Patent Publication Number: US-2023154820-A1

Title: Power semiconductor device and power conversion device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a power semiconductor device and a power conversion device. 
     BACKGROUND ART 
     Conventionally, a screw has been often used to connect and fix a power module and a support member to each other. In particular, in a case where heat dissipation is required, a fixing method with a screw using heat dissipation grease on a joint surface has been adopted. However, this method entails a problem of an increase in size because the screw fixing part is large. This method also entails a problem of deterioration in thermal resistance and reduction in insulation due to deterioration of grease. 
     In recent years, a method for joining a support member and a power module using an adhesive sheet having high adhesiveness has been applied. Particularly, when the support member is formed from a heat dissipation member, a heat dissipation adhesive sheet having high thermal conductivity is selected as the adhesive sheet. When the power module and the support member are not at the same potential, the adhesive sheet is required to have insulation. Therefore, a multifunctional material having heat dissipation, insulation, and adhesiveness may be selected as the adhesive sheet. As a result, it is possible to reduce the mounting area and the cost of the power semiconductor device. 
     As the adhesive sheet having the above characteristics, a thermally conductive resin composition obtained by combining an inorganic substance and a thermosetting resin is used, for example. When the power module and the support member are joined, a method for heating an uncured adhesive sheet and applying pressure to the adhesive sheet during curing is used. The inorganic substance is not involved in adhesiveness, and the thermosetting resin ensures adhesiveness. In many cases, voids are present in the thermosetting resin. 
     In order to uniformly join the power module and the support member, it is necessary to first heat the adhesive sheet, and at a timing when the viscosity of the thermosetting resin decreases, apply pressure thereto. The pressing force needs to be appropriately set in consideration of influences such as deformation of the power module, deformation of the support member, and irregularities of the joined surface due to application of pressure. When the pressing force is too low, a gap is generated between the power module or the support member and the adhesive sheet. In addition, voids originally present inside the adhesive sheet may remain and cause internal cracks. As a result, the bonding reliability may be lowered. 
     In addition, when the adhesive sheet is made of a multifunctional material having insulation and heat dissipation, the influence of voids in the adhesive sheet is more remarkable. Regarding insulation, partial discharge due to voids in the adhesive sheet causes a decrease in insulation reliability. The relationship between the void size and the partial discharge is based on Paschen&#39;s law Paschen&#39;s law. Specifically, the larger the void, the lower the insulation reliability. Similarly, regarding heat dissipation, the thermal conductivity of a portion where the void is present may be lowered. 
     Commonly, the power module is bonded to the upper surface of the adhesive sheet, and the support member is bonded to the lower surface of the adhesive sheet. The lateral face of the adhesive sheet is not bonded to the power module and the support member. When the adhesive sheet is bonded to the power module and the support member, the power module, the support member, and the adhesive sheet are pressurized in the vertical direction of the adhesive sheet. Since the lateral face of the adhesive sheet is open, almost no internal pressure is generated inside the adhesive sheet. To address this problem, Japanese Patent Laying-Open No. 2012-174965 (Patent Literature 1) discloses a sheet volume increase/decrease absorbing portion provided in a peripheral portion of an adhesive sheet. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Laying-Open No. 2012-174965 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     As described in Patent Literature 1, it is considered that adhesiveness, heat dissipation, and insulation can be improved by providing a frame that defines an increase or decrease in volume of the adhesive sheet. However, in the technique disclosed in Patent Literature 1, a difference in an amount of flow of a thermosetting resin in the adhesive sheet occurs due to a difference in the distance from the center of pressure applied to the adhesive sheet to the inner peripheral surface of the sheet volume increase/decrease absorption portion. Therefore, a difference occurs in the internal pressure of the outer peripheral surface of the adhesive sheet. 
     Specifically, when the adhesive sheet is bonded to the power module and the support member, the adhesive sheet flows in the in-plane direction. The adhesive sheet includes, for example, ceramic, a thermosetting resin, and voids. The ceramic, the thermosetting resin, and the voids are considered as a liquid, the thickness direction of the adhesive sheet is considered as a flow path cross-sectional area, and the distance from the center of the adhesive sheet is considered as a flow path length. Applying hydrodynamics theory, when the adhesive sheet is rectangular, the corner portion of the adhesive sheet is the farthest from the center of the adhesive sheet. At the corner portion of the adhesive sheet, the flow path length is long, so that the fluid resistance increases. As a result, at the corner portion of the adhesive sheet, the liquid amount of the adhesive sheet is the smallest, so that the internal pressure is the lowest. When the internal pressure of the adhesive sheet is low, the number and size of voids remaining in the adhesive sheet increase, so that each of adhesiveness, heat dissipation, and insulation deteriorates. Therefore, the reliability of the power semiconductor device decreases. 
     The present disclosure has been accomplished in view of the above problems, and an object thereof is to provide a power semiconductor device capable of improving reliability. 
     Solution to Problem 
     A power semiconductor device according to the present disclosure includes a power module unit, an adhesive sheet, a support member, and a flow prevention frame. The adhesive sheet is bonded to the power module unit. The support member is connected to the power module unit with the adhesive sheet interposed between the power module unit and the support member. The flow prevention frame is sandwiched between the power module unit and the support member, and is placed around the adhesive sheet. The adhesive sheet has an outer peripheral surface adjoining an inner peripheral surface of the flow prevention frame. A value obtained by dividing a maximum value of an internal pressure on the outer peripheral surface by a minimum value of the internal pressure is less than or equal to 10. 
     Advantageous Effects of Invention 
     According to the power semiconductor device according to the present disclosure, it is possible to improve adhesiveness, heat dissipation, and insulation of the adhesive sheet by reducing the number and size of voids remaining in the adhesive sheet. As a result, the reliability of the power semiconductor device can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic perspective view illustrating a configuration of a power semiconductor device according to a first embodiment. 
         FIG.  2    is a cross-sectional view taken along line II-II in  FIG.  1   . 
         FIG.  3    is a cross-sectional view taken along line III-III in  FIG.  2   . 
         FIG.  4    is a schematic cross-sectional view illustrating a manufacturing process of the power semiconductor device according to the first embodiment. 
         FIG.  5    is a schematic cross-sectional view illustrating a configuration of a power semiconductor device according to a second embodiment. 
         FIG.  6    is a schematic perspective view illustrating a configuration of a power semiconductor device according to a third embodiment. 
