Semiconductor module, power conversion device, and method for manufacturing semiconductor module

Abstract

A semiconductor module comprising a conductor plate on which a semiconductor element is mounted, a sheet-shaped member which covers the surface of the conductor plate, and a resin member which integrally packages the conductor plate and the sheet-shaped member, wherein: an end of the sheet-shaped member is covered by the resin member in a state in which the region of the sheet-shaped member overlapping the surface of the conductor plate is exposed; the sheet-shaped member has an outer peripheral surface which is formed on the outer periphery thereof, an inner peripheral surface which is formed so as to be further toward the inner periphery than the outer peripheral surface, an outer peripheral ramp which connects the outer edge of the sheet-shaped member and the outer peripheral surface, and an inner peripheral ramp which connects the outer peripheral surface and the inner peripheral surface; the outer peripheral surface is further from the semiconductor element in comparison to the outer edge; and the inner peripheral surface is further from the semiconductor element in comparison to the outer peripheral surface.

Description

Semiconductor module, power conversion device, and method for manufacturing semiconductor module

[0001] The present invention relates to a semiconductor module, a power conversion device, and a method for manufacturing a semiconductor module.

[0002] Power conversion devices that use switching power semiconductor elements have high conversion efficiency and are therefore widely used in consumer, automotive, railway, and substation equipment. Power semiconductor elements generate heat when current is applied, so high heat dissipation is required. In particular, for automotive applications, highly efficient cooling systems using water cooling are used to reduce size and weight. Patent Document 1 discloses an electric circuit body comprising: a power semiconductor element; a first conductor plate connected to one side of the power semiconductor element; a first sheet-like member having a first resin insulating layer and covering at least the surface of the first conductor plate; a sealing material that seals ends of the power semiconductor element, the first conductor plate, and the first sheet-like member; and a first cooling member that is in close contact with the first sheet-like member, wherein the first sheet-like member has a buried portion where the end of the first sheet-like member is covered by the sealing material, a heat dissipation surface portion that is an area that overlaps the surface of the first conductor plate, and a margin portion that is an area between the buried portion and the heat dissipation surface portion, wherein the margin portion is recessed inward from the heat dissipation surface portion and the buried portion is recessed inward from the margin portion.

[0003] Japanese Patent Application Publication No. 2021-141275

[0004] The invention described in Patent Document 1 leaves room for improvement in the way the resin member extends around the heat dissipation surface.

[0005] A semiconductor module according to a first aspect of the present invention comprises a conductor plate on which a semiconductor element is mounted, a sheet-like member covering the surface of the conductor plate, and a resin member integrally molding and sealing the conductor plate and the sheet-like member, wherein an end of the sheet-like member is covered with the resin member while an area overlapping the surface of the conductor plate is exposed, and the sheet-like member has an outer peripheral surface formed on the outer periphery, an inner peripheral surface formed inner than the outer peripheral surface, an outer peripheral step connecting the outer edge of the sheet-like member to the outer peripheral surface, and an inner peripheral step connecting the outer peripheral surface and the inner peripheral surface, wherein the outer peripheral surface is farther from the semiconductor element than the outer edge, and the inner peripheral surface is farther from the semiconductor element than the outer peripheral surface.A power conversion device according to a second aspect of the present invention is a power conversion device comprising a plurality of the aforementioned semiconductor modules, wherein the heights of the outer peripheral steps of the plurality of semiconductor modules are the same but the heights of the inner peripheral steps are not the same. A manufacturing method for a semiconductor module according to a third aspect of the present invention includes a clamping process in which the sheet-like member, the conductive plate, and the semiconductor element are arranged in a space formed by a mold having a variable step in the center and a fixed step on the periphery, and a molding process in which the conductive plate and the sheet-like member are molded and sealed together by filling the space with the resin member, thereby forming the outer peripheral step and the inner peripheral step.

[0006] According to the present invention, it is possible to prevent the resin member from getting around the heat dissipation surface of the sheet-like member.

[0007] 1A plan view of an electric circuit body A cross-sectional view taken along the line II-II of FIG. 1A cross-sectional view taken along the line III-III of FIG. 1A cross-sectional perspective view of a semiconductor module A semi-transparent view showing the internal structure of a semiconductor module A circuit diagram of a semiconductor module A view showing a manufacturing method for a semiconductor module A view showing a manufacturing method for a semiconductor module A view showing a manufacturing process for an electric circuit body A view showing the characteristics of a material A view explaining the principle of preventing resin from wrapping around the heat dissipation surface A view explaining the effect of this embodiment A circuit diagram of a power conversion device using a semiconductor module A perspective view of the appearance of a power conversion device A cross-sectional view taken along the line XV-XV of FIG. 14 A cross-sectional view of a semiconductor module in Modification 1

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and appropriate omissions and simplifications will be made for clarity of explanation. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural. The position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc., in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0009] -Embodiments- Hereinafter, embodiments of a semiconductor module and a power conversion device will be described with reference to FIGS.

[0010] FIG. 1 is a plan view of an electric circuit body 400. In this embodiment, mutually orthogonal X, Y, and Z axes are also shown to clarify the correlation between the drawings. In FIG. 1, the rightward direction in the figure is the positive side of the X axis, the upward direction in the figure is the positive side of the Y axis, and the forward direction in the figure is the positive side of the Z axis. The electric circuit body 400 includes a semiconductor module 300 and a cooling member 340. As will be described in more detail below, the semiconductor module 300 and the cooling member 340 overlap in the Z axis direction, and in FIG. 1, most of the semiconductor module 300 is hidden by the cooling member 340.

