Method for manufacturing a touch and force sensor, in particular a backlit one

Abstract

The invention relates to a miniature sensor (601) comprising, on an active part (621, 622), an assembly of conductive nanoparticles in an insulating ligand, a substrate on which are deposited conductive tracks (611, 612, 613, 650) and the assembly of nanoparticles, a thin stiffener (630) bonded to the substrate by a rigid glue on a first face of the stiffener and extending under the active part and a pressure-sensitive adhesive, bonded to a second face of the stiffener (630), opposite the first face, configured for bonding the miniature sensor to a surface to be functionalized. The invention also relates to a method for manufacturing such a miniature sensor. Fig. 6

Description

Title of the invention: Method for manufacturing a touch and force sensor, in particular backlit Technical field

[0001] The invention belongs to the field of sensors capable in particular of detecting a touch and of delivering information proportional to the force applied during this touch.

[0002] Such a sensor can in particular be used instead of a control button, more particularly, but not exclusively, backlit for mass-produced applications in the fields of computer terminals, control buttons in vehicle interiors, on household electrical products, without this list being exhaustive or limiting.

[0003] These sensors allow proportional tactile controls to be integrated on any type of surface, rigid or flexible, by simple gluing, and thus advantageously replace controls traditionally made with push buttons or mechanical selectors, offering in particular the advantages of low thickness, adjustable sensitivity, much simpler integration, the absence of moving parts and the absence of mechanical contact closing / opening. Prior art

[0004] The invention implements sensors comprising an assembly of nanoparticles as described in document EP 2 601 491 AL

[0005] The sensors described in this document have very high sensitivity and, through their operation, can be attached to the surface of any substrate, rigid or flexible, in order to functionalize this surface.

[0006] By way of non-limiting example, such a sensor can be glued to an automobile accessory, such as an armrest, a dashboard or a console, directly on the surface exposed to touch or on an opposite surface (below) the surface exposed to touch, pressure on the area where the sensor is located making it possible to control an action, such as lowering or raising an electric window, turning on the windshield wipers, etc., thus avoiding the mechanical installation of any switch or commutator.

[0007] In addition, since these sensors have a variable response depending on the force applied, this information can be used directly to control the targeted device; for example, a stronger pressure results in a higher windshield wiper wiping speed.

[0008] Examples of application of such sensors in the automotive field are given in document EP 4 111 151 A1.

[0009] According to embodiments, the sensors suitable for this type of application are of the touch and force type as described in document WO 2021 170883 and comprise a proximity sensor comprising conductive tracks configured to produce a capacitive sensor and a force sensor comprising an assembly of conductive or semi-conductive nanoparticles in colloidal suspension in an electrically insulating ligand, said assembly or assemblies of nanoparticles being deposited between electrodes, advantageously interdigitated as described in document WO 2023 111344 and releasing an open or transparent central zone to allow in particular the appearance of a backlit or non-backlit pictogram.

[0010] These prior art sensors have many advantages but are poorly suited to large-scale applications for at least two stages of their implementation:

[0011] - the manufacture of the sensor or a set of sensors which according to these prior arts are made by microprinting;

[0012] - the installation of said sensors on the surfaces to be functionalized.

[0013] Indeed, the surface functionalization techniques such as described in document EP 2 877 911 B1, although effective for the applications targeted in this document, are poorly suited to the installation of sensors dispersed on various flexible and rigid surfaces in a cluttered and inaccessible environment, for example in a car interior and where the elements can be manufactured from various sources. Furthermore, this technique is not conventional and requires the development of expensive installations for implementation in very large series.

[0014] Even if the sensor is deposited on a first substrate, for example flexible, and this assembly is attached to the rigid or flexible surface to be functionalized, the first substrate + sensor assembly must be bonded to the surface to be functionalized, for example by means of a polymerizable liquid adhesive of the cyanoacrylate or epoxy type so as to ensure a firm support and an excellent mechanical coupling between the first substrate + sensor assembly with the surface thus functionalized.

