Sensor, process of manufacturing a sensor, and use of certain polymers for covering a thermistor component

Abstract

The present application addresses having a thermistor component and a cover covering the thermistor component at least partially. The material of the cover comprises a polyaryletherketone, a polyphenylene sulfide, an aromatic thermosetting copolyester, a liquid crystal polymer, a polyamide, a polyimide, a polyamide imide, or a polybenzimidazole.

Description

[0001] Description

[0002] Sensor, process of manufacturing a sensor, and use of certain polymers for covering a thermistor component

[0003] The present application concerns a sensor, a process of making a sensor and the use of certain polymers for covering a thermistor component .

[0004] Sensors such as temperature sensors , for example using NTC ceramic thermistor components , can have polymer covers . These can provide protection or electrical insulation .

[0005] In this field there is a demand for the provision of sustainable cover materials . Also , topics such as environmental friendliness are of importance .

[0006] Accordingly, it is the task of the present application to provide new materials for covering thermistors . A further task is to provide means for forming a cover .

[0007] At least one task is ful filled by the subj ect-matter of claim 1 . Further preferred embodiments are provided in the dependent claims . Furthermore , other embodiments are also provided in further independent claims .

[0008] According to an embodiment , a sensor is described which has a thermistor component . The sensor can be a temperature sensor . The thermistor component can be any functional component that can provide thermistor functionality . This may, for example , be a PTC or NTC thermistor component . In particular, an NTC thermistor component is preferably used . Such an NTC thermistor component may comprise a perovskite or spinel NTC ceramic material. Furthermore, in the present embodiment a cover is provided to cover the thermistor component. The cover at least partially covers the thermistor component.

[0009] According to a preferred embodiment, the entire thermistor component is covered by the cover.

[0010] The material of the cover can comprise a polyaryletherketone (abbreviated: PAEK) , a polyphenylene sulfide (abbreviated: PPS) , an aromatic thermosetting copolyester (abbreviated: ATSP) , a liquid crystal polymer (abbreviated: LCP) , a poylamide (PA) , a polyimide (abbreviated: PI) , a polyamide imide (abbreviated: PAI) , or a polybenzimidazole (abbreviated: PBI) .

[0011] According to an embodiment, the cover may have said substances or a mixture of said substances as a main component. This main component can make up above 50% and preferably above 90% of the material of the cover. The cover can consist of said substances or a mixture of said substances except for minor technical impurities.

[0012] The inventors of the present invention have found that the above substances can at least partially replace per- and polyfluoroalkyl substances (abbreviated: PEAS) in covers. PEAS are so called "forever chemicals" which do not break down via natural processes. Also, health impacts are associated with PEAS. In conventional covers for sensors, often PEAS are used. Replacing PEAS may help to provide a more environmentally friendly or more sustainably produced sensors . Furthermore , for at least some of the above-listed substances , surprisingly, the inventors found that further advantages can be achieved besides simply replacing PFAS- based materials . In particular, the substances may provide high temperature resistivity of above 200 ° C, such as up to 260 ° C for long-term use . At least for short term use , at least some of the substances can withstand temperatures of up to 300 ° C . Furthermore , at least some of the substances perform better at water storage tests compared to PFAS- containing substances . Furthermore , at least some of the substances provide better mechanical stability and / or better shore hardness than PFAS-containing substances . Furthermore , they can show better adhesion than PFAS components . In this case they also have better gluability . In such cases a higher pull-out strength at a glue test can be achieved compared to covers containing PFAS . Furthermore , for at least some of the substances homogeneous and smooth surfaces can be achieved .

[0013] Furthermore , at least some of the substances allow for thin cover thicknesses which helps to improve the response time of the sensors . Further, at least some of the substances show a higher electrical insulation strength than PFAS-based materials . At least some of the above substances are nontransparent . The same applies to the fact that a uni form optical appearance can be achieved with at least some of the substances .

[0014] Furthermore , at least some of the substances show better performance at temperatures of 0 ° C or below when compared to PFAS-containing covers . The latter tend to crack at temperatures of 0 ° C or lower, whereas no cracks can be observed for at least some of the above-described materials . Furthermore , at least some of the materials are more cost- efficient than PFAS-based materials. Furthermore, at least some of the above-described materials have lower density than the PFAS-based materials.

[0015] According to an embodiment, the material cover comprises a polyaryletherketone (abbreviated: PAEK) , an aromatic thermosetting copolyester (abbreviated: ATSP) , a liquid crystal polymer (abbreviated: LCP) , a poylamide (PA) , a polyimide (abbreviated: PI) , or a polybenzimidazole (abbreviated: PBI) .

[0016] According to an embodiment the cover comprises polyetheretherketone (abbreviated: PEEK) or polyetherketoneketone (abbreviated: PEKK) .

