High-stability lead-free solder paste without inner cover and preparation method thereof

Abstract

The application relates to the technical field of welding materials, in particular to a high-stability lead-free soldering paste without an inner cover and a preparation method thereof, the lead-free soldering paste contains the following components in parts by weight: 10-14 parts of a soldering paste, 86-90 parts of lead-free soldering powder; the lead-free soldering powder is selected from one or more of Sn99Ag0.3Cu0.7, Sn98.5Ag1Cu0.5 and Sn96.5Ag3Cu0.5; the soldering paste contains the following components in parts by weight: 30-50 parts of rosin, 4-10 parts of resin, 30-50 parts of a solvent, 3-15 parts of an additive, 4-8 parts of a thixotropic agent, 5-10 parts of an organic acid, 0.5-3 parts of a halogen compound and 0.5-2 parts of an antioxidant. In the application, the prepared low-water absorption additive is introduced into the lead-free soldering paste to obtain a high-stability, low-water absorption soldering paste, the soldering paste can be stored for a long time without covering the inner cover, the material for producing the inner cover is saved, the packaging process is simplified, the storage time is prolonged, small and micro enterprises can concentrate on furnace welding, the welding time is reduced, and the energy consumption is reduced.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, specifically to a highly stable lead-free solder paste that does not require an inner cap and its preparation method. Background Technology

[0002] Solder paste, a new type of soldering material developed alongside surface mount technology (SMT), is an extremely important auxiliary material in modern electronic product manufacturing. Its quality directly affects the quality of SMT components, thus receiving widespread attention in the electronics industry. Currently, the electronics industry still widely uses traditional SnPb-based lead-containing solders and solder powders, and the technology in this environment is quite mature. Among them, tin-silver-copper lead-free solders have properties close to tin-lead solders and have the potential to replace them. Research and production of tin-silver-copper lead-free solders are undoubtedly a hot topic in solder and solder powder development.

[0003] For example, the invention patent with announcement number CN102198567A discloses a Sn-Zn-based lead-free solder paste. This Sn-Zn-based lead-free solder paste includes the following components and contents (by weight percentage): 80-91% Sn-Zn lead-free solder powder; 9-20% zinc-based flux. In this invention, DD, as a metal activity inhibitor, significantly improves the solderability (brazing performance) of the solder paste; simultaneously, the shelf life of the tin-zinc solder paste is also greatly extended. However, this lead-free solder paste easily absorbs moisture from the air, therefore the packaging must be airtight, with both inner and outer caps sealed. Furthermore, due to its poor stability after printing or surface mounting, it cannot be stored for long periods and must be quickly reflowed. This is difficult for some small and micro-enterprises because of their low production capacity. To reduce reflow soldering time, they often accumulate a certain amount before using reflow soldering, which can take anywhere from 4 hours to 2 days or even longer, thus increasing their economic costs and hindering widespread adoption. Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this invention is to provide a highly stable lead-free solder paste that does not require an inner cover and a method for preparing the same.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A highly stable lead-free solder paste that does not require an inner cap, the lead-free solder paste comprising the following components by weight: 10-14 parts flux, 3-8 parts low water absorption additive, and 86-90 parts lead-free solder powder.

[0007] The lead-free solder powder is selected from one or more of Sn99Ag0.3Cu0.7, Sn98.5Ag1Cu0.5, and Sn96.5Ag3Cu0.5;

[0008] The flux paste contains the following components by weight: 30-50 parts rosin, 4-10 parts resin, 30-50 parts solvent, 3-15 parts additives, 4-8 parts thixotropic agent, 5-10 parts organic acid, 0.5-3 parts halogen compound, and 0.5-2 parts antioxidant.

[0009] As a further preferred embodiment of the present invention, the rosin is composed of KE-604 rosin, AX-E rosin and CH-60 rosin in a mass ratio of (3-5):(3-5):1;

[0010] The resin is a hydrogenated petroleum resin.

[0011] As a further preferred embodiment of the present invention, the solvent is composed of diethylene glycol dibutyl ether, tripropylene glycol butyl ether, and diethylene glycol hexyl ether in a mass ratio of (1.5-2.0):(1.5-2.0):1;

[0012] The additive is composed of polyisobutylene 300R and dimer acid in a mass ratio of (2-3):1;

[0013] The thixotropic agent consists of equal masses of polyamide wax and ethylene bis-12-hydroxystearamide.

