Low-adsorbability flux paste and preparation method thereof

Abstract

The invention discloses low-adsorbability flux paste and a preparation method thereof.The low-adsorbability flux paste comprises, by weight, 13-15% of isopropanol, 20-25% of modified rosin, 1-1.2% of hydroquinone, 5-8% of triethanolamine, 1-1.5% of OP-10, 4-6% of hydrogenated castor oil and the balance xylene, molecules of the modified rosin can be adsorbed to the metal surface, and then a protective film is formed on the metal surface. The polysiloxane chain segment in the protective film endows the protective film with high flexibility and elasticity, welding thermal stress can be effectively buffered, cracking can be prevented, benzene rings provide rigid support, the strength and adhesive force of a film layer are enhanced, the compact and tough protective film is formed, surface energy can be further finely regulated and controlled through introduction of C-F bonds, and the welding performance of the protective film is improved. The flux paste has better fluidity and spreadability during preheating and welding, so that the protective film is more compact, and the metal surface is effectively prevented from being eroded.

Description

Technical Field

[0001] This invention relates to the field of flux preparation technology, specifically to a low-adsorption flux and its preparation method. Background Technology

[0002] As electronic components evolve towards miniaturization, high density, and high reliability, surface mount technology places increasingly stringent demands on the performance of solder paste. As a key material in the soldering process for removing oxides and promoting solder wetting, the performance of solder paste directly determines the soldering quality and the long-term reliability of the product. In high-end electronics manufacturing fields, such as smartphones, wearable devices, automotive electronics, and aerospace electronics, the requirements for solder paste have evolved from good solderability to a comprehensive performance requirement: a clean, residue-free, dust-free board surface after soldering, and high probe test pass rate—that is, low-adsorption solder paste. Rosin, due to its excellent film-forming properties, soldering activity, and low cost, has long been used as the main film-forming agent in solder pastes. However, with the popularization of lead-free soldering processes and the improvement of product reliability, the defects of traditional rosin-based solder pastes have become increasingly prominent. Rosin is prone to oxidation and carbonization at high temperatures. Ordinary rosin is easily oxidized, discolored, or even carbonized at the peak temperature of lead-free soldering, forming dark residues that not only affect the appearance of the board surface but may also reduce insulation performance. More seriously, the residue formed by the low molecular weight components of rosin after welding is viscoelastic at room temperature, which easily adsorbs dust and impurities in the air, and the protective film produced has limited anti-corrosion ability. Summary of the Invention

[0003] The purpose of this invention is to provide a low-adsorption flux and its preparation method, which solves the problem that the residual activator in the current low-adsorption flux will continue to react with the metal substrate after use, leading to corrosion of the metal substrate.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] A method for preparing a low-adsorption flux paste specifically includes the following steps:

[0006] Step A1: Mix the modified additive, rosin, tetrabutyl titanate and xylene, purge with nitrogen, and react for 10-15 hours at a speed of 120-150 r / min and a temperature of 145-150℃ to obtain pretreated rosin.

[0007] Step A2: Mix pretreated rosin, zinc chloride and mesitylene, purge with nitrogen for protection, stir and add fumaric acid at a speed of 150-200 r / min and a temperature of 170-180℃, and react for 8-10 h to obtain modified rosin.

[0008] Step A3: Weigh the following raw materials in the following percentages: 13-15% isopropanol, 20-25% modified rosin, 1-1.2% hydroquinone, 5-8% triethanolamine, 1-1.5% OP-10, 4-6% hydrogenated castor oil, and the balance is xylene. Mix the raw materials evenly to obtain a low-adsorption flux.

[0009] Furthermore, the molar ratio of the modified additive and rosin mentioned in step A1 is 1:2, and the amount of tetrabutyl titanate used is 0.02% of the mass of rosin.

[0010] Furthermore, in step A2, the molar ratio of the pretreated rosin to fumaric acid is 1:2.2, and the amount of zinc chloride used is 0.1% of the mass of fumaric acid.