[0011] The semiconductor module 300 converts DC current and AC current mutually using semiconductor elements 150 (described later). The semiconductor module 300 generates heat when energized, so it is cooled by a cooling member 340. The coolant contained in the cooling member 340 can be water or an antifreeze solution made by mixing ethylene glycol with water. The semiconductor module 300 includes power terminals through which large currents flow, such as a positive terminal 315B and a negative terminal 319B connected to the capacitor module 500 in the DC circuit, and an AC terminal 320B connected to the motor-generators 192 and 194 in the AC circuit. The semiconductor module 300 also includes signal terminals used to control the semiconductor module, such as a lower arm gate terminal 325L, an upper arm gate terminal 325U, an emitter signal terminal 325E, and a collector signal terminal 325C.

[0012] FIG. 2 shows a cross-sectional view taken along line II-II of FIG. 1 , and FIG. 3 shows a cross-sectional view taken along line III-III of FIG. 1 . Also, FIG. 4 shows a cross-sectional perspective view of semiconductor module 300, FIG. 5 shows a semi-transparent view illustrating the internal structure of semiconductor module 300, and FIG. 6 shows a circuit diagram of semiconductor module 300. As shown in FIG. 5 , semiconductor module 300 includes a first power semiconductor element 155 that constitutes an upper arm circuit and a second power semiconductor element 157 that constitutes a lower arm circuit. Hereinafter, first power semiconductor element 155 and second power semiconductor element 157 will be collectively referred to as "semiconductor element" 150. For example, silicon (Si), silicon carbide (SiC), gallium nitride (GaN), gallium oxide (GaO), carbon (C), or the like can be used for semiconductor element 150.

[0013] The semiconductor element 150 can be used in an insulated gate bipolar transistor (IGBT) device structure or a metal oxide semiconductor field effect transistor (MOSFET) device structure. IGBTs have low on-resistance even at high breakdown voltages, making them suitable for high-power applications, but are unsuitable for high-speed switching. On the other hand, MOSFETs are suitable for high-speed switching, but as the breakdown voltage increases, the drift layer becomes thicker and the on-resistance increases, making it difficult to achieve high power output. However, by using next-generation devices such as SiC, which has a high breakdown field, as the semiconductor element, high power output can be achieved even with MOSFETs, and low loss can be achieved through high-speed switching. However, because next-generation devices are more expensive than Si, multiple small-sized power semiconductor elements connected in parallel can be used.

[0014] In this case, a common gate terminal may be provided, but providing a gate terminal for each element is preferable because it allows for more precise control. Furthermore, in high-voltage applications, a guard ring is provided around the periphery of the chip to reduce the surface electric field strength. Because the size of the guard ring is determined by the electric field strength, the guard ring size cannot be reduced even when the chip size is reduced. Therefore, as the chip size decreases, the area ratio of the source-side active region to the chip area decreases. In a transfer molding process in which the sheet-like member 440 is bonded and resin-encapsulated simultaneously, when a small chip is used, even if the same pressure is applied to the chip area, stress increases at the joint between the source-side active region and the first conductor plate 421, making the joint more susceptible to peeling.

[0015] The drain side of the first power semiconductor element 155 is bonded to the second conductor plate 422. Hereinafter, the first conductor plate 421 and the second conductor plate 422 are collectively referred to as the "conductor plate" 420. Solder or sintered metal may be used to bond the semiconductor element 150 and the conductor plate 420. The conductor plate 420 is not particularly limited as long as it has high electrical conductivity and thermal conductivity, but a copper-based material or an aluminum-based material is desirable. The copper-based material or aluminum-based material may be used alone, but may be plated with nickel (Ni), silver (Ag), or the like to improve bonding with the solder or sintered metal. The conductor plate 420 is bonded to the source side of the first power semiconductor element 155.

[0016] The drain side of the second power semiconductor element 157 is joined to the second conductor plate 422. The source side of the second power semiconductor element 157 is joined to the first conductor plate 421. A substrate carrying circuit components may be mounted on the conductor plate 420 to add functions such as a current sensor and lifespan diagnosis to the electric circuit body 400. In addition to passing current, the conductor plate 420 also serves as a heat transfer member that transfers heat generated by the first power semiconductor element 155 and the second power semiconductor element 157 to the cooling member 340.

[0017] Because the conductive plate 420 has a different potential from the cooling member 340, a sheet-like member 440 having a resin insulating layer 441 is placed between the conductive plate 420 and the cooling member 340. A heat-conducting member 453 is disposed between the sheet-like member 440 and the cooling member 340 to reduce contact thermal resistance. The first power semiconductor element 155, the second power semiconductor element 157, the conductive plate 420, the internal connection portions, part of the insulating resin sheet, part of the laminated substrate, and part of the external terminals are sealed with a resin member 360 by transfer molding.

