Method for manufacturing a monolithic functional ceramic element and a contact for a functional ceramic element

Abstract

The present invention relates to a method for manufacturing a contact for a functional ceramic (3), comprising the steps of providing a functional ceramic (2, 3), applying a metal paste (4) onto two opposing surfaces of the functional ceramic (2, 3), laminating a ceramic substrate green film (9) onto the two opposing surfaces of the functional ceramic (2, 3) on the metal paste (4), and co-sintering the functional ceramic (2, 3), the ceramic substrate green film (9) to form an electrically insulating ceramic layer (10), and the metal paste (4) to form an electrically conductive metal structure (5). The present invention further relates, in particular, to a monolithic functional ceramic element manufactured by the described method.

Description

[Technical Field]

[0001] The present invention relates to a functional ceramic element, a method for manufacturing a functional ceramic contact, and the use of the element in a heating module. [Background technology]

[0002] The use of functional ceramic elements in the heating module, in particular PTC ("Positive Temperature Coefficient" = Kaltleiter) thermistor elements, has the advantage that due to their behavior as temperature-dependent resistors, they automatically limit the power consumption when a certain temperature is reached. This property in particular prevents overloading of the heating module.

[0003] Such heating modules are increasingly used as heating resistors in electric vehicles. In these cases, the resistor must be driven directly by the high-voltage battery (usually 200-800 V). Therefore, the insulation strength must be designed accordingly.

[0004] Typically, the PTC element is electrically contacted by conductor tracks on two opposite sides, which are carried by the substrate, and the generated heat is dissipated to the other side.

[0005] The available heat output is highly dependent on the thermal path through the layer structure described above. Heat must travel from the source (PTC), through the contacts, through the substrate, and to the coupling surface. Thermal and electrical considerations for optimizing the heating element are often in conflict with each other. Prior art designs offer compromise solutions between power density, thermal agility, isolation capability or robustness, and reliability.

[0006] The PTC element itself acts as a heat source when an electric current is passed through it, generating Joule heating. However, this is not generated uniformly within the material, and depending on the geometry and inhomogeneity of the material, temperature gradients can be created by the electric field distribution within the component. Starting from hot spots, heat can first reach the surface of the element before being transmitted further. The relatively low thermal conductivity of PTC ceramics (typically around 5 W / mK) means that heat transfer can be very slow and gradual.

[0007] Document DE 11 2017 006 124 T5 describes a corresponding prior art electric heating device which has an insulating layer between the conductor tracks and the cooling fins.

[0008] EP 1 182 908 A1 describes a similar PTC heating device that has at least one PTC element and two contact plates that contact the PTC element. To connect the surfaces of the PTC element to the contact plates, a metal foil coated with adhesive is provided on both sides. Insulation of the contact plates is not considered here.

[0009] Furthermore, a PTC heater with reduced inrush current is known from DE 2017 101 946 A1.

[0010] Document DE 10 2016 108 604 A1 further describes how similar functional ceramics can be embedded in ceramic substrates. Summary of the Invention

[0011] It is an object of the present invention to provide an improved functional ceramic element that can also be used in a heating module.

[0012] The present invention relates to a method for producing a contact of a functional ceramic, in particular a PTC ceramic, and to a method for producing a functional ceramic element, particularly preferably a monolithic thermistor element, which method comprises at least the following steps:

[0013] In a first step, a functional ceramic is provided, hereinafter referred to as functional ceramic, which is preferably a thermistor ceramic, more preferably a PTC ceramic.

[0014] The functional or PTC ceramic is provided in a green state or in a sintered state. The functional ceramic is preferably provided as a film in the green state, which has a small film thickness compared to the film surface. Only in the sintered state does the functional ceramic have the desired functionality. The functional ceramic is also referred to herein as a green ceramic, which only has functionality in the sintered state. The same is true for PTC ceramics.

[0015] The functional ceramic can include any suitable ceramic material. A possible ceramic material is, for example, barium titanate ceramic. The ceramic can also include, for example, lead and / or strontium. The ceramic can further be doped with an appropriate amount of a suitable dopant, for example, yttrium or manganese, to provide the desired functionality, in particular thermistor functionality.

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

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

[0018] The metal paste preferably comprises a conductive metal such as nickel, cobalt, copper, silver, other precious metals, or powdered metal alloys, and may further comprise, for example, a suitable suspending agent.

