Patent Abstract:
A printed circuit board unit with a cooling device includes a printed circuit board; a ventilation fan including blades rotating around a rotation axis intersecting the printed circuit board; a housing wall standing from a surface of the printed circuit board at a periphery of the ventilation fan; an inlet defined in the printed circuit board inside the housing wall and located under the blades of the ventilation fan; and an outlet defined in the housing wall to open in parallel with the surface of the printed circuit board. An electronic apparatus is also provided which further includes an electronic component mounted on the printed circuit board.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a continuation of application Ser. No. 11/369,840, filed Mar. 8, 2006, now U.S. Pat. No. 7,298,616; which is a continuation of application Ser. No. 11/120,979, filed May 4, 2005, now U.S. Pat. No. 7,019,970; which is a divisional of application Ser. No. 10/664,933, filed Sep. 22, 2003, now U.S. Pat. No. 6,909,604; which is a divisional of application Ser. No. 10/096,509, filed Mar. 13, 2002, now U.S. Pat. No. 6,665,181, and claims the benefit of foreign priority of JP 2001-281683, filed Sep. 17, 2001, the entire disclosures of which are hereby incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a printed circuit board unit with a cooling device in general incorporated within an electronic apparatus such as a portable digital assistant (PDA), a notebook personal computer, and the like. In particular, the invention relates to a printed circuit board unit comprising a printed circuit board, a ventilation fan rotatable around the rotation axis intersecting the printed circuit board, and a fan housing accommodating the ventilation fan. 
   2. Description of the Prior Art 
   As disclosed in Japanese Patent Application Publication P2000-77877A, a so-called fan unit includes a fan housing accommodating a ventilation fan rotating around the rotation axis. When the ventilation fan rotates, air is allowed to flow in the centrifugal direction of the rotation axis. The fan housing serves to guide the air toward the outlet. The air is discharged out of the outlet. At the same time, air surrounding the fan housing is introduced into the fan housing through the inlet. The inlet is defined to face the surface of the printed circuit board. When the air is sucked into the fan housing, air is allowed to flow along the surface of the printed circuit board. In general, a number of electronic components are mounted on the surface of the printed circuit board. The respective electronic components protrude from the surface of the printed circuit board, so that the electronic components hinder a smooth flow of the air. The turbulence in the air is supposed to constrain the ventilation fan from sucking the air into the fan housing. The suction quantity of the air may be reduced. The ventilation fan suffers from reduction in the cooling efficiency. As the printed circuit board gets thinner, the space is reduced between the fan housing and the surface of the printed circuit board. The cooling efficiency of the ventilation fan may still get deteriorated. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the present invention to provide a printed circuit board unit with a cooling device contributing to reduction in the thickness of an electronic apparatus. 
   According to the present invention, there is provided a printed circuit board unit with a cooling device, comprising: a printed circuit board; a ventilation fan rotating around a rotation axis intersecting the printed circuit board; a housing wall standing from a surface of the printed circuit board at a periphery of the ventilation fan; and an outlet defined in the housing wall. 
   The printed circuit board and the housing wall cooperate to define a space for accommodating the ventilation fan. When the ventilation fan rotates, the movement of air, namely, airflow can be generated within the space. The printed circuit board and the housing wall lead the air toward the outlet. In this manner, the printed circuit board can be utilized to form the cooling device. 
   In particular, a high speed airflow can be generated within the space in the printed circuit board unit and the housing wall. The airflow efficiently absorbs the heat from the surface of the printed circuit board. The heat radiation from the printed circuit board can be promoted. In general, an electrically conductive metallic wiring pattern extends over the surface of the printed circuit board. The metallic wiring pattern usually has a superior heat conductivity as compared with the material of the printed circuit board. The metallic wiring pattern thus contributes to promotion of the heat radiation from the printed circuit board. In particular, the metallic wiring pattern inside the housing wall leads to an improved promotion of the heat radiation from the printed circuit board. 
   The printed circuit board unit of the aforementioned type may further comprise: a ceiling wall connected to an upper end of the housing wall and extending along a datum plane parallel to the surface of the printed circuit board; and an inlet defined in the ceiling wall. 
