Water-soluble solder paste and method for producing the same

Abstract

Water-soluble soldering paste and preparation method thereof, A flux includes, A solvent, rosin-based material, A thixotropic agent, A active agent, corrosion inhibitor, surfactant; Rosin-based material includes at least one of acrylic modified rosin, hydrogenated rosin or polyoxyethylene rosin; B flux includes, B solvent, rosin derivative, B active agent, B thixotropic agent; B solvent is hydrophobic solvent; Rosin derivative includes at least one of polyoxyethylene rosin amine, polyoxyethylene polymerized rosin; A flux and B flux are compounded into emulsion structure. Cold storage A flux B flux is taken out, return to normal temperature, is emulsified under the stirring speed of 1000rpm above 5-10 minutes to obtain C flux; 85-92% soldering tin powder is added to 8-15% C flux, and is uniformly mixed under the stirring speed of 20-40rpm, to obtain water-soluble soldering paste.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of soldering paste, and particularly relates to a superfine tin powder water-soluble lead-free soldering paste and a preparation method thereof. BACKGROUND

[0002] Soldering paste (especially soft soldering paste) is mainly used in the manufacturing of electronic circuits. Through a reflow process, the soldering powder in the soldering paste is melted to respectively react with the metal on the pins of the electronic components and the metal on the pads of the circuit board (or substrate) to generate intermetallic compounds, thereby completing the mechanical and electrical connection between the electronic components and the circuit board (or substrate) and forming an effective circuit system.

[0003] Recently, due to the bottleneck of quantum effect encountered in the miniaturization process of chips, the feature size of CMOS is difficult to further decrease to 1-2 nanometers, and thus the design of electronic systems evolves from system on chip (SoC) to system in packaging (SiP, also known as More-than-Moore in the industry) to meet the practical needs of edge computing in the Internet of Things and other scenarios. The SiP needs to integrate several different types of chips and electronic components (resistors, capacitors, etc.) in a packaging module to form a complex and independent functional module.

[0004] In the field of electronic packaging, the chips and components in the SiP module are required to be continuously miniaturized, and the welding is completed under the condition of continuously reduced pad size and pitch, and high reliability is maintained throughout the application cycle of the SiP. A classic scenario in such packaging is the copper pillar bump technology, and the pad size corresponding to this technology has been reduced to 55 microns, and the pad pitch has been reduced to 35 microns. The residue of traditional no-clean soldering paste cannot meet the reliability requirements, so the industry requires the use of water-soluble soldering paste.

[0005] However, the traditional cleaning water-soluble soldering paste (as disclosed in US Patent 5069730) before 1991 used water-soluble PEG (polyethylene glycol) polymers as the carrier; the PEG polymer is a water-soluble high molecular polymer polymerized from ethylene oxide. Before 2016, the water-soluble soldering paste in the industry still followed this path of water-soluble polymers, such as the technologies disclosed in CN103909358A and CN105290650A. Due to the lack of protection of rosin, the amount of active agent in the flux is large, which leads to poor stability of such products, mainly manifested as rapid increase in the viscosity of the soldering paste during the printing process.

[0006] However, a common defect of the water-soluble solder paste on the market is that the printing performance is not good enough, and the stencil life is usually less than 8 hours. After 8 hours of continuous printing, the paste viscosity increases too high to cause significant printing defects.

[0007] The disclosed technology provides a superior comprehensive performance solution. Not only does it have excellent stencil life, but after 8 hours of continuous printing, the paste viscosity increases by less than 10%, and it can maintain normal printing quality. The solder paste prepared by the technology also has good heat collapse resistance and easy residue cleaning. The solder paste is obtained by inhibiting solder powder corrosion to achieve excellent stencil life, while retaining good heat collapse resistance of the solder paste. The solder paste prepared by the technology can meet the needs of fine-pitch printing and is easy to clean. SUMMARY

[0008] To address the problem of insufficient stencil life of existing solder paste, the present application provides a solder paste that alleviates solder powder corrosion to achieve long stencil life, excellent overall performance, solder spot brightness, easy residue cleaning, and smooth soldering.

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

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

[0011] The A solvent may be a hydrophilic organic alcohol or organic alcohol ether containing hydroxyl groups;

[0012] The A solvent can include one or more of organic alcohol or organic alcohol ether solvents, including 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, glycerol (glycerin);

[0013] The rosin-based material can include any one or more of acrylic modified rosin, hydrogenated rosin, and polyoxyethylene rosin.

[0014] The rosin-based material can include acrylic modified rosin, hydrogenated rosin, and polyoxyethylene rosin; and the mass ratio of the acrylic modified rosin, the hydrogenated rosin, and the polyoxyethylene rosin is (0-0.2):(0-0.2):1.

[0015] The rosin-based material can include polyoxyethylene rosin having an HLB value in the range of 8-20; and the polyoxyethylene rosin includes polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; the polyoxyethylene rosin amine is polyoxyethylene rosin amine having an HLB value in the range of 8-20; and the polyoxyethylene polymerized rosin is polyoxyethylene polymerized rosin having an HLB value in the range of 8-20.

[0016] The A active agent can include organic acid and halogen active agent.

[0017] The A active agent used by the A flux, i.e., the active system, can include organic acid and halogen active agent; the organic acid can include any one or more of oxalic acid, malonic acid, succinic acid, adipic acid, phenylsuccinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid; and the halogen active agent can include any one or more of triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutene diol, 2-bromo-1-methyl-1H-imidazole.

[0018] The A thixotropic agent used by the A flux, i.e., the thixotropic system, can include hydrogenated castor oil, polyamide thixotropic agent, and a compound thereof; and the polyamide thixotropic agent and the compound thereof can be water-soluble polyamide thixotropic agent.

[0019] The surfactant can have an HLB value in the range of 8-20.

[0020] The surfactant can include any one or more of Tween 20 and 2-bromo-1-methyl-1H-imidazole.

[0021] The corrosion inhibitor can include any one or more of 2-bromo-1-methyl-1H-imidazole, ethylimidazole, and 1,2,3-benzotriazole.

[0022] The B flux can include, in mass percentage, B solvent 40-80%, rosin derivative 10-45%, B active agent 2-8%, and B thixotropic agent 2-10%.

[0023] The B solvent can include any one or more of hydrophobic hydroxyl-free organic alcohol ethers or alkanes having a boiling point of 215-270°C or rosin solvents.

