High-temperature halogen-free flux, solder paste and preparation method

Abstract

The high-temperature halogen-free flux, solder paste, and preparation method include 30%–50% high-boiling-point solvent, 30%–40% rosin, 1%–8% modified thermoplastic resin, 5%–10% activator, 0.5%–1.0% modified surfactant, 4%–8% thixotropic agent, 0.5%–3% metal salt, and 3%–5% antioxidant. The solder paste includes 85%–88% lead-free metal alloy powder and 12%–15% high-temperature halogen-free flux. The organic solvent is weighed and added to a container, heated to 80–95°C; the thixotropic agent is added and stirred until homogeneous; the temperature is lowered to 60–70°C, and rosin, modified thermoplastic resin, activator, metal salt, antioxidant, and modified surfactant are weighed and added, stirred at a constant temperature until dissolved, air bubbles in the flux are removed, and the mixture is cooled to a paste consistency. The material is then ground to obtain the high-temperature halogen-free flux.

Description

Technical Field

[0001] This invention belongs to the field of electronic component soldering materials technology, specifically relating to a halogen-free flux and solder paste preparation method for high-temperature soldering of electronic components. Background Technology

[0002] Solder paste is mainly used in the manufacture of electronic circuits. Through the reflow process, the solder powder in the solder paste melts and reacts with the metal on the lead of the component and the metal on the pad of the circuit board (or substrate) to form intermetallic compounds, thereby completing the mechanical and electrical connection between the electronic component and the circuit board (or substrate), thus forming an effective circuit system.

[0003] In existing high-temperature semiconductor packaging processes, high-lead solder paste is widely used due to its high melting point and good wettability. However, the contradiction between its heavy metal pollution problem and the approaching expiration of the EU RoHS exemption is becoming increasingly prominent.

[0004] While existing lead-free solders (such as Sn-Ag-Cu systems) are environmentally friendly, during high-temperature reflow soldering, the peak temperature exceeds the tolerance threshold of the silver pads. This causes the silver layer on the pad surface to dissolve or even alloy, forming a brittle intermetallic compound layer, reducing the mechanical strength and conductivity of the solder joint, and even leading to cracks. Halogen-containing fluxes, while improving soldering activity, cause circuit board corrosion and excessive VOC emissions. Although research has attempted to replace halogens with rosin derivatives, problems such as residual organic carbonization at high temperatures and the mismatch between the wettability of high-melting-point lead-free alloy powders remain unresolved. Therefore, developing a new flux and solder paste preparation method that combines high-temperature stability, halogen-free environmental friendliness, and compatibility with multi-element alloy systems is crucial to overcoming industry bottlenecks.

[0005] The high-temperature solder Sn5Pb92.5 has a melting point of 296℃, and Au80Sn20 has a melting point of 280℃. For example... Figure 1 As shown, in the prior art, the peak temperature of the reflow curve is usually 310 to 330°C. Under special circumstances (such as double-sided, multi-layer, thick substrate welding), when the peak temperature is increased to 350°C to 360°C, the negative effects of flux and solder oxidation at high temperature are obvious.

[0006] In some existing high-temperature lead-free solder pastes, the flux activator formulations mostly use dicarboxylic acids or organic amines combined with halogen salts. These are easily oxidized, volatilized, decomposed, and ineffective at high temperatures, leading to decreased wettability and a solder joint void rate greater than 5%. A high solder joint void rate affects the reliability and stability of high-temperature soldering.

[0007] In the preparation process of some high-temperature lead-free solder pastes disclosed in the prior art, the flux is prone to volatilization (VOCs release ≥50ppm), the rheological properties of the paste are damaged and delaminated under high pressure, and the alloy powder is deformed. This not only causes risks in the preparation process, but also results in poor consistency of the output solder paste, and the reliability and stability of high-temperature soldering need to be improved.

[0008] In this application document, the particle size specifications in the electronic industry standard SJ / T 11391 to 2019 Tin Alloy Powder for Soldering Electronic Products or IPC J-STD-005A:2012 are adopted; symbols such as T3 to T8 represent particle diameter range signals; the unit is micrometer, i.e., μm;

[0009] The T3 type powder indicates that the particle diameter range is 25μm~45μm;

[0010] T4 grade powder indicates that the particle diameter range is 20μm~38μm;

[0011] T5 grade powder indicates that the particle diameter range is 15μm~25μm;

[0012] T6 type powder indicates that the particle diameter range is 5μm~15μm;

[0013] The T7 type powder indicates that the particle diameter range is 2μm to 11μm;

[0014] The T8 type powder indicates that the particle diameter range is 2μm to 8μm. Summary of the Invention

[0015] To address the shortcomings of existing fluxes and solder pastes, such as poor high-temperature resistance and susceptibility to voids and organic carbonization residues, a high-temperature halogen-free flux and solder paste, along with their components and preparation method, were designed. By modifying thermoplastic resins, the flux acquires excellent high-temperature resistance, meeting the requirements for halogen-free high-temperature reflow soldering. The prepared high-temperature halogen-free flux and solder paste exhibit high soldering reliability and minimal organic carbonization residues. In this application, "high temperature" refers to a reflow curve peak temperature of 260–360℃.

[0016] The technical solution of this application to solve the above-mentioned technical problems can also be a high-temperature halogen-free flux, the composition of which by weight percentage includes: 40% to 50% high-boiling-point solvent, 25% to 40% rosin, 1% to 8% modified thermoplastic resin, 5% to 10% activator, 0.5% to 1.0% modified surfactant, and 4% to 8% thixotropic agent; the above-mentioned high-boiling-point solvent is two or more combinations of tetraethylene glycol dimethyl ether, tetraethylene glycol butyl ether, diethylene glycol dibutyl ether, polyethylene glycol butyl ether, diethylene glycol, triethylene glycol, tetraethylene glycol, 2-ethyl-1,3-hexanediol, and polypropylene glycol 400; the above-mentioned rosin is modified rosin, which is two or more combinations of rosin; the modified surfactant is octadecylamine polyoxyethylene ether; and the modified thermoplastic resin is terpene phenolic resin.

[0017] The modified thermoplastic resin may be a terpene phenolic resin; the preparation method of the terpene phenolic resin includes the following steps:

[0018] Step A1: Preparation of terpene resin matrix: α-terpene monomer and toluene solvent were added to the reactor at a mass ratio of 1:1.2 and the temperature was raised to 45°C. Anhydrous aluminum trichloride catalyst, equivalent to 7% of the mass of α-terpene, was slowly added under stirring, and the reaction was carried out at 45°C for 5 hours. After the reaction was completed, deionized water was added for neutralization, and the aqueous phase was washed until neutral. The aqueous layer was separated, and the organic phase was distilled under reduced pressure to remove toluene, resulting in a pale yellow terpene resin matrix. The softening temperature of the terpene resin matrix was 90-110°C.

[0019] Step A2: Preparation of terpene phenolic resin: A2.1 Preparation of phenolic resin prepolymer: In a reactor equipped with a reflux condenser, stirrer and thermometer, phenol and 37% formaldehyde aqueous solution are added, with a molar ratio of phenol to formaldehyde of 1:1.05; 36% hydrochloric acid is slowly added, with a mass ratio of 36% hydrochloric acid to phenol of 1.6:100; the temperature is raised to 85-90℃ under stirring, and the reaction is refluxed for 2.5-3 hours; then the mixture is dehydrated under reduced pressure at 70-75℃ and -0.09 MPa for 1 hour to obtain a viscous thermoplastic phenolic resin prepolymer, which is then cooled to 80℃ for later use.

