Environment-friendly chemical nanogold liquid and application thereof

Abstract

The invention relates to the technical field of chemical gold plating, in particular to environment-friendly chemical nanogold liquid and application thereof. An environment-friendly chemical nanogold solution comprises the following preparation raw materials including, by mass concentration, 1-3 g / L of sodium gold sulfite, 12-20 g / L of a reducing agent, 48-62 g / L of a composite coordination agent, 25-32 g / L of a pH buffering agent, 20-50 mg / L of a stabilizer, 0.10-0.20 mg / L of a crystal nucleus refiner, 4-7 g / L of a corrosion inhibitor and 0.08-0.12 g / L of a water-soluble ruthenium compound, and the reducing agent is composed of sodium hypophosphite and thiosemicarbazone according to the mass ratio of 5: (2-3). Through synergistic innovation of the components, the environmental protection property, the plating speed, the plating layer quality and the process cost are balanced, the industrial pain points that a traditional chemical gold plating system is high in toxicity, the plating layer is easy to strip, welding is poor and the like are solved, and the industrial application value is remarkable.

Description

Technical Field

[0001] The present application relates to the technical field of chemical gold plating, and in particular to an environmentally friendly chemical nano-gold solution and its application. Background Art

[0002] In the PCB industry, surface treatment is required to ensure reliability and operability in downstream assembly. Chemical nickel-gold (CEGA) is a surface treatment that coats the original substrate with a layer of nickel followed by a layer of gold. This treatment offers the following advantages: 1) high-temperature resistance and excellent solderability; 2) high flatness, making it suitable for the assembly of highly integrated products; and 3) low contact resistance. Consequently, CEGA is widely used.

[0003] While electroless nickel-gold (ENG) offers various advantages, its process also presents difficult-to-overcome technical challenges. Nickel corrosion can occur during the actual process, leading to voids between the gold and nickel layers. This can cause gold shedding, which can cause solder joints on the gold layer to lose their support points, ultimately impacting the electrical performance of the PCB. This nickel corrosion phenomenon is difficult to completely eliminate for the following reasons: First, the nickel deposition reaction is accompanied by hydrogen release, which produces gas. Some of this gas is not promptly removed during the deposition process or remains in the nickel layer as microbubbles. Second, gold is larger than nickel, and the displacement of one nickel layer for two gold layers creates a crowding effect. Third, the nickel layer contains approximately 7% phosphorus, which cannot react with gold, resulting in voids. Industry research on nickel corrosion during ENG has primarily focused on reducing the extent of nickel corrosion during the ENG process to achieve control over terminal soldering reliability and electrical performance. For example, Chinese patent CN201510424488.5 discloses a process for preparing circuit boards using nickel-plated gold (IPG). The IPG process includes, in order, board loading and degreasing; first water washing; pickling; second water washing; pre-dip and activation; third water washing; nickel deposition; fourth water washing; IPG; fifth water washing; and board removal. Existing technologies mitigate nickel corrosion by optimizing pretreatment processes and nickel tank control, but the results are limited. Summary of the Invention

[0004] The present application aims to address the deficiencies of current technologies by providing an environmentally friendly chemical nano-gold solution and its application. The environmentally friendly chemical nano-gold solution of the present application combines fast gold plating rate, high stability, long service life, and excellent adhesion between the gold-plated layer and the nickel-plated layer, good plating solderability, less attack on the nickel layer, good uniformity of the gold-plated layer, and high corrosion resistance. Furthermore, the chemical nano-gold solution does not contain harmful substances such as cyanide and lead compounds, does not affect the production safety of operators or cause pollution to the environment, is safe, and has convenient waste liquid disposal, thus having broad application prospects.

[0005] In the first aspect, the present application provides an environmentally friendly chemical nano-gold solution, which adopts the following technical solution: An environmentally friendly chemical nano-gold liquid comprises the following raw materials, measured by mass concentration: 1-3 g / L of sodium gold sulfite, 12-20 g / L of a reducing agent, 48-62 g / L of a composite ligand, 25-32 g / L of a pH buffer, 20-50 mg / L of a stabilizer, 0.10-0.20 mg / L of a crystal nucleus refiner, 4-7 g / L of a corrosion inhibitor, and 0.08-0.12 g / L of a water-soluble ruthenium compound. The reducing agent is composed of sodium hypophosphite and thiosemicarbazide in a mass ratio of 5:2-3.