[0024] The B flux can include, in mass percentage, B solvent 40-80%, rosin derivative 10-45%, B active agent 2-8%, and B thixotropic agent 2-10%.

[0025] The B solvent can include any one or more of hydrophobic hydroxyl-free organic alcohol ethers or alkanes having a boiling point of 215-270°C or rosin solvents.

[0026] The B solvent can be a rosin solvent, and the rosin solvent can be a rosin modifier including methyl abietate.

[0027] The rosin derivative can be any one or more of polyoxyethylene abietamine having an HLB value in the range of 8-20 and polyoxyethylene polymerized rosin having an HLB value in the range of 8-20.

[0028] The B thixotropic agent can include any one or more of hydrogenated castor oil, hydrogenated castor oil modifier, or amide thixotropic agent.

[0029] The B active agent can include any one or more of malonic acid, oxalic acid, and citric acid.

[0030] The solder powder can be an alloy of Sn as a base material with a small amount of metal elements, and the solder powder can include any one or two of Ag 0-4%, Cu 0-1%, Sb 0-10%, Bi 0-3%, Ni 0-0.15%, and In 0-10%, and the solder powder can have a particle size of 2-25 um and a particle size type including T5 / T6 / T7 / T8.

[0031] The technical solution of the present application to solve the above technical problems can also be an A flux including, in mass percentage, A solvent 30-45%, rosin-based material 30-50%, A thixotropic agent 4-12%, A active agent 3-19%, corrosion inhibitor 0.2-3%, and surfactant 0-4%.

[0032] The A solvent can be a hydrophilic hydroxyl-containing organic alcohol or organic alcohol ether.

[0033] The A solvent can include one or more of organic alcohol or organic alcohol ether solvents, including 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.

[0034] The rosin-based material can include any one or more of acrylic modified rosin, hydrogenated rosin, and polyoxyethylene rosin.

[0035] The rosin-based material can include acrylic modified rosin, hydrogenated rosin, and polyoxyethylene rosin; and the mass ratio of the acrylic modified rosin, the hydrogenated rosin, and the polyoxyethylene rosin is (0-0.2):(0-0.2):1.

[0036] The rosin-based material can include polyoxyethylene rosin having an HLB value in the range of 8-20; and the polyoxyethylene rosin includes polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; the polyoxyethylene rosin amine is polyoxyethylene rosin amine having an HLB value in the range of 8-20; and the polyoxyethylene polymerized rosin is polyoxyethylene polymerized rosin having an HLB value in the range of 8-20.

[0037] The A active agent can include organic acid and halogen active agent.

[0038] The A active agent used by the A flux, i.e., the active system, can include organic acid and halogen active agent; the organic acid can include any one or more of oxalic acid, malonic acid, succinic acid, adipic acid, phenylsuccinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid; and the halogen active agent can include any one or more of triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutene diol, and 2-bromo-1-methyl-1H-imidazole.

[0039] The A thixotropic agent used by the A flux, i.e., the thixotropic system, can include hydrogenated castor oil, polyamide thixotropic agent, and a compound thereof; and the polyamide thixotropic agent and the compound thereof can be water-soluble polyamide thixotropic agent.

[0040] The surfactant can have an HLB value in the range of 8-20.

[0041] The surfactant can include any one or more of Tween 20 and 2-bromo-1-methyl-1H-imidazole.

[0042] The corrosion inhibitor can include any one or more of 2-bromo-1-methyl-1H-imidazole, ethylimidazole, and 1,2,3-benzotriazole.

[0043] The technical solution of the application for solving the above technical problem can also be a B flux, in mass percentage, the B flux comprises B solvent 40-80%, rosin derivative 10-45%, B active agent 2-8%, B thixotropic agent 2-10%; the B solvent comprises any one or more of hydrophobic organic alcohol ether without hydroxyl group or alkane with boiling point of 215-270 DEG C or rosin solvent.

[0044] The B solvent without hydroxyl group in the B flux can be organic alcohol ether, comprising any one or more of diethylene glycol diethyl ether, diethylene glycol dibutyl ether.

[0045] The alkane with boiling point of 215-270 DEG C in the B solvent can comprise any one or more of dodecane, tridecane, tetradecane, pentadecane or cycloalkane.

[0046] The B solvent can be rosin solvent, and the rosin solvent is rosin modifier, comprising methyl abietate.

[0047] The rosin derivative can be any one or more of polyoxyethylene abietamine with HLB value in the range of 8-20 and polyoxyethylene polymerized rosin with HLB value in the range of 8-20.

[0048] The B thixotropic agent can comprise any one or more of hydrogenated castor oil, hydrogenated castor oil modifier or amide thixotropic agent.

[0049] The B active agent can comprise any one or more of malonic acid, oxalic acid, citric acid.

[0050] The technical solution of the application for solving the above technical problem can also be a preparation method of A flux, for preparing A flux; step A comprises: step A10, mixing and stirring rosin-based material, A solvent, A active agent, corrosion inhibitor and heating, heating temperature is 70-90 DEG C; step A20, after mixing and dissolving, reducing the temperature to 40-55 DEG C, step A30, adding A thixotropic agent, applying high-speed stirring, stirring speed is between 2000-3000 rpm, activating for 20-30 minutes, step A40, reducing the stirring speed, slowly stirring and cooling, cooling to 30 DEG C; step A50, adding surfactant at 30 DEG C, mixing uniformly; step A60, cooling to room temperature, and grinding during cooling; step A70, after grinding, placing in 2-10 DEG C refrigerator for more than 10 hours, standby.

[0051] The technical scheme for solving the above technical problem of the application can also be a preparation method of B flux, for preparing B flux; step B includes: step B10, adding a mixture of B active agent and rosin derivative after heating B solvent at 60-75 DEG C, stirring at a speed higher than 1500 rpm for 3-5 minutes; step B20, adding B thixotropic agent at 60-75 DEG C, and activating by high-speed stirring for 20-30 minutes; step B30, slowly stirring and cooling to 30 DEG C; and step B40, discharging, grinding, and placing in a 2-10 DEG C refrigerator for more than 10 hours for standby.

