JP2009117701A - Power module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power module quickly dissipating a heat and absorbing a thermal stress and generating no junction damage even when the thermal stress resulting from a heat cycle is generated in the section of a solder joint. <P>SOLUTION: The power module has a plurality of power elements 10 and 20 adjacently arranged on a plane at predetermined internals. The power module has an electrode 30 arranged while being stretched to a plurality of both power elements and solder-joined with a plurality of both power elements. The electrode has a conductive elastomer 32 in a part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power module, and more particularly, to a power module having a plurality of power elements arranged adjacent to each other with a predetermined interval on a plane.

Conventionally, IGBTs (Insulated Gate Bipolar Transistors) and FWDs (Free-Wheeling Diodes), which are semiconductor chips, are mounted on a wiring pattern on an insulating substrate so that they are closely arranged, and IGBTs A heat pipe that also serves as a current-carrying conductor is stacked on the upper main electrode surface across both the FWD and FWD, and is electrically and thermally transferred by soldering, etc., and heat generated in the IGBT and FWD is passed through the heat pipe. A technique is known in which heat is radiated to the wiring pattern of the insulating substrate to enhance the cooling effect (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2004-6603

  However, in the configuration described in Patent Document 1 described above, since a heat pipe enclosing a working fluid is used for heat propagation, an evaporation / condensation cycle is required, and when a large current flows instantaneously There is a problem that a time difference is caused in the propagation of heat, resulting in a delay.

  In addition, it is good if the heat can be sufficiently dissipated using the heat pipe, but if the heat transport by the heat pipe is insufficient, the heat expansion coefficient of the insulating substrate, heat pipe, semiconductor chip There has been a problem that thermal stress due to the heat cycle is generated, and a joint failure such as a crack occurs in a soldered portion which is a joint portion.

  Furthermore, when the heat pipe cracks and the hydraulic fluid leaks, the power element may be damaged, and there is a problem in terms of reliability.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power module in which heat dissipation is quick and heat damage is generated in a soldered joint due to heat cycles so that the thermal stress is absorbed and no joint breakage occurs. .

To achieve the above object, a power module according to a first aspect of the present invention is a power module having a plurality of power elements arranged adjacent to each other at a predetermined interval on a plane,
It is disposed across both of the plurality of power elements, and has electrodes soldered to both of the plurality of power elements,
The electrode includes a conductive elastic body in a part thereof.

  Thereby, even when a thermal stress is applied due to a difference in thermal expansion coefficient between the electrode and the semiconductor element, the thermal stress is absorbed by the conductive elastic body portion, and solder joint breakage can be prevented. Further, since the conductive elastic body is provided only on a part of the electrode, it is possible to absorb thermal stress without reducing the conductivity of the electrode.

2nd invention is the power module which concerns on 1st invention,
The conductive elastic body is provided in a region not soldered.

  Thereby, even if the electrode is deformed by the heat cycle, it is possible to absorb the thermal stress in a region where the load on the power element is the smallest, and the influence of the thermal stress on the power element can be minimized. Further, since soldering is performed on a normal metal electrode portion, the soldering process can be easily performed.

3rd invention is the power module which concerns on 1st or 2nd invention,
The electrodes are arranged on upper surfaces of the plurality of power elements.

  Thereby, since the upper part of the electrode is free, thermal stress can be effectively released.

A fourth invention is the power module according to any one of the first to third inventions,
The conductive elastic body is a conductive rubber.

  Thereby, a thermal stress can be effectively absorbed in the part of a conductive elastic body.

A fifth invention is the power module according to any one of the first to fourth inventions,
The region where the electrode is solder-bonded is made of copper.

  Thereby, although the difference with the power element of a thermal expansion coefficient is large, it becomes possible to use a metal material with high heat conductivity and high heat dissipation for an electrode, and can improve a cooling effect.

A sixth invention is the power module according to any one of the first to fifth inventions,
One of the plurality of power elements is an insulated gate bipolar transistor, and the other includes a combination of diodes.

  Thereby, in the inverter for power conversion, a thermal stress can be absorbed effectively and destruction of a solder joint part can be prevented.

