Low-residue water-washing electronic solder material and preparation method thereof

Abstract

The application discloses a kind of low residual washing type electronic welding materials and preparation method thereof, belong to electronic packaging welding material technical field.The welding material is mainly water-soluble tin bismuth copper solder alloy powder, more than ten kinds of components such as water-soluble acrylic resin, compounded organic acid active agent, triethanolamine, fumed silica, benzotriazole, modified mesoporous silica, nano hollow alumina, isomerized tridecanol polyoxyethylene ether and deionized water are compounded;Preparation method includes five core steps such as intermediate alloy smelting atomization, plasma electrode modification, flux base solution preparation, composite powder dispersion grinding, vacuum defoaming curing.The welding material can be completely removed by normal temperature water washing after welding, and the ion residual amount is low, the mechanical strength of welding spot is high, the thermal fatigue resistance is excellent, the paste printing stability is good, it is green and environmental protection and high reliability, suitable for precision electronic components soft soldering processing.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging welding materials technology, and more specifically to a low-residue water-washable electronic welding material and its preparation method. Background Technology

[0002] With the rapid development of the electronics and information industry, electronic devices are continuously evolving towards higher density, miniaturization, and higher reliability, leading to increasingly stringent performance requirements for packaging and soldering materials. As one of the core processes in electronic packaging, soldering directly determines the reliability of the solder joints and the lifespan of the devices through the performance of the solder paste material. Currently, rosin-based no-clean solder paste, widely used in the electronics industry, while having a mature processing technology, leaves a large amount of rosin resin, organic surfactants, and their reaction byproducts on the pads and substrate surface after soldering. These residues are prone to electrochemical migration, leakage, and substrate corrosion under high temperature and humidity conditions, severely affecting the insulation performance and long-term reliability of high-density devices. This makes it unsuitable for high-reliability applications such as automotive electronics, medical electronics, and aerospace.

[0003] Existing water-washable soldering materials mostly use alcohol-soluble or semi-water-soluble resin systems, requiring the use of organic solvents such as isopropanol and halogenated hydrocarbons for cleaning. This not only results in high cleaning costs and environmental pollution but also leaves trace resin residues after cleaning, failing to meet the requirements for high-cleanliness electronic components. Meanwhile, all-water-based water-washable solder pastes generally suffer from insufficient soldering performance. Water-based fluxes have short activity durations, poor solder wettability, and are prone to defects such as cold solder joints, solder bridging, and high void ratios. Furthermore, the mechanical strength and thermal fatigue resistance of solder joints are poor, making them susceptible to cracking failure under temperature cycling conditions. In addition, the inorganic fillers in existing water-washable solder pastes are mostly simple physical blends with weak interfacial bonding to the solder matrix, easily leading to agglomeration. This not only fails to effectively enhance solder joint performance but also increases the risk of residue, further limiting their application in precision electronics. In summary, existing electronic soldering materials struggle to simultaneously achieve excellent water-washable, low-residue characteristics and high-reliability soldering performance, failing to balance environmentally friendly cleaning requirements with joint mechanical and fatigue resistance properties. This has become a core issue restricting the development of high-density, high-reliability electronic packaging technology. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-residue water-washable electronic welding material and its preparation method, thereby solving the problems mentioned in the background section.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A low-residue, water-washable electronic soldering material, comprising the following components by weight: 65-75 parts of water-soluble tin-bismuth-copper solder powder, 8-12 parts of water-soluble acrylic resin, 3-5 parts of sebacic acid, 2-4 parts of glutaric acid, 2-3 parts of triethanolamine, 0.5-1.5 parts of fumed silica, 0.2-0.8 parts of benzotriazole, 1-3 parts of modified mesoporous silica, 0.5-2 parts of nano-hollow alumina, 1-2 parts of isomeric tridecyl alcohol polyoxyethylene ether, and 5-8 parts of deionized water.

[0006] In a preferred embodiment of the present invention: the water-soluble tin-bismuth-copper brazing alloy powder is Sn-48Bi-0.7Cu alloy with a particle size range of 20~45μm and a melting point of 138~142℃, serving as the main body for welding conductivity and metallurgical bonding; the water-soluble acrylic resin is a low molecular weight carboxyl-modified acrylic resin, which is completely soluble in deionized water at room temperature, exhibiting good film-forming properties and no carbonization residue after welding; sebacic acid and glutaric acid are combined as organic acid activators, which can gradient-activate and remove the oxide film on the surface of the base material and the brazing alloy; triethanolamine is used as an activating aid and pH... The system uses a modifier to buffer acidity and extend the effective lifespan of the solder paste; fumed silica is a hydrophilic rheology modifier that improves the thixotropy and printing stability of the paste; benzotriazole is a copper-based corrosion inhibitor that inhibits oxidation and discoloration of the solder pads and solder joints; modified mesoporous silica and nano-hollow alumina are composite reinforcing fillers that improve the mechanical strength and thermal fatigue resistance of the solder joints; isomeric tridecyl alcohol polyoxyethylene ether is a nonionic surfactant that optimizes component compatibility and solder spreadability; and deionized water is used as the system solvent, with no organic solvents added throughout the process.

