JP5899680B2 - Power semiconductor module - Google Patents

Description

  The present invention relates to an insulated power semiconductor module, and more particularly to a power semiconductor module that requires high-temperature operation.

  As a typical insulated power semiconductor module, there is an IGBT (Insulated Gate Bipolar Transistor) module used in a power converter such as an inverter. Standards for insulated power semiconductor modules such as IGBT modules are established in JEC-2407-2007 and IEC60747-15. Moreover, it is disclosed by p289 of nonpatent literature 1 as a structure of a general insulated type power semiconductor module.

  FIG. 9 shows a configuration of a power semiconductor module described in Non-Patent Document 1. A semiconductor element 20 such as an IGBT or a diode serving as a switching element is connected to the DBC substrate 21 via a lower electrode layer of the semiconductor element 20. The DBC substrate 21 is soldered onto the copper circuit foil 22, and the DBC substrate 21 is bonded to the copper base 24 for heat dissipation via the soldering portion 25. Here, the DBC (Direct Bond Copper) substrate 21 is obtained by directly bonding a copper circuit foil 22 to an insulating plate 23 made of ceramics or the like.

  The upper electrode layer of the semiconductor element 20 is bonded with an aluminum wire 26 with ultrasonic waves and electrically connected to, for example, a copper circuit foil 22 on the DBC substrate 21. Then, it is led out from the copper circuit foil 22 on the DBC substrate 21 through a copper terminal 27 made of a lead frame or a bus bar. In this case, the connection between the copper circuit foil 22 and the copper terminal 27 is performed by soldering, and the surroundings are surrounded by a (super) engineering plastic case 28, and the inside thereof is a silicone gel for electrical insulation, etc. Is filled. Here, generally, the solder for joining the semiconductor element 20 and the DBC substrate 21 has a higher melting point than the solder for joining the DBC substrate 21 and the copper base 24, and is joined by two reflows.

In recent years, the operating temperature of semiconductor elements has been increased, and the operating temperature of 175 ° C. to 200 ° C. is close to the melting point of the solder material. Therefore, Bi, Zn, Au metal-based high-temperature solder, Sn—Cu Compound-based high-temperature solder, Ag powder, nanoAg low-temperature sintered metal, and the like have been proposed.
In addition, it has been reported that SiC, which is a next-generation semiconductor element, can operate at 250 ° C. to 300 ° C.

  Japanese Patent Application Laid-Open No. H10-228561 is known as a material that relieves stress based on heat generated during use and improves heat dissipation characteristics.

On the other hand, power semiconductor modules that do not use solder are disclosed as non-patent document 1 p336 and non-patent document 2 as a flat pressure contact structure package.
FIG. 10 shows the package, which is placed on the Mo plate 34 with the upper electrode layer of the semiconductor element 30 in contact with the contact terminal 33. A guide 35 for positioning the semiconductor element 30 and the contact terminal 33 is provided at the end of the semiconductor element 30.

  The thus configured flat pressure contact structure package can cool the semiconductor element 30 from the upper and lower surfaces, and can be electrically and thermally connected to the outside with a structure without soldering. Therefore, in general, both sides of the flat pressure contact structure package are cooled by pressing both ends of the shape pressure contact structure package with a heat sink, and the heat sink is used as a conductive member.

JP-A-10-303340 Japanese Patent No. 4621531

Corona "Power Device / Power IC Handbook" p289, p336 The Institute of Electrical Engineers of Japan Vol. 118, p276, 1996

In order to improve the reliability of temperature cycle, power cycle, etc., it is necessary to solve the problem caused by the difference in thermal expansion of semiconductor elements, metals, ceramics, etc. which are members constituting the semiconductor module. In other words, between the DBC substrate and the copper base, between the DBC substrate and the copper terminal, the solder used due to the difference in thermal expansion coefficient between copper and ceramics causes a shear stress to occur in the solder, resulting in increased thermal resistance and terminals. May peel off. Furthermore, cracks may also occur in the solder between the semiconductor element and the DBC substrate.
Further, depending on conditions, even at the connection portion of the aluminum wire on the semiconductor element, stress is generated due to the difference in thermal expansion between the aluminum and the semiconductor element, and the aluminum wire is fatigued.

