High-performance lead-free tin paste, preparation method and application thereof

Abstract

The application belongs to the technical field of lead-free tin paste, and particularly relates to high-performance lead-free tin paste, a preparation method and application thereof; the high-performance lead-free tin paste comprises lead-free alloy powder, carbon nanotube composite and fluxing agent in a mass ratio of 12-15:0.5-1:84.5-87; the carbon nanotube composite comprises carbon nanotubes, carbon nanohorns, nano indium tin oxide, quaternary ammonium salt surfactant and liquid rosin; the fluxing agent comprises, in terms of mass percentage, hydrogenated rosin 30-40%, activating agent 5-10%, thixotropic agent 4-8%, stabilizer 1-5% and solvent to make up the balance to 100%; the high-performance lead-free tin paste provided by the application has low welding point cavity rate, high shear strength and good temperature cycle impact resistance.

Description

Technical Field

[0001] This invention belongs to the field of lead-free solder paste technology, specifically relating to a high-performance lead-free solder paste, its preparation method, and its application. Background Technology

[0002] Currently, the solder paste industry is developing towards lead-free, non-toxic, and environmentally friendly directions. Lead-free solder paste, due to its low toxicity, low pollution, and compliance with environmental requirements, is gradually becoming the market mainstream. With the trend of miniaturization and high integration of electronic products, the performance requirements for lead-free solder paste are also increasing. However, compared with leaded solder paste, traditional lead-free solder paste is prone to void defects during the soldering process, which leads to a decrease in the mechanical strength of the solder joint and a shortened thermal fatigue life, seriously threatening the long-term stability of high-reliability electronic equipment (such as aerospace, automotive electronics, and medical equipment).

[0003] Chinese patent CN 118720518 B discloses a low-voidity precision lead-free solder paste and its preparation method. It is prepared from the following raw materials in parts by weight: 70-90 parts tin, 1-2 parts silver, 3-6 parts copper, 2-5 parts magnesium fluorosilicate, 3-6 parts nano-carbon powder, 4-5 parts rare earth oxides, and 20-30 parts flux. This formula can reduce the void rate during soldering, improve the wettability of the lead-free solder paste, and enhance the quality and reliability of the solder joints. However, the void rate of this technical solution is 5.4-15.6%, which cannot meet the aerospace requirement of ≤5% void rate.

[0004] Chinese Patent Publication No. CN 118162799 A discloses a formic acid lead-free solder paste and its application. The formic acid lead-free solder paste, by mass percentage, contains 7-20 wt% flux and 80-93 wt% lead-free alloy powder. The lead-free alloy powder is...

[0005] The solder paste can be any one of Sn96.5Ag3Cu0.5, Sn99Ag0.3Cu0.7, Sn89.5Sb10Ni0.5, Sn90Sb10, or Sn95Sb5. This technical solution uses lead-free alloy powder in its formic acid-based lead-free solder paste, making it safe and environmentally friendly. It can be used for automated printing and dispensing. Through reflow in a formic acid reducing atmosphere, it meets the requirements for ultra-low void ratio soldering and zero residue for IGBTs and automotive-grade power devices. It can completely replace existing cleaning-type solder paste and soldering processes, achieving high reliability without cleaning and significantly reducing costs in terms of process and materials. However, lead-free formic acid solder paste requires specific formic acid reflow soldering, which is more complex: precise control of parameters such as temperature, time, and solder ratio is required, demanding higher operational skills from operators. Summary of the Invention

[0006] Based on the deficiencies of existing technologies, the purpose of this invention is to provide a high-performance lead-free solder paste, its preparation method, and its application. The high-performance lead-free solder paste provided by this invention has low solder joint void ratio, high shear strength, and good resistance to temperature cycling shock.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of the present invention provides a high-performance lead-free solder paste, comprising lead-free alloy powder, carbon nanotube composite and flux in a mass ratio of 12-15:0.5-1:84.5-87;

[0009] The carbon nanotube composite includes carbon nanotubes, carbon nanohorns, nano-indium tin oxide, quaternary ammonium salt surfactant, and liquid rosin.

