The invention relates to a heat sink according to the preamble of claim 1 or 3 and to an assembly or module unit or arrangement according to the preamble of claim 22.
It is generally standard and necessary practice to cool electrical or electronic components or assemblies, in particular also power components or assemblies or modules to dissipate heat loss, namely by means of at least one heat sink (cooler) comprising at least one cooling element. For this purpose, the prior art uses in particular also heat sinks with cooling elements in which at least one, preferably highly branched cooling channel structure is provided, through which a liquid and/or gaseous and/or vaporous heat-transporting or medium or cooling medium, for example water, can flow.
For optimal cooling, it is advantageous in many cases to connect such components or assemblies by means of a solder bond to an outer cooling surface of the cooling element of the heat sink. The cooling element in this case, at least in the area of its outer cooling surface, is made of a metal material with high thermal conductivity, in particular of copper or aluminum. The solder bond between the component or assembly and the cooling element features the advantage, for example, that both components can be manufactured separately and connected with each other after being manufactured.
Problematic, however, is the fact that the solder bond or solder layer between the respective cooling element and the part of the constructional or modular unit comprising the at least one electric component, due to the generally widely differing thermal expansion coefficients of the components connected with each other by the solder layer, is subjected to considerable mechanical stress caused by thermal factors. This is especially pronounced in case of frequent changes in temperature, such as in the case of a constant load variation in the electrical component or electrical assembly, as is the case with electric drive controls, for example. This thermally related mechanical stress causes premature aging of the solder bond and in extreme cases even partial or total separation of the solder bond and therefore loss of the required cooling of the component or assembly.
The “DCB process” (direct copper bond technology) is known in the art, for example for connecting metal layers or sheets (e.g. copper sheets or foils) with each other and/or with ceramic or ceramic layers, namely using metal or copper sheets or metal or copper foils, the surfaces of which are provided with a layer or coating (melt-on layer) resulting from a chemical bond between the metal and a reactive gas, preferably oxygen. In this method, which is described for example in U.S. Pat. No. 3,744,120 and in DE-PS 23 19 854, this layer or coating (hot-melt layer) forms a eutectic with a melting temperature below the melting temperature of the metal (e.g. copper), so that the layers can be bonded to each other by placing the foil on the ceramic and heating all layers, namely by melting the metal or copper essentially only in the area of the hot-melt layer or oxide layer.
This DCB method then comprises the following steps:
Also known is the so-called active soldering method (DE 22 13 115; EP-A-153 618) for bonding metal layers or metal foils forming metallizations, in particular also of copper layers or copper foils, with ceramic material. In this process, which is used especially for manufacturing a metal-ceramic substrate, a bond is produced at a temperature of ca. 800-1000° C. between a metal foil, for example copper foil, and a ceramic substrate, for example aluminum-nitride ceramic, using a hard solder, which in addition to a main component such as copper, silver and/or gold also contains an active metal. This active metal, which is at least one element of the group Hf, Ti, Zr, Nb, Ce, creates a bond between the solder and the ceramic through a chemical reaction, while the bond between the solder and the metal is a metallic hard solder bond.
The object of the invention is to present a heat sink that eliminates the above disadvantages. This object is achieved by a heat sink according to claim 1 or 3. An assembly or module unit with a heat sink is the subject matter of claim 22.
The compensating layer which is provided on the at least one cooling surface of the cooling element and which is applied directly to the metal of the cooling element achieves or provides for effective compensation of the differing thermal expansion coefficients between the cooling element and the functional elements or components of an assembly or module connected with it by means of the solder bond, in particular also between the metal cooling element and a metal-ceramic substrate connected with the former by means of the solder bond, or another substrate or intermediate carrier made of a material differing from that of the cooling element, for example of a material or metal that is softer than the cooling element or has a reduced thermal expansion coefficient as compared with the cooling element.
Further embodiments, advantages and applications of the invention are disclosed in the following description of exemplary embodiments and the drawings. All characteristics described and/or pictorially represented, alone or in any combination, are subject matter of the invention, regardless of their being summarized or referenced in the claims. The content of the claims is also an integral part of the description.
The invention is described below in detail based on exemplary embodiments with reference to the drawings, in which:
In
The metallization 4 of the top side of the ceramic layer 3 is structured for forming conductors, contact surfaces, etc. Electronic components are attached to the metallization 4, namely for example a power component 6, e.g. in the form of an electronic switch element (IGBT) and further controlling components 7. The components 6 and 7 are housed in a closed housing 8, which is made of plastic, for example. The interior 9 of the housing 8 is compound-filled with a suitable material. Corresponding connectors 10 lead through the top side of the housing 8 for the power supply and control of the module 1.
For cooling of the module 1, said module is provided on a cooling element 11 generally designated 11 in
As shown in
If the module 1 is not operated continuously, but rather in switching mode or intermittently, as is generally the case with a module for controlling or switching drives, for example, the solder layer 12 is subjected to very strong, constantly changing mechanical tensions, which especially also in the case of a water- or liquid-cooled cooling element 11 cause a high shock load to the solder layer 12. This can destroy the solder bond between the module 1 and the cooling element 11 and, as a result of insufficient cooling, can also ultimately destroy the module 1.
