Abstract:
In a laminating direction of first to fifth ceramic sheets, a first slit and a second slit are positioned closer to a first mounting section and a second mounting section than a first communication hole, a second communication hole, a third communication hole and a fourth communication hole. Moreover, an overlapping section where each first slit and the first communication hole overlap, and an overlapping section where each second slit and the third communication hole overlap, are positioned in the vicinity of an area where the first mounting section and the second mounting section are disposed when viewed from the laminating direction of the first to fifth ceramic sheets.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a National Stage of International Application No. PCT/JP2013/069515 filed Jul. 18, 2013, claiming priority based on Japanese Patent Application No. 2012-159734 filed Jul. 18, 2012, Japanese Patent Application No. 2012-284011 filed Dec. 27, 2012, and Japanese Patent Application No. 2012-284012 filed Dec. 27, 2012, the contents of all of which are incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a heat dissipation device, formed by stacking ceramic sheets, and a semiconductor device, formed by mounting a metal plate to which a semiconductor element is coupled on a heat dissipation device. 
     BACKGROUND OF THE INVENTION 
     For example, patent document 1 discloses this type of a heat dissipation device. The heat dissipation device of patent document 1 is formed by baking a lamination in which a plurality of ceramic sheets are stacked. The ceramic sheets include a ceramic sheet having a plurality of slits, which are elements of a coolant passage, and a ceramic sheet having a communication passage that communicates the coolant passage and the exterior. A metal plate to which a semiconductor element is coupled is joined with a heat dissipation device to form a semiconductor device. Heat is transmitted from the semiconductor element to the heat dissipation device through the metal plate and dissipated to the coolant flowing through the coolant passage. This cools the semiconductor element. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: International Publication No. WO2011/136362 
     SUMMARY OF THE INVENTION 
     In such a heat dissipation device, it is desired that the performance for cooling a cooling subject such as a semiconductor element be further improved. 
     It is an object of the present disclosure to provide a heat dissipation device and a semiconductor device that can improve the performance for cooling a cooling subject. 
     One aspect of a heat dissipation device of the present disclosure includes a base body formed by stacking a plurality of ceramic sheets, a coolant passage located in the base body and through which coolant flows, at least one mounting portion defined in a first surface of the base body as a location where a cooling subject is mounted, a slit formation layer formed by at least one of the ceramic sheets, and a communication passage formation layer formed by at least one of the ceramic sheets. The slit formation layer includes a plurality of slits that form a portion of the coolant passage. The slits are formed to be at least partially overlapped with a region that includes the mounting portion as viewed from a stacking direction of the ceramic sheets. The communication passage formation layer forms a portion of the coolant passage and includes a communication passage that communicates the slits. The slits are located toward the mounting portion from the communication passage in the stacking direction of the ceramic sheets. An overlapping portion of the slits and the communication passage is located proximate to a region where the mounting portion is located as viewed from the stacking direction. 
     Another aspect of the heat dissipation device of the present disclosure includes a base body formed by stacking a plurality of ceramic members, a coolant passage located in the base body, and at least one mounting portion defined in a first surface of the base body as a location where a cooling subject is mounted. The coolant passage includes an underneath-lying passage that is formed underneath the mounting portion, a supply passage in communication with an upstream side of the underneath-lying passage in a direction coolant flows, a discharge passage in communication with a downstream side of the underneath-lying passage in the direction the coolant flows, and an expulsion passage located between the supply passage and the discharge passage. The supply passage supplies the coolant to the underneath-lying passage. The discharge passage discharges the coolant from the underneath-lying passage. The expulsion passage expels the coolant to the underneath-lying passage from a vertically lower side toward a vertically upper side. 
     One aspect of a semiconductor device of the present disclosure includes the above heat dissipation device, a metal plate mounted on the mounting portion of the heat dissipation device, and a semiconductor element coupled to the metal plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first embodiment of a semiconductor device. 
         FIG. 2  is a perspective view of a heat dissipation device of the semiconductor device of  FIG. 1 . 
         FIG. 3  is a plan view of a plurality of ceramic sheets, which are elements of the heat dissipation device of  FIG. 2 . 
         FIG. 4  is a cross-sectional view of the semiconductor device of  FIG. 1 . 
         FIG. 5A  is a cross-sectional view of  FIG. 4  taken along line  1 - 1 , and  FIG. 5B  is a cross-sectional view of  FIG. 4  taken along line  2 - 2 . 
         FIG. 6  is a partially enlarged cross-sectional view of the semiconductor device of  FIG. 4 . 
         FIG. 7  is a plan view of another embodiment of a ceramic sheet. 
         FIG. 8  is a cross-sectional view of a semiconductor device that includes the ceramic sheet of  FIG. 7 . 
         FIG. 9  is a partially enlarged cross-sectional view of another embodiment of a semiconductor device. 
         FIG. 10  is a partially enlarged cross-sectional view of another embodiment of a semiconductor device. 
         FIG. 11  is a cross-sectional view of another embodiment of a semiconductor device. 
         FIG. 12  is a plan view of another embodiment of a ceramic sheet. 
         FIG. 13  is a cross-sectional view of another embodiment of a semiconductor device. 
         FIG. 14  is a partially enlarged cross-sectional view of the semiconductor device of  FIG. 13 . 
         FIG. 15  is a plan view of a plurality of ceramic sheets, which are elements of a heat dissipation device of the semiconductor device of  FIG. 13 . 
         FIG. 16  is a perspective view of a second embodiment of a heat dissipation device. 
         FIG. 17  is a perspective view of a semiconductor device that includes the heat dissipation device of  FIG. 16 . 
         FIG. 18  is a cross-sectional view of  FIG. 17  taken along line  3 - 3 . 
         FIG. 19  is a cross-sectional view of  FIG. 17  taken along line  4 - 4 . 
         FIG. 20  is a plan view of a plurality of ceramic sheets, which are elements of a base body of the heat dissipation device of  FIG. 16 . 
         FIG. 21  is a cross-sectional view of another embodiment of a semiconductor device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present invention will now be described with reference to  FIGS. 1 to 6 . 
     A semiconductor device  10  shown in  FIG. 1  is formed by mounting a metal plate  13   b  to which a semiconductor element  13   a  is coupled and a metal plate  14   b  to which a semiconductor element  14   a  is coupled on one surface  12   a  (first surface) of a base body  12  of a heat dissipation device  11 . The metal plates  13   b  and  14   b , which function as wiring layers and joining layers, are formed from pure aluminum (e.g., 1000 series aluminum, which is pure aluminum for industrial use) or copper. For example, insulated gate bipolar transistors (IGBTs) or diodes are used as the semiconductor elements  13   a  and  14   a . The semiconductor elements  13   a  and  14   a  are joined with the metal plates  13   b  and  14   b  by performing metallic joining, for example, soldering or brazing. Also, the metal plates  13   b  and  14   b  are joined with the heat dissipation device  11  by performing metallic joining, for example, soldering or brazing. In this manner, the metal plates  13   b  and  14   b  are mounted on the first surface  12   a  of the base body  12 . 
     As shown in  FIG. 2 , in the first surface  12   a  of the base body  12 , locations where the metal plates  13   b  and  14   b  are mounted (indicated by broken lines in  FIG. 2 ) are respectively a first mounting portion  121  and a second mounting portion  131 , which function as mounting portions on which the metal plates  13   b  and  14   b  are mounted. That is, a plurality of the mounting portions (two in the first embodiment) are arranged side by side on the first surface  12   a  of the base body  12 . 
