Patent Publication Number: US-2023164958-A1

Title: Power conversion device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a power conversion device and a method of manufacturing a power conversion device. 
     BACKGROUND ART 
     In general, a power conversion device includes such electronic components as a switching element, a rectifier element, and a magnetic component. Such electronic components generate heat as the power conversion device operates. Heat generated in these electronic components conducts through a heat radiation path to a cooling body and radiated from the cooling body. A temperature of these electronic components is thus suppressed to a temperature not higher than an allowable temperature of each electronic component. 
     With higher demand for a smaller size and higher output of a power conversion device, an amount of heat generation in electronic components mounted on the power conversion device has recently increased. Therefore, enhancement of heat radiation performance of the power conversion device and suppression of temperature increase of the power conversion device have strongly been demanded. 
     Japanese Patent No. 4231626 (PTL 1) describes a motor drive apparatus for vehicle by way of example of a power conversion device. In the motor drive apparatus for vehicle described in this literature, a power conversion element which is a high-heat-generating component among electronic components accommodated in a housing is arranged on a bottom surface of the housing. The bottom surface of the housing where the power conversion element is arranged is integrated with a cooling body. A printed circuit board on which a control element is mounted is fixed to a plate-like substrate mounting member formed in the housing. Heat generated in the control element conducts to the housing through the plate-like substrate mounting member. The printed circuit board is layered on the power conversion element. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent No. 4231626 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the motor drive apparatus for vehicle described in the literature, the power conversion element which is the high-heat-generating component is arranged on the bottom surface of the housing. Therefore, increase in number of high-heat-generating components with increase in output from the power conversion device necessitates increase in area of the bottom surface of the housing for arranging these high-heat-generating components. Consequently, the power conversion device increases in size. In the motor drive apparatus for vehicle described in the literature, heat generated in the control element conducts to the housing through the plate-like substrate mounting member. Therefore, a heat radiation path is long, and consequently heat radiation performance is lowered. For the motor drive apparatus for vehicle described in the literature, a technique for electrical connection between the component and the printed circuit board is not described in detail. Therefore, for example, when two printed circuit boards are connected to each other through a harness and a screw and a terminal block to fix the harness, Joule heat generated in the screw and the terminal block increases the temperature of the power conversion device. 
     The present disclosure was made in view of problems above, and an object thereof is to provide a power conversion device capable of achieving suppression of increase in bottom surface area of a power conversion device, enhancement of heat radiation performance, and suppression of increase in temperature thereof, and a method of manufacturing the power conversion device. 
     Solution to Problem 
     A power conversion device in the present disclosure includes an electronic component, a first substrate, a first cooling body, a second substrate, a second cooling body, and a first wiring member. The electronic component includes a first component and a second component. The first substrate includes a first main surface on which the first component of the electronic component is mounted and a second main surface opposed to the first main surface. The first cooling body is thermally connected to the second main surface of the first substrate. The second substrate includes a third main surface on which the second component of the electronic component is mounted and a fourth main surface opposed to the third main surface. The second cooling body is thermally connected to the fourth main surface of the second substrate. A first wiring member electrically connects the first substrate and the second substrate to each other. The second cooling body extends in a direction from the second main surface of the first substrate toward the first main surface. The first wiring member is connected to the first main surface of the first substrate and the third main surface of the second substrate by any of direct connection and solder joint. 
     Advantageous Effects of Invention 
     According to the power conversion device in the present disclosure, electronic components are mounted not only on the first substrate but also on the second substrate. Therefore, even when the number of electronic components which are high-heat-generating components increases, increase in size of the first cooling body can be suppressed by mounting the electronic components on the second substrate. Therefore, increase in bottom surface area of the power conversion device can be suppressed. By mounting electronic components on the second substrate, a heat radiation distance over which heat generated in the electronic components mounted on the second substrate conducts to the second cooling body can be shorter. Therefore, heat radiation performance of the second substrate can be enhanced. The first wiring member is connected to the first main surface of the first substrate and the third main surface of the second substrate by any of direct connection and solder joint. Therefore, since a screw and a terminal block are not used for connection between substrates, Joule heat generated in the screw and the terminal block is reduced and hence increase in temperature of the first wiring member can be suppressed. 
     Therefore, increase in temperature of the power conversion device can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a circuit diagram of a power conversion device according to a first embodiment. 
         FIG.  2    is a perspective view schematically showing a construction of the power conversion device according to the first embodiment. 
         FIG.  3    is a perspective view schematically showing a construction of a first printed circuit board module of the power conversion device according to the first embodiment. 
         FIG.  4    is a perspective view schematically showing a construction of a second printed circuit board module of the power conversion device according to the first embodiment. 
         FIG.  5    is a perspective view schematically showing a construction of a third printed circuit board module of the power conversion device according to the first embodiment. 
         FIG.  6    is a cross-sectional view schematically showing the construction of the power conversion device according to the first embodiment. 
         FIG.  7    is a perspective view for illustrating electrical connection between the printed circuit board modules of the power conversion device according to the first embodiment. 
         FIG.  8    is a flowchart showing a method of manufacturing a power conversion device according to the first embodiment. 
         FIG.  9    is a cross-sectional view schematically showing the construction of the power conversion device according to a first modification of the first embodiment. 
         FIG.  10    is a perspective view for illustrating electrical connection between the printed circuit board modules of the power conversion device according to a second modification of the first embodiment. 
         FIG.  11    is a cross-sectional view schematically showing the construction of the power conversion device according to the second modification of the first embodiment. 
         FIG.  12    is a perspective view schematically showing the construction of the power conversion device according to a third modification of the first embodiment. 
         FIG.  13    is a perspective view schematically showing the construction of the power conversion device according to a fourth modification of the first embodiment. 
         FIG.  14    is a perspective view schematically showing the construction of the power conversion device according to a fifth modification of the first embodiment. 
         FIG.  15    is a perspective view schematically showing the construction of the power conversion device according to a sixth modification of the first embodiment. 
         FIG.  16    is a perspective view schematically showing the construction of the power conversion device according to a second embodiment. 
         FIG.  17    is a perspective view schematically showing the construction of the power conversion device according to a modification of the second embodiment. 
         FIG.  18    is a perspective view schematically showing the construction of the power conversion device according to a third embodiment. 
         FIG.  19    is a perspective view for illustrating electrical connection among the printed circuit board modules of the power conversion device according to the third embodiment. 
         FIG.  20    is a perspective view for illustrating electrical connection among the printed circuit board modules of the power conversion device according to a modification of the third embodiment. 
         FIG.  21    is a cross-sectional view schematically showing the construction of the power conversion device according to a fourth embodiment. 
         FIG.  22    is a perspective view for illustrating electrical connection between the printed circuit board modules of the power conversion device according to a fifth embodiment. 
         FIG.  23    is a cross-sectional view schematically showing the construction of the power conversion device according to a sixth embodiment. 
         FIG.  24    is a cross-sectional view schematically showing the construction of the power conversion device according to a first modification of the sixth embodiment. 
         FIG.  25    is a cross-sectional view schematically showing the construction of the power conversion device according to a second modification of the sixth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present disclosure will be described below with reference to the drawings. The same or corresponding elements below have the same reference characters allotted and redundant description will not be repeated. 
     First Embodiment 
       FIG.  1    is an exemplary circuit diagram of a power conversion device according to a first embodiment. The power conversion device shown in the circuit diagram in  FIG.  1    is, for example, a direct-current (DC)-DC converter mounted on an electric vehicle, the DC-DC converter converting an input voltage of a lithium ion battery of DC 100 V to 300 V to a voltage of DC 12 to 15 V and providing the resultant voltage to charge a lead acid battery. The power conversion device shown in the circuit diagram in  FIG.  1    includes an input capacitor  1 , an inverter circuit unit  11  constituted of four switching elements  2   a ,  2   b ,  2   c , and  2   d , a transforming unit  12  constituted of transformers  3  and  4 , a rectifier circuit unit  13  constituted of eight rectifier elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g , and  5   h , a smoothing circuit unit  14  constituted of reactors  6  and  7  and a smoothing capacitor  8 , an input terminal  9 , an output terminal  10 , and a control circuit unit  15 . Each electronic component shown with a circuit sign in  FIG.  1    may be configured with any number of components connected in series or parallel. 
     Each of switching elements  2   a ,  2   b ,  2   c , and  2   d  is a power semiconductor element such as a transistor, a metal oxide semiconductor field effect transistor (MOSFET), or an insulated gate bipolar transistor (IGBT). Rectifier elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g , and  5   h  are each a power semiconductor element such as a diode, a MOSFET, or a thyristor. 
     The power conversion device shown in the circuit diagram in  FIG.  1    converts a DC voltage provided from input terminal  9  into an alternating-current (AC) voltage by controlling switching of inverter circuit unit  11  by means of control circuit unit  15 . Transforming unit  12  converts the AC voltage obtained by conversion by inverter circuit unit  11  into any voltage based on a turns ratio of transformers  3  and  4 . Transformers  3  and  4  electrically isolate input terminal  9  and output terminal  10  from each other. Rectifier circuit unit  13  converts the AC voltage supplied from transformers  3  and  4  again into a DC voltage. Smoothing circuit unit  14  smoothens the DC voltage obtained by conversion by rectifier circuit unit  13  to stabilize an output voltage. 
     In the power conversion device thus configured and shown in the circuit diagram in  FIG.  1   , four switching elements  2   a ,  2   b ,  2   c , and  2   d , transformers  3  and  4 , eight rectifier elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g , and  5   h , and reactors  6  and  7  fall under high-heat-generating components. Heat generated in these high-heat-generating components should be radiated to lower a temperature of the high-heat-generating components to a temperature not higher than an allowable temperature of each component. The allowable temperature of each component is, for example, not lower than 100° C. and not higher than 120° C. 
     Since a high current flows through a line that electrically connects these high-heat-generating components to each other, an electrical resistance of the line itself causes generation of Joule heat therein. Therefore, the line itself that electrically connects the high-heat-generating components to each other also generates a large amount of heat. Therefore, when high-heat-generating components are electrically connected to each other in a circuit pattern formed on or in the inside of a printed circuit board, heat generated in the circuit pattern should be radiated to lower the temperature of the printed circuit board to a temperature not higher than the allowable temperature. The allowable temperature of the printed circuit board is, for example, not lower than 100° C. and not higher than 120° C. 
       FIG.  2    is a perspective view of a power conversion device  100  according to the first embodiment.  FIG.  3    is a perspective view of a first printed circuit board module  71  included in power conversion device  100 .  FIG.  4    is a perspective view of a second printed circuit board module  72  included in power conversion device  100 .  FIG.  5    is a perspective view of a third printed circuit board module  73  included in power conversion device  100 . For the sake of convenience of description,  FIGS.  2  to  5    do not show a wiring member  86  and a joint portion  87  which will be described later. 
