Patent Document

The entire disclosure of Japanese Patent Application No. 2008-006867 filed on Jan. 16, 2008, including specification, claims, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     One aspect of the present invention relates to a casing of an electronic apparatus with improved reliability of joints, and a supporting structure of a circuit board on which electronic components are mounted. 
     2. Description of the Related Art 
     With sophistication, multi-functionalization, etc., of instruments mounted with electronic apparatuses, the number of electrical joints which joins a circuit board and an electronic apparatus becomes an extremely large number. As a result, ensuring of joint reliability is not easy. 
     In electronic apparatuses, there is a tendency that thermal stress resulting from a difference between coefficients of linear expansion of a casing and a circuit board, and stress resulting from external load become large especially around a boss portion. Therefore, when the circuit board is fastened and fixed to the casing via the boss portion, the load of electronic components on the circuit board in a vicinity of the boss portion increases. Especially, more large-sized electronic components are there in the vicinity of a middle of the circuit board. This problem is actualized. Hereinafter, a cause of deterioration of reliability of a joint will be specifically described with reference to  FIG. 13 . A circuit board  13  is fixed to casing boss portions  27 ,  28 , and  29 . When the circuit board  13 , the upper casing  11 , and the lower casing  12  are fixed at the boss portions  27 ,  28 , and  29 , and the stress of the circuit board  13  around the boss portions  27  and  28  by temperature fluctuation and the  29  becomes large due to the difference between the coefficients of linear expansion of the circuit board  13 , and the upper casing  11  or the lower casing  12 . 
     Also, in a case where external load is generated, since deformation of the upper casing  11  and the lower casing  12  is transmitted to the circuit board via the boss portions  27 ,  28 , and  29 , the stress of the circuit board  13  around the boss portions  27  and  28  and the  29  becomes large. In particular, the tendency that the load of electronic components  19  in the vicinity of the boss portion  27  increases is observed in the middle of the circuit board  13 . 
     A method of fastening a shielding plate and a boss portion of a casing is suggested in connection with a circuit board (see JP-A-9-8488 (FIG. 2), for instance). 
     This method is a method of arranging a solder pattern, and jointly fastening the circuit board having a solder portion formed thereon and the shielding plate to the boss portion of the casing while the solder portion is interposed therebetween. 
     In the invention disclosed in JP-A-9-8488, the circuit board is soldered to the casing, and electrical connection is secured. Thus, thermal stress can be reduced. However, the concentration of stress caused around an attaching portion by external load onto an electronic component mounted on the circuit board cannot be reduced. 
     SUMMARY 
     According to one aspect of the invention, there is provided an electronic apparatus having a circuit board supporting structure, the circuit board supporting structure including: a casing including a first body and a second body, the first body having a first boss portion, the second body having a second boss portion; a jig including a cylindrical portion having an inner peripheral wall of the cylindrical portion, and a flange portion formed on an outer periphery, the cylindrical portion configured to slidably receive the first boss portion and the second boss portion in the inner peripheral wall; and a circuit board disposed in the casing, wherein: the first boss portion and the second boss portion are configured to be fastened by a bolt member; the circuit board has a hole and a joining region provided around the hole, the hole configured to allow the cylindrical portion to penetrate therethrough; and the joining region is configured to be soldered to the flange portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiment may be described in detail with reference to the accompanying drawings, in which: 
         FIG. 1  is an exemplary perspective view schematically showing a supporting structure of a circuit board related to a first embodiment of the invention; 
         FIG. 2  is an exemplary schematic sectional view of the supporting structure of the circuit board related to the first embodiment; 
         FIG. 3  is an exemplary perspective view of a jig in the supporting structure; 
         FIG. 4  is an exemplary perspective view schematically showing a supporting structure of a circuit board related to a second embodiment of the invention; 
         FIG. 5  is an exemplary schematic sectional view of the supporting structure of the circuit board related to the second embodiment; 
         FIG. 6  is an exemplary perspective view of a jig in the supporting structure; 
         FIG. 7  is an exemplary schematic sectional view of a supporting structure of a circuit board related to a third embodiment of the invention; 
         FIG. 8  is an exemplary schematic sectional view of the supporting structure of the circuit board related to a fourth embodiment of the invention; 
         FIG. 9  is an exemplary perspective view showing a circuit board, and wirings on the circuit board; 
         FIGS. 10A and 10B  are another exemplary perspective view of a jig in the supporting structure; 
         FIG. 11  is an exemplary schematic sectional view of a supporting structure of a circuit board related to a sixth embodiment of the invention; 
         FIG. 12  is another exemplary perspective view showing a circuit board, and wirings on the circuit board; 
         FIG. 13  is an exemplary schematic sectional view showing a support state of a circuit board in the related electronic apparatus; and 
         FIG. 14  is an exemplary schematic sectional view showing an electronic apparatus related to the first embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the invention will be described with reference to the drawings. In each of the drawings, the same elements are denoted by the same reference numerals, and duplicate description thereof is omitted. 
