Baths for the production of copper electroplates

United States Patent Office „ 3,051,634 ' Patented Aug. 28, 1962

3,051,634

BATHS FOR THE PRODUCTION OF COPPER ELECTROPLATES

Wennemar Strauss and Wolf-Dieter Willmund, Dusseldorf-Holthausen, Germany, assignors to Dehydag, 5 Deutsche Hydrierwerhe G.m.b.H., Dusseldorf, Germany, a corporation of Germany

No Drawing. Filed Nov. 21,1958, Ser. No. 775,354 Claims priority, application Germany Nov. 30, 1957

Claims. (CI. 204—52)

This invention relates to a process for producing bright copper electrodeposits from acid copper plating baths using organic compounds as brightening additives. It more specifically relates to supplementary additives for such copper plating baths to permit operation of the bath over wider ranges of temperature and current density without reducing the effectiveness of the bath and the quality of the electrodeposits.

It is known that organic brighteners may be added to copper electroplating baths to achieve bright copper electrodeposits. . These brighteners produce a substantial improvement in the brighteners, depending upon their nature, but in many cases their effectiveness is strongly dependent upon temperature, i.e., they can be used effectively only within relatively narrow temperature limits.

It is an object of this invention to provide a method and bath for producing bright copper electrodeposits at higher temperature conditions.

Another object is to provide a method and bath for producing bright copper electrodeposits at lower current density.

A further object of this invention is to provide additives for an acid bright copper electroplating bath which will permit operation of the bath over wider temperature and current density ranges without loss of brightness in the metal deposits.

These and other objects of our invention will become apparent as the description thereof proceeds.

We have now found that this temperature range can be widened by adding acyclic or cyclic thioamides or isothioamides to the baths in addition to the brightening agents. The effect achieved thereby is that the undesirable dull zones which form at higher temperatures in the range of low current densities of about 0-4 amp./dm.² no longer occur.

Suitable brighteners are the known, previously customary agents such as thiourea, thiourea derivatives, safranins or also, with particular advantage, modern highquality brighteners. The latter are characterized by a carbon atom linked only to heteroatoms, the carbon atom being also linked through a sulfur or nitrogen atom to an aliphatic radical which in turn has a water-solubilizing group, such as a sulfonic acid group, attached thereto.

The thioamides or isothioamides which are the subject matter of this invention, have a general structural formula as follows:

s y s-r'(r)

R— C—N or R—

R ^XN—R(R') wherein R, R' and R are aliphatic, cycloaliphatic, alkylaromatic or aromatic hydrocarbon radicals, and R' or R may also be hydrogen. R and R' (or R'') as well as R' and R may also form a polymethylene chain which may, in the latter case, be interrupted by heteroatoms. The radicals R, R' and R may carry substituents, such as halogen, cyano, thiocyano and/or hydroxyl groups, or may be interrupted by heteroatoms or heteroatom groups; particularly, they may contain additional thioamide groups. Products of this type are soluble in the acid copper baths in the customary concentrations. They may be improved with respect to solubility properties, if necessary, by introducing non-ionic, water-solubilizing groups, such as polyethylene-oxide groups.

The addition of these compounds permits operation at bath temperatures up to 55° C. and produces from bright to full bright electrodeposits, depending upon the nature of the brightener, over the entire current density range. If desired, two or more of these agents may be used simultaneously. Mixtures of halogen-free and halogen containing thioamides or isothioamides have been found to be particularly advantageous and result in a considerable increase in the effect.

Examples of thioamides or isothioamides which may be used in accordance with the present invention are:

Thioacetamide

Thiopropionamide

Thiobutyramide

Adipic acid dithioamide ₂θ Thiobenzamide

2-hydroxy-thiobenzamide

Phenyl-thioacetamide

Thionaphthamide

N,N-diethyl-thioacetamide ₂₅ N,N-diethanol-thioacetamide N-ethyl-thioacetamide

Thioacetanilide

Thioacet-m-chloroanilide

N-cyclohexyl-thioacetamide ^N- (AA^-trichloro-a-hydroxy-ethyl) -thioacetamide Thioacet-morpholide

Thioacet-piperidide

1,2-ethylene-bis- (thioacetiminoester-S,S') Thioacetimino-allylester

N-methyl-N-^-chloroethyl-thiopropionamide N-methyl-N-7-chloropropyl-thiopropionamide N-methyl-N-jS-chloroethyl-thiobenzamide N-cyclohexyl-thiobutyramide

2-hydroxy-thiobenz-piperidide

Butyrothiolactam

Valerothiolactam

Caprothiolactam

N-chloroalkyl-caprothiolactams, such as N-/3-chloroethyl-caprothiolactam

N-7-chloropropyl-methyl-valerothiolactam Ν,Ν'-bis- (thioacet) -ethylenediamine

The addition product of 5 mols of ethylenoxide to thioacetamide.

