Circuit Boards and Electronic Devices

Abstract

To suppress reduction of insulation property while improving heat dissipation property of heat generated from a heating element in a multilayer board comprising through holes.SOLUTION: A circuit board 10 comprises: a plurality of wiring layers including a wiring layer 11 of an outermost layer at the side of a front face F1 of the circuit board and a wiring layer 12 of an outermost layer at the side of a rear face F2; a plurality of through holes 13 connecting two or more wiring layers including the wiring layer 11 and the wiring layer 12 and including openings 131 in the wiring layer 11 and the wiring layer 12; a semiconductor switching element 16 disposed on the front face of the circuit board; and a resist layer 17 provided closer to a front layer than at least the wiring layers 12. The wiring layer 12 and the opening are exposed in an area A2 corresponding to a predetermined portion of the semiconductor switching element 16 disposed on the front face in an area A1 for opposing with a heat sink 211, and the wiring layer 12 and the opening are covered by the resist layer in an area A3, which is not the area A2, in the area A1.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a circuit board and an electronic device including the circuit board. [Background technology]

[0002] Conventionally, techniques for improving heat dissipation have been known for electronic devices including 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 in a portion facing the circuit board, and the heat sink portion is provided in close proximity to the circuit board. The circuit board has a resist-removed portion formed on a second surface opposite to a first surface on which the switching elements are mounted, at a position corresponding to the position where the switching elements are mounted, where the resist is removed. The resist-removed portion and the holder are connected via an adhesive that is insulating and thermally conductive. As a result, heat generated by the switching elements is dissipated to the outside via the resist-removed portion and the holder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-136534 Summary of the Invention [Problem to be solved by the invention]

[0004] Multilayer boards, in which multiple wiring layers are laminated with insulating layers, are often used for circuit boards used in inverter circuits and the like 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 plating layers for connecting the wiring layers. In such multilayer boards, when configured as in the prior art, insulating members must be provided between the holder and the heat sink in the area where the through holes are open to ensure insulation between the through holes and the holder except in the areas where the resist is removed. However, increasing the number of members disposed between the circuit board and the heat sink of the holder affects the durability of the circuit board due to the stress applied to the circuit board by the members when the circuit board is fixed.

[0005] In view of the above problems, the circuit board and electronic device equipped with the circuit board according to the present invention are multilayer boards having through holes, which enable improvement in the heat dissipation properties of heat generated from heat-generating elements while suppressing deterioration in insulation properties. [Means for solving the problem]

[0006] One form of a 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 a 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 surface insulating layer provided on the second surface side of the circuit board relative to the second wiring layer, and a plurality of insulating layers stacked with the plurality of wiring layers, a plurality of through holes connecting two or more wiring layers including the first wiring layer and the second wiring layer among the plurality of wiring layers and having openings in the first wiring layer and the second wiring layer, respectively, and a heat generating element disposed on the first surface of the circuit board, wherein the surface insulating layer is configured such that in a first region of the second surface that faces a heat sink and corresponds to a predetermined portion of the heat generating element disposed on the first surface, the second wiring layer and the openings 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 openings are covered by the surface insulating layer. and an 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 with the insulating layer. The present invention is characterized in that it is provided so that

[0007] Furthermore, in order to solve the above problem, one embodiment of an electronic device according to the present invention is characterized by having the above circuit board, a heat sink, and a thermally conductive member that thermally connects the circuit board and the heat sink. [Effects of the Invention]

