Abstract:
The computer having a module board with semiconductor elements mounted on both sides thereof, a motherboard on which a plurality of units of the module board are mounted, and a rack cabinet on which a plurality of units of the motherboard are mounted includes a thermo-siphon that is thermally connected to the semiconductor elements mounted on one side of the module board, a metal plate that is thermally connected to the semiconductor elements mounted on one side of the module board, a thermally-conductive member that transfers the heat of the metal plate to the thermo-siphon in a situation where the heat of the semiconductor elements mounted on one side of the module board is transferred to the metal plate, and a pressing member that presses the thermo-siphon and the metal plate against the semiconductor elements mounted on the module board.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a computer provided with a cooling system. 
       BACKGROUND ART 
       [0002]    IT devices are configured so that several CPUs, memories, and control elements are mounted on a circuit board. A backplane on the rear side of a rack supplies electrical power to the circuit board and exchanges signals with the circuit board. 
         [0003]    In recent years, high-density packaging of CPUs and memories is essential in order to process an enormous amount of data, thereby providing an improved capability. Therefore, one-hundred or more module boards, which are prepared by mounting CPUs, memories, and control elements on both sides of the module boards, are mounted on a large-size motherboard. As such being the case, the module boards have to be unmounted and remounted whenever they need to be accessed for the purpose of maintaining and servicing the CPUs and memories. 
         [0004]    As a prior-art technology concerning the above-mentioned module boards, a heat dissipation structure and its manufacturing method are disclosed in Japanese Patent Application Laid-Open No. 2009-16605 (PTL 1). This heat dissipation structure makes it possible to eliminate the variation of a heat dissipation surface, achieve heat dissipation with high efficiency, reduce the size and weight of a device, and provide increased ease of device assembly. 
         [0005]    Further, a prior-art technology disclosed in Japanese Patent Application Laid-Open No. 2005-223099 (PTL 2) provides a first electronic component heat transfer cover and a second electronic component heat transfer cover. The first electronic component heat transfer cover, which is shaped like an inverted dish, covers all electronic components mounted on the upside of an electronic circuit board. The second electronic component heat transfer cover, which is also shaped like an inverted dish, covers all electronic components mounted on the underside of the electronic circuit board. 
         [0006]    Furthermore, a prior-art technology disclosed in Japanese Patent Application Laid-Open No. 2008-010768 (PTL 3) provides a circuit board that is sandwiched between a first heat sink and a second heat sink. The first heat sink is equipped with a heat pipe and attached to the upside of the circuit board. The second heat sink is attached to the underside of the circuit board. 
         [0007]    Moreover, a prior-art technology disclosed in Japanese Patent Application Laid-Open No. 2010-080507 (PTL 4) provides a method of thermally connecting a CPU, which is a major heat source mounted on a wiring board, to one outer surface of a thermo-siphon, attaching a plurality of heat pipes to the other outer surface of the thermo-siphon, and establishing a thermal connection by attaching one end of each heat pipe to the upside of an element generating a small amount of heat. 
         [0008]    Besides, a prior-art technology disclosed in Japanese Patent Application Laid-Open No. Hei 08 (1996)-125371 (PTL 5) provides a method of cooling heat-generating components through a metal core incorporated in an inner layer of a printed circuit board, disposing a retaining member between the printed circuit board and a guide section, thermally connecting a cooling plate to the guide section in order to transfer heat to a fluid, and securing the printed circuit board to the guide section to thermally connect the metal core in the printed circuit board to the guide section. 
       CITATION LIST 
     Patent Literature 
       [0009]    PTL 1: Japanese Patent Application Laid-Open No. 2009-16605 
         [0010]    PTL 2: Japanese Patent Application Laid-Open No. 2005-223099 
         [0011]    PTL 3: Japanese Patent Application Laid-Open No. 2008-010768 
         [0012]    PTL 4: Japanese Patent Application Laid-Open No. 2010-080507 
         [0013]    PTL 5: Japanese Patent Application Laid-Open No. Hei 08 (1996)-125371 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0014]    As described earlier, IT devices are configured so that several CPUs, memories, and control elements are mounted on a circuit board. A backplane on the rear side of a rack supplies electrical power to the circuit board and exchanges signals with the circuit board. 
