US2694377A

US2694377A - System of gas plating

Info

Publication number: US2694377A
Application number: US250303A
Authority: US
Inventors: Pawlyk Peter
Original assignee: Commonwealth Engineering Company of Ohio
Current assignee: Commonwealth Engineering Company of Ohio
Priority date: 1951-10-08
Filing date: 1952-09-22
Publication date: 1954-11-16
Anticipated expiration: 1971-11-16

Description

Nov. 16, 1954 P. PAWLYK 2,694,377

SYSTEM OF GAS PLATING Original Filed Oct. 8, 1951 gsheeis-sheet 1 INVENTOR PETER PAWLYK 8Y7: 7.1;;

ATTORNEYS SYSTEM OF GAS PLATING Original Filed Oct. 8, 1951 2 Sheets-Sheet 2 FIG-2 FIG-.3

INVENTOR PETER PAWLYK BY W Fm ATTORN EYS United States Patent SYSTEM OF GAS PLATIN G Peter Pawlylr, Dayton, Ohio, assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio 2 Claims. (Cl. 118-48) This invention relates to a gas plating system and process for the production of semi-conductive and non-conductive coatings on insulating materials and to the products produced by the process.

This application is a division of application Serial No. 250,303, tiled October 8, 1951, and assigned to the same assignee as the present invention.

This application is related to applications, Serial Nos. 250,301; 250,302; 250,304; 250,303; 250,306; and 250,307, all filed October 8, 19 51, and all by the same inventor as the present application.

it has been round that electrically resistant layers of high quality may be produced by the formation of the mixed copper oxides, particularly cuprous oxide, on metallic and non-metallic bases for contacting the base under carefully controlled conditions, tobe more particularly discussed hereinafter, with copper acetylacetonate in the gaseous state to effect decomposition thereof. The process of formation of the oxides may be facilitated by carrying out the decomposition in an oxidizing atmosphere to achieve selective oxidation of any deposited metallic component present as decomposition of the copper acetylacetonate occurs.

This invention accordingly contemplates the provision of a unique method for the attainment of films of mixed oxides of copper on non-conductive materials.

The invention also contemplates the provision of unique resistive elements attained by depositing from the gaseous state mixed oxides of copper on non-conductive base materials.-

The method of invention is practiced by heating a dielectric base material to a temperature range below that at which copper acetylacetonate will decompose to copper metal and contacting the base material with heated vapors of copper acetylacetonate at a rate sufiicient to maintain the temperature of the material below the said range and at a pressure substantially equal to that of the atmosphere. Under these conditions the plating deposited on the insulating base will comprise essentially the mixed oxides of copper.

The resistance characteristics of the deposited layer,

for a given concentration of metal-bearing gas in the plating chamber, will vary with the velocity of gas flow, the higher flow rates contributing to the formation of a greater proportion of the cupric oxide, although some cuprous oxide will always be present. Similarly lower flow rates may contribute to the formation of more cuprous oxide but the cupric phase will exist in the coating.

In the preferred embodiment of the invention the copper acetylacetonate is vaporized from the solid compound by contacting the heated solid with a heated inert gas, which gas carries the metal-bearing vapors to a plating chamber. The copper acetylacetonate decomposes at approximately 455 F. and accordingly the temperature of the solid compound and the inert carrier gas must be maintained considerably below this temperature point.

The plating chamber to which the heated gas mixture is carried is itself heated, and the arrangement thereof is such that the workpiece therein which is to be plated is at a lower temperature than the atmosphere surrounding it. This is accomplished by exposing the workpiece in the chamber only to the heat of the flowing gases and to radiation from the element which heats the chamber. The object to be plated is not itself heated directly as is normally the custom in the gas plating art.

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2 Preferably control is achieved by regulating the temperature of the flowing gases at a point, spaced slightly from the workpiece, and between the workpiece and plating chamber heater.

The hot gases when they strike the workpiece of lower temperature will only partially decompose, and depending upon the exact conditions of the system, a mixture of cuprous oxide and cupric oxide, or a mix containing the oxides plus a small amount of copper metal will be attained. For example, films may be obtained on /2 inch diameter ceramic discs with resistances varying from 10 ohms to substantially infinity. The control of the resistance is attained primarily by controlling the rate of gas flow over the discs in the plating chamber.