     The base body  12  is formed by stacking a plurality of ceramic sheets (five sheets in the first embodiment). The base body  12  is baked to form the heat dissipation device  11 . Aluminum oxide, silicon nitride, silicon carbide, aluminum nitride, alumina zirconium, or the like, is used as the material of the ceramic. Preferably, a ceramic material has high water resistance when water cooling is employed to cool the heat dissipation device  11 . 
     As shown in  FIG. 3 , the heat dissipation device  11  of the first embodiment includes first to fifth ceramic sheets  21 ,  22 ,  23 ,  24 , and  25  as elements serving as ceramic sheets. In the description, hereafter, in the heat dissipation device  11 , the first ceramic sheet  21  is located at the upper side, and the fifth ceramic sheet  25  is located at the lower side. The first ceramic sheet  21  forms a top plate portion of the heat dissipation device  11  and includes a surface (upper surface) defining the first surface  12   a  of the base body  12 . A coolant supply hole  21   a  and a coolant discharge hole  21   b  extend through the first ceramic sheet  21 . The coolant supply hole  21   a  and the coolant discharge hole  21   b  have the same open area. The coolant supply hole  21   a  is connected to a supply pipe P 1  (shown in  FIGS. 1 and 2 ) that supplies a coolant to the heat dissipation device  11 . The coolant discharge hole  21   b  is connected to a discharge pipe P 2  (shown in  FIGS. 1 and 2 ) that discharges the coolant out of the heat dissipation device  11  to the exterior. 
     A first coolant inlet hole  22   a  extends through the second ceramic sheet  22 . The first coolant inlet hole  22   a  is located at a position where the first coolant inlet hole  22   a  is overlapped with the coolant supply hole  21   a  as viewed from a stacking direction of the first to fifth ceramic sheets  21 ,  22 ,  23 ,  24 , and  25 . A first coolant outlet hole  22   b  extends through the second ceramic sheet  22 . The first coolant outlet hole  22   b  is located at a position where the first coolant outlet hole  22   b  is overlapped with the coolant discharge hole  21   b  as viewed from the stacking direction of the first to fifth ceramic sheets  21 ,  22 ,  23 ,  24 , and  25  (hereafter, may be simply referred to as a stacking direction A). The first coolant inlet hole  22   a  and the first coolant outlet hole  22   b  are located in symmetric positions. The first coolant inlet hole  22   a  and the first coolant outlet hole  22   b  have the same open area. 
     The second ceramic sheet  22  also includes a plurality of first slits  22   c , which serve as slits, between the first coolant inlet hole  22   a  and the first coolant outlet hole  22   b . Each first slit  22   c  extends through the second ceramic sheet  22  and extends straight in the second ceramic sheet  22  from a position that is closer to the first coolant inlet hole  22   a  toward a central portion of the second ceramic sheet  22 . The first slits  22   c  have the same length. The first slits  22   c  have the same open area. The first slits  22   c  are at least partially located underneath the first mounting portion  121  (metal plate  13   b  and semiconductor element  13   a ). That is, the first slits  22   c  are at least partially overlapped with the first mounting portion  121  as viewed from the stacking direction A. 
     The second ceramic sheet  22  also includes a plurality of second slits  22   d , which serve as slits, between the first coolant inlet hole  22   a  and the first coolant outlet hole  22   b . Each second slit  22   d  extends through the second ceramic sheet  22  and extends straight in the second ceramic sheet  22  from a position that is closer to the first coolant outlet hole  22   b  toward the central portion of the second ceramic sheet  22 . The second slits  22   d  have the same length. The second slits  22   d  have the same open area. The second slits  22   d  are at least partially located underneath the second mounting portion  131  (metal plate  14   b  and semiconductor element  14   a ). That is, the second slits  22   d  are at least partially overlapped with the second mounting portion  131  as viewed from the stacking direction A. 
     A second coolant inlet hole  23   a  extends through the third ceramic sheet  23 . The second coolant inlet hole  23   a  is located in a position where the second coolant inlet hole  23   a  is overlapped with the first coolant inlet hole  22   a  as viewed from the stacking direction A. A second coolant outlet hole  23   b  extends through the third ceramic sheet  23 . The second coolant outlet hole  23   b  is located in a position where the second coolant outlet hole  23   b  is overlapped with the first coolant outlet hole  22   b  as viewed from the stacking direction A. The second coolant inlet hole  23   a  and the second coolant outlet hole  23   b  have the same open area. 
     The third ceramic sheet  23  also includes a first communication hole  23   c , which extends in a direction orthogonal to the extending direction of each first slit  22   c . The first communication hole  23   c  is partially overlapped with each first slit  22   c  at one end that is located toward the first coolant inlet hole  22   a  as viewed from the stacking direction A. This communicates each first slit  22   c  and the first communication hole  23   c . Additionally, the third ceramic sheet  23  includes a second communication hole  23   d  at a position closer to the second coolant outlet hole  23   b  than the first communication hole  23   c . The second communication hole  23   d  extends in the direction orthogonal to the extending direction of each first slit  22   c . The second communication hole  23   d  is partially overlapped with each first slit  22   c  at the other end, which is located toward the first coolant outlet hole  22   b , as viewed from the stacking direction A. This communicates each first slit  22   c  and the second communication hole  23   d.    
     The third ceramic sheet  23  also includes a third communication hole  23   e , which extends in a direction orthogonal to the extending direction of each second slit  22   d . The third communication hole  23   e  is partially overlapped with each second slit  22   d  at one end that is located toward the first coolant inlet hole  22   a  as viewed from the stacking direction A. This communicates each second slit  22   d  and the third communication hole  23   e . Additionally, the third ceramic sheet  23  includes a fourth communication hole  23   f  at a position closer to the second coolant outlet hole  23   b  than the third communication hole  23   e . The fourth communication hole  23   f  extends in the direction orthogonal to the extending direction of each second slit  22   d . The fourth communication hole  23   f  is partially overlapped with each second slit  22   d  at the other end, which is located toward the first coolant outlet hole  22   b , as viewed from the stacking direction A. This communicates each second slit  22   d  and the fourth communication hole  23   f.    
     The fourth ceramic sheet  24  includes a first through hole  24   a , a second through hole  24   b , and a third through hole  24   c . The first through hole  24   a  is overlapped with the second coolant inlet hole  23   a  and a portion of the first communication hole  23   c  as viewed from the stacking direction A. This communicates the second coolant inlet hole  23   a  and the first communication hole  23   c . The second through hole  24   b  is overlapped with a portion of the second communication hole  23   d  and a portion of the third communication hole  23   e  as viewed from the stacking direction A. This communicates the second communication hole  23   d  and the third communication hole  23   e . The third communication hole  24   c  is overlapped with a portion of the fourth communication hole  23   f  and the second coolant outlet hole  23   b  as viewed from the stacking direction A. This communicates the fourth communication hole  23   f  and the second coolant outlet hole  23   b . The fifth ceramic sheet  25  forms a bottom plate portion of the heat dissipation device  11  and includes a surface (lower surface) defining a second surface  12   b  of the base body  12 . That is, the first surface  12   a  and the second surface  12   b  are located at opposite sides of the base body  12 . 
