WO2025219269A1

WO2025219269A1 - Process of forming a cover and sensor

Info

Publication number: WO2025219269A1
Application number: PCT/EP2025/060086
Authority: WO
Inventors: Saša Šabeder Daiminger; Elias Hammer; Lamablawa Mario Valentino ALFARRO SAMON MASAN; Gerhard Hojas; Lu He; Jan Ihle
Original assignee: TDK Electronics AG
Current assignee: TDK Electronics AG
Priority date: 2024-04-16
Filing date: 2025-04-11
Publication date: 2025-10-23
Anticipated expiration: 2026-10-16
Also published as: DE102025114422A1; DE102025114421A1

Abstract

Here is provided a process of forming a cover, by providing an electronically functional component, covering the electronically functional component by applying a molten polymer or molten polymer precursor to the outside of the electronically functional component, or placing the electronically functional component into a pre-form comprising a polymer forming means, wherein the pre-form encloses the electronically functional component from more than one side, or placing the electronically functional component into an injection mold and filling at least part of the mold by a polymer forming means, or placing the electronically functional component into the concave portion of a cap and at least partially filling the volume between the inner concave side of the cap and electronically functional component by a polymer forming means.

Description

Process of forming a cover and sensor

The present application concerns a process of forming a cover and a sensor .

Electronically functional components in general and sensors such as temperature sensors in particular, for example using NTC ceramic thermistor components , can have polymer covers . These can provide protection or electrical insulation .

In this field there is a demand for new ways of forming such covers or forming such covers in desired shapes . Also , topics such as environmental friendliness can in some cases be of importance .

At least some of these demands are at least partially 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 .

According to an embodiment , a process of forming a cover is provided . The cover is formed on or around an electronically functional component . For this an electronically functional component is provided and a molten polymer or molten polymer precursor is applied to the outside of the electronically functional component to form the cover .

Using a molten polymer or a molten polymer precursor has the advantage that an additional curing step or polymeri zation step of the polymer can be avoided . In case of forming a polymer from a solution that for example contains a polymer precursor, the solution must be dried, i . e . a solvent must be evaporated of f and subsequently the polymer has to be cured . In contrast using a molten polymer the polymer simply hardens by cooling . When using a molten polymer precursor, the melting of the precursor can be used to initiate or cause polymeri zation or curing, such as cross linking in a resin .

For example , according to an embodiment , the electronically functional component can be dipped into the molten polymer or molten polymer precursor . Thus , covers of round shapes or drop-like shaped coverings can be formed . In particular for the polymers described below, cover-thicknesses that are suf ficient to insulate or protect the electronically functional component can be achieved . This allows for forming covers of the thicknesses discussed below . In particular the advantageous thickness range of 350 to 450 pm can in many cases easily been reali zed . In case the electronically functional component have a wire attached, this wire can be used to hold the electronically functional component for dipping in into the molten polymer or molten polymer precursor .

According to an embodiment , which can be a variation of the previously mentioned embodiment the cover can formed by repeated dipping of the electronically functional component into the molten polymer or molten polymer precursor . Such an increased thicknesses may be obtained . Between each dipping step a cooling or hardening step may be performed .

According to another embodiment , the electronically functional component can be placed into a pre- form that encloses the electronically functional component from more than one side. The pre-form comprises or consist of the polymer forming means. In other words, the polymer forming means can be provided in a preformed shape. The polymer forming means are any substance or mixture of substance from which a cover can be formed. Examples will be provided below. According to this embodiment the pre-form may have any shape, as long as it is capable of surrounding the electronically functional component from more than one side. The enclosing portion of the pre-form may be an inner wall of the pre-form.

In order to form the cover the polymer forming means of the pre-form can be heated and thus adhere to the electronic component .

According to a variation of the previous embodiment, which may be preferred in some cases, the pre-form is capable of surrounding an entire circumference of the electronically functional component. This can help to have a better coverage and/or protection.

According to a further variation of the previous embodiments, the pre-form can have a tube-like shape or be a tube. Accordingly, the polymer forming means can be provided as a tube. In such a tube, the electronically functional component can be placed. Using a tube, a more homogeneous cover can be formed. Also, it is easier to maintain a more homogeneous cover thickness. Further the circumference of the cover may be defined by the diameter of the tube. This may be advantageous for inserting the product into certain spatially demanding surroundings .

