Gold plating methods, components for gold plating, and plating solutions

Abstract

This invention provides a gold plating method for achieving soft gold plating, a composition for gold plating, and a plating solution. The gold plating method uses a plating solution containing at least one of gold sulfite salts, thiosulfate ions, and trithiosulfate ions.

Description

[Technical Field]

[0001] This invention relates to a gold plating method, a composition for gold plating, and a plating solution. [Previous Technology]

[0002] Japanese Patent Application Publication No. 2006-322037 (Patent Document 1) discloses a gold plating solution. This gold plating solution contains 0.1 to 50 g / L of potassium sulfite in a gold plating solution containing sodium gold sulfite or its ethylenediamine complex at a gold concentration of 5 to 20 g / L, sodium sulfite at a concentration of 10 to 100 g / L, and a thallium compound at a concentration of 1 to 50 ppm. This plating solution can be used for gold plating processes suitable for bump formation. Patent Document 1 discloses that gold plating is widely used in the formation of bumps for semiconductor power components, etc., to ensure electrical bonding. To achieve good bonding characteristics, a gold plating solution with relatively low hardness after heat treatment is required.

[0003] Japanese Patent Application Publication No. 2000-319016 (Patent Document 2) discloses a method for manufacturing a sodium gold sulfite solution. This method comprises (a) reacting Na(AuCl4) with sodium hydroxide and barium hydroxide to generate barium aurate and additional byproducts, (b) reacting sodium sulfite with an aqueous solution of barium aurate to generate sodium gold sulfite and additional byproducts, and (c) recovering the sodium gold sulfite solution, thereby producing a solution of sodium gold sulfite. Patent Document 2 describes a sodium gold sulfite solution useful for use in gold plating baths, and can be used for applications requiring a pure and soft gold plating film. [Prior Art Documents] [Patent Documents]

[0004] Patent Document 1: Japanese Patent Application Publication No. 2006-322037; Patent Document 2: Japanese Patent Application Publication No. 2000-319016 [Summary of the Invention]

[0005] [Problem to be solved by the invention] As disclosed in Patent Documents 1 and 2, gold plating for applications such as electrical components is sometimes desired to be of low hardness, that is, soft.

[0006] This invention was made in view of this situation, and its object is to provide a gold plating method, a composition for gold plating, and a plating solution for achieving soft gold plating. [Means for solving the problem]

[0007] The gold plating method of the present invention for achieving the above-mentioned objective is to perform gold plating using a plating solution containing at least one of gold sulfite salt, thiosulfate ions and trithiosulfate ions.

[0008] The gold plating composition of the present invention for achieving the above-mentioned objective comprises: a gold sulfite salt, and at least one of thiosulfate ions and trithiosulfate ions.

[0009] The gold plating composition of the present invention for achieving the above-mentioned objective comprises: sulfite, and at least one of thiosulfate and trithionate.

[0010] The gold plating composition of the present invention for achieving the above-mentioned objective comprises: at least one of a disulfite, a thiosulfate, and a trithionate.

[0011] The gold plating solution of the present invention, used to achieve the above-mentioned objective, comprises: a gold sulfite salt, and at least one of thiosulfate ions and trithiosulfate ions. [Effects of the Invention]

[0012] Based on the present invention, a gold plating method for achieving soft gold plating, gold plating components and plating solution can be provided.

Implementation Method

[0013] The gold plating method, gold plating composition and plating solution of the present invention will be described in relation to an embodiment of the present invention.

[0014] The plating method of this embodiment is to perform gold plating using a plating solution containing at least one of gold sulfite salt, thiosulfate ions and trithiosulfate ions.

[0015] The composition for gold plating in this embodiment includes gold sulfite salt, and at least one of thiosulfate ions and trithiosulfate ions.

[0016] The composition for gold plating in this embodiment includes at least one of sulfite, thiosulfate and trithionate.

[0017] The composition for gold plating in this embodiment includes at least one of bisulfite, thiosulfate and trithionate.

[0018] The gold plating solution of this embodiment (hereinafter, sometimes simply referred to as plating solution) contains at least one of sulfite, thiosulfate and trithiosulfate.

[0019] The plating method based on this embodiment can achieve soft gold plating. Based on the gold plating composition and plating solution of this embodiment, the plating method of this embodiment can be realized, resulting in soft gold plating. Furthermore, in this embodiment, the gold plating includes gold, and is not limited to cases containing only gold. In this embodiment, gold plating only needs to include gold, including cases where gold and other metal elements are plating.

