Cyanide-based silver alloy electroplating solution

Abstract

The present invention provides a cyanide-based silver alloy electroplating solution characterized by containing 10 to 100 g / L of silver cyanide complex in terms of silver, 5 to 300 q / L of electroconductive salt, 0.1 to 10 g / L of germanium compound in terms of germanium, and 1 to 100 g / L of a coordinating polymer additive.

Description

Cyanide-based electrolytic silver alloy plating solution

[0001] The present invention relates to a cyanide-based electrolytic silver alloy plating solution, specifically to an electrolytic silver-germanium alloy plating solution that uses cyanide as a silver source and can produce a plating film with high hardness.

[0002] Silver has been widely used in jewelry since ancient times due to its white luster. Because silver is relatively abundant and inexpensive among precious metals, even today, it is silver-plated for decorative purposes, such as silver accessories and tableware. Furthermore, because silver has the highest electrical conductivity of all metals at room temperature, silver plating is also widely used on lead frames and substrates for electronic devices such as ICs and transistors. Furthermore, because silver has the highest reflectance of all metals for visible light, silver plating is often applied to lead frames and various substrates for light-emitting devices, such as LEDs. Silver plating is also used for bearing parts and other applications that take advantage of silver's antibacterial properties.

[0003] In recent years, industrial demand for silver plating has increased due to the need for lower electrical resistance in electrical and electronic components. However, silver is a relatively soft metal, and various efforts have been made to deposit harder coatings. For example, silver-antimony alloy plating, in which antimony is co-deposited with silver, is widely used. However, because antimony is highly toxic to the human body, regulations on it are becoming stricter every year, and the development of alternative technologies is required.

[0004] Patent Document 1 discloses a silver plating solution containing a curing agent and graphene oxide. In addition to antimony, other curing agents for silver plating include selenium, copper, tin, nickel, cobalt, tellurium, and bismuth. However, there is no mention of hardness when elements other than antimony are used. Patent Document 2 discloses an electrolytic silver plating solution for optical semiconductor devices that contains at least one of a selenium compound and a sulfur compound as an essential component, along with water-soluble compounds of Ti, Zr, V, Mo, W, Co, Pd, Au, Cu, Zn, Ga, Ge, In, Sn, Tl, Sb, Bi, As, Te, Br, and I. However, there is no discussion of the effects of these elements on the hardness of the plating film. Patent Document 3 discloses a technology for improving the heat resistance of palladium plating films by adding germanium to a palladium plating solution.

[0005] JP 2018-199839 A Patent No. 6230778 Patent No. 4598782

[0006] Germanium has been studied as an alternative to antimony in silver plating hardeners. High hardness can be expected by codepositing germanium with silver. Research into silver-germanium alloy plating solutions has been conducted for a long time, but there have been no examples of industrial success. This is because, with conventional technology, it is not easy to codeposit germanium with silver, and there is no electroplating technology that can consistently achieve a glossy appearance. Therefore, there is a need for a silver-germanium alloy plating technology that can sufficiently codeposit germanium and achieve a glossy appearance.

[0007] Therefore, an object of the present invention is to provide a silver-germanium alloy plating solution capable of forming a film having performance equal to or better than that of silver-antimony alloy plating.

[0008] As a result of extensive research, the inventors discovered that by adding a germanium compound and a coordination polymer additive to an electrolytic silver plating solution, several percent of germanium can be co-deposited into the silver film, resulting in a glossy, hard silver film.

[0009] [1] A cyanide-based electrolytic silver alloy plating solution comprising: a silver cyanide complex in an amount of 10 to 100 g / L, calculated as silver; an electrically conductive salt in an amount of 5 to 300 g / L; a germanium compound in an amount of 0.1 to 10 g / L, calculated as germanium; and a coordination polymer additive in an amount of 1 to 100 g / L.

[0010] [2] The cyanide-based electrolytic silver alloy plating solution according to [1], wherein the electrically conductive salt contains at least one selected from the group consisting of cyanide salts, phosphate salts, pyrophosphate salts, nitrate salts, citrate salts, tartrate salts, sulfate salts, boric acid and salts thereof.

[0011] [3] The cyan-based electrolytic silver alloy plating solution according to [1], wherein the germanium compound contains at least one selected from the group consisting of germanium dioxide, germanium halide, tetraalkoxygermanium, germanium sulfide, germanic acid, and its salts.

