Patent Publication Number: US-2015062821-A1

Title: Cooling Structure for Electronic Circuit Board, and Electronic Device Using the Same

Description:
TECHNICAL FIELD 
     The present invention relates to cooling structures for electronic circuit boards to be plugged into a motherboard of an electronic device and, in particular, to a cooling structure for an electronic circuit board, and an electronic device using the same employing an ebullient cooling system in which heat transport and heat radiation are performed by a phase-change cycle of vaporization and condensation of a refrigerant. 
     BACKGROUND ART 
     In electronic equipment such as a computer, various types of electronic circuit boards, which are called an expansion card or an expansion board, are plugged into slots provided on a motherboard to extend and enhance its functions. High performance computing (HPC) has been developed in recent years, in which a plurality of graphics processing unit (GPU) boards, each of which includes a GPU of a type of processor, are plugged into slots on a motherboard. 
     With regard to an electronic circuit board on which a high performance processor and the like are mounted, electronic components such as a processor and a memory element generate a large amount of heat. Since the increase in operation temperature causes the decline in the performance of a processor and the like, it is necessary to cool the electronic components. An example of cooling structures for such an electronic circuit board is described in Patent Literature 1. 
     The cooling structure for an electronic circuit board described in Patent Literature 1 includes an augmented heat removal system that includes a fan provided for a GPU on a card, heat sinks for removal of heat from memory chips, and a flow directing device. The fan is a vertical blower with an axis perpendicular to both the heat sinks and the GPU. The flow directing device has a top with an aperture and an outer edge, and a housing for mounting the fan and diverting airflow along the card. 
     The configuration mentioned above enables the air flow provided by the fan and the flow directing device to be drawn in perpendicularly towards the GPU and redirected by the flow directing device towards other components to be cooled, specifically heat sinks, and in turn to cool the plurality of memory chips. It is said that the cooling structure for the electronic circuit board described in Patent Literature 1 provides air flow along various heat generating components to cool the components to or within a specified temperature or temperature range. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     
         
         Japanese Patent Application Laid-open Publication No. 2008-235932 (Paragraphs [0019] to [0027] and FIGS. 3 to 5) 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The cooling structure for the electronic circuit board described in Patent Literature 1 mentioned above requires an additional height to draw cooling air into the fan in addition to physical heights of the electronic components such as a GPU and a memory chip, the fan, and the heat sink in order to cool the electronic circuit board suitably. Accordingly, the cooling structure for the electronic circuit board described in Patent Literature 1 has a problem that the occupied space larger than the cooling structure is required. 
       FIGS. 7A and 7B  illustrate a configuration of a related electronic device using a heat sink as a cooling structure for an electronic circuit board on which a GPU and the like are mounted.  FIG. 7A  is an elevation view of the related electronic device  500  and  FIG. 7B  is a top view of the related electronic device  500 . It is necessary in the related electronic device  500  to attach a heat sink  530  to a whole surface of a slot card board  520  as illustrated in the figures when a heating element  510  generating a large amount of heat, such as a GPU, is mounted. Additionally, because the cooling performance is insufficient by this, there is a need to extend the length of heat radiation fins  532  in the heat sink  530  as illustrated on the right-hand side of  FIG. 8  in order to enlarge an area of the heat radiation fins  532 . The slot card board  520  is plugged into a slot  542  on a motherboard  540  with a connector  522 . A pitch of the slots  542  is equal to 0.8 inches (20.32 mm) in the PCI (peripheral component interconnect) standard. Accordingly, if the length of the heat radiation fins  532  is extended, the heat radiation fins  532  occupy two times as much space as the volume occupied by one of the slot card board  520  on the motherboard  540 . That is to say, there has been a problem that the package density is decreased and the device size is increased in the related electronic device  500  using a heat sink as a cooling structure for electronic circuit boards. 
     Thus, the related cooling structure for electronic circuit boards has a problem that using a heating element with a large amount of heat generation makes an electronic device grow in size. 
     The object of the present invention is to provide a cooling structure for an electronic circuit board, and an electronic device using the same that solve the problem mentioned above that the size of an electronic device using a cooling structure for an electronic circuit board is increased when using a heating element with a large amount of heat generation. 
