Abstract:
An electronic device includes: a circuit board having a convex-curved component and a housing having a support member with a concave-curved end and receiving the convex-curved component of the circuit board. The convex-curved component is freely turnable in the concave-curved end. Thereby, a simple structure prevents moments from being transmitted to the circuit board from a housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Application No. 2005-060839 filed on Mar. 4, 2005, the entire contents of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic device and convex member for a circuit board, and more particularly to an electronic device and convex member holding up a circuit board in a housing. 
     2. Description of the Related Art 
     At present, laptops (i.e., portable microcomputers) are designed to be compact, light in weight and easy to carry. Such a portable microcomputer (called the “microcomputer”) may be dropped while it is carried by a user. When dropped, a housing of the microcomputer may be deformed and undergo dropping impacts or external static loads. 
     It is assumed that a circuit board is fixedly mounted in the housing. If moments caused by the deforming housing are transmitted to the circuit board, the circuit board will be gradually warped. In such a case, interconnections on the circuit board and joints between the circuit board and semiconductor chips will be broken or damaged. 
     Especially, when the circuit board is made of materials having low rigidity in order to meet weight and thickness saving requirements, there is a large difference between the rigidity of the circuit board and that of elements mounted thereon. Therefore, the mounted elements will become defective when the circuit board is deformed. 
     In order to overcome the foregoing problem, a resin material is inserted between the circuit board and elements mounted thereon, thereby locally enhancing joints of the circuit board and elements. This measure is called the under-filling method. Refer to the Japanese patent No. 3,348,973. 
     However, it is very difficult in the foregoing method to exchange elements mounted on the circuit board. Further, the circuit board itself has to be exchanged when mounted elements are found to be defective. Therefore, the method is considered to be insufficient as a countermeasure. 
     Further, it has been proposed to support a circuit board using springs. In this case, cylindrical supports are fitted in openings on the circuit board. Each cylindrical support has one end thereof fixed to a housing, and has a flange on a side surface thereof. The circuit board is supported by springs inserted in the flanges of the cylindrical supports. This structure protects the circuit board against moments caused by the deformation of the housing. 
     However, the circuit board tends to be displaced in a direction which is vertical to the plane where elements are mounted. Especially, some connectors are directly mounted on the circuit board and extend outward via an open area of the housing. Further, the connectors have to be fixed to the housing in order that cables or the like are reliably attached to and detached from the connectors. In such a case, the connectors are a little bit displaced while the circuit board tends to be extensively displaced. Since the connectors and the circuit board are displaced in different amounts, joints between the connectors and the circuit board undergo an excessive deformation. Poor connections will be caused at the joints where the connectors and the circuit board are connected. 
     SUMMARY OF THE INVENTION 
     The present invention has been contemplated to overcome the foregoing problems of the related art and provides a microcomputer, a circuit board and convex members holding elements on the circuit board, all of which have simple structures and prevent moments from being transmitted to the circuit board from a housing. 
     According to a first aspect of the embodiment of the invention, there is provided an electronic device including: a circuit board including support structures which have convex-curved components; and a housing including support structures which have support members having concave-curved ends and receive the convex-curved components of the support structure of the circuit board. 
     In accordance with a second aspect, there is provided a circuit board including an element mounting surface and support structures provided on both surfaces of the element mounting surface and having convex-curved components. 
     In accordance with a third aspect, there is provided a convex member including first parts attached on one surface of a circuit board, and second parts received in concavities on a support member of the circuit board housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a microcomputer according to a first embodiment of the invention; 
         FIG. 2  is a perspective view of the microcomputer which is closed while it is carried; 
         FIG. 3  is a cross section of support structures for a circuit board in the microcomputer; 
         FIG. 4  is a cross section of the support structures of  FIG. 3 ; 
         FIG. 5  is a perspective view of the support structures of  FIG. 3 ; 
         FIG. 6A  is a cross section of the circuit board when a housing of the microcomputer is deformed by moments applied in opposite directions; 
         FIG. 6B  is a cross section of the circuit board when the housing is deformed by moments applied in the same direction; 
         FIG. 7  is a cross section of the support structures of  FIG. 5 , which are fixedly attached to the circuit board; 
         FIG. 8  is a cross section of support structures for the circuit board in a second embodiment of the invention; 
         FIG. 9  is a cross section of support structures for the circuit board in a third embodiment of the invention; 
         FIG. 10  is a cross section of support structures fixedly attached to the circuit board in a fourth embodiment of the invention; 
         FIG. 11  is a cross section of support structures for the circuit board in a modified example of the fourth embodiment; 
         FIG. 12  is a cross section of support structures fixedly attached to the circuit board in a fifth embodiment of the invention; 
         FIG. 13  is a cross section of support structures fixedly attached to the circuit board in a modified example of the fifth embodiment; 
         FIG. 14  is a cross section of support structures fixedly attached to the circuit board in a sixth embodiment; 
         FIG. 15  is a cross section of support structures in a modified example of the sixth embodiment; 
         FIG. 16A  and  FIG. 16B  are cross sections of the support structures showing how the circuit board is attached in a further embodiment; and 
         FIG. 17A  and  FIG. 17B  are cross sections of the support structures showing how the circuit board is attached in a still further embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that the same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified. 
