Aqueous solution of gold(I) compound, method for producing the same, and gold plating solution

Abstract

The objective is to provide an aqueous solution of gold(I) compounds that can be used as a gold source for gold plating solutions without causing precipitation over a wide pH range and with long-term oxidation stability. [Solution] An aqueous solution of a gold(I) compound having a structure represented by the following general formula (1), wherein the cyanide concentration is 500 mg / L or less, the sulfite ion concentration is 1000 ppm by mass or less, and the halogen ion concentration is 1000 mg / L or less. RS - -Au-S-(CH2) n -SO3 - ...(1) (In formula (1), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and n is an integer from 3 to 10.)

Description

[Technical Field]

[0001] This invention relates to an aqueous solution of a gold(I) compound, a method for producing the same, and a gold plating solution. [Background technology]

[0002] Traditionally, potassium gold cyanide (hereinafter also known as PGC) has been used as a gold source for electrolytic and electroless gold plating. However, while PGC has high stability, the cyanide (CN) it contains binds almost irreversibly to the iron ions of mitochondrial cytochrome C oxidase, inhibiting the transport of electrons to oxygen in the electron transport chain of aerobic respiration, which can lead to cellular cessation and even death. Furthermore, PGC is easily soluble in water and, if not properly managed, can easily be released into the environment through wastewater, potentially causing harm to the human body. In addition, when using cyanide-based gold plating solutions, excess cyanide can peel and damage the resist patterns of semiconductor components, making it difficult to form fine circuit patterns.

[0003] Due to these problems, in recent years it has become desirable to use plating solutions containing gold salts or gold complexes that are substantially free of cyanide. Examples include gold plating solutions containing gold sulfite or hydantoin gold that are substantially free of cyanide.

[0004] However, gold plating solutions using gold sulfite solutions have a problem in that they have poor oxidative stability, and the gold sulfite can decompose during plating operations. For example, in plating solutions using sodium gold sulfite (hereinafter also called SGS), the sulfite ions in the solution are easily oxidized and decomposed by dissolved oxygen in the plating solution and air entrainment due to stirring or the insertion and removal of the object to be plated, causing a decrease in their concentration. This reduces the oxidative stability of the gold complex, which can lead to the decomposition of the plating solution. When such decomposition occurs, a gold precipitate phenomenon occurs in the plating solution tank or piping, which interferes with the plating work. In addition, with SGS, black precipitate due to the decomposition of gold salts is likely to occur during storage, making storage in a light-shielded state essential, and its management is not easy.

[0005] In addition, due to the poor oxidation stability of the above-mentioned SGS, in the gold plating solution using SGS as the gold source, it has to be limited to use in neutral to alkaline conditions. Therefore, when used for a resist pattern with weak alkalinity, the plating solution may penetrate into the resist, resulting in pattern-out deposition or the like. In addition, in an alloy plating solution that requires high hardness for connector applications or the like, considering the stability of the eutectic metals (Co, Ni), the pH of the plating solution has to be in acidic to neutral conditions, and alloy plating using SGS cannot be used.

[0006] In addition, although the hydantoin gold plating solution has oxidation resistance, it has poor thermal and pH stability, and there is also a problem of salting out due to running.

[0007] Therefore, in order to solve the pH stability and air stability of the gold salt for the cyanide-free gold plating solution, thiol compounds are widely used. (Patent Documents 1, 2, 3)

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, many thiol ligands are slightly soluble in water, and many of the gold salts using these ligands are also slightly soluble in water. Further, even when a water-soluble thiol ligand is used, side reactions are likely to occur due to the presence of highly reactive functional groups other than the thiol moiety that coordinates to gold ions, which can cause changes in the properties of the gold salt. As an example, thiolate gold salts having a carboxy group, which is one of the water-soluble functional groups, are known to dissolve in an alkaline solution but precipitate in an acidic solution. Due to these reasons, the gold salts that can be used in a wide pH range from acidic to alkaline conditions have been limited.

[0010] Therefore, an object of the present invention is to provide an aqueous solution of a gold(I) compound that can be used as a gold plating solution source having long-term oxidation stability without causing precipitation in a wide pH range.

Means for Solving the Problems

[0011] In order to achieve the above object, the present inventors conducted a study on the development of water-soluble gold complexes. In order to achieve the above object, it is required that there can exist a water-soluble gold complex that does not cause precipitation of gold even in a wide pH range and can be stably used for a long period. The present inventors mixed and heated gold sulfite or its salt, which is known as a monovalent water-soluble gold complex, with a thiol having a specific structure to react both of them to obtain a solution containing a gold complex. Further, by reacting the insoluble gold complex obtained by cooling such a solution with a water-soluble organic compound (R-SH) having a thiol group to solubilize the gold complex again, the present inventors found that an aqueous solution of a gold(I) compound that can be used as a gold plating solution source having long-term oxidation stability without causing precipitation of gold even in a wide pH range can be obtained, and thus completed the present invention.

[0012] That is, the present invention is as follows. 〔1〕 It contains a gold(I) compound having a structure represented by the following general formula (1), the cyanide concentration is 500 mg / L or less, the sulfite ion concentration is 1000 mass ppm or less, The halogen ion concentration is 1000 mg / L or less. Gold(I) compound aqueous solution. RS - -Au-S-(CH2) n -SO3 - ...(1) (In formula (1), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and n is an integer from 3 to 10.) [2] An aqueous solution of the gold(I) compound described in [1] above, wherein the gold concentration is adjusted to 1.0 g / L or more in the pH range of 1 to 12, and no precipitate is formed when heated at 90°C for 8 hours. [3] The gold(I) compound aqueous solution described in [1] above, wherein when an air bubbling test is performed on the gold(I) compound aqueous solution with a pH of 6.0 or higher and less than 8.0 at an air flow rate of 1.0 L / min for 6 hours, the pH does not decrease by 40% or more. [4] The gold(I) compound aqueous solution described in [1] above, wherein the pH does not decrease by 10% or more when an air bubbling test is performed on the gold(I) compound aqueous solution with a pH of 8.0 or higher and less than 12.0 at an air flow rate of 1.0 L / min for 6 hours. [5] An aqueous solution of the gold(I) compound described in [1] above, wherein a fragment is obtained at the position m / z = 596.87 ± 0.5 when subjected to nano ESI MS. [6] An aqueous solution of the gold(I) compound described in [1] above, wherein when subjected to nano ESI MS, a fragment equivalent to a dimer is obtained at the position m / z = 596.87 + 573.9 ± 0.5. [7] An aqueous solution of the gold(I) compound described in [1] above, wherein when subjected to nano ESI MS, a trimer-equivalent fragment is obtained at the position m / z = 596.87 + 1147.8 ± 0.5. [8] An aqueous solution of the gold(I) compound described in [1] above, wherein when subjected to nano ESI MS, a fragment with an intensity equivalent to 15-20% of the main fragment ratio is obtained at the position m / z = 596.87 ± 0.5 + 1.99. [9] A step of mixing and heating gold sulfite or its salt with a thiol having a structure represented by the following general formula (2) to obtain an insoluble gold complex, and A step of mixing and heating the insoluble gold complex with a water-soluble organic compound having a thiol group to obtain a gold(I) compound having a structure represented by the following general formula (1), A method for producing an aqueous solution of a gold(I) compound, comprising: R-S - -Au-S-(CH2) n -SO3 - ···(1) (In formula (1), R is an organic group containing at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at the terminal or side chain, and n is an integer of 3 to 10) HS-(CH2) m -SO3 - ···(2) (In formula (2), m is an integer of 3 to 10)