[0052] The technical scheme for solving the above technical problem of the application can also be a preparation method of water-soluble solder paste, for preparing the water-soluble solder paste, step A, preparation of A flux, and cold storage after preparation; step B, preparation of B flux, and cold storage after preparation; step C, taking out the cold-stored A flux and B flux, warming to room temperature, mixing and stirring to emulsify to obtain C flux; and placing in a 2-10 DEG C refrigerator for more than 10 hours for standby after emulsification; the above mixing, stirring and emulsifying process includes emulsifying at a stirring speed higher than 1000 rpm for 5-10 minutes; and step D, taking out the above C flux, warming to room temperature, adding solder powder with a weight percentage of 85-92% into 8-15% of the above C flux, and uniformly mixing in vacuum at a stirring speed of 20-40 rpm to obtain water-soluble solder paste.

[0053] The application has the beneficial effect that A flux and B flux are used to compound C flux with emulsion structure, which has excellent heat collapse resistance and long on-board life.

[0054] The application has the beneficial effect that A solvent is hydrophilic organic alcohol or organic alcohol ether containing hydroxyl, A flux is composed of molecules with strong polarity and capable of forming hydrogen bonds, in the process of solder paste standing, due to the existence of three-dimensional network structure with swollen thixotropic agent particles as the skeleton or self-assembled structure of small molecule thixotropic agent in A flux, most of the solvent molecules are 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 existence of free solvent, the diffusion of water molecules in the flux is limited at this time. Therefore, the surface corrosion of solder powder is effectively reduced, and the on-board life of solder paste standing is improved.

[0055] The application has the beneficial effect that B solvent without hydroxyl in B flux is organic alcohol ether, and hydrogen bond-deficient B flux (dispersed phase) in the process of printing and rolling, such as Figure 9, the interface line Flux B between the scraper and the solder paste is constantly exposed to the solder paste rolling front surface, due to the relatively low surface tension of the solvent in B flux (for example, the surface tension of tetradecane is only 26.5 dyne / cm), which spreads to the rolling front surface of the solder paste, and forms a layer of hydrophobic liquid film on the rolling front surface of the solder paste by the hydrophobic properties of the dispersed phase solvent, thereby inhibiting the absorption of moisture, preventing corrosion of the tin powder, and improving the printed board life of the solder paste.

[0056] The beneficial effects of the present application are that the organic alcohol and organic alcohol ether substances containing hydroxyl groups in A solvent can form hydrogen bonds or other interactions with certain active ingredients in the flux, and these interactions will be destroyed during heating, thereby promoting the release of active ingredients and improving the activity of the flux. At the same time, the rheological properties of the solder paste can be adjusted, the viscosity can be controlled, other solid particle components in the flux can be dissolved, the viscosity of the post-weld residue can be reduced, and cleaning is facilitated.

[0057] The beneficial effects of the present application are that the rosin-based materials in A flux have a high HLB value in the range of 8-20, which have both lipophilicity (combined with solder metal) and hydrophilicity (compatible with polar components in flux), and the high HLB value (close to hydrophilic) promotes the wetting of the solder to the copper and pad surface, reduces welding defects (such as virtual welding), and the HLB value gives the solder paste good thixotropy, prevents printing collapse, and ensures the filling accuracy of fine lines. It is suitable for playing the roles of emulsification, wetting, and stabilizing residues during the welding process.

[0058] The beneficial effects of the present application are that the active agent A is an organic acid or halogen active agent, which provides welding activity for the solder paste and efficiently removes the oxide film on the surface of the solder powder. With the development of advanced packaging technology, the solder joint is becoming more and more fine, and the surface area of the ultra-fine solder powder increases exponentially as the particle size decreases, and the oxide also increases exponentially, and the deoxidation load of the flux increases. The active agent A has strong activity and can quickly remove the oxide film on the surface of the ultra-fine solder powder.

[0059] The beneficial effects of the present application are that the alkane with a boiling point of 215-270°C in B solvent in B flux has a long chain, which can adjust the viscosity of the solder paste as a thickening agent to prevent printing collapse. It can be converted into a low-surface-energy protective film at high welding temperatures to reduce solder oxidation, cover the metal surface during the use of the solder paste, form a hydrophobic temporary protective film, delay oxidation, and prevent the absorption of environmental moisture and oxygen.

[0060] The beneficial effects of the present application are: the B fluxing agent is a rosin-based solvent, the rosin-based solvent is a rosin modifier, including methyl rosinate, the carboxyl group contained in the structure can react with metal oxides to generate soluble salt, the saturated structure can reduce high-temperature carbonization, and the residue is more easily saponified and cleaned after methyl esterification, thereby increasing the post-weld cleaning performance.

[0061] The beneficial effects of the present application are: the rosin derivative is a polyoxyethylene rosin amine with an HLB value of 8-20, the hydrophilicity of which has excellent surface activity, can significantly reduce the contact angle of solder and metal surface, promote the spreading of solder on the PCB pads and pins, reduce false welding and cold welding, and the amine group in the structure also participates in the deoxidation at high temperature. In addition, the flexible structure of the polyoxyethylene chain can increase the viscoelasticity of the flux, so that the solder paste maintains good thixotropy, that is, anti-collapse, during screen printing or stencil printing, avoids excessive diffusion or blockage of the stencil opening, adjusts the rheological properties and demolding properties of the solder paste, and improves the printing accuracy and efficiency. The polyoxyethylene rosin amine with a high HLB value not only stabilizes the emulsion structure of the flux, but also enhances the cleaning ability of the residue.

[0062] The beneficial effects of the present application are: the B active agent in the B fluxing agent can effectively increase the heat collapse resistance of the solder paste through the cold welding mechanism by using strong acids such as oxalic acid, malonic acid, citric acid, etc., but also adversely affects the stability of the solder paste, the present patent technology limits the corrosion of the tin powder by the strong acidity of the organic salt by dispersing the salt in the B fluxing agent, thereby achieving the stability of the solder paste, and in the reflow process, the organic salt decomposes and releases strong organic acid molecules at a certain temperature, which are released in time due to the increased thermal motion in the flux, thereby achieving the heat collapse resistance of the solder paste.

[0063] The beneficial effects of the present application are: the corrosion inhibitor includes 2-bromo-1-methyl-1H-imidazole, which functions as both an active agent and a corrosion inhibitor.

[0064] The beneficial effects of the present application are: the particle size of the solder powder is 2-25 um, and the particle size types include T5 / T6 / T7 / T8, the water-soluble solder paste of the present application has good adaptability and is suitable for various particle sizes.

[0065] The beneficial effects of the present application are: the A fluxing agent is separately packaged and prepared, which is convenient for storage and use.