[0006] By adopting the above technical solution, the gold source: sodium gold sulfite replaces traditional potassium aurous cyanide, providing a cyanide-free gold source that is environmentally friendly and safe. Au⁺ ions are released through dissociation and serve as the basis for metal deposition. A composite reducing agent (sodium hypophosphite + thiosemicarbazide) is used. Sodium hypophosphite serves as the primary reducing agent, catalytically decomposing to produce H⁻ for Au⁺ reduction. Thiosemicarbazide synergistically accelerates electron transfer, inhibits side reactions (such as hydrogen evolution), and improves reduction efficiency. A synergistic ratio (5:2-3) optimizes the reduction kinetics, increasing plating speed while reducing the risk of bath self-decomposition. A composite ligand, such as disodium EDTA, sodium EDTA (sodium ethylenediaminetetramethylenephosphite), and triammonium citrate, is used. Disodium EDTA has strong chelating properties, stabilizing Au⁺ and preventing hydrolysis and precipitation. Sodium EDTA (sodium ethylenediaminetetramethylenephosphite) enhances the coordination network and suppresses interference from metal impurities. Triammonium citrate provides pH buffering and synergistic coordination, promoting uniform nucleation. Synergistic effect: Multiple ligands form a dynamically stable system, improving the plating bath's lifespan and deposition uniformity. A pH buffer maintains the bath's pH. Potassium dihydrogen phosphate offsets pH fluctuations caused by the reduction reaction, ensuring deposition reaction stability. Stabilizers: Capable of capturing free radicals, quenching singlet oxygen, and selectively oxidizing, they exhibit a strong electron-withdrawing effect, stabilizing the gold plating composition and reducing the risk of gold ion precipitation, thereby extending the bath's lifespan and saving costs. They also significantly improve the uniformity of gold deposition during gold plating, resulting in a dense, smooth, and highly corrosion-resistant gold layer. Nucleation refiners adsorb onto active sites, inhibiting grain coarsening, promoting nanoscale nucleation, and increasing coating density. Corrosion inhibitors, such as those described above, are composed of sodium polyepoxysuccinate, C8-10-fatty alcohol polyoxyethylene ether phosphate monoester, and triethanolamine. The C8-10-fatty alcohol polyoxyethylene ether phosphate monoester forms a dense monolayer on the gold surface. Sodium polyepoxysuccinate fills micropores and enhances film continuity. Triethanolamine: Regulates interfacial wettability and promotes uniform film spreading. Synergistic Effect: Reduces coating porosity and inhibits corrosion current. A water-soluble ruthenium compound co-deposits to form an Au-Ru alloy phase, enhancing the coating's corrosion resistance. Optimizing lattice orientation reduces the formation of brittle intermetallic compounds at the weld interface, improving solder joint reliability. In summary, this formulation achieves efficient deposition, ultra-long life, and comprehensive improvements in corrosion resistance, weldability, and bonding strength through molecular-level functional design and multi-scale synergistic control.

[0007] Preferably, the composite ligand is composed of disodium edetate, sodium edetate tetramethylene phosphine and triammonium citrate in a mass ratio of 5:1:9-11.

[0008] By employing the above technical solution, disodium ethylenediaminetetraacetate (EDTA) forms a stable hexadentate complex with gold ions (Au⁺) through its four carboxylic acid groups and two amino groups, reducing the concentration of free gold ions and delaying spontaneous reduction reactions. It maintains coordination stability in weakly alkaline plating solutions, preventing hydrolysis and precipitation of gold ions. Sodium ethylenediaminetetramethylenephosphonate (EDTMPS): The phosphonic acid group (-PO₃H₂) has superior coordination ability for gold ions compared to the carboxylic acid group, maintaining the complex structure, especially under high temperature or high pH conditions. It preferentially binds to heavy metal impurities such as Fe⁺ and Ni⁺ in the plating solution, reducing their negative impact on the gold plating reaction. Triammonium citrate forms a dynamic coordination equilibrium with gold ions through its hydroxyl and carboxylic acid groups, enhancing the dispersion of gold ions in the solution. The synergistic mechanism of the three agents: 1) Multiple coordination hierarchies are constructed. Disodium EDTA (primary ligand) and sodium EDTMPS (auxiliary ligand) form a rigid-flexible composite coordination network. The strong chelation of disodium EDTA stabilizes the gold ion core structure; the phosphonic acid groups of sodium EDTMPS enhance the complex's resistance to decomposition in the dynamic plating bath environment through steric hindrance and hydrogen bonding. Triammonium citrate serves as a dynamic modulator: its moderate coordination strength allows for gradual dissociation and release of Au⁺ during gold ion deposition, ensuring a controllable deposition rate. 2) Electrochemical synergy: The combined coordination of disodium EDTA and sodium EDTMPS lowers the reduction potential of gold ions, making the reduction reaction more easily controlled by the sodium hypophosphite-thiosemicarbazide system and avoiding localized excessive deposition. The weak reducing properties of triammonium citrate assist the reducing agent, improving gold ion reduction efficiency. Furthermore, its small molecular weight facilitates the diffusion of gold ions onto the substrate surface. 3) Optimized steric hindrance and dispersibility: The long chain structure of sodium EDTMPS creates steric hindrance in the plating solution, inhibiting gold particle agglomeration and ensuring grain refinement in the coating (synergistically with the nucleation refiner). The hydroxyl groups of triammonium citrate adsorb on the gold particle surface, further inhibiting abnormal grain growth and improving coating uniformity. Technical Effects: 1) Improved bath stability: The complex ligand inhibits the spontaneous reduction and precipitation of gold ions through multiple coordination mechanisms, extending the bath life (reducing ineffective gold ion loss). 2) Optimized plating rate and bonding strength: Dynamic coordination equilibrium ensures a stable gold ion release rate, synergistically achieving rapid and uniform deposition with the reducing agent. The ligand adsorbs on the nickel coating surface, forming transitional chemical bonds that strengthen the chemical bonding between the gold and nickel layers (not just physical attachment). 3) Enhanced coating density: The steric hindrance effect of the ligand refines the grain size. Combined with the lattice-directing effect of the ruthenium compound, this results in a dense, porosity-free coating, significantly improving corrosion resistance. The mass ratio of 5:1:9-11 has been verified through experiments to achieve the best balance among bath stability, deposition rate and coating quality.

[0009] Preferably, the stabilizer is composed of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidoxy and 4-tert-butoxycarbonylamino-thiophene-3-carboxylic acid in a mass ratio of 3:2-3.

[0010] By employing the above technical solution, 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidinoyloxy has been developed as a nitroxide compound with free radical scavenging capabilities, combining the hydrophilicity of the amino group with the rigid structure of the pyrrolidine ring. 4-tert-Butoxycarbonylamino-thiophene-3-carboxylic acid: A carboxylic acid derivative containing a thiophene ring, it possesses an electron-withdrawing group (tert-butoxycarbonylamino) and an acidic functional group, enabling selective oxidation of impurities. Its role in gold plating solutions: 1) Free radical scavenging and oxidation inhibition: 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidinoyl, through its stable nitroxide structure, efficiently scavenges free radicals (such as ·OH and ·O⁻) generated by reduction reactions in the plating solution, inhibiting chain oxidation reactions and preventing self-decomposition of the plating solution. The electron-withdrawing group of 4-tert-butyloxycarbonylaminothiophene-3-carboxylic acid reduces the molecular electron cloud density through a conjugation effect, selectively oxidizing metal impurities (such as Fe²⁺ and Ni²⁺), thereby reducing impurity-induced bath failure. 2) Bath Stability and Gold Ion Control: The amino group of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl can weakly coordinate with gold ions ([Au(SO³)²]³⁻) in sodium gold sulfite, slowing down the rapid reduction of gold ions and preventing "empty" plating. The carboxylic acid group of 4-tert-butyloxycarbonylaminothiophene-3-carboxylic acid electrostatically adsorbs onto the surface of gold particles, forming a dynamic protective layer that inhibits gold particle aggregation and improves plating uniformity. 3) Synergistically Enhanced Coating Performance: The rigid structure of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy provides steric hindrance, complementing the planar thiophene ring of 4-tert-butyloxycarbonylamino-thiophene-3-carboxylic acid. Together, they hinder the disordered deposition of gold ions and promote the formation of a dense coating. The positively charged amino groups of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy and the negatively charged carboxylic acid groups of 4-tert-butyloxycarbonylamino-thiophene-3-carboxylic acid form a "molecular network" through electrostatic attraction, enhancing the colloidal stability of the plating solution and reducing microporous defects. In summary, this stabilizer significantly improves plating solution stability and coating quality through a multi-stage synergistic mechanism of free radical capture, oxidation inhibition, charge regulation, and steric hindrance, while simultaneously reducing attack on the nickel substrate.

[0011] Preferably, the pH buffer is dipotassium hydrogen phosphate.

[0012] Preferably, the crystal nucleus refiner is potassium thiosulfate.

[0013] Preferably, the corrosion inhibitor is composed of sodium polyepoxysuccinate, C8-10-fatty alcohol polyoxyethylene ether phosphate monoester and triethanolamine in a mass ratio of 5:92:3.

