Electrical heating device and method for producing an electrical heating device

Abstract

The invention relates to an electric heating device (10), in particular an electric heating unit for a vehicle, comprising:-a heating conductor layer (14), which is thermally connected to a heat exchanger (12),-a first attachment point (16) and at least one second electrical attachment point (18), the invention relates to a heating element (10) comprising a heating conductor layer (14) having a first attachment point and at least one second electrical attachment point (16, 18), which are formed by the heating conductor layer (14) or adjoin the heating conductor layer (14), and electrical attachment means (20), which are connected to the first attachment point and to the at least one second electrical attachment point (16, 18), according to the invention, the electrical attachment means (20) comprises a first bonding conductor (22), which is directly bonded to the first electrical attachment point (16), and a second bonding conductor (24), which is directly bonded to the second electrical attachment point (18), the first bonding conductor (22) and the second bonding conductor (24) each forming a bonded connection.

Description

TECHNICAL FIELD

[0001] The present application relates to an electric heating device, in particular a vehicle electric heating section, and to a method for producing such an electric heating device. BACKGROUND

[0002] Conventional electric heating devices, in particular such electric heating devices for vehicle heating sections, as used for example in electric and / or hybrid vehicles, generally comprise an electric heating conductor layer which is arranged on a heat exchanger and converts electrical energy into heat. Here, a "heating conductor layer" in the sense of the present application is only to be understood as an electric resistance layer whose main purpose is to convert electrical energy into heat. In particular, a heating conductor layer is not to be understood here as an electronic (semi)conductor element, for example an IC, which generates waste heat as an undesired by-product in its operation.

[0003] Such a heating conductor layer is generally electrically connected to an energy source by means of stamped meshes for generating heat. For example, these stamped meshes can be used to bridge the electrical contact between a circuit board on which power switching elements for a corresponding high-voltage heating operation are provided and the heating conductor layer. Such stamped meshes generally comprise a plastic body for electrical insulation and a stamped metal mesh embedded in the plastic body, which stamped metal mesh configures a conductor circuit (so-called Fahnen) made of copper material and / or stainless steel material.

[0004] Here, the stamped meshes used can be fastened to the attachment points provided for this purpose on the heating conductor layer, for example by means of different known joining techniques. In particular, for this purpose, laser welding methods, resistance spot welding methods or soldering methods are used. However, the soldering method has the disadvantage of poor automatability of the joining process, high space requirements in terms of contact area due to the wetting behavior of the solder used, and susceptibility to reduced durability under temperature alternating loads, as well as a relatively low liquidus temperature of the solder, which is even below the temperatures that are still permissible in the event of overheating. In any case, mass production cannot be reconciled with the desired cost advantages.

[0005] Furthermore, the thickness of the heating conductor layer required for laser welding or resistance spot welding is generally greater than the layer thickness actually required for heating. An outlet is to use a heating conductor layer which is overall thicker, but this again means an undesired waste of resources. This thus reduces the possible cost advantages in mass production.

[0006] The task of achieving cost advantages in large series has become even more pressing, since modern, modularly configured electric heating devices have a large number of connections to be closed on the heating conductor layer in order to achieve the required heating power, since in this case a plurality of stamped grids or stamped grids with a more complex configuration are required. SUMMARY

[0007] On the basis thereof, the invention is based on the task of providing an electric heating device which can be produced more efficiently. Furthermore, the invention is based on the task of proposing a corresponding production method for an electric heating device.

[0008] With regard to the electric heating device, the task according to the invention is solved by an electric heating device having the features of claim 1. With regard to the method for manufacturing such an electric heating device, the task is solved by a method having the features of claim 12.

[0009] Advantageous refinements and configurations result from the dependent claims.

[0010] The aspect relates to an electric heating device, in particular a vehicle electric heating section. Preferably, this is a liquid heating section. The liquid heating section discharges heat onto a liquid heat carrier medium of a heat carrier cycle which flows through the heating section. The heat carrier medium can in particular be a liquid coolant of a vehicle which transports heat in the vehicle and can discharge heat at different locations. Alternatively, the liquid heating section can also be, for example, a component part of a heat pump of a vehicle, so that the heat carrier medium can be, for example, a refrigerant of the heat pump. It is possible in this case that the refrigerant only exists in a completely liquid form under certain conditions and only temporarily or possibly never, and is also partially or completely gaseous in other cases. This is nevertheless also understood as a liquid heating section.

[0011] In principle, the vehicle for which the electric heating device can be determined is to be understood as all possible mobile applications, in particular passenger cars, lorries, construction machines, aircraft and watercraft. This also includes, for example, construction machines or cranes and trailers which can be towed and transported by other vehicles, for example motor homes.

[0012] Preferably, the liquid heating section has a heating power of at least 5 kW, preferably at least 7 kW, for example at least 9 kW. The heating power is preferably less than or equal to 13 kW, respectively. The operating voltage with which the vehicle heating section is operated, which can be the same as the on-board voltage of an electrically driven vehicle, is greater than or equal to 400 V, preferably greater than or equal to 700 V, for example 800 V, 900 V or 1000 V.

[0013] The electric heating portion according to these aspects comprises a heating conductor layer, which is in a heat-acting connection with the heat exchanger, a first electric attachment site and at least one second electric attachment site, and an electric attachment device, which is connected with the first and the second electric attachment site, wherein the electric attachment device comprises a first bonding conductor and a second bonding conductor, the first bonding conductor being directly bonded onto the first electric attachment site, and the second bonding conductor being directly bonded onto the second electric attachment site. The first and the at least one second electric attachment site are formed by or adjoin the heating conductor layer.

[0014] An electric attachment site (English: pad) is to be understood as a conductor circuit section, which is designed for allowing a contact for establishing an electrically conductive connection with the heating conductor layer. In particular, the electric attachment site is designed for enabling a material-locked connection with an electric attachment partner (here: an end of a bonding conductor) which is contacted from the outside. The material-locked connection can require a mutual compatibility of the materials or metals of the respective contact partners as a property. If the heating conductor layer is structured as a heating conductor circuit, this can optionally be a conductor circuit section which is widened with respect to the width of the heating conductor circuit, which allows a larger tolerance during the contacting process. Furthermore, in order to ensure a chemical compatibility with the material of the contact partner, the conductor circuit section of the attachment site can be formed from a different material than the heating conductor layer, which is in turn adjoined to the heating conductor layer or the heating conductor circuit, in particular consisting of a well-conducting material, depending on the material of the contact partner.

