CA1295889C - Refractory coated article - Google Patents
Refractory coated articleInfo
- Publication number
- CA1295889C CA1295889C CA000499446A CA499446A CA1295889C CA 1295889 C CA1295889 C CA 1295889C CA 000499446 A CA000499446 A CA 000499446A CA 499446 A CA499446 A CA 499446A CA 1295889 C CA1295889 C CA 1295889C
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- CA
- Canada
- Prior art keywords
- layer
- article
- refractory
- metal
- keying
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
- H01B3/10—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances metallic oxides
- H01B3/105—Wires with oxides
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
- H01B13/06—Insulating conductors or cables
- H01B13/065—Insulating conductors with lacquers or enamels
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/29—Protection against damage caused by extremes of temperature or by flame
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Inorganic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Ceramic Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Insulated Conductors (AREA)
- Coating By Spraying Or Casting (AREA)
- Furnace Housings, Linings, Walls, And Ceilings (AREA)
- Insulating Bodies (AREA)
- Physical Vapour Deposition (AREA)
- Chemical Vapour Deposition (AREA)
Abstract
ABSTRACT
An article of manufacture, for example an electri-cal conductor, as on the surface of a metal part an adherent, dense refractory keying layer and, on the keying layer a further electrically insulating refrac-tory layer that has been formed by a faster deposition method.
The keying layer is preferably formed by a vacuum deposition process, e.g. sputtering evaporation, ion-plating or chemical vapour deposition, and the further refractory layer is preferably formed by a sol-gel deposition method, plasma ashing method, a solution coating method or a plasma spraying method. The articles are particularly suitable for high temperature wires.
An article of manufacture, for example an electri-cal conductor, as on the surface of a metal part an adherent, dense refractory keying layer and, on the keying layer a further electrically insulating refrac-tory layer that has been formed by a faster deposition method.
The keying layer is preferably formed by a vacuum deposition process, e.g. sputtering evaporation, ion-plating or chemical vapour deposition, and the further refractory layer is preferably formed by a sol-gel deposition method, plasma ashing method, a solution coating method or a plasma spraying method. The articles are particularly suitable for high temperature wires.
Description
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~ Refractory Coated Article This invention relates to articles that are formed from metal, for example from copper or copper alloys, and especially to such articles that may be subjected to high temperatures.
one area in which the present invention is par-ticularly applicable i9 that oE electrical wires and cables~ For example so called "magnet wire" which is used in electromagnet windings in transformers, motors and other equipment, may experience severe temperature excursions under overload conditions in service. Also, in certain fields where cables are used, for example in military, marine or offshore applications, it is desired to use cables that are capable of functioning for a period of time during a fire without failing.
Such cables are called circuit integrity cables or signal integrity cables depending on their use. The previously proposed circuit and signal integrity cables have generally used the principle that the individual conductors should be;separated from one another by mica tapes or by large volumes of packing materials or sili-eones or by combinations thereof in order to prevent the formation of~short circuits duriny a fire, with the result that the~previously proposed cables are relati-~ vely heavy or large or both.
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~ Refractory Coated Article This invention relates to articles that are formed from metal, for example from copper or copper alloys, and especially to such articles that may be subjected to high temperatures.
one area in which the present invention is par-ticularly applicable i9 that oE electrical wires and cables~ For example so called "magnet wire" which is used in electromagnet windings in transformers, motors and other equipment, may experience severe temperature excursions under overload conditions in service. Also, in certain fields where cables are used, for example in military, marine or offshore applications, it is desired to use cables that are capable of functioning for a period of time during a fire without failing.
Such cables are called circuit integrity cables or signal integrity cables depending on their use. The previously proposed circuit and signal integrity cables have generally used the principle that the individual conductors should be;separated from one another by mica tapes or by large volumes of packing materials or sili-eones or by combinations thereof in order to prevent the formation of~short circuits duriny a fire, with the result that the~previously proposed cables are relati-~ vely heavy or large or both.
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The pr~sent ln~en~ion pro~lde~ an ~rticl~ of manu~
f~ur~ ~hi~h h~s at leas~ ~ p~rt that i~ ~Qrm~A rom metal the ~rtlcle llatr1ns~, on a sur~ace of th~t l?art, an adherent dense ref r~tory lc~3yin~ layer formed ~rom an oxi~e of ~ meta~ or ~emi~ t~1, a~ le~t p~rt c~f ~h~
k~yir~g layer bolng el~c~xi~ally in~ a~ing, an~, ~n ~h~
k~yi~g l~y~r, a ~u~h~I~ r~fr~ctory lay~r ~ch~t ba~ ~Qn ~ormed ~y a rel.~tlvely ~t ~epo~ m~hod, ~ y 'che phr~se ~relatlvely f~J~t ~ it~or~ m~th~d!' i~ meant tha~ ~he rate o~ deposi~lQn o ~he furth6~r r~ractOry 12~yer ~ ms~U~ or example in m~c~ometre~
o~ thickne~i3 per unlt ~ime ~ r~t~r th2i~D th~ rato o~
depoRiti~n o~ the ref raotory keylng l~y~r . ~h~ ~xop-o o~ r~tory aoatings ar~ know~ to d~nd~igni~i~antly on th~ h~ y which they are ~orm~ or dep~ d on~ ubst~at~, and in sen~ral t th~ t~ch-niq~e3 that ~hll~l~ th~ l~west do~o~ltiorl rat~s w~
f c~rr~ ref rF~ tC,sy laye~3 havia~g ~lativ~ly hi~h d.~n~ity, ~L e ~ot 43~ng p~rou~, and h~ving bi ~h~r ~llR~ion to met~ sub~trate~. PreerabLy kh~ ~ractory keylng layer h~ be~n o~ d by ~ Y~CUUm d~po3itior~ ~roce~, e .g. a sputtering ~ ~vaporation ~ ior~ plAt~ t or cheJm-i~al ~rapour d~posltlon, and the fu:rther refrflctory laye~ pre~erab}y ha~ n ~ormed by ~ sol-gel depo-o~ m~thoa, a plaam~ a~hin~ method, a solution oo~ti~g m~thod or a ~la~ma spI~ayin~ m~thod e,g, a ~l~Lm~
6pr~ying method, or m~y b~ forme~ by anoth~r ,, fa~r, v~uum deE~sitlon pro~es~, Acoordin~ to the inv~ntion lt 1~ 1?o~s1ble t~ ~ ~o~
ar~i~les h~vlng A re~ractory ~o~ing which, although bela~ rel~iYely thic)c an~ ~ h~ving go~d electriaal inslllati~n chara~teri~ti~, also exhibi~ very good ~dhe ion to ~he und~rlying metal even wh~n ~h je~te~ to meahan~al or th~rmaI ~resse~, ~:
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The pr~sent ln~en~ion pro~lde~ an ~rticl~ of manu~
f~ur~ ~hi~h h~s at leas~ ~ p~rt that i~ ~Qrm~A rom metal the ~rtlcle llatr1ns~, on a sur~ace of th~t l?art, an adherent dense ref r~tory lc~3yin~ layer formed ~rom an oxi~e of ~ meta~ or ~emi~ t~1, a~ le~t p~rt c~f ~h~
k~yir~g layer bolng el~c~xi~ally in~ a~ing, an~, ~n ~h~
k~yi~g l~y~r, a ~u~h~I~ r~fr~ctory lay~r ~ch~t ba~ ~Qn ~ormed ~y a rel.~tlvely ~t ~epo~ m~hod, ~ y 'che phr~se ~relatlvely f~J~t ~ it~or~ m~th~d!' i~ meant tha~ ~he rate o~ deposi~lQn o ~he furth6~r r~ractOry 12~yer ~ ms~U~ or example in m~c~ometre~
o~ thickne~i3 per unlt ~ime ~ r~t~r th2i~D th~ rato o~
depoRiti~n o~ the ref raotory keylng l~y~r . ~h~ ~xop-o o~ r~tory aoatings ar~ know~ to d~nd~igni~i~antly on th~ h~ y which they are ~orm~ or dep~ d on~ ubst~at~, and in sen~ral t th~ t~ch-niq~e3 that ~hll~l~ th~ l~west do~o~ltiorl rat~s w~
f c~rr~ ref rF~ tC,sy laye~3 havia~g ~lativ~ly hi~h d.~n~ity, ~L e ~ot 43~ng p~rou~, and h~ving bi ~h~r ~llR~ion to met~ sub~trate~. PreerabLy kh~ ~ractory keylng layer h~ be~n o~ d by ~ Y~CUUm d~po3itior~ ~roce~, e .g. a sputtering ~ ~vaporation ~ ior~ plAt~ t or cheJm-i~al ~rapour d~posltlon, and the fu:rther refrflctory laye~ pre~erab}y ha~ n ~ormed by ~ sol-gel depo-o~ m~thoa, a plaam~ a~hin~ method, a solution oo~ti~g m~thod or a ~la~ma spI~ayin~ m~thod e,g, a ~l~Lm~
6pr~ying method, or m~y b~ forme~ by anoth~r ,, fa~r, v~uum deE~sitlon pro~es~, Acoordin~ to the inv~ntion lt 1~ 1?o~s1ble t~ ~ ~o~
ar~i~les h~vlng A re~ractory ~o~ing which, although bela~ rel~iYely thic)c an~ ~ h~ving go~d electriaal inslllati~n chara~teri~ti~, also exhibi~ very good ~dhe ion to ~he und~rlying metal even wh~n ~h je~te~ to meahan~al or th~rmaI ~resse~, ~:
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Preferably, the refractory keying layer is sub-stantially contaminant-free, that is to say, it con-tains only those species that are intended in order for the layer to fulfill its intended function, and contains substantially no species that result from the manufacturing process. An important feature of the refractory Xeying layer is good control of composition to optimise the high temperature performance of the article. The composition is totally inorganic and therefore does not rely on conversion processes to occur during exposure to normal or emergency high tem-perature service, as is the case for example in many mica filled or glass filled silicone resin s~stems.
The composition is also improved by removing the use of polymeric binders to support inorganic materials which may be consolidated by firing processes to form the inorganic insulation. Similarly, articles in which the refractory coatings have been formed by electrochemical conversion of metal layers e.g. by anodising an alumi-nium layer, do not form part of the invention, such layers usually being porous and often being heavily contaminated with ionic residue from the electrolytic solutions e.g. sulphates from sulphuric acid anodisa-tion processes.
Preferably the underlying metal from which the part of the article is formed has a melting point of at least 800C, more preferably at least 900C, and espe-cialIy at least 1000C. The present invention is par-ticularly applicable to articles in which the metal is copper or an alloy thereof for example wire and cable that need to be capable of functioning at high tem-peratures for significant lengths of time without failure e.g. circuit and signal integrity cable and ,:
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_ 4 _ RK265 magnet wire, and the invention will be described below with reference to wire and cable.
In the case where the article c:omprises an elec-trical wire or cable, so that the underlying copper forms the conductor of the cable, the conductor may be a single, solid conductor or it may be a stranded con-ductor in which individual strands are laid together to form a bundle which preferably contains 7, 19 or 37 strands. Where the conductor is stranded it is pre-ferred for the bundle to be coated rather than the individual strands, that is to say, the refractory coating extends around the circumference of the bundle but not around the individual strands so that substan-tially only the outwardly lying surEaces of the outer-most layer of strands are coated.
This form of conductor has the advantage that the inter strand electrical contact is retained and the dimensions of the bundle are kept to a minimum (since the thickness of the coating may constitute a signif-icant proportion of the strand dimensions for fine gauge conductors) and also it aids the formation of good electrical connections, e.g. crimp connections, to the conductor because a large proportion of the surface of the strands, and the entire surface of the strands in the central region of the conductor, will be un-coated by the refractory layer.
