Cooling device, method for manufacturing a cooling device and power circuit

Abstract

Cooling device (10) comprising an aluminum heat sink (26) and at least one soldering layer (90, 90') which is designed as a nickel or nickel alloy layer and is connected to the aluminum heat sink (26) by means of a solder layer (36), wherein the cooling device (10) has a mounting surface (92, 92') for mounting and heat absorption, which is formed on one side of the soldering layer (90) facing away from the aluminum heat sink (26), and wherein the aluminum heat sink (26) is formed from several stacked and connected aluminum sheets (20, 22, 24), wherein at least one aluminum sheet (22) has recesses (50) which form a cooling channel which is covered by at least one of the aluminum sheets (20, 24), wherein the soldering layer (90, 90') has a thickness of not more than 150 µm.

Description

[0001] The invention relates to a cooling device, a method for manufacturing the cooling device and a power circuit equipped with a cooling device.

[0002] Especially in automotive applications, electrical or electronic circuits, power semiconductors, or other electronic or electrical components are used, the heat generated during operation of which must be dissipated by heat sinks. Typically, the heat sinks are made of aluminum due to its good thermal conductivity, while the circuitry is implemented using a copper-based printed circuit board or similar substrates. To ensure good heat dissipation, cooling channels are incorporated into the aluminum heat sinks. However, manufacturing these cooling channels in the aluminum heat sink is complex, and extrusion processes for creating them require an aluminum alloy with less than optimal soldering properties.

[0003] The publication DE 10 2014 213 490 A1, which constitutes a subsequently published prior art, describes a cooling device in which a mounting surface is formed by means of a nickel sheet metal piece, wherein the sheet metal piece is soldered onto the aluminum heat sink. The aluminum heat sink is formed from stacked aluminum sheets that are soldered together.

[0004] The publication DE 20 2011 000 448 U1 describes a cooler with fins made of aluminum. The cooler assembly is fixed in place by a soldering process in which the entire assembly is placed in an oven, with the fins in particular being attached to the side walls of the cooler using holders.

[0005] German patent application DE 10 2009 022 877 A1 describes a connection of semiconductor elements with a cooling structure. A soldering compound layer is applied directly to the cooling structure.

[0006] It is therefore an object of the invention to demonstrate a way in which cooled circuits can be manufactured in a simple manner. Disclosure of the invention

[0007] This task is accomplished by the subject matter of the independent claims. Advantageous embodiments are described by the features of the dependent claims and the present description.

[0008] It was recognized that aluminum heat sinks can be manufactured simply and using conventional methods through a layered construction. This allows the use of aluminum sheets with any composition. Cooling channels can be created very cost-effectively and precisely by punching or milling. The stacked construction enables simple manufacturing by alternately stacking and joining at least one aluminum sheet with cutouts (created, for example, by punching) and aluminum sheets without cutouts. The aluminum sheets can be joined by a brazing process, in which additional components, such as a copper sheet or a carrier with a copper surface, are bonded to the aluminum sheet (via a nickel layer) while simultaneously bonding the aluminum sheets to each other.These connections can be made using a soldering compound that is applied before stacking, for example by melting it in an oven.

[0009] Similarly, the side of the sheet metal facing away from the heat sink offers good soldering properties for mounting copper, particularly through the nickel layer, or, more generally, through a soldering agent layer. Therefore, a transition between different materials (copper and aluminum) is also possible thanks to the soldering agent layer, which is designed as a nickel or nickel alloy layer.

[0010] A cooling device is described that comprises an aluminum heat sink and at least one soldering interface layer. The cooling device is designed for mounting on a circuit, particularly on a copper layer of a circuit assembly. The soldering interface layer forms the (planar) heat transfer interface in the form of a mounting surface onto which the copper layer is attached. The at least one soldering interface layer is metallurgically bonded and preferably directly attached to or applied to the aluminum heat sink. The at least one soldering interface layer is, in particular, vapor-deposited onto the aluminum heat sink or applied by electroplating. Furthermore, the soldering interface layer can be in the form of a foil that is attached by means of a solder layer. This solder layer directly bonds the soldering interface layer to the aluminum heat sink. The solder layer is, in particular, a hard solder layer.

