A lead-free solder flux and lead-free solder paste

Abstract

The present invention discloses a lead-free solder flux and a lead-free solder paste, wherein the flux comprises a rosin derivative; wherein the rosin derivative is obtained by subjecting rosin to an addition reaction with maleic anhydride and then to an amidation reaction with aminoimidazole. The present invention provides a lead-free solder flux and a lead-free solder paste, wherein the flux uses a synthetically obtained rosin derivative as a flux component, which not only overcomes the defects of the rosin flux in the prior art such as low activity, poor wettability, and poor thermal stability, but also has good soldering performance, and the residue after soldering is a colorless and transparent film, which is stable at room temperature and does not absorb moisture, and is more in line with environmental protection requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular relates to a flux for lead-free solder and a lead-free solder paste. Background Art

[0002] During the welding process, certain chemicals must be used to remove oxides on the surface of the materials to be welded, so that the solder and the materials to be welded can be well melted to achieve the effect of flux. This substance that can purify the surface of the metal to be welded and help welding is called flux. The composition of flux usually includes solvents, activators, surfactants, film formers and other additives (matting agents, corrosion inhibitors, stabilizers, etc.). According to the different active ingredients, flux can be divided into inorganic acid flux, organic acid flux and rosin flux. Among them, rosin flux is a high-efficiency flux with rosin or modified rosin as the main component, which is widely used in electronic welding technology. Rosin plays a multifaceted role in the welding process. First, the resin acid in rosin contains carboxyl groups, which can remove metal oxides at welding temperature; second, rosin has film-forming properties, which can protect the metal surface from oxidation during welding, and form a dense hydrophobic organic film after welding. This organic film has good electrical insulation and moisture-proof properties, which can protect the solder joints to a certain extent; in addition, rosin in the molten state has good fluidity and thermal conductivity, which can effectively promote heat transfer during welding and avoid poor welding. Different rosin products often have different softening points and activation temperature ranges, so most rosin fluxes use two or more rosin products in combination to improve their fluxing effect.

[0003] With the implementation of lead-free electronic products, the use of lead-free solder has become more and more common. Compared with traditional lead-containing solder, lead-free solder has a high melting point, is easy to oxidize and has poor wettability. The increase in melting point means that the welding temperature must be increased, which brings about the serious problem of high-temperature oxidation during the welding process, increases the volatilization of the activator in the flux, causes the failure of the flux performance, and reduces the activation and protection effects. Therefore, more stringent requirements are placed on the performance of the flux. In-depth research and development of flux products that can be used for lead-free solder is of great practical significance to the current welding field. Summary of the invention

[0004] Based on the above technical problems, the present invention provides a lead-free solder flux and lead-free solder paste. The flux uses a synthetic rosin derivative as a flux component, which not only overcomes the defects of the rosin flux in the prior art such as low activity, poor wettability, and poor thermal stability, but also has good flux performance. The residue after soldering is a colorless and transparent film, which is stable at room temperature and does not absorb moisture, and is more in line with environmental protection requirements.

[0005] The present invention provides a lead-free solder flux, the flux comprising a rosin derivative;

[0006] The rosin derivative is obtained by subjecting rosin to an addition reaction with maleic anhydride and then subjecting the rosin to an amidation reaction with aminoimidazole.

[0007] In the present invention, the levorotatory pimaric acid contained in the rosin can be subjected to Diels-Alder (DA) addition with maleic anhydride as a dienophile to obtain maleopimaric anhydride, and the maleopimaric anhydride can undergo an amidation reaction with aminoimidazole under certain conditions, thereby introducing aminoimidazole into the rosin derivative; on the one hand, the aminoimidazole can be used as an activator to enhance the activation ability of the rosin, thereby effectively improving the wettability and expansion rate of the soldering flux; on the other hand, while introducing the aminoimidazole, the anhydride is ring-opened, thereby enabling the carboxyl group contained in the rosin derivative to better exert the soldering activity; therefore, the activity of the rosin derivative of the present invention is significantly stronger than that of other rosin modified products, and the problems of low activation ability of the existing rosin soldering flux, the need to add a halogen-containing activator when the surface lead-free solder has limited wettability, and the problems of environmental pollution caused by the need to add a halogen-containing activator, easy moisture absorption in a humid environment, corrosion of soldering components, etc., can also achieve a good soldering effect under the condition of low usage, which is conducive to reducing the post-soldering solid residue of the soldering flux.

