JP2008270292A - Power module and heat dissipation fin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a structure between a mounting portion of a semiconductor switching element and a radiating fin, there is no problem of peeling at an interface between a metal and a ceramic in a wiring board, and a semiconductor device and power capable of enhancing heat radiation Provide modules and heat dissipation fins.
SOLUTION: A base flat plate portion 5b, a Si-SiC heat radiation portion 5 having a plurality of fins 5f protruding downward from the lower surface of the base flat plate portion 5b, an insulating layer 5s formed on the upper surface of the base flat plate portion 5b, The wiring board 2 is fixed to the insulating layer 5 s, and the semiconductor switching element 3 is connected to the wiring board 2 by a solder joint 9.
[Selection] Figure 3

Description

  The present invention relates to a power module and a heat radiating fin used for an automobile motor.

The motor has a function of converting electrical energy into mechanical energy, and is used in various transportation means together with an engine that extracts mechanical energy from fossil fuel. Of the means of transportation, engine vehicles have been overwhelmingly used for automobiles. However, electric vehicles have been used against the backdrop of soaring fossil fuels and increasing efforts to curb CO ₂ emissions to prevent global warming. The number of hybrid vehicles used has increased, and in particular, the number of hybrid vehicles has increased dramatically due to the high mileage per unit fuel.

  Not only motors used for transportation, but the power supplied to the motors is often converted into power by various power converters. At this time, since a large amount of power is supplied to the motor, the power conversion device also handles a large amount of power, and it is required to reduce power loss of the power conversion device itself and perform efficient power conversion. In the power conversion device, a semiconductor device that operates as a switch that repeatedly turns on and off, that is, a switching element is used.However, since there is actually an on-resistance and a time lag occurs during switching, power consumption is not zero in the switching element. Heat is generated as a loss.

  The temperature rise of semiconductor elements is not limited to power converters for automobile motors, and has long been a problem, and many efforts have been made. For example, a structure in which a baffle plate for generating turbulent flow is attached so that the airflow does not pass straight through the gap between the fins in order to improve the heat dissipation of the parallel fins used for heat dissipation of the semiconductor device, Or the structure of the cylindrical fin of a staggered arrangement is disclosed (patent document 1). According to this structure, a turbulent flow is generated by the baffle plate or the staggered columnar fins attached obliquely, and the heat dissipation effect can be enhanced. Also, in order to enhance the heat dissipation effect of the liquid refrigerant in contact with the metal radiating fins, there is a method of providing a gap between the radiating fins and covering with a porous cover (which does not allow liquid refrigerant to pass but allows its vapor to pass). It is disclosed (Patent Document 2). According to this method, when heated to a predetermined temperature or higher, the liquid refrigerant injected into the gap evaporates all at once and takes the heat of vaporization, thereby preventing the semiconductor switching element from reaching a predetermined temperature or higher.

In addition to the heat dissipation problem of the heat dissipation fins, efforts have been made to reduce the manufacturing cost of the heat dissipation fins. In other words, an integrally molded product in which a metal substrate on which a wiring board for mounting a semiconductor element is mounted and a heat radiation fin are integrated is expensive to work. Therefore, the metal substrate and the heat radiation fin are used as separate members, and the heat radiation fin is attached to the metal substrate. There has been proposed a method of attaching the material with brazing material (Patent Document 3). In this method, there is a problem of quality deterioration (such as generation of voids) of the solder joint connecting the semiconductor element and the wiring board due to heating of the heat dissipating fin attached by the brazing material. That is, in a multilayer structure of {semiconductor element (brazing material layer 1) insulating substrate with circuit pattern (brazing material layer 2) metal base (brazing material layer 3) radiating fin} from the semiconductor element which is a heat source to the radiation fin, By making the melting point of the material layer 3 lower than the melting points of the other brazing material layer 1 and the brazing material layer 2, while preventing quality deterioration due to remelting of the solder layer (brazing material) caused by the final heat radiation fin attachment, The manufacturing cost of the power module with the radiation fins can be reduced. And now, the brazing material layer 3 has reached a stage where it is replaced with heat conductive grease that does not require heating.
JP 2001-345585 A JP 9-45829 A JP 2004-273479 A

