GB2167774A - Apparatus and methods for coating substrates with metal coatings - Google Patents

Abstract

A substrate (10) as illustrated in Fig 1 is coated with protective metals at least in part evaporated from a metallic electrode (1) with which an arc is struck at low voltage and current to deposit metal from the electrode (1) on the substrate (10) in a vacuum chamber. The electrode (1) may be heated and the substrate (10) may be sandblasted and preheated. More specifically a method of coating a ceramic with a metal is disclosed comprising the steps of roughening a surface of a ceramic substrate by subjecting it to blasting with particles; preheating said substrate to a temperature of at least 200 DEG C but less than the melting point of a metal to be applied thereto; juxtaposing said surface of said substrate with an electrode composed of said metal; evacuating the space in which said electrode is juxtaposed with said substrate to at most 10<-6>torr (133x 10<-6>Pa) and maintaining the pressure in said space substantially no higher than 10<-5> torr (133 x 10<-5>Pa); and striking an arc with said electrode by intermittently attacking same with another electrode while applying a voltage in the range of from 30 to 60 volts across said electrodes and passing a current in the range of from 50 to 90 amperes through said electrodes to evaporate the electrode composed of said metal and deposit said metal on said surface. <IMAGE>

Description

SPECIFICATION Apparatus and methods for coating substrates with metals The invention relates to apparatus and methods for coating substrates. Such coatings can be effected with a material which is brought into the vapor phase by electrical means.

The deposition of material from a vapor phase onto a substrate is well known in the coating art and in the field of surface transformation of a substrate. General ly speaking, a body ofthe material to be transferred to the substrate is heated in the region of this substrate and transformed first into a molten state and then into a vaporstate. The material thus undergoestwo phase transformations, namely,thetransformation from the solid phase to the liquid phase and then from the liquid phasetothevaporphase.

The coating is generally effected in a vacuum and usually a relatively high vacuum must be drawn to permit transfer of vapors from the source to the substrate.

Earlier systems may use induction heating to effect the aforementioned phase transformation.

A particular problem has been encountered with respectto the application of metals to ceramics. While many metals can be coated onto ceramics, the refractory metals such as tungsten and titanium have been applied heretofore in a mannerwhich is less than satisfactory and practically in all cases adhesion problems are encountered by the methods used heretofore.

As will be described hereinafter there is provided a method for the vapor deposition of material on large-area and/orcomplexconfiguration substrates at relatively low-energy cost and with improved uniformity.

There is also provided a methodforthe high-speed coating of complex and/or large-area surfaces.

There is yetfurther provided an improved method of applying metal coatings to ceramics whereby the poor adhesion problems characterizing prior art systems are avoided.

The method of vapor desposition which will hereinafter be described is based upon the discovery that especially large-area surface deposits can be formed by juxtaposing an elongated electrode ofthe depositing material, laterally with the surface of the substrate to be coated over a substantial portion ofthe length of the electrode in a vacuum, and striking an arc between one end ofthis electrode and a counterelec trode such that the arc currentshould be between 50 and 90 amperes with a voltage applied across the electrode of 30 to 60 volts.

Surprisingly, once the arc is struck as the two electrodes are separated, the arc, a portion ofthe arc or a heating effect generated by the arc appears to spiral around the long electrode and cause vaporiza tion of the material ofthe electrode in a generally helical or spiral pattern progressively moving away from the counterelectrode.

It is indeed a remarkable surprise that the arc is not confined to the space between the two electrodes but rather has a component or an effectwhich spirals away from the counterelectrode toward a region ofthe length of the long electrode which is further removed from the counterlectrode in spite ofthe fact that the greatestconductivitywould appear to lie in a line directly between the two electrodes where the major portion of the arc appears to be confined.This effect is manifest in the fact the long electrode. i.e. the deposition electrode, while originally of uniform cross section, develops a taper toward the counterelectrodes and coating from the blank ofthe deposition electrode onto the substrate can be observed at considerable distance from the arc's striking face of the deposition electrode.

In fact, the effect appears to survive for a brief period following extinction ofthe original arc and hence it is preferred to periodically contact and separate the electrodes to generate the arc and then allow extinction thereof.

Means are provided at an end ofthe electrode ofthe material to be deposited, remote from the arc-striking electrode to control the temperature ofthe materialsupplying electrode, generally to maintain it in the range of 800"F to 1 000 F (427to 538 C), the speed underthe lower voltage, lower current and temperature conditions of the present invention, at which the material evaporates from the material-supplying electrode, can be increased by 1.5 to 2.0 times the speed of evaporation of the earlier systems. Practically all metals and alloys can be used in making the materialsupplying electrode.

