Low-residual lead-free tin paste and preparation method thereof

Abstract

The application relates to the technical field of lead-free tin paste, in particular to low-residue lead-free tin paste and a preparation method thereof. The raw materials of the low-residue lead-free tin paste include, by mass fraction, 100 parts of tin powder, 1-2 parts of nickel powder, 0.1-0.5 parts of gallium powder, 1-2 parts of bismuth powder, 0.1-1 parts of copper powder, 0.01-0.1 parts of silver powder, 0.01-0.1 parts of nanocellulose aerogel, 1-2 parts of 2-phenylimidazoline, 0.01-0.1 parts of cerium ammonium nitrate, 0.01-0.1 parts of Gemini quaternary ammonium salt, 0.01-0.1 parts of acrylic anhydride, 0.01-0.1 parts of potassium nitrate, 1-5 parts of hydrogenated rosin pentaerythritol ester and 1-10 parts of a soldering flux. The application effectively realizes low residue under the premise of guaranteeing welding quality, the tin paste is not only excellent in storage stability and good in process adaptability, but also high in solder joint strength and low in solder wire defect rate, and is particularly suitable for high-end electronic packaging fields such as new energy automobile power modules.

Description

Technical Field

[0001] This invention relates to the field of lead-free solder paste technology, and in particular to a low-residue lead-free solder paste and its preparation method. Background Technology

[0002] Electronic packaging technology is the core of the electronic information industry. Currently, electronic packaging technology is mainly developing towards high power, high density, miniaturization, high reliability, and greenness. Most electronic components are automated in packaging through processes such as reflow soldering and wave soldering. Reflow soldering is mainly achieved through processes such as screen printing solder paste, component placement, and reflow soldering.

[0003] In the field of electronic packaging, lead-free solder paste, as a core material to replace traditional lead-containing solder, directly determines the soldering reliability and long-term stability of electronic devices. However, as electronic products develop towards miniaturization and high density, existing lead-free solder pastes still have significant technical shortcomings in terms of low residue control, low-temperature soldering adaptability, and long-term reliability.

[0004] CN201410404368.4 discloses an electronic no-clean solder paste and its preparation method, comprising the following raw materials in parts by weight: 55-60 parts of lead-free solder micro powder, 0.3-0.5 parts of activator, 0.2-0.5 parts of rosin, 7.5-8.5 parts of solvent, 0.05-0.1 parts of film-forming agent, 1-1.5 parts of resin, 0.1-0.15 parts of benzotriazole, and 0.01-0.02 parts of antioxidant. This method uses lead-free tin alloy micro powder combined with halogen-free flux active ingredients and solvents to prepare a low-residue, non-corrosive, lead-free, halogen-free, environmentally friendly no-clean solder paste for soldering electronic components. The components have good compatibility and exhibit good antioxidant, rheological, and stability properties. However, long-term storage may lead to metal particle stratification, affecting the uniformity of the solder paste and its soldering performance.

[0005] The development of a novel lead-free solder paste system that is stable for long-term storage, while ensuring the mechanical strength of the solder joints and achieving adequate flux residue, presents a promising research prospect. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a low-residue lead-free solder paste and its preparation method.

[0007] A low-residue lead-free solder paste, comprising the following raw materials by weight: 100 parts tin powder, 1-2 parts nickel powder, 0.1-0.5 parts gallium powder, 1-2 parts bismuth powder, 0.1-1 parts copper powder, 0.01-0.1 parts silver powder, 0.01-0.1 parts nanocellulose aerogel, 1-2 parts 2-phenylimidazoline, 0.01-0.1 parts cerium ammonium nitrate, 0.01-0.1 parts Gemini quaternary ammonium salt, 0.01-0.1 parts acrylic anhydride, 0.01-0.1 parts potassium nitrate, 1-5 parts hydrogenated rosin pentaerythritol ester, and 1-10 parts flux.

[0008] Preferably, the specific surface area of ​​the nanocellulose aerogel is >600m² / g.

[0009] Preferably, the flux comprises, by weight, 0.1-1 parts of activator, 0.1-0.2 parts of defoamer, 1-2 parts of surfactant, 1-2 parts of corrosion inhibitor, 10-20 parts of hydrogenated rosin, and 20-50 parts of solvent.

