High-reliability water-based low-solid soldering flux for electronic welding and preparation method of high-reliability water-based low-solid soldering flux

Abstract

The invention discloses a high-reliability water-based low-solid soldering flux for electronic welding and a preparation method of the high-reliability water-based low-solid soldering flux. The soldering flux is prepared from the following raw materials: 1.80 to 4.00 w percent of organic acid, 0.50 to 0.80 w percent of organic amine, 0.13 to 0.22 w percent of halogen-containing activity enhancer, 0.40 to 0.80 w percent of halogen-free activity enhancer, 0.10 to 0.20 w percent of surfactant, 0.50 to 0.80 w percent of film-forming agent, 0.30 to 0.50 w percent of antioxidant, 0.20 to 0.50 w percent of corrosion inhibitor, 6.00 to 10.00 w percent of cosolvent and the balance of deionized water. The soldering flux has the characteristics of high reliability, low solid content, no halogen and low corrosion, has the characteristics of high welding activity, bright welding spots, no halogen residue, low solid content and extremely few residues after welding and does not need to be cleaned, and is particularly suitable for welding scenes with extremely high requirements on cleanliness and reliability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electronic welding materials, and particularly relates to an environmentally-friendly water-based flux with high reliability and a preparation method thereof. BACKGROUND

[0002] With the rapid development of the electronic information industry, electronic components are increasingly evolving towards miniaturization, high density and high reliability. This puts forward higher standards for the key material in the electronic assembly process, namely, flux, which not only needs to have excellent welding performance, but also must meet multiple requirements such as environmental protection, safety and subsequent process compatibility.

[0003] At present, the fluxes widely used in the market mainly include the following types: (1) traditional rosin-based flux: which relies heavily on high content of natural or modified rosin as a film-forming material, and the solid content is generally higher than 5%. The viscous residue formed after welding covers the solder joints and PCB board surface, which not only affects the contact reliability of the subsequent in-circuit test (ICT) probe, but also easily causes electrochemical migration of the residual organic acid under a humid and hot environment, resulting in line corrosion and insulation resistance reduction. (2) alcohol-based flux: which uses solvents such as ethanol and isopropyl alcohol to improve processability, but the emission of a large amount of volatile organic compounds (VOCs) has the potential safety hazard of being flammable and explosive, and violates the green manufacturing concept; in addition, the halogen activator is generally introduced to pursue high activity, and the ion residue will directly erode the precision pads and device pins, which is a potential threat to long-term reliability. (3) first-generation water-based flux: which takes a key step in solving the VOC problem, but its formula design often has to give up something to get something: in order to compensate for the lack of water as a solvent in wetting and permeability, the content of organic acid or halide is often increased to ensure activity, which passively increases the solid content (usually >3%), increases the residue, and loses the advantage of "cleaning-free", and has strong corrosion after welding, poor system stability, and easy precipitation.

[0004] In recent years, research on water-based fluxes in China has become increasingly active, with numerous patents proposing improvement solutions from different perspectives. However, a series of problems remain unresolved. For example, CN109530971A discloses a low-carbon, low-volatility water-based flux with advantages such as halogen-free, rosin-free, low solid content, low cost, and no irritating odor, and it can avoid solder splattering. However, its formulation still contains alkylphenol polyoxyethylene ethers, which are regulated by the EU REACH regulation. CN108655609A provides a high-wetting water-based flux with strong wetting ability, good solder joint shear strength, and good corrosion resistance, but the system has a relatively high solid content. CN116604222A introduces an environmentally friendly, no-clean water-based flux suitable for photovoltaic modules, in which deionized water accounts for more than 96%. It is easy to use, has fewer welding defects, strong solder joint adhesion, and low residue. However, due to the lack of key components such as corrosion inhibitors and antioxidants, its long-term reliability is still unclear. In CN116944729A, by adding film-forming agents, aqueous organic acids, and cationic surfactants, the flux possesses excellent welding performance and post-soldering reliability, especially in inhibiting corrosion of special materials. However, its high solid content limits its application in applications requiring low residue. CN115338562A reports a water-based flux that uses only 3.0–4.0% succinic acid as an activator, resulting in a narrow activity range. CN120347425A develops a water-based flux for photovoltaic N-type cell OBB modules, employing a composite solvent system of deionized water and alcohols, effectively mitigating the negative impact on thermosetting adhesive pull strength and fine grid alloying. However, this formulation has a limited water content, essentially making it closer to a "semi-aqueous" system. In addition, CN119681497A and CN114406524A respectively proposed pre-coated water-based flux solutions for photovoltaic welding strips. The former emphasizes wettability and insulation performance, while the latter focuses on environmental protection and process compatibility. However, both have high solid content due to the high proportion of film-forming agents and organic acids. CN119216873A innovatively uses microencapsulated activators to make welding activity more durable, especially suitable for medium and low temperature photovoltaic welding scenarios. However, there is still room for improvement in the overall performance under high solid content systems.

