Silver thiodiglycol-containing electroplating solution and preparation method thereof

Abstract

The invention relates to a silver thiodiglycol-containing electroplating solution and a preparation method thereof, and belongs to the technical field of silver plating. The electroplating solution is composed of a pre-plating solution, a main plating solution, a cylinder opening agent and a supplement, wherein the pre-plating solution contains Ag < + >, thiodiglycol, a nitrogen heterocyclic ring complexing agent and methanesulfonic acid; a main plating solution cylinder opening agent contains Ag < + >, thiodiglycol, a complexing agent, methanesulfonic acid and a thiourea derivative; and the supplement contains thiodiglycol, silver sulfamate and a corrosion inhibitor. Wherein the replenisher contains high-concentration silver sulfamate, so that the replenishment volume is reduced; 5% of sulfamic acid and 0.1% of thiourea derivative anti-displacement treatment liquid improve the binding force of a matrix; the cyanide-free silver plating process is achieved, uniform silver plating is achieved, no sediment exists, and a wear-resistant silver plating layer is provided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silver plating and relates to a silver plating solution containing thiodiglycol and a preparation method thereof. BACKGROUND

[0002] Traditional silver plating technology mainly relies on cyanide as a complexing agent. Cyanide solution has good stability and plating layer gloss, and has been widely used in various industrial silver plating processes for a long time. However, the toxicity of cyanide and its potential harm to the environment have prompted people to seek safer alternatives. Traditional silver plating processes usually require strict operating conditions and waste liquid treatment measures to reduce the risk of environmental pollution, which greatly increases the production cost and operating difficulty. In addition, the management and treatment of cyanide solution need to comply with strict regulations and standards to ensure the safety of operating personnel and environmental protection.

[0003] In recent years, in order to reduce the environmental and safety problems caused by the use of cyanide, cyanide-free silver plating technology has been gradually developed and applied. These technologies usually use non-cyanide complexing agents such as thiosulfate, sulfamate or other organic complexing agents to replace cyanide. In the cyanide-free silver plating process, the use of more environmentally friendly chemicals can significantly reduce the toxicity and environmental risk of the process, and also reduce the complexity of waste liquid treatment. These alternative technologies can usually provide plating layer quality comparable to traditional cyanide silver plating, with lower production cost and operating difficulty. However, the promotion of cyanide-free silver plating technology is still limited by some technical challenges.

[0004] Although cyanide-free silver plating technology has obvious advantages in environmental protection and safety, there are still some deficiencies in the existing technology. First, the stability of the cyanide-free silver plating solution and the quality of the plating layer may not be as good as that of the cyanide solution under certain conditions, which may result in slightly lower gloss and durability of the plating layer than the traditional process. In addition, some cyanide-free silver plating technologies may require more complex chemical formulations or more stringent operating conditions, increasing the complexity of the process. Therefore, further optimization of cyanide-free silver plating technology to improve plating layer quality and reduce operating difficulty is a current problem to be solved. SUMMARY

[0005] The purpose of the present application is to provide a silver plating solution containing thiodiglycol and a preparation method thereof, which reduces environmental pollution in a cyanide-free system.

[0006] The purpose of the present application can be achieved by the following technical solutions: A silver plating solution containing thiodiglycol, comprising: Pre-plating solution: containing Ag + : 1.0-3.0 g / L, thiodiglycol: 20-35 vol%, nitrogen-containing heterocyclic compound auxiliary complexing agent: 25-60 g / L, methyl sulfonic acid: 25-45 mL / L; Main plating solution opening agent: contains Ag + : 30-50 g / L, thiodiglycol: 20-35vol%, nitrogen-containing heterocyclic compound auxiliary complexing agent: 70-130 g / L, methanesulfonic acid: 25-45 mL / L, thiourea derivative additive: 5-20 g / L; Supplement: Contains thiodiglycol: 0.05-0.5vol%, silver sulfamate: 350-550 g / L, corrosion inhibitor: 5-20g / L.