While it is not fully understood why the rate of evaporation of the material to be deposited increases with the lower energy utilization, it is possible that the migration of the arc may spread the otherwise pooled moltion phase over a wider area ofthe materialsupplying electrode to allow, in effect, evaporation of the molten metal in thin film form.

The principles set forth above can be utilized in the application of metal coating to synthetic resins, the synthetic resins in the form of cabinets or housings for electronic components. It has been found, most surprisingly, that since the substrate is unaffected by the large area coatings applied the method of coating described is highly advantageous when utilized to coat the interiors of synthetic resin cabinets or housings which may be utilized for electronic components, the coating forming an electromagnetic shield.

It has also been found, most surprisingly, that the described method is highly effective in applying metal coatings to ceramics, with improved adhesion, even when the applied metals are nickel, tungsten, titanium,tantalum and like refractory metals which have been difficult to apply heretofore to ceramic substrates. Practically any ceramic substrate may be utilized and it is preferred to subjectthe surface adapted to receive the coating to a sandblasting or other blast-roughening procedure. The term "sand- blasting" is here utilized to describe the entrainment of abrasive pariculates against the surface, the abrasive particulates being generally metal particles, silicon carbide, silicone nitride, diamond dust, iron oxide, silicon dioxide or any other material capable of surface roughening.The entraining gascan be arrow any other available gas. In addition, the substrate may be preheated within the vacuum chamber or prior to introduction into the vacuum chamberto a temperature lessthan the melting point of the metal. The preheating temperature shou Id be at least several hundred degrees, however.

Ceramic coating is effected in accordance with the present invention, by juxtaposing two electrodes of different metals, preferably a highly conductive and a highly refractory metal with a substrate which is preferably a ceramic body, and striking an arc between these electrodes in an evacuating chamber containing the electrodes and the substrate. The electrodes are first given a relative polarity, i.e. one is poled positvely while the other is poled negatively to deposit the metal upon one ofthese electrodes selectively while at the same time, it appears, depositing a small amount of this latter metal on the second electrode.

When polarity is then reversed, the metal vaporizes preferentiallyfrom the second electrode, initially including the small portion ofthe metal from thefirst electrode which is deposited thereon so that at the interface between the two layers a mixed composition ofthe metals is formed.

The disadvantages, which have hitherto been encountered when high conductivity metals, especially copper but also gold and silver, are applied to a ceramic substrate with respect to adhesion and especiallywith respectto adhesion afterorduring soldering or other welding of conductivity elements thereto, can be obviated if, priortothe application of the high conductivity metal, the ceramic is coated with a refractory metal in a comparatively small thickness and this intermediate layer of coating is in turn coated with the conductive metal.

More particularly, it has been found that it is possible to deposit a coating of a thickness of, say, 5 to 10 microns oftungsten, molybdenum, titanium or zirconium as the refractory metal upon the substrate and thereafter to apply a coating of greaterthickness, say, 0.001 to 0.02 inches (0.004 cm to 0.0041 cm) of copper or a copper alloy, gold, silverorsome other nonrefractory metal, i.e. metal having a substantially lower boiling pointthan that ofthe refractory metal which is used.

It has been found that, when a two-electrode method is used, it is possible to constitute one electrode as the refractory metal and the other electrode as the nonrefractory metal and by regulating the polarityofthe electrodes during the deposition, the particular metal which is deposited can be controlled.

It has also been found that it is possible to increase the adhesion, in terms of the force required to separatethecoatingfrom thesubstrate by 100 or moretimes, all otherthings being equal, when the thin refractory metal coating is applied between the copper coating and the ceramic substrate.

Aceramic substrate can be used in accordance with the method described and masking techniques can be employed to ensure the formation ofthe deposit in any desired pa'tern.

One ofthe two electrodes which are juxtaposed with the substrate can be moved out of alignment with the other electrode and replaced by a substitute electrode and the process repeated with the latterto additionally deposit at least a layer ofthe metal ofthe third electrode upon the second layer.

