Chemical tin solution for flexible printed circuit boards

Abstract

The application discloses a kind of softness printed circuit board with chemical tin solution, belong to the technical field of circuit board.The chemical tin solution includes stannous sulfate, methyl sulfonic acid, reducing agent, thiourea, complexing agent, phytic acid, ethylenediaminetetraacetic acid disodium, active agent, lanthanum chloride and fluorine-substituted benzimidazole protective agent.Compared with prior art, the hydrophobic network constructed by fluorine-substituted benzimidazole protective agent of the application effectively blocks the penetration of environmental humidity, improves the salt fog resistance and tin thickness of the chemical tin solution, optimizes the grain boundary structure by synergistic effect of rare earth metal additive and composite complexing agent, significantly improves the compactness and uniformity of the coating, meets the fine pitch wiring requirement.In addition, the application can also promote the uniform nucleation of tin ions, inhibit the growth of tin whiskers, achieve high flatness coating, reduce local micropores and cracks, and has high reliability and good application prospect.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board technology, and more particularly to a chemical tin solution for flexible printed circuit boards. Background Technology

[0002] In modern electronics manufacturing, flexible printed circuit boards (FPCs) are widely used in consumer electronics, automotive electronics, and medical devices due to their thinness, lightness, and flexibility. Chemical tin plating, as an important surface treatment process, provides FPCs with excellent conductivity, oxidation resistance, and solderability, thus meeting the high performance and high reliability requirements of electronic devices.

[0003] Traditional chemical tin plating solutions mainly consist of stannous ions, reducing agents, and complexing agents. For example, Chinese patent application CN106939417A discloses a chemical tin plating solution for printed circuit boards, whose formulation includes stannous ions, thiourea, methanesulfonic acid, citric acid, tetrasodium iminodisuccinate, carbazide, surfactant, bismuth acetate, and polyaminopolyether methylenephosphonic acid. This formulation stabilizes stannous ions through multiple complexing agents and uses reducing agents to remove dissolved oxygen from the plating solution, preventing the oxidation of stannous ions, thereby achieving a stable tin deposition rate and good solution stability. However, the addition of bismuth only partially alleviates whisker growth, and in high humidity environments, it is prone to delamination and peeling of the plating layer due to interfacial stress concentration.

[0004] Another Chinese patent application, CN117888094A, discloses a chemical tin-plating composite solution, comprising a tin-plating base agent, a tin-plating corrector, a SnTech tin solution, a special acid SF, and tin-plating additives. This invention's chemical tin-plating process exhibits excellent tinning performance and tin whisker suppression capabilities, and the resulting tin-plated layer maintains the longest tin whisker length and quantity within the stringent IPC-4554 standard during storage. However, the process is relatively complex, involving multiple steps and various specialized chemicals, increasing production costs and process control difficulty.

[0005] Despite the progress made in electroless tin plating, several problems remain to be solved. For example, traditional electroless tin plating solutions are prone to producing tin whiskers under high temperature and humidity conditions, leading to plating failure and affecting the reliability and lifespan of electronic devices. Furthermore, some existing electroless tin plating solutions still need improvement in terms of plating uniformity, density, and corrosion resistance, especially in the manufacture of fine-pitch wiring and high-precision electronic devices, where they struggle to meet increasingly stringent performance requirements.

[0006] Therefore, it is crucial to develop a novel chemical tin solution for flexible printed circuit boards and to address the problems existing in the prior art by optimizing the formulation and process. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a chemical tin solution for flexible printed circuit boards.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A chemical tin solution for flexible printed circuit boards, comprising the following components:

[0010] Stannous sulfate 10-30 g / L, methanesulfonic acid 20-60 g / L, reducing agent 10-30 g / L, thiourea 80-120 g / L, complexing agent 20-60 g / L, phytic acid 20-40 g / L, disodium ethylenediaminetetraacetate 20-40 g / L, activator 20-60 mg / L, lanthanum chloride 0.05-0.15 g / L, fluorinated benzimidazole protectant 1-3 g / L;

[0011] The above component solutions are mixed to prepare a chemical tin plating solution.

