Preparation method of cleaning agent for cleaning circuit board

Abstract

The invention discloses a preparation method of a cleaning agent for cleaning a circuit board, and belongs to the technical field of cleaning agents, and the preparation method comprises the following steps: S1, mixing lignin and a sodium hydroxide solution, heating, pressurizing, and carrying out a high-pressure reaction to obtain activated lignin; s2, mixing and stirring the activated lignin and maleic anhydride with N, N-dimethylformamide at the same time, and heating for reaction to obtain grafted lignin; s3, the grafted lignin, sodium hydrogen sulfite and nano titanium dioxide are mixed and stirred in deionized water and heated for a reaction, and a nano-hybridized lignin dispersion liquid is obtained; s4, putting a thermal initiator and a cross-linking agent into the nano-hybridized lignin dispersion liquid, stirring, and heating for reaction to obtain nano-hybridized lignin composite liquid; s5, uniformly mixing and stirring the nano-hybridized lignin composite liquid with a cosolvent, a chelating agent, a corrosion inhibitor and deionized water to obtain a cleaning agent; the cleaning agent disclosed by the invention has a relatively high removal rate on pollutants in the circuit board.

Description

Technical Field

[0001] This invention relates to the field of cleaning agent technology, and more specifically to a method for preparing a cleaning agent for cleaning circuit boards. Background Technology

[0002] Currently, circuit board cleaning typically employs traditional techniques such as organic solvents, ultrasonic cleaning, and water-based cleaning. Organic solvent cleaning may have limitations in removing fine particulate contaminants and suffers from rapid evaporation and environmental pollution. Ultrasonic cleaning may damage precision components and is incomplete in cleaning complex structures such as deep holes or blind holes. Water-based cleaning is prone to corroding metal parts and has weak ability to remove grease stains. Therefore, the circuit board cleaning industry has been exploring other, better technologies. Adding nanoparticles to cleaning agents holds great potential. Nanoparticles, with their high specific surface area, strong adsorption, and penetration capabilities, can penetrate deep into the tiny crevices of circuit boards and efficiently adsorb and remove contaminants such as flux residue, solder paste, and metal ions. However, the strong adsorption of nanoparticles also makes them prone to adsorption on the circuit board surface, leading to residues in crevices and other areas after cleaning. These residues can easily form conductive bridges on the circuit board surface, causing micro-short circuits. Therefore, there are still areas for improvement in cleaning agents containing nanoparticles.

[0003] Based on the above, Chinese patent document CN118909702A discloses a cleaning agent for printed circuit boards and its preparation method. The cleaning agent includes a nonionic surfactant, anionic surfactant, N-methylpyrrolidone, pH adjuster, modified carbon nanotubes, and water. The preparation method of the cleaning agent includes the following steps: weigh each component according to the formula, and stir and mix the nonionic surfactant, anionic surfactant, N-methylpyrrolidone, pH adjuster, modified carbon nanotubes, and water evenly to obtain the cleaning agent.

[0004] The aforementioned patent document discloses a cleaning agent for printed circuit boards containing modified carbon nanotubes and its preparation method. The cleaning agent reduces the accumulation of static electricity by dispersing and conducting away static charges on the surface of the circuit board through carbon nanotubes. Furthermore, N-methylpyrrolidone adheres tightly to the surface of the circuit board through adsorption to form a complex film. This complex film and the film layer formed by the modified carbon nanotubes can jointly prevent corrosion of the circuit board substrate and the adhesion of dirt to its surface. However, carbon nanotubes are conductive, and the film layer formed on the circuit board surface can also act as a conductive layer. This conductive layer can bridge different components on the circuit board surface. Short circuits may occur during the operation of the circuit board, leading to damage to the short-circuited components. Based on the potential hazards after cleaning the circuit board with this cleaning agent, it can be seen that there is still room for improvement in this cleaning agent. Summary of the Invention

[0005] To address the technical deficiencies in the background art, this invention proposes a method for preparing a cleaning agent for cleaning circuit boards, which solves the aforementioned technical problems and meets practical needs. The specific technical solution is as follows: A method for preparing a cleaning agent for cleaning circuit boards includes the following steps: S1. Mix lignin with sodium hydroxide solution and add it into a reaction vessel. Heat the reaction vessel and subject the mixture inside to a high-pressure reaction. After the reaction is completed, activated lignin is obtained. S2. Activated lignin and maleic anhydride are simultaneously added to a container containing N,N-dimethylformamide. The mixture is stirred and heated to carry out the reaction. After the reaction is completed, grafted lignin is obtained. S3. Grafted lignin is mixed with sodium bisulfite and nano titanium dioxide in deionized water to form a dispersion. The dispersion is stirred and heated to carry out the reaction. After the reaction is completed, a nano-hybrid lignin dispersion is obtained. S4. Add the thermal initiator and crosslinking agent into the nano-hybrid lignin dispersion, stir and heat to react. After the reaction is completed, a nano-hybrid lignin composite solution is obtained. S5. The nano-hybrid lignin composite liquid is mixed with a co-solvent, chelating agent, corrosion inhibitor, and deionized water until homogeneous to obtain a cleaning agent for cleaning circuit boards.