Apparatus and methods for coating substrates will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which: FIG. lisa diagram in elevational view illustrating an apparatusforcarrying outvapordeposition in accordance with an embodiment ofthe present invention; FIG. 2 isa similarviewofanotherapparatus wherein, however, the vapor deposited material is collected on a vertically reciprocal electrode; FIG. 3 is a vertical section, also in diagrammatic form, illustrating an apparatus for depositing material upon a substrate disposed below the pool of metal; FIG. 4 is a view similarto FIG. 3 illustrating another embodimentofthe invention;; FIG. 5 is an axial cross-sectional view of another apparatusfordepositing material upon a substrate according to this invention; FIG. 6 is an axial cross-sectional view of a highly compact portable apparatusfor carrying outthe method of the invention; FIG. 7 is a diagrammatic cross-sectional view of anotherapparatusforcarrying outthe presentinven- tion; FIG. 8 is a view of still another device diagrammatically illustrating the application of large area coatings to ceramic substrates according to the invention; FIG. 9 is a diagram of an apparatus for carrying out the ceramic-coating method of the present invention; FIG. 10 is a cross-sectional view drawn to a larger scale of a productofthe present invention;; FIG. 11 is a view similarto FIG. 9 but illustrating another apparatus for carrying outthe invention; FIG. 12 is a diagram showing an effect obtained during the depositofthe metal for the first layer before the commencement ofthe second layer; and FIG. 13 is a cross-sectional view through the product in the lattercase.

In FIG. 1 there is shown a system utilizing a simple arc method for obtaining mirror-like protective coatings upon substrates orfor evaporating various metals or metal alloys, including heat-resistant and refractory metals,to apply coatings thereof to the substrate.

As is apparentfrom FIG. 1 ,the basic apparatus can include a vacuum chamber, not shown, which can be similarto the vacuum chamber of FIG. 6 and in which a metal electrode 1 can be fed byan electrodefeeder7 toward an electrode body 2to form the pool of molten metal with which the arc 4 is struck.

The electrode body 2 is held in a fixture or holder 5 and the direct-current source applies the arc current across the electrode 1 and the body 2via a conventional arc stabilizing circuit represented at8.

It has been found to be advantageous to provide the relatively small cross-section electrode 1 with a thermal regulator 6 tending to prevent overheating of this electrode.

Since the cross-section of body 2 is substantially largerthan that of the electrode 1, the pool 3 lies in a concave recess formed in situ in the body 2.

Example 1 The apparatus of FIG. 1, utilizing electrodes 1 and 2 oftitanium, aluminium, tungsten, tantalum or copper, strikes an arc at a temperature of 5000 to 7000"F (2760 C to 3871 "C) to generate vapor ofthe metal of the pool 3 which traverses the distance of 10 to 15 cm to the substrate 10 and forms a coating ofthe metal thereon. The pool 3 can be formed by a mixture of metal contributed by the electrodes 1 and 2, thereby depositing an allow of the metals of the two electrodes upon the substrate. Preferably the electrode is composed oftitanium while the molten metal predominantly consists of aluminium, tungsten, tantalum or copper.

The apparatus of FIG. 2 is generally similar to that of FIG. 1 but operates under somewhat different principles, the evaporation being effected at least in part from the wetted upper electrode 101.

In this Figure, elements which correspondtothose of FIG. 1 utilize similar reference numerals differing in the hundreds position.

In FIG. 2, the electrode feeder 107 is coupled with a vertical reciprocator 112 which imparts a reciprocation to the electrode 101 in the direction of the arrow 1 l4so asto periodically plungethetip ofthe electrode 101 into the pool 103 ofthe molten metal formed in the electrode body 102.

Upon rising from this pool to restrike the arc 104, the coating 113 of molten metal upon the electrode 101 is evaporated and the deposit is formed upon the substrate 110.

The electrode body 102 is shown in the holder 105 and the arc current supply is formed by the direct current source 109 and the stabilizer 108 in the manner described, the electrode 101 being provided with the thermoregulator 106.

This system has been found to be particularly effective, in a modification oftheforegoing example, when the electrode 101 is composed oftitanium and the pool 103 is formed of aluminium.

In FIG. 3 the vapor is deposited upon a substrate 210 disposed below a crucible 217 in the form of an upwardly open ring containing the molten metal 203, the crucible being mounted in a holderorframe 205.

Here the upper electrode 201 is in the form of a spherical segment which functions as a reflector so that, when an arc 204 is struck between the electrode 201 and the melt in the crucible 217, the vapors pass upwardly as represented by the arrows 219 and are reflected downwardlytofocus upon the substrate 210 as represented by the arrows 218.