         [0015]    Meanwhile, as described earlier, module boards prepared by mounting CPUs, memories, and control elements on both sides are frequently used in recent years in order to process an enormous amount of data. One-hundred or more module boards are mounted on a large-size motherboard. As such being the case, the module boards have to be unmounted and remounted whenever they need to be accessed for maintenance and service purposes. 
         [0016]    In other words, it is necessary to provide a cooling structure that is capable of transferring the heat of the double-sided module boards mounted on the motherboard to the outside, such as a remote location, and allowing the module boards to be easily unmounted and remounted. 
         [0017]    However, when the prior-art technologies described in PTLs 1 to 5 are used in a situation where air cooling is provided, a large-size blower fan is required due to a narrow space. Further, when the double-sided module boards are used, the semiconductor elements mounted on the underside cannot be cooled by the theme-siphon. Besides, as the thermo-siphon is screwed down to the CPUs, the module boards cannot be unmounted and remounted. Solutions to these problems are not given in PTLs 1 to 5. 
         [0018]    An object of the present invention is to provide a computer provided with a power-saving, low-noise cooling system that transfers the heat of semiconductor elements on the underside of a module board to a thermo-siphon in order to cool the entire module board. 
       Solution to Problem 
       [0019]    In order to achieve the above object, the present invention provides a computer that has a module board with semiconductor elements mounted on both sides thereof, a motherboard on which a plurality of units of the module board are mounted, and a rack cabinet on which a plurality of units of the motherboard are mounted. The computer includes a thermo-siphon, a metal plate, a thermally-conductive member, and a pressing member. The thermo-siphon is thermally connected to the semiconductor elements mounted on one side of the module board. The metal plate is thermally connected to the semiconductor elements mounted on one side of the module board. The thermally-conductive member transfers the heat of the metal plate to the thermo-siphon in a situation where the heat of the semiconductor elements mounted on one side of the module board is transferred to the metal plate. The pressing member presses the thermo-siphon and the metal plate against the semiconductor elements mounted on the module board. 
         [0020]    In order to achieve the above object, the present invention is preferably configured so that the pressing member is formed of a screw that penetrates through the thermo-siphon and brings a protrusion of the metal plate into contact with the surface of the thermo-siphon. 
         [0021]    In order to achieve the above object, the present invention is preferably configured so that the pressing member is formed of a clip that holds the thermo-siphon and the metal plate together. 
         [0022]    In order to achieve the above object, the present invention is preferably configured so that the clip is formed of an elastic metal member and shaped like a U-shaped hair pin. 
         [0023]    In order to achieve the above object, the present invention is preferably configured so that the pressing member is formed of a leaf spring disposed between the metal plate and the motherboard. 
         [0024]    In order to achieve the above object, the present invention is preferably configured so that the leaf spring is formed of an elastic metal member and provided with a flat surface that comes into contact with the metal plate. 
       Advantageous Effects of Invention 
       [0025]    The present invention makes it possible to provide a computer provided with a power-saving, low-noise cooling system that transfers the heat of semiconductor elements on the underside of a module board to a thermo-siphon in order to cool the entire module board. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0026]      FIG. 1  illustrates how a CPU board according to an embodiment of the present invention is implemented. 
           [0027]      FIG. 2  is a perspective view illustrating how a motherboard according to an embodiment of the present invention is implemented. 
           [0028]      FIG. 3  is a partial perspective view illustrating a rack for a computer system according to an embodiment of the present invention. 
           [0029]      FIG. 4  is a perspective view illustrating the rack for the computer system according to an embodiment of the present invention. 
           [0030]      FIG. 5  is a front view illustrating a section around the motherboard before the insertion of the CPU board according to a first embodiment of the present invention. 
           [0031]      FIG. 6  is a front view illustrating the section around the motherboard after the insertion of the CPU board according to the first embodiment. 
           [0032]      FIG. 7  is a front view illustrating the section around the motherboard after the mounting of the CPU board according to the first embodiment. 
           [0033]      FIG. 8  is a front view illustrating the section around the motherboard after the insertion of the CPU board according to a second embodiment of the present invention. 
