Patent Application
20230360988
This application relates to and claims priority to DE 10 2022 111 320.5 filed May 6, 2022, the entire contents of which are incorporated herein fully by reference.
The present invention is directed to an electronic circuit,
An electronic circuit has to be operationally reliable. A safeguard against inadvertent touching of the conductor tracks and the electronic components is often also required for this purpose. To ensure such touch safety, the conductor tracks and the electronic components are often covered using a potting compound. In many cases, the potting compound is permanently elastic. In other cases, the potting compound is a hard potting compound, for example a potting compound consisting of an epoxy resin.
An electronic circuit is furthermore often subjected to significant temperature variations in operation. Such temperature variations can result in significant mechanical loads of the electronic circuit due to different coefficients of expansion of materials used. In some cases, such mechanical loads can result in fractures. It often occurs in practice that electrical contacts are interrupted due to such fractures or undesired—sometimes even hazardous, in the extreme case even life-threatening—electrical contacts are created or creepage distances, which are required for safety reasons, are no longer maintained. Cracks can also arise in the base layer, into which moisture can penetrate. This can also have the result that properties of the electronic circuit required for safety reasons are no longer maintained.
Attempts have been made in practice to counter this problem in that the conductor tracks and the electronic components are covered using a potting compound. In some cases, however, cracks arise in the base layer in spite of such a potting compound and sometimes even because of such a potting compound. It may also occur that the base layer detaches from the metal layer.
An electronic circuit is known from DE 10 2013 013 842 A1, which includes a circuit carrier. The circuit carrier includes a metal layer and an electrically insulating base layer on the metal layer. Conductor tracks are arranged on the base layer, and electronic components are arranged on the conductor tracks. Possible cracks in the base layer are closed by pressing a free-flowing compound into the cracks.
The object of the present invention is to create possibilities by means of which cracks occurring in the base layer, in particular due to mechanical stresses can be avoided.
The object is achieved by an electronic circuit having the features of one or more of the proposed claims.
According to the invention, an electronic circuit of the type mentioned at the outset is designed in that a separating layer, which consists of an electrically insulating material that is different from both the material of the base layer and the material of the potting compound, is arranged at least in the areas between the conductor tracks between the base layer and the potting compound.
The use of a material which is different from both the material of the base layer and the material of the potting compound has the result in particular that direct contact no longer exists between the base layer and the potting compound. It is thus possible to avoid in particular that forces are transmitted directly to the base layer via the potting compound, which can result therein in the mentioned cracks.
In a minimal embodiment, the separating layer is applied to the base layer in such a way that it is arranged exclusively in the area between the conductor tracks, but not also on the conductor tracks and the electronic components. Alternatively, it is possible that the separating layer is applied flatly to the base layer in such a way that it is arranged not only in the area between the conductor tracks, but rather also on the conductor tracks, but not on the electronic components. In a further alternative, it is possible that the separating layer is applied flatly to the base layer in such a way that it is arranged not only in the area between the conductor tracks, but rather also on the conductor tracks and the electronic components. A person skilled in the art will choose which of these designs is used.
The separating layer can consist of a permanently elastic material. In particular—but not only—in this case, the separating layer can have a hardness between 5 and 70 Shore A and/or a dielectric strength of at least 1 kV/mm. The dielectric strength is preferably significantly greater, in particular at least 5 kV/mm. The numeric specifications relate to the final state of the electronic circuit, thus when the electronic circuit can be continuously operated, not to possible intermediate states in the context of the production of the electronic circuit.
It has proven to be advantageous in experiments if the separating layer consists of an epoxy lacquer, of an acrylate, or of a polyurethane, in the last-mentioned case in particular of a polyurethane resin.
The potting compound can be formed in the specific case as a soft, in particular permanently elastic potting compound. However, the potting compound is generally formed as a hard potting compound. The potting compound can consist, for example, of an epoxy resin.
To increase the mechanical strength and/or the dielectric strength, it is advantageous if the potting compound contains grains made of silicon dioxide and/or antimony trioxide and/or boron nitride. Analogously, it is often advantageous if the base layer contains grains made of aluminum oxide.
The separating layer preferably has a height which is less than the height of the conductor tracks. The electrical properties are thus still determined by the potting compound—in particular between the conductor tracks. This applies to a greater extent the less the height of the separating layer is. The height of the separating layer is therefore preferably at most 80% of the height of the conductor tracks, in particular at even smaller values, for example at most 50%, at most 30%, and very preferably at most 10%.
The separating layer preferably consists of a material wetting the base layer and the conductor tracks. It is thus ensured in particular that the separating layer is also applied in the particularly critical boundary area between the base layer and a conductor track. The wetting property applies at least for the state upon application of the still free-flowing—at this point in time—separating layer.
The distance of the conductor tracks from one another is preferably at least as great as the height of the conductor tracks. This embodiment facilitates the application of the separating layer to the area between the conductor tracks.
In specific cases, it can be sufficient if the separating layer is only arranged in the areas between the conductor tracks. However, the separating layer is usually also arranged between the base layer and the potting compound in the areas between the conductor tracks and the edge of the base layer.
The distance of the conductor tracks from the edge of the base layer is preferably at least as great as the height of the conductor tracks. It is thereby achieved that the separating layer is also able to be reliably applied in the areas between the conductor tracks and the edge of the base layer.