  Although various improvements have been made as described above, the heat resistance temperature of the current power module wiring board (including the insulating board) is low, and a large number of layers are interposed from the semiconductor element to the heat radiating part. However, there is a problem that the thermal conductivity of the thermal conductive grease itself is not good. In particular, in the next generation technology, when the current is higher than the current level, the insulating substrate included in the wiring board, which insulates the mounting structure of the semiconductor element from the heat dissipation structure, peels off at the joint between the ceramic and the metal. There is a problem that it is likely to occur. More specifically, in the wiring substrate, wiring is directly connected to the front and back surfaces of the insulating substrate by DBA (Direct Bonding Aluminum) or DBC (Direct Bonding Copper). These DBAs and DBCs have a complicated structure, and the heat-resistant temperature is limited to about 150 ° C. because peeling between ceramics and metal occurs at high temperatures.

  An object of this invention is to provide the power module and the radiation fin which enable simplification of the structure of a thermal radiation part, ensuring heat dissipation.

  The power module of the present invention is a power module used for power conversion between DC power and AC power. This power module includes a base plate portion and a plurality of fins projecting downward from the bottom surface of the base plate portion, a heat sink made of Si-SiC, an insulating layer formed on the top surface of the base plate portion, and fixed to the insulating layer. And a semiconductor switching element connected to the wiring board by solder bonding.

According to said structure, since the wiring board which uses a metal plate as a main member without using a wiring board is used, the insulating substrate which occupied the principal part of the wiring board is not used. Further, the heat radiating metal plate (heat sink) is also excluded from the linear heat radiation path from the semiconductor element to the heat radiation fin. For this reason, in the wiring board, peeling of ceramics and metal caused by the increase in power is prevented, and an improvement in thermal conductivity can be obtained by simplifying the multilayer structure. In addition, since the thermal expansion coefficient of Si—SiC is approximately 3 × 10 ⁻⁶ / K, the heat radiation fin has a thermal expansion coefficient substantially equal to that of the semiconductor element, and the warpage of the semiconductor device is reduced, thereby providing a highly reliable semiconductor device. Can be provided. In addition, by reducing the number of parts, parts management costs and processing steps can be omitted, and a significant reduction in manufacturing cost can be realized in parts other than the Si-SiC radiating fins.

The heat radiation fins mainly dissipate heat in contact with a liquid cooling medium, but may be a gaseous cooling medium. Si-SiC is known to have a high thermal conductivity, and has a substantially large surface area due to the porosity even after Si impregnation, which is inferior to metal radiating fins such as aluminum. A heat dissipation effect can be obtained. In addition, the insulating layer on the upper surface of the base plate portion may be SiO ₂ or other insulating films formed by CVD (Chemical Vapor Deposition) or sputtering, or may be obtained by oxidizing Si-SiC on the upper surface of the base plate portion. Thus, an oxide film insulating layer (SiO ₂ ) that is integral with the heat dissipating fins may be used.

Further, when the above insulating layer is an oxide film insulating layer formed by oxidizing the upper surface layer of the base plate portion made of Si-SiC, the heat radiation fin and the insulating film can be integrated, and further the heat conduction path Simplification is possible, and miniaturization of the semiconductor device is promoted. When Si—SiC is thermally oxidized, a strong and dense silicon oxide film (SiO ₂ ) can be obtained, and a highly reliable insulating film without fear of peeling can be obtained.

  The insulating layer may be formed in a region corresponding to the wiring board and not formed in a region on the upper surface of the base flat plate portion outside the insulating layer. By this structure, the area | region in which the insulating layer of the base plate part upper surface of a radiation fin is not formed can also contribute to heat radiation, and can improve heat dissipation. Further, the edge portion where the insulating layer is not disposed can be used as a margin portion for fixing the heat radiation fin in the cooling medium path with an adhesive.

