METHOD FOR PRODUCING A HEAT LOCK BY HARD SOLDERING

Description

State of the art

[0001] The present invention relates to a method for manufacturing a heat sink for a power electronics component and to an arrangement comprising a heat sink manufactured in this manner.

[0002] Power semiconductors in power electronics, for example in electric or hybrid vehicles, carry high electrical currents. During operation, this can generate heat loss, which can only be dissipated via very small areas. Heat flux densities of up to 1000 W / cm² can be reached. Therefore, liquid cooling is necessary to prevent overheating, for example, of the vehicle's control unit. Furthermore, vehicle control units must possess a certain robustness to withstand temperature fluctuations, vibrations, shocks, and the like without damage during operation. For this reason, such liquid coolers are often designed as die-cast components, which, in addition to being heavy, also involve relatively high manufacturing costs.An alternative is aluminum heat sinks made from multiple components. However, joining the aluminum requires a very high temperature in a brazing process, which negatively affects the aluminum material, for example, by causing distortion. Another problem with aluminum as a heat sink material is that a solderable surface is necessary for joining power electronic components. A copper coating is often used for this purpose. However, copper cannot be joined to aluminum in a conventional brazing process because a low-melting-point aluminum-copper phase forms at temperatures as low as 548°C, which can lead to the melting of both components. Therefore, there is a great need for improved manufacturing methods for such heat sinks.US patent 2013 / 277034 A1 discloses a method for manufacturing an aluminum heat sink with a stress-reducing component and a substrate layer. Furthermore, JP patent 2020 131251 A discloses a method for joining an aluminum component with a nickel-containing component. Disclosure of the invention

[0003] The inventive method for manufacturing a heat sink for power electronics components with the features of claim 1 has the advantage that at least two components of the heat sink are joined by means of a brazing process using a low-melting-point brazing alloy in the temperature range between 520° and 540°. This allows the use of a brazing process that remains below the critical temperature of 548°C, at which melting of the joining partners aluminum and copper can occur. This prevents the formation of a low-melting-point aluminum-copper phase to which a power electronics component could later be fixed by a soft soldering process, which uses significantly lower temperatures below 420°C.According to the invention, this is achieved by the heat sink comprising at least two components, selected from: an aluminum base, an aluminum top, an aluminum insert, and a copper plate. At least two of the aforementioned components are joined by means of a brazing process using a low-melting-point brazing alloy, the brazing joint being produced in a temperature range between 520°C and 540°C. This reliably prevents melting to the aluminum-copper phase described above. Thus, the heat sink, in particular, has a low-melting-point brazing alloy joint between the aluminum base and the copper plate or between the aluminum top and the copper plate.

[0004] The dependent claims describe preferred embodiments of the invention.

[0005] Preferably, the brazing process is carried out with the low-melting-point brazing alloy at a temperature of 530°C. This ensures a sufficient margin from the temperature limit of 548°C.

[0006] According to the invention, the low-melting-point hard solder comprises aluminum, silver, copper, and silicon. Preferably, the low-melting-point hard solder comprises silicon in a range of 1 to 2% by mass.

[0007] Alternatively, and in accordance with the invention, the low-melting-point hard solder comprises exclusively aluminium, silver and copper in a ratio of 40 wt% aluminium, 40 wt% silver and 20 wt% copper.

[0008] The inventive method is particularly preferably carried out such that the aluminum lower part, the aluminum upper part, and the aluminum insert are joined by brazing with a hard solder at a temperature of ≥ 590°C, and subsequently the copper plate is joined to the aluminum lower part or the aluminum upper part using the low-melting-point hard solder at a brazing temperature of 520°C to 540°C. Thus, the low-melting-point hard solder joint is formed on the copper plate. As a result, the heat sink preferably has a low-melting-point hard solder joint for fixing the copper plate, and the other components of the heat sink are made using a conventional brazing process at temperatures ≥ 590°C. Preferably, a power electronics component is then attached to the copper plate using a soft soldering process (temperature ≤ 420°C).

[0009] Alternatively, the inventive method is carried out such that the aluminum lower part, the aluminum upper part, and the aluminum insert are joined using low-melting-point brazing alloy, wherein a copper coating is applied to the aluminum lower part or the aluminum upper part, and the power electronics component is then attached exclusively to the copper coating using a soft soldering process. Thus, all components of the heat sink can be joined together using low-melting-point brazing alloy, with the power electronics component then being attached using a soft soldering process. Alternatively, instead of the copper coating, the aluminum lower part and / or the aluminum upper part can be designed as copper-roll-clad aluminum sheet.

[0010] It should also be noted that it is of course possible for the heat sink to have an aluminum base, an aluminum top, an aluminum insert and a copper plate, with all components being joined together by means of a brazing process using low-melting hard solder.

[0011] To attach the power electronics component, a soft solder in printed form is preferably arranged on the power electronics component, or alternatively, a soft solder foil is arranged on the power electronics component to carry out the soft soldering process.

