Water-soluble flux and method for producing the same

Abstract

The application relates to the field of welding technology, and particularly discloses a water-soluble flux and a preparation method thereof. The water-soluble flux comprises the following raw materials in parts by weight: 6-12 parts of a borate ester covalent activator; 3-8 parts of cucurbituril hydrate; 0.01-2 parts of an inhibitor; 1-3 parts of a modified graphene quantum dot solution; 1-5 parts of a cyclic ether solvent; 0.5-2 parts of a metal-organic framework material containing mercapto groups; and 68-88.5 parts of deionized water. The modified graphene quantum dot solution is obtained by modifying graphene quantum dots with dioctadecyldimethylammonium chloride. The flux of the application can effectively solve the problem of water residue in the later stage after the activator is decomposed and volatilized in the early stage of welding by combining the water-soluble flux with the cyclic ether solvent, thereby reducing the problems of virtual welding, bubble defects and the like of the welding points, and effectively improving the strength and reliability of the welding points.

Description

Technical Field

[0001] This application relates to the field of welding technology, and more specifically, to a water-soluble flux and a method for preparing the same. Background Technology

[0002] Flux, also known as soldering flux, is a chemical substance used in the soldering process to clean, prevent oxidation, and enhance solder quality. It is commonly used in soldering processes to remove oxide layers from metal surfaces, provide better contact performance, and aid in the melting and diffusion of solder and welding materials. Flux is essential for both dip soldering and wave soldering of electronic components. The two most widely used fluxes are rosin-based and water-soluble. Rosin-based fluxes offer good solderability but require a large amount of organic solvents. Large amounts of organic solvents are detrimental to environmental protection and human health; therefore, in recent years, the application of water-soluble fluxes in the electronics industry has received increasing attention.

[0003] In related technologies, such as the patent document with publication number CN108465984B, a halogen-free water-soluble flux and its preparation method are disclosed. It is prepared from the following components by weight percentage: 4-8% activator, 6-10% surfactant, 0.05-1% corrosion inhibitor, 1-5% alcohol ether solvent, 20-30% co-solvent, and the balance being deionized water. This water-soluble flux does not contain halides, has low corrosiveness, is less prone to product breakage, and exhibits good performance.

[0004] However, the above-mentioned fluxes have the following problems in actual use: Since the activator is mainly composed of traditional organic acids (such as succinic acid and adipic acid), under high-temperature welding environments, especially wave soldering or long-term continuous welding, the acidic substances are prone to volatilization or decomposition, leading to a decrease in oxide film removal ability during the middle and later stages of welding, which may cause problems such as incomplete soldering and poor solder joint gloss. Furthermore, because water has a higher boiling point, its evaporation rate is slower than that of organic solvents. During high-speed welding, residual water may form bubbles or cause poor welding. The presence of water molecules may affect the contact and reaction between the activator and the metal surface, thereby reducing the strength and reliability of the solder joint. Summary of the Invention

[0005] In order to improve the strength and reliability of solder joints and avoid problems such as bubbles, incomplete soldering, and poor solder joint gloss, this application provides a water-soluble flux and its preparation method.

[0006] The water-soluble flux provided in this application adopts the following technical solution:

[0007] A water-soluble flux, comprising the following raw materials in parts by weight:

[0008] 6-12 parts of borate ester covalent activator;

[0009] 3-8 parts of cucurbituril hydrate;

[0010] Corrosion inhibitor 0.01-2 parts;

[0011] 1-3 parts of modified graphene quantum dot solution;

[0012] 1-5 parts of cyclic ether solvents;

[0013] 0.5-2 parts of a thiol-containing metal-organic framework material;

[0014] 68-88.5 parts deionized water;

[0015] The modified graphene quantum dot solution was obtained by modifying graphene quantum dots with dioctadecyldimethylammonium chloride.

[0016] By adopting the above technical solution, the borate ester covalent activator anchors organic acids (such as 4-boronic acid-phenylacetic acid) to polyol molecules through the borate ester bond, thereby reducing the vapor pressure of organic acids and solving the problem of activator volatilization at room temperature. At the high temperature of welding, the borate ester bond hydrolyzes and breaks, releasing free organic acids to react with metal oxides. At the same time, the generated polyol acts as a co-solvent to improve wettability. The "anchoring-release" of the activator is achieved through the borate ester bond, with high response temperature accuracy, effectively solving the problem of premature exposure of the activator leading to easy volatilization or decomposition. This allows the flux to maintain a high efficiency in oxide film removal under long-term welding conditions, thereby improving the strength and reliability of the solder joint.