[10] A gold plating solution containing a gold(I) compound having a structure represented by the following general formula (1), a chelating agent, a buffer, and an additive, having a cyanide concentration of 500 mg / L or less, having a sulfite ion concentration of 1000 mass ppm or less, having a halogen ion concentration of 1000 mg / L or less, a gold plating solution. R-S - -Au-S-(CH2) n -SO3 - ···(1) (In formula (1), R is an organic group containing at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at the terminal or side chain, and n is an integer of 3 to 10)

[11] The gold plating solution according to

[10] above, wherein the additive contains at least one selected from the group consisting of potassium thiocyanate, sodium thiocyanate, and ammonium thiocyanate, and the gold plating solution is an electroless plating solution. [Advantages of the Invention]

[0013] According to the present invention, it is possible to provide an aqueous solution of a gold(I) compound that can be used as a gold source for a plating solution that does not precipitate gold over a wide pH range and has long-term oxidation stability, a method for producing the same, and a gold plating solution containing the same. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a spectral diagram obtained by nano ESI MS analysis of the gold(I) compound aqueous solution of Example 1. [Figure 2] Figure 2 is a graph showing the results of the air stability tests in Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0015] The embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below, and can be modified and implemented as desired without departing from the spirit of the invention. In this specification, gold(I) compounds are also referred to as gold(I) compounds and mean monovalent gold compounds. The "~" in a numerical range indicates a range that includes the numbers before and after it. For example, "0 mass%~100 mass%" means a range that is greater than or equal to 0 mass% and less than or equal to 100 mass%.

[0016] <Gold(I) compound aqueous solution> The following describes the aqueous solution of the gold(I) compound according to this embodiment. The gold(I) compound aqueous solution of this embodiment contains a gold(I) compound having the structure represented by the following general formula (1), and is characterized by having a cyanide concentration of 500 mg / L or less, a sulfite ion concentration of 1000 ppm by mass or less, and a halogen ion concentration of 1000 mg / L or less. RS - -Au-S-(CH2) n -SO3 - ...(1) (In formula (1), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and n is an integer from 3 to 10.)

[0017] (gold(I) compound) The gold(I) compound aqueous solution of this embodiment contains a gold(I) compound having the structure represented by the general formula (1) described above. The gold(I) compound may be obtained by mixing gold sulfite or a salt thereof, which is known as a monovalent water-soluble gold complex, with a thiol having a specific structure described later for coordinating to gold ions, heating the mixture, and then reacting the insoluble gold complex obtained with a water-soluble organic compound having a thiol group to re-soluble it. According to this method, the gold complex is first insoluble, then separated by solid-liquid separation by filtration or the like to extract the gold complex, and then re-solubled to obtain the gold complex, thereby reducing the concentration of sulfite ions originating from the raw materials. Thus, the gold(I) compound aqueous solution of this embodiment has a low concentration of sulfite ions, and therefore exhibits excellent oxidation stability and pH stability without precipitation over a wide pH range.

[0018] In the above general formula (1), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and these organic groups are preferably highly hydrophilic. In this specification, an organic group means a group having at least carbon atoms as a skeletal atom, and may be linear, branched, or cyclic. The above sulfonic acid group, carboxyl group, and amino group may be salts thereof. In R, the number of carbon atoms of the organic group is preferably 1 to 5, and more preferably 1 to 3. R is preferably an alkyl group, etc. Furthermore, it is preferable that R has a sulfonic acid group at its terminal or side chain. Particularly preferable, from the viewpoint of coordination stability of the gold(I) compound, R is an alkyl sulfonic acid group having 1 to 3 carbon atoms.

[0019] In the general formula (1) above, n is an integer between 3 and 10. If n is less than 3, the precipitate formed during the production of the gold(I) compound may become an impurity, and the aqueous solution of the gold(I) compound may not achieve the desired properties. If n is greater than 10, the compound may not be able to be made water-soluble. An integer between 3 and 5 is preferred for n.

[0020] The above gold(I) compound is particularly preferably a compound having the structure shown in formula (3) below, from the viewpoint of economy and other factors. That is, in the above general formula (1), R is (CH2)3-SO3 - It is particularly preferable that n is 3.

[0021] [ka]

[0022] If the gold(I) compound is a compound having the structure shown in formula (3) above, when the aqueous solution of the gold(I) compound of this embodiment is subjected to nano ESI MS, a monomer-equivalent fragment is obtained at the position m / z (mass / charge) = 596.87 ± 0.5, a dimer-equivalent fragment is obtained at the position m / z = 596.87 + 573.9 ± 0.5, and a trimer-equivalent fragment is obtained at the position m / z = 596.87 + 1147.8 ± 0.5. Figure 1 shows the spectrum obtained by nano ESI MS analysis when the gold(I) compound is the compound represented by formula (4) below, and the monomer is [Au / MPS / Na][Na / MPS / Na]Na + This means (C6H 12 O6AuNa4S4), the dimer is 2[Au / MPS / Na]2[Na / MPS / Na]Na + Meaning (C 12 H 24 O 12 Au2Na7S8), the trimer is 3[Au / MPS / Na]3[Na / MPS / Na]Na + (C 18 H 36 O 18 Au3Na 10S 12 ). MPS stands for "3-mercapto-1-propanesulfonate sodium".

[0023] [ka]

[0024] Furthermore, if the gold(I) compound is a compound having the structure shown in formula (3) above, when the aqueous solution of the gold(I) compound in this embodiment is subjected to nano ESI MS, a fragment with an intensity equivalent to 15-20% of the main fragment ratio is obtained at the position m / z = 596.87 ± 0.5 + 1.99. For example, in Figure 1, the "S isotope ion peak of the monomeric fragment" is the fragment at the position m / z = 596.87 ± 0.5 + 1.99.

[0025] In Figure 1, the vertical axis represents intensity, and the horizontal axis represents the mass-to-charge ratio (m / z). When the gold(I) compound is a compound having the structure shown in formula (3) above, the monomer of the compound is C6H in its chemical formula. 12 It can be represented as O6AuNa4S4, and when subjected to nano ESI-MS, a fragment is obtained at the position m / z = 596.87 ± 0.5. Also, C6H 12 O6AuNa4S4 (monomer) contains a sulfur atom, and sulfur is the main component present in the monomer. 32 In addition to S (atomic weight: 31.972071), (94.93%), 34 It is known that sulfur (atomic weight: 33.9678) is present in nature at approximately 4.29%. From this, it can be inferred that one of the sulfur atoms is located at the position corresponding to +1.99 of the monomer molecular ion fragment (m / z = 596.87 ± 0.5). 34 C6H replaced by S 12 O6AuNa4S4( 32 S x 3, 34 A fragment of S×1) was obtained, and its strength was C6H 12 O6AuNa4S4( 32The relative intensity with respect to the S×4 fragment (main fragment) is approximately 15-20% (theoretically 17%).