[0011] The cooling device has a mounting surface for attachment and heat absorption, which functions as a heat transfer interface. The mounting surface is formed by one side of the solder deposit layer. This side faces away from the aluminum heat sink (and thus also from the solder layer between the sheet metal and the heat sink). This side is essentially flat, but can also be adapted to the contour of the printed circuit board to be mounted. The thickness of the solder deposit layer is preferably essentially uniform throughout the layer (i.e., with a tolerance of no more than + / - 10% or + / - 5%).

[0012] One or more soldering layers can be attached to the heat sink. Multiple soldering layers can be arranged directly on the surface of the heat sink or at lateral distances from one another. Multiple soldering layers can be provided on the same, different, or opposite sides of the heat sink. In particular, one or more soldering layers can be attached to each of two opposite (preferably parallel) sides of the heat sink. As already mentioned, the at least one soldering layer is bonded to the heat sink, in particular by means of a bonded connection such as vapor deposition or electroplating. In particular, the heat sink is provided with at least one soldering layer on both sides to allow printed circuit boards or circuits to be mounted on both sides.

[0013] The heat sink is particularly flat and preferably substantially cuboid in shape. The heat sink may have cooling fingers to transfer heat to a surrounding heat medium (air) on the outside of the heat sink, and especially at the cooling fingers. The heat sink has at least one cooling channel extending through it to transfer heat to a heat medium (liquid, particularly oil or water) flowing through the cooling channel.

[0014] The aluminum heat sink is formed from several aluminum sheets stacked on top of each other. These sheets are joined to one another, preferably by means of a brazing alloy, and ideally a hard brazing alloy. At least one aluminum sheet has recesses. This recessed aluminum sheet is covered on both sides by two further aluminum sheets, or on one side by the aluminum sheet and on the other by the sheet metal piece. The recesses form a cooling channel. The recesses extend through the entire thickness of the aluminum sheet or only through a portion of the total thickness of the respective aluminum sheet. The recess is approximately in the form of a groove. The recess extends to the edge of the aluminum sheet.The recess can have a meandering longitudinal path, extending in one and preferably two different longitudinal directions of the aluminum sheet. The recesses therefore preferably extend across the entire surface. The recesses can be formed in one or two directions according to a grid pattern. The recesses are, for example, punched, milled, or cast. The aluminum sheets are joined together, in particular, by means of solder layers. The solder layers seal the aluminum sheets against each other.

[0015] Another sealing element (a layer of sealing, elastic material such as silicone) can also be provided between the aluminum sheets, with the aluminum sheets being connected to each other by means of fasteners, such as a screw connection extending through the aluminum sheets. One of the aluminum sheets (in particular an outer and / or an inner one) can also have flat or rod-shaped cooling fins, which preferably project into the cooling channel. An embodiment with rod-shaped cooling fins is also referred to as a "pin fin" structure, wherein the cooling fins are distributed over a flat (and preferably uniform) area. The cooling fins extend, in particular, inside the aluminum heat sink, i.e., into the at least one cooling channel, and can thus also be considered (in a functional sense) as turbulators.

[0016] The aluminum sheets are preferably rolled aluminum sheets. These can be brazed using hard solder. The heat sink and, in particular, the aluminum sheets preferably have a melting point of at least 590°C, with aluminum containing 8–15% silicon by mass being preferably used as the hard solder (for joining the aluminum sheets and / or for attaching the nickel-plated sheet, i.e., as a solder layer). The hard solder preferably has a casting temperature of 670–740°C and a solidification range of 570–590°C. AlSi12 can be used as the hard solder, in particular. All aluminum alloys with a silicon content of 7–13% by mass are suitable as hard solder. Furthermore, the melting range of the hard solder can be 575–615°C.