   In general, a number of electronic components are mounted on the surface of the printed circuit board. The electronic components protrude from the surface of the printed circuit board. The electronic components is supposed to hinder a smooth flow of the air along the surface of the printed circuit board. If the inlet is defined at a position spaced from the surface of the printed circuit board in the aforementioned manner, a smooth flow of the air can be established irrespective of the existence of the electronic components. The air can smoothly be sucked-into the inlet. A large quantity of the air can be sucked, so that the cooling efficiency of the cooling device can be improved. 
   For example, if the printed circuit board of the aforementioned type is incorporated within an electronic apparatus, the inlet can be opposed to the inner surface of the enclosure of the electronic apparatus. Airflow can be generated along the inner surface of the enclosure in response to the suction of the air into the inlet. In general, a generally flat surface is defined on the inner surface of the enclosure. Less obstacles can be found on the inner surface of the enclosure as compared with the surface of the printed circuit board. A smooth airflow can thus be generated along the inner surface of the enclosure. The air is smoothly sucked into the inlet. Since the air is smoothly introduced into the inlet in this manner, a higher cooling efficiency can be kept even when the space is reduced between the inlet and the inner surface of the enclosure in the electronic apparatus. The thickness of the electronic apparatus can reliably be reduced. 
   The printed circuit board unit of the aforementioned type may further comprise an inlet defined in the printed circuit board inside the housing wall. Air can be introduced not only from the space adjacent the front side of the printed circuit board but also from the space adjacent the back side of the printed circuit board. A larger quantity of air can be sucked into the space defined by the printed circuit board and the housing wall, so that the cooling efficiency of the cooling device can further be improved. Moreover, the front and back sides of the printed circuit board can simultaneously be cooled down enough. It should be noted that the inlet in the printed circuit board may be established in place of the inlet in the ceiling wall. This structure contributes to a further reduction in the thickness of the electronic apparatus. 
   In addition, the printed circuit board unit of the aforementioned type may further comprise: an electronic component mounted on the printed circuit board; and an electrically conductive wiring pattern extending over the surface of the printed circuit board inside the housing wall and connected to the electronic component. The ventilation fan serves to promote the heat radiation from the electrically conductive wiring pattern. The heat radiation from the printed circuit board can still be improved. Moreover, since the electrically conductive wiring pattern is allowed to receive the heat from the electronic component, the electronic component can efficiently be cooled down. 
   A heat radiation fin may be attached to the printed circuit board and connected to the electronic component. The heat radiation fin promotes the heat radiation from the electrically conductive wiring pattern. The heat radiation fin may be located within the outlet. Alternatively, the heat radiation fin may be located to face the outlet. 
   An electronic component may be mounted on the printed circuit board inside the housing wall. A high speed airflow can be generated inside the housing wall based on the rotation of the ventilation fan in the aforementioned manner. Accordingly, the electronic component can efficiently be cooled down. The electronic component may be located within the outlet, for example. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiment in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view schematically illustrating a notebook personal computer according to an example of an electronic apparatus; 
       FIG. 2  is a plan view schematically illustrating the inner structure of a main body and the front surface of a printed circuit board unit; 
       FIG. 3  is an enlarged plan view schematically illustrating the back surface of the printed circuit board unit; 
       FIG. 4  is an enlarged plan view of a printed circuit board for schematically illustrating the main portion of a cooling device according to a first embodiment of the present invention; 
       FIG. 5  is an enlarged partial sectional view taken along the line  5 - 5  in  FIG. 2 ; 
       FIG. 6  is an enlarged partial sectional view, corresponding to  FIG. 5 , for schematically illustrating a modification of the cooling device; 
       FIG. 7  is an enlarged plan view, corresponding to  FIG. 4 , for schematically illustrating the structure of a cooling device according to a second embodiment of the present invention; and 
       FIG. 8  is an enlarged plan view, corresponding to  FIG. 4 , for schematically illustrating the structure of a cooling device according to a third embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates a notebook personal computer  11  as an example of an electronic apparatus. The notebook personal computer  11  includes a thin main body  12  and a display enclosure  13  coupled to the main body  12 . The display enclosure  13  is allowed to swing relative to the main body  12 . Input devices such as a keyboard  14  and a pointing device  15  are embedded in the surface of the main body  12 . The user may utilize the keyboard  14  and the pointing device  15  so as to manipulate the notebook personal computer  11 . 
