US2255057A - Electroplating copper - Google Patents

Description

Patented Sept. 9, 1941 ELECTBOPLATING oorrna Donald Holt, Niagara Falls, N. Y., assignor to E. I. du Pont de Nemours 8: Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application October 2, 1939, Serial No. 297,433

4 Claims. (01. 204-52) This invention relates to electroplating copper and more particularly to the electroplating of copper from cyanide solutions.

Excellent, adherent, dense coatings of copper are advantageously electroplated from cyanide copper solutions. Such solutions contain the double cyanide of copper and an alkali metal, for example copper sodium cyanide, with or without other salts andwith or without an excess of free cyanide. An excellent type of copper plating bath contains the double copper alkali metal cyanide in high concentration (e. g. 12 to 20 oz. per gallon of CuCN), with little or no free cyanide and a high concentration of alkali metal hydroxide. Ordinarily, electrodeposits from cyanide copper plating baths are dull and bumng is required to obtain a bright, smooth finish; However, methods have been developed for directly electroplating bright, smooth copper deposits, for example by the method described in the copending application Serial No. 206,002, filed May 4, 1938 by Christian J. Wernlund, Harry L. Benner and Robert R. Bair.

A difflculty sometimes experienced in electroplating copper cyanide solutions is the formation of pits in the electroplated surface. This is particularly troublesome when abright copper plating process is utilized. The formation of pits is especially apparent when a process is utilized for electroplating smooth, bright copper deposits.

- Also, it has been observed that pitting generally is most likely to occur in baths having relatively high concentrations of copper cyanide.

An object of the present invention is an improved method for electroplating smooth bright copper deposits. Another object is to provide means for the prevention of pitting in cyanide copper plating baths. A further object is to provide for cyanide copper plating baths certain addition agents which will prevent pitting and act as brighteners. Other objects will be hereinafter apparent.

The above objects may be attained in accordance with the present invention by adding small amounts of certain betaine-type organic compounds to cyanide copper plating baths. These materials, which are more fully described hereinafter, have been found to inhibit or completeand gamma betaines, which have the following structural formulae, wherein R stands for an alkyl radical, e. g. methyl, ethyl, etc. or a modified alkyl radical, e. g., hydroxyethyl and the like.

R R R R such as 'hydroxyl, amino and the like. These hy-.

drocarbon radicals, are substituted either for one of the alkyl groups on the nitrogen atom of the betaine or for one of the hydrogen atoms on the alkylene group in the betaine or both. For example, trimethyl-C-cetyl alpha betaine which is a siliitable addition agent, has the. following formu a:

.Similarly, the formula of trimethyl-C-cetyl beta betaine is as follows:

The other type of betaine -utilized in my invention is one in which the long chain hydrocarbon radical is substituted on the nitrogen atom as exemplified by the following:

CH: CnHu Dlmethyl-N-eetyl alpha betaine Dimethyl-N-stenyl" alpha betaine In the N-stenyl betaine shown above the term stenyl is used to designate a mixture of essentially C16 and Cm carbon length chains with some C12, C14 and C20 carbon length chains also present. Thus, the N-stenyl betaine is a mixture of betaines having substituted hydrocarbons of the nature indicated by the above definition of the term "stenyll The preparation of the above 'pyl, hydroxyethyl and the like.

N-stenyl betaine and similar betainea is described in U. 8. Patent 2,129,264, Downing et al.

It is understood that in the various betaines utithe two methyl groups may be replaced by other alkyl or modified alkyl groups such as ethyl, pro- Trimethyi-C-decyl alpha betaine The following examples further illustrate my invention:

Exnlru: No. l

Plating bath NaCN 17 oz./gal. CuCn 16 oz./gal. NaOH 4 oz./gal. NaCNS 2 oz./gal.

Trimethyl-C-cetylalpha be- No pitting could be produced in these 501 11110115 8t 15 to 45 amps. per sq. ft.

. Exam: No. 2

' PloflM both NaON 18 oa/gal.

