1. Field of the Invention
The present invention relates to a power module and a method for manufacturing the same, and particularly, relates to a power module operated at high temperature and a method for manufacturing the same.
2. Description of the Background Art
In a conventional power module, in usual, a insulating substrate is formed of ceramics such as aluminum nitride (hereinafter, AlN, alumina (Al2O3), and silicon nitride (Si3N4), and a metal pattern such as copper or aluminum is formed on front and back surfaces of the insulating substrate. Power elements arranged on the insulating substrate are bonded by solder onto such metal pattern of the insulating substrate, wiring is made from electrodes of the power elements to terminal portions by aluminum wires, and the power modules is entirely sealed by a sealing material such as silicone gel. A configuration example of this power module is described in Japanese Patent Application Laid-Open No. H06-5742 (1994).
When the power module is operated, a current flows through resistor components of the power elements, and the elements generate heat. This heat passes through the insulating substrates, the solder and a base plate to an external radiator, and is then radiated.
However, bonded portions of the aluminum wires bonded to the power elements have a problem that temperature thereof rises by receiving the heat of the power elements, resulting in a decrease of reliability of the bonded portions. Moreover, in some cases, the bonded portions have a problem that a thermal stress is repeatedly applied thereto due to a difference between a thermal expansion coefficient (linear expansion coefficient) of the power elements and a thermal expansion coefficient (linear expansion coefficient) of the aluminum wires, and fatigue breakage occurs in the vicinity of interfaces therebetween, resulting in a fracture. In particular, in a device such as a SiC device capable of a high-temperature operation, operation temperature further rises, and the reliability of the bonded portions is significantly decreased.
It is an object of the present invention to provide a power module that prevents a deterioration of the reliability of the bonded portions of the aluminum wires, and enables the high-temperature operation of the Si or SiC device, and to provide a method for manufacturing the power module.
A power module according to the present invention includes an insulating substrate arranged in a case, a power element bonded onto the insulating substrate, a first wiring member as rectangular tube-like metal, the first wiring member having a first side surface bonded to a surface electrode of the power element, a wire connected to a second side surface of the first wiring member, the second side surface being opposite to the first side surface, and a sealing material filled into the case while covering the insulating substrate, the power element, the first wiring member and the wire.
In accordance with the power module according to the present invention, a distance between the surface of the power element and the bonded portion of the wire is increased, the heat can be suppressed from directly passing therebetween, and the deterioration of the reliability of the bonded portions can be prevented. Moreover, the thermal stress due to the difference between the thermal expansion coefficient of the power elements and that of the wire is suppressed, and fracture possibility of such bonding can be suppressed.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
First, a power module according to the underlying technology of the present invention is described below.
As shown in
When the power module is operated, a current flows through resistor components of the power elements 1, and the power elements 1 generate heat. This heat passes through the insulating substrates 5, the solder 6 and the base plate 7 to an external radiator (not shown), and is then radiated therefrom.
However, bonded portions of the aluminum wires 3 bonded to the power elements 1 have a problem that temperature thereof rises by receiving the heat of the power elements 1, resulting in a decrease of reliability of bonding thereof. Moreover, in some cases, the bonded portions have a problem that a thermal stress is repeatedly applied thereto due to a difference between a thermal expansion coefficient (linear expansion coefficient) of the power elements 1 and that of the aluminum wires 3, and fatigue breakage occurs in the vicinity of interfaces therebetween, resulting in a fracture. In particular, in a device such as a SiC device capable of a high-temperature operation, an operation temperature further rises, and the reliability of the bonded portions is significantly decreased.
In the following preferred embodiments, a power module that solves such problems is described.
A power module according to Embodiment 1 of the present invention is described with reference to the drawings. As shown in
The wiring members 9 are made of, for example, a copper material or a copper alloy material, which has good electric conductivity, and a shape thereof is a rectangular tube shape. One main surface (first side surface) of each of the wiring members 9 is bonded to a surface electrode portion of each of the power elements 1 by the bonding material 10 that is, for example, a low-temperature sintering material such as solder, silver and copper. The aluminum wire 3 is bonded to a main surface (second side surface) of each of the wiring members 9, which is opposite to the one main surface. As a material of the wiring members 9, a material having a larger thermal expansion coefficient (linear expansion coefficient) than a thermal expansion coefficient (linear expansion coefficient) of the power elements 1 is selected. The wiring member 9 has an effect of absorbing the heat generated in the power elements 1 though not being required to adopt such an insulating structure as required for a cooling medium electrode allowing a cooling medium to be inserted through a tube.
