EP1192297A1 - Acid bath for galvanic deposition of shining gold and gold alloy layers and brightener therefor - Google Patents

Abstract

The invention relates to an acid bath for galvanic deposition of shining gold and gold alloy layers and to a brightener therefor, using compounds of formula (I): R - SOm-H, wherein m represents 3 or 4 and R represents a straight or branched-chained or cyclic alkyl group having up to 20 C atoms and also an aryl or heteroaryl group having up to 10 C atoms if m = 4, which can be optionally substituted one or more times by straight or branched-chained alkyl groups having 1 to 14 C atoms. The utilization of said compounds as an additional brightener expands the current density work area with little negative influences due to pH value changes and increases current efficiency and deposition performance.

Description

 Acidic bath for the galvanic deposition of shiny gold and gold alloy layers and a gloss additive therefor

Description:

The invention relates to an acid bath for the galvanic deposition of shiny gold and gold alloy layers and a gloss additive therefor.

Galvanic gold baths usually contain gold and optionally one or more alloy elements in dissolved form.

Such electrolytes are mainly based on gold cyanide complexes. It is necessary to adjust these electrolytes to a weak to moderately acidic pH using inorganic and / or organic acids and buffer salts.

So that shiny gold or gold alloy layers are deposited from such baths, they usually contain certain inorganic or organic compounds as so-called "gloss additives".

A typical, very frequently used gloss additive is, as described for example in DE 23 55 581, the compound pyridine-3-sulfonic acid.

Such additives shift or expand the working range, that is the range of applicable current density, in which a shiny gold plating is deposited, in the direction of high current densities. The use of higher current densities in turn allows deposition at a higher speed.

On the other hand, the working range of such gold baths also depends on the pH of the electrolyte. It applies here that the working range (applicable current density range) is narrowed at a higher pH value, but at the same time the current yield and thus the separation speed is increased.

It was therefore an object of the invention to optimize the working conditions and the separation performance of such acidic gold baths in such a way that, on the one hand, a maximum current density working range is achieved with the least possible negative influence by pH changes and, on the other hand, a maximum current efficiency and separation speed is achieved.

Surprisingly, it has now been found that this can be achieved if such acid baths for the deposition of shiny gold layers as a further additive to the gloss add at least one compound of the general formula I.

R - SO _m -H (I)

is added in which

m the numbers 3 or 4 and

R is a straight-chain or branched-chain or cyclic alkyl group with up to 20 C atoms and in the case of m = 4 also an aryl or heteroaryl group with up to 10 C atoms, which may be one or more times with straight or branched-chain alkyl groups with 1 to 14 C atoms can be substituted,

means.

The invention thus relates to an acidic bath for the electrodeposition of shiny gold and gold alloy layers, containing gold and optionally one or more alloy elements in dissolved form and at least one organic compound as an additive, characterized in that the bath as at least one compound of the additive general formula R - SO _m -H (I)

contains what

m the numbers 3 or 4 and

R is a straight-chain or branched-chain or cyclic alkyl group with up to 20 C atoms and in the case of m = 4 also an aryl or heteroaryl group with up to 10 C atoms, which may be one or more times with straight or branched-chain alkyl groups with 1 to 14 C atoms can be substituted,

means.

The gloss additives according to formula I are selected compounds from the classes of the alkyl sulfonates and the alkyl, aryl or heteroaryl sulfates. In formula I, when m stands for the numbers 3 or 4, R means a straight or branched chain or cyclic alkyl group with up to 20 C atoms. If m stands for the number 4, then R can also be an aryl or heteroaryl group with up to 10 C atoms, it being possible for these to be substituted one or more times with straight-chain or branched-chain alkyl groups with 1 to 14 C atoms .

The compounds of the formula I are known per se and are either commercially available or can be prepared readily by standard processes.

These compounds are sufficiently water soluble and compatible with the electroplating bath. The compounds have surfactant properties, the corresponding action being reduced by less than 4 for a total number of carbon atoms and generally no longer providing adequate solubility if the total number of carbon atoms is more than 20. Preferred gloss additives are compounds of the formula I in which R represents straight-chain or branched-chain or cyclic alkyl groups having 5 to 12 carbon atoms and in particular branched-chain alkyl groups having 6 to 10 carbon atoms.

Typical gloss additives according to the invention are

Pentyl sulfonate Pentyl sulfate Hexyl sulfonate Hexyl sulfate Heptyl sulfonate Heptyl sulfate Octyl sulfonate Octyl sulfate Nonyl sulfonate Nonyl sulfate Decyl sulfonate Decyl sulfate Dodecyl sulfonate Dodecyl sulfate Cyclohexyl sulfonate Cyclohexyl sulfate.

These compounds can also be in the form of their salts.

Branched-chain and short-chain connections are particularly suitable due to their lower tendency to foam, especially in processes and systems in which strong foam formation interferes, e.g. in air-moving electrolytes where

Drum processing, in systems for high-speed separation (spraying systems) and in systems for selective separation, e.g. Diving cells.

