Patent Application
20100282459
The present invention is directed to a heat sink.
Heat sinks made of homogeneous metal-carbon composite materials and in particular metal matrix-ceramic composite (MMC) materials are described in Japanese Patent Application No. JP 2005 044 841 A, PCT Application No. WO 2004/005 566 A2, European Patent No. 1 168 438 A2, U.S. Pat. No. 5,886,407 A and European Patent No. 0 859 410 A2. These composite materials include a matrix made of metals, for example, copper or aluminum, and carbon particles dispersed in the matrix. These homogeneous composite materials are provided for dissipating heat, in particular from a semiconductor component situated on a first side of the heat sink. In addition, to reduce thermal stresses between the semiconductor component and the heat sink, the aim is to provide a heat sink having a thermal expansion coefficient comparable to the thermal expansion coefficient of the semiconductor component substrate. In modules having an MMC base plate structure, the semiconductor component is contacted electrically via copper on an insulation layer, the insulation layer being situated on the MMC heat sink and in particular being adhesively bonded, the aim being to match the thermal expansion coefficient of the heat sink to the thermal expansion coefficient of the insulation layer.
An example heat sink according to the present invention and an example method according to the present invention for manufacturing a heat sink may have the advantage that an insulation layer of the first material is integrated into the heat sink itself, so that the thermal expansion coefficient of the insulation layer is much better matched to the thermal expansion coefficient of the remaining heat sink, while at the same time a substantially better thermal coupling of the insulation layer to the remaining heat sink is achieved, and furthermore, the insulation layer is joined to the remaining heat sink in a much more stable manner mechanically, so that an adhesive layer for a materially bonded joint of the insulation layer to the remaining heat sink is completely eliminated in a particularly advantageous manner. Therefore, on the one hand, heat at the insulation layer is dissipated much more rapidly by the heat sink, thus preventing overheating damage to a semiconductor structure in particular, while on the other hand, mechanical stresses on the insulation layer or between the insulation layer and the remaining heat sink due to the extreme difference in thermal expansion coefficients between the insulation layer and the remaining heat sink are much lower or are completely suppressed. The heat sink is a composite body, the material component of the insulating first material on the first side being greater than that on the second side, the first side of the heat sink preferably being an insulation layer made of the first material, and the second side including primarily the second material. A combination of a comparatively good thermal conductivity of the second material with a comparatively low electric conductivity of the first material is thus made possible in a particularly advantageous manner, so that a comparatively good adaptation of the thermal expansion coefficients is achieved within the composite body and thus the thermomechanical stresses within the composite body are much lower in comparison with those in the related art.
According to a preferred refinement, it is provided that the material component of the second material in the composite material is greater in the area of the second side than the material component of the second material in the area of the first side, the first side preferably having generally only the first material and/or the second side having generally only the second material, so that the first side as the insulation layer has a minimal electrical conductivity and the second side has a maximal thermal conductivity in a particularly advantageous manner, and at the same time a maximum thermal coupling is implementable between the first and second sides and a maximal adaptation of the thermal expansion coefficient of the first side to the thermal expansion coefficient of the second side is implemented.
According to another preferred refinement, the proportion of the first material in the composite material decreases from the first side to the second side perpendicularly to the main direction of extent, in particular continuously, monotonously and/or in steps, while the proportion of the second material in the composite material increases from the first side to the second side perpendicularly to the main direction of extent, in particular continuously, monotonously and/or in steps. Thermal stresses within the composite material are thus minimized in a particularly advantageous manner, because there are no comparatively strongly pronounced discontinuities in the thermal expansion coefficients in this direction due to a preferably continuous transition from a high proportion of the first material to a high proportion of the second material in a direction perpendicular to the main direction of extent, the thermal coupling between the first and second materials being maximized at the same time.
According to another preferred refinement, the first material has a porosity which increases from the first side to the second side perpendicularly to the main direction of extent and the pore size and/or the pore density of the first material preferably increases on the average from the first side to the second side perpendicularly to the main direction of extent, the pores particularly preferably being filled with the second material. A different proportion of the first material between the first and second sides is thus implementable in a particularly simple and inexpensive manner by a variation in the pore size and/or pore density in the first material. Alternatively, a variation in the porosity of the second material is also possible, in particular with regard to the pore size and/or pore density perpendicularly to the main direction of extent.
According to another preferred refinement, the composite material has a plurality of composite material layers perpendicularly to the main direction of extent, such that in particular the ratio of the first material to the second material is different between the composite material layers so that a composite body having a different proportion of the first material may be formed between the first side and the second side in a particularly simple and inexpensive manner. In particular, a composite body having a plurality of composite material layers is possible, the ratio of the first material to the second material changing from a composite material layer close to the first side to a composite material close to the second side in comparatively small gradations and/or monotonously increasing or decreasing.
According to another preferred refinement, the first material is joined to the second material by a form-fit and/or force-fit connection and/or the first material forms interpenetrating networks with the second machine. A form-fit and/or force-fit connection between the first and second materials is preferably formed by filling the pores of the first material with the second material. The mechanical load-bearing capacity within the heat sink is particularly advantageously increased to a substantial extent in comparison with the related art by a form-fit and/or force-fit connection between the first and second materials.