  The wiring board may be fixed to the insulating layer on the upper surface of the base plate portion of the Si—SiC radiating fin by an adhesive layer. Thereby, the mounting structure portion of the semiconductor element and the heat radiation fin can be integrated very easily, and the manufacturing cost can be reduced.

  The wiring board may be fixed to a metal layer formed on the insulating layer on the upper surface of the base plate portion of the Si-SiC radiating fin by solder bonding. As a result, the thermal conductivity can be further increased, and the mechanical strength between the layers of the multilayer structure can be easily increased.

  The power module of the present invention is a power module mounted on an automobile, and the semiconductor switching element is used for power conversion between direct-current power and alternating-current power exchanged between a rotating device and a battery. It is a semiconductor switching element. Problems caused by the increase in current and miniaturization in power modules such as hybrid cars in recent years, (1) Peeling of the bonding portion between ceramics and metal in the wiring board (low heat resistance temperature in the wiring board including the insulating board), (2) The Si-SiC radiation fin can solve the warpage of the power module. For this reason, the Si—SiC radiating fin described above can exhibit a particularly useful effect in a power module for automobiles that is highly required to have a large current and a small size.

  The above-described arrangement plate has a plurality of openings, and the edges of the base plate portions of the heat dissipating fins are closely bonded and fixed along the openings. The insulating layer, the wiring board, and the semiconductor switching element can be configured to be located outside the cooling medium path from the opening. Thereby, the cooling in a power module can be strengthened reliably.

  The radiating fin of the present invention is a radiating fin formed of an integral Si-SiC, and includes a base flat plate portion and a plurality of fins protruding downward from the lower surface of the base flat plate portion.

  By using the Si—SiC radiating fin, the heat radiating portion can be simplified and the heat radiating property can be secured.

  Moreover, it is preferable that the base flat portion includes an oxide film insulating layer formed by oxidizing the upper surface layer of the base flat portion. As a result, since a strong and dense silicon oxide film is provided on the upper surface of the base flat portion, there is no need to use a wiring substrate including an insulating substrate or a heat sink (heat sink), and a heat conduction path extending from the semiconductor element to the heat radiating fin is eliminated. The configuration can be simplified.

  Further, the oxide film insulating layer can be formed in the inner region excluding the upper surface of the base flat plate portion or the edge of the back surface. Thereby, the heat radiation effect from the region of the upper surface where the oxide film is not formed can be obtained, and the heat radiation performance can be enhanced.

  The manufacturing method of the radiation fin of the present invention includes a step of forming a radiation fin having a base flat plate portion and a plurality of fins protruding downward from the lower surface of the base flat plate portion with a sintered body containing SiC, and a SiC-containing sintered body. And a step of forming Si—SiC radiation fins by impregnating with Si, and a step of forming an oxide film insulating layer on the upper surface of the base plate portion of the Si—SiC radiation fins.

  Si-SiC heat dissipation fins made by reactive sintering with Si impregnation can be manufactured without adding other metal compounds as sintering aids like ordinary SiC, so high purity and dense sintering You can get a body. Moreover, since the dimensional change is small at the time of manufacture, it is also suitable for manufacturing large products. For this reason, it is possible to manufacture a radiating fin having a dense and strong oxide film insulating layer that is unlikely to peel off from the metal layer and having high thermal conductivity with high dimensional accuracy.

  According to the power module and the heat radiation fin of the present invention, it is possible to simplify the structure of the heat radiation portion while ensuring heat radiation.

