TWI837305B - Electrolytic gold plating solution, its manufacturing method and gold plating method, gold complex - Google Patents

Abstract

The present invention provides an electrolytic gold plating solution that does not contain cyanide and has excellent oxidation stability and is advantageous in terms of current efficiency during gold electroplating.

The electrolytic gold plating solution of the present invention uses a gold complex as a gold source and contains a chelating agent, a conductive salt, and a buffer. The gold complex has a structure in which a hydantoin compound represented by the following chemical formula (1) is coordinated with a monovalent gold ion.

(In the chemical formula (1), R ₁ to R ₄ independently represent a hydrogen atom or a monovalent organic group, both or either of R ₁ and R ₂ are hydrogen atoms, and both or either of R ₃ and R ₄ are hydrogen atoms. This excludes the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms).

Description

Electrolytic gold plating solution, its manufacturing method and gold plating method, gold complex

The present invention relates to an electrolytic gold plating solution used in gold plating on wafers, substrates, etc., and its manufacturing method, as well as a gold plating method, and further to a gold complex that can be used as a raw material for the electrolytic gold plating solution.

As the plating solution used in electroplating and electroless plating, cyanide gold plating solution has been used as the gold supply source in the past, and the cyanide gold plating solution uses a cyanide gold complex with excellent oxidation stability in the liquid. However, cyanide gold salts are highly toxic, so they have problems such as poor work safety and wastewater treatment. In addition, when using cyanide gold plating solution, the remaining cyanide will cause the photoresist pattern of semiconductor parts to peel off and damage, and it is also difficult to form fine circuit patterns.

In view of such problems, it is considered desirable to apply a plating solution using a gold salt or gold complex that does not contain cyanide. As an example, there is a non-cyanide gold plating solution such as a gold sulfite salt (Na ₃ Au(SO ₃ ) ₂ ) solution.

However, the gold salts or gold complexes contained in these non-cyanide gold plating solutions lack oxidation stability and have the problem of decomposition during the electroplating process. For example, in the above-mentioned gold sulfite salt, the sulfite ions in the solution are easily oxidized and decomposed due to the dissolved oxygen in the electroplating solution and the air mixed in by stirring or taking the electroplated material, which leads to a decrease in its concentration. As a result, the oxidation stability of the gold complex is reduced, and the electroplating solution may decompose. Then, when this decomposition occurs, gold will precipitate out of the electroplating solution and precipitate in the electroplating solution tank or piping, which will hinder the electroplating process. Therefore, for non-cyanide electroplating, additives such as stabilizers or chelating agents are added to the electroplating solution to prevent the decomposition of the electroplating solution, and the electroplating treatment is performed. However, in such a countermeasure, the cost of the stabilizer and the complicated manufacturing steps of the electroplating solution lead to an increase in cost.

In addition, plating solutions containing gold salts or gold complexes with low oxidation stability also have problems from the perspective of storage. In the case of the above-mentioned gold sulfite salt, black precipitates are easily generated due to the decomposition of the gold salt during storage, and it must be stored in a light-shielded state, which makes its management difficult.

Therefore, Patent Documents 1 and 2 disclose a gold complex which does not contain cyanide and has excellent oxidation stability, and uses a hydantoin compound as a ligand. The gold complex described in Patent Document 1 is a complex in which chloroauric acid or chloroaurate salt is reacted with a hydantoin compound in an aqueous solution to coordinate the hydantoin compound with a gold ion. Furthermore, the gold complex described in Patent Document 2 is a complex in which gold hydroxide is reacted with a hydantoin compound in an aqueous solution by heating it to coordinate the hydantoin compound with a gold ion.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2005-256072

[Patent Document 2] Japanese Patent Publication No. 2003-183258

These gold complexes have greatly improved oxidation stability compared to conventional non-cyanide gold salts or gold complexes such as the above-mentioned sulfites. Here, Patent Documents 1 and 2 recommend the use of 5,5-dimethylhydantoin as the hydantoin compound coordinated to the gold ion because the oxidation stability of the complex after the reaction is particularly excellent. However, 5,5-dimethylhydantoin itself does not oxidize because it does not have a hydrogen atom at the 5-carbon position, and therefore does not induce a reaction that reduces gold from trivalent to monovalent, but is stable as a trivalent gold ion complex. As a result, when gold electroplating is performed using an electrolytic gold plating solution made from the gold ion complex, the cathode current density must be matched with the trivalent gold ion complex, which is disadvantageous in terms of current efficiency.

The present invention was completed in view of the above situation, and its purpose is to provide an electrolytic gold plating solution that does not contain cyanide and has excellent oxidation stability, and is advantageous in terms of current efficiency during gold electroplating.

As a result of detailed research conducted by the inventors of this case to solve the above-mentioned problem, they found that the above-mentioned problem can be solved by using a gold complex having a structure in which a specific hydantoin-based compound is coordinated to a monovalent gold ion as a gold source.

That is, the electrolytic gold plating solution of the present invention is formed by the following composition [1].

[1] An electrolytic gold plating solution which uses a gold complex as a gold source and contains a chelating agent, a conductive salt, and a buffer, wherein the gold complex has a structure in which a hydantoin compound represented by the following chemical formula (1) is coordinated to a monovalent gold ion.

[Chemical formula (1)]

In the chemical formula (1), R ₁ to R ₄ independently represent a hydrogen atom or a monovalent organic group, both or either of R ₁ and R ₂ are hydrogen atoms, and both or either of R ₃ and R ₄ are hydrogen atoms, excluding the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms.

