Low-residue lead-free solder paste and preparation method thereof

Abstract

The invention relates to the technical field of lead-free solder paste, in particular to low-residue lead-free solder paste and a preparation method thereof. The low-residue lead-free solder paste is prepared from the following raw materials in parts by mass: 100 parts of tin powder, 1 to 2 parts of nickel powder, 0.1 to 0.5 part of gallium powder, 1 to 2 parts of bismuth powder, 0.1 to 1 part of copper powder, 0.01 to 0.1 part of silver powder, 0.01 to 0.1 part of nano cellulose aerogel, 1 to 2 parts of 2-phenylimidazoline, 0.01 to 0.1 part of ceric ammonium nitrate, 0.01 to 0.1 part of Gemini quaternary ammonium salt, 0.01 to 0.1 part of acrylic anhydride, 0.01 to 0.1 part of potassium nitrate, 1 to 5 parts of pentaerythritol ester of hydrogenated rosin and 1 to 10 parts of soldering flux. On the premise of guaranteeing the welding quality, low residues are effectively achieved, the solder paste is excellent in storage stability, good in process adaptability, high in welding spot strength and low in welding wire defect rate, and the solder paste is particularly suitable for the field of high-end electronic packaging of new energy automobile power modules and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of lead-free solder paste, and in particular to a low-residue lead-free solder paste and a preparation method thereof. Background Art

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

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

[0004] CN201410404368.4 discloses an electronic no-clean solder paste and a preparation method thereof, comprising the following raw materials by mass: 55-60 parts of lead-free solder 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 former, 1-1.5 parts of resin, 0.1-0.15 parts of benzotriazole, and 0.01-0.02 parts of antioxidant. A low-residue, non-corrosive lead-free, halogen-free, environmentally friendly no-clean solder paste for electronic component welding is prepared by combining lead-free tin alloy powder with halogen-free flux active ingredients and solvents. Each component has good adaptability, good oxidation resistance, rheology and stability, but long-term storage may cause metal particles to delaminate, affecting the uniformity and welding performance of the solder paste.

[0005] How to prepare a new lead-free solder paste system that is stable for long-term storage and achieve a low flux residue while ensuring the mechanical strength of the solder joint has excellent research prospects. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a low-residue lead-free solder paste and a preparation method thereof.

[0007] A low-residue lead-free solder paste, the raw materials of which include, by mass, 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 soldering flux.

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

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

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

[0011] Preferably, the defoaming agent is polyoxypropylene glyceryl ether.

[0012] Preferably, the surfactant is ricinoleyl diethanolamide.

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

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

[0015] The method for preparing the low-residue lead-free solder paste comprises the following steps: S1. In high-purity hydrogen, tin powder and nickel powder are mixed, treated at 300-350°C for 15-20min, the temperature is reduced to below 200°C, gallium powder is added, and the pressurized environment is treated for 3-6min to obtain a pre-treated tin liquid; copper powder, bismuth powder, silver powder and hydrogen are mixed to form a metal dust gas, and the tin liquid is pre-treated at 180-200°C and 2-4MPa high pressure impact until the melting chamber is filled with droplets and mist, and 5-10°C low-temperature hydrogen is blown in to cool it down, and solder powder is obtained by ball milling; S2, adding nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester, stirring evenly, ultrasonically treating for 10-30 minutes, and then adding Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and ultrasonically treating for 10-30 minutes to obtain a coating material; S3. Mix the solder powder and the 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 at 110-120°C for 10-30 minutes under vacuum, treat with a pulse magnetic field for 5-10 minutes with a pulse intensity of 0.1-0.2T and a pulse frequency of 50-100Hz, and cool to room temperature.

[0016] Preferably, in S1, the concentration of the metal dust gas is 100-150 mg / L.

[0017] Preferably, in S2, the frequency of ultrasonic treatment after adding to hydrogenated rosin pentaerythritol ester is 35-45 kHz, and the frequency of ultrasonic treatment after adding potassium nitrate is 50-60 kHz.

