Water-soluble soldering paste and preparation method thereof

Abstract

The invention discloses water-soluble soldering paste and a preparation method thereof. A soldering flux A comprises a solvent A, a rosin-based material, a thixotropic agent A, an active agent A, a corrosion inhibitor and a surfactant; the rosin-based material comprises at least one of acrylic acid modified rosin, hydrogenated rosin or polyoxyethylene rosin; the soldering flux B comprises a solvent B, a rosin derivative, an active agent B and a thixotropic agent B; the solvent B is a hydrophobic solvent; the rosin derivative comprises at least one of polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; and the soldering flux A and the soldering flux B are compounded into an emulsion structure. Refrigerating the soldering flux A, taking out the soldering flux B, returning to normal temperature, mixing, and emulsifying for 5-10 minutes at the stirring speed of more than 1000rpm to obtain the soldering flux C; and 85-92% of soldering powder is added into 8-15% of the soldering flux C, vacuum uniform mixing is carried out at the stirring speed of 20-40 rpm, and the water-soluble soldering paste is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of solder paste, and particularly relates to an ultrafine tin powder water-soluble lead-free solder paste and a preparation method thereof. Background Art

[0002] Solder paste (especially soft solder paste) is primarily used in the manufacture of electronic circuits. The reflow process melts the solder powder in the paste, where it reacts with the metal on component pins and the metal on the pads of the circuit board (or substrate) to form intermetallic compounds. This creates the mechanical and electrical connection between the electronic component and the circuit board (or substrate), ultimately forming an effective circuit system.

[0003] Recently, due to quantum effects bottlenecks encountered in chip manufacturing during miniaturization, CMOS feature sizes have been difficult to reduce further near 1-2 nanometers. Consequently, electronic system design has evolved from System on Chip (SoC) to System in Package (SIP) (known in the industry as "More-than-Moore") to meet the real-world needs of scenarios such as edge computing in the Internet of Things. A System in Package (SiP) integrates several different types of chips and electronic components (such as resistors and capacitors) into a single package module to form complex and independent functional modules.

[0004] In the electronic packaging field, the ever-decreasing miniaturization of chips and components within SiP modules requires soldering to shrinking pad sizes and pitches, while maintaining high reliability throughout the SiP's lifecycle. A classic example of this type of package is copper pillar bumping technology, where pad sizes have been reduced to 55 microns and pad pitches to 35 microns. Traditional no-clean solder residues are difficult to meet reliability requirements, leading the industry to adopt water-soluble solder paste.

[0005] However, prior to 1991, conventional cleaning water-soluble solder pastes (such as disclosed in U.S. Patent 5,069,730) used water-soluble PEG (polyethylene glycol) polymers as carriers. PEG polymers are water-soluble polymers formed by the polymerization of ethylene oxide. Prior to 2016, the industry still relied on water-soluble polymers for water-soluble solder pastes, as exemplified by the technologies disclosed in CN103909358A and CN105290650A. Without the protective effect of rosin, the flux required a high amount of activator, resulting in poor stability. This was primarily manifested in a rapid increase in solder paste viscosity during the printing process.

[0006] However, a common drawback of water-soluble solder paste currently on the market is its poor printing performance. Stencil life on printed boards usually does not exceed 8 hours. After 8 hours of continuous printing, the paste viscosity increases so much that significant printing defects occur.

[0007] The technology disclosed in this invention provides a comprehensive solution with superior performance. It not only offers excellent stencil life, but also maintains normal print quality with a viscosity increase of less than 10% after 8 hours of continuous printing. The resulting solder paste also exhibits excellent thermal collapse resistance and easy residue cleaning. This solder paste achieves excellent stencil life by inhibiting solder powder corrosion while maintaining excellent thermal collapse resistance. The resulting solder paste meets the requirements of fine-pitch printing and easily cleans residual solder. Summary of the Invention

[0008] In response to the problem of insufficient life of existing solder paste on printed boards, the present invention provides a solder paste that alleviates solder powder corrosion to extend the life of the printed board, has excellent other comprehensive properties, such as solder joint brightness, easy cleaning of residue, and smooth tin printing.

[0009] The technical solution of the present application to solve the above-mentioned technical problems is a water-soluble solder paste, which includes, by mass percentage, 85-92% of solder powder and 8-15% of C flux; C flux includes 85-95% of A flux and 5-15% of B flux; A flux includes A solvent, rosin-based material, A thixotropic agent, A activator, corrosion inhibitor, and surfactant; A solvent is a hydrophilic solvent; the rosin-based material includes at least one of acrylic modified rosin, hydrogenated rosin or polyoxyethylene rosin; B flux includes B solvent, rosin derivative, B activator, and B thixotropic agent; B solvent is a hydrophobic solvent; the rosin derivative includes at least one of polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; A flux and B flux are compounded into C flux with an emulsion structure; C flux is used to be mixed with solder powder to form a water-soluble solder paste.

[0010] The flux A may include, by mass percentage, 30-45% of solvent A, 30-50% of rosin-based material, 4-12% of thixotropic agent A, 3-19% of active agent A, 0.2-3% of corrosion inhibitor, and 0-4% of surfactant.

[0011] Solvent A may be a hydrophilic organic alcohol or organic alcohol ether containing a hydroxyl group; Solvent A may include organic alcohols or organic alcohol ether solvents, including one or more of 2,5-dimethyl-2,5-hexanediol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, tripropylene glycol n-butyl ether, diethylene glycol monooctyl ether, and glycerol; The rosin-based material may include any one or more of acrylic acid-modified rosin, hydrogenated rosin and polyoxyethylene rosin; The rosin-based material may include acrylic acid-modified rosin, hydrogenated rosin and polyoxyethylene rosin; and the mass ratio of acrylic acid-modified rosin, hydrogenated rosin and polyoxyethylene rosin is (0-0.2):(0-0.2):1.

[0012] The rosin-based material may include polyoxyethylene rosin with an HLB value in the range of 8-20; polyoxyethylene rosin includes polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; polyoxyethylene rosin amine is polyoxyethylene rosin amine with an HLB value in the range of 8-20; polyoxyethylene polymerized rosin is polyoxyethylene polymerized rosin with an HLB value in the range of 8-20.

[0013] Alternatively, the active agent A includes an organic acid and a halogen active agent.

[0014] It can be that the A active agent used in the A flux, that is, the active system includes organic acids and halogen active agents; the organic acid includes any one or more of oxalic acid, malonic acid, succinic acid, adipic acid, phenylsuccinic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid; the halogen active agent includes any one or more of triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutenediol, and 2-bromo-1-methyl-1H-imidazole.

[0015] It can be that the thixotropic agent A used in the A flux, that is, the thixotropic system includes: hydrogenated castor oil, polyamide thixotropic agent and its compound; the polyamide thixotropic agent and its compound are water-soluble polyamide thixotropic agents.

[0016] It may be that the HLB value of the surfactant is in the range of 8-20.

[0017] The surfactant may include any one or more of Tween 20 and 2-bromo-1-methyl-1H-imidazole.

[0018] The corrosion inhibitor may include any one or more of 2-bromo-1-methyl-1H-imidazole, ethylimidazole, and 1,2,3-benzotriazole.

