Rotating electric machine

Abstract

This rotating electric machine comprises: a substrate mounted with a power circuit for supplying power to a motor body; and a heat sink. The power circuit includes a heat generation element. The substrate has: a pattern circuit formed on the surface of the substrate and joined to the heat generation element; and a plurality of thermal vias connected to the pattern circuit and being in thermal contact with the heat sink. The pattern circuit has: a joint portion to which the heat generation element is joined; and an extension portion extending from the joint part in a first direction. The pattern circuit has a connection region positioned outside the heat generation element in the first direction and not positioned outside the heat generation element in a second direction intersecting with both the thickness direction of the substrate and the first direction. Each of the plurality of thermal vias is not disposed in the connection region.

Description

Rotating electric machines

[0001] The present disclosure relates to a rotating electric machine.

[0002] Conventionally, a motor (rotating electric machine) is known that includes a substrate on which a power circuit that supplies power to a motor body is mounted, and a heat sink. The power circuit includes a heat-generating element, such as a switching element or a shunt resistor.

[0003] In the rotating electric machine described in Patent Document 1, multiple thermal vias are arranged directly below the source and drain of the switching element and in the pattern circuit located around the switching element. Each thermal via is in thermal contact with the heat sink via thermal grease. With this heat dissipation structure, heat generated by the switching element is dissipated to the heat sink via the thermal vias and thermal grease.

[0004] Japanese Patent Application Laid-Open No. 2022-160336

[0005] For example, in the heat dissipation structure described in Patent Document 1, increasing the number of thermal vias arranged directly under or around the heat-generating element improves the efficiency of heat conduction between the heat-generating element and the thermal vias. However, the thermal vias arranged around the heat-generating element may cause the pattern circuit formed around the thermal vias to generate heat. Such heat generation from the pattern circuit may reduce the efficiency of heat dissipation from the heat-generating element to the heat sink.

[0006] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a rotating electric machine with improved heat dissipation performance.

[0007] In order to solve the above problem, a rotating electric machine according to aspect 1 of the present disclosure comprises a substrate on which a power circuit that supplies power to a motor body is mounted, and a heat sink, wherein the power circuit includes a heat-generating element, and the substrate has a pattern circuit formed on the surface of the substrate and joined to the heat-generating element, and a plurality of thermal vias that are connected to the pattern circuit and are in thermal contact with the heat sink, the pattern circuit having a joint portion to which the heat-generating element is joined and an extension portion extending from the joint portion in a first direction, the pattern circuit having a connection region that is located outward from the heat-generating element in the first direction but is not located outward from the heat-generating element in a second direction that intersects both the thickness direction of the substrate and the first direction, and each of the plurality of thermal vias is not positioned in the connection region.

[0008] According to the above aspects of the present disclosure, it is possible to provide a rotating electric machine with improved heat dissipation performance from heat generating elements.

[0009] 4A is a cross-sectional view showing a rotating electric machine according to embodiment 1. FIG. 4B is a plan view showing a substrate according to embodiment 1. FIG. 4C is a cross-sectional view showing an example of thermal vias. FIG. 4D is a cross-sectional view showing a heat dissipation structure according to embodiment 1. FIG. 4E is a cross-sectional view taken along line BB shown in FIG. 4A, showing the arrangement of thermal vias according to embodiment 1. FIG. 4F is a view showing a conventional example of the arrangement of thermal vias. FIG. 4G is a view showing the arrangement of thermal vias according to embodiment 2. FIG. 4H is a cross-sectional view showing a heat dissipation structure according to embodiment 3.

[0010] Embodiment 1. Figure 1 is a cross-sectional view showing a rotating electric machine 1 according to embodiment 1. The rotating electric machine 1 according to this embodiment includes a motor body 10, a substrate 20, a heat sink 30, a frame 40, a connector 50, and a cover 60. The motor body 10 has a shaft 13 that rotates about a rotation axis O. The rotating electric machine 1 according to this embodiment is used, for example, to generate a steering assist force in an electric power steering device of a vehicle. However, the use of the rotating electric machine 1 is not limited to this and can be changed as appropriate.

[0011] In the following description, the thickness direction of the substrate 20 will be simply referred to as the thickness direction Z. The substrate 20, heat sink 30, and motor main body 10 are arranged in this order in the thickness direction Z. In this embodiment, the thickness direction Z coincides with the direction in which the rotation axis O extends. Hereinafter, the direction from the heat sink 30 (motor main body 10) toward the substrate 20 in the thickness direction Z will be referred to as the upward direction and represented by the +Z direction in the drawings. The direction from the substrate 20 toward the heat sink 30 (motor main body 10) in the thickness direction Z will be referred to as the downward direction and represented by the -Z direction in the drawings. Furthermore, the view from the thickness direction Z will be referred to as the planar view. In the planar view, the direction perpendicular to the rotation axis O will be referred to as the radial direction. In the radial direction, the direction approaching the rotation axis O will be referred to as the radially inward direction, and the direction away from the rotation axis O will be referred to as the radially outward direction. In the planar view, the direction going around the rotation axis O will be referred to as the circumferential direction.

