Gold plating solution containing gold sulfite and replenishing solution for gold plating solution containing gold sulfite

Abstract

The object is to provide a gold plating solution and a replenishing solution for the same which can solve the problem of variation in plating performance. The object is solved by a non-cyanide gold plating solution containing a gold sulfite salt, an electrolyte and water and having a cyanide ion concentration of 1 mg / L or less and a replenishing solution for the same.

Description

Technical Field

[0001] This invention relates to gold plating solutions containing gold sulfite salts and replenishing solutions for gold plating solutions containing sodium gold sulfite. Background Technology

[0002] As a gold raw material contained in gold plating solution and replenishment solution for gold plating solution, gold sulfite salts such as sodium gold sulfite are used, and the manufacturing method thereof is disclosed, for example, in Patent Document 1.

[0003] In addition, Patent Document 2 discloses a method for manufacturing a chemical gold plating solution and a method for manufacturing an aqueous solution of gold sulfite for the gold plating solution. By controlling the particle increase rate of the aqueous solution of gold sulfite, a plating solution with excellent plating operation stability can be provided.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 2773931

[0007] Patent Document 2: Japanese Patent Application Publication No. 2006-249485 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] The method described in Patent Document 2 can suppress the formation of a gold coating on the inner wall of the plating bath, etc., but no research has been conducted on the formed coating. After research, the inventors discovered that when forming a coating using a gold plating solution containing gold sulfite, the formed coating has deviations. Particularly in the formation of electroless gold plating, sometimes the desired gold film thickness cannot be obtained, and poor color tone of the gold coating occurs.

[0010] The objective of this invention is to provide a gold plating solution and a replenishing solution for the gold plating solution that can solve the problem of deviation in such gold plating coating.

[0011] Methods for solving problems

[0012] To solve the aforementioned problem, the inventors conducted repeated research and discovered that a specific substance present in the gold plating solution and the replenishing solution is the cause of deviations in the gold plating film. Specifically, they clarified that the presence of cyanide ions (CN) in the gold plating solution is the cause. - This results in reduced plating performance of the gold plating solution, such as decreased film thickness and poor color tone.

[0013] Then, based on the above insights, it was found that by reducing the concentration of cyanide ions in the gold plating solution and the replenishment solution to a certain level, the degradation of the gold plating performance could be suppressed.

[0014] One aspect of the present invention is a non-cyanide gold plating solution comprising gold sulfite, an electrolyte, and water, with a cyanide ion concentration of less than 1 mg / L. Another aspect of the present invention is a replenishing solution for the non-cyanide gold plating solution comprising gold sulfite and water, with a cyanide ion concentration of less than 1 mg / L.

[0015] Invention Effects

[0016] According to the present invention, a gold plating solution and a replenishing solution for the gold plating solution are provided, which can suppress the reduction in plating performance of the gold plating solution, such as the reduction in film thickness and poor color of the gold plating film. Detailed Implementation

[0017] The present invention will now be described in detail. However, the description of the constituent elements described below is only one example (representative example) of the implementation of the present invention. The present invention is not limited to these contents and can be implemented in various modifications within the scope of its spirit.

[0018] One embodiment of the present invention is a non-cyanide gold plating solution comprising gold sulfite, electrolyte and water, and having a cyanide ion concentration of less than 1 mg / L.

[0019] This invention is based on the discovery that specific substances are present in the solution during gold plating, specifically cyanide ions (CN) in the gold plating solution. - This reduces the plating performance (plating formation capability) of the gold plating solution. Furthermore, based on this understanding, by setting the cyanide ion concentration in the gold plating solution to below 1 mg / L, the reduction in plating performance can be suppressed.

[0020] The reason why cyanide ions can be mixed into the gold plating solution is unclear, but it is believed that most gold is obtained through recycling, and therefore gold refining is sometimes carried out in the environment where the gold plating solution is manufactured. Then, potassium cyanide, which is used as a solvent for precious metals at this time, volatilizes, inevitably leading to its contamination into the gold plating solution.

[0021] As a method to reduce cyanide ions in gold plating solution, methods such as using ion exchange resins or chelating resins to remove cyanide ions from the gold plating solution can be cited.

[0022] There are no particular restrictions on the gold sulfite salts used in gold plating solutions; examples include sodium gold sulfite, potassium gold sulfite, and ammonium gold sulfite, with sodium gold sulfite being the preferred choice.

[0023] There are no particular limitations on the preparation method of the gold plating solution of this embodiment. It can be prepared by adding gold sulfite and an electrolyte to an aqueous medium containing water and mixing them. As the electrolyte, a known electrolyte that can be contained in the gold plating solution can be used.

[0024] There are no particular restrictions on the content of gold sulfite in the gold plating solution, which is generally converted to a gold concentration of 0.2 g / L or more and 100 g / L or less, preferably 0.5 g / L or more and 30 g / L or less. In addition, there are no particular restrictions on the content of electrolyte in the gold plating solution, which is generally 20 g / L or more and 300 g / L or less.

[0025] In addition, it may contain other components that are commonly found in gold plating solutions, such as pH adjusters and complexing agents. Adding complexing agents can improve the stability of the gold plating solution.

[0026] Another embodiment of the present invention is a replenishing solution for a non-cyanide gold plating bath comprising gold sulfite and water, and having a cyanide ion concentration of 1 mg / L or less. The replenishing solution is a solution used to replenish the gold component in the gold plating bath. There is no particular limitation on the content of gold sulfite in the replenishing solution, but it is generally converted to a gold concentration of 30 g / L or more and 200 g / L or less, preferably 50 g / L or more and 150 g / L or less.