[0019] The B flux may include, by mass percentage, 40-80% of B solvent, 10-45% of rosin derivative, 2-8% of B activator, and 2-10% of B thixotropic agent.

[0020] Solvent B may include any one or more of hydrophobic hydroxyl-free organic alcohol ethers, alkanes with a boiling point of 215-270° C., or rosin solvents.

[0021] The B flux may include organic alcohol ethers, wherein the organic alcohol ethers are hydroxyl-free organic alcohol ethers, including any one or more of diethylene glycol diethyl ether and diethylene glycol dibutyl ether.

[0022] The alkane with a boiling point of 215-270° C. in the solvent B may include any one or more of dodecane, tridecane, tetradecane, pentadecane or cycloalkanes.

[0023] The solvent B may be a rosin-based solvent, and the rosin-based solvent is a modified rosin, including methyl abietic acid.

[0024] The rosin derivative may be any one or more of polyoxyethylene rosin amine having an HLB value in the range of 8-20 and polyoxyethylene polymerized rosin having an HLB value in the range of 8-20; The thixotropic agent B may include any one or more of hydrogenated castor oil, modified hydrogenated castor oil, or amide thixotropic agents.

[0025] The active agent B may include any one or more of malonic acid, oxalic acid, and citric acid.

[0026] Yes, solder powder is an alloy composed of Sn as the base and a small amount of metal elements added. The solder powder includes any one or two of: Ag 0~4%, Cu 0~1%, Sb 0~10%, Bi 0~3%, Ni 0~0.15%, In 0~10%. The particle size of the solder powder is 2~25um, and the particle size models include T5 / T6 / T7 / T8.

[0027] The technical solution of the present application to solve the above technical problems can also be a flux A, which includes, by mass percentage, 30-45% of solvent A, 30-50% of rosin-based material, 4-12% of thixotropic agent A, 3-19% of active agent A, 0.2-3% of corrosion inhibitor, and 0-4% of surfactant.

[0028] Solvent A may be a hydrophilic organic alcohol or organic alcohol ether containing a hydroxyl group.

[0029] It can be that solvent A includes organic alcohol or organic alcohol ether solvents, including one or more of 2,5-dimethyl-2,5-hexanediol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, tripropylene glycol n-butyl ether, diethylene glycol monooctyl ether, and glycerol.

[0030] The rosin-based material may include any one or more of acrylic acid-modified rosin, hydrogenated rosin, and polyoxyethylene rosin.

[0031] The rosin-based material may include acrylic acid-modified rosin, hydrogenated rosin and polyoxyethylene rosin; and the mass ratio of acrylic acid-modified rosin, hydrogenated rosin and polyoxyethylene rosin is (0-0.2):(0-0.2):1.

[0032] The rosin-based material may include polyoxyethylene rosin with an HLB value in the range of 8-20; polyoxyethylene rosin includes polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; polyoxyethylene rosin amine is polyoxyethylene rosin amine with an HLB value in the range of 8-20; polyoxyethylene polymerized rosin is polyoxyethylene polymerized rosin with an HLB value in the range of 8-20.

[0033] Alternatively, the active agent A includes an organic acid and a halogen active agent.

[0034] It can be that the A active agent used in the A flux, that is, the active system includes organic acids and halogen active agents; the organic acid includes any one or more of oxalic acid, malonic acid, succinic acid, adipic acid, phenylsuccinic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid; the halogen active agent includes any one or more of triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutenediol, and 2-bromo-1-methyl-1H-imidazole.

[0035] It can be that the thixotropic agent A used in the A flux, that is, the thixotropic system includes: hydrogenated castor oil, polyamide thixotropic agent and its compound; the polyamide thixotropic agent and its compound are water-soluble polyamide thixotropic agents.

[0036] It may be that the HLB value of the surfactant is in the range of 8-20.

[0037] The surfactant may include any one or more of Tween 20 and 2-bromo-1-methyl-1H-imidazole.

[0038] The corrosion inhibitor may include any one or more of 2-bromo-1-methyl-1H-imidazole, ethylimidazole, and 1,2,3-benzotriazole.

[0039] The technical solution of the present application to solve the above technical problems can also be a B flux, which includes, by mass percentage, 40-80% B solvent, 10-45% rosin derivative, 2-8% B activator, and 2-10% B thixotropic agent; B solvent includes any one or more of hydrophobic hydroxyl-free organic alcohol ethers or alkanes with a boiling point of 215-270°C or rosin solvents.

[0040] Alternatively, the hydroxyl-free solvent B in the flux B may be an organic alcohol ether, including any one or more of diethylene glycol diethyl ether and diethylene glycol dibutyl ether.

[0041] The alkane with a boiling point of 215-270° C. in the solvent B may include any one or more of dodecane, tridecane, tetradecane, pentadecane or cycloalkanes.

[0042] The solvent B may be a rosin-based solvent, and the rosin-based solvent is a modified rosin, including methyl abietic acid.

[0043] The rosin derivative may be any one or more of polyoxyethylene rosin amine having an HLB value within the range of 8-20 and polyoxyethylene polymerized rosin having an HLB value within the range of 8-20.

[0044] The thixotropic agent B may include any one or more of hydrogenated castor oil, modified hydrogenated castor oil, or amide thixotropic agents.

[0045] The active agent B may include any one or more of malonic acid, oxalic acid, and citric acid.

[0046] The technical solution of the present application to solve the above-mentioned technical problems can also be a method for preparing flux A, which is used to prepare flux A; step A includes, step A10: mixing, stirring and heating the rosin-based material, solvent A, active agent A, and corrosion inhibitor, the heating temperature being 70-90°C; step A20: after mixing and dissolving, lowering the temperature to 40-55°C, step A30: adding thixotropic agent A, applying high-speed stirring, the stirring speed being between 2000-3000 rpm, and activating for 20-30 minutes, step A40: reducing the stirring speed, slowly stirring and cooling, and cooling to 30°C; step A50: adding a surfactant at 30°C and mixing evenly; step A60: cooling to room temperature, and grinding while cooling; step A70: after grinding, placing in a refrigerator at 2-10°C, leaving for more than 10 hours, and set aside.

[0047] The technical solution of the present application to solve the above-mentioned technical problems can also be a method for preparing B flux, which is used to prepare B flux; step B includes, step B10: heating B solvent to a temperature of 60-75°C, adding a mixture of B active agent and rosin derivative, and stirring at a speed higher than 1500 rpm for 3-5 minutes; step B20: adding B thixotropic agent at 60-75°C, and activating at high speed for 20-30 minutes; step B30: slowly stirring and cooling to 30°C, step B40: discharging the material, grinding it, and placing it in a refrigerator at 2-10°C after grinding for more than 10 hours for standby use.