If a circuit or signàl integrity cable is formed according to the invention from a stranded; conductor, it has the ad~antage that it is very flexible as com-pared with other signal and circuit integrity cables, especially if a stranded conductor is used. The abi-: :
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_ 5 _ RK265 lity of the wire to be bent around tight bends (smallbend radii) without deleterious effect is partly due to - the fact that the layer providing the integrity is thinner than with other signal and circuit integrity cables~ However, when the conductor is a stranded con-ductor it may be bent around tight bends without undue stress on the surface of the strands because the strands are displaced from a regular hexagonal packing at the apex of the bend thereby exposing uncoated areas of the strands to the eye. It is highly surprising that even though uncoated strands may be exposed when the wire conductor is bent there is no electrical con-tact between adjacent stranded conductors. It i9 believed that in this case the integrity is retained because the profile of a stranded conductor is not cylindrical but rather is in the form of a hexagon that rotates along the length of the conductors, so that adjacent stranded conductors will touch one another only at a few points along their length, which points are always provided by the outwardly oriented part of the surface of the strands in the outer layer of the conductors. It is these points of contact that are always provided with the refractory coating.
The further refractory layer preferably has a thickness of at least 0.5, more preferably at least 1 and especially at least 2 micrometres. The exact thickness desired will depend on a number of factors including the type of layer and the voltage rating of ~ the wire, circuit integrity cables usually requiring a ; ~ somewhat thicker coating~ than signal integrity cables and sometimes above 15 micro-metres. The lower limits for the layer thickness are usually determined by the required voltage rating of the wire whilst the upper ;,~
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6 270~5-123 limits are usually determined by the tlme, and therefore the cos~, of the coating operation.
The refractory keying layer wlll usually be thinner than the further refractory layer, and preferably has a thiakness of not more than 0.5 micrometres and most preferably not more ~han 0.3 micxometre~, but usually a~ least 0.1 micro~etres.
In order to optimise the adhesion between the refractory keying layer and the further refractory layer it is preferred for them both to have the same nominal chemlcal composition, that is to say, they both preferably have the same general ¢hemical formula although, a~ explained below, the preai~e stoichiometry o~ one or bokh layer~ may dlf~er ~rom the stoichlometric formula.
In order to improve further the high temperature propertieæ of the article, and e3peci~ally in the case where the underlying metal is copper or an alloy thereof, it i5 preferred ~or the article to include a metallic intermediate layer located between the metal ~rom which the part is formed and the refraatory keying layer. The metal is preferably one whlch forms a good bond between the underlying metal and the re~ractory keying layer and also, as de~crlbed in Canadian Patent No.
1,264,616, one which acts as a barrier to diffusion o$ oxygen or oopper or both or which acts to reduce stre~s in the refraatory layer isposed bV sub~trate ~train resu1ting from mechanical ,, ~ . ~
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~ 7 ~ 2706~-123 or thermal strPss. Preferred metallic inter~nediate layers include those formed from aluminium, titanium, tantalum chrom-ium, manganese, silicon or nickel although other metals may be used. Examples articles in which they may be used ~re described in Canadian Patent No. 1,241,395.
In the case of electrical equipment the refractory layers may provïde the entire elec~rical insulation or one or more additional iDsulating layers may be pro-vided thereon. The additional insulating layer may be inorganic or organic or a combination of ino~ganic and organic layer~ may be provided.
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In the case of wires according to the invention, the po1ymeric insulation may be provided in order to provide additional insulation to the conductor during ; normal service conditions and also to enable the wire to have the desired dielectric properties and other properties e.~. mechanical properties, scu~f resis-tance, colour coding ability etc. ~owever, an im-portant advantage of the present invention is that since a significant proportion of or all the service insulating properties are provided by the refractory coating, the electrical properties of the polymeric insulation are not as critical as with other wire contructions in which the polymeric insulation provides the sole insulation between the conductors. Of the known polymeric materials that are used for electrical insulation, polye~thylene probably has the most suitable ~ electrical properties but is highly flammable, and has `: :
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poor mechanical properties. Attempts to flame retard polyethylene have either required halogenated flame retardants which, by their nature, liberate corrosive and toxic hydrogen halides when subjected to fire, or have required relatively large quantities of halogen free flame retardants which have a deleterious effect on the electrical properties and often also the mechan-ical properties of the polymer. Accordingly~ an accep-table wire has in the past only been achieved by a compromise between different properties which is often resolved by using a relatively thick-walled polymeric insulation and/or dual wall constructions. Although such forms of polymeric insulation may be used with the wire according to the present invention, the presence of the refractory layer does obviate these problems to a large extent since the polymer used for the insul-ation may be chosen for its flammability and/or its mechanical properties at the expense of its electrical properties. As examples of polymers that may be used to form the polymeric insulation there may be mentioned polyolefins e.g. ethylene homopolymers and copolymers with alpha olefins, halogenated polymers e.g. tetra-fluoroethylene, vinylidene fluoride, hexafluoropropy-lene and vinyl chloride homo or copolymers polyamides, oolyesters, polyimides, polyether ketones e.g. poly-arylether ketones, aromatic polyether imides and sulphones, silicones, alkene/vinyl acetate copolymers and the like. The polymers may be used alone or as blends with~one another and may contain fillers e.g.
silica and metal oxides e.g. treated and untreated metal oxide flame retardants such as hydrated alumina and titania. 'The polymers may be used in single wall constructions or in multiple wall constructions, for example a polyvinylidine fluoride Iayer may be located :. . .
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on for exampLe a polyethylene layer. The polymers may be uncross-linked but preferably are crosslinked, for example by chemical crosslinking a~ents or by electron or gamma irradiation, in order to improve their mechanical properties and to reduce flowing when heated. They may also contain other materials e.g. anti-oxidants, stabilizers, crosslinking promotors, processing aids and the like.
The polymeric insulation may, if desired, contain a filler e.g.
hydrated alumina, hydrated titania, ~awsonite, silica and the like, and especially a filler that has the same chemical composi-tion, at least under pyrolysis conditions, as the refractory coat-ing, so that the ~iller in the polymeri~ insulation will provide additional insulation when the wire or cable is subjected to a fire. A preEerred type of polymeric insulation is one that wil:L
cllar, for instance certa:in aromatic polymers mentioned above, or that will ash e.g. a silicone polymer, when subjected to a fire so that the char or ash, together with the refractory coating, will provide the necessary insulation during a fire. Examples of poly-mers, compositions, their manufacture and wires using them are described in U.S. Patent Specifications Nos. 3,269,862, 20 3,580,829, 3,953,400, 3,956,240, 4,155,823, 4,121,001 and 4,320, 224, British Patent Specifications Nos. 1,473,972, 1,603,205, 2,068,347 and 2,035,333, 1,604,405 and in European Patent Specification No. 69,598. In some instances, for example when certain aromatic polymers are used, i-t may be appropriate to form the insulation on the conductor by a plasma or therma] polymerisa-~ tion process. Preferab1y the wire is substantiall~ halogen reé.
;~ As stated~above, the preferred methods of forming the :::
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keying layer include evaporation, plasma assisted chemical vapour deposition and sputtering methods.
An advantage oE using a relatively slow deposition method such as a sputtering ~ethod for Eorming the keying layer is that it allows greater control over the chemical composition and mechanical properties of the keying layer to be exercised. For example, it is often advantageous for the keying layer to be non-stoichiometric since this may increase the adhesion between the keying layer and the underlying layer, and especially if the stoi-chiometry oE the keying layer varies through at least part of its thickness so that stresqes that may be induced in the coatiny, for example due to clifEerential thermal expansion, are not localised to a boundary oE the layer and so that diEferent parts oE the layer will exibit di~ferent properties. For example, a relatively metal-rich part of the keying layer may exhibit good adhesion to the conductor or intermediate layer while part of the coating having least metal or semi-metal may exhibit the best electrical properties or better adhesion to the further refractory layer.
Preferably the insulating refractory coating is formed from an electrically insulating infusible or refractory me-tal or semi-metal oxide or nitride and the invention will be described below in many cases with respect to oxides and nitrides although other refractory-coatings are included. By the term "infusible"
or "refractory" is meant that the coatiDg material in its bulk form should not fuse or decompose when subjected to a temperature of 800C, for 3 hours. Preferably the oxide or nitride should be able to~withstand higher -temperatures also, for example it should ::
- lOa - 5 ~ ~ 27065-123 be able to withstand a temperature of 1000C for a-t least 20 to 30 minutes. The preferred oxides are those oE aluminium, titanium, tantalum and silicon or mixtures thereof with themselves or with other oxides and the preferred nitrides are those of aluminium and silicon. Thus, for example, the use of mixed metal oxides for the refractory coating are also encompassed by the present invention.
If desired, the stoichiometry of the keying layer may vary continuously throughout the thickness of the ]ayer or it may contain one or more layers or strata of relatively uniform stoichiometry. Thus the keying layer may have an outer region of :: :
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relatively uni~orm stoichiometry and preferably of a relatively high oxygen content in order to exhibit the optimum electrical properties or adhesion to the further refractory layer. The relative thicknesses of the non-uniform and uniform layers may vary widely. ~or example the major part of the keying may have a non-uniform stoichiometry or the major part of the layer's thick-ness may be of uniform stoichiometry, in wliich latter case the non-uniform part of the layer could even by considered as an intermediate layer that improves adhesion of the rest of the layer especially at high temperatures. If the underlying metal- or semi-metal-rich part of the keying layer is intended to improve the adhesion of the refractory coating, its particular composition will depend on the composition of any underlying layer, and in some cases it may be desirable for the metal or semi-metal rich part to consist substantially entirely of the metal or semi-metal so that there is a gradual change from the metal or seml-metal to the oxide. This is particularly preferred if the system includes an underlying layer o the same metal or semi-metal.
The precise stoichiometry of the uniform top layer can be determined experimentally using wavelength dispersive electron mlcroprobe analysis or by using x-ray photoelectron spectroscopy ;(XPS). The composition of the coating as it changes from metal to refractory throughout~its depth can be assessed using Auger elec-tron spectroscopy (~AE5) in which the film is con-tinuously sputter-ed away~to expose fresh surface for composition analysis.
The variation in s-toichiometry is not limited to a variation in~the metal or semi-metal/oxygen proportions. In addi-tion or alternatively the relative proportions of two difEerent metals or semi~metals may be varied so that, for example, there is a gradual change from one metal, which may constitute an interme-diate layer, to the oxide of a different metal.
The outer region of the keying layer preferably has a molar oxygen content that is at least 50~, more preferably at least 65% and especially at least 80~ of the oxygen content of that required for the formal stoichiometry o~ the insulating refractory oxide. Thus the preferred oxide composition of the outer region may be represented as M0x where x is at least 0.75, preerably at least :l and especially at least 1.25 in the case of aluminium, at least 1, preerably at least 1.3 and especially at least 1.5 in the case of titanium or silicon, and at least 1.25, preferably at least 1.6 and especially at least 2 in the case of tantalum.
The most preferred method of forming keying layer in which the composition varies throughout i-ts thickness i9 a sputtering method.
In the sputtering method, predominantly neutral atomic or molecular species are ejected from a target, which may be formed from the material to be deposited, under the bombardment of : inert gas positive ions e.g. argon ions. The high energy species e~ected will travel considerable distances to be deposited on the wire , 5~
conductor substrate held in a medium vacuum, e.g. 10-4 to 10-2 mbar. The positive ions required for bombard-ment may be generated in a glow discharge where the sputtering target serves as the cathode electr~de to the glow discharge system. The r~egative potential (with respect to ground and the glow discharge) is maintained in the case of insulating target materials by the use of radio frequency power applied to the cathode, which maintains the target surface at a nega-tive potential throughout the process, DC power may be applied when the, target is an electrically conducting material. The advantage of such techniques is that control over the coating material is greatly enhanced, and the energy of the species ejected is very much higher than with evaporation methods e.g. typically 1 to 10 eV for sputtering as compared with 0.1 to 0.5 eV
for evaporation methods. Considerable improvements in interfacial bonding are achieved but the deposition rate in the sputtering process described will be lower than that for electron beam evaporation.
