Semiconductor module and method for manufacturing semiconductor module

Abstract

Provided is a semiconductor module which suppresses pump-out of a heat dissipation member.　The semiconductor module comprises: a semiconductor device (1) provided with a heat dissipation plate (2), an insulating layer (3) disposed on an upper surface of the heat dissipation plate (2), a circuit electrode (4) disposed on an upper surface of the insulating layer (3), a semiconductor chip (5) disposed on an upper surface of the circuit electrode (4), and a case (8) that is formed in a frame shape surrounding the heat dissipation plate (2) while leaving the bottom surface of the heat dissipation plate (2) exposed and is in contact with a peripheral portion of the upper surface of the insulating layer (3) so as to enclose the semiconductor chip (5); a heatsink (12) fastened to the case (8); a heat dissipation member (14) sandwiched between an upper surface of the heatsink (12) and a lower surface of the heat dissipation plate (2); and a flexible sheet (15) formed in a frame shape surrounding the heat dissipation member (14) and sandwiched between the upper surface of the heatsink (12) and a bottom surface of the case (8), wherein the heatsink (12) is fastened to the case (8) via the flexible sheet (15).

Description

Semiconductor module and method for manufacturing the same

[0001] The present disclosure relates to a semiconductor module and a method for manufacturing a semiconductor module.

[0002] Semiconductor modules such as semiconductor power modules are used as power conversion devices. In semiconductor modules equipped with semiconductor devices, semiconductor chips (IGBT: Insulated Gate Bipolar Transistor, MOSFET: Metal-Oxide-Semiconductor Field Effect Transistor) included in the semiconductor device generate heat during operation, so a heat sink is provided to cool the semiconductor device to efficiently dissipate the heat. The semiconductor device is equipped with, for example, a metal heat sink, and heat is dissipated by contacting the heat sink with the heat sink. If the mounting surfaces of the heat sink and the heat sink are not flat or have irregularities, the contact area becomes small, resulting in reduced heat dissipation performance. Therefore, heat dissipation performance is improved by sandwiching thermal grease between the heat sink and the heat sink and deforming it to fit the shape of the mounting surface.

[0003] However, when a semiconductor module is used for a long period of time, warping deformation of the heat sink due to temperature changes can cause a pump-out phenomenon in which the thermal grease is gradually expelled. In such a case, if a space is created between the heat sink and the heat sink, discharge may occur. As a countermeasure, it has been proposed to prevent discharge by connecting the heat sink and the heat sink with a conductive material (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2022-048552

[0005] Conventional semiconductor modules do not prevent the pumping out of the heat dissipation grease, which is a heat dissipation material, and therefore have the problem that the heat dissipation material may pump out, resulting in a decrease in heat dissipation performance.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a semiconductor module that suppresses the occurrence of pump-out of a heat dissipation member, and a method for manufacturing the semiconductor module.

[0007] The semiconductor module according to the present disclosure is characterized in that it comprises a semiconductor device including a heat sink, an insulating layer arranged on the upper surface of the heat sink, circuit electrodes arranged on the upper surface of the insulating layer, a semiconductor chip arranged on the upper surface of the circuit electrode, a case formed in a frame shape surrounding the periphery of the heat sink with the lower surface of the heat sink exposed and in contact with the peripheral portion of the upper surface of the insulating layer so as to surround the semiconductor chip, a heat sink fastened to the case, a heat dissipation member sandwiched between the upper surface of the heat sink and the lower surface of the heat sink, and a flexible sheet formed in a frame shape surrounding the periphery of the heat dissipation member and sandwiched between the upper surface of the heat sink and the bottom surface of the case, and the heat sink is fastened to the case via the flexible sheet.