[0014] As a further preferred embodiment of the present invention, the organic acid is composed of adipic acid, stearic acid, succinic acid, tetracosic acid, and dodecanoic acid in a mass ratio of 1:(2-3):(2-3):1:(2-3);

[0015] The halogen compound is composed of dibromobutenediol and diphenylguanidine hydrobromide in a mass ratio of 1:(2-5);

[0016] The antioxidant is composed of equal masses of antioxidant 245 and antioxidant 1010.

[0017] As a further preferred embodiment of the present invention, the method for preparing the low water absorption additive is as follows:

[0018] 1) Add carbon nanotubes to an acidic solution composed of concentrated sulfuric acid and concentrated nitric acid, and react at 70-75℃ for 3-5 hours. After the reaction is complete, dilute the solution thoroughly with deionized water, centrifuge, filter and wash to make the pH of the solution neutral, and prepare a carbon nanotube dispersion.

[0019] 2) Soak activated carbon in hydrochloric acid solution for 10-15 hours, wash it repeatedly with deionized water and dry it to obtain pretreated activated carbon for later use. Then dissolve divinylbenzene in tetrahydrofuran, add azobisisobutyronitrile, sonicate for 1-2 hours and transfer it to a high-pressure reactor. Continue to react at 110-115℃ for 24-30 hours. After the reaction is completed, cool to room temperature and evaporate the residual tetrahydrofuran to obtain a hydrophobic modifier for later use.

[0020] 3) Add the hydrophobic modifier to anhydrous ethanol and dissolve it completely to obtain a suspension. Then add the pretreated activated carbon to the suspension and impregnate it at room temperature for 6-10 hours. After impregnation, centrifuge and filter the carbon, then transfer it to a constant temperature oven and dry it at 105-110℃ for 12-15 hours to obtain the modified activated carbon.

[0021] 4) Add the modified activated carbon to the carbon nanotube dispersion, ultrasonically disperse for 1-2 hours, centrifuge and dry, repeat the operation 3-5 times, then add it to the polyethyleneimine ethanol solution, soak for 10-30 minutes, centrifuge and filter again, dry at 60-70℃ for 30-50 minutes, then add it to polydimethylsiloxane, soak again for 30-50 minutes, centrifuge and filter, and dry to obtain the low water absorption additive.

[0022] As a further preferred embodiment of the present invention, in step 1), the ratio of carbon nanotubes, concentrated sulfuric acid, and concentrated nitric acid is (1-3) g: (12-18) mL: (4-5) mL;

[0023] The concentration of the concentrated sulfuric acid is 70-75 wt%.

[0024] The concentration of the concentrated nitric acid is 68-72 wt%.

[0025] The concentration of the carbon nanotube dispersion is 5-15 mg / mL.

[0026] As a further preferred embodiment of the present invention, in step 2), the concentration of the hydrochloric acid solution is 0.1-0.3 mol / L;

[0027] The ratio of divinylbenzene, tetrahydrofuran, and azobisisobutyronitrile is (10-20) g: (10-20) mL: (0.1-0.2) g.

[0028] As a further preferred embodiment of the present invention, in step 3), the ratio of the amount of hydrophobic modifier, anhydrous ethanol and pretreated activated carbon is (1-3)g: (60-100)mL: (8-15)g.

[0029] As a further preferred embodiment of the present invention, in step 4), the ratio of the amount of modified activated carbon, carbon nanotube dispersion, polyethyleneimine ethanol solution and polydimethylsiloxane is (5-10) g: (300-500) mL: (80-120) mL: (60-80) mL;

[0030] The concentration of the polyethyleneimine ethanol solution is 1-3 wt%.

[0031] A method for preparing a highly stable, capless lead-free solder paste includes the following steps:

[0032] 1) Weigh each component according to the formula. Heat the rosin, resin, solvent, additives and thixotropic agent together to 160-165℃. After the system is dissolved and mixed evenly, reduce the temperature to 140-143℃ and add organic acid, halogen compound and antioxidant. After it is completely dissolved, continue to stir for 2-5 minutes to mix evenly. Transfer the evenly mixed flux to a sealed beaker and cool it in ice water for 1-3 hours. Take it out and return it to room temperature. Grind it 1-2 times to obtain the flux.

