JP7724105B2 - Circuit Boards and Electronic Devices - Google Patents

Description

The present invention relates to a circuit board and an electronic device equipped with the circuit board.

Conventionally, techniques for improving heat dissipation have been known for electronic devices that include circuit boards for inverter circuits or motor drive circuits, which are equipped with heat-generating elements such as switching elements (bipolar transistors, field effect transistors (FETs)) that generate a large amount of heat. For example, Patent Document 1 discloses a control device that can improve heat dissipation. The control device includes a circuit board whose entire surface is coated with resist, switching elements mounted on the circuit board, and a holder that supports the circuit board. The holder has a portion that functions as a heat sink facing the circuit board, and the heat sink portion is located adjacent to the circuit board. The circuit board has a resist-removed portion on its second surface, opposite the first surface on which the switching elements are mounted, formed in a location corresponding to the location where the switching elements are mounted, where the resist is removed. The resist-removed portion and the holder are connected via an insulating and thermally conductive adhesive. This allows heat generated by the switching elements to be dissipated to the outside via the resist-removed portion and the holder.

Japanese Patent Application Laid-Open No. 2020-136534

For circuit boards used in inverter circuits and the like, multilayer boards with multiple wiring layers laminated with insulating layers are sometimes used to achieve high integration. Such multilayer boards have through holes that electrically and thermally connect the topmost wiring layer on the front side to the topmost wiring layer on the back side. These through holes have openings on the front and back sides of the circuit board, exposing the plating layer that connects the wiring layers. When such multilayer boards are configured as in the prior art, it is necessary to provide insulating material between the through-hole openings and the holder heat sink in areas other than the resist-removed areas to ensure insulation between the through-holes and the holder. However, increasing the number of materials placed between the circuit board and the holder heat sink affects the durability of the circuit board due to the stress applied to the circuit board by the materials when the circuit board is secured.

In consideration of the above issues, the circuit board and electronic device equipped with the circuit board according to the present invention are multilayer boards with through holes, which improve the heat dissipation properties of heat generated by heat-generating elements while suppressing a decrease in insulation properties.

One form of circuit board for solving the above problem includes a plurality of wiring layers including a first wiring layer that is an outermost layer on a first surface side of the circuit board and a second wiring layer that is an outermost layer on a second surface side of the circuit board opposite the first surface, a plurality of insulating layers including a surface insulating layer provided on the second surface side of the second wiring layer and stacked with the plurality of wiring layers, a plurality of through holes that connect two or more wiring layers including the first wiring layer and the second wiring layer among the plurality of wiring layers and have openings in the first wiring layer and the second wiring layer, respectively, and a heat generating element that is disposed on the first surface of the circuit board. and the surface insulating layer is arranged so that in a second region of the second surface corresponding to a predetermined portion of the heat generating element arranged on the first surface within a first region of the second surface for facing a heat sink, the second wiring layer and the opening are not covered by the surface insulating layer, and in a third region of the first region that is not the second region, the second wiring layer and the opening are covered by the surface insulating layer , and the opening on the second surface side of a through hole provided in a fourth region of the second surface that is not the first region is covered by the insulating layer .

Furthermore, in order to solve the above problem, one embodiment of the electronic device according to the present invention is characterized by having the above-mentioned circuit board, a heat sink, and a thermally conductive member that thermally connects the circuit board and the heat sink.

As described above, the present invention provides a circuit board that is a multilayer substrate with through holes and that can improve the heat dissipation properties of heat generated by heat-generating elements while suppressing a decrease in insulation properties, as well as an electronic device that includes such a circuit board.

1 is an exploded perspective view of an electronic device according to a first embodiment of the present invention; 1 is a plan view of a circuit board according to a first embodiment of the present invention, viewed from the front surface side. 1 is a plan view of a circuit board according to a first embodiment of the present invention, seen from the front surface side with a switching element seen through; FIG. 2 is a bottom view of the circuit board of the first embodiment according to the present invention, as viewed from the rear surface side. 1 is a cross-sectional view of a circuit board according to a first embodiment of the present invention. FIG. 4 is a cross-sectional view of a circuit board according to a second embodiment of the present invention. FIG. 10 is a cross-sectional view of a circuit board according to a third embodiment of the present invention. FIG. 1 is an exploded perspective view of an electronic device according to the prior art. FIG. 1 is a cross-sectional view of a part of an electronic device and a circuit board according to the prior art.