  According to the present invention, it is possible to prevent the joint failure due to the thermal stress of the power module.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating an inverter circuit as an example of an application target of a power module according to an embodiment to which the present invention is applied. In FIG. 1, the inverter circuit includes six IGBTs (Insulated Gate Bipolar Transistors) 10 and six FWDs (Free-Wheeling Diodes) connected in parallel between the collector and the emitter. , Hereinafter referred to as “diodes”) 20 as power elements.

  In FIG. 1, the inverter circuit includes one IGBT 10 and one diode 20 connected in parallel to each other to form one set, and includes a set of six IGBT 10 and diode 20 power elements. Of the six power element sets, two power element sets are connected in series, and each series connection point constitutes the U output, V output, and W output, and constitutes the output of the three-phase inverter circuit. is doing. The series connection is made by connecting the emitter of one high potential side IGBT 10 and the collector of the other low potential side IGBT 10. The collector of the high potential side IGBT 10 is connected to the P line 91 on the high potential side. It is connected. Similarly, the emitter of the IGBT 10 on the low potential side is connected to the N line 92 on the low potential side. With such an inverter circuit, the DC power applied to the P line 91 and the N line 92 can be converted into three-phase AC power and output to drive an AC motor or the like.

  The power module according to the present embodiment can be suitably applied to, for example, an inverter circuit having a plurality of power elements 10 and 20 as shown in FIG. In this embodiment, an example in which a power module is applied to an inverter circuit will be described below. However, a power module having a plurality of power elements can be applied to various applications.

  FIG. 2 is a side view of the power module according to the first embodiment to which the present invention is applied. In FIG. 2, the power module according to the first embodiment includes the IGBT 10 and the diode 20 that are power elements, the upper electrode 30 that also functions as a heat sink, and the lower electrode 40 that also functions as a heat sink. And an insulating substrate 50 made of an insulating material, a cooler 60, a solder 70 for soldering each element or component, and a sealing material 80 for sealing the whole. The upper electrode 30 includes a conductive elastic material 32 in a part thereof.

  In FIG. 2, only one set of the plurality of power elements 10 and 20 including the IGBT 10 and the diode 20 is shown. However, for example, there are 6 combinations of the IGBT 10 and the diode 20 as shown in FIG. For example, six configurations similar to those in FIG. 2 may be provided on the plane. This is the same for the other embodiments.

  The IGBT 10 and the diode 20 are semiconductor elements each functioning as a power element, and are configured as a semiconductor chip formed on a semiconductor substrate. In the inverter circuit described with reference to FIG. 1, the IGBT 10 serves as a switching element. The diode 20 serves as a free-wheeling diode that releases current due to counter electromotive force generated by a motor driving coil (not shown). In FIG. 1, the IGBT 10 and the diode 20 are connected in parallel in a circuit to form one set. However, as shown in FIG. 2, the IGBT 10 and the diode 20 are physically disposed on the planar electrode 40. Are arranged adjacent to each other with a predetermined interval. By adopting such an adjacent arrangement, the area required for the power module can be reduced, and the connection resistance between the IGBT 10 and the diode 20 can be reduced.

  The electrode 40 is disposed below the IGBT 10 and the diode 20 that are power elements, and constitutes a lower electrode. The electrode 40 is a lead electrode below the IGBT 10 and the diode 20 and also serves as a heat sink. In general, the collector of the IGBT 10 is disposed on the lower side and the electrode 40 is disposed as a collector extraction electrode. However, the emitter of the IGBT 10 may be disposed on the lower side and disposed as the extraction electrode 40. The diode 20 is arranged so that the n-type diffusion layer or the p-type diffusion layer is on the lower side in conformity to the arrangement direction of the IGBT 10, and the electrode 40 also plays a role as an extraction electrode of the diode 20 in common.