[0015] In the present case, a heating conductor circuit is to be understood as a region of the heating conductor layer, in which an electric current flows after a voltage is applied on the existing attachment site. The heating conductor circuit extends from the first electric attachment site to the at least one second electric attachment site. Further heating conductor circuits can be attached directly or seamlessly to the section of the heating conductor circuit which forms one of the attachment sites. This is to say that the term "end" does not necessarily imply that the heating conductor circuit actually ends there, like the "attachment site". Rather, the heating conductor circuit can continue to extend therefrom, for example towards a third attachment site. Such a third attachment site can be arranged, for example, on the actual end of the conductor circuit. The heating conductor circuit is in particular laterally delimited in the plane of the heating conductor circuit by an insulating interruption, wherein no electric current flows in the region of the insulating interruption.

[0016] By means of the features described according to the above-mentioned aspects, a highly automatable bonding method can be used instead of the hitherto used soldering method or laser welding method. Direct bonding offers additional advantages over soldering. Thus, in direct bonding, less space is required for the attachment face on the heating conductor layer, since the solder, which is required in other cases for the soldering process, is dispensed with and, due to its flow properties, could "short-circuit" hitherto adjacent regions of the heating conductor layer. The flux, which is likewise required in soldering, can also be dispensed with. Thus, after direct bonding, there is no longer a need to additionally clean the heating conductor layer in order to prevent chemical corrosion of the heating conductor layer by flux residues. By means of direct bonding, the susceptibility of the resulting attachment connection to frequently occurring temperature alternating loads is also reduced, so that the service life of the heating device is increased. Finally, it is to be noted that, in the case of (permitted) overheating, the melting temperature of the solder used is often reached, which likewise often leads to a defect due to an undesired breakage of the soldered attachment connection.

[0017] Furthermore, by means of the bonding, an improved quality of the electrical connection between the heating conductor and the energy source is also achieved, since the required tolerances can be adhered to more easily and more reliably. On the one hand, the bonding process generally permits a higher positioning accuracy in itself. On the other hand, the bonding process can easily be automated, so that manual errors no longer have to be taken into account. In addition, since the stamped grid does not come into spatial contact directly or at least very close with the heating conductor circuit, the dynamic expansion of the stamped grid at different temperatures no longer has to be taken into account. Finally, by means of the possible use of fewer components, such as corresponding connectors, the tolerance chain in successive manufacturing steps can also be reduced, which increases the permissible tolerances for each process step in the present case.

[0018] The bonding conductor generally has two end portions, wherein one end portion is bonded to the corresponding attachment site, while the opposite end portion of the bonding conductor can be connected with an attachment end that provides electrical energy, for example with a corresponding output end of a power switch or a controller on a circuit board. The bonding conductor is thus a bonded connection between the corresponding attachment site in or adjacent to the heating conductor layer and an opposite attachment point, at which electrical energy is provided. Here, the heating conductor layer can first be arranged on a substrate, for example a ceramic substrate, which serves as an electrical insulator and carrier element for the heating conductor layer. In the case of a ceramic substrate, this can in particular be formed from aluminum oxide (AI2O3). The proportion by mass of the aluminum oxide can be, for example, 96%.

[0019] The heating conductor layer can be a resistance alloy which provides the respective heating resistance. According to a specific embodiment, the thickness of the heating conductor layer can be between 5 and 35 pm, preferably between 7 and 30 pm, further preferably between 10 and 20 pm. These values relate to the thickness of the heating conductor layer in the fired state (according to predetermined process steps of the manufacturing), not to the wet layer thickness, which can be higher in value.

[0020] Here, the two attachment sites can be configured end region of the heating conductor layer which is structured as a heating conductor circuit. The heating conductor layer can be configured, for example, as a metallization made of a resistance alloy, which is the respective heating resistance. This structuring can be introduced into a planar heating conductor layer, for example, in the form of insulation interruptions, which do not have the insulation interruptions. In particular, the structuring can be produced in the heating conductor layer, for example, by means of laser ablation or has already been produced when applying by means of a screen printing process.

[0021] It is further possible that, as described above, the two attachment sites can consist of a well-conducting material, which can in particular differ from the material of the actual heating conductor layer. This can be the case with an additional layer, which can directly adjoin the heating conductor layer and serves to provide the respective attachment site. Such a layer can be provided for each attachment site, which does not exclude that the respective adjoining layer is formed from the same material in the same process step.

[0022] Such an additional layer consisting of a well-conducting material can be formed, for example, on a substrate, onto which the material of the heating conductor layer is applied in a subsequent manufacturing step. This can be, for example, copper, aluminum or gold, etc. The heating conductor layer is thus partially placed on the material of the additional layer consisting of a well-conducting material. The additional layer configures the respective first or second attachment site in the area of the exposed part of its surface, while the part not exposed, which configures a double-layer section, configures a sufficiently planar contact area between the well-conducting material and the heating conductor layer material.

[0023] Alternatively, a third possibility, which is not exhaustively listed as a configuration of the attachment site, also includes the following: The heating conductor layer and the additional layer consisting of a well-conducting and material-compatible material of the bonding conductor can also be arranged in a stacked manner. Here, the additional layer consisting of a well-conducting material is placed on top of the heating conductor layer and thus configures the attachment site as a stack together with the section of the heating conductor layer located below it. In this case, the material of the additional layer can be applied locally afterwards.

[0024] According to the specific configuration of the attachment site, the thickness of the section of the heating conductor layer complementary to the attachment site can be increased compared to the remaining sections, but can also be reduced, or even.

[0025] In the case where the attachment site is itself configured by heating predetermined sections of the heating conductor layer, the thickness at the attachment site is preferably essentially the same as the thickness of the remaining heating conductor layer (the preferred interval for the value of the thickness is listed above: [5...35 mm], [7...30 pm], [10...20 pm]). In such an embodiment, the material of the heating conductor layer can preferably be a ferro-nickel alloy. This ferro-nickel alloy is suitable for a direct material-locked connection with the material of the bonding connection (for example copper and / or aluminum, or gold, etc.). The preferred composition is further described below. For example, the relative deviation of the thickness of the attachment site from the thickness of the remaining heating conductor layer can be less than 70%. Preferably, however, such a deviation is less than 50%, further preferably less than 30%, and particularly preferably the relative deviation is less than 10%.

