Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing single metal
Reexamination Certificate
1998-07-13
2001-02-06
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing single metal
C205S067000, C205S296000
Reexamination Certificate
active
06183622
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to additives for producing ductile and pure copper deposits from electrowinning, electrorefining and electroforming baths. More specifically, the present invention relates to polyepichlorohydrin trimethylamine quarternary additives useful in the electrowinning, electrorefining and electroforming of copper.
Electrowinning and electrorefining are methods of purifying and collecting copper for use in wire circuit boards or the like. In electrowinning, copper is plated directly from solution, using insoluble anodes such as lead. In electrorefining, the copper is plated onto a cathode from a soluble copper anode. These processes are known to those skilled in the art and have been in use since the 1800's.
In electrowinning applications, it has long been desirable to provide electrodeposits which do not require further purification. This has been problematic in two respects. First of all, additives commonly in use tend to oxidize on the insoluble lead anodes when they evolve oxygen. This anode phenomenon also leads to lead oxides which flake off during electrolysis. These unwanted particles will then tend to migrate to the cathodes, causing impurities of lead in the copper deposit. These impurities lead to low ductility in these deposits.
Guar gum has typically been used as a brightening additive for electrowinning. The drawback in using this additive is that it is hard to dissolve into solution and tends to readily break down. This creates erratic electroplating results. In electrorefining, thiourea is often used as an additive. This can result in sulfur co-deposition from the plating residues in the solution. Sulfur then co-deposits as an undesirable impurity in the copper deposit. Therefore, an additive without these disadvantages is desirable.
However, any additive used in electrowinning must also be compatible with solvent extraction of copper from the raw ore and the copper stripping process used in line for replenishing copper to the electrowinning baths. Typically, in order to extract copper from a raw ore, the copper ore is initially dissolved with a sulfuric acid solution. This also leaches many undesirable impurities from the ore. The copper is selectively extracted from the sulfuric acid solution via a solvent-solvent extraction technique. Such techniques are known. In brief, an organic solvent which is not soluble in the aqueous sulfuric acid solution is used. The organic solvent acts to exchange a hydrogen atom to the aqueous solution for a copper atom from the aqueous solution. After this is completed, the organic solvent having the copper ions attached is separated from the aqueous solution, leaving the impurities in the aqueous solution. After separation, the copper must then be stripped from the organic molecule.
Additives, to be useful, must not interfere or hinder this solvent extraction process. Hindrance of solvent extraction can occur in many ways. If an additive is too surface active, it will interfere with the organic water separation, leading to problems. Many organic molecules may interfere with the kinetics of the exchange reaction, reducing the efficiency thereof. Additionally, copper selectivity over iron is somewhat sensitive in the extraction system. Organic additives must not interfere with the selectivity of copper. Additives also must not interfere with the copper stripping process.
Improvements in purity of electrowinned and electroformed copper have been realized, such as by the use of novel polyacrylic acid additives, which are the subject of commonly assigned U.S. Pat. No. 5,733,429, issued Mar. 31, 1998, entitled “Polyacrylic Acid Additives for Copper Electrorefining and Electrowinning”.
Ductility has increasingly become important in copper production. With the advent of micro-electronics, wired connections have gotten smaller and smaller. This means that the circuit conductors in microchips have become thinner and thinner. The limits, or the “fineness”, of these conductors is directly proportional to the ductility of the copper used. The more the ductility of the copper, the more malleable it is. This allows the copper to be drawn or formed into thinner strands without breaking. As ductility decreases, copper becomes more brittle, hindering fine formation of thin circuit leads. Thus, high ductility copper is very much in demand.
Typically, in order to provide the purity and ductility necessary for such applications, it has been necessary for the electrowinned “rough” copper to be refined further, using various time consuming and expensive processes. Improvement in existing electrowinning and electrorefining baths is, therefore, desirable. Additionally, improvements in the ductility of electroformed copper is desirable, such that thinner gauge wire can be drawn from more ductile copper.
SUMMARY OF THE INVENTION
Therefore, in accordance with the present invention, there is provided a method for electrowinning, electrorefining or electroforming copper from a copper electrolyte. The method includes the steps of providing an electroplating bath, including ionic copper and an effective amount of an additive which is a bath soluble adduct of a tertiary alkyl amine, and electroplating a copper deposit from the bath onto a cathode.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the present invention, there is provided a method for electrowinning, electrorefining or electroforming of copper from a standard bath, including new and useful additives therefor. The method, in its broad aspects, includes providing an electrolysis bath, including ionic copper. A bath addition of an effective amount of a bath soluble adduct of a tertiary alkyl amine with an epichlorohydrin is included in the bath of the present invention. A copper deposit is deposited onto a cathode by electroplating with the additive added to the solution.
In the method of the present invention, a preferred ductility additive adduct of a tertiary alkyl amine with an epichlorohydrin has the formula:
wherein:
R is methyl, ethyl or mixtures of a methyl and ethyl;
A is an integer greater than 0;
B is either 0 or an integer greater than 0;
the sum of A+B is from about 4 to about 500; and
In a preferred composition, B is 0 in the above formula. Preferably, the molecular weight of the composition is from about 600 to about 100,000. Further details of process for manufacture of the additives of the subject invention may be found in U.S. Pat. Nos. 3,320,317 and 4,336,114, which are incorporated herein by reference.
The above ductility additive of the present invention is generally effective for providing improved ductility when used in amounts of from about 0.1 mg/l to about 1 gram per liter. Typically, the additives are used in amounts of from about 1-65 mg/l with preferred amounts of from about 6-12 mg/l. Ductility of deposits in accordance with the present invention have been found to be greater than 50%, and preferably greater than 100%, using ASTM B-490-68 as the standard.
The additives of the present invention do not build up in the bath and, therefore, have no detrimental effects in the bath. These additives also do not co-deposit in the copper deposit. Without wishing to be bound by theory, it is believed that the additives break down into carbon dioxide and nitrogen gases which evolve from the solution as such. The additives do not impart sulfur and are compatible with bath chemistry, including the polyacrylic additives discussed above in the “Background of the Invention”.
Typically, the copper which is formed from baths of the present invention has improved ductility and purity and may be drawn sufficiently thin for use in computer chip manufacture.
Copper electrolyte baths in which the additives of the present invention are operable are those commercially used for electrowinning, electroforming and electrorefining.
Typically, electrowinning baths of the present invention include sulfuric acid, copper and chlorides in similar amounts as electrorefining baths. However, electrowinning baths typically di
Enthone-OMI Inc.
Gorgos Kathryn
Leader William T.
Warn IP Law Office
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