[0019] In one embodiment, the metal paste is not applied flat, but in a form that can be transformed into a comb-shaped metal structure by a sintering step. To this end, the metal paste can be applied to a comb-like structure. Preferably, both comb-like structures are applied on opposite surfaces so that they do not overlap each other, but are rather offset. Each comb-like structure has a continuous section as a main strand and sections branching off therefrom as secondary strands.

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

[0021] In the next step, ceramic substrate green films are applied to two opposing surfaces of the functional ceramic and laminated together.

[0022] The ceramic substrate green film can include a ceramic material similar to the functional ceramic or another ceramic material. The ceramic material formed from the ceramic substrate green film after sintering is advantageously electrically insulating and highly thermally conductive.

[0023] The ceramic substrate green film is preferably applied so as to cover the entire surface of the functional ceramic and the metal paste applied thereon, either directly on the surface of the functional ceramic or on the metal paste applied thereon.

[0024] The above steps are preferably performed in the order described to provide a layer stack comprising two ceramic substrate green sheets sandwiching a functional ceramic, with a further structure consisting of a metal paste disposed between the functional ceramic and the ceramic substrate green film to create electrical contact with the functional ceramic.

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

[0026] In a preferred embodiment, the functional ceramic element is monolithic. By "monolithic" we mean that the functional ceramic element is made up of a single element rather than multiple separate elements, i.e., there is no need for mechanical connection or bonding of the (sub)elements.

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

[0028] The term "sintering" herein specifically refers only to the heat treatment process described above. The term "sintering" does not specifically mean that everything being sintered was previously in a green state. Also, even an already sintered structure can be subjected to a corresponding temperature treatment step, which then has little or no effect on the already sintered structure.

[0029] The functional ceramic element is preferably a thermistor element having thermistor functionality, in which case the functional ceramic is a ceramic having thermistor properties, in particular an NTC ceramic, or preferably a PTC ceramic.

[0030] A monolithic functional ceramic element is formed by co-sintering a functional ceramic to form a functional ceramic layer, a ceramic substrate green film to form an electrically insulating ceramic layer, and a metal paste to form an electrically conductive metal structure.

[0031] The functional ceramic element thus formed includes a functional ceramic layer, an electrically insulating ceramic layer, and an electrically conductive metal structure.

[0032] By forming a monolithic functional ceramic element, defects that may occur when assembling a single functional ceramic element from different sub-elements can be avoided. For example, voids that may occur during bonding can be avoided. Furthermore, adhesive leaks and contamination can be prevented. Furthermore, incomplete connections between the individual functional ceramic elements and the insulating ceramic element can be avoided.

[0033] Also, the method is simplified since there is no need to assemble various sub-elements.

[0034] By forming the functional ceramic layer, the conductive structure and the insulating ceramic layer in one monolithic element, the stability and time stability of the functional ceramic element can be improved.

[0035] Furthermore, this improves the thermal coupling between the individual layers, so that when the functional ceramic layer designed as a thermistor layer is heated by applying a voltage, the generated heat can be easily dissipated to the outside via the electrically insulating ceramic layer. For this reason, it is preferable that the ceramic layer is thin.

[0036] By applying film technology to the production of functional ceramic elements, it is possible to provide very thin functional ceramic elements with large areas. The thickness of the functional ceramic elements can be reduced. Furthermore, a single functional ceramic film can replace multiple conventional functional ceramic blocks, such as PTC blocks, each of which has a significantly smaller area dimension.

[0037] Furthermore, thin films allow the creation of a uniform electric field, and therefore, in the case of a thermistor element, uniform heating thereof, without the need for two-dimensional application of conductive structures.

[0038] Furthermore, the functional ceramic elements can be easily manufactured using existing automated processes for manufacturing multilayer ceramic elements.

[0039] Additionally, producing monolithic functional ceramic elements eliminates the need to provide individual components, such as conventional functional ceramic blocks, insulating ceramic parts, and conductive metal films, which must be manufactured in different locations and then assembled.

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

[0041] In the region of the cutout, the metal structure can be electrically contacted, for example, with a wire. The wire can be soldered to the metal structure, for example. Alternatively, the metal structure can be electrically contacted, for example, by a clamp contact. Other suitable contact methods are also possible.