     First Embodiment 
     Referring to  FIG. 1 , a microcomputer  10  includes a main body  12  installed in a lower housing  15 , and a display unit  13  installed in an upper housing  17 . The main body  12  includes a keyboard  11 , a central processing unit (CPU), a circuit board  21  with a memory and so on mounted thereon, and a hard disk drive (HDD). The CPU, circuit board  21  and hard disk drive HDD are installed in the lower housing  15 . The display unit  13  is provided in the upper housing  17 , and includes a liquid crystal display panel  16 . 
     The upper and lower housings  17  and  15  are hinged, which enables the upper housing  17  to be opened and closed with respect to the lower housing  15 . When the upper housing  17  is opened, the keyboard  11  and the display unit  13  are oriented as shown in  FIG. 1 . On the other hand, the keyboard  11  and the display panel  16  face with each other when the upper and lower housings  17  and  15  are closed as shown in  FIG. 2 . 
       FIG. 3  shows that the circuit board  21  has its front and rear surfaces backed up by a support structure of the lower housing  15 . The support structure of the lower housing  15  includes support shafts (support members)  24  and  25  having concave-curved ends, and upper and lower plates  22  and  23 . The circuit board  21  has a support structure constituted by convex-curved components  26  and  27 , which are received in the concave-curved ends of the support shafts  24  and  25 . The convex-curved components  26  and  27  are opposite to each other on the front and rear surfaces of the circuit board  21 . In other words, the upper and lower plates  22  and  23  constitute the lower housing  15  where the circuit board  21  is mounted. As shown in  FIG. 4 , the concave-curved ends of the support shafts  24  and  25  have a curvature radius R which is equal to that of the convex-curved components  26  and  27  of the support structure of the circuit board  21 . 
     The convex-curved components  26  and  27  and the concave-curved ends of the support shafts  24  and  25  are in the shape of a sphere which is concentric to the thickness center of the circuit board  21 .  FIG. 5  shows that the convex-curved components  26  and  27  are in slidable contact with the concave-curved ends of the support shafts  24  and  25 . In short, the support shafts  24  and  25  are slidable in a desired direction with the central focus on the convex-curved components  26  and  27 . 
     When external forces are applied to the microcomputer, the upper and lower plates  22  and  23  will be deformed in the lower housing  15 , and make the support shafts  24  and  25  tilted. In such a case, the support shafts  24  and  25  slide on the convex-curved components  26  and  27 , which prevents moments from being transmitted to the circuit board  21 . For example, if reverse moments are applied as shown in  FIG. 6A , the support shafts  24  and  25  slide via their concave-curved ends on the convex-curved components  26  and  27 . This effectively prevents the moments from being transmitted to the circuit board  21 . On the other hand, when moments are applied in the same direction as shown in  FIG. 6B , the support shafts  24  and  25  slide via their concave-curved ends on the convex-curved components  26  and  27 . This also effectively prevents the moments from being transmitted to the circuit board  21 . 
       FIG. 7  shows that a support structure of the circuit board  21  includes convex-curved components  26   b  and  27   b  which are independent from the circuit board  21 . The support structure is bonded to the circuit board  21  using adhesives  39  and  40 . Alternatively, the support structure may be attached using an adhesive tape, or may be soldered. In the latter case, the circuit board  21  is heated in a furnace with elements mounted thereon, and the support structure having the convex-curved components  26   b  and  27   b  is attached thereon in a reflow process. 
     In the first embodiment, the simplified structure can protect the circuit board  12  against the moments caused by the deformed lower housing  15 . Therefore, it is possible to protect wirings on the circuit board  21  against breaking, and against poor joints between semiconductor chips and the circuit board  21 . 
