Electrolytic gold plating solution, method for manufacturing the same, and plating method using the plating solution.

Abstract

To provide an electrolytic gold plating solution having a long lifespan without toxicity, in which plating can be performed with the solution temperature of 35°C or lower and the plating film can uniformly be electrodeposited with excellent plating properties, and a production method of the solution.SOLUTION: An electrolytic gold plating solution includes a non-cyanide soluble gold salt (A) and a complexing agent (B) for complexing gold ions of the gold salt. The complexing agent (B) is a mercaptotetrazole compound expressed by the following general formula (1). The molar ratio (B / A) of the complexing agent (B) to the soluble gold salt (A) is between 10 and 260. The pH of the gold plating solution is less than 3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electrolytic gold plating solution used for gold plating on a wafer, a substrate, etc., a method for producing the same, and a plating method using the plating solution. More specifically, the present invention relates to an electrolytic gold plating solution suitably used for forming gold plating bumps, a method for producing the same, and a plating method using the plating solution.

Background Art

[0002] Conventionally, since cyanide has a strong complex-forming ability, a gold plating solution in which the gold salt is a cyanide gold salt has been disclosed (see, for example, Patent Document 1 (Claims 1, Claims 2, Claims 3, Paragraph

[0012] , Paragraph

[0025] )). Patent Document 1 describes that this gold plating solution contains a cyanide gold salt, a soluble cobalt salt and / or a nickel salt, an organic acid conductive salt, a chelating agent, and a substitution inhibitor for an electrolytic hard gold plating solution. Further, Patent Document 1 states that according to this gold plating solution, since a predetermined organic substitution inhibitor is blended in the gold plating solution, a protective film can be formed on a nickel substrate in a state where no current is passed through the gold plating solution, and this protective film can be easily removed by passing a current through the gold plating solution. Due to the presence of the protective film formed on the nickel substrate, even when the gold plating solution comes into contact in a state where no current is passed, no substitution reaction occurs with the nickel substrate, enabling selective plating. Also, since no substitution reaction occurs with the nickel substrate, it is described that features such as deposition of gold on the inner wall of the plating tank caused by the generation of gold particles can be suppressed.

[0003] As described in Patent Document 1, plating solutions containing gold cyanide salts are highly toxic. For this reason, cyanide-free electrolytic gold plating solutions have been disclosed (see, for example, Patent Document 2 (Claim 1, paragraphs

[0012] ,

[0037] ,

[0040] ,

[0051] ,

[0054] ,

[0061] )). Patent Document 2 states that this gold plating solution contains a predetermined monovalent gold complex, an electrolyte, and a crystal modifier selected from metals, the pH of the gold plating solution is, for example, 3 to 14, preferably 5 to 8, and the conditions for electrolytic gold plating using this gold plating solution are, for example, a solution temperature of 20 to 80°C and a current density of 0.1 to 6 A / dm². 2 It is stated that this gold plating solution is extremely stable, remains unchanged for one year after preparation, and that changes in the physical properties of deposited gold during the gold plating process are unlikely to cause the gold plating solution to decompose. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2016 / 208340 [Patent Document 2] International Publication No. 2016 / 098789 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Generally, when forming gold-plated bumps using the gold plating method, gold plating is performed within a pattern formed on the substrate with organic resist. However, although the gold plating solution described in Patent Document 2 is non-toxic, when gold plating is performed in the alkaline region where the plating solution pH exceeds 7 within the pH range of 3 to 14, the resist pattern dissolves, making pattern plating difficult, and the electrical conductivity of the plating solution decreases, resulting in the problem of uneven electrodeposition of the plating film. On the other hand, when the plating solution pH is in the acidic to neutral range of 3 to 7, and the plating temperature is in the range of 20°C to 80°C, but the temperature is above 40°C, the resist pattern is easily damaged, and the problem of uneven electrodeposition of the plating film still remains.