[0012] The preparation method of the fluorinated benzimidazole protectant is as follows:

[0013] An o-phenylenediamine compound, a phenylacetic acid compound, and boric acid were mixed, heated, and stirred to react. After cooling to room temperature, methanol was added to the reactants and stirred to dissolve them. The solution was added to an aqueous triethylamine solution and filtered to obtain a crude product. The crude product was dissolved in methanol and decolorized. After filtration, the filtrate was collected, cooled to room temperature, and then added to water. The filtrate was filtered and dried to obtain a fluorinated benzimidazole protectant.

[0014] The mixing temperature is 60-80℃ and the mixing time is 10-30 min.

[0015] The reducing agent is at least one of carbazide, sodium hypophosphite, ascorbic acid, and hydroxylamine hydrochloride.

[0016] The complexing agent is at least one of citric acid and oxalic acid.

[0017] The active agent is fatty alcohol polyoxyethylene ether.

[0018] The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight:

[0019] Mix 10-20 parts of o-phenylenediamine compounds, 15-25 parts of phenylacetic acid compounds, and 0.05-0.2 parts of boric acid, heat to 140-150℃, and stir continuously for 4-8 hours. Cool to room temperature, add 4000-6000 parts of methanol to the reactants, stir to dissolve, and add the solution dropwise to 15000-25000 parts of triethylamine aqueous solution with pH 8-9. Filter to obtain crude product. Dissolve the crude product in 4000-6000 parts of methanol at 40-60℃, and decolorize with activated carbon at 40-60℃ for 1-3 hours. Filter and collect the filtrate, cool to room temperature, and add the filtrate dropwise to 8000-12000 parts of water. Filter and dry under vacuum at 40-60℃ to obtain fluorinated benzimidazole protective agent.

[0020] The o-phenylenediamine compound is at least one of 4-bromo-o-phenylenediamine, 4-nitro-o-phenylenediamine, and 4-chloro-5-fluoro-o-phenylenediamine.

[0021] The phenylacetic acid compound is at least one of 2,4-difluorophenylacetic acid, 4-(trifluoromethyl)phenylacetic acid, and 5-fluorophenylacetic acid.

[0022] The roles of each component in the chemical tin solution of this invention are as follows:

[0023] Stannous sulfate, as a source of tin ions (Sn²⁺), is deposited to form a metallic tin plating layer under the action of a reducing agent.

[0024] Methylsulfonic acid provides an acidic environment, maintaining solution stability and tin ion solubility.

[0025] Reducing agents (such as carbazide / hydroxylamine hydrochloride) reduce Sn²⁺ to metallic tin (Sn 0 ), driving chemical deposition reactions.

[0026] Thiourea complexes tin ions, controlling the deposition rate and inhibiting tin whisker growth.

[0027] Complexing agents (oxalic acid / citric acid) stabilize stannous ions through chelation, preventing oxidation and hydrolytic precipitation.

[0028] Phytic acid enhances the dispersibility of the plating solution, helps form a dense tin layer, and improves adhesion.

[0029] Disodium EDTA enhances the chelation ability of heavy metal ions and reduces interference from impurities.

[0030] Fatty alcohol polyoxyethylene ether (activator) reduces the surface tension of the solution, improves substrate wettability and coating uniformity.

[0031] Lanthanum chloride ions are co-deposited to form a tin-lanthanum alloy, which suppresses tin whiskers and increases the hardness of the coating.

[0032] Fluorinated benzimidazole protectants construct a hydrophobic network through the condensation of o-phenylenediamine compounds and phenylacetic acid compounds, forming coordination bonds and a hydrophobic barrier on the copper surface, blocking salt spray penetration and enhancing corrosion resistance.

[0033] The fluorinated benzimidazole protective agent of this invention exhibits excellent chemical stability, process compatibility, and synergistic enhancement properties in electroless tin solutions. In acidic plating environments, its benzimidazole ring structure remains stable, without side reactions with other components in the plating solution, maintaining a uniform and transparent solution. Its high-temperature resistance allows it to maintain molecular integrity during immersion tin processes, significantly increasing immersion tin thickness. The formed bisfluorinated hydrophobic network effectively blocks ambient moisture, reduces interfacial tension, and improves coating uniformity and corrosion resistance. Simultaneously, it synergistically inhibits tin whisker growth with rare earth additives without inducing component competition and has no negative effects on the performance of electroless tin solutions.