The direct current source 209 is here connected across the electrode 201 and the crucible 217 via the arc stabilizer 208 and the upper electrode 201, mounted on the rod 216, is vertically positioned by the feeder 207 and horizontally positioned by an auxiliary mechanism 215 which adjusts the position ofthe electrode 201 over the evaporating metal.

In this embodiment, the electrode 201 can be composed oftitanium, molybdenum ortungsten while the molten metal can be composed of alumi nium or copper and the crucible 217 of graphite.

In FIG.4there is shownanotherembodiment ofthe invention in which the vapors flow downwardly to deposit upon the substrate 310.

In this case, the upwardly open crucible 317 containing the molten metal 303 can be supplied with additional molten metal from a ladle or other sources represented at 322 or with solid metal which is melted in the crucible 317. The lattercari be heated by auxiliary means such as an inductive heater 323 and is supported in a holder305.

The bottom of the crucible 317 is formed with apertures 321 at which droplets of the molten metal appear, these droplets being vaporized by the arc 304 struck between the electrode 301 and the bottom of the crucible 317.

The temperature in the region ofthearccan be controlled by an auxiliary inductive means 324 and the electrode 301 can be cooled as represented by the cooling element 306.

Electrode 301 is fed toward the crucible 317 by the electrode holder307 andthearc is maintained byan arc stabilizer 308 connected to the direct current source 309.

In this embodiment, the molten metal may be copper.

In place ofthe auxiliary device 324, a substrate to be coated may be provided at this location, e.g. in the form of a titanium ring, which can collectthe vapor in the form of a coating.

The embodiment of FIG. 5 evaporates the molten metal as it is formed in a closed space, the vapors being discharged through apertures 425 on the substrate 410.

In this case, the pool of liquid is formed by melting the electrode402 supported by the holder 405 by feeding the counter electrode 401 via the electrode feeder 407 through a central bore 426 in the electrode 402, the electrode 401 passing through an insulating sleeve 427 forming a guide. Atemperature regulator 406 is provided coaxially around the two electrodes adjacent the arc 404 to prevent overheating in the region ahead of the apertures 425. The deposit is formed on the substrate 41 0.

The current is supplied between the electrodes through the arc stabilizer 408 and the direct current source 409 in the manner described previously.

FIG. 6 shows a portable voltaic arc device for depositing reflective, anticorrosive, protective and semiconductor type metal, silicide and carbide coatings using the principles described previously.

This apparatus comprises a vacuum chamber 500 which is formed at its upperendwith a handle 530 enabling the portable unit to be readily transported.

Within this chamber, there is provided a hollow sphere 517, the lower part of which forms a crucible for the molten metal 503, coated internally with a high-temperature heat resistant (refractory) material such as aluminium oxide.

The upper portion ofthis sphere is coated at 531 with a reflective layer concentrating the heat reflected from the bath back onto the latter.

An arc 504 is struck between the electrode 501 and the bath 503, the electrode being fed by the unit 507 toward the bath as the electrode material is consumed.

Additional metal, e.g. in solid form, is fed to the bath as a rod 532 which also is connected to the feeder 533' so that as the bath is consumed, additional metal is supplied thereto.

The electrode 501 and the bath 503 are connected to opposite terminals of an arcstabilizerand a direct currentsource in the manner previously described.

Atubular electrode 502 surrounds the rod 532.

The lower part ofthe chamber 500 is provided with an airpump as represented at 533, the latterevacuat- ing the chamber containing the hollow sphere 517 and, via a vacuum hose 534, via a vaive 535, an adaptor 536 of outwardly divergent configuration which can be connected to a iateral aperture 525 ofthe hollow sphere 517.

The chamber 500 can be formed with a heating coil 537 to prevent undesired condensation of vapour thereon.

Between the aperture 525 and the adaptor 536 there is provided a vacuum lock 538 and a mounting arrangement 539 for holding a variety of adaptors of different shapes and sizes.

The adaptor 536 is alsoformedwith a vacuum gasket 540 wherebythe adaptor can bearagainstthe substrate 510 to be coated.

The portable unit shown in FIG. 6 is carried to the location ofthe substrate 510 to be coated and the appropriate adaptor 536 is mounted on the fitting 539 and the gasket 540 pressed againstthe surface 510 to be coated. The arc current is supplied and the system is evacuated by the air pump 533, thereby melting the metal andformingthe bath 503 within the hollow sphere. The gate 538 isthen opened and the vapors permitted to pass onto the substrate 510 at least in part by pressure differential as controlled by the valve 535 maintained betweenthe interiorofthesphere 517 and the adaptor 536.