[0017] The hydrophobic cavities of cucurbituril hydrate selectively encapsulate water molecules, forming supramolecular complexes with a particle size of approximately 2 nm. This effectively reduces water activity and inhibits the formation of bubbles from water evaporation at high temperatures. When the temperature exceeds 150°C, water molecules are released from the cage-like structure of the cucurbituril hydrate and evaporate rapidly, preventing residual water from forming bubbles. By employing cyclic ether solvents, which have higher boiling points, the difference in boiling points with water can be reduced, minimizing the difference in their evaporation rates and further reducing residual water. This avoids affecting the contact and reaction between the activator and the metal surface, thereby enhancing the strength and reliability of the solder joint.

[0018] The long-chain alkyl groups of modified graphene quantum dots are oriented to form a hydrophobic layer, reducing the solder contact angle and thus promoting solder spread, which in turn improves the strength and reliability of the weld. Metal-organic framework materials containing thiol groups have pores that can adsorb residual organic acids. The thiol groups (-SH) form a sulfide passivation layer on the metal surface, repairing micro-corrosion defects within one hour after welding. This reduces the adverse effects of flux residue on the solder joint, ensuring weld strength and reliability.

[0019] Optionally, the borate ester covalent activator is prepared by the following method:

[0020] A. Add 4-bromophenylacetic acid, isopropanol pinacol boronic acid ester, palladium catalyst and sodium hydroxide to tetrahydrofuran, heat to 80-90℃ under nitrogen protection and reflux for 6-12h. After cooling, add dilute hydrochloric acid to acidify the solution system to pH 2, and dry the precipitated product to obtain 4-boronic acid phenylacetic acid.

[0021] B. Mix 4-boronic acid phenylacetic acid and glycerol in acetate buffer and stir at 50-60℃ for 2-3 hours to obtain a borate ester covalent activator.

[0022] Optionally, the mass ratio of 4-bromophenylacetic acid, isopropanol pinacol boronic acid ester, palladium catalyst and sodium hydroxide is 1:(1-1.1):(0.2-0.3):(0.3-0.4); the concentration of the dilute hydrochloric acid is 5-6 mol / L.

[0023] Optionally, the mass ratio of the 4-boronic acid phenylacetic acid to glycerol is 1:(0.5-0.6).

[0024] By adopting the above technical solution, the above preparation method can effectively improve the yield of borate esters. Acetic acid buffer can promote the esterification reaction of boric acid and glycerol hydroxyl groups to form a stable five-membered ring structure, ensuring the stability of storage at room temperature and the accurate release of organic acids to participate in activation at high temperature. Excess glycerol shifts the reaction towards the formation of borate esters, inhibits the reverse reaction hydrolysis, and improves the stability of the complex.

[0025] Optionally, the modified graphene quantum dot solution is prepared by the following method:

[0026] Dioctadecyldimethylammonium chloride was added to the aqueous solution of graphene quantum dots and stirred for 5-10 min. The mixture was then transferred to a three-necked flask and heated to 60-70 °C under nitrogen protection. The mixture was refluxed and stirred for 2-3 h. After the reaction was completed, the mixture was cooled to room temperature and dialyzed for 18-24 h using a dialysis bag with a molecular weight cutoff of 1000 to obtain the modified graphene quantum dot solution.

[0027] By employing the above technical solution, bis(octadecyldimethylammonium chloride) forms a coating structure on the surface of graphene quantum dots through electrostatic adsorption and hydrophobic interaction. Dialysis removes unreacted surfactants, ensuring uniform dispersion of the quantum dots. This modified graphene quantum dot effectively increases the solder spreading area, thereby ensuring good solder joint quality and effectively reducing the resistance of the welding interface.

[0028] Optionally, the mass concentration of the graphene quantum dot aqueous solution is 5-10 mg / mL; the mass ratio of bis(octadecyldimethylammonium chloride) to the graphene quantum dot aqueous solution is (2-3):1.

[0029] Optionally, the thiol-containing metal-organic framework material includes either ZIF-90-SH or ZIF-8-SH.

[0030] By adopting the above technical solution, the pores of the zeolite imidazole ester framework material and methyl imidazole in the above metal-organic framework material can adsorb residual organic acids, and the thiol group (-SH) forms a sulfide passivation layer with the metal surface, thereby quickly repairing micro-corrosion defects during welding, and reducing the adverse effects caused by flux residue on the weld joint, which is conducive to ensuring the weld joint strength and reliability.

[0031] Optionally, the cyclic ether solvent includes any one of tetrahydrofuran, methyltetrahydrofuran, and tetrahydropyran.

[0032] By adopting the above technical solution, the aforementioned cyclic ether solvent can form a low azeotrope with water, allowing water and solvent to evaporate simultaneously in the early stage of welding, avoiding water residue at high temperatures, and thus effectively enhancing the strength and reliability of the weld joint.

[0033] Optionally, the corrosion inhibitor may be any one of diethanolamine, triethanolamine, and triisopropanolamine.

[0034] This application also provides a method for preparing a water-soluble flux, using the following technical solution:

[0035] A method for preparing a water-soluble flux, comprising the following steps:

[0036] Under nitrogen protection, deionized water, cyclic ether solvent, borate ester covalent activator, cucurbituril hydrate and modified graphene quantum dot solution are added sequentially to the reactor. After stirring evenly, a metal-organic framework material containing thiol groups is added. The mixture is stirred at 30-40℃ for 1-2 hours. Finally, a corrosion inhibitor is added and the mixture is stirred for 10-15 minutes to obtain the water-soluble flux.

[0037] The flux prepared by the above method exhibits the following characteristics: the borate ester covalent activator remains highly stable at room temperature, effectively inhibiting activator volatilization and loss. At the high-temperature welding environment, it precisely hydrolyzes, releasing organic acids to efficiently remove the oxide film on the metal surface. Simultaneously, the polyol improves wettability, ensuring strong deoxidation capabilities throughout the welding process. The synergistic effect of cucurbituril hydrate and cyclic ether solvents allows for simultaneous evaporation of the cyclic ether solvent and water as a low-level azeotrope in the initial welding stage, reducing residual moisture. Meanwhile, the cucurbituril hydrate releases water molecules and evaporates rapidly at high temperatures, preventing bubble formation. Through the synergistic effect of these components, precise control of the welding process is achieved, effectively avoiding problems such as activator failure, moisture interference, poor interfacial wettability, and corrosion. This significantly improves the mechanical strength and electrical properties of the weld joint, enhancing its strength and reliability, and preventing issues such as bubbles, incomplete welds, and poor weld gloss.

[0038] In summary, this application has the following beneficial effects:

[0039] 1. This application employs a borate ester covalent activator, which combines organic acids and polyols through dynamic covalent bonds to form an activation system that is stable at room temperature and responsive at high temperatures. At room temperature, the activator exists in a stable cyclic structure, avoiding the volatilization loss of traditional organic acids. In the high-temperature welding environment, the covalent bonds break precisely, releasing the active ingredients to continuously and efficiently remove the metal oxide film, while the generated polyol improves wettability. This "low-temperature lock-in, high-temperature activation" mechanism solves the problem of insufficient deoxidation capacity in the mid-to-late stages caused by the volatilization or decomposition of traditional activators at high temperatures, ensuring stable oxide film removal capacity throughout the welding cycle, reducing defects such as incomplete solder joints and poor solder joint gloss from the root, and significantly improving solder joint strength and reliability.

[0040] 2. This application constructs a precise moisture control system through the synergistic effect of cucurbituril hydrate and cyclic ether solvents. The hydrophobic cavities of cucurbituril selectively encapsulate water molecules, reducing water activity and inhibiting high-temperature bubble formation; the cyclic ether solvent forms an azeotropic system with water, regulating the evaporation rate and preventing moisture residue during high-speed welding. In the initial welding stage, the solvent and encapsulated water evaporate simultaneously, maintaining system wettability; during the high-temperature stage, the encapsulated water is released and rapidly evaporates, ensuring no moisture interference at the welding interface. This design effectively solves the problems of bubbles, cold welding, and poor activator contact caused by slow water evaporation in traditional water-based fluxes, improving solder joint density and interfacial reaction efficiency, and significantly enhancing solder joint strength and reliability.

