DE1097231B - Acid galvanic copper bath - Google Patents

Description

Acid electroplating copper bath The invention relates to an acid electroplating copper bath Copper bath; it is based on the task by adding a novel additive to the galvanic acid copper bath during galvanizing lighter and smoother copper deposits to create.

Numerous additives have been proposed which acidic copper electrolytes are to be incorporated, so that improved copper coatings can be generated. However, the additives heretofore proposed were not satisfactory. For example, one has with some of the previously proposed additives can only achieve poor results in terms of brightness and smoothness. Also is the range of brightness achievable with some of these additives relatively tight, and in some cases the plating solution's ability to Depositing metal evenly on an irregularly shaped cathode is considerable by adding the additive.

Another disadvantage of using many of the previously available additives occurred, is that that from electrolytic baths, which contain such additives, precipitated copper is often quite crumbly is. This friable condition is undesirable because it makes the processing of the galvanized parts much more difficult. Stripes and ribs also usually appear when acidic copper electrolytes contain previously known additives.

There are also additives for copper sulfate and sulfuric acid plating baths become known, which consist of acetylthiourea. Even with these well-known Additives should produce uniform, high-gloss coatings. Acetylthiourea however, it is only suitable if it is accompanied by another known addition such as dextrin, caramel or molasses is used and when the content of chloride anions is kept within relatively narrow limits in the electroplating bath. Better ones Results are obtained by adding a 2-thiohydantoin, e.g. B. of 1-acetyl-2-thiohydantoin, won, but even with this addition, the coatings still had veil streaks on, at least at certain current densities. Also was the shine of the galvanized Coatings sometimes uneven; matt and coarse-grained structures resulted, when working with direct current of high current density.

All these disadvantages are eliminated by the proposed invention. A bath for the electrodeposition of copper coatings is proposed, which consists of copper sulfate and sulfuric acid and is characterized by a content of a reaction product obtained during mixing and heating in equimolar amounts of at least one compound with the core and at least one alkylolamine from the group of primary, secondary and tertiary alkylolamines in which the groups substituted for the nitrogen atom are hydrogen, alkyl or alkylol groups having at least 1 to 4 carbon atoms, at least one alkylol group being present in one molecule.

From the description that follows, further details of the Invention.

This description also describes process steps for production of the additive described. However, these procedural steps are not the subject matter the invention.

If these reaction products are added to the electrolyte, one obtains a bath whose ability to make metal uniformly on an irregularly shaped Cathode, like body with depressions, to deposit, is relatively large. In addition, the brightness range is at both the upper and lower limits the current density is expanded far beyond the extent normally achieved with the previously available additives is achieved. The expansion of the brightness range for high current density allows higher current densities to be used, thereby the duration of precipitation can be shortened with the same precipitation intensity.

Another advantage of incorporating the additive according to the invention in acidic copper electrolytes it can be seen that the polishing ability of the precipitated Copper is improved. However, it is common the downcast Copper, which is obtained from baths with additives according to the invention, already so bright that polishing is not necessary at all. But it should be for some If the copper coating obtained does not have its full shine, it can because of its high quality and its fine-grained consistency through very light Polishing to keep its shine, then with bright coatings of nickel, Chrome or the like. To be provided.

