JPH031383B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an electroless gold plating bath, and particularly to a reasonably stable electroless gold plating bath and its use,
Concerning giving a way to replenish. BACKGROUND OF THE INVENTION Autocatalytic or electroless gold plating baths are widely used to form gold deposits on conductive and non-conductive substrates, particularly in electronics where optimal electrical properties of the deposit are desired. used for purposes.
For optimum electrical properties, it is desirable that the gold be of high purity, ie, greater than 99.9%, and that the deposit be substantially uniform over the surface of the workpiece. Generally, such electroless gold plating solutions contain alkali metal gold cyanide and free cyanide,
and water-soluble borohydrides or amineboranes have been used as reducing agents. As the bath is refilled, the cyanide concentration increases, which has an undesirable effect on the deposition rate and stability of the composition. “Elektrochemische Stabili” by Martin Ulrich Kitztel and Christoph Julius Raob
−taetsbestimmung Reduktiv Arbeitender
Gold-elektrollyte” [Metalloberflaeche Publishing,
Vol. 41 (1987) pp. 309-313],
The effectiveness of various compounds as stabilizers in gold plating compositions has been discussed. None of the compounds reported by the authors serve effectively to provide a stable electroless gold plating bath that can be refilled many times without adversely affecting performance. It is therefore an object of the present invention to provide a novel and highly effective method which provides useful rates of autocatalytic deposition of gold onto substrates and which can be replenished many times without significantly adversely affecting plating rates or properties. The object of the present invention is to provide a composition for electroless gold plating. It is also an object to provide such electroless gold plating compositions that are easy to formulate and relatively stable in industrial plating environments. Yet another objective is to autocatalytically deposit substantially pure gold onto workpieces using a relatively stable composition that can be easily replenished many times without significantly adversely affecting plating rates. It's about giving a method. SUMMARY OF THE INVENTION The foregoing and related objects and advantages include: 1.0-16.6
gold (calculated as metal) in an amount of g/
It has now been found that this is easily accomplished with an electroless gold plating composition containing an aqueous solution of alkali metal gold cyanide sufficient to provide an amount of alkali metal cyanide of 110 g/l. These are included in an amount of a boron compound selected from alkylamine borane, alkali metal borohydride and mixtures thereof in an amount of 2 to 10 g/a and an alkali metal hydroxide in an amount of 10 to 1100 g/a. Good too. Finally, 0.1~
A stabilizer with the following formula in an amount of 0.3 g/:

[Detailed description of preferred embodiments]

As previously indicated, the baths of the present invention consist essentially of alkali metal gold cyanide, alkali metal cyanide, sufficient alkali metal hydroxide to maintain the desired pH and stabilize the cyanide ions, Requires a boron compound reducing agent and a nitroaromatic compound as a stabilizer. These components must be maintained within certain ranges and/or ratios to maintain a stable composition and reasonably uniform plating rate. First, regarding the gold component, potassium gold cyanide is preferred, but sodium salts can also be used.
Lithium compounds generally require additional cost.
The amount of gold cyanide (calculated as metal) is 1~
Although it will vary within a range of 16.6g/, the plating rate will be significantly affected when the gold content is lower than 2.0g/. Ideally, the gold content (as metal) is maintained within the range of 4-6 g/. The second component of the composition is sufficient alkali metal cyanide to provide free cyanide to the bath.
The amount of cyanide compound will vary from as little as 3 g/ to as high as 110 g/ as the bath is refilled from time to time. In preparation for the initial bath, the cyanide salt concentration is preferably in the range of about 4-10 g/g. The preferred cyanide salt is potassium cyanide, although sodium cyanide and lithium cyanide may also be used. Alkali metal hydroxides are necessary to provide the desired bath operating pH of 12.5-14 and are used to stabilize the cyanide ions and participate in the reduction reaction with boron compounds. Therefore, the hydroxide to cyanide ratio should be within the range of 4.0 to 10.0. For other salts, potassium hydroxide is preferred, but sodium hydroxide is a reasonable alternative thereto. Conventional boron compounds are used as reducing agents in the composition. These may consist of alkali metal borohydride and alkylamine borane in the range from 2 to 10 g/, preferably from 4 to 7 g/. A preferred reducing agent is dimethylamine borane, alone or in combination with an alkali metal borohydride. To give the composition the necessary stability, the general formula:

[Formula] [In the formula, R ₁ is -COOH, -OH, -CH ₂ OH, or -SO ₃ H (or an alkali metal salt thereof), and R ₂ is -COOH, -OH, -Cl, - H (or an alkali metal salt thereof) attached at the 2, 5 or 6 ring position, and the -NO ₂ group is at the 3 or 4 ring position. This is essential. This stabilizer is blended in an amount of 0.1 to 0.3 g/, preferably 0.15 to 0.25 g/. It has been observed that the concentration of stabilizer in the solution can drop severely during replenishment additions, causing the redox potential to exceed the -700 mV limit. Therefore, it is desirable that the potential is continuously monitored and the stabilizer is added in small amounts of 0.05 to 0.1 g per plating solution to maintain the redox potential within the operating range of -550 to 700 mV. It is added in As a result, the total amount of stabilizer added over the life of the solution can range as large as 10 g/ml. As indicated earlier, the pH of the aqueous composition is between 12.5 and 12.5.
14.0, preferably within the range of 13.4 to 14.0. To obtain the desired plating speed, the bath should be 85-95
℃, preferably 88-93℃. Using preferred compositions and temperatures, 3.75 to
Provides an effective plating rate of 6.75 μ/hr, with a density of at least 18 g/cc (on average) and at least 85
This will result in a gold deposit of at least 99.9% purity with a Knoop hardness (25 g maximum load). As the gold content of the solution decreases below 2 g/(as metal), the plating rate begins to decrease and replenishment of the composition becomes necessary. This is achieved by adding alkali metal hydroxides, alkali metal gold cyanides and additional stabilizers. As will be appreciated, alkali metal hydroxide is necessary to maintain the desired hydroxide to cyanide ratio. Generally, potassium hydroxide is 1 to 10
Potassium gold cyanide will be added in an amount ranging from 70 to 90 g/g (as metallic gold) to the gold replenishment solution. The amount of stabilizer added will be about 2-6 g/g. It has generally been found that the bath may be refilled for up to 10 strokes before the desirable properties of the plating formulation are significantly lost. One pass is defined as the time until the metal in a given volume of solution has been plated. To avoid contamination of the bath, the workpiece should be thoroughly cleaned before being placed therein according to conventional gilding methods. If the workpiece is a synthetic resin or ceramic, it is necessary to first form a base metal deposit thereon, which typically involves etching with chromic acid, application of palladium/tin chloride, and electroless copper deposition. Or it may require immersion in a nickel bath. Both such non-metallic and metal fabricated articles must be subjected to an initial treatment to form an immersion gold strike. A suitable composition for forming the initial thin gold deposit includes potassium gold cyanide, potassium dihydrogen phosphate and citric acid and is maintained at a temperature of about 140-160°C. Following deposition of the gold strike, the workpieces can be rinsed and then placed in the electroless gold plating composition of the present invention to produce the desired deposit. To illustrate the advantages of the present invention, the following specific examples are described in which all parts are by weight unless otherwise indicated. EXAMPLE 1 A preferred bath embodying the invention was prepared with 43 g of potassium hydroxide, 4 g of potassium cyanide, 6 g of potassium gold cyanide, 0.2 g of m ^- nitrobenzene sulfonic acid sodium salt in a previously cleaned and leached tank. , 6.5 g of methylamine borane and deionized water to make a solution of 1. The ratio of potassium hydroxide to total cyanide (as potassium cyanide) was 6.5 and the pH was 13.4. The resulting bath was heated to a temperature of approximately 91°C, and the redox potential of the solution was determined using an Orion SA230 model ORP.