[0014] By employing this technical solution, sodium polyepoxysuccinate, an environmentally friendly polymer, chelates metal ions through its carboxylic acid groups, preventing metal salts from precipitating and forming scale on the coating surface. Through adsorption within the molecular chain, a primary protective film framework is preferentially formed on the gold surface. The C8-10-fatty alcohol polyoxyethylene ether phosphate monoester exhibits the following effects: 1) Interfacial adsorption: The phosphate groups chemically adsorb onto the gold surface to form a dense monolayer, blocking the penetration of corrosive media (such as Cl⁻ and O₂). 2) Steric hindrance: The long-chain fatty alcohol polyoxyethylene ether structure provides a hydrophobic barrier, reducing the dissolution rate of gold in the electrolyte. 3) Pore filling: The molecular chains penetrate microscopic defects in the coating (pores and grain boundaries), physically blocking them and improving corrosion resistance. Triethanolamine, through its amine groups, neutralizes localized acidic corrosion products (such as H⁺), inhibiting pitting corrosion. It forms a hydrogen bond network with the C8-10-fatty alcohol polyoxyethylene ether phosphate monoester, enhancing the stability of the adsorption film. Three-component synergistic mechanism: (1) Molecular orientation synergy: The linear molecular chains of sodium polyoxysuccinate are first adsorbed on the gold surface, forming a directional base film layer; the phosphate groups of C8-10-fatty alcohol polyoxyethylene ether phosphate monoester are embedded in the film layer through chemical bonding, and its long-chain alkyl groups extend outward to form a hydrophobic barrier; triethanolamine connects the two through hydrogen bonds, filling the molecular gaps and forming a continuous and dense composite film. (2) Dynamic synergy, rapid film formation: The high concentration of the C8-10 component (92%) ensures rapid surface coverage, sodium polyoxysuccinate prevents particle agglomeration through electrostatic repulsion, and triethanolamine regulates interfacial wettability, accelerating the uniform expansion of the film layer. Long-term protection: The chelating ability of sodium polyoxysuccinate inhibits the redeposition of metal ions, the chemical adsorption of the C8-10 component provides a long-lasting barrier, and the dynamic repair mechanism of triethanolamine maintains the integrity of the film. (3) Functional complementarity and improved welding performance: The hydrophobic chain of the C8-10 component reduces surface oxidation of the coating, sodium polyepoxysuccinate inhibits poor solder wetting, and triethanolamine removes residual oxides. The three components work together to reduce the rate of false solder joints / leaked solder joints. Environmental compatibility: All three components do not contain heavy metals / cyanides. Sodium polyepoxysuccinate and triethanolamine are biodegradable and meet the requirements of green chemistry. In short, the corrosion inhibitor achieves multiple performance breakthroughs while maintaining environmental protection through molecular structure complementarity, dynamic film formation synergy and functional integration design. The mass ratio of 5:92:3 is set based on the critical micelle concentration (CMC) of each component, adsorption kinetics and cost optimization, ultimately achieving a synergistic improvement in coating corrosion resistance, welding reliability and plating solution life.

[0015] Preferably, the water-soluble ruthenium compound is one of ruthenium chloride, ruthenium nitrate and ruthenium sulfate.

[0016] By adopting the above technical solution and adding the special rare element ruthenium, the corrosion resistance, density, uniformity and welding performance of the chemical gold plating layer are significantly improved.

[0017] Preferably, the operating temperature is 65-70°C.

[0018] In a second aspect, the present application provides an application of an environmentally friendly chemical nano-gold solution, which adopts the following technical solution: As a general technical concept, the present application also provides a gold plating process of the above-mentioned environmentally friendly chemical nano-gold liquid, wherein the circuit board after the chemical nickel plating treatment is immersed in the environmentally friendly chemical nano-gold liquid at a temperature of 65-70°C and the gold is precipitated for 15-25 minutes.

[0019] In summary, the beneficial technical effects of this application are: 1. Improved environmental protection and safety No harmful substances: Abandoning traditional toxic ingredients such as cyanide and lead compounds, reducing health hazards to operators and reducing environmental pollution risks.

[0020] Easy to handle waste liquid: The components are environmentally friendly, simplifying the waste liquid treatment process and meeting green manufacturing requirements.

[0021] 2. Optimization of plating bath performance High stability and long life: The complex ligand (disodium EDTA, sodium ethylenediaminetetramethylenephosphine, and triammonium citrate) forms a multi-coordination network, enhancing the stability of gold ions and inhibiting spontaneous reduction and precipitation. The stabilizer slows down the decomposition of the plating solution by capturing free radicals and inhibiting singlet oxygen activity, thereby extending the life of the plating solution.

[0022] High-efficiency gold plating rate: Sodium hypophosphite-thiosemicarbazide composite reducing agent synergistically accelerates gold ion reduction, with a plating rate of 0.15-0.18 μm / 20min, a 15%-25% increase over traditional systems.