[0026] The deviation can also result from an intentional design of the specific attachment site to be thicker than the remaining area of the heating conductor layer. For example, this can be achieved in the framework of a screen printing method, which in principle also enables a subsequent thinning of the remaining area outside the attachment site.

[0027] In the case of an additional layer composed of a well-conducting material, which is configured next to the heating conductor layer on the substrate and contacts the heating conductor layer in a lapped manner, the respective attachment site (bond pad) is configured as described above by the area not covered by the heating conductor layer, the surface of which (before the bonding and possible filling by means of a casting mass) is bare. In an embodiment with copper as the well-conducting material, the wet layer thickness is for example about 45-55 pm, and in the fired state purely exemplarily about 35 pm. In such an embodiment, the material of the heating conductor layer can preferably be a nickel-chromium alloy. However, for the material of the heating conductor layer, a ferro-nickel alloy can also be considered. In this case, the layer thickness of the heating conductor layer can (in the fired case) be for example 12-15 pm.

[0028] Here, the desired structure in the heating conductor layer can for example be produced in an abrading manner or in a configured manner by means of a screen printing method, the use of which is preferred. For example, according to a particularly preferred embodiment, the direct bonding of the bonding conductor can be performed by means of a cold pressure welding method, in particular an ultrasonic bonding method, wherein in the following text ultrasonic bonding is always exemplarily referred to, even though the bonding can be performed with any method. In addition to ultrasound, for example laser, plasma, electric arc, gas flame, reaction energy or combinations thereof can also be used as a heat source for the bonding in order to establish the desired, material-locked bonding connection.

[0029] However, the following particularly advantageous applicability has been found for ultrasonic bonding: the bonding can be carried out directly on the material of the heating conductor layer, which enables that the attachment site can be configured in one step with the formation of the heating conductor layer, for example in a screen printing method, without the need for an additional adjoining layer, so that the production is simplified and less costly. This can also be due to the interaction of the cold pressure welding method with the surface of the material of the heating conductor layer, which is porous in embodiments. Here, the ultrasonic bonding is suitable for establishing the heating element contact as a mature, highly scalable, automatable and cost-advantageous production method. The same advantages of direct contact of the heating conductor layer are achieved for further bonding methods (English: wire bonding) mentioned above. Here, not only the Front-Cut method can be used, but also the Back- or Rear-Cut method.

[0030] Thus, in summary, by possibly dispensing with the additional thickening of the attachment site of the configuration of the heating conductor circuit including the heating conductor layer, a cost-efficient production of the heating element can be combined with a directly bonding method which can be easily realized and automatable, whereby ultimately a cost-advantageous electric heating device can be provided.

[0031] As mentioned above, the dispensing with the thickening of the attachment site can be preferred, however, embodiments of the application provide that, especially if a thickening arises for structural / methodical reasons (see above, for example an additional layer with a larger thickness composed of a well-conducting material), the direct bonding is also carried out on the thickened attachment site. In correspondence therewith, the attachment site can also be configured to have a relatively large thickness for structural / methodical reasons completely with respect to the remaining area of the configuration of the heating conductor circuit there, which is formed only by the heating conductor layer.

[0032] As mentioned above, the attachment site can preferably consist only of the material of the actual heating conductor layer, however, alternatively, in the case of the provision of an additional layer, also other well-conducting materials, for example copper, can be included. In this particular case, the well-conducting material can be applied to the substrate by means of a similar method as the material of the actual heating conductor layer, for example by means of a screen printing method. First, the corresponding additional layer composed of a well-conducting material, which later has the attachment site, is configured in the screen printing method, then, subsequently, the heating conductor layer is configured in the screen printing process, here in a partial overlap of the additional layer. Here, too, alternative bonding methods known to the person skilled in the art can be used for the direct bonding to the attachment site.

[0033] According to an advantageous development, it can be provided that the first bonding conductor is a first thick wire or a first thick ribbon and the second bonding conductor is a second thick wire or a second thick ribbon. In this way, the electrical energy required for operating the electrical heating device or the heating conductor layer can be brought into the heating conductor layer using bonding conductors which do not heat up strongly. Here, the bonding conductors or the bonding connections used, i.e. the thick wires or thick ribbons, can consist, for example, of aluminum, copper or gold (coating) or alloys of these metals. In ultrasonic bonding, aluminum ribbons with or without nickel addition are usually used, aluminum ribbons without nickel addition being preferred. In laser bonding, copper round wires (so-called CU-cor-AL, i.e. copper core with aluminum sheath) can be used.

[0034] According to a further embodiment, the bonding conductors used can have a Brinell hardness of between 20 and 40 HB, in particular in the case of aluminum or aluminum alloys. Preferably, the thick wires used can have a diameter of between 125 and 500 pm. However, larger diameters are also possible. The thick ribbons used can have a width of between 0.5 and 2.5 mm and a thickness of between 50 and 350 pm, for example. However, it is also possible to use thick ribbons with a larger width and / or thickness. The bonding conductors used can be insulated or uninsulated.

[0035] According to a particular embodiment, two or three or more bonds can be provided for each attachment point of the heating conductor loop.

[0036] Furthermore, it is possible, in particular in the case of a 400 V heating device with 3 heating elements, to provide nine contacts, which can be distributed, for example, over three thick ribbons for each heating element, wherein each heating element comprises 2 heating loops and one of the thick ribbons bonds one attachment point for both heating loops. In another example, in particular in the case of an 800 V heating device, it is possible to provide six contacts, wherein for each heating element with only one heating conductor loop, two thick ribbons (English: Bond-Ribbons) can be used.