Monitoring was performed using a Machee and coupled redox electrode model 9678. When the potential of the solution reaches -550mV,
The solution could be used as is. Example 2 The fabricated article was a flat sheet of an alloy sold by Westinghouse Electric Co. under the mark KOVAR, nominally 29% nickel and 17% cobalt. , had a composition consisting of 0.3% manganese and the balance iron. These sheets had a thickness of approximately 0.025 inches and were electrolytically cleaned in a hot caustic solution and then rinsed. The workpieces were then immersed in 50% by volume hydrochloric acid and rinsed, following which they were placed in an immersion plating bath consisting of potassium gold cyanide, potassium dihydrogen phosphate, and citric acid at a pH of about 2.5. They were removed after a uniform gold color developed on the surface. These processed articles were then suspended in the bath of Example 1 and magnetic stirring was used to maintain agitation of the bath around them. The bath temperature was maintained at 91°C. After 20 minutes, remove the workpiece from the bath and rinse.
And dried. The deposit was found to have a thickness of approximately 72 μin. The purity of the deposit was found to be 99.97. The deposit exhibited a satin matte finish and a lemon yellow color and was uniform and amorphous upon microscopic examination. Example 3 A Hull cell panel was thoroughly cleaned and immersed in the dip gold plating solution of Example 2 to produce a uniform gold color thereon. Rinse it and
Next, in the electroless gold plating composition of Example 1, 3.5%
It was hung for an hour, then removed, rinsed, and dried. A cross section of the plated panel was taken and the microhardness was determined to be 93 Knoop at 25g load. Example 4 A ceramic fabricated article was obtained consisting of an alumina substrate with a sintered dungsten coating and sputtered gold deposits thereon. The processed articles were immersed in a hot alkaline solution, rinsed, and then immersed in boiling hot deionized water to bring them to bath temperature. Thereafter, they were suspended in the bath of Example 1 for 30 minutes, removed, rinsed, and dried. The deposits are
Found to be 102 microns of electroless gold, the light yellow gold deposit was found to have a uniform matte finish with an amorphous structure. Example 5 The plating solution of Example 1 was subjected to long term process testing, including plating of Hull Cell panels. The bath composition was monitored hourly to determine gold content. When the gold content decreased to a level lower than 3 g/g, the bath was treated with 80 g/g potassium gold cyanide, 2
It was replenished with a formulation consisting of an aqueous solution of g/g potassium hydroxide and 4 g/m ^{-nitrobenzene} sulfonic acid sodium salt. The amount of replenishment solution added was an amount calculated to restore the gold content of the plating bath to 4 g/g/. This procedure was repeated and it was observed that the plating rate was essentially stable until the seventh pass, after which it began to decline to removal. The plating speed is the first 300μin/
It was found that it changes within a range of about 150 μin/hour from the 10th stroke. Thus, from the foregoing detailed description and examples, it can be seen that the electroless plating compositions of the present invention provide stable and effective baths for the autocatalytic deposition of gold on metal and non-metallic fabricated articles. The deposits exhibit good amorphous structure, high purity and relatively large hardness, thus making them highly suitable for electronics applications.

Claims (1)

Claims: 1. (a) an alkali metal gold cyanide sufficient to provide gold (calculated as metal) in an amount of 1.0 to 16.6 g/; (b) an alkali metal in an amount of 3 to 110 g/ cyanide; (c) a boron compound selected from the group consisting of alkylamine borane, alkali metal borohydride, and mixtures thereof in an amount of 2 to 10 g/; (d) an alkali metal in an amount of 10 to 1100 g/. hydroxide, and (e) 0.1 to 0.3 g/stabilizer having the following formula: [Formula] [wherein R ₁ is -COOH, -OH, -CH ₂ OH, or -SO ₃ H] (or an alkali metal salt thereof), R ₂ is -COOH, -OH, -Cl, -H (or an alkali metal salt thereof), bonded to the 2, 5 or 6 ring position, -NO ₂ is at the 3rd or 4th ring position] An electroless gold plating composition comprising an aqueous solution of
It has a pH of 12.5 to 14.0 and a weight ratio of OH ^- /CN ^- of 4.0.
