Abstract:
An electric device includes: first and second electric elements, wherein electric power consumption and operation temperature limit of the first electric element is larger than the second electric element; a substrate made of a rigid flexible board; and a casing that accommodates the substrate with the first and second electric elements. The substrate includes first and second rigid portions and a flexible portion. The first and second electric elements are disposed on the first and second rigid portion, respectively. The flexible portion connects the first and second rigid portions. The thickness of the flexible portion is smaller than the first and second rigid portions. The flexible portion further includes a wiring for electrically coupling the first and second electric elements so that high speed communication is performed between the first and second electric elements.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on Japanese Patent Application No. 2007-43853 filed on Feb. 23, 2007, the disclosure of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to an electric device having first and second electric elements. 
   BACKGROUND OF THE INVENTION 
   Dimensions of a printed circuit board can be reduced by using an element built-in technique and a multi-layered technique. Further, the size of the entire electric device also can be reduced. 
   As shown in  FIG. 6 , when a printed circuit board  1  includes a large heat generation electric element  2 , which consumes a large amount of electricity and generates a large amount of heat, if the dimensions of the printed circuit board  1  are minimized, the operation specifications of a small heat generation electric element  3 ,  4 ,  5  may be not satisfied. Here, the small heat generation electric element  3 ,  4 ,  5  consumes a small amount of electricity and has a low proper operation temperature limit. The large heat generation electric element  2  consumes a large amount of electricity and has a high proper operation temperature limit. The heat generated in the large heat generation electric element  2  affects the small heat generation electric element  3 ,  4 ,  5  by heat conduction of the printed circuit board  1 . Therefore, the temperature may exceed the low proper operation temperature limit of the small heat generation electric element  3 ,  4 ,  5 . 
   In view of the above difficulty, it is necessary to have a large heat radiation fin for radiating heat from the large heat generation electric element  2 . Thus, the dimensions of the device increase. Further, as shown in  FIG. 7 , when a cooling fan  7  is formed on a casing  6 , it is necessary to increase air blow volume of the fan  7 . In this case, noise from the fan  7  may cause difficulty. The fan may generate an operation noise. Further, when the small heat generation electric element  3 ,  4 ,  5  is disposed on a downstream side of the large heat generation electric element  2 , heat convection from the large heat generation electric element  2  and/or heat radiation from the large heat generation electric element  2  may affect the small heat generation electric element  3 ,  4 ,  5 . 
   Thus, the printed circuit board  1  may be divided into two independent boards, so that the large heat generation electric element  2  is mounted on one independent board, and the small heat generation electric element  3 ,  4 ,  5  is mounted on the other independent board. Thus, the heat from the large heat generation electric element  2  does not affect the small heat generation electric element  3 ,  4 ,  5 . However, in this case, when it is necessary to connect between the large heat generation electric element  2  and the small heat generation electric element  3 ,  4 ,  5  in order to communicate therebetween with high speed, impedance mismatch may be caused by a contact resistance when a connector connects the large heat generation electric element  2  and the small heat generation electric element  3 ,  4 ,  5 . 
   Thus, it is required to connect between the large heat generation electric element  2  and the small heat generation electric element  3 ,  4 ,  5  with high speed communication. 
   SUMMARY OF THE INVENTION 
   In view of the above-described problem, it is an object of the present disclosure to provide an electric device having first and second electric elements. 
   According to an aspect of the present disclosure, an electric device includes: first and second electric elements, wherein electric power consumption of the first electric element is larger than that of the second electric element, and wherein operation temperature limit of the first electric element is higher than that of the second electric element; a substrate, on which the first and second electric elements are disposed; and a casing that accommodates the substrate with the first and second electric elements. The substrate is made of a rigid flexible board. The substrate includes first and second rigid portions and a flexible portion. The first electric element is disposed on the first rigid portion, and the second electric element is disposed on the second rigid portion. The flexible portion connects the first and second rigid portions. The flexible portion has a thickness, which is smaller than the first and second rigid portions. The flexible portion further includes a wiring. The first and second electric elements are electrically coupled with the wiring so that high speed communication is performed between the first and second electric elements. 