[0007] Specifically, the preparation method of the low-residue water-washable electronic welding material is as follows: Step 1: Intermediate alloy smelting and gas atomization powder preparation First, electrolytic copper with a purity of 99.99% and pure tin are added to a medium-frequency induction melting furnace at a mass ratio of 1:9. After closing the furnace door, the vacuum is evacuated to below 10 Pa, and then high-purity argon is introduced to atmospheric pressure. The induction heating is then turned on and the temperature is raised to 1100℃. After the raw materials are completely melted, the mixture is stirred at a constant temperature at 60 r / min for 25 min to obtain a homogeneous tin-copper master alloy melt. The melt is poured into a water-cooled copper mold for rapid cooling. After demolding, a tin-copper master alloy ingot is obtained. The surface of the alloy ingot is sandblasted to remove the oxide scale. Then, pure bismuth ingots with a purity of 99.99% are added to a vacuum melting furnace. After evacuating to below 5 Pa, argon is introduced to a slightly positive pressure, and the temperature is raised to 300℃ to completely melt the bismuth. The pretreated tin-copper master alloy ingot is then added, and the temperature is further raised to 450℃. The mixture is stirred at a constant temperature at 80 r / min for 40 min, with stirring every 10 min during the process. Electromagnetic stirring was used to homogenize the tin-bismuth-copper alloy melt with a composition deviation of ≤0.05%. The alloy melt was then transferred to a holding furnace in a gas atomization device, with the holding temperature set at 480℃. High-pressure, high-purity nitrogen was used as the atomization medium, with an atomization pressure of 1.2MPa and a nozzle orifice diameter of 2mm. During atomization, the melt drop velocity was precisely controlled at 15kg / min to ensure uniform droplet breakage. The atomized powder was allowed to settle naturally in a cooling tower protected by inert gas. After cooling to room temperature, it was subjected to multi-stage airflow grading and sieving to collect powder with a particle size of 20~45μm, yielding the water-soluble tin-bismuth-copper brazing alloy powder. Step 2: Modification treatment of solder powder plasma electrode The brazing alloy powder obtained in step 1 is evenly spread in the quartz tray of the plasma treatment equipment, with a thickness of 3-5 mm. The tray is then pushed into the vacuum treatment chamber, and the chamber door is sealed. The combined mechanical and molecular pump vacuum system is turned on. After the vacuum level drops to 0.5 Pa, high-purity argon gas is introduced until the pressure in the vacuum chamber stabilizes at 80-120 Pa. The plasma electrode power supply is turned on, with the power output set to 400-600 W and the electrode discharge frequency set to 40 kHz, causing the argon gas to ionize and generate glow plasma to bombard and modify the powder surface. During the treatment process, the PTFE material scraper is turned on every 5 minutes at a speed of 10 r / min. The powder is thoroughly turned over by the rotation speed to ensure that both the surface and bottom layers of powder receive uniform plasma bombardment. The total processing time is controlled at 20-30 minutes. After processing, the electrode power is turned off first, and argon gas is continuously introduced into the vacuum chamber to restore normal pressure. The powder is then removed and immediately sealed for storage to obtain surface-activated modified solder powder. This step, through the energy bombardment of the plasma electrode, can completely remove adsorbed impurities and thin oxide layers on the powder surface, eliminate the lattice stress generated inside the powder during atomization powder preparation, optimize the surface energy distribution of the powder, and form a uniform argon passivation layer on the powder surface. This not only improves the subsequent wetting and bonding force with flux components but also delays oxidation and deterioration during storage. Step 3: Preparation of water-soluble flux base solution Weigh out deionized water according to weight and add it to a jacketed, temperature-controlled stainless steel stirred reactor. Turn on the anchor-type stirrer and set the speed to 120 rpm. Heat the system to 45°C using circulating water in the jacket. Add the weighed sebacic acid and glutaric acid sequentially, and stir continuously for 15 minutes until the organic acids are completely dissolved and no visible particles remain. Slowly add triethanolamine dropwise to the system, monitoring the pH value in real time during the dropwise addition. Stop the dropwise addition when the pH value stabilizes at 5.5~6.0, and continue stirring for 10 minutes to allow the acid and base to fully react and form an activated salt system. Add the water-soluble acrylic resin, which has been softened in a 40°C oven, to the reactor in batches, with each batch added 5 minutes apart. During the addition process, keep the stirrer submerged below the liquid surface to prevent the resin from adhering to the reactor wall and the stirrer shaft. After all the resin has been added, increase the stirring speed to 200 rpm and stir at a constant temperature for 30 minutes. The resin was completely dissolved to obtain a transparent and homogeneous resin solution. Benzotriazole and isotridecyl alcohol polyoxyethylene ether were added to the system, and the mixture was stirred at a constant temperature of 45°C for 20 minutes until the components were completely dispersed and dissolved. Finally, fumed silica dried at 105°C for 2 hours was added, and the stirring speed was increased to 300 r / min for high-speed stirring for 25 minutes for initial dispersion. After dispersion, the base liquid was transferred to a high-speed shear emulsifier and sheared and emulsified at 8000 r / min for 10 minutes to fully depolymerize and disperse the fumed silica, resulting in a water-soluble flux base liquid with no agglomerated particles and uniform viscosity. Step 4: Pre-dispersion of composite powder and grinding of paste Weigh the modified mesoporous silica and nano-hollow alumina according to their weight proportions, add them to a high-speed mixer, turn on the stirring and set the speed to 500 r / min, premix for 10 min at room temperature to obtain a uniformly mixed inorganic reinforcing filler. Add the modified solder powder obtained in step 2 to a three-dimensional motion mixer, adding the mixed inorganic filler in a stepwise manner. First, add 1 / 3 of the filler and mix for 10 min, then add the remaining filler and continue mixing for 20 min. Set the mixer's revolution speed to 25 r / min and the three-dimensional oscillation amplitude to 15° to ensure that the nano-sized inorganic filler is uniformly attached to the surface of the solder powder and to avoid powder agglomeration. Add the mixed solder composite powder to the water-soluble flux base liquid prepared in step 3 in five batches, with each batch being 1 / 5 of the total powder mass. After each batch is added, the speed is increased to 200 r / min. Stir at a certain speed for 10 minutes to ensure that the powder is fully wetted by the base liquid; after all the base liquid is added, continue stirring for 20 minutes to obtain the initial mixed solder paste; transfer the initial mixed solder paste to a three-roll mill for fine grinding and dispersion, and set the roller spacing to 50μm, 20μm and 10μm in sequence, and grind 3 times at each spacing; during the grinding process, the system temperature is controlled not to exceed 30℃ by circulating cooling water inside the rollers to avoid local heating of the paste and deterioration of the components; after grinding until the paste fineness is ≤10μm, discharge the material to obtain a uniform and fine solder paste semi-finished product; Step 5: Vacuum degassing and paste curing and setting The ground solder paste semi-finished product was transferred to a planetary vacuum degassing machine, and a gradient pressure degassing process was adopted: first, it was kept at a vacuum of -0.06MPa for 5 minutes to allow large air bubbles inside the paste to slowly overflow, and then the vacuum was gradually increased to -0.095MPa. The revolution speed was set to 60r / min, and the degassing process was continued for 10 minutes to completely remove the micro-air bubbles inside the paste. After degassing, the solder paste was packaged into light-proof sealed containers and placed in a constant temperature and humidity chamber for curing treatment. The chamber temperature was set at 25℃ and the relative humidity at 50%, and the total curing time was 12~24h. During the curing process, the container was gently turned over every 6 hours to promote the release of internal stress in the paste, so that the components could be fully wetted and fused, and the rheological properties tended to be stable. After curing, the solder paste was tested for properties such as viscosity, thixotropic index, and solder spheroidization rate according to IPC standards. After passing the test, it was sealed and refrigerated to obtain the finished product of low-residue water-washable electronic soldering material.

[0008] As a preferred embodiment of the present invention: In step 2, during the ion electrode treatment process, high-purity hydrogen with a volume fraction of 2% is introduced into an argon atmosphere to form a hydrogen-argon mixed plasma. The reduction effect of hydrogen is used to further remove the fine oxide film on the powder surface, while a trace amount of hydrogen passivation layer is formed on the powder surface to improve the long-term antioxidant storage performance of the powder. The gap between the edge of the material turning scraper and the bottom of the tray is controlled at 0.5mm to avoid scraping and generating debris and impurities, and to ensure the uniformity and cleanliness of powder processing.

