Soldering flux for gold-tin soldering paste, gold-tin soldering paste and preparation method and application of soldering flux

Abstract

The invention relates to soldering flux for gold-tin soldering paste, the gold-tin soldering paste and a preparation method and application of the soldering flux. The soldering flux for the gold-tin soldering paste comprises the following components: rosin, a film-forming agent, a thixotropic agent, an anti-settling agent, an alcohol compound, an organic acid compound and a solvent. According to the soldering flux for the gold-tin soldering paste, through cooperation of the rosin, the film-forming agent, the thixotropic agent, the anti-settling agent, the alcohol compound and the organic acid compound, the gold-tin soldering paste can have low voidage, good wettability and good printing performance, and the gold-tin soldering paste does not settle after being stored and placed for a long time.

Description

Technical Field

[0001] The present invention relates to the technical field of solder, and more specifically to a flux for gold-tin solder paste, gold-tin solder paste, and a preparation method and application thereof. Background Art

[0002] Gold-tin solder paste is widely used in aerospace, optoelectronics, radio frequency, high-power semiconductor devices, lasers and other fields because of its excellent properties after welding, such as high tensile strength, high melting point, high thermal conductivity, resistance to thermal fatigue and corrosion resistance.

[0003] In recent years, the development trend of electronic products is diversification, high density, high performance and miniaturization. In the welding of micro-small devices, prefabricated parts have become increasingly difficult to adapt to the current development trend of electronic products. Gold-tin solder paste has excellent performance, and due to the characteristics of its paste, it can flexibly adjust the coating position and coating amount according to the size and shape of the device, which can effectively cope with the welding of current micro-small devices. Therefore, gold-tin solder paste has an increasingly important position in the electronic product market.

[0004] The reliability of gold-tin solder paste has a great impact on the performance of welded parts, among which voids and wettability are important factors affecting device reliability. Voids are very harmful to solder joints. High void rates will weaken soldering strength and reduce reliability. Voids will crowd out solder paste and may cause short circuits between solder joints. According to industry statistics, void-related failures account for 20% of PCBA failures. There are many existing fluxes that can reduce the void rates of Sn64Bi35Ag1, Sn62Pb36Ag2, Sn90Sb10 and other solder pastes, but these fluxes do not significantly improve the high void rate problem of gold-tin solder paste.

[0005] Wettability refers to the degree of spreading of molten solder on the metal surface of the body, which characterizes the ability of solder to diffuse on the surface of the pad and form a metallurgical connection with the pad to generate specific intermetallic compounds. Insufficient wettability can lead to problems such as low solder-pad bonding ability, low solder joint strength, poor solder joint size, irregular solder joint shape, and multiple tin beads. For gold-tin solder paste, the use of gold-tin alloy solder powder with large particle size (25~45μm) can improve the wettability of gold-tin solder paste to a certain extent, but large-particle gold-tin alloy solder powder is prone to sedimentation in gold-tin solder paste, especially after long-term storage (more than 2 months).

[0006] The Chinese patent application with publication number CN114378483A provides a flux for a no-clean gold-tin solder paste, which can make the gold-tin solder paste have good wettability, but the amount of rosin used in the flux of this patent is small, which will lead to poor printing performance of the solder paste; in addition, this patent does not pay attention to the high void rate of the solder paste and the sedimentation problem after long-term storage. Summary of the invention

[0007] The primary purpose of the present invention is to overcome the problems of the above-mentioned existing gold-tin solder paste, such as high void rate, poor wettability, easy sedimentation after long-term storage or poor printing performance, and provide a flux for gold-tin solder paste. The flux for gold-tin solder paste is prepared by combining rosin, film-forming agent, thixotropic agent, anti-settling agent, alcohol compound and organic acid compound, so that the gold-tin solder paste has low void rate, good wettability and good printing performance, and does not settle after long-term storage.

[0008] A further object of the present invention is to provide a method for preparing the above-mentioned soldering flux for gold-tin solder paste.

[0009] A further object of the present invention is to provide the use of the above-mentioned flux for gold-tin solder paste in the preparation of gold-tin solder paste.

[0010] A further object of the present invention is to provide a gold-tin solder paste.

[0011] A further object of the present invention is to provide a method for preparing the gold-tin solder paste.

[0012] A further object of the present invention is to provide application of the gold-tin solder paste in the preparation of electronic products.