[0006] As a further technical solution of the present invention, the water content of the nano-hybrid lignin composite liquid is 65%~75%; The cleaning agent comprises the following components by weight: 10% to 20% nano-hybrid lignin composite liquid, 5% to 10% co-solvent, 0.5% to 2% chelating agent, 0.3% to 0.8% corrosion inhibitor, and 70% to 84% deionized water.

[0007] As a further technical solution of the present invention, in step S1, the concentration of sodium hydroxide solution is 30%~50%, and the mass ratio of lignin to sodium hydroxide solution is 1:(4~6).

[0008] As a further technical solution of the present invention, in step S1, the temperature of the mixture of lignin and sodium hydroxide solution and the heating reaction is 110~130℃, the pressure is 0.2~0.3MPa, and the time is 1.5~2.5h. After the mixture reaction is complete, the pH is adjusted to 6-7 and a solid product is precipitated. Then, the product is filtered, washed, and dried to obtain activated lignin.

[0009] As a further technical solution of the present invention, in step S2, activated lignin and maleic anhydride are added to sufficient N,N-dimethylformamide at a mass ratio of 1:(0.7~0.9), and the mixture is heated to react at a temperature of 75~85℃ for 3.5~4.5h. After the mixture reaction is complete, it is distilled. Acetone is added to the viscous liquid obtained by distillation to produce a solid precipitate. Then, it is filtered, and the solid product obtained by filtration is washed and dried to obtain grafted lignin.

[0010] As a further technical solution of the present invention, in step S3, the mass ratio of grafted lignin, sodium bisulfite and nano titanium dioxide in the dispersion is 1:(0.4~0.6):(0.1~0.15), and the temperature of the dispersion heating reaction is 85~95℃ and the time is 2.5~3.5h; After the reaction is complete, adjust the pH of the nano-hybrid lignin dispersion to 6-7.5.

[0011] As a further technical solution of the present invention, in step S4, the temperature of the thermal initiator and the crosslinking agent added to the nano-hybrid lignin dispersion for heating reaction is 60~80℃ and the time is 1~2h.

[0012] As a further technical solution of the present invention, the nano-titanium dioxide undergoes surface modification treatment, which includes the following steps: dispersing nano-titanium dioxide in anhydrous ethanol, adding 1%~3% by mass of silane coupling agent KH-550 to nano-titanium dioxide, refluxing at 70°C for 4~6 hours, and after the reaction is completed, obtaining silane-coupled modified nano-titanium dioxide by filtration, washing, and drying.

[0013] As a further technical solution of the present invention, the thermal initiator is selected as ammonium persulfate or potassium persulfate, and the amount of thermal initiator added is 0.5% to 2% of the quality of the grafted wood. The crosslinking agent is selected from N,N'-methylenebisacrylamide or polyethylene glycol diacrylate, and the amount of crosslinking agent added is 2% to 6% of the quality of the grafted wood.

[0014] As a further technical solution of the present invention, the cosolvent is selected from ethyl lactate or propylene glycol methyl ether; The chelating agent is selected from one of tetrasodium glutamate diacetate, trisodium ethylenediamine disuccinate, and trisodium methylglycine diacetate. The corrosion inhibitor is selected from one of benzotriazole, methylbenzotriazole, and sodium sarcosinate.

[0015] The beneficial effects of this invention are as follows: The main technical solution of this invention is to process lignin and load it with nano-titanium dioxide to form the core component of a circuit board cleaning agent. The lignin is activated by demethylation pretreatment, grafted with maleic anhydride, and sulfonated to introduce sulfonic acid groups, and then transformed into a water-based surfactant, which can load nano-titanium dioxide. The lignin molecular chains loaded with nano-titanium dioxide form a three-dimensional network structure through cross-linking. The chelating groups, sulfonic acid groups, and nano-titanium dioxide in the three-dimensional network structure achieve spatial synergy, and achieve functional synergy through surfactant-driven wetting and penetration, physical embedding of the three-dimensional network structure, chemical chelation of multifunctional groups, and photocatalytic degradation of nano-titanium dioxide. This results in a cleaning agent with a high removal rate of contaminants in the circuit board. Detailed Implementation

[0016] The embodiments of the present invention will be described below with reference to relevant examples. The embodiments of the present invention are not limited to the following examples, and the present invention relates to relevant necessary components in this technical field, which should be regarded as well-known technology in this technical field and can be known and mastered by those skilled in this technical field.