  As the power density increases year by year, the junction temperature inside the semiconductor element to be used increases, so that the shear stress of the solder and the stress of the aluminum wire are increasing. On the other hand, it is necessary to prevent the above problem from becoming apparent during the period until the influence of thermal expansion reaches the design life of the semiconductor module. This is due to the emergence of wideband cap semiconductor elements that can be used at high temperatures such as SiC and GaN, and further reduction of the effects of thermal expansion is required.

Therefore, in order to achieve high reliability, environmental friendliness, and convenience at the same time, it is possible to easily realize double-sided cooling without using solder bonding or wire bonding, and a pressure-welded insulation type that is advantageous in terms of heat dissipation characteristics. Power semiconductor modules are again in the limelight.
Further, power semiconductor modules that make use of the performance of semiconductor elements that can be used at high temperatures such as SiC and GaN are also required to have improved reliability such as temperature cycle and power cycle.

FIG. 11 shows a main part of a general pressure contact type power semiconductor module. The following problems (a) and (b) exist in the pressure contact type power semiconductor module.
(A). Heat dissipation changes due to subtle changes due to contact pressure between members. In order to maintain high heat dissipation, it is necessary to ensure that the contact pressure between the members exceeds a certain pressure such as 1 MPa, and in order to increase the reliability of the module, it is as uniform as possible over the entire contact surface. It is necessary to ensure a sufficient contact pressure.

  That is, if there is a part with a low contact pressure, the electrical conductivity of the part decreases, and as a result, the current concentrates on a part where good contact is maintained, and the path for radiating Joule heat generated by energization becomes narrow. As a result, the temperature of a specific member rises locally. As a result, the member thermally expands locally to thermally change into a complicated shape, and it becomes difficult to maintain a uniform contact pressure on the contact surface between the members. At the same time, stress is concentrated locally, which causes a decrease in module reliability. In addition, an electrode layer such as Al is formed on the surface of the semiconductor chip by vapor deposition or the like, and there is a concern that the surface of the chip may be damaged if the pressure contact force to the semiconductor chip becomes excessive. It is important to maintain an appropriate contact pressure.

  (B). In the double-sided cooling structure, as shown in FIG. 9, heat is exchanged with an insulating material, a base (heat radiating plate) having a thickness of about 3 to 5 mm, and a coolant flowing through the cooler via grease. Even when good contact can be secured between the interfaces, there is a problem that the thermal resistance from the semiconductor chip to the refrigerant cannot be lowered below a certain value.

  Patent Documents 1 and 2 are publicly known for disposing an elastic metal plate between an insulating plate and a heat sink. Patent Document 1 describes that a metal plate with protrusions having an elastic action for relaxing thermal stress is disposed on a semiconductor element. Patent Document 2 describes that a metal plate with protrusions having an elastic action for heat conduction and thermal stress relaxation is disposed between an insulating plate and a heat sink. However, both patent documents relate to a conventional module that is sealed using a resin or the like using solder.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pressure semiconductor power semiconductor module that improves the heat dissipation characteristics of a power semiconductor module that does not use solder, improves the reliability while achieving downsizing. is there.

Claim 1 of the present invention is a pressure-contact type power semiconductor module in which a cooling block is laminated on both sides of a semiconductor chip and a contact material, an electrode material and an insulating material toward the outer surface direction on each side of the semiconductor chip.
Between the insulating material and the cooling block, a plurality of protrusions are provided on the surface facing the cooling block, and a thin plate having a leaf spring characteristic that receives force on the surface is disposed, respectively.
Providing a plurality of grooves on the surface of the cooling block facing the protrusion provided on the thin plate,
Surrounding and fixing the outer peripheral surface of each member of the laminated semiconductor chip, contact material, electrode material, insulating material and thin plate with a case made of an insulator,
The cooling block arranges the formed groove at a position avoiding the protrusion of the thin plate,
The protrusion of the thin plate is brought into contact with the cooling block surface and fixed integrally with the thin plate via a bolt.

