US2700019A - Acid copper plating - Google Patents

Description

1955 G. w. JERNSTEDT ETAL 2,700,019

ACID COPPER PLATING Filed July 5, 1951 Acid Copper Electrolyte Plus z -Thiohydontoin Compound us on additional Agent.

Fig.2.

SM m m Y I d. mm. e V. mw m, n A w .wM 1 mm V| M 8 mm B m i s 0. n .0. .m m m C mm y m mm X m .t 9. .YO W. F E 0 L 28 3- Y B C A n o c e S O m e .w m m m 9n m .m m e m5 0 m s s x m s e E A W W v O B 0 3.2.60 230 I United States Patent ACID COPPER PLATING George W. Jernstedt and Myron Ceresa, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 5, 1951, Serial No. 235,135

Claims. (Cl. 204-52) advantages are encountered in using them. Many of these addition agents must be employed in such minute amounts in the acid copper electrolyte thaLsatisfactOry determinations of the quantity present are almost impossible to make and it requires guesswork on the part of the operator either to determine how much to add to begin with or to replenish the amount present to some desired optimum amount. Furthermore, the effect of most previously employed addition agents has been relatively meager so that a high level of consistently good results has been difficult to obtain in acid copper plating.

One disadvantage in acid copper plating as carried out at the present time is the necessity for staying within a restricted range of temperatures during plating within which the electrolytes must be kept to produce satisfactory plating. In commercial installations of acid copper plating baths at the present time, temperatures of approximately 100 F. are regarded as the maximum permissible using known addition agents in the baths. Artificial cooling of the bath is practiced to keep the temperature below this value. and higher present day acid copper plating baths produce definitely inferior copper plate which is ordinarily regarded as inacceptable.

Copper plated from acid copper plating electrolytes containing any of the number of addition agents now used in industry today tends to be quite brittle. This brittleness is undesirable in that it makes the machining or other processing of members plated with such copper quite difiicult. Also striations or ribbing are commonly encountered while plating from acid copper electrolytes containing these previously known addition agents.

The object of the present invention is to provide an acid copper electrolyte containing thiohydantoin and certain substitution derivatives of 2-thiohydantoin.

A further object of the invention is to provide-a process for electroplating copper from an acid copper electrolyte containing thiohydantoin or certain substitution derivatives of 2-thiohydantoin.

Another object of the invention is to provide-an addition agent for acid copper baths comprising essentially thiohydantoin or certain substitution derivatives of. 2- thiohydantoin, with or without other additives.

A still further object of the invention is to provide an acid copper electroplating electrolyte with an addition agent comprising 2-thiohydantoin and certain derivatives of 2-thiohydantoin in combination with either organic carboxylic acids or with dextrin or both.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description and drawing, in which:

Figure l is a view in cross section, and

Fig. 2 is a graph. We have discovered that the addition of either 2-thiohydantoin or substitution derivatives of 2-thiohydantoin or two or more of such compounds, to acid copper electrolytes will enable electrodeposits with a highly refined grain size and having smooth, bright surfaces to be plated from the electrolytes so treated. Many of the dis- At temperatures of 120 F.

r6 ce advantages encountered with additions of previously known addition agents to the same electrolytes are eliminated by the addition of these 2-thiohydantoin compounds.

More particularly, the present invention is based on the addition of predetermined amounts of at least one 2-thiohydantoin compound having at least one organic snbstituent in any one of the 1, 3 and 5 positions. The base of these compounds is the following thiohydantoin structure:

H O (i-- 4 5 I 3 1 2 /N. C

Various organic radicals may be substituted at any one or more of the 1, 3, or 5 positions, so long as the com- 1 pound is not rendered so insoluble that it will not dissolve in the acid copper electrolyte in an amount sufficient to produce an appreciable result. Examples of suitable compounds are:

2-thiohydantoin l-acetyl-Z-thiohydantoin 5(2-hydroxylbenzal)-2-thiohydantoin S-furfural-Z-thiohydantoin l-benzoyl-2-thiohydantoin S-benzal-Z-thiohydantoin 1-methyl-2-thiohydantoin 3-acetyl-2-thiohydantoin The best results have been secured with Z-thiohydantoin derivatives having a carbonyl group ..C ll 0 attached at any one or all of the 1, 3 and 5 positions, and with an organic radical being attached to the carbonyl group.