[0018] The thermal conductive member 453 can be made of an inorganic, highly thermally conductive material such as a carbon-based material. Materials that have fluidity at room temperature or high temperatures, such as grease, gel grease, and phase change sheet, can also be used for the thermal conductive member 453. To ensure workability and long-term reliability, the thermal conductive member 453 can be made of a curable thermal conductive material that is fluid when uncured but loses its fluidity after curing. Using a curable material for the thermal conductive member 453 offers the advantages of low viscosity during application, excellent workability, and improved mechanical properties upon curing. Curing can be achieved by heat curing, moisture curing, ultraviolet curing, or other methods, but heat curing is preferred for deep curing. The thermal conductive member 453 can be made of a highly thermally conductive material such as a metal, ceramic, or carbon-based material, or a mixture of these with resin, or a combination of these.

[0019] The sheet-shaped member 440 and the resin member 360 are cured simultaneously in a transfer molding process described below. The transfer molding process also simultaneously bonds the conductive plate 420 and the sheet-shaped member 440. The heat dissipation surface of the sheet-shaped member 440 is the adhesive region between the conductive plate 420 and the sheet-shaped member 440, which are connected to the semiconductor element 150, and is a region that is responsible for both dissipating heat from the semiconductor element 150 and providing insulation.

[0020] The resin insulating layer 441 of the sheet-shaped member 440 is not limited to any particular material as long as it is adhesive to the heat sink. However, from the viewpoint of balancing adhesiveness and heat dissipation, it is preferable to use an epoxy resin-based resin insulating layer with a powdered inorganic filler dispersed therein for the resin insulating layer 441. It is preferable to provide a metal foil 444 on the side of the sheet-shaped member 440 that contacts the thermally conductive member 453. To prevent adhesion to the mold when the sheet-shaped member 440 is placed in the mold during the transfer molding process, a release sheet or metal foil 444 is provided on the surface of the sheet-shaped member 440 that contacts the mold. Because release sheets have poor thermal conductivity, they require a peeling process after transfer molding. However, metal foils can be used without peeling after transfer molding by selecting a metal with high thermal conductivity, such as copper or aluminum. Transfer molding the sheet-shaped member 440 includes the resin member 360, covering the edges of the sheet-shaped member 440 and improving reliability.

[0021] As shown in FIG. 4 , the sheet-like member 440 has an innermost peripheral surface 461, an inner peripheral surface 462, an outer peripheral surface 463, an innermost peripheral step 431, an inner peripheral step 432, and an outer peripheral step 433. The innermost peripheral surface 461 is the innermost surface, and the innermost peripheral step 431, the inner peripheral surface 462, the inner peripheral step 432, the outer peripheral surface 463, and the outer peripheral step 433 are arranged in this order toward the outside. The innermost peripheral step 431 is a step located at the boundary between the innermost peripheral surface 461 and the inner peripheral surface 462. The inner peripheral step 432 is a step located at the boundary between the inner peripheral surface 462 and the outer peripheral surface 463. The outer peripheral step 433 is a step located at the boundary between the outer peripheral surface 463 and the outer edge of the sheet-like member 440. The distance from the outer peripheral step 433 to the inner peripheral step 432 is greater than the distance from the inner peripheral step 432 to the innermost peripheral step 431 .

[0022] The positions of the innermost circumferential surface 461, the inner circumferential surface 462, and the outer circumferential surface 463 in the Z direction are such that the innermost circumferential surface 461 is furthest on the positive side of the Z axis, and the outer circumferential surface 463 is furthest on the negative side of the Z axis. Since the semiconductor element 150 is located in the center of the figure, of the three surfaces, the innermost circumferential surface 461 is furthest from the semiconductor element 150. Specifically, this is as follows: The outer circumferential surface 463 is further from the semiconductor element 150 than the outer edge of the sheet-like member 440. The inner circumferential surface 462 is further from the semiconductor element 150 than the outer circumferential surface 463. The innermost circumferential surface 461 is further from the semiconductor element 150 than the inner circumferential surface 462.

[0023] The outer edge of the sheet-shaped member 440 can also be referred to as the "end" of the sheet-shaped member 440. The outer peripheral step 433 is provided near the resin-coated portion of the end of the sheet-shaped member 440. The outer peripheral step 433 is a step of 100 μm, preferably 150 μm or more. Based on the principle shown in FIG. 11 , which will be described later, the outer peripheral step 433 prevents the resin member 360 from wrapping around the surface of the sheet-shaped member 440 due to the molding pressure in the transfer molding process.

[0024] Furthermore, an innermost peripheral step 431 is formed on the sheet-like member 440 according to the principle shown in FIG. 11 (described later). The innermost peripheral step 431 makes the heat dissipation surface, i.e., the innermost peripheral surface 461, which bonds the sheet-like member 440 and the conductive plate 420, convex, effectively adhering to the cooling member 340 and improving cooling performance. The inner peripheral step 432 is created by a pressure mechanism using springs 602 in the transfer mold die, which absorbs height variations when connecting power semiconductor elements. The inner peripheral step 432 absorbs height variations in the circuit body 310. Because the sheet-like member 440 has the inner peripheral step 432, the sheet-like member 440 and the conductive plate 420 can be pressed with a constant surface pressure even if the circuit body 310 varies in height. This allows the sheet-like member 440 and the conductive plate 420 to be effectively bonded together.

