A cyanide-free gold plating solution and its preparation method and application

Abstract

The present invention relates to the technical field of gold plating liquid, and in particular to a cyanide-free gold plating liquid and a preparation method and application thereof. The preparation method comprises the following steps: preparing a main ligand; preparing an auxiliary ligand; preparing a stabilizing additive; and preparing a cyanide-free gold plating liquid. The present invention prepares an ionic liquid by using choline chloride and compounding it with 5,5-dimethylhydantoin as a main ligand. The ionic liquid of choline chloride has a wide electrochemical window and good conductivity, and many single metals can be electrodeposited. Urea is required in the ionic liquid of choline chloride, and urea cannot be used as a metal ligand. 5,5-dimethylhydantoin has a good coordination effect with chloroauric acid. Through the strong coordination effect of 5,5-dimethylhydantoin and chloroauric acid, the remaining chloride ions in the chloroauric acid can form a strong coordination effect with urea, reduce the activity of chloride ions, thereby improving the deposition of gold elements during gold plating, and the thickness and strength of the formed gold layer are improved.

Description

Technical Field

[0001] The invention relates to the technical field of gold plating solution, and in particular to a cyanide-free gold plating solution and a preparation method and application thereof. Background Art

[0002] With the increasing requirements for large-scale integrated circuits and miniaturization of component circuits, the requirements for chemical gold plating are also getting higher and higher. Cyanide-containing gold plating liquid has long dominated the market due to its good stability, but cyanide is a highly toxic substance and there are safety issues in the preparation, operation and storage processes. With the increasing environmental protection requirements, the application of cyanide-containing gold plating will be strictly controlled and will eventually withdraw from the market. Therefore, the demand for cyanide-free chemical gold plating will become increasingly important.

[0003] The gold salts used in the common cyanide-free gold plating solutions on the market are mostly gold sulfite salts, and hydantoin derivatives are used as coordination agents. Hydantoin derivatives have a coordination effect with gold salts. However, although the use of hydantoin derivatives alone has a certain coordination effect on gold salts, the deposition effect on gold elements is not significant. Therefore, although hydantoin derivatives can be used for gold plating, the coating thickness is slightly thin and difficult to compare with cyanide-containing gold plating solutions. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a cyanide-free gold plating solution and a preparation method and application thereof.

[0005] A cyanide-free gold plating solution comprises the following components: 30-120 parts by volume of a main complexing agent, 20-140 parts by volume of an auxiliary complexing agent, 10-150 parts by volume of chloroauric acid, 0.1-15 parts by volume of a stabilizing additive, and 20-200 parts by volume of methanol;

[0006] The main ligand is prepared by mixing choline chloride, urea and 5,5-dimethylhydantoin; the auxiliary ligand is prepared by mixing potassium citrate, boric acid and sodium dodecyl sulfate; and the stabilizing additive is prepared by mixing histidine, sodium 2-mercaptoethane sulfonate and 3-mercaptopropionic acid.

[0007] A method for preparing a cyanide-free gold plating solution comprises the following steps:

[0008] S1: Preparation of primary ligand

[0009] Add choline chloride to a desiccator, seal and heat to dry, to obtain dry choline chloride, take urea and add it to another desiccator, seal and dry to obtain dry urea, mix the dry choline chloride and dry urea, seal and heat, and stir until the system is gradually converted into a uniform and transparent liquid to obtain an ionic liquid, add dry 5,5-dimethylhydantoin powder to the ionic liquid to obtain a main ligand, and place it in a sealed desiccator for standby use;

[0010] S2: Preparation of auxiliary complexing agent

[0011] Dilute chloroauric acid with deionized water and centrifuge for 10-20 minutes to obtain liquid A, dissolve potassium citrate and boric acid in water, add sodium dodecyl sulfate under stirring, and then slowly add KOH to adjust the pH value of the solution to obtain liquid B, stir liquid A and liquid B in a water bath, cool to room temperature after the reaction is completed, and then put into an oven for drying to obtain an auxiliary coordination agent, which is placed in a sealed desiccator for standby use;

[0012] S3: Preparation of stabilizing additives

[0013] A histidine solution and a sodium 2-mercaptoethane sulfonate solution are prepared, and the histidine solution and the sodium 2-mercaptoethane sulfonate solution are mixed under vigorous stirring to obtain a mixed solution, and 3-mercaptopropionic acid is then added dropwise under stirring. After the addition of 3-mercaptopropionic acid is completed, the mixture is allowed to stand in the dark to obtain a stabilizing additive, and the stabilizing additive is stored at 2-4° C. for later use;

[0014] S4: Preparation of cyanide-free gold plating solution

[0015] Nitrogen is continuously introduced into the reactor. After removing the air, 30-120 parts by volume of the main ligand, 20-140 parts by volume of the auxiliary ligand, 10-150 parts by volume of chloroauric acid, 0.1-15 parts by volume of the stabilizing additive and 20-200 parts by volume of methanol are added into the reactor, stirred with a magnetic rotor and in an oil bath until the solid in the system is completely dissolved to obtain a cyanide-free gold plating solution.