[0010] Preferably, the activator includes sodium succinate and sodium malate.

[0011] Preferably, the defoamer is polyoxypropylene glycerol ether.

[0012] Preferably, the surfactant is ricinoleoyl diethanolamine.

[0013] Preferably, the corrosion inhibitor is an imidazoline-based corrosion inhibitor, specifically imidazoline quaternary ammonium salt MZJ-1.

[0014] Preferably, the solvent includes diethylene glycol butyl ether.

[0015] The preparation method of the above-mentioned low-residue lead-free solder paste includes the following steps:

[0016] S1. In high-purity hydrogen, tin powder and nickel powder are mixed and treated at 300-350℃ for 15-20 minutes. The temperature is then reduced to below 200℃, gallium powder is added, and the mixture is treated under pressure for 3-6 minutes to obtain pretreated tin liquid. Copper powder, bismuth powder, and silver powder are mixed with hydrogen to form metal dust gas. The pretreated tin liquid is then impacted at 180-200℃ and 2-4MPa high pressure until the melting chamber is filled with droplet mist. Low-temperature hydrogen gas at 5-10℃ is blown in to cool the mixture, and then ball milling is performed to obtain solder powder.

[0017] S2. Add nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stir evenly. Ultrasonic treatment for 10-30 min, then add Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and ultrasonic treatment for 10-30 min to obtain the coating material.

[0018] S3. Mix the solder powder and coating material, and treat with low-frequency ultrasonic waves for 10-20 minutes to obtain pre-coated solder powder; then add flux and mix evenly, stir under vacuum at 110-120℃ for 10-30 minutes, treat with pulsed magnetic field for 5-10 minutes, pulse intensity of 0.1-0.2T, pulse frequency of 50-100Hz, and cool to room temperature.

[0019] Preferably, in S1, the concentration of metal dust gas is 100-150 mg / L.

[0020] Preferably, in S2, the ultrasonic treatment frequency after adding hydrogenated rosin pentaerythritol ester is 35-45 kHz, while the ultrasonic treatment frequency after adding potassium nitrate is 50-60 kHz.

[0021] Preferably, in S3, the frequency of the low-frequency ultrasonic treatment is 20-30kHz, and the ultrasonic power is 200-300W.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] This invention uses a composite of tin, nickel, gallium, copper, bismuth, and silver to prepare solder powder. In the pretreatment stage, the pre-mixing of gallium and nickel forms a highly active interface, reducing the activation energy of subsequent tin-nickel alloying. A gas atomization-stage heat treatment process ensures the uniform distribution of tin-nickel intermetallic compounds. This process also inhibits excessive growth of intermetallic compounds, allowing copper, bismuth, and silver to be distributed in a metastable state within the alloy matrix, synergistically improving the fatigue resistance of the solder joint. Pulsed magnetic field treatment optimizes the physical arrangement of solder powder particles through magnetothermal effects, reducing internal stress concentration. Combined with the magnetic response characteristics of nickel, this enhances the creep resistance of the solder joint, effectively increasing its strength while lowering the melting point.

[0024] This invention uses a combination of solder powder and coating material to effectively enhance welding strength and reduce the defect rate of solder wires. Nanocellulose aerogel serves as a molecular carrier, on which 2-phenylimidazoline is loaded. Coating the solder powder with this material effectively forms a slow-release active system. The porous structure of the nanocellulose aerogel gradually releases 2-phenylimidazoline through capillary action during the preheating stage. During the high-temperature stage, the collapse of the aerogel skeleton accelerates the diffusion of active substances, solving the problem of premature consumption of activators in traditional systems. Low-frequency ultrasonic treatment can break down nanocellulose aggregates. The combined effect effectively achieves a low-residue effect.

[0025] This invention effectively achieves low residue while ensuring welding quality. The solder paste not only has excellent storage stability and good process adaptability, but also has high solder joint strength and low wire defect rate, making it particularly suitable for high-end electronic packaging fields such as power modules for new energy vehicles. Attached Figure Description

[0026] Figure 1 This is a comparison chart of the melting points of the solder pastes obtained in Example 5 and Comparative Examples 1-3.

