Printable paste, printed thin film, manufacturing method, temperature sensor, inrush current limiter, use of the printed thin film in an electrical component

Abstract

The invention relates to a printable paste 20 for producing an electrical component, comprising a printable, non-conductive coating 22, electrically conductive particles 25 and and ceramic NTC particles 30, wherein the electrically conductive particles 25 and the ceramic NTC particles 30 are homogeneously distributed in the printable, non-conductive coating 22. The invention also relates to a method for producing a printable paste, to a thin film comprising the printable paste, to a method for producing the thin film, and to a temperature sensor and an inrush current limiter comprising the thin film having the printable paste.

Description

[0001] Printable paste, manufacturing process of a printable paste, printed thin film with the printable paste, manufacturing process of the printed thin film, as well as temperature sensors and inrush current limiters with the printed thin film, use of the printed thin film in an electrical component

[0002] The present invention relates to a printable paste according to claim 1, a method for producing the printable paste according to claim 15, a printed thin film comprising the printable paste according to claim 17, a method for producing the printed thin film according to claim 19, and a temperature sensor according to claim 20, an inrush current limiter according to claim 21 and the use of the printed thin film in an electrical component according to claim 22.

[0003] Technological background

[0004] In the field of printed electronics, it is often necessary to integrate circuit elements with defined temperature dependence and accuracy, such as temperature sensors or inrush current limiters. This can be achieved by mounting components on printed or etched circuits or by printing functional pastes. Mounted SMD (surface mounted device) components, such as platinum resistors or ceramic NTCs (negative temperature coefficient), have the disadvantage that expensive conductive adhesives are often used when mounting printed electrodes. Etched electrodes require reflow soldering processes, which require the base material to be highly temperature stable. Furthermore, the geometric dimensions of the components result in locally increased thickness in the integration area. This can be disadvantageous, especially in applications where a flat design without elevations is required.Furthermore, populated components lead to a reduction in flexibility or reduced mechanical strength. Due to the manufacturing tolerances in cost-effective printing processes, state-of-the-art printed temperature sensors often require complex calibration to achieve acceptable measurement accuracy. Furthermore, the calibration data must be transferred to the control or measuring device. To achieve accurate measurement results, a four-wire measurement may also be necessary.

[0005] EP 2 919239 A1 is known from the prior art. It discloses an NTC sensor with a printable NTC paste based on silicon-carbon nanoparticles, which are printed on gold electrodes. The silicon crystals are selected from doped or undoped silicon, and the carbon particles are selected from the group consisting of carbon black, graphite flakes, and graphene nanoplatelets.

[0006] The disadvantage of the known solution is that silicon is used as the NTC material, and both undoped and doped silicon are very energy-intensive to produce. The change in NTC resistance with temperature is determined by the silicon (an intrinsic property) and can only be influenced to a limited extent by doping. In the presence of oxygen, silicon forms an oxide layer (SiO2). This layer can be up to 7 nm thick under natural ambient conditions. This changes the contact resistance from particle to particle, leading to reduced long-term stability.

[0007] WO 2018 / 164570 A1 is known from the prior art. It discloses a printed temperature sensor comprising an electrical circuit with a pair of electrodes. The sensor material disposed between the electrodes comprises semiconducting microparticles comprising an NTC material with a negative temperature coefficient (NTC), wherein the microparticles are mixed in a dielectric matrix. The dielectric matrix serves as a binder for printing the sensor material, with the microparticles contacting each other to form an interconnected network through the dielectric matrix, wherein the interconnected network of microparticles acts as a conductive path with a negative temperature coefficient between the electrodes.

[0008] A disadvantage of these known solutions is that, due to the very high solids content in the sensor material, the sensor material, comprising the matrix and the microparticles, becomes brittle, thereby reducing the flexibility of the temperature sensor. Another disadvantage is that the particle shape and particle size strongly depend on the conductivity of the NTC material, so that a volume fraction of greater than 50% of NTC material is necessary. US 2022 / 065707 A1 is known from the prior art. This discloses various thin films for a temperature sensor, with at least one embodiment being a thin film created using a drop-deposition technique. This embodiment comprises a lacquer and conductive components. Conjugated polymer units doped with alkali metals are provided as the conductive component.