[0017] In particular, the heat sink, and especially the aluminum sheets, have a magnesium content of less than 2% by mass, thus ensuring good wettability (with solder). The heat sink, and especially the aluminum sheets, have an aluminum content of at least 70% by mass to guarantee corrosion resistance. Rolled (or cast) aluminum sheets can be used, including AlMg5Si2Mn. The lower melting point of the aluminum sheets in this case is, for example, 594 °C. If the aluminum body is not designed as a stack of aluminum sheets, it can be made of the same material as the aluminum sheets mentioned here. The preceding information therefore applies equally to aluminum sheets and aluminum heat sinks.

[0018] The terms "aluminium sheets" and "aluminium heat sinks" contain the word component "aluminium," indicating that the component is predominantly aluminum. Therefore, the use of the word component "aluminium" does not necessarily mean a 100% aluminum content (by mass), but rather that it may refer to an alloy consisting primarily of aluminum, although, as mentioned, additives are not excluded.

[0019] The at least one soldering layer can, in particular, be a nickel layer. The at least one nickel layer has a nickel content of at least 70%, 85%, or even at least 95%, 98%, or 99% by mass. The thermal conductivity of the soldering layer is preferably at least 70 or 75 W / m*K, and particularly preferably at least 85 or 90 W / m*K. If the soldering layer is a soldered foil, it can have a hard solder layer on one side (facing the aluminum heat sink) or on both sides before being bonded to the aluminum heat sink or the relevant aluminum sheet. If the soldering layer is a foil, it can have a hard solder layer facing the aluminum heat sink and a soft solder layer on the opposite side.This soldering interface layer, provided with at least one layer of solder (or a corresponding soldering compound), is stacked together with the aluminum heat sink and soldered (for example in an oven).

[0020] The soldering agent layer can have a thickness of approximately 5–150 µm, particularly 10–100 µm or 20–50 µm. The soldering agent layer is not thicker than 150 µm, and particularly not thicker than 100 µm, preferably not thicker than 50 or 30 µm. In particular, the soldering agent layer is applied before or after the aluminum sheets are joined together. The application of the soldering agent layer can therefore be a separate step from the step of joining the aluminum sheets together. The heat sink may include cooling channels with a free internal cross-section or channels in which turbulators are incorporated.The turbulators are physically independent bodies (such as a folded piece of sheet metal) that are connected to the inner wall of the cooling channel, or are formed by lateral recesses, or are formed by body sections that project into the channel.

[0021] Furthermore, a method for manufacturing a cooling device described herein is presented. As an exemplary method for joining the aluminum sheets, solder is applied to a joining surface of at least one of the aluminum sheets, for example by printing or rolling, and in particular by applying or inserting a preform in the form of a sheet or foil, which constitutes the solder (especially the brazing compound within the cooling device). The aluminum sheets are stacked. In particular, the aluminum sheets already coated with solder are stacked, or the aluminum sheets are stacked alternately with the solder in the form of a sheet or foil. The solder is melted to form at least one solder layer between the aluminum sheets. This is carried out, for example, by heating the aluminum sheets together with the solder, such as in an oven.The furnace can be evacuated or have a nitrogen atmosphere inside. This creates the aluminum heat sink as a stacked aluminum sheet structure. Flux can be used, particularly as an additive to the soldering compound.

[0022] The at least one soldering agent layer is applied before or after joining the aluminum sheets, in particular before or after melting the solder and optionally before or after applying the solder and / or before or after stacking the aluminum sheets. If the soldering agent layer is designed as a foil, this at least one foil representing the soldering agent layer can also be applied to one of the aluminum sheets, in particular to one of the aluminum sheets that forms an outer surface of the aluminum heat sink. Solder is located between the soldering agent layer and the aluminum sheet. Therefore, it can be provided that solder is applied to a bonding surface of the foil (i.e., the soldering agent layer) or of the aluminum sheet in question.

[0023] The solder between the soldering agent layer and the aluminum sheet is melted in the same step as the solder between the aluminum sheets. Therefore, the solder between the soldering agent layer and the aluminum sheet, and the solder between the aluminum sheets, can be heated and melted in a single step, for example, by placing the stacked aluminum sheets and the soldering agent layer (formed as a foil) in an oven that heats and melts the solder. A solder layer is formed between the soldering agent layer (formed as a foil) and the aluminum heat sink, particularly in a single heating step (e.g., in an oven).