[0020] A2.2 Blending and Reaction: The terpene resin matrix obtained in step A1 is added to the phenolic prepolymer, wherein the mass ratio of the terpene resin matrix to the initial mass of phenol in step A2.1 is 1:0.7; under nitrogen protection, the mixture is stirred and heated to 125-135℃ for 1.5-2 hours; then the temperature is raised to 145-150℃ and solvent volatiles are removed under a vacuum of -0.095 MPa or higher for 1-1.5 hours to obtain molten modified terpene phenolic resin.

[0021] Step A3: Product molding and refining: The molten modified terpene phenolic resin obtained in step A2.2 is discharged under nitrogen protection, cooled and granulated in a cold water bath to obtain a branched terpene phenolic resin.

[0022] In this application, the branched terpene phenolic resin has a three-dimensional network in which the branched chain encapsulates the high-boiling-point solvent in a three-dimensional network through steric hindrance, thereby reducing the evaporation rate of the solvent at high temperatures above 200°C by 30% to 40%.

[0023] The method for preparing the octadecylamine polyoxyethylene ether includes the following steps: Step B1: Stearamine is added to a high-pressure reactor, nitrogen is introduced to replace the air, and then a vacuum is drawn to ≤-0.08MPa. The temperature is raised to 100℃ and dehydrated for 1.5 hours.

[0024] Step B2: Add 0.8% (by weight of stearylamine) of sodium hydroxide (NaOH) catalyst, heat to 150°C, and introduce ethylene oxide in stages: initially add 5% (by weight of total ethylene oxide) to induce the reaction, and add the remaining amount after confirming that the temperature is stable. Control the reaction pressure at 0.2 MPa, the stirring speed at 400 rpm, and the total reaction time at 2.5 hours. In Step B2, the total amount of ethylene oxide to the mass ratio of stearylamine is 82:100.

[0025] Step B3: After the reaction is complete, cool down to 70°C and purge with nitrogen to remove unreacted ethylene oxide;

[0026] Step B4: Add acetic acid to neutralize the catalyst, and filter to obtain octadecylamine polyoxyethylene ether with an oxyethylene addition number of 5 moles.

[0027] Modified surfactant, namely octadecylamine polyoxyethylene ether.

[0028] It is possible that the above-mentioned active agent is at least one of pyromellitic acid, tetracarboxylic acid, DL-pyroglutamic acid, azelaic acid, hexadecenedicarboxylic acid, octadecenedicarboxylic acid, and trididecenedicarboxylic acid.

[0029] It can be at least one of the above-mentioned thixotropic agent-modified polyamide wax DISPARLON 6500, EBS, and modified hydrogenated castor oil ST.

[0030] Yes, it can also include 0.5% to 3% metal salts and 1.5% to 5% antioxidants.

[0031] It is possible that the metal salt mentioned above is at least one of ferrous sulfate, copper sulfate, nickel citrate, cobalt oxalate, and stannous oxalate.

[0032] It is possible that the antioxidant mentioned above is at least one of 5-methylbenzotriazole, benzotriazole octadecylamine salt, p-tert-butylcatechol, antioxidant 330, and antioxidant 264.

[0033] The technical solution of this application to solve the above-mentioned technical problems can also be a high-temperature halogen-free solder paste, the composition of which by weight percentage includes: 85% to 88% lead-free metal alloy powder; and 12% to 15% of the above-mentioned high-temperature halogen-free flux.

[0034] The lead-free metal alloy powder may include at least one alloy powder of SnSb, SnSbCu, SnAgCu, and SnSbAgCu; and may also include 0 to 0.5% trace metal elements; the trace metal elements may include one or more of Ni, In, Bi, Mn, and Co; and the lead-free metal alloy powder may include one or more of T4, T5, T6, T7, and T8 type powders.

[0035] The technical solution of this application to solve the above-mentioned technical problems can also be a method for preparing high-temperature halogen-free flux, which includes: Step D1: Weigh 40% to 50% organic solvent by weight and add it to a container, and heat it to 80℃ to 135℃; Step D2: Add 4% to 8% thixotropic agent and stir until uniform; Step D3: Reduce the temperature to 60 to 70℃, weigh 25% to 40% rosin, 1% to 8% modified thermoplastic resin, 5% to 10% activator, 0.5% to 3% metal salt, 1.5% to 5% antioxidant, and 0.5% to 1.0% modified surfactant by mass and add them to the container, and stir at a constant temperature until dissolved; Step D4: Stir to remove air bubbles in the flux, take it out and cool it into a paste; Step D5: Grind the material to obtain the above-mentioned high-temperature halogen-free flux.

[0036] It can be as follows: In step D2: after adding the thixotropic agent, stir at high speed of 1200 rpm / min for 30 to 60 minutes until uniform; In step D4: stir to remove air bubbles from the flux, reduce the speed to 100 to 200 rpm / min, stir for 20 minutes to remove air bubbles from the flux, take it out and cool it into a paste; In step D5: place the material in a three-roll mill and grind it until the crystals are less than 10 microns.

[0037] The technical solution of this application to solve the above-mentioned technical problems can also be a solder paste preparation method, used to prepare the above-mentioned high-temperature solder paste, including step C1: under the conditions of ambient temperature 25±2℃ and humidity 40%~60%, the above-mentioned high-temperature halogen-free flux and lead-free metal alloy powder are added to a mixer; step C2: the mixer is sealed and the stirring speed is set to 15rpm~60rpm, the stirring time is 10min, the machine is stopped to deal with the dead corners of the stirring, and the mixing of the above-mentioned lead-free metal alloy powder and the high-temperature halogen-free flux is repeated once; step C3: the mixed solder paste is thoroughly stirred and defoamed in a vacuum mixer at a high speed of 30~100rpm for 10~20 minutes; step C4: large-diameter particles in the solder paste are removed by a vacuum negative pressure filtration device to obtain high-temperature lead-free solder paste.

[0038] It can be that in step C4: large-diameter particles in the solder paste are removed by a vacuum negative pressure filtration device; the vacuum negative pressure filtration device is equipped with a multi-layer filter screen with a pore size of 5 to 50 μm to remove large-diameter particles in the solder paste.

[0039] It is possible that the mixed solder paste undergoes segmented vacuuming in a vacuum negative pressure filtration device; the segmented vacuuming includes: a first stage and a second stage. The first stage is a fast vacuuming stage, reaching a negative pressure of -0.05MPa in ≤10 seconds; the second stage is a slow vacuuming stage, with a pressure gradient of ≤-0.01MPa / min.

[0040] One of the beneficial effects of this application is that the formulation contains 40%–50% high-boiling-point solvent, 25%–40% rosin, 1%–8% modified thermoplastic resin, 5%–10% activator, 0.5%–1.0% modified surfactant, and 4%–8% thixotropic agent. This formulation gives the flux excellent high-temperature performance, making it suitable for preparing solder paste for high-temperature halogen-free soldering applications. The high-boiling-point solvent has a high-boiling-point range of 150–300°C.

[0041] One of the beneficial effects of this application is that the modified thermoplastic resin prepared by combining the terpene resin matrix with the components of the phenolic and aldehyde formulations and the corresponding steps has a special structure. Specifically, the modified resin containing branched structures forms three-dimensional steric hindrance through its side chains, which can encapsulate solvent molecules and restrict their diffusion paths. This makes it very suitable for producing high-temperature halogen-free fluxes, effectively preventing solvent evaporation at high temperatures, thereby improving the high-temperature resistance of the aforementioned high-temperature halogen-free fluxes and maintaining the active atmosphere of the flux at high temperatures. This makes it suitable for high-temperature reflow soldering processes. Therefore, the terpene resin-modified phenolic resin possesses the ability to remove metal oxides and has high-temperature resistance, while existing phenolic resins do not have the function of removing metal oxides.

