US2774728A - Addition agent for copper plating - Google Patents

Description

United States Patent.

ADDITION AGENT-.FORZ COPPER PLATING Christian J. Werrilund', Niagara Falls, N. Y., assignor to Del., a corporation of Delaware No Drawing. Application September 29, 1955,- Serial No. 537,556

Claims. .(Cl. 204-52) E. L du Pont de Nemours anrLCompany, Wilmington,

This application, a continuation-in-part of my copending application Serial Number 352,269, filed April 30, 1953, and now abandoned, relates to bright copper electroplating.

Various methods have heretofore been, proposed for the electrodeposition of brightcopper on such bases as iron, steel, pewter, zinc and the like. Several of these methods are quite good and are widely used but all suffer from disadvantages. In some instances the brightness obtained is not suflicient. too expensive or difficult to procure. The most common defect, however, is probably the restricted current density range within which the bright'copper is obtained. The distribution of current densities over individual surfaces,

particularly those of irregular shape possessing both recessed and exposed areas, may thus sometimes extend outside the bright plating range available. Unsightlyvariations in the brightness of the deposit are the result,; v

An object of the present invention is, therefore, to provide a novel and useful process for electroplating bright copper. V

A second object is to provide a process with an unusually wide current density range for electrodepositing bright copper.

Another object is to-provide a process'for electroplating copper in which both recessed and exposed areas ofjirregularly shaped objects will be electroplated to the same brightness.

A further object is to provide a coppercyanide-con tain ing bath to accomplish the novel electroplating process.

' The above-mentioned and additional objectsgare achieved in accordance with this invention by electroplating copper with direct current from an otherwise substantially conventional solution of copper cyanide which contains a compound of. trivalent antimony '(Sb+ Tartar emetic, potassium antimonyl tartrate.

In others an addition agent employed is 2,774,728 Patented Dec. 18, 7 I956 "ice,

Preferred Range,

Component oz./gal.

Sodium hydroxide 0 Free sodium cyanide Copper cyanide In another, and preferred, embodiment equivalent amounts of potassium compounds are substituted in whole or in part for those of sodium enumerated. Although they. are more expensive, potassium baths possess several advantages over sodium baths. Thus, the potassium ion increases to some extent the width of the brightness range obtainable. It furthermore aids in keeping the antimony in solution, particularly when pentavalent antimony is present.

Other embodiments of the invention may be based on the sodium or. potassiumbaths. Thiocyanate ion for example may advantageously be included as a brightener of rather low intensity as disclosed in U. S. Patent 2,287,- 654. About 0.05-10. oz./gal. of potassium or sodium thiocyanate may be added to the formulations given. About 1-4 oz./ gal. is preferred. Additional tartrate may also, though optionally, be added to the baths in the form of Rochelle. salts, sodiumpotassium tartrate. This compound seems to broaden slightly the brightness range obtainable with the antimony. 1 to 8 or 10 oz./gal. of Rochelle salts is usable. Rochelle salts may be included in the same bath with the thiocyanate ion if it is so desired. Other conventional basic solutions will be apparent to those skilled in the electroplating art.

In all the antimony-containing baths mentioned, it is advisable to include an organic anti-pitting agent to insure smoothness of the deposit. Conventional agents such as C-decyl betaine and trimethyl benzyl ammonium chloride are quite satisfactory and may be employed in conven tional amounts, i. e., around 0.05 to 0.3 oz./ gal.

The preferred agent, however, is methylene-bis(ea-naphthalene sulfonic acid). This compound not only serves to eliminate pitting of the deposits but co-operateswith the antimony in brightening the deposit. A mixture of trivalent antimony and methylene-bis(oz-naphthalene sulfonic acid) maldehyde. The corresponding fl-cornpound is also ef- There are numerous substantially conventional cyanidecopper baths to which the antimony brightening agent thus serves as a brightener of extremely high intensity, producingalmost brilliant plate. About 0.01 to 0.5 oz./ gal. will achieve thisresult within the Weight limits of antimony specified. About 0.10 oz./ gal. of the methylene sulfonic acidis preferred. This sulfonicj acid is the condensation product of a-naphthalene sulfonic acid and for- Conditions for operation of the bath, except for the usabledirect current density range, are substantially those normally encountered in direct current cyanide copper plating. Thus the temperature may be varied between about 60 and 95 C., with about C. preferred. Conventional agitation as by stirring is also preferably utilized. The preferred anti-pitting agent, methylene-bismnaphthalene sulfonic acid), is also an anti-foaming agent and permits the use of air agitation.

