Heat dissipation base, semiconductor module, and energy conversion device

Abstract

According to the present invention, a wiring board is prevented from being damaged by deformation of a heat dissipation base to which the wiring board is joined. This heat dissipation base (3) has a first surface to which a wiring board (4) is joined and a second surface which faces a cooler (10), and the second surface has a convex curved surface that has a substantially rectangular shape having a side extending in a first direction and another side extending in a second direction when viewed in plan view. When the second surface is directed downward, a first curve representing the shape of the second surface on a first straight line passing through the center of the second surface and extending in the first direction, and a second curve representing the shape of the second surface on a second straight line passing through the center of the second surface and extending in the second direction are each represented by a curve which includes end parts and the shape change of which in a direction from the end parts toward the center has a downward convex shape, while a third curve representing the shape of the second surface on a straight line in a diagonal direction is represented by a curve which includes end parts and the shape change of which in a direction from the end parts toward the center has an upward convex shape, and a curve which includes the center and the shape change of which in a direction from the center toward the end parts has a downward convex shape.

Description

[Technical Field]

[0001] The present invention relates to a heat dissipation base, a semiconductor module, and an energy conversion device. [Background technology]

[0002] Among semiconductor devices used in power conversion devices such as inverter devices, there are those in which a heat dissipation base on which a wiring board, semiconductor elements, etc. are arranged is attached to a cooler. Some heat dissipation bases used in this type of semiconductor device are shaped so that a second surface facing the cooler, opposite to a first surface on which the wiring board, semiconductor elements, etc. are arranged, is convex (see, for example, Patent Documents 1 to 7). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-195717 [Patent Document 2] Japanese Patent Publication No. 2020-188152 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-167548 [Patent Document 4] International Publication No. 2012 / 108073 [Patent Document 5] Japanese Patent Application Laid-Open No. 2007-88045 [Patent Document 6] Japanese Patent Application Laid-Open No. 2005-39081 [Patent Document 7] U.S. Patent No. 7,511,961 Summary of the Invention [Problem to be solved by the invention]

[0004] A wiring board is bonded to the first surface of the heat dissipation base with a bonding material. When the heat dissipation base is molded so that the second surface is convex, the second surface deforms in a direction that changes from a convex curved surface to a flat surface when it is attached to the cooler. Therefore, deformation of the heat dissipation base applies deformation stress to the wiring board bonded to the first surface of the heat dissipation base with the bonding material, which can damage the wiring board.

[0005] In one aspect, the present invention aims to prevent damage to a wiring board due to deformation of a heat dissipation base to which the wiring board is bonded. [Means for solving the problem]

[0006] A heat dissipation base according to one embodiment has a first surface to which a wiring board is bonded and a second surface opposite the first surface and facing a cooler, wherein the second surface of the heat dissipation base is a convex curved surface and has a shape in a plan view that is approximately rectangular with a side extending in a first direction and a side extending in a second direction, and when the second surface is facing downward, a first curve representing the shape of the second surface on a first line that passes through the center of the second surface and extends in the first direction. a second curve representing the shape of the second surface on a second straight line passing through the center of the second surface and extending in the second direction, each of which includes the end and is represented by a downward convex curve in the direction from the end to the center, and a third curve representing the shape of the second surface on a diagonal line of the heat dissipation base, each of which includes the end and is represented by an upward convex curve in the direction from the end to the center, and which includes the center and is represented by a downward convex curve in the direction from the center to the end. [Effects of the Invention]

[0007] According to the above-described aspect, it is possible to prevent damage to the wiring board due to deformation of the heat dissipation base to which the wiring board is joined. [Brief explanation of the drawings]

[0008] [Figure 1]1 is a top view illustrating a configuration example of an energy conversion device according to an embodiment. [Figure 2] 2 is a cross-sectional side view showing an example of the internal configuration of the energy conversion device taken along line AA' in FIG. [Figure 3] 2 is a cross-sectional side view of the energy conversion device taken along line BB' in FIG. [Figure 4] FIG. 2 is a diagram illustrating an example of a circuit configuration of a semiconductor module. [Figure 5] 10A and 10B are bottom views illustrating examples of application patterns of thermally conductive material when the heat dissipation base is attached to the cooler. [Figure 6] 10A and 10B are diagrams illustrating the spreading of the thermally conductive material when the heat dissipation base is attached to the cooler. [Figure 7] 10A and 10B are diagrams illustrating an example of a problem that occurs when a heat dissipation base is attached to a cooler. [Figure 8] 10A and 10B are top views illustrating examples of shapes of a heat dissipation base according to an embodiment. [Figure 9] 9 is a graph illustrating the tendency of warpage in three directions in the heat dissipation base illustrated in FIG. 8. FIG. [Figure 10] 9 is a graph illustrating a specific example of warpage in the diagonal direction in the heat dissipation base illustrated in FIG. 8. FIG. [Figure 11] 9A and 9B are diagrams illustrating deformation of the heat dissipation base illustrated in FIG. 8 when the heat dissipation base is attached to a cooler. [Figure 12] 10A and 10B are diagrams providing supplementary information regarding the shape of a convex curved surface in a heat dissipation base according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The X, Y, and Z axes in each of the referenced figures are shown for the purpose of defining planes and directions in the illustrated energy conversion device, semiconductor module, and the like. The X, Y, and Z axes are orthogonal to each other and form a right-handed system. In the following description, the Z direction may be referred to as the up-down direction. A plane including the X and Y axes may be referred to as the XY plane, a plane including the Y and Z axes may be referred to as the YZ plane, and a plane including the Z and X axes may be referred to as the ZX plane. These directions and planes are terms used for convenience of explanation, and their correspondence with the X, Y, and Z directions may change depending on the mounting orientation of the energy conversion device, etc. For example, in this specification, a surface facing the positive side of the Z direction (+Z direction) of a component constituting the energy conversion device is referred to as the upper surface, and a surface facing the negative side of the Z direction (-Z direction) is referred to as the lower surface. However, a surface facing the negative side of the Z direction may also be referred to as the upper surface, and a surface facing the positive side of the Z direction may also be referred to as the lower surface. In this specification, a plan view refers to a view of the top or bottom surface (XY plane) of an energy conversion device or the like as seen from the Z direction.