[0023] 3. Breakthrough in coating quality Bonding and Density: Water-soluble ruthenium compounds form nanoscale crystal nuclei within the coating, refining the structure and strengthening the bond between the gold layer and the nickel substrate. Crystalline refiners regulate the deposition process and reduce porosity.

[0024] Improved corrosion resistance: The corrosion inhibitor (sodium polyepoxysuccinate / C8-10 phosphate / triethanolamine) forms a dense passivation film, significantly improving corrosion resistance.

[0025] Optimized welding performance: Ruthenium and corrosion inhibitors work together to eliminate oxidation on the coating surface, improve the wettability of the solder joints, and significantly reduce the welding rate. DETAILED DESCRIPTION

[0026] The embodiments of the present application will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0027] Example 1, an environmentally friendly chemical nano-gold solution, comprising the following raw materials, measured by mass concentration: 1g / L of sodium gold sulfite, 12g / L of reducing agent, 48g / L of composite ligand, 25g / L of dipotassium hydrogen phosphate, 20mg / L of stabilizer, 0.10mg / L of potassium thiosulfate, 4g / L of corrosion inhibitor, and 0.08g / L of ruthenium chloride, wherein the reducing agent is composed of sodium hypophosphite and thiosemicarbazide in a mass ratio of 5:2, and the composite ligand is 0.08g / L of ruthenium chloride. The invention is composed of disodium ethylenediaminetetraacetate, sodium ethylenediaminetetramethylenephosphine and triammonium citrate in a mass ratio of 5:1:9, the stabilizer is composed of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidoxy and 4-tert-butoxycarbonylamino-thiophene-3-carboxylic acid in a mass ratio of 3:2, and the corrosion inhibitor is composed of sodium polyepoxysuccinate, C8-10-fatty alcohol polyoxyethylene ether monophosphate and triethanolamine in a mass ratio of 5:92:3.

[0028] Example 2, an environmentally friendly chemical nano-gold solution, comprising the following raw materials, measured by mass concentration: 3g / L of sodium gold sulfite, 20g / L of reducing agent, 62g / L of composite ligand, 32g / L of dipotassium hydrogen phosphate, 50mg / L of stabilizer, 0.20mg / L of potassium thiosulfate, 7g / L of corrosion inhibitor, and 0.12g / L of ruthenium nitrate, wherein the reducing agent is composed of sodium hypophosphite and thiosemicarbazide in a mass ratio of 5:3, and the composite ligand is 0.12g / L of ruthenium nitrate. The invention is composed of disodium ethylenediaminetetraacetate, sodium ethylenediaminetetramethylenephosphine and triammonium citrate in a mass ratio of 5:1:11, the stabilizer is composed of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidoxy and 4-tert-butoxycarbonylamino-thiophene-3-carboxylic acid in a mass ratio of 3:3, and the corrosion inhibitor is composed of sodium polyepoxysuccinate, C8-10-fatty alcohol polyoxyethylene ether monophosphate and triethanolamine in a mass ratio of 5:92:3.

[0029] Example 3, an environmentally friendly chemical nano-gold solution, comprising the following raw materials, measured by mass concentration: 2g / L of sodium gold sulfite, 16g / L of reducing agent, 55g / L of composite ligand, 28g / L of dipotassium hydrogen phosphate, 35mg / L of stabilizer, 0.15mg / L of potassium thiosulfate, 5.5g / L of corrosion inhibitor, and 0.1g / L of ruthenium sulfate, wherein the reducing agent is composed of sodium hypophosphite and thiosemicarbazide in a mass ratio of 5:2.5, and the composite ligand is 0.1g / L of ruthenium sulfate. The invention is composed of disodium ethylenediaminetetraacetate, sodium ethylenediaminetetramethylenephosphine and triammonium citrate in a mass ratio of 5:1:10, the stabilizer is composed of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidoxy and 4-tert-butoxycarbonylamino-thiophene-3-carboxylic acid in a mass ratio of 3:2.5, and the corrosion inhibitor is composed of sodium polyepoxysuccinate, C8-10-fatty alcohol polyoxyethylene ether monophosphate and triethanolamine in a mass ratio of 5:92:3.

[0030] Comparative Example 1 The same as Example 3, except that the composite ligand is composed of disodium ethylenediaminetetraacetate and sodium ethylenediaminetetramethylenephosphine in a mass ratio of 5:1.

[0031] Comparative Example 2 The same as Example 3, except that the composite ligand is composed of disodium edetate and triammonium citrate in a mass ratio of 5:10.

