A cyanide-free electrolyte for hard gold electroforming and its preparation process

Abstract

The present invention provides a cyanide-free electrolyte for hard gold electroforming and a preparation process thereof, belonging to the technical field of gold plating processes; the preparation process comprises the following steps: adding 4-dimethylaminopyridine to react and prepare additive A; adding lithium tert-butoxide to react and prepare additive B; preparing an AuCl3 solution; dissolving 5,5-dimethylhydantoin and adding each component. The present invention is prepared by stirring and mixing N-acetyl-L-cysteine, triphenylmethanol and dichloromethane and mixing them with trifluoroacetic acid; after vacuum distillation, purification and elution, triethylamine, 4-dimethylaminopyridine and acetic anhydride are added to react, and trifluoroacetic acid and triethylsilane are added to react to prepare additive A. After adding the cyanide-free electrolyte, during the gold electroplating process, the additive A can effectively promote the formation of crystal nuclei, prevent excessive grain growth, and promote gold grain refinement. The fine and evenly distributed grain structure can significantly improve the hardness and wear resistance of the coating.

Description

Technical Field

[0001] The invention relates to the technical field of gold plating technology, and in particular to a cyanide-free electrolyte for hard gold electroforming and a preparation process thereof. Background Art

[0002] Gold plating, with its excellent corrosion resistance, stable conductivity, and low contact resistance, is widely used as a functional coating in printed circuit boards (PCBs), precision electronic devices, electronic interconnects, plug-and-play devices, and other fields. Gold plating is typically electroplated using a gold electroforming solution. In traditional electroforming processes, cyanide is widely used as a primary component in the plating solution because it effectively promotes metal deposition and ensures the smoothness and continuity of the coating. However, the high toxicity of cyanide poses a serious threat to production safety, environmental protection, and worker health. Its storage, transportation, use, and waste disposal require strict compliance with environmental regulations, resulting in increased costs and significant risks.

[0003] In recent years, with the increasingly stringent environmental protection regulations and the urgent demand of society for sustainable development, the development of cyanide-free electroforming technology has become an inevitable trend in the development of the industry. Cyanide-free electroforming liquid can not only avoid the hazards of cyanide, but also meet the requirements of modern production for high efficiency and environmental protection, and promote the green transformation of the gold electroforming industry. Although some cyanide-free electroforming liquids have been developed and applied, these solutions often have limitations in electroforming efficiency, coating hardness, wear resistance and stability, and it is difficult to completely replace traditional cyanide electroplating liquids, resulting in a relatively short service life of the gold plating obtained by electroplating with cyanide-free electroforming liquid.

[0004] In view of this, it is necessary to propose a cyanide-free electrolyte for hard gold electroforming and a preparation process thereof that can improve the hardness and wear resistance of the gold plating layer, so as to extend the service life of the gold plating layer. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a cyanide-free electrolyte for hard gold electroforming and a preparation process thereof.

[0006] A cyanide-free electrolyte for hard gold electroforming, comprising, by weight:

[0007] 10-12 parts of AuCl3 solution, 30-35 parts of 5,5-dimethylhydantoin, 70-80 parts of potassium chloride, 20-30 parts of anhydrous ethanol, 10-20 parts of additive A, 10-20 parts of additive B, 1-3 parts of cinnamaldehyde, 8-10 parts of polyacrylamide, 30-35 parts of a composite buffer and 50-60 parts of deionized water, wherein the composite buffer is prepared by mixing citric acid and disodium hydrogen phosphate in a mass ratio of (1-3):1.

[0008] A process for preparing a cyanide-free electrolyte for hard gold electroforming comprises the following steps:

[0009] S1: Add 4-dimethylaminopyridine to react and prepare additive A

[0010] N-acetyl-L-cysteine ​​and triphenylmethanol are stirred and mixed with dichloromethane, and then trifluoroacetic acid is added. After distillation under reduced pressure, purification and elution, the mixture is dissolved in dichloromethane, and triethylamine, 4-dimethylaminopyridine and acetic anhydride are added to react. Finally, the mixture is mixed with trifluoroacetic acid and triethylsilane to react to obtain additive A.

[0011] S2: Add lithium tert-butoxide to react and prepare additive B

[0012] Ethylene oxide and 1,3-dimethyl-2-imidazolidinone are stirred and mixed with dimethylformamide, and lithium tert-butoxide is added, heated for reaction, and then poured into deionized water, stirred, filtered and recrystallized to obtain additive B;

[0013] S3: Prepare AuCl3 solution

[0014] After pretreatment, pure gold is added to aqua regia, heated and stirred to dissolve, and then added to deionized water to prepare a gold-containing solution. Then, sodium hydroxide solution is added to adjust the pH to obtain an AuCl3 solution.

