Abstract:
The disclosed invention provides power conversion equipment in which the thermal resistance of thermal connections is reduced. A structure for cooling a heat generator includes a heat generator having at least one cooled surface having protruding convex portions formed thereon, a heat receiving spacer in which hollow portions into which the convex portions are inserted are formed, clamping members which press and clamp the heat receiving space and the heat generator sandwiched therebetween, and a cooler which cools the heat receiving spacer. In an engagement state in which the heat generator and the heat receiving spacer are engaged by the clamping members, a distance between the cooled surface and the end faces of the convex portions is smaller than a distance between the cooled surface and a face, facing either of the clamping members, of the heat receiving spacer.

Description:
BACKGROUND 
       [0001]    The present invention relates to a structure for cooling a heat generator and power conversion equipment. 
         [0002]    An Uninterruptible Power-supply System (hereinafter abbreviated to UPS) is equipment for stable supply of electric power to a load without interruption in case abnormal condition occurs with a utility power source or the like which is a steady power source. There is a high demand of UPS for application in, inter alia, data centers along with ongoing innovation of IT utilization. Because UPSs for data centers center are installed in urban neighborhood where land prices are high, reduction in installation area, in other words, equipment downsizing is hoped for. 
         [0003]    To downsize an UPS, it is important to downsize the components of the UPS. Above all, power conversion equipment occupies a large physical volume and, therefore, its downsizing is significantly effective. To pursue downsizing of the power conversion equipment, what is required is downsizing of a mechanism for cooling a power semiconductor module which is a heat generator and a more efficient cooling method through that mechanism. 
         [0004]    As a method for air-cooling a power semiconductor module, for example, in Japanese Unexamined Patent Application Publication No. 2000-269671, there is the following description. “A first heat sink  25  is mounted on a CPU  23  with the intermediate positioning of a heat transfer sheet  26 . A plurality of heat transfer portions  25   a  are formed on the first heat sink  25 . A second heat sink  27  is placed on the first heat sink  25 . On the second heat sink  27 , openings  29  are formed such that the heat transfer portions  25   a  can be inserted therein with a gap. The gaps between the heat transfer portions  25   a  and the openings  29  are filled with heat conductive grease.” 
       SUMMARY 
       [0005]    The air-cooling method described in Japanese Unexamined Patent Application Publication No. 2000-269671 enables expanding heat dissipation areas by the connections between the convex portions and the openings and reducing the thermal resistance of a heat conductive grease layer, while reducing the load applied to an electronic part. However, since heat that has once been conducted to a holding member is allowed to conduct up to the rear surface of a heat generating member and dissipated to a substrate, there is large thermal resistance in conduction, and heat dissipation performance is limited. 
         [0006]    An object of the present invention is to provide power conversion equipment downsized by reducing the thermal resistance of thermal connections and improving heat dissipation performance. 
         [0007]    In order to achieve the above object, a structure for cooling a heat generator is provided, including, for example, a heat generator having at least one cooled surface having protruding convex portions formed thereon, a heat receiving spacer in which hollow portions into which the convex portions are inserted are formed, clamping members which press and clamp the heat receiving space and the heat generator sandwiched therebetween, and a cooler which cools the heat receiving spacer. In an engagement state in which the heat generator and the heat receiving spacer are engaged by the clamping members, a distance between the cooled surface and the end faces of the convex portions is smaller than a distance between the cooled surface and a face, facing either of the clamping members, of the heat receiving spacer. 
         [0008]    According to the present invention, the convex portions are connected to the cooler via a heat conductive material and, therefore, heat from a power semiconductor module can be transferred to the cooler efficiently. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a circuit diagram of power conversion equipment pertaining to one embodiment of the present invention; 
           [0010]      FIG. 2  is a circuit diagram of a converter in the power conversion equipment; 
           [0011]      FIG. 3  is a circuit diagram of an inverter in the power conversion equipment; 
           [0012]      FIG. 4  is a circuit diagram of a charging/discharging chopper in the power conversion equipment; 
           [0013]      FIG. 5  is a circuit diagram of a dual-side cooled power module which is used in the present embodiment; 
           [0014]      FIG. 6  is an external view of the dual-side cooled power module which is used in the present embodiment; 
           [0015]      FIG. 7  is a perspective view of a heat receiving spacer; 
           [0016]      FIG. 8  is a diagram depicting a state in which heat receiving spacers are attached to the dual-side cooled power module; 
           [0017]      FIG. 9  is a cross-sectional view through line A-A′ in  FIG. 8 ; 
           [0018]      FIG. 10  is a perspective view depicting a state in which two dual-side cooled power modules are attached to a cooler; 
           [0019]      FIG. 11  is an exploded view of region B surrounded by dashed lines presented in  FIG. 10 ; 
           [0020]      FIG. 12  is a cross-sectional view through line C-C′ in.  FIG. 11 ; 
           [0021]      FIG. 13  is an enlarged view of portion D presented in  FIG. 12 ; 
           [0022]      FIG. 14  depicts a second embodiment of the present invention, in which thermal connections in the first embodiment are provided by heat conductive sheets  451 ; 
           [0023]      FIG. 15  is an enlarged view of portion E in  FIG. 14 ; 
           [0024]      FIG. 16  depicts a third embodiment of the present invention, in which the power semiconductor module of the first embodiment is configured as a one side cooled power module; and 
           [0025]      FIG. 17  is an enlarged view of portion F in  FIG. 16 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    In the following, embodiments for carrying out the present invention will be described with reference to the drawings. 
       First Embodiment 
       [0027]      FIG. 1  is a circuit diagram of power conversion, equipment  1  pertaining to one embodiment of the present invention. 
         [0028]    This system assumed to operate as UPS is an uninterrupted inverter-fed power supply system which can continue to supply electric power without instantaneous interruption in case of electric power outage. Three-phase AC voltage from a utility power source  2  is supplied through a steady power source side switch  21  and a filtering circuit for input  17  for eliminating harmonics and to a converter  11  and converted from AC to DC by the converter  11  which is a rectification circuit. After rectification at the converter  11 , a DC voltage  4  smoothed by a capacitor  20  is applied to an inverter  12  and inversely converted to AC of a desired voltage and frequency. After inverse conversion, three-phase AC voltage  5  which is output by the inverter  12 , after its harmonic components are eliminated by a filtering circuit for output  18 , is supplied via a load side switch  24  to a load  3 . In the uninterrupted inverter-fed power supply system, the utility power source  2  of three-phase AC voltage constantly supplies power via the converter  11  and inverter  12  to the load  3 . Therefore, in case a voltage fluctuation such as instantaneous voltage drop occurs with the utility power source  2 , it is enabled to stably supply power that is equivalent to normal utility power by controlling the converter  11  and inverter  12 . The operations of the converter  11  and inverter  12  and ON/OFF of the steady power source side switch  21  and the load side switch are controlled by a signal from a higher level control circuit  201 . 
         [0029]    In the meantime, a charging/discharging chopper  13  is connected to a stage preceding the inverter  12 . When normal utility power is supplied, the charging/discharging chopper  13  operates as a step-down chopper which decreases the DC voltage  4  and outputs charging power  7  for charging a battery  14 . A non-steady power source side switch  22  has a role to make connections to power feeding paths when feeding power from the battery  14  to the converter  11 . A battery protecting switch  23  has a role to protect the battery from overcurrent or the like. The charging/discharging chopper  13 , non-steady power source side switch  22 , and battery protecting switch  23  are controlled by a signal from the higher level control circuit  201 . 
         [0030]    The converter  11 , inverter  12 , and charging/discharging chopper  13  generate heat during their operation and their temperature rises. To suppress this temperature rise, cooling wind  10  generated by a cooling fan  9  (air blower) is fed in to circulate and cool the inside of the power conversion equipment  1 . 
         [0031]      FIG. 2  is a circuit diagram of the converter  11  which is a component of the power conversion equipment  1 . 
         [0032]    The converter  11  converts a three-phase AC voltage from the utility power source  2  to a DC voltage  4 . When normal utility power is supplied, incoming three-phase AC power is supplied to AC terminals  41   r ,  41   s ,  41   t  of the converter  11  and rectified with switching elements  31  and rectification elements  33  in an upper arm and switching elements  32  and rectification elements  34  in a lower arm, these elements being provided for the respective phases. In the present embodiment, Insulated Gate Bipolar Transistors (IGBTs) are used as the switching elements and diodes are used as the rectification elements; however, these are non-limiting and other types of elements can also be applied (the same applies hereinafter). The switching elements  31 ,  32  of the converter  11  are driven by a signal from a control circuit  202 . 
         [0033]      FIG. 3  is a circuit diagram of the inverter  12  which is a component of the power conversion equipment  1 . 
         [0034]    The inverter  12  converts DC power smoothed by the capacitor which is not depicted to three-phase AC power. DC voltage produced by the converter  11  is converted to a three-phase AC voltage with switching elements  31  and rectification elements  33  in an upper arm and switching elements  32  and rectification elements  34  in a lower arm, these elements being provided for the respective phases, and the three-phase AC voltage is output to AC terminals  42   u ,  42   v ,  42   w . The switching elements  31 ,  32  of the inverter  12  are driven by a signal from a control circuit  203 . The inverter  12  converts a DC voltage to an AC voltage regardless of condition of the utility power source  2  and outputs rated electric power to the filtering circuit for output  18 . 
         [0035]      FIG. 4  is a circuit diagram of the charging/discharging chopper  13  which is a component of the power conversion equipment  1 . 
         [0036]    The charging/discharging chopper  13  decrease the DC voltage and outputs charging power, when normal utility power is supplied by the utility power source  2 . While switching elements  31  in an upper arm are ON, first, electromagnetic energy is accumulated in a reactor, which is not depicted, connected between the battery  14  and the charging/discharging chopper  13 . Then, upon switching of the switching elements  31  in the upper arm to OFF, counter electromotive force is generated in the reactor and the electromagnetic energy in the reactor is discharged to charge the battery  14 . On the other hand, when abnormal condition occurs with the utility power source, the charging/discharging chopper  13  converts a low DC voltage to a high DC voltage. First, electric power discharged by the battery  14  is supplied to the reactor and electromagnetic energy is accumulated in the reactor, while switching elements  32  in a lower arm are ON. Then, upon switching of the switching elements  32  in the lower arm to OFF, rectification elements  33  in the upper arm are turned ON by counter electromotive force of the reactor. Thereby, a voltage that is the sum of the DC voltage of the battery  14  and the counter electromotive voltage of the reactor appears at the output terminal of the charging/discharging chopper  13 , which thus results in a voltage increase. The switching elements  31 ,  32  of the charging/discharging chopper  13  are driven by a signal from a control circuit  204 . Although, in the present embodiment, there are two parallel legs in the charging/discharging chopper  13 , the number of parallel legs is determined by the amount of electric power to be supplied to the charging/discharging chopper  13  when discharging takes place. 
         [0037]    As will be noted from the foregoing, the converter  11 , inverter  12 , and charging/discharging chopper  13  which are installed in the power conversion equipment  1  of the present embodiment are basically configured with legs  35  in which the switching elements  31  and the rectification elements  33  are connected in series in the upper arm and the switching elements  32  and the rectification elements  34  are connected in series in the lower arm. In a case where electric power that is supplied to the load  3  exceeds rated power of the power conversion equipment  1 , the rated power should be increased by increasing the number of parallel legs  35  in the converter  11 , inverter  12 , and charging/discharging chopper  13 . 
