Monolithic functional ceramic element and method for establishing contact for functional ceramic

Abstract

The invention relates to a method for establishing a contact for a functional ceramic (3), comprising the following steps: providing a functional ceramic (2, 3); applying a metal paste (4) to two opposite surfaces of the functional ceramics (2, 3); laminating a ceramic substrate green film (9) on the metal paste (4) on two opposite surfaces of the functional ceramics (2, 3); the functional ceramics (2, 3) and the ceramic substrate green film (9) are co-sintered to form an electrically insulating ceramic layer (10) and the metal paste (4) is co-sintered to form an electrically conductive metal structure (5). The invention further relates to a monolithic functional ceramic element, in particular a monolithic functional ceramic element produced according to the described method.

Description

Technical Field

[0001] The invention relates to a functional ceramic component, a method for producing contact of a functional ceramic and the use of the component in a heating module. Background Art

[0002] The advantage of using functional ceramic elements, in particular PTC (Positive Temperature Coefficient) thermistor elements in the heating module is that their properties as temperature-dependent resistors automatically limit the power consumption when a certain temperature is reached. This property prevents overloading of the heating module in particular.

[0003] Such heating modules are increasingly being used as temperature registers in electric vehicles. Such applications require operating the register directly from a high-voltage battery (typically 200-800 V). Therefore, the insulation strength must be designed accordingly.

[0004] The PTC element is usually electrically contacted on two opposite sides by means of conductor tracks, which are carried by a substrate which couples out the generated heat on the other side.

[0005] The heat power that can be coupled out depends largely on the heat path through the layer structure described above. The heat must be transferred from the source (PTC) via the contacts and through the substrate to the coupling-out surface. Here, thermal and electrical considerations for optimizing the heating element are often subject to conflicting arguments, i.e. the design according to the prior art is a compromise solution between power density, thermal flexibility and insulation capacity or robustness and reliability.

[0006] The PTC element itself acts as a heat source when Joule heat is generated by passing an electric current. However, the Joule heat is not generated uniformly in the material, but the electric field distribution in the component causes a temperature gradient, depending on the geometry and possible material inhomogeneities. The heat must first reach the component surface from the hot spot before it can be transported further. Since the thermal conductivity of PTC ceramics is relatively poor (typically ~5 W / mK), this is very slow and sluggish.

[0007] Document DE 112017006124 T5 describes a corresponding electric heating device according to the prior art, which has an insulating layer between the conductor track and the cooling fins.

[0008] Document EP 1182908 A1 describes a similar PTC heating device having at least one PTC element and two contact plates in contact with the PTC element. In order to connect the surface of the PTC element to the contact plates, a metal film is provided, which is coated with an adhesive on both sides. In this case, no insulation of the contact plates is provided.

[0009] Furthermore, a PTC heater with reduced inrush current is known from document DE 2017101946 A1.

[0010] Document DE 10 2016 108 604 A1 also describes how similar functional ceramics can be embedded in a ceramic substrate. Summary of the invention

[0011] The object of the present invention is to provide an improved functional ceramic component which can also be used in heating modules.

[0012] The present invention relates to a method for establishing contact with a functional ceramic, in particular a PTC ceramic, or a method for producing a functional ceramic component, in particular a preferably monolithic thermistor component. The method comprises at least the steps described below.

[0013] In the first step, a functional ceramic is provided. The ceramic referred to below as the functional ceramic is preferably a thermistor ceramic, and more preferably a PTC ceramic.

[0014] Functional ceramics or PTC ceramics can be provided in a green state or in a sintered state. Preferably, the functional ceramic is provided as a film in a green state, wherein the film has a small film thickness compared to the film surface. Functional ceramics can only play their desired functions in a sintered state. In this application, green ceramics that only have functions in a sintered state are also referred to as functional ceramics. This also applies to PTC ceramics.

[0015] Functional ceramics can include any suitable ceramic material. Possible ceramic materials are, for example, barium titanate ceramics. In addition, the ceramics can also include, for example, lead and / or strontium. The ceramics can also be doped with appropriate doping materials, such as yttrium or manganese, in appropriate amounts to provide the desired function, in particular a thermistor function.

[0016] In a further step, a metal paste is applied to two opposite surfaces of the functional ceramic.

[0017] The metal paste is preferably applied at a thickness of a few micrometers or a few hundred nanometers.

[0018] The metal paste preferably comprises a conductive metal in powder form, such as nickel, cobalt, copper, silver, other noble metals or metal alloys. In addition, the metal paste also comprises a suitable suspending agent, for example.

[0019] In one embodiment, the metal paste can be applied not in a planar manner, but can be applied in the form of a comb-like metal structure converted by a sintering step. For this purpose, the metal paste can be applied in a comb-like structure. Preferably, two comb-like structures are applied to opposite surfaces so that the comb-like structures do not overlap, but are staggered. The comb-like structures each include a continuous section as a trunk and sections branching therefrom as branches.