[0024] As mentioned, joining the aluminum sheets using solder is one of several possibilities. In particular, they can also be glued, or a force-fit or form-fit connection can be created using a clamp, a screw connection, or similar to join the aluminum sheets to each other.

[0025] At least one of the aluminum sheets can be punched before stacking. Punching creates the recesses that form the cooling channel, which is enclosed by adjacent sheets or sheet sections. This aluminum sheet can be inserted between two aluminum sheets during stacking, or optionally between an aluminum sheet and the soldering agent layer (designed as a foil). Stacking, together with the surrounding aluminum sheets, creates a cooling channel. The punching produces the recesses that, together with the adjacent components, form the at least one cooling channel. During stacking, a turbulator (as a separate component) can also be inserted into the recess and / or attached there.In this process, solder can be introduced between the turbulator and the adjacent aluminum sheet, so that, if necessary, along with the solder between the aluminum sheets and one of the aluminum sheets, the solder between the turbulator and the adjacent sheet or sheet piece is also melted to form a solder layer. This can be combined with the melting of the solder between the soldering interface layer, provided this layer is designed as a foil.

[0026] In the process for manufacturing a cooling device, the aluminum sheets are stacked to form an aluminum heat sink. At least one of the stacked aluminum sheets has recesses to form a cooling channel.

[0027] The stacked aluminum sheets (20, 22, 24) are joined together to form the aluminum heat sink. This joining can be achieved, for example, by creating a friction-fit or form-fit connection, such as by screwing the edges of the aluminum sheets together with a clamp, or by soldering the aluminum sheets. When creating a friction-fit or form-fit connection, sealant such as silicone or, preferably, elastic sealing elements can be introduced between the aluminum sheets to create a fluid-tight seal between them. The sealant or sealing elements define the cooling channel.

[0028] Therefore, creating a soldered joint between the aluminum sheets is optional and can generally be regarded as a mechanical (and preferably fluid-tight) joining of the stacked aluminum sheets.

[0029] Furthermore, the soldering agent layer is arranged on at least one of the aluminum sheets (24) that forms an outer surface of the aluminum heat sink (26). This can be achieved by directly bonding the soldering agent layer to at least one of the aluminum sheets before or after the stacking and / or joining steps. Alternatively, the soldering agent layer can be arranged (i.e., attached or applied) by soldering. In this case, solder may be present between the soldering agent layer and the aluminum sheet. The solder between the soldering agent layer and the aluminum sheet is preferably melted by heating. This forms a solder layer between the soldering agent layer and the aluminum heat sink.

[0030] The stacked aluminum sheets can be joined by attaching a screw connection that extends through all the aluminum sheets, or by attaching a clamp that grips the edges of all the aluminum sheets. Alternatively, soldering can be used, whereby the stacked aluminum sheets are joined to each other by applying solder to a joining surface of at least one aluminum sheet, preferably before the stacking step.

[0031] The solder can then be melted to form at least a solder layer between the aluminum sheets by heating the aluminum sheets together with the solder. This creates the aluminum heat sink as a stacked aluminum sheet structure.

[0032] The soldering agent layer can be applied by soldering. Solder can be placed between the soldering agent layer and the aluminum sheet, for example, by applying the solder to the aluminum sheet or to the soldering agent layer (formed as a foil) before stacking, and then placing the soldering agent layer onto the aluminum sheet. The solder is then in its green state and positioned between the soldering agent layer and the aluminum sheet. The solder located between the soldering agent layer and the aluminum sheet is preferably melted during the melting step of the layer located between the aluminum sheets. Melting the solder located between the soldering agent layer and the aluminum sheet forms a solder layer between the soldering agent layer and the aluminum heat sink.

[0033] A hard solder compound is used, in particular an aluminum solder with silicon content. The solder compound preferably has a melting point of at least 450 °C.