We have found as little as 0.0005 ounce per gallon of one or more of these Z-thiohydantoin derivatives will produce an improvement in the acid copper electrolyte. In some cases as much as 0.05 ounce per gallon of the compounds may be added. It will be appreciated that the relative solubility of the compounds will determine the maximum amount that may be applied. Extremely good results have been secured with 1-acety1-2-thiohydantoin and specific reference will be made hereinafter to this compound, though, it will be understood that others may be substituted in whole or in part therefor.

Acid copper electrolytes suitable for plating copper are well known. Ordinarily they comprise an aqueous solution having dissolved therein from 20 to 33 ounces per gallon of copper sulfate and from 1.3 to 13 ounces per gallon of sulfuric acid. In industry at the present time, the acid copper bath most widely used is one comprising a solution of 27.5 ounces per gallon of copper sulfate crystals and 6 ounces per gallon'of sulfuric acid (98% Into the acid copper electrolyte there may be added l-acetyl- 2-thiohydantoin in an amount of from 0.0005 to 0.05 ounce per gallon. The optimum proportions appear to be from 0.005 to 0.01 ounce per gallon. It will be appreciated that as the electrolyte is used in plating the addition agent will require replenishing from time to time. When. treated with acetyl thiohydantoin, very satisfactory copper plating can be done with the bath at any temperature from room temperature up to 150 F. We have secured fine smooth copper deposits from bathsoperating at temperatures of R, which appears to be the optimum temperature.

One or more of the 2-thiohydantoin compounds may be employed in the bath alone or in combination with other known addition agents. For example, We have added l-acetyl-Z-thiohydantoin to acid copper bathscontaining phenol sulphonic acid, thiourea, glue, metallic addition agents such as cadmium and the like. In every case, we have secured better copper electrodepositsbyi the addition of the l-acetyl-Z-thiohydantoin to each of these baths.

As a result of numerous tests run under comparable conditions, both in the laboratories and in the shop, we have found that l-acetyl-Z-thiohydantoin, for instance, enables the brightest copper to be deposited that we have secured with any single known addition agent, and furtherrlnore the electrodeposited copper is relatively nonbritt e.

In order to enable the l-acetyl-2-thiohydantoin, for instance, to function at the maximum efficiency for long periods of time, it is desirable to associate it with an organic carboxyl acid in amounts of up to about 3.00 ounces per gallon of the electrolyte or up to the limit of solubility for the less soluble carboxylic acids. The organic carboxyl acid should be water soluble and not decompose in the acid electrolyte. Examples of suitable organic carboxyl acids are:

Adipic acid Phthalic acid Malic acid Linoleic acid Pimelic acid, and Aconitic acid A number of these acids may be added if desired. Hereinafter specific reference will be made to citric acid, but it will be understood that one or more of the other water soluble organic acids may be substituted in whole or in part therefor.

We have found further that the addition of dextrin to the acid copper electrolytes containing 2-thiohydantoin and its 1, 3 and 5 derivatives, with or without a carboxylic acid, enables further benefits to be obtained. The dextrin prolongs the period of effectiveness of the 2- thiohydantoin additives in the electrolyte. The combination in an acid copper electrolyte of a 2-thiohydautoin compound, a carboxylic acid such as citric acid or aconitic acid, and dextrin has given the optimum quality in copper plating, and the most uniform plating for the longest periods have been produced from this combination. The amount of dextrin for best results is from 0.1 to 1.0 ounce per gallon of electrolyte, though as little as 0.01 ounce and as much as 5 ounces per gallon of electrolyte constitute an efiective amount.

Acid copper aqueous electroplating electrolytes with l-acetyl-Z-thiohydantoin added thereto, with or Without citric acid, and dextrin, or any other additive, may be employed for plating metal by passing either continuous direct current or periodically reversed electrical current or other suitable electrical current therethrough. Excellent results have been obtained with direct current plating from such electrolytes. However, periodic reverse current has given outstanding electrodeposits characterized by an absence of nodules, and having smooth edges, smooth surfaces and refined grain not attainable with direct current.

