VOC-free water-soluble environmentally friendly soldering flux and its preparation method and application

Abstract

The present invention discloses a VOC-free water-soluble environmentally friendly soldering flux and a preparation method and application thereof, which belongs to the field of electronic packaging technology, wherein the soldering flux is composed of the following components by mass percentage: 30-70% ionic liquid; 5-30% organic acid; 0.2-10% cosolvent; the boiling point of the ionic liquid is greater than 300°C; the water-soluble soldering flux is prepared by heating, mixing, stirring and cooling, and can be used in electronic soldering processes. The present invention utilizes the low vapor pressure characteristics of ionic liquids to avoid the use of conventional solvents with low boiling points that are volatile at high temperatures, such as ethers or alcohols, thereby reducing VOC emissions in electronic soldering processes; at the same time, ionic liquids play a corrosion-inhibiting role in the high-temperature welding process, which is more efficient than traditional corrosion inhibitors and can significantly improve welding quality.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic packaging, and specifically relates to a VOC-free water-soluble environmentally friendly soldering flux and a preparation method and application thereof. Background Art

[0002] According to rough estimates, more than 70% of chemical and chemical processes use solvents in the preparation of chemicals and materials, separation, etc., and production efficiency is closely related to the properties and functions of solvents. Traditional organic solvents generally have problems such as volatility, low efficiency, and limited functions. At the same time, it is becoming increasingly difficult to achieve major technological breakthroughs using traditional solvents. The effective use of green solvents can not only avoid the use of harmful solvents and reduce environmental pollution, but also use their characteristics to often optimize and strengthen many chemical and chemical processes, reduce energy consumption, improve raw material utilization, and realize some chemical and chemical processes that are difficult or impossible to carry out under traditional conditions, providing broad space for the development of new, efficient, green technologies and solving major problems that are difficult to solve with traditional solvents. The use of environmentally friendly media is crucial to achieving green chemical processes.

[0003] Green solvents should be non-toxic, environmentally friendly, and easy to recycle. Their use should promote efficiency and save energy. Environmentally friendly media include water, ionic liquids, supercritical fluids, liquid polymers, biomass-based solvents and their mixed systems.

[0004] In the flux used for electronic welding, solvents are needed to dissolve functional materials, and their usage accounts for a large proportion. However, traditional organic solvent-based fluxes evaporate in large quantities during the high-temperature 260°C welding process, causing serious VOC emissions. As a substitute for volatile organic solvents, green solvents (such as water, ionic liquids, etc.) have good environmental friendliness and can therefore be used to replace toxic and harmful volatile organic solvents in the traditional chemical industry to achieve the goal of green chemistry.

[0005] Water-soluble flux is designed for use in high-temperature welding. After high temperature, it needs to be removed by water or aqueous cleaning fluid to remove residues. In order to improve welding quality, organic acid products are usually used to remove oxides on the solder surface, and corrosion inhibitors are used to inhibit oxidation and prevent the flux from oxidative decomposition under high temperature conditions. Because the solvent in the flux needs to be considered comprehensively to meet the solubility of various materials and needs to maintain high-temperature stability, the choice of solvent is particularly important. Taking corrosion inhibitors as an example, the amount of corrosion inhibitor added is limited by its solubility in the solvent, so the oxidation inhibition performance that can be produced is limited. However, due to the designability of its functional groups, ionic liquids take into account the role of solvents and corrosion inhibitors, broaden their dosage and selectivity in water-soluble fluxes, and can play an excellent role in oxidation inhibition, thereby making it possible to improve the welding quality of water-soluble fluxes.

[0006] Development status of water-soluble flux: CN 102398124 B / CN 100408257C use water to reduce VOC emissions. However, the two patents retain a certain weight ratio of solvents such as alcohols and ethers, with a mass ratio of 5~20% and 3~4% respectively; a large amount of VOC will still be generated during high-temperature welding. The use of ionic liquids as solvents in flux has never been reported. At the same time, the two patents use organic amines or nitrogen heterocyclic compounds as corrosion inhibitors to inhibit oxidation, and the use of functional groups of ionic liquids as corrosion inhibitors in flux has never been reported. Summary of the invention

[0007] In order to solve the problems raised in the above background technology, the present invention provides a VOC-free water-soluble environmentally friendly soldering flux and a preparation method and application thereof.