The use of the further gloss additive according to the invention in acid baths for the electrodeposition of shiny gold and gold alloy layers is advantageously carried out in a concentration range from 0.01 to 10 g / l. Baths according to the invention which contain the gloss additive according to formula I in a concentration of 0.1 to 5 g / l are particularly advantageous. Through the use of the compounds of the formula I according to the invention as a further gloss additive in galvanic gold baths of otherwise customary composition, the applicable current density working range is expanded in an unexpected manner and at the same time the current yield and the separation efficiency are drastically increased in part.

To produce the gold baths according to the invention, it is possible to start from many common and commercially available galvanic, weakly acidic gold baths by adding the corresponding amount of compound of the formula I to them. The qualitative and quantitative composition of such gold baths is well known to the person skilled in the art from literature and practice and therefore requires no further explanation. In any case, these contain gold in dissolved form, starting from gold salts or gold complex salts, predominantly gold cyanide complexes being used. The Bader can also contain alloying elements in the form of dissolved salts or complex salts. The bathers also contain inorganic and / or organic acids, corresponding salts and, if appropriate, buffer and conductive salts in order to adjust the pH and the conductivity. In order to deposit shiny, smooth gold layers, organic compounds are usually contained, which mostly have surfactant properties and act as brighteners. A typical and well-preserved brightener of this type is pyridine-3-sulfonic acid.

Furthermore, conventional gloss additives also come

Nicotmic acid,

Nicotmsaureamid,

3- (3-pyπdyl) acrylic acid

3- (4-Imιdazolyl) acrylic acid

3-pyπdylhydroxymethanesulfonic acid Pyridine

Picolin

Quinoinsulfonic acid

3-aminopyridine

2,3-diaminopyridine

2,3-di- (2-pyridyl) pyrazine

2- (pyridyl) -4-ethanesulfonic acid

1- (3-sulfopropyl) pyridinium betaine

1- (3-sulfopropyl) isoquinolinium betaine

and their salts and derivatives. The galvanic gold baths according to the invention typically contain approximately

0.1 - 50 g / 1 gold as a gold cyanide complex

0 - 50 g / 1 alloy metals such as iron, cobalt, nickel, indium, silver, copper, cadmium, tin, zinc, bismuth, arsenic, antimony as salt or complex salt

10 - 200 g / 1 citric acid / citrate as buffer and / or conductive salts

0.1 - 10 g / 1 pyridine-3-sulfonic acid as a brightener

0.1 - 5 g / 1 compound of the formula I as a further gloss additive according to the invention,

wherein the pH of the bath is adjusted to 3 to 6, preferably 4 to 5. The use of the gloss additive according to the invention brings about a number of practical advantages. The separation performance can be increased significantly under otherwise unchanged conditions. Due to the wider working area, the fine adjustment of the working method is less critical, whereby the risk of sudy separation is significantly reduced.

However, it is also possible to work with higher pH values with an unchanged working range. This also makes it possible to increase the separation performance.

Alternatively, a low gold content can be used with the same separation performance. The advantages are the lower carry-over due to electrolytes adhering to the goods and the lower capital commitment.

Example 1:

In a gold-cobalt electrolyte with

10 g / 1 gold in the form of potassium gold (I) cyanide 0.5 g cobalt as cobalt sulfate 100 g / 1 citric acid

3 g / 1 pyridine-3-sulfonic acid adjusted to pH 4.2 with potassium hydroxide

is in a Hull cell (test conditions: platinized titanium anode, temperature 50 ° C, duration 2 min, movement 500

U / min by magnetic stirring bar 25 mm) with a cell current of 2 A a working range up to 3 A / dm ² achieved. The current yield at 3 A / dm ² is 48%; the deposition speed is 0.98 μm / min.

By adding 1 g / 1 nonyl sulfate, the maximum applicable current density is increased to over 5 A / dm ² . This speaks of widening the work area by over 66

When the pH is then raised to 4.4, a working range of up to 44 .A / dm ^{2 is} achieved; the separation rate is 1.05 μm / min.

At pH 4.6 the working range extends up to 3 A / dm ² and a deposition speed of 1.15 μm / min is achieved

Example 2:

In a gold-nickel electrolyte with

10 g / 1 gold in the form of potassium gold (I) cyanide 0.7 g nickel in the form of nickel sulfate 100 g / 1 citric acid

3 g / 1 pyridine-3-sulfonic acid adjusted to pH 4.2 with potassium hydroxide

a maximum current density of 3 A / dm ² is reached on pre-nickel-plated sheets of size 25 x 40 mm (experimental setup: 1 liter beaker, platinum-coated titanium anode, bath movement 200 rpm using a magnetic stirring bar 60 mm, movement of goods 5 cm / s). The cathodic current yield at 3 A / dm ² is 52% and the deposition rate is 1.0 μm / min.

