Cyanide electrolytic silver alloy plating solution

Abstract

According to the present invention, a cyanide-based electrolytic silver alloy plating solution is provided, characterized in that it contains: a silver cyanide complex at a concentration of 10 to 100 g / L (based on silver), a conductive salt at a concentration of 5 to 300 g / L, a germanium compound at a concentration of 0.1 to 10 g / L (based on germanium), and a coordination polymer additive at a concentration of 1 to 100 g / L.

Description

Technical Field

[0001] This invention relates to cyanide-based electrolytic silver alloy plating solutions. Specifically, it relates to electrolytic silver-germanium alloy plating solutions that use cyanide as the silver source to obtain a high-hardness plating film. Background Technology

[0002] Silver, with its white luster, has been used in jewelry since ancient times. Because silver is relatively abundant and inexpensive among precious metals, it is also used in modern decorative items and tableware. Furthermore, since silver has the highest electrical conductivity of all metals at room temperature, silver plating is widely used for lead frames and substrates in electronic devices such as ICs and transistors. Moreover, because silver has the highest visible light reflectance of all metals, it is frequently used for lead frames and various substrates in light-emitting devices such as LEDs. In addition, silver plating is used in bearing components and applications utilizing silver's antibacterial properties.

[0003] In recent years, the demand for lower resistance in electrical and electronic components has increased the industrial demand for silver plating. However, silver is a relatively soft metal, and various combinations have been developed to deposit a harder film. For example, silver-antimony alloy plating with antimony co-deposition is widely used. However, due to the high toxicity of antimony to humans, there is a tendency for increasingly stringent restrictions to be imposed annually, necessitating the development of alternative technologies.

[0004] Patent Document 1 discloses a silver plating solution containing a hardener and graphene oxide. Besides antimony, other hardeners for silver plating include selenium, copper, tin, nickel, cobalt, tellurium, and bismuth. However, it does not describe the hardness when using materials other than antimony.

[0005] Patent Document 2 discloses an electrolytic silver plating solution for an optical semiconductor device, which uses at least one of a selenium compound and a sulfur compound as essential components, and combines it with a water-soluble compound of Ti, Zr, V, Mo, W, Co, Pd, Au, Cu, Zn, Ga, Ge, In, Sn, Tl, Sb, Bi, As, Te, Br, or I. However, no research has been conducted on the effect of these elements on the hardness of the plating film.

[0006] Patent document 3 discloses a technique for improving the heat resistance of palladium-plated films by adding germanium to the palladium plating solution.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2018-199839

[0010] Patent Document 2: Japanese Patent No. 6230778

[0011] Patent Document 3: Japanese Patent No. 4598782 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] Germanium has been studied as a substitute for antimony in silver plating. High hardness can be expected by co-deposition of germanium and silver. Research on silver-germanium alloy plating solutions has a long history, but there are no successful industrial examples. This is because, in previous techniques, co-deposition of germanium and silver was not easy, and there was no electroplating technique that consistently yielded a bright appearance. Therefore, a silver-germanium alloy plating technique that fully co-deposits germanium and achieves a bright appearance is needed.

[0014] Therefore, the object of the present invention is to provide a silver-germanium alloy plating solution capable of forming a film with properties equivalent to or higher than those of silver-antimony alloy plating.

[0015] Methods for solving problems

[0016] The inventors conducted in-depth research and discovered that by adding germanium compounds and coordination polymer additives to the silver plating solution, a germanium co-deposition of approximately several percentage points (a few percent) is achieved in the silver film, resulting in a bright-looking silver film with high hardness, thus completing this invention. The invention that solves the above-mentioned problems is described below.

[0017] [1] A cyanide-based electrolytic silver alloy plating solution, characterized in that it contains: 10 to 100 g / L of silver cyanide complex, 5 to 300 g / L of conductive salt, 0.1 to 10 g / L of germanium compound, and 1 to 100 g / L of coordinating polymer additive.

[0018] [2] According to the cyanide-based electrolytic silver alloy plating solution of [1], wherein the conductive salt contains at least one selected from cyanide salts, phosphates, pyrophosphates, nitrates, citrates, tartrates, sulfates, boric acids and their salts.

[0019] [3] According to the cyanide electrolytic silver alloy plating solution described in [1], wherein the germanium compound contains at least one selected from germanium dioxide, germanium halide, germanium tetraalkoxy, germanium sulfide, germanic acid and its salts.

[0020] [4] According to the cyanide electrolytic silver alloy plating solution of [1], wherein the coordination polymer additive is selected from at least one of polyacrylic acid, polyethyleneimine, and copolymers thereof in the structure.