[0015] In order to functionalize the surface, said miniature sensors are bonded to a surface of the substrate by means of a polymerizable liquid adhesive of the cyanoacrylate or epoxy type. This type of rigid adhesive ensures firm support and excellent mechanical coupling of the sensor to the surface of the substrate.

[0016] However, the application of these liquid adhesives, which must be applied on a small surface and with precision, is not suitable for a manufacturing process in large series, such as in the automotive industry, which prefers to use pressure-sensitive adhesives (PSA) in film form.

[0017] But the use of a pressure-sensitive adhesive film to achieve such bonding reduces, on the one hand, the capacity of the system to detect a force, which results in an apparent reduction in the sensitivity of the sensor, and on the other hand, leads to relaxation phenomena which modify the response of the device. Summary of the invention

[0018] The invention aims to resolve the drawbacks of the prior art and to this end relates to a miniature sensor comprising, on an active part, an assembly of conductive nanoparticles in an insulating ligand, a substrate on which conductive tracks and the assembly of nanoparticles are deposited, a thin stiffener bonded to the substrate by a rigid glue on a first face of the stiffener and extending under the active part and a pressure-sensitive adhesive bonded to a second face of the stiffener, opposite the first face, configured for bonding the miniature sensor to a surface to be functionalized.

[0019] Thus, the presence of the thin stiffener makes it possible to fix the sensor to a surface to be functionalized, whether this is flexible or rigid, by means of a pressure-sensitive adhesive without the disadvantage of relaxation phenomena.

[0020] The sensitivity of the area to low deformations due to the sensor technology makes it possible to maintain very high sensitivity despite the presence of the stiffener.

[0021] The invention can be implemented according to the embodiments and variants set out below, which are to be considered individually or according to any technically effective combination.

[0022] According to an exemplary embodiment, the thin stiffener is made of a polycarbonate with a thickness of between 0.05 mm and 0.2 mm.

[0023] According to exemplary embodiments, the substrate is transparent and chosen from: a polyethylene terephthalate, a cycloolefinic (co-)polymer and a polyimide.

[0024] The conductive tracks may comprise metal tracks chosen from: copper, gold, nickel and a cupronickel alloy.

[0025] Advantageously, the conductive tracks may comprise transparent tracks of a composition chosen from: an indium-doped tin oxide and an electrically conductive transparent polymer.

[0026] According to one embodiment, the miniature sensor comprises a transparent central zone, the active zone comprising the assembly of nanoparticles being located at the edge of the transparent central zone. This embodiment makes it possible to position a backlit pictogram at the level of the transparent zone.

[0027] The invention also relates to a method for manufacturing a miniature combined proximity and force sensor, comprising the steps of:

[0028] obtaining a laminate comprising a conductive thin film on a polymer substrate;

[0029] photoetching tracks in the conductive thin film;

[0030] depositing by micro-printing at least one assembly of conductive nanoparticles in an insulating ligand on an active zone between two tracks so as to create a force sensor;

[0031] gluing with a rigid glue a thin stiffener under the substrate and extending at least under the active zone; and

[0032] bonding a pressure sensitive adhesive to the thin stiffener.

[0033] This process makes it possible to use a laminate and printed circuit etching techniques for producing the sensor in large series with very high precision in producing the tracks compared to micro-printing techniques on substrate.

[0034] According to one embodiment, the laminate comprises a thin conductive film chosen from: copper, gold, nickel and a cupronickel alloy, the polymer substrate is transparent and the force and proximity sensor comprises a transparent central zone.

[0035] According to a variant of this embodiment, the laminate comprises a transparent conductive thin film and the method comprises a step of photoetching the transparent conductive thin film in the transparent central zone to create at least one transparent conductive zone configured as a capacitive sensor.

[0036] The conductive thin film is, for example, removed by photoetching in the transparent central area.

[0037] Advantageously, the method may comprise micro-printing at least one conductive central area in the transparent central area with a transparent conductive polymer, configured to create a capacitive sensor.

[0038] According to an alternative, the micro-printing of the tracks in the transparent zone is carried out by inkjet.