[0010] The flux, by weight percentage, comprises: 30-40% hydrogenated rosin, 5-10% activator, 4-8% thixotropic agent, 1-5% stabilizer, and solvent to make up to 100%.

[0011] As some preferred embodiments, the lead-free alloy powder is selected from...

[0012] At least one of SnBi, SnBiAg, SnBiCu, SnBiIn and SnBiZn.

[0013] As some preferred embodiments, the particle size of the lead-free alloy powder is at least one of 3# (diameter: 25-45μm), 4# (diameter: 20-38μm), 5# (diameter: 15-25μm), and 6# (diameter: 5-15μm).

[0014] In a preferred embodiment, the lead-free alloy powder is SnBi58, particle size 5#, purchased from Yunnan Tin Industry Tin Materials Co., Ltd.

[0015] In a preferred embodiment, the carbon nanotube is a single-walled carbon nanotube.

[0016] In a preferred embodiment, the single-walled carbon nanotubes have a diameter of 1-2 nm and a length of 5-30 μm, and are purchased from Beijing Deco Island Gold Technology Co., Ltd., model: CNT100.

[0017] In a preferred embodiment, the carbon nanotubes have a diameter of 2-5 nm and a length of 10-20 nm, and are purchased from Beijing Deco Island Technology Co., Ltd.

[0018] As some preferred embodiments, the nano-indium tin oxide contains 90-95 wt% indium oxide and 5-10 wt% tin oxide.

[0019] As some preferred embodiments, the nano-indium tin oxide has a particle size of 20-50 nm.

[0020] In a preferred embodiment, the nano-indium tin oxide contains 90 wt% indium oxide and 10 wt% tin oxide, with a particle size of 20-30 nm, and was purchased from Beijing Deco Island Gold Technology Co., Ltd.

[0021] As some preferred embodiments, the quaternary ammonium salt surfactant is selected from at least one of rosin-based monoquaternary ammonium salt, rosin-based bisquaternary ammonium salt, and rosin-based triquaternary ammonium salt.

[0022] In a preferred embodiment, the quaternary ammonium salt surfactant is a rosin-based bisquaternary ammonium salt, purchased from Henan Daochun New Material Technology Co., Ltd.

[0023] As some preferred embodiments, the liquid rosin is selected from at least one of hydrogenated rosin methyl ester, hydrogenated rosin diethylene glycol ester, and hydrogenated rosin triethylene glycol.

[0024] In a preferred embodiment, the liquid rosin is hydrogenated rosin methyl ester, purchased from Guangxi Wuzhou Richeng Forest Products Chemical Co., Ltd., model: M-HDR.

[0025] As some preferred embodiments, the method for preparing the carbon nanotube composite includes the following steps:

[0026] (1) Mix nano-indium tin oxide, quaternary ammonium salt surfactant and water evenly, stir, filter and dry to obtain the first intermediate product; (2) Mix the first intermediate product, carbon nanotubes, carbon nanoparticles and water evenly, let stand, filter and dry to obtain the second intermediate product; (3) Mix the second intermediate product and liquid rosin to obtain carbon nanotube composite.

[0027] As some preferred embodiments, the mass ratio of the nano-indium tin oxide, the quaternary ammonium salt surfactant, and water is 8-10:1:30-50.

[0028] As some preferred embodiments, the mass ratio of the first intermediate product, carbon nanotubes, carbon nanotubes and water is 1:3-5:0.01-0.03:15-25.

[0029] As some preferred embodiments, the mass ratio of the second intermediate product to liquid rosin is 1:8-10.

[0030] As some preferred embodiments, the stirring speed in step (1) is 4000-6000 rpm, and the stirring time is 20-30 min.

[0031] As some preferred options, the settling time in step (2) is 20-40 minutes.

[0032] As some preferred embodiments, the stirring speed in step (3) is 1000-2000 rpm, and the stirring time is 10-20 min.