[0012] [4] The cyan-based electrolytic silver alloy plating solution according to [1], wherein the coordinating polymer additive is at least one selected from polyacrylic acid, polyethyleneimine, and copolymers containing these in their structure.

[0013] The cyanide-based electrolytic silver alloy plating solution of the present invention does not contain antimony and produces a silver-germanium alloy film with a glossy appearance and high hardness. This allows for the provision of electrical contact materials, which are in increasing demand due to the spread of electric vehicles, while also complying with increasingly stringent environmental regulations. Furthermore, it is economical because it allows for the thinning of silver plating thickness.

[0014] The electrolytic silver plating solution of the present invention contains a silver cyanide complex as a silver salt, an electrically conductive salt, a germanium compound, and a coordination polymer additive. Each component constituting the electrolytic silver plating solution of the present invention will be described below.

[0015] [Silver Cyanide Complex] In the cyanide-based electrolytic silver alloy plating solution of the present invention, any known silver cyanide complex can be used as the silver source without limitation. Examples of silver cyanide complexes include silver cyanide, silver potassium cyanide, and silver sodium cyanide.

[0016] The concentration of the silver cyanide complex is 10 to 100 g / L, preferably 20 to 70 g / L, in terms of silver ion concentration. If the silver ion concentration is less than 10 g / L, the deposition efficiency decreases and the desired silver film thickness may not be obtained. On the other hand, if the silver ion concentration exceeds 100 g / L, the loss of silver salt due to the plating solution being carried away by the object to be plated increases, which is not economical.

[0017] [Electrically Conductive Salt] The electrically conductive salt to be incorporated into the cyanide-based electrolytic silver alloy plating solution of the present invention is not particularly limited as long as it has electrical conductivity in aqueous solution. However, for industrially stable use and economical production of the plating solution, it is preferable to contain at least one selected from cyanide salts, phosphate salts, nitrate salts, citrate salts, tartrate salts, sulfate salts, boric acid and its salts. Soluble organic acid salts are also preferable. These may be used alone or in combination of two or more. Examples of cyanide salts include potassium cyanide and sodium cyanide. Examples of phosphate salts include potassium phosphate, sodium phosphate, and ammonium phosphate. Examples of pyrophosphate salts include potassium pyrophosphate, sodium pyrophosphate, and ammonium pyrophosphate. Examples of nitrate salts include potassium nitrate, sodium nitrate, and ammonium nitrate. Examples of citrate salts include potassium citrate, sodium citrate, and ammonium citrate. Examples of tartaric acid salts include potassium tartrate, sodium tartrate, and sodium potassium 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.

[0018] The concentration of the electrically conductive salt in the cyan-based electrolytic silver alloy plating solution of the present invention is 5 to 300 g / L, preferably 50 to 250 g / L, and more preferably 100 to 240 g / L. If the concentration of the electrically conductive salt is less than 5 g / L, the electrical resistance of the plating solution becomes too high, making it impossible to perform plating at an appropriate cathode current density.

[0019] [Germanium Compound] The germanium compound to be incorporated into the cyanide-based electrolytic silver alloy plating solution of the present invention is a compound containing germanium, and is particularly preferably germanium dioxide, germanium halide, tetraalkoxygermanium, germanium sulfide, germanic acid, or a salt thereof. Examples of germanate salts include sodium germanate and potassium germanate.

[0020] The concentration of the germanium compound in the cyanide-based electrolytic silver alloy plating solution of the present invention is 0.1 to 10 g / L, preferably 1 to 6 g / L, in terms of germanium concentration. If the amount of the germanium compound blended is outside the above range, a glossy silver film may not be obtained, or plating may not be possible at an appropriate cathode current density.

[0021] [Coordinating Polymer Additive] The coordinating polymer additive for the cyanide-based electrolytic silver alloy plating solution of the present invention is at least one selected from polyacrylic acid, polyethyleneimine, and copolymers containing these in their structure, and is preferably polyacrylic acid or polyethyleneimine. The molecular weight of the coordinating polymer additive is not limited, but the number average molecular weight is generally about 300 to 5,000,000.

[0022] The concentration of the coordinating polymer additive in the cyan-based electrolytic silver alloy plating solution of the present invention is 1 to 100 g / L, preferably 2 to 84 g / L. If the concentration of the coordinating polymer additive is less than 1 g / L, germanium may not be sufficiently co-deposited. If the concentration of the coordinating polymer additive exceeds 100 g / L, the viscosity of the plating solution may increase too much, making it impossible to plate at an appropriate cathode current density or increasing the amount of plating solution carried out.