         FIG.  7    is a schematic perspective view illustrating a configuration of a power module of the power semiconductor device according to the third embodiment. 
         FIG.  8    is a cross-sectional view taken along line VIII-VIII in  FIG.  6   . 
         FIG.  9    is a cross-sectional view taken along line IX-IX in  FIG.  8   . 
         FIG.  10    is a schematic perspective view illustrating a configuration of a power semiconductor device according to a fourth embodiment. 
         FIG.  11    is a schematic perspective view illustrating a configuration of a support member of the power semiconductor device according to the fourth embodiment. 
         FIG.  12    is a cross-sectional view taken along line XII-XII in  FIG.  10   . 
         FIG.  13    is a cross-sectional view taken along line XIII-XIII in  FIG.  12   . 
         FIG.  14    is a schematic cross-sectional view illustrating a configuration of a power semiconductor device according to a fifth embodiment. 
         FIG.  15    is a schematic cross-sectional view illustrating a configuration of a power semiconductor device according to a sixth embodiment. 
         FIG.  16    is a schematic cross-sectional view illustrating a configuration of a power semiconductor device according to a seventh embodiment. 
         FIG.  17    is a schematic cross-sectional view illustrating a configuration of a power semiconductor device according to an eighth embodiment. 
         FIG.  18    is a cross-sectional view taken along line XVIII-XVIII in  FIG.  17   . 
         FIG.  19    is a schematic cross-sectional view illustrating a configuration of a power semiconductor device according to a ninth embodiment. 
         FIG.  20    is a cross-sectional view taken along line XX-XX in  FIG.  19   . 
         FIG.  21    is a block diagram illustrating a configuration of a power conversion system to which a power conversion device according to a tenth embodiment is applied. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present disclosure will be described below in detail. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the redundant description thereof will not be repeated. 
     First Embodiment 
       FIG.  1    is a schematic perspective view illustrating a configuration of a power semiconductor device according to a first embodiment.  FIG.  2    is a cross-sectional view taken along line II-II in  FIG.  1   . 
     As illustrated in  FIGS.  1  and  2   , a power semiconductor device  100  according to the first embodiment mainly includes a power module unit  200 , an adhesive sheet  6 , a support member  7 , and a flow prevention frame  8 . Power module unit  200  mainly includes a power semiconductor element  1 , a first metal wiring member  2   a , a second metal wiring member  2   b , a third metal wiring member  2   c , a heat spreader  3 , a first metal bonding member  4   a , a second metal bonding member  4   b , and a mold resin portion  5 . Power semiconductor element  1  is sealed by mold resin portion  5 . Power semiconductor element  1  is bonded to heat spreader  3  using first metal bonding member  4   a . Power semiconductor element  1  is bonded to first metal wiring member  2   a  using second metal bonding member  4   b.    
     First metal wiring member  2   a  and second metal wiring member  2   b  are made of, for example, solder or metal such as silver or aluminum. Power semiconductor element  1  is bonded to second metal wiring member  2   b  using third metal wiring member  2   c . Third metal wiring member  2   c  is, for example, a wire made of aluminum, copper, or the like. Power semiconductor element  1  is, for example, a voltage-driven metal oxide semiconductor field effect transistor (MOSFET), insulated gate bipolar transistor (IGBT), diode, or the like. Power semiconductor element  1  is made of, for example, a semiconductor such as silicon, silicon nitride, gallium nitride, or silicon carbide. Power semiconductor element  1  is a main heat source in power module unit  200 . 
     Each of first metal wiring member  2   a  and second metal wiring member  2   b  is molded with a part thereof being exposed to the outside of mold resin portion  5 . Each of first metal wiring member  2   a  and second metal wiring member  2   b  serves as a connection portion with the outside. Support member  7  is, for example, a heat sink that diffuses heat generated by power semiconductor element  1  during operation to the outside. Support member  7  is made of metal such as aluminum or copper, for example. Support member  7  is connected to power module unit  200  with adhesive sheet  6  therebetween. Support member  7  includes, for example, a body portion  7   a  and a plurality of fins  7   b . Since support member  7  has the plurality of fins  7   b , heat dissipation is improved. A cooling solution may be put into support member  7  to cool support member  7 . Support member  7  may be connected to a peripheral component such as a radiator (not illustrated). The cooling solution is, for example, water. 
     At least one surface of power module unit  200  is connected to support member  7  using adhesive sheet  6 . For example, power module unit  200  may have a structure in which a part of heat spreader  3  having no insulating function is exposed from mold resin portion  5 , and the exposed surface and support member  7  are connected by adhesive sheet  6  having insulation, adhesiveness, and heat dissipation. Power module unit  200  may have a structure in which an insulating substrate holding ceramic is used as heat spreader  3  which is partly exposed from mold resin portion  5 , and the exposed surface and support member  7  are connected by adhesive sheet  6  having adhesiveness and heat dissipation. Power module unit  200  may have a structure in which all surfaces are sealed with a mold resin and any one of the surfaces is joined to support member  7  using adhesive sheet  6  having adhesiveness and heat dissipation. 
     Adhesive sheet  6  is bonded to power module unit  200 . Adhesive sheet  6  is in contact with each of heat spreader  3  and mold resin portion  5 , for example. Adhesive sheet  6  is, for example, a mixture of ceramic and a thermosetting resin. The ceramic is, for example, boron nitride. The thermosetting resin is, for example, an epoxy resin or a polyimide resin. Adhesive sheet  6  may be formed by simply mixing ceramic grains in a thermosetting resin, or may be formed by impregnating a ceramic skeleton with a thermosetting resin. The ceramic functions as a heat dissipation path. The thermosetting resin ensures adhesiveness. The ceramic and the thermosetting resin have insulating properties. 
     It is only sufficient that adhesive sheet  6  is made of a material having heat dissipation, insulation, and adhesiveness, and the material of adhesive sheet  6  is not limited to the above materials. Adhesive sheet  6  as described above generally contains voids within about a range of 1 vol % or more and 14 vol % or less, for example. There may be a possibility that adhesiveness, insulation, and heat dissipation of adhesive sheet  6  are deteriorated due to the voids. 
