Semiconductor device

Abstract

Provided is a semiconductor device, in particular, a power semiconductor device that needs to operate stably at high temperatures, wherein moisture that has penetrated into the device interior is prevented from penetrating into an insulating material, voids or cracking are prevented from occurring in the insulating material upon heating, and partial discharge and electrical breakdown are prevented.　This semiconductor device comprises a semiconductor substrate onto which a semiconductor element is mounted, and a housing in which the semiconductor substrate is hermetically sealed, wherein the housing is provided with a pressure regulation unit for changing the volume of the housing interior in accordance with the pressure in the housing interior.

Description

Semiconductor Devices

[0001] The present invention relates to a semiconductor device, and more particularly to a power semiconductor device that is required to operate stably at high temperatures.

[0002] In recent years, environmental and resource issues have come to the forefront on a global scale, and in order to make effective use of resources, promote energy conservation, and reduce greenhouse gas emissions, high-efficiency power conversion devices, such as inverter devices that utilize switching of power semiconductor elements, have been attracting attention. Such power conversion devices are being widely applied to a wide range of applications, including home appliances such as refrigerators and air conditioners, industrial machinery, hybrid electric vehicles (HEVs), electric vehicles (EVs), railways, and power and social infrastructure-related equipment.

[0003] A power conversion system is composed of numerous components, such as a power semiconductor device (power module) incorporating a power semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor), bus bars, capacitors, inductors, various sensors, and control circuits. To reduce installation space and ensure safety, compact, highly reliable power conversion systems are in demand. To achieve this, it is important to reduce the size and improve the reliability of power semiconductor devices, which are the main components of power conversion systems.

[0004] Currently, IGBTs, diodes, and the like made mainly of Si are used as power semiconductor elements in power semiconductor devices. As mentioned above, power semiconductor devices are becoming smaller and larger in capacity, and as a result, stable operation at high temperatures is required. Power semiconductor elements are also required to have "high breakdown voltage," "low on-resistance," and "high-speed switching" characteristics. SiC, which has a breakdown field strength 10 times that of Si and a band gap 3 times that of Si, has begun to be applied as a next-generation power semiconductor element and is expected to become more widespread. These next-generation power semiconductor elements will be able to be used at even higher temperatures than Si devices, so power semiconductor devices must have high reliability under high-temperature operation.

[0005] Patent Document 1, for example, is a power semiconductor device that aims to achieve high reliability during high-temperature operation. Patent Document 1 discloses a power semiconductor device in which a lead pin block includes a base portion from which many lead pins stand, a lid receiving step portion, engaging claws on the inner surface of a frame portion, guide pins that are inserted into guide holes in a female connector of the lead pins during use, and an air vent hole that penetrates the base portion in the thickness direction from a recess in the lid receiving step portion to the step portion of the engaging claw. In Patent Document 1, when the lead pin block is dropped onto the inner surface of the frame portion and the engaging claws are engaged with the engaging claws, the block is tightly secured to prevent removal, but the gap between the block and the frame portion is sealed with a sealing member. The space inside the semiconductor device is in communication with the outside air via the air vent hole.

[0006] According to the configuration of Patent Document 1, when the lead pin block is inserted into the frame and assembled, the fitting gap with the frame is sealed by a sealing member on the internal space side. Therefore, even if the temperature of the gel resin encapsulant rises due to heating for fixing the insulating lid to the insulating case frame or heat generated by the semiconductor element, causing the gel resin encapsulant to thermally expand, the gel resin encapsulant will not seep out of the gap. Furthermore, while the expansion of the gel resin encapsulant increases the air pressure of the residual air in the internal space, the air vent holes prevent this internal pressure from increasing, allowing the gel resin encapsulant to expand freely. This is said to suppress the occurrence of excessive thermal stress and improve reliability.

[0007] Furthermore, Patent Document 2 discloses a power semiconductor device that will not break even if the volume of a soft sealing material expands due to heat generation during testing or operation, and that has a case to which a substrate used as a bottom plate is attached, a semiconductor element and an electrical connection member are attached to the side of the substrate facing the inside of the case, a soft sealing material is injected into the case, and a hard sealing material is injected on top of that, and that the power semiconductor device has a protection space connected to the space inside the case into which the soft sealing material has been injected, and is formed so that the soft sealing material expands into the protection space when the temperature rises, and that the protection space is in communication with the atmosphere surrounding the power semiconductor device through an opening provided in the case.

[0008] According to the configuration of Patent Document 2, by providing a compensation space inside, the soft sealing material can expand in volume, and it is possible to prevent high pressure that could damage the power semiconductor device from occurring inside the power semiconductor device. It is also considered preferable to provide an opening in the wall of the case that forms the compensation space, thereby communicating the air inside the compensation space with the outside air surrounding the device, so that the power semiconductor device can breathe.

[0009] The power semiconductor devices of Patent Documents 1 and 2 both have a substrate with a semiconductor element mounted inside a case, the semiconductor element and substrate are insulated and sealed with a gel resin sealant, and have a structure in which an air vent (an "air vent hole" in Patent Document 1, and an "opening" in Patent Document 2) is formed in a part of the case or in a part of the lead pin block. It is said that this prevents overflow of the gel resin sealant from gaps due to volume expansion when the semiconductor element generates heat during operation, prevents an increase in internal pressure, and suppresses the generation of excessive thermal stress.

[0010] Meanwhile, in the shipping test of a power semiconductor device in which a substrate carrying a power semiconductor element is bonded to a heat-dissipating base plate with a bonding material such as solder, there is a process to inspect the bonding condition between the heat-dissipating base plate and the substrate. The power semiconductor device is immersed in water, and ultrasonic waves are used to inspect the presence of solder voids or sink marks at the bonding interface between the heat-dissipating base plate and the substrate. This is an important inspection to confirm the heat dissipation performance of the power semiconductor element to the base plate and the reliability of the power semiconductor device.

[0011] JP-A-8-162571 JP-A-63-28052

[0012] In the technologies described in Patent Documents 1 and 2, water may enter the device through a vent hole formed in a part of the case or a part of the lead pin block. The water that has entered the device creates a high-temperature, high-humidity environment inside the device due to heating, such as during a high-temperature blocking test performed in the inspection process of the aforementioned shipping test. This vaporizes the water and penetrates into the gel resin encapsulant. Furthermore, the vaporized water forms voids and cracks in the gel resin encapsulant. Subsequently, when a high voltage is applied during a partial discharge test or a withstand voltage test, partial discharges or dielectric breakdown may occur. These issues needed to be addressed in conventional power semiconductor devices.

[0013] Furthermore, power semiconductor devices are incorporated into power converters for use. In this case, depending on the housing structure of the power converter and the environment in which it is used, it is possible that water such as rainwater or condensation may get on the power semiconductor device. Furthermore, in a hot and humid environment such as during the rainy season, the inside of the device may also become humid through the ventilation holes. When the temperature drops under such conditions, moisture may be trapped inside the device. In the technologies of Patent Documents 1 and 2, it is possible that water may enter the device during use through ventilation holes formed in a part of the case or a part of the lead pin block. Moisture that has entered the device may degrade the insulation and reliability of the device, and this point also needed to be improved.

[0014] The present invention has been made in consideration of the above circumstances, and aims to provide a power semiconductor device that prevents partial discharge and dielectric breakdown by suppressing the penetration of moisture that has entered the device into the insulating material and the generation of voids and cracks in the insulating material when heated.

[0015] The present invention provides a semiconductor device that solves the above problems as follows: The semiconductor device includes a semiconductor substrate on which a semiconductor element is mounted and a housing that hermetically seals the semiconductor substrate, the housing including a pressure adjusting unit that changes the volume inside the housing in accordance with the pressure inside the housing.

[0016] According to the present invention, it is possible to prevent moisture from penetrating into the device, and to suppress voids and cracks that occur in the insulating material when heated by moisture that has penetrated the insulating material, thereby preventing partial discharge and dielectric breakdown.

[0017] Furthermore, since an excessive increase in internal pressure when the temperature rises can be prevented, stress applied to the gel insulating material can be prevented, and crushing and cracking of the gel insulating material can be prevented.

[0018] 1 is a cross-sectional view schematically illustrating the structure of a power semiconductor device according to a first embodiment of the present invention. FIG. 2 is a view explaining deformation of an expandable / contractible part in response to pressure inside the device in the power semiconductor device according to the first embodiment of FIG. 1. FIG. 3 is a cross-sectional view schematically illustrating the structure of a power semiconductor device according to a second embodiment of the present invention. FIG. 4 is a cross-sectional view schematically illustrating the structure of a power semiconductor device according to a third embodiment of the present invention. FIG. 5 is a cross-sectional view schematically illustrating the structure of a power semiconductor device according to a comparative example 1 (conventional example 1), and a view for explaining a problem that occurs in the conventional power semiconductor device. FIG. 6 is a cross-sectional view schematically illustrating the structure of a power semiconductor device according to a comparative example 2 (conventional example 2), and a view for explaining a problem that occurs in the conventional power semiconductor device. FIG. 7 is a diagram showing partial discharge test results for the power semiconductor device according to the first to third embodiments of the present invention, and comparative examples 1 and 2. FIG. 8 is a diagram showing dielectric strength test results for the power semiconductor device according to the first to third embodiments of the present invention, and comparative examples 1 and 2. FIG. 9 is a diagram showing test pass / fail judgment results for the power semiconductor device according to the first to third embodiments of the present invention, and comparative examples 1 and 2.