[0008] To achieve the above purpose, the present invention provides the following technical solution: a VOC-free water-soluble environmentally friendly flux, which is composed of the following components by mass percentage: 30-70% ionic liquid; 5-30% organic acid; 0.2-10% co-solvent; the boiling point of the ionic liquid is greater than 300°C.

[0009] The boiling point of ionic liquids is usually very high, and the specific value cannot be measured by experimental methods. This is because ionic liquids have already decomposed or sublimated before reaching the boiling point. In order to compare with conventional solvents, the group contribution method is selected to predict the boiling point of ionic liquids, and then the boiling points of ionic liquids and conventional solvents are compared. From the perspective of boiling point, it is proved that the flux of the present invention uses ionic liquids to replace conventional organic solvents, which produces less VOC.

[0010] The group contribution method was calculated according to the reference “JO Valderrama, PA Roldes, Critical Properties, Normal Boiling Temperatures, and Acentric Factors of Fifty Ionic Liquids, Industrial & Engineering Chemistry Research, 2007, 46(4), 1338-1344”.

[0011] In the present invention, the boiling point of the ionic liquid is limited to greater than 300°C because in the electronic welding process, the welding temperature is generally below 300°C, and the common temperature is between 220 and 260°C. By limiting the boiling point to greater than 300°C, the welding process can basically be carried out below the boiling point of the ionic liquid, thereby fundamentally controlling the generation of VOCs.

[0012] Furthermore, the ionic liquid includes one or two of imidazole and pyridine. Imidazole ring and pyridine ring have corrosion inhibition function. By using the above-mentioned group contribution method, ionic liquids with imidazole ring and pyridine ring structure and boiling point greater than 300°C are screened as the main solvent of the flux of the present invention, which can reduce VOC and have a slow release effect.

[0013] Further, the ionic liquid includes 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium methyl sulfate or 1-ethylpyridinium tetrafluoroborate. These ionic liquids contain structural units with corrosion inhibition properties, so the ionic liquids have the function of solvents and corrosion inhibitors at the same time.

[0014] Furthermore, the organic acid includes one or more of citric acid, oxalic acid, itaconic acid, iminodiacetic acid, succinic acid, glutaric acid, adipic acid, acrylic acid, lactic acid, malic acid, and benzoic acid.

[0015] Furthermore, the co-solvent includes water and a surfactant.

[0016] Furthermore, the surfactant includes one or more of polyethylene glycol 200-4000, fatty alcohol polyoxyethylene ether, alkyl polyglycoside, N-alkyl pyrrolidone, and ethylene oxide-propylene oxide block copolymer.

[0017] The present invention also claims protection for a method for preparing the above-mentioned VOC-free water-soluble environmentally friendly soldering flux, which comprises first adding an ionic liquid and a cosolvent into a reactor with an agitator, stirring evenly, and then adding an organic acid under stirring until the solid matter is completely dissolved, mixing the materials evenly, cooling, standing, filtering, and retaining the filtrate to obtain the soldering flux.

[0018] Furthermore, during the stirring process, the system temperature is controlled to be 40-80°C and the stirring speed is controlled to be 80-1500 rpm.

[0019] The present invention also requires an application of the above-mentioned VOC-free water-soluble environmentally friendly flux for electronic soft soldering soldering process, which is a high-temperature lead-free solder welding process, such as surface mounting process, BGA ball planting process, wafer-level bumping process, SIP and other packaging processes.