[0020] Hereinafter, the gold plating method, gold plating components and plating solution of this embodiment will be described in detail.

[0021] In the plating method of this embodiment, a gold plating composition comprising a gold sulfite salt such as sodium gold sulfite, and at least one of thiosulfate ions and trithiosulfate ions can be used. One example of a gold plating composition (plating solution composition) is a gold plating solution.

[0022] One example of the gold plating solution is a plating solution containing at least one of gold sulfite salt, thiosulfate ions, and trithiosulfate ions. The plating solution may contain thiosulfate ions and trithiosulfate ions. The plating solution may further contain other gold plating components (gold plating additives) described later. In addition, in this embodiment, the term "plating solution" includes a plating replenishing solution used to replenish the plating solution in use. The plating solution may be, for example, an aqueous solution. The plating method of this embodiment involves preparing the plating solution and performing gold plating using the plating solution. The plating method of this embodiment may include a preparation step of preparing the plating solution and a plating step of performing gold plating using the plating solution.

[0023] The composition for gold plating (additive for gold plating) may be a first composition comprising at least one of a sulfite, a thiosulfate that generates a thiosulfate ion, and a trithiosulfate that generates a trithiosulfate ion. For example, the first composition may comprise a sulfite, a thiosulfate ion, and a trithiosulfate ion. The first composition will be described in detail below.

[0024] Furthermore, the composition for gold plating (additive for gold plating) may be a second composition comprising at least one of a bisulfite, a thiosulfate, and a trithionate. For example, the second composition may comprise a bisulfite, a thiosulfate, and a trithionate. The second composition will be described in detail below.

[0025] That is, in addition to gold sulfite salts such as sodium gold sulfite, thiosulfate ions and trithiosulfate ions, the plating solution may further contain sulfites such as sodium sulfite that are different from gold sulfite salts, and bisulfites such as sodium bisulfite.

[0026] The plating solution may contain chelating agents, buffers, crystallization modifiers, brighteners, alloy metal salts, reducing agents, and surfactants as other additives. Examples of chelating agents include sulfites, EDTA, NTA, and amine compounds. Examples of buffers include various inorganic acid salts and various organic acid salts. Examples of crystallization modifiers include salts of thallium, lead, bismuth, antimony, and arsenic. Examples of brighteners include amine compounds and aromatic compounds. Examples of alloy metal salts include salts of cobalt, nickel, iron, and silver. Examples of reducing agents include SBH, DMAB hydrazine, hydroquinone, thiourea, and ascorbic acid salts. Examples of surfactants include anionic surfactants, cationic surfactants, and amphiphilic surfactants. For example, when the plating solution contains thallium, the concentration of thallium ions in the plating solution may be set between 1 mg / L and 50 mg / L.

[0027] The pH of the plating solution is between 6.0 and 10.0, preferably between 7.0 and 9.0. The pH of the plating solution can be adjusted by adding sodium hydroxide or sodium bisulfite.

[0028] When evaluating the specific gravity of the plating solution using Baumé (heavy Baumé), it is 0.2 Bh or more and 33.3 Bh or less.

[0029] When the plating solution is for electroplating, especially for a plating bath, its specific gravity is 2.0 Bh or more and 22.0 Bh or less, preferably 3.3 Bh or more and 19.9 Bh or less, and even more preferably 4.1 Bh or more and 17.8 Bh or less.

[0030] The plating solution is for electroplating, especially when it is a replenishing solution, and its specific gravity is above 12.0 Bh and below 33.3 Bh.

[0031] The plating solution is for electroless plating, especially when it is a building bath solution, and its specific gravity is 0.2Bh or more and 14.3Bh or less, preferably 0.4Bh or more and 13.0Bh or less, and even more preferably 0.6Bh or more and 11.8Bh or less.

[0032] The plating solution is for electroless plating, especially when it is a replenishment solution, and its specific gravity is 12.0 Bh or more and 33.3 Bh or less.

[0033] Gold sulfite salts can be alkali gold sulfite salts such as sodium gold sulfite or ammonium gold sulfite. When the gold sulfite salt is an alkali gold sulfite salt, sodium gold sulfite or potassium gold sulfite are particularly suitable.

[0034] Thiosulfate ions can be derived from thiosulfates such as sodium thiosulfate, ammonium thiosulfate, potassium thiosulfate, and calcium thiosulfate.

