Low-residue water-washable flux paste and preparation method thereof

Abstract

The present invention provides a low-residue water-washable soldering flux paste and a preparation method thereof, belonging to the field of soldering technology. The low-residue water-washable soldering flux paste comprises a solder flux, solder powder, and nickel-copper microspheres loaded with cerium oxide. The raw materials of the solder flux include modified hydrogenated rosin, a solvent, and modified titanium dioxide particles. The present invention also provides a preparation method for the soldering flux paste. The present invention effectively prevents oxidation reactions in high-temperature environments and improves the thermal stability of the welded joint. Modified titanium dioxide is added to enhance the shear resistance of the solder layer after welding, achieves grain refinement, and increases the hardness of the product. The introduction of the nickel-copper microspheres loaded with cerium oxide facilitates the solder to spread and wet on the welding surface, inhibits crack propagation, and improves the mechanical properties of the solder joint, such as tensile strength and shear strength. The preparation method of the present invention is simple to operate, and the prepared solder paste has good solderability and strong spreadability, and a high maximum shear resistance after welding.

Description

Technical Field

[0001] The present invention relates to the technical field of welding, and in particular to a low-residue water-washable soldering paste and a preparation method thereof. Background Art

[0002] In the modern electronics manufacturing industry, electronic soldering is a critical process for connecting electronic circuits. As electronic products continue to evolve toward miniaturization, multifunctionality, and high performance, the packaging density of electronic components is increasing, and the pitch between pins is shrinking. This places higher demands on soldering quality and reliability. As a key auxiliary material in the soldering process, flux paste primarily removes oxides from the soldering surface, preventing re-oxidation of the metal surface, reducing the surface tension of the solder, and promoting solder wetting and spreading across the solder joint, thereby ensuring good soldering quality, forming reliable electrical and mechanical connections, and guaranteeing the proper operation of electronic devices.

[0003] Traditional soldering paste has many technical problems.

[0004] Insufficient solder joint strength: The mechanical properties of solder joints formed by traditional flux paste after soldering may not meet the stringent requirements of modern electronic products. For example, some portable electronic devices, such as smartphones and tablets, are often subjected to external forces such as drops and vibrations. Solder joints welded with traditional flux paste may crack and desolder under these external forces, causing electronic equipment failure. This is because traditional flux paste may not effectively promote the full fusion of solder and the soldering surface during the soldering process, resulting in a less dense internal structure of the solder joint and the presence of defects such as pores, which reduces the mechanical properties of the solder joint, such as tensile strength and shear strength.

[0005] Poor creep resistance: Over long-term use, electronic devices are exposed to varying temperatures, and solder joints are subject to thermal stress. Conventional soldering solder joints can experience creep during temperature cycling, where they slowly plastically deform under prolonged, constant stress. This can cause changes in the shape and size of the solder joint, affecting the stability of the electrical connection, increasing circuit resistance, and even causing short circuits.

[0006] Storage stability issues: Traditional solder flux pastes are prone to delamination and drying out during storage. Flux pastes are typically a paste-like mixture of solder powder and flux. Due to differences in physical properties such as density and particle size, these components can easily delaminate during prolonged storage. For example, some solid components (such as solder powder) in solder pastes may settle to the bottom, while liquid components (such as the solvent in the flux) float to the top. This can lead to uneven composition and affect performance. Furthermore, some volatile components in the flux may gradually evaporate during storage, causing the solder paste to dry out and lose its original soldering properties.

[0007] Insufficient thermal stability: During the soldering process, solder joints are exposed to high temperatures. Conventional flux pastes can undergo decomposition and oxidation reactions at high temperatures, producing harmful gases or forming unstable compounds. These reactions not only affect the air quality of the soldering environment and pose health risks to operators, but can also cause defects such as porosity and inclusions in the solder joints, reducing their quality and reliability. Furthermore, during the use of electronic products, solder joints may be subject to certain temperature fluctuations. Conventional flux paste solder joints may not maintain stable performance under these temperature fluctuations, thus affecting the long-term stability of electronic devices.

[0008] In summary, the soldering paste in the prior art has poor solderability and spreadability, and low shear resistance after soldering. Summary of the Invention

[0009] The invention provides a low-residue water-washable soldering paste and a preparation method thereof, so as to solve the problems of poor solderability and spreadability of the soldering paste in the prior art and low shear resistance after soldering.