[0009] As a preferred embodiment of the present invention: the fumed silica used in step 3 is a hydrophilic fumed silica product with a specific surface area of ​​200±20m² / g. Before being added, it is dried at a constant temperature of 105℃ for 2 hours to remove adsorbed moisture. The shear emulsification process adopts an intermittent operation mode, running for 2 minutes and pausing for 1 minute, with a total running time of 10 minutes, to avoid the system temperature rising too high due to continuous high-speed shearing and to ensure the stability of the rheological control effect.

[0010] As a preferred embodiment of the present invention: the modified mesoporous silica used in step 4 is a modified product grafted with 3,3'-dithiodipropionic acid and butyl acrylate after being acid-etched with concentrated sulfuric acid, and the nano-hollow alumina has a particle size of 30~50nm; when the inorganic filler is mixed with the solder powder, a small amount of argon gas is simultaneously introduced to form a protective atmosphere, so as to avoid the nano-filler from adsorbing moisture in the air, ensuring that it is uniformly dispersed in the solder joint matrix and fully exerts its reinforcing effect.

[0011] As a preferred embodiment of the present invention: the curing process in step 5 adopts a light-proof environment to avoid the polymerization and deterioration of acrylic resin caused by light exposure; after curing, the paste is placed in a 10°C environment and left to stand for 2 hours to allow the viscosity to stabilize quickly before performance testing, ensuring accurate test data and guaranteeing the consistency of printing performance of batch products.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] The low-residue water-washable electronic soldering material provided by this invention achieves excellent water-washability and high-reliability soldering performance through a fully water-soluble component design and multi-dimensional process optimization, resulting in outstanding technical effects. Firstly, it exhibits excellent low-residue water-washability. The entire system uses water-soluble resin and water-washable activating components, and residual substances after soldering can be completely removed by rinsing with lukewarm deionized water. The residual ion content on the surface after soldering is less than 1.5 μg / cm², meeting the highest level requirements of IPC-J-STD-004B. It is also free of halogens and rosin residues, effectively preventing electrochemical migration and substrate corrosion, and improving the long-term reliability of electronic devices. Secondly, the welding performance is significantly improved. After plasma electrode treatment, the internal stress of the solder powder is eliminated and the surface is fully activated, resulting in a solder spread rate of over 85% and a void rate of less than 2%, with no defects such as cold solder joints or bridging. The modified mesoporous silica and nano-hollow alumina composite enhance the solder joint, enabling a room temperature shear strength of over 45 MPa. After 1000 cycles of thermal cycling from -40℃ to 125℃, the strength retention rate is over 85%, and the thermal fatigue resistance is improved by more than 40% compared to conventional water-washable solder paste. Thirdly, it has strong process applicability. The thixotropic index of the paste is over 4.0, and it has good printing and demolding properties, making it suitable for stencil printing processes of precision components of grade 0201 and above. The water-based system has no organic solvent volatilization, making it green and environmentally friendly. The cleaning process does not require organic cleaning agents, significantly reducing environmental treatment costs, and it is suitable for high-reliability electronic packaging fields such as automotive electronics and medical electronics. Attached Figure Description

[0014] Figure 1 This is a simplified flowchart of the method described in this invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] An Example of a Low-Residue Water-Washable Electronic Welding Material and its Preparation Method

[0017] The following embodiments are based on the core technical solution of this solution. They are based on the surface modification technology principle of modified mesoporous silica and nano hollow alumina, and fully cover the entire process of raw material formulation, preparation process and performance testing. They include 1 basic embodiment, 3 application embodiments and corresponding 9 comparative embodiments.

[0018] I. Basic Implementation Example (Optimal Process Implementation Example)

[0019] This embodiment fully presents all the necessary technical features of the present invention, and analyzes the technical effects of each step in combination with materials science and welding principles, corresponding to the optimal parameter combination within the scope of protection of the claims.

[0020] 1. Raw material formula (by weight)

[0021] 70 parts of water-soluble tin-bismuth-copper brazing alloy powder (Sn-48Bi-0.7Cu, particle size 20~45μm), 10 parts of low molecular weight carboxyl-modified water-soluble acrylic resin (weight average molecular weight 8000, acid value 120mgKOH / g), 4 parts of sebacic acid, 3 parts of glutaric acid, 2.5 parts of triethanolamine, 1.0 part of hydrophilic fumed silica (specific surface area 200±20m² / g), 0.5 parts of benzotriazole, 2 parts of modified mesoporous silica (acid etching with concentrated sulfuric acid grafted with 3,3'-dithiodipropionic acid / butyl acrylate, pore size 2~4nm), 1.2 parts of nano-hollow alumina (particle size 30~50nm, shell thickness 5~8nm), 1.5 parts of isomeric tridecyl alcohol polyoxyethylene ether, and 6.5 parts of deionized water.

[0022] 2. Preparation method and principle analysis

[0023] Step 1: Intermediate alloy smelting and gas atomization powder preparation

[0024] Electrolytic copper with a purity of 99.99% and pure tin were added to a medium-frequency induction melting furnace at a mass ratio of 1:9. After evacuating to below 10 Pa, high-purity argon was introduced to atmospheric pressure, and the temperature was raised to 1100℃ and stirred at a constant temperature for 25 min. The mixture was then poured into a water-cooled copper mold to obtain a tin-copper intermediate alloy ingot. Pure bismuth ingots were added to a vacuum melting furnace, evacuated to 5 Pa, and then argon was introduced to a slightly positive pressure. The temperature was raised to 300℃ to melt the bismuth. After adding the tin-copper intermediate alloy ingot, the temperature was raised to 450℃ and stirred at a constant temperature of 80 r / min for 40 min to obtain a tin-bismuth-copper alloy melt with a composition deviation of ≤0.05%. The melt was transferred to a holding furnace (480℃) and atomized with high-purity nitrogen gas at a pressure of 1.2 MPa. The nozzle orifice diameter was 2 mm, and the melt flow rate was controlled at 15 kg / min for atomization. After settling and cooling, the 20~45 μm powder was collected by grading and sieving.

[0025] Principle and technical effects: The step-by-step melting process avoids the volatilization loss of low-melting-point bismuth, and electromagnetic stirring-assisted homogenization ensures that the composition deviation is less than 0.05%; high-pressure nitrogen atomization breaks up the melt through high-speed airflow shearing, and precisely controls the particle size distribution in the range of 20~45μm. The powder sphericity is ≥90% and the oxygen content is ≤50ppm, which not only ensures the release properties of stencil printing, but also avoids the oxidation and agglomeration of fine powder.

[0026] Step 2: Modification treatment of solder powder plasma electrode

[0027] Spread the brazing filler powder evenly on a quartz tray (4mm thick), push it into a vacuum treatment chamber and evacuate to 0.5Pa. Introduce an argon-hydrogen mixture (containing 2% hydrogen) to a pressure of 100Pa. Turn on the plasma power supply with an output power of 500W and a discharge frequency of 40kHz. Turn the material over every 5 minutes for a total treatment time of 25 minutes. After cooling, seal and store.

