Patent ID: 12256523

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First, embodiments of the present disclosure will be listed and described.

The board unit according to the present disclosure is as follows.

First Aspect

In accordance with a first aspect, a board unit includes: a board stack including a first circuit board and a second circuit board that are supported while being spaced apart from each other; an electronic component mounted on the first circuit board; a first heat dissipation member that covers the board stack from outside of the first circuit board; a second heat dissipation member that covers the board stack from outside of the second circuit board; a first heat transfer portion that thermally connects the electronic component and the first heat transfer portion; and a second heat transfer portion that thermally connects the electronic component and the second circuit board, wherein the electronic component has a body located between the first circuit board and the second circuit board, and the second heat transfer portion is partially provided at a position that corresponds to the body of the electronic component. As a result of the electronic component being thermally connected to the first heat dissipation member and the second circuit board by the first heat transfer portion and the second heat transfer portion, the heat dissipation of the electronic component is enhanced. Since the second heat transfer portion is partially provided at a position corresponding to the body of the electronic component, it is possible to prevent such a situation that the land design of the circuit boards is restricted due to the provision of the second heat transfer portion.

Second Aspect

In a second aspect, in the board unit according to the first aspect, the second heat transfer portion may thermally connect the electronic component and the second heat dissipation member. As a result of the electronic component being thermally connected to the second heat dissipation member by the second heat transfer portion, the heat dissipation of the electronic component is further enhanced.

Third Aspect

In a third aspect, in the board unit according to the first or the second aspect, the second heat transfer portion may include a metal member, and the metal member may include a fixed portion fixed to the second circuit board, and a first protruding portion that protrudes from the second circuit board toward the body. With this, the heat conductivity of the second heat transfer portion is enhanced. Also, the metal member being fixed to the second circuit board enables reflow processing on the second circuit board.

Fourth Aspect

In a fourth aspect, in the board unit according to the third aspect, the metal member may include a second protruding portion that protrudes from the second circuit board toward the second heat dissipation member, and a coupling portion that couples the first protruding portion and the second protruding portion, and is received in a hole formed in the second circuit board. With this, the metal member can extend to a position close to the second heat dissipation member, and the heat conductivity of the second heat transfer portion is further enhanced.

Fifth Aspect

In a fifth aspect, in the board unit according to the fourth aspect, a horizontal cross-sectional area of the second protruding portion may be greater than a horizontal cross-sectional area of the coupling portion. Accordingly, the area of the surfaces of the metal member and the second heat dissipation member that face with each other is increased, and thus the heat conductivities of the metal member and the second heat dissipation member are enhanced.

Sixth Aspect

In a sixth aspect, in the board unit according to the fourth aspect, a horizontal cross-sectional area of the first protruding portion may be greater than a horizontal cross-sectional area of the coupling portion. This enables reflow processing on the side of the second circuit board that faces the first circuit board.

Seventh Aspect

In a seventh aspect, in the board unit according to the fourth aspect, a horizontal cross-sectional area of the second protruding portion and a horizontal cross-sectional area of the coupling portion may be smaller than a horizontal cross-sectional area at a leading end of the first protruding portion. With this, a reduction in a mountable area of the second circuit board is suppressed.

Eighth Aspect

In an eighth aspect, in the board unit according to the disclosure, the second heat transfer portion may include a flexible heat transfer member, the flexible heat transfer member being interposed between the first protruding portion and the body, being more flexible than the metal member, and filling up a gap between the first protruding portion and the body. With this, the heat conductivity between the electronic component and the metal member is enhanced.

Ninth Aspect

In a ninth aspect, in the board unit according to the disclosure, a region of the first circuit board covered by the first heat transfer portion may be greater than a region of the first circuit board covered by the second heat transfer portion. With this, the heat conductivity between the first circuit board and the first heat dissipation member is enhanced.

The following will describe specific examples of the board unit of the present disclosure with reference to the drawings. Note that the present disclosure is not limited to the examples but is defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

Embodiment 1

The following will describe a board unit according to Embodiment 1.FIG.1is a schematic cross-sectional view of a board unit10according to Embodiment 1.

The board unit10includes a board stack20, an electronic component30, a first heat dissipation member42, a second heat dissipation member47, a first heat transfer portion50, and a second heat transfer portion60.