[0012] The frame 40 according to this embodiment has a housing 41 for the stator 11, a connector connection surface 42, and a flange portion (not shown) that connects to a gear (not shown) of an output device. The housing 41 has a generally cylindrical shape with a bottom. A bare box portion 41a is provided at the bottom of the housing 41, to which an output-side bearing 14b (described later) is fixed. The connector connection surface 42 extends radially outward from the opening edge (upper edge) of the housing 41. The connector connection surface 42 according to this embodiment has an opening 42a formed therein through which a terminal 51 (described later) of the connector 50 is inserted. The frame 40 may be manufactured, for example, by molding an aluminum alloy by die casting or the like and then machining the molded product.

[0013] The heat sink 30 according to this embodiment includes a base 31 and a protrusion 32. The base 31 is fixed to the opening edge (upper edge) of the housing 41 by, for example, press-fitting. A bare box portion 31a is provided on the underside of the base 31, to which the input-side bearing 14a (described later) is fixed. The base 31 has a heat-absorbing surface 31b facing upward. The heat-absorbing surface 31b is in thermal contact with a heat-generating element (described later) of the substrate 20, and absorbs heat generated by the heat-generating element into the base 31 (heat sink 30). Note that the term "thermal contact" in this specification encompasses both direct contact with an object and contact via one or more thermally conductive members. The protrusion 32 protrudes upward from the outer periphery of the heat-absorbing surface 31b.

[0014] The motor body 10 has a stator 11, a rotor 12, and a shaft 13. The stator 11 and the rotor 12 are housed inside the housing portion 41 (more specifically, the housing space surrounded by the lower surface of the base portion 31 and the inner surface of the housing portion 41).

[0015] The shaft 13 has a counter-output end 13a located at an upper position and an output end 13b located at a lower position. The counter-output end 13a is held by an input-side bearing 14a so as to be rotatable about the rotation axis O. The output end 13b is held by an output-side bearing 14b so as to be rotatable about the rotation axis O. The input-side bearing 14a is fixed to a bare box portion 31a of the heat sink 30, and the output-side bearing 14b is fixed to a bare box portion 41a of the frame 40. A sensor magnet 16 is attached to the counter-output end 13a to transmit magnetism to a rotation sensor 73 (described below) mounted on the substrate 20. A boss 15 is attached to the output end 13b to be fitted with a gear (not shown) of an output device.

[0016] The rotor 12 is provided radially outward of the shaft 13 and is fixed to the shaft 13. The rotor 12 according to this embodiment has a rotor core (not shown), a permanent magnet (not shown), and a protective cover 12 a.

[0017] The stator 11 is disposed radially outward of the rotor 12. The stator 11 according to this embodiment includes a stator core 11a and a motor coil 11c wound around the stator core 11a via an insulator 11b. The stator core 11a may have a laminated structure of electromagnetic steel sheets. The stator 11 is formed into a circular shape in a plan view. The stator 11 is fixed to the housing 41 by a fixing method such as shrink fitting or press fitting.

[0018] The substrate 20 is fixed to the heat sink 30 so that the lower surface of the substrate 20 faces the heat absorption surface 31b of the heat sink 30. Specifically, the substrate 20 according to this embodiment is screwed to the protrusions 32 of the heat sink 30 with screws SC. This forms a gap GP in the thickness direction Z between the lower surface of the substrate 20 and the heat absorption surface 31b of the heat sink 30. However, the method of fixing the substrate 20 to the heat sink 30 is not limited to screwing to the protrusions 32 and can be changed as appropriate.

[0019] At least a portion of the gap GP is filled (applied) with thermal grease GL. The thermal grease GL is in thermal contact with a heat-generating element (described later) of the substrate 20, and transfers heat generated in the heat-generating element to the heat sink 30. In this embodiment, the thermal grease GL is in direct contact with both the underside of the substrate 20 and the heat-absorbing surface 31b of the heat sink 30.

[0020] The connector 50 transmits signals to the circuit board 20 and supplies power to the circuit board 20, for example. When the rotating electric machine 1 is used in an electric power steering device of a vehicle, the signal transmitted by the connector 50 to the circuit board 20 is, for example, a torque signal (a signal acquired by a torque sensor) sent from the vehicle. The connector 50 may also supply power to the circuit board 20 from a battery or the like mounted on the vehicle. The connector 50 has terminals 51 connected to the circuit board 20. In this embodiment, the connector 50 is provided on the lower surface of the connector connection surface 42, and the terminals 51 are inserted into the openings 42a from below. As a result, the connector 50 is positioned below (on the output side of) the circuit board 20.