[0005] In summary, although various water-based flux solutions have emerged in the existing technology, each with its own advantages in specific performance, they still generally face problems such as being "pseudo-water-based" or "semi-water-based", having high solid content, insufficient long-term reliability, and unsatisfactory corrosion control. An ideal balance has not yet been achieved between environmental friendliness, welding performance, and post-weld reliability. Summary of the Invention

[0006] To address the aforementioned technical bottlenecks, the core objective of this invention is to provide a water-based flux with high reliability, low solid content, halogen-free and low-corrosion properties, as well as its preparation method, to solve the problems of high solid content, halogen contamination and excessive residues in traditional products.

[0007] The technical solution adopted in this invention is as follows: A high-reliability water-based low-solids flux for electronic soldering, wherein the raw material composition of the flux is as follows (by weight percentage): Organic acids 1.80-4.00 w% Organic amines 0.50-0.80 w% Halogenated activity enhancer 0.13-0.22 w% Halogen-free activity enhancer 0.40-0.80 w% Surfactant 0.10-0.20 w% Film-forming agent 0.50-0.80 w% Antioxidant 0.30-0.50 w% Corrosion inhibitor 0.20-0.50 w% Cosolvent 6.00-10.00 w% Deionized water balance; The organic acids are used in a compound active system, composed of high-boiling-point organic acids and low-boiling-point organic acids, to ensure excellent activation performance over a wide temperature range. The high-boiling-point organic acids are selected from one or two of sebacic acid, octanoic acid, glutaric acid, and adipic acid; the low-boiling-point organic acids are selected from one or two of malonic acid, succinic acid, malic acid, and maleic acid. Through the synergistic effect of these high- and low-boiling-point organic acids, the activation efficiency is maximized.

[0008] The organic amine is one of ethanolamine, diethanolamine, and triethanolamine; The halogenated activity enhancer is one or more of n-butylamine hydrochloride, ammonium chloride, dibromobutenediol, and higher iodates; The halogen-free activity enhancer is one of ST-200, ST-400, and FR-500; The surfactant is one of Tween 80, Span 80, and AP-8; The film-forming agent is one of PEG-600, PEG-2000, PEG-4000, and PEG-6000; The antioxidant is one of tea polyphenols, ascorbic acid, hydroquinone, and resorcinol; The corrosion inhibitor is one of imidazole, 2-ethylimidazol, and benzotriazole; The co-solvent is two of the following: ethanol, isopropanol, diethylene glycol butyl ether, propylene glycol methyl ether, and diethylene glycol hexyl ether.

[0009] The preparation method of a high-reliability water-based low-solids flux for electronic welding according to the present invention comprises the following steps: (1) Dissolving the ingredients: Place the organic acid, halogenated active agent, halogen-free active agent, film-forming agent, corrosion inhibitor and antioxidant in a container, add the measured amount of cosolvent and deionized water, and stir at 20-45 °C for at least 30 minutes until the solid components are completely dissolved to obtain a clear solution; (2) Homogenization: Add organic amine and surfactant to the solution obtained in step (1), and continue stirring at 20-45 °C for 10-15 minutes until the mixture forms a homogeneous and transparent liquid, which is the flux.

[0010] This invention provides a truly water-based flux. Its activation system is composed of organic acids, organic amines, and selective activity enhancers. The design comprehensively considers the solubility of each component in water-based solvents, its wetting and spreading properties on metal surfaces, and its thermal stability to ensure continuous activation across the entire soldering temperature range. A strategy of combining high- and low-boiling-point organic acids is employed, utilizing the rapid action of low-boiling-point acids in the initial soldering stage and the sustained action of high-boiling-point acids in the high-temperature soldering zone, thereby widening the activation temperature window and improving the tinning speed and soldering efficiency. Organic amines simultaneously provide multiple synergistic functions, including pH adjustment, complexation stabilization, and corrosion inhibition. Furthermore, the addition of trace amounts of activity enhancers specifically strengthens the removal ability of stubborn oxide layers, enabling the application of flux under extreme solderability conditions.