[0009] The disadvantage of this known solution is that the resistance is largely dominated by the resistance of the gaps between the non-contacting conductive polymer units. This resistance is temperature-dependent and results in an NTC (electron hopping transport) effect.

[0010] US 3408311 A is known from the prior art. It discloses a temperature sensor made of a thin film, the base being a powder comprising an inorganic binder.

[0011] The disadvantage of this solution is that such thin films have to be sintered and are therefore unusable for printed electronics.

[0012] Description of the invention

[0013] An object of the invention is to avoid at least one of the disadvantages of the prior art, and in particular to create an improved printable paste, which is preferably a functional paste for electrical components, with which a thin film can be printed in the wet state, which thereby has a weak electrical conductivity, and in the dry state is not brittle and becomes increasingly electrically conductive, while exhibiting a strongly exponential temperature dependence. Furthermore, improved manufacturing methods are to be created, as well as improved temperature sensors or improved inrush current limiters. In addition, the printed thin film comprising the printed paste is to be usable in an electrical component.

[0014] This object is achieved by the features of the independent patent claims. Advantageous further developments are set forth in the figures and in the dependent patent claims. A printable paste according to the invention for producing an electrical component comprises a printable, electrically non-conductive lacquer, electrically conductive particles, and ceramic NTC particles, wherein the electrically conductive particles and the ceramic NTC particles are homogenized and distributed throughout the printable, electrically non-conductive lacquer. In the homogenized, printable paste, the particles are evenly distributed and form a weakly electrically conductive network, whereby the printable paste is easy to process and can be printed reproducibly. For example, when homogenizing the printable paste, a stirrer with a crossbar stirrer is used, with a stirring speed of 500 revolutions per minute being used for 5 minutes.The quantity and shape of the conductive particles in the paste determine the resistance of a thin film at, for example, 25°C (R25). By adding conductive particles to the printable resist and the ceramic NTC particles, percolation in the paste is significantly improved, with the conductive particles improving the contact between the ceramic NTC particles. The resistance behavior in the paste, or in the thin film produced with it, is largely determined by the intrinsic properties of the NTC particles. The selection of the NTC particle materials in the paste enables the resistance behavior in the thin film to be adjusted, in particular its slope (B value) or the adjustment of the exponential temperature dependence of the thin film. This allows the NTC resistance behavior to be adjusted independently of the resistance at, for example, 25°C.Through sufficient percolation of the NTC particles in the dried thin film, the resistance is largely dominated by the ceramic NTC particles, while the resistance in the non-conductive lacquer between the particles plays only a minor role. Carbon, carbon black, nanotubes, silver, iron, steel, copper, or similar electrically conductive particles are particularly used as conductive particles. Without conductive particles in the printable paste, at least 50% by volume, or up to 70% by volume, of ceramic NTC particles is required to ensure the desired percolation in the dried state, for example, in the form of a printed thin film, and thus a conductive thin film layer with a strongly exponential temperature dependence. This means that the improved printable paste can be produced with less energy consumption per kilogram of paste produced than comparable printable pastes from the state of the art.This protects the environment because fewer CO2 emissions are generated. Furthermore, costs, especially CO2 taxes, can be saved. The printable varnish is electrically non-conductive, so electrical contact in the wet paste is impossible. The printable paste has a viscosity of 15 Pa s to 100 Pa s in its flowable state, with the viscosity being determined using a Brookfield method. Brookfield viscosity usually refers to a viscosity measurement using a Brookfield viscometer. A viscometer motor rotates a spindle at a specific speed (measured in rpm) or shear rate, and the viscometer measures the resistance to rotation and provides a viscosity value.The printable paste in its flowing form has a viscosity of preferably 20 Pa s to 60 Pa s, so that a suitable thin film between 10 micrometers and 250 micrometers can be produced easily and reproducibly, for example using a screen printing technique.

[0015] Preferably, the conductive particles in the printable varnish are arranged such that the percolation threshold in the paste is exceeded. This requires a smaller quantity of ceramic NTC particles in the printable paste. The conductive particles improve the contact between the ceramic NTC particles. In the flowing or wet paste, the ceramic NTC particles are spaced apart from each other on average, with at least one conductive particle essentially being located between at least two ceramic NTC particles on average.