[0048] The technical solution for solving the above-mentioned technical problem can also be a method for preparing a water-soluble solder paste, which is used for preparing the water-soluble solder paste, comprising the following steps: A: preparing flux A, and refrigerating and placing the flux after preparation; B: preparing flux B, and refrigerating and placing the flux after preparation; C: removing the refrigerated flux A and flux B, returning them to room temperature, and mixing and stirring the two to emulsify them to obtain flux C; after emulsification, placing them in a refrigerator at 2-10°C for more than 10 hours for standby use; the mixing and emulsification process includes emulsifying at a stirring speed of more than 1000 rpm for 5-10 minutes; and D: removing the flux C, returning it to room temperature, and then adding solder powder with a weight percentage of between 85% and 92% to 8-15% of the flux C, and mixing them uniformly in a vacuum at a stirring speed of 20-40 rpm to obtain the water-soluble solder paste.

[0049] The beneficial effects of the present application are: the flux A and the flux B are compounded into the flux C with an emulsion structure, which has excellent anti-thermal collapse performance and long service life on the board.

[0050] The beneficial effects of the present application are as follows: Solvent A is a hydrophilic organic alcohol or organic alcohol ether containing hydroxyl groups, and flux A is composed of molecules with strong polarity and functional groups capable of forming hydrogen bonds. During the static process of the solder paste, due to the presence of a three-dimensional network structure with swollen thixotropic agent particles as the skeleton formed by the hydrogen bonding mechanism, or the presence of a self-assembled structure of a small molecule thixotropic agent, the solvent molecules are mostly bound in the three-dimensional structure of the swollen thixotropic particles or trapped in the self-assembled structure of the small molecule thixotropic agent, and the free solvent molecules are limited. Since the diffusion of water molecules in the flux depends on the presence of free solvent, the diffusion of water molecules in the flux is limited at this time. Therefore, the surface corrosion of the solder powder is effectively reduced, and the life of the solder paste on the board during static state is increased.

[0051] The beneficial effects of the present application are as follows: the B solvent containing no hydroxyl group in the B flux is an organic alcohol ether, and the hydrogen bond-deficient B flux (dispersed phase) is in the process of printing and rolling, such as Figure 9 , it is continuously exposed to the front surface of the solder paste on the interface line FluxB where the scraper and the solder paste are separated. Due to the relatively low surface tension of the solvent in the B flux (for example, the surface tension of tetradecane is only 26.5 dyne / cm), it spreads to the front surface of the solder paste. By virtue of the hydrophobic properties of the dispersed phase solvent, a hydrophobic liquid film is formed on the front surface of the solder paste, thereby effectively inhibiting the absorption of moisture, preventing the corrosion of tin powder, and improving the life of the solder paste on the printed board.

[0052] The beneficial effects of this application are as follows: The organic alcohols and alcohol ethers containing hydroxyl groups in solvent A can form hydrogen bonds or other interactions with certain active ingredients in the flux. During heating, these interactions are disrupted, thereby promoting the release of the active ingredients and enhancing the activity of the flux. Furthermore, the rheological properties of the solder paste can be adjusted, the viscosity can be controlled, other solid particles in the flux can be dissolved, and the viscosity of the post-solder residue can be reduced, making it easier to clean.

[0053] The beneficial effects of this application are as follows: The rosin-based material in flux A has a high HLB value in the range of 8-20. This rosin-based material has a certain degree of oleophilicity (bonding with the solder metal) and hydrophilicity (compatibility with the polar components of the flux). The high HLB value (close to hydrophilicity) promotes solder wetting on copper and pad surfaces, reducing soldering defects (such as cold solder joints). The HLB value imparts good thixotropy to the solder paste, preventing print collapse and ensuring fill accuracy in fine circuits. It is suitable for emulsifying, wetting, and stabilizing residues during the soldering process.

[0054] The beneficial effects of the present application are as follows: the activator A is an organic acid or a halogen activator, which provides soldering activity to the solder paste and efficiently removes the oxide film on the surface of the solder powder. With the development of advanced packaging technology, solder joints are becoming more and more refined. As the particle size of ultrafine solder powder decreases, its surface area increases exponentially, and its oxides also increase exponentially, increasing the deoxidation load of the flux. The activator A has strong activity and can quickly remove the oxide film on the surface of the ultrafine solder powder.

[0055] The beneficial effects of this application are as follows: the alkanes with a boiling point of 215-270°C in the B solvent in the B flux have long chains and can act as thickeners to adjust the viscosity of the solder paste and prevent printing collapse. At high soldering temperatures, they can be converted into a low-surface-energy protective film, reducing solder oxidation. During the use of the solder paste, they cover the metal surface, forming a hydrophobic temporary protective film, delaying oxidation and preventing the absorption of water vapor and oxygen from the environment.

[0056] The beneficial effects of the present application are as follows: the B solvent in the B flux is a rosin solvent, and the rosin solvent is a rosin modified substance, including methyl abietic acid. The carboxylic acid groups contained in the structure can react with metal oxides to form soluble salts. Its saturated structure can reduce high-temperature carbonization. The residue is more easily cleaned by water saponification after methyl esterification, thereby improving the post-weld cleaning performance.

[0057] The beneficial effects of this application are as follows: The hydrophilicity of the rosin derivative, a polyoxyethylene rosin amine with an HLB value between 8 and 20, gives it excellent surface activity, significantly reducing the contact angle between solder and metal surfaces, promoting solder spreading on PCB pads and pins, and reducing false and cold solder joints. The amino groups in the structure also participate in the deoxidation process at high temperatures. In addition, the flexible structure of the polyoxyethylene chain can increase the viscoelasticity of the flux, allowing the solder paste to maintain good thixotropy, i.e., anti-collapse properties, during screen printing or stencil printing, preventing excessive solder paste diffusion or clogging of stencil openings, regulating the solder paste's rheological properties and demolding properties, and improving printing accuracy and efficiency. The high HLB value of the polyoxyethylene rosin amine not only stabilizes the flux's emulsion structure but also enhances its ability to clean residues.

[0058] The beneficial effects of the present application are as follows: the B active agent in the B flux can effectively increase the anti-thermal collapse effect of the solder paste through the cold welding mechanism due to the use of strong acids (such as oxalic acid, malonic acid, citric acid, etc.), but it also has an adverse effect on the stability of the solder paste. The patented technology uses a method of reacting an organic strong acid with a rosin-type amine to form a salt, which is then dispersed in the B flux to limit the corrosive effect of its strong acidity on the tin powder, thereby achieving the stability of the solder paste. At the same time, during the reflow process, when heated to a certain temperature, the organic salt decomposes to release strong organic acid molecules, which are released in time in the flux due to the intensified thermal motion, so that the anti-thermal collapse property of the solder paste can also be achieved.

[0059] The beneficial effect of the present application is that the corrosion inhibitor includes 2-bromo-1-methyl-1H-imidazole, which acts as an activator and a corrosion inhibitor at the same time.

[0060] The beneficial effects of the present application are: the particle size of the solder powder is 2~25um, and the particle size models include T5 / T6 / T7 / T8. The water-soluble solder paste of the present application has good adaptability and is suitable for a variety of particle sizes.

[0061] The beneficial effects of the present application are: A soldering flux is individually packaged and prepared, making it convenient to store and use.

[0062] The beneficial effects of the present application are: B flux is individually packaged and prepared, which is convenient for storage and use.