[0015] S4: Dissolve 5,5-dimethylhydantoin and add the components

[0016] 5,5-dimethylhydantoin is dissolved in deionized water, and then sodium hydroxide solution is added to adjust the pH, and then the AuCl3 solution, the additive A, the additive B, potassium chloride, cinnamaldehyde, polyacrylamide and a composite buffer are added to obtain a cyanide-free electrolyte.

[0017] Furthermore, S1 specifically includes the following steps:

[0018] S1.1: Add N-acetyl-L-cysteine ​​and triphenylmethanol to dichloromethane at a solid-liquid ratio of 1 g:(1.6-2) g:(13-15) mL and stir to mix thoroughly to obtain a mixed solution;

[0019] S1.2: Add trifluoroacetic acid to the above mixed solution and continue stirring for 2-3 hours. Then, remove the solvent by distillation under reduced pressure. Purify by silica gel column chromatography and elution with an eluent to obtain intermediate A.

[0020] S1.3: Add the above intermediate A to dichloromethane at a solid-liquid ratio of 1 g:(30-40) mL. Stir and mix, then place in an ice-water bath at 1-3°C. Add triethylamine, 4-dimethylaminopyridine, and acetic anhydride. Stir and react for 10-12 hours. Then, remove the solvent by distillation under reduced pressure. Purify by silica gel column chromatography using an eluent to obtain intermediate B.

[0021] S1.4: Dissolve the intermediate B in dichloromethane at a solid-liquid ratio of 1 g:(40-50) mL. Add trifluoroacetic acid and triethylsilane. Stir the mixture for 3-4 h. Remove the solvent by distillation under reduced pressure. Purify the mixture by silica gel column chromatography and elute with an eluent to obtain additive A.

[0022] Furthermore, S2 specifically includes the following steps:

[0023] S2.1: Add equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone to dimethylformamide and stir thoroughly to obtain a mixed solution;

[0024] S2.2: Add lithium tert-butoxide to the mixed solution, stir thoroughly, heat to 60-70°C, and keep the mixture for 1-2 hours to obtain a precursor solution;

[0025] S2.3: Pour the above precursor solution into deionized water, stir at a rate of 200-300 r / min for 10-20 min, and then filter and recrystallize to obtain additive B.

[0026] Furthermore, S3 specifically includes the following steps:

[0027] S3.1: Chop pure gold, wash, and dry it. Add it to aqua regia at a solid-to-liquid ratio of 1 g:(11-13) mL. Heat and stir at 80-90°C to dissolve until a blood-red, thick substance forms.

[0028] S3.2: Deionized water is added to the above blood-red viscous material to prepare a gold-containing solution with a mass fraction of 20-30%, and sodium hydroxide solution is added to adjust the pH to 6-7 to obtain an AuCl3 solution.

[0029] Furthermore, S4 specifically includes the following steps:

[0030] S4.1: Add 5,5-dimethylhydantoin to deionized water, heat to 40-50°C, and stir to dissolve. Then, add sodium hydroxide solution to adjust the pH to 10-11 to obtain Solution A.

[0031] S4.2: Add the AuCl3 solution prepared in step S3.2 to the above solution A while stirring, and heat at 40-50°C until the solution becomes colorless to obtain solution B;

[0032] S4.3: Add anhydrous ethanol, additive A obtained in step S1.4, and additive B obtained in step S2.3 to the above-mentioned liquid B, stir and mix evenly, then add potassium chloride, cinnamaldehyde, and polyacrylamide, continue stirring and mixing, and then add a composite buffer to adjust the pH to 9-10 to obtain a cyanide-free electrolyte.

[0033] Furthermore, the volume ratio of trifluoroacetic acid to dichloromethane is 1:(3-5), and the eluent is dichloromethane and methanol in a volume ratio of (70-80):1.

[0034] Furthermore, the mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A is 1:(9-11):(30-36), and the solid-liquid ratio of intermediate A to triethylamine is 1 g:(0.8-1) mL.

[0035] Furthermore, the solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane is 1 g: (6-8) mL: (0.6-0.8) mL.

[0036] Furthermore, the solid-liquid ratio of ethylene oxide to dimethylformamide is 1 g: (40-50) mL, and the mass ratio of lithium tert-butoxide to ethylene oxide is (1.5-2.5):1.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention comprises the following steps: stirring and mixing N-acetyl-L-cysteine, triphenylmethanol and dichloromethane and mixing them with trifluoroacetic acid; performing reduced pressure distillation, purification and elution; and then adding triethylamine, 4-dimethylaminopyridine and acetic anhydride to react; and adding trifluoroacetic acid and triethylsilane to react. Additive A is prepared by adding the additive to a cyanide-free electrolyte. When the additive is added to a gold electroplating process, the additive can effectively promote the formation of crystal nuclei, prevent excessive grain growth, and promote gold grain refinement. The fine and evenly distributed grain structure can significantly improve the hardness and wear resistance of the coating.

