US2195454A - Electrodeposition of copper - Google Patents

Description

Patented Apr. 2, 1940 UNITED STATES ELECTRODEPOSITION OF COPPER Lawrence Greenspan, New York, N. Y., assignor to Louis Weisberg, Inc., New York, N. Y., a corporation of New York No Drawing. Application January 7, 1939, Serial No. 249,721

26 Claims.

This invention relates to methods for producing lustrous electrodeposits of copper.

Copper deposits produced by ordinary electrolytic methods, unless they are very thin, often require bufiing in order toproduce a surface with satisfactory lustre. So-called flash deposits are usually very thin and often possess excellent brightness, but for thicker deposits, the best that can be obtained from ordinary copper plating solutions are deposits which are smooth and fine-grained but not lustrous or bright.

An object of the invention is the provision of a method of producing thick (0.001 inch or more) copper electrodeposits that are lustrous,

or bright, and therefore require no bumng after plating.

Another object is to produce bright copper electrodeposits which possess good physical properties and, particularly, are free from brittleness.

Other objects and advantages will appear from the more detailed description, it being understood, however, that this more detailed description is given by way of explanation and illustra- 5 tion only, and not by way of limitation.

Most copper plating solutions in general use at this time being to one of two types, either the acid type or the cyanide type. The solutions I employed in connection with this invention are 30 of still another type, the main ingredient of which is a complex copper salt formed by interaction of copper sulphate with a sultable'amine.

Nearly all commercially available amines have been tried at one time or another in the hope 35 t tja' satisfactory bright copper plating soluti M uld be produced .in this way, but for the n 't the results obtained heretofore have not own much promise of utility. In most cases,',the deposits are too brittle to be used ex- 4 ceptjjperhaps for thin "fiash coatings. Deposits from: these solutions are often dark in color, and it has been observed that this dark color seems to be associated with deposits that are brittle.

Another difficulty relates to the behavior of 45 such solutions at different current densities. With some amines, the maximum current density that can be employed is too low for commercial use in applying relatively thick coatings; with certain others a higher average current density 50 may be used without producing burned deposits, but the deposits are unsatisfactory in the low current density range, and the solutions therefore are unsuitable for plating recessed objects. Solutions made with diethylene triamine, for

example, give bright deposits at current densities up to 100 amperes per square foot, but the deposits are dull on the parts of the object which. receive a low current density, say 10 or 20 amperes per square foot.

An obvious way to try to widen the permissible 5 range of current densities would be to mix various amines; for example, diethylene triamine, whose behavior has just been described, might be mixed with ethylene diamine, which works best at low current densities. As a matter of 10 fact, it has been found that such a mixture can be used over a wider range than either amine alone. Since there are quite a few amines commercially available, including besides those already mentioned, monoethanolamine, diethanol- 15 amine, triethanolamine', morpholine and various amyl and butylamines, there area considerable number of possible combinations. Unfortunately, mixing amines does not overcome the brittleness of the deposits, and something less obvi- 0 ous is required to overcome this difl'iculty.

This invention is based on the discovery that good ductile lustrous deposits can be obtained from solutions containing complex copper salts formed by interaction with amines, provided the solution also contains ammonium compounds such as ammonia and/or ammonium salts. The presence of ammonia in sumcient amount overcomes brittleness, but it is preferable to use an andmonium salt such as ammonium sulphate, either alone or in conjunction with free ammonia, because the solutions made in this way have a wider'range of current densities within which bright deposits can be obtained than solutions to which ammonia alone has been added. It is believed that the use of the ammonium salt is beneficial, in part at least, by reason of its buffer action. It has been found, however, that the amount of ammonia needed to give optimum results is governed by the degree of relative mo- 40 tion between the cathode and the solution. If the solution is agitated vigorously, little or no ammonia has to be added. With less agitation, increasing, amounts of ammonia are necessary.

It appears from these results that a certain minimum concentration of ammonia in the cathode film is necessary for-good results, and that this concentration in the fllm can be maintained with varying concentrations in the bulk of the solution according to the degree of relative motion provided. It is to be understood that this view is put forward merely as an attempt to explain the results observed and that it is not intended to limit the -invention by any theory as to how the results are produced.

. bined ammonia.

While to get the best results may require adding both ammonia and an ammonium salt, such as ammonium sulphate, it is possible to get excellent results, under favorable conditions, with either one alone. This arises from the fact that regardless of the form in which ammonia is introduced-whether free, as in aqua ammonia, or in the combined state, as in ammonium sulphate, an equilibrium state is established in the solution so that it contains both free and com- The proportions in which the two forms are present depend, not alone on the proportions in which they are added, but also on the amounts of other salts such as copper sulphate, the alkalinity of the amine, and the quantity of excess amine present. The equilibrium state accordingly will be characterized by a definite pH value. From this it will be apparent that the essential feature of the invention is the addition to the amine type of copper plating solution of ammonium compounds such as ammonia and/or an ammonium salt.