The preferred embodiment of the electrolytic gold plating solution of the present invention is formed by the following structures [2] to [4].

[2] The electrolytic gold plating solution of [1] above, wherein the chlorine concentration in the electrolytic gold plating solution is less than 1000 ppm.

[3] In the electrolytic gold plating solution of [1] or [2] above, the gold complex is derived from an alkaline metal salt.

[4] An electrolytic gold plating solution as described in any one of [1] to [3] above, wherein the chelating agent comprises at least one of a hydantoin compound and succinimide.

Furthermore, the electrolytic gold plating solution of the present invention is formed by the following composition [5].

[5] An electrolytic gold plating solution, which uses a gold complex as a gold source and contains a chelating agent, a conductive salt, and a buffer, wherein the gold complex has a structure in which a hydantoin compound represented by the following chemical formula (2) is coordinated to a monovalent gold ion; and the chlorine concentration in the electrolytic gold plating solution is less than 1000 ppm.

[Chemical formula (2)]

In the chemical formula (2), R ₅ to R ₈ each independently represent a hydrogen atom or a monovalent organic group, both or either of R ₅ and R ₆ are hydrogen atoms, and both or either of R ₇ and R ₈ are hydrogen atoms.

The preferred embodiment of the electrolytic gold plating solution of the present invention is formed by the following structure [6] or [7].

[6] An electrolytic gold plating solution as described in [5] above, wherein the gold complex is derived from an alkaline metal salt.

[7] The electrolytic gold plating solution of [5] or [6] above, wherein the chelating agent comprises at least one of a hydantoin compound and succinimide.

Furthermore, the method for manufacturing the electrolytic gold plating solution of the present invention is formed by the following structure [8] or [9].

[8] A method for producing an electrolytic gold plating solution, which is the method for producing an electrolytic gold plating solution of any one of [1] to [4] above, characterized by comprising: a step of reacting chloroauric acid or chloroaurate, a hydantoin compound represented by the chemical formula (1), and an alkali metal hydroxide in an aqueous solution to form the gold complex; a step of cooling the aqueous solution containing the gold complex to extract the alkali metal salt of the gold complex; and a step of using the alkali metal salt of the gold complex to produce the electrolytic gold plating solution.

[9] A method for producing an electrolytic gold plating solution, which is a method for producing an electrolytic gold plating solution as described in any one of [5] to [7] above, characterized by comprising: a step of reacting chloroauric acid or chloroaurate, a hydantoin compound represented by the chemical formula (2), and an alkali metal hydroxide in an aqueous solution to form the gold complex; a step of cooling the aqueous solution containing the gold complex to extract the alkali metal salt of the gold complex; and a step of using the alkali metal salt of the gold complex to produce the electrolytic gold plating solution.

Furthermore, the gold electroplating method of the present invention is formed by the following structure [10].

[10] A gold electroplating method, which is a method for electroplating using an electrolytic gold plating solution as described in any one of [1] to [7] above, characterized in that the electroplating is carried out under the conditions of pH: 5.0~10.0, liquid temperature: 20~80℃ and current density: 0.1~4.5A/ ^dm2 .

Furthermore, the gold alloy of the present invention is formed by the following structure [11].

[11] A gold complex characterized by having a structure in which a hydantoin compound represented by the following chemical formula (1) is coordinated to a monovalent gold ion.

In the chemical formula (1), R ₁ to R ₄ independently represent a hydrogen atom or a monovalent organic group, both or either of R ₁ and R ₂ are hydrogen atoms, and both or either of R ₃ and R ₄ are hydrogen atoms, excluding the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms.

According to the present invention, a cyanide-free electrolytic gold plating solution can be provided, which has excellent oxidation stability and is advantageous in terms of current efficiency during gold electroplating.

The following is a detailed description of the form used to implement the present invention. In addition, the present invention is not limited to the implementation form described below, and can be implemented in any manner without departing from the scope of the present invention.

<Electrolytic gold plating solution>

The electrolytic gold plating solution of this embodiment is described. The electrolytic gold plating solution of this embodiment uses a gold complex as a gold source and contains at least a chelating agent, a conductive salt and a buffer. The gold complex has a structure in which a hydantoin compound represented by the following chemical formula (1) is coordinated to a monovalent gold ion.

In the chemical formula (1), R ₁ to R ₄ independently represent a hydrogen atom or a monovalent organic group, both or either of R ₁ and R ₂ are hydrogen atoms, and both or either of R ₃ and R ₄ are hydrogen atoms, excluding the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms.

The gold complex of this embodiment is characterized in that the valence of the gold ion in the electrolytic gold plating solution is 1. This is because by making the valence of the gold ion 1, when gold plating is performed using an electrolytic gold plating solution, the cathode current density can be matched with the univalent gold ion complex, and compared to the trivalent case, the cathode current density can be made 1/3, so compared to the case of using a trivalent gold ion complex, it is advantageous in terms of current efficiency. In addition, compared to the trivalent case, the anode current density can also be made 1/3, so the oxidative decomposition of the plating solution near the anode can be reduced, and the life of the plating solution can be extended.

Next, in the gold complex using a hydantoin compound as a ligand, a specific one among the hydantoin compounds is used in order to make the valence of the gold ion 1. Specifically, a hydantoin compound represented by the following chemical formula (1) is used as a ligand. In addition, the identification of the ligand can be simply performed by separating and qualitatively analyzing the ligand released in the gold complex solution due to the complex equilibrium by methods such as liquid chromatography.