     Solution to Problem 
     A cooling structure for an electronic circuit board according to an exemplary aspect of the present invention includes an evaporator with an evaporation container storing a refrigerant; a condenser condensing and liquefying a vapor-phase refrigerant vaporized in the evaporator and radiating heat; and a pipe connecting the evaporator to the condenser, wherein the evaporator includes a heat receiving area, on one side of the evaporation container, thermally connecting to a heating element disposed on the electronic circuit board, and a plurality of flow path plates, in an area including the heat receiving area, extending in the direction parallel to the electronic circuit board; and a vapor-liquid interface of the refrigerant is positioned above or at the level of a lower end and below an upper end of the heat receiving area in the vertical direction, in the arrangement condition that the drawing direction of the flow path plates is approximately parallel to the vertical direction. 
     An electronic device using a cooling structure for an electronic circuit board according to an exemplary aspect of the present invention includes a heating element; an electronic circuit board on which the heating element is disposed; and a cooling structure for the electronic circuit board, wherein the cooling structure for the electronic circuit board includes an evaporator with an evaporation container storing a refrigerant; a condenser condensing and liquefying a vapor-phase refrigerant vaporized in the evaporator and radiating heat; and a pipe connecting the evaporator to the condenser, wherein the evaporator includes a heat receiving area, on one side of the evaporation container, thermally connecting to the heating element disposed on the electronic circuit board, and a plurality of flow path plates, in an area including the heat receiving area, extending in the direction parallel to the electronic circuit board; and a vapor-liquid interface of the refrigerant is positioned above or at the level of a lower end and below an upper end of the heat receiving area in the vertical direction, in the arrangement condition that the drawing direction of the flow path plates is approximately parallel to the vertical direction. 
     Advantageous Effects of Invention 
     According to the cooling structure for an electronic circuit board of the present invention, it is possible to avoid the increase in size of an electronic device even when used for a heating element with a large amount of heat generation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a diagram illustrating a configuration of a cooling structure for an electronic circuit board in accordance with the first exemplary embodiment of the present invention and is a partially perspective elevation view. 
         FIG. 1B  is a diagram illustrating the configuration of the cooling structure for the electronic circuit board in accordance with the first exemplary embodiment of the present invention and is a partially perspective bottom view viewed from the direction indicated by arrow B in  FIG. 1A . 
         FIG. 1C  is a diagram illustrating the configuration of the cooling structure for the electronic circuit board in accordance with the first exemplary embodiment of the present invention and is a cross-sectional view taken along the line C-C of  FIG. 1A . 
         FIG. 2  is an elevation view illustrating a configuration of an electronic device using a cooling structure for an electronic circuit board in accordance with the second exemplary embodiment of the present invention. 
         FIG. 3A  is a top view illustrating another configuration of the electronic device using the cooling structure for the electronic circuit board in accordance with the second exemplary embodiment of the present invention. 
         FIG. 3B  is a side view illustrating another configuration of the electronic device using the cooling structure for the electronic circuit board in accordance with the second exemplary embodiment of the present invention. 
         FIG. 4A  is an elevation view illustrating yet another configuration of the electronic device using the cooling structure for the electronic circuit board in accordance with the second exemplary embodiment of the present invention. 
         FIG. 4B  is a side view illustrating yet another configuration of the electronic device using the cooling structure for the electronic circuit board in accordance with the second exemplary embodiment of the present invention. 
         FIG. 5A  is a top view illustrating a configuration of an electronic device using a cooling structure for an electronic circuit board in accordance with the third exemplary embodiment of the present invention. 
         FIG. 5B  is a side view illustrating the configuration of the electronic device using the cooling structure for the electronic circuit board in accordance with the third exemplary embodiment of the present invention. 
         FIG. 6  is a top view illustrating another configuration of the electronic device using the cooling structure for the electronic circuit board in accordance with the third exemplary embodiment of the present invention. 
         FIG. 7A  is an elevation view illustrating a configuration of a related electronic device. 
         FIG. 7B  is a top view illustrating the configuration of the related electronic device. 