In magnetron sputtering processes the plasma is concentrated immediately in front of the cathode (target) by means of a magnetic field. The effect of the magnetic field on the gas discharge is dramatic.
In that area of discharge where permanent magnets, usually installed behind the cathode, create a suff-iciently strong magnetic field vertically to the electric field, secondary electrons resulting from the sputter bombardment process will be deflected by means of the Lorentz force into circular or helical paths.
Thus the density of electrons immediately in front of the cathode as well as the number of ionised argon atoms bombarding the cathode are substantially in-.
creased. There is an increase in plasma density and a considerable increase in deposition rate. Bias sput-tering (or sputter ion plating) may be employed as a variation of this technique. In this case the wire conductor is held at a negative potential relative to the chamber and plasma. The bombardment of the wire conductor by Argon ions results in highly cleaned sur-faces. Sputtering of the target material onto the wire conductor thoughout this process results in a simulta-neous deposition/cleaning mechanism. This has the advantage that the interfacial bonding is considerably improved. In sputter ion plating systems both target and the wire conductor are held at a negative poten-tial. In this case the relative potentials are balanced to promote preferential sputtering of the target material. The target voltage will be typically less than lkV, dependent on system design and target material. The wire substrate, may be immersed in its own localised plasma dependent upon its bias potential, which will be lower than that of the target. The exact voltage/power relationship achieved at either target or substrate is dependant upon many variables and will differ in detail from system to system. Typical power densities on the target are 10-20W/cm2. The load to the substrate may be substantially lower, often as little as 5% of the target load.
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The preferred technique that is used to apply the oxide or nitride coating is a reactive bias sputtering method in which reactive gas is introduced into the vacuum chamber in addition to argon so that the oxide/
nitride of the target material, which in this case is a metal or semi metal rather than the oxide/nitride will be deposited. Experimental results have shown that the ', ' :
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level of reactive gas and its admission rate have a significant effect on deposition rates. The precision control of partial pressure of the reactive gas and the analysis of the sputtering atmosphere in a closed loop control system is considered highly desirable~ Apart from the simultaaeous deposition/cleaning advantages mentioned above, the ion bombardment of the substrate enhances surface reaction between the reactive gas and depositing species, resulting in more efficient for-mation of the coating with the required stoichiometry.
Partial pressure of reactive gas is determined experimentally but will normally be between 2 ancl 25%
but sometimes up to 30%, the exact level depending on the required stoichiometry of the coating and depostion rate. Reactive sputtering is also the preferred tech-nique because it facilitates alterations to the stoichiometry of the coating. For example, an inter-mediate "layer" of the pure metal used for the oxide/
nitride coating may be deposited in such a way that there is no defined boundary between the conductor metal, oxide/nitride metal and oxide/nitride layers.
The vacuum chambers and ancillary equipment, including micro-processor gas control units and a variety of targets used in these methods may be pur-chased commercially. Many variations in design are possible but most employ the use of "box" shaped cham-bers which can be pumped down to high vacuum for use in any of the vacuum deposition processes mentioned.
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Systems are normally, but not exclusively, dedicated to one deposition process. One system which may be employed to coat wire uses air to air transfer tech-niques for passage of the wire ~conductor through the ~, ' .
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deposition chambers and employs one or more ancillary vacuum chambers either side of the main deposition chamber.
These ancillary chambers are held at progressively higher pressures as they extend from deposition chamber to air. This reduces the load on individual vacuum sealsO The system described has the advan~age of con-tinuous feed of the wire conductor over batch process arrangements. In the vacuum deposition chamber the pressure is held constant at a pressure normally bet-ween 10-4 and 10-2 Torr.
The targets employed are commercially available Planar Magnetron Sputtering sources. Their size may vary widely, and targets in excess of 2 metres in length may be employed. Between two and four such sources may be arranged opposite one another so as to surround the wire conductor passing through the chamber or to sputter from at least two sides. The arrangement may be employed in series to increase wire throughput rates. As described above a negative bias is applied to the magnetron to initiate the sputtering process.
The wire may be held at a lower negative bias as described earlier.
Refinements to the system can, if desired, be employed. For example, the use of an intermediate vacuum~ station between the air (input side) and the deposition chamber may be employed to generate an Argon ion glow disch~arge which cleans the wire conductor suface by ion bombardment prior to its entry into the vacuum deposition chamber and also heats the wire con-ductor.
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, , Further intermediate chambers can be employed bet-ween the cleaning and deposition chamber to deposit intermediate layers.
Conditions may be controlled to produce`any of the conductor coatings described above in which no deflned boundries occur between the layers. For example an intermediate "layer" of the pure metal used for the refractory coating may be deposited in such a way that there is no defined boundary between the conductor metal, the intermediate layer and the oxide or nitride coating. In a similar fashion additional chambers can be employed between the deposition chamber ancl air ~output side) to deposit different metal, metal oxide or metal alloys onto the refractory coating for improved lubrication or wear resistance.
; Evaporation and the related processes of ac~iva~ed evaporation and ion plating offer alternative tech-niques for deposition of either the keying layer or the ~ further refractory layer.
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Evaporation of the coating material is achieved by heating the material such that its vapour pressure exceeds 10~2mbar. Evaporation temperatures vary according to coating material, e.g. 1300-3500C for refractory metal~ oxides~, the chamber pressure being usually 10-4 to 10~6mbar. Similar wire transport systems to those described may be used to hold the substrate about 30-40 cm~above the source. Several heating methods exist e.g. resistive, inductive, electron beam }mpingement etc~ although the preferred method; is an electron beam source where a beam of high energy electrons e.g. lO,OOOeV impinge onto the coating .: ~ :
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material contained in a water-cooled crucible. The use of multi-pot crucibles or twin source guns, enable multiple layers and graded stoichiometry layers to be deposited with the aid of electronic monitoring and control equipment.
Compound coatings can be made either by direct evaporation from that compound e.g. A1203 or by reac-tive evaporatrion, e.g. aluminium evaporated into a par-tial pressure of oxygen to give aluminium oxide.
Variations in the process exist either to promote reac-tions or adhesion, e.g. Activated reactive evaporation (ARE) can be used to increase the reaction probability between the evaporant and the reactive gas.
In ion-plating, negative bias applied to the substrate in an inert gas promotes simultaneous cleaning/deposition mechanisms for optimising adhesion as described in the sputtering process. Bias levels of -2kV are typically used but these can be reduced to suit wire substrates. Alternatively, high bias can be applied to a plate positioned behind the traverse wire to achieve a similar effect. As operating pressures are higher in the ion plating technique, e.g. 10-3 to 10~2mbar, gas scattering results in a more even coating distribution. To protect the filament the electron beam gun in the ion plating technique is differentially pumped to maintain vacuum higher than 10-4 mbar.
In the Plasma assisted chemical vapour deposition (PACVD) method the substrate to be coated is immersed in a low pressure ~0.1 to 10 Torr) plasma of the appro-priate gases/volatile compounds. This pressure is maintained by balancing the total gas flow-rate against , " ,.
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', '. ,~ ; , the throughput of the pumping system. The plasma is electrically activated and sustained by coupling the energy from a power generator through a matching net-work into the gas medium. Thin films have been suc-cessfully deposited from direct current and higher frequency plasmas well into the microwave range. At high frequencies the energy may be capacitatively or inductively coupled depending on chamber design and electrode configuration. Typically a 13.56 MHz radio-frequency generator would be used having a rating which would allow a power density of between 0.1 - lOW/cm2 in a capacitatively-coupled parallel-plate type reactor.
The substrate, which could be set at a temperature of up to 40~C, may be groùnded, floating or subjected to a dc voltage bias as required. Typically deposition rates for this technique can be favourably compared with those obtained by sputtering. The deposition of alumina may be achieved by immersing a substrate in a plasma containing a volatile alumina compound ~e.g.
Tri-methyl aluminium or Aluminium butoxide) and oxygen under appropriate processing conditions.
After the keying layer has been formed, the further refractory insulating coating is applied. As stated above the further refractory insulating coating may be formed on the vacuum deposited refractory coating by any technique which is relatively fast, for example sol-gel, flame sprayed, or evaporated coatings.
The sol-gel process involves the hydrolysis and polycondensation of a metal alkoxide, for example, silicon tetraethoxide, titanium butoxide or aluminium butoxide to produce an inorganic oxide gel which is converted to an inorganic oxide glass by a low temper-' 5~
ature heat treatment. The metal alkoxides can be used as precursors to inorganic glass preparation via the sol-gel route. The alumina gel can be prepared by adding an alkoxide of aluminium, such as aluminium secondary butoxide, to water which is heated to a tem-perature above 80C and stirred at high `speed.
Approximately two litres of water pex mole of alkoxide are suitable quantities. The solution is maintained at 90C and approximately 0.5 - 1 hour after the addition of the alkoxide a quantity of acid, for example 0.07 moles of hydrochloric acid per mole of alkoxide, is added to peptise the sol particles. The sol i5 main-tained at the boiling temperature to evaporate excess butanol and reflux conditions are established and main-tained until peptisation is complete. The soLs can be reduced in volume by removal of water until a viscosity suitable for wire coating is reached Wires are provided with the alumina gel for sub-sequent conversion to an inorganic insulation by a dip or extrusion process. In this process the wire is drawn through the gel prepared to a suitable viscosity, as described above, such that a controlled thickness of gel adheres to the wire. The thickness is best con-trolled by wiping excess gel from the wire using sizing dies. The gel coated wire then undergoes suitable ; dryin~ and firing stages to convert the coating into an inorganic oxide glass. The precise conditions with respect to temperature and residence time in the various stages of conversion are dependent upon the gel composition pr~pared and its tolerance to relatively rapid changes in its environment. Porosity and integ-rity of the coating can be significantly affected by these s-~ges. A suitable conversion process would : ~"' ~: :
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' include drawing the wire through drying o~ens in which the temperature is controlled at approximately 80C and subsequently through progressive heat treatment stages which expose the wire for a few minutes to temperatures of 300C to 500C. The required exposure times are dependent upon the initial thickness of the gel coating, but the general guidelines above are used with the recommendation that the drying process is carxied out as slowly as practical. It may be desirable to build thickness in a multipass process in which several thin layers are deposited sequentially.
Flame (or plasma) spraying involves injecting a powder of the refractory compound into a high tem-perature, high velocity gas stream. This process occurs within a specially designed gun or torch, and the refractory compound is ejected as a molten or semi-molten spray. This spray condenses to form a dense refractory film when it strikes a substrate. The high temperature gas stream can be produced either by controlled burning of a combustible mixture of gases (e.g. acetylene and oxygen), or by striking a low voltage high current arc in an inert gas (e.g. argon) between metal electrodes.
Flame spraying torches are available commercially, and comprise a powder dispenser, gas flow controlsl and a shaped nozzle. Several powder dispensing methods are used, including gravity and Archimedean screw. The gas temperature may reach several thousand C. Plasma spraying is very similar to flame spraying, but the heat source is supplied by an electric arc. In addi-tion to gas control, a special dc power supply is needed that can deliver up to lOOOA at lOOV. The ,, .,~,,",, :
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cathode is often made of t~oriated tungsten, and the anode is usually wat~r-~ooled copper. ~ ~lasma ~et is blown out of the torch nozzle, and refractory powaer is injected into this }et. The temperature of the plasma jet may be more than 10000C, and the gas velocity is ~ up to lOOOm/sec.