           [0034]      FIG. 9  is a front view illustrating the section around the motherboard after the mounting of the CPU board according to a third embodiment of the present invention. 
           [0035]      FIG. 10  includes a front view illustrating the section around the motherboard after the insertion of the CPU board according to the third embodiment and a perspective view illustrating a leaf spring. 
           [0036]      FIG. 11  is a front view illustrating the section around the motherboard after the mounting of the CPU board according to the third embodiment. 
           [0037]      FIG. 12  is a top view illustrating the section around the motherboard after the mounting of the CPU board according to the first, second, and third embodiments. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0038]    Embodiments of the present invention will now be described with reference to the accompanying drawings. 
       First Embodiment 
       [0039]      FIG. 1  shows the shape of a CPU board.  FIG. 1(   a ) is a perspective view of the upside of the CPU board.  FIG. 1(   b ) is a perspective view of the underside of the CPU board.  FIG. 1(   c ) is a cross-sectional view taken along line A-A of  FIG. 1(   a ). In this document, a module board on which at least a CPU is mounted is referred to as the CPU board. 
         [0040]    Referring to  FIG. 1(   a ), a CPU  2 , memories  3 , and a controller element  4  are mounted on the upside  5  of the CPU board  1 . 
         [0041]    Referring to  FIG. 1(   b ), the memories  3  are exposed to view from the underside  6  of the CPU board  1 . The reason is that the memories  3  are mounted on both the upside  5  and the underside  6  of the CPU board  1  as shown in  FIG. 1(   c ). 
         [0042]      FIG. 2  is a perspective view illustrating a motherboard on which a large number of units of the CPU board described with reference to  FIG. 1  are mounted. 
         [0043]    Referring to  FIG. 2 , a large number of units of an optical module  10  and a large number of units of the CPU board  10  are mounted on the motherboard  7 . The motherboard  7  can be inserted in an insertion direction  11  from the front end  12  and extracted. Thus, the rear end  8  of the motherboard  7  is provided with an optical connector  14 , a signal connector  9 , and a power connector  13  and is to be connected to another motherboard. 
         [0044]    The motherboard  7  is to be inserted in the insertion direction  11  from the front end  12 . The CPU board  1  can be accessed for maintenance when the front end  12  of the motherboard  7  is extracted. 
         [0045]      FIG. 3  is a partial top perspective view illustrating how the motherboard  7  described with reference to  FIG. 2  is mounted on a rack  19 . 
         [0046]    Referring to  FIG. 3 , a power supply unit  16  is mounted on both sides of the rack  19  for power feeding purposes. A thermo-siphon  17  is mounted on the motherboard  7 . A thermal highway  18  is mounted in the power supply unit  16  to provide thermal transport by means of vaporization heat. The thermo-siphon  17  is capable of collectively cooling four units of the CPU board  1 . In other words, one unit of the thermo-siphon  17  covers four units of the CPU board  1  while maintaining thermal contact with them. As eight units of the thermo-siphon  17  are disclosed in the present embodiment, there are a total of 32 units of the CPU board  1 . 
         [0047]    One unit of the thermal highway  18  is extended to cover the width of two units of the thermo-siphon  17  in order to provide thermal transport for the two units of the thermo-siphon  17 . In the present embodiment, thermal transport is provided by using one unit of the thermo-siphon  17  for four units of the CPU board  1  and by using one unit of the thermal highway  18  for two units of the thermo-siphon  17 . However, the number of units may vary with an employed structure. In  FIG. 3 , the reference sign  12  denotes the front end. 
         [0048]      FIG. 4  is a side perspective view illustrating the rack  19  described with reference to  FIG. 3 . 
         [0049]    Referring to  FIG. 4 , an infinite number of units of the motherboard  7  are vertically mounted on the rack  19 . A power supply busbar  30  is disposed on the rear end  8  of the rack  19  in order to efficiently feed electrical power to each motherboard  7 . No structure is mounted on the front end  12  so as to facilitate the unmounting and remounting of each motherboard  7 . A heat exchanger  20  is disposed on the top of the rack  19  and thermally connected to the thermal highway  18  mounted on a lateral surface of the rack  19 . 
