Abstract:
A semiconductor device and a method of producing the same, wherein a joining member and a joined member are bonded by means of brazing in a way such that no voids are left inside the joining layer. The semiconductor device comprises a joined member and a joining member which is joined to the joined member by means of brazing. The joined member is provided with a through hole which is open on the joining surface with the joining member, and a path communicating with the through hole is provided on at least one of the joining surface of the joining member with the joined member or the joining surface of the member with the joining member.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a semiconductor device including a joining member and a joined member joined to each other by brazing, and a method of producing the semiconductor device. 
     BACKGROUND OF THE INVENTION 
     For a semiconductor device, when a joining member such as an insulating member (an insulating substrate) is to be joined or bonded by brazing to a member to be joined (a joined member) such as a lid of a cooler, for example, a brazing material placed between the joining member and the joined member is heated to be melted. At that time, if a clearance or gap between the joining member and the joined member is uniform, the melted brazing material is wetted and spread with no regularity. When the brazing material is cooled and solidified to form a joining layer, a peripheral portion of the joining member is apt to become cold first, causing the brazing material to begin solidifying from an outer peripheral edge. 
     Thus, air existing in the brazing material is kept in the joining layer. This may leave voids (air layers) with unspecified width or area inside the joining layer. In case such voids are left, it is impossible to stably transfer and release the heat generated in an electronic component such as a semiconductor element to a cooler. Thus, a cooling performance of the cooler could not sufficiently be brought out on the electronic component. 
     Patent document 1 discloses a technique of releasing such air. To be concrete, a pair of electrodes to which an electronic component is to be soldered are formed with guide passages for air release. These guide passages open in a clearance located under the electronic component and in the outside of the electronic component. With this configuration, the air that occurs in the clearance under the electronic component when resin is supplied to form an insulating layer is released through open ends located in the outside of the electronic component via the guide passages. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: JP 2007-258605 A 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the case where the guide passages are open in the outside of the electronic component as disclosed in Patent Document 1, outside air is liable to enter from the open ends located in the outside of the electronic component into an insulating layer formed in the clearance under the electronic component through the guide passages. Further, since the brazing material tends to begin solidifying from the outer peripheral edge when the joined member is joined to the joining member by brazing as mentioned above, the air could not be sufficiently released to the outside of the joining member. This results in remaining voids in the insulating layer formed in the clearance under the electronic component. 
     During joining and after joining between a joining member (e.g., the electronic component in Patent Document 1) and a joined member (e.g., the electrode in Patent Document 1), when heat is added to the joining member and the joined member which are different in linear expansion coefficient, thermal stress occurs. At that time, peeling and cracking are likely to occur particularly in an outer peripheral area of the joining portion. Therefore, in the case where the guide passage is provided to extend up to the outside of the joining portion between the joining member and the joined member as disclosed in Patent Document 1, thermal stress may concentrate on the guide passage located in the outside of the joining portion, causing deformation of the joining member and the joined member, leading to their disjoining. 
     The present invention has been made to solve the above problems and has a purpose to provide a semiconductor device and a method of producing the semiconductor device, whereby a joining member and a joined member are joined by brazing without leaving voids in a joining layer. 
     Means of Solving the Problems 
     To achieve the above purpose, one aspect of the invention provides a semiconductor device including a joining member and a joined member to which the joining member is joined by brazing, wherein the joined member includes a joining surface to be joined to the joining member and a through hole opening in the joining surface, and a passage communicated with the through hole is provided with at least one of a joining surface of the joining member to be joined to the joined member and the joining surface of the joined member to be joined to the joining member, the passage is provided between a position apart from an edge of a joining portion between the joining member and the joined member toward the through hole and a position of the through hole, and the passage is a groove. 
