EP3155871B1 - Planar heating element with a structure of ptc resistance - Google Patents

Description

The invention relates to a planar heating element with a PTC resistance structure, which is arranged in a defined surface area of a first surface of a carrier substrate, with the PTC resistance structure being assigned electrical connection contacts for connection to an electrical voltage source. Furthermore, the invention relates to a heating arrangement in which the planar heating element according to the invention is used. Furthermore, the invention describes preferred uses of the heating element according to the invention or the heating arrangement according to the invention. In addition, a method for producing the heating element according to the invention is described.

It is known from the prior art, for example, to determine or monitor the temperature by evaluating the electrical resistance of a resistance structure. Corresponding resistance structures are applied to a carrier substrate either using thin-film technology or using thick-film technology. The resistance structures are often designed in a meandering or spiral shape.

Furthermore, it has become known to heat a surrounding medium to a predetermined temperature via corresponding resistance structures. For this purpose, the resistance structure is connected to an electrical voltage source. For example, heatable resistance structures are used in thermal flowmeters to determine and/or monitor the mass flow of a medium through a measuring tube.

Resistance structures that are used for temperature measurement and heatable resistance structures are usually made of a PTC (Positive Temperature Coefficient) material, preferably made of nickel or platinum. PTC resistance structures are characterized by the fact that the ohmic resistance increases as the temperature rises, with the functional dependency being highly linear over a large temperature range.

The disadvantage of the known resistance structures, in particular when they are designed in a meandering manner, lies in the relatively high resistance of these structures. As a result, a relatively high voltage must be provided for the power supply. If, in addition, a uniform temperature distribution is required within a defined surface area, this cannot be achieved with a known meander structure. Such a structure has the disadvantage that - caused by process fluctuations in the production of the coatings - can result in different line widths. This leads to the formation of hotspots, since the resistance is greater in the area of smaller line widths. This leads to locally stronger heating (hotspot), which is intensified by the fact that the heating also increases the resistance. On the other hand, such a solution means that high current densities can result in electromigration.

the DE 195 23 301 A1 describes a heating structure in which an external and an internal conductor track have the same width. Because the outside trace is longer than the inside trace, the resistance of the outside trace is greater than the resistance of the inside trace.

The one in the WO 2011/078063 A1 The image heating device shown in FIG.

the DE 10 2005 057 566 A1 refers to a gas sensor for measuring a physical property of a measurement gas. The property is, for example, the concentration of a gas component, such as oxygen, or the temperature. For the even distribution of the temperature in the heating area, the resistance heater has current paths connected in parallel, which extend over an extensive heating area.

the U.S.A. 4,970,376 describes a transparent heating element for heating a glass substrate. The transparent heating element is part of a glass cell or container and is applied to its surface. The heating element applied to the glass cell or glass container is transparent to visible light or to IR radiation.

The invention is based on the object of proposing a planar heating element which has at least approximately a homogeneous or uniform temperature distribution in a defined surface area.

The object is achieved by the heating element described in claim 1. Starting from the two electrical connection contacts, the PTC resistor structure has at least one inner conductor track and one outer conductor track connected in parallel, with the inner conductor track having a greater resistance than the outer conductor track and with the resistances of the inner conductor track and the outer conductor track being dimensioned in this way are that when a voltage is applied, there is a substantially uniform temperature distribution within the defined surface area. Here, the effect is exploited that the conductor track with the lower resistance makes a higher contribution to the heating output. Therefore, the parallel connection of the two traces has a self-stabilizing effect. If, for example, one of the two conductor tracks has a narrowing caused by the process technology, no hotspot usually forms at this point.

Outside of the largely uniformly heated surface area, there is a high temperature gradient, so that the heating zone is essentially limited to the defined surface area. Small ohmic resistances can be realized with the at least two conductor tracks running in parallel and connected in parallel. In particular, the total resistance of the PTC resistance structure at room temperature without applied heating voltage is preferably less than 3 ohms.

The PTC resistance structure is preferably designed in such a way that, in addition to the heating function, it also provides measured temperature values, so that the PTC resistance structure serves as a heating element and as a temperature sensor.

According to a first advantageous embodiment of the heating element according to the invention, the conductor track lying on the inside and the conductor track lying on the outside are made of the same material; the different resistances are realized via different cross-sectional areas and/or length extensions of the internal conductor track and the external conductor track. This first configuration has the advantage that the resistance structure consists of a single material, which can be produced in one production step. Nickel or platinum is preferably used as the material for the PTC resistance structure. Platinum has the advantage that it can also be used in a high-temperature range above 300°C without any problems.