[0010] To achieve the above-mentioned purpose, the present invention provides the following technical solutions:

[0011] A low-residue water-washable soldering paste comprises a soldering flux, solder powder, and nickel-copper microspheres loaded with cerium oxide. The raw materials of the soldering flux include modified hydrogenated rosin, a solvent, modified titanium dioxide particles, and a composite activator. The atomic molar ratio of nickel, copper, and cerium in the nickel-copper microspheres loaded with cerium oxide is 3-4:2:1, and the average particle size of the nickel-copper microspheres loaded with cerium oxide is 200-300 nm.

[0012] Preferably, the mass ratio of the soldering flux, solder powder, and nickel-copper microspheres loaded with cerium oxide is 9-12:90:0.05-0.08.

[0013] Preferably, the raw materials of the flux include, by mass, 25-30 parts of modified hydrogenated rosin, 50-60 parts of solvent, 1-1.4 parts of modified titanium dioxide particles, 4-7 parts of compound activator, 0.5-1 part of emulsifier, 0.5-1 part of anionic surfactant, 0.3-0.4 part of corrosion inhibitor and / or 1-1.5 parts of film-forming agent.

[0014] Among them, ethanol: glycerol: 1,2-propylene glycol: ethylene glycol butyl ether are mixed in a mass ratio of 2:4:3:1 to obtain a solvent; oxalic acid: citric acid: triethanolamine are mixed in a mass ratio of 1:1:2 to obtain a compound activator; the emulsifier is a commercially available OP-10 emulsifier, the anionic surfactant is a commercially available sodium dodecylbenzene sulfonate, the corrosion inhibitor is corrosion inhibitor BTA, and the film-forming agent is polyethylene glycol 2000.

[0015] Preferably, the solder powder is a Sn-Ag-Cu alloy powder with an average particle size of 20-30 microns.

[0016] Preferably, the modified hydrogenated rosin is one or more of hydrogenated rosin yttrium, hydrogenated rosin calcium, and hydrogenated rosin zinc.

[0017] Preferably, the modified titanium dioxide particles are alumina-modified titanium dioxide particles.

[0018] A method for preparing the low-residue water-washable flux paste of the present invention comprises the following steps:

[0019] S1. Modified hydrogenated rosin, solvent, modified titanium dioxide particles, compound activator, emulsifier, anionic surfactant, corrosion inhibitor and / or film-forming agent are mixed to obtain soldering flux;

[0020] S2, dissolving copper sulfate and nickel sulfate in water to obtain a metal salt solution;

[0021] S3, adding polyvinyl pyrrolidone to the metal salt solution to obtain a pre-reaction solution;

[0022] S4, adjusting the pH value of the pre-reaction solution, adding hydrazine hydrate, and carrying out a reduction reaction at 70-75 ° C., wherein the molar amount of the hydrazine hydrate is 3-4 times the total molar amount of the copper sulfate and nickel sulfate. Foam will be generated during the reduction reaction, and the reaction is terminated when the foam subsides;

[0023] S5, after the reduction reaction is completed, a black precipitate is obtained, and the black precipitate is dried to obtain nickel-copper microspheres;

[0024] S6. placing the nickel-copper microspheres into a cerium nitrate alcohol solution to obtain a microsphere reaction solution, and ultrasonically impregnating the solution at an ultrasonic power of 500-600 W for 1-2 h;

[0025] S7, taking out the microspheres from the impregnation solution, drying them at 90-120° C. for 6 h to obtain nickel-copper microspheres loaded with cerium oxide;

[0026] S8. Mixing the soldering flux, solder powder, and nickel-copper microspheres loaded with cerium oxide to obtain the soldering flux paste.

[0027] Preferably, the solute mass concentration of the metal salt solution in S2 is 20-30%.

[0028] Preferably, the mass of the polyvinyl pyrrolidone in S3 is 10-12% of the total mass of copper sulfate and nickel sulfate.

[0029] Preferably, the concentration of the cerium nitrate alcohol solution in S6 is 1-1.5 g / mL.

[0030] Preferably, since cerium oxide is adsorbed and loaded, it does not produce the effect that all cerium is loaded on the microspheres. Therefore, in actual preparation, according to the loading ratio, the mass ratio of nickel-copper microspheres to cerium nitrate alcohol solution needs to be selected as 1:5-10.

