Gold plating solution composition and gold plating method

Abstract

The object of the present invention is to provide a gold plating method that can form a uniform gold film with good adhesion, low porosity, and sufficient thickness in a single step, and that has a low environmental impact. [Solution] The present invention relates to a plating solution composition for gold plating a metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium, and nickel, or a metal layer made of an alloy containing said metal, wherein the plating solution composition comprises 3-pyridinesulfonic acid and / or its salts.

Description

Technical Field

[0001] The present invention relates to a gold plating solution composition used when forming a gold plating film on electronic industrial parts such as printed wiring boards, a gold plating method, and the like.

Background Art

[0002] A printed circuit board has a metal circuit pattern on and / or inside the board. A metal with low electrical resistance such as copper is used for the circuit, and a barrier metal layer for preventing oxidation, corrosion, and / or migration with gold of the circuit is further provided. As the metal used as the barrier metal layer, in addition to nickel and nickel alloys, palladium, platinum, silver, cobalt, and alloys thereof can be used. There is also a technique of forming a palladium layer on the nickel layer for the purpose of preventing diffusion of nickel by heat treatment. After forming these underlying metal layers, the circuit is further covered with a gold film. Generally, since the gold film is used for preventing corrosion of the circuit and / or as a contact, a film with a high porosity is not preferable, and a dense and smooth surface is required.

[0003] As gold plating methods, an electrolytic gold plating method and an electroless gold plating method are known. As electroless gold plating methods, a displacement gold plating method and a reduction gold plating method are generally known. The displacement gold plating method is a gold plating method in which gold deposition is performed by an electrical displacement reaction between the underlying metal on the plating surface and gold ions and / or a gold ion complex. The reduction gold plating method is a method in which gold deposition is performed by a reducing agent using gold as a catalyst, and continuous deposition is possible and an arbitrary film thickness can be obtained. In order to form a gold plating film having a sufficient thickness, it is often performed in a two-step process in which a thin gold film is formed by displacement gold plating and then thickened using a reduction gold plating bath.

[0004] Under Bump Metal (UBM), widely used as the final surface treatment for printed circuit boards, is a coating formed to prevent oxidation of wiring materials such as Cu and Al during soldering or wire bonding between metal pads on semiconductor chips, thereby ensuring bonding reliability. From the viewpoint of barrier properties and surface protection during bonding, it is formed with compositions such as Ni / Au or Ni / Pd / Au. In particular, Ni / Pd / Au is widely used in automotive applications due to its relatively high reliability, but it involves many steps, and electroless gold plating alone generally requires two steps: displacement gold plating followed by reduction gold plating.

[0005] Therefore, with the aim of reducing the gold plating process, electroless displacement-reduction gold plating has been reported, which combines displacement gold plating solution and reduction gold plating solution into a single solution. Patent Document 1 reports an electroless displacement-reduction gold plating bath, but it contains toxic hydrazines as a reducing agent. Furthermore, Patent Document 2 reports a cyanide-free electroless displacement-reduction gold plating bath, but it contains toxic thallium compounds as an accelerator.

[0006] On the other hand, Patent Document 3 describes a cyanide-free electroless gold plating bath and states that pyridine derivatives such as pyridine sulfonic acid may be added as a brightener, but this only suggests its use as a brightener when further plating gold autocatalyzably on a gold plated surface that has already been electroplated. Patent document 4 describes gold plating solutions for nickel, palladium, platinum, silver, cobalt, etc., but it does not mention the addition of 3-pyridinesulfonic acid or its salts. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-058312 [Patent Document 2] Patent No. 6594077 [Patent Document 3] Japanese Patent Application Publication No. 8-239768 [Patent Document 4] Japanese Patent Publication No. 2003-221674 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention aims to provide a novel gold plating solution composition and a gold plating method using the same, which can form a uniform gold film with sufficient thickness on a wide range of underlying metal films in a single step. Furthermore, in substitution-reduction gold plating methods, unless highly reactive but also highly toxic compounds such as cyanide and thallium are used, the substitution reaction will not proceed smoothly, resulting in uneven gold plating. Hydrazines, the reducing agents used in Patent Document 2, are also highly reactive but toxic. Therefore, substitution-reduction gold plating methods have had the problem of requiring the use of highly toxic compounds. Accordingly, in one aspect, the present invention also aims to provide a substitution-reduction gold plating method that has a low environmental impact. [Means for solving the problem]

[0009] In order to solve the above problems, the inventors of the present invention have diligently conducted research and have discovered that by using 3-pyridinesulfonic acid in a gold plating method for a specific metal layer, it is possible to form a coating with sufficient thickness on various metal layers, thus completing the present invention.