[0017] A method for preparing a cleaning agent for cleaning circuit boards includes the following steps: S1. Mix lignin with sodium hydroxide solution and add it into a reaction vessel. Heat the reaction vessel and subject the mixture inside to a high-pressure reaction. After the reaction is completed, activated lignin is obtained. S2. Activated lignin and maleic anhydride are simultaneously added to a container containing N,N-dimethylformamide. The mixture is stirred and heated to carry out the reaction. After the reaction is completed, grafted lignin is obtained. S3. Grafted lignin is mixed with sodium bisulfite and nano titanium dioxide in deionized water to form a dispersion. The dispersion is stirred and heated to carry out the reaction. After the reaction is completed, a nano-hybrid lignin dispersion is obtained. S4. Add the thermal initiator and crosslinking agent into the nano-hybrid lignin dispersion, stir and heat to react. After the reaction is completed, a nano-hybrid lignin composite solution is obtained. S5. The nano-hybrid lignin composite liquid is mixed with a co-solvent, chelating agent, corrosion inhibitor, and deionized water until homogeneous to obtain a cleaning agent for cleaning circuit boards.

[0018] This invention discloses a method for preparing a circuit board cleaning agent with added nano-titanium dioxide. The cleaning agent uses lignin as a carrier to load nano-titanium dioxide. In the preparation process of the cleaning agent, the lignin is first activated, grafted, and sulfonated in sequence, so that the lignin is transformed into a water-soluble polymer after treatment. The nano-titanium dioxide is embedded in the water-soluble polymer network under the action of hydrogen bonds. Subsequently, under the action of thermal initiator and crosslinking agent, an aqueous free radical copolymerization reaction occurs, forming a polymer with a three-dimensional network structure loaded with nano-titanium dioxide. This polymer can improve the problem of nano-titanium dioxide agglomeration and sedimentation. Moreover, its three-dimensional network can effectively capture contaminants peeled off from the surface of the circuit board through physical embedding and steric hindrance effects. The nano-titanium dioxide can be activated by ultraviolet light to generate strong oxidizing free radicals to degrade some of the captured contaminants. In the preparation method of the cleaning agent for cleaning circuit boards of the present invention, step S1 is to pretreat lignin by demethylation. The principle of this step is based on the ether bond cleavage reaction catalyzed by a strong base. In the reaction system of this step, the concentration of sodium hydroxide solution is 30%~50%, the mass ratio of lignin to sodium hydroxide solution is 1:(4~6), and the temperature of the reaction after mixing lignin and sodium hydroxide solution is 110~130℃, the pressure is 0.2~0.3MPa, and the time is 1.5~2.5h. Lignin is a complex three-dimensional polymer composed of phenylpropane units linked by ether bonds and carbon-carbon bonds. Its structure contains a large number of methoxy groups. In the high temperature and pressure strong alkaline solution environment, the carbon-oxygen bonds in the methoxy groups undergo hydrolysis and release methanol, while new phenolic hydroxyl groups are generated on the aromatic ring of lignin. The newly generated phenolic hydroxyl groups in lignin have stronger nucleophilicity than methoxyl groups, providing more reaction sites for the subsequent esterification reaction with maleic anhydride, thus improving the reactivity of lignin. Furthermore, phenolic hydroxyl groups are excellent metal ion ligands, and their increased number significantly enhances the chelating ability of the final product for metal ions such as lead, tin, and copper on the circuit board surface. In addition, the reaction system needs to be carried out under pressure to ensure that the aqueous solution temperature exceeds 100°C, thereby achieving the required reaction temperature and ensuring that the demethylation reaction proceeds efficiently, resulting in a significant increase in the methyl removal rate of lignin. It should be noted that in step S1, after the mixture reaction is completed, the pH value is adjusted to 6-7 and a solid product is precipitated. Then, the product is filtered, washed, and dried to obtain activated lignin. Since lignin is a water-insoluble solid, an alkaline suspension will be formed in the reaction vessel during the reaction process. That is, the lignin solid particles are dispersed in a strong alkaline solution. Some of the phenolic hydroxyl groups of lignin dissociate into sodium phenolate, causing it to swell and appear partially dissolved. After the reaction is completed, after the methoxy group is removed by the demethylation reaction, the polarity of the lignin molecules is enhanced. It will still exist in the solution in the form of flocculent solid, but its swelling degree is improved. After the solution is cooled, the pH value is adjusted to 6-7 with dilute hydrochloric acid. The sodium phenolate of lignin is converted into the form of phenolic hydroxyl groups, which reduces its water solubility and causes it to precipitate. Subsequently, the solid product can be separated by vacuum filtration through a Buchner funnel. After washing the solid product with deionized water to remove impurities, it is dried to obtain solid activated lignin.