[0031] The use of modified hydrogenated rosin (e.g., yttrium hydrogenated rosin, calcium hydrogenated rosin, zinc hydrogenated rosin) in the flux of this invention improves the thermal stability of the solder paste. The modified hydrogenated rosin contains elements such as yttrium (Y), calcium (Ca), and zinc (Zn), which exhibit excellent oxidation resistance and thermal stability. These elements form stable chemical bonds with rosin molecules, further enhancing the antioxidant properties of the hydrogenated rosin. The modified hydrogenated rosin forms a stable protective layer at the interface between the solder and the substrate, effectively preventing oxidation reactions in high-temperature environments and reducing oxidation of the solder and substrate. The yttrium, calcium, and zinc in the modified hydrogenated rosin have high thermal conductivity, effectively conducting heat during the soldering process, reducing thermal stress and improving the thermal stability of the welded joint. The modified hydrogenated rosin is evenly distributed throughout the solder, enabling rapid and uniform heat transfer to the weld area, reducing localized overheating and thermal stress concentration, thereby improving overall thermal stability. Modified hydrogenated rosin exhibits excellent wettability, providing superior coverage of both the solder and substrate surfaces, promoting uniform bonding. This uniform bonding helps reduce interfacial defects such as pores and cracks during soldering, thereby improving the overall thermal stability of the solder joint. Modified hydrogenated rosin effectively diffuses at the solder-substrate interface, forming a uniform protective layer that reduces interfacial oxidation and corrosion, improves the thermal stability of the solder joint, and effectively prevents the decomposition of rosin molecules at high temperatures, maintaining the stability and functionality of the flux.

[0032] The addition of modified titanium dioxide (20 nm particle size) can also enhance the shear resistance of the weld layer after welding. Modified titanium dioxide particles act as second-phase particles in the weld joint and interface, producing significant second-phase strengthening. During welding, some TiO2 particles dissolve in the Sn-rich phase, some settle on the Ag3Sn phase, and some settle on the Cu6Sn5 phase. Doping with modified titanium dioxide reduces the thickness of the IMC layer and the size of the IMC grains at the weld joint interface, achieving grain refinement and enhancing the hardness of the product.

[0033] The present invention also introduces nickel-copper microspheres loaded with cerium oxide. Cerium oxide reduces the surface tension of the solder, making it easier for the solder to spread and wet the solder surface, reducing poor wetting and cold solder joints during the soldering process. For example, when soldering electronic component pins to circuit board pads, the solder can be evenly applied to the solder joint, forming a good solder joint. The nickel-copper microspheres themselves act as an excellent heat transfer medium, rapidly transferring heat during the soldering process, allowing the solder to reach a molten state more quickly and distribute evenly, further promoting solder spreading and wetting, and improving soldering quality and efficiency.

[0034] Secondly, cerium oxide has a certain degree of activity. At high welding temperatures, it may react slightly with the soldering surface (such as interfacial reactions with metals such as copper and tin), forming a more stable chemical bond and strengthening the adhesion between the solder joint and the substrate. At the same time, the nickel-copper microspheres can act like a reinforcing phase during the solder solidification process, forming a good metallurgical bond with the solder, preventing crack propagation and improving the tensile strength, shear strength and other mechanical properties of the solder joint. For example, when subjected to external forces (such as vibration and impact), the solder joint is less likely to crack or desolder, thereby improving the reliability and durability of the welded structure.

[0035] Finally, cerium oxide is an effective antioxidant. The cerium ions in its crystal structure can, to a certain extent, capture and neutralize the oxygen free radicals generated during the welding process, preventing further oxidation of the weld metal surface. During the welding process, the nickel-copper microspheres loaded with cerium oxide may chemically react with the existing oxides on the weld surface, reducing or converting the oxides into more volatile or soluble substances, thereby effectively removing the oxides from the weld surface and enabling the solder to better bond with the metal substrate. For example, for some metal surfaces that are easily oxidized (such as copper oxide that easily forms on copper surfaces), it can clean the surface and improve the weldability.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] Modified hydrogenated rosin (hydrogenated rosin yttrium, hydrogenated rosin calcium, hydrogenated rosin zinc, etc.) is used in the present invention.

[0038] The invention forms a stable protective layer at the interface between the solder and the substrate, effectively preventing oxidation reactions in high-temperature environments, reducing interfacial oxidation and corrosion, and improving the thermal stability of the welded joint. Modified titanium dioxide is added to enhance the shear resistance of the solder layer after welding, achieving grain refinement and increasing the hardness of the product. The introduction of nickel-copper microspheres loaded with cerium oxide facilitates solder spreading and wetting on the welding surface, preventing crack propagation and improving the tensile strength, shear strength, and other mechanical properties of the solder joint. The invention also provides a method for preparing the flux paste, which is simple to operate and highly operable. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The modified titanium dioxide particles involved in the following specific embodiments can be prepared by referring to the preparation method in Example 1 of invention patent CN1454939A.