  As long as the electrode 40 is a metal for wiring, various materials may be applied. For example, copper may be applied. Copper has higher thermal conductivity and conductivity than aluminum, and has preferable characteristics over aluminum as a wiring material and a heat dissipation material. However, since the difference in coefficient of thermal expansion from the power elements 10 and 20 which are semiconductor elements is larger than that of aluminum, when deformation occurs due to a heat cycle, a thermal stress is applied to the soldered portion, resulting in a junction failure. There was a problem that it was easy to invite. The upper electrode 30 will be described later in detail. In the power module according to the present embodiment, the electrode 30 is configured so that the solder joint portion is not easily broken by the thermal stress, so that the electrode 40 can be made of copper. . In addition, in the case of copper, a copper alloy may be sufficient and CuMo, CuC, etc. may be suitably applied according to a use other than pure copper (Cu). As described above, various metal materials for wiring such as copper and aluminum can be applied to the electrode 40 according to the application.

  The upper surface of the electrode 40 is solder-bonded to the IGBT 10 and the diode 20 of the power element by the solder 70 and supports the power elements 10 and 20 from below. Further, the lower surface of the electrode 40 is soldered to the insulating substrate 50 disposed below by the solder 70 and supported from below by the insulating substrate 50.

The insulating substrate 50 is a substrate made of an insulating material, and insulates the electrode 40 from the metal used in the cooler 60 and supports the power elements 10 and 20 and the electrodes 30 and 40 from below. Yes. As the insulating substrate 50, for example, a material such as AlN (aluminum nitride), epoxy resin, Si ₃ N ₄ (silicon nitride), a DBA substrate which is a kind of ceramic substrate, or the like may be applied.

  The cooler 60 is means for supporting the insulating substrate 50 from below and cooling the heat released from the insulating substrate 50 by water cooling. The cooler 60 includes a base portion 61 and fins 62, and is configured to circulate and cool water inside the base portion 61 so that the heat dissipation efficiency is increased by the fins 62. By providing such a cooler 60, the heat radiation efficiency from the lower side of the heat generation of the power elements 10 and 20 can be increased. The cooler 60 may be made of a metal having high thermal conductivity such as copper or aluminum, and the cooler 60 and the insulating substrate 50 may be joined by soldering with the solder 70.

  The electrode 30 is disposed above the power elements 10 and 20 and constitutes an upper electrode. The electrode 30 constitutes a lead electrode for the power elements 10 and 20 and also functions as a heat sink. In the IGBT 10, the emitter is generally arranged on the upper side. In this case, the electrode 30 serves as an extraction electrode for the emitter. On the other hand, there is a case where the collector is disposed on the upper side in the reverse arrangement, and in this case, the electrode 30 serves as an extraction electrode of the collector. The electrode 30 also serves as a common extraction electrode for the p-type diffusion layer or the n-type diffusion layer in the diode 20 connected in parallel to the IGBT 10 depending on the orientation of the IGBT 10. Thus, the electrode 30 that is the upper electrode of the power elements 10 and 20 constitutes a common electrode that straddles both the IGBT 10 that is the power element and the diode 20.

  The electrode 30 is soldered to the upper surfaces of the power elements 10 and 20 with solder 70. Thereby, electrical connection and physical fixation are made.

  Although most of the electrode 30 is a metal part 31 made of a wiring metal such as copper or aluminum, a part of the electrode 30 is made of a conductive elastic body 32. In FIG. 2, the portion immediately above the power elements 10 and 20 is configured as a metal portion 31, but the central portion is configured with a conductive elastic body 32. Thus, the electrode 30 includes the conductive elastic body 32 in a part thereof, so that even if thermal stress is generated, the electrode 30 can be absorbed by the conductive elastic body.

  The conductive elastic body 32 is an elastic body having conductivity, and for example, conductive rubber is applied. Although the conductive elastic body 32 is an elastic body and has conductivity, the function as the electrode 30 can be maintained as it is.

  For the metal part 31 of the electrode 30, various wiring metals such as copper and aluminum may be applied depending on the application. For example, copper may be applied. As described above, copper is a metal material excellent in conductivity and thermal conductivity, and thus can be suitably applied to the electrode 30. Also, copper has a thermal expansion coefficient significantly different from that of the power elements 10 and 20 which are semiconductor elements as compared with aluminum, but in the power module according to the present embodiment, it is conductive as a stress relaxation material that releases thermal stress. Since the elastic body 32 is provided between the metal parts 31 and the metal part 31 of the electrode 30 is deformed, the thermal stress generated thereby can be absorbed. can do.