     According to the above configuration, the joined member is provided with the through hole opening in the joining surface to be joined to the joining member, and the passage communicated with the through hole is provided in at least one of the joining surface of the joining member to be joined to the joined member and the joining surface of the joined member to be joined to the joining member. Accordingly, in brazing the joining member and the joined member, a brazing material is guided in the passage, and wetted and spread with regularity. Thus, air which may be present in the brazing material passes through the passage and is removed through the through hole. Accordingly, the joining member and the joined member can be joined to each other by brazing so that no voids are left in the joining layer formed by solidification of the brazing material. 
     Further, the passage is provided between the position apart from the edge of the joining portion between the joining member and the joined member toward the through hole and the position of the through hole. 
     Thus, the passage is not open in the position corresponding to the outer peripheral edge of the joining member during joining between the joining member and the joined member. Therefore, there is no possibility that outside air enters in the passage, thus more reliably ensuring that no voids are left in the joining layer. 
     The joining member and the joined member are joined to each other more reliably with the brazing material. Even when heat is added to the joining member and the joined member during joining and after joining, therefore, the joining member and the joined member are not disjoined. 
     Further, the brazing material is easy to be guided in the groove, and wetted and spread, thereby allowing air which may be present in the brazing material to easily pass through the groove and be removed through the through hole. 
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     In the above configuration, preferably, the passage has a depth gradually increasing toward the through hole. 
     Herein, the brazing material has the property of being solidified from a portion located in a small clearance to a portion located in a large clearance. 
     According to the above configuration, therefore, the passage has the depth gradually increasing as it approaches to the through hole. The brazing material will be wetted and spread toward the through hole. Thus, air which may be present in the brazing material is more reliably removed through the through hole. This can further ensure that no voids are left in the joining layer. 
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     In the above configuration, preferably, the joined member is a lid member of a cooler for cooling an electronic component placed on the joining member. 
     According to the above configuration, no voids are left in the joining layer between the lid member of the cooler and the joining member. Thus, the electronic component placed on the joining member can be more reliably cooled. 
     In the above configuration, preferably, the through hole includes an open end that opens in a surface opposite the joining surface of the joined member and is located on a gap between a plurality of fins provided in the cooler. 
     According to the above configuration, the through hole has the open end that opens in the surface opposite the joining surface of the joined member and is located on the gap between the fins. This makes it possible to release the air which may be present in the brazing material into the cooler. This further ensures that no voids are left in the joining layer. 
     To achieve the above object, another aspect of the invention provides a method of producing a semiconductor device including a joining member and a joined member joined to each other by brazing, wherein the joined member is formed with a through hole that opens in a joining surface to be joined to the joining member, a passage communicated with the through hole is provided in at least one of a joining surface of the joining member to be joined to the joined member and the joining surface of the joined member to be joined to the joining member, the method including: placing a brazing material between the joining surface of the joining member to be joined to the joined member and the joining surface of the joined member to be joined to the joining member, and melting and solidifying the brazing material to join the joining member and the joined member to each other, wherein the passage is provided between a position apart from an edge of a joining portion between the joining member and the joined member toward the through hole and a position of the through hole, and the passage is a groove. 
     According to the above configuration, the joined member is formed with a through hole that opens in a joining surface to be joined to the joining member, a passage communicated with the through hole is provided in at least one of a joining surface of the joining member to be joined to the joined member and the joining surface of the joined member to be joined to the joining member. The method includes: placing a brazing material between the joining surface of the joining member to be joined to the joined member and the joining surface of the joined member to be joined to the joining member, and melting and solidifying the brazing material to join the joining member and the joined member to each other. Therefore, in joining the joining member and the joined member, the brazing material is guided in the passage, and wetted and spread out with regularity. Accordingly, the air which may be present in the brazing material is allowed to pass through the passage and be removed through the through hole. Thus, the joining member and the joined member can be joined by brazing so that no voids are left in the joining layer formed by solidification of the brazing material. 
     Further, the passage is provided between the position apart from the edge of the joining portion between the joining member and the joined member toward the through hole and the position of the through hole. 
