Abstract:
An intake opening is defined in a printed circuit board inside a fan cover mounted on the printed circuit board. The intake opening has a particular extent inside the fan cover. This intake opening contributes to improvement in the cooling efficiency of a fan as compared with a conventional intake opening. Moreover, the intake opening allows a sufficient space to remain on the front and back surfaces of the printed circuit board inside the fan cover. Electronic components and/or wiring patterns may be disposed in the space. This contributes to disposition of electronic components and/or wiring patterns at a higher density on the printed circuit board.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a printed circuit board unit and a fan unit incorporated in an electronic apparatus such as a notebook personal computer, for example. In particular, the invention relates to a fan unit including a fan rotating around the rotation axis, and a fan cover defining an inner space for containing the fan. 
   2. Description of the Prior Art 
   A fan unit is in general incorporated within a notebook personal computer as disclosed in Japanese Patent Application Publication No. 2001-284863. The fan unit includes a fan cover for containing a fan rotating around the rotation axis. When the fan rotates, air is forced to flow away from the rotation axis in the centrifugal direction. The fan cover serves to guide the air toward a discharge opening. At the same time, an intake opening is defined in the fan cover. Ambient air is introduced inside the fan cover through the intake opening. Airflow is generated along the surface of the printed circuit board. 
   In general, many electronic components are mounted on the surface of a printed circuit board. Wiring patterns are formed on the surface of the printed circuit board so as to connect the electronic components. A reduction in the size of the notebook personal computer induces a reduction in the size of the printed circuit board. The electronic components and wiring patterns are located on the printed circuit board at a higher density. The tight location of the electronic components and wiring patterns requires an efficient heat radiation from the printed circuit board. The cooling efficiency of the fan should be improved. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the present invention to provide an electronic apparatus having a larger space for electronic components and contributing to an efficient cooling. It is also an object of the present invention to provide a printed circuit board unit and fan unit greatly contributing to realization of the electronic apparatus. 
   According to a first aspect of the present invention, there is provided a printed circuit board unit comprising: a printed circuit board; a fan rotating about the rotation axis intersecting the surface of the printed circuit board; a fan cover mounted on the printed circuit board, said fan cover defining an inner space for containing the fan; a discharge opening defined in the fan cover at a location outside the fan in the centrifugal direction; a curved wall defined in the fan cover, said curved wall extending on the printed circuit board along an outer periphery of the fan; and a guiding wall defined in the fan cover, said guiding wall extending on the printed circuit board along a plane from the downstream end of the curved wall toward the discharge opening, wherein an intake opening extends in the printed circuit board from a first reference plane to a fourth reference plane across second and third reference planes, where the first reference plane extends from the rotation axis to the guiding wall in the direction perpendicular to the guiding wall, the second reference plane located downstream of the first reference plane and perpendicularly intersecting the first reference plane at the rotation axis, the third reference plane located downstream of the second reference plane and perpendicularly intersecting the second reference plane at the rotation axis, and the fourth reference plane located downstream of the third reference plane and perpendicularly intersecting the third reference plane at the rotation axis. 
   The fan rotates around the rotation axis in the printed circuit board unit. The rotating fan serves to generate a high speed airflow within the inner space of the fan cover. Air is sucked into the inner space of the fan cover through the intake opening defined in the printed circuit board. Airflow is thus generated along the front and back surfaces of the printed circuit board. The airflow serves to efficiently absorb heat from the front and back surfaces of the printed circuit board. The rotating fan also forces the sucked air to flow within the fan cover. The curved wall and the guiding wall serve to guide the air toward the discharge opening. The air is allowed to flow out of the fan cover through the discharge opening. The heat radiation is thus promoted from the printed circuit board. 
   The intake opening extends from the first reference plane to the fourth reference plane across the second and third reference planes in the printed circuit board unit. According to an examination of the inventors, it has been proved that the intake opening contributes to improvement in the cooling efficiency of the fan as compared with a conventional intake opening. Moreover, a sufficient space can be maintained on the front and back surfaces of the printed circuit board between the fourth and first reference planes. Electronic components and/or wiring patterns may be disposed in the space, for example. This contributes to disposition of electronic components and/or wiring patterns at a higher density on the printed circuit board. 
