A flux for gold-tin solder paste, the gold-tin solder paste, and their preparation methods and applications

Abstract

The present invention relates to a soldering flux for AuSn solder paste, an AuSn solder paste, and a preparation method and application thereof. The soldering flux for AuSn solder paste comprises the following components: rosin, film-forming agent, thixotropic agent, anti-settling agent, alcohol complex, organic acid complex, and solvent. By the cooperation of rosin, film-forming agent, thixotropic agent, anti-settling agent, alcohol complex, and organic acid complex, the soldering flux for AuSn solder paste of the present invention can endow the AuSn solder paste with a low void rate, good wettability, good printing performance, and prevent the AuSn solder paste from settling after long-term storage.

Description

Technical Field

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

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

[0003] In recent years, the development trend of electronic products has been towards diversification, high density, high performance, and miniaturization. In the welding of micro-miniature devices, it has become increasingly difficult for prefabricated parts to adapt to the current development trend of electronic products. Gold-tin solder paste has excellent properties, and due to the characteristics of its paste, it can flexibly adjust the coating position and coating amount according to the device size and shape, and can effectively cope with the welding of current micro-miniature 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 the welded parts. Among them, voids and wettability are important factors affecting the reliability of the device. Voids are very harmful to solder joints. A high void rate will weaken the welding strength and reduce the reliability. Moreover, voids will squeeze the solder paste, which may cause short circuits between solder joints. According to industry statistics and analysis, failures related to voids account for 20% of PCBA failures. There are many existing fluxes that can reduce the void rate of solder pastes such as Sn64Bi35Ag1, Sn62Pb36Ag2, Sn90Sb10, etc., but the improvement of these fluxes on the high void rate problem of gold-tin solder paste is not obvious.

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

[0006] The Chinese patent application with the publication number CN114378483A provides a flux for no-clean gold-tin solder paste, which can make the gold-tin solder paste have good wettability. However, the rosin dosage of the flux in 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 object of the present invention is to overcome the problems of high void ratio, poor wettability, easy sedimentation after long-term storage or poor printing performance existing in the existing gold-tin solder paste, and to provide a soldering flux for gold-tin solder paste. By the combination of rosin, film-forming agent, thixotropic agent, anti-settling agent, alcohol complex and organic acid complex, the gold-tin solder paste made with this soldering flux can have a low void ratio, good wettability and good printing performance, and will not settle after long-term storage.

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

[0009] A further object of the present invention is to provide the application of the above-mentioned soldering 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 preparation method of the above-mentioned gold-tin solder paste.

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

[0013] The above objects of the present invention are achieved by the following technical solutions:

[0014] A soldering flux for gold-tin solder paste, comprising components in the following mass percentages:

[0015] Rosin 30 - 50%,

[0016] Film-forming agent 8 - 15%,

[0017] Thixotropic agent 5 - 8%,

[0018] Anti-settling agent 0.4 - 1.5%,

[0019] Alcohol complex 2 - 3%,

[0020] Organic acid complex 4 - 6%,

[0021] The balance is solvent;

[0022] The alcohol complex includes D-mannitol and erythritol with a mass ratio of 1:(0.2 - 1);

[0023] The organic acid complex includes a first organic acid, a second organic acid and a third organic acid with a mass ratio of 1:(0.5 - 0.6):(0.15 - 0.3). 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.

[0024] The rosin mass content of the soldering flux for 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 the film-forming agent is beneficial to improving the wettability of the gold-tin solder paste; the addition of the thixotropic agent is beneficial to improving the printing performance of the gold-tin solder paste; the addition of the anti-settling agent has an improvement effect on the sedimentation problem during the storage of the gold-tin solder paste.