The stress on the solder layer 12 due to the different thermal expansion coefficients of the adjoining ceramic-metal substrate 2 and of the cooling element 11 increases with the reduction of the thickness of the solder layer and is also dependent on the composition of the solder in the solder layer 12. The stress on the solder layer 12 is especially high if lead-free solder is used for this layer, which is increasingly being required to reduce environmental impact. Examples of such lead-free solders are SnAg5 and SnCu3.
To prevent this disadvantage, as shown in
The intermediate or compensating layer 13 especially achieves equalization of the thermal expansion coefficients of the ceramic-metal substrate and the cooling element 11 in the area of the bond between these components, i.e. on both sides of the solder layer 11. Since the thermal expansion coefficient e of the ceramic-metal substrate 2 depends for example on the thickness of the ceramic layer 3, the thickness of the compensating layer 13 is also adapted to the thickness of the ceramic layer 3, preferably so the ratio of “thickness of the compensating layer 13/thickness of the ceramic layer 3” is between 1.3 and 0.25. In a preferred embodiment of the invention the thickness of the compensating layer 13 is between 0.05 and 3 mm.
The application of the compensating layer 13 to the metal surface of the cooling element 11 is achieved with a suitable surface process, for example cladding, e.g. explosion cladding, by metal cold spraying, by thermal metal spraying, for example molten bath spraying, flame shock spraying, flame spraying, electric arc spraying, plasma spraying, etc.
The compensating layer 13 achieves equalization of the thermal expansion coefficients of the components provided on both sides of the solder layer 12 and therefore a reduction of the stress on the solder layer 12, especially also in stop-and-go operation of the module 1 and also a reduction of the resulting constant temperature change of the module 1 and of the ceramic-metal substrate 2. This reduction is especially advantageous due to the high temperature gradient in the case of an active heat sink, i.e. a heat sink that comprises cooling channels within its cooling element 11 through which a gaseous and/or vaporous and/or liquid medium can flow and which is designed for optimal cooling, for example, so that the inner heat exchange or cooling surface that is in contact with the coolant is considerably larger, for example at least by a factor of 2 or 4, than the outer cooling surface that is in contact with the module 1.
To achieve a symmetrical design, especially also with respect to the temperature curve, the cooling element 11 is also provided on its bottom side facing away from the module 1 with an additional layer 13a corresponding to the compensating layer 13, the additional layer then preferably having a thickness that is greater than the thickness of the compensating layer 13.
At least in the area of the face side 11.5, a compensating layer 13 is again applied to the top side 11.1 and the bottom side 11.2. The laser bar 16, which is provided with a plate-shaped intermediate carrier 17, is soldered onto the compensating layer 13 on the top side 11.1, namely by means of the solder layer 18 provided between the compensating layer 13 and the intermediate carrier 17 (submount). The bond between the laser bar 16 and the intermediate carrier 17 is likewise formed by a solder layer 19, namely so that the laser bar lies with its laser light emitting side flush with a longitudinal side or longitudinal edge of the intermediate carrier 17 extending along the entire length of the laser bar 16, the intermediate carrier however projecting with its other longitudinal side over the back of the laser bar 16.
Due to the compensating layer 13, in this embodiment equalization is also achieved between the different thermal expansion coefficients of the cooling element 11 made of copper or aluminum and of the intermediate carrier 17 made of Cu—Mo and therefore reduction of the stress on the solder layer 18. To maintain a symmetrical design, especially also with respect to the thermal aspects, the compensating layer 13 is provided with a corresponding layer 13a to the bottom side 11.2, namely so that the thickness of the layer 13a is greater than the thickness of the compensating layer 13, but less than the sum of the thicknesses of the compensating layer 13 and of the intermediate carrier 17.
The invention was described above based on exemplary embodiments. It goes without saying that numerous modifications and variations are possible without abandoning the underlying inventive idea upon which the invention is based.
For example, the compensating layer 13 and/or counter-layer 13a can also be made of sputtered ceramic or high-strength metals.
It is also possible to manufacture the compensating layer 13 and/or counter-layer 13a as composite layers, namely as single or multi-ply layers, in which case the single plies are made of several different materials, for example metals or alloys of different metals, or different plies of different materials or material mixtures (e.g. metal alloys), which then for example are applied using different processes. It is possible, for example, to apply a metal ply (e.g. Cu ply) by cold spraying and a further ply (e.g. ceramic ply) by plasma spraying.
Special layers or plies made of diamond, carbon and/or carbon nanofibers can be applied by chemical vapor deposition (CVD), in which case these layers or plies can then be coated with Cu powder cold gas.
The cooling element 11 can also be part of a heat pipe, in which case the layers 13 and/or 13a also serve to seal risk zones against leaking and for this reason alone already contribute to improving the service life of a constructional of modular unit.
Number | Date | Country | Kind |
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10 2007 015 771.3 | Mar 2007 | DE | national |
10 2007 027 991.6 | Jun 2007 | DE | national |
10 2007 030 389.2 | Jun 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE2007/002186 | 12/4/2007 | WO | 00 | 3/22/2010 |