[0020] The metal paste can be applied by, for example, (screen) printing or sputtering.

[0021] In a further step, a ceramic substrate green film is applied to two opposite surfaces of the functional ceramic and laminated.

[0022] The ceramic substrate green film may include a ceramic material similar to the functional ceramic or another ceramic material. The ceramic material formed by the ceramic substrate green film after sintering is preferably electrically insulating and has good thermal conductivity.

[0023] The ceramic substrate green film is applied in such a way that it preferably covers the entire surface of the functional ceramic and the metal paste applied thereto, respectively. The ceramic substrate green film is applied directly to the surface of the functional ceramic or to the metal paste applied thereto.

[0024] The above steps, which are preferably performed in the order described, provide a layer stack, which includes two ceramic substrate green films, which wrap the functional ceramic in a sandwich structure. A structure composed of a metal paste is also arranged between the functional ceramic and the ceramic substrate green films, which is used to establish electrical contact with the functional ceramic.

[0025] In a further step, the layer stack is sintered together to form the functional ceramic component.

[0026] In a preferred embodiment, the functional ceramic element is monolithic. "Monolithic" means that the functional ceramic element is not composed of different individual elements, but of a single element. Therefore, no (sub)elements need to be mechanically connected or glued.

[0027] In one embodiment, the functional ceramic element is a monolithic thermistor element.

[0028] The term "sintering" here refers in particular only to a so-called temperature treatment step. In particular, the term "sintering" does not imply that all sintered materials are previously in the green state. Already sintered structures can also be subjected to corresponding temperature treatment steps, which then have little or no effect on the already sintered structure.

[0029] The functional ceramic element is preferably a thermistor element having a thermistor function. The functional ceramic is then a ceramic having thermistor properties, in particular an NTC ceramic or preferably a PTC ceramic.

[0030] The monolithic functional ceramic component is formed by co-sintering a functional ceramic for forming a functional ceramic layer, a ceramic substrate green film for forming an electrically insulating ceramic layer, and a metal paste for forming an electrically conductive metal structure.

[0031] The functional ceramic component formed in this way therefore comprises a functional ceramic layer, an electrically insulating ceramic layer and an electrically conductive metal structure.

[0032] By forming a monolithic functional ceramic component, defects that occur when assembling a functional ceramic component from different subcomponents can be avoided. For example, cavities that may be formed during gluing can be avoided. In addition, seepage or smearing of the adhesive can be avoided. In addition, incomplete connections between separate functional ceramic components and insulating ceramic components can be avoided.

[0033] Furthermore, the method is simplified since the assembly of different subcomponents can be dispensed with.

[0034] By forming a functional ceramic layer, a conductive structure and an insulating ceramic layer in a monolithic component, the stability and durability of the functional ceramic component can be improved.

[0035] In addition, the thermal coupling between the individual layers is improved so that when the functional ceramic layer designed as a thermistor layer is heated by applying a voltage, the generated heat can be well dissipated to the outside via the electrically insulating ceramic layer. For this purpose, the ceramic layer is preferably formed thinly.

[0036] By using film technology when manufacturing functional ceramic elements, large-area and very thin functional ceramic elements can be provided. Therefore, the thickness of the functional ceramic element can be reduced. In addition, the functional ceramic film can replace a variety of traditional functional ceramic tiles, such as PTC tiles, which each have a significantly smaller surface size.

[0037] Even without a flat application of the electrically conductive structure, the film still allows a uniform electric field to be formed and thus, in the case of a thermistor element, a uniform heating of the thermistor element.

[0038] Functional ceramic components can also be produced in a simple manner using existing automated processes for producing multilayer ceramic components.

[0039] By producing a monolithic functional ceramic component, it is also possible to dispense with the provision of individual components, such as conventional functional ceramic tiles or insulating ceramic components and conductive metal films, which have to be produced at different locations and subsequently assembled.

[0040] The electrically conductive metal structure can be electrically contacted to the outside. For this purpose, for example, a recess is provided in the electrically insulating ceramic layer. For example, the recess can be formed by incompletely covering the metal structure with a ceramic film or by subsequently removing the ceramic material.

[0041] Then, in the region of the recess, the metal structure can be electrically contacted by means of a wire. For example, the wire is welded to the metal structure. Alternatively, the metal structure can be electrically contacted, for example, by means of terminal contacts. Other suitable contact methods are also possible.

[0042] Preferably, the metallic structure does not extend as far as the edge of the ceramic layer, in order to form regions at the edge of the functional ceramic element which are not subjected to voltage even during operation.

[0043] In one embodiment, the functional ceramic is provided as a functional ceramic film in a green state. In one embodiment, the functional ceramic is provided in particular as a film in a green state and the metal slurry and the ceramic substrate green film are directly applied to the functional ceramic film in a green state. Preferably, no other processing steps are performed between the above steps. In an alternative embodiment, the functional ceramic is provided as a film in a green state and the green functional ceramic is first sintered to form a functional ceramic layer. Then, the metal slurry and the ceramic substrate green film are applied to the functional ceramic layer in a sintered state.

[0044] In one embodiment, the functional ceramic is provided as a green film and sintered at a high temperature above 1000° C., preferably above 1300° C., to form a functional ceramic layer before applying the metal paste and the ceramic substrate green film. The functional ceramic preferably comprises a HTCC (high temperature co-sintered ceramic) ceramic material.

[0045] Preferably, the metal slurry is dried at an elevated temperature prior to sintering to evaporate the suspending agent or solvent.

[0046] In an alternative embodiment, the functional ceramic is provided in a sintered state.

[0047] The ceramic substrate green film preferably comprises a LTCC (low temperature co-fired ceramic) ceramic material. The subsequent co-sintering is preferably performed at a relatively low temperature below 1000°C, preferably below 800°C.

[0048] For example, by sintering at low temperature, the thermistor function of the functional ceramic remains unchanged. In particular, undesired oxidation of the functional ceramic is avoided by subsequent sintering at low temperature.

[0049] In an alternative embodiment, the metal paste and the ceramic substrate green film are applied to the functional ceramic provided as a film in the green state. The layer stack thus formed is then co-sintered. The co-sintering is preferably carried out at a high temperature of more than 1000° C., preferably at a high temperature of more than 1300° C.

[0050] Preferably, in this embodiment, both the functional ceramic and the further ceramic layer comprise HTCC ceramic.

[0051] The ceramics can thus be sintered at the same temperature. By selecting ceramics that are as similar as possible, the formation of mechanical stresses during sintering can also be reduced or avoided.

[0052] In a preferred embodiment, the functional ceramic film and the ceramic substrate green film have substantially the same composition.

[0053] Preferably, the components of the functional ceramic film and the ceramic substrate green film differ only in the proportion of the doping material in the components. Such a doping material can be, for example, yttrium or manganese. In particular, the resistance of the ceramic material can be increased by the higher proportion of the proposed doping material, thereby providing an electrically insulating ceramic material.

[0054] In general, it can be preferred if the functional ceramic film and the ceramic substrate green film have the same ceramic base material, wherein the PTC function or the substrate function is set or defined via the selection of the dopant and / or the concentration of the dopant.

[0055] By selecting ceramics that are as similar as possible for the different ceramic layers, the formation of mechanical stresses during sintering can be reduced or avoided. As a result, the formation of defects in the functional ceramic component, such as the formation of cavities between the layers, is suppressed. In addition, the thermal coupling between the individual layers can be improved by selecting similar materials.

[0056] In a preferred method, a plurality of functional ceramic membranes are separated from a larger functional ceramic membrane. This enables simple mass production of functional ceramic components. By separating the functional ceramic from the membrane, large-area but very thin functional ceramics can be provided in a simple manner.

[0057] For example, the functional ceramic membrane is divided by cutting or punching.

[0058] Each divided functional ceramic film preferably has a rectangular shape with dimensions of at least 3 cm×10 cm. The thickness of the film is preferably a maximum of 150 μm. Then, due to the usual sintering shrinkage, the dimensions of the functional ceramic layer are smaller.

[0059] The present invention also relates to a monolithic functional ceramic component, in particular a monolithic thermistor component. The functional ceramic component is preferably produced according to the above method. All features and embodiments described with respect to the method are also applicable to the functional ceramic component. In particular, in all embodiments and examples, the functional ceramic component can be a thermistor component.

[0060] In particular, the present invention also relates to a monolithic functional ceramic component, preferably a monolithic thermistor component, which comprises at least the following layers laminated in a stacking direction perpendicular to the outer surface of the monolithic functional ceramic component.

[0061] All features and embodiments described with respect to the method are also applicable to the monolithic functional ceramic component.

[0062] The monolithic functional ceramic component comprises, on the one hand, a functional ceramic layer, preferably a PTC ceramic layer, having two opposite surfaces.

[0063] In addition, the monolithic functional ceramic element comprises two electrically conductive metal structures having different polarities in the operating state, which are arranged in direct contact on each of the opposite surfaces of the functional ceramic layer. Here, direct contact means that the electrically conductive metal structure is directly placed on the surface of the functional ceramic layer without forming any other intermediate structures.

[0064] The conductive metal structure is also electrically connected to the conductive functional ceramic layer, which means that an electric field or a voltage can be applied to the functional ceramic layer via the conductive metal structure.

[0065] Furthermore, the functional ceramic element comprises two electrically insulating ceramic layers which are arranged on each of the opposite surfaces of the functional ceramic layer and the metal structure arranged thereon. The electrically insulating ceramic layers are applied directly to the surface of the functional ceramic layer or the metal structure.