[0063] The beneficial effects of the present application are: the C flux is ready for use, and the ratio of the A flux and the B flux can be adjusted according to the chemical composition, particle size model and oxide level of the solder powder to prepare the C flux that matches different solder powders and is suitable for different process windows and characteristic requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 Table 1 shows the formula of flux A in Examples 1 to 5; Figure 2Table 2 shows the formulations of flux B in Examples 1 to 5; Figure 3 is Table 3, showing the formulation of the comparative example; Figure 4 is Table 4, showing the continuous printing test results of Examples and Comparative Examples; Figure 5 Table 5 shows the thermal collapse test results of the embodiments and comparative examples; Figure 6 This is a comparison diagram before and after solder joint cleaning; Figure 7 This is a schematic diagram of Raman spectroscopy analysis of residual materials before solder joint cleaning; Figure 8 This is a schematic diagram of Raman spectroscopy analysis of residual materials after solder joint cleaning; Figure 9 This is a schematic diagram of the separation between the scraper and the solder paste during the printing and rolling process of water-soluble solder paste. DETAILED DESCRIPTION

[0065] The content of this application is further described in detail below with reference to the accompanying drawings.

[0066] In solder, rosin, rosin derivatives and rosin modifications are common flux components, which play different roles in the soldering process.

[0067] Glossary: Rosin: It is a natural product extracted from the resin of pine trees. Its main component is abietic acid. It has good chemical stability and is a complex mixture, but it has low activity. It is suitable for welding scenarios that do not require high flux activity.

[0068] Rosin derivatives: Rosin is further processed through chemical reactions to produce compounds with different functional groups or structures. These compounds typically have different chemical properties and applications from rosin, enhance activity, and are suitable for soldering scenarios requiring high flux activity and reliability.

[0069] Rosin Modifiers: Rosin is treated physically or chemically to improve its properties or impart new functions. Modification methods include esterification, hydrogenation, and polymerization. They are suitable for applications requiring high soldering temperatures and quality.

[0070] Rosin-based materials include rosin modifications and rosin derivatives. They are derivatives or composite materials obtained from natural rosin as the main raw material through physical or chemical modification (such as hydrogenation, disproportionation, polymerization, esterification, acrylic acid grafting, etc.). They have special functions and high performance.

[0071] HLB value (Hydrophile-Lipophile Balance) is a quantitative indicator of the balance in size and strength between the hydrophilic and lipophilic groups in a surfactant molecule. A higher value indicates greater hydrophilicity, while a lower value indicates greater lipophilicity.

[0072] Although the surface of the solder powder is covered with a tin oxide film, the oxide layer still has defects, and the tin atoms still have the opportunity to be exposed to the flux, causing the solder paste to corrode during storage and printing. The process can be described by the following reaction formula: 4Sn+2H2O+4H + +O2=2H2+2Sn(OH - )2+2Sn 2+ As shown in the above reaction formula, the simultaneous presence of water and oxygen is necessary for the corrosion of solder powder.

[0073] Furthermore, some solder pastes with good thermal collapse resistance may have a shorter lifespan on printed boards due to the use of highly active activators. During storage and printing, highly active activators, such as strong organic acids, can come into contact with solder powder, causing corrosion reactions that can also affect the lifespan of the solder paste on printed boards.

[0074] Activators in solder: Their primary function is to remove oxides from the surface of the pad and solder at soldering temperatures, thereby improving wettability between the solder and pad. They chemically react with metal oxides, removing the oxide layer and providing a clean metal surface for soldering, thereby promoting metallurgical bonding between the solder and the metal being soldered.

[0075] Traditional activators include inorganic substances, rosin, and organic halides, but now most of them are organic acids and organic amines. For example, organic acids include succinic acid, glutaric acid, and o-hydroxybenzoic acid, while organic amines are used to adjust the acidity of the flux.

[0076] The stronger the activity of the activator, the greater the corrosiveness after soldering, so it is necessary to reasonably select and control the dosage. The presence of activator is one of the factors affecting the life of solder paste on the board.

[0077] Surfactants: Their primary function is to reduce the surface tension of the flux and increase its wettability with the solder powder and pads. They help the liquid solder blend better into the weld, improving soldering quality. This is particularly true when using lead-free solder, which has a higher melting point and greater surface tension.

[0078] Surfactants can be categorized into nonionic surfactants, such as the OP series and fluoroaliphatic polyethers; anionic surfactants, such as sodium diethyl sulfosuccinate; cationic surfactants, such as cetyltrimethylammonium bromide; and amphoteric surfactants. Ionic surfactants can affect the activity of the active agent, so nonionic surfactants are generally used. Furthermore, surfactants are not very volatile and can leave hygroscopic residues after welding, so excessive amounts should generally be avoided.

[0079] In the present application, a water-soluble solder paste comprises, by mass percentage, 85-92% solder powder and 8-15% C flux; C flux comprises 85-95% A flux and 5-15% B flux; A flux comprises A solvent, rosin-based material, A thixotropic agent, A activator, corrosion inhibitor, and surfactant; A solvent is a hydrophilic solvent; rosin-based material comprises at least one of acrylic modified rosin, hydrogenated rosin, or polyoxyethylene rosin; B flux comprises B solvent, rosin derivative, B activator, and B thixotropic agent; B solvent is a hydrophobic solvent; rosin derivative comprises at least one of polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; A flux and B flux are compounded into C flux with an emulsion structure; C flux is used to be mixed with solder powder to form a water-soluble solder paste.

[0080] Calculated by mass percentage, flux A includes 30-45% of solvent A, 30-50% of rosin-based material, 4-12% of thixotropic agent A, 3-19% of active agent A, 0.2-3% of corrosion inhibitor, and 0-4% of surfactant.

[0081] Solvent A is a hydrophilic organic alcohol or organic alcohol ether containing a hydroxyl group.

[0082] Solvent A includes organic alcohols or organic alcohol ether solvents, including one or more of 2,5-dimethyl-2,5-hexanediol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, tripropylene glycol n-butyl ether, diethylene glycol monooctyl ether, and glycerol.

[0083] The rosin-based material includes any one or more of acrylic acid-modified rosin, hydrogenated rosin and polyoxyethylene rosin.

[0084] The rosin-based materials include acrylic acid-modified rosin, hydrogenated rosin and polyoxyethylene rosin; the mass ratio of acrylic acid-modified rosin, hydrogenated rosin and polyoxyethylene rosin is (0-0.2): (0-0.2):1.

[0085] Rosin-based materials include polyoxyethylene rosin with an HLB value in the range of 8-20; polyoxyethylene rosin includes polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; polyoxyethylene rosin amine is polyoxyethylene rosin amine with an HLB value in the range of 8-20; polyoxyethylene polymerized rosin is polyoxyethylene polymerized rosin with an HLB value in the range of 8-20.

[0086] A activator includes organic acid and halogen activator.

[0087] The A active agent used in the A flux, that is, the active system includes organic acids and halogen active agents; the organic acid includes any one or more of oxalic acid, malonic acid, succinic acid, adipic acid, phenylsuccinic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid; the halogen active agent includes any one or more of triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutenediol, and 2-bromo-1-methyl-1H-imidazole.

[0088] The A thixotropic agent used in the A flux, namely the thixotropic system, includes: hydrogenated castor oil, polyamide thixotropic agent and its compound; the polyamide thixotropic agent and its compound are water-soluble polyamide thixotropic agents.