     As shown in  FIG. 4 , the base body  12  of the heat dissipation device  11  is formed by sequentially stacking the fourth ceramic sheet  24 , the third ceramic sheet  23 , the second ceramic sheet  22 , and the first ceramic sheet  21  on the fifth ceramic sheet  25 . The interior of the base body  12  includes the coolant supply hole  21   a , the first coolant inlet hole  22   a , the second coolant inlet hole  23   a , the first through hole  24   a , the first communication hole  23   c , each first slit  22   c , the second communication hole  23   d , the second through hole  24   b , the third communication hole  23   e,  each second slit  22   d , the fourth communication hole  23   f , the third through hole  24   c , the second coolant outlet hole  23   b,  the first coolant outlet hole  22   b , and the coolant discharge hole  21   b , which form a coolant passage  15  through which a coolant flows. The coolant supply hole  21   a  and the coolant discharge hole  21   b  open in the first surface  12   a  of the base body  12 . 
     The second communication hole  23   d , the second through hole  24   b , and the third communication hole  23   e  form a portion of the coolant passage  15  that is located between the first mounting portion  121  and the second mounting portion  131 . That is, the second communication hole  23   d , the second through hole  24   b , and the third communication hole  23   e  form a portion of the coolant passage  15  that extends from the first mounting portion  121  toward the second surface  12   b  and extends from the second surface  12   b  toward the second mounting portion  131 . 
     In the first embodiment, the second ceramic sheet  22  corresponds to a slit formation layer that includes the first slits  22   c  and the second slits  22   d , which form a portion of the coolant passage  15 . The first communication hole  23   c  corresponds to a communication passage that is overlapped with each first slit  22   c  at a portion closer to the first coolant inlet hole  22   a  and communicates with each first slit  22   c . The second communication hole  23   d  corresponds to a communication passage that is overlapped with each first slit  22   c  at a portion closer to the first coolant outlet hole  22   b  and communications with each first slit  22   c . The third communication hole  23   e  corresponds to a communication passage that is overlapped with each second slit  22   d  at a portion closer to the first coolant inlet hole  22   a  and communicates with each second slit  22   d . The fourth communication hole  23   f  corresponds to a communication passage that is overlapped with each second slit  22   d  at a portion closer to the first coolant outlet hole  22   b  and communicates with each second slit  22   d . The third ceramic sheet  23  corresponds to a communication passage formation layer that includes the first communication hole  23   c , the second communication hole  23   d , the third communication hole  23   e , and the fourth communication hole  23   f , which correspond to the communication passages. 
     The first slits  22   c  and the second slits  22   d  are located toward the first mounting portion  121  and the second mounting portion  131  from the first communication hole  23   c,  the second communication hole  23   d , the third communication hole  23   e , and the fourth communication hole  23   f  in the stacking direction A. 
     In the heat dissipation device  11 , the second communication hole  23   d  is continuous to the first slit  22   c  at a downstream side of the coolant flow, and the second through hole  24   b  is continuous to the second communication hole  23   d . This forms an extension passage W that extends from the first surface  12   a  to the second surface  12   b  of the base body  12 . As shown in  FIGS. 4 and 6 , the extension passage W includes a passage surface X 1  and a passage surface Y 1  that are opposed in the stacking direction of the first to fifth ceramic sheets  21  to  25 . The passage surface X 1  is a portion of a passage formed by the first slit  22   c,  which is located closer to the first surface  12   a  of the base body  12 . The passage surface Y 1  is a portion of a passage formed by the second through hole  24   b , which is located closer to the second surface  12   b.    
     The passage surface X 1  is formed by a surface of the first ceramic sheet  21 , which is located above the second ceramic sheet  22 . The passage surface Y 1  is formed by a surface of the fifth ceramic sheet  25 , which is located below the fourth ceramic sheet  24 . That is, a passage formed by the first slit  22   c  forms the coolant passage  15  that is located on the uppermost position in the stacking direction. The passage surface X 1  corresponds to an upper surface of the passage. A passage formed by the second through hole  24   b  forms the coolant passage  15  that is located at the lowermost position in the stacking direction. The passage surface Y 1  corresponds to a lower surface of the passage. 
     As shown in  FIG. 5A , a first fin  31  is located between adjacent ones of the first slits  22   c . As shown in  FIG. 5B , a second fin  32  is located between adjacent ones of the second slits  22   d.    
     As shown in  FIG. 6 , the length H of the first fin  31  (length of the first slit  22   c ) is set to be within a region Z (dotted region in  FIG. 6 ) as viewed from the stacking direction A. In a cross-section of the first ceramic sheet  21 , the region Z is located between straight lines A and B. The straight lines A and B extend from opposite ends  131   b  and  132   b  of the metal plate  13   b  at an angle θ of 45° relative to the first surface  12   a  of the base body  12 . The angle θ of the straight lines A and B relative to the first surface  12   a  of the base body  12  only needs to be within 30° to 60°. The region Z, which is located between the straight lines A and B, forms a heat transmission region where the heat generated by the semiconductor element  13   a  is transmitted to the heat dissipation device  11  through the metal plate  13   b.    
     In the first embodiment, a portion of the first communication hole  23   c  that corresponds to the region Z as viewed from the stacking direction A serves as an overlapping portion  35  of each first slit  22   c  and the first communication hole  23   c . Thus, the overlapping portion  35  is located in the heat transmission region, where the heat generated by the semiconductor element  13   a  is transmitted to the heat dissipation device  11  through the metal plate  13   b.  That is, the overlapping portion  35  is located proximate to a region where the first mounting portion  121  is located as viewed from the stacking direction A. The overlapping portion  35  is located toward an inner side of the first slit  22   c  from one end  221   c  of each first slit  22   c  that is closer to the first coolant inlet hole  22   a . The same description can be given for the length of the second fin  32  (length of the second slit  22   d ) and an overlapping portion  36  of each second slit  22   d  and the third communication hole  23   e  as the length H of the first fin  31  and the overlapping portion  35  of each first slit  22   c  and the first communication hole  23   c.  Thus, a detailed description will not be given. 
     As shown in  FIG. 6 , in a cross-sectional view of the heat dissipation device  11 , the overlapping portion  35  includes a first overlapping portion  35   a , which is located underneath the first mounting portion  121 , and a second overlapping portion  35   b , which excludes the first overlapping portion  35   a . The length of the second overlapping portion  35   b  is greater than the length of the first overlapping portion  35   a . In this case, the phrase “the length of the second overlapping portion  35   b  is greater than the length of the first overlapping portion  35   a ” means, in the cross-sectional view of the heat dissipation device  11 , the second overlapping portion  35   b  extends toward the first coolant inlet hole  22   a , which results in the length of the second overlapping portion  35   b  being greater than the length of the first overlapping portion  35   a . Although the first mounting portion  121  has been described here, the second mounting portion  131  has the same form. Here, the phrase of “underneath a mounting portion” refers to a region that is located toward the coolant passage  15  from the mounting portion and corresponds to a region that is overlapped with the mounting portion as viewed from the stacking direction A. 
     The operation of the first embodiment will now be described. 
     The coolant supplied from the coolant supply source flows from the supply pipe P 1  to each first slit  22   c  through the coolant supply hole  21   a , the first coolant inlet hole  22   a , the second coolant inlet hole  23   a , the first through hole  24   a , and the first communication hole  23   c . In this case, when the coolant flows from the first communication hole  23   c  to each first slit  22   c , the coolant is expelled from the first communication hole  23   c  into each first slit  22   c  and directed toward the first mounting portion  121  (semiconductor element  13   a  and metal plate  13   b ). This generates a jet flow in the coolant flowing from the first communication hole  23   c  to each first slit  22   c  and agitates the coolant flowing through each first slit  22   c . As a result, the heat, which is transmitted from the semiconductor element  13   a  to the heat dissipation device  11  (each first fin  31 ) through the metal plate  13   b , is dissipated to the coolant flowing through each first slit  22   c  more effectively than when, for example, the coolant flows through each first slit  22   c  along the first mounting portion  121  (first surface  12   a  of the base body  12 ) after flowing along the first surface  12   a . This improves the performance for cooling the semiconductor element  13   a . In the first embodiment, the semiconductor element  13   a  corresponds to a first cooling subject. 