     First Embodiment 
       FIG. 1  is a perspective view schematically showing a supporting structure of a circuit board related to a first embodiment of the invention.  FIG. 2  is a schematic sectional view of the supporting structure of the circuit board related to the first embodiment.  FIG. 3  is a perspective view of a jig in the supporting structure. Further,  FIG. 14  is an exemplary schematic sectional view showing an electronic apparatus related to the first embodiment. 
     The supporting structure of this circuit board includes an upper casing  11 , a lower casing  12 , and a jig  17 , for housing and holding a circuit board  13  as interposed between the upper casing  11  and the lower casing  12  from the up-down direction. A boss portion  14  is formed in the upper casing  11  toward the circuit board  13 . In this embodiment, the boss portion  14  is formed in a shape recessed from the upper casing  11 . Moreover, a hole is formed in the recessed portion of the boss portion  14 , and a boss screw  16  is inserted through the hole. 
     Similarly, a boss portion  15  is formed in the lower casing  12  toward the circuit board  13 . As shown in  FIG. 2 , the boss portion  14  of the upper casing  11  and the boss portion  15  of the lower casing  12  face each other. In this embodiment, the boss portion  15  is formed in a shape protruding from the lower casing  12 . Moreover, an internal thread into which the boss screw  16  is threadedably inserted from the upper casing  11  is fabricated in the boss portion  15 . In addition, reinforcing ribs  15   a  can be suitably formed at a peripheral wall of the boss portion  15  to increase rigidity. 
     The jig  17  assumes a cylindrical shape, and the boss portions  14  and  15  are slidably inserted into an inside  17   c  of a cylindrical portion  17   a  of the jig  17 . A flange portion  17   b  is formed at an intermediate portion of the cylindrical portion  17   a  of the jig  17 . 
     A hole  13   a  of a larger diameter than the external diameter of the cylindrical portion  17   a  of the jig  17  is formed in the circuit board  13 , and the jig  17  is adapted to pass through the hole  13   a . A solder joint  18  is provided around the hole  13   a  of the circuit board  13 , and the flange portion  17   b  of the jig  17 , and the circuit board  13  are solder-joined, thereby securing electric conduction. Further, an electronic component  19  is mounted on the circuit board  13 . In this embodiment, the jig  17  is mounted by a soldering process similarly to other components. 
     For example, when an electronic apparatus on which the circuit board  13  is mounted is used at an environmental temperature of 0° C. to 40° C., outer peripheries  14   a  and  15   a  of the boss portions  14  and  15 , and the inside  17   c  of the cylindrical portion  17   a  of the jig  17  are slidable in the fastening direction of the boss portions  14  and  15  within a temperature range of the electronic apparatus. 
     In addition, as shown in  FIG. 14 , the circuit board  13  is fixed at both ends thereof.  FIG. 14  shows an electronic apparatus related to the first embodiment. The electronic apparatus has the circuit board supporting structure  10 . 
     Since the supporting structure of the circuit board  13  is configured as described above, the circuit board  13  is not fixed at the boss portions  14  and  15 , but is slidable in the fastening direction of the boss portions  14  and  15 . Therefore, for example, even in a case where the upper casing  11  is pushed, the external load from right above the boss portions  14  and  15  is not applied to the circuit board  13 . Accordingly, since the stress by the external load is not concentrated on the peripheries of the boss portions  14  and  15  in the circuit board  13 , the load to a joint of the electronic component  19  which exists in the vicinity of the boss portions  14  and  15  can be reduced. 
     Even in a case where excessive deformation is caused in the upper casing  11  or the lower casing  12  by the external load from right above the boss portions  14  and  15 , an end  17   d  of the cylindrical portion  17   a  of the jig  17  contacts the upper casing  11  or the lower casing  12 . Therefore, the electronic component  19  mounted on the circuit board  13  can be prevented from contacting the upper casing  11 . 