A? ^aIready indicated, suitable brighteners are the known ^υ previously customary agents such as thiourea derivatives, safranins and the full brightening agents which may be used are primarily those organic compounds which are characterized by one or more carbon atoms linked only to heteroatoms, and which contain a short aliphatic radical linked to the carbon atom through a sulfur or nitrogen atom, the aliphatic radical having attached thereto a water-solubilizing group, especially a sulfonic acid group. Examples of such full brightening agents are water-soluble an ^Sa!l^S N,N-diethyl-dithiocarbamic acid-n-propylester-ωsulfonic acid; Ν,Ν-pentamethylene-dithiocarbamic acid-npropylester-w-SO_sH; l,3,5-triazine-2,4,6-tris-(mercapto-2'hydroxy-propane-sulfonic acid); and other full brightening agents of similar structure, such as those which are described in French Patent No. 1,097,123 and Belgian ^bS Patents Nos. 543,413 and 540,564 or which are the subject matter of copending application Serial No. 618,183 filed October 25, 1956, now Patent No. 2,849,352.

Furthermore, the baths may be modified with agents which render bath impurities harmless and which improve ⁷⁰ the ductility of the electrodeposits. If desired, the baths may contain.additional brightening and/or wetting agents.

The addition of agents which render bath impurities

3,051,634 harmless has the effect that inorganic impurities, such as the hardness components of water or impurities in technical grade metal salts, do not exert a detrimental effect upon the properties of metal electrodeposits which are produced with the aid of the above full brighteners. Furthermore, these compounds have the property of increasing the ductility of the electrodeposits.

Examples of compounds of this type are: N,N,N',N'-tetraethyl-l,3-diamino-propanol-2,N,N,N',N'tetraethanol-ethylenediamine

2-diethylamino-ethylchloride-1 N,N,-dimethyl-4-bromaniline 3 -diethylamino-1 -chloro-propanol-2 as well as halogen salts of quaternary ammonium compounds which have been formed by intramolecular rearrangement from the last-mentioned substances, and piperazine-N,N'-bis-(2-hydroxypropane-sulfuric acid) Ν,Ν,Ν', N'-tetra-n-butyl-l,3-diamino-propanol-2-monosulfuric acid ester and similar compounds, such as those which are described in German Patents 934,508 and 1,000,204, German published specification 1,014,404, and in copending application Serial No. 714,687, now U.S. Patent No. 2,986,498.

The additives according to the present invention may also be used conjointly with the above-described hardnessbinding and ductility-improving amino compounds free from carboxyl groups, as well as with the full brighteners in the process for directly copper plating non-precious metals in accordance with copending application Serial No. 458,983, now U.S. Patent No. 2,903,403. According to that process it is possible to deposit firmly adhering copper electroplates on non-precious metals, such as iron, without a cyanide pre-dip by pre-treating the metal objects to be copper plated in an acid pickling bath in the presence of inhibitors having a high inhibiting effect, and subsequently directly electroplating them in a copper bath without intermediate rinsing.

The additives according to the present invention are employed in amounts of about 0.001 to 6 gm./liter, preferably in amounts of 0.01 to 1 gm./liter of bath.

From German Patent 837,029 it is known that thioacetamides may be added to copper electroplating baths in order to improve the brightness of the electrodeposits. However, it was found that only a very moderate brightening effect could be achieved with these substances alone. In contrast thereto, the present invention concerns the improvement of baths which contain known full brighteners, because the addition of thioamides achieves a substantial widening of the effective temperature range of the copper electroplating process.

The following examples are set forth to enable persons skilled in the art to better understand and practice the invention. It will be understood that there is no intention of limiting the invention to these examples.