• einen ersten endseitigen Teilbereich, der sich an die elektrischen Kontaktanschlüsse/Verbindungsleitungen anschließt, über die die Verbindung mit der elektrischen Spannungsquelle erfolgt,
• einen mittleren Teilbereich, der sich an den ersten endseitigen Teilbereich anschließt, und einen zweiten sich an den mittleren Teilbereich anschließenden zweiten endseitigen Teilbereich.

The heating element according to the invention shows a PTC resistance structure, which - is structured in three sub-areas - quasi virtual:

• a first partial area at the end, which adjoins the electrical contact terminals/connecting lines via which the connection to the electrical voltage source is made,
• a central portion adjoining the first end portion, and a second end portion adjoining the central portion.

According to the invention, the conductor track lying on the inside and the conductor track lying on the outside run essentially parallel in the central partial area. Preferably, the inner conductor track and the outer conductor track also run essentially parallel in the second partial area at the end. In the first partial area at the end, the conductor track lying on the inside and the conductor track lying on the outside are each connected to run towards one another with each of the two electrical connection contacts. The two conductor tracks in the first partial area at the end therefore preferably have a V-shape. If there are no abrupt changes in the geometry of the PTC resistance structure, high temperature stability can be achieved in the defined surface area. In particular, the formation of so-called hot spots is avoided.

However, it is also possible for the two conductor tracks to be connected to one another in the first partial area at the end via a section running at right angles to the two conductor tracks.

Likewise, both the internal conductor track and the external conductor track in the second partial area at the end can have either a V-shape or a rectangular shape. In the second partial area at the end, too, the conductor track lying on the inside and the conductor track lying on the outside run essentially parallel to one another. Another shape is also possible, for example a semicircular shape. Furthermore, it is possible to select a first shape, e.g. a rectangular shape, in one of the two end-side partial areas and a second shape deviating therefrom, e.g. a V-shape, in the other end-side partial area.

Furthermore, an advantageous embodiment proposes that the resistance per length of the inner conductor track and/or the resistance per length of the outer conductor track in the first partial area at the end and/or in the second partial area at the end are/is greater than the resistance per length of the inner conductor track and/or or the external conductor track in the middle section.

The heating element according to the invention provides that at least one geometric parameter of the inner conductor track and/or the outer conductor track, such as line width and filling thickness, is varied at least in a subsection of at least one subarea in such a way that a locally occurring deviation from the uniform temperature distribution in the affected Section is at least approximately balanced.

The carrier substrate preferably consists of a material with a thermal conductivity that is below a predetermined limit value, so that between the defined surface area with a uniform temperature distribution and the connection contacts large heat gradient occurs that is above a specified limit value, typically above 50°C/mm. This ensures that the heated 'hot' zone is essentially limited to the defined surface area and is thermally decoupled from the 'cold' zone lying outside. A material is preferably used as the carrier material whose thermal conductivity (thermal conductivity) is less than 5 watts/m*K. The thermal conductivity is preferably less than 3 watts/m·K

The defined surface area has a limitation that is essentially given by the outer dimensions of the outer conductor track. This defined surface area characterizes the so-called heating zone or hot zone, in which the temperature is at least 300°C. The limitation of the heating zone to the area defined by the outer dimensions of the outer conductor track is achieved in particular by the fact that the carrier material is characterized by low thermal conductivity. In addition, it preferably has a thickness of less than or equal to 1 mm.

In order to achieve heat exchange between the heating zone and the cold zone, which is usually at room temperature and in which the connection contacts are located, electrical connecting lines with a low filling density are provided. These are made of preferably high-purity gold (gold content at least greater than 95%, preferably greater than 99%). The connection contacts are made of silver or a silver alloy.

The resistance of the PTC resistance structure is below 10Ω at room temperature, preferably below 3Ω or even 1Ω. This is achieved by choosing at least one suitable material (preferably platinum) and a suitable dimensioning of the corresponding conductor track structure.