[0019] The principle involved in step S2 is based on the esterification reaction of acid anhydrides. Activated lignin and maleic anhydride are added to sufficient N,N-dimethylformamide at a mass ratio of 1:(0.7~0.9). The mixture is heated to a temperature of 75~85℃ for 3.5~4.5h. The phenolic hydroxyl groups of the activated lignin undergo a nucleophilic ring-opening reaction with the five-membered ring of maleic anhydride to form an ester bond, thereby introducing a carboxyl group and an unsaturated carbon-carbon double bond into the lignin skeleton. The introduced carboxyl group is a very strong metal ion chelating group, which can work synergistically with the phenolic hydroxyl group to achieve a strong chemical scavenging ability. In addition, the carboxyl group itself also has good hydrophilicity, which helps the subsequent grafted lignin to disperse in water. Furthermore, the unsaturated carbon-carbon double bond formed by grafting is the basis for the free radical copolymerization and crosslinking of the lignin skeleton to form a three-dimensional network structure in the subsequent steps. It should be noted that in step S2, after the mixture reaction is completed, distillation is performed. Acetone is added to the viscous liquid obtained from distillation to produce a solid precipitate. Then, the precipitate is filtered, and the solid product obtained from the filtration is washed and dried to obtain grafted lignin. During the reaction process in this step, when the activated lignin and maleic anhydride are added to N,N-dimethylformamide and heated and stirred, N,N-dimethylformamide will break the hydrogen bonds between lignin molecules, causing the activated lignin to gradually swell and partially dissolve in N,N-dimethylformamide. This provides conditions for the esterification reaction between maleic anhydride and lignin phenolic hydroxyl groups. After distillation of the product after the reaction, the product in the container is a viscous mixture of grafted maleic anhydride dissolved in a small amount of residual N,N-dimethylformamide. When acetone is added, since acetone is a poor solvent for grafted maleic anhydride, it reduces the solvent's ability to dissolve grafted lignin through dilution, thereby causing the grafted maleic anhydride to precipitate. After filtering, the precipitate is washed and dried to obtain solid grafted lignin.

[0020] The principle involved in step S3 is mainly based on sulfonation reaction and nanoparticle hybridization. The mass ratio of grafted lignin, sodium bisulfite and nano titanium dioxide in the dispersion is 1:(0.4~0.6):(0.1~0.15). The temperature of the dispersion is 85~95℃ and the time is 2.5~3.5h. Under heating conditions, sodium bisulfite undergoes a free radical addition reaction on the unsaturated carbon-carbon double bond of grafted lignin, introducing a strongly hydrophilic sulfonic acid group on the carbon chain, transforming it into a water-soluble polymer. After the reaction, the pH value of the nano-hybridized lignin dispersion is adjusted to 6~7.5 to make it stable in the form of sulfonate. It should be noted that the nano-titanium dioxide undergoes surface modification treatment, which includes the following steps: dispersing nano-titanium dioxide in anhydrous ethanol, adding 1%~3% by mass of silane coupling agent KH-550, and refluxing at 70℃ for 4~6 hours. After the reaction, the nano-titanium dioxide is obtained by filtration, washing, and drying. After modification with silane coupling agent KH-550, the silanol groups on the surface of the nano-titanium dioxide form strong hydrogen bonds with the carboxyl groups, phenolic hydroxyl groups, and other groups on the lignin molecules. The nano-titanium dioxide is uniformly embedded in the lignin polymer network under ultrasonic or mechanical stirring, which can effectively prevent the nano-titanium dioxide from agglomerating or settling. Introducing sulfonic acid groups into the lignin polymer network significantly enhances its hydrophilicity, making it a highly efficient surfactant that can significantly reduce the surface tension of the cleaning solution, achieving excellent wetting, penetration, and detergency effects. After nano-titanium dioxide is loaded into the lignin polymer network, the steric hindrance effect of the nanoparticles can prevent the lignin molecular chains from re-aggregating and stabilizing the aqueous dispersion system formed by the nano-hybrid lignin dispersion. Furthermore, nano-titanium dioxide possesses photocatalytic activity, which can be supplemented with ultraviolet light during the circuit board cleaning process to degrade stubborn organic contaminants and reduce the difficulty of cleaning circuit boards.

[0021] The principle involved in step S4 is mainly based on aqueous free radical copolymerization. The thermal initiator is selected from ammonium persulfate or potassium persulfate, and the amount of thermal initiator added is 0.5%~2% of the grafted lignin mass. The crosslinking agent is selected from N,N'-methylenebisacrylamide or polyethylene glycol diacrylate, and the amount of crosslinking agent added is 2%~6% of the grafted lignin mass. The thermal initiator and crosslinking agent are added to the nano-hybrid lignin dispersion and heated to a temperature of 60~80℃ for 1~2 hours. The thermal initiator decomposes at 60~80℃ to generate sulfate free radicals. These free radicals attack the double bonds in the grafted lignin and crosslinking agent, initiating a chain growth reaction. Finally, through the bridging effect of the crosslinking agent, multiple linear lignin molecules are linked into a three-dimensional network polymer with a pore size of 50~200nm. The polymer surface is loaded with many nano-titanium dioxide molecules, which serve as an effective component in the nano-hybrid lignin composite liquid. The three-dimensional network structure of the nano-hybrid lignin composite liquid, composed of lignin molecules loaded with nano-titanium dioxide, can effectively capture organic pollutant particles and colloids peeled off from the circuit board surface through physical encapsulation and steric hindrance effects, preventing their secondary deposition. Furthermore, the three-dimensional network structure enriches a large number of chelating groups on a single macromolecule, producing a synergistic effect, and its ability to capture metal ions is superior to that of small molecule chelating agents. In addition, nano-titanium dioxide plays a physical abrasive role in the three-dimensional network structure, assisting in the removal of stubborn pollutants. More importantly, it endows the cleaning agent with potential photocatalytic self-cleaning ability, degrading stubborn organic pollutants.