Practically any productatany site can be coated and the use of a variety of adaptors of different shapes and sizes enables coating of even intricate bodies without moving then from the area in which they are to be used. The device can be collapsible so as to be used to provide coatings inside ducts and the like.

The apparatus shown in the drawing, withoutthe adaptor 536, can be used as a propellant for individuals or equipment in space.

Upon generation ofthe arc, one need onlyopenthe gate 538 to discharge a stream through the aperture 525 and effect propulsion in the opposite direction.

Thevacuum in space provides a natural vacuum for the device and no air pump 533 is then required.

Practically any waste found in space applications can be utilized inthevessel 517to generate such propulsion.

FIG. 7 combinesfeatures previously described and concepts developed above.

In this system, which can be used to deposit a coating 610' on the inner surface 61 0a of a tube 610, forming a substrate, of complex shape, a materialsupplying electrode 602 of corresponding shape is mounted centrally ofthe tube on a support 602a and is provided with an induction heating coil 606a of a temperature controller 606 which can have athermocouple 606b or a liketemperature sensor responsive to the temperature ofthe material-supplying electrode 602 for maintaining the temperature ofthe latter constant in the range of 800 to 1 000"F (427"C to 5380C) by conventional feedback control circuitry.

As in the previous embodiment, the substrate and the source of the material to be deposited on the substrate are enclosed in a vacuum chamber 600 which can be evacuated to 10-6 torr so thatvapor deposition can be effected at a pressure of 1 0-5 to rr (133x10-5Pa).

The end ofthe material-supplying electrode 602 is provided with an arc-striking electrode 601 which can be reciprocated toward and away from the electrode 602 by an electrically controlled reciprocating drive 607. The latter can be operated in response to a zero current detector 607a so that when the arc current decays completely, the electrode 601 is displaced to the left into contact with the end 602a of the electrode 602 and is then withdrawn to reestablish an arc. The arc current is provided by a pulsating direct current source 609 across which an arc stabilizer 608 the parameters of the arc current and arc voltage are adjusted within the range of 50 to 90 amperes and 30 to 60 volts by these circuit elements.

In practice, utilizing the system illustrated once the arc is struck, the arc itself, an evaporation effect or some other electromagnetic phenomenon appearsto progress as represented by the arrow A generally helical and spiral where arc-striking location and vapor deposition takes place overthe entire length of the material-supply electrode 602 which is subjected to this phenomenon, i.e. overthe length atwhichthe phenomenon is effective until the arc decays.

The material loss from the electrode 602 gradually transforms it into a tapered shape as represented by the dot-dash lines as 602b in FIG. 7.

The fact that the taper results in a recession of the electrode from the substrate does not create any problem of significance because the greatest depposit is at the region of greatest recession and consequent- ly,the ultimate coating as it progresses along the substrate is highly uniform.

The system is especially useful in coating temperatu re-sensitive materials with very small thicknesses of metal coatings since the coating is especially rapid and it is possible to carry out the deposition without significantly heating up the substrate.

Example 2 A copper electrode 602 of the shape shown is provided in a substrate tube with an initial spacing of electrode 602 from the substrate of about 10cam. The electrode is maintained at a temperature of 900"F (428"C) and an arc is struck in the manner previously described at one end. The arc current is about 70 amperes and thevoltage applied aftertheelectrode 601 is withdrawn to form the arc is about 40 volts. The speed of evaporation from electrode 602 under these conditions exceeds the speed of evaporation in Example 1.

In FIG. 8 there is shown a system for the large area coating of a ceramic substrate 801 which prior to introduction into the vacuum chamber can be initially preheated, after its coating-receiving surface has been sandblasted, by the movement of a burner 820 along the underside of the substrate. The electrode 801 can be composed of a refractory metal or nickel and via the actuator 807 is urged into contact with and withdrawn from contactfrom the counterelectrode 802 which may also be composed of the same metal.

The power supply has been represented at 809. The electrodes are here mounted on a track 821 and are moved along the substrate so that the arc is repeatedly struck and the arc travels along the electrode 801 in the vacuum chamber receiving the entire assembly, the entire surface ofthe substrate is coated utilizing the principles described in FIG. 7.

Example 3 Utilizing an apparatus operating with the principles shown in FIG. 8, an aluminium oxide plate is coated to a thickness of 1 to 2 mils with tungsten utilizing tungsten electrodes. The arc current is 50 amperes and the arc voltage 40 volts for a maximum electrode spacing of approximately 4 mm. The eiectrode diameter was about 1 cm. The tungsten coating was highly adherentto the alumina plate.