[0035] The trithiolate ion can be derived from trithiolates such as sodium trithiolate, ammonium trithiolate, potassium trithiolate, and calcium trithiolate.

[0036] The gold concentration of the plating solution can be set to be 0.50 g / L or more and 20.0 g / L or less. When the plating solution is used for electroplating, the gold concentration of the plating solution is preferably 5.0 g / L or more and 20.0 g / L or less, and more preferably 10.0 g / L or more and 16.0 g / L or less.

[0037] The plating solution may contain thiosulfate ions at a concentration of 0.02 mg / L to 4.00 mg / L, preferably 0.03 mg / L to 3.55 mg / L. This facilitates the softening of the plating layer. Furthermore, in this embodiment, when "ppm" is used, it refers to "mass ppm".

[0038] The plating solution may contain trisulfonate ions at a concentration of 0.10 mg / L to 2.50 mg / L, preferably 0.13 mg / L to 2.19 mg / L. This makes the plating layer easier to soften.

[0039] The plating solution preferably contains thiosulfate ions and trithiosulfate ions. The plating solution may contain thiosulfate ions and trithiosulfate ions in a total concentration of 0.20 mg / L to 4.00 mg / L, preferably 0.20 mg / L to 3.68 mg / L. This makes the plating layer easier to soften.

[0040] By softening the coating as described above, the surface of the coating becomes smoother. In other words, the surface roughness of the coating surface decreases. At this time, under visual observation, for example, the surface of the coating appears glossy.

[0041] The plating step can be, for example, electrolytic gold plating. The preferred plating conditions are a current density of 0.1 A / dm² to 2.0 A / dm² and a liquid temperature of 40°C to 80°C. Even more preferred are a current density of 0.2 A / dm² to 1.0 A / dm² and a liquid temperature of 50°C to 70°C.

[0042] The preparation step is assumed to be a sulfation step in which the plating solution is prepared to contain sulfonated gold hydroxide. One example of gold hydroxide is Ba[Au(OH)4]2 (barium tetrahydroxyaluminate, sometimes referred to as barium gold hydroxide) as a hydroxide of barium and gold.

[0043] In the sulfonation step, gold hydroxide may be sulfonated using a first component containing a sulfite. Furthermore, in the sulfonation step, gold hydroxide may be sulfonated using a second component containing a bisulfite. The sulfonation step may use both the first and second components to sulfonate gold hydroxide.

[0044] The first component preferably contains sulfite, thiosulfate, and trithionate. This makes the coating easier to soften. As an example, the first component can be obtained by a first heat treatment step of heat treating sulfite. The first heat treatment step is described later.

[0045] The first component contains 95.0% by mass of sulfite, and the remainder may be thiosulfate, trithionate and impurities.

[0046] The first composition may contain thiosulfate, preferably 1 ppm to 3000 ppm based on thiosulfate ions, and more preferably 10 ppm to 1500 ppm.

[0047] The first composition may contain trithionate, preferably 1 ppm to 3000 ppm based on trithionate ions, and more preferably 10 ppm to 1500 ppm.

[0048] In the first heat treatment step, the sulfite may be heated at a temperature of 28°C to 60°C, preferably 40°C to 60°C. In the first heat treatment step, through heat treatment, salts capable of generating thiosulfate ions (thiosulfate) and salts capable of generating trithiosulfate ions (trithiosulfate) are generated from the sulfite. When the first heat treatment step is performed at a temperature of 40°C to 60°C, the heating time is sufficient for 100 to 200 hours. When the temperature of the first heat treatment step is less than 40°C, the heating time may be set to 10 days or more.

[0049] The second component preferably comprises bisulfite, thiosulfate and trithionate. As an example, the second component can be obtained by a second heat treatment step of heat treatment of bisulfite.

[0050] The second component contains more than 95.0% by mass of bisulfite, and the remainder may be thiosulfate ions, trithiosulfate ions and impurities.

[0051] The second component may contain thiosulfate, preferably 1 ppm to 300 ppm based on thiosulfate ions, and more preferably 10 ppm to 1500 ppm.

[0052] The second component may contain trithionate, preferably at a concentration of 1 ppm to 3000 ppm based on trithionate ions, and even more preferably at a concentration of 10 ppm to 1500 ppm.

[0053] In the second heat treatment step, the bisulfite may be heated at a temperature of 28°C to 60°C, preferably 40°C to 60°C. During the second heat treatment step, the bisulfite decomposes to produce salts that can generate thiosulfate ions (thiosulfate) and salts that can generate trithiosulfate ions (trithiosulfate). When the second heat treatment step is performed at a temperature of 40°C to 60°C, a heating time of 100 to 200 hours is sufficient. If the temperature of the second heat treatment step is less than 40°C, the heating time may be set to 10 days or more.

[0054] One example of a sulfite is sodium sulfite. Other sulfites may be potassium sulfite, ammonium sulfite, magnesium sulfite, or calcium bisulfite.

[0055] One example of a sulfite is sodium bisulfite. Other sulfites may be potassium bisulfite, ammonium bisulfite, magnesium bisulfite, or calcium bisulfite. Furthermore, in this embodiment, the concept of sodium bisulfite includes sodium disulfite (Na₂S₂O₅) and sodium bisulfite (NaHSO₃) obtained by hydrolysis of sodium disulfite. When only sodium bisulfite or sodium bisulfite (Na₂S₂O₅) is mentioned, it includes the cases of sodium disulfite, sodium bisulfite, and a mixture of sodium disulfite and sodium bisulfite.

[0056] Thiosulfate, as an example, can be sodium thiosulfate, which can generate thiosulfate ions. Other thiosulfates can be thiosulfate, sodium thiosulfate, ammonium thiosulfate, magnesium thiosulfate, potassium thiosulfate, etc., which can generate thiosulfate ions.

[0057] As an example, a trithiosulfate may be sodium trithiosulfate, which can generate trithiosulfate ions. Other trithiosulfate ions may be potassium trithiosulfate, ammonium trithiosulfate, magnesium trithiosulfate, calcium trithiosulfate, etc., which can generate trithiosulfate ions. [Example]

[0058] Hereinafter, the gold plating method, gold plating composition and plating solution of this embodiment will be described based on the embodiments.

[0059] The gold plating process shown in Table 1 for Experimental Examples 1-14 was performed as follows to form gold-plated bumps, and these bumps were evaluated.

[0060]

[0061] (Experimental Examples 1-12) In Experimental Examples 1-12, gold plating was performed on the test substrate as follows.

[0062] First, barium gold hydroxide (Ba[Au(OH)4]2) is prepared using auric acid chloride (HAuCl4), barium hydroxide (Ba(OH)2) and sodium hydroxide.

[0063] The first component is manufactured as follows. Sodium sulfite (Na2SO3, manufactured by AIR WATER PERFORMANCE CHEMICAL INC., specification: industrial grade, purity ≥97%) is kept at 50°C for 168 hours (first heat treatment) and is used as the first component.

[0064] When sodium sulfite and the first component are determined (analyzed) by liquid chromatography (LC-TOFMS), thiosulfate ions and trithiosulfate ions are detected in the first component.

[0065] Here, the determination of sodium sulfite and the first component by LC-TOFMS is performed as follows.

[0066] In the LC determination, the measuring apparatus used was a Prominence UFLC manufactured by Shimadzu Corporation. The column used in this determination was an Intrade Organic Acid (2.0 mm × 150 mm, 3.0 μm). The column temperature was set to 40 °C. The mobile phase A used acetonitrile / water / formic acid = 10 / 90 / 0.1. The mobile phase B used acetonitrile / 100 mM ammonium formate = 10 / 90. The assay profile was varied in the following order: A:B = 100:0 (0 min), A:B = 100:0 (1 min), A:B = 0:100 (7 min), A:B = 0:100 (10 min). The flow rate of the mobile phase was set to 0.2 mL / min. The analyte sample was dissolved in ultrapure water at a concentration of 10 mg / mL to prepare the assay sample. The volume of the assay sample injected into the LC was 5 μL.

[0067] In the determination using MS, the measuring apparatus used was an AB SCIEX Triple TOF 5600+. The ionization method was set to ESI, and the IonSpray Voltage Floating was set to 4.5kV (Negative mode) and 5.5kV (Positive mode). The mass range was set to m / z 50-1500.

[0068] In this determination, before the determination of the analyte (sodium sulfite or the first component), the sodium thiosulfate (10 mg / mL, the concentration of the sample used for determination) is first determined as a reference substance, and the area of ​​the peak of the thiosulfate ion (the peak at about 7.5 minutes) is calculated (S1).