[0016] Percolation describes the formation of connected areas (clusters) between the ceramic NTC particles and the conductive particles in the printable paste or in the thin film produced with it. In its flowing or wet form, the printable paste in question therefore statistically exhibits no electrically conductive connection or very weak electrical conductivity, since the printable coating is electrically non-conductive and there are hardly any continuous clusters between the ceramic NTC particles and the conductive particles. The resistance in the flowing or wet form is therefore high-ohmic or infinite.

[0017] Preferably, the conductive particles are smaller than 100 micrometers. A paste with conductive particles with an average diameter of less than 100 micrometers can be printed easily and reproducibly. In particular, the resistance behavior in a thin film produced with the printable paste can be reproducibly adjusted. Preferably, conductive particles smaller than 20 micrometers are present. Conductive particles with an average diameter of less than 20 micrometers diffuse better on average between the ceramic NTC particles, thus improving percolation and resulting in an improved, strongly exponential temperature behavior in the thin film produced with the printable paste.

[0018] Preferably, the printable paste contains at least less than 50% conductive particles by volume. By varying the volume fraction of the conductive particles, the conductivity in the printable paste can be finely tuned. This allows production variations in the particle shape, size, and conductivity of the ceramic NTC particles to be compensated for without changing the steepness of the resistance behavior. Thus, the shape or steepness of the NTC curve can be adjusted independently of each other by selecting the NTC ceramic, and the resistance at 25°C, for example, can be adjusted by varying the proportion of conductive particles.

[0019] Preferably, the ceramic NTC particles are powder particles so that the addition of the ceramic NTC particles to the printable paste is easy to dose.

[0020] Preferably, the ceramic NTC particles have a diameter of less than 100 micrometers, so that the temperature behavior of the ceramic NTC particles is adjustable. Preferably, the ceramic NTC particles have a diameter between 10 micrometers and 60 micrometers, so that printed thin films can be produced reproducibly.

[0021] Preferably, the conductive particles have a diameter of less than 50% of the diameter of the ceramic NTC particles. This allows the conductive particles to diffuse more easily between the ceramic NTC particles during thin film formation, thereby exceeding the percolation threshold. A thin film formed using the printable paste is sufficiently elastic to allow it to be printed onto film substrates without forming cracks or craters in the thin film.

[0022] Preferably, the conductive particles have a diameter of less than 30% of the diameter of the ceramic NTC particles. This further improves the diffusion of the conductive particles, and the thin film formed from the printable paste is not brittle. Preferably, the conductive particles are rod-shaped or disc-shaped. This ensures stable and reliable percolation between the ceramic NTC particles with even smaller amounts of conductive particles. For example, a rod-shaped conductive particle is a nanotube, and a disc-shaped conductive particle is a silver particle, carbon particle, or graphite particle.

[0023] The ceramic NTC particles preferably comprise metal oxides, for example, metal oxides of the elements manganese, iron, nickel, cobalt, or titanium. This allows for improved NTC behavior to be achieved in order to achieve the desired highly exponential temperature behavior. NTC materials, also called thermistors, are temperature-dependent resistors that have a negative temperature coefficient as their key property and conduct electrical current better at high temperatures than at low temperatures.

[0024] The printable paste preferably contains at least less than 50% by volume of ceramic NTC particles. The lower solids content of the NTC material in the printable paste increases the flexibility and mechanical stability of an applied thin film comprising the printable paste. A processed thin film (printed and dried) with the printable paste is very stable and insensitive to resistance drift, i.e., changes in electrical resistance over time, even under high thermal cycling. On average, the NTC particles thus form a maximally weakly conductive, continuous network throughout the printable paste. This makes the printable paste particularly easy to print and process.

[0025] Preferably, the printable paste contains more than 10% by volume of ceramic NTC particles to ensure sufficiently high percolation, so that a strongly exponential temperature behavior is guaranteed.

[0026] Preferably, the printable, electrically non-conductive varnish is solvent-based. Ceramic NTC particles can be water-sensitive, so the use of a solvent-based printable varnish in the printable paste keeps the temperature behavior of the printable paste reproducibly stable over many temperature cycles. Solvent-based printable varnishes comprise at least acrylic, epoxy, silicone, polyurethane, or polyamide, and other components. Any resistance drifts can be minimized. Alternatively, the printable varnish is water-based, allowing the printable paste to be produced in a more environmentally friendly manner.

