Ultra-low roughness chemical silver plating solution for 6g communication and preparation method thereof

Abstract

This invention discloses an ultra-low roughness chemical silver plating solution for 6G communication, comprising 2-5 g / L silver nitrate, 10-15 g / L complexing agent, 5-8 g / L nicotinic acid, 2-5 g / L reducing agent, 1-3 g / L stabilizer, 0.1-0.5 g / L surfactant, 10-30 g / L pH adjuster, 0.01-0.1 g / L grain refiner, 0.1-0.5 g / L antioxidant, and water. The invention also provides a method for its preparation. Compared with existing technologies, this invention uses specific halogenated compounds to modify uracil, improving its defects and making it less prone to ionization. The introduced groups also impart crystal plane guiding function, thereby achieving an ultra-low surface roughness of the plating layer.

Description

Technical Field

[0001] This invention relates to the field of chemical silver plating technology, and more particularly to a chemical silver plating solution with extremely low roughness for 6G communication and its preparation method. Background Technology

[0002] Chemical silver plating solutions are solution systems that autocatalytically deposit silver layers on solid surfaces without the influence of external current, based on the principle of redox reactions. Their core components include silver salts, complexing agents, reducing agents, and functional additives. Silver salts include silver nitrate and silver methanesulfonate; common complexing agents are HEDTA and disodium EDTA, which control the silver ion release rate by forming stable coordination compounds with silver ions; reducing agents such as glucose and formaldehyde reduce silver ions to metallic silver on catalytically active surfaces, achieving autocatalytic deposition. In recent years, environmental requirements have spurred the development of cyanide-free chemical silver plating systems. Systems represented by phosphorus-based complexing agents THPP and hydantoin derivatives can achieve over 99% coating uniformity while meeting RoHS standards.

[0003] In the field of 6G communication technology, chemical silver plating solutions have become a key material for high-frequency device manufacturing due to their excellent conductivity, machinability, and surface uniformity. In the terahertz band (0.1-1.0 THz), signal transmission is extremely sensitive to surface roughness. Studies have shown that reducing the surface roughness of the silver plating layer from Ra0.5 μm to Ra0.2 μm can reduce signal transmission loss in the 300 GHz band by more than 3 dB. Therefore, this material is widely used in the surface treatment of core components such as terahertz antennas and waveguides to effectively reduce signal attenuation. In the technology system of high-frequency ceramic filters, surface metallization is a core component. This process, by forming a metal coating on the surface of a ceramic substrate, can effectively suppress leakage of high-frequency microwave signals and reduce attenuation loss during signal transmission. Its key technical indicators include the interfacial bonding strength between the metal layer and the ceramic substrate, and the insertion loss parameter (or the resonator quality factor Q value) reflecting signal transmission efficiency. With the large-scale growth of filter demand in future high-frequency communication infrastructure, cost control of the metallization process has also become a key factor to consider in process design.

[0004] In 6G filters, the surface roughness requirements for the chemically plated silver layer are extremely stringent, as they directly determine the high-frequency signal transmission efficiency. Millimeter-wave and terahertz electromagnetic waves propagate only within an extremely thin layer on the conductor surface; a rough surface exacerbates electron scattering, significantly increasing resistive losses and leading to a degradation of the filter's core performance—specifically manifested as a decrease in the quality factor (Q value), an increase in insertion loss, and a deterioration in frequency selectivity. To ensure the filter's accurate signal processing capabilities at ultra-high frequencies, the silver plating layer must achieve a nanoscale smooth surface, which is one of the core manufacturing challenges in overcoming the performance bottlenecks of 6G communication.

[0005] CN116288289A discloses a method for nickel and silver plating on a ceramic copper-clad substrate, belonging to the field of ceramic copper-clad substrate processing technology. Its core lies in solving the technological challenge of nickel plating on the front and silver plating on the back. The specific process route is as follows: First, vacuum sintering is performed, followed by cleaning the surface of the ceramic copper-clad substrate through a chemical pretreatment process; patterning is performed using chemical etching, followed by selective chemical printing, exposure and development, and then selective chemical silver plating is performed on the etched pattern surface; after silver plating, excess dry film layer is removed and the substrate is cleaned and dried; then, a peelable colloid is coated onto the product surface by printing a blank screen, and cured by baking to form a masking layer; then, chemical nickel plating is performed on the non-masked areas, and finally, the colloid is removed and the substrate is cleaned and dried. This method achieves differentiated metallization treatment on both sides of the ceramic copper-clad substrate, effectively avoiding cross-contamination of chemicals during the production process while meeting product performance requirements.