[0010] The aspect ratios and relative sizes of components in each drawing are merely schematic representations and do not necessarily correspond to the relationships in an energy conversion device that is actually manufactured. For the sake of convenience, the relative sizes of components may be exaggerated. Furthermore, the shapes of the same components may differ between different drawings.

[0011] In the following description, an example of an energy conversion device according to the present disclosure will be a device applied to a power conversion device such as an inverter device for an industrial or automotive motor, and therefore, in the following description, detailed descriptions of configurations, functions, operations, assembly methods, etc. that are the same as or similar to those of known energy conversion devices will be omitted.

[0012] FIG. 1 is a top view showing an example of the configuration of an energy conversion device according to an embodiment. FIG. 2 is a cross-sectional side view showing an example of the internal configuration of the energy conversion device taken along line A-A' in FIG. 1. FIG. 3 is a cross-sectional side view of the energy conversion device taken along line B-B' in FIG. 1. FIG. 4 is a diagram showing an example of the configuration of a circuit of a semiconductor module. Note that FIG. 1 does not show a sealing material that seals a wiring board, semiconductor elements, etc. FIG. 2 schematically shows an example of the configuration of a portion of the energy conversion device taken along line A-A' in FIG. 1, located on the left side of the line A-A', as viewed from the right. FIG. 2 does not show hatching that indicates a cross section of the sealing material. FIG. 3 schematically shows an example of the configuration of a portion of the energy conversion device taken along line B-B' in FIG. 1, located on the left side of the line B-B', as viewed from the right.

[0013] The energy conversion device 1 illustrated in FIGS. 1 to 3 includes a semiconductor module 2 as a semiconductor device and a cooler 10. The semiconductor module 2 includes a heat dissipation base 3, a wiring board 4, semiconductor elements 5A and 5B, a plurality of bonding wires 7A to 7F, a case 8, and a sealing material 9. The cooler 10 includes fins 11 and a water jacket 12. The semiconductor module 2 is attached to the cooler 10 by screws 13 that are inserted into through holes in the heat dissipation base 3 and have male threads that screw into screw holes (female threads) provided on the upper surfaces 1110 of the fins 11 of the cooler 10. The heat dissipation base 3 of the semiconductor module 2 and the fins 11 of the cooler 10 are connected via a thermally conductive material 14 such as thermal grease or a thermal compound.

[0014] The semiconductor module 2 illustrated in FIGS. 1 to 3 constitutes a single-phase voltage-type half-bridge inverter circuit as illustrated in FIG. 4. A wiring board 4 is disposed on the upper surface of a heat dissipation base 3 in this type of semiconductor module 2. The wiring board 4 includes an insulating substrate 400, a first conductor pattern 401 and a second conductor pattern 402 provided on the upper surface (first surface) of the insulating substrate 400, and a third conductor pattern 403 provided on the lower surface (second surface) of the insulating substrate 400. The wiring board 4 may be, for example, a DCB (Direct Copper Bonding) substrate or an AMB (Active Metal Brazing) substrate. The wiring board 4 may also be called a laminated substrate or an insulating circuit board.

[0015] The insulating substrate 400 is not limited to a specific substrate. The insulating substrate 400 may be a ceramic substrate formed from a ceramic material such as aluminum oxide (Al2O3), aluminum nitride (AlN), silicon nitride (Si3N4), or a composite material of aluminum oxide (Al2O3) and zirconium oxide (ZrO2). The insulating substrate 400 may be, for example, a substrate formed from an insulating resin such as epoxy resin, a substrate formed by impregnating a base material such as glass fiber with an insulating resin, or a substrate formed by coating the surface of a flat metal core with an insulating resin.

[0016] The third conductor pattern 403 is a member that functions as a heat conduction member that conducts heat generated in the inverter circuit to the heat dissipation base 3, and is formed of, for example, a metal plate or metal foil such as copper or aluminum. The third conductor pattern 403 is joined to the heat dissipation base 3 by a joining material 21 such as solder. The third conductor pattern 403 may also be called a heat dissipation layer or a heat dissipation pattern.

[0017] The first conductor pattern 401 and the second conductor pattern 402 are members that function as wiring members in the inverter circuit, and are formed of, for example, a metal plate or metal foil made of copper, aluminum, etc. The first conductor pattern 401 and the second conductor pattern 402 may also be called a conductor layer, a conductor plate, a conductive layer, or a wiring pattern.

[0018] A first semiconductor element 5A is disposed on the first conductor pattern 401 and bonded to the first conductor pattern 401 with a bonding material (not shown). A second semiconductor element 5B is disposed on the second conductor pattern 402 and bonded to the second conductor pattern 402 with a bonding material 2122. The first semiconductor element 5A and the second semiconductor element 5B are bonded to the first conductor pattern 401 and the second conductor pattern 402, respectively, with a conductive bonding material such as solder.

[0019] Each of the first semiconductor element 5A and the second semiconductor element 5B is configured, for example, by an RC (Reverse Conducting)-IGBT element, which integrates an IGBT (Insulated Gate Bipolar Transistor) element serving as a switching element with a diode element such as an FWD (Free Wheeling Diode) element connected in anti-parallel to the switching element. The switching element and diode element in the semiconductor elements 5A and 5B are not limited to a Si substrate, but may be formed on a semiconductor substrate using a wide bandgap semiconductor such as SiC (Silicon Carbide) or GaN (Gallium Nitride). Each of these semiconductor elements 5A and 5B has a first main electrode (not shown) on its bottom surface and a second main electrode and a control electrode (gate electrode) (not shown) on its top surface. That is, the first conductor pattern 401 is electrically connected to the first main electrode of the first semiconductor element 5A by a conductive bonding material, and the second conductor pattern 402 is electrically connected to the first main electrode of the second semiconductor element 5B by a conductive bonding material 22.