The board stack20includes a first circuit board22and a second circuit board24supported while being spaced apart from each other. Between the first circuit board22and the second circuit board24, there is a space in which components mounted on these first circuit board22and second circuit board24can be accommodated. The circuit boards22and24may each be a rigid board. The circuit boards22and24may have a wiring pattern on only one side or on both sides. The circuit boards22and24may each be a multi-layer board, but the board stack20is not a multi-layer board itself.

The electronic component30is mounted on the first circuit board22. A body32of the electronic component30is located between the first circuit board22and the second circuit board24. The electronic component30is mounted as appropriate according to the usage of the board unit10, and includes, for example, a switching element such as a FET (Field Effect Transistor), a resistor, a coil, a capacitor, and the like.

Note that in the example shown inFIG.1, only one electronic component30is shown, but the board unit10may of course include, in addition to the electronic component30, electronic components mounted on the first circuit board22and the second circuit board24.

Here, the electronic component30is mounted on only one side of the first circuit board22. Also, the side of the first circuit board22on which the electronic component30is mounted faces the second circuit board24, and the side of the first circuit board22on which no electronic component30is mounted faces the first heat dissipation member42. Of course, electronic components may also be mounted on both sides of the first circuit board22. Electronic components may be mounted on only one side of the second circuit board24, or on both sides thereof. When electronic components are mounted on only one side of the second circuit board24, the side on which the electronic components are mounted may face the first circuit board22, or the second heat dissipation member47.

The first heat dissipation member42and the second heat dissipation member47cover the board stack20from the opposite sides. The first heat dissipation member42covers the board stack20from outside of the first circuit board22. The second heat dissipation member47covers the board stack20from outside of the second circuit board24. Here, the first heat dissipation member42and the second heat dissipation member47constitute parts of a housing40that houses the board unit10.

The housing40includes a case41and a cover46. For example, the case41and the cover46are each made of a metal material such as aluminum, an aluminum alloy, iron, or an iron alloy, or are made of a resin material such as a high thermal conductivity resin.

The first circuit board22and the second circuit board24are housed in the case41. The case41is box-shaped with an open top, and has a bottom wall42and a side wall43. The bottom wall42serves as the first heat dissipation member42. The first circuit board22is disposed above the bottom wall42. The case41includes support portions44and45. The support portion44supports an outer edge portion of the first circuit board22. The support portion45supports an outer edge portion of the second circuit board24. As a result of being supported by the corresponding support portions44and45, the first circuit board22and the second circuit board24are supported while being spaced apart from each other. The support portions44and45protrude to the housing space from the bottom wall42and the side wall43. For example, the first circuit board22and the second circuit board24are fixed to the corresponding support portions44and45by screwing or the like. The first circuit board22and the second circuit board24may be supported while being spaced apart from each other by a spacer provided separately from the case41.

The cover46covers the case41. The cover46has a top wall47and a side wall48. The top wall47serves as the second heat dissipation member47. When the side wall43and the side wall48abut against each other, the inside of the housing40is closed. Fins or the like may be provided on the outer surfaces of the bottom wall42and the top wall47.

Here, the distance between the first circuit board22and the second circuit board24is greater than the distance between the first circuit board22and the bottom wall42. The distance between the first circuit board22and the second circuit board24may also be smaller than or equal to the distance between the first circuit board22and the bottom wall42. Also, here, the distance between the first circuit board22and the second circuit board24is greater than the distance between the second circuit board24and the top wall47. The distance between the first circuit board22and the second circuit board24may also be smaller than or equal to the distance between the second circuit board24and the top wall47. Also, here, the distance between the first circuit board22and the bottom wall42is smaller than the distance between the second circuit board24and the top wall47. The distance between the first circuit board22and the bottom wall42may also be greater than or equal to the distance between the second circuit board24and the top wall47.

The first heat transfer portion50thermally connects the electronic component30and the bottom wall42. In the present disclosure, “thermally connecting” means increasing the heat conductivity between two portions spaced apart from each other relative to the heat conductivity of air. Accordingly, the heat conductivity of the first heat transfer portion50is higher than the heat conductivity of air. The first heat transfer portion50includes a flexible heat transfer member52and a thermal via54, which is a conductor.