[0066] In one embodiment, the functional ceramic layer includes or consists of a HTCC ceramic, and the electrically insulating ceramic layer includes or consists of a LTCC ceramic.

[0067] Preferably, in the described embodiment, the electrically insulating ceramic layer comprises alumina ceramic.

[0068] The electrically insulating ceramic layer should also be thermally well conductive and consist of a material with high thermal conductivity.

[0069] In an alternative embodiment, the functional ceramic layer and the electrically insulating ceramic layer each include or consist of HTCC ceramic.

[0070] Preferably, the functional ceramic layer and the electrically insulating ceramic layer then have essentially the same ceramic composition.

[0071] In one embodiment, the ceramic components of the functional ceramic layer and the electrically insulating ceramic layer differ only with regard to the proportion of the dopant in the ceramic component.

[0072] Such functional ceramic components have a particularly high thermal coupling between the individual layers, which is advantageous, for example, for use as a thermistor element in a heating module.

[0073] In any embodiment, the functional ceramic layer includes barium titanate ceramic, which may further include strontium compounds (such as strontium oxide) and / or lead compounds (such as lead oxide) and doping materials (such as yttrium or manganese).

[0074] In one embodiment, the functional ceramic layer has a layer thickness of at most 150 μm. Preferably, the functional ceramic layer has a smaller layer thickness of at most 100 μm or at most 50 μm. The layer thickness should be at least 40 μm.

[0075] In such thin layers, a uniform electric field can be easily generated. Even with non-planar metal structures, for example comb-shaped metal structures, an electric field can be applied which is uniform over the entire area of ​​the functional ceramic layer covered by the metal structure.

[0076] In one embodiment, the electrically insulating ceramic layer has a layer thickness of at most 200 μm.

[0077] The insulating ceramic layer preferably covers the entire functional ceramic layer along two opposite surfaces. The thin design of the layer can reduce the size of the entire functional ceramic component.

[0078] The thin insulating ceramic layer also enables good conduction of heat to the outer side of the functional ceramic component.

[0079] According to one embodiment, the functional ceramic component has a thickness in the stacking direction of the mentioned layers of a maximum of 800 μm, preferably 500 μm, more preferably 400 μm.

[0080] In one embodiment, the electrically conductive metal structure is designed as a comb-like structure.

[0081] The comb-like structures each include a continuous section and a plurality of sections branching from the continuous section. Preferably, the conductive metal structures are arranged without overlapping in the stacking direction, so that during operation, all conduction paths in the functional ceramic layer, via which the current is guided through the functional ceramic layer, extend diagonally. Thus, despite the small thickness of the functional ceramic layer, a minimum conduction path through the layer, preferably at least 4 mm, can be provided.

[0082] The minimum conduction path, ie the shortest path through which an electric current can flow between two metallic structures of different polarity during operation, is preferably formed in the functional ceramic component between two branch sections of each electrically conductive metallic structure.

[0083] By forming a comb-like structure, metal material can also be saved.

[0084] The minimum conduction path thus ensured can comply with the specified creepage distance, so that the desired insulation strength is achieved and the thickness of the functional ceramic layer can be further reduced. Despite the low film thickness, voltages of preferably 450 to 800 volts, more preferably up to 1000 volts, can be applied.

[0085] The guaranteed minimum conduction path also reduces the maximum current flow when a certain voltage is applied to the ceramic layer. Thus, for example, the energy consumption of a connected battery can be reduced. In addition, surge current peaks that are a high load for the battery or the connected switching electronics can also be reduced.

[0086] The present invention also relates to a heating module, which comprises one or more monolithic thermistor elements as described above.

[0087] The efficiency of the heating module may be increased through the described improved thermal coupling, thermal conduction, and heat transfer characteristics of the monolithic thermistor element.

[0088] The heating module is, for example, a finned heating module, which comprises a plurality of the described monolithic thermistor elements, on the surface of which fins are applied, through which a thermal fluid flows. The thermal fluid is heated by the thermistor elements during operation. For example, a corresponding heating module can be used in the automotive sector and should have a thermal power of preferably at least 5 kW. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] The present invention will be described in more detail below based on embodiments and the associated drawings.

[0090] The invention is not limited to the examples shown in the figures.

[0091] Similar or seemingly identical elements in the figures are provided with the same reference numerals. The figures and the dimensional ratios in the figures are not necessarily drawn strictly to scale.

[0092] in:

[0093] Figure 1 A schematic diagram showing a method of manufacturing a first embodiment of a monolithic thermistor component.

[0094] Figure 2 A cross section of a first embodiment of a monolithic thermistor element is shown with the minimum conduction paths depicted.

[0095] Figure 3 A microscopic image of a portion of a first embodiment of a monolithic thermistor component is shown in the edge region.