  FIG. 1 is a diagram for explaining a power module 10 according to an embodiment of the present invention. This power module 10 has a U-phase terminal, a V-phase terminal, and a W-phase terminal that are terminals for motor distribution of a hybrid vehicle, and has a + terminal and a − terminal that are terminals for a generator. As the switching elements, motor switching elements 3 and 31 and a generator switching element 33 are arranged. The motor switching element includes an IGBT (Insulated Gate Bipolar Transistor) 3 and a free wheel diode (FWD) 31. In this description, both transistors and diodes are called semiconductor switching elements. These semiconductor switching elements 3, 31 and 33 are mounted on a mounting structure or the like (not shown), and an arrangement plate (heat radiating plate) 61 is provided so as to arrange the mounting structure. The semiconductor switching elements 3, 31, 33 and the mounting structure are housed in a housing 65. In the housing 65, a control signal mounting board (not shown) is mounted, on which a semiconductor element or the like for controlling the gate signal of the switching element is mounted with an insulating plate interposed on the switching element. A cooling medium path 67 through which a cooling medium flows is provided below the arrangement plate (heat radiating plate) 61 so as to be in contact with the arrangement plate 61. An ethylene glycol aqueous solution that is an antifreeze can be used as the cooling medium.

  In FIG. 1, a distribution terminal U-phase, V-phase or W-phase terminal for a three-phase AC motor is provided, and AC power is distributed from these distribution terminals. Two switching elements 3 and 31 are connected in series between the positive side and the negative side of the power supply terminal, and distribution terminals U, V, and W are connected therebetween. FIG. 2 is an enlarged view of a region A in FIG. In the region A, the high-potential-side IGBT 3 and FWD 31 or the low-potential-side IGBT 3 and FWD 31 are arranged. In the U phase distribution area for motors, there are a total of four areas corresponding to area A. As described above, there are two types of voltage division (high potential side and low potential side), and a large current. Since the same thing as the above is connected in parallel, a total of four regions are formed. The number of paths provided in parallel is not limited to two, and three paths are arranged in parallel when the current is larger. Further, when the switching element is reduced in size and increased in current, if only the capacity of the switching element is limited, only one path may be required.

In FIG. 2, the arrangement plate (heat radiating plate) 61 forming the ceiling of the cooling medium passage is provided with an opening 61h, and the Si-SiC radiating fin 5 is formed on the upper surface or the back surface (lower surface) of the edge of the opening 61h. The edge of the upper surface of the base flat plate portion 5b is bonded and fixed with an adhesive or the like. An oxide film insulating layer (SiO ₂ ) 5s formed by thermal oxidation of Si—SiC is located on the upper surface of the Si—SiC radiating fin 5, and a wiring board 2 made of a metal plate or almost a metal plate is formed thereon. It is fixed. The semiconductor switching elements 3 and 31 are mounted on the wiring board 2 by solder layers (not shown), and the surface electrodes 3a and 31a are electrically connected to surrounding bus bars not shown by wires or the like (not shown). Connected. The wiring board 2 that is electrically connected to the back electrodes (not shown) of the semiconductor switching elements 3 and 31 via the solder layer is also connected to the bus bar (power supply / distribution conductor) by wires or the like.

  FIG. 3 is a cross-sectional view showing a heat dissipation path of the semiconductor switching element in the power module according to the embodiment of the present invention. FIG. 4 is a modification of the structure of FIG. 3 and has a configuration in which fins are attached to the opening of the arrangement plate 61 from above. Hereinafter, the configuration of FIG. 3 will be described, but the configuration of FIG. 4 is applicable unless otherwise specified. In FIG. 3, the semiconductor switching element 3 is connected to the wiring board 2 by the solder layer 9, and the wiring board 2 is joined to the oxide film insulating layer 5s having a metal surface formed by plating or the like by the solder layer 9. It is fixed. The oxide film insulating layer 5s is formed by thermally oxidizing the upper surface of the base flat plate portion 5b of the Si-SiC radiation fin 5, and is a dense and strong insulating layer. The edge of the upper surface or the back surface (lower surface) of the heat radiating fin 5 is bonded and fixed to the edge back surface of the opening 61 h of the arrangement plate (heat radiating plate) 61 forming the cooling medium path by an adhesive 29.