Control of the oxide formation may also be in- 1 fluenced by the bleeding into the system of small amounts of oxygen which tends to develop cupric oxide formation. As the system will contain both carbon dioxide and the carbon monoxide decomposition product, care must be exercised to prevent water vapor or any appreciable amounts of hydrogen bearing carbon compounds forming in the chamber, for mixes of oxygen,

carbon monoxide and carbon dioxide may be rendered slightly explosive in the presence of such constituents. Normally if the oxygen is introduced as -dry air the presence of the nitrogen of the air will serve as a sufficiently effective diluent to prevent any deleterious reactions.

The invention will be more fully understood by reference to the following detailed description and accompanying drawings wherein:

Figure 1 is a schematic representation of the apparatus for the carrying out of one embodiment of the invention;

Figure 2 illustrates a carrier for the objects to be plated; and

Figure 3 illustrates schematically apparatus for the carrying out of another embodiment of the invention.

in Figure l the major components of the apparatus utilized to carry out the invention are indicated at 1, 2, 3 and 4. Numeral 1 indicates a source of carrier gas; the numeral 2 a constant temperature bath containing a carburetor and the compounds to be vvaporized; the numeral 3 indicates the plating chamber; while the numeral 4 designates generally a recovery system.

The tank 5 of inert carrier gas (carbon dioxide) is provided with a valve 6 and flow meter 34 having conthe carburetor. The carburetor 9 and coil 8 are each immersed in oil 10 contained in tank 11 and maintained at a constant temperature by means of heater 12 and the thermostat unit indicated generally at.13. Since such thermostats in themselves are well known no detailed description thereof will be given herein.

The bath is also provided with a stirrer 14 actuated through belt 15 my motor 16. The carburetor contains solid layers of copper acetylacetonate 17 and a length of insulated tubing extends from the top of the carburetor and passes to the gas plating chamber 19 of plating chamber unit 3. v

The connection between tubing 18 and chamber 19 may be made throughstopper 20 although any suitable means of connection may be employed, the only requirement being that the seal be gas tight.

Gas chamber 19 is provided externally thereof with a resistance heating element 21 provided with electrical energy from a source not shown. Mounted in chamber 19 i; an object carrier 22, more clearly shown in Figure The carrier 22 consists of a rack of insulating material extending the length of chamber 19 on a wall thereof and having supports thereon for the carrying of ceramic discs 23 of substantially /2 inch diameter. Chamber 19 is provided at the remote end thereof with an outlet in which tubing 25 is secured, the tubing 25 passing directly to the recovery system 4 where it is secured in the bulb of trap 26. Trap 26 is surrounded by cooling water 0 27 contained in tank 28 having inlet 2 and outlet 30 for the passage of the cooling water. The remote end of the trap 15 provided with tube 31 for the emission of exhaust gases to the temperature.

Positioned between the constant temperature bath 2 and the plating unit 3 in the line 18 is a pump 32 for the mgaintenance of a steady flow of gases to the cham- In the operation of the apparatus of invention, to attain a resistive coating having a resistance value of approximately 300 ohms per centimeter, a ceramic disc or discs 23 are inserted on the carrier 22 in the plating chamber 19. The resistance heater 21 is adjusted to supply a temperature of about 600 F. within the chamber 19 at a point approximately of an inch above the positioned ceramic disc. The temperature of the oil is adjusted to about 375 F.

Under these conditions the valve 6 on tank 5 is open to permit a flow of carbon dioxide of about one liter per minute through line 7 and coil 8 wherein it is heated to approximately 375 F. The gas then passes into the carburetor where it contacts the copper acetylacetonate. The copper acetylacetonate having already been subjected to a temperature of 375 F. by means of the oil bath will have built up a considerable vapor pressure and the enterligig CO2 will sweep these vapors out through tubing As the packing of the copper compound in the carburetor 9 may tend to restrict to some extent the gas flow, pump 32 is actuated to insure of the steady flow of gas to the plating chamber 19. The gases passing into chamber 19 at the flow rate specified will contact the object or workpiece 23 and will tend to maintain the same cool, that is below the temperature of the surrounding atmosphere and below the temperature at the thermocouple 24. The gases under this condition will decompose and deposit on the cooler workpiece, forming a film consisting substantially only of cuprous and cupric oxide. The waste gases together with any undecomposed copper compound will then pass through tubing 25 to the trap 26 where the cooling effect of water 27 will cause the copper acetylacetonate to deposit out from the decomposition vapors, the decomposition vapors themselves then flow on to the atmosphere.