   A liquid crystal display (LCD) panel module  16  is incorporated within the display enclosure  13 , for example. The screen of the LCD panel module  16  is positioned in a window  17  defined in the display enclosure  13 . The user is allowed to observe the operation of the notebook personal computer  11  based on texts and graphics, for example, displayed on the screen of the LCD display panel module  16 . The display enclosure  13  may be superposed over the upper surface of the main body  12  through the swinging movement. 
   As shown in  FIG. 2 , a printed circuit board unit  18  is incorporated within the main body  12 . The printed circuit board unit  18  includes a printed circuit board  19  and a central processing unit (CPU) package  21  mounted on the front surface of the printed circuit board  19 , for example. The CPU package  21  may include a small-sized ceramic substrate  22  and a CPU chip  23  mounted on the ceramic substrate  22 , for example. Not only the CPU package  21  but also various electronic components  24   a ,  24   b  are mounted on the front surface of the printed circuit board  19 . An electrically conductive wiring pattern, not shown, is formed to extend over the front surface of the printed circuit board, for example. The electrically conductive wiring pattern serves to establish electric connections between the CPU package  21  and the electronic components  24   a ,  24   b  as well as between the electronic components  24   a ,  24   b.    
   Within the main body  12 , a secondary battery  25  as well as a hard disk drive (HDD)  26  is connected to the printed circuit board unit  18 , for example. The secondary battery  25  and the HDD  26  may be detachably incorporated within the main body  12 . The secondary battery  25  supplies an electric power to the printed circuit board  18  in place of an AC power supply, for example. The HDD  26  is allowed to hold application software programs to be processed at the CPU chip  23  as well as various data utilized during the execution of the application software programs. 
   A cooling device  27  according to a first embodiment of the present invention is coupled to the CPU package  21 . The cooling device  27  includes a heat receiving plate  28 , of a higher heat conductive material, superposed on the upper surface of the CPU chip  23 . One end of a heat conductive member such as a heat pipe  29  is connected to the heat receiving plate  28 . The other end of the heat pipe  29  is connected to heat radiation fins  31  attached to the printed circuit board  19 . Heat of the CPU chip  23  is transmitted to the heat radiation fins  31  via the heat receiving plate  28  and the heat pipe  29 . The heat radiation fins  31  are allowed to protrude, out of a recess  32  defined in the printed circuit board  19 , into a space at the back of the printed circuit board  19 . 
   As shown in  FIG. 3 , electronic components such as a memory module  35  including a random access memory (RAM), a PC card slot  36 , a local area network (LAN) module  37  are mounted on the back surface of the printed circuit board  19 . In this manner, relatively taller electronic components are mounted on the back surface of the printed circuit board  19  as compared with the front surface. 
   A fan unit  38  is further incorporated within the cooing device  27 . The fan unit  38  is attached to the back surface of the printed circuit board  19 , as shown in  FIG. 3 . The fan unit  38  includes a fan housing  39  fixed to the back surface of the printed circuit board  19 . A top or ceiling wall  41  is defined in the fan housing  39 . The ceiling wall  41  is allowed to extend along a datum plane parallel to the back surface of the printed circuit board  19 . An inlet  42  is defined in the ceiling wall  41 . The inlet  42  serves to interconnect the space inside the fan housing  39  and the space outside the fan housing  39  to each other. 
   Referring also to  FIG. 4 , a rotary member  43  is accommodated within the fan housing  39 . The rotary member  43  is designed to rotate around the rotation axis CR extending in a direction perpendicular to the back surface of the printed circuit board  19 . Blades  44  are integrally formed on the peripheral surface of the rotary member  43 . The blades  44  may be located at equal intervals, for example. The respective blades  44  are designed to extend in the centrifugal directions from the rotary member  43 . The individual blade  44  extends in a plane intersecting, by a predetermined inclination angle α, the vertical plane VP including the rotation axis CR. When the rotary member  43  rotates, the blades  44  serve to generate airflow in the centrifugal direction from the rotation axis CR. The rotary member  43  and the blades  44  constitute a so-called fan or ventilation fan. 