[0020] A second main electrode provided on the upper surface of first semiconductor element 5A is electrically connected to output terminal 803 provided on case 8 by bonding wire 7A. A control electrode provided on the upper surface of first semiconductor element 5A is electrically connected to first control terminal 804 provided on case 8 by bonding wire 7C. First conductor pattern 401 electrically connected to the first main electrode provided on the lower surface of first semiconductor element 5A is electrically connected to first input terminal (P terminal) 801 provided on case 8 by bonding wire 7B. That is, the first main electrode of first semiconductor element 5A is electrically connected to first input terminal 801 provided on case 8 via the bonding material, first conductor pattern 401, and bonding wire 7B.

[0021] A second main electrode provided on the upper surface of the second semiconductor element 5B is electrically connected to a second input terminal (N terminal) 802 provided on the case 8 by a bonding wire 7D. A control electrode provided on the upper surface of the second semiconductor element 5B is electrically connected to a second control terminal 805 provided on the case 8 by a bonding wire 7F. A second conductor pattern 402 electrically connected to a first main electrode provided on the lower surface of the second semiconductor element 5B is electrically connected to an output terminal 803 provided on the case 8 by a bonding wire 7E. That is, the first main electrode of the second semiconductor element 5B is electrically connected to the output terminal 803 provided on the case 8 via the bonding material 22, the second conductor pattern 402, and the bonding wire 7E.

[0022] The first input terminal 801, the second input terminal 802, the output terminal 803, the first control terminal 804, and the second control terminal 805 are provided integrally with an insulating member 800 of the case 8. The insulating member 800 has openings on the top and bottom, and has a hollow portion capable of accommodating the wiring board 4, semiconductor elements 5A and 5B, bonding wires 7A to 7F, and the like, which are arranged on the top surface of the heat dissipation base 3. The insulating member 800 is formed using an insulating resin material such as PPS (Poly Phenylene Sulfide) or PA (Poly Amide). The first input terminal 801, the second input terminal 802, the output terminal 803, the first control terminal 804, and the second control terminal 805 are formed using, for example, a metal plate such as a copper plate, and are integrated with the insulating member 800 by, for example, insert molding.

[0023] The first input terminal 801, the second input terminal 802, and the output terminal 803 are bent so that the portions protruding from the upper surface of the insulating member 800 extend along the upper surface of the insulating member 800. On the upper surface of the insulating member 800, in an area overlapping with the first input terminal 801, in an area overlapping with the second input terminal 802, and in an area overlapping with the output terminal 803, a receiving portion (not shown) capable of receiving a nut 15 with the axis of the screw hole oriented in the vertical direction is provided. The first input terminal 801, the second input terminal 802, and the output terminal 803 are each provided with a through hole (not shown) that allows a threaded fastener such as a bolt to be screwed onto the nut 15 received in the receiving portion of the insulating member 800.

[0024] One end of each of the first input terminal 801, the second input terminal 802, the output terminal 803, the first control terminal 804, and the second control terminal 805 is exposed on the inner circumferential surface that defines the hollow portion of the insulating member 800. One end of each of the bonding wires 7A to 7F is electrically connected to the part of the corresponding terminal that is exposed on the inner circumferential surface of the insulating member 800.

[0025] The case 8 is attached to the heat dissipation base 3 by adhering the bottom surface of the insulating member 800 to the top surface of the heat dissipation base 3. The adhesive 16 that adheres the insulating member 800 to the heat dissipation base 3 may be, for example, an epoxy-based or silicone-based adhesive. The wiring board 4, semiconductor elements 5A and 5B, and bonding wires 7A to 7F arranged on the top surface of the heat dissipation base 3 are located in a recessed space defined by the heat dissipation base 3 and the insulating member 800 of the case 8, and are sealed by the sealing material 9 that fills the recessed space. The sealing material 9 may be, for example, epoxy resin, silicone gel, etc.

[0026] As shown in FIG. 1 , the heat dissipation base 3 is a plate-like member having a generally rectangular shape with rounded corners in a plan view, with through-holes (not shown) formed at the corners through which the shafts of the screws 13 can be inserted. The heat dissipation base 3 functions as a heat-conducting member that conducts heat generated by the semiconductor elements 5A and 5B to the cooler 10, and is formed of a metal plate such as a copper plate or an aluminum plate. The heat dissipation base 3 is formed by warping a flat metal plate, for example, by pressing or the like, so that the lower surface 301 has a convex curved surface. The corners of the insulating member 800 of the case 8 are cut off so as not to overlap with the through-holes of the heat dissipation base 3 in a plan view (more specifically, so that the screws 13 can be threaded into the threaded holes of the fins 11).

[0027] As described above, the semiconductor module 2 described above with reference to FIGS. 1 to 3 configures a single-phase voltage-type half-bridge inverter circuit (hereinafter referred to as a "half-bridge inverter circuit") as illustrated in FIG. 4. The half-bridge inverter circuit includes a switching element 503 and a diode element 504 connected between a first input terminal IN(P) and an output terminal OUT, and a switching element 505 and a diode element 506 connected between a second input terminal IN(N) and an output terminal OUT. The section between the first input terminal IN(P) and the output terminal OUT may be referred to as an upper arm, and the section between the second input terminal IN(N) and the output terminal OUT may be referred to as a lower arm. In the semiconductor module 2 described above with reference to FIGS. 1 to 3, the switching element 503 and the diode element 504 of the upper arm are formed in a first semiconductor element 5A, and the switching element 505 and the diode element 506 of the lower arm are formed in a second semiconductor element 5B.