[0017] PEEK and PEKK are examples of PAEK. PAEK in general and in particular PEEK and PEKK are preferable in many applications as they tend to fulfill many of the above-described advantages. In particular, PEEK has lower density than PFAS- containing covers. PEEK materials can have a density of 1.3 g / ml, whereas PEAS based materials have a density of 2.1 g / ml. Furthermore, PEEK and PEKK showed no failure after 1000 hours of testing in a water storage test, whereas PFAS- containing covers already failed after 500 hours. Also, PEEK and PEKK materials showed particularly good stability and chemical inertness at 0°C or below. Furthermore, PEEK and PEKK have enhanced mechanical stability, superior adhesion and superior durability when compared to PFAS-containing covers. PFAS-based materials can easily be peeled off from a sensor, whereas PEEK and PEKK containing cover materials adhere firmly and can only be removed using destructive force. The PEEK and PEKK-based covers adhere strongly to the thermistor component, the glass encapsulation and the wires. For example , in a peel-of f test a failure mode for PFAS- containing covers has been observed to be peeling of f from the coating . In contrast , for PEEK and PEKK containing covers no peeling of was observed . The failure mode observed was that the wire elongated and broke rather than material being peeled of f . The PEEK and PEKK-based covers have better gluability . For example , for PEEK and PEKK a seven times higher pull-out strength at glue test compared to PFAS-based materials was observed . PEKK showed an even higher pull-out strength than PEEK . Furthermore , PEEK and PEKK have up to two times higher electrical insulation strength than PFAS-based covers .

[0018] According to a preferred embodiment , the cover can be closed . Also , according to an embodiment , the cover may have a homogeneous structure . "Homogeneous" may mean that macroscopically or optically the cover has a uni form structure . For example , the structure of the cover can be non-granular . Also , the cover may be non-porous . The embodiments described here , may preferably be combined . They are particularly relevant for PAEK and even more particularly relevant for PEEK . This , for example , may help to provide protection from moisture or other substances that could af fect the thermistor or the electrodes on the thermistor . Certain procedural features which are described below may aid to form a closed and / or homogeneous cover . Moisture reaching the thermistor component can lead to corrosion, migration of components of the electrodes or the thermistor component , short circuiting, or delamination of electrodes .

[0019] According to an embodiment , the thermistor component can be a multilayer component , which for example has inner electrodes . According to another embodiment , the thermistor component is based on or has a monolithic ceramic component . For such a thermistor component , the inventive cover is particularly preferred . The monolithic component can be sintered as an entire block from a green material or can be assembled from green sheets which are subsequently sintered . The latter is preferable due to a simpler manufacturing process . A monolithic thermistor can be di f ferent from a multilayer thermistor, in that the monolithic thermistor has no inner electrodes .

[0020] According to an embodiment , two sides of the thermistor which are preferably opposite to each other, are metalli zed . A metalli zation may, for example , comprise gold or silver . The electrode can also have multiple layers of which some may increase adhesion to a thermistor material or facilitate contacting of the thermistor component .

[0021] According to an embodiment , the thermistor component is contacted by a first wire . The first wire can, for example , be in contact to one of the sides of the thermistor component . This side may be a metalli zed side of the thermistor component . Likewise , a second wire can be provided according to another embodiment . The second wire is preferably in electrical contact to a di f ferent side , in particular a side opposite to the with which the first wire is in contact .

[0022] According to an embodiment , the first and / or the second wire can be applied via sintering, such as paste sintering using a sinter paste suitable for the electrode . For example , a paste complementary to the material of the metalli zation can be used . For example , a gold or silver paste can be used . According to other embodiments the first and / or second wire can be applied by bonding, welding or soldering . In particular, the inventors found that welding can provide a mechanically stable connection between wire and thermistor . For example , welding can be advantageously applied together with hard cover materials , such as PEAK or in particular PEEK, to form a mechanically highly durable sensor .

[0023] According to an embodiment , the cover covers the region, in which the first wire makes contact with the thermistor component . This can, for example , mean that the cover covers at least a region of the electrode of the thermistor component to which the first wire is attached . Thus , the cover may provide a protection to this region .

[0024] According to a variation of the previous embodiment , in a similar manner the cover also covers the region where the second wire is applied to the thermistor component in the case that a second wire is provided .

[0025] Alternatively, to a second wire , the thermistor component can also be attached to a di f ferent type of external contact such as a contact area or a metal platelet . Such contact areas may be part of a substrate or of a printed circuit board . Depending on the type and intended use of the thermistor also instead of the first wire , electrical contact can be established also via a contact area, metal platelet or similar .

[0026] According to an embodiment the wires can comprise at least a conductive portion . The conductive portion preferably comprises or consists of a metal or a metal alloy . The wires can, for example , contain copper, silver, nickel or iron in the conductive portion . For example , a copper clad nickeliron wire can be used . In particular, the wires can be Dumet wires . Also , silverplated nickel wires can be used .

[0027] According to an embodiment , the cover may cover parts of the first and / or the second wire . In particular, according to an embodiment in a setup with a first wire and a second wire which contact two opposite sides of an NTC thermistor ceramic component , the cover can cover the entire thermistor component , and also portions of the wire leading away from the regions in which the wires make contact with a thermistor component . In this case at least the contact regions of the wires are covered by the cover . According to an embodiment also additional portions of the wires may be covered . This has the advantage , that all the covered areas and components can have a continues layer of the cover, which may provide insulation and / or chemical and / or mechanical protection .

[0028] According to another embodiment , the wires can have portions which are insulated . In particular, pre-insulated wires may be used for contacting the thermistor component . In the regions where the wires make contact with the thermistor component , the insulation is preferably removed . It is preferred that the cover covers all of the regions from which the insulation has been removed, as well as the thermistor component . In the case that the wires are pre-insulated, smaller portions of the wires can be covered by the cover than in the case where no pre-insulation is present and still insulation and / or chemical and / or mechanical protection can be provided to a signi ficant portion of a sensor . According to an embodiment , the insulation of the preinsulated wires can be one of the above-mentioned materials discussed for the cover .