[0008] In the present invention, the synthetic route of rosin derivatives can be referred to the following route:

[0009]

[0010] Preferably, the aminoimidazole is at least one of 5-aminobenzimidazole, 2-aminobenzimidazole or 2-imidazolylethylamine.

[0011] In the present invention, the rosin derivative comprises a compound represented by the following structural formula (1), (2) or (3):

[0012]

[0013] Preferably, based on the total mass of the soldering flux, the rosin derivative accounts for 10-35%.

[0014] In the present invention, when the content of the rosin derivative used is less than 10%, the activity of the soldering flux is insufficient, and when the content of the rosin derivative used exceeds 35%, excessive residues will remain on the surface, and cracks will easily occur after heating and cooling.

[0015] Preferably, the soldering flux further includes at least one of an organic acid activator, a surfactant, a thixotropic agent or a solvent.

[0016] Preferably, the organic acid activator is at least one of oxalic acid, succinic acid, glutaric acid, adipic acid, citric acid, malic acid or tartaric acid;

[0017] Preferably, the organic acid activator comprises oxalic acid, glutaric acid and adipic acid, and the mass ratio of the three is 1:0.5-2:0.5-2;

[0018] Preferably, based on the total mass of the soldering flux, the organic acid activator accounts for 1-10%.

[0019] In the present invention, when the rosin derivative is compounded with an organic acid activator, the organic acid activator can form an ammonium salt with the imidazole group in the rosin derivative, further improving the flux's ability to remove the solder powder oxide layer and wettability to the solder joint; and the inventors have found that when oxalic acid, glutaric acid and adipic acid are compounded as the organic acid activator, not only is the wettability the best, the solder joint spreading area is the largest, but also less residue after welding and less corrosiveness.

[0020] Preferably, the surfactant is at least one of alkylphenol polyoxyethylene ether, 2-ethylhexyl phosphate, nonylphenol polyoxyethylene ether or pentaerythritol hexadecanoate;

[0021] Preferably, based on the total mass of the soldering flux, the surfactant accounts for 0.5-5%.

[0022] In the present invention, the surface tension is reduced by the surfactant, the dissolution of various additives in the soldering flux is promoted, the solder and the soldering surface are quickly wetted, and the rosin derivative is coordinated to play a soldering role.

[0023] Preferably, the thixotropic agent is at least one of hydrogenated castor oil, polyamide wax, stearic acid amide or fumed silica;

[0024] Preferably, based on the total mass of the soldering flux, the thixotropic agent accounts for 0.5-5%.

[0025] In the present invention, the shear thinning behavior of the flux fluid is enhanced by a thixotropic agent, and the printing performance of the solder paste is changed, so that the solder paste is easy to demould without collapse.

[0026] Preferably, the solvent includes an alcohol solvent and an ether solvent;

[0027] Preferably, the alcohol solvent is at least one of ethylene glycol, propylene glycol, glycerol, butylene glycol or diethylene glycol, and the ether solvent is at least one of ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, dipropylene glycol butyl ether or tripropylene glycol;

[0028] Preferably, based on the total mass of the soldering flux, the solvent accounts for 50-80%.

[0029] In the present invention, the alcohol solvent has a certain viscosity and has a good effect of dissolving auxiliary agents such as activators. At this time, the addition of an ether solvent can further enhance the dissolution effect on the rosin derivative, increase the viscosity and ensure that the solder paste will not dry out during storage.

[0030] The present invention also provides a lead-free solder paste, which comprises, by mass percentage, 80-90wt% of lead-free solder alloy powder and the remainder of the above-mentioned soldering flux.

[0031] Preferably, the lead-free solder alloy powder includes at least one metal of Sn, Ag, Cu, In, Zn, Bi, Ni or Al.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) It does not contain halogens and contains a small amount of rosin derivatives; it has high activity, good wettability, good solderability, bright and full solder joints, little residue after welding, low corrosion, and no need for cleaning; (2) The flux has good fluidity and no precipitation and stratification; (3) The surface insulation resistance of the substrate after welding is much greater than 1×10 8 Ω, meeting the standard requirements of the electronics industry; (4) The soldering effect is good and meets the requirements of green environmental protection. DETAILED DESCRIPTION

[0034] Hereinafter, the present invention will describe the technical solution in detail through specific embodiments, but it should be clearly stated that these embodiments are for illustration only and are not to be construed as limiting the scope of the present invention.

[0035] Example 1

[0036] This embodiment provides a lead-free solder flux, which includes, by mass percentage, 18% of rosin derivatives, 2% of oxalic acid, 2% of glutaric acid, 2% of adipic acid, 3% of nonylphenol polyoxyethylene ether, 2% of hydrogenated castor oil, 22% of ethylene glycol, 36% of ethylene glycol monobutyl ether, and 13% of diethylene glycol monomethyl ether;

[0037] Wherein, the rosin derivative is prepared by the following method:

[0038] Under nitrogen protection, after heating Masson pine rosin to 180° C., maleic anhydride in an amount of 30% by mass of Masson pine rosin is added, and the mixture is kept warm for reaction for 4 hours, and then poured into turpentine oil in an amount of 4 times by mass of Masson pine rosin while hot, and heated until completely dissolved, and solid is precipitated after standing overnight, and maleopimaric anhydride is obtained after suction filtration; the obtained maleopimaric anhydride is added to acetone, and after stirring and dissolving completely, 5-aminobenzimidazole in an amount of 35% by mass of maleopimaric anhydride and pyridine in an amount of 5% by mass of maleopimaric anhydride are added, and the mixture is kept warm for reaction for 6 hours after heating to 30° C., and then ethanol is added to precipitate solid, and the rosin derivative is obtained after suction filtration.

[0039] The lead-free solder flux is prepared by the following method:

[0040] A rosin derivative is added to a mixed solvent of ethylene glycol, ethylene glycol monobutyl ether and diethylene glycol monomethyl ether, and the rosin derivative is mixed evenly under stirring, and then the temperature is raised to 70° C., and then oxalic acid, glutaric acid and adipic acid are added to the resulting solution, followed by nonylphenol polyoxyethylene ether and hydrogenated castor oil. After keeping warm and stirring for 3 hours, the solution is naturally cooled to obtain the flux.

[0041] In this embodiment, 11% of the above-mentioned flux and 89% of lead-free solder alloy powder are mixed according to mass percentage to obtain solder paste, and the lead-free solder alloy powder can use Sn0.7Cu lead-free solder alloy.

[0042] Example 2

[0043] This embodiment provides a lead-free solder flux, which includes, by mass percentage, 21% of rosin derivative, 1% of oxalic acid, 2% of glutaric acid, 2% of adipic acid, 2% of 2-ethylhexyl phosphate, 3% of stearic acid amide, 16% of glycerol, 28% of ethylene glycol monobutyl ether, and 25% of dipropylene glycol butyl ether;

[0044] Wherein, the rosin derivative is prepared by the following method:

[0045] Under nitrogen protection, after heating Masson pine rosin to 180° C., maleic anhydride in an amount of 30% by mass of Masson pine rosin is added, and the mixture is kept warm for reaction for 4 hours, and then poured into turpentine oil in an amount of 4 times by mass of Masson pine rosin while hot, and heated until completely dissolved, and solid is precipitated after standing overnight, and then maleopimaric anhydride is obtained after suction filtration; the obtained maleopimaric anhydride is added to acetone, and after stirring and dissolving completely, 2-aminobenzimidazole in an amount of 35% by mass of maleopimaric anhydride and pyridine in an amount of 5% by mass of maleopimaric anhydride are added, and the mixture is kept warm for reaction for 6 hours after heating to 30° C., and then ethanol is added to precipitate solid, and then the rosin derivative is obtained after suction filtration.

[0046] The lead-free solder flux is prepared by the following method:

[0047] The rosin derivative is added to a mixed solvent of propylene glycol, ethylene glycol monobutyl ether and dipropylene glycol butyl ether, and the rosin derivative is mixed evenly under stirring, and then the temperature is raised to 70°C. Then, oxalic acid, glutaric acid and adipic acid are added to the obtained solution, followed by adding stearic acid amide and 2-ethylhexyl phosphate. After keeping warm and stirring for 3 hours, the flux is obtained by natural cooling.