[0018] Preferably, in S3, the frequency of the low-frequency ultrasonic treatment is 20-30kHz, and the ultrasonic power is 200-300W.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts tin, nickel, gallium, copper, bismuth and silver to prepare solder powder, wherein in the pretreatment stage, the premixing of gallium and nickel forms a highly active interface, reduces the activation energy of subsequent tin-nickel alloying, and realizes the uniform distribution of tin-nickel intermetallic compounds through atomization-grading heat treatment process; the excessive growth of intermetallic compounds is suppressed through atomization-grading heat treatment process, and copper, bismuth and silver are distributed in the alloy matrix in a metastable form, which synergistically improves the fatigue resistance of solder joints. Pulsed magnetic field treatment optimizes the physical arrangement of solder powder particles through magnetocaloric effect, reduces internal stress concentration, and combines the magnetic response characteristics of nickel element to improve the creep resistance of solder joints, effectively improving the strength of solder joints while reducing the melting point.

[0020] The present invention adopts solder powder and coating material compound, which can effectively enhance welding strength and reduce welding line defect rate. Nanocellulose aerogel is used as a molecular carrier, 2-phenylimidazoline is loaded on it, and then the solder powder is coated to effectively form a slow-release active system. The porous structure of the nanocellulose aerogel gradually releases 2-phenylimidazoline through capillary action in the preheating stage. The aerogel skeleton collapses in the high temperature stage to accelerate the diffusion of active substances, solving the problem of premature consumption of activators in traditional systems. Low-frequency ultrasonic treatment can break up nanocellulose agglomerates, and the combined effect effectively achieves the effect of low residue.

[0021] The present 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 solder wire defect rate. It is particularly suitable for high-end electronic packaging fields such as new energy vehicle power modules. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1It is a comparison chart of the melting points of the solder pastes obtained in Example 5 and Comparative Examples 1-3.

[0023] Figure 2 The figure is a comparison chart of the surface insulation resistance and organic residue rate of solder wires soldered by using the solder pastes obtained in Example 5 and Comparative Examples 1-3.

[0024] Figure 3 The figure is a comparison chart of the tensile strength after soldering of the solder pastes obtained by Example 5 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0025] The present invention will be further explained below in conjunction with specific embodiments.

[0026] The following nanocellulose aerogel was purchased from Xi'an Mouyue Biotechnology Co., Ltd., and its specific surface area was 855m² / g.

[0027] Embodiment 1: A low-residue lead-free solder paste, whose raw materials include: tin powder 100g, nickel powder 1g, gallium powder 0.1g, bismuth powder 1g, copper powder 0.1g, silver powder 0.01g, nanocellulose aerogel 0.01g, 2-phenylimidazoline 1g, cerium ammonium nitrate 0.01g, Gemini quaternary ammonium salt 0.01g, acrylic anhydride 0.01g, potassium nitrate 0.01g, hydrogenated rosin pentaerythritol ester 1g, and flux 1g.

[0028] The soldering flux is composed of sodium succinate, sodium malate, polyoxypropylene glycerol ether, ricinoleyl 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.