   As is apparent from  FIG. 4 , a housing wall  45  is defined in the fan housing  39 . The housing wall  45  is designed to stand upright from the back surface of the printed circuit board  19  at the periphery of the blades  44 , so that the housing wall  45  mostly surrounds the ventilation fan. Specifically, the inner surface of the housing wall  45  is opposed to the outer ends of the blades  44  at positions spaced from the outer ends of the blades  44 . An outlet  46  is defined in the fan housing  39  at the break of the housing wall  45 . The outlet  46  is located to face the heat radiation fins  31 . An inlet  47  is also defined in the printed circuit board  19  inside the housing wall  45 . The inlet  47  likewise serves to interconnect the space inside the fan housing  39  and the space outside the fan housing  39  to each other, in the same manner as the aforementioned inlet  42 . Part of the printed circuit board  19  constitutes the fan housing  39 . 
   As is apparent from  FIG. 5 , the rotary member  43  is mounted on a rotary shaft  51  extending in the vertical direction perpendicular to the back surface of the printed circuit board  19 . The rotary shaft  51  is received on a bearing  52  fixed to the ceiling wall  41  of the fan housing  39 . A thin electric motor  53  is interposed between the rotary member  43  and the bearing  52 . The electric motor  53  may include permanent magnets  54  attached to the rotary member  43 , and stationary coils  55  fixed to the bearing  52  and opposed to the permanent magnets  54 . A controller board  56  is also fixed to the ceiling wall  41  of the fan housing  39 . A controller circuit is established on the controller board  56 . The controller circuit operates to control the operation of the electric motor  53 . 
   Now, when an electric power is supplied to the electric motor  53 , the rotary member  43  rotates around the rotation axis CR. The blades  44  generate airflow in the centrifugal direction of the rotation axis CR. The generated airflow is guided along the housing wall  45  to the outlet  46 . The air is discharged out of the outlet  46  in this manner. 
   An opening  58  is defined in an enclosure  57  of the main body  12 . The opening  58  is located to face the outlet  46  of the fan unit  38 . The air discharged out of the outlet  46  is allowed to flow through the heat radiation fins  31  and gets out of the main body  12  through the opening  58 . The air absorbs the heat from the heat radiation fins  31 . In this manner, the heat radiation from the heat radiation fins  31  is efficiently promoted. 
   A high speed airflow is generated based on the rotation of the blades  44  within the inner space surrounded by the printed circuit board  19 , the housing wall  45  and the ceiling wall  41 . The airflow efficiently absorbs the heat from the surface of the printed circuit board  19 . The heat radiation from the printed circuit board  19  can be promoted. In general, an electrically conductive metallic wiring pattern extends over the surface of the printed circuit board  19 . The metallic wiring pattern usually has a superior heat conductivity as compared with the material of the printed circuit board  19 . The metallic wiring pattern thus contributes to promotion of the heat radiation from the printed circuit board  19 . In particular, the metallic wiring pattern inside the housing wall  45  leads to an improved promotion of the heat radiation from the printed circuit board  19 . 
   While the air is discharged out of the outlet  46  in the aforementioned manner, air is sucked into the fan housing  39  through the inlet  42 . Since the inlet  42  in the ceiling wall  41  is opposed to the inner surface of the enclosure  57 , airflow  61  can be generated along the inner surface of the enclosure  57  in response to the suction of the air into the inlet  42 . In general, a number of electronic components are mounted on the back surface of the printed circuit board  19 . The electronic components protrude from the back surface of the printed circuit board  19 . The electronic components thus hinder a smooth flow of the air along the back surface of the printed circuit board  19 . On the other hand, a generally flat surface is defined on the inner surface of the enclosure  57  of the main body  12 . Less obstacles can be found on the inner surface of the enclosure  57 . The smooth airflow  61  can be generated along the inner surface of the enclosure  57  of the main body  12 . The air is smoothly sucked into the inlet  42 . A large quantity of the air can be sucked into the fan housing  39 , so that the cooling efficiency of the fan unit  38  can be improved. Since the air is smoothly introduced into the inlet  42  in this manner, a higher cooling efficiency can be kept even when the space is reduced between the ceiling wall  41  of the fan housing  39  and the inner surface of the enclosure  57 . 