[0041] Yttrium hydrogenated rosin, calcium hydrogenated rosin, and zinc hydrogenated rosin can be prepared in the laboratory.

[0042] Preparation of yttrium hydrogenated rosin: 3.00 g of propylene pimaric acid (purchased from Guangxi Wuzhou Richeng Forest Products Chemical Co., Ltd.) was weighed and dissolved in 30 mL of anhydrous ethanol. 70 mL of distilled water was added to obtain a clear, transparent hydrogenated rosin solution. 1.11 g of yttrium acetate (purchased from Xiya Reagent Company) was dissolved in 30 mL of anhydrous ethanol by ultrasonication to obtain a milky white solution. 70 mL of distilled water was then added to obtain a clear, transparent yttrium acetate solution. The yttrium acetate solution was then added dropwise to the hydrogenated rosin solution with mechanical stirring. The reaction was allowed to proceed for 1.5 hours to produce a white precipitate. This was filtered and washed with anhydrous ethanol and deionized water (20:6 by volume). The precipitate was then dried in a vacuum oven at 70°C for 6 hours to obtain yttrium hydrogenated rosin.

[0043] Preparation of hydrogenated rosin calcium: Weigh 20.00 g of hydrogenated rosin (purchased from Guangxi Wuzhou Richeng Forestry Chemical Co., Ltd.), dissolve it in 250 mL of anhydrous ethanol, weigh 3.68 g of KOH, and dissolve it in 30 mL of distilled water.

[0044] Dissolve the calcium chloride solution and prepare a KOH solution. Add the KOH solution dropwise to the hydrogenated rosin ethanol solution. When the solution becomes turbid, add 50 mL of distilled water. The solution becomes a yellow, transparent liquid. After the KOH solution is added, the pH of the solution is approximately 9. Weigh 3.65 g of CaCl2 and dissolve it in 100 mL of anhydrous ethanol under ultrasonication. Add 32 mL of distilled water to obtain a clear, transparent calcium chloride solution. Then, add the calcium chloride solution dropwise to the hydrogenated rosin potassium salt solution while stirring. A white precipitate will form. Let it react for 2 hours, filter, and wash with anhydrous ethanol and deionized water (20:7 by volume). The washing endpoint is detected with silver nitrate solution to obtain a white solid. The product is placed in a vacuum drying oven at 70°C and dried under vacuum for 6 hours to obtain hydrogenated rosin calcium.

[0045] Preparation of hydrogenated rosin zinc: Weigh 4.00 g of hydrogenated rosin and dissolve it in 100 mL of anhydrous ethanol. Weigh 0.74 g of KOH and dissolve it in 20 mL of distilled water to prepare a KOH aqueous solution. Add the KOH aqueous solution dropwise to the hydrogenated rosin ethanol solution, until the solution becomes turbid. Then add 30 mL of distilled water, and the solution becomes a light yellow, transparent liquid. After the KOH aqueous solution is added dropwise, the solution pH is approximately 9. Weigh 0.90 g of ZnCl2 and dissolve it in 100 mL of anhydrous ethanol under ultrasonication. Then add 33 mL of distilled water to obtain a clear, transparent zinc chloride solution. The zinc chloride solution is then added dropwise to the hydrogenated rosin potassium salt solution with mechanical stirring. A white precipitate is formed by the reaction. The reaction is continued for 2 hours, filtered, and washed with anhydrous ethanol and deionized water (3:1 by volume). The washing endpoint is detected with silver nitrate solution to obtain a white solid. The product is vacuum dried in a vacuum oven at 70°C for 6 hours to obtain hydrogenated rosin zinc.

[0046] The Sn-Ag-Cu alloy powder used in the specific embodiment is YT-688 Sn-3.0wt.% Ag-0.5w.%Cu alloy powder produced by Yoshida Corporation of Japan.

[0047] Example 1

[0048] A low-residue water-washable soldering paste is prepared by mixing soldering flux, solder powder, and nickel-copper microspheres loaded with cerium oxide in a mass ratio of 9:90:0.05.

[0049] The atomic molar ratio of nickel, copper and cerium in the nickel-copper microspheres loaded with cerium oxide is 3:2:1, and the average particle size of the nickel-copper microspheres loaded with cerium oxide is 200 nm.

[0050] The raw materials of the soldering flux include, by mass, 25 parts of hydrogenated rosin yttrium, 50 parts of solvent, 1 part of modified titanium dioxide particles, 4 parts of compound activator, 0.5 parts of emulsifier, 0.5 parts of anionic surfactant, 0.3 parts of corrosion inhibitor and 1 part of film-forming agent.