; Several variations on the above methods exist including, for example, detonation gun coating and low pressure sprayinq. In a detonation gun, pulses of powder are melted and accelerated by the controlled explosion of acetylene-oxygen within a water-cooled cylindrical chamber. This gives high gas velocities ~several thou,sand m/sec), leading to improved coating adhesion. Low pressure plasma spraying is similar to conventional plasma spraying, except the plasma jet (with molten powder) escapes into a rough vacuum, giving a denser, less contaminated coating.
; After the keying layer and further refractory layer have been deposited on the wire conductor it may be desirable to coat the oxide layer with a thin coating of a polymeric resin or lacquer in order to provide mechanical protection and a barrier against water or electrolytes during service. Further poly-meric insulation may then be extruded onto the coated conductor by methods well known in the art~ - ~
In order to form a circuit or signal integrity cable the appropriate wires according to the invention ~ ~ may simply be' Iaid together and be enclosed in a ; jacket. If desired the wires may be provided with a screen or electromagnetic interference shield before the cable ~acket is applied. Thus a cable may be .
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formed in a continuous process by means well known in the art by braiding the wire bundle and extruding a cable ]acket thereon. Any of the materials described above for the wire polymeric insulation may be used although halogen-fxee compositions e.g. compositions as described in the U.K. Patent Specifications Nos.
1,603,205 and 2,068,347A mentioned above are preferred.
It is of course possible to employ additional means for providing integrity of the cable such as mica tape wraps, but these are not necessary nor are they desir-able in view of the increased size and weight of the cable.
The present invention is also suitable for Eorming flat cables which, as wlll be ~ppreciated, are not susceptible to being wrapped with mica tape. Thus it is possible by means of the present invention to form flat cables that are capable of functioning as circuit and signal integrity cables.
Several embodiments of the invention and a method of production thereof will now be described by way of example with reference to the accompanying drawings in which:
Figure 1 is a cross-section through one form of wire according to the present invention;
Figure 2 is a cross-section through a signal ~ integrity cable employing the wires of figure : ' l;
Figure 3 is a cross-section through part of a flat ~ conductor flat cable;
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Figure 4 is a schematic view of part of the sputtering apparatus showing its wire hand-ling mechanism; and Figure 5 is a schematic section through part of the thickness of article ln accordance with the invention.
Referring to figure 1 of the drawings a 26 AWG
stranded copper conductor formed from 19 copper strands 1 is coated with ~ 0.5 micrometre thick keying layer of aluminium oxide by the sputter ion plating method described above and a further refractory aluminium oxide layer 6 micrometres thick by the sol-gel method described above, both layers being indicated by refer-ence numeral 2. Before deposition of the aluminium oxide, the outer surface of the stranded conductor was provided with a 3 micrometre thick layer of aluminium (not shown). A coating 3 based~ on a polyetherimide sold under the trade name "ULTEM'' is then extruded on ~ , :
the oxlde coated conductor to form a polymeric "insulating" layer of mean wall thickness 0.2 mm.
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Figure 2 shows a signal integrity cable formed by laying together seven wires shown in figure lj forming an electromagnetic interference screen 4 about the bundle by braiding and then extruding thereon a jacket 5 based on a~halogen-free composltion as described in British Patent Specification No. 2,068~,347 Example lA.
The cable so ~formed is particularly lightweight and~has a relatively small overall diameter in relation;
to the volume of the copper conductor.
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~ 25 - RK265 Figure 3 shows a flat conductor flat cable com-prising an array of flat copper conductors 1 with a 100 mil (2.54 mm) spacing. Each copper conductor 1 is pro-vided with a 3 micrometre thick aluminium intermediate layer (not shown), an 0.5 micrometre thick alumina keying layer thereon and a 6 micrometre thick further alumina layer thereon as described above, both alumina layers shown by reference numberal 2, and the coated conductors are embedded in a single polymeric insu-lating layer 3 formed for example from the polyether imide sold under the trade name "ULTEM" or from a polyether ether ketone or polyether ketone.
Apparatus for use in a batch process for providing the keying layer on a wire conductor substrate is illustrated in Fig. 4. The apparatus comprises a vacuum chamber into which a complete wire transport mechanism which includes wire pay-off reel 2 and take-up reel 3, wire support rolls 10 and tensioning rolls i5 loaded. The mechanism engages motor drives which control the passage of wire 4 so that the wire traver-ses a vertically mounted target 5 a number of times.
Deposition occurs by the processes previously described, As before, variations in set-up are poss-ible. An additional target (not shown) may be employed on the other side of the wire to increase coating rates and additional targets, e.g. target 6 can be employed to deposit intermediate layers before and/or after deposition ~of the primary oxide/ nitride coating.
Suitable design of the gas inlet system to suit the specific geometries employed can facilitate deposition of layers whic~ have no defined boundaries as described previously. Batch length will depend on chamber dimen-sions and transport system design.
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In the operation of such a batch process wire 4 is transferred from one reel 2 to the other 3 within the chamber. The route taken by the wire may cause it to pass before the smaller ancillary target 6 to deposit an intermediate layer of any desirecl material. Power to this target, combined with wire speed and the number of passes in front of the target will control the thickness of the intermediate layer deposit. The wire 4 may then pass in front of the larger primary target S
to deposit the main coating. Again thickness will be dictated by a combination of power, wire speed and a number of passes. The ratio of thicknesses between the intermediate and the primary coating is controlled in the same way. Multi-layers can be built up by reversing the mechanism as desired such that the wire 4 passes back past the targets 5,6 in reverse order.
Thickness and composition may be altered in the reverse pass as required, e.g. the process employed at the smaller magnetron may be reactive on the reverse pass to deposit a compound of the metal on the intermediate layer, e.g. Ti and TiNX. Deposition of layers with no defined boundary between the metal intermediate layers (or substrates) and the oxide/ nitride coatings may be achieved by setting up gradients of reactive gas in front of the primary target, such that wire at the top edge of the target 5 is subjected to deposition in an Argon rich atmosphere which gradually increases in reactive gas content as the wire progresses down the face of the t:arget. A gradient can be achieved by a baffle system (not shown) which progressively leaks oxygen introduced at the bottom end of the target towards the upper end.
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A simpler techni~ue for~ producing the layer with '~ no defined boundary involves use of a multipass process ': ~
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in which wire 4 is passed back and forth through the system, and with each pass the level of reactive gas is increased to a final level required to obtain the correct stoichiometry. Thus the stoichiometry of the intermediate layer increases in a series of small incremental steps from metal to required stoichiometry.
Composite targets may also be used to produce inter-mediate layers with stoichiometry gradients. In the case of discrete articles, the articles may instead be held in front of the target by means of a rotating sample holder.
Figure 5 is a schematic section through parts of an article according to the invention showing a typical arrangement of layers that may be formed on the copper substrate, the thickness of the layers being exaggerated for the sake of clarity.
A copper substrate 21 is provided with a thick (e.g. 1 to 3 micrometres) layer 22 of nickel followed by a layer 23 of aluminium metal, a layer 24 of non~
stoichiometric aluminium oxide A120x and a layer 25 of stoichiometric aluminium oxide A1203, the Iayers 23, 24 and 25 having been formed e.g. by a sputtering method.
An additional, relatively thick layer 26 of aluminium oxide (e.g. of about 5 to 15 micrometres thickness) has been deposited on the layer 25 by a sol-gel method.
Although~the layers are clearly demarcated in the drawing by means of lines, it will be appre~iated that such boundaries,may, and preferably will, not be formed in practise, especially between the copper/aluminium, aluminium/A120x and A120x/Al203 layers. Indeed, the aluminium, A120X and stoichiometric alumina layers may , ~
' :
, all be formed in the same sputtering process in which case the stoichiometry of the layers will depend on the oxygen gradient used.
The following Examples illustrate the invention:
Examples 1 and 2 Copper conductors were provided with 3.3 micro-metres thick aluminium intermediate layer by use of the sputtering apparatus shown schematically in figure 4 of the drawings. The sputtering conditions were as follows: the wire 4 was precleaned by vapour degreas-ing in l,l,l-trichloroethalle prior to depo5ition. The cleaning was achieved by passing the wire through a vapour degreasing bath such that a residence time of 3 minutes was achieved. The wire 4 was then loaded into the vacuum chamber. The chamber was then evacuated o a pressure of 1 x 10-6 mbar prior to starting the pro-cess. At this stage argon was admitted to attain a pressure of 1.5x10-2 mbar whereupon a high frequency (80 kHz) bias potential was applied to the wire hand-ling system which was isolated from ground. A bias potential of -850V was achieved, and the wire was transferred from reel 3 to reel 4 such that a residence time of 10 minutes was achieved. On completion of the cleaning cycle the pressure was reduced to 8.10-3 mbar and the deposition process started.
:
3 kW of ~DC power was applied to the aluminium target 5. The wire passed from ~reel 2 to reel 3 being coated as it~passed the target 5. Residence time in this region was controlled by wire speed and ad~justed to give the~required thickness. The roller mechanism : :
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alternated the wire face exposed to the target as it progressed down the target length.
The wire sample of copper conductor coated with aluminium as described above was subsequently coated with aluminium oxide in a similar process. For this second coating, an aluminium oxide target powered with an RF power supply was used. The wire residence time and target power were adjusted to give a constant thickness of aluminium oxide, of about 0.2 micro-metres. During déposition of both aluminium and alumi-nium oxide the copper conductors were held at an appropriate bias potential relative to the chamber to promote adhesion.
Wire samples of copper conductor, in some cases coated with a 3.3 micrometre thickness of aluminium, and in some cases coated with an additional 0.2 micro-metre thickness of aluminium oxide as described above, were subsequently coated with a gel-derived aluminium oxide by the sol-gel process described above.
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The samples were then tested to determine the adhesion of the top coat as follows. A fixed Length of wire was subjected to a tensile stress whilst the strain was continuously recorded. During testing the wire sample~was viewed through an optical mircoscope.
When the coating was seen to significantly spall the strain was recorded. The strain value recorded at this point gave a measure of the adhesion of the coating.
The composition of the samples and the results obtained are shown in Table No. 1.
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_ 30 _ RK265 Table 1 Example l(Comparison) . 2 Substrate 22 awg Stranded 22 awg Stranded Copper Cu .
Metallic Aluminium layer (micrometres) 0 3.3 Vacuum deposited ^
Aluminium Oxide Layer (micrometres) 0 0.2 Sol gel deposited Aluminium Oxide layer (micrometres) 12 12 Adhesion (arbitary units) 0* 600 ~ ~ ;
* The adhesion of the coating to bare copper was very poor, rendering the samples unable to be tested due to immediate spalling.
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The. results show a clear improvement in adhesion of the gel ~derived alumina coating with the vacuum deposited aluminium oxide layer.
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: Examples 3 and 4 The elect~ical:~performance of wires prepared as those~ in example: 2,: were tested by twisti:ng pairs of identical wires~(2 twists~per 2.5 cms length) to form a ;: :
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~L ~ '~ J '~ 9 twisted pair cable, connecting one end of the wires to a 30V peak to peak lMHz square wave generator, and observing the wave form across a 200 ohm load connected between the wires by means of an c>scilloscope. The twisted pair cables were subjected to heating in a pro-pane gas burner having a flat flame 8cm wide. The tem-perature of the flame just below the twisted pairs was maintained at the required temperature and the time to failure recorded.
In example 3 the sample was found to survive for 70 seconds in a flame at 900C. In example 4 the wires had still not failed after a flame exposure time of 72 minutes at 650C. The substrate material onto which the sol-gel derived aluminium oxide was deposited for examples 3 and 4 had a dense 0.2 micrometres coating of ; vacuum deposited aluminium oxide on its surface.
Although this layer is insulating, it was incapable alone of supporting 30V at room temperature.
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Examples 5 to 7 22 AWG 19 strand copper wire conductors were pro-vided with sputtered aluminium and aluminium oxide layers using the method detailed in examples l and 2.