[0026] The above nano ESI MS is performed by the method described in the examples below.

[0027] (gold concentration) In this embodiment, the gold concentration in the aqueous solution of the gold(I) compound is preferably 100 g / L or less, preferably 20 g / L or more, and more preferably 50 g / L or more, from the viewpoint of long-term storage stability of the aqueous solution of the gold(I) compound in this embodiment and from the viewpoint of gold supply to the gold plating solution. The gold concentration in the gold(I) compound aqueous solution of this embodiment can be determined, for example, by high-frequency inductively coupled plasma atomic emission spectroscopy as described in the examples.

[0028] (Cyanide concentration) The gold(I) compound aqueous solution in this embodiment has a cyanide concentration of 500 mg / L or less. Because the cyanide concentration of the gold(I) compound aqueous solution in this embodiment is low (500 mg / L or less), it does not suffer from the effects on the human body or the environment caused by cyanide as described above. The aqueous solution of the gold(I) compound in this embodiment preferably has a cyanide concentration of 500 mg / L or less, more preferably 100 mg / L or less, even more preferably 10 mg / L or less, particularly preferably 5 mg / L or less, and most preferably 0 mg / L. The cyanide concentration in the gold(I) compound aqueous solution of this embodiment can be determined, for example, by ion chromatography as described in the example.

[0029] (Sulfite ion concentration) The gold(I) compound aqueous solution of this embodiment has a sulfite ion concentration of 1000 ppm by mass or less. Because the sulfite ion concentration of the gold(I) compound aqueous solution of this embodiment is low (1000 ppm by mass or less), it can maintain oxidation stability. Furthermore, it does not precipitate over a wide pH range, thus exhibiting excellent pH stability. The aqueous solution of the gold(I) compound of this embodiment preferably has a sulfite ion concentration of 1000 ppm by mass or less, more preferably 500 ppm by mass or less, still more preferably 0.5 ppm by mass or less, particularly preferably 0.1 ppm by mass or less, and most preferably 0 ppm by mass. The sulfite ion concentration in the aqueous solution of the gold(I) compound of this embodiment can be determined by, for example, capillary electrophoresis as described in the examples.

[0030] (Halide ion concentration) The aqueous solution of the gold(I) compound of this embodiment has a halide ion concentration of 1000 mg / L or less. Since the aqueous solution of the gold(I) compound of this embodiment has a low halide ion concentration of 1000 mg / L or less, substrate corrosion during plating caused by halogens is unlikely to occur. Examples of the halide ions include chloride ions, bromide ions, fluoride ions, iodide ions, and the like. The aqueous solution of the gold(I) compound of this embodiment preferably has a halide ion concentration of 1000 mg / L or less, more preferably 500 mg / L or less, still more preferably 100 mg / L or less, particularly preferably 10 mg / L or less, and most preferably 0 mg / L. The halide ion concentration in the aqueous solution of the gold(I) compound of this embodiment can be determined by, for example, ion chromatography as described in the examples.

[0031] (Properties) The aqueous solution of the gold(I) compound of this embodiment is preferably adjusted so that the gold concentration is 1.0 g / L or more in the range of pH from 1 to 12 and no precipitation occurs when heated at 90 °C for 8 hours. Here, "no precipitation occurs" means that no precipitation occurs when the aqueous solution is visually observed, and preferably, no metal residue with a diameter of 0.2 μm or more is observed on the filter and no coloring is observed on the filter after passing the liquid through a 0.2-μm filter. Specifically, the above properties can be confirmed by the method described in the <pH stability test> in the examples described later.

[0032] The aqueous solution of the gold(I) compound of the present embodiment preferably has a pH that does not decrease by 40% or more when subjected to an air bubbling test at an air flow rate of 1.0 L / min for 6 hours with respect to the aqueous solution of the gold(I) compound having a pH of 6.0 or more and less than 8.0. More preferably, the above pH does not decrease by 30% or more, still more preferably does not decrease by 20% or more, and particularly preferably does not decrease by 10% or more.

[0033] The aqueous solution of the gold(I) compound of the present embodiment preferably has a pH that does not decrease by 10% or more when subjected to an air bubbling test at an air flow rate of 1.0 L / min for 6 hours with respect to the aqueous solution of the gold(I) compound having a pH of 8.0 or more and less than 12.0. More preferably, the above pH does not decrease by 5% or more.

[0034] The above air bubbling test is carried out by the method described in <Air Stability Test> in the examples described later. In this specification, "when the pH does not decrease by X% or more when subjected to an air bubbling test at an air flow rate of 1.0 L / min for 6 hours" means that the pH before the start of the above air bubbling test (pre-test pH) and the pH after the end of the above air bubbling test (post-test pH) satisfy the following formula (1). {(Pre-test pH - Post-test pH) / Pre-test pH}×100 < X ··· Formula (1)

[0035] <Method for Producing Aqueous Solution of Gold(I) Compound> Hereinafter, the method for producing the aqueous solution of the gold(I) compound of the present embodiment (hereinafter, also referred to as the production method of the present embodiment) will be described. The production method of the present embodiment includes a step of mixing and heating gold sulfite or a salt thereof with a thiol having a structure represented by the following general formula (2) to obtain an insoluble gold complex, and a step of mixing and heating the insoluble gold complex with a water-soluble organic compound having a thiol group to obtain a gold(I) compound having a structure represented by the following general formula (1).

[0036] R-S - -Au-S-(CH2) n -SO3- ...(1) (In formula (1), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and n is an integer from 3 to 10.)

[0037] HS-(CH2) m -SO3 - ...(2) (In equation (2), m is an integer between 3 and 10.)

[0038] According to the manufacturing method of this embodiment, an aqueous solution of a gold(I) compound having the structure represented by the general formula (1) is obtained by mixing gold sulfite or a salt thereof, which is known as a monovalent water-soluble gold complex, with a thiol having the structure represented by the general formula (2) above for coordination with gold ions, heating the mixture, and reacting the insoluble gold complex obtained with a water-soluble organic compound having a thiol group to re-solubilize it. In this manufacturing method, the gold complex is first insoluble, then separated by solid-liquid separation to extract the gold complex, and then re-solubilized to obtain the gold complex, thus reducing the concentration of sulfites originating from the raw materials. Therefore, the aqueous solution of the gold(I) compound obtained by this manufacturing method can maintain oxidation stability and does not precipitate over a wide pH range, exhibiting excellent pH stability.

[0039] [Process for obtaining an insoluble gold complex] The manufacturing method of this embodiment includes the step of mixing gold sulfite or a salt thereof with a thiol having a structure represented by the following general formula (2), and heating to obtain an insoluble gold complex.

[0040] Examples of gold sulfite or its salts used in this process include gold sulfite, sodium gold sulfite, potassium gold sulfite, and ammonium gold sulfite. From the viewpoint of economics and other factors, sodium gold sulfite is preferred.