  According to a second aspect of the present invention, the protrusion of the thin plate is provided at a position corresponding to the position directly above the semiconductor chip.

  According to a third aspect of the present invention, the thin plate is formed by increasing the thickness of the peripheral portion, and the thick layer of the formed thin plate is integrated with the cooling block.

According to a fourth aspect of the present invention, after the thick layer of the thin plate and the cooling block are integrated, a pressure contact force is propagated to the semiconductor chip through the thin plate by a bolt inserted from the cooling block. Is.
The fifth aspect of the present invention is characterized in that the integration between the thick layer of the thin plate and the cooling block is based on an adhesive.

  The sixth aspect of the present invention is characterized in that the thin plate and the cooling block joint surface are provided with a periodic protrusion shape during the circulation of the cooling medium.

  The seventh aspect of the present invention is characterized in that the thin plate is formed with a thickness of the flat plate portion of 0.1 to 0.5 mm and a thickness of the protruding portion of 0.1 to 1.0 mm. .

  Claim 8 of the present invention is configured such that when the thin plate and the cooling block are joined, the projection of the thin plate first contacts the cooling block, and contact pressure is applied to the projection of the thin plate when the adhesive or bolt is tightened. It is characterized by.

  As described above, according to the present invention, a projection is provided on a thin plate to act as a leaf spring that receives a force by a surface. As a result, the spring constant can be controlled by the thickness of the thin plate, the number of protrusions provided on the surface, etc., and it can act as a leaf spring that receives the force distributed over a wide area. The possibility of tightening can be greatly reduced, and the module can be downsized.

Also, a groove is provided in the cooling block, and a cooling water circulation channel is formed by the groove and the protrusion provided on the surface of the thin plate, so that the thermal resistance between the circulation channel and the semiconductor chip is reduced, and the heat exchange rate is increased. It improves and heat dissipation improves.
Furthermore, in the present invention, when the cooling block and the thin plate are integrated, the peripheral part of the internal part is tightened with an adhesive and a bolt, and then the adhesive is cured to prevent leakage of the refrigerant to the outside. .

Sectional drawing which shows embodiment of this invention. The block diagram of the thin plate used for this invention. Bonding explanatory drawing of a thin plate and a cooling block. The model figure by the simulation of this invention. Modeling explanatory drawing by simulation of this invention. Displacement diagram of internal parts by simulation. The stress distribution map by simulation. The pressure figure to the semiconductor chip by simulation. The conventional power semiconductor module partial block diagram. The block diagram of the conventional flat type press-contacting structure package. The block diagram of the conventional press-contact type power semiconductor module.

In the present invention, a base (heat radiating plate) used in a power semiconductor module is formed into a thin film shape, has a small spring constant, and is elastically deformed in proportion to the applied pressure. This elastic base and cooling block are integrated to provide a constant pressure while absorbing tolerances caused by component tolerances, thermal expansion in the thickness direction, etc., and flowing refrigerant between the base and cooling block. It has improved heat dissipation.
Hereinafter, it will be described in detail based on the drawings.