     Further, the inside  17   c  of the cylindrical portion  17   a  of the jig  17  generally contacts and faces the whole peripheries of outer peripheral surfaces  14   a  and  15   a  of the boss portions  14  and  15  parallel to the fastening direction of the boss portions  14  and  15 . Therefore, the force in the in-plane direction of the circuit board  13 , and the moment around the in-plane axis thereof can be transmitted. Accordingly, with respect to loads other than the load from right above the boss portions  14  and  15 , a load is transmitted to the circuit board  13 , thereby increasing the rigidity of the whole casing. 
     On the other hand, since the jig  17  is fixed to the solder joint  18 , a flexible structure is obtained as compared with other parts. Accordingly, even in a case where temperature fluctuation occurs around or inside an electronic apparatus, since any stress is not concentrated on the peripheries of the boss portions  14  and  15  in the circuit board  13 , the load to a joint of the electronic component  19  which exists in the vicinity of the boss portions  14  and  15  can be reduced. 
     Second Embodiment 
     Next, a second embodiment of the invention will be described.  FIG. 4  is a perspective view schematically showing a supporting structure of a circuit board related to the second embodiment of the invention.  FIG. 5  is a schematic sectional view of the supporting structure of the circuit board related to the second embodiment. Further,  FIG. 6  is a perspective view of a jig  30  in the supporting structure. 
     In this embodiment, configurations other than the jig  30  are the same as those of the first embodiment. As shown in  FIG. 4  and  FIG. 6 , the jig  30  is formed in such a shape that a portion thereof is cut out in a longitudinal direction, unlike the first embodiment. 
     Even if a cylindrical portion  30   a  and the flange portion  30   b  are cut out partially, the same effect as the first embodiment can be exhibited. Further, a sliding surface  30   c  inside the cylindrical portion  30   a  a portion of which is cut out generally contacts and faces portions of the outer peripheral surfaces of the boss portions  14  and  15  parallel to the fastening direction of the boss portions  14  and  15 . Therefore, since the force in the in-plane direction of the circuit board  13 , and the moment around the in-plane axis thereof is transmitted in a direction in which the sliding surface  30   c  face the peripheral surfaces  14   a  and  15   a  of the boss portions, the rigidity of the whole casing is increased. On the other hand, the force in the in-plane direction of the circuit board  13 , and the moment around the in-plane axis thereof is transmitted in a direction in which the sliding surface  30   c  does not face the peripheral surfaces  14   a  and  15   a  of the boss portions  14  and  15 . Therefore, when the jig  30  is arranged such that the direction in which the electronic component  19  is mounted become the direction in the direction in which the sliding surface does not face the peripheral surfaces  14   a  and  15   a  of the boss portions, the load to a joint of the electronic component  19  can be reduced even against loads other than the load from right above the boss portions  14  and  15 . 
     Third Embodiment 
     Next, a third embodiment of the invention will be described.  FIG. 7  is a schematic sectional view of a supporting structure of a circuit board related to the third embodiment of the invention. 
     The supporting structure of this circuit board generally includes an upper casing  11 , a lower casing  12 , and a jig  31 , for housing and holding the circuit board  13  as interposed between the upper casing  11  and the lower casing  12  from the up-down direction. A boss portion  14  is formed in the upper casing  11  toward the circuit board  13 . In this embodiment, the boss portion  14  is formed in a shape recessed from the upper casing  11 . Moreover, a hole is formed in the recessed portion of the boss portion  14 , and a boss screw  16  is inserted through the hole. 
     Similarly, a boss portion  15  is formed on the lower casing  12  so as to protrude toward the circuit board  13 . As shown in  FIG. 7 , the boss portion  14  of the upper casing  11  and the boss portion  15  of the lower casing  12  face each other. Moreover, an internal thread into which the boss screw  16  is threadedably inserted from the upper casing  11  is fabricated in the boss portion  15 . 
     The jig  31  assumes a cylindrical shape, and the boss screw  16  is slidably inserted into an inside  31   c  of a cylindrical portion  31   a  of the jig  31 . A flange portion  31   b  is formed at an intermediate portion of the jig  31 . 