[0027] The printable, non-conductive coating preferably comprises at least one organic polymer. This is simply dried at low temperatures, below 200°C. During drying, the particles in the paste do not fuse together; instead, the solvents are simply removed and any cross-linking reactions are activated. This allows for easy production of thin films on film substrates without damaging the film, making them particularly suitable for printed electronics.

[0028] A method according to the invention for producing a printable paste, in particular a paste as described above, comprises the following steps: a) Providing a printable, electrically non-conductive varnish b) Adding electrically conductive particles to the printable, electrically non-conductive varnish, wherein the addition takes place below the percolation threshold c) Adding ceramic NTC particles to the printable, electrically non-conductive varnish d) Homogenizing the electrically conductive particles and the NTC particles in the printable, electrically non-conductive varnish.

[0029] This allows for a uniform distribution of the particles in the printable paste, forming a weakly electrically conductive network. The printable paste is easy to process and prints reproducibly. By adding conductive particles to the printable, electrically non-conductive lacquer and the ceramic NTC particles, percolation in the paste is significantly improved, with the conductive particles improving the contact between the ceramic NTC particles. Without conductive particles in the printable paste, at least 50% by volume, and preferably 70% by volume, of ceramic NTC particles is required to achieve the desired percolation in the dried state, for example, in the form of a thin film, and thus a conductive layer with a strongly exponential temperature dependence.Thus, the printable paste according to the invention can be produced using the process with less energy consumption per kilogram of paste produced than comparable printable pastes from the prior art. This protects the environment because fewer CO2 emissions are generated. Furthermore, costs, especially taxes, can be saved. In particular, the process is carried out at least in the previously specified order a) to d), so that the setting of a target value for the temperature dependence is improved without having to change the design of the printed thin film.

[0030] Preferably, at least less than 50% by volume of the ceramic NTC particles are added. The lower solids content of the NTC material in the printable paste increases the flexibility and mechanical stability of a deposited thin film. A processed thin film layer (printed and dried) with the printable paste is very stable and insensitive to resistance drift.

[0031] Preferably, more than 10% by volume of the ceramic NTC particles are added to ensure a sufficiently high percolation so that a strongly exponential temperature behavior can be guaranteed.

[0032] A printed thin film according to the invention for an electrical component comprises at least one printable paste, as described above. The printed thin film can be configured as a thin film layer in an electrical component. The lower solids content of the NTC material increases the flexibility and mechanical stability of the dried thin film. Fracture of the thin film under mechanical stress on the electrical component can be prevented because the thin film is not brittle in the dry state. Furthermore, the electrical resistance of the dried thin film layer can be adjusted to a target value without having to change the design of the electrical component. The shape of the strongly exponential temperature dependence of the resistance is retained (temperature difference -100°C). Change in resistance greater than a factor of 20). As a result, high manufacturing tolerances of the ohmic resistance only lead to a relatively small measurement inaccuracy. The dried printed thin film is comparable in its properties to a ceramic NTC. The resistance of the finished component can be influenced by the electrical properties of the ceramic NTC particles used or the conductive particles in the printable paste, their concentration, the printed thin film thickness, the printed area, and the electrode spacing and width of the printed electrodes. The thin film can be less than 250 micrometers thick, and especially between 10 and 100 micrometers thick, without becoming brittle and breaking. Furthermore, the thin film can be produced with less energy consumption per kilogram of paste than comparable thin films of printable pastes from the state of the art.

[0033] The printed thin film is preferably produced using a screen printing process. Screen printing is primarily used, but offset, inkjet, or pad printing processes are also suitable. The screen printing used here is carried out using a screen mesh, whereby the wet film thickness can be roughly adjusted by varying the screen printing parameters (squeegee speed, squeegee angle, etc.). It is preferred that the mesh size of the screen mesh is larger than the particle size to prevent clogging of the screen mesh during printing. The maximum particle size limits the selection of possible screen meshes used for the screen printing process. The particle size must be smaller than the mesh size of the screen mesh or the characteristic size for the other printing processes mentioned above.