[0066] The beneficial effects of the present application are: the B fluxing agent is separately packaged and prepared, which is convenient for storage and use.

[0067] The beneficial effects of the present application are: the C flux is ready-to-use, and the ratio of A flux and B can be adjusted according to the chemical composition, particle size, and the level of oxide of the solder powder, so as to prepare C flux matching different solder powders, and suitable for different process windows and performance requirements. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 Table 1 shows the formula of A flux in Example 1 to Example 5;

[0069] Figure 2 Table 2 shows the formula of B flux in Example 1 to Example 5;

[0070] Figure 3 Table 3 shows the formula of the comparative example;

[0071] Figure 4 Table 4 shows the continuous printing test results of the examples and the comparative example;

[0072] Figure 5 Table 5 shows the hot collapse test results of the examples and the comparative example;

[0073] Figure 6 Figure 1 is a schematic diagram of the comparison before and after cleaning the solder joint;

[0074] Figure 7 Figure 2 is a schematic diagram of Raman spectrum analysis of the residual material before cleaning the solder joint;

[0075] Figure 8 Figure 3 is a schematic diagram of Raman spectrum analysis of the residual material after cleaning the solder joint;

[0076] Figure 9 Figure 4 is a schematic diagram of the separation of the doctor blade and the solder paste during the printing process of the water-soluble solder paste. DETAILED DESCRIPTION

[0077] The content of the present application is further described in detail below in combination with the drawings.

[0078] In the solder, rosin, rosin derivatives and rosin modifiers are common flux ingredients, which play different roles in the welding process.

[0079] Glossary:

[0080] Rosin: is a natural product extracted from the resin of pine trees, the main component is rosin acid, and it has good chemical stability. It is a complex mixture, but the activity is low, and it is suitable for welding scenes with low activity requirements for flux.

[0081] Rosin derivatives: refers to the deep processing of rosin through chemical reactions to generate compounds with different functional groups or structures, usually with different chemical properties and applications from rosin, enhanced activity, suitable for soldering scenes with high activity requirements and high reliability requirements.

[0082] Rosin modification: is the treatment of rosin by physical or chemical methods to improve its performance or give new functional products, modification methods include esterification, hydrogenation, polymerization, etc. Suitable for scenes with high requirements on welding temperature and quality.

[0083] Rosin-based materials include rosin modification and rosin derivatives, which are derivatives or composite materials obtained by physical modification or chemical modification (such as hydrogenation, disproportionation, polymerization, esterification, acrylic acid grafting, etc.) with natural rosin as the main raw material, with special functions and high performance.

[0084] HLB value: English full name: Hydrophile-Lipophile Balance; Chinese meaning: Hydrophile-Lipophile Balance; It is a quantitative index of the balance between the size and strength of the hydrophilic and lipophilic groups in the surfactant molecule. The larger the value, the stronger the hydrophilicity, and vice versa.

[0085] Although the solder powder surface is wrapped with a tin oxide film, due to the defects in the oxide layer, tin atoms still have the opportunity to be exposed to the flux, causing corrosion of the solder paste during storage and printing, which can be described by the following reaction equation: 4Sn + 2H2O + 4H + + O2 = 2H2 + 2Sn(OH - )2 + 2Sn 2+

[0086] As shown in the above reaction equation, the simultaneous presence of water and oxygen is necessary for the corrosion of solder powder.

[0087] Not only that, some solder pastes with good thermal collapse resistance have a shorter board life, which is due to the use of active agents with strong activity. During storage and printing, the contact between active agents with strong activity such as strong organic acids and solder powder triggers a corrosion reaction, which also affects the board life of the solder paste.

[0088] Active agent in solder: The main role is to remove the oxide on the solder pad and solder surface at the welding temperature, thereby improving the wettability between the solder and the solder pad. It removes the oxide layer by chemical reaction with metal oxide, providing a clean metal surface for welding, thereby promoting the metallurgical bonding of the solder and the welded metal.

[0089] Traditional active agents are inorganic substances, rosin, organic halides, etc. Nowadays, they are mostly organic acids and organic amines. For example, organic acids include succinic acid, glutaric acid, o-hydroxybenzoic acid, etc. Organic amines are used to adjust the acidity value of the flux.

[0090] The stronger the activity of the active agent, the greater the corrosion after soldering may be, and thus the amount needs to be reasonably selected and controlled. The presence of the active agent is one of the factors affecting the shelf life of the solder paste on the board.

[0091] Surfactant: The main function is to reduce the surface tension of the flux, increase the wettability of the flux to the solder powder and the pad. It can make the liquid solder better melt into the weld, improve the welding quality, especially in lead-free solder welding, its role is more prominent, because the melting point of lead-free solder is higher, the surface tension is greater.

[0092] Surfactant: can be divided into non-ionic surfactants, such as OP series, fluorinated aliphatic polyether; anionic surfactants, such as diethyl succinate sodium sulfonate; cationic surfactants, such as cetyltrimethylammonium bromide; amphoteric surfactants, etc. Ionic surfactants will affect the activity of the active agent, so non-ionic surfactants are generally selected. In addition, the surfactant is not easy to volatilize, and will leave a hygroscopic residue after soldering, so the amount should not be too much.

[0093] In the present application, a water-soluble solder paste includes, in mass percentage, 85-92% of solder powder and 8-15% of C flux; the C flux includes 85-95% of A flux and 5-15% of B flux; the A flux includes A solvent, rosin-based material, A thixotropic agent, A active agent, corrosion inhibitor, and surfactant; the A solvent is a hydrophilic solvent; the rosin-based material includes at least one of acrylic modified rosin, hydrogenated rosin, or polyoxyethylene rosin; the B flux includes B solvent, rosin derivative, B active agent, and B thixotropic agent; the B solvent is a hydrophobic solvent; the rosin derivative includes at least one of polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; the A flux and the B flux are compounded into the C flux with an emulsion structure; and the C flux is used to mix with the solder powder to form the water-soluble solder paste.

[0094] The A flux includes, in mass percentage, 30-45% of A solvent, 30-50% of rosin-based material, 4-12% of A thixotropic agent, 3-19% of A active agent, 0.2-3% of corrosion inhibitor, and 0-4% of surfactant.

[0095] The A solvent is a hydrophilic organic alcohol or organic alcohol ether containing a hydroxyl group.

[0096] The solvent A includes one or more of organic alcohol or organic alcohol ether solvents, including 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 one or more of glycerol.