[0012] Preferably, the copper plate has a thickness less than the aluminum base or top. The copper plate preferably has a thickness of approximately 1.5 mm, and the aluminum base or top preferably has a thickness of 2.5 mm.

[0013] Furthermore, the present invention relates to a power electronics arrangement comprising a power electronics component and a liquid cooling heat sink made of aluminum, which includes an aluminum lower part, an aluminum upper part, an aluminum insert and a copper plate, wherein at least one connection between the components of the heat sink is made by a brazing alloy with a low-melting-point solder with a brazing temperature of approximately 530°C, or wherein the heat sink has an aluminum lower part, an aluminum upper part, an aluminum insert and a copper coating on the aluminum lower part and / or on the aluminum upper part, and a component connection between the components of the heat sink is formed by means of a low-melting-point brazing alloy with a brazing temperature of approximately 530°C or a melting range between 490 and 506°C. drawing

[0014] Preferred embodiments of the invention are described in detail below with reference to the accompanying drawing. The drawing shows: Figure 1 is a schematic view of a power electronics arrangement with a heat sink, Figure 2 is a schematic view of a power electronics arrangement with a heat sink which was manufactured according to a first preferred embodiment of the invention, and Figure 3 is a schematic view of a power electronics arrangement with a heat sink which was manufactured according to a second preferred embodiment of the invention. Preferred embodiments of the invention

[0015] The following refers to the Figure 1 A power electronics arrangement 1 and a method for manufacturing a heat sink are described in detail.

[0016] As from Figure 1As can be seen, the power electronics arrangement 1 comprises a power electronics component 2 with a heat sink 3. The heat sink 3 comprises an aluminum lower part 30, an aluminum upper part 31 and an aluminum insert 32. The aluminum insert 32 is, for example, a strip-fin insert.

[0017] As from Figure 1 As can be seen, the heat sink 3 is located directly below the power electronics component 2. The heat sink 3 is designed to be cooled by a coolant flow for improved cooling performance. For this purpose, the heat sink 3 has an inlet and an outlet (both not shown) for supplying and removing the coolant. It should be noted that the aluminum insert could also, for example, be an insert for meandering fluid flow.

[0018] What's next? Figure 1As can be seen, a copper coating 6 is provided on an outer surface of the aluminum top part 31. This makes it possible to connect the power electronics component 2 to the aluminum top part 31 by means of a soft solder joint 8.

[0019] Furthermore, as can be seen from Figure 1 As can be seen, a low-melting-point brazing alloy 4 is formed between the aluminum lower part 30 and the aluminum insert 32. A similar low-melting-point brazing alloy 4 is also formed between the aluminum lower part 30 and the aluminum upper part 31.

[0020] In this embodiment, the brazed joints of the heat sink 3, which are otherwise provided by means of hard solder joints at temperatures ≥ 590°C, are replaced by low-melting-point hard solder joints 4, which are executed at temperatures of approximately 530°C. The low-melting-point hard solder is an alloy comprising aluminum, silver, copper, and silicon.

[0021] The copper coating 6 can, for example, be applied to the surface of the aluminum top part 31 using a cold gas process. The thickness of the copper coating 6 is preferably approximately 100 µm.

[0022] Thus, an aluminum heat sink 3 can be provided which can be brazed at temperatures significantly below the critical temperature of 548°C and still has a copper coating on the aluminum component, which does not form an undesirable aluminum-copper phase despite the brazing process. This has the particular advantage that an aluminum component can be used which already has the copper coating 6 before the brazing process. This also offers particular advantages in terms of manufacturing. It should be noted that, alternatively, a copper-roll-clad aluminum sheet can be used instead of the copper coating, which can also be produced before the brazing process. Furthermore, the copper coating 6 also enables excellent thermal contact between the power electronics component 2 and the heat sink 3.

[0023] The following refers to the Figure 2 a power electronics arrangement 1 and a method for manufacturing a heat sink according to a second embodiment of the invention are described in detail.

[0024] Figure 2 essentially corresponds to the Figure 1 , in contrast to Figure 1 In the first embodiment, a copper plate 7 is provided instead of the copper coating 6. As shown in the following: Figure 2 As can be seen, the copper plate 7 is connected to the aluminum top part 31 by means of a low-melting-point hard solder joint 4. The power electronics component 2 is then connected to the copper plate 7 by means of a soft solder joint 8.

[0025] Thus, in the first embodiment, all components of the heat sink 3, namely the aluminum lower part 30, the aluminum upper part 31, the aluminum insert 32, and the copper plate 7, are joined together by means of low-melting-point brazing alloys 4. This significantly reduces the thermal stress on the heat sink 3 during its manufacture, preventing any manufacturing-related thermal distortion. As a result, the accuracy of the heat sink 3 can be significantly improved compared to the prior art. Otherwise, this embodiment corresponds to the first embodiment, so reference can be made to the description given therein.

[0026] The following refers to the Figure 3 a power electronics arrangement 1 and a method for manufacturing a heat sink according to a second embodiment of the invention are described in detail.