[0006] CN112746295A provides a silver plating solution for electrochemical silver plating, the formulation of which includes silver salt, complexing agent, accelerator, surfactant, pH adjuster, and water. The innovation of this invention lies in the introduction of rare earth elements such as cerium and lanthanum. By adjusting the electrochemical properties of the plating solution, the static potential is shifted positively, significantly increasing polarizability and cathode overpotential, thereby reducing the resistivity of the plating layer and enhancing its oxidation resistance. The addition of rare earth elements also refines the micrograin structure, promoting a uniform and dense plating structure, which improves the adhesion between the plating layer and the ceramic substrate while significantly improving corrosion resistance. Furthermore, rare earth elements can accelerate the metal deposition reaction kinetics, resulting in a significant increase in plating speed. The accompanying process, through coarsening, neutralizing, and activating pretreatment of the ceramic substrate, followed by pre-plating an intermediate nickel layer before silver plating, further enhances the gloss of the silver layer and the interfacial bonding strength.

[0007] Currently, the mainstream cyanide-free silver plating process mainly uses thiosulfate system and sulfite system. However, such processes have inherent technical bottlenecks: slow plating rate, weak adhesion between silver layer and substrate, insufficient resistance to discoloration, and poor uniformity of plating thickness, making it difficult to meet the requirements of low roughness and high flatness of silver plating layer for 6G communication. Summary of the Invention

[0008] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a chemical silver plating solution with extremely low roughness for 6G communication and a method for preparing the same.

[0009] In silver plating solutions, complexing agents play a crucial role, controlling the release rate of silver ions by forming stable coordination compounds with them. Uracil, as a complexing agent in cyanide-free silver plating, can produce excellent silver deposits on copper substrates without the need for a separate silver pressing process; however, its performance in terms of deposit quality and solution stability is inferior to that of cyanides. This invention improves uracil's solubility and pH sensitivity by modifying it with hydrophilic groups. The modified uracil binds to silver ions through coordination, and it is less prone to ionization under alkaline conditions. The introduced groups also impart crystal plane guiding functionality, thereby achieving extremely low surface roughness of the plating layer.

[0010] To achieve the above objectives, the present invention provides an extremely low roughness chemical silver plating solution for 6G communication, comprising 2-5 g / L silver nitrate, 10-15 g / L complexing agent, 5-8 g / L nicotinic acid, 2-5 g / L reducing agent, 1-3 g / L stabilizer, 0.1-0.5 g / L surfactant, 10-30 g / L pH adjuster, 0.01-0.1 g / L grain refiner, 0.1-0.5 g / L antioxidant, and water.

[0011] The preparation method of the complexing agent includes the following steps:

[0012] The complexing agent is obtained by mixing uracil with a halogenated compound, adding alkali, and then recrystallizing after post-treatment.

[0013] Furthermore, the preparation method of the complexing agent includes the following steps:

[0014] Uracil and sodium 2-chloroethylsulfonate were mixed in water, and sodium hydroxide was added. The mixture was stirred at 60-80°C under a nitrogen atmosphere for 6-10 hours. After cooling to 5-10°C, acid was added to adjust the pH to 2-4, and the mixture was centrifuged. The complexing agent was obtained by recrystallization. The mass ratio of uracil, sodium 2-chloroethylsulfonate, water, and sodium hydroxide was 1:1.8-2:15-25:0.7-0.8.

[0015] Preferably, the method for preparing the complexing agent includes the following steps:

[0016] Uracil and 2-chloroethanol were mixed in N,N-dimethylformamide, and potassium carbonate was added. The mixture was stirred at 70-90°C under a nitrogen atmosphere for 4-6 hours, then filtered. The filtrate was concentrated under reduced pressure, and water was added to crystallize the mixture. The crystals were then freeze-dried to obtain the complexing agent. The mass ratio of uracil, 2-chloroethanol, N,N-dimethylformamide, and potassium carbonate was 1:1.1-1.2:5-15:1-1.2.

[0017] More preferably, the method for preparing the complexing agent includes the following steps:

[0018] After mixing uracil and chloroacetyl chloride in pyridine, stirring at 0-5°C for 1-2 hours, ammonia water was added, and stirring at room temperature for 10-14 hours. After concentration under reduced pressure, the mixture was washed with water and recrystallized to obtain the complexing agent. The mass ratio of uracil, chloroacetyl chloride, pyridine, and ammonia water was 1:1.3-1.4:5-6:4-5.

[0019] Furthermore, the reducing agent is sodium hypophosphite.

[0020] Furthermore, the stabilizer is sodium thiosulfate.

[0021] Furthermore, the surfactant is polyethylene glycol octylphenyl ether.

[0022] Furthermore, the pH adjuster is a borax-boric acid buffer solution.

[0023] Furthermore, the grain refiner is polyvinylpyrrolidone.

[0024] Furthermore, the antioxidant is L-ascorbic acid.

[0025] A method for preparing an ultra-low roughness chemical silver plating solution for 6G communication includes the following steps:

[0026] S1. Dissolve the complexing agent, nicotinic acid, and pH adjuster in water under light-protected conditions, and adjust the pH to a slightly alkaline level before use.

[0027] S2. Dissolve silver nitrate in water, then add the solution from S1, stir until homogeneous, then add stabilizer, grain refiner, and surfactant, and stir and mix thoroughly at 30~45℃.

[0028] S3. Dissolve the reducing agent in water at 30~40℃, add the antioxidant, cool to 20~25℃, add to the solution of S2, stir evenly in the dark to obtain the chemical silver plating solution.

[0029] The beneficial effects of this invention are:

[0030] 1. Compared with existing technologies, this invention improves the solubility and pH sensitivity of uracil by modifying it. The introduction of hydrophilic groups enhances solubility, and the modified uracil binds to silver ions through coordination, resulting in stronger complexation ability. After modification, it is less prone to ionization under alkaline conditions, and the introduced groups also impart crystal plane guiding function, thereby achieving extremely low surface roughness of the coating.

[0031] 2. The chemical silver plating solution of this invention uses silver nitrate as the silver source. Sodium thiosulfate can both stabilize silver ions and prevent spontaneous decomposition of the plating solution. Polyvinylpyrrolidone effectively inhibits dendrite growth by adsorbing onto specific crystal faces of silver crystal nuclei. Polyethylene glycol octylphenyl ether acts as a wetting agent to ensure uniform coating in deep-hole areas. Ascorbic acid not only has antioxidant properties but also forms a redox pair with sodium hypophosphite that can regulate the deposition rate. Modified uracil and nicotinic acid complex silver ions, and the components work precisely and synergistically during the nano-deposition process to obtain a chemical silver plating solution with extremely low roughness suitable for 6G communication. Detailed Implementation

[0032] Polyethylene glycol octylphenyl ether, model: Triton X-100, is sourced from Shanghai Lianmai Biotechnology Co., Ltd.

[0033] Borax-boric acid buffer solution, pH=9.0, 0.2mol / L.

[0034] Polyvinylpyrrolidone, model number: PVPK30, is sourced from BASF.

[0035] Example 1

[0036] A method for preparing an ultra-low roughness chemical silver plating solution for 6G communication includes the following steps:

[0037] S1. Dissolve 12g of complexing agent, 6g of nicotinic acid, and 20g of borax-boric acid buffer in 600mL of water under light protection, adjust the pH to 9, and set aside.

[0038] S2. Dissolve 3g of silver nitrate in 200mL of water, then add the solution from S1, stir well, and then add 1.5g of sodium thiosulfate, 0.05g of polyvinylpyrrolidone, and 0.2g of polyethylene glycol octylphenyl ether. Stir and mix well at 40℃.

[0039] S3. Dissolve 4g of sodium hypophosphite in 200mL of water at 35℃, add 0.3g of ascorbic acid, cool to 25℃, add to the solution in S2, stir evenly in the dark to obtain the chemical silver plating solution.

[0040] The preparation method of the complexing agent includes the following steps:

[0041] Uracil was mixed with sodium 2-chloroethylsulfonate in water, and sodium hydroxide was added. The mixture was stirred at 70°C under a nitrogen atmosphere for 8 hours. After cooling to 5°C, acid was added to adjust the pH to 3, and the mixture was centrifuged. The complexing agent was obtained by recrystallization. The mass ratio of uracil, sodium 2-chloroethylsulfonate, water and sodium hydroxide was 1:1.9:20:0.75.

