TW201333275A - Selective hard gold deposition - Google Patents

Abstract

The present invention relates to a process for the electrolytic deposition of gold on, in particular, electric contacts. The process is characterized in that particular additives which allow undesirable deposition of gold in regions of low current density to be prevented are added to the electrolyte.

Description

Selective hard gold deposition

The invention relates to a method for electrolytic deposition of gold, in particular on electrical contacts. The method is characterized in that a plurality of special additives are added to the electrolyte to prevent undesired gold deposition in the low current density region.

The use of specific additives in the field of metal plating is well known. In the case of gold and gold alloys, particularly hard gold (for example, AuNi, AuCo, AuFe), there are many additives for electrochemical methods and electrolysis. The commercial gold electroplating bath therefore contains not only gold and optionally one or more alloying elements in dissolved form, but also generally contains conductive salts and buffer salts and as a brightening agent or for other auxiliary purposes. Different inorganic and/or organic substances formed by deposition and layer formation.

Fine and hard gold coatings are used in a large number of industrial applications where wear resistance, chemical resistance, adhesion, weldability or wear properties are particularly important. For the electroplating of gold on electrical contacts, the prior art uses a masking technique in a continuous device (Edelmetallschichten; H. Kaiser; Eugen G. Leuze Verlag, 2002, 1st edition, pages 74-89 and Selektive Hochgeschwindigkeitsabscheidung von Edelmetallen Auf Bandanlagen; P. Wingenfeld, Galvanotechnik, 2/2004, page 335ff, Eugen G. Leuze Verlag) in order to selectively coat metal deposits in the functional area of the stylus. However, the bias below the mask In the runout zone (gap), there are a plurality of low current density regions in the case of electrolytic deposition. Here, in order to reduce costs, the deposition of the coating from the hard gold electrolyte should be avoided as much as possible. For this purpose, additives should be found which selectively inhibit the deposition of gold in this region.

Thus, for example, WO0028108 discloses a method for the reduction deposition of gold in which an anti-gold deposition agent is used. The compounds used herein are said to prevent, among other things, etch or corrosive secondary reactions between the metal surface and the gold during the deposition process. Such compounds are considered to be, in particular, certain amines or their reaction products with epoxy-carrying compounds.

According to GB 2028873, the addition of an alkyl polyamine such as tetraethylenepentamine to an electrolytic gold cadmium bath results in an abnormally stable gold deposit having a low contact resistance. In addition, the polyamine ensures that the carbon content in the gold deposits appears to be a special value and the cathode efficiency is reduced by up to 80%. However, it is recommended to use the corresponding gold cobalt or gold nickel alloy for this purpose.

No. 3,642,589 discloses additives which are added to an electrolytic bath containing gold and silver. These baths are used to deposit gold-based alloys. The additives mentioned above consist of a polymeric condensate of epichlorohydrin and an alkylene polyamine. For example, a condensate of epichlorohydrin and tetraethylenepentamine is added to an electrolyte containing gold and other alloy components such as nickel and cobalt. Very thick gold alloy layers can be deposited in this way without defects. However, since the electrolyte will contain free cyanide, the electrolytes discussed herein are used in the alkaline pH range. From the perspective of labor hygiene, this seems to be a disadvantage.

DE 3432784 likewise relates to an electrolytic bath from which a hard coating of gold-cobalt alloy can be deposited. The process described herein operates at current densities ranging from 0.1 to 3.0 A/dm ² and pH from 3.5 to 6.5, and it is recommended to add a reaction product having about one part of epichlorohydrin and two Part of the diaminoalkane, and also a part of the α,ω-dihaloalkane. The purpose of this article is to provide a high alloy steel product with a tightly bonded coating and to increase the current density upper limit for this process.

Gold or gold alloys may also be electrolytically deposited from a bath comprising, as mentioned in US Pat. No. 4,062, 736, which contains gold cyanide complex and a polyamine and epoxy chloride in a ratio of 1:2.5. a condensation product of propane. This bath operates in a pH range from 6 to 10 and additionally contains arsenic compounds as well as mild reducing agents. Such baths are said to ensure improved uniformity of the coating as well as better color stability.