   The printed circuit board may include: a central portion extending around the rotation axis of the fan inside the intake opening; and an area extending from the central portion to the curved wall in an extent from the fourth reference plane to the first reference plane, said area excluding the intake opening. Electronic components and/or wiring patterns can be positioned within the central portion as well as the aforementioned area excluding the intake opening. The aforementioned area may be opposed to a space occupied at least by blades of the fan rotating around the rotation axis in an extent from the fourth reference plane to the first reference plane without interruption. The printed circuit board unit may be incorporated within an electronic apparatus such as a notebook personal computer, for example. 
   The intake opening may comprise: a first intake opening or separate component defined in the printed circuit board between first and second reference planes; a second intake opening or separate component defined in the printed circuit board between third and the second reference planes; and a third intake opening or separate component defined in the printed circuit board between fourth and the third reference planes. 
   According to a second aspect of the present invention, there is provided a fan unit comprising: a bottom plate; a fan rotating about the rotation axis intersecting the surface of the bottom plate; a fan cover coupled to the bottom plate, said fan cover defining an inner space for containing the fan; a discharge opening defined in the fan cover at a location outside the fan in the centrifugal direction; a curved wall defined in the fan cover, said curved wall extending on the bottom plate along the outer periphery of the fan; and a guiding wall defined in the fan cover, said guiding wall extending on the bottom plate along a plane from the downstream end of the curved wall toward the discharge opening, wherein an intake opening extends in the bottom plate from a first reference plane to a fourth reference plane across second and third reference planes, where the first reference plane extends from the rotation axis to the guiding wall in a direction perpendicular to the guiding wall, the second reference plane located downstream of the first reference plane and perpendicularly intersecting the first reference plane at the rotation axis, the third reference plane located downstream of the second reference plane and perpendicularly intersecting the second reference plane at the rotation axis, and the fourth reference plane located downstream of the third reference plane and perpendicularly intersecting the third reference plane at the rotation axis. 
   The fan unit serves to improve the cooling efficiency of the fan as described above. If the fan unit is mounted no the printed circuit board within an electronic apparatus, for example, the heat radiation can be promoted in the printed circuit board. 
   The bottom plate may include: a central portion extending around the rotation axis of the fan; and an area extending from the central portion to the curved wall in an extent from the fourth reference plane to the first reference plane, said area excluding the intake opening. The area may be opposed to a space occupied at least by blades of the fan rotating around the rotation axis in an extent from the fourth reference plane to the first reference plane without interruption. 
   The intake opening may comprise: a first intake opening or separate component defined in the printed circuit board between first and second reference planes; a second intake opening or separate component defined in the printed circuit board between third and the second reference planes; and a third intake opening or separate component defined in the printed circuit board between fourth and the third reference planes. 
   According to a third aspect of the present invention, there is provided a printed circuit board comprising an intake opening for a fan unit, said intake opening located at a position where the fan unit is mounted, said intake opening being defined within an area located on a discharge side of the fan unit, said area being divided into a pair of portions with a reference line extending through a rotation axis of a fan in the fan unit in the direction of discharge of the fan unit, and said intake opening further being defined in a portion located within an area opposite to the discharge side at a position upstream of the reference line according to the direction of rotation of the fan. 
   According to a fourth aspect of the present invention, there is provided a printed circuit board unit including a printed circuit board as defined in the third aspect of the present invention and a fan unit. In this case, the fan unit may include a fan rotating around the rotation axis intersecting the surface of the printed circuit board, and a discharge opening located outside the fan in the centrifugal direction. 
   The intake opening may include three separate components. Two of the components may respectively be located in the portions on the discharge side of the fan unit. The other of the components may be located in the portion within the area opposite to the discharge side with respect to the reference line. 
   Said two of the components may respectively be shaped into a near sector. The near sector may have a contour along a first circle having the center at the rotation axis of the fan. The other of the components may be shaped into a near sector. This near sector may have a contour along a second circle concentric to the first circle and having a diameter different from that of the first circle. 
   The fan unit may comprise a fan cover including an intake opening having the center at the rotation axis of the fan and a diameter identical to that of the first circle. The outer diameter of the intake opening in the printed circuit board corresponds to the outer diameter of the intake opening in the fan cover. This avoids a discharge of air out of one of the intake openings due to the difference of the areas of the intake openings. Air is efficiently sucked and discharged. 
