GB2462823A

GB2462823A - A switch

Info

Publication number: GB2462823A
Application number: GB0815095A
Authority: GB
Inventors: Frank Ferdinandi; Rodney Edward Smith; Mark Robson Humphries
Original assignee: CROMBIE 123 Ltd; Semblant Ltd
Current assignee: CROMBIE 123 Ltd; Semblant Ltd
Priority date: 2008-08-18
Filing date: 2008-08-18
Publication date: 2010-02-24
Also published as: GB0815095D0

Abstract

A switch comprising one or more contacts, wherein at least one of said contacts is coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2 µm. The switch may be of use in keypads or mobile telephones, safety switches or alarm systems etc.

Description

DEVICES

The present invention relates to devices comprising contacts or contact coated with halo..

hydrocarbon polymers, or any configuration where it is desirable to create an electrical contact between two or more entities.

Many devices rely on the ability of contacts in the device to make electrical contact with, for example, other contacts or connectors, thereby forming an electrical circuit. Such devices include a range of different switch types and connectors such as keypads on mobile telephones, which comprise a plurality of upper and lower contacts that are brought into electrical contact with each other when required.

Contacts such as these are very susceptible to environmental damage and corrosion, leading to a far shorter device lifetime than would normally be expected or desirable.

Such conditions arise normally but can be more pronounced, for example, when a device is used in very humid environments, especially where microscopic droplets of water containing dissolved gases such as sulfur dioxide, hydrogen sulfide, nitrogen dioxide, hydrogen chloride, chlorine and water vapour form a corrosive solution. Additionally, droplets of moisture may form a thin film or deposit of corrosion on the contacts in the device.

When contacts become environmentally damaged and/or corroded or merely oxidized through normal exposure to the environment, it may no longer make the desired electrical contact and indeed it may, in the extreme, interfere with bringing the contacts into electrical contact with each other. This may arise because an insulating layer of corrosion has formed over the surface of the contact or a physical change to the surface has occurred which prevents a good contact. This could be the case, for example, for safety switches or contacts for alarm systems. Such systems are frequently inactive for long periods of time, but must function correctly when required.

Environmental corrosion may also cause electrical contacts to become disconnected where the corrosion forms an insulating barrier between the mating contacts. Examples of this are fuse-holders and battery terminals. Additionally the corrosion could lead to alternative current paths.

Alternatively, the corrosion may prevent movement of the contact, thereby preventing physical contact between the contact and other contact(s) in the device. These problems lead to a shortened lifespan for the device. Another problem is that the resistance of the contact may change, in which case reference currents in measurement circuits or circuit performance may be changed as the resistance of the circuit changes.

Devices that rely on electrical contact between contacts on removable elements and the main body of the device are also susceptible to physical and/or environmental damage and corrosion. Such devices include contact pads on semiconductor chips, smart cards, etc and disposable devices such as sensors and test strips.

Disposable sensors can be used to detect analytes, such as toxic gases, liquid based or physiological fluid based chemical compounds. Such devices typically comprise a sensor element and a means of powering and making a measurement. Contact pads on the electrodes are in electrical contact with the main body of the measuring device, so that an electrical circuit is made with the main body of the measuring device. An analyte interacts with the sensing element, creating a signal that can be electrical or converted into an electrical signal. The device is configured and calibrated such that the signal can be measured to provide a read out of the presence of an analyte or its concentration.

The lifetime of devices that rely on electrical contact between contacts on removable sensor elements and the main body of the device is reduced by environmental damage and corrosion of the contacts. It is also desirable to prevent build up of soft' contact material from the contact on sensor element on the connector in the measuring device.

Thus, in devices comprising contacts, such as keypads and sensor devices, there is a need to protect the surfaces of the contacts with a coating. It is however important to ensure that the contacts can still make electrical contact with, for example, contacts or connectors. Typical coating substances, such as polymers and plastics, are normally insulators and therefore unsuitable for use in the devices.

The present inventors have found that coatings of compositions that comprise one or more halo-hydrocarbon polymers at a thickness of 1 nm to 2 jim demonstrate low z-axis impedance compared to the impedance in the x-and y-axis. By z-axis it is meant the axis pointing into the plane of surface of the coating on the electrode or contact. The coating exhibits high impedance in the x-and y-axis, thus demonstrating good insulating properties. However, the impedance is relatively low in the z-axis. This enables electrical contact to be made through the coating.