  FIG. 1 is a block diagram showing an embodiment of the present invention. Reference numeral 1 denotes a semiconductor chip (semiconductor element), and electrode materials 3 (3a, 3b) are stacked via contact materials 2 (2a, 2b) in the vertical (front and back) directions of a plurality of provided semiconductor chips. . The contact material 2 presses a predetermined region on the surface of the semiconductor chip 1 with a controlled predetermined pressure to reduce shear stress at the interface with the semiconductor chip 1. For this reason, the contact material 2 is made of a material having a thermal expansion coefficient close to that of the semiconductor chip 1. For example, when the semiconductor chip 1 is made of silicon, a material having a thermal expansion coefficient close to 3 ppm / ° C. is used. From the condition of high, graphite materials, molybdenum, tungsten, and other metals containing graphite (alloy, C-CuMo, etc.) can be exemplified.

The electrode material 3 for taking out an electric current to the outside through the contact material 2 is made of Cu alloy or the like, and one end of each of 3a and 3b penetrates the case 7 and protrudes to the outside. In addition, insulating materials 4a and 4b made of silicon nitride or the like for insulating the current-carrying region from the outside are disposed outside the electrode materials 3a and 3b. Furthermore, outside the insulating materials 4a and 4b,
A thin plate 5 (5a, 5b) made of carbon steel, austenitic stainless or the like, which is a general spring material, is disposed.

The thin plate 5 is, for example, a flat portion having a thickness of about 0.3 mm (0.1 to 0.5 mm), and even a flat plate is elastically deformed in proportion to the applied force, and the applied force is removed. However, in the present invention, in order to lower the spring constant (increase the displacement with respect to the force), the protrusion 5c having a constant thickness on one surface as shown in FIG. Is formed. The protrusion 5c has, for example, a height of about 0.5 mm (0.1 to 1.0), and when the protrusion is square, the height is about 4 mm. Further, as shown in FIG. 3, the peripheral portion of the thin plate 5 has a thickness approximately the same as the height of the protruding portion 5c, and screw holes for integrating the cooling block 6 are screwed through bolts. ing.
Of course, the dimension and shape of the thin plate and the protruding portion of the thin plate are not limited, and the shape and size can be freely selected depending on the size of the semiconductor chip and the like.

  The case 7 surrounds the outer peripheral portion of each member in which 1 to 5 are stacked. The case 7 is an insulator made of resin such as PPS, and surrounds the laminated thin plates 5a and 5b so as to sandwich them, and is fixed with an adhesive, and the components 1 to 5 are cut off from the outside to oxidize and contaminate parts. Prevents deterioration. Cooling blocks 6 (6a, 6b) are laminated on the outer side of the thin plate 5.

  The cooling block 6 is made of aluminum or a copper alloy, and a groove 6c serving as a refrigerant flow path is provided on the inner surface side, and an inflow port 6d is formed at an arbitrary position. When the cooling block 6 is laminated on the thin plate 5, the protrusion 5 c of the thin plate 5 is integrated in a state where it is positioned and in contact with the position avoiding the groove 6 c provided in the cooling block 6 as shown in FIGS. 1 and 3. Is done. For the integration, it may be integrated by packing (O-ring) or the like, but, for example, an adhesive that cures and adheres at room temperature to 200 ° C. is poured from the outside between the thin plate 5 and the cooling block 6, and then into the hole 6e. When the bolt is inserted and the distance between the thin plate 5 and the cooling block 6 becomes an appropriate thickness, the bolt is tightened so as to have an appropriate tightening torque, and the adhesive is cured.

The downward vertical pressure (or upward) generated when the bolts are tightened transmits stress in the order of the cooling block 6 → the projection 5c of the thin plate 5 → the insulating material 4 → the electrode material 3 → the contact material 2 → the semiconductor chip 1. be able to.
It should be noted that the adhesive between the cooling block 6 and the thin plate 5 is a case caused by a slight deviation in the thickness of the case 7 and its internal components (insulating material, electrode material 3, contact material 2, semiconductor chip 1), and thermal expansion of the internal components. The thickness of the adhesive layer is adjusted so that a contact pressure of, for example, 2 to 24 MPa is applied between the members when the power semiconductor module is operated.