[0027] The replenishing solution for gold plating solution is a replenishing solution to replenish the gold component of the gold plating solution. Therefore, the replenishing solution for gold plating solution is the same as that for gold plating solution. By keeping the cyanide ion concentration below 1 mg / L, the plating performance of the gold plating solution can be suppressed.

[0028] In this embodiment, the molar ratio of gold concentration to sulfite ion concentration in the replenishment solution of the gold plating bath (SO3) 2- The preferred value for ( / Au) is 2.1 or higher and 2.9 or lower. According to the inventors' research, sulfite ions affect the redox potential of the plating solution; therefore, within the above range, the gold plating solution becomes a stable liquid and exhibits good plating performance, thus this is preferred.

[0029] It should be noted that the gold concentration in the replenishment solution of the gold plating solution can be determined by ICP-based luminescence spectrophotometry.

[0030] Example

[0031] The present invention will now be described in more detail using examples, but it is clear that the scope of the present invention is not limited to the examples described herein.

[0032] <Comparative Example 1 Regarding Cyanide Concentration>

[0033] A non-cyanide gold plating solution 1 was prepared, which contained, in water, 14 g / L of sodium gold(I) sulfite (based on gold concentration), 80 g / L of sodium sulfite as an electrolyte, 20 g / L of disodium ethylenediaminetetraacetate as a buffer, and 10 mg / L (thallium concentration) of thallium formate as a crystallization regulator. The cyanide concentration was determined to be 1.1 mg / L.

[0034] The test piece (pure copper plate, 0.3 mm thick, 25 mm × 40 mm in size, substrate: 1 μm nickel plating, 0.1 μm gold touch plating) was immersed in non-cyanide gold plating solution 1 at a bath temperature of 50 °C for 30 minutes, with a current density of 0.5 A / dm³. 2 Electroplating was performed, and the resulting coating thickness was 9.12 μm.

[0035] <Examples 1-2 regarding cyanide concentration>

[0036] Non-cyanide gold plating solution 1 was subjected to adsorption and cyanide removal treatment to prepare non-cyanide gold plating solution 2 (Example 1) with a cyanide concentration of 0.8 mg / L and non-cyanide gold plating solution 3 (Example 2) with a cyanide concentration of 0.4 mg / L. These non-cyanide gold plating solutions were used to electroplate test pieces in the same manner as in Comparative Example 1, resulting in coating thicknesses of 9.49 μm and 9.50 μm, respectively.

[0037]

[0038] (Comparative Examples 2-6 and Examples 3-7)

[0039] Preparation of sodium gold(I) sulfite solution:

[0040] The gold concentration is planned to be set at 100 g / L and the cyanide concentration (CN) at 100 g / L. - ) and sulfite ion concentration (SO3) 2- Various sodium gold(I) sulfite solutions from Comparative Examples 2-6 and Examples 3-7.

[0041] Chemical plating (displacement plating) method:

[0042] Using the sodium gold(I) sulfite solutions prepared in Comparative Examples 2-6 and Examples 3-7 above, electroless gold plating solutions were prepared containing 2 g / L gold, 5.0 g / L citrate monohydrate as a pH buffer, 65.0 g / L trisodium citrate dihydrate, 0.1 g / L thiourea as a precipitation promoter, and 5 mg / L (thallium equivalent concentration) thallium formate as a crystallization regulator. The bath temperature was set to 70°C and the pH was set to 6.0.

[0043] A 5μm to 7μm nickel plating layer is formed on a copper plate using a commercially available pretreatment agent and a chemical nickel plating solution. The nickel-plated copper plate is then immersed in the chemical plating solution prepared above for 15 minutes, followed by rinsing with water and drying.

[0044] Visual inspection and a fluorescence X-ray thickness gauge were used to confirm the presence of gold deposits on the copper plate material. A 0° mark was awarded when the lemon-yellow gold plating film was deposited with a thickness of 0.1 μm or more; a △ mark was awarded when the gold plating film was 0.1 μm or more with slight color unevenness; and an × mark was awarded when the gold plating film thickness was insufficient (less than 0.1 μm). A 0° or △ mark was considered acceptable.

[0045] Stability evaluation method for sodium gold(I) sulfite solution:

[0046] Add 50 mL of the sodium gold(I) sulfite solution prepared in Comparative Examples 2-6 and Examples 3-7 as described above to a 100 mL polypropylene container, and impregnate a piece of quantitative filter paper cut into 15 mm × 15 mm pieces. Then, close the lid of the polypropylene container.

[0047] Next, the polypropylene container was immersed in a warm water bath maintained at 70°C, and a sodium gold(I) sulfite solution was added indirectly. After 5 hours, the polypropylene container was removed, the lid was opened, and the immersed quantitative filter paper was taken out with tweezers. The color of the filter paper was visually confirmed.

[0048] When the sodium gold sulfite (I) solution is unstable, heating produces colloidal gold particles, which adsorb onto quantitative filter paper, causing the paper to turn purple, brown, or black. If no color change in the quantitative filter paper is visually observed before and after heating, the solution is considered stable and acceptable (○). If a color change in the quantitative filter paper is visually observed before and after heating, the solution is considered unstable and unacceptable (×). The results are shown in Table 2 below.

[0049]

Claims

1. A replenishing solution for a non-cyanide gold plating bath, wherein the replenishing solution comprises gold sulfite and water, the cyanide ion concentration is below 1 mg / L, and the molar ratio of sulfite ion concentration to gold concentration in the replenishing solution (SO3) 2- / Au) is above 2.1 and below 2.9.

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