In the chemical formula (1), R ₁ to R ₄ independently represent a hydrogen atom or a monovalent organic group, both or either of R ₁ and R ₂ are hydrogen atoms, and both or either of R ₃ and R ₄ are hydrogen atoms, excluding the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms.

These hydantoin compounds react to reduce gold from trivalent to monovalent under alkaline conditions and stabilize as monovalent gold ion complexes.

In addition, in the chemical formula (1), examples of the monovalent organic group represented by R ₁ to R ₄ include: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, pentyl, neopentyl, dodecyl, hexadecyl, etc., including linear and isomeric forms; alkyl, hydroxyalkyl, vinyl, allyl, isopropenyl, etc., including second-order and third-order structural isomers; alkenyl, alkoxy groups such as methoxy and ethoxy, carboxylic acids such as acetyl and propionyl, acyl groups such as acetyl and propionyl, aromatic hydrocarbon groups, hydroxyl groups such as phenyl, methylphenyl, hydroxyphenyl, benzyl, etc., including second-order and third-order structural isomers. Furthermore, the organic group preferably has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and most preferably 1 carbon atoms, from the viewpoint of water solubility and economic efficiency.

Specific examples of the hydantoin compounds represented by the chemical formula (1) include hydantoin (when R ₁ to R ₄ are all hydrogen atoms), 3-methylhydantoin (when R ₂ is a methyl group and R ₁ , R ₃ and R 4 are all hydrogen atoms), 5-methylhydantoin (when R ₃ is a methyl group and R ₁ , R ₂ and R _{4 are} all hydrogen atoms), and 5-hydantoinacetic acid (when R ₃ is acetic acid and R ₁ , R ₂ and R ₄ are all hydrogen atoms). Among them, hydantoin is preferably used as the material from the viewpoint of being the lowest price and being economical.

In the above chemical formula (1), "excluding the case where _R1 is a methyl group and _R2 to _R4 are all hydrogen atoms" means excluding the case where _R1 is a methyl group and _R2 to _R4 are all hydrogen atoms in the hydantoin-based compound, that is, "1-methylhydantoin".

On the other hand, other hydantoin compounds, such as 5,5-dimethylhydantoin or 1,5,5-trimethylhydantoin, do not have hydrogen at the 5-carbon (see the above chemical formula (1)). Therefore, they do not oxidize under alkaline conditions and do not induce a reaction that reduces gold from trivalent to monovalent. They are therefore stable as trivalent gold ion complexes. In addition, ureaacetic acid does not have a hydantoin ring structure and does not oxidize under alkaline conditions. Therefore, similar to the above, it does not induce a reaction that reduces gold from trivalent to monovalent. Therefore, it is stable as a trivalent gold ion complex.

Furthermore, gold and hydantoin compounds form complexes due to the hydrogen release from the 1- or 3-position nitrogen, and the 1- or 3-position nitrogen bonds with gold (see the above chemical formula (1)). Therefore, 1,3-dimethylhydantoin, in which both the 1- and 3-position nitrogens are bonded to alkyl groups, cannot form gold complexes.

In addition, another electrolytic gold plating solution of the present embodiment also uses a gold complex as a gold source and contains a chelating agent, a conductive salt, and a buffer. The gold complex has a structure in which a hydantoin compound represented by the following chemical formula (2) is coordinated to a monovalent gold ion, and the chlorine concentration in the electrolytic gold plating solution is less than 1000 ppm.

In the chemical formula (2), R ₅ to R ₈ each independently represent a hydrogen atom or a monovalent organic group, both or either of R ₅ and R ₆ are hydrogen atoms, and both or either of R ₇ and R ₈ are hydrogen atoms.

These hydantoin compounds will also undergo a reaction to reduce gold from trivalent to monovalent under alkaline conditions, and stabilize as monovalent gold ion complexes.

In addition, in the chemical formula (2), the monovalent organic group represented by R ₅ to R ₈ may include, for example, linear and isomeric forms of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl, dodecyl, hexadecyl, etc.; linear and isomeric forms of alkyl, hydroxyalkyl, vinyl, allyl, isopropenyl, etc. including second-order and third-order structural isomers; alkenyl, alkoxy groups such as methoxy and ethoxy, carboxylic acids such as acetyl and propionyl, acyl groups such as acetyl and propionyl, aromatic hydrocarbon groups, hydroxyl groups such as phenyl, methylphenyl, hydroxyphenyl, benzyl, etc. including second-order and third-order structural isomers. Furthermore, the organic group preferably has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and most preferably 1 carbon atoms, from the viewpoint of water solubility and economic efficiency.

Specific examples of the hydantoin compounds represented by the chemical formula (2) include hydantoin (when R ₅ to R ₈ are all hydrogen atoms), 1-methylhydantoin (when R ₅ is a methyl group and R ₆ to R ₈ are all hydrogen atoms), 3-methylhydantoin (when R ₆ is a methyl group and R ₅ , R ₇ and R ₈ are all hydrogen atoms), 5-methylhydantoin (when R ₇ is a methyl group and R ₅ , R ₆ and R ₈ are all hydrogen atoms), and 5-hydantoinacetic acid (when R ₃ is acetic acid and R ₅ , R ₆ and R ₈ are all hydrogen atoms). Among them, hydantoin is preferably used as the material from the viewpoint of the lowest price and economy.