[0027] Figure 2 The graph shows a comparison of the surface insulation resistance and organic residue rate of the solder paste obtained in Example 5 and Comparative Examples 1-3.

[0028] Figure 3 The image shows a comparison of the tensile strength of the solder paste obtained in Example 5 and Comparative Examples 1-3 after soldering. Detailed Implementation

[0029] The present invention will be further explained below with reference to specific embodiments.

[0030] The nanocellulose aerogel described below was purchased from Xi'an Mouyue Biotechnology Co., Ltd., and its specific surface area is 855 m² / g.

[0031] Example 1: A low-residue lead-free solder paste, the raw materials of which include: 100g tin powder, 1g nickel powder, 0.1g gallium powder, 1g bismuth powder, 0.1g copper powder, 0.01g silver powder, 0.01g nanocellulose aerogel, 1g 2-phenylimidazoline, 0.01g cerium ammonium nitrate, 0.01g Gemini quaternary ammonium salt, 0.01g acrylic anhydride, 0.01g potassium nitrate, 1g hydrogenated rosin pentaerythritol ester, and 1g flux.

[0032] The flux is composed of sodium succinate, sodium malate, polyoxypropylene glycerol ether, ricinoleoyl diethanolamine, imidazoline quaternary ammonium salt MZJ-1, hydrogenated rosin, and diethylene glycol butyl ether in a mass ratio of 0.05:0.05:0.1:1:1:10:20.

[0033] The preparation method of the above-mentioned low-residue lead-free solder paste includes the following steps:

[0034] S1. In high-purity hydrogen gas, where the hydrogen purity is >99.9%, tin powder and nickel powder are mixed and fed into the melting chamber. The mixture is treated at 300°C for 15 minutes. When the temperature is reduced to below 200°C, gallium powder is added and the mixture is treated under pressure for 3 minutes to obtain pretreated tin liquid.

[0035] Copper powder, bismuth powder, silver powder and hydrogen are mixed to form a 100mg / L metal dust gas. The molten tin is pretreated by impacting the melting chamber at 180℃ and 2MPa high pressure until the melting chamber is filled with droplet mist. Low-temperature hydrogen gas at 5℃ is blown in to cool it down. The tin powder is then ball-milled and sieved to obtain solder powder with a particle size of 5-10μm.

[0036] S2. Add nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stir evenly. Sonicate for 10 min at a frequency of 35 kHz. Then add Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and sonicate for 10 min at a frequency of 50 kHz to obtain the coating material.

[0037] S3. Mix solder powder and coating material, treat with low-frequency ultrasonic for 10 minutes, ultrasonic frequency is 20kHz, ultrasonic power is 200W, to obtain pre-coated solder powder; then add flux and mix evenly, stir under vacuum at 110℃ for 10 minutes at 200r / min, treat with pulsed magnetic field for 5 minutes, pulse intensity is 0.1T, pulse frequency is 50Hz, and then cool to room temperature.

[0038] Example 2: A low-residue lead-free solder paste, the raw materials of which include: 100g tin powder, 2g nickel powder, 0.5g gallium powder, 2g bismuth powder, 1g copper powder, 0.1g silver powder, 0.1g nanocellulose aerogel, 2g 2-phenylimidazoline, 0.1g cerium ammonium nitrate, 0.1g Gemini quaternary ammonium salt, 0.1g acrylic anhydride, 0.1g potassium nitrate, 5g hydrogenated rosin pentaerythritol ester, and 10g flux.

[0039] The flux is composed of potassium succinate, potassium malate, polyoxypropylene glycerol ether, ricinoleoyl diethanolamine, imidazoline quaternary ammonium salt MZJ-1, hydrogenated rosin, and diethylene glycol butyl ether in a mass ratio of 0.5:0.5:0.2:2:2:20:50.

[0040] The preparation method of the above-mentioned low-residue lead-free solder paste includes the following steps:

[0041] S1. In high-purity hydrogen gas, where the hydrogen purity is >99.9%, tin powder and nickel powder are mixed and fed into the melting chamber. The mixture is treated at 350°C for 20 minutes. When the temperature is reduced to below 200°C, gallium powder is added and the mixture is treated under pressure for 6 minutes to obtain pretreated tin liquid.

