JP2008042020A - Semiconductor module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve cooling characteristics of a semiconductor module and reliability to a cold cycle from a low temperature to a high temperature. <P>SOLUTION: The semiconductor module comprises an Mo board 11; a GaN element 13; an AlN sheet 12 for electrically insulating the GaN element 13 and the Mo board; and a cooler 20 formed on the side not provided with the GaN element 13 of the Mo board 11 and provided with a flow path 21 where cooling water is distributed, and an Al board 22 to be reversibly deformed by thermal stress is housed. The Mo board 11 forms the path wall of the flow path 21 of the cooler 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor module, and more particularly to a semiconductor module including a heat-generating power semiconductor element.

  Conventionally, circuit boards used with heat radiating members have a structure in which individually prepared metal circuit boards, ceramic boards, solid metal boards, etc. are laminated, and their thermal stresses are unbalanced. In this case, the circuit board is warped, or peeling or cracking occurs at the joint interface due to thermal stress generated when the circuit board is cooled by the heat radiating member.

  Such a phenomenon is largely due to the difference in thermal expansion coefficient between the combined materials. The higher the temperature, the greater the thermal stress, and the degree of warpage, delamination and cracking worsens.

In particular, GaN and SiC, which are next-generation power semiconductor elements, can operate at 200 ° C. or higher. However, since these thermal expansion coefficients are as small as 3 to 4 ppm / K, aluminum (Al; thermal expansion coefficient 23 ppm / K) or copper (Cu; thermal expansion coefficient 17 ppm / K) generally used for cooling members such as coolers is used. For example, in a power module in which these are combined and bonded in a layered manner, a large thermal stress or a large stress is applied to each bonded portion by a cooling cycle between a low temperature (eg, 0 ° C. or lower) and a high temperature (eg, 200 ° C. or higher). Distortion occurs, warping occurs in a short time, or destruction is accompanied by peeling or cracking.
The linear expansion coefficient is a dimensional change per unit length when the temperature changes by 1 ° C.

  As a technique related to the above, in the structure of the inverter power module, heat transfer grease is used to provide a layer for relaxing the thermal stress caused by the difference in thermal expansion coefficient between the power semiconductor element and the cooler. Is described (for example, see Non-Patent Document 1).

Also, an insulating substrate such as aluminum nitride (AlN) or aluminum oxide (Al ₂ O ₃ ) is directly bonded to the Cu plate, and the cooling water is allowed to flow through the cooler by bonding partially perforated Cu. A cooler-integrated module having a structure is disclosed (for example, see Patent Document 1).

In addition to the above, a technique is known in which the gap between the metal circuit boards is filled with an insulator to avoid the occurrence of warp due to heat.
Japanese Patent Laid-Open No. 10-261886 “Efforts to ensure the quality of HV inverters”, Yoichiro Baba (2005 Fall National Convention Forum, “Electronics Packaging Technology Trends and Future Developments—From Environmentally Friendly Automotive Electronics Packaging to Next-Generation Power Electronics Packaging Development”, Chair : Yasuo Takahashi etc.)

  However, when grease is used to relieve the thermal stress as described above, the grease is easily deformed because it has a low viscosity and approaches a liquid state at a high temperature, and the effect of relieving the thermal stress accompanying the cooling cycle is not effective. Although obtained, the thermal conductivity of the grease is as low as 1 W / mK or less, so that the thermal resistance between the grease portion, that is, the power semiconductor element and the cooler is increased, and the cooling characteristics are deteriorated as a whole. Furthermore, when the temperature is higher than 200 ° C., the grease is liquefied remarkably and the viscosity is greatly reduced, so that it easily oozes out to the surroundings. This also causes a problem that the thermal resistance becomes high.

In the above-described cooler-integrated module, AlN or Al ₂ O ₃ which is an insulating material and Cu are directly joined, but the difference in thermal expansion coefficient between AlN or Al ₂ O ₃ and Cu is large. On the high temperature side, a large thermal stress or strain is generated in a cooling cycle exceeding 200 ° C., and defects such as cracks are generated in the insulating material in a short time. Similarly, the vicinity of the semiconductor of this structure has low thermal expansion, while the cooler is configured with high thermal expansion, causing warpage during the cooling / heating cycle, and further causing breakage such as cracks in brittle parts such as insulating materials. Arise.