[0089] The HLB value of the surfactant is in the range of 8-20.

[0090] The surfactant includes any one or more of Tween 20 and 2-bromo-1-methyl-1H-imidazole.

[0091] The corrosion inhibitor includes any one or more of 2-bromo-1-methyl-1H-imidazole, ethylimidazole, and 1,2,3-benzotriazole. Among the surfactants used in flux A, 2-bromo-1-methyl-1H-imidazole is also a halogen activator.

[0092] Flux A has a strong polarity and a high hydrogen bond density. Solvent A is a highly polar organic alcohol or organic alcohol ether containing hydroxyl groups. Polyoxyethylene rosin is a polyoxyethylene rosin with a high HLB value (HLB value range of 8-20). High HLB value refers to an HLB value within the range of 8-20. For high-HLB polyoxyethylene rosin amines and high-HLB polyoxyethylene polymerized rosins, high HLB value refers to an HLB value within the range of 8-20.

[0093] By mass percentage, flux B consists of 40-80% solvent B, 10-45% rosin derivative, 2-8% activator B, and 2-10% thixotropic agent B. Solvent B includes hydrophobic, hydroxyl-free organic alcohol ethers, alkanes with a boiling point of 215-270°C, or rosin-based solvents. Solvent B is a hydroxyl-free, low-polarity solvent. Flux B has a weak polarity and low hydrogen bond density. Activator B is a strong acid.

[0094] The B solvent containing no hydroxyl group in the B flux is an organic alcohol ether, including any one or more of diethylene glycol diethyl ether and diethylene glycol dibutyl ether.

[0095] The alkane with a boiling point of 215-270° C. in the solvent B includes any one or more of dodecane, tridecane, tetradecane, pentadecane or cycloalkanes.

[0096] Solvent B is a rosin-based solvent, which is a modified rosin, including methyl abietic acid.

[0097] The rosin derivative is any one or more of polyoxyethylene rosin amine having an HLB value within the range of 8-20 and polyoxyethylene polymerized rosin having an HLB value within the range of 8-20.

[0098] The thixotropic agent B includes any one or more of hydrogenated castor oil, modified hydrogenated castor oil or amide thixotropic agents.

[0099] The active agent B includes any one or more of malonic acid, oxalic acid, and citric acid. The active agent B is a strong acid.

[0100] High HLB value polyoxyethylene rosin amine, high HLB value polyoxyethylene polymerized rosin, high HLB value means HLB value is in the range of 8-20.

[0101] The present invention provides a water-soluble solder paste, wherein the solder powder content is between 85-92wt%, and the solder powder composition is an alloy composed of Sn as a matrix and a small amount of metal elements such as Ag 0-4wt%, Cu 0-1wt%, Sb 0-10wt%, Bi 0-3wt%, Ni 0-0.15wt%, and In 0-10wt%. The particle size of the solder powder is 2-25um, and the particle size of the solder powder meets the electronic industry standard SJ / T1 1391-2019 solder alloy powder for electronic product soldering or particle size requirements for T5, T6, T7, and T8 powders as specified in IPCJ-STD-005A-2012; C flux consists of two parts, A flux and B flux, with a ratio of 85-95wt%:5-15wt%. A flux and B flux are compounded in the above ratio and stirred at high speed to form an emulsion structure with A flux as the continuous phase and B flux as the dispersed phase, namely C flux.

[0102] Solder flux C consists of two types of solvents. One is the hydroxyl-containing organic alcohols or organic alcohol ethers in flux A, and the other is the hydroxyl-free organic alcohol ethers, alkanes, and rosin modifications in flux B. Through the emulsification process of flux A and flux B, flux C is produced with an emulsion structure. Flux B, primarily composed of the hydroxyl-free solvent B, forms the dispersed phase, while flux A, primarily composed of the hydroxyl-containing solvent A and containing the majority of the active agent, forms the continuous phase.

[0103] The continuous phase A flux is composed of molecules with highly polar functional groups capable of hydrogen bonding. During the stagnant state of the solder paste, hydrogen bonding facilitates the formation of a three-dimensional network structure within the flux, with swollen thixotropic agent particles as the backbone, or a self-assembled structure of small-molecule thixotropic agents. Solvent molecules are mostly bound within the three-dimensional structure of the swollen thixotropic particles or trapped within the self-assembled structure of the small-molecule thixotropic agents, resulting in a limited number of free solvent molecules. Since the diffusion of water molecules in the flux depends on the presence of free solvent, this is limited. This, in turn, hinders the surface corrosion of the solder powder. In the absence of strong organic acids with high water absorption in the continuous phase, solder paste stability is excellent.

[0104] However, when the solder paste begins to flow under external force (such as the rolling of the solder paste during the printing process), the three-dimensional structure of the solder paste with the thixotropic agent particles as the skeleton is destroyed. The hydrogen bond-deficient type B flux (dispersed phase) unique to this technology product is continuously exposed to the surface before the solder paste rolls at the interface line where the scraper and the solder paste separate during the printing and rolling process. Due to the relatively low surface tension of the B flux solvent (for example, the surface tension of tetradecane is only 26.5 dyne / cm), it spreads to the surface before the solder paste rolls. Due to the hydrophobic properties of the dispersed phase solvent, a hydrophobic liquid film is formed on the surface before the solder paste rolls, which can effectively inhibit the absorption of moisture, prevent the corrosion of tin powder, and increase the life of the solder paste on the printed board.

[0105] The hydrophobic solvent B in flux B is composed of organic alcohol ethers, alkanes, and modified rosin. Examples include diethylene glycol diethyl ether, diethylene glycol dibutyl ether, dodecane to pentadecane, and methyl hydrogenated abietic acid. Its weight percentage in flux B is 40-80% by weight. To minimize interference with the overall properties of the solder paste, flux B is used in a much smaller amount than flux A, with a weight ratio of 5-15% to 85-95%.

[0106] In order to preserve the comprehensive performance of the entire solder paste, flux A needs to provide the thixotropy, activity, and coating protection of solder powder required by the solder paste. Therefore, flux A uses conventional hydroxyl-containing solvents, such as: diethylene glycol monohexyl ether, diethylene glycol monobutyl ether, diethylene glycol monooctyl ether, 2,5-dimethyl-2,5-hexanediol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, tripropylene glycol n-butyl ether, glycerol, or a mixture of multiple solvents. The total amount of solvent used accounts for 30-45wt% of flux A.

[0107] The organic acids and halogen activators used in flux A of the present invention include succinic acid, adipic acid, phenylsuccinic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutenediol, and 2-bromo-1-methyl-1H-imidazole, with a total amount of 3-19wt%. The thixotropic agent system used in the present invention is preferably a water-soluble polyamide thixotropic agent to achieve a high thixotropic coefficient. Alternatively, a combination of a conventional polyamide thixotropic agent and hydrogenated castor oil can be used. The total amount is 4-12wt%. To ensure water solubility, rosin and its derivatives used in flux A include acrylic acid-modified rosin, hydrogenated rosin, and high-HLB polyoxyethylene rosin. High-HLB polyoxyethylene rosin includes high-HLB polyoxyethylene rosin amine and high-HLB polyoxyethylene polymerized rosin. The ratio of acrylic acid-modified rosin, hydrogenated rosin, and high-HLB polyoxyethylene rosin is 0-0.2:0-0.2:1, with a total weight of 30-50 wt%. The present invention prioritizes the use of polyoxyethylene rosin amine, which has good water solubility and a high HLB value, to not only stabilize the flux emulsion structure but also enhance the ability to clean residues.

