly electronic components and the like) for the sake of easy understanding but shows a part of first wiring substrate  20  in a cut away view. 
     As shown in  FIG. 8 , external connection terminal  60  has: a base portion  61  that covers rear wall  10   b  of housing  10 ; a pair of external connection portions  62  that cover right-side wall  10   e  and left-side wall  10   f  of housing  10 ; and a plate spring-shaped contact  63  that is disposed to face the above-mentioned opening provided in rear wall  10   b  of housing  10 . Among these components, the pair of external connection portions  62  serves to electrically connect external connection terminal  60  to a component unit disposed adjacent to electronic device  1 . 
     Plate spring-shaped contact  63  is inserted into the above-mentioned opening and thereby positioned to protrude into the space inside housing  10 . Thereby, plate spring-shaped contact  63  is disposed at a position on the deepest side of housing  10  in the depth direction of electronic device  1  (in the X-axis direction shown in the figure). 
     In this case, when electronic device  1  is manufactured, the assembly formed of first wiring substrate  20 , second wiring substrate  30 , fixing member  40 , and the like is inserted from the front side into rear-side housing  12  and thereby attached to rear-side housing  12 , as described above. At this time, the pair of guide grooves  14  receives and guides first wiring substrate  20 , and thereby, the above-mentioned assembly is guided in the depth direction of electronic device  1 . 
     Thus, by inserting the above-mentioned assembly toward the deepest side of rear-side housing  12 , a prescribed position of plate-shaped base portion  41  provided in fixing member  40  is pressed into contact with plate spring-shaped contact  63  of external connection terminal  60  disposed on the deepest side of housing  10 . Thereby, fixing member  40  is electrically connected to external connection terminal  60 , and thus, external connection terminal  60  is electrically conductive via fixing member  40  to both first electrically conductive portion  22  of first wiring substrate  20  and second electrically conductive portion  32  of second wiring substrate  30 . 
     &lt;D. Conclusion&gt; 
     As in the above description, according to electronic device  1  in the present embodiment, first wiring substrate  20  and second wiring substrate  30  can be firmly fixed by using fixing member  40 , and external connection terminal  60  for transmitting a reference potential can be electrically connected via fixing member  40  to first wiring substrate  20  and second wiring substrate  30 , as described above. In other words, fixing member  40  allows both: the physical fixation between first wiring substrate  20  and second wiring substrate  30 ; and the electrical connection between external connection terminal  60  and each of first wiring substrate  20  and second wiring substrate  30 . 
     Thus, adopting the above-described configuration eliminates the need to firmly fix second wiring substrate  30  to housing  10  and also eliminates the need to separately provide spaces for the above-mentioned physical fixation and electrical connection. Therefore, electronic device  1  that is reduced in size and fabricated in easy assembly operation can be implemented. 
     Further, according to electronic device  1  in the present embodiment described above, fixing member  40  can be formed of, what is called, a press-molded product, and therefore, the component cost can be significantly reduced. Further, since fixing member  40  has plate-shaped base portion  41  extending in the above-mentioned facing direction, the mechanical strength of fixing member  40  can also be increased while reducing the material cost. 
     Further, according to electronic device  1  in the present embodiment described above, tongue-shaped first fixing portion  42   a  and tongue-shaped second fixing portion  42   b  can be disposed to face first main surface  20   a  of first wiring substrate  20  and first main surface  30   a  of second wiring substrate  30 , respectively. Thus, first fixing portion  42   a  and second fixing portion  42   b  can be fixed to first wiring substrate  20  and second wiring substrate  30 , respectively, in a wide area in the in-plane direction of first wiring substrate  20  and second wiring substrate  30 . Therefore, adopting the above-described configuration can increase the strength of attachment of fixing member  40  to first wiring substrate  20  and second wiring substrate  30 , and also can increase the strength of fixation between first wiring substrate  20  and second wiring substrate  30 . 
     Further, according to electronic device  1  in the present embodiment described above, the position at which fixing members  40  is fixed to first wiring substrate  20  and the position at which fixing members  40  is fixed to second wiring substrate  30  can be displaced from each other in the direction orthogonal to the above-mentioned facing direction in a simple configuration in which bent portion  41   a  is provided in plate-shaped base portion  41  of fixing member  40 . Accordingly, these fixing positions are not necessarily located to face each other, so that the degree of freedom in designing first wiring substrate  20  and second wiring substrate  30  can be significantly increased. 