Aluminum oxide, quartz glass or zirconium oxide can be used as the carrier material. Zirconium oxide is preferably used as the carrier substrate in connection with the invention. The thickness of the carrier substrate is preferably less than 1 mm. Zirconium oxide has the following advantages: low thermal conductivity (which is, however, sufficient to compensate for any local hotspots that may occur), high mechanical stability even with small thicknesses and, with regard to thermal expansion, optimal adaptation to metallic components of the heating element, especially if the conductor tracks are made of pass platinum. This configuration ensures that the homogeneous temperature distribution is limited to the surface area that is defined by the external dimensions of the resistance structure. Outside the PTC resistance structure, the temperature drops a lot due to the high temperature gradient off quickly. The shape of the carrier substrate is preferably adapted to the shape of the PTC resistance structure. In particular, the carrier material is therefore V-shaped or rectangular in the second partial area at the end. If the second partial area at the end has a V-shape—that is, if it has a point—then the heating element can be inserted into a medium to be heated. An example of a chip arrangement with a tip is the EP 1 189 281 B1 refer to.

According to an advantageous embodiment of the heating element according to the invention, at least one essentially electrically insulating separating layer, which is preferably made of glass, is provided on or in the carrier substrate. It was already mentioned above that the carrier substrate is preferably made of zirconium oxide. As already described above, zirconium oxide has properties that predestine it for use in the heating element according to the invention. However, zirconium oxide has the disadvantage that it becomes conductive at temperatures above 200°C. The application of a separating layer prevents the conductivity from occurring. More information about this known solution can be found in the EP 1 801 548 A2 .

Furthermore, the carrier substrate is assigned at least one passivation layer, which is preferably applied to the surface of the carrier substrate. The passivation layer preferably consists at least partially of the material of the separating layer. The passivation layer serves to protect against mechanical, chemical and electrical influences. The passivation layer is preferably applied to both surfaces of the heating element. This makes it possible to prevent mechanical bending of the carrier substrate. In particular, the material of the passivation layer can be a tightly sealed glass. More information on a passivation layer that can be used in connection with the present invention can be found in WO 2009/016013 A1 .

As already mentioned above, the PTC resistance structure is preferably made of a conductive material that is suitable for use in the high-temperature range. The PTC resistance structure is preferably made of platinum. Platinum has the advantage that, in addition to its good temperature stability, it has a well-defined, almost linear temperature characteristic and a very high electromigration resistance. In addition, due to the PTC characteristics of a platinum resistance structure, a self-regulation of the temperature can be approximately achieved when the resistance structure is connected to a quasi-constant voltage source (eg a battery). In addition, a platinum PTC resistor structure is recognized as an industry-standard temperature sensor.

According to an advantageous embodiment of the heating element according to the invention, the electrical connection contacts are made of a precious metal or a precious metal alloy, the precious metal preferably being silver and the precious metal alloy preferably being a silver alloy. Silver also enjoys recognition as an industry standard and has the advantage that it can be easily soldered or welded. However, silver has the disadvantage that it diffuses laterally into platinum at temperatures above 300°C. Therefore, when used in the high-temperature range (above 250°C), no direct connection between a platinum resistor structure and silver connection contacts is possible. It should be mentioned that in practice silver is only used as an alloy. This is due to the fact that a certain proportion of palladium, or here preferably a certain proportion of platinum, blocks the mobility of the silver atoms and thus prevents material migration.

In order to circumvent the problem described above, electrical connecting lines are provided between the electrical connection contacts and the first partial area at the end of the first resistance structure. These are also made of a precious metal, preferably gold. Gold ensures a stable transition to platinum up to 850°C, it is characterized by good electrical conductivity and is technologically available in a very pure form for compact thin layers.

According to a preferred embodiment of the solution according to the invention, both the connecting lines and the conductor tracks in the first partial area at the end of the PTC resistor structure and the connecting lines and the electrical connection contacts have a defined overlap. The overlap ensures reliable electrical contact. According to an advantageous embodiment of the heating element according to the invention, it is provided that the length of the overlap between the connecting lines and the conductor tracks in the first partial area of the PTC resistor structure at the end is greater than the distance between the inner conductor track and the outer conductor track.

The depth of the overlap between the connecting lines and the conductor tracks in the first end-side partial area of the PTC resistor structure is preferably greater than 100 μm, in particular in the case of a linear or V-shaped overlap. It is considered to be particularly advantageous in connection with the invention if the length and the depth of the overlap between the connecting lines and the conductor tracks in the first partial area at the end of the PTC resistor structure are approximately greater than 5:1.