[0033] 2) Pour the above flux into the tank and start pre-stirring at a speed of 20-26 r / min for 3-8 minutes. Then add the low water absorption additive and lead-free solder powder into the tank, set the speed to 10-18 r / min, stir for 10-15 minutes, and then evacuate to a vacuum state. Stir at a speed of 6-10 r / min for 1-5 minutes to uniformly evacuate the vacuum to 0.07-0.09 MPa. Close the vacuum valve and stop stirring to obtain lead-free solder paste.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] In this invention, activated carbon is acidified to remove impurities from the pores and increase its porosity. Polyvinylbenzene (PVB) is used as a hydrophobic modifier, and a simple liquid-phase impregnation method is employed to modify the activated carbon. PVB porous nanoparticles can penetrate the pore structure of the activated carbon, improving its porous structure properties, enhancing specific surface area and micropore volume, thereby effectively increasing the loading capacity of carbon nanotubes during subsequent impregnation. Furthermore, after PVB modification, the activated carbon exhibits certain hydrophobic properties, effectively preventing water intrusion and achieving a low water absorption effect. Simultaneously, the carbon nanotubes are immersed in an acid solution composed of concentrated sulfuric acid and concentrated nitric acid... The activated carbon was modified by carboxylation, and then added to a carbon nanotube dispersion. Under ultrasonication, the carboxylated carbon nanotubes were loaded onto the modified activated carbon. Polyethyleneimine was then loaded onto the modified activated carbon through hydrogen bonding between the amino groups of polyethyleneimine and the carboxyl groups of the carboxylated carbon nanotubes, forming a strong cross-linked structure. Finally, polydimethylsiloxane was used to further modify its hydrophobic effect. When applied to lead-free solder paste, it can form a multi-layered hydrophobic layer, effectively preventing moisture from the outside air from penetrating into the lead-free solder paste, thereby reducing the water absorption rate and improving the stability of the lead-free solder paste.

[0036] In this invention, by introducing the prepared low-water-absorption additive into lead-free solder paste, a highly stable, low-water-absorption flux paste is obtained. It can be stored for a long time without an inner cap, which saves materials for producing the inner cap, simplifies the packaging process, and extends the storage time. This allows small and micro enterprises to perform centralized reflow soldering, reducing soldering time and energy consumption. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In this embodiment of the invention, the rosin is composed of KE-604 rosin, AX-E rosin, and CH-60 rosin in a mass ratio of 3:3:1; the resin is hydrogenated petroleum resin; the solvent is composed of diethylene glycol dibutyl ether, tripropylene glycol butyl ether, and diethylene glycol hexyl ether in a mass ratio of 1.5:2.0:1; the additive is composed of polyisobutylene 300R and dimer acid in a mass ratio of 2:1; the thixotropic agent is composed of equal masses of polyamide wax and ethylene bis-12-hydroxystearamide; the organic acid is composed of adipic acid, octadecanoic acid, succinic acid, teicosuccinic acid, and dodecanoic acid in a mass ratio of 1:3:3:1:3; the halogen compound is composed of dibromobutenediol and diphenylguanidine hydrobromide in a mass ratio of 1:2; and the antioxidant is composed of equal masses of antioxidant 245 and antioxidant 1010.

[0039] Example 1: A highly stable lead-free solder paste that does not require an inner cap, the lead-free solder paste comprising the following components by weight: 10 parts flux, 3 parts low water absorption additive, and 86 parts lead-free solder powder.

[0040] The lead-free solder powder is selected from Sn99Ag0.3Cu0.7;

[0041] The flux contains the following components by weight: 30 parts rosin, 4 parts resin, 30 parts solvent, 3 parts additives, 4 parts thixotropic agent, 5 parts organic acid, 0.5 parts halogen compound, and 0.5 parts antioxidant.

[0042] The preparation method of this lead-free solder paste specifically includes the following steps:

[0043] 1) Weigh each component according to the formula, heat the rosin, resin, solvent, additives and thixotropic agent together to 160℃, and after the system is dissolved and mixed evenly, the temperature is reduced to 140℃ and organic acid, halogen compound and antioxidant are added. After it is completely dissolved, continue to stir for 2 minutes to make it evenly mixed. Transfer the evenly mixed flux to a sealed beaker, put it in ice water to cool for 1 hour, take it out and return it to room temperature, grind it once to obtain the flux.