         [0038]    In the converter  11 , inverter  12 , and charging/discharging chopper  13 , the resistors incorporated in the switching elements  31 ,  32  and the rectification elements  33 ,  34  give rise to loss, when these components carry current. Besides, switching from a current carrying state to a current blocking state gives rise to loss. Because heat is generated during operation entailing this loss, the temperature of the converter  11 , inverter  12 , and charging/discharging chopper  13  rises. 
         [0039]      FIG. 5  is a circuit diagram of a dual-side cooled power module  100  which is used in the present embodiment. In the dual-side cooled power module  100 , switching elements  31 ,  32  and rectification elements  33 ,  34  mounted on an insulator  112  are included. Respective semiconductors are interconnected to form a leg  35  which is depicted in  FIGS. 2 to 4 . Onto the insulator  112 , a P terminal  113 P (DC positive terminal), an N terminal  113 N (DC negative terminal), an AC terminal.  113 AC (AC terminal), and a gate terminal  111  for ON/OFF control of the switching elements are attached. 
         [0040]      FIG. 6  is an external view of the dual-side cooled power module  100  which is used in the present embodiment. The dual-side cooled power module  100  is comprised of a substantially cuboidal main body part  101 , a substantially cuboidal flange part  102  formed to expand one lateral side of the main body part  101 , and a terminal block part  103  which is comprised of a plurality of terminals, protruding from a face of the flange part  102  on the side opposite to the main body part  101 . Terminals constituting the terminal block part  103  are as follows: P terminal  113 P, N terminal  113 N, AC terminal  113 AC, and gate terminal  111  depicted in  FIG. 5 . 
         [0041]    One face  121 A of the main body part  101  has a great number (e.g., a total of approx. 200 or more) of protruding pin fins  122 A which are very small, columnar projections. On another face  121 B of the main body part  101 , opposite to the face  121 A, as many pin fins  122 B (not depicted) as the number of the pin fins  122 A are also formed. Hereinafter, the pin fins  122 A and  122 B will be collectively termed “pin fins  122 ”. The pin fins  122  may be any convex portions formed to protrude from the faces  121 A,  121 B, besides the form of pin fins as depicted in this drawing. The main body part  101  has cooled surfaces  121 A,  121 B which are regions where the pin fins  122  are formed on the faces  121 A,  121 B. The cooled surfaces  121 A and  121 B are collectively termed “cooled surfaces”. The thickness of the main body part  101  with the exception of the pin fins  122 , that is, the distance between the cooled surfaces  121 ,  121 B is denoted by “d 1 ”. 
         [0042]      FIG. 7  is a perspective view of a heat receiving spacer. A pair of heat receiving spacers  300 A,  300 B is fit onto the cooled surfaces  300 A,  300 B of the dual-side cooled power module  100 . A heat receiving spacer  300 A is comprised of a heat receiving part  301 A which has a substantially rectangular plate form and a pair of hollow space providing sections  302 A which have a substantially cuboidal form, protruding toward a heat receiving spacer  300 B from both edges of the heat receiving part  301 A. In the heat receiving part  301 A, a great number of columnar through holes  303 A (concave portions) are formed. These through holes  303 A are formed in positions facing the pin fins  122 A of the cooled surface  121 A and have a diameter that is slightly larger than the diameter of a pin fin  122 A. Like the heat receiving spacer  300 A, the heat receiving spacer  300 B is also comprised, of a heat receiving part  301 B which has a substantially rectangular plate form and a pair of hollow space providing sections  302 B which have a substantially cuboidal form, protruding toward the heat receiving spacer  300 B from both edges of the heat receiving part  301 B. The heat receiving spacer  300 B has a shape that is upside down symmetrical with respect to the heat receiving spacer  300 A, but, in the heat receiving part  301 B, through holes  303 B are formed in positions facing the respective pin fins  122 B protruding from the cooled surface  121 B of the dual-side cooled power module  100 . 