[0029] The method for preparing the low-residue lead-free solder paste comprises the following steps: S1. In high-purity hydrogen, wherein the purity of hydrogen is greater than 99.9%, tin powder and nickel powder are mixed and sent into a melting chamber, treated at a temperature of 300°C for 15 minutes, the temperature is reduced to below 200°C, gallium powder is added, and the pressurized environment is treated for 3 minutes to obtain a pretreated tin liquid; Copper powder, bismuth powder, silver powder and hydrogen are mixed to form 100mg / L metal dust gas, and the molten tin is pre-treated at 180℃ and 2MPa high pressure impact until the melting chamber is full of droplets and mist, and 5℃ low-temperature hydrogen is blown in to cool it down, and the solder powder with a particle size of 5-10μm is obtained by ball milling and sieving; S2, adding nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester, stirring evenly, ultrasonically treating for 10 min at an ultrasonic frequency of 35 kHz, and then adding Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate for ultrasonic treatment for 10 min at an ultrasonic frequency of 50 kHz to obtain a coating material; S3. Mix the solder powder and the coating material, and treat them with low-frequency ultrasound for 10 minutes at a frequency of 20 kHz and a power of 200 W to obtain pre-wrapped solder powder. Add flux and mix well. Stir for 10 minutes at 110°C in a vacuum state at a speed of 200 r / min. Treat with a pulsed magnetic field for 5 minutes at a pulse intensity of 0.1 T and a pulse frequency of 50 Hz, and then cool to room temperature.

[0030] Embodiment 2: A low-residue lead-free solder paste, whose raw materials include: tin powder 100g, nickel powder 2g, gallium powder 0.5g, bismuth powder 2g, copper powder 1g, silver powder 0.1g, nanocellulose aerogel 0.1g, 2-phenylimidazoline 2g, cerium ammonium nitrate 0.1g, Gemini quaternary ammonium salt 0.1g, acrylic anhydride 0.1g, potassium nitrate 0.1g, hydrogenated rosin pentaerythritol ester 5g, and flux 10g.

[0031] The soldering flux is composed of potassium succinate, potassium malate, polyoxypropylene glycerol ether, ricinoleyl 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.

[0032] The method for preparing the low-residue lead-free solder paste comprises the following steps: S1. In high-purity hydrogen, wherein the purity of hydrogen is greater than 99.9%, tin powder and nickel powder are mixed and sent into a melting chamber, treated at a temperature of 350°C for 20 minutes, the temperature is reduced to below 200°C, gallium powder is added, and the pressurized environment is treated for 6 minutes to obtain a pretreated tin liquid; Copper powder, bismuth powder, silver powder and hydrogen are mixed to form 150mg / L metal dust gas, and the molten tin is pre-treated at 200℃ and 4MPa high pressure impact until the melting chamber is full of droplets and mist, and 10℃ low-temperature hydrogen is blown in to cool it down, and the solder powder with a particle size of 5-10μm is obtained by ball milling and sieving; S2, adding nanocellulose aerogel, 2-phenylimidazoline, and ammonium cerium nitrate to hydrogenated rosin pentaerythritol ester, stirring evenly, ultrasonically treating for 30 minutes at an ultrasonic frequency of 45 kHz, and then adding Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate for ultrasonic treatment for 30 minutes at an ultrasonic frequency of 60 kHz to obtain a coating material; S3. Mix the solder powder and the coating material, and treat them with low-frequency ultrasound for 20 minutes at a frequency of 30 kHz and a power of 300 W to obtain pre-wrapped solder powder. Add flux and mix them evenly. Stir them at 120°C for 30 minutes under vacuum at a speed of 300 r / min. Treat them with a pulsed magnetic field for 10 minutes at a pulse intensity of 0.2 T and a pulse frequency of 100 Hz, and then cool them to room temperature.

[0033] Example 3: A low-residue lead-free solder paste, whose raw materials 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.

[0034] The soldering flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleyl 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.

