Water-soluble tin paste, preparation method and application thereof

Abstract

This application relates to the field of electronic soldering materials technology, and discloses a water-soluble solder paste, its preparation method, and its application. The water-soluble solder paste of this application comprises a water-soluble flux and solder powder, with a mass ratio of water-soluble flux to solder powder of 1:(7~10). The water-soluble flux comprises the following components by weight: 45~55 parts film-forming agent; 8~12 parts organic acid activator; 6~8 parts thixotropic agent; 0.3~3 parts surfactant; 1~3 parts corrosion inhibitor; 3~5 parts antioxidant; and 25~35 parts solvent. The raw materials for preparing the film-forming agent include polyethylene glycol 400, sodium hydroxypropyl methylcellulose, VYBAR 825 polymer, triethylamine, 1,6-hexanediol, tripropylene glycol, and polyoxyethylene glycerol ether MF-200A. The water-soluble solder paste of this application, prepared by adding a specific film-forming agent and combining it with vacuum stirring, has advantages such as no need for organic solvent cleaning, moisture resistance, and long shelf life.

Description

Technical Field

[0001] This application relates to the field of electronic soldering materials technology, and in particular to a water-soluble solder paste, its preparation method, and its application. Background Technology

[0002] In the electronics manufacturing industry, processes such as surface mount technology (SMT) of electronic circuit boards and IC pin soldering are crucial, especially in specific scenarios such as sensor soldering inside ultrasonic radars and photosensitive sensors, where strict requirements are placed on soldering materials and processes. With the continuous development of electronic technology, the demands for soldering quality and efficiency are also increasing. High-quality soldering materials can ensure stable connections of electronic components, improving the reliability and performance of electronic products. This not only helps improve the stability of the entire electronic system but also meets the development trend of miniaturization and high performance in modern electronic products.

[0003] In existing technologies, natural rosin is used to improve the adhesion of solder paste and prevent displacement. However, in actual soldering operations, rosin / flux residues remain on the circuit board after soldering. To remove these residues, organic solvents are typically used as cleaning agents to remove the flux and water-insoluble natural rosin. However, cleaning soldering residues with organic solvents can be corrosive to the circuit board. To address this, water-soluble solder pastes are available on the market that can be cleaned with water after soldering, thus resolving the corrosive effects of organic solvents on the circuit board.

[0004] However, existing water-soluble solder pastes are prone to absorbing moisture when used in the air for extended periods, leading to reduced viscosity and solder spattering. To address this, a reflow oven filled with protective gas is typically used to solve the moisture absorption problem of water-soluble solder pastes. However, current water-soluble solder pastes still suffer from issues such as short shelf life, easy delamination, and poor wetting properties. Summary of the Invention

[0005] To at least overcome one of the problems existing in the prior art, one objective of this application is to provide a water-soluble solder paste that has advantages such as no need for organic solvent cleaning, moisture resistance, long shelf life (can be stored for 6 months), good wetting properties, resistance to delamination, and high soldering strength. This avoids problems such as solder paste delamination and easy moisture absorption, and can meet the requirements of people for solder paste electronic soldering materials in practical applications. A second objective of this application is to provide a method for preparing the water-soluble solder paste. A third objective of this application is to provide applications of the water-soluble solder paste.

[0006] Therefore, this application adopts the following technical solution:

[0007] The first aspect of this application provides a water-soluble solder paste, comprising a water-soluble flux and solder powder, wherein the mass ratio of the water-soluble flux to the solder powder is 1:(7-10); the water-soluble flux comprises the following components in parts by weight:

[0008] 45-55 parts of film-forming agent;

[0009] 8-12 parts of organic acid surfactant;

[0010] 6-8 parts of thixotropic agent;

[0011]

[0012] The raw materials for preparing the film-forming agent include polyethylene glycol 400, sodium hydroxypropyl methylcellulose, VYBAR 825 polymer, triethylamine, 1,6-hexanediol, tripropylene glycol, and polyoxyethylene glycerol ether MF-200A.