In order to ensure that as a result of the overlap, in particular between the connecting lines and the PTC resistance structure, no disruption occurs in the area of the dimensions of the heating zone defined by the dimensions of the PTC resistance structure, the first end-side partial area of the PTC resistance structure is, according to the invention, with regard to its geometric parameters designed so that the physical heating properties of the PTC resistance structure are at least approximately unchanged. The adaptation preferably takes place by changing the filling density or the line width of the conductor tracks or the connecting lines in the vicinity of the respective overlap.

As already mentioned above, the overlap between the connecting lines and the conductor tracks in the first partial area at the end of the PTC resistance structure is preferably V-shaped or line-shaped; however, it can also be designed in the form of a web.

Some preferred dimensions for the individual components of the heating element according to the invention are given below. The filling thickness of the conductor tracks of the PTC resistance structure, which preferably consist of platinum, is between 5-10 μm, at least in the first partial area at the end. The filling thickness of the connecting lines, which are preferably made of gold, is preferably between 3-10 μm. The thickness of the connection contacts, which preferably consist of silver or a silver alloy, is preferably in the range of 10-30 μm. The linear expansion of the PTC resistance structure is on the order of a few millimeters, preferably in a range of 2-10 mm. In addition, the resistance of the PTC resistor structure at room temperature without an applied heating voltage is preferably below 3Ω, preferably below 1Ω. Since the PTC resistance structure has a very low resistance, it is possible to heat the PTC resistance structure to a high temperature with a relatively low energy supply. A voltage source with a few volts, e.g. 3 volts, is sufficient to operate the heating element.

Preferred dimensions and materials of a planar heating element using thick-film technology are specified below. It goes without saying that other dimensions and materials can also be found by a technically qualified person. The overall length of the planar heating element is 19 mm and the width is 5 mm. The conductor track on the outside is about twice as wide as the one on the inside (eg 800 µm to 400 µm). The carrier substrate made of zirconium oxide has a thickness of 0.3 mm. The separation layer and the passivation layer each have a thickness of 15 µm and are arranged on both surfaces of the planar heating element. That The planar heating element described above can easily reach a heating temperature of 450°C.

The planar heating element according to the invention can be produced using thin or thick film technology. However, due to the more cost-effective manufacturing processes, it is preferably manufactured using thick-film technology. The heating element according to the invention is characterized by high dynamics. After switching on, the operating temperature is reached very quickly; after switching off, the planar heating element cools down very quickly to the ambient room temperature.

The temperature in the defined surface area with a substantially uniform temperature distribution is preferably in a temperature range between 300°C and 750°C. It goes without saying that, depending on the design and use of materials for the heating element according to the invention, temperatures outside the previously specified range can also be covered.

• Eine möglichst hohe thermische Leitfähigkeit der PTC-Widerstandsstruktur minimiert die thermischen Effekte der Verlustleistung infolge von Spannungsabfällen an den Leiterbahnen und Leitungen.
• Die thermische Leitfähigkeit der Leiterbahnen muss relativ gering sein, um die unerwünschte Wärmeabfuhr aus der Heizzone zu vermeiden.
• Die elektrische Leitfähigkeit muss aber genügend hoch bleiben, um die Erzeugung zusätzlicher Wärme durch Verlustleistung in diesem Bereich in Grenzen zu halten.

When choosing the material, the following points in particular must be observed:
The following two effects must be kept in balance:

• A thermal conductivity of the PTC resistance structure that is as high as possible minimizes the thermal effects of the power loss as a result of voltage drops on the conductor tracks and lines.
• The thermal conductivity of the conductor tracks must be relatively low in order to avoid unwanted heat dissipation from the heating zone.
• However, the electrical conductivity must remain high enough to limit the generation of additional heat due to power loss in this area.

An overlap of the two conductor tracks, which are preferably made of platinum, with the connecting lines, which are preferably made of gold, is necessary in order to ensure reliable electrical contact. In the area of the overlap (PI/Au), the requirements placed on the components of the heating element made of pure metals (eg Au and PI) are not met. These degraded properties in the areas of the overlap must be taken into account when designing the PTC resistor structure. The ideal choice of the geometry of the lap is the highest possible length with the smallest possible depth of the lap, so the V-shape is particularly suitable. The depth of the overlap is preferably 100 μm. In general, the depth of the overlap should be selected so that it can be reproduced in terms of process technology. A small depth can also have disadvantages, for example if it is between 25 µm and 30µm varies. With a small depth, the influence of a process-related inaccuracy, eg of 5 µm, on the overall performance is of course much greater than if you set the depth of the overlap to 100 µm.