     A hole  13   a  of a larger diameter than the external diameter of the cylindrical portion  31   a  of the jig  31  is formed in the circuit board  13 , and the jig  31  is adapted to pass through the hole  13   a . A solder joint  18  is provided around the hole  13   a  of the circuit board  13 , and the flange portion  31   b  of the jig  31 , and the circuit board  13  are solder-joined, thereby securing electric conduction. Further, an electronic component  19  is mounted on the circuit board  13 . 
     Since the supporting structure of the circuit board  13  is configured as described above, the circuit board  13  is not fixed at the boss screw  16 , but the boss screw  16  and the jig  31  are slidable. Therefore, for example, even in a case where the upper casing  11  is pushed, the external load from right above the boss portions  14  and  15  is not applied to the circuit board  13 . Accordingly, since the stress by the external load is not concentrated on the peripheries of the boss portions  14  and  15  in the circuit board  13 , the load to a joint of the electronic component  19  which exists in the vicinity of the boss portions  14  and  15  can be reduced. 
     Even in a case where excessive deformation is caused in the upper casing  11  or the lower casing  12  by the external load from right above the boss portions  14  and  15 , an end  31   d  of the cylindrical portion  31   a  of the jig  31  contacts THE boss portion  14  or THE boss portion  15 . Therefore, the electronic component  19  mounted on the circuit board  13  can be prevented from contacting the upper casing  11 . 
     Further, the inside  31   c  of the cylindrical portion  31   a  of the jig  31  generally contacts and faces the whole periphery of an outer peripheral surface of the boss portion  16 . Therefore, the force in the in-plane direction of the circuit board  13 , and the moment around the in-plane axis thereof can be transmitted. Accordingly, with respect to loads other than the load from right above the boss portions  14  and  15 , a load is transmitted to the circuit board  13 , thereby increasing the rigidity of the whole casing. 
     On the other hand, since the jig  31  is fixed to the solder joint  18 , a flexible structure is obtained as compared with other parts. Accordingly, even in a case where temperature fluctuation occurs around or inside an electronic apparatus, since any stress is not concentrated on the peripheries of the boss portions  14  and  15  in the circuit board  13 , the load to a joint of the electronic component  19  which exists in the vicinity of the boss portions  14  and  15  can be reduced. 
     Fourth Embodiment 
     Next, a fourth embodiment of the invention will be described.  FIG. 8  is a schematic sectional view of a supporting structure of a circuit board related to the fourth embodiment.  FIG. 9  is a perspective view showing a circuit board, and wirings on the circuit board. In this embodiment, a solder joint includes a first solder joint  22  and a second solder joint  23 . The first solder joint  22  and the second solder joint  23  are respectively connected to wirings  20  and  21  formed on the circuit board  13 . Although this embodiment differs from the first embodiment in this regard, other configurations are the same as those of the first embodiment. Accordingly, the same effects as those described in the first embodiment can be achieved. 
     For example, metallic conductors, such as aluminum, are suitable for the jig  17 . As shown in  FIG. 9 , the wiring  20 , the first solder joint  22 , the jig  37 , the second solder joint  23 , and the wiring  21  are electrically connected in this order on the circuit board  13 , and a circuit network which measures the electric resistance value of this connection path is provided. In addition, it is needless to say that a voltage value or a current value can be measured if necessary. 
     Normally, the relative displacement of the upper casing  11  or the lower casing  12 , and the circuit board  13  resulting from the difference between the coefficients of linear expansion thereof is larger compared with the relative displacement of a semiconductor package  24  and the circuit board  13  resulting from the difference between the coefficients of linear expansion thereof. Accordingly, the distortion caused at the boss portions  14  and  15  at which the upper casing  11  and the lower casing  12  are joined to the circuit board  13  is larger than the distortion caused at the joint of the semiconductor package  24  and the circuit board  13 . Since the value obtained by dividing the relative displacement by the height of the joint is an average distortion, in a case where the height of the first solder joint  22  and the second solder joint  23  is equal to or slightly greater than the joint of the semiconductor package  24 , a fatigue life slightly shorter than that of the semiconductor package  24  can be set. 
     Specifically, design can be made as follows. 