[0029] According to an embodiment , the material of the pre-insulated wires can be the same material or comprise the same material as the cover . As pre-insulated wires , PEEK pre-insulated wires can be used . In this case preferably the silver-plated wires can be employed .

[0030] According to an embodiment , an encapsulation comprising glass is arranged between the cover and the thermistor component . This encapsulation can be addressed in the following also as a glass encapsulation . The thermistor component can at least be partially or can preferably be fully covered by the glass encapsulation . In this case , the cover covers at least portions of the thermistor component by covering portions of the glass encapsulation or by covering a portion of the thermistor component that is not covered by the glass encapsulation . According to a preferred embodiment the entire glass encapsulation is covered by the cover .

[0031] According to an embodiment the NTC ceramic thermistor component can be contacted by two wires , wherein the thermistor component together with portions of the wires contacting the thermistor component and portions of the wires leading away from the thermistor component covered by the glass encapsulation . The cover surrounds and covers the glass encapsulation as well as , optionally, further portions of the wires . In case further portions of the wires are covered by the cover, this can have the advantage that the point at which a wire sticks out of the glass encapsulation is protected by the cover . Alternatively, according to an embodiment , the sensor may also have no cover . Having no cover can be facilitated by having a welded connection of wires . Also , the hardness of the described cover materials helps in this case . In particular in this case the hard cover comprises or consists of PAEK and even more preferably of PEEK . The hardness of the cover material can contribute to the mechanical stability of the sensor . For example , in such a case , a glass encapsulation may not be needed or be less advantageous . Having no glass encapsulation may help to have a more ef ficient manufacturing of the sensor . Also , welding of the wires provides a mechanically stable connection . Having both a hard cover and a welded connection helps to ensure a mechanically robust sensor . Also , it can help to reduce the thermal load on the sensor, as the high temperatures of melting glass may be avoided . Furthermore , the dimensions of the sensor may be smaller, i f no cover is required . Accordingly, it may be easier to use the senor in a sterically challenging environment . Also , welding of the wires provides a mechanically stable connection . Having both a hard cover and a welded connection helps to ensure a mechanically robust sensor .

[0032] According to an embodiment , the thickness of the cover is between 5 to 500 pm . Preferably, the thickness of the cover lies 100 pm and 150 pm . A thickness of at least 5 pm can help to ensure suf ficient chemical stability, corrosion resistance and insulation . A thickness of below 500 pm can help to achieve suf ficiently short sensor response times . These advantages are more prominent for the preferred ranges . According to an embodiment , the wires can be straight and lead away from the thermistor component in a V-shape . The wires can also only be V-shaped and straight in the vicinity of the thermistor component but are kinked or bent slightly at some distance from the thermistor component , for example to have a smaller angle between them, or in order to have parallel wires .

[0033] According to another embodiment , use of the above-described cover materials for covering a thermistor component is described . All of the above-described embodiments and advantages also apply to the use .

[0034] Also , a process of manufacturing a sensor is provided . As far as applicable , the above-described embodiments and advantages also apply to the process . In the process a thermistor component is contacted by a first wire and a second wire . A cover is applied to the thermistor component . Alternatively, a pre-assembled sensor can be provided . The pre-assembled sensor has every component of the final sensor except the cover . For example , a thermistor already provided with wires can be provided . For example , at least the parts of the wires which are attached to the thermistor component may be covered in the process of applying the cover . Preferably the entire thermistor component is covered . The material of the cover comprises the above-described materials .

[0035] According to an embodiment of the process , the cover is applied via dip coating or electrostatic coating . In particular for PEEK and PEKK electrostatic coating can preferably be applied, as a good homogeneity can be achieved by this method . For PPS (polyphenylene sul fide ) , dip coating has been found to be preferable because of better coverage of the sensor head and wires .

[0036] According to an embodiment , the electrostatic coating can comprise a deposition step, wherein powderi zed coating material is electrostatically adhered to the thermistor and / or parts of the wires . For example , the particles of the powderi zed coating material can be electrostatically charged and thus adhere to a natural or grounded thermistor or preassembled sensor . Alternatively or additionally, a voltage may be applied to the thermistor or pre-assembled sensor and the powder electrostatically adheres to it . The powderi zed coating material can be sprayed on the thermistor or preassembled sensor . The spraying can be carried out through a noz zle . For example , the noz zle may comprise means to charge the particles .

[0037] Alternatively, according to an embodiment , in electrostatic coating the powder can be applied without a spraying mechanism, for example by charging the stationary powder with a sheet metal grid .

[0038] According to an embodiment that preferably is combined with the previous embodiment , the adhered coating material is cured . Generally, according to an embodiment , curing conditions may be chosen such that the coating material adheres to the thermistor component without additional means , such as electrostatic adhesion, and a closed and / or homogeneous structure of the coating is achieved . For example , the formed cover preferably is non-granular or not lumpy . For example, the curing conditions may include or address a curing temperature and / or a curing time. In this case, the cover can be heated to a curing temperature. The curing temperature may be held for a curing time. For example, according to an embodiment, the curing temperature can be the specific temperature at which the coating material adheres to the thermistor component and forms a closed and / or homogeneous structure of the coating.