According to EP 37535, when an amine carboxylic acid or a phosphonic acid is added to the bath in addition to the alloy component and a pH of less than 3 is set in the bath, the pure amine is also suitable for electrolysis of the gold (III) bath as well as gold ( III) A bright and highly ductile deposit is formed in the alloy bath. As the amine, for example, tetramethylenetetramine is used.

In FR 2410 082, polyamines and epichlorohydrin are also used in electrolytic baths having arsenic compounds and reducing agents as additional components. The bath used should have a pH of 6-10. The gold deposits produced in this way are said to have a particularly uniform thickness.

EP 2014801 describes a gold electrolyte that can be used to plate (among other things) contact materials. Such electrolytes contain a wide variety of additives. except In addition to hexamethylenetetramine, a complexing agent based on a nitrogen-containing and sulfur-containing carboxylic acid or alcohol and a brightening agent are also used. The deposition of gold in the low current density region is said to be prevented by means of such electrolytes.

Accordingly, it is an object of the present invention to indicate how excessive deposition of gold or gold alloy in the deflection zone of the mask can be avoided or at least reduced. The proposed method should be capable of operating with an electrolyte having a very simple composition and should be superior to the methods established in the prior art from an economic and ecological point of view.

This and other objects which will be apparent to those skilled in the art from the prior art can be achieved by a method having the characteristic features of item 1 of the scope of the patent application. A number of preferred embodiments of the method of the present invention are indicated in the scope of a plurality of patent applications that are subject to claim 1 of the patent application.

In a method for selective electrolytic deposition of gold or a gold alloy, in particular hard gold, an aqueous electrolyte having a pH of from 3 to 6 is used, the aqueous electrolyte comprising: gold ions in the form of a soluble complex; Optionally additional ions selected from the group consisting of cobalt, nickel, iron or mixtures thereof; aliphatic polyamines which are soluble in the electrolyte and which have at least 4 ethylene groups Units and at least 2 primary or secondary amine groups, and/or molar ratios from 1:1 to 1:5 are only aliphatic or aromatic a reaction product of an aromatic amine with an epoxy group-bearing compound, particularly epichlorohydrin; and a corresponding deposit by the following steps: immersing the substrate as a cathode in an electrolyte and an anode in contact with the electrolyte The setting of a sufficient current between the cathode and the electrolytic deposition of gold or a gold alloy, in particular hard gold, is completely unexpected but still advantageously achieves the stated purpose. This method presented here makes it possible for the first time to reduce the deposition of gold or gold alloys in low current density regions and at the same time to make the deposition factor a better current density range from a process point of view. Not affected internally. This causes a savings of about 10%-30% of the gold used.

The gold will be present in the form of ions dissolved in the electrolyte. As regards the source of gold, it is possible for all cyanide complexes, chlorinated complexes, sulfite complexes and nitriamide complexes of gold to be considered by those skilled in the art for this purpose. use. Known gold compounds can be found in the following reference (Edelmetallschichten; H. Kaiser; Eugen G. Leutze Verlag, 2002, 1st edition, pages 35-45). For this purpose, it is preferred to use a cyanate (I) complex. Very particularly preferred in this context is the potassium salt of the gold cyanide complex: K[Au(CN) ₂ ]. The gold compound is used in the electrolyte to be used in the following concentrations: 0.005-0.2 mol/l, preferably 0.025-0.1 mol/l, and very particularly preferably 0.05-0.08 mol/l. It may be noted that the electrolyte desirably does not contain additional free cyanide. All of the cyanide used is introduced into the electrolyte in the form of the complex shown above.