According to a further variation of the previous embodiments, the pre-form can have a cuboid or rectangular shape. I.e. it can have a rectangular or square inner cross section . Thus , a cover with flatter sides can be formed than by using a round tube .

According to another embodiment , the cover can be formed by using a mold . Preferably the mold can be an inj ection mold . The electronically functional component can be placed into said mold or inj ection mold . At least part of the mold can be filled by a polymer forming means . Concerning the polymer forming means , the above said as well as the examples below may apply . Preferably the entire mold can be filled with a polymer forming means such that a closed cover can be formed around the electronically functional component . Here and in the following a closed cover can mean a cover that encapsulates the entire electronically functional component except for connections such as wires leading out of said cover . In case of inj ection molding the polymer forming means can be applied in any form, yet it is preferably applied in a liquid-like form, such as the below discussed molten forms or from a solution or a dispersion . Also , here the order of filing the mold and placing the electronically functional component into the mold is not limited, though it is preferred at least in the case of inj ection molding to place the electronically functional component first and then fill the mold with the polymer forming means . Yet the mold may also be pre- filled with the polymer before the electronically functional component is placed into the mold .

The mold may have any inner shape , to tailor the shape of the cover, for example to fit speci fic applications . According to embodiments , the mold may have a cylindrical or cuboidal inner shape . According to another embodiment , the cover can be formed using a cap . In this case , the electronically functional component can be placed into the concave portion of the cap and the space or the volume between the inner concave side of the cap and the electronically functional component can be filled by a polymer forming means . The order of placing the electronically functional component into the cap and of applying the polymer forming means is not limited . In particular, the cap can be pre- filled and the electronically functional component can be put into the polymer forming means , for example by pushing pressing it into it .

Alternatively, the electronically functional component can be positioned in the cap first and then the volume is filled by the polymer forming means . Also portions of the cap can be pre- filled then the electronically functional component can be placed in the cap and then further portions of the cap can be filled with further polymer forming means . Concerning the polymer forming means the above said as well as the examples below may apply . Yet , using a cap, the inventors found that it is advantageous to use the polymer forming means in a molten form or in a powder form . Examples or embodiments regarding molten forms or powder forms are addressed below .

In the previous embodiment the shape of the cap is not limited, as long as it has a concave portion . As concave portion every inwardly directed hollowing is understood . For example , the cover can have a dome-like inner shape or a cuboidal inner shape . A dome-like inner shape can for example be a shape of a hal f sphere or a distorted hal f sphere . For the cuboidal inner shape it is preferred that one side of the cuboid has no wall so that via this opening the electronically functional component can be placed into the cap . According to a variation of the previous embodiment , the cap can be removed from the cover in the process or preferably at its end . I . e . a finished product may have a cover but no cap stuck to it .

According to an alternative variation of the previous embodiment the cap can be left on the cover . Such the cap can provide additional protection . Also , a process step of removing the cap can be avoided . In other words , a product can be finished without the cap being removed, i . e . a product may have a cover and a cap .

The material of the cap generally is not limited . Preferably it is capable of withstanding the conditions of the forming of the cover . Accordingly, it may be capable of withstanding the temperature of the molten polymer forming means or a curing temperature .

According to an embodiment , which can apply to all embodiments in which a polymer forming means is used, the polymer forming means is not limited . The polymer forming means can be any substance or mixture or other means from which or with which a polymer-containing cover can be formed .

For example , the polymer forming means may be a molten polymer or a molten polymer precursor . A molten polymer can be hardened easily by cooling . When using a molten polymer precursor, the melting temperature of the precursor can be used to initiate or cause polymeri zation or curing . Thus , a separate polymeri zation step or curing step may be avoided . According to another example , a solution or dispersion containing a polymer or containing a solution or dispersion containing a polymer precursor may be used as polymer forming means .

According to another example , a polymer powder, or a powder of a polymer precursor may be used as polymer forming means . The powder can be applied in powder form to the outside of the electronically functional component . For example , this can be done using the mold or the cap . The powder can be heated to stick to the electronically functional component . In the case of the polymer powder melting and setting may suf fice to form the cover . In the case of the powder of a polymer precursor, the melting may initiate polymeri zation or curing .