  For semiconductor modules that require cooling, such as power modules, various studies have been made including cooling characteristics such as cooling efficiency. However, as described above, it is intended to relieve the thermal stress caused by temperature changes between low and high temperatures. There is a conflict between maintaining the cooling characteristics and preventing the occurrence of cracks (ensuring reliability), in which the cooling characteristics cannot be maintained and the thermal conductivity (cooling characteristics) is to be secured, resulting in breakage due to cracks. Since it includes technical elements, it is expected to provide a semiconductor module that maintains the cooling characteristics and also ensures the reliability to withstand a thermal cycle with a large temperature difference.

  The present invention has been made in view of the above, and an object of the present invention is to provide a semiconductor module having high cooling efficiency and excellent cooling characteristics and having high reliability for a cooling cycle from low temperature to high temperature. This is the issue.

  In order to achieve the above object, the semiconductor module of the present invention has a thermal expansion coefficient difference of ± 5 ppm / K between a power semiconductor element and a power semiconductor element, and a thermal conductivity of 50 W / It is formed on the opposite side of the low thermal expansion substrate on which the power semiconductor element is provided, and the refrigerant flows and deforms (preferably reversibly) against thermal stress. And a cooler that cools at least the power semiconductor element by heat exchange with the refrigerant, and is disposed between the power semiconductor element and the low thermal expansion substrate. In addition, an insulating member that electrically insulates the power semiconductor element and the cooler is provided, and a part of the cooler wall is formed of a low thermal expansion base material.

  The power semiconductor element in the present invention is a semiconductor for controlling electric energy typified by a rectifier element and an inverter element, and includes, for example, a semiconductor such as gallium nitride (GaN) or silicon carbide (SiC).

  In the semiconductor module of the present invention, an element mounting portion is formed by joining at least a power semiconductor and an insulating member on one side of the low thermal expansion base material, with the low thermal expansion base material as a center, and one side of the instrument wall on the other side. Part (preferably, a part of the wall of the flow path of the cooler) has an integral structure in which a cooler composed of the low thermal expansion substrate is formed, and the low thermal expansion substrate has a thermal conductivity. Power semiconductor and cooling by making the element mounting part in a joined state without using grease, etc., and configuring the cooler directly on the surface where the element mounting part is not formed on the low thermal expansion substrate. Since thermal conductivity is ensured by reducing the thermal resistance between the vessels, the cooling efficiency can be improved and the cooling characteristics can be improved.

  Furthermore, the thermal expansion coefficient of the low thermal expansion base material that defines the power semiconductor element and the cooler is set within a range in which the difference from the thermal expansion coefficient of the power semiconductor element having a relatively small thermal expansion coefficient is ± 5 ppm / K, The appearance of the cooler is arranged by disposing a material that is thermally conductive and deformable (preferably reversibly) against heat stress in a position where it can contact and exchange heat with the refrigerant flowing in the flow path of the cooler. The thermal expansion coefficient can be reduced, the weight and cost can be reduced, the cooling efficiency can be improved, and the thermal stress and strain caused by the cooling cycle between low temperature (for example, 0 ° C. or lower) and high temperature (for example, 200 ° C. or higher) can be eliminated. Therefore, the module can be effectively prevented from being warped, peeled off, or cracked.

  As described above, the semiconductor module of the present invention has high cooling efficiency and excellent cooling characteristics, and at the same time, is prevented from being destroyed by a cooling cycle and has high reliability.

  The low thermal expansion base material constituting the semiconductor module of the present invention can be configured using a base material having a thermal expansion coefficient of 7 ppm / K or less and a thermal conductivity of 100 W / mK or more.

  When the thermal expansion coefficient is 7 ppm / K or less, the difference in thermal expansion coefficient with the power semiconductor element is small, the occurrence of thermal stress and distortion, and consequently breakdown, generated in the cooling / heating cycle is suppressed, and the reliability is improved. Further, when the thermal conductivity is 100 W / mK or more, heat transfer characteristics between the power semiconductor element and the cooler are enhanced.