     Also, the coolant flows from each first slit  22   c  to each second slit  22   d  through the second communication hole  23   d,  the second through hole  24   b , and the third communication hole  23   e . In this case, when the coolant flows from the third communication hole  23   e  to each second slit  22   d , the coolant is expelled from the third communication hole  23   e  into each second slit  22   d  to be directed toward the second mounting portion  131  (semiconductor element  14   a  and metal plate  14   b ). This generates a jet flow in the coolant flowing from the third communication hole  23   e  to each second slit  22   d  and agitates the coolant flowing through each second slit  22   d . As a result, the heat, which is transmitted from semiconductor element  14   a  to the heat dissipation device  11  (each second fin  32 ) through the metal plate  14   b , is dissipated to the coolant flowing through each second slit  22   d  more effectively then when, for example, the coolant flows through each second slit  22   d  along the second mounting portion  131  (first surface  12   a  of the base body  12 ) after flowing along the first surface  12   a . This improves the performance for cooling the semiconductor element  14   a . In the first embodiment, the semiconductor element  14   a  corresponds to a second cooling subject. 
     The coolant flows through each second slit  22   d  and is discharged from the discharge pipe P 2  and out of the heat dissipation device  11  through the fourth communication hole  23   f , the third through hole  24   c , the second coolant outlet hole  23   b , the first coolant outlet hole  22   b , and the coolant discharge hole  21   b.    
     Accordingly, the first embodiment has the advantages described below. 
     (1) The first slit  22   c  and the second slit  22   d  are located toward the first mounting portion  121  and the second mounting portion  131  from the first communication hole  23   c,  the second communication hole  23   d , the third communication hole  23   e , and the fourth communication hole  23   f  in the stacking direction A. The overlapping portion  35  of each first slit  22   c  and the first communication hole  23   c  and the overlapping portion  36  of each second slit  22   d  and the third communication hole  23   e  are respectively located proximate to regions where the first mounting portion  121  and the second mounting portion  131  are arranged. Thus, the coolant flowing from the first communication hole  23   c  to each first slit  22   c  may be directed toward the first mounting portion  121 . The coolant flowing from the third communication hole  23   e  to each second slit  22   d  may be directed toward the second mounting portion  131 . This cools the semiconductor elements  13   a  and  14   a  more effectively than when, for example, the coolant flows through each first slit  22   c  and each second slit  22   d  along the first mounting portion  121  and the second mounting portion  131 . Thus, the performance for cooling the semiconductor elements  13   a  and  14   a  may be improved. 
     (2) In the region Z corresponding to the first mounting portion  121  on which a cooling subject is mounted, that is, the region Z serving as the heat transmission region described above, the length of the second overlapping portion  35   b  is greater than the length of the first overlapping portion  35   a . When the coolant enters a coolant passage of a thin slit, turbulent flow is generated. However, there is a time-lag until the turbulent flow contributes to a thermal exchange. The length of the second overlapping portion  35   b  is greater than the length of the first overlapping portion  35   a . This allows the coolant to cool the heat transmission region from a portion located at the upstream side and effectively cools the semiconductor element  13   a . Thus, the performance for cooling the semiconductor element  13   a  may be improved. In the same manner as the first mounting portion  121 , when the second mounting portion  131  and a third mounting portion  171  which will be described later, have the same form, the same advantage may be obtained even when a plurality of semiconductor elements are mounted on each mounting portion. 
     (3) A portion of the coolant passage  15  that is formed by the second communication hole  23   d , the second through hole  24   b , and the third communication hole  23   e  extends from the first mounting portion  121  in a direction toward the second surface  12   b  and extends from the second surface  12   b  in a direction toward the second mounting portion  131 . Thus, the flow of the coolant flowing through the coolant passage  15  may be directed toward the first mounting portion  121  and the second mounting portion  131 . Therefore, when the metal plate  13   b , to which the semiconductor element  13   a  is coupled, is mounted on the first mounting portion  121  and the metal plate  14   b , to which the semiconductor element  14   a  is coupled, is mounted on the second mounting portion  131 , the semiconductor elements  13   a  and  14   a  can be effectively cooled and the performance for cooling the semiconductor elements  13   a  and  14   a  may be improved. 
     (4) The first communication hole  23   c  and the first slit  22   c , and the third communication hole  23   e  and the second slit  22   d , are each directed to the corresponding mounting portion in a stepped manner. The stepped coolant passage  15  can generate a jet flow and a turbulent flow in the coolant. This effectively cools each first slit  22   c  from the end  221   c , which is located at the upstream side, and each second slit  22   d  from an end of the passage surface X 1  that is located at the upstream side. Thus, the cooling performance may be improved. This reduces the size of the heat dissipation device  11  without the need to lengthen the passage to improve the cooling performance. 
     (5) The coolant supply hole  21   a  and the coolant discharge hole  21   b  open in the first surface  12   a  of the base body  12 . This allows the first surface  12   a  of the base body  12  to be connected to the supply pipe P 1 , which is used to supply the coolant, and the discharge pipe P 2 , which is used to discharge the coolant. Thus, components needed for the heat dissipation device  11  may be collectively located at the side of the first surface  12   a  of the base body  12 . This reduces the size of the heat dissipation device  11 . 
     (6) The length H of the first fin  31  (length of the first slit  22   c ) is set to be within the region Z as viewed from the stacking direction A. The region Z is located between the straight lines A and B, which extend from the opposite ends  131   b  and  132   b  of the metal plate  13   b  at an angle θ of 45° relative to the first surface  12   a  of the base body  12 . In this case, the length H of the first fin  31  may be the minimum length needed for the heat dissipation of the semiconductor element  13   a . That is, the length of the first slit  22   c  can be minimized. This limits pressure loss of the coolant flowing through the first slit  22   c  as compared to when the first slit  22   c  is formed to extend beyond the region Z to a position outside the region Z. 
     (7) In the extension passage W, the passage surfaces X 1  and Y 1  are opposed to each other in the stacking direction. This reduces portions that decrease the area of the passage. Thus, the pressure loss of the coolant may be decreased. When the passage surfaces X 1  and Y 1  are opposed to each other, the extension passage W becomes almost straight in the stacking direction A. Thus, the reduction of steps in the extension passage W limits expansion of the coolant passage  15  in the lateral direction. This decreases the size of the heat dissipation device  11 . 
     The first embodiment may be modified as follows. 
     As shown in  FIG. 7 , the second ceramic sheet  22  may include a communication portion  22   h  that communicates each first slit  22   c  and each second slit  22   d . As shown in  FIG. 8 , the second communication hole  23   d , the second through hole  24   b , and the third communication hole  23   e  may be removed. In this case, the coolant may flow from each first slit  22   c  to each second slit  22   d  through the communication portion  22   h  only in the second ceramic sheet  22 . This smoothly flows the coolant compared to when the coolant flows from each first slit  22   c  to each second slit  22   d  through the second communication hole  23   d , the second through hole  24   b , and the third communication hole  23   e . Thus, the pressure loss of the coolant may be limited. In this case, preferably, a metal plate including a semiconductor element that should be cooled the most is mounted on the first mounting portion  121 . 