[0041] The thiol used to coordinate with the gold ions in this process has a structure represented by the following general formula (2). HS-(CH2) m -SO3- ...(2)

[0042] In the general formula (2) above, m is an integer between 3 and 10. If m is less than 3, there is a high possibility that an insoluble gold complex cannot be obtained, in which case the concentration of sulfites due to the raw materials cannot be reduced, and the resulting aqueous solution of the gold(I) compound may not achieve the desired properties. If m is greater than 10, the resulting gold(I) compound may not be water-soluble. It is preferable that m is an integer between 3 and 5.

[0043] Examples of thiols having the structure represented by the above general formula (2) include sodium 3-mercapto-1-propanesulfonate, sodium 4-mercapto-1-butanesulfonate, sodium 5-mercapto-1-pentanesulfonate, sodium 6-mercapto-1-hexanesulfonate, sodium 7-mercapto-1-heptanesulfonate, sodium 8-mercapto-1-octanesulfonate, sodium 9-mercapto-1-nonanesulfonate, and sodium 10-mercapto-1-decanesulfonate.

[0044] In this process, it is preferable to mix 1 to 5 equivalents of a thiol having the structure represented by the general formula (2) above with 1 equivalent of gold sulfite or its salt, more preferably 1 to 3 equivalents, and even more preferably 1 to 2 equivalents. By keeping the amount to 5 equivalents or less, the amount of unreacted thiol can be reduced, and the formation of disulfide-bonded thiols such as 3,3'-dithiobis(1-propanesulfonic acid) disodium (SPS), which are reaction byproducts, can be suppressed, resulting in a good yield for forming the gold complex.

[0045] In the manufacturing method of this embodiment, the heating temperature when heating gold sulfite or its salt and the thiol having the structure represented by the general formula (2) is preferably 60 to 100°C, and more preferably 80 to 95°C. The heating time is preferably 1 to 5 hours, and more preferably 2 to 3 hours. The pH of the mixture of gold sulfite or its salt and the thiol having the structure represented by the general formula (2) during heating is preferably 4 to 9, more preferably 5 to 8, and even more preferably 6 to 7.

[0046] After heating a mixture of gold sulfite or a salt thereof and a thiol having the structure represented by the general formula (2) above, the insoluble gold complex in the solution may be precipitated by cooling the mixture, for example, and then the insoluble gold complex may be separated by solid-liquid separation using conventionally known methods such as filtration. The cooling of the above mixture is preferably carried out to a temperature of 40°C or lower, more preferably to 30°C or lower, even more preferably to 25°C or lower, and also preferably to 0°C or higher, and more preferably to 10°C or higher. The insoluble gold complex obtained in this process is preferably isolated as a polymer of the gold complex. By polymerizing the gold complex and then separating the solid and liquid by filtration or the like to extract the gold complex, a gold complex with a low impurity concentration and high purity can be obtained.

[0047] [Process for obtaining gold(I) compounds] The manufacturing method of this embodiment includes the step of mixing the insoluble gold complex with a water-soluble organic compound having a thiol group, heating the mixture, and obtaining a gold(I) compound having the structure represented by the general formula (1) described above.

[0048] Examples of water-soluble organic compounds having a thiol group used in this process are represented by the following general formula (5). R-SH ···(5) In the above general formula (5), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and these organic groups are preferably highly hydrophilic. The above sulfonic acid group, carboxyl group, and amino group may also be salts thereof. In R, the number of carbon atoms of the organic group is preferably 1 to 5, and more preferably 1 to 3. R is preferably an alkyl group, etc. Furthermore, it is preferable that R contains a sulfonic acid group at its terminal or side chain. Particularly preferable, from the viewpoint of coordination stability of the gold(I) compound, R is an alkyl sulfonic acid group having 1 to 3 carbon atoms.

[0049] Examples of water-soluble organic compounds having thiol groups used in this process include sodium 3-mercapto-1-propanesulfonate (MPS), sodium 2-mercaptoethanesulfonate, thiomalic acid, cysteine, thioglucolic acid, 3-mercaptopropionic acid, thioacetic acid, 2-mercaptoethanol, 3-mercapto-1-propanol, and thiosulfate.

[0050] In this process, it is preferable to mix 0.5 to 5 equivalents of the above-mentioned water-soluble organic compound having a thiol group with 1 equivalent of the insoluble gold complex, and more preferably 1 to 2 equivalents.

[0051] In this process, the heating temperature when heating the insoluble gold complex and the water-soluble organic compound having a thiol group is preferably 60 to 100°C, more preferably 70 to 95°C, and even more preferably 70 to 80°C. The heating time is preferably 0.5 to 3 hours, and more preferably 1 to 2 hours. Furthermore, the pH of the mixture of the insoluble gold complex and the water-soluble organic compound having a thiol group during heating is preferably 6 or higher, more preferably 7 or higher, preferably 12 or lower, and even more preferably 10 or lower.

[0052] If unreacted, insoluble gold complexes remain, the gold(I) compound aqueous solution may be obtained by removing them through a process such as filtration.

[0053] <Gold Plating Solution> The gold plating solution of this embodiment will be described below. The gold plating solution of this embodiment contains a gold(I) compound having the structure represented by the following general formula (1), a chelating agent, a buffering agent, and an additive, and is characterized by having a cyanide concentration of 500 mg / L or less, a sulfite ion concentration of 1000 ppm by mass or less, and a halogen ion concentration of 1000 mg / L or less. RS - -Au-S-(CH2) n -SO3 - ...(1) (In formula (1), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and n is an integer from 3 to 10.)

[0054] (gold(I) compound) The gold(I) compound having the structure represented by general formula (1) contained in the gold plating solution of this embodiment can be the same as that described in the section on <Aqueous solution of gold(I) compound> and can be used as is in the gold plating solution of this embodiment. The gold plating solution of this embodiment may also be obtained using a diluted or concentrated solution of the aqueous solution of gold(I) compound of this embodiment.

[0055] In this embodiment, the gold concentration in the gold plating solution is preferably 0.1 g / L or more, more preferably 0.2 g / L or more, from the viewpoint of uniformity of the plating film and plating deposition rate, and preferably 10 g / L or less, from the viewpoint of adhesion to the electroless nickel plating film and economic efficiency.

[0056] (Chelating agent) The gold plating solution of this embodiment contains a chelating agent. The chelating agent is added separately from the ligand of the gold complex and preferably includes ethylenediaminetetraacetate disodium dihydrate (EDTA-2Na), hydantoin, 1-methylhydantoin, 5-methylhydantoin, 5,5-dimethylhydantoin, succinimide, triethanolamine, nitrilotriacetic acid, trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, hydroxyethylethylenediaminetriacetic acid or its alkali metal (e.g., sodium, potassium) salts, alkaline earth metal salts, ammonium salts, etc. Particularly preferred are ethylenediaminetetraacetate disodium dihydrate (EDTA-2Na), nitrilotriacetic acid, trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, and hydroxyethylethylenediaminetriacetic acid. By using a chelating agent in the gold plating solution, an extremely stable gold plating solution is obtained. That is, gold precipitation is less likely to occur during the plating process. This is because these chelating agents maintain equilibrium with the ligands of the gold complex and, unlike reducing agents such as sulfurous acid, are less likely to cause oxidative decomposition.