[0021] The cover 60 covers and protects the substrate 20. The cover 60 may be made of, for example, resin and metal. The cover 60 according to this embodiment has a housing portion 61 and a flange portion 62. The housing portion 61 has a topped shape. The substrate 20 is housed inside the housing portion 61. The outer shape of the housing portion 61 may substantially match the outer shape of the substrate 20. The flange portion 62 extends radially outward from the opening edge (lower edge) of the housing portion 61. The flange portion 62 is fixed to the connector connection surface 42 of the frame 40.

[0022] The connector 50 may be located above (on the opposite side to the output side of) the board 20. In this case, an opening may be formed in the cover 60. The terminals 51 may be inserted into the opening from above.

[0023] Fig. 2 is a plan view showing the board 20 according to the first embodiment. The board 20 is also referred to as a control board 20. As shown in Figs. 1 and 2, a control circuit 70 and a power circuit 80 are mounted on the board 20 according to this embodiment. The power circuit 80 supplies power to the motor main body 10. The control circuit 70 controls the power circuit 80. The control circuit 70 according to this embodiment includes a microcontroller 71, a driver 72, a rotation sensor 73, and the like. The power circuit 80 according to this embodiment includes a switching element 81, a shunt resistor 82, a ripple capacitor 83, and the like. The switching element 81 may be, for example, a field effect transistor (FET), etc.

[0024] 2, the terminal 51, the microcontroller 71, the driver 72, the switching element 81, the shunt resistor 82, and the ripple capacitor 83 are arranged symmetrically with respect to a line L in a plan view. Here, the line L is a line passing through the center of the rotation sensor 73 in a plan view. However, the arrangement of these electronic components can be changed as appropriate.

[0025] As shown in FIG. 2 , the power circuit 80 according to this embodiment includes two inverter circuits 84a and 84b. Each inverter circuit 84a and 84b includes nine switching elements 81 and other components. One inverter circuit 84a is located on one side of a line L, and the other inverter circuit 84b is located on the other side of the line L. The nine switching elements 81 in each inverter circuit 84a and 84b form three upper arms 81A, three lower arms 81B, and three motor relays 81C. That is, each inverter circuit 84a and 84b includes three sets, each including one upper arm 81A, one lower arm 81B, and one motor relay 81C. The three sets correspond one-to-one to the three phases (i.e., U-phase, V-phase, and W-phase) of the motor. In this embodiment, the inverter circuits 84a and 84b supply three-phase current to the motor coil 11c of the motor main body 10, and the current flows to ground via a shunt resistor 82. The switching element 81, the shunt resistor 82, etc. are heat-generating elements that generate heat when a current (specifically, a current for generating an output from the motor main body 10) flows through them. The power circuit 80 according to this embodiment has a plurality of heat-generating elements (the switching element 81, the shunt resistor 82, etc.) arranged in close proximity to one another. However, the number and arrangement of the heat-generating elements included in the power circuit 80 can be changed as appropriate.

[0026] The current flowing through the inverter circuits 84a and 84b is controlled by the microcontroller 71 and the driver 72. The ripple capacitor 83 suppresses the fluctuation range of the current ripple flowing through the motor coil 11c. The terminal 51, switching element 81, shunt resistor 82, ripple capacitor 83, and motor coil 11c (not shown in FIG. 2) are electrically connected by a pattern circuit 21a (not shown in FIG. 2; see FIGS. 4A and 4B) on the circuit board 20. Therefore, a large current flows through the pattern circuit 21a to generate output from the motor main body 10. This large current causes the pattern circuit 21a to generate heat.

[0027] Here, heat generation by the substrate 20 will be described. Generally, the amount of heat generated per unit time by an object, P (unit: W), is calculated by the following formula (1). R (unit: Ω) is the electrical resistance of the object, and I (unit: A) is the current flowing through the object. P = R x I ２ ...(1) The temperature of an object rises according to the duration of the heat generation. If a heat dissipation path for dissipating heat is connected to the object, the temperature of the object will stabilize at a constant temperature when the amount of heat dissipated from the heat dissipation path and the amount of heat generated in the object are balanced. However, if the amount of heat generated is excessive, the temperature of the object will rise.

[0028] In the substrate 20 according to this embodiment, heat generation in the heat generating elements (switching elements 81 and shunt resistors 82) through which a large current flows and in the pattern circuit 21 a becomes a problem. If the amount of heat generated is excessive, the temperatures of the heat generating elements (switching elements 81 and shunt resistors 82) and the pattern circuit 21 a may exceed their heat resistance temperatures, which may result in damage to the heat generating elements and deformation of the substrate 20.