     Further, according to electronic device  1  in the present embodiment described above, fixing member  40  can be readily attached to first wiring substrate  20  and second wiring substrate  30  with first screw  45   a  and second screw  45   b,  respectively. Thus, adopting the above-described configuration allows further easy assembly operation. Note that first screw  45   a  and second screw  45   b  may be replaced with a rivet and the like. 
     Further, according to electronic device  1  in the present embodiment described above, in a simple operation of introducing first wiring substrate  20  into guide groove  14  provided in housing  10  and then inserting first wiring substrate  20  into housing  10 , the assembly formed of first wiring substrate  20 , second wiring substrate  30 , fixing member  40 , and the like can be fixed to housing  10 . Further, fixing member  40  is pressed into contact with external connection terminal  60  during insertion, to thereby establish electrical connection between external connection terminal  60  and each of first wiring substrate  20  and second wiring substrate  30 . Thus, adopting the above-described configuration can dramatically improve the assembly operation. 
     In addition, according to electronic device  1  in the present embodiment described above, contact  63  provided on external connection terminal  60  has a plate spring shape, so that pressure contact between external connection terminal  60  and fixing member  40  can be ensured during the above-mentioned insertion of the assembly into housing  10 . Thus, adopting the above-described configuration can prevent occurrence of contact failure between external connection terminal  60  and fixing member  40 . 
     &lt;E. Additional Description&gt; 
     The following summarizes the characteristic configuration of electronic device  1  according to the above-described present embodiment. 
     [Configuration 1] 
     An electronic device comprising: 
     a first wiring substrate ( 20 ) and a second wiring substrate ( 30 ) each having a first main surface ( 20   a,    30   a ) and a second main surface ( 20   b,    30   b ) that are located on a front surface and a rear surface, respectively, as a pair of main surfaces ( 20   a,    30   a ), the first wiring substrate and the second wiring substrate being spaced apart from each other in a facing direction in which the first main surface of the first wiring substrate faces the first main surface of the second wiring substrate; 
     a housing ( 10 ) that accommodates the first wiring substrate and the second wiring substrate; 
     a fixing member ( 40 ) including a first fixing portion ( 42   a ) fixed to the first wiring substrate and a second fixing portion ( 42   b ) fixed to the second wiring substrate, the fixing member being interposed between the first wiring substrate and the second wiring substrate to fix the first wiring substrate and the second wiring substrate to each other; and 
     an external connection terminal ( 60 ) provided in the housing, wherein 
     the fixing member is formed of an electrically conductive member, 
     the first wiring substrate is provided with a first electrically conductive portion ( 22 ), 
     the second wiring substrate is provided with a second electrically conductive portion ( 32 ), 
     the fixing member is electrically conductive to the first electrically conductive portion by fixing the first fixing portion to the first wiring substrate, 
     the fixing member is electrically conductive to the second electrically conductive portion by fixing the second fixing portion to the second wiring substrate, and 
     the external connection terminal is electrically conductive to the fixing member by electrically connecting the fixing member to the external connection terminal. 
     [Configuration 2] 
     The electronic device according to Configuration 1, wherein the fixing member is formed of a metal plate-shaped member having a bent shape and including at least a plate-shaped base portion ( 41 ) extending in the facing direction. 
     [Configuration 3] 
     The electronic device according to Configuration 2, wherein 
     the first fixing portion is formed of a tongue-shaped portion standing upright from one end portion of the plate-shaped base portion to extend along the first main surface of the first wiring substrate, the one end portion of the plate-shaped base portion being located close to the first wiring substrate, and 
     the second fixing portion is formed of a tongue-shaped portion standing upright from the other end portion of the plate-shaped base portion to extend along the first main surface of the second wiring substrate, the other end portion of the plate-shaped base portion being located close to the second wiring substrate. 
     [Configuration 4] 
     The electronic device according to Configuration 2 or 3, wherein the fixing member has a reinforcement portion ( 43 ) having a tongue shape standing upright from an end portion of the plate-shaped base portion in a direction orthogonal to the facing direction and extending in the facing direction. 
     [Configuration 5] 
     The electronic device according to any one of Configurations 2 to 4, wherein 
     the fixing member includes
         a first positioning protrusion ( 44   a ) protruding in the facing direction with respect to the first fixing portion toward the first wiring substrate, and   a second positioning protrusion ( 44   b ) protruding in the facing direction with respect to the second fixing portion toward the second wiring substrate,       

     the first positioning protrusion is inserted into a cut-out portion ( 23 ) or a recessed portion ( 23 ) provided in the first wiring substrate to position the fixing member with respect to the first wiring substrate, and 
     the second positioning protrusion is inserted into a cut-out portion ( 33 ) or a recessed portion ( 33 ) provided in the second wiring substrate to position the fixing member with respect to the second wiring substrate. 