[0025] For the solder paste system of gold-tin alloy solder powder with large particle size (25 - 45μm), the inventors of the present invention have found that the molecule of D-mannitol contains 6 hydroxyl groups, with a relatively large molecular weight, long molecular chain, and a significant contribution to the viscosity of the solder paste, while the molecule of erythritol contains 4 hydroxyl groups, with a relatively small molecular weight, small steric hindrance, and can be better dispersed in the solder paste. This enables the mutual interactions between molecules such as hydrogen bonds formed synergistically between the two to not only help improve the uniformity and stability of the components and thus improve the printing performance and the stability during long-term storage of the gold-tin solder paste, but also help expel the bubbles generated during the soldering of the solder paste from the system and reduce the void ratio of the solder paste. In addition, when D-mannitol and erythritol are compounded, the active interval formed by the boiling point difference between the two has a good match with the welding temperature interval of the gold-tin solder paste, which is beneficial to removing metal oxides during the welding process and has a certain help in improving the wettability of the gold-tin solder paste.

[0026] The present invention also adds an organic acid complex, which can adjust the surface tension of the gold-tin solder paste, and the different active intervals of its first organic acid, second organic acid, and third organic acid further cooperate with the alcohol complex, thereby reducing the void ratio of the gold-tin solder paste and significantly improving the wettability of the gold-tin solder paste.

[0027] That is, the soldering flux for gold-tin solder paste of the present invention, through the cooperation of rosin, film-forming agent, thixotropic agent, anti-settling agent, alcohol complex, and organic acid complex, can make the gold-tin solder paste have a low void ratio, good wettability, good printing performance, and prevent the solder paste from settling after long-term storage.

[0028] In the present invention, the mass ratio of D-mannitol to erythritol in the alcohol complex can specifically be 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.

[0029] Preferably, the mass ratio of the D-mannitol to the erythritol is 1:(0.4 - 1).

[0030] Preferably, the rosin is at least one of hydrogenated rosin, polymerized rosin, or water-white rosin.

[0031] Preferably, the film-forming agent is at least one of polyethylene oxide, hydrogenated rosin glyceride, or polyacrylic acid resin.

[0032] Preferably, the thixotropic agent is at least one of hydrogenated castor oil and vinyl bisstearamide.

[0033] Preferably, the anti-settling agent is polyamide wax.

[0034] Preferably, the flux for gold-tin solder paste further comprises 0.5 - 2.0% of a corrosion inhibitor.

[0035] More preferably, the corrosion inhibitor is at least one of alcohol amine corrosion inhibitors and imidazole corrosion inhibitors.

[0036] Further preferably, the alcohol amine corrosion inhibitor includes but is not limited to triethanolamine.

[0037] Further preferably, the imidazole corrosion inhibitor includes but is not limited to at least one of 2-phenylimidazole, 2-methylimidazole, and 2-ethylimidazole.

[0038] Preferably, the flux for gold-tin solder paste further comprises 0.8 - 3.0% of an antioxidant and 0.5 - 2.0% of a surfactant.

[0039] More preferably, the antioxidant is at least one of benzotriazole and 5-hydroxy salicylic acid.

[0040] More preferably, the surfactant is at least one of fluorosurfactant, antioxidant oil surfactant, and rosin alcohol ether surfactant.

[0041] Preferably, the solvent comprises a high-boiling solvent and a low-boiling solvent with a mass ratio of 1:(3 - 4); the boiling point of the high-boiling solvent is 240 - 340°C, and the boiling point of the low-boiling solvent is 170 - 230°C.

[0042] More preferably, the high-boiling solvent is at least one of diethanolamine, tetraethylene glycol, 3-hexanol, glycerol ether, propylene glycol phenyl ether, and 2-ethyl-1,3-hexanediol.

[0043] More preferably, the low-boiling solvent is at least one of 1,2,6-hexanetriol, propylene glycol, diethylene glycol butyl ether, ethylene glycol, and 1,4-butanediol.

[0044] The preparation method of the above-mentioned flux for gold-tin solder paste comprises the following steps: mixing each component to obtain the flux for gold-tin solder paste.

[0045] Preferably, the temperature of the mixing is 110 - 180°C.

[0046] The application 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.

[0047] A gold-tin solder paste comprises the following components in parts by weight:

[0048] 7 - 12 parts of the soldering flux for Au - Sn solder paste,

[0049] 88 - 93 parts of Au - Sn alloy powder.

[0050] More preferably, the particle size distribution of the Au - Sn alloy powder is 25 - 45 μm.