[0010] In other words, the present invention relates to the following: [1] A plating solution composition for gold plating a metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium, and nickel, or a metal layer made of an alloy containing said metal, wherein the plating solution composition comprises 3-pyridinesulfonic acid and / or its salts. [2] The metal layer to be gold plated is A metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, and iridium, or a metal layer made of an alloy containing such metal, is laminated on a metal selected from the group consisting of nickel, nickel alloys, titanium, chromium, aluminum, and copper. The plating solution composition according to [1], wherein the nickel or nickel alloy layer is laminated on a metal selected from the group consisting of titanium, chromium, aluminum, and copper. [3] The metal layer to be gold plated is It is a nickel layer, or A metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, and iridium, or a metal layer made of an alloy containing such metal, laminated on nickel or a nickel alloy. The plating solution composition according to [1] or [2], wherein the plating is substitution reduction plating.

[0011] [4] A plating solution composition according to any one of the above [1] to [3], comprising a gold salt, a gold complexing agent, a metal layer complexing agent, a reducing agent, and a gold deposition accelerator. [5] A plating solution composition according to any one of [1] to [4], wherein the gold salt is selected from the group consisting of gold sulfites and gold chloride salts, the gold complexing agent is selected from sulfites and disulfites, the metal layer complexing agent is selected from the group consisting of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and ethylenediaminetetramethylphosphonic acid and its salts, the reducing agent is selected from the group consisting of ascorbic acid and its salts, and the gold deposition accelerator is selected from the group consisting of alkali salts, alkaline earth salts and ammonium salts of halogens. [6] The gold salt is selected from the group consisting of gold sulfite and chloroaurate, the gold complexing agent is selected from sulfite and disulfite, the metal layer complexing agent is ethylenediaminetetraacetic acid, the reducing agent is selected from the group consisting of ascorbic acid and its salts, and the gold deposition accelerator is selected from potassium iodide, sodium iodide, and ammonium iodide. The plating solution composition according to any one of [1] to [5] above. [7] The plating solution composition according to any one of [1] to [6] above, further comprising an aromatic compound having a nitro group. [8] The plating solution composition according to any one of [1] to [7] above, which does not contain a cyanide compound, thallium, and hydrazine.

[0012] [9] A plating method comprising a step of plating gold on a metal layer using the plating solution composition according to any one of [1] to [8] above.

[10] The plating method according to [9] above, wherein the plating solution composition comprises a gold salt selected from the group consisting of 3-pyridinesulfonate, gold sulfite, and chloroaurate, a gold complexing agent selected from sulfite and disulfite, ethylenediaminetetraacetic acid, a reducing agent selected from the group consisting of ascorbic acid and its salts, a gold deposition accelerator selected from potassium iodide, sodium iodide, and ammonium iodide, and an aromatic compound having a nitro group. [Advantages of the Invention]

[0013] According to the present invention, since a uniform gold film having a sufficient thickness can be formed on a wide range of base films (such as Ni, Ni / Au, Ni / Pd, Ni / Pd-P, Ni / Pt, Pt, Ru, etc.) in one step, the process cost can be reduced. In addition, since it does not contain highly toxic compounds such as thallium and hydrazine, which are commonly used in electroless gold plating, the burden on the environment and the human body is small. Furthermore, since it can be plated on Pd films with various film thicknesses, it can meet the wide range of requirements for various devices. Also, by controlling the reaction of gold by displacement plating, the amount of gold deposition can be adjusted as appropriate, and the erosion effect on the base film that occurs in conventional displacement plating can also be controlled.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in detail based on preferred embodiments of the present invention. The present invention relates to a plating solution composition for gold plating on a metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium and nickel or a metal layer made of an alloy containing the metal, which contains 3-pyridinesulfonic acid and / or its salts. Examples of salts of 3-pyridinesulfonic acid include salts of 3-pyridinesulfonic acid with alkali metals and ammonium, such as salts with sodium, potassium, ammonium, etc. 3-Pyridinesulfonic acid and its salts not only act as brighteners, but can also promote the formation of a homogeneous thick film of gold plating on a specific metal layer of the present invention. In particular, when the metal layer is a multilayer film, for example, when gold plating a palladium film on nickel or a nickel alloy, if the palladium film is thick, the number of palladium pinholes decreases, making it difficult for the substitution reaction between the underlying nickel or nickel alloy and gold to occur through the pinholes. As a result, a homogeneous gold film is not formed on the palladium through the substitution reaction, and plating defects occur during the subsequent reduction reaction to deposit gold. However, if non-toxic 3-pyridinesulfonic acid or a salt thereof is present in the plating solution, plating defects do not occur even if the palladium film is thick. The mechanism is not entirely clear, but it is speculated that 3-pyridinesulfonic acid ions adhere to the palladium through the substitution-reduction reaction and retain gold ions on the palladium.