[0033] The carbon nanotube composite in this invention can significantly reduce the void ratio and improve the shear strength of solder joints, while also exhibiting excellent resistance to temperature cycling shock. This is especially true due to the presence of carbon nanotubes and nano-indium tin oxide (ITO): the nanoscale porous structure of the carbon nanotubes acts as a microchannel for the flow of liquid solder, accelerating the diffusion and filling of molten metal, reducing voids caused by obstructed gas escape, and forming a composite structure with the carbon nanotubes, thereby reducing the void ratio and improving the shear strength of the solder joints; the nano-indium tin oxide is uniformly dispersed at the solder interface, forming a continuous intermetallic compound layer, inhibiting bubble aggregation while refining alloy grains through heterogeneous nucleation, reducing the size and segregation tendency of the brittle phase at the interface; the combined effect of carbon nanotubes, carbon nanotubes, and nano-indium tin oxide results in lead-free solder paste with low void ratio, high shear strength, and good resistance to temperature cycling shock.

[0034] In the preparation of carbon nanotube composites, quaternary ammonium salt surfactants were used to modify nano-indium tin oxide to obtain positively charged nano-indium tin oxide, which then combined with negatively charged carbon nanotubes and carbon nanoparticles through electrostatic adsorption. Unexpectedly, it was found that using traditional alkyl quaternary ammonium salts resulted in high void ratios, low shear strength, and poor resistance to temperature cycling shock. However, when rosin-based quaternary ammonium salt surfactants were used, the rosin-based quaternary ammonium salt molecules contained rosin derivatives, and their benzene ring structure formed a π-π conjugation with liquid rosin, which significantly improved the compatibility of the composite with the flux, thereby reducing the void ratio of the solder joints and improving the shear strength and resistance to temperature cycling shock.

[0035] As some preferred embodiments, the hydrogenated rosin has a tetrahydroresin acid content ≥30%, an abietic acid content ≤1%, and a dehydroabietic acid content ≤8%.

[0036] In a preferred embodiment, the hydrogenated rosin has a tetrahydroresin acid content ≥30%, an abietic acid content ≤0.5%, and a dehydroabietic acid content ≤8%, and was purchased from Guangxi Wuzhou Richeng Forest Products Chemical Co., Ltd., model: Special Grade X.

[0037] While existing technologies disclose various types and grades of rosin, they do not provide technical specifications for rosin selection in practice. However, the inventors unexpectedly discovered that, in this invention, when hydrogenated rosin with a tetrahydropolymer content ≥30%, abietic acid content ≤1%, and dehydroabietic acid content ≤8%, under the action of the carbon nanotube composite, it is possible to achieve a solder joint void rate of less than 5%, a solder joint shear strength greater than 35 MPa, and no cracking after 1000 cycles of temperature cycling impact testing, with the shear strength still greater than 31 MPa. Conversely, when the specifications of the selected rosin or hydrogenated rosin are outside these ranges, the performance of the resulting lead-free solder paste is suboptimal.

[0038] As some preferred embodiments, the activator comprises an organic acid and cyclohexylamine hydrochloride in a mass ratio of 5-8:1.

[0039] As some preferred embodiments, the organic acid is selected from at least one of glutaric acid, adipic acid, azelaic acid, and glycolic acid.

[0040] As some preferred embodiments, the organic acid is glutaric acid and phenylsuccinic acid in a mass ratio of 3-6:1-2.

[0041] In a preferred embodiment, the organic acid is glutaric acid and phenylsuccinic acid in a mass ratio of 4:2.

[0042] As some preferred embodiments, the thixotropic agent is selected from at least one of castor oil, polyamide wax, microcrystalline wax and beeswax.

[0043] In a preferred embodiment, the thixotropic agent is castor oil.

[0044] As some preferred embodiments, the castor oil is selected from at least one of hydrogenated castor oil, methyl hydrogenated castor oil, and polyamide-modified hydrogenated castor oil.

[0045] In a preferred embodiment, the castor oil is polyamide-modified hydrogenated castor oil, purchased from Shenzhen Jintenglong Industrial Co., Ltd., model: CRAYVALLAC SF.