[0097] The rosin-based material A includes one or more of acrylic modified rosin, hydrogenated rosin, and polyoxyethylene rosin.

[0098] The rosin-based material A includes one or more of acrylic modified rosin, hydrogenated rosin, and polyoxyethylene rosin; the mass ratio of the acrylic modified rosin, the hydrogenated rosin, and the polyoxyethylene rosin is (0-0.2):(0-0.2):1.

[0099] The rosin-based material A includes polyoxyethylene rosin with an HLB value in the range of 8-20; the polyoxyethylene rosin includes polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; the polyoxyethylene rosin amine is polyoxyethylene rosin amine with an HLB value in the range of 8-20; the polyoxyethylene polymerized rosin is polyoxyethylene polymerized rosin with an HLB value in the range of 8-20.

[0100] The active agent A includes organic acid and halogen active agent.

[0101] The active agent A used by the flux A includes organic acid and halogen active agent; the organic acid includes one or more of oxalic acid, malonic acid, succinic acid, adipic acid, phenylsuccinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid; the halogen active agent includes one or more of triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutene diol, and 2-bromo-1-methyl-1H-imidazole.

[0102] The thixotropic agent A used by the flux A includes hydrogenated castor oil, polyamide thixotropic agent, and a compound thereof; the polyamide thixotropic agent and the compound thereof are water-soluble polyamide thixotropic agent.

[0103] The HLB value of the surfactant is in the range of 8-20.

[0104] The surfactant includes one or more of Tween 20 and 2-bromo-1-methyl-1H-imidazole.

[0105] The corrosion inhibitor includes one or more of 2-bromo-1-methyl-1H-imidazole, ethylimidazole, and 1,2,3-benzotriazole; the 2-bromo-1-methyl-1H-imidazole is also a halogen active agent in the surfactant used by the flux A.

[0106] The A flux has a strong polarity and a large hydrogen bond density. The A solvent is an organic alcohol or an organic alcohol ether containing a hydroxyl group and having a strong polarity. The polyoxyethylene rosin is a polyoxyethylene rosin having a high HLB value (the HLB value is in the range of 8-20). The high HLB value means that the HLB value is in the range of 8-20. The high HLB value of the polyoxyethylene rosin amine having a high HLB value and the polyoxyethylene polymerized rosin having a high HLB value means that the HLB value is in the range of 8-20.

[0107] The B flux includes, in mass percentage, 40-80% of the B solvent, 10-45% of the rosin derivative, 2-8% of the B active agent, and 2-10% of the B thixotropic agent. The B solvent includes a hydrophobic organic alcohol ether containing no hydroxyl group or an alkane having a boiling point in the range of 215-270°C or a rosin solvent. The B solvent is a solvent containing no hydroxyl group and having a low polarity. The B flux has a weak polarity and a small hydrogen bond density. The B active agent is a strong acid.

[0108] 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.

[0109] The alkane having a boiling point in the range of 215-270°C in the B solvent includes any one or more of dodecane, tridecane, tetradecane, pentadecane, or a cycloalkane.

[0110] The B solvent is a rosin solvent, and the rosin solvent is a rosin modifier, including methyl abietate.

[0111] The rosin derivative is any one or more of a polyoxyethylene rosin amine having a HLB value in the range of 8-20 and a polyoxyethylene polymerized rosin having a HLB value in the range of 8-20.

[0112] The B thixotropic agent includes any one or more of hydrogenated castor oil, a hydrogenated castor oil modifier, or an amide thixotropic agent.

[0113] The B active agent includes any one or more of malonic acid, oxalic acid, and citric acid. The B active agent is a strong acid.

[0114] The polyoxyethylene rosin amine having a high HLB value and the polyoxyethylene polymerized rosin having a high HLB value, the high HLB value means that the HLB value is in the range of 8-20.

[0115] The application provides a water-soluble soldering paste, soldering powder content is between 85-92wt%, soldering powder composition is Sn as a matrix adding a small amount of metal elements such as Ag0~4wt%, Cu0~1wt%, Sb0~10wt%, Bi0~3wt%, Ni0~0.15wt%, In0~10wt% one or more than two components of an alloy, the particle size of the soldering powder is 2~25um, the particle size of the soldering powder meets the particle size requirements of T5, T6, T7, T8 powder specified in electronic industry standard SJ / T11391-2019 soldering alloy powder for electronic products or IPC J-STD-005A-2012; C flux includes two parts of A flux and B flux, the ratio is between 85-95wt%:5-15wt%, A flux and B flux are compounded by the above ratio, and an emulsion structure of A flux as a continuous phase and B flux as a dispersed phase is formed under the condition of high-speed stirring, that is, C flux.

[0116] The solvent of C flux includes two types. One is the organic alcohol or organic alcohol ether containing hydroxyl in A flux, and the other is the organic alcohol ether, alkane and rosin modifier not containing hydroxyl in B flux. Through the emulsification process of A flux and B, a C flux with an emulsion structure is obtained. The B flux with the B solvent not containing hydroxyl as the main body forms a dispersed phase, and the A flux with the A solvent containing hydroxyl as the main body and containing most of the active agents forms a continuous phase.

[0117] The continuous phase A flux is composed of molecules with strong polarity and hydrogen bond forming functional groups. In the process of standing of the soldering paste, due to the existence of the three-dimensional network structure formed by the swelling thixotropic agent particles assisted by the hydrogen bond mechanism in the soldering paste flux, or the self-assembly structure of the small molecule thixotropic agent, most of the solvent molecules are bound in the three-dimensional structure of the swelling thixotropic particles or trapped in the self-assembly 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 existence of free solvent, the diffusion of water molecules in the flux is limited at this time. Therefore, the surface corrosion reaction of the soldering powder is not conducive to proceed, and in the case that there is a lack of strong organic acid with strong water absorption in the continuous phase, the stability of the soldering paste is good.

[0118] But when the solder paste is subjected to external force to start flowing (for example, the rolling of solder paste in the printing process), the three-dimensional structure of the thixotropic agent particles in the solder paste is destroyed, and the unique hydrogen bond in the product of the present technology is constantly exposed to the solder paste rolling front surface at the interface line between the scraper and the solder paste during the printing 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), the B flux solvent spreads on the rolling front surface of the solder paste, and a layer of hydrophobic liquid film is formed on the rolling front surface of the solder paste by the hydrophobic property of the dispersed phase solvent, thereby effectively inhibiting the absorption of moisture and preventing the corrosion of the tin powder, and improving the printed board life of the solder paste.