  The low thermal expansion substrate is particularly preferably a molybdenum substrate or a substrate containing molybdenum. Molybdenum has a thermal expansion coefficient close to that of the power semiconductor element as described above, and has a high Young's modulus and can be made thin. Therefore, it is possible to reduce the thermal resistance, which is advantageous for improving the cooling efficiency.

  The “thermally conductive material that can be deformed (preferably reversibly) against thermal stress” accommodated in the flow path of the cooler constituting the semiconductor module of the present invention includes copper, aluminum, or copper and aluminum. A metal material containing at least one is preferable.

  This heat conductive material has a relatively small weight and cost, and is a material for exchanging heat with the refrigerant flowing in the flow path, so that it has heat conductivity and does not deform the module structure. Desirably, from such a viewpoint, a material using copper or aluminum is preferable.

  Copper and aluminum are metals with high thermal conductivity, are relatively soft, and self-deform even if thermal stress or distortion occurs in the thermal cycle, ensuring cooling efficiency and preventing destruction of the module structure. It is effective for.

  Further, a part of the cooler wall (for example, the wall facing the power semiconductor element of the flow path) is composed of the above-described low thermal expansion base material, but at least one of the wall walls excluding a part of the cooler wall. The part can be formed of a material having a thermal expansion coefficient of 7 ppm / K or less.

  All or a part of the road wall other than the road wall constituted by the low thermal expansion base material (for example, the cooler is configured in the shape of a hexahedron in which one surface is formed by the low thermal expansion base material. In this case, if one surface (all or a part of the other five surfaces other than the low thermal expansion substrate) is formed of a material having a thermal expansion coefficient of 7 ppm / K or less, the difference in thermal expansion coefficient from the power semiconductor element Therefore, the occurrence of thermal stress and strain, and consequently destruction, caused by the cooling and heating cycle can be suppressed more effectively, so that the reliability can be further improved.

  As the material having a coefficient of thermal expansion of 7 ppm / K or less, a metal material containing at least one of molybdenum, FeNi alloy, or molybdenum and FeNi alloy is particularly preferable.

The metal plate for wiring having a thermal conductivity of 50 W / m · K or more and an electric resistivity of 10 × 10 ⁻⁶ Ωcm or less on the side where the power semiconductor element of the insulating member in the semiconductor module of the present invention is provided. The power semiconductor element can be arranged on the wiring metal plate. Since this wiring metal plate has good thermal conductivity and low electrical resistance, it is possible to satisfactorily supply power to the power semiconductor element without impairing the cooling characteristics between the power semiconductor element and the cooler.

  The power semiconductor element in the present invention is desirably a semiconductor element using GaN or SiC in view of the effect. Since these semiconductor elements generate heat up to a high temperature and are susceptible to thermal stress and distortion in the module structure during the cooling and heating cycle, the effects of the present invention for ensuring reliability as well as cooling characteristics can be exhibited more effectively. it can.

  The semiconductor module of the present invention is a system that combines high thermal cycle reliability and cooling characteristics for operation at 200 ° C. or higher using power semiconductor elements such as GaN and SiC in the next-generation power electronics field. Can be built.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in a cooling characteristic, the reliable semiconductor module with respect to the thermal cycle from low temperature to high temperature can be provided.

  Embodiments of a semiconductor module of the present invention will be described below with reference to the drawings. However, the present invention is not limited to these embodiments.

  In the semiconductor module of the present embodiment, a GaN power device is provided on one side of a molybdenum (Mo) plate, and on the other side, a square (hexahedron) cooler with this Mo plate as one surface is formed. A plurality of relatively thin thin film aluminum (Al) plates are arranged in the flow path of the cooler, and cooling water is passed through the flow path so that heat can be exchanged with the Al plate. is there.

  As shown in FIG. 1, the semiconductor module of the present embodiment includes a molybdenum (Mo) plate 11 that is a low thermal expansion base material and an insulating film (insulating member) that is laminated on one side of the Mo plate 11. An aluminum nitride (AlN) sheet 12 and a GaN power device (hereinafter also referred to as “GaN element”) 13 which is a power semiconductor element, and the Mo plate 11 are joined to the Mo plate on the other side. And a cooler 20.

  The molybdenum (Mo) plate 11 is a molybdenum plate member having a length of 40 mm, a width of 50 mm, and a thickness of 3 mm, a thermal expansion coefficient of 4 ppm / K, and a thermal conductivity of 140 W / mK.

