US 2475974 A
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Patented July 12, 1949 ELECTRODEPOSITION OF COPPER Abraham M. Max, Indianapolis, Ind., assignor to Radio Corporation of America, a corporation of Delaware No Drawing. Application August 28, 1945,
Serial No. 613,215 r 2 Claims. (01. 204-52) This invention relates to electroforming copper deposits, and more particularly to a copper plat ing solution from which fine-grain deposits of copper may be plated.
One of the aims of electroforming deposits of various metals is to obtain metal matrices the surfaces of which duplicate the surfaces on which electroforming takes place. The surface of an electroformed matrix is the negative of the original surface, the impressions or depressions in the original surface becoming elevations in the electroformed surface.
Acid copper plating solutions have been used heretofore for electroforming copper deposits. Such solutions have the advantages, among others, that (1) they have comparatively wide limits of operation, (2) they can be easily controlled, (3) they provide smooth, heavy deposits of copper, and (4) they have the ability to cover a thin, conductive film on a non-conductive material. Hence, acid copper plating solutions are preferred to other types. However, copper deposits obtained from an acid copper plating solution are very soft and have a tendency to tree. Consequently, addition agents are employed to produce harder and smoother deposits.
Electroformed copper deposits from an acid copper plating solution consists of columnar crystals perpendicular to the starting surface, or surface on which the copper is being plated, the crystals becoming larger, by lateral growth, as the deposits become heavier. If the surface being plated has an impression or depression therein, there results in the columnar, crystal structure a weakness perpendicular to the impression where the columnar crystals come together. Most commonly used addition agents retard the lateral growth of crystals, but due to the retained columnar structure, the weaknesses in irregular surfaces remain. Thus, many addition agents.
result in a brittle electroformed structure which splits under the stresses to which matrices are subjected.
It is apparent that a desirable structure for electroformed deposits is one in which the columnar growth is retarded completely. I have found that if triethanolamine is added to a standard acid copper plating solution, the resulting solution will produce fine-grain deposits both laterally and perpendicularly to the surface which is plated, the columnar crystal growth being retarded. Tensile tests made with specimens of such copper deposits show a tensile strength equal to a strong copper alloy.
In accordance with my present invention, there is added to a more or less standard, acid copper plating solution triethanolamine in the proportions of approximately 0.7 ounce to 1 ounce per gallon of plating solution. The plating solution may consist of approximately 25 ounces to 32 ounces of copper sulfate and approximately 3 ounces to 10 ounces of sulfuric acid per gallon of plating solution. The copper may be plated out in known manner at suitable current densities and suitable plating solution temperatures. I have found that a copper deposit plated out from a solution according to my present invention has an extremely fine and uniform grain structure which gives the copper considerable strength.
Copper deposits resulting from my improved plating solution have a tensile strength of from about 60,000 pounds per square inch to about 73,000
pounds per square inch with an elongation of approximately 6 per cent to 9 per cent. This is about per cent stronger than known samples of electroformed copper obtained from standard, conventional, plating solutions employing various addition agents proposed heretofore.
It will be apparent to those skilled in the art that the various proportions of the addition agent indicated above. are not necessarily limiting and that they may be varied more or less depending upon the particular application or the particular articles to be plated. It will also be obvious, no doubt, that my improved plating solution may be employed in providing electroformed copper deposits on a great many articles other than phonograph record matrices, printing plates, and the like.
I claim as my invention:
1. An acid copper plating solution consisting essentially of approximately 25 ounces to 32 ounces of copper sulfate, approximately 3 ounces to 10 ounces of sulfuric acid, and an addition agent comprising approximately 0.7 ounce to 1 ounce of triethanolamine per gallon of plating solution.
2. The method of producing on an article a fine-grain deposit of copper comprising immersing said article in a solution consisting essentially of approximately 25 to 32 ounces of copper sulfate, approximately 3 to 10 ounces of sulfuric acid and approximately 0.7 to 1 ounce of triethanola (References on following page) I I I The following references are of record in the Number. count Date file this 503,095 Great Britain Mar. 31, 1939 UNITED STATES PATENTS OTHER'REFERENCES Number Name Date I f 694,658 Meurant Mar. 4, 1902 f gf g 'ggfi gfl fi w 1,642,238 Gardner Sept. 13, 1927 1,805,920 Muschler May 19, 1931 v 2,391,289 Beaver Dec. 18', 1945