Abstract:
An electrical junction box may include a casing with a lower casing member and an upper casing member. A multi-layered circuit board may be retained in the electrical junction box. The multi-layered circuit board may contain a lower layer circuit board, an upper layer circuit board and an insulation plate that is disposed between and supports the lower layer circuit board and the upper layer circuit board. A rib and a boss may project from the lower casing member and may contact the insulation plate without contacting either the lower layer circuit board or the upper layer circuit board. In this manner, no physical stress is applied to a surface of either the lower layer circuit board or the upper layer circuit board thereby preventing detachment of an electronic component from the multi-layered circuit board.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to JP 2008-277474 filed in Japan on Oct. 28, 2008, the entire disclosure of which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    This invention relates to an electrical junction box and a method for assembling the same. Particularly, the electrical junction box may includes features that allow a circuit board to be securely mounted within the electrical junction box in a manner that prevents a load placed on a supporting member that supports the circuit board from being transferred to the circuit board, thereby protecting the circuit board from stress, damage and deformation and thereby preventing an electronic component mounted on the circuit board from being detached from the circuit board. 
         [0003]    A vehicle-mounted electrical junction box or the like may contain, in high density, a wide range of circuit members stacked on one another. In some embodiments, a multilayered circuit board assembly that mounts a circuit member such an electronic component is contained in the electrical junction box. 
         [0004]    Embodiments of the electrical junction box may include a casing that includes an upper casing member and a lower casing member. The stacked circuit member may be contained in the casing. Accordingly, it is necessary to hold the multilayered circuit board assembly in the electrical junction box. 
         [0005]    For example,  FIG. 11  shows a related art electrical junction box, which has been disclosed in JP 2007-134506 A. As shown in  FIG. 11 , a circuit board  101  is mounted on lower bosses  100   a  and  100   b  projecting from a bottom wall of a lower casing member  100 . A plate  102  disposed above the circuit board  101  is provided on a bottom surface at positions faced to the lower bosses  100   a  and  100   b  with upper bosses  102   a  and  102   b . The lower boss  100   a  and upper boss  102   a  clamp the circuit board  101  in a vertical direction. The upper boss  102   b  passes through the circuit board  101  and enters a receiving aperture  100   b - 1  provided in an upper end of the lower boss  100   b . Thus, the circuit board  101  is positioned and held on the lower casing member  100 . 
         [0006]    As described above, when the circuit board  101  is clamped directly between the upper bosses  102   a ,  102   b  and the lower bosses  100   a ,  100   b , a load is applied directly to the points of contact between the circuit board  101  and the bosses  100   a  to  102   b . Consequently, there is a possibility that the circuit board will be subject to strain, deformation and/or damage and, thus, there is a possibility that an electronic component mounted on the multilayered circuit board assembly will be detached from the assembly. 
         [0007]    In view of the above problems and other problems, the exemplary embodiments provide an electrical junction box that can position and hold a circuit board in a casing so that a positioning member does not contact directly with the circuit board, thereby preventing detachment of electronic components from the circuit board. 
       SUMMARY 
       [0008]    An electrical junction box in accordance with an exemplary embodiment may include a casing including a lower casing member and an upper casing member, and a multilayered circuit board assembly that may include a lower layer circuit board, an upper layer circuit board, and an insulation plate disposed between the upper and lower circuit boards. An electronic component may be mounted through the insulation plate on a top surface of the lower layer circuit board without contacting a bottom surface of the upper layer circuit board. The upper and lower layer circuit boards may be secured to the insulation plate. A rib assembly and a boss may project from the lower casing member. The rib assembly and the boss may contact the insulation plate to support the plate without contacting surfaces of the upper and lower circuit boards in the multilayered circuit board assembly on which the electronic component is mounted. 
         [0009]    The boss may be a cylindrical support post standing upward from the bottom wall of the lower casing member at a position apart from the peripheral wall of the lower casing member. The rib assembly may stand upward from the bottom wall of the lower casing member and may be continued to the peripheral wall of the lower casing member. 