A heat radiation path from the semiconductor switching element 3 to the heat radiation fin 5 is shown below in comparison with a conventional power module.
(Example of the present invention (structure illustrated in FIG. 3)): semiconductor switching element 3 / (1) solder layer 9 / (2) wiring board 2 / (3) solder layer 9 / (4) oxide film insulating layer 5s / Si -SiC heat radiation fin 5
(Conventional example (for comparison)): semiconductor switching element / (1) solder layer / wiring substrate ((2) front surface side wiring layer; (3) insulating substrate; (4) back metal surface) / (5) solder layer / (6) Radiation plate / (7) Radiation grease / Metal radiation fin

  According to the above comparison result, in the conventional structure, seven types of layers are interposed between the semiconductor switching element and the heat radiating fin. In the example of the present invention illustrated in FIG. Simplified into layers. For this reason, heat transfer from the semiconductor switching element 3 to the Si—SiC radiation fin 5 is promoted, and the temperature rise of the semiconductor switching element 3 can be efficiently suppressed. Other advantages are as follows.

(1) Since the wiring board is not used, it is not necessary to consider the heat-resistant temperature of the wiring board. As described above, the wiring board has the wiring layers directly connected to the front and back surfaces of the insulating substrate by DBA (Direct Bonding Aluminum) or DBC (Direct Bonding Copper). These DBAs and DBCs have low heat resistance because peeling between ceramics and metal occurs at high temperatures, and are limited to about 150 ° C. In the example of the present invention, DBA and DBC are not used, and the above-described simple configuration is adopted, so that it can be used at 200 ° C. or higher. For this reason, the semiconductor device in the present invention provides a useful mounting technique when a SiC or GaN semiconductor element having a high heat-resistant temperature is put into practical use in the next generation. In other words, the semiconductor device of the present invention can provide a mounting technique with a heat resistant temperature exceeding 200 ° C. by suppressing the temperature rise of the semiconductor switching element by a simple heat dissipation path.
(2) Since a wiring board (including an insulating plate) and heat radiation grease are not used, the number of parts can be suppressed, and the parts management cost and the number of processing steps can be reduced. Parts other than Si-SiC heat radiation fins Can greatly reduce the cost.
(3) The power module can be reduced in size and weight. Although the downsizing is clear from the above explanation, the weight can be significantly reduced by simplifying the heat dissipation path, forming the opening of the arrangement plate (heat dissipating plate), and replacing the metal heat dissipating fins with Si-SiC heat dissipating fins. Can be achieved.
(4) Since the thermal expansion coefficient of Si—SiC is about 3 × 10 ⁻⁶ / K, the heat radiating fin has a thermal expansion coefficient almost equal to that of the semiconductor element, and the warpage of the semiconductor device is reduced and the reliability is high. A semiconductor device can be provided.

The reason why the above great effect could be obtained is that (1) the radiation fin is made of Si-SiC and the upper surface is oxidized to form an oxide film insulating layer (SiO ₂ ) integrated with the radiation fin. (2) Abolishing the insulating substrate in the wiring board by utilizing the above oxide film insulating layer, and (3) refraining from interposing a metal heat dissipation plate in the heat dissipation path. Can do. Regarding (2) above, it can also be said that the insulating substrate in the wiring substrate is replaced with an oxide film insulating film on the Si—SiC radiating fin.

  Said Si-SiC radiation fin 5 can be manufactured as follows. First, the porous precursor which has the shape of a radiation fin is produced by sintering using the mixed powder which contains SiC as a main component. At this time, it heats to 1400 degreeC or more or 1900 degreeC or more. Next, this porous precursor is impregnated with Si at 1400 ° C. or higher to form Si-SiC heat radiation fins 5. Next, a predetermined region on the upper surface of the base plate portion of the heat radiating fin is thermally oxidized to form an oxide film insulating layer (silicon oxide) 5s. Since the heat dissipation fin made of Si—SiC manufactured by the above process does not contain a metal compound which general SiC contains as a sintering aid, it becomes a high-purity and dense sintered body.