[0034] Furthermore, a method according to the invention for producing an electrically conductive thin film for an electrical component using a previously described printable paste is disclosed. The printable paste is printed onto a substrate, and at least the printable paste is dried at a temperature of less than 200°C, so that the paste becomes electrically conductive and, in particular, an electrical connection is formed between the electrically conductive particles and the ceramic NTC particles, thereby creating a strongly exponential temperature dependence in the electrically conductive thin film. In this process, an adjacent network is formed with the electrically conductive particles and the ceramic NTC particles, without the particles fusing together. The drying temperature and time depend on the printable paste in its flowing state and the substrate thickness.However, it must be ensured that the solvents have completely evaporated from the printed thin film. To assist this process, the printed thin film can also be additionally irradiated with infrared radiation. A suitable drying oven setting would be, for example, a continuous oven at 140°C and a dwell time of 10 minutes in the continuous oven (belt speed 1 m / min, oven length 10 m). In particular, the printable paste is printed directly onto a substrate that is at least partially electrically conductive. This eliminates the need for additional contacting of the printed thin film. The substrate can, for example, have a silver layer as the first electrode.

[0035] The substrate can be a thin film, so that heat flows are only slightly distorted at high thermal conductivity coefficients. A processed thin film (printed and dried) with the printable paste is very stable and insensitive to resistance drift.

[0036] A temperature sensor according to the invention comprises a first electrode and a second electrode, as well as at least one printed thin film, as described above. This creates a cost-effective printed temperature sensor that can be easily integrated into an electrical component, such as a heating foil for heating the surface of a vehicle interior. The printed temperature sensor cannot be felt or sensed in the vehicle interior. The thin temperature sensor has only very small elevations and a very high heat transfer coefficient. The temperature sensor is calibration-free. High manufacturing tolerances when producing the temperature sensor as a thin film with the printed paste lead to only small measurement inaccuracies. Due to the thin film, the thermal inertia is very low, so that the temperature can be measured almost in real time.The resistance of the finished temperature sensor can be influenced by the electrical properties of the ceramic NTC thermistors or the conductive particles in the printable paste, their concentration, the thin-film thickness, the printed area, and the electrode spacing and width of the printed electrodes. The temperature sensor can be easily integrated into a flexible heating foil. The printed temperature sensors can be manufactured in very thin thicknesses and can therefore also be used in areas where localized irregularities are undesirable. Furthermore, temperature sensors based on thin foils can be manufactured, which have a high heat transfer coefficient and thus minimize heat flow distortion.

[0037] An inrush current limiter according to the invention comprises at least one printed thin film as disclosed here. This creates a cost-effective printed inrush current limiter for electrical components. The resistance of the finished inrush current limiter can be influenced by the electrical properties of the ceramic NTC particles used or the conductive particles in the printable paste, their concentration, the thin film thickness, and / or the printed area. Theoretically, the inrush current limitation is maximal in the idle state (=de-energized), as this is an inherent property of an NTC material. The effectiveness as an inrush current limiter decreases with increasing temperature. The effectiveness as an inrush current limiter can be influenced by the design of the printed thin film with the ceramic NTC particles in the printable paste.A larger (=more massive) thin-film layer will achieve inrush current limitation with a less steep gradient than a smaller (=less massive) thin-film layer. Alternatively, the thickness of the substrate and / or the overall thickness or the printed thin film of the inrush current limiter can be varied to achieve a desired inrush current limitation.

[0038] Furthermore, an inventive use of at least one printed thin film as disclosed here in an electrical component is claimed. The thin film is imperceptible, adhesive-free, and inexpensive. The printed temperature sensor electrode can be manufactured simultaneously with a heating electrode, for example, thus simplifying and reducing the time required to manufacture a heating foil including a temperature sensor. The thin film can be easily applied to the temperature sensor electrode in a subsequent process step.

[0039] Further advantages, features and details of the invention will become apparent from the following description, in which embodiments of the invention are described with reference to the drawings.

[0040] The list of reference symbols, as well as the technical content of the patent claims and figures, is part of the disclosure. The figures are described coherently and comprehensively. Identical reference symbols indicate identical components; reference symbols with different indices indicate functionally identical or similar components. The invention is explained in more detail with reference to exemplary embodiments in the following figures.

[0041] Positional designations such as "top," "bottom," "right," or "left" refer to the respective illustrations and are not to be understood as limiting. Although the invention is illustrated and described in detail by means of the figures and the associated description, this illustration and this detailed description are to be understood as illustrative and exemplary and not as limiting the invention. It is understood that those skilled in the art may make changes and modifications without departing from the scope of the following claims. In particular, the invention also encompasses embodiments having any combination of features mentioned or shown above for various aspects and / or embodiments.