FIG. 9 shows an apparatus, in a highly diagrammatic form,forcarrying outthe method of the invention.

This apparatus comprises a chamber 1010 which can be evacuated by a suction pump 1011 to the desired degree of vacuum, generally 10-5 fo 1 0-6 torr (133x 10-5to 133x 1 0-6Pa). With in th is chamber, by means not shown, a ceramic substrate 1012 can be disposed and can be shielded by a mask diagrammatically illustrated at 1013 so that coating can only occur in regions defined bythewindows 1014 in the mask.

With in the vacuum chambertheportionsofthe substrate to be coated is juxtaposed with a pair of electodes, i.e. a copper electrode 1015 and a tungsten electrode 1016,the electrodes being provided with means such as the electromagnetic motors (solenoids) 1017 and 1018 for briefly bringing them into contact to strike the arc and then drawing them apart.

The pulserfor periodically energizing the devices 1017 and 1018 have been shown at 1019.

The power supply comprises the alternating current source 1020 which is connected to a rectifier 1021 and the latter is provided with a reversing switch 1022 which can reverse the polarity ofthe electrodes 1015 and 1016 underthe control of a timer 1023.

In operation with the copper electrode 1015 poled positively and the tungsten 16 poled negatively an arc can be struck by passing an electric current of 30 to 100 amperes at a voltage of 40to 100 voltsthrough and across the gap after the electrodes briefly touch tp preferentially vaporize tungsten and thus deposit tungsten through the window 1 014 of the mask 1013 on the substrate. The duration of coating is controlled by the timer 1023 which, afterthe coating ofthe order of microns in thickness has been applied, reverses the polarity so that the copper electrode 1015 is now poled negatively and the tungsten electrode 1016 is poled positively whereupon copper is vaporized from the electrode 1015 and deposited upon the substrate.

As can be seen from FIG. 11 ,the resulting article has a substrate 1030, e.g. of aluminium oxide, bearing a copper coating 1032 which is separated by the refractory metal coating 1031 (tungsten) ofsmaller thickness.

Example 4 Utilizing the principles described, a current of about 70 amperes, a voltage of 80 watts and a vacuum of about 1 0-Storr(133 x 10-5Pa), an aluminium oxide plate is coated with tungsten to a thickness of about 8 microns and with copper to a thickness of about 0.002 inches (0.008 cm). The adhesion is measured and for the coating isfound to be 500 to 700 Ibs per square inch (87500 to 122,500 N/m) (force required to remove the coating). When under identical conditions a copper coating ofthe same thickness is applied to the same substrate, the adhesion is only 6 to 8 Ibs per square inch (1050 to 1400 N/m). The direct coppper-toceramic bond is found to be sensitive to both mechanical and thermal effects when a solder connection is made to it and with the copper/tungsten contact, no similar sensitivity was found.

Practically identical results could be obtained by substituting molybdenum, titanium and zirconium for the tungsten and with combinations ofthese refractory metals with one another and with tungsten as intermediate layers. Similarly, high degrees of adhesion were obtained with nickel, gold, silver and alloys thereof with one another and with copper.

FIG. 11 shows a modification ofthe apparatus of FIG.9 in which the chamber 1110,evacuated bythe pump 1111, includes a ceramic substrate 1 112 which is to be coated with a plurality of metals. In this case, in addition to the common electrode 1116 and its actuator 1118 driven by the pulser/timer 1119, a pair of counter-electrodes 1115 and 1115a, respectively of copper and gold, are provided each with a respective actuator 1117, 1117a. The counter-electrode assembly is provided on a track 11124 having a drive enabling shifting ofthetwo electrodes to the left as illustrated by the showing ofthe electrodes 1115 in its shifted position in dot-dash lines. Naturally, in the latter position,the electrode 111 5a is aligned with the common electrode 1116.A reversing switch 1122 as described in connectiion wuth FIG. 9 is here also provided and the apparatus is energized from the alternating current lines 1120 through the rectifier 1121.

In this mode of operation, once the chamber is evacuated, the actuators 1117 and 1118 are operated to move the electrodes 1115 and 1116 together and apartto strike an arc, the electrode 1116 oftungsten being poled positively while the electrode 1115 of copper is poled negatively.

This process is continued in the manner described until the initial coating oftungsten has been brought up to the desired thickness.