[0022] Step S5 mainly involves compounding the product obtained in step S4 with other raw materials to prepare a cleaning agent for cleaning circuit boards. The nano-hybrid lignin composite liquid obtained in step S4 has a water content of 65%~75%. As the core functional component of the cleaning agent, the nano-hybrid lignin composite liquid integrates multiple functions such as surface activity, chelation, and physical adsorption. The cleaning agent includes the following components by mass: 10%~20% nano-hybrid lignin composite liquid, 5%~10% co-solvent, 0.5%~2% chelating agent, 0.3%~0.8% corrosion inhibitor, and 70%~84% deionized water. The cosolvent is selected from ethyl lactate or propylene glycol methyl ether. Both ethyl lactate and propylene glycol methyl ether are green solvents. The cosolvent is mainly responsible for dissolving non-polar or weakly polar organic pollutants such as rosin and resin. The chelating agent is selected from one of tetrasodium glutamate diacetate, trisodium ethylenediamine disuccinate, and trisodium methylglycine diacetate. The chelating agent can quickly penetrate and work synergistically with the three-dimensional network structure formed by the lignin molecular chain to ensure that free metal ions are completely complexed. The corrosion inhibitor is selected from one of benzotriazole, methylbenzotriazole, and sodium sarcosinate. The chelating agent can adsorb onto the surface of metals such as copper and tin to form a monomolecular protective film, effectively preventing the cleaning agent from corroding precision circuits and solder joints.

[0023] In summary, the main technical solution of this invention is to process lignin and load it with nano-titanium dioxide to form the core component of circuit board cleaning agent. Regarding lignin, it has an amorphous three-dimensional spatial network structure. This characteristic is highly homologous to the molecular trapping network target to be constructed in this invention. Modification starting from the molecular chain of lignin can efficiently form a stable three-dimensional network structure with specific pore sizes. Analogous to processing on an existing framework, it is much simpler and more robust than building a complex network structure from scratch. Furthermore, lignin molecules are rich in active functional groups such as phenolic hydroxyl groups, alcoholic hydroxyl groups, and carboxyl groups. These functional groups provide great convenience for subsequent operations such as grafting, sulfonation, nanoparticle loading, and cross-linking. Lignin possesses a three-dimensional network framework and abundant functional groups, which contain enormous processing potential. In the process of processing lignin in this invention, the first step is to perform demethylation pretreatment to activate it. By opening the methoxy group, more and more reactive phenolic hydroxyl groups are exposed, laying the foundation for improving the efficiency of subsequent grafting, sulfonation and other reactions. Grafting the activated lignin endows it with the ability to participate in free radical cross-linking, transforming it from a macromolecule into a more stable network building unit. Sulfonation of the grafted lignin introduces sulfonic acid groups to improve hydrophilicity and significantly enhance surface activity. Grafting and sulfonation transform lignin from a water-insoluble material into a highly efficient water-based surfactant. The loading of nanoparticles and the cross-linking of lignin molecular chains enable spatial and functional synergy. Spatial synergy is achieved by constructing a three-dimensional network structure through cross-linking, which orderly arranges and enriches a large number of chelating groups, sulfonic acid groups, and nano-titanium dioxide at the nanoscale, resulting in a high concentration of functional groups in the three-dimensional network structure. Functional synergy is based on surfactant-driven wetting and penetration, physical embedding of the three-dimensional network structure, chemical chelation of multifunctional groups, and photocatalytic degradation of nano-titanium dioxide. These four mechanisms are unified and can act synchronously in the three-dimensional network structure, realizing the sequential stripping, transport, fixation, and degradation of pollutants, and more thoroughly removing pollutants from circuit boards through the entire process.

[0024] The present invention will be further illustrated below through examples and comparative examples.

[0025] Example 1 S1. A mixture of lignin and a 40% sodium hydroxide solution at a mass ratio of 1:5 is added to a reaction vessel. The reaction vessel is pressurized to 0.25 MPa and heated to 120°C for reaction. After 2 hours of reaction, the reaction is stopped and the mixture inside the reaction vessel is cooled. After cooling, the pH value of the mixture is adjusted to 7 with dilute hydrochloric acid and a solid product is precipitated. The product is then filtered, and the solid product obtained by filtration is washed with deionized water and dried to obtain activated lignin. S2. Activated lignin and maleic anhydride are added to a container containing sufficient N,N-dimethylformamide at a mass ratio of 1:0.8. The mixture is stirred and heated to 80°C for reaction. After 4 hours of reaction, the product is distilled. Acetone is added to the viscous liquid obtained by distillation to produce a solid precipitate. The precipitate is then filtered and the solid product obtained by filtration is washed with acetone and deionized water in sequence and then dried to obtain grafted lignin. S3. Grafted lignin, sodium bisulfite, and nano titanium dioxide are mixed in an appropriate amount of deionized water at a mass ratio of 1:0.5:0.12 and stirred to form a dispersion. While stirring the dispersion, it is heated to 90°C to carry out the reaction. After reacting for 3 hours, a nano-hybrid lignin dispersion is obtained. S4. Ammonium persulfate and N,N'-methylenebisacrylamide were added to the nano-hybrid lignin dispersion, stirred, and heated to 70°C for reaction. After 1.5 h of reaction, a nano-hybrid lignin composite solution with a water content of 70% was obtained. The amount of ammonium persulfate added was 1% of the grafted lignin mass, and the amount of N,N'-methylenebisacrylamide added was 4% of the grafted lignin mass. S5. The nano-hybrid lignin composite liquid is mixed with ethyl lactate, tetrasodium diacetate of glutamic acid, benzotriazole and deionized water to obtain a cleaning agent for cleaning circuit boards. The cleaning agent includes the following components by mass: 10% nano-hybrid lignin composite liquid, 7% co-solvent, 1% chelating agent, 0.5% corrosion inhibitor and 81.5% deionized water.

[0026] Example 2 S1. A mixture of lignin and a 40% sodium hydroxide solution at a mass ratio of 1:5 is added to a reaction vessel. The reaction vessel is pressurized to 0.25 MPa and heated to 120°C for reaction. After 2 hours of reaction, the reaction is stopped and the mixture inside the reaction vessel is cooled. After cooling, the pH value of the mixture is adjusted to 7 with dilute hydrochloric acid and a solid product is precipitated. The product is then filtered, and the solid product obtained by filtration is washed with deionized water and dried to obtain activated lignin. S2. Activated lignin and maleic anhydride are added to a container containing sufficient N,N-dimethylformamide at a mass ratio of 1:0.8. The mixture is stirred and heated to 80°C for reaction. After 4 hours of reaction, the product is distilled. Acetone is added to the viscous liquid obtained by distillation to produce a solid precipitate. The precipitate is then filtered and the solid product obtained by filtration is washed with acetone and deionized water in sequence and then dried to obtain grafted lignin. S3. Grafted lignin, sodium bisulfite, and nano titanium dioxide are mixed in an appropriate amount of deionized water at a mass ratio of 1:0.5:0.12 and stirred to form a dispersion. While stirring the dispersion, it is heated to 90°C to carry out the reaction. After reacting for 3 hours, a nano-hybrid lignin dispersion is obtained. S4. Ammonium persulfate and N,N'-methylenebisacrylamide were added to the nano-hybrid lignin dispersion, stirred, and heated to 70°C for reaction. After 1.5 h of reaction, a nano-hybrid lignin composite solution with a water content of 70% was obtained. The amount of ammonium persulfate added was 1% of the grafted lignin mass, and the amount of N,N'-methylenebisacrylamide added was 4% of the grafted lignin mass. S5. The nano-hybrid lignin composite liquid is mixed with ethyl lactate, tetrasodium diacetate of glutamic acid, benzotriazole and deionized water to obtain a cleaning agent for cleaning circuit boards. The cleaning agent includes the following components by mass: 15% nano-hybrid lignin composite liquid, 7% co-solvent, 1% chelating agent, 0.5% corrosion inhibitor and 76.5% deionized water.

[0027] Example 3 S1. A mixture of lignin and a 40% sodium hydroxide solution at a mass ratio of 1:5 is added to a reaction vessel. The reaction vessel is pressurized to 0.25 MPa and heated to 120°C for reaction. After 2 hours of reaction, the reaction is stopped and the mixture inside the reaction vessel is cooled. After cooling, the pH value of the mixture is adjusted to 7 with dilute hydrochloric acid and a solid product is precipitated. The product is then filtered, and the solid product obtained by filtration is washed with deionized water and dried to obtain activated lignin. S2. Activated lignin and maleic anhydride are added to a container containing sufficient N,N-dimethylformamide at a mass ratio of 1:0.8. The mixture is stirred and heated to 80°C for reaction. After 4 hours of reaction, the product is distilled. Acetone is added to the viscous liquid obtained by distillation to produce a solid precipitate. The precipitate is then filtered and the solid product obtained by filtration is washed with acetone and deionized water in sequence and then dried to obtain grafted lignin. S3. Grafted lignin, sodium bisulfite, and nano titanium dioxide are mixed in an appropriate amount of deionized water at a mass ratio of 1:0.5:0.12 and stirred to form a dispersion. While stirring the dispersion, it is heated to 90°C to carry out the reaction. After reacting for 3 hours, a nano-hybrid lignin dispersion is obtained. S4. Ammonium persulfate and N,N'-methylenebisacrylamide were added to the nano-hybrid lignin dispersion, stirred, and heated to 70°C for reaction. After 1.5 h of reaction, a nano-hybrid lignin composite solution with a water content of 70% was obtained. The amount of ammonium persulfate added was 1% of the grafted lignin mass, and the amount of N,N'-methylenebisacrylamide added was 4% of the grafted lignin mass. S5. The nano-hybrid lignin composite liquid is mixed with ethyl lactate, tetrasodium diacetate of glutamic acid, benzotriazole and deionized water to obtain a cleaning agent for cleaning circuit boards. The cleaning agent includes the following components by mass: 20% nano-hybrid lignin composite liquid, 7% co-solvent, 1% chelating agent, 0.5% corrosion inhibitor and 71.5% deionized water.