[0037] Advantageously, in the case of the iron-nickel alloy described above for the heating conductor layer, it can be provided that the heating conductor layer comprises a proportion of iron of between 30 and 80 mass-%, preferably between 40 and 70 mass-%, with respect to 100 mass-% of the total mass of the heating conductor layer. Furthermore, it can also be provided that the heating conductor layer comprises a proportion of nickel of between 10 and 30 mass-%, preferably between 15 and 25 mass-%, with respect to 100 mass-% of the total mass of the heating conductor layer, wherein the proportion of nickel and the proportion of iron, if present, together amount to ≤ 100 mass-% of the total mass of the heating conductor layer. In this way, a heating conductor layer which is well suited for the conversion of electrical energy into heat can be provided, which at the same time can also be bonded directly to the bonding conductor used in a reliable manner. By adding further, well bondable metal proportions, such as aluminum, copper, etc., to the heating conductor material, the bondability of the heating conductor layer as well as the electrical and thermal-mechanical properties can be improved.

[0038] Alternatively, in the case of an additional layer composed of a well-conducting material, a nickel-chromium alloy can be used as the heating conductor layer. In this case, the heating conductor layer comprises a proportion of chromium of between 0.5 and 10 mass-%, preferably between 1 and 7 mass-%, with respect to 100 mass-% of the total mass of the heating conductor layer. Furthermore, it can also be provided that the heating conductor layer comprises a proportion of nickel of between 60 and 99 mass-%, preferably between 70 and 95 mass-%, with respect to 100 mass-% of the total mass of the heating conductor layer (14), wherein the proportion of nickel and the proportion of chromium together amount to ≤ 100 mass-% of the total mass of the heating conductor layer (14).

[0039] It is also possible to provide that the heating conductor layer has a porous structure and that the first and / or second attachment site is machined or prepared in the manufactured frame in such a way that the oxide layer is broken or such that the first and / or second attachment site no longer has an oxide layer. In this way, it is possible, firstly, to carry out the manufacture of the heating conductor layer by means of a simple and reliable firing process in which, firstly, a screen printing process for applying the heating conductor layer is carried out and, next, a firing process is carried out in which a porous structure is produced, wherein, next, the adhesion of the directly bonded bonding conductor on the respective attachment site is improved by breaking or removing the oxide layer on the surface of the two attachment sites. The machining of the first and / or second attachment site can be seen, for example, as a surface treatment of the respective attachment site and can be carried out, for example, by means of brushing, grinding, polishing or cleaning by means of laser and / or plasma. Impurities, such as oxides, grease, oil, etc., which affect, in particular impair, the quality of the bonding connection, can thus be compensated for. In addition, rough edges are smoothed, which likewise improves bondability. The ablation of the material of the respective layer, in particular of the heating conductor layer as a whole or in sub-areas, for example in the attachment sites formed therein, or also of the material of an optional additional layer, for example a copper pad or an aluminum pad, etc., caused by the removal or breaking of the oxide layer by the surface treatment, is negligibly low, such that the thickness of the layer(s) involved remains virtually unchanged by the surface treatment, i.e. the thickness of the layer(s) after the surface treatment and before the surface treatment is virtually the same. A heat treatment is also possible. A consistent and in particular significantly better bondability and a good bonding connection with the required tear-off force and shear force on the respective attachment site is thus produced. The porous structure of the heating conductor layer can be, for example, a porous morphology with a porosity of preferably between 3% and 20%. However, greater porosities are also possible.

[0040] It is further possible to provide that the first and / or second attachment face is covered with an electrically insulating casting mass together with the end of the bonding conductor bonded thereon. In this way, the connection between the bonding conductor and the respective attachment face can additionally be protected. The casting mass can be applied to the complete heating element (substrate with structures formed thereon, in particular a heating conductor circuit with attachment sites). Since one end of the bonding conductor is part of the heating element, this end can also be covered by the casting mass. However, in principle, it is not necessarily necessary to cover one end of the bonding conductor by means of the casting mass. However, when bonding is carried out on an additional layer consisting of a well-conducting material comprising copper and when the bonding wire or the thick strip comprises aluminum, it will be necessary to cover one end of the bonding conductor by means of the casting mass, in which case special protective measures against corrosion are desirable.

[0041] Furthermore, a method for manufacturing an electric heating device, in particular a vehicle electric heating section, is proposed, the method comprising the following steps: providing a substrate, preferably a ceramic substrate; arranging a heating conductor layer or a heating conductor layer together with a layer adjoining the heating conductor layer on the substrate by means of a first electrical attachment site configured by the heating conductor layer or by the adjoining layer and a second electrical attachment site configured by the heating conductor layer or the adjoining layer; directly bonding a first bonding conductor to the first attachment site; directly bonding a second bonding conductor to the second attachment site; and merging the substrate with a heat exchanger and / or further components of the electric heating device.

[0042] It is noted here that the last-mentioned step of merging with a heat exchanger does not necessarily have to be the last step in the sequence of steps. Rather, according to the proposed aspect, this step can also be performed, for example, directly after the provision of the substrate. In such a case, the subsequent steps can then be performed, for example, on the substrate which has already been fixed on the heat exchanger.

[0043] Here, advantageously, the first attachment site and / or the second attachment site can be prepared or processed in such a way that the first attachment site and / or the second attachment site no longer has an oxide layer or that the oxide layer is broken.

[0044] Advantageously, the method can further comprise applying an electrically insulating casting mass to the first attachment face and to the end of the first bonding conductor bonded thereto and / or to the second attachment face and to the end of the second bonding conductor bonded thereto. Further method steps result from the aspects, refinements, embodiments, configurations and examples relating to the apparatus. This relates in particular to the bonding configuration as a cold pressure welding process, which is further preferably configured as ultrasonic bonding here. BRIEF DESCRIPTION OF DRAWINGS

[0045] The above-mentioned invention is now explained exemplarily with reference to the attached drawings according to preferred embodiments.