[0028] When the switching elements 503 and 505 are IGBT elements, the first main electrodes on the lower surfaces of the first semiconductor element 5A and the second semiconductor element 5B are called collector electrodes, and the second main electrodes on the upper surfaces are called emitter electrodes. The collector electrode of the upper-arm switching element 503 is connected to a first input terminal IN(P), which may be a first input terminal 801, and the emitter electrode of the lower-arm switching element 505 is connected to a second input terminal IN(N), which may be a second input terminal 802. The first input terminal IN(P) and the second input terminal IN(N) are connected to the positive and negative poles of a DC power supply, respectively. The emitter electrode of the upper-arm switching element 503 and the collector electrode of the lower-arm switching element 505 are connected to an output terminal OUT, which may be an output terminal 803. The gates of the switching elements 503 and 505 are connected to a control circuit (not shown) via a first control terminal 804 and a second control terminal 805, respectively.

[0029] The half-bridge inverter circuit illustrated in Fig. 4 can convert direct current between the first input terminal IN(P) and the second input terminal IN(N) into alternating current and output it from the output terminal OUT by a control signal applied to the gate of the switching element 503 of the upper arm and a control signal applied to the gate of the switching element 505 of the lower arm. Also, by connecting three half-bridge inverter circuits illustrated in Fig. 4 in parallel between the first input terminal IN(P) and the second input terminal IN(N) and controlling the control signals applied to each circuit, a three-phase alternating current inverter circuit can be formed.

[0030] The semiconductor module 2 including the half-bridge inverter circuit described above with reference to FIG. 4 is not limited to the configuration described above with reference to FIGS. 1 to 3. The switching elements 503 and 505 may be configured, for example, as power metal oxide semiconductor field effect transistors (MOSFETs) or bipolar junction transistors (BJTs). When the switching elements are MOSFETs, the main electrodes on the lower surfaces of the semiconductor elements 5A and 5B may be referred to as drain electrodes, and the main electrodes on the upper surfaces may be referred to as source electrodes. The diode elements 504 and 506 may be configured, for example, as Schottky barrier diodes (SBDs), junction barrier Schottky diodes (JBSs), merged pn Schottky diodes (MPSs), or pn diodes. The substrates on which the switching elements 503 and 505 and the diode elements 504 and 506 are formed are not limited to Si substrates, and may be substrates using wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN).

[0031] Furthermore, in the semiconductor module 2, for example, the switching element 503 and the diode element 504 of the upper arm and the switching element 505 and the diode element 506 of the lower arm may each be separate semiconductor elements. For example, the switching element 503 and the diode element 504 of the upper arm are not limited to being formed on a single semiconductor substrate (single semiconductor chip), but may be formed from one or more semiconductor elements (one or more semiconductor chips) on which the switching element 503 is formed and one or more semiconductor elements (one or more semiconductor chips) on which the diode element 504 is formed. The shape, number, and location of the semiconductor elements may be changed as appropriate. The layout of the conductor pattern serving as the wiring member provided on the upper surface of the wiring board 4 may be changed depending on the type, shape, number, and location of the semiconductor elements to be mounted. Furthermore, some or all of the bonding wires 7A to 7F in the semiconductor module 2 described above may be replaced with leads formed by processing a metal plate such as a copper plate.

[0032] Furthermore, the control electrodes provided on the upper surfaces of the semiconductor elements 5A and 5B may include gate electrodes and auxiliary electrodes. For example, the auxiliary electrodes may be auxiliary emitter electrodes or auxiliary source electrodes that are electrically connected to the main electrodes on the upper surfaces and serve as a reference potential for the gate potential. The auxiliary electrodes may also be temperature sensing electrodes that are electrically connected to a temperature sensing unit that may be included in an inverter device or the like having the semiconductor module 2 and measure the temperatures of the semiconductor elements 5A and 5B. These electrodes (main electrodes and control electrodes including gate electrodes and auxiliary electrodes) formed on the upper surfaces of the semiconductor elements 5A and 5B may be collectively referred to as upper surface electrodes.

[0033] The circuit configuration of the semiconductor module 2 is not limited to the half-bridge inverter circuit described above with reference to Fig. 4. The inverter circuit of the semiconductor module 2 may be, for example, a single-phase full-bridge inverter circuit. Furthermore, the inverter circuit in one semiconductor module 2 is not limited to a single-phase inverter circuit, and may be, for example, a three-phase AC inverter circuit as described above.

[0034] The cooler 10 attached to the semiconductor module 2 described above with reference to FIGS. 1 to 3 includes fins 11 and a water jacket 12. The fins 11 include a base 1101 having an upper surface 1110 on which the semiconductor module 2 is attached, and a plurality of fins 1102 extending downward from the lower surface of the base 1101. When attached to the fins 11, the water jacket 12 is shaped to define a coolant flow path in which the fins 1102 are arranged. The energy conversion device 1 of this embodiment conducts and dissipates a portion of the heat generated by the semiconductor elements 5A and 5B during operation of the semiconductor module 2 to the cooler 10 via the wiring board 4 and the heat dissipation base 3. In this type of energy conversion device 1, the heat can be efficiently conducted from the heat dissipation base 3 to the cooler 10 (fins 11) by improving the adhesion between the heat dissipation base 3 and the fins 11 using a thermally conductive material 14 such as thermal grease.

[0035] Fig. 5 is a bottom view illustrating an example of a pattern of application of the thermally conductive material when the heat dissipation base is attached to the cooler. Fig. 6 is a diagram illustrating the spreading of the thermally conductive material when the heat dissipation base is attached to the cooler. Fig. 7 is a diagram illustrating an example of a problem that occurs when the heat dissipation base is attached to the cooler. Note that the fin portion 1102 of the fin 11 is omitted in Figs. 6 and 7.