[0042] One of the beneficial effects of this application is that the temperature and catalyst settings for adding terpene monomers to toluene solvent are conducive to a full reaction and the formation of a terpene resin matrix.

[0043] One of the beneficial effects of this application is that the weight ratio of phenol to formaldehyde is set so that the reaction is sufficient and appropriate. The phenolic resin formed after the terpene resin matrix is ​​purified by polycondensation according to the above steps has low impurity content, low boiling point and low residual catalyst, and is suitable for the preparation of high temperature halogen-free flux.

[0044] One of the beneficial effects of this application is that the modified surfactant is prepared by stearylamine and ethylene oxide with a catalyst. The modified surfactant with such a formulation is a low-volatility surfactant, which is very beneficial for use under high temperature conditions and improves the wettability of solder to the substrate.

[0045] One of the beneficial effects of this application is that the low-volatility modified surfactant can not only improve the wettability of the solder to the substrate, but also reduce the wetting angle of the solder joint by combining the self-leveling properties of the branched modified resin.

[0046] One of the beneficial effects of this application is that the activators, such as pyromellitic acid, tetracarboxylic acid, DL-pyroglutamic acid, azelaic acid, hexadecenedicarboxylic acid, octadecenedicarboxylic acid, octadecenedicarboxylic acid, and trididecenedicarboxylic acid, which are high-melting-point organic acids, remain active at temperatures ≥300℃, effectively removing metal oxides and reducing the surface tension of the solder, improving the spreadability of the molten solder, and reducing the rate of cold solder joints and voids.

[0047] One of the beneficial effects of this application is that metal salts, such as oxalate (C2O4), act as synergistic activators. 2- It has two carboxylic acid groups and can coordinate with Sn via bidentate coordination. 4+ They combine to form a highly stable octahedral complex [Sn(C2O4)3] 2- This weakens the Sn-O bond, significantly reducing the lattice energy of SnO2, causing it to dissociate from the solid lattice and enter the solution, thus improving the dissolution efficiency. Oxalate remains stable under weakly acidic to neutral conditions, and its coordination ability increases with increasing pH. However, excessive acidity (pH < 2) may lead to oxalate molecularization (H2C2O4), reducing coordination efficiency. The conditions used in this application are weakly acidic to neutral.

[0048] One of the beneficial effects of this application is that metal salts act as synergistic activators, such as the citrate ion (C6H5O7) in nickel citrate. 3- It contains three carboxylic acid groups and one hydroxyl group, and can react with Sn under acidic conditions. 4+ Formation of multidentate complexes such as [Sn(C6H5O7)2] 2- to further enhance Sn 4+ The solubility of Sn is affected by the chelation reaction. 4+The positive charge inhibits the redeposition of SnO2, preventing secondary oxidation of tin alloys at high temperatures. Citric acid can simultaneously donate protons (H+) within the pH range of 2–4. + ) and ligand (C6H5O7) 3- ), which dissolves SnO 2 Surface oxides, in turn, promote Sn through complexation. 4+ Mass transfer and diffusion. Fe 2+ High-valence tin Sn 4+ Restore to Sn 2+ This lowers the oxidation state of tin, making it more soluble in acidic environments. Metal cations (Ni) 2+ Sn 2+ Adsorbed on the surface of tin oxide, it lowers the activation energy of the reaction and accelerates the reaction rate between carboxylic acid and the oxide layer.

[0049] One of the beneficial effects of this application is that metal salts act as synergistic activators, and the oxalate ions (C2O4) in oxalates such as cobalt and stannous oxalate... 2- It has two carboxylic acid groups and can coordinate with Sn via bidentate coordination. 4+ They combine to form a highly stable octahedral complex [Sn(C2O4)3] 2- This weakens the Sn-O bond, significantly reducing the lattice energy of SnO2, causing it to dissociate from the solid lattice and enter the solution, thus improving dissolution efficiency. Oxalate remains stable under weakly acidic to neutral conditions.

[0050] One of the beneficial effects of this application is that it removes large-diameter particles from the solder paste using a vacuum negative pressure filtration device, thereby producing high-temperature lead-free solder paste and ensuring that the particle diameter in the high-temperature lead-free solder paste meets the design requirements.

[0051] One of the beneficial effects of this application is the use of segmented vacuum technology for negative pressure filtration of solder paste. The rapid extraction stage (≤10 seconds to -0.05MPa) quickly establishes a vacuum environment, reducing the paste exposure time. The slow extraction stage (pressure gradient ≤ -0.01MPa / min) precisely controls impurity separation and prevents filter clogging.

[0052] One of the beneficial effects of this application is that the modified thermoplastic resin and modified surfactant, together with high-boiling-point solvents, rosin, activators, and thixotropic agents, form a unique formulation that enables the halogen-free flux to withstand high temperatures and ensures the reliability of welding during high-temperature reflow soldering.

[0053] One of the beneficial effects of this application is that the ratio of lead-free metal alloy powder and high-temperature halogen-free flux is suitable for high-temperature reflow soldering.

[0054] One of the advantages of this application is that the lead-free metal alloy powder includes alloy powders of various different metals and alloy powders of various particle sizes, making the flux applicable to a wide range of applications.

[0055] One of the advantages of this application is that the method for preparing high-temperature halogen-free flux and solder paste is simple, efficient, and has high production efficiency.

[0056] One of the beneficial effects of this application is that vacuum negative pressure filtration in the solder paste preparation method can effectively remove large-diameter particles, ensure product consistency, and is very suitable for fine printing, dispensing, and inkjet printing processes.

[0057] One of the advantages of this application is that the solder powder has a particle size of 2~25um and the particle size models include T4 / T5 / T6 / T7 / T8, which has good adaptability and is suitable for packaging processes of various sizes of components. Attached Figure Description

[0058] Figure 1 It is a high-temperature solder welding reflow temperature and time curve;

[0059] Figure 2 This demonstrates the test results of weld void rate and surface insulation resistance after welding in the examples and comparative examples.

[0060] Figure 3 These are the formulation components of Example 1 of the high-temperature halogen-free flux;

[0061] Figure 4 This is the formulation component of Example 2 of the high-temperature halogen-free flux;

[0062] Figure 5 These are the formulation components of Examples 1-10 of high-temperature halogen-free flux;

[0063] Figure 6 These are the formulation components of comparative examples 1-6 of high-temperature halogen-free flux;

[0064] Figure 7 This is an X-ray image of the weld point location after welding in Example 3;

[0065] Figure 8 This is an X-ray image of the weld point location after welding in Comparative Example 3;

[0066] Figure 9 This is an X-ray image of the weld point location after welding in Example 4;

[0067] Figure 10 This is an X-ray image of the weld point location after welding in Comparative Example 4.

[0068] Figure 11 This is an X-ray image of the weld point location after welding in Example 6;

[0069] Figure 12 This is an X-ray image of the weld point location after welding, as shown in Comparative Example 6. Detailed Implementation

[0070] The contents of this application will be further described in detail below with reference to the accompanying drawings.

[0071] Rosin and modified rosin are common flux components in solder, and they play different roles in the soldering process.

[0072] Definitions:

[0073] Rosin is a natural product extracted from the resin of pine trees. Its main component is rosin acid. It has good chemical stability and is a complex mixture, but its activity is low, making it suitable for welding scenarios where the flux activity requirements are not high.

[0074] Modified rosin: This refers to rosin that has been treated using physical or chemical methods to improve its properties or impart new functional products. Modification methods include esterification, hydrogenation, and polymerization. It is suitable for applications requiring high welding temperatures and quality.