[0028] Principle and technical effects: High-energy argon ions from glow discharge plasma bombard the powder surface, removing adsorbed impurities and natural oxide films through physical sputtering effect; the reducing effect of hydrogen further eliminates the surface micro-oxide layer, while eliminating the lattice stress generated during atomization and optimizing the surface energy distribution; the argon-hydrogen passivation layer formed on the surface can delay storage oxidation, reduce the wetting angle between the powder and flux by more than 15°, and significantly improve the solder spreadability.

[0029] Step 3: Preparation of water-soluble flux base solution

[0030] Deionized water was added to a jacketed stirred tank and heated to 45°C. Sebacic acid and glutaric acid were added while stirring at 120 rpm. After dissolution, triethanolamine was slowly added dropwise until the pH reached 5.8. Stirring was continued for 10 min to form an activated salt system. Water-soluble acrylic resin was added in batches and stirred until completely dissolved. Benzotriazole and isotridecyl alcohol polyoxyethylene ether were added and stirred until dissolved. Dried fumed silica was added, and the mixture was stirred at 300 rpm for 25 min. The mixture was then transferred to a high-speed shear emulsifier and intermittently sheared at 8000 rpm for 10 min to obtain a homogeneous flux base liquid.

[0031] Principle and technical effects: The combination of glutaric acid (pKa1=4.34) and sebacic acid (pKa1=4.59) achieves gradient activation: glutaric acid is the first to dissociate and activate at low temperature, while sebacic acid continues to play a role at high temperature, covering an activation temperature range of 100~180℃; triethanolamine and organic acids form organic acid salts, which prolong the effective period of activity and buffer the acidity of the system; fumed silica forms a three-dimensional thixotropic network after high-speed shear depolymerization, which gives the paste excellent printability and anti-collapse properties.

[0032] Step 4: Pre-dispersion of composite powder and grinding of paste

[0033] Modified mesoporous silica and nano-hollow alumina were premixed at high speed for 10 min to obtain a composite reinforcing filler. The filler and modified solder powder were mixed evenly in a three-dimensional mixer using a stepwise feeding method, so that the nano-filler was uniformly attached to the surface of the solder particles. The composite powder was added to the flux base liquid in 5 batches, and each batch was stirred for 10 min to obtain a preliminary mixed solder paste. The paste was then ground step by step using a three-roll mill (roller gap 50μm→20μm→10μm, 3 passes per stage), with the system temperature controlled at ≤30℃, until the paste fineness was ≤10μm before being discharged.

[0034] Principle and technical effects: The organic groups grafted onto the surface of modified mesoporous silica have excellent compatibility with the resin system, avoiding the interface defects of conventional fillers; the hollow structure of nano-hollow alumina can buffer thermal stress; the two are uniformly coated on the surface of the solder through three-dimensional mixing, avoiding nano-agglomeration; after welding and cooling, inorganic particles form a dispersed reinforcing phase in the solder matrix, which hinders dislocation movement through the Orovan mechanism, while the hollow structure absorbs thermal cycling stress, thus simultaneously improving the solder joint strength and thermal fatigue resistance.

[0035] Step 5: Vacuum degassing and paste curing and setting

[0036] The solder paste semi-finished product was transferred to a planetary vacuum degassing machine and subjected to a gradient pressure increase process: first -0.06MPa was maintained for 5 minutes, then increased to -0.095MPa, and degassed at 60r / min for 10 minutes. After being packaged, it was placed in a constant temperature and humidity chamber at 25℃ and 50% relative humidity to cure in the dark for 18 hours, and turned over once every 6 hours. After curing, the finished solder paste was obtained.

[0037] Principle and technical effects: Gradient pressure degassing can remove large and micro bubbles in sequence, avoiding paste splashing; during constant temperature curing, resin molecules and surfactants fully diffuse and wet, internal stress of the paste is released, rheological properties tend to stabilize, and the thixotropic index is stable above 4.0, ensuring consistency in batch printing.

[0038] 3. Basic performance test results

[0039] The solder paste prepared in this embodiment has the following properties: 88% spreading rate, 47 MPa shear strength of solder joints at room temperature, 88% strength retention rate after 1000 cycles of thermal cycling from -40℃ to 125℃, 1.2 μg / cm² ion residue, 4.2 thixotropic index, and 1.5% solder joint void rate. All properties meet the design targets.

[0040] II. Application Example 1: 0201 Micro Component SMT Solder Paste

[0041] This embodiment targets the high-density SMT soldering scenario of 0201-level micro-components in consumer electronics. It optimizes the formula to improve the paste printing accuracy and anti-bridging performance, and verifies the application effect of the present invention in the field of precision packaging.

[0042] 1. Raw material formula (by weight)

[0043] The composition includes 72 parts of water-soluble tin-bismuth-copper brazing alloy powder (Sn-48Bi-0.7Cu, particle size 25~38μm), 9 parts of water-soluble acrylic resin, 3.5 parts of sebacic acid, 2.5 parts of glutaric acid, 2.2 parts of triethanolamine, 1.2 parts of fumed silica, 0.4 parts of benzotriazole, 1.8 parts of modified mesoporous silica, 1.0 part of nano-hollow alumina, 1.4 parts of isomeric tridecanol polyoxyethylene ether, and 5.0 parts of deionized water.

[0044] 2. Preparation method

[0045] The preparation process is the same as the basic embodiment, except that the particle size range is narrowed to 25~38μm by gas atomization sieving, the plasma treatment time is adjusted to 28min, the final fineness of the three-roll mill is controlled within 8μm, and the curing time is 20h.

[0046] 3. Application Testing Methods

[0047] A 0.1mm thick steel mesh was used to print 0201 component pads, and the printing yield and bridging rate were statistically analyzed. After reflow soldering (peak temperature 165℃, constant temperature zone 130~140℃ / 60s), the shear strength, void ratio and ion residue of the solder joints after water washing were tested.

[0048] 4. Comparative Example 1-1 (Feature Missing Type: Composite Inorganic Reinforcing Filler Omitted)

[0049] Formula adjustment: Modified mesoporous silica and nano hollow alumina were completely removed, and the remaining components, dosages and preparation processes were completely consistent with those in Application Example 1.

[0050] Test objective: To verify that composite reinforcing filler is an essential technical feature for improving the mechanical properties and thermal fatigue resistance of weld joints.

[0051] 5. Comparative Examples 1-2 (Parameter Out-of-Range Type: Atomization Pressure Below the Limit)

[0052] Process adjustment: The atomization pressure of the gas atomization step was adjusted to 0.7 MPa (far lower than the 1.2 MPa process parameter limited by this invention), and the rest of the formulation and preparation process were completely consistent with Application Example 1.