[0006] The object of the present invention is to provide an electrolytic gold plating solution and a method for producing the same, which allows plating at a liquid temperature of 35°C or lower, has excellent plating properties that result in uniform electrodeposition of the plating film, has a long plating solution life, and is non-toxic. Another object of the present invention is to provide a plating method using this plating solution. [Means for solving the problem]

[0007] The present inventors have observed that the gold plating solution described in Patent Document 2 has a neutral pH to facilitate the complexation of gold ions, but this results in uneven electrodeposition of the plating film. Therefore, they have focused on the fact that by setting the pH of the gold plating solution to a strongly acidic range of less than 3 to increase the electrical conductivity of the plating solution, while simultaneously selecting a specific complexing agent and setting the molar ratio of this complexing agent to the gold salt to a predetermined ratio, they can promote the complexation of gold ions, thereby improving the plating performance by ensuring uniform electrodeposition of the plating film and extending the life of the plating solution, leading to the present invention.

[0008] A first aspect of the present invention is an electrolytic gold plating solution comprising a non-cyanide soluble gold salt (A) and a complexing agent (B) for complexing the gold ions of the gold salt, wherein the complexing agent (B) is a mercaptotetrazole compound represented by the following general formula (1), the molar ratio (B / A) of the complexing agent (B) to the soluble gold salt (A) is 10 or more and 260 or less, and the pH of the gold plating solution is less than 3.

[0009] [ka]

[0010] However, in formula (1), '*' represents a methyl group, ethyl group, propyl group, carboxyl group, acetyl group, phenyl group, hydroxyphenyl group, methoxyphenyl group, alboxyl group, dimethylaminoethyl group, or acetamidophenyl group.

[0011] A second aspect of the present invention is an invention based on the first aspect, further comprising sulfuric acid or an alkyl sulfonic acid having 1 to 5 carbon chains, which is an electrolytic gold plating solution.

[0012] A third aspect of the present invention is an invention based on the first or second aspect, which is an electrolytic gold plating solution that does not contain cyanide compounds or cyanide ions.

[0013] A plating method according to a fourth aspect of the present invention is a plating method that forms a gold plating film within a resist pattern using an electrolytic gold plating solution according to the first, second, or third aspect.

[0014] A method for producing the product according to the fifth aspect of the present invention involves electrolyzing a gold metal in sulfuric acid or an alkyl sulfonic acid having 1 to 5 carbon chains in the presence of the complexing agent (B) according to the first aspect to obtain an electrolyte containing a non-cyanide soluble gold salt (A), and then producing the electrolytic gold plating solution according to the first aspect. [Effects of the Invention]

[0015] In the electrolytic gold plating solution according to the first aspect of the present invention, a specific mercaptotetrazole compound shown in formula (1) above is used as a complexing agent, and by setting the molar ratio (B / A) of the complexing agent (B) to the gold salt (A) to a predetermined ratio of 10 to 260, gold ions can be complexed even at a pH of less than 3. Furthermore, because the pH is less than 3, the electrical resistance of the plating solution is low and the electrical conductivity of the plating solution is high, which allows the plating film to be uniformly electrodeposited during plating and results in excellent plating performance. In addition, because this electrolytic plating solution contains a specific mercaptotetrazole compound, gold plating can be performed under relatively low temperature conditions (e.g., 35°C or below), and the acidic pH of less than 3 has the advantage of reducing damage to the resist pattern during plating. Furthermore, because the gold ions are complexed with a specific mercaptotetrazole compound, it exhibits high oxidation stability and has the effect of extending the life of the plating solution after it has been manufactured.

[0016] In the electrolytic gold plating solution according to the second aspect of the present invention, since the gold plating solution further contains sulfuric acid or an alkylsulfonic acid having a carbon chain of 1 to 5, there is an effect of dissolving gold in an aqueous solution by electrolysis.

[0017] In the electrolytic gold plating solution according to the third aspect of the present invention, since the gold plating solution does not contain a cyanide compound or cyanide ions, it has low toxicity.

[0018] In the plating method according to the fourth aspect of the present invention, since a gold plating solution having a pH less than 3 is used, a uniform gold plating film can be formed in the resist pattern without dissolving the resist pattern during gold plating.

[0019] In the production method according to the fifth aspect of the present invention, gold metal is electrolyzed in sulfuric acid or an alkylsulfonic acid having a carbon chain of 1 to 5 in the presence of the complexing agent (B) according to the first aspect to prepare an aqueous solution of a non-cyanide soluble gold salt (A) having a pH less than 1, and the pH of this aqueous solution is adjusted to less than 3 using a pH adjuster, thereby producing the electrolytic gold plating solution according to the first aspect. Therefore, this method has the effect of coordinating only the complexing agent (B) to gold ions.