     As shown in  FIG. 9 , for example, the open area of the first communication hole  23   c  may be set to be smaller than that of the first embodiment. This increases the flow speed of the coolant when passing through the first communication hole  23   c . In this case, jet flow may be generated in the coolant flowing from the first communication  23   c  to each first slit  22   c . As a result, the performance for cooling the semiconductor element  13   a  may be further improved. In the same manner, the open area of the third communication hole  23   e  may be set to be smaller than that of the first embodiment. This increases the flow speed of the coolant when passing through the third communication hole  23   e.    
     As shown in  FIG. 10 , for example, the open area of the first through hole  24   a  may be set to be larger than that of the first embodiment. Also, in the same manner, the open area of the second through hole  24   b  may be set to be larger than that of the first embodiment. 
     As shown in  FIG. 11 , a third mounting portion  171 , which serves as a mounting portion, may be additionally located on a position of the second surface  12   b  that is located beyond a portion of the coolant passage  15  that is located between the first mounting portion  121  and the second mounting portion  131  and extends in a direction from the first mounting portion  121  toward the second surface  12   b  of the base body  12 . In this case, the second through hole  24   b  is replaced with a plurality of slits  41 , and a plurality of fins  42  are arranged in the fourth ceramic sheet  24 . The fins  42  are at least partially overlapped with the third mounting portion  171  as viewed from the stacking direction A. A metal plate  17   b  to which a semiconductor element  17   a  is coupled is mounted on the third mounting portion  171 . The semiconductor element  17   a  is cooled by dissipating heat to the coolant flowing through the slits  41 . The semiconductor element  17   a  corresponds to a third cooling subject. In this case, the maximum number of semiconductor elements may be mounted on the heat dissipation device  11 , the total volume may be reduced, and the performance for cooling the semiconductor elements  13   a ,  14   a , and  17   a , which are mounted on the heat dissipation device  11 , may be improved. 
     As shown in  FIG. 12 , the second ceramic sheet  22  may include a plurality of first slits  43  and second slits  44 , each of which are undulated. This increases the heat dissipation surface area as compared to the first slits  22   c  and the second slits  22   d , which are straight in a plan view. Also, the agitation effect is obtained. This further improves the performance for cooling the semiconductor elements  13   a  and  14   a.    
     In the first embodiment, the positions of the coolant supply hole and the coolant discharge hole of the coolant passage  15  may be changed. For example, the coolant supply hole and the coolant discharge hole may open in the second surface  12   b  of the base body  12 . 
     In the first embodiment, the first slits  22   c  and the second slits  22   d  only need to be at least partially overlapped with a region that includes the first mounting portion  121  and the second mounting portion  131  as viewed from the stacking direction A. 
     In the first embodiment, the number of the first slits  22   c  and the second slits  22   d  may be changed. The number of slits is changed in accordance with the area of a semiconductor element, the passage width of the coolant passage  15 , and the like. For example, when the region area forming the coolant passage  15  is the same, the number of slits decreases if the passage width increases, and the number of slits increases if the passage width decreases. 
     In the first embodiment, the number of ceramic sheets that are stacked to form the base body  12  of the heat dissipation device  11  may be changed. For example, the number of ceramic sheets stacked is increased or decreased in accordance with the cross-sectional area (passage area) of the coolant passage  15  formed in the heat dissipation device  11 . 
     The first embodiment does not particularly limit the number of semiconductor elements or metal plates. 
     The first embodiment does not particularly limit the number of mounting portions. 
     In the first embodiment, the heat dissipation device  11  may be cooled by undergoing air cooling. In this structure, a cooling gas, such as air, flows to the coolant passage  15 . 
     The heat dissipation device  11  of the first embodiment shown in  FIG. 4  may include an extension passage, which has the same structure as the extension passage W, at the side of the second slit  22   d  in addition to the extension passage W connected to the first slit  22   c.    
     As shown in  FIGS. 13 and 14 , extension passages W 1  and W 2  extending straight in the stacking direction of the first to fifth ceramic sheets  21  to  25  may be arranged as the extension passage W. The extension passage W 1  is a portion of the coolant passage  15  that is formed by the first slit  22   c , the second communication hole  23   d , and the second through hole  24   b . The extension passage W 2  is a portion of the coolant passage  15  that is formed by the second slit  22   d , the fourth communication hole  23   f , and the third through hole  24   c . As shown in  FIG. 14 , in the extension passage W 1 , the passage surface X 1 , which is formed by a surface of the first ceramic sheet  21 , is opposed in the stacking direction to the passage surface Y 1 , which is formed by a surface of the fifth ceramic sheet  25 . The same applies to the extension passage W 2 . The straight extension passages W 1  and W 2  further decrease the pressure loss of the coolant compared to when the passage is formed in a stepped manner. Also, the reduction of steps further limits expansion of the coolant passage  15  in the lateral direction. This further decreases the size of the heat dissipation device  11 . 
     As shown in  FIG. 15 , when forming the straight extension passage W 1 , the position of the second communication hole  23   d  at an end (end that is located closer to the second coolant outlet hole  23   b ) opposite to the end that is located closer to the second coolant inlet hole  23   a  is aligned with the position of the first slit  22   c  at an end (end that is located closer to the first coolant outlet hole  22   b ) opposite to the end that is located closer to the first coolant inlet hole  22   a . Also, when forming the extension passage W 1 , the position of the second communication hole  23   d  at the end that is located closer to the second coolant inlet hole  23   a  is aligned with the position of the second through hole  24   b  at an end that is located closer to the first through hole  24   a . When forming the straight extension passage W 2 , the position of the fourth communication hole  23   f  at an end that is located closer to the second coolant outlet hole  23   b  is aligned with the position of the second slit  22   d  at an end that is located closer to the first coolant outlet hole  22   b . Also, when forming the extension passage W 2 , the position of the fourth communication hole  23   f  at an end (end that is located closer to the second coolant inlet hole  23   a ) opposite to the end that is located closer to the second coolant outlet hole  23   b  is aligned with the position of the third through hole  24   c  at an end that is located closer to the second through hole  24   b.    
     Second Embodiment 
     A second embodiment of the present invention will now be described with reference to  FIGS. 16 to 20 . 
     As shown in  FIG. 16 , a heat dissipation device  11  includes a base body  218 , which is formed by stacking a plurality of sheets (six sheets in the second embodiment) of first to sixth ceramic members  212 ,  213 ,  214 ,  215 ,  216 , and  217 . Aluminum oxide, silicon nitride, silicon carbide, aluminum nitride, alumina zirconium, or the like, is used as the material of the ceramic member. Preferably, a ceramic material has high water resistance when water cooling is employed to cool the heat dissipation device  11 . 
     The base body  218  includes a coolant supply hole  219  and a coolant discharge hole  220 . A coolant is supplied from the exterior to a coolant passage formed in the base body  218  through the coolant supply hole  219 . The coolant flowing through the coolant passage is discharged from the coolant passage to the outside of the base body  218  through the coolant discharge hole  220 . The coolant supply hole  219  and the coolant discharge hole  220  each open in the first ceramic member  212 , which is an element of the base body  218 . That is, the coolant supply hole  219  and the coolant discharge hole  220  each open in one surface (first surface) of the base body  218 . The coolant supply hole  219  is connectable to the supply pipe P 1 , which is connected to an external coolant supply source. The coolant discharge hole  220  is connectable to the discharge pipe P 2 , which discharges the coolant to the exterior. The base body  218  also includes a mounting portion  222  (indicated by broken lines in  FIG. 16 ) of an electronic component  221  at a position where the mounting portion  222  is at least partially overlapped with the coolant passage as viewed from a stacking direction of the first to sixth ceramic members  212 ,  213 ,  214 ,  215 ,  216 , and  217  (hereafter, may be simply referred to as a stacking direction B). In the second embodiment, the mounting portion  222  is arranged on a surface (first face) of the first ceramic member  212  located at the exterior of the base body  218  in which the coolant supply hole  219  and the coolant discharge hole  220  open. 