The deposits produced in accordance with the present invention may likewise be composed of a gold alloy. For alloys, hard gold is found to be useful in this regard because The contacts should be able to withstand specific mechanical stresses. Hard gold is generally understood to be an alloy of gold and one of the metals selected from the group consisting of iron, cobalt, nickel or a mixture thereof. The latter are likewise advantageously present in the form of ions which they dissolve in the electrolyte. As the compound which can be dissolved as a corresponding ion in the electrolyte, mention may be made especially of their water-soluble salts having an anion selected from the group consisting of chloride ion, bromide ion, carbonic acid. Roots, bicarbonate, phosphate, hydrogen phosphate, sulfate, citrate, mesylate, tartrate, oxalate, and nitrate. The salts mentioned herein are advantageously used in the electrolyte at a concentration of 0.0001 to 0.1 mol/l, particularly preferably 0.0025 to 0.02 mol/l, and very particularly preferably 0.005 to 0.015 mol/l. It may be noted that the presence of other metals as well as non-metal additional ions in the electrolyte is not excluded according to the invention. However, for cost reasons, the electrolyte should be as simple as possible. From this point of view, the addition of additional salts or other inorganic compounds can be dispensed with, among other things. In particular, no additional (non)metals should be present in the electrolyte other than those mentioned herein as optional. It is very particularly preferable to dispense with the addition of arsenic, silver and/or cadmium.

It is possible in this case to act as an aliphatic polyamine for the deposition of a current density specific inhibitor of gold or gold alloy from an electrolytic bath, particularly advantageously having at least 4 ethylene units and at least 2 primary amines or two Those of the amine group. This definition encompasses polyamines having at least 4 ethylene units in a row between terminal amine groups and polyamines having amine groups on either side of all or at least some of the ethylene units. The two general formulas for the latter are shown by the following examples:

1. NH ₂ -(CH ₂ -CH ₂ -NR ₁ -) _n CH ₂ -CH ₂ -NH ₂

n 3 R _1,2,3,4 =H or an aliphatic group (for example, methyl, ethyl, (iso)propyl, (normal, secondary, iso)butyl)

It may be noted that the aliphatic polyamines are aliphatic polyamines soluble in the electrolytes of the invention at the amounts shown below. Thus, at a given pH of 3-6 (specifically 4-5) of the electrolyte, there is an upper limit to the chain length or number of amine groups in the polyamine. The upper limit of the chain length between the two amine groups of the aliphatic amine is expected to be 8 carbon atoms, preferably 6 carbon atoms, and especially good is 4 carbon atoms. The number of secondary amines and/or primary amine groups may likewise have an upper limit of 10. Particularly preferred are polyamines having from 3 to 9 amine groups in the backbone, preferably from 4 to 7 amine groups, and particularly preferably from 5 or 6 amine groups. Advantageous polyamines are those which can be found in the literature cited at the outset and which comply with the standards herein. It is particularly preferred to use a polyamine selected from the group consisting of tetraethylenepentamine and pentaethylenehexamine. The aliphatic polyamine is used in the electrolyte to be used in the following concentrations: 0.001-0.5 mmol/l, particularly preferably 0.005-0.4 mmol/l, and very particularly preferably 0.01-0.03 mmol/l.

As an alternative or in addition, the reaction product of an aliphatic or aromatic amine with an epoxy-carrying compound, in particular an epihalohydrin such as epichlorohydrin, can likewise be used as an additive in the electrolyte. It may be noted that the reaction product referred to herein is formed solely from the amine and the epoxy-carrying compound. Such compounds are known from the prior art. In this respect, reference is made to the literature cited in the opening paragraph, in particular to WO 0028108, the disclosure of which is incorporated herein by reference. The reaction product between the two types of compounds can advantageously be formed in a ratio of epoxy derivative to amine from 1:1 to 1:5. Particularly preferred is a range from 1:2 to 1:4, very particularly preferably about 1:3 (based on the amount of moles). With regard to aliphatic or aromatic amines, it is possible here to select all compounds which will be considered by one of ordinary skill in the art in this context. Those compounds disclosed in the literature cited at the outset are particularly suitable. Particularly preferred for such amines are those selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, pentaethylenehexamine, and tetrakiene. Ethylpentamine, hexamethyleneheptaamine, heptaethylene octaamine, imidazole, pyridazine, diaminopropylamine. The reaction product under consideration here is used in the electrolyte to be used in the following concentrations, namely: 0.00001-2 g/l, particularly preferably 0.0001-0.5 g/l, very particularly preferably 0.0001-0.1 g/ l, and the best is 0.0001-0.05 g/l. Advantageously, a polyamine having a molar ratio of about 1:3 containing 4 to 6 amine groups (particularly 5 amine groups) and epichlorohydrin, or a molar ratio of about 1:1 A reaction product of a tertiary amine with epichlorohydrin is present in the electrolyte.