The same considerations also apply in the area of the overlap (Ag/Au) of connection contacts (e.g. Ag) and connecting lines (e.g. Au). Since the temperatures that occur in this overlap are much lower (→ cold zone: the temperature essentially corresponds to the prevailing ambient temperature) than in the area of the overlap of connecting lines and conductor tracks (hot zone or heating zone: the temperature corresponds to the temperature in the defined area of the PTC resistance structure, i.e. the temperature of the heating zone), the properties of the PTC resistance structure are less affected.

Furthermore, the invention relates to a heating arrangement which uses the above-described PTC resistance structure in a suitable but arbitrary configuration. For this purpose, in addition to the heating element according to the invention, an electrical power supply is provided, which supplies the PTC resistance structure with energy, and a control/evaluation unit, which regulates the PTC resistance structure to a predetermined temperature value.

The electrical voltage supply is a voltage source that has a limited energy supply. The electrical voltage is preferably supplied by a battery.

Furthermore, in connection with the heating arrangement according to the invention, it is suggested that a separate resistance structure be provided for determining the temperature of the medium that is heated by the heating element. The resistance structure for temperature measurement and for heating is preferably applied to the second surface of the carrier substrate, which is opposite the first surface on which the PTC resistance structure is arranged. Based on the measured temperature, the temperature control is carried out preferentially and heating is carried out from both surfaces.

The planar heating element according to the invention or the heating arrangement according to the invention is preferably used in a compact semiconductor-based gas sensor, in a compact heater for pocket devices or in a calorimetric flow sensor.

For example, a gas-sensitive structure, such as a metal oxide and an interdigital electrode structure, can be located on the passivation layer. The invention can therefore also generally serve as a basis for sensors in which heating is essential for the sensor function.

The planar heating element according to the invention is preferably manufactured using the method described below:
A separating layer is applied—usually one after the other—to each of the two surfaces of the carrier substrate. It is common, when using the thick layer technique, to print the coatings on. However, as already mentioned above, thin-film technology can also be used in connection with the invention. The PTC resistance structure is applied to one of the two dry separating layers. As soon as the PTC resistance structure has hardened, the electrical connection lines are applied and subjected to a drying process. The connection contacts are then applied and also cured. The overlapping areas of the connection contacts and electrical connecting lines are preferably cured again separately. The passivation layers are applied—preferably successively—to the two surfaces of the planar heating element and cured.

• Fig. 1: eine Draufsicht auf eine bevorzugte Ausgestaltung des erfindungsgemäßen Heizelements,
• Fig. 1a: einen Längsschnitt gemäß der Kennzeichnung A-A durch das in Fig. 1 dargestellte erfindungsgemäße Heizelement,
• Fig. 2: eine schematische Teilansicht des erfindungsgemäßen Heizelements, das eine erste Ausgestaltung des Überlapps zwischen einer Verbindungs-leitung und den Leiterbahnen zeigt,
• Fig. 3: eine schematische Teilansicht des erfindungsgemäßen Heizelements, das eine zweite Ausgestaltung des Überlapps zwischen einer Verbindungs-leitung und den Leiterbahnen zeigt,
• Fig. 4: eine schematische Teilansicht des erfindungsgemäßen Heizelements, das eine dritte Ausgestaltung des Überlapps zwischen einer Verbindungs-leitung und den Leiterbahnen zeigt,
• Fig. 5a: eine Draufsicht auf eine zweite Ausgestaltung des erfindungsgemäßen Heizelements mit PTC-Widerstandsstruktur und
• Fig. 5b: eine Draufsicht auf die Rückseite des in Fig. 5a gezeigten Heizelements.

The invention is explained in more detail with reference to the following figures. It shows:

• 1 : a plan view of a preferred embodiment of the heating element according to the invention,
• Fig. 1a : a longitudinal section according to the marking AA through the in 1 illustrated heating element according to the invention,
• 2 : a schematic partial view of the heating element according to the invention, showing a first embodiment of the overlap between a connecting line and the conductor tracks,
• 3 : a schematic partial view of the heating element according to the invention, showing a second embodiment of the overlap between a connecting line and the conductor tracks,
• 4 : a schematic partial view of the heating element according to the invention, showing a third embodiment of the overlap between a connecting line and the conductor tracks,
• Figure 5a : a plan view of a second embodiment of the heating element according to the invention with a PTC resistance structure and
• Figure 5b : a top view of the back of the in Figure 5a shown heating element.