         [0050]    The above-mentioned thermal connection is made, for example, by vapor on the side toward the thermal highway  18  and by the single liquid-phase of the heat exchanger  20  on the top. In  FIG. 4 , the reference sign  12  denotes the front end. 
         [0051]      FIG. 5  is a front view illustrating a section around the motherboard before the insertion of the CPU board. 
         [0052]    Referring to  FIG. 5 , a flat heat pipe or metal plate  23  (hereinafter referred to as the metal plate  23 ) is mounted on the top of the motherboard  7 . The thermo-siphon  17  is mounted above the metal plate  23  with a space  23   b  provided in-between. A thermally-conductive sheet  31  is disposed on opposing surfaces of the metal plate  23  and thermo-siphon  17  and on protrusions  23   a  of the metal plate  23 . 
         [0053]    The vertical distance between the motherboard  7  and the thermo-siphon  17  is fixed. The metal plate  23  moves between the motherboard  7  and the thermo-siphon  17 . 
         [0054]      FIG. 6  is a front view illustrating the section around the motherboard after the insertion of the CPU board. 
         [0055]    Referring to  FIG. 6 , screws  25  are attached to the thermo-siphon  17 . The screws  25  are positioned to oppose the protrusions  23   a , which protrude upward from the metal plate  23  below the thermo-siphon  17 . The thermally-conductive sheet  31  described with reference to  FIG. 5  is disposed in contact with the upside or underside of the CPU  2 , memories  3 , and controller element  4  (not shown) mounted on the CPU board  1 . 
         [0056]    More specifically, first of all, the metal plate  23  is disposed in the space  23   b  between the motherboard  7  and the thermo-siphon  17  as shown in  FIG. 6 . The metal plate  23  has the protrusions  23   a , which form the space  23   b  having a predetermined height. The CPU board  1  is then inserted into the space  23   b . The screws  25  fasten the protrusions  23   a  to the thermo-siphon  17 . 
         [0057]    Therefore, when the screws  25  are tightened, the protrusions  23   a  of the metal plate  23  become attracted to the thermo-siphon  17 , and the CPU  2  and memories  3  on the upside of the CPU board  1  come into thermal contact with the thermo-siphon  17 . Meanwhile, the memories  3  on the underside of the CPU board  1  come into thermal contact with the metal plate  23  through the thermally-conductive sheet  31 . 
         [0058]      FIG. 7  is a front view illustrating the section around the motherboard after the mounting of the CPU board  1  in the first embodiment. 
         [0059]    Referring to  FIG. 7 , tightening the screws  25  moves the metal plate  23  from the motherboard  7  toward the thermo-siphon  17 . Through the thermally-conductive sheet  31  attached to the thermo-siphon  17  and the thermally-conductive sheet  31  attached to the metal plate  23 , the upper surface (upside) of the CPU board  1  is thermally joined to the thermo-siphon  17  and the lower surface (underside) of the CPU board  1  is thermally joined to the metal plate  23 . Further, the protrusions  23   a  of the metal plate  23  thermally join the metal plate  23  to the thermo-siphon  17 . 
         [0060]    As is obvious from the above, the heat of the semiconductor elements (CPU  1 , memories  2 , and controller element  4 ) on the upside of the CPU board  1  can be thermally transported to the thermo-siphon  17 . Further, the heat of the semiconductor elements (memories  2 ) on the underside of the CPU board  1  can be thermally transported from the metal plate  23  to the thermo-siphon  17  through the protrusions  23   a.    
         [0061]    According to the present embodiment, the heat of the memories  3  mounted on the underside of the CPU board  1  can be transferred from the metal plate  23  to the thermo-siphon  17  through the protrusions  23   a  as described above. Therefore, the memories  3  can be efficiently cooled while a simple structure is employed. 
         [0062]    When the CPU board  1  is to be replaced or extracted for maintenance purposes, loosening the screws  25  moves the metal plate  23  downward to enlarge the space  23   b . When the space  23   b  is enlarged, the CPU board  1  can be extracted with ease. 
       Second Embodiment 
       [0063]      FIG. 8(   a ) is a front view of the section around the motherboard according to a second embodiment of the present invention.  FIG. 8(   b ) is a side view of a clip. 