[0008] The semiconductor module of the present disclosure comprises a semiconductor device including a heat sink, an insulating layer arranged on the upper surface of the heat sink, circuit electrodes arranged on the upper surface of the insulating layer, a semiconductor chip arranged on the upper surface of the circuit electrode, a case formed in a frame shape surrounding the periphery of the heat sink and exposing the lower surface of the heat sink, and in contact with the peripheral portion of the upper surface of the insulating layer so as to surround the semiconductor chip, a heat sink fastened to the case, a heat dissipation member sandwiched between the upper surface of the heat sink and the lower surface of the heat sink, and a flexible sheet formed in a frame shape surrounding the periphery of the heat dissipation member and sandwiched between the upper surface of the heat sink and the bottom surface of the case, and since the heat sink is fastened to the case via the flexible sheet, the occurrence of pump-out of the heat dissipation member is suppressed.

[0009] 1 is a schematic cross-sectional view of a semiconductor device according to a first embodiment. FIG. 2 is a bottom view of the semiconductor device according to the first embodiment. FIG. 3 is a schematic cross-sectional view of a semiconductor module according to a first comparative example. FIG. 4 is a schematic cross-sectional view of a semiconductor module according to the first embodiment. FIG. 5 is a bottom view of a flexible sheet and a semiconductor device according to the first embodiment. FIG. 6 is a bottom view of the semiconductor device after the flexible sheet according to the first embodiment has been installed. FIG. 7 is a process diagram of a method for manufacturing a semiconductor module according to the first embodiment. FIG. 8 is a view of a semiconductor module according to the first embodiment in the middle of manufacture. FIG. 9 is a view of a semiconductor module according to the first embodiment in the middle of manufacture. FIG. 10 is a view of a semiconductor module according to the first embodiment in the middle of manufacture. FIG. 11 is a view of a semiconductor module according to the second comparative example in the middle of manufacture. FIG. 12 is a view of a semiconductor module according to the first embodiment in the middle of manufacture. FIG. 13 is a view of a semiconductor module according to the second embodiment in the middle of manufacture. FIG. 14 is a view of a semiconductor module according to the third embodiment in the middle of manufacture. FIG. 15 is a view of a semiconductor module according to the third embodiment in the middle of manufacture.

[0010] Hereinafter, a semiconductor module and a method for manufacturing the semiconductor module according to an embodiment of the present disclosure will be described in detail with reference to the drawings. Note that the same reference numerals in the various drawings indicate the same or corresponding parts.

[0011] First Embodiment. FIG. 1 is a cross-sectional schematic diagram of a semiconductor device 1 according to a first embodiment. An insulating layer 3 is disposed on the upper surface (front surface) of a metal heat sink 2. Circuit electrodes 4 are disposed on the upper surface of the insulating layer 3. A semiconductor chip 5 is disposed on the upper surface of the circuit electrodes 4. The semiconductor chip 5 is connected to terminals 7 via the circuit electrodes 4 and wires 6. The semiconductor chip 5 is surrounded by a case 8, the interior of which is insulated by an insulating sealant 9. The insulating sealant 9 fills the space surrounded by the case 8, the insulating layer 3, the circuit electrodes 4, the semiconductor chip 5, and the terminals 7. The case 8 is formed in a frame shape surrounding the periphery of the heat sink 2, exposing its lower surface (the rear surface) of the heat sink 2. The case 8 is in contact with the peripheral portion of the upper surface of the insulating layer 3 so as to surround the semiconductor chip 5. FIG. 2 is a bottom view of the semiconductor device 1 according to the first embodiment as viewed from the lower surface (the rear surface). The case 8 has through holes 10a at its four corners for screw fastening.

[0012] FIG. 3 is a schematic cross-sectional view of a semiconductor module according to a first comparative example. During operation of the semiconductor device 1, heat generated from the semiconductor chip 5 is transferred to the heat sink 2. To dissipate heat from the heat sink 2, the case 8 and the heat sink 12 are fastened together with screws 13. When fastening the case 8 and the heat sink 12, if the contact surface between the heat sink 2 and the heat sink 12 is uneven and the contact area is small, the heat dissipation efficiency decreases. Therefore, by sandwiching a heat dissipation member 14 between the upper surface of the heat sink 12 and the lower surface of the heat sink 2, the contact area can be increased, thereby improving the heat dissipation efficiency. The heat dissipation member 14 is, for example, thermal grease, such as silicone mixed with a filler of a highly thermally conductive material. The heat dissipation member 14 is, for example, a thermal dissipation sheet, such as a resin mixed with a highly thermally conductive filler. However, because a thermal dissipation sheet may not be able to accommodate the warping of the heat sink 2 due to temperature changes, it is preferable to use thermal grease for the heat dissipation member 14.

[0013] Because heat is generated during operation of the semiconductor device 1, the difference in thermal expansion coefficients causes warping of the heat sink 2, and in the semiconductor module of the first comparative example shown in Figure 3, repeated deformation causes pump-out, in which the heat dissipation grease serving as the heat dissipation member 14 leaks out. When the amount of heat dissipation grease serving as the heat dissipation member 14 between the heat sink 2 and the heat sink 12 decreases, a space is created where the heat dissipation member 14 is no longer present, which is a factor in reducing heat dissipation.

[0014] Furthermore, in the semiconductor module of the first comparative example shown in FIG. 3 , partial discharge may occur in the gap 11 between the side surface of the heat sink 2 and the case 8 due to an electric field generated between a high-voltage portion such as the terminal 7 and the end of the heat sink 2. For example, even if partial discharge does not occur at the operating voltage in a ground environment, in a high-altitude environment (such as a mountaintop or inside an aircraft in flight), the air pressure decreases, making discharge more likely, and increasing the likelihood of partial discharge in the semiconductor module of the first comparative example. Partial discharge is a cause of insulation degradation or a source of noise, so it must be suppressed. One method of suppressing discharge in the gap 11 between the side surface of the heat sink 2 and the case 8 is to fill the gap 11 with an insulating material, but this requires a process of filling the insulating material without leaving voids, which increases costs.

[0015] 4 is a schematic cross-sectional view of a semiconductor module according to the first embodiment. The semiconductor module according to the first embodiment shown in FIG. 4 differs from the semiconductor module according to the first comparative example shown in FIG. 3 in that a flexible sheet 15 is added. The flexible sheet 15 is formed in a frame shape surrounding the periphery of the heat dissipation member 14, and is sandwiched between the top surface of the heat sink 12 and the bottom surface of the case 8 when the case 8 and the heat sink 12 are fastened together. The flexible sheet 15 may surround the periphery of the heat dissipation member 14 without any gaps. The flexible sheet 15 is made of, for example, silicone rubber and is elastic.

[0016] FIG. 5 is a bottom view showing the flexible sheet 15 and the semiconductor device 1 before the flexible sheet 15 is installed on the semiconductor device 1. The bottom view of FIG. 5 is a bottom view of the semiconductor device 1 viewed from the underside of the heat sink 2, and the top view of FIG. 5 is a bottom view of the semiconductor device 1 viewed from the underside of the flexible sheet 15. FIG. 6 is a bottom view of the flexible sheet 15 after it has been installed on the semiconductor device 1, showing the semiconductor device 1 with the flexible sheet 15 installed viewed from the underside of the heat sink 2. The heat sink 12 and the heat dissipation member 14 are not shown in FIG. 6. The flexible sheet 15 is formed in a frame shape with a through hole 16 in the portion overlapping with the heat sink 2. The size of the through hole 16 in the flexible sheet 15 is larger than the size of the heat sink 2 and smaller than the size of the outer periphery of the case 8. For example, the inner peripheral edge of flexible sheet 15 when viewed from the bottom of heat sink 2 is located outside the outer peripheral edge of heat sink 2 when viewed from the bottom of heat sink 2. Flexible sheet 15 has through holes 10b at positions corresponding to through holes 10a in case 8, and when flexible sheet 15 is placed on case 8, through holes 10a and 10b become a single through hole, and case 8 and heat sink 12 are fastened together via flexible sheet 15 with screws 13. In the semiconductor module in which case 8 and heat sink 12 are fastened together, heat dissipation member 14 is sandwiched between the upper surface of heat sink 12 and the lower surface of heat sink 2 at the position of through holes 16 in flexible sheet 15. This brings the entire lower surface of heat sink 2 into contact with heat dissipation member 14, thereby achieving a high heat dissipation effect.