[0039] 2. The present invention obtains an additive B by stirring and mixing equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone with dimethylformamide, and then adding lithium tert-butoxide to react. After the additive B is added to a cyanide-free electrolyte, the additive B has good surface activity and can form an effective adsorption layer between the cyanide-free electrolyte and the substrate. The adsorption effect can change the double electric layer structure of the electrode interface and affect the charge distribution, thereby promoting the uniform deposition of gold ions during the electroplating process, reducing uneven growth, making the coating smoother, and affecting the crystallization process, prompting the metal deposition to appear in the form of smaller and more uniform grains, reducing scattering between crystal planes, enhancing the reflection effect, and thus increasing the gloss of the coating. In addition, by adding the additive B and the additive A to the cyanide-free electrolyte at the same time, the hardness and corrosion resistance of the gold coating formed by electroplating can be improved while ensuring high deposition efficiency.

[0040] 3. After adding cinnamaldehyde to the cyanide-free electrolyte, the present invention regulates the electrodeposition process through complexation with gold ions, promotes the formation of a more uniform and fine grain structure, and thus enhances the wear resistance of the coating. In addition, cinnamaldehyde and additive A have a synergistic effect, and the two further improve the hardness and wear resistance of the coating through the synergistic effect.

[0041] 4. After polyacrylamide is added to the cyanide-free electrolyte in the present invention, the active groups on the polyacrylamide molecules can be adsorbed to the surface of the solid particles in the electrolyte, so that the surface of the particles is fully wetted, the mutual attraction between the particles is reduced, and the uniform dispersion of the particles is promoted. At the same time, the surface tension of the system is reduced and the dynamic stability of the system is increased, thereby helping gold ions to be more evenly deposited on the surface of the substrate, forming a denser and smoother coating, which can effectively resist the penetration of corrosive media and improve the corrosion resistance of the formed gold coating. DETAILED DESCRIPTION

[0042] The following describes in detail a cyanide-free electrolyte for hard gold electroforming and its preparation process, provided by the present invention, with reference to specific examples. It is also noted that, for the sake of completeness, the following examples are best and preferred embodiments, and those skilled in the art may employ alternative methods for implementing known techniques.

[0043] Example 1

[0044] A process for preparing a cyanide-free electrolyte for hard gold electroforming comprises the following steps:

[0045] S1: Add 4-dimethylaminopyridine to react and prepare additive A

[0046] N-acetyl-L-cysteine ​​and triphenylmethanol were added to dichloromethane at a solid-liquid ratio of 1g:1.6g:13mL, stirred and mixed to obtain a mixed solution, and then trifluoroacetic acid was added to the mixed solution, and the stirring was continued for 2h. The solvent was then distilled off under reduced pressure, and the mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A, wherein the volume ratio of trifluoroacetic acid to dichloromethane was 1:3. The intermediate A was added to dichloromethane at a solid-liquid ratio of 1g:30mL, stirred and mixed, and placed in an ice-water bath at 1°C, and triethylamine, 4-dimethylaminopyridine and acetic anhydride were added. The mixture was stirred and reacted for 10h, and the solvent was then distilled off under reduced pressure. The mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A. Purification by column chromatography and elution with an eluent to obtain intermediate B, wherein the mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A is 1:9:30, and the solid-liquid ratio of intermediate A to triethylamine is 1 g:0.8 mL. Subsequently, intermediate B is dissolved in dichloromethane at a solid-liquid ratio of 1 g:40 mL, and trifluoroacetic acid and triethylsilane are added, and the reaction is stirred for 3 hours, wherein the solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane is 1 g:6 mL:0.6 mL. The solvent is then removed by distillation under reduced pressure, and the additive A is obtained by purification by column chromatography on silica gel and elution with an eluent, wherein the eluent is dichloromethane and methanol at a volume ratio of 70:1;

[0047] S2: Add lithium tert-butoxide to react and prepare additive B

[0048] Equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone were added to dimethylformamide, and the mixture was thoroughly stirred to obtain a mixed solution. Lithium tert-butoxide was then added to the mixed solution, and the mixture was thoroughly stirred. The mixture was heated to 60° C. and kept warm for 1 hour to obtain a precursor solution, wherein the solid-liquid ratio of ethylene oxide to dimethylformamide was 1 g:40 mL, and the mass ratio of lithium tert-butoxide to ethylene oxide was 1.5:1. The precursor solution was then poured into deionized water, stirred at a rate of 200 r / min for 10 minutes, and then filtered and recrystallized to obtain additive B.

[0049] S3: Prepare AuCl3 solution

[0050] The pure gold was chopped, washed and dried, and then added to aqua regia at a solid-liquid ratio of 1g:11mL, and heated and stirred at 80°C to dissolve until a blood-red viscous substance was formed. Deionized water was then added to the blood-red viscous substance to prepare a gold-containing solution with a mass fraction of 20%, and sodium hydroxide solution was added to adjust the pH to 6-7 to obtain an AuCl3 solution.

[0051] S4: Dissolve 5,5-dimethylhydantoin and add the components

[0052] 30 parts by weight of 5,5-dimethylhydantoin were added to 50 parts of deionized water, heated to 40° C. and stirred to dissolve, and then sodium hydroxide solution was added to adjust the pH to 10 to obtain liquid A. Then, 10 parts of the AuCl3 solution prepared in step S3 were added to liquid A while stirring, and the mixture was heated at 40° C. until the solution became colorless to obtain liquid B. Then, 20 parts of anhydrous ethanol, 10 parts of additive A prepared in step S1, and 10 parts of additive B prepared in step S2 were added to liquid B, and the mixture was stirred and mixed uniformly. Then, 70 parts of potassium chloride, 1 part of cinnamaldehyde, and 8 parts of polyacrylamide were added, and the stirring and mixing was continued. Then, 30 parts of a composite buffer was added to adjust the pH to 9 to obtain a cyanide-free electrolyte, wherein the composite buffer was prepared by mixing citric acid and disodium hydrogen phosphate in a mass ratio of 1:1.

[0053] Then, a copper sheet was used as a substrate, and the copper sheet was wrapped with polyimide tape, leaving a plating area of ​​10 mm × 10 mm in the middle. The above-mentioned cyanide-free electrolyte was used as a plating solution to electroplate gold to obtain a gold-plated copper sheet. The process conditions for electroplating gold were: temperature 40°C, magnetic stirring rate 400 r / min, current density 0.5 A / dm 2 , time: 10 minutes.

[0054] The performance test results are shown in Table 1 below:

[0055] 1. Make small cuts on the surface of the gold-plated layer, touching the base material when making cuts. The distance between the cuts should be less than 2mm. After making cuts, use 3M tape to stick firmly, tear it off quickly, and observe whether the gold-plated layer falls off.

[0056] 2. According to GB / T10125-2021 "Artificial atmosphere corrosion test salt spray test", a neutral salt spray (NSS) test was conducted on an LX-60A salt spray tester, using a continuous spray of 5% NaCl solution, a temperature of 35°C, a pressure of 197.2 kPa, and a test time of 48 hours;

[0057] 3. Use the Junnengda MM6 gloss meter to measure the gloss of the gold-plated layer at a measuring angle of 60°;

[0058] 4. Use HXD-1000B microhardness tester to measure the hardness of the gold-plated layer. The test conditions are: load 25g, load time 15s.

[0059] Example 2

[0060] S1: Add 4-dimethylaminopyridine to react and prepare additive A

[0061] N-acetyl-L-cysteine ​​and triphenylmethanol were added to dichloromethane at a solid-liquid ratio of 1g:1.8g:14mL, stirred and mixed to obtain a mixed solution, and then trifluoroacetic acid was added to the mixed solution, and the stirring was continued for 2.5h. The solvent was removed by distillation under reduced pressure, and the mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A, wherein the volume ratio of trifluoroacetic acid to dichloromethane was 1:4. The intermediate A was added to dichloromethane at a solid-liquid ratio of 1g:35mL, stirred and mixed, and placed in a 2°C ice water bath, and triethylamine, 4-dimethylaminopyridine and acetic anhydride were added, and the reaction was stirred for 11h. The solvent was then removed by distillation under reduced pressure, and the mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A. Purification by column chromatography and elution with an eluent afforded an intermediate B, wherein the mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A was 1:10:33, and the solid-liquid ratio of intermediate A to triethylamine was 1 g:0.9 mL. Subsequently, the intermediate B was dissolved in dichloromethane at a solid-liquid ratio of 1 g:45 mL, and trifluoroacetic acid and triethylsilane were added, and the reaction was stirred for 3.5 hours, wherein the solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane was 1 g:7 mL:0.7 mL. The solvent was then removed by distillation under reduced pressure, and the additive A was obtained by purification by column chromatography on silica gel and elution with an eluent, wherein the eluent consisted of dichloromethane and methanol at a volume ratio of 75:1;

[0062] S2: Add lithium tert-butoxide to react and prepare additive B

[0063] Equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone were added to dimethylformamide, and the mixture was thoroughly stirred to obtain a mixed solution. Lithium tert-butoxide was then added to the mixed solution, and the mixture was thoroughly stirred. The mixture was heated to 65° C. and kept warm for 1.5 hours to obtain a precursor solution, wherein the solid-liquid ratio of ethylene oxide to dimethylformamide was 1 g:45 mL, and the mass ratio of lithium tert-butoxide to ethylene oxide was 2:1. The precursor solution was then poured into deionized water, stirred at a rate of 250 r / min for 15 minutes, and then filtered and recrystallized to obtain additive B.

[0064] S3: Prepare AuCl3 solution

[0065] The pure gold was chopped, washed and dried, and then added to aqua regia at a solid-liquid ratio of 1 g: 12 mL. The mixture was heated and stirred at 80-90°C to dissolve until a blood-red viscous substance was formed. Deionized water was then added to the blood-red viscous substance to prepare a gold-containing solution with a mass fraction of 25%. Sodium hydroxide solution was then added to adjust the pH to 6.5 to obtain an AuCl3 solution.

[0066] S4: Dissolve 5,5-dimethylhydantoin and add the components

[0067] 33 parts of 5,5-dimethylhydantoin by weight were added to 55 parts of deionized water, heated to 45° C. and stirred to dissolve, and then sodium hydroxide solution was added to adjust the pH to 10.5 to obtain liquid A. Then, 11 parts of the AuCl3 solution prepared in step S3 were added to liquid A while stirring, and the mixture was heated at 45° C. until the solution became colorless to obtain liquid B. Then, 25 parts of anhydrous ethanol, 15 parts of additive A prepared in step S1, and 15 parts of additive B prepared in step S2 were added to liquid B, and the mixture was stirred and mixed uniformly. Then, 75 parts of potassium chloride, 2 parts of cinnamaldehyde, and 9 parts of polyacrylamide were added, and the stirring and mixing was continued. Then, 33 parts of a composite buffer was added to adjust the pH to 9.5 to obtain a cyanide-free electrolyte, wherein the composite buffer was prepared by mixing citric acid and disodium hydrogen phosphate in a mass ratio of 2:1.

[0068] Then, the performance test was performed according to the performance test method in Example 1.

[0069] Example 3

[0070] S1: Add 4-dimethylaminopyridine to react and prepare additive A

[0071] N-acetyl-L-cysteine ​​and triphenylmethanol were added to dichloromethane at a solid-liquid ratio of 1g:2g:15mL, stirred and mixed to obtain a mixed solution, and then trifluoroacetic acid was added to the mixed solution, and the stirring was continued for 3h. The solvent was then distilled off under reduced pressure, and the mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A, wherein the volume ratio of trifluoroacetic acid to dichloromethane was 1:5. The intermediate A was added to dichloromethane at a solid-liquid ratio of 1g:40mL, stirred and mixed, and placed in a 3°C ice water bath. Triethylamine, 4-dimethylaminopyridine and acetic anhydride were added, and the mixture was stirred and reacted for 12h. The solvent was then distilled off under reduced pressure, and the mixture was purified by silica gel column chromatography and eluted with an eluent to obtain an intermediate A. Purification by column chromatography and elution with an eluent to obtain intermediate B, wherein the mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A is 1:11:36, and the solid-liquid ratio of intermediate A to triethylamine is 1 g:1 mL. Subsequently, intermediate B is dissolved in dichloromethane at a solid-liquid ratio of 1 g:50 mL, and trifluoroacetic acid and triethylsilane are added, and the reaction is stirred for 4 hours, wherein the solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane is 1 g:8 mL:0.8 mL. The solvent is then removed by distillation under reduced pressure, and the additive A is obtained by purification by column chromatography on silica gel and elution with an eluent, wherein the eluent is dichloromethane and methanol at a volume ratio of 80:1;

[0072] S2: Add lithium tert-butoxide to react and prepare additive B

[0073] Equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone were added to dimethylformamide, and the mixture was thoroughly stirred to obtain a mixed solution. Lithium tert-butoxide was then added to the mixed solution, and the mixture was thoroughly stirred. The mixture was heated to 70° C. and kept warm for 2 hours to obtain a precursor solution, wherein the solid-liquid ratio of ethylene oxide to dimethylformamide was 1 g:50 mL, and the mass ratio of lithium tert-butoxide to ethylene oxide was 2.5:1. The precursor solution was then poured into deionized water, stirred at a rate of 300 r / min for 20 minutes, and then filtered and recrystallized to obtain additive B.

[0074] S3: Prepare AuCl3 solution

[0075] Pure gold was chopped, washed, and dried, and then added to aqua regia at a solid-liquid ratio of 1 g:13 mL, and heated and stirred at 90°C to dissolve until a blood-red viscous substance was formed. Deionized water was then added to the blood-red viscous substance to prepare a gold-containing solution with a mass fraction of 30%, and sodium hydroxide solution was added to adjust the pH to 7 to obtain an AuCl3 solution.

[0076] S4: Dissolve 5,5-dimethylhydantoin and add the components

[0077] 35 parts of 5,5-dimethylhydantoin by weight were added to 60 parts of deionized water, heated to 50° C. and stirred to dissolve, and then sodium hydroxide solution was added to adjust the pH to 11 to obtain liquid A. Then, 12 parts of the AuCl3 solution prepared in step S3 were added to liquid A while stirring, and the mixture was heated at 50° C. until the solution became colorless to obtain liquid B. Then, 30 parts of anhydrous ethanol, 20 parts of additive A prepared in step S1, and 20 parts of additive B prepared in step S2 were added to liquid B, and the mixture was stirred and mixed uniformly. Then, 80 parts of potassium chloride, 3 parts of cinnamaldehyde, and 10 parts of polyacrylamide were added, and the stirring and mixing was continued. Then, 35 parts of a composite buffer was added to adjust the pH to 10 to obtain a cyanide-free electrolyte, wherein the composite buffer was prepared by mixing citric acid and disodium hydrogen phosphate in a mass ratio of 3:1.

[0078] Then, a copper sheet was used as a substrate, and the copper sheet was wrapped with polyimide tape, leaving a plating area of ​​10 mm × 10 mm in the middle. The above-mentioned cyanide-free electrolyte was used as a plating solution to electroplate gold to obtain a gold-plated copper sheet. The process conditions for electroplating gold were: temperature 40°C, magnetic stirring rate 400 r / min, current density 0.5 A / dm 2 , time: 10 minutes.

[0079] The performance test results are shown in Table 1 below:

[0080] 1. Make small cuts on the surface of the gold-plated layer, touching the base material when making cuts. The distance between the cuts should be less than 2mm. After making cuts, use 3M tape to stick firmly, tear it off quickly, and observe whether the gold-plated layer falls off.

[0081] 2. According to GB / T10125-2021 "Artificial atmosphere corrosion test salt spray test", a neutral salt spray (NSS) test was carried out on an LX-60A salt spray tester, using 5% NaCl solution for continuous spraying, a temperature of 35°C, a pressure of 197.2 kPa, and a test time of 48 hours;

[0082] 3. Use the Junnengda MM6 gloss meter to measure the gloss of the gold-plated layer at a measuring angle of 60°;

[0083] 4. Use HXD-1000B microhardness tester to measure the hardness of the gold-plated layer. The test conditions are: load 25g, load time 15s.

[0084] Table 1: Summary of performance test results of Examples 1-3

[0085]

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 1 is that step S1 is removed, and the additive A in step S4 is removed, and then the performance test is performed according to the performance test method in Example 1. The results are shown in Table 2 below.

[0088] Table 2: Comparative Example 1 and Example 1 Performance Test Results Comparison

[0089] Test items Gold plating adhesion Gold plating corrosion Hardness value (HV) Example 1 Not falling off Uncorroded 82.65 Comparative Example 1 Local shedding More pitting 74.52

[0090] As shown in Table 2 above, the gold-plated layer of Comparative Example 1 partially fell off after the tape was quickly torn off, indicating that the bonding force between the gold-plated layer and the substrate was poor, and the hardness value of the gold-plated layer in Comparative Example 1 was 74.52HV, which was relatively small compared with the gold-plated layer in Example 1. That is, the bonding force and hardness value of the gold-plated layer to the substrate in Example 1 were relatively high, so that the wear resistance of the gold-plated layer in Example 1 was excellent. It can be seen that by stirring and mixing N-acetyl-L-cysteine, triphenylmethanol and dichloromethane and mixing them with trifluoroacetic acid, after reduced pressure distillation, purification and elution, triethylamine, 4-dimethylaminopyridine and acetic anhydride were added to react, and trifluoroacetic acid and triethylsilane were added to react to prepare additive A. After adding it to the cyanide-free electrolyte, in the process of electroplating the gold layer, it can effectively promote the formation of crystal nuclei, prevent excessive growth of grains, and promote the refinement of gold grains. The fine and evenly distributed grain structure can significantly improve the hardness and wear resistance of the coating.

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 1 is that step S2 is removed, and the additive B in step S4 is removed. The performance test is then performed according to the performance test method in Example 1, and the results are shown in Table 3 below.

[0093] Table 3: Comparative Example 2 and Example 1 Performance Test Results Comparison

[0094] Test items Gold plating corrosion Gloss (GU) Hardness value (HV) Example 1 Uncorroded 96.26 82.65 Comparative Example 2 More pitting 74.62 75.18

[0095] As shown in Table 3 above, the gloss of the gold-plated layer in Comparative Example 2 is 74.62GU, which is less than that in Example 1. It can be seen that by stirring and mixing equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone with dimethylformamide, and then adding lithium tert-butoxide to react, an additive B is obtained. After adding the additive to the cyanide-free electrolyte, the additive B has good surface activity and can form an effective adsorption layer between the cyanide-free electrolyte and the substrate. This adsorption can change the double layer structure of the electrode interface and affect the charge distribution, thereby promoting the uniform deposition of gold ions during the electroplating process, reducing uneven growth, making the coating smoother, and affecting the crystallization process, prompting the metal deposition to appear in the form of smaller and more uniform grains, reducing scattering between crystal planes, and enhancing the reflection effect, thereby increasing the gloss of the coating;

[0096] In addition, more pitting appeared on the surface of the gold-plated layer in Comparative Example 1 and Comparative Example 2, and the hardness values ​​were both lower than those in Example 1, indicating that adding Additive B and Additive A to the cyanide-free electrolyte at the same time can ensure high deposition efficiency while also improving the hardness and corrosion resistance of the gold-plated layer formed by electroplating.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 1 is that the cinnamaldehyde in step S4 is replaced by an equal amount of additive A, and the performance test is performed according to the performance test method in Example 1. The results are shown in Table 4 below.

[0099] Comparative Example 4

[0100] The difference between this comparative example and Example 1 is that the additive A in step S4 is replaced with an equal amount of cinnamaldehyde, and the performance test is performed according to the performance test method in Example 1. The results are shown in Table 4 below.

[0101] Table 4: Comparative Example 3-4 and Example 1 Performance Test Results Comparative Example 3-4 and Example 1

[0102]

[0103] As shown in Table 4 above, the gold-plated layers in Comparative Examples 3 and 4 both showed slight detachment, and the hardness values ​​of both were lower than those in Example 1, indicating that the addition of a single additive A and a single cinnamaldehyde resulted in a gold-plated layer with lower bonding strength and hardness than when cinnamaldehyde and additive A were added simultaneously. It can be seen that after adding cinnamaldehyde to the cyanide-free electrolyte, it complexes with gold ions, regulates the electrodeposition process, promotes the formation of a more uniform and fine grain structure, and thus enhances the wear resistance of the coating. In addition, cinnamaldehyde and additive A have a synergistic effect, and the two further improve the hardness and wear resistance of the coating through the synergistic effect.

[0104] Comparative Example 5

[0105] The difference between this comparative example and Example 1 is that the polyacrylamide in step S4 is removed, and then the performance test is performed according to the performance test method in Example 1. The results are shown in Table 5 below.

[0106] Table 5: Comparative Example 5 and Example 1 Performance Test Results Comparative Example 5 and Example 1

[0107] Test items Gold plating corrosion Example 1 Uncorroded Comparative Example 5 Slight pitting

[0108] As shown in Table 5 above, slight pitting occurs on the surface of the gold-plated layer in Comparative Example 5, indicating that after polyacrylamide is added to the cyanide-free electrolyte, the active groups on the polyacrylamide molecules can be adsorbed to the surface of the solid particles in the electrolyte, so that the surface of the particles is fully wetted, the mutual attraction between the particles is reduced, and the uniform dispersion of the particles is promoted. At the same time, the surface tension of the system is reduced and the dynamic stability of the system is increased, thereby helping the gold ions to be more evenly deposited on the surface of the substrate, forming a denser and smoother plating layer, which can effectively resist the penetration of the corrosive medium and improve the corrosion resistance of the formed gold plating layer.

[0109] 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 skilled in 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 one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A cyanide-free electrolyte for hard gold electroforming, characterized in that: In parts by weight, comprising: 10-12 parts of AuCl3 solution, 30-35 parts of 5,5-dimethylhydantoin, 70-80 parts of potassium chloride, 20-30 parts of anhydrous ethanol, 10-20 parts of additive A, 10-20 parts of additive B, 1-3 parts of cinnamaldehyde, 8-10 parts of polyacrylamide, 30-35 parts of a composite buffer and 50-60 parts of deionized water, wherein the composite buffer is prepared by mixing citric acid and disodium hydrogen phosphate in a mass ratio of (1-3):1; N-acetyl-L-cysteine ​​and triphenylmethanol are stirred and mixed with dichloromethane, and then trifluoroacetic acid is added. After distillation under reduced pressure, purification and elution, the mixture is dissolved in dichloromethane, and triethylamine, 4-dimethylaminopyridine and acetic anhydride are added to react. Finally, the mixture is mixed with trifluoroacetic acid and triethylsilane to react to obtain additive A. Ethylene oxide, 1,3-dimethyl-2-imidazolidinone and dimethylformamide are stirred and mixed, and lithium tert-butoxide is added. The mixture is heated for reaction, and then poured into deionized water. Additive B is obtained after stirring, filtering and recrystallization.

2. A process for preparing a cyanide-free electrolyte for hard gold electroforming, characterized in that: The steps include: S1: Add 4-dimethylaminopyridine to react and prepare additive A N-acetyl-L-cysteine ​​and triphenylmethanol are stirred and mixed with dichloromethane, and then trifluoroacetic acid is added. After distillation under reduced pressure, purification and elution, the mixture is dissolved in dichloromethane, and triethylamine, 4-dimethylaminopyridine and acetic anhydride are added to react. Finally, the mixture is mixed with trifluoroacetic acid and triethylsilane to react to obtain additive A. S2: Add lithium tert-butoxide to react and prepare additive B Ethylene oxide and 1,3-dimethyl-2-imidazolidinone are stirred and mixed with dimethylformamide, and lithium tert-butoxide is added, heated for reaction, and then poured into deionized water, stirred, filtered and recrystallized to obtain additive B; S3: Prepare AuCl3 solution After pretreatment, pure gold is added to aqua regia, heated and stirred to dissolve, and then added to deionized water to prepare a gold-containing solution. Then, sodium hydroxide solution is added to adjust the pH to obtain an AuCl3 solution. S4: Dissolve 5,5-dimethylhydantoin and add the components 5,5-dimethylhydantoin is dissolved in deionized water, and then sodium hydroxide solution is added to adjust the pH, and then the AuCl3 solution, the additive A, the additive B, potassium chloride, cinnamaldehyde, polyacrylamide and a composite buffer are added to obtain a cyanide-free electrolyte.

3. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 2, wherein: S1 specifically includes the following steps: S1.1: Add N-acetyl-L-cysteine ​​and triphenylmethanol to dichloromethane at a solid-liquid ratio of 1 g:(1.6-2) g:(13-15) mL and stir to mix thoroughly to obtain a mixed solution; S1.2: Trifluoroacetic acid was added to the mixed solution, and stirring was continued for 2-3 hours. The solvent was then removed by distillation under reduced pressure. The product was purified by silica gel column chromatography using an eluent to obtain intermediate A, wherein the volume ratio of trifluoroacetic acid to dichloromethane was 1:(3-5). S1.3: Add the above intermediate A to dichloromethane at a solid-liquid ratio of 1 g:(30-40) mL. Stir and mix, then place in an ice-water bath at 1-3°C. Add triethylamine, 4-dimethylaminopyridine, and acetic anhydride. Stir and react for 10-12 hours. Then, remove the solvent by distillation under reduced pressure. Purify by silica gel column chromatography using an eluent to obtain intermediate B. S1.4: Dissolve the intermediate B in dichloromethane at a solid-liquid ratio of 1 g:(40-50) mL. Add trifluoroacetic acid and triethylsilane. Stir the mixture for 3-4 h. Remove the solvent by distillation under reduced pressure. Purify the mixture by silica gel column chromatography and elute with an eluent to obtain additive A.

4. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 3, wherein: S2 specifically includes the following steps: S2.1: Add equimolar amounts of ethylene oxide and 1,3-dimethyl-2-imidazolidinone to dimethylformamide and stir thoroughly to obtain a mixed solution; S2.2: Add lithium tert-butoxide to the mixed solution, stir thoroughly, heat to 60-70°C, and keep the mixture for 1-2 hours to obtain a precursor solution; S2.3: Pour the above precursor solution into deionized water, stir at a rate of 200-300 r / min for 10-20 min, and then filter and recrystallize to obtain additive B.

5. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 4, wherein: S3 specifically includes the following steps: S3.1: Chop pure gold, wash, and dry it. Add it to aqua regia at a solid-to-liquid ratio of 1 g:(11-13) mL. Heat and stir at 80-90°C to dissolve until a blood-red, thick substance forms. S3.2: Deionized water is added to the above blood-red viscous material to prepare a gold-containing solution with a mass fraction of 20-30%, and sodium hydroxide solution is added to adjust the pH to 6-7 to obtain an AuCl3 solution.

6. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 5, characterized in that: S4 specifically includes the following steps: S4.1: Add 5,5-dimethylhydantoin to deionized water, heat to 40-50°C, and stir to dissolve. Then, add sodium hydroxide solution to adjust the pH to 10-11 to obtain Solution A. S4.2: Add the AuCl3 solution prepared in step S3.2 to the above solution A while stirring, and heat at 40-50°C until the solution becomes colorless to obtain solution B; S4.3: Add anhydrous ethanol, additive A obtained in step S1.4, and additive B obtained in step S2.3 to the above-mentioned liquid B, stir and mix evenly, then add potassium chloride, cinnamaldehyde, and polyacrylamide, continue stirring and mixing, and then add a composite buffer to adjust the pH to 9-10 to obtain a cyanide-free electrolyte.

7. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 6, characterized in that: The eluent is dichloromethane and methanol in a volume ratio of (70-80):

1.

8. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 7, characterized in that: The mass ratio of 4-dimethylaminopyridine and acetic anhydride to intermediate A is 1:(9-11):(30-36), and the solid-liquid ratio of intermediate A to triethylamine is 1 g:(0.8-1) mL.

9. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 8, characterized in that: The solid-liquid ratio of intermediate B to trifluoroacetic acid and triethylsilane is 1 g: (6-8) mL: (0.6-0.8) mL.

10. The process for preparing a cyanide-free electrolyte for hard gold electroforming according to claim 9, characterized in that: The solid-liquid ratio of ethylene oxide to dimethylformamide is 1 g: (40-50) mL, and the mass ratio of lithium tert-butoxide to ethylene oxide is (1.5-2.5):1.

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