[0016] Furthermore, step S1 of preparing a primary coordination agent comprises the following steps:

[0017] S1.1: Add choline chloride to a dryer, evacuate it, seal it with three layers of plastic film, heat it to 70-80℃ and dry it for 20-24h to obtain dry choline chloride, add urea to another dryer, seal it and dry it in an oven at 80-100℃ for 15-20h to obtain dry urea;

[0018] S1.2: Mix dry choline chloride and dry urea in a molar ratio of 1:(1.5-2), heat in a sealed state at 75-80°C, and stir at a speed of 500-800 r / min until the system is gradually converted into a uniform transparent liquid to obtain an ionic liquid;

[0019] S1.3: Add dry 5,5-dimethylhydantoin powder to the ionic liquid with a solid-liquid ratio of 1:(5-10), cool to 50-60℃ and centrifuge for 10-20min to obtain the main ligand, which is then placed in a sealed desiccator for later use.

[0020] Furthermore, step S2 of preparing an auxiliary coordination agent comprises the following steps:

[0021] S2.1: dilute chloroauric acid and deionized water in a ratio of 1:(2-10), centrifuge at 500-800 rpm for 10-20 min, and obtain solution A;

[0022] S2.2: Dissolve 0.2-0.4 mol / L potassium citrate and 0.5-0.8 mol / L boric acid in water, add 0.5-1 mol / L sodium dodecyl sulfate under stirring, then slowly add KOH to adjust the pH value of the solution to 4-5, stir well for 0.5-1h, and obtain solution B;

[0023] S2.3: Stir liquid A and liquid B in a water bath at 65-70°C for 2-3 hours. After the reaction is completed, cool to room temperature and dry in an oven at 100-120°C for 15-20 hours to obtain an auxiliary complexing agent, which is then placed in a sealed desiccator for later use.

[0024] Furthermore, step S3 of preparing a stabilizing additive comprises the following steps:

[0025] S3.1: preparing 15-20 parts by volume of a histidine solution having a concentration of 0.1-0.2 mol / L and 5-8 parts by volume of a sodium 2-mercaptoethane sulfonate solution having a concentration of 0.01-0.05 mol / L;

[0026] S3.2: Mix the histidine solution and the sodium 2-mercaptoethane sulfonate solution under vigorous stirring to obtain a mixed solution, and then add 3-mercaptopropionic acid dropwise at a rate of 1-5 ml / s under stirring;

[0027] S3.3: After the addition of 3-mercaptopropionic acid is completed, the reaction bottle is placed at 20-25°C in the dark for 1-2 hours to obtain a stabilizing additive, and the stabilizing additive is stored at 2-4°C for later use.

[0028] Furthermore, in step S2.2, the volume ratio of potassium citrate, boric acid and sodium dodecyl sulfate is 3:1:3.

[0029] Furthermore, in step S2.3, the volume ratio of liquid A to liquid B is 1:1.

[0030] Furthermore, in step S3.2, the volume ratio of 3-mercaptopropionic acid to the mixed solution is 1:1.

[0031] The application of cyanide-free gold plating solution in gold plating includes the following steps:

[0032] The degreasing powder is dissolved in water to prepare a degreasing solution with a mass fraction of 5-8%, the nickel substrate is placed in the degreasing solution, heated to 60-70°C, soaked for 1-5 minutes, taken out and washed with ultrapure water to obtain a degreasing nickel substrate, and then the electrolytic degreasing powder is dissolved in water to prepare an electrolytic degreasing solution with a mass fraction of 5-8%, the degreasing nickel substrate is placed in the electrolytic degreasing solution, heated to 60-70°C, soaked for 1-5 minutes, taken out and washed with ultrapure water to obtain an electrolytic degreasing nickel substrate Then, the electrolytically degreased nickel substrate is placed in a dilute sulfuric acid solution with a mass fraction of 5-10%, activated for 1-2 minutes, taken out and washed with ultrapure water, and dried to obtain a treated nickel substrate. The treated nickel substrate is immersed in a cyanide-free gold plating solution. The electroplating gold adopts a high-frequency DC power supply, a circuit density of 0.01-0.5A / dm2, a platinum-plated titanium mesh anode, a temperature of 20-40°C, a pH of 8.5-10.5, a time of 30-200s, and the anode is moved and stirred to obtain a gold-plated nickel plate.

[0033] Furthermore, the degreasing powder is specifically HJ-W122 degreasing powder.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] 1. The present invention prepares an ionic liquid by using choline chloride and uses the ionic liquid and 5,5-dimethylhydantoin as a main ligand. The ionic liquid of choline chloride has a wide electrochemical window and good conductivity, and can electrodeposit many single metals. Urea is required in the ionic liquid of choline chloride, and urea cannot be used as a metal ligand. 5,5-dimethylhydantoin has a good coordination effect with chloroauric acid. Through the strong coordination effect of 5,5-dimethylhydantoin and chloroauric acid, the remaining chloride ions in the chloroauric acid can form a strong coordination effect with urea, reduce the activity of chloride ions, thereby improving the deposition of gold elements during gold plating, and the thickness and strength of the formed gold layer are improved.

[0036] 2. The present invention prepares a stabilizing additive by compounding histidine, sodium 2-mercaptoethane sulfonate and 3-mercaptopropionic acid. Sodium 2-mercaptoethane sulfonate can act as a stabilizer in the gold plating process to ensure stable Au deposition during the gold plating process. Histidine can act in combination with sodium 2-mercaptoethane sulfonate to provide electrons to the Au nucleus. 3-mercaptopropionic acid is used to carry histidine and sodium 2-mercaptoethane sulfonate to contact with chloroauric acid, thereby stabilizing the gold plating process and forming a denser gold layer.

[0037] 3. The present invention uses potassium citrate and sodium dodecyl sulfate to assist in coordination. Sodium dodecyl sulfate can improve ion activity. The combined effect of potassium citrate and sodium dodecyl sulfate can make the gold element more active, thereby improving the efficiency of gold plating. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate embodiments of the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art to make and use the present disclosure.

[0039] Figure 1 The invention discloses a method for preparing the cyanide-free gold plating solution used in the embodiment of the present invention. DETAILED DESCRIPTION

[0040] Embodiment 1:

[0041] A method for preparing a cyanide-free gold plating solution, such as Figure 1 As shown, the following steps are included:

[0042] S1: Preparation of primary ligand

[0043] S1.1: Add choline chloride to a desiccator, evacuate it, seal it with three layers of plastic film, heat it to 80°C and dry it for 24 hours to obtain dry choline chloride, add urea to another desiccator, seal it and dry it in an oven at 80°C for 20 hours to obtain dry urea;

[0044] S1.2: Dry choline chloride and dry urea are mixed in a molar ratio of 1:2, sealed and heated at 80°C, and stirred at a speed of 500 r / min until the system is gradually converted into a uniform transparent liquid to obtain an ionic liquid;

[0045] S1.3: Add dry 5,5-dimethylhydantoin powder to the ionic liquid with a solid-liquid ratio of 1:5, and cool to 60°C and centrifuge and stir for 20 minutes to obtain the main ligand, which is then placed in a sealed desiccator for later use.

[0046] S2: Preparation of auxiliary complexing agent

[0047] S2.1: dilute chloroauric acid and deionized water in a ratio of 1:10 and centrifuge at 500 rpm for 10 min to obtain solution A;

[0048] S2.2: Dissolve 0.2 mol / L potassium citrate and 0.5 mol / L boric acid in water, add 0.5 mol / L sodium dodecyl sulfate while stirring, the volume ratio of potassium citrate, boric acid and sodium dodecyl sulfate is 3:1:3, then slowly add KOH to adjust the pH value of the solution to 5, stir well for 1 hour, and obtain solution B;

[0049] S2.3: Stir liquid A and liquid B in a water bath at 70°C for 2 hours. The volume ratio of liquid A to liquid B is 1:1. After the reaction is completed, cool to room temperature and dry in an oven at 100°C for 20 hours to obtain an auxiliary complexing agent, which is placed in a sealed desiccator for later use.

[0050] S3: Preparation of stabilizing additives

[0051] S3.1: prepare 15 parts by volume of a 0.1 mol / L histidine solution and 5 parts by volume of a 0.01 mol / L sodium 2-mercaptoethane sulfonate solution;

[0052] S3.2: Mix the histidine solution and the sodium 2-mercaptoethane sulfonate solution under vigorous stirring to obtain a mixed solution, and then add 3-mercaptopropionic acid dropwise at a rate of 1 ml / s under stirring, with the volume ratio of 3-mercaptopropionic acid to the mixed solution being 1:1;

[0053] S3.3: After the addition of 3-mercaptopropionic acid is completed, the reaction bottle is placed at 20°C in the dark for 2 hours to obtain a stabilizing additive, and the stabilizing additive is stored at 4°C for later use.

[0054] S4: Preparation of cyanide-free gold plating solution

[0055] Nitrogen was continuously introduced into the reactor. After removing the air, 30 parts by volume of the main ligand, 20 parts by volume of the auxiliary ligand, 10 parts by volume of chloroauric acid, 0.1 parts by volume of the stabilizing additive and 20 parts by volume of methanol were added into the reactor. The mixture was stirred with a magnetic rotor and in an oil bath until the solids in the system were completely dissolved to obtain a cyanide-free gold plating solution.

[0056] Embodiment 2:

[0057] A method for preparing a cyanide-free gold plating solution, such as Figure 1 As shown, the following steps are included:

[0058] S1: Preparation of primary ligand

[0059] S1.1: Add choline chloride to a desiccator, evacuate it, seal it with three layers of plastic film, heat it to 80°C and dry it for 24 hours to obtain dry choline chloride, add urea to another desiccator, seal it and dry it in an oven at 80°C for 20 hours to obtain dry urea;

[0060] S1.2: Dry choline chloride and dry urea are mixed in a molar ratio of 1:2, sealed and heated at 80°C, and stirred at a speed of 500 r / min until the system is gradually converted into a uniform transparent liquid to obtain an ionic liquid;

[0061] S1.3: Add dry 5,5-dimethylhydantoin powder to the ionic liquid with a solid-liquid ratio of 1:5, and cool to 60°C and centrifuge and stir for 20 minutes to obtain the main ligand, which is then placed in a sealed desiccator for later use.

[0062] S2: Preparation of auxiliary complexing agent

[0063] S2.1: dilute chloroauric acid and deionized water in a ratio of 1:10 and centrifuge at 500 rpm for 10 min to obtain solution A;

[0064] S2.2: Dissolve 0.2 mol / L potassium citrate and 0.5 mol / L boric acid in water, add 0.5 mol / L sodium dodecyl sulfate while stirring, the volume ratio of potassium citrate, boric acid and sodium dodecyl sulfate is 3:1:3, then slowly add KOH to adjust the pH value of the solution to 5, stir well for 1 hour, and obtain solution B;

[0065] S2.3: Stir liquid A and liquid B in a water bath at 70°C for 2 hours. The volume ratio of liquid A to liquid B is 1:1. After the reaction is completed, cool to room temperature and dry in an oven at 100°C for 20 hours to obtain an auxiliary complexing agent, which is placed in a sealed desiccator for later use.

[0066] S3: Preparation of stabilizing additives

[0067] S3.1: prepare 20 parts by volume of a 0.1 mol / L histidine solution and 8 parts by volume of a 0.01 mol / L sodium 2-mercaptoethane sulfonate solution;

[0068] S3.2: Mix the histidine solution and the sodium 2-mercaptoethane sulfonate solution under vigorous stirring to obtain a mixed solution, and then add 3-mercaptopropionic acid dropwise at a rate of 1 ml / s under stirring, with the volume ratio of 3-mercaptopropionic acid to the mixed solution being 1:1;

[0069] S3.3: After the addition of 3-mercaptopropionic acid is completed, the reaction bottle is placed at 20°C in the dark for 2 hours to obtain a stabilizing additive, and the stabilizing additive is stored at 4°C for later use.

[0070] S4: Preparation of cyanide-free gold plating solution

[0071] Nitrogen was continuously introduced into the reactor. After removing the air, 120 parts by volume of the main ligand, 140 parts by volume of the auxiliary ligand, 150 parts by volume of chloroauric acid, 15 parts by volume of the stabilizing additive and 200 parts by volume of methanol were added into the reactor. The mixture was stirred with a magnetic rotor and in an oil bath until the solids in the system were completely dissolved to obtain a cyanide-free gold plating solution.

[0072] Embodiment 3:

[0073] A method for preparing a cyanide-free gold plating solution, such as Figure 1 As shown, the following steps are included:

[0074] S1: Preparation of primary ligand

[0075] S1.1: Add choline chloride to a desiccator, evacuate the container, seal it with three layers of plastic film, heat it to 70°C and dry it for 20 hours to obtain dry choline chloride, add urea to another desiccator, seal it, and dry it in an oven at 100°C for 15 hours to obtain dry urea;

[0076] S1.2: Dry choline chloride and dry urea are mixed in a molar ratio of 1:2, sealed and heated at 75°C, and stirred at a speed of 800 r / min until the system is gradually converted into a uniform transparent liquid to obtain an ionic liquid;

[0077] S1.3: Add dry 5,5-dimethylhydantoin powder to the ionic liquid with a solid-liquid ratio of 1:5, and cool to 50°C and centrifuge and stir for 10 minutes to obtain the main ligand, which is then placed in a sealed desiccator for later use.

[0078] S2: Preparation of auxiliary complexing agent

[0079] S2.1: dilute chloroauric acid and deionized water in a ratio of 1:10 and centrifuge at 800 rpm for 10 min to obtain solution A;

[0080] S2.2: Dissolve 0.2 mol / L potassium citrate and 0.5 mol / L boric acid in water, add 0.5 mol / L sodium dodecyl sulfate while stirring, the volume ratio of potassium citrate, boric acid and sodium dodecyl sulfate is 3:1:3, then slowly add KOH to adjust the pH value of the solution to 4, stir thoroughly for 0.5 h, and obtain solution B;

[0081] S2.3: Stir liquid A and liquid B in a water bath at 65°C for 3 hours. The volume ratio of liquid A to liquid B is 1:1. After the reaction is completed, cool to room temperature and dry in an oven at 100°C for 20 hours to obtain an auxiliary complexing agent, which is placed in a sealed desiccator for standby use.

[0082] S3: Preparation of stabilizing additives

[0083] S3.1: prepare 15 parts by volume of a 0.1 mol / L histidine solution and 5 parts by volume of a 0.01 mol / L sodium 2-mercaptoethane sulfonate solution;

[0084] S3.2: Mix the histidine solution and the sodium 2-mercaptoethane sulfonate solution under vigorous stirring to obtain a mixed solution, and then add 3-mercaptopropionic acid dropwise at a rate of 5 ml / s under stirring, wherein the volume ratio of 3-mercaptopropionic acid to the mixed solution is 1:1;

[0085] S3.3: After the addition of 3-mercaptopropionic acid is complete, the reaction bottle is placed at 25°C in the dark for 2 hours to obtain a stabilizing additive, and the stabilizing additive is stored at 2°C for later use.

[0086] S4: Preparation of cyanide-free gold plating solution

[0087] Nitrogen was continuously introduced into the reactor. After removing the air, 30 parts by volume of the main ligand, 20 parts by volume of the auxiliary ligand, 10 parts by volume of chloroauric acid, 0.1 parts by volume of the stabilizing additive and 20 parts by volume of methanol were added into the reactor. The mixture was stirred with a magnetic rotor and in an oil bath until the solids in the system were completely dissolved to obtain a cyanide-free gold plating solution.

[0088] Comparative Example 1:

[0089] Compared with Example 1, Comparative Example 1 is a commercially available cyanide-free gold plating solution, product number: Q / YS.805 (Yishun brand).

[0090] Comparative Example 2:

[0091] Compared with Example 1, Comparative Example 2 is an ionic liquid prepared by using only choline chloride in step S1 without adding 5,5-dimethylhydantoin, specifically: "S1.1: Add choline chloride to a dryer, evacuate and seal with three layers of plastic film to make it sealed, heat to 80°C and dry for 24h to obtain dry choline chloride, take urea and add it to another dryer, seal and dry in an oven at 80°C for 20h to obtain dry urea;

[0092] S1.2: Dry choline chloride and dry urea are mixed in a molar ratio of 1:2, sealed and heated at 80°C, and stirred at a speed of 500 r / min until the system is gradually converted into a uniform transparent liquid to obtain an ionic liquid;

[0093] S1.3: Add dry choline chloride to the ionic liquid at a material-liquid ratio of 1:5, cool to 60°C and centrifuge for 20 minutes to obtain a main complexing agent, which is placed in a sealed desiccator for standby use. The prepared cyanide-free gold plating solution is recorded as Comparative Example 2.

[0094] Comparative Example 3:

[0095] Compared with Example 1, Comparative Example 3 is an ionic liquid prepared by using only 5,5-dimethylhydantoin in step S1 without adding choline chloride, specifically: "Dry the 5,5-dimethylhydantoin powder to prepare a main ligand for standby use." The prepared cyanide-free gold plating solution is recorded as Comparative Example 3.

[0096] Comparative Examples 1-3 and Examples 1-3 were applied to gold plating on a nickel substrate, specifically in the following steps:

[0097] The degreasing powder is dissolved in water to prepare a degreasing solution with a mass fraction of 8%, the nickel substrate is placed in the degreasing solution, heated to 70°C, soaked for 5 minutes, taken out and washed with ultrapure water to obtain a degreasing nickel substrate, and then the electrolytic degreasing powder is dissolved in water to prepare an electrolytic degreasing solution with a mass fraction of 8%, the degreasing nickel substrate is placed in the electrolytic degreasing solution, heated to 70°C, soaked for 5 minutes, taken out and washed with ultrapure water to obtain an electrolytic degreasing nickel substrate, then the electrolytic degreasing nickel substrate is placed in a dilute sulfuric acid solution with a mass fraction of 5-10%, activated for 2 minutes, taken out and washed with ultrapure water, and dried to obtain a treated nickel substrate, the treated nickel substrate is immersed in the cyanide-free gold plating solution of Example 1-3 and Comparative Example 1-3, the electroplating gold adopts a high-frequency DC power supply, the circuit density is 0.1A / dm2, the anode is a platinum-plated titanium mesh, the temperature is 20°C, pH=10.5, the time is 200s, the anode is moved and stirred to obtain a gold-plated nickel plate.

[0098] The coating thickness of the gold-plated nickel plate was tested by an X-ray film thickness tester and recorded in a table, as shown in Table 1.

[0099] Table 1: Coating film thickness table

[0100]

[0101] It can be seen that the coating film thickness of Examples 1-3 is above 0.146 μm, and can reach up to 0.157 μm, while Comparative Example 1 is a commercially available cyanide-free gold plating solution, and its coating film thickness is only 0.115 μm, which is not as high as the embodiment of the present invention. Comparative Example 2 is a cyanide-free gold plating solution without adding 5,5-dimethylhydantoin, and the coating film thickness is only 0.095 μm, which is lower than the thickness of the commercially available cyanide-free gold plating solution, and has obvious defects, because 5,5-dimethylhydantoin has a good coordination with chloroauric acid. The effect of choline chloride on the gold deposition effect is shown in Figure 2. It is difficult to form a stable coating without 5,5-dimethylhydantoin. Comparative Example 3 is a cyanide-free gold plating solution without the addition of ionic liquid prepared by choline chloride, and the coating film thickness is 0.092 μm. It can be seen that without the choline chloride ionic liquid with a wide electrochemical window and good conductivity, the deposition effect of gold element decreases, and the coating film thickness also decreases accordingly. The ionic liquid prepared by choline chloride and compounded with 5,5-dimethylhydantoin can significantly improve the deposition of gold element, thereby increasing the thickness of the gold plating film.

[0102] Comparative Example 4:

[0103] Compared with Example 1, Comparative Example 4 is a method of preparing a stabilizing additive by compounding only sodium 2-mercaptoethane sulfonate and 3-mercaptopropionic acid in step S3, specifically: “S3.1: preparing 20 parts by volume of a sodium 2-mercaptoethane sulfonate solution having a concentration of 0.01 mol / L;

[0104] S3.2: under stirring, 3-mercaptopropionic acid is added dropwise to the sodium 2-mercaptoethane sulfonate solution at a rate of 1 ml / s, and the volume ratio of 3-mercaptopropionic acid to sodium 2-mercaptoethane sulfonate is 1:1;

[0105] S3.3: After the addition of 3-mercaptopropionic acid is completed, the reaction bottle is placed at 20° C. in the dark for 2 h to obtain a stabilizing additive, and the stabilizing additive is stored at 4° C. for standby use. The prepared cyanide-free gold plating solution is recorded as Comparative Example 4.

[0106] Comparative Example 5:

[0107] Compared with Example 1, Comparative Example 5 is a method of preparing a stabilizing additive by compounding only sodium 2-mercaptoethane sulfonate and a histidine solution in step S3, specifically: “S3.1: preparing 15 parts by volume of a histidine solution with a concentration of 0.1 mol / L and 5 parts by volume of a sodium 2-mercaptoethane sulfonate solution with a concentration of 0.01 mol / L;

[0108] S3.2: Mix the histidine solution and the sodium 2-mercaptoethane sulfonate solution under vigorous stirring to obtain a mixed solution, place the mixed solution at 20° C. in the dark for 2 hours to obtain a stabilizing additive, and store the stabilizing additive at 4° C. for standby use. The prepared cyanide-free gold plating solution is recorded as Comparative Example 5.

[0109] Comparative Example 6:

[0110] Compared with Example 1, Comparative Example 5 is a step S3 in which only histidine solution and 3-mercaptopropionic acid are used to prepare a stabilizing additive, specifically: “S3.1: preparing 20 parts by volume of a histidine solution with a concentration of 0.1 mol / L, and adding 3-mercaptopropionic acid dropwise at a rate of 1 ml / s under stirring, wherein the volume ratio of 3-mercaptopropionic acid to the histidine solution is 1:1;

[0111] S3.3: After the addition of 3-mercaptopropionic acid is completed, the reaction bottle is placed at 20° C. in the dark for 2 h to obtain a stabilizing additive, and the stabilizing additive is stored at 4° C. for standby use. The prepared cyanide-free gold plating solution is recorded as Comparative Example 6.

[0112] Comparative Examples 4-6 and Examples 1-3 were applied to gold plating on a nickel substrate, specifically in the following steps:

[0113] The degreasing powder is dissolved in water to prepare a degreasing solution with a mass fraction of 8%, the nickel substrate is placed in the degreasing solution, heated to 70°C, soaked for 5 minutes, taken out and washed with ultrapure water to obtain a degreasing nickel substrate, and then the electrolytic degreasing powder is dissolved in water to prepare an electrolytic degreasing solution with a mass fraction of 8%, the degreasing nickel substrate is placed in the electrolytic degreasing solution, heated to 70°C, soaked for 5 minutes, taken out and washed with ultrapure water to obtain an electrolytic degreasing nickel substrate, then the electrolytic degreasing nickel substrate is placed in a dilute sulfuric acid solution with a mass fraction of 5-10%, activated for 2 minutes, taken out and washed with ultrapure water, and dried to obtain a treated nickel substrate, the treated nickel substrate is immersed in the cyanide-free gold plating solution of Examples 1-3 and Comparative Examples 4-6, the electroplating gold adopts a high-frequency DC power supply, the circuit density is 0.1A / dm2, the anode is a platinum-plated titanium mesh, the temperature is 20°C, pH=10.5, the time is 200s, the anode is moved and stirred to obtain a gold-plated nickel plate.

[0114] According to GB / T6458-1986 "Neutral Salt Spray Test for Metal Covering (NSS Test)", a neutral smoke test was conducted for 192 hours. The appearance of Examples 1-3 and Comparative Examples 1-3 was observed to see whether there were obvious corrosion spots, and the results were recorded in a table as shown in Table 2.

[0115] Table 2 Corrosion points and corrosion degree table

[0116]

[0117] It can be seen that after the salt spray test, no corrosion spots appeared in Examples 1-3, which have good strength and corrosion resistance. However, due to the lack of histidine, corrosion spots appeared in Comparative Example 4 after 192h of salt spray test, and a smaller corrosion area of ​​about 0.5% was produced. It can be seen that after the loss of histidine, the ability of sodium 2-mercaptoethane sulfonate to provide electrons to the Au nucleus is weakened, the gold plating process is unstable, and the thickness of the coating film is uneven, resulting in corrosion spots in some positions. Comparative Example 5 lacks 3-mercaptopropionic acid, which makes its plating solution more unstable. The corrosion area of ​​the coating film after the salt spray test is larger than that of Comparative Example 4, reaching 1.6%. Comparative Example 6, which does not add sodium 2-mercaptoethane sulfonate, lacks a stabilizer and cannot make Au deposited stably, resulting in a thin and uneven coating as a whole, resulting in a corrosion area of ​​up to 5.4%.

[0118] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A cyanide-free gold plating solution, characterized in that The invention comprises the following components: 30-120 parts by volume of a main ligand, 20-140 parts by volume of an auxiliary ligand, 10-150 parts by volume of chloroauric acid, 0.1-15 parts by volume of a stabilizing additive and 20-200 parts by volume of methanol; The main ligand is prepared by mixing choline chloride, urea and 5,5-dimethylhydantoin; the auxiliary ligand is prepared by mixing potassium citrate, boric acid and sodium dodecyl sulfate; and the stabilizing additive is prepared by mixing histidine, sodium 2-mercaptoethane sulfonate and 3-mercaptopropionic acid.

2. A method for preparing a cyanide-free gold plating solution, characterized in that: The following steps are involved: S1: Preparation of primary ligand Add choline chloride to a desiccator, seal and heat to dry, to obtain dry choline chloride, take urea and add it to another desiccator, seal and dry to obtain dry urea, mix the dry choline chloride and dry urea, seal and heat, and stir until the system is gradually converted into a uniform and transparent liquid to obtain an ionic liquid, add dry 5,5-dimethylhydantoin powder to the ionic liquid to obtain a main ligand, and place it in a sealed desiccator for standby use; S2: Preparation of auxiliary complexing agent Dilute chloroauric acid with deionized water and centrifuge for 10-20 minutes to obtain liquid A, dissolve potassium citrate and boric acid in water, add sodium dodecyl sulfate under stirring, and then slowly add KOH to adjust the pH value of the solution to obtain liquid B, stir liquid A and liquid B in a water bath, cool to room temperature after the reaction is completed, and then put into an oven for drying to obtain an auxiliary coordination agent, which is placed in a sealed desiccator for standby use; S3: Preparation of stabilizing additives A histidine solution and a sodium 2-mercaptoethane sulfonate solution are prepared, and the histidine solution and the sodium 2-mercaptoethane sulfonate solution are mixed under vigorous stirring to obtain a mixed solution, and 3-mercaptopropionic acid is then added dropwise under stirring. After the addition of 3-mercaptopropionic acid is completed, the mixture is allowed to stand in the dark to obtain a stabilizing additive, and the stabilizing additive is stored at 2-4° C. for later use; S4: Preparation of cyanide-free gold plating solution Nitrogen is continuously introduced into the reactor. After removing the air, 30-120 parts by volume of the main ligand, 20-140 parts by volume of the auxiliary ligand, 10-150 parts by volume of chloroauric acid, 0.1-15 parts by volume of the stabilizing additive and 20-200 parts by volume of methanol are added into the reactor, stirred with a magnetic rotor and in an oil bath until the solid in the system is completely dissolved to obtain a cyanide-free gold plating solution.

3. The method for preparing a cyanide-free gold plating solution according to claim 2, wherein: Step S1: preparing a primary coordination agent, comprising the following steps: S1.1: Add choline chloride to a dryer, evacuate it, seal it with three layers of plastic film, heat it to 70-80℃ and dry it for 20-24h to obtain dry choline chloride, add urea to another dryer, seal it and dry it in an oven at 80-100℃ for 15-20h to obtain dry urea; S1.2: Mix dry choline chloride and dry urea in a molar ratio of 1:(1.5-2), heat in a sealed state at 75-80°C, and stir at a speed of 500-800 r / min until the system is gradually converted into a uniform transparent liquid to obtain an ionic liquid; S1.3: Add dry 5,5-dimethylhydantoin powder to the ionic liquid with a solid-liquid ratio of 1:(5-10), cool to 50-60℃ and centrifuge for 10-20min to obtain the main ligand, which is then placed in a sealed desiccator for later use.

4. The method for preparing a cyanide-free gold plating solution according to claim 3, wherein step S2 prepares an auxiliary coordination agent, comprising the following steps: S2.1: Dilute chloroauric acid and deionized water in a ratio of 1:(2-10), then centrifuge at 500-800 rpm for 10-20 min to obtain solution A; S2.2: Dissolve 0.2-0.4 mol / L potassium citrate and 0.5-0.8 mol / L boric acid in water, add 0.5-1 mol / L sodium dodecyl sulfate under stirring, then slowly add KOH to adjust the pH value of the solution to 4-5, stir well for 0.5-1h, and obtain solution B; S2.3: Stir liquid A and liquid B in a water bath at 65-70°C for 2-3 hours. After the reaction is completed, cool to room temperature and dry in an oven at 100-120°C for 15-20 hours to obtain an auxiliary complexing agent, which is then placed in a sealed desiccator for later use.

5. The method for preparing a cyanide-free gold plating solution according to claim 4, wherein: Step S3 prepares a stabilizing additive, comprising the following steps: S3.1: preparing 15-20 parts by volume of a histidine solution having a concentration of 0.1-0.2 mol / L and 5-8 parts by volume of a sodium 2-mercaptoethane sulfonate solution having a concentration of 0.01-0.05 mol / L; S3.2: Mix the histidine solution and the sodium 2-mercaptoethane sulfonate solution under vigorous stirring to obtain a mixed solution, and then add 3-mercaptopropionic acid dropwise at a rate of 1-5 ml / s under stirring; S3.3: After the addition of 3-mercaptopropionic acid is completed, the reaction bottle is placed at 20-25°C in the dark for 1-2 hours to obtain a stabilizing additive, and the stabilizing additive is stored at 2-4°C for later use.

6. The method for preparing a cyanide-free gold plating solution according to claim 5, wherein: The volume ratio of potassium citrate, boric acid and sodium dodecyl sulfate in step S2.2 is 3:1:

3.

7. The method for preparing a cyanide-free gold plating solution according to claim 6, wherein: The volume ratio of liquid A to liquid B in step S2.3 is 1:

1.

8. The method for preparing a cyanide-free gold plating solution according to claim 7, wherein: In step S3.2, the volume ratio of 3-mercaptopropionic acid to the mixed solution is 1:

1.

9. The use of the cyanide-free gold plating solution in gold plating according to claim 1, characterized in that: The method comprises the following steps: dissolving degreasing powder in water to prepare a degreasing solution with a mass fraction of 5-8%, placing a nickel substrate in the degreasing solution, heating the solution to 60-70°C, soaking the substrate for 1-5 minutes, taking the substrate out and washing it with ultrapure water to obtain a degreasing nickel substrate, and then dissolving the electrolytic degreasing powder in water to prepare an electrolytic degreasing solution with a mass fraction of 5-8%, placing the degreasing nickel substrate in the electrolytic degreasing solution, heating the solution to 60-70°C, soaking the substrate for 1-5 minutes, taking the substrate out and washing it with ultrapure water to obtain an electrolytic degreasing nickel substrate. The electrolytically degreased nickel substrate is then placed in a dilute sulfuric acid solution with a mass fraction of 5-10%, activated for 1-2 minutes, taken out and washed with ultrapure water, and dried to obtain a treated nickel substrate, and the treated nickel substrate is immersed in a cyanide-free gold plating solution. The gold plating adopts a high-frequency DC power supply, a circuit density of 0.01-0.5A / dm2, a platinum-plated titanium mesh as the anode, a temperature of 20-40°C, a pH of 8.5-10.5, a time of 30-200s, and the anode is moved and stirred to obtain a gold-plated nickel plate.

10. The use of a cyanide-free gold plating solution according to claim 9, characterized in that: The degreasing powder is specifically HJ-W122 degreasing powder.

Images