The wires were then transferred to another vacuum chamber equipped with a 25Kw electron beam gun. This chamber was pumped down to a base pressure of 5~.10~5mbar,~and a further refractory insulating layer of aluminium oxide deposited by electron beam evapora-tion. The elèctron beam power was about 6kW (25Kv, 240mA), and the refractory was evaporated directly from highly sintered alumina pieces, contained in a water-cooled copper crucible. The deposition rate of alumi-- :
' - 32 - R~65 nium oxide by evaporation was about 3um/min, much faster than the refractory keying layer deposition rate, which was about O.Olum/min.
Samples manufactured as described above were adhe-sion tested using the tensile method described in examples 1 and 2. The results are given in Table 2, from which it is clear that a thin refractory keying layer deposited by a relatively slow method improved the adhesion of a further refractory layer deposited by a faster method.
Table 2 Example Al intermediate A1203 keying A1203 further Adhesion layer thickness layer thickness layer thickness (arbitary ~um) (um) (um) units) 6 0 0.5 7 1200 7 7 0.5 7 2150 The wire of Example 7 was tested for electrical performance as described in Example 3 (900C) and no failure was recorded after 4 hours, whereas the wire of .
: Example 5 could not be tested due to immediate spalling on lmmersion in the flame.
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The composition is also improved by removing the use of polymeric binders to support inorganic materials which may be consolidated by firing processes to form the inorganic insulation. Similarly, articles in which the refractory coatings have been formed by electrochemical conversion of metal layers e.g. by anodising an alumi-nium layer, do not form part of the invention, such layers usually being porous and often being heavily contaminated with ionic residue from the electrolytic solutions e.g. sulphates from sulphuric acid anodisa-tion processes.
Preferably the underlying metal from which the part of the article is formed has a melting point of at least 800C, more preferably at least 900C, and espe-cialIy at least 1000C. The present invention is par-ticularly applicable to articles in which the metal is copper or an alloy thereof for example wire and cable that need to be capable of functioning at high tem-peratures for significant lengths of time without failure e.g. circuit and signal integrity cable and ,:
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_ 4 _ RK265 magnet wire, and the invention will be described below with reference to wire and cable.
In the case where the article c:omprises an elec-trical wire or cable, so that the underlying copper forms the conductor of the cable, the conductor may be a single, solid conductor or it may be a stranded con-ductor in which individual strands are laid together to form a bundle which preferably contains 7, 19 or 37 strands. Where the conductor is stranded it is pre-ferred for the bundle to be coated rather than the individual strands, that is to say, the refractory coating extends around the circumference of the bundle but not around the individual strands so that substan-tially only the outwardly lying surEaces of the outer-most layer of strands are coated.
This form of conductor has the advantage that the inter strand electrical contact is retained and the dimensions of the bundle are kept to a minimum (since the thickness of the coating may constitute a signif-icant proportion of the strand dimensions for fine gauge conductors) and also it aids the formation of good electrical connections, e.g. crimp connections, to the conductor because a large proportion of the surface of the strands, and the entire surface of the strands in the central region of the conductor, will be un-coated by the refractory layer.
If a circuit or signàl integrity cable is formed according to the invention from a stranded; conductor, it has the ad~antage that it is very flexible as com-pared with other signal and circuit integrity cables, especially if a stranded conductor is used. The abi-: :
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_ 5 _ RK265 lity of the wire to be bent around tight bends (smallbend radii) without deleterious effect is partly due to - the fact that the layer providing the integrity is thinner than with other signal and circuit integrity cables~ However, when the conductor is a stranded con-ductor it may be bent around tight bends without undue stress on the surface of the strands because the strands are displaced from a regular hexagonal packing at the apex of the bend thereby exposing uncoated areas of the strands to the eye. It is highly surprising that even though uncoated strands may be exposed when the wire conductor is bent there is no electrical con-tact between adjacent stranded conductors. It i9 believed that in this case the integrity is retained because the profile of a stranded conductor is not cylindrical but rather is in the form of a hexagon that rotates along the length of the conductors, so that adjacent stranded conductors will touch one another only at a few points along their length, which points are always provided by the outwardly oriented part of the surface of the strands in the outer layer of the conductors. It is these points of contact that are always provided with the refractory coating.
The further refractory layer preferably has a thickness of at least 0.5, more preferably at least 1 and especially at least 2 micrometres. The exact thickness desired will depend on a number of factors including the type of layer and the voltage rating of ~ the wire, circuit integrity cables usually requiring a ; ~ somewhat thicker coating~ than signal integrity cables and sometimes above 15 micro-metres. The lower limits for the layer thickness are usually determined by the required voltage rating of the wire whilst the upper ;,~
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6 270~5-123 limits are usually determined by the tlme, and therefore the cos~, of the coating operation.
The refractory keying layer wlll usually be thinner than the further refractory layer, and preferably has a thiakness of not more than 0.5 micrometres and most preferably not more ~han 0.3 micxometre~, but usually a~ least 0.1 micro~etres.
In order to optimise the adhesion between the refractory keying layer and the further refractory layer it is preferred for them both to have the same nominal chemlcal composition, that is to say, they both preferably have the same general ¢hemical formula although, a~ explained below, the preai~e stoichiometry o~ one or bokh layer~ may dlf~er ~rom the stoichlometric formula.
In order to improve further the high temperature propertieæ of the article, and e3peci~ally in the case where the underlying metal is copper or an alloy thereof, it i5 preferred ~or the article to include a metallic intermediate layer located between the metal ~rom which the part is formed and the refraatory keying layer. The metal is preferably one whlch forms a good bond between the underlying metal and the re~ractory keying layer and also, as de~crlbed in Canadian Patent No.
1,264,616, one which acts as a barrier to diffusion o$ oxygen or oopper or both or which acts to reduce stre~s in the refraatory layer isposed bV sub~trate ~train resu1ting from mechanical ,, ~ . ~
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~ 7 ~ 2706~-123 or thermal strPss. Preferred metallic inter~nediate layers include those formed from aluminium, titanium, tantalum chrom-ium, manganese, silicon or nickel although other metals may be used. Examples articles in which they may be used ~re described in Canadian Patent No. 1,241,395.
In the case of electrical equipment the refractory layers may provïde the entire elec~rical insulation or one or more additional iDsulating layers may be pro-vided thereon. The additional insulating layer may be inorganic or organic or a combination of ino~ganic and organic layer~ may be provided.
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In the case of wires according to the invention, the po1ymeric insulation may be provided in order to provide additional insulation to the conductor during ; normal service conditions and also to enable the wire to have the desired dielectric properties and other properties e.~. mechanical properties, scu~f resis-tance, colour coding ability etc. ~owever, an im-portant advantage of the present invention is that since a significant proportion of or all the service insulating properties are provided by the refractory coating, the electrical properties of the polymeric insulation are not as critical as with other wire contructions in which the polymeric insulation provides the sole insulation between the conductors. Of the known polymeric materials that are used for electrical insulation, polye~thylene probably has the most suitable ~ electrical properties but is highly flammable, and has `: :
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poor mechanical properties. Attempts to flame retard polyethylene have either required halogenated flame retardants which, by their nature, liberate corrosive and toxic hydrogen halides when subjected to fire, or have required relatively large quantities of halogen free flame retardants which have a deleterious effect on the electrical properties and often also the mechan-ical properties of the polymer. Accordingly~ an accep-table wire has in the past only been achieved by a compromise between different properties which is often resolved by using a relatively thick-walled polymeric insulation and/or dual wall constructions. Although such forms of polymeric insulation may be used with the wire according to the present invention, the presence of the refractory layer does obviate these problems to a large extent since the polymer used for the insul-ation may be chosen for its flammability and/or its mechanical properties at the expense of its electrical properties. As examples of polymers that may be used to form the polymeric insulation there may be mentioned polyolefins e.g. ethylene homopolymers and copolymers with alpha olefins, halogenated polymers e.g. tetra-fluoroethylene, vinylidene fluoride, hexafluoropropy-lene and vinyl chloride homo or copolymers polyamides, oolyesters, polyimides, polyether ketones e.g. poly-arylether ketones, aromatic polyether imides and sulphones, silicones, alkene/vinyl acetate copolymers and the like. The polymers may be used alone or as blends with~one another and may contain fillers e.g.
silica and metal oxides e.g. treated and untreated metal oxide flame retardants such as hydrated alumina and titania. 'The polymers may be used in single wall constructions or in multiple wall constructions, for example a polyvinylidine fluoride Iayer may be located :. . .
, S ~
on for exampLe a polyethylene layer. The polymers may be uncross-linked but preferably are crosslinked, for example by chemical crosslinking a~ents or by electron or gamma irradiation, in order to improve their mechanical properties and to reduce flowing when heated. They may also contain other materials e.g. anti-oxidants, stabilizers, crosslinking promotors, processing aids and the like.
The polymeric insulation may, if desired, contain a filler e.g.
hydrated alumina, hydrated titania, ~awsonite, silica and the like, and especially a filler that has the same chemical composi-tion, at least under pyrolysis conditions, as the refractory coat-ing, so that the ~iller in the polymeri~ insulation will provide additional insulation when the wire or cable is subjected to a fire. A preEerred type of polymeric insulation is one that wil:L
cllar, for instance certa:in aromatic polymers mentioned above, or that will ash e.g. a silicone polymer, when subjected to a fire so that the char or ash, together with the refractory coating, will provide the necessary insulation during a fire. Examples of poly-mers, compositions, their manufacture and wires using them are described in U.S. Patent Specifications Nos. 3,269,862, 20 3,580,829, 3,953,400, 3,956,240, 4,155,823, 4,121,001 and 4,320, 224, British Patent Specifications Nos. 1,473,972, 1,603,205, 2,068,347 and 2,035,333, 1,604,405 and in European Patent Specification No. 69,598. In some instances, for example when certain aromatic polymers are used, i-t may be appropriate to form the insulation on the conductor by a plasma or therma] polymerisa-~ tion process. Preferab1y the wire is substantiall~ halogen reé.
;~ As stated~above, the preferred methods of forming the :::
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keying layer include evaporation, plasma assisted chemical vapour deposition and sputtering methods.
An advantage oE using a relatively slow deposition method such as a sputtering ~ethod for Eorming the keying layer is that it allows greater control over the chemical composition and mechanical properties of the keying layer to be exercised. For example, it is often advantageous for the keying layer to be non-stoichiometric since this may increase the adhesion between the keying layer and the underlying layer, and especially if the stoi-chiometry oE the keying layer varies through at least part of its thickness so that stresqes that may be induced in the coatiny, for example due to clifEerential thermal expansion, are not localised to a boundary oE the layer and so that diEferent parts oE the layer will exibit di~ferent properties. For example, a relatively metal-rich part of the keying layer may exhibit good adhesion to the conductor or intermediate layer while part of the coating having least metal or semi-metal may exhibit the best electrical properties or better adhesion to the further refractory layer.
Preferably the insulating refractory coating is formed from an electrically insulating infusible or refractory me-tal or semi-metal oxide or nitride and the invention will be described below in many cases with respect to oxides and nitrides although other refractory-coatings are included. By the term "infusible"
or "refractory" is meant that the coatiDg material in its bulk form should not fuse or decompose when subjected to a temperature of 800C, for 3 hours. Preferably the oxide or nitride should be able to~withstand higher -temperatures also, for example it should ::
- lOa - 5 ~ ~ 27065-123 be able to withstand a temperature of 1000C for a-t least 20 to 30 minutes. The preferred oxides are those oE aluminium, titanium, tantalum and silicon or mixtures thereof with themselves or with other oxides and the preferred nitrides are those of aluminium and silicon. Thus, for example, the use of mixed metal oxides for the refractory coating are also encompassed by the present invention.