Next, the electrolytic gold plating solution of this embodiment preferably has a chlorine concentration of less than 1000 ppm. By making the chlorine concentration in the electrolytic gold plating solution less than 1000 ppm, that is, the electrolytic gold plating solution substantially does not contain chlorine, it can be applied to the electroplated objects that repel chlorine.

Here, as in Patent Document 1, in the electrolytic gold plating solution produced by reacting chloroauric acid or chloroaurate with a hydantoin compound, a large amount of chlorine ions derived from chloroauric acid or chloroaurate are contained in the electrolytic gold plating solution, so it is difficult to apply to the electroplated object that rejects chlorine.

In this embodiment, as an indicator for indicating that the electrolytic gold plating solution does not substantially contain chlorine, the chlorine concentration in the electrolytic gold plating solution is set to be below 1000ppm. However, as the reason why the chlorine in the electrolytic gold plating solution is rejected, it is considered that the residual chlorine on the surface of the gold film will reduce the adhesion with the base layer or cause corrosion of the film, or it is difficult to adjust the hardness due to its presence in the grain boundaries of the gold film. In order to be able to be applied to the electroplated object that rejects chlorine without problems, the chlorine concentration in the electrolytic gold plating solution is preferably below 500ppm, more preferably below 300ppm, and even more preferably below 200ppm.

In addition, the method for obtaining an electrolytic gold plating solution that is substantially free of chlorine is described in the following paragraph.

Next, the chelating agent, conductive salt and buffer that constitute the electrolytic gold plating solution of this embodiment are described respectively.

As a chelating agent, it is added separately from the ligand of the gold complex, and hydantoin, 1-methylhydantoin, 5-methylhydantoin, 5,5-dimethylhydantoin and succinimide can be used ideally. Among them, for the oxidation stability and precipitation uniformity of the gold complex in the electroplating solution, it is preferred that the chelating agent contains at least one of 5,5-dimethylhydantoin and succinimide. By using a chelating agent in the electrolytic gold plating solution, an extremely stable gold plating solution can be obtained. That is, gold precipitation is not easy to occur during the electroplating process. This is because such chelating agents maintain equilibrium with the ligands of the gold complex and are not reductive like sulfurous acid, but are not easily oxidized and decomposed.

In addition, the equilibrium state and mixed concentration of the chelating agent and the ligand of the gold complex can be distinguished by ion chromatography or liquid chromatography.

The amount of chelating agent is preferably more than 0 times molar and less than 4 times molar relative to gold at pH 5-7. If the amount is large and the gold complex is frequently replenished, the ligands of the gold complex will be freed, so the chelating agent may not be included in the initial stage. If the amount exceeds 4 times molar, it will become a burnt appearance.

In addition, in the case of pH 8-10, the concentration is preferably 4 times molar or more and 10 times molar or less relative to gold. If it is less than 4 times molar, a burnt appearance may be observed, and the gold complex ligands are alkaline and the oxidation decomposition reaction will take precedence compared to the balance between the chelating agent and the gold complex ligands, so gold precipitation may be observed. In addition, if it exceeds 10 times molar, the appearance and oxidation stability will not change, and the effect of increasing the chelating agent cannot be expected.

As the conductive salt, it is preferred to use hydrochloric acid, sulfuric acid, sulfurous acid, sulfamic acid, nitric acid, phosphoric acid or any one or more of these salts. If these are used alone or in combination as the conductive salt, the solution stability of the electrolytic gold plating solution of this embodiment becomes extremely good.

When the electrolytic gold plating solution of the present embodiment contains the above-mentioned conductive salt, the conductive salt concentration is preferably in the range of 0.05~1.95mol/L. If the conductive salt concentration is less than 0.05mol/L, the current efficiency is reduced due to the reduction in conductivity, and the plating appearance is also prone to poor. If it exceeds 1.95mol/L, the conductivity and appearance are not changed, and salt precipitation is prone to occur depending on the pH.

As a buffer, it is preferred to use any one or more of boric acid, succinic acid, phthalic acid, tartaric acid, citric acid, phosphoric acid or their salts. If these are used alone or in combination as buffers, the pH of the electrolytic gold plating solution of this embodiment will not change significantly, and it is easy to maintain the plating solution at a pH of weakly acidic to weakly alkaline (pH about 5.0~10.0) near neutral.

When the electrolytic gold plating solution of this embodiment contains the above-mentioned buffer, the buffer concentration is preferably in the range of 0.05~1.95mol/L. If the buffer concentration is less than 0.05mol/L, the effect of stabilizing pH is lost. If it exceeds 1.95mol/L, the stability of pH does not change, and salt precipitation is likely to occur depending on the pH.

In addition, the total concentration of the conductive salt and the buffer is preferably in the range of 0.1~2.0mol/L. If the total concentration of the conductive salt and the buffer is 0.1~2.0mol/L, the gold plating solution of this embodiment can achieve the best complete balance in practical operation. That is, the solution has excellent stability, high current efficiency, and the pH of the plating solution does not change significantly.

In addition, from the perspective of preventing salt precipitation in winter, the total concentration of conductive salt and buffer is preferably in the range of 0.1~1.0mol/L.

The gold concentration in the electrolytic gold plating solution of this embodiment is also related to the concentration of the chelating agent, but the best concentration is in the range of 0.5~15g/L. If it is less than 0.5g/L, gold electrolysis will not occur unless a voltage of 3V or more is applied. If it exceeds 15g/L, the electroplated material will be taken out of the electroplating tank, which is considered to be economically inconvenient and prone to salt precipitation in winter.