Examples of particularly suitable compounds with the core are acetylthiourea, 2-thiohydantoin and substitution derivatives of 2-thiohydantoin with at least one organic substituent in positions 1 and 5. The core of these substitution derivatives of 2-thiohydantoin has the following structure: Various organic radicals can be substituted at the 1 or 5 position, or both, so long as the compound does not become so insoluble that it does not dissolve in the acidic copper electrolyte sufficiently to cause a substantial improvement in the brightness and smoothness of the deposited copper. Examples of suitable compounds are: 1-acetyl-2-thiohydantoin, 5- (2-hydroxylbenzal) 2-thiohydantoin, 5-furfural-2-thiohydantoin, 5-benzal-2-thiohydantoin, 1-methyl-2-thiohydantoin. More examples of connections to the core which are suitable for reaction with alkylolamines to produce compounds according to the invention are 2-thiobarbituric acid and substitution derivatives of 2-thiobarbituric acid. The core of these 2-thiobarbituric acid derivatives has the following structure: Various organic radicals can be substituted for the hydrogen in the 1, 5 and / or 6 position, provided that the resulting compound obtained after the reaction with the alkylolamine is soluble in the acidic plating bath. Examples of suitable compounds of this type are: 2-thiobarbituric acid, 1-acetyl-2-thiobarbituric acid, 1-benzoyl-2-thiobarbituric acid, 1,5-diacetyl-2-thiobarbituric acid. Examples of alkylolamines are: monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, tripropanolamine, monobutanolamine, dibutanolamine, tributanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, monoisobutanolamine, diisobutanolamine, methylethanutanolamine, methylethanutanolamine, methylethanutanolamine, and methylethanutanolamine.

The novel reaction product according to the present invention can can easily be prepared by taking approximately equimolar amounts of the two essential starting compounds mixed together and heated so that they react and produce the desired additional substances. It should in general Alkylolamine can be used in excess. The preparation of the reaction products is clear from the following specific example. Example A 1 mole of acetylthiourea and 1 mole of 1-acetyl-2-thiohydantoin are in 1.5 moles of monoethanolamine and 1 mole of isopropanolamine dissolved; the mixture is heated to a temperature above 80 ° C. After After cooling, a solid product crystallizes out of the solution. The crystals are washed with alcohol and are then suitable as an additive for the acidic copper bath.

The additives according to the invention can alone or together with certain already known additives added to the acidic copper plating baths will. So one has z. B. the reaction product of 1-acetyl-2-thiohydantoin and monoethanolamine added to a series of acidic copper baths, which firstly contain phenolsulfonic acid, secondly, thiourea, thirdly, glue, and fourthly, metallic additives such as Contained cadmium and the like. In each case, bathrooms that either do that additives according to the invention contained alone or together with known additives, Better copper precipitation is achieved than with baths which only use the known additives contained.

The addition of the novel reaction products to acidic copper baths enables a copper coating with a fine grain, high smoothness and a shiny appearance.

The increased gloss and smoothness of the copper deposit occur with an addition of 7.5-10-4 g per liter of additive. That Additive can be used in amounts up to 3.75 g / l. The most favorable proportion is 7.5 .10-3 to 7.5 # 10-2 g per liter.

It has been found that even better results are obtained if a smaller amount of chlorides in the form of chloride ions is added to the bath containing the additives according to the invention. Commercial hydrochloric acid (370/1) can be used for this purpose, in an amount sufficient to produce about 7.5-10-3 to 0.45 g of chloride ions per liter of electrolyte, depending on the amount of in the additive contained in the electroplating bath. The known acidic copper baths usually consist of an aqueous solution containing 150 to 300 g of copper sulfate and 9.75 to 97.5 g of sulfuric acid per liter. An acidic copper bath currently in widespread use in industry consists of a solution of 210 g of copper sulfate crystals and 60 g of 98% sulfuric acid per liter. In these acidic copper electrolytes, the additives according to the invention are used in an amount of 7.5. 10-4 to 3.75 g per liter of electrolyte introduced. The best results have been obtained with an additive of 7.5 # 10-3 to 7.5-10-2 per liter. Of course, the additive must be renewed from time to time. When using these additives, very good results are obtained when the temperature of the electrolytic bath is between 4.5 and 65 ° C. Excellent copper deposits are obtained at bike temperatures of 21 to 52 ° C. These latter temperatures correspond to the most favorable temperature range.

The electric current can flow either continuously or periodically change direction. Using direct current will give very good results achieved. However, excellent coatings are obtained with periodic currents changing direction. The precipitates generated with such streams stand out due to the lack of nodes as well as due to edges and faces which are essential are smoother than those achieved with direct current.