     As shown in  FIG. 17 , in the same manner as the first embodiment, a semiconductor device  10  is formed by mounting a metal plate  227  on the mounting portion  222  located on the base body  218  of the heat dissipation device  11 . A semiconductor element  226 , which serves as the electronic component  221 , is coupled to the metal plate  227 . The metal plate  227 , which functions as a wiring layer and a bonding layer, is pure aluminum (e.g., 1000 series aluminum, which is pure aluminum for industrial use) or copper. The semiconductor element  226  is, for example, an insulated gate bipolar transistor (IGBT) or a diode. The semiconductor element  226  and the metal plate  227 , and the metal plate  227  and the heat dissipation device  11 , are each joined by performing metallic joining, for example, soldering or brazing. 
     The heat dissipation device  11  of the second embodiment will now be described in detail. 
     As shown in  FIGS. 18 and 19 , a coolant passage  228  that communicates the coolant supply hole  219  and the coolant discharge hole  220  is formed in the base body  218  of the heat dissipation device  11 . In the description hereafter, the first ceramic member  212 , which is the element of the base body  218  and includes the mounting portion  222 , is located at the upper side, and the sixth ceramic sheet  217 , which is located at the farthest position from the first ceramic member  212 , is located at the lower side. 
     The coolant passage  228  includes first to seventh passages L 1  to L 7 . More specifically, the first passage L 1  is straight and continuous to the coolant supply hole  291 . The coolant flows through the first passage L 1  in a vertically lower direction. The second passage L 2  branches from the first passage L 1 . The coolant flows through the second passage L 2  obliquely upward. The third passage L 3  is straight, continuous to the second passage L 2 , and formed underneath the mounting portion  222 . The coolant flows through the third passage L 3  in the horizontal direction. The fourth passage L 4  is straight and continuous to the third passage L 3 . The coolant flows through the fourth passage L 4  in the vertically lower direction. The fifth passage L 5  is straight and continuous to the fourth passage L 4 . The coolant flows through the fifth passage L 5  in the horizontal direction. The sixth passage L 6  is straight and continuous to the fifth passage L 5 . The coolant flows through the sixth passage L 6  in a vertically direction. The seventh passage L 7  is straight and branches from the first passage L 1  together with the second passage L 2 . The coolant flows through the seventh passage L 7  from the vertically lower side to the vertically upper side toward the third passage L 3  located underneath the mounting portion  222 . The first to sixth ceramic members  212  to  217  includes a plurality of passage holes, which are elements of the coolant passage  228 . The passage holes are joined in the stacking direction of the first to sixth ceramic members  212  to  217  to form the first to seventh passages L 1  to L 7 . 
     Each member of the heat dissipation device  11  will now be described with reference to  FIG. 20 . In  FIG. 20 , a sheet forming the ceramic member is referred to as a ceramic sheet. The same reference numeral as the ceramic member is given to the ceramic sheet. 
     As shown in  FIG. 20 , in the second embodiment, the first to sixth ceramic sheets  212  to  217 , which are elements of the heat dissipation device  11 , are rectangle and have the same length and the same width. 
     The first ceramic sheet  212  forms a top plate of the heat dissipation device  11  where the mounting portion  222  is located. A first passage hole  212   a  including the coolant supply hole  219  and a sixth passage hole  212   b  including the coolant discharge hole  220  are located at opposite ends of the mounting portion  222 . The first passage hole  212   a  and the sixth passage hole  212   b  have the same open area. 
     The second ceramic sheet  213  is located below the first ceramic sheet  212  when stacked. The second ceramic sheet  213  includes a first passage hole  213   a  and a sixth passage hole  213   b . The first passage hole  213   a  is located at a position corresponding to the first passage hole  212   a  of the first ceramic sheet  212  and communicates with the first passage hole  212   a . The first passage hole  213   a  has the same open area as the first passage hole  212   a . The sixth passage hole  213   b  is located at a position corresponding to the sixth passage hole  212   b  of the first ceramic sheet  212  and communicates with the sixth passage hole  212   b . The sixth passage hole  213   b  has the same open area as the sixth passage hole  212   b . Also, the second ceramic sheet  213  includes a plurality of slit-like third passage holes  213   c  (five slits in the second embodiment) between the first passage hole  213   a  and the sixth passage hole  213   b . Each third passage hole  213   c  has the same shape and extends straight. The length of the third passage hole  213   c  in the extending direction (longitudinal direction) is greater than the length of the mounting portion  222  in the same direction. The third passage holes  213   c  are arranged along a direction orthogonal to the extending direction (longitudinal direction) at regular intervals. As shown in  FIGS. 18 and 19 , a portion of the third passage hole  213   c  is located underneath the mounting portion  222 . The other portion of the third passage hole  213   c  is located outside the mounting portion  222  as viewed from the stacking direction B. 
     The third ceramic sheet  214  is located below the second ceramic sheet  213  when stacked. The third ceramic sheet  214  includes a first passage hole  214   a  and a sixth passage hole  214   b . The first passage hole  214   a  is located at a position corresponding to the first passage hole  213   a  of the second ceramic sheet  213  and communicates with the first passage hole  213   a . The first passage hole  214   a  has the same open area as the first passage hole  213   a . The sixth passage hole  214   b  communicates with the sixth passage hole  213   b  of the second ceramic sheet  213  and has the same open area as the sixth passage hole  213   b . The third ceramic sheet  214  also includes a plurality of slit-like third passage holes  214   c  (five slits in the second embodiment) between the first passage hole  214   a  and the sixth passage hole  214   b . Each third passage hole  214   c  has the same shape and extends straight. Each third passage hole  214   c  is located in a position where the third passage hole  214   c  is partially overlapped with the third passage hole  213   c  of the second ceramic sheet  213  as viewed from the stacking direction B. The length of each third passage hole  214   c  in the extending direction (longitudinal direction) is greater than the length of the third passage hole  213   c  of the second ceramic sheet  213  in the same direction. The third passage holes  214   c  are arranged along a direction orthogonal to the extending direction (longitudinal direction) at regular intervals. When the second ceramic sheet  213  and the third ceramic sheet  214  are stacked, opposite ends of the third passage hole  214   c  are located at positions that are projected by the same length outward from opposite ends of the third passage hole  213   c  as viewed from the stacking direction B. 
     As shown in  FIG. 19 , when the second ceramic sheet  213  and the third ceramic sheet  214  are stacked, each third passage hole  213   c  are overlapped with each third passage hole  214   c  in the stacking direction. This forms the third passage L 3 , which has the height of two ceramic sheets. 
     The fourth ceramic sheet  215  is located below the third ceramic sheet  214  when stacked. The fourth ceramic sheet  215  includes a first passage hole  215   a . When the third ceramic sheet  214  is stacked, the first passage hole  215   a  is located at a position where the first passage hole  215   a  is entirely overlapped with the first passage hole  214   a  and partially overlapped with the third passage hole  214   c  that is located closer to the first passage hole  214   a  as viewed from the stacking direction B. The open area of the first passage hole  215   a  is greater than the open area of the first passage hole  214   a  of the third ceramic sheet  214 . The length of the first passage hole  215   a  in a direction orthogonal to the extending direction of the third passage hole  214   c  of the third ceramic sheet  214  is the same as the length between inner surfaces of the third passage holes  214   c  that are located at the opposite outermost positions. 
     The fourth ceramic sheet  215  includes a sixth passage hole  215   b . The sixth passage hole  215   b  is located at a position corresponding to the sixth passage hole  214   b  of the third ceramic sheet  214  and communicates with the sixth passage hole  214   b . The sixth passage hole  215   b  has the same open area as the sixth passage hole  214   b . The fourth ceramic sheet  215  also includes a fourth passage hole  215   c  between the first passage hole  215   a  and the sixth passage hole  215   b.  The fourth passage hole  215   c  is located in a position where the fourth passage hole  215   c  is partially overlapped with each third passage hole  214   c  that is located closer to the sixth passage hole  214   b  as viewed from the stacking direction B. 
     The fourth ceramic sheet  215  also includes a plurality of slit-like seventh passage holes  215   d  (five slits in the second embodiment) between the first passage hole  215   a  and the fourth passage hole  215   c . Each seventh passage hole  215   d  has the same shape and extends straight. Each seventh passage hole  215   d  is located in a position where the seventh passage hole  215   d  is overlapped with the third passage hole  214   c  of the third ceramic sheet  214  as viewed from the stacking direction B. The length of each seventh passage hole  215   d  in the extending direction (longitudinal direction) is less than the length of each of the third passage holes  213   c  and  214   c  of the second and third ceramic sheets  213  and  214  in the same direction. The seventh passage holes  215   d  are arranged along a direction orthogonal to the extending direction (longitudinal direction) at regular intervals. The centers of the seventh passage holes  215   d  are arranged along a line that extends through the center of the mounting portion  222  in a direction orthogonal to the extending direction of the third passage holes  213   c  and  214   c.    
     The fifth ceramic sheet  216  is located below the fourth ceramic sheet  215  when stacked. The fifth ceramic sheet  216  includes a first passage hole  216   a  and a fifth passage hole  216   b . When the fourth ceramic sheet  215  is stacked, the first passage hole  216   a  is located at a position where the first passage hole  216   a  is entirely overlapped with the first passage hole  215   a  and each seventh passage hole  215   d  as viewed from the stacking direction B. Also, when the fourth ceramic sheet  215  is stacked, the fifth passage hole  216   b  is located at a position where the fifth passage hole  216   b  is entirely overlapped with the sixth passage hole  215   b  and the fourth passage hole  215   c  as viewed from the stacking direction B. The sixth ceramic sheet  217  is located below the fifth ceramic sheet  216  when stacked. The sixth ceramic sheet  217  forms a bottom plate of the heat dissipation device  11 . 
     The base body  218  of the heat dissipation device  11  is formed by sequentially stacking the fifth ceramic member  216 , the fourth ceramic member  215 , the third ceramic member  214 , the second ceramic member  213 , and the first ceramic member  212  on the sixth ceramic member  217 . As described above, the coolant passage  228  is formed in the base body  218  having such a structure. 
     The first passage L 1  is formed by connecting each first passage hole  212   a ,  213   a ,  214   a ,  215   a ,  216   a  of the first to fifth ceramic members  212  to  216 . The second passage L 2  is formed by connecting a portion of the first passage hole  215   a  of the fourth ceramic member  215 , a portion of the third passage hole  214   c  of the third ceramic member  214 , and a portion of the third passage hole  213   c  of the second ceramic member  213  in a stepped manner. The third passage L 3  is formed by connecting the third passage hole  213   c  of the second ceramic member  213  and the third passage hole  214   c  of the third ceramic member  214 . 
     The fourth passage L 4  is formed by connecting a portion of the third passage hole  214   c  of the third ceramic member  214 , the fourth passage hole  215   c  of the fourth ceramic member  215 , and a portion of the fifth passage hole  216   b  of the fifth ceramic member  216  in a straight line. The fifth passage L 5  is formed by the fifth passage hole  216   b  of the fifth ceramic member  216 , which is connected to the fourth passage hole  215   c  of the fourth ceramic member  215 . The sixth passage L 6  is connected to the fifth passage hole  216   b  of the fifth ceramic member  216  and formed by connecting each sixth passage hole  212   b ,  213   b ,  214   b ,  215   b  of the first to fourth ceramic members  212  to  215 . The seventh passage L 7  is formed by the seventh passage holes  215   d  of the fourth ceramic member  215 , which are connected to the first passage hole  216   a  of the fifth ceramic member  216 . 
     The third passage L 3  of the second embodiment serves as an underneath-lying passage through which coolant flows underneath the mounting portion  222 . The second passage L 2  of the second embodiment is in communication with the third passage L 3  at the upstream side in a flow direction of the coolant and forms a supply passage that supplies the coolant to the third passage L 3  together with the first passage L 1  connected to the second passage L 2 . The fourth passage L 4  of the second embodiment is in communication with the third passage L 3  at the downstream side in the flow direction of the coolant and forms a discharge passage that discharges the coolant from the third passage L 3  together with the fifth passage L 5  connected to the fourth passage L 4  and the sixth passage L 6  connected to the fifth passage L 5 . The seventh passage L 7  of the second embodiment is located between the supply passage and the discharge passage and serves as an expulsion passage that expels the coolant to the third passage L 3  from the vertically lower side toward the vertically upper side. The seventh passage L 7  serving as the expulsion passage expels the coolant toward a central section of the mounting portion  222 . 
     As shown in  FIG. 19 , the base body  218  includes fins  230  and  231 . The fin  230  is located between the third passage holes  213   c  of the second ceramic member  213  forming the third passage L 3 . The fin  231  is located between the third passage holes  214   c  of the third ceramic member  214  forming the third passage L 3 . The fins  230  and  231  are overlapped in the stacking direction B. The fins  230  and  231  are straight fins. 
     The operation of the second embodiment will now be described. 
     In the heat dissipation device  11  of the second embodiment, the coolant supplied through the coolant supply hole  219  to the coolant passage  228  first flows through the first passage L 1  toward a lower side of the heat dissipation device  11 . The coolant in the first passage L 1  is separated to flow into the second passage L 2  and the seventh passage L 7 , which branch from the first passage L 1 . Then, the coolant flows from the second passage L 2  and the seventh passage L 7  to the third passage L 3 . The heat of the electronic component  221  (semiconductor element  226  and metal plate  227 ) is dissipated to the coolant flowing through the third passage L 3  by way of the surface of the first ceramic member  212 , which covers the third passage L 3 , and the fins  230  and  231 . After heat is exchanged, the coolant flows from the third passage L 3  through the fourth passage L 4 , the fifth passage L 5 , and the sixth passage L 6 , and out of the coolant discharge hole  220 . 
     The heat dissipation device  11  of the second embodiment includes the second passage L 2 , through which the coolant flows toward the third passage L 3  in an oblique direction from a peripheral region of the mounting portion  222  of the electronic component  221  toward the mounting portion  222 , and the seventh passage L 7 , through which the coolant flows toward the central section of the mounting portion  222  from the lower side to the upper side. The coolant flowing through the second passage L 2  and the seventh passage L 7  are expelled toward the third passage L 3  from the lower side to the upper side. This generates a jet flow in the coolant flowing through the third passage L 3  and agitates the coolant. The agitation thins a temperature boundary layer of the coolant flowing through the third passage L 3 . Particularly, the coolant is expelled from the seventh passage L 7  toward the central portion of the electronic component  221 , which has the highest temperature in the mounting portion  222 . This allows the coolant to directly strike a heating surface and effectively thins the temperature boundary layer. 