The following describes an embodiment of the present invention with reference to the drawings. The following describes an example of an electronic device incorporating a motor control unit (so-called Electronic Control Unit, ECU) for an electric power steering device as an example of a circuit board and an electronic device having the circuit board according to the present invention. An electric power steering device is a device for controlling or assisting steering in a vehicle. The ECU in the electric power steering device controls the motor to generate a force corresponding to the detected torque of the steering wheel operated by the driver. The force generated by the motor is transmitted via a gear to a rack that controls the tilt of the tires, and acts as a force to assist steering. Note that the functions of the ECU are not limited to those described above and can also perform known controls for controlling an electric power steering device. The circuit board includes a motor drive control circuit. Furthermore, the circuit board according to the present invention is not limited to motor control units in electric power steering devices, but can also be applied to various other circuit boards, such as circuit boards used in motor control units for vehicle power window systems. The following describes an electronic device comprising a circuit board that functions as an ECU and a housing that houses the circuit board. The housing is at least partially made of metal and has a heat sink that transfers heat from the circuit board to the outside to cool the circuit board.

First, a circuit board 10Z and an electronic device 100Z according to the prior art will be described. FIG. 8 is a schematic diagram showing the overall configuration of an electronic device 100Z according to the prior art. FIG. 9 is a cross-sectional view showing the installation state of the circuit board 10Z in the electronic device 100Z. The circuit board 10Z is housed in a housing 20 composed of a base 21 and a cover member 22. The electronic device 100Z includes a circuit board 10Z, a heat sink 211 integrally molded with the base 21 that supports the circuit board 10Z, and a thermally conductive member 30 that thermally connects the circuit board 10Z and the heat sink 211. The thermally conductive member 30 is an adhesive material (adhesive) that provides close contact. Furthermore, a so-called insulating material is used for the thermally conductive member 30 to ensure electrical insulation between the circuit board 10Z and the heat sink 211. The thermally conductive member 30 fills the entire space between the circuit board 10Z and the heat sink 211. The circuit board 10Z has a semiconductor switching element 16, which generates a large amount of heat, mounted on its surface.

The circuit board 10Z is a multilayer board constructed by laminating an insulating base material IB and a conductive copper foil CB, and has hollow through holes that electrically and thermally connect multiple wiring layers, including the top wiring layer on the front side and the top wiring layer on the back side. The through holes are created by drilling a multilayer board in which copper foil (wiring layer) CB and substrate (insulating layer) IB are laminated, followed by a plating process to form a plated layer that connects the multiple wiring layers with the through holes, and then a process to form a resist layer (surface insulating layer) that ensures insulation of the top wiring layer. Because the through holes formed in the drilling process have a hollow structure, the process of forming a resist layer made of resist material sometimes fails to adequately cover the end openings of the through holes.

In addition, in the heat dissipation area where the semiconductor switching elements 16 are located, the resist layer is removed from both the front and back surfaces of the circuit board 10Z, forming a resist-removed area that exposes the plated layer MB. The semiconductor switching elements 16 are placed directly on the plated layer MB in the resist-removed area on the front surface of the circuit board 10Z. Heat generated by the semiconductor switching elements 16 is dissipated from the highly thermally conductive plated layer MB, which is made of metal, via the side of the through-hole, the resist-removed area on the back surface, and the thermally conductive member 30 to the heat sink 211. This allows the heat generated by the semiconductor switching elements 16 to be dissipated efficiently.

On the other hand, if the thermally conductive member 30 is filled in the entire space between the circuit board 10Z and the heat sink 211, the thermally conductive member 30 can get caught when the circuit board 10Z is fixed to the base 21 with screws, causing stress on the circuit board 10Z and affecting the durability of the circuit board 10Z. However, if the amount of thermally conductive member 30 applied is reduced in areas other than the resist-removed areas, the plated portion can become exposed from the end openings of the through-holes in areas other than the resist-removed areas, potentially compromising insulation from the heat sink 211.