As can be seen from FIG. 12,this procedure not only results in erosion of the tungsten electrode 1016 but it also gives rise to a small deposit 1025 oftungsten on the copper electrode 1015.

When the polarity is now reversed, i.e. the copper electrode 1015 is poled positively and the tungsten electrode is poled negatively, the arc is struck and evaporation is effected from the copper electrode, the tungsten deposit 1025, which has been exaggerated in thickness in FIG. 12, vaporizestogetherwith copper and a mixedtungsten/copperdepositis produced as in interface.

In FIG. 13, for example, the substrate 112 is shown to have been coated at 1131 with the tungsten layer. The mixed or tungsten layer 1126 is then applied thereto before, with continuation of the generation of vapor by arc-striking between the electrodes 1115 and 1116, the copper coating 1132 is applied.

When the copper coating has reached the desired thickness, the electrode assembly 1115, 1117 is shifted to the left and replaced bythe assembly 111 5a, 11 17a and the arc is struck between the electrodes 111 spa, 1116to depositgold in a layer 1133 upon the copper coating.

A controller 1127 may be provided forthe electrode shifting device 1124, the pulser/timer 1119 and the reversing switch 1122 and may be controlled by a preprogrammed microprocessorto effect the polarity reversal and the switching of electrodes when layer thicknesses ofthe desired magnitude have been achieved.

Example5 The method ofExample4is practised exceptthat the copper electrode is shifted away and replaced by a gold electrode. Utilizing the same vacuum and striking a similar arc, a flash coating in the order ofthe 5 microns range of gold was deposited upon the copper coating underthecondition recitedforcopperdeposi- tion.

The adhesion was not diminished and the resulting gold layerwas found to make an ideal contact for micro-electronic purposes. Investigations of the interface between copper and tungsten showed mixed transition zone 1126 which was traced to the vaporize tion of a minor deposit oftungsten from the copper electrode.

Claims (31)

1. A method of coating a ceramic with a metal, comprising the steps of roughening a surface of a ceramic substrate by subjecting it to blasting with particles; preheating said substrate to a temperature of at least200 C but less than the melting point of a metal to be applied thereto; juxtaposing said surface of said substrate with an electrode composed of said metal; evacuatingthespace in which said electrode is juxtaposed with said substrate to at most 10~5torr(133 xl 06Pa) and maintaining the pressure in said space substantially no higherthan 10-5 (133 X1OSPa); and striking an arowith said electrode by intermittently attacking same with another electrode while applying a voltage in the range of from 30 to 60 volts across said electrodes and passing a current in the range offrom 50 to 90 amperes through said electrodes to evaporate the electrode composed of said metal and deposit said metal on said surface.

2. The method defined in Claim 1 wherein said metal is composed of nickel, copper, tungsten, titanium ortantalum.

3. The method defined in Claim 1 or Claim 2 wherein said ceramic is a body of alumina.

4. A method of bonding a material to a ceramic which comprises the steps of applying to a ceramic substanceathin layerofa refractory metal; and thereafter bonding said material to said layer.

5. The method defined in Claim 4wherein said material is a high-conductivity metal.

6. The method defined in Claim 5 wherein said high-conductivity metal is copper, gold, silver or an alloy thereof.

7. The method defined in any of of Claims 4to 6 wherein said refractory metal is tungsten, molybdenum, titanium, zirconium or an alloy or combination thereof.

8. The method defined in any one of Claims 4to 7 wherein said refractory metal is applied to said substrateto a thickness ofthe order of microns and said metal is applied to a thickness of 0.001 to 0.02 inch (0.0025 to 0.05 cm ).

9. The method defined in Claim 8wherein said refractory metal is applied in a layer of 5 to 10 microns thick.

10. The method defined in Claim 9 wherein said high-conductivity metal is copper and said refractory metal is tungsten.

11. The method defined in any one of Claims 4 to 10 wherein the metal is applied by striking an arc between a pair of electrodes to vaporize the metal from one of said electrodes in an evacuating chamber

12. The method defined in Claim 11 wherein an electrode of said refractory metal is juxtaposed with an electrode of said high-conductivity metal, said electrodes are brought into contact and drawn apart to strike said arc, and said electrodes are initially energized with positive and negative polarities in one sense to initially deposit said refractory metal on said substrate and the polarity is thereafter reversed to deposit said high-conductivity metal upon said substrate.

13. Aceramic body comprising a ceramicsubs- tratehaving a thin refractory metal bonded thereto ion a first layer and a second relatively thick layers a high-conductivity metal bonded to said first layer.