[0051] Among them, ethanol: glycerol: 1,2-propylene glycol: ethylene glycol butyl ether are mixed in a mass ratio of 2:4:3:1 to obtain a solvent; oxalic acid: citric acid: triethanolamine are mixed in a mass ratio of 1:1:2 to obtain a compound activator; the emulsifier is a commercially available OP-10 emulsifier, the anionic surfactant is a commercially available sodium dodecylbenzene sulfonate, the corrosion inhibitor is corrosion inhibitor BTA, and the film-forming agent is polyethylene glycol 2000.

[0052] The solder powder is a Sn-Ag-Cu alloy powder with an average particle size of 20 μm.

[0053] The modified titanium dioxide particles are aluminum oxide modified titanium dioxide particles.

[0054] A method for preparing the low-residue water-washable flux paste of the present invention comprises the following steps:

[0055] S1, hydrogenated rosin yttrium, solvent, modified titanium dioxide particles, compound activator, emulsifier, anionic surfactant, corrosion inhibitor and film-forming agent are mixed to obtain a soldering flux;

[0056] S2, adding copper sulfate and nickel sulfate in a molar ratio of 3:2 into water to obtain a metal salt solution with a solute mass concentration of 20%;

[0057] S3, adding polyvinyl pyrrolidone to the metal salt solution to obtain a pre-reaction solution, wherein the mass of polyvinyl pyrrolidone is 10% of the total mass of copper sulfate and nickel sulfate;

[0058] S4, adjusting the pH value of the pre-reaction solution to 10, adding hydrazine hydrate, and carrying out a reduction reaction at 70° C. for about 4 hours, wherein the molar amount of the hydrazine hydrate is 3 times the total molar amount of the copper sulfate and nickel sulfate;

[0059] S5, after the reduction reaction is completed, a black precipitate is obtained, and the black precipitate is dried to obtain nickel-copper microspheres;

[0060] S6. Place the nickel-copper microspheres into a 1 g / mL cerium nitrate alcohol solution to obtain a microsphere reaction solution, wherein the mass ratio of the nickel-copper microspheres to the cerium nitrate alcohol solution is 1:5, and ultrasonic immerse the microspheres at an ultrasonic power of 500 W for 1 h.

[0061] S7, taking out the microspheres from the immersion solution, drying them at 90°C for 6 hours to obtain nickel-copper microspheres loaded with cerium oxide. After testing the elemental composition, the atomic molar ratio of nickel, copper, and cerium was 3:2:1;

[0062] S8. Mixing the soldering flux, solder powder, and nickel-copper microspheres loaded with cerium oxide to obtain the soldering flux paste.

[0063] Example 2

[0064] A low-residue, water-washable soldering paste is prepared by mixing flux, solder powder, and nickel-copper microspheres loaded with cerium oxide in a mass ratio of 12:90:0.08. The atomic molar ratio of nickel, copper, and cerium in the cerium oxide-loaded nickel-copper microspheres is 4:2:1, and the average particle size of the cerium oxide-loaded nickel-copper microspheres is 300 nm. The raw materials for the soldering paste, by mass, include 30 parts of hydrogenated calcium rosin, 60 parts of solvent, 1.4 parts of modified titanium dioxide particles, 7 parts of a composite activator, 1 part of an emulsifier, 1 part of an anionic surfactant, 0.4 parts of a corrosion inhibitor, and 1.5 parts of a film-forming agent. The solvent is prepared by mixing ethanol, glycerol, 1,2-propylene glycol, and ethylene glycol butyl ether in a mass ratio of 2:4:3:1. The compound activator is prepared by mixing oxalic acid, citric acid, and triethanolamine in a mass ratio of 1:1:2. The emulsifier is commercially available OP-10 emulsifier, the anionic surfactant is commercially available sodium dodecylbenzenesulfonate, the corrosion inhibitor is BTA, and the film-forming agent is polyethylene glycol 2000. The solder powder is a Sn-Ag-Cu alloy powder with an average particle size of 30 microns.

[0065] The modified titanium dioxide particles are aluminum oxide modified titanium dioxide particles.