1 shows a plan view of a preferred embodiment of the heating element 1 according to the invention. The external dimensions of the PTC resistance structure 2 delimit the defined surface area 3 or the heating zone. Virtually, the PTC resistance structure is divided into three different sub-areas: a first end-side sub-area 10, which adjoins the connection contacts 6 or the electrical connecting lines 15, a middle sub-area 11, which adjoins the first end-side sub-area 10, and a second end portion 12 which adjoins the middle portion 11 . There is an overlap 16b of a defined length between the connection contacts 6 and the electrical connecting lines 15 . There is also an overlap 16a between each connecting line 15 and the conductor tracks 8, 9.

The inner conductor track 8 and the outer conductor track 9 of the PTC resistance structure 2 run approximately parallel and are electrically connected in parallel. The inner conductor track 8 has a higher resistance than the outer conductor track 9. The resistances of the inner conductor track 8 and the outer conductor track 9 are dimensioned such that when a voltage is applied, there is a substantially uniform temperature distribution within the defined surface area 3. This defined surface area is also referred to as the heating zone and is 1 indicated by the dashed line on the outer edge of the PTC resistance structure 2.

The cold zone, i.e. the area where essentially room temperature prevails, is in the area of the connection contacts 6. In the transition area between the heating zone and the cold zone, as well as in the outer area of the defined surface area 3, the temperature gradient is very high. As a result of the high temperature gradient, the heating zone is largely limited to the defined surface area 3 . The high temperature gradient is achieved by choosing a carrier substrate 5 with low thermal conductivity. Further information on this can be found in the previous description.

In the embodiment shown, the conductor track 8 lying on the inside and the conductor track 9 lying on the outside are made of the same material. It has already been described above that platinum is preferably used as the material for the conductor tracks 8 , 9 . The different resistances of the conductor tracks 8, 9 are realized by means of different cross-sectional areas and/or linear expansions of the inner conductor track 8 and the outer conductor track 9.

A preferred dimensioning of the planar heating element according to the invention or of the chip according to the invention has already been specified above.

Out of 1 it can be seen that the connecting lines 15, which - as already described in detail above - are preferably made of gold, also vary in diameter: Following the first partial area 10, the width is smaller and thus the resistance is greater than in the area that adjoins the connection contacts 6 connects. This ensures that the thermal conductivity does not increase. In connection with the lower thermal conductivity of gold compared to platinum, the desired large temperature gradient is achieved in the transition area between the heating and cold zones.

Fig. 1a shows a longitudinal section according to the marking AA through the in 1 illustrated heating element 1 according to the invention. On both surfaces 4, 19 of a carrier substrate 5, a separating layer 14 is arranged. The carrier substrate 5 is preferably zirconium oxide with a thickness of 300 μm, the separating layers 14 each have a thickness of 15 μm. The PTC resistance structure 2 is arranged on the separating layer 14 applied to the surface 4 of the carrier substrate 5 . The PTC resistor structure consists of platinum with a thickness of 8 µm. It goes without saying that the previously described dimensioning of the PTC resistance structure 2 is not limited to the stated values. Each of the explicitly mentioned values can be varied up or down as desired. How the dimensioning of the variants is designed in detail is at the discretion of the person skilled in the art.

In a preferred embodiment of the invention, the connection contacts 6 are made of silver and have a thickness of 10 μm. The electrical connecting line 15 between the connection contacts 6 and the PTC resistance structure 2 are made of gold and are 4 μm thick. In the area of the overlap 16b, the connection contacts 6 and the electrical connecting lines 15 overlap, in the area of an overlap 16a the electrical connecting lines 15 and the conductor tracks 8, 9 of the PTC resistance structure overlap. The surfaces 4, 19 of the planar heating element 1 are sealed with a passivation layer 13. the Passivation layer 13 has a thickness of 15 μm. The functions of the individual layers have already been described in detail above. The sensitivity of the planar heating element is 3700ppm/K (+- 100ppm/K) at room temperature without applying the heating voltage. It goes without saying that the specified thicknesses of the individual layers are exemplary. Each of the explicitly mentioned values of the preferred embodiment can be varied up or down as desired. How the dimensioning is designed in detail is at the discretion of the specialist.