     As illustrated in  FIG.  2   , flow prevention frame  8  is sandwiched between power module unit  200  and support member  7 . Flow prevention frame  8  is placed around adhesive sheet  6 .  FIG.  3    is a cross-sectional view taken along line III-III in  FIG.  2   . As illustrated in  FIG.  3   , flow prevention frame  8  has an inner peripheral surface  18  and an outer wall surface  28 . Outer wall surface  28  is located outside inner peripheral surface  18 . Outer wall surface  28  surrounds inner peripheral surface  18 . Adhesive sheet  6  has a central portion  6   a , an outer peripheral portion  6   b , and an outer peripheral surface  6   c . Outer peripheral portion  6   b  is located outside central portion  6   a . Outer peripheral portion  6   b  is continuous with central portion  6   a . Outer peripheral portion  6   b  constitutes outer peripheral surface  6   c . Flow prevention frame  8  is constituted by, for example, a single layer. Flow prevention frame  8  is constituted by, for example, a single material. 
     As illustrated in  FIG.  3   , outer peripheral portion  6   b  surrounds central portion  6   a  as viewed in the thickness direction of adhesive sheet  6 . Outer peripheral portion  6   b  constitutes outer peripheral surface  6   c . Outer peripheral surface  6   c  adjoins inner peripheral surface  18  of flow prevention frame  8 . As illustrated in  FIG.  3   , inner peripheral surface  18  has, for example, a rectangular shape with rounded corners as viewed in the thickness direction of adhesive sheet  6 . Inner peripheral surface  18  has a rounded corner portion  18   a  and a side portion  18   b . Side portion  18   b  has a linear shape. Rounded corner portion  18   a  is continuous with side portion  18   b . The radius of curvature of rounded corner portion  18   a  is greater than or equal to 1/30 of the length of the long side of the rectangle. The radius of curvature of rounded corner portion  18   a  may be greater than or equal to 1/20 or 1/10 of the length of the long side of the rectangle. As illustrated in  FIG.  3   , outer peripheral surface  6   c  may have, for example, a rectangular shape with rounded corners as viewed in the thickness direction of adhesive sheet  6 . As illustrated in  FIG.  9   , outer peripheral surface  6   c  may have a rectangular shape as viewed in the thickness direction of adhesive sheet  6 . Corner portion  18   a  of outer peripheral surface  6   c  may have a right angle instead of a rounded shape as viewed in the thickness direction of adhesive sheet  6 . 
       FIG.  4    is a schematic cross-sectional view illustrating a manufacturing process of the power semiconductor device according to the first embodiment. As illustrated in  FIG.  4   , adhesive sheet  6  before thermal pressure bonding is placed inside inner peripheral surface  18  of flow prevention frame  8  with a gap  61  being provided between adhesive sheet  6  and inner peripheral surface  18 . Next, power module unit  200  and support member  7  are firmly joined with adhesive sheet  6  therebetween. Specifically, power module unit  200  is bonded by being pressurized and heated at a pressure and a temperature by which the power module unit is not broken. 
     During thermal pressure bonding, the viscosity of the thermosetting resin contained in adhesive sheet  6  temporarily decreases. Adhesive sheet  6  flows with the application of pressure. Adhesive sheet  6  is deformed in each of a thickness direction (vertical direction in  FIG.  2   ) and an in-plane direction (horizontal direction in  FIG.  2   ). During deformation, a part of the ceramic, the thermosetting resin, and voids contained in adhesive sheet  6  flow. That is, gap  61  provided between adhesive sheet  6  and flow prevention frame  8  in the planar direction before the thermal pressure bonding is filled with outer peripheral portion  6   b  (flow portion) due to adhesive sheet  6  flowing by the thermal pressure bonding. After the thermal pressure bonding, the contact region between outer peripheral surface  6   c  of adhesive sheet  6  and inner peripheral surface  18  of flow prevention frame  8  may be a part of or entire circumference of outer peripheral surface  6   c  of adhesive sheet  6 . 
     When adhesive sheet  6  is open in the in-plane direction (that is, when there is no flow prevention frame  8  of power semiconductor device  100  illustrated in  FIG.  2   ), the pressure at the central portion of adhesive sheet  6  is the highest and the pressure at outer peripheral surface  6   c  is the lowest. Adhesive sheet  6  flows from the central portion of adhesive sheet  6  toward the outer peripheral side due to a pressure difference between the central portion and outer peripheral surface  6   c . Adhesive sheet  6  deforms and flows under a pressure of, for example, about 10 MPa. 
     A part of the ceramic, the thermosetting resin, and the void flow from the central portion of adhesive sheet  6  toward the outer peripheral side under the pressing force at the time of bonding as a driving force and the fluid resistance in adhesive sheet  6  as a reaction force. The corner portion of outer peripheral surface  6   c  of adhesive sheet  6  is the farthest from the central portion of adhesive sheet  6 . Therefore, the corner portion of outer peripheral surface  6   c  of adhesive sheet  6  has higher fluid resistance than the portions other than the corner portion of outer peripheral surface  6   c . As a result, an amount of flow at the corner portion of outer peripheral surface  6   c  of adhesive sheet  6  is smaller than that at portions other than the corner portion of outer peripheral surface  6   c . Therefore, in the corner portion of outer peripheral surface  6   c  of adhesive sheet  6 , the internal pressure generated in adhesive sheet  6  decreases, and the void present in adhesive sheet  6  cannot be sufficiently crushed. As a result, a large number of voids remain in adhesive sheet  6 , and bonding reliability, heat dissipation, and insulation reliability may be deteriorated. 
     According to power semiconductor device  100  according to the first embodiment, the internal pressure of outer peripheral surface  6   c  of adhesive sheet  6  is uniform. Specifically, a value obtained by dividing the maximum value of the internal pressure on outer peripheral surface  6   c  of adhesive sheet  6  by the minimum value of the internal pressure on outer peripheral surface  6   c  of adhesive sheet  6  is less than or equal to 10. The value obtained by dividing the maximum value of the internal pressure on outer peripheral surface  6   c  of adhesive sheet  6  by the minimum value of the internal pressure on outer peripheral surface  6   c  of adhesive sheet  6  may be less than or equal to 5 or less than or equal to 2. When the outer shape of adhesive sheet  6  is rectangular, it is likely that the internal pressure at the corner portion of the rectangle is minimized, and the internal pressure at the center of the long side of the rectangle is maximized. The internal pressure at the center of the long side of the rectangle may be less than or equal to 10 times the internal pressure at the corner portion of the rectangle. 
     Next, a method for calculating the internal pressure on the outer peripheral surface of the adhesive sheet will be described. The internal pressure on the outer peripheral surface of the adhesive sheet is obtained by calculation using structural parameters of the flow prevention frame, the adhesive sheet, and the like. The method for calculating the internal pressure on the outer peripheral surface of the adhesive sheet includes, for example, a method for applying the Ergun equation. 