If desired, the stoichiometry of the keying layer may vary continuously throughout the thickness of the ]ayer or it may contain one or more layers or strata of relatively uniform stoichiometry. Thus the keying layer may have an outer region of :: :
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relatively uni~orm stoichiometry and preferably of a relatively high oxygen content in order to exhibit the optimum electrical properties or adhesion to the further refractory layer. The relative thicknesses of the non-uniform and uniform layers may vary widely. ~or example the major part of the keying may have a non-uniform stoichiometry or the major part of the layer's thick-ness may be of uniform stoichiometry, in wliich latter case the non-uniform part of the layer could even by considered as an intermediate layer that improves adhesion of the rest of the layer especially at high temperatures. If the underlying metal- or semi-metal-rich part of the keying layer is intended to improve the adhesion of the refractory coating, its particular composition will depend on the composition of any underlying layer, and in some cases it may be desirable for the metal or semi-metal rich part to consist substantially entirely of the metal or semi-metal so that there is a gradual change from the metal or seml-metal to the oxide. This is particularly preferred if the system includes an underlying layer o the same metal or semi-metal.
The precise stoichiometry of the uniform top layer can be determined experimentally using wavelength dispersive electron mlcroprobe analysis or by using x-ray photoelectron spectroscopy ;(XPS). The composition of the coating as it changes from metal to refractory throughout~its depth can be assessed using Auger elec-tron spectroscopy (~AE5) in which the film is con-tinuously sputter-ed away~to expose fresh surface for composition analysis.
The variation in s-toichiometry is not limited to a variation in~the metal or semi-metal/oxygen proportions. In addi-tion or alternatively the relative proportions of two difEerent metals or semi~metals may be varied so that, for example, there is a gradual change from one metal, which may constitute an interme-diate layer, to the oxide of a different metal.
The outer region of the keying layer preferably has a molar oxygen content that is at least 50~, more preferably at least 65% and especially at least 80~ of the oxygen content of that required for the formal stoichiometry o~ the insulating refractory oxide. Thus the preferred oxide composition of the outer region may be represented as M0x where x is at least 0.75, preerably at least :l and especially at least 1.25 in the case of aluminium, at least 1, preerably at least 1.3 and especially at least 1.5 in the case of titanium or silicon, and at least 1.25, preferably at least 1.6 and especially at least 2 in the case of tantalum.
The most preferred method of forming keying layer in which the composition varies throughout i-ts thickness i9 a sputtering method.
In the sputtering method, predominantly neutral atomic or molecular species are ejected from a target, which may be formed from the material to be deposited, under the bombardment of : inert gas positive ions e.g. argon ions. The high energy species e~ected will travel considerable distances to be deposited on the wire , 5~
conductor substrate held in a medium vacuum, e.g. 10-4 to 10-2 mbar. The positive ions required for bombard-ment may be generated in a glow discharge where the sputtering target serves as the cathode electr~de to the glow discharge system. The r~egative potential (with respect to ground and the glow discharge) is maintained in the case of insulating target materials by the use of radio frequency power applied to the cathode, which maintains the target surface at a nega-tive potential throughout the process, DC power may be applied when the, target is an electrically conducting material. The advantage of such techniques is that control over the coating material is greatly enhanced, and the energy of the species ejected is very much higher than with evaporation methods e.g. typically 1 to 10 eV for sputtering as compared with 0.1 to 0.5 eV
for evaporation methods. Considerable improvements in interfacial bonding are achieved but the deposition rate in the sputtering process described will be lower than that for electron beam evaporation.
In magnetron sputtering processes the plasma is concentrated immediately in front of the cathode (target) by means of a magnetic field. The effect of the magnetic field on the gas discharge is dramatic.
In that area of discharge where permanent magnets, usually installed behind the cathode, create a suff-iciently strong magnetic field vertically to the electric field, secondary electrons resulting from the sputter bombardment process will be deflected by means of the Lorentz force into circular or helical paths.
Thus the density of electrons immediately in front of the cathode as well as the number of ionised argon atoms bombarding the cathode are substantially in-.
creased. There is an increase in plasma density and a considerable increase in deposition rate. Bias sput-tering (or sputter ion plating) may be employed as a variation of this technique. In this case the wire conductor is held at a negative potential relative to the chamber and plasma. The bombardment of the wire conductor by Argon ions results in highly cleaned sur-faces. Sputtering of the target material onto the wire conductor thoughout this process results in a simulta-neous deposition/cleaning mechanism. This has the advantage that the interfacial bonding is considerably improved. In sputter ion plating systems both target and the wire conductor are held at a negative poten-tial. In this case the relative potentials are balanced to promote preferential sputtering of the target material. The target voltage will be typically less than lkV, dependent on system design and target material. The wire substrate, may be immersed in its own localised plasma dependent upon its bias potential, which will be lower than that of the target. The exact voltage/power relationship achieved at either target or substrate is dependant upon many variables and will differ in detail from system to system. Typical power densities on the target are 10-20W/cm2. The load to the substrate may be substantially lower, often as little as 5% of the target load.
.
The preferred technique that is used to apply the oxide or nitride coating is a reactive bias sputtering method in which reactive gas is introduced into the vacuum chamber in addition to argon so that the oxide/
nitride of the target material, which in this case is a metal or semi metal rather than the oxide/nitride will be deposited. Experimental results have shown that the ', ' :
~z~
level of reactive gas and its admission rate have a significant effect on deposition rates. The precision control of partial pressure of the reactive gas and the analysis of the sputtering atmosphere in a closed loop control system is considered highly desirable~ Apart from the simultaaeous deposition/cleaning advantages mentioned above, the ion bombardment of the substrate enhances surface reaction between the reactive gas and depositing species, resulting in more efficient for-mation of the coating with the required stoichiometry.
Partial pressure of reactive gas is determined experimentally but will normally be between 2 ancl 25%
but sometimes up to 30%, the exact level depending on the required stoichiometry of the coating and depostion rate. Reactive sputtering is also the preferred tech-nique because it facilitates alterations to the stoichiometry of the coating. For example, an inter-mediate "layer" of the pure metal used for the oxide/
nitride coating may be deposited in such a way that there is no defined boundary between the conductor metal, oxide/nitride metal and oxide/nitride layers.
The vacuum chambers and ancillary equipment, including micro-processor gas control units and a variety of targets used in these methods may be pur-chased commercially. Many variations in design are possible but most employ the use of "box" shaped cham-bers which can be pumped down to high vacuum for use in any of the vacuum deposition processes mentioned.
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Systems are normally, but not exclusively, dedicated to one deposition process. One system which may be employed to coat wire uses air to air transfer tech-niques for passage of the wire ~conductor through the ~, ' .
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deposition chambers and employs one or more ancillary vacuum chambers either side of the main deposition chamber.
These ancillary chambers are held at progressively higher pressures as they extend from deposition chamber to air. This reduces the load on individual vacuum sealsO The system described has the advan~age of con-tinuous feed of the wire conductor over batch process arrangements. In the vacuum deposition chamber the pressure is held constant at a pressure normally bet-ween 10-4 and 10-2 Torr.
The targets employed are commercially available Planar Magnetron Sputtering sources. Their size may vary widely, and targets in excess of 2 metres in length may be employed. Between two and four such sources may be arranged opposite one another so as to surround the wire conductor passing through the chamber or to sputter from at least two sides. The arrangement may be employed in series to increase wire throughput rates. As described above a negative bias is applied to the magnetron to initiate the sputtering process.
The wire may be held at a lower negative bias as described earlier.
Refinements to the system can, if desired, be employed. For example, the use of an intermediate vacuum~ station between the air (input side) and the deposition chamber may be employed to generate an Argon ion glow disch~arge which cleans the wire conductor suface by ion bombardment prior to its entry into the vacuum deposition chamber and also heats the wire con-ductor.
:
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, , Further intermediate chambers can be employed bet-ween the cleaning and deposition chamber to deposit intermediate layers.
Conditions may be controlled to produce`any of the conductor coatings described above in which no deflned boundries occur between the layers. For example an intermediate "layer" of the pure metal used for the refractory coating may be deposited in such a way that there is no defined boundary between the conductor metal, the intermediate layer and the oxide or nitride coating. In a similar fashion additional chambers can be employed between the deposition chamber ancl air ~output side) to deposit different metal, metal oxide or metal alloys onto the refractory coating for improved lubrication or wear resistance.
; Evaporation and the related processes of ac~iva~ed evaporation and ion plating offer alternative tech-niques for deposition of either the keying layer or the ~ further refractory layer.
,:
Evaporation of the coating material is achieved by heating the material such that its vapour pressure exceeds 10~2mbar. Evaporation temperatures vary according to coating material, e.g. 1300-3500C for refractory metal~ oxides~, the chamber pressure being usually 10-4 to 10~6mbar. Similar wire transport systems to those described may be used to hold the substrate about 30-40 cm~above the source. Several heating methods exist e.g. resistive, inductive, electron beam }mpingement etc~ although the preferred method; is an electron beam source where a beam of high energy electrons e.g. lO,OOOeV impinge onto the coating .: ~ :
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material contained in a water-cooled crucible. The use of multi-pot crucibles or twin source guns, enable multiple layers and graded stoichiometry layers to be deposited with the aid of electronic monitoring and control equipment.
Compound coatings can be made either by direct evaporation from that compound e.g. A1203 or by reac-tive evaporatrion, e.g. aluminium evaporated into a par-tial pressure of oxygen to give aluminium oxide.
Variations in the process exist either to promote reac-tions or adhesion, e.g. Activated reactive evaporation (ARE) can be used to increase the reaction probability between the evaporant and the reactive gas.
In ion-plating, negative bias applied to the substrate in an inert gas promotes simultaneous cleaning/deposition mechanisms for optimising adhesion as described in the sputtering process. Bias levels of -2kV are typically used but these can be reduced to suit wire substrates. Alternatively, high bias can be applied to a plate positioned behind the traverse wire to achieve a similar effect. As operating pressures are higher in the ion plating technique, e.g. 10-3 to 10~2mbar, gas scattering results in a more even coating distribution. To protect the filament the electron beam gun in the ion plating technique is differentially pumped to maintain vacuum higher than 10-4 mbar.
In the Plasma assisted chemical vapour deposition (PACVD) method the substrate to be coated is immersed in a low pressure ~0.1 to 10 Torr) plasma of the appro-priate gases/volatile compounds. This pressure is maintained by balancing the total gas flow-rate against , " ,.
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', '. ,~ ; , the throughput of the pumping system. The plasma is electrically activated and sustained by coupling the energy from a power generator through a matching net-work into the gas medium. Thin films have been suc-cessfully deposited from direct current and higher frequency plasmas well into the microwave range. At high frequencies the energy may be capacitatively or inductively coupled depending on chamber design and electrode configuration. Typically a 13.56 MHz radio-frequency generator would be used having a rating which would allow a power density of between 0.1 - lOW/cm2 in a capacitatively-coupled parallel-plate type reactor.
The substrate, which could be set at a temperature of up to 40~C, may be groùnded, floating or subjected to a dc voltage bias as required. Typically deposition rates for this technique can be favourably compared with those obtained by sputtering. The deposition of alumina may be achieved by immersing a substrate in a plasma containing a volatile alumina compound ~e.g.
Tri-methyl aluminium or Aluminium butoxide) and oxygen under appropriate processing conditions.
After the keying layer has been formed, the further refractory insulating coating is applied. As stated above the further refractory insulating coating may be formed on the vacuum deposited refractory coating by any technique which is relatively fast, for example sol-gel, flame sprayed, or evaporated coatings.