[0042] Copper powder, bismuth powder, silver powder and hydrogen are mixed to form a 150 mg / L metal dust gas. The molten tin is pretreated by impacting the melting chamber at 200°C and 4 MPa to fill the melting chamber with droplet mist. Then, 10°C low-temperature hydrogen is blown in to cool it down. After ball milling and sieving, solder powder with a particle size of 5-10 μm is obtained.

[0043] S2. Add nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stir evenly. Sonicate for 30 min at a frequency of 45 kHz. Then add Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and sonicate for 30 min at a frequency of 60 kHz to obtain the coating material.

[0044] S3. Mix solder powder and coating material, treat with low-frequency ultrasonic for 20 minutes, ultrasonic frequency is 30kHz, ultrasonic power is 300W, to obtain pre-coated solder powder; then add flux and mix evenly, stir under vacuum at 120℃ for 30 minutes at a stirring speed of 300r / min, treat with pulsed magnetic field for 10 minutes, pulse intensity is 0.2T, pulse frequency is 100Hz, and then cool to room temperature.

[0045] Example 3: A low-residue lead-free solder paste, the raw materials of which include: 100g tin powder, 1.3g nickel powder, 0.4g gallium powder, 1.3g bismuth powder, 0.8g copper powder, 0.03g silver powder, 0.08g nanocellulose aerogel, 1.2g 2-phenylimidazoline, 0.07g cerium ammonium nitrate, 0.03g Gemini quaternary ammonium salt, 0.08g acrylic anhydride, 0.02g potassium nitrate, 4g hydrogenated rosin pentaerythritol ester, and 3g flux.

[0046] The flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleoyl diethanolamine, imidazoline quaternary ammonium salt MZJ-1, hydrogenated rosin, and diethylene glycol butyl ether in a mass ratio of 0.3:0.5:0.12:1.7:1.4:16:30.

[0047] The preparation method of the above-mentioned low-residue lead-free solder paste includes the following steps:

[0048] S1. In high-purity hydrogen gas with a purity > 99.9%, tin powder and nickel powder are mixed and fed into the melting chamber. The mixture is treated at 340°C for 17 minutes. The temperature is then reduced to below 200°C, gallium powder is added, and the mixture is treated under pressure for 4 minutes to obtain pretreated tin liquid.

[0049] Copper powder, bismuth powder, silver powder and hydrogen are mixed to form a 130 mg / L metal dust gas. The molten tin is pretreated by impacting it at 185℃ and 3.5 MPa high pressure until the melting chamber is filled with droplet mist. Low-temperature hydrogen gas at 6℃ is blown in to cool it down. The molten tin is then ball-milled and sieved to obtain solder powder with a particle size of 5-10 μm.

[0050] S2. Add nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stir evenly. Sonicate for 25 min at a frequency of 36 kHz. Then add Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and sonicate for 25 min at a frequency of 51 kHz to obtain the coating material.

[0051] S3. Mix solder powder and coating material, treat with low-frequency ultrasonic waves for 18 minutes (ultrasonic frequency 21kHz, ultrasonic power 280W) to obtain pre-coated solder powder; then add flux and mix evenly, stir under vacuum at 112℃ for 25 minutes (stirring speed 220r / min), treat with pulsed magnetic field for 9 minutes (pulse intensity 0.12T, pulse frequency 90Hz), and cool to room temperature.

[0052] Example 4: A low-residue lead-free solder paste, the raw materials of which include: 100g tin powder, 1.7g nickel powder, 0.2g gallium powder, 1.7g bismuth powder, 0.2g copper powder, 0.07g silver powder, 0.02g nanocellulose aerogel, 1.8g 2-phenylimidazoline, 0.03g cerium ammonium nitrate, 0.07g Gemini quaternary ammonium salt, 0.02g acrylic anhydride, 0.08g potassium nitrate, 2g hydrogenated rosin pentaerythritol ester, and 7g flux.

[0053] The flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleoyl diethanolamine, imidazoline quaternary ammonium salt MZJ-1, hydrogenated rosin, and diethylene glycol butyl ether in a mass ratio of 0.1:0.1:0.18:1.3:1.8:12:40.