     Generally, for example, resin materials, such as ABS resin, or magnesium alloys, are used as the material for the upper casing  11  or the lower casing  12 . The coefficient of linear expansion of the resin casing is 80 ppm/° C., and the coefficient of linear expansion of the magnesium casing is about 26 ppm/° C. For example, in a case where the upper casing  11  and the lower casing  12  are made of resin, the coefficient of linear expansion thereof is about 80 ppm/° C. Further, when the coefficient of linear expansion of the circuit board  13  is set to about 15 ppm/° C., the coefficient of linear expansion of the semiconductor package  24  is set to about 13 ppm/° C., the temperature range of fluctuation inside a casing is set to 20° C., the distance between the boss portions in a plane is set to 150 mm, and the size of an electronic component is set to 35 mm×35 mm, the expansion difference between the upper casing  11  or the lower casing  12 , and the circuit board  13  becomes about 0.2 mm, the expansion difference between the semiconductor package  24  and the circuit board  13  is set to about 0.002 mm. 
     As such, it is provided that the relative displacement of the upper casing  11  or the lower casing  12 , and the circuit board  13  resulting from the difference between the coefficients of linear expansion thereof is larger compared with the relative displacement of the semiconductor package  24  and the circuit board  13  resulting from the difference between the coefficients of linear expansion thereof. 
     Accordingly, before the joint of the semiconductor package  24  is ruptured, the first solder joint  22  or the second solder joint  23  is ruptured and an electric resistance value rises. As a result, it can be detected in advance that rupture of the joint of the semiconductor package  24  on the circuit board  13  is approaching. 
     Fifth Embodiment 
     Next, a fifth embodiment of the invention will be described.  FIG. 10A  is a perspective view of a jig in the supporting structure, and  FIG. 10B  is a perspective view of a portion of the jig. 
     In this embodiment, the jig  17  is configured of a resinous portion  25 , and a portion  26  made of, for example, metal, such as aluminum. The other configurations are the same as those of the above-described fourth embodiment. Accordingly, the same effects as those described in the fourth embodiment can be achieved. 
     The resinous portion  25  of the jig  17  is outsert-molded so as to be attached and fixed to the metallic portion  26 . Similarly to that shown in  FIG. 9 , the wiring  20 , the first solder joint  22 , the metallic portion  26  of the jig  17 , the second solder joint  23 , and the wiring  21  are electrically connected in this order on the circuit board  13 , and forms a circuit network which measures the electric resistance value of this connection path. In addition, it is needless to say that a voltage value or a current value can be measured. 
     According to this embodiment, since most of the jig  17  is the resinous portion  25 , light-weight and easy molding can be achieved. 
     Sixth Embodiment 
     Next, a sixth embodiment of the invention will be described.  FIG. 11  is a schematic sectional view of a supporting structure of a circuit board related to the sixth embodiment.  FIG. 12  is a perspective view showing a circuit board, and wirings on the circuit board. 
     As shown in  FIG. 11 , the jig  32  has a taper  32   a , and a boss portion  33  of the lower casing also has a taper such that its diameter becomes smaller toward the boss portion  14  of the upper casing. In this embodiment, the shapes of the jig  32  and the boss portion  33  of the lower casing differ from those of the above-described fourth embodiment. The other configurations are the same as those of the fourth embodiment. Accordingly, the same effects as those described in the fourth embodiment can be achieved. 
     When the relative displacement of the upper casing  11  or the lower casing  12  and the circuit board  13  resulting from the difference between the coefficients of linear expansion thereof is caused by temperature fluctuation, the jig  32  contacts the boss portion  33  of the lower casing, and the force in the direction in which the flange portion  32   b  of the jig  32  is separated from the circuit board  13  act on the jig  32  by the taper. Therefore, the force in the direction of tension acts on the first solder joint  22  or the second solder joint  23 . Even if the first solder joint  22  or the second solder joint  23  is ruptured, since electrical connection is made when the ruptured surfaces partially contact each other, an electric resistance value may not change. However, in this embodiment, the force in the direction of tension acts on the first solder joint  22  or the second solder joint  23 . Therefore, even if the first solder joint  22  or the second solder joint  23  is ruptured, the phenomenon that an electric resistance value does not change can be prevented. 
     It is to be understood that the present invention is not limited to the specific embodiments described above and that the present invention can be embodied with the components modified without departing from the spirit and scope of the present invention. The present invention can be embodied in various forms according to appropriate combinations of the components disclosed in the embodiments described above. For example, some components maybe deleted from the configurations as described as the embodiments. Further, the components in different embodiments may be used appropriately in combination.

Technology Category: 5