[0046] As some preferred embodiments, the stabilizer is selected from at least one of 2,6-di-tert-butyl-4-methylphenol, dilaurate thiodipropionate, butylated hydroxyanisole, and butylated hydroxytoluene.

[0047] In a preferred embodiment, the stabilizer is butylated hydroxyanisole.

[0048] As some preferred embodiments, the solvent is selected from at least one of triethylene glycol, tripropylene glycol, butanediol, 2-ethyl-1,3-hexanediol, 2-hexyl-1-decyl alcohol, diethylene glycol hexyl ether, diethylene glycol butyl ether, diethylene glycol ethyl ether, and tripropylene glycol butyl ether.

[0049] As some preferred embodiments, the solvent comprises tripropylene glycol and diethylene glycol hexyl ether in a mass ratio of 1:2-4.

[0050] In a preferred embodiment, the solvent comprises tripropylene glycol and diethylene glycol hexyl ether in a mass ratio of 1:3.

[0051] The second aspect of the present invention provides a method for preparing the above-mentioned high-performance lead-free solder paste, comprising the following steps: mixing hydrogenated rosin, activator, thixotropic agent, stabilizer and solvent evenly to obtain flux; mixing flux, lead-free alloy powder and carbon nanotube composite evenly to obtain high-performance lead-free solder paste.

[0052] The third aspect of this invention provides the application of the above-mentioned high-performance lead-free solder paste in the soldering of electronic components.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] This invention utilizes a quaternary ammonium salt surfactant to form a carbon nanotube composite from carbon nanotubes, carbon nanoparticles, and nano-indium tin oxide. The combined action of these three components results in a lead-free solder paste with low solder joint void ratio, high shear strength, and excellent resistance to temperature cycling shock. Simultaneously, by employing a specific hydrogenated rosin, the high-performance lead-free solder paste, under the influence of the carbon nanotube composite, exhibits a solder joint void ratio of less than 5%, a solder joint shear strength greater than 35 MPa, and after 1000 cycles of temperature cycling shock testing, no cracking occurs in the solder joints, with the shear strength still exceeding 31 MPa. Detailed Implementation

[0055] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific implementation schemes are now described in detail.

[0056] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0057] Unless otherwise specified, all raw materials used in the following examples and comparative examples are commercially available or prepared by conventional methods in the art.

[0058] Example 1

[0059] A high-performance lead-free solder paste is composed of lead-free alloy powder, carbon nanotube composite and flux in a mass ratio of 12:1:87.

[0060] The lead-free alloy powder is SnBi58, particle size 5#, purchased from Yunnan Tin Industry Tin Materials Co., Ltd.

[0061] The carbon nanotube composite is composed of carbon nanotubes, carbon nanohorns, nano-indium tin oxide, quaternary ammonium salt surfactant, and liquid rosin.

[0062] The carbon nanotubes are single-walled carbon nanotubes with a diameter of 1-2 nm and a length of 5-30 μm. They were purchased from Beijing Deco Island Gold Technology Co., Ltd., model number: CNT100.

[0063] The carbon nanotubes have a diameter of 2-5 nm and a length of 10-20 nm and were purchased from Beijing Deco Island Gold Technology Co., Ltd.

[0064] The nano-indium tin oxide contains 90wt% indium oxide and 10wt% tin oxide, with a particle size of 20-30nm, and was purchased from Beijing Deco Island Gold Technology Co., Ltd.

[0065] The quaternary ammonium salt surfactant is a rosin-based bisquaternary ammonium salt, purchased from Henan Daochun New Material Technology Co., Ltd.

[0066] The liquid rosin is hydrogenated rosin methyl ester, purchased from Guangxi Wuzhou Richeng Forest Products Chemical Co., Ltd., model: M-HDR.

[0067] The preparation method of the carbon nanotube composite is as follows: (1) Nano-indium tin oxide, quaternary ammonium salt surfactant and water are mixed evenly, stirred, filtered and dried to obtain the first intermediate product; (2) The first intermediate product, carbon nanotubes, carbon nanoparticles and water are mixed evenly, allowed to stand, filtered and dried to obtain the second intermediate product; (3) The second intermediate product and liquid rosin are stirred to obtain the carbon nanotube composite.