[0041] 3. The flux of this application constructs a cross-scale protection system through the multiple effects of modified graphene quantum dots, mercapto-containing metal-organic frameworks (MOFs), and corrosion inhibitors. Modified graphene quantum dots form a hydrophobic layer on the metal surface, reducing the solder contact angle and promoting spread, thereby improving the conductivity and mechanical strength of the solder interface. Mercapto-containing MOFs adsorb residual acid through pores and repair micro-corrosion defects through mercapto film formation. The corrosion inhibitor neutralizes free acid and forms an adsorbed protective film. The synergistic effect of these multiple components optimizes immediate soldering wettability and inhibits long-term corrosion through a dynamic repair mechanism, solving the problem of residual corrosion in traditional fluxes. This allows solder joints to maintain high insulation and mechanical stability even in harsh environments such as humid heat, comprehensively improving the long-term reliability of electronic devices. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the embodiments.

[0043] The various raw materials used in the embodiments and comparative examples of this application were obtained commercially available. ZIF-90-SH and ZIF-8-SH were purchased from Xi'an Ruixi Biotechnology Co., Ltd., and their thiol loading was 3 mmol / g. Graphene quantum dot solution was purchased from Suzhou Carbon-Feng Graphene Technology Co., Ltd. 4-Bromophenylacetic acid was purchased from Hangzhou Hairui Chemical Co., Ltd. Isopropanol pinacol borate was purchased from Hubei Hongxin Ruiyu Fine Chemical Co., Ltd. and cucurbituril hydrate was purchased from Hubei Jusheng Technology Co., Ltd.

[0044] Preparation example of borate ester covalent activators

[0045] Preparation Example 1

[0046] The borate ester covalent activator was prepared by the following method:

[0047] A. Add 1 kg of 4-bromophenylacetic acid, 1 kg of isopropanol pinacol boronic acid ester, 0.2 kg of tetraphenylphosphine palladium, and 0.3 kg of sodium hydroxide to 5 kg of tetrahydrofuran. Heat to 80 °C and reflux for 12 h under nitrogen protection. After cooling, add 5 mol / L dilute hydrochloric acid to acidify the solution to pH 2. Dry the precipitated product to obtain 4-boronic acid phenylacetic acid.

[0048] B. Mix 1 kg of 4-boronic acid phenylacetic acid and 0.5 kg of glycerol in 5 kg of acetate buffer and stir at 50 °C for 3 h to obtain a borate ester covalent activator.

[0049] Preparation Example 2

[0050] The borate ester covalent activator was prepared by the following method:

[0051] A. Add 1 kg of 4-bromophenylacetic acid, 1.05 kg of isopropanol pinacol boronic acid ester, 0.25 kg of tetraphenylphosphine palladium, and 0.35 kg of sodium hydroxide to 5 kg of tetrahydrofuran. Heat to 85 °C and reflux for 9 h under nitrogen protection. After cooling, add 5.5 mol / L dilute hydrochloric acid to acidify the solution to pH 2. Dry the precipitated product to obtain 4-boronic acid phenylacetic acid.

[0052] B. Mix 1 kg of 4-boronic acid phenylacetic acid and 0.55 kg of glycerol in 5 kg of acetate buffer and stir at 55 °C for 2.5 h to obtain a borate ester covalent activator.

[0053] Preparation Example 3

[0054] The borate ester covalent activator was prepared by the following method:

[0055] A. Add 1 kg of 4-bromophenylacetic acid, 1.1 kg of isopropanol pinacol borate, 0.3 kg of tetraphenylphosphine palladium, and 0.4 kg of sodium hydroxide to 5 kg of tetrahydrofuran. Heat to 90 °C and reflux for 6 h under nitrogen protection. After cooling, add 6 mol / L dilute hydrochloric acid to acidify the solution to pH 2. Dry the precipitated product to obtain 4-boronic acid phenylacetic acid.

[0056] B. Mix 1 kg of 4-boronic acid phenylacetic acid and 0.6 kg of glycerol in 5 kg of acetate buffer and stir at 60 °C for 2 h to obtain a borate ester covalent activator.

[0057] Example of preparation of modified graphene quantum dot solution

[0058] Preparation Example 4

[0059] The modified graphene quantum dot solution was prepared using the following method:

[0060] 2 kg of bis(octadecyl)dimethylammonium chloride was added to 1 kg of graphene quantum dot aqueous solution with a concentration of 10 mg / mL. The mixture was stirred for 5 min, then transferred to a three-necked flask. Under nitrogen protection, the mixture was heated to 60 °C and refluxed with stirring for 3 h. After the reaction was completed, the mixture was cooled to room temperature and dialyzed for 18 h using a dialysis bag with a molecular weight cutoff of 1000 to obtain a modified graphene quantum dot solution.