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0020] 1 is a schematic cross-sectional view showing the structure of a power semiconductor device according to a first embodiment of the present invention. This embodiment is an example in which the semiconductor device is applied to a power semiconductor device including a power semiconductor element.

[0021] As shown in FIG. 1 , the power semiconductor device 100A comprises an insulating circuit board 2 having a power semiconductor element 1 mounted on one surface thereof, a heat dissipation base plate 3 (heat dissipation base) joined to the surface of the insulating circuit board 2 opposite to the surface on which the power semiconductor element 1 (semiconductor element) is mounted, a case 4 fixed to the heat dissipation base plate 3 and surrounding the insulating circuit board 2, a gel-like insulating material 5 that insulates and seals the power semiconductor element 1 and the insulating circuit board 2 inside the case 4, and a lid 6 that covers the entire upper part of the power semiconductor device 100A and is fixed to the case 4, and at least a portion of the portion of the lid 6 that is not in contact with the insulating material 5 is provided with a movable part 50 that deforms in response to the pressure in a space 31 inside the device.

[0022] The movable part 50 has a hole 7 opened in the case 4 or the lid 6, an expandable movable part 21 that is arranged to close the hole 7 and deforms due to the pressure in the space 31 inside the device, and a frame part 22 that bonds the expandable movable part to the side wall of the hole in the lid. The expandable movable part 21 and the frame part 22 in this embodiment are made of a rubber-like organic material that is impermeable to air and water.

[0023] Except for the frame portion 22 that is bonded to the sidewall of the hole in the lid via the adhesive 10, the rubber-like organic material of the expandable movable portion 21 is formed thinner than the frame portion 22 so that it deforms in response to pressure changes in the space 31 inside the device. In this embodiment, the movable portion 50 is provided in a portion of the lid 6, but it is also possible to provide the movable portion 50 in the case 4. In the claims, the insulated circuit board 2 on which the power semiconductor element 1 is mounted is referred to as the "semiconductor substrate," and the state in which the lid 6 is fixed to the case 4 and the "semiconductor substrate" is hermetically sealed is referred to as the "housing." Furthermore, the movable portion 50, which deforms in response to the pressure in the space 31 inside the device, thereby changing the volume inside the "housing," corresponds to the "pressure adjusting portion" described in the claims.

[0024] A method for manufacturing the power semiconductor device 100A configured as described above will now be described.

[0025] As shown in FIG. 1, the insulating circuit board 2 of the power semiconductor device 100A has a circuit electrode 2b bonded to one surface of an insulating substrate 2a and a back electrode 2c bonded to the other surface thereof via a brazing material 2d.

[0026] The insulating substrate 2a is selected from the following materials depending on the normal device breakdown voltage of the power semiconductor device 100A. That is, for the power semiconductor device 100A with a normal device breakdown voltage of 1200V or more, ceramics such as aluminum oxide, aluminum nitride, and silicon nitride are used for the insulating substrate 2a. Also, for the power semiconductor device 100A with a device breakdown voltage of less than 1200V, a high thermal conductivity resin substrate in which a high thermal conductivity filler is dispersed in an organic resin is used. In the case of a high thermal conductivity resin substrate, the circuit electrode 2b and the back electrode 2c are bonded to the substrate by the adhesive force of the resin, so no brazing material is required.

[0027] The circuit electrodes 2b are formed with a circuit using a technique such as etching in a circuit shape required for the circuit operation of the power semiconductor device 100A.

[0028] First, the power semiconductor element 1 is bonded to the circuit electrodes 2b of the insulated circuit board 2 via a bonding material 8 such as solder or sintered metal. Next, the electrodes of the power semiconductor element 1 and the circuit electrodes 2b of the insulated circuit board 2 are connected using thin metal wires such as aluminum to form the required circuit (thin metal wires are omitted from Figure 1). The heat dissipating base plate 3 and the backside electrodes of the insulated circuit board 2 are then bonded via a bonding material 9 such as solder. Next, adhesive 10 is applied to the outer periphery of the heat dissipating base plate 3 to secure the case 4 to the heat dissipating base plate 3. In addition to the adhesive, the heat dissipating base plate 3 and the case 4 may also be secured together with screws (screws are not shown). Finally, terminals 11 are bonded to the circuit electrodes 2b of the insulated circuit board 2 using a technique such as ultrasound.

[0029] Thereafter, a lid 6 is placed on top of the power semiconductor device 100A, and the case 4 and the lid 6 are bonded and fixed together using adhesive 10. Here, a hole 7 (in which a movable part 50 will later be formed) is formed in advance in the lid 6 so that a gel insulating material can be injected into the device. Then, the gel insulating material 5 is injected through the hole 7, and the gel insulating material 5 is hardened under predetermined hardening conditions. Silicone gel is generally used as the gel insulating material 5, but any material having insulating properties may be used, and other resins other than silicone may also be used.