[0054] The preparation method of the above-mentioned low-residue lead-free solder paste includes the following steps:

[0055] S1. In high-purity hydrogen gas, where the hydrogen purity is >99.9%, tin powder and nickel powder are mixed and fed into the melting chamber. The mixture is treated at 320°C for 19 minutes. When the temperature is reduced to below 200°C, gallium powder is added and the mixture is treated under pressure for 5 minutes to obtain pretreated tin liquid.

[0056] Copper powder, bismuth powder, silver powder and hydrogen are mixed to form a 110 mg / L metal dust gas. The molten tin is pretreated by impacting it at 195℃ and 2.5 MPa high pressure until the melting chamber is filled with droplet mist. Low-temperature hydrogen gas at 8℃ is blown in to cool it down. The molten tin is then ball-milled and sieved to obtain solder powder with a particle size of 5-10 μm.

[0057] S2. Add nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stir evenly. Sonicate for 15 min at a frequency of 42 kHz. Then add Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and sonicate for 15 min at a frequency of 57 kHz to obtain the coating material.

[0058] S3. Mix solder powder and coating material, treat with low-frequency ultrasonic waves for 12 minutes (ultrasonic frequency 27kHz, ultrasonic power 220W) to obtain pre-coated solder powder; then add flux and mix evenly, stir under vacuum at 118℃ for 15 minutes (stirring speed 280r / min), treat with pulsed magnetic field for 7 minutes (pulse intensity 0.18T, pulse frequency 60Hz), and cool to room temperature.

[0059] Example 5: A low-residue lead-free solder paste, the raw materials of which include: 100g tin powder, 1.5g nickel powder, 0.3g gallium powder, 1.5g bismuth powder, 0.5g copper powder, 0.05g silver powder, 0.05g nanocellulose aerogel, 1.5g 2-phenylimidazoline, 0.05g cerium ammonium nitrate, 0.05g Gemini quaternary ammonium salt, 0.05g acrylic anhydride, 0.05g potassium nitrate, 3g hydrogenated rosin pentaerythritol ester, and 5g flux.

[0060] The flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleoyl diethanolamine, imidazoline quaternary ammonium salt MZJ-1, hydrogenated rosin, and diethylene glycol butyl ether in a mass ratio of 0.3:0.2:0.15:1.5:1.6:14:35.

[0061] The preparation method of the above-mentioned low-residue lead-free solder paste includes the following steps:

[0062] S1. In high-purity hydrogen gas with a purity > 99.9%, tin powder and nickel powder are mixed and fed into the melting chamber. The mixture is treated at 330°C for 18 minutes. When the temperature is reduced to below 200°C, gallium powder is added and the mixture is treated under pressure for 3 minutes to obtain pretreated tin liquid.

[0063] Copper powder, bismuth powder, silver powder and hydrogen are mixed to form a 120 mg / L metal dust gas. The molten tin is pretreated by impacting the molten tin at 190°C and 3 MPa high pressure until the melting chamber is filled with droplet mist. Low-temperature hydrogen gas at 7°C is blown in to cool it down. The tin powder is then ball-milled and sieved to obtain solder powder with a particle size of 5-10 μm.

[0064] S2. Add nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stir evenly. Sonicate for 18 min at a frequency of 39 kHz. Then add Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and sonicate for 20 min at a frequency of 54 kHz to obtain the coating material.

[0065] S3. Mix solder powder and coating material, treat with low-frequency ultrasonic for 15 minutes, ultrasonic frequency is 24kHz, ultrasonic power is 250W to obtain pre-coated solder powder; then add flux and mix evenly, stir under vacuum at 115℃ for 20 minutes at a stirring speed of 250r / min, treat with pulsed magnetic field for 8 minutes, pulse intensity is 0.15T, pulse frequency is 75Hz, and then cool to room temperature.

[0066] Comparative Example 1

[0067] A low-residue lead-free solder paste comprises the following raw materials: 100g tin powder, 1.5g nickel powder, 1.5g bismuth powder, 0.5g copper powder, 0.05g silver powder, 0.05g nanocellulose aerogel, 1.5g 2-phenylimidazoline, 0.05g cerium ammonium nitrate, 0.05g Gemini quaternary ammonium salt, 0.05g acrylic anhydride, 0.05g potassium nitrate, 3.3g hydrogenated rosin pentaerythritol ester, and 5g flux.