[0013] Preferably, the film-forming agent is a mixture of polyethylene glycol 400, sodium hydroxypropyl methylcellulose, VYBAR 825 polymer, triethylamine, 1,6-hexanediol, tripropylene glycol and polyoxyethylene glycerol ether MF-200A in a mass ratio of (4-6):(2-4.5):(1.5-3.5):(0.8-1.2):(0.3-0.7):(0.1-0.4):(0.5-0.7).

[0014] In the preparation of the film-forming agent, polyethylene glycol 400 is a water-soluble polymer with good solubility and stability. It can form a protective film during the soldering process to prevent the solder powder from oxidizing, thus providing protection. Sodium hydroxypropyl methylcellulose is a cellulose ether compound with thickening and film-forming properties, which helps improve the viscosity and stability of the water-soluble flux. VYBAR 825 polymer has good thermal and chemical stability, which can improve the overall performance of the water-soluble flux. Triethylamine is an organic base that regulates the pH of the water-soluble flux and maintains its stability. 1,6-Hexanediol has certain solubility and volatility, which helps in the uniform mixing of the flux and its volatilization during the soldering process. Tripropylene glycol has good solubility and a moderate boiling point, making it suitable as a solvent and additive. Polyoxyethylene glycerol ether MF-200A is a nonionic surfactant that reduces surface tension, allowing the flux to spread better. These components are mixed in a certain proportion to form a film-forming agent. During the soldering process, the film-forming agent will form a uniform thin film at the soldering site. This thin film can isolate the air and prevent the solder powder from oxidizing. It also helps the flux to be evenly distributed and the soldering to proceed smoothly. It also avoids the problem of existing water-soluble solder paste easily absorbing moisture, which leads to a decrease in viscosity and solder splattering. It can also prevent the solder powder in the solder paste from sinking or separating, and improve the shelf life of water-soluble solder paste.

[0015] Preferably, the organic acid activator is selected from at least one of dodecanoic acid, phenylsuccinic acid, glycolic acid, octanoic acid, succinic acid, and hexadecanoic acid. More preferably, the organic acid activator is selected from at least one of dodecanoic acid, phenylsuccinic acid, octanoic acid, succinic acid, and hexadecanoic acid. Even more preferably, the organic acid activator is selected from at least one of dodecanoic acid, phenylsuccinic acid, and octanoic acid.

[0016] Choosing at least one of dodecanoic acid, phenyl succinic acid, glycolic acid, octanoic acid, succinic acid, and hexadecanoic acid as an organic acid activator can effectively remove metal surface oxides and improve welding wettability during the welding process.

[0017] Preferably, the thixotropic agent is a diamide-based thixotropic agent.

[0018] Preferably, the diamide thixotropic agent is selected from at least one of ethylene bis(12-hydroxystearamide), phenylene bisstearamide, and hexamethylenediamine bisstearamide. More preferably, the diamide thixotropic agent is selected from at least one of ethylene bis(12-hydroxystearamide) and phenylene bisstearamide.

[0019] Diamide thixotropic agents are key additives in water-soluble solder paste. These molecules contain polar groups (such as hydroxyl and amide bonds) and long-chain alkyl groups (hydrophobic ends). In water-soluble systems, they self-assemble into a three-dimensional network structure through hydrogen bonding and van der Waals forces. When stationary, this structure encapsulates solder powder and flux components, maintaining high viscosity and preventing solder powder sedimentation and solvent stratification, thus ensuring the uniformity of the solder paste. However, under external forces such as shear forces, the network structure of the diamide is disrupted, causing a rapid decrease in solder paste viscosity and increased fluidity. When the shear force disappears, the network structure recovers, and the solder paste viscosity rebounds. Therefore, using diamide thixotropic agents enables water-soluble solder paste to possess excellent thixotropic properties, ensuring the fluidity and stability of the solder paste under different application scenarios.

[0020] Preferably, the surfactant is selected from at least one of dimethyl silicone oil, oleyl alcohol polyoxyethylene ether, Surfynol 104 surfactant, and GE-511 surfactant. More preferably, the surfactant is selected from at least one of dimethyl silicone oil, oleyl alcohol polyoxyethylene ether, and Surfynol 104 surfactant. Even more preferably, the surfactant is selected from at least one of dimethyl silicone oil and Surfynol 104 surfactant.