Thus, the present invention relates to a device comprising one or more contacts, wherein at least one of said contacts is coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2 jim.

The contact can comprise any conductive material, and preferably comprises stainless steel, silver, carbon, nickel, gold, tin or alloys thereof. The contacts may also comprise conductive inks, silver loaded epoxy, conductive plastics and the like.

Thus, in one embodiment, the present invention relates to devices comprising: an upper contact and a lower contact, wherein: the device is configured such that said upper contact and lower contact are capable of being brought into electrical contact with each other; and said upper and/or lower contacts are coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2 rim.

The device may also comprise inner and outer contacts, or any other combination of contact pairs. Typically both upper and the lower contact are coated with the

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composition, but in some devices it may be preferably that only one of the upper and lower contact is coated.

The device can for example be a keypad, which comprises (a) printed conductors on a substrate as the lower contacts, and (b) upper contacts, which may comprise metal "snap domes" or silicone rubber with carbon inserts. Alternatively, the keypad may be a membrane keypad, where both the upper and lower contacts are typically silver inks printed on a substrate, which is typically a plastic or a polymer.

Other devices of the present invention include: elastomeric connectors (also known as Zebra strips); connectors, including sockets and plugs; terminators; crimped connectors; press fit connectors; sliding contacts such as those used on chip or smart cards/tokens including the contacts in the reader mechanism.

The contacts in the above devices may comprise any conductive material, but typically comprise stainless steel, silver, carbon, nickel, gold, tin or alloys thereof. The contacts may also comprise conductive inks, conductive plastics and the like.

The present invention also relates to a sensor device comprising one or more sensor elements, each sensor element further comprising a contact, wherein the contacts are coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2 tm.

The contacts on the sensor elements in the sensor device typically comprise any soft contact material. Preferably the contacts comprise carbon, conductive inks and/or silver load epoxy, more preferably carbon.

The sensor elements are typically electrodes.

The contacts on the sensor elements typically make electrical contact with another contact or connector on the main body of the device. That contact or connector may also be coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2 pm, but may also be uncoated. The device is thus preferably configured such that an electrical circuit forms between the sensor element and the main body of the device via the contact on the sensor element.

A typical electrochemical sensor device comprises two or more measurement or sensing electrodes as sensor elements. One or more of the electrodes is typically coated with a catalyst or a material and/or structure which will interact with an analyte. Preferably, the electrochemical sensor device is configured such that an analyte can diffuse through a membrane and react at an electrolyte-catalyst interface, creating a current. The device is preferably configured and calibrated such that the current can be measured to provide a read out of the analyte concentration. This is the description of a gas sensor, but this can also apply to liquid sensors where the liquid is in direct contact with the sensor electrodes or diffuses through a membrane.

Preferably the electrochemical sensor device has a reusable main body and disposable sensor elements, which are typically only used once. The sensor elements may also be multi-use or have a long lifetime. The connection between the device and the sensor, through the contacts, is preferably reproducible, giving a constant or essentially constant resistance. The coating preferably does not allow build up of soft' contact material from the sensor element on the connector in the main body of the device.

The present invention also relates to a sensor element comprising a contact, wherein the contact is coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2 pm. The sensor element is typically used in a sensor device described above.

In our description of polymer coatings of the invention below we include polymers formed in-situ from single or multiple monomers, linear, branched, grafted and crossl inked copolymers, ol igomers, mu Itipolymers, multimonorner polymers, polymer mixtures, grafted copolymers, blends and alloys of polymers, as well as interpenetrating networks of polymers (IPNs).

The thickness of the coating of the invention is typically from mm to 2p.m, more typically from mm to 500nm, still more typically from 3nm to 500nm, still more typically from lOnm to 500nm, and most typically from lOnm to 250nm. The coating is preferably at a thickness of from lOnm to lOOnm, in various gradients, with lOOnm being a preferred thickness. In another embodiment, the thickness of the coating is lOnm to 3Onm. In yet another embodiment, the coating is a monolayer (usually a few angstroms (A). The coating may be in single or multiple layers.