Brief Description of the Drawings

[0020] [Figure 1] It is a configuration diagram of an apparatus for preparing a non-cyanide soluble gold salt of the present invention.

Embodiments for Carrying Out the Invention

[0021] Next, embodiments for carrying out the present invention will be described with reference to the drawings.

[0022] 〔Electrolytic Gold Plating Solution〕 The electrolytic gold plating solution of this embodiment comprises a non-cyanide soluble gold salt (A) and a complexing agent (B) that complexes the gold ions of the gold salt, wherein the complexing agent (B) is a mercaptotetrazole compound represented by the general formula (1) described above, the molar ratio of the complexing agent (B) to the soluble gold salt (A) (B / A) is 10 or more and 260 or less, and the pH of the gold plating solution is less than 3.

[0023] As the complexing agent (B) for the electrolytic gold plating solution, a mercaptotetrazole compound represented by the general formula (1) described above is used. Such a complexing agent (B) has a high electron density in the tetrazole ring and a strong coordinating power of the lone pair of electrons of the mercapto group, which allows it to accurately complex with gold ions and result in a highly stable plating solution that does not cause deposition or precipitation of gold components. Among the mercaptotetrazole compounds, 5-mercapto-1-methyltetrazole and I-(2-dimethylaminoethyl)-5-mercaptotetrazole are preferred because they have high solubility in aqueous solutions.

[0024] The molar ratio (B / A) of the complexing agent (B) to the soluble gold salt (A) in an electrolytic gold plating solution is between 10 and 260. If the molar ratio (B / A) is less than 10, there is insufficient complexing agent, resulting in inadequate complexing of gold ions eluted from the soluble gold salt. This leads to deposition or precipitation of the gold component in the plating solution, and the stability of the plating solution deteriorates. If the ratio exceeds 260, there is an excess of complexing agent, excessively suppressing the electrodeposition of gold ions, resulting in the failure to obtain a dense plating film. The preferred molar ratio (B / A) is between 10 and 100.

[0025] The concentration of the non-cyanide soluble gold salt (A) in the electrolytic gold plating solution is preferably 0.001 mol / L to 0.1 mol / L. If it is less than 0.001 mol / L, the plating rate tends to be slow, and if it exceeds 0.1 mol / L, the plating bath may become too expensive. Furthermore, the concentration of the complexing agent (B) in the electrolytic gold plating solution is preferably 0.01 mol / L to 3 mol / L. If it is less than 0.01 mol / L, the complexation of gold ions tends to be insufficient, and the gold component of the plating solution tends to precipitate. If it exceeds 3 mol / L, it tends to be difficult to dissolve the complexing agent in the aqueous solution.

[0026] The pH of the electrolytic gold plating solution is less than 3 to ensure high electrical conductivity. If the pH exceeds 3, the electrical conductivity of the plating solution decreases, resulting in poor plating performance. A preferred pH is between 0 and 2.

[0027] In electrolytic gold plating solutions, it is preferable that the solution contains sulfuric acid or an alkyl sulfonic acid with a carbon chain of 1 to 5. The concentration of sulfuric acid or alkyl sulfonic acid with a carbon chain of 1 to 5 is preferably in the range of 0.01 mol / L to 5 mol / L. If the concentration is less than 0.01 mol / L, the conductivity of the plating solution tends to be low, making it difficult to uniformly electrodeposit the plating film. If the concentration exceeds 5 mol / L, the viscosity of the plating solution becomes too high, making it difficult to obtain a dense plating film.

[0028] In electrolytic gold plating solutions, it is preferable that they do not contain cyanide compounds or cyanide ions. Because they do not contain cyanide compounds or cyanide ions, they have low toxicity. "Not containing cyanide compounds or cyanide ions" means that when the electrolytic gold plating solution is measured by a test method specified in JIS-K0102 (such as pyridine-pyrazolone spectrophotometric method, 4-pyridinecarboxylic acid-pyrazolone spectrophotometric method, ion electrode method, or flow analysis method using 4-pyridinecarboxylic acid-pyrazolone color development), the concentration of cyanide compounds or cyanide ions is 1 ppm or less.