[0119] The hydrophobic B solvent in the B flux is an organic alcohol ether, alkane and rosin modifier, for example, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, dodecane to pentadecane, hydrogenated rosin acid methyl ester and other rosin solvents, which account for 40-80wt% in the B flux. In order to not interfere with the overall characteristics of the entire solder paste, the amount of B flux is much smaller than that of A flux, and the weight ratio of the two is 5-15wt%:85-95wt%.

[0120] In order to preserve the overall performance of the entire solder paste, the A flux needs to provide the thixotropy, activity and protective coating of the solder powder required by the solder paste, so the A flux uses conventional solvents containing hydroxyl groups, 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, and a mixture of one or more of glycerol, which accounts for 30-45wt% of the total amount of A flux.

[0121] The organic acid and halogen active agent used in the A flux of the present application are: butanedioic acid, hexanedioic acid, phenyl butanedioic acid, succinic acid, pentanedioic acid, heptanedioic acid, octanedioic acid, nonanedioic acid, decanedioic acid, triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutene glycol, 2-bromo-1-methyl-1H-imidazole, etc., the total amount being 3-19 wt%; the thixotropic agent system used in the present application is preferably a water-soluble polyamide thixotropic agent to obtain a high thixotropic coefficient, or a combination of a conventional polyamide thixotropic agent and hydrogenated castor oil can also be selected. The total amount is 4-12 wt%, in order to meet the water-soluble characteristics, the rosin and its derivatives used in the A flux are: acrylic modified rosin, hydrogenated rosin, high HLB value polyoxyethylene rosin. The high HLB value polyoxyethylene rosin includes high HLB value polyoxyethylene rosin amine, high HLB value polyoxyethylene polymerized rosin. The ratio of acrylic modified rosin, hydrogenated rosin and high HLB value polyoxyethylene rosin is 0-0.2:0-0.2:1. The total amount is 30-50 wt%. The present application preferably uses water-soluble high HLB value polyoxyethylene rosin amine which can not only stabilize the emulsion structure of the flux, but also enhance the cleaning ability for the residual.

[0122] Due to the use of strong acids such as oxalic acid, malonic acid, citric acid, the heat slump resistance of the solder paste can be effectively increased by the cold welding mechanism, but it also adversely affects the stability of the solder paste. The present patent technology uses the method of reacting organic strong acid with rosin amine to generate salt and dispersing it in the B flux to limit the corrosion of the tin powder by the strong acidity, so that the stability of the solder paste can be achieved. 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 can be released in time in the flux due to the increase of thermal motion, so that the heat slump resistance of the solder paste can also be achieved. The strong organic acid active agent in the B flux is malonic acid, oxalic acid, citric acid, etc., the total content being 2-8 wt%. The B flux also needs to have a certain protection for the solder powder, the rosin derivative used is high HLB value, i.e. HLB value between 8-20, polyoxyethylene rosin amine, polyoxyethylene polymerized rosin, the total amount being 10-45 wt%; the thixotropic agent is hydrogenated castor oil and its modified product, amide thixotropic agent, the total amount being 2-10 wt%.

[0123] The present application pays attention to the emulsion structure of the flux which can effectively block the absorption of water vapor in the air in the flux during the printing and rolling of the solder paste, thereby inhibiting the corrosion of the solder powder and improving the stencil life. Due to the lack of water and the fact that the organic acid is confined in the B flux, the corrosion on the surface of the tin powder is very limited. This structural feature enables the stability and good heat slump resistance of the solder paste to be achieved simultaneously in one product.

[0124] The present application provides a preparation method of the water-soluble solder paste.

[0125] The preparation process of the flux A: the rosin derivative, the organic alcohol ether solvent containing hydroxyl, the active agent, the corrosion inhibitor are added into the temperature-controllable heating device, and slowly stirred and mixed to dissolve under the condition that the temperature is in the range of 70-90°C; the temperature of the system is reduced to 40-55°C, the thixotropic agent is added, and the high-speed stirring (the rotating speed is between 2000-3000 rpm) is applied for 20-30 minutes to activate the thixotropic agent, then the surface active agent is added under the slow stirring and the cooling to below 30°C, and mixed uniformly. After being cooled to the normal temperature, the grinding is carried out, then it is placed into the refrigerator at 2-10°C for more than 10 hours, and is ready for use.

[0126] The preparation process of the flux B: the solvent without hydroxyl is added into the temperature-controllable heating device, and the mixture of the organic acid and the rosin modifier is added under the condition that the temperature is in the range of 60-75°C, the high-speed stirring (1500 rpm and above) is applied for 3-5 minutes, then the thixotropic agent is added under the temperature range, the high-speed stirring is applied for 20-30 minutes to activate, then the slow stirring is applied for the cooling to 30°C, and the grinding is carried out, then it is placed into the refrigerator at 2-10°C for more than 10 hours, and is ready for use.

[0127] The refrigerated fluxes A and B are taken out, and are warmed to the normal temperature, then they are compounded in the proportion between 85-95%: 15-5%, and are emulsified under the stirring speed of more than 1000 rpm for 5-10 minutes to obtain the flux. The flux is placed into the refrigerator at 2-10°C for more than 10 hours, and is ready for use.

[0128] The obtained flux is taken out, and is warmed to the normal temperature, then the solder powder in the weight percentage of 85-92 wt% is added into the above flux in 8-15 wt%, and is mixed uniformly under the stirring speed of 20-40 rpm in vacuum to obtain the solder paste.

[0129] One of the beneficial effects of the present application is that the existence of the hydrophobic dispersed phase B in the structure of the emulsion flux C can form a hydrophobic film on the front surface of the solder paste during the solder paste printing process. The existence of the hydrophobic film can effectively inhibit the absorption of water; and during the standing process of the solder paste, due to the existence of the three-dimensional structure (self-assembly structure of the small molecule thixotropic agent) formed by the hydrogen bond in the swelling thixotropic particles of the flux, the absence of the free solvent molecules makes the water absorbed on the surface of the flux unable to effectively diffuse in the paste body, and the corrosion speed of the solder paste is limited in this stage. By the above mechanism, the product can significantly reduce the corrosion of the solder powder, thereby effectively preventing the viscosity rise of the solder paste during the continuous printing process and the standing process, and thereby improving the service life on the printed board.