     The material of flow prevention frame  8  has strength enough to restrict adhesive sheet  6  that deforms and flows under high pressure of, for example, 10 MPa. Before thermal pressure bonding, the height of flow prevention frame  8  is desirably larger than the height of adhesive sheet  6 . Flow prevention frame  8  is deformed by the thermal pressure bonding. After the thermal pressure bonding, the thickness of flow prevention frame  8  is desirably equal to or larger than the thickness of adhesive sheet  6 . 
     According to power semiconductor device  100  according to the first embodiment, the internal pressure of outer peripheral surface  6   c  of adhesive sheet  6  is uniform. Therefore, the number and size of voids remaining in adhesive sheet  6  are reduced. The size (diameter) of the void present in adhesive sheet  6  may be less than or equal to 20 for example. With this configuration, the adhesiveness, heat dissipation, and insulation of adhesive sheet  6  can be improved. As a result, the reliability of power semiconductor device  100  can be improved. Therefore, it is possible to suppress an increase in the mounting area and an increase in cost due to the formation of an extra design margin. 
     Second Embodiment 
     Next, a configuration of power semiconductor device  100  according to the second embodiment will be described. The same components as those of power semiconductor device  100  according to the first embodiment are denoted by the same reference numerals as those of power semiconductor device  100  according to the first embodiment, and the description thereof will not be repeated. A configuration different from power semiconductor device  100  according to the first embodiment will be mainly described below. 
       FIG.  5    is a schematic cross-sectional view illustrating a configuration of power semiconductor device  100  according to the second embodiment. The cross section in  FIG.  5    corresponds to the cross section taken along line III-III in  FIG.  2   . As illustrated in  FIG.  5   , inner peripheral surface  18  of flow prevention frame  8  is circular as viewed in the thickness direction of adhesive sheet  6 . Similarly, outer peripheral surface  6   c  of adhesive sheet  6  is circular. Flow prevention frame  8  has a ring shape. When viewed in the thickness direction of adhesive sheet  6 , the distance between the center of adhesive sheet  6  and inner peripheral surface  18  of flow prevention frame  8  (or outer peripheral surface  6   c  of adhesive sheet  6 ) is the same at any point on inner peripheral surface  18 . As a result, the fluid resistance during thermal pressure bonding can be made constant. As a result, an amount of flow of adhesive sheet  6  can be made uniform in all directions in the plane as viewed from the center of adhesive sheet  6 . Thus, the internal pressure of outer peripheral surface  6   c  of adhesive sheet  6  can be made uniform. 
     Third Embodiment 
     Next, a configuration of power semiconductor device  100  according to the third embodiment will be described. The same components as those of power semiconductor device  100  according to the first embodiment are denoted by the same reference numerals as those of power semiconductor device  100  according to the first embodiment, and the description thereof will not be repeated. A configuration different from power semiconductor device  100  according to the first embodiment will be mainly described below. 
       FIG.  6    is a schematic perspective view illustrating a configuration of power semiconductor device  100  according to the third embodiment.  FIG.  7    is a schematic perspective view illustrating a configuration of power module unit  200  of power semiconductor device  100  according to the third embodiment. 
     As illustrated in  FIG.  7   , power module unit  200  has a joint surface  9 . Joint surface  9  is a surface in contact with adhesive sheet  6 . Joint surface  9  includes heat spreader  3  and mold resin portion  5 . Joint surface  9  has a curved shape. Power module unit  200  is the thinnest at the corner portion (first corner portion  9   b ) of joint surface  9  and the thickest at the center (first center  9   a ) of joint surface  9 . Joint surface  9  may be a convex curved surface radially and continuously extending from the center (first center  9   a ). 
       FIG.  8    is a cross-sectional view taken along line VIII-VIII in  FIG.  6   .  FIG.  8    illustrates the cross section parallel to the thickness direction of adhesive sheet  6 . As illustrated in  FIG.  8   , in the cross section, the thickness of adhesive sheet  6  may increase from central portion  6   a  toward outer peripheral surface  6   c . In the cross section, the thickness of outer wall surface  28  of flow prevention frame  8  may be larger than the thickness of inner peripheral surface  18  of flow prevention frame  8 . The thickness of outer peripheral surface  6   c  of adhesive sheet  6  may be larger than the maximum value of the thickness of central portion  6   a  of adhesive sheet  6 . 
     Flow prevention frame  8  has a first face  38  and a second face  48 . Second face  48  is on the opposite side of first face  38 . First face  38  is in contact with mold resin portion  5 . Second face  48  is in contact with support member  7 . The distance between first face  38  and second face  48  may increase from inner peripheral surface  18  toward outer wall surface  28 . First face  38  may be curved. Second face  48  may be flat. 
       FIG.  9    is a cross-sectional view taken along line IX-IX in  FIG.  8   . As illustrated in  FIG.  9   , inner peripheral surface  18  of flow prevention frame  8  may be square or rectangular as viewed in the thickness direction of adhesive sheet  6 . Similarly, outer shape of adhesive sheet  6  may be square or rectangular. Outer wall surface  28  of flow prevention frame  8  may be square or rectangular. The thickness of adhesive sheet  6  at the corner portion of outer peripheral surface  6   c  of adhesive sheet  6  may be larger than the thickness of adhesive sheet  6  at the center of one side of outer peripheral surface  6   c  of adhesive sheet  6 . 
     In power semiconductor device  100  according to the third embodiment, the gap between adhesive sheet  6  and power module unit  200  in the thickness direction is the widest at the corner portion of outer peripheral surface  6   c  farthest from the center of adhesive sheet  6  before the thermal pressure bonding. In general, the larger the cross-sectional area of a flow path, the easier the fluid flows. Therefore, by increasing the gap between adhesive sheet  6  and power module unit  200  in the thickness direction, an effect of increasing an amount of flow of adhesive sheet  6  can be expected. 
     In power semiconductor device  100  according to the third embodiment, power module unit  200  is the thinnest at the corner portion (first corner portion  9   b ) of joint surface  9  and the thickest at the center (first center  9   a ) of joint surface  9 . Therefore, the difference in amount of flow of adhesive sheet  6  on the outer periphery of adhesive sheet  6  can be reduced. Thus, it can be expected to uniformize the internal pressure of adhesive sheet  6 . As a result, the bonding reliability, heat dissipation, and insulation reliability of power semiconductor device  100  can be improved. Therefore, it is possible to suppress an increase in the mounting area and an increase in cost due to the formation of an extra design margin. 