[0061] Preparation Example 5

[0062] The modified graphene quantum dot solution was prepared using the following method:

[0063] 2.5 kg of bis(octadecyl)dimethylammonium chloride was added to 1 kg of graphene quantum dot aqueous solution with a concentration of 8 mg / mL. The mixture was stirred for 8 min, then transferred to a three-necked flask. The mixture was heated to 65 °C under nitrogen protection and stirred under reflux for 2.5 h. After the reaction was completed, the mixture was cooled to room temperature and dialyzed for 22 h using a dialysis bag with a molecular weight cutoff of 1000 to obtain the modified graphene quantum dot solution.

[0064] Preparation Example 6

[0065] The modified graphene quantum dot solution was prepared using the following method:

[0066] 3 kg of bis(octadecyl)dimethylammonium chloride was added to 1 kg of a 10 mg / mL aqueous solution of graphene quantum dots and stirred for 10 min. The mixture was then transferred to a three-necked flask and heated to 70 °C under nitrogen protection. The mixture was refluxed and stirred for 3 h. After the reaction was completed, the mixture was cooled to room temperature and dialyzed for 24 h using a dialysis bag with a molecular weight cutoff of 1000 to obtain a modified graphene quantum dot solution.

[0067] Example

[0068] Example 1

[0069] A water-soluble flux, the components and formulations of which are shown in Table 1, wherein the borate ester covalent activator is the borate ester covalent activator prepared in Preparation Example 1; the corrosion inhibitor is diethanolamine; the modified graphene quantum dot solution is the modified graphene quantum dot solution prepared in Preparation Example 4; the cyclic ether solvent is tetrahydrofuran; and the mercapto-containing metal-organic framework material is ZIF-90-SH.

[0070] A method for preparing a water-soluble flux, comprising the following steps:

[0071] Under nitrogen protection, deionized water, cyclic ether solvent, borate ester covalent activator, cucurbituril hydrate and modified graphene quantum dot solution were added sequentially to the reactor. After stirring evenly, a metal-organic framework material containing thiol groups was added, and the mixture was stirred at 30°C for 1 hour. Finally, a corrosion inhibitor was added and stirred for 10 minutes to obtain the water-soluble flux.

[0072] Example 2

[0073] A water-soluble flux, the components and formulations of which are shown in Table 1, wherein the borate ester covalent activator is the borate ester covalent activator prepared in Preparation Example 1; the corrosion inhibitor is triethanolamine; the modified graphene quantum dot solution is the modified graphene quantum dot solution prepared in Preparation Example 5; the cyclic ether solvent is methyltetrahydrofuran; and the mercapto-containing metal-organic framework material is ZIF-8-SH.

[0074] A method for preparing a water-soluble flux, comprising the following steps:

[0075] Under nitrogen protection, deionized water, cyclic ether solvent, borate ester covalent activator, cucurbituril hydrate and modified graphene quantum dot solution were added sequentially to the reactor. After stirring evenly, a metal-organic framework material containing thiol groups was added, and the mixture was stirred at 35°C for 1.5 h. Finally, a corrosion inhibitor was added and stirred for 12 min to obtain the water-soluble flux.

[0076] Example 3

[0077] A water-soluble flux, the components and formulations of which are shown in Table 1, wherein the borate ester covalent activator is the borate ester covalent activator prepared in Preparation Example 1; the corrosion inhibitor is triisopropanolamine; the modified graphene quantum dot solution is the modified graphene quantum dot solution prepared in Preparation Example 6; the cyclic ether solvent is tetrahydropyran; and the mercapto-containing metal-organic framework material is ZIF-8-SH.

[0078] A method for preparing a water-soluble flux, comprising the following steps:

[0079] Under nitrogen protection, deionized water, cyclic ether solvent, borate ester covalent activator, cucurbituril hydrate and modified graphene quantum dot solution were added sequentially to the reactor. After stirring evenly, a metal-organic framework material containing thiol groups was added, and the mixture was stirred at 40°C for 2 hours. Finally, a corrosion inhibitor was added and stirred for 15 minutes to obtain the water-soluble flux.