  FIG. 5 is a cross-sectional view showing a heat dissipation path of a semiconductor device or power module showing another embodiment of the present invention. FIG. 6 is a modification of the structure of FIG. 5, and has a configuration in which fins are attached to the opening of the arrangement plate 61 from above. Hereinafter, the configuration of FIG. 5 will be described. However, the configuration of FIG. 6 is applicable unless otherwise specified. The power module 10 is characterized in that an adhesive 19 is used to fix the wiring board 2 to the oxide film insulating layer 5s. In the structure shown in FIG. 3 or 4, a metal surface layer is formed on the oxide film insulating layer 5 s by plating or the like, and the wiring board 2 is fixed by the solder layer. It becomes unnecessary, and it becomes possible to make a radiation fin and a mounting structure continue more easily.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  In the power module and the heat radiation fin of the present invention, since a heat radiation part made of Si-SiC is used, a simple structure is possible, and it is possible to obtain an increase in the heat resistance temperature of the mounted component and to suppress the temperature rise by improving the heat radiation performance. it can. Therefore, it is possible to provide a powerful mounting technology for the next-generation power module.

It is a general-view figure of the power module in an embodiment of the invention. It is an enlarged view of the A area | region of FIG. It is sectional drawing of the power module of the embodiment of this invention. It is sectional drawing of the power module of the modification of the structure of FIG. It is sectional drawing of the power module of another embodiment of this invention. It is sectional drawing of the power module of the modification of the structure of FIG.

Explanation of symbols

  2 Wiring board, 3 Semiconductor switching element, 3a Surface electrode, 5 Radiation fin, 5b Base flat plate part, 5f Fin part, 5s Oxide film insulating layer, 9 Solder layer, 10 Power module (semiconductor device), 19 Adhesive, 29 Adhesion Agent, 31 FWD, surface electrode of 31a FWD, 33 semiconductor switching element, 61 arrangement plate (heat radiating plate), 61h heat radiating plate opening, 65 housing, 67 cooling path.

Claims (8)

A power module used for power conversion between DC power and AC power,
A heat sink made of Si-SiC having a base flat plate portion and a plurality of fins protruding downward from the lower surface of the base flat plate portion;
An insulating layer formed on the upper surface of the base plate portion;
A wiring board fixed to the insulating layer;
A power module comprising: a semiconductor switching element connected to the wiring board by solder bonding.   The power module according to claim 1, wherein the insulating layer is an oxide film insulating layer formed by oxidizing Si—SiC in an upper surface layer of the base flat plate portion.   3. The power module according to claim 1, wherein the insulating layer is formed in a region corresponding to the wiring board and is not formed in a region of an upper surface of the base flat plate portion outside the insulating layer.   The power module according to any one of claims 1 to 3, wherein the wiring board is fixed to an insulating layer on an upper surface of a base plate portion of the Si-SiC radiation fin by an adhesive layer.   The said wiring board is being fixed to the metal layer formed in the insulating layer of the base plate part of the base fin part of the said Si-SiC radiation fin by solder joining, The one in any one of Claims 1-3 characterized by the above-mentioned. The described power module.   A placement plate that forms a ceiling of the cooling medium path, the placement plate having a plurality of openings, and the edges of the base plate portions of the radiation fins are closely bonded and fixed along the openings; The power module according to claim 1, wherein the insulating layer, the wiring board, and the semiconductor switching element are disposed outside the cooling medium path from the opening. A heat dissipating fin formed from a monolithic Si-SiC,
A base plate,
And a plurality of fins projecting downward from the lower surface of the base flat plate portion.   The heat radiating fin according to claim 1, further comprising an oxide film insulating layer formed by oxidizing an upper surface layer of the base flat plate portion on the base flat plate portion.

Images