[0039] According to an alternative, the micro-printing in the transparent area is carried out by screen printing. Brief description of the drawings

[0040] The invention is implemented according to the preferred embodiments, which are in no way limiting, described below with reference to [Fig.l] to [Fig.8] in which: Fig.l

[0041] [Fig.l] relating to the prior art represents in a sectional view the installation of a miniature sensor on a surface to be functionalized; Fig.2

[0042] [Fig.2] relating to the prior art shows the comparative temporal responses of a miniature sensor subjected to stress levels in the case of bonding with a rigid glue and in the case of bonding with a pressure-sensitive adhesive film; Fig. 3

[0043] [Fig.3] shows in a sectional view a miniature sensor glued to a surface to be functionalized by a pressure-sensitive adhesive film and implementing the invention; Fig.4

[0044] [Fig.4] shows the comparative time responses of a sensor subjected to stress levels in the case of a sensor glued to a substrate with a rigid glue and in the case of a sensor glued to a substrate with a pressure-sensitive adhesive film but using a thin stiffener; Fig.5

[0045] [Fig.5] schematically illustrates in top view and in detail, two examples of embodiment of the active part (force sensor) of a miniature sensor comprising a transparent central zone; Fig.6

[0046] [Fig.6] shows schematically in top view an example of the embodiment of a miniature sensor comprising a force sensor and a proximity sensor located in its transparent central area; Fig.7

[0047] [Fig.7] shows in a perspective view in cutaway two examples of production of a laminate suitable for the production of conductive tracks by photoengraving; Fig.8

[0048] [Fig.8] shows according to a simplified view in partial section AA defined [Fig.6] a example of the realization of a miniature sensor. Description of the embodiments

[0049] [Fig. 1] relating to the prior art illustrates the bonding of a miniature sensor (110) on a surface (101) to be functionalized. The sensor (110) is bonded to said surface by a layer of rigid polymerizable glue (120) of cyanoacrylate or epoxy type, applied in the liquid state.

[0050] However, the application in a large-scale work situation of such a liquid glue, which must be applied to a reduced surface and with precision, is not suitable for such a manufacturing process as in the automobile industry, requires maintaining the miniature sensor (110) in contact with the surface to be functionalized (101) for the polymerization time of the glue and is difficult to carry out by a robot. This is why for this type of application, pressure sensitive adhesives (PSA) in film form are preferred.

[0051] [Fig.2], however, if the adhesive layer (120) of [Fig.l] is replaced by a film pressure-sensitive adhesive, on the one hand, the system's ability to detect force is reduced, which results in an apparent drop in the sensor's sensitivity, on the other hand, relaxation phenomena occur and modify the device's response.

[0052] Thus, [Fig.2] shows in a time (201) - output quantity (202) diagram, an example of time response (210) of a miniature sensor glued with a rigid glue, as shown [Fig.l], at stress levels, and an example of time response (220) of the same miniature sensor but where the layer of rigid glue (120 [Fig.l]), has been replaced by a pressure-sensitive adhesive film, at similar stress levels.

[0053] These result curves (210, 220) are independent of the nature of the object carrying the surface to be functionalized (101), whether it is flexible (textile) or rigid (metal, wood), whether the miniature sensor (110) is directly exposed to touch or whether it is installed on a face of the object opposite a surface exposed to touch.

[0054] [Fig.3] according to an exemplary embodiment the miniature sensor (110) is glued to the at the time of its manufacture on a thin stiffener (310) for example made of a polycarbonate with a thickness of between 0.05 mm and 0.2 mm, by a rigid glue (not shown), for example of the epoxy or cyanoacrylate type.

[0055] The miniature sensor (110) and thin stiffener (310) assembly is then attached to the surface to be functionalized (101) by means of a pressure-sensitive adhesive film (330).