[0007] In this application, the sulfide group (-S-) of thiodiglycol provides a lone pair of electrons to react with Ag. + Forming a tetrahedral complex with a higher stability constant than silver cyanide; nitrogen-containing heterocyclic compounds (such as 2-mercaptobenzimidazole) coordinate with nitrogen heterocyclic rings through mercapto (-SH) to form mixed ligand complexes, which shift the deposition potential negatively and inhibit the replacement reaction; thiourea derivatives are adsorbed on the cathode surface to form a steric layer, inhibiting the disordered deposition of silver ions, and breaking the C=S bond in the molecule to produce S 2- , with Ag + Generate nano-Ag2S crystal nuclei, leading to the growth of dense coating.

[0008] Furthermore, the method for preparing the silver electroplating solution containing thiodiglycol comprises the following steps: Prepare the pre-plating solution: dissolve thiodiglycol and nitrogen-containing heterocyclic compound auxiliary complexing agent in water and stir to dissolve; add methanesulfonic acid dropwise and stir evenly; then add AgNO3 solution dropwise and mix thoroughly; adjust the pH to 3.5-5.5; Prepare the main plating solution opening agent: dissolve thiodiglycol and auxiliary complexing agent in water and stir to dissolve; add methanesulfonic acid dropwise and stir evenly; then add AgNO3 solution dropwise and mix thoroughly; add thiourea derivative additive and stir to dissolve; adjust the pH to 4.0-6.0; Prepare the supplement: dissolve silver sulfamate in water and stir to dissolve; add thiodiglycol and corrosion inhibitor dropwise and mix thoroughly to dissolve.

[0009] As a preferred technical solution of the present invention, the nitrogen-containing heterocyclic compound auxiliary complexing agent is at least one of 2-mercaptobenzimidazole, benzotriazole, nicotinic acid, isonicotinic acid, 2-aminopyrimidine, and 2,2'-bipyridine.

[0010] As a preferred technical solution of the present invention, the thiourea derivative additive is at least one of thiourea, diphenylthiourea, N,N'-diethylthiourea, and allylthiourea.

[0011] As a preferred technical solution of the present invention, the corrosion inhibitor is at least one of benzotriazole, methylbenzotriazole, and mercaptobenzothiazole.

[0012] Further, a silver plating method using the silver plating solution containing thiodiglycol, comprising the steps of: (1) pre-treating the substrate; (2) immersing the pre-treated substrate into the pre-plating solution, and pre-plating at 20-30 DEG C, cathode current density 0.5-1.5 A / dm 2 2 for 1-5 min; (3) immersing the pre-plated substrate into the main plating solution, and plating at 25-35 DEG C, cathode current density 1-3 A / dm 2 2, and adding the replenisher.

[0013] As a preferred technical solution of the present application, the pre-treatment in step (1) is immersing the substrate into the alkaline cleaning solution at 60-70 DEG C for 5-10 min, and then immersing into 10% H2SO4 for 30-60 s for activation, and immersing into the anti-displacement treatment solution for 20-30 s after the acid activation.

[0014] As a preferred technical solution of the present application, the alkaline cleaning solution contains 40-60 g / L NaOH, 20-30 g / L Na2CO3, 4-6 g / L fatty acid methyl ester ethoxylate, and the rest is deionized water.

[0015] As a preferred technical solution of the present application, the anti-displacement treatment solution contains 4-6% sulfamic acid and 0.02-0.2% thiourea derivative.

[0016] As a preferred technical solution of the present application, in step (3), the replenisher is added to the main plating solution during the plating process, and the amount of the replenisher added is V=K*Q / (C*η); wherein K=0.85-0.95, Q=the cumulative electric current Ah / L of per liter of the main plating solution, C=the concentration of sulfamic acid silver in the replenisher, and η=cathode current efficiency.

[0017] The present application has the following advantages: (1) The silver plating solution and the silver plating process of the present application adopt a cyanide-free system, completely avoiding the risk of cyanide toxicity, improving the complexation of silver ions through the synergistic complexation of thiodiglycol and nitrogen-containing heterocyclic compounds, reducing the free Ag + concentration, and further reducing environmental pollution.

[0018] (2) The present application uses the selective adsorption of thiourea derivative to the crystal face of the plated layer to control the orientation of silver crystal grains to be the preferred growth of the crystal face, improve the hardness and wear resistance of the plated layer, and reduce the friction coefficient; through the anti-displacement treatment solution containing 5% sulfamic acid and 0.1% thiourea derivative, a transition layer is formed in the pre-plating pretreatment, and the adhesion is improved. DETAILED DESCRIPTION

[0019] In order to further clarify the technical means adopted by the present application and the effects achieved by the present application, the following describes the specific embodiments, structures, features and effects of the present application in detail in combination with examples.

[0020] Example 1 A silver electroplating solution containing thiodiglycol, comprising: A pre-plating solution containing 2 g / L Ag + , 28 vol% thiodiglycol, 42 g / L nitrogen-containing heterocyclic compound auxiliary complexing agent, 35 mL / L methyl sulfonic acid; A main plating solution opening agent containing 40 g / L Ag + , 27 vol% thiodiglycol, 100 g / L nitrogen-containing heterocyclic compound auxiliary complexing agent, 35 mL / L methyl sulfonic acid, 13 g / L thiourea derivative additive; A replenisher containing 0.3 vol% thiodiglycol, 450 g / L silver sulfamate, 12 g / L corrosion inhibitor.

[0021] The preparation method of the silver electroplating solution containing thiodiglycol, comprising the following steps: Preparation of a pre-plating solution: dissolve thiodiglycol and nitrogen-containing heterocyclic compound auxiliary complexing agent in water and stir to dissolve; add methyl sulfonic acid dropwise and stir until uniform; then add AgNO3 solution dropwise and mix thoroughly; adjust the pH to 4.5; Preparation of a main plating solution opening agent: dissolve thiodiglycol and auxiliary complexing agent in water and stir to dissolve; add methyl sulfonic acid dropwise and stir until uniform; then add AgNO3 solution dropwise and mix thoroughly; add thiourea derivative additive and stir to dissolve; adjust the pH to 5.0; Preparation of a replenisher: dissolve silver sulfamate in water and stir to dissolve; add thiodiglycol and corrosion inhibitor dropwise and mix thoroughly to dissolve.

[0022] The nitrogen-containing heterocyclic compound auxiliary complexing agent is 2-mercaptobenzimidazole.

[0023] The thiourea derivative additive is thiourea.

[0024] The corrosion inhibitor is benzotriazole.

[0025] A silver plating method using the silver electroplating solution containing thiodiglycol, comprising the steps of: (1) Pre-treatment of the substrate; (2) Immersing the pre-treated substrate in the pre-plating solution at 25°C, with a cathode current density of 1 A / dm 2 , and pre-plating for 3 min; (3) The pre-plated substrate is immersed in the main plating solution opening agent, and silver plating is carried out at 30℃ with a cathode current density of 2A / dm 2 , and a supplement is added.

[0026] The pre-treatment in step (1) is to immerse the substrate in an alkaline cleaning solution at 65℃ for 8 min, then immerse it in 10% H2SO4 for 45 s for activation, and then immerse it in a displacement prevention treatment solution for 25 s after acid activation.

[0027] The alkaline cleaning solution contains 50 g / L NaOH, 25 g / L Na2CO3, 5 g / L fatty acid methyl ester ethoxylate, and the balance is deionized water.

[0028] The displacement prevention treatment solution contains 5% sulfamic acid and 0.1% thiourea derivative.

[0029] In the plating process, the supplement is added to the main plating solution, and the supplement addition amount V = K × Q / (C × η); Wherein K = 0.9, Q = cumulative electric energy Ah / L per liter of main plating solution; C = sulfamic acid silver concentration in the supplement, taking 450 g / L; η = cathode current efficiency, taking 93%.

[0030] On the basis of Example 1, the composite complexing agent is compounded and adjusted: Example 2 The pre-plating solution contains 2 g / L Ag + , 28 vol% thiodiglycol, 42 g / L nitrogen-containing heterocyclic compound auxiliary complexing agent, and 35 mL / L methyl sulfonic acid; The main plating solution opening agent contains 40 g / L Ag + , 27 vol% thiodiglycol, 100 g / L nitrogen-containing heterocyclic compound auxiliary complexing agent, 35 mL / L methyl sulfonic acid, and 13 g / L thiourea derivative additive; The supplement contains 0.3 vol% thiodiglycol, 450 g / L sulfamic acid silver, and 12 g / L corrosion inhibitor.

[0031] The preparation method of the silver plating solution containing thiodiglycol includes the following steps: Preparation of pre-plating solution: dissolve thiodiglycol and nitrogen-containing heterocyclic compound auxiliary complexing agent in water and stir to dissolve; add methyl sulfonic acid dropwise and stir evenly; then add AgNO3 solution dropwise and mix thoroughly; adjust the pH to 4.5; Preparation of main plating solution opening agent: dissolve thiodiglycol and auxiliary complexing agent in water and stir to dissolve; add methyl sulfonic acid dropwise and stir evenly; then add AgNO3 solution dropwise and mix thoroughly; add thiourea derivative additive and stir to dissolve; adjust the pH to 5.0; Preparation of the supplement: dissolve silver sulfamate in water, stir and dissolve; drop in thiodiglycol and corrosion inhibitor, mix and dissolve thoroughly.

[0032] The nitrogen-containing heterocyclic compound auxiliary complexing agent in the pre-plating solution contains 30 g / L of nicotinic acid and 10 g / L of benzotriazole; the nitrogen-containing heterocyclic compound auxiliary complexing agent in the main plating solution opening agent contains 80 g / L of nicotinic acid and 20 g / L of benzotriazole.

[0033] The thiourea derivative additive is thiourea.

[0034] The corrosion inhibitor is benzotriazole.

[0035] A method for silver plating using the silver plating solution containing thiodiglycol, comprising the steps of: (1) pre-treating the substrate; (2) immersing the pre-treated substrate in the pre-plating solution at 25°C, with a cathode current density of 1 A / dm 2 , for pre-plating for 3 min; (3) immersing the pre-plated substrate in the main plating solution opening agent, at 30°C, with a cathode current density of 2 A / dm 2 , for silver plating with the addition of the supplement.

[0036] The pre-treatment in step (1) is to immerse the substrate in an alkaline cleaning solution at 65°C for 8 min, then immerse it in 10% H2SO4 for 45 s for activation, and then immerse it in a displacement prevention treatment solution for 25 s after acid activation.

[0037] The alkaline cleaning solution contains 50 g / L of NaOH, 25 g / L of Na2CO3, 5 g / L of fatty acid methyl ester ethoxylate, and the rest is deionized water.

[0038] The displacement prevention treatment solution contains 5% of sulfamic acid and 0.1% of thiourea derivative.

[0039] In step (3), the supplement is added to the main plating solution during the plating process, and the amount of supplement added is V = K × Q / (C × η); wherein K = 0.9, Q = cumulative electrically charged ampere-hour value Ah / L per liter of main plating solution; C = concentration of silver sulfamate in the supplement, with a value of 450 g / L; and η = cathode current efficiency, with a value of 93%.

[0040] Set the extreme parameter boundary test: Example 3 A silver plating solution containing thiodiglycol, comprising: a pre-plating solution containing 1.0 g / L of Ag + , 20 vol% of thiodiglycol, 25 g / L of a nitrogen-containing heterocyclic compound auxiliary complexing agent, and 25 mL / L of methyl sulfonic acid; A main plating solution opening agent comprising 30 g / L Ag + , 20 vol% thiodiglycol, 70 g / L nitrogen-containing heterocyclic compound auxiliary complexing agent, 25 mL / L methyl sulfonic acid, 5 g / L thiourea derivative additive; A replenisher comprising 0.05 vol% thiodiglycol, 350 g / L silver sulfamate, 5 g / L corrosion inhibitor.

[0041] The preparation method of the silver electroplating solution containing thiodiglycol comprises the following steps: Preparation of a pre-plating solution: dissolve thiodiglycol and nitrogen-containing heterocyclic compound auxiliary complexing agent in water and stir to dissolve; add methyl sulfonic acid dropwise and stir until uniform; then add AgNO3 solution dropwise and mix thoroughly; adjust the pH to 3.5; Preparation of a main plating solution opening agent: dissolve thiodiglycol and auxiliary complexing agent in water and stir to dissolve; add methyl sulfonic acid dropwise and stir until uniform; then add AgNO3 solution dropwise and mix thoroughly; add thiourea derivative additive and stir to dissolve; adjust the pH to 4.0; Preparation of a replenisher: dissolve silver sulfamate in water and stir to dissolve; add thiodiglycol and corrosion inhibitor dropwise and mix thoroughly to dissolve.

[0042] The nitrogen-containing heterocyclic compound auxiliary complexing agent is 2-aminopyrimidine.

[0043] The thiourea derivative additive is N,N'-diethyl thiourea.

[0044] The corrosion inhibitor is methyl benzotriazole.

[0045] A method for silver plating using the silver electroplating solution containing thiodiglycol, comprising the steps of: (1) Pre-treatment of the substrate; (2) Immersion of the pre-treated substrate in the pre-plating solution at 20°C with a cathode current density of 0.5 A / dm 2 for 1 min of pre-plating; (3) Immersion of the pre-plated substrate in the main plating solution opening agent at 25°C with a cathode current density of 1 A / dm 2 for silver plating with the addition of the replenisher.

[0046] The pre-treatment in step (1) is immersion of the substrate in an alkaline cleaning solution at 60°C for 5 min, followed by immersion in 10% H2SO4 for 30 s of activation, and then immersion in a displacement prevention treatment solution for 20 s after acid activation.

[0047] The alkaline cleaning solution contains 40 g / L NaOH, 20 g / L Na2CO3, 4 g / L fatty acid methyl ester ethoxylate, and the balance is deionized water.

[0048] The replacement-preventing treatment solution contains 5% sulfamic acid and 0.1% thiourea derivative.

[0049] In the electroplating process, the replenishing agent is added to the main plating solution, and the amount of the replenishing agent added V = K × Q / (C × η); Wherein K = 0.85, Q = cumulative electric current Ah / L per liter of the main plating solution; C = the concentration of silver sulfamate in the replenishing agent, taking 350 g / L; η = cathode current efficiency, taking 92%.

[0050] Set the extreme parameter boundary test: Example 4 A silver electroplating solution containing thioglycol, comprising: A pre-plating solution containing 3.0 g / L Ag + , 35 vol% thioglycol, 60 g / L nitrogen-containing heterocyclic compound auxiliary complexing agent, 45 mL / L methyl sulfonic acid; A main plating solution opening agent containing 50 g / L Ag + , 35 vol% thioglycol, 130 g / L nitrogen-containing heterocyclic compound auxiliary complexing agent, 45 mL / L methyl sulfonic acid, 20 g / L thiourea derivative additive; A replenishing agent containing 0.5 vol% thioglycol, 550 g / L silver sulfamate, 20 g / L corrosion inhibitor.

[0051] The preparation method of the silver electroplating solution containing thioglycol, comprising the following steps: Preparation of pre-plating solution: dissolve thioglycol and nitrogen-containing heterocyclic compound auxiliary complexing agent in water, stir to dissolve; add methyl sulfonic acid dropwise, stir evenly; then add AgNO3 solution dropwise, mix thoroughly; adjust the pH to 5.5; Preparation of main plating solution opening agent: dissolve thioglycol and auxiliary complexing agent in water, stir to dissolve; add methyl sulfonic acid dropwise, stir evenly; then add AgNO3 solution dropwise, mix thoroughly; add thiourea derivative additive, stir to dissolve; adjust the pH to 6.0; Preparation of replenishing agent: dissolve silver sulfamate in water, stir to dissolve; add thioglycol and corrosion inhibitor dropwise, mix thoroughly and dissolve.

[0052] The nitrogen-containing heterocyclic compound auxiliary complexing agent is isonicotinic acid.

[0053] The thiourea derivative additive is propenyl thiourea.

[0054] The corrosion inhibitor is mercaptobenzothiazole.

[0055] A method for silver plating using the silver electroplating solution containing thioglycol, comprising the steps of: (1) pretreat the substrate; (2) immerse the pretreated substrate in the pre-plating solution, and pre-plate at 30°C for 5 min at a cathode current density of 1.5 A / dm 2 (3) immerse the pre-plated substrate in the main plating solution, and plate silver at 35°C for 30 min at a cathode current density of 3 A / dm 2 , and add a replenisher.

[0056] The pretreatment in step (1) is to immerse the substrate in an alkaline cleaning solution at 70°C for 10 min, then immerse in 10% H2SO4 for 60 s for activation, and then immerse in a displacement prevention treatment solution for 30 s after acid activation.

[0057] The alkaline cleaning solution contains 40-60 g / L NaOH, 20-30 g / L Na2CO3, 4-6 g / L fatty acid methyl ester ethoxylate, and the balance is deionized water.

[0058] The displacement prevention treatment solution contains 5% sulfamic acid and 0.1% thiourea derivative.

[0059] In step (3), the replenisher is added to the main plating solution during plating, and the amount of replenisher added V = K × Q / (C × η); wherein K = 0.95, Q = cumulative electrically connected ampere-hour value Ah / L per liter of main plating solution; C = silver sulfamate concentration in the replenisher, with a value of 550 g / L; η = cathode current efficiency, with a value of 95%.

[0060] Comparative Example 1 On the basis of Example 1, the thiodiglycol in the pre-plating solution and the main plating solution is replaced by 250 g / L sodium thiosulfate and 50 g / L EDTA, and the rest is the same as Example 1.

[0061] Comparative Example 2 On the basis of Example 1, the silver sulfamate concentration of the replenisher is changed to 150 g / L, and the volume is increased by 3 times under the same electrically connected amount; the rest is the same as Example 1.

[0062] Comparative Example 3 On the basis of Comparative Example 1, the pretreatment omits the immersion step of the displacement prevention treatment solution, and the rest is the same as Example 1.

[0063] Comparative Example 4 On the basis of Example 1, the main plating solution does not add thiourea derivative additive, and the rest is the same as Example 1.

[0064] Performance test: Test the copper sheet after silver plating according to the above examples and comparative examples;​ Precipitation rate: 100 mL of plating solution was filtered through a 0.45 μm filter membrane, dried at 105°C and weighed, and the precipitation rate = precipitate mass / plating solution mass; Bonding strength: according to ASTM B571 thermal shock test, the peeling condition was observed; Porosity: according to ASTM B765-03(2023) standard, the coating porosity was tested; Wear resistance: according to ISO 4527 standard, the wear resistance was tested.

[0065] From the test results, the precipitation rates of Examples 1-4 were all within 0.01%, and the thiodiglycol-nitrogen-containing heterocyclic complexing agent effectively inhibited Ag2S precipitation; in Comparative Example 1, the traditional cyanide-free silver plating system of sodium thiosulfate and EDTA was used, the complexing was unstable, and EDTA was easily oxidized; in Comparative Example 2, the concentration of the silver sulfamate supplement was low, and the addition of the supplement had a great influence on the complexing concentration, and the porosity and wear loss of the coating were significantly increased; in Comparative Example 3, the anti-displacement treatment liquid immersion was omitted, and the glass filter was significantly high, which was probably due to the displacement reaction of the copper substrate; in Comparative Example 4, the thiourea derivative was missing, and the coarse grains had many defects.

[0066] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any indirect modification, equivalent change and modification of the above embodiments according to the technical essence of the present application, which does not depart from the technical solution of the present application, are still within the scope of the technical solution of the present application.

Claims

1. A silver electroplating solution containing thiodiglycol, characterized in that: include: Pre-plating solution containing 1.0-3.0 g / L of + , 20-35vol% thiodiglycol, 25-60 g / L nitrogen-containing heterocyclic compound auxiliary complexing agent, 25-45 mL / L methanesulfonic acid; Main plating bath opening agent, which contains 30-50 g / LAg + , 20-35vol% thiodiglycol, 70-130 g / L nitrogen-containing heterocyclic compound auxiliary complexing agent, 25-45 mL / L methanesulfonic acid, 5-20 g / L thiourea derivative additive; A supplement comprising 0.05-0.5 vol% thiodiglycol, 350-550 g / L silver sulfamate, and 5-20 g / L corrosion inhibitor.

2. A method for preparing the silver electroplating solution containing thiodiglycol as claimed in claim 1, characterized in that: The following steps are involved: Prepare the pre-plating solution: dissolve thiodiglycol and nitrogen-containing heterocyclic compound auxiliary complexing agent in water and stir to dissolve; add methanesulfonic acid dropwise and stir evenly; then add AgNO3 solution dropwise and mix thoroughly; adjust the pH to 3.5-5.5; Prepare the main plating solution opening agent: dissolve thiodiglycol and auxiliary complexing agent in water and stir to dissolve; add methanesulfonic acid dropwise and stir evenly; then add AgNO3 solution dropwise and mix thoroughly; add thiourea derivative additive and stir to dissolve; adjust the pH to 4.0-6.0; Prepare the supplement: dissolve silver sulfamate in water and stir to dissolve; add thiodiglycol and corrosion inhibitor dropwise and mix thoroughly to dissolve.

3. The silver electroplating solution containing thiodiglycol according to claim 1, wherein: The nitrogen-containing heterocyclic compound auxiliary complexing agent is at least one of 2-mercaptobenzimidazole, benzotriazole, nicotinic acid, isonicotinic acid, 2-aminopyrimidine, and 2,2'-bipyridine.

4. The silver electroplating solution containing thiodiglycol according to claim 1, wherein: The thiourea derivative additive is at least one of thiourea, diphenylthiourea, N,N'-diethylthiourea, and allylthiourea.

5. The silver electroplating solution containing thiodiglycol according to claim 1, wherein: The corrosion inhibitor is at least one of benzotriazole, methylbenzotriazole and mercaptobenzothiazole.

6. A method for silver plating, characterized in that: Using the silver electroplating solution containing thiodiglycol as described in any one of claims 1 to 5, comprising the steps of: (1) Pre-treating the substrate; (2) Immerse the pre-treated substrate in the pre-plating solution at 20-30°C and a cathode current density of 0.5-1.5A / dm 2 , pre-plating for 1-5 minutes; (3) Immerse the pre-plated substrate in the main plating solution at 25-35°C and a cathode current density of 1-3A / dm 2 , silver plating and addition of supplements.

7. A silver plating method according to claim 6, characterized in that: The pretreatment in step (1) is to immerse the substrate in an alkaline cleaning solution at 60-70°C for 5-10 minutes, then immerse it in 10% H2SO4 for 30-60 seconds for activation, and then immerse it in an anti-displacement treatment solution for 20-30 seconds after acid washing and activation.

8. A silver plating method according to claim 7, characterized in that: The alkaline cleaning solution contains: 40-60 g / L NaOH, 20-30 g / L Na2CO3, 4-6 g / L fatty acid methyl ester ethoxylate, and the balance is deionized water.

9. A silver plating method according to claim 7, characterized in that: The anti-displacement treatment liquid contains 4-6% aminosulfonic acid and 0.02-0.2% thiourea derivative.

10. The silver plating method according to claim 6, wherein: In step (3), during the electroplating process, the supplement is added to the main plating solution, and the amount of the supplement added is V=K×Q / (C×η); Where K = 0.85-0.95, Q = the cumulative ampere-hour value of the main plating solution per liter Ah / L; C = the concentration of silver sulfamate in the supplement, which is 350-550g / L; η = cathode current efficiency, which is 92%-95%.

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