[0035] The method for preparing the low-residue lead-free solder paste comprises the following steps: S1. In high-purity hydrogen, wherein the purity of hydrogen is greater than 99.9%, tin powder and nickel powder are mixed and sent into a melting chamber, treated at a temperature of 340°C for 17 minutes, the temperature is reduced to below 200°C, gallium powder is added, and the pressurized environment is treated for 4 minutes to obtain a pretreated tin liquid; Copper powder, bismuth powder, silver powder and hydrogen are mixed to form 130mg / L metal dust gas, and the molten tin is pre-treated at 185℃ and 3.5MPa high pressure impact until the melting chamber is full of droplets and mist, and 6℃ low-temperature hydrogen is blown in to cool it down, and the solder powder with a particle size of 5-10μm is obtained by ball milling and sieving; S2, adding nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester, stirring evenly, ultrasonically treating for 25 minutes at an ultrasonic frequency of 36 kHz, and then adding Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate for ultrasonic treatment for 25 minutes at an ultrasonic frequency of 51 kHz to obtain a coating material; S3. Mix the solder powder and the coating material, and treat them with low-frequency ultrasound for 18 minutes. The ultrasonic frequency is 21kHz and the ultrasonic power is 280W to obtain pre-wrapped solder powder. Then add flux and mix them evenly. Stir them at 112℃ for 25 minutes under vacuum and the stirring speed is 220r / min. Treat them with a pulse magnetic field for 9 minutes with a pulse intensity of 0.12T and a pulse frequency of 90Hz, and then cool them to room temperature.

[0036] Example 4: A low-residue lead-free solder paste, whose raw materials 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.

[0037] The soldering flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleyl 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.

[0038] The method for preparing the low-residue lead-free solder paste comprises the following steps: S1. In high-purity hydrogen, wherein the purity of hydrogen is greater than 99.9%, tin powder and nickel powder are mixed and sent into a melting chamber, treated at a temperature of 320°C for 19 minutes, the temperature is reduced to below 200°C, gallium powder is added, and the pressurized environment is treated for 5 minutes to obtain a pretreated tin liquid; Copper powder, bismuth powder, silver powder and hydrogen are mixed to form 110mg / L metal dust gas, and the molten tin is pre-treated at 195°C and 2.5MPa high pressure impact until the melting chamber is full of droplets and mist, and 8°C low-temperature hydrogen is blown in to cool it down, and the solder powder with a particle size of 5-10μm is obtained by ball milling and sieving; S2, adding nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester, stirring evenly, ultrasonically treating for 15 minutes at an ultrasonic frequency of 42kHz, and then adding Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate for ultrasonic treatment for 15 minutes at an ultrasonic frequency of 57kHz to obtain a coating material; S3. Mix the solder powder and the coating material, and treat them with low-frequency ultrasound for 12 minutes at a frequency of 27kHz and a power of 220W to obtain pre-wrapped solder powder. Add flux and mix them evenly. Stir them at 118°C for 15 minutes under vacuum at a speed of 280r / min. Treat them with a pulsed magnetic field for 7 minutes at a pulse intensity of 0.18T and a pulse frequency of 60Hz, and then cool them to room temperature.

[0039] Example 5: A low-residue lead-free solder paste, whose raw materials 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.

[0040] The soldering flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleyl 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.

[0041] The method for preparing the low-residue lead-free solder paste comprises the following steps: S1. In high-purity hydrogen, wherein the purity of hydrogen is greater than 99.9%, tin powder and nickel powder are mixed and sent into a melting chamber, treated at a temperature of 330°C for 18 minutes, the temperature is reduced to below 200°C, gallium powder is added, and the pressurized environment is treated for 3 minutes to obtain a pretreated tin liquid; Copper powder, bismuth powder, silver powder and hydrogen are mixed to form 120mg / L metal dust gas, and the molten tin is pre-treated at 190℃ and 3MPa high pressure impact until the melting chamber is full of droplets and mist, and 7℃ low-temperature hydrogen is blown in to cool it down, and the solder powder with a particle size of 5-10μm is obtained by ball milling and sieving; S2, adding nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stirring evenly, ultrasonically treating for 18 minutes at an ultrasonic frequency of 39 kHz, and then adding Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and ultrasonically treating for 20 minutes at an ultrasonic frequency of 54 kHz to obtain a coating material; S3. Mix the solder powder and the coating material, and treat them with low-frequency ultrasound for 15 minutes at a frequency of 24 kHz and a power of 250 W to obtain pre-wrapped solder powder. Add flux and mix them evenly. Stir them at 115°C for 20 minutes under vacuum at a speed of 250 r / min. Treat them with a pulsed magnetic field for 8 minutes at a pulse intensity of 0.15 T and a pulse frequency of 75 Hz, and then cool them to room temperature.