     As shown in  FIGS.  2  to  5   , power conversion device  100  includes an external cooling body  21 , a first printed circuit board  31 , a first insulating member  41 , a first cooling body  51 , a first fixing member  61 , a second printed circuit board  32 , a second insulating member  42 , a second cooling body  52 , a second fixing member  62 , a third printed circuit board  33 , a third insulating member  43 , a third cooling body  53 , a third fixing member  63 , an electronic component, and wiring member  86 . External cooling body  21  includes a main surface  21   a.    
     First printed circuit board (a first substrate)  31  includes a front surface (a first main surface) S 1  on which an electronic component (a first component) is mounted and a rear surface (a second main surface) S 2  opposed to first cooling body  51 . Second main surface S 2  is opposed to first main surface S 1 . First insulating member  41  is arranged between second main surface S 2  of first printed circuit board  31  and first cooling body  51 . First cooling body  51  is thermally connected to second main surface S 2  of first printed circuit board  31 . First cooling body  51  is thermally connected to second main surface S 2  of first printed circuit board  31  with first insulating member  41  being interposed. First cooling body  51  is thermally coupled to external cooling body  21 . External cooling body  21  is thermally connected to first cooling body  51 . First cooling body  51  is thermally connected to second main surface S 2  of first printed circuit board  31 . First fixing member  61  is constructed to fix first printed circuit board  31  to first cooling body  51 . 
     Second printed circuit board (a second substrate)  32  includes a front surface (a third main surface) S 3  on which an electronic component (a second component) is mounted and a rear surface (a fourth main surface) S 4  opposed to second cooling body  52 . Fourth main surface S 4  is opposed to third main surface S 3 . Second insulating member  42  is arranged between fourth main surface S 4  of second printed circuit board  32  and second cooling body  52 . Second cooling body  52  is thermally connected to fourth main surface S 4  of second printed circuit board  32 . Second cooling body  52  is thermally connected to fourth main surface S 4  of second printed circuit board  32  with second insulating member  42  being interposed. Second cooling body  52  is constructed to vertically extend with a surface connected to a surface S 1   a  of first cooling body  51  opposed to first printed circuit board  31  being defined as a bottom surface. Second cooling body  52  extends in a direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . Second cooling body  52  is thermally connected to first cooling body  51 . Second fixing member  62  is constructed to fix second printed circuit board  32  to second cooling body  52 . 
     Third printed circuit board (a third substrate)  33  includes a front surface (a fifth main surface) S 5  on which an electronic component (a third component) is mounted and a rear surface (a sixth main surface) S 6  opposed to third cooling body  53 . Sixth main surface S 6  is opposed to fifth main surface S 5 . Third insulating member  43  is arranged between sixth main surface S 6  of third printed circuit board  33  and third cooling body  53 . Third cooling body  53  is thermally connected to sixth main surface S 6  of third printed circuit board  33 . Third cooling body  53  is thermally connected to sixth main surface S 6  of third printed circuit board  33  with third insulating member  43  being interposed. Third cooling body  53  is constructed to vertically extend with a surface connected to surface S 1   a  of first cooling body  51  being defined as a bottom surface. Third cooling body  53  extends in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . Third cooling body  53  is thermally connected to first cooling body  51 . Third fixing member  63  is constructed to fix third printed circuit board  33  to third cooling body  53 . 
     Each of second printed circuit board  32  and third printed circuit board  33  extends in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . Second printed circuit board  32  and third printed circuit board  33  are arranged to face each other. 
     In the present embodiment, first printed circuit board  31 , the second printed circuit board, and third printed circuit board  33  are constructed in a space defined by the cooling bodies. 
     Though second printed circuit board  32  and third printed circuit board  33  are arranged to face each other in the present embodiment, they may be arranged adjacently to each other. At that time, second printed circuit board  32  and third printed circuit board  33  are thermally coupled to each other. 
     The vertical direction is defined as a direction substantially perpendicular to main surface  21   a  of external cooling body  21 . First cooling body  51  defines a bottom surface of a support body of power conversion device  100 . Second cooling body  52  and third cooling body  53  each define a side surface of the support body of power conversion device  100 . 
     Input power is connected to first printed circuit board  31  (not shown) from an upper opening of second cooling body  52  or third cooling body  53 , for example, through a harness or a line of the printed circuit board. 
     Output power is provided from second printed circuit board  32  or third printed circuit board  33 . For example, a harness or a line of the printed circuit board for providing output power is connected to second printed circuit board  32  or third printed circuit board  33  (not shown) from an upper opening of the housing. 
     Control circuit unit  15  is arranged above second cooling body  52  or third cooling body  53  (not shown). 
     External cooling body  21  has a thermal conductivity not lower than 1.0 W/(m·K), preferably not lower than 10.0 W/(m·K), and further preferably not lower than 100.0 W/(m·K). External cooling body  21  is formed of a metal material such as copper, iron, aluminum, an iron alloy, or an aluminum alloy or a resin high in thermal conductivity. External cooling body  21  may include a pipe for passage of cooling water therein. External cooling body  21  may include a heat radiation fin for promoting heat radiation to the atmosphere therearound. 
     A not-shown circuit pattern may be formed on a surface or in the inside of each of first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33 . This circuit pattern has a thickness not smaller than 1 μm and not larger than 2000 μm. This circuit pattern is formed of a conductive material. This circuit pattern is formed, for example, of copper, nickel, gold, aluminum, silver, or tin, or an alloy thereof. First printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33  may each be composed, for example, of a glass fiber reinforced epoxy resin, a phenol resin, polyphenylene sulfide (PPS), or polyether ether ketone (PEEK). In other words, each of first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33  may be composed of a material generally assumed as being low in thermal conductivity. In other words, each of first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33  may be a general-purpose printed circuit board. Each of first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33  may be composed of ceramics such as aluminum oxide, aluminum nitride, or silicon carbide. 
     Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  is electrically insulating. Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  may be elastic. Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  may have a Young&#39;s modulus not lower than 1 MPa and not higher than 100 MPa. Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  has a thermal conductivity not lower than 0.1 W/(m·K) and preferably not lower than 1.0 W/(m·K). Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  may be composed, for example, of a rubber material such as silicon or urethane, a resin material such as acrylonitrile butadiene styrene (ABS), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), or phenol, a polymeric material such as polyimide, a ceramic material such as alumina or aluminum nitride, or a phase change material mainly composed of silicon. Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  may be composed of a material obtained by mixing particles of aluminum oxide, aluminum nitride, or boron nitride in a silicon resin. 
     Each of first cooling body  51 , second cooling body  52 , and third cooling body  53  has a thermal conductivity not lower than 1.0 W/(m·K), preferably not lower than 10.0 W/(m·K), and further preferably not lower than 100.0 W/(m·K). Each of first cooling body  51 , second cooling body  52 , and third cooling body  53  is formed of a metal material such as copper, iron, aluminum, an iron alloy, or an aluminum alloy, or a resin high in thermal conductivity. In the present embodiment, first cooling body  51 , second cooling body  52 , and third cooling body  53  are composed of an aluminum alloy in a form of a plate. First cooling body  51 , second cooling body  52 , and third cooling body  53  may electrically be connected to another member to be equal in potential to the ground. Each of second cooling body  52  and third cooling body  53  is connected and fixed to first cooling body  51  directly or with another member being interposed. Each of second cooling body  52  and third cooling body  53  is thermally connected to first cooling body  51 . 
     A thermally conductive member (a first thermally conductive member) HC 1  such as thermally conductive grease, a thermally conductive sheet, or a thermally conductive adhesive may be arranged on a surface of contact between first cooling body  51  and second cooling body  52  and a surface of contact between first cooling body  51  and third cooling body  53 . Thermally conductive member (first thermally conductive member) HC 1  includes at least any one of the thermally conductive grease, the thermally conductive sheet, and the thermally conductive adhesive. First cooling body  51  is thermally connected to each of second cooling body  52  and third cooling body  53  with thermally conductive member (first thermally conductive member) HC 1  being interposed. 
     First cooling body  51  may be in surface contact with external cooling body  21 . When first cooling body  51  and external cooling body  21  are in surface contact with each other, the thermally conductive member such as the thermally conductive grease, the thermally conductive sheet, or the thermally conductive adhesive may be arranged on the surface of contact between first cooling body  51  and external cooling body  21 . 
     Since first cooling body  51  and external cooling body  21  are thermally coupled to each other, performance of radiation of heat generated in first printed circuit board module  71  is higher than performance of radiation of heat generated in second printed circuit board module  72  and third printed circuit board module  73 . Therefore, though electronic components arranged in first printed circuit board module  71 , second printed circuit board module  72 , and third printed circuit board module  73  may be interchanged, electronic components (high-heat-generating components) that generate a particularly large amount of heat are arranged preferably on first printed circuit board module  71 . In the present embodiment, with each of switching elements  2   a ,  2   b ,  2   c , and  2   d  being assumed as a particularly high-heat-generating component, each of switching elements  2   a ,  2   b ,  2   c , and  2   d  is arranged in first printed circuit board module  71 . 
     Rectifier elements  5   a ,  5   b ,  5   c ,  5   e ,  5   f ,  5   g , and  5   h  or transformers  3  and  4  less in heat generation than the switching elements are arranged in second printed circuit board module  72  and/or third printed circuit board module  73 . 
     Exemplary first printed circuit board module  71 , second printed circuit board module  72 , and third printed circuit board module  73  will be described in succession with reference to  FIGS.  3  to  5   . 
     As shown in  FIG.  3   , first printed circuit board module  71  includes first printed circuit board  31 , first insulating member  41 , first cooling body  51 , first fixing member  61 , and an electronic component (first electronic component). The electronic component (first component) is mounted on first printed circuit board  31 . The electronic component (first component) is each of switching elements  2   a ,  2   b ,  2   c  and  2   d  that are particularly high-heat-generating components. First insulating member  41  is provided between first printed circuit board  31  and first cooling body  51 . First insulating member  41  is preferably in surface contact with first printed circuit board  31  and first cooling body  51 . First fixing member  61  fixes first printed circuit board  31  to first cooling body  51 . 