The sol-gel process involves the hydrolysis and polycondensation of a metal alkoxide, for example, silicon tetraethoxide, titanium butoxide or aluminium butoxide to produce an inorganic oxide gel which is converted to an inorganic oxide glass by a low temper-' 5~
ature heat treatment. The metal alkoxides can be used as precursors to inorganic glass preparation via the sol-gel route. The alumina gel can be prepared by adding an alkoxide of aluminium, such as aluminium secondary butoxide, to water which is heated to a tem-perature above 80C and stirred at high `speed.
Approximately two litres of water pex mole of alkoxide are suitable quantities. The solution is maintained at 90C and approximately 0.5 - 1 hour after the addition of the alkoxide a quantity of acid, for example 0.07 moles of hydrochloric acid per mole of alkoxide, is added to peptise the sol particles. The sol i5 main-tained at the boiling temperature to evaporate excess butanol and reflux conditions are established and main-tained until peptisation is complete. The soLs can be reduced in volume by removal of water until a viscosity suitable for wire coating is reached Wires are provided with the alumina gel for sub-sequent conversion to an inorganic insulation by a dip or extrusion process. In this process the wire is drawn through the gel prepared to a suitable viscosity, as described above, such that a controlled thickness of gel adheres to the wire. The thickness is best con-trolled by wiping excess gel from the wire using sizing dies. The gel coated wire then undergoes suitable ; dryin~ and firing stages to convert the coating into an inorganic oxide glass. The precise conditions with respect to temperature and residence time in the various stages of conversion are dependent upon the gel composition pr~pared and its tolerance to relatively rapid changes in its environment. Porosity and integ-rity of the coating can be significantly affected by these s-~ges. A suitable conversion process would : ~"' ~: :
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.
' include drawing the wire through drying o~ens in which the temperature is controlled at approximately 80C and subsequently through progressive heat treatment stages which expose the wire for a few minutes to temperatures of 300C to 500C. The required exposure times are dependent upon the initial thickness of the gel coating, but the general guidelines above are used with the recommendation that the drying process is carxied out as slowly as practical. It may be desirable to build thickness in a multipass process in which several thin layers are deposited sequentially.
Flame (or plasma) spraying involves injecting a powder of the refractory compound into a high tem-perature, high velocity gas stream. This process occurs within a specially designed gun or torch, and the refractory compound is ejected as a molten or semi-molten spray. This spray condenses to form a dense refractory film when it strikes a substrate. The high temperature gas stream can be produced either by controlled burning of a combustible mixture of gases (e.g. acetylene and oxygen), or by striking a low voltage high current arc in an inert gas (e.g. argon) between metal electrodes.
Flame spraying torches are available commercially, and comprise a powder dispenser, gas flow controlsl and a shaped nozzle. Several powder dispensing methods are used, including gravity and Archimedean screw. The gas temperature may reach several thousand C. Plasma spraying is very similar to flame spraying, but the heat source is supplied by an electric arc. In addi-tion to gas control, a special dc power supply is needed that can deliver up to lOOOA at lOOV. The ,, .,~,,",, :
.
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cathode is often made of t~oriated tungsten, and the anode is usually wat~r-~ooled copper. ~ ~lasma ~et is blown out of the torch nozzle, and refractory powaer is injected into this }et. The temperature of the plasma jet may be more than 10000C, and the gas velocity is ~ up to lOOOm/sec.
; Several variations on the above methods exist including, for example, detonation gun coating and low pressure sprayinq. In a detonation gun, pulses of powder are melted and accelerated by the controlled explosion of acetylene-oxygen within a water-cooled cylindrical chamber. This gives high gas velocities ~several thou,sand m/sec), leading to improved coating adhesion. Low pressure plasma spraying is similar to conventional plasma spraying, except the plasma jet (with molten powder) escapes into a rough vacuum, giving a denser, less contaminated coating.
; After the keying layer and further refractory layer have been deposited on the wire conductor it may be desirable to coat the oxide layer with a thin coating of a polymeric resin or lacquer in order to provide mechanical protection and a barrier against water or electrolytes during service. Further poly-meric insulation may then be extruded onto the coated conductor by methods well known in the art~ - ~
In order to form a circuit or signal integrity cable the appropriate wires according to the invention ~ ~ may simply be' Iaid together and be enclosed in a ; jacket. If desired the wires may be provided with a screen or electromagnetic interference shield before the cable ~acket is applied. Thus a cable may be .
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formed in a continuous process by means well known in the art by braiding the wire bundle and extruding a cable ]acket thereon. Any of the materials described above for the wire polymeric insulation may be used although halogen-fxee compositions e.g. compositions as described in the U.K. Patent Specifications Nos.
1,603,205 and 2,068,347A mentioned above are preferred.
It is of course possible to employ additional means for providing integrity of the cable such as mica tape wraps, but these are not necessary nor are they desir-able in view of the increased size and weight of the cable.
The present invention is also suitable for Eorming flat cables which, as wlll be ~ppreciated, are not susceptible to being wrapped with mica tape. Thus it is possible by means of the present invention to form flat cables that are capable of functioning as circuit and signal integrity cables.
Several embodiments of the invention and a method of production thereof will now be described by way of example with reference to the accompanying drawings in which:
Figure 1 is a cross-section through one form of wire according to the present invention;
Figure 2 is a cross-section through a signal ~ integrity cable employing the wires of figure : ' l;
Figure 3 is a cross-section through part of a flat ~ conductor flat cable;
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Figure 4 is a schematic view of part of the sputtering apparatus showing its wire hand-ling mechanism; and Figure 5 is a schematic section through part of the thickness of article ln accordance with the invention.
Referring to figure 1 of the drawings a 26 AWG
stranded copper conductor formed from 19 copper strands 1 is coated with ~ 0.5 micrometre thick keying layer of aluminium oxide by the sputter ion plating method described above and a further refractory aluminium oxide layer 6 micrometres thick by the sol-gel method described above, both layers being indicated by refer-ence numeral 2. Before deposition of the aluminium oxide, the outer surface of the stranded conductor was provided with a 3 micrometre thick layer of aluminium (not shown). A coating 3 based~ on a polyetherimide sold under the trade name "ULTEM'' is then extruded on ~ , :
the oxlde coated conductor to form a polymeric "insulating" layer of mean wall thickness 0.2 mm.
:
Figure 2 shows a signal integrity cable formed by laying together seven wires shown in figure lj forming an electromagnetic interference screen 4 about the bundle by braiding and then extruding thereon a jacket 5 based on a~halogen-free composltion as described in British Patent Specification No. 2,068~,347 Example lA.
The cable so ~formed is particularly lightweight and~has a relatively small overall diameter in relation;
to the volume of the copper conductor.
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~ 25 - RK265 Figure 3 shows a flat conductor flat cable com-prising an array of flat copper conductors 1 with a 100 mil (2.54 mm) spacing. Each copper conductor 1 is pro-vided with a 3 micrometre thick aluminium intermediate layer (not shown), an 0.5 micrometre thick alumina keying layer thereon and a 6 micrometre thick further alumina layer thereon as described above, both alumina layers shown by reference numberal 2, and the coated conductors are embedded in a single polymeric insu-lating layer 3 formed for example from the polyether imide sold under the trade name "ULTEM" or from a polyether ether ketone or polyether ketone.
Apparatus for use in a batch process for providing the keying layer on a wire conductor substrate is illustrated in Fig. 4. The apparatus comprises a vacuum chamber into which a complete wire transport mechanism which includes wire pay-off reel 2 and take-up reel 3, wire support rolls 10 and tensioning rolls i5 loaded. The mechanism engages motor drives which control the passage of wire 4 so that the wire traver-ses a vertically mounted target 5 a number of times.
Deposition occurs by the processes previously described, As before, variations in set-up are poss-ible. An additional target (not shown) may be employed on the other side of the wire to increase coating rates and additional targets, e.g. target 6 can be employed to deposit intermediate layers before and/or after deposition ~of the primary oxide/ nitride coating.
Suitable design of the gas inlet system to suit the specific geometries employed can facilitate deposition of layers whic~ have no defined boundaries as described previously. Batch length will depend on chamber dimen-sions and transport system design.
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In the operation of such a batch process wire 4 is transferred from one reel 2 to the other 3 within the chamber. The route taken by the wire may cause it to pass before the smaller ancillary target 6 to deposit an intermediate layer of any desirecl material. Power to this target, combined with wire speed and the number of passes in front of the target will control the thickness of the intermediate layer deposit. The wire 4 may then pass in front of the larger primary target S
to deposit the main coating. Again thickness will be dictated by a combination of power, wire speed and a number of passes. The ratio of thicknesses between the intermediate and the primary coating is controlled in the same way. Multi-layers can be built up by reversing the mechanism as desired such that the wire 4 passes back past the targets 5,6 in reverse order.
Thickness and composition may be altered in the reverse pass as required, e.g. the process employed at the smaller magnetron may be reactive on the reverse pass to deposit a compound of the metal on the intermediate layer, e.g. Ti and TiNX. Deposition of layers with no defined boundary between the metal intermediate layers (or substrates) and the oxide/ nitride coatings may be achieved by setting up gradients of reactive gas in front of the primary target, such that wire at the top edge of the target 5 is subjected to deposition in an Argon rich atmosphere which gradually increases in reactive gas content as the wire progresses down the face of the t:arget. A gradient can be achieved by a baffle system (not shown) which progressively leaks oxygen introduced at the bottom end of the target towards the upper end.
::
A simpler techni~ue for~ producing the layer with '~ no defined boundary involves use of a multipass process ': ~
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in which wire 4 is passed back and forth through the system, and with each pass the level of reactive gas is increased to a final level required to obtain the correct stoichiometry. Thus the stoichiometry of the intermediate layer increases in a series of small incremental steps from metal to required stoichiometry.
Composite targets may also be used to produce inter-mediate layers with stoichiometry gradients. In the case of discrete articles, the articles may instead be held in front of the target by means of a rotating sample holder.
Figure 5 is a schematic section through parts of an article according to the invention showing a typical arrangement of layers that may be formed on the copper substrate, the thickness of the layers being exaggerated for the sake of clarity.
A copper substrate 21 is provided with a thick (e.g. 1 to 3 micrometres) layer 22 of nickel followed by a layer 23 of aluminium metal, a layer 24 of non~
stoichiometric aluminium oxide A120x and a layer 25 of stoichiometric aluminium oxide A1203, the Iayers 23, 24 and 25 having been formed e.g. by a sputtering method.
An additional, relatively thick layer 26 of aluminium oxide (e.g. of about 5 to 15 micrometres thickness) has been deposited on the layer 25 by a sol-gel method.
Although~the layers are clearly demarcated in the drawing by means of lines, it will be appre~iated that such boundaries,may, and preferably will, not be formed in practise, especially between the copper/aluminium, aluminium/A120x and A120x/Al203 layers. Indeed, the aluminium, A120X and stoichiometric alumina layers may , ~
' :
, all be formed in the same sputtering process in which case the stoichiometry of the layers will depend on the oxygen gradient used.
The following Examples illustrate the invention:
Examples 1 and 2 Copper conductors were provided with 3.3 micro-metres thick aluminium intermediate layer by use of the sputtering apparatus shown schematically in figure 4 of the drawings. The sputtering conditions were as follows: the wire 4 was precleaned by vapour degreas-ing in l,l,l-trichloroethalle prior to depo5ition. The cleaning was achieved by passing the wire through a vapour degreasing bath such that a residence time of 3 minutes was achieved. The wire 4 was then loaded into the vacuum chamber. The chamber was then evacuated o a pressure of 1 x 10-6 mbar prior to starting the pro-cess. At this stage argon was admitted to attain a pressure of 1.5x10-2 mbar whereupon a high frequency (80 kHz) bias potential was applied to the wire hand-ling system which was isolated from ground. A bias potential of -850V was achieved, and the wire was transferred from reel 3 to reel 4 such that a residence time of 10 minutes was achieved. On completion of the cleaning cycle the pressure was reduced to 8.10-3 mbar and the deposition process started.