As described above, the present invention constitutes a pressure contact type power semiconductor module that can impart spring characteristics by making the thin plate 5 into an uneven shape, and can apply compressive stress to the internal components.
4 to 8 show verification results for verifying whether the thin plate 5 gives a considerable contact pressure to the internal components.

  The analysis was performed using ANSYS. FIG. 4 shows an analytical model and FIG. 5 shows boundary conditions. In this analysis, in order to simplify the model, the power semiconductor module is provided with a thin plate 5 and a cooling block 6 on the upper surface side, and the pressure due to bolting around the cooling block has a constant thickness as shown in FIG. The simulation was performed by applying a downward pressure of 10 MPa to the periphery. The thickness of the thin plate 5 used for verification was 0.3 mm, and the thickness (height) of the protrusions 5 c was 0.5 mm. Six protrusions 5 c were provided at positions corresponding to directly above the semiconductor chip 1. Further, it is assumed that the thickness (height) of the internal components 1 to 4 stacked with the semiconductor chip 1 interposed therebetween is 0.1 mm thinner than the height of the inner surface of the case, and the thin plate 5 is deformed by the downward stress due to the bolt tightening. The situation where pressure contact force is applied to the part was simulated.

  FIG. 6 shows the displacement in the thickness direction of each member with respect to that before bolting when the temperature is returned to room temperature after bolting and adhesive curing. According to FIG. 6, when the dimension error in the thickness direction of the case and the internal part is 0.1 mm, the displacement in the thickness direction of each member after the pressure contact by bolt tightening is, for example, -20 to 20 at the part surrounded by the dotted line. It is displaced by about −40 [μm], and is displaced by about −0.0001 [m] in the portion “a”, and is in contact with the lower insulating material 4 to propagate the stress.

FIG. 7 shows the equivalent stress distribution applied to each internal component and the thin plate 5. FIG. 7 (a) shows the equivalent stress distribution, and FIG. 7 (b) shows the equivalent stress distribution applied to the thin plate.
The material of the thin plate is SUS301. As a result, the stress applied to the inner peripheral side wall of the case 7 and the deformed portion of the thin plate 5 is 4e7 to 2e8 [Pa], which is about 200 MPa at maximum, as shown by the portion surrounded by the dotted line. It has become. Compared to the upper limit of elasticity (spring limit value) of 500 MPa or more for carbon steel and austenitic stainless steel (for example, SUS301-CSP H), the material SUS301 has no problem as a spring function for thin plates. it is obvious. As for the material of the thin plate, it is desirable that the heat dissipation, workability, and water resistance are higher. For example, an aluminum alloy and a copper alloy can be used by designing them with appropriate thicknesses and shapes, respectively.

FIG. 8 shows the contact pressure distribution applied to the upper surface of the plurality of (here, six) semiconductor chips. The portion surrounded by the dotted line is the shape of the contact surface of the contact material 2 located on the semiconductor chip, and is 1e7 to 2.4e7 [Pa] on the upper surface side of the semiconductor chip, and the pressure at the position in contact with the contact material 2 Was confirmed to be applied at a pressure of 2 to 24 MPa.
The contact pressure can be controlled by the pressure value applied to the peripheral portion of the cooling block, that is, the tightening degree of screwing the thin plate 5 through the hole 6e, the arrangement and number of bolts, and the like.

Further, by configuring the power semiconductor module as shown in FIG. 1, the heat dissipation is improved for the following reason.
(1) Since the thickness of the cooling block can be reduced, the thermal resistance of the cooling block itself can be reduced.
(2) The presence of the periodic protrusions in the flow area of the refrigerant including the groove 6c disturbs the flow of the refrigerant instead of being a stable flow or a laminar flow, so that the heat between the refrigerant, the thin plate, and the cooling block. Exchange rate is increased.
Therefore, it is possible to provide a power semiconductor module with good heat dissipation and high reliability.