The current density established in the electrolyte between the cathode and the anode during the deposition process can be selected by one of ordinary skill in the art based on the efficiency and quality of the deposition. The current density in the electrolyte is advantageously set from 0.5 to 100 A/dm ² depending on the application and type of plating apparatus. The current density can optionally be increased or decreased by matching device parameters such as the structure of the coating unit, flow rate, anode and cathode conditions, and the like. 1-100 A/dm ² , preferably 2-90 A/dm ² , and very particularly preferably a current density of 4-80 A/dm ² is advantageous. The pH range can be set by those of ordinary skill in the art at the regions mentioned at the outset. A pH of from about 4 to 5, particularly preferably about 4.5, of the electrolyte is advantageous.

When using an electrolyte, it is possible to use different insoluble anodes. For the insoluble anode, it is preferred to use an insoluble anode composed of a material selected from the group consisting of platinumd titanium, graphite, ruthenium-transition metal mixed oxide, and a special carbon material (" Diamond-like carbon", DLC) or a combination of such anodes. Particularly preferred are mixed oxide anodes composed of cerium mixed oxide, cerium-titanium mixed oxide or cerium mixed oxide. Further suitable anode materials can be found in Cobley, AJ, et al. (The use of insoluble Anodes in Acid Sulphate Copper Electrodeposition Solutions, Trans IMF, 2001, 79(3), 113. And found in page 114). If an insoluble anode is used, a particularly preferred embodiment of the method is obtained when using a direct contact membrane anode as described in DE 102010055143.

In the electrolyte according to the invention, anionic and nonionic surfactants, such as polyethylene glycol adducts, fatty alcohol sulfates, alkyl sulfurs Acid esters, alkyl sulfonates, aryl sulfonates, alkyl aryl sulfonates, and heteroaryl sulfates, as well as their salts and derivatives, are typically used as wetting agents (see also: Kanani) , N: Galvanotechnik; Hanser Verlag, Munich Vienna, 2000; page 84ff).

For suitable brighteners, it is possible to use, for example, DE 2355581 and DE 1000 7325 A1 for 3-(4-imidazolyl)acrylic acid, 3-pyridylhydroxymethanesulfonic acid, pyridine, pyridinesulfonic acid, pyridinecarboxylic acid. , nicotinamide, 3-(3-pyridyl)acrylic acid, quinoline sulfonic acid, 3-aminopyridine, 2,3-diaminopyridine, 2,3-bis(2-pyridyl)pyrazine, 2 -(pyridyl)-4-ethanesulfonic acid, 1-(3-sulfopropyl)pyridinium betaine, 1-(3-sulfopropyl)isoquinolinium betaines, and salts and derivatives thereof.

It may be noted that the method of the present invention preferably ensures that only a deposit of gold or gold alloy is ensured by the use of electrical current. The use of additional reducing agents can therefore be completely dispensed with, which is advantageous. Likewise, it is not necessary to use any compound selected from the group consisting of arsenic compounds, salicylates, polyvinylpyrrolidone, nitrogen-containing or sulfur-containing carboxylic acids in the process of the invention. , phosphonic acid, alcohol and aromatic nitro compounds.

Can be clearly seen from the graph depicted in the low current density range of less than 4 A / dm ^2, the additive has great influence on the deposition rate of the hard gold electrolyte. Here, a suitable polyamine (alone) and a reaction product of epichlorohydrin and an amine have an inhibitory effect on hard gold deposition. The use of an optimal amount of inhibiting species in the low current density range from 0.5 to 4 A/dm ² resulted in a reduction in deposition rate of up to 80%, from about 80 mg/Amin to 15 mg/Amin. This causes less or even no hard gold to be deposited in these areas, which ultimately illustrates the savings in expensive precious metals and thus reduces the cost of coating the coating. The method described herein and described with all its advantageous and preferred embodiments is therefore suitable for producing electrical contacts.