[0096] Figure 4 Microscope image showing a cross section of a second embodiment of a monolithic thermistor element.

[0097] Figure 5 A top view of one embodiment of a monolithic thermistor element with external contacts made by wires is shown.

[0098] Figure 6 Show the change of the cold resistance of the PTC ceramic layer of the exemplary thermistor element according to the present invention and the cycle number.In each cycle, 450 volts of direct current are loaded on the thermistor element for 5 seconds, and then cool for 30 seconds.

[0099] Figure 7 The surge current curve of an exemplary thermistor element according to the present invention is shown. The current flow I through the PTC ceramic layer when a 450 V DC voltage U is applied is shown in relation to the time t since switching on.

[0100] Figure 8 A photograph showing a heating module including a monolithic thermistor element. DETAILED DESCRIPTION

[0101] exist Figure 1 The production of a first embodiment of a functional ceramic component according to the present invention is shown in FIG. In this example, the functional ceramic component is in particular a monolithic thermistor component 100 .

[0102] In the first step, a PTC ceramic film 1 is provided as a functional ceramic film with a large surface extension and a small thickness. For example, the extension of the large PTC ceramic film 1 is 4 inches by 4 inches. Alternatively, the extension can be any other preferably larger size. The thickness of the PTC ceramic film 1 is between 40 and 250 microns, preferably between 50 and 150 microns, and more preferably less than 100 microns.

[0103] Any number of PTC ceramic films 2 with smaller extensions can be separated from the provided large PTC ceramic film 1. The individual PTC ceramic films 2 are punched or cut out from the large PTC ceramic film 1, for example.

[0104] For example, three PTC ceramic films 2 are cut out from an exemplary large PTC ceramic film 1 having an extension of 4 inches×4 inches. The cut PTC ceramic films 2 preferably have a rectangular shape with an extension of approximately 3 cm×10 cm respectively. The PTC ceramic film 2 may also have an extension greater than 3 cm×10 cm.

[0105] The PTC ceramic film 2 manufactured in this way has a significantly larger surface extension at a smaller thickness than the conventionally used PTC ceramic tiles. Therefore, a monolithic thermistor element comprising a single PTC ceramic film 2 can be manufactured, whereas in conventional methods, a plurality of PTC ceramic tiles are used. In addition, by using a thin PTC ceramic film 2, the thickness of the thermistor element can be reduced.

[0106] In a subsequent step, the segmented PTC ceramic film 2 is sintered. Preferably, the PTC ceramic film 2 is sintered at a high temperature, for example between 1240° C. and 1320° C., in order to produce the desired thermistor function.

[0107] During sintering, the expansion of the PTC ceramic film 2 is reduced by an amount typical for sintering shrinkage. By sintering, the green PTC ceramic film 2 is converted into a sintered functional ceramic layer, namely the PTC ceramic layer 3. The surface expansion of the PTC ceramic layer 3 is, for example, 26 mm×78 mm and preferably not more than 3 mm×9 mm.

[0108] Then, an electrically conductive metal structure 5 is applied to the sintered PTC ceramic layer 3. For this purpose, for example, a metal paste 4 is printed or sputtered onto two opposite surfaces of the PTC ceramic layer 3. Preferably, the metal paste 4 is applied in the form of a comb.

[0109] The metal paste 4 includes, for example, nickel, copper, aluminum, a noble metal, or an alloy of any of the above metals.

[0110] As shown, the comb comprises a continuous section 6, the main trunk of the comb, from which a plurality of sections 7, the branches of the comb, preferably branch off at right angles. The metal paste 4 is therefore not applied to the surface in a flat manner.

[0111] Despite the absence of a planar application of metal paste 4, the advantageously thin layer thickness of the PTC ceramic layer 3 according to the invention enables a uniform electric field to form in the PTC ceramic layer 3 during operation. This has the effect, in particular, that the current is converted uniformly into heat energy in the PTC ceramic layer 3 during operation.

[0112] The heat energy is released to the environment via the preferably well-conducting further ceramic layer 10. The heat release to the environment is further promoted by the good thermal coupling between the individual co-sintered layers of the monolithic thermistor element 100.

[0113] The two combs on the two surfaces of the PTC ceramic layer 3 are structured so that the two combs do not overlap in a direction perpendicular to the surface of the PTC ceramic layer 3. That is, in the theoretical case where the PTC ceramic layer 3 is transparent, the two comb-like structures are visible side by side from the direction of one surface of the PTC ceramic layer 3. The trunk 6 of the comb is applied on different sides of the respective surface. The branch sections 7 are therefore applied side by side with a recessed portion located therebetween, so that the sections 7 of the two combs do not overlap, but point in the direction of the respective other comb structure.