In order to ensure insulation between the heat sink 211 and the through holes provided in areas other than the resist-removed area, processing such as forming grooves in the heat sink 211 increases the distance between the heat sink 211 and the circuit board 10Z, but this can lead to issues such as burrs being generated by processing the heat sink 211 and increased costs.

<First Example>
1 to 5 , a circuit board 10 and an electronic device 100 including the circuit board 10 according to this embodiment will be described. As shown in FIG. 1 , the electronic device 100 includes a housing 20 and the circuit board 10 housed within the housing 20. The housing 20 includes a base 21 that supports the circuit board 10 and a cover member 22 that fits around the edge of the base 21. The base 21 has a heat sink 211 integrally molded into the bottom of its inner surface. This allows the electronic device 100 to be provided with a housing that has excellent heat dissipation capabilities for heat generated by the circuit board 10. While the heat sink 211 is integrally molded with the base 21 in this embodiment, this is not a limitation and the heat sink 211 may be a separate heat sink inserted from the outside of the housing into the interior through an opening in the base. The housing 20 is appropriately provided with female threads for attaching the circuit board 10 to the inner surface of the base 21.

The circuit board 10 has multiple semiconductor switching elements 16 mounted on its front surface F1, the side opposite the base 21. The circuit board 10 is attached to the base 21 with screws at several locations, and a heat sink 211 is provided in a position corresponding to the semiconductor switching elements 16 arranged on the attached circuit board 10. As will be described in more detail below, for example, on the back surface F2 of the circuit board 10 facing the heat sink 211, there is no resist layer (surface insulating layer) in the area corresponding to a certain semiconductor switching element 16a, and a thermal conductive member 30 is provided in the corresponding position, thereby efficiently dissipating heat from the semiconductor switching element 16 and preventing a decrease in insulation.

The electronic device 100 includes a circuit board 10, a heat sink 211, and a thermally conductive member 30 that thermally connects the circuit board 10 and the heat sink 211, and may also include connectors and terminal blocks that are connected to the bottom and side surfaces of the base 21 as appropriate. The circuit board 10 is electrically connected to an external motor via these connectors and is equipped with a control circuit for driving the motor using semiconductor switching elements 16. This provides a circuit board 10 that includes a motor drive control circuit using semiconductor switching elements 16 with excellent heat dissipation and insulation properties. The electronic device 100 and circuit board 10 are, of course, not limited to this, and can be used in all circuit boards on which heat-generating elements are mounted, and in all electronic devices that include such circuit boards.

Figure 2 is a top view of circuit board 10 as viewed from the front side of circuit board 10 (the upper side of electronic device 100). Circuit board 10 has multiple semiconductor switching elements 16 mounted on its front surface F1, and numerous through holes 13 provided directly below and around the semiconductor switching elements 16. For example, double or triple through holes 13 are provided around a certain semiconductor switching element 16a. Figure 3 is a top view of circuit board 10 as viewed from the front side of circuit board 10 (the upper side of electronic device 100), showing the semiconductor switching elements 16 from a perspective. As shown in Figure 3, a through hole 13 is also provided directly below semiconductor switching element 16. The through hole 13 penetrates both the front surface F1 and the back surface F2 of circuit board 10, which is made up of multiple layers of insulators and conductors, and has openings on both sides.

Figure 4 is a bottom view of the circuit board 10 as seen from its rear side (the underside of the electronic device 100). Figure 4 shows the rear surface F2 facing the base 21. In Figure 4, the region A1 on the rear surface F2 facing the heat sink 211 is indicated by a thick dashed dotted line. This figure also shows the region A2 of region A1 corresponding to the semiconductor switching element 16 arranged on the front surface F1 by a thin dashed dotted line. While region A2 is shown in this figure to correspond to a single semiconductor switching element 16a, it is not limited to this size and range. It may be slightly larger than the semiconductor switching element 16a (for example, a range larger than the thickness of the circuit board 10), or it may correspond only to a specific portion of the semiconductor switching element 16a (for example, the drain terminal portion, which generates the most heat). By aligning region A2 with a specific portion of the semiconductor switching element 16, high heat dissipation can be achieved in the region that generates the most heat, in accordance with the characteristics of the heat-generating element. Note that in this diagram, only one area A2 corresponding to one semiconductor switching element 16a is shown, and areas A2 corresponding to the other multiple semiconductor switching elements 16 are omitted.