     Thus, the passage is not open in the position corresponding to the outer peripheral edge of the joining member during joining between the joining member and the joined member. Therefore, there is no possibility that outside air enters in the passage, thus more reliably ensuring that no voids are left in the joining layer. 
     The joining member and the joined member are joined to each other more reliably with the brazing material. Even when heat is added to the joining member and the joined member during joining and after joining, therefore, the joining member and the joined member are not disjoined. 
     Further, the brazing material is easy to be guided in the groove, and wetted and spread, thereby allowing air which may be present in the brazing material to easily pass through the groove and be removed through the through hole. 
     Effects of the Invention 
     According to a semiconductor device and a method of producing the semiconductor device according to the present invention, a joining member and a joined member can be joined to each other by brazing without leaving voids in a joining layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a semiconductor device of a present invention; 
         FIG. 2  is a top view showing a state where a cooler and an insulating member are mounted in a brazing jig; 
         FIG. 3  is a sectional view taken along a line A-A in  FIG. 2 ; 
         FIG. 4  is a perspective view showing the insulating member and a lid of the cooler in an exploded state in Example 1; 
         FIG. 5  is a top view showing the insulating member and the lid of the cooler in a joined state in Example 1; 
         FIG. 6  is a side view showing the insulating member and the lid of the cooler in the joined state in Example 1; 
         FIG. 7  is a perspective view showing an insulating member and a lid of a cooler in an exploded state in Example 2; 
         FIG. 8  is a side view showing the insulating member and the lid of the cooler in a joined state in Example 2; 
         FIG. 9  is a perspective view showing an insulating member and a lid of a cooler in an exploded state in Example 3; 
         FIG. 10  is a top view showing the insulating member and the lid of the cooler in a joined state in Example 3; 
         FIG. 11  is a top view showing an insulating member and a lid of a cooler in a joined state in Example 4; 
         FIG. 12  is a side view showing the insulating member and the lid of the cooler in the joined state in Example 4; 
         FIG. 13  is a view showing another example of Example 4. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of a preferred embodiment of the present invention will now be given referring to the accompanying drawings. 
       FIG. 1  is a side view of a semiconductor device  1  of the present invention. As shown in  FIG. 1 , the semiconductor device  1  includes a cooler  10 , insulating members  12 , electronic components  14 , and others. 
     The cooler  10  includes a frame  16 , a plurality of fins  18 , lids  20 , and others. The frame  16  is made of for example aluminum (linear expansion coefficient: about 25 ppm/° C.) and formed in a box-like shape. The fins  18  are arranged in the frame  16  so that adjacent fins  18  are spaced apart from each other with gaps  22 . The gaps  22  serve as channels of cooling water. 
     The lids  20  are made of for example aluminum (linear expansion coefficient: about 25 ppm/° C.) and formed in a flat-plate shape. Each lid  20  is formed with a through hole  40  as mentioned later. An open end  40   b  of the through hole  40  opening on the fin  18  side is located in a position to open in a gap  22 . The through hole  40  has a size enough to allow passage of air but not allow a brazing material  32  (see  FIG. 3 ) held on the interior surface of the through hole  40  by surface tension to drop out. To be specific, the through hole  40  has a hole diameter of several millimeters or less. 
     The insulating members  12  are insulating substrates placed on the lid  20  of the cooler  10 . A linear thermal coefficient of the insulating members  12  is for example 4 to 4.5 ppm/° C. Between the insulating members  12  and the lid  20 , joining layers  24  formed of the solidified brazing material  32  (see  FIG. 3 ) are provided. The electronic components  14  are semiconductor modules placed on the upper surfaces of the insulating members  12  and are each internally provided with a semiconductor element such as IGBT and a diode to control a large amount of power. 