[0029] Next, the heat resistance of the substrate 20 will be described. As an example, the substrate 20 may be a glass cloth epoxy resin substrate (hereinafter referred to as a glass epoxy substrate). By using a glass epoxy substrate as the substrate 20, the cost of the substrate 20 can be reduced. For example, the glass transition temperature of a glass epoxy substrate used for vehicles is approximately 145°C, which is lower than the heat-resistant temperature (e.g., 170°C) of the heating elements. In this embodiment, it is preferable to adopt a design in which the temperatures of the heating elements (switching elements 81 and shunt resistors 82) and the pattern circuit 21a when heated are equal to or lower than the glass transition temperature of the substrate 20.

[0030] Specifically, a possible method is to suppress the heat generation of the heating elements by employing heating elements with low internal resistance. Another possible method is to reduce the wiring resistance of the pattern circuit 21a by increasing the width or thickness of the pattern circuit 21a, thereby reducing the heat generation of the pattern circuit 21a. The wiring resistance (heat generation) of the pattern circuit 21a can also be reduced by connecting the pattern circuit 21a to the pattern circuits 21b to 21f (not shown in FIG. 2; see FIG. 4B) located on other layers using vias or the like. Reducing the distance between heating elements is also effective in reducing the wiring resistance (heat generation). However, employing heating elements with low internal resistance increases the cost of the heating elements. Furthermore, reducing the wiring resistance of the pattern circuit 21a by increasing the width or thickness of the pattern circuit 21a also increases the cost of the substrate 20. Therefore, a new method is desired that can achieve stable heat dissipation from the heating elements (switching elements 81 and shunt resistors 82) and the pattern circuit 21a while suppressing increases in the cost of the substrate 20.

[0031] In this embodiment, thermal vias 90 are introduced that are connected to both the heating element and the pattern circuit 21a (see also FIGS. 4A and 4B). Heat dissipation performance is ensured by the placement of the thermal vias 90. A heat dissipation structure that uses thermal vias 90 has the advantage of being easy to achieve low costs.

[0032] 3 is a diagram showing an example of a thermal via 90 that can be formed in the substrate 20. In this embodiment, the substrate 20 has a plurality of layers L (La to Lf) on which a plurality of pattern circuits 21 (21a to 21f) are arranged. The plurality of pattern circuits 21a to 21f correspond one-to-one to the plurality of layers La to Lf, and each pattern circuit 21a to 21f is arranged on the corresponding layer La to Lf. The layers La to Lf (pattern circuits 21a to 21f) are arranged at intervals in the thickness direction Z. The layers La and Lf correspond to the outer layers (surface) of the substrate 20. The layers Lb to Le correspond to the inner layers of the substrate 20.

[0033] The thermal vias 90 are via holes that connect the layers La to Lf in the thickness direction Z. Here, the via hole is a general term for a conductor structure having a thin-film tubular shape (e.g., a thin-film cylindrical shape) obtained by copper plating the inside of a hole H formed in the substrate 20. That is, the thermal via 90 according to this embodiment includes a tubular (e.g., cylindrical) copper plating layer PL formed on the inner surface of the hole H of the substrate 20. Each thermal via 90 (via hole) electrically and mechanically connects at least two pattern circuits out of the plurality of pattern circuits 21a to 21f.

[0034] Thermal vias 90 (via holes) are classified into two types, through via holes 91 and non-through via holes 92, depending on their structure. The through via holes 91 are via holes that penetrate the substrate 20 in the thickness direction Z. That is, the through via holes 91 are via holes that connect the outer layers La and Lf (pattern circuits 21a and 21f) to each other. The through via holes 91 can be manufactured, for example, by drilling a through hole in the substrate 20 and then copper plating the through hole. The non-through via holes 92 are via holes that do not penetrate the substrate 20 in the thickness direction Z. The non-through via holes 92 are further classified into two types, blind via holes 92a and buried via holes 92b, depending on their structure. The blind via holes 92a are via holes that connect the outer layers La and Lf (pattern circuits 21a and 21f) to the inner layers Lb to Le (pattern circuits 21b to 21e). The buried via holes 92b are via holes that connect the inner layers Lb to Le (pattern circuits 21b to 21e) to each other. The non-through via holes 92 can be manufactured, for example, by using a small-diameter drill and a laser to form holes only between the necessary layers and then plating the holes with copper. Note that while the interior of the through via holes 91 is hollow (space), the interior of the non-through via holes 92 is filled with an insulating material such as epoxy resin.

[0035] Fig. 4A is a cross-sectional view showing the heat dissipation structure according to embodiment 1. Fig. 4B is a cross-sectional view taken along line BB in Fig. 4A, showing the arrangement of thermal vias 90 according to embodiment 1. In the following description, switching element 81 will be described as a representative example of a heat-generating element. The heat dissipation structure described below can also be applied to heat-generating elements other than switching element 81 (for example, shunt resistor 82).