   In the above device, thermal conduction from the first electric element to the second electric element is limited by the flexible portion. Thus, the heat from the first electric element does not affect the second electric element substantially, so that the device can function appropriately. Further, since the first and second electric elements are connected with the wiring, the high speed communication can be performed between the first and second electric elements without causing impedance mismatching. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
       FIG. 1  is a plan view showing a rigid flexible board according to an example embodiment; 
       FIG. 2  is a cross sectional view showing the rigid flexible board in a casing; 
       FIG. 3  is a cross sectional view showing arrangement of the rigid flexible board in the casing; 
       FIG. 4  is a front view showing the arrangement of the rigid flexible board in the casing; 
       FIGS. 5A to 5C  are cross sectional views showing a method for manufacturing the rigid flexible board; 
       FIG. 6  is a plan view showing a circuit board according to a related art; and 
       FIG. 7  is a cross sectional view showing the circuit board in a casing according to the related art. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An electric device having a large heat generation electric element and a small heat generation electric element is, for example, a vehicle navigation device according to an example embodiment. The navigation device is mounted on a vehicle. The navigation device shown in  FIG. 2  includes a casing  11  and a control unit  12 , which is accommodated in the casing  11 . The control unit  12  is mainly composed of a rigid flexible board  13 .  FIG. 1  shows the rigid flexible board  13 . The board  13  includes first to fourth rigid portions  13   a - 13   d  and a flexible portion  13   e . The first to fourth rigid portions  13   a - 13   d  are connected to each other with the flexible portion  13   e . A CPU (i.e., central processing unit)  14  and a periphery circuit (not shown) such as a clock circuit, a reset circuit, a I/O circuit and the like are formed on the first rigid portion  13   a . The CPU  14  controls a control unit, and corresponds to, for example, a large heat generation electric element and a micro processor. The CPU  14  performs high speed operation, so that the CPU  14  consumes large amount of electricity. Thus, the CPU  14  generates large amount of heat. Further, proper operation temperature limit of the CPU  14  is high. A high speed memory  15  (corresponding to a small heat generation electric element) is mounted on the second rigid portion  13   b . The high speed memory  15  is a DDR (i.e., double data rate) memory so that communication speed of the DDR memory is twice higher than that of a normal memory. The high speed memory  15  consumes small amount of electricity and generates small amount of heat. Thus, proper operation temperature limit of the high speed memory  15  is low. 
   A boot strap memory  16  is mounted on the third rigid portion  13   c . When the CPU  14  starts to operate, the CPU  14  firstly accesses the boot strap memory  16 . The boot strap memory  16  stores a boot strap program, which performs to read and input an OS (i.e., operating system) from a hard disk (not shown) to the CPU  14 . The boot strap memory  16  consumes small amount of electricity and generates small amount of heat. Thus, proper operation temperature limit of the boot strap memory  16  is low. 
   A power source circuit such as a power source IC  17  and the like is mounted on the fourth rigid portion  13   d . When a driver of the vehicle turns on an ignition switch so that accessories of the vehicle turn on, a voltage output from a battery maintains to be a predetermined voltage. Under this stable condition of the voltage, the power source IC  17  supplies electricity to electric elements such as the CPU  14 , the high speed memory  15  and the boot strap memory  16 . The power source IC  17  functions efficiently. Thus, electricity consumption of the power source IC  17  is quite small, and heat generation is also quite small. Thus, proper operation temperature limit of the power source IC  17  is low. 
   Each electric element such as the high speed memory  15 , the boot strap memory  16  and the power source IC  17  is mounted on a backside of the rigid portion  13   b - 13   d . This is because the rigid portions  13   b - 13   d  are arranged to be reversed when the rigid flexible board  13  is mounted in the casing  11 . 
   The first rigid portion  13   a  is connected to the second to fourth rigid portions  13   b - 13   d  with the flexible portion  13   e  having a small thickness. Further, electric elements in the rigid portions  13   a - 13   d  are electrically connected to each other with a wiring pattern of the flexible portion  13   e . The flexible portion  13   e  has a lattice shape, which is divided by a slit  13   f.    
   When the rigid flexible board  13  is mounted in the casing  11 , the first rigid portion  13   a  is arranged in parallel to the second to fourth rigid portions  13   b - 13   d . Specifically, the first rigid portion  13   a  is spaced a part from the second to fourth rigid portions  13   b - 13   d  by a predetermined distance in an up and down direction. The first rigid portion  13   a  is disposed over the second to fourth rigid portions  13   b - 13   d . In this case, the second to fourth rigid portions  13   b - 13   d  are reversed so that an element mounting surface of each rigid portion  13   b - 13   d  faces the first rigid portion  13   a . The flexible portion  13   e  connecting between the first rigid portion  13   a  and the second to fourth rigid portions  13   b - 13   d  is bent, as shown in  FIGS. 3 and 4 . The flexible portion  13   e  is divided by the slit  13   f  in a longitudinal direction of the flexible portion  13   e  so that the flexible portion  13   e  has a stripe shape. 