         FIG. 8  is a side view illustrating the configuration of the related electronic device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The exemplary embodiments of the present invention will be described with reference to drawings below. 
     The First Exemplary Embodiment 
       FIGS. 1A ,  1 B, and  1 C are diagrams illustrating the configuration of a cooling structure for an electronic circuit board  100  in accordance with the first exemplary embodiment of the present invention.  FIG. 1A  is a partially perspective elevation view,  FIG. 1B  is a partially perspective bottom view viewed from the direction indicated by arrow B in  FIG. 1A , and  FIG. 1C  is a cross-sectional view taken along the line C-C of  FIG. 1A . 
     The cooling structure for an electronic circuit board  100  includes an evaporator  110  with an evaporation container  112  storing a refrigerant  111 , and a condenser  120  condensing and liquefying a vapor-phase refrigerant vaporized in the evaporator  110  and radiating heat. The evaporator  110  and the condenser  120  are connected by a vapor pipe  131  and a liquid pipe  132  as a pipe  130 . The evaporator  110  includes a heat receiving area  113 , on one side of the evaporation container  112 , thermally connecting to a heating element  140  disposed on the electronic circuit board, and a plurality of flow path plates  114 , in the area including the heat receiving area  113 , extending in the direction parallel to the electronic circuit board. 
     The vapor-liquid interface of the refrigerant is positioned above or at the level of the lower end of the heat receiving area  113  and below the upper end of the heat receiving area  113  in the vertical direction, in the arrangement condition that the drawing direction of the flow path plates  114  is approximately parallel to the vertical direction as illustrated in  FIG. 1A . The vapor-liquid interface of the refrigerant means an interface between the refrigerant in liquid state and the refrigerant in vapor state, and is represented by the dotted line on the hatching region in the evaporation container  112  in  FIG. 1A . 
     It is possible to keep the pressure within the evaporator  110  equal to a saturated vapor pressure of the refrigerant constantly by using a low-boiling material as the refrigerant and evacuating the evaporator  110  after having injected the refrigerant into it. It is possible to use as the refrigerant a low-boiling refrigerant such as hydrofluorocarbon and hydrofluoroether which are insulating and inactive materials, for example. As the materials composing the evaporator  110  and the condenser  120 , it is possible to use the metal having an excellent thermal conductive property such as aluminum and copper. It is possible to use for the pipe  130  a pipe made of resin such as rubber whose inner surface is coated with metal, for example. The flow path plate  114  is formed by using the metal having an excellent thermal conductive property such as aluminum and copper, and can have a fin shape composed of a plurality of thin plates as illustrated in  FIGS. 1A and 1B . 
     Next, the operation of the cooling structure for an electronic circuit board  100  in accordance with the present exemplary embodiment will be described in detail. The cooling structure for an electronic circuit board  100  is used disposing a heating element  140  such as a central processing unit (CPU) on the side of the evaporation container  112  composing the evaporator  110 , thermally connected to the evaporator  110 . The heat from the heating element  140  is conducted to the refrigerant  111  through the evaporation container  112 , so that the refrigerant  111  vaporizes. At this time, since the heat from the heating element is drawn by the refrigerant as vaporization heat, the increase in temperature of the heating element is suppressed. 
     The refrigerant vapor evaporated in the evaporator  110  flows into the condenser  120  through the vapor pipe  131 . The refrigerant vapor releases heat in the condenser  120 , condenses and liquefies. As mentioned above, the cooling structure for an electronic circuit board  100  is configured to employ the ebullient cooling system in which heat transport and heat radiation are performed by a cycle of vaporization and condensation of the refrigerant. 