[0114] By structuring the metal paste 4 and thus also the conductive metal structure 5 subsequently formed from the metal paste, the conduction paths 8 in the PTC ceramic layer 3 are maximized, such as Figure 2Here, the distance traveled by the current in the PTC ceramic layer 3 in the operating state is referred to as the conduction path 8. The shortest conduction path 8 in the PTC ceramic layer 3 between the two metal structures 5 should preferably be at least 4 mm. The shortest conduction path 8 is preferably formed between two branch sections 7 of each of the two conductive metal structures 5 that are adjacent to each other.

[0115] Despite the low ceramic thickness, the described minimum conducting paths 8 still enable the use of high voltages, for example in the range between 400 and 1000 volts, preferably in the range above 800 volts.

[0116] The applied metal paste 4 is then dried at a temperature of, for example, at least 180° C. for a period of, for example, at least 30 minutes.

[0117] Then, if Figure 3 As shown in FIG. 1 , a ceramic substrate green film 9 is applied on both surfaces of the PTC ceramic layer 3, and the ceramic substrate green film covers the entire surface of the PTC ceramic layer 3 and the metal paste 4 applied thereon. The thickness of the structure composed of the metal paste 4 is negligible compared to the thickness of the ceramic layer or ceramic film, and is in the micrometer or submicrometer range.

[0118] The PTC ceramic layer 3 preferably comprises a HTCC ceramic sintered at a high temperature, whereas the further ceramic layer 10 formed from the ceramic substrate green film 9 preferably comprises a LTCC ceramic material sintered at a relatively low temperature.

[0119] The material of the PTC ceramic layer 3 is, for example, barium titanate ceramic or a similar material, which may also include other metals, such as lead or strontium. However, the material of the PTC ceramic layer 3 is preferably lead-free ceramic. In order to manufacture thermistor function, the ceramic of the PTC ceramic layer 3 is preferably doped with other elements, such as yttrium and / or manganese.

[0120] The LTCC ceramic of the further ceramic layer 10 is, for example, an aluminum oxide ceramic or a similar material which is preferably a good thermal conductor but electrically insulating.

[0121] The ceramic substrate green film 9 preferably has a film thickness between 50 and 200 micrometers.

[0122] After laminating the ceramic substrate green film 9, the entire layer stack is compacted and sintered together. Preferably, the sintering is carried out at low temperature, for example between 850 and 950° C. in an air atmosphere, so that the ceramic substrate green film 9 is converted into an electrically insulating ceramic layer 10 and the metal paste 4 is converted into an electrically conductive metal structure 5.

[0123] The low sintering temperature during the co-sintering ensures that the PTC ceramic layer 3 is not oxidized or is hardly oxidized, so that the desired thermistor function is maintained.

[0124] For an alternative embodiment, the method can be modified in a simple manner. In the modified method, all steps that are not described in detail again are performed similarly to the previous method. In contrast to the previously described method, in the modified method, the PTC ceramic film 2 is not sintered before applying the metal paste 4 and the ceramic substrate green film 9. Rather, the metal paste 4 and the ceramic substrate green film 9 are applied to the unsintered green PTC ceramic film 2.

[0125] Unlike the previously described method, it is necessary that the ceramic substrate green film 9 has a material similar to that of the PTC ceramic film 2. Therefore, the ceramic substrate green film 9 includes HTCC ceramics like the PTC ceramic film 2.

[0126] Preferably, the PTC ceramic film 2 and the ceramic substrate green film 9 basically comprise the same ceramic material, which differs only in the amount of doping elements incorporated. A suitable material would be, for example, a barium titanate ceramic provided with a boron nitride sintering additive. The thermistor function of the PTC ceramic layer 3 or the electrical insulation properties of the other ceramic layer 10 is set by the amount of doping other elements (e.g. yttrium and / or manganese).

[0127] Alternatively, however, two different HTCC ceramics may also be selected for the PTC ceramic film 2 and the ceramic substrate green film 9 .

[0128] The entire stack including the films 2 and 9 and the metal paste 4 is sintered together at high temperature. Exemplary sintering temperatures are between 1000° C. and 1300° C. For example, the stack is sintered at 1150° C.

[0129] In a subsequent step, the formed monolithic thermistor element 100 may be reoxidized by heating to 600 to 800° C. in an air atmosphere to produce the thermistor function of the PTC ceramic layer 2 .

[0130] exist Figure 4 , a scanning electron microscope image of a cross section of the corresponding manufactured monolithic thermistor element 100 is shown.

[0131] For external electrical contacting, the wire 11 can then be connected to the conductive structure 5, for example. Figure 5 as shown in .

[0132] For example, for this purpose, the wire 11 is soldered on the surface of the conductive structure 5. For this purpose, a recess 12 can be provided in the electrically insulating ceramic layer 10, or the recess 12 can be formed subsequently by removing the ceramic material at the corresponding position. Preferably, the recess 12 is formed at or near the corner of the monolithic thermistor element 100.