     Second Embodiment 
     In a second embodiment, convex-curved components  26  and  27  of the circuit board  21  have a curvature radius which is smaller than that of the concave-curved ends of the support shafts  24  and  25 . 
     Specifically, as shown in  FIG. 8 , the curvature radius of the convex-curved components  26  and  27  is smaller than that of concave-curved ends  30   b  and  31   b  of the support shafts  24  and  25 . The convex-curved components  26  and  27  are freely turnable in the concave-curved ends of the support shafts  24  and  25  in a direction along the plane of the circuit board  21 . Even if the circuit board  21  laterally expands or is constricted due to temperature variations and the convex-curved components  26  and  27  are moved along the circuit board  21 , no loads will be applied to the circuit board  21  or the support shafts  24  and  25 . 
     Therefore, the shafts  24  and  25  prevent the circuit board  21  from being deformed by loads. 
     In addition to the advantage of the first embodiment, the second embodiment can protect the circuit board  21  against thermal strains. 
     Third Embodiment 
     In a third embodiment, support shafts  24  and  25  are partly hollow as shown in  FIG. 9 . Ring-shaped peripheries  30   c  and  31   c  of the support shafts  24  and  25  are beveled by a curvature radius which is equal to that of convex-curved components  26  and  27  of the circuit board  21 . 
     It is possible to reduce the volume of the support shafts  24  and  24 , which makes the microcomputer light in weight as a whole. 
     Alternatively, the convex-curved components  26  and  27  may be supported by support shafts  24  and  25  of which peripheral edges are partially cut. 
     Fourth Embodiment 
     In this embodiment, the circuit board  21  is fastened to the support structure of the lower housing  15  using a cylindrical screw  32 . Referring to  FIG. 10 , the support shaft  24  has an opening which receives the screw  32 . A through-hole  33  extends through convex-curved components  26  and  27  and a circuit board  21 . The through-hole  33  is larger than the screw  32 . The screw  32  is inserted into the circuit board  21  through a support shaft  25  and the through-hole  33 , so that the support shafts  24  and  25  are connected. 
     The inner diameter of the through-hole  33  is larger than the diameter of the screw  32 , so that the screw  32  fixed in the support shafts  24  and  25  is rotatable through the circuit board  21 . The support shafts  24  and  25  are turnably connected to each other via the convex-curved components  26  and  27 . The support shafts  24  and  25  also function as a joint connecting the upper and lower plates  22  and  23 . 
     The support shafts  24  and  25  support not only the convex-curved components  26  and  27  of the circuit board  21  but also connect the upper and lower plates  22  and  23 . This is effective in reliably preventing the support shafts  24  and  25  from being disengaged from the convex-curved components  26  and  27  even when an external force is applied to the microcomputer. 
     In addition to the advantage of the first embodiment, the fourth embodiment can prevent the support shafts  24  and  25  from being disengaged from the convex-curved components  26  and  27  of the circuit board  21 . 
     If the support shafts  24  and  25  are too thin to make an opening for the screw  32 , as shown in  FIG. 11 , fastening parts  34  and  35  may be provided near the support shafts  24  and  25  in order to join the upper and lower plates  22  and  23  using a screw  36 . 
     Fifth Embodiment 
     In this embodiment, the convex-curved components  26  and  27  are movable along the circuit board  21 . Referring to  FIG. 12 , the circuit board  21  has a through-hole  37  along its thickness, into which a projection  38  of a convex-curved component  27   e  is fitted. The projection  38  is fixed to a convex-curved component  26 e, using an adhesive  41 , or an adhesive tape or the like as shown in  FIG. 13 . 
     An inner diameter of the through-hole  37  of the circuit board  21  is larger than an outer diameter of the projection  38  of the convex-curved component  27 , so that there is a gap between the through-hole  37  and the projection  38 . This structure enables the projection  38  to be movable in the through-hole  37  at maximum in a direction where the circuit board  21  extends. 
     The convex-curved components  26  and  27  are movable along the circuit board  21 . For instance, when there is a difference between a thermal expansion coefficient of the upper and lower plates  22  and  23  and a thermal expansion coefficient of the circuit board  21 , the convex-curved components  26  and  27  can absorb a lateral expansion or constriction of the circuit board  21  due to temperature variations. 
     The foregoing structure can protect wirings on the circuit board  21  against breaking, and prevent poor connections between the circuit board  21  and elements mounted thereon. 