Referring to the drawing there is illustrated in Fig. 1 an apparatus for practicing the present invention. This apparatus comprises a tank 12 provided with a suitable liner 14 of rubber, glass or the like, resistant to the acid electrolyte, carrying an electrolyte 16 composed of an aqueous solution of copper sulfate, sulfuric acid and at least one 2-thiohydantoin derivative as described herein. Disposed within the electrolyte is an anode 18 that may be composed of copper or lead, or separate anodes of both. If lead anodes are used, the copper must be replenished by introducing copper sulfate into the electrolyte 16 from time to time. The anode 18 is suspended from a conductor bar 20. A base 22 to be plated with copper is suspended by a support 24 from a second conductor bar 26. The conductor bars 20 and 26 are provided with electrical current from a suitable source 28 which may be a generator, a rectifier, storage batteries or the like. Electrical current passing from the source 28 to the conductor bars 20 and 26 passes through the anode 18, electrolyte 16 and the base 22 to cause copper to be deposited from the electrolyte upon the base. The l.-acetyl-2-thiohydantoin will cause the copper to be deposited as a smooth bright layer substantially free from brittleness and striation or ribbing. The copper deposited will exhibit a highly refined grain and will be 'superior to copper deposited from any known acid copper electrolyte bath.

Copper may be plated from the electrolyte by means of a reversed electrical current composed of cycles, each of which passes electrical current through the base for a period of time of from 0.01 second to 100 seconds to plate copper on the base and then the direction of flow of the current is reversed to deplate a part of the previously deplated copper. The time and the magnitude of the deplating current is such that it applies from 8% to of the coulombs applied during the previous plating period. Assuming efficiency during the deplating period, this means that from 8% to 90% of the copper deposited during the previous plating period in each cycle is deplated. The increment of copper remaining on the base after the cycle consists of smooth, sound copper upon which a second layer of copper is plated by the plating portion 'of the next cycle of period reversed current and then a portion of this second increment is deplated by passing of deplating current leaving a second increment of still smoother copper than the first increment, and so on.

Referring to Fig. 2 of the drawing, there is illustrated in a graph the period reverse current as it is applied to the base. It is assumed that the base when first immersed in the electrolyte is at a zero potential so that no current flows. When the first cycle of periodically reversed current is applied, a cathodic or plating current of a density of the value A is applied and metal is plated for a period of time X to a point B, then the direction of flow of the current is reversed so that the current density in the member drops from the value B to zero and then becomes anodic and will deplate copper, reaching a deplating current density of C. Metal is deplated for a period of time Y, which is at least 6 of the length of period X, at the current density of C to D until sufficient coulombs of deplating current have been applied to equal from 8% to 90% of the coulombs applied during the plating period X. The cycle A-B-C-D deposits an increment of sound, smooth copper on the base. The direction of current flow is again reversed from D through zero and then plating current of a density value of F is applied to begin another cycle which will plate a second increment of copper. It will be understood that the showing in Fig. 2 is merely schematic and that the current is not necessarily uniform from A to B or C to D, as shown, but will vary and be relatively non-uniform. Also in reversing from B to C and from D to F the time required is finite and these lines will not be vertical, as shown, but will take an appreciable period of time, depending upon the various factors involved in the plating installation. The deplating or anodic current density C-D may be equal to the plating current density A-B, or exceed it or may be as low as 35% of the plating current density. Reference should be had to Patents 2,451,- 341 and 2,470,775 for additional information as to periodic reverse current cycles.

The following examples are illustrative of the practice of the invention:

Example I An aqueous electroplating electrolyte of the following composition was prepared:

Ounces per gallon Copper sulfate (crystals) [CuSO4.5H2O] 27.5

Sulfuric acid (98%) 6 1-acetyl-2-thiohydantoin l 0.007

This bath was operated at various temperatures from 60 F. to 150? F. with excellent results. Both temperatures of from F. to F. appeared to give optimum plating results.

Copper was plated from the bath of this Example I us ing direct current at current densities of from 50 to 100 amperes ,per square foot. In each case the copper had a highly refined grain and was quite bright.

Copper was plated from the bath of Example I using a periodic reverse current having the following cycles:

Plating time: Deplating time, seconds (a) 2 seconds /3 (b) 5 seconds (c) 10 seconds 2 (d) '15 seconds 3 The current density during each portion of the cycles (1:) and (b) was 50 amperes per square foot and 60 amperes per square foot for cycles (0) and (d). The periodic reverse current cycles in each case produced excellent smooth deposits of copper better than anything securedunder the same conditions using many other addition agents previously known in the art.

In another test 3-acetyl-2-thiohydantoin was used instead of l-acetyI-Z-thiohydantoin in this Example I. The plating solution produced copper deposits fully equivalent to those described in Example I.

Example II To the bath of Example I there was added 0.25 ounce per gallon of citric acid. A base immersed in the bath was plated by applying continuous direct current thereto. The deposited copper was bright "and showed a fine grain structure without any ribbing or striations. The citric acid enabled good plating to be obtained for longer periods than possible with the bath of Example I without citric acid. In another test a periodic reverse current comprising a cycle of 20 seconds plating and seconds deplating applied at a current density of 75 amperes per square foot during both portions of the cycle produced on members excellent bright copper deposits free from any surface defects.

Example 111 An electrolyte having the following composition was prepared:

Copper was plated from this electrolyte with both direct current and a periodic reverse current having cycles with 15 seconds plating period and 3 seconds deplating perlod. The deposits of copper were brighter than from the electrolyte without the dextrin.

To six separate portions of the electrolyte of this Example III, there was added 0.25 ounce per gallon of citric acid, malic acid, maleic acid, linoleic acid, oxalic acid and aconitic acid, respectively. These portions were used in plating over a period of many days. Throughout this period the plated copper was of excellent color and characterized by a smooth, extremely fine grain structure.

We have found it to be desirable to prepare a composition by combining the Z-thiohydantoin compounds as disclosed herein with either a water soluble organic car boxylic acid or dextrin, or both, and copper sulfate may be included, which composition may be added to water and sulfuric acid to prepare the bath originally and to replenish the bath as required from time to time. Sultable compositions of this type comprise essentially at least 0.1% by weight of at least one Z-thiohydantoin compound or derivatives thereof having at least 1 organic substituent at the l, 3 and the 5 positions, not exceeding 80% by weight of at least 1 water soluble organic carboxylic acid or dextrin or both, and the balance being copper sulfate crystals, or other additive such as thiourea or metal salts. An example of such composition to be added to the electrolyte is the following:

Example IV The following in powdered form were admixed:

Parts by weight l-acetyl-Z-thiohydantoin l1 Citric acid 1475 Copper sulfate crystals 13,170

This composition was added in the amount of 0.25 ounce per gallon of acid copper electrolyte and would provide therein 0.002 ounce per gallon of l-acetyl-2-thiohydantoin.

Since certain changes may be made in the above invention and different embodiments of the invention may be made Without departing from the scope hereof, it is intended that all matter contained in the disclosure shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. An aqueous electroplating electrolyte comprising essentially copper sulfate, sulfuric acid, from 0.0005 to 0.05 ounce per gallon of at least one 2-thiohydantoin compound and from efiective amounts up to 3.0 ounces per gallon of an organic carboxylic acid soluble in water, the organic carboxylic acid being selected from the group consisting of citric acid, malic acid, maleic acid, linoleic acid, oxalic acid, adipic acid, and aconitic acid.

2. An aqueous electroplating electrolyte comprising es-' sentially copper sulfate, sulfuric acid, from 0.0005 to 0.05 ounce per gallon of at least one 2-thiohydantoin compound from effective amounts, up to 3 ounces per gallon of an organic carboxylic acid soluble in water, the organic carboxylic acid being selected from the group consisting of citric acid, malic acid, maleic acid, linoleic acid, oxalic acid, adipic acid, and aconitic acid, and from 0.1 to 5 ounces per gallon of dextrin.

In the process of plating on a base copper from an aqueous electrolyte, the electrolyte comprising as its essential ingredients copper sulfate and sulfuric acid, the steps comprising adding from 0.0005 to 0.05 ounce per gallon of at least one Z-thiohydantoin compound and dextrin in an amount of from 0.1 to 5 ounces per gallon and then passing a plating electrical current from an anode through the electrolyte and to the base to deposit copper on the base.

4. The process of claim 3 wherein up to 3 ounces per gallon of at least one water soluble organic carboxylic acid is added to the electrolyte, the organic carboxylic acid being selected from the group consisting of citric acid, malic acid, maleic acid, linoleic acid, oxalic acid, adipic acid, and aconitic acid.