[0025] The height of the innermost step 431, i.e., the width in the Z direction, is referred to as the innermost step height 431H. The height of the inner step 432, i.e., the width in the Z direction, is referred to as the innermost step height 432H. The height of the outer step 433, i.e., the width in the Z direction, is referred to as the outermost step height 433H. Note that while the innermost step height 432H and the outermost step height 433H are shown in Figure 3, the innermost step height 431H is not shown for convenience of drawing.

[0026] The conductor plate 420 is preferably made of a material with high electrical conductivity and high thermal conductivity. Metallic materials such as copper or aluminum, or composite materials of metallic materials and high thermal conductivity materials such as diamond, carbon, or ceramic, may also be used for the conductor plate 420. The cooling member 340 is preferably made of aluminum or copper, which have high thermal conductivity and are lightweight. The cooling member 340 is manufactured by extrusion molding, forging, brazing, or the like.

[0027] The method for manufacturing the electric circuit body 400 will be described below with reference to FIGS. 7 to 9. FIGS. 7 and 8 show the first to sixth steps of the method for manufacturing the semiconductor module 300, and FIG. 9 shows the manufacturing process for the electric circuit body 400 using the semiconductor module 300 completed at the end of FIG. 8. The method for manufacturing the semiconductor module 300 will be described with reference to FIGS. 7 and 8. FIG. 7 shows the first to third steps, and FIG. 8 shows the fourth to sixth steps. First, FIG. 7 will be described. The first step shown in FIG. 7(a) is a bonding step. First, the drain side of the semiconductor element 150 is connected to the first conductor plate 421, the gate electrode (not shown) is connected by wire bonding, and the source side of the semiconductor element 150 is connected to the second conductor plate 422, thereby producing the circuit body 310.

[0028] The second step shown in Figure 7(b) is a temporary attachment step in which the sheet-like member 440 is temporarily attached to the conductive plate 420. Temporary attachment means that the sheet-like member 440 is attached using its adhesive force under conditions that leave room for the sheet-like member 440 to harden and adhere in the subsequent transfer molding step. The third step shown in Figure 7(c) is a mounting step in which the circuit body 310 to which the sheet-like member 440 has been temporarily attached is mounted on a mold 601 of a transfer molding device. The transfer molding step using the mold 601 will be described with reference to Figure 8.

[0029] The fourth step shown in FIG. 8A is the forming and molding step, which involves clamping and transfer molding. The transfer molding device includes a spring 602 inside a mold 601. The spring 602 creates a variable step using its elastic force. Even if the height of the circuit body 310 varies, the spring 602 allows a predetermined load to be applied by the spring force without excessive compression to the semiconductor element 150. The transfer molding device also includes a vacuum degassing mechanism (not shown). Vacuum degassing reduces the size of any voids that may be present, improving insulation.

[0030] Furthermore, a release film (not shown) can be used. Using the release film can prevent resin burrs from entering the drive portion of the spring 602. In this clamping process, the upper and lower molds 601 are clamped. At this time, the spring 602 applies pressure to the sheet-like member 440 and the conductive plate 420, causing them to adhere tightly to each other. After this, a molding process is performed in which the resin member 360 is injected by transfer molding. At this time, an inner peripheral step 432 and an outer peripheral step 433 are formed.

[0031] Inner peripheral step 432 changes according to the height of circuit body 310. On the other hand, outer peripheral step 433 has dimensions carved into mold 601 and is therefore not affected by the height of circuit body 310. In other words, inner peripheral step 432 is formed by a variable step achieved by spring 602, while outer peripheral step 433 is formed by a fixed step carved into mold 601. The height of outer peripheral step 433 is 50 μm or more, preferably 150 μm or more, and can prevent resin transfer molding resin from seeping onto the surface of sheet-like member 440 according to the principle shown in FIG. 11 , which will be described later.

[0032] The fifth step shown in FIG. 8( b) is a release step in which the mold 601 is released. The resin member 360 is cooled during the curing process and when the mold 601 is released, forming an innermost peripheral step 431. The presence of the innermost peripheral step 431 makes the heat dissipation surface, i.e., the innermost peripheral surface 461, convex, allowing the heat dissipation surface to be effectively in close contact with the cooling member 340, improving heat dissipation. The sixth step shown in FIG. 8( c) is a post-curing step. The resin-sealed semiconductor module 300 is removed from the mold 601 and post-cured at 175° C. for two hours or more.

[0033] The manufacturing process of the electric circuit body 400 will be described with reference to FIG. 9 . The semiconductor module 300 shown in FIG. 9( a) is obtained upon completion of the sixth step shown in FIG. 8( c). First, as shown in FIG. 9( a), a thermally conductive member 453 is applied to the cooling member 340 and the semiconductor module 300. Then, as shown in FIG. 9( b), the cooling member 340 and the semiconductor module 300 are brought into close contact with each other, and the thermally conductive member 453 is cured, thereby producing the electric circuit body 400. By applying the thermally conductive member 453 to the convex portions of the steps of the innermost peripheral step 431 and the inner peripheral step 432, i.e., the innermost peripheral surface 461 and the inner peripheral surface 462, excess thermally conductive member 453 can flow to the outer peripheral step 433. This prevents the thermally conductive member 453 from flowing near the terminals, thereby preventing a deterioration in insulation between the terminals.