[0011] Furthermore, the modified additive is prepared by the following steps:

[0012] Step B1: Mix trimethylsilyl lithium and tetrahydrofuran, purge with nitrogen, stir and add hexamethylcyclotrisiloxane and trifluoropropylmethylcyclotrisiloxane at 200-300 r / min and 0℃, heat to 25-30℃ and react for 7-9 h, add diethylenedichlorosilane and continue the reaction for 3-5 h to obtain branched polysiloxane;

[0013] Step B2: Mix octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide and deionized water, purge with nitrogen, and react for 10-12 hours at a rotation speed of 150-200 r / min and a temperature of 90-95℃. Then raise the temperature to 105-110℃ and continue the reaction for 2-3 hours to obtain pretreated polysiloxane.

[0014] Step B3: Mix pretreated polysiloxane, 2-vinyl-1H-benzimidazole, benzoin dimethyl ether and xylene, purge with nitrogen, and react for 15-20 minutes under the conditions of 120-150 r / min, 20-25℃ and 365nm ultraviolet light irradiation to obtain functionalized polysiloxane.

[0015] Step B4: Functionalized polysiloxane, branched polysiloxane, caster catalyst and xylene are mixed, nitrogen gas is introduced for protection, and the reaction is carried out at a speed of 200-300 r / min and a temperature of 80-85℃ for 6-8 hours. Then, allyl alcohol is added to continue the reaction to obtain the modified additive.

[0016] Furthermore, the molar ratio of Si-Cl on lithium trimethylsilanolate, hexamethylcyclotrisiloxane, trifluoropropylmethylcyclotrisiloxane and diethylenedichlorosilane in step B1 is 1:2:2:1.

[0017] Furthermore, the ratio of octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide and deionized water in step B2 is 1 mol: 1 mol: 0.4 mol: 2 mol: 3 mol: 40 mL.

[0018] Furthermore, in step B3, the molar ratio of the thiol group on the pretreated polysiloxane to 2-vinyl-1H-benzimidazole is 1:1, and the amount of benzoin dimethyl ether used is 0.02% of the mass of 2-vinyl-1H-benzimidazole.

[0019] Furthermore, the molar ratio of the functionalized polysiloxane, branched polysiloxane, and allyl alcohol in step B4 is n+1:n:2, where n is a natural number greater than 0, and the amount of cassette catalyst is 0.01% of the mass of the branched polysiloxane.

[0020] The beneficial effects of the present invention are as follows: The low-adsorption flux disclosed in this application comprises the following raw materials: isopropanol, modified rosin, hydroquinone, triethanolamine, OP-10, hydrogenated castor oil, and the balance being xylene. The modified rosin is prepared by using modified additives and rosin as raw materials, thereby esterifying the hydroxyl groups on the modified additives and the carboxyl groups on the rosin to obtain pretreated rosin. The pretreated rosin is then reacted with Diels-Alder fumarate to obtain modified rosin.

[0021] The modified additive uses lithium trimethylsilanolate as an initiator and hexamethylcyclotrisiloxane and trifluoropropylmethylcyclotrisiloxane as polymerization monomers to prepare a polysiloxane with lithium silanolate at one end. Then, divinyldichlorosilane is added, causing the Si-Cl bonds on the divinyldichlorosilane to react with the lithium silanolate, yielding a branched polysiloxane. Octamethylcyclotetrasiloxane and tetramethyltetraphenylcyclotetrasiloxane are ring-opened, hydrolyzed and condensed with 3-mercaptopropylmethyldimethoxysilane, and then end-capped with tetramethyldisiloxane to form a side chain containing benzene rings and mercapto groups, with both ends containing... A pretreated polysiloxane with Si-H bonds was prepared. The pretreated polysiloxane and 2-vinyl-1H-benzimidazole were reacted under ultraviolet light in the presence of dimethyl benzoate, causing the thiol groups on the side chains of the pretreated polysiloxane to react with the vinyl groups on the 2-vinyl-1H-benzimidazole, thus preparing a functionalized polysiloxane. The functionalized polysiloxane was then reacted with a branched polysiloxane, causing the Si-H bonds on the functionalized polysiloxane to react with the double bonds on the branched polysiloxane. Finally, the end-capping was performed with allyl alcohol to prepare a modified additive.