14. A method of making multilayermetalcoatings on a substrate which comprises the steps ofjuxtapos- ing a first electrode of a first metal with a second electrode of a second metal with one another and disposing a substrate in vapor-receiving relationship with said electrodes in a chamber; evacuating said chamber; striking an arc between said electrodes in said evacuated chamber while applying one electrical polarityto said first electrode and another electrical polarity to said second electrodeto selectively vaporize metal from said first electrode and deposit same upon said substrate; thereafter reversing the polarities of said electrodes and striking an arc between them to selectively deposit metal from said second electrode on the metal from said first electrode previously deposited upon said substrate; and thereafterjuxtaposing with one of said electrodes a substitute electrode and striking an arc between said substitute electrode and said one of said electrodes in said chamberto vaporize metal from said substitute electrode and deposit same on said layer of the metal of said second electrode on said substrate.

15. The method defined in Claim 14wherein said substrate is a ceramic.

16. The method defined in Claim 13 or Claim 14 wherein said first electrode is composed of a refractory metal.

17. The method defined in Claim 16wherein said refractory metal is selected from the group which consists oftungsten, molybdenum, titanium, zirconium and alloys and combinations thereof.

18. The method defined in any one of Claims 14to 17 wherein at least one of said second and substitute electrodes is composed of a metal selected from the group which consists of nickel, copper, gold, silver and alloys thereof.

19. The method defined in any one of Claims 14to 18 wherein the layer ofthe metal of said first electrode is applied in a thickness of the order of microns and the layerformed by one of said second and substitute electrodes has a thickness of 0.001 to 0.02 inches (0.0025 cm to 0.058 cm).

20. A method of coating a substrate which comprises the steps of juxtaposing a pair of electrodes of different metals with a substrate in a chamber; evacuating said chamber; applying one electrical polarity to one of said electrodes and the opposite electrical polarity to the other of said electrodes and striking an arc between said electrodes by approximating them into contact and drawing them apart to vaporize material from said one of said electrodes and deposit the vaporized material on said substrate in a first layer while simultaneously transferring a portion of said material onto the other of said electrodes; and thereupon reversing the electrical polarity of said electrodes and striking an arc between them to vaporize material from said other electrode including said portion and deposit a mixed layer of materials from both of said electrodes on said first layer as a transition layer and thereafter deposit material from said second electrode onto said transition layer.

21. The method defined in Claim 20 wherein said substrate is a ceramic.

22. The method defined in Claim 20 or Claim 21 wherein the material of said one of said electrodes is a refractory material.

23. The method defined in Claim 22 wherein said refractory metal is tungsten, moiybdenum,zirconium or an alloy or combustion thereof.

24. The method defined in any one of Claims 20 to 27 wherein said other electrode is composed of nickel, copper, gold, silver or an alloythereof.

25. The method defined in any one Claims 22 to 24 wherein said one of said electrodes is composed of tungsten.

26. The method defined in any one of Claims 20 to 25 wherein said other electrode is thereafter shifted out of alignment with said one of said electrodes and is replaced by a substitute electrode with which an arc is struck in said chamberto deposit a further material on said material of said other electrode.

27. An apparatus for multilayer coating of a substrate as defined in one ofthe preceding claims which comprises a chamber; means for evacuating said chamber; a substrate adapted to be coated being positioned in said chamber; a pair of first electrodes juxtaposed with one another in said chamber; means for applying an electrical potential to said electrodes with one ofsaid electrodes having one electrical polarity and the other of said electrodes having the opposite electrical polarity; means for approximating said electrodes and drawing them apartto strike an arc between said electrodes selectively vaporizing material of said one of said electrodes for deposit upon said substrate in a first layer; means for reversing the polarities on said electrodes whereby said electrodes strike an arcto deposit material selectively from said other of said electrodes on said first layer; and means in said chamberfor automatically replacing one ofthe first mentioned electrodes with a substitute electrode and striking an arc between the remaining one ofthefirst mentioned electrodes and said substitute electrode to deposit material of said substitute electrode selectively on said substrate.

28. A body made by the method of any one of Claims 1 to 12 and 14to 26.

29. A method of coating according to any preceding claim and substantially as hereinbefore described with reference to the accompanying drawings.

30. Apparatus for effecting a bond according to Claim 27 substantially as hereinbefore described with reference to the accompanying drawings.

31. Apparatus for carrying out the method of any one of Claims 1 to 25 and 29.