[0034] Furthermore, the convex portion of the outer peripheral step 433, i.e., the outer peripheral surface 463, is an area where the thermal conductive material 453 is not completely applied. Furthermore, because the outer peripheral surface 463 is separated from the conductive plate 420 and does not affect the insulation, repairs can be made by inserting a thin plate into this area and using the principle of leverage to separate the semiconductor module and the water channel. Even if the sheet-like member 440 on the outer peripheral surface 463 is damaged during repairs, it can be reused because it does not affect the insulation. Furthermore, when the circuit body 310 is formed using multiple semiconductor modules 300, the uniform height dimensions of the outer peripheral step 433 facilitate the insertion of the thin plate used for the repairs described above, making it easier to remove multiple semiconductor elements 150 all at once.

[0035] FIG. 10 is a diagram showing material characteristics. The horizontal axis of FIG. 10 represents temperature, and the vertical axis represents volume per unit mass. T1 represents the minimum operating temperature of the semiconductor element 150, T2 represents the maximum operating temperature of the semiconductor element 150, and Tmold represents the temperature during molding. T1 is, for example, -40°C, T2 is, for example, 125°C, and Tmold is, for example, 175°C. The vertical axis indicates a larger volume at the top and a smaller volume at the bottom. The four straight lines shown in FIG. 10 represent the characteristics of copper, resin A, resin B, and resin C. Resins A to C are hypothetical resins shown for convenience of explanation. In FIG. 10, the characteristics of copper are shown with a solid line and the symbol Cu. In FIG. 10, the characteristics of resin A are shown with a dashed line and the symbol Ra. In FIG. 10, the characteristics of resin B are shown with a dashed line and the symbol Rb. In FIG. 10, the characteristics of resin C are shown with a dashed line and the symbol Rc.

[0036] The principle of forming the peripheral step 433 will be explained with reference to FIG. 10 . Resin member 360 is injected into a transfer mold at a temperature of, for example, 175°C. The shrinkage of the power module components in the Z-axis direction is noted based on the dimensions immediately after injection. Looking from the source side to the drain side, the steel members are arranged as follows: sheet member 440, conductor plate 420, solder, semiconductor element 150, solder, conductor plate 420, and sheet member 440. Sheet member 440 is composed of a resin insulating layer 100 μm to 500 μm thick and a metal foil 444 30 μm to 200 μm thick. Conductor plate 420 is composed of a copper-based material 1 mm to 5 mm thick. Solder is composed of a tin-based material 50 μm to 200 μm thick. Semiconductor element 150 is composed of a material 80 μm to 200 μm thick. The semiconductor element 150 is made up of various materials, but since we are focusing on the amount of shrinkage in the Z-axis direction here, we will represent it with a copper-based material, which is the thickest constituent material, and explain the amount of thermal shrinkage of the semiconductor element 150 by approximating it with the amount of thermal shrinkage of pure copper.

[0037] After being injected into the mold 601 of the transfer molding device, the resin member 360 cures and shrinks as the curing reaction progresses. The amount of cure shrinkage depends on the composition of the resin member 360 and the amount of temperature change. The greater the proportion of epoxy resin components that undergo a curing reaction in the resin member 360, the greater the amount of cure shrinkage. Furthermore, even if the proportion of epoxy resin components is the same, the greater the proportion of epoxy groups, which are reactive components in the epoxy resin components, the greater the amount of cure shrinkage.

[0038] The semiconductor element 150 removed from the mold 601 of the transfer molding device is cooled to room temperature. If the glass transition temperature is lower than Tmold, the semiconductor element 150 shrinks at a large shrinkage rate up to the glass transition temperature, and then at a smaller shrinkage rate once the temperature drops below the glass transition temperature. If the glass transition temperature is higher than Tmold, the semiconductor element 150 shrinks at a constant shrinkage rate. Focus is now on the temperature range from T1 to T2, which is the range of ambient temperatures in which the semiconductor element 150 is used. If the shrinkage amount is greater than Cu within this temperature range, i.e., if the shrinkage amount of the resin member 360 falls within the hatched area in FIG. 10 , an innermost peripheral step 431 is formed within the operating temperature range, and the innermost peripheral surface 461, which is the heat dissipation surface, becomes convex. In other words, the innermost peripheral step 431 can be formed by using resin B or resin C in the example shown in FIG. 10 for the resin member 360. If resin A were used for the resin member 360, the innermost peripheral step 431 would not be formed.

[0039] With reference to FIG. 11 , the principle of preventing resin from seeping around the surface of the sheet-shaped member 440 at the peripheral step 433 will be described. The surface of the sheet-shaped member 440 refers to the side where the sheet-shaped member 440 and the mold 601 contact, i.e., the surface on the positive Z-axis side of the sheet-shaped member 440 in FIG. 11 . The surface of the sheet-shaped member 440 can also be called a heat dissipation surface for dissipating heat from the semiconductor element 150. By providing a step near the edge of the sheet-shaped member 440, resin burrs are prevented from infiltrating between the sheet-shaped member 440 and the mold 601. Resin burrs are made of the resin member 360 filled in by transfer molding and the resin components of the resin member 360. Prevention of resin burr infiltration will be described in detail.