[0029] [Method for manufacturing electrolytic gold plating solution] The method for manufacturing the electrolytic gold plating solution in this embodiment will now be described in detail. In the method for producing the electrolytic gold plating solution of this embodiment, it is preferable to utilize the electrolysis of gold metal by an ion exchange membrane. In the electrolytic gold plating solution obtained using this method, the mercaptotetrazole compound is reliably coordinated to the gold ions, so gold plating can be reliably performed.

[0030] As shown in Figure 1, non-cyanide soluble gold salts are prepared in an electrolytic apparatus 10 in which an anode tank 1 and a cathode tank 2 are connected with a hydrogen ion exchange membrane 3 in between. First, sulfuric acid or alkyl sulfonic acid with a carbon chain of 1 to 5, the complexing agent (B) shown in the general formula (1) described above, and pure water are placed in anode tank 1. Here, the concentration of sulfuric acid or alkyl sulfonic acid with a carbon chain of 1 to 5 is preferably 0.1 to 5 mol / L. The concentration of the complexing agent (B) is preferably 0.01 to 3 mol / L. Deionized water can be used as the pure water.

[0031] Next, sulfuric acid or an alkyl sulfonic acid with a carbon chain of 1 to 5 and pure water are added to the cathode tank 2. Here, the concentration of sulfuric acid or the alkyl sulfonic acid with a carbon chain of 1 to 5 is preferably 0.01 to 5 mol / L. Next, a soluble plate-shaped or rod-shaped gold metal 4 is used for the anode, and an insoluble Pt / Ti plate 5, which is made by plating platinum (Pt) on a titanium (Ti) base, is used for the cathode. As the gold metal 4, it is preferable to use gold with a purity of 99% or higher that has been processed into a plate-shaped or rod-shaped form.

[0032] In the electrolytic apparatus 10 with this configuration, the gold metal 4 is electrolyzed to elute gold ions and complex them with a complexing agent (B). The obtained electrolyte 6 is removed from the anode tank 1, and the electrolyte 6 is subjected to solid-liquid separation using a solid-liquid separation apparatus (not shown) to obtain a liquid containing a non-cyanide soluble gold salt (A). The electrolysis here can be carried out at a liquid temperature of 10°C to 50°C and a current density of 0.01 ASD to 10 ASD, and it is preferable that the gold concentration (concentration of the non-cyanide soluble gold salt (A)) be 0.001 mol / L to 1 mol / L.

[0033] Next, the solution containing the non-cyanide soluble gold salt (A) is diluted to produce the electrolytic gold plating solution of this embodiment. Dilution is carried out with pure water such as deionized water or distilled water, and it is preferable to dilute it so that the concentration of the non-cyanide soluble gold salt (A) is in the range of 0.001 mol / L to 0.1 mol / L. In this case, if the concentration of the complexing agent (B) has decreased, it is preferable to add more so that it is in the range of 0.01 mol / L to 3 mol / L. Furthermore, when plating objects that are unstable to strong acids, the pH of the plating solution can be adjusted by neutralization as needed, within a range where the pH does not exceed 3. Neutralization is preferably carried out with a hydroxide such as sodium hydroxide or a base such as ammonia. This produces the electrolytic gold plating solution of this embodiment. [Examples]

[0034] Next, embodiments of the present invention will be described in detail along with comparative examples.

[0035] First, Table 1 below shows the six types of complexing agents (types: A to F) used in Examples 1 to 12 and Comparative Examples 1 to 6, along with their respective molecular weights.

[0036] [Table 1]

[0037] <Example 1> First, a solution containing the non-cyanide soluble gold salt (A) described below was prepared, and then an electrolytic gold plating solution was prepared using this solution. (Preparation of a solution containing a non-cyanide soluble gold salt (A)) A solution containing a non-cyanide soluble gold salt (A) was prepared using a complexing agent of type A (B) as shown in Table 1 above, with the following composition. The prepared solution was placed in the anode tank 1 shown in Figure 1. Methanesulfonic acid: 100g / L 5-Mercapto-1-methyltetrazole (complexing agent of type A (B)): 100 g / L Remainder: pure water

[0038] Next, a solution with the following composition was prepared and added to the cathode tank 2 shown in Figure 1. Methanesulfonic acid: 100g / L Remainder: pure water In the soluble gold salt preparation apparatus 10 with the above configuration, the liquid temperature was set to 25°C and the anode current density to 0.1ASD, and the gold metal 4 was electrolyzed for 50 hours. The pH of the electrolyte 6 was less than 1. This electrolyte 6 was filtered using three types of filter paper for qualitative analysis, and a yellow, transparent, non-cyanide soluble gold salt (A) solution was obtained as the filtrate. The gold ion concentration in this solution was measured using an ICP emission spectrometer (ICP-OES) and was found to be 10 g / L.

[0039] (Preparation of electrolytic gold plating solution) An electrolytic gold plating solution was prepared using the following procedure. A solution containing a non-cyanide soluble gold salt (A) with a gold ion concentration of 10 g / L and a pH of less than 1 was diluted with pure water to adjust the gold ion concentration to 0.5 g / L (0.002538 mol / L). Next, 5-mercapto-1-methyltetrazole, a complexing agent of type A (B), was added to the diluted solution and mixed to prepare the electrolytic gold plating solution. The concentration of the complexing agent (B) in the electrolytic gold plating solution was 10 g / L (0.086103 mol / L), and the pH of the electrolytic gold plating solution was less than 1. The molar ratio (B / A) calculated from the gold ion concentration and the complexing agent concentration was 34.

[0040] The details of Example 1 described above are shown in Table 2 below. Table 2 also shows the details (molar ratio (B / A) and pH value) of Examples 2 to 12 and Comparative Examples 1 to 6, which will be described next.

[0041] [Table 2]

[0042] <Examples 2-12 and Comparative Examples 1-6> As shown in Table 2 above, in Examples 2 to 12 and Comparative Examples 1 to 6, the gold ion concentration of the non-cyanide soluble gold salt (A) was changed to a different value from that in Example 1 by altering the dilution ratio when diluting the solution containing the non-cyanide soluble gold salt (A) with pure water. In addition, the complexing agent (B) was prepared in the amounts listed in Table 2. Furthermore, the same complexing agent (B) was used in Examples 2-9 and Comparative Examples 1-3 and 6 as in Example 1. Examples 10-12 and Comparative Examples 4 and 5 used different complexing agents than in Example 1. In Comparative Examples 4 and 5, a mercaptotriazole compound was used instead of a mercaptotetrazole compound. Furthermore, in Examples 2 to 12 and Comparative Examples 1 to 6, the concentration of the complexing agent in the electrolytic gold plating solution was adjusted by adding the same or different amounts of the complexing agent (B) when preparing the solution containing the non-cyanide soluble gold salt (A) as in Example 1. Furthermore, in Examples 2-12 and Comparative Examples 1-6, after adding and mixing the complexing agent to the diluted solution from Example 1, a 0.1 mol / L sodium hydroxide aqueous solution was added dropwise to this mixture to change the pH of the mixture as shown in Table 2.

[0043] <Comparative Tests and Evaluations> The stability and plating properties of the 18 electrolytic gold plating solutions (Examples 1-12 and Comparative Examples 1-6) were investigated after preparation using the following method. The results are shown in Table 2 above.

[0044] (1) Stability of the plating solution The stability of the electrolytic gold plating solution was tested by taking 50 mL of the prepared solution and sealing it in a clear glass bottle. This bottle was stored for 6 months in a clean oven maintained at 40°C. The appearance of the solution after storage was visually inspected. In the visual inspection, if no precipitate formed at the bottom of the glass bottle, the stability of the plating solution was judged to be "good," and if precipitate formed, the stability of the plating solution was judged to be "poor."

[0045] (2) Regarding plating properties A 1 mm diameter rod-shaped gold metal was used as the anode of the electroplating apparatus. A silicon wafer with a resist pattern consisting of 2000 vias with a diameter of 100 μm was formed on its surface as the cathode. 100 mL each of the 18 electrolytic gold plating solutions obtained in Examples 1-12 and Comparative Examples 1-6 were placed in glass beakers and stirred with a stirrer. These stirred solutions were placed in the plating tank of the electrolytic plating apparatus, and the solution temperature was set to 30°C and the cathode current density to 0.1 ASD, and the via openings of the resist pattern were plated for 1 hour. After removing the silicon wafer from the plating apparatus, cleaning and drying it, the resist pattern was removed using an organic solvent. Plating performance was determined to be "good" if gold plating bumps formed along the shape of the resist pattern, and "poor" if gold plating bumps did not form according to the resist pattern. The results are shown in Table 2 above.