[0042] Preferably, the metal structure does not extend to the edge of the ceramic layer, in order to create areas on the edge of the functional ceramic element to which no voltage is applied even during operation.

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

[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 prior to application of the metal paste and ceramic substrate. The functional ceramic preferably comprises an HTCC (High temperature cofired ceramics) ceramic material.

[0045] The metal paste is preferably dried at higher temperatures to evaporate the suspension or solvent before sintering.

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

[0047] The ceramic substrate green film preferably comprises LTCC (low temperature cofired ceramics) ceramic material. Subsequent co-sintering is preferably carried out at lower temperatures below 1000°C, preferably below 800°C.

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

[0049] In an alternative embodiment, a green film of the metal paste and ceramic substrate is applied onto the green functional ceramic provided as a green film, after which the layer stack thus formed is co-sintered, preferably at temperatures above 1000°C, preferably above 1300°C.

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

[0051] This allows the ceramics to be sintered at the same temperature. Furthermore, by selecting ceramics that are as similar as possible, the occurrence of mechanical stresses during sintering can 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] The functional ceramic film and the ceramic substrate green film preferably differ in composition only by the proportion of dopant in the composition. Such dopant may be, for example, yttrium or manganese. In particular, a high proportion of the dopant can increase the electrical resistivity of the ceramic material, providing an electrically insulating ceramic material.

[0054] Generally speaking, the functional ceramic film and the ceramic substrate green film can preferably have the same ceramic base material, with the PTC functionality or substrate functionality being tailored or defined by the choice of 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, which prevents the formation of defects in the functional ceramic element, such as the formation of voids between the layers. Furthermore, the selection of similar materials improves the thermal bonding between the individual layers.

[0056] In a preferred method, multiple functional ceramic films are separated from a larger functional ceramic film, which allows for simple continuous production of functional ceramic elements. By separating the functional ceramic from the film, large-area yet very thin functional ceramics can be easily produced.

[0057] The functional ceramic film is separated, for example, by cutting or punching.

[0058] The individual functional ceramic films preferably have a rectangular shape with dimensions of at least 3 cm x 10 cm. The thickness of the films is preferably 150 μm or less. The dimensions of the functional ceramic layers are reduced accordingly due to the usual sintering shrinkage.

[0059] The present invention further relates to a monolithic functional ceramic element, in particular a monolithic thermistor element. The functional ceramic element is preferably manufactured by the method described above. All features and embodiments described with respect to the method can also be applied to the functional ceramic element. In particular, the functional ceramic element can be a thermistor element in all embodiments and examples.

[0060] In particular, the present invention also relates to a monolithic functional ceramic element, preferably a monolithic thermistor element, comprising at least the following layers stacked in a stacking direction perpendicular to the outer surface of the monolithic functional ceramic element:

[0061] All features and embodiments described with respect to the method can also be applied to the monolithic functional ceramic element.

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

[0063] Furthermore, the monolithic functional ceramic element includes two electrically conductive metal structures that have different polarities in the operating state, and these metal structures are arranged in direct contact with one of the opposing surfaces of each of the functional ceramic layers, where direct contact means that the electrically conductive metal structures are directly present on the surface of the functional ceramic layer without the formation of 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] The functional ceramic element further includes two electrically insulating ceramic layers disposed on opposite surfaces of the functional ceramic layer and the metal structure disposed thereon, respectively, and the electrically insulating ceramic layers are disposed directly on the surfaces of the functional ceramic layer or the metal structure.

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

[0067] In this embodiment, preferably the electrically insulating ceramic layer comprises an aluminum oxide ceramic.

[0068] The electrically insulating ceramic layer should be a good thermal conductor rather than being made of a material with a high thermal conductivity.

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

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

[0071] In one embodiment, the ceramic compositions of the functional ceramic layer and the electrically insulating ceramic layer differ only in the percentage of dopant in the ceramic composition.

[0072] Such functional ceramic elements have a particularly high thermal coupling between the individual layers, which is advantageous for application as thermistor elements in heating modules, for example.

[0073] In any embodiment, the functional ceramic layer comprises a barium titanate ceramic and may further comprise, for example, a strontium compound, such as strontium oxide, and / or a lead compound, such as lead oxide, and a dopant, such as yttrium or manganese.