[0013] The above-mentioned object of the present invention is achieved by the following technical solutions: A soldering flux for gold-tin solder paste, comprising the following components in percentage by mass: Rosin 30~50%, Film former 8~15%, Thixotropic agent 5~8%, Anti-settling agent 0.4~1.5%, Alcohol complex 2~3%, Organic acid complex 4~6%, The balance is solvent; The alcohol complex comprises D-mannitol and erythritol in a mass ratio of 1:(0.2-1); The organic acid complex comprises a first organic acid, a second organic acid and a third organic acid in a mass ratio of 1: (0.5-0.6): (0.15-0.3), wherein the first organic acid is at least one of adipic acid or glutaric acid, the second organic acid is at least one of itaconic acid or salicylic acid, and the third organic acid is at least one of succinic acid or malic acid.

[0014] The rosin mass content of the flux for the gold-tin solder paste of the present invention reaches 30-50%, which can provide a basis for the wettability and printing performance of the gold-tin solder paste; the addition of a film-forming agent is beneficial to improving the wettability of the gold-tin solder paste; the addition of a thixotropic agent is beneficial to improving the printing performance of the gold-tin solder paste; and the addition of an anti-settling agent has an improving effect on the storage and placement sedimentation problem of the gold-tin solder paste.

[0015] For the gold-tin alloy solder powder solder paste system with large particle size (25~45μm), the inventors of the present invention have found that the molecule of D-mannitol contains 6 hydroxyl groups, has a large molecular weight, a long molecular chain, and a more significant contribution to the viscosity of the solder paste, while the molecule of erythritol contains 4 hydroxyl groups, has a small molecular weight, a small steric hindrance, and can be better dispersed in the solder paste, so that the molecular interactions such as hydrogen bonds formed synergistically between the two not only help to improve the uniformity and stability of the components and improve the printing performance and long-term storage stability of the gold-tin solder paste, but also help to discharge the bubbles generated during soldering of the solder paste from the system and reduce the void rate of the solder paste. In addition, the active range formed by the difference in boiling points of D-mannitol and erythritol is well matched with the welding temperature range of the gold-tin solder paste, which is conducive to removing metal oxides in the welding process and has a certain help in improving the wettability of the gold-tin solder paste.

[0016] The present invention also adds an organic acid complex, which can adjust the surface tension of the gold-tin solder paste, and the different activity ranges of the first organic acid, the second organic acid and the third organic acid further cooperate with the alcohol complex, thereby reducing the void rate of the gold-tin solder paste and significantly improving the wettability of the gold-tin solder paste.

[0017] That is, the flux for gold-tin solder paste of the present invention can make the gold-tin solder paste have low void rate, good wettability and good printing performance through the combination of rosin, film-forming agent, thixotropic agent, anti-settling agent, alcohol complex and organic acid complex, and prevent the gold-tin solder paste from settling after long-term storage.

[0018] In the present invention, the mass ratio of D-mannitol to erythritol in the alcohol complex can be specifically 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1.

[0019] Preferably, the mass ratio of D-mannitol to erythritol is 1:(0.4~1).

[0020] Preferably, the rosin is at least one of hydrogenated rosin, polymerized rosin or water-white rosin.

[0021] Preferably, the film-forming agent is at least one of polyethylene oxide, hydrogenated rosin glycerol ester or polyacrylic acid resin.

[0022] Preferably, the thixotropic agent is at least one of hydrogenated castor oil or vinyl bisstearamide.

[0023] Preferably, the anti-settling agent is polyamide wax.

[0024] Preferably, the gold-tin solder paste flux further includes 0.5-2.0% of a corrosion inhibitor.

[0025] More preferably, the corrosion inhibitor is at least one of an olamine corrosion inhibitor or an imidazole corrosion inhibitor.

[0026] Further preferably, the alcoholamine corrosion inhibitor includes but is not limited to triethanolamine.

[0027] Further preferably, the imidazole corrosion inhibitor includes but is not limited to at least one of 2-phenylimidazole, 2-methylimidazole or 2-ethylimidazole.

[0028] Preferably, the gold-tin solder paste flux further comprises 0.8-3.0% antioxidant and 0.5-2.0% surfactant.

[0029] More preferably, the antioxidant is at least one of benzotriazole or 5-hydroxysalicylic acid.

[0030] More preferably, the surfactant is at least one of a fluorine-containing surfactant, an antioxidant oil surfactant or a rosin alcohol ether surfactant.