5. In the process of plating on a base copper from an aqueous electrolyte, the electrolyte comprising as its essential ingredients copper sulfate and sulfuric acid, the steps comprising adding 0.0005 to 0.05 ounce per gallon of at least one 2-thiohydantoin compound and up to 3.0 ounces per gallon of at least one water soluble organic carboxylic acid, the organic carboxylic acid being selected from the group consisting of citric acid, malic acid, maleic acid, linoleic acid, oxalic acid, adipic acid, and aconitic acid, and then passing an electrical current from an anode, through the electrolyte and to the base to deposit copper on the base.

6. In the process of plating on a base copper from an aqueous electrolyte, the electrolyte comprising as its essential ingredients copper sulfate and sulfuric acid, the steps comprising adding from 0.0005 to 0.05 ounce per gallon of at least one 2-thiohydantoin compound selected from the group consisting of 2-thiohydantoin and its derivatives having at least one organic radical substituted at the l, 3 and 5 positions, and from effective amounts up to 3.0 ounces per gallon of at least one water soluble organic carboxylic acid, the organic carboxylic acid being selected from the group consisting of citric acid, malic acid, maleic acid, linoleic acid, oxalic acid, adipic acid, and aconitic acid, and then passing cycles of periodically reversed electrical current through the base, the aqueous electrolyte and an anode, each cycle of current first flowing in one direction to plate'copper on the base for a period of time of from 0.01 second to 100 seconds, then the direction of current flow reversing for a period of time to deplate a portion of the previously plated copper, the coulombs applied during the deplating period equal to from 8% to 90% of the coulombs applied during the plating period, the plurality of cycles of periodically reversed current electrodepositing smooth sound copper on the base.

7. An addition agent composition to be added to acid copper electrolytes comprising essentially a mixture of at least 0.1% by weight of at least one 2-thiohydantoin compound and a substantial amount but not exceeding 80% by weight of at least one Water soluble organic carboxylic acid, the organic carboxylic acid being selected from the group consisting of citric acid, malic acid, maleic acig, linoleic acid, oxalic acid, adipic acid, and aconitic ac1 8. An addition agent composition to be added to acid copper electrolytes comprising essentially a mixture of at least 0.1% by weight of acetyl 2-thiohydantoin compound, and a substantial amount but not exceeding 80% by weight of citric acid.

9. An addition agent composition to be added to acid copper electrolytes comprising essentially about 118 parts by weight of at least one Z-thiohydantoin compound having at least one organic substituent at the l, 3 and 5 positions, about 1475 parts by weight of citric acid andv about 13,170 parts of powdered copper sulfate crystals.

10. An addition agent composition to be added to acid copper plating electrolytes comprising essentially a mixdantoin compound, and a substantial amount but not exceeding 80% by weight of a mixture of dextrin and at 7. least one water soluble organic carbo'xylic acid, the organic carboxylic acid being selected from the group consisting of citric acid, malic acid, maleic acid, linoleic 'acid, oxalic acid, adipic acid, 'and acon'itic acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,391,289 Beaver Dec. 18, 1945 8 Wilsfin Nov. 26, 1 946 Jem'st'edt Oct. 12, 1948 Phillips et 31. n. Aug. 7, 1 951 FOREIGN PATENTS Canada Nov. 22, 1949

Claims (1)

1. 2. AN AQUEOUS ELECTROPLATING ELECTROLYTE COMPRISING ESSENTIALLY COPPER SULFATE, SULFURIC ACID, FROM 0.0005 TO 0.05 OUNCE PER GALLON OF AT LEAST ONE 2-THIOHYDANTOIN COMPOUND FROM EFFECTIVE AMOUNTS, UP TO 3 OUNCES PER GALLON OF AN ORGANIC CARBOZYLIC ACID SOLUBLE IN WATER, THE ORGANIC CARBOXYLIC ACID BEING SELECTED FROM THE GROUP CONSISTING OF CITRIC ACID, MALIC ACID, MALEIC ACID, LINOLEIC ACID, OXALIC ACID, ADIPIC ACID, AND ACONITIC ACID, AND FROM 0.1 TO 5 OUNCES PER GALLON OF DEXTRIN.

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