[0074] In one embodiment, the functional ceramic layer has a thickness of up to 150 μm. The functional ceramic layer preferably has a smaller layer thickness of 100 μm or less, or 50 μm or less. The layer thickness should be 40 μm or more.

[0075] Such a thin layer allows for easy generation of a uniform electric field, and even non-planar metal structures, such as comb-shaped structures, can be applied with a uniform electric field across the entire area of ​​the functional ceramic layer covered by the metal structure.

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

[0077] The insulating ceramic layer preferably covers the entire functional ceramic layer along two opposing surfaces, and the thin layer allows the overall size of the functional ceramic element to be reduced.

[0078] The thin insulating ceramic layer further allows good heat conduction to the outside of the functional ceramic element.

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

[0080] In one embodiment, the conductive metal structures are formed into a comb-like structure.

[0081] Each comb-like structure includes a continuous section and multiple sections branching off from the continuous section. The conductive metal structures are preferably arranged so that they do not overlap each other in the stacking direction, so that, during operation, all conductive paths in the functional ceramic layers, through which current flows, extend diagonally. Therefore, despite the thin thickness of the functional ceramic layers, a minimum conductive path of preferably at least 4 mm through the layers can be available.

[0082] The minimum conduction path, i.e., the shortest path along which current can flow between two metal structures with different polarities during operation, is preferably defined within the functional ceramic layer between two branch sections of one of the conductive metal structures.

[0083] Furthermore, by forming the comb-like structure, it is possible to save metal material.

[0084] The minimal conductive path thus ensured makes it possible to maintain a certain leakage path, thus achieving the desired insulating strength while still allowing the thickness of the functional ceramic layer to be further reduced.Despite the small film thickness, voltages of preferably 450 to 800 volts, even more preferably up to 1000 volts, can be applied in this way.

[0085] The guaranteed minimum conduction path also reduces the maximum current flow when a certain voltage is applied to the ceramic layer, thus reducing the energy consumption of a connected battery, for example, and reducing inrush current peaks that place a heavy load on the battery and connected switching electronics.

[0086] The present invention further relates to a heating module including one or more of the monolithic thermistor elements described above.

[0087] The improved thermal coupling, conduction, and transfer properties of the monolithic thermistor element improve the efficiency of the heating module.

[0088] The heating module is a fin heating module that includes a plurality of the described monolithic thermistor elements, for example, with fins applied to the surface through which a thermal fluid flows. During operation, the thermal fluid is heated by the thermistor elements. Corresponding heating modules can be used, for example, in the automotive sector and preferably have a thermal output of at least 5 kilowatts.

[0089] The present invention will now be described in more detail with reference to examples and related drawings.

[0090] The invention is not limited to the embodiments shown in the drawings.

[0091] Similar or apparently identical elements in the drawings are assigned the same reference signs.The drawings and proportions therein are not necessarily to scale. [Brief explanation of the drawings]

[0092] [Figure 1] FIG. 1 is a diagram showing an outline of a method for manufacturing a first embodiment of a monolithic thermistor element. [Figure 2] FIG. 2 shows a cross-sectional view of a first embodiment of a monolithic thermistor element showing minimum conductive paths. [Figure 3] FIG. 3 shows a microscope image of a portion of the edge region of the first embodiment of the monolithic thermistor element. [Figure 4] FIG. 4 shows a microscope image of a cross section of a second embodiment of a monolithic thermistor element. [Figure 5] FIG. 5 shows a top view of an embodiment of a monolithic thermistor element having external wire contacts. [Figure 6] 6 is a graph showing the change in cold resistance of the PTC ceramic layer of an exemplary thermistor element of the present invention as a function of the number of cycles, in which a DC voltage of 450 volts was applied to the thermistor element for 5 seconds, followed by a 30 second cooling period. [Figure 7] 7 shows the inrush current curve of an exemplary thermistor element of the present invention, showing the current I through the PTC ceramic layer as a function of time t from switch-on when a DC voltage U of 450 volts is applied. [Figure 8] FIG. 8 shows a heating module including a monolithic thermistor element. DETAILED DESCRIPTION OF THE INVENTION

[0093] 1 illustrates the fabrication of a first embodiment of a functional ceramic element of the invention, in this example specifically a monolithic thermistor element 100.