[0040] In the process of the resin member 360 flowing into the mold 601, first, the molding pressure generated by the flowing resin member 360 presses the sheet-like member 440 against the mold 601. Next, after the interior of the cavity of the mold 601 is almost completely filled with the resin member 360, a final molding pressure that is one step greater than before is applied to the resin member 360 as hydrostatic pressure. At this time, the resin member 360 flows into even minute gaps, and the resin member 360 and resin burrs flow into the narrow gap between the sheet-like member 440 and the mold 601. However, because the gap is narrow, a loss occurs in the pressure with which the resin member 360 flows in.

[0041] Let us focus on the location where a convex step exists after the resin member 360 flows into the gap between the sheet-shaped member 440 and the mold 601, i.e., the location circled by a dashed line in FIG. 11 . Here, the pressure of the resin member 360 flowing into the narrow gap between the sheet-shaped member 440 and the mold 601 acts in a direction opposite to the molding pressure that presses the sheet-shaped member 440 against the mold 601. At this time, the molding pressure that presses the sheet-shaped member 440 against the mold 601 is defined as Pa. Furthermore, the molding pressure of the resin member 360 that flows through the narrow gap and causes a pressure loss is defined as Pb. In this case, since the relationship Pa > Pb holds, the resin member 360 flowing between the sheet-shaped member 440 and the mold 601 stops at this step.

[0042] The closer the angle of the peripheral step 433 is to a right angle and the higher the height, the more effective it is in preventing the resin from seeping onto the surface of the sheet-like member 440. The angle of the peripheral step 433 with respect to the horizontal plane must be, for example, 10 degrees or more, preferably 30 degrees or more. The height of the step must be, for example, 50 μm or more, preferably 150 μm or more. Configuration example 1 shown in the lower part of Figure 11 illustrates a case where the angle of the peripheral step 433 is 10 degrees and the height is 50 μm. Similarly, configuration example 2 illustrates a case where the angle of the peripheral step 433 is 90 degrees and the height is 150 μm. As described above, the molding pressure pressing the sheet-like member 440 against the mold 601 counters the pressure that tries to cause the resin member 360 to flow into the narrow gap between the sheet-like member 440 and the mold 601, and is therefore extremely effective in preventing the resin member 360 from seeping into and forming resin burrs.

[0043] The effect of this embodiment will be described with reference to Fig. 12. Fig. 12(a) shows the pressure distribution during molding in this embodiment, and Fig. 12(b) shows the pressure distribution during molding in a comparative example. The comparative example has only one step.

[0044] The area of ​​the pressure mechanism in this embodiment is S1, and the area of ​​the pressure mechanism in the comparative example is S2. Furthermore, the value obtained by subtracting S1 from S2 is S3, the area of ​​the source-side active region of semiconductor element 150 is S4, and the molding pressure during transfer molding is P. In this embodiment, the force pushing up on spring 602 is the value obtained by subtracting S4 from S1 and multiplying the result by the molding pressure P. On the other hand, the force pushing up on spring 602 in the comparative example is the value obtained by subtracting S4 from S2 and multiplying the result by the molding pressure P. In other words, this embodiment has the effect of being able to reduce the force that the molding pressure P pushes up on the spring mechanism by the amount of S3, which is obtained by subtracting S1 from S2.

[0045] If the force due to the molding pressure exceeds the force pushing up the spring mechanism, a force in the peeling direction is generated in the semiconductor element 150. Because the semiconductor element 150 has a structure in which electrodes and elements are stacked, it is weak against forces in the peeling direction but is strong against forces in the compression direction. However, the bonding material that bonds the semiconductor element 150 may undergo plastic deformation due to the strong compressive stress, causing peeling.

[0046] In other words, in the comparative example, when a force from the spring mechanism that exceeds the force from the molding pressure is applied, a strong compressive stress acts on the region S4 by the spring mechanism, which may cause the joining member to peel off. On the other hand, in the example, even if a force from the spring mechanism that exceeds the force from the molding pressure is applied, the pressure force from the spring mechanism can be reduced by the area of ​​S3, so the compressive stress acting on the region S4 can be reduced, which has the effect of improving reliability.

[0047] Furthermore, in the example, the outer peripheral step 433 is formed to the dimensions of the mold 601, so even if the height of the circuit body 310 changes, the height of the innermost peripheral step 431 does not change, and it is possible to stably prevent the resin from leaking in. On the other hand, in the comparative example, if the height of the circuit body 310 changes, the height of the step inevitably changes, which may result in the step becoming lower and making it impossible to prevent the resin from leaking in.

[0048] FIG. 13 is a circuit diagram of a power conversion device 200 using the semiconductor module 300 described above. The power conversion device 200 includes a first inverter circuit unit 140, a second inverter circuit 142, an auxiliary inverter circuit unit 43, and a capacitor module 500. The first inverter circuit unit 140 and the second inverter circuit 142 each include a plurality of semiconductor modules 300, which are connected to form a three-phase bridge circuit. For larger current capacities, additional semiconductor modules 300 can be connected in parallel, corresponding to each phase of the three-phase inverter circuit. Furthermore, an increase in current capacity can also be achieved by connecting the first power semiconductor element 155 and the second power semiconductor element 157, which are power semiconductor elements built into the semiconductor module 300, in parallel.

[0049] The first inverter circuit unit 140 and the second inverter circuit 142 have the same basic circuit configuration, and also have the same control method and operation. The outline of the circuit operation of the first inverter circuit unit 140 and the like is well known, so a detailed description will be omitted here.