         [0010]    As described above, in an embodiment in which the multilayered circuit board assembly is mounted in the electrical junction box, the circuit boards may be attached to the insulation plate in the box. Using such an approach, the circuit boards may contact the insulation plate and the boss projecting from the lower casing member may contact the insulation plate, thereby supporting the multilayered circuit board assembly without contacting a surface of the circuit board on which the electronic component is mounted. 
         [0011]    Thus, no load is applied to the surface of the circuit board, because the rib assembly and boss do not contact directly with the surfaces of the circuit board on which the electronic component is not mounted. Accordingly, no stress or strain is applied to a surface of the circuit board and it is possible to prevent the mounted electronic component from being detached from the circuit board. 
         [0012]    The multilayered circuit board assembly may include embodiments in which a single upper layer circuit board and a single lower layer circuit board are used, and embodiments in which the upper and lower circuit boards are stacked on each other without interposing any insulation plate between them. 
         [0013]    The rib assembly may include a first rib member and a second rib member. The first rib member may pass a peripheral edge of the lower layer circuit board and may contact a bottom surface of a peripheral edge of the insulation plate. The boss may pass through a through-hole in the lower layer circuit board and may contact a bottom surface of the insulation plate or a bottom surface of the upper layer circuit board. The second rib member may pass a peripheral edge of the insulation plate and may contact a bottom surface of the upper layer circuit board. 
         [0014]    Also, the lower layer circuit board and insulation plate may be connected by a second screw. The insulation plate and upper layer circuit board may include screw apertures that may be aligned with each other. A first screw may be screwed through the screw apertures into a screw cylinder projecting from an inner surface of the upper casing member. 
         [0015]    In the electrical junction box of the present invention, as described after, the upper casing member may be turned upside down and held on an assembling jig. The upper layer circuit board, insulation plate, and lower layer circuit board may be installed in order in the upper casing member. Then, the lower casing member, from which the boss and the rib assembly project, may be aligned with, mounted and locked on the upper casing member. Accordingly, the upper layer circuit board may attach to the upper casing member before the insulation plate is attached to the upper casing member. A screw cylinder projecting from the upper casing member may be inserted into the screw apertures in the upper layer circuit board and insulation plate, and a first screw may be used to fasten the upper layer circuit board and the insulation plate to the screw cylinder. A second screw may be used to fasten the lower layer circuit board to the insulation plate. 
         [0016]    Thus, the upper and lower layer circuit boards are positioned and held in the upper and lower casing members. 
         [0017]    The circuit boards may be previously bonded to the insulation plate by an adhesive without using any screws. 
         [0018]    Preferably, the boss may be positioned substantially in a central position of a triangular area defined by three first screws. 
         [0019]    By positioning the boss in a central position relative to the triangular area defined by three first screws, the boss and the vertices of the triangle may absorb and moderate stress from the upper casing member. 
         [0020]    Embodiments of the present invention provide a method for assembling an electrical junction box described above. The method may include, turning the upper casing member topside down to direct an opening upward, disposing the turned upper casing member on an assembling jig, inserting the upper layer circuit board and the insulation plate in order in the upper casing member, interconnecting the insulation plate and upper layer circuit board by an upper casing screw, inserting the lower layer circuit board into the upper casing member, interconnecting the lower layer circuit board and insulation plate by a screw, attaching the lower casing member to the upper casing member, and bringing the first rib member and boss projecting from an inner surface of the lower casing member into contact with the insulation plate and bringing the second rib member into contact with a bottom surface of the upper layer circuit board to position and hold the circuit board assembly in the casing. 
         [0021]    After the electrical junction box is assembled by the above manner, the electrical junction box may be turned so that the bottom surface of the lower casing member is directed downward. The boss and the rib assembly projecting from the inner surface of the bottom wall of the lower casing member can position and hold the insulation plate and the upper and lower layer circuit boards mounted on the upper and lower surfaces of the insulation plate. 