[0056] [Fig.4] compares the time response (210) of the miniature sensor (110) installed according to the assembly shown [Fig.l] and glued with a rigid glue on the surface to be functionalized (101), and the time response (420) of the same miniature sensor (110) installed on the same surface to be functionalized (101) but according to the installation shown [Fig.3] implementing a pressure-sensitive adhesive film (330) and a thin stiffener (310) in both cases at the same series of stress levels.

[0057] The presence of the thin stiffener (310) eliminates the relaxation phenomena in the time response (420) of the miniature sensor attached to the surface to be functionalized by a pressure-sensitive adhesive film (330).

[0058] This result curve (420) is independent of the nature of the object carrying the surface to be functionalized (101) whether it is flexible (textile) or rigid (metal, wood), whether the miniature sensor (110) is directly exposed to touch or whether it is installed on a face of the object opposite a surface exposed to touch.

[0059] [Fig.5] according to exemplary embodiments, the miniature sensor (501, 502) comprises a transparent central zone (590).

[0060] This configuration makes it possible in particular to display a backlit pictogram in said transparent zone (590) when the miniature sensor is fixed on a surface to be functionalized comprising such a pictogram.

[0061] In these two exemplary embodiments, the miniature sensor (501, 502) comprises a force sensor extending around and outside the transparent zone (590), thus constituting an active zone and comprising two conductive tracks (511, 512, 521, 522), for example made of copper, at least locally interdigitated.

[0062] According to a first exemplary embodiment of the miniature sensor (501) the two conductive tracks (511, 512) are interdigitated all around the transparent zone (590), according to a second exemplary embodiment of the miniature sensor (502) the two conductive tracks (521, 522) are interdigitated in two zones on either side of the transparent zone (590).

[0063] Thus, the active zone of the force sensor is at least a zone extending under the interdigitation zones of the conductive tracks (511, 512, 521, 522).

[0064] These embodiments are only examples where the transparent zone (590) is substantially rectangular. Those skilled in the art understand that it can take any other shape and that the number of interdigitation zones of the electrodes around this transparent zone can be any, depending on the intended application.

[0065] To produce the force sensor, assemblies of conductive nanoparticles in an insulating ligand (560) are deposited between the conductive tracks (521, 522) in the areas where they are interdigitated, so that an assembly of nanoparticles (560) extends between the two tracks (521, 522) and is in electrical contact with each of them.

[0066] A person skilled in the art adapts this configuration shown in a detailed view of the second exemplary embodiment of the miniature sensor (502) to the first exemplary embodiment of the miniature sensor (501).

[0067] As non-limiting examples, the nanoparticles of the assembly are nanoparticles of gold, copper, carbon or indium-doped tin oxide (ITO). The ligand is for example based on phosphonic acid.

[0068] The nanoparticle assemblies (560) are, for example, deposited by inkjet or screen printing microprinting techniques.

[0069] To attach this type of miniature sensor (501, 502) to a surface to be functionalized by means of a pressure-sensitive adhesive film, a thin stiffener extending between the active area(s), where the conductive tracks are interdigitated, and the adhesive film is bonded to the sensor by gluing using a rigid glue.

[0070] According to exemplary embodiments, the thin stiffener does not cover the transparent central zone or covers it, in the latter case the thin stiffener is also made of a transparent material.

[0071] The miniature sensor (501, 502) can then be attached to an object whose surface is to be functionalized, either directly on this surface, the miniature sensor then being exposed to touch, or on a surface opposite the surface exposed to touch.

[0072] [Fig.6] according to another exemplary embodiment, the miniature sensor (601) comprises a transparent central zone (690) and at least two conductive tracks (611, 612) comprising active zones (621, 622) where the two conductive tracks (611, 612) are interdigitated and where assemblies of nanoparticles are deposited between said conductive tracks so as to create a force sensor.

[0073] Additionally, the miniature sensor comprises at least one conductive track (650, 651) which extends into the transparent central area (690) and configured to create a capacitive sensor capable of detecting proximity.

[0074] Thus, according to an exemplary embodiment, the transparent central zone (690) comprises a connection track (650) at the periphery of said zone, the latter being for example made of copper by etching, and a conductive zone (651) made by a technique of printing a transparent conductive ink, for example of the PEDOT type, covering most of the transparent central zone (690) and the connection track (650).