[0075] The activator in solder primarily functions to remove oxides from the solder pads and solder surface at soldering temperatures, thereby improving the wettability between the solder and pads. It removes the oxide layer through a chemical reaction with metal oxides, providing a clean metal surface for soldering and promoting metallurgical bonding between the solder and the metal being soldered. The stronger the activator's activity, the greater the potential for post-soldering corrosion; therefore, proper selection and control of its dosage are necessary. The presence of the activator is one of the factors affecting the lifespan of solder paste on the board.

[0076] Surfactants: Their main function is to reduce the surface tension of the flux and increase its wettability to solder powder and pads. They enable liquid solder to better integrate into the weld, improving solder quality. This effect is particularly pronounced in lead-free soldering because lead-free solder has a higher melting point and greater surface tension.

[0077] Surfactants can be classified into nonionic surfactants, such as OP series and fluorinated aliphatic polymeric ethers; anionic surfactants, such as sodium diethyl succinate sulfonate; cationic surfactants, such as hexadecyltrimethylammonium bromide; and amphoteric surfactants. Ionic surfactants can affect the activity of the active agent, so nonionic surfactants are generally preferred. Furthermore, surfactants are not easily volatile and may leave hygroscopic residues after soldering; therefore, their usage should generally be limited.

[0078] Ethylene oxide-induced reaction (EO-Induced Reaction) refers to a chemical process in which ethylene oxide (EO) serves as a key reaction intermediate or initiator, inducing the polymerization or functionalization of other molecules (such as compounds containing active hydrogen) through ring-opening reactions under specific catalytic conditions. Its core mechanism involves the release of the three-membered ring strain of EO to generate a highly reactive oxonium ion intermediate, which then drives subsequent nucleophilic addition or chain propagation reactions.

[0079] In this application, mass percentage % means weight percentage wt%. In this application, the modified resin in the accompanying drawings means modified thermoplastic resin.

[0080] like Figure 3 Example 1 of the high-temperature halogen-free flux comprises the following components by weight percentage: 34.7% tetraethylene glycol dimethyl ether; 10.0% triethylene glycol; 4.8% polypropylene glycol 400; 18.0% rosin KE-604; 15.0% rosin KR330; 3.0% modified thermoplastic resin; 1.0% pyromellitic acid; 3.5% azelaic acid; 1.0% dodecyl dicarboxylic acid; 0.2% ferrous sulfate; 0.4% stannous oxalate; 1.9% antioxidant 330; 0.5% modified surfactant; and 6.0% modified polyamide wax DISPARLON 6500.

[0081] The preparation steps of the high-temperature halogen-free flux in Example 1 are as follows:

[0082] Step 1: Weigh out 34.7% tetraethylene glycol dimethyl ether, 10% triethylene glycol, and 4.8% polypropylene glycol by weight percentage and add them to a container, then heat to 80°C.

[0083] Step 2: Add 6% DISPARLON 6500 thixotropic agent and stir at 1200 rpm for 60 minutes until homogeneous.

[0084] Step 3: Reduce the temperature to 70℃, and weigh out the following components by mass percentage: 18% rosin KE-604, 15% rosin KR330, 3.0% modified thermoplastic resin, 1% trimesic acid, 3.5% azelaic acid, 1.0% dodecenedicarboxylic acid, 0.2% ferrous sulfate, 0.4% stannous oxalate, 1.9% antioxidant 330, and 0.5% modified surfactant. Add these components to a container and stir at a constant temperature until dissolved.

[0085] Step 4: Reduce the speed to 100 rpm / min, stir for 20 minutes to remove air bubbles from the flux, remove and cool to a paste consistency.

[0086] Step 5: Place the material in a three-roll mill and grind it until the crystals are less than 10 micrometers to complete the production of high-temperature flux.

[0087] The preparation method of the above-mentioned modified surfactant includes:

[0088] Step B1: Add stearylamine to the high-pressure reactor, purge with nitrogen to replace the air, then evacuate to -0.08 MPa and heat to 100°C to dehydrate for 1.5 hours;

[0089] Step B2: Add 0.8% (by weight of stearylamine) of sodium hydroxide (NaOH) catalyst, heat to 150°C, and introduce ethylene oxide in stages: initially add 5% (by weight of total ethylene oxide) to induce the reaction, and add the remaining amount after confirming that the temperature is stable. Control the reaction pressure at 0.2 MPa, the stirring speed at 400 rpm, and the total reaction time at 2.5 hours. In Step B2, the total amount of ethylene oxide to the mass ratio of stearylamine is 82:100.

[0090] Step B3: After the reaction is complete, cool down to 70°C and purge with nitrogen to remove unreacted ethylene oxide;

[0091] Step B4: Add acetic acid to neutralize the catalyst, and filter to obtain octadecylamine polyoxyethylene ether with an oxyethylene addition number of 5 moles.

[0092] The preparation method of the above-mentioned modified thermoplastic resin includes:

[0093] Step A1: Preparation of terpene resin matrix: α-terpene monomer and toluene solvent were added to the reactor at a mass ratio of 1:1.2 and the temperature was raised to 45°C. Anhydrous aluminum trichloride catalyst, equivalent to 7% of the mass of α-terpene, was slowly added under stirring, and the reaction was carried out at 45°C for 5 hours. After the reaction was completed, deionized water was added for neutralization, and the aqueous phase was washed until neutral. The aqueous layer was separated, and the organic phase was distilled under reduced pressure to remove toluene, resulting in a pale yellow terpene resin matrix. The softening temperature of the terpene resin matrix was 90-110°C.

[0094] Step A2: Preparation of terpene phenolic resin: A2.1 Preparation of phenolic resin prepolymer: In a reactor equipped with a reflux condenser, stirrer and thermometer, phenol and 37% formaldehyde aqueous solution are added, with a molar ratio of phenol to formaldehyde of 1:1.05; 36% hydrochloric acid is slowly added, with a mass ratio of 36% hydrochloric acid to phenol of 1.6:100; the temperature is raised to 85-90℃ under stirring, and the reaction is refluxed for 2.5-3 hours; then the mixture is dehydrated under reduced pressure at 70-75℃ and -0.09 MPa for 1 hour to obtain a viscous thermoplastic phenolic resin prepolymer, which is then cooled to 80℃ for later use.

[0095] A2.2 Blending and Reaction: The terpene resin matrix obtained in step A1 is added to the phenolic prepolymer, wherein the mass ratio of the terpene resin matrix to the initial mass of phenol in step A2.1 is 1:0.7; under nitrogen protection, the mixture is stirred and heated to 125-135℃ for 1.5-2 hours; then the temperature is raised to 145-150℃ and solvent volatiles are removed under a vacuum of -0.095 MPa or higher for 1-1.5 hours to obtain molten modified terpene phenolic resin.

[0096] Step A3: Product molding and refining: The molten modified terpene phenolic resin obtained in step A2.2 is discharged under nitrogen protection, cooled and granulated in a cold water bath to obtain a branched terpene phenolic resin.

[0097] A method for preparing high-temperature lead-free solder paste includes the following steps:

[0098] Step 1: Mix 88% of T4 type lead-free metal alloy powder with 12% of the high-temperature halogen-free flux prepared in the above embodiment by weight percentage;

[0099] Step 2: Under ambient temperature of 25℃ and humidity of 50%, add the solder paste mixed in Step 1 into the mixer;

[0100] Step 3: Seal the mixer, set the mixing speed to 18 rpm, mix for 25 minutes, stop the machine to remove any dead spots, and repeat the mixing of the alloy powder once more.