         [0022]    As described above, in the electrical junction box that contains the multilayered circuit board assembly in the casing comprising the upper and lower casing members, because the boss and the rib assembly for positioning and holding the multilayered circuit board assembly do not directly contact the surfaces of circuit boards on which an electronic component is mounted, it is possible to prevent the circuit boards from deforming or straining by the stress caused by contact between them and thereby prevent detachment of an electronic component from the circuit boards. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1A  is a plan view of an embodiment of an electrical junction box in accordance with an example embodiment of the present invention.  FIG. 1B  is a front elevation view of the electrical junction box shown in  FIG. 1A .  FIG. 1C  is a bottom view of the electrical junction box shown in  FIG. 1A ; 
           [0024]      FIG. 2  is a longitudinal section view of the electrical junction box taken along lines II-II in  FIG. 1A ; 
           [0025]      FIG. 3  is a plan view of a lower casing member, illustrating an interior of the lower casing member; 
           [0026]      FIG. 4A  is a longitudinal section view of the lower casing member.  FIG. 4B  is a cross section view of the lower casing member; 
           [0027]      FIG. 5A  is a top view of an upper layer circuit board.  FIG. 5B  is a bottom view of the upper layer circuit board; 
           [0028]      FIG. 6  is a bottom view of a multilayered circuit board assembly interposing an insulation plate between an upper layer circuit board and a lower layer circuit board; 
           [0029]      FIG. 7A  is a bottom view of an insulation plate.  FIG. 7B  is a bottom view of the insulation plate, illustrating the insulation plate attached to the upper layer circuit board; 
           [0030]      FIG. 8A  is a bottom view of an upper casing member, illustrating an interior of the upper casing member.  FIG. 8B  is a side elevation view of the upper casing member shown in  FIG. 8A .  FIG. 8C  is an enlarged view of a main part of the upper casing member shown in  FIG. 8B ; 
           [0031]      FIG. 9  is an exploded schematic view of a casing and a multilayered circuit board assembly, illustrating a method for assembling the electrical junction box in accordance with an example embodiment of the present invention; 
           [0032]      FIG. 10  is a sectional view of a main part of the casing and multilayered circuit board assembly, illustrating them under an assembled position; and 
           [0033]      FIG. 11  is a sectional view of a main part of a prior art electrical junction box. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0034]    Referring now to the drawings, an example embodiment of an electrical junction box in accordance with the present invention will be described below. 
         [0035]    An electrical junction box  1  shown in  FIGS. 1A to 1C  may be mounted in a motor vehicle.  FIG. 1A  is a plan view of an example embodiment of electrical junction box  1  in accordance with the present invention.  FIG. 1B  is a front elevation view of electrical junction box  1  shown in  FIG. 1A .  FIG. 1C  is a bottom view of electrical junction box  1  shown in  FIG. 1A .  FIG. 2  is a longitudinal section view of electrical junction box  1  taken along lines II-II in  FIG. 1A . 
         [0036]    Electrical junction box  1  may include a casing that may include an upper casing member  2  and a lower casing member  3 . The casing members  2  and  3  may be locked to each other to constitute the casing. A multilayered circuit board assembly may be contained in an interior of the casing. As shown in  FIG. 2 , the multilayered circuit board assembly may include an upper layer circuit board  7 , a lower layer circuit board  5 , and an insulation plate  6  disposed between lower layer circuit board  5  and upper layer circuit board  7 . Also, an insulation plate  8  may be disposed between upper layer circuit board  7  and an upper wall  2   a  of upper casing member  2 . 
         [0037]      FIG. 9  schematically shows a method of assembling electrical junction box  1 . Upper casing member  2  may be turned upside down so that an upper wall  2   a  becomes a bottom side. Turned upper casing member  2  may be held on an assembling jig  50 . Insulation plate  8 , upper layer circuit board  7 , insulation plate  6 , lower layer circuit board  5  may be installed in order in the upper casing member  2 . Finally, lower casing member  3  may be mounted and locked on the upper casing member  2 . 
         [0038]    Upper casing member  2  and lower casing member  3  may be resin molding products and may be formed into elongated configurations. 