[0008] As described above, according to the present invention, it is possible to provide a circuit board that is a multilayer board having through holes and that can improve the heat dissipation properties of heat generated from heat-generating elements while suppressing a decrease in insulation properties, and an electronic device that includes such a circuit board. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an exploded perspective view of an electronic device according to a first embodiment of the present invention; [Figure 2] 1 is a plan view of a circuit board according to a first embodiment of the present invention, viewed from the front surface side. [Figure 3]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; [Figure 4] 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. [Figure 5] 1 is a cross-sectional view of a circuit board according to a first embodiment of the present invention. [Figure 6] FIG. 4 is a cross-sectional view of a circuit board according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a cross-sectional view of a circuit board according to a third embodiment of the present invention. [Figure 8] FIG. 1 is an exploded perspective view of an electronic device according to the prior art. [Figure 9] FIG. 1 is a cross-sectional view of a part of an electronic device and a circuit board according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Hereinafter, an electronic device incorporating a motor control unit (so-called Electronic Control Unit, ECU) for an electric power steering device will be described as an example of a circuit board and an electronic device having the circuit board according to the present invention. The 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 is a circuit board including a motor drive control circuit. Furthermore, the circuit board according to the present invention is not limited to the motor control unit in an electric power steering device, but can also be applied to various circuit boards, such as a circuit board used in a motor control unit of a power window system of a vehicle. Hereinafter, an electronic device including a circuit board functioning as an ECU and a housing that houses the circuit board will be described. 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.

[0011] First, a circuit board 10Z and an electronic device 100Z according to the related art will be described. FIG. 8 is a schematic diagram showing the overall configuration of an electronic device 100Z according to the related 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 formed of a base 21 and a cover member 22. The electronic device 100Z includes the 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 as 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 semiconductor switching elements 16, which generate a large amount of heat, mounted on its surface.

[0012] The circuit board 10Z is a multilayer board formed by laminating an insulating substrate IB and a conductive copper foil CB, and includes 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 a drilling process in a multilayer board formed by laminating copper foil (wiring layer) CB and substrate (insulating layer) IB, 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 a resist material sometimes fails to adequately cover the end openings of the through-holes.

[0013] In the heat dissipation area where the semiconductor switching elements 16 are disposed, the resist layer is removed from both the front and back surfaces of the circuit board 10Z, forming a resist-removed portion to expose the plated layer MB. The semiconductor switching elements 16 are disposed directly on the plated layer MB in the resist-removed portion on the front surface of the circuit board 10Z. Heat generated by the semiconductor switching elements 16 is dissipated from the plated layer MB, which is made of a highly thermally conductive metal, via the side surfaces of the through-holes, the resist-removed portion on the back surface, and the heat-conducting member 30 to the heat sink 211. This allows the heat generated by the semiconductor switching elements 16 to be dissipated efficiently.

[0014] On the other hand, if the thermal conductive member 30 is filled in the entire space between the circuit board 10Z and the heat sink 211, stress is generated in the circuit board 10Z when the circuit board 10Z is fixed to the base 21 with screws, which causes a problem of affecting the durability of the circuit board 10Z. However, if the amount of thermal conductive member 30 applied is reduced in areas other than the resist-removed areas, the plated portion may be exposed from the end openings of the through-holes in areas other than the resist-removed areas, which may impair the insulation with the heat sink 211.

[0015] In order to ensure insulation between the heat sink 211 and the through holes provided in areas other than the resist-removed area, if a groove is formed in the heat sink 211 to increase the distance between the heat sink 211 and the circuit board 10Z, problems arise such as the generation of burrs due to the processing of the heat sink 211 and increased costs.

[0016] <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 limiting 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.

[0017] The circuit board 10 has a plurality of semiconductor switching elements 16 mounted on its front surface F1 opposite the base 21. The circuit board 10 is attached to the base 21 with screws at several locations, and the heat sink 211 is provided in positions corresponding to the semiconductor switching elements 16 arranged on the attached circuit board 10. As will be described in detail later, 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 an 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 suppressing a decrease in insulation properties.

[0018] The electronic device 100 includes the circuit board 10, the heat sink 211, and the thermally conductive member 30 that thermally connects the circuit board 10 and the heat sink 211, and also includes connectors, terminal blocks, and the like that are connected to the bottom or side of the base 21 as appropriate. The circuit board 10 is electrically connected to an external motor via these connectors, and is mounted with a control circuit for driving the motor using semiconductor switching elements 16. This makes it possible to provide a circuit board 10 that includes a motor drive control circuit using semiconductor switching elements 16 that have excellent heat dissipation and insulation properties. The electronic device 100 and the circuit board 10 are, of course, not limited to these, 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.