[0036] When using a thermally conductive material 14 such as thermal grease to improve the adhesion between the heat dissipation base 3 and the fins 11, for example, as shown in FIGS. 5 and 6A, a plurality of thermally conductive materials 14 are arranged in a predetermined pattern on the underside 301 of the heat dissipation base 3. The heat dissipation base 3 has a rectangular shape in plan view with rounded corners, and through-holes 303 for inserting screws 13 are formed in the corners. The heat dissipation base 3 is formed, for example, by warping a flat metal plate by press working or the like so that the underside 301 has a convex curve. The underside 301 of the heat dissipation base 3 shown in FIGS. 6A to 6C is a curved surface in which the center of the underside 301 is the apex in plan view, and the change in the relative position of each point on the underside 301 in the Z direction with respect to the center is represented by a downwardly convex curve.

[0037] The plurality of thermally conductive materials 14 are arranged on the lower surface 301 of the heat dissipation base 3 excluding the areas around the through holes 303. The arrangement pattern of the plurality of thermally conductive materials 14 is not limited to the pattern in which materials of the same shape and size are aligned as illustrated in FIG. 5. The plurality of thermally conductive materials 14 arranged on the lower surface 301 of the heat dissipation base 3 may have, for example, a plurality of different shapes, or may have the same shape and a plurality of different sizes. The arrangement pattern of the plurality of thermally conductive materials 14 may vary depending on, for example, the distance from the center of the lower surface 301 of the heat dissipation base 3 in a plan view.

[0038] When the lower surface 301 of the heat dissipation base 3 is placed on the fins 11 facing the upper surfaces 1110 of the fins 11, the thermally conductive material 14 placed at the center and its periphery of the lower surface 301 first comes into contact with the upper surfaces 1110 of the fins 11, as shown in FIG. 6A. Then, for example, when the heat dissipation base 3 is pressed against the upper surfaces 1110 of the fins 11, the thermally conductive material 14 in contact with the fins 11 is integrated between the lower surface 301 of the heat dissipation base 3 and the upper surfaces 1110 of the fins 11 while spreading radially outward from the center of the lower surface 301, as shown in FIG. 6B and FIG. 6C. In this case, if the lower surface 301 of the heat dissipation base 3 is made a convex curved surface, the thermally conductive material 14 will be more likely to spread radially outward from the center of the lower surface 301 of the heat dissipation base 3, and voids will be less likely to occur within the integrated thermally conductive material 14.

[0039] However, when the heat dissipation base 3 is attached to the fins 11 of the cooler 10, the wiring board 4 is joined to the upper surface 302 of the heat dissipation base 3, as illustrated in Figures 6A to 6C. Furthermore, when attaching the heat dissipation base 3 to the fins 11 of the cooler 10, the heat conductive material 14 is spread between the heat dissipation base 3 and the fins 11, and then the heat dissipation base 3 is fixed to the fins 11 using the screws 13.

[0040] 7 is a schematic diagram showing deformation of heat dissipation base 30 used in a conventional semiconductor device (semiconductor module) when the heat dissipation base 30 is attached to fins 11 of a cooler 10. When the lower surface 301 of the conventional heat dissipation base 30 faces downward, the shape of the lower surface 301 as viewed on a diagonal line passing through through-holes 303 for screwing is represented by a downwardly convex curve.

[0041] When the lower surface 301 of the heat dissipation base 30 has through-holes 303 at the corners thereof, when the screws 13 inserted through the through-holes 303 are threaded into the screw holes 1111 in the upper surface 1110 of the fins 11, the heat dissipation base 30 deforms from the convex curved surface of the lower surface 301 (the curved surface represented by the curved solid line) to a nearly flat curved surface with a small curvature (the curved surface represented by the curved two-dot chain line), as illustrated in FIG. 7 . That is, when the heat dissipation base 30 is attached to the fins 11 with the screws 13, the heat dissipation base 30 deforms in a direction that reduces warping compared to before attachment. When the heat dissipation base 30 deforms in a direction that reduces warping, a deformation stress is applied to the wiring board 4 bonded to the upper surface 302 of the heat dissipation base 30, causing damage to the wiring board 4, such as cracking of the insulating substrate 400 or peeling of the conductor patterns 401 to 403 from the insulating substrate 400. Such damage to the wiring board 4 is likely to occur when the area of ​​the lower surface 301 of the heat dissipation base 30 is large, the wiring board 4 is positioned close to the through hole 303, and the through hole 303 for inserting the screw 13 is formed in the corner of the lower surface 301.

[0042] Fig. 8 is a top view illustrating an example of the shape of a heat dissipation base according to an embodiment. Fig. 9 is a graph illustrating the tendency of warpage in three directions in the heat dissipation base illustrated in Fig. 8. Fig. 10 is a graph illustrating a specific example of warpage in the diagonal direction in the heat dissipation base illustrated in Fig. 8. Fig. 11 is a diagram illustrating deformation of the heat dissipation base illustrated in Fig. 8 when the heat dissipation base is attached to a cooler.

[0043] FIG. 8 illustrates the definitions of parameters used to describe the shape of the heat dissipation base 3 according to this embodiment. The convex curved shape of the lower surface 301 of the heat dissipation base 3 according to this embodiment can be described by a curve representing the shape of the lower surface 301 as viewed on a line S1 in the longitudinal direction (X direction), a curve representing the shape of the lower surface 301 as viewed on a line S2 in the lateral direction (Y direction), and a curve representing the shape of the lower surface 301 as viewed on a line S3 in the diagonal direction (D direction), all of which pass through the center P of the lower surface 301 in a plan view. The heat dissipation base 3 illustrated in FIG. 8 has a longitudinal dimension Lx (mm), a lateral dimension Ly (mm), and a diagonal dimension Ld (mm). For ease of explanation, the lower surface 301 of the heat dissipation base 3 is assumed to be a convex curved surface with the center P as a vertex in a plan view.