[0042] Comparative Example 1 A low-residue lead-free solder paste, whose raw materials include: 100g of tin powder, 1.5g of nickel powder, 1.5g of bismuth powder, 0.5g of copper powder, 0.05g of silver powder, 0.05g of nanocellulose aerogel, 1.5g of 2-phenylimidazoline, 0.05g of cerium ammonium nitrate, 0.05g of Gemini quaternary ammonium salt, 0.05g of acrylic anhydride, 0.05g of potassium nitrate, 3.3g of hydrogenated rosin pentaerythritol ester, and 5g of flux.

[0043] The soldering flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleyl 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.

[0044] The method for preparing the low-residue lead-free solder paste comprises the following steps: S1. In high-purity hydrogen, wherein the purity of hydrogen is greater than 99.9%, tin powder and nickel powder are mixed and sent into a melting chamber, and treated at a temperature of 330° C. for 18 minutes to obtain a pretreated tin liquid; Copper powder, bismuth powder, silver powder and hydrogen are mixed to form 120mg / L metal dust gas, and the molten tin is pre-treated at 190℃ and 3MPa high pressure impact until the melting chamber is full of droplets and mist, and 7℃ low-temperature hydrogen is blown in to cool it down, and the solder powder with a particle size of 5-10μm is obtained by ball milling and sieving; S2, adding nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stirring evenly, ultrasonically treating for 18 minutes at an ultrasonic frequency of 39 kHz, and then adding Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and ultrasonically treating for 20 minutes at an ultrasonic frequency of 54 kHz to obtain a coating material; S3. Mix the solder powder and the coating material, and treat them with low-frequency ultrasound for 15 minutes at a frequency of 24 kHz and a power of 250 W to obtain pre-wrapped solder powder. Add flux and mix them evenly. Stir them at 115°C for 20 minutes under vacuum at a speed of 250 r / min. Treat them with a pulsed magnetic field for 8 minutes at a pulse intensity of 0.15 T and a pulse frequency of 75 Hz, and then cool them to room temperature.

[0045] Comparative Example 2 A low-residue lead-free solder paste, whose raw materials include: 100g of tin powder, 1.5g of nickel powder, 0.3g of gallium powder, 0.05g of nanocellulose aerogel, 1.5g of 2-phenylimidazoline, 0.05g of cerium ammonium nitrate, 0.05g of Gemini quaternary ammonium salt, 0.05g of acrylic anhydride, 0.05g of potassium nitrate, 5.05g of hydrogenated rosin pentaerythritol ester, and 5g of flux.

[0046] The soldering flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleyl 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.

[0047] The method for preparing the low-residue lead-free solder paste comprises the following steps: S1. In high-purity hydrogen, wherein the purity of hydrogen is greater than 99.9%, tin powder and nickel powder are mixed and sent into a melting chamber, treated at a temperature of 330°C for 18 minutes, the temperature is reduced to below 200°C, gallium powder is added, and the pressurized environment is treated for 3 minutes to obtain a pretreated tin liquid; The temperature was lowered by blowing in 7°C low-temperature hydrogen, and the solder powder with a particle size of 5-10μm was obtained by ball milling and sieving; S2, adding nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester and stirring evenly, ultrasonically treating for 18 minutes at an ultrasonic frequency of 39 kHz, and then adding Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and ultrasonically treating for 20 minutes at an ultrasonic frequency of 54 kHz to obtain a coating material; S3. Mix the solder powder and the coating material, and treat them with low-frequency ultrasound for 15 minutes at a frequency of 24 kHz and a power of 250 W to obtain pre-wrapped solder powder. Add flux and mix them evenly. Stir them at 115°C for 20 minutes under vacuum at a speed of 250 r / min. Treat them with a pulsed magnetic field for 8 minutes at a pulse intensity of 0.15 T and a pulse frequency of 75 Hz, and then cool them to room temperature.