[0031] Preferably, the solvent comprises a high boiling point solvent and a low boiling point solvent in a mass ratio of 1:(3-4); the boiling point of the high boiling point solvent is 240-340°C, and the boiling point of the low boiling point solvent is 170-230°C.

[0032] More preferably, the high boiling point solvent is at least one of diethanolamine, tetraethylene glycol, 3-hexanol, glycerol ether, propylene glycol phenyl ether or 2-ethyl-1,3-hexanediol.

[0033] More preferably, the low boiling point solvent is at least one of 1,2,6-hexanetriol, propylene glycol, diethylene glycol butyl ether, ethylene glycol or 1,4-butanediol.

[0034] The preparation method of the above-mentioned soldering flux for gold-tin solder paste comprises the following steps: mixing the components to obtain the soldering flux for gold-tin solder paste.

[0035] Preferably, the mixing temperature is 110-180°C.

[0036] The use of the above-mentioned flux for gold-tin solder paste in the preparation of gold-tin solder paste is also within the protection scope of the present invention.

[0037] A gold-tin solder paste comprising the following components in parts by weight: 7~12 parts of flux for the above gold-tin solder paste, 88~93 parts of gold-tin alloy powder.

[0038] More preferably, the particle size distribution of the gold-tin alloy powder is 25-45 μm.

[0039] The preparation method of the gold-tin solder paste comprises the following steps: mixing a gold-tin solder paste flux and a gold-tin alloy powder to obtain the gold-tin solder paste.

[0040] Preferably, the gold-tin solder paste flux and gold-tin alloy powder are first stirred at -50 to -60 kPa and 70 to 90 RPM for 0.5 to 2 hours, collected, then stirred at -50 to -60 kPa and 150 to 180 RPM for 0.5 to 2 hours, and then stirred at 250 to 300 RPM for 3 to 5 hours to obtain the gold-tin solder paste.

[0041] The application of the above-mentioned gold-tin solder paste in the preparation of electronic products is also within the protection scope of the present invention.

[0042] Compared with the prior art, the present invention has the following beneficial effects: The flux for gold-tin solder paste of the present invention can make the gold-tin solder paste have low void rate, good wettability and good printing performance through the combination of rosin, film-forming agent, thixotropic agent, anti-settling agent, alcohol compound and organic acid compound, and prevent the gold-tin solder paste from settling after long-term storage. DETAILED DESCRIPTION

[0043] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0044] The raw materials used in each embodiment and comparative example are as follows: Rosin 1#: Hydrogenated rosin, Ryan, 65997-06-0; Rosin 2#: polymerized rosin, Eastman, Staybelite; Film former 1#: polyethylene oxide, McLean, 68441-17-8; Film former 2#: Hydrogenated rosin glycerol ester, McLean, 65997-13-9; Thixotropic agent: hydrogenated castor oil, Nippon Seika, HCO; Alcohol complex 1#: comprising D-mannitol and erythritol in a mass ratio of 1:0.4; Alcohol complex 2#: comprising D-mannitol and erythritol in a mass ratio of 1:0.2; Alcohol complex 3#: including D-mannitol and erythritol in a mass ratio of 1:1; Alcohol complex 4#: comprising D-mannitol and xylitol in a mass ratio of 1:0.4; Alcohol complex 5#: comprising sorbitol and erythritol in a mass ratio of 1:0.4; Organic acid complex 1#: comprising adipic acid, itaconic acid and succinic acid in a mass ratio of 1:0.6:0.15; Organic acid complex 2#: comprising adipic acid, itaconic acid and succinic acid in a mass ratio of 1:0.5:0.3; Organic acid complex 3#: including glutaric acid, salicylic acid and malic acid in a mass ratio of 1:0.6:0.15; Organic acid complex 4#: comprising adipic acid and itaconic acid in a mass ratio of 1:0.6; Organic acid complex 5#: comprising adipic acid and succinic acid in a mass ratio of 1:0.15; Organic acid complex 6#: comprising itaconic acid and succinic acid in a mass ratio of 0.6:0.15; Corrosion inhibitor 1#: triethanolamine; Corrosion inhibitor 2#: 2-methylimidazole; Antioxidant: Benzotriazole (BTA); Surfactant: Fluorinated surfactant, Chemours, Capstone FS-63; Anti-settling agent: polyamide wax, HIMAX, THIXATROL® P2100W; Solvent 1#: including tetraethylene glycol (boiling point 328°C, CAS number: 31692-85-0) and propylene glycol (boiling point 187°C) in a mass ratio of 1:3; Solvent 2#: includes tetraethylene glycol and propylene glycol in a mass ratio of 1:4.