[0030] Finally, adhesive 10 (jointing means) is applied around hole 7 in lid 6, and movable section 50, which deforms in response to the pressure in device internal space 31, specifically frame section 22 of movable section 50, is adhesively fixed to hole 7 to complete power semiconductor device 100A. Note that, although lid 6 is fixed to case 4 with adhesive 10, which is a jointing means, in FIG. 1, case 4 and lid 6 may be formed integrally. The material of case 4 and lid 6 is, for example, an organic insulating material such as PPS (polyphenylene sulfide) or PBT (polybutylene terephthalate).

[0031] A rubber-like organic material was used for the movable portion 50 (expandable movable portion 21, frame portion 22) of the power semiconductor device 100A. Here, silicone rubber was used, but any material would be acceptable as long as it does not easily allow water or air to penetrate the power semiconductor device and deforms in response to pressure changes in the device's internal space 31. The frame portion 22 of the movable portion 50 is thick in the vertical direction, while the expandable movable portion 21 inside the frame portion is thin in the vertical direction to allow deformation and movement. For example, the frame portion 22 is 5 mm thick, and the expandable movable portion 21 is 200 μm thick. In addition to silicone rubber, other rubber materials such as natural rubber, nitrile rubber, urethane rubber, acrylic rubber, isoprene rubber, butadiene rubber, and styrene rubber may also be used as the rubber-like organic material for the movable portion 50. A rubber material with excellent heat resistance, cold resistance, aging resistance, ozone resistance, and weather resistance, so that it can withstand the environment in which the semiconductor device is used for a long period of time, is preferred.

[0032] By making the housing of the power semiconductor device 100A have the above-mentioned airtight structure, it is possible to prevent moisture from entering the inside of the device, and as shown in Figure 2, when the temperature rises during operation of the device, the expandable movable part 21 of the movable part 50 expands outward from the device in a direction (21a) that expands the volume of the space 31 inside the device, thereby minimizing the increase in pressure in the space 31 inside the device. Also, when the temperature drops during shutdown of the device, it expands inward from the device in a direction (21b) that reduces the volume of the space inside the device, thereby changing the volume inside the housing and minimizing the decrease in pressure in the space 31 inside the housing, thereby minimizing the occurrence of voids and cracks in the silicone gel.

[0033] As will be described later, in a semiconductor device with ventilation holes, such as in Comparative Example 1 ( FIG. 5 ), moisture penetrates the device through the ventilation holes and gradually penetrates the silicone gel. At high temperatures, the penetrated moisture evaporates, creating voids 32 in the silicone gel, potentially resulting in partial discharges and poor pressure resistance. In a sealed semiconductor device without ventilation holes, such as in Comparative Example 2 ( FIG. 6 ), the pressure inside the device increases at high temperatures. When the adhesive between the case and lid can no longer withstand the increased pressure, air leaks from the internal space of the device through the adhesive interface between the case and lid. When the device temperature drops, the internal space of the device becomes negative pressure, which causes the case and lid to seal tightly together, preventing air from entering the semiconductor device from the outside and maintaining the negative pressure for a long period of time. This negative pressure can create voids 32 in the silicone gel, potentially resulting in partial discharges and poor pressure resistance. In contrast, the power semiconductor device 100A of this embodiment includes a movable part 50 that deforms in response to the pressure in the space inside the device, located in a portion of the lid 6 that is not in contact with the insulating material 5. This prevents moisture from entering the device and prevents voids from forming in the silicone gel due to the evaporation of moisture at high temperatures. Furthermore, even when there is a temperature change from low to high or from high to low, the deformation of the movable part reduces the pressure change in the space inside the device. This prevents voids and cracks from forming in the silicone gel. Because voids and cracks can be prevented from forming in the gel insulating material, partial discharge and dielectric breakdown can be prevented, resulting in a compact, highly reliable power semiconductor device.

[0034] Furthermore, if the temperature of the semiconductor device becomes abnormally higher than expected and the expandable / contractable part 21 is no longer able to accommodate the pressure change in the space inside the device within its deformation range, as in Comparative Example 2, it is expected that air will leak from the adhesive interface between the case and the lid, causing the space inside the device to enter a negative pressure state when the device is returned to room temperature. In this case, the expandable / contractable part 21 will deform in a direction that reduces the volume of the space inside the device at the same temperature compared to its initial, unexpanded state. The soundness of the semiconductor device can also be determined by checking this deformation. If no change is observed in the movable part even when the temperature of the device changes, this indicates that the device is not sealed, which may indicate that the device is absorbing moisture. Monitoring the change in the movable part (the amount of change in operation) when the temperature changes allows the soundness of the semiconductor device to be evaluated (soundness evaluation part).