The aluminum wire 3 may also be sheet-like aluminum ribbon or copper wire, or copper ribbon wire.
In Embodiment 1, the thermal conductivity of the sealing material 2 is increased, whereby heat radiation properties from the wiring members 9 are enhanced, and the temperature of the bonded portions of the aluminum wires 3 can be further reduced. As a method for enhancing the thermal conductivity from the sealing material 2, it is possible to mix powder of silica, alumina, silicon nitride, aluminum nitride, boron nitride or the like into the sealing material 2.
As the low expansive material 103 as described above, a material with a linear expansion coefficient approximately ranging from 4×10−6/K to 10×10−6/K is desirable, and for example, a cladding material (linear expansion coefficient: 7×10−6/K) formed by bonding copper with a thickness ratio of 1 to both sides of invar with a thickness ratio of 3 is adaptive. In the cladding material as described above, the thickness ratio of invar and copper is adjusted, whereby a desired thermal expansion coefficient (linear expansion coefficient) can be obtained. Brazing, welding and the like are usable for bonding the low expansive material 103 and the wring member 9 to each other.
A wiring member 9 in
In accordance with Embodiment 1 according to the present invention, the power module includes the insulating substrates 5 arranged in the case 8, the power elements 1 bonded onto the insulating substrates 5, the wiring members 9 as the first wiring members which are the rectangular tube-like metal, in which the first side surfaces are bonded to the surface electrodes of the power elements 1, the aluminum wires 3 as the wires connected to the second side surfaces of the wiring members 9, which are opposite to the first side surfaces, and the sealing material 2 filled into the case 8 while covering the insulating substrates 5, the power elements 1, the wiring members 9 and the aluminum wires 3. In such a way, a distance between the surfaces of the power elements 1 and the bonded portions of the aluminum wires 3 is increased, the heat can be suppressed from directly passing therebetween, and a deterioration of reliability of such bonded portions can be prevented. Moreover, the thermal stress due to the difference between the thermal expansion coefficient of the power elements 1 and the thermal expansion coefficient of the aluminum wires 3 is suppressed, and the fracture possibility of the bonding can be suppressed.
Moreover, in accordance with Embodiment 1 according to the present invention, in the power module, the thermal expansion coefficient of the wiring member 9 as the first wiring members is larger than the thermal expansion coefficient of the power elements 1. In such a way, the thermal stress owing to the difference between the thermal expansion coefficient of the power elements 1 and the thermal expansion coefficient of the aluminum wires 3 is suppressed, and the fracture possibility of the bonding can be suppressed.
Furthermore, in accordance with Embodiment 1 according to the present invention, in the power module, in the wiring members 9 as the first wiring members, the low expansive material 103 as members corresponding to the first side surfaces thereof is a member having a lower thermal expansion coefficient than the metal materials 102 and 104 as members corresponding to other side surfaces. In such way, a stress in the bonding material 10, which occurs due to the difference in thermal expansion coefficient between the power elements 1 and the wiring members 9, is reduced, and the fatigue lifetime of the bonding material 10 can be extended.
Moreover, in accordance with Embodiment 1 according to the present invention, in the power module, the power elements 1 are the wide band gap semiconductor elements, whereby it becomes possible to realize a device capable of the higher-temperature operation.
Here, in a similar way to Embodiment 1, it is possible to fill the sealing material 2 into the case 8. However, in this Embodiment 2, the case 8 is filled with a sealing material 100 (first sealing material) such as epoxy resin so that at least the side surfaces (second side surfaces) where the aluminum wires 3 are bonded to the wiring members 9 and the wiring members 91 can be exposed, followed by curing of the sealing material 100, and thereafter, the aluminum wires 3 are bonded to exposed surfaces of the wiring members 9 and the wiring members 91. Thereafter, a sealing material 101 (second sealing material) for ensuring insulating properties is filled into an exposed portion as the rest. Note that a filling height of the sealing material 100 is adjustable by setting strength to be described later, and so on.
By adopting such a configuration, a structure capable of enduring a load and ultrasonic vibrations, which are applied at the time of bonding the aluminum wires 3, is realized, so that more stable bonding properties are obtained, and quality is enhanced. Moreover, the wiring members 9 and the wiring members 91 can be fixed by the sealing material 100, and accordingly, a height of the wiring members 9 and the wiring members 91 can be maintained to be high, whereby the temperature of the bonded portions of the aluminum wires 3 can be decreased.