  The low thermal expansion base material has a small difference in thermal expansion coefficient from the power semiconductor element (≦ 7 ppm / K; more preferably, the difference from the thermal expansion coefficient of the power semiconductor element is within ± 5 ppm / K), and is thermally It can be appropriately selected depending on the purpose or the like from a substrate having good conductivity (thermal conductivity ≧ 100 W / mK). For example, in addition to a molybdenum base material, a base material made of a mixed material of molybdenum and another metal (for example, Cu), a laminated material of these, and the like can be used.

  The thickness of the Mo plate (low thermal expansion substrate) 11 is selected in consideration of module warpage prevention and thermal conductivity (cooling efficiency), and in addition to the above thickness, preferably 0.5 to 8 mm. You can select from a range. From the viewpoint of thinness, Mo is preferable.

The AlN sheet 12 is an insulating film of aluminum nitride having an insulating property of 30 mm long × 40 mm wide × 0.6 mm thick and having an electrical resistivity of 10 ¹⁴ Ωcm or more (after firing). The GaN element 13 (specifically, the Al wiring board 14 in FIG. 1 to which the GaN element is bonded) and the cooler 20 are electrically insulated from each other.

  The thickness of the AlN sheet 12 can be selected in the range of 0.2 to 3 mm in consideration of the material, insulation performance, strength, and the like.

The AlN sheet 12 is made by mixing and kneading an aluminum nitride powder, an organic binder such as polyvinyl butyral, a plasticizer such as dibutyl phthalate, and an organic solvent such as toluene, and the obtained slurry is uniformly mixed with a doctor blade. After the sheet was formed so as to have a thickness and the thickness after firing was 0.6 mm, the sheet was cut and molded by performing die cutting such as a press, Furthermore, it can produce by performing drying, degreasing | defatting, and baking.
Since the AlN sheet 12 shrinks in size by 10 to 20% by drying, degreasing, and firing, it is desirable that the AlN sheet 12 be formed thicker than a desired thickness in advance.

Other than the AlN sheet, the insulating member can be suitably selected from ceramic materials having high thermal conductivity and a small linear expansion coefficient. Examples of the ceramic material include aluminum nitride, aluminum oxide (Al ₂ O ₃ ), silicon nitride (Si ₂ N ₄ ), silicon oxide, beryllium oxide, silicon carbide, and the like. Alternatively, two or more types can be selected and used.

  In the AlN sheet 12 of this embodiment, an Al wiring board 14 made of an aluminum (Al) plate having a thickness of 0.4 mm is bonded to the element side surface on which the GaN element 13 is provided. Further, an aluminum film (not shown) having a thickness of 0.4 mm is bonded to the surface opposite to the element side surface.

  The Al wiring board 14 is a wiring metal plate on which a semiconductor element is arranged. In this embodiment, a GaN element (power semiconductor element; coefficient of thermal expansion: 3 to 4 ppm / K) 13 is bonded to the surface of the Al wiring board 14 and externally. The GaN element 13 can be operated by being electrically connected to the power source. As shown in FIG. 1, the GaN element 13 is bonded to an Al plate with solder 15 interposed therebetween.

  The wiring metal plate can be appropriately selected and configured from an electrically conductive metal material according to the purpose and the like, in addition to the aluminum plate, for example, copper, tungsten, molybdenum, invar (Fe-Ni alloy) ), And laminated materials thereof.

The metal plate for wiring is preferably a metal material having a thermal conductivity of 50 W / m · K or more in terms of ensuring heat transfer efficiency, increasing the cooling efficiency of the GaN element 13, and avoiding warpage due to thermal stress. Copper, aluminum, tungsten, molybdenum and the like are preferable. In addition, a metal material having an electric resistivity of 10 × 10 ⁻⁶ Ωcm or less is preferable, and copper, aluminum, tungsten, molybdenum, and the like are preferable from the viewpoint of ensuring electric conductivity and maintaining the operation performance of the element. .

  The thickness of the Al wiring board (wiring metal plate) is not particularly limited, but is usually about 0.1 to 1 mm, and 0.2 to 0.7 mm is preferable in terms of thermal stress and wiring resistance. is there. In addition, what is necessary is just to select suitably about sizes other than the thickness of Cu wiring board according to the objective.