The figures 2, 3, 4 show schematic partial views of heating elements 1 according to the invention with different configurations of the overlap 16a between one of the connecting lines 15 and the connected conductor tracks 8, 9. The overlap 16a in 2 has a web-like configuration, the overlap 16a in 3 is rectangular and the overlap 16a in 4 has a V shape. The overlap 16a between the connecting lines 15 and the conductor tracks 8, 9 in the first partial area 10 at the end of the PTC resistance structure 2 is designed with regard to its geometric parameters in such a way that the physical heating properties of the PTC resistance structure 2 are at least approximately unchanged or are almost identical with the properties in the defined area 3, in which the heating zone is located. The materials and the special features that occur in the areas of the overlap 16a, 16b have already been described at the previous point, so that they will not be repeated at this point.

Figure 5a shows a plan view of a second embodiment of the heating element 1 according to the invention with a PTC resistance structure 2, Figure 5b a plan view of the back 19 of the in Figure 5a shown heating element 1, on which a meandering temperature sensor 18 is arranged. Furthermore, in Figure 5a also the heating arrangement according to the invention with heating element 1, electrical voltage source 7 and control/evaluation unit 17 is shown schematically.

Reference List

1

heating element

2

PTC resistance structure

3

defined area

4

surface

5

carrier substrate

6

connection contact

7

electrical voltage source

8th

internal conductor track

9

external conductor track

10

first terminal section

11

middle section

12

second end portion

13

passivation layer

14

release layer

15

electrical connection line

16a

overlap

16b

overlap

17

control/evaluation unit

18

Resistance structure for temperature measurement

19

opposite surface

Claims (26)

1. Planar heating element (1) with a PTC resistor structure (2), which is arranged in a defined surface area (3) of a first surface (4) of a carrier substrate (5), wherein electrical connection contacts (6) are assigned to the PTC resistor structure (2) for connection to an electrical voltage source (7), wherein the electrical connection contacts (6) are connected to the PTC resistor structure (2) via electrical connection lines (15), wherein the PTC resistor structure (2) has a first end section (10), a middle section (11) and a second end section (12),

   wherein, starting from a defined overlap (16a), the PTC resistor structure (2) is made from interlocking conductive tracks (8, 9) and has an interior conductive track (8) and an exterior conductive track (9),

   wherein the interior conductive track (8) and the exterior conductive track (9) are essentially parallel in the middle section (11),

   wherein the interior conductive track (8) and the exterior conductive track (9) are switched in parallel,

   characterized in that

   the connection lines (15) and the conductive tracks (8, 9) each have the defined overlap (16a) in the first end section (10) of the PTC resistor structure (2),

   the interior conductive track (8) has a bigger resistance than the exterior conductive track (9),

   the resistances of the interior conductive track (8) and the exterior conductive track (9) are sized in such a way that, when voltage is applied, there is an essentially even distribution of temperature within the defined surface area (3),

   and

   the first end section (10) of the PTC resistor structure is designed in such a way, with regard to the filling thickness and/or the line width of the conductive tracks (8, 9) in the area of the specific overlap (16a), that the physical heating properties of the PTC resistor structure are at least approximately unchanged in the first section (10).
2. Heating element as claimed in Claim 1,
   wherein the PTC resistor structure (2) makes temperature measured values available in such a way that the PTC resistor structure (2) serves as a heating element and as a temperature sensor.
3. Heating element as claimed in Claim 1 or 2,

   wherein the interior conductive track (8) and the exterior conductive track (9) are made from the same material, and