[0011] The flux of the present invention has the following advantages: (1) Wide applicability and balanced performance: The flux formulation exhibits excellent welding compatibility with both copper-plated and tin-plated parts. According to IPC-TM-650 2.3.13A:2004, its acid value is controlled within the range of 30-38 mg KOH / g; according to IPC-TM-650 2.3.28.1:2004 automatic potentiometric titration, its halogen content (as Cl%) is at a low level of 0.03-0.07%. This design achieves a good balance between low corrosivity and high welding activity.

[0012] (2) Few residues after welding and high reliability: There are very few residues on the board surface after welding, and the residues are chemically inert and highly insulating. No secondary cleaning is required to meet the stringent requirements of cleanliness and long-term reliability of precision electronic assembly.

[0013] (3) Stable soldering process and excellent spatter control: During the soldering process, this flux exhibits significant low spatter characteristics. When evaluated according to the solder spatter test methods specified in standards such as J-STD-006 or IPC-TM-650 2.6.30, its spatter area is small and there are basically no solder beads falling, which is beneficial to improving the process window and production first pass rate.

[0014] (4) Wide range of applications and significant comprehensive benefits: This product can be widely used in wave soldering, dip soldering and other processes in precision electronic products, photovoltaic soldering ribbons, home appliances and automotive electronic control units. It has a fast tinning speed, full and bright solder joints and high welding yield, providing a high-quality material solution for green and high-reliability electronic assembly in related fields.

[0015] The flux and its preparation method of this invention aim to simultaneously achieve the following key characteristics: high welding activity to ensure excellent solder joint yield; complete halogen-free to guarantee long-term reliability; and by controlling the solid content to an extremely low level (e.g., ≤2.0%), enabling the solder residue to possess inherent insulation and chemical inertness, thereby achieving true "no-cleaning" and completely eliminating the need for subsequent cleaning processes. This product is specifically designed to address the challenges of high reliability and green manufacturing in wave soldering and dip soldering processes faced by precision electronics, automotive electronics, and new energy photovoltaic industries. Detailed Implementation

[0016] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the contents described in the embodiments. Example

[0017] A high-reliability water-based low-solids flux for electronic soldering, with the following raw material composition by weight percentage: Sebacic acid 1.50 w% 1.50 w% malonic acid Ethanolamine 0.60 w% ST-200 0.40 w% Dibromobutenediol 0.08 w% n-Butylamine hydrochloride 0.05 w% Tween 80 0.10 w% PEG-600 0.80 w% Tea polyphenols 0.30 w% Imidazole 0.20 w% Ethanol 5.00 w% Diethylene glycol butyl ether 5.00 w% Deionized water 84.47 w.

[0018] The preparation method of the high-reliability electronic welding water-based low-solids flux is as follows: At 40-45 °C, sebacic acid, malonic acid, ST-200, dibromobutenediol, n-butylamine hydrochloride, PEG-600, tea polyphenols, and imidazole are placed in a beaker and mixed with ethanol, diethylene glycol butyl ether, and deionized water. The mixture is stirred continuously at 800 rpm for 30 minutes until the solids are completely dissolved, yielding a clear solution. Then, ethanolamine and Tween 80 are added to the above solution, and the mixture is stirred at this temperature for 10-12 minutes at 800 rpm until a homogeneous, transparent, and stable liquid is formed, thus obtaining the water-based flux. Example

[0019] A high-reliability water-based low-solids flux for electronic soldering, with the following raw material composition by weight percentage: Caprylic acid 1.30 w% Succinic acid 1.20 w% Diethanolamine 0.50 w% ST-400 0.50 w% Dibromobutenediol 0.08 w% Higher iodate 0.10 w% Span 80 0.15 w% PEG-2000 0.50 w% Ascorbic acid 0.40 w% 2-Ethylimidazole 0.35 w% Isopropanol 4.00 w% Diethylene glycol hexyl ether 4.00 w% Deionized water 86.92 w.

