Method for encapsulating electronic module and electronic module

Abstract

The invention relates to a method for encapsulating an electronic module (1) with at least one molding compound (8), in which in a first step the electronic module (1) is at least partially encapsulated with a thermoset molding compound by injection molding, wherein the electronic module (1) is subsequently post-processed in an oven in a post-curing process at a temperature above the glass transition temperature for a predetermined time, the electronic module (1) being subjected to a defined bending load at least temporarily during the post-curing process; the invention also relates to an electronic module (1).

Description

Technical Field

[0001] The present invention relates to a method for encapsulating an electronic module with a molding compound and such an electronic module. Background Art

[0002] An electronic module is known from DE 10 2012 112 738 A1, which has at least one substrate having at least one electronic component and contact portions, wherein the electronic component and at least partially the substrate are covered with at least one molding compound (Moldmasse, sometimes also referred to as encapsulating material), wherein at least one contact portion is not completely covered by the at least one molding compound. The molding compound can also be understood as an encapsulation portion and is usually composed of plastic. In addition, the molding compound also has a protective function for the electronic component.

[0003] A power module is known from DE 10 2019 200 884 A1, the surface of which is encapsulated with an encapsulating resin.

[0004] Especially in the case of a power module as an electronic module (such as an inverter circuit), relatively large heat losses occur, which usually have to be dissipated through a cooling body. The temperature fluctuations occurring here are related to the different thermal expansion behaviors of the materials contained, resulting in bending or a change in the bending of the electronic module. In extreme cases, the bending direction flips via a flat state opposite to the original shape, for example from convex to concave. This can lead to the separation of the electronic module from the cooling body or to the rupture of the substrate, which is usually made of ceramic. Summary of the Invention

[0005] The present invention is based on the technical problem of improving the method for encapsulating an electronic module in such a way that the above problems are reduced. Another technical problem is to create an improved electronic module to reduce the above problems.

[0006] The solution to this technical problem results from a method for encapsulating an electronic module with at least one molding compound and an electronic module having at least one substrate.

[0007] In the first step of the method for encapsulating an electronic module with at least one molding compound, the electronic module is at least partially encapsulated with a thermosetting molding compound (Duroplastformmasse, sometimes also called thermosetting molding compound) by injection molding. This injection molding is also called transfer molding. Subsequently, the electronic module is post-treated in an oven for a predetermined time at a temperature above the glass transition temperature of the encapsulation material during a post-curing process. This process is also called post-mold curing. Here, the electronic module is at least temporarily subjected to a defined bending load during this post-curing process. Due to the high temperature, the stress additionally introduced into the package is relaxed as much as possible during aging in the oven, so that the minimum stress state is moved to a higher temperature. This reduces the bending problems caused by high temperatures in electrical operation.

[0008] Here, the bending load can occur via an axis or in a point-like manner. For example, in the case of a point-like bending load, the punch presses onto the electronic module. For example, in the case of a bending load via an axis, the cylinder presses radially against the electronic module.

[0009] The defined bending load is preferably selected in such a way that it amounts to approximately 1% to 10%, more preferably 1.5% to 3%, of the edge fiber elongation in relation to the height of the module.

[0010] Preferably, the electronic module is subjected to a defined bending load during the entire post-hardening process. This does not exclude that no bending load is applied temporarily during introduction and removal from the oven. This improves relaxation.

[0011] In another embodiment, a defined bending load is maintained during the subsequent cooling process. As already explained above, the bending load can be briefly interrupted, in particular if the bending load is applied by different devices in the oven and during the cooling process. This prevents the stress state from changing indefinitely during the cooling process. In this case, a temperature can be predefined up to which the bending load is maintained.

[0012] In a further embodiment, the post-curing process lasts at least 30 minutes, wherein further preferably the process temperature during the post-curing process is at least 180° C.

[0013] The electronic module comprises at least one substrate, at least one electronic component and contacts, wherein the electronic component and at least part of the substrate are covered with at least one molding compound, wherein the molding compound is produced according to the above-described method. As a result, the lowest stress state in the molding compound or the electronic module is shifted to a higher temperature, thereby reducing the risk of the substrate cracking or separating from the cooling body or the cooling system due to high temperatures.

[0014] In one embodiment, a metal plate is disposed below the substrate, and a part of the metal plate is embedded in the molding compound. The metal plate is the base. In addition to mechanical stability, the metal plate can also be more easily connected to the cooling body, where the heat transfer is very good. The metal plate is preferably made of copper. The connection between the electronic module and the cooling body can be, for example, a sintered connection, a welded connection or a threaded connection.

[0015] In another embodiment, at least one contact portion is not completely covered by the at least one molding compound.

[0016] In one embodiment, the electronic module is connected to at least one cooling body.