[0057] The equilibrium state and mixed concentration of the chelating agent and the ligand of the gold complex can be determined by ion chromatography or liquid chromatography.

[0058] The amount of chelating agent is preferably greater than 0 molars and less than or equal to 4 molars relative to the gold when the pH is 5 to 7. If a large amount is used and the gold complex is replenished frequently, the ligands of the gold complex will be liberated, so it is not necessary to include the chelating agent initially. If the amount exceeds 4 molars, it will have a burnt appearance.

[0059] Furthermore, the amount of chelating agent is preferably between 4 moles and 10 moles relative to the gold when the pH is 8-10. If the amount is less than 4 moles, a burnt appearance may occur, and the reaction in which the ligands of the gold complex are oxidized and decomposed by alkalinity takes precedence over the chelating agent maintaining equilibrium with the ligands of the gold complex, which may result in gold deposition. Also, if the amount exceeds 10 moles, the appearance and oxidative stability tend to be similar to that when it is 10 moles or less, and the increased effect of the chelating agent is not expected to be significant, making it economical and potentially preventing further remarkable effects.

[0060] (buffering agent) The gold plating solution of this embodiment contains a buffering agent. As a buffering agent, it is preferable to use one or more of the following: boric acid, succinic acid, phthalic acid, tartaric acid, citric acid, phosphoric acid, or salts thereof. If these are used individually or in combination as buffering agents, the pH of the gold plating solution according to this embodiment will not fluctuate significantly, and it will be easy to maintain the plating solution at a pH close to neutral, ranging from weakly acidic to weakly alkaline (pH approximately 5.0 to 10.0).

[0061] When the buffering agent described above is included in the gold plating solution according to this embodiment, the buffering agent concentration is preferably in the range of 0.1 to 250 g / L. If the buffering agent concentration is less than 0.1 g / L, the effect of stabilizing the pH is lost. Also, if the buffering agent concentration exceeds 250 g / L, the pH stability tends to become similar to that when the buffering agent concentration is 250 g / L or less, and salting out is more likely to occur depending on the pH.

[0062] (Additives) The gold plating solution of this embodiment contains additives. Additives include bath stabilizers, deposition regulators, deposition rate regulators, leveling agents, crystallization regulators, stress relaxants, etc. The gold plating solution of this embodiment preferably contains at least one of "Additive-1" and "Additive-2" described later as additives. In the gold plating solution of this embodiment, commonly used known additive components can be used as appropriate. However, additives are substances different from chelating agents.

[0063] (Additive-1) In the gold plating solution of this embodiment, it is preferable to include a thiocyanate deposition modifier. By using such a thiocyanate additive, a stable gold film (improved deposition film thickness) can be achieved. In this specification, thiocyanates are also referred to as "additive-1". Preferred examples of thiocyanates include thiocyanates such as sodium thiocyanate, potassium thiocyanate, and ammonium thiocyanate.

[0064] (Additive-2) Specifically, additive-2 includes thiosulfate and its compounds, thiourea and its compounds, water-soluble metal salts, polyamines and their salts, and polyamines include, but are not limited to, ethylenediamine, diethylenetriamine, triethylenetetramine, pentaethylenehexamine, hexamethylenediamine, ethylenediaminetetramethylene phosphate, diethylenetriaminepentamethylene phosphate, aminotrimethylene phosphate, and diaminodipropylamine. Examples of water-soluble metal salts and salts of polyamines include, but are not limited to, sulfates, hydrochlorides, nitrates, and acetates. Examples of water-soluble metal salts include nickel compounds for potential adjustment and thallium nitrate, thallium sulfate, thallium formate, and thallium malonate for precipitation rate adjustment. Examples of such nickel compounds include known water-soluble nickel compounds such as nickel sulfate and nickel sulfamate. However, EDTA-2Na is not included in the polyamines listed as examples of additive-2.

[0065] The content of additive-1 in the gold plating solution of this embodiment is preferably 5 g / L or more, more preferably 10 g / L or more, preferably 150 g / L or less, and more preferably 120 g / L or less. The content of additive-2 in the gold plating solution of this embodiment is preferably 1 g / L or more, more preferably 5 g / L or more, preferably 200 g / L or less, and more preferably 150 g / L or less.

[0066] (pH) As described above, the gold plating solution of this embodiment can be used over a wide pH range due to the stability of the gold complex. The pH range of the gold plating solution of this embodiment is preferably 5 to 10, and more preferably 4 to 8. To adjust the pH as needed, well-known adjusting solutions such as aqueous sodium hydroxide solution or aqueous sulfuric acid solution can be used.

[0067] (Plated metal) Examples of metals to be plated using the gold plating solution of this embodiment include metals, alloys, or substrates having a film of these metals or alloys, i.e., substrates having a metallic surface. Examples of substrates having a metallic surface include copper and copper alloys, nickel and nickel alloys, silver and silver alloys, and palladium and palladium alloys. The surface of the metal to be plated may be a solid metal body or a laminated structure of one or more layers of metal or alloy coated on a non-metallic body such as plastic or ceramic. When the metal to be plated contains nickel or a nickel alloy, the gold plating solution of this embodiment may or may not contain a nickel compound as an additive, but from the viewpoint of stability of the plating rate, it is preferable to include a nickel compound. Examples of such nickel compounds include known water-soluble nickel compounds such as nickel sulfate and nickel sulfamate.

[0068] (Application) The gold plating solution of this embodiment is preferably used for electroless plating, and the electroless plating may be displacement plating or reduction plating. When the gold plating solution of this embodiment is used for electroless plating, particularly displacement plating, the solution temperature is not particularly limited, but generally, the range of the solution temperature is 60 to 95°C, preferably 70 to 90°C. A solution temperature of 60°C or higher allows for a sufficiently fast displacement rate, while a temperature of 95°C or lower suppresses evaporation loss of the displacement gold plating solution.

[0069] When forming a plating film using the gold plating solution of this embodiment, the underlying metal to be plated is not particularly limited. Even non-conductive ceramics and plastics can be used as the plated object by various methods. Preferred underlying metals have a surface of copper, nickel, or palladium. [Examples]

[0070] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0071] <Gold Solution Manufacturing 1> (Example 1) Aqueous solution of gold(I) compound An aqueous solution of sodium gold sulfite (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., 80.00 g / L) was mixed with 1.5 molar equivalents of sodium 3-mercapto-1-propanesulfonate (MPS) to obtain a mixture, which was then heated at 90°C for 3 hours using a constant temperature water bath with a magnetic stirrer. The heated mixture was cooled to 25°C using a low-temperature constant-temperature water bath. A white precipitate formed in the mixture, and solid-liquid separation was performed by vacuum filtration to remove the precipitated white solid from the mixture. One molar equivalent of the obtained white solid and one molar equivalent of 3-mercapto-1-propanesulfonate sodium (MPS) (MPS / MPS-Au ratio: 1) were mixed using a constant temperature water bath with a magnetic stirrer. The resulting mixture was adjusted to pH 12 with a 100 g / L sodium hydroxide aqueous solution, and then heated at 80°C for 1 hour using a constant temperature water bath with a magnetic stirrer. The gold(I) compound aqueous solution of Example 1 was prepared as described above. In this specification, the gold(I) compound of Example 1 will be abbreviated as MPS gold.