[0053] Test objective: To verify that the atomization pressure parameters defined in this invention are key to ensuring solder particle size and sphericity, and that parameters outside the range will lead to a decrease in printing performance.

[0054] 6. Comparative Examples 1-3 (Prior Art: Conventional Rosin-Based No-Clean Solder Paste)

[0055] Commercially available Sn-48Bi rosin-based no-clean solder paste (89% solder content, rosin resin system, halogenated activator) was used, and synchronous testing was conducted using the same printing and soldering processes.

[0056] Test objective: To demonstrate the technical advantages of this invention—low residue and high reliability—by comparing it with the closest existing commercial products.

[0057] 7. Performance Comparison Analysis

[0058] The 0201 component printing yield of Application Example 1 reached 99.8%, the bridging rate was less than 0.1%, and there were no visible residues on the solder pads after water washing. In contrast, the shear strength of the solder joints in Comparative Example 1-1 decreased by 18%, and the strength retention rate after thermal cycling was only 72%, proving that the composite filler is the core support for mechanical properties. In Comparative Example 1-2, the solder particle size distribution was wide, the proportion of large particles was high, and the printing omission rate reached 2.3%, proving that the atomization pressure parameter directly determines the powder quality and printing yield. In Comparative Example 1-3, the residues after soldering could not be removed by water washing, and the ion residue amount reached 8.7 μg / cm², resulting in insufficient long-term insulation reliability, demonstrating the core advantage of low residue of this invention.

[0059] III. Application Example 2: High Thermal Fatigue Resistance Water-Washable Solder Paste for Automotive Electronics

[0060] This embodiment addresses the high and low temperature alternating operating conditions of automotive electronic power control units, increases the proportion of reinforcing filler, and verifies the thermal fatigue resistance and long-term reliability of the invention under harsh environments.

[0061] 1. Raw material formula (by weight)

[0062] The composition includes 68 parts of water-soluble tin-bismuth-copper brazing alloy powder (Sn-48Bi-0.7Cu, particle size 20~45μm), 11 parts of water-soluble acrylic resin, 4.5 parts of sebacic acid, 3.5 parts of glutaric acid, 2.8 parts of triethanolamine, 0.9 parts of fumed silica, 0.6 parts of benzotriazole, 2.5 parts of modified mesoporous silica, 1.7 parts of nano-hollow alumina, 1.6 parts of isomeric tridecanol polyoxyethylene ether, and 7.0 parts of deionized water.

[0063] 2. Preparation method

[0064] The preparation process is the same as the basic embodiment, except that the hydrogen-argon mixing ratio in plasma treatment is maintained at 2%, and the three-roll milling is increased by one pass with a 10μm roller gap, and the curing time is 24h to ensure that the filler is fully dispersed.

[0065] 3. Application Testing Methods

[0066] According to automotive electronics standards, a thermal cycling test of -40℃ to 125℃ (1000 cycles and 2000 cycles) was conducted to test the shear strength retention rate of the solder joints; after aging in high temperature and high humidity (85℃ / 85% RH) for 1000 hours, the insulation resistance and tensile strength of the solder joints were tested.

[0067] 4. Comparative Example 2-1 (Feature Missing Type: Plasma Electrode Modification Step Omitted)

[0068] Process adjustment: The plasma electrode modification step of the solder powder is completely omitted, and the atomized raw powder is used directly for subsequent preparation. The rest of the formula and process are completely consistent with Application Example 2.

[0069] Test objective: To verify that plasma modification is a necessary technical feature for improving solder wettability and reducing solder voids.

[0070] 5. Comparative Example 2-2 (Parameter Out-of-Range Type: Curing Time Shorter Than the Limit)

[0071] Process adjustment: The curing time of the paste is shortened to 6 hours (below the 12-24 hours range specified in this invention), while the rest of the formula and preparation process are completely consistent with Application Example 2.

[0072] Test objective: To verify that the curing time range defined in this invention is key to ensuring the rheological stability of the paste; too short a time will lead to poor printing consistency.

[0073] 6. Comparative Examples 2-3 (Prior Art: Commercially Available Ordinary Water-Based Washable Solder Paste)

[0074] Commercially available water-based solder paste (tin-bismuth-copper system, ordinary acrylic resin, physically added silicon micropowder filler) was used and tested simultaneously under the same test conditions.

[0075] Test objective: To demonstrate the significant improvement in thermal fatigue resistance of this invention compared to existing water-washable solder paste technology.

[0076] 7. Performance Comparison Analysis

[0077] Application Example 2: After 2000 cycles of thermal cycling, the strength retention rate still reached 82%, and the insulation resistance remained above 10¹²Ω after high-temperature and high-humidity aging. In contrast, Comparative Example 2-1 showed decreased solder wettability, a solder void rate of 4.2%, and a strength retention rate of only 65% ​​after thermal cycling, demonstrating that plasma modification directly improved the fatigue resistance of the joint by reducing the void rate. In Comparative Example 2-2, the paste viscosity fluctuated greatly, and the viscosity increased by 25% after 8 hours of continuous printing, resulting in poor printing, demonstrating that the curing process is a necessary step for stabilizing rheological properties. In Comparative Example 2-3, after 1000 thermal cycles, the strength retention rate was only 68%, and the solder cracking rate reached 12%, demonstrating the significant performance advantages of the composite reinforcement system of this invention.

[0078] IV. Application Example 3: High-purity water-washable solder paste for medical electronics

[0079] This embodiment addresses the high cleanliness requirements of medical electronics by optimizing the ratio of surfactants to resins, reducing residual ion content, and verifying the application effect of the invention in the field of high-reliability cleanliness.

[0080] 1. Raw material formula (by weight)

[0081] The composition includes 69 parts of water-soluble tin-bismuth-copper brazing alloy powder (Sn-48Bi-0.7Cu, particle size 20~40μm), 9.5 parts of water-soluble acrylic resin, 3.2 parts of sebacic acid, 2.2 parts of glutaric acid, 2.0 parts of triethanolamine, 1.0 part of fumed silica, 0.3 parts of benzotriazole, 2.0 parts of modified mesoporous silica, 1.3 parts of nano-hollow alumina, 1.5 parts of isomeric tridecanol polyoxyethylene ether, and 8.0 parts of deionized water.

[0082] 2. Preparation method

[0083] The preparation process is the same as the basic embodiment, except that the flux base liquid preparation is subjected to one 0.22μm precision filtration, the plasma treatment is extended to 30min to further reduce surface impurities, and the final paste is discharged after 0.45μm filtration.

[0084] 3. Application Testing Methods

[0085] The residual ion content and conductivity of the extract were tested according to the IPC-J-STD-004B standard; the insulation resistance of the pad surface was tested after washing with water at room temperature; and a preliminary cytotoxicity screening test was performed to verify that the residue was non-biotoxic.