~10.0, and the redox potential of the solution is −550 to −
A composition for electroless gold plating with a voltage of 700 mV. 2. The composition for electroless gold plating according to claim 1, wherein the boron compound is dimethylamine borane in an amount of 4 to 7 g/g. 3. The electroless gold plating composition according to claim 1, wherein the stabilizer is nitrobenzene sulfonic acid or an alkali metal salt thereof. 4. Electroless gold plating composition according to claim 1, wherein the stabilizer is present in an amount of 0.15 to 0.25 g/g. 5. An electroless gold plating composition according to claim 1, wherein the composition has in its initial preparation an amount of alkali metal cyanide of 4 to 6 g/a and an amount of alkali metal hydroxide of 40 to 50 g/a. 6 The composition is 4 to 5 g/calculated as metallic gold.
2. The electroless gold plating composition of claim 1, having an amount of gold. 7. The electroless gold plating composition of claim 1, wherein the solution has a pH of about 13.4-14.0. 8. A method for electrolessly plating gold on a workpiece, comprising: (a) dip-plating a thin deposit of immersion gold onto the surface of the workpiece, and (b) said plated workpiece: (i) calculated as metal; (ii) an alkali metal cyanide in an amount of 3 to 110 g/m; (iii) an alkylamine borane, an alkali metal borohydride; (iv) an alkali metal hydroxide in an amount of 10 to 1100 g/, and (v) a stabilizer having the formula: :
[Formula] [In the formula, R ₁ is -COOH, -OH, -CH ₂ OH, or -SO ₃ H (or an alkali metal salt thereof), and R ₂ is -COOH, -OH, -Cl, - H (or an alkali metal salt thereof), bonded to the 2nd, 5th or 6th ring position, and the -NO ₂ group is at the 3rd or 4th ring position. With things,
It has a pH of 12.5 to 14.0 and a weight ratio of OH ^- /CN ^- of 4.0.
~10.0, and when the amount of stabilizer is in the range of 0.1 to 0.3 g/, the redox potential of the solution is -550 to -
Electroless plating of gold on a fabricated article consists of steps of immersing the workpiece in an electroless gold plating composition maintained within the range of 700 mV for a period of time sufficient to plate high purity gold to the desired thickness. how to. 9. A method for electrolessly plating gold on a workpiece according to claim 8, wherein the solution is maintained at a temperature of about 85-95C. 10. A method for electroless plating gold on an article according to claim 8, wherein the boron compound is dimethylamine borane in an amount of 4 to 7 g/g. 11. The method of electroless plating gold on a processed article according to claim 8, wherein the stabilizer is nitrobenzene sulfonic acid or an alkali metal salt thereof. 12. The method of electroless plating gold on a fabricated article according to claim 8, wherein the stabilizer is present in an amount of 0.15 to 0.25 g/g. 13. Electrolessly plating gold on the article of claim 8, wherein the composition has, in its initial preparation, an amount of alkali metal cyanide in an amount of 4.0 to 6.0 g/a and an amount of alkali metal hydroxide in an amount of 40 to 50 g/a. Method. 14 Gold content (as metal) is 1.5-3g/
(a) alkali metal gold cyanide (as metal) in an amount of 60 to 100 g/; (b) alkali metal hydroxide in an amount of 1 to 10 g/;
and (c) a stabilizer in an amount of 2 to 6 g/g to the composition. 15 A composition for electroless gold plating is prepared by first preparing an aqueous solution of an alkali metal hydroxide, an alkali metal cyanide, an alkali metal gold cyanide, a stabilizer, and a boron compound, and then redoxing the heated solution. 9. A method for electroless plating gold on a workpiece according to claim 8, which is produced by monitoring the potential until it reaches a value of -550 to -700 mV. 16. The processed article according to claim 8, wherein the redox potential is monitored during the plating step, and the stabilizer is added in portions in an amount of 0.05 to 0.1 g/l to maintain the potential within the range of -550 to -700 mV. How to electroless plate gold.