[0039] In particular, the inventors of the present invention have found it to be highly advantageous to heat the coating material to a higher temperature than the formal melting temperature of the material. Thus, according to an embodiment, the curing temperature can be higher than the formal melting temperature of the cover. Alternatively, according to an embodiment the curing temperature may be over 25 °C higher than the melting temperature. For example, it may be at least 30°C higher than the melting temperature, or at least 35°C higher than the melting temperature or at least 40°C higher than the melting temperature.

[0040] In particular for PEEK the inventors found in extensive studies that it is highly preferable to heat the electrostatically adhered PEEK powder to a temperature of at least 370 °C. Thereby a closed cover can be formed. The inventors found that often temperatures closer to the formal melting temperature, such as 350°C may not be sufficient to form a closed and homogeneous cover. More preferably, for PEEK a curing temperature is higher than 370°C, such as for example 375°C or higher, 380°C or higher. At these temperatures above 370°C homogeneity can be improved. According to a further embodiment, the curing temperature may be chosen such that any thermal and / or oxidative degeneration is not compromising the capability of the function and properties of the cover, as defined above. Accordingly, according to embodiment, this may define an upper limit for the curing temperature. Preferably the curing temperature is chosen such that no visible thermal and / or oxidative degeneration takes place. For example, in the case of PEEK, the inventors found that a curing temperature may be 430°C or below under normal atmosphere. At 430 °C in a PEEK cover thermal and / or oxidative degeneration may optically be visible, however the cover can still be functional. More preferably, the curing temperature is lower than 430°C. For example the curing temperature may be 425°C or lower, or 420°C or lower, or 415°C or lower, or 410°C or lower.

[0041] According to embodiments the curing temperature can be between the above-described temperatures. For example, the curing temperature for PEEK can be between 370°C and 430°C or more preferably it may be between 375°C and 425°C. According to a preferred embodiment, the curing temperature for PEEK can be between 380 °C and 410 °C. For example, for a curing temperature of 390 ± 5°C the inventors found that good homogeneity with hardly any degeneration takes place.

[0042] Accordingly, curing can be performed at 390°C but also at temperatures between 370°C to below 390°C and at temperatures above 390°C, such as above 390°C to 430°C. The abovedescribed preferred values may apply to these ranges.

[0043] According to an embodiment, the curing time is chosen such that a closed and / or homogeneous cover is formed. For example, in the case of PEEK the inventors found that a curing time of at least 5 min may help to form a high quality cover . In particular, a curing time of at least 10 min, such as 15 min or more can be preferable . In principle there is no upper limit for the curing time . The inventors found it preferable , according to an embodiment , to have a curing time of 30 min or below, as this may minimi ze thermal stress on the sensor and also helps to reduce process time . Also at higher temperatures shorter curing times may help to minimi ze degradation of the cover .

[0044] According to an embodiment , repeated cycles of dip coating or electrostatic coating can be used .

[0045] The coating methods are preferably applied by applying a source material or starting material for the cover . This starting material is subsequently preferably hardened, dried or cured .

[0046] According to an embodiment of the process , an encapsulation comprising glass can be applied to the thermistor component before the cover is applied .

[0047] This glass encapsulation can, for example , be formed by melting of a glass tube around the thermistor component .

[0048] Application of a glass cover is preferable in particular in cases where the wires are only sintered to the thermistor component . In the case of welding or soldering, a more mechanically stable connection can be provided which may allow setups without the glass cover . Omitting the glass encapsulation can help to reduce the response times of the sensor or reduce complexity and production costs .

[0049] In the following the invention is explained with respect to exemplary embodiments . These exemplary embodiments do not limit the invention to the embodiments . Furthermore , any schematic drawing which is explicitly labeled schematic or appears to be schematic is not true to scale and dimensions of the components may vary, for example to better visuali ze certain features .

[0050] Figure 1 shows a schematic cross-section of a first exemplary embodiment of a sensor .

[0051] Figure 2 shows a photographic image of a sensor according to the first exemplary embodiment of a sensor .

[0052] Figure 3 shows a schematic cross-section of the head portion of the first exemplary embodiment of a sensor .

[0053] Figure 4 shows a cross-section photograph of the head portion of a sensor according to the first exemplary embodiment of a sensor .

[0054] Figure 5 shows a schematic cross-section of a second exemplary embodiment of a sensor .

[0055] Figure 6 shows a schematic cross-section of the head portion of the second exemplary embodiment of a sensor .

[0056] Figure 7 shows a schematic cross-section of a third exemplary embodiment of a sensor . Figure 8 shows a schematic cross-section of the head portion of the third exemplary embodiment of a sensor .

[0057] Figure 9 shows a schematic cross-section of a fourth exemplary embodiment of a sensor .

[0058] Figure 10 shows a photograph of a sensor according to the fourth exemplary embodiment of a sensor .

[0059] Figure 11 shows a schematic cross-section of the head portion of the fourth exemplary embodiment of a sensor .

[0060] Figure 12 shows a cross-section photograph of the head portion of a sensor according to the fourth exemplary embodiment of a sensor .

[0061] Figure 13 shows a schematic cross-section of a fi fth exemplary embodiment of a sensor .

[0062] Figure 14 shows a schematic cross-section of the head portion of the fi fth exemplary embodiment of a sensor .

[0063] Figure 15 shows a schematic cross-section of a sixth exemplary embodiment of a sensor .

[0064] Figure 16 shows a schematic cross-section of the head portion of the sixth exemplary embodiment of a sensor .