[0017] In another embodiment, the electronic module is configured as part of an inverter. Description of the Drawings

[0018] The present invention will be explained in more detail below based on preferred embodiments. In the figures:

[0019] Figure 1 A perspective view of the electronic module before applying the molding compound is shown,

[0020] Figure 2 A perspective view of the electronic module after applying the molding compound is shown,

[0021] Figure 3 A schematic side view of the electronic module after the injection process is shown,

[0022] Figure 4 A schematic side view of the electronic module during the post-curing process is shown,

[0023] Figure 5 A schematic side view of the electronic module during the cooling process is shown, and

[0024] Figure 6 A schematic side view of the electronic module after connection to the cooling body is shown. Detailed Description of the Invention

[0025] In Figure 1 , an electronic module 1 before applying the molding compound is schematically shown. The electronic module 1 has a substrate 2 on which a metallization layer 3 is applied. The substrate 2 is preferably ceramic and the metallization layer 3 is preferably made of copper and is structured accordingly to form conductor tracks. Four electronic components 4 are arranged on the metallization layer 3. The electronic components 4 in the form of chips are, for example, power transistors. In addition, contact portions 5 are arranged on the metallization layer 3, and the contact portions 5 form the external contact portions of the electronic module 1. Finally, control pins 6 are also arranged on the metallization layer 3. A metal plate 7 preferably made of copper is arranged on the lower side of the substrate 2. The metal plate 7 forms the base of the electronic module 1.

[0026] Figure 2 , the electronic module 1 is shown after being cast with at least one molding compound 8 .

[0027] Figure 3 A schematic side view of an electronic module 1 after injection molding is shown in . The temperature of the thermosetting molding compound is, for example, 170° C. to 180° C. In this case, the electronic module 1 is already slightly bent.

[0028] Figure 4 , the electronic module 1 is now shown during a post-curing process, for which the electronic module 1 is post-treated in an oven at a temperature above 180° C., wherein the post-treatment time is preferably between 30 and 120 minutes. During this time, the electronic module 1 is subjected to a defined additional bending load. In this case, a force F is applied to the electronic module 1 from above, for example by means of a punch, which results in a defined bending load, which, for example, increases the edge fiber elongation by approximately 1.5% to 3%. In this case, the electronic module 1 is supported on the support 10 in such a way that the electronic module 1 is bendable. Due to the high temperature, these bending stresses can be relaxed very well. As a result, the state of lowest stress shifts to a higher temperature. After the end of the post-curing process, the electronic module 1 can then, if necessary, immediately reach the assembly line, where it can be connected to the cooling body 9 (see Figure 6 )connect.

[0029] However, a defined cooling process is preferably carried out after the post-hardening process. During this cooling process, the electronic module is further subjected to defined bending loads, which Figure 5 In this case, the bending load can be combined with the force F during the post-hardening process. Figure 4 The electronic module is then subsequently connected to the cooling body 9. If the electronic module 1 is then heated during operation, the bend of the electronic module 1 will only be inclined at a higher temperature than the electronic module that was post-hardened without bending load.

[0030] Reference Symbols List

[0031] 1 Electronic module

[0032] 2 Base

[0033] 3 Metallization layer

[0034] 4 Electronic components

[0035] 5 Contact Department

[0036] 6 Control pins

[0037] 7 Metal Plate

[0038] 8 Molding Compound

[0039] 9 Cooling body

[0040] 10 Support member

Claims

1. A method for encapsulating an electronic module (1) with at least one molding compound (8), wherein in a first step the electronic module (1) is at least partially encapsulated with a thermosetting molding compound by injection molding, wherein subsequently the electronic module (1) is post-treated in an oven in a post-hardening process at a temperature above the glass transition temperature for a predetermined time, Features The electronic module (1) is at least temporarily subjected to a defined bending load during the post-hardening process.

2. The method according to claim 1, characterized in that The electronic module (1) is subjected to defined bending loads during the entire post-hardening process.

3. The method according to claim 1 or 2, characterized in that: During the subsequent cooling process the defined bending load is maintained.

4. The method according to any one of the preceding claims, characterized in that The post-hardening process lasts at least 30 minutes.

5. The method according to any one of the preceding claims, characterized in that The process temperature during the post-curing process is at least 180°C.

6. An electronic module (1) comprising at least one substrate (2), the at least one substrate (2) having at least one electronic component (4) and a contact (5), wherein the electronic component (4) and at least part of the substrate (2) are covered with at least one molding compound (8), Features The at least one molding compound (8) is produced according to a method according to any one of claims 1 to 5.

7. The electronic module according to claim 6, characterized in that: A metal plate (7) is arranged below the substrate (2), which is partially embedded in the molding compound.

8. The electronic module according to claim 6 or 7, characterized in that: At least one contact (5) is not completely covered by the at least one molding compound (8).

9. The electronic module according to any one of claims 6 to 8, characterized in that: The electronic module (1) is connected to at least one cooling body (9).

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