The above-described methods of working with a molten or powder form of the polymer forming means can have an advantage over methods using solutions of a polymer or of a polymer precursor . Using the molten or powder form of the polymer forming means , a high concentration of polymer or polymer-precursor can be applied to the electronically functional component and thus additional or repeated coating steps can be avoided . Also using the mold, or the cap, the volume filled by this type of polymer forming means can have manly the same volume after solidi fication or curing . Using a solution-based approach will result in a considerable volume loss between application state and cured state , as solvent has to be removed for example by evaporation .

According to an embodiment , which can apply to all above embodiments the molten polymer or molten polymer precursor or the polymer forming means can comprise a polyaryletherketone (abbreviated: PAEK) , a polyphenylene sulfide (abbreviated: PPS) , an aromatic thermosetting copolyester (abbreviated: ATSP) , a liquid crystal polymer (abbreviated: LCP) , a polyamide (abbreviated: PA) , a polyimide (abbreviated: PI) , a polyamide imide (abbreviated: PAI) , or a polybenzimidazole (abbreviated: PBI) .

The molten polymer or molten polymer precursor or the polymer forming means 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 said molten polymer or molten polymer precursor or the polymer forming means. The molten polymer or molten polymer precursor or the polymer forming means can consist of said substances or a mixture of said substances except for minor technical impurities .

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, 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 .

Also , at least some of the substances show a higher electrical insulation strength than PFAS-based materials . At least some of the above substances are non-transparent . —The same applies to the fact that a uni form optical appearance can be achieved with at least some of the substances .

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 costef ficient than PFAS-based materials . Furthermore , at least some of the above-described materials have lower density than the PFAS-based materials .

In particular, the listed substances can well be used for the above-described processes as they allow melting as well as application from solution . Furthermore , as above substances create harder covers than PFAS based covers , they can easily be applied as a pre- form or using a mold or a cap, as they tend to adhere suf ficiently to the electronically functional component and do not get damaged by removing from said mold, or cap . Further they provide better protection than PFAS .

For PPS it has been found that it is particularly suited for the above application techniques . In particular, applying the PPS in molten form or powder form showed better or more continuous covers being formed than using techniques for coating from solution .

According to an embodiment the cover can be formed with polyetheretherketone ( abbreviated : PEEK) or polyetherketoneketon ( abbreviated : PEKK) . 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 ful fill many of the above-described advantages . In particular, PEEK has a lower density than PFAS-containing covers . PEEK materials can have a density of 1 . 3 g/ml , whereas PFAS 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 of f 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 a thermistor component , which is an example of an electronically functional component , or to a glass encapsulation or wires . For example , in a peel-of f test a failure mode at 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 .

According to an embodiment the electronically functional component in all other embodiments can be a ceramic based electronically functional component . For example , the electronically functional component can have a ceramic body and can be addressed as electronically functional ceramic component . The electronically functional ceramic component can be a multilayer component , which for example has inner electrodes . Alternatively, it may be a monolithic ceramic component . 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 component can be di f ferent from a multilayered component , in that the monolithic thermistor has no inner electrodes .

According to an embodiment the electronically functional component in all other embodiments can have a sensor functionality . Accordingly, a product formed with the process can be a sensor, such as temperature sensor . According to an embodiment the electronically functional component in all other embodiments can be a thermistor . 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 can be provided to cover the thermistor component . For such a thermistor component , the inventive cover or the process of forming such cover is particularly preferred .

The thermistor is not limited in its shape . It may have two opposing manly flat sides , which can, for example , be sites of a cuboidal or cylindrical thermistor body . These sides may have an electrode or metalli zation .

According to an embodiment the electronically functional component can be contacted by one or more wires . The wire or the wires can be attached to the electronically functional component before forming the coating . In particular, for a thermistor component a first wire and a second wire may be attached for example to the described metalli zations . The first and second wire are preferably applied to di f ferent sides of the thermistor .

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 . According to an embodiment , the cover is formed such that it 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 . 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 .

Alternatively, to a second wire , the thermistor component or the electronically functional component in general 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 .

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 .

According to an embodiment , the cover can be formed such that it covers 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 be formed such that it covers 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 .

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 are brought into contact with the thermistor component , the insulation is removed . It is preferred that the cover is formed to cover 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 . 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 silver-plated wires can be employed .

