Patent Publication Number: US-2011056650-A1

Title: Heat sink

Description:
This application is based upon and claims the benefit of priority from Japanese patent application No. 2009-204655, filed on Sep. 4, 2009, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heat sink for radiating heat generated by an electronic part or the like. 
     2. Description of the Related Art 
     One of electronic parts used for an information device and the like is an LSI (Large Scale Integration). In recent years, there has been a preference for LSIs that feature enhanced functions and performance. For this reason, a highly integrated LSI having a larger number of elements such as transistors, resistors, and capacitors than a conventional LSI has been manufactured. In the LSI that is more highly integrated than the conventional LSI, electric power consumed when the LSI is operated is increased by an increase in the number of elements. Hence, heat generated by the LSI when the LSI is operated becomes large, so that there is a danger of causing a thermal runaway which causes the LSI to malfunction. In order to prevent the malfunction of not only the LSI but also a heating element that generates heat when operated, it is necessary to prevent a temperature increase caused by heat generated by the heating element to thereby keep the temperature of the heating element constant. 
     One of the parts for keeping the temperature of a heating element constant is a heat sink. An example of the related art is a heat sink constructed by laminating a plurality of layers each of which has a flow channel (for example, Japanese Patent Laid-Open No. 2007-534973). The flow channel in the heat sink is connected to a cooling system provided outside the heat sink. A refrigerant is sent to the flow channel from the cooling system. The refrigerant passes through the flow channel in the heat sink and returns to the cooling system. In this heat sink is provided a temperature detecting member for detecting the temperature of the heat sink. The data of temperature detected by the temperature detecting member is sent to a control system provided outside the heat sink. The control system gives the cooling system an instruction to control the flow rate of the refrigerant flowing through the flow channel in such a way as to bring the heat sink into an optimal temperature. In this manner, the data of temperature of the heat sink is fed back to the cooling system, whereby the temperature of the heat sink can be kept constant. 
     Further, a heat sink of another example of the related art will be described. A schematic view of the heat sink of another example of the related art is shown in  FIG. 1 . This heat sink  27  has enclosure  22  the one face of which is constructed of heat transfer plate  21 , the one face having heating elements  26  arranged thereon. Furthermore, heat sink  27  has a multitude of external fins  23  that are provided on faces other than heat transfer plate  21  of enclosure  22  and that are extended vertically and outward from the respective faces of enclosure  22 . A multitude of internal fins  24  are provided in enclosure  22  in such a way as to be vertical to heat transfer plate  21 . In addition, enclosure  22  is filled with heat storage material  25  whose melting point ranges from 40 to 100 ° C. (for example, Japanese Patent Laid-Open No. 11-111898). 
     When heating elements  26  generate heat in a state where heat transfer plate  21  and heating elements  26  are brought into contact with each other, a portion of heat generated by heating elements  26  is radiated outside from external fins  23  provided on the periphery of enclosure  22  via heat transfer plate  21 . Further, another portion of the heat generated by heating element  26  is transferred to heat storage material  25  in enclosure  22  from heat transfer plate  21  and internal fins  24 . The temperature of heat storage material  25  is increased by the transferred heat and when the temperature of heat storage material  25  reaches a melting point, heat storage material  25  starts to melt. During the period of time that elapses after heat storage material  25  starts to melt until heat storage material  25  melts completely, the heat generated by heating elements  26  and transferred to heat storage material  25  is used as melting heat by which heat storage material  25  is melted, so that the temperature of heat storage material  25  is not increased. Hence, during the period of time that elapses after heat storage material  25  starts to melt until heat storage material  25  melts completely, the temperature of heating elements  26  is not increased either but is kept constant. When heat storage material  25  melts completely, heat storage material  25  cannot absorb the heat generated by heating element  26  and hence radiates the heat from external fins  23  provided on the periphery of enclosure  22 . 
     In the case of the heat sink of one example of the related art, that is, the heat sink in which the temperature of the heating elements is kept constant, it is necessary to provide the flow channel and the temperature detecting member in the heat sink and to provide the cooling system outside the heat sink and in addition to construct the control system to control the temperature of the heat sink. For this reason, the configuration of the heat sink is very complicated. 
