Spray Process For Creating Electrical Circuits

Abstract

Electrically conductive pathways are applied to a metallic base by means of the plasma flame spray process, which process is also employed to apply an intermediate layer of ceramic insulation. The conductor pattern is formed into a kaolin template through which the powdered copper conductor material is sprayed.

Description

BACKGROUND OF INVENTION

In the past, several problems have made it virtually impossible to fabricate acceptable high current capacity conductors by the spray process. One such problem was that the copper deposited by the spray was relatively porous and therefore had too high electrical resistance. Another problem was that there was no rapid and economical way to apply the conductor material in the desired pattern, mainly because of the extremely high temperatures of the plasma stream which have heretofor disintegrated any material used to mask the areas not to be coated by the copper spray. Metal templates are undesirable because the free electrons present in metals are readily surrendered to the plasma stream thus overheating the template.

Hence, it is the principal object of this invention to create a process for economically depositing a high current capacity conductor path pattern upon a supporting base by a spray process.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is an exploded perspective view of a base structure to which an insulating layer and circuit conductors have been applied using a template in accordance with the process of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, there is illustrated a metallic base 10 upon which electrical circuit conductors 12 are to be formed by spraying a powdered electrical conductor through template 14. Base 10 may be steel or aluminum or any other metallic surface upon which it is desired to place an electrical circuit. The surface of base 10 is first prepared by a cleaning and roughening process, which may be accomplished by a grit blast or by grinding.

Next, the surface of base 10 is coated with a bond-enhancing material 16. This material is applied by the plasma flame spray process, a well-known process for applying powdered metals and ceramics in a stream of high-temperature ionized gas. One such bonding material which has been successfully employed is a nickel alumina powder manufactured by the Metco Company of Long Island, New York, and is identified as Metco 450. During the application of this bonding material to base 10, it is desirable to keep the base cool by the application of an air or nitrogen stream to the base. The thickness of this layer of bonding material 16 is preferably two- or three-thousandths of an inch, depending upon the thickness of the circuit to be applied thereto.

The next step is to apply an insulation layer 18 on top of the bonding material 16. The purpose of such a layer 18 is to insulate the subsequently applied electrical circuit conductors from metallic base 10. An insulator which has worked successfully is an aluminum oxide ceramic powder identified as Metco 105. This is a white powder chosen for its color and abrasion resistance and hardness as well as its excellent properties as a dielectric and thermal insulator. Another ceramic which can be used is Metco 1161, an alumina-type titanium composite. The important criteria is ohmic resistance. Layer 18 should be sprayed on rather heavily, up to one-sixteenth of an inch, so that the resistance through it will be on the order of 10 megohms.

To prevent moisture absorption by the ceramic, a Metcoseal phenolic resin can be applied to the ceramic after it has been cleaned by grit blasting.

The next step is the preparation of the template 14. The template must be fabricated of a material capable of withstanding the extremely high temperatures present in the plasma flame spray. A material which has been successfully employed is a ceramic fiber paper known as kaolin manufactured by the Nickel Lead Company of Hamilton, Ohio. More specifically, kaolin is a hydrous silicate of aluminum having a formula of H.sub.4 A1.sub.2 Si.sub.2 O.sub.9. This material comes in a thickness of 1/16 to 1/18 of an inch, and can be readily cut by a knife or diecutting machine. Kaolin is capable of withstanding temperatures of well over 3,200.degree. F. without disintegrating. If water is applied to the kaolin, it becomes pliable to permit it to conform to curved supports if necessary.

Depending upon the production circumstances, the template can either be expendable or it can be processed to be reusable indefinitely. Such processing to increase its useful life preferably comprises applying by the plasma flame process a ceramic coating to both sides of the template, the ceramic having a slightly higher melting point than the copper formulation which will be subsequently sprayed through the template. During this preparation of the template, it is desirable to cool the kaolin with water or air. A Metco masking compound can thereafter be brush applied to the surface to prevent further buildup of metal during the subsequent copper spraying operation. This masking compound should be reapplied after each copper spray operation.

An alternative treatment is to apply a silica slurry to the underside of the template, so as to increase its rigidity. A further alternative is to apply a boric acid powder to the surface and melt the powder with a low-temperature plasma flame to create a boric glass to provide greater rigidity. Boric acid also prevents subsequent oxidation of the template. A rigid peripheral frame may also be used. Such a frame could be made magnetic to aid in anchoring it.

The template is then placed upon the ceramic insulating layer 18. It has been found that retention and adherence of the kaolin template to a flat or curved ceramic surface 18 can be improved by wetting the template with water. This also functions to keep the template from overheating.

Next, the plasma flame spray gun is utilized to spray the copper through the template onto the ceramic surface. The copper may be in the form of a glass copper powder manufactured by Metco and identified as XT1159, in a mixture of 140 and 235 meshes.

After the copper has been applied, the conductor surface can be polished if desired. Furthermore, a layer of ceramic insulation can be spray applied over the surface if desired in order to prevent impact and abrasion damage to the circuitry and also to protect persons from electrical shock.

Although this invention has been described as applied to the making of electrically conductive pathways, the template disclosed and claimed herein could similarly be employed in conjunction with the plasma flame spray process to form artistic designs or signs, as well as other types of metallic patterns.

This invention may be further developed within the scope of the following claims. Accordingly, the above specification is to be interpreted as illustrative of only one operative embodiment of this invention, rather than in a strictly limited sense.

Claims

I claim:

1. The method of applying the current conductors of an electrical circuit to a metallic supporting base surface which comprises the steps of:

cleaning and roughening the supporting base surface;

spraying a powdered bonding material onto the supporting base surface by means of a high-temperature flame spray process;

spraying a powdered ceramic insulation layer onto the bonding material on the supporting base surface by means of the high-temperature flame spray process;

applying a reusable self-supporting supporting template of high heat resistant kaolin fiber paper to the ceramic-coated supporting base surface, said template conforming to the desired configuration of the electrical circuit conductors;

spraying a powdered electricity-conducting material through said template and onto said ceramic-coated base surface by means of the high-temperature flame spray process without destroying said template, whereby an electrical circuit corresponding to the configuration of said template is formed on top of said ceramic-coated base surface, with said ceramic coating insulating said current conductors from said metallic supporting base surface.

2. The method of claim 1 wherein said paper template is pretreated on both sides by the application of a ceramic coating by means of the plasma flame spray process.