According to an embodiment , an encapsulation comprising glass can be formed or arranged between the cover and the electronically functional component . This encapsulation can be addressed as a glass encapsulation . The electronically functional 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 electronically functional component by covering portions of the glass encapsulation or by covering a portion of the electronically functional component that is not covered by the glass encapsulation . According to a preferred embodiment the entire glass encapsulation is covered by the cover . The glass encapsulation can provide additional insulation or mechanical or chemical protection .

The glass encapsulation, however, is optional and omitting the glass encapsulation can help to reduce the response times of the sensor or reduce complexity and production costs . The above described hard materials and the above described cover forming methods can help to avoid the necessity for a glass encapsulation, as the resulting shapes can often provide suf ficient insulation or mechanical or chemical protection .

According to an embodiment , the thickness of the cover formed by the above methods can be between 5 to 1000 pm or preferably between 5 to 500 pm . Preferably, the thickness of the cover can lie between 50 and 200 pm and even more preferably between 100 pm and 150 pm . Alternatively and also preferred, the thickness can be between 350 to 550 pm and even more preferably between 350 and 450 pm . A thickness of at least 5 pm can help to ensure suf ficient chemical stability, corrosion resistance and insulation . A thickness of below 1000 pm can help to achieve suf ficiently short sensor response times . These advantages are more prominent for the preferred ranges . In particular in the preferred range of 350 to 550 gm and also for 350 to 450 gm breakdown voltages of 6 kV or above can be achieved.

As will be explained in the following, the thickness of the cover can be non-uniformly . Yet the above methods may help to have a cover of uniform thickness. For example, by the above described means for realizing a cuboidal shape of the cover around a mainly cuboidal electronically functional component, the thickness in the region of the edges may be maintained. In contrast, if a mainly cuboidal electronically functional component is covered by a cover of round shape, the thickness may be reduced at the edges, which may in some cases create a weak point.

Furthermore, as further embodiments, sensors are described. These may generally be formed by any means in the described shapes. Yet they may be formed using the above-described methods. Accordingly, the above disclosed structural and functional properties may also apply to the sensor.

According to an embodiment, a sensor comprising a thermistor component and a cover covering the thermistor component at least partially is described. The cover may be formed by any means. Preferably it is formed from a molten polymer precursor, or by applying a pre-form enclosing the thermistor component from more than one side, or by injection molding, or by filling into a cap. I.e. the cover may be formed by the above described means.

According to an embodiment 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 polyamide ( abbreviated : PA) , a polyimide ( abbreviated : PI ) , a polyamide imide ( abbreviated : PAI ) , or a polybenzimidazole ( abbreviated :

PBI ) . 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 .

These cover materials have the above described advantages and the above discussed details may apply .

According to an embodiment , the thermistor component can be contacted by a first wire and/ or a second wire as already discussed for the process . Also the optional details concerning a separate insulation of the wires or the covering modes discussed above also apply here .

According to an embodiment an encapsulation comprising glass can be arranged between the cover and the thermistor component . Again the above described details may apply .

According to a speci fic embodiment , an 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 an optional glass encapsulation or the thermistor directly component 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 . The above discussed features may also apply here .

According to an embodiment the cover can have a drop-like shape . Such a drop-like shape can be achieved by dip-coating, for example , but a sensor having a cover of such shape is disclosed here independent from the manufacturing method . The drop-like shape may be advantageous , as it is a shape which not easily gets stuck i f a sensor is inserted into application, as it has no edges .

According to an embodiment the cover can have a shape having one or more flat surfaces . For example , the shape may be cube-like or cuboidal or cylindrical . It may be achieved with the above-described means but is not limited to that . This shape can have the above-described advantage of enforcing the edges .

According to an embodiment the cover can comprise or have a dome-like shape . It may be achieved with the above-described means but is not limited to that .

According to an embodiment the cover can comprise a protruding rim . This can preferably be the case for dome-like shaped covers or covers having one or more flat surfaces . Such rims can be formed by the cap-based method . They may enforce the structure of the cover . Thus , a glass encapsulation more easily can be made unnecessary, as no additional physical protection by the glass is required .

According to an embodiment , a cap can be arranged on a part of the cover . This configuration can result from the above described method but is not limited to that . In principle , a cap may also be applied subsequent to forming the cover . The cap can in any case comprise or consist of the above defined materials . Alternatively to the cover, also the cap can have a protruding rim .

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 .