Furthermore, the above gold concentration is preferably in the range of 4~8g/L. Within this concentration range, it can be controlled in accordance with various electroplated materials, and it is also easy to manage the concentration changes caused by the consumption of gold.

In addition, in the electrolytic gold plating solution of the present embodiment, the gold complex is preferably derived from an alkaline metal salt. As described later, the specific hydantoin compound used in the present embodiment is stable as a monovalent gold ion complex under alkaline conditions, and the gold complex alkaline metal salt extracted thereafter is substantially free of chlorine. By using the gold complex alkaline metal salt to manufacture the electrolytic gold plating solution, it can be an electrolytic gold plating solution that can be applied to an object to be plated that rejects chlorine.

As the above-mentioned alkaline metal salts, lithium salts, sodium salts, potassium salts, cadmium salts, and cesium salts can be cited as examples, among which sodium salts or potassium salts are preferred. This is because these are common to the previous gold compounds, namely potassium cyanide gold or sodium sulfite gold, and are salts of alkaline metals with excellent economical properties.

<Method for manufacturing electrolytic gold plating solution>

The method for producing the electrolytic gold plating solution of the present embodiment is described. The method for producing the electrolytic gold plating solution of the present embodiment comprises the following steps: reacting chloroauric acid or chloroaurate, a hydantoin compound represented by the above chemical formula (1) or the above chemical formula (2), and an alkali metal hydroxide in an aqueous solution to form a gold complex alkali metal salt, and extracting the gold complex alkali metal salt; and using the gold complex alkali metal salt to produce the electrolytic gold plating solution.

As mentioned above, the electrolytic gold plating solution of this embodiment is characterized by being substantially free of chlorine. Therefore, although the gold complex with hydantoin compounds as ligands can be formed using the gold hydroxide described in Patent Document 2 as a raw material, the yield of gold hydroxide is usually only about 60% at most, which is not high. Therefore, the cost of gold used as the electrolytic gold plating solution becomes high and is not economical.

Therefore, in this embodiment, in order to suppress the cost of gold used and obtain an electrolytic gold plating solution that can be applied to an object to be plated that rejects chlorine, the electrolytic gold plating solution is obtained by the following manufacturing method as its characteristic.

First, as a raw material for obtaining a gold complex, chloroauric acid or chloroaurate is prepared in the same manner as in the prior art. In addition, a hydantoin compound represented by the above chemical formula (1) or the above chemical formula (2) is prepared for coordination with gold ions, and further alkali metal hydroxides such as lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), arsenic hydroxide (RbOH), and cesium hydroxide (CsOH) are prepared.

Next, chloroauric acid or chloroaurate salt, the above-mentioned hydantoin compound, and alkali metal hydroxide are reacted in an aqueous solution to obtain a gold complex having a structure in which the hydantoin compound represented by the above-mentioned chemical formula (1) or the above-mentioned chemical formula (2) is coordinated with a monovalent gold ion.

Here, the reaction conditions of chloroauric acid or chloroaurate with hydantoin compounds in this embodiment are preferably a temperature of 40 to 80°C and a reaction time of 30 to 360 minutes. Next, the reaction temperature is particularly preferably 60 to 75°C, and the reaction time is particularly preferably more than 180 minutes.

In addition, even if chloroauric acid or chloroaurate is simply mixed with a hydantoin compound, the hydantoin compound in the liquid also has the function of a so-called chelating agent, but gold maintains the state of a gold chloride complex and complex formation cannot occur. Then, although gold electroplating can be performed using such a liquid, the amount of gold precipitated is 1/3 because gold is in a trivalent state, and its precipitation mechanism is different from that of the gold complex of this embodiment.

Here, although the raw material of the gold complex of this embodiment is chloroauric acid or chloroaurate salt, the chloroaurate salt is preferably a salt of chloroauric acid and an alkali metal (lithium, sodium, potassium, cadmium, cesium) or an alkali earth metal (magnesium, calcium, strontium, barium), and particularly preferably sodium chloroaurate or potassium chloroaurate.

Then, if the solution containing the gold complex obtained above is cooled to below room temperature (25°C), a gold complex alkali metal salt crystal without chlorine in the structure is precipitated, so solid-liquid separation is performed and the gold complex alkali metal salt is extracted from the above solution. By such treatment, the solution becomes a state of residual chlorine, and the extracted gold complex alkali metal salt does not contain chlorine in substance. In addition, according to this operation method, the gold complex alkali metal salt can be obtained from the above solution at a very high yield without using gold salt hydroxide.

Afterwards, as long as the gold complex alkaline metal salt extracted from the solution is used as a raw material to manufacture electrolytic gold plating solution, an electrolytic gold plating solution that is substantially free of chlorine can be obtained.

In addition, for reference, paragraph 0017 of the above-mentioned patent document 1 and paragraph 0013 of the above-mentioned patent document 2 state that "although a gold complex formation reaction occurs in an aqueous solution, when the complex is supplied to a plating solution, the solution after the reaction can be directly used as a raw material for the plating solution." However, for example, when a gold complex is formed using chloroauric acid or chloroaurate as a raw material, when the solution after the reaction is directly used as a raw material for the plating solution, the solution after the reaction contains a large amount of chlorine ions, so that the electrolytic gold plating solution also contains a large amount of chlorine ions, and it is difficult to apply it to the electroplated product that rejects chlorine.