[0048] Comparative Example 3 A low-residue lead-free solder paste, whose raw materials include: 100g of tin powder, 1.5g of nickel powder, 0.3g of gallium powder, 1.5g of bismuth powder, 0.5g of copper powder, 0.05g of silver powder, 4.75g of hydrogenated rosin pentaerythritol ester, and 5g of flux.

[0049] The soldering flux is composed of calcium succinate, calcium malate, polyoxypropylene glycerol ether, ricinoleyl 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.

[0050] The method for preparing the low-residue lead-free solder paste comprises the following steps: S1. In high-purity hydrogen, wherein the purity of hydrogen is greater than 99.9%, tin powder and nickel powder are mixed and sent into a melting chamber, treated at a temperature of 330°C for 18 minutes, the temperature is reduced to below 200°C, gallium powder is added, and the pressurized environment is treated for 3 minutes to obtain a pretreated tin liquid; Copper powder, bismuth powder, silver powder and hydrogen are mixed to form 120mg / L metal dust gas, and the molten tin is pre-treated at 190℃ and 3MPa high pressure impact until the melting chamber is full of droplets and mist, and 7℃ low-temperature hydrogen is blown in to cool it down, and the solder powder with a particle size of 5-10μm is obtained by ball milling and sieving; S2. Add flux to solder powder and mix evenly. Stir at 115°C for 20 minutes under vacuum, with a stirring speed of 250 r / min. Treat with pulse magnetic field for 8 minutes with a pulse intensity of 0.15 T and a pulse frequency of 75 Hz, and then cool to room temperature.

[0051] The solder pastes obtained in Example 5 and Comparative Examples 1-3 were tested with reference to SJ / T 11186-2019 "General Specification for Solder Paste". The viscosities of the four were all within the range of 180-185 Pa·s, the collapse was 0.20 mm, the solder bead level was level 1, and the wettability level was level 1, indicating that the solder pastes obtained in Example 5 and Comparative Examples 1-3 met the solder paste standards.

[0052] The melting points of the solder pastes obtained in Example 5 and Comparative Examples 1-3 were measured, and the results are as follows: Figure 1 As shown, the solder paste obtained in Example 5 has the lowest melting point, which is better than that in Comparative Examples 1-3 (P < 0.05).

[0053] The solder paste obtained in Example 5 and Comparative Examples 1-3 was smoothed and then placed in a humid environment (30°C×100%RH). When more than 10% of the solder paste surface had black spots, the oxidation time was recorded. If more than 90% of the solder paste surface did not have black spots after 48 hours, the oxidation test was terminated. The solder pastes obtained in Example 5 and Comparative Examples 1-2 did not have more than 10% of the surface black spots after more than 48 hours, while the oxidation time of the solder paste obtained in Comparative Example 3 was only 4.7 hours.

[0054] A vertical laser reflow oven was used, a PCB aluminum substrate was set, the laser zone temperature was controlled at 260±10°C, the solder paste obtained in Example 5 and Comparative Examples 1-3 was used for pre-coating, followed by manual patching and reflow soldering, and 1mm×5mm×50mm solder wires were soldered; and the surface insulation resistance of the solder wires was tested according to the IPC-TM-650 standard. After the above groups of soldering were completed, they were cleaned and dried, the total weight of the solder wires was tested, and the organic residue rate was calculated.

[0055] Organic residue rate = (total weight of solder wire - metal mass in solder paste) ÷ (mass of solder paste - metal mass in solder paste) × 100% like Figure 2 As shown, the surface insulation resistance of the solder wire welded by the solder paste obtained in Example 5 is the highest, which is better than that of Comparative Examples 1-3 (P < 0.05); and the organic residue rate of the solder paste welded by Example 5 is the smallest, but there is no significant difference with Comparative Examples 1-2.