   At the same time, air can be sucked from the inlet  47  in the printed circuit board  19  in the fan unit  38 . The air is introduced into the fan unit  38  not only from the space adjacent the back surface of the printed circuit board  19  but also from the space adjacent the front surface of the printed circuit board  19 . A still larger quantity of the air can be sucked into the fan housing  39 , so that the cooling efficiency of the fan unit  38  can further be improved. Moreover, the front surface of the printed circuit board  19  can be cooled down enough even when the fan unit  19  is located on the back surface of the printed circuit board  19 . 
   When the inlet  47  is defined in the printed circuit board  19  in the aforementioned manner, the ceiling wall  41  of the fan housing  39  may completely superposed over the inner surface of the enclosure  57 , as shown in  FIG. 6 . Air can be sucked enough into the fan housing  39  from the inlet  47  irrespective of the closure of the inlet  42 . A sufficient cooling efficiency can be maintained in the fan unit  38 . This structure is supposed to contribute to an additional reduction in the thickness of the main body  12 . 
     FIG. 7  illustrates a cooling device  62  according to a second embodiment of the present invention. The cooling device  62  includes an electrically conductive wiring pattern  63  extending over the front surface of the printed circuit board  19 , and heat radiation fins  64  attached to the front surface of the printed circuit board  19 . The electrically conductive wiring pattern  63  is connected to a power consumption circuit, namely, the CPU package  21  and to the heat radiation fins  64 . Soldering may be employed to fix the heat radiation fins  64  to the electrically conductive wiring pattern  63  on the printed circuit board  19 . The electrically conductive wiring pattern  63  may function as a ground wire of the CPU package  21 . It should be noted that like reference numerals are attached to the structure or components equivalent to those of the aforementioned first embodiment. 
   A fan unit  38   a  is attached to the front surface of the printed circuit board  19  in the cooling device  62 . The fan unit  38   a  may have the structure identical to that of the fan unit  38  according to the first embodiment. The heat radiation fins  64  may be located within the outlet  46  of the fan unit  38   a , for example. In addition, the electrically conductive wiring pattern  63  is allowed to extend from the CPU package  21  to the heat radiation fins  64  inside the housing wall  45 . 
   The cooling device  62  induces the heat radiation of a higher efficiency from the printed circuit board  19  based on a high speed airflow generated within the fan housing  39  of the fan unit  38   a  in the same manner as described above. The electrically conductive wiring pattern  63  promotes the heat radiation from the printed circuit board  19 . In addition, since the electrically conductive wiring pattern  63  is allowed to efficiently receive the heat from the CPU package  21 , the CPU package  21  can efficiently be cooled down. 
   The air discharged from the outlet  46  is allowed to pass through the heat radiation fins  64 . The air absorbs the heat from the heat radiation fins  64 . The air thereafter gets out of the enclosure  57  of the main body  12  from the opening  58 . The heat radiation from the heat radiation fins  64  can thus be promoted. Otherwise, any electrically wiring pattern for the ground of the electronic components  24   a ,  24   b  may likewise be connected to the heat radiation fins  64 . 
     FIG. 8  illustrates a cooling device according to a third embodiment of the present invention. The cooling device  66  likewise includes the aforementioned fan unit  38 . Electronic components  67  are mounted on the back surface of the printed circuit board  19  inside the housing wall  45  in the fan unit  38 . The electronic components  67  may be located at the outlet  46  of the fan unit  38 , for example. The cooling device  66  of this type serves to promote the heat radiation from the electronic components  67  based on a high speed airflow generated within the fan housing  39  of the fan unit  38  in the same manner as described above. It should be noted that like reference numerals are attached to the structure or components equivalent to those of the aforementioned first embodiment. 
   The printed circuit board unit  18 , along with the cooling device  27 ,  62 ,  66  may be incorporated not only in a portable electronic apparatus such as the aforementioned notebook personal computer  11  and a personal digital assistant (PDA) but also in a desktop type electronic apparatus. The bearing  52  for the rotary shaft  51  may be supported directly on the printed circuit board  19  in the fan unit  38 ,  38   a .

Technology Classification (CPC): 6