[0020] Furthermore, the flux is evenly coated on the PCB to be soldered by spraying, dispensing or transfer coating, the PCB is heated to below 260° C. in a preset reflow oven, then taken out, cooled and washed with water, and the soldering is completed.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention adopts high-boiling-point ionic liquid to effectively reduce the VOC emission problem originally generated in the welding process; and the functional groups of the ionic liquid, such as the imidazole ring of the imidazole class and the pyridine ring of the pyridine class, are excellent corrosion inhibitors themselves, and their corrosion inhibition effect can be used to avoid the limited corrosion inhibition performance of conventional corrosion inhibitors due to solubility limitations and ultimately improve the welding quality of the flux; the ionic liquid has excellent water solubility and can be directly removed by washing with water after welding, which fully meets the needs of water-soluble flux in electronic packaging applications. DETAILED DESCRIPTION

[0023] The technical problem to be solved by the present invention is to replace the organic solvents with high VOC emissions in the existing water-soluble soldering flux, and solve the problem that the amount of corrosion inhibitor added in the conventional soldering flux is limited by solubility and cannot effectively improve the welding quality. The present invention cleverly introduces a special ionic liquid as the main solvent, and uses its low vapor pressure and structural design characteristics to combine the solvent and the corrosion inhibitor functional group into one, thereby reducing VOC emissions. At the same time, due to the high content of the main solvent, it helps to increase the content of the corrosion inhibition functional component and thus improve the welding quality.

[0024] Example 1

[0025] Add 50 parts of ionic liquid 1-ethyl-3-methylimidazolium acetate, 2 parts of polyethylene glycol 1000 and 5 parts of water into a reaction kettle and heat and stir. When the temperature reaches 70°C, add 20 parts of oxalic acid and stir at a high speed of 1500 rpm for 1 hour. After filtering, cool and stand to retain the filtrate to obtain the flux.

[0026] Example 2

[0027] Add 50 parts of ionic liquid 1-ethyl-3-methylimidazole acetate, 2 parts of fatty alcohol polyoxyethylene ether and 5 parts of water into a reaction kettle and heat and stir. When the temperature reaches 70°C, add 20 parts of organic acid oxalic acid, rotate and stir at a high speed of 1500 rpm for 1 hour, filter, cool and stand, and retain the filtrate to obtain the flux.

[0028] Example 3

[0029] Add 50 parts of ionic liquid 1-ethyl-3-methylimidazolium acetate, 2 parts of polyethylene glycol 1000 and 5 parts of water into a reaction kettle and heat and stir. When the temperature reaches 70°C, add 20 parts of organic acid citric acid and stir at a high speed of 1500 rpm for 1 hour. After filtering, cool and stand to retain the filtrate to obtain the flux.

[0030] Example 4

[0031] Add 50 parts of ionic liquid 1-ethyl-3-methylimidazolium methyl sulfate, 2 parts of polyethylene glycol 1000 and 5 parts of water into a reaction kettle and heat and stir. When the temperature reaches 70°C, add 20 parts of organic acid oxalic acid and stir at a high speed of 1500 rpm for 1 hour. After filtering, cool and stand to retain the filtrate to obtain the flux.

[0032] Example 5

[0033] Add 50 parts of ionic liquid 1-ethylpyridinium tetrafluoroborate, 2 parts of polyethylene glycol 1000 and 5 parts of water into a reaction kettle and heat and stir. When the temperature reaches 70°C, add 20 parts of organic acid oxalic acid and stir at a high speed of 1500 rpm for 1 hour. After filtering, cool and stand to retain the filtrate to obtain the flux.

[0034] Comparative Example 1

[0035] Add 50 parts of solvent triethylene glycol butyl ether and 5 parts of water into a reaction kettle and heat and stir. When the temperature reaches 70°C, add 20 parts of organic acid oxalic acid and 2 parts of benzotriazole. Rotate and stir at 1500 rpm for 1 hour. After filtering, cool and let stand to retain the filtrate to obtain the flux.

[0036] Comparative Example 2

[0037] Add 50 parts of solvent triethylene glycol butyl ether and 5 parts of water into a reaction kettle and heat and stir. When the temperature reaches 70°C, add 20 parts of organic acid oxalic acid and stir at 1500 rpm for 1 hour. After filtering, cool and let stand to retain the filtrate to obtain the flux.

[0038] The main evaluation standard for welding quality is the expansion rate. The evaluation method for the expansion rate is as follows:

[0039] According to the JEDEC expansion rate test method: a certain amount of flux is applied on the copper sheet, a 1mm diameter 96.5Sn-3.0Ag-0.5Cu solder ball is placed in the flux, and the copper sheet is placed on a 260℃ heating platform for 30 seconds. The height difference before and after welding is measured to obtain the expansion rate of the solder ball on the copper sheet.