The following examples show the use of additives according to the invention. Example I. Copper sulfate [Cu SO, -5 H2 O]. . . . . . . . . . . 210 g / 1 Sulfuric acid (98%). . . . . . . . . . . . . . . . . . . 60 g / 1 Reaction product from 1-acetyl- 2-thiohydantoin and monoethanol amine (see example A). . . . . . . . . . . . . 2.25-10-2 g / 1 This bath was used at various temperatures between 4.5 and 65 ° C with very good results. Bath temperatures of 21 to 52 ° C gave the best results.

Copper is deposited on rectangular brass plates, namely using direct current at a current density of 0.5 to 20 A / dm2. In in all cases there was a copper coating of fine grain and good gloss.

Periodically changing currents were also used. The course of the current was as follows: Deposition time Removal time (a) 2 seconds i / 3 seconds (b) 5 seconds I second (c) 10 seconds 2 seconds (d) 15 seconds 3 seconds (e) 5 seconds 5 seconds (f) 40 seconds 20 seconds (g) 60 seconds 30 seconds For the course (a) and (b) the current density was 5A / dm2, for the course (c) and (d) 6 A / dm2 in both current directions. During the deposition time of periods (e), (f) and (g) the current density was 7.5 A / dm2. During the removal time of course (e), the current density was 0.75 A / dm2 (10% of the amount of charge that had passed through flowed back). During the ablation periods of course (f) and (g) the current density was 7.5 A / dm2. Because of the periodically changing direction of the current, extremely smooth copper precipitates were obtained in all cases.

In the course of further testing, 0.375 g of the reaction product was obtained of 2-thiohydantoin and monoethanolamine per liter instead of that used in Example I. Reaction product used. This solution was used for direct current methods Copper coatings made on bodies that fully match those described in Example I. were equivalent.

In a further investigation, 7.5-10-4 g of the reaction product of acetylthiourea and diethanolamine per liter were used in place of the reaction product from Example I. The solution so formed provided copper deposits which were semi-glossy and of such a quality that a very light polish was sufficient to prepare the surfaces for the subsequent deposition of glossy nickel or chromium. Example II Copper sulfate [Cu SO, -5 H20]. . . . . . . . . . . 210 g / 1 Sulfuric acid (98 ° / o). . . . . . . . . . . . . . . . . . . 60 g j1 Reaction product from 2-thio- hydantoin and monoethanolamine ... 7.5-10-3 g / l If direct current is applied to this electrolyte, excellent precipitations are achieved at current densities between 0.5 and 20 A / dm2. A periodically changing current with a deposition time of 20 seconds per period and an ablation time of 4 seconds per period produced excellent copper coatings at current densities of up to 20 A / dm.

The bath of Example II was changed by gradually larger amounts of the reaction product (up to) 4.5-10-2 g / l would be added. the The quality of the copper precipitates gradually increased. The downcast Copper is particularly characterized by the fact that the grain size of the copper is very fine was.

It was also found that by adding water-soluble Carboxylic acids or from dextrin or dextrose to the acidic copper electrolyte, which contains the additives according to the invention, the service life of the additives at maximum Effectiveness is longer than when using the reaction products according to the invention alone.

Citric acid, aconitic acid, and succinic acid are examples of acids that which have proven themselves as such additives. Any of these acids, but also mixtures Such acids can be used in proportions of 7.5-10-3 to 22.5 g / 1 or up to to their solubility limit in the electrolyte can be used, dextrin or dextrose can be added in amounts between 6-10-2 and 1.875 g / l of the electrolyte; however, quantities down to 7.5-10-3 and up to 37.5 g of the electrolyte can also be used can be applied. Dextrin, dextrose and carboxylic acid can be used alone or together can be applied.