   The aforementioned printed circuit board and printed circuit board unit serve to improve the cooling efficiency of the fan as described above. Moreover, the printed circuit board includes an area, excluding any intake opening, opposite to the discharge side of the fan unit at a position upstream of the reference line. A sufficient space can be maintained on the front and back surfaces of the printed circuit board. Electronic components and/or wiring patterns may be disposed in the space, for example. This contributes to disposition of electronic components and/or wiring patterns at a higher density on the printed circuit board. 
   According to a fifth aspect of the present invention, there is provided a fan unit comprising: a bottom plate: a fan rotating about a rotation axis intersecting a surface of the bottom plate; and a discharge opening disposed at a location outside the fan in a centrifugal direction, wherein said bottom plate includes an intake opening, said intake opening being defined within an area located on a discharge side of the fan unit, said area being divided into a pair of portions with a reference line extending through a rotation axis of a fan in the fan unit in a direction of discharge of the fan unit, and said intake opening further being defined in a portion located within an area opposite to the discharge side at a position upstream of the reference line according to a direction of rotation of the fan. This fan unit also serves to improve the cooling efficiency of the fan as described above. 
   The printed circuit board, the printed circuit board unit, and the fan unit contribute to improvement of the heat radiation from the printed circuit board. 

   
     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 embodiments in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view schematically illustrating the entire structure of a notebook personal computer as an example of an electronic apparatus; 
       FIG. 2  is a plan view schematically illustrating the front surface of a printed circuit board unit within a main body of the notebook personal computer; 
       FIG. 3  is an enlarged plan view of the printed circuit board unit for schematically illustrating the main portion of the printed circuit board unit according to the present invention; 
       FIG. 4  is an enlarged plan view of a printed circuit board of the printed circuit board unit for schematically illustrating the structure of an intake opening; 
       FIG. 5  is an enlarged partial sectional view taken along the line  5 - 5  in  FIG. 2 ; 
       FIGS. 6A to 6L  are a plan view illustrating samples of the intake opening; 
       FIGS. 7A to 7C  are a table illustrating the result of an examination; 
       FIG. 8  is an enlarged plan view of a printed circuit board unit for schematically illustrating the main portion of a fan unit according to another example of the present invention; and 
       FIG. 9  is an enlarged plan view illustrating the positional relationship between the intake opening in the ceiling wall of the fan cover and the intake opening in the printed circuit board or bottom plate of the fan cover. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  schematically 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  14  coupled to the main body  12 . The display enclosure  14  is allowed to swing around a predetermined axis  13  relative to the main body  12 . Input devices such as a keyboard  15  and a pointing device  16  are embedded in the upper surface of the main body  12 . A liquid crystal display (LCD) panel  17  is contained in the display enclosure  14 . The user recognizes the operation of the notebook personal computer  11  based on texts and graphics displayed on the screen of the LCD panel  17 , for example. 
   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 CPU chip, not shown, mounted on a small-sized ceramic substrate, for example. The CPU chip is designed to execute operations based on an operating system (OS) and application softwares, for example. The user is allowed to input various data and instructions through the input devices  15 ,  16  to the CPU chip. 
   A cooling device  22  is connected to the CPU package  21 . The cooling device  22  includes a thermally-conductive plate  23  superposed on the upper surface of the CPU chip. The thermally-conductive plate  23  is connected to one end of a thermally-conductive member such as a heat pipe  24 . The other end of the heat pipe  24  is connected to radiation fins  25 . The radiation fins  25  are supported on the heat pipe  24 . Heat of the CPU chip is transmitted to the radiation fins  25  through the thermally-conductive plate  23  and the heat pipe  24 . The radiation fins  25  are designed to protrude out of the back of the printed circuit board  19  through a recess  26  defined in the edge of the printed circuit board  19 . 
   A fan unit  27  is further mounted on the front surface of the printed circuit board  19 . The fan unit  27  includes a fan cover  28  fixed to the front surface of the printed circuit board  19 . The fan cover  28  defines an inner space between the printed circuit board  19  and the fan cover  28  itself. A ceiling wall  29  is defined in the fan cover  28 . The ceiling wall  29  is designed to extend along a datum plane parallel to the front surface of the printed circuit board  19 . An intake opening  31  is defined in the ceiling wall  29 . The intake opening  31  serves to connect the inner space of the fan cover  28  and the exterior space of the fan cover  28  to each other. The intake opening  31  comprises three separate components  32 ,  33 ,  34 , in this case. 