[0028] It should be noted that the nano-titanium dioxide in all the above embodiments has undergone silane coupling modification treatment. The silane coupling modification treatment of nano-titanium dioxide includes the following steps: dispersing nano-titanium dioxide in sufficient anhydrous ethanol, adding 2% by mass of silane coupling agent KH-550 of nano-titanium dioxide, refluxing at 70°C for 5 hours, and after the reaction is completed, filtering, washing and drying are performed to obtain silane coupling modified nano-titanium dioxide.

[0029] Comparative Example 1 S1. A mixture of lignin and a 40% sodium hydroxide solution at a mass ratio of 1:5 is added to a reaction vessel. The reaction vessel is pressurized to 0.25 MPa and heated to 120°C for reaction. After 2 hours of reaction, the reaction is stopped and the mixture inside the reaction vessel is cooled. After cooling, the pH value of the mixture is adjusted to 7 with dilute hydrochloric acid and a solid product is precipitated. The product is then filtered, and the solid product obtained by filtration is washed with deionized water and dried to obtain activated lignin. S2. Activated lignin and maleic anhydride are added to a container containing sufficient N,N-dimethylformamide at a mass ratio of 1:0.8. The mixture is stirred and heated to 80°C for reaction. After 4 hours of reaction, the product is distilled. Acetone is added to the viscous liquid obtained by distillation to produce a solid precipitate. The precipitate is then filtered and the solid product obtained by filtration is washed with acetone and deionized water in sequence and then dried to obtain grafted lignin. S3. Grafted lignin and sodium bisulfite are mixed in an appropriate amount of deionized water at a mass ratio of 1:0.5 and stirred to form a dispersion. While stirring the dispersion, it is heated to 90°C to carry out the reaction. After 3 hours of reaction, a lignin dispersion is obtained. S4. Ammonium persulfate and N,N'-methylenebisacrylamide were added to the lignin dispersion, stirred, and heated to 70°C for reaction. After 1.5 h of reaction, a lignin composite solution with a water content of 70% was obtained. The amount of ammonium persulfate added was 1% of the mass of the grafted lignin, and the amount of N,N'-methylenebisacrylamide added was 4% of the mass of the grafted lignin. S5. The lignin composite liquid is mixed with ethyl lactate, tetrasodium diacetate of glutamic acid, benzotriazole and deionized water to obtain a cleaning agent for cleaning circuit boards. The cleaning agent includes the following components by mass: 10% lignin composite liquid, 7% co-solvent, 1% chelating agent, 0.5% corrosion inhibitor and 81.5% deionized water.

[0030] Comparative Example 2 The cleaning agent obtained according to the technical solution of Example 2 in the specification of Chinese Patent Document CN118909702A.

[0031] According to the standard document SJ / T 11639-2016 "Water-based Cleaning Agents for Electronic Manufacturing", the surface insulation resistance of the circuit boards before and after cleaning with the cleaning agents obtained in all the above examples and comparative examples was tested. The results are shown in Table 1 below. The ionic cleanliness, corrosivity to metals, and corrosivity to polymers of the cleaning agents were also tested. The results are shown in Table 2 below.

[0032]

[0033] Table 1

[0034] Table 2 Analyzing the data in Table 1 above, all cleaning agents resulted in a decrease in the surface insulation resistance of the circuit board after cleaning. Since the cleaning agent of Comparative Example 1 did not contain nano-titanium dioxide, the surface insulation resistance of the circuit board was not affected by the residue of nanoparticles. Therefore, the circuit board cleaned with this cleaning agent maintained a higher surface insulation resistance. Comparing Examples 1, 2, and 3 with Comparative Example 2, the surface insulation resistance of the circuit board cleaned with the cleaning agent of Comparative Example 2 was significantly lower. Furthermore, scanning electron microscopy revealed a large number of fibrous carbon nanotubes attached to the surface of the circuit board cleaned with the cleaning agent of Comparative Example 2, while fewer nano-titanium dioxide particles were observed on the surface of the circuit boards cleaned with the cleaning agents of Examples 1, 2, and 3. Therefore, it can be seen that the cleaning agents of Examples 1, 2, and 3 based on the technical solution of this invention leave fewer nanoparticles on the surface of the circuit board after cleaning, thus maintaining a higher surface insulation resistance.

[0035] Analyzing the data in Table 2 above, Examples 1, 2, and 3 were compared with Comparative Examples 1 and 2. Since the cleaning agent of Comparative Example 1 did not contain nano-titanium dioxide, its cleaning effect on the circuit board was poor. In addition, since the carbon nanotubes in the cleaning agent of Comparative Example 2 were prone to remain on the surface of the circuit board, the pollutants adsorbed by them were also prone to remain on the surface of the circuit board along with the carbon nanotubes, resulting in a cleaning effect that was not as good as the cleaning agent based on the technical solution of the present invention.