[0048] Example 3

[0049] This embodiment provides a lead-free solder flux, which includes, by mass percentage, 18% of rosin derivatives, 2% of oxalic acid, 2% of glutaric acid, 2% of adipic acid, 3% of nonylphenol polyoxyethylene ether, 2% of hydrogenated castor oil, 22% of ethylene glycol, 36% of ethylene glycol monobutyl ether, and 13% of diethylene glycol monomethyl ether;

[0050] Wherein, the rosin derivative is prepared by the following method:

[0051] Under nitrogen protection, after heating Masson pine rosin to 180° C., maleic anhydride in an amount of 30% by mass of Masson pine rosin is added, and the mixture is kept warm for reaction for 4 hours, and then poured into turpentine oil in an amount of 4 times by mass of Masson pine rosin while hot, and heated until completely dissolved, and solid is precipitated after standing overnight, and then filtered to obtain maleopimaric anhydride; the obtained maleopimaric anhydride is added to acetone, and after stirring and dissolving completely, 45% by mass of 2-imidazolylethylamine and 5% by mass of pyridine are added, and the mixture is heated to 30° C. and kept warm for reaction for 6 hours, and then ethanol is added to precipitate solid, and then filtered to obtain the rosin derivative.

[0052] The lead-free solder flux is prepared by the following method:

[0053] A rosin derivative is added to a mixed solvent of ethylene glycol, ethylene glycol monobutyl ether and diethylene glycol monomethyl ether, and the rosin derivative is mixed evenly under stirring, and then the temperature is raised to 70° C., and then oxalic acid, glutaric acid and adipic acid are added to the resulting solution, followed by nonylphenol polyoxyethylene ether and hydrogenated castor oil. After keeping warm and stirring for 3 hours, the solution is naturally cooled to obtain the flux.

[0054] Example 4

[0055] This embodiment provides a lead-free solder flux, which includes, by mass percentage, 18% of rosin derivatives, 3% of succinic acid, 3% of citric acid, 3% of nonylphenol polyoxyethylene ether, 2% of hydrogenated castor oil, 22% of ethylene glycol, 36% of ethylene glycol monobutyl ether, and 13% of diethylene glycol monomethyl ether;

[0056] Wherein, the rosin derivative is prepared by the following method:

[0057] Under nitrogen protection, after heating Masson pine rosin to 180° C., maleic anhydride in an amount of 30% by mass of Masson pine rosin is added, and the mixture is kept warm for reaction for 4 hours, and then poured into turpentine oil in an amount of 4 times by mass of Masson pine rosin while hot, and heated until completely dissolved, and solid is precipitated after standing overnight, and maleopimaric anhydride is obtained after suction filtration; the obtained maleopimaric anhydride is added to acetone, and after stirring and dissolving completely, 5-aminobenzimidazole in an amount of 35% by mass of maleopimaric anhydride and pyridine in an amount of 5% by mass of maleopimaric anhydride are added, and the mixture is kept warm for reaction for 6 hours after heating to 30° C., and then ethanol is added to precipitate solid, and the rosin derivative is obtained after suction filtration.

[0058] The lead-free solder flux is prepared by the following method:

[0059] A rosin derivative is added to a mixed solvent of ethylene glycol, ethylene glycol monobutyl ether and diethylene glycol monomethyl ether, and the mixture is stirred to be uniformly mixed, and then the temperature is raised to 70° C., and then succinic acid and citric acid are added to the obtained solution, followed by nonylphenol polyoxyethylene ether and hydrogenated castor oil. After keeping the mixture warm and stirring for 3 hours, the mixture is naturally cooled to obtain the flux.

[0060] Comparative Example 1

[0061] This comparative example proposes a flux for lead-free solder, which includes, by mass percentage, 18% of masson pine rosin, 2% of oxalic acid, 2% of glutaric acid, 2% of adipic acid, 3% of nonylphenol polyoxyethylene ether, 2% of hydrogenated castor oil, 22% of ethylene glycol, 36% of ethylene glycol monobutyl ether, and 13% of diethylene glycol monomethyl ether.

[0062] The lead-free solder flux is prepared by the following method:

[0063] Add masson pine rosin to a mixed solvent of ethylene glycol, ethylene glycol monobutyl ether and diethylene glycol monomethyl ether, stir to mix the masson pine rosin evenly, then heat to 70°C, add oxalic acid, glutaric acid and adipic acid to the resulting solution, then add nonylphenol polyoxyethylene ether and hydrogenated castor oil, keep warm and stir for 3 hours, and cool naturally to obtain the flux.

[0064] Comparative Example 2

[0065] This comparative example proposes a soldering flux for lead-free solder, which comprises, by mass percentage, 9% water-white rosin, 9% hydrogenated rosin, 2% oxalic acid, 2% glutaric acid, 2% adipic acid, 3% nonylphenol polyoxyethylene ether, 2% hydrogenated castor oil, 22% ethylene glycol, 36% ethylene glycol monobutyl ether, and 13% diethylene glycol monomethyl ether.