     Further, in the case of heat sink  27  of another example of the related art, in which heat storage material  25  is used, the heat of heating elements  26  is radiated through two routes of A: heating elements  26 →heat transfer plate  21 →internal fins  24 →heat storage material  25 →external fins  23 , and B: heating elements  26 →heat transfer plate  21 →external fins  23 . In the route A, an increase in the temperature of heating elements  26  can be kept constant to some extent by heat storage material  25 . However, when heat radiated from external fins  23  is small as compared with the total quantity of heat transferred to external fins  23  from the route A and heat transferred to external fins  23  from the route B, the heat generated by heating elements  26  cannot be completely radiated from external fins  23 . Hence, the temperature of heating elements  26  cannot be kept constant and the temperature of heating elements  26  is increased. In order to solve this problem and to keep the temperature of heat sink constant, the heat sink needs to be provided with a temperature detecting member and a cooling fan or the like needs to be provided separately from the heat sink. Further, it is necessary to provide a mechanism for operating the cooling fan according to the temperature of the heat sink to cool the heat sink or to make the flow of air. 
     SUMMARY OF THE INVENTION 
     The present invention provides a heat sink capable of solving a problem in which a unit other than a heat sink is required so as to keep a heating element at a desired temperature. 
     A heat sink of the present invention includes: a closed container covered with a heat insulation material; a heat transfer member constructed of a heat transfer part brought into contact with a heating element and a heat transfer fin provided in such a way as to extend from a face on a side opposite to a face that belongs to the heat transfer part and at which the heat transfer part is brought into contact with the heating element; a heat radiation fin for radiating heat; and a heat storage material enclosed in the closed container. The heat transfer part of the heat transfer member is built in one face of the closed container in such a way as to penetrate the one face. The face that belongs to the heat transfer part and at which the heat transfer part is brought into contact with the heating element is protruded to the outside. The heat transfer fin is located in the closed container. The heat radiation fin penetrates a face that belongs to the closed container and that is opposed to a face at which heat transfer part is located, and has one end portion thereof located inside the closed container, and has the other end portion thereof located outside the closed container. Further, the heat radiation fin and the heat transfer fin are arranged in such a way as not to be brought into contact with each other. 
     The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrates examples of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a heat sink of the related art; 
         FIG. 2  is a schematic view to illustrate one exemplary embodiment of a heat sink according to the present invention; 
         FIG. 3  is a graph to show a temperature change when a heat storage material changes from a solid phase to a liquid phase; 
         FIG. 4A  is a schematic view to illustrate a state in which a heat storage material changes and a schematic view to illustrate a state immediately after the time when the heat storage material starts to melt; 
         FIG. 4B  is a schematic view to illustrate a state in which the heat storage material changes and a schematic view to illustrate a state when the heat storage material further melts; 
         FIG. 5A  is a graph to show a relationship between electric power applied to a heating element and time; and 
         FIG. 5B  is a graph to show a relationship between the temperature of the heating element and time when the electric power shown in  FIG. 5A  is applied to the heating element. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Hereinafter, an exemplary embodiment of the present invention will be described in detail on the basis of the accompanying drawings. In this regard, a configuration having the same function is denoted by the same reference number in the accompanying drawings and the description of the configuration will be omitted in some cases. 
       FIG. 2  is a schematic view to illustrate one exemplary embodiment of a heat sink according to the present invention. 
     Heat sink  11  of the present invention is constructed of: heat transfer member  12  constructed of heat transfer part  10  and heat transfer fins  5  that transfer the heat of heating element  1  such as an LSI to the inside of heat sink  11 ; heat radiation fins  7  for radiating heat inside heat sink  11  to the outside of heat sink  11 ; closed container (enclosure)  3  covered with heat insulation material  2  for preventing heat transfer between the inside and the outside of heat sink  11  so as to prevent heat, which is transferred from heating element  1  to heat transfer member  12 , from radiating from a part other than heat radiation fins  7 ; and heat storage material  4  enclosed in closed container  3 . 
     Next, the structure of heat sink  11  will be described in detail. 
     Heat transfer member  12  is constructed in such a way that heat transfer fins  5  are provided on one face of heat transfer part  10  and that a face, which belongs to heat transfer part  10  and is opposite to the one face on which heat transfer fins  5  are provided, is brought into contact with heating element  1 . Heat transfer part  10  of heat transfer member  12  is built in one face of closed container  3  in such a way as to penetrate the one surface and the face, which belongs to heat transfer part  10  and is brought into contact with heating element  1 , is protruded outside. Heat transfer fins  5  are housed in closed container  3 . 