Such a method of filling the sealing material 100 and the sealing material 101 is applicable even to the case of a structure in which the wiring members 91 are not provided on the insulating substrates 5 (that is, the structure of Embodiment 1).
In accordance with Embodiment 2 according to the present invention, the sealing material 2 includes: the sealing material 100 as the first sealing material filled into the case 8 while covering the insulating substrates 5, the power elements 1 and the wiring members 9 so that at least the second side surfaces of the wiring members 9 as the first wiring members can be exposed, and the sealing material 101 as the second sealing material further filled onto the sealing material 100 while covering at least the second side surfaces of the wiring members 9 and the aluminum wires 3 as the wires. In such a way, the structure capable of enduring the load and the ultrasonic vibrations, which are applied at the time of bonding the aluminum wires 3, is realized, so that more stable bonding properties are obtained, and the quality is enhanced. Moreover, the wiring members 9 and the wiring members 91 can be fixed by the sealing material 100, and accordingly, the height of the wiring members 9 and the wiring members 91 can be maintained to be high, so that the temperature of the bonded portions of the aluminum wires 3 can be decreased.
Moreover, in accordance with Embodiment 2 according to the present invention, the power module further includes the wiring members 91 as the second wiring members which are the rectangular tube-like metal, and have first side surfaces bonded onto the surface patterns of the insulating substrates 5. In the power module, the sealing material 100 as the first sealing member is filled while covering the wiring members 91 so that at least the second side surfaces of the wiring members 91 as the second wiring members, which are opposite to the first side surfaces, can be exposed, and the sealing material 101 as the second sealing material is filled while covering at least the second side surfaces of the wiring members 91. In such a way, the distance between the power elements 1 and the bonded portions of the aluminum wires 3 is increased, whereby a heat radiation effect is enhanced, and the reliability of the bonded portions can be enhanced. Moreover, the structure capable of enduring the load and the ultrasonic vibrations, which are applied at the time of bonding the aluminum wires 3, is realized, so that more stable bonding properties are obtained, and the quality is enhanced.
Furthermore, in accordance with Embodiment 2 according to the present invention, in the power module, the sealing material 2 is the epoxy resin, whereby the thermal conductivity of the sealing material is enhanced, whereby the heat radiation effect can be enhanced.
Moreover, in accordance with Embodiment 2 according to the present invention, a method for manufacturing the power module includes (a) filling the sealing material 100 as the first sealing material into the case 8 while covering the insulating substrates 5, the power elements 1 and the wiring members 9 so that at least the second side surfaces of the wiring members 9 as the first wiring members can be exposed, (b) connecting the aluminum wires 3 as the wires to the second side surfaces of the wiring members 9, which are exposed after the case 8 is filled with the sealing material 100, and (c) further filling the sealing material 101 as the second sealing material onto the sealing material 100 while covering at least the second side surfaces of the wiring members 9 and the aluminum wires 3. In such a way, the structure capable of enduring the load and the ultrasonic vibrations, which are applied at the time of bonding the aluminum wires 3, is realized, so that more stable bonding properties are obtained, and the quality is enhanced.
The wiring members 90 have an integral structure lying astride the plurality of power elements 1. With such a configuration, the strength for enduring the load and the ultrasonic vibrations, which are applied at the time of bonding the aluminum wires 3, is increased more than in the case of Embodiment 2, and moreover, since connection portions are formed, an area of a surface from which the heat is radiated is also increased, and accordingly, a further heat radiation effect can be expected.
In accordance with Embodiment 3 according to the present invention, in the power module, the plurality of power elements 1 are arranged on the insulating substrate 5, the wiring members 90 as the first wiring members are provided to correspond to the plurality of power elements 1, the respective first side surfaces of the wiring members 90 are bonded to the respective surface electrodes of the plurality of power elements 1 in a corresponding manner, and the respective second surfaces of the respective wiring members 90 are bonded to each other. In such a way, the strength for enduring the load and the ultrasonic vibrations, which are applied at the time of bonding the aluminum wires 3, is further increased, and moreover, since the connection portions are formed, the area of the surface from which the heat is radiated is also increased, and accordingly, the further heat radiation effect can be expected.
In the embodiments of the present invention, materials of the respective constituent elements, embodying conditions and the like are also described; however, these are illustrations, and materials and the like in the present invention are not limited to those described above.
While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.
Number | Date | Country | Kind |
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2010-223505 | Oct 2010 | JP | national |