[0034] In a subsequent step, a printed circuit board or other substrate with a copper conductive layer (or even just the copper conductive layer itself) can be soldered onto the soldering interface layer using soft soldering. The temperature used here is below the melting point of the aforementioned solder.

[0035] Furthermore, a power circuit is described, comprising a cooling device with an aluminum heat sink (made of stacked sheets) and a soldering interface layer, as mentioned herein, and a printed circuit board (PCB). The PCB is provided on both sides with a conductive layer, in particular a copper conductive layer. The conductive layer, and thus also the PCB, is connected to the soldering interface layer, in particular to the mounting surface formed by the soldering interface layer, via a solder layer (preferably soft solder). The power circuit further comprises at least one semiconductor or other electrical or electronic component, which is mounted on the side of the PCB facing away from the soldering interface layer (i.e., on the opposite conductive layer). The solder layer between the PCB and the mounting surface, or between the component and the PCB, is in particular made of soft solder.Sn-based soft solder can be used, preferably with Ag addition, in particular soft solder of the group SnAg3.5, alternatively with the modifications SnAg3Cu0.5 and Sn95.75Ag3.5Cu0.75.

[0036] The semiconductor can be a power semiconductor in the form of an unpackaged semiconductor. This is attached to the printed circuit board (PCB) by means of a soft solder layer. The semiconductor (or component) can be soldered to the PCB in the same step in which the PCB is soldered to the cooling device (i.e., to the aluminum heat sink or to the mounting surface / solder layer) by heating the relevant (soft) solder in an oven (together with the cooling device, the PCB, and the semiconductor / component). The oven temperature is maintained at a level above the melting point of the solder between the component and the PCB, and of the solder between the PCB and the heat sink, but below the melting point of the solder or solder layers located within the cooling device.

[0037] The power circuit is, in particular, an electric motor power control system for a vehicle, a voltage or current power converter in a vehicle electrical system, or an inverter or rectifier circuit. The power circuit is preferably multi-phase, especially three-phase. Circuits with a current-carrying capacity of at least 50 A, 100 A, 200 A, or 500 A are specifically referred to as power circuits.

[0038] Printed circuit boards (PCBs) are primarily made of "direct copper bonded" material, although printed circuit boards with copper cladding are also possible. Additionally, substrates can be used as PCBs where the conductive layer is first structured as a single sheet, for example by stamping to create individual conductor tracks or the interconnect structure. This interconnect structure is then bonded to the substrate, for example by overmolding the interconnect structure with the material of the (electrically insulating) substrate. Brief description of the drawing The Fig. 1 shows a power circuit and a heat sink belonging to the power circuit in cross-section Detailed description of the drawing

[0039] Fig. Figure 1 shows a cross-section of a cooling device 10 comprising several stacked aluminum sheets 20, 22, 24. The aluminum sheets (including associated elements such as solder layers, inlet, outlet, turbulators, fasteners, etc.) form an aluminum heat sink. The aluminum sheets are stacked flush. The aluminum sheet 22, located between the aluminum sheets 20 and 24, has recesses 50, 52 that form a cooling channel. This cooling channel extends to an outer surface of the heat sink 10, specifically to an edge that is approximately offset from the plane of the drawing (and therefore not shown). An inlet and an outlet may be provided at the ends of the cooling channel.

[0040] The aluminum sheets 20-24 are joined to each other by means of solder layers 30 and 32, respectively, with a solder layer located between each pair of adjacent aluminum sheets. The solder layer is located particularly where the aluminum sheets meet, whereas no solder or solder layer may be provided at the recesses 50 and 52. Turbulators 40, which are formed from corrugated sheet metal as shown, may be located within the recesses 50 and 52. These are connected to the adjacent aluminum sheets 20 and 24 via individual solder layer sections 34. However, the turbulators 50 and 52 are optional and can also be omitted. The recesses 50 and 52 extend through the entire thickness of the intervening aluminum sheet 22.As a result, the recesses 50, 52 each form a cooling channel (or cooling channel section of a common cooling channel) which is closed off by the sheets 20, 24, between which the sheet 22 with the recesses lies.