[0065] Figure 17 shows a thermistor component with electrodes .

[0066] Figures 18 to 21 show results of a melting experiment . Figure 22 shows a photograph of a seventh exemplary embodiment of a sensor .

[0067] Figure 23 shows a photograph of an eighth exemplary embodiment of a sensor .

[0068] Figure 24 shows a photograph of a ninth exemplary embodiment of a sensor .

[0069] In Figures 1 to 4 a first exemplary embodiment of a sensor 1 is shown . In Figure 1 a schematic cross-section of the entire sensor 1 is shown . Figure 2 shows an exemplary photograph of a sensor 1 according to the first exemplary embodiment . It can be seen from the line of symmetry S in Figure 1 , that the sensor 1 can be fairly symmetric . In the photo of Figure 2 it can be seen that reali zations of the first exemplary embodiment may vary in their shape from the schematic representation of Figure 1 . In Figure 3 and Figure 4 the head portion 2 of the sensor is shown in schematic cross-section and in an exemplary cross-sectional photograph, respectively .

[0070] As can be seen, in Figure 1 , internal components of the sensor are depicted with dashed lines . Figure 3 provides a more detailed view on these components with continuously drawn lines .

[0071] The sensor 1 according to the first exemplary embodiment is a temperature sensor . It has a thermistor component 3 , which is electrically contacted by a first contact portion 4 and a second contact portion 5 which establish the contact between the thermistor component 3 and the first wire 8 and the second wire 9 , respectively . As can be seen in the cross sectional image in Figure 4 , the contact portions 4 and 5 may be portions of the wires 8 and 9 , respectively .

[0072] What is not explicitly labeled in Figure 1 is that the thermistor 3 has , on two opposing surfaces , a first electrode 3a and a second electrode 3b, via which the electrical contacts 4 and 5 are contacting the thermistor . Also , in Figures 3 and 4 the electrodes 3a and 3b are thin layers , which are mainly represented by the surface of the thermistor component in the drawings .

[0073] A more detailed image of a senor component 3 can be seen in Figure 17 . Here the electrodes are explicitly shown . The electrodes 3a and 3b may be gold or silver electrodes or may be multilayered electrodes having a gold or silver surface .

[0074] The shape of the thermistor component 3 in Figure 17 is rectangular . Generally, the shape of the thermistor component 3 is not limited . It can also be a platelet or a disc . The thermistor is a monolithic thermistor made from stacked green sheets which are sintered together .

[0075] The thermistor can comprise any suitable thermistor material . In particular here it is an NTC thermistor with a perovskite or spinel ceramic .

[0076] The wires 8 and 9 are Dumet wires . These Dumet wires are connected by paste sintering to the electrodes 3a and 3b . In the case the electrodes 3a and 3b comprise gold or silver a gold or silver containing sintering paste can be used . As can be seen in particular in Figure 3 and also as a lighter colored region in Figure 4 , the thermistor component 3 as well as portions of the first and the second wire 8 and 9 neighboring the thermistor component 3 are encapsulated in a glass encapsulation 6 . The glass encapsulation 6 is made from a material that comprises or consists of glass .

[0077] Around the glass encapsulation 6 and thereby covering the thermistor component , a cover 7 is arranged . The cover 7 also covers at least portions of the wires 9 and 8 . The cover 7 has a cloudy and non-transparent beige color . This can be seen in the color image of Figure 2 .

[0078] In the present example , the cover 7 consists of polyetheretherketone ( short : PEEK) . Using PEEK has the advantage of achieving a per- and polyfluoroalkyl substances free cover (per- and polyfluoroalkyl substances are abbreviated as PEAS ) .

[0079] Furthermore , the present cover 7 showed high temperature resistivity of up to 260 ° C for long time use . The sensor having this cover 7 can even withstand short-time heating of up to 300 ° C .

[0080] The sensor showed enhanced climatical performance with respect to a similar sensor having a PFAS-based cover . For the present sensor there was no failure after 1000 hours of testing in a water storage test . In contrast , a PFAS-coated NTC thermistor failed already after 500 hours of testing due to migration and / or corrosion .

[0081] Furthermore , the present sensor showed enhanced mechanical stability . In particular, the present cover 7 has a superior shore hardness when compared to PFAS-based materials . In particular, the PFAS coating can easily be removed or peeled of f from the NTC thermistor by hand or by tweezers . The present material can only be removed by using a blade and force. Furthermore, superior adhesion is achieved using the present cover material. In particular, good adhesion to the glass encapsulation 6 and the Dumet wires has been achieved. In contrast, PFAS-based covers easily peel off. For the present cover 7 no peeling can be achieved without breaking of the wire. Furthermore, the present cover material showed superior gluability compared to PFAS-based materials. In particular, a seven times higher value for the pull-out strength at a glue test was measured compared to PFAS-coated NTC thermistors.

[0082] Furthermore, as can be seen in Figure 2, a homogenous covering can be achieved. Also, a smooth surface, which allows for different assemblies depending on the requirements of the application, can be achieved. In principle, the present cover 7 can be provided in different colors, which for example allows easy differentiation of different sensors, for example.

[0083] Furthermore, the present material allows for thin and mainly homogenous coverings. This can help to achieve short response times for the sensor.

[0084] Furthermore, the present material shows higher electrical insulation strength compared to PFAS-based materials. In particular, a two times higher average short circuit voltage was recorded for the present material compared to PFAS-based materials .