[0051] The preparation method of the above - mentioned Au - Sn solder paste includes the following steps: Mix the soldering flux for Au - Sn solder paste and the Au - Sn alloy powder to obtain the Au - Sn solder paste.

[0052] Preferably, the soldering flux for Au - Sn solder paste and the Au - Sn alloy powder are first stirred under the conditions of - 50~ - 60 kPa and 70~90 RPM for 0.5~2 hours, then the material is collected, and then stirred under the conditions of - 50~ - 60 kPa and 150~180 RPM for 0.5~2 hours, and then stirred at 250~300 RPM for 3~5 hours to obtain the Au - Sn solder paste.

[0053] The application of the above - mentioned Au - Sn solder paste in the preparation of electronic products is also within the protection scope of the present invention.

[0054] Compared with the prior art, the beneficial effects of the present invention are:

[0055] The soldering flux for Au - Sn solder paste of the present invention, through the cooperation of rosin, film - forming agent, thixotropic agent, anti - settling agent, alcohol complex and organic acid complex, can make the Au - Sn solder paste have a low void ratio, good wettability and good printing performance, and prevent the Au - Sn solder paste from settling after long - term storage. Detailed embodiments

[0056] In order to more clearly and completely describe the technical solution of the present invention, the following further details the present invention through specific embodiments. 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, and various changes can be made within the scope defined by the claims of the present invention.

[0057] The raw materials used in each embodiment and comparative example are as follows:

[0058] Rosin 1#: Hydrogenated rosin, Rayne, 65997 - 06 - 0;

[0059] Rosin 2#: Polymerized rosin, Eastman, Staybelite;

[0060] Film - forming agent 1#: Polyethylene oxide, Macklin, 68441 - 17 - 8;

[0061] Film - forming agent 2#: Hydrogenated rosin glyceride, Macklin, 65997 - 13 - 9;

[0062] Thixotropic agent: Hydrogenated castor oil, Nippon Fine Chemical Co., Ltd., HCO;

[0063] Alcohol complex 1#: Comprising D-mannitol and erythritol in a mass ratio of 1:0.4;

[0064] Alcohol complex 2#: Comprising D-mannitol and erythritol in a mass ratio of 1:0.2;

[0065] Alcohol complex 3#: Comprising D-mannitol and erythritol in a mass ratio of 1:1;

[0066] Alcohol complex 4#: Comprising D-mannitol and xylitol in a mass ratio of 1:0.4;

[0067] Alcohol complex 5#: Comprising sorbitol and erythritol in a mass ratio of 1:0.4;

[0068] Organic acid complex 1#: Comprising adipic acid, itaconic acid and succinic acid in a mass ratio of 1:0.6:0.15;

[0069] Organic acid complex 2#: Comprising adipic acid, itaconic acid and succinic acid in a mass ratio of 1:0.5:0.3;

[0070] Organic acid complex 3#: Comprising glutaric acid, salicylic acid and malic acid in a mass ratio of 1:0.6:0.15;

[0071] Organic acid complex 4#: Comprising adipic acid and itaconic acid in a mass ratio of 1:0.6;

[0072] Organic acid complex 5#: Comprising adipic acid and succinic acid in a mass ratio of 1:0.15;

[0073] Organic acid complex 6#: Comprising itaconic acid and succinic acid in a mass ratio of 0.6:0.15;

[0074] Corrosion inhibitor 1#: Triethanolamine;

[0075] Corrosion inhibitor 2#: 2-Methylimidazole;

[0076] Antioxidant: Benzotriazole (BTA);

[0077] Surfactant: Fluorinated surfactant, Chemours, Capstone FS-63;

[0078] Anti-settling agent: Polyamide wax, Elementis, THIXATROL® P2100W;

[0079] Solvent 1#: Comprising 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;

[0080] Solvent 2#: It includes tetraethylene glycol and propylene glycol with a mass ratio of 1:4.

[0081] Examples 1 to 10

[0082] Examples 1 to 10 provide a series of soldering fluxes for gold-tin solder pastes, and their formulations are shown in Table 1 and Table 2 below.