[0045] Embodiments 1 to 10 Examples 1 to 10 provide a series of fluxes for gold-tin solder pastes, the formulations of which are shown in Tables 1 and 2 below.

[0046] Table 1 Components and their mass percentages (%) of each embodiment

[0047] Table 2 Components and mass percentages (%) of each embodiment

[0048] Comparative Examples 1 to 7 Comparative Examples 1 to 7 provide a series of fluxes for gold-tin solder pastes, and their formulas are shown in Table 3 below.

[0049] Table 3 Components and mass percentages of each comparative example (%)

[0050] The preparation method of the gold-tin solder paste flux of the above embodiment and comparative example comprises the following steps: 1) Add rosin and tetraethylene glycol in the solvent into the reactor and mix them evenly at 170°C; 2) After the temperature drops to 150°C, add propylene glycol, film-forming agent, the first organic acid (if any) and the second organic acid (if any) in the organic acid complex and alcohol (alcohol complex, D-mannitol or erythritol) in the solvent, mix well, then add thixotropic agent and mix thoroughly; 3) Cool down to 120℃, add the third organic acid (if any), corrosion inhibitor, anti-settling agent, antioxidant and surfactant in the organic acid complex, mix well and then cool down to <60℃, take out and obtain the flux for gold-tin solder paste.

[0051] Performance Testing The gold-tin solder pastes of the embodiments and comparative examples were made into gold-tin solder pastes with flux, and then the performance tests were performed.

[0052] The gold-tin solder paste includes the following components by weight: 8 parts of flux for gold-tin solder paste and 92 parts of gold-tin alloy powder, wherein the gold-tin alloy powder is 3# Au80Sn20 alloy, and the particle size distribution of the gold-tin alloy powder is 25-45 μm.

[0053] The preparation method of gold-tin solder paste comprises the following steps: placing a gold-tin solder paste flux and a gold-tin alloy powder into a double planetary agitator, stirring at a speed of 80RPM for 1 hour in a vacuum degree of -50 to -60kPa, then collecting the materials at the center of the agitator, stirring at a speed of 160RPM for 1 hour in a vacuum degree of -50 to -60kPa, and then increasing the speed to 280RPM and stirring for 4 hours to obtain the gold-tin solder paste.

[0054] The test standards or test methods for each performance test are as follows: 1) Void rate: Use micro-focus X-RAY perspective inspection equipment to test the void rate of gold-tin solder paste after welding. The industry usually requires the void rate to be below 10%.

[0055] 2) Wettability: Tested in accordance with GBT 31475-2015 standard. Usually the wettability is required to reach level 1 or 2; if the wettability is level 3 or 4, it is considered poor.

[0056] 3) Sedimentation: The gold-tin solder paste is stored in a cool cabinet at a temperature of 5°C for 3 months to observe whether the gold-tin solder paste is stratified. If there is no stratification, it means that no sedimentation has occurred. If there is stratification, it means that sedimentation has occurred.

[0057] 4) Printing performance: Test in accordance with the Chip 1608, 2125, 3216 solder paste printing standards, observe and record the following 4 aspects: ① The solder paste covers more than 90% of the pad area; ② The solder paste has no offset; ③ The solder paste quantity and thickness are uniform, with a thickness of 8.31 MILS; ④ The solder paste is well formed, without collapse or fracture. The evaluation criteria are: if all of the above 4 aspects are met, the printing performance is excellent; if 3 of the above 4 aspects are met, the printing performance is good; if 0 to 2 of the above 4 aspects are met, the printing performance is poor.

[0058] The performance test results of the gold-tin solder pastes prepared with the gold-tin solder paste fluxes of the embodiments and comparative examples are shown in Table 4.

[0059] Table 4 Performance test results of various embodiments and comparative examples

[0060] From Table 4, we can see that: The void rates of Examples 1 to 10 are all below 6%, the wettability is level 1 or level 2, no sedimentation occurs after storage for 3 months, and the printing performance is excellent or good, indicating that the flux for gold-tin solder paste of the present invention can make the gold-tin solder paste have low void rate, good wettability and good printing performance, and prevent the gold-tin solder paste from sedimentation after long-term storage.

[0061] Comparing Example 1 with Example 4, it can be seen that the use of hydrogenated rosin to obtain the gold-tin solder paste flux can make the gold-tin solder paste have a lower void rate.