The direct currentbright plating range is, of course, broadened by the use of antimony. In the absence of special aids such as the antimony, this range may be nonexistent or very narrow. When sodium salts are utilized as the basis of an antimony-containing plating solution, the bright range can readily be extended up to 45 A./ S. F. When potassium salts are substituted in whole or in part for the sodium, the range is extended up to 60 A./S. F. If vigorous stirring such as is available from air agitation is employed, the bright range, in potassium formula tions particularly, may extend up to 90 A./S. F. Interrupted current and current reversal may be used with antimony but are not essential.

It Will be understood that the concentration of trivalent antimony must be maintained at a satisfactory level. Maintenance may readily be accomplished by separate additions of a trivalent antimony compound such as tartar emetic as desired.

So far the discussion has been largely restricted to trivalent antimony compounds, the actual brightening agent of the invention. The presence of pentavalent antimony (Sb+ is, however, not harmful. Pentavalent compounds are, in any case, usually formed from the trivalent upon several days exposure of the latter to air. They can also be added as such to the baths but contribute little,

if any, brightening action.

Several advantages of the present method of producing bright copper will be obvious, largely paralleling the ob jectives of the invention. There are, however, two remaining advantages that have not been touched upon. One is the fact that copper electrodeposits from the antimony-containing baths are very ductile. Thus, if additional brightness is desired, it can be obtained by an easily accomplished buffing operation.

The second remaining advantage is the effect of trivalent antimony on hexavalent chromium. Copper plating baths often become contaminated with hexavalent chromium within a short time. This impurity is undesirable because as little as 3 or 4 p. p. m. will dull the copper plate produced from the bath. Sodium hydrosulfite has been used heretofore to remove hexavalent chromium by reducing it to the harmless trivalent state but this compound is itself unstable and must be frequently renewed. It has now been found that trivalent antimony will reduce hexavalent chromium. In addition, it is stable and easily maintained in the bath. Control of copper cyanide baths is thus greatly simplified by use of trivalent antomony.

There follow some examples which illustrate the invention in more detail. In these examples all percentages are' by weight. Free cyanide was determined by the Liebig silver nitrate titration.

. Example 1 This example shows the effect of adding antimony to an otherwise conventional sodium copper cyanide bath.

A copper plating solution was made up according to the formula:

Oz./ gal. Sodium cyanide (96-98%) 17.0 Copper cyanide 14.0 Sodium hydroxide 4.0 Potassium thiocyanate 1.33 Trimethyl benzyl ammonium chloride 0.12 C-decyl betaine 0.05

0.07 gallon of this electrolyte was placed in a modified Hull cell equipped with pure copper anodes and sheet steel cathodes with a ratio of anode to cathode surface of approximately 2 to 1. Thebath was raised to a temperature of 80 C. and agitated by motion of the cathode in the horizontal plane at a rate of approximately feet per minute. Direct current was passed between the electrodes, the current densities at the cathode varying from approximately 4 to 90 A./S. F. A hazy copper deposit was obtained overthe current density range of 8 to 24 A./S. F., the remainder being dull.

0.02 oz./gal. of potassium antimonyl tartrate was then 4 added to the bath. Under these conditions bright copper deposits were secured in the current density range extending between 4 and 35 A./S. F.

Example 2 Sodium thiocyanate 0.8 Potassium hydroxide (100%) 4.5 Trimethyl benzyl ammonium chloride 0.16 C-decyl betaine 0.07

Analysis showed that the solution contained 4.15 oz./ gal. of KOH and 1.25 oz./ gal. of free KCN.

Plating tests were carried out in a 0.08 gallon Hull cell at a current of 2.0 amperes, the cathode current density range extending from 4 to 90 A./S. F. The cathodes consisted of polished sheet steel while the anode consisted of pure copper screen the ratio of anode to cathode surface being slightly greater than 2 to 1. The solution temperature was C.i2. The solution was stirred by a vertical glass rod passing along the cathode horizontally at a rate of 12 feet per minute.

The current density range for bright copper in the basic solution was 50 to 60 A./S. F., the range from 4 to 50 A./ S. F. being hazy bright and the rest dull. Addition of 0.01 oz./ gal. of potassium antimonyl tartrate to the bath resulted in bright deposits over the entire range from 4 to 55 A./S. F.

Example 3 This example shows the effect of tartrate in the form of Rochelle salts added along with antimony. A basic electrolyte was prepared as follows:

Oz./gal. Sodium cyanide 12.5 Copper cyanide 10.0 Potassium hydroxide 5.0 Sodium thiocyanate 1.25 Trimethyl benzyl ammonium chloride 0.12 C-decyl betaine 0.05

Example 4 Q This example shows the effect obtained by adding both antimony and methylene-bis(rat-naphthalene sulfonic acid) to copper cyanide baths.