Examples I and 11 below illustrate compositions of solution which have been successfully used when the solution is vigorously agitated.

I II Copper sulphate grams per liter lgiims fiftleilter griii i i i ii i fil i i l r rli ia gr m s pi a r l i ter 0 ii-mi per liter When the solution is notagitated, but the common oscillating cathode arrangement is employed, from 10 to c. c. of 28% aqua ammonia per liter are added.

For general use, the more concentrated solution is preferable on account of its greater conductivity and plating rate. The temperature of the solution and the current densities employed may be varied over a fairly wide range, but for average use a temperature between 50 and 60 degrees centigrade and a current density of 40 to 50 amperes per square foot are recommended. On articles not too complicated in shape, current densities up to 130 amperes per square foot have been used with good results.

The composition of the solution may be varied over wide limits, provided certain limiting conditions are observed. In theflrst place, the quantity of amine present should be somewhat in excess of that which is required to redissolve the precipitate formed when the amine is first added to a solutionbf copper sulphate. In the examples above, this excess of amine is approximately 10 c. e. per liter.' The concentration of copper, and hence of amine, may vary within wide limits, but there is little advantage in having the copper sulphate much above 100 or 150 grams per liter, since at higher concentrations the solution is viscous and drag-out losses become excessive. Substantially all of the commercially available amines may be used in the method as 1 described.

The quantity of ammonium sulphate for optimum results is shown in the above examples. It will be observed the ammonium sulphate required is less with the greater amount of copper sulphate, and it is interesting to note that the total sulphate radical is very nearly the same in the two solutions. However, this rule does not hold over too wide a range. For example, with 200 grams of copper sulphate per liter, the quantity of ammonium sulphate required is 15 to 20 grams per liter. In general, the addition of small amounts of ammonium sulphate brings about an immediate improvement in brightness and throwing power. This improvement continues until the optimum is reached. On increasing the ammonium sulphate beyond the optimum, the deposit begins to lose in lustre and eventually becomes dull. This efl'ect is observable when the excess over the optimum reaches approximately 10 grams per liter.

As already stated, the quantity of free ammonia varies with the degree of relative motion between cathode and solution, but it also varies for different amines and, to some degree also, with the concentration of copper and of amine. Thus with diethylene triamine, it may vary from none at all for vigorous agitation of the solution up to about 40 c. e. per liter for a slow oscillating motion of the cathode. On the other hand, with ethylene diamine as much as 50 to 100 c. 0. must be used to overcome brittleness. Too much ammonia causes the deposit to become dull again at low current densities and thus lowers the throwing power for bright deposits. Obviously, in practice it is desirable to work with as low free ammonia content as possible so as to minimize loss of ammonia by evaporation.

The deposits obtained from solutions such as those described in the examples above are uniformly bright over a wide range of current densities, so that parts with deep recesses can be satisfactorily plated in these solutions. The deposits are light in color and free from brittleness. Articles plated in such solutions can be bent or twisted without seriously damaging the deposit until the base metal itself fails.

The current efliciency in these solutions is generally'better than 90 percent and comparatively little hydrogen is evolved. Under certain conditions, however, this hydrogen causes pitting. It has been found that this is most likely to happen when the solution has become contaminated and when the free ammonia content is too low. Pitting therefore can sometimes be overcome merely by adding ammonia, or in more stubborn cases, by treating the solution with activated carbon or clay, or by electrolysing to remove impurities.

The nature of the impurities which cause pitting is not known. However. certain impurities that are definitely detrimental to the solution are known. Iron is perhaps the most important, but as it can be very readily removed if it does get into the solution, it does not present a serious problem.

Another method of overcoming pitting is to use a suitable surface tension depressant. It has been found, however, that a number of the most common surface tension depressants are definitely detrimental in other ways. Accordingly, it is necessary to choose such agents with care. The ones that have been found best for the purpose are the sulphate esters of certain secondary higher alcohols, such as Tergitol 08, for example. About 2 c; c. of Tergitol 08 per liter is the proper quantity to use. Too much is deleterious and results in rough deposits. In practice, the amount of Tergitol 08 or other surface tension depressants required depends on the condition of the solution; when the solution is in really good condition, none at all may be required.