[0108] While strong acids, such as oxalic acid, malonic acid, and citric acid, can effectively enhance the solder paste's thermal collapse resistance through the cold soldering mechanism, they can also negatively impact the paste's stability. This patented technology utilizes a method whereby a strong organic acid reacts with a rosin-based amine to form a salt, which is then dispersed in flux B to limit the corrosive effects of the strong acid on tin powder, thereby achieving solder paste stability. Furthermore, during the reflow process, when heated to a certain temperature, the organic salt decomposes to release strong organic acid molecules, which are promptly released into the flux due to increased thermal motion, thereby achieving solder paste thermal collapse resistance. The strong organic acid activators in flux B are malonic acid, oxalic acid, citric acid, and the like, with a total content of 2-8wt%. B flux also needs to have a certain degree of protection against solder powder. The rosin derivatives used are high HLB values, that is, polyoxyethylene rosin amines and polyoxyethylene polymerized rosin with an HLB value between 8-20, with a total amount of 10-45wt%; the thixotropic agent is hydrogenated castor oil and its modifications, and amide thixotropic agents, with a total amount of 2-10wt%.

[0109] The present invention notes that the flux's emulsion structure effectively blocks the absorption of atmospheric moisture into the flux during solder paste printing and rolling, thereby inhibiting corrosion of the solder powder and improving stencil life. Due to the lack of moisture and the trapping of organic acids within flux B, corrosion of the solder powder surface is significantly limited. This structural feature enables both solder paste stability and excellent thermal collapse resistance to be achieved in a single product.

[0110] The present invention provides a method for preparing the water-soluble solder paste, and the preparation method is as follows: Preparation of flux A: Add rosin derivatives, hydroxyl-containing organic alcohol ether solvents, activators, and corrosion inhibitors to a temperature-controlled heating device and slowly stir to dissolve at 70-90°C. Lower the system temperature to 40-55°C, add the thixotropic agent, and activate the thixotropic agent by stirring at high speed (2000-3000 rpm) for 20-30 minutes. Cool the mixture to below 30°C while slowly stirring, add the surfactant, and mix thoroughly. After cooling to room temperature, grind the mixture and place it in a refrigerator at 2-10°C for at least 10 hours before use.

[0111] Preparation process of B flux: Add a hydroxyl-free solvent to a temperature-controlled heating device, add a mixture of organic acid and rosin modifier under the condition of temperature range of 60-75℃, stir at high speed (1500rpm and above) for 3-5 minutes, add thixotropic agent within the temperature range, stir at high speed for 20-30 minutes, slowly stir and cool to 30℃, discharge the material, grind it, and then put it into a refrigerator at 2-10℃ for more than 10 hours for standby use.

[0112] Remove the refrigerated fluxes A and B and return them to room temperature. Then, mix them in a ratio of 85-95%:15-5%. Emulsify for 5-10 minutes under high-speed stirring at a speed of 1000 rpm or higher to obtain the flux. Place the flux in a refrigerator at 2-10°C for at least 10 hours before use.

[0113] The flux obtained above is taken out and returned to room temperature, and then 85-92 wt% of solder powder is added to 8-15 wt% of the flux above, and mixed evenly in a vacuum at a stirring speed of 20-40 rpm to obtain solder paste.

[0114] One of the beneficial effects of this application is that the presence of the hydrophobic dispersed phase B within the structure of the emulsion flux C forms a hydrophobic film on the front surface of the solder paste during printing. This hydrophobic film effectively inhibits water absorption. During the resting phase of the solder paste, the three-dimensional structure (the self-assembled structure of the small molecule thixotropic agent) formed by hydrogen bonding within the swollen thixotropic particles of the flux and the absence of free solvent molecules prevents water absorbed by the flux surface from effectively diffusing within the paste, limiting the corrosion rate of the solder paste during this phase. Through this mechanism, this product significantly reduces solder powder corrosion, effectively preventing the increase in solder paste viscosity during continuous printing and during the placement process, thereby extending the life of the printed board.

[0115] One of the beneficial effects of the present application is that the present invention uses a confined strong organic acid in the hydrophobic dispersed phase B, which can effectively inhibit its corrosion while exerting its cold welding effect in the early stage of reflow, so that the solder paste can simultaneously obtain excellent on-net life and good heat collapse resistance.

[0116] One of the beneficial effects of the present application is that a large amount of high HLB rosin-based surfactant in the continuous phase can provide effective protection for solder powder during the reflow process, thereby ensuring activity and residual cleaning performance.

[0117] like Figure 1 , i.e. Table 1, shows the formula of flux A in Examples 1 to 5. Figure 2 , i.e. Table 2, shows the formula of flux B in Examples 1 to 5.

[0118] The preparation process of Example 1: Add 23 parts of diethylene glycol monobutyl ether, 3 parts of glycerin, and 14 parts of diethylene glycol monohexyl ether to an oil bath container. Raise the system temperature to 82°C. Then add 5 parts of succinic acid, 10 parts of sebacic acid, 0.6 parts of dibromobutylene glycol, 2.4 parts of ethylimidazole, 16 parts of polyoxyethylene polymerized rosin, and 20 parts of polyoxyethylene rosin amine. Slowly stir until dissolved. Further lower the system temperature to 45°C. Add 6 parts of water-soluble polyamide thixotropic agent RE-127. Stir at high speed for 20-30 minutes to complete activation. Cool to room temperature under slow stirring, grind, and then place in a refrigerator at 2-10°C for more than 10 hours before use.

[0119] Slowly stir and mix 50 parts of n-tetradecane and 10 parts of diethylene glycol diethyl ether at a temperature of 65°C, add a mixture of 26 parts of polyoxyethylene rosin amine and 4 parts of malonic acid, stir at high speed (1500rpm) for 3-5 minutes, then add 10 parts of polyamide thixotropic agent 6650, stir at high speed (3000rmp) for activation for 25 minutes, slowly stir and cool to 30°C, discharge the material, and grind it after cooling to room temperature. Then, place it in a refrigerator at 2-10°C for more than 10 hours and set aside.

[0120] Remove the refrigerated fluxes A and B and return them to room temperature. Then, mix them in a ratio of 90wt%:10wt% and emulsify them at a high-speed stirring speed of 1500rpm for 5 minutes to obtain the flux. Place the flux in a refrigerator at 2-10℃ for at least 10 hours before use.

[0121] The flux obtained above was taken out and returned to room temperature, and then 87 wt % of 6# solder powder was added to 13 wt % of the flux above, and mixed evenly at a stirring speed of 25 rpm to obtain solder paste.

[0122] Example 2. The formula of Example 2 is shown in Tables 1 and 2. The production process is the same as that of Example 1, except that the weight ratio of flux A to flux B is 85wt%:15wt%.