[0021] Preferably, the corrosion inhibitor is selected from at least one of mercaptobenzothiazole, ethylidene thiourea, and 2-mercaptoethanol. More preferably, the corrosion inhibitor is selected from at least one of mercaptobenzothiazole and 2-mercaptoethanol.

[0022] Preferably, the antioxidant is selected from at least one of 2-ethylimidazole, benzimidazole, methylbenzotriazole, and benzotriazole. More preferably, the antioxidant is selected from at least one of 2-ethylimidazole, benzimidazole, and methylbenzotriazole. Even more preferably, the antioxidant is selected from at least one of 2-ethylimidazole and benzimidazole.

[0023] Preferably, the solvent is selected from at least one of tetrahydrofurfuryl alcohol, tetraethylene glycol, diethylene glycol dibutyl ether, propylene glycol methyl ether, and dipropylene glycol dimethyl ether. More preferably, the solvent is selected from at least one of tetrahydrofurfuryl alcohol, tetraethylene glycol, diethylene glycol dibutyl ether, and propylene glycol methyl ether. Even more preferably, the solvent is selected from at least one of tetrahydrofurfuryl alcohol, tetraethylene glycol, and diethylene glycol dibutyl ether.

[0024] The surfactants in this application help reduce the surface tension of the system, improve wettability, and disperse tin powder while preventing agglomeration. The corrosion inhibitors bind to active sites on the tin powder surface, forming a dense adsorption film that blocks contact between acidic substances, moisture, and the metal, thereby inhibiting corrosion reactions. The antioxidants inhibit tin powder oxidation, prevent solder pad substrate corrosion, and protect the stability of the flux components, ultimately ensuring extended shelf life of the water-soluble solder paste and reliable soldering.

[0025] Preferably, the tin powder has a particle size of 22–35 μm. More preferably, the tin powder has a particle size of 25–32 μm.

[0026] By adopting the above technical solution, water-soluble flux and solder powder are mixed in a specific mass ratio to ensure the basic performance of solder paste; film-forming agent, organic acid activator, thixotropic agent, surfactant, corrosion inhibitor, antioxidant and solvent are combined in a specific weight percentage, and the film-forming agent is prepared from specific raw materials, so that the solder paste has good wetting properties, long life, and suitable viscosity. After soldering, it can be cleaned, has a high solder climb height, large spread rate and high strength. At the same time, it can solve the problems of existing water-soluble solder paste such as moisture absorption, solder splattering, short storage life and easy delamination.

[0027] The second aspect of this application provides a method for preparing the water-soluble solder paste according to the first aspect of this application, comprising the following steps:

[0028] S1: Weigh the raw materials of each component of the water-soluble flux according to the weight parts, mix them, and then heat, stir, cool, grind and let stand to obtain the water-soluble flux.

[0029] S2: Weigh out the water-soluble flux and solder powder according to the weight parts, mix and stir to obtain the water-soluble solder paste.

[0030] Preferably, in step S1, the heating temperature is 50–70°C, the stirring speed is 1200–1800 r / min, the stirring time is 3–5 h, and the settling time is 2–3 days. More preferably, in step S1, the heating temperature is 50–65°C, the stirring speed is 1300–1800 r / min, the stirring time is 3–4.5 h, and the settling time is 2–2.5 days. Even more preferably, in step S1, the heating temperature is 55–65°C, the stirring speed is 1400–1800 r / min, the stirring time is 3–4 h, the particle size of the ground material is ≤10 μm, and the settling time is 2.5 days.

[0031] Preferably, in step S2, the stirring speed is 20-30 r / min, the stirring time is 35-50 min, the vacuum degree of the vacuum stirring is -0.09 MPa to -0.1 MPa, the vacuum stirring speed is 20-30 r / min, and the vacuum stirring time is 15-20 min. More preferably, in step S2, the stirring speed is 20-30 r / min, the stirring time is 35-45 min, the vacuum degree of the vacuum stirring is -0.09 MPa to -0.1 MPa, the vacuum stirring speed is 20-25 r / min, and the vacuum stirring time is 15-18 min. More preferably, in step S2, the stirring speed is 20-26 r / min, the stirring time is 40-45 min, the vacuum degree of the vacuum stirring is -0.09 MPa to -0.1 MPa, the vacuum stirring speed is 20-25 r / min, and the vacuum stirring time is 15-18 min.