[0066] A method for preparing the low-residue water-washable flux paste of the present invention comprises the following steps:

[0067] S1, hydrogenated rosin calcium, solvent, modified titanium dioxide particles, compound activator, emulsifier, anionic surfactant, corrosion inhibitor and / or film-forming agent are mixed to obtain a soldering flux;

[0068] S2, copper sulfate and nickel sulfate are added to water in a molar ratio of 4:2 to obtain a metal salt solution with a solute mass concentration of 30%;

[0069] S3, adding polyvinyl pyrrolidone to the metal salt solution to obtain a pre-reaction solution, wherein the mass of polyvinyl pyrrolidone is 12% of the total mass of copper sulfate and nickel sulfate;

[0070] S4, adjusting the pH value of the pre-reaction solution to 10, adding hydrazine hydrate, and carrying out a reduction reaction at 75 ° C. for about 4 hours, wherein the molar amount of the hydrazine hydrate is 4 times the total molar amount of the copper sulfate and nickel sulfate;

[0071] S5, after the reduction reaction is completed, a black precipitate is obtained, and the black precipitate is dried to obtain nickel-copper microspheres;

[0072] S6, placing the nickel-copper microspheres into a 1.5 g / mL cerium nitrate alcohol solution to obtain a microsphere reaction solution, wherein the mass ratio of the nickel-copper microspheres to the cerium nitrate alcohol solution is 1:10, and ultrasonic immersion is performed at an ultrasonic power of 600 W for 2 h;

[0073] S7, taking out the microspheres from the immersion solution, drying them at 120°C for 6 hours to obtain nickel-copper microspheres loaded with cerium oxide. After testing the elemental composition, the atomic molar ratio of nickel, copper, and cerium was 4:2:1;

[0074] S8. Mixing the soldering flux, solder powder, and nickel-copper microspheres loaded with cerium oxide to obtain the soldering flux paste.

[0075] Example 3

[0076] A low-residue, water-washable soldering paste is prepared by mixing flux, solder powder, and nickel-copper microspheres loaded with cerium oxide in a mass ratio of 10:90:0.06. The atomic molar ratio of nickel, copper, and cerium in the cerium oxide-loaded nickel-copper microspheres is 3.5:2:1, and the average particle size of the cerium oxide-loaded nickel-copper microspheres is 250 nm. The raw materials for the soldering paste, by mass, include 27 parts hydrogenated rosin zinc, 55 parts solvent, 1.3 parts modified titanium dioxide particles, 6 parts compound activator, 0.8 parts emulsifier, 0.7 parts anionic surfactant, 0.35 parts corrosion inhibitor, and / or 1.3 parts film-forming agent. The solvent is prepared by mixing ethanol, glycerol, 1,2-propylene glycol, and ethylene glycol butyl ether in a mass ratio of 2:4:3:1. The compound activator is prepared by mixing oxalic acid, citric acid, and triethanolamine in a mass ratio of 1:1:2. The emulsifier is commercially available OP-10 emulsifier, the anionic surfactant is commercially available sodium dodecylbenzenesulfonate, the corrosion inhibitor is BTA, and the film-forming agent is polyethylene glycol 2000. The solder powder is a Sn-Ag-Cu alloy powder with an average particle size of 25 microns.

[0077] The modified titanium dioxide particles are aluminum oxide modified titanium dioxide particles.

[0078] A method for preparing the low-residue water-washable flux paste of the present invention comprises the following steps:

[0079] S1, hydrogenated rosin zinc, solvent, modified titanium dioxide particles, compound activator, emulsifier, anionic surfactant, corrosion inhibitor and / or film-forming agent are mixed to obtain soldering flux;

[0080] S2, copper sulfate and nickel sulfate are added to water in a molar ratio of 3.5:2 to obtain a metal salt solution with a solute mass concentration of 27%;

[0081] S3, adding polyvinyl pyrrolidone to the metal salt solution to obtain a pre-reaction solution, wherein the mass of polyvinyl pyrrolidone is 11% of the total mass of copper sulfate and nickel sulfate;

[0082] S4, adjusting the pH value of the pre-reaction solution to 10, adding hydrazine hydrate, and carrying out a reduction reaction at 73 ° C. for about 4 hours, wherein the molar amount of the hydrazine hydrate is 3.5 times the total molar amount of the copper sulfate and nickel sulfate;

[0083] S5, after the reduction reaction is completed, a black precipitate is obtained, and the black precipitate is dried to obtain nickel-copper microspheres;

[0084] S6. Place the nickel-copper microspheres into a 1.2 g / mL cerium nitrate alcohol solution to obtain a microsphere reaction solution, wherein the mass ratio of the nickel-copper microspheres to the cerium nitrate alcohol solution is 1:8, and ultrasonically immerse the microspheres at an ultrasonic power of 550 W for 1.5 h.