[0036] As shown in FIG. 4A , the switching element 81 according to this embodiment includes a heating element 81a and lead frames 81b and 81c. The lead frames 81b and 81c are connected via the heating element 81a and are not in direct contact with each other. The lead frame 81b corresponds to the drain of the switching element 81, and the lead frame 81c corresponds to the source of the switching element 81. The switching element 81 includes a resin package 81d formed around the heating element 81a and the lead frames 81b and 81c. The lower surfaces of the lead frames 81b and 81c are joined to a pattern circuit 21a on the substrate 20 by solder SL. The pattern circuit 21a includes a first portion P1 joined to the lead frame 81b and a second portion P2 joined to the lead frame 81c. The first portion P1 and the second portion P2 are spaced apart in the first direction X.

[0037] As shown in FIG. 4A , the substrate 20 according to this embodiment has a plurality of thermal vias 90 that are connected to the pattern circuit 21a and are in thermal contact with the heat sink 30 (base 31). The upper end of each thermal via 90 is in contact with the lower surface of the switching element 81 (specifically, the lead frame 81b). In this embodiment, all of the thermal vias 90 are through-hole vias 91. The lower ends of the thermal vias 90 are in thermal contact with the heat sink 30 (base 31) via thermal grease GL. Because the thermal vias 90 are in contact with both the switching element 81 and the pattern circuit 21a, heat generated in the switching element 81 and the pattern circuit 21a is dissipated to the heat sink 30 by the thermal vias 90 and the thermal grease GL.

[0038] As shown in FIG. 4B , the pattern circuit 21a according to this embodiment includes a bonding portion 21A to which a switching element 81 (heat-generating element) is bonded, and an extension portion 21B extending in one direction from the bonding portion 21A. In the following description, the direction in which the extension portion 21B extends from the bonding portion 21A (the direction in which the bonding portion 21A and the extension portion 21B are aligned) is referred to as the first direction X. Furthermore, the direction intersecting (e.g., perpendicular to) both the thickness direction Z and the first direction X is referred to as the second direction Y. One direction in the first direction X is represented as the +X direction, and the other direction is represented as the −X direction. Furthermore, one direction in the second direction Y is represented as the +Y direction, and the other direction is represented as the −Y direction. As shown in FIG. 4B , the dimension of the bonding portion 21A in the second direction Y is larger than the dimension of the extension portion 21B. In the second direction Y, the dimension of the joint portion 21A is larger than the dimension of the switching element 81 (lead frames 81b, 81c).

[0039] The arrangement of the thermal vias 90 in this embodiment will be described below. In this embodiment, the thermal vias 90 are arranged in the overlapping region A1 and the outer region A2 shown in FIG. 4B , but not in the connection region A3. Here, regions A1 to A3 are regions included in the pattern circuit 21a. The overlapping region A1 is a region that overlaps with the switching element 81 (heat-generating element) in a planar view. The outer region A2 is a region located outside the switching element 81 (heat-generating element) in the second direction Y. In the illustrated example, the pattern circuit 21a has two outer regions A2. The two outer regions A2 are located on both sides of the switching element 81 (heat-generating element) in the second direction Y. In other words, the switching element 81 (heat-generating element) is located between the two outer regions A2 in the second direction Y. The connection region A3 is a region that is located outside the switching element 81 (heat-generating element) in the first direction X, but is not located outside the switching element 81 (heat-generating element) in the second direction Y. "Not located outside the switching element 81 (heating element) in the second direction Y" can also be rephrased as "located inside in the second direction Y of both ends (side edges) of the switching element 81 (heating element) in the second direction Y."

[0040] The reason why thermal vias 90 are not disposed in the connection region A3 will be explained. The diameter of a via hole drilled with a small-diameter drill is approximately 0.3 mm to 0.4 mm. In contrast, the thickness of a typical copper plating layer obtained by copper plating the inner surface of a via hole is approximately 0.02 mm to 0.05 mm. Therefore, the heat dissipation area of ​​the thermal via 90 is approximately 20% to 30% of the cross-sectional area of ​​the via hole. Therefore, the heat dissipation performance of the thermal via 90 is lower than that of a solid, columnar heat dissipation component such as a copper inlay (not shown). Therefore, it is desirable to ensure heat dissipation performance by providing multiple thermal vias 90 rather than a single one. The arrangement pitch of the thermal vias 90 is, for example, approximately 0.9 mm. However, forming holes in the pattern circuit 21a to provide the thermal vias 90 (via holes) reduces the cross-sectional area of ​​the pattern circuit 21a. This increases the wiring resistance of the pattern circuit 21a, potentially causing the pattern circuit 21a to generate heat.