[0050] As described above, the upper arm circuit includes the upper arm power semiconductor element 155 as a switching power semiconductor element, and the lower arm circuit includes the lower arm power semiconductor element 157 as a switching power semiconductor element. The first power semiconductor element 155 and the second power semiconductor element 157 perform switching operations in response to drive signals output from one or the other of the two driver circuits that make up the driver circuit 174, and convert the DC power supplied from the battery 136 into three-phase AC power.

[0051] As described above, the first power semiconductor element 155 and the second power semiconductor element 157 have a drain electrode, a source electrode, and a gate electrode. The positive terminal 315B and the negative terminal 319B of each upper and lower arm series circuit are connected to DC terminals for connecting capacitors of the capacitor module 500, respectively. AC power is generated at the junction between the upper arm circuit and the lower arm circuit, and the junction between the upper arm circuit and the lower arm circuit of each upper and lower arm series circuit is connected to the AC terminal 320B of each semiconductor module 300. The AC terminal 320B of each semiconductor module 300 of each phase is connected to the AC output terminal of the power conversion device 200, and the generated AC power is supplied to the stator winding of the motor generator 192 or 194.

[0052] The control circuit 172 generates timing signals for controlling the switching timing of the first power semiconductor element 155 and the second power semiconductor element 157 based on input information from a vehicle-side control device or sensor, such as a current sensor 180. The driver circuit 174 generates drive signals for performing switching operations on the first power semiconductor element 155 and the second power semiconductor element 157 based on the timing signals output from the control circuit 172. Note that reference numerals 181, 182, and 188 each denote connectors.

[0053] The upper and lower arm series circuits each include a temperature sensor (not shown), and temperature information about the upper and lower arm series circuits is input to the microcomputer. Voltage information about the DC positive poles of the upper and lower arm series circuits is also input to the microcomputer. The microcomputer detects overtemperatures and overvoltages based on this information, and if an overtemperature or overvoltage is detected, the microcomputer stops the switching operations of all of the first power semiconductor elements 155 and the second power semiconductor elements 157, thereby protecting the upper and lower arm series circuits from overtemperature or overvoltage.

[0054] FIG. 14 is an external perspective view of the power conversion device 200. FIG. 15 is a cross-sectional view of the power conversion device 200 taken along the line XV-XV. The power conversion device 200 includes a housing 12 formed in a substantially rectangular parallelepiped shape, including a lower case 11 and an upper case 10. An electric circuit body 400, a capacitor module 500, and the like are housed inside the housing 12. The electric circuit body 400 has a cooling flow path, and a cooling water inlet pipe 13 and a cooling water outlet pipe 14 communicating with the cooling flow path protrude from one side of the housing 12. The lower case 11 has an opening on the upper side (Z direction) in the cross-sectional view shown in FIG. 15. The upper case 10 is attached to the lower case 11, closing the opening of the lower case 11. The upper case 10 and the lower case 11 are formed of an aluminum alloy or the like, and are fixed in place while being sealed from the outside. The upper case 10 and the lower case 11 may be integrally configured. The housing 12 has a simple rectangular parallelepiped shape, which makes it easy to mount on a vehicle or the like and also easy to manufacture.

[0055] 14 , a connector 17 is attached to one longitudinal side surface of the housing 12. An AC terminal 18 is connected to the connector 17. A connector 21 is provided on the surface of the housing 12 from which the cooling water inlet pipe 13 and the cooling water outlet pipe 14 are led out.

[0056] As shown in FIG. 15 , an electric circuit body 400 is housed within the housing 12. The control circuit 172 and the driver circuit 174 are disposed above the electric circuit body 400, and a capacitor module 500 is housed on the DC terminal side of the electric circuit body 400. By disposing the capacitor module 500 at the same height as the electric circuit body, the power conversion device 200 can be made thinner, improving the degree of freedom in installation in a vehicle. The AC side terminal 320B of the electric circuit body 400 is connected to the bus bar 361, passing through the current sensor 180. In addition, the positive side terminal 315B and the negative side terminal 319B, which are DC terminals of the semiconductor module 300, are connected to the positive terminal 362A and the negative terminal 362B of the capacitor module 500, respectively.

[0057] The above-described embodiment provides the following advantageous effects. (1) The semiconductor module 300 includes a conductive plate 420 on which a semiconductor element 150 is mounted, a sheet-like member 440 that covers the surface of the conductive plate 420, and a resin member 360 that integrally molds and seals the conductive plate 420 and the sheet-like member 440. The sheet-like member 440 has an exposed area that overlaps the surface of the conductive plate 420. As shown in FIG. 11 , the edge of the sheet-like member 440 is covered with the resin member. As shown in FIG. 4 , the sheet-like member 440 has an outer peripheral surface 463 formed on the outer periphery, an inner peripheral surface 462 formed on the inner periphery of the sheet-like member 440, an outer peripheral step 433 connecting the outer edge of the sheet-like member 440 to the outer peripheral surface 463, and an inner peripheral step 432 connecting the outer peripheral surface 463 to the inner peripheral surface 462. The outer peripheral surface 463 is farther from the semiconductor element 150 than the outer edge. The inner peripheral surface 462 is farther from the semiconductor element than the outer peripheral surface 463. This prevents the resin member 360 from wrapping around the heat dissipation surface of the sheet-like member 440, and prevents the resin member 360 from reducing heat dissipation.