         [0039]    As shown in  FIG. 1A , upper casing member  2  may be provided on the upper wall  2   a  with a fuse-containing section  12 , a relay-containing section  13 , and a connector-containing section  14 . As shown in  FIG. 2 , an attaching piece  9   a  bent from a bus bar  9  may be pressed into and held in a receiving aperture provided in an inner surface of the upper wall  2   a . Tabs provided on bus bar  9  may be inserted into terminal apertures in the fuse-containing section  12 , relay-containing section  13 , and connector-containing section  14 . 
         [0040]    Peripheral wall  2   b  of upper casing member  2  may have dimensions that are matched to the dimensions of insulation plate  8 , which may be disposed inside the peripheral wall  2   b . Therefore, a height of peripheral wall  2   b  may be relatively small in a vertical direction. On the other hand, a peripheral wall  3   b  of the lower casing member  3  may have dimensions that surround the multilayered circuit board assembly including upper lower circuit board  7  and lower circuit board  5  and insulation plate  6 , so a height of peripheral wall  3   b  may be relatively great in the vertical direction. 
         [0041]    Upper casing member  2  may include locking portions  2   c  ( FIG. 2 ) on an outer surface of the peripheral wall  2   b , while the lower casing member  3  may include locked portions  3   c  ( FIG. 2 ) on an outer surface of the peripheral wall  3   b . When locking portions  2   c  lock the locked portion  3   c , the upper and lower casing members  2  and  3  are interlocked to each other to form the casing. 
         [0042]    As shown in  FIG. 3 , the lower casing member  3  may include a cylindrical boss  20  projecting from a central area on an inner surface of a bottom wall  3   a . Also, as shown in  FIGS. 4A and 4B , an L-shaped rib assembly including first rib members  21  and second rib members  22  may project from an inner peripheral surface of the bottom wall  3   a  to the inner surface of the peripheral wall  3   b.    
         [0043]    As shown in  FIGS. 5A and 5B , upper layer circuit board  7  may be a rectangular configuration. An outer peripheral surface of upper layer circuit board  7  may have a size that may be fitted inside the peripheral wall  3   b  of the lower casing member  3 . As shown in  FIG. 5A , terminals  30  may be directly soldered on a top surface  7   x  of upper layer circuit board  7 . Although connectors  31  are soldered on the top surface  7   x , no electronic component is mounted on the upper surface  7   x . Although a connector  32  is soldered on a bottom surface  7   y  of upper layer circuit board  7 , as shown in  FIG. 5B , no electronic component is mounted on the bottom surface  7   y.    
         [0044]    As shown in  FIG. 6 , when upper layer circuit board  7  is mounted on insulation plate  6 , lower layer circuit board  5  becomes a rectangular configuration except for a cutout space  5   b  in a part of a side edge  5   a . The connector  32  mounted on the bottom surface  7   y  of the upper layer  7  may be disposed in the cutout space  5   b . A part of side edge  5   a  (a portion that is not provided with the cutout space  5   b ) may extend along the peripheral wall  3   b  of the lower casing member  3 . A side edge  5   c  may be faced to the side edge  5   a  and spaced apart from the peripheral wall  3   b  of the lower casing member  3  by a given distance, so that a part of the insulation plated  6  is exposed. Side edges  5   d  and  5   e  perpendicular to the side edges  5   a  and  5   c  may extend along the peripheral wall  3   b  of the lower casing member  3  and are provided with rib-receiving cutout spaces  5   f  spaced apart from one another. 
         [0045]    As shown in  FIG. 6 , an electronic component mounting section  35  including microchips (not shown) may be provided on the bottom surface  5   y  of lower layer circuit board  5  and a connector may be soldered on the bottom surface  5   y.    
         [0046]      FIG. 7A  is a bottom view of the insulation plate  6  that may be interposed between the lower circuit board  5  and upper layer circuit board  7 .  FIG. 7B  is a bottom view of the insulation plate  6  attached to upper layer circuit board  7 . As shown in  FIG. 7A , parts of the insulation plate  6  may be cut out at three edges B-B, C-C, and D-D. A whole edge A-A of the peripheral wall  6   a  of the insulation plate  6  may extend along the inner surface of the peripheral wall  3   b  of the lower casing member  3 . The insulation plate  6  may be provided on three edges B-B, C-C, and D-D of the peripheral wall  6   a  with cutout spaces C 3 , C 1 , and C 2 , respectively. Peripheral walls  6   b ,  6   c , and  6   d , which are not provided with the cutout spaces C 1 , C 2 , and C 3 , may extend along the peripheral wall  3   b  of the lower casing member  3 . 