     Fourth Embodiment 
     Next, a configuration of power semiconductor device  100  according to the fourth embodiment will be described. The same components as those of power semiconductor device  100  according to the first embodiment are denoted by the same reference numerals as those of power semiconductor device  100  according to the first embodiment, and the description thereof will not be repeated. A configuration different from power semiconductor device  100  according to the first embodiment will be mainly described below. 
       FIG.  10    is a schematic perspective view illustrating a configuration of power semiconductor device  100  according to the fourth embodiment.  FIG.  11    is a schematic perspective view illustrating a configuration of a support member of power semiconductor device  100  according to the fourth embodiment. 
     As illustrated in  FIG.  11   , support member  7  has a top face  15 . Top face  15  is a surface facing adhesive sheet  6 . Top face  15  is constituted by body portion  7   a . Top face  15  has an upper face  16 , a lateral face  11   a , and a bottom face  11   b . Upper face  16  is continuous with lateral face  11   a . Lateral face  11   a  is continuous with bottom face  11   b . Upper face  16  is separated from bottom face  11   b . Top face  15  is provided with a groove  11 . Groove  11  is defined by lateral face  11   a  and bottom face  11   b . Groove  11  is the deepest at the corner portion (second corner portion  15   b ) of bottom face  11   b  and the shallowest at the center (second center  15   a ) of the bottom face. Bottom face  11   b  may be a convex curved surface radially and continuously extending from the center (second center  15   a ). 
       FIG.  12    is a cross-sectional view taken along line XII-XII in  FIG.  10   .  FIG.  12    illustrates the cross section parallel to the thickness direction of adhesive sheet  6 . As illustrated in  FIG.  12   , adhesive sheet  6  and flow prevention frame  8  may be provided inside groove  11 . Adhesive sheet  6  and flow prevention frame  8  may be in contact with bottom face  11   b  of groove  11 . Flow prevention frame  8  may be in contact with lateral face  11   a  of groove  11 . As illustrated in  FIG.  12   , in the cross section, the thickness of adhesive sheet  6  may increase from central portion  6   a  toward outer peripheral surface  6   c . In the cross section, the thickness of outer wall surface  28  of flow prevention frame  8  may be larger than the thickness of inner peripheral surface  18  of flow prevention frame  8 . The thickness of outer peripheral surface  6   c  of adhesive sheet  6  may be larger than the maximum value of the thickness of central portion  6   a.    
     Flow prevention frame  8  has first face  38  and second face  48 . Second face  48  is on the opposite side of first face  38 . First face  38  is in contact with mold resin portion  5 . Second face  48  is in contact with support member  7 . The distance between first face  38  and second face  48  may increase from inner peripheral surface  18  toward outer wall surface  28 . First face  38  may be flat. Second face  48  may be curved. 
       FIG.  13    is a cross-sectional view taken along line XIII-XIII in  FIG.  12   . As illustrated in  FIG.  13   , inner peripheral surface  18  of flow prevention frame  8  may be square or rectangular as viewed in the thickness direction of adhesive sheet  6 . Similarly, outer peripheral surface  6   c  of adhesive sheet  6  may be square or rectangular. Outer wall surface  28  of flow prevention frame  8  may be square or rectangular. The thickness of adhesive sheet  6  at the corner portion of outer peripheral surface  6   c  of adhesive sheet  6  may be larger than the thickness of adhesive sheet  6  at the center of one side of outer peripheral surface  6   c  of adhesive sheet  6 . 
     In power semiconductor device  100  according to the fourth embodiment, the gap between adhesive sheet  6  and power module unit  200  in the thickness direction is the widest at the corner portion of outer peripheral surface  6   c  farthest from the center of adhesive sheet  6  before the thermal pressure bonding. In general, the larger the cross-sectional area of a flow path, the easier the fluid flows. Therefore, by increasing the gap between adhesive sheet  6  and power module unit  200  in the thickness direction, an effect of increasing an amount of flow of adhesive sheet  6  can be expected. 
     In power semiconductor device  100  according to the fourth embodiment, the depth of groove  11  is the largest at the corner portion (second corner portion  15   b ) of bottom face  11   b  and the smallest at the center (second center  15   a ) of bottom face  11   b . Therefore, the difference in amount of flow of adhesive sheet  6  on the outer periphery of adhesive sheet  6  can be reduced. Thus, it can be expected to uniformize the internal pressure of adhesive sheet  6 . As a result, the bonding reliability, heat dissipation, and insulation reliability of power semiconductor device  100  can be improved. Therefore, it is possible to suppress an increase in the mounting area and an increase in cost due to the formation of an extra design margin. 
     Fifth Embodiment 
     Next, a configuration of power semiconductor device  100  according to the fifth embodiment will be described. The same components as those of power semiconductor device  100  according to the first embodiment are denoted by the same reference numerals as those of power semiconductor device  100  according to the first embodiment, and the description thereof will not be repeated. A configuration different from power semiconductor device  100  according to the first embodiment will be mainly described below. 
       FIG.  14    is a schematic cross-sectional view illustrating a configuration of power semiconductor device  100  according to the fifth embodiment. The cross section in  FIG.  14    corresponds to the cross section taken along line III-III in  FIG.  2   . As illustrated in  FIG.  14   , inner peripheral surface  18  has corner portion  18   a  and side portion  18   b  as viewed in the thickness direction of adhesive sheet  6 . Side portion  18   b  is continuous with corner portion  18   a . Side portion  18   b  is curved so as to protrude inward. As illustrated in  FIG.  14   , the width of flow prevention frame  8  decreases from the center of side portion  18   b  toward corner portion  18   a  as viewed in the thickness direction of adhesive sheet  6 . Outer wall surface  28  of flow prevention frame  8  may be rectangular or square. 
     Flow prevention frame  8  is, for example, a solid material. Before thermal pressure bonding, the thickness of flow prevention frame  8  is greater than or equal to the thickness of adhesive sheet  6 . Flow prevention frame  8  is deformed during thermal pressure bonding. After the thermal pressure bonding, the thickness of flow prevention frame  8  is greater than or equal to the thickness of adhesive sheet  6 . The material having the above characteristics is, for example, soft metal such as tin or a silicone-based rubber material. 