     The cooling structure for an electronic circuit board  100  in accordance with the present exemplary embodiment is configured to include a plurality of flow path plates  114  extending in the direction parallel to the electronic circuit board in a region including the heat receiving area  113  of the evaporation container  112 . Flow paths of the refrigerant are formed between the flow path plates  114 , and a vapor-liquid two-phase flow of the refrigerant arises in the heat receiving area below the vapor-liquid interface of the refrigerant in the vertical direction. Here, the vapor-liquid two-phase flow is defined as flowing with two phases of a vapor phase and a liquid phase being mixed. Since the vapor-liquid two-phase flow of the refrigerant rises with bubbles of the refrigerant taking in the liquid-phase refrigerant around them, the liquid-phase refrigerant reaches the heat receiving area located above the vapor-liquid interface of the refrigerant in the vertical direction. Accordingly, it is possible to cool the entire heat receiving area  113  by means of the phase change of the refrigerant even though the vapor-liquid interface of the refrigerant is located below the upper end of the heat receiving area  113  in the vertical direction. 
     A distance between the flow path plates  114  is determined by the condition under which a vapor-liquid two-phase flow arises. Specifically, the distance can be determined based on physical property values of the refrigerant such as surface tension, molecular weight, and kinetic viscosity of the refrigerant. When hydrofluorocarbon, hydrofluoroether, or the like mentioned above is used as the refrigerant, the distance between the flow path plates  114  can preferably take a range of values from approximately 0.5 mm to approximately 2 mm. 
     Since it is possible to lower the vapor-liquid interface of the refrigerant in the cooling structure for an electronic circuit board  100  in accordance with the present exemplary embodiment as mentioned above, it is possible to enlarge the space occupied by the vapor-phase refrigerant without increasing the volume of the evaporation container  112 . As a result, even when used for a heating element with a large amount of heat generation, the elevation in the internal pressure of the vapor-phase refrigerant is suppressed, and it does not result in deterioration in the cooling performance due to an elevation of the boiling point of the refrigerant. That is to say, according to the cooling structure for an electronic circuit board  100  of the present exemplary embodiment, it is possible to avoid the increase in size of an electronic device even when used for a heating element with a large amount of heat generation. 
     It is acceptable for the condenser  120  to be configured to include a plurality of condensation flow paths  121  extending in the direction approximately parallel to the drawing direction of the flow path plates  114 , and heat radiation plates (heat radiation fins)  122  between the condensation flow paths  121 . Since the plurality of condensation flow paths  121  makes it possible to reduce the flow resistance of the refrigerant vapor (vapor-phase refrigerant) in the condenser  120 , it is possible to suppress the elevation in the internal pressure of the vapor-phase refrigerant. Since the condensation heat-transfer efficiency is improved because of increasing the condensation area, it is possible to improve the cooling performance. 
     The condenser  120  can be configured in which its lower end in the vertical direction is located on roughly the same level as the lower end in the vertical direction of the evaporator  110  in the arrangement state that the drawing direction of the flow path plates  114  is nearly parallel to the vertical direction as illustrated in  FIG. 1A . That is to say, it is possible to dispose the condenser  120  on nearly the same level as the evaporator  110 . This is because according to the cooling structure for an electronic circuit  100  of the present exemplary embodiment, it is unnecessary to fill the entirety of the heat receiving area  113  with liquid-phase refrigerant and it is possible to lower the vapor-liquid interface of the refrigerant in the vertical direction. This makes it possible to further miniaturize an electronic device using the cooling structure for an electronic circuit board  100 . 
     The Second Exemplary Embodiment 
     Next, the second exemplary embodiment of the present invention will be described.  FIG. 2  is an elevation view illustrating a configuration of an electronic device  200  using a cooling structure for an electronic circuit board in accordance with the second exemplary embodiment of the present invention. The electronic device  200  using the cooling structure for an electronic circuit board includes a heating element  140 , an electronic circuit board  210  on which the heating element  140  is disposed, and the cooling structure for an electronic circuit board  100  including the evaporator  110  and the condenser  120 . 
     It is possible to use, as the heating element  140 , an LSI (large scale integration) element, especially a micro processing unit (MPU), a graphics processing unit (GPU) or the like which generates a large amount of heat. It is possible to use, as the electronic circuit board  210 , an expansion card, an expansion board or the like which is plugged into a slot set on a motherboard with the surface of the board parallel to the vertical direction. Specific examples include a PCI card, a slot card, and a GPU board, for example. The configuration of the cooling structure for an electronic circuit board  100  is the same as that according to the first exemplary embodiment, and therefore, the description of the configuration will be omitted. 