However, the optimal thickness of the coating will depend on the properties that are required. For example, if very high environmental toughness is required (high corrosion and abrasion resistance), a thicker coating may be used. Additionally the coating thickness may be optimised with thfferent thicknesses at different locations, depending on which feature is being optimised (for example, environmental protection versus Z axis conductivity).

Thus, the coating can be optimised for compliance to avoid cracking when flexed; to minimise wear on the coating, or by the coating; for environmental protection; for physical protection of an underlying material that may be softer; for controlled resistance for circuit trimming; for stability for reference measurements of sensors/electrodes; or for surface energy or charge dissipation or blooming.

The halo-hydrocarbon coating may be Continuous, substantially continuous or non-continuous. For a very high level of environmental protection, a substantially continuous coating may be required. Flowever, a non-continuous coating may be sufficient for other purposes.

By halo-hydrocarbon polymer it is meant a polymer with a straight or branched chain or ring carbon structure with 0, 1, 2 or 3 halogen atoms bound to each carbon atom in the

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structure. The halogen atoms could be the same halogens (for example fluorine) or a mixture of halogens (for example fluorine and chlorine). The term "halo-hydrocarbon polymer" as used herein includes polymers that contain one or more unsaturated groups, such as carbon-carbon double and triple bonds, and polymer that contain one or more heteroatoms (atoms which are not C, H or halogen), for example N, S or 0. Preferably the polymer contains less than 5 % heteroatoms as a proportion of the total number of atoms in the polymer.

The molecular weight of the polymer is preferably greater than 500 amu.

The polymer chains may be straight or branched, and there may be crosslinking between polymer chains. The halogen may be fluorine, chlorine, bromine or iodine. Preferably the polymer is a fluoro-hydrocarbon polymer, a chioro-hydrocarbon polymer or a fluoro-chioro-hydrocarbon polymer wherein 0, 1, 2 or 3 fluoro or chloro atoms are bonded to each carbon atom in the chain. The chain may be conjugated or highly conjugated or have extended conjugated chains or rings or branches.

Examples of preferred polymers include: -PTFE, PTFE type material, fluorinated-hydrocarbons, chlorinated-fluorinated-hydrocarbons, halogenated-hydrocarbons, halo-hydrocarbons or co-polymers, ol igomers, multipolymers, multimonomer polymers, polymer mixtures, blends, alloys, branched chain, grafted copolymers, cross-linked variants of these materials and also interpenetrating polymer networks (IPNs).

-PCTFE (polychiorotrifluoroethylene) and copolymers, oligomers, mu Itipolymers, multimonomer polymers, polymer mixtures, blends, alloys, branched chain, grafted copolymers, cross-linked variants of this material and also interpenetrating polymer networks (IPNs).

-EPCTFE (ethylene copolymer of polychiorotrifluoroethylene) and copolymers, oligomers, inultipolymers, multimonomer polymers, polymer mixtures, blends, alloys, branched chain, grafted copolymers, cross-linked variants of this material and also interpenetrating polymer networks (IPNs).

-Other fluoroplastics including the materials below and co-polymers, oligomers, multipolymers, multimonomer polymers, polymer mixtures, blends, alloys, branched chain, grafted copolymers, cross-linked variants of these materials as well as interpenetrating polymer networks (IPNs): ETFE (copolymer of ethylene and tetrafluoroethylene), FEP (copolymer of tetrafluoroethylene and hexafluoropropylene), PFA (copolymer of tetrafluoroethylene and perfluorovinyl ether), PVDF (polymer of vinylidenefluoride), THV (copolymer of tetrafluoroethylene, hexafluoropropylene and vinylidenefluoride), PVDFHFP (copolymer of vinylidene fluoride and hexafluoropropylene), MFA (copolymer of tetrafluoroethylene and perfluoromethylvinylether), EFEP (copolymer of ethylene, tetrafluoroethylene and hexafluoropropylene), HTE (copolymer of hexfluoropropylene, tetrafluoroethylene and ethylene) or copolymer of vinylidene fluoride and chiorotrifluoroethylene and other fluoroplastics.

Most preferably the polymer is a polytetrafluoroethylerie (PTFE) type material, and in particular modified polytetrafluoroethylene (PTFE).