[0075] The advantages of this combination of proximity sensor (touch) and force sensor are explained in particular in document WO 2021 170883.

[0076] The conductive area (651) of the transparent central area is connected via the connection track (650) and via at least one conductive track (613), to an electrical connection end (640) of the miniature sensor (601).

[0077] To bond this miniature sensor to a surface to be functionalized, a thin stiffener is glued to the miniature sensor, for example under the hatched area (630) of [Fig.6].

[0078] [Fig.7] one or more miniature sensors each comprising a transparent central zone comprising a transparent proximity sensor and a force sensor at the edge of the transparent central zone, can be produced economically in large series by techniques used for producing printed circuits, starting from a laminate (701, 702) comprising a metallic conductive layer (711) on a transparent polymer substrate (710).

[0079] As non-limiting examples, the polymer substrate (711) is made of a polyethylene terephthalate (PET), a cycloolefinic (co-)polymer (COP, COC) or a polyimide with a thickness commonly between 100 qm and 300 qm.

[0080] The metallic conductive layer (711) is for example made of copper, gold, nickel or an alloy of these elements with a thickness of between 150 nm and 15 pm (1 nm = 10 9 m, 1 pm = 106 m).

[0081] According to another embodiment, the laminate (702) comprises, between the transparent substrate (710) and the metallic conductive layer (711), a transparent conductive intermediate layer (712), consisting for example of an indium-doped tin oxide (ITO). The thickness of this intermediate layer (712) is also between 150 nm and 15 pm.

[0082] The use of such a laminate (701, 702) makes it possible to produce all of the conductive tracks using a photoetching technique such as that used for the production of printed circuits in large series and in an economical manner.

[0083] Returning to [Fig. 6], according to an exemplary embodiment all of the non-transparent conductive tracks (611, 612, 613, 650) can be etched in the copper layer, the transparent conductive area (651) can be etched in the transparent conductive layer (712 [Fig. 7]) if the laminate comprises such a layer and the conductive layers are eliminated by photoetching outside the conductive tracks (611, 612, 613, 650).

[0084] A large quantity of such miniature sensors (601) can be photoetched at the same time on a laminated plate.

[0085] The precision of photoengraving can reach 10 pm for precision engraving while remaining compatible with large-scale production.

[0086] Of course, the laminate (701, 702) can comprise coating layers (711, 712) on its two faces which makes it possible, for example, to produce the proximity sensor on one face and the force sensor on the other face, or to produce force sensors on each face so as to achieve thermal compensation as explained in document US 11,366,029 B2.

[0087] The nanoparticle assemblies are deposited between and on the conductive tracks in the active parts by inkjet or screen printing microprinting techniques.

[0088] Screen printing also makes it possible to carry out all the nanoparticle deposits on an entire engraved laminated plate comprising several miniature sensors at once with a positioning precision of the order of ± 50 pm.

[0089] According to another exemplary embodiment, starting from a laminate (701) not comprising a transparent conductive layer (712), the transparent conductive zone (651) is also produced by a micro-printing technique, for example with a transparent conductive polymer of the PEDOT type (poly(3,4-ethylenedioxythiophene).

[0090] Microprinting can be done by inkjet or screen printing.

[0091] Preferably, a surface of the laminated plate receiving microprinting is pretreated by a plasma treatment so as to clean it and activate it in a step prior to microprinting.

[0092] Advantageously, a protective film, for example made of polyimide or PET, with a thickness of, for example, between 25 qm and 50 qm, can be deposited on each miniature sensor produced on the laminated plate, also by a screen printing method in one or more layers.

[0093] According to an exemplary implementation, the laminate plate comprising the miniature sensors is attached and glued to the face of a plate capable of constituting a thin stiffener, then a film of pressure-sensitive adhesive comprising for example a peelable protection is attached to an opposite face of the thin stiffener.

[0094] The individual miniature sensors can then be cut from the plate.