[0101] Step 4: The mixed solder paste is thoroughly stirred and defoamed in a vacuum mixer at 80 rpm for 18 minutes;

[0102] Step 5: Using a vacuum negative pressure filtration device with segmented vacuum technology, the fast vacuum stage reaches a negative pressure of -0.05MPa in 10 seconds, and the slow vacuum stage has a pressure gradient of -0.01MPa / min; the upper layer has a 50um pore size filter screen and the lower layer has a 30um pore size filter screen to remove large particle impurities in the solder paste, thus producing high-temperature lead-free solder paste.

[0103] like Figure 4 Example 2 of a high-temperature halogen-free flux comprises the following components by weight percentage: 30.0% diethylene glycol dibutyl ether; 12.0% tetraethylene glycol; 6.1% polypropylene glycol 400; 14.0% rosin R-140; 11.0% rosin KHR130; 8.0% modified thermoplastic resin; 3.0% DL-pyroglutamic acid; 3.5% azelaic acid; 1.0% hexadecenedicarboxylic acid; 0.6% nickel citrate; 0.3% cobalt oxalate; 4.5% antioxidant 330; 0.5% modified surfactant; and 5.5% modified hydrogenated castor oil THIXATROL ST.

[0104] The preparation steps for high-temperature halogen-free flux are as follows:

[0105] Step 1: Weigh out 30.0% diethylene glycol dibutyl ether, 12% tetraethylene glycol trioxide, and 6.1% polypropylene glycol by weight percentage and add them to a container, then heat to 80°C.

[0106] Step 2: Add 5.5% modified hydrogenated castor oil THIXATROL ST and stir at 1200 rpm for 60 minutes until homogeneous.

[0107] Step 3: Reduce the temperature to 60℃, and weigh out the following components by mass percentage: 14% rosin R-140, 11% rosin KHR130, 8.0% modified thermoplastic resin, 3.0% DL-pyroglutamic acid, 3.5% azelaic acid, 1.0% hexadecenedicarboxylic acid, 0.6% nickel citrate, 0.3% cobalt oxalate, 4.5% antioxidant 330, and 0.5% modified surfactant. Add these components to a container and stir at a constant temperature until dissolved.

[0108] Step 4: Reduce the speed to 150 rpm / min, stir for 20 minutes to remove air bubbles from the flux, remove and cool to a paste consistency.

[0109] Step 5: Place the material in a three-roll mill and grind it until the crystals are less than 10 micrometers to complete the production of high-temperature flux.

[0110] The preparation method of the above-mentioned modified surfactant includes:

[0111] Step B1: Add stearylamine to the high-pressure reactor, purge with nitrogen to replace the air, then evacuate to -0.09 MPa and heat to 100°C to dehydrate for 1.5 hours;

[0112] Step B2: Add 0.8% (by weight of stearylamine) of sodium hydroxide (NaOH) catalyst, heat to 150°C, and introduce ethylene oxide in stages: initially add 5% (by weight of total ethylene oxide) to induce the reaction, and add the remaining amount after confirming that the temperature is stable. Control the reaction pressure at 0.2 MPa, the stirring speed at 400 rpm, and the total reaction time at 2.5 hours. In Step B2, the total amount of ethylene oxide to the mass ratio of stearylamine is 82:100.

[0113] Step B3: After the reaction is complete, cool down to 70°C and purge with nitrogen to remove unreacted ethylene oxide;

[0114] Step B4: Add acetic acid to neutralize the catalyst, and filter to obtain octadecylamine polyoxyethylene ether with an oxyethylene addition number of 5 moles.

[0115] The preparation method of the above-mentioned modified thermoplastic resin includes:

[0116] Step A1: Preparation of terpene resin matrix

[0117] α-terpene monomer and toluene solvent were added to a reaction vessel at a mass ratio of 1:1.2, and the temperature was raised to 45°C. Anhydrous aluminum trichloride catalyst, equivalent to 7% of the mass of α-terpene, was slowly added under stirring, and the reaction was carried out at 45°C for 5 hours. After the reaction was complete, deionized water was added for neutralization and the mixture was washed until the aqueous phase was neutral, and the aqueous layer was separated. The organic phase was distilled under reduced pressure to remove toluene, yielding a pale yellow terpene resin matrix (softening point 90-110°C).

[0118] Step A2: Preparation of Terpene Phenolic Resin A2.1 Preparation of Phenolic Prepolymer: In a reactor equipped with a reflux condenser, stirrer, and thermometer, add phenol and a 37% formaldehyde aqueous solution (phenol:formaldehyde molar ratio = 1:1.05). Slowly add 36% hydrochloric acid (hydrochloric acid to phenol mass ratio = 1.6:100). Heat to 85-90℃ with stirring and reflux for 2.5-3 hours. Then dehydrate under reduced pressure at 70-75℃ and -0.09 MPa for 1 hour to obtain a viscous thermoplastic phenolic resin prepolymer, which is then cooled to 80℃ for later use. A2.2 Blending and Reaction: Add the terpene resin matrix obtained in Step A1 to the phenolic prepolymer at an initial mass ratio of terpene resin matrix to phenol of 1:0.7. Under nitrogen protection, stir and heat to 125-135℃ for 1.5-2 hours. The temperature was then raised to 145-150℃, and solvent volatiles were removed under a vacuum of -0.095 MPa or higher for 1-1.5 hours to obtain molten modified terpene phenolic resin.

[0119] Step A3: Product Shaping and Refining

[0120] The molten resin obtained in step A2.2 is discharged under nitrogen protection, cooled and granulated in a cold water bath to obtain a branched terpene phenolic resin.

[0121] A method for preparing high-temperature lead-free solder paste includes the following steps:

[0122] Step 1: Mix 87% of T6 type lead-free metal alloy powder with 13% of the high-temperature halogen-free flux prepared in the above embodiment by weight percentage;

[0123] Step 2: Under ambient temperature of 25℃ and humidity of 50%, add the solder paste mixed in Step 1 into the mixer;

[0124] Step 3: Seal the mixer, set the mixing speed to 25 rpm, mix for 15 minutes, stop the machine to remove any dead spots, and repeat the mixing of the alloy powder once more.

[0125] Step 4: The mixed solder paste is thoroughly stirred and defoamed in a vacuum mixer at 100 rpm for 18 minutes;

[0126] Step 5: Using a vacuum negative pressure filtration device with segmented vacuum technology, the fast vacuum stage reaches a negative pressure of -0.05MPa in 15 seconds, and the slow vacuum stage has a pressure gradient of -0.01MPa / min; the upper layer has a 30um pore size filter screen and the lower layer has a 15um pore size filter screen to remove large particle impurities in the solder paste, thus producing high-temperature lead-free solder paste.

[0127] Example 3 of a method for preparing high-temperature lead-free solder paste uses the same high-temperature halogen-free flux as in Example 2. The method for preparing high-temperature lead-free solder paste includes the following steps:

[0128] Step 1: Mix 86% of T7 type lead-free metal alloy powder with 14% of the high-temperature halogen-free flux prepared in Example 1 by weight percentage;

[0129] Step 2: Under ambient temperature of 27℃ and humidity of 45%, add the solder paste mixed in Step 1 into the mixer;

[0130] Step 3: Seal the mixer, set the mixing speed to 35 rpm, mix for 12 minutes, stop the machine to remove any dead spots in the mixing, and repeat the mixing of the above alloy powder once;

[0131] Step 4: After mixing, the solder paste is thoroughly stirred and defoamed in a vacuum mixer at 50 rpm for 20 minutes;

[0132] Step 5: Using a vacuum negative pressure filtration device with segmented vacuum technology, the fast vacuum stage reaches a negative pressure of -0.05MPa in 18 seconds, and the slow vacuum stage has a pressure gradient of -0.01MPa / min; the upper 15um pore size filter and the lower 10um pore size filter remove large particle impurities from the solder paste to produce high-temperature lead-free solder paste.