[0041] On an outer surface of the stacked aluminum sheets, in particular on a main surface of an outer aluminum sheet 20, 24 facing away from the recesses 50, 52, there is a soldering agent layer 90, which is connected to the aluminum sheet 24 via an optional solder layer 36. The solder layers 30–34 and the optional solder layer 36 are brazing alloys and can be produced in a single melting process within a furnace. As mentioned, the solder layer 36 can be omitted by producing the soldering agent layer 90 by deposition or coating processes, such as an electroplated layer or a vapor-deposited layer. In this case, the soldering agent layer 90 is directly adjacent to the aluminum sheet (or the aluminum heat sink).

[0042] The soldering layer 90 forms a mounting surface 92, which faces away from the aluminum sheets 20-24. This mounting surface 92 is formed by a top surface of the soldering layer 90 and, in particular, by a surface of the soldering layer 90 provided with a solder layer 70. The solder layer 70 is, in particular, made of soft solder and serves, in particular, to facilitate further assembly. Electronic or electrical components requiring cooling can be mounted onto the mounting surface.

[0043] The Fig. Figure 1 shows, in addition to the heat sink 10 according to the invention, a populated circuit board 60, which is located on the mounting surface 92. Thus, the Fig. In addition to the heat sink 10 according to the invention, a power circuit is also provided, which includes the heat sink 10 and further forms the power circuit. The printed circuit board 60 is a double-sided printed circuit board with a first conductor layer 62 and a second conductor layer 64. The first conductor layer 62 is connected to the soldering layer 70 via the soft solder layer 70, so that the printed circuit board 60 is connected to the mounting surface of the heat sink 10 via the first conductor layer 62. The opposite, second conductor layer 62 serves for mounting a semiconductor 80, which can also represent other electrical or electronic components, in particular power components.

[0044] A solder layer 72, which, like layer 70, is a soft solder layer, connects the semiconductor 80 to the second conductor layer 64, which faces away from the heat sink 10. The semiconductor 80 is an unpackaged semiconductor, such as a transistor, in particular an IGBT or a MOSFET. The semiconductor 80 is only one example of the many components that can be mounted on the circuit board 60.

[0045] For better presentation, in Fig. 1 The circuit board 60 is shown to be narrower than the nickel sheet piece, wherein in further embodiments the circuit board can extend laterally beyond the solder layer and also beyond the heat sink 10. In this case, in particular, power semiconductors or power components that generate heat to be dissipated are preferably arranged above the mounting surface 92, so that the heat conduction path for the heat to be dissipated remains short.

[0046] Furthermore, the heat sink 10 can not only have a soldering layer 90 and thus a mounting surface 92 on one side, but can also be provided with soldering layers on both sides. The optional soldering layer 90' is shown as an example; it is located on the opposite side of the aluminum body (formed by the aluminum layers 20-24) from the soldering layer 90. This second soldering layer 90' has another mounting surface 92' to which components or circuit boards can be attached to dissipate their heat. Like the soldering layer 90, the soldering layer 90' is connected to the aluminum heat sink (i.e., to the aluminum sheets) by means of a hard solder layer 36'. However, this is only one of many possibilities. For example, the soldering layer 90' can be directly bonded to the aluminum body, just like the soldering layer 90.be bonded to the aluminum sheets, for example as a galvanized or vapor-deposited layer.

[0047] As already noted, the aluminium heat sink is formed by the aluminium sheets 20, 22 and 24 and the solder layers 30 and 32 in between, possibly including the turbulators 40.