[0095] [Fig.8] thus each miniature sensor appears as a sandwich comprising a transparent polymer substrate (710), this is rigidly bonded by one of its faces to a thin stiffener (830) at the level of the active zones, thin stiffener on which is attached a pressure-sensitive adhesive film (840) to allow the miniature sensor to be bonded to a surface to be functionalized.

[0096] On its opposite face, the transparent substrate (710) comprises conductive tracks (611, 612, 650) obtained by photoengraving. On and between some of these conductive tracks, in active areas, assemblies of nanoparticles (560) are deposited by a micro-printing technique.

[0097] A transparent conductive area (651) is produced in a transparent central area by photoengraving or by a micro-printing technique.

[0098] A first protective layer (851) is deposited for example by screen printing, layer on which a second protective layer (852) is deposited.

[0099] The total thickness (890) of the miniature sensor thus produced is between 0.15 mm and 0.3 mm.

Claims

Claims

1. Miniature sensor (110, 501, 502, 601) comprising, on an active part (621, 622), an assembly of conductive nanoparticles (560) in an insulating ligand, a substrate on which are deposited conductive tracks (511, 512, 521, 522, 611, 612, 613, 650, 651) and the assembly of nanoparticles, a thin stiffener (330) bonded to the substrate by a rigid glue on a first face of the stiffener and extending under the active part and a pressure-sensitive adhesive (840), bonded to a second face of the stiffener (330, 630, 830) opposite the first face, configured for bonding the miniature sensor to a surface to be functionalized (101).

2. A miniature sensor according to claim 1, wherein the thin stiffener (330, 630, 830) is made of a polycarbonate having a thickness of between 0.05 mm and 0.2 mm.

3. Miniature sensor according to claim 1, wherein the substrate is transparent (710) and selected from: a polyethylene terephthalate, cycloolefinic (co-)polymer and a polyimide.

4. A miniature sensor according to claim 1, wherein the conductive tracks (511, 512, 521, 522, 611, 612, 613, 650) comprise metal tracks selected from: copper, gold, nickel and a cupronickel alloy.

5. Miniature sensor according to claim 1, in which the conductive tracks comprise a transparent conductive zone (651) of a composition chosen from: an indium-doped tin oxide and an electrically conductive transparent polymer.

6. Miniature sensor according to claim 1, comprising a transparent central zone (590, 690) the active zone comprising the assembly of nanoparticles being located at the edge of the transparent central zone.

7. A method for manufacturing a miniature combined proximity and force sensor (601), comprising the steps of: providing a laminate (701, 702) comprising a conductive thin film (711, 712) on a polymer substrate (710); photoetching tracks (611, 612, 613, 650) in the conductive thin film; microprinting at least one assembly (560) of conductive nanoparticles in an insulating ligand on an area active (621, 622) between and on two tracks (611, 612) so as to create a force sensor; bonding, with a rigid glue, a thin stiffener (330, 630, 830) to the substrate (710) and extending at least under the active area (621, 622); and bonding a pressure-sensitive adhesive film (840) to the thin stiffener (330, 630, 830).

8. The method of claim 7, wherein the laminate (702) comprises a conductive thin film (711) selected from: copper, gold, nickel and a cupronickel alloy, the polymer substrate (710) is transparent and wherein the force and proximity sensor (601) comprises a transparent central area (690).

9. The method of claim 8, wherein the laminate (702) comprises a transparent conductive thin film (712) and comprises a step of photoetching the transparent conductive thin film (712) in the transparent central area (690) to create at least one transparent conductive area (651) configured as a capacitive sensor.

10. The method of claim 8 wherein the conductive thin film (711) is removed by photoetching in the transparent central area (690).

11. The method of claim 10, comprising microprinting at least one transparent conductive area (651) in the transparent central area (690) with a transparent conductive polymer, configured to create a capacitive sensor.

12. The method of claim 11, wherein the microprinting in the transparent central area (690) is performed by inkjet.

13. The method of claim 11, wherein the microprinting in the transparent central area (690) is performed by screen printing.

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