[0042] Example 2

[0043] This is essentially the same as Example 1, except that the complexing agent is different. The preparation method of the complexing agent includes the following steps:

[0044] Uracil and 2-chloroethanol were mixed in N,N-dimethylformamide, and potassium carbonate was added. The mixture was stirred at 80°C under a nitrogen atmosphere for 5 hours and then filtered. The filtrate was concentrated under reduced pressure, and water was added to crystallize the mixture. The crystals were then freeze-dried to obtain the complexing agent. The mass ratio of uracil, 2-chloroethanol, N,N-dimethylformamide and potassium carbonate was 1:1.15:10:1.1.

[0045] Example 3

[0046] This is essentially the same as Example 1, except that the complexing agent is different. The preparation method of the complexing agent includes the following steps:

[0047] The preparation method of the complexing agent includes the following steps:

[0048] Uracil and chloroacetyl chloride were mixed in pyridine and stirred at 0°C for 1 h. Then, 25 wt% ammonia water was added and stirred at room temperature for 12 h. After concentration under reduced pressure, the mixture was washed with water and recrystallized to obtain the complexing agent. The mass ratio of uracil, chloroacetyl chloride and pyridine was 1:1.35:5.5:4.3.

[0049] Compare with Example 1

[0050] A method for preparing an ultra-low roughness chemical silver plating solution for 6G communication includes the following steps:

[0051] S1. Dissolve 12g of uracil, 6g of nicotinic acid, and 20g of borax-boric acid buffer in 600mL of water under light-protected conditions, and adjust the pH to 9 before use.

[0052] S2. Dissolve 3g of silver nitrate in 200mL of water, then add the solution from S1, stir well, and then add 1.5g of sodium thiosulfate, 0.05g of polyvinylpyrrolidone, and 0.2g of polyethylene glycol octylphenyl ether. Stir and mix well at 40℃.

[0053] S3. Dissolve 4g of sodium hypophosphite in 200mL of water at 35℃, add 0.3g of ascorbic acid, cool to 25℃, add to the solution in S2, stir evenly in the dark to obtain the chemical silver plating solution.

[0054] Compare with Example 2

[0055] A method for preparing an ultra-low roughness chemical silver plating solution for 6G communication includes the following steps:

[0056] S1. Dissolve 12g of disodium EDTA, 6g of nicotinic acid, and 20g of borax-boric acid buffer in 600mL of water under light protection, and adjust the pH to 9 before use.

[0057] S2. Dissolve 3g of silver nitrate in 200mL of water, then add the solution from S1, stir well, and then add 1.5g of sodium thiosulfate, 0.05g of polyvinylpyrrolidone, and 0.2g of polyethylene glycol octylphenyl ether. Stir and mix well at 40℃.

[0058] S3. Dissolve 4g of sodium hypophosphite in 200mL of water at 35℃, add 0.3g of ascorbic acid, cool to 25℃, add to the solution in S2, stir evenly in the dark to obtain the chemical silver plating solution.

[0059] Test Example 1

[0060] The surfaces of components to be silver-plated were degreased, pickled, sensitized, and activated before being immersed in a chemical silver plating solution. After silver plating, the components were washed with water, passivated, and dried to obtain the silver plating layer. The adhesion strength between the silver layer and the substrate on the silver-plated components in the examples and control examples was tested according to GB / T 5270-2005, "Test Method for Adhesion Strength of Electrodeposition and Chemical Deposition Layers on Metal Substrates". The Q-value of the silver-plated components was tested using a network vector analyzer.

[0061] Table 1

[0062]

[0063] Q-factor is a parameter that measures the ratio of energy storage to energy loss. In the 6 GHz millimeter-wave band, the skin depth is extremely small, and the influence of the conductor surface condition on the Q-factor is amplified dramatically. Controlling the crystal orientation of the coating can reduce electron scattering; secondly, a surface roughness below 50 nm is required to meet terahertz transmission requirements; and thirdly, residual organic impurities in the coating can form grain boundary barriers. All of these factors affect the Q-factor, thus impacting signal transmission.