[0041] FIG. 5 shows a conventional example of the arrangement of thermal vias 90. In the example of FIG. 5, the thermal vias 90 are arranged not only in the overlap region A1 and the outer region A2 but also in the connection region A3. In the example of FIG. 5, the size of the switching element 81 is 5 mm × 6 mm, and the width (dimension in the second direction Y) of the lead frames 81b and 81c is 4 mm. Four via rows R0 are arranged in the connection region A3. Each via row R0 includes a plurality of thermal vias 90 arranged in the first direction X. The diameter of each thermal via 90 is 0.4 mm, and the arrangement pitch of the thermal vias 90 is 0.9 mm. By arranging the thermal vias 90 in this manner, the pattern width is reduced from a minimum of 4 mm to 2.6 mm (-40%). This reduces the cross-sectional area of ​​the pattern circuit 21a, increasing the wiring resistance of the pattern circuit 21a and the amount of heat generated by the pattern circuit 21a. As a result of the large heat generation in the portion of the pattern circuit 21a near the thermal via 90, the heat generated in this portion accounts for the majority of the heat dissipated to the heat sink 30 by the thermal via 90. This reduces the efficiency of heat dissipation from the switching element 81 (heat-generating element) to the heat sink 30.

[0042] In consideration of the above problem, in this embodiment, as shown in Fig. 4B, the thermal vias 90 are not provided in the connection area A3. This suppresses heat generation from the pattern circuit 21a and a decrease in the efficiency of heat dissipation from the switching elements 81 (heat-generating elements) to the heat sink 30, which are caused by the arrangement of the thermal vias 90. In other words, it is possible to achieve an improvement in the heat dissipation efficiency.

[0043] More specifically, in this embodiment, a plurality of thermal vias 90 constitute an overlapping via row R1 and an outer via row R2. In each of the via rows R1 and R2, a plurality of thermal vias 90 (four in the illustrated example) are arranged in the first direction X. The overlapping via row R1 is arranged in the overlapping region A1, and the outer via row R2 is arranged in the outer region A2. That is, in this embodiment, each thermal via 90 is arranged in either the overlapping region A1 or the outer region A2. Arranging the thermal vias 90 in the regions A1 and A2 does not affect the wiring resistance in the connection region A3. Therefore, heat generation in the pattern circuit 21a can be suppressed.

[0044] Specifically, a plurality of (four in the illustrated example) overlapping via rows R1 are arranged in the overlapping region A1 at intervals (e.g., equal intervals) in the second direction Y. A single outer via row R2 is arranged in each outer region A2. Heat generated by the switching element 81 (heat-generating element) is dissipated to the heat sink 30 from the thermal vias 90 (overlapping via row R1) arranged in the overlapping region A1 (see also FIG. 4A ). Heat generated by the switching element 81 (heat-generating element) is also dissipated to the heat sink 30 from the thermal vias 90 (outer via row R2) arranged in the outer region A2 via the pattern circuit 21a (see also FIG. 4A ).

[0045] The reason why a single (single row) outer via row R2 is arranged in each outer region A2, and not multiple (multiple rows) outer via rows R2, will be explained. When multiple outer via rows R2 spaced apart in the second direction Y are arranged in each outer region A2, it appears that heat generated by the switching element 81 (heat-generating element) flows to all of these outer via rows R2 via the pattern circuit 21a. However, as a result of heat transfer analysis using the finite element method, it was found that almost no heat flows to the outer via rows R2 other than the outer via row R2 closest to the switching element 81 (heat-generating element). Therefore, in this embodiment, by arranging a single (single row) outer via row R2 in each outer region A2, it is possible to simultaneously ensure heat dissipation efficiency, suppress the wiring resistance of the pattern circuit 21a, and reduce the size of the board 20.

[0046] As described above, when forming thermal vias 90 (via holes) in the substrate 20, for example, holes are first drilled in the substrate 20, and then copper plating is performed on the inner surfaces of the holes. If the same drill is used to drill all of the via holes, uneven diameters among the multiple via holes can be prevented. Meanwhile, the thickness of the copper plating layer PL tends to be uneven within a single via hole and among multiple via holes. The heat dissipation performance of each portion of each thermal via 90 is determined by the cross-sectional area (cross-sectional area intersecting the thickness direction Z) of the copper plating layer PL at that portion. Therefore, uneven thickness of the copper plating layer PL among portions of the thermal via 90 means uneven heat dissipation performance among these portions.

[0047] In light of this, in this embodiment, as shown in FIG. 4A , pattern circuits 21b-21f are arranged not only on the surface layer (outer layer La) of the substrate 20 on which the switching element 81 (heat-generating element) is mounted, but also on the other layers Lb-Lf. In a plan view, the pattern circuits 21a-21f at least partially overlap the switching element 81 (heat-generating element). More specifically, the pattern circuits 21a-21f may at least partially overlap the lead frames 81b and 81c in a plan view. Furthermore, all of the thermal vias 90 belonging to the via rows R1 and R2 are made into through-holes 91 (see also FIG. 4B ), and each through-hole 91 is connected to all of the pattern circuits 21a-21f. This prevents uneven heat dissipation performance in the thermal vias 90 and ensures stable heat dissipation performance. The number of pattern circuits 21a-21f on the substrate 20 can be changed as needed. In a plan view, the shape of the pattern circuits 21a-21f may be substantially identical to one another.