[0046] The drawings show: Figure 1 a simplified schematic diagram of an exemplary electric heating device; Figure 2 a schematic detail view of an exemplary attachment site; Figure 3 a further simplified schematic diagram of an exemplary electric heating device; Figure 4 a schematic view of an exemplary bonding apparatus; and Figure 5 a flowchart of an exemplary method for manufacturing an electric heating device; Figure 6A top view of a heat exchanger according to an embodiment of the electric heating device is shown, having substrates 42 (here three pieces, each with two heating circuits) and a circuit board 34 mounted thereon and a stamped grid 60. DETAILED DESCRIPTION

[0047] It is to be understood that the embodiments disclosed are not limited to the details of the construction and arrangement of components set forth in the following description and accompanying drawings, which are provided as examples only. All embodiments, even if not explicitly described or shown herein, can be practiced or implemented in various ways. Also, it is to be understood that the terminology and phraseology employed herein are for the purpose of description and should not be regarded as limiting. Rather, the scope of the disclosure is broader, as set forth in the appended claims. Furthermore, in the following description, like reference numerals are used to denote like features or objects in the figures, such that repeated description is omitted for the sake of brevity and clarity.

[0048] Figure 1 A simplified schematic of an exemplary electric heating device 10 is shown. The electric heating device 10 can be, for example, a high-voltage electric heater, in particular a vehicle electric heating unit, which operates at an operating voltage of more than 100 V, in particular more than 400 V, preferably about 800 V. Inside the heating device 10 a heat exchanger 12 is indicated, on the surface of which substrates 42 are arranged. For the sake of simplification of the schematic, possible thermally conductive intermediate layers, such as thermally conductive pads, adhesive layers or the like, are not shown. The heat exchanger 12 can be made of a metallic material, for example of aluminum, and formed into the desired shape by means of a die-casting method or configured as a brazed structure group, in particular. The heat exchanger 12 is designed for transferring the heat absorbed thereby to a fluid flowing past or an adjoining mass.

[0049] The substrate 42 can be, for example, a ceramic layer or, in particular, an aluminum oxide layer (ceramic substrate). The substrate 42 can be used as a carrier element for the heating conductor layer 14 arranged on the substrate 42. The heating conductor layer 14 serves for converting electrical energy into heat. To achieve this, the heating conductor layer 14 comprises a first attachment site 16 and a second attachment site 18, on which the heating conductor layer 14 is conductively connected with the controller 46, in particular with a circuit board 36 belonging to the controller 46, by means of attachment means 20. This connection with the controller 46 can be direct or, alternatively, be achieved by means of a power switching element, for example arranged on the circuit board. The attachment means 20 can comprise, in particular, a first bonding conductor 22 and a second bonding conductor 24 here. The first bonding conductor 22 and / or the second bonding conductor 24 can be bonded directly to the first attachment site 16 or the second attachment site 18 and to an associated attachment pad on the circuit board 36. The first attachment site 16 and the second attachment site 18 can be distinguished from the remaining surface 28 of the heating conductor layer 14 not used as an attachment site by an additional surface processing, which will be described in the following in connection with Figure 2 The remaining surface is explained in more detail.

[0050] Alternatively, it is also possible that, in the region of the two attachment sites 16, 18, an additional layer (not shown in the drawing) is provided which adjoins the heating conductor layer 14 or is partially covered by the heating conductor layer 14, which additional layer consists of a well-conducting material, for example copper or aluminum or one of its alloys, wherein the adjoining additional layer configures the respective attachment site 16, 18 in the uncovered, exposed section.

[0051] In Figure 1 Only two attachment sites 16, 18 of a single heating loop in the heating conductor layer 14 are shown in Fig. 1. It is possible, however, that the heating conductor layer 14 comprises a plurality of consecutive heating conductor loops, which are each electrically connected with the circuit board 36 by means of their own bonding conductor, but also share one bonding connection or one bonding conductor, which configures the positive or negative pole for two heating loops.

[0052] Figure 2 A schematic detail view of an exemplary attachment site 16 is shown. The heating conductor layer 14 can consist, in particular, of a ferro-nickel alloy. In this case, it can be advantageous to bond directly to the material of the heating conductor layer in the region of the attachment site 16, as shown in the figure. In this case, the thickness of the heating conductor layer 14 on the attachment site 16 can be increased compared to the rest of the heating conductor layer 14 - in the case of a ferro-nickel alloy, for example, by 10 to 20 μιη. Figure 2In the case shown, the thickness is drawn in the same way for simplicity. Preferably, however, the thickness of the attachment site 16 is in fact substantially similar to the thickness of the remaining heating conductor layer 14. The deviation of the thickness of the attachment site 54 from the thickness of the remaining heating conductor layer 14 can be less than 70%. Preferably, however, such a deviation is less than 50%, further preferably less than 30%, and particularly preferably the relative deviation is less than 10%.

[0053] It can be seen that the substrate 42, on the surface of which the heating conductor layer 14 can be seen, has a first attachment site 16 and a portion of the remaining surface 28. As mentioned above, the heating conductor layer 14 can consist in particular of a nickel-iron alloy, in which case it is advantageous to bond directly to the heating conductor layer 14. The heating conductor layer 14 can comprise a proportion of iron of between 30% and 80% by mass, preferably between 40% and 70% by mass. In addition, the heating conductor layer 14 can also comprise a proportion of nickel of between 10% and 30% by mass, preferably between 15% and 25% by mass, wherein the proportion of nickel and the proportion of iron present together amount to ≤ 100% by mass of the total mass of the heating conductor layer 14. The heating conductor layer 14 can in particular exhibit an open-porous, sponge-like structure, which can be relatively uneven. When the surface of the heating conductor layer 14 in the region of the first attachment site 16 is post-processed, an oxide layer is removed from the surface or is broken up. Thereby, if necessary, the surface roughness can also be reduced.

[0054] According to an alternative which is not shown, Figure 2 The attachment site 16 in the case shown can also be formed by a well-conducting material which is different from the material of the heating conductor layer 14, in particular copper or aluminium or the like. In the case shown, Figure 2 In the case shown, the section of the heating conductor layer 14 would in this case extend partially over an additional layer composed of the well-conducting material of the attachment site 16 and thus partially cover and lap over the additional layer in order to establish a mechanically stable and electrically conductive contact between the two. In this case, the thickness of the attachment site 16, which in this case is composed of the non-lapped region of the additional layer, would be significantly greater than the thickness of the heating conductor layer 14.