It is desirable that the coating composition have any one or more, and preferably substantially all, of the following properties: capable of being deposited as continuous films, free of cracks, holes or defects; relatively low gaseous permeability which provides a significant barrier to gaseous permeation and avoids gaseous corrosion and oxidation through' the coating; chemical resistance to corrosive gases, liquids and salt solutions, particularly environmental pollutants; exhibit low surface energy and wettability'; to be stable inert material at normal device temperatures; have good mechanical properties, good mechanical abrasion resistance; and modified electrostatic protection.

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Z-axis conductivity can be controlled by regulating one or more of the following features: * The halo-hydrocarbon coating material. This includes combining different halo-hydrocarbon materials and controlling the gradation between layers of the different materials * The ratio of halogens/hetero-atoms/carbon in the halo-hydrocarbon coating material.

* The proportion of carbon in the halo-hydrocarbon coating material.

* The degree of conjugation in halo-hydrocarbon coating material.

* The average molecular weight halo-hydrocarbon coating material.

* The degree of branching and cross-linking in the halo-hydrocarbon coating material.

* The molecular size distribution of molecules in the halo-hydrocarbon coating material.

* Density of the halo-hydrocarbon coating material.

* Presence of additional doping agents in the halo-hydrocarbon coating material.

* The presence of ionic/salt and covalent components in the halo-hydrocarbon coating material.

* The presence of organic/polymer and inorganic compounds comprising transition metals, including complex cations and anions in the halo-hydrocarbon coating material.

* The presence of compounds and elements having variable oxidation states in the halo-hydrocarbon coating material.

* The presence of chemical compounds having delocalized character in the halo-hydrocarbon coating material.

* The presence of occluded components in the coating in the halo-hydrocarbon coating material.

* Adjustment of plasma conditions e.g. power, gas pressure, electrode arrangement during deposition of the halo-hydrocarbon coating material if a plasma deposition method is used.

* The thickness of the halo-hydrocarbon coating material. As shown in the Examples, thicker coatings typically have a greater resistance than thinner coatings of the same material.

* The continuity of the coating.

The z-axis conductivity of the coatings of the invention can be measured by determining the resistance of the coating. This can be achieved by soldering electrical wires to the contacts in a device of the invention and connecting the wires to a resistance meter. The contacts can then be brought into electrical contact with a predetermined force and the resistance between the contacts measured. The resistance of the contacts themselves can be determined using an uncoated device. A typical arrangement that is suitable for achieving this is the keypad arrangement shown in Figure 1.

Preferably the z-axis conductivity is in the range 0 to 10 kilo ohms (kfl). More preferably the z-axis conductivity is in the range 0 to 1 ohms (fI).

The contacts can be coated with the halo-hydrocarbon polymer before or after construction of the device but are typically coated prior to construction. The coating may be applied to one or more of the surfaces of the contact, or to all of its surfaces. The coating may optionally be applied to all the surfaces of the component or device.

Typically the coating will be applied to the surface(s) that will be environmentally exposed in the device, and will typically be the surface that acts as the electrical contact area between two parts of a circuit. Applying the coating over the remainder of the device increases protection of the device and prevents other spoilage routes to the contact area.

Thus, the present invention also relates to a method of protecting one or more upper and lower contacts in a device, the device being configured such that said upper contact and lower contact are capable of being brought into electrical contact with each other, which method comprises coating the contacts with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2tm prior to manufacture of the device.

The present invention also relates to a method of protecting one or more contacts in a sensor device, which comprises coating the contacts with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2p.m prior to manufacture of the sensor device.

The halo-hydrocarbon polymer coating may be applied by a thin film deposition technique such as plasma deposition, chemical vapour deposition (CVD), molecular beam epitaxy (MBE), creation of inter-penetrating polymer networks (IPNs), surface absorption of monolayers (SAMs) of polymers of monomers to form in-situ polymers, polymer alloys, or sputtering. Plasma enhanced-chemical vapour deposition (PE-CVD), high pressure/atmospheric plasma deposition, metallo-organic-chemical vapour deposition (MO-CVD) and laser enhanced-chemical vapour deposition (LE-CVD) are alternative deposition techniques. Liquid coating techniques such as liquid dipping, spray coating, spin coating and sol/gel techniques are further alternatives.