[0022] The carboxyl groups in the modified rosin molecule can gently dissolve metal oxides, and the nitrogen atoms on the benzimidazole nitrogen heterocycle in the molecular structure have lone pairs of electrons, which can interact more strongly with metal ions in the metal oxide. The synergistic effect of the two can more efficiently destroy the oxide film. At the same time, the benzimidazole structure allows the modified rosin molecules to adsorb onto the metal surface, thereby forming a protective film on the metal surface. The polysiloxane segments in the protective film give the protective film high flexibility and elasticity, which can effectively buffer welding thermal stress and prevent cracking. The benzene ring provides rigid support, enhances the strength and adhesion of the film layer, and forms a dense and tough protective film. The introduction of CF bonds can further finely control the surface energy, making the flux paste more fluid and spreadable during preheating and welding, making the protective film denser and effectively preventing the metal surface from being corroded. Detailed Implementation

[0023] 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.

[0024] Example 1: A method for preparing a low-adsorption flux, specifically including the following steps:

[0025] Step A1: Mix the modified additive, rosin, tetrabutyl titanate and xylene, purge with nitrogen, and react for 10 h at a speed of 120 r / min and a temperature of 145℃ to obtain pretreated rosin.

[0026] Step A2: Mix pretreated rosin, zinc chloride and mesitylene, purge with nitrogen for protection, stir and add fumaric acid at 150 r / min and 170 °C, and react for 8 h to obtain modified rosin.

[0027] Step A3: Weigh the following raw materials in the following percentages: 13% isopropanol, 20% modified rosin, 1% hydroquinone, 5% triethanolamine, 1% OP-10, 4% hydrogenated castor oil, and the balance is xylene. Mix the raw materials evenly to obtain a low-adsorption flux.

[0028] The molar ratio of the modified additive and rosin mentioned in step A1 is 1:2, and the amount of tetrabutyl titanate is 0.02% of the mass of rosin.

[0029] The molar ratio of the pretreated rosin and fumaric acid in step A2 is 1:2.2, and the amount of zinc chloride used is 0.1% of the mass of fumaric acid.

[0030] The modified additive is prepared by the following steps:

[0031] Step B1: Trimethylsilyl lithium and tetrahydrofuran were mixed and protected with nitrogen. Under the conditions of 200 r / min and 0℃, hexamethylcyclotrisiloxane and trifluoropropylmethylcyclotrisiloxane were added while stirring. The temperature was raised to 25℃ and the reaction was carried out for 7 h. Diethylenedichlorosilane was added and the reaction was continued for 3 h to obtain branched polysiloxane.

[0032] Step B2: Mix octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide and deionized water, purge with nitrogen, and react for 10 h at a speed of 150 r / min and a temperature of 90 °C. Then raise the temperature to 105 °C and continue the reaction for 2 h to obtain pretreated polysiloxane.

[0033] Step B3: Mix pretreated polysiloxane, 2-vinyl-1H-benzimidazole, benzoin dimethyl ether and xylene, purge with nitrogen, and react for 20 min under the conditions of 150 r / min rotation speed, 25℃ temperature and 365nm ultraviolet light irradiation to obtain functionalized polysiloxane.

[0034] Step B4: Functionalized polysiloxane, branched polysiloxane, caster catalyst and xylene are mixed, nitrogen gas is introduced for protection, and the reaction is carried out for 8 hours at a rotation speed of 300 r / min and a temperature of 85℃. Then allyl alcohol is added to continue the reaction to obtain the modified additive.

[0035] The molar ratio of Si-Cl on lithium trimethylsilanolate, hexamethylcyclotrisiloxane, trifluoropropylmethylcyclotrisiloxane and diethylenedichlorosilane in step B1 is 1:2:2:1.

[0036] The ratio of octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide, and deionized water in step B2 is 1 mol: 1 mol: 0.4 mol: 2 mol: 3 mol: 40 mL.

[0037] In step B3, the molar ratio of the thiol group on the pretreated polysiloxane to 2-vinyl-1H-benzimidazole is 1:1, and the amount of benzoin dimethyl ether used is 0.02% of the mass of 2-vinyl-1H-benzimidazole.

[0038] The molar ratio of functionalized polysiloxane, branched polysiloxane and allyl alcohol in step B4 is 2:1:2, and the amount of cassette catalyst is 0.01% of the mass of branched polysiloxane.