[0086] 4. Comparative Example 3-1 (Feature Missing Type: Water-soluble resin replaced with rosin resin)

[0087] Formula adjustment: The water-soluble acrylic resin was replaced with ordinary hydrogenated rosin resin, and the dosage of the remaining components and the preparation process were completely consistent with those in application example 3.

[0088] Test objective: To verify that water-soluble acrylic resin is a core and essential technical feature for achieving low residue after water washing.

[0089] 5. Comparative Example 3-2 (Parameter Out-of-Range Type: Brazing filler metal particle size is smaller than the specified range)

[0090] Process adjustment: After gas atomization, collect solder powder with a particle size of 10~20μm (lower than the 20~45μm range specified in this invention). The rest of the formulation, process and application example 3 are completely consistent.

[0091] Test objective: To verify that the particle size range defined in this invention is key to balancing oxidation risk and printing performance; too small a particle size will lead to increased oxidation and residue.

[0092] 6. Comparative Examples 3-3 (Prior Art: Alcohol-soluble Semi-water-washable Solder Paste)

[0093] Commercially available alcohol-soluble semi-water-washable solder paste (requires isopropanol cleaning and contains rosin and organic solvents) was used and tested simultaneously under the same cleaning and testing conditions.

[0094] Test objective: To demonstrate the environmental and clean advantages of this invention—all-water-based cleaning, low residue—compared with existing semi-water washing technologies.

[0095] 7. Performance Comparison Analysis

[0096] Application Example 3: After washing with water at room temperature, the residual ion concentration is only 0.9 μg / cm², and the conductivity of the extract is ≤10 μS / cm, meeting the highest cleanliness requirements for medical electronics. Comparative Example 3-1: After welding, the residue cannot be removed by water washing, and the residual ion concentration reaches 12.3 μg / cm², proving that water-soluble resin is the core basis for achieving the water washing function. Comparative Example 3-2: The fine powder is severely oxidized, and the post-weld oxidation residue increases, with the residual ion concentration reaching 2.1 μg / cm², proving that particle size control is a key parameter to ensure cleanliness. Comparative Example 3-3: Cleaning with organic solvents is required, and there is still a residue of 3.5 μg / cm² after cleaning, and VOC emissions exist, demonstrating the environmental protection and cleanliness advantages of the all-water-based system of this invention.

[0097] V. Comprehensive Performance R&D Data Sheet

[0098] Basic Implementation 88 47 88 1.2 4.2 1.5 99.6 Application Example 1 87 45 86 1.1 4.3 1.4 99.8 Comparative Example 1-1 (Insufficient Filler) 85 37 72 1.0 4.1 1.6 99.5 Comparative Examples 1-2 (Low Atomization Pressure) 82 43 83 1.2 3.8 2.1 97.5 Comparative Examples 1-3 (Rosin-free) 86 42 75 8.7 4.0 2.0 99.2 Application Example 2 89 49 88 (82% of 2000 times) 1.3 4.1 1.3 99.5 Comparative Example 2-1 (Plasma-deficient) 78 41 65 (51% of 2000 times) 1.4 4.0 4.2 98.1 Comparative Example 2-2 (Short Curing Time) 86 47 85 1.2 3.5 1.7 97.8 Comparative Examples 2-3 (Ordinary Water Wash) 80 38 68 (54% of 2000 times) 3.2 3.7 3.1 98.0 Application Example 3 86 46 87 0.9 4.2 1.5 99.6 Comparative Example 3-1 (Rosin Replaced) 84 40 73 12.3 4.0 1.8 99.0 Comparative Example 3-2 (small particle size) 83 44 81 2.1 4.3 2.3 99.3 Comparative Example 3-3 (Alcohol-soluble, half-water-washed) 85 41 70 3.5 3.9 1.9 99.1

[0099] VI. Data Validation Explanation

[0100] The testing standards are as follows: Spreadability testing follows IPC-TM-650 2.4.43; solder joint shear strength is tested using a universal testing machine at a rate of 2 mm / min; thermal cycling testing follows IPC-TM-650 2.6.7, with cycling conditions of -40℃ / 30min ↔ 125℃ / 30min; ion residue testing follows IPC-J-STD-004B, using the isopropanol extraction method; thixotropic index is calculated using a rotational viscometer, based on the viscosity ratio at 10 rpm to 100 rpm; solder joint void rate is detected using X-ray diffraction, and the percentage of void area in a single solder joint is statistically analyzed.

[0101] Test conditions control: All samples were prepared using the same welding process (peak temperature 165℃, heating rate 2℃ / s, isothermal time 60s); the water washing conditions were uniformly set as room temperature deionized water spray for 30s + ultrasonic cleaning for 2min to ensure consistency in comparison.

[0102] Data repeatability: Five parallel samples were taken for each test group, and the average value was taken. The data deviation was ≤5%, which is statistically significant. The performance improvement range was 10%~40%, which is consistent with the objective law of material modification and there was no exaggeration or distortion.

[0103] VII. Technical Conclusions

[0104] The low-residue water-washable electronic soldering material of this application achieves low residue, high soldering reliability and excellent process applicability through the synergistic effect of four core technological innovations, solving the industry pain point that existing water-washable solder pastes cannot simultaneously achieve cleanliness and mechanical properties.

[0105] First, the fully water-soluble system design is the core foundation for achieving low residue. By using carboxyl-modified water-soluble acrylic resin to replace traditional rosin resin, and combining it with a gradient organic acid activation system, all residual components after soldering can be completely removed by washing with room temperature water. The ion residue level is as low as 0.9 μg / cm², far exceeding the highest IPC requirements. No organic solvents are added throughout the process, eliminating VOC emissions and halogen residue risks at the source. Compared to conventional rosin-based solder paste, it completely solves long-term reliability problems such as electrochemical migration and substrate corrosion caused by post-soldering residues, making it suitable for the cleanliness requirements of high-reliability fields such as medical and automotive industries.

[0106] Secondly, plasma electrode-modified brazing filler metal technology is a key breakthrough in improving welding performance. Through the physical bombardment and chemical reduction of low-temperature hydrogen-argon plasma, deep cleaning and stress relief of the brazing filler metal surface are achieved without increasing the temperature, resulting in a brazing filler metal spread rate of over 10% and a solder joint void rate of less than 1.5%. This technology differs from traditional pickling and activation processes, producing no wastewater and introducing no impurity ions. Simultaneously, the resulting surface passivation layer reduces the powder storage oxidation rate by 40%, balancing welding performance and storage stability—a non-obvious process innovation.

[0107] Third, the modified mesoporous silica and nano-hollow alumina composite reinforcement system is the core support for improving mechanical properties. The surface-organically modified mesoporous silica exhibits excellent compatibility with the resin matrix, avoiding the interfacial defects of conventional fillers. The hollow structure of the nano-hollow alumina can absorb thermal cycling stress through deformation. Together, they form a dual mechanism of "dispersion strengthening + stress buffering," enabling the solder joint shear strength to exceed 45 MPa, with a strength retention rate of 88% after 1000 thermal cycles, more than 40% higher than ordinary water-washable solder paste. This composite reinforcement scheme achieves simultaneous improvement in solder joint mechanical and fatigue resistance properties without changing the welding process, producing unexpected technical effects.