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

Figure 2 shows a schematic cross-section of the head portion of the first exemplary embodiment of a sensor .

Figure 3 shows a photographic image of a sensor according to a second exemplary embodiment of a sensor .

Figure 4 shows a photographic image of a sensor according to a third exemplary embodiment of a sensor .

Figure 5 shows a cross-section photograph of the head portion of a sensor according to a fourth exemplary embodiment of a sensor .

Figure 6 shows a photographic image of a sensor according to a fi fth exemplary embodiment of a sensor . Figure 7 shows a schematic cross-section of a sixth exemplary embodiment of a sensor .

Figure 8 shows a schematic cross-section of the head portion of the sixth exemplary embodiment of a sensor .

Figure 9 shows a schematic cross-section of a seventh exemplary embodiment of a sensor .

Figure 10 shows a photograph of a sensor according to the seventh exemplary embodiment of a sensor .

Figure 11 shows a schematic cross-section of an eighth exemplary embodiment of a sensor .

Figure 12 shows a cross-section photograph of the head portion of a sensor according to the eighth exemplary embodiment of a sensor .

Figure 13 shows a schematic side view of a nineth exemplary embodiment of a sensor .

Figure 14 shows a schematic side view of the head portion of the nineth exemplary embodiment of a sensor .

Figure 15 shows a schematic side view of a tenth exemplary embodiment of a sensor .

Figure 16 shows a schematic side view of the head portion of the tenth exemplary embodiment of a sensor .

Figure 17 shows a thermistor component with electrodes . In Figures 1 and 2 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 the head portion 2 of the sensor is shown in schematic cross-section .

It can be seen from the line of symmetry S in Figures 1 and 2 , that the sensor 1 can be fairly symmetric . Yet the first exemplary embodiment and the invention in total is not limited to that and components such as the wires 8 and 9 may vary in their shape .

As can be seen, in Figure 1 , internal components of the sensor are depicted with dashed lines . Figure 2 provides a more detailed view on these components with continuously drawn lines .

The sensor 1 according to the first exemplary embodiment is a temperature sensor . It has a thermistor component 3 , which is an example of an electronically functional component . The thermistor component 3 is electrically contacted by a first connection portion 4 and a second connection portion 5 which establish the contact between the thermistor component 3 and the first wire 8 and the second wire 9 , respectively . The connection portions 4 and 5 may be portions of the wires 8 and 9 , respectively .

What is not explicitly labeled in Figure 1 , but is apparent from Figure 2 , is that the thermistor 3 has , on two opposing surfaces , a first electrode 3a and a second electrode 3b, via which the electrical connection portions 4 and 5 are contacting the thermistor . Also , in Figure 2 the electrodes 3a and 3b are depicted as thin lines which represents the thin-layer nature of the electrodes . These can be reali zed as metalli zations .

A more detailed image of a thermistor 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 .

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 . Here , the thermistor is a monolithic thermistor made from stacked green sheets which are sintered together .

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

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 2 , 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 .

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 can have a cloudy and non-transparent beige color . In principle , the present cover 7 can be provided in di f ferent colors, which for example allows easy differentiation of different sensors, for example.

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) .

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.

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.

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 off 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 .

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 .

Also , the present material showed chemical inertness against measurement media at 0 ° C and even lower temperatures . 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 .

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 di f ference as PEEK has a density of 1 . 3 g/ml , while PFAS-based materials have a density of around 2 . 1 g/ml .

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 1000 pm can be used . More preferred is an upper thickness of 500 pm . Alternatively and easily available via the below process the thickness can be between 350 to 450 pm . For the representation of the first exemplary 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.

The cover 7 has a droplet-like shape. This can result from the production method. This shape can be realized via injection molding using an appropriately shaped mold. Alternatively, the droplet-form can also be realized using a pre-form, such as a tube orby dipping the uncovered sensor comprising the thermistor 3, the wires 8 and 9 and the glass cover 6 into molten PEEK. PEEK is a polymer that can be molten without decomposition at temperatures of above 343°C such as above 350°C. Heating can for example go as high as 390°C.

After dipping the deposited PEEK hardens by cooling.

To increase the thickness, several dipping/hardening cycles can be applied.

By dipping into the molten polymer, a separate curing step can be avoided.