[0039] Example 2, a method for preparing a low-adsorption flux, specifically includes the following steps:

[0040] Step A1: Mix the modified additive, rosin, tetrabutyl titanate and xylene, purge with nitrogen, and react for 13 hours at a speed of 120 r / min and a temperature of 150℃ to obtain pretreated rosin.

[0041] Step A2: Mix pretreated rosin, zinc chloride and mesitylene, purge with nitrogen for protection, stir and add fumaric acid at a speed of 150 r / min and a temperature of 175℃, and react for 9 h to obtain modified rosin.

[0042] Step A3: Weigh the following raw materials in the following percentages: 14% isopropanol, 23% modified rosin, 1.1% hydroquinone, 6.5% triethanolamine, 1.3% OP-10, 5% hydrogenated castor oil, and the balance is xylene. Mix the raw materials evenly to obtain a low-adsorption flux.

[0043] The molar ratio of the modified additive and rosin mentioned in step A1 is 1:2, and the amount of tetrabutyl titanate is 0.02% of the mass of rosin.

[0044] The molar ratio of the pretreated rosin and fumaric acid in step A2 is 1:2.2, and the amount of zinc chloride used is 0.1% of the mass of fumaric acid.

[0045] The modified additive is prepared by the following steps:

[0046] Step B1: Trimethylsilyl lithium and tetrahydrofuran were mixed and protected with nitrogen. Under the conditions of 200 r / min and 0℃, hexamethylcyclotrisiloxane and trifluoropropylmethylcyclotrisiloxane were added while stirring. The temperature was raised to 30℃ and the reaction was carried out for 8 h. Diethylenedichlorosilane was added and the reaction was continued for 4 h to obtain branched polysiloxane.

[0047] Step B2: Octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide and deionized water are mixed, and nitrogen gas is introduced for protection. The mixture is reacted at a speed of 150 r / min and a temperature of 95 °C for 11 h. Then the temperature is raised to 105 °C and the reaction is continued for 3 h to obtain pretreated polysiloxane.

[0048] Step B3: Mix pretreated polysiloxane, 2-vinyl-1H-benzimidazole, benzoin dimethyl ether and xylene, purge with nitrogen, and react for 15 min under the conditions of 120 r / min rotation speed, 25℃ temperature and 365nm ultraviolet light irradiation to obtain functionalized polysiloxane.

[0049] Step B4: Functionalized polysiloxane, branched polysiloxane, caster catalyst and xylene are mixed, nitrogen gas is introduced for protection, and the reaction is carried out for 8 hours at a rotation speed of 300 r / min and a temperature of 80℃. Then allyl alcohol is added to continue the reaction to obtain the modified additive.

[0050] The molar ratio of Si-Cl on lithium trimethylsilanolate, hexamethylcyclotrisiloxane, trifluoropropylmethylcyclotrisiloxane and diethylenedichlorosilane in step B1 is 1:2:2:1.

[0051] The ratio of octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide, and deionized water in step B2 is 1 mol: 1 mol: 0.4 mol: 2 mol: 3 mol: 40 mL.

[0052] In step B3, the molar ratio of the thiol group on the pretreated polysiloxane to 2-vinyl-1H-benzimidazole is 1:1, and the amount of benzoin dimethyl ether used is 0.02% of the mass of 2-vinyl-1H-benzimidazole.

[0053] The molar ratio of functionalized polysiloxane, branched polysiloxane and allyl alcohol in step B4 is 3:2:2, and the amount of cassette catalyst is 0.01% of the mass of branched polysiloxane.

[0054] Example 3, a method for preparing a low-adsorption flux, specifically includes the following steps:

[0055] Step A1: Mix the modified additive, rosin, tetrabutyl titanate and xylene, purge with nitrogen, and react for 15 hours at a speed of 150 r / min and a temperature of 150℃ to obtain pretreated rosin.

[0056] Step A2: Mix pretreated rosin, zinc chloride and mesitylene, purge with nitrogen for protection, stir and add fumaric acid at a speed of 200 r / min and a temperature of 180℃, and react for 10 h to obtain modified rosin.