[0094] First, a PTC ceramic film 1 is provided as a functional ceramic film having a large area and a thin thickness. For example, the area or dimension of a large PTC ceramic film 1 is 4 inches by 4 inches. Alternatively, the area can be any other, preferably larger, dimension. The thickness of the PTC ceramic film 1 is 40 to 250 μm, preferably 50 to 150 μm, and more preferably less than 100 μm.

[0095] Any number of PTC ceramic films 2 having smaller areas can be cut out from the provided large PTC ceramic film 1. The individual PTC ceramic films 2 are, for example, punched or cut out from the large PTC ceramic film 1.

[0096] For example, three PTC ceramic films 2 are separated from a large PTC ceramic film 1 measuring 4 inches by 4 inches. The individual PTC ceramic films 2 are preferably rectangular, each measuring approximately 3 cm by 10 cm. The PTC ceramic film 2 can also have dimensions larger than 3 cm by 10 cm.

[0097] The PTC ceramic film 2 produced in this manner has a thinner thickness and a significantly larger surface area than conventionally used PTC ceramic blocks. As a result, whereas conventional processes use multiple PTC ceramic blocks, it is possible to produce a monolithic thermistor element including a single PTC ceramic film 2. Furthermore, the use of the PTC ceramic film 2 allows the thickness of the thermistor element to be reduced.

[0098] The singulated PTC ceramic film 2 is then fired in a subsequent step. Preferably, the PTC ceramic film is sintered at a high temperature, for example, between 1240°C and 1320°C, to produce the desired thermistor function.

[0099] During sintering, the area of ​​the PTC ceramic film 2 is reduced by the typical sintering shrinkage. Sintering converts the green PTC ceramic film 2 into a sintered functional ceramic layer, i.e., the PTC ceramic layer 3. The area of ​​the PTC ceramic layer 3 is, for example, 26 mm x 78 mm, preferably 3 mm x 9 mm or less.

[0100] Next, a conductive metal structure 5 is applied onto the sintered PTC ceramic layer 3. For this purpose, for example, a metal paste 4 is printed or sputtered onto two opposing surfaces of the PTC ceramic layer 3. The metal paste 4 is preferably applied in a comb-like pattern.

[0101] The metal paste 4 contains, for example, nickel, copper, aluminum, a noble metal, or an alloy of these metals.

[0102] As shown, the comb comprises a continuous section 6, which is the main strand of the comb, from which a number of sections 7, which are the secondary strands of the comb, branch off, preferably at right angles. The metal paste 4 is therefore not spread evenly on the surface.

[0103] Even if the metal paste 4 is not applied in a planar manner, the advantageously thin thickness of the PTC ceramic layer 3 of the present invention makes it possible to form a uniform electric field in the PTC ceramic layer 3 in an operating state. This, in particular, allows the PTC ceramic layer 3 to convert electric current into thermal energy uniformly during operation.

[0104] The thermal energy is preferably dissipated to the surroundings via the highly thermally conductive ceramic layer 10. The dissipation of heat to the surroundings is further facilitated by the excellent thermal bonding between the co-sintered individual layers of the monolithic thermistor element 100.

[0105] The comb-like structures on both surfaces of the PTC ceramic layer 3 are configured so that they do not overlap each other in the direction perpendicular to the surface of the PTC ceramic layer 3. This means that when viewed from one side of the PTC ceramic layer 3, in the theoretically transparent PTC ceramic layer 3, both comb-like structures are visible next to each other. The main strands 6 of the comb-like structures are applied to different sides of each surface. The branch sections 7 are applied next to each other with recesses between the sections 7 so that the sections 7 of the two comb-like structures do not overlap but each points toward the other comb-like structure.

[0106] This structuring of the metal paste 4, and therefore the conductive metal structure 5 subsequently formed therefrom, maximizes the conductive path 8 in the PTC ceramic layer 3, as shown in Figure 2. Here, the conductive path 8 is the distance over which current flows in the PTC ceramic layer 3 in an operating state. The shortest conductive path 8 in the PTC ceramic layer 3 between two metal structures 5 is preferably 4 mm or longer. This shortest conductive path 8 is preferably formed between two adjacent branch sections 7 of one of the two conductive metal structures 5.

[0107] The described minimum conductive path 8 allows the application of high voltages, for example in the range of 400 to 1000 volts, preferably in the range above 800 volts, despite the small ceramic thickness.

[0108] The applied metal paste 4 is then dried at a temperature of, for example, 180° C. or higher for a time span of, for example, 30 minutes or more.