   As shown in  FIG. 3 , a fan  36  is incorporated within the inner space of the fan cover  28 . The fan  36  is designed to rotate around the rotation axis  35  perpendicular to the front surface of the printed circuit board  19 . The fan  36  includes a rotary member  37  and blades  38  respectively extending in radial directions from the rotary member  37 . The blades  38  are designed to extend along imaginary planes parallel to the rotation axis  35 . The blades  38  are integral to the rotary member  37 . The blades  38  may be arranged at equal intervals, for example, around the rotary member  37 . When the rotary member  37  rotates, the blades serve to force air to flow in the centrifugal direction from the rotation axis  35 . The rotary member  37  and the blades  38  in combination establish a so-called centrifugal fan. 
   A discharge opening  39  is defined in the fan cover  28 . The discharge opening  39  is located outside the fan  36  in the centrifugal direction. The discharge opening  39  is opposed to the radiation fins  25 . A curved wall  41  is also defined in the fan cover  28  so as to extend on the printed circuit board  19 . The curved wall  41  stands upright on the front surface of the printed circuit board  19  outside the fan  36  in the centrifugal direction. The curved wall  41  curves along the outer periphery of the fan  36 . It should be noted that the curved wall  41  may at least define a curved “surface” along the outer periphery of the fan  36 . The upper end of the curved wall  41  is connected to the ceiling wall  29 . 
   A guiding wall  42  is defined in the fan cover  28 . The guiding wall  42  is designed to extend along an imaginary plane upright to the front surface of the printed circuit board  19 . The guiding wall  42  extends from the downstream end of the curved wall  41  toward the discharge opening  39 . The guiding wall  42  is designed to stand upright on the front surface of the printed circuit board  19  outside the fan  36  in the centrifugal direction. The inner surface of the guiding wall  42  is opposed to the outer ends of the blades  38 . It should be noted that the guiding wall  42  may at least define a flat inner “surface” along the imaginary plane. The upper end of the guiding wall  42  is connected to the ceiling wall  29 . 
   A first reference plane  43  is established in the inner space of the fan cover  28 . The first reference plane  43  extends from the rotation axis toward the guiding wall  42 . The first reference plane  43  perpendicularly intersects the guiding wall  42 . A second reference plane  44  is likewise defined downstream of the first reference plane. The term “downstream” and “upstream” should be defined based on the direction of the rotation of the fan  36 . The second reference plane  44  intersects the first reference plane  43  at the rotation axis  35  in the direction perpendicular to the first reference plane  43 . A third reference plane  45  is likewise defined downstream of the second reference plane  44 . The third reference plane  45  intersects the second reference plane  44  at the rotation axis  35  in the direction perpendicular to the second reference plane  44 . A fourth reference plane  46  is also defined downstream of the third reference plane  45 . The fourth reference plane  46  intersects the third reference plane  45  at the rotation axis  35  in the direction perpendicular to the third reference plane  45 . 
   An intake opening  47  is defined in the printed circuit board  19  inside the curved wall  41  and the guiding wall  42 . The intake opening  47  is located at a position where the fan unit  27  is mounted. The intake opening  47  serves to connect the inner space of the fan cover  28  and the exterior space of the fan cover  28  to each other. The intake opening  47  is designed to extend downstream from the first reference plane  43  to the fourth reference plane  46  across the second and third reference planes  44 ,  45 . The intake opening  47  is opposed to a space occupied at least by the blades  38  of the rotating fan  36 . 
   AS shown in  FIG. 4 , a central portion  48  is defined in the printed circuit board  19 . The central portion  48  extends around the rotation axis  35  of the fan  36  inside the intake opening  47 . The rotary member  37  of the fan  36  is opposed to the central portion  48 . A continuous wall or portion  49  is defined in the printed circuit board  19 . The continuous portion  49  extends from the central portion  48  toward the curved wall  41  between the fourth and first reference planes  46 ,  43 . An intake opening is excluded from the continuous portion  49 . The continuous portion  49  is continuously opposed to the space occupied at least by the blades  38  of the rotating fan  36  between the fourth and first reference planes  46 ,  43 . 