[0044] In the graph of FIG. 9, curve R1 indicates the shape of the lower surface 301 as viewed on a straight line S1 in the longitudinal direction (X direction) of the heat dissipation base 3 illustrated in FIG. 8, and curve R2 indicates the shape of the lower surface 301 as viewed on a straight line S2 in the lateral direction (Y direction) of the heat dissipation base 3 illustrated in FIG. 8. In the graph of FIG. 9, curve R3 indicates the shape of the lower surface 301 as viewed on a straight line S3 in the diagonal direction (D direction) of the heat dissipation base 3 illustrated in FIG. 8. The shape of the lower surface 301 indicated by straight line S3 includes the opening ends of the through holes 303 on the lower surface 301 side. In the graph of FIG. 9, the horizontal axis indicates the distance from the center P of the lower surface 301, with positive values ​​indicating the distance to the part located on the positive side of the center P in each of the X direction, Y direction, and D direction, and negative values ​​indicating the distance to the part located on the negative side of the center P. In the graph of FIG. 9, the vertical axis represents the relative position of each point in the Z direction with respect to the position of the center P in the Z direction when the lower surface 301 of the heat dissipation base 3 faces downward (negative side in the Z direction).

[0045] The lower surface 301 of the heat dissipation base 3 of this embodiment is represented as a downward convex curve as a whole, such that the relative position in the Z direction of each point on a straight line S1 in the longitudinal direction (X direction) passing through the center P is represented by a curve R1. On the straight line S1, the relative position in the Z direction from the end point of the straight line S1 toward the center P, including the end point (end point), and the relative position in the Z direction from the center P toward the end point, including the center P, both change as represented by a downward convex curve. Similarly, the lower surface 301 of the heat dissipation base 3 of this embodiment is represented as a downward convex curve as a whole, such that the relative position in the Z direction of each point on a straight line S2 in the lateral direction (Y direction) passing through the center P is represented by a curve R2. On the straight line S2, the relative position in the Z direction from the end point of the straight line S2 toward the center P, including the end point (end point), and the relative position in the Z direction from the center P toward the end point, including the center P, both change as represented by a downward convex curve.

[0046] In contrast, the lower surface 301 of the heat dissipation base 3 of this embodiment has a section where the relative position in the Z direction of each point on a straight line S3 in the diagonal direction (direction D) passing through the center P changes as represented by a curve R3, and a section where the relative position changes as represented by a curve convex downward and a curve convex upward. On the straight line S3, the relative position in the Z direction from the end point toward the center P, including the end point (end point) of the straight line S3, changes as represented by a curve convex upward, and the relative position in the Z direction from the center P toward the end point, including the center P, changes as represented by a curve convex downward. Specifically, the section where the distance Lp from the center is Li > Lp > -Li changes as represented by a curve convex downward, and the section where Lp > Li changes as represented by a curve convex upward. That is, the curve R3 has an inflection point Q at distances -Li and Li from the center P.

[0047] The distances -Li and Li associated with the position of the inflection point Q are set, for example, between the minimum value Lk1 and the maximum value Lk2 of the distance from the center of the screw-use through-hole 303 formed at the corner of the heat dissipation base 3. The minimum value Lk1 and the maximum value Lk2 of the distance are set, for example, based on the longitudinal dimension Lx and the lateral dimension Ly of the heat dissipation base 3, as well as the diameter of the screw-use through-hole 303. If the longitudinal dimension Lx and the lateral dimension Ly of the heat dissipation base 3 are Lx = approximately 120 mm and Ly = approximately 60 mm, respectively, and the diameter of the screw-use through-hole 303 is approximately 5 mm, the minimum value Lk1 and the maximum value Lk2 of the distance can be set, for example, to Lk1 = 5 mm and Lk2 = 20 mm.

[0048] In the curve R3 shown in Fig. 9, it is desirable that the downward convex curve and the upward convex curve that share an inflection point Q as a boundary are arranged so that the tangent to the upward convex curve at the position of the inflection point Q coincides with the tangent T to the downward convex curve, as shown in Fig. 10. By doing so, it is possible to make the relative position in the Z direction at each point in the end section from the end point on the diagonal line S3 to the nearest inflection point Q smaller than the relative position when the change in relative position in the Z direction in the central section between the two inflection points Q is extended to the end section (the relative position shown by the dotted line in Fig. 10).

[0049] If the change in the convex curve in the diagonal direction (direction D) of the heat dissipation base 3 satisfies the above-mentioned condition (condition of curve R3), the distance Li from the center is approximately 48 mm, and the relative position in the Z direction at the distance Li is 160 μm, the relative position in the Z direction at the end of the diagonal direction can be, for example, approximately 240 μm. On the other hand, if the change in the relative position in the Z direction in the diagonal direction is limited to a downwardly convex curve without inflection point Q, similar to the change in the longitudinal direction and the change in the lateral direction, the change in the relative position in the Z direction at the end section will be the change shown by the dotted line in Figure 10. In this case, the relative position in the Z direction at the end of the diagonal direction will be, for example, approximately 310 μm.

[0050] In this way, by making the convex curved surface of the lower surface 301 of the heat dissipation base 3 into the shape described above with reference to Figures 8 to 10, it is possible to reduce the amount of deformation in the direction that reduces the warping of the heat dissipation base 3 that occurs when the heat dissipation base 3 is attached to the cooler 10 (fins 11).

[0051] That is, when the heat dissipation base 3 of this embodiment is attached to the fins 11 of the cooler 10, as shown in Fig. 11, the distance in the Z direction from the corner of the heat dissipation base 3 to the upper surface 1110 of the fin 11 can be made shorter than that in the case of the heat dissipation base 30 (see Fig. 7) whose curved surface is represented by a downwardly convex curve extending to the end indicated by the dotted line. Therefore, the amount of deformation of the heat dissipation base 3 caused when the screws 13 are inserted into the through holes 303 of the heat dissipation base 3 and screwed into the screw holes 1111 of the fins 11 can be made smaller than that of the conventional heat dissipation base 30 described above with reference to Fig. 7. Therefore, by using the heat dissipation base 3 of this embodiment, the deformation stress caused in the wiring board 4 due to the deformation of the heat dissipation base 3 when the heat dissipation base 3 is attached to the fins 11 can be made smaller, and damage to the wiring board 4 due to the deformation stress can be prevented.