In this region A2, to ensure heat dissipation, the resist layer (surface insulating layer) covering the opening ends of the highly thermally conductive through holes 13 and the outermost conductor (wiring layer) on the back surface F2 side is not present and is exposed. Meanwhile, in region A3 of region A1, which is not region A2, the opening ends of the through holes 13 and the outermost conductor (wiring layer) on the back surface F2 side are covered with a resist layer (surface insulating layer) to ensure insulation from the heat sink 211. That is, in region A2 of region A1 on the back surface F2, which faces the heat sink 211 and corresponds to a predetermined portion of the semiconductor switching element 16a arranged on the front surface F1, the resist layer 17 is provided so that the wiring layer 12 and the opening ends of the through holes 13 are not covered by the resist layer 17. Furthermore, in region A3 of region A1, which is not region A2, the resist layer 17 is provided so that the wiring layer 12 and the opening ends of the through holes 13 are covered by the resist layer 17. In this figure, through holes 13 are also provided in the area of the back surface F2 that does not face the heat sink 211, i.e., area A4, which is not area A1.

Figure 5 shows a cross section of the circuit board 10, thermally conductive member 30, and heat sink 211 near a semiconductor switching element 16a. The circuit board 10 is a multilayer substrate formed by laminating an insulating substrate IB and a conductive copper foil CB. It includes wiring layer 11, which is the topmost copper foil CB on the front surface F1 side, and wiring layer 12, which is the topmost copper foil CB on the back surface F2 side. Note that wiring layer 11 includes the topmost copper foil CB on the front surface F1 side and a plating layer MB formed on the front surface F1 side. Similarly, wiring layer 11 includes the topmost copper foil CB on the back surface F2 side and a plating layer MB formed on the front surface F1 side. Multiple through holes 13 are formed in each region, connecting two or more wiring layers, including wiring layer 11 and wiring layer 12, with openings 131 in wiring layer 11 and wiring layer 12, respectively. This diagram shows that two through holes 13 are provided in area A2 and two through holes 13 are provided in area A3.

The semiconductor switching element 16a is located on the front surface F1 of the circuit board 10. The resist layer 17 is absent from the surface where the semiconductor switching element 16a is located. The highly thermally conductive plating layer MB and the open ends of the through-holes 13 are exposed, while the resist layer 17 is present in the remaining areas. That is, the area of the front surface F1 of the circuit board 10 where the semiconductor switching element 16a is located is a region where the resist layer 17 is absent (a resist-removed region). The area A2 on the back surface F2 corresponding to the location of the semiconductor switching element 16a is absent from the resist layer 17 and is in contact with the highly thermally conductive thermal conductive member 30. That is, the area A2 on the back surface F2 of the circuit board 10 is a region where the resist layer 17 is absent (a resist-removed region). On the other hand, the resist layer 17 is present in the area A3 to ensure insulation from the heat sink 211. Because the area A3 is sufficiently distant from the heat-generating semiconductor switching element 16a in the direction parallel to the board, the through-holes 13 in the area A3 contribute little to heat dissipation. Therefore, by covering the open ends of the through holes 13 in area A3 with an insulating resist layer 17, insulation between the heat sink 211 is ensured while minimizing the impact on the heat dissipation of the semiconductor switching elements 16a.

In this way, in the circuit board 10, in the region A1 on the back surface F2 facing the heat sink 211, the wiring layer 12 and opening 131 are exposed in the region A2 on the back surface F2 that corresponds to a predetermined portion of the semiconductor switching element 16a arranged on the front surface F1 (in this figure, the entire semiconductor switching element 16a), and in the region A3 of the region A1 that is not region A2, the wiring layer 12 and opening 131 are covered by the resist layer 17 (surface insulating layer).