     With the above configuration, the electronic components  14  in the semiconductor device  1  are cooled in the following manner. Heat generated in each electronic component  14  is transferred to the fins  18  via the insulating member  12 , the joining layer  24 , and the lid  20 . At that time, cooling water not shown is supplied through an inlet port  26  (see  FIG. 2 ) provided in the lid  20  of the cooler  10 . When the cooling water flows in the gaps  22 , therefore, heat exchange is performed between the cooling water and the fins  18 . Thus, the heat generated in the electronic components  14  is absorbed by the cooling water. Thereafter, the cooling water absorbing the heat is discharged out through an outlet port  28  (see  FIG. 2 ) provided in the lid  20 . As above, the heat generated in the electronic components  14  is released out of the semiconductor device  1  and the electronic components  14  are cooled. 
     In the present embodiment, one example of joining between a joining member and a joined member is explained below as joining between the insulating members  12  and the lid  20 . 
       FIGS. 2 and 3  are views showing a part of a process of producing the semiconductor device  1 , showing a state where the cooler  10  and the insulating members  12  are mounted in a brazing jig  30 . Specifically,  FIG. 2  is a top view and  FIG. 3  is a sectional view taken along a line A-A in  FIG. 2 . In  FIG. 2 , press members  36  are not illustrated for convenience of explanation. 
     As shown in  FIG. 2 , four insulating members  12  in total are provided to one cooler  10 . 
     As shown in  FIG. 3 , the insulating members  12  are placed on the lid  20  by interposing the brazing material  32  (a metal joining material and so on) and further the press members  36  supported in the brazing jig  30  are disposed respectively on the insulating members  12 . 
     The brazing jig  30  has for example an outer frame  38  having a box-like shape as shown in  FIG. 3  and is configured to place the cooler  10  inside the outer frame  38 . 
     The brazing jig  30  configured as above, in which the cooler  10  and the insulating members  12  are mounted, is put in a heating furnace not shown. An internal temperature of the heating furnace is increased to a melting temperature of the brazing material  32  or higher, thereby melting the brazing material  32 , and then is decreased to the melting temperature of the brazing material  32  or lower. Accordingly, the brazing material  32  is melted once, wetted and spread in clearances between the insulating members  12  and the lid  20  and then solidified, forming the joining layers  24  (see  FIG. 1 ). Thus, the insulating members  12  and the lid  20  are joined or bonded to one another by brazing. 
     Therefore, the following explanation is given to examples of the present invention related to the above joining between the insulating members  12  and the lid  20  of the cooler  10  by brazing. 
     EXAMPLE 1 
     In Example 1,  FIGS. 4 to 6  show one insulating member  12  indicated by a chain double-dashed line in  FIG. 2  to show a joining portion  39  between the insulating member  12  and the lid  20 . Specifically,  FIG. 4  is a perspective view showing the insulating member  12  and the lid  20  in an exploded state.  FIGS. 5 and 6  are views showing the insulating member  12  and the lid  20  in a joining state; specifically,  FIG. 5  is a top view and  FIG. 6  is a sectional view taken along a line B-B in  FIG. 5 . 
     As shown in  FIGS. 4 to 6 , the lid  20  is provided with the through hole  40  and grooves  42 . The lid  20  includes a joining surface  20   a  to be joined to the insulating member  12  and the other surface  20   b  opposite the joining surface  20   a . The surface  20   b  is located on the side where the fins  18  are placed. 
     The through hole  40  is formed through the lid  20  in a pressing direction of the press member  36  (see  FIG. 3 ) and includes an open end  40   a  opening in the joining surface  20   a , i.e., on the joining surface  20   a  side, and an open end  40   b  opening in the other surface  20   b , i.e., on the fin  18  side. The open end  40   b  is located in a position corresponding to the gap  22  between the fins  18  in an assembled state as the cooler  10  as shown in  FIG. 1 . In the example shown in  FIGS. 4 to 6 , the through hole  40  is provided one per insulating member  12  and located near the center of the joining portion  39  between the insulating member  12  and the lid  20 . However, not limited to the example shown in  FIGS. 4 to 6 , the through hole  40  may be provided anywhere in the joining portion  39  between the insulating member  12  and the lid  20  other than the center thereof. As an alternative, a plurality of through holes  40  may be provided in one area in the joining portion  39  between the insulating member  12  and the lid  20 . 