[0130] One of the benefits of the present application is that the invention uses a strong organic acid which is confined in the hydrophobic dispersed phase B, which can well inhibit its corrosion effect and at the same time can play its role in the early stage of reflow, so that the solder paste can obtain excellent on-line life and good thermal collapse resistance.

[0131] One of the benefits of the present application is that a large amount of high HLB rosin surfactant in the continuous phase can provide effective protection to the solder powder during reflow, thereby ensuring the activity and residual cleaning performance.

[0132] As Figure 1 Table 1, which shows the formulation of A flux in Examples 1 to 5. As Figure 2 Table 2, which shows the formulation of B flux in Examples 1 to 5.

[0133] Preparation process of Example 1:

[0134] Put 23 parts of diethylene glycol monobutyl ether, 3 parts of glycerol, 14 parts of diethylene glycol monohexyl ether into an oil bath heated container, the system temperature is raised to 82℃, add 5 parts of succinic acid, 10 parts of sebacic acid, 0.6 parts of dibromobutane diol, 2.4 parts of ethyl imidazole, 16 parts of polyoxyethylene polymerized rosin and 20 parts of polyoxyethylene rosin amine, slowly stir until dissolved, further reduce the system temperature to 45℃, add 6 parts of water-soluble polyamide thixotropic agent RE-127, high-speed stirring for 20-30 minutes to complete activation, slowly stir until cooled to room temperature, then grind, then put into a 2-10℃ refrigerator, and place for more than 10 hours for standby.

[0135] Slowly stir and mix 50 parts of n-tetradecane, 10 parts of diethylene glycol diethyl ether at a temperature range of 65℃, add a mixture of 26 parts of polyoxyethylene rosin amine and 4 parts of malonic acid, high-speed stirring (1500rpm) for 3-5 minutes, then add 10 parts of polyamide thixotropic agent 6650, high-speed stirring activation (3000rmp) for 25 minutes, slowly stir and cool to 30℃, discharge, then grind after cooling to room temperature, then put into a 2-10℃ refrigerator, and place for more than 10 hours for standby.

[0136] Take out the refrigerated flux A and B, warm them to room temperature, then mix and compound them at a ratio of 90wt%:10wt%, emulsify at a stirring speed of 1500rpm for 5 minutes to obtain the flux. Put the flux into a 2-10℃ refrigerator, and place for more than 10 hours for standby.

[0137] Take out the above obtained flux, warm it to room temperature, then add 6# solder powder at a weight percentage of 87wt% to the above flux 13wt%, mix uniformly at a stirring speed of 25rpm to obtain the solder paste.

[0138] Example 2. The formulation of Example 2 is shown in Tables 1 and 2 and was made in the same way as Example 1 except that the ratio of A flux to B flux was 85wt%: 15wt%.

[0139] Example 3. The formulation of Example 3 is shown in Tables 1 and 2 and was made in the same way as Example 1. The difference is that the ratio of A flux to B flux was 95wt%: 5wt%.

[0140] Example 4. The formulation of Example 4 is shown in Tables 1 and 2 and was made in the same way as Example 1 except that the ratio of A flux to B flux was 85wt%: 15wt%.

[0141] Example 5. The formulation of Example 5 is shown in Tables 1 and 2 and was made in the same way as Example 1. The difference is that the ratio of A flux to B flux was 95wt%: 5wt%.

[0142] To better illustrate the effect of the technical solutions in this application, the following comparative examples are designed for effect comparison. The formulation of Comparative Example 1 is shown in Table 3, which is exactly the same as the A flux of Example 1.

[0143] The comprehensive performance comparison of the solder paste made from the formulations of Example 1 and Comparative Example 1 can well reflect the role of B flux in Example 1 in improving the board life of the solder paste. The formulation of Comparative Example 2 is shown in Table 3, and the main difference between the formulation and the A flux of Example 2 is that in Example 2, malonic acid is dispersed in B flux, while in Comparative Example 2, it is added to the only main flux.

[0144] As Figure 4 i.e. Table 4, which shows the results of the continuous printing test of the examples and comparative examples; the continuous printing test (viscosity unit Pa.S) conditions are: Malcom PCU02V@10 rpm 25°C. The board life of each sample is represented by the viscosity value of the continuous printing. Since the solder paste made from Comparative Example 2 has too high viscosity in the initial stage, no subsequent tests of various types are carried out.

[0145] From Figure 4 It can be seen that Examples 1 to 5 not only have suitable initial viscosity, but also have smaller viscosity changes at 8 hours and 12 hours, and more stable viscosity performance. Comparative Example 1 can also test the initial viscosity, 8-hour viscosity and 12-hour viscosity, but the viscosity changes at 8 hours and 12 hours are relatively larger than those of the examples.

[0146] As Figure 5Table 5, which shows the hot collapse test results of the examples and the comparative example. Hot collapse performance: according to the test method of SJT11186-2019. The unbonding distance of Examples 1 to 5 is smaller than that of Comparative Example 1. Comparative Example 1 has no unbonding distance because it cannot be printed.

[0147] As Figure 6 is a schematic diagram of the comparison of residues before and after cleaning of the solder joint; Solder joint performance: the solder joints of all sample tests are shiny, without tin beads, and good spreading and wetting under a nitrogen atmosphere. Water washing performance: all sample tests can completely clean the residues near the solder joint.

[0148] As Figure 7 is a schematic diagram of Raman spectrum analysis of the residues before cleaning of the solder joint; Figure 8 is a schematic diagram of Raman spectrum analysis of the residues after cleaning of the solder joint. The residues are mainly rosin substances, and the characteristic peaks near 2000-3000 cm -1 -1,450 cm -1 The characteristic peaks near 2000-3000 cm

[0149] In this application, the mass percentage % is the weight percentage wt%. In this application, the flux C is C flux, the flux A is A flux, and the flux B is B flux. The solvent A is A solvent, the thixotropic agent A is A thixotropic agent, and the active agent A is A active agent. The solvent B is B solvent, the active agent B is B active agent, and the thixotropic agent B is B thixotropic agent.