[0032] Comparative Example 3 The same as Example 3, except that the composite ligand is composed of sodium ethylenediaminetetramethylenephosphine and triammonium citrate in a mass ratio of 1:10.

[0033] Comparative Example 4 The same as Example 3, except that the stabilizer is 4-tert-butoxycarbonylamino-thiophene-3-carboxylic acid.

[0034] Comparative Example 5 The same as Example 3, except that the stabilizer is 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidoxy.

[0035] Comparative Example 6 The method is the same as Example 3, except that the corrosion inhibitor is composed of sodium polyepoxysuccinate and C8-10-fatty alcohol polyoxyethylene ether phosphate monoester in a mass ratio of 5:92.

[0036] Comparative Example 7 The method is the same as Example 3, except that the corrosion inhibitor consists of C8-10-fatty alcohol polyoxyethylene ether phosphate monoester and triethanolamine in a mass ratio of 92:3.

[0037] Comparative Example 8 The same as Example 3, except that ruthenium sulfate is 0 mg / L.

[0038] Performance Testing The environmentally friendly chemical nanogold solutions prepared in Examples 1 to 3 and Comparative Examples 1 to 8 were sampled, part of the sample solution was tested for stability, and part of the sample solution was subjected to chemical gold plating. The process conditions were: temperature 68° C., time 20 minutes, and the part to be plated was a circuit board after chemical nickel deposition treatment. The following tests were performed, and the test results are shown in Table 1.

[0039] The preparation process of the circuit board after chemical nickel deposition treatment is as follows: (1) Grinding plate sandblasting: After grinding the plate, remove the residue on the copper surface, and sandblast to make the copper surface uniform; (2) Degreasing: Use an acidic degreasing agent to degrease the circuit board to remove organic matter and oxides on the copper surface. Use S-31 acidic degreasing agent provided by SMIT for 3 minutes at a temperature of 60°C. After completion, rinse with water. (3) Microetching: Immerse the circuit board treated in step (2) in a mixture of sodium persulfate and sulfuric acid for 0.5 minutes, and then rinse with water. The concentration of sodium persulfate in the mixture is 120 g / L, and the concentration of sulfuric acid is 40 g / L. (4) pickling: immerse the circuit board treated in step (3) in a 70 g / L sulfuric acid solution for 2 min to remove the oxides remaining on the copper surface after micro-etching, and then rinse with water; (5) Activation: Immerse the circuit board treated in step (4) in the S-32 activator solution provided by SMIT for 1 min, and then rinse with water; (6) Chemical nickel deposition: Immerse the circuit board treated in step (5) in a chemical nickel plating solution containing 20.56 g / L nickel aminosulfate, 27.87 g / L sodium hypophosphite, 21.4 g / L lactic acid (90%), 14.3 g / L malic acid, 15.6 g / L glycine, 5.6 g / L sodium acetate, 4.97 g / L ethylenediamine, and 3.31 ppm thiodiacetic acid. Deposit for 15 min at 78°C, and then rinse with water. 1. Stability test: Take 50mL of chemical nanogold solution and heat it continuously in an 80℃ water bath. Observe and record the time when gold precipitation begins to appear in the bath solution to evaluate the stability of the chemical nanogold solution. 2. Adhesion test: After baking at 290℃ for 3 minutes, if no cracks are seen in the gold layer at 3000 times magnification, it is excellent; after baking at 290℃ for 3 minutes, if occasional cracks are seen in the gold layer at 3000 times magnification, it is good; after baking at 290℃ for 3 minutes, if occasional cracks are seen in the gold layer at 1000 times magnification, it is poor; after baking at 290℃ for 3 minutes, if obvious cracks are seen in the gold layer at 1000 times magnification, it is poor. 3. Coating soldering performance test: 1. Immerse the sample to be tested in a tin furnace (235±5℃), remove it after 4 seconds, cool it down, clean it, and then blow it dry. 2. Check the solder joints under a 30X magnifying glass to see if they are wet and have defects such as pinholes. If the solder joints are wet and free of pinholes, the coating soldering performance is good; if the solder joints have pinholes and are not wet, the coating soldering performance is poor. 4. Corrosion resistance test: According to GB / T10125-2012 artificial atmosphere corrosion test, copper accelerated acetic acid salt spray test (CASS) was carried out. The salt solution used in the salt spray test was added with copper chloride at a concentration of 0.26g / L, and the corrosion resistance time was recorded. 5. Deposition rate: A fluorescence thickness gauge (XRF-2000L) from the Korean Micro Pioneer brand was used to measure the coating thickness and calculate the deposition rate.