[0068] The flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleoyl diethanolamine, imidazoline quaternary ammonium salt MZJ-1, hydrogenated rosin, and diethylene glycol butyl ether in a mass ratio of 0.3:0.2:0.15:1.5:1.6:14:35.

[0069] The preparation method of the above-mentioned low-residue lead-free solder paste includes the following steps:

[0070] S1. In high-purity hydrogen gas with a purity > 99.9%, tin powder and nickel powder are mixed and fed into the melting chamber, and treated at 330°C for 18 minutes to obtain pretreated tin liquid.

[0071] Copper powder, bismuth powder, silver powder and hydrogen are mixed to form a 120 mg / L metal dust gas. The molten tin is pretreated by impacting the molten tin at 190°C and 3 MPa high pressure until the melting chamber is filled with droplet mist. Low-temperature hydrogen gas at 7°C is blown in to cool it down. The tin powder is then ball-milled and sieved to obtain solder powder with a particle size of 5-10 μm.

[0072] S2. Add nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stir evenly. Sonicate for 18 min at a frequency of 39 kHz. Then add Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and sonicate for 20 min at a frequency of 54 kHz to obtain the coating material.

[0073] S3. Mix solder powder and coating material, treat with low-frequency ultrasonic for 15 minutes, ultrasonic frequency is 24kHz, ultrasonic power is 250W to obtain pre-coated solder powder; then add flux and mix evenly, stir under vacuum at 115℃ for 20 minutes at a stirring speed of 250r / min, treat with pulsed magnetic field for 8 minutes, pulse intensity is 0.15T, pulse frequency is 75Hz, and then cool to room temperature.

[0074] Comparative Example 2

[0075] A low-residue lead-free solder paste comprises the following raw materials: 100g tin powder, 1.5g nickel powder, 0.3g gallium powder, 0.05g nanocellulose aerogel, 1.5g 2-phenylimidazoline, 0.05g cerium ammonium nitrate, 0.05g Gemini quaternary ammonium salt, 0.05g acrylic anhydride, 0.05g potassium nitrate, 5.05g hydrogenated rosin pentaerythritol ester, and 5g flux.

[0076] The flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleoyl diethanolamine, imidazoline quaternary ammonium salt MZJ-1, hydrogenated rosin, and diethylene glycol butyl ether in a mass ratio of 0.3:0.2:0.15:1.5:1.6:14:35.

[0077] The preparation method of the above-mentioned low-residue lead-free solder paste includes the following steps:

[0078] S1. In high-purity hydrogen gas with a purity > 99.9%, tin powder and nickel powder are mixed and fed into the melting chamber. The mixture is treated at 330°C for 18 minutes. When the temperature is reduced to below 200°C, gallium powder is added and the mixture is treated under pressure for 3 minutes to obtain pretreated tin liquid.

[0079] The solder powder with a particle size of 5-10μm was obtained by blowing in 7℃ low-temperature hydrogen gas to cool it down, then ball milling and sieving.

[0080] S2. Add nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stir evenly. Sonicate for 18 min at a frequency of 39 kHz. Then add Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and sonicate for 20 min at a frequency of 54 kHz to obtain the coating material.

[0081] S3. Mix solder powder and coating material, treat with low-frequency ultrasonic for 15 minutes, ultrasonic frequency is 24kHz, ultrasonic power is 250W to obtain pre-coated solder powder; then add flux and mix evenly, stir under vacuum at 115℃ for 20 minutes at a stirring speed of 250r / min, treat with pulsed magnetic field for 8 minutes, pulse intensity is 0.15T, pulse frequency is 75Hz, and then cool to room temperature.

[0082] Comparative Example 3

[0083] A low-residue lead-free solder paste, the raw materials of which include: 100g tin powder, 1.5g nickel powder, 0.3g gallium powder, 1.5g bismuth powder, 0.5g copper powder, 0.05g silver powder, 4.75g hydrogenated rosin pentaerythritol ester, and 5g flux.