         [0047]    Connectors  37  mounted on upper layer circuit board  7  may be disposed in cutout space C 1  and in cutout space C 2 . Connector  32  mounted on upper layer circuit board  7  may be disposed in cutout space C 3 . Connectors  37  may serve to interconnect conductors on upper layer circuit board  7  and lower layer circuit board  5  to one another. 
         [0048]    As shown in  FIG. 4A , a height H 1  of each of first rib members  21  provided on lower casing member  3  may be set to be smaller than a height H 2  of each of second rib members  22  provided on lower casing member  3  by a thickness of insulation plate  6 , e.g., H 1 &lt;H 2 . 
         [0049]    An upper end  21   a  of each first rib member  21  may pass an outside of a peripheral edge of lower layer circuit board  5  and cutout spaces  5   f  in the peripheral edge to contact a bottom surface of the peripheral edge of insulation plate  6 . 
         [0050]    An upper end  22   a  of each second rib member  21  may pass the peripheral edge of lower layer circuit board  5  and cutout spaces  5   f  in the peripheral edge to contact bottom surface  7   y  of upper layer circuit board  7  on which no electronic component is mounted. 
         [0051]    As shown in  FIGS. 4A and 4B , reinforcing ribs  23 , each having a height lower than that of each first rib member  21 , may be provided between first rib member  21  and second rib member  22  in order to reinforce peripheral wall  3   b  of lower casing member  3 . Upper ends of reinforcing ribs  23  do not contact the bottom surface of lower layer circuit board  5 . 
         [0052]    Boss  20  may penetrate a through-hole  5   k  ( FIG. 9 ) in lower layer circuit board  5  and contacts with the bottom surface of insulation plate  6 . A height of boss  20  may have substantially the same height of each first rib member  21 . 
         [0053]    Furthermore, lower layer circuit boar  5  and insulation plate  6  may be provided substantially on central parts with screw apertures  5   n  and  6   n  that are aligned with each other upon assembling. A second screw  40  is screwed into the aligned screw apertures  5   n  and  6   n.    
         [0054]    Insulation plate  6  and upper layer circuit boar  7  may also be provided with three screw apertures  6   m  and  7   m  that are aligned with one another upon assembling them. As shown in  FIG. 8C  in greater detail, each screw aperture  6   m  in insulation plate  6  may be provided with an upper opening  6   m - 1 , a lower opening  6   m - 2 , and an intermediate opening  6   m - 3  in a thickness direction of the insulation plate  6 . Intermediate opening  6   m - 3  may be provided between the upper and lower openings  6   m - 1  and  6   m - 2  and may have a smaller opening area than that of each of the openings  6   m - 1  and  6   m - 2 . Each screw aperture  6   m  may include a space S 1  for receiving a head of a first screw mentioned after and a space S 2  for receiving a distal end of a screw cylinder  43 . 
         [0055]    As shown in  FIGS. 8A to 8C , the respective screw apertures  6   m  and  7   m  may be provided in portions corresponding to the three screw cylinders  43  projecting from the inner surface of the upper wall  2   a  of the upper casing member  2 . Screw apertures  6   m ,  7   m , and screw cylinders  43  may be aligned on the same line and each of the first screws  44  may be screwed into each of the screw apertures  6   m . Thus, because the head of each first screw  44  is contained in each space S 1  without exposing the head outward, and because the distal end of each screw cylinder  43  is contained in each space S 2 , the upper casing member  2 , upper layer circuit board  7 , and insulation plate  6  are securely fastened to one another. 