[0133] The monolithic thermistor element 100 manufactured by the described method can be implemented significantly thinner than the thermistor element known so far. Due to the described layer structure and the whole layer stacked together to form the monolithic element, the additional assembly steps such as pressing and pasting each device are omitted. By omitting the steps, possible assembly errors are also avoided or minimized, such as forming gaps or cavities between each element. Therefore, the reliability of thermistor element 100 in operation and the durability of its function over time can be improved.

[0134] Furthermore, the described method enables flexible production of thermistor components 100 of different sizes and with different desired electrical properties by means of established automated production processes from multilayer ceramic technology.

[0135] Figure 6 The diagram of the cold resistance of the PTC ceramic layer 3 is shown as a function of the number of switching cycles. In each switching cycle, a DC voltage of 450 volts is applied to the PTC ceramic layer for 5 seconds, and then the current is cut off and the thermistor element 100 is cooled for 30 seconds. The cold resistance is measured in the cooling state. Then the next switching cycle is started.

[0136] This graph shows that the cold resistance is almost independent of the number of switching cycles, so the characteristics of the thermistor element 100 are not changed by the separation of the layers, for example. The fluctuations shown are due to the short cycle time, which prevents the establishment of thermal equilibrium.

[0137] Figure 7 Another diagram is shown, which shows the surge current curve of the monolithic thermistor element 100 according to the present invention. The thermistor element with a room temperature resistance of about 25 kΩ reaches the maximum surge current or minimum resistance after about 50 ms (milliseconds) when a DC voltage of 450 V is applied. With regard to the resistance-temperature data of the PTC ceramic used, this corresponds to a temperature of about 170 ° C. The voltage curve is also shown in the diagram in a stepped manner.

[0138] Since the conducting paths 8 are relatively long due to the diagonal arrangement of the conductive structures 5 on the PTC ceramic layer 3 , the current peak after switching on the current, which is visible in the diagram at approximately 50 ms, is reduced, thereby reducing power consumption and protecting the material under load.

[0139] The monolithic thermistor element 100 according to the present invention is preferably used in a heating module 200 . Figure 8 The heating module 200 shown in FIG. 1 includes a plurality of, for example, six, thermistor elements 100 .

[0140] Then, a fin structure 201 is applied to the surface of the electrically insulating but well-heat-conducting ceramic layer 10 , through which a fluid heat medium is conducted.

[0141] The heat medium is heated when flowing through the fin structure 201 , and can then output the heat to a location to be heated.

[0142] Corresponding heating modules are used, for example, in the automotive sector to heat the passenger compartment or in the electric vehicle sector to heat the battery to a uniform desired temperature of, for example, 40° C. The heating power of such a heating module 200 should preferably be at least 5 kW.

[0143] Due to the monolithic structure of the thermistor element 100 , no special requirements, such as high mechanical driving force, need be imposed when assembling the heating module 200 .

[0144] Reference numerals list

[0145] 1 Large PTC ceramic membrane

[0146] 2 PTC ceramic film

[0147] 3 PTC ceramic layer

[0148] 4 Metal slurry

[0149] 5 Conductive structure

[0150] 6 Continuous comb sections

[0151] 7-branch comb segment

[0152] 8 Transmission routes

[0153] 9 Ceramic substrate film

[0154] 10 Electrically insulating ceramic layer

[0155] 11 lines

[0156] 12 Depression in the ceramic layer

[0157] 100 Monolithic Thermistor Element

[0158] 200 Heating Module

[0159] 201 Fin structure

Claims

1. A method for establishing contact for a functional ceramic (3), comprising the following steps: Providing functional ceramics (2, 3); Applying metal slurry (4) on two opposite surfaces of the functional ceramic (2, 3); Laminating a ceramic substrate green film (9) on the metal slurry (4) on two opposite surfaces of the functional ceramic (2, 3); The functional ceramic (2, 3) and the ceramic substrate green film (9) are sintered together to form an electrically insulating ceramic layer (10), and the metal paste (4) is sintered together to form an electrically conductive metal structure (5).

2. The method according to claim 1, wherein the functional ceramic is provided as a functional ceramic film (2) in a green state.

3. The method according to claim 2, wherein a plurality of functional ceramic membranes (2) are separated from a larger-sized functional ceramic membrane (1).

4. The method according to claim 3, wherein each functional ceramic membrane (2) has a rectangular shape with dimensions of at least 3 cm x 10 cm.

5. The method according to any one of claims 1 to 4, wherein the functional ceramic (3) is a thermistor ceramic.

6. The method according to claim 5, wherein the functional ceramic (2, 3) is a PTC ceramic (2, 3).

7. The method according to claim 1, wherein a monolithic functional ceramic component (100) is formed.

8. The method according to claim 1, wherein the functional ceramic (3) is provided in a sintered state.

9. A method according to any one of claims 1 to 7, wherein the functional ceramic is provided as a film (2) in a green state and is sintered at a high temperature above 1000°C to form a functional ceramic layer (3) before applying the metal slurry (4) and the ceramic substrate green film (9), and wherein the subsequent co-sintering to form the functional ceramic element (100) is performed at a lower temperature below 1000°C.