[0052] 10, heat dissipation base 3 of the present embodiment can smoothly change lower surface 301 from a downwardly convex curved surface to an upwardly convex curved surface at inflection point Q, which occurs when viewed on diagonal line S3. By smoothly changing the curve of lower surface 301 at inflection point Q in this way, stress concentration at inflection point Q is less likely to occur and deformation stress in wiring board 4 due to deformation of heat dissipation base 3 can be more easily reduced than, for example, when bending is performed in which the tangent line changes discontinuously around inflection point Q.

[0053] FIG. 12 is a diagram providing additional information regarding the shape of the convex curved surface of the heat dissipation base according to one embodiment.

[0054] As an example of the shape of the lower surface 301 on the diagonal line S3 of the heat dissipation base 3 of this embodiment, the curve R3 shown in FIGS. 9 and 10 represents the shape of the lower surface 301 before the wiring board 4 is bonded to the upper surface 302 of the heat dissipation base 3. When the wiring board 4 is bonded to the upper surface of the heat dissipation base 3 of this embodiment, the relative position in the Z direction at each point on the diagonal line S3 may change, for example, as represented by the curve R4 shown in FIG. 12. Like the curve R3, the curve R4 has a section where the relative position in the Z direction changes as represented by a downward convex curve and a section where the relative position in the Z direction changes as represented by an upward convex curve. The curve R4 has two end sections, including the end points of the curve R4, divided by the distances -Li and Li, where the relative position in the Z direction in the direction from the end points toward the center P changes as represented only by an upward convex curve, and a central section located between the two end sections. The change in relative position in the Z direction in the central section of curve R4 differs from the change in the central section of curve R3 and includes a section represented by a downwardly convex curve and a section represented by an upwardly convex curve.

[0055] Furthermore, although explanations with reference to the figures are omitted, when the wiring board 4 is joined to the heat dissipation base 3, the relative positions in the Z direction at each point on a longitudinal line passing through the center of the lower surface 301, and the relative positions in the Z direction at each point on a short-side line, can also be represented by a curve having a section represented by a downward convex curve, such as the central section of curve R4, and a section represented by an upward convex curve.

[0056] However, even when the central section has a section represented by a downwardly convex curve and a section represented by an upwardly convex curve, the change in relative position in the Z direction, including the end points (ends) and in the direction from the end points toward the center, will be the change described with reference to Figures 9 and 10. Therefore, even when the central section has a section represented by a downwardly convex curve and a section represented by an upwardly convex curve, the amount of deformation that occurs when the heat dissipation base 3 is attached to the cooler 10 (fins 11) can be reduced.

[0057] As described above, the heat dissipation base 3 according to this embodiment has a convexly curved lower surface 301 that faces the fins 11 of the cooler 10, and the shape of the lower surface 301 along the longitudinal line S1 passing through the center P of the lower surface 301 and along the lateral line S2 include the ends and are represented by a downwardly convex curve that changes from the ends toward the center P, while the shape of the lower surface 301 along the diagonal line S3 includes the ends and is represented by an upwardly convex curve. Therefore, the heat dissipation base 3 according to this embodiment can reduce the amount of deformation when attached to the fins 11, and can reduce deformation stress generated in the wiring board 4 bonded to the upper surface of the heat dissipation base 3, compared to the heat dissipation base 30 (see FIG. 7 ) in which the shape of the lower surface 301 along the diagonal line S3 also includes the ends and is represented by a downwardly convex curve that changes from the ends toward the center P. Therefore, in the energy conversion device 1 using the heat dissipation base 3 according to this embodiment, damage to the wiring board 4 due to deformation stress can be prevented, and failure of the energy conversion device 1 (semiconductor module 2) can be prevented.

[0058] The embodiments of the heat dissipation base 3 and the energy conversion device 1 according to the present invention are not limited to the above-described embodiments, and may be variously changed, substituted, or modified without departing from the spirit of the technical idea. Furthermore, if the technical idea can be realized in a different way due to technological advances or derived other technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea.

[0059] For example, the heat dissipation base 3 according to the above-described embodiment has a flat base plate warped by press processing or the like to form a convexly curved lower surface 301, and a concavely curved upper surface 302 to which the wiring board 4 is bonded. However, the heat dissipation base 3 according to the present invention is not limited to such a shape. For example, the heat dissipation base 3 according to the present invention may have a convexly curved lower surface 301 facing the fins 11 of the cooler 10, and a flat upper surface 302 to which the wiring board 4 is bonded. Furthermore, the position of the apex of the convexly curved lower surface 301 of the heat dissipation base 3 does not have to be at the center of the lower surface 301 in a plan view, but may be off-center. Furthermore, the number of wiring boards 4 bonded to one heat dissipation base 3 may be two or more. Furthermore, it is desirable that the inflection point Q of the heat dissipation base 3 be located outside the area to which the wiring board 4 is bonded in a plan view, from the viewpoint of preventing the wiring board 4 from cracking, for example, starting from the inflection point Q when fastened with screws. However, for example, as illustrated in Fig. 8, some of the inflection points Q distributed in a curved line on the lower surface 301 of the heatsink base 3 may be located inside the region of the heatsink base 3 where the wiring board 4 is bonded. Furthermore, the through holes 303 for screwing in the heatsink base 3 may be formed in the middle of the longitudinal end edges, in addition to the corners of the lower surface 301. Furthermore, the shape of the heatsink base 3 in plan view is not limited to the roughly rectangular planar shape with the sides extending in the X direction and the Y direction having different lengths as described above with reference to Fig. 8, but may also be a roughly square planar shape with the sides extending in the X direction and the Y direction having approximately the same lengths.

[0060] The features of the above-described embodiment will be summarized below.