     Accordingly, the second embodiment has the advantages described below. 
     (8) The seventh passage L 7  is arranged to expel the coolant into the third passage L 3  from the vertically lower side to the vertically upper side. This allows the coolant to directly strike a location corresponding to the mounting portion  222 . This effectively agitates the coolant flowing through the third passage L 3  and thins the temperature boundary layer of the coolant flowing through the third passage L 3 . Thus, the performance for cooling the cooling subject can be improved. 
     (9) The seventh passage L 7  branches from the first passage L 1 . This simplifies the structure of the coolant passage  228  formed in the base body  218 . 
     (10) The seventh passage L 7  expels the coolant toward the central section of the mounting portion  222 . This effectively thins the temperature boundary layer of the coolant flowing through the third passage L 3 . Thus, the performance for cooling the cooling subject can be further improved. 
     (11) The coolant supply hole  219  and the coolant discharge hole  220  open in the surface (first surface) of the base body  218  where the mounting portion  222  is arranged. This allows for a collective arrangement of components needed for the heat dissipation device  11 , such as, the supply pipe P 1  connected to the coolant supply hole  219 , and the discharge pipe P 2  connected to the coolant discharge hole  220 . As a result, the heat dissipation device  11  can be reduced in size. 
     (12) The coolant is expelled from the second passage L 2  and the seventh passage L 7  toward the third passage L 3 . This effectively agitates the coolant flowing through the third passage L 3  and thins the temperature boundary layer of the coolant flowing through the third passage L 3 . 
     (13) The straight fourth passage L 4  decreases pressure loss of the coolant as compared to when the fourth passage L 4  includes steps. Also, the straight fourth passage L 4  reduces steps in the coolant passage  228  and limits expansion of the coolant passage  228  in the lateral direction. This reduces the size of the heat dissipation device  11 . 
     (14) The semiconductor device  10  having the heat dissipation device  11  can effectively cool the electronic component  221  (semiconductor element  226  and metal plate  227 ). This improves the performance for cooling the electronic component  221 . 
     (15) The ceramic heat dissipation device  11  may have a cooling function and an insulative property. This allows for the formation of the semiconductor device  10  by directly joining the heat dissipation device  11  with the electronic component  221  (semiconductor element  226  and metal plate  227 ). Thus, the semiconductor device  10  may be reduced in size and the number of components. 
     The second embodiment may be modified as follows. 
     As shown in  FIG. 21 , in the second embodiment, a plurality of the seventh passages L 7  may be arranged in the coolant passage  228 . When a plurality of the seventh passages L 7  are used, coolant expelling positions of the seventh passages L 7  are located within the region of the mounting portion  222  as viewed from the stacking direction B. This further increases the effect of the jet flow. Preferably, at least one of the seventh passages L 7  is located in a position where the coolant is expelled toward the central section of the mounting portion  222 . In this structure, the seventh passages L 7  allow the coolants to directly strike a location corresponding to the mounting portion  222  from a wide range. This effectively thins the temperature boundary layer of the coolant flowing through the third passage L 3  and further improves the performance for cooling the cooling subject. 
     In the second embodiment, the base body  218  may include undulated fins by forming undulated third passage holes  213   c  and  214   c . The undulated fins increase the area that contacts the coolant and has a coolant agitating effect. This improves the cooling performance. 
     In the second embodiment, a passage that supplies the coolant to the second passage L 2  may differ from a passage that supplies the coolant to the seventh passage L 7 . For example, the coolant may be directly supplied to the seventh passage L 7  from the exterior. 
     In the second embodiment, the coolant supply hole  219  and the coolant discharge hole  220  may be located at different positions in the base body  218 . For example, the coolant supply hole  219  and the coolant discharge hole  220  may be located in the sixth ceramic member  217 . One of the coolant supply hole  219  and the coolant discharge hole  220  may be located in the first ceramic member  212  when the other is located in the sixth ceramic member  217 . 
     In the second embodiment, the fourth passage L 4  may extend obliquely downward by connecting a portion of the third passage hole  214   c  of the third ceramic member  214 , the fourth passage hole  215   c  of the fourth ceramic member  215 , and a portion of the fifth passage hole  216   b  of the fifth ceramic member  216  in a stepped manner. 
     In the second embodiment, the number of the third passage holes  213   c  and  214   c  may be changed. The number is changed in accordance with the area of a semiconductor element, the passage width of the coolant passage  228 , and the like. For example, when the area of the region forming the coolant passage  228  is the same, the number of the third passage holes  213   c  and  214   c  decreases if the passage width increases, and the number increases if the passage width decreases. 
     In the second embodiment, the number of ceramic members that are stacked to form the base body  218  of the heat dissipation device  11  may be changed. For example, the number of ceramic members stacked is increased or decreased in accordance with the cross-sectional area (passage area) of the coolant passage  228  formed in the heat dissipation device  11 . 
     In the second embodiment, the heat dissipation device  11  may be cooled by undergoing liquid cooling or air cooling. 
     In the second embodiment, the number of the electronic components  221  mounted on the heat dissipation device  11  may be changed. The coolant passage  228  in the base body  218  may be modified in accordance with the number or the layout of the mounting portions  222  on which the electronic components  221  are mounted. 
     DESCRIPTION OF REFERENCE SYMBOLS 
       10  semiconductor device 
       11  heat dissipation device 
       12 ,  218  base body 
       12   a  first surface 
       12   b  second surface 
       13   a ,  14   a ,  17   a ,  226  semiconductor element (cooling subject) 
       13   b ,  14   b ,  17   b ,  227  metal plate 
       15 ,  228  coolant passage 
       21  first ceramic sheet serving as ceramic sheet 
       21   a ,  219  coolant supply hole 
       21   b ,  220  coolant discharge hole 
       22  second ceramic sheet serving as ceramic sheet corresponding to slit formation layer 
       22   c ,  43  first slit serving as slit 
       22   d ,  44  second slit serving as slit 
       22   h  communication portion 
       23  third ceramic sheet serving as ceramic sheet corresponding to communication passage formation layer 
       23   c  first communication hole corresponding to communication passage 
       23   d  second communication hole corresponding to communication passage 
       23   e  third communication hole corresponding to communication passage 
       23   f  fourth communication hole corresponding to communication passage 
       24  fourth ceramic sheet serving as ceramic sheet 
       25  fifth ceramic sheet serving as ceramic sheet 
       35 ,  36  overlapping portion 
       41  slit 
       121  first mounting portion serving as mounting portion 
       131  second mounting portion serving as mounting portion 
       171  third mounting portion serving as mounting portion 
       212  to  217  first to sixth ceramic members (ceramic sheets) 
       222  mounting portion 
       212   a ,  213   a ,  214   a ,  215   a ,  216   a  first passage hole 
       212   b ,  213   b ,  214   b ,  215   b  sixth passage hole 
       213   c ,  214   c  third passage hole 
       215   c  fourth passage hole 
       215   d  seventh passage hole 
       216   b  fifth passage hole 
     W, W 1 , W 2  extension passage 
     X 1 , Y 1  passage surface 
     L 1  to L 7  first to seventh passages