     The grooves  42  are formed in the joining surface  20   a  of the lid  20  by fine processing using laser or the like. The grooves  42 , which are one example of a passage communicated with the through hole  40 , are arranged to extend radially from the through hole  40  as a center. In the example shown in  FIGS. 4 to 6 , for one through hole  40 , eight grooves  42  in total are arranged in eight positions spaced at equal intervals in a circumferential direction about the center point of the through hole  40 . The total number of grooves  42  is not limited to eight and, for example, may be appropriately determined according to the area of the joining surface  12   b  of the insulating member  12  to be joined to the lid  20 . 
     Each groove  42  is formed between a position X at a predetermined distance apart from an edge  39   a  of the joining portion  39  between the insulating member  12  and the lid  20  toward the through hole  40  and the position of the through hole  40  as shown in  FIGS. 4 to 6 . Thus, when the insulating member  12  is to be joined to the lid  20 , the grooves  42  are not open in positions corresponding to an outer peripheral edge  12   a  of the insulating member  12 . 
     As shown in  FIG. 6 , furthermore, a bottom  42   a  of each groove  42  is sloped downward from the edge  39   a  of the joining portion  39  between the insulating member  12  and the lid  20  toward the through hole  40 . Accordingly, the depth of each groove  42  gradually increases as it approaches the through hole  40 . Alternatively, the grooves  42  may be designed to each have a uniform depth without making the bottoms  42   a  slant. 
     The above configuration in Example 1 can provide the following operations and effects. 
     During melting and solidifying, the brazing material  32  placed between the joining surfaces  12   b  and the joining surface  20   a  is guided in the grooves  42  and hence wetted and spread out regularly. Accordingly, the air which may be present in the brazing material  32  is guided in the grooves  42  and passes through the grooves  42 , and then released into the cooler  10  through the through holes  40 . 
     Especially, the bottom  42   a  of each groove  42  is sloped downward from the edge  39   a  side of the joining portion  39  between the insulating member  12  and the lid  20  toward the through hole  40  so that the depth of each groove  42  gradually increases as it approaches toward the through hole  40 . Herein, the brazing material  32  has the property of being solidified from a portion located in a small clearance between the joining member and the joined member toward a portion located in a large clearance. Accordingly, the air which may be present in the brazing material  32  is allowed to flow toward a large-depth portion of each groove  42  near the through hole  40  and then be released into the cooler  10  through the through hole  40 . Since the open end  40   b  of the through hole  40  is located on the gap  22  between the fins  18 , the air which may be present in the brazing material  32  is released into the gap  22 . Thus, no voids are left in the joining layer  24  formed by solidification of the brazing material  32 . Therefore, the heat generated from the electronic component  14  stably transferred and released to the cooler  10 , so that the electronic component  14  and others can be cooled stably. 
     Further, the groove  42  is provided between the position X at the predetermined distance apart from the edge  39   a  of the joining portion  39  between the insulating member  12  and the lid  20  toward the through hole  40  and the position of the through hole  40 . Thus, the grooves  42  are not open in the positions corresponding to the outer peripheral edge  12   a  when the insulating member  12  is joined to the lid  20 . Consequently, there is no possibility that outside air enters in the grooves  42 . This can further ensure that no voids are left in the joining layer  24 . 
     Furthermore, the grooves  42  are not open in the positions corresponding to the outer peripheral edge  12   a  of each insulating member  12  during joining of the insulating members  12  to the lid  20 . Even in the edge  39   a  of each joining portion  39 , the insulating members  12  and the lid  20  are reliably joined to each other with the brazing material  32 . Accordingly, even when thermal stress occurs by the heat applied to the insulating members  12  and the lid  20  during and after joining, the thermal stress does not concentrate on specific portions. Thus, the insulating members  12  and the lid  20  are not disjoined. 