     On a surface  31   a  of first printed circuit board  31  opposite to a surface opposed to first cooling body  51 , input capacitor  1  and switching elements  2   a ,  2   b ,  2   c , and  2   d  are mounted. Not-shown input terminal  9  is mounted on surface  31   a . Other electronic components may be mounted on surface  31   a . Other electronic components may be mounted on the surface of first printed circuit board  31  opposed to first cooling body  51 . The surface of first printed circuit board  31  opposed to first cooling body  51  corresponds to second main surface S 2 . Surface  31   a  of first printed circuit board  31  opposite to the surface opposed to first cooling body  51  corresponds to first main surface S 1 . 
     As shown in  FIG.  4   , second printed circuit board module  72  includes second printed circuit board  32 , second insulating member  42 , second cooling body  52 , second fixing member  62 , and an electronic component (second component). The electronic component (second component) is mounted on second printed circuit board  32 . The electronic component (second component) is transformers  3  and  4  and rectifier elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g , and  5   h  which are particularly high-heat-generating components. Second insulating member  42  is provided between fourth main surface S 4  of second printed circuit board  32  and second cooling body  52 . Second insulating member  42  is preferably in surface contact with second printed circuit board  32  and second cooling body  52 . Second fixing member  62  fixes second printed circuit board  32  to second cooling body  52 . 
     On a surface  32   a  of second printed circuit board  32  opposite to a surface opposed to second cooling body  52 , rectifier elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g , and  5   h  and transformers  3  and  4  are mounted. Other electronic components may be mounted on surface  32   a . Other electronic components may be mounted on the surface of second printed circuit board  32  opposed to second cooling body  52 . The surface of second printed circuit board  32  opposed to second cooling body  52  corresponds to fourth main surface S 4 . Surface  32   a  of second printed circuit board  32  opposite to the surface opposed to second cooling body  52  corresponds to third main surface S 3 . 
     As shown in  FIG.  5   , third printed circuit board module  73  includes third printed circuit board  33 , third insulating member  43 , third cooling body  53 , third fixing member  63 , and an electronic component (third component). The electronic component (third component) is mounted on third printed circuit board  33 . The electronic component (third component) is reactors  6  and  7  which are particularly high-heat-generating components. Third insulating member  43  is provided between third printed circuit board  33  and third cooling body  53 . Third insulating member  43  is preferably in surface contact with third printed circuit board  33  and third cooling body  53 . Third fixing member  63  fixes third printed circuit board  33  to third cooling body  53 . 
     On a surface  33   a  of third printed circuit board  33  opposite to a surface opposed to third cooling body  53 , smoothing capacitor  8  and reactors  6  and  7  are mounted. Not-shown output terminal  10  is mounted on surface  33   a . Other electronic components may be mounted on surface  33   a . Other electronic components may be mounted on the surface of third printed circuit board  33  opposed to third cooling body  53 . The surface of third printed circuit board  33  opposed to third cooling body  53  corresponds to sixth main surface S 6 . Surface  33   a  of third printed circuit board  33  opposite to the surface opposed to third cooling body  53  corresponds to fifth main surface S 5 . 
     Control circuit unit  15  shown in  FIG.  1    may be mounted on any of first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33 . Control circuit unit  15  may be mounted as being divided, on at least two of first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33 . 
     Wiring member  86  will be described in further detail with reference to  FIGS.  2 ,  6 , and  7   . 
     As shown in  FIG.  2   , power conversion device  100  according to the first embodiment includes external cooling body  21 , first printed circuit board module  71 , second printed circuit board module  72 , and third printed circuit board module  73 . Wiring member  86  electrically connects first printed circuit board module  71  and second printed circuit board module  72  to each other and electrically connects first printed circuit board module  71  and third printed circuit board module  73  to each other. 
     Wiring member  86  includes a first wiring member  86   a  and a second wiring member  86   b . First wiring member  86   a  electrically connects first printed circuit board  31  of first printed circuit board module  71  and second printed circuit board  32  of second printed circuit board module  72  to each other. Second wiring member  86   b  electrically connects first printed circuit board  31  of first printed circuit board module  71  and third printed circuit board  33  of third printed circuit board module  73  to each other. 
     First wiring member  86   a  is connected to first main surface S 1  of first printed circuit board  31  and third main surface S 3  of second printed circuit board  32  by any of direct connection and solder joint. Second wiring member  86   b  is joined to first main surface S 1  of first printed circuit board  31  and fifth main surface S 5  of third printed circuit board  33 . Joint here refers to joint by soldering, ultrasonic bonding, a conductive adhesive, and welding. 
     Joint portion  87  is provided on first main surface S 1  of first printed circuit board module  71 . Joint portion  87  is provided on third main surface S 3  of second printed circuit board module  72 . Joint portion  87  is provided on fifth main surface S 5  of third printed circuit board module  73 . Wiring member  86  is electrically connected to joint portion  87 . A current from 0 to 300 A flows to wiring member  86  and joint portion  87 . 
     Wiring member  86  is formed of a conductive material. Wiring member  86  is formed of copper, nickel, gold, aluminum, silver, or tin, or an alloy thereof. 
     Regarding a shape of wiring member  86 , too small a thickness, too small a width, or too long a length causes a large amount of heat generation at the time of conduction to wiring member  86 . Therefore, the temperature of wiring member  86  increases. Therefore, the shape of wiring member  86  preferably satisfies a condition below. 
     Wiring member  86  has a thickness preferably not smaller than 0.05 mm and smaller than 0.3 mm. Wiring member  86  has a width preferably not smaller than 3 mm and smaller than 50 mm. Wiring member  86  has a length preferably not shorter than 10 mm and shorter than 100 mm. Wiring member  86  has a current density preferably not lower than 50 A/mm 2  and not higher than 100 A/mm 2 . Wiring member  86  has an aspect ratio preferably lower than 1:300. Wiring member  86  should only have, for example, a thickness of 0.1 mm, a width of 10 mm, and a length of 50 mm and should only allow conduction of a current at 90 A. 
       FIG.  6    is a cross-sectional view schematically showing the construction of power conversion device  100 . For the sake of convenience of description, hatching is not provided in  FIG.  6   . 
       FIG.  7    is a developed view of first printed circuit board module  71 , second printed circuit board module  72 , and third printed circuit board module  73  of power conversion device  100 . 
     With a large thickness of wiring member  86 , a crack is likely in a portion of soldering between wiring member  86  and joint portion  87  when second printed circuit board module  72  and third printed circuit board module  73  are erected as shown in  FIG.  6    from a state shown in  FIG.  7   . With a thickness smaller than 0.3 mm, when second printed circuit board module  72  and third printed circuit board module  73  are erected perpendicularly to first printed circuit board module  71  in a direction of a Z axis, deflection is produced in a direction of a Y axis. This flexed portion deforms in the direction of the Y axis to thereby absorb position displacement. Therefore, as the thickness is smaller, position displacement in the direction of the Y axis can more be absorbed. 
     As wiring member  86  has a smaller width, position displacement in the direction of the Y axis at the time when second printed circuit board module  72  and third printed circuit board module  73  are erected perpendicularly to first printed circuit board module  71  in the direction of the Z axis can more be absorbed. 
     As wiring member  86  has a longer length, position displacement in the direction of the Y axis at the time when second printed circuit board module  72  and third printed circuit board module  73  are erected perpendicularly to first printed circuit board module  71  in the direction of the Z axis can more be absorbed. 
     As shown in  FIG.  6   , wiring member  86  is bent at a right angle and connected to joint portion  87 . Joint portion  87  is a part of a circuit pattern. Wiring member  86  can be bent not only at the right angle but also at any angle from 0 degree to 180 degrees. By bending wiring member  86 , as shown in  FIG.  6   , second printed circuit board module  72  and third printed circuit board module  73  can be erected with respect to first printed circuit board module  71  in the direction of the Z axis. Therefore, each of second printed circuit board module  72  and third printed circuit board module  73  can be arranged perpendicularly to external cooling body  21 . A structure obtained by assembling first printed circuit board module  71 , second printed circuit board module  72 , and third printed circuit board module  73  can thus be smaller in bottom surface area with respect to external cooling body  21 , so that this structure can be mounted on external cooling body  21 . 
     As shown in  FIG.  7   , a direction in parallel to a longitudinal direction of wiring member  86  on a rectangular thin plate is defined as an X axis and a direction perpendicular to the longitudinal direction is defined as the Y axis. A direction perpendicular to a cooling surface is defined as the direction of the Z axis. A position of joint portion  87  may be displaced in the direction of the Y axis from a designed position at the time of screwing of the printed circuit board module to the cooling body. Position displacement in the direction of the Y axis may occur at the time of connection of joint portion  87  to wiring member  86 . In a state shown in  FIG.  6   , when second printed circuit board module  72  and third printed circuit board module  73  are erected perpendicularly to first printed circuit board module  71  in the direction of the Z axis, wiring member  86  is flexed. Therefore, wiring member  86  can absorb position displacement in the direction of the Z axis. 
     A method of manufacturing power conversion device  100  according to the first embodiment will now be described with reference to  FIGS.  6 ,  7 , and  8   . 
     As shown in  FIGS.  6 ,  7 , and  8   , power conversion device  100  is manufactured through a preparation step S 100 , an assembly step S 200 , and a connection step S 300 . 
     In preparation step S 100 , electronic components including the first component, the second component, and the third component, first printed circuit board  31 , the second printed circuit board, and third printed circuit board  33 , first cooling body  51  and second cooling body  52 , and wiring member  86  are prepared. The printed circuit board may be obtained by division of a single substrate. In this case, division into individual printed circuit boards is made by cutting by a rooter along perforations provided in a single substrate. 
     In assembly step S 200 , each printed circuit board may be connected by wiring member  86  with joint portion  87  being interposed. The perforations may be arranged so as not to be superimposed on wiring member  86 . 
     In assembly step S 200 , each of first printed circuit board module  71 , second printed circuit board module  72 , and third printed circuit board module  73  is assembled. In assembly step S 200 , each of first printed circuit board module  71 , second printed circuit board module  72 , and third printed circuit board module  73  is manufactured through an electronic component mounting step, a printed circuit board combination step, and a printed circuit board fixing step. 
     A step of assembling first printed circuit board module  71  will be described. In the electronic component mounting step, the electronic component (first component) is mounted on first main surface S 1  of first printed circuit board  31  by flow soldering or reflow soldering. In the printed circuit board combination step, first cooling body  51 , first insulating member  41 , and first printed circuit board  31  where the electronic component is mounted on surface  31   a  are combined. At this time, first cooling body  51  is thermally connected to second main surface S 2  opposed to first main surface S 1  of first printed circuit board  31 . In the printed circuit board fixing step, first fixing member  61  fixes first printed circuit board  31  to first cooling body  51  with first insulating member  41  being interposed. 
