Electronics module and method for producing same

Abstract

The invention relates to an electronics module, comprising an electronics unit (2) and a metal heat sink (3) having a plurality of protruding cooling elements (6), and comprising a metal housing (7) attached to the heat sink (3), wherein a cavity (9) having an inlet (12) and an outlet (13) is formed between the heat sink (3) and the housing (7), with the cooling elements (6) projecting into said cavity, wherein that surface (10) of the housing (20) that delimits the cavity (9) is provided with a non-metallic anti-corrosion coating (14) at least in the region opposite the cooling elements (6).

Description

[0001] Electronic module and method for its manufacture

[0002] The invention relates to an electronic module comprising an electronic unit and a metal heat sink with a plurality of projecting cooling elements and a metal housing attached to the heat sink, wherein a cavity with an inlet and an outlet into which the cooling elements protrude is formed between the heat sink and the housing.

[0003] Such an electronic module is often designed as a power module, with an electronic unit comprising one or more power components such as high-performance transistors, capacitors, and the like. The components of the electronic unit heat up during operation, especially if they are power components, which is why appropriate cooling is required. For this purpose, the electronic module has, in addition to the electronic unit, which is usually embedded in a potting compound, a metal heat sink on which several protruding cooling elements are provided, for example in the form of pins or webs, often also called pins or fins. A housing is attached to the metal heat sink. This housing is also made of metal and, together with the heat sink, defines a cavity into which a coolant inlet opens and from which a coolant outlet leads, so that the electronic module can be integrated into a cooling circuit.The cooling elements protrude into the cavity into which the coolant, for example water or a water-glycol mixture, flows, so that heat generated at the power components can be transferred via the heat sink and the cooling elements to the fluid coolant and dissipated via this.

[0004] After the electronic module has been manufactured from the module-specific components in the factory, it undergoes a functional test at the end of the production line, where it is regularly connected to an associated unit, such as an electric machine. This test is known as an end-of-line test. This also tests the cooling of the electronic module, i.e., the coolant circulates and necessarily flows through the cavity. After the test is completed, the unit along with the electronic module, or, if disassembled, the electronic module itself, is often not installed immediately but stored for a certain period of time.

[0005] After the test, a certain residual amount of coolant remains in the cooling circuit or in the cavity, which is divided by the cooling elements, for example, into a meandering, relatively long cooling channel extending from the inlet to the outlet. The cooling elements extend, as described, from the surface of the cooling element that defines the cavity into the cavity to the opposite surface of the housing, separated from this only by a narrow gap. The heat sink and thus the cooling elements are made of metal, for example copper, with the surface optionally coated with a galvanic layer of nickel or containing nickel. The housing, in turn, which is also made of metal, is usually made of a different, less noble material, usually aluminum. It is usually manufactured using a die-casting process, for example an aluminum die-casting process.The problem here is that when the remaining coolant comes into contact with air or the oxygen contained in the air, corrosion occurs in the narrow gap, for example, only a few tenths of a millimeter wide, between the cooling elements and the surface of the housing. This corrosion is caused by the different metals and the residual amount of coolant present in the gap area, which solidifies due to a chemical reaction with the air or atmospheric oxygen, resulting in a type of "gelling." This corrosion is naturally detrimental, as it impairs the cooling structure and damages the housing. To counteract this problem, it is known from DE 10 2020 214 397 A1 to thermally treat the electronic module after the end-of-line test has been carried out, i.e., bake it out so that any coolant residues present in the cavity evaporate. However, this thermal treatment is complex.

[0006] The invention is based on the problem of providing an electronic module which is improved compared to the above.

[0007] To solve the problem, in an electronic module of the type mentioned at the outset, the invention provides that the surface of the housing delimiting the cavity is provided with a non-metallic corrosion protection coating, at least in the area opposite the cooling elements.

