US3037918A - Semi-bright copper - Google Patents

Description

United States Patent No Drawing. Filed .iuly 14, 1960, Ser. No. 42,755 8 Claims. (Cl. 204-52) The present invention is directed to alkaline cyanide copper plating baths and more particularly to semi-bright baths having a leveling or smoothing eifect to reduce surface micro-roughness.

In certain applications of copper deposits it is more desirable to obtain leveling than to obtain a high degree of brightness. Of the bright cyanide copper baths in the prior art, none had the ability of depositing coatings which would hide or level surface imperfections on the basis metal without using periodic reverse currents. Actually, such prior baths often exerted a negative leveling; i.e., they magnified the imperfections. The prior art addition agents further tended to accentuate the negative leveling effect of the bath. It is known that the prior art acid copper plating baths can be made to level or reduce surface roughness of the basis metal when certain organic addition agents are incorporated in the bath. For instance, such acid baths are capable of reducing the surface roughness of a comparatively rough surface to R.M.S. value of about 30.

On the other hand, the prior art cyanide copper baths even with addition agents were unable to reduce surface roughness or hide imperfections on comparatively smooth surfaces (R.M.S. values of 10 or below) unless periodic reverse current was used. The baths described in this invention are capable of producing positive leveling in cyanide copper baths without the use of periodic reverse current on surfaces that had initial roughness of approximately 10 R.M.S. or less. If periodic reverse current is utilized with the baths of this invention, then the degree of leveling becomes considerably enhanced, in fact far better than that secured from prior art periodic reverse cyanide copper baths.

The present invention is intended and adapted to overcome the deficiencies and disadvantgaes inherent in cyanide copper plating baths, it being among the objects thereof to introduce into such baths an addition agent which will have a leveling effect on a copper deposit without using periodic reverse current, to eliminate surface roughness of about 10-15 R.M.S. and lower.

It is also among the objects of the invention to provide a bath of the character described which is adapted to produce a crystal structure of the deposited copper which, while only semi-bright, can be readily brightened by the subsequent bright nickel coatings.

It is further among the objects of the invention to provide a bath of such character that even if the copper deposit is burned, the subsequent nickel coating tends to brighten readily.

' ing or leveling eifect and brighten the deposit. The bright- It is still further among the objects of the invention to provide a cyanide copper bath that will produce leveling with or without reverse current from the same bath.

In practicing the present invention there is provided the usual cyanide copper plating baths, for instance:

G./l. CuCN 45-75 Total KCN 75-120 KOH 15-30 ness approximates that obtained by the practice of US. Patent No. 2,287,654, describing the use of ,thiocyanate in the bath, which has no leveling elfect without periodic reverse current. Actually in such prior baths, selenium or sulfur in the 2 state and tellurium in the 2 and +4 state, destroy leveling when present in concentrations required or recommended to give full or maximum brightness of the deposit.

The compounds which are the addition agents of the present invention are of the type set forth in Table I below:

The compounds of the present invention may be included in the following general formula:

wherein R is a hydrocarbon radical having 2 to 3 carbon atoms, X is hydrogen or [OR] OH and n is 0 to 20.

The leveling efiect of the above class of compounds is enhanced by the presence of a small amount of zinc in the soluble form, such as sodium zincate or zinc cyanide. In high efliciency cyanide copper baths the concentration of the zinc in the range of 0.01 to 1.0 g./l. gives excellent results. The optimum range is between 0.1 and 0.2 g./l.

In order to obtain good leveling it is important that the bath contain a limited concentration of the selenium, tellurium, or sulfur type brighteners. Selenium having a valence of -2, sulfur in the sulfide state and tellurium should not be present in amounts exceeding 0.0005 g./l. However, controlled amounts of selenium (in the -2 state) or sulfidic sulfur may be utilized within the above limits, say from 0.0001 to 0.0005 g./l. whereby increased brightness of deposit is obtained without impairing appreciably the micro-leveling characteristic of the bath.

Table II attached hereto contains a number of specific examples which will illustrate the nature of the invention.

ROX

ROX

Table 11 CuCN .l- 60 75 45 75 60 75 6O 60 i 94 KOH 15 20 15 30 30 15 15 15' Znaszineateor Cyanie 0.2 0.3 0.15 0.2 0.5 0.4

The Plating is conducted at temperatures of 7 1 5. A plating bath according to claim 1 characterized in F. with a current density of 10 to 40 amperes per square foot. Mild to vigorous agitation is provided.

Among the present addition agents, those of larger molecular weight or of more complex structure are preferred'. Those hydroxy polyamines which have ether linkages have a greater leveling efiect than those which do not contain such ether linkages. Mixtures of hydroxy 'polyamines are more effective than single compounds.

While the amounts used may vary from 0.01 to 50.0 g./l., it is preferred to employ from 0.5 to 10.0 g./l, in most applications.

The present cyanide baths exhibit micro-leveling whereas the acid copper baths exhibit macro-leveling. However, it is possible to obtain microas well as macroleveling from these cyanide baths by utilizing periodic reverse current.

' We claim: 7

1. An aqueous alkaline cyanide copper plating bath having incorporated therein a compound having the following formula:

/R 0 X -RN X-O R BOX wherein R represents a hydrocarbon radical having from 2 to 3 carbon atoms, X represents hydrogen and -[OR] -OH, and n is 0 to 20, the amount of said compound present in the bath being sufiicient to produce micro-leveling in the deposit.

2. A plating bath according to claim 1 characterized in that the amount of said compound is about 0.1 to 50.0 g./l.

3. A plating bath according to claim 1 characterized in that said bath contains less than 1.0 g./l. of a soluble zinc salt.

4. A plating bath according to claim 1 characterized in that said bath contains about 0.01 to 1.0 g./l. of a soluble zinc salt.

that said bath is substantially free from soluble compounds of selenium, tellurium and sulfur.

' 6. A plating bath according to claim 1 characterized in that said bath contains not over 0.0005 g./l. of soluble compounds of selenium, tellurium and sulfur.

"I. A plating bath according to claim 1 characterized in that saidcompound has from 1 to 4 free OH groups.

and at least one ether group.

' References Cited in the file of this patent UNITED STATES PATENTS Portzer Nov. 26, 1957 Winters May 6, 1958

Claims (1)

1. AN AQUEOUS ALKALINE CYANIDE COPPER PLATING BATH HAVING INCORPORATED THEREIN A COMPOUND HAVING THE FOLLOWING FORMULA: