Cyanide-free electrolytic pure silver plating solution

Abstract

To provide a non-cyanide electrolytic pure silver plating film with high hardness having excellent abrasion resistance in a high temperature environment, not containing a highly toxic cyanide, and to provide a non-cyanide electrolytic pure silver plating solution for forming the film.SOLUTION: A film is formed on a material to be plated using a non-cyanide electrolytic pure silver plating solution containing: a silver-ion supply source; at least one of an inorganic acid and an inorganic acid salt; and a five-membered ring compound having a thiol structure or a thiocarbonyl structure. The non-cyanide electrolytic pure silver plating film thus obtained retains high hardness and does not deteriorate in abrasion resistance even when subjected to a high temperature environment because the hardness is held to be HV120 or more even after a heat treatment has been performed at 150°C for 1000 hours.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pure silver plating film prepared using a non-cyanide electrolytic plating solution that does not contain highly toxic cyanide compounds, and in particular to a non-cyanide electrolytic pure silver plating film with excellent abrasion resistance and high hardness, and to a non-cyanide electrolytic pure silver plating solution used for forming the same. [Background technology]

[0002] Because silver plating has high electrical conductivity, it is widely used for contacts and terminal parts of electronic devices such as connectors, switches, relays, etc. Silver plating is also used for electrical wiring connectors in automobiles, and in recent years, with the spread of hybrid cars and electric cars, it is also used for the coating of connector terminals of high voltage cables.

[0003] In connectors for high-power motors, such as those used in hybrid and electric cars, large currents flow, which generates a lot of heat in the connector. For parts that are repeatedly inserted and removed, such as contacts and terminal parts, the silver plating film must maintain its hardness and wear resistance even when exposed to high-temperature environments for long periods of time.

[0004] Generally, when a silver plating film is placed in a high-temperature environment for a long time, the silver crystal grains grow, causing the hardness to decrease and the wear resistance to deteriorate. Therefore, as a method for increasing the hardness of a silver plating film and improving its wear resistance, Patent Document 1 proposes a high-hardness silver plating film in which a second plating layer containing antimony is formed by cyan-based electrolytic silver plating on a first silver plating layer with controlled crystal orientation, and Patent Document 2 proposes a high-hardness plating film containing a selenium compound formed by cyan-based electrolytic silver plating.

[0005] The plating films proposed in Patent Documents 1 and 2 are all formed using a cyanide-based electrolytic silver plating solution. However, in recent years, cyanide-based silver plating solutions contain highly toxic cyanide compounds, which have raised concerns about operational safety and environmental impact. In addition, unlike pure silver plating films, silver plating films containing antimony have a problem in that an oxide film is formed and contact resistance increases when exposed to a high-temperature environment for a long period of time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-189680 A [Patent Document 2] JP 2016-204719 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-cyanide electrolytic pure silver plating film that does not contain highly toxic cyanide compounds and has excellent abrasion resistance in high-temperature environments and high hardness, and a non-cyanide electrolytic pure silver plating solution for forming the same. [Means for solving the problem]

[0008] (1) The non-cyanide electrolytic pure silver plating film of the present invention has a Vickers hardness (HV) of 120 or more before and after heat treatment at 150° C. for 1,000 hours.

[0009] (2) In (1), the contact resistance is 2 mΩ or less before and after heat treatment at 150°C for 1,000 hours.

[0010] (3) The non-cyanide electrolytic pure silver plating solution of the present invention is a non-cyanide electrolytic pure silver plating solution for forming a non-cyanide electrolytic pure silver plating film as described in (1) or (2), which contains a silver ion source, at least one of an inorganic acid or an inorganic acid salt, and a five-membered ring compound represented by the general formula (1): [ka] (In the general formula (1), M is any one of hydrogen (H), sodium (Na), and potassium (K), and A1 to A3 are each any one of carbon (C), nitrogen (N), oxygen (O), and sulfur (S). However, the number of nitrogens (N) constituting the five-membered ring is three or less. In addition, C bonded to a thiol group (-SM) has a double bond structure with N constituting the five-membered ring, N and A3 are single bonds, and the bonds between A1 and A2 and between A2 and A3 are single bonds or double bonds.) [ka] A non-cyanide electrolytic pure silver plating solution which is a five-membered ring compound having a thiocarbonyl structure represented by the following general formula (2): (In the general formula (2), A1 to A3 are either carbon (C), nitrogen (N), oxygen (O) or sulfur (S). However, the number of nitrogens (N) constituting the five-membered ring is 3 or less. Furthermore, the C of the thiocarbonyl group has a structure in which it is single-bonded to the N constituting the five-membered ring, and the bonds between N and A3, between A1 and A2, and between A2 and A3 are single bonds or double bonds.)

[0011] (4) In (3), the five-membered ring compound having a thiol structure includes at least one selected from 2-mercaptobenzothiazole sodium, 2-mercaptothiazole, 2-mercapto-1-methylimidazole, 4-methyl-2-mercaptobenzothiazole, 3-mercapto-4-methyl-1,2,4-triazole, 2-mercaptobenzoxazole, 6-amino-8-mercaptopurine, and 5,7-dimethyl[1,2,4]triazolo[1,5-A]pyrimidin-2-yl hydrosulfide.

[0012] (5) In (3), the five-membered ring compound having a thiocarbonyl structure includes at least one selected from 2-imidazolinethione, 2-mercapto-2-thiazoline, 1,3-dimethyl-2-imidazolidinethione, thiazole-2-thiol, 3-amino-5-mercapto-1,2,4-triazole, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, 3-aminorhodanine, 2-oxazolidinethione, and 3-(2-hydroxyethyl)oxazolidine-2-thione.

[0013] (6) In any one of (3) to (5), the content of the five-membered ring compound is 0.05 g / L or more and 2 g / L or less.

[0014] (7) In any one of (3) to (6), the silver ion source contains at least silver sulfite or silver oxide, and the content of silver ions is 0.5 g / L or more and 50 g / L or less in terms of metallic silver concentration.

[0015] (8) In any one of (3) to (7), the inorganic acid or inorganic acid salt contains at least one selected from sulfuric acid, sulfurous acid, phosphoric acid, thiosulfuric acid, and sulfamic acid, and a salt thereof, and the content of the inorganic acid or inorganic acid salt is 1 g / L or more and 500 g / L or less.

[0016] (9) In any one of (3) to (8), the composition contains at least one of an organic acid containing a carbonyl group and an organic acid salt containing a carbonyl group.

[0017] (10) In any one of (3) to (9), the organic acid containing a carbonyl group is glutamic acid, aspartic acid, pyruvic acid 、 The acid solution contains at least one selected from citric acid, tartaric acid, succinic acid, fumaric acid, L-malic acid, or a salt thereof, and the content is 1 g / L or more and 200 g / L or less.

[0018] (11) In any one of (3) to (10), the pH is 4 to 7. Effect of the Invention

[0019] According to the present invention, it is possible to provide a non-cyanide electrolytic pure silver plating film that does not contain highly toxic cyanide compounds and has excellent abrasion resistance in high-temperature environments and high hardness, and a non-cyanide electrolytic pure silver plating solution for forming the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present inventors have found that by adding a heterocyclic compound having a specific structure to a non-cyanide electrolytic pure silver plating solution, a silver plating film having high hardness without adding any metal element other than silver and which maintains its high hardness even when exposed to a high temperature environment for a long period of time can be formed, and as a result of further investigation, have completed the present invention. Hereinafter, an example of an embodiment of the present invention will be described in detail, but the present invention is not limited thereto. In the present invention, the pure silver plating film refers to a plating film having a silver purity of 99.9 mass% or more, which is formed using a plating solution that does not contain any source of metal ions such as antimony, selenium, or tellurium other than a source of silver ions.

[0021] The non-cyanide electrolytic pure silver plating solution of the present invention contains a silver ion source, at least one of an inorganic acid or an inorganic acid salt, and a five-membered ring compound as follows: The five-membered ring compound contained in the non-cyanide electrolytic pure silver plating solution of the present invention is a five-membered ring compound having a thiol structure in which N and C are represented by a double bond in an NCS sequence and a structure represented by the following general formula (1) (hereinafter sometimes referred to as a "first five-membered ring compound"), or a five-membered ring compound having a thiocarbonyl structure in which C and S are represented by a double bond and a structure represented by the following general formula (2) (hereinafter sometimes referred to as a "second five-membered ring compound").

[0022] [ka]

[0023] In the general formula (1), M is any one of hydrogen (H), sodium (Na), and potassium (K), and A1 to A3 are any one of carbon (C), nitrogen (N), oxygen (O), and sulfur (S). However, the number of nitrogens (N) constituting the five-membered ring is three or less. In addition, C bonded to the thiol group (-SM) has a double bond structure with N constituting the five-membered ring, N and A3 are single bonds, and the bonds between A1 and A2 and between A2 and A3 are single bonds or double bonds.

[0024] [ka]

[0025] In the general formula (2), A1 to A3 are either carbon (C), nitrogen (N), oxygen (O), or sulfur (S). However, the number of nitrogens (N) constituting the five-membered ring is three or less. In addition, C of the thiocarbonyl group has a structure in which it is single-bonded to N constituting the five-membered ring, and the bonds between N and A3, between A1 and A2, and between A2 and A3 are single bonds or double bonds.

[0026] The first five-membered ring compound and the second five-membered ring compound may be polycyclic compounds as long as they have a structure represented by general formula (1) or general formula (2).

[0027] The first five-membered ring compound may include sodium 2-mercaptobenzothiazole, 2-mercaptothiazole, 2-mercapto-1-methylimidazole, 4-methyl-2-mercaptobenzothiazole, 3-mercapto-4-methyl-1,2,4-triazole, 2-mercaptobenzoxazole, 6-amino-8-mercaptopurine, and 5,7-dimethyl[1,2,4]triazolo[1,5-A]pyrimidin-2-yl hydrosulfide. The use of these compounds is not limited to one type, and two or more types may be used in combination.

[0028] The second five-membered ring compound may include 2-imidazolinethione, 2-mercapto-2-thiazoline, 1,3-dimethyl-2-imidazolidinethione, thiazole-2-thiol, 3-amino-5-mercapto-1,2,4-triazole, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, 3-aminorhodanine, 2-oxazolidinethione, and 3-(2-hydroxyethyl)oxazolidine-2-thione. The use of these compounds is not limited to one type, and two or more types may be used in combination.

[0029] The content of the first or second five-membered ring compound in the non-cyanide electrolytic pure silver plating solution is preferably 0.05 g / L or more and 2 g / L or less. If the concentration is lower than 0.05 g / L, the initial film hardness will be low, and if it exceeds 2 g / L, the plating deposit film may be burned or clouded, or the current efficiency may be reduced.

[0030] The silver ion source is not particularly limited as long as it does not contain a cyanide compound, but examples include silver sulfite and silver oxide. The content in the non-cyanide electrolytic pure silver plating solution is preferably 0.5 g / L or more and 50 g / L or less in terms of metallic silver concentration. If it is 0.5 g / L or less, silver deposition becomes difficult, and if it is 50 g / L or more, the silver compound may not be completely dissolved, which is not preferable.

[0031] Examples of inorganic acids or inorganic acid salts contained in the non-cyanide electrolytic pure silver plating solution include sulfuric acid, sulfurous acid, phosphoric acid, thiosulfuric acid, and sulfamic acid, or their salts. The content of inorganic acids or inorganic acid salts is preferably 1 g / L or more and 500 g / L or less. If the concentration is lower than 1 g / L, the conductivity of the plating solution cannot be ensured, and if the concentration is higher than 500 g / L, there is a risk that all the plating solution components will not be dissolved.

[0032] The non-cyanide electrolytic pure silver plating solution contains at least one of an organic acid containing a carbonyl group or an organic acid salt containing a carbonyl group. Specific examples of such organic acids or organic acid salts include glutamic acid, aspartic acid, pyruvic acid, and the like. 、Examples of the organic acid or salt thereof include citric acid, tartaric acid, succinic acid, fumaric acid, and L-malic acid. The content of the organic acid or salt thereof is preferably 1 g / L or more and 200 g / L or less, and more preferably 10 g / L or more and 100 g / L or less.

[0033] Non-cyanide electrolytic pure silver plating solutions have a pH of 4 to 7. If the pH is less than 4 or more than 7, the solution stability decreases and precipitation may occur. A chelating agent may be added to non-cyanide electrolytic pure silver plating solutions as a measure against impurity metal ions in the plating solution. Examples of chelating agents include ethylenediaminetetraacetic acid (EDTA), trisodium nitrilotriacetate (NTA), diethylenetriaminepentamic acid (DTPA), and cyclohexanediaminetetraacetic acid (CyDTA). The content of the chelating agent is preferably 0.5g / L to 50g / L.

[0034] In addition, other components may be added to the non-cyanide electrolytic pure silver plating solution of the present invention as necessary within the range that does not impair the object of the present invention. For example, surfactants, leveling agents, antioxidants, etc. may be added.

[0035] The non-cyanide electrolytic pure silver plating film of the present invention, which maintains high hardness and excellent wear resistance even when exposed to a high-temperature environment, can be formed by electrolytic plating using the non-cyanide electrolytic pure silver plating solution as described above. More specifically, the Vickers hardness before heat treatment is HV120 or more, and remains HV120 or more even after heat treatment at 150°C for 1000 hours. In addition, there is no need to add metal elements other than silver, such as antimony, to increase the hardness of the silver plating film. For contacts and terminal parts such as connectors, switches, and relays of electronic devices, the contact resistance of the plating film is preferably 2 mΩ or less. In the present invention, an oxide film of metal elements other than silver, such as antimony, is not formed on the film surface to increase the contact resistance, so the initial contact resistance is 2 mΩ or less, and the contact resistance is maintained at 2 mΩ or less even after heat treatment at 150°C for 1000 hours. EXAMPLES

[0036] As examples of the present invention, a silver plating film was formed on a plated material using the non-cyanide electrolytic pure silver plating solutions of Examples 1 to 5, and the hardness and contact resistance were measured before and after heat treatment.

[0037] [Example 1] The substrate for the silver plating was prepared by plating pure copper with 1 μm of matte nickel sulfamate (Ni sulfamate = 450 g / L, solution temperature: 55°C, current density: 2 ASD, solution volume: 2 L) and 0.01 μm of silver strike plating (Ag = 2 g / L, solution temperature: 30°C, current density: 1 ASD, solution volume: 2 L).

[0038] The non-cyanide electrolytic pure silver plating solution of Example 1 was prepared using silver sulfite as the silver ion source, sodium sulfite and sodium thiosulfate as inorganic acid salts, and 2-mercaptobenzothiazole sodium (first five-membered ring compound) as the five-membered ring compound, with sodium citrate further added to obtain the following composition. Silver sulfite 10g / L (as metallic silver concentration) Sodium sulfite 30g / L Sodium thiosulfate 100g / L Sodium citrate 50g / L Sodium 2-mercaptobenzothiazole 0.2g / L

[0039] A pure silver plate was placed as the anode and the material to be plated as the cathode in the non-cyanide electrolytic pure silver plating solution (liquid volume: 2 L) of Example 1. The plating solution was kept at pH 6 and the plating solution temperature at 30°C, and the plating solution was stirred with a stirrer at a current density of 0.5 A / dm 2 The plating process was carried out under the above conditions, forming a non-cyanide electrolytic pure silver plating film having a thickness of 10 μm.

[0040] [Example 2] The non-cyanide electrolytic pure silver plating solution of Example 2 was prepared using 2-imidazolinethione (a second five-membered ring compound) as the five-membered ring compound, so as to have the following composition. Silver sulfite 30g / L (as metallic silver concentration) Sodium sulfite 75g / L Sodium thiosulfate 200g / L Citric acid 60g / L 2-Imidazolinethione 0.4g / L

[0041] A pure silver plate was placed as the anode and the same plated material as in Example 1 as the cathode in the non-cyanide electrolytic pure silver plating solution (liquid volume 2 L) of Example 2. The plating solution was kept at pH 6 and the plating solution temperature 30°C, and the plating solution was stirred with a stirrer at a current density of 2.0 A / dm 2 The plating process was carried out under the above conditions, forming a non-cyanide electrolytic pure silver plating film having a thickness of 10 μm.

[0042] [Example 3] The non-cyanide electrolytic pure silver plating solution of Example 3 was prepared using 2-mercapto-2-thiazoline (a second five-membered ring compound) as the five-membered ring compound, so as to have the following composition. Silver sulfite 10g / L (as metallic silver concentration) Potassium sulfite 20g / L Sodium thiosulfate 100g / L Fumaric acid 10g / L 2-Mercapto-2-thiazoline 0.2g / L

[0043] A pure silver plate was placed as the anode and the same plated material as in Example 1 as the cathode in the non-cyanide electrolytic pure silver plating solution (liquid volume 2 L) of Example 3. The plating solution was kept at pH 6 and the plating solution temperature 30°C, and the plating solution was stirred with a stirrer at a current density of 0.5 A / dm 2 The plating process was carried out under the above conditions, forming a non-cyanide electrolytic pure silver plating film having a thickness of 10 μm.

[0044] [Example 4] The non-cyanide electrolytic pure silver plating solution of Example 4 was prepared using 2-mercaptothiazole (first five-membered ring compound) as the five-membered ring compound, so as to have the following composition. Silver sulfite 20g / L (as metallic silver concentration) Sodium sulfite 60g / L Sodium thiosulfate 150g / L Glutamic acid 40g / L 2-Mercaptothiazole 0.2g / L

[0045] In the non-cyanide electrolytic pure silver plating solution (liquid volume 2 L) of Example 4, a pure silver plate was placed as the anode and the same plated material as in Example 1 was placed as the cathode. The plating solution was kept at pH 6 and the plating solution temperature at 30°C, and the plating solution was stirred with a stirrer at a current density of 1.0 A / dm 2 The plating process was carried out under the above conditions, forming a non-cyanide electrolytic pure silver plating film having a thickness of 10 μm.

[0046] [Example 5] The non-cyanide electrolytic pure silver plating solution of Example 5 was prepared using 2-mercapto-1-methylimidazole (first five-membered ring compound) as the five-membered ring compound, so as to have the following composition. Silver ion source: Silver sulfite 10g / L (as metallic silver concentration) Sodium sulfite 30g / L Sodium thiosulfate 100g / L Aspartic acid 20g / L 2-Mercapto-1-methylimidazole 0.1g / L

[0047] A pure silver plate was placed as the anode and the same plated material as in Example 1 as the cathode in the non-cyanide electrolytic pure silver plating solution (liquid volume 2 L) of Example 5. The plating solution was kept at pH 6 and the plating solution temperature 30°C, and the plating solution was stirred with a stirrer at a current density of 0.5 A / dm 2 The plating process was carried out under the above conditions, forming a non-cyanide electrolytic pure silver plating film having a thickness of 10 μm.