   Reinforcing portions  51  are formed in the intake opening  47 . The reinforcing portions  51  are designed to reinforce the central portion  48 . The reinforcing portions  51  extend from the central portion  48  in the centrifugal directions of the fan  36 . One of the reinforcing portions  51  is formed to extend along the second reference plane  44 . The other of the reinforcing portions  51  is formed to extend along the third reference plane  45 . The reinforcing portions  51  serve to establish a first partial intake opening or separate component  52  between the first and second reference planes  43 ,  44 . A second partial intake opening or separate component  53  is established between the second and third reference planes  44 ,  45 . A third partial intake opening or separate component  54  is likewise established between the third and fourth reference planes  45 ,  46 . In other words, the first and second partial intake openings  52 ,  53  are located within an area near the discharge opening  39 . Such an area is divided into partial areas with a reference line  55  extending through the rotation axis  35  of the fan  36  toward the discharge opening  39 . The first and second partial intake openings  52 ,  53  are defined within the partial areas, respectively. The third partial intake opening  54  is located within an area remoter from the discharge opening  39 , namely, opposite to the area near the discharge opening  39  with respect to the rotation axis  35 . The third partial intake opening  54  is defined upstream of the reference line  55  within the area. 
   The first and second partial intake openings  52 ,  53  are shaped into a near sector having the inner contour along a first circle  56 . The first circle  56  has the center at the rotation axis  35  of the fan  36 . The first and second partial intake openings  52 ,  53  are set symmetric with respect to the second reference plane  44 . The first and second partial intake openings  52 ,  53  are thus allowed to have the identical area. On the other hand, the third partial intake opening  54  is shaped into a near sector having the inner contour along a second circle  57 . The second circle  57  is set concentric to the first circle  56  and has a diameter larger than that of the first circle  56 . The third partial intake opening  54  is thus set smaller than the first or second partial intake opening  52 ,  53 . 
   As shown in  FIG. 5 , the rotary member  37  of the fan unit  27  is mounted on a vertical rotary shaft  61  perpendicular to the front surface of the printed circuit board  19 . The rotary shaft  61  is supported on a bearing  62  fixed to the ceiling wall  29  of the fan cover  28 . Permanent magnets  63  are fixed to the rotary member  37 . Coils  64  are attached to the bearing  62 . The coils  64  are opposed to the permanent magnets  63 . The rotary member  37 , the rotary shaft  61  and the bearing  62  establish an electric motor  65 . A controller circuit may be utilized to control the operation of the electric motor  65 . The controller circuit may be mounted on a controller board, for example. 
   Now, when electric power is supplied to the electric motor  65 , the rotary member  37  is driven to rotate around the rotation axis  35 . The blades  38  force air to flow in the centrifugal direction from the rotation axis  35 . The curved wall  41  and the guiding wall  42  serve to guide the air toward the discharge opening  39 . The air is then discharged out of the discharge opening  39 . An enclosure  66  of the main body  12  defines an opening  67  opposed to the discharge opening  39  of the fan unit  27 . The air from the discharge opening  39  absorbs heat from the radiation fins  25 . The air is thereafter allowed to flow out of the main body  12  through the opening  67  of the enclosure  66 . The heat radiation of the radiation fins  25  is in this manner efficiently promoted. 
   The blades  38  on the rotating fan  36  serve to cause a high speed airflow within the inner space of the fan cover  28 . Air is introduced into the fan cover  28  through the intake opening  31  as well as the first, second and third partial intake openings  52 ,  53 ,  54 . Airflow is generated along the inner surface of the enclosure  66  of the main body  12 . The airflow serves to efficiently absorb heat from the front and back surfaces of the printed circuit board  19 . The airflow is allowed to flow out of the enclosure  66  through the discharge opening  39  and the opening  67 . The heat radiation is in this manner promoted from the printed circuit board  19 . 
   Moreover, the intake opening  47  extends from the first reference plane  43  to the fourth reference plane  46  across the second and third reference planes  44 ,  45 . Since any intake opening is excluded from the area ranging downstream from the fourth reference plane  46  to the first reference planes  43 , electronic components and/or wiring patterns can be located on the front and back surfaces of the printed circuit board  19  within the area, for example. Electronic components and/or wiring patterns can be located on the printed circuit board  19  at a higher density. It should be noted that a small-sized through via, not shown, can be formed in the printed circuit board  19  around the fan  36 . The via should have a diameter small enough to avoid hindrance to introduction of air into the fan cover  28 . 