     As illustrated in  FIG. 2 , the evaporator  110  composing the cooling structure for an electronic circuit board  100  is disposed on the electronic circuit board  210  sandwiching the heating element  140 . A chassis  220  housing the electronic circuit board  210  and the cooling structure for an electronic circuit board  100  is included. The condenser  120  composing the cooling structure for an electronic circuit board  100  and the electronic circuit board  210  can be configured to be connected to the chassis  220 . This configuration makes it possible to transport the heat generation from the heating element  140  to the condenser  120  fixed on the chassis  220  outside the electronic circuit board  210  by phase-change cooling. Accordingly, since the condenser  120  can be configured without being limited by the size, the arrangement and the like of the electronic circuit board  210 , it is possible to improve the cooling performance. 
       FIGS. 3A and 3B  illustrate configurations of an electronic device  250  including a plurality of electronic circuit boards  210  and using the cooling structure for an electronic circuit board.  FIG. 3A  is a top view and  FIG. 3B  is a side view. The electronic device  250  using the cooling structure for an electronic circuit board is configured to include a motherboard  260  on which a plurality of electronic circuit boards  210  are mounted at a predetermined alignment interval (slot pitch). The plurality of electronic circuit boards  210  are disposed on the motherboard  260  in the state that the drawing direction of the flow path plates  114  composing the evaporator  110  is nearly parallel to the vertical direction. That is to say, the electronic circuit board  210  is plugged with its principal surface parallel to the vertical direction. Specifically, for example, the electronic circuit board  210  is plugged through a slot  262  provided for the motherboard  260 . The electronic circuit board  210  is fixed to a boss provided for the chassis  220  by using a screw or the like. 
     By the configuration described above, the condenser  120  composing the cooling structure for an electronic circuit board  100  can be configured so that the width in the direction perpendicular to the electronic circuit board  210  may be extended to a width nearly equal to the alignment interval (slot pitch). In addition, it is possible to extend the heat radiation plate  122  between the condensation flow paths  121  composing the condenser  120  to a width nearly equal to the alignment interval (slot pitch). Since a crossflow heat exchanger is configured by setting the heat radiation plates  122 , the heat radiation capability can be improved as compared with a parallel-flow heat sink using the sensible heat. 
     As illustrated in  FIGS. 4A and 4B , it is also acceptable for the condenser  120  to be configured so that the upper end of the condenser  120  in the vertical direction may be above the level of the upper end of the electronic circuit board  210  in the vertical direction, in the arrangement state that the drawing direction of the flow path plates  114  is nearly parallel to the vertical direction. This configuration makes it possible to increase the inner volume of the condenser  120  and to further improve the heat radiation capability. 
     As described above, according to the electronic device using the cooling structure for an electronic circuit board of the present exemplary embodiment, by adopting the cooling structure for an electronic circuit board  100  according to the present exemplary embodiment, it is possible to avoid the increase in size of the electronic device even when used for a heating element with a large amount of heat generation. In addition, since the condenser  120  can be configured without being limited by the size, the arrangement and the like of the electronic circuit board  210 , it is possible to improve the cooling performance. 
     The Third Exemplary Embodiment 
     Next, the third exemplary embodiment of the present invention will be described.  FIGS. 5A and 5B  illustrate a configuration of an electronic device  300  using the cooling structure for an electronic circuit board according to the third exemplary embodiment of the present invention, and  FIG. 5A  is a top view and  FIG. 5B  is a side view. The electronic device  300  using the cooling structure for an electronic circuit board is configured to include a motherboard  260  on which a plurality of electronic circuit boards  210  are mounted at a predetermined alignment interval (slot pitch). The plurality of electronic circuit boards  210  are disposed on the motherboard  260  in the state that the drawing direction of the flow path plates  114  composing the evaporator  110  is nearly parallel to the vertical direction. That is to say, the electronic circuit board  210  is plugged with its principal surface parallel to the vertical direction. 