[0015] The metal layer plated with the plating solution composition of the present invention may be a single layer or a multilayer film. The single-layer metal layer is a metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium, and nickel, or a metal layer made of an alloy containing such metal. In one embodiment, the single-layer metal layer is a metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, and iridium, or a metal layer made of an alloy containing said metal. The metal layers of the laminated film include two or more laminated films in which the uppermost layer is a metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium, and nickel, or a metal layer made of an alloy containing said metal. Examples of the metal layer in the laminated film include, but are not limited to, a laminated film in which a metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium, and nickel, or a metal layer made of an alloy containing such a metal, is laminated on a metal selected from the group consisting of nickel, nickel alloys, titanium, chromium, aluminum, and copper. Alloys containing metals selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium, and nickel include phosphorus alloys such as palladium-phosphorus alloys and nickel-phosphorus alloys. The preferred metal layers of the multilayer film are, in the order of bottom layer / top layer, nickel or nickel alloy / palladium, nickel or nickel alloy / palladium-phosphorus alloy, or nickel or nickel alloy / platinum.

[0016] The plating solution composition of the present invention may be a plating solution composition for substitution reduction plating. In this specification, substitution reduction plating can be performed when gold plating a metal layer consisting of a single layer of nickel, a metal layer consisting of a single layer of nickel alloy, or a metal layer consisting of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, and iridium, or an alloy containing said metal, which is laminated on nickel or a nickel alloy. When the plating solution composition of the present invention is used in substitution reduction plating, the metal layer complexing agent forms a complex with the dissolved metal layer, promoting the substitution reaction between nickel or nickel alloy and gold, and forming a gold plating that is firmly bonded to the metal layer. Subsequently, using the deposited gold as a catalyst, gold ions in the plating bath are reduced by the reducing agent, and gold is deposited, resulting in a thicker film. In this case, if 3-pyridinesulfonic acid is present, uniform and thickness-controlled gold plating becomes possible without using highly toxic components.

[0017] The present invention also relates to a substitution reduction plating solution composition comprising 3-pyridinesulfonic acid or a salt thereof, a gold salt, a metal layer complexing agent, a reducing agent, and a gold deposition accelerator.

[0018] Specifically, the gold source used in this invention can be water-soluble gold salts such as gold sulfites and gold chlorides. From the standpoint of safety and wastewater treatment, it is preferable to use a gold source that does not contain cyanide. The gold source can be used alone or in combination of two or more types. The concentration of the gold source is preferably 0.3 to 5 g / L, and more preferably 0.5 to 4 g / L, when converted to gold concentration.

[0019] Examples of reducing agents used in the present invention include aromatic compounds having hydroxyl groups, such as ascorbic acid, ascorbates, hydroquinone, catechol, and gallic acid. From the viewpoint of bath stability, ascorbic acid and ascorbates are preferred. It is preferable that the mixture does not contain formaldehyde or hydrazine, which are highly toxic. The reducing agent can be used alone or in combination of two or more types. The concentration of the reducing agent is preferably 1 to 50 g / L, and more preferably 10 to 40 g / L.

[0020] The plating solution composition of the present invention may contain a complexing agent having a gold complexing effect. Examples of gold complexing agents include sulfites and disulfites, specifically potassium sulfite, sodium sulfite, ammonium sulfite, potassium bisulfite, sodium bisulfite, ammonium bisulfite, potassium disulfite, sodium disulfite, and ammonium disulfite. These can be used individually or in combination of two or more. The concentration of the gold complexing agent is preferably 1 to 100 g / L, and more preferably 5 to 30 g / L. Since thiosulfates tend to cause uneven plating and can worsen wire bonding performance, the present invention, in one embodiment, does not contain thiosulfates.