     In power semiconductor device  100  according to the fifth embodiment, the clearance in the in-plane direction between inner peripheral surface  18  of flow prevention frame  8  and outer peripheral surface  6   c  of adhesive sheet  6  continuously changes so as to be widest at the corner portion. When coming into contact with flow prevention frame  8 , outer peripheral surface  6   c  of adhesive sheet  6  that flows at the time of thermal pressure bonding cannot flow any more. Therefore, adhesive sheet  6  easily flows to the side where the clearance is wide, that is, the corner side of adhesive sheet  6 . Thus, the internal pressure of outer peripheral surface  6   c  of adhesive sheet  6  can be made uniform. 
     Sixth Embodiment 
     Next, a configuration of power semiconductor device  100  according to the sixth embodiment will be described. The same components as those of power semiconductor device  100  according to the first embodiment are denoted by the same reference numerals as those of power semiconductor device  100  according to the first embodiment, and the description thereof will not be repeated. A configuration different from power semiconductor device  100  according to the first embodiment will be mainly described below. 
       FIG.  15    is a schematic cross-sectional view illustrating a configuration of power semiconductor device  100  according to the sixth embodiment. The cross section in  FIG.  15    corresponds to the cross section taken along line III-III in  FIG.  2   . In power semiconductor device  100  according to the sixth embodiment, flow prevention frame  8  is formed of a porous body. Unlike the first to fifth embodiments, adhesive sheet  6  flowing during thermal pressure bonding enters the inside of flow prevention frame  8 . When adhesive sheet  6  passes through the inside of flow prevention frame  8 , fluid resistance is generated against adhesive sheet  6 . Therefore, the flow of adhesive sheet  6  can be restricted. Thus, the internal pressure of adhesive sheet  6  can be made uniform. As the material of flow prevention frame  8 , a material by which adhesive sheet  6  deforms in the similar manner as in the fifth embodiment is selected. The material of flow prevention frame  8  is, for example, a porous body such as cellulose fiber, glass fiber, foamed resin, or porous ceramics. 
     As illustrated in  FIG.  15   , inner peripheral surface  18  has corner portion  18   a  and side portion  18   b  as viewed in the thickness direction of adhesive sheet  6 . Side portion  18   b  is continuous with corner portion  18   a . Side portion  18   b  has a linear shape. The pore diameter of the porous body increases from the center of side portion  18   b  toward corner portion  18   a . Specifically, the pore diameter of flow prevention frame  8  at corner portion  18   a  is the largest, and the pore diameter of flow prevention frame  8  at the center of side portion  18   b  is the smallest. 
     As illustrated in  FIG.  15   , flow prevention frame  8  may include a first region  8   a , a second region  8   b , a third region  8   c , a fourth region  8   d , a fifth region  8   e , a sixth region  8   f , and a seventh region  8   g . First region  8   a  constitutes the center of the side portion. Fifth region  8   e  constitutes the corner portion. Second region  8   b  is located on each side of first region  8   a . Third region  8   c  is located between second region  8   b  and fourth region  8   d . Fourth region  8   d  is located between third region  8   c  and fifth region  8   e . Fifth region  8   e  is located between fourth region  8   d  and sixth region  8   f . Sixth region  8   f  is located between fifth region  8   e  and seventh region  8   g . Seventh region  8   g  is a corner portion of flow prevention frame  8 . 
     The pore diameter in second region  8   b  is larger than the pore diameter in first region  8   a . The pore diameter in third region  8   c  is larger than the pore diameter in second region  8   b . The pore diameter in fourth region  8   d  is larger than the pore diameter in third region  8   c . The pore diameter in fifth region  8   e  is larger than the pore diameter in fourth region  8   d . The pore diameter in sixth region  8   f  is larger than the pore diameter in fifth region  8   e . The pore diameter in seventh region  8   g  is larger than the pore diameter in sixth region  8   f.    
     As another mode, in a case where the pore diameters are the same, the density of the pores of flow prevention frame  8  at the corner portion may be the highest, and the density of the pores of flow prevention frame  8  at the center of the side portion may be the lowest. Specifically, the density of the pores in second region  8   b  may be higher than the density of the pores in first region  8   a . The density of the pores in third region  8   c  may be higher than the density of the pores in second region  8   b . The density of the pores in fourth region  8   d  may be higher than the density of the pores in third region  8   c . The density of the pores in fifth region  8   e  may be higher than the density of the pores in fourth region  8   d . The density of the pores in sixth region  8   f  may be higher than the density of the pores in fifth region  8   e . The density of the pores in seventh region  8   g  may be higher than the density of the pores in sixth region  8   f.    
     In power semiconductor device  100  according to the sixth embodiment, when adhesive sheet  6  passes through the inside of flow prevention frame  8 , the fluid resistance is the largest at the center of the side portion, and the fluid resistance is the smallest at the corner portion. Therefore, adhesive sheet  6  easily flows to the corner side of adhesive sheet  6 . Thus, the internal pressure of outer peripheral surface  6   c  of adhesive sheet  6  can be made uniform. 
     Seventh Embodiment 
     Next, a configuration of power semiconductor device  100  according to the seventh embodiment will be described. The same components as those of power semiconductor device  100  according to the first embodiment are denoted by the same reference numerals as those of power semiconductor device  100  according to the first embodiment, and the description thereof will not be repeated. A configuration different from power semiconductor device  100  according to the first embodiment will be mainly described below. 
       FIG.  16    is a schematic cross-sectional view illustrating a configuration of power semiconductor device  100  according to the seventh embodiment. The cross section in  FIG.  16    corresponds to the cross section taken along line III-III in  FIG.  2   . In power semiconductor device  100  according to the seventh embodiment, flow prevention frame  8  is formed of a porous body. As illustrated in  FIG.  16   , inner peripheral surface  18  has corner portion  18   a  and side portion  18   b  as viewed in the thickness direction of adhesive sheet  6 . Side portion  18   b  is continuous with corner portion  18   a . Side portion  18   b  has a linear shape. As illustrated in  FIG.  16   , the width of flow prevention frame  8  decreases from the center of side portion  18   b  toward corner portion  18   a . From another point of view, the width of flow prevention frame  8  at the center of side portion  18   b  is the largest, and the width of flow prevention frame  8  at corner portion  18   a  is the smallest. 