Example: Illustrative electrolyte 1:

Aqueous hard gold electrolyte having a reaction product of an epihalohydrin and an aliphatic amine

Illustrative electrolyte 2:

Expanding the working range of aqueous hard gold electrolyte by means of a reaction product

Illustrative electrolyte 3:

Aqueous hard gold electrolyte with polyamine

Illustrative electrolyte 4 (not according to the invention)

Hard gold electrolyte with ineffective polyamine (See Figure 4)

Overall experimental description: Method steps of the electroplating experiment in the illustrative electrolyte mentioned above:

A polished brass plate pre-plated with gold was used as the substrate. The cleaning and coating of the substrates are as follows:

1. Cathode degreasing 30 sec/5V

2. Rinsing

3. Immersed in acid 10 sec

4. Rinse

5. Coating of the substrate in the hard gold electrolyte was carried out under the following conditions: the article was moved horizontally (5 m/min) according to the scale of 11, and the electrolyte was agitated at a different current density (200 rpm / 6 cm stirrer) .

6. Rinsing

7. Dry the coated substrate with compressed air

After the drying operation, the deposition speed was determined via the weight difference of the substrate (before coating and weight after coating) and is depicted in the following chart. (See Figure 1 - Figure 5)

Drawings:

Figure 1 shows the deposition rate [mg/Amin] in a hard gold electrolyte using different concentrations of additives according to the present invention (reaction product of epihalohydrin with aliphatic amine = epichlorohydrin and pentaethylene) amine).

Figure 2 shows the deposition rate [mg/Amin] in the hard gold electrolyte in the presence and absence of additives (the working range is extended by means of the reaction product of epichlorohydrin and dimethylaminopropylamine).

Figure 3 shows the deposition rate [mg/Amin] in a hard gold electrolyte with and without the addition of a polyamine (tetraethylenepentamine) having 4 ethylene units.

Figure 4 shows the deposition rate [mg/Amin] in a hard gold electrolyte with and without the addition of a polyamine (triethylenetetramine) having 3 ethylene units.

Figure 5 shows a comparison between the polyamines having 3 and 4 ethylene units from Examples 3 and 4.

Claims (5)

A method of using an aqueous electrolyte for selective electrodeposition of gold or a gold alloy having a pH of from 3 to 6 and comprising: gold ions in the form of a soluble complex; optionally additional ions, The plasma is selected from the group consisting of cobalt, nickel, iron or mixtures thereof; aliphatic polyamines which are soluble in the electrolyte and which have at least 4 ethylene units and at least 2 stages An amine or a secondary amine group, and/or a molar ratio of only an aliphatic or aromatic amine to a compound carrying an epoxy group from 1:1 to 1:5; the method is carried out by the following steps It is carried out: a substrate as a cathode is immersed in the electrolyte and a sufficient current is set between an anode in contact with the electrolyte and the cathode, so that corresponding deposition occurs. The method of claim 1, wherein the aliphatic polyamines soluble in the electrolyte are used in the electrolyte at a concentration of 0.001 to 0.5 mmol/l, and/or aliphatic. Or such reaction products of an aromatic amine and epichlorohydrin are used in the electrolyte at a concentration of 0.00001-2 g/l. The method of claim 2, characterized in that the polyamine having a molar ratio of about 1:3 and having 4 to 6 amine groups and epichlorohydrin, or a molar ratio of about 1 a tertiary amine and epoxy chloride of 1: The reaction product of propane is present in the electrolyte. A method according to one or more of the preceding claims, characterized in that the current density is set from 1 to 100 A/dm ² . A method according to one or more of the preceding claims, characterized in that the pH of the electrolyte is set to a value of from about 4 to 5.