10. A method according to any one of claims 1 to 7, wherein the functional ceramic is provided as a film (2) in a green state, and wherein the metal slurry (4) and the ceramic substrate green film (9) are applied to the functional ceramic (2) in a green state, and wherein subsequent co-sintering to form the functional ceramic element (100) is performed at a high temperature above 1000°C.

11. The method according to claim 10, wherein the functional ceramic film (2) and the ceramic substrate green film (9) have substantially the same composition, and the composition of the functional ceramic film (2) and the ceramic substrate green film (9) differ only in the proportion of doping materials in the composition.

12. The method according to any one of claims 1 to 11, wherein the functional ceramic membrane (2) has a rectangular shape with dimensions of at least 3 cm x 10 cm.

13. The method according to claim 1, wherein the metal paste (4) is applied in a structure which is converted into a comb-shaped metal structure (5) by the co-sintering.

14. The method according to claim 2, wherein in addition to the functional ceramic film (2), a ceramic substrate green film (9) in a green state is also applied, and the ceramic substrate green film (9) is converted into a non-green sintered state by a co-sintering step.

15. A monolithic functional ceramic element (100), comprising at least the following layers, which are laminated along a stacking direction perpendicular to an outer surface of the functional ceramic element (100): A functional ceramic layer (3) having two opposite surfaces, two electrically conductive metallic structures (5) having different polarities during operation, which are arranged in direct contact on each of the opposite surfaces of the functional ceramic layer (3), Two electrically insulating ceramic layers (10) are arranged on each of the opposite surfaces of the functional ceramic layer (3) and on the metal structure (5) arranged thereon.

16. The monolithic functional ceramic component (100) according to claim 15, wherein the functional ceramic layer (3) comprises or consists of a HTCC ceramic, and the electrically insulating ceramic layer (10) comprises or consists of a LTCC ceramic.

17. The monolithic functional ceramic component (100) according to claim 16, wherein the electrically insulating ceramic layer (10) comprises an aluminum oxide ceramic.

18. The monolithic functional ceramic component (100) according to claim 15, wherein the functional ceramic layer (3) and the electrically insulating ceramic layer (10) respectively comprise or consist of HTCC ceramic.

19. A monolithic functional ceramic element (100) according to claim 18, wherein the functional ceramic layer (3) and the electrically insulating ceramic layer (10) have substantially the same ceramic composition, and the ceramic composition of the functional ceramic layer (3) and the electrically insulating ceramic layer (10) differ only in the proportion of doping material in the ceramic composition.

20. The monolithic functional ceramic component (100) according to any one of claims 15 to 19, wherein the functional ceramic layer (3) comprises barium titanate ceramic.

21. The monolithic functional ceramic component (100) according to one of claims 15 to 20, wherein the electrically insulating ceramic layer (10) has a high thermal conductivity.

22. The monolithic functional ceramic component (100) according to claim 15, wherein the functional ceramic layer (3) has a layer thickness of at most 150 μm.

23. The monolithic functional ceramic component (100) according to claim 15, wherein the electrically insulating ceramic layer (10) has a layer thickness of at most 200 μm. 24 . The monolithic functional ceramic component ( 100 ) according to claim 15 , which has a thickness of a maximum of 500 μm in the stacking direction of the mentioned layers.

25. The monolithic functional ceramic component (100) according to claim 15, wherein the electrically conductive metal structure (5) is designed as a comb-like structure, each comprising a continuous section (6) and a plurality of sections (7) branching off from the continuous section.

26. A monolithic functional ceramic element (100) according to claim 25, wherein the conductive metal structures (5) are arranged non-overlappingly in the stacking direction, so that during operation all conduction paths (8) in the functional ceramic layer (3) extend diagonally, wherein the current is guided through the functional ceramic layer (3) via the conduction paths.

27. The monolithic functional ceramic component (100) according to claim 26, wherein the smallest conducting path (8) in the functional ceramic layer (3) is formed between two branch sections (7) of each conductive metal structure (5) and is at least 4 mm.

28. The monolithic functional ceramic component (100) according to one of claims 15 to 27, wherein the monolithic functional ceramic component (100) is a monolithic thermistor component (100).

29. The monolithic functional ceramic component (100) according to claim 28, wherein the functional ceramic (2, 3) is a PTC ceramic (2, 3).

30. The monolithic functional ceramic component (100) according to any one of claims 15 to 29, wherein the functional ceramic layer (3) originates from a functional ceramic film having dimensions of at least 3 cm x 10 cm.

31. A heating module (200) comprising the monolithic thermistor element (100) according to claim 28 or 29.

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