     A step of assembling second printed circuit board module  72  will be described. In the electronic component mounting step, the electronic component (second component) is mounted on third main surface S 3  of second printed circuit board  32  by flow soldering or reflow soldering. In the printed circuit board combination step, second cooling body  52 , second insulating member  42 , and second printed circuit board  32  where the electronic component is mounted on surface  32   a  are combined. Upper and lower cores are combined with each other. At this time, second cooling body  52  is thermally connected to fourth main surface S 4  opposed to third main surface S 3  of second printed circuit board  32 . In the printed circuit board fixing step, second fixing member  62  fixes second printed circuit board  32  to second cooling body  52  with second insulating member  42  being interposed. 
     A step of assembling third printed circuit board module  73  will be described. In the electronic component mounting step, the electronic component (third component) is mounted on fifth main surface S 5  of third printed circuit board  33  by flow soldering or reflow soldering. In the printed circuit board combination step, third cooling body  53 , third insulating member  43 , and third printed circuit board  33  where the electronic component is mounted on surface  33   a  are combined. Upper and lower cores are combined with each other. At this time, third cooling body  53  is thermally connected to sixth main surface S 6  opposed to fifth main surface S 5  of third printed circuit board  33 . In the printed circuit board fixing step, third fixing member  63  fixes third printed circuit board  33  to third cooling body  53  with third insulating member  43  being interposed. 
     First wiring member  86   a  of wiring member  86  electrically connects first printed circuit board  31  and second printed circuit board  32  to each other. First wiring member  86   a  is connected to first main surface S 1  of first printed circuit board  31  and third main surface S 3  of second printed circuit board  32  by any of direct connection and solder joint. First wiring member  86   a  may electrically connect first printed circuit board  31  and second printed circuit board  32  to each other before first printed circuit board  31  is fixed to first cooling body  51  and before second printed circuit board  32  is fixed to second cooling body  52 . First wiring member  86   a  may electrically connect first printed circuit board  31  and second printed circuit board  32  to each other after first printed circuit board  31  is fixed to first cooling body  51  and after second printed circuit board  32  is fixed to second cooling body  52 . 
     Second wiring member  86   b  of wiring member  86  electrically connects first printed circuit board  31  and third printed circuit board  33  to each other. Second wiring member  86   b  is connected to first main surface S 1  of first printed circuit board  31  and fifth main surface S 5  of third printed circuit board  33  by any of direct connection and solder joint. First wiring member  86   a  may electrically connect first printed circuit board  31  and third printed circuit board  33  to each other before first printed circuit board  31  is fixed to first cooling body  51  and before third printed circuit board  33  is fixed to third cooling body  53 . First wiring member  86   a  may electrically connect first printed circuit board  31  and third printed circuit board  33  to each other after first printed circuit board  31  is fixed to first cooling body  51  and after third printed circuit board  33  is fixed to third cooling body  53 . 
     As shown in  FIG.  7   , each of second printed circuit board module  72  and third printed circuit board module  73  is electrically connected to first printed circuit board module  71  through wiring member  86 . Joint portion  87  is mounted on each of first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33 . Wiring member  86  is electrically connected to joint portion  87 . As wiring member  86  and joint portion  87  are fixed, each of second printed circuit board module  72  and third printed circuit board module  73  is electrically connected to first printed circuit board module  71 . Though first printed circuit board  31  is connected to second printed circuit board  32  and third printed circuit board  33  through wiring members  86  in  FIG.  7   , three or more substrates may be connected to a single substrate. 
     Joint portion  87  is a part of the circuit pattern, and connected to joint portion  87  by soldering without using such a fastening member as a screw and a terminal block. Joint portion  87  may be connected to joint portion  87  not only by soldering but also by welding, swaging, or ultrasonic bonding. 
     In assembly step S 200 , the electronic component (second component) and the electronic component (third component) are fixed into respective grooves G provided in second printed circuit board  32  and third printed circuit board  33 . 
     In connection step S 300 , each of second printed circuit board module  72  and third printed circuit board module  73  is connected and fixed to first printed circuit board module  71 . At this time, second cooling body  52  is arranged to extend in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . 
     Third cooling body  53  is arranged to extend in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . 
     In connection step S 300 , second cooling body  52  included in second printed circuit board module  72  and third cooling body  53  included in third printed circuit board module  73  are connected and fixed to first cooling body  51  included in first printed circuit board module  71 , directly or with another member being interposed. At this time, each of second cooling body  52  and third cooling body  53  is arranged to extend in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . First cooling body  51  is thermally coupled to external cooling body  21  with such a method as surface contact with external cooling body  21 . 
     In connection step S 300 , second cooling body  52  and third cooling body  53  are thermally connected to first cooling body  51 . At that time, in assembly of second cooling body  52  and third cooling body  53  to first cooling body  51  as in  FIG.  6    from the state in  FIG.  7   , positions of facing joint portions  87  in first printed circuit board  31  and second printed circuit board  32  and positions of facing joint portions  87  in first printed circuit board  31  and third printed circuit board  33  may be displaced. Even when the positions of joint portions  87  are displaced, connection can be maintained by deformation of wiring member  86 . 
     Effects of Power Conversion Device  100  According to the First Embodiment Will Now be Described. 
     According to the power conversion device in the first embodiment, electronic components are mounted not only on first printed circuit board  31  but also on second printed circuit board  32 . Therefore, even when the number of components which are high-heat-generating components increases, increase in size of first cooling body  51  can be suppressed by mounting the electronic components on second printed circuit board  32 . Therefore, increase in bottom surface area of power conversion device  100  can be suppressed. By mounting the electronic components on second printed circuit board  32 , the heat radiation distance over which heat generated in the electronic components mounted on second printed circuit board  32  conducts to second cooling body  52  can be shorter. Therefore, heat radiation performance of second printed circuit board  32  can be enhanced. First wiring member  86   a  is connected to first main surface S 1  of first printed circuit board  31  and third main surface S 3  of second printed circuit board  32  by any of direct connection and solder joint. Therefore, since a screw and a terminal block are not used in connection between substrates, a conduction path is accordingly shorter and an electrical resistance is lowered. Since Joule heat produced in the screw and the terminal block is thus reduced, increase in temperature of first wiring member  86   a  can be suppressed. Therefore, increase in temperature of power conversion device  100  can be suppressed. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     According to power conversion device  100  in the first embodiment, electronic components are mounted also on third printed circuit board  33 . Therefore, even when the number of electronic components which are high-heat-generating components increases, increase in size of first cooling body  51  can be suppressed by mounting the electronic components on third printed circuit board  33 . Therefore, increase in bottom surface area of power conversion device  100  can be suppressed. By mounting the electronic components on third printed circuit board  33 , the heat radiation path through which heat generated in the electronic components mounted on third printed circuit board  33  conducts to third cooling body  53  can be shorter. Therefore, heat radiation performance of third printed circuit board  33  can be enhanced. Second wiring member  86   b  is connected to first main surface S 1  of first printed circuit board  31  and fifth main surface S 5  of third printed circuit board  33  by any of direct connection and solder joint. Therefore, since a screw and a terminal block are not used in connection between substrates, a conduction path is accordingly shorter and an electrical resistance is lowered. Since Joule heat produced in the screw and the terminal block is thus reduced, increase in temperature of second wiring member  86   b  can be suppressed. Therefore, increase in temperature of power conversion device  100  can be suppressed. 
     Power conversion device  100  according to the first embodiment will be described in comparison to a comparative example. In the comparative example, a terminal block provided at joint portion  87  provided at an end of each of first printed circuit board  31  and second printed circuit board  32  is connected with the use of a screw and a harness. When second printed circuit board  32  is mounted with respect to first printed circuit board  31  perpendicularly and closely, the terminal block and the screw provided at joint portion  87  of second printed circuit board  32  interfere with the terminal block, the screw, and an electronic component provided at the end of first printed circuit board  31 . Therefore, first printed circuit board  31  and second printed circuit board  32  should be mounted at a distance from each other so as to avoid interference between components of first printed circuit board  31  and second printed circuit board  32 . Then, a volume and the bottom surface area of power conversion device  100  increase. 
     According to power conversion device  100  in the first embodiment, a copper plate in a form of a thin ribbon rather than the screw and the terminal block is employed as wiring member  86  between first printed circuit board  31  and second printed circuit board  32 , to connect joint portions  87  of first printed circuit board  31  and second printed circuit board  32  to each other by soldering. Then, in mount of second printed circuit board  32  with respect to first printed circuit board  31  perpendicularly and closely, power conversion device  100  can be assembled without providing substrates at a distance from each other. Consequently, space-saving wiring can be realized. Therefore, power conversion device  100  according to the first embodiment can further be reduced in size. 
     According to power conversion device  100  in the first embodiment, a shape of wiring member  86  is larger in surface area in contact with air, as compared with an annular wiring member equal in cross-sectional area. Therefore, performance of power conversion device  100 , of radiation of heat generated by conduction to the wiring member can be enhanced. Therefore, a current that flows in power conversion device  100  can be increased. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     According to power conversion device  100  in the first embodiment, second printed circuit board  32  and third printed circuit board  33  are arranged to face each other. Therefore, power conversion device  100  can be reduced in size. 