The amine solutions here described do not deposit copper on iron or zinc when these metals are immersed in the solution. Iron. nevertheless, undergoes severe attack if it,remains in contact with the solution 'for any length of time. Accordingly, it is sometimes advisable to flash iron or steel parts in a cyanide copper solution before putting them in the amine solution. The same procedure helps to avoid blistering in connection with zinc base die castings, especially when the castings are porous.

It has been found that the presence of ammonium compounds such as ammonia and ammonium sulphate in copper plating solution containing an amine increases the permissible current density at the anode. It has also been found that electrolytic copper anodes dissolve more rapidly and smoothly in these solutions than ordinary copper.

Various changes may be made in the procedure and in the character and composition of the bath without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The process of electrolytically obtaining bright deposits of copper which comprises electrolysing an aqueous solution containing 30 to 150 grams per liter of copper sulphate in the presence of 30 to 120 grams per liter of diethylene triamine, and 15 to 50 grams per liter of ammonium sulphate.

2. The process of electrolytically obtaining bright deposits of copper which comprises electrolysing an aqueous solution containing 30 to 150 grams per liter of copper sulphate in the presence of 30 to 120 grams per liter of diethylene triamine, 15 to 50 grams per liter of ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol suflicient substantially to prevent pitting.

3. An electrolyte for depositing bright copper coatings consisting of a water solution containing 30 to 150 grams per liter of copper sulphate, -30 to 120 grams per liter of diethylene triamine and 15 to 50 grams per liter of ammonium sulphate.

4. An electrolyte for depositing bright copper coatings consisting of a water solution containing 30 to 50 grams per liter of copper sulphate, 30 to 120 grams per liter of diethylene triamine, 15 to 50 grams of.ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol" sufficient substantially to prevent pitting.

5. An electrolyte for depositing bright copper coatings consisting of a water solution containing 100 grams per liter of copper sulphate, grams per liter of diethylene triamine, 20 grams per liter of ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol sufficient substantially to prevent pitting 6. An electrolyte for depositing bright copper coatings consisting of a water solution containing grams per liter of copper sulphate, 80 grams per liter of diethylene triamine, and 20 grams per liter of ammonium sulphate.

7. The process of electrolytically obtaining bright deposits of copper which comprises electrolysing an aqueous solution containing copper sulphate in the presence of 30 to grams per liter of an alkyl amine and 15 to 50 grams per liter of ammonium sulphate.

8. The process of electrolytically obtaining bright deposits of copper which comprises electolysing an aqueous solution containing copper sulphate in the presence of 30 to 120 grams per liter of an alkyl amine, 15 to 50 grams per liter of ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol sufficient substantially to prevent pitting.

9. An electrolyte for depositing bright copper coatings consisting of a water solution containing copper sulphate, 30 to 120 grams per liter of an alkyl amine, and 15 to 50 grams per liter of ammonium sulphate.

10. An electrolyte for depositing bright copper coatings consisting of a water solution containing copper sulphate, 30 to 120 grams per liter of an alkyl amine, 15 to 50 grams of ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol sumcient substantially to prevent pitting.

11. An electrolyte for depositing bright copper coatings consisting of a water solution containing 100 grams per liter of copper sulphate, 80 grams per liter 01 an alkyl amine, and 20 grams per liter of ammonium sulphate.

12. An electrolyte for depositing bright copper coatings consisting of a water solution containing 100 grams per liter of copper sulphate, 80 grams per liter of an alkyl amine, 0 to 30 cubic centimeters per liter of 28% aqua ammonia, 20 grams per liter of ammonium sulphate, and a quantity of a sulphate ester 01' a secondary higher alcohol suilicient substantially to prevent pitting.

13. The process of electrolytically obtaining bright deposits of copper which comprises electrolysing an aqueous solution containing 30 to 150 grams per liter of copper sulphate in the presence of 30 to 120 grams per liter of diethylene triamine, an effective amount of free ammonia up to that equivalent to 50 cubic centimeters per liter of 28% aqua ammonia, and 15 to 50 grams per liter of ammonium sulphate.

14. The process of electrolytically obtaining bright deposits of copper which comprises electrolysing an aqueous solution containing 30 to 150 grams per liter of copper sulphate in the presence of 30 to 120 grams per liter of diethylene triamine, an effective amount of free ammonia up to that equivalent to 50 cubic centimeters per liter of 28% aqua ammonia, 15 to 50 grams per liter of ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol sufficient substantially to prevent pitting.

15. The process of electrolytically obtaining bright deposits of copper which comprises electrolysing an aqueous solution containing copper sulphate in the presence of 30 to 120 grams per liter of an alkyl amine, an eflective amount of free ammonia up to that equivalent to 50 cubic centimeters per liter of 28% aqua ammonia, and 15 to 50 grams per liter of ammonium sulphate.