[0017] When the case 8 and the heat sink 12 are fastened with the screws 13, the flexible sheet 15 deforms, bringing the flexible sheet 15 into tight contact with the case 8 and the heat sink 12. Because the peripheral portion of the upper surface of the insulating layer 3 is in tight contact with the case 8, the space surrounded by the heat sink 12, the flexible sheet 15, the case 8, the heat sink 2, and the insulating layer 3 is sealed, and the heat sink 14 is enclosed by the flexible sheet 15 in the sealed space. This prevents the heat sink 14 from leaking out of the sealed space, even when heat is generated during operation of the semiconductor device 1 and the heat sink 2 warps, thereby preventing the heat sink 14 from flowing out due to pump-out. Furthermore, because the gap 11 is a sealed space from the outside of the semiconductor module, the air pressure in the gap 11 does not decrease even in low-pressure environments such as high-altitude environments, and partial discharge in the gap 11 is suppressed.

[0018] A method for manufacturing a semiconductor module according to the first embodiment will be described. FIG. 7 is a process diagram of the method for manufacturing a semiconductor module according to the first embodiment, illustrating a method for manufacturing a semiconductor module from the semiconductor device 1 shown in FIG. 1 , a heat dissipation member 14, a flexible sheet 15, and a heat sink 12. In a first step, step S1, the flexible sheet 15 is placed on the top surface of the heat sink 12, and the process proceeds to a second step, step S2. In a second step, step S2, the heat dissipation member 14 is placed on the top surface of the heat sink 12 inside the inner periphery of the flexible sheet 15 so that the heat dissipation member 14 is surrounded by the flexible sheet 15, and the process proceeds to a third step, step S3. In a third step, step S3, the heat dissipation member 14 is sandwiched between the heat sink 12 and the heat dissipation plate 2, and the case 8 and the heat sink 12 are fastened together via the flexible sheet 15.

[0019] 8 and 9 are diagrams showing the semiconductor module according to the first embodiment during manufacturing. FIG. 8 shows the state before the third step, when the heat sink 12 and the heat plate 2 are in contact with each other, and FIG. 9 shows the state when the heat sink 14 and the heat plate 2 are in contact with each other, when the case 8 and the heat sink 12 are fastened together. Before the case 8 and the heat sink 12 are fastened together, the difference between the vertical height of the bottom surface of the heat sink 2 and the vertical height of the bottom surface of the case 8 is defined as t1, the vertical thickness of the heat sink 14 is defined as t2, and the vertical thickness of the flexible sheet 15 is defined as t3. If the heat sink 14 is thermal grease, the thickness of the applied thermal grease is defined as t2. At this time, as shown in FIG. 9, before the case 8 and the heat sink 12 are fastened together with the screws 13, t1 + t2 > t3. That is, before the case 8 and the heat sink 12 are fastened together, the difference in height between the bottom surface of the heat sink 2 and the bottom surface of the case 8 plus the thickness of the heat dissipation member 14 is greater than the thickness of the flexible sheet 15.

[0020] 10 is a diagram showing a semiconductor module of a second comparative example during manufacturing. As in the semiconductor module of the second comparative example shown in FIG. 10 , if t1 + t2 < t3 holds before the case 8 and heat sink 12 are fastened together, air remains between the heat sink 2 and the heat dissipation member 14. In the semiconductor module of the second comparative example, even if the thickness of the flexible sheet 15 is reduced by fastening the case 8 and heat sink 12 together with the screws 13 in the third step, the space surrounded by the heat sink 12, flexible sheet 15, case 8, heat sink 2, and insulating layer 3 is sealed, preventing air from leaking outside. This increases the likelihood of air remaining between the heat sink 2 and the heat dissipation member 14, resulting in reduced heat dissipation. Therefore, in the manufacturing method of the semiconductor module according to the first embodiment, t1 + t2 > t3 holds before the case 8 and heat sink 12 are fastened together with the screws 13, as shown in FIG. 9 .