[0008] In the electronic module according to the invention, the housing surface that defines the cavity and, as described, is prone to corrosion, is provided with a non-metallic anti-corrosive coating, wherein this anti-corrosive coating is provided at least in the area opposite the cooling elements. This anti-corrosive coating, which consists of a non-metallic material, preferably plastic, separates the two metallic components in this area—i.e., the cooling elements made of a more noble material from the housing surface made of a less noble material—so that galvanic corrosion caused by the connection of the cooling elements to the housing surface via the coolant residue and its reaction with air or atmospheric oxygen does not occur in this area.As a result, a coolant residue can easily remain in the cavity after the end-of-line test has been carried out, since corrosion of the housing material does not occur even in the long term, as it is protected by the corrosion protection coating.

[0009] As described, the corrosion protection coating is preferably made of plastic, for which thermoplastic polymers such as fluoropolymers, but also other thermoplastic polymers as well as thermosetting polymers are suitable.

[0010] The corrosion protection coating can be applied to the surface of the housing in various forms. According to the invention, the corrosion protection coating can be a prefabricated coating element arranged on the surface of the housing. The coating element is, for example, an appropriately dimensioned foil or plate that is, for example, glued to the housing surface. The coating element is dimensioned such that it covers at least the area of ​​the housing surface opposite the cooling elements, but preferably also beyond.

[0011] Alternatively, it is also conceivable for the corrosion protection coating to be applied in the form of a cured coating. The corrosion protection coating is applied to the housing surface using a liquid, e.g., polymeric material and then cured, comparable to a type of paint. The coating can be applied to the separate housing itself or after completion of the electronic module by flooding the cavity, draining the excess material, and then curing.

[0012] The cooling elements can also be spaced from the corrosion protection coating by a narrow gap of just a few tenths of a millimeter. They can also be flush with the corrosion protection coating.

[0013] It is advisable to arrange a sealing element between the heat sink and the housing, which runs around the cavity and laterally delimits the cavity. This sealing element, which completely seals the cavity on all sides and, of course, also seals the surface of the heat sink and the surface of the housing, ensures that the coolant only wets the surfaces of the heat sink or cooling elements that are not in contact with each other and the housing surface, but not the connection area where the heat sink directly rests against the housing. The sealing element can be, for example, a circumferential seal made of a suitable sealing material; here, too, a polymer material, such as a thermoplastic or elastomeric material, can be used.

[0014] In addition to the electronic module itself, the invention also relates to a method for producing such an electronic module, comprising the following steps:

[0015] Applying a prefabricated coating element as a non-metallic corrosion protection coating to the surface of the housing delimiting the cavity, connecting the housing to the heat sink in such a way that the cooling elements projecting from the heat sink protrude into the cavity and end adjacent to the coating element.

[0016] In this process variant, a prefabricated coating element, as described above, for example in the form of a plastic film or a plastic plate, is used to form the non-metallic corrosion protection coating. This coating element is placed on the surface of the housing that defines the cavity and secured there, for example, by gluing. In a next step, the housing is connected to the heat sink, closing the cavity and allowing the cooling elements to protrude into the cavity and, accordingly, end adjacent to the coating element via the very narrow gap, which, as described, is only a few tenths of a millimeter wide, or rest against the coating element.

[0017] If a sealing element is to be arranged in the cavity which laterally limits the cavity, such a sealing element can be arranged on the housing before or after the lining element is applied.

[0018] As an alternative to the variant described, the invention provides a method for producing such an electronic module, comprising the following steps:

[0019] Connecting the housing to a heat sink dummy comprising cooling element dummies, which is identical to the heat sink of the electronic module, such that the cooling element dummies projecting on the heat sink dummy protrude into the cavity and end adjacent to the surface of the housing, wherein before connecting, a sealing element is arranged on the housing or on the heat sink dummy, which laterally delimits the cavity after connecting the housing to the heat sink dummy,

[0020] Flooding the cavity with a hardenable fluid,

[0021] Draining the fluid, whereby the surface of the housing that defines the cavity is covered with a fluid coating, either hardening of the fluid to form the corrosion protection coating and removal of the heat sink dummy, or vice versa,

[0022] Connecting the housing to the heat sink in such a way that the cooling elements projecting on the heat sink protrude into the cavity and end adjacent to the corrosion protection coating, wherein, if appropriate, a sealing element is arranged on the housing or on the heat sink before the connection, which sealing element laterally delimits the cavity after the housing is connected to the heat sink.