[0085] Also, the present material showed chemical inertness against measurement media at 0°C and even lower temperatures when stored under these conditions. In particular, for perfluoropolyethers such as Galden cracks appear in the PFAS- coating after emersion in fluorinated measurement media at 0°C or lower temperatures. In contrast, no cracks are observed for the present cover material.

[0086] Furthermore, also commercially the present material can have some advantages. In particular, at the time of filing of the application, the present PEEK material costs around 100 EUR per kilogram compared to around 170 EUR per kilogram for PFAS-based materials. Additionally, these materials benefit from a density difference as PEEK has a density of 1.3 g / ml, while PFAS-based materials have a density of around 2.1 g / ml.

[0087] The thickness of the cover 7 lies in the range of 100 to 150 pm. In this thickness range good chemical and also mechanical protection is provided by the cover. Generally, a thickness in the range of 5 to 500 pm and preferably between 100 to 150 pm can be used.

[0088] For the representation of the first embodiment in Figure 1, the line of symmetry S is indicated. As is partly already addressed above, in a general sense the sensor only is approximately symmetrical. In particular, as can be seen in Figure 2, the shape of the head portion 2 may be slightly offset with respect to the shape of the symmetry axis defined by the wires. Furthermore, the wires do not have to be perfectly straight but may be slightly curved as indicated in Figure 2.

[0089] Instead of PEEK, other polyaryletherketones (short: PAEK) such as polyetherketoneketone (short: PEKK) can be used. With these and in particular with PEKK, similar advantages as with PEEK can be achieved. Alternatively, polyphenylene sulfides ( PPS ) , aromatic thermosetting copolyesters (ATSP ) , liquid crystal polymers ( LCP ) , polyimides ( PI ) , polyamides ( PA) , polyamide imides ( PAI ) or polybenzimidazoles ( PBI ) can be used as a material comprised in the cover . The cover 7 can be made from these materials .

[0090] The sensor according to the first exemplary embodiment can be provided by providing the thermistor component 3 . Thermistor component 3 can have first electrode 3a and a second electrode 3b, for example as depicted in Figure 17 . Subsequently the first wire 8 and the second wire 9 are connected to the thermistor component 3 via the electrodes 3a and 3b by paste sintering .

[0091] Subsequently the glass encapsulation 6 is provided by melting of a glass tube around the thermistor component 3 . The glass encapsulation 6 is preferred in the present case , as the paste-sintered connections are mechanically weak and the glass encapsulation 6 can provide stability . In addition, the glass encapsulation 6 can provide chemical protection .

[0092] After that the thermistor component is covered with the cover 7 by covering the outside of the glass encapsulation 6 as well as portions of the wires 8 and 9 . Electrostatic coating is advantageous as by this method a suf ficiently thick cover can be applied, which nonetheless is not too thick, which would be disadvantageous for sensor response times . Electrostatic coating has been found to work particularly well for PEEK and PEKK . It also works good for other PAEK substances . Further details regarding the electrostatic coating are described below and also in connection with Figures 18 to 21 and with respect to Figures 22 , 23 and 24 . Alternatively dip coating can be used to apply the cover. Dip coating is particularly preferable for DPS.

[0093] To apply the cover 7 with sufficient thickness, several cycles of dip coating and / or electrostatic coating can be used .

[0094] After applying the coating from a liquid precursor or from a solution or dispersion, the cover is dried, cured or otherwise hardened.

[0095] For example, after electrostatic coating, curing can be performed using a defined temperature profile adjusted on selected material and design. After dip coating, a drying step or several such steps in case of repeated coating can be performed. Subsequently the dried layer can be cured with a defined temperature profile adjusted on selected material and design. For example, for PEEK a temperature profile can be a heating from room temperature to a temperature of 370°C or above, such as up to 430°C, such as at 390°C for example. A curing profile for PEEK used in this case can be heating from room temperature with 15°C / min to 390°C, a dwell time (curing time) 15 min at 390°C and then slow cooling to room temperature (not specifically controlled) .

[0096] In Figures 5 and 6 a second exemplary embodiment of a sensor

[0097] 1 is shown. Figure 5 shows a schematic cross-section of the entire sensor 1 with internal components shown in dashed lines in a manner similar to Figure 1. Figure 6 shows the head portion 2 of the sensor 1. In Figure 5 the head portion

[0098] 2 is indicated by a circle to highlight which portion of the sensor is shown in Figure 6. The setup of the sensor is identical to the first exemplary embodiment except for that no glass encapsulation is provided between the cover 7 and the thermistor component 3 . Accordingly, the thermistor component 3 is directly covered by the cover 7 . As can be seen, the connection portions 4 and 5 at which the first and second wires 8 and 9 connect to the thermistor component 3 as well as portions of the wires 8 and 9 are covered by the cover 7 .

[0099] The cover 7 using PEEK allows for stabili zing the mechanically comparatively weak paste-sintered connections suf ficiently . Accordingly, a glass encapsulation is made disposable . This can enhance response times of the sensor .

[0100] Furthermore , PEEK also showed good adhesion directly on the thermistor component 3 .