[0055] The first bonding conductor 22 is bonded directly, for example by ultrasonic bonding, on the first attachment site 16, wherein in particular a compression face 44 is designated, by means of which bonding Figure 4 The method, which will be described in more detail, establishes the first bonding conductor 22 on the compression face for providing an electrically conductive connection between the heating conductor layer 14 and the first bonding conductor 22 on the first attachment site 16. In the case shown, Figure 2In the case of protection, the essentially entire area of the substrate 42, including the first attachment site 16, is covered by means of an electrically insulating casting mass 30. The first bonding conductor can be, inter alia, a thick wire or a thick strip, which can consist, for example, of an aluminum, copper or gold alloy. In order to reduce the current strength in the first bonding conductor 22, it can optionally be provided that further bonding conductors are connected to the first attachment face 16 "stacked-like", i.e., for example, in the manner of a meander. Figure 2 Further bonding conductors, which are not shown in the figure, can be bonded to the first bonding conductor 22, in particular on the compression face 44.

[0056] The casting mass 30 can be realized, inter alia, by means of a partially cross-linked silicone gel. This silicone gel advantageously exerts no significant weight on the bonding connection, but is temperature-resistant and remains "tacky". In preparation of the first attachment site 16, it can be provided, inter alia, that the first attachment face 16 is brushed by means of a nylon brush in order to break up or remove an oxide layer which can be present on the surface of the heating conductor layer in the area of the attachment site 16. The sponge-like, porous structure can have a cavernous pore morphology with open pores, wherein the porosity of the heating conductor layer 14 can be, inter alia, between 3% and 20%.

[0057] Figure 3 A further simplified schematic diagram of an exemplary electric heating device 10 is shown. In Figure 3 The electric heating device 10, which is shown from above, comprises a heat exchanger 12, on the surface of which a substrate 42, for example a ceramic substrate, is arranged, which has a heating conductor layer 14 arranged thereon. The heating conductor layer 14 shown is structured, wherein the structure provided configures two mutually symmetrically configured heating conductor loop lines. The structure can be realized, for example, retroactively by means of insulation interruptions 48 in the form of line-like structures in the heating conductor layer 14. Alternatively, it is also possible that the structure is produced directly when the heating conductor layer 14 is arranged on the substrate 42, for example by means of a silk screen printing method or a thick coating method.

[0058] Here, the heating conductor circuit 50 comprises a first attachment site 16 and a second attachment site 18, and the further heating conductor circuit 50' likewise comprises the same first attachment site 16 and a further second attachment site 18. That is, the heating conductor circuits 50, 50' share the first attachment site 16. Here, the thickness of the heating conductor layer 14 at the attachment sites 16, 18 and the further attachment sites 16', 18' can also be increased compared to the remaining portion of the heating conductor layer. Preferably, however, the thickness of all attachment sites 16, 18' here can also be substantially at least similar to the thickness in the region of the remaining heating conductor layer 14. For example, the relative deviation of the thickness of the respective attachment sites 16, 18, 18' from the thickness of the remaining heating conductor layer 14 can be less than 70%. Preferably, however, such a deviation is less than 50%, further preferably less than 30%, and particularly preferably, the relative deviation is less than 10%.

[0059] For the sake of clarity, in Figure 3 the attachment means 20 are not shown in Figure 1 the schematic representation. The arrows drawn on the heating conductor circuits 50, 50' respectively illustrate the possible current flow direction within the respective heating conductor circuit 50, 50'. From their respective first attachment site 16, the current flows in the heating conductor circuit 50, 50' up to the second attachment face 18, 18', wherein, centrally, a turnaround region 52 is passed around.

[0060] The combination of the heating conductor layer 14 or the heating conductor circuits 50, 50' formed thereon and the substrate 42 (ceramic substrate) is referred to as a heating element. The heating device 10 as a whole can have a plurality of heating elements, which can each be bonded in a similar manner and can thereby be connected with the circuit board 36 and / or, if necessary, with a controller, the circuit board having power switching elements. A particular embodiment provides for different thicknesses of the thick wires or thick strips for different attachment sites, more precisely, the thicknesses are provided in accordance with the power requirement that can be expected in the respective heating loop or heating loop portion due to the wiring. This individual adjustability advantageously complements the automated production in the bonding process and allows flexible configuration of the heating elements. For example, one heating element can have one positive pole but two negative poles as attachment sites 16, 18, so that two heating loops are formed. The one positive pole is implemented by means of thick wires or thick strips having a greater thickness or a greater cross section in order to take into account the greater current flow here. Similar measures (different thicknesses / cross sections) can be taken in different voltage drop situations (for example, series or parallel connection of the heating loops).

[0061] Figure 4 A schematic view showing a fragment of an exemplary bonding apparatus, which is set up for ultrasonic bonding.Figure 4 In particular, a bonding tool 32, a guide 40 for a bonding wire or a bonding ribbon and a knife 34 for separating a bonded bonding wire or bonding ribbon are shown. The bonding tool 32, the guide 40 and the knife 34 are fastened on a holding element, not shown in Figure 4 which, together with the holding element, configures a "bonding head", i.e. a machine part which is movable relative to a substrate, which machine part can establish a bonding connection.

[0062] In the bonding, first the bonding tool 32 and the substrate 42 with the heating conductor layer 14 and the first attachment site 16 arranged thereon are positioned on top of one another. Then, a suitable length of bonding wire or bonding strip is fed through the guide 40 and wire manipulation (looping) is performed, for example, by means of a suitable movement of the bonding head, so that the bonding wire or bonding strip is bent such that a portion of the bonding wire or bonding strip is positioned on the first attachment site 16. The bonding tool 32 comprises means for generating sufficient heat so that the first bonding conductor 22 is welded on the particular bonding site 56 within the tolerance range for the bonding constituted by the first attachment site 16. For example, the bonding tool 32 can be configured for performing a cold pressure welding method between the bonding wire or bonding strip and the first attachment site 16. The cold pressure welding method can be, in particular, an ultrasonic bonding process, but other bonding processes are likewise possible, so that, in addition to ultrasound, for example, also laser light, plasma, electric arc, gas flame, reaction energy or a combination thereof can be used as a heat source for the bonding in order to establish the desired, materially bonded bonding connection. Then, while the bonding wire or bonding strip, now referred to as the first bonding conductor 22, is being fed through the guide 40, the bonding tool 32 is moved by moving the bonding head relative to the further attachment site 38 on the circuit board 36 in order to also cause welding of the first bonding conductor 22 there, this time on the particular bonding site 58 within the further attachment site 38. The circuit board 36 can generally be understood as a further substrate. The two substrates can be arranged at the same or different heights relative to one another and, in addition, can also have a variable angle relative to one another. The bonding device can comprise, in particular, optical detection means in order to recognize a relative positioning deviation between the substrates and to adjust the looping in accordance with the recognized position of the substrates so that an electric contact that remains precisely the same can be established. Next, the first bonding conductor 22 is severed by the knife 34 so that the bonding of the electric connection is completed. The process is repeated with further attachment sites of the heating conductor layer 14 until these are bonded at least once with the corresponding further attachment sites 38 on the circuit board 36. It is also possible to stack a plurality of bonding conductors on top of one another so that a parallel attachment connection is produced, for example, in order to reduce the current strength in the bonding conductors. All bonding connections produced by the bonding conductors 22, 24 can be direct bonding connections to the material of the heating conductor layer so that, in this particular embodiment, it is possible to dispense with the provision of contact pads / interface layers or the like, in particular contact layers composed of a well-conducting material in the region of the attachment face, which support the connection.