[0019] FIG. 2 is a top view of the circuit board 10 as viewed from the front side of the circuit board 10 (the upper side of the electronic device 100). The circuit board 10 has a plurality of semiconductor switching elements 16 mounted on the front surface F1, and a large number of 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. FIG. 3 is a top view of the circuit board 10 as viewed from the front side of the circuit board 10 (the upper side of the electronic device 100) with the semiconductor switching elements 16 seen through. As shown in FIG. 3, a through hole 13 is also provided directly below the semiconductor switching element 16. The through hole 13 penetrates the front surface F1 and the back surface F2 of the circuit board 10, which is made up of multiple layers of insulators and conductors, and has openings on both sides.

[0020] FIG. 4 is a bottom view of the circuit board 10 as seen from its rear side (the lower side of the electronic device 100). FIG. 4 shows the rear surface F2 facing the base 21. In FIG. 4, a region A1 on the rear surface F2 facing the heat sink 211 is indicated by a thick dashed dotted line. Furthermore, within region A1, a region A2 corresponding to the semiconductor switching element 16 disposed on the front surface F1 is indicated by a thin dashed dotted line. While region A2 is shown to correspond to a single semiconductor switching element 16a in this figure, it is not limited thereto. It may be a region slightly larger than the semiconductor switching element 16a (e.g., a region larger than the thickness of the circuit board 10), or it may correspond only to a specific portion of the semiconductor switching element 16a (e.g., the drain terminal portion, which generates a large amount of 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. In this figure, only one area A2 corresponding to one semiconductor switching element 16a is shown, and areas A2 corresponding to the other semiconductor switching elements 16 are omitted.

[0021] In this region A2, in order to ensure heat dissipation, the resist layer (surface insulating layer) that covers 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. On the other hand, in a region A3 of the region A1 that is not the 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) in order to ensure insulation from the heat sink 211. That is, in a region A2 of the back surface F2 region A1 that 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 opening ends of the wiring layer 12 and the through holes 13 are not covered by the resist layer 17. Furthermore, in a region A3 of the region A1 that is not the region A2, the resist layer 17 is provided so that the opening ends of the wiring layer 12 and the through holes 13 are covered by the resist layer 17. In this figure, through holes 13 are also provided in an area of the rear surface F2 that does not face the heat sink 211, that is, an area A4 that is not the area A1.

[0022] FIG. 5 shows a cross section of the circuit board 10, the thermally conductive member 30, and the 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. The circuit board 10 includes a wiring layer 11, which is the copper foil CB located on the front surface F1, and a wiring layer 12, which is the copper foil CB located on the back surface F2. The wiring layer 11 includes the copper foil CB located on the front surface F1 and a plating layer MB formed on the front surface F1. Similarly, the wiring layer 11 includes the copper foil CB located on the back surface F2 and a plating layer MB formed on the front surface F1. Multiple through holes 13 are formed in each region, connecting two or more wiring layers, including the wiring layer 11 and the wiring layer 12. The figure shows two through holes 13 in region A2 and two through holes 13 in region A3.

[0023] The semiconductor switching elements 16a are disposed on the front surface F1, and the resist layer 17 is not formed on the surface of the circuit board 10 where the semiconductor switching elements 16a are disposed. The highly thermally conductive plating layer MB and the open ends of the through-holes 13 are exposed, and the resist layer 17 is formed on the remaining portions. That is, the region of the front surface F1 of the circuit board 10 where the semiconductor switching elements 16a are disposed is a region where the resist layer 17 is not formed (resist-removed region). The region A2 on the back surface F2 corresponding to the position where the semiconductor switching elements 16a are disposed is a region where the resist layer 17 is not formed (resist-removed region). On the other hand, the resist layer 17 is formed in a region A3 to ensure insulation from the heat sink 211. Because the region A3 is sufficiently separated from the heat-generating semiconductor switching elements 16a in the direction parallel to the substrate, the through-holes 13 in the region A3 can be said to contribute little to heat dissipation. Therefore, by covering the open end of the through hole 13 in the region A3 with the insulating resist layer 17, the insulation between the heat sink 211 is ensured while the influence on the heat dissipation of the semiconductor switching element 16a is suppressed.