[0101] Figures 7 and 8 show a third exemplary embodiment of a sensor 1 . In Figure 7 the entire sensor 1 is shown, in a manner similar to Figure 1 or 5 . In Figure 8 a head portion 2 is shown . Again, similar as for the second exemplary embodiment , the circle in Figure 7 indicates the head portion 2 of the sensor 1 . The sensor 1 shown in Figure 7 is nearly identical to the first exemplary embodiment shown in Figure 1 . The third exemplary embodiment di f fers from the first exemplary embodiment only in that the electric connection of the wires 8 and 9 to the thermistor component 3 are formed via welding .

[0102] In Figures 9 to 12 a fourth exemplary embodiment is shown . The manner of depiction is similar as for the first exemplary embodiment . In Figure 9 , a schematic cross-section of the entire sensor 1 according to the fourth exemplary embodiment is shown . Figure 10 shows a photograph of a sensor 1 according to the fourth exemplary embodiment . Please note that here the angle of the wires di f fers from that shown in Figure 9 . The explanations with regard to symmetry with respect to the first exemplary embodiment apply here accordingly . Furthermore , in Figures 11 and 12 a schematic cross-section of the head portion 2 as well as a photograph of the head portion 2 of a sensor 1 according to the fourth exemplary embodiment are shown . The fourth exemplary embodiment is identical to the third exemplary embodiment except that no glass encapsulation is provided . Similar as in the case of the third exemplary embodiment here the wires are welded to the thermistor component 3 . The welding provides a mechanically comparatively stable connection . This helps to achieve a stable setup without a glass encapsulation . This allows to have a thinner layer of the cover 7 around the thermistor component 3 for which response times can be shorter . Also , the high mechanical durability of the PEEK- cover in combination with the welded connection helps to provide a mechanically stable construction . Also , it may help to provide short response times for the senor .

[0103] In Figure 13 and 14 a fi fth exemplary embodiment of a sensor 1 is shown . The depiction is in a manner similar as to the previous embodiments . The fi fth exemplary embodiment is identical to the fourth exemplary embodiment except for that pre-insulated wires are used as first and second wires 8 and 9 . The wires 8 and 9 have a conductive core 8a and 9a, respectively . This conductive core 8a or 9a is covered by an insulation 8b or 9b . The insulation may consist of or comprise PEEK . In a portion of the wires 8 and 9 next to the contact portions 4 and 5 , the insulation 8b and 9b is removed . This allows to establish electrical contact . Having a pre-insulation allows for the cover 7 to not be extend far along the length of the wires 8 and 9 . The cover 7 covers the regions in which the wires 8 and 9 are connected to the thermistor component 3 . Also , all the uninsulated regions are covered .

[0104] Furthermore , the fi fth exemplary embodiment has a kink 8c and a kink 9c in the first wire 8 and in the second wire 9 , respectively . Having such a bending or kink allows a parallel arrangement of the wires . This can be advantageous for implementing the sensor 1 into applications . The PEEK and PEKK containing covers 3 in connection with electrostatic have shown to be advantageous for sensors with kinked wires . In PFAS-containing coatings the thickness of the cover at the kinks is often strongly reduced or the cover even becomes penetrated at these points . In the inventive setup, a thickness of at least 5 pm or preferably of at least 100 pm can be reali zed more easily .

[0105] In Figures 15 and 16 a sixth exemplary embodiment of sensor 1 is shown . Figure 15 shows a schematic cross-section of the entire sensor, and Figure 16 shows a schematic cross-section of the sensor head, both in manner of depiction similar to the previous embodiments . The sixth exemplary embodiment of the sensor 1 is identical to the fi fth exemplary embodiment except for that the connection of the first wire 8 and the second wire 9 is provided via soldering . The solders 4a and 5a which are part of the first connection portion 4 and the second connection portion 5 are represented by dotted droplets covering flattened portions of the first wire 8 and the second wire 9 , respectively . Furthermore , the inventors have conducted extensive studies regarding the curing of a cover applied using electrostatic coating .

[0106] Electrostatic coating can be carried out as described in the introduction or as described above . In particular, PEEK powder is electrostatically adhered to the assembly of thermistor and wires , optionally including a glass encapsulation .

[0107] Subsequently the adhered coating material is cured .

[0108] Initially, the inventors assumed that curing PEEK can be carried out at any temperature above the formal melting temperature of 343 ° C ( 616 K

[0109] Figures 18 to 21 show curing experiments , in which PEEK applied by electrostatic coating was cured at 350 ° C for 30 min . Under these conditions only a kind of sintering of the particles takes place . However, no closed layer or closed cover is formed . The material clearly remains granular, and a cover formed under these conditions would be porous and remain permeable to water . Accordingly, a nonfunctional cover would be formed by curing at 350 ° C even when a comparatively long curing time of 30 min is applied .

[0110] The inventors found that for PEEK it is required to cure a cover at a higher temperature than 350 ° C . In particular, the inventors found that a closed cover can be formed at a temperature of at least 370 ° C ( 643 K) , which is over 25 ° C higher than the formal melting temperature . This was observed experimentally in the exemplary embodiment of Figure 22 . In this embodiment , the electrostatically adhered PEEK material was cured for 15 minutes at 370 ° C . The resulting cover is closed but not fully homogenous. At this temperature, lumps in the cover material may still be visible.