[0023] In this process variant, the corrosion protection coating is created via a coating on the housing surface. For this purpose, a dummy heat sink comprising dummy cooling elements is first connected to the housing. The dummy heat sink is identical in its geometry to the heat sink to be subsequently attached. A sealing element is also arranged in the cavity. The formed cavity is then flooded with the liquid material forming the coating, which is then drained away again, for example after a certain holding time. This results in the surface of the housing that borders the cavity being covered with a fluid coating. The fluid can then be cured, with the dummy heat sink still in place, to form the corrosion protection coating. After curing, the dummy heat sink is removed.Alternatively, it is conceivable that the dummy heat sink is removed after the fluid has been drained, allowing the coating to harden only then. In any case, after removing the dummy heat sink, the housing, now coated on its hollow surface, is connected to the actual heat sink of the electronics unit in such a way that the cooling elements protruding from the heat sink extend into the cavity and either end over the still narrow gap adjacent to the corrosion protection coating, i.e., the coating, or rest against it. Of course, the sealing element is inserted into the cavity beforehand, if necessary.

[0024] The invention is explained below using an exemplary embodiment with reference to the drawing. The drawing is a schematic representation.

[0025] Shown is an electronic module 1 comprising an electronic unit 2, preferably a power electronics unit, comprising a plurality of high-performance power components such as transistors, capacitors, etc., which are regularly arranged on a circuit board. The power electronics unit 2 is accommodated in a heat sink 3 made of metal, for example, copper, in a corresponding recess and encapsulated with a potting compound 4. During operation, the power components heat up, and the resulting heat can be dissipated via the heat sink 3.

[0026] On the underside 5 of the heat sink, a plurality of cooling elements 6 are arranged in a projecting manner, which are preferably webs, so-called fins, over which a quasi-meander-shaped cooling channel can be formed in the assembly configuration.

[0027] Furthermore, a housing 7 is provided, which is connected, in particular screwed, to the heat sink 3 via fastening elements 8 (only indicated here). The housing 7 is also made of metal, but of a different, less noble metal than the heat sink 3. The heat sink 3 is made of copper, for example, and preferably has an additional coating, for example of nickel or nickel-based, on the underside 5 and the cooling elements 6. In contrast, the housing 7 is made of aluminum, for example, and is thus a die-cast aluminum housing.

[0028] A cavity 9 is formed above the heat sink 3 and the housing 7, which in the figure is limited at the top by the surface of the underside 5, and at the bottom by the surface 10 of the housing 7. To the side, the cavity 9 is limited and sealed by a circumferential sealing element 11 such as a seal, preferably made of a suitable elastic plastic material, wherein the sealing element 11 extends to the underside 5, thus also sealing the connection area between the heat sink 3 and the housing 7.

[0029] The housing 7 has an inlet 12 leading into the cavity 9, and an outlet 13 leading out of the cavity 9. Both the inlet 12 and the cavity 13 are preferably designed as elongated slots in the housing 7. Via the inlet 12 and the outlet 13, the electronics module 1 can be connected to a coolant circuit in which a coolant, for example a water-glycol mixture, circulates in an airtight manner. The coolant flows into the cavity 9 via the inlet 12, flows through it along the meandering channel defined by the web-shaped cooling elements 6, and exits again via the outlet 13.

[0030] The cooling elements 6 extend toward the surface 10 of the housing, said surface 10 being coated with a non-metallic anti-corrosion coating 14. This anti-corrosion coating 14 is provided at least in the region of the surface 10 adjacent to the ends of the cooling elements 6. The anti-corrosion coating 14 is, for example, a prefabricated coating element that is arranged, in particular glued, on the surface 10. The coating element can be a cut-to-size film or a correspondingly dimensioned plate. Any thermoplastic or thermosetting plastic can be used as the plastic material, provided that it is chemically stable enough that it is not attacked by the coolant used, and that it is sufficiently thermally stable enough to withstand the temperatures prevailing in the cavity or within the coolant.Alternatively, the corrosion protection coating 14 can also be realized via an applied coating, which is first applied to the surface 10 in a fluid form and then hardens.