[0042] The invention also encompasses individual features in the figures, even if they are shown there in conjunction with other features and / or not mentioned above. Furthermore, the term "comprising" and derivatives thereof do not exclude other elements or steps. Likewise, the indefinite article "a" or "an" and derivatives thereof do not exclude a plurality. The functions of several features listed in the claims may be fulfilled by a single unit. The terms "essentially," "about," "approximately," and the like, in connection with a property or value, specifically define the property or value. All reference signs in the claims are not to be understood as limiting the scope of the claims.

[0043] Character description

[0044] The figures are described in a coherent and comprehensive manner. The same reference symbols refer to the same components.

[0045] Fig. 1 : a strongly exponential temperature behavior of a printable paste or a printed thin film comprising a printable paste,

[0046] Fig. 2: a printable paste according to the invention in a schematic view,

[0047] Fig. 3: another printable paste according to the invention in a schematic view,

[0048] Fig. 4a-4c: a simplified representation of a method for producing a printable paste according to Fig. 2 in a schematic view, Fig. 5: a thin film according to the invention with a printable paste according to Fig. 2 in a schematic view,

[0049] Fig. 6: an inrush current limiter according to the invention with a printed thin film according to Fig. 5 in a schematic view, and

[0050] Fig.7: a temperature sensor according to the invention with a printed thin film according to Fig. 5 in a schematic view.

[0051] Fig. 1 shows a graph 15 with a strongly exponential temperature behavior of a printable paste or a printed thin film with the printable paste, which are described below. The abscissa represents the temperature in °C, which is shown linearly, and the ordinate represents the electrical resistance in ohms, which is shown logarithmically.

[0052] Fig. 2 shows a first embodiment of the printable paste 20 for producing an electrical component, comprising a solvent-based, printable electrically non-conductive lacquer 22, electrically conductive particles 25, and ceramic NTC particles 30, wherein the electrically conductive particles 25 and the ceramic NTC particles 30 are homogenized and evenly distributed in the printable electrically non-conductive lacquer 22. The particles 25, 30 form an electrically weakly conductive network 35 through the printable paste. By adding the conductive particles 25 to the printable lacquer 22 and the ceramic NTC particles 30, the percolation in the paste 20 is significantly improved, wherein the conductive particles 25 improve the contact between the ceramic NTC particles 30. Carbon in powder form is used as the conductive particles 25, as shown here. The printable paste 20 has a viscosity of 20 Pa s to 60 Pa s in the flowable state.The conductive particles 25 in the printable varnish 22 are arranged such that the percolation threshold in the printable paste 20 is exceeded. In the flowing or moist paste 20, the ceramic NTC particles 30 are spaced apart from one another on average, with at least one conductive particle 25 being located between at least two ceramic NTC particles 30 on average.

[0053] The conductive particles 25 are smaller than 100 micrometers, with disc-shaped conductive particles 25 being present that are smaller than 20 micrometers. Conductive particles 25 with an average diameter of less than 20 micrometers diffuse, on average, more effectively between the ceramic NTC particles 30. The printable paste 20 comprises less than 25% by volume of conductive particles 25 and less than 50% by volume of ceramic NTC particles 30.

[0054] The ceramic NTC particles 30 are powder particles and have a diameter between 10 micrometers and 100 micrometers. The ceramic NTC particles 30 are metal oxides containing nickel.

[0055] Fig. 3 shows a further embodiment of the printable paste 20a for producing an electrical component, as disclosed in Fig. 2, wherein the printable paste 20a comprises at least less than 50% by volume of conductive particles 25a and more than 10% of ceramic NTC particles 30a. The ceramic NTC particles 30a are metal oxides of manganese, and the conductive particles 25a are rod-shaped nanotubes. The ceramic NTC particles 30a are powder particles and have a diameter between 30 micrometers and 60 micrometers, although these diameters are also possible for other NTC materials.