     Power conversion device  100  according to the first embodiment includes external cooling body  21  thermally connected to first cooling body  51 . A first heat radiation path for heat radiation to external cooling body  21  through first printed circuit board  31 , first insulating member  41 , and first cooling body  51  can be formed as a heat radiation path for radiation of heat generated in the circuit pattern formed at the surface or in the inside of first printed circuit board  31  and heat generated in switching elements  2   a ,  2   b ,  2   c , and  2   d  which are high-heat-generating components mounted on first printed circuit board  31 . Therefore, performance of power conversion device  100 , of radiation of heat generated in the circuit pattern formed at the surface or in the inside of first printed circuit board  31  and heat generated in the high-heat-generating components mounted on first printed circuit board  31  can be enhanced. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     When first insulating member  41  is in surface contact with first printed circuit board  31  and first cooling body  51 , an area of the surface of contact between first insulating member  41  and first printed circuit board  31  and an area of the surface of contact between first insulating member  41  and first cooling body  51  can be increased. Therefore, a contact thermal resistance of the surface of contact between first insulating member  41  and first printed circuit board  31  and a contact thermal resistance of the surface of contact between first insulating member  41  and first cooling body  51  can be lowered, and thus heat radiation performance of the first heat radiation path can be enhanced. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     A second heat radiation path for heat radiation to external cooling body  21  through second printed circuit board  32 , second insulating member  42 , second cooling body  52 , and first cooling body  51  can be formed as a heat radiation path for radiation of heat generated in the circuit pattern formed at the surface or in the inside of second printed circuit board  32  and heat generated in rectifier elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g , and  5   h  and transformers  3  and  4  which are high-heat-generating components mounted on second printed circuit board  32 . Since the second heat radiation path does not include the plate-like substrate mounting member as compared with the construction described in PTL 1, the heat radiation path can be shorter in length and heat radiation performance can be enhanced. Therefore, performance of power conversion device  100 , of radiation of heat generated in the circuit pattern formed at the surface or in the inside of second printed circuit board  32  and heat generated in the high-heat-generating components mounted on second printed circuit board  32  can be enhanced. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     When second insulating member  42  is in surface contact with second printed circuit board  32  and second cooling body  52 , an area of the surface of contact between second insulating member  42  and second printed circuit board  32  and an area of the surface of contact between second insulating member  42  and second cooling body  52  can be increased. Therefore, the contact thermal resistance of the surface of contact between second insulating member  42  and second printed circuit board  32  and the contact thermal resistance of the surface of contact between second insulating member  42  and second cooling body  52  can be lowered and heat radiation performance of the second heat radiation path can be enhanced. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     When a lower surface of the core is in direct contact with second cooling body  52 , when the lower surface of the core is in contact with second cooling body  52  with a thermally conductive member such as the thermally conductive grease, the thermally conductive sheet, or the thermally conductive adhesive being interposed, or when the lower surface of the core is in contact with second cooling body  52  with the insulating member being interposed, heat generated in transformers  3  and  4  can be radiated to external cooling body  21  through second cooling body  52  and first cooling body  51 . Therefore, performance of power conversion device  100 , of radiation of heat generated in transformers  3  and  4  can be enhanced. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     A third heat radiation path for heat radiation to external cooling body  21  through third printed circuit board  33 , third insulating member  43 , third cooling body  53 , and first cooling body  51  can be formed as a heat radiation path for radiation of heat generated in the circuit pattern formed at the surface or in the inside of third printed circuit board  33  and heat generated in reactors  6  and  7  which are high-heat-generating components mounted on third printed circuit board  33 . Since the third heat radiation path does not include the plate-like substrate mounting member as compared with the construction described in PTL 1, the heat radiation path can be shorter in length and heat radiation performance can be enhanced. Therefore, performance of power conversion device  100 , of radiation of heat generated in the circuit pattern formed at the surface or in the inside of third printed circuit board  33  and heat generated in the high-heat-generating components mounted on third printed circuit board  33  can be enhanced. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     When third insulating member  43  is in surface contact with third printed circuit board  33  and third cooling body  53 , an area of the surface of contact between third insulating member  43  and third printed circuit board  33  and an area of the surface of contact between third insulating member  43  and third cooling body  53  can be increased. Therefore, the contact thermal resistance of the surface of contact between third insulating member  43  and third printed circuit board  33  and the contact thermal resistance of the surface of contact between third insulating member  43  and third cooling body  53  can be lowered and heat radiation performance of the third heat radiation path can be enhanced. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     When the lower surface of the core is in direct contact with third cooling body  53 , when the lower surface of the core is in contact with third cooling body  53  with a thermally conductive member such as the thermally conductive grease, the thermally conductive sheet, or the thermally conductive adhesive being interposed, or when the lower surface of the core is in contact with third cooling body  53  with the insulating member being interposed, heat generated in reactors  6  and  7  can be radiated to external cooling body  21  through third cooling body  53  and first cooling body  51 . Therefore, performance of power conversion device  100 , of radiation of heat generated in reactors  6  and  7  can be enhanced. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     Since first cooling body  51  and external cooling body  21  are thermally coupled to each other, the first heat radiation path is higher in heat radiation performance than the second heat radiation path and the third heat radiation path. Therefore, by mounting particularly high-heat-generating electronic components among high-heat-generating electronic components on first printed circuit board  31 , performance of power conversion device  100 , of radiation of heat generated in those components can be enhanced. Consequently, power conversion device  100  according to the first embodiment can operate at high output. 
     The thickness of first cooling body  51  in a direction substantially perpendicular to surface  31   a  of first printed circuit board  31  is preferably small. Since the first heat radiation path, the second heat radiation path, and the third heat radiation path can thus be shorter in length, heat radiation performance can be enhanced. 
     The thickness of second cooling body  52  in a direction substantially perpendicular to surface  32   a  of second printed circuit board  32  is preferably large. Since a thermal resistance of second cooling body  52  included in the second heat radiation path can thus be lowered, heat radiation performance can be enhanced. 
     The thickness of third cooling body  53  in a direction substantially perpendicular to surface  33   a  of third printed circuit board  33  is preferably large. Since a thermal resistance of third cooling body  53  included in the third heat radiation path can thus be lowered, heat radiation performance can be enhanced. 
     In power conversion device  100  according to the first embodiment, first cooling body  51  can thermally be connected to first printed circuit board  31  with first insulating member  41  being interposed. Second cooling body  52  can thermally be connected to second printed circuit board  32  with second insulating member  42  being interposed. Third cooling body  53  can thermally be connected to third printed circuit board  33  with third insulating member  43  being interposed. 
     In power conversion device  100  according to the first embodiment, second cooling body  52  is thermally connected to first cooling body  51  and third cooling body  53  is thermally connected to first cooling body  51 . Therefore, heat generated in electronic components mounted on second printed circuit board  32  can be radiated through second cooling body  52  from first cooling body  51 , and heat generated in electronic components mounted on third printed circuit board  33  can be radiated through third cooling body  53  from first cooling body  51 . 
     In power conversion device  100  according to the first embodiment, first cooling body  51  is thermally connected to each of second cooling body  52  and third cooling body  53  through first thermally conductive member HC 1 . Therefore, with first thermally conductive member HC 1 , heat conduction efficiency from second cooling body  52  to first cooling body  51  can be enhanced and heat conduction efficiency from third cooling body  53  to first cooling body  51  can be enhanced. 
     According to power conversion device  100  in the first embodiment, wiring member  86  has a thickness not smaller than 0.05 mm and smaller than 0.3 mm and a current density not lower than 50 A/mm 2  and not lower than 100/mm 2 . Therefore, conduction of a high current to wiring member  86  having a small thickness can be achieved. 
     In the construction described in PTL 1, electronic components are arranged in the space provided in the housing. When the printed circuit board is fixed to the bottom surface and the side surface of the housing with the insulating member being interposed in the construction described in PTL 1 as in the present embodiment, arrangement of the insulating members, arrangement of the printed circuit boards, fixing of the printed circuit boards, and electrical connection of the printed circuit boards to each other should be done in the substantially surrounded space and hence workability is poor. Consequently, variation in thickness of the insulating member is likely and thermal design taking into account that fact is required. 
     In contrast, the method of manufacturing power conversion device  100  according to the first embodiment includes preparation step S 100 , assembly step S 200 , and connection step S 300 . Therefore, it is not necessary to do works to arrange first insulating member  41 , second insulating member  42 , and third insulating member  43  on first cooling body  51  that defines the bottom surface of the support body and second cooling body  52  and third cooling body  53  that define the side surfaces of the support body and to fix first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33  and works to electrically connect first printed circuit board module  71 , second printed circuit board module  72 , and third printed circuit board module  73  to one another within the substantially surrounded space. Consequently, thermal design in consideration of variation in thickness of first insulating member  41 , second insulating member  42 , and third insulating member  43  due to poor workability is not required. 
     In the method of manufacturing power conversion device  100  according to the first embodiment, second cooling body  52  is arranged to extend in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . First wiring member  86   a  electrically connects first printed circuit board  31  and second printed circuit board  32  to each other. First wiring member  86   a  is connected to first main surface S 1  of first printed circuit board  31  and third main surface S 3  of second printed circuit board  32  by any of direct connection and solder joint. Therefore, power conversion device  100  can be reduced in size, heat radiation performance thereof can be enhanced, and increase in temperature of power conversion device  100  can be suppressed. 
     According to the method of manufacturing power conversion device  100  according to the first embodiment, switching elements  2   a ,  2   b ,  2   c , and  2   d  which are high-heat-generating components are arranged in first printed circuit board module  71 . Rectifier elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g , and  5   h  or transformers  3  and  4  less in heat generation than the switching elements are arranged in second printed circuit board module  72  and third printed circuit board module  73 . The high-heat-generating components can thus lower a thermal resistance to the external cooling body. Therefore, power conversion device  100  can be reduced in size, heat radiation performance thereof can be enhanced, and increase in temperature of power conversion device  100  can be suppressed. 
     In the method of manufacturing power conversion device  100  according to the first embodiment, third cooling body  53  is arranged to extend in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . Second wiring member  86   b  electrically connects first printed circuit board  31  and third printed circuit board  33  to each other. Second wiring member  86   b  is connected to first main surface S 1  of first printed circuit board  31  and fifth main surface S 5  of third printed circuit board  33  by any of direct connection and solder joint. Therefore, power conversion device  100  can be reduced in size, heat radiation performance thereof can be enhanced, and increase in temperature of power conversion device  100  can be suppressed. 
     In the method of manufacturing power conversion device  100  according to the first embodiment, in connection step S 300 , second cooling body  52  and third cooling body  53  are thermally connected to first cooling body  51 . Therefore, power conversion device  100  can be reduced in size, heat radiation performance thereof can be enhanced, and increase in temperature of power conversion device  100  can be suppressed. 
     In the method of manufacturing power conversion device  100  according to the first embodiment, in assembly step S 200 , the electronic component (second component) and the electronic component (third component) are fixed into respective grooves G provided in second printed circuit board  32  and third printed circuit board  33 . Therefore, power conversion device  100  can be reduced in size, heat radiation performance thereof can be enhanced, and increase in temperature of power conversion device  100  can be suppressed. Furthermore, the electronic components can reliably be fixed. 
     Power conversion device  100  according to a modification of the first embodiment will now be described. The modification of the first embodiment is identical in construction, operations, and effects to the first embodiment unless particularly described. Therefore, features the same as those in the first embodiment have the same reference characters allotted and description will not be repeated. 
     Power conversion device  100  according to a first modification of the first embodiment will be described with reference to  FIG.  9   .  FIG.  9    is a cross-sectional view showing a state after assembly of first cooling body  51 , second cooling body  52 , and third cooling body  53  as in  FIG.  2   . For the sake of convenience of description, hatching is not provided in  FIG.  9   . 
     Power conversion device  100  according to the first modification of the first embodiment is basically similar in construction to power conversion device  100  according to the first embodiment. Power conversion device  100  according to the first modification of the first embodiment is different from power conversion device  100  according to the first embodiment in shape of wiring member  86 . 