   The casing  11  has a suction opening  18  disposed on a front side of the casing  11 , and a cooling fan  19  is mounted on a back side of the casing  11 . When the cooling fan  19  works, air introduced from the suction opening  18  passes through the casing  11 , and then, the air is discharged to the outside of the casing  11 . The cooling fan  19  is connected to the battery with the ignition switch. Therefore, when the ignition switch turns on so that the accessories are switched on, the cooling fan  19  is energized and operated. 
   The rigid flexible board  13  is manufactured by using a method disclosed in JP-A-2003-264369 corresponding to U.S. Pat. No. 7,036,214. 
     FIGS. 5A to 5C  show a manufacturing process of the rigid flexible board  13 . A conductive pattern  20  is formed on a one-side conductive pattern film  23 . The film  23  has a via hole  21 , in which a conductive paste  22  is filled. Multiple films  23  are stacked in such a manner that each conductive pattern  20  turns upward. In  FIG. 5A , six films  23  are stacked. A copper film  24  as a conductive foil is formed on an utmost down side of the stacked films  23  so that the copper film  24  is formed on an outer side of the stacked films  23 . Further, the one-side conductive pattern film  23  disposed on an utmost upside of the stacked films  23  has no conductive pattern  20 , but has the copper film  24 , which is not patterned. Before stacked, a slit  26  is preliminarily formed on a side of a remove region  25 , and a separation sheet  27  is formed on a bottom of the remove region  25 . After stacked, the remove region  25  is removed so that the flexible portion  13   e  is formed. Thus, the remove region  25  is disposed over and under the flexible portion  13   e.    
   The stacked films  23  is pressed and heated by a pair of hot press plates in a vacuum hot press equipment so that both sides of the stacked films  23  are pressed and heated. As shown in  FIG. 5B , the one-side conductive pattern film  23  and the copper film  24  are bonded to each other so that the films  23  are thermally bonded and integrated. Further, the conductive paste  22  in the via hole  21  connects adjacent conductive patterns  20  and copper film  24  so that interlayer connection is performed. Thus, a multi-layer board  28  is formed. In the board  28 , both sides of the board  28  are covered with the copper film  24 . 
   Next, the copper film  24  disposed on a surface of the multi-layer board  28  is etched so that a predetermined pattern is formed. Accordingly, as shown in  FIG. 5C , the conductive pattern is formed on an utmost outer side of the multi-layer board  28 . 
   Finally, the remove region  25  is separated from the multi-layer board  28 . In this case, the side of the remove region  25  is surrounded with the slit  26 , and further, the separation sheet  27  is arranged on the bottom of the remove region  25 . Thus, the remove region  25  is easily removed from the multi-layer board  28 . 
   The slit  13   f  of the flexible portion  13   e  can be easily formed by arranging two separation sheets  27  in the multi-layer board  28 , the two sheets  27  which are stacked, so that two remove regions  25  facing each other are easily removed. 
   Thus, the first rigid portion  13   a  is connected to the second to fourth rigid portions  13   b - 13   d  with the flexible portion  13   e . Further, the first to fourth rigid portions  13   a - 13   d  are electrically coupled with the wiring pattern on the flexible portion  13   e  so that the rigid flexible board  13  is manufactured. Furthermore, the conductive pattern including an electrode may be formed on both sides of the first to fourth rigid portions  13   a - 13   d . Then, an electric element is mounted on the rigid flexible board  13  with solder. Thus, the control unit  12  is completed. 
   Then, the control unit  12  is mounted in the casing  11  so that the control unit  12  is connected to a hard disk (not shown), a display element (not shown) and the like. Thus, the vehicle navigation device is formed. 
   When the navigation device is mounted on the vehicle, and a driver turns on the ignition switch, a power source IC  17 , which is mounted on the fourth rigid portion  13   d , is energized. Thus, a voltage, which is stabilized by the power source IC  17 , is supplied to the CPU  14 . At the same time, a battery energizes the cooling fan  19 , so that the cooling fan  19  functions to discharge the air in the casing  11  to the outside of the casing  11 . 
   When the CPU  14  starts to function, a boot strap program outputted from the boot strap memory  16  is performed, so that an OS memorized in the hard disk is output and executed. By using the OS, a program for the navigation device is performed. In accordance with the program for the navigation device, a data is read out form the hard disk. If necessary, the data is memorized as a working data in the high speed memory  15 . Further, the data is read out from the high speed memory  15  in order to output to the display element. 
   When the CPU  14  functions with high speed, the CPU  14  generates heat because electric power consumption in the CPU  14  is large. Thus, the temperature of the CPU  14  increases. When the temperature of the CPU  14  increases, the heat from the CPU  14  conducts to the first rigid portion  13   a . Thus, the temperature of the first rigid portion  13   a  increases. In this case, the operation temperature limit of the CPU  14  is sufficiently high. Further, the cooling fan  19  cools the CPU  14  intensively. Thus, even if the temperature of the CPU  14  increases, the operational specification of the navigation device is satisfied. 
   Each of the memory  15  mounted on the second rigid portion  13   b , the memory  16  mounted on the third rigid portion  13   c  and the IC  17  mounted on the fourth rigid portion  13   d  has comparatively small electric power consumption, so that each generates comparatively small amount of heat. However, the heat conducted from the first rigid portion  13   a  may affect the second to fourth rigid portions  13   b - 13   d  so that the temperature exceeds the operation temperature limit of the memory  15 , the memory  16  or the IC  17 , and the operational specification of the navigation device may not be satisfied. However, in this embodiment, since the second to fourth rigid portions  13   b - 13   d  are connected to the first rigid portion  13   a  with the flexible portion  13   e  having a small thickness, the heat conduction from the first rigid portion  13   a  to the second to fourth rigid portions  13   b - 13   d  is limited. Thus, although the temperature of the first rigid portion  13   a  increases with heat generation of the CPU  14 , the temperature of each of the second to fourth rigid portions  13   b - 13   d  does not increase excessively. Thus, the structure of the navigation device prevents the temperature of each of the memory  15 , the memory  16  and the IC  17  from increasing excessively. Thus, even when the operation temperature limit of each of the memory  15 , the memory  16  and the IC  17  is comparatively low, the memory  15 , the memory  16  and the IC  17  function appropriately, compared with a case where the elements  2 ,  3  having different operation temperature limits are mounted on one printed circuit board  1  shown in  FIG. 6 . Further, the dimensions of the navigation device are reduced. 
   Since the CPU  14  is connected to the high speed memory  15  with the wiring pattern on the flexible portion  13   e , high speed communication between the first and second rigid portions  13   a - 13   b  can be performed without causing impedance mismatch, which is generated by a contact resistance when a connector connects the CPU  14  and the memories  15 ,  16  and the IC  17 . 
   The flexible portion  13   e  connecting between the first and second rigid portions  13   a ,  13   b  has a stripe shape, which is divided by the slit  13   f . Therefore, the flexible portion  13   e  does not prevent the air from flowing through the device when the cooling fan  19  forcibly air-cools the CPU  14 . Further, heat radiation from the flexible portion  13   e  is effectively improved. 
   The first rigid portion  13   a , on which the CPU  14  is mounted, is arranged over the memories  15 ,  16  and the IC  17 . Therefore, heat radiation and heat convection from the CPU  14  does not affect the memories  15 ,  16  and the IC  17  substantially. 
   Further, since the cooling fan  19  cools the CPU  14  effectively, the performance of the cooling fan  19  is designed by considering the cooling of the CPU  14  only. Thus, the dimensions of the cooling fan  19  are reduced, so that the device includes a small size cooling fan  19 . 
   Although no electric element is mounted on a front side of the second to fourth rigid portions  13   b - 13   d , electric elements may be mounted on the front side of the second to fourth rigid portions  13   b - 13   d.    
   Although the flowing direction of the air from the cooling fan  19  is perpendicular to the surface of the flexible portion  13   e , the flexible portion  13   e  may be arranged in the casing  11  so that the flowing direction of the air is parallel to the surface of the flexible portion  13   e.    
   Alternatively, the device may have no cooling fan  19 . 
   The rigid flexible board  13  may be manufactured by another method other than the above described method. 
   The device may be another equipment other than the vehicle navigation device. Although the CPU  14  is mounted on the first rigid portion  13   a  and the memories  15 ,  16  and the IC  17  are mounted on the second to fourth rigid portions  13   b - 13   d , respectively, other electric elements may be mounted on the first to fourth rigid portions  13   a - 13   d . Although the number of the rigid portions  13   a - 13   d  is four, the number of the rigid portions  13   a - 13   d  may be two or more. 
   While the invention has been described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the preferred embodiments and constructions. The invention is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, which are preferred, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.