[0040] Table 1 Performance test

[0041] Analyzing the data in Table 1, we can see that: 1) The environmentally friendly chemical nano-gold liquid obtained in Examples 1 to 3 has the advantages of fast gold plating rate, high stability, long service life, excellent adhesion between the gold-plated layer and the nickel-plated layer, good plating welding performance, less attack on the nickel layer, good uniformity of the gold-plated layer and high corrosion resistance. At the same time, the chemical nano-gold liquid does not contain harmful substances such as cyanide and lead compounds, will not affect the production safety of operators and cause pollution to the environment, has good safety, convenient waste liquid treatment, and has broad application prospects.

[0042] 2) A comparative analysis of the performance of the environmentally friendly chemical nanogold solutions prepared in Example 3 and Comparative Examples 1-3 shows that the composite ligand is composed of disodium EDTA, sodium EDTP, and triammonium citrate in a mass ratio of 5:1:10. Utilizing their synergistic mechanism: 1) A multi-coordination hierarchy is constructed, with disodium EDTA (primary ligand) and sodium EDTMPS (auxiliary ligand) forming a rigid-flexible composite coordination network. The strong chelation of disodium EDTA stabilizes the gold ion core structure; the phosphonic acid groups of sodium EDTMPS enhance the complex's resistance to decomposition in the dynamic plating bath environment through steric hindrance and hydrogen bonding. Triammonium citrate serves as a dynamic modulator: its moderate coordination strength allows it to gradually dissociate and release Au⁺ during gold ion deposition, ensuring a controllable deposition rate. 2) Electrochemical synergistic effect: The combined coordination of disodium EDTA and sodium EDTMPS lowers the reduction potential of gold ions, making the reduction reaction more easily controlled by the sodium hypophosphite-thiosemicarbazide system and avoiding localized excessive deposition. The weak reducing properties of triammonium citrate complement the reducing agent, improving the efficiency of gold ion reduction. Its small molecular weight facilitates the diffusion of gold ions to the substrate surface. 3) Steric hindrance and optimized dispersibility: The long chain structure of sodium EDTMPS creates steric hindrance in the plating bath, inhibiting gold particle agglomeration and ensuring grain refinement in the coating (synergistically with the core refiner). The hydroxyl groups of triammonium citrate adsorb on the gold particle surface, further inhibiting abnormal grain growth and improving coating uniformity. Technical Effects: 1) Improved bath stability: The combined coordination agent inhibits the spontaneous reduction and precipitation of gold ions through multiple coordination mechanisms, extending the bath life (reducing ineffective gold ion loss). 2) Optimized plating rate and binding strength: Dynamic coordination equilibrium ensures a stable gold ion release rate, synergistically achieving rapid and uniform deposition with the reducing agent. The complexing agent adsorbs onto the surface of the nickel plating, forming a transitional chemical bond that strengthens the chemical bonding between the gold and nickel layers (not just physical adhesion). 3) The density of the plating layer is enhanced. The steric hindrance effect of the complexing agent refines the grain size. Combined with the lattice-directing effect of the ruthenium compound, this forms a dense, porous coating, significantly improving corrosion resistance.

[0043] 3) A comparative analysis of the performance of the environmentally friendly chemical nano-gold solution prepared in combination with Example 3 and Comparative Examples 4-5 shows that the stabilizer is composed of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidone and 4-tert-butoxycarbonylamino-thiophene-3-carboxylic acid in a mass ratio of 3:2.5. The two work together to improve the coating performance: the rigid structure of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidone provides steric hindrance, which complements the planar thiophene ring of 4-tert-butoxycarbonylamino-thiophene-3-carboxylic acid, jointly hindering the disordered deposition of gold ions and promoting the formation of a dense coating. The positively charged amino group of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidone and the negatively charged carboxylic acid group of 4-tert-butoxycarbonylamino-thiophene-3-carboxylic acid form a "molecular network" through electrostatic attraction, enhancing the colloidal stability of the plating solution and reducing micropore defects. In summary, this stabilizer significantly improves the stability of the plating solution and the quality of the coating through a multi-level synergistic mechanism of free radical capture-oxidation inhibition-charge regulation-steric hindrance, while reducing the attack on the nickel substrate.