[0048] For comparison, the plating solutions of Comparative Examples 1 to 6 were prepared, and a silver plating film having a thickness of 10 μm was formed on the surface of a material to be plated. [Comparative Example 1] The non-cyanide electrolytic pure silver plating solution of Comparative Example 1 was prepared to have the following composition. Silver sulfite 10g / L (as metallic silver concentration) Sodium sulfite 30g / L Sodium thiosulfate 100g / L

[0049] [Comparative Example 2] The non-cyanide electrolytic pure silver plating solution of Comparative Example 2 was prepared to have the following composition. Silver sulfite 10g / L (as metallic silver concentration) Sodium sulfite 30g / L Sodium thiosulfate 100g / L Trimethylthiourea 0.1g / L

[0050] [Comparative Example 3] The non-cyanide electrolytic pure silver plating solution of Comparative Example 3 was prepared to have the following composition. Silver sulfite 10g / L (as metallic silver concentration) Sodium sulfite 30g / L Sodium thiosulfate 100g / L 2-Mercaptopyridine 0.1g / L

[0051] [Comparative Example 4] The cyanide-based electrolytic silver plating solution of Comparative Example 4 was prepared to have the following composition. Silver cyanide 50g / L (as metallic silver concentration) Potassium cyanide 160g / L Potassium carbonate 20g / L Sodium 2-mercaptobenzothiazole 0.2g / L

[0052] [Comparative Example 5] The cyanide-based electrolytic silver plating solution of Comparative Example 5 was prepared to have the following composition. Silver cyanide 50g / L (as metallic silver concentration) Potassium cyanide 160g / L Potassium carbonate 20g / L Potassium antimony tartrate 4.0g / L Potassium selenocyanate 0.02g / L

[0053] [Comparative Example 6] The cyanide-based electrolytic silver plating solution of Comparative Example 6 was prepared to have the following composition. Silver cyanide 50g / L (as metallic silver concentration) Potassium cyanide 160g / L Potassium carbonate 20g / L Potassium selenocyanate 0.02g / L

[0054] In the non-cyanide electrolytic pure silver plating solutions (volume 2 L) of Comparative Examples 1 to 3, a pure silver plate was placed as the anode and the same plated material as in Example 1 was placed as the cathode. The plating solution was kept at pH 6 and the plating solution temperature at 30°C, and the plating solution was stirred with a stirrer while applying a current density of 0.5 A / dm 2 The plating process was carried out under the above conditions, and a non-cyanide electrolytic pure silver plating film having a thickness of 10 μm was formed on each sample.

[0055] In the cyanide-based electrolytic silver plating solution (volume 2 L) of Comparative Example 4, a pure silver plate was placed as the anode and the same plated material as in Example 1 was placed as the cathode. The plating solution was kept at pH 12 and temperature 30°C, and the plating solution was stirred with a stirrer while a current density of 1.0 A / dm 2 A plating treatment was carried out under the above conditions to form a cyanide-based electrolytic silver plating film having a thickness of 10 μm.

[0056] The cyanide-based electrolytic silver plating solutions of Comparative Example 5, which contained antimony and selenium in addition to silver, and Comparative Example 6, which contained selenium in addition to silver, were plated under the same plating conditions as Comparative Example 4, except that the plating solution temperatures were kept at 15° C. and 20° C., respectively, to form cyanide-based electrolytic silver plating films having a thickness of 10 μm.

[0057] The obtained plating films of Examples 1 to 5 and Comparative Examples 1 to 6 were subjected to a heat treatment at 150°C for 1000 hours in an air atmosphere, and the Vickers hardness (HV) and contact resistance were evaluated before and after the heat treatment. In addition, the appearance of the plating film was visually observed to check whether the appearance of the film had changed after the heat treatment.

[0058] The Vickers hardness was measured using a micro Vickers hardness tester (HMV-2) manufactured by Shimadzu Corporation, with a measurement load of 0.098 N and a holding time of 5 seconds. The contact resistance was measured using a four-terminal contact resistance tester (CRS-113-Au) manufactured by Yamazaki Seiki Kenkyusho Co., Ltd., with an open terminal voltage of 20 mV or less, an applied current of 10 mA, and a measurement load of 0.245 N. The plating conditions and evaluation results of the examples and comparative examples are shown in Tables 1 and 2.