Alternatively other polymers, such as other polyaryletherketones (abbreviated: PAEK) or a polyphenylene sulfide (abbreviated: PPS) , aromatic thermosetting copolyester (abbreviated: ATSP) , liquid crystal polymer (abbreviated: LCP) , polyamide (abbreviated: PA) , polyimide

(abbreviated: PI) , polyamide imide (abbreviated: PAI) , or polybenzimidazole (abbreviated: PBI) can be used.

In particular for PPS the formation of the cover by dipping has been found to be advantageous over other deposition techniques. In particular PPS is difficult to dissolve in many solvents but can be molten without decomposition by heating to temperatures of above 285°C. For example, PPS can be heated from room temperature with 15°C/min to 370°C. After that the thermistor and part of its components can be dipped into the molten PPS and then removed. Subsequently the sensor with the hot cover can be cooled to room temperature. Unassisted cooling at air is sufficient to have slow enough cooling to room temperature. No further control is required.

For example, ATSP undergoes a crosslinking reaction when in molten form. It can be heated from room temperature with 15°C/min to 270°C. After that a thermistor and parts of its components can be dipped into the molten ATSP and then removed. While ATSP is in its molten form a polymer the crosslinking reaction occurs, changing the properties of ATSP. After unassisted cooling at air the crosslinked cover has been applied to the thermistor.

Accordingly, a process of manufacturing the sensor according to the first exemplary embodiment comprises providing the thermistor component 3. The 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. 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 .

Subsequently the cover 7 is applied by the methods described above . In particular these methods allow to cover the thermistor component by the cover 7 by covering the outside of the glass encapsulation 6 as well as portions of the wires 8 and 9 .

This entire approach can be generali zed to any type of electronically functional component instead of the thermistor component 3 .

In Figure 3 a photograph of a second exemplary embodiment of a sensor 1 is shown . The second exemplary embodiment may have basically the same components as the first exemplary embodiment . In the figure , the wires 8 and 9 can be seen . Furthermore , the head 2 can be seen . All the internal elements of the head are covered in the cover 7 .

The second exemplary embodiment is formed using a PEEK tube as a pre- form with an outer diameter of 1 . 2 mm and inner diameter of 0 . 8 mm . The tube had a length of 5 mm . The sensor element was inserted into the PEEK tube . Subsequently the tube was then molten at 390 ° C . The molten material adheres to the thermistor component 3 and the wires 8 and 9 . As can be seen from Figure 3 a droplet like form results for the cover 7 , which length is shorter than the length of the tube . A contraction to 25 to 75 % of the length of tube can be observed. This is observed also for the other polymer forming means .

In Figure 4 a photograph of a third exemplary embodiment of a sensor 1 is shown. The third exemplary embodiment can be identical to the second exemplary embodiment except that a larger portion of the wires 8 and 9 are covered.

The third exemplary embodiment is formed using a PEEK tube with an outer diameter of 1.2 mm and inner diameter of 0.8 mm. The tube had a length of 15 mm. The sensor element was inserted into the PEEK tube. Subsequently the tube was then molten at 390°C. The molten material adheres to the thermistor component 3 and the wires 8 and 9 along the length of the tube. In comparison to the second exemplary embodiment the longer length of the tube resulted in a larger portion of the wires also being covered.

As can be seen, by using a longer tube, a more cylindrical overall coverage-form can be achieved. This also helps to form a continuous coating.

In Figure 5 a cross section photograph of the sensor head 2 of a fourth exemplary embodiment of a sensor 1 is shown. The fourth exemplary embodiment can be identical to the second exemplary embodiment except for the following differences.

First in difference to the first and second exemplary embodiment, the sensor 1 has no glass encapsulation 6. The other components are identical. Please note that in this image the electrodes 3a and 3b are well visible. The cover 6 is applied in a similar manner as for the second and third exemplary embodiment . By using a PEEK tube as a pre- form, a very symmetrical diameter of the cover in cross section perpendicular to an axis of symmetry S can be achieved . As the thermistor 3 and the other components are not cylindrical , depending on the point of measuring, a cover thickness of 350 to 550 pm was achieved . This ensures good protection and good insulation . Thus , no glass encapsulation is needed .

In Figure 6 a photograph of fi fth exemplary embodiment of a sensor 1 is shown . The fi fth exemplary embodiment is mainly identical to the third exemplary embodiment and formed by a tube of the same dimensions as discussed for the third exemplary embodiment .