[0021] 11 is a diagram showing the semiconductor module according to embodiment 1 after the third step. When the case 8 and the heat sink 12 are fastened together with the screws 13 in the third step, the heat dissipation member 14 expands laterally, reducing its thickness, and the bottom surface of the case 8 comes into contact with the flexible sheet 15. The thickness of the flexible sheet 15 is then slightly compressed, sealing the space surrounded by the heat sink 12, the flexible sheet 15, the case 8, the heat sink 2, and the insulating layer 3. After the case 8 and the heat sink 12 are fastened together with the screws 13 in the third step, if the vertical thickness of the heat dissipation member 14 is t21 and the vertical thickness of the flexible sheet 15 is t31, then t1 + t21 = t31, as shown in FIG.

[0022] When the case 8 and the heat sink 12 are fastened together with the screws 13 in the third step, the heat dissipation member 14 reduces in thickness and expands laterally, contacting the flexible sheet 15 as shown in FIG. 11 . Therefore, when the heat dissipation member 14 is installed on the top surface of the heat sink 12 inside the frame of the flexible sheet 15 in the second step, it is preferable to provide a space between the heat dissipation member 14 and the flexible sheet 15 as shown in FIG. 8 . When the case 8 and the heat sink 12 are fastened together with the screws 13 in the third step, the heat dissipation member 14 reduces in thickness and expands laterally. When the heat dissipation member 14 contacts the flexible sheet 15 and can no longer expand laterally, the screws 13 cannot be tightened any further. If excessive force is applied to the flexible sheet 15 by tightening the screws 13 too tightly, creep may occur over the long term, potentially reducing the sealing performance of the space surrounded by the heat sink 12, the flexible sheet 15, the case 8, the heat dissipation plate 2, and the insulating layer 3. However, in the semiconductor module according to embodiment 1, the thickness t31 of the flexible sheet 15 shown in FIG. 11 does not fall below t1 + t21. Therefore, by assuming the thickness t31 of the flexible sheet 15 after deformation and the thickness t21 of the heat dissipation member 14 after deformation, the thickness t3 of the flexible sheet 15 before deformation and the thickness t2 of the heat dissipation member 14 before deformation are set, thereby preventing excessive force from being applied to the flexible sheet 15 and suppressing the occurrence of creep.

[0023] As described above, the semiconductor module according to the first embodiment comprises a semiconductor device 1 including a heat sink 2, an insulating layer 3 arranged on the upper surface of the heat sink 2, a circuit electrode 4 arranged on the upper surface of the insulating layer 3, a semiconductor chip 5 arranged on the upper surface of the circuit electrode 4, a case 8 formed in a frame shape surrounding the periphery of the heat sink 2 with the lower surface of the heat sink 2 exposed and in contact with the peripheral portion of the upper surface of the insulating layer 3 so as to surround the semiconductor chip 5, a heat sink 12 fastened to the case 8, a heat dissipation member 14 sandwiched between the upper surface of the heat sink 12 and the lower surface of the heat sink 2, and a flexible sheet 15 formed in a frame shape surrounding the periphery of the heat dissipation member 14 and sandwiched between the upper surface of the heat sink 12 and the bottom surface of the case 8, and since the heat sink 12 is fastened to the case 8 via the flexible sheet 15, the occurrence of pump-out of the heat dissipation member 14 is suppressed.

[0024] Embodiment 2. In the semiconductor module according to embodiment 1, the width of through-hole 16 in flexible sheet 15 is made larger than the width of heat sink 2. That is, the inner peripheral edge of flexible sheet 15, as viewed from the bottom of heat sink 2, is positioned outside the outer peripheral edge of heat sink 2, as viewed from the bottom of heat sink 2. In this structure, if there is a narrow portion on the bottom of case 8 (for example, a narrow portion on the upper or lower side of case 8 in FIG. 5 ), the narrow portion of the bottom of case 8 may enter through-hole 16 in flexible sheet 15 if the positioning accuracy when attaching case 8 to flexible sheet 15 is low. If the narrow portion of the bottom of case 8 enters through-hole 16 in flexible sheet 15, the space surrounded by heat sink 12, flexible sheet 15, case 8, heat sink 2, and insulating layer 3 in the semiconductor module will no longer be sealed, and the effects of the semiconductor module according to embodiment 1 will not be obtained. In the semiconductor module according to embodiment 2, the width of the through hole 16 in the flexible sheet 15 is made smaller than the width of the heat sink 2, thereby preventing the narrow portion of the bottom surface of the case 8 from entering the through hole 16 in the flexible sheet 15.