[0020] The preparation method of the high-reliability electronic welding water-based low-solids flux is as follows: At 40-45 °C, succinic acid, succinic acid, ST-400, dibromobutenediol, higher iodate, PEG-2000, ascorbic acid, and 2-ethylimidazole are placed in a beaker and mixed with isopropanol, diethylene glycol hexyl ether, and deionized water. The mixture is stirred continuously at 800 rpm for 30 minutes until the solids are completely dissolved, yielding a clear solution. Then, diethanolamine and Span 80 are added to the above solution, and the mixture is stirred at this temperature for 10-12 minutes at 800 rpm until a homogeneous, transparent, and stable liquid is formed, thus obtaining the water-based flux. Example

[0021] A high-reliability water-based low-solids flux for electronic soldering, with the following raw material composition by weight percentage: Glutaric acid 1.00 w% maleic acid 1.00 w% Triethanolamine 0.50 w% FR-500 0.60 w% Dibromobutenediol 0.10 w% Higher iodate 0.10 w% AP-8 0.20 w% PEG-6000 0.60 w% Hydroquinone 0.30 w% Imidazole 0.20 w% Ethanol 3.00 w% Propylene glycol methyl ether 3.00 w% Deionized water 89.40 w.

[0022] The preparation method of the above-mentioned high-reliability electronic welding water-based low-solids flux is as follows: At 40-45 °C, glutaric acid, maleic acid, FR-500, dibromobutenediol, higher iodates, PEG-6000, hydroquinone, and imidazole are placed in a beaker and mixed with ethanol, propylene glycol methyl ether, and deionized water. The mixture is stirred continuously at 800 rpm for 30 minutes until the solids are completely dissolved, yielding a clear solution. Triethanolamine and AP-8 are then added to the solution, and the mixture is stirred at this temperature for 10-12 minutes at 800 rpm until a homogeneous, transparent, and stable liquid is formed, thus obtaining the water-based flux. Example

[0023] A high-reliability water-based low-solids flux for electronic soldering, with the following raw material composition by weight percentage: Adipic acid 1.00 w% Malic acid 0.80 w% Diethanolamine 0.80 w% ST-400 0.80 w% Dibromobutenediol 0.08 w% Higher iodate 0.07 w% Span 80 0.10 w% PEG-4000 0.50 w% Resorcinol 0.50 w% Benzotriazole 0.50 w% Ethanol 5.00 w% Diethylene glycol hexyl ether 4.00 w% Deionized water 85.85 w.

[0024] The preparation method of the above-mentioned high-reliability electronic welding water-based low-solids flux is as follows: At 40-45 °C, adipic acid, malic acid, ST-400, dibromobutenediol, higher iodate, PEG-4000, resorcinol, and benzotriazole are placed in a beaker and mixed with ethanol, diethylene glycol hexyl ether, and deionized water. The mixture is stirred continuously at 800 rpm for 30 minutes until the solids are completely dissolved, yielding a clear solution. Then, diethanolamine and Span 80 are added to the above solution, and the mixture is stirred at this temperature for 13-15 minutes at 800 rpm until a homogeneous, transparent, and stable liquid is formed, thus obtaining the water-based flux. Example

[0025] A high-reliability water-based low-solids flux for electronic soldering, with the following raw material composition by weight percentage: 1.50 w% of octanoic acid 0.80 w% malonic acid Succinic acid 0.90 w% Diethanolamine 0.80 w% ST-400 0.50 w% Ammonium chloride 0.08 w% Higher iodate 0.10 w% Span 80 0.10 w% PEG-4000 0.50 w% Hydroquinone 0.30 w% Benzotriazole 0.50 w% Isopropanol 5.00 w% Diethylene glycol hexyl ether 4.00 w% Deionized water 84.92 w.

[0026] The preparation method of the above-mentioned high-reliability electronic welding water-based low-solids flux is as follows: At 40-45 °C, succinic acid, malonic acid, succinic acid, ST-400, ammonium chloride, higher iodate, PEG-4000, hydroquinone, and benzotriazole are placed in a beaker and mixed with isopropanol, diethylene glycol hexyl ether, and deionized water. The mixture is stirred continuously at 800 rpm for 30 minutes until the solids are completely dissolved, yielding a clear solution. Then, diethanolamine and Span 80 are added to the above solution, and the mixture is stirred at this temperature for 13-15 minutes at 800 rpm until a homogeneous, transparent, and stable liquid is formed, thus obtaining the water-based flux. Example

[0027] A high-reliability water-based low-solids flux for electronic soldering, with the following raw material composition by weight percentage: Glutaric acid 2.00 w% Malic acid 1.00 w% Succinic acid 1.00 w% Triethanolamine 0.50 w% FT-500 0.50 w% Ammonium chloride 0.05 w% Dibromobutenediol 0.07 w% Higher iodate 0.10 w% AP-8 0.10 w% PEG-2000 0.80 w% Resorcinol 0.50 w% Benzotriazole 0.50 w% Ethanol 4.00 w% Diethylene glycol butyl ether 5.00 w% Deionized water 83.88 w.