[0069] Next, the analyte is measured, and the area of ​​the peak of thiosulfate ions (approximately 7.5 minutes) (S21) and the area of ​​the peak of trithiosulfate ions (approximately 8.5 minutes) (S22) are calculated. Then, based on the concentration of the reference substance, the area S1, the concentration of the analyte, and the area S21, the mass of thiosulfate ions in the analyte (sodium sulfite and each of the first component) is calculated. Similarly, based on the concentration of the reference substance, the area S1, the concentration of the analyte, and the area S21, the mass of trithiosulfate ions in the analyte is calculated. From these results, the thiosulfate ion content in sodium sulfite is 3 ppm, and the trithiosulfate ion content is 1 ppm. Furthermore, the thiosulfate ion content in the first component is 54 ppm, and the trithiosulfate ion content is 460 ppm.

[0070] The second component is manufactured as follows. Anhydrous sodium bisulfite (Na2S2O5, manufactured by AIR WATER PERFORMANCE CHEMICAL INC., specification: industrial grade, purity ≥ 97%) is kept at 50°C for 168 hours (second heat treatment) and used as the second component.

[0071] When sodium bisulfite and the second component were determined (analyzed) by liquid chromatography (LC-TOFMS) in the same manner as sodium bisulfite and the first component, thiosulfate ions and trithiosulfate ions were detected in the second component.

[0072] In this determination, before determining the analyte (anhydrous sodium bisulfite or the second component), the sodium thiosulfate, serving as a reference substance, is first determined. Based on the results of this determination, the mass of thiosulfate ions and the mass of trithiosulfate ions in each analyte are calculated. The anhydrous sodium bisulfite contains 5 ppm of thiosulfate ions and 230 ppm of trithiosulfate ions, as determined from these results. Furthermore, the second component contains 650 ppm of thiosulfate ions and 2190 ppm of trithiosulfate ions.

[0073] Next, a plating solution containing sodium gold sulfite (Na3Au(SO3)2) is prepared as follows.

[0074] Sodium gold sulfite is manufactured from barium gold hydroxide as follows. Specifically, sodium gold sulfite is prepared by adding an aqueous solution of sodium sulfite and a first component (hereinafter referred to as the first aqueous solution), an aqueous solution of sodium bisulfite and a second component (hereinafter referred to as the second aqueous solution), and a bonding agent (EDTA·2Na) to barium gold hydroxide and stirring, then filtering the precipitate (barium sulfate). Thallium formate is added to this sodium gold sulfite, and then sodium thiosulfate is added to adjust the pH to prepare a plating solution.

[0075] In addition, the concentration of the first aqueous solution (the total concentration of sodium sulfite and the first component) is set to 126 g / L. The concentration of the second aqueous solution (the total concentration of sodium bisulfite and the second component) is set to 84 g / L.

[0076] The ratio of sodium sulfite to the first component in the first aqueous solution is shown in Table 1, and varies depending on the experimental example. Similarly, the ratio of sodium bisulfite to the second component in the second aqueous solution is also shown in Table 1, and varies depending on the experimental example. In addition, in Table 1, the proportion (mass %) of the first component in the first aqueous solution relative to the total amount of sodium sulfite and the first component is recorded as "Proportion of the first component (%)". Also, the proportion (mass %) of the second component in the second aqueous solution relative to the total amount of sodium bisulfite and the second component is recorded as "Proportion of the second component (%)".

[0077] The plating solution prepared in the above manner has an approximate thallium ion concentration of 10 mg / L, contains 10 g / L of gold ions in the solution, has a pH of 8.0, and a specific gravity of 4.5 Bh. In Table 1, the items "Thiosulfate ions from the first aqueous solution (mg / L)," "Trithiosulfate ions from the first aqueous solution (mg / L)," "Thiosulfate ions from the second aqueous solution (mg / L)," and "Trithiosulfate ions from the second aqueous solution (mg / L)" indicate the concentrations in the plating solution. In addition, when preparing the plating solution, in order to increase the concentration of thiosulfate ions in the plating solution only to the concentration shown in Table 1 ("Added thiosulfate ions" in Table 1), a specified amount of sodium thiosulfate was added to the plating solution in each experimental example.

[0078] Next, gold plating was performed on the test substrate using the above plating solution.