  On this Al wiring board 14, as shown in FIG. 1, one GaN element and one diode (not shown) are provided, and a unit which is a minimum unit necessary for forming an inverter is configured. ing.

  For example, in the case of a three-phase inverter used in a hybrid vehicle or the like, as shown in FIG. 2, three sets (arms) of two units in series (or multiples thereof) are combined in parallel.

  As shown in FIG. 1, the cooler 20 is configured as a rectangular parallelepiped having a rectangular cross section, and one of the six surfaces is formed of a Mo plate 11. That is, the GaN element 13 and the cooler 20 are demarcated on different sides via the Mo plate 11, and at the same time, the GaN element 13 is on the cooler (specifically, a flow path through which cooling water as a coolant flows). The road wall surface) is directly provided via an AlN sheet or the like, so that the cooling can be performed efficiently.

  The cooler 20 includes a flow channel 21 through which coolant, which is a coolant, circulates on the opposite side of the Mo plate 11 forming the device wall (flow channel wall) to which the AlN sheet 12 is joined, and a part of the flow channel 21. And a plurality of thin aluminum (Al) plates 22 that are reversibly deformable heat conductive materials joined to the inner surface of the flow path of the Mo plate 11.

  The flow path 21 includes a concave member 23 having an outer shape composed of four side walls 23a and a bottom wall 23b of the same size as the Mo plate 11 (the surface facing the bottom wall is open), and each side wall of FIG. -It is formed by joining to the outer peripheral surface (surface for thickness) of Mo board 11, and fixing to Mo board 11 like (c). This concave member is manufactured using the side wall 23a and the bottom wall 23b which consist of a board | plate material of a 5-mm-thick FeNi alloy.

  Of the four side walls 23a of the concave member 23, a pair of two walls facing each other are each provided with a taper screw joint, as shown in FIG. 1, and an inlet for supplying cooling water to the inside. 25 and an outlet 26 for discharging the heat-warmed cooling water to the outside, and the cooling water supplied from the inlet 25 flows through the passage and is discharged from the outlet 26 to the outside. Thus, the GaN element and the diode can be cooled by exchanging heat with the cooling water.

  The material used for the concave member 23 constituting the cooler 20 is a material having a thermal expansion coefficient of 7 ppm / K or less (more preferably, the difference from the thermal expansion coefficient of the power semiconductor element is within ± 5 ppm / K) such as FeNi alloy. Is preferable in that the difference in coefficient of thermal expansion between the GaN element (power semiconductor element) can be reduced. In addition to the FeNi alloy, for example, molybdenum, or one or both of molybdenum and FeNi alloy, and other metals (for example, A material made of a mixed material with Cu) can be used.

  The Al plate 22 in the flow channel 21 is formed by cutting a thin aluminum plate having a thickness of 0.2 mm (purity 99.99%) by wire cutting into a size of 10 mm × 20 mm. The parts are joined to the inner surface of the flow path of the Mo plate 11 with a brazing material, and a plurality of aluminum plates are accommodated in a three-dimensionally arranged state with a pitch of about 1 mm.

  The Al plate 22 is for heat exchange in contact with cooling water flowing through the flow channel 21 in the same manner as so-called fins and pillars generally used as heat exchange members. Because of its high and relatively soft properties, it deforms itself even when subjected to thermal stress, absorbs thermal stress and strain, and avoids breakage due to peeling or cracks in the module structure, while preventing damage to the GaN element 13 and the diode. The cooling can be performed efficiently.

  In addition to the Al plate, the thermally conductive material has a lower thermal rigidity and a thermal conductivity (preferably a thermal conductivity of 150 W / mK or more) than the structural skeleton such as the low thermal expansion base material and the concave member of the cooler. A material made of a mixed material of copper, or any one or both of copper and aluminum and another metal can be preferably used.

  The Al plate 22 is heated in a temperature range of 700 ° C. to 1000 ° C. after a plurality of Al plates are sandwiched between tungsten slits and brought into contact with the flow channel inner surface of the AlN sheet 12. May be joined directly.