[0035] As a method of monitoring, the movable part of the extendable / retractable part 21 may be color-coded to indicate normal and abnormal ranges, allowing visual inspection to determine whether the device is healthy or not, or a scale may be provided to allow the user to read the values ​​displayed on the scale. Specifically, by providing a concentric pattern on the rubber-like member, the size of the concentric circles changes when the rubber-like member stretches due to a change in pressure, and the state of the pressure change can be estimated from the size. Also, by coloring each of the multiple concentric circles in a different color, the color tone changes as the rubber-like member stretches (the color becomes lighter as it stretches), and the state of the pressure change can be estimated based on the change in color tone.

[0036] If necessary, a device such as a strain sensor that converts the amount of movement of the movable part of the expandable movable part 21 into an electrical signal can be provided, and a system that automatically monitors the soundness based on the electrical signal can be provided.

[0037] Furthermore, semiconductor devices may be used in high-altitude areas. If the semiconductor device is hermetically sealed at the factory, the internal volume of the housing may be large from the start (in the configuration of Example 1, the rubber-like member is used in a protruding state), potentially making it unable to absorb pressure changes inside the housing. Therefore, a pressure adjustment hole may be provided in part of the housing to adjust the internal pressure of the housing to the local pressure. After transporting the semiconductor device to the area where it will be used, the hole is opened to adjust the internal pressure of the housing to the local atmospheric pressure, and then the hole is closed with a screw, thereby adapting the semiconductor device to the area where it will be used. Reference numeral 60 in FIG. 1 is an example of a pressure adjustment screw. Any device other than a screw that can temporarily open the interior of the housing to the outside may be used. In the claims, this screw-like member is referred to as an "air opening portion." Furthermore, when the semiconductor device according to the present invention is mounted on an aircraft, the air pressure outside the housing fluctuates repeatedly and to a large extent. Under such operating conditions, adjusting the pressure inside the housing to match the external air pressure may actually promote the formation of voids and cracks in the silicone gel. For semiconductor devices used under such conditions, it may be effective to provide a limiter that limits the adjustment amount of the pressure adjustment unit. An effective limiter is a plate-shaped member that prevents the rubber-like member from expanding further upward. Reference numeral 70 in Figure 2 is an example of a limiter. A pipe-shaped member 70 with one closed end is provided to cover the rubber-like member. The pipe-shaped member 70 has a side that is connected to the external air, allowing the external air pressure to be applied to the rubber-like member.

[0038] 3 is a cross-sectional view showing the structure of a power semiconductor device according to a second embodiment of the present invention, in which the same components as those in FIG.

[0039] The structure and manufacturing method of the power semiconductor device 100B of the second embodiment are almost the same as those of the power semiconductor device 100A of FIG. 1, and only the differences will be described.

[0040] 3, a movable part 51 composed of a frame part 24 and a bellows-shaped expandable movable part 23 is disposed in a hole 7 formed in the lid 6. This point differs from the power semiconductor device 100A of the first embodiment. Adhesive 10 (jointing means) is applied around the hole 7 of the lid 6, and the frame part 24 of the movable part 51, which deforms in response to pressure inside the device, is adhesively fixed to the hole 7 to complete the power semiconductor device 100B.

[0041] A power semiconductor device 100B ( FIG. 3 ) of the second embodiment includes an insulating substrate 2a having a power semiconductor element 1 mounted on one surface thereof, a heat dissipation base plate 3 joined to the surface of the insulating circuit board 2 opposite to the surface on which the power semiconductor element 1 is mounted, a case 4 fixed to the heat dissipation base plate 3 and surrounding the insulating circuit board 2, an insulating material 5 that insulates and seals the power semiconductor element 1 and the insulating circuit board 2 inside the case 4, and a lid 6 formed integrally with the case 4 or fixed to the case 4 by a joining means (e.g., an adhesive), and includes a movable part 51 that expands and contracts in response to the pressure in the space inside the semiconductor device in at least a part of a portion of the case 4 or the lid 6 that is not in contact with the insulating material 5. That is, the power semiconductor device 100A includes a movable part 51 that expands and contracts in response to the pressure in the space inside the semiconductor device in at least a part of a portion of the lid 6 that is not in contact with the gel-like insulating material 5. By doing this, by disposing a movable part 51 that expands and contracts in response to the pressure in the space inside the semiconductor device on the part of the case 4 or lid 6 facing the space inside the device, it is possible to prevent moisture from entering the device, and when the temperature rises during operation of the device, the bellows-shaped movable part 23 expands outward from the device in the direction that expands the volume of the space inside the device, thereby minimizing the increase in pressure in the space inside the device 31. Also, when the temperature drops during shutdown of the device, it contracts inward from the device in the direction that reduces the volume of the space inside the device, thereby minimizing the decrease in pressure in the space inside the device 31, thereby suppressing the occurrence of voids and cracks in the silicone gel. Also, instead of the bellows-shaped movable part 23, a disk-shaped member such as a diaphragm can be used, or a bellows-shaped movable part can be combined with a diaphragm to accommodate greater pressure changes inside the housing.