[0057] Step A3: Weigh the following raw materials in percentage: 15% isopropanol, 25% modified rosin, 1.2% hydroquinone, 8% triethanolamine, 1.5% OP-10, 6% hydrogenated castor oil, and the balance is xylene. Mix the raw materials evenly to obtain a low-adsorption flux.

[0058] The molar ratio of the modified additive and rosin mentioned in step A1 is 1:2, and the amount of tetrabutyl titanate is 0.02% of the mass of rosin.

[0059] The molar ratio of the pretreated rosin and fumaric acid in step A2 is 1:2.2, and the amount of zinc chloride used is 0.1% of the mass of fumaric acid.

[0060] The modified additive is prepared by the following steps:

[0061] Step B1: Trimethylsilyl lithium and tetrahydrofuran were mixed and protected with nitrogen. Under the conditions of 300 r / min and 0℃, hexamethylcyclotrisiloxane and trifluoropropylmethylcyclotrisiloxane were added while stirring. The temperature was raised to 30℃ and the reaction was carried out for 9 h. Diethylenedichlorosilane was added and the reaction was continued for 5 h to obtain branched polysiloxane.

[0062] Step B2: Mix octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide and deionized water, purge with nitrogen, and react for 12 hours at a speed of 200 r / min and a temperature of 95°C. Then raise the temperature to 110°C and continue the reaction for 3 hours to obtain pretreated polysiloxane.

[0063] Step B3: Mix pretreated polysiloxane, 2-vinyl-1H-benzimidazole, benzoin dimethyl ether and xylene, purge with nitrogen, and react for 20 min under the conditions of 150 r / min rotation speed, 25℃ temperature and 365nm ultraviolet light irradiation to obtain functionalized polysiloxane.

[0064] Step B4: Functionalized polysiloxane, branched polysiloxane, caster catalyst and xylene are mixed, nitrogen gas is introduced for protection, and the reaction is carried out for 8 hours at a rotation speed of 300 r / min and a temperature of 85℃. Then allyl alcohol is added to continue the reaction to obtain the modified additive.

[0065] The molar ratio of Si-Cl on lithium trimethylsilanolate, hexamethylcyclotrisiloxane, trifluoropropylmethylcyclotrisiloxane and diethylenedichlorosilane in step B1 is 1:2:2:1.

[0066] The ratio of octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide, and deionized water in step B2 is 1 mol: 1 mol: 0.4 mol: 2 mol: 3 mol: 40 mL.

[0067] In step B3, the molar ratio of the thiol group on the pretreated polysiloxane to 2-vinyl-1H-benzimidazole is 1:1, and the amount of benzoin dimethyl ether used is 0.02% of the mass of 2-vinyl-1H-benzimidazole.

[0068] The molar ratio of functionalized polysiloxane, branched polysiloxane and allyl alcohol in step B4 is 4:3:2, and the amount of cassette catalyst is 0.01% of the mass of branched polysiloxane.

[0069] Comparative Example 1: This comparative example uses pretreated rosin instead of modified rosin, while the other steps are the same as in Example 1.

[0070] Comparative Example 2: Compared with Example 1, this comparative example uses octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, tetramethyldisiloxane, tetramethylammonium hydroxide and deionized water, under nitrogen protection, and reacts at a speed of 150 r / min and a temperature of 90°C for 10 h. Then, the temperature is raised to 105°C and the reaction continues for 2 h. The product obtained replaces the functionalized polysiloxane, and the remaining steps are the same.

[0071] Comparative Example 3: This comparative example differs from Example 1 in that trifluoropropylmethylcyclotrisiloxane was added, while the other steps were the same.

[0072] Comparative Example 4: This comparative example did not include branched polysiloxanes compared to Example 1, but the remaining steps were the same.

[0073] The fluxes prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to copper plate corrosion, copper mirror corrosion, and wetting coverage tests according to IPC-TM-650. At the same time, it was observed whether pores appeared on the surface of the plate after welding. The test results are shown in Table 1 below.

[0074] Table 1

[0075] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Copper plate corrosion Non-corrosive Non-corrosive Non-corrosive Non-corrosive Slight corrosion Slight corrosion Slight corrosion Corrosion of bronze mirrors L-class L-class L-class L-class M-Class M-Class M-Class Wetting coverage ＞95% ＞95% ＞95% 85-95% 85-95% ＜85% ＜85% Are pores present? Not found Not found Not found Not found Not found Appear Appear

[0076] As shown in Table 1, this application has excellent corrosion resistance and wetting properties.