[0048] The lead frame 81c corresponding to the source has a smaller bonding surface area with respect to the pattern circuit 21a than the lead frame 81b corresponding to the drain (see FIG. 4B). Therefore, if a thermal via 90 is disposed in the lead frame 81c corresponding to the source, the pattern circuit 21a is likely to generate heat in that portion. Therefore, it is preferable to not dispose a thermal via 90 in the lead frame 81c corresponding to the source, but to dispose the thermal via 90 in the lead frame 81b corresponding to the drain. The term "bonding surface with respect to the pattern circuit 21a" refers to a surface of the lead frames 81b, 81c that is bonded directly to the pattern circuit 21a or the thermal via 90 or indirectly via solder SL or the like.

[0049] As described above, the rotating electric machine 1 according to this embodiment includes a substrate 20 on which a power circuit 80 for supplying power to a motor main body 10 is mounted, and a heat sink 30. The power circuit 80 includes a heat generating element (a switching element 81, a shunt resistor 82). The substrate 20 includes a pattern circuit 21a formed on a surface (an outer layer La) of the substrate 20 and joined to the heat generating element, and a plurality of thermal vias 90 connected to the pattern circuit 21a and in thermal contact with the heat sink 30. The pattern circuit 21a includes a joint 21A to which the heat generating element is joined and an extension 21B extending from the joint 21A in a first direction X. The pattern circuit 21a has a connection region A3 located outside the heat generating element in the first direction X but not outside the heat generating element in a second direction Y intersecting both the thickness direction Z of the substrate 20 and the first direction X. None of the thermal vias 90 are located in the connection region A3. This configuration improves heat dissipation efficiency.

[0050] The pattern circuit 21a also includes an overlapping region A1 that overlaps with the heat generating element when viewed from the thickness direction Z, and an outer region A2 that is located outside the heat generating element in the second direction Y, and the multiple thermal vias 90 are configured as an overlapping via row R1 in which the thermal vias 90 are aligned in the first direction X and arranged in the overlapping region A1, and an outer via row R2 in which the thermal vias 90 are aligned in the first direction X and arranged in the outer region A2, and the multiple overlapping via rows R1 that are spaced apart in the second direction Y are arranged in the overlapping region A1, and a single outer via row R2 is arranged in the outer region A2. This configuration makes it possible to ensure heat dissipation efficiency, suppress wiring resistance of the pattern circuit 21a, and reduce the size of the substrate 20 all at once.

[0051] The substrate 20 also has pattern circuits 21b to 21f (second pattern circuits) that are spaced apart from the pattern circuit 21a in the thickness direction Z that intersects the substrate 20, and the thermal vias 90 are connected to the pattern circuits 21b to 21f. This configuration allows stable heat dissipation performance to be obtained.

[0052] Embodiment 2 Next, embodiment 2 will be described, but the basic configuration is the same as embodiment 1. For this reason, the same components are given the same reference numerals and their description will be omitted, and only the differences will be described.

[0053] 6 is a diagram showing the arrangement of thermal vias 90 according to embodiment 2. As shown in FIG. 6 and FIG. 4B, this embodiment differs from embodiment 1 in the shape of the pattern circuit 21a and the arrangement of the thermal vias 90.

[0054] As shown in FIG. 6 , in the pattern circuit 21a according to this embodiment, not only the first portion P1 but also the second portion P2 include a joint portion 21A having a width greater than the width (dimension in the second direction Y) of the extension portion 21B. Furthermore, each outer region A2 included in the portions P1 and P2 includes an extension region A2a. The extension region A2a is located outward of the switching element 81 (heat-generating element) in the first direction X. At least one thermal via 90 (one in the illustrated example) is disposed in each extension region A2a. That is, each outer via row R2 includes at least one thermal via 90 (one in the illustrated example) disposed in the extension region A2a. This configuration can further suppress heat generation in the pattern circuit 21a.

[0055] Embodiment 3 Next, embodiment 3 will be described, but the basic configuration is the same as embodiment 1. For this reason, the same components are given the same reference numerals and their description will be omitted, and only the differences will be described.

[0056] 7 is a cross-sectional view showing a heat dissipation structure according to embodiment 3. As shown in FIG. 7 and FIG. 4A, this embodiment differs from embodiment 1 in the configuration of thermal vias 90.