[0068] The mass ratio of the nano-indium tin oxide, quaternary ammonium salt surfactant, and water is 9:1:40.

[0069] The mass ratio of the first intermediate product, carbon nanotubes, carbon nanotubes and water is 1:4:0.02:20.

[0070] The mass ratio of the second intermediate product to liquid rosin is 1:9.

[0071] The stirring speed in step (1) is 5000 rpm, and the stirring time is 30 min.

[0072] The settling time in step (2) is 30 minutes.

[0073] The stirring speed in step (3) is 2000 rpm, and the stirring time is 20 min.

[0074] The flux, by weight percentage, consists of: 30% hydrogenated rosin, 5% activator, 4% thixotropic agent, 2% stabilizer, and solvent to make up to 100%.

[0075] The hydrogenated rosin has a tetrahydroresin acid content ≥30%, an abietic acid content ≤0.5%, and a dehydroabietic acid content ≤8%. It was purchased from Guangxi Wuzhou Richeng Forest Products Chemical Co., Ltd., and is grade X.

[0076] The activator comprises an organic acid and cyclohexylamine hydrochloride (CAS:4998-76-9) in a mass ratio of 6:1.

[0077] The organic acids are glutaric acid (CAS: 110-94-1) and phenyl succinic acid (CAS: 635-51-8) in a mass ratio of 4:2.

[0078] The thixotropic agent is polyamide-modified hydrogenated castor oil. It was purchased from Shenzhen Jintenglong Industrial Co., Ltd., model: CRAYVALLAC SF.

[0079] The stabilizer is butylated hydroxyanisole (CAS: 25013-16-5).

[0080] The solvent comprises tripropylene glycol (CAS: 24800-44-0) and diethylene glycol hexyl ether (CAS: 112-59-4) in a mass ratio of 1:3.

[0081] The preparation method of the above-mentioned high-performance lead-free solder paste is as follows: hydrogenated rosin, activator, thixotropic agent, stabilizer and solvent are mixed evenly to obtain flux. The flux, lead-free alloy powder and carbon nanotube composite are mixed evenly to obtain high-performance lead-free solder paste.

[0082] Example 2

[0083] The only difference from Example 1 is that the high-performance lead-free solder paste is composed of lead-free alloy powder, carbon nanotube composite and flux in a mass ratio of 13:0.8:86.2; all other aspects are the same.

[0084] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0085] Example 3

[0086] The only difference from Example 1 is that the high-performance lead-free solder paste is composed of lead-free alloy powder, carbon nanotube composite and flux in a mass ratio of 15:0.5:84.5; all other aspects are the same.

[0087] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0088] Example 4

[0089] The only difference from Example 1 is that the flux, by mass percentage, consists of: 35% hydrogenated rosin, 8% activator, 6% thixotropic agent, 3% stabilizer, and solvent to make up to 100%; all other components are the same.

[0090] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0091] Example 5

[0092] The only difference from Example 1 is that the flux, by mass percentage, consists of: 40% hydrogenated rosin, 10% activator, 8% thixotropic agent, 5% stabilizer, and solvent to make up to 100%; all other components are the same.

[0093] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0094] Comparative Example 1

[0095] The only difference from Example 1 is that there is no carbon nanotube corner. The preparation method of the carbon nanotube composite is as follows: (1) mix nano-indium tin oxide, quaternary ammonium salt surfactant and water evenly, stir, filter and dry to obtain a first intermediate product; (2) mix the first intermediate product, carbon nanotubes, carbon and water evenly, let stand, filter and dry to obtain a second intermediate product; (3) mix the second intermediate product and liquid rosin, stir to obtain a carbon nanotube composite; the mass ratio of the first intermediate product, carbon nanotubes and water is 1:4:20; the rest are the same.