[0083] Components and their mass percentages (%) of each example in Table 1

[0084]

[0085] Components and their mass percentages (%) of each example in Table 2

[0086]

[0087] Comparative Examples 1 to 7

[0088] Comparative Examples 1 to 7 provide a series of soldering fluxes for gold-tin solder pastes, and their formulations are shown in Table 3 below.

[0089] Components and their mass percentages (%) of each comparative example in Table 3

[0090]

[0091] The preparation methods of the soldering fluxes for gold-tin solder pastes in the above examples and comparative examples include the following steps:

[0092] 1) Add rosin and tetraethylene glycol in the solvent into the reaction kettle, and mix evenly at 170 °C;

[0093] 2) Wait until the temperature drops to 150 °C, add propylene glycol in the solvent, 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), after mixing evenly, add thixotropic agent and mix thoroughly;

[0094] 3) Cool down to 120 °C, add the third organic acid (if any) in the organic acid complex, corrosion inhibitor, anti-settling agent, antioxidant, surfactant, after mixing thoroughly, cool down to <60 °C, take out, and obtain the soldering flux for gold-tin solder paste.

[0095] Performance test

[0096] The soldering fluxes for gold-tin solder pastes of each example and each comparative example are made into gold-tin solder pastes, and then performance tests are carried out.

[0097] The gold-tin solder paste includes the following components in parts by weight: 8 parts of the soldering flux for gold-tin solder paste and 92 parts of gold-tin alloy powder. Among them, the gold-tin alloy powder is 3# Au80Sn20 alloy, and the particle size distribution of the gold-tin alloy powder is 25 - 45 μm.

[0098] The preparation method of the gold-tin solder paste includes the following steps: Put the gold-tin solder paste, flux, and gold-tin alloy powder into a double planetary mixer, stir at a rotation speed of 80 RPM for 1 h under a vacuum of -50 to -60 kPa, then collect the material at the center of the mixer and stir at a rotation speed of 160 RPM for 1 h under a vacuum of -50 to -60 kPa, and then increase the rotation speed to 280 RPM and stir for 4 h to obtain the gold-tin solder paste.

[0099] The test standards or test methods for each performance test are as follows:

[0100] 1) Void ratio: Use a microfocus X-RAY fluoroscopy detection device to test the void ratio of the gold-tin solder paste after welding. The industry usually requires the void ratio to be below 10%.

[0101] 2) Wettability: Test according to the 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 that the wettability is poor.

[0102] 3) Sedimentation: Store the gold-tin solder paste in a cool cabinet at a temperature of 5°C for 3 months, and observe whether the gold-tin solder paste is stratified. If it is not stratified, it indicates that sedimentation has not occurred; if it is stratified, it indicates that sedimentation has occurred.

[0103] 4) Printing performance: Test according to the "Solder Paste Printing Standard for Chip 1608, 2125, 3216", and 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 amount and thickness are uniform, and the thickness is 8.31 MILS; ④ The solder paste has good formation and no collapse or fracture. The evaluation criteria are as follows: 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.

[0104] The performance test results of the gold-tin solder paste prepared with the flux of each example and comparative example are shown in Table 4.

[0105] Table 4 Performance test results of each example and comparative example

[0106]

[0107] As can be seen from Table 4:

[0108] The void ratios of Examples 1 to 10 are all below 6%, the wettability is level 1 or 2, no sedimentation occurs after 3 months of storage, and the printing performance is excellent or good, indicating that the flux for the gold-tin solder paste of the present invention can make the gold-tin solder paste have a low void ratio, good wettability and good printing performance, and prevent the gold-tin solder paste from sedimenting after long-term storage.

[0109] Comparing Example 1 and Example 4, it can be seen that when hydrogenated rosin is selected, the soldering flux for Au-Sn solder paste can make the Au-Sn solder paste have a lower void ratio.

[0110] Comparing Example 1 and Example 5, it can be seen that when hydrogenated rosin glyceride is selected as the film-forming agent, the soldering flux for Au-Sn solder paste can make the Au-Sn solder paste have a lower void ratio.