[0085] S7, taking out the microspheres from the immersion solution, drying them at 110°C for 6 hours to obtain nickel-copper microspheres loaded with cerium oxide. After testing the elemental composition, the atomic molar ratio of nickel, copper, and cerium was 3.5:2:1;

[0086] S8. Mixing the soldering flux, solder powder, and nickel-copper microspheres loaded with cerium oxide to obtain the soldering flux paste.

[0087] Comparative Example 1

[0088] This comparative example is the same as Example 1, except that in this comparative example, an equal amount of nickel-copper microspheres loaded with cerium oxide are replaced by solder powder.

[0089] Comparative Example 2

[0090] This comparative example is the same as Example 1, except that steps S6-7 are omitted in this comparative example, and the nickel-copper microspheres loaded with cerium oxide are replaced by the nickel-copper microspheres in S5.

[0091] Comparative Example 3

[0092] This comparative example is the same as Example 1, except that in this comparative example, the modified titanium dioxide particles are replaced with an equal amount of a film-forming agent.

[0093] Comparative Example 4

[0094] This comparative example is the same as Example 1, except that in this comparative example, the mass ratio of the flux, the solder powder, and the nickel-copper microspheres loaded with cerium oxide is 9:90:0.03.

[0095] Comparative Example 5

[0096] This comparative example is the same as Example 1, except that in this comparative example, the mass ratio of the flux, the solder powder, and the nickel-copper microspheres loaded with cerium oxide is 9:90:0.1.

[0097] Comparative Example 6

[0098] This comparative example is the same as Example 1, except that steps S6-7 are omitted in this comparative example, and the nickel-copper microspheres loaded with cerium oxide are replaced by the cerium oxide microspheres in S5 in equal amounts.

[0099] The solder pastes in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests, primarily including solderability, spreadability, and maximum shear resistance. Solderability is an indicator used to evaluate the solder paste's soldering performance. The solderability test was conducted using a SAT5100 solderability tester. The test method included setting the instrument's measurement parameters, including the solder bath heating temperature at (260 ± 5)6, the Cu sheet immersion depth at 5mm, and the wetting time at 10s. The solder paste sample was placed in the solder bath and heated to melt, and three standard Cu sheets were immersed in the solder paste sample for testing. The wetting force curve was obtained, and the wetting time, maximum wetting force, and other related indicators were measured and their average values ​​calculated. For solder paste, the shorter the wetting time, the greater the maximum wetting force, indicating better wetting of the Cu sheet by the solder paste sample during soldering, i.e., stronger solderability.

[0100] Spreadability testing, based on the IPC-TM-650 standard, is a key research method for evaluating solder paste performance. The test method involves printing three solder paste patterns on a Cu substrate using a stencil with a 6.5mm hole diameter and 0.2mm thickness. The Cu substrate with the printed solder paste patterns is heated in a T200N flow soldering furnace at a peak temperature of (260 ± 5)6. After cooling, the sample is removed and the solder joint's spread morphology is observed. The spread area, spread rate, and wetting angle are measured, and the average value of the three solder joint samples is taken.

[0101] The maximum shear resistance test used a lap-shear model, using a 30x5x1mm copper bar as the base material. During the soldering process, solder paste was printed onto the copper surface using a stencil with a 5x5x0.2mm opening, ensuring consistent solder paste usage for each soldering session. Finally, soldering was completed in a reflow oven at a maximum temperature of 260°C for 1 minute, and the maximum shear resistance after soldering was measured.

[0102] The solderability test results are shown in Table 1;

[0103] Table 1 Solderability test results

[0104] Group Maximum wetting force (mN) Final wetting force (mN) Zero crossing time (s) Wetting time (s) Example 1 4.31 4.23 1.01 1.32 Example 2 4.42 4.26 0.93 1.13 Example 3 4.26 4.12 1.12 1.21 Comparative Example 1 3.21 3.10 1.51 1.63 Comparative Example 2 4.11 3.92 1.21 1.28 Comparative Example 3 3.55 3.45 1.33 1.37 Comparative Example 4 4.13 4.1 1.19 1.22 Comparative Example 5 4.32 4.3 0.98 1.1 Comparative Example 6 3.98 3.87 1.26 1.31

[0105] The results of the spreadability test are shown in Table 2;

[0106] Table 2 Spreadability test results

[0107] Group Spreading area (mm) Spreading rate (%) Wetting angle Example 1 64.3 90.5 10.6 Example 2 65 91.1 9.8 Example 3 65.6 91.8 9.6 Comparative Example 1 53 84.8 13.2 Comparative Example 2 61.1 87.9 11.2 Comparative Example 3 58.3 86.5 12.4 Comparative Example 4 60.2 86.3 11.7 Comparative Example 5 66.1 91.4 9.7 Comparative Example 6 59.2 87.1 12.1