[0123] Example 3. The formula of Example 3 is shown in Table 1 and Table 2, and the preparation process is the same as that of Example 1. The difference is that the weight ratio of flux A to flux B is 95wt%:5wt%.

[0124] Example 4. The formula of Example 4 is shown in Table 1 and Table 2. The production process is the same as that of Example 1, except that the weight ratio of flux A to flux B is 85wt%:15wt%.

[0125] Example 5. The formula of Example 5 is shown in Table 1 and Table 2, and its preparation process is the same as that of Example 1. The difference is that the weight ratio of flux A to flux B is 95wt%:5wt%.

[0126] In order to better illustrate the effect of the technical solution in this application, the following comparative examples are designed for effect comparison. The formula of comparative example 1 is shown in Table 3, which is exactly the same as the flux A in Example 1.

[0127] A comparison of the overall performance of the solder pastes prepared using the formulations of Example 1 and Comparative Example 1 clearly demonstrates the role of flux B in Example 1 in improving the on-board life of the solder paste. The formulation of Comparative Example 2 is shown in Table 3. The main difference between this formulation and flux A in Example 2 is that malonic acid is dispersed in flux B in Example 2, while in Comparative Example 2 it is added to the sole main flux.

[0128] like Figure 4 Table 4 shows the results of continuous printing tests for Examples and Comparative Examples. The continuous printing test conditions (viscosity in Pa.S) were: Malcom PCU02V @ 10 rpm, 25°C. The on-board life of each sample was characterized by the viscosity during continuous printing. Because the solder paste prepared in Comparative Example 2 had high initial viscosity, subsequent tests were not performed.

[0129] from Figure 4 As can be seen, Examples 1 to 5 not only have suitable initial viscosities, but also have smaller viscosity changes after 8 and 12 hours, indicating more stable viscosity performance. Comparative Example 1 can also test initial viscosity, viscosity after 8 and 12 hours, but the viscosity changes after 8 and 12 hours are greater than those of the Examples.

[0130] like Figure 5Table 5 shows the thermal collapse test results for Examples and Comparative Examples. Thermal collapse performance: Tested according to the SJT11186-2019 test method. The non-bonding spacing for Examples 1 through 5 is smaller than that for Comparative Example 1. The non-bonding spacing for Comparative Example 1 was not measured because printing was not possible.

[0131] like Figure 6 The figure below compares solder joints before and after cleaning. Solder joint performance: Under nitrogen, all samples tested exhibited bright solder joints, free of tin beads, and exhibited good spreading and wetting. Water-washability: All samples tested completely cleaned away any residue near the solder joints.

[0132] like Figure 7 This is a schematic diagram of Raman spectroscopy analysis of residual materials before solder joint cleaning; Figure 8 This is a schematic diagram of Raman spectroscopy analysis of residual materials after solder joint cleaning. The residual materials are mainly rosin-like substances, with visible wavelengths of 2000-3000 cm -1 The Raman shift of the hydroxyl peak near 1450 cm -1 The characteristic peaks of the Raman shift accessory disappeared after cleaning.

[0133] In this application, mass percentage (%) refers to weight percentage (wt%). In this application, flux C refers to flux C, flux A refers to flux A, and flux B refers to flux B. Solvent A refers to solvent A, thixotropic agent A refers to thixotropic agent A, and activator A refers to activator A. Solvent B refers to solvent B, activator B refers to activator B, and thixotropic agent B refers to thixotropic agent B.

[0134] The above are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A water-soluble solder paste, characterized in that : In percentage by mass, Including solder powder 85-92%, C flux 8-15%; C flux contains 85-95% A flux and 5-15% B flux; The flux A comprises a solvent A, a rosin-based material, a thixotropic agent A, an activator A, a corrosion inhibitor, and a surfactant; the solvent A is a hydrophilic solvent; the rosin-based material comprises at least one of acrylic acid-modified rosin, hydrogenated rosin, or polyoxyethylene rosin; The B flux includes a B solvent, a rosin derivative, a B thixotropic agent, and a B activator; the B solvent is a hydrophobic solvent; the rosin derivative includes at least one of polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; Flux A and flux B are compounded into flux C with an emulsion structure; flux C is used to mix with solder powder to form a water-soluble solder paste.

2. The water-soluble solder paste according to claim 1, characterized in that : In terms of mass percentage, flux A includes: A solvent 30-45%, rosin-based material 30-50%, A thixotropic agent 4-12%, A active agent 3-19%, corrosion inhibitor 0.2-3%; surfactant 0-4%.

3. The water-soluble solder paste according to claim 2, characterized in that : Include any one or more of the following technical features: TA 10: Solvent A is a hydrophilic organic alcohol or organic alcohol ether containing hydroxyl groups; TA20: A solvent includes organic alcohol or organic alcohol ether solvents, including one or more of 2,5-dimethyl-2,5-hexanediol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, tripropylene glycol n-butyl ether, diethylene glycol monooctyl ether, and glycerol; TA30: Rosin-based materials include any one or more of acrylic acid-modified rosin, hydrogenated rosin, and polyoxyethylene rosin; TA31: Rosin-based materials include acrylic acid-modified rosin, hydrogenated rosin, and polyoxyethylene rosin; the mass ratio of acrylic acid-modified rosin, hydrogenated rosin, and polyoxyethylene rosin is (0-0.2): (0-0.2): 1; TA32: Rosin-based materials include polyoxyethylene rosin with an HLB value in the range of 8-20; Polyoxyethylene rosin, including polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; Polyoxyethylene rosin amine is a polyoxyethylene rosin amine with an HLB value in the range of 8-20; polyoxyethylene polymerized rosin is a polyoxyethylene polymerized rosin with an HLB value in the range of 8-20; TA60: A surfactant includes organic acid and halogen surfactant; TA61: The A active agent used in A flux, i.e., the active system, includes organic acids and halogen active agents; the organic acid includes any one or more of oxalic acid, malonic acid, succinic acid, adipic acid, phenylsuccinic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid; the halogen active agent includes any one or more of triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutenediol, and 2-bromo-1-methyl-1H-imidazole; TA70: The thixotropic agent A used in A flux, namely the thixotropic system, includes: hydrogenated castor oil, polyamide thixotropic agent and its compound; the polyamide thixotropic agent and its compound are water-soluble polyamide thixotropic agents; TA80: The HLB value of the surfactant is in the range of 8-20; TA81: Surfactants include any one or more of Tween 20 and 2-bromo-1-methyl-1H-imidazole; TA90: The corrosion inhibitor includes any one or more of 2-bromo-1-methyl-1H-imidazole, ethylimidazole, and 1,2,3-benzotriazole.

4. The water-soluble solder paste according to claim 1, characterized in that : In percentage by mass, B flux includes, B solvent 40-80%, rosin derivative 10-45%, B active agent 2-8%, B thixotropic agent 2-10%; Solvent B includes any one or more of hydrophobic hydroxyl-free organic alcohol ethers, alkanes with a boiling point of 215-270° C., or rosin solvents.