[0025] 12 is a diagram showing a semiconductor module according to the second embodiment during manufacturing, illustrating the semiconductor device 1, heat sink 12, flexible sheet 15, and heat dissipation member 14 after the first and second steps and before the third step of FIG. 7 . The manufacturing process of the semiconductor module according to the second embodiment is the same as the manufacturing process of the semiconductor module according to the first embodiment shown in FIG. 7 . In the semiconductor module according to the second embodiment, the width of the through-hole 16 in the flexible sheet 15 is smaller than the width of the heat sink 2, and a portion of the flexible sheet 15 overlaps the edge of the heat sink 2. For example, the inner peripheral edge of the flexible sheet 15, as viewed from the bottom of the heat sink 2, is located inside the outer peripheral edge of the heat sink 2, as viewed from the bottom of the heat sink 2. Note that, in order to fasten the case 8 and the heat sink 12 via the flexible sheet 15, the outer peripheral edge of the flexible sheet 15, as viewed from the bottom of the heat sink 2, is located outside the outer peripheral edge of the heat sink 2, as viewed from the bottom of the heat sink 2. A portion of the flexible sheet 15 near the inner peripheral edge overlaps the edge of the heat sink 2. This allows the case 8 to be easily placed on the flexible sheet 15 even when the positioning accuracy when attaching the case 8 to the flexible sheet 15 is low.

[0026] In the semiconductor module according to the second embodiment, if the vertical thickness t2 of the heat dissipation member 14 is smaller than the vertical thickness t3 of the flexible sheet 15 before the case 8 and the heat sink 12 are fastened together, air will remain between the heat dissipation plate 2 and the heat dissipation member 14 in the semiconductor module after the third step. Therefore, as shown in Fig. 12, the vertical thickness t2 of the heat dissipation member 14 is made larger than the vertical thickness t3 of the flexible sheet 15 before the case 8 and the heat sink 12 are fastened together with the screws 13. Furthermore, since the heat dissipation member 14 expands laterally when the case 8 and the heat sink 12 are fastened together with the screws 13 in the third step, a space is provided between the heat dissipation member 14 and the flexible sheet 15 before the case 8 and the heat sink 12 are fastened together.

[0027] 13 is a diagram showing the semiconductor module according to the second embodiment after the third process. By fastening the case 8 and the heat sink 12 with the screws 13, the vertical thickness of the flexible sheet 15 at the position where it contacts the heat sink 2 is smaller than the vertical thickness of the flexible sheet 15 at the position where it is not contacting the heat sink 2. That is, the thickness of the flexible sheet 15 at a position inside the outer circumferential edge of the heat sink 2 is smaller than the thickness at a position outside the outer circumferential edge of the heat sink 2. As a result, the vertical thickness of the flexible sheet 15 at the position where it contacts the heat sink 2 is smaller than the vertical thickness of the flexible sheet 15 at the position where it contacts the case 8. As a result, the semiconductor module according to the second embodiment can reduce the volume of the heat dissipation member 14 compared to the semiconductor module according to the first embodiment. Furthermore, in the semiconductor module according to embodiment 2, the space surrounded by the heat sink 12, flexible sheet 15, case 8, heat sink 2, and insulating layer 3 is sealed, suppressing the occurrence of pump-out of the heat dissipation member 14 and suppressing the occurrence of partial discharge in the gap 11 even in a low-pressure environment such as a high-altitude environment.

[0028] Embodiment 3 In the semiconductor module according to embodiment 2, the thickness t2 of the heat dissipation member 14 is determined in accordance with the thickness t3 of the flexible sheet 15. Therefore, if it is desired to reduce the thickness t2 of the heat dissipation member 14, it is necessary to reduce the thickness t3 of the flexible sheet 15. However, if the thickness t3 of the flexible sheet 15 is made too small, it becomes impossible to maintain a tight seal between the bottom surface of the case 8 and the upper surface of the flexible sheet 15, and between the lower surface of the flexible sheet 15 and the upper surface of the heat sink 12.