     In power semiconductor device  100  according to the seventh embodiment, when adhesive sheet  6  passes through the inside of flow prevention frame  8 , the fluid resistance is the largest at the center of the side portion, and the fluid resistance is the smallest at the corner portion. Therefore, adhesive sheet  6  easily flows to the corner side of adhesive sheet  6 . Thus, the internal pressure of outer peripheral surface  6   c  of adhesive sheet  6  can be made uniform. 
     Eighth Embodiment 
     Next, a configuration of power semiconductor device  100  according to the eighth embodiment will be described. The same components as those of power semiconductor device  100  according to the first embodiment are denoted by the same reference numerals as those of power semiconductor device  100  according to the first embodiment, and the description thereof will not be repeated. A configuration different from power semiconductor device  100  according to the first embodiment will be mainly described below. 
       FIG.  17    is a schematic cross-sectional view illustrating a configuration of power semiconductor device  100  according to the eighth embodiment. The cross section in  FIG.  17    corresponds to the cross section taken along line III-III in  FIG.  2   .  FIG.  18    is a cross-sectional view taken along line XVIII-XVIII in  FIG.  17   . As illustrated in  FIG.  18   , in power semiconductor device  100  according to the eighth embodiment, flow prevention frame  8  may include two or more layers of different materials. As illustrated in  FIG.  18   , flow prevention frame  8  has a plurality of layers laminated in the thickness direction. Specifically, flow prevention frame  8  includes, for example, a first layer  13   a , a second layer  13   b , and a third layer  13   c . Second layer  13   b  is on third layer  13   c . First layer  13   a  is on second layer  13   b . Second layer  13   b  is located between first layer  13   a  and third layer  13   c . The material of first layer  13   a  is different from the material of second layer  13   b . The material of third layer  13   c  is different from the material of second layer  13   b . For example, the material of first layer  13   a  may be a porous body, and the material of second layer  13   b  may be a solid material. The solid material is, for example, soft metal such as tin or a silicone-based rubber material. 
     According to power semiconductor device  100  according to the eighth embodiment, flow prevention frame  8  having a desired thickness can be formed by laminating a plurality of materials each of which is difficult to be increased in thickness. This makes it possible to enlarge the range of choice for the material of flow prevention frame  8 , which is advantageous in terms of simple choice and material cost. 
     Next, a configuration of power semiconductor device  100  according to a first modification of the eighth embodiment will be described. Power semiconductor device  100  according to the first modification of the eighth embodiment uses flow prevention frame  8  having the shape illustrated in  FIG.  14   . Specifically, as illustrated in  FIG.  14   , inner peripheral surface  18  of flow prevention frame  8  has corner portion  18   a  and side portion  18   b  as viewed in the thickness direction of adhesive sheet  6 . Side portion  18   b  is continuous with corner portion  18   a . Side portion  18   b  is curved so as to protrude inward. The width of flow prevention frame  8  decreases from the center of side portion  18   b  toward corner portion  18   a.    
     Next, a configuration of power semiconductor device  100  according to a second modification of the eighth embodiment will be described. Power semiconductor device  100  according to the second modification of the eighth embodiment uses flow prevention frame  8  having the shape illustrated in  FIG.  15   . Specifically, flow prevention frame  8  is made of a porous body. As illustrated in  FIG.  15   , inner peripheral surface  18  has corner portion  18   a  and side portion  18   b  as viewed in the thickness direction of adhesive sheet  6 . Side portion  18   b  is continuous with corner portion  18   a . Side portion  18   b  has a linear shape. The pore diameter of the porous body increases from the center of side portion  18   b  toward corner portion  18   a . The density of the pores of the porous body may increase from the center of side portion  18   b  toward corner portion  18   a.    
     Next, a configuration of power semiconductor device  100  according to a third modification of the eighth embodiment will be described. Power semiconductor device  100  according to the third modification of the eighth embodiment uses flow prevention frame  8  having the shape illustrated in  FIG.  16   . Specifically, flow prevention frame  8  is made of a porous body. As illustrated in  FIG.  16   , inner peripheral surface  18  has corner portion  18   a  and side portion  18   b  as viewed in the thickness direction of adhesive sheet  6 . Side portion  18   b  is continuous with corner portion  18   a . Side portion  18   b  has a linear shape. The width of flow prevention frame  8  decreases from the center of side portion  18   b  toward corner portion  18   a.    
     Ninth Embodiment 
     Next, a configuration of power semiconductor device  100  according to the ninth embodiment will be described. The same components as those of power semiconductor device  100  according to the first embodiment are denoted by the same reference numerals as those of power semiconductor device  100  according to the first embodiment, and the description thereof will not be repeated. A configuration different from power semiconductor device  100  according to the first embodiment will be mainly described below. 
       FIG.  19    is a schematic cross-sectional view illustrating a configuration of power semiconductor device  100  according to the ninth embodiment. The cross section in  FIG.  19    corresponds to the cross section taken along line III-III in  FIG.  2   .  FIG.  20    is a cross-sectional view taken along line XX-XX in  FIG.  19   . As illustrated in  FIG.  19   , inner peripheral surface  18  has corner portion  18   a  and side portion  18   b  as viewed in the thickness direction of adhesive sheet  6 . Side portion  18   b  is continuous with corner portion  18   a . As illustrated in  FIGS.  19  and  20   , power semiconductor device  100  according to the ninth embodiment has a plurality of recesses  12  provided in inner peripheral surface  18 . The density of the plurality of recesses  12  decreases from the center of the side portion toward the corner portion. The material of flow prevention frame  8  is, for example, a solid material. The plurality of recesses  12  may be distributed in the thickness direction of flow prevention frame  8  as illustrated in  FIG.  20   , or may be distributed in the width direction of flow prevention frame  8 . Adhesive sheet  6  enters at least a part of the plurality of recesses  12 . The plurality of recesses  12  may be exposed on outer wall surface  28  of flow prevention frame  8 . 
     In power semiconductor device  100  according to the ninth embodiment, when adhesive sheet  6  passes through the inside of flow prevention frame  8 , the fluid resistance is the largest at the center of the side portion, and the fluid resistance is the smallest at the corner portion. Therefore, adhesive sheet  6  easily flows to the corner side of adhesive sheet  6 . Thus, the internal pressure of outer peripheral surface  6   c  of adhesive sheet  6  can be made uniform. 
     Tenth Embodiment 
     In the present embodiment, power semiconductor device  100  according to any one of the first to ninth embodiments is applied to a power conversion device. The tenth embodiment will describe a case where the present disclosure is applied to a three-phase inverter, although the present disclosure is not limited to a specific power conversion device. 