:
3 kW of ~DC power was applied to the aluminium target 5. The wire passed from ~reel 2 to reel 3 being coated as it~passed the target 5. Residence time in this region was controlled by wire speed and ad~justed to give the~required thickness. The roller mechanism : :
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alternated the wire face exposed to the target as it progressed down the target length.
The wire sample of copper conductor coated with aluminium as described above was subsequently coated with aluminium oxide in a similar process. For this second coating, an aluminium oxide target powered with an RF power supply was used. The wire residence time and target power were adjusted to give a constant thickness of aluminium oxide, of about 0.2 micro-metres. During déposition of both aluminium and alumi-nium oxide the copper conductors were held at an appropriate bias potential relative to the chamber to promote adhesion.
Wire samples of copper conductor, in some cases coated with a 3.3 micrometre thickness of aluminium, and in some cases coated with an additional 0.2 micro-metre thickness of aluminium oxide as described above, were subsequently coated with a gel-derived aluminium oxide by the sol-gel process described above.
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The samples were then tested to determine the adhesion of the top coat as follows. A fixed Length of wire was subjected to a tensile stress whilst the strain was continuously recorded. During testing the wire sample~was viewed through an optical mircoscope.
When the coating was seen to significantly spall the strain was recorded. The strain value recorded at this point gave a measure of the adhesion of the coating.
The composition of the samples and the results obtained are shown in Table No. 1.
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_ 30 _ RK265 Table 1 Example l(Comparison) . 2 Substrate 22 awg Stranded 22 awg Stranded Copper Cu .
Metallic Aluminium layer (micrometres) 0 3.3 Vacuum deposited ^
Aluminium Oxide Layer (micrometres) 0 0.2 Sol gel deposited Aluminium Oxide layer (micrometres) 12 12 Adhesion (arbitary units) 0* 600 ~ ~ ;
* The adhesion of the coating to bare copper was very poor, rendering the samples unable to be tested due to immediate spalling.
::
The. results show a clear improvement in adhesion of the gel ~derived alumina coating with the vacuum deposited aluminium oxide layer.
:: : : : : ~ : ~ : :
: Examples 3 and 4 The elect~ical:~performance of wires prepared as those~ in example: 2,: were tested by twisti:ng pairs of identical wires~(2 twists~per 2.5 cms length) to form a ;: :
~ :
~L ~ '~ J '~ 9 twisted pair cable, connecting one end of the wires to a 30V peak to peak lMHz square wave generator, and observing the wave form across a 200 ohm load connected between the wires by means of an c>scilloscope. The twisted pair cables were subjected to heating in a pro-pane gas burner having a flat flame 8cm wide. The tem-perature of the flame just below the twisted pairs was maintained at the required temperature and the time to failure recorded.
In example 3 the sample was found to survive for 70 seconds in a flame at 900C. In example 4 the wires had still not failed after a flame exposure time of 72 minutes at 650C. The substrate material onto which the sol-gel derived aluminium oxide was deposited for examples 3 and 4 had a dense 0.2 micrometres coating of ; vacuum deposited aluminium oxide on its surface.
Although this layer is insulating, it was incapable alone of supporting 30V at room temperature.
:
Examples 5 to 7 22 AWG 19 strand copper wire conductors were pro-vided with sputtered aluminium and aluminium oxide layers using the method detailed in examples l and 2.
The wires were then transferred to another vacuum chamber equipped with a 25Kw electron beam gun. This chamber was pumped down to a base pressure of 5~.10~5mbar,~and a further refractory insulating layer of aluminium oxide deposited by electron beam evapora-tion. The elèctron beam power was about 6kW (25Kv, 240mA), and the refractory was evaporated directly from highly sintered alumina pieces, contained in a water-cooled copper crucible. The deposition rate of alumi-- :
' - 32 - R~65 nium oxide by evaporation was about 3um/min, much faster than the refractory keying layer deposition rate, which was about O.Olum/min.
Samples manufactured as described above were adhe-sion tested using the tensile method described in examples 1 and 2. The results are given in Table 2, from which it is clear that a thin refractory keying layer deposited by a relatively slow method improved the adhesion of a further refractory layer deposited by a faster method.
Table 2 Example Al intermediate A1203 keying A1203 further Adhesion layer thickness layer thickness layer thickness (arbitary ~um) (um) (um) units) 6 0 0.5 7 1200 7 7 0.5 7 2150 The wire of Example 7 was tested for electrical performance as described in Example 3 (900C) and no failure was recorded after 4 hours, whereas the wire of .
: Example 5 could not be tested due to immediate spalling on lmmersion in the flame.
~ :
::
~, .
:i :
.
.~
~: :
~;
': ,
Claims (28)
1. An article of manufacture which has at least a part that is formed from a metal the article having, on a surface of that part, an adherent dense refractory keying layer formed from an oxide of a metal or semi-metal, at least a part of the keying layer being electrically insulating, and, on the keying layer, a further electrically insulating refractory layer that has been formed by a relatively fast deposition method.
2. An article as claimed in claim 1, wherein the further refractory layer has a thickness that is greater than that of the refractory keying layer.
3. An article as claimed in claim 1 or claim 2, wherein the further refractory layer has a thickness greater than 1 micro-metre.
4. An article as claimed in claim 1 or claim 2, wherein the further refractory layer has a thickness greater than 2 micro-metres.
5. An article as claimed in claim 1 or claim 2, wherein the refractory keying layer has a thickness of not more than 0.5 micrometres.
6. An article as claimed in claim 1, wherein the refractory keying layer and the further refractory layer have the same nominal chemical composition.
7. An article as claimed in claim 1, wherein the further refractory layer comprises a metal oxide.
8. An article as claimed in claim 7, wherein the further refractory layer comprises an oxide of aluminium, silicon, tita-nium, or tantalum.
9. An article as claimed in claim 1, wherein the refractory keying layer has been formed by a vacuum deposition process.
10. An article as claimed in claim 9, wherein the refractory keying layer has been formed by a sputter ion plating method, a chemical vapour deposition method or an evaporation method.
11. An article as claimed in claim 1, wherein the further refractory layer has been formed by a flame spraying method, a sol-gel method, a plasma ashing method or a solution coating method.
12. An article as claimed in claim 1, wherein the further refractory layer has been formed by an evaporation process.
- 34a - 27065-123
- 34a - 27065-123
13. An article as claimed in claim 1, wherein the metal from which the part of the article is formed comprises copper or an alloy thereof.
14. An article as claimed in claim 1, which includes a metallic intermediate layer located between the metal from which the part is formed and the refractory keying layer.
15. An article as claimed in claim 14, wherein the interme-diate layer has a thickness of at least 1 micrometre.
16. An article as claimed in claim 14, wherein the intermediate layer has been formed by a vacuum deposi-tion technique.
17. An article as claimed in claim 16, wherein the intermediate layer has been formed by a sputter ion plating method.
18. An article as claimed in claim 14, wherein the intermediate layer has been formed by a metal rolling electroplating method or a melt coating method.
19. An article as claimed in claim 14, wherein the intermediate layer is formed from aluminium, silicon, titanium, tantalum, nickel, manganese, chromium or an alloy thereof.
20. An article as claimed in claim 14, wherein the refractory keying layer comprises an inorganic metal compound and the intermediate layer comprises the same metal as that present in the refractory keying layer.
21. An article as claimed in claim 14, wherein the intermediate layer is formed from a metal that forms an intermetallic compound with copper when heated.
22. An article as claimed in claim 14, wherein the intermediate layer comprises aluminium.
23. An article as claimed in claim 1, wherein the refractory keying layer has a stoichiometry that varies throughout at least part of its thickness such that the proportion of metal or semi-metal in the layer decreases towards the outer surface of the layer.
24. An article as claimed in claim 14, wherein the refractory keying layer has a stoichiometry that varies throughout at least part of its thickness such that there is no defined boundry between the metallic inter-mediate layer and the refractory keying layer.
25. An article as claimed in claim 1, which has one or more additional layers on top of the further refrac-tory layer or between the refractory keting layer and the further refractory layer.
26. An article as claimed in claim 1, which is in the form of an electrical wire.
27. An article as claimed in claim 26 which is pro-vided with an additional outer polymeric insulation.
28. An article as claimed in claim 27, wherein the polymeric insulation will char when subjected to a fire.
23. An article as claimed in claim 27 or claim 28, wherein the polymeric insulation has been deposited by a pyrolytic or plasma deposition process.
**********
23. An article as claimed in claim 27 or claim 28, wherein the polymeric insulation has been deposited by a pyrolytic or plasma deposition process.
**********
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8500818 | 1985-01-14 | ||
| GB8500818 | 1985-01-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1295889C true CA1295889C (en) | 1992-02-18 |
Family
ID=10572788
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000499446A Expired - Fee Related CA1295889C (en) | 1985-01-14 | 1986-01-13 | Refractory coated article |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0188369B1 (en) |
| JP (1) | JPS61165909A (en) |
| AT (1) | ATE48047T1 (en) |
| CA (1) | CA1295889C (en) |
| DE (1) | DE3666993D1 (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS63281313A (en) * | 1987-05-12 | 1988-11-17 | Sumitomo Electric Ind Ltd | Heat-resistant electric wire |
| JPH02177212A (en) * | 1988-12-28 | 1990-07-10 | Furukawa Electric Co Ltd:The | Heat-proof electric wire and manufacture thereof |
| JPH02215010A (en) * | 1989-02-14 | 1990-08-28 | Sumitomo Electric Ind Ltd | Insulated electric wire |
| CA2027553C (en) * | 1989-02-14 | 1996-09-17 | Kazuo Sawada | Insulated wire for high-temperature environment |
| US5372886A (en) * | 1989-03-28 | 1994-12-13 | Sumitomo Electric Industries, Ltd. | Insulated wire with an intermediate adhesion layer and an insulating layer |
| JP2890631B2 (en) * | 1989-03-28 | 1999-05-17 | 住友電気工業株式会社 | Insulated wire |
| EP1612295A1 (en) * | 2004-06-07 | 2006-01-04 | Fachhochschule Schmalkalden | Coated metal substrate and process for its preparing |
| JP2006117999A (en) * | 2004-10-21 | 2006-05-11 | Hitachi Cable Ltd | Thin film forming method and thin film forming device |
| CN102969053A (en) * | 2012-11-30 | 2013-03-13 | 苏州贯龙电磁线股份有限公司 | Single-surface film little-glue mica tape flatly-wrapping flat copper wire and manufacturing method thereof |
| PL3226258T3 (en) * | 2016-04-01 | 2019-04-30 | Gebauer & Griller Metallwerk Gmbh | Insulated electrical conductor |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH587548A5 (en) * | 1973-11-30 | 1977-05-13 | Battelle Memorial Institute | Surface insulation for copper conductors - includes thin layer of aluminium oxide pyrohydrolysed on keying layer of alloy |
| GB8318612D0 (en) * | 1983-07-08 | 1983-08-10 | Raychem Ltd | Wire and cable |
-
1986
- 1986-01-13 CA CA000499446A patent/CA1295889C/en not_active Expired - Fee Related
- 1986-01-14 JP JP61006136A patent/JPS61165909A/en active Pending
- 1986-01-14 AT AT86300207T patent/ATE48047T1/en not_active IP Right Cessation
- 1986-01-14 DE DE8686300207T patent/DE3666993D1/en not_active Expired
- 1986-01-14 EP EP86300207A patent/EP0188369B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| ATE48047T1 (en) | 1989-12-15 |
| DE3666993D1 (en) | 1989-12-21 |
| EP0188369A3 (en) | 1987-01-07 |
| EP0188369A2 (en) | 1986-07-23 |
| JPS61165909A (en) | 1986-07-26 |
| EP0188369B1 (en) | 1989-11-15 |
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