[0032] In the preparation method of water-soluble solder paste in this application, step S1 adopts a combined process of "heating and dispersing - grinding and refining - static stabilization" to ensure that the flux is uniform, has a compact and stable internal structure, and that the internal and surface temperatures are consistent. This ensures that the subsequently prepared water-soluble solder paste has good wetting properties, a long lifespan, and suitable viscosity. At the same time, the particle fineness of the grinding is ≤10μm, which can enhance the contact area during water washing and improve the water washing effect of residual solder paste after soldering.

[0033] In step S2, maintaining a vacuum prevents air from entering the system, thus preventing the solder powder from oxidizing due to contact with oxygen during stirring. Simultaneously, it promptly removes air bubbles introduced by mechanical stirring during mixing. No oxidation of the solder powder and no air bubbles in the solder paste ensure that there are no "cold solder joints" during soldering. Low-speed stirring helps the flux evenly and fully coat the surface of the solder powder, forming a "flux-solder powder" interface layer, while avoiding surface wear and accelerated oxidation of the solder powder caused by high-speed stirring.

[0034] Preferably, the preparation method of the film-forming agent includes the following steps:

[0035] The film-forming agent is prepared by mixing polyethylene glycol 400, sodium hydroxypropyl methylcellulose, VYBAR 825 polymer, triethylamine, 1,6-hexanediol, tripropylene glycol and polyoxyethylene glycerol ether MF-200A and then stirring.

[0036] During stirring, shear force promotes the dissolution of components and intermolecular interactions. For example, the hydroxyl groups of polyethylene glycol 400 and sodium hydroxypropyl methylcellulose form hydrogen bonds, creating a composite film with both flexibility and strength. The uniform dispersion of VYBAR 825 polymer in the film-forming agent allows it to synergistically work with diamide thixotropic agents in the subsequent solder paste system, enhancing the thixotropic properties of the water-soluble solder paste. The film-forming agent in this application exhibits stable performance and does not separate when mixed with other components, ultimately providing the solder paste with excellent post-soldering film protection.

[0037] A third aspect of this application provides the application of a water-soluble solder paste in electronic soldering materials, wherein the water-soluble solder paste is the water-soluble solder paste described above, or is prepared by the preparation method described above.

[0038] Compared with the prior art, this application has at least the following beneficial effects:

[0039] 1) The raw materials of the water-soluble solder paste of this application are all soluble in water or can be washed off with water after soldering, thus avoiding the circuit board corrosion problem caused by cleaning with organic solvents.

[0040] 2) This application utilizes a specifically formulated film-forming agent to enable the water-soluble solder paste to form a uniform thin film on the soldering surface. This film isolates the solder from air, preventing oxidation of the solder powder. It also facilitates the uniform distribution of flux and smooth soldering, while avoiding the problems of existing water-soluble solder pastes absorbing moisture, leading to viscosity reduction and solder spattering. When the solder joints of the water-soluble solder paste from this application are placed at 85°C and 85% humidity for 72 hours, the residue on the solder joints shows no discoloration or corrosion, demonstrating excellent moisture resistance.

[0041] 3) The water-soluble solder paste of this application has a compact internal structure and stable materials through a specific process during preparation, and its shelf life can reach 6 months, which solves the problem of short shelf life of existing water-soluble solder paste.

[0042] 4) By adding organic acid activators, the water-soluble solder paste can effectively remove metal surface oxides during the soldering process and improve the soldering wetting performance. The flux and solder powder of the water-soluble solder paste of this application have strong bonding force, are not easy to delaminate, and have good wetting performance. The solder climb height is ≥0.8mm and the spread rate is ≥83% during soldering, which meets the soldering requirements of high-precision electronic components. Detailed Implementation

[0043] The following detailed description of the contents of this application is provided through specific embodiments, comparative examples, and tables, but is not limited to all the arguments and data.