[0061] The heat dissipation base according to the above-described embodiment has a first surface to which a wiring board is bonded and a second surface opposite to the first surface and facing a cooler, and the second surface of the heat dissipation base is a convex curved surface and has a shape in a plan view that is approximately rectangular having a side extending in a first direction and a side extending in a second direction, and when the second surface is facing downward, the shape of the second surface is represented on a first straight line that passes through the center of the second surface and extends in the first direction. A first curve representing the shape of the second surface on a diagonal line extending in the second direction and a second curve representing the shape of the second surface on a diagonal line extending in the second direction are each represented by a curve that is convex downwards, with the shape including the end portion and changing from the end portion to the center, and a third curve representing the shape of the second surface on a diagonal line are each represented by a curve that is convex upwards, with the shape including the center and changing from the center to the end portion being represented by a curve that is convex downwards.

[0062] The heat dissipation base according to the above embodiment has a through hole formed at a corner of the second surface in a plan view, through which a male screw for attaching the heat dissipation base to the cooler can be inserted.

[0063] In the heat dissipation base of the above embodiment, the third curve representing the shape of the second surface on the diagonal straight line has an inflection point at a position closer to the center than the through hole, and the section of the third curve between the end and the inflection point is an upward convex curve.

[0064] In the heat dissipation base according to the above embodiment, the inflection point is located outside the area where the wiring board is bonded.

[0065] In the heat dissipation base according to the above embodiment, the inflection point is located at a distance from the center of the through hole within a range of 5 mm to 20 mm.

[0066] In the heat dissipation base according to the above embodiment, the first surface is a concave curved surface corresponding to the convex curved surface of the second surface.

[0067] In the heat dissipation base of the above embodiment, the third curve representing the shape of the second surface on the diagonal straight line includes the end portions, and has two end sections in which the change in shape from the end portions toward the center is represented by the upward convex curve, and a central section located between the two end portions, and has a subsection within the central section represented by an upward convex curve.

[0068] In the heat dissipation base according to the above embodiment, the length of the side extending in the first direction is different from the length of the side extending in the second direction.

[0069] The semiconductor module of the above embodiment comprises a heat dissipation base of the above embodiment, a wiring board joined to the first surface of the heat dissipation base, and a semiconductor element arranged on the upper surface of the wiring board.

[0070] The energy conversion device according to the above embodiment comprises a semiconductor module according to the above embodiment, a cooler arranged facing the second surface of the heat dissipation base and attached to the heat dissipation base, and a thermally conductive material filled between the heat dissipation base and the cooler. [Industrial Applicability]

[0071] As described above, the present invention has the effect of preventing damage to the wiring board due to deformation of the heat dissipation base when the heat dissipation base to which the wiring board is bonded is attached to a cooler, and is particularly useful for inverter devices for industrial or electrical equipment.

[0072] This application is based on Japanese Patent Application No. 2023-038214, filed on March 13, 2023, the contents of which are incorporated herein in their entirety. [Explanation of symbols]

[0073] 1 Energy conversion device 2. Semiconductor Module 3 Heat dissipation base 301 Bottom surface 302 Top surface 303 Through Hole 4 Wiring board 400 insulating substrate 401, 402, 403 Conductor patterns 5A, 5B Semiconductor elements 7A~7F Bonding Wire 8 cases 800 Insulating materials 801, 802 input terminals 803 output terminal 804, 805 control terminals 9. Encapsulating materials 10 Cooler 11 Finn 1110 Top surface 1111 screw hole 12 Water Jacket 13 Screws 14 Thermal Conductive Materials 15 Nut 16 Adhesive

Claims

1. a heat dissipation base having a first surface to which a wiring board is bonded and a second surface opposite to the first surface and facing a cooler, The second surface of the heat dissipation base is a convex curved surface, and has a generally rectangular shape in a plan view having a side extending in a first direction and a side extending in a second direction, and when the second surface is facing downward, a first curve representing the shape of the second surface on a first straight line passing through the center of the second surface and extending in the first direction, and a second curve representing the shape of the second surface on a second straight line passing through the center of the second surface and extending in the second direction, each of which includes an end portion and in which the change in shape in a direction from the end portion to the center is represented by a downwardly convex curve, a third curve representing the shape of the second surface on a diagonal line of the heat dissipation base includes an end portion, and a change in shape from the end portion toward the center is represented by an upward convex curve, and includes the center, and a change in shape from the center toward the end portion is represented by a downward convex curve; Heat dissipation base.

2. The heat dissipation base according to claim 1 , wherein a through hole is formed at a corner of the second surface in a plan view, and through which a male screw for attaching the heat dissipation base to the cooler can be inserted.

3. The heat dissipation base of claim 2, wherein the third curve representing the shape of the second surface on the diagonal line has an inflection point at a position closer to the center than the through hole, and the section of the third curve between the end and the inflection point is an upward convex curve.

4. The heat dissipation base according to claim 3 , wherein the inflection point is outside the area where the wiring board is bonded.

5. The heat dissipation base according to claim 3 , wherein the inflection point is located at a distance from the center of the through hole within a range of 5 mm to 20 mm.

6. The heat dissipation base according to claim 1 , wherein the first surface has a concave curved surface that corresponds to the convex curved surface of the second surface when the second surface faces downward.

7. 2. The heat dissipation base according to claim 1, wherein the third curve representing the shape of the second surface on the diagonal line includes the end portion, and has two end sections in which the change in shape from the end portion toward the center is represented by the upward convex curve, and a central section located between the two end sections, and the central section has a partial section represented by an upward convex curve.

8. The heat dissipation base according to claim 1 , wherein the length of the side extending in the first direction is different from the length of the side extending in the second direction.

9. A heat dissipation base according to any one of claims 1 to 8; a wiring board joined to the first surface of the heat dissipation base; a semiconductor element disposed on an upper surface of the wiring board; A semiconductor module comprising:

10. The semiconductor module according to claim 9 ; the cooler disposed opposite the second surface of the heat dissipation base and attached to the heat dissipation base; a thermally conductive material filled between the heat dissipation base and the cooler; An energy conversion device comprising:

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