The addition of 0.5 g / 1 decyl sulfate increases the maximum applicable current density to over 7 A / dm ² . At 7 A / dm ² , the current yield is still 26%, the separation efficiency increases to 1.18 μm / min. This corresponds to a speed increase of 18%. Example 3:

In a gold-iron electrolyte with

10 g / 1 gold in the form of potassium gold (I) cyanide 0.05 g iron as iron (III) citrate 100 g / 1 citric acid

3 g / 1 pyridine-3-sulfonic acid adjusted to pH 4.2 with potassium hydroxide

a maximum current density of 5 A / dm ^{2 is} achieved on sheets of size 25 x 40 mm (conditions see example 2). The cathodic current yield is 31% and the deposition rate is 1.0 μm / min.

By adding 4 g / 1 hexyl sulfate, the maximum applicable current density is increased to over 6 A / dm ² . At 6 A / dm ² , the current yield is still 30%; the separation rate increases to 1.16 μm / min. This corresponds to a speed increase of 16%.

Example 4:

In a gold-cobalt electrolyte with

10 g / 1 gold in the form of potassium gold (I) cyanide 0.5 g cobalt as cobalt sulfate 100 g / 1 citric acid

1 g / 1 of 3- (3-pyridyl) acrylic acid adjusted to pH 4.2 with potassium hydroxide

a working range of up to 5 A / dm ^{2 is} achieved in a Hull cell (test conditions: platinum-plated titanium anode, temperature 50 ° C., duration 2 min, movement 500 rpm by means of a magnetic stirring bar 25 mm) with a cell current of 2 A. The current yield at 5 A / dm ² is 26%; the separation speed is 0.83 μm / min. By adding 1.5 g / 1 octyl sulfate, the maximum applicable current density is increased to over 8 A / dm ² . At 8 A / dm ^{2, the} current yield is still 19%; the separation rate increases to 1.0 μm / min.

Example 5:

In the gold-cobalt electrolyte from Example 1, the maximum applicable current density is increased to over 5 A / dm ² by the addition of 1 g / 1 hexyl sulfonate. At 5 A / dm ² the current yield is 35.1%, the separation efficiency increases to 1.13 μm / min. This corresponds to a speed increase of 15%.

Example 6:

In the gold-cobalt electrolyte from Example 1, the maximum applicable current density is increased to over 7 A / dm ² by the addition of 1 g / 1 octyl sulfonate. At 7 A / dm ^{2 the} current yield is 26.2%, the separation efficiency increases to 1.18 μrα / min. This corresponds to a 20% increase in speed.

Example 7: Comparative example

In a gold-cobalt electrolyte (see example 1)

10 g / 1 gold in the form of potassium gold (I) cyanide 0.5 g cobalt as cobalt sulfate 100 g / 1 citric acid adjusted to pH 4.2 with potassium hydroxide

under the test conditions of Example 1, the influence on the working range and deposition rate Addition of octyl sulfate alone, pyridine-3-sulfonic acid alone and both substances determined together as gloss additives. Table 1 shows the result.

The combination of both substances drastically extends the work area and causes a significant increase in the separation speed.

Table 1:

Claims

Claims: 1. Acid bath for the electrodeposition of shiny gold and gold alloy layers, containing gold and optionally one or more alloy elements in dissolved form and at least one organic compound as a brightener, characterized in that the bath as a further brightener at least one compound of the general formula R - SO _m -H (I) contains what the numbers 3 or 4 and R is a straight-chain or branched-chain or cyclic alkyl group with up to 20 C atoms and in the case of m = 4 also an aryl or heteroaryl group with up to 10 C atoms, which may be one or more times with straight or branched-chain alkyl groups with 1 to 14 C atoms can be substituted, means. 2. Galvanic bath according to claim 1, characterized in that it contains as a further gloss additive at least one compound of formula I, wherein R is a straight or is a branched-chain alkyl group with 5 to 12 carbon atoms, preferably a branched-chain alkyl group with 6 to 10 carbon atoms. 3. Galvanic bath according to claim 1 or 2, characterized in that it contains the compounds pentyl sulfonate, hexyl sulfonate, heptyl sulfonate, octyl sulfonate, nonyl sulfonate, decyl sulfonate, dodecyl sulfonate, cyclohexyl sulfonate, pentyl sulfate, hexyl sulfate, hexyl sulfate, hexyl sulfonate Contains octyl sulfate, nonyl sulfate, decyl sulfate, dodecyl sulfate, cyclohexyl sulfate or their isomers. 4. Galvanic bath according to claims 1 to 3, characterized in that it contains 0.01 to 10 g / 1, preferably 0.1 to 5 g / 1, of compound of formula I. 5. Use of compounds of the general formula R - SO _m -H (I) wherein m the numbers 3 or 4 and R is a straight-chain or branched-chain or cyclic alkyl group with up to 20 C atoms and, in the case of m = 4, also or an aryl or heteroaryl group with up to 10 C atoms, which may be one or more times with straight or branched-chain alkyl groups with 1 to 14 C atoms can be substituted, means as a further gloss additive in acid baths for the galvanic deposition of shiny gold and gold alloy layers, containing gold and optionally one or more alloy elements in dissolved form and at least one organic compound as a gloss additive. 6. A method for the electrodeposition of shiny gold and gold alloy layers, characterized in that the deposition from a bath according to claims 1 to 4 takes place at a pH value of 3 to 6, preferably 4 to 5.