     When the brazing material  32  held on the interior surface of each through hole  40  by surface tension is solidified, finally, it serves as a stopper that blocks off the through holes  40 . Accordingly, there is no possibility that the cooling water flowing through the cooler  10  leaks to the outside through the through holes  40 . 
     EXAMPLE 2 
     In Example 2,  FIGS. 7 and 8  show one insulating member  12  indicated by a chain double-dashed line in  FIG. 2  to show a joining portion between the insulating member  12  and the lid  20 . Specifically,  FIG. 7  is a perspective view showing the insulating member  12  and the lid  20  in an exploded state.  FIG. 8  is a view showing the insulating member  12  and the lid  20  in a joining state, corresponding to a sectional view taken along a line B-B in  FIG. 5 . A top view of this example is identical to  FIG. 5  and hence is omitted herein. 
     As shown in  FIGS. 7 and 8 , the lid  20  is provided with the through hole  40  and the insulating member  12  is provided with grooves  44 . 
     In this example, the details of the through hole  40  are identical to those in Example 1 and omitted herein. 
     The grooves  44  are formed in the joining surface  12   b  of the insulating member  12  by fine processing using laser or the like. The grooves  44  are arranged to extend radially from a position corresponding to the position in which the through hole  40  is located when the insulating member  12  and the lid  20  are joined. Accordingly, the grooves  44  are communicated with the through hole  40  when the insulating member  12  and the lid  20  are joined. As above, the grooves  44  are one example of a passage communicated with the through hole  40 . 
     In the example shown in  FIG. 7 , the through hole  40  is provided in the position corresponding to the center of the insulating member  12  when the insulating member  12  and the lid  20  are joined. Thus, the grooves  44  are arranged radially from the position near the center of the insulating member  12 . 
     In the example shown in  FIG. 7 , per one insulating member  12 , eight grooves  44  in total are arranged in eight positions spaced at equal intervals in a circumferential direction about near the center of the insulating member  12 . The total number of grooves  44  is not limited to eight and, for example, may be appropriately determined according to the area of the joining surface  12   b  of the insulating member  12 . 
     It is to be noted that the brazing material  32  is placed between the joining surface  12   b  of the insulating member  12  and the joining surface  20   a  of the lid  20  as shown in  FIG. 7  to join the insulating member  12  and the lid  20  to each other. 
     Each groove  44  is formed between a position Y at a predetermined distance apart from the outer peripheral edge  12   a  of the insulating member  12  toward the center and the center position of the insulating member  12 , as shown in  FIGS. 7 and 8 . This means that the groove  44  is provided between the position Y at the predetermined distance apart from the outer peripheral edge  12   a  of the insulating member  12  toward the through hole  40  and the position of the through hole  40  as shown in  FIG. 8 . Accordingly, the grooves  44  are not open in the outer peripheral edge  12   a  of the insulating member  12 . 
     Furthermore, as shown in  FIG. 8 , a bottom  44   a  of each groove is sloped upward from the outer peripheral edge  12   a  toward the center of the insulating member  12 . Accordingly, the depth of each groove  44  gradually increases as it approaches the through hole  40 . As an alternative, the grooves  44  may be designed to each have a uniform depth without making the bottoms  44   a  slant. 
     The above configuration in Example 2 can provide the following operations and effects. 
     During melting and solidifying, the brazing material  32  placed between the joining surface  12   b  and the joining surface  20   a  is guided in the grooves  44  and hence wetted and spread regularly. Accordingly, the air which may be present in the brazing material  32  is guided in the grooves  44  to pass through the grooves  44 , and then released into the cooler  10  through the through hole  40 . 