         [0064]    Referring to  FIG. 8(   a ), the second embodiment is configured so that the clip  26  is disposed to thermally connect the thermo-siphon  17  to the metal plate  23 . As shown in  FIG. 8(   b ), the clip  26  is shaped like a U-shaped hair pin and used to hold the thermo-siphon  17  and the metal plate  23  together. The CPU board  1 , which is sandwiched between the thermo-siphon  17  and the metal plate  23 , is then pressurized. 
         [0065]    The thermally-conductive sheet  31  is attached to the surface of the thermo-siphon  17  that comes into contact with the semiconductor elements (CPU  1 , memories  2 , controller element  4 ) on the upside of the CPU board  1 . The thermally-conductive sheet  31  is also attached to the surface of the metal plate  23  that comes into contact with the semiconductor elements (memories  2 ) on the underside of the CPU board  1 . 
         [0066]      FIG. 9  is a front view illustrating the section around the motherboard after the mounting of the CPU board according to the second embodiment. 
         [0067]    Referring to  FIG. 9 , inserting the clip  26  in a horizontal direction moves the metal plate  23  from the motherboard  7  toward the thermo-siphon  17 . As is the case with  FIG. 7 , the present embodiment is configured so that, through the thermally-conductive sheet  31 , the thermo-siphon  17  and the flat heat pipe or metal plate  23  thermally join the upper surface (upside) of the CPU board  1  to the thermo-siphon  17  and thermally join the lower surface (underside) of the CPU board  1  to the flat heat pipe or metal plate  23 . Further, the protrusions of the flat heat pipe or metal plate  23  thermally join the flat heat pipe or metal plate  23  to the thermo-siphon  17 . 
         [0068]    As is obvious from the above, the heat of the semiconductor elements (CPU  1 , memories  2 , and controller element  4 ) on the upside of the CPU board  1  can be thermally transported to the thermo-siphon  17 . Further, the heat of the semiconductor elements (memories  2 ) on the underside of the CPU board  1  can be thermally transported to the thermo-siphon  17  through the flat heat pipe or metal plate  23 . 
         [0069]    According to the present embodiment, the heat of the memories  3  can be transferred from the metal plate  23  to the clip  26  and then transferred from the clip  26  to the thermo-siphon  17  as described above. Therefore, the heat of the memories  3  can be efficiently dissipated. Further, the present embodiment is configured so that the clip  26  provides the thermal connection between the thermo-siphon  17  and the metal plate  23 . This not only makes it extremely easy to attach and detach the clip  26 , but also permits the use of a low-cost configuration. 
         [0070]    In the present embodiment, the clip  26  is U-shaped. However, the present invention is not limited to the use of a U-shaped clip. The clip  26  may alternatively be in horizontal U shape. 
       Third Embodiment 
       [0071]      FIG. 10(   a ) is a front view illustrating the section around the motherboard according to a third embodiment of the present invention.  FIG. 10(   b ) shows the shape of a leaf spring. 
         [0072]    Referring to  FIG. 10(   a ), the third embodiment is configured so that the leaf spring  27  is inserted between the metal plate  23  and the motherboard  7 . The leaf spring  27  is disposed on the entire surface of the metal plate  23  or on a portion corresponding to the protrusions  23   a  of the metal plate  23 . Further, as is the case with  FIG. 6 , the thermally-conductive sheet  31  described with reference to  FIG. 5  is disposed to face the upside or underside of the CPU  2 , memories  3 , and controller element  4  mounted on the CPU board  1 . 
         [0073]    As shown in  FIG. 10(   b ), the leaf spring is prepared by bending an elastic metal plate into the shape of a mountain. As the flat metal plate  23  needs to be pushed upward in the present embodiment, the leaf spring  27  has a flat portion  27   a  that comes into planar contact with the metal plate  23 . As the leaf spring  27  is compressed when it is inserted between the metal plate  23  and the motherboard  7 , the metal plate  23  is constantly pushed upward. 
         [0074]    The shape of the leaf spring  27  is not limited to the one shown in  FIG. 10(   b ). The leaf spring  27  may be of any shape as far as it pushes up the metal plate  23 . 