[0080] Table 1. Flux raw material ratios (kg) in Examples 1-3

[0081]

[0082] Example 4

[0083] A water-soluble flux, which differs from Example 1 in that: in this example, the borate ester covalent activator is the borate ester covalent activator prepared in Preparation Example 2.

[0084] Example 5

[0085] A water-soluble flux, which differs from Example 1 in that: in this example, the borate ester covalent activator is the borate ester covalent activator prepared in Preparation Example 3.

[0086] Comparative Example

[0087] Comparative Example 1

[0088] A water-soluble flux, which differs from Example 1 in that an equal amount of succinic acid is used instead of borate ester covalent activator in this comparative example.

[0089] Comparative Example 2

[0090] A water-soluble flux, which differs from Example 1 in that: no cucurbita hydrate was added in this comparative example, and the difference was made up with deionized water.

[0091] Comparative Example 3

[0092] A water-soluble flux, which differs from Example 1 in that: no modified graphene quantum dot solution was added in this comparative example, and the difference was made up with deionized water.

[0093] Comparative Example 4

[0094] A water-soluble flux, which differs from Example 1 in that: no mercapto-containing metal-organic framework material was added in this comparative example, and the difference was made up with deionized water.

[0095] Comparative Example 5

[0096] A water-soluble flux, which differs from Example 1 in that methanol is used as the solvent in this comparative example.

[0097] Performance testing

[0098] Test method: Soldering tests were conducted using the fluxes provided in Examples 1-5 and Comparative Examples 1-5. The test substrate was a standard PCB board with OSP surface treatment and a substrate size of 10mm×10mm. The soldering component was a pin-type SOIC-8 chip. The soldering equipment was a manual soldering iron, and the soldering temperature was set to 250±10℃. Ten parallel samples were prepared for each test group, and the average value of the test results was taken.

[0099] Test instruments: precision balance (accuracy 0.1mg), ultrasonic cleaning equipment, tensile tester, special fixtures, AOI equipment, X-ray detector.

[0100] Experimental results: See Table 2

[0101] Table 2 Experimental Results

[0102]

[0103] As shown in Table 2, the fluxes prepared in Examples 1-5 of this application exhibit good performance during the welding process. The flux residue in Examples 1-5 remains at 0.22-0.28%, the welding tensile strength remains above 2.8N, and the solder joints have good gloss and no surface defects. The flux provided in this application, due to the use of a high-boiling-point solvent and a borate ester covalent activator, effectively prevents premature decomposition and volatilization of the activator in the early stages of welding, thus maintaining a good activation effect. This, in turn, helps to improve the welding strength and reliability of the solder joints. The synergistic effect of cucurbituril hydrate and cyclic ether solvents allows the cyclic ether solvent and water to form a low azeotrope and volatilize simultaneously in the early stages of welding, reducing residual moisture and preventing bubble formation.

[0104] In Comparative Example 1, a traditional succinic acid activator was used as the flux, resulting in a flux residue of 1.92%, a welding tensile strength of only 1.26 N, and a dull and rough solder joint. Because traditional succinic acid activator is volatile at room temperature, insufficient activator concentration in the later stages of welding prevents effective removal of the oxide film, leading to poor solder joints and reduced bonding strength. Furthermore, the decomposition of succinic acid at high temperatures generates bubbles, and residual moisture exacerbates interface defects, resulting in a rough and dull surface structure due to oxidation and bubbles.

[0105] In Comparative Example 2, due to the absence of cucurbitacin hydrate in the flux, the final flux residue was 1.34%, the welding tensile strength was 1.42 N, and the solder joint gloss was dull and rough. The lack of hydrophobic cavity encapsulation by cucurbitacin resulted in the presence of free water molecules, which rapidly evaporated at high temperatures, generating bubbles and consequently reducing the strength and deteriorating the gloss of the solder joint.

[0106] In Comparative Example 3, the flux without modified graphene quantum dot solution was not added. Final testing showed that the residual flux level was similar to that of the example, and the solder joints were bright and defect-free. However, the tensile strength of the solder joints was only 1.42 N. Due to the lack of a hydrophobic layer with oriented modified graphene quantum dots, the solder contact angle increased, resulting in insufficient solder spread and inadequate interfacial contact, leading to a decrease in the mechanical strength of the solder joints.