[0077] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a low-adsorption flux, characterized in that: Specifically, the steps include the following: Step A1: Mix the modified additive, rosin, tetrabutyl titanate and xylene, purge with nitrogen, and react for 10-15 hours at a speed of 120-150 r / min and a temperature of 145-150℃ to obtain pretreated rosin. Step A2: Mix pretreated rosin, zinc chloride and mesitylene, purge with nitrogen for protection, stir and add fumaric acid at a speed of 150-200 r / min and a temperature of 170-180℃, and react for 8-10 h to obtain modified rosin. Step A3: Weigh the following raw materials in the following percentages: 13-15% isopropanol, 20-25% modified rosin, 1-1.2% hydroquinone, 5-8% triethanolamine, 1-1.5% OP-10, 4-6% hydrogenated castor oil, and the balance is xylene. Mix the raw materials evenly to obtain a low-adsorption flux.

2. The method for preparing low-adsorption flux according to claim 1, characterized in that: The molar ratio of the modified additive and rosin mentioned in step A1 is 1:

2.

3. The method for preparing low-adsorption flux according to claim 1, characterized in that: The molar ratio of the pretreated rosin and fumaric acid described in step A2 is 1:2.

2.

4. The method for preparing low-adsorption flux according to claim 1, characterized in that: The modified additive is prepared by the following steps: Step B1: Mix trimethylsilyl lithium and tetrahydrofuran, purge with nitrogen, stir and add hexamethylcyclotrisiloxane and trifluoropropylmethylcyclotrisiloxane at 200-300 r / min and 0℃, heat to 25-30℃ and react for 7-9 h, add diethylenedichlorosilane and continue the reaction for 3-5 h to obtain branched polysiloxane; Step B2: Mix octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide and deionized water, purge with nitrogen, and react for 10-12 hours at a rotation speed of 150-200 r / min and a temperature of 90-95℃. Then raise the temperature to 105-110℃ and continue the reaction for 2-3 hours to obtain pretreated polysiloxane. Step B3: Mix pretreated polysiloxane, 2-vinyl-1H-benzimidazole, benzoin dimethyl ether and xylene, purge with nitrogen, and react for 15-20 minutes under the conditions of 120-150 r / min, 20-25℃ and 365nm ultraviolet light irradiation to obtain functionalized polysiloxane. Step B4: Functionalized polysiloxane, branched polysiloxane, caster catalyst and xylene are mixed, nitrogen gas is introduced for protection, and the reaction is carried out at a speed of 200-300 r / min and a temperature of 80-85℃ for 6-8 hours. Then, allyl alcohol is added to continue the reaction to obtain the modified additive.

5. The method for preparing low-adsorption flux according to claim 4, characterized in that: The molar ratio of Si-Cl on lithium trimethylsilanolate, hexamethylcyclotrisiloxane, trifluoropropylmethylcyclotrisiloxane and diethylenedichlorosilane in step B1 is 1:2:2:

1.

6. The method for preparing low-adsorption flux according to claim 4, characterized in that: The ratio of octamethylcyclotetrasiloxane, tetramethyltetraphenylcyclotetrasiloxane, 3-mercaptopropylmethyldimethoxysilane, tetramethyldisiloxane, tetramethylammonium hydroxide, and deionized water in step B2 is 1 mol: 1 mol: 0.4 mol: 2 mol: 3 mol: 40 mL.

7. The method for preparing low-adsorption flux according to claim 4, characterized in that: The molar ratio of the thiol group on the pretreated polysiloxane and the 2-vinyl-1H-benzimidazole in step B3 is 1:

1.

8. The method for preparing low-adsorption flux according to claim 4, characterized in that: The molar ratio of functionalized polysiloxane, branched polysiloxane and allyl alcohol mentioned in step B4 is n+1:n:2, where n is a natural number greater than 0.

9. A low-adsorption solder paste, characterized in that: Prepared according to any one of the preparation methods described in claims 1-8.