The above-described circuit board provides a circuit board 10 that can improve heat dissipation from the semiconductor switching elements 16 while suppressing degradation of insulation. Specifically, the thermally conductive member 30 is disposed to cover the area A2 of the back surface F2 where the resist layer 17 is not present, thermally connecting the circuit board 10 to the heat sink 211. This allows the heat generated by the semiconductor switching elements 16a to be efficiently dissipated through the highly thermally conductive plating layer MB on the front surface F1 of the circuit board 10, the opening ends and side surfaces of the through holes 13, the thermally conductive member 30, and the heat sink 211, while suppressing degradation of insulation due to the absence of the resist layer 17. Meanwhile, since the opening ends of the through holes 13 in the area A3 are covered with the resist layer 17, insulation from the heat sink 211 can be ensured without disposing the thermally conductive member 30 between the area A3 and the heat sink 211. Therefore, by providing the thermally conductive member 30 only in the area A2 facing the heat sink 211, which contributes greatly to heat dissipation, it is possible to reduce the amount of insulating material (thermally conductive member 30) provided between the circuit board and the heat sink 211. This minimizes the stress on the circuit board 10 caused by the thermally conductive member 30, and prevents a decrease in the durability of the circuit board 10.

Next, we will explain a circuit board formation method for covering the openings on the back surface F2 side of the through-holes in region A3 with a resist layer. As described above, through-hole formation involves forming openings at the through-hole formation positions in a substrate consisting of alternating insulating substrates IB and copper foils CB (wiring layers). Next, a plating layer MB is formed to connect the wiring layers. To form a resist layer covering the through-hole openings 131, a process is performed in which an insulating resin material 14 is filled into the openings corresponding to the through-holes in region A3. When the resist layer formation process is performed with the resin material 14 filled inside the through-holes in region A3, a resist layer is formed over the openings of the through-holes in region A3. The resin material 14 may be removed from the openings in a later process, or it may remain in the openings as is. Filling the through-holes 13 in region A3 with the insulating resin material 14 forms a resist layer with the openings of the through-holes 13 filled, thereby enabling the openings of the through-holes 13 to be more reliably covered with the resist layer. This ensures reliable insulation in region A3. The hollow portions of the through holes 13 in area A3 may be filled with a thermally conductive material. This can improve the heat dissipation effect of the through holes 13 in area A3.

Furthermore, as in the above example, it is preferable that the openings of the through holes 13 provided in region A4 are covered with a resist layer at least on the back surface F2 side. Covering the openings 131 of the through holes 13 in region A4 that do not face the heat sink 211 with a resist layer 17 improves insulation from the base 21. The interiors of the through holes 13 provided in region A4 may also be filled with insulating resin material 14. This makes it possible to more reliably cover the openings of the through holes 13 in region A4 with the resist layer. The interiors of the through holes 13 provided in region A2 may also be filled with insulating resin material 14. Filling the interiors of the through holes 13 in region A2 with insulating resin material 14 makes it possible to suppress contamination inside the through holes 13 when assembling the circuit board 10 to the housing 20.

<Second Example>
A circuit board 10A according to this embodiment will be described with reference to FIG. 6 . The circuit board 10A according to this embodiment is characterized in that the hollow interior portions of the through holes 13 provided in the region A2 are filled with a thermally conductive material 15. To avoid repetition, the same components as those in the above embodiment are denoted by the same reference numerals, and their description will be omitted. The circuit board 10A is housed in a housing 20 and is a multilayer board on which a plurality of semiconductor switching elements 16 are mounted on the surface F1 opposite the base 21. A heat sink 211 of the housing 20 is provided at a position corresponding to the semiconductor switching elements 16, and heat generated by the circuit board 10A is dissipated via a thermally conductive member 30 that thermally connects the circuit board 10A and the heat sink 211.

The circuit board 10A has multiple semiconductor switching elements 16 mounted on its front surface F1, and numerous through holes 13 provided directly below and around the semiconductor switching elements 16. The back surface F2 of the circuit board 10A has an area A1 facing the heat sink 211, an area A2 within area A1 that corresponds to the semiconductor switching elements 16 arranged on the front surface F1, an area A3 within area A1 that is not area A2, and an area A4 within the back surface F2 that is not area A1.

The circuit board 10A is formed by laminating a substrate IB and copper foil CB, and includes wiring layer 11, which is the copper foil CB located on the surface F1 side, and wiring layer 12, which is the copper foil CB located on the back surface F2 side. Wiring layer 11 includes the copper foil CB located on the surface F1 side and a plating layer MB formed on the surface F1 side. Similarly, wiring layer 11 includes the copper foil CB located on the back surface F2 side and a plating layer MB formed on the surface F1 side. Multiple through holes 13 are formed, connecting two or more wiring layers including wiring layer 11 and wiring layer 12, with openings 131 formed in wiring layer 11 and wiring layer 12, respectively.