     In a state similar to the state in  FIG.  7    before assembly of first cooling body  51 , second cooling body  52 , and third cooling body  53 , wiring member  86  is in a linear shape. Pleat lines are provided in advance in wiring member  86  such that wiring member  86  is folded a plurality of times when the printed circuit board module is erected. Thereafter, as shown in  FIG.  9   , wiring member  86  is formed like bellows including a plurality of bent portions BP. In other words, wiring member  86  includes the plurality of bent portions BP. Adjacent bent portions BP of the plurality of bent portions BP are arranged as being superimposed on each other. 
     An effect of power conversion device  100  according to the first modification of the first embodiment will now be described. According to power conversion device  100  according to the first modification of the first embodiment, wiring member  86  includes the plurality of bent portions BP and hence wiring member  86  is reduced in size by being folded. Adjacent bent portions BP of the plurality of bent portions BP are arranged as being superimposed on each other. Therefore, when wiring member  86  is bent, crests of bent wiring member  86  are superimposed on each other and a conduction path in wiring member  86  becomes shorter. An electrical resistance of wiring member  86  is thus further lowered and hence heat generation can be reduced. Consequently, power conversion device  100  according to the first modification of the first embodiment can operate at high output. 
     Power conversion device  100  according to a second modification of the first embodiment will be described with reference to  FIGS.  10  and  11   . For the sake of convenience of description, hatching is not provided in  FIG.  11   . 
     Power conversion device  100  according to the second modification of the first embodiment is basically similar in construction to power conversion device  100  according to the first embodiment. Power conversion device  100  according to the second modification of the first embodiment is different from power conversion device  100  according to the first embodiment in shape of wiring member  86 . 
     As shown in  FIG.  10   , in a state before first cooling body  51 , second cooling body  52 , and third cooling body  53  are assembled, wiring member  86  is warped like an arch in advance in a positive direction along the Z axis and is in a structure where a space is provided under a central portion thereof. Wiring member  86  is in a curved shape as being adjacent to joint portions  87  at opposing ends thereof. A component can be placed in the space under the central portion of wiring member  86  warped in the positive direction along the Z axis. 
     In a state shown in  FIG.  11   , the center of wiring member  86  is curved like an arc and wiring member  86  is in a shape opposed to joint portions  87 , so that two curved portions CP provided in wiring member  86  are proximate to each other. Curved portions CP of wiring member  86  may be provided adjacently to ends of first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33 , and curved portions CP of wiring member  86  may be in contact with each other. As curved portions CP of wiring member  86  come in contact with each other, the conduction path becomes shorter when the printed circuit board modules are brought closer to each other. 
     An effect of power conversion device  100  according to the second modification of the first embodiment will now be described. According to power conversion device  100  in the first embodiment, the center of wiring member  86  is curved like an arch so that wiring member  86  is opposed to joint portions  87 . As two curved portions CP provided in wiring member  86  come in contact with each other, the conduction path becomes shorter. Since an electrical resistance of wiring member  86  is thus lowered, heat generation can be reduced. Consequently, power conversion device  100  according to the second modification of the first embodiment can operate at high output. 
     Power conversion device  100  according to a third modification of the first embodiment will be described with reference to  FIG.  12   . 
     Power conversion device  100  according to the third modification of the first embodiment is basically similar in construction to power conversion device  100  according to the first embodiment. Power conversion device  100  according to the third modification of the first embodiment is different from power conversion device  100  according to the first embodiment in arrangement of first cooling body  51 , second cooling body  52 , and third cooling body  53 . 
     In power conversion device  100  according to the third modification of the first embodiment, first cooling body  51  is arranged as lying between second cooling body  52  and third cooling body  53 . 
     Power conversion device  100  according to a fourth modification of the first embodiment will be described with reference to  FIG.  13   . 
     Power conversion device  100  according to the fourth modification of the first embodiment is basically similar in construction to power conversion device  100  according to the first embodiment. Power conversion device  100  according to the fourth modification of the first embodiment is different from power conversion device  100  according to the first embodiment in construction of first cooling body  51  and external cooling body  21 . 
     In power conversion device  100  according to the fourth modification of the first embodiment, first cooling body  51  is formed integrally with external cooling body  21 . In this case, first cooling body  51  serves also as external cooling body  21 . First cooling body  51  is thermally coupled to external cooling body  21  with such a method as formation integral with external cooling body  21 . 
     Power conversion device  100  according to a fifth modification of the first embodiment will be described with reference to  FIG.  14   . 
     Power conversion device  100  according to the fifth modification of the first embodiment is basically similar in construction to power conversion device  100  according to the first embodiment. Power conversion device  100  according to the fifth modification of the first embodiment is different from power conversion device  100  according to the first embodiment in arrangement of second printed circuit board module  72 . 
     In power conversion device  100  according to the fifth modification of the first embodiment, second printed circuit board module  72  and third printed circuit board module  73  are arranged adjacently to each other. Second printed circuit board  32  and third printed circuit board  33  are arranged adjacently to each other. 
     According to power conversion device  100  according to the fifth modification of the first embodiment, second printed circuit board  32  and third printed circuit board  33  are arranged adjacently to each other. Therefore, power conversion device  100  can be reduced in size. 
     Power conversion device  100  according to a sixth modification of the first embodiment will be described with reference to  FIG.  15   . 
     Power conversion device  100  according to the sixth modification of the first embodiment is basically similar in construction to power conversion device  100  according to the first embodiment. Power conversion device  100  according to the sixth modification of the first embodiment is different from power conversion device  100  according to the first embodiment in that third printed circuit board module  73  is not arranged. 
     Power conversion device  100  according to the sixth modification of the first embodiment does not include third printed circuit board module  73 . 
     Second Embodiment 
     Power conversion device  100  according to a second embodiment will now be described with reference to  FIG.  16   . The second embodiment is identical in construction, operations, and effects to the first embodiment unless particularly described. Therefore, features the same as those in the first embodiment have the same reference characters allotted and description will not be repeated. 
     Power conversion device  100  according to the second embodiment is basically similar in construction to power conversion device  100  according to the first embodiment. Power conversion device  100  according to the second embodiment is different from power conversion device  100  according to the first embodiment in including a fourth cooling body  54  and a fifth cooling body  55 . 
     Fourth cooling body  54  is constructed to vertically extend with a surface connected to surface S 1   a  of first cooling body  51  being defined as a bottom surface. Fourth cooling body  54  extends in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . Fifth cooling body  55  is constructed to vertically extend with a surface connected to surface S 1   a  of first cooling body  51  being defined as a bottom surface. Fifth cooling body  55  extends in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . 
     Each of fourth cooling body  54  and fifth cooling body  55  is connected and fixed to at least one of first cooling body  51 , second cooling body  52 , and third cooling body  53  directly or with another member being interposed. Each of fourth cooling body  54  and fifth cooling body  55  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53 . Fourth cooling body  54  is thermally connected to first cooling body  51 , second cooling body  52 , and third cooling body  53 . Fifth cooling body  55  is thermally connected to first cooling body  51 , second cooling body  52 , and third cooling body  53 . 
     At a surface of contact between each of fourth cooling body  54  and fifth cooling body  55  and each of first cooling body  51 , second cooling body  52 , and third cooling body  53 , a thermally conductive member such as the thermally conductive grease, the thermally conductive sheet, or a thermally conductive adhesive (second thermally conductive member) HC 2  may be arranged. Thermally conductive member (second thermally conductive member) HC 2  includes at least any one of the thermally conductive grease, the thermally conductive sheet, and the thermally conductive adhesive. Fourth cooling body  54  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53  with thermally conductive member (second thermally conductive member) HC 2  being interposed. Fifth cooling body  55  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53  with thermally conductive member (second thermally conductive member) HC 2  being interposed. Each of fourth cooling body  54  and fifth cooling body  55  defines the side surface of the support body of power conversion device  100 . 
     By doing so as well, power conversion device  100  according to the second embodiment can achieve effects equivalent to those of power conversion device  100  according to the first embodiment. Furthermore, as a heat radiation path for radiation of heat generated in the circuit pattern formed at the surface or in the inside of second printed circuit board  32  and heat generated in rectifier elements  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g , and  5   h  and transformers  3  and  4  which are high-heat-generating components mounted on second printed circuit board  32 , two following heat radiation paths are formed in addition to the second heat radiation path for heat radiation to external cooling body  21  through second printed circuit board  32 , second insulating member  42 , second cooling body  52 , and first cooling body  51 . The first heat radiation path is a heat radiation path for heat radiation to external cooling body  21  through second printed circuit board  32 , second insulating member  42 , second cooling body  52 , fourth cooling body  54 , and first cooling body  51 . The second heat radiation path is a heat radiation path for heat radiation to external cooling body  21  through second printed circuit board  32 , second insulating member  42 , second cooling body  52 , fifth cooling body  55 , and first cooling body  51 . Therefore, performance of power conversion device  100 , of radiation of heat generated in the circuit pattern formed at the surface or in the inside of second printed circuit board  32  and heat generated in the high-heat-generating components mounted on second printed circuit board  32  can be enhanced. As a heat radiation path for radiation of heat generated in the circuit pattern formed at the surface or in the inside of third printed circuit board  33  and heat generated in reactors  6  and  7  which are high-heat-generating components mounted on third printed circuit board  33 , two following heat radiation paths are formed in addition to the third heat radiation path for heat radiation to external cooling body  21  through third printed circuit board  33 , third insulating member  43 , third cooling body  53 , and first cooling body  51 . The first heat radiation path is a heat radiation path for heat radiation to external cooling body  21  through third printed circuit board  33 , third insulating member  43 , third cooling body  53 , fourth cooling body  54 , and first cooling body  51 . The second heat radiation path is a heat radiation path for heat radiation to external cooling body  21  through third printed circuit board  33 , third insulating member  43 , third cooling body  53 , fifth cooling body  55 , and first cooling body  51 . Therefore, performance of power conversion device  100 , of radiation of heat generated in the circuit pattern formed at the surface or in the inside of third printed circuit board  33  and heat generated in the high-heat-generating components mounted on third printed circuit board  33  can be enhanced. Consequently, power conversion device  100  according to the second embodiment can operate at high output. 
     In power conversion device  100  according to the second embodiment, fourth cooling body  54  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53  with thermally conductive member (second thermally conductive member) HC 2  being interposed. Fifth cooling body  55  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53  with thermally conductive member (second thermally conductive member) HC 2  being interposed. Therefore, with second thermally conductive member HC 2 , heat conduction efficiency from fourth cooling body  54  to first cooling body  51 , second cooling body  52 , and third cooling body  53  can be enhanced and heat conduction efficiency from fifth cooling body  55  to first cooling body  51 , second cooling body  52 , and third cooling body  53  can be enhanced. 