[0079] The plating process was performed using the following method. The test substrate was made by coating a silicon wafer with a resist patterned in a manner that could form 60μm square bumps (thickness from 14μm to 17μm). Next, the current density was set to 0.5A / dm2, and the temperature of the plating solution was set to 60°C. The plating process was performed while stirring the plating solution. The plating process time was set to 48 minutes.

[0080] (Experimental Example 13) Experimental Example 13 used sodium sulfite and sodium bisulfite from different batches than those used in Experimental Examples 1-12, and gold plating was performed on the test substrate in the same manner as in Experimental Example 1.

[0081] (Experimental Example 14) Experimental Example 14 used sodium sulfite and sodium bisulfite from different batches than those used in Experimental Examples 1-12 and Experimental Example 13. The rest of the process was the same as in Experimental Example 1, and gold plating was performed on the test substrate.

[0082] After plating in each experimental example, the resist was removed from the test substrate. The test substrate was then heat-treated. The heat treatment was performed at 300°C for 30 minutes. Next, the Vickers hardness of the gold-plated surface (bump surface) after heat treatment was measured, the surface roughness (Ra) was measured, and visual observation (presence or absence of nodules / clumps) was conducted using an optical microscope. These results are shown in Table 1. In Table 1, "Hardness (HV)" refers to the Vickers hardness of the gold-plated surface after heat treatment, and "Ra (nm)" refers to the surface roughness (Ra).

[0083] In this embodiment, the Vickers hardness is measured using a micro Vickers hardness tester (manufactured by Mitutoyo Co., Ltd., model: HM-200). Furthermore, in this embodiment, the Vickers hardness is measured using a micro Vickers hardness tester (manufactured by Mitutoyo Co., Ltd., model: HM-200) according to Japanese Industrial Standard JIS Z 2244:2009, with a test force set to 10 gf (98.07 mN) and a holding time set to 10 seconds.

[0084] In this embodiment, a nodule is a type of uneven structure formed on the surface of the coating, which is a slightly rounded protrusion on the surface of the coating when viewed from the front. A nodule is a structure that protrudes from the surface of the coating. When a nodule is formed on the surface of the coating, the top of the nodule often has an arc (spherical shape). The presence or absence of a nodule is determined when a nodule with a long side of 3 μm or more can be identified (marked as "present" in Table 1), otherwise it is determined as not having a nodule (marked as "absent" in Table 1).

[0085] In Table 1, the item "Total of Thiosulfate Ions and Trithiosulfate Ions (mg / L)" indicates the total amount of thiosulfate ions and trithiosulfate ions in 1L of plating solution. Similarly, the item "Total of Thiosulfate Ions (mg / L)" in Table 1 indicates the total amount of thiosulfate ions in 1L of plating solution.

[0086] As shown in Table 1, in experimental examples (Examples 3, 4, 6-11, and 13) where the total concentration of thiosulfate ions and trithiosulfate ions in the plating solution was 0.20 mg / L or more and 4.00 mg / L or less (3.68 mg / L or less), the Vickers hardness (hardness in Table 1) of the gold-plated coating surface after heat treatment was 60 Hv or less, achieving a sufficiently soft and good gold-plated film. When the total concentration of thiosulfate ions and trithiosulfate ions was less than 0.20 mg / L or more than 4.00 mg / L, the Vickers hardness of the coating surface exceeded 60 Hv. In addition, in Experiment 14, the coating surface was significantly uneven, making it impossible to properly measure the hardness.

[0087] When the total concentration of thiosulfate ions and trithiosulfate ions in the plating solution is 0.20 mg / L or more and 4.00 mg / L or less, the plating solution may contain thiosulfate ions of 0.02 mg / L or more (0.03 mg / L or more) and 4.00 mg / L or less (3.55 mg / L or less), and trithiosulfate ions of 0.10 mg / L or more (0.13 mg / L or more) and 2.50 mg / L or less (2.19 mg / L or less).

[0088] In Table 1, based on the Vickers hardness results above, Experimental Examples 1-14 are classified as Examples 1-9 and Comparative Examples 1-5.

[0089] Evaluation results other than the Vickers hardness of the coating surface are as follows. A surface roughness (Ra) of 82 nm to 220 nm is considered good. In this embodiment, the surface roughness (Ra) of the coating surface in the experimental examples other than Experimental Example 14 is considered good if it is in the range of 82 nm to 220 nm. Furthermore, in the experimental examples other than Experimental Example 14, the formation of significant nodules (clumps) on the coating surface could not be confirmed. As described above, the coating surface (plated surface) possesses the necessary and sufficient smoothness.