[0058] (2) The sheet-shaped member 440 has an innermost peripheral surface 461 located further inward from the inner peripheral surface 462, with an innermost peripheral step 431 sandwiched therebetween. The innermost peripheral surface 461 is farther from the semiconductor element 150 than the inner peripheral surface 462. Therefore, heat can be dissipated from the conductive plate 420 to the cooling member 340 via the innermost peripheral surface 461 of the sheet-shaped member 440.

[0059] (3) The distance from the outer peripheral step 433 to the inner peripheral step 432 is greater than the distance from the inner peripheral step 432 to the innermost peripheral step 431. Therefore, the area of ​​S1 shown in FIG. 12 is reduced, and the force applied to the semiconductor element 150 can be reduced.

[0060] (4) The innermost circumferential surface 461 and the inner circumferential surface 462 are coated with the heat conductive member 453 that is in close contact with the cooling member 340, and a portion of the outer circumferential surface 463 is not coated with the heat conductive member 453. This prevents the heat conductive member 453 from flowing out to the vicinity of the terminals, and prevents a decrease in insulation between the terminals.

[0061] (5) The semiconductor modules 300 included in the power conversion device 200 have the same outer peripheral step height 433H but different inner peripheral step heights 432H. The inner peripheral step 432 absorbs the variations in height of the circuit body 310, and the outer peripheral step height 433H can be made constant, improving the efficiency of repair work and the like.

[0062] (6) The manufacturing method of the semiconductor module 300 includes a clamping process in which the sheet-like member 440, the conductive plate 420, and the semiconductor element 150 are arranged in a space formed by a mold 601 having a variable step in the center and a fixed step on the periphery, and a molding process in which the conductive plate 420 and the sheet-like member 440 are molded and sealed together by filling the space with a resin member 360, thereby forming an outer peripheral step 433 and an inner peripheral step 432.

[0063] 16 is a cross-sectional view of a semiconductor module 300 in Modification 1. In the above-described embodiment, the semiconductor module 300 houses two semiconductor elements 150. However, the semiconductor module 300 may house only one semiconductor element 150.

[0064] The above-described embodiments and modifications may be combined with each other. Although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments conceivable within the scope of the technical concept of the present invention are also included within the scope of the present invention.

[0065] 150: Semiconductor element 200: Power conversion device 300: Semiconductor module 310: Circuit body 340: Cooling member 360: Resin member 400: Electric circuit body 420: Conductive plate 431: Innermost peripheral step 432: Inner peripheral step 433: Outer peripheral step 440: Sheet-like member 453: Heat conduction member 601: Mold 602: Spring

Claims

1. A semiconductor module comprising: a conductor plate on which a semiconductor element is mounted; a sheet-like member covering a surface of the conductor plate; and a resin member that molds and seals the conductor plate and the sheet-like member together, wherein an end of the sheet-like member is covered by the resin member with an area that overlaps with the surface of the conductor plate being exposed, the sheet-like member has an outer circumferential surface formed on the outer periphery, an inner circumferential surface formed inner than the outer circumferential surface, an outer circumferential step connecting an outer edge of the sheet-like member and the outer circumferential surface, and an inner circumferential step connecting the outer circumferential surface and the inner circumferential surface, wherein the outer circumferential surface is farther from the semiconductor element than the outer edge, and the inner circumferential surface is farther from the semiconductor element than the outer circumferential surface.

2. A semiconductor module as claimed in claim 1, wherein the sheet-like member has an innermost surface with an innermost step located further inward from the inner surface, and the innermost surface is farther from the semiconductor element than the inner surface.

3. A semiconductor module according to claim 2, wherein the distance from the outer peripheral step to the inner peripheral step is greater than the distance from the inner peripheral step to the innermost peripheral step.

4. A semiconductor module as described in claim 2, wherein the innermost circumferential surface and the inner circumferential surface are coated with a heat conductive material that is in close contact with a cooling member, and a portion of the outer circumferential surface is not coated with the heat conductive material.

5. A power conversion device comprising a plurality of semiconductor modules according to claim 1, wherein the heights of the outer peripheral steps of the plurality of semiconductor modules are the same, but the heights of the inner peripheral steps are not the same.

6. A method for manufacturing a semiconductor module comprising: a conductor plate on which a semiconductor element is mounted; a sheet-like member covering a surface of the conductor plate; and a resin member integrally molding and sealing the conductor plate and the sheet-like member, wherein an end of the sheet-like member is covered by the resin member with an area overlapping the surface of the conductor plate exposed; the sheet-like member has an outer circumferential surface formed on the outer periphery, an inner circumferential surface formed inner than the outer circumferential surface, an outer circumferential step connecting an outer edge of the sheet-like member and the outer circumferential surface, and an inner circumferential step connecting the outer circumferential surface and the inner circumferential surface, wherein the outer circumferential surface is farther away from the semiconductor element than the outer edge, and the inner circumferential surface is farther away from the semiconductor element than the outer circumferential surface, the method comprising: a clamping step of arranging the sheet-like member, the conductor plate, and the semiconductor element in a space formed by a mold having a variable step due to elastic force in a central portion and a fixed step on an outer periphery; and a molding process of integrally molding and sealing the conductor plate and the sheet-like member while forming the outer peripheral step and the inner peripheral step by filling the space with the resin member.

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