  As described above, by providing the conductive elastic body 32 on a part of the electrode 30, it is possible to reduce the joint breakdown of the solder 70. Further, by having such a configuration, it is possible to use copper with high heat dissipation for the electrode 30, the cooling performance itself can be improved, and the power elements 10 and 20 and the power module can be configured more compactly. It becomes possible.

  The conductive elastic body 32 may be provided immediately above the spacing region 15 in which the power elements 10 and 20 are disposed with a predetermined interval, in which the power elements 10 and 20 and the electrode 30 are not soldered. preferable. Immediately above the power elements 10 and 20, the electrical connection between the power elements 10 and 20 and the electrode 30 is ensured and the heat generated in the power elements 10 and 20 is dissipated more to the electrode 30. It is preferable to arrange a high metal part 31 and perform reliable bonding by solder bonding. On the other hand, the gap region 15 between the IGBT 10 and the diode 20 is a region where the electrode 30 and the power elements 10 and 20 are not solder-bonded and are not fixed. Therefore, even if the electrode 30 expands due to thermal deformation, the conductive elastic body 32 can be deformed without being fixedly restrained, and stress can be absorbed with the highest cushioning effect.

  As described above, in the power module according to the present embodiment, the metal part 31 having a high heat dissipation effect is disposed on the entire upper surface of the power elements 10 and 20 that are the heat generation sources so as to improve the transient thermal characteristics. By providing the conductive elastic body 32 in a non-bonded region that is not joined, the structure is configured to effectively exhibit the ability to absorb stress by the conductive elastic body 32.

  Further, in the power module according to the present embodiment, the conductive elastic body 32 is provided only in a partial region of the electrode 30, so that thermal stress can be applied without reducing the conductivity and heat dissipation as the electrode 30. It can absorb and prevent the solder 70 from being broken.

  The conductive elastic body 32 may be adjusted by appropriately changing its thickness and characteristics according to the amount of heat generated by the power elements 10 and 20 and the amount of deformation of the metal portion 31 of the electrode 30. For example, if the deformation amount of the metal part 31 is large, the conductive elastic body 32 may be configured to be thicker. For example, when the width of the electrode 30 is about 30 mm, the conductive elastic body 32 may have a thickness of about 0.05 to 2 mm, which is the amount of heat generated by the power elements 10 and 20 of the metal part 31. Depending on the amount of deformation based on the above, an appropriate thickness may be used.

  Further, in the power module according to the present embodiment, the example in which the conductive elastic body 32 is provided in the center of the electrode 30 where solder bonding is not performed has been described. However, the position where the conductive elastic body 32 is provided. However, the present invention is not limited to this, and may be provided in a portion where solder bonding is performed depending on the application. For example, when the amount of deformation of the metal part 31 of the electrode 30 is particularly large in the metal part 31 at the upper part of the IGBT 10, the conductive elastic material 32 is provided at the center part, and further, the part directly above the IGBT 10 is electrically conductive. It is also possible to provide the elastic body 32.

  The sealing material 80 serves to seal components such as the power elements 10 and 20 from above using gel or resin, and prevent these components from being contaminated by dust. When resin is applied, resin sealing may be performed by processing such as potting, transfer molding, etc., but according to the power module according to the present embodiment, resin sealing is performed to restrain thermal expansion, Since there is less need for molding, sealing may be performed using gel.

  As described above, according to the power module according to the first embodiment, the stress load of the solder joint portion can be reduced to prevent joint breakage, and the reliability of the power module can be improved. In addition, since the configuration has a high thermal stress resistance, it is possible to reduce the number of steps for thermal stress design.

  FIG. 3 is a side view of a power module according to a second embodiment to which the present invention is applied. In FIG. 3, most of the components are the same as those of the power module according to the first embodiment. However, the conductive elastic body 42 is also provided on the electrode 40a that is the lower electrode. It is different from the power module concerning.