[0056] Cut equal length (1mm, area is about 5mm 2 ) are placed in an optical microscope matrix, observed and marked with red circles to mark the approximate range of defects, and the number of circles and the sum of the areas of each circle are calculated. The sum of the areas of each circle is divided by 5 to obtain the defect rate. The defect rate of solder paste soldering wires obtained by Example 5 or Comparative Examples 1-2 is less than 0.2%, while the defect rate of solder paste soldering wires obtained by Comparative Example 3 is 0.6%.

[0057] The tensile strength of the above solder joints is measured. Figure 3 As shown, the solder paste obtained by Example 5 has the highest tensile strength after soldering, which is better than that of Comparative Examples 1-3 (P < 0.05).

[0058] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A low-residue lead-free solder paste, characterized in that: The raw materials include, by mass, 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 flux.

2. The low-residue lead-free solder paste according to claim 1, characterized in that: The specific surface area of ​​nanocellulose aerogel is >600m² / g.

3. The low-residue lead-free solder paste according to claim 1, characterized in that: The soldering flux comprises, by mass, 0.1-1 part of an activator, 0.1-0.2 part of a defoamer, 1-2 parts of a surfactant, 1-2 parts of a corrosion inhibitor, 10-20 parts of hydrogenated rosin, and 20-50 parts of a solvent.

4. The low-residue lead-free solder paste according to claim 3, characterized in that: Activators include: Sodium succinate, sodium malate.

5. The low-residue lead-free solder paste according to claim 3, characterized in that: The defoaming agent is polyoxypropylene glyceryl ether (molecular weight is less than 2000); the surfactant is ricinoleyl diethanolamine; and the corrosion inhibitor is an imidazoline corrosion inhibitor, specifically imidazoline quaternary ammonium salt MZJ-1.

6. The low-residue lead-free solder paste according to claim 3, characterized in that: The solvent included diethylene glycol butyl ether.

7. A method for preparing the low-residue lead-free solder paste according to any one of claims 1 to 6, characterized in that: The steps include: S1. In high-purity hydrogen, tin powder and nickel powder are mixed, treated at 300-350°C for 15-20min, the temperature is reduced to below 200°C, gallium powder is added, and the pressurized environment is treated for 3-6min to obtain a pre-treated tin liquid; copper powder, bismuth powder, silver powder and hydrogen are mixed to form a metal dust gas, and the tin liquid is pre-treated at 180-200°C and 2-4MPa high pressure impact until the melting chamber is filled with droplets and mist, and 5-10°C low-temperature hydrogen is blown in to cool it down, and solder powder is obtained by ball milling; S2, adding nanocellulose aerogel, 2-phenylimidazoline, and cerium ammonium nitrate to hydrogenated rosin pentaerythritol ester, stirring evenly, ultrasonically treating for 10-30 minutes, and then adding Gemini quaternary ammonium salt, acrylic anhydride, and potassium nitrate and ultrasonically treating for 10-30 minutes to obtain a coating material; S3. Mix the solder powder and the 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 at 110-120°C for 10-30 minutes under vacuum, treat with a pulse magnetic field for 5-10 minutes with a pulse intensity of 0.1-0.2T and a pulse frequency of 50-100Hz, and cool to room temperature.

8. The method for preparing the low-residue lead-free solder paste according to claim 7, characterized in that: In S1, the concentration of metal dust gas is 100-150 mg / L.

9. The method for preparing the low-residue lead-free solder paste according to claim 7, characterized in that: In S2, the ultrasonic treatment frequency after adding to hydrogenated rosin pentaerythritol ester is 35-45 kHz, while the ultrasonic treatment frequency after adding potassium nitrate is 50-60 kHz.

10. The method for preparing the low-residue lead-free solder paste according to claim 7, characterized in that: In S3, the frequency of low-frequency ultrasonic treatment is 20-30kHz, and the ultrasonic power is 200-300W.

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