[0133] like Figure 5 Example 4 of a high-temperature halogen-free flux comprises the following components by weight percentage: 25.0% tetraethylene glycol butyl ether; 16.0% diethylene glycol; 24.0% rosin KE604; 14.0% rosin KHR130; 5.0% modified thermoplastic resin; 3.0% DL-pyroglutamic acid; 2.0% azelaic acid; 1.0% octadecene dicarboxylic acid; 1.0% nickel citrate; 1.0% copper sulfate; 2.0% 5-methylbenzotriazole and 1.0% p-tert-butylcatechol; 1.0% modified surfactant; and 4.0% modified hydrogenated castor oil THIXATROL ST.

[0134] The preparation steps for high-temperature halogen-free flux are as follows:

[0135] Step 1: Weigh out 25.0% tetraethylene glycol butyl ether and 16.0% diethylene glycol by weight percentage and add them to a container, then heat to 80°C.

[0136] Step 2: Add 4.0% modified hydrogenated castor oil THIXATROL ST and stir at 1200 rpm for 60 minutes until homogeneous.

[0137] Step 3: Reduce the temperature to 60℃, and weigh out the following components by mass percentage: 24% rosin KE604, 14% rosin KHR130, 5.0% modified thermoplastic resin, 3.0% DL-pyroglutamic acid, 2.0% azelaic acid, 1.0% octadecene dicarboxylic acid, 1.0% nickel citrate, 1.0% copper sulfate, 2.0% 5-methylbenzotriazole, 1.0% p-tert-butylcatechol, and 1.0% modified surfactant. Add these components to a container and stir at a constant temperature until dissolved.

[0138] Step 4: Reduce the speed to 70 rpm / min, stir for 20 minutes to remove air bubbles from the flux, remove and cool to a paste consistency.

[0139] Step 5: Place the material in a three-roll mill and grind it until the crystals are less than 10 micrometers to complete the production of high-temperature flux.

[0140] The modified thermoplastic resin, modified surfactant, and solder paste preparation method used in the examples are the same as in Example 2.

[0141] like Figure 5 Example 5 of a high-temperature halogen-free flux comprises the following components by weight percentage: 25.0% tetraethylene glycol butyl ether; 12% 2-ethyl-1,3-hexanediol; 7.0% polypropylene glycol 400; 14.0% rosin R 140; 16.0% rosin KHR130; 7.0% modified thermoplastic resin; 3.0% tetracarboxybenzoic acid; 5.0% azelaic acid; 0.8% ferrous sulfate; 0.7% cobalt oxalate; 1.8% antioxidant 264; 0.6% modified surfactant; 5.5% modified hydrogenated castor oil THIXATROL ST; and 1.6% EBS.

[0142] The preparation steps for high-temperature halogen-free flux are as follows:

[0143] Step 1: Weigh out 25.0% tetraethylene glycol butyl ether, 12% 2-ethyl-1,3-hexanediol, and 7.0% polypropylene glycol 400 by weight percentage and add them to a container, then heat to 130°C.

[0144] Step 2: Add 5.5% modified hydrogenated castor oil THIXATROL ST and 1.6% EBS, and stir at 1200 rpm / min for 60 minutes until homogeneous.

[0145] Step 3: Reduce the temperature to 60℃, and weigh out the following components by mass percentage: 14% rosin R 140, 16% rosin KHR130, 7.0% modified thermoplastic resin, 3.0% tetraformylbenzoic acid, 5.0% azelaic acid, 0.8% ferrous sulfate, 0.7% cobalt oxalate, 1.8% antioxidant 264, and 0.6% modified surfactant. Add these components to a container and stir at a constant temperature until dissolved.

[0146] Step 4: Reduce the speed to 150 rpm / min, stir for 20 minutes to remove air bubbles from the flux, remove and cool to a paste consistency.

[0147] Step 5: Place the material in a three-roll mill and grind it until the crystals are less than 10 micrometers to complete the production of high-temperature flux.

[0148] The modified thermoplastic resin, modified surfactant, and solder paste preparation method used in the examples are the same as in Example 2.

[0149] like Figure 5 Example 6, a high-temperature halogen-free flux, uses the same flux preparation method, modified thermoplastic resin, modified surfactant, and solder paste preparation method as Example 2. The ratio of alloy tin powder to flux in the solder paste is as follows: Figure 2 .

[0150] like Figure 5 Example 7 of high-temperature halogen-free flux: The flux preparation method, the modified thermoplastic resin and modified surfactant used, and the solder paste preparation method in this example are the same as in Example 2. The ratio of alloy tin powder to flux used in the solder paste is as follows: Figure 2 .

[0151] like Figure 5 Example 8, a high-temperature halogen-free flux, uses the same flux preparation method, modified thermoplastic resin, modified surfactant, and solder paste preparation method as Example 2. The ratio of alloy tin powder to flux in the solder paste is as follows: Figure 2 .

[0152] like Figure 5 Example 9 of a high-temperature halogen-free flux: The flux preparation method, the modified thermoplastic resin and modified surfactant used, and the solder paste preparation method in this example are the same as in Example 2. The ratio of alloy tin powder to flux used in the solder paste is as follows: Figure 2 .

[0153] like Figure 5 Example 10, a high-temperature halogen-free flux, uses the same flux preparation method, modified thermoplastic resin, modified surfactant, and solder paste preparation method as Example 2. The ratio of alloy tin powder to flux in the solder paste is as follows: Figure 2 .

[0154] To better compare the technical effects, a comparative example was designed during the development process of this application.

[0155] The difference between Comparative Example 1 and Example 1 is that the flux used is a conventional halogen-containing flux; the preparation method of the high-temperature lead-free solder paste of Comparative Example 1 is the same as that of Example 1.

[0156] The difference between Comparative Example 2 and Example 2 is that the flux formulation used in Comparative Example 2 did not contain modified thermoplastic resin, but was replaced with KE604 rosin. The material formulation used is as follows: Figure 6 .

[0157] The preparation method of the high-temperature lead-free solder paste of Comparative Example 2 is the same as that of Example 2.

[0158] The difference between Comparative Example 3 and Example 2 is that the flux formulation used in Comparative Example 3 did not contain a modified surfactant, but instead used the conventional surfactant GE511. The material formulation used is as follows: Figure 6 The preparation method of the high-temperature lead-free solder paste in Comparative Example 3 is the same as that in Example 2.

[0159] The difference between Comparative Example 4 and Example 4 is that the flux formulation used in Comparative Example 4 does not contain metal salts, but is replaced with rosin KE604. The material formulation used is as follows: Figure 6 The preparation method of the high-temperature lead-free solder paste in Comparative Example 4 is the same as that in Example 4. Figure 9 This is an X-ray cavity image of the weld joint location in Example 4. Figure 10 This is an X-ray void image of the solder joint location in Comparative Example 4; the red area in the image represents the void region. Figure 9 and Figure 10 As can be seen from the comparison, Example 4 showed a significant reduction in welding void rate compared to Comparative Example 4.

[0160] The difference between Comparative Example 5 and Example 5 is that the flux formulation used does not contain modified thermoplastic resin, but is replaced with rosin KE604; and the modified surfactant is replaced with azelaic acid. The material formulation used is as follows: Figure 6 The preparation method of the high-temperature lead-free solder paste in Comparative Example 5 is the same as that in Example 5.

[0161] The difference between Comparative Example 6 and Example 6 is that the flux formulation used does not contain metal salts, but is replaced with pyromellitic acid; octadecene dicarboxylic acid is replaced with sebacic acid, and the material formulation used is as follows: Figure 6 The preparation method of the high-temperature lead-free solder paste in Comparative Example 6 is the same as that in Example 6. Figure 11 This is an X-ray cavity image of the weld joint location in Example 6. Figure 12 This is an X-ray void image of the solder joint location shown in Scale 6; the red area in the image represents the void region. Figure 11 and Figure 12 As can be seen from the comparison, Example 6 showed a significant reduction in welding void rate compared to Comparative Example 6.

[0162] Performance testing: The solder paste provided in Examples 1-10 and Comparative Examples 1-6 of this application was used for printed surface mount reflow soldering. The mounted chip was a QFN24 (4×4mm), and the substrate was a ceramic silver-plated pad. The high-temperature solder reflow temperature and time curves are shown in the attached figure. Figure 1 The solder joints underwent performance testing; detailed test results are attached. Figure 2 Performance testing methods include testing void ratio, surface insulation resistance, and spread rate.

[0163] Solder joint void ratio is one of the most direct indicators for inspecting solder paste. The specific method for detecting void ratio involves using an SMX-1000 X-ray device to penetrate the solder joint, capturing its internal structure through an imaging system, and detecting the location, size, and distribution density of voids. This information is then combined with grayscale analysis software to quantitatively calculate the void area. A lower solder joint void ratio indicates better wettability of the solder paste to the pads, better thermal and electrical conductivity, and consequently, higher solder joint reliability.

[0164] Surface insulation resistance (SIR) is one of the indicators of the environmental reliability of packaged solder. SIR measurement is performed according to IPC-TM-650 2.6.3.3 "Surface Insulation Resistance". A bias voltage (e.g., 50V DC) is applied to the PCB in a high-temperature, high-humidity environment (e.g., 85℃ / 85%RH) for 168 hours, and the trend of SIR change is monitored. Packaged devices, especially power devices, operate in harsh environments with complex temperature and humidity conditions, requiring high solder joint reliability. Devices with high SIR exhibit better performance in temperature and humidity environments.

[0165] Flux spread rate is a key performance indicator for measuring its wetting ability and activity. The spread rate test method is as follows: Refer to the national standard GB / T31474-2015 Flux for High-Quality Internal Interconnection in Electronic Assembly, section 6.8.1, Spread Rate Method. Cut five flat test pieces (50 mm × 50 mm × 0.5 mm) from a copper plate (grade T2) conforming to GB / T2040. After degreasing, remove the oxide film with 500-grit sandpaper and polish with polishing compound. Then clean with anhydrous ethanol and dry thoroughly. Place the test pieces in an oven at 150℃±2℃ for 1 hour for oxidation, ensuring all test pieces are at the same height within the oven. After removing the test pieces from the oven, place them in a sealed desiccator for later use. The solder bath temperature was set 50°C above the liquefaction temperature (the alloy was Sn90Sb10, melting point 245°C, solder bath temperature set to 295°C). 0.1g of the flux to be tested was placed in the center of the sample, and then 0.3g of SnSb10 alloy solder balls were placed on the flux. The sample was held horizontally on the molten solder surface of the solder bath for 30 seconds. The sample was removed and placed horizontally to cool to room temperature. Flux residue was wiped away with anhydrous ethanol, and the height h of each solder joint was measured. The equivalent ball diameter of 0.3g SnSb alloy is D, then the flux spread rate is E = (Dh) / D × 100%.

[0166] From the appendix Figure 2 The performance test results show that the spread rate reflects the flux's ability to remove oxides from the metal surface and reduce the surface tension of the molten solder, allowing it to more fully wet the copper surface and spread out. A higher spread rate indicates stronger wetting ability and better activity of the flux.

[0167] From the appendix Figure 2 The performance test results show that the high-temperature lead-free solder paste prepared by adapting the modified thermoplastic resin and modified surfactants proposed in this application to ultrafine lead-free alloy powder of T4 or above significantly improves the soldering performance.

[0168] In Example 3, the void ratio after welding was 3.8%, a decrease of 68.6% compared to the void ratio of 12.1% in Comparative Example 3. Figure 7 This is an X-ray cavity image of the weld joint location in Example 3. Figure 8 This is an X-ray void image of the solder joint location in Comparative Example 3; the red area in the image represents the void region. Figure 7 and Figure 8 As can be seen from the comparison, Example 3 showed a significant reduction in weld void rate compared to Comparative Example 3, demonstrating that modified thermoplastic resin and modified surfactant can improve the welding performance of high-temperature weld joints.

[0169] The surface insulation resistance (SIR) of the example group was stable at 10. 8 ~10 9Ω level, far exceeding the comparative example (10 5 ~10 7 (Ω), the flux spreading power of the example group is generally greater than 75%, exceeding that of the comparative example (65-74%). The high-temperature halogen-free flux prepared in this application, under the conditions of high-temperature reflow temperature curve, still obtains solder joints with good wetting, high spreading rate, bright solder joints and low void ratio after a long period of high temperature, which meets the requirements of high reliability electronic devices.

[0170] The high-temperature lead-free solder paste provided by this invention, under the conditions of high-temperature reflow temperature profile, undergoes a long high-temperature holding period. However, by improving the temperature resistance of the flux and alloy powder, this invention significantly enhances the high-temperature resistance of the solder paste, thereby ensuring good wetting, bright solder joints, and no solder beads during the soldering process.

[0171] Of particular importance is that this application uses materials resistant to high temperatures of 330–360°C, such as high-acid-value, high-temperature-resistant modified rosin KR330, tetramethylbenzoic acid, and tetraethylene glycol, which enable the solder paste to maintain high activity in the 330–360°C high-temperature range and form good soldering.

[0172] In this application, the applicable high-temperature range for the high-temperature halogen-free flux and high-temperature lead-free solder paste is a reflow peak temperature of 260-360℃. Their alloy melting point is 240-340℃.

[0173] The high-temperature halogen-free flux, solder paste, and their components and preparation methods described in this application include 40%–50% high-boiling-point solvent, 25%–40% rosin, 1%–8% modified thermoplastic resin, 5%–10% activator, 0.5%–1.0% modified surfactant, 4%–8% thixotropic agent, 0.5%–3% metal salt, and 1.5%–5% antioxidant. The modified thermoplastic resin is obtained by modifying a terpene resin matrix with phenols and aldehydes. The modified surfactant is obtained by reacting stearyl amine with ethylene oxide and a catalyst. The solder paste includes 85%–88% lead-free metal alloy powder and 12%–15% high-temperature halogen-free flux. Weigh the organic solvent and add it to a container, then heat it to 80-95℃. Add the thixotropic agent and stir until homogeneous. Reduce the temperature to 60-70℃, then weigh and add rosin, modified thermoplastic resin, activator, metal salt, antioxidant, and modified surfactant. Stir at a constant temperature until dissolved, remove the air bubbles from the flux, and cool it into a paste. Grind the material to obtain a high-temperature halogen-free flux.