Example I

Metal objects were electroplated at room temperature in an acid copper bath which contained 200 gm./liter CuSo₄,5H₂O, 60 gm./liter concentrated H₂SO₄, 0.2 gm./ liter Ν,Ν-diethyl-dithiocarbamic acid-n-propylester-w-sulfonic acid (sodium salt) and 0.4 gm./liter 1,3,5-triazine2,4,6-tris- (mercapto-ethane sulfonic acid) (sodium salt) as a brightening agent, 0.25 gm./liter Ν,Ν,Ν',Ν'-tetraethyl-ethylenediamine as a ductility-improving agent, and 3 gm./liter of a condensation product formed from dodecylalcohol and 10 mols ethyleneoxide, which had been 25% converted into the sulfuric acid ester, as a wetting agent. Full bright copper electroplates were obtained in a current density range of about 0-7 amp./dm.². However, if the objects are electroplated in the same bath at a higher temperature, for example at 35° C., only dull electroplates were obtained in the range of 0-4 amp./dm.², whereas full bright deposits were obtained in the range of 4-8 amp./dm.². However, when the bath was modified with 0.002 gm./liter caprothiolactam, the range of full bright deposits was extended to about 0-8 amp./dm.², i.e., full brightness again occurred over the active current density range.

In place of caprothiolactam, the following thioamides may be used with comparable results: N-/3-chloroethylcaprothiolactam, methyl-valerothiolactam, N,N -bis-(thioacet)-ethylenediamine, thioacetmorpholide, N,N-diethanol-thioacetamide thioacetimino-allylester, N-cyclohexylthioacetamide.

Example II

The copper electroplating bath described in Example I was modified in additon with 0.008 gm./liter thioacet-mchloroanilide. Full bright copper electrodeposits were obtained even at 55° C. In this case the effective current density range was 0.5-8.5 amp./dm.².

Example III

In an acid copper electroplating bath, containing 200 gm./liter CuSO₄.5H₂O, 60 gm./liter concentrated H₂SO₄, 0.025 gm./liter of the sodium salt of N,N-dimethyl-dithiocarbamic acid-ethyl ester-w-sulfonic acid, 0.5 gm./liter dimethyl-jS-chlcroethyl-amine hydrochloride, 4 gm./liter of a condensation product of dodecyl alcohol and 10 mols ethyleneoxide, which had been completely transformed into the sulfuric acid ester, full bright electrodeposits were obtained at a temperature of 35° C. within a current density range of 0—8 amp./dm.² when 0.003 gm./liter phenyl thioacetamide was added to the bath.

Corresponding results were obtained if thiobenzanilide, thio-jS-naphthamide, 2-hydroxy-thiobenzamide and others were used in place of phenyl-thioacetamide.

Example IV

To an acid copper bath, containing 200 gm./liter CuSO₄.5H₂O gm./liter concentrated H₂SO₄ and 4 gm./liter of Jhe acid-n-propylester-w-sodium sulfonate brightening agents, 2.5 gm./liter of the wetting agent of Example III, 0.1 gm./liter N,N-diethyldithiocarbamic were added compound as

-C₂Hs CH₂ '''ch OH .οίΗ,^ΟΗ, as the agent to render bath impurities harmci45 were added as the agent to render bath impurities barmless and to improve the ductility, and 0.003 gm./liter l,2-ethylene-bis-(S,S'-caprothiolactam) were added. Full bright copper electrodeposits were obtained at temperatures of about 35-40° C. within a current density range of 0-7 amp./dm.².

Example V

In place of the brightener, ductility-improving agent acid additive for increasing the temperature range indicated in Example IV, 0.25 gm./liter N,N-diethyl-dithiocarbamic acid-n-2-hydroxy propyl ester-w-sodium sulfonate, 0.15 gm./liter l,3-diamino-propanol-2-sulfuric acid ester and 0.02 gm./liter N-(ftft/9-trichloro-a-hydroxyethyl)-thioacetamide were added to the acid copper bath. Full bright copper electrodeposits were obtained in this bath at a temperature of 38° C.

Example VI

In an acid copper bath, containing 200 gm./liter

CuSO₄.5H₂O gm./liter concentrated H₂SO₄, 4 gm./liter of the wetting agent used in Example III, and 0.02 gm./liter N,N-diethyldithiocarbamic acid-ethyl ester-w-sodium sulfonate, full bright electrodeposits were obtained up to a temperature of 28° C. Where 0.01 gm./liter thioacetamide are added to this bath, it was possible to obtain full° bright copper electrodeposits even at a temperature of 37 ° C.

While we have disclosed certain specific embodiments of our invention, we wish it to be understood that these

3,051,634 are not intended to be limitative, and that various changes and modifications may be made without departing from the spirit of our invention or the scope of the appended claims.