[0021] The effects of the invention

[0022] The cyanide-based electrolytic silver alloy plating solution of this invention is antimony-free, resulting in a silver-germanium alloy film with a bright appearance and high hardness. This allows for the provision of electrical contact materials that meet increasing demands due to the growing popularity of electric vehicles, while simultaneously addressing increasingly stringent environmental restrictions. Furthermore, the thinner silver plating film thickness also makes it economical. Detailed Implementation

[0023] The electroplating silver solution of the present invention contains: a silver cyanide complex as a silver salt, a conductive salt, a germanium compound, and a coordination polymer additive. The components constituting the electroplating silver solution of the present invention will be described below.

[0024] [Silver cyanide complex]

[0025] In the cyanide-based electrolytic silver alloy plating solution of the present invention, known silver cyanide complexes can be used as the silver source without limitation. Examples of silver cyanide complexes include silver cyanide, potassium silver cyanide, and sodium silver cyanide.

[0026] Regarding the concentration of the silver cyanide complex, expressed as silver ion concentration, it is 10–100 g / L, preferably 20–70 g / L. When the silver ion concentration is less than 10 g / L, the precipitation efficiency decreases, and sometimes the desired silver film thickness cannot be obtained. On the other hand, when the silver ion concentration exceeds 100 g / L, the loss of silver salts due to carryover from the plating solution caused by the substrate increases, which is uneconomical.

[0027] [Conductive Salt]

[0028] The conductive salt incorporated in the cyanide-based electrolytic silver alloy plating solution of the present invention is not particularly limited in type, as long as it is conductive in aqueous solution. For stable industrial use and economical production of the plating solution, it is preferable to contain at least one salt selected from cyanide salts, phosphates, nitrates, citrates, tartrates, sulfates, boric acid, and their salts. Furthermore, soluble organic acid salts are also preferred. These can be used individually or in combination. Examples of cyanide salts include potassium cyanide and sodium cyanide. Examples of phosphates include potassium phosphate, sodium phosphate, and ammonium phosphate. Examples of pyrophosphates include potassium pyrophosphate, sodium pyrophosphate, and ammonium pyrophosphate. Examples of nitrates include potassium nitrate, sodium nitrate, and ammonium nitrate. Examples of citrates include potassium citrate, sodium citrate, and ammonium citrate. Examples of tartaric acid include potassium tartrate, sodium tartrate, and potassium sodium tartrate. Examples of sulfates include potassium sulfate, sodium sulfate, and ammonium sulfate. Examples of boric acid and its salts include boric acid, sodium borate, and potassium borate.

[0029] The concentration of conductive salt in the cyanide-based electrolytic silver alloy plating bath of the present invention is 5–300 g / L, preferably 50–250 g / L, and more preferably 100–240 g / L. When the concentration of conductive salt is less than 5 g / L, the resistance of the plating bath becomes too high, making it impossible to perform plating with an appropriate cathode current density.

[0030] [Germanium compounds]

[0031] The germanium compound incorporated in the cyanide-based electrolytic silver alloy plating solution of the present invention is a germanium-containing compound, and germanium dioxide, germanium halide, germanium tetraalkoxy, germanium sulfide, germanic acid, and their salts are particularly preferred. Examples of germanates include sodium germanate and potassium germanate.

[0032] Regarding the concentration of the germanium compound in the cyanide-based electrolytic silver alloy plating solution of the present invention, expressed as germanium concentration, it is 0.1 to 10 g / L, preferably 1 to 6 g / L. If the amount of germanium compound deviates from the above concentration, a bright silver film may not be obtained, or plating with an appropriate cathode current density may not be possible.

[0033] [Coordination polymer additives]

[0034] The coordination polymer additive in the cyanide-based electrolytic silver alloy plating solution of the present invention is selected from at least one of polyacrylic acid, polyethyleneimine, and copolymers containing them in their structure, preferably polyacrylic acid or polyethyleneimine. There is no limitation on the molecular weight of the coordination polymer additive; generally, the number average molecular weight is around 300 to 5,000,000.

[0035] The concentration of the coordination polymer additive in the cyanide-based electrolytic silver alloy plating bath of the present invention is 1 to 100 g / L, preferably 2 to 84 g / L. When the concentration of the coordination polymer additive is less than 1 g / L, germanium sometimes cannot be sufficiently co-deposited. When the concentration of the coordination polymer additive exceeds 100 g / L, sometimes plating with an appropriate cathode current density cannot be performed due to an excessive increase in the viscosity of the plating bath, or the carryover from the plating bath increases.