16. The process of electrolytically obtaining bright deposits of copper which comprises electrolysing an aqueous solution containing copper sulphate in the presence of 30 to 120 grams per liter of an alkyl amine, an effective amount of free ammonia up to that equivalent to 50 cubic centimeters per liter of 28% aqua ammonia, 15 to 50 grams per liter of ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol sufficient substantially to prevent pitting.

17. The process of electrolytically obtaining bright deposits of copper which comprises electrolysing an aqueous solution containing copper sulphate in the presence of 30 to 120 grams per liter of an alkyl amine, and 15 to 50 grams per liter of ammonium sulphate at a current density of from about 40 to amperes per square foot.

18. The process of electrolytically obtaining bright deposits of copper which comprises electrolysing an aqueous solution containing copper sulphate in the presence of 30 to 120 grams per liter of an alkyl amine, an eflective amount 01' tree ammonia up to that equivalent to 50 cubic centimeters of 28% aqua ammonia, and to 50 grams per liter of ammonium sulphate at a current density of from about to 130 amperes per square foot.

19. An electrolyte for depositing bright copper coatings consisting of a water solution containing 30 to 150 grams per liter of copper sulphate, 30 to 120 grams per liter of diethylene triamine, an efiective amount of free ammonia up to that equivalent to cubic centimeters per liter of 28% aqua ammonia, and 15 to 50 grams per liter of ammonium sulphate.

20. An electrolyte for depositing bright copper coatings consisting of a water solution containing 30 to 150 grams per liter of copper sulphate, 30 to 120 grams per liter of diethylene trlamine, an effective amount of free ammonia up to that equivalent to 50 cubic centimeters per liter oi. 28% aqua ammonia, 15 to 50 grams of ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol sufficient substantially to prevent pitting.

21. An electrolyte for depositing bright copper coatings consisting of a water solution containing copper sulphate, 30 to 120 grams per liter of an alkyl amine, an efiective amount of free ammonia up to that equivalent to 50 cubic centimeters per liter of 28% aqua ammonia, and 15 to 50 grams per liter of ammonium sulphate.

22. An electrolyte for depositing bright copper coatings consisting of a water solution containing copper sulphate, 30 to 120 grams per liter of an alkyl amine, an efiective amount of free ammonia up to that equivalent to 50 cubic centimeters per liter of 28% aqua ammonia, 15 to 50 grams of ammonium sulphate, and a quantity of a sulphate ester oi a secondary higher alcohol sufllcient substantially to prevent pitting.

23. An electrolyte for depositing bright copper coatings consisting of a water solution containing 100 grams per liter of copper sulphate, grams per liter of diethylene triamine, an effectlve amount of free ammonia up to that equivalent to 30 cubic centimeters per liter of 28% aqua ammonia, and 20 grams per liter of ammonium sulphate.

24. An electrolyte for depositing bright copper coatings consisting of a water solution containing grams per liter of copper sulphate, 80 grams per liter of dlethylene triamine, an effective amount of free ammonia up to that equivalent to 30 cubic centimeters per liter of 28% aqua ammonia, 20 grams per liter of ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol suilicient substantially to prevent pitting.

- 25. An electrolyte for depositing bright copper coatings consisting of a water solution containing 100 grams per liter of copper sulphate, 80 grams per liter of an alkyl amine, an eflective amount of free ammonia up to that equivalent to 30 cubic centimeters per liter of 28% aqua ammonia, and. 20 grams per liter of ammonium sulphate.

26. An electrolyte for depositing bright copper coatings consisting of a water solution containing 100 grams per liter of copper sulphate, 80 grams per liter of an alkyl amine, an effective amount of free ammonia up to that equivalent to 30 cubic centimeters per liter of 28% aqua ammonia, 20 grams per liter of ammonium sulphate, and a quantity of a sulphate ester of a secondary higher alcohol suillcient substantially to prevent pitting.

LAWRENCE GREENSPAN;

- CERTIFICATE OF CORRECTION. Patent No. 2,19 ,151 Apriiz, 191p.

' LAWRENCE GREENSPAN.

It ishereby certified that error aopearsin the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, line 27, for the word "Being" read --bel'ong-; page 5, first column, line 67-68, elaimB, for 'felectolysing" read --electro1ysiz 1g--; same 'page, second column, lines 19 and-20, claim 12, strike out "0 to 50 cubic centimeters per liter of 28;! aqua ammonia); and that the said Letters Patent shouldbe read with this correction therein that the same may conform to therecord of the case in the Patent Office.

I Signed "and sealed this lhth day of May,- A. D. 19 40.

' Henry van Arsdale, (Seal) Acting Commissioner of Patents.