The resist layer 17 is absent on the front surface F1 where the semiconductor switching element 16a is located, leaving the highly thermally conductive plating layer MB and the open ends of the through holes 13 exposed, with the resist layer 17 remaining in the rest of the surface. The back surface F2, corresponding to the position where the semiconductor switching element 16a is located, similarly does not have the resist layer 17, but is in direct contact with the highly thermally conductive heat conduction member 30, and a resist layer 17 is formed in region A3 to ensure insulation from the heat sink 211.

As a result, in the region A2 of the region A1 facing the heat sink 211, which corresponds to the semiconductor switching element 16a, the wiring layer 12 and opening 131, which have high thermal conductivity and electrical conductivity, are exposed, and in the region A3, the wiring layer 12 and opening 131 are covered with the resist layer 17, thereby providing a circuit board 10A that can improve the dissipation of heat generated by the semiconductor switching element 16 while suppressing a decrease in insulation properties.

The hollow interior portions of the through-holes 13 in region A2 are filled with a thermally conductive material 15. This improves the heat dissipation effect of the through-holes 13 in region A2 compared to when the through-holes 13 are hollow (air). The thermally conductive material 15 contains, for example, a metallic filler to enhance thermal conductivity. Similar to the thermal conductive member 30, the thermally conductive material 15 may be made of any material with high thermal conductivity, and is not limited to the above example. As with the first embodiment, the hollow interior portions of the through-holes 13 in region A3 may be filled with an insulating resin material 14. By filling the hollow interior portions of the through-holes 13 in region A3 with resin material 14, a resist layer is formed with the openings of the through-holes 13 filled, allowing the openings of the through-holes 13 to be more reliably covered with the resist layer. This may ensure reliable insulation in region A3.

The through holes in region A3 may be hollow. The hollow portions of the through holes 13 in region A3 may be filled with thermally conductive material 15, similar to the through holes 13 in region A2. This allows the heat dissipation effect of the through holes 13 in region A3 to be improved.

<Third Example>
A circuit board 10B according to the third embodiment will be described with reference to FIG. 7 . The circuit board 10B according to the third embodiment is characterized in that the through holes 13 formed in the regions A3 and A4 are filled with an insulating resin material 14. To avoid duplication, the same components as those in the above embodiments are designated by the same reference numerals and will not be described again. The circuit board 10B is housed in a housing 20 and is a multilayer board on which a plurality of semiconductor switching elements 16 are mounted on the surface F1 opposite the base 21. A heat sink 211 of the housing 20 is provided at a position corresponding to the semiconductor switching elements 16, and heat generated by the circuit board 10B is dissipated via a thermally conductive member 30 that thermally connects the circuit board 10B to the heat sink 211.

The circuit board 10B has multiple semiconductor switching elements 16 mounted on its front surface F1, and numerous through holes 13 provided directly below and around the semiconductor switching elements 16. The back surface F2 of the circuit board 10B is divided into an area A1 facing the heat sink 211, an area A2 within area A1 that corresponds to the semiconductor switching elements 16 arranged on the front surface F1, an area A3 within area A1 that is not the second area, and an area A4 within the back surface F2 that is not area A1 (and does not face the heat sink 211).

Circuit board 10B is formed by laminating a substrate IB and copper foil CB, and includes wiring layer 11, which is the copper foil CB located on the surface F1 side, and wiring layer 12, which is the copper foil CB located on the back surface F2 side. Wiring layer 11 includes the copper foil CB located on the surface F1 side and a plating layer MB formed on the surface F1 side. Similarly, wiring layer 11 includes the copper foil CB located on the back surface F2 side and a plating layer MB formed on the surface F1 side. Multiple through holes 13 are formed, connecting two or more wiring layers including wiring layer 11 and wiring layer 12, and wiring layer 11 and wiring layer 12 each have an opening 131.