I 5 NaOH. 4 oalgal. NaCNB 2 oz./gal. Trimethyl-c-decyl alpha betalne 2 8:4 cc./gal.

(25% E20 soln.)

Operating conditions as in Example No. 1.

.Various of the betaines which may be used to gamma concentration 2 m W L practice my invention are listed below by way of illustration: I cum and; Tim M Trlmethyl-C-decyl alpha betaine Mm lTrim-ethyl'c'cetyl alpha betame amps./sq it m Bdhtno m methyl-cam $33543 A2 B3- Dimethyl, beta-hydroxyethyl-C-cetyl alpha beaine Methy dubetadlydmxyethyl) t 1 alpha 20 B. Betaine concentration, 4 cc. per aal.

betaine 'lrimethyl-c-lauryl alpha betain cumin Time e lt Trimethyl-C-lauryl gamma betaine Mm wethyl'c'stearyl betalne m l v t Not bright-no p mmethyl-N-stenyl alpha betaine ma u-lsqt 1t right-mp1. Dimethyl-N-stenyl-C-methyl alpha betalne W Methyl-N-distenyl alpha betaine Emu, No 3 Dimethyl-N-stenyl-C-cetyl beta betaine pl ti bath Dimethy1-N-decyL'beta-hydroxy gamma ta e N c M/gaL Dimethyl-N-heptadecyI alpha betaine cucN 02 Dimethyl-N-octadecyl-C-mcthyl alpha betaine NaQH (mi/83L Dlmethyl-N-o t e yl beta betaine NQCNS 2 oz /ga1 Dimethyl-N-octadecyl. beta-hydroxy gamma be m t N stenyl tame alpha betaine 0.2 to 10 gms./gal.

Operating condltions Same as in Example No. 1 Of the variousbetaines which may be utilized current density 45 min/sq. it. in practicing my invention I prefer to use trimethyl-C-cetyl alpha betaine, dimethyl-N-s'tenyl alpha betaine and trimethyhC-decyl alpha be- 2 Run lizt a i ia e aigime Mum taine. The latter betaine has the formula:

E """'8." gmw c i... ggght b1 2 H-C=0 g 01%" 0:11 3&2... mu'i o 1o oooos"ou.. Very bright-no pitting.

' The betaine was added as a 10% water solution.

The amounts of the betaines required in the copper plating solution are small and usually will not exceed about one ounce per gallon. Generally, the betaines are effective as anti-pitting agents in amounts as low as 0.01 oz. per gallon. The optimum amount will vary, depending upon the betaine used and the composition of the copper plating bath. For. electroplating copper from a copper plating bath containing 8 or more ounces per gallon of copper cyanide and sumcient alkali metal cyanide to form the copper double salt. I prefer to use from about 0.02 to 0.2 ounce-per gallon of trimethyl-C-cetyl alpha betaine, trlmethyl-N-stenyl alpha betalne; or trimethyl-C-decyl alpha betaine.

I have found the betalnes to be substantially plating solutions, even when the electroplating operation is carried out at elevated temperatures of 60 to 80 C. in baths of low or high alkalinity. It is therefore only necessary to add sumcient of the betaine from time to time to replace that lost by adherence to the work removed from the plating bath. Other addition agents or brightening agents may be added to the bath in addition to the betaine, for example, the brightening agents specified in the aforesaid patent application, Serial No. 206,002. The betaines are chemchemically stable in the copper cyanide ele'ctroically compatible with the various addition electrolyzing a copper sodium cyanide solution to 10 which has been added 0.02 to 0.2 ounce per gallon of trimethyl-C-cetyl alpha betaine.

3. A copper plating process which comprises electrolyzing a copper sodium cyanide solution to which has been added 0.02 to 0.2 ounce per gallon of trimethyl-C-decyl alpha betaine.

4. A copper plating process which comprises electrolyzing a copper sodium cyanide solution to which has-been added 0.02 to 0:2 ounce per gallon of dimethyl-N-stenyl alpha betaine.

. DONALD A. HOLT.