   The inventors have examined the effect of the first, second and third partial intake openings  52 ,  53 ,  54 . The inventors have prepared the printed circuit board unit  18  as a specific example of the present invention, as shown in  FIG. 6A . The inventors also prepared various printed circuit board units according to comparative examples. The printed circuit board units were not assembled within the main body  12  during the examination. Various types of intake openings were established in the printed circuit board units of the comparative examples, as shown in  FIGS. 6B to 6L . Air was discharged in the direction of the bold arrows. An air measurement apparatus was set at the discharge opening in the printed circuit board unit under the examination. The measurement apparatus was utilized to measure the maximum volume [m 3 /min] of the discharged air and the maximum static pressure [Pa] of the discharge air during the rotation of the fan. A sound level meter was also set in the vicinity of the printed circuit board unit under the examination. The sound level meter was utilized to measure the loudness [dB] of the rotating fan. 
   As shown in  FIGS. 7A to 7C , the printed circuit board unit  18  according to the Example of the Invention exhibits the maximum volume of the displacement nearly identical to those of the printed circuit board units of the comparative Examples Nos. 4-6. However, the printed circuit board units of the comparative Examples Nos. 4-6 were designed to define the intake opening extending from the first reference plane to the first reference plane across the second to fourth reference planes, namely, all around the rotation axis. The printed circuit board units of the comparative Examples Nos. 4-6 suffer from a smaller space for disposition of electronic components and/or wiring patterns. Additionally, the printed circuit board units of the comparative Examples Nos. 4-6 tend to suffer from a larger noise. The printed circuit board unit  18  of the Invention exhibits a superior maximum volume of the displacement to the comparative Examples Nos. 1-3 and 7-11. Although the comparative Examples Nos. 1-3 and 7-11 were designed to enjoy a larger space for electronic components and/or wiring patterns on the printed circuit board, they cannot enjoy a sufficient maximum volume of the displacement. It has been confirmed that the printed circuit board unit  18  of the Invention ensures a large space for disposition of electronic components and/or wiring patterns on the printed circuit board  19  while the printed circuit board unit  18  serves to improve the cooling efficiency of the fan  36 . 
   As shown in  FIG. 8 , the fan cover  28  may be mounted on a predetermined bottom plate  68  in place of the aforementioned printed circuit board  19  in the printed circuit board unit  18 . The first, second and third partial intake openings  52 ,  53 ,  54  may be defined in the bottom plate  68 . The fan unit  27   a  of the type may be located within a recess  69  formed in the printed circuit board  19 , for example. The fan unit  27   a  may be fixed to the enclosure  66  of the main body  12 , for example. Like reference numerals are attached to components or structures equivalent to those of the aforementioned embodiment. 
     FIG. 9  illustrates the positional relationship between the intake openings  32 ,  33 ,  34  at the ceiling wall  29  of the fan cover  28  and the partial intake openings  52 ,  53 ,  54  at the printed circuit board  19  in the printed circuit board unit  18 . It should be noted that the identical positional relationship may be established between the intake openings  32 ,  33 ,  34  and the partial intake openings  52 ,  53 ,  54  at the bottom plate  62  of the fan unit  27   a.    
   Assume that the intake openings  32 ,  33 ,  34  are projected on the front surface of the printed circuit board  19  in the direction perpendicular to the front surface of the printed circuit board  19 . The intake openings  32 ,  33  are superposed over the partial intake openings  52 ,  53 ,  54 . The intake opening  34  is superposed over the area  49  excluding an intake opening. A small part of the intake opening  34  is also superposed on the partial intake opening  52 . 
   The outer radius of the first, second and third partial openings  52 ,  53 ,  54  may be set at 15 mm approximately, for example, around the rotation axis  35 . The outer radius of the intake openings  32 ,  33 ,  34  may also be set at 15 mm approximately around the rotation axis  35 . The inner radius of the first and second partial intake openings  52 ,  53  may be different from that of the third partial intake opening  54 . The first and second partial intake openings  52 ,  53  may have a radius of 6 mm while the third partial intake opening  54  may have a radius of 9 mm, for example. 
   The aforementioned printed circuit board units  18  and the fan units  27 ,  27   a  may be incorporated not only in a portable electronic apparatus such as the aforementioned notebook personal computer  11  and a personal digital assistance (PDA) but also in a floor model or desktop model of an electronic apparatus.