[0042] 4 is a cross-sectional view showing the structure of a power semiconductor device according to a third embodiment of the present invention. In explaining FIG. 4, the same components as those in FIGS. 1 and 3 are denoted by the same reference numerals.

[0043] The structure and manufacturing method of the power semiconductor device 100C of the third embodiment are almost the same as those of the power semiconductor device 100A of FIG. 1 and the power semiconductor device 100B of FIG. 2, and only the differences will be described.

[0044] 4, a movable part 52 composed of an outer tubular part 27, a gasket 25, and a plunger 26 is disposed in a hole 7 formed in the lid 6. This point differs from the power semiconductor device 100A of the first embodiment and the power semiconductor device 100B of the second embodiment. The power semiconductor device 100C is completed by applying adhesive 10 (jointing means) around the hole 7 of the lid 6, and adhesively fixing the outer tubular part 27 of the movable part 52, which deforms in response to the pressure inside the device, to the hole 7.

[0045] The power semiconductor device 100C of the third embodiment comprises an insulating substrate 2a having a power semiconductor element 1 mounted on one surface thereof, a heat dissipation base plate 3 joined to the surface of the insulating circuit board 2 opposite to the surface on which the power semiconductor element 1 is mounted, a case 4 fixed to the heat dissipation base plate 3 and surrounding the insulating circuit board 2, an insulating material 5 that insulates and seals the power semiconductor element 1 and the insulating circuit board 2 inside the case 4, and a lid 6 formed integrally with the case 4 or fixed to the case 4 by a joining means (for example, an adhesive), and at least a portion of the portion of the case 4 or the lid 6 that is not in contact with the insulating material 5 comprises a movable part 52 that expands and contracts in response to the pressure in the space inside the semiconductor device.

[0046] That is, the power semiconductor device 100A is provided with a movable part 52 that expands and contracts in response to the pressure in the space inside the semiconductor device, in at least a part of the portion (space 31) of the lid 6 that is not in contact with the gel-like insulating material 5. By arranging the movable part 52 that expands and contracts in response to the pressure in the space inside the semiconductor device on the portion of the case 4 or the lid 6 that faces the space inside the device, it is possible to prevent moisture from entering the device, and the movable part composed of the gasket 25 and the plunger 26 expands outward from the device in a direction that expands the volume of the space 31 inside the device when the temperature rises during operation, thereby minimizing the increase in pressure in the space 31 inside the device, and also shrinks inward from the device in a direction that reduces the volume of the space inside the device when the temperature drops during shutdown of the device, thereby minimizing the decrease in pressure in the space 31 inside the device, thereby suppressing the generation of voids and cracks in the silicone gel.

[0047] By using the plunger 26, it becomes easier to monitor changes in the movable part due to temperature changes, as described in Example 1. When the rubber-like member of Example 1 is used, it is somewhat difficult to accurately determine how much the movable part has moved, but monitoring the vertical movement of the plunger 26 allows for more quantitative understanding than when a rubber-like member is used. By providing a scale on the vertical bar of such plunger 26 or displaying the scale in different colors, it becomes possible to monitor (manage) changes in the movable part more quantitatively and easily.

[0048] Furthermore, by increasing the plunger's range of motion (operation range) as needed, it is possible to accommodate larger volume changes. Furthermore, limiters can be provided vertically on the plunger, and a system can be installed to detect and alert when the plunger attempts to move beyond the limiter. In other words, if the plunger attempts to move beyond the limiter, some abnormality may have occurred in the semiconductor device, and by alerting this, accidents in vehicles equipped with the semiconductor device can be prevented. Furthermore, as described in Example 1, limiting the plunger's range of motion can limit pressure fluctuations within the housing to a predetermined pressure range, preventing the development of voids and cracks in the silicone gel in semiconductor devices used under conditions where pressure fluctuations are repeated, such as in aircraft. [Comparative Example] The following describes the reliability test results of the power semiconductor devices of the first to third embodiments and Comparative Examples 1 and 2. <Configuration of Comparative Example 1> Figure 5 is a cross-sectional view showing the structure of the power semiconductor device of Comparative Example 1. The same components as in Figure 1 are designated by the same reference numerals.

[0049] The power semiconductor device of the comparative example shown in FIG. 5 has a hole 7 formed in a part of the lid 6 for injecting a gel insulating material, and an air vent 14 formed to prevent the internal pressure in the device from increasing when the power semiconductor device generates heat.

