Patent Publication Number: US-7213338-B2

Title: Cooler, electronic apparatus, and method for fabricating cooler

Description:
RELATED APPLICATION DATA 
   This application is a divisional of application Ser. No. 10/250,528 filed Jun. 30, 2003, now U.S. Pat. No. 6,999,314. The present and foregoing applications claim priority to Japanese Application No. P2001-380561 filed on Dec. 13, 2001, and PCT application No. PCT/JP02/12643. Each of these applications is incorporated herein by reference to the extent permitted by law. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a cooler for transferring heat generated from a driver for card-typed storage medium as a component in a personal computer, a digital camera, and the like, to cool the storage medium, and a method for fabricating the cooler. The present invention also relates to an electronic apparatus such as a personal computer, and a digital camera, which is equipped with the cooler. 
   BACKGROUND ART 
   Since a compact and low-profile storage medium such as a memory stick (registered trademark), smart media (registered trademark), and a compact flash (registered trademark) as compared with conventional one such as a floppy (registered trademark) disks may have a large amount of storage capacity, the storage medium has been generically used in an electronic apparatus such as a personal computer, and a digital camera. 
   In such the storage medium, there are memories wherein a driver and a flash memory are integral parts, and wherein a driver is provided with a memory main body or another card-typed memory, for example. At any rate, this storage medium has recently had a considerable amount of storage capacity. 
   Such the considerable amount of storage capacity of the storage medium causes the driver to generate a great amount of heat, thereby resulting in a malfunction therein. 
   In order to avoid the malfunction, it is conceivable that a cooler will be provided with the electronic apparatus side wherein a technology using a heat pipe is used as cooling method. 
   The heat pipe is a metallic pipe having a wick structure on an inside wall thereof, maintained under vacuum, and filled with a small amount of water, alternatives for chlorofluorocarbons or the like. An end of the heat pipe is attached to heat source to be heated and a working fluid then evaporates or is vaporized in the heat pipe, whereby heat is acquired as latent heat (of evaporation). The vapor is moved toward a low-temperature portion thereof rapidly (almost at the velocity of sound) and it then turns back to a liquid condition by cooling of the low-temperature portion and extracts heat (liberated heat as latent heat when vapor condenses). The working fluid returns to its original position through the wick structure (or by gravity) so that heat transfer can be successively performed with efficiency. 
   Since the conventional heat pipe has a pipe shape and occupies a large space, it is unsuitable for a cooler for an electronic apparatus such as a personal computer, and a digital camera because the cooler is required to be downsized and low-profiled. 
   In order to downsize the heat pipe, a cooler has proposed such that silicon and glass board members each having grooves on their mating surfaces are connected together to form a passage between them as the heat pipe. Note that as connecting them, the passage is filled with a small amount of water, alternatives for chlorofluorocarbons or the like and sealed. Such the liquid changes in phase into and from the vapor inside the heat pipe, thereby serving as the heat pipe. 
   If, however, the heat pipe is formed using the silicon board member as described above, an object to be cooled diffuses too much heat because of high thermal conductivity of silicon itself. This causes inadequate or no evaporation of the working liquid inside the heat pipe, thereby failing to suitably deliver a performance of the heat pipe. 
   In order to improve the inconvenience, the inventors have proposed such a technology that a plastic board member having low thermal conductivity can be used instead of silicon board member, thereby preventing the heat from being improperly diffused at a surface of the board member to allow a performance of the heat pipe to improve. 
   In this case, however, it is difficult to transfer the heat from an object to be cooled into the working liquid inside the heat pipe because of low thermal conductivity of the plastic material itself, thereby resulting in inadequate evaporation of the working liquid inside the heat pipe. This may fails to suitably deliver a performance of the heat pipe. 
   SUMMARY OF THE INVENTION 
   The present invention has been contrived in the above circumstances and an object of the present invention is to provide a cooler having an excellent cooling performance, which is capable of being downsized and low-profiled, an electronic apparatus and a method for fabricating the cooler. 
   A cooler according to first aspect of the present invention comprises first board member having a cavity portion formed on a surface thereof, the cavity portion corresponding to a part of a heat pipe excluding at least a wick part (a structure for allowing capillary action to be generated) therefrom, second board member having at least a groove for the wick part formed on a surface thereof, the second board member being made from material having higher thermal conductivity than the first board member has, the surface of the second board member being adhered to the first board member, and third board member incorporating the second board member through a surface thereof, the surface of the third board member being adhered to the first board member. 
   According to the invention, the first and third board members are adhered to each other. Their surfaces opposed to each other are matched so that the cavity portion can be served as a passage for heat pipe. This allows the cooler to be downsized and low-profiled. Since the wick part is made from the material having higher thermal conductivity such as copper and nickel, thermal transfer can be effectively performed in this part. Additionally, a condenser part and the wick part are removable and the condenser part is also made from material having higher thermal conductivity such as copper and nickel. This allows a cooling performance of the heat pipe to be improved. Since the first and third board members are made from plastic or glass material, they are available for being processed in actuality. They, however, have poor adhesion properties. According to the invention, an adhesive member is provided between the first and third board members to complement their adhesion properties. Incidentally, as a combination of the first and third board members in this case, both members are preferably glass or plastic board members. It is also preferable that one is glass board member and the other is plastic board member. Further, as a matter of course, silicon board member is available. If taking a cost performance, a suitable assembly, and the like into account, silicon, copper and the like may be preferably used as the suitable adhesive. 
   An electronic apparatus according to second aspect of the invention comprises a slot portion into which a card-typed storage medium having a flush memory and a driver is detachably inserted, or a driver provided with the device side or a driver equipped with a portion separated from the device, and a cooler having the above configuration for transferring heat generated from the driver. 
   In the invention, the above configured cooler having an excellent cooling performance, which is downsized and low-profiled, is equipped with the electronic apparatus. This prevents the apparatus itself from suffering from thermal malfunction. 
   A method for fabricating a cooler according to third aspect of the invention comprises the steps of forming first board member having a cavity portion on a surface thereof the cavity portion corresponding to a part of a heat pipe excluding at least a wick part therefrom, forming second board member having at least a groove for the wick part on a surface thereof, said second board member being made from material having higher thermal conductivity than said first board member has, incorporating the second board member to third board member through a surface thereof, and adhering a surface of the third board member to a surface of the first board member. According to the invention, it is possible to effectively fabricate the cooler having the above configuration with reliability. 
   According to an embodiment of the invention, in the method for fabricating the cooler, the steps of forming fourth board member having at least a groove for a condenser part on a surface thereof, the forth board member being made form material having higher thermal conductivity than the first board member has, and incorporating the forth board member to the third board member through a surface thereof are provided. According the embodiment having such the configuration, the condenser part also has higher thermal conductivity. This allows heat to be much transferred. 
   According to another embodiment of the invention, in the method for fabricating the cooler, the second board member or the fourth board member is formed under a process of UV-Lithografie Galvanoformung Abformung (UV-LIGA). According the embodiment having such the configuration, it is possible to effectively form a narrow groove. 
   Finally, according to further embodiment of the invention, in the method for fabricating the cooler, a step of forming adhesive members on any of a surface of the first board member and a surface of the third board member to adhere the first and third board members is further provided. This allows an adhesion between the first and third board members with reliability. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view illustrating a configuration of a cooler embodying the invention; 
       FIG. 2  is a side view illustrating an assembled condition of the cooler embodying the invention; 
       FIG. 3  is a top plan view showing a lower board member in the cooler embodying the invention; 
       FIG. 4  is a top plan view showing upper complex board members in the cooler embodying the invention; 
       FIG. 5  is a top plan view showing an assembled condition of the upper complex board members and the lower board member in the cooler embodying the invention; 
       FIG. 6A  is a diagram showing an area where heat is diffused as plastic board member is used; 
       FIG. 6B  is a diagram showing an area where heat is diffused as complex board members made from plastic material and metallic material are used according to the invention; 
       FIG. 7  is a flow diagram showing a fabrication method for fabricating the cooler of the invention; 
       FIG. 8A  is a schematic diagram illustrating a step for forming a groove on each of the board members for the condenser and the wick, respectively, used in the cooler of the invention; 
       FIG. 8B  is a schematic diagram illustrating a step for forming a groove on each of the board members for the condenser and the wick, respectively, used in the cooler of the invention; 
       FIG. 8C  is a schematic diagram illustrating a step for forming a groove on each of the board members for the condenser and the wick, respectively, used in the cooler of the invention; 
       FIG. 8D  is a schematic diagram illustrating a step for forming a groove on each of the board members for the condenser and the wick, respectively, used in the cooler of the invention; 
       FIG. 9  is a schematic diagram illustrating a step for making board members for the condenser and the wick, respectively, incorporated to the upper board member used in the cooler of the invention; 
       FIG. 10A  is a schematic diagram illustrating a step for adhering the upper complex board member to the lower board member, both members being used in the cooler of the invention; 
       FIG. 10B  is a schematic diagram illustrating a step for adhering the upper complex board member to the lower board member, both members being used in the cooler of the invention; 
       FIG. 11  is a schematic diagram illustrating another cooler embodying the invention; and 
       FIG. 12  is a schematic perspective view of a personal computer equipped with a cooler according to the invention. 
   

   DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described more in detail with reference to the drawings. 
   (Cooler) 
     FIG. 1  is an exploded perspective view of a cooler embodying the invention and  FIG. 2  is a side view illustrating an assembled condition of the cooler. 
   As shown in  FIGS. 1 and 2 , the cooler  1  comprises four board members  10 ,  20 ,  30  and  40 . Lower board member  10  is made from plastic material and has a rectangular shape, which is set on a lower location. The board member  20  for a condenser part and the board member  40  for a wick part are made from metallic material such as nickel and have a rectangular shape, respectively. The upper board member  30  is made from plastic material and has a rectangular shape, which is set on an upper location. The board member  20  for the condenser part and the board member  40  for the wick part are inserted into openings  32  and  34  of the upper board member  30 , respectively, with them being made integral thereto. These four board members  10 ,  20 ,  30  and  40  are adhered and fixed through an adhesive member such as silicon member  50 . The respective board members  10 ,  20 ,  30  and  40  have a cavity portion  11 , a groove  21 , a hollow portion  31  and a groove  41  at their surfaces,  10   a ,  20   b ,  30   b  and  40   b . The cavity portion  11 , the groove  21 , the hollow portion  31 , and the groove  41  are formed so that they can be served as a looped heat pipe as these four board members are adhered. 
   Configurations of the cavity, the grooves, and the hollow formed in the board members  10 ,  20 ,  30  and  40  will be described more in detail with reference to the  FIGS. 3 and 4 . 
   As shown in  FIG. 3 , the lower board member  10  has the cavity portion  11  at its surface  10   a  This cavity portion  11  has a major empty space comprising a portion forming a passage for flowing working liquid and a vapor and a portion serving as a storage tank for supplying the working liquid. With reference to more detailed explanation of the configuration thereof the portion forming the passage  12  for flowing the working liquid such as water is provided, and the liquid is introduced into the board member  40  for the wick part, which will be explained, through the passage  12 . The introduced liquid is made evaporated through the board member  40  for the wick part and a vapor thus evaporated is then introduced into a portion forming a vapor receiver  14 . The vapor is introduced through a portion forming a passage  15  into a condenser part  22  for transition from the vapor to liquid, and the condensed liquid is then moved to a portion forming low temperature part  16 . It then returns to the passage  12 . Thus, circulation from liquid to vapor and vice versa can be performed. 
   A reservoir  13  and a storage portion  17  keep the liquid stored. The liquid in the reservoir  13  is flowed into the vapor receiver  14  when an amount of liquid in the receiver  14  lowers below a set level. The liquid in the storage portion  17  is flowed into the low temperature part  16  when an amount of liquid in the low temperature part  16  lowers below a set level. Thus, the reservoir  13  and the storage portion  17  keep the liquid stored to prevent a space inside the heat pipe from being dried out so that the liquid can be flowed into the reservoir  13  and the storage portion  17  when necessary. 
   A heat insulation hall  18  exists at a center of the lower board member  10  and at a location adjacent to the passages  12 ,  15 . This prevents the heat from being diffused. 
   As shown in  FIG. 4 , the upper board member  30  incorporates the board member  20  for the condenser part and the board member  40  for the wick part, respectively, thereby forming an upper complex board member  100 . 
   The board member  20  for the condenser part has a groove  21  on its surface  20   b . The groove  21  serves as the condenser part for allowing the vapor introduced via the passage  15  to be condensed to the liquid and circulates it to the low temperature part  16 . 
   The board member  40  for the wick part has a groove  41  on its surface  40   b . The groove  41  serves as the cooler part for allowing the liquid introduced via the passage  12  and the reservoir  13  to be vaporized and the vapor thus vaporized to be flowed into the receiver  14 . 
   A heat insulation hall  34  exists at a location opposed to that of the above heat insulation hall  18 . The respective upper and lower board members  10 ,  30  have the heat insulation halls  18 ,  34  as a hollow and a cavity, for preventing the heat from being diffused. 
     FIG. 5  shows an adhered condition of the upper complex board member  100  and the lower board member  10  through the silicon member  50  as shown in  FIG. 2 . 
   The heat pipe formed as the upper complex board member  100  and the lower board member  10  are adhered is filled with the working liquid. The filled liquid is circulated inside the heat pipe with making a liquid to vapor transition or a vapor to liquid transition. This allows the heat to be transferred, thereby serving as the cooler  1 . 
   The circulation from the liquid to the vapor and vice versa will be explained with starting at the passage  12  for convenience of explanation. 
   The liquid, first, flows from the passage  12  into the wick part  42 . When an amount of liquid flowed into the wick part  42  lowers below a set level at this time, the reservoir  13  supplies the sufficient liquid thereto to order to avoid drying out the heat pipe. 
   In the wick part  42 , the flowed liquid is heated and boiled. The vapor evaporated according to the boil flows into the reservoir  14 . The vapor then flows through the passage  15  into the condenser part  22  for condensing it to the liquid. Thus, the condensed liquid flows into the low temperature portion  16  positioned below the condenser part  22 . The liquid again flows from the low temperature portion  16  to the passage  12  to circulate it. When an amount of liquid flowed from the low temperature portion  16  to the passage  12  lowers below a set level, the storage portion  17  allows the stored liquid to flow into the low temperature portion  16 . 
   Although the embodiment using the board members made from the plastic material has been explained, the board member made from the glass material or a combination of the plastic material and the glass material may be used instead thereof. 
   Although the embodiment using the board member  20  for the condenser part and the board member  40  for the wick part each made from nickel has been explained, cooper can be used for them. 
     FIGS. 6A and 6B  are diagrams for comparing the board member made from plastic material and the complex board member of the plastic material and the metallic material according to the invention in terms of the heat diffusion, each schematically showing an area where heat is diffused for a set time on the board member.  FIG. 6A  shows an area where the heat is diffused as the board member made from plastic material is used.  FIG. 6B  shows an area where the heat is diffused as the complex board members made from the plastic material and the metallic material are used with the plastic board member incorporating the metal such as nickel. 
   If the board member is made from the plastic material, as shown in  FIG. 6A , the heat from heat source (the wick part) A- 1  diffuses in a little area in the directions indicated by arrows (A- 2 ). On the other hands, if the complex board member made from the plastic material and the metallic material is used as shown in  FIG. 6B , the heat from heat source (the wick part) B- 1  highly diffuses in a metallic portion but little heat diffuse in the plastic portion around the metallic portion (B- 2 ). 
   The wick part is required for having thermal conductivity higher than a set level in order to serve as the heat pipe. Since the board member made from the plastic material, as shown in  FIG. 6A , has little conductivity, it does not sufficiently serve as the heat pipe. On the other hands, in the complex board member made from the plastic material and the metallic material, as shown in  FIG. 6B , according to the invention, the heat is sufficiently transferred in the wick part but it is hard to diffuse in the plastic portion around the wick part. This means that the heat concentrates in the wick part, thereby sufficiently serving as the heat pipe. 
   (A Method for Fabricating the Cooler) 
     FIG. 7  shows a fabrication method for fabricating the cooler. 
   The lower board member  10  and the upper board member  30  are first formed so that the cavity and hollow portions can be served as the heat pipe (Step  701 ). The cavity portion  11  working as a passage, a storage tank for storing working liquid, and a heat insulation hall is formed on the surface  10   a  of the lower board member  10  made from the plastic material. The hollow portion  31  working as a heat insulation hall is formed on the surface  30   b  of the upper board member  30  made from the plastic material. As the method for forming these cavity and hollow portions, it is conceivable that a mould for each of the board members is previously made, and the board members may be shaped into a particular form using the mold. The upper and lower board members may be made from glass. If so, the cavity and hollow portions may be etched into a piece of glass after patterning thereof. 
   Next, the board member  20  for the condenser part and the board member  40  for the wick part are formed (Step  702 ). Each of the board members  20 ,  40  that have grooves is formed according to the so-called UV-LIGA, for example. 
   Detailed steps of the UV-LIGA will be explained with reference to  FIGS. 8A through 8D . 
   Photoresist layer  81  made from organic material such as SU-8 is first formed on a plate  82  and patterned photoresist film  83  is then formed on the layer  81 , as shown in  FIG. 8A . They are referred to as a pattern board  80 . 
   The photoresist layer  81  is then etched applying ultraviolet light UV toward the pattern board  80  from above, as shown in  FIG. 8B . 
   Further, as shown in  FIG. 8C , the photoresist film  83  is removed from the pattern board  80  and nickel layer  84  is then formed on a surface thereof by electroforming of nickel Ni. 
   Next, as shown in  FIG. 8D , the nickel layer  84  is removed from the pattern board  80 . Accordingly, the nickel layer thus removed becomes available for the board member  20  for the condenser part and the board member  40  for the wick part, which have grooves. 
   The board members  20 ,  40  thus formed are inserted into the openings  32 ,  34  opened through the upper board member  30  as shown in  FIG. 9  (Step  703 ). When the upper board member  30  made from plastic material is heated resulting in semi-solid condition, the board member  20  for the condenser part and the board member  40  for the wick part are inserted into the openings  32 ,  34  of the upper board member  30  thus heated to make the board members  20 ,  30 , and  40  integral without a crack. 
   Additionally, as shown in  FIG. 10A , a copper thin film  10   b  as an adhesive member is formed on the surface  10   a  of the lower board member  10  using, for example, the spattering. The lower board member  10  and the upper complex board member  100  are then bonded to each other using, for example, an ultrasonic bonding or a heat fusion bonding (Step  704 ). 
   The above method allows the heat pipe to be effectively fabricated. 
   (Another Embodiment of Cooler) 
     FIG. 11  illustrates a flexible cooler  120  comprising a board device  122  for a condenser part, a board device  124  for wick part, and a flexible board member  121  connecting the board devices  122  and  124 . 
   The board device  122  for the condenser part and the board device  124  for wick part are respectively made from plastic materials, into which the board member  20  for the condenser part and the board member  40  for the wick part are respectively inserted according to the above method. 
   The flexible board member  121  is made from plastic material and includes a passage  123  for heat pipe. The heat pipe is formed with these board member and devices being made integral. 
   The flexible board member  121  is made flexible without restraint. It is illustratively capable of equipping its board device  124  for the wick part for a heat source portion of an electronic apparatus and closely connecting the flexible board member along an outer surface of the electronic apparatus. 
   According to the cooler having such the configuration, the heat pipe may be effectively equipped even when the space therefor is limited, thereby allowing the electronic apparatus to be downsized and low-profiled. 
   (Electronic Apparatus) 
     FIG. 12  is a schematic perspective view of a personal computer equipped with a cooler according to the invention. 
   The personal computer  130  has a slot  131  for inserting and withdrawing storage medium  134  having a flush memory  133  and a driver  132 . The cooler  135  of the invention is placed in the personal computer  130  with its wick part being illustratively situated directly under the driver  132  as the storage medium  134  is inserted into the personal computer through the slot  131 . 
   Although the electronic apparatus has been explained as the personal computer, the cooler according to the invention may be used for other electronic apparatus such as digital cameras and video cameras. 
   (Others) 
   Although it has been explained according to the above embodiments of the invention that the upper board member  30  and the lower board member  10  are made from plastic or glass material and the board members  20 ,  40  for the condenser part and the wick part are made from metallic material, this invention is not limited thereto. The invention has such a feature that each of the board members  20 ,  40  has a grater (higher) thermal conductivity than the upper and lower board members  10 ,  30  have. 
   The following table 1 illustratively indicates materials suitably applied for the board members  20 ,  40  for the condenser part and the wick part and their thermal conductivity. The following table 2 illustratively indicates materials suitably applied for the upper and lower board members  10 ,  30  and their thermal conductivity. 
   
     
       
         
             
             
             
           
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
                 
               THERMAL CONDUCTIVITY 
             
             
                 
               MATERIALS 
               (Wm −1 K −1 ) 
             
             
                 
                 
             
           
          
             
                 
             
          
         
         
             
             
             
          
             
                 
               Silicon 
               168 
             
             
                 
               Aluminum 
               240 
             
             
                 
               Copper 
               395 
             
             
                 
               Nickel 
               83 
             
             
                 
               Iron 
               72 
             
             
                 
               Titanium 
               17 
             
             
                 
               Special Plastic 
               100 
             
             
                 
                 
             
          
         
       
     
   
   
     
       
         
             
             
             
           
             
                 
               TABLE 2 
             
             
                 
                 
             
             
                 
                 
               THERMAL CONDUCTIVITY 
             
             
                 
               MATERIALS 
               (Wm −1 K −1 ) 
             
             
                 
                 
             
           
          
             
                 
               Pyrex Glass 
               About 1 
             
             
                 
               Plastic 
               About 1 
             
             
                 
                 
             
          
         
       
     
   
   Further, special plastic having more than 100 times the thermal conductivity of conventional plastic has been recently developed by mixing good thermal conductive ceramic powder and low temperature soluble alloy powder with granular plastic raw material, heating and molding them. Thus, it is conceivable that, if such the special plastic is used for materials for the board members for the condenser part and the wick part, and plastic or glass having a normal thermal conductivity such as Pyrex (registered trademark) glass is used for materials for the upper and lower board members, the board members for the condenser part and the wick part have grater thermal conductivity than the upper and lower board members have. 
   Note that, if plastic or glass having a normal thermal conductivity such as Pyrex glass is used for materials for the upper and lower board members, the board members for the condenser part and the wick part may have more than 10 times the thermal conductivity of the upper and lower board members when the board members for the condenser part and the wick part are made from titanium. 
   Similarly, if the board members for the condenser part and the wick part are made from iron or nickel, they may have more than 50 times the thermal conductivity of upper and lower board members. Additionally, if the board members for the condenser part and the wick part are made from the above special plastic, aluminum or silicon, they may have more than 50 times the thermal conductivity of upper and lower board members. Further, if the board members for the condenser part and the wick part are made from copper, they may have more than 300 times the thermal conductivity of upper and lower board members. 
   As described above, according to the invention, it is possible to provide the cooler having an excellent cooling performance, which is capable of being downsized and low-profiled, an electronic apparatus, and a method for fabricating the cooler. 
   INDUSTRIAL APPLICABILITY 
   As described above, the present invention is useful when it is applicable to a compact cooler for cooling card-typed storage medium. The present invention is also useful when it is applicable to a compact electronic apparatus such as note-typed personal computer, and digital cameras, which include the card-typed storage medium. The present invention is further useful when it is applicable to a method for fabricating a compact cooler for cooling card-typed storage medium