[0064] As can be seen from Table 1, compared with the control example, the coating of the examples has a stronger bond with the component and a higher Q value. This may be because the uracil deposit in control example 1 has lower quality and poorer solubility, making Ag⁺ more easily released, resulting in an uncontrollable reduction rate and high coating roughness. In contrast, the disodium EDTA complex in control example 2 is too strong, leading to slow Ag⁺ release and a low deposition rate, which may result in a thin and discontinuous coating.

[0065] The embodiments improve the defects of uracil in terms of solubility and pH sensitivity by modifying uracil. The solubility is improved by introducing hydrophilic groups. The modified uracil binds to silver ions through coordination. It is not easy to ionize under alkaline conditions after modification. The introduced groups can also give crystal plane guiding function, thereby achieving extremely low surface roughness of the coating.

[0066] In Example 1, uracil reacts with sodium 2-chloroethylsulfonate to generate a complexing agent containing sulfonic acid groups. The SO₃⁻ in this agent's structure can form a stable complex ion with Ag⁺. Simultaneously, the hydrophilicity of the sulfonic acid groups ensures uniform dispersion of the complex ion in the solution, preventing excessively high local concentrations. This derivative forms a complex ion with Ag⁺, ensuring slow release of Ag⁺ and resulting in a uniform coating. In Example 2, uracil reacts with 2-chloroethanol to obtain modified uracil, which not only introduces a hydrophilic hydroxyl group but also prevents ionization. In Example 3, modified uracil is obtained by reacting uracil with chloroacetyl chloride and ammonia. The introduced carbamoyl group forms a bidentate coordination, which is much more stable than the single-point adsorption in Examples 1 and 2. Therefore, it has the best complexing ability for Ag⁺. The bidentate coordination slows down the release rate of silver ions, resulting in more ordered deposition, smaller grain size, and the highest quality coating. Since coating quality directly affects the bonding with the substrate and the Q value, the coating in Example 3 performs best.

[0067] The chemical silver plating solution of this invention uses silver nitrate as the silver source, and sodium thiosulfate can both stabilize silver ions and prevent spontaneous decomposition of the plating solution. Polyvinylpyrrolidone effectively inhibits dendrite growth by adsorbing onto specific crystal faces of silver crystal nuclei. Polyethylene glycol octylphenyl ether acts as a wetting agent to ensure uniform plating in deep-hole areas. Ascorbic acid not only has antioxidant properties but also forms a redox pair with sodium hypophosphite that can regulate the deposition rate. Modified uracil and nicotinic acid complex silver ions, and the components work precisely and synergistically during the nano-deposition process to obtain a chemical silver plating solution with extremely low roughness suitable for 6G communication.

[0068] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. An ultra-low roughness chemical silver plating solution for 6G communication, characterized in that, Silver nitrate 3 g / L, complexing agent 12 g / L, nicotinic acid 6 g / L, reducing agent 4 g / L, stabilizer 1.5 g / L, surfactant 0.2 g / L, pH adjuster 20 g / L, grain refiner 0.05 g / L, antioxidant 0.3 g / L and water; The preparation method of the complexing agent comprises the following steps: After mixing the uracil and chloroacetyl chloride in pyridine, stirring at 0-5℃ for 1-2h, adding ammonia water, stirring at room temperature for 10-14h, concentrating under reduced pressure, washing with water and recrystallizing, the complexing agent is obtained; the mass ratio of uracil, chloroacetyl chloride, pyridine and ammonia water is 1:1.35:5.5:4.3; The reducing agent is sodium hypophosphite; The stabilizer is sodium thiosulfate; The surfactant is polyethylene glycol octylphenyl ether; The pH adjuster is borax-boric acid buffer; The grain refiner is polyvinylpyrrolidone; The antioxidant is L-ascorbic acid.

2. A method of preparing an extremely low roughness chemical silver plating solution for 6G communication as claimed in claim 1, characterized in that, The preparation method comprises the following steps: S1, dissolving the complexing agent, nicotinic acid and pH adjuster in water under light protection, adjusting the pH to weak alkaline and reserving; S2, dissolving the silver nitrate in water, then adding the solution in S1, stirring uniformly, then adding the stabilizer, grain refiner and surfactant, stirring and mixing uniformly at 30-45℃; S3, dissolving the reducing agent in water by stirring at 30-40℃, adding the antioxidant, cooling to 20-25℃, adding the solution in S2, stirring uniformly under light protection and obtaining the chemical silver plating solution.

Images