[0059] [Table 1]

[0060] [Table 2]

[0061] In Examples 1 to 5, the coating hardness before heat treatment was high at HV120 or more, and the contact resistance was 2 mΩ or less. Furthermore, even after heat treatment at 150°C for 1000 hours, no change in appearance was observed, and the coating hardness was maintained at HV120 or more, and the contact resistance was also maintained at 2 mΩ or less.

[0062] In Comparative Examples 1 and 2, the film hardness before heat treatment was HV110 and HV114, which were lower than those of Examples 1 to 5, and decreased to HV100 and HV81 after heat treatment. In Comparative Examples 3 to 6, the film hardness before heat treatment was high, HV130, HV162, HV150, and HV141, respectively, but decreased to HV100 or less after heat treatment. In Comparative Examples 3 to 6, changes in appearance such as unevenness and discoloration were observed due to heat treatment. In Comparative Example 5, the film contact resistance value after heat treatment exceeded 2 mΩ.

[0063] As described above, by using the non-cyanide electrolytic pure silver plating solution of the present invention, it is possible to form a non-cyanide electrolytic pure silver plating film having a hardness of HV120 or more and a contact resistance of 2 mΩ or less before and after heat treatment at 150°C. Since the hardness remains at HV120 or more even after heat treatment, the high hardness is maintained and the wear resistance does not deteriorate even when exposed to a high-temperature environment. In addition, since it does not contain highly toxic cyanide compounds, it is safer to work with and has a smaller environmental impact than cyanide-based plating solutions. The present invention is not limited to the above-described embodiment, and various modifications and changes are possible within the scope of the gist of the present invention as defined in the claims.

Claims

1. A non-cyanide electrolytic pure silver plating solution for forming an electrolytic pure silver plating film having a Vickers hardness (HV) of 120 or more before and after a heat treatment at 150°C for 1000 hours, and a contact resistance of 2 mΩ or less before and after a heat treatment at 150°C for 1000 hours, The silver ion source includes at least one of an inorganic acid and an inorganic acid salt, and a five-membered ring compound represented by the general formula (2): 【Chemistry 2】 (In the general formula (2), A1 to A3 are either carbon (C), nitrogen (N), oxygen (O), or sulfur (S). However, the number of nitrogens (N) constituting the five-membered ring is three or less. In addition, C of the thiocarbonyl group has a structure in which it is single-bonded to N constituting the five-membered ring, and the bonds between N and A3, between A1 and A2, and between A2 and A3 are single bonds or double bonds.) The content of the five-membered ring compound is 0.05 g / L or more and 2 g / L or less, Contains at least one of an organic acid containing a carbonyl group or an organic acid salt containing a carbonyl group, the carbonyl group-containing organic acid includes at least one selected from glutamic acid, aspartic acid, pyruvic acid, citric acid, tartaric acid, succinic acid, fumaric acid, L-malic acid, and salts thereof, and the content is 1 g / L or more and 200 g / L or less; The five-membered ring compound having a thiocarbonyl structure includes at least one selected from 2-imidazolinethione, 2-mercapto-2-thiazoline, 1,3-dimethyl-2-imidazolidinethione, thiazole-2-thiol, 3-amino-5-mercapto-1,2,4-triazole, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, 3-aminorhodanine, 2-oxazolidinethione, and 3-(2-hydroxyethyl)oxazolidine-2-thione; A non-cyanide electrolytic pure silver plating solution with a pH of 4 to 7.

2. the silver ion source comprises at least silver sulfite or silver oxide; 2. The non-cyanide electrolytic pure silver plating solution according to claim 1, wherein the content of silver ions is 0.5 g / L or more and 50 g / L or less in terms of metallic silver concentration.

3. The inorganic acid or inorganic acid salt includes at least one selected from sulfuric acid, sulfurous acid, phosphoric acid, thiosulfuric acid, and sulfamic acid, or salts thereof; 3. The non-cyanide electrolytic pure silver plating solution according to claim 1, wherein the content of said inorganic acid or inorganic acid salt is 1 g / L or more and 500 g / L or less.

Images