[0044] 4) The performance comparison analysis of the environmentally friendly chemical nano-gold liquid prepared in combination with Example 3 and Comparative Examples 6-7 shows that the corrosion inhibitor is composed of sodium polyepoxysuccinate, C8-10-fatty alcohol polyoxyethylene ether phosphate monoester and triethanolamine in a mass ratio of 5:92:3, and the synergistic mechanism between them is utilized: (1) Molecular orientation synergy: the linear molecular chain of sodium polyepoxysuccinate is first adsorbed on the gold surface to form a directional base film layer; the phosphate group of C8-10-fatty alcohol polyoxyethylene ether phosphate monoester is embedded in the film layer through chemical bonding, and its long-chain alkyl group extends outward to form a hydrophobic barrier; triethanolamine connects the two through hydrogen bonding, filling the molecular gap to form a continuous and dense composite film. (2) Kinetic synergy and rapid film formation: the high concentration of the C8-10 component (92%) ensures rapid surface coverage, sodium polyepoxysuccinate prevents particle agglomeration through electrostatic repulsion, and triethanolamine adjusts the interfacial wettability to accelerate the uniform expansion of the film layer. Long-term protection: The chelating ability of sodium polyepoxysuccinate inhibits the redeposition of metal ions, the chemical adsorption of the C8-10 component provides a long-lasting barrier, and the dynamic repair mechanism of triethanolamine maintains the integrity of the film. (3) Functional complementarity, improved welding performance: The hydrophobic chain of the C8-10 component reduces surface oxidation of the coating, sodium polyepoxysuccinate inhibits poor solder wetting, and triethanolamine removes oxide residues. The three work together to reduce the rate of cold solder joints / leaked solder joints. Environmental compatibility: All three do not contain heavy metals / cyanide, and sodium polyepoxysuccinate and triethanolamine are biodegradable, meeting the requirements of green chemistry. In short, the corrosion inhibitor achieves multiple performance breakthroughs while maintaining environmental protection through molecular structure complementarity, dynamic film formation synergy and functional integrated design, ultimately achieving a synergistic improvement in coating corrosion resistance, welding reliability and plating solution life.

[0045] 5) Comparative analysis of the performance of the environmentally friendly chemical nano-gold solutions prepared in Example 3 and Comparative Example 8 demonstrates that the addition of a water-soluble ruthenium compound (e.g., ruthenium sulfate) co-deposits an Au-Ru alloy phase, improving the corrosion resistance of the coating. It also optimizes the lattice orientation, reduces the formation of brittle intermetallic compounds at the weld interface, and enhances solder joint reliability.

[0046] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the above embodiments provide a detailed description of the present application, relevant technical personnel should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the scope of protection of the present application.

Claims

1. An environmentally friendly chemical nano-gold solution, characterized in that: Calculated by mass concentration, the preparation comprises the following raw materials: 1-3 g / L of sodium gold sulfite, 12-20 g / L of reducing agent, 48-62 g / L of composite ligand, 25-32 g / L of pH buffer, 20-50 mg / L of stabilizer, 0.10-0.20 mg / L of crystal nucleus refiner, 4-7 g / L of corrosion inhibitor, and 0.08-0.12 g / L of water-soluble ruthenium compound, wherein the reducing agent is composed of sodium hypophosphite and thiosemicarbazide in a mass ratio of 5:2-3; the composite ligand is composed of disodium ethylenediaminetetraacetic acid, sodium ethylenediaminetetramethylenephosphine and triammonium citrate in a mass ratio of 5:1:9-11; and the corrosion inhibitor is composed of sodium polyepoxysuccinate, C8-10-fatty alcohol polyoxyethylene ether phosphate monoester and triethanolamine in a mass ratio of 5:92:

3.

2. The environmentally friendly chemical nano-gold solution according to claim 1, wherein The stabilizer is composed of 3-(aminomethyl)-2,2,5,5-tetramethyl-1-pyrrolidyloxy and 4-tert-butoxycarbonylamino-thiophene-3-carboxylic acid in a mass ratio of 3:2-3.

3. The environmentally friendly chemical nano-gold solution according to claim 1, characterized in that: The pH buffer is dipotassium hydrogen phosphate.

4. The environmentally friendly chemical nano-gold solution according to claim 1, characterized in that: The crystal nucleus refiner is potassium thiosulfate.

5. The environmentally friendly chemical nano-gold solution according to claim 1, characterized in that: The water-soluble ruthenium compound is one of ruthenium chloride, ruthenium nitrate and ruthenium sulfate.

6. The environmentally friendly chemical nano-gold solution according to claim 1, characterized in that: The operating temperature of the environmentally friendly chemical nano-gold solution is 65-70°C.

7. An environmentally friendly chemical nano-gold plating process, characterized in that: The environmentally friendly chemical nano-gold solution according to any one of claim 16 is heated to 65-70° C.; the circuit board after the chemical nickel plating treatment is immersed in the environmentally friendly chemical nano-gold solution at a temperature of 65-70° C. and the gold is precipitated for 15-25 minutes.

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