         [0075]      FIG. 11  is a front view illustrating the section around the motherboard after the mounting of the CPU board according to the third embodiment. 
         [0076]    Referring to  FIG. 11 , when the metal plate  23  is pushed up from the motherboard  7  toward the thermo-siphon  17  due to the elasticity of the leaf spring  27 , the protrusions  23   a  come into contact with the thermo-siphon  17 . The thermally-conductive sheet  31  attached to the thermo-siphon  17  and the thermally-conductive sheet  31  attached to the metal plate  23  thermally join the upper surface (upside) of the CPU board  1  to the thermo-siphon  17  and thermally join the lower surface (underside) of the CPU board  1  to the metal plate  23 . Further, the protrusions  23   a  of the metal plate  23  thermally join the metal plate  23  to the thermo-siphon  17 . 
         [0077]    As is obvious from the above, the heat of the semiconductor elements (CPU  1 , memories  2 , and controller element  4 ) on the upside of the CPU board  1  can be thermally transported to the thermo-siphon  17 . Further, the heat of the semiconductor elements (memories  2 ) on the underside of the CPU board  1  can be thermally transported to the thermo-siphon  17  through the flat heat pipe or metal plate  23 . 
         [0078]    According to the present embodiment, the leaf spring  27  pushes up the metal plate  23 . Therefore, the protrusions  23   a  of the metal plate  23  come into contact with the thermo-siphon  17  to dissipate the heat of the memories  3 . 
         [0079]      FIG. 12  is a top view illustrating the section around the motherboard after the mounting of the CPU board according to the first, second, and third embodiments. 
         [0080]    Referring to  FIG. 12 , which does not depict the screws  25 , clip  26 , and leaf spring  27  in the first to third embodiments, a thermal connector  29  is a joint between thermo-siphon  17  and the protrusions  23   a  of the metal plate  23 . The signal connector  9  and the power connector  13  provide a signal or power connection between the CPU board  1  and the motherboard. The signal connector  9 , the power connector  13 , and the thermal connector  29  are oriented so that they do not interfere with each other in the insertion direction  11  of the CPU board  1 . Thus, the CPU board  1  can be unmounted and remounted with ease. 
         [0081]    When the above-described configuration is employed, a cooling system that facilitates the unmounting and remounting of a module board can be provided for a computer that is used, for instance, in a server, a storage device, or a network device and formed of a large-size circuit board on which the module board having a CPU, memories, and controller element for processing is mounted. 
         [0082]    According to the present invention, which has been described above, the cooling system and the computer provided with the cooling system do not have a cooling fan. This makes it possible to provide increased energy savings and reduce fan-induced noise. Further, the heat of the semiconductor elements on the underside of the module board can be transferred to the thermo-siphon in order to cool the entire module board. Furthermore, the present invention provides the computer that makes it easy to unmount and remount the module board because it can be unmounted and remounted by removing or reinstalling the screws, the clip, or the leaf spring. 
         [0083]    Moreover, the present invention facilitates the unmounting and remounting of the module board included in a computer that is used, for instance, in a server, a storage device, or a network device and formed of a large-size circuit board on which the module board having a CPU, memories, and controller element for processing is mounted. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  . . . CPU board, 
               2  . . . CPU, 
               3  . . . memory, 
               4  . . . controller element, 
               5  . . . upside, 
               6  . . . underside, 
               7  . . . motherboard, 
               8  . . . rear end, 
               9  . . . signal connector, 
               10  . . . optical module, 
               11  . . . insertion direction, 
               12  . . . front end, 
               13  . . . power connector, 
               14  . . . optical connector, 
               16  . . . power supply unit, 
               17  . . . thermo-siphon, 
               18  . . . thermal highway, 
               19  . . . rack, 
               20  . . . heat exchanger, 
               23  . . . metal plate, 
               23   a  . . . protrusion, 
               23   b  . . . space, 
               25  . . . screw, 
               26  . . . clip, 
               27  . . . leaf spring, 
               27   a  . . . flat portion, 
               29  . . . thermal connector, 
               30  . . . power supply busbar, 
               31  . . . thermally-conductive sheet