[0056] Fig. 4a to Fig. 4c show an embodiment of a method according to the invention for producing a printable paste 20 according to Fig. 2, comprising the following steps: a) Providing the solvent-based printable electrically non-conductive varnish 22 b) Adding electrically conductive particles 25 to the printable electrically non-conductive varnish 22, wherein the addition takes place below the percolation threshold c) Adding ceramic NTC particles 30 to the printable electrically non-conductive varnish 22 d) Homogenizing the electrically conductive particles 25 and the NTC particles 30 in the printable electrically non-conductive varnish 22.

[0057] At least less than 50% by volume of the ceramic NTC particles 30 are added.

[0058] Fig. 5 shows a printed thin film 40 for an electrical component comprising at least one printable paste 20 according to Fig. 2, as previously described. The thin film 40 is printed onto a flexible substrate, a thin foil 41. As a result, high manufacturing tolerances of the ohmic resistance lead to only a relatively small measurement inaccuracy. The dried and printed thin film 40 is comparable in its properties to a ceramic NTC. The resistance in the printed thin film 40 in a finished electrical component can be influenced by the electrical properties of the ceramic NTC particles 30 used or the conductive particles 25 in the printable paste 20, their concentration, the printed thin film thickness, and the printed area. The thin film 40 is less than 250 micrometers thick without being brittle or breaking and was produced using a screen printing process.During the production of the thin film 40, the printable paste 20 is dried at a temperature of less than 200°C, so that the paste 20 becomes electrically conductive and an electrical connection forms between the electrically conductive particles 25 and the ceramic NTC particles 30, thus creating a strongly exponential temperature dependence in the electrically conductive thin film 40. In this case, an adjacent network is formed with the electrically conductive particles 25 and the ceramic NTC particles 30, without the particles 25 and 30 fusing together. An applicable oven setting is, for example, a continuous oven 45 at 140°C and a residence time of 10 minutes in the continuous oven 45 (belt speed 1 m / min, oven length 10 m).

[0059] Fig. 6 shows an embodiment of the inventive inrush current limiter 50 comprising at least one printed thin film 40, as shown in Fig. 5. The printed inrush current limiter for electrical components is arranged between two electrodes 51, 52. The resistance of the finished inrush current limiter is influenced by the electrical properties of the ceramic NTC particles 30 used or the conductive particles 25 in the thin film 40, the concentration of the particles 30, 25, the thin film thickness, and / or the printed area. Theoretically, the inrush current limitation is maximal at the switch-on time in the idle state, as this is an inherent property of an NTC material. The effectiveness as an inrush current limiter 50 decreases with increasing temperature. A larger (=more massive) thin film layer will realize the inrush current limitation with a less steep gradient than a smaller (=less massive) thin film layer.Alternatively, the thickness of the substrate and / or the total thickness of the inrush current limiter can be varied to achieve a desired inrush current limit. Typically, smaller resistors are required than for a temperature sensor (thus requiring either a larger area printed with paste, smaller electrode spacing, or more conductive paste).

[0060] Fig. 7 shows an embodiment of the temperature sensor 60 according to the invention, comprising a first electrode 61 and a second electrode 62, as well as at least one printed thin film 40, as described above. The printed temperature sensor 60 can be easily integrated into an electrical component, such as a heating foil for heating the surface of a vehicle interior. A possible circuit design is shown here. The printable paste 20 is screen-printed onto a previously generated electrode image (left). The electrodes 61, 62 are made of silver and are also printed. The electrodes 61, 62 have webs 63, 64 that are spaced apart from one another and interlock on the thin film 41. The printable paste 20 is printed over the electrodes 61, 62 in the area of ​​the webs 63, 64 and, when dry, forms the previously described thin film (right). Alternatively, the electrodes can also be connected via a

[0061] Etching process on the thin foil 41.

[0062] Reference symbol I iste

[0063] 15 Graph

[0064] 20 printable paste

[0065] 22 Printable, electrically non-conductive varnish

[0066] 25 conductive particles

[0067] 30 ceramic NTC particles

[0068] 20a printable paste

[0069] 25a conductive particles

[0070] 30a ceramic NTC particles

[0071] 35 leading network

[0072] 40 thin film with 20

[0073] 41 thin foil

[0074] 45 continuous furnace

[0075] 50 inrush current limiters

[0076] 51 Electrode

[0077] 52 Electrode

[0078] 60 temperature sensor

[0079] 61 Electrode

[0080] 62 Electrode

[0081] 63 bridge of 61

[0082] 64 bridge of 62

Claims

Patent claims 1. Printable paste (20; 20a) for producing an electrical component comprising a printable, electrically non-conductive lacquer (22), electrically conductive particles (25; 25a) and ceramic NTC particles (30; 30a), wherein the electrically conductive particles (25; 25a) and the ceramic NTC particles (30; 30a) are distributed in a homogenized manner in the printable, electrically non-conductive lacquer (22).