The flexible heat transfer member52is interposed between the first circuit board22and the bottom wall42. The flexible heat transfer member52fills up the gap between the first circuit board22and the bottom wall42. The flexible heat transfer member52is, for example, heat conductive grease (referred to also as heat dissipation grease), a heat conductive sheet (referred to also as a heat dissipation sheet), or the like. The flexible heat transfer member52may be made of a silicone-based material, or a non-silicone-based material such as an acrylic resin. The flexible heat transfer member52preferably has insulation properties. By being interposed between the first circuit board22and the bottom wall42, the flexible heat transfer member52is deformed to the shape that corresponds to the gap between the first circuit board22and the bottom wall42, and is in areal contact with the first circuit board22and the bottom wall42.

A region of the first circuit board22that is covered by the flexible heat transfer member52of the first heat transfer portion50is greater than a region of the first circuit board22that is covered by the second heat transfer portion60. For example, the flexible heat transfer member52of the first heat transfer portion50may be entirely provided on the first circuit board22.

The thermal via54is formed by providing copper foil, solder, or the like on the inner surface of a through hole formed in the first circuit board22. The thermal via54allows heat to be transferred from one side of the first circuit board22to another side. Here, a thermal via54is formed in the first circuit board22at a position directly below or around the body32, or at positions directly below and around the body32. A portion of the first circuit board22that is covered by the body32serves as a land that is electrically connected to a terminal of the electronic component30, and the thermal via54may be formed partially in the land. In the portion of the first circuit board22in which the thermal via54is formed, flexible heat transfer members similar to the flexible heat transfer member52may also be provided between the first circuit board22and the body32.

The second heat transfer portion60thermally connects the electronic component30and the top wall47. The heat conductivity of the second heat transfer portion60is higher than the heat conductivity of air. The second heat transfer portion60is partially provided at a position corresponding to the body32of the electronic component30. The position corresponding to the body32refers to a position on a path connecting the electronic component30and the top wall47as short as possible. Here, the second heat transfer portion60is provided directly above the electronic component30. Here, the second heat transfer portion60includes a metal member62and flexible heat transfer members68and70.

The metal member62includes a fixed portion63and a first protruding portion64. Here, the metal member62further includes a second protruding portion65and a coupling portion66. The metal member62is made of copper, a copper alloy, aluminum, an aluminum alloy, or the like. The metal member62is a member that is referred to also as a rivet, which is provided separately from solders and wiring patterns of the circuit boards. The metal member62has a melting point higher than that of solders. The metal member62is thicker than the wiring patterns of the circuit boards. If an electronic component is mounted only on one side of the second circuit board24, and the metal member62is soldered to the second circuit board24, it will be preferable that the metal member62be soldered to a surface of the second circuit board24on which the electronic component is mounted.

The fixed portion63is a portion fixed to the second circuit board24. The fixed portion63may be fixed via a fixing member. In the example shown inFIG.1, such a fixing member is solder SO. The fixing member does not need to be solder but may also be screws, an adhesive, or the like. If the metal member62is made of aluminum or an aluminum alloy, and the metal member62is fixed to the second circuit board24by the solder SO, a terminal made of copper or a copper alloy is preferably provided as the fixed portion63. The fixed portion63may also be fixed without using any fixing member. The fixed portion63may also be a press-fit structure or an engaging structure with respect to the hole.

The first protruding portion64is a portion that protrudes from the second circuit board24toward the body32. The second protruding portion65is a portion that protrudes from the second circuit board24toward the top wall47. Here, the protrusion length of the first protruding portion64from the second circuit board24is greater than the protrusion length of the second protruding portion65from the second circuit board24. The protrusion length of the first protruding portion64from the second circuit board24may also be smaller than or equal to the protrusion length of the second protruding portion65from the second circuit board24. The coupling portion66is a portion that couples the first protruding portion64and the second protruding portion65. The coupling portion66is received in a hole formed in the second circuit board24.

Here, the metal member62has a shape that includes a columnar body portion and a flange portion protruding to the outer circumferential side of the body portion. Here, the flange portion is provided at one end of the body portion. The body portion and the flange portion may have any outer shape, such as a circular shape or a square shape, for example. The body portion passes through the second circuit board24. A portion of the body portion that includes a first end on the side without any flange portion serves as the first protruding portion64. The flange portion and a portion of the body portion that includes a second end on the side on which the flange portion is provided serve as the second protruding portion65. An intermediate portion of the body portion that extends along an axial direction thereof serves as the coupling portion66.