[0036] [Other ingredients]

[0037] In the cyanide-based electrolytic silver alloy plating solution of the present invention, in addition to the above-mentioned components, surfactants and other components may be included to reduce viscosity and suppress unevenness of the silver film, without compromising the purpose of the present invention. Examples of surfactants include anionic surfactants such as sodium polyoxyethylene alkyl ether sulfate and nonionic surfactants such as polyoxyethylene alkyl ether condensates.

[0038] The cyanide-based electrolytic silver alloy plating solution of the present invention may not contain either selenium compounds or sulfur compounds (except for germanium sulfide and the surfactants mentioned above). That is, it may not contain any of the following: selenium compounds such as potassium selenium cyanide, selenium cyanide, selenite, selenic acid oxide, and selenium oxide; or sulfur compounds such as carbon disulfide, thiourea, thiolactic acid, thiouracil, thiobarbituric acid, cysteine, cystine, thioacetic acid, and mercaptobenzothiazole.

[0039] Regarding the concentration of selenium compounds and sulfur compounds in the cyanide-based electrolytic silver alloy plating solution of the present invention, expressed as selenium concentration and sulfur concentration, it is preferably less than 1 g / L, more preferably less than 0.1 g / L, and even more preferably substantially free (less than 0.01 g / L).

[0040] The solvent used in the cyanide-based electrolytic silver alloy plating solution of the present invention is water, and may contain aqueous solvents (solvents dissolved in water at a suitable concentration).

[0041] The cyanide-based electrolytic silver alloy plating solution of the present invention can be manufactured by dissolving the above-mentioned components in a solvent. There is no limitation on the order of dissolution. The cyanide-based electrolytic silver alloy plating solution of the present invention can be in a concentrated state (including a solvent-free state) during circulation and storage. Alternatively, it can be configured to be circulated or stored without dissolving a portion of the components, and then dissolved just before use.

[0042] Example

[0043] The present invention will now be specifically described through examples. However, the present invention is not limited to these examples.

[0044] As the object to be plated, use 0.1dm 2 The copper plate was first degreased with an alkaline degreasing solution, then neutralized with dilute sulfuric acid, and then plated with a matte copper plating of approximately 1.7 μm using a cyanide bath. Then, a silver plating of approximately 0.1 μm was performed using a cyanide strike bath.

[0045] The plating solutions for Examples 1-12 and Comparative Examples 1-5 were prepared with the compositions described in Tables 1 and 2 (the balance of any plating solution was water). The objects to be plated were immersed in 1 L of the prepared plating solution and electroplated with silver under the conditions described in Tables 1 and 2 until the silver film thickness reached 20 μm. After washing with clean pure water, the objects were dried.

[0046] For the silver films of Examples 1-12 and Comparative Examples 1-5 obtained as described above, their appearance and hardness were measured. For appearance, a bright appearance without uneven plating was rated as ○, and any other appearance was rated as ×. Hardness was measured using a Mitsutoyo MVK-H300 micro hardness tester at a test force of 10g for 10 seconds. Five measurements were performed, and the results of the three measurements after removing the minimum and maximum values ​​were averaged.

[0047] [Table 1]

[0048]

[0049] [Table 2]

[0050]

[0051] The silver films obtained in Examples 1-12 all exhibit a hardness of 180.0 or higher. They are silvery-white in color, without any unevenness, and have a good appearance. They also demonstrate good bath stability.

[0052] Regarding the silver films obtained in Comparative Examples 1-7, the hardness was below 130.0 for all of them. The hue was generally matte brown, with some areas exhibiting a semi-gloss appearance; unevenness was prevalent, resulting in a poor appearance. For ease of measurement, hardness was determined in the semi-gloss areas. Bath stability was good.

Claims

1. A cyanide-based electrolytic silver-germanium alloy plating solution, characterized in that, It contains: a silver cyanide complex at a concentration of 10 to 100 g / L based on silver, a conductive salt at a concentration of 5 to 300 g / L, a germanium compound at a concentration of 0.1 to 10 g / L based on germanium, and a coordination polymer additive at a concentration of 1 to 100 g / L, wherein the coordination polymer additive comprises at least one selected from polyacrylic acid, polyethyleneimine, and copolymers thereof that contain them in their structure.

2. The cyanide-based electrolytic silver-germanium alloy plating solution according to claim 1, wherein, The conductive salt contains at least one selected from cyanide salts, phosphates, pyrophosphates, nitrates, citrates, tartrates, sulfates, boric acids, and their salts.

3. The cyanide-based electrolytic silver-germanium alloy plating solution according to claim 1, wherein, The germanium compound contains at least one selected from germanium dioxide, germanium halide, germanium tetraalkoxy, germanium sulfide, germanic acid and its salts.

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