     [Configuration 6] 
     The electronic device according to any one of Configurations 2 to 5, wherein the plate-shaped base portion is provided with a bent portion ( 41   a ) such that the plate-shaped base portion has a stepped surface extending in a direction intersecting with the facing direction. 
     [Configuration 7] 
     The electronic device according to any one of Configurations 2 to 6, wherein the first fixing portion and the first wiring substrate are fastened with a first fastening member ( 45   a ) to fix the first fixing portion to the first wiring substrate, and the second fixing portion and the second wiring substrate are fastened with a second fastening member ( 45   b ) to fix the second fixing portion to the second wiring substrate. 
     [Configuration 8] 
     The electronic device according to any one of Configurations 1 to 7, wherein the housing is provided with a guide groove ( 14 ) that receives the first wiring substrate to be inserted into the housing in a direction orthogonal to the facing direction, 
     the external connection terminal is provided at a position on a deepest side in an insertion direction in which the first wiring substrate is inserted into the housing, and 
     the first wiring substrate is inserted into the housing in the insertion direction to press the fixing member into contact with the external connection terminal. 
     [Configuration 9] 
     The electronic device according to Configuration 8, wherein a portion ( 63 ) of the external connection terminal that is pressed into contact with the fixing member has a plate spring shape. 
     &lt;F. Other Embodiments and the Like&gt; 
     The above embodiment has been described with reference to an example of a configuration in which the fixing member is fixed with screws to both the paired wiring substrates, but may be fixed by other fixing methods to one or both of the wiring substrates. In addition to the above-mentioned riveting, examples of other fixing methods include bonding using a brazing material such as solder, bonding using an electrically conductive adhesive, fixing by means of welding, caulking, and the like. 
     Further, the above embodiment has been described with reference to an example of a case where a bent portion is provided in the plate-shaped base portion of the fixing member, but the bent portion is not necessarily provided. In addition, the above embodiment has been described with reference to an example of a case where a reinforcement portion and a positioning protrusion are provided in the fixing member, but these portions are not necessarily provided. 
     Further, the above embodiment has been described with reference to an example of a configuration in which the fixing member and the external connection terminal are pressed into contact with each other so as to be electrically connected to each other, but the method of connecting the fixing member and the external connection terminal is not limited thereto, and any other connection methods may be used. 
     Further, the above embodiment has been described with reference to an example of a configuration in which a reference potential is transmitted from the external connection terminal to the first wiring substrate and the second wiring substrate via the fixing member, but other electrical signals and the like may be transmitted from the external connection terminal to the first wiring substrate and the second wiring substrate via the fixing member, or other electrical signals and the like may be transmitted from the first wiring substrate and the second wiring substrate to the external connection terminal via the fixing member. 
     Further, the above embodiment has been described with reference to an example of a case where the present invention is applied to a component unit of a programmable multi-axis motion controller, but the present invention can also be naturally applicable to other electronic devices represented by a component unit of a PLC or the like. Further, the present invention can also be applicable to electronic devices having various configurations without being limited to a building block-type electronic device. 
     The above embodiments disclosed herein are illustrative in all respects and should not be construed as being restrictive. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
       1  electronic device,  10  housing,  10   a  front wall,  10   b  rear wall,  10   c  upper wall,  10   d  lower wall,  10   e  right-side wall,  10   f  left-side wall,  11  front-side housing,  12  rear-side housing,  13  rail attachment groove portion,  14  guide groove,  15  locking portion,  20  first wiring substrate,  20   a  first main surface,  20   b  second main surface,  21  first through portion,  22  first electrically conductive portion,  23  first positioning hole portion,  30  second wiring substrate,  30   a  first main surface,  30   b  second main surface,  31  second through portion,  32  second electrically conductive portion,  33  second positioning hole portion,  40  fixing member,  41  plate-shaped base portion,  41   a  bent portion,  42   a  first fixing portion,  42   a   1  first screw hole,  42   b  second fixing portion,  42   b   1  second screw hole,  43  reinforcement portion,  44   a  first positioning protrusion,  44   b  second positioning protrusion,  45   a  first screw,  45   b  second screw,  51  to  54  connector,  60  external connection terminal,  61  base portion,  62  external connection portion,  63  contact.