[0107] In Comparative Example 4, the flux did not contain a mercapto-based metal-organic framework (MOF), resulting in a final flux residue of 0.89%, a welding tensile strength of 1.21 N, and good weld gloss. However, the strength decreased significantly after humid heat aging, and the residue was substantial. Without the addition of a mercapto-based MOF, residual organic acids could not be adsorbed, and micro-corrosion defects on the metal surface were not passivated and repaired by the mercapto groups. Although the immediate weld gloss met the requirements, the weld bond strength decreased.

[0108] In Comparative Example 5, the flux residue was 2.35%, and the welding tensile strength was 1.06 N. The boiling point of methanol differs significantly from that of water. In the initial stage of welding, methanol evaporates rapidly, leaving water behind and forming a "water film." This hinders solder spread and induces bubbles, leading to reduced solder joint strength. High water residue dilutes the activator, and incomplete evaporation at high temperatures results in voids within the solder joint, significantly reducing mechanical strength and reliability.

[0109] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A water-soluble flux, characterized by, The raw materials include the following parts by weight: 6-12 parts of borate ester covalent activator; 3-8 parts of cucurbituril hydrate; Corrosion inhibitor 0.01-2 parts; 1-3 parts of modified graphene quantum dot solution; 1-5 parts of cyclic ether solvents; 0.5-2 parts of a thiol-containing metal-organic framework material; 68-88.5 parts deionized water; The modified graphene quantum dot solution was obtained by modifying graphene quantum dots with dioctadecyldimethylammonium chloride. The thiol-containing metal-organic framework material includes either ZIF-90-SH or ZIF-8-SH; The borate ester covalent activator was prepared by the following method: A. Add 4-bromophenylacetic acid, isopropanol pinacol boronic acid ester, palladium catalyst and sodium hydroxide to tetrahydrofuran, heat to 80-90℃ under nitrogen protection and reflux for 6-12h. After cooling, add dilute hydrochloric acid to acidify the solution system to pH 2, and dry the precipitated product to obtain 4-boronic acid phenylacetic acid. B. Mix 4-boronic acid phenylacetic acid and glycerol in acetate buffer and stir at 50-60℃ for 2-3 hours to obtain a borate ester covalent activator.

2. The water-soluble flux according to claim 1, characterized in that: The mass ratio of 4-bromophenylacetic acid, isopropanol pinacol boronic acid ester, palladium catalyst and sodium hydroxide is 1:(1-1.1):(0.2-0.3):(0.3-0.4); the concentration of the dilute hydrochloric acid is 5-6 mol / L.

3. The water-soluble flux according to claim 1, characterized in that: The mass ratio of 4-boronic acid phenylacetic acid to glycerol is 1:(0.5-0.6).

4. The water-soluble flux according to claim 1, characterized in that: The modified graphene quantum dot solution was prepared by the following method: Dioctadecyldimethylammonium chloride was added to the aqueous solution of graphene quantum dots and stirred for 5-10 min. The mixture was then transferred to a three-necked flask and heated to 60-70 °C under nitrogen protection. The mixture was refluxed and stirred for 2-3 h. After the reaction was completed, the mixture was cooled to room temperature and dialyzed for 18-24 h using a dialysis bag with a molecular weight cutoff of 1000 to obtain the modified graphene quantum dot solution.

5. The water-soluble flux according to claim 4, characterized in that: The mass concentration of the graphene quantum dot aqueous solution is 5-10 mg / mL; the mass ratio of bis(octadecyldimethylammonium chloride) to the graphene quantum dot aqueous solution is (2-3):

1.

6. The water-soluble flux according to claim 1, characterized in that: The cyclic ether solvents include any one of tetrahydrofuran, methyltetrahydrofuran, and tetrahydropyran.

7. The water-soluble flux according to claim 1, characterized in that: The corrosion inhibitor includes any one of diethanolamine, triethanolamine, and triisopropanolamine.

8. A method for preparing a water-soluble flux as described in any one of claims 1-7, characterized in that, The steps are as follows: Under nitrogen protection, deionized water, cyclic ether solvent, borate ester covalent activator, cucurbituril hydrate and modified graphene quantum dot solution are added sequentially to the reactor. After stirring evenly, a metal-organic framework material containing thiol groups is added. The mixture is stirred at 30-40℃ for 1-2 hours. Finally, a corrosion inhibitor is added and the mixture is stirred for 10-15 minutes to obtain the water-soluble flux.

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