The flange portion is formed so as to be greater than a hole in the second circuit board24through which the coupling portion66is passed, so that the flange portion and the surface of the second circuit board24face each other. Also, the solder SO is provided between the flange portion and the second circuit board24, and the flange portion and the second circuit board24are fixed to each other by the solder SO. Accordingly, in the present example, the fixed portion63is provided on the second protruding portion65. The fixed portion63is in contact with the surface of the second circuit board24that faces the top wall47, directly or indirectly by the solder or the like. Accordingly, the metal member62is thermally connected to the second circuit board24at the fixed portion63. Also, the coupling portion66may be in contact with the inner surface of the hole in the second circuit board24, directly or indirectly by the solder or the like. The metal member62may also be thermally connected to the second circuit board24at a position of the coupling portion66.

The horizontal cross-sectional area of the second protruding portion65is greater than the horizontal cross-sectional area of the coupling portion66. In the present disclosure, “horizontal cross-sectional area” refers to an area of a cross section of an object member taken along a plane orthogonal to a direction (here, the vertical direction ofFIG.1) connecting the bottom wall42and the top wall47. Here, the second protruding portion65includes both the body portion and the flange portion, and the coupling portion66only includes the body portion, out of the body portion and the flange portion, and as a result, the horizontal cross-sectional area of the second protruding portion65is greater than the horizontal cross-sectional area of the coupling portion66. Similarly, the horizontal cross-sectional area of the second protruding portion65is greater than the horizontal cross-sectional area of the first protruding portion64.

A flexible heat transfer member68is interposed between the first protruding portion64and the body32. The flexible heat transfer member68fills up the gap between the first protruding portion64and the body32. A flexible heat transfer member70is interposed between the second protruding portion65and the top wall47. The flexible heat transfer member70fills up the gap between the second protruding portion65and the top wall47. Similar to the flexible heat transfer member52of the first heat transfer portion50, the flexible heat transfer members68and70are, for example, heat conductive grease, a heat conductive sheet, or the like. The flexible heat transfer members68and70preferably have insulation properties. By being interposed between the first protruding portion64and the body32, the flexible heat transfer member68is deformed to the shape that corresponds to the gap between the first protruding portion64and the body32, and is in areal contact with the first protruding portion64and the body32. By being interposed between the second protruding portion65and the top wall47, the flexible heat transfer member70is deformed to the shape that corresponds to the gap between the second protruding portion65and the top wall47, and is in areal contact with the second protruding portion65and the top wall47.

A part of heat generated by the electronic component30reaches the bottom wall42via the thermal via54and the flexible heat transfer member52. When the flexible heat transfer member52and the thermal via54of the first heat transfer portion50are provided directly below the electronic component30, a part of heat generated by the electronic component30easily reaches the bottom wall42, thus enhancing the heat dissipation of the electronic component30.

Another part of the heat generated by the electronic component30reaches the second circuit board24via the flexible heat transfer member68and the metal member62. Also, another part of the heat generated by the electronic component30reaches the top wall47via the flexible heat transfer member68, the metal member62, and the flexible heat transfer member70. When the flexible heat transfer member68and the metal member62of the second heat transfer portion60, and the flexible heat transfer member70are provided directly above the electronic component30, another part of the heat generated by the electronic component30easily reaches the second circuit board24and the top wall47, thus enhancing the heat dissipation of the electronic component30.

Effects and the Like of Embodiment 1

According to the board unit10having the above-described configuration, the electronic component30is thermally connected to the bottom wall42and the second circuit board24by the first heat transfer portion50and the second heat transfer portion60, thereby enhancing the heat dissipation of the electronic component30. Since the second heat transfer portion60is partially provided at a position corresponding to the body32of the electronic component30, it is possible to prevent such a situation that the land design of the circuit boards22and24is restricted due to the provision of the second heat transfer portion60. Furthermore, the second heat transfer portion60thermally connects the electronic component30and the top wall47. With this, the heat dissipation of the electronic component30are further enhanced.

Also, the second heat transfer portion60includes the metal member62, and the metal member62includes the fixed portion63fixed to the second circuit board24, and the first protruding portion64that protrudes from the second circuit board24toward the body32. The metal member62typically has a heat conductivity higher than those of a heat dissipation grease, a heat dissipation sheet, and the like. With this, the heat conductivity of the second heat transfer portion60is enhanced. Also, since the metal member62is fixed to the second circuit board24, reflow processing can be easily performed on the second circuit board24.