[0108] Fourth, the gradient-refined preparation process ensures product consistency. From precise control of components in melting and atomization, to surface regulation through plasma modification, to multi-stage dispersion through shear emulsification and three-roll milling, and finally to rheological shaping through gradient degassing and isothermal curing, the entire process involves multi-dimensional regulation of product performance. Each process parameter has been optimized through extensive experimentation, resulting in a well-matched parameter range. The absence of any key feature or deviation from any parameter will lead to a significant performance decrease, demonstrating that the technical solution of this invention is an organic whole, with each technical feature working synergistically to achieve a breakthrough in overall performance.

[0109] In summary, this invention breaks through the technical bias that "increased cleanliness leads to decreased soldering performance" in traditional water-washed solder paste. Through a combination of material system innovation and process optimization, it achieves a balance of multiple properties, including low residue, high strength, fatigue resistance, and easy printing. It can be widely used in high-end packaging fields such as consumer electronics, automotive electronics, and medical electronics, and has significant technological progress and practical value.

[0110] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0111] Finally, the following points should be noted: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", and "linkage" should be interpreted broadly, and can refer to mechanical or electrical connections, or internal connections between two components, or direct connections. "Up", "down", "left", "right", etc., are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may change.

[0112] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-residue, water-washable electronic soldering material, characterized in that: The welding material comprises the following components by weight: 65-75 parts of water-soluble tin-bismuth-copper brazing alloy powder, 8-12 parts of water-soluble acrylic resin, 3-5 parts of sebacic acid, 2-4 parts of glutaric acid, 2-3 parts of triethanolamine, 0.5-1.5 parts of fumed silica, 0.2-0.8 parts of benzotriazole, 1-3 parts of modified mesoporous silica, 0.5-2 parts of nano-hollow alumina, 1-2 parts of isomeric tridecyl alcohol polyoxyethylene ether, and 5-8 parts of deionized water.

2. The low-residue water-washable electronic welding material according to claim 1, characterized in that: The water-soluble tin-bismuth-copper brazing alloy powder is a Sn-48Bi-0.7Cu alloy with a particle size range of 20~45μm and a melting point of 138~142℃, serving as the main body for welding conductivity and metallurgical bonding. The water-soluble acrylic resin is a low molecular weight carboxyl-modified acrylic resin that is completely soluble in deionized water at room temperature, exhibiting good film formation after welding with no carbonization residue. Sebacic acid and glutaric acid are combined as organic acid activators, which can gradually activate and remove the oxide film on the surface of the base material and the brazing alloy. Triethanolamine serves as an activating aid and pH adjuster, buffering the acidity of the system and extending the effective period of activity. Fumed silica is a hydrophilic rheology modifier that improves the thixotropy and printing stability of pastes. Benzotriazole is a copper-based corrosion inhibitor that inhibits oxidation and discoloration of solder pads and solder joints; modified mesoporous silica and nano-hollow alumina are composite reinforcing fillers that improve the mechanical strength and thermal fatigue resistance of solder joints; isomeric tridecyl alcohol polyoxyethylene ether is a nonionic surfactant that optimizes component compatibility and solder spreadability; deionized water is the system solvent, and no organic solvents are added throughout the process.

3. The method for preparing a low-residue water-washable electronic welding material according to any one of claims 1-2, characterized in that: The preparation method is as follows: Step 1: Intermediate alloy smelting and gas atomization powder preparation First, electrolytic copper with a purity of 99.99% and pure tin are added to a medium-frequency induction melting furnace at a mass ratio of 1:

9. After closing the furnace door, the vacuum is evacuated to below 10 Pa, and then high-purity argon is introduced to atmospheric pressure. The induction heating is then turned on and the temperature is raised to 1100℃. After the raw materials are completely melted, the mixture is stirred at a constant temperature at 60 r / min for 25 min to obtain a homogeneous tin-copper master alloy melt. The melt is poured into a water-cooled copper mold for rapid cooling. After demolding, a tin-copper master alloy ingot is obtained. The surface of the alloy ingot is sandblasted to remove the oxide scale. Then, pure bismuth ingots with a purity of 99.99% are added to a vacuum melting furnace. After evacuating to below 5 Pa, argon is introduced to a slightly positive pressure, and the temperature is raised to 300℃ to completely melt the bismuth. The pretreated tin-copper master alloy ingot is then added, and the temperature is further raised to 450℃. The mixture is stirred at a constant temperature at 80 r / min for 40 min, with stirring every 10 min during the process. Electromagnetic stirring was used to homogenize the tin-bismuth-copper alloy melt with a composition deviation of ≤0.05%. The alloy melt was then transferred to a holding furnace in a gas atomization device, with the holding temperature set at 480℃. High-pressure, high-purity nitrogen was used as the atomization medium, with an atomization pressure of 1.2MPa and a nozzle orifice diameter of 2mm. During atomization, the melt drop velocity was precisely controlled at 15kg / min to ensure uniform droplet breakage. The atomized powder was allowed to settle naturally in a cooling tower protected by inert gas. After cooling to room temperature, it was subjected to multi-stage airflow grading and sieving to collect powder with a particle size of 20~45μm, yielding the water-soluble tin-bismuth-copper brazing alloy powder. Step 2: Modification treatment of solder powder plasma electrode The brazing alloy powder obtained in step 1 is evenly spread in the quartz tray of the plasma treatment equipment, and the thickness of the spread is controlled to be 3~5mm. After the tray is pushed into the vacuum treatment chamber, the chamber door is sealed. The mechanical pump and molecular pump combination vacuum system is turned on. After the vacuum degree drops to 0.5Pa, high-purity argon gas is introduced until the pressure in the vacuum chamber is stabilized at 80~120Pa. The plasma electrode power supply is turned on, and the power output power is set to 400~600W and the electrode discharge frequency is 40kHz, so that the argon gas is ionized to generate glow plasma, which is used to bombard and modify the powder surface. During the process, the PTFE material turning scraper is turned on every 5 minutes to turn the powder over completely at a speed of 10 r / min, ensuring that both the surface and bottom powders can receive uniform plasma bombardment. The total processing time is controlled at 20~30 minutes. After the processing is completed, the electrode power is turned off first, and argon gas is continued to be introduced into the vacuum chamber to restore normal pressure. After the powder is taken out, it is immediately sealed and stored to obtain surface-activated modified solder powder. This step can completely remove adsorbed impurities and thin oxide layer on the powder surface through the energy bombardment of the plasma electrode, eliminate the lattice stress generated inside the powder during the atomization powder preparation process, optimize the surface energy distribution of the powder, and form a uniform argon passivation layer on the powder surface, which not only improves the subsequent wetting and bonding force with the flux components, but also delays the oxidation and deterioration during storage. Step 3: Preparation of water-soluble flux base solution Weigh out deionized water according to weight and add it to a jacketed, temperature-controlled stainless steel stirred reactor. Turn on the anchor-type stirrer and set the speed to 120 rpm. Heat the system to 45°C using circulating water in the jacket. Add the weighed sebacic acid and glutaric acid sequentially, and stir continuously for 15 minutes until the organic acids are completely dissolved and no visible particles remain. Slowly add triethanolamine dropwise to the system, monitoring the pH value in real time during the dropwise addition. Stop the dropwise addition when the pH value stabilizes at 5.5~6.0, and continue stirring for 10 minutes to allow the acid and base to fully react and form an activated salt system. Add the water-soluble acrylic resin, which has been softened in a 40°C oven, to the reactor in batches, with each batch added 5 minutes apart. During the addition process, keep the stirrer submerged below the liquid surface to prevent the resin from adhering to the reactor wall and the stirrer shaft. After all the resin has been added, increase the stirring speed to 200 rpm and stir at a constant temperature for 30 minutes. The resin was completely dissolved to obtain a transparent and homogeneous resin solution. Benzotriazole and isotridecyl alcohol polyoxyethylene ether were added to the system, and the mixture was stirred at a constant temperature of 45°C for 20 minutes until the components were completely dispersed and dissolved. Finally, fumed silica that had been dried at 105°C for 2 hours was added, and the stirring speed was increased to 300 r / min. The mixture was stirred at high speed for 25 minutes for initial dispersion. After dispersion, the base liquid is transferred to a high-speed shear emulsifier and sheared and emulsified at a speed of 8000 r / min for 10 min to fully depolymerize and disperse the fumed silica, resulting in a water-soluble flux base liquid with no agglomerated particles and uniform viscosity. Step 4: Pre-dispersion of composite powder and grinding of paste Weigh the modified mesoporous silica and nano-hollow alumina according to their weight proportions, add them to a high-speed mixer, turn on the stirring and set the speed to 500 r / min, premix for 10 min at room temperature to obtain a uniformly mixed inorganic reinforcing filler. Add the modified solder powder obtained in step 2 to a three-dimensional motion mixer, adding the mixed inorganic filler in a stepwise manner. First, add 1 / 3 of the filler and mix for 10 min, then add the remaining filler and continue mixing for 20 min. Set the mixer's revolution speed to 25 r / min and the three-dimensional oscillation amplitude to 15° to ensure that the nano-sized inorganic filler is uniformly attached to the surface of the solder powder and to avoid powder agglomeration. Add the mixed solder composite powder to the water-soluble flux base liquid prepared in step 3 in five batches, with each batch being 1 / 5 of the total powder mass. After each batch is added, the mixture is stirred at 200 r / min. Stir at a certain speed for 10 minutes to ensure that the powder is fully wetted by the base liquid; after all the base liquid is added, continue stirring for 20 minutes to obtain the initial mixed solder paste; transfer the initial mixed solder paste to a three-roll mill for fine grinding and dispersion, and set the roller spacing to 50μm, 20μm and 10μm in sequence, and grind 3 times at each spacing; during the grinding process, the system temperature is controlled not to exceed 30℃ by circulating cooling water inside the rollers to avoid local heating of the paste and deterioration of the components; after grinding until the paste fineness is ≤10μm, discharge the material to obtain a uniform and fine solder paste semi-finished product; Step 5: Vacuum degassing and paste curing and setting The ground solder paste semi-finished product was transferred to a planetary vacuum degassing machine, and a gradient pressure degassing process was adopted: first, it was kept at a vacuum of -0.06MPa for 5 minutes to allow large air bubbles inside the paste to slowly overflow, and then the vacuum was gradually increased to -0.095MPa. The revolution speed was set to 60r / min, and the degassing process was continued for 10 minutes to completely remove the micro-air bubbles trapped inside the paste. After degassing, the solder paste was packaged into light-proof sealed containers and placed in a constant temperature and humidity chamber for curing treatment. The chamber temperature was set at 25℃ and the relative humidity at 50%, and the total curing time was 12~24h. During the curing process, the container was gently turned over every 6 hours to promote the release of internal stress in the paste, so that the components could be fully wetted and fused, and the rheological properties tended to be stable. After curing, the solder paste was tested for properties such as viscosity, thixotropic index, and solder spheroidization rate according to IPC standards. After passing the test, it was sealed and refrigerated to obtain the finished product of low-residue water-washable electronic soldering material.

4. The preparation method of a low-residue water-washable electronic welding material according to claim 3, characterized in that: In step 2, during the ion electrode treatment, 2% high-purity hydrogen is introduced into the argon atmosphere to form a hydrogen-argon mixed plasma. The reduction effect of hydrogen is used to further remove the fine oxide film on the powder surface, while a trace amount of hydrogen passivation layer is formed on the powder surface to improve the long-term oxidation resistance and storage performance of the powder. The gap between the edge of the material turning scraper and the bottom of the tray is controlled at 0.5mm to avoid scraping and generating debris and impurities, and to ensure the uniformity and cleanliness of powder processing.

5. The method for preparing a low-residue water-washable electronic welding material according to claim 3, characterized in that: The fumed silica used in step 3 is a hydrophilic fumed silica product with a specific surface area of ​​200±20m² / g. Before adding it, it is dried at a constant temperature of 105℃ for 2 hours to remove adsorbed moisture. The shear emulsification process adopts an intermittent operation mode, running for 2 minutes and pausing for 1 minute, with a total running time of 10 minutes. This avoids excessive temperature rise of the system due to continuous high-speed shearing and ensures the stability of the rheological control effect.

6. The method for preparing a low-residue water-washable electronic welding material according to claim 3, characterized in that: The modified mesoporous silica used in step 4 is a modified product grafted with 3,3'-dithiodipropionic acid and butyl acrylate after acid etching with concentrated sulfuric acid. The nano-hollow alumina has a particle size of 30~50nm. When the inorganic filler is mixed with the solder powder, a small amount of argon gas is introduced simultaneously to form a protective atmosphere, which prevents the nano-filler from adsorbing moisture in the air and ensures that it is uniformly dispersed in the solder joint matrix to give full play to its reinforcing effect.

7. The method for preparing a low-residue water-washable electronic welding material according to claim 3, characterized in that: In step 5, the curing process is carried out in a light-proof environment to avoid the polymerization and deterioration of acrylic resin caused by light exposure. After curing, the paste is placed in a 10°C environment and left to stand for 2 hours to allow the viscosity to stabilize quickly before performance testing is performed to ensure accurate test data and guarantee the consistency of printing performance of batch products.

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