     In addition to the advantage of the first embodiment, the fifth embodiment can prevent the circuit board  21  from being deformed due to thermal strains. 
     Sixth Embodiment 
     According to this embodiment, the circuit board  21  has a support structure constituted by a pair of semi-cylindrical ribs  26   a  and  27   a  in place of the convex-curved components  26  and  27 . As shown in  FIG. 14 , the semi-cylindrical ribs  26   a  and  27   a  are attached to the circuit board  21  using an adhesive or the like. Support walls  24   a  and  25   a  are provided on the upper and lower plates  22  and  23 , and have concave-curved ends thereof. The concave-curved ends have a curvature radius equal to that of the semi-cylindrical ribs  26   a  and  27   a.    
     If only uniaxial moments are transmitted to the circuit board  21 , an amount of rotational freedom of the walls  24   a  and  25   a  may be equal to an amount of freedom of the moments. Therefore, the walls  24   a  and  25   a  can reliably support the circuit board  21  via the semi-cylindrical ribs  26   a  and  27   a.    
     The walls  24   a  and  25   a  extend along the semi-cylindrical ribs  26   a  and  27   a,  can make the upper and lower plates  22  and  23  more rigid, and increase contact areas with the semi-cylindrical ribs  26   a  and  27   a.  This structure is effective in preventing the circuit board  21  from warping due to its own weight. 
     In the sixth embodiment, the support walls  24   a  and  25   a  have the uniaxial rotational freedom and extend in the direction of the rotary shaft, and support the semi-cylindrical ribs  26   a  and  27   a , which enables the circuit board  21  to be free from moments caused by the deformed housing, and from warping by its own weight. 
     Other Embodiments 
     In the foregoing embodiments, the convex-curved components  26  and  27  are provided on both surfaces of the circuit board  21 . Alternatively, a ball  42  may be fitted into a through-hole in the circuit board  21  as shown in  FIG. 15 . The ball  42  has a flange  43  which is fixed to the circuit board  21  using an adhesive  44  or an adhesive tape. Further, the flange  43  may be soldered. In this case, the balls  42  function as the convex-curved components  26  and  27 . 
     The use of the ball  42  as the support structure is effective in reducing the number of components. Further, the ball  42  may be swaged or screwed to the circuit board  21 . 
       FIG. 16A  shows that a pair of hemispherical components  56  and  57  are attached to the circuit board  21 . Specifically, the hemispherical component  56  has a cylindrical projection  56   a  on the bottom thereof, and a cylindrical part  56   b.  The cylindrical projection  56   a  has a tapered end. The curved component  57  has, on its bottom, a cylindrical part  57   a  and a cylindrical part  57   b  surrounding the cylindrical part  57   a.    
     The circuit board  21  has a through-hole  52  which is slightly thicker than the cylindrical part  57   b.  Via the through-hole  52 , the cylindrical projection  56   a  is fitted in the cylindrical part  57   a , and the cylindrical part  56   b  is engaged with the cylindrical part  57   b.    
     The hemispherical components  56  and  57  are swaged, and fixedly and reliably attached to the circuit board  21  as shown in  FIG. 16B . 
     In this case, an outer diameter of the cylindrical part  57   b  is smaller than the diameter of the through-hole  52 , so that a gap  58  is formed between the cylindrical part  57   b  and the through-hole  52 . Therefore, the hemispherical components  56  and  57  are movable along the circuit board  21 , which prevents the circuit board  21  from being deformed due to thermal strains. 
     Alternatively, the hemispherical components  66  and  67  may be screwed to the circuit board  21  as shown in  FIGS. 17A and 17B . Referring to  FIG. 17A , the hemispherical component  66  has a threaded projection  66   a  at the bottom thereof while the hemispherical component  67  has a cylindrical projection  67   b  which has a threaded hole  67   a.    
     The circuit board  21  has a through-hole  68 , via which the threaded projection  66   a  is engaged in the threaded hole  67   a.    
     The hemispherical components  66  and  67  are reliably fixed to the circuit board  21  similarly to the convex-curved components  56  and  57  shown in  FIG. 16B . 
     When an outer diameter of the projection  67   b  is smaller than an inner diameter of the through-hole  68  of the circuit board  21 , the hemispherical components  66  and  67  are movable along the circuit board  21 . This is effective in preventing the circuit board  21  from being deformed due to thermal strains. 
     The present invention is applicable to portable walkie-talkies and various electronic devices as well as the portable microcomputer  10 .