       FIG.  21    is a block diagram illustrating a configuration of a power conversion system to which the power conversion device according to the tenth embodiment is applied. 
     The power conversion system illustrated in  FIG.  21    includes a power supply  150 , a power conversion device  250 , and a load  300 . Power supply  150  is a DC power supply, and supplies DC power to power conversion device  250 . Power supply  150  can be of any type. For example, power supply  150  can be a DC system, a solar cell, and a storage battery, or may be constituted by a rectifier circuit or an AC/DC converter connected to an AC system. Alternatively, power supply  150  may be constituted by a DC/DC converter that converts DC power output from the DC system into predetermined power. 
     Power conversion device  250  is a three-phase inverter connected between power supply  150  and load  300 , converts DC power supplied from power supply  150  into AC power, and supplies the AC power to load  300 . As illustrated in  FIG.  21   , power conversion device  250  includes a main conversion circuit  251  that converts DC power into AC power and outputs the AC power, and a control circuit  253  that outputs a control signal for controlling main conversion circuit  251  to main conversion circuit  251 . 
     Load  300  is a three-phase electric motor driven by the AC power supplied from power conversion device  250 . Load  300  is not limited to a specific application, and is an electric motor mounted on various electric devices such as an electric motor for a hybrid vehicle, an electric vehicle, a railway vehicle, an elevator, or an air conditioner. 
     The detail of power conversion device  250  will be described below. Main conversion circuit  251  includes a switching element and a freewheeling diode (not illustrated), converts DC power supplied from power supply  150  into AC power by switching of the switching element, and supplies the AC power to load  300 . Although there are various specific circuit structures of main conversion circuit  251 , main conversion circuit  251  according to the present embodiment can be a two-level three-phase full bridge circuit including six switching elements and six freewheeling diodes antiparallel to the respective switching elements. Each switching element and each freewheeling diode of main conversion circuit  251  are constituted by a semiconductor module  252  corresponding to any one of the above-described first to ninth embodiments. The six switching elements are connected in series for every two switching elements to constitute upper and lower arms, and each of the upper and lower arms constitutes each phase (U-phase, V-phase, W-phase) of the full bridge circuit. The output terminals of the upper and lower arms, that is, the three output terminals of main conversion circuit  251 , are connected to load  300 . 
     Further, main conversion circuit  251  includes a drive circuit (not illustrated) that drives each switching element. The drive circuit may be built in semiconductor module  252 , or may be provided separately from semiconductor module  252 . The drive circuit generates a drive signal for driving the switching elements of main conversion circuit  251 , and supplies the drive signal to control electrodes of the switching elements of main conversion circuit  251 . Specifically, the drive circuit outputs, to the control electrode of each switching element, a drive signal for turning on the switching element and a drive signal for turning off the switching element in accordance with a control signal from control circuit  253  to be described later. When the switching element is maintained in the ON state, the drive signal is a voltage signal (ON signal) equal to or higher than a threshold voltage of the switching element, and when the switching element is maintained in the OFF state, the drive signal is a voltage signal (OFF signal) equal to or lower than the threshold voltage of the switching element. 
     Control circuit  253  controls the switching elements of main conversion circuit  251  so that desired power is supplied to load  300 . Specifically, control circuit  253  calculates, on the basis of power to be supplied to load  300 , a time (ON time) during which each switching element of main conversion circuit  251  is to be turned on. For example, control circuit  253  can control main conversion circuit  251  by PWM control that modulates the ON time of the switching element according to the voltage to be output. Then, control circuit  253  outputs a control command (control signal) to the drive circuit included in main conversion circuit  251  such that, at each time point, the ON signal is output to the switching element to be turned on and the OFF signal is output to the switching element to be turned off. The drive circuit outputs the ON signal or the OFF signal as a drive signal to the control electrode of each switching element in accordance with the control signal. 
     The power conversion device according to the present embodiment uses power semiconductor device  100  according to any one of the first to ninth embodiments as the switching element and the freewheeling diode of main conversion circuit  251 , whereby the reliability of the power conversion device can be improved. 
     The present embodiment has described the example in which the present invention is applied to a two-level three-phase inverter. However, the present disclosure is not limited thereto, and can be applied to various power conversion devices. In the present embodiment, the two-level power conversion device has been described. However, a three-level or multi-level power conversion device may be used, or the present disclosure may be applied to a single-phase inverter in a case where power is supplied to a single-phase load. In addition, in a case where power is supplied to a DC load or the like, the present disclosure can also be applied to a DC/DC converter or an AC/DC converter. 
     In addition, the power conversion device to which the present disclosure is applied is not limited to the one described above used for an electric motor serving as a load, and can be used as, for example, a power supply device of an electric discharge machine, a laser beam machine, an induction heating cooker, or a non-contact power feeding system, and as a power conditioner of a solar power generation system, a power storage system, or the like. 
     It should be understood that the embodiments disclosed herein are illustrative in all respects and not restrictive. At least two of the embodiments disclosed herein may be combined as long as there is no contradiction. The scope of the present application is defined not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 : power semiconductor element,  2   a : first metal wiring member,  2   b : second metal wiring member,  2   c : third metal wiring member,  3 : heat spreader,  4   a : first metal bonding member,  4   b : second metal bonding member,  5 : mold resin portion,  6 : adhesive sheet,  6   a : central portion,  6   b : outer peripheral portion,  6   c : outer peripheral surface,  7 : support member,  7   a : body portion,  7   b : fin,  8 : flow prevention frame,  8   a : first region,  8   b : second region,  8   c : third region,  8   d : fourth region,  8   e : fifth region,  8   f : sixth region,  8   g : seventh region,  9 : joint surface,  9   a : first center,  9   b : first corner portion,  11 : groove,  11   a : lateral face,  11   b : bottom face,  12 : recess,  13   a : first layer,  13   b : second layer,  13   c : third layer,  15 : top face,  15   a : second center,  15   b : second corner portion,  16 : upper face,  18 : inner peripheral surface,  18   a : corner portion,  18   b : side portion,  28 : outer wall surface,  38 : first face,  48 : second face,  61 : gap,  100 : power semiconductor device,  150 : power supply,  200 : power module unit,  250 : power conversion device,  251 : main conversion circuit,  252 : semiconductor module,  253 : control circuit,  300 : load