     Especially, the bottom  44   a  of each groove  44  is sloped upward from the outer peripheral edge  12   a  toward the center of the insulating member  12  so that the depth of each groove  44  gradually increases as it approaches toward the vicinity of the center of the insulating member  12 . Herein, the brazing material  32  has the property of being solidified from a portion located in a small clearance between the joining member and the joined member toward a portion located in a large clearance. Accordingly, the air which may be present in the brazing material  32  is allowed to flow toward a large-depth portion of each groove  44  near the center of the insulating member  12  and then released into the cooler  10  through the through hole  40 . Since the open end  40   b  of the through hole  40  is located on the gap  22  between the fins  18 , the air which may be present in the brazing material  32  is released into the gap  22 . Thus, no voids are left in the joining layer  24  formed by solidification of the brazing material  32 . Therefore, the heat generated from the electronic component  14  can be stably transferred and released to the cooler  10 , so that the electronic component  14  and others can be cooled stably. 
     Further, the groove  44  is provided between the position Y at the predetermined distance apart from the outer peripheral edge  12   a  of the insulating member  12  toward the center and the center of the insulating member  12 . Thus, the grooves  44  are not open in the outer peripheral edge  12   a . Consequently, there is no possibility that outside air enters in the grooves  44 . This can further ensure that no voids are left in the joining layer  24 . 
     Furthermore, the grooves  44  are not open in the outer peripheral edge  12   a  and thus the insulating member  12  and the lid  20  are reliably joined to each other with the brazing material  32  even in the edge  39   a  of the joining portion  39 . Accordingly, even when thermal stress occurs by the heat applied to the insulating member  12  and the lid  20  during and after joining, the thermal stress does not concentrate on specific portions. Thus, the insulating member  12  and the lid  20  are not disjoined. 
     When the brazing material  32  held on the interior surface of each through hole  40  by surface tension is solidified, finally, it serves as a stopper that blocks off the through holes  40 . Accordingly, there is no possibility that the cooling water flowing through the cooler  10  leaks to the outside through the through holes  40 . 
     EXAMPLE 3 
     In Example 3,  FIGS. 9 and 10  show one insulating member  12  indicated by a chain double-dashed line in  FIG. 2  to show a joining portion between the insulating member  12  and the lid  20 . Specifically,  FIG. 9  is a perspective view showing the insulating member  12  and the lid  20  in an exploded state.  FIG. 10  is a top view showing the insulating member  12  and the lid  20  in a joining state. A sectional view taken along a line C-C in  FIG. 10  is identical to  FIG. 6  and omitted herein. 
     As shown in  FIGS. 9 and 10 , the lid  20  is provided with the through hole  40  and a sloping portion  46 . 
     In this example, the details of the through hole  40  are identical to those in Example 1 or Example 2 and omitted herein. 
     The sloping portion  46  is a cone-shaped sloping hollow centered at the through hole  40  as shown in  FIG. 9 . This sloping portion  46  is one example of a passage communicated with the through hole  40  as with the grooves  42  of Example 1 and the grooves  44  of Example 2. The sloping portion  46  is provided between a position Z at a predetermined distance apart from the edge  39   a  of the joining portion  39  between the insulating member  12  and the lid  20  toward the through hole  40  and the position of the through hole  40 . Accordingly, the sloping portion  46  is not open in the position corresponding to the outer peripheral edge  12   a  of the insulating member  12  when the insulating member  12  and the lid  20  are joined. 
     The above configuration in Example 3 can provide the following operations and effects. 
     During melting and solidifying, the brazing material  32  placed between the joining surface  12   b  and the joining surface  20   a  is guided in the sloping portion  46  and hence wetted and spread regularly. Accordingly, the air which may be present in the brazing material  32  is guided in the sloping portion  46  to pass through the sloping portion  46 , and then released into the cooler  10  through the through hole  40 . 
     Especially, the sloping portion  46  is sloped downward from the edge  39   a  of the joining portion  39  between the insulating member  12  and the lid  20  toward the through hole  40  so that the depth of the sloping portion  46  is gradually larger as it approaches toward the through hole  40 . Herein, the brazing material  32  has the property of being solidified from a portion located in a small clearance between the joining member and the joined member to a portion located in a large clearance. Accordingly, the air which may be present in the brazing material  32  is released into the cooler  10  through the through hole  40 . Since the open end  40   b  of the through hole  40  is located on the gap  22  between the fins  18 , the air which may be present in the brazing material  32  is released into the gap  22 . Thus, no voids are left in the joining layer  24  formed by solidification of the brazing material  32 . Therefore, the heat generated from the electronic component  14  can be stably transferred and released to the cooler  10 , so that the electronic component  14  and others can be cooled stably. 