[0063] Figure 5A flow chart of an exemplary method 100 for manufacturing an electric heating device is shown. The method 100 starts for example with providing a heat exchanger 12. Next, a heating conductor layer 14 is arranged 120 on the heat exchanger 12, the heating conductor layer having a first electrical attachment site 16 and a second electrical attachment site 18. Here, the heating conductor layer 14 can also be arranged first on a separate substrate 42, for example a ceramic substrate, which substrate is then arranged on the heat exchanger 12. Alternatively, the substrate 42 can be fixed first on the heat exchanger 12, and then the process steps described later for forming the heating conductor layer 14 and the bonding are carried out. In an optional step, the first attachment site 16 and / or the second attachment site 18 are processed 130 such that the first attachment site and / or the second attachment site no longer have an oxide layer, i.e. the oxide layer is removed or broken. It is also possible that the oxide layer is removed over the entire heating conductor layer - the oxide layer can then be formed again in areas which are not involved in the bonding.

[0064] The processing 130 can be provided before or after arranging 120 the ceramic substrate 42 on or at the heat exchanger 12. In processing 130 the heating conductor layer 14 in the area of the first and second attachment sites 16, 18, for example porous, cavity-like, the surface properties of the attachment sites provided later with different roughness and impurities, for example oxides, grease, oil, etc., which affect, in particular impair, the quality of the bonding connection, can be compensated. For this purpose, by preparing the heating conductor layer 14 in the area of the first and second attachment sites 16, 18, for example by (grind)ing, brushing, polishing, cleaning, activation and / or heat treatment, plasma activation, laser processing, etc., the surface properties are influenced so that a consistent and in particular significantly better bondability and a good bonding connection with the required tear-off force and shear force and connection area can be achieved. By means of the described surface treatment, in particular the oxide layer in the area of the attachment sites is removed or broken, for example mechanically.

[0065] After this optional step, the first bonding conductor 22 is directly bonded 140 to the first attachment site 16. Then, the second bonding conductor 24 is directly bonded 150 to the second attachment site 18. Optionally, an electrically insulating casting mass 30 can then be applied 160 to the first attachment site 16 and the end of the first bonding conductor 22 bonded thereon and / or to the second attachment site 18 and the end of the second bonding conductor 24 bonded thereon. Finally, the method is completed by incorporating 170 the bonded substrate 42 or heating element (substrate 42 with heating conductor layer 14) and the heat exchanger 12 with the further components of the electric heating device 10. Of course, the steps of direct bonding 140, 150 also include connecting the first bonding conductor 22 or the second bonding conductor 24 with the respectively assigned further attachment pad on the circuit board 36.

[0066] The features disclosed in the foregoing description, in the claims and in the

[0067] In Figure 6 a top view of a heat exchanger 12 according to an embodiment is shown, which has a substrate 42 mounted thereon, said substrate having thermally conductive layers (here three substrates, each having two heating circuits) and a circuit board 34 and punched grids 60. Here, the heat exchanger 12 can only be seen as a flat floor plate, onto which the substrate 42 as well as the circuit board 34 are arranged. The three punched grids are located in openings of the floor plate and allow access to plated vias of a controller 46, which is not visible in Figure 6 , since the controller is located on the back side of the floor plate. In the top view, the cavities of the heat exchanger, which are for example traversed by a coolant, extend behind the floor plate at the height of the heating elements 66a, 66b, 66c, which are formed by the three substrates 42 having heating conductor structures arranged thereon. The heating elements can for example be fastened on the heat exchanger by means of an adhesive. In Figure 6 , power switching elements are arranged on the circuit board 34, which are connected with the heating conductor layer 14 or the respective heating conductor circuit 50 by further attachment sites 38, first and second bonding conductors 22, 24 and first and second attachment sites 16, 18 and thus configure heating circuits which can be controlled accordingly.

[0068] In Figure 3 , a heating element 66a is shown, which corresponds to the heating element shown in Figure 6 . Instead of three substrates 42, it is also possible to arrange three pairs of heating circuits on a common substrate 42.

[0069] The shown embodiment is only one specific implementation, further modifications are possible within the scope of protection defined by the attached claims. It is emphasized here that the heating conductor layer can also be configured from other materials (as an iron-nickel alloy) which have metallizations composed of a resistance alloy, which set the respective heating resistance according to the requirements. In particular, the mentioned nickel-chromium alloy is also considered here, in which case the first and second attachment sites can be configured as additional layers on the substrate, which are partially overlapped by the heating conductor layer in order to establish an electrical contact.

[0070] List of reference signs 10 electric heating device 12 heat exchanger 14 heating conductor layer 16 first attachment site 16' further first attachment site 18 second attachment site 18' further second attachment site 20 attachment means 22 first bonding conductor 24 second bonding conductor 28 remaining surface 30 cast mass 32 bonding tool 34 knife 36 printed circuit board 38 further attachment site 40 guide 42 substrate 44 pressing surface 46 controller 48 insulation interruption 50 heating conductor circuit 52 central turning region 56 bonding site 58 bonding site 60 stamping grid 62 further bonding conductor 66a-c heating element 100 method 110 providing 120 arranging 130 processing 140 bonding 150 bonding 160 applying 170 merging.