Also, a flexible heat transfer member such as a heat dissipation grease or a heat dissipation sheet is, due to its flexibility, likely to come into areal contact with an object, but if the flexible heat transfer member locally has a large thickness, the shape retention properties thereof will be likely to decrease. Therefore, if the distance between the first circuit board22and the second circuit board24is large, it is difficult to locally provide a flexible heat transfer member such as a heat dissipation grease or a heat dissipation sheet. In contrast, because of high shape retention properties of the metal member62, even if the distance between the first circuit board22and the second circuit board24is large, the state in which the metal member62is partially provided at a position corresponding to the body32will be likely to become stabilized.

Also, the metal member62includes the second protruding portion65that protrudes from the second circuit board24toward the top wall47, and the coupling portion66that couples the first protruding portion64and the second protruding portion65and is received in a hole formed in the second circuit board24. With this, the metal member62can extend to a position close to the top wall47, and the heat conductivity of the second heat transfer portion60is further enhanced.

Also, the horizontal cross-sectional area of the second protruding portion65is greater than the horizontal cross-sectional area of the coupling portion66. Accordingly, the area of the surfaces of the metal member62and the top wall47that face with each other is increased, and thus the heat conductivities of the metal member62and the top wall47are enhanced.

Also, the second heat transfer portion60includes the flexible heat transfer member68that is interposed between the first protruding portion64and the body32, is more flexible than the metal member62, and fills up the gap between the first protruding portion64and the body32. With this, the heat conductivity between the electronic component30and the metal member62is enhanced.

Also, a region of the first circuit board22that is covered by the first heat transfer portion50is greater than a region of the first circuit board22that is covered by the second heat transfer portion60. With this, the heat conductivity between the first circuit board22and the bottom wall42is enhanced.

Embodiment 2

The following will describe a board unit according to Embodiment 2.FIG.2is a schematic cross-sectional view of a board unit110according to Embodiment 2. Note that in descriptions of following embodiments, the same reference numerals are given to the same constituent components as those described above, and descriptions thereof are omitted.

In the board unit110, the shape of a metal member162is different from the shape of the above-described metal member62. The horizontal cross-sectional area of a second protruding portion165of the metal member162, and the horizontal cross-sectional area of a coupling portion166are smaller than the horizontal cross-sectional area at the leading end of a first protruding portion164. With this, a reduction in a mountable area of the second circuit board24is suppressed.

The metal member162has, for example, a shape that includes a bottom plate portion and a side plate portion that stands upright from one side of the bottom plate portion. Such a metal member162may be obtained by, for example, bending a flat plate-shaped metal plate member at an intermediate portion into an L-shape. The bottom plate portion is disposed so as to face the body32. Also, the side plate portion extends toward the top wall47. The side plate portion passes through the second circuit board24. Here, the bottom plate portion corresponds to the leading end of the first protruding portion164. Also, an end of the side plate portion on the bottom plate portion side corresponds to a base end of the first protruding portion164, an end on the opposite side corresponds to the second protruding portion165, and an intermediate portion corresponds to the coupling portion166. A hole in the second circuit board24through which the side plate portion is passed is a long hole elongated in one side. For example, solder SO or the like is provided between the metal member162and the inner surface of the long hole, so that the metal member162and the second circuit board24are fixed to each other. Accordingly, in the present example, a fixed portion163is provided at the coupling portion166.

A recess47his formed in the top wall47at a position corresponding to the leading end of the second protruding portion165. Also, the leading end of the second protruding portion165is located in the recess47h. With this, the area of the surfaces of the second protruding portion165and the top wall47that face with each other is increased, and the heat dissipation properties are enhanced. In the present example, a flexible heat transfer member170located between the metal member162and the top wall47is provided between the inner surface of the recess47hand the leading end of the second protruding portion165.

Also, in the present example, the first heat transfer portion50includes a metal member56, instead of the thermal via54. A hole is formed in a portion of the first circuit board22that is covered by the body32, and the metal member56is received in the hole. In the example shown inFIG.2, the metal member56is smaller than the hole, and is fixed to the first circuit board22by the solder SO provided between the inner surface of the hole and the metal member56. The metal member56may also be press fit into the hole. Also, similar to the metal member62, the metal member56may include a body portion and a flange portion. This flange portion may protrude from the first circuit board22toward the bottom wall42. Also, this flange portion may be fixed to the first circuit board22.