[0072] (Comparative Example 1) Sodium gold sulfite solution A sodium gold sulfite solution (SGS) (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., 80.00 g / L) was diluted with water to prepare the sodium gold sulfite solution of Comparative Example 1.

[0073] (Comparative Example 2) Hydantoin Gold Complex Solution A solution containing 1 molar equivalent of hydantoin was prepared by adjusting the pH to 11 with a 100 g / L aqueous sodium hydroxide solution. To this solution, 0.2 molar equivalents of gold were added using a chlorauric acid solution (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., 100 g / L). This solution was heated at 60°C for 3 hours using a constant temperature water bath with a magnetic stirrer. The heated mixture was cooled to 25°C using a low temperature constant temperature water bath, and the filtrate was collected by vacuum filtration. A hydantoin-gold complex solution was thus prepared.

[0074] <Component analysis> The concentrations of gold, chloride ions, sulfite ions, sulfate ions, and cyanide in the solutions of each example and comparative example are shown in Table 1 below. In Table 1, "ND" indicates that measurement was not possible due to the detection limit. The gold concentration was determined by inductively coupled plasma emission spectroscopy, the chloride ion and cyanide concentrations by ion chromatography, and the sulfite and sulfate ions by capillary electrophoresis. The detection limits for each analytical method were 10 mg / L for chloride ions, 0.1 mg / L for sulfite ions, 0.1 mg / L for sulfate ions, and 0.01 mg / L for cyanide ions. Note that cyanide ion concentration and cyanide concentration are synonymous.

[0075] [Table 1]

[0076] <Gold Solution Manufacturing 2> To investigate the conditions for the gold compound aqueous solution, the gold(I) compound aqueous solutions of Examples 2 to 9 were prepared in the same manner as in Example 1, except that each condition was adjusted as shown in Table 2 below.

[0077] [Table 2]

[0078] As shown in Table 2, in Examples 1 to 8, it was confirmed that gold(I) compound aqueous solutions could be produced in high yield, and the amount of SPS, a by-product, was also low. In particular, Example 1 showed high yield and low SPS content.

[0079] <MS analysis of gold(I) compounds> The gold(I) contained in the gold(I) compound aqueous solution of Example 1 was analyzed by MS under the following conditions. ·Mass spectrometer: Thermo Fisher Scientific, “Q Exactive Plus” • Ionization method: nano electrospray ionization (nanoESI) TriVersa NanoMate (registered trademark) • Mass range: Full scan (positive / negative m / z 200~3000) Production scan • Gas pressure: N20.3psi Voltage: 2.0kV • Sample: A solution obtained by diluting the solution from Example 1 to an Au concentration of 20 g / L, and then further diluting it 10 times. The results are shown in Figure 1. As shown in Figure 1, a monomer-equivalent fragment was obtained at m / z (mass / charge) = 596.87 ± 0.5, a dimer-equivalent fragment was obtained at m / z = 596.87 + 573.9 ± 0.5, and a trimer-equivalent fragment was obtained at m / z = 596.87 + 1147.8 ± 0.5.

[0080] In addition, when the aqueous solution of the gold(I) compound of Example 1 was subjected to nano ESI MS, as shown in Fig. 1, fragments with an intensity equivalent to 15 - 20% of the main fragment ratio were obtained at a position of m / z = 596.87 ± 0.5 + 1.99.

[0081] <pH Stability Test> (Example 1) The aqueous solution of the gold(I) compound of Example 1 was added to a 30 mL screw tube (made of borosilicate glass, transparent), and diluted with pure water to prepare 12 aqueous solutions with a gold concentration of 5 g / L (colorless and transparent solutions). The solutions in the 30 mL screw tubes were adjusted to pH 1 - 12 one by one using 10% sulfuric acid and 10% sodium hydroxide. The volume of the solution in the 30 mL screw tube was made 15 mL. After heating these solutions to 90 °C in a warm bath and standing for 8 hours, the appearance of the liquid was visually confirmed. The results are shown in Table 3. As shown in Table 3, no change in the appearance of the liquid was confirmed within the range of pH 1 - 12.

[0082] (Comparative Example 1) Twelve aqueous solutions with a gold concentration of 5 g / L at pH 1 - 12 were prepared in the same manner as in Example 1, except that the aqueous solution of the gold(I) compound of Example 1 was changed to the sodium sulfite gold solution of Comparative Example 1. After heating these solutions to 90 °C in a warm bath and standing for 8 hours, the appearance of the liquid was visually confirmed. The results are shown in Table 3. As shown in Table 3, no change in the liquid color was confirmed at pH 6 or below, but a precipitate of metallic gold was confirmed. At pH 7 or above, there was no change in the appearance of the liquid and no precipitate was confirmed.

[0083] (Comparative Example 2) Twelve aqueous solutions with a gold concentration of 5 g / L at pH 1 - 12 were prepared in the same manner as in Example 1, except that the aqueous solution of the gold(I) compound of Example 1 was changed to the hydantoin gold complex solution of Comparative Example 2. After heating these solutions to 65 °C in a warm bath and standing for 8 hours, the appearance of the liquid was visually confirmed. The results are shown in Table 3. As shown in Table 3, black precipitates were confirmed at pH 4 or below and pH 10 or above. No precipitate was confirmed within the range of pH 5 - 9, and the liquid color changed to light purple. When heating was carried out under the condition of 90 °C, the change in the liquid color became even faster.

[0084] [Table 3]

[0085] <Air Stability Test> (Example 1) Two 5 g / L gold aqueous solutions were prepared by adding the gold(I) compound aqueous solution from Example 1 to a 100 mL vial (borosilicate glass, transparent) and diluting it with pure water. The solution in one vial was adjusted to pH 7.0 with 10% sulfuric acid (total 50 mL). The solution in the other vial was adjusted to pH 10.0 (total 50 mL). An air pump (NISSO CHIKARA Nα1500) was set to an air flow rate of 1.0 L / min, and bubbling was performed at room temperature (25 °C ± 1 °C) using a diffuser (Kinoshita Rika Kogyo Co., Ltd., Kinoshita glass ball filter, material: Pyrex®, standard 502G, type No. 2, spherical diameter Φ15 mm, tube diameter 7 mm, tube length 250 mm). The pH of each solution was measured after each bubbling time as described in Table 4. The pH measurement results are shown in Table 4 and Figure 2. Furthermore, the appearance of each solution was checked after 0, 2, 4, 6, 12, 18, 24, 32, and 40 hours of bubbling. In the sample starting at pH 7.0, the pH hardly decreased even 40 hours after the start of bubbling (pH 7.23). In the sample starting at pH 10.0, the pH decreased to 9.23 after 6 hours of bubbling, but no further decrease in pH was observed during subsequent bubbling times. In terms of liquid appearance, neither the pH 7.0 nor the pH 10.0 samples showed any precipitation or discoloration in the vial even 40 hours after the start of bubbling. Furthermore, even when the airflow rate was increased to 2.0 L / min, no changes were observed in pH or liquid appearance over a long period of time.