[0096] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0097] Comparative Example 2

[0098] The only difference from Example 1 is that nano-indium tin oxide is replaced with nano-cerium oxide of equal mass, with an average particle size of 20 nm, purchased from Beijing Deco Island Gold Technology Co., Ltd.; the preparation method of the carbon nanotube composite is as follows: (1) nano-cerium oxide, quaternary ammonium salt surfactant and water are mixed evenly, stirred, filtered and dried to obtain the first intermediate product; (2) the first intermediate product, carbon nanotubes, carbon nanoparticles and water are mixed evenly, allowed to stand, filtered and dried to obtain the second intermediate product; (3) the second intermediate product and liquid rosin are stirred to obtain the carbon nanotube composite; the mass ratio of nano-cerium oxide, quaternary ammonium salt surfactant and water is 9:1:40; all others are the same.

[0099] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0100] Comparative Example 3

[0101] The only difference from Example 1 is that the rosin-based bisquaternary ammonium salt is replaced with an equal mass of dodecyltrimethylammonium chloride (CAS No.: 112-00-5); all other aspects are the same.

[0102] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0103] Comparative Example 4

[0104] The only difference from Example 1 is that the hydrogenated rosin contains ≥30% tetrahydroresin acid, ≤1% abietic acid, and ≤10% dehydroabietic acid, and was purchased from Guangxi Wuzhou Richeng Forest Products Chemical Co., Ltd., model: Grade 1 WW; all other aspects are the same.

[0105] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0106] Comparative Example 5

[0107] The only difference from Example 1 is that the hydrogenated rosin contains ≤30% tetrahydroabietic acid, ≤2% abietic acid, and ≤10% dehydroabietic acid, and was purchased from Guangxi Dinghong Resin Co., Ltd., model: DH-HR; all other aspects are the same.

[0108] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0109] Comparative Example 6

[0110] The only difference from Example 1 is that the hydrogenated rosin is replaced with KE604 rosin from Arakawa, Japan; everything else is the same.

[0111] The preparation method of the above-mentioned high-performance lead-free solder paste is the same as that in Example 1.

[0112] To verify the performance of the high-performance lead-free solder paste of the present invention, the lead-free solder pastes prepared in Examples 1-5 and Comparative Examples 1-6 were subjected to the following performance tests:

[0113] (1) Void rate test: The pads are copper-nickel and gold pads with a nickel layer thickness of 6mm and a gold layer thickness of 0.02mm. The reflow soldering temperature is 180℃ and the reflow time is 90s, forming a solder joint with a diameter of 0.8mm. The void rate of the solder joint is detected by X-ray inspection equipment.

[0114] (2) Shear strength: The pads are copper-nickel and gold pads with a nickel layer thickness of 6 mm and a gold layer thickness of 0.02 mm. The reflow soldering temperature is 180℃ and the reflow time is 90s to form a solder joint with a diameter of 0.8 mm. The shear strength of the solder joint is tested at a shearing speed of 50 mm / min.

[0115] (3) Temperature Cyclic Shock Test: The pads are copper-nickel and gold pads, with a nickel layer thickness of 6 mm and a gold layer thickness of 0.02 mm. The reflow soldering temperature is 180℃, and the reflow time is 90 s, forming solder joints with a diameter of 0.8 mm. The pads are then subjected to a temperature cyclic shock test. The temperature cyclic shock test is as follows:

[0116] -40℃×10min, 125℃×10min constitute one cycle, and a total of 1000 cycles are performed. After these cycles, observe whether there is any cracking at the weld joint and test the shear strength of the weld joint at a shear rate of 50mm / min.

[0117] Table 1

[0118]

[0119]