In this example, a part of heat generated by the electronic component30reaches the bottom wall42via the metal member56and the flexible heat transfer member52. Another part of the heat generated by the electronic component30reaches the top wall47via the flexible heat transfer member68, the metal member162, and the flexible heat transfer member170.

Embodiment 3

The following will describe a board unit according to Embodiment 3.FIG.3is a schematic cross-sectional view of a board unit210according to Embodiment 3.

In the board unit210, the shape of a metal member262is different from the shape of the above-described metal member62. The metal member262is interposed between the first circuit board22and the second circuit board24. The metal member262has a shape obtained by omitting, from the above-described metal member62, the coupling portion66and the second protruding portion65. With this, in the board unit210, it is possible to realize a configuration in which the metal member262does not pass through the second circuit board24.

The metal member262is shorter than the distance between the first circuit board22and the second circuit board24. The metal member262may be columnar such that, for example, the same cross section continues from a first end on the body32side to a second end on the second circuit board24side. Solder SO or the like is provided between the second end of the metal member262and the second circuit board24, so that the metal member262and the second circuit board24are fixed to each other. Accordingly, in the present example, a fixed portion263is provided at a base end of a first protruding portion264.

In the present example, instead of the flexible heat transfer member70, a flexible heat transfer member72is interposed between the second circuit board24and the top wall47. Note that thermal via74may also be provided in the second circuit board24at a position covered by a base end of the first protruding portion264. In the present example, a part of heat generated by the electronic component reaches the top wall47via the flexible heat transfer member68, the metal member262, the solder SO, the thermal via74, and the flexible heat transfer member72.

Embodiment 4

The following will describe a board unit according to Embodiment 4.FIG.4is a schematic cross-sectional view of a board unit310according to Embodiment 4.

In the board unit310, the fixation structure of the metal member62to the second circuit board24is different from the fixation structure of the metal member62to the second circuit board24in the above-described board unit10. In the board unit310, the metal member62and the second circuit board24are screwed and fixed to each other by screws SC.

The present example is the same as the above-described board unit10in terms of the shape of the metal member62, and the positional relationship between the second circuit board24and the metal member62. In the present example, the flange portion of the metal member62and the second circuit board24have holes through which the screws SC are passed. Using these holes, the screws SC are fastened. Note that when, as inFIG.4, the heads of the screws SC are located on the outer side of the second circuit board24, female screws may also be provided in the holes in the flange portion, or nuts may also be provided on the outer side of the flange portion, separately from the flange portion. Also, if the heads of the screws SC are provided on the outer side of the flange portion, nuts are preferably provided on the outer side of the second circuit board24, separately from the second circuit board24. In the present example, a part of heat generated by the electronic component30reaches the top wall47via the flexible heat transfer member68, the metal member62, and the flexible heat transfer member70.

Embodiment 5

The following will describe a board unit according to Embodiment 5.FIG.5is a schematic cross-sectional view of a board unit410according to Embodiment 5.

In the board unit410, the shape of a metal member462is different from the shape of the above-described metal member62. Similar to the metal member62in the above-described board unit310, the metal member462is screwed and fixed to the second circuit board24by screws SC. Similar to the metal member262of the board unit210, the metal member462does not pass through the second circuit board24.

The metal member462is shorter than the distance between the first circuit board22and the second circuit board24. Similar to the metal member62, the metal member462has a shape such that it includes a body portion and a flange portion, and the body portion is shorter than the body portion of the metal member62. The flange portion and the second circuit board24have holes through which the screws SC are passed. Using these holes, the screws SC are fastened. A fixed portion463is provided at a base end of a first protruding portion464of the metal member462. Note that when, as inFIG.5, the heads of the screws SC are located on the outer side of the second circuit board24, female screws may also be provided in the holes in the flange portion, or nuts may also be provided on the outer side of the flange portion, separately from the flange portion. Also, if the heads of the screws SC are provided on the outer side of the flange portion, nuts may be provided on the outer side of the second circuit board24, separately from the second circuit board24.

In the present example, a part of heat generated by the electronic component30reaches the top wall47via the flexible heat transfer member68, the metal member462, the thermal via74, and the flexible heat transfer member72. A flexible heat transfer member may also be interposed between the metal member462and the second circuit board24.