[0028] The preparation method of the above-mentioned high-reliability electronic welding water-based low-solids flux is as follows: At 40-45 °C, glutaric acid, malic acid, succinic acid, FT-500, ammonium chloride, dibromobutenediol, higher iodates, PEG-2000, resorcinol, and benzotriazole are placed in a beaker and mixed with ethanol, diethylene glycol butyl ether, and deionized water. The mixture is stirred continuously at 800 rpm for 30 minutes until the solids are completely dissolved, yielding a clear solution. Triethanolamine and AP-8 are then added to the solution, and the mixture is stirred at this temperature for 13-15 minutes at 800 rpm until a homogeneous, transparent, and stable liquid is formed, thus obtaining the water-based flux.

[0029] According to the relevant test methods specified in the international standard IPC-TM-650, the acid value, halogen, non-volatile content, spread rate, copper plate corrosion, surface insulation resistance, RoHS and REACH tests were performed on Examples 1-6 above. The test results are shown in Table 1.

[0030] Table 1. Summary of Performance Testing of Water-Based Fluxes

[0031] As shown in Table 1, the water-based flux of this invention possesses the following characteristics: 1. Halogen-free; 2. Low corrosiveness; 3. Low solid content; 4. Low volatile gas emissions; 5. Excellent electrical reliability. Based on these characteristics, the flux demonstrates broad compatibility and applicability to various forms of solder, including solder wire, solder bar, and solder paste. Therefore, its application areas comprehensively cover the manufacturing processes of precision electronic products, photovoltaic solder ribbons, household appliances, and automotive electronic control units, which require extremely high cleanliness and reliability. It is particularly suitable for continuous production processes such as wave soldering and dip soldering.

Claims

1. A high-reliability water-based low-solids flux for electronic welding, characterized in that: The flux, by weight percentage, has the following raw material composition: Organic acids 1.80-4.00 w% Organic amines 0.50-0.80 w% Halogenated activity enhancer 0.13-0.22 w% Halogen-free activity enhancer 0.40-0.80 w% Surfactant 0.10-0.20 w% Film-forming agent 0.50-0.80 w% Antioxidant 0.30-0.50 w% Corrosion inhibitor 0.20-0.50 w% Cosolvent 6.00-10.00 w% Deionized water balance; The organic acid is a compound active system composed of high-boiling-point organic acid and low-boiling-point organic acid; wherein, the high-boiling-point organic acid is selected from one or two of sebacic acid, octanoic acid, glutaric acid and adipic acid; and the low-boiling-point organic acid is selected from one or two of malonic acid, succinic acid, malic acid and maleic acid. The organic amine is one of ethanolamine, diethanolamine, and triethanolamine; The halogenated activity enhancer is one or more of n-butylamine hydrochloride, ammonium chloride, dibromobutenediol, and higher iodates; The halogen-free activity enhancer is one of ST-200, ST-400, and FR-500; The surfactant is one of Tween 80, Span 80, and AP-8; The film-forming agent is one of PEG-600, PEG-2000, PEG-4000, and PEG-6000; The antioxidant is one of tea polyphenols, ascorbic acid, hydroquinone, and resorcinol; The corrosion inhibitor is one of imidazole, 2-ethylimidazol, and benzotriazole; The co-solvent is two of the following: ethanol, isopropanol, diethylene glycol butyl ether, propylene glycol methyl ether, and diethylene glycol hexyl ether.

2. The method for preparing a high-reliability water-based low-solids flux for electronic welding as described in claim 1, characterized in that, The steps are as follows: (1) Dissolving the ingredients: Place the organic acid, halogenated active agent, halogen-free active agent, film-forming agent, corrosion inhibitor and antioxidant in a container, add the measured amount of cosolvent and deionized water, and stir at 20-45 °C for at least 30 minutes until the solid components are completely dissolved to obtain a clear solution; (2) Homogenization: Add organic amine and surfactant to the solution obtained in step (1), and continue stirring at 20-45 °C for 10-15 minutes until the mixture forms a homogeneous and transparent liquid, which is the flux.

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