[0044] In the water-soluble solder paste raw materials, the tin powder is selected from a Sn-Ag-Cu alloy with a particle size range of 22-35 μm, wherein the mass fraction of Ag is 3.0% and the mass fraction of Cu is 1.5%; the film-forming agent is prepared according to the formulation and preparation method of this application. In the examples and comparative examples, the mass ratio of flux to tin powder is 11.5:88.5.

[0045] Example of film-forming agent preparation:

[0046] Preparation Example 1:

[0047] The preparation method of a film-forming agent has the following steps:

[0048] The film-forming agent was prepared by mixing 4g polyethylene glycol 400, 3g sodium hydroxypropyl methylcellulose, 1.8g VYBAR 825 polymer, 0.9g triethylamine, 0.3g 1,6-hexanediol, 0.2g tripropylene glycol and 0.55g polyoxyethylene glycerol ether MF-200A and stirring.

[0049] Preparation Example 2:

[0050] The preparation method of a film-forming agent has the following steps:

[0051] The film-forming agent was prepared by mixing 5g of polyethylene glycol 400, 2.3g of sodium hydroxypropyl methylcellulose, 3.1g of VYBAR 825 polymer, 0.9g of triethylamine, 0.5g of 1,6-hexanediol, 0.2g of tripropylene glycol and 0.6g of polyoxyethylene glycerol ether MF-200A and stirring.

[0052] Preparation Example 3:

[0053] The preparation method of a film-forming agent has the following steps:

[0054] The film-forming agent was prepared by mixing 5.5g polyethylene glycol 400, 3.6g sodium hydroxypropyl methylcellulose, 2.8g VYBAR 825 polymer, 1.1g triethylamine, 0.6g 1,6-hexanediol, 0.3g tripropylene glycol and 0.6g polyoxyethylene glycerol ether MF-200A and stirring.

[0055] Preparation of Comparative Example 1:

[0056] The preparation method of a film-forming agent has the following steps:

[0057] The film-forming agent was prepared by mixing 8g of polyethylene glycol 400, 3g of sodium hydroxypropyl methylcellulose, 1.8g of VYBAR 825 polymer, 0.9g of triethylamine, 0.3g of 1,6-hexanediol, 0.2g of tripropylene glycol and 0.55g of polyoxyethylene glycerol ether MF-200A and stirring.

[0058] Preparation of Comparative Example 2:

[0059] The preparation method of a film-forming agent has the following steps:

[0060] The film-forming agent was prepared by mixing 4g of polyethylene glycol 400, 5g of sodium hydroxypropyl methylcellulose, 1.8g of VYBAR 825 polymer, 0.9g of triethylamine, 0.3g of 1,6-hexanediol, 0.2g of tripropylene glycol and 0.55g of polyoxyethylene glycerol ether MF-200A and stirring.

[0061] Preparation of Comparative Example 3:

[0062] The preparation method of a film-forming agent has the following steps:

[0063] The film-forming agent was prepared by mixing 4g polyethylene glycol 400, 3g sodium hydroxypropyl methylcellulose, 1g VYBAR 825 polymer, 0.9g triethylamine, 0.3g 1,6-hexanediol, 0.2g tripropylene glycol and 0.55g polyoxyethylene glycerol ether MF-200A and stirring.

[0064] Preparation of Comparative Example 4:

[0065] The preparation method of a film-forming agent has the following steps:

[0066] The film-forming agent was prepared by mixing 4g of polyethylene glycol 400, 3g of sodium hydroxypropyl methylcellulose, 0.9g of triethylamine, 0.3g of 1,6-hexanediol, 0.2g of tripropylene glycol and 0.55g of polyoxyethylene glycerol ether MF-200A and stirring.

[0067] It is particularly important to emphasize that, unless otherwise specified, the raw materials, reagents or devices used in this application can be obtained from conventional commercial sources.