[0086] (Comparative Example 1) Except for replacing the gold(I) compound aqueous solution in Example 1 with the sodium gold sulfite solution in Comparative Example 1, samples for the air stability test were prepared in the same manner as in Example 1 in the <Air Stability Test>, and a bubbling test was performed under the same conditions. The pH measurement results are shown in Table 4 and Figure 2. In the sample starting at pH 7.0, the pH dropped to 4.03 after 6 hours of bubbling, a decrease of approximately 57% from the initial pH, and precipitation of metallic gold was observed after 12 hours of bubbling. In the sample starting at pH 10.0, the pH dropped to 8.01 after 6 hours of bubbling (a decrease of approximately 80%), but no further decrease in pH was observed thereafter. Furthermore, when the airflow rate was increased to 1.5 L / min, the rate of pH decrease due to oxidation accelerated.

[0087] [Table 4]

[0088] <Substitution gold plating on electrolytic nickel plating> (Preparation of the metal to be plated: Test piece A) Test piece A, used to evaluate the plating solutions in Test Examples 1-3, was prepared using a brass plate (20mm x 20mm x 0.2mm thick) as follows. In the acidic degreasing process, "E-Trex® 15" manufactured by EEJA Corporation was used, and the brass plate was immersed at 25°C for 30 seconds. In the subsequent electrolytic degreasing process, "E-Trex® 12" electrolytic degreasing solution manufactured by EEJA Corporation was used, and a voltage of 6V was applied to the brass plate, which was then immersed at 60°C for 30 seconds. In the following sulfuric acid activation process, the brass plate was immersed in a 10% sulfuric acid aqueous solution at 25°C for 30 seconds. In the following electrolytic nickel plating process, "Microfab® Ni100" manufactured by EEJA Corporation, adjusted to 55°C, was used, and the brass plate was plated at a cathode current efficiency of 3ASD (Ampere per Square Decimator) for 16 minutes, depositing 10 μm of nickel. This is designated as Test Piece A.

[0089] (Replacement gold plating) A displacement gold plating solution was prepared with the composition shown in Table 5 below, and the pH was adjusted to 5.6 using an aqueous sodium hydroxide solution. The plating solution was placed in a constant temperature bath with a magnetic stirrer and heated to the specified temperature. Then, test piece A, which was prepared as described above, was immersed in the plating solution and displacement gold plating was performed. After 10 minutes of immersion, it was removed, rinsed with water, and dried. The specific formulation of the displacement gold plating solution and the plating conditions are shown in Table 5 below.

[0090] [Table 5]

[0091] The buffering agents, chelating agents, and additives used in Table 5 are as follows: (buffering agent) • Sodium dihydrogen phosphate (anhydrous): Manufactured by Kanto Chemical Co., Ltd. (Chelating agent) • EDTA-2Na: "Ethylenediaminetetraacetate disodium dihydrate" manufactured by Kanto Chemical Co., Ltd. (Additive-1) • Potassium thiocyanate: Manufactured by Kanto Chemical Co., Ltd. (Additive-2) • Ethylenediamine sulfate: Manufactured by Kanto Chemical Co., Ltd. • Thallium formate: Manufactured by Fujifilm Wako Pure Chemical Corporation

[0092] The film thickness of the displacement gold plating was measured using an X-ray fluorescence film thickness meter (Hitachi High-Tech Corporation's "FT150 series" X-ray fluorescence film thickness meter), and the average film thickness was calculated. The results are shown in Table 6 below.

[0093] [Table 6]

[0094] When displacement gold plating was performed under the same conditions using IM FAB(registered trademark) Au-IGS4000, a gold sulfite-based displacement gold plating solution, the film thickness was approximately 60-70 nm. In contrast, the average film thickness obtained by displacement gold plating using the plating solution containing the gold(I) compound aqueous solution of this embodiment was comparable to that obtained when using a conventional gold sulfite-based plating solution.

[0095] <Wettability of substitution gold plating on electrolytic nickel> (Preparation of the metal to be plated: Test piece B) Test piece B, used to evaluate the plating solutions in Test Examples 4-9, was manufactured using a Cu-Cr alloy lead frame (Furukawa Electric Co., Ltd., "EFTEC64T") and was produced by the same acidic degreasing process followed by an electrolytic nickel plating process as test piece A.

[0096] (Replacement gold plating) The test piece B, the metal to be plated as described above, was subjected to displacement gold plating. A displacement gold plating solution was prepared with the composition shown in Table 7 below, and the pH was adjusted to 5.4 using an aqueous sodium hydroxide solution. The plating solution was placed in a constant temperature bath with a magnetic stirrer and heated to the specified temperature. Then, the test piece B, which was prepared as described above, was immersed in the plating solution and displacement gold plating was performed. After 5 minutes of immersion, it was removed, rinsed with water, and dried. The specific formulation of the displacement gold plating solution and the plating conditions are shown in Table 7 below.

[0097] [Table 7]

[0098] Of the buffers, chelating agents, and additives listed in Table 7, the following were used that differed from those used in the evaluation of the plating solutions in Test Examples 1-3. (Additive-1) • Ammonium thiocyanate: Manufactured by Kanto Chemical Co., Ltd. (Additive-2) • Nickel sulfate: "Nickel(II) sulfate hexahydrate" manufactured by Kanto Chemical Co., Ltd.

[0099] (Wettability evaluation) As comparative examples, IM FAB® Au-IGS4000 (manufactured by EEJA Co., Ltd., 70°C, pH 6.0, 6.5 min, average film thickness 50 nm) and IM FAB® Au-IGS8600 (manufactured by EEJA Co., Ltd., 70°C, pH 6.5, 25 min, average film thickness 150 nm), both gold sulfite-based displacement gold plating solutions, were used in the gold plating tests described in Test Examples 4-9 above. After the gold plating was performed using these solutions, the plated objects were heat-treated at 350°C for 30 seconds. Subsequently, wettability was evaluated using the zero-cross time (Dip Wetting Tester SWB-2, manufactured by mlacom). The measurement conditions are shown in Table 8 below, and the evaluation results are shown in Table 9 below. Note that the Zero Cross Time (ZCT) test in Table 9 is a test to evaluate the solder wettability of the coating. A short ZCT indicates good solder wettability. The evaluation sample was immersed in the solder bath (SAC305) described in Table 8, and the time (in seconds) required until the force from the solder bath became zero was measured five times, and the average value was calculated.