     Further, there are provided heat radiation fins  7  that extend from the inside of closed container  3  to the outside thereof. These heat radiation fins  7  extend through a face belongs to the closed container  3  and that is opposed to a face at which heat transfer part  10  is located, in such a way that portions of one end thereof are located inside closed container  3  and that portions of the other end thereof are located outside closed container  3 . Inside closed container  3 , heat radiation fins  7  are arranged so as not to be brought into contact with heat transfer fins  5 . The number of heat transfer fins  5  and the number of heat transfer fins  7  may be singular or plural, respectively. In the case where the number of them is plural, it is preferable that heat transfer fins  5  are separated from each other at regular intervals and that each of heat radiation fins  7  is located in the center between adjacent heat transfer fins  5 . 
     It is desirable that heat transfer part  10 , heat transfer fins  5 , and heat radiation fins  7  are made of material having a high thermal conductivity, for example, metal such as copper. Further, heat transfer fins  5  and heat radiation fins  7  can be formed in a planar shape or in a columnar shape, or in the combination of the planar shape and the columnar shape. 
     Heat storage material  4  that is in a solid phase at the room temperature is enclosed in closed container  3 . When heat storage material  4  is heated and is changed from a solid phase to a liquid phase, heat storage material  4  is increased in volume: Hence, it is necessary to prevent heat storage material  4  from overflowing from closed container  3  or from pressing and breaking closed container  3 , heat transfer fins  5 , or heat radiation fins  7  when heat storage material  4  is heated. In other words, it is necessary not to fill the inside of closed container  3  with heat storage material  4  at the room temperature but to provide clearance  8 . 
     Here, the function of heat storage material  4  will be described. 
       FIG. 3  is a graph to show a temperature change when heat storage material  4  changes from a solid phase to a liquid phase. Here, it is assumed that heat storage material  4  is paraffin (paraffin wax) having a melting point of 60° C. When heat is applied to heat storage material  4  that is in a solid phase at the room temperature (20° C.), the temperature of heat storage material  4  is increased (in a range shown by A). When the temperature of heat storage material  4  is increased to 60° C. of the melting point of heat storage material  4 , heat storage material  4  starts to melt. Heat applied to heat storage material  4  during the period in which heat storage material  4  changes from the solid phase to the liquid phase is consumed as melting heat for melting heat storage material  4 , so that an increase in the temperature of heat storage material  4  is almost stopped (in a range shown by B). When heat storage material  4  is completely melted, the temperature of heat storage material  4  is again increased (in a range shown by C). In other words, the heat of heating element  1 , which is transferred to heat storage material  4  through heat transfer part  10  and heat transfer fins  5 , is continuously consumed as the melting heat of heat storage material  4  until heat storage material  4  is completely melted. For this reason, an increase in the temperature of heating element  1  can almost be stopped. 
     Next, the principle of operation of heat sink  11  of the present invention will be described by the use of  FIG. 4A  to illustrate a state immediately after the time when heat storage material  4  starts to melt and  FIG. 4B  to illustrate a state when heat storage material  4  further melts. 
     When heating element  1  generates heat, the heat of heating element  1  is transferred to heat storage material  4  through heat transfer part  10  and heat transfer fins  5 . In other words, as the temperature of heating element  1  is increased, the temperature of heat storage material  4  is also increased. When the temperature of heat storage material  4  reaches a melting point, as shown in  FIG. 4A , heat storage material  4  starts to melt and changes to heat storage material  4 ′ that is in a liquid phase. When heat storage material  4  starts to melt, the heat of heat storage material  4  is consumed as melting heat for melting heat storage material  4 , so that an increase in the temperature of heating element  1  and an increase in the temperature of heat storage material  4  are stopped. 
     Further, when the temperature of heat storage material  4  becomes higher than the temperature of the outside of heat sink  11 , the heat of heat storage material  4  is radiated to the outside by heat radiation fins  7 , so that heat storage material  4  is cooled. Hence, the time that elapses after heat is applied to heat storage material  4  until heat storage material  4  starts to melt can be extended. Furthermore, as shown in  FIG. 4B , even when heat storage material  4  further melts and heat storage material  4 ′ that has changed to the liquid phase increases in volume, the heat of heat storage material  4 ′ of the liquid phase can be radiated to the outside of heat sink  11  by heat radiation fins  7 . For this reason, a portion of heat storage material  4 ′ that changed to the liquid phase can be solidified again. Hence, an increase in the temperature of heat storage material  4  can be made more moderate than a case where heat radiation fins  7  are not provided, so that the mixed state of the solid phase and the liquid phase of heat storage material  4  can be kept for a longer period, which makes it possible to stop an increase in the temperature of heating element  1  for a longer period. 