[0090] In Experiment 14, as described above, the surface of the coating was significantly uneven, and nodules were observed. In Experiment 14, the surface of the coating was significantly uneven, therefore the surface roughness (Ra) measurement method used in this embodiment could not measure the surface roughness.

[0091] As shown in the above experimental examples, it is known that if the plating solution contains thiosulfate ions and trisulfonic acid ions in a specified amount, soft gold plating can be achieved.

[0092] The above methods can provide a gold plating method for achieving soft gold plating, gold plating components and plating solution.

[0093] Furthermore, the embodiments disclosed in this specification are illustrative, and the embodiments of the present invention are not limited thereto. Appropriate modifications may be made without departing from the scope of the present invention. [Industrial Applicability]

[0094] The present invention is applicable to gold plating methods, gold plating compositions and plating solutions.

Claims

1. A gold plating method comprising: a plating step of plating gold using a plating solution containing sodium gold sulfite, thiosulfate ions, and trithiosulfate ions; wherein the plating solution contains: 0.50 g / L to 20.0 g / L of gold, 0.03 mg / L to 3.55 mg / L of thiosulfate ions, 0.13 mg / L to 2.19 mg / L of trithiosulfate ions, and a combined concentration of 0.20 mg / L to 3.68 mg / L of thiosulfate ions and trithiosulfate ions; and the pH of the plating solution is 7.0 to 9.

0.

2. The gold plating method of claim 1, wherein the aforementioned plating solution further comprises thallium ions.

3. The gold plating method of claim 1 further includes a sulfation step of preparing the aforementioned plating solution by sulfation of gold hydroxide.

4. The gold plating method of claim 3 further includes a first heat treatment step of heat-treating sulfite to obtain a first composition comprising at least one of sulfite, thiosulfate and trithiosulfate, wherein the aforementioned sulfonation step uses the aforementioned first composition to sulfonate the aforementioned gold hydroxide.

5. The gold plating method of claim 4, wherein the aforementioned first component comprises thiosulfate and trithionate.

6. The gold plating method of claim 3, further comprising a second heat treatment step of heat-treating bisulfite to obtain a second composition comprising at least one of bisulfite, thiosulfate and trithionate, wherein the aforementioned sulfonation step uses the aforementioned second composition to sulfonate the aforementioned gold hydroxide.

7. The gold plating method of claim 6, wherein the aforementioned second component comprises thiosulfate and trithionate.

8. The gold plating method as claimed in claim 1 or 2, wherein the aforementioned plating solution contains gold at a concentration of 9 g / L to 11 g / L.

9. The gold plating method of claim 1 or 2, wherein the specific gravity of the aforementioned plating solution is 0.2 Bh or more and 33.3 Bh or less.

10. A composition for gold plating, comprising: sodium gold sulfite at a concentration of 0.50 g / L to 20.0 g / L based on gold, thiosulfate ions at a concentration of 0.03 mg / L to 3.55 mg / L, and trithiosulfate ions at a concentration of 0.13 mg / L to 2.19 mg / L; wherein the total concentration of thiosulfate ions and trithiosulfate ions is 0.20 mg / L to 3.68 mg / L; and the pH is 7.0 to 9.

0.

11. The composition for gold plating as claimed in claim 10 further includes thallium ions.

12. The composition for gold plating as claimed in claim 10 or 11 contains sodium gold sulfite at a concentration of 9 g / L to 11 g / L based on gold.

13. The composition for gold plating as claimed in item 10 or 11, wherein the specific gravity is more than 0.2 Bh and less than 33.3 Bh.

14. A gold plating solution comprising: sodium gold sulfite at a concentration of 0.50 g / L to 20.0 g / L (based on gold), thiosulfate ions at a concentration of 0.03 mg / L to 3.55 mg / L, and trithiosulfate ions at a concentration of 0.13 mg / L to 2.19 mg / L; wherein the total concentration of thiosulfate ions and trithiosulfate ions is 0.20 mg / L to 3.68 mg / L; and the pH is 7.0 to 9.

0.

15. The gold plating solution of claim 14 further contains thallium ions.

16. The gold plating solution of claim 14 or 15 contains sodium gold sulfite at a concentration of 9 g / L to 11 g / L based on gold.

17. The plating solution for gold plating as requested in item 14 or 15, wherein the specific gravity is 0.2 Bh or more and 33.3 Bh or less.