[0027] As from Figure 3As can be seen, the second embodiment, like the first, also features a copper plate 7. However, in the second embodiment, a conventional brazing joint 5 is provided between the aluminum lower part 30, the aluminum insert 32, and the aluminum upper part 31, which is produced at temperatures ≥ 590°C. The copper plate 7, on the other hand, is connected to the aluminum upper part 31 by means of a low-melting-point brazing joint 4 at a brazing temperature of approximately 530°C. Thus, the heat sink 3 can be connected without the copper plate 7 using the conventional brazing joints 5. After this pre-assembly of the heat sink 3 has been produced, the copper plate 7 can then be applied to the aluminum upper part 31 using a low-melting-point brazing joint at temperatures of approximately 530°C.Subsequently, as in the first embodiment, the power electronics component 2 can be fixed to the copper plate 7 by means of a soft solder joint 8. Otherwise, this embodiment corresponds to the preceding embodiments, so reference can be made to the description given there.

[0028] Thus, the invention enables a significant improvement in the manufacture of the heat sink 3 by using a low-melting-point brazing alloy, which in particular has a melting range between 490 and 506°C, as illustrated in the two exemplary embodiments. Either a single low-melting-point brazing alloy joint 4 can be provided between two components of the heat sink 3, or alternatively, more than two or all components of the heat sink 3 can be joined together by a low-melting-point brazing alloy joint 4. Both manufacturing methods have in common that no undesirable aluminum-copper phase occurs, since the soft soldering process for fixing the power electronics component 2 to the aluminum heat sink 3 requires the application of copper, as the power electronics component 2 cannot be fixed directly to aluminum by means of a soft soldering process.

[0029] Thus, the heat sink 3, as illustrated in the two exemplary embodiments, can have a structure made of aluminum and copper, resulting in significantly improved thermal performance. In particular, the invention also allows for variation of the required copper surface area with respect to its length, width, and height. This does not require any changes to the manufacturing process. If necessary, according to the invention, a heat sink in its basic form can still be produced by an aluminum-to-aluminum brazing process at temperatures above 590°C, and the copper plate 7 can then be attached to the heat sink by means of the low-melting-point brazing alloy 4 at a temperature of approximately 530°C.

Claims

1. Method of producing a heat sink (3) for liquid cooling of power electronics components (2), wherein the heat sink (3) has at least two components: - an aluminium lower portion (30), - an aluminium upper portion (31), - or an aluminium insert portion (32) and a copper plate (7), - wherein at least two components are bonded to one another with a low-melting brazing solder by a brazing method, wherein the brazing method is conducted at a temperature between 520°C and 540°C in order to form a low-melting brazing solder bond (4) between the at least two components, wherein the low-melting brazing solder comprises aluminium and silver and copper and silicon, or wherein the low-melting brazing solder comprises exclusively aluminium, silver or copper, in particular in a ratio of 40% by mass of aluminium, 40% by mass of silver and 20% by mass of copper, wherein the heat sink (3) includes a low-melting brazing solder bond between the aluminium lower portion (30) and the copper plate (7), or the aluminium upper portion (31) and the copper plate (7).

2. Method according to Claim 1, wherein the temperature for conducting the brazing method is 530°C.

3. Method according to either of the preceding claims, wherein all components of the heat sink (3) are bonded to one another by the low-melting brazing solder.

4. Method according to either of Claims 1 and 2, wherein the components of the heat sink (3) are the aluminium lower portion (30), the aluminium upper portion (31) and the aluminium insert (32) and the copper plate (7), and the aluminium lower portion (30), the aluminium upper portion (31) and the aluminium insert (32) are bonded by a brazing solder bond (5) by a brazing solder at a brazing temperature of > 590°C, and then the copper plate (7) is bonded to the aluminium lower portion (30) or the aluminium upper portion (31) by the low-melting brazing solder bond (4).

5. Method according to any of the preceding claims, wherein the power electronics component (2) is fixed to the copper plate (7) by a soft soldering method.

6. Method according to Claim 5, wherein a soft solder is arranged in printed form on the power electronics component (2) or wherein a soft solder foil is arranged on the power electronics component (2).

7. Power electronics arrangement comprising: - a power electronics component (2) and - a heat sink (3) for liquid cooling, where the heat sink (3) has been produced from a plurality of components of aluminium and a copper plate (7), - wherein the copper plate is arranged between the power electronics component (2) and the heat sink (3), and - wherein at least one component bond of the aluminium lower portion (30), of the aluminium upper portion (31) or of the aluminium insert portion (32) to the copper plate (7) of the heat sink (3) is a low-melting brazing solder bond (4) formed by means of a brazing operation at a temperature within a range from 520°C to 540°C, in particular 530°C, wherein the low-melting brazing solder comprises aluminium and silver and copper and silicon, or wherein the low-melting brazing solder comprises exclusively aluminium, silver or copper, in particular in a ratio of 40% by mass of aluminium, 40% by mass of silver and 20% by mass of copper.