A copper plating solution of the following composition was prepared:

Oz./gal. Copper cyanide 11.25 Potassium cyanide 4.7 Sodium cyanide 10.1 Sodium hydroxide. 4.0 Sodium carbonate 4.0 Sodium thiocyanate 1.0

The solution was adjusted to contain 1.5 oz./gal. of free KCN and 4.0 02/ gal. of NaOH.

(a) Copper plate was deposited from the original bath to a thickness of 1 mil. The deposits were semi-bright over most of the plating range and dull over the remainder.

(b) Addition of 0.02 02/ gal. of potassium antimonyl tartrate to the basic bath greatly improved the brightness of the deposits.

Addition of 0.1 to 0.2 oz./ gal. of trimethylbenzyl ammonium chloride and 0.05 to 0.10 oz./gal. C-decyl betaine to the bath containing potassium antimonyl tartrate did not increase the brightness of the deposits.

(d) Substitution of 0.05 to 0.2 oz./ gal. of methylenebis(a-naphtha1ene sulfonic acid) for trirnethylbenzyl ammonium chloride and C-decyl betaine resulted in the production of panels clearly brighter than those of (b). Traces of haze exist in parts of the bright range of baths containing potassium antimonyl tartrate alone. These traces are practically invisible when the plate is considered by itself. They are quite noticeable, however, when plate from such a bath is compared with the extremely bright or liquid-bright plate from a bath containing both the trivalent antimony and the sulfonic acid. The sulfonic acid removes the haze.

Having described my invention, I claim:

1. An aqueous copper cyanide bath for electrodepositing a bright, ductile, copper electroplate, said bath containing about -20 oz./gal. ofcopper cyanide, about 0.0060.06 oz./gal. of potassium antimonyl tartrate and methylene-bis(naphthalene sulfonic acid).

2. An aqueous copper cyanide bath for electrodepositing a bright, ductile copper electroplate, said bath containing about 5-20 oz./gal. of copper cyanide, about 005- 02/ gal. of an alkali metal thiocyanate and about 0.006-0.6 oz./gal. of potassium antimonyl tartrate.

3. The bath of claim 2 containing additionally an organic anti-pitting agent.

4. The bath of claim 3 in which the organic antipitting agent is methylene-bis(naphthalene sulfonic acid).

5. The bath of claim 2 containing additionally sodium potassium tartrate.

6. The method of producing a bright, ductile copper electroplate which comprises electrodepositing said elecq troplate from an aqueous bath containing about 5-20 0z./ gal. of copper cyanide, about 0.006-0.06 oz./ gal. of potassium antimonyl tartrate and methylene-bis(naphthalene sulfonic acid).

7. The method of producing a bright, ductile copper electroplate which comprises electrodepositing said electroplate from an aqueous bath containing about 5-20 oz./ gal. of copper cyanide, about 0.05-10 oz./ gal. of an alkali metal thiocyanate and about 0.0060.06 oz./gal. of potassium antimonyl tartrate.

8. The method of claim 7 in which the bath contains additionally an organic anti-pitting agent.

9. The method of claim 8 in which the organic antipitting agent is methylene-bis(naphthalene sulfonic acid).

10. The method of claim 7 in which the bath contains additionally sodium potassium tartrate.

References Cited in the file of this patent UNITED STATES PATENTS 1,120,794 Daft Dec. 15, 1914 2,636,850 Jernstedt Apr. 28, 1953 2,700,126 Janner Jan. 18, 1955 2,701,234 Wernlund Feb. 1, 1955 2,732,336 Ostrow Jan. 24, 1956

Claims (2)

1. AN AQUEOUS COPPER CYANIDE BATH OF ELECTRODEPOSITING A BRIGHT, DUCTILE, COPPER ELECTROPLATE, SAID BATH CONTAINING ABOUT 5-20 OZ./GAL. OF COPPER CYANIDE, ABOUT 0.006-0.06 OZ./GAL. OF POTASSIUM ANTIMONYL TARTRATE AND METHYLENE-BIS(NAPHTHALENE SULFONIC ACID).

2. AN AQUEOUS COPPER CYANIDE BATH FOR ELECTRODEPOSITING A BRIGHT, DUCTILE COPPER ELECTROPLATE, SAID BATH CONTAINING ABOUT 5-20 OZ./GAL. OF COPPER CYANIDE, ABOUT 0.05-10 OZ./GAL. OF AN ALKALI METAL THIOCYANATE AND ABOUT 0.006-0.6 OZ./GAL. OF POTASSIUM ANTIMONYL TARTRATE.