[0120] As shown in Table 1: The lead-free solder pastes of Examples 1-5 had a void ratio of less than 5%, a shear strength greater than 35 MPa, and no cracking after temperature cycling impact testing, with a shear strength greater than 30 MPa. In Comparative Example 1, the absence of carbon nanoparticles resulted in a lead-free solder paste with a void ratio greater than 5%, a shear strength less than 30 MPa, and cracking after temperature cycling impact testing, with a shear strength less than 25 MPa. In Comparative Example 2, replacing nano-indium tin oxide with an equal mass of nano-cerium oxide resulted in a lead-free solder paste with a void ratio greater than 5%, a shear strength less than 35 MPa, and no cracking after temperature cycling impact testing, with a shear strength less than 30 MPa. In Comparative Example 3, replacing rosin-based bisquaternary ammonium salt with an equal mass of dodecyltrimethylammonium chloride resulted in a lead-free solder paste with a void ratio greater than 5%. The shear strength was less than 30 MPa, and the solder joints cracked after the temperature cycling impact test. The shear strength was less than 25 MPa. The contents of tetrahydroresin acid, abietic acid, and dehydroabietic acid in the hydrogenated rosin of Comparative Examples 4 and 5 changed. Among them, the void ratio of the solder joints of the lead-free solder paste obtained by Comparative Example 4 was greater than 5%, the shear strength was less than 35 MPa, and the solder joints did not crack after the temperature cycling impact test. The shear strength was less than 30 MPa. The void ratio of the solder joints of the lead-free solder paste obtained by Comparative Example 5 was greater than 5%, the shear strength was less than 30 MPa, and the solder joints cracked after the temperature cycling impact test. The shear strength was less than 25 MPa. Comparative Example 6 replaced the hydrogenated rosin with rosin. The void ratio of the solder joints of the obtained lead-free solder paste was greater than 5%, the shear strength was less than 30 MPa, and the solder joints did not crack after the temperature cycling impact test. The shear strength was less than 25 MPa.

[0121] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A high-performance lead-free solder paste, characterized in that, Including a mass ratio of 12-15: 0.5-1: 84.5-87 lead-free alloy powder, carbon nanotube composite and flux; The carbon nanotube composite includes carbon nanotubes, carbon nanohorns, nano-indium tin oxide, quaternary ammonium salt surfactant, and liquid rosin. The nano-indium tin oxide contains 90-95 wt% indium oxide and 5-10 wt% tin oxide; The flux, by weight percentage, comprises: 30-40% hydrogenated rosin, 5-10% activator, 4-8% thixotropic agent, 1-5% stabilizer, and solvent to make up to 100%.

2. The high-performance lead-free solder paste according to claim 1, characterized in that, The carbon nanotubes are single-walled carbon nanotubes; the diameter of the single-walled carbon nanotubes is 1-2 nm and the length is 5-30 µm.

3. The high-performance lead-free solder paste according to claim 2, characterized in that, The diameter of the carbon nanotubes is 2-5 nm, and the length is 10-20 nm.

4. The high-performance lead-free solder paste according to claim 3, characterized in that, The quaternary ammonium salt surfactant is selected from at least one of rosin-based monoquaternary ammonium salt, rosin-based bisquaternary ammonium salt, and rosin-based triquaternary ammonium salt.

5. The high-performance lead-free solder paste according to claim 4, characterized in that, The liquid rosin is selected from at least one of hydrogenated rosin methyl ester, hydrogenated rosin diethylene glycol ester, and hydrogenated rosin triethylene glycol.

6. The high-performance lead-free solder paste according to any one of claims 1-5, characterized in that, The preparation method of the carbon nanotube composite includes the following steps: (1) mixing nano-indium tin oxide, quaternary ammonium salt surfactant and water evenly, stirring, filtering and drying to obtain a first intermediate product; (2) mixing the first intermediate product, carbon nanotubes, carbon nanoparticles and water evenly, letting stand, filtering and drying to obtain a second intermediate product; (3) mixing the second intermediate product and liquid rosin to obtain a carbon nanotube composite.

7. The high-performance lead-free solder paste according to claim 1, characterized in that, The hydrogenated rosin contains ≥30% tetrahydroresinic acid, ≤1% abietic acid, and ≤8% dehydroabietic acid.

8. The method for preparing the high-performance lead-free solder paste according to any one of claims 1-7, characterized in that, Includes the following steps: Hydrogenated rosin, activator, thixotropic agent, stabilizer and solvent are mixed evenly to obtain flux. High-performance lead-free solder paste is obtained by mixing flux, lead-free alloy powder and carbon nanotube composite evenly.

9. The application of the high-performance lead-free solder paste according to any one of claims 1-7 in the soldering of electronic components.

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