     As shown in  FIG.  17   , power conversion device  100  according to the second embodiment may be constructed such that first cooling body  51  is arranged as lying between fourth cooling body  54  and fifth cooling body  55 . 
     Third Embodiment 
     Power conversion device  100  according to a third embodiment will now be described with reference to  FIGS.  18  and  19   . The third embodiment is identical in construction, operations, and effects to the second embodiment unless particularly described. Therefore, features the same as those in the second embodiment have the same reference characters allotted and description will not be repeated. 
     Power conversion device  100  according to the third embodiment is basically similar in construction to power conversion device  100  according to the second embodiment. Power conversion device  100  according to the third embodiment is different from power conversion device  100  according to the second embodiment in including a fourth printed circuit board module  74  and a fifth printed circuit board module  75 . 
     Fourth printed circuit board module  74  includes a fourth printed circuit board  34 , a fourth insulating member  44 , fourth cooling body  54 , a fourth fixing member  64 , an electronic component, and wiring member  86 . 
     Fourth printed circuit board (fourth substrate)  34  includes a front surface (seventh main surface) S 7  on which an electronic component (a fourth component) is mounted and a rear surface (an eighth main surface) S 8  opposed to fourth cooling body  54 . Seventh main surface S 7  is opposed to eighth main surface S 8 . Fourth insulating member  44  is arranged between eighth main surface S 8  of fourth printed circuit board  34  and fourth cooling body  54 . Fourth cooling body  54  is thermally connected to eighth main surface S 8  of fourth printed circuit board  34 . Fourth cooling body  54  is thermally connected to eighth main surface S 8  of fourth printed circuit board  34  with fourth insulating member  44  being interposed. Fourth cooling body  54  is constructed to vertically extend with a surface connected to surface S 1   a  of first cooling body  51  opposed to first printed circuit board  31  being defined as a bottom surface. Fourth cooling body  54  extends in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . Fourth cooling body  54  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53 . Fourth fixing member  64  is constructed to fix fourth printed circuit board  34  to fourth cooling body  54 . 
     Fifth printed circuit board module  75  includes a fifth printed circuit board  35 , a fifth insulating member  45 , fifth cooling body  55 , a fifth fixing member  65 , and an electronic component. 
     Fifth printed circuit board (fifth substrate)  35  includes a front surface (a ninth main surface) S 9  on which an electronic component (a fifth component) is mounted and a rear surface (a tenth main surface) S 10  opposed to fifth cooling body  55 . Ninth main surface S 9  is opposed to tenth main surface S 10 . Fifth insulating member  45  is arranged between tenth main surface S 10  of fifth printed circuit board  35  and fifth cooling body  55 . Fifth cooling body  55  is thermally connected to tenth main surface S 10  of fifth printed circuit board  35 . Fifth cooling body  55  is thermally connected to tenth main surface S 10  of fifth printed circuit board  35  with fifth insulating member  45  being interposed. Fifth cooling body  55  is constructed to vertically extend with a surface connected to surface S 1   a  of first cooling body  51  opposed to first printed circuit board  31  being defined as a bottom surface. Fifth cooling body  55  extends in the direction from second main surface S 2  of first printed circuit board  31  toward first main surface S 1 . Fifth cooling body  55  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53 . Fifth fixing member  65  is constructed to fix fifth printed circuit board  35  to fifth cooling body  55 . 
     Joint portion  87  is provided in each of fourth printed circuit board  34  and fifth printed circuit board  35 . First printed circuit board  31  and fourth printed circuit board  34  are electrically connected to each other and first printed circuit board  31  and fifth printed circuit board  35  are electrically connected to each other, through wiring member  86  at joint portions  87 . 
     Fourth printed circuit board module  74  and fifth printed circuit board module  75  are made also through the preparation step, the assembly step, and the connection step as in the first embodiment. 
     In power conversion device  100  in the third embodiment, as shown in  FIG.  19   , joint portion  87  is provided in each of second printed circuit board  32  and fourth printed circuit board  34  and in each of third printed circuit board  33  and fourth printed circuit board  34 . Second printed circuit board  32  and fourth printed circuit board  34  are electrically connected to each other and third printed circuit board  33  and fourth printed circuit board  34  are electrically connected to each other, through wiring member  86  at joint portions  87 . Similarly, second printed circuit board  32  and fifth printed circuit board  35  may electrically be connected to each other and third printed circuit board  33  and fifth printed circuit board  35  may electrically be connected to each other, through wiring member  86  at joint portions  87 . Though wiring member  86  that connects second printed circuit board  32  and fourth printed circuit board  34  to each other and wiring member  86  that connects third printed circuit board  33  and fourth printed circuit board  34  to each other are each in an L shape in  FIG.  19   , the shape is not limited thereto. Wiring member  86  should only be in a shape that allows mitigation of position displacement in the direction of the Z axis of second printed circuit board  32  and fourth printed circuit board  34  when second printed circuit board  32  and fourth printed circuit board  34  are erected with respect to first printed circuit board  31  in the direction of the Z axis. In addition, wiring member  86  should only be in a shape that allows mitigation of position displacement in the direction of the Z axis of third printed circuit board  33  and fourth printed circuit board  34  when third printed circuit board  33  and fourth printed circuit board  34  are erected with respect to first printed circuit board  31  in the direction of the Z axis. 
     In power conversion device  100  according to the third embodiment, as shown in  FIG.  20   , second printed circuit board  32  and third printed circuit board  33  may electrically be connected to each other. In this case, wiring member  86  includes a third wiring member  86   c . Third wiring member  86   c  electrically connects second printed circuit board  32  and third printed circuit board  33  to each other. Third wiring member  86   c  is connected to third main surface S 3  of second printed circuit board  32  and fifth main surface S 5  of third printed circuit board  33  by any of direct connection and solder joint. 
     An Effect of Power Conversion Device  100  According to the Third Embodiment Will Now be Described. 
     According to power conversion device  100  according to the third embodiment, in conduction from second printed circuit board  32  to fourth printed circuit board  34 , direct conduction without passing through first printed circuit board  31  can be achieved. Therefore, the conduction path from second printed circuit board  32  to fourth printed circuit board  34  can be shortest and a conduction pattern in the first printed circuit board can be omitted. Since an electrical resistance of the conduction pattern is thus lowered, heat generation can be reduced. Since first printed circuit board  31  can also be smaller in area, it can be reduced in size. Consequently, power conversion device  100  according to the third embodiment can operate at high output. 
     In addition, in conduction from third printed circuit board  33  to fourth printed circuit board  34 , direct conduction without passing through first printed circuit board  31  can be achieved. Therefore, the conduction path from third printed circuit board  33  to fourth printed circuit board  34  can be shortest and a conduction pattern in the first printed circuit board can be omitted. Since an electrical resistance of the conduction pattern is thus lowered, heat generation can be reduced. Since first printed circuit board  31  can also be smaller in area, it can be reduced in size. Consequently, power conversion device  100  according to the third embodiment can operate at high output. 
     Power conversion device  100  according to the third embodiment can achieve effects equivalent to those of power conversion device  100  according to the second embodiment. Furthermore, in power conversion device  100  according to the third embodiment, a fourth heat radiation path for heat radiation to external cooling body  21  through fourth printed circuit board  34 , fourth insulating member  44 , fourth cooling body  54 , and first cooling body  51  can be formed as the heat radiation path for radiation of heat generated in the circuit pattern formed at the surface or in the inside of fourth printed circuit board  34  and heat generated in smoothing capacitor  8  and reactor  6  which are high-heat-generating components mounted on fourth printed circuit board  34 . Since the fourth heat radiation path does not include the plate-like substrate mounting member as compared with the construction described in PTL 1, the heat radiation path can be shorter in length and heat radiation performance can be enhanced. Therefore, performance of power conversion device  100 , of radiation of heat generated in the circuit pattern formed at the surface or in the inside of fourth printed circuit board  34  and heat generated in the high-heat-generating components mounted on fourth printed circuit board  34  can be enhanced. Consequently, power conversion device  100  according to the third embodiment can operate at high output. 
     When fourth insulating member  44  is in surface contact with fourth printed circuit board  34  and fourth cooling body  54 , an area of the surface of contact between fourth insulating member  44  and fourth printed circuit board  34  and an area of the surface of contact between fourth insulating member  44  and fourth cooling body  54  can be increased. Therefore, since the contact thermal resistance of the surface of contact between fourth insulating member  44  and fourth printed circuit board  34  and the contact thermal resistance of the surface of contact between fourth insulating member  44  and fourth cooling body  54  can be lowered, heat radiation performance of the fourth heat radiation path can be enhanced. Consequently, power conversion device  100  according to the third embodiment can operate at high output. 
     A fifth heat radiation path for heat radiation to external cooling body  21  through fifth printed circuit board  35 , fifth insulating member  45 , fifth cooling body  55 , and first cooling body  51  can be formed as the heat radiation path for radiation of heat generated in the circuit pattern formed at the surface or in the inside of fifth printed circuit board  35  and heat generated in smoothing capacitor  8  and reactor  7  which are high-heat-generating components mounted on fifth printed circuit board  35 . Since the fifth heat radiation path does not include the plate-like substrate mounting member as compared with the construction described in PTL 1, the heat radiation path can be shorter in length and heat radiation performance can be enhanced. Therefore, performance of power conversion device  100 , of radiation of heat generated in the circuit pattern formed at the surface or in the inside of fifth printed circuit board  35  and heat generated in the high-heat-generating components mounted on fifth printed circuit board  35  can be enhanced. Consequently, power conversion device  100  according to the third embodiment can operate at high output. 
     When fifth insulating member  45  is in surface contact with fifth printed circuit board  35  and fifth cooling body  55 , an area of the surface of contact between fifth insulating member  45  and fifth printed circuit board  35  and an area of the surface of contact between fifth insulating member  45  and fifth cooling body  55  can be increased. Therefore, since the contact thermal resistance of the surface of contact between fifth insulating member  45  and fifth printed circuit board  35  and the contact thermal resistance of the surface of contact between fifth insulating member  45  and fifth cooling body  55  can be lowered, heat radiation performance of the fifth heat radiation path can be enhanced. Consequently, power conversion device  100  according to the third embodiment can operate at high output. 
     A thickness of fourth cooling body  54  in a direction substantially perpendicular to a surface  34   a  of fourth printed circuit board  34  is preferably large. Since a thermal resistance of fourth cooling body  54  included in the fourth heat radiation path can thus be lowered, heat radiation performance can be enhanced. 