[0029] 14 and 15 are diagrams showing a semiconductor module according to the third embodiment in the middle of manufacture. Fig. 14 is a diagram showing the state before the third step, when the heat sink 2 and the heat dissipation member 14 have not yet come into contact with each other, and Fig. 15 is a diagram showing the state when the heat sink 2 and the heat dissipation member 14 have come into contact with each other, when the case 8 and the heat sink 12 are fastened together. The steps of the method for manufacturing a semiconductor module according to the third embodiment are the same as the steps of the method for manufacturing a semiconductor module according to the first embodiment shown in Fig. 7. As with the semiconductor module according to the second embodiment, the inner peripheral edge of the flexible sheet 15, when viewed from the bottom of the heat sink 2, is located inside the outer peripheral edge of the heat sink 2 when viewed from the bottom of the heat sink 2, and the outer peripheral edge of the flexible sheet 15, when viewed from the bottom of the heat sink 2, is located outside the outer peripheral edge of the heat sink 2 when viewed from the bottom of the heat sink 2. In the semiconductor module according to embodiment 3, before the case 8 and the heat sink 12 are fastened together, the vertical thickness of the flexible sheet 15 at a position where it overlaps with the heat sink 2 when viewed from the underside of the heat sink 2 after the case 8 and the heat sink 12 are fastened together is made smaller than the vertical thickness of the flexible sheet 15 at a position where it contacts the bottom surface of the case 8 after the case 8 and the heat sink 12 are fastened together, and the vertical thickness of the heat dissipation member 14 is made larger than the vertical thickness of the flexible sheet 15 at a position where it overlaps with the heat sink 2 when viewed from the underside of the heat sink 2 after the case 8 and the heat sink 12 are fastened together. For example, before the case 8 and the heat sink 12 are fastened together, the vertical thickness of the flexible sheet 15 at the position where it will come into contact with the heat sink 2 after the case 8 and the heat sink 12 are fastened together is made smaller than the vertical thickness of the flexible sheet 15 at the position where it will come into contact with the bottom surface of the case 8 after the case 8 and the heat sink 12 are fastened together, and the vertical thickness of the heat dissipation member 14 is made larger than the vertical thickness of the flexible sheet 15 at the position where it will come into contact with the heat sink 2 after the case 8 and the heat sink 12 are fastened together.The flexible sheet 15 of the semiconductor module according to embodiment 3 has, for example, a stepped cross section, and when the vertical thickness of the step portion 151, which is located at a position that overlaps with the heat sink 2 after the case 8 and the heat sink 12 are fastened, is t4 before the case 8 and the heat sink 12 are fastened, the relationships "t2 > t4" and "t1 + t2 > t3" are satisfied.

[0030] 16 is a diagram showing the semiconductor module according to the third embodiment after the third process. Like the flexible sheet 15 of the semiconductor module according to the second embodiment, the flexible sheet 15 of the semiconductor module according to the third embodiment has a smaller vertical thickness at the position where it contacts the heat sink 2 than at the position where it contacts the case 8. After the case 8 and the heat sink 12 are fastened together with the screws 13 in the third process, the vertical thickness of the heat sink member 14 is t21, the vertical thickness of the flexible sheet 15 at the portion sandwiched between the case 8 and the heat sink 12 is t31, and the vertical thickness of the step portion 151 at the portion sandwiched between the heat sink 2 and the heat sink 12 is t41. As shown in FIG. 16 , t21 = t41, and thus t1 + t21 = t31. In the semiconductor module according to the third embodiment, the thickness of the heat sink member 14 can be reduced while maintaining the thickness of the flexible sheet 15 necessary for fastening. That is, the space surrounded by the heat sink 12, flexible sheet 15, case 8, heat sink 2, and insulating layer 3 is sealed, and the thickness of the heat sink 14 can be made smaller than that of the semiconductor module according to embodiment 2. Furthermore, for example, by aligning the position of the step portion 151 of the flexible sheet 15 with the position of the outer peripheral edge of the heat sink 2, it is possible to suppress misalignment of the installation in the third step.