<Gold electroplating method>

The gold electroplating method of this embodiment is described below. The gold electroplating method of this embodiment is a method of using the above-mentioned electrolytic gold electroplating solution for electroplating treatment, and the electroplating is performed under the conditions of pH: 5.0~10.0, liquid temperature: 20~80℃ and current density: 0.1~4.5A/ ^dm2 .

The pH value of the gold plating solution is in the range of pH 5.0 to 10.0, depending on the concentration of the buffer and the conductive salt. As long as it is within this range, the appearance of the deposited gold will not be abnormal. If the pH is less than 5.0, the appearance of the plating will be uneven. If it exceeds 10.0, if the electroplated object is covered by photoresist (hereinafter referred to as PR), it has a tendency to dissolve the PR.

The temperature of the gold electroplating solution is set at 20~80℃ because if it is less than 20℃, the unevenness of the electroplating process will become too large and it will not be suitable for actual operation. If it exceeds 80℃, it will affect the gloss of the deposited gold and the life of the solution will be sharply reduced.

The current density during electrolysis is set to 0.1~4.5A/dm ² in consideration of the pH value, liquid temperature, and gold concentration of the above-mentioned electroplating solution, and to ensure that the properties of the deposited gold are in a very good state. The electroplating properties in this case include comprehensive conditions such as appearance, adhesion, leveling, and hardness.

<Gold complex>

The gold complex of this embodiment is described. The gold complex of this embodiment has a structure in which a hydantoin compound represented by the following chemical formula (1) is coordinated to a monovalent gold ion.

Chemical formula 1

In the chemical formula (1), R ₁ to R ₄ independently represent a hydrogen atom or a monovalent organic group, both or either of R ₁ and R ₂ are hydrogen atoms, and both or either of R ₃ and R ₄ are hydrogen atoms, excluding the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms.

These hydantoin compounds react to reduce gold from trivalent to monovalent under alkaline conditions, and stabilize as monovalent gold ion complexes.

In addition, in the chemical formula (1), the monovalent organic group represented by R ₁ to R ₄ includes, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, pentyl, neopentyl, dodecyl, hexadecyl and the like, linear and isomeric groups; alkyl, hydroxyalkyl, vinyl, allyl, isopropenyl and the like, linear and isomeric groups including secondary and tertiary structural isomers; alkenyl, methoxy, ethoxy and the like alkoxy groups, acetoxy, propionyl and the like carboxylic acids, acetyl, propionyl and the like acyl groups, phenyl, methylphenyl, hydroxyphenyl, benzyl and the like aromatic hydrocarbon groups, hydroxy groups and the like. Furthermore, the organic group preferably has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and most preferably 1 carbon atoms, from the viewpoint of water solubility and economic efficiency.

Specific examples of the hydantoin compounds represented by the chemical formula (1) include hydantoin (when R ₁ to R ₄ are all hydrogen atoms), 3-methylhydantoin (when R ₂ is a methyl group and R ₁ , R ₃ and R ₄ are all hydrogen atoms), 5-methylhydantoin (when R ₃ is a methyl group and R ₁ , R ₂ and R ₄ are all hydrogen atoms), and 5-hydantoinacetic acid (when R ₃ is acetic acid and R ₁ , R ₂ and R ₄ are all hydrogen atoms). Among them, hydantoin is preferably used as a material from the viewpoint of the lowest price and economy.

In the above chemical formula (1), "excluding the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms" means excluding the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms in the hydantoin-based compound, that is, "1-methylhydantoin".

The method for obtaining the gold complex is described in the above-mentioned <Method for producing electrolytic gold plating solution>. By using the gold complex as a gold supply source to obtain an electrolytic gold plating solution, the above-mentioned various effects can be obtained.

In addition, the paper "Nouman A.Malik, "X-Ray Crystal Structure of Sodium Bis(N-methylhydantoinato)gold(I)Tetrahydrate; a Linear Planar Complex of Pharmacological Interest Stabilised by Two Nitrogen Ligands", J.C.S.CHEM.COMM., 1978, p.711-712" as a prior art document discloses a gold complex having a structure in which 1-methylhydantoin is coordinated to a monovalent gold ion. However, the paper is a study on monovalent Au complexes for the treatment of rheumatic arthritis, and does not describe its use as an electrolytic gold plating solution as in the present embodiment.

[Implementation example]

The following examples are given to illustrate the present invention in more detail, but the present invention is not limited to these examples.

<Extraction of gold complex alkali metal salts>

[Extraction of sodium hydantoin gold complex]

50 g of hydantoin was dissolved in 250 mL of water to form a hydantoin aqueous solution, which was adjusted to pH 11.5-12.5 with sodium hydroxide, and 25 g of chloroauric acid (HAuCl ₄ ) was added based on gold conversion. The mixture was stirred at 65° C. for 180 minutes to react and obtain a hydantoin gold complex.

Then, sodium hydroxide is added to the aqueous solution containing the obtained gold complex to adjust the pH to 9.0, and the aqueous solution is cooled to below room temperature (25°C) to precipitate crystals of sodium hydantoin gold complex. Thereafter, sodium hydantoin gold complex, which is a gold complex alkali metal salt, is extracted from the aqueous solution by filtration separation (solid-liquid separation).

[Extraction of potassium hydantoin gold complex]

Potassium hydantoin gold complex was extracted in the same manner as in [Extraction of sodium hydantoin gold complex].