[0100] [Table 8]

[0101] [Table 9]

[0102] As shown in Table 9, it was found that the gold(I) compound aqueous solution of Example 1 could be adjusted to a composition that could achieve wettability equivalent to that of IM FAB® Au-IGS4000, a gold sulfite-based substitution gold plating solution. In other words, it was found that the substitution gold plating solution using the gold(I) compound aqueous solution of Example 1 could achieve wettability equivalent to that of a gold sulfite-based substitution gold plating solution. Furthermore, it was found that good solder wettability could be achieved even when compared with IM FAB Au-IGS8600, a gold sulfite-based substitution gold plating solution with a different target film thickness. Good solder wettability results in a uniform and dense gold film with good adhesion to the substrate metal, making it possible to obtain highly reliable electronic components.

[0103] <Displacement gold plating on electroless NiP> (Preparation of the metal to be plated: Test piece C) Test piece C, used to evaluate the plating solutions in test examples 10-14, was prepared using a copper plate as follows. In the acidic degreasing process, "E-Trex® 15" manufactured by EEJA Corporation was used, and the copper plate was immersed at 25°C for 1 minute. In the subsequent electrolytic degreasing process, "Microfab® 74" electrolytic degreasing solution manufactured by EEJA Corporation was used, and a soft etching treatment was performed at 25°C for 1 minute. In the following sulfuric acid activation process, the copper plate was immersed in a 10% sulfuric acid aqueous solution at 25°C for 1 minute. In the following palladium catalyst application process, the copper plate was immersed in "IM FAB® Pd-AC2" manufactured by EEJA Corporation at 25°C for 1 minute. In the subsequent electroless nickel plating process, "AC Meister® NP7600" (electroless nickel, medium phosphorus bath) manufactured by EEJA Corporation was used, and the plate was plated at 85°C for 25 minutes to deposit 5 μm of nickel, obtaining a Cu / Ni layered structure test piece C.

[0104] (Replacement gold plating) Substitution gold plating was performed on the test piece C (Cu / Ni layered structure), which was the metal to be plated as described above. A displacement gold plating solution was prepared with the composition shown in Table 10 below, and the pH was adjusted to 5.4 using an aqueous sodium hydroxide solution. The plating solution was placed in a constant temperature bath with a magnetic stirrer and heated to the specified temperature. Then, test piece C, which was prepared as described above, was immersed in the plating solution and displacement gold plating was performed. After 10 minutes of immersion, it was removed, rinsed with water, and dried. The specific formulation of the displacement gold plating solution and the plating conditions are shown in Table 10 below.

[0105] [Table 10]

[0106] Of the buffering agents, chelating agents, and additives listed in Table 10, the following were used that differed from those used to evaluate the plating solutions in Test Examples 1 to 9. (Additive-2) • Thiourea: Manufactured by Tokyo Chemical Industry Co., Ltd.

[0107] The film thickness of the displacement gold plating was measured using an X-ray fluorescence film thickness meter (Hitachi High-Tech Corporation, FT150 series). The average film thickness was calculated from these measurement results, and the results are shown in Table 11 below.

[0108] [Table 11]

[0109] In the aforementioned <Substitution Gold Plating on Electrolytic Nickel Plating>, it was shown that substitution gold plating on electroless nickel could be performed using the plating solutions of Test Examples 1 to 3, which included the gold(I) compound aqueous solution of Example 1, at a plating speed comparable to that of conventional plating solutions containing gold sulfite. Table 11 shows that in the plating solutions of Test Examples 10-14, a higher thiourea content resulted in an increased plating film thickness. Therefore, it was found that the substitution gold plating rate can be adjusted by controlling the thiourea content in the plating solution. Furthermore, it was demonstrated that substitution Au plating could be formed without any problems on test piece C, i.e., on the electroless Ni-P coating (medium phosphorus).

Claims

1. The material contains a gold(I) compound having the structure represented by the following general formula (1), The cyanide concentration is 500 mg / L or less. The sulfite ion concentration is 1000 ppm by mass or less. The halogen ion concentration is 1000 mg / L or less. Gold(I) compound aqueous solution. R-S － -Au-S-(CH ２ ) ｎ -SO ３ － ・・・(1) (In formula (1), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and n is an integer from 3 to 10.)

2. An aqueous solution of a gold(I) compound according to claim 1, wherein the gold concentration is adjusted to 1.0 g / L or more in the pH range of 1 to 12, and no precipitate is formed when heated at 90°C for 8 hours.

3. The aqueous solution of a gold(I) compound according to claim 1, wherein when an air bubbling test is performed on an aqueous solution of a gold(I) compound with a pH of 6.0 or higher and less than 8.0 at an air flow rate of 1.0 L / min for 6 hours, the pH does not decrease by 40% or more.

4. The aqueous solution of a gold(I) compound according to claim 1, wherein when an air bubbling test is performed on an aqueous solution of a gold(I) compound with a pH of 8.0 or higher and less than 12.0 at an air flow rate of 1.0 L / min for 6 hours, the pH does not decrease by 10% or more.

5. An aqueous solution of a gold(I) compound according to claim 1, wherein a fragment is obtained at the position m / z = 596.87 ± 0.5 when subjected to nano ESI MS.

6. An aqueous solution of a gold(I) compound according to claim 1, wherein when subjected to nano ESI MS, a fragment equivalent to a dimer is obtained at the position m / z = 596.87 + 573.9 ± 0.

5.

7. An aqueous solution of a gold(I) compound according to claim 1, wherein when subjected to nano ESI MS, a trimer-equivalent fragment is obtained at the position m / z = 596.87 + 1147.8 ± 0.

5.

8. An aqueous solution of a gold(I) compound according to claim 1, wherein when subjected to nano ESI MS, a fragment of intensity equivalent to 15-20% of the main fragment ratio is obtained at the position m / z = 596.87 ± 0.5 + 1.

99.

9. A step of mixing gold sulfite or a salt thereof with a thiol having a structure represented by the following general formula (2), heating it to obtain an insoluble gold complex, and The process involves mixing the aforementioned insoluble gold complex with a water-soluble organic compound having a thiol group, heating the mixture, and obtaining a gold(I) compound having a structure represented by the following general formula (1). A method for producing an aqueous solution of a gold(I) compound containing the compound. R-S － -Au-S-(CH ２ ) ｎ -SO ３ － ・・・(1) (In formula (1), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and n is an integer from 3 to 10.) HS-(CH ２ ) ｍ -SO ３ － ・・・(2) (In equation (2), m is an integer between 3 and 10.)

10. It contains a gold(I) compound having a structure represented by the following general formula (1), a chelating agent, a buffering agent, and an additive, The cyanide concentration is 500 mg / L or less. The sulfite ion concentration is 1000 ppm by mass or less. The halogen ion concentration is 1000 mg / L or less. Gold plating solution. R-S － -Au-S-(CH ２ ) ｎ -SO ３ － ・・・(1) (In formula (1), R is an organic group having at least one group selected from the group consisting of a sulfonic acid group, a carboxyl group, and an amino group at its terminal or side chain, and n is an integer from 3 to 10.)

11. The gold plating solution according to claim 10, wherein the additive comprises at least one selected from the group consisting of potassium thiocyanate, sodium thiocyanate, and ammonium thiocyanate, and the gold plating solution is an electroless plating solution.

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