     Further, if all of heat storage material  4  changes to the liquid phase, convection is caused in liquid heat storage material  4  by the heat, so that the heat can be radiated more efficiently by heat radiation fins  7  as compared with a case where heat storage material  4  is not provided. Hence, the increase in the temperature of heating element  1  can be made moderate. 
     Next, an example of a change in the temperature of heating element  1  when heating element  1  generates heat will be described. 
       FIG. 5A  is a graph to show a relationship between electric power applied to heating element  1  and time, and  FIG. 5B  is a graph to show a relationship between the temperature of heating element  1  and the time when the electric power shown in  FIG. 5A  is applied to heating element  1 . In this regard, paraffin (paraffin wax) that has a melting point of 60° C. is used as heat storage material  4 . 
     As shown in  FIG. 5A , Constant electric power (100 W) is applied to heating element  1  during the period of time that elapses from when heating element  1  starts to have electric power applied thereto until heat storage material  4  starts to melt and some time elapses thereafter. Thereafter, the applied electric power is changed. As a result, as shown in  FIG. 5B , the temperature of heating element  1  is increased at a nearly constant rate until heat storage material  4  starts to melt. However, even if the applied electric power is changed thereafter, the temperature of heating element  1  is almost constantly kept at 60° C. that is the melting point of heat storage material  4 . 
     In heat sink  27  (for example, Japanese Patent Laid-Open No. 11-111898) using heat storage material  25 , which is another example of the related art described above, the heat of heating element  26  is radiated through two routes of A: heating element  26 →heat transfer plate  21 →internal fins  24 →heat storage material  25 →external fins  23 , and B: heating element  26 →heat transfer plate  21 →external fins  23 . However, in the present invention, heat sink  11  is covered with heat insulation material  2 , so that the heat of heating element  1  is radiated through one route of: heating element  1 →heat transfer part  10 →heat transfer fins  5 →heat storage material  4 →heat radiation fins  7 . In other words, if the temperature of this one route can be controlled, the temperature of heat sink  11  can be controlled. Further, unlike a heat sink of an example of the related art (for example, Japanese Patent Laid-Open No. 2007-534973) in which a cooling system is provided to keep temperature constant, Heat sink  11  of the present invention can keep the temperature of heating element  1  at a desired temperature by matching the temperature at which heating element  1  is desired to be kept with the melting point of heat storage material  4  even if other constituent elements are not used. 
     As an example of heat storage material  4 , paraffin (paraffin wax) can be used. The melting point of paraffin varies depending on the number of chains of a carbon molecule that compose the paraffin. Hence, it is recommended that paraffin having a desired melting point be selected and used as heat storage material  4 . 
     In heat sink  11  of the present invention, the heat of heating element  1  is radiated through one route of: heating element  1 →heat transfer part  10 →heat transfer fins  5  → 0  heat storage material  4 →heat radiation fins  7 . For this reason, by utilizing a melting state in which heat storage material  4  changes from a solid phase to a liquid phase, heating element  1  can be kept at a desired temperature even if an external unit is not provided. Further, heat radiation fins  7  are in direct contact with heat storage material  4 , so that the heat of heat storage material  4  can be efficiently radiated to the outside. Hence, both the time that elapses from when heating element  1  starts to have electric power applied thereto until heat storage material  4  starts to melt and the time that elapses while heat storage material  4  completely changes from a solid phase to a liquid phase can be elongated, so that the temperature of heating element  1  can be kept constant for a long time without being affected by the electric power applied thereto. Further, this effect can be acquired only by a single unit of heat sink  11  without using another external unit or the like, so that a currently used heat sink can be replaced by heat sink  11 . Furthermore, in heat sink  11  of the present invention, the temperature of heating element  1  can be kept at the melting point of heat storage material  4 , so that even if various kinds of heat sinks are not prepared, heating element  1  can be kept at a desired temperature only by replacing heat storage material  4 . 
     In addition, when an atmospheric temperature outside heating element  1  such as LSI is low and hence heating element  1  needs to be warmed, it is also possible to warm heating element  1  by providing a heater in closed container  3  at a position in which the heater is not in contact with heat transfer member  12  and heat radiation fins  7 . 
     According to the present invention, it is possible to provide a heat sink capable of keeping a heating element at a desired temperature without using a unit other than the heat sink. 
     While the invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims.