Patent Publication Number: US-2020278161-A1

Title: Composite heat transfer member and method for producing composite heat transfer member

Description:
TECHNICAL FIELD 
     The present invention relates to a composite heat transfer member and a method for producing a composite heat transfer member. 
     BACKGROUND ART 
     As a material of heat spreaders that transfer heat generated from electronic components or electronic instruments, a copper plate or a graphene laminate is used. 
     Among these, the graphene laminate has higher thermal conductivity and lower specific gravity compared to the copper plate. Therefore, the graphene laminate is useful as a material of heat spreaders because this material can be compactified and lightened. 
     On the other hand, the graphene laminate generally has a brittle composition. Therefore, the graphene laminate is likely to be broken due to the stress caused in a case where the laminate is brought into contact with heat sources such as electronic components or electronic instruments or mounted on a mounting portion. 
     Accordingly, a composite heat transfer member is used which is obtained by covering the graphene laminate with a metal such as copper or aluminum so as to improve the overall strength. 
     CITATION LIST 
     Patent Literature 
     [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2011-23670 
     [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2012-238733 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     However, in the aforementioned composite heat transfer member, high thermal resistance occurs in the bonding interface between the graphene laminate and the metal, and accordingly, the overall thermal conductivity of the composite heat transfer member is reduced. 
     According to an aspect, an object of the present invention is to provide a composite heat transfer member which can improve thermal conductivity and a method for producing the composite heat transfer member. 
     Solution to Problem 
     According to an aspect of a technique that will be disclosed below, there is provided a composite heat transfer member having a carbon plate and a metal cast-molded article covering a surface of the plate. 
     According to another aspect of the technique that will be disclosed below, there is provided a method for producing a composite heat transfer member having a step of disposing a carbon plate in a cavity of a casting mold and a step of covering a surface of the plate with a cast-molded article by supplying a molten metal into the cavity so as to form the cast-molded article of the metal. 
     Advantageous Effects of Invention 
     According to the technique that will be disclosed below, the surfaces of the carbon plate are covered with the metal cast-molded article. Therefore, the cast-molded article contacts the surfaces of the plate by surface-to-surface contact. Furthermore, due to the difference in shrinkage between the cast-molded article and the plate at the time of forming the cast-molded article, the cast-molded article is pressed on the surfaces of the plate. 
     As a result, the cast-molded article is in tight contact with the surfaces of the plate. Therefore, the thermal resistance in the bonding interface between the cast-molded article and the plate is reduced, and the thermal conductivity of the composite heat transfer member can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a cross-sectional view ( 1 ) of a composite heat transfer member according to a first embodiment that is in the production process. 
         FIG. 1B  is a cross-sectional view ( 2 ) of the composite heat transfer member according to the first embodiment that is in the production process. 
         FIG. 2  is a cross-sectional view ( 3 ) of the composite heat transfer member according to the first embodiment that is in the production process. 
         FIG. 3  is a perspective view showing the structure of a plate of the first embodiment. 
         FIG. 4A  is a perspective view showing the structure of the composite heat transfer member according to the first embodiment. 
         FIG. 4B  is a cross-sectional view taken along the line I-I in  FIG. 4A . 
         FIG. 5A  is a top view showing the positional relationship among a model used for calculating a thermal resistance ratio, a pointlike heat source as a heating portion, and a cooling portion. 
         FIG. 5B  is a lateral view showing the positional relationship among the model used for calculating a thermal resistance ratio, the pointlike heat source as a heating portion, and the cooling portion. 
         FIG. 6  is a graph showing the results obtained by calculating a thermal resistance ratio of each of the composite heat transfer member of the first embodiment and a heat transfer member of a comparative example. 
         FIG. 7  is a perspective view showing the structure of a plate of a first modification example of the first embodiment. 
         FIG. 8A  is a perspective view showing the structure of a composite heat transfer member according to the first modification example of the first embodiment. 
         FIG. 8B  is a cross-sectional view taken along the line III-III in  FIG. 8A . 
         FIG. 9A  is a perspective view showing the structure of a plate of a second modification example of the first embodiment. 
         FIG. 9B  is a cross-sectional view taken along the line IV-IV in  FIG. 9A . 
         FIG. 10A  is a perspective view showing the structure of a composite heat transfer member according to the second modification example of the first embodiment. 
         FIG. 10B  is a cross-sectional view taken along the line V-V in  FIG. 10A . 
         FIG. 11A  is a cross-sectional view ( 1 ) of a composite heat transfer member according to a second embodiment that is in the production process. 
         FIG. 11B  is a cross-sectional view ( 2 ) of the composite heat transfer member according to the second embodiment that is in the production process. 
         FIG. 12  is a cross-sectional view ( 3 ) of the composite heat transfer member according to the second embodiment that is in the production process. 
         FIG. 13A  is a perspective view showing the structure of a tray of the second embodiment. 
         FIG. 13B  is a cross-sectional view taken along the line VI-VI in  FIG. 13A . 
         FIG. 14A  is a perspective view showing the structure in a state where a plate is accommodated in the tray in the second embodiment. 
         FIG. 14B  is a cross-sectional view taken along the line VII-VII in  FIG. 14A . 
         FIG. 15  is a view showing the constitution of a casting device. 
         FIG. 16A  is a perspective view showing the structure of the composite heat transfer member according to the second embodiment. 
         FIG. 16B  is a cross-sectional view taken along the line VIII-VIII in  FIG. 16A . 
         FIG. 17A  is a perspective view showing the structure of a plate of a modification example of the second embodiment. 
         FIG. 17B  is a cross-sectional view taken along the line IX-IX in  FIG. 17A . 
         FIG. 18A  is a perspective view showing the structure of a tray of a modification example of the second embodiment. 
         FIG. 18B  is a cross-sectional view taken along the line X-X in  FIG. 18A . 
         FIG. 19A  is a perspective view showing the structure in a state where the plate is accommodated in the tray in the modification example of the second embodiment. 
         FIG. 19B  is a cross-sectional view taken along the line XI-XI in  FIG. 19A . 
         FIG. 20A  is a perspective view showing the structure of a composite heat transfer member according to the modification example of the second embodiment. 
         FIG. 20B  is a cross-sectional view taken along the line XII-XII in  FIG. 20A . 
         FIG. 21A  is a perspective view showing the structure of a composite heat transfer member according to a third embodiment. 
         FIG. 21B  is a cross-sectional view taken along the line XIII-XIII in  FIG. 21A . 
         FIG. 22  is a perspective view showing the structure of a plate of a fourth embodiment. 
         FIG. 23A  is a perspective view showing the structure of a composite heat transfer member according to the fourth embodiment. 
         FIG. 23B  is a cross-sectional view taken along the line XIV-XIV in  FIG. 23A . 
         FIG. 24  is a view showing an example of a heat transfer pathway in the plate of the fourth embodiment. 
         FIG. 25A  is a perspective view showing the structure of a plate of a modification example of the fourth embodiment. 
         FIG. 25B  is a cross-sectional view taken along the line XV-XV in  FIG. 25A . 
         FIG. 26A  is a perspective view showing the structure of a composite heat transfer member according to the modification example of the fourth embodiment. 
         FIG. 26B  is a cross-sectional view taken along the line XVI-XVI in  FIG. 26A . 
         FIG. 27A  is a perspective view showing the structure in a state where a plate is accommodated in a tray in a fifth embodiment. 
         FIG. 27B  is a cross-sectional view taken along the line XVII-XVII in  FIG. 27A . 
         FIG. 28A  is a perspective view showing the structure of a composite heat transfer member according to the fifth embodiment. 
         FIG. 28B  is a cross-sectional view taken along the line XVIII-XVIII in  FIG. 28A . 
         FIG. 29A  is a perspective view showing the structure of a plate of a modification example of the fifth embodiment. 
         FIG. 29B  is a cross-sectional view taken along the line XIX-XIX in  FIG. 29A . 
         FIG. 30A  is a perspective view showing the structure in a state where the plate is accommodated in a tray in the modification example of the fifth embodiment. 
         FIG. 30B  is a cross-sectional view taken along the line XX-XX in  FIG. 30A . 
         FIG. 31A  is a perspective view showing the structure of a composite heat transfer member according to the modification example of the fifth embodiment. 
         FIG. 31B  is a cross-sectional view taken along the line XXI-XXI in  FIG. 31A . 
         FIG. 32A  is a perspective view showing the structure of a composite heat transfer member according to a sixth embodiment. 
         FIG. 32B  is a cross-sectional view taken along the line XXII-XXII in  FIG. 32A . 
         FIG. 33  is a perspective view showing the structure of a tray of a seventh embodiment. 
         FIG. 34  is a perspective view showing the structure in a state where an XZ heat transfer member and an XY heat transfer member are accommodated in the tray in the seventh embodiment. 
         FIG. 35A  is a perspective view showing the structure of a composite heat transfer member according to the seventh embodiment. 
         FIG. 35B  is a cross-sectional view taken along the line XXIII-XXIII in  FIG. 35A . 
         FIG. 36  is a perspective view showing the structure of a tray of a modification example of the seventh embodiment. 
         FIG. 37  is a perspective view showing the structure in a state where an XZ heat transfer member and an XY heat transfer member are accommodated in the tray in the modification example of the seventh embodiment. 
         FIG. 38A  is a perspective view showing the structure of a composite heat transfer member according to a modification example of the seventh embodiment. 
         FIG. 38B  is a cross-sectional view taken along the line XXIV-XXIV in  FIG. 38A . 
         FIG. 39  is a perspective view showing a composite heat transfer member according to an eighth embodiment. 
         FIG. 40  is a perspective view showing the constitution of a plate included in the composite heat transfer member according to the eighth embodiment. 
         FIG. 41  is a perspective view showing the constitution of a portion of the plate included in the composite heat transfer member according to the eighth embodiment. 
         FIG. 42  is a view showing an example of a heat transfer pathway in the plate of the eighth embodiment. 
         FIG. 43  is a partial cross-sectional view showing a composite heat transfer member according to a ninth embodiment. 
         FIG. 44  is a partial cross-sectional view showing a composite heat transfer member according to a first modification example of the ninth embodiment. 
         FIG. 45  is a partial cross-sectional view showing a composite heat transfer member according to a second modification example of the ninth embodiment. 
         FIG. 46  is a partial cross-sectional view showing a composite heat transfer member according to a third modification example of the ninth embodiment. 
         FIG. 47A  is a perspective view showing the constitution of a composite heat transfer member according to a tenth embodiment. 
         FIG. 47B  is a top view showing the structure of the composite heat transfer member according to the tenth embodiment. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     The composite heat transfer member according to the present embodiment will be described along with the production method thereof. 
       FIG. 1A  to  FIG. 2  are cross-sectional views of the composite heat transfer member according to the present embodiment that is in the production process. 
     In the present embodiment, as the composite heat transfer member, a heat spreader is produced in the following manner. 
     First, as shown in  FIG. 1A , as one of the heat transfer members constituting the composite heat transfer member, a carbon plate  1  is prepared. 
       FIG. 3  is a perspective view showing the structure of the plate  1 . 
     As shown in  FIG. 3 , the plate  1  is a plate-like heat transfer member obtained by laminating graphenes  2 . 
     In the plate  1 , the graphenes  2  are laminated in the Y direction. That is, the graphenes  2  are laminated in a direction perpendicular to the thickness direction (Z direction) of the plate  1 . 
     The in-plane direction of the graphenes  2  is the X-Z direction. 
     Generally, in the laminate of the graphenes  2 , the thermal conductivity in the in-plane direction of the graphenes  2  is higher than the thermal conductivity in the lamination direction of the graphenes  2 . 
     Accordingly, the plate  1  has anisotropic thermal conductivity in which the thermal conductivity in the X direction and the Z direction is higher than the thermal conductivity in the Y direction. Hereinafter, the heat transfer member in which the thermal conductivity in the X direction and the Z direction is higher than the thermal conductivity in the Y direction will be called XZ heat transfer member as well. 
     In this case, in the plate  1 , the thermal conductivity in the X direction and the Z direction is about 800 W/m·k, and the thermal conductivity in the Y direction is about 10 to 20 W/m·k. 
     The material of the plate  1  is not limited to the laminate of the graphenes  2 . For example, as the material, graphite, Highly Oriented Pyrolytic Graphite (HOPG), or diamond can be used. 
     A top surface la and a bottom surface  1   b  of the plate  1  are rectangular. The direction along which long sides of the top surface  1   a  and the bottom surface  1   b  extend is the X direction, and the direction along which short sides of the top surface la and the bottom surface  1   b  extend is the Y direction. 
     As shown in  FIG. 1A , in the plate  1  having the structure described above, a fixing tool  3  is mounted on both ends in the X direction thereof. The plate  1  with the fixing tools is installed in the internal space of a lower portion  4   b  of a casting mold  4 . 
     Then, an upper portion  4   a  of the casting mold is loaded on and fixed to the lower portion  4   b . As a result, a cavity  6  is formed between the lower portion  4   b  and the upper portion  4   a.    
     In this way, the plate  1  is disposed in the cavity  6  of the casting mold  4 . 
     Thereafter, as shown in  FIG. 1B , as a material of a cast-molded article which will be described later, a metal  7 , which is melted at a temperature of about 700° C., is prepared and injected into the casting mold  4  from an injection port  4   c  of the upper portion  4   a  of the casting mold. 
     In this way, the molten metal  7  is supplied into the cavity  6  of the casting mold  4 . 
     The type of the metal  7  is not particularly limited. For example, as the metal  7 , a magnesium alloy or an aluminum alloy can be used. 
     In the present embodiment, as the metal  7 , a magnesium alloy is used which is constituted with magnesium containing aluminum and zinc and has a thermal conductivity of about 51 to 100 W/m·k. By heating the magnesium alloy at a temperature of about 700° C., the molten metal  7  is formed. 
     The temperature of the casting mold  4  is lower than the solidification temperature (about 400° C.) of the magnesium alloy. 
     Therefore, the molten metal  7  starts to be solidified immediately after being supplied into the cavity  6 . 
     Then, as shown in  FIG. 2 , by decreasing the temperature of the metal  7  to about room temperature, a cast-molded article  8  is formed which covers the surfaces of the plate  1  except for the portions on which the fixing tool  3  is mounted. 
     At this time, the patterns of the surface asperities of the plate  1  are transferred to the cast-molded article  8 , and consequently, the cast-molded article  8  contacts the surfaces of the plate  1  by surface-to-surface contact. 
     The magnesium alloy as a material of the cast-molded article  8  shrinks while the temperature thereof is being decreased to room temperature from the solidification temperature thereof. In contrast, while the temperature is being decreased as described above, the laminate of the graphenes  2  as a material of the plate  1  substantially does not shrink or slightly expands. 
     In this way, due to the difference in a coefficient of thermal expansion, a difference in shrinkage is caused between the cast-molded article  8  and the plate  1 . Consequently, the cast-molded article  8  is pressed on the surfaces of the plate  1  as being indicated by the arrows in the circles of broken lines in  FIG. 2 . 
     As a result, the cast-molded article  8  is in tight contact with the surfaces of the plate  1 . 
     Accordingly, the thermal resistance in the bonding interface between the cast-molded article  8  and the plate  1  is reduced, and the thermal conduction efficiency between the cast-molded article  8  and the plate  1  is improved. 
     Then, the upper portion  4   a  of the casting mold  4  is detached from the lower portion  4   b , and the plate  1  and the cast-molded article  8  are taken out of the lower portion  4   b  together with the fixing tools  3 . Thereafter, a portion of the plate  1  and the cast-molded article  8  is cut, and the fixing tools  3 , residues, and the like are removed. 
     By the process described above, the basic structure of a composite heat transfer member  9  according to the present embodiment is completed. 
       FIG. 4A  is a perspective view showing the structure of the composite heat transfer member  9 .  FIG. 4B  is a cross-sectional view taken along the line I-I of the structure. 
     As shown in  FIG. 4A  and  FIG. 4B , the composite heat transfer member  9  includes the plate  1 , which is the laminate of the graphenes  2 , as a heat transfer member on one side and the cast-molded article  8  of a magnesium alloy, which covers the surfaces of the plate  1  except for lateral surfaces  1   c  in the X direction, as a heat transfer member on the other side. 
     The plate  1  is an XZ heat transfer member in which the thermal conductivity in the X direction and the Z direction is higher than the thermal conductivity in the Y direction. Therefore, basically, the composite heat transfer member  9  including the plate  1  is also an XZ heat transfer member. 
     However, because the surfaces of the plate  1  are covered with the cast-molded article  8  of a magnesium alloy, the thermal conductivity in the Y direction that is relatively low can also be increased. 
     As described above, in the composite heat transfer member  9  according to the present embodiment, the surfaces of the carbon plate  1  are covered with the metal cast-molded article  8 . 
     Accordingly, the cast-molded article  8  contacts the surfaces of the plate  1  by surface-to-surface contact, and a difference in shrinkage is caused between the cast-molded article  8  and the plate  1 . As a result, the cast-molded article  8  is pressed on the surfaces of the plate  1  as being indicated by the arrows in the circles of broken lines in  FIG. 2 . 
     As a result, the cast-molded article  8  is in tight contact with the surfaces of the plate  1 . Consequently, the thermal resistance in the bonding interface between the cast-molded article  8  and plate  1  is reduced, and the thermal conductivity of the composite heat transfer member  9  can be improved even though a thermally conductive member or a thermally conductive adhesive is not used. 
     Furthermore, due to the difference in shrinkage that is caused between the cast-molded article  8  and the plate  1  at the time of forming the cast-molded article  8 , even after the composite heat transfer member  9  is produced, residual tensile stress exists in the cast-molded article  8  while residual compressive stress exists in the plate  1 . 
     For example, in a case where the composite heat transfer member  9  is used in a high-temperature environment with a temperature of about 150° C., the residual stresses are not lost even if being reduced. Therefore, the cast-molded article  8  remains pressed on the surfaces of the plate  1  as being indicated by the arrows in the circles of broken lines in  FIG. 4B . 
     Accordingly, the excellent thermal conductivity between the cast-molded article  8  and the plate  1  can be maintained. 
     In the composite heat transfer member  9  according to the present embodiment, by the removal of the fixing tools  3 , the lateral surfaces  1   c  of the plate  1  are exposed without being covered with the cast-molded article  8 . 
     As described above, residual compressive stress exists in the plate  1 . Therefore, in a case where the composite heat transfer member  9  is used in a high-temperature environment, it is possible to inhibit the composite heat transfer member  9  from thermally expanding along the X direction. 
     In the composite heat transfer member  9 , by combining the plate  1 , which is the laminate of the graphenes  2 , with the cast-molded article  8  of a magnesium alloy, it is possible to obtain thermal conductivity approximately the same as the thermal conductivity of copper (391 W/m·k) and to greatly reduce the specific gravity of the composite heat transfer member  9  ( 2 . 1  g/cm 3 ) compared to the specific gravity of copper (8.9 g/cm 3 ). 
     Therefore, the composite heat transfer member  9  can be lightened or compactified. 
     In order to confirm that the thermal resistance in the composite heat transfer member  9  is really reduced, the inventor of the present application prepared a heat transfer member formed only of copper as a comparative example and calculated a thermal resistance ratio of each of the heat transfer member and the composite heat transfer member  9  according to the present embodiment. 
       FIG. 5A  is a top view showing the positional relationship among a model used for calculating the thermal resistance ratio, a pointlike heat source as a heating portion, and a cooling portion.  FIG. 5B  is a lateral view showing the positional relationship among these. 
     As shown in  FIG. 5A  and  FIG. 5B , each of the composite heat transfer member  9  as a model  10  and the copper heat transfer member is 37 mm long in the Y direction and 3 mm long in the Z direction, that is, 3 mm thick. Furthermore, the thermal resistance ratio between a pointlike heat source  11  and a cooling portion  12  was calculated while varying the length of the model  10  in the X direction. 
     The pointlike heat source  11  is  1  mm long in the X direction and  1  mm long in the Y direction. The pointlike heat source  11  was disposed at a position  5  mm distant from one end of the model  10  in the X direction. Furthermore, the cooling portion  12  was disposed in a region extending 10 mm from another end of the model  10  in the X direction. 
       FIG. 6  is a graph showing the results obtained by calculating the thermal resistance ratio of the composite heat transfer member  9  of the present embodiment and the heat transfer member of the comparative example. In  FIG. 6 , the abscissa shows the length of the model  10  in the X direction, and the ordinate shows the thermal resistance ratio of a sample. 
     As shown in  FIG. 6 , until the length of the model  10  in the X direction is increased to 70 mm, the thermal resistance ratio of the heat transfer member of the comparative example remains lower than the thermal resistance ratio of the composite heat transfer member  9  of the present embodiment. 
     However, after the length of the model  10  in the X direction becomes greater than 70 mm, the thermal resistance ratio of the composite heat transfer member  9  of the present embodiment becomes lower than the thermal resistance ratio of the heat transfer member of the comparative example. For example, in a case where the length of the model  10  is 150 mm, the thermal resistance ratio of the composite heat transfer member  9  is reduced and becomes about  74 % of the thermal resistance ratio of the heat transfer member of the comparative example. 
     By this result, it was confirmed that the composite heat transfer member  9  of the present embodiment has a thermal resistance reducing effect. 
     Next, modification examples of the present embodiment will be described. 
     FIRST MODIFICATION EXAMPLE 
     In the first embodiment described above, as the plate  1 , a plate of an XZ heat transfer member was used. However, in the present modification example, a plate of a heat transfer member having anisotropic thermal conductivity different from the anisotropic thermal conductivity of the XZ heat transfer member will be used. 
     In the present modification example, the same elements as those in the first embodiment will be marked with the same reference signs as those in the first embodiment and will not be described in the following section. 
       FIG. 7  is a perspective view showing the structure of the plate of the present modification example. 
     As shown in  FIG. 7 , a plate  13  is a thin plate-like heat transfer member formed of the laminate of the graphenes  2 . 
     In the plate  13 , the graphenes  2  are laminated in the thickness direction, that is, in the Z direction. 
     Therefore, the plate  13  has anisotropic thermal conductivity in which the thermal conductivity in the X direction and the Y direction is higher than the thermal conductivity in the Z direction. Hereinafter, the heat transfer member in which the thermal conductivity in the X direction and the Y direction is higher than the thermal conductivity in the Z direction will be called XY heat transfer member as well. 
     For the plate  13  having the structure described above, by performing the steps in the first embodiment shown in  FIG. 1A  to  FIG. 2  and then removing the fixing tools  3 , residues, and the like, the structure of a composite heat transfer member according to the present modification example is obtained. 
       FIG. 8A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 8B  is a cross-sectional view taken along the line III-III of the structure. 
     As shown in  FIG. 8A  and  FIG. 8B , a composite heat transfer member  14  according to the present modification example includes the plate  13 , which is the laminate of the graphenes  2 , and the cast-molded article  8  of a magnesium alloy covering the surfaces of the plate  13  except for lateral surfaces  13   c  in the X direction. 
     As described above, the plate  13  is an XY heat transfer member in which the thermal conductivity in the X direction and the Y direction is higher than the thermal conductivity in the Z direction. Therefore, basically, the composite heat transfer member  14  including the plate  13  is also an XY heat transfer member. 
     However, because the surfaces of the plate  13  are covered with the cast-molded article  8  of a magnesium alloy, the thermal conductivity in the Z direction that is relatively low can also be increased. 
     SECOND MODIFICATION EXAMPLE 
     In the present modification example, a plate having a shape different from the shape of the plate  1  will be used. 
     In the present modification example, the same elements as those in the first embodiment will be marked with the same reference signs as those in the first embodiment and will not be described in the following section. 
       FIG. 9A  is a perspective view showing the structure of the plate of the present modification example.  FIG. 9B  is a cross-sectional view taken along the line IV-IV of the structure. 
     As shown in  FIG. 9A  and  FIG. 9B , just as the plate  1  of the first embodiment, a plate  15  is a thin plate-like XZ heat transfer member formed of the laminate of the graphenes  2 . 
     However, unlike the plate  1  of the first embodiment, the plate  15  of the present modification example is provided with through holes  15   d  that extend from a top surface  15   a  to a bottom surface  15   b.    
     The position where the through holes  15   d  are provided and the number of the through holes  15   d  are not particularly limited. In the present embodiment, at the center of the plate  15  in the X direction, two through holes  15   d  that are spaced in the Y direction are provided. 
     For the plate  15  having the structure described above, by performing the steps in the first embodiment shown in  FIG. 1A  to  FIG. 2  and then removing the fixing tools  3 , residues, and the like, the structure of a composite heat transfer member according to the present modification example is obtained. 
       FIG. 10A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 10B  is a cross-sectional view taken along the line V-V of the structure. 
     As shown in  FIG. 10A  and  FIG. 10B , a composite heat transfer member  16  according to the present modification example includes the plate  15 , which is the laminate of the graphenes  2 , and the cast-molded article  8  of a magnesium alloy covering the surfaces of the plate  15  except for lateral surfaces  15   c  in the X direction. 
     According to the present modification example, a portion  8   a  of the cast-molded article  8  fills up the through holes  15   d  of the plate  15 . 
     As a result, through the portion  8   a , the cast-molded article  8 , which covers the top surface  15   a  of the plate  15 , is connected to the cast-molded article  8  which covers the bottom surface  15   b.    
     As described above, due to the difference in shrinkage that is caused between the cast-molded article  8  and the plate  15  at the time of forming the cast-molded article  8 , residual tensile stress TS exists in the cast-molded article  8  as being indicated by the arrows. 
     Even though the composite heat transfer member  16  is used in a high-temperature environment, the residual tensile stress TS is not lost. Therefore, the cast-molded article  8  remains pressed on the surfaces of the plate  15  as being indicated by the arrows in the circles of broken lines. Accordingly, the excellent thermal conductivity between the cast-molded article  8  and the plate  15  can be maintained. 
     Second Embodiment 
     In the present embodiment, a composite heat transfer member is produced by a casting method different from the method in the first embodiment. 
       FIG. 11A  to  FIG. 12  are cross-sectional views of a composite heat transfer member according to the present embodiment that is in the production process. In  FIG. 11A  to  FIG. 12 , the same elements as those in the first embodiment will be marked with the same reference signs as those in the first embodiment and will not be described in the following section. 
     In the present embodiment, as the composite heat transfer member, a heat spreader will be produced in the following manner. 
     First, as shown in  FIG. 11A , a carbon plate  1 , which is one of the heat transfer members constituting the composite heat transfer member, and a metal tray  17  accommodating the plate  1  are prepared. 
     Among these, the plate  1  is a thin plate-like XZ heat transfer member formed of the laminate of the graphenes  2 . 
     In contrast, the tray  17  has the following structure. 
       FIG. 13A  is a perspective view showing the structure of the tray  17 .  FIG. 13B  is a cross-sectional view taken along the line VI-VI of the structure. 
     As shown in  FIG. 13A  and  FIG. 13B , the tray  17  is an open-top metal container with bottom. 
     The lower portion of each of outer lateral surfaces  17   a  of the tray  17  is provided with a depression  17   b . The function of the depression  17   b  will be described later. 
     The type of metal forming the tray  17  is not particularly limited. For example, as the metal forming the tray  17 , a magnesium alloy or an aluminum alloy can be used. In the present embodiment, as the metal, a magnesium alloy is used which is constituted with magnesium containing aluminum and zinc and has a thermal conductivity of about 51 to 100 W/m·k. 
     The method for preparing the tray  17  is not particularly limited. For example, the tray  17  can be obtained by a thixomolding method or a die casting method which will be described later. 
     After the plate  1  and the tray  17  having the structure described above are prepared, the plate  1  is accommodated in the tray  17 . 
       FIG. 14A  is a perspective view showing a structure in a state where the plate  1  is accommodated in the tray  17 .  FIG. 14B  is a cross-sectional view taken along the line VII-VII of the structure. 
     As shown in  FIG. 14A  and  FIG. 14B , the plate  1  is accommodated in the tray  17  such that the bottom surface  1   b  among the surfaces of the plate  1  contacts an inner bottom surface  17   c  of the tray  17  (see  FIG. 13A  and  FIG. 13B ). 
     As a result, the bottom surface  1   b  and the lateral surfaces  1   c  of the plate  1  are covered with the tray  17 , and only the top surface la of the plate  1  is exposed. 
     Furthermore, in a state where the plate  1  is accommodated in the tray  17 , the plate  1  and the tray  17  are disposed in the cavity of a mold of a casting device. 
       FIG. 15  is a view showing the constitution of the casting device. In  FIG. 15 , the cross-sectional structure of a portion of a molding portion, which will be described later, is also shown. 
     As shown in  FIG. 15 , a casting device  18  is a device producing a metal cast-molded article by a thixomolding method, and includes a raw material supply portion  19 , a molten metal injection portion  20 , and a molding portion  21 . 
     Among these, the raw material supply portion  19  is connected to the molten metal injection portion  20 , and supplies metal chips as a raw material of a molten metal, which will be described later, to the molten metal injection portion  20 . 
     The type of metal chips as a raw material is not particularly limited. For example, as the metal chips, magnesium alloy chips or aluminum alloy chips can be used. In the present embodiment, as the metal chips, magnesium alloy chips are used which are constituted with magnesium containing aluminum and zinc and have a thermal conductivity of about 51 to 100 W/m·k. 
     The molten metal injection portion  20  melts the metal chips supplied from the raw material supply portion  19  and injects the molten metal into the molding portion  21  while applying pressure to the molten metal. 
     The molten metal injection portion  20  includes a cylinder  22 , a heater  23  covering the outer surface of the cylinder  22 , and a screw (not shown in the drawing) installed in the internal space of the cylinder  22 . The operation of the cylinder  22 , the heater  23 , and the screw will be described later. 
     The molding portion  21  includes an immovable mold  25  mounted on a fixing board  24  and a movable mold  27  mounted on a moving board  26 . By the movement of the movable mold  27 , a cavity  28  between the immovable mold  25  and the movable mold  27  is closed (formed) or opened. 
     As shown in  FIG. 11A , in the casting device  18  having the structure described above, in a state where the plate  1  is accommodated in the tray  17 , the plate  1  and the tray  17  are loaded on a surface  25   a  of the immovable mold  25  and fixed by fixing tools not shown in the drawing, such that an outer bottom surface  17   d  of the tray  17  contacts the surface  25   a  of the immovable mold  25 . 
     Then, the movable mold  27  is moved to the immovable mold  25  such that the cavity  28  is formed between the immovable mold  25  and the movable mold  27 . 
     In this way, in the cavity  28  between the molds  25  and  27 , the plate  1  and the tray  17  are disposed in a state where the plate  1  is accommodated in the tray  17 . 
     Thereafter, a molten metal is supplied into the cavity  28  in the following manner. 
     First, in the molten metal injection portion  20  of the casting device  18 , the cylinder  22  is preheated by the heater  23 . In the present embodiment, magnesium allow chips are used as a raw material. Therefore, by the heater  23 , the cylinder  22  is preheated to a temperature of about 600° C. which is close to the melting point of the magnesium alloy. 
     In the molding portion  21 , by a heater not shown in the drawing, the immovable mold  25  and the movable mold  27  are preheated to a temperature of about 300° C. 
     In the casting device  18  in this state, as a raw material, the magnesium alloy chips are put into the cylinder  22  from the raw material supply portion  19 . Then, the screw not shown in the drawing is rotated in the cylinder  22 . 
     As a result, in the cylinder  22 , the magnesium alloy chips become in a semi-molten state in which solids and a liquid coexist. Furthermore, by the rotation of the screw, shear stress is applied to the magnesium alloy in the aforementioned state. Consequently, dendritic solid phases are finely shredded and become in the form of particles. 
     As a result, a thixotropic magnesium alloy with reduced viscosity and increased fluidity is formed in the cylinder  22 . Furthermore, by the rotation of the screw, the thixotropic magnesium alloy is injected into the molding portion  21  as a molten metal  29  under pressure. 
     In this way, as shown in  FIG. 11B , the molten metal  29  is supplied into the cavity  28  between the molds  25  and  27  of the molding portion  21 . 
     As described above, the molds  25  and  27  are at a temperature of about 300° C. which is lower than the solidification temperature (about 40 0 ° C.) of the magnesium alloy. Therefore, the molten metal  29  starts to be solidified immediately after being supplied into the cavity  28 . 
     Subsequently, as shown in  FIG. 12 , a heater (not shown in the drawing) of the molds  25  and  27  is turned off, such that the temperature of the metal  29  is reduced to about room temperature, and a cast-molded article  30  is formed which covers the outer lateral surfaces  17   a  of the tray  17  and the top surface  1  a of the plate  1 . 
     At this time, the patterns of the asperities of the outer lateral surfaces  17   a  of the tray  17  and the top surface la of the plate  1  are transferred to the cast-molded article  30 . As a result, the cast-molded article  30  contacts the outer lateral surfaces  17   a  of the tray  17  and the top surface la of the plate  1  by surface-to-surface contact. 
     The magnesium alloy as a material of the cast-molded article  30  shrinks while the temperature thereof is being decreased to room temperature from the solidification temperature thereof. In contrast, while the temperature is being decreased as described above, the laminate of the graphenes  2  as a material of the plate  1  substantially does not shrink or slightly expands. 
     In this way, a difference in shrinkage is caused between the cast-molded article  30  and the plate  1  after the solidification of the molten metal  29 , and accordingly, the cast-molded article  30  is pressed on the top surface la of the plate  1  as being indicated by the arrows in the circles of broken lines in  FIG. 12 . 
     As a result, the cast-molded article  30  is in tight contact with the top surface la of the plate  1 . 
     Accordingly, the thermal resistance in the bonding interface between the cast-molded article  30  and the plate  1  is reduced, and the thermal conductivity between the cast-molded article  30  and the plate  1  is improved. 
     Furthermore, at the time of forming the cast-molded article  30 , a portion of the cast-molded article  30  fills up the depression  17   b  of the outer lateral surfaces  17   a  of the tray  17 . Consequently, a projection  30   b  fitted with the depression  17   b  is formed. 
     Then, the movable mold  27  is moved to be separated from the immovable mold  25 , and the cast-molded article  30  that is covering the plate  1  and the tray  17  is taken out of the immovable mold  25 . 
     Thereafter, a portion of the plate  1 , the tray  17 , and the cast-molded article  30  is cut, and the fixing tools not shown in the drawing, residues, and the like are removed. 
     In this way, the basic structure of a composite heat transfer member  31  according to the present embodiment is completed. 
       FIG. 16A  is a perspective view showing the structure of the composite heat transfer member  31 .  FIG. 16B  is a cross-sectional view taken along the line VIII-VIII of the structure. 
     As shown in  FIG. 16A  and  FIG. 16B , the composite heat transfer member  31  includes the plate  1 , which is the laminate of the graphenes  2 , as a heat transfer member on one side, the tray  17  of a magnesium alloy, which covers the surfaces of the plate  1  except for the top surface  1   a,  as a heat transfer member on the other side, and the cast-molded article  30  of a magnesium alloy which covers the top surface  1   a  of the plate  1 . 
     The plate  1  is an XZ heat transfer member in which the thermal conductivity in the X direction and the Z direction is higher than the thermal conductivity in the Y direction. Therefore, basically, the composite heat transfer member  31  including the plate  1  is also an XZ heat transfer member. 
     However, because the surfaces of the plate  1  are covered with the tray  17  and the cast-molded article  30  of a magnesium alloys, the thermal conductivity in the Y direction that is relatively low can also be increased. 
     As described above, in the composite heat transfer member  31  according to the present embodiment, the surfaces of the carbon plate  1  are covered with the metal tray  17  and the cast-molded article  30 . 
     Particularly, the top surface  1   a  of the plate  1  is covered with the cast-molded article  30 . 
     Accordingly, the cast-molded article  30  contacts the top surface  1   a  of the plate  1  by surface-to-surface contact, and a difference in shrinkage is caused between the cast-molded article  30  and the plate  1  at the time of forming the cast-molded article  30 . As a result, the cast-molded article  30  is pressed on the top surface la of the plate  1 . 
     Therefore, the cast-molded article  30  is in tight contact with the top surface la of the plate  1 . 
     Consequently, the thermal resistance in the bonding interface between the cast-molded article  30  and the plate  1  is reduced, and as a result, it is possible to improve the thermal conductivity between the cast-molded article  30  and the plate  1  without using a thermally conductive member or a thermally conductive adhesive. 
     Furthermore, due to the difference in shrinkage that occurs between the cast-molded article  30  and the plate  1  at the time of forming the cast-molded article  30 , even after the composite heat transfer member  31  is produced, residual tensile stress exists in the cast-molded article  30  while residual compressive stress exists in the plate  1 . 
     In a case where the composite heat transfer member  31  is used in a high-temperature environment, the residual stresses are not lost. Therefore, the cast-molded article  30  remains pressed on the top surface  1   a  of the plate  1  as being indicated by the arrows in the circles of broken lines in  FIG. 16B . 
     Accordingly, the excellent thermal conductivity between the cast-molded article  30  and the plate  1  can be maintained. 
     In the composite heat transfer member  31 , by combining the plate  1 , which is the laminate of the graphenes  2 , with the tray  17  and the cast-molded article  30  of a magnesium alloy, it is possible to obtain thermal conductivity approximately the same as the thermal conductivity of copper and to greatly reduce the specific gravity of the composite heat transfer member  31  compared to the specific gravity of copper. 
     Therefore, the composite heat transfer member  31  can be lightened or compactified. 
     In addition, because the plate  1  is accommodated in the metal tray  17 , it is easy to handle the plate  1  which has a brittle composition and is easily broken. 
     Moreover, according to the present embodiment, the projection  30   b  of the cast-molded article  30  is fitted with the depression  17   b  of the outer lateral surfaces  17   a  of the tray  17 . Therefore, it is possible to inhibit the cast-molded article  30  from being detached from the tray  17 . 
     In the embodiment described above, the cast-molded article  30  is formed by a thixomolding method. However, the method for forming the cast-molded article  30  is not particularly limited. For example, the cast-molded article may be formed by a die casting method. 
     Furthermore, although the plate  1  as an XZ heat transfer member is accommodated in the tray  17 , the plate  13  as an XY heat transfer member shown in  FIG. 7  may be accommodated in the tray  17 . In addition, a desired heat transfer pathway may be formed of a plate as an XZ heat transfer member and a plate as an XY heat transfer member, and the plates may be accommodated in the tray  17 . 
     MODIFICATION EXAMPLE 
     In the present modification example, a plate and a tray having shapes different from the shapes of the plate and the tray in the second embodiment will be used. 
     In the present modification example, the same elements as those in the second embodiment will be marked with the same reference signs as those in the second embodiment and will not be described in the following section. 
       FIG. 17A  is a perspective view showing the structure of the plate of the present modification example.  FIG. 17B  is a cross-sectional view taken along the line IX-IX of the structure. 
     As shown in  FIG. 17A  and  FIG. 17B , just as the plate  1  of the second embodiment, a plate  32  is a thin plate-like XY heat transfer member formed of the laminate of the graphenes  2 . 
     However, unlike the plate  1  of the second embodiment, the plate  32  of the present modification example is provided with through holes  32   d  that penetrate the plate from a top surface  32   a  to a bottom surface  32   b.    
     The position where the through holes  32   d  are provided and the number of the through holes  32   d  are not particularly limited. In the present embodiment, at the left end, center, and right end of the plate  32  in the X direction, two through holes  32   d  that are spaced in the Y direction are provided. 
       FIG. 18A  is a perspective view showing the structure of the tray of the present modification example.  FIG. 18B  is a cross-sectional view taken along the line X-X of the structure. 
     As shown in  FIG. 18A  and  FIG. 18B , a tray  33  is an open-top metal container with bottom. 
     The lower portion of outer lateral surfaces  33   a  of the tray  33  is provided with a depression  33   b.    
     First openings  33   e  are provided at the center of the bottom of the tray  33 , and second openings  33   f  larger than the first opening  33   e  are provided at the left end and the right end of the bottom of the tray  33 . The position where the openings  33   e  and  33   f  are provided and the number of the openings will be described later. 
     Each of the first openings  33   e  and the second openings  33   f  has a tapered shape having width decreasing toward an inner bottom surface  33   c  from an outer bottom surface  33   d  of the tray  33 . 
     The type of metal forming the tray  33  is not particularly limited. 
     For example, as a metal forming the tray  33 , a magnesium alloy or an aluminum alloy can be used. In the present embodiment, as the metal, a magnesium alloy is used which is constituted with magnesium containing aluminum and zinc and has a thermal conductivity of about 51 to 100 W/m·k. 
     The method for preparing the tray  33  is not particularly limited. For example, the tray  33  can be prepared by a thixomolding method or a die casting method. 
     After the plate  32  and the tray  33  having the structure described above are prepared, the plate  32  is accommodated in the tray  33 . 
       FIG. 19A  is a perspective view showing a structure in a state where the plate  32  is accommodated in the tray  33 .  FIG. 19B  is a cross-sectional view taken along the line XI-XI of the structure. 
     As shown in  FIG. 19A  and  FIG. 19B , the plate  32  is accommodated in the tray  33  such that a bottom surface  32   b  among the surfaces of the plate  32  contacts an inner bottom surface  33   c  of the tray  33  (see  FIG. 18A  and  FIG. 18B ). 
     As a result, the bottom surface  32   b  and lateral surfaces  32   c  of the plate  32  are covered with the tray  33 , and only the top surface  32   a  of the plate  32  is exposed. 
     Furthermore, among the through holes  32   d  of the plate  32 , two through holes  32   d  at the center communicate with two first openings  33   e  at the center of the tray  33  along the thickness direction (Z direction) of the plate  32 . 
     Two through holes  32   d  at the right end portion communicate with two second openings  33   f , which are larger than the through holes  32   d  and positioned at the left end of the tray  33 , along the Z direction. Two through holes  32   d  at the right end communicate with two second openings  33   f , which are larger than the through holes  32   d  and positioned at the right end of the tray  33 , along the Z direction. 
     For the plate  32  and the tray  33  that are in a state where the plate  32  is accommodated in the tray  33 , by performing the steps in the second embodiment shown in  FIG. 11A  to  FIG. 12  and then removing the fixing tools, residues, and the like, a structure of a composite heat transfer member according to the present modification example is obtained. 
       FIG. 20A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 20B  is a cross-sectional view taken along the line XII-XII of the structure. 
     As shown in  FIG. 20A  and  FIG. 20B , a composite heat transfer member  34  according to the present modification example includes the plate  32 , which is the laminate of the graphenes  2 , as a heat transfer member on one side, the tray  33  of a magnesium alloy, which covers the surfaces of the plate  32  except for the top surface  32   a , as a heat transfer member on the other side, and the cast-molded article  30  of a magnesium alloy which covers the top surface  32   a  of the plate  32 . 
     According to the present modification example, a portion  30   a  of the cast-molded article  30  fills up the through holes  32   d  of the plate  32  and the openings  33   e  and  33   f  of the tray  33 . 
     As a result, through the portion  30   a , the cast-molded article  30  covering the top surface  32   a  of the plate  32  is connected to the cast-molded article  30  covering the bottom surface  32   b.    
     As described above, due to the difference in shrinkage that is caused between the cast-molded article  30  and the plate  32  at the time of forming the cast-molded article  30 , even after the composite heat transfer member  34  is produced, residual tensile stress TS exists in the cast-molded article  30  as being indicated by the arrows. 
     In a case where the composite heat transfer member  34  is used in a high-temperature environment, the residual tensile stress TS is not lost. Therefore, the cast-molded article  30  remains pressed on the top surface  32   a  of the plate  32  as being indicated by the arrows in the circles of broken lines. 
     The second openings  33   f  of the tray  33  are larger than the through holes  32   d  of the plate  32  that communicate with the second openings  33   f.    
     Accordingly, by the portion  30   a  of the cast-molded article  30  that fills up the second openings  33   f , the cast-molded article  30  can also remain pressed on the bottom surface  32   b  of the plate  32  as being indicated by the arrows in the circles of broken lines. 
     As a result, further improved thermal conductivity can be maintained between the cast-molded article  30  and the plate  32 . 
     In addition, according to the present modification example, the projection  30   b  of the cast-molded article  30  is fitted with the depression  33   b  of outer lateral surfaces  33   a  of the tray  33 . Furthermore, the portion  30   a  of the cast-molded article  30  is fitted with the tapered first openings  33   e  and the tapered second openings  33   f  at the bottom of the tray  33 . 
     Consequently, it is possible to more reliably inhibit the cast-molded article  30  from being detached from the tray  33 . 
     Third Embodiment 
     In the first embodiment and the second embodiment, as a composite heat transfer member, a heat spreader was produced. However, in the present embodiment, as a composite heat transfer member, a heat spreader that also functions as a heat sink will be produced. 
       FIG. 21A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 21B  is a cross-sectional view taken along the line XIII-XIII of the structure. In  FIG. 21A  and  FIG. 21B , the same elements as those in the second embodiment will be marked with the same reference signs as those in the second embodiment and will not be described in the following section. 
     As shown in  FIG. 21A  and  FIG. 21B , basically, a composite heat transfer member  35  according to the present embodiment has the same structure as the structure of the composite heat transfer member  31  according to the second embodiment. 
     That is, the composite heat transfer member  35  also includes the plate  1 , which is the laminate of the graphenes  2 , as a heat transfer member on one side, the tray  17  of a magnesium alloy, which covers the surfaces of the plate  1  except for the top surface  1  a, as a heat transfer member on the other side, and the cast-molded article  30  of a magnesium alloy which covers the top surface  1  a of the plate  1 . 
     In the composite heat transfer member  35 , a plurality of fins  30   d  are provided on the outer top surface  30   c  of the cast-molded article  30 . 
     In a case where a movable mold for forming the fins  30   d  is used instead of the movable mold  27  used in the second embodiment, the composite heat transfer member  35  having the structure described above can be obtained by performing the same steps as the steps in the second embodiment shown in  FIG. 11A  to  FIG. 12 . 
     In this way, according to the present embodiment, the fins  30   d  are provided on the cast-molded article  30 . 
     Therefore, by the composite heat transfer member  35 , the heat generated from electronic components or electronic instruments can be moved and dissipated from the fins  30   d.    
     The cast-molded article  30  and the fins  30   d  are integrated. Accordingly, in this case, thermal resistance can be further reduced than in a case where a cast-molded article and fins are separately provided, because a thermally conductive member or a thermally conductive adhesive for bonding the cast-molded article to the fins is not used. 
     Basically, the composite heat transfer member  35  according to the present embodiment has the same structure as the structure of the composite heat transfer member  31  according to the second embodiment. However, the composite heat transfer member  35  is not limited to the structure. 
     For example, the composite heat transfer member according to the present embodiment may have a structure that is basically the same as the structure of the composite heat transfer member  9  according to the first embodiment. In this case, a plurality of fins may be provided on the outer top surface of the cast-molded article  8 . 
     Fourth Embodiment 
     In the first embodiment, as the plate  1 , a plate which is an XZ heat transfer member was used. However, in the present modification example, a plate will be used which is constituted with heat transfer members having two kinds of anisotropic thermal conductivity. 
     In the present embodiment, the same elements as those in the first embodiment will be marked with the same reference signs as those in the first embodiment and will not be described in the following section. 
       FIG. 22  is a perspective view showing the structure of the plate of the present embodiment. 
     As shown in  FIG. 22 , a plate  41  includes a heat transfer member  101  and a heat transfer member  43 . 
     The heat transfer member  101  has the same structure as the structure of the plate  1 . That is, in the heat transfer member  101 , the graphenes  2  are laminated in the Y direction, and the in-plane direction of the graphenes  2  is the X-Z direction. Accordingly, the heat transfer member  101  is an XZ heat transfer member. 
     The heat transfer member  43  is a thin plate-like heat transfer member formed of the laminate of the graphenes  2 . In the heat transfer member  43 , the graphenes  2  are laminated in the thickness direction of the heat transfer member  43 , that is, in the Z direction, and the in-plane direction of the graphenes  2  is the X-Y direction. Accordingly, the heat transfer member  43  is an XY heat transfer member. 
     For example, the dimension of the heat transfer member  43  in the Y direction is identical to the dimension of the heat transfer member  101  in the Y direction, one lateral surface of the heat transfer member  101  in the X direction contacts a lateral surface of the heat transfer member  43  in the X direction, and one end of the heat transfer member  101  in the X direction is connected to the heat transfer member  43 . 
     A top surface  41   a  and a bottom surface  4   1   b  of the plate  41  are rectangular. The direction along which long sides of the top surface  41   a  and the bottom surface  4   1   b  extend is the X direction, and the direction along which short sides of the top surface  41   a  and the bottom surface  41   b  extend is the Y direction. 
     For the plate  41  having the structure described above, by performing the steps in the first embodiment shown in  FIG. 1A  to  FIG. 2  and then removing the fixing tools  3 , residues, and the like, a structure of a composite heat transfer member according to the present embodiment is obtained. 
       FIG. 23A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 23B  is a cross-sectional view taken along the line XIV-XIV of the structure. 
     As shown in  FIG. 23A  and  FIG. 23B , a composite heat transfer member  49  according to the present embodiment includes the plate  41 , which the laminate of the graphenes  2 , and the cast-molded article  8  of a magnesium alloy which covers the surfaces of the plate  41  except for lateral surfaces  41   c  in the X direction. 
     The heat transfer pathway in the composite heat transfer member  49  will be described.  FIG. 24  is a view showing an example of a heat transfer pathway in the plate  41  of the fourth embodiment.  FIG. 24  shows the heat transfer pathway in the X-Y plane. In  FIG. 24 , a heat source  100  is assumed to be at the center of the bottom surface  41   b  of the plate  41 . 
     First, the heat generated from the heat source  100  is transferred along the Z direction through graphene positioned around the center of the Y direction among the graphenes  2  constituting the heat transfer member  101 , and transferred along the X direction as well (arrow A). Thereafter, a portion of the heat is transferred to the heat transfer member  43  at one end of the heat transfer member  101  in the X direction. The heat is then transferred along the X direction through the heat transfer member  43  and transferred along the Y direction as well (arrow B). A portion of the heat transferred through the heat transfer member  43  is transferred to the heat transfer member  101 . The heat is then transferred along the Z direction through the heat transfer member  101  and transferred along the X direction as well (arrow C). Because the plate  41  is in tight contact with the cast-molded article  8 , the heat is released out of the cast-molded article  8 . 
     Therefore, according to the fourth embodiment, it is possible to obtain the same effect as that in the first embodiment and to obtain excellent thermal conductivity in the X direction and the Y direction. For example, due to the difference in shrinkage that is caused between the cast-molded article  8  and the plate  41  at the time of forming the cast-molded article  8 , even after the composite heat transfer member  49  is produced, residual tensile stress exists in the cast-molded article  8  while residual compressive stress exists in the plate  41 . 
     Furthermore, for example, even though the composite heat transfer member  49  is used in a high-temperature environment with a temperature of about 150° C., the residual stresses are not lost even if being reduced. Therefore, the cast-molded article  8  remains pressed on the surfaces of the plate  41  as being indicated by the arrows in the circles of broken lines in  FIG. 23B . Accordingly, the excellent thermal conductivity between the cast-molded article  8  and the plate  41  can be maintained. 
     MODIFICATION EXAMPLE 
     In the present modification example, a plate having a shape different from the shape of the plate  41  will be used. 
     In the present modification example, the same elements as those in the fourth embodiment will be marked with the same reference signs as those in the fourth embodiment and will not be described in the following section. 
       FIG. 25A  is a perspective view showing the structure of the plate of the present modification example.  FIG. 25B  is a cross-sectional view taken along the line XV-XV of the structure. 
     As shown in  FIG. 25A  and  FIG. 25B , a plate  44  includes a heat transfer member  115  instead of the heat transfer member  101 . The heat transfer member  115  has the same structure as the structure of the plate  15 . That is, the heat transfer member  115  is a thin plate-like XZ heat transfer member which is formed of the laminate of the graphenes  2  and is provided with through holes  44 d that extend from a top surface  44   a  to a bottom surface  44   b.    
     For the plate  44  having the structure described above, by performing the steps in the first embodiment shown in  FIG. 1A  to  FIG. 2  and then removing the fixing tools  3 , residues, and the like, a structure of a composite heat transfer member according to the present modification example is obtained. 
       FIG. 26A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 26B  is a cross-sectional view taken along the line XVI-XVI of the structure. 
     As shown in  FIG. 26A  and  FIG. 26B , a composite heat transfer member  46  according to the present modification example includes the plate  44 , which is the laminate of the graphenes  2 , and the cast-molded article  8  of a magnesium alloy which covers the surfaces of the plate  44  except for lateral surfaces  44   c  in the X direction. 
     According to the present modification example, a portion  8   a  of the cast-molded article  8  fills up the through holes  44 d of the plate  44 . 
     As a result, through the portion  8   a , the cast-molded article  8  covering the top surface  44   a  of the plate  44  is connected to the cast-molded article  8  covering the bottom surface  44   b.    
     As in the second modification example of the first embodiment, due to the difference in shrinkage that is caused between the cast-molded article  8  and the plate  44  at the time of forming the cast-molded article  8 , residual tensile stress TS exists in the cast-molded article  8  as being indicated by the arrows. 
     Even though the composite heat transfer member  46  is used in a high-temperature environment, the residual tensile stress TS is not lost. Therefore, the cast-molded article  8  remains pressed on the surfaces of the plate  44  as being indicated by the arrows in the circles of broken lines. Therefore, the excellent thermal conductivity between the cast-molded article  8  and the plate  44  can be maintained. 
     Fifth Embodiment 
     In the present embodiment, a composite heat transfer member will be produced by a casting method different from the method in the fourth embodiment. That is, in the present embodiment, the plate  41  and the tray  17  shown in  FIG. 13A  and  FIG. 13B  are prepared, and a composite heat transfer member is produced by the same method as that in the second embodiment. 
       FIG. 27A  is a perspective view showing a structure in a state where the plate  41  is accommodated in the tray  17 .  FIG. 27B  is a cross-sectional view taken along the line XVII-XVII of the structure. 
     As shown in  FIG. 27A  and  FIG. 27B , the plate  41  is accommodated in the tray  17  such that the bottom surface  4   1   b  among the surfaces of the plate  41  contacts the inner bottom surface  17   c  of the tray  17  (see  FIG. 13A  and  FIG. 13B ). 
     As a result, the bottom surface  4   1   b  and the lateral surfaces  41   c  of the plate  41  are covered with the tray  17 , and only the top surface  41   a  of the plate  41  is exposed. 
     As in the second embodiment, the plate  41  and the tray  17  that are in a state where the plate  41  is accommodated in the tray  17  are disposed in the cavity  28  between the movable mold  27  and the immovable mold  25  of the casting device  18 , and a molten metal is supplied into the cavity  28 , thereby forming the cast-molded article  30 . 
     Then, the movable mold  27  is moved to be separated from the immovable mold  25 , and the cast-molded article  30  that is covering the plate  41  and the tray  17  is taken out of the immovable mold  25 . 
     Thereafter, a portion of the plate  41 , the tray  17 , and the cast-molded article  30  is cut, and the fixing tools not shown in the drawing, residues, and the like are removed. 
     In this way, the basic structure of a composite heat transfer member  51  according to the present embodiment is completed. 
       FIG. 28A  is a perspective view showing the structure of the composite heat transfer member  51 .  FIG. 28B  is a cross-sectional view taken along the line XVIII-XVIII of the structure. 
     As shown in  FIG. 28A  and  FIG. 28B , the composite heat transfer member  51  includes the plate  41 , which is the laminate of the graphenes  2 , as a heat transfer member on one side, the tray  17  of a magnesium alloy, which covers the surfaces of the plate  41  except for the top surface  41   a , as a heat transfer member on the other side, and the cast-molded article  30  of a magnesium alloy which covers the top surface  41   a  of the plate  41 . 
     According to the fifth embodiment, it is possible to obtain the effects of the fourth embodiment and the second embodiment. For example, due to the difference in shrinkage that is caused between the cast-molded article  30  and the plate  41  at the time of forming the cast-molded article  30 , even after the composite heat transfer member  51  is produced, residual tensile stress exists in the cast-molded article  30  while residual compressive stress exists in the plate  41 . Furthermore, for example, even though the composite heat transfer member  51  is used in a high-temperature environment, the residual stresses are not lost. Therefore, the cast-molded article  30  remains pressed on the top surface  41   a  of the plate  41  as being indicated by the arrows in the circles of broken lines in  FIG. 28B . Accordingly, the excellent thermal conductivity between the cast-molded article  30  and the plate  41  can be maintained. 
     MODIFICATION EXAMPLE 
     In the present modification example, a plate and a tray having shapes different from the shapes of the plate and the tray in the fifth embodiment will be used. 
     In the present modification example, the same elements as those in the fifth embodiment will be marked with the same reference signs as those in the fifth embodiment and will not be described in the following section. 
       FIG. 29A  is a perspective view showing the structure of the plate of the present modification example.  FIG. 29B  is a cross-sectional view taken along the line XIX-XIX of the structure. 
     As shown in  FIG. 29A  and  FIG. 29B , a plate  52  includes a heat transfer member  132  instead of the heat transfer member  101 . The heat transfer member  132  has the same structure as the plate  32 . That is, the heat transfer member  132  is a thin plate-like XZ heat transfer member which is formed of the laminate of the graphenes  2  and is provided with through holes  52   d  that extend from a top surface  52   a  to a bottom surface  52   b.    
     As a tray, as in the modification example of the second embodiment, the tray  33  shown in  FIG. 18A  and  FIG. 18B  is used. The plate  52  and the tray  33  are prepared, and then the plate  52  is accommodated in the tray  33 . 
       FIG. 30A  is a perspective view showing a structure in a state where the plate  52  is accommodated in the tray  33 .  FIG. 30B  is a cross-sectional view taken along the line XX-XX of the structure. 
     As shown in  FIG. 30A  and  FIG. 30B , the plate  52  is accommodated in the tray  33  such that the bottom surface  52   b  among the surfaces of the plate  52  contacts the inner bottom surface  33   c  of the tray  33  (see  FIG. 18A  and  FIG. 18B ). 
     As a result, the bottom surface  52   b  and the lateral surfaces  52   c  of the plate  52  are covered with the tray  33 , and only the top surface  52   a  of the plate  52  is exposed. 
     Among the through holes  52   d  of the plate  52 , two through holes  52   d  at the center communicate with two first openings  33   e  at the center of the tray  33  along the thickness direction (Z direction) of the plate  52 . 
     Two through holes  52   d  at the left end communicate with the second opening  33   f , which is larger than the through holes  52   d  and positioned at the left end of the tray  33 , along the Z direction. Furthermore, two through holes  52   d  at the right end communicate with the second opening  33   f , which is larger than the through holes  52   d  and positioned at the right end of the tray  33 , along the Z direction. 
     For the plate  52  and the tray  33  that are in a state where the plate  52  is accommodated in the tray  33 , by performing the steps in the second embodiment shown in  FIG. 11A  to  FIG. 12  and then removing the fixing tools, residues, and the like, a structure of a composite heat transfer member according to the present modification example is obtained. 
       FIG. 31A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 31B  is a cross-sectional view taken along the line XXI-XXI of the structure. 
     As shown in  FIG. 31A  and  FIG. 31B , a composite heat transfer member  54  according to the present modification example includes the plate  52 , which is the laminate of the graphenes  2 , as a heat transfer member on one side, the tray  33  of a magnesium alloy, which covers the surfaces of the plate  52  except for the top surface  52   a , as a heat transfer member on the other side, and the cast-molded article  30  of a magnesium alloy which covers the top surface  52   a  of the plate  52 . 
     According to the present modification example, a portion  30   a  of the cast-molded article  30  fills up the through holes  52   d  of the plate  52  and the openings  33   e  and  33   f  of the tray  33 . 
     As a result, through the portion  30   a , the cast-molded article  30  covering the top surface  52   a  of the plate  52  is connected to the cast-molded article  30  covering the bottom surface  52   b.    
     As in the modification example of the second embodiment, due to the difference in shrinkage that is caused between the cast-molded article  30  and the plate  52  at the time of forming the cast-molded article  30 , even after the composite heat transfer member  54  is produced, residual tensile stress TS exists in the cast-molded article  30  as being indicated by the arrows. 
     In a case where the composite heat transfer member is used in a high-temperature environment, the residual tensile stress TS is not lost. Therefore, the cast-molded article  30  remains pressed on the top surface  52   a  of the plate  52  as being indicated by the arrows in the circles of broken lines. 
     The second openings  33   f  of the tray  33  are larger than the through holes  52   d  of the plate  52  that communicate with the second openings  33   f.    
     Accordingly, by the portion  30   a  of the cast-molded article  30  that fills up the second openings  33   f , the cast-molded article  30  can also remain pressed on the bottom surface  52   b  of the plate  52  as being indicated by the arrows in the circles of broken lines. 
     As a result, further improved thermal conductivity can be maintained between the cast-molded article  30  and the plate  52 . 
     In addition, according to the present modification example, as in the modification example of the second embodiment, the projection  30   b  of the cast-molded article  30  is fitted with the depression  33   b  of outer lateral surfaces  33   a  of the tray  33 . Furthermore, the portion  30   a  of the cast-molded article  30  is fitted with the tapered first openings  33   e  and the tapered second openings  33   f  at the bottom of the tray  33 . 
     Consequently, it is possible to more reliably inhibit the cast-molded article  30  from being detached from the tray  33 . 
     Sixth Embodiment 
     In the fourth embodiment and the fifth embodiment, as a composite heat transfer member, a heat spreader was produced. However, in the present embodiment, as in the third embodiment, as a composite heat transfer member, a heat spreader that also functions as a heat sink will be produced. 
       FIG. 32A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 32B  is a cross-sectional view taken along the line XXII-XXII of the structure. In  FIG. 32A  and  FIG. 32B , the same elements as those in the fifth embodiment will be marked with the same reference signs as those in the fifth embodiment and will not be described in the following section. 
     As shown in  FIG. 32A  and  FIG. 32B , basically, a composite heat transfer member  55  according to the present embodiment has the same structure as the structure of the composite heat transfer member  54  according to the modification example of the fifth embodiment. 
     That is, the composite heat transfer member  55  also includes the plate  52 , which is the laminate of the graphenes  2 , as a heat transfer member on one side, the tray  33  of a magnesium alloy, which covers the surfaces of the plate  52  except for the top surface  52   a , as a heat transfer member on the other side, and the cast-molded article  30  of a magnesium alloy which covers the top surface  52   a  of the plate  52 . 
     In the composite heat transfer member  55 , as in the third embodiment, a plurality of fins  30   d  are provided on the outer top surface  30   c  of the cast-molded article  30 . 
     In a case where a movable mold for forming the fins  30   d  is used instead of the movable mold  27  used in the second embodiment, the composite heat transfer member  55  having the structure described above can be obtained by performing the same steps as the steps in the second embodiment shown in  FIG. 11A  to  FIG. 12 . 
     In this way, according to the present embodiment, the fins  30   d  are provided on the cast-molded article  30 . 
     Therefore, by the composite heat transfer member  55 , the heat generated from electronic components or electronic instruments can be moved and dissipated from the fins  30   d.    
     The cast-molded article  30  and the fins  30   d  are integrated. Accordingly, in this case, thermal resistance can be further reduced than in a case where a cast-molded article and fins are separately provided, because a thermally conductive member or a thermally conductive adhesive for bonding the cast-molded article to the fins is not used. 
     The composite heat transfer member  55  according to the present embodiment has a structure that is basically the same as the structure of the composite heat transfer member  54  according to the modification example of the fifth embodiment. However, the composite heat transfer member  55  is not limited to the structure. 
     For example, the composite heat transfer member according to the present embodiment may have a structure that is basically the same as the structure of the composite heat transfer member  49  according to the fourth embodiment. In this case, a plurality of fins may be provided on the outer top surface of the cast-molded article  8 . The composite heat transfer member according to the present embodiment may have a structure that is basically the same as the structure of the composite heat transfer member  51  according to the fifth embodiment. 
     Seventh Embodiment 
     In the present embodiment, a tray having a shape different from the shape of the tray in the fifth embodiment will be used. 
       FIG. 33  is a perspective view showing the structure of the tray of the seventh embodiment. 
     A tray  117  used in the seventh embodiment is a metal container just as the tray  17 . As in the tray  17 , a depression  117   b  is provided on the lower side of outer lateral surfaces  117   a  of the tray  117 . Furthermore, on the top surface of the tray  117 , five grooves  117   s  for an XZ heat transfer member and a groove  117   t  for an XY heat transfer member are formed. One end of each of the grooves  117   s  is connected to the groove  117   t . The tray  117  can be prepared by the same method as that used for preparing the tray  17  by using the same material as the material of the tray  17 . 
     XZ heat transfer members  72  to be accommodated in the grooves  117   s  and an XY heat transfer member  73  to be accommodated in the groove  117   t  are prepared. The XZ heat transfer members  72  and the XY heat transfer member  73  can be prepared, for example, by the same method as that used for preparing the plate  1  or  13 . 
       FIG. 34  is a perspective view showing a structure in a state where the XZ heat transfer members  72  and the XY heat transfer member  73  are accommodated in the tray  117 . 
     The XZ heat transfer members  72  are accommodated in the grooves  117   s  such that the bottom surface among the surfaces of each of the XZ heat transfer members  72  contacts the inner bottom surface of the tray  117 . The XY heat transfer member  73  is accommodated in the groove  117   t  such that the bottom surface among the surfaces of the XY heat transfer member  73  contacts the inner bottom surface of the tray  117 . One lateral surface of each of the XZ heat transfer members  72  in the X direction contacts a lateral surface of the XY heat transfer member  73  in the X direction, and one end of each of the XZ heat transfer members  72  in the X direction is connected to the XY heat transfer member  73 . A plate  71  is constituted with the XZ heat transfer members  72  and the XY heat transfer member  73 . 
     In the seventh embodiment, the bottom surface and the lateral surfaces of the plate  71  are covered with the tray  117 , and only a top surface  71   a  of the plate  71  is exposed. 
     For the plate  71  and the tray  117  that are in a state where the plate  71  is accommodated in the tray  117 , by performing the steps in the second embodiment shown in  FIG. 11A  to  FIG. 12  and then removing the fixing tools, residues, and the like, a structure of a composite heat transfer member according to the present embodiment is obtained. 
       FIG. 35A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 35B  is a cross-sectional view taken along the line XXIII-XXIII of the structure. 
     As shown in  FIG. 35A  and  FIG. 35B , a composite heat transfer member  74  according to the present embodiment includes the plate  71 , which is the laminate of the graphenes  2 , as a heat transfer member on one side, the tray  117  of a magnesium alloy, which covers the surfaces of the plate  71  except for the top surface  71   a , as a heat transfer member on the other side, and the cast-molded article  30  of a magnesium alloy which covers the top surface  71   a  of the plate  71 . 
     According to the present embodiment, it is possible to obtain the same effect as the effect of the fifth embodiment. For example, due to the difference in shrinkage that is caused between the cast-molded article  30  and the plate  71  at the time of forming the cast-molded article  30 , even after the composite heat transfer member  74  is produced, residual tensile stress exists in the cast-molded article  30  while residual compressive stress exists in the plate  71 . In a case where the composite heat transfer member  74  is used in a high-temperature environment, the residual stresses are not lost. Therefore, the cast-molded article  30  remains pressed on the top surface  71   a  of the plate  71  as being indicated by the arrows in the circles of broken lines in  FIG. 35B . Accordingly, the excellent thermal conductivity between the cast-molded article  30  and the plate  71  can be maintained. 
     Furthermore, by the combination of the XZ heat transfer members  72  and the XY heat transfer member  73 , it is possible to obtain excellent thermal conductivity substantially in all directions in the X-Y plane. 
     In addition, because the magnesium alloy is lighter than graphene, the overall weight can be reduced. Moreover, the use of the magnesium alloy is effective for reducing the material cost. 
     In the seventh embodiment, the XZ heat transfer members  72  and the XY heat transfer member  73  are accommodated in the tray  117 . However, a plurality of heat transfer members of one kind may be accommodated in one tray. For example, in a case where a plurality of heat sources are included in an electronic component or an electronic instrument, XZ heat transfer members may be accommodated in the tray at sites corresponding to the heat sources. In this case, other XZ heat transfer members may be accommodated in the tray such that heat can be transferred to the vicinity of the outer lateral surfaces of the tray. 
     MODIFICATION EXAMPLE 
     In the present modification example, a tray having a shape different from the shape of the tray of the seventh embodiment will be used. 
       FIG. 36  is a perspective view showing the structure of the tray of the present modification example. 
     A tray  118  used in the present modification example is a metal container just as the tray  17 . As in the tray  17 , a depression  117   b  is provided on the lower side of outer lateral surfaces  117   a  of the tray  118 . Furthermore, on the top surface of the tray  118 , three grooves  118   s  for an XZ heat transfer member and two grooves  118   t  for an XY heat transfer member are formed. Both ends of each of the grooves  118   s  are connected to both the grooves  118   t . The tray  118  can be prepared by the same method as that used for preparing the tray  17  by using the same material as the material of the tray  17 . 
     An XZ heat transfer member  76  to be accommodated in the grooves  118   s  and an XY heat transfer member  77  to be accommodated in the grooves  118   t  are prepared. The XZ heat transfer member  76  and the XY heat transfer member  77  can be prepared, for example, by the same method as that used for preparing the plate  1  or  13 . 
       FIG. 37  is a perspective view showing a structure in a state where the XZ heat transfer member  76  and the XY heat transfer member  77  are accommodated in the tray  118 . 
     The XZ heat transfer member  76  is accommodated in the grooves  118   s  such that the bottom surface among the surfaces of the XZ heat transfer member  76  contacts the inner bottom surface of the tray  118 . The XY heat transfer member  77  is accommodated in the grooves  118   t  such that the bottom surface among the surfaces of the XY heat transfer member  77  contacts the inner bottom surface of the tray  118 . Furthermore, lateral surfaces of the XY heat transfer member  77  in the X direction contact both the lateral surfaces of each of the XZ heat transfer members  76  in the X direction, and both ends of each of the XZ heat transfer members  76  in the X direction are connected to the XY heat transfer member  77 . A plate  75  is constituted with the XZ heat transfer members  76  and the XY heat transfer members  77 . 
     In the present modification example, the bottom surface and the lateral surfaces of the plate  75  are covered with the tray  118 , and only a top surface  75   a  of the plate  75  is exposed. 
     For the plate  75  and the tray  118  that are in a state where the plate  75  is accommodated in the tray  118 , by performing the steps in the second embodiment shown in  FIG. 11A  to  FIG. 12  and then removing the fixing tools, residues, and the like, a structure of a composite heat transfer member according to the present modification example is obtained. 
       FIG. 38A  is a perspective view showing the structure of the composite heat transfer member.  FIG. 38B  is a cross-sectional view taken along the line XXIV-XXIV of the structure. 
     As show in  FIG. 38A  and  FIG. 38B , a composite heat transfer member  79  according to the present modification example includes the plate  75 , which is the laminate of the graphenes  2 , as a heat transfer member on one side, the tray  118  of a magnesium alloy, which covers the surfaces of the plate  75  except for the top surface  75   a , as a heat transfer member on the other side, and the cast-molded article  30  of a magnesium alloy which covers the top surface  75   a  of the plate  75 . 
     Accordingly, by the present modification example, the same effect as the effect of the seventh embodiment can also be obtained. 
     At the time of using the composite heat transfer member  74  according to the seventh embodiment, it is preferable that a heat source is positioned in the vicinity of a site where the XZ heat transfer member  72  and the XY heat transfer member  73  positioned at the center in the Y direction are connected to each other. In contrast, at the time of using the composite heat transfer member  79  according to the modification example, it is preferable that a heat source is positioned at the center of the XZ heat transfer member  76 , which is positioned at the center in the Y direction, in the X direction. In a case where the heat source is positioned in the vicinity of the XZ heat transfer member  72  or  76 , heat can be transferred with high efficiency. 
     Furthermore, in order to obtain higher heat dissipation efficiency, it is preferable that fins are provided on five XZ heat transfer members  72  in the composite heat transfer member  74  and on three XZ heat transfer members  76  in the composite heat transfer member  79  such that the composite heat transfer members also function as a heat sink. 
     Eighth Embodiment 
     In the present embodiment, as a composite heat transfer member, a heat spreader that also functions as a heat sink will be produced. 
       FIG. 39  is a perspective view showing a composite heat transfer member according to an eighth embodiment.  FIG. 40  is a perspective view showing the constitution of a plate included in the composite heat transfer member according to the eighth embodiment.  FIG. 41  is a perspective view showing the constitution of a portion of the plate included in the composite heat transfer member according to the eighth embodiment. 
     As shown in  FIG. 39 , a composite heat transfer member  80  according to the eighth embodiment has a plate-like base portion  81  and a fin  82  erecting on the base portion  81 . For example, the base portion  81  has a top surface  81   a  and a bottom surface  8   1   b  that are parallel to the X-Y plane, and the fin  82  extends along the Z direction from the top surface  81   a . A heat source contacts the bottom surface  81   b . The composite heat transfer member  80  includes a plate  88 , which is the laminate of the graphenes  2 , as a heat transfer member on one side, and a cast-molded article  89  of a magnesium alloy, which covers the surfaces of the plate  88 , as a heat transfer member on the other side. The plate  88  and the cast-molded article  89  are constituted such that these are in tight contact with each other by the same method as the method in the first embodiment, the second embodiment, or the like. 
     As shown in  FIG. 40  and  FIG. 41 , the plate  88  includes an XZ heat transfer member  85 , XY heat transfer members  86 , and an YZ heat transfer member  87 . The XZ heat transfer member  85  is constituted with the graphenes  2  laminated in the Y direction. Each of the XY heat transfer members  86  is constituted with the graphenes  2  laminated in the Z direction. The YZ heat transfer member  87  is constituted with the graphenes  2  laminated in the X direction. 
     A lateral surface of each of the XY heat transfer members  86  contacts each of both the lateral surfaces of the XZ heat transfer member  85  in the X direction, and the XY heat transfer members  86  are connected to the XZ heat transfer member  85 . The dimension (height) of the XZ heat transfer member  85  in the Z direction is approximately the same as the dimension (height) of each of the XY heat transfer members  86  in the Z direction, and the XZ heat transfer member  85  and the XY heat transfer members  86  are included in the base portion  81 . 
     A portion of a lateral surface of the YZ heat transfer member  87  in the Y direction contacts a lateral surface of the XZ heat transfer member  85  in the Y direction, and the YZ heat transfer member  87  is connected to the XZ heat transfer member  85 . The dimension of the XZ heat transfer member  85  in the X direction is approximately the same as the dimension of the YZ heat transfer member  87  in the X direction. The portion of the YZ heat transfer member  87  that contacts the XZ heat transfer member  85  is included in the base portion  81 , and a portion that protrudes in the Z direction from the aforementioned portion is included in the fin  82 . 
     The heat transfer pathway in the composite heat transfer member  80  will be described.  FIG. 42  is a view showing an example of the heat transfer pathway in the plate  88  of the eighth embodiment. Herein, a heat source  200  is assumed to be at the center of the bottom surface side of the XZ heat transfer member  85 . 
     First, the heat generated from the heat source  200  is transferred along the Z direction through graphene, which is positioned in the vicinity of the center in the Y direction among the graphenes  2  constituting the XZ heat transfer member  85 , and transferred along the X direction as well (arrow D). Thereafter, the heat is transferred to the XY heat transfer members  86  at the end of the XZ heat transfer member  85  in the X direction. The heat is then transferred along the X direction through the XY heat transfer members  86  and transferred along the Y direction as well (arrow E). A portion of the heat transferred through the XY heat transfer members  86  is transferred to a portion of the XZ heat transfer member  85 . The heat is then transferred along the Z direction through the XZ heat transfer member  85  and transferred along the X direction as well (arrow F). Furthermore, the heat transferred through graphene contacting the YZ heat transfer member  87  among the graphenes  2  constituting the XZ heat transfer member  85  is transferred to the YZ heat transfer member  87 . The heat is then transferred along the Y direction through the YZ heat transfer member  87  and transferred along the Z direction as well (arrow G). Because the plate  88  and the cast-molded article  89  are in tight contact with each other, the heat is released out of the cast-molded article  89 . 
     Ninth Embodiment 
     The present embodiment relates to a composite heat transfer member which is a heat spreader that functions as a heat sink as well. 
       FIG. 43  is a partial cross-sectional view showing a composite heat transfer member according to a ninth embodiment. 
     As shown in  FIG. 43 , a composite heat transfer member  90  according to the ninth embodiment has a plate-like base portion  91  and fins  92  erecting on the base portion  91 . For example, the base portion  91  has a top surface  91   a  and a bottom surface  9   1   b  that are parallel to the X-Y plane, and the fins  92  extend in the Z direction from the top surface  91   a . A heat source contacts the bottom surface  91   b . The base portion  91  has an XZ heat transfer member  95 , which is constituted with graphenes laminated in the Y direction, and an XY heat transfer member  96  which is constituted with graphenes laminated in the Z direction. Each of the fins  92  has an YZ heat transfer member  97  which is constituted with graphenes laminated in the X direction. The YZ heat transfer member  97  contacts the XZ heat transfer member  95  and erects on the XZ heat transfer member  95  along the Z direction. The composite heat transfer member  90  has a cast-molded article  99 B of a magnesium alloy, which covers the surfaces of each of the YZ heat transfer members  97 , and a cast-molded article  99 A of a magnesium alloy which covers the surfaces of the XZ heat transfer member  95  and the XY heat transfer member  96 . The XZ heat transfer member  95 , the XY heat transfer member  96 , the YZ heat transfer members  97 , and the cast-molded articles  99 A and  99 B are constituted such that these are in tight contact with each other by the same method as the method in the first embodiment, the second embodiment, or the like. 
     In the ninth embodiment constituted as above, as in the eighth embodiment, the heat from the heat source mounted on the bottom surface  9   1   b  is released out of the cast-molded articles  99 A and  99 B through the XZ heat transfer member  95 , the XY heat transfer member  96 , and the YZ heat transfer members  97 . 
     FIRST MODIFICATION EXAMPLE 
     The present modification example is different from the ninth embodiment in terms of the constitution of the cast-molded article  99 B. 
       FIG. 44  is a partial cross-sectional view showing a composite heat transfer member according to a first modification example of the ninth embodiment. 
     As shown in  FIG. 44 , in a composite heat transfer member  90 A according to the present modification example, the cast-molded article  99 B also covers the surface of each of the YZ heat transfer members  97  that contacts the XZ heat transfer member  95 , and the YZ heat transfer members  97  erect on the XZ heat transfer member  95  along the Z direction in a state where a portion of the cast-molded article  99 B is interposed between each of the YZ heat transfer members  97  and the XZ heat transfer member  95 . Other constitutions are the same as the constitutions of the ninth embodiment. 
     In the first modification example constituted as above, as in the ninth embodiment, the heat from the heat source mounted on the bottom surface  9   1   b  is released out of the cast-molded articles  99 A and  99 B through the XZ heat transfer member  95 , the XY heat transfer member  96 , and the YZ heat transfer members  97 . 
     SECOND MODIFICATION EXAMPLE 
     The present modification example is different from the ninth embodiment in terms of the constitutions of the YZ heat transfer members  97  and the cast-molded article  99 B. 
       FIG. 45  is a partial cross-sectional view showing a composite heat transfer member according to a second modification example of the ninth embodiment. 
     As shown in  FIG. 45 , in a composite heat transfer member  90 B according to the present modification example, the dimension of each of the YZ heat transfer members  97  in the Z direction is smaller than the dimension in the ninth embodiment. Other constitutions are the same as the constitutions in the ninth embodiment. 
     In the second modification example constituted as above, as in the ninth embodiment, the heat from the heat source mounted on the bottom surface  91   b  is released out of the cast-molded articles  99 A and  99 B through the XZ heat transfer member  95 , the XY heat transfer member  96 , and the YZ heat transfer members  97 . 
     In the first modification example, as in the second modification example, the dimension of each of the YZ heat transfer members  97  in the Z direction may be smaller than the dimension in the ninth embodiment. 
     THIRD MODIFICATION EXAMPLE 
     The present modification example is different from the ninth embodiment in terms of the constitution of the cast-molded article  99 A. 
       FIG. 46  is a partial cross-sectional view showing a composite heat transfer member according to a third modification example of the ninth embodiment. 
     As shown in  FIG. 46 , in a composite heat transfer member  90 C according to the present modification example, the cast-molded article  99 A covers the surface of the XZ heat transfer member  95  that contacts the YZ heat transfer members  97 , and the YZ heat transfer members  97  erect on the XZ heat transfer member  95  along the Z direction in a state where a portion of the cast-molded article  99 A is interposed between each of the YZ heat transfer members  97  and the XZ heat transfer member  95 . Other constitutions are the same as the constitutions in the ninth embodiment. 
     In the third modification example constituted as above, as in the ninth embodiment, the heat from the heat source mounted on the bottom surface  91   b  is released out of the cast-molded articles  99 A and  99 B through the XZ heat transfer member  95 , the XY heat transfer member  96 , and the YZ heat transfer members  97 . 
     Tenth Embodiment 
     The present embodiment relates to a composite heat transfer member suited for a specific heat source. 
       FIG. 47A  is a perspective view showing the structure of a composite heat transfer member according to a tenth embodiment.  FIG. 47B  is a top view of the structure. 
     A composite heat transfer member  109  according to the tenth embodiment has a carbon plate  107  and a cast-molded article  108  of a magnesium alloy covering the surfaces of the plate  107 . The plate  107  has an XZ heat transfer member  105  constituted with graphenes laminated in the Y direction perpendicular to the thickness direction (Z direction) of the plate  107 . 
     The composite heat transfer member  109  is used by being mounted on a heat source  102  whose dimension in the Y direction is W 2 . Furthermore, the dimension of the XZ heat transfer member  105  in the Y direction is W 1 . In the present embodiment, the dimension W 1  is identical to the dimension W 2 . 
     In the tenth embodiment, as shown in  FIG. 47A  and  FIG. 47B , the composite heat transfer member  109  is mounted such that the heat source  102  overlaps the XZ heat transfer member  105  along the Y direction when seen in a plan view. Accordingly, the heat generated from the heat source  102  is transferred along the X direction and the Y direction by the XZ heat transfer member  105  with high efficiency and released to the outside. 
     In the XZ heat transfer member  105 , the heat transfer performance in the Y direction (lamination direction) is lower than the heat transfer performance in the X direction and the Z direction. Therefore, even though the XZ heat transfer member  105  is provided to cover a wider range in the Y direction, the heat transfer performance remains substantially the same. Generally, a magnesium alloy is less expensive than graphene. Therefore, in a case where substantially the same heat transfer performance is obtained, a composite heat transfer member in which a small amount of graphene is used is preferable. 
     “Identical” mentioned herein does not means that the dimensions are identical in a strict sense, and may mean dimensions that can be regarded as being “identical” according to common sense. Even though the dimensions are not identical in a strict sense, the heat generated from the heat source can be released to the outside with high efficiency. For example, the width W 1  is preferably 100% to 110% of the width W 2 , and more preferably 100% to 105% of the width W 2 . 
     (Application Examples of Composite Heat Transfer Member) 
     The composite heat transfer members according to the first embodiment to the tenth embodiment described above can be applied to various components involved in heat transfer. 
     For example, the first embodiment, the second embodiment, the fourth embodiment, the fifth embodiment, the seventh embodiment, and the tenth embodiment which are heat spreaders or the composite heat transfer members  9 ,  16 ,  31 ,  34 ,  49 ,  46 ,  51 ,  54 ,  74 ,  79 , and  109  according to modification examples of the above embodiments can be applied to water cooling jacket and cooling water piping made of copper for heating components such as Central Processing Unit (CPU) of a server or applied to a base substrate for a power module. 
     Furthermore, the third embodiment, the sixth embodiment, the eighth embodiment, and the ninth embodiment which are heat spreaders that also function as heat sinks or the composite heat transfer members  35 ,  55 ,  80 ,  90 ,  90 A,  90 B, and  90 C according to modification examples of the above embodiments can be applied to a heat sink of an LED headlamps for automobiles made of aluminum or applied to a heat sink for a mobile base station. 
     The present application claims priorities based on Japanese Patent Application No.  2017 - 222862  filed to Japanese Patent Office on November  20 ,  2017  and Japanese Patent Application No.  2018 - 131470  filed to Japanese Patent Office on July  11 ,  2018 , the entire content of which is incorporated into the present specification. 
     REFERENCE SIGNS LIST 
       1 ,  13 ,  15 ,  32 ,  41 ,  44 ,  52 ,  71 ,  75 ,  88 ,  107  . . . plate,  1   a,    15   a ,  32   a ,  41   a ,  44   a ,  52   a ,  71   a ,  75   a  . . . top surface of plate,  1   b,    15   b ,  32   b ,  41   b ,  44   b ,  52   b  . . . bottom surface of plate,  1   c,    13   c ,  15   c ,  41   c ,  44   c ,  52   c  . . . lateral surface of plate,  2  . . . graphene,  4  . . . casting mold,  4   b  . . . lower portion of casting mold,  4   a  . . . upper portion of casting mold,  6  . . . cavity of casting mold,  7 ,  29  . . . molten metal,  8 ,  30 ,  99 A,  99 B,  108  . . . cast-molded article,  8   a ,  30   a  . . . a portion of cast-molded article,  9 ,  14 ,  16 ,  31 ,  34 ,  35 ,  46 ,  49 ,  51 ,  54 ,  55 ,  74 ,  79 ,  80 ,  90 ,  90 A,  90 B,  90 C,  109  . . . composite heat transfer member,  15   d ,  32   d ,  44 d,  52   d  . . . through hole of plate,  17 ,  33 ,  117 ,  118  . . . tray,  17   a ,  33   a ,  117   a  . . . outer lateral surface of tray,  17   b ,  33   b ,  117   b  . . . depression of tray,  17   c ,  33   c  . . . inner bottom surface of tray,  17   d ,  33   d  . . . outer bottom surface of tray,  18  . . . casting device,  25  . . . immovable mold,  25   a  . . . surface of immovable mold,  27  . . . movable mold,  28  . . . cavity of mold,  30   b  . . . projection of cast-molded article,  30   c  . . . outer top surface of cast-molded article,  30   d  . . . fin,  33   e  . . . first opening of tray,  33   f  . . . second opening of tray,  72 ,  76 ,  85 ,  95  . . . XZ heat transfer member,  73 ,  77 ,  86 ,  96  . . . XY heat transfer member,  87 ,  97  . . . YZ heat transfer member,  81 ,  91  . . . base portion,  102  . . . heat source,  82 ,  92  . . . fin,  117   s ,  117   t ,  118   s ,  118   t  . . . groove