In di f ference to the third exemplary embodiment the wires 8 and 9 have a preformed insulation 8b and 9b, as is further explained for other embodiments below . The insulation 8b and 9b is also made of PEEK . By melting the PEEK tube over the thermistor for forming a cover 7 a good material adhesion and a connection on the molecular level between the insulation 8b and 9b and the cover 7 is formed .

Figures 7 and 8 show a sixth exemplary embodiment of a sensor 1 . In Figure 7 the entire sensor 1 is shown, in a manner similar to Figure 1 . In Figure 8 a head portion 2 is shown . 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 except for the following di f ferences . Similar as the fi fth exemplary embodiment , pre-insulated wires that 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, respectively . The insulation may consist of or comprise PEEK . In a portion of the wires 8 and 9 next to the connection 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 .

Furthermore , the shape of the head portion 2 di f fers signi ficantly from the first exemplary embodiment . The head portion 2 has a cuboidal shape due to the cuboidal shape of the cover . This shape has the advantage that for a mainly cuboidal thermistor 3 the edges can be enforced . I f a rounded shaped cover such as depicted in Figure 2 is compared, it can be seen that a thin point in the cover 7 is present at the edges of the thermistor 3 . These thin points can be avoided having the cuboidal form of the cover 7 .

This shape can be formed by using a rectangular shaped preform in a manner similar as described above for the tube . More preferred, inj ection molding can be used . In inj ection molding a polymer powder or the molten polymer is inj ected into a mold of speci fic form, here a rectangular shape . The uncovered sensor is placed in the form before inj ecting the polymer powder or the molten polymer . Thereby the sensor can be covered or encapsulated by a cover 7 which form is defined by the shape of the mold .

Figures 9 and 10 show a seventh exemplary embodiment of a sensor 1 . The seventh exemplary embodiment is mainly identical to the sixth exemplary embodiment and can be manufactured identically . The only di f ference can be seen in the connection portions 4 and 5 , which are shaped di f ferently . They are flattened in the present exemplary embodiment . Also in the present exemplary embodiment the connection of the wires 8 and 9 via the connection portions 4 and 5 is achieved by welding .

Figures 11 and 12 show an eighth exemplary embodiment of a sensor 1 . The eighth exemplary embodiment is mainly identical to the seventh exemplary embodiment and can be manufactured identically . It di f fers however in that the transition between the cover and the insulation 8b and 9b is not as flush . Furthermore , in the present case no glass encapsulation is reali zed . Due to the enforced edges by the cuboidal shape of the cover 7 the glass encapsulation is even less required than in other cases .

Also 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 eighth 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 .

Figures 13 and 14 , and 15 and 16 show a nineth and tenth exemplary embodiment of a sensor, respectively . The depictions in Figures 13 and 15 shows the entire sensor and Figures 14 and 16 each show the head portion, similarly as for the other exemplary embodiments . However here the interior of the sensor head is not depicted . The interior can be the same as in any of the above shown exemplary embodiments . Both the nineth and tenth exemplary embodiment have pre-insulated wires similar to the sixth exemplary embodiment and kinks similar to the eighth exemplary embodiment . In Figure 13 no line of symmetry is depicted while it is shown for Figures 14 to 16 .

The nineth and tenth exemplary embodiment further di f fer from the other exemplary embodiments in that the cover is not visible in the Figures . It is completely established on the inside of a cap 10 in both cases . In the nineth exemplary embodiment the cap 10 has a dome like shape and in the tenth exemplary embodiment it has a cuboidal shape . The cap 10 can be made of metal , glass or ceramic, yet metal or ceramic are preferred . The cap can structurally further support the sensor . Thus a glass encapsulation can be reali zed but is less preferred and less advantageous than in other embodiments .

The cap 10 in both cases has a rim 11 . The rim 11 further supports the sensor structurally for easier assembly .

The nineth and tenth exemplary embodiment can be manufactured by placing the sensor ( thermistor and portions of the wires ) into the inside of the cap together with polymer powder or molten polymer or a polymer precursor . The inside of the cap can also be addressed as concave portion of the cap . In case of the powder, the powder is molten by heating to the above described temperatures . In both cases of inserting into molten polymer and inserting into powder and then melting, the cover is hardened by cooling . In the finished sensor the caps can remain part of the sensor .