[0050] Gel insulating material is injected through hole 7 for injecting the gel insulating material, and the gel insulating material is cured under predetermined curing conditions. After that, hole 7 for injecting the gel is covered with cap 13. Hole 7 for injecting the gel insulating material is covered with cap 13. However, ventilation holes 14 allow ventilation between the inside and outside of the power semiconductor device. This ventilation hole 14 allows water or moisture to easily penetrate into the inside of the device from the outside. <Configuration of Comparative Example 2> Figure 6 is a cross-sectional view showing the structure of a power semiconductor device of Comparative Example 2. The same components as in Figure 1 are designated by the same reference numerals.

[0051] In the power semiconductor device of the comparative example shown in FIG. 6, a hole 7 for injecting a gel insulating material is formed in a part of the lid 6 .

[0052] A gel insulating material was injected through the hole 7 for injecting the gel insulating material, cured under predetermined curing conditions, and then the hole 7 for injecting the gel insulating material was closed with the cap 13. The hole 7 for injecting the gel insulating material was closed with the cap 13. Unlike Comparative Example 1, no air vent was provided, and the device was sealed. Water and moisture did not easily penetrate into the device from the outside. <Reliability Test of Power Semiconductor Device> [Reliability Test of Power Semiconductor Device] Reliability tests were performed on the power semiconductor devices of the first to third embodiments and Comparative Examples 1 and 2 to confirm the effects of the present invention. The reliability test method will be described. (1) Water Immersion Test During shipping tests for power semiconductor devices, ultrasonic inspection was used to inspect the bonding condition between the heat dissipation base plate and the insulating circuit board. Ultrasonic inspection involves immersing the power semiconductor device in water. Therefore, to simulate this inspection, the power semiconductor device was immersed in water for approximately 20 minutes. (2) High-Temperature Storage Test In a shipping test for a power semiconductor device, after an ultrasonic flaw detection test, the power semiconductor device is heated multiple times for drying the device and a high-temperature blocking test. To simulate these tests, the power semiconductor device was placed in a high-temperature chamber and subjected to heat treatments at 80°C for 1 hour and 100°C for 4 hours. (3) Insulation Test In a shipping test for a power semiconductor device, a partial discharge test and a withstand voltage test are performed as insulation tests to inspect the insulation properties of the device. Depending on the withstand voltage of the power semiconductor device, standards such as the IEC (International Electrotechnical Commission) and JIS (Japanese Industrial Standards) specify the partial discharge test voltage and the withstand voltage test voltage. In order to verify the reliability of the power semiconductor devices 100A to 100C of the first to third embodiments and the comparative examples 100D and 100E, (1) a water immersion test, (2) a high-temperature storage test, and finally (3) an insulation test, a partial discharge test and a dielectric strength test were performed.

[0053] Both the partial discharge test and the dielectric strength test are carried out by short-circuiting all terminals of the power semiconductor device and applying a high voltage between all terminals and the heat sink base.

[0054] In the partial discharge test, a voltage of 7 kVrms was applied for 1 minute, then reduced to 5.1 kVrms and applied for 30 seconds, and the amount of discharged charge of partial discharge was measured in the last 5 seconds. If a partial discharge occurred and the amount of discharged charge exceeded 10 pC, the insulation was judged to be "poor," and if it was within 10 pC, it was judged to be "good."

[0055] In the withstand voltage test, a voltage of 10.2 kVrms was applied for 1 minute, and if no breakdown occurred, the insulation was judged to be "bad," and if no breakdown occurred, the insulation was judged to be "good."

[0056] Referring to Comparative Example 2 in FIG. 6, the problems of a conventional power semiconductor device (high-voltage power module, hereinafter referred to as module) will be described.

[0057] The air leak test at the blocking test temperature is carried out according to the following procedure.

[0058] The module of Comparative Example 2 was immersed in Fluorinert and heated on a hot plate, and a test was conducted to check the change in the internal pressure of the module and whether or not there was any air leakage to the outside.

[0059] When a module that has an air leak at high temperature is returned to room temperature, the inside of the device is placed in a negative pressure state, which is maintained for a long time. This negative pressure causes voids 32 (see Figure 6) in the silicone gel, resulting in a pressure resistance failure.

[0060] In a voltage resistance test of the module, dielectric breakdown occurs at a rate of 3 to 4%, resulting in a decrease in yield. The above problem was discovered for the first time by the present inventors. The present inventors speculated that the cause of the dielectric breakdown was voids 32 (Figure 6) that occurred in the silicone gel.

[0061] 7A to 7C are diagrams showing, in tables, the results of reliability tests on the power semiconductor devices 100A to 100C of the first to third embodiments and the power semiconductor device of the comparative example. FIG. 7A is a diagram showing the partial discharge test results, and FIG. 7B is a diagram showing the dielectric strength test results. FIG. 7C is a diagram showing the pass / fail judgment of the partial discharge test (FIG. 7A) and the dielectric strength test (FIG. 7B) after the water immersion test and the high-temperature storage test. In the diagram, a circle indicates a "pass" judgment, and an x ​​indicates a "fail" judgment.