[0068] Table 1. Mass ratios and process parameters of water-soluble solder paste raw material components in Examples 1-8 (unit: g)

[0069]

[0070]

[0071]

[0072] Table 2. Mass ratio of water-soluble solder paste raw material components for Comparative Examples 1–4 (unit: g)

[0073]

[0074] Example 1:

[0075] A water-soluble solder paste is prepared by the following steps:

[0076] S1: Weigh the raw materials of each component of the water-soluble flux corresponding to Example 1 in Table 1 according to the weight parts, put them into the reaction furnace and mix them. Then heat to 50°C, set the stirring speed to 1600 r / min, and stir for 3 hours. Cool to room temperature and keep for 1 hour. Put them into a three-roll mill for grinding until the particle fineness is ≤10μm. Let stand for 2 days to obtain the water-soluble flux.

[0077] S2: Weigh 11.5g of water-soluble flux and 88.5g of solder powder according to the weight ratio, mix them, stir at 20r / min for 35min, clean off the residue, control the vacuum degree to -0.09MPa, the vacuum stirring speed to 20r / min, and the vacuum stirring time to 18min to obtain water-soluble solder paste.

[0078] Example 2:

[0079] A method for preparing a water-soluble solder paste is the same as in Example 1, except that the types, amounts, and process conditions of each raw material are added according to those in Example 2.

[0080] Example 3:

[0081] A method for preparing a water-soluble solder paste is the same as in Example 1, except that the types, amounts, and process conditions of each raw material are added in accordance with those in Example 3.

[0082] Example 4:

[0083] A method for preparing a water-soluble solder paste is the same as in Example 1, except that the types, amounts, and process conditions of each raw material are added in accordance with those in Example 4.

[0084] Example 5:

[0085] A method for preparing a water-soluble solder paste is the same as in Example 1, except that the types, amounts, and process conditions of each raw material are added according to those in Example 5.

[0086] Example 6:

[0087] A method for preparing a water-soluble solder paste is the same as in Example 1, except that the types, amounts, and process conditions of each raw material are added in accordance with those in Example 6.

[0088] Example 7:

[0089] A method for preparing a water-soluble solder paste is the same as in Example 1, except that the types, amounts, and process conditions of each raw material are added in accordance with those in Example 7.

[0090] Example 8:

[0091] A method for preparing a water-soluble solder paste is the same as in Example 1, except that the types, amounts, and process conditions of each raw material are added in accordance with those in Example 8.

[0092] Comparative Example 1:

[0093] A method for preparing a water-soluble solder paste and the process conditions are the same as in Example 1, except that the types and amounts of each raw material are added according to Comparative Example 1.

[0094] Comparative Example 2:

[0095] A method for preparing a water-soluble solder paste, with the same process conditions as in Example 1, differs in that the types and amounts of each raw material are added according to Comparative Example 2.

[0096] Comparative Example 3:

[0097] A method for preparing a water-soluble solder paste and the process conditions are the same as in Example 1, except that the types and amounts of each raw material are added according to Comparative Example 3.

[0098] Comparative Example 4:

[0099] A method for preparing a water-soluble solder paste and the process conditions are the same as in Example 1, except that the types and amounts of each raw material are added according to Comparative Example 4.

[0100] Material performance testing:

[0101] The water-soluble solder pastes obtained in Examples 1-8 and Comparative Examples 1-4 were subjected to various performance tests, and the test methods are as follows:

[0102] Cleaning procedure: After welding, any residue is washed directly with water to check if it is clean.

[0103] Room temperature viscosity: At room temperature, stir the water-soluble solder paste to ensure that the components are evenly distributed and stir in the same direction for 3 to 5 minutes, avoiding air entrapment. Insert the viscometer rotor into the middle of the solder paste, set the speed to 10 r / min, record once every 5 minutes, and take the average value for three times.

[0104] Lifespan: Store at 0-10℃. Take it out monthly to observe for stratification (separation of solder powder and flux) and sedimentation (hard lumps at the bottom). Record the storage time. When stratification or clumping appears and cannot be restored to uniformity by stirring, the lifespan ends.