[0046] As is clear from Table 2, in Comparative Example 1, a mercaptotetrazole compound was used as the complexing agent (B), the pH of the electrolytic gold plating solution was 1, and the gold plating bumps were formed according to the resist pattern, indicating "good" plating performance. However, the molar ratio (B / A) of soluble gold salt (A) to complexing agent (B) was too small at 8, resulting in insufficient complexing of the gold ions, precipitation, and "poor" stability of the plating solution.

[0047] In Comparative Example 2, a mercaptotetrazole compound was used as the complexing agent (B), and the molar ratio of soluble gold salt (A) to complexing agent (B) (B / A) was 170. The stability of the plating solution was "good," but because the pH of the electrolytic gold plating solution was too high at 3, hydrogen was generated, causing the resist pattern to peel off, and the gold plating bumps were not formed according to the resist pattern, resulting in "poor" plating performance.

[0048] In Comparative Example 3, a mercaptotetrazole compound was used as the complexing agent (B), but the molar ratio (B / A) of the soluble gold salt (A) to the complexing agent (B) was too small at 8, resulting in precipitation and "poor" stability of the plating solution. Furthermore, the pH of the electrolytic gold plating solution was too high at 4, causing hydrogen to be generated, the resist pattern to peel off, and the gold plating bumps were not formed according to the resist pattern, resulting in "poor" plating performance.

[0049] In Comparative Examples 4 and 5, the pH of the electrolytic gold plating solution was 1 and 2, respectively, and gold plating bumps were formed according to the resist pattern, resulting in "good" plating performance in both cases. Furthermore, the molar ratio (B / A) of soluble gold salt (A) to complexing agent (B) was appropriate at 97 and 171, respectively. However, because a mercaptotriazole compound was used as the complexing agent, under the aforementioned plating conditions, the gold ions did not reliably complex, precipitation occurred, and the stability of the plating solution was "poor" in both cases.

[0050] In Comparative Example 6, a mercaptotetrazole compound was used as the complexing agent (B). However, the molar ratio (B / A) of the soluble gold salt (A) to the complexing agent (B) was too high at 305. As a result, the electrodeposition of gold ions by the complexing agent was excessively suppressed, and the plating film formed within the resist pattern was not dense, resulting in "poor" plating performance.

[0051] In contrast to these comparative examples, Examples 1 to 12 were electrolytic gold plating solutions that met the requirements of the first aspect of the present invention. As a result, no gold sedimentation occurred after 6 months of storage, and gold plating bumps were formed according to the resist pattern. The stability and plating properties of the plating solution were all "good". [Industrial applicability]

[0052] The electrolytic gold plating solution of the present invention can be suitably used for gold plating on wafers or substrates, particularly for gold plating bumps.

Claims

1. An electrolytic gold plating solution comprising a non-cyanide soluble gold salt (A) and a complexing agent (B) that complexes the gold ions of the gold salt, An electrolytic gold plating solution characterized in that the complexing agent (B) is a mercaptotetrazole compound represented by the following general formula (1), the molar ratio (B / A) of the complexing agent (B) to the soluble gold salt (A) is 10 or more and 260 or less, and the pH of the gold plating solution is less than 3. 【Chemistry 1】 However, in formula (1), '*' represents a methyl group, ethyl group, propyl group, carboxyl group, acetyl group, phenyl group, hydroxyphenyl group, methoxyphenyl group, alboxyl group, dimethylaminoethyl group, or acetamidophenyl group.

2. The electrolytic gold plating solution according to claim 1, further comprising sulfuric acid or an alkyl sulfonic acid having 1 to 5 carbon chains.

3. The electrolytic gold plating solution according to claim 1 or 2, which does not contain cyanide compounds or cyanide ions.

4. A plating method for forming a gold plating film in a resist pattern using the electrolytic gold plating solution described in Claim 1.

5. A method for producing an electrolytic gold plating solution according to claim 1, which involves electrolyzing a gold metal in sulfuric acid or an alkyl sulfonic acid having 1 to 5 carbon chains in the presence of the complexing agent (B) according to claim 1 to obtain an electrolyte containing a non-cyanide soluble gold salt (A).

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