[0024] In this way, in the circuit board 10, in the region A1 of the back surface F2 facing the heat sink 211, the wiring layer 12 and the opening 131 are exposed in the region A2 of the back surface F2 corresponding 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 the region A2, the wiring layer 12 and the opening 131 are covered by the resist layer 17 (surface insulating layer).

[0025] The above-described circuit board can provide a circuit board 10 that can improve heat dissipation from the semiconductor switching elements 16 while suppressing deterioration in insulation. Specifically, the thermally conductive member 30 is provided to cover the region A2 of the back surface F2 where the resist layer 17 is not present, thereby thermally connecting the circuit board 10 and the heat sink 211. This allows the heat generated from 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 deterioration in insulation due to the absence of the resist layer 17. Meanwhile, since the opening ends of the through holes 13 in the region A3 are covered with the resist layer 17, insulation from the heat sink 211 can be ensured without providing the thermally conductive member 30 between the region A3 and the heat sink 211. Therefore, it is possible to provide the thermal conductive member 30 only in the region A2 that faces the heat sink 211 and that contributes greatly to heat dissipation, thereby reducing the amount of insulating member (thermal 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 thermal conductive member 30, and prevents a decrease in the durability of the circuit board 10.

[0026] Next, a circuit board forming method for covering the openings on the back surface F2 side of the through-holes in region A3 with a resist layer will be described. As described above, the through-holes are formed by alternately laminating insulating substrates IB and copper foils CB (wiring layers) on a substrate, forming openings at the through-hole formation positions. Next, a plating layer MB is formed for connection between the wiring layers. To form a resist layer to cover 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 filled in the openings as is. By filling the through-holes 13 in region A3 with the insulating 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 ensures reliable insulation in region A3. The hollow portions of the through holes 13 provided in the region A3 may be filled with a thermally conductive material, thereby improving the heat dissipation effect of the through holes 13 in the region A3.

[0027] As in the above example, it is also 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 the resist layer 17 improves insulation from the base 21. The through holes 13 provided in region A4 may be filled with an insulating resin material 14. This allows the openings of the through holes 13 in region A4 to be more reliably covered with the resist layer. The through holes 13 provided in region A2 may also be filled with the insulating resin material 14. Filling the through holes 13 in region A2 with the insulating resin material 14 makes it possible to prevent contamination of the through holes 13 when assembling the circuit board 10 to the housing 20.

[0028] <Second Example> A circuit board 10A according to the present embodiment will be described with reference to FIG. 6. The circuit board 10A according to the second 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 a surface F1 opposite to 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.

[0029] The circuit board 10A has a plurality of semiconductor switching elements 16 mounted on its front surface F1, and a large number of 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 in area A1 corresponding to the semiconductor switching elements 16 arranged on the front surface F1, an area A3 in area A1 that is not area A2, and an area A4 in area F2 that is not area A1.

[0030] The circuit board 10A is formed by laminating a base material IB and a copper foil CB, and includes a wiring layer 11, which is the copper foil CB located on the front surface F1 side, and a wiring layer 12, which is the copper foil CB located on the back surface F2 side. The wiring layer 11 includes the copper foil CB located on the front surface F1 side and a plating layer MB formed on the front surface F1 side. Similarly, the wiring layer 11 includes the copper foil CB located on the back surface F2 side and a plating layer MB formed on the front surface F1 side. A plurality of through holes 13 are formed, connecting two or more wiring layers including the wiring layer 11 and the wiring layer 12, and the wiring layer 11 and the wiring layer 12 each have an opening 131.

[0031] The resist layer 17 is not formed on the front surface F1 where the semiconductor switching elements 16a are arranged, and the highly thermally conductive plating layer MB and the open ends of the through holes 13 are exposed, with the remaining portions being formed with the resist layer 17. The back surface F2 corresponding to the position where the semiconductor switching elements 16a are arranged similarly does not have the resist layer 17, and is in direct contact with the highly thermally conductive heat conducting member 30, and the resist layer 17 is formed in the region A3 to ensure insulation from the heat sink 211.

[0032] 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 heat dissipation properties of the heat generated from the semiconductor switching element 16 while suppressing a decrease in insulation properties.