  As described above, the conductive elastic body 42 may be provided also on the electrode 40 a disposed below the power elements 10 and 20. In FIG. 3, the electrode 40 a includes a metal part 41 and a conductive elastic body 42, and the metal part 41 is disposed immediately below the power elements 10 and 20 and soldered to the power elements 10 and 20. In addition, the conductive elastic body 42 is provided in a portion immediately below the spacing region 15 between the power elements 10 and 20. With this configuration, even if heat generated in the power elements 10 and 20 propagates to the electrode 40a and the metal part 41 is deformed, the conductive elastic body 42 absorbs stress due to the deformation, and the power elements 10 and 20 and the electrode 40a. The stress load applied to the solder 70 and the solder 70 between the electrode 40a and the insulating substrate 50 can be reduced.

  Since the other components are the same as those of the power module according to the first embodiment, the same components are denoted by the same reference numerals, and the description thereof is omitted.

  According to the power module according to the second embodiment, the conductive elastic body 42 is provided not only on the upper electrode 30 of the power elements 10 and 20, but also on the lower electrode 40a. Can be effectively dissipated from the upper and lower sides, and the stress can be relieved for the lower electrode 40a, so that a more reliable power module can be obtained in which the solder 70 is less damaged.

  In the power module according to the second embodiment, the example in which the conductive elastic bodies 32 and 42 are provided on both the electrode 30 that is the upper electrode and the electrode 40 that is the lower electrode has been described. The conductive elastic body 42 may be provided only on the lower electrode 40a. Furthermore, in the second embodiment, the example in which the conductive elastic body 42 is provided immediately below the predetermined space region 15 has been described. However, as described in the first embodiment, the conductive elastic body 42 is provided at other positions depending on the application. The elastic body 32 may be provided.

  FIG. 4 is a side view of a power module according to a third embodiment to which the present invention is applied. In FIG. 4, the power module according to the third embodiment includes a power element IGBT 10 and a diode 20, an electrode 30 a provided on the upper side of the power elements 10, 20, a radiator plate 45, a cooler 60, and a bus bar 90. And a bonding 95 and a sealing material 80.

  The IGBT 10 and the diode 20 are semiconductor elements that function as power elements, and the configuration and function thereof are exactly the same as those in the first and second embodiments, and thus the same reference numerals are given and description thereof is omitted. To do.

  The heat radiating plate 45 is a means for radiating heat generated in the power elements 10 and 20, and serves as both the lower electrode 40 and the insulating substrate 50 described in the first embodiment. That is, since the heat radiating plate 45 is supported from the lower side by the cooler 60, the heat generated in the power elements 10 and 20 is thermally propagated and released to the cooler 60.

  For example, a DBA substrate formed of a three-layer laminated structure of aluminum, silicon nitride, and aluminum may be applied to the heat radiating plate 45. In this case, the upper aluminum layer functions as the lower electrode 40 for the power elements 10 and 20, and silicon nitride functions as the insulating substrate 50. The heat radiating plate 45 and the power elements 10 and 20 are soldered together by solder 70.

  The cooler 60 includes a base portion 61 and fins 62, and the configuration and function thereof are exactly the same as those in the first and second embodiments, so the same reference numerals are given and the description thereof is omitted.

  The electrode 30a is an upper electrode for the power elements 10 and 20, has a function as an emitter or collector extraction electrode for the IGBT 10, and similarly corresponds to the arrangement direction of the IGBT 10 for the diode 20. The p-type diffusion layer or the n-type diffusion layer functions as an extraction electrode. Therefore, since the electrode 30a is a common electrode for the plurality of power elements 10 and 20, the electrode 30a is disposed across both the plurality of power elements 10 and 20.

  The electrode 30a includes a metal portion 31a and a conductive elastic body 32a, as in the first embodiment. For the metal portion 31a, a wiring metal such as copper or aluminum may be applied, but for example, aluminum may be applied. Aluminum is not as electrically conductive and thermally conductive as copper, but the difference in thermal expansion coefficient from the semiconductor elements constituting the power elements 10 and 20 is not as great as that of copper. This is less than when it is used. However, since the thermal expansion coefficient of aluminum is still different from the thermal expansion coefficient of the power elements 10 and 20, depending on the amount of heat generated by the power elements 10 and 20, the electrode 30a and the power elements 10 and 20 A stress load is applied to the solder 70 that joins.