[0111] Optimal coating for PEEK can be achieved using a curing temperature of 390°C. Also, it is particularly preferred to use the above-described conditions, and in particular a curing time of 15 min. For example, the above-described curing profile for PEEK can be used (heating from room temperature with 15°C / min to 390°C, a curing time of 15 min at 390°C and then slow cooling to room temperature, which is not specifically controlled) . In this way, the coating as shown in Figure 23 can be obtained. As can be seen, there is hardly any change in coloring of the material, which means that there are no or hardly any negative effects from thermal or oxidative degeneration. Furthermore, the cover is not only closed but fully homogenous and smooth.

[0112] A further experiment is shown in Figure 24. Here, a curing temperature of 430°C and a curing time of 10 min was applied. As can be seen in the color image originally submitted, a considerable browning of the PEKK material can be observed. This can indicate thermal and / or oxidative degeneration. Nevertheless, even at this high curing temperature the cover material is closed. Also, the cover material is sufficiently homogenous. In addition, the sensor still produces reliable test results.

[0113] From the experiments conducted here, the inventors conclude that a curing temperature of 370°C to 430°C can be used for forming a cover using PEKK. They found that an optimal coating can be achieved around 390°C, for example between 380°C and 400°C, or at 390 ± 5 °C. Reference sign list

[0114] 1 sensor

[0115] 2 head portion

[0116] 3 thermistor component

[0117] 3a first electrode

[0118] 3b second electrode

[0119] 4 first connection portion

[0120] 5 second connection portion

[0121] 4a, 5a solder

[0122] 6 glass encapsulation

[0123] 7 cover

[0124] 8 first wire

[0125] 8a conductive portion of the first wire

[0126] 8b insulation of the first wire

[0127] 8c kink in the first wire

[0128] 9 second wire

[0129] 9a conductive portion of the second wire

[0130] 9b insulation of the second wire

[0131] 9c kink in the second wire

[0132] S line of symmetry

Claims

Claims (We claim)1 . Sensor comprising a thermistor component and a cover covering the thermistor component at least partially, wherein the material of the cover comprises a polyaryletherketone , a polyphenylene sul fide , an aromatic thermosetting copolyester, a liquid crystal polymer, a polyamide , a polyimide , a polyamide imide , or a polybenzimidazole .2 . Sensor according to claim 1 , wherein a first wire contacts the thermistor component .3 . Sensor according to claim 2 , wherein the cover covers at least the region wherein the first wire makes contact with the thermistor component .4 . Sensor according to claims 2 or 3 , wherein the sensor comprises a second wire which contacts the thermistor component , and wherein the region in which the second wire makes contact with the thermistor component is covered by the cover .5 . Sensor according to any of claims 2 to 4 , wherein, in addition to covering at least parts of thermistor component , the cover covers parts of the first wire other than the region wherein the first wire makes contact with the thermistor component , and wherein the part of the cover covering the thermistor component and covering the first wire forms a continuous layer .6 . Sensor according to any of claims 2 to 5 , wherein the first wire has an insulation separate from the cover .

7. Sensor according to any of claims 2 to 6, wherein the first wire is welded to the thermistor.

8. Sensor according to any of the preceding claims, wherein an encapsulation comprising glass is arranged between the cover and the thermistor component.

9. Sensor according to any of the preceding claims, wherein the cover covers the entire thermistor component.

10. Sensor according to any of the preceding claims, wherein the thickness of the cover is between 5 to 500 pm.

11. Sensor according to any of the preceding claims, wherein the cover material is polyetheretherketone or polyetherketoneketon .

12. Sensor according to any of the preceding claims, wherein the material of the cover comprises or is polyetheretherketone or polyetherketoneketon.

13. Sensor according to any of the preceding claims, wherein the cover is applied by electrostatic coating.

14. Sensor according to any of the preceding claims, wherein the cover is applied including a curing step at a temperature of 370°C or above.

15. Sensor according to any of the preceding claims, wherein the cover is closed.

16. Sensor according to any of the preceding claims, wherein the cover is homogeneous.

17. Use of a polyaryletherketone, a polyphenylene sulfide, an aromatic thermosetting copolyester, a liquid crystal polymer, a polyamide, a polyimide, a polyamide imide, or a polybenzimidazole for covering a thermistor component.

18. Process of manufacturing a sensor, wherein a thermistor component is contacted by a first wire and a second wire, applying a cover to the thermistor component and parts of the wires which are attached to the thermistor component, wherein the material of the cover comprises a polyaryletherketone, a polyphenylene sulfide, an aromatic thermosetting copolyester, a liquid crystal polymer, a polyamide, a polyimide, a polyamide imide, or a polybenzimidazole.

19. Process of manufacturing a sensor according to claim 18, wherein the material of the cover comprises or is polyetheretherketone or polyetherketoneketone.

20. Process of manufacturing a sensor according to claim 18 or 19, wherein the cover is applied via dip coating or electrostatic coating.

21. Process of manufacturing a sensor according to any of claims 18 to 20, wherein the cover is applied using repeated dip coating and / or electrostatic coating.

22. Process of manufacturing a sensor according to any of claims 18 to claim 21, wherein before applying the cover an encapsulation comprising glass is applied to the thermistor component .23 . Process of manufacturing a sensor according to any of claims 18 to claim 22 , wherein applying the cover includes drying and / or curing of a starting material for the cover . 24 . Process of manufacturing a sensor according to any of claims 18 to claim 23 , wherein the cover is applied including electrostatic coating and curing at a curing temperature of above 370 ° C . 25 . Process of manufacturing a sensor according to any of claims 18 to claim 24 , wherein the wires are applied via welding .

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