         [0056]    Three screw cylinders  43  may be provided substantially on the central part of upper wall  2   a  of upper casing member  2  and on opposite sides of at least one edge of peripheral wall  2   b . An area enclosed by a triangle defined by the three screw cylinders  43  may be disposed on a back side of the fuse-containing section  12 , relay-containing section  13 , and connector-containing section  14  on the upper casing member  2 . Also, boss  20  projecting from bottom wall  3   a  of lower casing member  3  may be disposed in the area enclosed by the triangle. Thus, it is possible for the three screw cylinders  43  and boss  20  to moderate a stress caused when electrical components (not shown) are coupled to fuse-containing section  12 , relay-containing section  13 , and connector-containing section  14 . Consequently, it is possible to prevent stress from affecting the electronic mounting section  35  (e.g., that may result in detachment of the electronic component), in particular, on lower layer circuit board  5 . 
         [0057]    Insulation plate  8  which may be interposed between upper circuit board  7  and upper casing member  2  may also be provided on positions corresponding to the screw cylinders  43  with screw apertures  8   m.    
         [0058]    In addition, a positioning boss  46  may project substantially from a central part of the upper wall  2   a  of upper casing member  2  while a position-adjusting boss  47  may project from a corner of the upper wall  2   a . On the other hand, insulation plate  8 , upper layer circuit board  7 , insulation plate  6 , and lower layer circuit board  5  may be provided in positions corresponding to boss  46  with circular apertures  8   h ,  7   h ,  6   h , and  5   h  and in positions corresponding to boss  47  with elongated apertures  8   i ,  7   i ,  6   i , and  5   i.    
         [0059]    Next, an example embodiment of a method for assembling electrical junction box  1  in accordance with the present invention will be described. 
         [0060]      FIG. 9  schematically shows a method of assembling electrical junction box  1 . When assembling electrical junction box  1 , upper casing member  2  may be turned upside down so that upper wall  2   a  becomes a bottom side. Turned upper casing member  2  may be held on an assembling jig  50 . 
         [0061]    Attaching piece  9   a , previously bent from each bus bar  9 , may be pressed into and held in the inner surface of upper wall  2   a  of upper casing member  2  to secure bus bar  9  to upper casing member  2 . However, bus bar  9  may be secured to upper casing member  2  with member  2  being held on assembling jig  50 . 
         [0062]    Insulation plate  8  may be inserted into upper casing member  2  held on assembling jig  50  described above. Then, boss  46  may pass through circular aperture  8   h , boss  47  may pass through elongated aperture  8   i , and screw cylinder  43  may pass through screw aperture  8   m.    
         [0063]    After insulation plate  8  is attached to upper casing member  2 , upper layer circuit board  7  may be attached to upper casing member  7 . Then, boss  46  and boss  47 , and each screw cylinder  43  may be inserted into circular aperture  7   h , elongated aperture  7   i , and screw aperture  7   m  in upper layer circuit board  7 , respectively. 
         [0064]    Next, insulation plate  6  may be attached to upper casing member  2 , and boss  46 , boss  47 , and each screw cylinder  43  may be inserted into spaces S 2  in circular aperture  6   h , elongated aperture  6   i , and screw aperture  6   m , respectively, in insulation plate  6 . 
         [0065]    Under this condition, each first screw  44  may be screwed into each screw cylinder  43 . In this manner, as shown in  FIG. 2  and  FIG. 10 , insulation plate  6 , upper layer circuit board  7 , and insulation plate  8  may be secured to the upper casing member  2 . 
         [0066]    Next, lower layer circuit board  5  may be attached to upper casing member  2 , and boss  46  and boss  47  may pass through circular aperture  5   h  and elongated aperture  5   i , respectively. Each screw aperture  5   n  in lower layer circuit board  5  may be aligned with each screw aperture  6   n  in insulation plate  6  to be communicated with each other. Each second screw  40  may be screwed into each of screw aperture  5   n  and screw aperture  6   n . In this manner, as shown in  FIG. 2  and  FIG. 10 , lower layer circuit board  5  may be secured to insulation plate  6 . Because insulation plate  6  together with upper layer circuit board  7  are secured to upper casing member  2  by first screws  44 , after lower layer circuit board  5  is mounted on insulation plate  6 , lower layer circuit board  5  can be secured to insulation plate  6  by a single step of fastening second screws  40 . 