[0084] The flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleoyl diethanolamine, imidazoline quaternary ammonium salt MZJ-1, hydrogenated rosin, and diethylene glycol butyl ether in a mass ratio of 0.3:0.2:0.15:1.5:1.6:14:35.

[0085] The preparation method of the above-mentioned low-residue lead-free solder paste includes the following steps:

[0086] S1. In high-purity hydrogen gas with a purity > 99.9%, tin powder and nickel powder are mixed and fed into the melting chamber. The mixture is treated at 330°C for 18 minutes. When the temperature is reduced to below 200°C, gallium powder is added and the mixture is treated under pressure for 3 minutes to obtain pretreated tin liquid.

[0087] Copper powder, bismuth powder, silver powder and hydrogen are mixed to form a 120 mg / L metal dust gas. The molten tin is pretreated by impacting the molten tin at 190°C and 3 MPa high pressure until the melting chamber is filled with droplet mist. Low-temperature hydrogen gas at 7°C is blown in to cool it down. The tin powder is then ball-milled and sieved to obtain solder powder with a particle size of 5-10 μm.

[0088] S2. Add flux to solder powder and mix evenly. Stir under vacuum at 115℃ for 20 minutes at a stirring speed of 250 r / min. Treat with pulsed magnetic field for 8 minutes at a pulse intensity of 0.15T and a pulse frequency of 75Hz. Cool to room temperature.

[0089] Referring to SJ / T 11186-2019 "General Specification for Solder Paste", the solder pastes obtained in Example 5 and Comparative Examples 1-3 were tested. The viscosity of all four was in the range of 180-185 Pa·s, the collapse was 0.20 mm, the solder ball level was Grade 1, and the wettability level was Grade 1. This indicates that the solder pastes obtained in Example 5 and Comparative Examples 1-3 all meet the solder paste standard.

[0090] The melting points of the solder pastes obtained in Example 5 and Comparative Examples 1-3 were determined, and the results are as follows: Figure 1 As shown, the solder paste obtained in Example 5 had the lowest melting point, which was better than that of Comparative Examples 1-3 (P < 0.05).

[0091] The solder pastes obtained in Example 5 and Comparative Examples 1-3 were smoothed and then placed in a humid environment (30°C × 100% RH). The oxidation time was recorded when more than 10% of the solder paste surface showed black spots. The oxidation test was terminated if more than 90% of the solder paste surface remained free of black spots after 48 hours. The solder pastes obtained in Example 5 and Comparative Examples 1-2 did not show black spots on more than 10% of their surfaces even after more than 48 hours, while the solder paste obtained in Comparative Example 3 only took 4.7 hours to oxidize.

[0092] A vertical laser reflow oven was used, with an aluminum PCB substrate set up. The laser zone temperature was controlled at 260±10℃. Solder paste obtained from Example 5 and Comparative Examples 1-3 was pre-applied, followed by manual placement and reflow soldering to solder 1mm×5mm×50mm wires. The surface insulation resistance of the wires was tested according to the IPC-TM-650 standard. After each group of soldering was completed, the wires were cleaned and dried, the total weight of the wires was measured, and the organic residue rate was calculated.

[0093] Organic residue rate = (Total weight of solder wire - Mass of metal in solder paste) ÷ (Mass of solder paste - Mass of metal in solder paste) × 100%

[0094] like Figure 2 As shown, the solder paste obtained in Example 5 has the highest surface insulation resistance for soldering wires, which is better than that of Comparative Examples 1-3 (P < 0.05); while the solder paste obtained in Example 5 has the lowest organic residue rate, but there is no significant difference compared with Comparative Examples 1-2.

[0095] Cut a piece of equal length (1mm, area approximately 5mm²) 2 For each group of solder lines, an optical microscope matrix was used to observe and mark the approximate area of ​​defects using red circles. The number of circles and the sum of the areas of each circle were calculated. The defect rate was obtained by dividing the sum of the areas of each circle by 5. The defect rate of the solder lines obtained using the solder paste from Example 5 or Comparative Examples 1-2 was <0.2%, while the defect rate of the solder lines obtained using the solder paste from Comparative Example 3 was 0.6%.

[0096] The tensile strength of the aforementioned weld joints was measured, such as... Figure 3 As shown, the solder paste obtained in Example 5 exhibits the highest tensile strength after soldering, which is superior to that of Comparative Examples 1-3 (P < 0.05).