[0066] The lead-free solder flux is prepared by the following method:

[0067] Water-white rosin and hydrogenated rosin are added to a mixed solvent of ethylene glycol, ethylene glycol monobutyl ether and diethylene glycol monomethyl ether, and the mixture is stirred to be uniformly mixed, and then the temperature is raised to 70° C., and then oxalic acid, glutaric acid and adipic acid are added to the obtained solution, and then nonylphenol polyoxyethylene ether and hydrogenated castor oil are added. After keeping the temperature and stirring for 3 hours, the mixture is naturally cooled to obtain the soldering flux.

[0068] According to the test method specified in SJ / T11389-2009 "Lead-free Soldering Flux", the performance of the flux obtained in this embodiment and the comparative example was tested. The physical stability, halogen content, copper plate corrosion, surface insulation resistance after welding and Sn 0.7 The wettability of Cu lead-free solder (expressed as expansion rate) is shown in Table 1 below:

[0069] Table 1 Performance test results of the soldering flux obtained in the embodiments and comparative examples

[0070]

[0071] As can be seen from Table 1 above, the soldering flux of the present invention uses the synthesized rosin derivative as the soldering flux component, which not only overcomes the defects of the rosin soldering flux in the prior art such as low activity, poor wettability, and poor thermal stability, but also has good soldering performance, is stable at room temperature and does not absorb moisture, and is more in line with environmental protection requirements.

[0072] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A lead-free solder flux, characterized in that: The soldering flux includes a rosin derivative; The rosin derivative is obtained by subjecting rosin to an addition reaction with maleic anhydride and then subjecting it to an amidation reaction with aminoimidazole; The aminoimidazole is at least one of 5-aminobenzimidazole, 2-aminobenzimidazole or 2-imidazolylethylamine.

2. The lead-free solder flux according to claim 1, characterized in that: Based on the total mass of the flux, the rosin derivative accounts for 10-35%.

3. The lead-free solder flux according to claim 1 or 2, characterized in that: The soldering flux further includes at least one of an organic acid activator, a surfactant, a thixotropic agent or a solvent.

4. The lead-free solder flux according to claim 3, characterized in that: The organic acid activator is at least one of oxalic acid, succinic acid, glutaric acid, adipic acid, citric acid, malic acid or tartaric acid.

5. The lead-free solder flux according to claim 3, characterized in that: The organic acid activator comprises oxalic acid, glutaric acid and adipic acid, and the mass ratio of the three is 1:0.5-2:0.5-2.

6. The lead-free solder flux according to claim 3, characterized in that: Based on the total mass of the soldering flux, the organic acid activator accounts for 1-10%.

7. The lead-free solder flux according to claim 3, characterized in that: The surfactant is at least one of alkylphenol polyoxyethylene ether, 2-ethylhexyl phosphate, nonylphenol polyoxyethylene ether or pentaerythritol hexadecanoate.

8. The lead-free solder flux according to claim 3, characterized in that: Based on the total mass of the soldering flux, the surfactant accounts for 0.5-5%.

9. The lead-free solder flux according to claim 3, characterized in that: The thixotropic agent is at least one of hydrogenated castor oil, polyamide wax, stearic acid amide or fumed silica.

10. The lead-free solder flux according to claim 3, characterized in that: Based on the total mass of the soldering flux, the thixotropic agent accounts for 0.5-5%.

11. The lead-free solder flux according to claim 3, characterized in that: The solvent includes an alcohol solvent and an ether solvent.

12. The lead-free solder flux according to claim 11, characterized in that: The alcohol solvent is at least one of ethylene glycol, propylene glycol, glycerol, butylene glycol or diethylene glycol, and the ether solvent is at least one of ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, dipropylene glycol butyl ether or tripropylene glycol.

13. The lead-free solder flux according to claim 3, characterized in that: Based on the total mass of the soldering flux, the solvent accounts for 50-80%.

14. A lead-free solder paste, characterized in that: Measured in percentage by mass, the solder paste comprises: 80-90wt% of lead-free solder alloy powder and the remainder of the soldering flux according to any one of claims 1-13.

15. The lead-free solder paste according to claim 14, characterized in that: The lead-free solder alloy powder includes at least one metal of Sn, Ag, Cu, In, Zn, Bi, Ni or Al.

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