[0031] In any case, the cooling elements 6 extend close to the corrosion protection coating 14 and are only spaced from it by a very narrow gap 15, which is, for example, only a few tenths of a millimeter, or can even rest against the collision protection coating made of the polymer material, i.e., be in contact. The corrosion protection coating 14 prevents corrosion from occurring in the area of ​​the narrow gap 15 between the cooling elements 6 and the metal housing 7, which would then corrode the housing 7 made of a less noble metal. Such corrosion would result from coolant residues that remain in the cavity orRemaining in the channel, through which residual coolant, in conjunction with a chemical reaction with air or atmospheric oxygen penetrating into the cavity 9, would bring the cooling elements 6 into contact with the uncoated surface 10. However, this is effectively prevented by the non-metallic corrosion protection coating 14, which effectively protects and encapsulates the surface 10. This enables, on the one hand, the performance of the end-of-line test after completion of production, and, on the other hand, also permits longer-term storage of the electronic module 1 before its final assembly, since any tendency to corrosion is prevented. List of reference symbols.

[0032] Electronic module Electronic unit Heat sink Potting compound Bottom Cooling element Housing

[0033] Fastening element cavity

[0034] Surface sealing element

[0035] To run out corrosion protection coating gap

Claims

Patent claims 1. Electronic module, comprising an electronic unit (2) and a metal heat sink (3) with a plurality of projecting cooling elements (6) and a metal housing (7) attached to the heat sink (3), wherein a cavity (9) with an inlet (12) and an outlet (13) is formed between the heat sink (3) and the housing (7), into which the cooling elements (6) protrude, characterized in that the surface (10) of the housing (20) delimiting the cavity (9) is provided with a non-metallic corrosion protection coating (14), at least in the region opposite the cooling elements (6).

2. Electronic module according to claim 1, characterized in that the corrosion protection coating (14) is made of plastic.

3. Electronic module according to claim 1 or 2, characterized in that the corrosion protection coating (14) is a prefabricated coating element which is arranged on the surface (10) of the housing (7).

4. Electronic module according to claim 1 or 2, characterized in that the corrosion protection coating (14) is applied in the form of a cured coating.

5. Electronic module according to one of the preceding claims, characterized in that a sealing element (11) is arranged between the heat sink (3) and the housing (7) and runs around the cavity (9) and laterally delimits the cavity (9).

6. A method for producing an electronic module according to one of claims 1 to 5, comprising the following steps: Applying a prefabricated coating element as a non-metallic corrosion protection coating (14) to the surface (10) of the housing (7) delimiting the cavity (9), Connecting the housing (7) to the heat sink (3) in such a way that the cooling elements (6) projecting on the heat sink (3) protrude into the cavity (9) and end adjacent to the covering element.

7. Method according to claim 6, characterized in that before or after the application of the covering element, a sealing element (11) is arranged on the housing (7), which laterally delimits the cavity (9) after the housing (7) has been connected to the heat sink (3).

8. A method for producing an electronic module according to one of claims 1 to 5, comprising the following steps: Connecting the housing (7) to a heat sink dummy comprising cooling element dummies, which is identical to the heat sink (3) of the electronic module (1), such that the cooling element dummies projecting on the heat sink dummy protrude into the cavity (9) and end adjacent to the surface (10) of the housing (7), wherein before connecting, a sealing element (11) is arranged on the housing (7) or on the heat sink dummy, which laterally delimits the cavity (9) after connecting the housing (7) to the heat sink dummy, Flooding the cavity (9) with a hardenable fluid, Draining the fluid, wherein the surface (10) of the housing (7) which delimits the cavity (9) is covered with a fluid coating, either hardening the fluid to form the corrosion protection coating (14) and removing the heat sink dummy, or vice versa, Connecting the housing (7) to the heat sink (3) in such a way that the cooling elements (6) projecting on the heat sink (3) protrude into the cavity (9) and end adjacent to the corrosion protection coating (14), wherein, if appropriate, a sealing element (11) is arranged on the housing (7) or on the heat sink (3) before the connection, which sealing element laterally delimits the cavity (9) after the housing (7) has been connected to the heat sink (3).

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