The preferred method may depend on the thickness of coating that is required. Liquid coating techniques may be preferred for thicker coatings, while plasma deposition techniques may be preferred for thinner coatings. The preferred method of applying the halo-hydrocarbon polymer to the blank contacts or electrodes is plasma deposition, although all the other techniques mentioned above would also be applicable.

Plasma deposition techniques are extensively used for deposition of coatings in a wide range of industrial applications. The method is an effective way of depositing continuous thin film coatings. The contacts or electrodes are coated in a vacuum chamber that generates a gas plasma comprising ionised gaseous ions, electrons, atoms and neutral species. In this method, the substrate or device or preferred areas to be contacted are introduced into a vacuum chamber that is first pumped down to pressures typically in the range to 10 mbar. A gas is then introduced into the vacuum chamber to generate a stable gas plasma and one or more precursor compounds are then introduced into the plasma as either a gas or liquid to enable the deposition process.

The precursor compounds are typically halogen-containing hydrocarbon materials, which are selected to provide the desired coating properties. When introduced into the gas plasma the precursor compounds are also ionized/decomposed to generate a range of active species that will react at the surface of contacts or electrodes, typically by a polymerisation process, to generate a thin halo-hydrocarbon coating. Preferred precursor compounds are perfluoroalkanes, perfluoroalkenes, perfluoroalkynes, fluoroalkanes, fluoroalkenes, fluoroalkynes, fluorochloroalkanes, fluorochloroalkenes, fluorochloroalkynes, or any other fluorinated and/or chlorinated organic material (such as fluorohydrocarbons, fluorocarbons, chiorofluorohydrocarbons and chlorofluorocarbons).

In another aspect of the invention, the coating on contacts may comprise a very thin layer (for example Snm or less) of metal halide (çreferably a metal fluoride) directly in contact with the metal surface. In one embodiment, the metal halide layer may be a monolayer or substantially a monolayer, or a few monolayers, or comprise a metal halide zone of layers at the surface. Such a metal halide layer may be very robust and inert, and prevents formation of oxide layers or other tarnishes which prevent effective electrical contact or subsequent processing. The metal halide layer may form when active species in the gas plasma react with the metal surface or may be enhanced using a higher concentration of fluorine species. The halo-hydrocarbon layer may then be deposited in combination with the metal halide layer. The two layers may be discrete, axially or spatially, or alternatively there may be a graded transition from metal halide to halo-hydrocarbon. It is possible that the metal halide layer protects the metal from oxidation, whilst the halo-hydrocarbon layer provides environmental protection from corrosive gases andlor liquids as well as oxidation protection. Furthermore, should the halo-hydrocarbon coating eventually be worn away by mechanical abrasion, the underlying metal fluoride layer will prevent oxidation build up, enabling contact to still be made.

The nature and composition of the plasma deposited coating depends on a number of conditions: the plasma gas selected; the precursor compound used; the plasma pressure; the coating time; the plasma power; the chamber electrode arrangement; the preparation of the incoming contacts or electrodes; and the size and geometry of the chamber.

Typically the plasma deposition technique can be used to deposit thin films from a monolayer (usually a few angstroms (A)) to 2gm, depending on the above settings and conditions.

In a variant of the plasma process, it is possible to use the plasma method for in situ cleaning of the surface of the electrodes or contacts prior to plasma deposition using an active gas plasma. In this variant, an active gas plasma is used typically in the same chamber for cleaning the electrodes or contacts ahead of introduction of the precursor compound for the plasma deposition stage. The active gas plasma is based on a stable gas, such as hydrogen, oxygen, nitrogen, argon, methane, ethane, other hydrocarbons, tetrafluoromethane (CF4), hexafluoroethane (C2F6), tetrachioromethane (CCL), other fluorinated or chlorinated hydrocarbons, other rare gases, or a mixture thereof. In one particular embodiment, the electrodes or contacts could be cleaned by the same material as to be deposited. For example, a fluorinated or chlorinated hydrocarbon such as tetrafluoromethane (CF4) or hexafluoroethane (C2F6) or hexafluoropropylene (C3F6) or octafluoropropane (C3F8) could be used in the plasma method both to clean the surface of the substrate and lay down a layer of a halo-hydrocarbon polymer and/or a layer of metal halide.

The present invention also relates to use of a halohydrocarbon polymer to coat a surface or surfaces of contacts in a device comprising: an upper contact and a lower contact, wherein: the device is configured such that said upper contact and lower contact are capable of being brought into electrical contact with each other.