[0034] Compared with existing technologies, it has the following advantages:

[0035] 1) This invention optimizes the grain boundary structure by using rare earth metal additives (such as lanthanum ions), which significantly improves the density and uniformity of the coating and meets the wiring requirements of fine pitch.

[0036] 2) This invention uses a hydrophobic network constructed by fluorine-substituted benzimidazole protective agent to block the penetration of environmental moisture, so that the coating does not produce whiskers after aging, thus breaking through the failure bottleneck of traditional pure tin coating in high temperature and high humidity environment.

[0037] 3) This invention can promote uniform nucleation of tin ions, reduce grain size, and significantly reduce surface undulation; at the same time, it fills the voids in the tin lattice, suppresses stress concentration caused by volume expansion, blocks tin whisker growth from the source, and achieves a highly flat coating that reduces local micropores and cracks. Detailed Implementation

[0038] Main source of materials:

[0039] Fatty alcohol polyoxyethylene ether, item number: AEO-3, brand: BASF, Germany.

[0040] Activated carbon, item number: 6741, particle size: 200 mesh, function: decolorization, Hubei Tongke Activated Carbon Co., Ltd.

[0041] All other raw materials used in the embodiments and comparative examples of this invention are commercially available products.

[0042] Example 1

[0043] A chemical tin solution for flexible printed circuit boards, comprising the following components:

[0044] Stannous sulfate 20 g / L, methanesulfonic acid 40 g / L, carbazide 20 g / L, thiourea 100 g / L, oxalic acid 40 g / L, phytic acid 30 g / L, disodium ethylenediaminetetraacetate 30 g / L, fatty alcohol polyoxyethylene ether 40 mg / L, lanthanum chloride 0.1 g / L, fluorinated benzimidazole protectant 2 g / L;

[0045] The above component solutions are mixed at 70°C for 20 minutes to prepare the chemical tin solution for flexible printed circuit boards.

[0046] The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight:

[0047] 15 parts of 4-chloro-5-fluoro-o-phenylenediamine, 19 parts of 5-fluorophenylacetic acid, and 0.12 parts of boric acid were mixed and heated to 145°C. The mixture was stirred continuously for 6 hours and then cooled to room temperature. 5000 parts of methanol were added to the reactants and stirred to dissolve them. The solution was then added dropwise to 20000 parts of triethylamine aqueous solution with a pH of 8.5. The mixture was filtered to obtain a crude product. The crude product was dissolved in 5000 parts of methanol at 50°C and decolorized with activated carbon at 50°C for 2 hours. The filtrate was collected after filtration, cooled to room temperature, and then added dropwise to 10000 parts of water. The mixture was filtered and dried under vacuum at 50°C to obtain a fluorinated benzimidazole protective agent.

[0048] Example 2

[0049] A chemical tin solution for flexible printed circuit boards is basically the same as that in Example 1, except that the preparation method of the fluorinated benzimidazole protective agent is different.

[0050] The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight:

[0051] 15 parts of 4-nitro-o-phenylenediamine, 19 parts of 5-fluorophenylacetic acid, and 0.12 parts of boric acid were mixed and heated to 145°C. The mixture was stirred continuously for 6 hours and then cooled to room temperature. 5000 parts of methanol were added to the reactants and stirred to dissolve them. The solution was then added dropwise to 20000 parts of triethylamine aqueous solution with a pH of 8.5. The mixture was filtered to obtain a crude product. The crude product was dissolved in 5000 parts of methanol at 50°C and decolorized with activated carbon at 50°C for 2 hours. The filtrate was collected after filtration, cooled to room temperature, and then added dropwise to 10000 parts of water. The mixture was filtered and dried under vacuum at 50°C to obtain a fluorinated benzimidazole protective agent.

[0052] Example 3

[0053] A chemical tin solution for flexible printed circuit boards is basically the same as that in Example 1, except that the preparation method of the fluorinated benzimidazole protective agent is different.

[0054] The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight:

[0055] 15 parts of 4-bromo-o-phenylenediamine, 19 parts of 5-fluorophenylacetic acid, and 0.12 parts of boric acid were mixed and heated to 145°C. The mixture was stirred continuously for 6 hours and then cooled to room temperature. 5000 parts of methanol were added to the reactants and stirred to dissolve them. The solution was then added dropwise to 20000 parts of triethylamine aqueous solution with a pH of 8.5. The mixture was filtered to obtain a crude product. The crude product was dissolved in 5000 parts of methanol at 50°C and decolorized with activated carbon at 50°C for 2 hours. The filtrate was collected, cooled to room temperature, and then added dropwise to 10000 parts of water. The mixture was filtered and dried under vacuum at 50°C to obtain a fluorinated benzimidazole protective agent.