[0109] Thereafter, as shown in Figure 3, a ceramic substrate green film 9 is applied on both surfaces of the PTC ceramic layer 3, covering the entire surface of the PTC ceramic layer 3 and the metal paste 4 applied thereon. The thickness of the metal paste 4 structure is negligible compared to the thickness of the ceramic layer or film and is in the micrometer or submicrometer range.

[0110] The PTC ceramic layer 3 preferably comprises a high temperature sintered HTCC ceramic, while the other ceramic layer 10 formed from the ceramic substrate green film 9 preferably comprises a relatively low temperature sintered LTCC ceramic material.

[0111] The material of the PTC ceramic layer 3 is, for example, a barium titanate ceramic or a similar material, which may further contain other metals such as lead or strontium. Advantageously, it is a lead-free ceramic. The ceramic of the PTC ceramic layer 3 is preferably doped with further elements, such as yttrium and / or manganese, so that a thermistor function is created.

[0112] The LTCC ceramic of the other ceramic layer 10 is, for example, an aluminum oxide ceramic or similar material, and is preferably a good thermal conductor but electrically insulating.

[0113] The ceramic substrate green film 9 preferably has a film thickness of 50 to 200 micrometers.

[0114] After laminating the ceramic substrate green film 9, the entire laminate is pressed and co-sintered, preferably at a low temperature of, for example, 850 to 950°C in an air atmosphere, to convert the ceramic substrate green film 9 into an electrically insulating ceramic layer 10 and the metal paste 4 into a conductive metal structure 5.

[0115] The low sintering temperature during co-sintering ensures that the PTC ceramic layer 3 is not or only slightly oxidized, thereby maintaining the desired thermistor function.

[0116] In an alternative embodiment, the method may be slightly modified, in which all steps not re-described in detail are performed in the same manner as the previously described method.

[0117] Unlike the previously described method, in the modified process, the PTC ceramic film 2 is not sintered before applying the metal paste 4 and ceramic substrate green sheet 9. Rather, the metal paste 4 and ceramic substrate green sheet 9 are applied onto the unsintered green PTC ceramic film 2. Unlike the previously described method, the ceramic substrate green film 9 must have the same material as the PTC ceramic sheet 2. Thus, the ceramic substrate green film 9, like the PTC ceramic sheet 2, is made of an HTCC ceramic.

[0118] Preferably, the PTC ceramic film 2 and the ceramic substrate green film 9 comprise essentially the same ceramic material, differing only in the amount of added doping elements. A suitable material is, for example, a barium oxide ceramic with an additive of boron nitride. The thermistor function of the PTC ceramic layer 3 and / or the electrical insulating properties of the additional ceramic layer 10 are adjusted by the doping amount of additional elements, such as yttrium and / or manganese.

[0119] However, alternatively, two different HTCC ceramics can be selected for the PTC ceramic film 2 and the ceramic substrate green film 9 .

[0120] The entire stack including the films 2 and 9 and the metal paste 4 is co-sintered at high temperature. An exemplary sintering temperature is 1000-1300°C. For example, the stack is sintered at 1150°C.

[0121] In a next step, the formed monolithic thermistor element 100 can be re-oxidized by heating to 600-800° C. in an air atmosphere to produce the thermistor function of the PTC ceramic layer 2 .

[0122] FIG. 4 shows a scanning electron microscope image of a cross section of a correspondingly manufactured monolithic thermistor element 100.

[0123] For external electrical contact, wires 11 can be connected to the conductive structure 5 as shown in FIG.

[0124] For example, wires 11 are soldered to the surface of the conductive structure 5. Here, notches 12 can be provided in the electrically insulating ceramic layer 10, or the notches 12 can be formed at appropriate positions by subsequently removing ceramic material. These notches 12 are preferably formed at or near the corners of the monolithic thermistor element 100.

[0125] The monolithic thermistor element 100 produced by the described method can be significantly thinner than known thermistor elements. The described layer structure and co-sintering of the entire layer stack to form the monolithic element eliminates the need for additional assembly steps, such as compressing and gluing individual devices. Eliminating these steps can avoid or minimize assembly errors, such as gaps or voids between individual elements. This can improve the reliability of the thermistor element 100 during operation and the stability of its functionality over time.