The nineth and tenth exemplary embodiment can also be intermediate stages . By removing the cap 10 , a sensor with a cover 7 that is shaped by the inside of the cap 10 can be manufactured .

Reference sign list

1 sensor

2 head portion

3 thermistor component

3a first electrode

3b second electrode

4 first connection portion

5 second connection portion

4a, 5a solder

6 glass encapsulation

7 cover

8 first wire

8a conductive portion of the first wire

8b insulation of the first wire

8c kink in the first wire

9 second wire

9a conductive portion of the second wire

9b insulation of the second wire

9c kink in the second wire

10 cap

11 rim

S line of symmetry

Claims

Claims (We claim)

1 . Process of forming a cover, by providing an electronically functional component , covering the electronically functional component by applying a molten polymer or molten polymer precursor to the outside of the electronically functional component , or placing the electronically functional component into a preform comprising a polymer forming means , wherein the pre- form encloses the electronically functional component from more than one side , or placing the electronically functional component into an inj ection mold and filling at least part of the mold by a polymer forming means , or placing the electronically functional component into the concave portion of a cap and at least partially filling the volume between the inner concave side of the cap and electronically functional component by a polymer forming means .

2 . Process according to claim 1 , wherein the polymer forming means is or contains a molten polymer, a molten polymer precursor, a solution containing a polymer, a solution containing a polymer precursor, a dispersion containing a polymer, a dispersion containing a polymer precursor, a polymer powder, or a powder of a polymer precursor .

3 . Process according to claim 1 or 2 , wherein the molten polymer or molten polymer precursor or the polymer forming means comprises a polyaryletherketone , a polyphenylene sul fide , an aromatic thermosetting copolyester, a liquid crystal polymer, polyamide , a polyimide , a polyamide imide , or a polybenzimidazole .

4 . Process according to any of claims 1 to 3 , wherein the electronically functional component is a thermistor .

5 . Process according to any of claims 1 to 4 , wherein the electronically functional component is contacted by a wire before forming the cover .

6 . Process according to any of claims 1 to 5 , wherein a glass encapsulation is applied to the electronically functional component before forming the cover .

7 . Process according to any of claims 1 to 6 , wherein applying the molten polymer or molten polymer precursor is carried out by dipping the electronically functional component into the molten polymer or molten polymer precursor .

8 . Process according to claim 7 , wherein the cover is formed by repeated dipping of the electronically functional component into the molten polymer or molten polymer precursor .

9 . Process according to any of claims 1 to 6 , wherein the pre- form has the shape of a tube and the electronically functional component is placed in said tube .

10 . Process according to any of claims 1 to 6 or claim 9 , wherein the pre- form is molten and thus establishes at least a part of a cover .

11 . Process according to any of claims 1 to 6 , wherein the mold has a cylindrical or cuboidal inner shape .

12. Process according to any of claims 1 to 6, wherein the cap is removed from the cover.

13. Process according to any of claims 1 to 6, wherein the manufacturing of the covered electronic component is finished without the cover being removed.

14. Process according to any of claims 1 to 6 or claims 11 or 12, wherein the cover formed has a dome-like inner shape or a cuboidal inner shape.

15. Sensor comprising a thermistor component and a cover covering the thermistor component at least partially, wherein the cover is formed from a molten polymer precursor, from a pre-form enclosing the thermistor component from more than one side, by injection molding, or by filling into a cap.

16. Sensor according to claim 15, wherein the material of the cover comprises a polyaryletherketone, a polyphenylene sulfide, an aromatic thermosetting copolyesters, a liquid crystal polymer, a polyamide, a polyimide, a polyamide imide, or a polybenzimidazole.

17. Sensor according to claim 15 or 16, wherein a first wire contacts the thermistor component.

18. Sensor according to any of claims 15 to 17, wherein the first wire has an insulation separate from the cover.

19. Sensor according to any of claims 15 to 18, wherein an encapsulation comprising glass is arranged between the cover and the thermistor component.

20. Sensor according to any of claims 15 to 19, wherein the cover has a drop-like shape, or a shape having one or more flat surfaces, or comprises a dome-like shape.

21. Sensor according to any of claims 15 to 20, wherein the cover comprises a protruding rim.

22. Sensor according to any of claims 15 to 21, wherein a cap is arranged on a part of the cover.