2. Paste according to claim 1, characterized in that the conductive particles (25; 25a) are arranged in the printable lacquer (22) such that the percolation threshold in the printable paste (20; 20a) is undershot.

3. Paste according to claim 1 or 2, characterized in that the conductive particles (25; 25a) are smaller than 100 micrometers, preferably conductive particles (25; 25a) are present which are smaller than 20 micrometers.

4. Paste according to one of the preceding claims, characterized in that the printable paste (25; 25a) has at least less than 50% by volume of conductive particles.

5. Paste according to one of the preceding claims, characterized in that the ceramic NTC particles (30; 30a) are powder particles.

6. Paste according to one of the preceding claims, characterized in that the ceramic NTC particles (30; 30a) have a diameter of less than 100 micrometers and preferably have a diameter between 10 micrometers and 60 micrometers.

7. Paste according to one of the preceding claims, characterized in that the conductive particles (25; 25a) have a diameter of less than 50% of the diameter of the ceramic NTC particles (30; 30a) and preferably have a diameter of less than 30% of the diameter of the ceramic NTC particles (30; 30a).

8. Paste according to one of the preceding claims, characterized in that the paste in the flowable state has a viscosity of 15 Pa s to 100 Pa s and preferably has a viscosity of 20 Pa s to 60 Pa s.

9. Paste according to one of the preceding claims, characterized in that the conductive particles (25; 25a) are rod-shaped or disc-shaped.

10. Paste according to one of the preceding claims, characterized in that the ceramic NTC particles (30; 30a) comprise metal oxides 11. Paste according to one of the preceding claims, characterized in that at least less than 50% by volume of ceramic NTC particles (30; 30a) are added and preferably more than 10% by volume of ceramic NTC particles (30; 30a) are added.

12. Paste according to one of the preceding claims, characterized in that at least more than 10% by volume of ceramic NTC particles (30; 30a) are added.

13. Paste according to one of the preceding claims, characterized in that the printable, non-conductive lacquer (22) is solvent-based.

14. Paste according to one of the preceding claims, characterized in that the printable, non-conductive lacquer (22) comprises at least one organic polymer.

15. A method for producing a printable paste, in particular a printable paste (20; 20a) according to one of claims 1 to 14, wherein the method comprises the following steps, in particular in the following order: a) providing a printable, electrically non-conductive lacquer (22) b) admixing electrically conductive particles (25; 25a) into the printable lacquer (22), wherein the admixture takes place below the percolation threshold c) admixing ceramic NTC particles (30; 30a) into the printable, electrically non-conductive lacquer (22) d) homogenizing the electrically conductive particles (25; 25a) and the NTC particles (30; 30a) in the printable, electrically non-conductive lacquer (22).

16. The method according to claim 15, characterized in that at least less than 50% by volume of the ceramic NTC particles (30; 30a) are added.

17. Printed thin film (40) for an electrical component comprising at least one printable paste (20; 20a) according to at least one of claims 1 to 14.

18. Thin film according to claim 17, characterized in that the printed thin film is produced by a screen printing process.

19. A method for producing an electrically conductive thin film (40) for an electrical component with a printable paste (20; 20a) according to one of claims 1 to 14, wherein the printable paste (20; 20a) is printed onto a substrate, in particular onto a substrate that is at least partially electrically conductive, and at least the printable paste (20; 20a) is dried at a temperature of less than 200 °C, so that the printable paste (20; 20a) becomes electrically conductive and in particular an electrical connection is formed between the electrically conductive particles (25; 25a) and the ceramic NTC particles (30; 30a) in order to form a strongly exponential temperature dependence in the electrically conductive thin film (40).

20. Temperature sensor (60) comprising a first electrode (61) and a second electrode (62), and at least one printed thin film (40) according to claim 17.

21. Inrush current limiter (50) comprising at least one printed thin film (40) according to claim 17.

22. Use of at least one printed thin film (40) according to claim 17 in an electrical component.

Images