[0105] Moisture resistance: The water-soluble solder paste of this application was placed in an environment of 85°C and 85% humidity for 72 hours, and the residual corrosion on the solder joints was observed.

[0106] Solder climb height: Tested according to IPC-A-610 standard.

[0107] Expansion rate: Tested according to JIS Z 3197 standard.

[0108] The test performance of the water-soluble solder pastes of Examples 1-8 and Comparative Examples 1-4 is shown in Table 3 below:

[0109] Table 3 shows the performance test results of Examples 1-8 and Comparative Examples 1-4.

[0110]

[0111]

[0112] The water-soluble solder pastes in Examples 1-5 are prepared by combining the film-forming agent of the formulation of this application with organic acid activators, thixotropic agents, surfactants, corrosion inhibitors, antioxidants, and solvents to obtain a water-soluble flux. The water-soluble flux combines with solder powder, allowing the prepared water-soluble solder paste to be washed off with water after soldering, avoiding the circuit board corrosion problems caused by cleaning with organic solvents. The viscosity at room temperature is in the range of 179-189 Pa·s. After being placed in an environment of 85°C and 85% humidity for 72 hours, the residue on the solder joints did not change color or show corrosion, demonstrating excellent moisture resistance. The shelf life can reach more than 7 months, it is not easy to delaminate, and it has good wetting properties. The soldering performance is excellent, with a solder climb height ≥0.82mm and an spread rate ≥83.1% during soldering, meeting the soldering requirements of high-precision electronic components.

[0113] Compared to Example 1, the film-forming agent in Example 6, which used the film-forming agent prepared in Comparative Example 1, showed a decrease in shelf life, solder climb height, and spread rate. Compared to Example 1, the film-forming agent in Example 7, which used the film-forming agent prepared in Comparative Example 2, showed better shelf life and moisture resistance, but residues were not completely removed after washing with water. Compared to Example 1, the film-forming agent in Example 8, which used the film-forming agent prepared in Comparative Example 3, also showed a short shelf life. Therefore, the film-forming agent prepared in this application using polyethylene glycol 400, sodium hydroxypropyl methylcellulose, VYBAR 825 polymer, triethylamine, 1,6-hexanediol, tripropylene glycol, and polyoxyethylene glycerol ether MF-200A in a specific ratio can improve the shelf life, moisture resistance, and water-washability of the water-soluble solder paste.

[0114] Compared with Example 1, Comparative Examples 1 and 2 used the film-forming agent prepared by Comparative Example 4. The results showed that after cleaning with water, Comparative Example 1 had a viscosity of only 152 Pa·s at room temperature. After being placed at 85°C and 85% humidity for 72 hours, the solder joint showed white residue and copper oxide corrosion, indicating poor moisture resistance. Its shelf life was only 3 months, it was prone to delamination, and its wetting properties were low. During soldering, the solder climb height was 0.70 mm, and the spread rate was 76.5%, indicating generally poor soldering performance. The test results for Comparative Example 2 were similar to those for Comparative Example 1.

[0115] Compared with Example 1, Comparative Examples 3 and 4 used polyethylene glycol 10000 as the film-forming agent. The results showed that Comparative Example 3 had incomplete residue removal after washing with water, a room temperature viscosity of only 147 Pa·s, and after being left at 85°C and 85% humidity for 72 hours, the residue on the solder joints turned white with corrosive verdigris, exhibiting poor moisture resistance. Its shelf life was only 4 months, it was prone to delamination, and its wetting properties were low. The solder climb height during soldering was 0.65 mm, and the spread rate was 75.3%, indicating generally poor soldering performance. Comparative Example 4, although clean after washing with water, still had low room temperature viscosity. After being left at 85°C and 85% humidity for 72 hours, the residue on the solder joints turned white with corrosive verdigris, exhibiting poor moisture resistance. Its shelf life, solder climb height during soldering, and spread rate were also generally poor.

[0116] Therefore, the film-forming agent of this application is beneficial for water-soluble solder paste to form a protective film during the soldering process, prevent tin powder oxidation, improve the stability of water-soluble solder paste, extend its shelf life, and improve the moisture resistance and soldering performance of water-soluble solder paste.