[0056] Example 4

[0057] A chemical tin solution for flexible printed circuit boards is basically the same as that in Example 1, except that the preparation method of the fluorinated benzimidazole protective agent is different.

[0058] The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight:

[0059] 15 parts of 4-chloro-5-fluoro-o-phenylenediamine, 19 parts of 4-(trifluoromethyl)phenylacetic acid, and 0.12 parts of boric acid were mixed and heated to 145°C. The mixture was stirred continuously for 6 hours and then cooled to room temperature. 5000 parts of methanol were added to the reactants and stirred to dissolve them. The solution was then added dropwise to 20000 parts of triethylamine aqueous solution with a pH of 8.5. The mixture was filtered to obtain a crude product. The crude product was dissolved in 5000 parts of methanol at 50°C and decolorized with activated carbon at 50°C for 2 hours. The filtrate was collected after filtration, cooled to room temperature, and then added dropwise to 10000 parts of water. The mixture was filtered and dried under vacuum at 50°C to obtain a fluorinated benzimidazole protective agent.

[0060] Example 5

[0061] A chemical tin solution for flexible printed circuit boards is basically the same as that in Example 1, except that the preparation method of the fluorinated benzimidazole protective agent is different.

[0062] The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight:

[0063] 15 parts of 4-chloro-5-fluoro-o-phenylenediamine, 19 parts of 2,4-difluorophenylacetic acid, and 0.12 parts of boric acid were mixed and heated to 145°C. The mixture was stirred continuously for 6 hours and then cooled to room temperature. 5000 parts of methanol were added to the reactants and stirred to dissolve them. The solution was then added dropwise to 20000 parts of triethylamine aqueous solution with a pH of 8.5. The mixture was filtered to obtain a crude product. The crude product was dissolved in 5000 parts of methanol at 50°C and decolorized with activated carbon at 50°C for 2 hours. The filtrate was collected, cooled to room temperature, and then added dropwise to 10000 parts of water. The mixture was filtered and dried under vacuum at 50°C to obtain a fluorinated benzimidazole protective agent.

[0064] Example 6

[0065] A chemical tin solution for flexible printed circuit boards is essentially the same as that in Example 1, except that the carbazide is replaced with an equal amount of hydroxylamine hydrochloride.

[0066] Comparative Example 1

[0067] A chemical tin solution for flexible printed circuit boards is basically the same as that in Example 1, except that the preparation method of the fluorinated benzimidazole protective agent is different.

[0068] The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight:

[0069] 15 parts of 4-chloro-o-phenylenediamine, 19 parts of 5-fluorophenylacetic acid, and 0.12 parts of boric acid were mixed and heated to 145°C. The mixture was stirred continuously for 6 hours and then cooled to room temperature. 5000 parts of methanol were added to the reactants and stirred to dissolve them. The solution was then added dropwise to 20000 parts of triethylamine aqueous solution with a pH of 8.5. The mixture was filtered to obtain a crude product. The crude product was dissolved in 5000 parts of methanol at 50°C and decolorized with activated carbon at 50°C for 2 hours. The filtrate was collected, cooled to room temperature, and then added dropwise to 10000 parts of water. The mixture was filtered and dried under vacuum at 50°C to obtain a fluorinated benzimidazole protective agent.

[0070] Comparative Example 2

[0071] A chemical tin solution for flexible printed circuit boards is basically the same as that in Example 1, except that the preparation method of the fluorinated benzimidazole protective agent is different.

[0072] The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight:

[0073] 15 parts of 4-chloro-5-fluoroo-phenylenediamine, 19 parts of 2-chloro-4-fluorophenylacetic acid, and 0.12 parts of boric acid were mixed and heated to 145°C. The mixture was stirred continuously for 6 hours and then cooled to room temperature. 5000 parts of methanol were added to the reactants and stirred to dissolve them. The solution was then added dropwise to 20000 parts of triethylamine aqueous solution with a pH of 8.5. The mixture was filtered to obtain a crude product. The crude product was dissolved in 5000 parts of methanol at 50°C and decolorized with activated carbon at 50°C for 2 hours. The filtrate was collected, cooled to room temperature, and then added dropwise to 10000 parts of water. The mixture was filtered and dried under vacuum at 50°C to obtain a fluorinated benzimidazole protective agent.