  Therefore, also in the power module according to the third embodiment, the conductive elastic body 32a is provided in a part of the electrode 30a. For example, conductive rubber may be applied to the conductive elastic body 32a as in the first embodiment. By providing the conductive elastic body 32a on a part of the electrode 30a, the deformation due to the thermal expansion of the metal part 31a of the electrode 30a is absorbed, the stress load applied to the solder 70 is relaxed, and the solder 70 is surely broken. Can be prevented. Thus, even when the metal of the material which is not extremely large in the difference in thermal expansion coefficient from the power elements 10 and 20 is applied to the metal portion 31a of the electrode 30a, the conductive elastic body 32a is used as the electrode. By providing it in a part of 30a, it is possible to reliably prevent the solder 70 from being broken and improve the reliability of the power module.

  In FIG. 4, the metal portion 31 a of the electrode 30 a is disposed on the upper surface immediately above the power elements 10 and 20 and is soldered to the power elements 10 and 20 by the solder 70. The conductive elastic body 32a is provided immediately above the predetermined spacing region 15 in which the power elements 10 and 20 are disposed on the planar heat radiating plate 45 with a predetermined spacing. As described above, also in the power module according to the third embodiment, the metal portion 31a is disposed immediately above the power elements 10 and 20 and soldered, and the conductive elastic body 32a is a region of the central portion that is not soldered. By providing in, it can be set as the structure which raised sufficiently both the electroconductivity and thermal conductivity in the metal part 31a, and the mobility in the electroconductive elastic body 32a.

  In addition, the arrangement position of the conductive elastic body 32a may be a position where the conductive elastic body 32a is solder-bonded depending on the application, as described in the first embodiment, or a plurality of the conductive elastic bodies 32a may be provided. You may make it provide both in the position directly above the space 15 which is not solder-joined, and the position where other solder is joined.

  The bus bar 90 is a potential supply means for supplying a power supply potential or a ground potential to the electrode 30a, and is electrically connected to the electrode 30a by bonding 95. The bonding 95 may be made of a wiring metal material such as aluminum.

  The sealing material 80 is means for covering the power elements 10 and 20 and other components to prevent adhesion of dust, and gel or various types of resins may be applied. Since the functions, types, and the like of the sealing material 80 are the same as those described in the first embodiment, the same reference numerals are used and the description thereof is omitted.

  In the second embodiment, an example in which aluminum is applied to the metal portion 31a of the electrode 30a has been described. However, other wiring metals such as copper may be similarly applied.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

It is the figure which showed the inverter circuit of the application object of the power module which concerns on a present Example. 1 is a side view of a power module according to Embodiment 1. FIG. 6 is a side view of a power module according to Embodiment 2. FIG. 6 is a side view of a power module according to Embodiment 3. FIG.

Explanation of symbols

10 IGBT (Power element)
15 spacing area 20 diode (power element)
30, 30a, 40 Electrode 31, 31a, 41 Metal part 32, 32a, 42 Conductive elastic body 45 Heat sink 50 Insulating substrate 60 Cooler 61 Base part 62 Fin 70 Solder 80 Sealing material 90 Bus bar 95 Bonding

Claims (6)

A power module having a plurality of power elements arranged adjacent to each other with a predetermined interval on a plane,
It is disposed across both of the plurality of power elements, and has electrodes soldered to both of the plurality of power elements,
The electrode includes a conductive elastic body in a part of the electrode.   The power module according to claim 1, wherein the conductive elastic body is provided in a region not soldered.   The power module according to claim 1, wherein the electrode is disposed on an upper surface of the plurality of power elements.   4. The power module according to claim 1, wherein the conductive elastic body is a conductive rubber. 5.   5. The power module according to claim 1, wherein the solder-bonded region of the electrode is made of copper.   6. The power module according to claim 1, wherein one of the plurality of power elements is an insulated gate bipolar transistor and the other includes a combination of diodes.

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