In principle, the base layer can consist of any electrically insulating material. However, it preferably consists of an epoxy resin.
The electronic circuit is preferably operable in a temperature range which extends at least from −40° C. to +125° C. The mentioned values characterize a minimum requirement. Of course, operability even at temperatures below −40° C. and/or above 125° C. is even better.
The above and other aspects, features, objects, and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings for exemplary but nonlimiting embodiments, in which like reference numerals designate the same elements.
Reference will now be made in detail to embodiments of the invention. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps. The drawings are in simplified form and are not to precise scale. The word ‘couple’ and similar terms do not necessarily denote direct and immediate connections, but also include connections through intermediate elements or devices. For purposes of convenience and clarity only, directional (up/down etc.) or motional (forward/back, etc.) terms may be used with respect to the drawings. These and similar directional terms should not be construed to limit the scope in any manner. It will also be understood that other embodiments may be utilized without departing from the scope of the present invention, and that the detailed description is not to be taken in a limiting sense, and that elements may be differently positioned, or otherwise noted as in the appended claims without requirements of the written description being required thereto.
According to
Solely by way of example, a half-bridge of an inverter circuit is shown in
However, the electronic circuit could also be designed differently at any time. The present invention is thus restricted neither to a half-bridge of an inverter circuit nor to an inverter circuit in general.
According to
It is possible that the base layer 2 is relatively thick (up to approximately 2 mm) and the metal layer 9 is relatively thin (up to 0.5 mm). In this case, the base layer 2 can assume a mechanical support function, thus effect the mechanical stability of the circuit carrier 1. Alternatively, it is possible that the base layer 2 is relatively thin, for example less than 0.5 mm, in particular only somewhat more than 0.1 mm. In this case, the base layer 2 is not capable of effecting the mechanical support function of the circuit carrier 1. In this case, the mechanical support function has to be assumed by the metal layer 9. The thickness of the metal layer 9 is in this case often in the range between 1 mm and 3 mm, usually at approximately 2 mm. Examples of such circuit carriers 1 are an IMS (=insulated metal substrate) and an IMB (=insulated metal baseplate).
Alternatively, the circuit carrier 1 can be designed like a typical printed circuit board, in which the base layer 2 as such is mechanically stable per se, thus can also assume the mechanical support function for the conductor tracks 3 and the electronic components 4.
According to
It is thus possible—see
The separating layer 11 is preferably arranged not only in the area between the conductor tracks 3 as such, but rather is arranged at least everywhere no conductor tracks are located. The separating layer 11 is therefore preferably also arranged between the base layer 2 and the potting compound 10 in the areas between the conductor tracks 3 and the edge of the base layer 2.
The separating layer 11 preferably consists of a permanently elastic material. In particular, it can have a hardness between 5 and 70 Shore A. Furthermore, the separating layer 11 is preferably to have a dielectric strength of at least 1 kV/mm. Greater values of, for example, at least 1 kV/mm or of at least 10 kV/mm are preferred. Furthermore, the separating layer 11 preferably consists of a material which wets the base layer 2 and the conductor tracks 3. For example, the separating layer 11 can consist of an epoxy lacquer, an acrylate, or a polyurethane. In the last-mentioned case, it can consist in particular of a polyurethane resin. Suitable polyurethane resins are sold, for example, by Lackwerke Peters GmbH & Co. KG, 47906 Kempen, under the name ELPEGUARD. In contrast, the potting compound 10 is generally designed as a hard potting compound in the scope of the present invention. It can consist of an epoxy resin, for example.
To improve the electric properties, the potting compound 10 can contain filler particles made of silicon dioxide (SiO2) and/or antimony trioxide (Sb2O3) and/or boron nitride (BN). For the same reasons, the base layer 2 can contain filler particles made of aluminium oxide (Al2O3).
It is apparent from
The electronic circuit is preferably to be able to be operated in a temperature range which extends from −40° C. (if possible, also even lower temperatures) to +125° C. (if possible also even higher temperatures). The material of which the separating layer 11 consists is therefore preferably to be selected in such a way that it is stable in this temperature range. Corresponding materials are known for the other components of the electronic circuit.
The present invention has many advantages. In particular, in the cases in which the base layer 2 consists of an epoxy resin and the potting compound 10 is a hard potting compound—in particular also consists of an epoxy resin—the service life of the electronic circuit is significantly improved even in the case of greater, repeated temperature variations.
The above description is used exclusively to explain the present invention. In contrast, the scope of protection of the present invention is to be defined exclusively by the appended claims.*
The preceding description is intended exclusively for the illustration of the present invention. Conversely, the scope of protection of the present invention is dictated exclusively by the attached claims.
Also, the inventors intend that only those claims which use the specific and exact phrase “means for” are intended to be interpreted under 35 USC 112. The structure herein is noted and well supported in the entire disclosure. Moreover, no limitations from the specification are intended to be read into any claims, unless those limitations are expressly included in the claims.
Having described at least one of the preferred embodiments of the present invention with reference to the accompanying drawings, it will be apparent to those skills that the invention is not limited to those precise embodiments, and that various modifications and variations can be made in the presently disclosed system without departing from the scope or spirit of the invention. Thus, it is intended that the present disclosure cover modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-111-320.5 | May 2022 | DE | national |