[0074] Comparative Example 3

[0075] A chemical tin solution for flexible printed circuit boards is basically the same as that in Example 1, except that the preparation method of the fluorinated benzimidazole protective agent is different.

[0076] The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight:

[0077] 15 parts of 4-chloro-o-phenylenediamine, 19 parts of 2-chloro-4-fluorophenylacetic acid, and 0.12 parts of boric acid were mixed and heated to 145°C. The mixture was stirred continuously for 6 hours and then cooled to room temperature. 5000 parts of methanol were added to the reactants and stirred to dissolve them. The solution was then added dropwise to 20000 parts of triethylamine aqueous solution with a pH of 8.5. The mixture was filtered to obtain a crude product. The crude product was dissolved in 5000 parts of methanol at 50°C and decolorized with activated carbon at 50°C for 2 hours. The filtrate was collected after filtration and cooled to room temperature. The filtrate was then added dropwise to 10000 parts of water and filtered. The mixture was then dried under vacuum at 50°C to obtain a fluorinated benzimidazole protective agent.

[0078] Comparative Example 4

[0079] A chemical tin solution for flexible printed circuit boards is essentially the same as that in Example 1, except that the fluorinated benzimidazole protective agent is not added.

[0080] Test Example 1

[0081] Flexible printed circuit boards (FPCs) were treated with the chemical tin solutions prepared in the embodiments and comparative examples of this invention. The pre-immersion plating time was 1 minute and the temperature was 30°C; the immersion plating time was 10 minutes and the temperature was 65°C.

[0082] Salt spray resistance test: The test shall be conducted in accordance with GB / T 2423.17-2024 "Environmental testing - Part 2: Test methods - Test Ka: Salt spray".

[0083] The test results are shown in Table 1.

[0084] Table 1

[0085]

[0086] Test Example 2

[0087] The thickness of the immersion tin layer was measured after treatment with the chemical tin solution prepared in the embodiments and comparative examples of the present invention in Test Example 1. Ten points were taken on the front side of the immersion tin flexible printed circuit board (FPC) and the tin thickness was measured by X-ray.

[0088] The test results are shown in Table 2.

[0089] Table 2

[0090]

[0091] The advantages of 4-chloro-5-fluoroo-phenylenediamine in the 5-fluorophenylacetic acid system stem from the synergistic effect of its molecular structure. The ortho-chlorine and fluorine form a strongly electronegative region, significantly enhancing the coordination ability with the copper substrate. Through chelation, a stable six-membered ring structure is constructed, increasing bond energy. Simultaneously, the small van der Waals radius of the fluorine atom in the 5-fluorosubstituted benzene ring greatly reduces steric hindrance, allowing the fluorinated benzimidazole protective agent molecules to be highly ordered and adsorbed on the copper surface, optimizing crystallization uniformity. Furthermore, this combination forms a bifluorinated hydrophobic network with 5-fluorophenylacetic acid, effectively blocking salt spray penetration. In contrast, the monochloro-substituted form, lacking fluorine atoms, results in weak interfacial bonding, leading to delamination and bubbling. This synergistic effect of the molecular structure enables the protective agent to form a uniform and dense protective layer on the copper substrate, providing a good foundation for the uniform deposition of tin ions. This helps improve the uniformity and stability of the tin deposition thickness, reduces uneven tin deposition caused by local defects, and ultimately increases the overall tin deposition thickness.

[0092] 5-Fluorophenylacetic acid, with its para-fluorine substitution, forms a complementary electron cloud distribution with the ortho-fluorine of the amine component, achieving strong coordination anchoring. Simultaneously, the small size of the fluorine atoms maintains molecular planarity, reduces steric hindrance, and promotes the crystallization of a dense tin layer. Furthermore, the two synergistically construct a continuous hydrophobic network, effectively blocking salt spray penetration. This combination, through dual optimization of electron and space, simultaneously improves tin deposition efficiency and corrosion resistance, exhibiting high reliability. This structural characteristic of 5-fluorophenylacetic acid facilitates the uniform adsorption and deposition of tin ions on its surface, reducing tin ion aggregation and uneven distribution during deposition, thereby improving the density and uniformity of the tin deposition layer and further increasing the tin deposition thickness.