[0044] 2) Pour the above flux into the tank and start pre-stirring at 20 r / min for 3 minutes. Then add the low water absorption additive and lead-free solder powder into the tank, set the speed to 10 r / min, stir for 10 minutes, and then evacuate to enter the vacuum state. Stir at 6 r / min and uniformly evacuate the vacuum to 0.07 MPa within 1 minute. Close the vacuum valve and stop stirring to obtain lead-free solder paste.

[0045] The preparation method of the low water absorption additive is as follows:

[0046] 1) Add 1g of carbon nanotubes to an acid solution consisting of 12mL of 70wt% concentrated sulfuric acid and 4mL of 68wt% concentrated nitric acid. React at 70℃ for 3h. After the reaction is complete, dilute the solution thoroughly with deionized water. Centrifuge, filter and wash to make the pH of the solution neutral, and prepare a carbon nanotube dispersion with a concentration of 5mg / mL.

[0047] 2) Soak activated carbon in 0.1 mol / L hydrochloric acid solution for 10 h, wash repeatedly with deionized water and dry to obtain pretreated activated carbon for later use. Then dissolve 10 g divinylbenzene in 10 mL tetrahydrofuran, add 0.1 g azobisisobutyronitrile, and sonicate at 100 W for 1 h. Then transfer to a high-pressure reactor and react at 110 °C for 24 h. After the reaction is completed, cool to room temperature and evaporate the residual tetrahydrofuran to obtain hydrophobic modifier for later use.

[0048] 3) Add 1g of hydrophobic modifier to 60mL of anhydrous ethanol and dissolve it completely to obtain a suspension. Then add 8g of pretreated activated carbon to the suspension and impregnate it at room temperature for 6h. After impregnation, centrifuge and filter the mixture, then transfer it to a constant temperature oven and dry it at 105℃ for 12h to obtain modified activated carbon.

[0049] 4) Add 5g of modified activated carbon to 300mL of carbon nanotube dispersion, ultrasonically disperse at 100W for 1h, centrifuge and dry, repeat the operation 3 times, then add to 80mL of 1wt% polyethyleneimine ethanol solution, soak for 10min, centrifuge and filter again, dry at 60℃ for 30min, then add to 60mL of polydimethylsiloxane, soak for 30min again, centrifuge and filter, and dry to obtain the low water absorption additive.

[0050] Example 2: A highly stable lead-free solder paste that does not require an inner cap, the lead-free solder paste comprising the following components by weight: 12 parts flux, 5 parts low water absorption additive, and 88 parts lead-free solder powder.

[0051] The lead-free solder powder is selected from Sn99Ag0.3Cu0.7;

[0052] The flux contains the following components by weight: 40 parts rosin, 7 parts resin, 40 parts solvent, 10 parts additives, 6 parts thixotropic agent, 7 parts organic acid, 2 parts halogen compound, and 1.5 parts antioxidant.

[0053] The preparation method of this lead-free solder paste specifically includes the following steps:

[0054] 1) Weigh each component according to the formula, heat the rosin, resin, solvent, additives and thixotropic agent together to 163℃, and after the system is dissolved and mixed evenly, the temperature is reduced to 142℃ and organic acid, halogen compound and antioxidant are added. After it is completely dissolved, continue to stir for 3 minutes to make it evenly mixed. Transfer the evenly mixed flux to a sealed beaker, put it in ice water to cool for 2 hours, take it out and return it to room temperature, grind it twice to obtain flux.

[0055] 2) Pour the above flux into the tank and start pre-stirring at 25 r / min for 5 minutes. Then add the low water absorption additive and lead-free solder powder into the tank, set the speed to 15 r / min, stir for 13 minutes, and then draw a vacuum to enter the vacuum state. Stir at 8 r / min and draw the vacuum to 0.08 MPa at a constant speed within 3 minutes. Close the vacuum valve and stop stirring to obtain lead-free solder paste.