[0031] Although various exemplary embodiments are described in this disclosure, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are contemplated within the scope of the technology of this disclosure. For example, this includes cases where at least one component is modified, added, or omitted, or where at least one component is extracted and combined with components of another embodiment.

[0032] REFERENCE SIGNS LIST 1 semiconductor device, 2 heat sink, 3 insulating layer, 4 circuit electrode, 5 semiconductor chip, 6 wire, 7 terminal, 8 case, 9 insulating sealing material, 10a, 10b through hole, 11 gap, 12 heat sink, 13 screw, 14 heat dissipation member, 15 flexible sheet, 16 through hole, 151 step portion.

Claims

1. A semiconductor module comprising: a semiconductor device comprising: a heat sink; an insulating layer disposed on an upper surface of the heat sink; circuit electrodes disposed on the upper surface of the insulating layer; a semiconductor chip disposed on the upper surface of the circuit electrodes; a case formed in a frame shape surrounding the periphery of the heat sink with the lower surface of the heat sink exposed and in contact with the peripheral portion of the upper surface of the insulating layer so as to surround the semiconductor chip; a heat sink fastened to the case; a heat dissipation member sandwiched between the upper surface of the heat sink and the lower surface of the heat sink; and a flexible sheet formed in a frame shape surrounding the periphery of the heat dissipation member and sandwiched between the upper surface of the heat sink and a bottom surface of the case, wherein the heat sink is fastened to the case via the flexible sheet.

2. The semiconductor module according to claim 1, wherein an inner peripheral edge of said flexible sheet is positioned outside an outer peripheral edge of said heat sink.

3. The semiconductor module according to claim 1, wherein an inner peripheral edge of said flexible sheet is located inside an outer peripheral edge of said heat sink.

4. The semiconductor module according to claim 3, wherein the flexible sheet has a smaller thickness at the position where it is in contact with the heat sink than at the position where it is in contact with the case.

5. A method for manufacturing a semiconductor module comprising: a semiconductor device comprising a heat sink, an insulating layer arranged on an upper surface of the heat sink, circuit electrodes arranged on an upper surface of the insulating layer, a semiconductor chip arranged on an upper surface of the circuit electrodes, and a case formed in a frame shape surrounding the periphery of the heat sink with the lower surface of the heat sink exposed and in contact with the peripheral portion of the upper surface of the insulating layer so as to surround the semiconductor chip, a heat dissipation member, a flexible sheet formed in a frame shape, and a heat sink, the method comprising: a first step of placing the flexible sheet on the upper surface of the heat sink; a second step of placing the heat dissipation member on the upper surface of the heat sink inside the inner circumference of the flexible sheet so as to be surrounded by the flexible sheet; and a third step of sandwiching the heat dissipation member between the heat sink and the heat sink, and fastening the case and the heat sink via the flexible sheet.

6. A method for manufacturing a semiconductor module, wherein the inner edge of the flexible sheet is positioned outside the outer edge of the heat sink, and the method for manufacturing a semiconductor module, as described in claim 5, is characterized in that before the case and the heat sink are fastened to each other, the difference in height between the bottom surface of the heat sink and the bottom surface of the case plus the thickness of the heat sink member is greater than the thickness of the flexible sheet.

7. A method for manufacturing a semiconductor module, characterized in that the inner edge of the flexible sheet is located more inward than the outer edge of the heat sink, and the thickness of the heat sink member is greater than the thickness of the flexible sheet before the case and the heat sink are fastened together.

8. A method for manufacturing a semiconductor module, in which the inner edge of the flexible sheet is located more inward than the outer edge of the heat sink, characterized in that, before the case and the heat sink are fastened together, the thickness of the flexible sheet at a position where it will overlap with the heat sink after the case and the heat sink are fastened together is smaller than the thickness of the flexible sheet at a position where it will contact the bottom surface of the case after the case and the heat sink are fastened together, and the thickness of the heat dissipation member is greater than the thickness of the flexible sheet at a position where it will overlap with the heat sink after the case and the heat sink are fastened together.

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