[0040] Water solubility evaluation method: Place a certain amount of flux on a 260°C heating platform for 30 seconds, then place it in water and stir it for 2 minutes to see if it is a clear solution.

[0041]

[0042] Note: The boiling point values ​​of ionic liquids listed in this table are all predicted values ​​obtained by the group contribution method.

[0043] It can be seen from the above table that the expansion rate of the flux using ionic liquid as the main solvent in Examples 1-5 can reach more than 80%. The greater the expansion rate, the stronger the sustained release effect. The sustained release effect is equivalent to that of Comparative Example 1 in which the conventional corrosion inhibitor benzotriazole is added; and the flux obtained in Examples 1-5 has excellent water solubility and can meet all requirements of water-soluble flux.

[0044] At the same time, the boiling points of the main solvents in Examples 1-5 are all above 300°C. In the electronic soldering process, the soldering temperature is usually below 260°C, which is significantly lower than the boiling point of the main solvent. Therefore, the volatility of the main solvent is low, thereby greatly reducing VOC emissions.

[0045] The present invention utilizes the low vapor pressure characteristics of ionic liquids to avoid the use of conventional solvents with low boiling points that are volatile at high temperatures, such as ethers or alcohols, thereby reducing VOC emissions in the electronic soldering process. Ionic liquids are a new type of environmentally friendly medium that complies with the principles of green chemistry. In addition, the functional groups of ionic liquids can be designed to form protective films on the metal surface with imidazole rings, pyridine rings, alkyl groups, etc., which play a role in corrosion inhibition during high-temperature welding. They are more efficient than traditional corrosion inhibitors and can significantly improve welding quality.

[0046] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. VOC-free water-soluble environmentally friendly flux, characterized by: The invention is composed of the following components by mass percentage: 30-70% of ionic liquid; 5-30% of organic acid; 0.2-10% of cosolvent; and the sum of the mass percentages of the components is 100%; and the boiling point of the ionic liquid is greater than 300°C.

2. The VOC-free water-soluble environmentally friendly soldering flux according to claim 1, characterized in that: The ionic liquid includes one or both of imidazoles and pyridines.

3. The VOC-free water-soluble environmentally friendly soldering flux as claimed in claim 2, characterized in that: The ionic liquid includes 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium methyl sulfate or 1-ethylpyridinium tetrafluoroborate.

4. The VOC-free water-soluble environmentally friendly soldering flux according to claim 1, characterized in that: The organic acid includes one or more of citric acid, oxalic acid, itaconic acid, iminodiacetic acid, succinic acid, glutaric acid, adipic acid, acrylic acid, lactic acid, malic acid, and benzoic acid.

5. The VOC-free water-soluble environmentally friendly soldering flux according to claim 1, characterized in that: The co-solvent includes water and a surfactant.

6. The VOC-free water-soluble environmentally friendly soldering flux according to claim 5, characterized in that: The surfactant includes one or more of polyethylene glycol 200-4000, fatty alcohol polyoxyethylene ether, alkyl polyglycoside, N-alkyl pyrrolidone, and ethylene oxide-propylene oxide block copolymer.

7. A method for preparing a VOC-free water-soluble environmentally friendly soldering flux as claimed in any one of claims 1 to 6, characterized in that: First, add the ionic liquid and the co-solvent into a reaction kettle with a stirrer, stir evenly, then add the organic acid under stirring until the solid matter is completely dissolved, mix the materials evenly, cool and stand, filter, and retain the filtrate to obtain the product.

8. The method for preparing the VOC-free water-soluble environmentally friendly soldering flux according to claim 7, characterized in that: During the stirring process, the system temperature was controlled at 40~80°C and the stirring speed was controlled at 800~1500 rpm.

9. An application of the VOC-free water-soluble environmentally friendly soldering flux as claimed in claim 1, characterized in that: Used in electronic soldering and welding processes.

10. The use according to claim 9, characterized in that: The flux is evenly applied on the PCB to be soldered by spraying, dispensing or transfer coating. The PCB is heated to below 260°C in a preset reflow oven, then taken out, cooled and washed with water, and the soldering is completed.

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