     The electronic device  300  using the cooling structure for an electronic circuit board includes a heating element  140 , an electronic circuit board  210  on which the heating element  140  is disposed, and the cooling structure for an electronic circuit board  100  including the evaporator  110  and a condenser  320 . The configuration and the operation of the cooling structure for an electronic circuit board  100  are the same as those according to the first exemplary embodiment except the configuration of the condenser  320  described below, and therefore, the description of the same part will be omitted. 
     As illustrated in  FIGS. 5A and 5B , the electronic device  300  using the cooling structure for an electronic circuit board is configured so that the width of the condenser  320  in the direction perpendicular to the electronic circuit board  210  may be larger than the alignment interval on the motherboard  260 . That is to say, the electronic device  300  using the cooling structure for an electronic circuit board is configured to connect a plurality of electronic circuit boards  210  such as slot cards to a single condenser  320  collectively. The vapor pipes  131  and the liquid pipes  132  as the pipe connect more than one evaporator  110  to one of the condenser  320 . 
     Since the configuration described above makes it possible to increase the volume of the condenser  320  even when the electronic circuit boards  210  are disposed on the motherboard  260  at a unit of alignment interval, it is possible to improve the cooling performance of the cooling structure for an electronic circuit board  100 . That is to say, since the interference between the adjacent condensers  320  can be reduced and accordingly the heat radiation area of the condenser  320  can be increased, it is possible to further improve the cooling performance. 
     The electronic device  300  using the cooling structure for an electronic circuit board is configured to connect more than one evaporator  110  to one of the condenser  320  through the vapor pipes  131  and the liquid pipes  132 . The configuration is not limited to this, however, as illustrated in  FIG. 6 , it can be also configured to dispose the condensers  320  in multistage and for the pipe  130  to connect the evaporator  110  to the condenser  320  one-on-one. That is to say, an electronic device  350  using the cooling structure for an electronic circuit board illustrated in  FIG. 6  includes a plurality of evaporators  110  and a plurality of condensers  320  including at least a first condenser  321  and a second condenser  322 . The second condenser  322  is disposed to be an extension of the straight line connecting one of the evaporators  110  to the first condenser  321 . In other words, the first condenser  321  and the second condenser  322  are disposed in multistage in the direction of a cooling air flow. 
     Since this also makes it possible to be configured so that the condenser  320  may have a width larger than the alignment interval on the motherboard  260 , it is possible to increase the volume of the condenser  320 . Therefore, since it is possible to suppress the elevation in the internal pressure of the cooling structure for an electronic circuit board even when the electronic circuit boards  210  are disposed on the motherboard  260  at a unit of alignment interval, it is possible to improve the cooling performance. 
     As described above, according to the electronic device using the cooling structure for an electronic circuit board of the present exemplary embodiment, by adopting the cooling structure for an electronic circuit board  100  according to the present exemplary embodiment, it is possible to avoid the increase in size of the electronic device even when used for a heating element with a large amount of heat generation. In addition, since the condenser  320  can be configured without being limited by the size, the arrangement and the like of the electronic circuit board  210 , it is possible to improve the cooling performance. 
     The present invention is not limited to the aforementioned exemplary embodiments. Various modifications can be made therein within the scope of the present invention as defined by the claims, and obviously, such modifications are included in the scope of the present invention. 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-066078, filed on Mar. 22, 2012, the disclosure of which is incorporated herein in its entirety by reference. 
     REFERENCE SIGNS LIST 
     
         
           100  Cooling structure for an electronic circuit board 
           110  Evaporator 
           111  Refrigerant 
           112  Evaporation container 
           113  Heat receiving area 
           114  Flow path plate 
           120 ,  320  Condenser 
           121  Condensation flow path 
           122  Heat radiation plate 
           130  Pipe 
           131  Vapor pipe 
           132  Fluid pipe 
           140  Heating element 
           200 ,  250 ,  300 ,  350  Electronic device using cooling structure for an electronic circuit board 
           210  Electronic circuit board 
           220  Chassis 
           260  Motherboard 
           262  Slot 
           321  First condenser 
           322  Second condenser 
           500  Electronic device 
           510  Heating element 
           520  Slot card board 
           522  Connector 
           530  Heat sink 
           532  Heat radiation fin 
           540  Motherboard 
           542  Slot