[0062] Comparing Example 1 with Example 5, it can be seen that when hydrogenated rosin glycerol ester is used as the film-forming agent, the obtained flux for gold-tin solder paste can make the gold-tin solder paste have a lower void rate.

[0063] Comparing Example 1 with Example 6, it can be seen that the corrosion inhibitor is an alcohol amine corrosion inhibitor (for example, triethanolamine), and the obtained flux for gold-tin solder paste can make the gold-tin solder paste have lower void rate, better wettability and printing performance.

[0064] By comparing Example 1 with Examples 7 to 8, it can be seen that by regulating the mass ratio of D-mannitol to erythritol within a certain range (1:0.4 to 1), the obtained flux for gold-tin solder paste can make the gold-tin solder paste have lower void rate, better wettability and printing performance.

[0065] Comparing Example 1 with Example 10, it can be seen that the organic acid composite is a combination of adipic acid, itaconic acid and succinic acid, and the obtained flux for gold-tin solder paste can make the gold-tin solder paste have a lower void rate.

[0066] Comparative Example 1 uses xylitol instead of erythritol, and the gold-tin solder paste made of the obtained gold-tin solder paste flux has a high void rate, sedimentation occurs after long-term storage, and the wettability and printing performance are not as good as Example 1. Comparative Example 2 uses sorbitol instead of D-mannitol, and the gold-tin solder paste made of the obtained gold-tin solder paste flux has a high void rate, sedimentation occurs after long-term storage, and the wettability and printing performance are not as good as Example 1. Comparative Example 3 does not use erythritol, and the gold-tin solder paste made of the obtained gold-tin solder paste flux has a high void rate, sedimentation occurs after long-term storage, and the printing performance is poor, and the wettability is not as good as Example 1. Comparative Example 4 does not use D-mannitol, and the gold-tin solder paste made of the obtained gold-tin solder paste flux has a high void rate, sedimentation occurs after long-term storage, and the printing performance is poor, and the wettability is not as good as Example 1. The organic acid composites of Comparative Examples 5 to 7 are compounded with only two organic acids, the void rate of the gold-tin solder paste is high, and the wettability of Comparative Example 5 is not as good as that of Example 1, and the wettability of Comparative Examples 6 to 7 is poor.

[0067] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A flux for gold-tin solder paste, characterized in that: The components include the following mass percentages: Rosin 30~50%, Film former 8~15%, Thixotropic agent 5~8%, Anti-settling agent 0.4~1.5%, Alcohol complex 2~3%, Organic acid complex 4~6%, The balance is solvent; The alcohol complex comprises D-mannitol and erythritol in a mass ratio of 1:(0.2-1); The organic acid complex comprises a first organic acid, a second organic acid and a third organic acid in a mass ratio of 1: (0.5-0.6): (0.15-0.3), wherein the first organic acid is at least one of adipic acid or glutaric acid, the second organic acid is at least one of itaconic acid or salicylic acid, and the third organic acid is at least one of succinic acid or malic acid.

2. The flux for gold-tin solder paste according to claim 1, characterized in that: The rosin is at least one of hydrogenated rosin, polymerized rosin or water-white rosin.

3. The flux for gold-tin solder paste according to claim 1, characterized in that: The film-forming agent is at least one of polyethylene oxide, hydrogenated rosin glycerol ester or polyacrylic acid resin.

4. The flux for gold-tin solder paste according to claim 1, characterized in that: The thixotropic agent is at least one of hydrogenated castor oil and vinyl bisstearamide.

5. The flux for gold-tin solder paste according to claim 1, characterized in that: The soldering flux for gold-tin solder paste also includes 0.5-2.0% of corrosion inhibitor.

6. The method for preparing the flux for gold-tin solder paste according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: mixing the components to obtain the soldering flux for the gold-tin solder paste.

7. Use of the flux for gold-tin solder paste according to any one of claims 1 to 5 in the preparation of gold-tin solder paste.

8. A gold-tin solder paste, characterized in that: The composition comprises the following components in parts by weight: 7 to 12 parts of the flux for gold-tin solder paste according to any one of claims 1 to 5, 88~93 parts of gold-tin alloy powder.

9. The method for preparing the gold-tin solder paste according to claim 8, characterized in that: The method comprises the following steps: mixing a gold-tin solder paste flux and a gold-tin alloy powder to obtain the gold-tin solder paste.

10. Use of the gold-tin solder paste according to claim 8 in the preparation of electronic products.

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