[0057] 7, in this embodiment, non-penetrating via holes 92 are used as the thermal vias 90. Specifically, blind via holes 92a connecting layers La to Lb (pattern circuits 21a to 21b), buried via holes 92b connecting layers Lb to Le (pattern circuits 21b to 21e), and blind via holes 92a connecting layers Le to Lf (pattern circuits 21e to 21f) are used.

[0058] In this configuration, heat is dissipated from the switching elements 81 (heat generating elements) or the pattern circuit 21a to the heat sink 30 via the pattern circuits 21b to 21e of the inner layers Lb to Le. Therefore, the heat dissipation performance is reduced compared to a configuration using the through via holes 91. Therefore, it is preferable to increase the number of thermal vias 90 (blind via holes 92) compared to when the through via holes 91 are used.

[0059] On the other hand, in a configuration using through via holes 91, when the amount of solder SL increases when mounting a heat-generating element, there is a possibility that the solder SL will flow into the through via holes 91 and flow out to layer Lf. In contrast, because the non-through via holes 92 are filled with a filler (epoxy resin or glass filler), the problem of solder SL flowing into the thermal vias 90 does not occur. In light of this, it is preferable to configure all of the thermal vias 90 arranged in the overlapping region A1 (belonging to the overlapping via row R1) as non-through via holes 92, and all of the thermal vias 90 arranged in the outer region A2 (belonging to the outer via row R2) as through via holes 91. The non-through via holes 92 also have the advantage of making it easier to shorten the mounting pitch of electronic components.

[0060] In this specification, expressions using "roughly" also include cases where the meaning indicated by the words following "roughly" can be considered to be valid if manufacturing errors are removed.

[0061] The technical scope of the present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure.

[0062] In addition, the components in the above-described embodiments may be replaced with known components as appropriate without departing from the spirit of the present disclosure, and the above-described embodiments may be combined as appropriate. For example, the features of embodiment 2 may be combined with the features of embodiment 3. That is, in embodiment 2, all of the thermal vias 90 belonging to the overlapping via row R1 may be non-through via holes 92, and all of the thermal vias 90 belonging to the outer via row R2 may be through via holes 91.

[0063] DESCRIPTION OF SYMBOLS 1...Rotating electric machine 10...Motor body 20...Substrate 21a...Patterned circuit 21b to 21f...Patterned circuit (second patterned circuit) 21A...Joint portion 21B...Extended portion 81...Switching element (heat generating element) 82...Shunt resistor (heat generating element) 90...Thermal via 91...Through via hole 92...Blind via hole A1...Overlapping region A2...Outer region A2a...Extended region A3...Connection region R1...Overlapping via row R2...Outer via row X...First direction Y...Second direction Z...Thickness direction

Claims

1. A rotating electric machine comprising: a substrate on which a power circuit for supplying power to a motor body is mounted; and a heat sink, wherein the power circuit includes a heat generating element; the substrate has a pattern circuit formed on a surface of the substrate and joined to the heat generating element; and a plurality of thermal vias connected to the pattern circuit and in thermal contact with the heat sink; the pattern circuit has a joint portion to which the heat generating element is joined, and an extension portion extending from the joint portion in a first direction; the pattern circuit has a connection region located outside the heat generating element in the first direction, but not outside the heat generating element in a second direction intersecting both the thickness direction of the substrate and the first direction; and none of the plurality of thermal vias is located in the connection region.

2. A rotating electric machine as described in claim 1, wherein the pattern circuit includes an overlapping region that overlaps with the heat generating element when viewed from the thickness direction, and an outer region that is located outside the heat generating element in the second direction, and the plurality of thermal vias constitute an overlapping via row in which the thermal vias are aligned in the first direction and arranged in the overlapping region, and an outer via row in which the thermal vias are aligned in the first direction and arranged in the outer region, and the overlapping region has a plurality of overlapping via rows arranged at intervals in the second direction, and the outer region has a single outer via row.

3. The rotating electric machine according to claim 2, wherein all of the thermal vias belonging to the outer via row penetrate the substrate, and all of the thermal vias belonging to the overlapping via row penetrate the substrate.

4. The rotating electric machine according to claim 2, wherein all of the thermal vias belonging to the outer via row penetrate the substrate, and all of the thermal vias belonging to the overlapping via row do not penetrate the substrate.

5. A rotating electric machine according to any one of claims 2 to 4, wherein the outer region has an extension region located outside the heat generating element in the first direction, and the outer via row includes the thermal vias arranged in the extension region.

6. A rotating electric machine according to any one of claims 1 to 5, wherein the thermal via includes a cylindrical copper plating layer formed on the inner surface of a hole in the substrate.

7. A rotating electric machine according to any one of claims 1 to 6, wherein the substrate has a second pattern circuit arranged at a distance from the pattern circuit in a thickness direction intersecting the substrate, and the plurality of thermal vias are connected to the second pattern circuit.

8. A rotating electric machine according to any one of claims 1 to 7, used in an electric power steering device.

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