As described above, according to the present invention, a projection is provided on a thin plate so as to act as a plate spring that receives a force by a surface.
In this case, the spring constant can be controlled by the thickness of the thin plate, the number of protrusions provided on the surface, and the like, and can act as a plate spring that receives a force distributed over a wide surface. Thereby, compared with the case where a plurality of springs having the same spring constant are provided on the outer periphery of the module as in Non-Patent Document 1, the possibility of the module being single-clamped is greatly reduced. Moreover, it is not necessary to provide a large spring provided conventionally on the outside of the module, and the module can be reduced in size.
In addition, when the surface unevenness provided on the thin plate is provided only directly above the semiconductor chip, it is possible to efficiently propagate the force to the semiconductor chip.

  A groove 6c is provided in the cooling block, and the groove 6c and the protrusion 5c provided on the surface of the thin plate form a cooling water circulation channel, and the functions of both are synergized to increase the area of the circulation channel for the semiconductor chip side. Therefore, the thermal resistance between the circulation channel and the semiconductor chip is reduced, the heat exchange rate is improved, and the heat dissipation is improved. In particular, when the uneven shape of the thin plate is positioned at a position directly above the semiconductor chip, the heat exchange rate between the refrigerant and the internal parts is maximized near the uneven shape. The heat dissipation in the direction is improved.

Further, in the present invention, when the cooling block and the thin plate are integrated, the peripheral portion of the internal part is fastened with an adhesive and a bolt, and then the adhesive is cured by a simple method to secure the external pressure of the refrigerant. It is possible to prevent leaks. By changing the layer (thickness) of the adhesive, it is possible to cope with the deviation (tolerance) in the thickness direction between the internal component and the case.

DESCRIPTION OF SYMBOLS 1 ... Semiconductor chip 2 ... Contact material 3 ... Electrode material 4 ... Insulating material 5 ... Thin plate 6 ... Cooling block 7 ... Case

Claims (8)

In a pressure contact type power semiconductor module in which a cooling block is laminated on both sides of a semiconductor chip and a contact material, an electrode material, and an insulating material toward the outer surface direction, respectively,
A plurality of protrusions are provided on the surface facing the cooling block between the insulating material and the cooling block, and a thin plate having a leaf spring characteristic that receives force on the surface is provided, respectively.
Providing a plurality of grooves on the surface of the cooling block facing the protrusion provided on the thin plate,
Surrounding and fixing the outer peripheral surface of each member of the laminated semiconductor chip, contact material, electrode material, insulating material and thin plate with a case made of an insulator,
The cooling block arranges the formed groove at a position avoiding the protrusion of the thin plate,
A power semiconductor module, wherein a protrusion of a thin plate is brought into contact with a cooling block surface and fixed integrally with the thin plate via a bolt. The power semiconductor module according to claim 1, wherein the protrusion of the thin plate is provided at a position just above the semiconductor chip. The power semiconductor module according to claim 1, wherein the thin plate is formed by increasing a thickness of a peripheral portion, and a thick layer of the formed thin plate is integrated with the cooling block. 4. The power semiconductor module according to claim 3, wherein after the thick layer of the thin plate and the cooling block are integrated, a pressure contact force is propagated to the semiconductor chip through the thin plate by a bolt inserted from the cooling block. . The power semiconductor module according to claim 3 or 4, wherein the integration between the thin layer of the thin plate and the cooling block is based on an adhesive. 6. The power semiconductor module according to claim 1, wherein the thin plate and the cooling block joining surface are provided with a periodic protrusion shape during the circulation of the cooling medium. 7. The thin plate according to claim 1, wherein a thickness of the flat plate portion is 0.1 to 0.5 mm and a thickness of the protrusion portion is 0.1 to 1.0 mm. Power semiconductor module. The protrusions of the thin plate first contact the cooling block when the thin plate and the cooling block are joined, and contact pressure is applied to the protrusions of the thin plate when the adhesive or bolts are tightened. The power semiconductor module according to any one of 6.

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