[0108] The shear resistance test results are shown in Table 3;

[0109] Table 3 Maximum shear resistance

[0110] Group Maximum shear resistance (MPa) Example 1 32.4 Example 2 33.6 Example 3 31.5 Comparative Example 1 26.8 Comparative Example 2 29.6 Comparative Example 3 27.4 Comparative Example 4 28.1 Comparative Example 5 27.2 Comparative Example 6 29.7

[0111] The test results in Tables 1-3 show that the flux paste of the present invention has good solderability and wettability, as well as high shear resistance after soldering. When the amount of nickel-copper microspheres loaded with cerium oxide is too low, the wettability, spreadability, and shear resistance after soldering decrease. When the amount of nickel-copper microspheres loaded with cerium oxide is too high, the wettability and spreadability after soldering decrease, but the shear resistance decreases. This may be because too much nickel-copper microspheres loaded with cerium oxide, while improving wettability, also have a negative impact on shear resistance.

[0112] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A low-residue water-washable flux paste, characterized in that: The invention comprises a flux, solder powder and nickel-copper microspheres loaded with cerium oxide. The raw materials of the flux are composed of modified hydrogenated rosin, a solvent, modified titanium dioxide particles and a compound activator. The atomic molar ratio of nickel, copper and cerium in the nickel-copper microspheres loaded with cerium oxide is 3-4:2:1, and the average particle size of the nickel-copper microspheres loaded with cerium oxide is 200-300 nm. The mass ratio of the flux, solder powder, and nickel-copper microspheres loaded with cerium oxide is 9-12:90:0.05-0.08; The raw materials of the soldering flux include, by mass, 25-30 parts of modified hydrogenated rosin, 50-60 parts of solvent, 1-1.4 parts of modified titanium dioxide particles, 4-7 parts of compound activator, 0.5-1 part of emulsifier, 0.5-1 part of anionic surfactant, 0.3-0.4 part of corrosion inhibitor and / or 1-1.5 parts of film-forming agent.

2. The low-residue water-washable flux paste according to claim 1, wherein: The solder powder is Sn-Ag-Cu alloy powder with an average particle size of 20-30 microns.

3. The low-residue water-washable flux paste according to claim 1, wherein: The modified hydrogenated rosin is one or more of hydrogenated rosin yttrium, hydrogenated rosin calcium, and hydrogenated rosin zinc.

4. The low-residue water-washable flux paste according to claim 1, wherein: The modified titanium dioxide particles are aluminum oxide modified titanium dioxide particles.

5. A method for preparing the low-residue water-washable flux paste according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Modified hydrogenated rosin, solvent, modified titanium dioxide particles, compound activator, emulsifier, anionic surfactant, corrosion inhibitor and / or film-forming agent are mixed to obtain soldering flux; S2, dissolving copper sulfate and nickel sulfate in water to obtain a metal salt solution; S3, adding polyvinyl pyrrolidone to the metal salt solution to obtain a pre-reaction solution; S4, adjusting the pH value of the pre-reaction solution, adding hydrazine hydrate, and performing a reduction reaction at 70-75° C., wherein the molar amount of the hydrazine hydrate is 3-4 times the total molar amount of the copper sulfate and nickel sulfate; S5, after the reduction reaction is completed, a black precipitate is obtained, and the black precipitate is dried to obtain nickel-copper microspheres; S6, placing the nickel-copper microspheres into a cerium nitrate alcohol solution to obtain a microsphere reaction solution, and ultrasonically impregnating the solution; S7, taking out the microspheres from the immersion solution and drying them to obtain nickel-copper microspheres loaded with cerium oxide; S8. Mixing the soldering flux, solder powder, and nickel-copper microspheres loaded with cerium oxide to obtain the soldering flux paste.

6. The preparation method according to claim 5, characterized in that The solute mass concentration of the metal salt solution in S2 is 20-30%.

7. The preparation method according to claim 5, characterized in that The mass of the polyvinyl pyrrolidone in S3 is 10-12% of the total mass of copper sulfate and nickel sulfate.

8. The preparation method according to claim 5, characterized in that The concentration of the cerium nitrate alcohol solution in S6 is 1-1.5 g / mL, and the mass ratio of the nickel-copper microspheres to the cerium nitrate alcohol solution is 1:5-10.