         [0067]    Finally, lower casing member  3  may be turned upside down, so that bottom wall  3   a  becomes an upper surface, and mounted onto upper casing member  2 . When assembling, boss  20  projecting from bottom wall  3   a  of lower casing member  3  may penetrate a through-hole  5   k  in lower layer circuit board  5  so that a distal end of boss  20  contacts the bottom surface of insulation plate  6 , thereby positioning and holding insulation plate  6 . 
         [0068]    First rib members  21  may be inserted into cutout spaces  5   f  provided in an outside and an outer peripheral edge of lower layer circuit board  5 , and distal ends of first rib members  21  contact with a bottom surface of a peripheral edge of insulation plate  6 . 
         [0069]    Second rib members  22  may pass through cutout spaces  5   f  provided in an outside and an outer peripheral edge of lower layer circuit board  5  and may further pass the peripheral edge of insulation plate  6 . Distal ends of second rib members  22  may contact a bottom surface of upper layer circuit board  7 , on which no electronic component is mounted. 
         [0070]    Thus, boss  20  and first rib members  21  position and hold insulation plate  6  fixed to lower layer circuit board  5  by second screws  40  and the second rib members position and hold upper layer circuit board  7  fixed to insulation plate  6  by first screws  44 . 
         [0071]    Finally, after lower casing member  3  is aligned with upper casing member  2 , and locking portions  2   c  and locked portions  3   c  are interlocked to one another. Boss  46  and boss  47  projecting from upper casing member  2  may be inserted into screw cylinders  25  on lower casing member  3  and third screws  48  ( FIG. 2 ) may be screwed into boss  46  and boss  47 . Thus, the process for assembling the electrical junction box  1  is completed. 
         [0072]    As described above, when positioning and holding lower layer circuit boards  5  and upper layer circuit board  7 , boss  20 , first rib member  21  and second rib member  22  projecting from the lower casing member  3  do not contact the bottom surface of lower layer circuit board  5 , on which an electronic component may be mounted. The distal ends of the second rib members  22  may contact a peripheral edge of the bottom surface of upper layer circuit board  7 , but no electronic component is mounted on the bottom surface of upper layer circuit board  7 . That is, boss  20 , first rib member  21  and second rib member  22  do not contact with the surface of the multilayered circuit board assembly on which the electronic component is mounted. Thus, no load is applied to upper layer circuit boards  7  and lower layer circuit board  5 . Consequently, no stress is caused on the surface of the multilayered circuit board assembly, on which an electronic component is mounted, thereby eliminating a possibility of detachment of the electronic component. 
         [0073]    The present invention is not limited to the exemplary embodiments described above. 
         [0074]    For example, upper layer circuit board  7  may be previously bonded to the top surface of insulation plate  6  by an adhesive, and lower layer circuit board  5  and insulation plate  6  may be connected by second screws  44  to previously integrate them. Alternatively, lower layer circuit board  5  and upper layer circuit board  7  may be bonded to the top and bottom surfaces of insulation plate  6  by an adhesive. 
         [0075]    Furthermore, insulation plate  6  may be provided with a through-hole that receives boss  20  projecting from lower casing member  3 , a distal end of boss  20  may contact with the bottom surface of upper layer circuit board  7 , on which no electronic component is mounted, so that boss  20  supports upper layer circuit board  7 . 
         [0076]    In addition, because bus bar  9  may be directly secured to the inner surface of upper wall  2   a  of upper casing member  2  in embodiments described above, insulation plate  8  may be disposed in upper casing  2 . However, in embodiments in which the bus bar  9  is not fixed directly on upper casing member  2 , it is not necessary to provide insulation plate  8 . 
         [0077]    Although upper casing member  2  may be turned topside down and upper layer circuit board  7  and lower layer circuit board  5  may be inserted into upper casing member  2  in embodiments described above, lower layer circuit board  5 , insulation plate  6 , upper layer circuit board  7 , and insulation plate  8 , in order, may be inserted into lower casing member  3  and then upper casing member  2  may be mounted on lower casing member  3 . 
         [0078]    The present invention is not limited to the embodiments described above and any embodiments that do not depart the spirit of the present invention fall within the scope of the present invention.