[0021] The metal layer complexing agent used in the present invention is thought to form complexes with the eluted metal layer, or with the underlying metal layer in the case of a multilayer film, thereby promoting the substitution reaction between the metal layer and gold. Examples of metal layer complexing agents used in the present invention include ethyleneamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, pentaethylenehexamine, and their salts (hydrochloride salts, etc.), glycine, and the like. These can be used individually or in combination of two or more. The concentration of the complexing agent is preferably 1 to 100 g / L, and more preferably 5 to 50 g / L.

[0022] The plating solution composition of the present invention can use other additives such as accelerators, brighteners, and stabilizers within an appropriate concentration range. The other additives are not particularly limited; for example, conventionally used additives can be used. Other additives that satisfy the above conditions can also be used.

[0023] The plating solution composition of the present invention contains a gold deposition accelerator. The gold deposition accelerator is preferably a component that strongly promotes the anodic reaction, and includes compounds that generate halogen ions in aqueous solution, such as sodium chloride, potassium chloride, sodium iodide, potassium iodide, etc., i.e., alkalis or alkaline earth salts of halogens. These may be used alone or in combination. Compounds containing metals known as UPD (under potential deposition) metals, specifically thallium, lead, arsenic, and antimony, can also be used as gold deposition accelerators, but are preferably omitted due to their high toxicity. Suitable plating accelerators for use in the present invention include potassium iodide, sodium iodide, and ammonium iodide. The concentration of the accelerator is preferably 1 to 100 g / L, and more preferably 5 to 50 g / L.

[0024] The concentration of 3-pyridinesulfonic acid and its salts (sodium, potassium, ammonium, etc.) contained in the plating solution composition of the present invention is preferably 0.1 to 10 g / L, and more preferably 0.5 to 5 g / L. If the concentration is less than 0.1 g / L, the gloss of the plating may decrease, and if it is greater than 10 g / L, the lifespan of the plating bath may decrease.

[0025] Aromatic compounds having a nitro group are preferred as plating stabilizers in the plating solution composition of the present invention. Examples include 5-amino-2-nitrobenzoic acid, 3,5-dinitrobenzoic acid, 2,4-dinitrotoluene, and 3-nitrobenzoic acid. The concentration of the stabilizer is preferably 0.1 to 5 g / L, and more preferably 0.5 to 3 g / L.

[0026] In a preferred embodiment of the present invention, the plating solution composition of the present invention comprises a gold salt selected from the group consisting of 3-pyridinesulfonic acid and / or its salts, gold sulfites and gold chloride salts, a gold complexing agent selected from sulfites and disulfites, a metal layer complexing agent selected from the group consisting of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and ethylenediaminetetramethylphosphonic acid and its salts, a reducing agent selected from the group consisting of ascorbic acid and its salts, and a gold deposition accelerator selected from the group consisting of alkali salts of halogens, alkaline earth salts and ammonium salts, and preferably further comprises an aromatic compound having a nitro group. A plating solution composition containing this particular component can achieve gold plating that is particularly easy to form a thick film, dense, even, and with good film thickness uniformity.

[0027] In a preferred embodiment of the present invention, the plating solution composition of the present invention comprises a gold salt selected from the group consisting of 3-pyridinesulfonic acid and / or its salts, gold sulfites and gold chloride salts, a gold complexing agent selected from sulfites and disulfites, a reducing agent selected from the group consisting of metal layer complexing agents such as ethylenediaminetetraacetic acid, ascorbic acid and its salts, and a gold deposition accelerator selected from potassium iodide, sodium iodide and ammonium iodide, and preferably further comprises an aromatic compound having a nitro group.

[0028] The present invention also relates to a plating method comprising the step of plating gold onto a metal layer using the plating solution composition of the present invention. The pH of the electroless gold plating bath containing the plating solution composition of the present invention is preferably 5 to 10, and more preferably 6 to 9, from the viewpoint of solution stability and deposition rate.

[0029] The pH of the plating bath can be adjusted using pH adjusters. These can include organic acids such as acetic acid and phosphoric acid, as well as pH adjusters such as sodium hydroxide and potassium hydroxide. These can be used individually or in combination of two or more.

[0030] From the viewpoint of deposition rate and bath stability, the temperature of the plating bath is preferably 40 to 90°C, and more preferably 50 to 80°C. Furthermore, the processing time for electroless gold plating is not particularly limited and can be set appropriately to achieve the desired film thickness. More specifically, it can be set to approximately 0.1 to 3 hours.