[0093] The improved salt spray resistance in Example 6 after replacing carbazide with hydroxylamine hydrochloride may be due to the fact that hydroxylamine hydrochloride has a lower reduction potential than carbazide, allowing for a more thorough reduction of Sn²⁺ to Sn. 0 This reduces residual stannous ions; the latter are easily oxidized to SnO in salt spray environments, causing volume expansion and stratification risks. Hydroxylamine hydrochloride has a stronger reducing power and can more effectively reduce Sn²⁺ to Sn.0 This improves the deposition efficiency of tin ions, allowing more tin ions to be deposited on the substrate surface, thereby increasing the thickness of the tin plating layer. Simultaneously, reducing residual tin ions avoids uneven deposition and defects that may be caused during the deposition process, further improving the quality and thickness uniformity of the tin plating layer.

Claims

1. A chemical tin solution for flexible printed circuit boards, characterized in that, Includes the following components: Stannous sulfate 10-30 g / L, methanesulfonic acid 20-60 g / L, reducing agent 10-30 g / L, thiourea 80-120 g / L, complexing agent 20-60 g / L, phytic acid 20-40 g / L, disodium ethylenediaminetetraacetate 20-40 g / L, activator 20-60 mg / L, lanthanum chloride 0.05-0.15 g / L, fluorinated benzimidazole protectant 1-3 g / L; The above component solutions are mixed to prepare a chemical tin plating solution; The preparation method of the fluorinated benzimidazole protectant is as follows: An o-phenylenediamine compound, a phenylacetic acid compound, and boric acid were mixed, heated, and stirred to react. After cooling to room temperature, methanol was added to the reactants and stirred to dissolve them. The solution was added to an aqueous triethylamine solution and filtered to obtain a crude product. The crude product was dissolved in methanol and decolorized. After filtration, the filtrate was collected, cooled to room temperature, and then added to water. The filtrate was filtered and dried to obtain a fluorinated benzimidazole protective agent. The o-phenylenediamine compound is at least one of 4-bromo-o-phenylenediamine, 4-nitro-o-phenylenediamine, and 4-chloro-5-fluoro-o-phenylenediamine; The phenylacetic acid compound is at least one of 2,4-difluorophenylacetic acid, 4-(trifluoromethyl)phenylacetic acid, and 5-fluorophenylacetic acid.

2. The chemical tin solution for flexible printed circuit boards as described in claim 1, characterized in that, The mixing temperature is 60-80℃ and the mixing time is 10-30 min.

3. The chemical tin solution for flexible printed circuit boards as described in claim 1, characterized in that, The reducing agent is at least one of carbazide, sodium hypophosphite, ascorbic acid, and hydroxylamine hydrochloride.

4. The chemical tin solution for flexible printed circuit boards as described in claim 1, characterized in that, The complexing agent is at least one of citric acid and oxalic acid.

5. The chemical tin solution for flexible printed circuit boards as described in claim 1, characterized in that, The active agent is fatty alcohol polyoxyethylene ether.

6. The chemical tin solution for flexible printed circuit boards as described in claim 1, characterized in that, The preparation method of the fluorinated benzimidazole protectant is as follows, in parts by weight: Mix 10-20 parts of o-phenylenediamine compounds, 15-25 parts of phenylacetic acid compounds, and 0.05-0.2 parts of boric acid, heat to 140-150℃, and stir continuously for 4-8 hours. Cool to room temperature, add 4000-6000 parts of methanol to the reactants, stir to dissolve, and add the solution dropwise to 15000-25000 parts of triethylamine aqueous solution with pH 8-9. Filter to obtain crude product. Dissolve the crude product in 4000-6000 parts of methanol at 40-60℃, and decolorize with activated carbon at 40-60℃ for 1-3 hours. Filter and collect the filtrate, cool to room temperature, and add the filtrate dropwise to 8000-12000 parts of water. Filter and dry under vacuum at 40-60℃ to obtain fluorinated benzimidazole protective agent.

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