Embodiment 6

The following will describe a board unit according to Embodiment 6.FIG.6is a schematic cross-sectional view of a board unit510according to Embodiment 6.

In the board unit510, the shape of a metal member562is different from the shape of the above-described metal member62. Similar to the metal member62in the above-described board unit310, the metal member562is screwed and fixed to the second circuit board24by screws SC, while passing through the second circuit board24. The metal member562has a flange portion at an intermediate position in the longitudinal direction. The flange portion is provided between the first circuit board22and the second circuit board24. The flange portion and the second circuit board24have holes through which the screws are passed. Using these holes, the screws SC are fastened. A fixed portion563is provided at a base end of a protruding portion564of the metal member562. Note that when, as inFIG.6, the heads of the screws SC are located on the outer side of the second circuit board24, female screws may also be provided in the holes in the flange portion, or nuts may also be provided on the outer side of the flange portion, separately from the flange portion. Also, if the heads of the screws SC are provided on the outer side of the flange portion, nuts may also be provided on the outer side of the second circuit board24, separately from the second circuit board24.

In the present example, a part of heat generated by the electronic component30reaches the top wall47via the flexible heat transfer member68, the metal member562, and the flexible heat transfer member70.

The metal member562of the present example may also be fixed to the second circuit board24by solder SO, instead of being screwed. In this case, the protruding portion564of the metal member562serves as a first protruding portion. Also, a portion of the metal member562that is received in a hole formed in the second circuit board24serves as a coupling portion. Also, a portion of the metal member562that protrudes from the second circuit board24to the side opposite to the protruding portion564serves as a second protruding portion. In this case, the horizontal cross-sectional area of the portion of the metal member562in which the flange portion is provided is greater than the horizontal cross-sectional area of the coupling portion. Accordingly, the horizontal cross-sectional area of the first protruding portion is greater than the horizontal cross-sectional area of the coupling portion. This enables reflow processing on the side of the second circuit board24that faces the first circuit board22.

Embodiment 7

The following will describe a board unit according to Embodiment 7.FIG.7is a schematic cross-sectional view of a board unit610according to Embodiment 7.

In the board unit610, a plurality of electronic components30,34, and36are provided on the first circuit board22. Second heat transfer portions60are provided not only at a position corresponding to the electronic component30but also at a position corresponding to the electronic component34. The second heat transfer portion60for the electronic component30and the second heat transfer portion60for the electronic component34are provided while being detached from each other. No second heat transfer portion is provided at a position corresponding to the electronic component36. For example, the electronic component36is considered to be an electronic component that generates a smaller amount of heat than the electronic components30and34.

A first heat transfer portion50is provided so as to correspond to the plurality of electronic components30. The first heat transfer portion50is provided in a region over the two electronic components30and34at which the second heat transfer portions60are provided. The first heat transfer portion50is provided in a region over the two electronic components34and36, namely, the electronic component34for which the second heat transfer portion60is provided, and the electronic component36for which no electronic component is provided.

Modifications

Although the second heat transfer portion has been described so far as thermally connecting the corresponding electronic component30and the top wall47, at a position corresponding to the electronic component30, this configuration is not essential. The second heat transfer portion does not need to thermally connect, at a position corresponding to the electronic component30, the electronic component30and the top wall47. For example, in Embodiment 3, a configuration is also possible in which the flexible heat transfer member72is omitted, and at a position corresponding to the electronic component30, the second heat transfer portion does not needs to thermally connect the electronic component30and the top wall47although the metal member262of the second heat transfer portion thermally connects the electronic component30and the second circuit board24.

Although the second heat transfer portion has been described so far as including a metal member, this configuration is not essential. The second heat transfer portion does not need to include a metal member. In this case, the second heat transfer portion may be constituted by a flexible heat transfer member.

Although the second heat transfer portion60has been described so far as including the flexible heat transfer member68, this configuration is not essential. The metal member62may directly abut against the body32.

Also, although a region of the first circuit board22that is covered by the first heat transfer portion50has been described so far as being greater than a region of the first circuit board22that is covered by the second heat transfer portion60, this configuration is not essential. Also, a region of the first circuit board22that is covered by the first heat transfer portion50may also be smaller than or equal to a region of the first circuit board22that is covered by the second heat transfer portion60.

Note that the above-described embodiments and modifications can be freely combined unless they contradict each other.