         [0043]    When attaching the heat receiving spacers  300 A,  300 B to the dual-side cooled power module  100 , apply heat conductive grease over the cooled surfaces  121 A,  121 B and put the hollow space providing sections  302 A,  302 B abutting against each other, while positioning the through holes  303 A,  303 B in alignment with the respective pin fins  122 . A state in which heat receiving spacers  300 A,  300 B are attached to the dual-side cooled power module  100  in this way is depicted in  FIG. 8 . As depicted, the cooled surfaces  121 A,  121 B of the main body part  101  are mostly covered by the heat receiving spacers  300 A,  300 B, though a side end face  101   a  of the main body part is exposed. 
         [0044]      FIG. 9  is a cross-sectional view through line A-A′ in  FIG. 8 . When the hollow space providing sections  302 A,  302 B are put abutting against each other, the surfaces, facing a heat generator, of the heat receiving parts  301 A,  301 B face with each other with an interval as long as a distance d 2  between them. That is, the heat receiving spacers  300 A,  300 B are formed so that the distance d 2  is slightly longer than the thickness d 1  of the main body part  101  of the dual-side cooled power module  100 . In consequence, gaps  310 A,  310 B are formed between the heat receiving part  301 A and the main body part  101  and between the heat receiving part  301 B and the main body part  101 , respectively. The gaps  310 A,  310 B do not necessarily have an equal width, since the dual-side cooled power module  100  has play with respect to the heat receiving spacers  300 A,  300 B. 
         [0045]    When the hollow space providing sections  302 A,  302 B are put abutting against each other, heat conductive grease (not depicted) applied over the pin fins is pushed to enter the gaps  310 A,  310 B and the gaps  310 A,  310 B are also filled with heat conductive grease without space. Given that d 4  denotes the thickness of the main body part  101  from the tips of the pin fins  122 A to the tips of the pin fins  122 B and d 5  denotes the entire width when the heat receiving spacers  300 A,  300 B are put abutting against each other, the heat receiving spacers  300 A,  300 B are formed so that the width d 5  will be slightly wider than the thickness d 4 . Thereby, gaps  311 A,  311 B are formed between the upper surface of the heat receiving spacer  300 A and the tips of the pin fins  122 A and between the lower surface of the heat receiving spacer  300 B and the tips of the pin fins  122 B in the drawing, respectively. The gaps  311 A,  311 B do not necessarily have an equal width, since the dual-side cooled power module  100  has play with respect to the heat receiving spacers  300 A,  300 B as described previously. 
         [0046]    When the heat receiving spacers  300 A,  300 B are attached to a cooler  400  (which will be detailed later) pressing force  320  is applied, as indicated by hatched arrows. This pressing force  320  is applied to portions where hollow space providing sections  302 A,  302 B abut against each other. That is, this pressing force  320  is not applied to the main body part  101 , since the gaps  310 A,  310 B are formed between the main body part  101  and the heat receiving spacers  300 A,  300 B and the gaps  311 A,  311 B are formed in the portions adjacent to the tips of the pin fins  122 A,  122 B, these gaps being made by the hollow space providing sections  302 A and  302 B. 
         [0047]      FIG. 10  is a perspective view depicting a state in which two dual-side cooled power modules  100  are attached to the cooler  400 . The cooler  400  is comprised of a pair of coolers  400 A,  400 B. The coolers  400 A,  400 B have clamping members  410 A,  410 B formed in a substantially cuboidal block, respectively. Two dual-side cooled power modules  100 , to each of which the heat receiving spacers  300 A,  300 B are attached, are sandwiched between and clamped by these clamping members  410 A,  410 B. 