Hereinafter, a method for manufacturing the semiconductor module of the present embodiment will be described in detail with an example.
Power semiconductor element (GaN element), Mo plate (length 40 mm x width 50 mm x thickness 3 mm), AlN sheet (0.4 mm thick Al film on one side and 0.1 mm thick Al film on the other) ), And a thin plate-like Al plate (purity 99.99%) having a thickness of 0.2 mm. Here, on the AlN sheet, a mask is formed by photolithography on an Al film having a thickness of 0.4 mm, which is an Al wiring board, and is arranged so that only the surface of the Al wiring board is immersed in the etching solution. The wiring pattern (circuit) was formed on the Al wiring board by etching.

  Next, using a FeNi alloy plate material having a thickness of 5 mm, as shown in FIG. 1- (c), a concave box material having an outer shape composed of four side walls 23a and a Mo wall 11 and a bottom wall 23b of the same size ( The surface facing the bottom wall is open). A through hole is provided in each of two paired side walls of the manufactured concave box material 23, and taper screw joints are attached to the two through holes provided as shown in FIG. 1- (a). As a result, the cooling water inlet 25 and the outlet 26 were formed.

  First, the end of the thin Al plate was brazed to one surface of the Mo plate and joined. Subsequently, the Mo plate is arranged so that the Al plate joining surface of the Mo plate enters the concave portion of the concave box material, and the side wall of the concave box material and the outer peripheral surface (surface corresponding to the thickness) of the Mo plate are welded and joined. . Subsequently, an AlN sheet was brazed to the surface of the Mo plate on which the Al plate was not joined, with a 0.4 mm thick Al film surface, and joined. Thereafter, a GaN element was soldered to the surface of an Al wiring board (0.4 mm thick Al film) on which an AlN sheet wiring pattern was formed using a reflow furnace to obtain a power module.

Next, the performance of the semiconductor module of this embodiment will be described.
(1) Measurement of thermal resistance The inlet 25 and outlet 26 provided in the cooler 20 constituting the semiconductor module of the present invention and the circulating nozzle of the cooling water / warm water circulating device are connected by a hose, and the temperature is 65 ° C. Hot water (hereinafter abbreviated as “Tw”) is circulated at a constant flow rate. This cooling water / warm water circulation device plays a role of, for example, a radiator and a pump mounted in an automobile.

Next, a voltage (hereinafter abbreviated as “Vge”) is applied between the gate electrode and the emitter electrode. At this time, when a Vge exceeding a threshold value (Vge (th); usually 4V to 8V) is applied, the GaN element is turned on. In this embodiment, 15 V is applied as Vge.
When a voltage (hereinafter abbreviated as “Vce”) is applied between the collector electrode and the emitter electrode, a current (hereinafter abbreviated as “Ice”) starts to flow between the collector electrode and the emitter electrode. In the saturated state, current hardly flows until Vce is about 2 V, but when it exceeds about 1 to 2 V, Ice increases as Vce increases. At this time, in the GaN element, heat Q corresponding to power loss represented by the product of Vce and Ice is generated. An insulated sheath thermocouple is brought into contact with the emitter electrode (the upper surface of the GaN element), the surface temperature of the GaN element is measured, and the measured value is defined as the junction temperature of the GaN element (hereinafter abbreviated as “Tj”). . The temperature difference ΔT between the GaN element and the cooling water is ΔT = Tj−Tw.
From the above, the thermal resistance from the semiconductor element to the cooling water (hereinafter abbreviated as “Rth”) is calculated as Rth = ΔT / Q.

  Based on the above, when the flow rate of the cooling water was 6 L / min, a current was passed through the GaN element 13 and Rth was measured, about 0.3 K / W was obtained. This value is compared with the thermal resistance of the conventional commercially available GaN power module (between the element and the case) of about 0.6 K / W, compared with the thermal resistance of the semiconductor module of the present embodiment configured in a water-cooled type. (Rth is the element and case plus the thermal resistance of the cooler), indicating that it is very small and good.

(2) Reliability test A thermal cycle test was conducted by the following method to evaluate the reliability.
Specifically, the semiconductor module was installed in a gas-phase cooling / heating cycle test apparatus, and the cooling / heating cycle was repeated 1000 times in the air between a low temperature atmosphere (−40 ° C.) and a high temperature atmosphere (+ 200 ° C.).