[Extraction of 5-methylhydantoin gold complex sodium salt]

5-methylhydantoin gold sodium complex was extracted in the same manner as in [Extraction of hydantoin gold sodium complex] except that 63 g of 5-methylhydantoin was used instead of 50 g of hydantoin.

In addition, the sodium salt of hydantoin gold complex, potassium salt of hydantoin gold complex and sodium salt of 5-methylhydantoin gold complex obtained above can be confirmed to have monovalent gold ions by the precipitation efficiency in gold electroplating (details will be described later).

<Manufacturing of electrolytic gold plating solution and gold plating treatment>

[Experiment No.1~12]

Using any of the above-obtained sodium hydantoin gold complex, potassium hydantoin gold complex, and sodium 5-methylhydantoin gold complex as the gold complex salt, electrolytic gold plating solutions of various specifications shown in Table 1 (Experiments No. 1 to 12) were prepared. In addition, in Experiment No. 1, no chelating agent was added.

[Experiment No.13]

64 g of 5,5-dimethylhydantoin was dissolved in 250 mL of water to form a 5,5-dimethylhydantoin aqueous solution, which was adjusted to pH 11.5-12.5 with sodium hydroxide, and 25 g of chloroauric acid (HAuCl ₄ ) was added based on gold conversion. The mixture was stirred at 65° C. for 180 minutes to react and obtain a 5,5-dimethylhydantoin gold complex.

After further adding sodium hydroxide to the aqueous solution containing the obtained gold complex to a pH of 9.0, the aqueous solution was cooled to below room temperature (25°C), but no crystals of 5,5-dimethylhydantoin gold complex sodium salt were precipitated. Afterwards, the aqueous solution was directly used as a raw material for the electroplating solution (5,5-dimethylhydantoin gold solution in Experiment No. 13 in Table 1) to produce an electrolytic gold plating solution of the specifications shown in Table 1 (Experiment No. 13).

[Experiment No.14]

50 g of hydantoin was dissolved in 250 mL of water to form a hydantoin aqueous solution, to which 25 g of sodium chloroaurate (NaAuCl ₄ ) in terms of gold was added, and the mixture was stirred at 65° C. for 180 minutes to react, thereby obtaining a hydantoin gold complex.

After further adding sodium hydroxide to the obtained aqueous solution with gold complex to pH 9.0, the aqueous solution was cooled to below room temperature (25°C), but crystals of sodium salt of hydantoin gold complex could not be precipitated. Afterwards, the aqueous solution was directly used as a raw material for electroplating solution (hydantoin gold solution in Experiment No. 14 in Table 1) to produce an electrolytic gold plating solution (Experiment No. 14) with the specifications shown in Table 1.

Then, the electrolytic gold plating solutions of Experiments No. 1 to 12, which used gold complex alkaline metal salts as the raw materials of the electrolytic gold plating solution, were subjected to ion chromatography analysis (manufactured by Thermo SCIENTIFIC, device name: Dionex ICS-2100, separation column: Dionex IonPacTM AS12A (4x200mm)). The results confirmed that the chlorine concentration in the electrolytic gold plating solution was 550ppm when the gold concentration was 8g/L, and the chlorine concentration in the electrolytic gold plating solution was 300ppm when the gold concentration was 4g/L (refer to "Chlorine concentration (ppm)" in Table 1).

On the other hand, for each electrolytic gold plating solution of Experiments No. 13 and 14, in which the aqueous solution that generates the gold complex was directly used as the plating solution raw material, ion chromatography analysis was performed in the same manner as above. The results showed that the chlorine concentration for Experiment No. 13 was 5800ppm, and the chlorine concentration for Experiment No. 14 was 5700ppm, both of which were very high chlorine concentrations (see "Chlorine concentration (ppm)" in the test results of Table 1).

In addition, the various electrolytic gold plating solutions of Experiment No. 1 to 14 were used, and as a common condition, the plating solution temperature was 60°C, and the test pieces made of brass and subjected to Ni: 5μm and Au impact plating were electroplated at a current density of 0.5A/ ^dm2 . The appearance results of each gold electroplated film obtained are also shown in Table 1. Here, "○" in "Appearance" of Table 1 indicates a bright lemon yellow tone, "×" indicates a dark brown burnt tone, and "-" indicates that the gold ion maintains a trivalent valence from the following precipitation efficiency results and no appearance evaluation is performed. In addition, for Experiment No. 12, the amount of chelating agent added was less than 4 times the molar amount relative to gold at pH 8 to 10. Therefore, in addition to the charred appearance, the ligands of the gold complex underwent oxidation and decomposition due to alkalinity. Although the amount was small, gold precipitation still occurred. Therefore, "×, gold precipitation phenomenon" is indicated in the "Appearance" column of Table 1.

Furthermore, the deposition efficiency in the electroplating treatment using each electrolytic gold plating solution of Experiment No. 1 to 14 was calculated. The results of the deposition efficiency are shown in Table 1. From the results of Table 1, the deposition efficiency (mg/A.min) in Experiment No. 1 to 12 showed a value of more than 95% (i.e., about 116.3 mg/A.min) of the theoretical value of 122.5 mg/A.min when the gold complex has monovalent gold ions, and it was confirmed that the electrolytic gold plating solution has monovalent gold ions.

On the other hand, the precipitation efficiency (mg/A.min) in Experiments No. 13 and 14 showed a theoretical value of about 40.8mg/A.min when the gold complex has trivalent gold ions, confirming that these electrolytic gold plating solutions have trivalent gold ions.