[0056] The preparation method of the low water absorption additive is as follows:

[0057] 1) Add 2g of carbon nanotubes to an acid solution consisting of 15mL of 72wt% concentrated sulfuric acid and 4mL of 70wt% concentrated nitric acid. React at 72℃ for 4h. After the reaction is complete, dilute the solution thoroughly with deionized water, centrifuge, filter and wash to make the pH of the solution neutral, and prepare a carbon nanotube dispersion with a concentration of 10mg / mL.

[0058] 2) Soak activated carbon in 0.2 mol / L hydrochloric acid solution for 13 h, wash repeatedly with deionized water and dry to obtain pretreated activated carbon for later use. Then dissolve 15 g divinylbenzene in 15 mL tetrahydrofuran, add 0.15 g azobisisobutyronitrile, and sonicate at 150 W for 1.5 h. Then transfer to a high-pressure reactor and react at 112 °C for 28 h. After the reaction is completed, cool to room temperature and evaporate the residual tetrahydrofuran to obtain hydrophobic modifier for later use.

[0059] 3) Add 2g of hydrophobic modifier to 80mL of anhydrous ethanol and dissolve it completely to obtain a suspension. Then add 12g of pretreated activated carbon to the suspension and impregnate it at room temperature for 8h. After impregnation, centrifuge and filter the mixture, then transfer it to a constant temperature oven and dry it at 108℃ for 13h to obtain modified activated carbon.

[0060] 4) Add 7g of modified activated carbon to 400mL of carbon nanotube dispersion, ultrasonically disperse at 150W for 1.5h, centrifuge and dry, repeat the operation 4 times, then add to 100mL of 2wt% polyethyleneimine ethanol solution, soak for 20min, centrifuge and filter again, dry at 65℃ for 40min, then add to 70mL of polydimethylsiloxane, soak for 40min again, centrifuge and filter, and dry to obtain the low water absorption additive.

[0061] Example 3: A highly stable lead-free solder paste that does not require an inner cap, the lead-free solder paste comprising the following components by weight: 14 parts flux, 8 parts low water absorption additive, and 90 parts lead-free solder powder.

[0062] The lead-free solder powder is selected from Sn99Ag0.3Cu0.7;

[0063] The flux contains the following components by weight: 50 parts rosin, 10 parts resin, 50 parts solvent, 15 parts additives, 8 parts thixotropic agent, 10 parts organic acid, 3 parts halogen compound, and 2 parts antioxidant.

[0064] The preparation method of this lead-free solder paste specifically includes the following steps:

[0065] 1) Weigh each component according to the formula, heat the rosin, resin, solvent, additives and thixotropic agent together to 165℃, and after the system is dissolved and mixed evenly, the temperature is reduced to 143℃ and organic acid, halogen compound and antioxidant are added. After it is completely dissolved, continue to stir for 5 minutes to make it evenly mixed. Transfer the evenly mixed flux to a sealed beaker, put it in ice water to cool for 3 hours, take it out and return it to room temperature, grind it twice to obtain flux.

[0066] 2) Pour the above flux into the tank and start pre-stirring at 26 r / min for 8 minutes. Then add the low water absorption additive and lead-free solder powder into the tank, set the speed to 18 r / min, stir for 15 minutes, and then evacuate to a vacuum state. Stir at 10 r / min and uniformly evacuate to 0.09 MPa within 5 minutes. Close the vacuum valve and stop stirring to obtain lead-free solder paste.

[0067] The preparation method of the low water absorption additive is as follows:

[0068] 1) Add 3g of carbon nanotubes to an acid solution consisting of 18mL of 75wt% concentrated sulfuric acid and 5mL of 72wt% concentrated nitric acid. React at 75℃ for 5h. After the reaction is complete, dilute the solution with deionized water, centrifuge, filter and wash to make the pH of the solution neutral, and prepare a carbon nanotube dispersion with a concentration of 15mg / mL.

[0069] 2) Soak activated carbon in 0.3 mol / L hydrochloric acid solution for 15 h, wash repeatedly with deionized water and dry to obtain pretreated activated carbon for later use. Then dissolve 20 g divinylbenzene in 20 mL tetrahydrofuran, add 0.2 g azobisisobutyronitrile, and sonicate at 200 W for 2 h. Then transfer to a high-pressure reactor and react at 115 °C for 30 h. After the reaction is completed, cool to room temperature and evaporate the residual tetrahydrofuran to obtain hydrophobic modifier for later use.