         [0048]    The clamping members  410 A,  410 B are mutually tightened with a plurality of fasteners  420  and pressing force  320  is applied to the clamping members  410 A,  410 B in a direction indicated by hatched arrows. However, as described for  FIG. 9 , this force  320  is applied to the heat receiving spacers  300 A,  300 B, but is not applied to the dual-side cooled power modules  100 . As the fasteners  420 , bolts and nuts which are commonly used can be used. 
         [0049]    In  FIG. 10 , four heat pipes  430  protrude from the clamping member  410 A, slanting at an angle of about 10° with respect to an x-y plane (horizontal plane) formed by x and y axes. A plurality of plate-like heat radiation fins  440  is welded to these heat pipes  430  in their radial direction. Therefore, each heat radiation fin  440  slants at an angle of about 10° with respect to an x-z plane (vertical plane) formed by x and z axes. A cooler  400 B is configured in the same way as for the cooler  400 A. By thus mounting two dual-side cooled power modules  100  to the cooler  400 , an air-cooled dual-side cooled power unit  500  is configured. 
         [0050]    When the dual-side cooled power modules  100  generate heat, the heat is transferred via the heat receiving spacers  300 A,  300 B to the clamping members  410 A,  410 B and further transferred backward (in the y-axis direction) through the heat pipes  430 . When cooling wind  441  directed from bottom to top (directed in the z-axis direction) is blown into this air-cooled dual-side cooled power unit  500 , the cooling wind  441  moves upward, while cooling the heat radiation fins  440  and, thus, the heat is expelled rapidly. Paths of such heat transfer are indicated by arrows  431  in the drawing. Heat transfer in a direction perpendicular to the direction of the cooling wind  441  is mainly due to the heat pipes  430 . 
         [0051]      FIG. 11  is an exploded view of region B surrounded by dashed lines presented in  FIG. 10 . In  FIG. 11 , heat conductive grease  450  is applied between the heat receiving spacer  300 A and the clamping member  410 A and between the heat receiving spacer  300 B and the clamping member  410 B, respectively. When the clamping members  410 A,  410 B are tightened with the fasteners  420 , the heat conductive grease  450  spreads over an interface plane between the heat receiving spacer  300 A and the clamping member  410 A and an interface plane between the heat receiving spacer  300 B and the clamping member  410 B and makes thin film layers as depicted. At the same time, the heat conductive grease  450  also enters the gaps  311 A,  311 B in the portions adjacent to the tips of the pin fins  122 A,  122 B (see  FIG. 9 ) and the outsides of the pin fins  122 A,  122 B are immersed in the heat conductive grease  450 . 
         [0052]      FIG. 12  is a cross-sectional view through line C-C′ in  FIG. 11 . Placing the clamping member  410 A on the upper surface of the heat receiving spacer  300 A provides a thermal connection surface at the interface between both. To transfer heat of the dual-side cooled power module  100  to the claiming member  410 A efficiently, the tips of the pin fins  122 A and the heat receiving part  301 A of the heat receiving spacer  300 A must connect with the clamping member  410 A in a smooth condition. 
         [0053]      FIG. 13  is an enlarged view of portion D presented in  FIG. 12 . In the present embodiment, a region (which is hatched in  FIG. 13 ) that is formed by the cooled surface  121 A, pins fins  122 A, heat receiving part  301 A, and clamping member  410 A is filled with heat conductive grease  450 . At this time, heat of the dual-side cooled power module  100  is transferred to the clamping member  410 A through heat dissipation paths  130 ,  131 ,  132  indicate by dashed lines. A heat dissipation path  130  is a path through which heat is transferred from the main body part  101  via the heat receiving part  301 A to the clamping member  410 A. A heat dissipation path  131  is a path through which heat is conducted from the main body part  101  to the pin fin  122 A and transferred via the heat conductive grease  450  to the clamping member  410 A. A heat dissipation path  132  is a path through which heat migrates from the pin fin  122 A to the heat receiving part  301 A and then the heat is transferred to the clamping member  410 A. The present embodiment enables dissipating heat of the dual-side cooled power module  100  through making effective use of the entire outer surfaces of the pin fins  122 A. As described above, it is enabled to dissipate heat through a plurality of paths via heat conductive grease in the present embodiment, and, therefore, heat can be dissipated efficiently. 