[0174] The above are merely embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of the application specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A high-temperature halogen-free flux, characterized in that, the component composition by weight percentage includes: 40-50% of high-boiling-point solvent, 25-40% of rosin, 1-8% of modified thermoplastic resin, 5-10% of active agent, 0.5-1.0% of modified surfactant, and 4-8% of thixotropic agent; the high-boiling-point solvent is two or more than two combinations of tetraethylene glycol dimethyl ether, tetraethylene glycol butyl ether, diethylene glycol dibutyl ether, polyethylene glycol butyl ether, diethylene glycol, triethylene glycol, tetraethylene glycol, 2-ethyl-1, 3-hexanediol, and polypropylene glycol 400; the modified surfactant is octadecylamine polyoxyethylene ether; the modified thermoplastic resin is terpene phenolic resin; the preparation method of the modified thermoplastic resin, i.e. terpene phenolic resin, includes the following steps: Step A1: Preparation of terpene resin matrix: α-terpene monomer and toluene solvent were added into a reaction kettle at a mass ratio of 1:1.2, and the temperature was raised to 45℃; 7% of anhydrous aluminum chloride catalyst based on the mass of α-terpene was slowly added under stirring, and reacted at 45℃ for 5 hours; after the reaction was completed, deionized water was added for neutralization, and washed until the aqueous phase was neutral; the organic phase was distilled under reduced pressure to remove toluene, and a light yellow terpene resin matrix was obtained, with a softening temperature point of 90-110℃; Step A2: Preparation of terpene phenolic resin: A2.1 Preparation of phenolic resin prepolymer: phenol and 37% formaldehyde aqueous solution were added into a reaction kettle equipped with a reflux condenser, a stirrer and a thermometer, and the molar ratio of phenol to formaldehyde was 1:1.05; 36% hydrochloric acid was slowly added, and the mass ratio of 36% hydrochloric acid to phenol was 1.6:100; the temperature was raised to 85-90℃ under stirring, and refluxed for 2.5-3 hours; then dehydrated under reduced pressure at 70-75℃ and -0.09 MPa for 1 hour to obtain a viscous thermoplastic phenolic resin prepolymer, which was cooled to 80℃ for standby; A2.2 Blending and reaction: the terpene resin matrix prepared in step A1 was added into the phenolic prepolymer, and the mass ratio of the terpene resin matrix to the initial mass of phenol in step A2.1 was 1:0.7; under nitrogen protection, the mixture was stirred and heated to 125-135℃, and reacted for 1.5-2 hours; then the temperature was raised to 145-150℃, and the solvent volatiles were removed under a vacuum degree of -0.095 MPa for 1-1.5 hours to obtain a molten modified terpene phenolic resin; Step A3: Product shaping and refining: the molten modified terpene phenolic resin obtained in step A2.2 was discharged under nitrogen protection, cooled and granulated in a cold water tank to obtain a branched terpene phenolic resin.

2. The high-temperature halogen-free flux according to claim 1, characterized in that, the preparation method of the octadecylamine polyoxyethylene ether includes the following steps: Step B1: Stearylamine was added into a high-pressure reaction kettle, and after replacing air with nitrogen, vacuum was applied to ≤-0.08 MPa, and the temperature was raised to 100℃ for dehydration for 1.5 hours; Step B2: add 0.8% stearic amine mass of NaOH catalyst, heat to 150℃, and then add ethylene oxide in stages: add 5% of the total mass of ethylene oxide to induce the reaction, and then add the remaining amount after confirming that the temperature is stable, control the reaction pressure at 0.2 MPa, the stirring speed at 400 rpm, and the total reaction time at 2.5 hours; in step B2, the total amount of ethylene oxide and the mass ratio of stearic amine are 82:100; Step B3: after the reaction is completed, reduce the temperature to 70℃, and remove the unreacted ethylene oxide by passing nitrogen gas; Step B4: add acetic acid to neutralize the catalyst, and filter to obtain octadecylamine polyoxyethylene ether with an oxyethylene addition number of 5 moles. 3.The high-temperature halogen-free flux according to claim 1, characterized in that, Any one of the following technical features is included: TB1: the active agent is at least one of trimesic acid, tetracarboxybenzoic acid, DL-pyroglutamic acid, azelaic acid, hexacosene diacid, octacosene diacid, and dodecane diacid; TB2: the thixotropic agent is at least one of modified polyamide wax DISPARLON 6500, EBS, and modified hydrogenated castor oil ST. 4.The high-temperature halogen-free flux according to claim 1, characterized in that, 0.5% to 3% of a metal salt and 1.5% to 5% of an antioxidant are further included. 5.The high-temperature halogen-free flux according to claim 4, characterized in that, Any one of the following technical features is included: TA1: the metal salt is at least one of ferrous sulfate, copper sulfate, nickel citrate, cobalt oxalate, and stannous oxalate; TA2: the antioxidant is at least one of 5-methylbenzotriazole, benzotriazole octadecylamine salt, p-tert-butyl catechol, antioxidant 330, and antioxidant 264.

6. A high temperature, halogen-free solder paste characterized in that, The composition of the ingredients by weight percentage includes: 85% to 88% of lead-free metal alloy powder; 12% to 15% of the high-temperature halogen-free flux according to any one of claims 1 to 5. 7.The high-temperature halogen-free tin paste according to claim 6, characterized in that, the lead-free metal alloy powder includes at least one of SnSb, SnSbCu, SnAgCu, and SnSbAgCu alloy powder; and further includes 0 to 0.5% of trace metal elements; the trace metal elements include one or more of Ni, In, Bi, Mn, and Co; the melting point of the alloy is between 240 and 340℃; the lead-free metal alloy powder includes one or more of T4, T5, T6, T7, and T8 type powders.

8. A process for the preparation of a high temperature halogen-free flux for the preparation of a high temperature halogen-free flux according to claim 4, characterized in that, It includes: Step D1: add 40% to 50% of the organic solvent by weight percentage to the container, and heat to 80℃ to 135℃; Step D2: add 4% to 8% of the thixotropic agent, and stir until uniform; Step D3: reduce the temperature to 60 to 70℃, add 25% to 40% of the rosin, 5% to 10% of the active agent, 0.5% to 3% of the metal salt, 1.5% to 5% of the antioxidant, 0.5% to 1.0% of the modified surfactant, and 1% to 8% of the modified thermoplastic resin to the container by mass percentage, and stir until dissolved at a constant temperature; Step D4: Stirring to remove the air bubbles in the flux, then remove and cool into paste; Step D5: Grinding the material to make the high temperature halogen-free flux.

9. The high temperature halogen-free flux preparation method of claim 8, wherein, Step D2: After adding the thixotropic agent, stirring at 1200 rpm for 30-60 min until uniform; Step D4: Stirring to remove the air bubbles in the flux, which is to reduce the stirring speed to 100-200 rpm / min, stirring for 20 min to remove the air bubbles in the flux, then remove and cool into paste; Step D5: Grinding the material to make the high temperature halogen-free flux.

10. A method of preparing a tin paste, characterized by: The high temperature halogen-free solder paste of claim 6, Step C1: At ambient temperature 25±2℃ and humidity 40%-60%, adding the high temperature halogen-free flux of claim 5 and lead-free metal alloy powder into the stirrer; Step C2: Sealing the stirrer, setting the stirring speed to 15-60 rpm, stirring for 10 min, stopping the stirring to deal with the dead angle, and repeating the mixing of the lead-free metal alloy powder and the high temperature halogen-free flux once; Step C3: After mixing, the solder paste is vacuumed to -0.06 MPa in the vacuum stirrer, and is fully stirred at 30-100 rpm for 10-20 min to remove the air bubbles; Step C4: Removing the large particle size particles in the solder paste through the vacuum negative pressure filtration device to make the high temperature lead-free solder paste.

11. The solder paste preparation method of claim 10, wherein, Step C4: Removing the large particle size particles in the solder paste through the vacuum negative pressure filtration device; The vacuum negative pressure filtration device is provided with a plurality of filter screens with a pore size of 5-50 μm for removing the large particle size particles in the solder paste; The mixed solder paste is subjected to staged vacuuming in the vacuum negative pressure filtration device; The staged vacuuming includes a first stage and a second stage, The first stage is a fast vacuuming stage ≤10 s to reach a negative pressure of -0.05 MPa; The second stage is a slow vacuuming stage with a pressure gradient ≤-0.01 MPa / min.

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