[0126] Furthermore, the described method allows for the flexible production of thermistor elements with different dimensions and different desired electrical properties by established automated manufacturing processes from multilayer ceramic technology.

[0127] 6 is a graph showing the cold resistance of the PTC ceramic layer 3 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 3 for 5 seconds, after which the current is turned off and the thermistor 100 is allowed to cool for 30 seconds. The cold resistance is measured in each case in the cooled state, after which the next switching cycle begins.

[0128] This figure shows that the cold resistance is largely independent of the number of switching cycles, i.e., delamination, for example, does not change the characteristics of the thermistor element 100. The variation shown here is due to the short cycle times preventing the establishment of thermal equilibrium.

[0129] 7 shows another diagram illustrating the inrush current curve of the monolithic thermistor element 100 of the present invention. A thermistor with a room temperature resistance of about 25 kΩ reaches its maximum inrush current or minimum electrical resistance after about 50 ms (milliseconds) when a DC voltage of 450 volts is applied. Referring to the resistance-temperature data of the PTC ceramic used, this corresponds to a temperature of about 170° C. The voltage curve is also displayed as a step in the graph.

[0130] The relatively long conductive paths 8 due to the diagonal arrangement of the conductive structures 5 on the PTC ceramic layer 3 allow to reduce the current spike after switching on the current, as can be seen in the figure at about 50 ms, thus reducing the power consumption and saving on the material required.

[0131] The monolithic thermistor element 100 of the present invention is preferably used in a heating module 200. The heating module 200 shown in Figure 8 includes a plurality of thermistor elements 100, for example six.

[0132] A layer structure 201 is then applied to the surface of the electrically insulating yet highly thermally conductive ceramic layer 10, through which a fluid heat transfer medium is passed.

[0133] The heat transfer medium is heated as it flows through the layered structure 201 and can then release the heat to the location to be heated.

[0134] 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, for example 40° C. The heating power of such a heating module 200 is preferably at least 5 kilowatts.

[0135] Due to the monolithic structure of the thermistor element 100, no special requirements such as high mechanical driving forces are necessary when assembling the heating module 200. [Explanation of symbols]

[0136] 1 Large PTC ceramic film (gross PTC-Keramikfolie) 2 PTC ceramic films (PTC-Keramikfolien) 3 PTC ceramic layer (PTC-Keramikschicht) 4 Metal paste 5 Conductive structures 6. Continuous pectinate sections (zusammenhaengender Kammabschnitt) 7 Branched comb sections 8 Wiring path (Leitungsweg) 9. Ceramic substrate green film 10 Electrically insulating ceramic layer 11 Wire 12 Cutting out the ceramic layers 100 Monolithic Thermistor Element 200 Heating Module (Heizmodul) 201 Laminated Structures

Claims

1. A method for manufacturing a contact for a functional ceramic (3), comprising the steps of: Providing a functional ceramic (2, 3); applying a metal paste (4) onto two opposing surfaces of said functional ceramic (2, 3); laminating a ceramic substrate green film (9) on the two opposing surfaces of the functional ceramic (2, 3) on the metal paste (4); and co-sintering the functional ceramic (2, 3), the ceramic substrate green film (9) to form an electrically insulating ceramic layer (10), and the metal paste (4) to form a conductive metal structure (5). method.

2. The functional ceramic is provided as a green functional ceramic film (2); The method of claim 1.

3. The plurality of functional ceramic films (2) are separated from the larger functional ceramic film (1); The method of claim 2.

4. Each of the functional ceramic films (2) has a rectangular shape with dimensions of at least 3 cm x 10 cm; The method of claim 3.

5. The functional ceramic (3) is a thermistor ceramic.

5. The method according to any one of claims 1 to 4.

6. The functional ceramic (2, 3) is a PTC ceramic (2, 3), The method of claim 5.

7. A monolithic functional ceramic element (100) is formed.

7. The method according to any one of claims 1 to 6.

8. The functional ceramic (3) is provided in a sintered state.

8. The method according to any one of claims 1 to 7.

9. The functional ceramic is provided as a green film (2), Before applying the metal paste (4) and the ceramic substrate green film, the green film is fired at a high temperature exceeding 1000°C to form a functional ceramic layer (3); The subsequent common sintering to form the functional ceramic element (100) is carried out at a low temperature below 1000°C.