[0036] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a cleaning agent for cleaning a circuit board, characterized by, The method comprises the following steps: S1, mixing lignin and sodium hydroxide solution into a reaction kettle, heating the reaction kettle and making the mixture in the reaction kettle react under high pressure, and obtaining activated lignin after the reaction is completed; S2, putting the activated lignin and maleic anhydride into a container containing N,N-dimethylformamide at the same time, stirring and heating the mixture to react, and obtaining grafted lignin after the reaction is completed; S3, mixing the grafted lignin, sodium bisulfite and nano titanium dioxide in deionized water to form a dispersion liquid, stirring and heating the dispersion liquid to react, and obtaining a nano hybrid lignin dispersion liquid after the reaction is completed; S4, putting the thermal initiator and crosslinking agent into the nano hybrid lignin dispersion liquid, stirring and heating to react, and obtaining a nano hybrid lignin composite liquid after the reaction is completed; S5, mixing the nano hybrid lignin composite liquid, a cosolvent, a chelating agent, a corrosion inhibitor and deionized water uniformly to obtain a cleaning agent for cleaning circuit boards.

2. The method for producing a cleaning agent for cleaning a circuit board according to claim 1, characterized by, The water content of the nano hybrid lignin composite liquid is 65% to 75%. The cleaning agent comprises the following components by mass: 10% to 20% of the nano hybrid lignin composite liquid, 5% to 10% of the cosolvent, 0.5% to 2% of the chelating agent, 0.3% to 0.8% of the corrosion inhibitor, and 70% to 84% of the deionized water.

3. The method for producing a cleaning agent for cleaning a circuit board according to Claim 1, wherein In step S1, the concentration of the sodium hydroxide solution is 30% to 50%, and the mass ratio of the lignin to the sodium hydroxide solution is 1:(4 to 6).

4. The method for producing a cleaning agent for cleaning a circuit board according to Claim 1, wherein In step S1, the temperature for heating the mixture of the lignin and the sodium hydroxide solution after mixing is 110 to 130℃, the pressure is 0.2 to 0.3MPa, and the time is 1.5 to 2.5h. After the reaction of the mixture is completed, the pH value is adjusted to 6 to 7, and the solid product is precipitated, then filtered, washed, dried, and the activated lignin is obtained.

5. The method for producing a cleaning agent for cleaning a circuit board according to Claim 1, wherein In step S2, the activated lignin and the maleic anhydride are put into sufficient N,N-dimethylformamide at a mass ratio of 1:(0.7 to 0.9), the temperature for heating the mixture to react is 75 to 85℃, and the time is 3.5 to 4.5h. After the reaction of the mixture is completed, distillation is performed, and after adding acetone to the viscous liquid obtained by distillation, solid precipitates are generated, then filtered, washed, dried, and the grafted lignin is obtained.

6. The method for producing a cleaning agent for cleaning a circuit board according to Claim 1, wherein In step S3, the mass ratio of the grafted lignin, the sodium bisulfite and the nano titanium dioxide in the dispersion liquid is 1:(0.4 to 0.6):(0.1 to 0.15), the temperature for heating the dispersion liquid to react is 85 to 95℃, and the time is 2.5 to 3.5h. After the reaction is completed, the pH value of the nano hybrid lignin dispersion liquid is adjusted to 6 to 7.

5.

7. The method for producing a cleaning agent for cleaning a circuit board according to Claim 1, wherein In step S4, the temperature for heating the nano hybrid lignin dispersion liquid after the thermal initiator and the crosslinking agent are put into the nano hybrid lignin dispersion liquid is 60 to 80℃, and the time is 1 to 2h.

8. The method for producing a cleaning agent for cleaning a circuit board according to Claim 1, wherein The nano-titanium dioxide is subjected to surface modification treatment, and the surface modification treatment of the nano-titanium dioxide comprises the following steps: dispersing the nano-titanium dioxide in anhydrous ethanol, adding 1-3% of silane coupling agent KH-550 by mass of the nano-titanium dioxide, refluxing at 70°C for 4-6 hours, and obtaining the nano-titanium dioxide subjected to silane coupling modification after filtration, washing and drying.

9. The method of producing a cleaning agent for cleaning a circuit board according to Claim 1, wherein The thermal initiator is selected from ammonium persulfate or potassium persulfate, and the addition amount of the thermal initiator is 0.5-2% of the mass of the grafted lignin; The crosslinking agent is selected from N,N'-methylene bisacrylamide or polyethylene glycol diacrylate, and the addition amount of the crosslinking agent is 2-6% of the mass of the grafted lignin.

10. The method of producing a cleaning agent for cleaning a circuit board according to Claim 1, wherein The cosolvent is selected from ethyl lactate or propylene glycol methyl ether; The chelating agent is selected from one of tetrasodium glutamate diacetate, trisodium ethylenediamine disuccinate and trisodium methylglycine diacetate; The corrosion inhibitor is selected from one of benzotriazole, methylbenzotriazole and sodium sarcosinate.

Images