         [0054]    When viewing the power module  100  which is a heat generator from a direction parallel to a direction in which the convex portions formed on the power module protrude (that is, when viewing the power module  100  from −X axis direction toward +X axis direction in  FIG. 13 ), a filler area where the heat conductive material is filled between the heat receiving spacer  300 A and the clamping member  410 A is larger than a filler area where the heat conductive material is filled between the through hole  303 A and the pin fin  122 A and between the cooled surface  121 A and the heat receiving part  301 A. When heat is transferred from the heat receiving spacer  300 A to the clamping member  410 A, heat will spread inside the heat receiving spacer  300 A; therefore, the filler area between the heat receiving spacer  300 A and the clamping member  410 A is enlarged for transferring heat more efficiently. This configuration makes it possible to dissipate heat more effectively, when heat diffuses from the heat generator via the pin fins  122 A and the heat receiving spacer  300 A. The same configuration can be adopted also in second and third embodiments which will be described later and the same advantageous effect can be obtained. 
         [0055]    Moreover, if the main body part  101  has swollen by thermal deformation of the dual-side cooled power module  100 , swelling stress is released by fluid deformation of the heat conductive grease  450 . At this time, because the gap  315  between the tips of the pin fins  122 A and the clamping member  410 A is larger than the gap  311 A between the upper surface of the heat receiving spacer  300 A and the tips of the pin fins  122 A, the tips of the pins fins  122 A do not abut against the clamping member  410 A and a good thermal connection condition is maintained. The side of the clamping member  410 B is configured in the same way as for the side of the clamping member  410 A. 
       Second Embodiment 
       [0056]      FIG. 14  depicts a second embodiment of the present invention, in which thermal connections in the first embodiment are provided by heat conductive sheets  451 . 
         [0057]      FIG. 15  is an enlarged view of portion E in  FIG. 14 . The heat receiving part  301 A of the heat receiving spacer  300 A and the clamping member  410 A as well as the heat receiving part  301 A and the cooled surface  121 A of the dual-side cooled power module  100  are thermally connected by heat conductive sheets  451  which are of sheet form. Commonly used heat conductive sheets  451  have a lower fluidity than heat conductive grease  450 , but their heat conduction performance is high. Therefore, even though it is impossible to connect each pin fin  122 A and the heat receiving part  301 A by a heat conductive sheet  451 , heat dissipation performance is compensated by heat transfer through heat dissipation paths  130 ,  131 . Although two heat conductive sheets  151  are layered over the tips of the pin fins  122 A in  FIG. 15 , this layer may be configured with one sheet, making effective use of the deformability of a heat conductive sheet  451  in its thickness direction. 
       Third Embodiment 
       [0058]      FIG. 16  depicts a third embodiment of the present invention, in which the power semiconductor module of the first embodiment is configured as a one side cooled power module  600 . The one side cooled power module  600  is comprised of an element mount part  651  in which elements are installed and a base  652  in which an insulation substrate providing electrical insulation is installed. The element mount part  651  and the base  652  are bonded by brazing, for example. 
         [0059]      FIG. 17  is an enlarged view of portion F in  FIG. 16 . In the present configuration, there are thermal connections between a heat receiving part  611  of a heat receiving spacer  610  and the base  652 , between a through hole  612  of the heat receiving spacer  610  and a pin fin  653  of the base  610 , and between the heat receiving part  611  and a clamping member  410 . In the present embodiment, gaps are filled with heat conductive grease  450  to provide the thermal connections, enabling heat dissipation making effective use of the entire outer surfaces of the pin fins  653 . Therefore, it is possible to transfer heat from the heat generator efficiently.