[0031] According to the plating solution composition of the present invention, a gold plating film can be produced on a metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium, and nickel, or an alloy containing such a metal, with a thickness of 1 to 300 nm, preferably 25 to 100 nm, and more preferably 40 to 70 nm, considering the price of gold and the reliability of the gold film. Furthermore, in substitution reduction plating, even if the thickness of the metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium, and nickel, or an alloy containing such a metal, is 100 nm or more, for example, 100 to 1000 nm, gold plating can be performed in a single step. Using the plating solution composition of the present invention, gold plating is possible without the use of toxic substances such as hydrazine and thallium. Furthermore, it is possible to produce a gold-plated film with a faster plating speed and higher bonding performance than when using hydrazine and thallium.

[0032] Next, the plating solution compositions of the present invention will be described in more detail by the following examples and comparative examples, but the present invention is not limited to these. [Examples]

[0033] [Preparation of gold plating solution composition] After preparing a gold plating solution by mixing the gold source, reducing agent, gold complexing agent, metal layer complexing agent, accelerator, 3-pyridine sulfonic acid, and stabilizer listed in Table 1, the pH was adjusted to 8 with an aqueous sodium hydroxide solution to obtain the gold plating solution compositions of Comparative Example 1 and Examples 1-4.

[0034] [Creation of gold plating film] Method for creating a gold plating film The samples for measuring the plating thickness were obtained as follows. ENIG (electroless Ni / Au) A Si wafer with Cu wiring formed on it was chipped to 20 mm, and a 4 μm Ni film was formed on this wiring using a general hypophosphorous acid type electroless Ni plating. Then, a Ni / Au film was formed using the electroless displacement reduction Au plating bath shown in Table 1. The plating bath temperature was 65°C and the plating time was 15 min.

[0035] ENEPIG (electroless Ni / Pd / Au) A Si wafer with Cu wiring was chipped to 20 mm, and a 4 μm Ni film was formed on this wiring using a general hypophosphorous acid type electroless Ni plating. Then, either a commercially available electroless pure Pd plating bath or an electroless Pd-P plating bath was selected to form Pd on the Ni. Finally, a Ni / Au film was formed using the electroless displacement reduction Au plating bath shown in Table 1. The plating bath temperature was 65°C and the plating time was 15 min.

[0036] On Pt A wafer with SI / Ti / Pt layers was chipped to a thickness of 20 mm, and an Au film was formed using the electroless displacement reduction Au plating bath shown in Table 1. The plating bath temperature was 65°C, and the plating time was 15 min. Ru top A wafer with Si / Ti / Ru (CVD, PVD deposition) layers was chipped to 20 mm thickness, immersed in ruthenium etching solution (REC-11, manufactured by Kanto Chemical Co., Ltd.) for 5 minutes to remove the surface oxide film, and then an Au film was formed using the electroless displacement reduction Au plating bath shown in Table 1. The plating bath temperature was 65°C and the plating time was 15 min.

[0037] [Evaluation of gold plating films] [Measurement of gold plating thickness] The thickness of the obtained gold plating film was measured using an X-ray fluorescence film thickness meter (Hitachi High-Tech Science, FT9500X).

[0038] [Evaluation method for gold-plated appearance] The surface of the formed Au film was visually inspected. A uniform golden appearance was judged as "○". On the other hand, if uneven plating occurred, it was judged as "×".

[0039] [Method for evaluating corrosion of Ni-plated films] The Au film on the surface of the prepared ENIG sample was removed using an Au stripping solution, and then the surface of the Ni plating was checked for corrosion using an FE-SEM (Hitachi High-Technologies, SU8220). Samples showing corrosion were marked with "×" for Ni plating corrosion, and those not showing corrosion were marked with "〇".

[0040] [Wire Bonding Test Method] Wire bonding was performed on samples prepared using the ENIG and ENEPIG processes using a MODEL-7700D from Hi-Sol, and then the bonding strength was measured using a PTR-1101 from Lesca. Measurements were taken n=12 times for each sample. If the pull strength was 7.0 gf or higher, it was evaluated as having excellent wire bonding properties ("○"), and if it was less than 7.0 gf, it was evaluated as having poor wire bonding properties ("×"). The wire bonding conditions are as follows: Wire bonder: MODEL-7700D (manufactured by Highsol Co., Ltd.) Wire: 25um gold wire Bonding temperature: 120℃ Ultrasonic wave (mW):300(1 st ),300(2 nd ) Bonding time (msec): 30 (1 st ),30(2 nd ) Wire pull device: PTR-1101 (manufactured by Resca Co., Ltd.) Tensile force (gf): 100 [Method for evaluating liquid stability] Each plating solution shown in Table 1 was placed in a constant temperature bath at the operating temperature of 65°C. Solutions in which Au precipitated and the solution disintegrated within 70 hours were evaluated as having a stability rating of "×", while solutions in which Au precipitated and the solution did not disintegrate after 70 hours were evaluated as having a stability rating of "〇".