  In the semiconductor module of this embodiment, when each part after the above cooling cycle was observed, the Al film bonded to the AlN sheet was slightly deformed, but structural defects such as cracks and peeling were recognized. It was not possible to keep it in good condition.

  Here, as a comparison with the semiconductor module of the present embodiment, (a) as shown in FIG. 3, a structure using grease was formed between the Cu—Mo alloy substrate provided with the GaN power device and the cooler. A structure in which an AlN insulating substrate is provided between a comparison module and (b) a Cu plate to which a GaN power device is bonded and a cooler in which partially perforated Cu is bonded, as shown in FIG. The comparison module configured as described above was manufactured, and the thermal resistance was measured and the reliability test was performed in the same manner as the method performed on the semiconductor module of the present embodiment.

As a result, in the comparison module (a), the thermal resistance Rth from the GaN element to the cooling water was 0.6 K / W. Further, when the thermal cycle was performed, remarkable cracks and voids were observed in the solder layer between the AlN insulating substrate and the heat sink. In addition, there was a problem that grease oozes out to the periphery.
Further, in the comparative module (b), although the thermal resistance Rth was 0.2 K / W, a remarkable crack was observed in the AlN insulating substrate when the thermal cycle was performed.

  In the above embodiment, the case where a GaN power device is used as the power semiconductor element has been mainly described. However, the present invention is not limited to the case where the power semiconductor element is made of GaN, and the same applies to the case where the semiconductor element is made of SiC.

(A) is a top view which shows the structure of the semiconductor module which concerns on embodiment of this invention, (b) is a side view when the semiconductor module which concerns on embodiment of this invention of (a) is seen from the side surface, (C) is the sectional view on the AA 'line of (a). It is explanatory drawing for briefly explaining the structural example of the circuit of a three-phase inverter. It is a schematic sectional drawing which shows the structural example using the grease of the conventional semiconductor module. It is a schematic sectional drawing which shows the other structural example of the conventional semiconductor module.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Molybdenum (Mo) board 12 ... AlN sheet 13 ... GaN power device (GaN element)
20 ... cooler 21 ... flow path 22 ... thin plate-like Al plate (heat conductive material that can be reversibly deformed)

Claims (8)

A power semiconductor element;
A low thermal expansion base material having a difference in thermal expansion coefficient between the power semiconductor elements within a range of ± 5 ppm / K and a thermal conductivity of 50 W / mK or more;
Formed on the side of the low thermal expansion substrate opposite to the side on which the power semiconductor element is provided, has a flow path in which a refrigerant flows and contains a thermally conductive material that is deformable against thermal stress, A cooler that cools at least the power semiconductor element by heat exchange with the refrigerant;
An insulating member disposed between the power semiconductor element and the low thermal expansion base material to electrically insulate the power semiconductor element and the cooler;
And the low thermal expansion substrate forms part of the cooler wall.   2. The semiconductor module according to claim 1, wherein the low thermal expansion base material has a thermal expansion coefficient of 7 ppm / K or less and a thermal conductivity of 100 W / mK or more.   The semiconductor module according to claim 2, wherein the low thermal expansion base material is a molybdenum base material or a base material containing molybdenum.   The semiconductor module according to claim 1, wherein the thermally conductive material is any one of copper, aluminum, and a metal material containing at least one of copper and aluminum.   The cooler is characterized in that at least a part of the vessel wall other than a part of the vessel wall formed of the low thermal expansion base material is formed of a material having a thermal expansion coefficient of 7 ppm / K or less. The semiconductor module of any one of 1-4.   6. The semiconductor module according to claim 5, wherein the material having a thermal expansion coefficient of 7 ppm / K or less is any one of molybdenum, FeNi alloy, and a metal material containing at least one of molybdenum and FeNi alloy. A wiring metal plate having a thermal conductivity of 50 W / m · K or more and an electrical resistivity of 10 × 10 ⁻⁶ Ωcm or less is further provided on the side of the insulating member where the power semiconductor element is provided, The semiconductor module according to claim 1, wherein a semiconductor element is disposed on the wiring metal plate.   The semiconductor module according to claim 1, wherein the power semiconductor element is a semiconductor element using GaN or SiC.

Images