[0070] 3) Add 3g of hydrophobic modifier to 100mL of anhydrous ethanol and dissolve it completely to obtain a suspension. Then add 15g of pretreated activated carbon to the suspension and soak it at room temperature for 10h. After soaking, centrifuge and filter the mixture, then transfer it to a constant temperature oven and dry it at 110℃ for 15h to obtain modified activated carbon.

[0071] 4) Add 10g of modified activated carbon to 500mL of carbon nanotube dispersion, ultrasonically disperse at 200W for 2h, centrifuge and dry, repeat the operation 5 times, then add to 120mL of 3wt% polyethyleneimine ethanol solution, soak for 30min, centrifuge and filter again, dry at 70℃ for 50min, then add to 80mL of polydimethylsiloxane, soak for 50min again, centrifuge and filter, and dry to obtain the low water absorption additive.

[0072] Comparative Example 1: This comparative example is basically the same as Example 1, except that it does not contain low water absorption additives.

[0073] Comparative Example 2: This comparative example is basically the same as Example 1, except that step 1 is omitted in the preparation of the low water absorption additive.

[0074] Comparative Example 3: This comparative example is basically the same as Example 1, except that step 2 is omitted in the preparation of the low water absorption additive.

[0075] Comparative Example 4: This comparative example is basically the same as Example 1, except that step 3 is omitted in the preparation of the low water absorption additive.

[0076] Comparative Example 5: This comparative example is basically the same as Example 1, except that in the preparation of the low water absorption additive, the activated carbon in step 2) was not pretreated.

[0077] Test experiment:

[0078] The lead-free solder pastes provided in Examples 1-3 and Comparative Examples 1-5 were completely exposed to room temperature with a relative humidity of 60% for 15 days, and the viscosity change rate of the solder pastes was recorded. The results are shown in Table 1.

[0079] Table 1

[0080] Example 1 Example 2 Example 3 Comparative Example 1 viscosity change rate % 1.0 0.7 0.9 4.3 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 viscosity change rate % 2.4 2.7 3.5 1.8

[0081] As shown in Table 1, the lead-free solder paste of this invention has low water absorption and can maintain good stability without the need for comprehensive sealing with inner and outer caps.

[0082] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A highly stable, capless lead-free solder paste, characterized in that, The lead-free solder paste comprises the following components by weight: 10-14 parts flux, 3-8 parts low water absorption additive, and 86-90 parts lead-free solder powder. The lead-free solder powder is selected from one or more of Sn99Ag0.3Cu0.7, Sn98.5Ag1Cu0.5, and Sn96.5Ag3Cu0.5; The flux paste comprises the following components by weight: 30-50 parts rosin, 4-10 parts resin, 30-50 parts solvent, 3-15 parts additives, 4-8 parts thixotropic agent, 5-10 parts organic acid, 0.5-3 parts halogen compound, and 0.5-2 parts antioxidant. The additive is composed of polyisobutylene 300R and dimer acid in a mass ratio of (2-3):1; The preparation method of the low water absorption additive is as follows: 1) Add carbon nanotubes to an acidic solution composed of concentrated sulfuric acid and concentrated nitric acid, and react at 70-75℃ for 3-5 hours. After the reaction is complete, dilute the solution thoroughly with deionized water, centrifuge, filter and wash to make the pH of the solution neutral, and prepare a carbon nanotube dispersion. 2) Soak activated carbon in hydrochloric acid solution for 10-15 hours, wash it repeatedly with deionized water and dry it to obtain pretreated activated carbon for later use. Then dissolve divinylbenzene in tetrahydrofuran, add azobisisobutyronitrile, sonicate for 1-2 hours and transfer it to a high-pressure reactor. Continue to react at 110-115℃ for 24-30 hours. After the reaction is completed, cool to room temperature and evaporate the residual tetrahydrofuran to obtain a hydrophobic modifier for later use. 3) Add the hydrophobic modifier to anhydrous ethanol and dissolve it completely to obtain a suspension. Then add the pretreated activated carbon to the suspension and impregnate it at room temperature for 6-10 hours. After impregnation, centrifuge and filter the carbon, then transfer it to a constant temperature oven and dry it at 105-110℃ for 12-15 hours to obtain the modified activated carbon. 4) Add the modified activated carbon to the carbon nanotube dispersion, ultrasonically disperse for 1-2 hours, centrifuge and dry, repeat the operation 3-5 times, then add it to the polyethyleneimine ethanol solution, soak for 10-30 minutes, centrifuge and filter again, dry at 60-70℃ for 30-50 minutes, then add it to polydimethylsiloxane, soak again for 30-50 minutes, centrifuge and filter, and dry to obtain the low water absorption additive.