[0150] The above is only an embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation using the content of the application specification and drawings, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A water-soluble solder paste, characterized by by mass percentage, The C flux includes 85-92% of solder powder and 8-15% of C flux; The C flux includes 85-95% of A flux and 5-15% of B flux; The A flux includes A solvent, rosin-based material, A thixotropic agent, A active agent, corrosion inhibitor, and surfactant; the A solvent is a hydrophilic solvent; the rosin-based material includes at least one of acrylic modified rosin, hydrogenated rosin, or polyoxyethylene rosin; The B flux includes B solvent, rosin derivative, B thixotropic agent, and B active agent; the B solvent is a hydrophobic solvent; the rosin derivative includes at least one of polyoxyethylene rosin amine and polyoxyethylene polymerized rosin; The A flux and the B flux are compounded into the C flux with emulsion structure; the C flux is used to mix with the solder powder to form the water-soluble solder paste; The A flux includes, by mass percentage, The A flux includes 30-45% of A solvent, 30-50% of rosin-based material, 4-12% of A thixotropic agent, 3-19% of A active agent, 0.2-3% of corrosion inhibitor, and 0-4% of surfactant; The B flux includes, by mass percentage, The B flux includes 40-80% of B solvent, 10-45% of rosin derivative, 2-8% of B active agent, and 2-10% of B thixotropic agent; The B solvent includes any one or more of hydroxyl-free hydrophobic organic alcohol ethers or alkanes with boiling point of 215-270°C or rosin solvents; The solder powder is an alloy with Sn as the matrix 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 solder powder has a particle size of 2-25 um, and the particle size type includes T5 / T6 / T7 / T8.

2. The water-soluble solder paste according to claim 1, wherein the A solvent is a hydrophilic organic alcohol or organic alcohol ether containing a hydroxyl group.

3. The water-soluble solder paste according to claim 1, wherein the A solvent includes an organic alcohol or organic alcohol ether solvent, and includes 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.

4. The water-soluble solder paste according to claim 1, wherein the rosin-based material includes any one or more of acrylic modified rosin, hydrogenated rosin, and polyoxyethylene rosin.

5. The water-soluble solder paste according to claim 1, wherein the rosin-based material includes acrylic modified rosin, hydrogenated rosin, and polyoxyethylene rosin; and the mass ratio of the acrylic modified rosin, the hydrogenated rosin, and the polyoxyethylene rosin is (0-0.2):(0-0.2):

1.

6. The water-soluble solder paste according to claim 1, wherein the rosin-based material includes 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 polyoxyethylene rosin amine with HLB value in the range of 8-20; polyoxyethylene polymerized rosin is polyoxyethylene polymerized rosin with HLB value in the range of 8-20.

7. The water-soluble solder paste according to claim 1, wherein: The A active agent used in the A flux includes an organic acid and a halogen active agent; 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, sebacic acid; the halogen active agent includes any one or more of triethanolamine hydrobromide, cyclohexylamine hydrobromide, dibromobutene diol, 2-bromo-1-methyl-1H-imidazole.

8. The water-soluble solder paste according to claim 1, wherein: The A thixotropic agent used in the A flux includes hydrogenated castor oil, polyamide thixotropic agent and its compound; the polyamide thixotropic agent and its compound is a water-soluble polyamide thixotropic agent.

9. The water-soluble solder paste according to claim 1, wherein: The HLB value of the surfactant is in the range of 8-20; The surfactant includes any one or more of Tween 20, 2-bromo-1-methyl-1H-imidazole.

10. The water-soluble solder paste according to claim 1, wherein: The corrosion inhibitor includes any one or more of 2-bromo-1-methyl-1H-imidazole, ethyl imidazole, 1,2,3-benzotriazole.

11. The water-soluble solder paste according to claim 1, wherein: The B flux includes an organic alcohol ether, which is a hydroxyl-free organic alcohol ether, including any one or more of diethylene glycol diethyl ether, diethylene glycol dibutyl ether.

12. The water-soluble solder paste according to claim 1, wherein: The alkane with boiling point in the range of 215-270℃ in the B solvent includes any one or more of dodecane, tridecane, tetradecane, pentadecane or cycloalkane.

13. The water-soluble solder paste according to claim 1, wherein: The B solvent is a rosin solvent, which is a rosin modifier, including methyl abietate.

14. The water-soluble solder paste according to claim 1, wherein: The rosin derivative is any one or more of polyoxyethylene rosin amine with HLB value in the range of 8-20 and polyoxyethylene polymerized rosin with HLB value in the range of 8-20.

15. The water-soluble solder paste according to claim 1, wherein: The B thixotropic agent includes any one or more of hydrogenated castor oil, hydrogenated castor oil modifier or amide thixotropic agent.

16. The water-soluble solder paste according to claim 1, wherein: The B active agent includes any one or more of malonic acid, oxalic acid, citric acid.

17. A water-soluble solder paste preparation method for the water-soluble solder paste according to any one of claims 1-16, wherein: Step A: preparation of the A flux, and after preparation, the A flux is stored in cold storage; Step A for preparing the A flux includes, Step A10: mix and stir the rosin-based material, A solvent, A active agent, corrosion inhibitor, and heat to a temperature of 70-90°C; Step A20: after mixing and dissolving, reduce the temperature to 40-55°C, Step A30: add A thixotropic agent, apply high-speed stirring at a speed of 2000-3000 rpm, and activate for 20-30 minutes, Step A40: reduce the stirring speed and slowly cool to 30°C; Step A50: add a surfactant at 30°C and mix well; Step A60: cool to room temperature and grind while cooling; Step A70: after grinding, place in a 2-10°C refrigerator for 10 hours or more for standby; Step B: preparation of B flux, and store after preparation; Step B for preparing B flux includes, Step B10: after heating the B solvent to a temperature of 60-75°C, add a mixture of B active agent and rosin derivative, and stir at a speed higher than 1500 rpm for 3-5 minutes; Step B20: add B thixotropic agent at 60-75°C, and activate by high-speed stirring for 20-30 minutes, Step B30: slowly stir and cool to 30°C, Step B40: discharge, grind, and place in a 2-10°C refrigerator for 10 hours or more for standby; Step C: take out the refrigerated A flux and B flux, warm to room temperature, mix and emulsify them to obtain C flux; after emulsification, place in a 2-10°C refrigerator for 10 hours or more for standby; the above mixing and emulsifying process includes emulsification at a stirring speed of 1000 rpm or higher for 5-10 minutes; Step D: take out the above C flux, warm to room temperature, then add solder powder with a weight percentage of 85-92% to the above C flux 8-15%, and mix uniformly under vacuum at a stirring speed of 20-40 rpm to obtain water-soluble solder paste.

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