NL8104859A - METHOD OF APPLYING A LOW GOLD. - Google Patents

Description

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Method of applying a layer of gold

The invention relates to the electrolytic deposition of gold on a substrate. In particular, the invention relates to an improvement in the corrosion resistance of a cobalt-hardened gold coating which has been electrolytically deposited on various substrates.

It is generally known in the coating technique to deposit a cobalt-hardened layer of gold on a substrate by electrolytic means. In the conventional method, a bath containing ions of the metal to be deposited as well as a suitable electrolyte is applied and the object to be coated is immersed or otherwise contacted with the bath while being connected as a cathode is with an external power source, and a metal electrode or anode is connected to the same power source. During electrolytic coating, ions of the metal to be deposited in the bath are reduced to the zero value metal state, which metal is deposited on the surface to be coated.

The use of cobalt to harden gold plating is discussed. example described in U.S. Patent 2,905,601.20, which is discussed in more detail below.

However, it has been found that such conventional cobalt hardened gold layers do not have the high degree of corrosion resistance, which is an important property for some commercial purposes.

For example, it would be desirable to provide a method of obtaining special cobalt hardened gold electrolytic layers having markedly improved erosion resistance and cosmetic appearance such as gloss and smoothness. In some cases, it has been found possible to obtain such desirable results with a significantly reduced metal thickness.

According to the invention it has now been found that hard gold layers having an improved corrosion resistance can be obtained by cobalt by first coating the substrate with a dual stress-free nickel layer.

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The necessary nickel layer on the substrate is obtained with a specially prepared electrolytic bath, which is preferably used with insoluble anodes. Generally, the electrolytic nickel baths will contain a nickel salt such as nickel-5 sulfate, as the source of nickel ions, and boric acid or citric acid as the electrolyte. Although other conventional additives may also be used, it has been found essential to use ortho-formylbenzenesulfonic acid as a brightener and as a wetting agent a mixture of potassium perfluoroalkyl sulfates which are, inter alia, commercially available under the trademark FC-98.

After the electrolytic deposition of the ductile, stress-free nickel layer, an upper layer is electrolytically deposited on the workpiece, which contains cobalt hardened gold.

By carrying out the above-mentioned successive electrolytic deposits, a cobalt hardened gold layer having an improved corrosion resistance is obtained, compared to the corrosion resistance of the same cobalt hardened gold layer without the underlying ductile, stress-free nickel layer. On the other hand, the improvement in corrosion was not achieved! 20 (not even when using a ductile, stress-free nickel intermediate layer), when the gold was hardened with, for example, iron, instead of cobalt. The corrosion resistance is measured according to Western Electrics

Manufacturing Specification WL-2316.

.25: The electrolytic nickel bath suitable for the first coating step of the invention will have the following composition:. . \.

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Component Concentration g / 1

Nickel salt. . 30 to 105 (as Ni) 30 Electrolyte 20 to 100 O-formylbenzenesulfonic acid 0.25 to 3.0 FC-98 0.02 to 0.2

The preferred nickel metal sources are. Nickel sulfate, nickel citrate, nickel carbonate, and the like.

- These salts are preferably used in an amount of "—Mt + tW -------; ---------- · - *" r. About 135-70 g / 1 cm to obtain the desired concentration of nickel metal.

The electrolytes most useful for the present purpose are hearing acid, citric acid and the like. The preferred amounts used for the preparation of the electrolytic baths of the invention will be between 22.5-5 g / l. The use of boric acid is particularly preferred.

The organic components of the nickel bath are usually the brighteners and the wetting agents. When formulating the special electrolytic bath of this invention, orthoformyl benzene sulfonic acid is used as the brightener. The wetting agent required is FC 98, a product marketed by Minnesota Mining and Manufacturing Co. or products of comparable composition.

For most purposes, the pH of the electrolysis bath is adjusted to a value of 2-5 and preferably 2.5-5.

The compounds used to adjust the pH include nickel carbonate, sulfuric acid, potassium citrate and citric acid.

The electrolysis baths according to the invention are used at temperatures of k6-5J ° C and at a relatively high current density up to about 108 amp / dm and preferably from 2 10-65 amp / dm. The ability to use such high current densities is another important advantage of the electrolysis baths used in the present invention. The nickel layers, which are applied on different surfaces when used. of the electrolysis baths according to the invention are characterized,. because they are semi-gloss and ductile and have little tension.

In addition, it is possible to use non-consumable anodes both when carrying out the first and second coating steps. Non-consumable anodes which can be used according to the invention include, for example, platinum-plated titanium, platinum-plated tantalum, platinum-plated niobium, or platinum itself.

In addition, it is also possible to use titanium anodes which are coated with mixed oxides, for example ruthenium oxide / titanium dioxide layers.

The electrolytic deposition of cured gold layers can be carried out using the baths and the method described in U.S. Pat. No. 2,905- 601 (1959)

The text of this patent is therefore incorporated herein by reference. Although kohalt-cured gold metal coatings are preferred, it will be appreciated that other metal hardeners such as indium or nickel can also be used in carrying out the process of the invention which involves the use of rapid deposition of gold, following rapid application of a nickel layer to form the first or intermediate layer on the substrate. The electrolysis bath used for coating with gold comprises: 1. a weak, stable organic acid, 2. gold in the form of cyanide (eg gold cyanide) and 3. one or more salts of base metals.