[0033] Furthermore, the hollow portions inside the through-holes 13 provided in the region A2 are filled with a thermally conductive material 15. This allows the heat dissipation effect of the through-holes 13 in the region A2 to be improved compared to when the through-holes 13 are hollow (air). Here, the thermally conductive material 15 is a material that contains, for example, a metallic filler to enhance thermal conductivity. Note that, like the thermally 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. Furthermore, as in the first embodiment, the hollow portions inside the through-holes 13 provided in the region A3 may be filled with an insulating resin material 14. By filling the hollow portions of the through-holes 13 in the region A3 with the 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 therefore ensure the insulation in the region A3.

[0034] 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.

[0035] <Third Example> A circuit board 10B according to the present 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 denoted by the same reference numerals, and their description will be omitted. 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 a 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 and the heat sink 211.

[0036] The circuit board 10B has a plurality of semiconductor switching elements 16 mounted on its front surface F1, and a large number of 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 corresponding 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 (not facing the heat sink 211).

[0037] The circuit board 10B is formed by laminating a base material IB and a copper foil CB, and includes a wiring layer 11, which is the copper foil CB located on the front surface F1 side, and a wiring layer 12, which is the copper foil CB located on the back surface F2 side. The wiring layer 11 includes the copper foil CB located on the front surface F1 side and a plating layer MB formed on the front surface F1 side. Similarly, the wiring layer 11 includes the copper foil CB located on the back surface F2 side and a plating layer MB formed on the front surface F1 side. A plurality of through holes 13 are formed, connecting two or more wiring layers including the wiring layer 11 and the wiring layer 12, and the wiring layer 11 and the wiring layer 12 each have an opening 131.

[0038] The resist layer 17 is not formed on the portion of the front surface F1 where the semiconductor switching element 16a is arranged, and the highly thermally conductive plating layer MB and the open end of the through hole 13 are exposed, while the resist layer 17 is formed on the other portions. Similarly, the resist layer 17 is not formed on the region A2 on the back surface F2 corresponding to the position where the semiconductor switching element 16a is arranged, and the highly thermally conductive heat conduction member 30 is in direct contact with the region. Furthermore, the resist layer 17 is formed on the regions A3 and A4 to ensure insulation from the heat sink 211 and the base 21.

[0039] As a result, in region A2 facing the heat sink 211 corresponding 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 regions A3 and A4 other than region A2, the wiring layer 12 and opening 131 are covered with the resist layer 17, thereby providing a circuit board 10B that can improve the heat dissipation properties of the heat generated from the semiconductor switching element 16 while suppressing a decrease in insulation properties.

[0040] Furthermore, through holes 13 in region A2 have no filler and have hollow portions 132, while the hollow portions of through holes 13 in regions A3 and A4 are filled with insulating resin material 14. By filling through holes 13 in regions A3 and A4 with insulating resin material 14 in this way, a resist layer is formed with the openings of through holes 13 filled, making it possible to more reliably cover the openings of through holes 13 with the resist layer. This ensures insulation in regions A3 and A4.

[0041] It should be noted that the present invention is not limited to the illustrated examples, and can be implemented in configurations that do not deviate from the scope of the claims. That is, although the present invention has been particularly shown 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 the number and other details without departing from the scope of the technical idea and purpose of the present invention. [Explanation of symbols]

[0042] 100 Electronic equipment 10 Circuit Board 11 Wiring layer 12 wiring layer 13 through holes 131 Aperture 132 Hollow part 14 Resin material 15 Thermally conductive materials 16 Semiconductor switching element (heat generating element) 17 Resist layer (surface insulating layer) IB substrate (insulator) CB copper foil (conductor) MB plating layer F1 surface F2 back A1 area A2 area A3 area A4 area 20 Case 21 Base 211 Heat sink 22 Cover member 30 Thermal Conduction Material

Claims

1. 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.

2. 2. The circuit board according to claim 1, further comprising an insulating resin material filled in a hollow portion of the through hole provided in the third region.

3. 2. The circuit board according to claim 1, further comprising a thermally conductive material filled in a hollow portion of the through hole provided in the third region.

4. 4. The circuit board according to claim 1, wherein 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. 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.

6. 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.

7. 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:

8. 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.

9. 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.

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