Claims

1. An electric heating device (10), particularly a vehicle electric heating unit, said electric heating device comprising: - A heating conductor layer (14) is thermally connected to the heat exchanger (12). - A first attachment site (16) and at least one second electrical attachment site (18), wherein the first attachment site and at least one second electrical attachment site (16, 18) are formed through or adjacent to the heating conductor layer (14), and - An electrical attachment device (20) connected to the first attachment site and at least one second electrical attachment site (16, 18), The electrical attachment device (20) includes a first bonding conductor (22) and a second bonding conductor (24). The first bonding conductor is directly bonded to the first electrical attachment site (16), and the second bonding conductor is directly bonded to the second electrical attachment site (18). The first bonding conductor (22) and the second bonding conductor (24) respectively constitute a bonding connection.

2. The electric heating device (10) according to claim 1, wherein, The first bonding conductor (22) is a first thick wire or a first thick strip, and the second bonding conductor (24) is a second thick wire or a second thick strip.

3. The electric heating device (10) according to claim 2, wherein, In the case of thick conductors, the diameter of the thick conductors is in the range of 125µm to 500µm, or in the case of thick strips, the cross-section of the thick strips is given by the dimensions of width and thickness respectively in the range of (0.5mm-3.0mm) x (0.05-0.35mm), including the boundary values ​​of the range respectively.

4. The electric heating device (10) according to any one of claims 1 to 3, wherein, The first bonding conductor (22) and / or the second bonding conductor (24) are formed of a bonding material with a hardness in the range of 20 HB to 40 HB, preferably including aluminum and / or copper or alloys thereof.

5. The electric heating device (10) according to any one of the preceding claims, wherein, The heating conductor layer (14) comprises an iron fraction between 30% and 80% by mass, preferably between 40% and 70% by mass, relative to 100% by mass of the total mass of the heating conductor layer (14), and The heating conductor layer (14) comprises a nickel fraction between 10% and 30% of the total mass of the heating conductor layer (14), preferably between 15% and 25% of the total mass of the heating conductor layer (14), wherein the nickel fraction and the iron fraction together are ≤ 100% of the total mass of the heating conductor layer (14).

6. The electric heating device (10) according to any one of claims 1 to 4, wherein, The heating conductor layer (14) comprises a chromium fraction between 0.5% and 10% by mass, preferably between 1% and 7% by mass, relative to 100% by mass of the total mass of the heating conductor layer (14), and The heating conductor layer (14) comprises a nickel share between 60% and 99% of the total mass of the heating conductor layer (14), preferably between 70% and 95% of the total mass of the heating conductor layer (14), wherein the nickel share and the chromium share together are ≤ 100% of the total mass of the heating conductor layer (14).

7. The electric heating device (10) according to any one of the preceding claims, wherein, The heating conductor layer (14) has a porous structure (26), and the first attachment site (16) and / or the at least one second attachment site (18) are processed such that there is no oxide layer between the first bonding conductor (22) and the second bonding conductor (24) on one hand and the corresponding surfaces of the first attachment site and at least one second attachment site (16, 18) on the other hand.

8. The electric heating device (10) according to any one of the preceding claims, wherein, The first attachment portion (16) and / or the at least one second attachment portion (18), together with the ends of the bonding conductors (22, 24) respectively bonded thereto, are covered by an electrically insulating casting quality (30).

9. The electric heating device (10) according to any one of the preceding claims, wherein, If the first attachment site and at least one second electrical attachment site (16, 18) are formed through the heating conductor layer (14), then the thickness of the heating conductor layer (14) in the region of the first attachment site (16) and / or the thickness in the region of the at least one second attachment site (18) is in the range of 5 to 35 µm, including the boundary values ​​of the range, or If the first attachment site and at least one second electrical attachment site (16, 18) are respectively adjacent to the heating conductor layer (14), then the first attachment site and at least one second electrical attachment site are respectively formed by a highly conductive layer, the thickness of which is preferably in the range of 20µm to 55µm, including the boundary value of the range, wherein the highly conductive layer is preferably formed of copper, aluminum or gold or an alloy thereof.

10. The electric heating device (10) according to any one of the preceding claims, the electric heating device further comprising a substrate (42), preferably a ceramic substrate, the heating conductor layer (14) being constructed on the substrate, and the substrate being configured to transfer electrical power converted into thermal energy by the heating conductor layer (14) during operation to the heat exchanger (12).

11. The electric heating device (10) according to any one of the preceding claims, wherein, The first bonding conductor (22) and the second bonding conductor (24) have a first end and a second end, respectively. The first end is connected to the first attachment site and the at least one second attachment site, and the second end is connected to the attachment pad on the circuit board. The circuit board has a power switching element that can selectively supply electrical power to the heating conductor layer.

12. A method (100) for manufacturing an electric heating device (10), particularly an electric heating unit for a vehicle, the method comprising the following steps: - Provides (110) substrate (42), preferably ceramic substrate; - A heating conductor layer (14) or a heating conductor layer (14) together with a layer adjacent to the heating conductor layer (14) is arranged (120) on the substrate (42) by means of a first electrical attachment portion (16) constructed through the heating conductor layer or the adjacent layer and a second electrical attachment portion (18) constructed through the heating conductor layer (14) or the adjacent layer; - The first bonding conductor (22) is directly bonded (140) to the first attachment site (16); - The second bonding conductor (24) is directly bonded (150) to the second attachment site (18); and - Combine the substrate with other components of the heat exchanger (12) and / or the electric heating device (10) (170).

13. The method (100) according to claim 12, wherein, The direct bonding includes cold pressure bonding methods, especially ultrasonic bonding.

14. The method (100) according to claim 12 or 13, further comprising: Prior to the bonding step, the first attachment site (16) and / or the second attachment site (18) are pre-processed (130) so that the first attachment site and / or the second attachment site no longer have an oxide layer.

15. The method (100) according to any one of claims 13 to 14, wherein the method further comprises: The casting quality (30) of electrical insulation is applied (160) to the first attachment site (16) and the end of the first bonding conductor (22) bonded to the first attachment site and / or the at least one second attachment site (18) and the end of the second bonding conductor (24) bonded to the at least one second attachment site.

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