5. The water-soluble solder paste according to claim 4, characterized in that : Include any one or more of the following technical features: TB11: B soldering flux includes organic alcohol ethers, wherein the organic alcohol ethers are hydroxyl-free organic alcohol ethers, including any one or more of diethylene glycol diethyl ether and diethylene glycol dibutyl ether; TB12: The alkane with a boiling point of 215-270°C in solvent B includes any one or more of dodecane, tridecane, tetradecane, pentadecane or cycloalkanes; TB13: Solvent B is a rosin-based solvent, which is a modified rosin, including methyl abietic acid; TB20: Rosin derivatives are any one or more of polyoxyethylene rosin amine with an HLB value in the range of 8-20 and polyoxyethylene polymerized rosin with an HLB value in the range of 8-20; TB30:B thixotropic agent includes any one or more of hydrogenated castor oil, hydrogenated castor oil modification or amide thixotropic agent; TB50: B active agent includes any one or more of malonic acid, oxalic acid, and citric acid.

6. The water-soluble solder paste according to claim 1, characterized in that : Solder powder is an alloy composed of Sn as the base and a small amount of metal elements added. The solder powder includes any one or more of: Ag 0~4%, Cu 0~1%, Sb 0~10%, Bi 0~3%, Ni 0~0.15%, and In 0~10%; The particle size of solder powder is 2~25um, and the particle size models include T5 / T6 / T7 / T8.

7. A soldering flux A, characterized in that, In terms of mass percentage, flux A includes: A solvent 30-45%, rosin-based material 30-50%, A thixotropic agent 4-12%, A active agent 3-19%, corrosion inhibitor 0.2-3%, surfactant 0-4%; Include any one or more of the following technical features: TA 10: Solvent A is a hydrophilic organic alcohol or organic alcohol ether containing hydroxyl groups; TA20: A solvent includes organic alcohol or organic alcohol ether solvent, including one or more of 2,5-dimethyl-2,5-hexanediol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, tripropylene glycol n-butyl ether, diethylene glycol monooctyl ether, and glycerol; TA30: Rosin-based materials include any one or more of acrylic acid-modified rosin, hydrogenated rosin, and polyoxyethylene rosin; TA31: Rosin-based materials include acrylic acid-modified rosin, hydrogenated rosin, and polyoxyethylene rosin; the mass ratio of acrylic acid-modified rosin, hydrogenated rosin, and polyoxyethylene rosin is (0-0.2): (0-0.2): 1; TA32: Rosin-based materials include polyoxyethylene rosin with an HLB value in the range of 8-20; Polyoxyethylene rosin, including polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; Polyoxyethylene rosin amine is a polyoxyethylene rosin amine with an HLB value in the range of 8-20; polyoxyethylene polymerized rosin is a polyoxyethylene polymerized rosin with an HLB value in the range of 8-20; TA60: A surfactant includes organic acid and halogen surfactant; TA61: The A active agent used in A flux, i.e., the active system, includes organic acids and halogen active agents; the organic acid includes any one or more of oxalic acid, malonic acid, succinic acid, adipic acid, phenylsuccinic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid; the halogen active agent includes any one or more of triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutenediol, and 2-bromo-1-methyl-1H-imidazole; TA70: The thixotropic agent A used in A flux, namely the thixotropic system, includes: hydrogenated castor oil, polyamide thixotropic agent and its compound; the polyamide thixotropic agent and its compound are water-soluble polyamide thixotropic agents; TA80: The HLB value of the surfactant is in the range of 8-20; TA81: Surfactants include any one or more of Tween 20 and 2-bromo-1-methyl-1H-imidazole; TA90: The corrosion inhibitor includes any one or more of 2-bromo-1-methyl-1H-imidazole, ethylimidazole, and 1,2,3-benzotriazole.

8. A B flux, characterized in that, In percentage by mass, B flux includes, B solvent 40-80%, rosin derivative 10-45%, B active agent 2-8%, B thixotropic agent 2-10%; Solvent B includes any one or more of hydrophobic hydroxyl-free organic alcohol ethers, alkanes with a boiling point of 215-270°C, or rosin solvents; Include any one or more of the following technical features: TB 11: The B solvent that does not contain hydroxyl groups in the B flux is an organic alcohol ether, including any one or more of diethylene glycol diethyl ether and diethylene glycol dibutyl ether; TB12: The alkane with a boiling point of 215-270°C in solvent B includes any one or more of dodecane, tridecane, tetradecane, pentadecane or cycloalkanes; TB13: Solvent B is a rosin-based solvent, which is a modified rosin, including methyl abietic acid; TB20: Rosin derivatives are any one or more of polyoxyethylene rosin amine with an HLB value in the range of 8-20 and polyoxyethylene polymerized rosin with an HLB value in the range of 8-20; TB30:B thixotropic agent includes any one or more of hydrogenated castor oil, hydrogenated castor oil modification or amide thixotropic agent; TB50: B active agent includes any one or more of malonic acid, oxalic acid, and citric acid; In the polyoxyethylene rosin amine with a high HLB value and the polyoxyethylene polymerized rosin with a high HLB value, the high HLB value refers to an HLB value in the range of 8-20.

9. A method for preparing flux A, characterized in that: Used to prepare the A soldering flux according to claim 7; Step A includes, Step A10: Mix and heat the rosin-based material, solvent A, active agent A, and corrosion inhibitor at a temperature of 70-90° C. Step A20: After mixing and dissolving, lower the temperature to 40-55°C. Step A30: Add thixotropic agent A, apply high-speed stirring at a speed of 2000-3000 rpm, and activate for 20-30 minutes. Step A40: Reduce the stirring speed, slowly stir and cool to 30°C; Step A50: Add surfactant at 30°C and mix well; Step A60: Cooling to room temperature, and grinding again while cooling; Step A70: After grinding, place in a 2-10℃ refrigerator for more than 10 hours and set aside.

10. A method for preparing B flux, characterized in that: Used to prepare the B flux according to claim 8; Step B includes, Step B10: After heating the solvent B to 60-75°C, add the mixture of the active agent B and the rosin derivative, and stir at a speed of more than 1500 rpm for 3-5 minutes; Step B20: Add thixotropic agent B at 60-75°C and activate with high-speed stirring for 20-30 minutes. Step B30: Stir slowly and cool to 30°C. Step B40: Discharge the material, grind it, and place it in a refrigerator at 2-10°C for more than 10 hours for later use.

11. A method for preparing a water-soluble solder paste, for preparing the water-soluble solder paste according to any one of claims 1 to 6, characterized in that : Step A: Preparation of flux A, refrigerated storage after preparation; Step B: Preparation of B flux, refrigerated storage after preparation; Step C: Take out the refrigerated flux A and flux B, return them to room temperature, and mix and emulsify them to obtain flux C; after emulsification, place them in a refrigerator at 2-10°C for more than 10 hours for standby use; the mixing and emulsification process includes emulsifying at a stirring speed of more than 1000 rpm for 5-10 minutes; Step D: Take out the above-mentioned C flux and return it to room temperature. Then, add 85-92% by weight of solder powder to 8-15% of the above-mentioned C flux, and mix them evenly under vacuum at a stirring speed of 20-40 rpm to obtain a water-soluble solder paste.

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