8. The method according to any one of claims 1 to 7.

10. The functional ceramic is provided as a green film (2), The metal paste (4) and the ceramic substrate green film (9) are applied onto the functional ceramic (2) in a green state; The subsequent common sintering to form the functional ceramic element (100) is carried out at high temperatures above 1000°C, 8. The method according to any one of claims 1 to 7.

11. The functional ceramic film (2) and the ceramic substrate green film (9) have substantially the same composition, The composition of the functional ceramic film (2) and the ceramic substrate green film (9) differs only in the proportion of dopant in the composition. The method of claim 10.

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

13. The metal paste (4) is applied to a structure that is transformed by common sintering into a comb-shaped metal structure (5), 13. The method of any one of claims 1 to 12.

14. In addition to the functional ceramic film (2), a green ceramic substrate green film (9) is also applied, converted to a non-green sintered state by a common sintering step; 3. The method of claim 2.

15. A monolithic functional ceramic element (100) stacked in a stacking direction perpendicular to the outer surface of the functional ceramic element (100), a functional ceramic layer (3) having two opposing surfaces; two electrically conductive metal structures (5) having different polarities during operation, the two electrically conductive metal structures (5) being arranged in direct contact with respective ones of the opposing surfaces of the functional ceramic layer (3); Two electrically insulating ceramic layers (10) disposed on opposite surfaces of the functional ceramic layer (3) and the metal structure (5) disposed thereon; A monolithic functional ceramic element having at least:

16. The functional ceramic layer (3) comprises or consists of a HTCC ceramic, The electrically insulating ceramic layer (10) comprises or consists of LTCC ceramic; 16. The monolithic functional ceramic component of claim 15.

17. The electrically insulating ceramic layer (10) comprises an aluminum oxide ceramic.

17. The monolithic functional ceramic component of claim 16.

18. The functional ceramic layer (3) and the electrically insulating ceramic layer (10) each contain or consist of an HTCC ceramic.

16. The monolithic functional ceramic component of claim 15.

19. the functional ceramic layer (3) and the electrically insulating ceramic layer (10) have substantially the same ceramic composition; The ceramic compositions of the functional ceramic layer (3) and the electrically insulating ceramic layer (10) differ only in the proportion of dopant in the ceramic composition.

20. The monolithic functional ceramic component of claim 18.

20. The functional ceramic layer (3) contains barium titanate ceramic, 20. A monolithic functional ceramic element according to any one of claims 15 to 19.

21. The electrically insulating ceramic layer (10) has a high thermal conductivity.

21. A monolithic functional ceramic element according to any one of claims 15 to 20.

22. The thickness of the functional ceramic layer (3) is 150 μm or less.

22. A monolithic functional ceramic element according to any one of claims 15 to 21.

23. The thickness of the electrically insulating ceramic layer (10) is 200 μm or less.

23. A monolithic functional ceramic element according to any one of claims 15 to 22.

24. having a thickness of up to 500 μm in the stacking direction of the layers; 24. A monolithic functional ceramic element according to any one of claims 15 to 23.

25. The plurality of conductive metal structures (5) are formed in a comb-like structure, each comprising a continuous section (6) and a plurality of branch sections (7) branching off from the continuous section.

25. A monolithic functional ceramic element according to any one of claims 15 to 24.

26. The conductive metal structures (5) are not arranged so as to overlap each other in the stacking direction, In operation, current is conducted through the functional ceramic layer (3), and all conductive paths (8) within the functional ceramic layer (3) extend obliquely.

26. The monolithic functional ceramic component of claim 25.

27. In the functional ceramic layer (3), a minimum conductive path (8) is formed between the two branch sections (7) of each of the conductive metal structures (5), and is at least 4 mm.

27. The monolithic functional ceramic component of claim 26.

28. The monolithic functional ceramic element (100) is a monolithic thermistor element (100).

28. A monolithic functional ceramic element according to any one of claims 15 to 27.

29. The functional ceramic (2, 3) is a PTC ceramic (2, 3), 30. The monolithic functional ceramic component of claim 28.

30. The functional ceramic layer (3) is obtained from a functional ceramic film having dimensions of at least 3 cm x 10 cm; 30. A monolithic functional ceramic element according to any one of claims 15 to 29.

31. A heating module (200) comprising a monolithic thermistor element (100) according to any one of claims 28 or 29.

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