[0062] As shown in Figures 7A to 7C, for the sample corresponding to the power semiconductor device 100A of the first embodiment, the sample corresponding to the power semiconductor device 100B of the second embodiment, and the sample corresponding to the power semiconductor device 100C of the third embodiment, all seven out of seven samples passed the partial discharge test and the dielectric breakdown test with a good result.

[0063] As described above, all of the power semiconductor devices 100A to 100C according to the first to third embodiments passed the partial discharge test and the dielectric breakdown test with a good result.

[0064] In contrast, in the samples corresponding to the power semiconductor device of Comparative Example 1, partial discharge occurred in five out of seven units in the partial discharge test ( FIG. 7A ), and insulation breakdown occurred in four out of seven units, resulting in a failure judgment, and the test could not be passed ( FIG. 7C ). Also, in the samples corresponding to the power semiconductor device of Comparative Example 2, partial discharge occurred in two out of seven units in the partial discharge test ( FIG. 7A ), and insulation breakdown occurred in one out of seven units, resulting in a failure judgment, and the test could not be passed ( FIG. 7C ).

[0065] Furthermore, after the insulation test, the lids 6 were opened to observe the interiors of the power semiconductor devices, one each of the power semiconductor devices 100A-100C of the first to third embodiments and the power semiconductor devices of Comparative Examples 1 and 2. It was confirmed that the power semiconductor devices 100A-100C of the first to third embodiments had no voids or cracks in the gel-like insulating material. In contrast, it was confirmed that the power semiconductor devices 100D and 100E of Comparative Examples 1 and 2 had voids in the gel-like insulating material. [Effects] As described above, the power semiconductor devices 100A-100C include a movable portion that expands and contracts in response to the pressure in the space inside the semiconductor device in at least a portion of the case 4 or lid 6 that is not in contact with the insulating material 5. This prevents water from entering the power semiconductor devices 100A-100C and minimizes changes in the pressure in the space inside the device even when the power semiconductor devices 100A-100C generate heat or are heated externally during testing, thereby preventing voids and cracks from occurring in the gel-like insulating material. As a result, it is possible to realize a power semiconductor device that can suppress the occurrence of partial discharge and maintain a dielectric strength voltage.

[0066] The above-described embodiments are merely examples, and the present invention is not limited to these embodiments as long as the features of the invention are not impaired.

[0067] The present invention is not limited to the above-described embodiment, and includes other modifications and applications within the scope of the claims.

[0068] DESCRIPTION OF SYMBOLS 1 Power semiconductor element (semiconductor element) 2 Insulated circuit board 2a Insulating board 2b Circuit electrode 2c Back electrode 2d Brazing material 3 Heat dissipation base plate (heat dissipation base) 4 Case 5 Gel insulating material (insulating material) 6 Lid 7 Hole 8 Bonding material (solder, sintered metal) 9 Bonding material (solder, sintered metal) 10 Adhesive 11 Terminal 12 Nut 13 Cap 14 Ventilation hole 21, 23 Expandable movable part 22, 24 Frame part 25 Gasket 26 Plunger 27 Outer cylinder 31 Space inside semiconductor device 32 Void 50, 51, 52 Movable part 70 Pipe-shaped member 71 Hole 100A, 100B, 100C, 100D, 100E Power semiconductor device (semiconductor device)

Claims

1. A semiconductor device comprising: a semiconductor substrate on which a semiconductor element is mounted; and a housing that hermetically seals the semiconductor substrate, wherein the housing comprises a pressure adjusting unit that changes the internal volume of the housing in accordance with the internal pressure of the housing.

2. A semiconductor device according to claim 1, wherein the pressure adjusting section comprises a movable section that expands and contracts in response to the pressure inside the casing.

3. A semiconductor device according to claim 2, wherein at least a portion of said movable portion is made of an elastic material.

4. A semiconductor device according to claim 3, wherein the elastic member is made of a rubber-like organic material or a spring.

5. A semiconductor device according to any one of claims 2 to 4, further comprising a soundness evaluation unit that evaluates the soundness of the semiconductor device based on the amount of change in the operation of the movable part.

6. A semiconductor device according to any one of claims 2 to 4, characterized in that a gel-like insulating material is provided inside the casing to insulate and seal the semiconductor substrate.

7. A semiconductor device according to any one of claims 2 to 4, characterized in that it comprises an air opening section for temporarily opening the inside of the casing to the outside air.

8. A semiconductor device according to any one of claims 2 to 4, further comprising a limiter for limiting the operating range of the movable part of the pressure adjusting part.

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