The present invention also relates to use of a halo-hydrocarbon polymer to coat a surface or surfaces of a contact in a sensor device comprising one or more sensor elements.

Description of the drawings

Figure 1 is a diagram of a typical arrangement, as used in Example 1, for measuring the z-axis conductivity in a keypad type device of the invention.

Figure 2 is a graph showing the resistance of the coatings as determined in Example 1.

Examples

Example 1 -measurement of z-axis conductivity The z-axis conductivity of coatings in a device of the invention was measured using the keypad arrangement shown in Figure 1. The tracks in this arrangement were coated with a PTFE type material. Electrical wires were soldered to the contacts and connected to a resistance meter. A conducting material was pushed down onto the keypad tracks with a predetermined force and the electrical resistance between these contacts was measured.

The force applied was predetermined using ENIG plated tracks and varying the force until a stable resistance measurement was made.

The measurement was carried out using a metal snapdome' as the conducting material and was repeated for coatings of different thicknesses. The resulting readings were adjusted to allow for the fact that two thicknesses of material were in the measurement path and also to take account of the resistance of the copper tracks. The resistance of the copper tracks was determined by using an uncoated PCB as a reference.

The results for these tests are described above are shown in the following table and in Figure 2.

Coating thickness Resistance of coating (flm) (f�=) 0.0704 0.1677 0.2095 0.4105 1.2775

Claims

CLAIMS1. A device comprising one or more contacts, wherein at least one of said contacts is coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from I nm to 2 jim.
2. A device according to claim I comprising: an upper contact and a lower contact, wherein: the device is configured such that said upper contact and lower contact are capable of being brought into electrical contact with each other; and said upper and/or lower contacts are coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from I nm to 2 jim.
3. A device according to claim 2, wherein said upper and said lower contact comprise stainless steel, silver, carbon, nickel, gold, tin or alloys thereof
4. A device according to any preceding claim, which is a keypad.
5. A device according to claim 1 which is a sensor device comprising one or more sensor elements, each sensor element further comprising a contact, wherein the contacts are coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from I nm to 2 jim.
6. A sensor device according to claim 5, wherein the one or more sensor elements are electrodes.
7. A sensor device according to claim 5 or 6, wherein the contacts comprise carbon, conductive Inks and/or silver loaded epoxy.
8. A sensor device according to claim 7 wherein the contacts comprise carbon.
9. A device according to any one of the preceding claims having a coating of a composition comprising one or more halo-hydrocarbon polymers at a thickness of from l0nm to lOOnm.10 A device according to any one of the preceding claims wherein the electrical conductivity of the coating in the z-axis is higher than the electrical conductivity in the x-axis and y-axis.11. A device according to any one of the preceding claims wherein the halo-hydrocarbon polymer coating provides environmental protection.12. A device according to any one of the preceding claims where the electrical resistance of the coating can be optimised for different applications 13. A method for preparing a device according to any one of the preceding claims, wherein the halo-hydrocarbon polymer coating is deposited by plasma deposition.14. A device according to any one of the preceding claims wherein the halo-hydrocarbon polymer is a fluoro-hydrocarbon.15. A sensor element comprising a contact, wherein the contact is coated with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2 un.16. A method of protecting one or more upper and lower contacts in a device, the device being configured such that said upper contact and lower contact are capable of being brought into electrical contact with each other, which method comprises coating the contacts with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 21.Lm.S17. A method according to claim 16 wherein the coating is applied prior to manufacture of the device.18. A method of protecting one or more contacts in a sensor device, which comprises coating the contact pads with a composition that comprises one or more halo-hydrocarbon polymers at a thickness of from 1 nm to 2p.m.19. A method according to claim 18 wherein the coating is applied prior to manufacture of the device.20. A method according to any one of claims 12 to 15 wherein the deposition technique is plasma deposition.21. Use of a halohydrocarbon polymer to coat a surface or surfaces of contacts in a device comprising: an upper contact and a lower contact, wherein: the device is configured such that said upper contact and lower contact are capable of being brought into electrical contact with each other.22 Use of a halohydrocarbon polymer to coat a surface or surfaces of a contact in a sensor device comprising one or more sensor elements.