2. The high-stability, capless lead-free solder paste according to claim 1, characterized in that, The rosin is composed of KE-604 rosin, AX-E rosin, and CH-60 rosin in a mass ratio of (3-5):(3-5):1; The resin is a hydrogenated petroleum resin.

3. The high-stability lead-free solder paste without inner cap according to claim 1, characterized in that, The solvent is composed of diethylene glycol dibutyl ether, tripropylene glycol butyl ether, and diethylene glycol hexyl ether in a mass ratio of (1.5-2.0):(1.5-2.0):1; The additive is composed of polyisobutylene 300R and dimer acid in a mass ratio of (2-3):1; The thixotropic agent consists of equal masses of polyamide wax and ethylene bis-12-hydroxystearamide.

4. The high-stability lead-free solder paste without inner cap according to claim 1, characterized in that, The organic acid is composed of adipic acid, stearic acid, succinic acid, tetracosic acid, and dodecanoic acid in a mass ratio of 1:(2-3):(2-3):1:(2-3); The halogen compound is composed of dibromobutenediol and diphenylguanidine hydrobromide in a mass ratio of 1:(2-5); The antioxidant is composed of equal masses of antioxidant 245 and antioxidant 1010.

5. The high-stability lead-free solder paste without inner cap according to claim 1, characterized in that, In step 1), the ratio of carbon nanotubes, concentrated sulfuric acid, and concentrated nitric acid is (1-3) g: (12-18) mL: (4-5) mL; The concentration of the concentrated sulfuric acid is 70-75 wt%. The concentration of the concentrated nitric acid is 68-72 wt%. The concentration of the carbon nanotube dispersion is 5-15 mg / mL.

6. The high-stability lead-free solder paste without inner cap according to claim 1, characterized in that, In step 2), the concentration of the hydrochloric acid solution is 0.1-0.3 mol / L; The ratio of divinylbenzene, tetrahydrofuran, and azobisisobutyronitrile is (10-20) g: (10-20) mL: (0.1-0.2) g.

7. The high-stability lead-free solder paste without inner cap according to claim 1, characterized in that, In step 3), the ratio of the hydrophobic modifier, anhydrous ethanol, and pretreated activated carbon is (1-3)g: (60-100)mL: (8-15)g.

8. The high-stability lead-free solder paste without inner cap according to claim 1, characterized in that, In step 4), the ratio of the amount of modified activated carbon, carbon nanotube dispersion, polyethyleneimine ethanol solution, and polydimethylsiloxane is (5-10) g: (300-500) mL: (80-120) mL: (60-80) mL; The concentration of the polyethyleneimine ethanol solution is 1-3 wt%.

9. A method for preparing a high-stability, capless lead-free solder paste according to any one of claims 1-8, characterized in that, Specifically, the steps include the following: 1) Weigh each component according to the formula. Heat the rosin, resin, solvent, additives and thixotropic agent together to 160-165℃. After the system is dissolved and mixed evenly, reduce the temperature to 140-143℃ and add organic acid, halogen compound and antioxidant. After it is completely dissolved, continue to stir for 2-5 minutes to mix evenly. Transfer the evenly mixed flux to a sealed beaker and cool it in ice water for 1-3 hours. Take it out and return it to room temperature. Grind it 1-2 times to obtain the flux. 2) Pour the above flux into the tank and start pre-stirring at a speed of 20-26 r / min for 3-8 minutes. Then add the low water absorption additive and lead-free solder powder into the tank, set the speed to 10-18 r / min, stir for 10-15 minutes, and then evacuate to a vacuum state. Stir at a speed of 6-10 r / min for 1-5 minutes to uniformly evacuate the vacuum to 0.07-0.09 MPa. Close the vacuum valve and stop stirring to obtain lead-free solder paste.