[0111] Comparing Example 1 and Example 6, it can be seen that when an alcohol amine corrosion inhibitor (such as triethanolamine) is selected as the corrosion inhibitor, the soldering flux for Au-Sn solder paste can make the Au-Sn solder paste have a lower void ratio, better wettability and printing performance.

[0112] Comparing Example 1 and Examples 7 to 8, it can be seen that when the mass ratio of D-mannitol to erythritol is regulated within a certain range (1:0.4 to 1), the soldering flux for Au-Sn solder paste can make the Au-Sn solder paste have a lower void ratio, better wettability and printing performance.

[0113] Comparing Example 1 and Example 10, it can be seen that when a combination of adipic acid, itaconic acid and succinic acid is selected as the organic acid complex, the soldering flux for Au-Sn solder paste can make the Au-Sn solder paste have a lower void ratio.

[0114] In Comparative Example 1, xylitol was used to replace erythritol, and the Au-Sn solder paste made from the soldering flux for Au-Sn solder paste had a high void ratio, settled after long-term storage, and its wettability and printing performance were inferior to those of Example 1. In Comparative Example 2, sorbitol was used to replace D-mannitol, and the Au-Sn solder paste made from the soldering flux for Au-Sn solder paste had a not-low void ratio, settled after long-term storage, and its wettability and printing performance were inferior to those of Example 1. In Comparative Example 3, erythritol was not used, and the Au-Sn solder paste made from the soldering flux for Au-Sn solder paste had a high void ratio, settled after long-term storage, poor printing performance, and its wettability was inferior to that of Example 1. In Comparative Example 4, D-mannitol was not used, and the Au-Sn solder paste made from the soldering flux for Au-Sn solder paste had a high void ratio, settled after long-term storage, poor printing performance, and its wettability was inferior to that of Example 1. For Comparative Examples 5 to 7, the organic acid complexes all used only two organic acids for compounding, and the Au-Sn solder paste had a high void ratio. Moreover, the wettability of Comparative Example 5 was inferior to that of Example 1, and the wettability of Comparative Examples 6 to 7 was poor.

[0115] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill 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 implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A soldering flux for gold-tin solder paste, characterized in that, Comprising components in the following mass percentages: rosin 30 - 50%, film-forming agent 8 - 15%, thixotropic agent 5 - 8%, anti-settling agent 0.4 - 1.5%, alcohol complex 2 - 3%, organic acid complex 4 - 6%, corrosion inhibitor 0.5 - 2.0%, the balance being solvent; the corrosion inhibitor is an alcohol amine corrosion inhibitor; the alcohol complex comprises D-mannitol and erythritol in a mass ratio of 1:(0.4 - 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), the first organic acid being at least one of adipic acid or glutaric acid, the second organic acid being at least one of itaconic acid or salicylic acid, and the third organic acid being at least one of succinic acid or malic acid.

2. The soldering flux for AuSn solder paste according to claim 1, wherein The rosin is at least one of hydrogenated rosin, polymerized rosin or water-white rosin.

3. The soldering flux for AuSn solder paste according to claim 1, characterized in that, The film-forming agent is at least one of polyethylene oxide, hydrogenated rosin glyceride or polyacrylic resin.

4. The soldering flux for AuSn solder paste according to claim 1, wherein The thixotropic agent is at least one of hydrogenated castor oil or vinyl bisstearamide.

5. The preparation method of the soldering flux for AuSn solder paste according to any one of claims 1 to 4, characterized in that, Comprising the following steps: mixing the components to obtain the soldering flux for Au-Sn solder paste.

6. Use of the soldering flux for Au-Sn solder paste according to any one of claims 1 - 4 in the preparation of Au-Sn solder paste.

7. A gold-tin solder paste, characterized in that, Comprising components in the following weight parts: the soldering flux for Au-Sn solder paste according to any one of claims 1 - 4, 7 - 12 parts, Au-Sn alloy powder, 88 - 93 parts.

8. The preparation method of the gold-tin solder paste according to claim 7, characterized in that, Comprising the following steps: mixing the soldering flux for Au-Sn solder paste and the Au-Sn alloy powder to obtain the Au-Sn solder paste.

9. Use of the Au-Sn solder paste according to claim 7 in the preparation of electronic products.

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