[0117] Obviously, the above embodiments of this application are merely examples for clearly illustrating this application, and are not intended to limit the implementation of this application. For those skilled in the art, other variations or modifications can be made based on the above description. Any obvious variations or modifications derived from the technical solutions of this application are still within the protection scope of this application.

Claims

1. A water-soluble solder paste, characterized in that, It includes a water-soluble flux and solder powder, wherein the mass ratio of the water-soluble flux to the solder powder is 1:(7~10). The water-soluble flux comprises the following components in parts by weight: 45-55 parts of film-forming agent; 8-12 parts of organic acid surfactant; 6-8 parts of thixotropic agent; Surfactant 0.3~3 parts; 1-3 parts corrosion inhibitor; Antioxidant 3-5 parts; Solvent 25-35 parts; The raw materials for preparing the film-forming agent include polyethylene glycol 400, sodium hydroxypropyl methylcellulose, VYBAR 825 polymer, triethylamine, 1,6-hexanediol, tripropylene glycol, and polyoxyethylene glycerol ether MF-200A. The film-forming agent is a mixture of polyethylene glycol 400, sodium hydroxypropyl methylcellulose, VYBAR 825 polymer, triethylamine, 1,6-hexanediol, tripropylene glycol and polyoxyethylene glycerol ether MF-200A in a mass ratio of (4~6):(2~4.5):(1.5~3.5):(0.8~1.2):(0.3~0.7):(0.1~0.4):(0.5~0.7). The preparation method of the film-forming agent includes the following steps: The film-forming agent is prepared by mixing polyethylene glycol 400, sodium hydroxypropyl methylcellulose, VYBAR 825 polymer, triethylamine, 1,6-hexanediol, tripropylene glycol and polyoxyethylene glycerol ether MF-200A and then stirring. The surfactant is selected from at least one of dimethyl silicone oil, oleyl alcohol polyoxyethylene ether, Surfynol 104 surfactant, and GE-511 surfactant; The antioxidant is selected from at least one of 2-ethylimidazole, benzimidazole, methylbenzotriazole, and benzotriazole; The solvent is selected from at least one of tetrahydrofurfuryl alcohol, tetraethylene glycol, diethylene glycol dibutyl ether, propylene glycol methyl ether, and dipropylene glycol dimethyl ether.

2. The water-soluble solder paste according to claim 1, characterized in that, The organic acid activator is selected from at least one of dodecanoic acid, phenyl succinic acid, glycolic acid, octanoic acid, succinic acid, and hexadecanoic acid; And / or, the thixotropic agent is a diamide-based thixotropic agent.

3. The water-soluble solder paste according to claim 2, characterized in that, The thixotropic diamide is selected from at least one of ethylene bis(12-hydroxystearamide), phenylene bisstearamide, and hexamethylenediamine bisstearamide.

4. The water-soluble solder paste according to claim 1, characterized in that, The particle size of the tin powder is 22~35μm.

5. A method for preparing a water-soluble solder paste as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Weigh the raw materials of each component of the water-soluble flux according to the weight parts, mix them, and then heat, stir, cool, grind and let stand to obtain the water-soluble flux. S2: Weigh out the water-soluble flux and solder powder according to the weight proportions, mix and stir, and then vacuum stir to obtain the water-soluble solder paste.

6. The method for preparing water-soluble solder paste according to claim 5, characterized in that, In step S1, the heating temperature is 50~70℃, the stirring speed is 1200~1800r / min, the stirring time is 3~5h, and the settling time is 2~3d.

7. The method for preparing water-soluble solder paste according to claim 5, characterized in that, In step S2, the stirring speed is 20-30 r / min, the stirring time is 35-50 min, the vacuum degree of the vacuum stirring is -0.09 MPa to -0.1 MPa, the vacuum stirring speed is 20-30 r / min, and the vacuum stirring time is 15-20 min.

8. The application of a water-soluble solder paste as described in any one of claims 1 to 4 or a water-soluble solder paste prepared by any one of claims 5 to 7 in electronic soldering materials.

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