[0048] In addition to internal cooling channels, the aluminum heat sink can also have cooling fins, especially on the surface of the aluminum heat sink, so that heat can be dissipated alternatively or additionally via the surface of the heat sink (and not only via the cooling channels). Reference symbol list 10 Cooling device 20, 22, 24 aluminum sheets 26 aluminum heat sinks 30, 32, 36 solder layers, especially hard solder layers 34 layers of hard solder for attaching the turbulators 40 turbulators 50, 52 cutouts in aluminum sheet or in aluminum heat sink 26 60 circuit boards 62, 64 conductor layers of the printed circuit board 60 70, 72 Solder layers, especially soft solder layers 80 semiconductors, preferably unpackaged 90, 90' Lot intermediation layer 92, 92' mounting surface

Claims

[1] Cooling device (10) comprising an aluminum heat sink (26) and at least one soldering layer (90, 90') which is designed as a nickel or nickel alloy layer and is connected to the aluminum heat sink (26) by means of a solder layer (36), wherein the cooling device (10) has a mounting surface (92, 92') for mounting and heat absorption, which is formed by a side of the soldering layer (90) facing away from the aluminum heat sink (26), and wherein the aluminum heat sink (26) is formed from several stacked and connected aluminum sheets (20, 22, 24), wherein at least one aluminum sheet (22) has recesses (50) which form a cooling channel which is covered by at least one of the aluminum sheets (20, 24), wherein the soldering layer (90, 90') has a thickness of not more than 150 µm. [2] Cooling device according to claim 1, wherein the aluminium sheets are joined together by means of solder layers (30, 32). [3] Cooling device according to claim 1 or 2, wherein the aluminium sheets (20 - 24) are rolled aluminium sheets which can be brazed together using hard solder. [4] Cooling device according to one of the preceding claims, wherein the solder mediation layer (90, 90') is formed as a nickel layer and has a mass fraction of nickel of at least 70%, 85% or preferably at least 95%, 98% or 99% nickel. [5] Method for manufacturing a cooling device 10) according to any one of the preceding claims, comprising: - Stacking the aluminium sheets (20, 22, 24) to form an aluminium heat sink, at least one of which has recesses to form a cooling channel; - Joining the stacked aluminum sheets (20, 22, 24) together to form the aluminum heat sink and - Arranging the soldering interface layer (90, 90') on at least one of the aluminum sheets (24) forming an outer surface of the aluminum heat sink (26) by soldering, wherein solder is located between the soldering interface layer (90) and the aluminum sheet (24), wherein the solder located between the soldering interface layer (90) and the aluminum sheet (24) is melted by heating to form a solder layer (36) between the soldering interface layer (90, 90') and the aluminum heat sink (26). [6] Method according to claim 5, wherein joining the stacked aluminium sheets (20, 22, 24) comprises: attaching a screw connection extending through all aluminium sheets, or a clamp that engages edges of all aluminium sheets, or wherein joining the stacked aluminium sheets (20, 22, 24) comprises: - Applying solder to a joining surface of at least one aluminium sheet (20, 22, 24) before the stacking step; and - Melting the solder to form at least one solder layer (30, 32) between the aluminum sheets by heating the aluminum sheets (20, 22, 24) together with the solder, thereby creating the aluminum heat sink (26) as a stacked aluminum sheet structure, wherein the solder mediation layer (90, 90') is arranged by soldering, wherein solder is located between the solder mediation layer (90) and the aluminum sheet (24), and the solder located between the solder mediation layer (90) and the aluminum sheet (24) is melted in the step of melting the solder between the aluminum sheets to form a solder layer (36) between the solder mediation layer (90, 90') and the aluminum heat sink (26). [7] Method according to claim 5, wherein at least one of the aluminium sheets (22) is punched before stacking in order to form a cooling channel by means of the surrounding aluminium sheets (20, 24). [8] Power circuit with a cooling device (10) according to one of claims 1-4, wherein the power circuit further comprises a printed circuit board (60) with a conductor layer (62, 64) on both sides, which is connected to the solder mediation layer (90) via a solder layer (70), and wherein the power circuit further comprises at least one semiconductor (80) which is mounted on the side of the printed circuit board (60) facing away from the solder mediation layer (90). [9] Power circuit according to claim 8, wherein the semiconductor (80) is a power semiconductor in the form of an unpackaged semiconductor which is attached to the printed circuit board by means of a soft solder layer (62).

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