   wherein the different resistances are implemented via different cross-sectional areas and/or elongations of the interior conductive track (8) and of the exterior conductive track (9).
4. Heating element as claimed in Claim 1 or 2,
   wherein the interior conductive track (8) and the exterior conductive track (9) are made from different materials, which have a different resistivity.
5. Heating element as claimed in one or more of the Claims 1 to 4,
   wherein, in the first end section (10), the interior conductive track (8) and the exterior conductive track (9) are put into contact with the corresponding electrical connection contacts (6) in a manner that they approach one another.
6. Heating element as claimed in one or more of the previous claims
   wherein the resistance of the interior conductive track (8) and/or the resistance of the exterior conductive track (9) in the first end section (10) and/or in the second end section (12) is greater than the resistance of the interior conductive track (8) and/or of the exterior conductive track (9) in the middle section (11).
7. Heating element as claimed in one or more of the Claims 1 to 6,
   wherein the carrier substrate (5) is made from a material with a thermal conductivity that is less than a predefined limit value, such that a thermal gradient occurs between the heated defined surface area (3) and the connection contacts (6) that is above a predefined limit value, preferably above 50 °C/mm.
8. Heating element as claimed in one or more of the previous claims,
   wherein at least a separation layer (14), which is essentially electrically isolating, is provided on or in the carrier substrate (5), wherein said layer is preferably made of glass.
9. Heating element as claimed in one or more of the previous claims,
   wherein at least a passivation layer (13) is assigned to the carrier substrate (5), said layer being preferably applied on the surface of the carrier substrate (5).
10. Heating element as claimed in one or more of the previous claims,
    wherein the PTC resistor structure (2) is made from a conductive material for use in the high-temperature range, said material being preferably platinum.
11. Heating element as claimed in one or more of the previous claims,
    wherein the electrical connection contacts (6) are made from a precious metal or a precious metal alloy, wherein the precious metal is preferably silver and wherein the precious metal alloy is preferably a silver alloy.
12. Heating element as claimed in one or more of the previous claims,
    wherein electrical connection lines (15) are provided between the electrical connection contacts (6) and the first end section (10) of the PTC resistor structure (2), wherein said lines are made from a precious metal, preferably gold, preferably with a purity of 99.9 %.
13. Heating element as claimed in Claim 11 or 12,
    wherein the overlap (16a) between the connection lines (15) and the conductive tracks (8, 9) in the first end section (10) of the PTC resistor structure (2) is in the form of a V, a square or a bar.
14. Heating element as claimed in Claim 13,
    wherein the width (b) of the overlap (16a) between the connection lines (15) and the conductive tracks (8, 9) in the first end section (10) of the PTC resistor structure (2) is greater than the distance between the interior conductive track (8) and the exterior conductive track (9).
15. Heating element as claimed in one or more of the Claims 13 to 14,
    wherein the depth of the overlap (16a) between the connection lines (15) and the conductive tracks (8, 9) in the first end section (10) of the PTC resistor structure (2) is greater than 100 µm for a linear or V-shaped overlap.
16. Heating element as claimed in one or more of the Claims 13 to 15,
    wherein the length and the depth of the overlap (16a) between the connection lines (15) and the conductive tracks (8, 9) in the first end section (10) of the PTC resistor structure (2) have approximately a ratio greater than 5:1.
17. Heating element as claimed in one or more of the previous claims,
    wherein the thickness (d) of the PTC resistor structure (2), which is preferably made of platinum, is between 5 and 10 µm at least in the first section (10).
18. Heating element as claimed in one or more of the previous claims,
    wherein the thickness of the connection lines (15), which are preferably made of gold, is between 3 and 10 µm.
19. Heating element as claimed in one or more of the previous claims,
    wherein the thickness of the connection contacts (6), which are preferably made of silver, is between 10 and 30 µm.
20. Heating element as claimed in one or more of the previous claims,
    wherein the temperature in the defined surface area (3) with an essentially even distribution of temperature is preferably in a temperature range between 300 °C and 750 °C.
21. Heating element as claimed in one or more of the previous claims,
    wherein the resistance of the PTC resistor structure (2) is less than 3 Ω, preferably less than 1 Ω, at room temperature without heating voltage applied.
22. Heating arrangement with a heating element as claimed in at least one of the Claims 1 to 21,

    wherein an electrical voltage source (7) is provided that supplies the PTC resistor structure (2) with energy, and

    wherein a control/evaluation unit (17) is provided which regulates the PTC resistor structure (2) to a predefined temperature value.
23. Heating arrangement as claimed in Claim 22,
    wherein the electrical voltage source (7) is a voltage source with a limited energy reserve, preferably a battery with a voltage less than or equal to 3 V.
24. Heating arrangement as claimed in Claim 22 or 23,

    wherein a resistance structure (18) is provided to determine the temperature and to heat the medium, and

    wherein the resistance structure (18) is applied to a second surface (19) of the carrier substrate (5), said second surface being opposite to the first surface (4).
25. Procedure for producing a planar heating element, which is described in at least one of the Claims 1 to 21, said procedure comprising the following steps:

    - Coating of each of the surfaces (4, 19) of the carrier substrate (5) with a separation layer (14)

    - Fitting of the resistor structure (2) on the separation layer (14) of the surface (4)

    - Fitting of the electrical connection lines (15)

    - Fitting of the connection contacts (6)

    - Application of the passivation layers (13) in the area of the two surfaces (4, 19).
26. Procedure as claimed in Claim 25,
    wherein thick film technology or thin film technology is used to produce the planar heating element (1).

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