     A thickness of fifth cooling body  55  in a direction substantially perpendicular to a surface  35   a  of fifth printed circuit board  35  is preferably large. Since a thermal resistance of fifth cooling body  55  included in the fifth heat radiation path can thus be lowered, heat radiation performance can be enhanced. 
     High-heat-generating components can be mounted not only on first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33  but also on each of fourth printed circuit board  34  and fifth printed circuit board  35 . Therefore, since a distance between high-heat-generating components mounted on the printed circuit boards can be longer, thermal interference of heat generated in the high-heat-generating components can be suppressed, and performance of power conversion device  100 , of radiation of heat generated in each high-heat-generating component can be enhanced. Consequently, power conversion device  100  according to the third embodiment can operate at high output. 
     Electronic components can be mounted not only on first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33  but also on each of fourth printed circuit board  34  and fifth printed circuit board  35 . Therefore, since a component mount area increases, first printed circuit board  31 , second printed circuit board  32 , and third printed circuit board  33  can be smaller in size than in the first and second embodiments. Consequently, power conversion device  100  according to the third embodiment can be reduced in size. 
     Power conversion device  100  according to the third embodiment does not have to include fifth printed circuit board  35 , fifth insulating member  45 , and fifth fixing member  65 . In other words, power conversion device  100  may include external cooling body  21 , first printed circuit board module  71 , the second printed circuit board module, third printed circuit board module  73 , and fourth printed circuit board module  74 , and fifth cooling body  55 . First printed circuit board module  71 , second printed circuit board module  72 , third printed circuit board module  73 , and fourth printed circuit board module  74  are electrically connected to one another through wiring member  86  at joint portions  87 . 
     Though electronic components arranged in first printed circuit board module  71 , second printed circuit board module  72 , third printed circuit board module  73 , fourth printed circuit board module  74 , and fifth printed circuit board module  75  may be interchanged, particularly high-heat-generating components are arranged preferably in first printed circuit board module  71 . 
     According to power conversion device  100  according to the third embodiment, third wiring member  86   c  is connected to third main surface S 3  of second printed circuit board  32  and fifth main surface S 5  of third printed circuit board  33  by any of direct connection and solder joint. Power conversion device  100  can thus be reduced in size. 
     Fourth Embodiment 
     Power conversion device  100  according to a fourth embodiment will now be described with reference to  FIG.  21   . The fourth embodiment is identical in construction, operations, and effects to the first embodiment unless particularly described. Therefore, features the same as those in the first embodiment have the same reference characters allotted and description will not be repeated.  FIG.  21    is a cross-sectional view showing a state after first cooling body  51 , second cooling body  52 , and third cooling body  53  are assembled as in  FIG.  2   . For the sake of convenience of description, hatching is not provided in  FIG.  21   . 
     As shown in  FIG.  21   , in power conversion device  100  according to the fourth embodiment, a through hole TH that passes through first main surface S 1  and second main surface S 2  is provided in first printed circuit board  31 . A through hole TH that passes through third main surface S 3  and fourth main surface S 4  is provided in second printed circuit board  32 . A through hole TH that passes through fifth main surface S 5  and sixth main surface S 6  is provided in third printed circuit board  33 . 
     In through hole TH, for example, copper plating of a thickness of several ten micrometers is provided on an inner wall of a hole made in the printed circuit board. A material for through hole TH is similar to that of a not-shown circuit pattern. The material for through hole TH may be identical to or different from that of the not-shown circuit pattern. 
     Through hole TH may be set to a potential as high as wiring member  86  through joint portion  87 . Through hole TH is isolated from first cooling body  51 , second cooling body  52 , and third cooling body  53  by first insulating member  41 , second insulating member  42 , and third insulating member  43 . 
     Through hole TH should only be arranged at least directly under joint portion (first joint portion)  87 . Furthermore, arrangement of through hole TH not only directly under joint portion  87  but also around joint portion  87  would enhance heat radiation performance. 
     Heat generated in wiring member  86  is mainly radiated through joint portion  87 , the printed circuit board, the insulating member, and the cooling body. Since a thermal resistance of the printed circuit board is highest in a heat radiation path in wiring member  86 , the thermal resistance of the printed circuit board should be lowered. 
     According to power conversion device  100  according to the fourth embodiment, through hole TH serves to increase a thermal conductivity in a direction of thickness of the printed circuit board directly under joint portion  87 . The thermal resistance in the direction of thickness of the printed circuit board is thus lowered. Therefore, performance of radiation of heat generated in wiring member  86  can be enhanced. 
     Fifth Embodiment 
     Power conversion device  100  according to a fifth embodiment will now be described with reference to  FIG.  22   . The fifth embodiment is identical in construction, operations, and effects to the first embodiment unless particularly described. Therefore, features the same as those in the first embodiment have the same reference characters allotted and description will not be repeated.  FIG.  22    is a developed view of first printed circuit board module  71 , second printed circuit board module  72 , and third printed circuit board module  73  of power conversion device  100 . 
     As shown in  FIG.  22   , in power conversion device  100  according to the fifth embodiment, a surface of wiring member  86  is covered with an insulating coating  86 X. Insulating coating  86 X is composed, for example, of vinyl chloride, fluoroplastic, or polyimide. 
     When second printed circuit board module  72  and third printed circuit board module  73  are erected with respect to first printed circuit board module  71 , curved wiring member  86  may come in contact with an unintended portion such as an electronic component, a cooling body, or a circuit pattern therearound, and short-circuiting may occur. 
     Since wiring member  86  is in contact with air, there is a path for heat radiation by direct emission from wiring member  86  to air other than the heat radiation path to the cooling body through the printed circuit board. Since wiring member  86  is composed of a metal, emissivity at the surface of wiring member  86  is low. Therefore, performance of emission to air is low. 
     According to power conversion device  100  according to the fifth embodiment, even when wiring member  86  comes in contact with an electronic component therearound when wiring member  86  is curved, insulating coating  86 X can prevent occurrence of short-circuiting. Since insulating coating  86 X can improve emissivity at the surface of wiring member  86 , performance of heat radiation to air can be enhanced. 
     Sixth Embodiment 
     Power conversion device  100  according to a sixth embodiment will now be described with reference to  FIG.  23   . The sixth embodiment is identical in construction, operations, and effects to the first embodiment unless particularly described. Therefore, features the same as those in the first embodiment have the same reference characters allotted and description will not be repeated.  FIG.  23    is a cross-sectional view showing a state after first cooling body  51 , second cooling body  52 , and third cooling body  53  are assembled as in  FIG.  2   . For the sake of convenience of description, hatching is not provided in  FIG.  23   . 
     As shown in  FIG.  23   , power conversion device  100  according to the sixth embodiment is different from power conversion device  100  according to the first embodiment in shape of wiring member  86 . 
     While first cooling body  51 , second cooling body  52 , and third cooling body  53  are assembled, wiring member  86  in a flexed state is in contact with a core K with a heat radiation member Q being interposed. Core K is a member that implements transformers  3  and  4  or reactors  6  and  7 . Heat generated in wiring member  86  conducts to heat radiation member Q, core K, second cooling body  52 , and third cooling body  53  and radiated. Heat radiation member Q is composed of an electrically insulating and highly thermally conductive material. 
     In the present embodiment, an electrically insulating adhesive is employed as heat radiation member Q. A sheet or grease in which particles of highly thermally conductive and electrically insulating aluminum oxide or aluminum nitride are mixed in a silicone resin may be employed as heat radiation member Q. 
     Wiring member  86  may have a long length at the time of manufacturing of power conversion device  100 . At this time, an electrical resistance value of wiring member  86  increases and the heat radiation path in wiring member  86  becomes long, and hence a temperature of wiring member  86  increases. 
     According to power conversion device  100  according to the sixth embodiment, wiring member  86  in a flexed state comes in contact with core K with heat radiation member Q being interposed. A central portion of wiring member  86  in contact with core K allows heat radiation from core K to the cooling body other than a heat radiation path to the cooling body through joint portion  87  and a heat radiation path to air. Therefore, heat radiation performance can further be enhanced. 
     Power conversion device  100  according to a modification of the sixth embodiment will now be described. The modification of the sixth embodiment is identical in construction, operations, and effects to the sixth embodiment unless particularly described. Therefore, features the same as those in the sixth embodiment have the same reference characters allotted and description will not be repeated. 
     Power conversion device  100  according to a first modification of the sixth embodiment will be described with reference to  FIG.  24   . For the sake of convenience of description, hatching is not provided in  FIG.  24   . 
     Wiring member  86  may radiate heat by coming in contact with a structure other than core K. As shown in  FIG.  24   , wiring member  86  may radiate heat by coming in contact with a sheet metal AL that fixes core K. In the present embodiment, core K is fixed by a screw N and sheet metal AL. A hole through which screw N passes is provided in each of second printed circuit board  32  and third printed circuit board  33 . Screw N is fixed to each of second cooling body  52  and third cooling body  53  through this hole. 
     So long as an object in contact with wiring member  86  is insulated, wiring member  86  may be in contact with any object such as first cooling body  51 , second cooling body  52 , third cooling body  53 , first printed circuit board  31 , or a circuit pattern (not shown) of the printed circuit board. 
     According to power conversion device  100  according to the first modification of the sixth embodiment, performance of radiation of heat generated in wiring member  86  can be enhanced. 
     Power conversion device  100  according to a second modification of the sixth embodiment will be described with reference to  FIG.  25   . For the sake of convenience of description, hatching is not provided in  FIG.  25   . 
     As shown in  FIG.  25   , parts of wiring member  86  may come in contact with each other and a conduction path may become shorter. 
     According to power conversion device  100  according to the second modification of the sixth embodiment, the conduction path in wiring member  86  is shorter. Since the electrical resistance of wiring member  86  is thus further lowered, heat generation can be reduced. 
     The embodiments above can be combined as appropriate. 
     It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the terms of the claims rather than the description above and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
     
         
         
           
               21  external cooling body;  31  first printed circuit board;  32  second printed circuit board;  33  third printed circuit board;  34  fourth printed circuit board;  35  fifth printed circuit board;  41  to  45  first insulating member to fifth insulating member;  51  to  55  first cooling body to fifth cooling body;  61  to  65  first fixing member to fifth fixing member;  71  to  75  first printed circuit board module to fifth printed circuit board module;  86  wiring member;  86   a  first wiring member;  86   b  second wiring member;  86   c  third wiring member;  87  joint portion;  100  power conversion device; BP bent portion; CP curved portion; HC 1  first thermally conductive member; HC 2  second thermally conductive member; S 1  to S 10  first main surface to tenth main surface; S 100  preparation step; S 200  assembly step; S 300  connection step.