According to another preferred refinement, the first material has a degree of porosity profile preferably from 0 vol % to 95 vol % and particularly preferably from 0 vol % to 65 vol % perpendicularly to the main plane of extent, and most particularly preferably the first side has a composite material layer generally completely made of the first material having a thickness of at least 50 μm perpendicularly to the main plane of extent, so that the properties of low electric conductivity of the insulation layer, good thermal conductivity of the heat sink, and good matching of the thermal expansion coefficients are implemented comparatively well.
According to another preferred refinement, the first material includes a ceramic material, preferably oxides, nitrides and/or carbides, particularly preferably Al2O3, AlN, Si3N4 and/or SiC and most particularly preferably Al2O3, and the second material is a metallic material, preferably copper, copper alloys, aluminum and/or aluminum alloys. Ceramic material particularly advantageously has a comparatively low electrical conductivity so that the requirements of a high insulation capacity of the insulation layer are met, and metallic material has a comparatively good thermal conductivity so that the requirements of good cooling capacity of the heat sink may also be met at the same time.
Another embodiment of the present invention includes an assembly having a heat sink, at least one electrical, electronic and/or micromechanical component and/or a printed conductor and/or a connecting layer being situated on the first side of the heat sink, the first side being covered preferably at least partially by a metal layer and particularly preferably at least partially by an aluminum layer and/or a copper layer. Due to the insulation layer of the heat sink, which provides electrical insulation, application of printed conductors directly to the insulation layer for contacting electrical, electronic and/or micromechanical components is thus made possible in a particularly advantageous manner, so that the implementation of a DBC stack becomes unnecessary due to the assembly described here.
Another embodiment of the present invention includes a method for manufacturing a heat sink; in a first method step, a preform having a porosity gradient perpendicularly to the main plane of extent is manufactured from the first material, and in a second method step, the pores of the preform are filled with the second material. It is thus possible to manufacture the heat sink according to the present invention in just two comparatively simple and easily controllable steps, so that manufacturing is comparatively inexpensive, and comparatively inexpensive materials may be used.
According to a preferred refinement, the preform is manufactured in the first method step by negative molding, in particular by negative molding of foams pressed together by using ceramic slips; polyurethane foams are preferably used or the preform is manufactured in the first method step via pressure filtration of the slip and subsequent sintering; preferably a slip mold is first filled with two slips having different compositions, the ratio between the two slips being varied continuously and then the preform being manufactured via a pressure filtration and sintering method, or the preform being manufactured via powder pressing in the first method step, powders of different compositions being preferably squeegeed into a female mold, one over the other, and then pressed, or the preform being manufactured in the first method step via coating and sintering of a plurality of greenware plates, the greenware plates preferably being stacked on top of each other, yielding different porosities in sintering, or the preform being manufactured in the first method step via stacking and joining plates of different porosities, ceramic plates preferably being stacked on top of each other and sintered subsequently for joining them, for example, or the preform being manufactured in the first method step via a casting method, in particular a film-casting method, slips of different compositions being cast one over the other, preferably via the film-casting technique, and are subsequently sintered, or the second method step includes an infiltration method, the preform preferably being infiltrated with the second material in a pressure-assisted method and the second material particularly preferably being converted into a liquid state before the second method step. Manufacturing of the heat sink is thus possible in a particularly advantageous manner using a plurality of manufacturing methods, whereby comparatively flexible and cost-optimized manufacturing is implementable. All the manufacturing methods are comparatively easily controllable and inexpensively implementable.
Exemplary embodiments of the present invention are illustrated in the figures and described in greater detail below.
a shows a schematic side view of a preform for manufacturing a heat sink according to a second exemplary specific embodiment of the present invention.
b shows a schematic side view of a heat sink according to the second exemplary specific embodiment of the present invention.
a shows a schematic side view of a preform 1′ for manufacturing a heat sink 1 according to a second exemplary specific embodiment of the present invention, preform 1′ including only first material 3, preform 1′ having a plurality of pores 10, and the pore density increasing continuously or in stages from first side 5 to second side 6 perpendicularly to main plane of extent 100, so that the material density of first material 1 decreases continuously or in stages from first side 5 to second side 6. Preform 1′ is manufactured via negative molding of polyurethane foams pressed together via ceramic slips or via a graduated pressure filtration of the slip, a slip mold being filled preferably from reservoirs having slips of different compositions, for example, with regard to the pore-forming substance or the grain size, the ratio of the two slips being varied continuously in particular, and then a greenware body, having a gradient in the proportion of the pore-forming substance, for example, is produced therefrom with the aid of pressure filtration, so that after a subsequent sintering procedure, preform 1′ having a porosity gradient is formed. Alternatively, preform 1′ is manufactured via graduated/stepped powder pressing, powders of different compositions preferably being squeegeed into a female mold one over the other and then pressed, thus permitting powder variations with regard to grain size or pore-forming substance, or preform 1′ is manufactured by stacking greenware plates on top of each other, which yield different porosities under the same sintering conditions due to variations in grain sizes or the proportions of the pore-forming substance, and then sintering the greenware plates. Alternatively, it is also possible to stack ceramic plates of differing porosities on top of each other, which are subsequently sintered to join them together, or to use a film-casting method, in which ceramic slips having different compositions, for example, with regard to grain size or the proportions of the pore-forming substance, are cast one over the other and subsequently sintered to manufacture the preform.
b shows a schematic side view of heat sink 1 according to the second exemplary specific embodiment of the present invention, in which heat sink 1 includes preform 1′ manufactured in the first method step and illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 005 529.8 | Jan 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/066290 | 11/27/2008 | WO | 00 | 6/30/2010 |