The following examples show the use of some of the last-mentioned additives in acidic copper electrolyte baths which contain the reaction products according to the invention. Example III Copper sulfate [GU S 04-5 H2 O]. . . . . . . . . . . . 210 g / 1 Sulfuric acid (98 0%). . . . . . . . . . . . . . . . . . . . 60 g / 1 Reaction product from 1-acetyl-2-thio- hydantoin and monoethanolamine .. 7.5 -10-3 g / 1 Dextrin (yellow). . . . . . . . . . . . . . . . . . . . . 6 - 10-2 g / 1 The copper precipitates obtained from this electrolyte had a better color appearance than those obtained from electrolytes without dextrin. Shiny copper coatings were produced from this electrolyte in approximately twice as long as with the electrolyte of Example I. Example IV Copper sulfate [Cu S 0, -5 H2 O]. . . . . . . . . . . . 210 g / 1 Sulfuric acid (98 0/0). . . . . . . . . . . . . . . . . . . . 60 g / 1 Reaction product from 1-acetyl 2-thio- hydantoin and monoethanolamine .. 7.5 - 10-3 g / 1 Hydrochloric acid (370/0) ... . . . . . . . . . . . . . . . . 4.5 -10-2 g / 1 The copper coatings obtained with this electrolyte had a slightly better color appearance than those obtained with the electrolyte of Example III, although they were not significantly stronger with their brightness. Example V Copper sulfate [Cu S 0, -5 H2 O]. . . . . . . . . . . . 210 g / 1 Sulfuric acid (98 0/0). . . . . . . . . . . . . . . . . . . . 60 g / 1 Reaction product from 1-acetyl-2-thio- hydantoin and monoethanolamine ... 7.5. 10-3 g / 1 Citric acid ......................... 1.875 g / 1 This electrolyte resulted in bright, shiny copper deposits, but the coatings took longer to produce than when the electrolyte of Example IV was used.

Another satisfactory electroplating bath is obtained by adding 6 # 10-2 g of dextrose per liter to the electrolyte of Example V. Example VI The following electrolyte is produced: Copper sulfate [Cu S 04-5 H2 O]. . . . . . . . . . . . 210 g / 1 Sulfuric acid (98 ° / 0). . . . . . ... ... . . . . . . . . 60 g Reaction product from 5-furfural 2-thiohydantoin and methyl mono- ethanolamine. . . . . . . . . . . . . . . . . . . 7.5 10-3 g / 1 Hydrochloric acid (370%). . . . . . . . . . . . . . . . . . 2.25 10-2 g / 1 Dextrin. . . . . . . . . . . . . . . . . . . . . . . . . 3 10-2 g / 1 Those generated using this electrolyte Precipitation has a better color appearance, but require a longer time for their production than that obtained from the electrolyte of Example I.

To introduce the chloride ions into the electrolyte, alkali metal chlorides, such as sodium chloride and other ionizable chloride salts can be added.

Claims (1)

PATENT CLAIMS: 1. Bath for the galvanic deposition of copper coatings, consisting of copper sulfate and sulfuric acid, characterized by a content of a reaction product obtained during mixing and heating in equimolar amounts of at least one compound with the core and at least one alkylolamine from the group of primary, secondary and tertiary alkylolamines in which the groups substituted for the nitrogen atom are hydrogen, alkyl or alkylol groups having at least 1 to 4 carbon atoms, at least one alkylol group being present in one molecule. z. Bath according to Claim 1, characterized by a content of the reaction product in an amount of 7.5-10-4 to 3.75 g / 1. 3. Bath according to claim 1 and 2, characterized by the content of a reaction product with 1-acetyl-2-thiohydantoin as a reaction component. 4. Bath according to claim 1 to 3, characterized by an additional content of chloride ions in an amount of 7.5-10-3 to 0.45 g / 1. 5. Bath according to claim 1 to 4, characterized by the additional content of a water-soluble carboxylic acid in an amount of 7.5-10-3 to 22.5 g / l. 6. Bath according to claim 1 to 5, characterized by an additional content of dextrin and / or dextrose in an amount of 7.5-10-3 to 37.5 g / 1. References considered: British Patent No. 710,474; U.S. Patent No. 2,602,774.