Examples of acids that can be used are mineral acid, acetic acid, citric acid, tartaric acid, lactic acid, kojic acid, or similar acids and mixtures thereof. This acid is preferably! present in an amount of 10-150 g / l and it can be partially neutralized with ammonium or alkali metal hydroxide to a pH of about 3-5- It is this weak organic acid and maintain it! of the pH of the bath within a limited range providing the desired effect of gold alloy deposition. The gold may be added as the double cyanide of gold and an alkali metal, for example potassium gold cyanide, and may be present in an amount of about 8-26 g / gold / l and preferably 12 g gold / l. . _! Base metal salts which can be added include the sulfates, sulfamates, formats, acetates, citrates, lactates, heartrates, fluoroborates, borates, phosphates, etc. of nickel, zinc, cobalt, indium, iron, manganese, antimony, copper, etc. These metal salts are added in an amount of 0.5-5 g / l. Very satisfactory results are obtained when two such base metal salts are incorporated in the bath. Although the addition of a base metal salt is necessary, it is not important which salt or mixture of salts is added as long as only the added salts are soluble and compatible with the other components of the bath. The bath can be operated at a current density of 0.1-11 amp / dm. Moderate to strong ^ 8104859::: ~ r -5 -......

stirring promotes proper operation. The bath can be used at room temperature (21 ° C), which is an advantage because it does not require thermostatic control, but higher or lower temperatures ranging from 10 to 50 ° C can also be used.

The maximum cathode / anode ratio is preferably about 4: 1.

The preferred second coating stage electrolysis bath will have the following composition:

Component Concentration (g / l)

Acetic acid and sodium citrate 100 to 300, 10 Formic acid 10 to 50 ml / 1

Gold (as potassium gold cyanide) 12 to 26

Cobalt (as sulfate) 0.5 to 1.75

Water Rest

The invention is illustrated by the following example.

15 Example. .

A first electrolysis bath was prepared by dissolving the following components:. - - 'Βίλ

Wrap (as sulfate) 75 20 Boric acid '40 O-formylbenzenesulfonic acid 1.5 FC 98 '. 0.1 -

Water. Rest -

A second electrolysis bath was prepared by dissolving the following components: & Ιλ

Citric acid (as potassium citrate) 200

Formic acid 20 ml / 1

Gold (as potassium gold cyanide) 12 30 Cobalt (as sulfate) 1.5

Water Rest

The pH of the latter bath is adjusted to 4.8-5.2 by —rRHH8-5 -: - - - - - -; “Λ» ». > -6- adding a base or an acid.

Trial A.

The substrate, a copper-clad commercial printed circuit board, is first treated in the nickel bath 5 to form a semi-gloss ductile and stress-free nickel layer about 2.5-5 microns thick. The substrate thus coated is then treated in the second electrolysis bath (gold) to form a shiny, smooth and hard gold layer.

This layer has a thickness of about 1-2 microns; The corrosion resistance of the product obtained, measured according to Western

Electric's Manufacturing Specification WL 2316 proved to be excellent.

Trial B.

When the electrolytic deposition of the nickel layer is left open, the corrosion resistance of the product obtained is found to be considerably reduced. .

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Claims (8)

A method of depositing a gold layer with improved corrosion resistance on a substrate, wherein (a) is first electrolytically deposited on the substrate electrolytically a nickel, stress-free layer of nickel from an electrolysis bath containing a nickel salt, an electrolyte from the group consisting of a boric acid and citric acid and further orthoformyl benzene sulfonic acid and contains as a wetting agent a mixture of potassium perfluoroalkyl sulfonates and 10 (b) electrolytically deposited a gold layer hardened gold base on the ductile, stress-free nickel layer thus obtained. an electrolysis bath containing a gold salt, an electrolyte selected from the group consisting of acetic acid, citric acid, formic acid and mixtures thereof and a salt of a metal selected from cobalt, indium, nickel and / or zinc. The method according to claim 1, characterized in that the nickel salt is nickel sulfate and that the electrolyte is boric acid. The method according to claim 1, characterized in that the electrolysis bath used under (a) has a pH of 2-5 ·. t 20 Ij ·. Method according to claim 1, characterized in that the two electrolysis stages (a) and (b) are carried out with non-usable anodes. Method according to claim 1, characterized in that the gold salt is a gold cyanide salt. Process according to claim 5, characterized in that the electrolysis bath used under (b) contains potassium gold cyanide. Method according to claim 1, characterized in that the electrolysis bath used under (b) contains acetic acid as the electrolyte. 8. Process according to claim 1, characterized in that the electrolysis bath used under (b) contains cobalt sulfate as a base metal salt. Method according to claim 1, characterized in that the electrolysis bath used under (b) contains citric acid as the electrolyte. 10. A method according to claim 1, characterized in that the electrolysis bath used under (b) comprises formic acid and citric acid as -8.1.QJL & -5-S ___-____-____________________ ....... '..... "-8- ..... ..... contains electrolyte. 11. A cobalt hardened gold clad layer with improved corrosion resistance obtained by the process of claims 1-10. * * V. "* '. - _” i' · · * ''. «* · 1 18 1 0 4 8 5 9____________ ·