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low-residue lead-free solder paste, characterized by, The raw materials include, by mass fraction: tin powder 100 parts, nickel powder 1-2 parts, gallium powder 0.1-0.5 parts, bismuth powder 1-2 parts, copper powder 0.1-1 part, silver powder 0.01-0.1 part, nanocellulose aerogel 0.01-0.1 part, 2-phenylimidazoline 1-2 parts, cerium ammonium nitrate 0.01-0.1 part, Gemini quaternary ammonium salt 0.01-0.1 part, acrylic anhydride 0.01-0.1 part, potassium nitrate 0.01-0.1 part, hydrogenated rosin pentaerythritol ester 1-5 parts, flux 1-10 parts.

2. The low-residue lead-free solder paste of claim 1, wherein, The specific surface area of the nanocellulose aerogel is > 600 m 2 / g.

3. The low-residue lead-free solder paste of claim 1, wherein, The flux includes, by mass fraction: activator 0.1-1 part, defoaming agent 0.1-0.2 part, surfactant 1-2 parts, corrosion inhibitor 1-2 parts, hydrogenated rosin 10-20 parts, solvent 20-50 parts.

4. The low-residue lead-free solder paste according to claim 3, wherein The activator includes: Sodium succinate, sodium malate.

5. The low-residue lead-free solder paste of claim 3, wherein the flux is a combination of a carboxylic acid and a carboxylate salt. The defoaming agent is polyoxypropylene glyceryl ether with a molecular weight less than 2000; the surfactant is castor oil acyl diethanolamine; the corrosion inhibitor is an imidazoline corrosion inhibitor, specifically imidazoline quaternary ammonium salt MZJ-1.

6. The low-residue lead-free solder paste of claim 3, wherein, The solvent includes diethylene glycol butyl ether.

7. A method of producing the low-residual lead-free solder paste according to any one of claims 1 to 6, characterized by, The method includes the following steps: S1, in high-purity hydrogen, tin powder and nickel powder are mixed, treated at 300-350℃ for 15-20min, the temperature is reduced to below 200℃, gallium powder is added, and the pressure environment is treated for 3-6min to obtain a pretreated tin liquid; copper powder, bismuth powder and silver powder are mixed with hydrogen to form a metal dust gas, and the pretreated tin liquid is impacted at 180-200℃ and 2-4MPa high pressure to fill the droplet mist gas in the melting chamber, 5-10℃ low-temperature hydrogen is blown to cool, and ball milling is performed to obtain solder powder; S2, nanocellulose aerogel, 2-phenylimidazoline and cerium ammonium nitrate are added to hydrogenated rosin pentaerythritol ester and stirred uniformly, ultrasonic treatment is performed for 10-30min, Gemini quaternary ammonium salt, acrylic anhydride and potassium nitrate are added and ultrasonic treatment is performed for 10-30min to obtain a coating material; S3, the solder powder and the coating material are mixed, low-frequency ultrasonic treatment is performed for 10-20min to obtain pre-wrapped solder powder; then the flux is added and mixed uniformly, stirring is performed at 110-120℃ under vacuum for 10-30min, pulse magnetic field treatment is performed for 5-10min, the pulse intensity is 0.1-0.2T, and the pulse frequency is 50-100Hz, and the temperature is reduced to room temperature.

8. The method of claim 7, wherein the low-residue lead-free solder paste is prepared by adding the flux to the solder powder and then mixing the flux and the solder powder. In S1, the concentration of the metal dust gas is 100-150mg / L.

9. The method of claim 7, wherein the low-residue lead-free solder paste is prepared by adding the flux to the solder powder and then mixing the flux and the solder powder. In S2, the ultrasonic treatment frequency after being added to the hydrogenated rosin pentaerythritol ester is 35-45kHz, and the ultrasonic treatment frequency after the potassium nitrate is added is 50-60kHz.

10. The method of claim 7, wherein the low-residue lead-free solder paste is prepared by adding the flux to the solder powder and then mixing the flux and the solder powder. In S3, the low-frequency ultrasonic treatment frequency is 20-30kHz, and the ultrasonic power is 200-300W.

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