The resist layer 17 is absent in the portion of the front surface F1 where the semiconductor switching element 16a is located, leaving the highly thermally conductive plating layer MB and the open end of the through hole 13 exposed, with the resist layer 17 formed in other areas. Similarly, the resist layer 17 is absent in area A2 on the back surface F2, which corresponds to the position where the semiconductor switching element 16a is located, and the highly thermally conductive heat conduction member 30 is in direct contact with it. Furthermore, in areas A3 and A4, the resist layer 17 is formed to ensure insulation from the heat sink 211 and base 21.

As a result, the wiring layer 12 and opening 131, which have high thermal conductivity and electrical conductivity, are exposed in region A2, which faces the heat sink 211 corresponding to the semiconductor switching element 16a, and the wiring layer 12 and opening 131 are covered with the resist layer 17 in regions A3 and A4 outside region A2. This allows for the provision of a circuit board 10B that can improve the dissipation of heat generated by the semiconductor switching element 16 while suppressing a decrease in insulation properties.

Furthermore, the through holes 13 in area A2 have no filler and have hollow portions 132, while the through holes 13 in areas A3 and A4 have their hollow portions filled with insulating resin material 14. In this way, by filling the through holes 13 in areas A3 and A4 with insulating resin material 14, a resist layer is formed with the openings of the through holes 13 filled, making it possible to more reliably cover the openings of the through holes 13 with the resist layer. This ensures reliable insulation in areas A3 and A4.

The present invention is not limited to the illustrated examples, but can be implemented in configurations that do not deviate from the scope of the claims. In other words, while the present invention has been particularly illustrated and described primarily with reference to specific embodiments, those skilled in the art can make various modifications to the above-described embodiments in terms of quantity and other details without departing from the scope of the technical concept and purpose of the present invention.

REFERENCE SIGNS LIST 100 Electronic device 10 Circuit board 11 Wiring layer 12 Wiring layer 13 Through hole 131 Opening 132 Hollow portion 14 Resin material 15 Thermally conductive material 16 Semiconductor switching element (heat generating element)
17 Resist layer (surface insulating layer)
IB Base material (insulator)
CB copper foil (conductor)
MB: plating layer F1: front surface F2: back surface A1: area A2: area A3: area A4: area 20: housing 21: base 211: heat sink 22: cover member 30: thermally conductive member

Claims (9)

a plurality of wiring layers including a first wiring layer that is the outermost layer on a first surface side of the circuit board and a second wiring layer that is the outermost layer on a second surface side opposite to the first surface of the circuit board;
a surface insulating layer provided on the second surface side of the second wiring layer, and a plurality of insulating layers stacked on the plurality of wiring layers;
a plurality of through holes that connect two or more wiring layers including the first wiring layer and the second wiring layer among the plurality of wiring layers, and have openings in the first wiring layer and the second wiring layer, respectively;
a heat generating element disposed on the first surface of the circuit board;
and
The surface insulating layer is
a first region of the second surface facing a heat sink, the second wiring layer and the opening are not covered by the surface insulating layer in a second region of the second surface corresponding to a predetermined portion of the heat generating element arranged on the first surface, the second wiring layer and the opening are covered by the surface insulating layer in a third region of the first region that is not the second region, and the opening on the second surface side of a through hole provided in a fourth region of the second surface that is not the first region is covered by the insulating layer . The circuit board according to claim 1, further comprising an insulating resin material filled in the hollow portion of the through hole provided in the third region. The circuit board of claim 1, further comprising a thermally conductive material filled in the hollow portion of the through hole provided in the third region. The circuit board described in any one of claims 1 to 3, characterized in that the heat-generating element is a semiconductor switching element, and the predetermined portion is a portion including a drain terminal of the semiconductor switching element. 5. The circuit board according to claim 1 , further comprising a thermally conductive material filled in a hollow portion of a through hole provided in the second region. the circuit board is a circuit board on which a control circuit for driving a motor is mounted,
6. The circuit board according to claim 1 , wherein the heat generating element is a semiconductor switching element for driving the motor. The circuit board according to any one of claims 1 to 6 ;
the heat sink;
a thermally conductive member that thermally connects the circuit board and the heat sink;
An electronic device having: The electronic device according to claim 7 , wherein the heat conducting member is provided so as to cover at least the second region of the first region on the second surface of the circuit board. the heat sink is integrally molded with a base that supports the circuit board;
9. The electronic device according to claim 7 , wherein the circuit board is housed by the base and a cover member.