The time of plating of the above noted process is approximately 30 minutes in order to secure a deposit having a resistance of 300 ohms.

In Figure 3 there is shown an embodiment in which there is provided an oxygen inlet to the system. Since the system is otherwise the same as shown in Figure 1 the same reference nmnerals will be employed. In line 18 there is shown an inlet 33 for dry air.

In the operation of the system shown in Figure 3 oxygen to the extent of .05 by volume of the plating gases is bled into the system in a dry condition. When the gases passing from the carburetor 9 through line 18 containing the dry air from inlet 33 enter the chamber 19 the presence of oxygen tends to prohibit the formation of any copper metal.

The system of plating of Figure 1 is preferred to that of Figure 3. However in some instances it may be necessary to use a high temperature in the plating chamber thus raising the temperature of the ceramic to such an extent that metallic copper may tend to deposit. In this circumstance the air bleed of Figure 3 provides in the chamber sufiicient air to convert the copper to copper oxide. Where temperature conditions in the chamber are lower and more favorable the system of Figure 1 offers. close control of the deposition and is preferred.

By way of illustration raising the temperature of the object to 650 F. and the temperature of the flowing gas to 400 F. results in a substantially electrically nonconductive layer after 30 minutes exposure of the insulated object in the system of Figure 1. Thus by adjusting the flow temperature'and/or the chamber atmosphere temperature, it is possible with relatively small temperature steps to attain layer resistance between 300 ohms and infinity.

A temperature rise in the chamber to 700 F. should 1 be avoided with the system of Figure 1 however for metallic copper may then deposit.

The inert gases useful in the system of invention include, as well as carbon dioxide, argon, helium, nitrogen, etc.

Substantially all materials of heat insulating nature are suitable for the practice of the invention. Metallic objects however do not in general maintain a sufficiently low surface temperature to permit the attainment of controlled resistive coatings in the fiow ranges presently explored. Flow. rates of between about 1 to 10 liters of carrier gas per minute are however effective with heat insulating materials and a particular flow condition may be readily chosen in conjunction with a specific carburetor temperature to attain a desired result.

It will be understood that this invention is susceptible to modification in order to adopt it to different usages and conditions and accordingly it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. In a gas plating system for the deposition of copper oxides on heat insulating material the structure comprising a plating chamber having a wall, rack means within said chamber extending the length thereof to support .an object therein whereby said object is insulated from heat transmitted through the wall of said chamber, to support an object in said chamber in heat insulated relation with the wall thereof, means to measure the temperature of the atmosphere in said chamber at a point .1 remote from said rack means, and means to supply a flow of heated plating gas between said rack means and said temperature measuring means at substantially aimospheric pressure.

2. In a gas plating system for the deposition of copper oxides on heat insulating material the structure comprising a plating chamber having a wall, means to heat said chamber, rack means within said chamber extending the length thereof to support an object therein whereby said object is insulated from heat transmitted through t-- the wall of said chamber, to support an object in heat insulated relationship with said wall of said chamber, means to measure the temperature of the atmosphere in said chamber at a point remote from said rack means, means to supply a flow of plating gas to said chamber 1,; between said rack means and said temperature measuring means at substantially atmospheric pressure, and means to control said plating gas flow rate whereby the temperature within said chamber at said workpiece may be regulated to less than the temperature at said temperaiiifture measuring means.

Claims

1. IN A GAS PLATING SYSTEM FOR THE DEPOSITION OF COPPER OXIDES ON HEAT INSULATING MATERIAL THE STRUCTURE COMPRISING A PLATING CHAMBER HAVING A WALL, RACK MEANS WITHIN SAID CHAMBER EXTENDING THE LENGTH THEREOF TO SUPPORT AN OBJECT THEREIN WHEREIN SAID OBJECT IS INSULATED FROM HEAT TRANSMITTED THROUGH THE WALL OF SAID CHAMBERS, TO SUPPORT AN OBJECT IN SAID CHAMBER IN HEAT INSULATED RELATION WITH THE WALL THEREOF, MEANS TO MEASURE THE TEMPERATURE OF THE ATMOSPHERE IN SAID CHAMBER AT A POINT REMOTE FROM SAID RACK MEANS, AND MEANS TO SUPPLY A FLOW OF HEATED PLATING GAS BETWEEN SAID RACK MEANS AND