The above experimental results confirm that the gold complex in the electrolytic gold plating solution of Experiment No. 1 to 12 has monovalent gold ions, which shows that it is beneficial in terms of current efficiency when performing gold plating. In addition, the electrolytic gold plating solution (Experiment No. 1 to 12) produced using the above-mentioned gold complex alkaline metal salt as the gold source is confirmed to be substantially free of chlorine, showing that it can be applied to the electroplated object that repels chlorine.

<Confirmation of the oxidation stability of gold complex>

A solution containing 5 g/L of the sodium salt of the hydantoin gold complex obtained above as gold was adjusted to pH 7.0 and divided into 5 portions. 3.45% hydrogen peroxide (H ₂ O ₂ ) was added so that the Au equivalent ratios were 0, 0.5, 1.0, 2.0, 3.0, and 5.0, respectively. After being stored at room temperature, no change in appearance occurred after 95 hours. In addition, the pH dropped by a maximum of 0.4.

In addition, the pH of a solution containing 5 g/L of sodium gold sulfite (Na ₃ Au(SO ₃ ) ₂ ) as gold was confirmed to be 9.8, and it was divided into 6 portions. 3.45% hydrogen peroxide (H ₂ O ₂ ) was added so that the Au equivalent ratio was 0, 0.5, 1.1, 1.4, 1.7, 2.0, and 5.4, respectively. After being stored at room temperature, precipitation believed to be gold was observed in the case where the amount of hydrogen peroxide added was large after several hours, and a large amount of precipitation was observed in the case where the amount of hydrogen peroxide added was 1.1 equivalents or more after 68 hours. In addition, the pH dropped significantly in the case where the amount of hydrogen peroxide added was 1.1 equivalents or more.

From the above comparative experiments, it is confirmed that the hydantoin gold complex obtained above has better oxidation stability than gold sulfite used as a non-cyanide gold source.

Claims (11)

An electrolytic gold plating solution uses a gold complex as a gold source and contains a chelating agent, a conductive salt, and a buffer, wherein the gold complex has a structure in which a hydantoin compound represented by the following chemical formula (1) is coordinated to a monovalent gold ion;

(In the chemical formula (1), R ₁ to R ₄ independently represent a hydrogen atom or a monovalent organic group, both or either of R ₁ and R ₂ are hydrogen atoms, and both or either of R ₃ and R ₄ are hydrogen atoms; excluding the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms). The electrolytic gold plating solution of claim 1, wherein the chlorine concentration in the electrolytic gold plating solution is less than 1000 ppm. An electrolytic gold plating solution as claimed in claim 1 or 2, wherein the gold complex is derived from an alkaline metal salt. The electrolytic gold plating solution of claim 1 or 2, wherein the chelating agent comprises at least one of a hydantoin compound and succinimide. An electrolytic gold plating solution, which uses a gold complex as a gold source and contains a chelating agent, a conductive salt, and a buffer, is characterized in that: the gold complex has a structure in which a hydantoin compound represented by the following chemical formula (2) is coordinated to a monovalent gold ion; the chlorine concentration in the electrolytic gold plating solution is less than 1000 ppm;

(In the chemical formula (2), R ₅ to R ₈ each independently represent a hydrogen atom or a monovalent organic group, both or either of R ₅ and R ₆ are hydrogen atoms, and both or either of R ₇ and R ₈ are hydrogen atoms). The electrolytic gold plating solution of claim 5, wherein the gold complex is derived from an alkaline metal salt. The electrolytic gold plating solution of claim 5 or 6, wherein the chelating agent comprises at least one of a hydantoin compound and succinimide. A method for producing an electrolytic gold plating solution, which is a method for producing an electrolytic gold plating solution as defined in any one of items 1 to 4 of the patent application, and is characterized by comprising: a step of reacting chloroauric acid or chloroaurate, a hydantoin compound represented by the chemical formula (1), and an alkali metal hydroxide in an aqueous solution to form the gold complex; a step of cooling the aqueous solution containing the gold complex to extract the alkali metal salt of the gold complex; and a step of using the alkali metal salt of the gold complex to produce the electrolytic gold plating solution. A method for producing an electrolytic gold plating solution, which is a method for producing an electrolytic gold plating solution as defined in any one of items 5 to 7 of the patent application, and is characterized by comprising: a step of reacting chloroauric acid or chloroaurate, a hydantoin compound represented by the chemical formula (2), and an alkali metal hydroxide in an aqueous solution to form the gold complex; a step of cooling the aqueous solution containing the gold complex to extract the alkali metal salt of the gold complex; and a step of using the alkali metal salt of the gold complex to produce the electrolytic gold plating solution. A gold electroplating method, which is a method for electroplating using an electrolytic gold electroplating solution as described in any one of items 1 to 7 of the patent application scope, characterized in that the electroplating is carried out under the conditions of pH: 5.0~10.0, liquid temperature: 20~80℃ and current density: 0.1~4.5A/ ^dm2 . A gold complex characterized by having a structure in which a hydantoin compound represented by the following chemical formula (1) is coordinated to a monovalent gold ion;

(In the chemical formula (1), R ₁ to R ₄ independently represent a hydrogen atom or a monovalent organic group, both or either of R ₁ and R ₂ are hydrogen atoms, and both or either of R ₃ and R ₄ are hydrogen atoms; excluding the case where R ₁ is a methyl group and R ₂ to R ₄ are all hydrogen atoms).