[0023] [Other Components] In addition to the above components, the cyanide-based electrolytic silver alloy plating solution of the present invention may contain other components such as surfactants to reduce viscosity and prevent unevenness in the silver film, provided that the object of the present invention is not impaired. Examples of surfactants include anionic surfactants such as sodium polyoxyethylene alkyl ether sulfate and nonionic surfactants such as polyoxyethylene alkyl ether condensates.

[0024] The cyanide-based electrolytic silver alloy plating solution of the present invention may be free of selenium compounds and sulfur compounds (except germanium sulfide and the above-mentioned surfactants). That is, it may be free of selenium compounds such as potassium selenium cyanide, selenium cyanide, selenious acid, selenium oxide, and selenium oxide; or sulfur compounds such as carbon disulfide, thiourea, thiolactic acid, thiouracil, thiobarbituric acid, cysteine, cystine, thioacetic acid, and mercaptobenzothiazole. The concentrations of selenium compounds and sulfur compounds in the cyanide-based electrolytic silver alloy plating solution of the present invention are 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), in terms of selenium concentration and sulfur concentration.

[0025] The solvent used in the cyan-based electrolytic silver alloy plating solution of the present invention is water, and may contain an aqueous solvent (a solvent that dissolves in water at the blending concentration).

[0026] The cyan-based electrolytic silver alloy plating solution of the present invention can be produced by dissolving the above-mentioned components in a solvent. The order of dissolution is not important. The cyan-based electrolytic silver alloy plating solution of the present invention may be in a concentrated state (including a state without a solvent) during distribution or storage. Alternatively, some of the components may be distributed or stored undissolved and dissolved immediately before use.

[0027] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0028] The object to be plated is 0.1 dm ２ The copper plate was first degreased with an alkaline degreasing solution, then neutralized with dilute sulfuric acid, and then plated with approximately 1.7 μm of matte copper in a cyanide bath. This was followed by approximately 0.1 μm of silver plating in a cyanide strike bath.

[0029] Plating solutions for Examples 1 to 12 and Comparative Examples 1 to 5 were prepared with the compositions shown in Tables 1 and 2 (the remainder of each plating solution was water). The workpiece was immersed in 1 L of the prepared plating solution and electrolytic silver plating was performed under the conditions shown in Tables 1 and 2 until the silver film thickness reached 20 μm. The workpiece was then washed with clean pure water and dried.

[0030] The appearance and hardness of the silver coatings obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were measured. The appearance referred to here was evaluated by visually inspecting a glossy appearance with no plating unevenness as ○, and any other appearance as ×. The hardness referred to here is the micro-Vickers hardness obtained when a test force of 10 g is held for 10 seconds using a Mitutoyo microhardness tester MVK-H300, and is the average of three results obtained by measuring five times and excluding the minimum and maximum values.

[0031]

[0032]

[0033] The silver films obtained in Examples 1 to 12 all had a hardness of 180.0 or more. The color tone was silvery white, with no unevenness and a good appearance. The bath stability was also good.

[0034] The hardness of all the silver films obtained in Comparative Examples 1 to 7 was 130.0 or less. The color tone was basically brown and matte, with a partially semi-gloss appearance, and there was much unevenness, resulting in a poor appearance. For convenience of measurement, the hardness was measured in the semi-gloss area. The bath stability was good.

Claims

1. A cyanide-based electrolytic silver alloy plating solution comprising: 10 to 100 g / L of a silver cyanide complex, calculated as silver; 5 to 300 g / L of an electrically conductive salt; 0.1 to 10 g / L of a germanium compound, calculated as germanium; and 1 to 100 g / L of a coordination polymer additive.

2. The cyanide-based electrolytic silver alloy plating solution according to claim 1, wherein the electrically conductive salt contains at least one selected from the group consisting of cyanide salts, phosphate salts, pyrophosphate salts, nitrates, citrates, tartrates, sulfates, boric acid and salts thereof.

3. The cyan-based electrolytic silver alloy plating solution according to claim 1, wherein the germanium compound contains at least one selected from the group consisting of germanium dioxide, germanium halides, tetraalkoxygermanium, germanium sulfide, germanic acid and its salts.

4. The cyan-based electrolytic silver alloy plating solution according to claim 1, wherein the coordinating polymer additive is at least one selected from the group consisting of polyacrylic acid, polyethyleneimine, and copolymers containing these in their structure.