[0041] The results are shown in the table above. [Table 1]

[0042] result A good plating appearance without unevenness was obtained on Ni, Pd, and Pd-P, and the bath stability and bonding properties were also good (Example 1). Au plating was possible without problems even when the film thickness of pure Pd and Pd-P was increased to about 240 nm, and the results for each specification were also good (Example 2). Even when changing from potassium sulfite to sodium sulfite or from EDTA·2H·2Na·2H2O to EDTMP, there were no problems with the plating speed, and each property was good (Examples 3-4). In addition, a good Au film could be formed on a Si / Ti / Pt 50 nm film, and film deposition was also possible on Si / Ti / Ru (CVD, PVD deposition). In Comparative Example 1, which did not contain sodium 3-pyridinesulfonate, plating unevenness occurred under all conditions, and bonding performance deteriorated. Thus, the plating solution composition of the present invention can perform gold plating without using highly toxic components.

[0043] Furthermore, it has been separately confirmed that using the plating solution composition of the present invention makes it possible to perform gold plating without using highly toxic components such as hydrazine and thallium, and that the gold plating speed is faster and a gold plating film with higher bonding performance can be produced when these components are not used compared to when hydrazine and thallium are used.

Claims

1. A plating solution composition for gold plating a metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, iridium, and nickel, or a metal layer made of an alloy containing said metal, wherein the plating solution composition comprises 3-pyridinesulfonic acid and / or its salts.

2. The metal layer to be gold plated is A metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, and iridium, or a metal layer made of an alloy containing such metal, is laminated on a metal selected from the group consisting of nickel, nickel alloys, titanium, chromium, aluminum, and copper. The plating solution composition according to claim 1, wherein the nickel or nickel alloy layer is laminated on a metal selected from the group consisting of titanium, chromium, aluminum, and copper.

3. The metal layer to be gold plated is It is a nickel layer, or A metal layer made of a metal selected from the group consisting of palladium, silver, platinum, rhodium, ruthenium, and iridium, or a metal layer made of an alloy containing such metal, laminated on nickel or a nickel alloy. The plating solution composition according to claim 1, wherein the plating is substitution reduction plating.

4. A plating solution composition according to claim 1, comprising a gold salt, a gold complexing agent, a metal layer complexing agent, a reducing agent, and a gold deposition accelerator.

5. The plating solution composition according to claim 4, wherein the gold salt is selected from the group consisting of gold sulfites and gold chloride salts, the gold complexing agent is selected from sulfites and disulfites, the metal layer complexing agent is selected from the group consisting of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and ethylenediaminetetramethylphosphonic acid and its salts, the reducing agent is selected from the group consisting of ascorbic acid and its salts, and the gold deposition accelerator is selected from the group consisting of alkali salts of halogens, alkaline earth salts, and ammonium salts.

6. The plating solution composition according to claim 4, wherein the gold salt is selected from the group consisting of gold sulfites and gold chloride salts, the gold complexing agent is selected from sulfites and disulfites, the metal layer complexing agent is ethylenediaminetetraacetic acid, the reducing agent is selected from the group consisting of ascorbic acid and its salts, and the gold deposition accelerator is selected from potassium iodide, sodium iodide and ammonium iodide.

7. The plating solution composition according to claim 4, further comprising an aromatic compound having a nitro group.

8. The plating solution composition according to claim 1, which does not contain cyanide compounds, thallium, and hydrazine.

9. A plating method comprising the step of plating gold onto a metal layer using a plating solution composition according to any one of claims 1 to 8.

10. The plating method according to claim 9, wherein the plating solution composition comprises a gold salt selected from the group consisting of 3-pyridine sulfonate, gold sulfite, and gold chloride salt, a gold complexing agent selected from sulfite and disulfite, a reducing agent selected from the group consisting of ethylenediaminetetraacetic acid, ascorbic acid and its salts, a gold deposition accelerator selected from potassium iodide, sodium iodide, and ammonium iodide, and an aromatic compound having a nitro group.

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