     Further, the sloping portion  46  is provided between the position Z at the predetermined distance apart from the edge  39   a  of the joining portion  39  between the insulating member  12  and the lid  20  toward the through hole  40  and the position of the through hole  40 . Thus, the sloping portion  46  is not open in the position corresponding to the outer peripheral edge  12   a  during joining of the insulating member  12  to the lid  20 . Consequently, there is no possibility that outside air enters in the sloping portion  46 . This can further ensure that no voids are left in the joining layer  24 . 
     Furthermore, as in Examples 1 and 2, when the brazing material  32  held on the interior surface of each through hole  40  by surface tension is solidified, finally, it serves as a stopper that blocks off the through holes  40 . Accordingly, there is no possibility that the cooling water flowing through the cooler  10  leaks to the outside through the through holes  40 . 
     EXAMPLE 4 
     In Example 4,  FIGS. 11 and 12  show one insulating member  12  indicated by a chain double-dashed line in  FIG. 2  to show a joining portion between the insulating member  12  and the lid  20 . Specifically,  FIG. 11  is a top view and  FIG. 12  is a sectional view taken along a line D-D in  FIG. 11 . 
     As shown in  FIGS. 11 and 12 , the lid  20  is provided with a single minute recess  48  near the center of the insulating member  12  when the insulating member  12  and the lid  20  are joined. As an alternative, as shown in  FIG. 13 , a single recess  50  may be provided near the center of the insulating member  12 . The position of the recess  48  or the recess  50  is not limited to the vicinity of the center of the insulating member  12 . Further, a plurality of such recesses may also be provided. 
     The above configuration in Example 4 can provide the following operations and effects. 
     The air which may be generated in the joining layer  24  when the brazing material  32  is melted and then solidified from its peripheral portion intensively collects in the recess  48  or  50 . This can ensure a joining rate in portions other than the recess  48  or  50 . Accordingly, the insulating member  12  and the lid  20  can be joined reliably by brazing. 
     The above embodiments are mere examples and do not give any limitations to the present invention. The present invention may be embodied in other specific forms without departing from the essential characteristics thereof. 
     In the above examples, the insulating member  12  is directly joined to the lid  20  of the cooler  10 . As an alternative, a metal plate not shown may be interposed between the lid  20  and the insulating member  12 . In this case, instead of the insulating member  12 , the metal plate is formed with grooves, recesses, or the like. 
     At the same time as joining between the insulating member  12  and the lid  20  of the cooler  10  in the aforementioned Examples 1 to 4, brazing joining may also be performed between the frame  16  and the lid  20  of the cooler  10  and between the fins  18  and the lid  20  of the cooler  10 . 
     The present invention may also be applied to a joined member other than the lid  20  of the cooler  10 . 
     Furthermore, it may be arranged that the lid  20  of the cooler  10  is provided with the grooves  42  and simultaneously the insulating member  12  is provided with the grooves  44 . 
     DESCRIPTION OF THE REFERENCE SIGNS 
     
         
           1  Semiconductor device 
           10  Cooler 
           12  Insulating member 
           12   a  Outer peripheral edge 
           12   b  Joining surface 
           14  Electronic component 
           18  Fin 
           20  Lid 
           20   a  Joining surface 
           20   b  Surface 
           22  Gap 
           24  Joining layer 
           32  Brazing material 
           39  Joining portion 
           39   a  Edge 
           40  Through hole 
           40   a  Open end 
           40   b  Open end 
           42  Groove 
           42   a  Bottom 
           44  Groove 
           44   a  Bottom 
           46  Sloping portion 
           48  Recess 
           50  Recess