High-melting-point high-temperature lead-free environment-friendly soldering paste and preparation method thereof

Abstract

The invention discloses a high-melting-point high-temperature lead-free environment-friendly soldering paste and a preparation method thereof. The soldering paste is composed of 85-89% of alloy powder and 11-15% of flux paste. The alloy powder comprises the following components in percentage by weight: 0.5 to 7.0 percent of tin, 0.2 to 3.0 percent of silver, 0.2 to 1.5 percent of copper, 0.5 to 5.0 percent of nickel, 0.02 to 0.8 percent of antimony and the balance of bismuth. A high-boiling-point solvent, modified resin, an active agent containing an antioxidant and a thixotropic agent are adopted in the flux paste, and the flux paste and the alloy powder are prepared into the soldering paste through a vacuum mixing technology. The problem of high-temperature secondary melting of traditional lead-free solder is solved, and the lead-free solder is suitable for high-temperature welding scenes such as ICs and power devices.

Description

Technical Field

[0001] The present application relates to the technical field of welding materials, and more specifically, to a high-melting-point, high-temperature, lead-free, environmentally friendly solder paste and a preparation method thereof. Background Art

[0002] With the trend toward lead-free soldering, conventional lead-free solder pastes, such as tin-silver-copper (SAC) alloys, generally have melting points between 217°C and 245°C. However, the manufacturing of ICs, IGBTs, semiconductor power devices (such as bridge rectifiers), automotive electronics, and high-power LED die bonding often requires secondary high-temperature soldering or high-temperature operating environments. This makes these solder joints susceptible to secondary melting during subsequent processing, leading to component displacement and solder joint failure, seriously impacting product reliability.

[0003] While bismuth (Bi)-based alloys are seen as a potential solution due to their higher melting points, existing Bi-based solders suffer from poor wettability and brittleness, and there is a lack of compatible high-performance fluxes. Conventional fluxes tend to prematurely burn and fail at temperatures above 255°C, resulting in insufficient wetting and spreading, and undesirable residue. Furthermore, they struggle to maintain the process stability required for continuous printing for more than 12 hours.

[0004] Therefore, there is an urgent need to develop an environmentally friendly, lead-free solder paste that has a high melting point, good soldering performance, excellent high-temperature stability, and is environmentally friendly to address the key pain points in the above-mentioned high-temperature application fields. The present invention is developed to address this need. Summary of the Invention

[0005] In order to solve the problem that conventional lead-free solder paste is prone to secondary melting in subsequent processes when secondary high-temperature soldering is required or in a high-temperature working environment, causing problems such as component displacement and solder joint failure, which seriously affects product reliability, the present application provides a high-melting-point, high-temperature, lead-free, environmentally friendly solder paste and its preparation method.

[0006] In the first aspect, the present application provides a high melting point, high temperature, lead-free, environmentally friendly solder paste, which adopts the following technical solutions:

[0007] A high-melting-point, high-temperature, lead-free, environmentally friendly solder paste comprising alloy powder and flux paste, wherein, by mass percentage, the alloy powder accounts for 85-89% and the flux paste accounts for 11-15%;

[0008] The alloy powder contains the following elements in percentage by mass:

[0009] 0.5-7.0% tin

[0010] 0.2-3.0% silver

[0011] 0.2-1.5% copper

[0012] 0.5-5.0% of nickel

[0013] 0.02-0.8% of antimony

[0014] balance % of bismuth;

[0015] The solder paste comprises the following components in mass percentage:

[0016] 30-50% of solvent

[0017] 10-25% of modified resin

[0018] 8-20% of active agent

[0019] 4-10% of thixotropic agent

[0020] balance % of rosin.

[0021] Preferably, the solvent comprises one or a combination of high boiling ethers, alcohols, vegetable oils, the high boiling ethers comprising at least one of tripropylene glycol butyl ether, diethylene glycol dibutyl ether, diethylene glycol hexyl ether, anisole, the alcohols comprising at least one of sunflower alcohol, dodecanol, benzyl alcohol, the vegetable oils comprising one or a combination of hydrogenated castor oil, palm oil derivatives.

[0022] Preferably, the modified resin comprises at least two of polyisobutylene, hydrocarbon resin, rosin ester, tackifying resin, the polyisobutylene being a combination of polyisobutylene 100 and polyisobutylene 300, the hydrocarbon resin being copolymerized from C5 resin and C9 resin, the rosin ester comprising one of rosin pentaerythritol ester, rosin glycerol ester, the tackifying resin being P-105 type tackifying resin.

[0023] Preferably, the active agent comprises one or a combination of organic acid component, amine component, halogen substitute, the organic acid component comprising at least two of sebacic acid, decanoyl tetradecanoic acid, adipic acid, succinic acid, glutaric acid, malic acid, the amine component comprising at least one of 2-ethylimidazole, 2-phenylimidazole, triethanolamine, triisopropanolamine, ethylenediamine derivative, the halogen substitute being organic halide or diphenyl phosphate.

[0024] Preferably, the thixotropic agent comprises at least one of polyamide modified hydrogenated castor oil, ethylene bis-stearamide, microcrystalline wax, organobentonite, fumed silica.

[0025] Preferably, the rosin comprises at least one of hydrogenated rosin, polymerized rosin, disproportionated rosin, maleated rosin.

[0026] Preferably, the solvent comprises a composition having a boiling point greater than 250° C., specifically a mixture of tripropylene glycol butyl ether and hydrogenated castor oil in a ratio of 3:1, or a mixture of diethylene glycol dibutyl ether and benzyl alcohol in a ratio of 3:1.

[0027] Preferably, the active agent further comprises 0.5-5% of an antioxidant component, wherein the antioxidant component comprises at least one of propyl gallate, butylated hydroxyanisole, and tocopherol.

[0028] In a second aspect, the present application provides a method for preparing a high-melting-point, high-temperature, lead-free, environmentally friendly solder paste, which adopts the following technical solution:

[0029] A method for preparing a high-melting-point, high-temperature, lead-free, environmentally friendly solder paste comprises the following steps:

[0030] Step S1: Add rosin, solvent and active agent into a reaction kettle and stir at 75-85°C for 1-2 hours until they are completely dissolved;

[0031] Step S2: cooling to 60-70° C., adding a thixotropic agent and a modified resin, and dispersing at a high speed of 1000-3000 rpm for 30-60 minutes to obtain a mixed paste;

[0032] Step S3: After the mixed paste is allowed to stand for 12-24 hours, it is ground 2-3 times with a three-roll grinder until the fineness is ≤15 μm to obtain a soldering paste;

[0033] Step S4: weigh the alloy powder and solder paste in proportion, and mix them in a vacuum mixer for 10-20 minutes;

[0034] Step S5: evacuate to -0.095 ~ -0.085 MPa and continue stirring for 3-8 minutes;

[0035] Step S6: packaging the finished solder paste in a nitrogen-filled environment.

[0036] In summary, the beneficial technical effects of this application are as follows: Through the synergistic effect of a bismuth-based alloy containing a specific ratio of tin, silver, copper, nickel, and antimony and a high-temperature stable soldering paste, the secondary melting problem caused by the insufficient melting point of traditional lead-free solder in high-temperature soldering scenarios is solved. The addition of nickel and antimony to the alloy significantly improves the mechanical strength and thermal fatigue resistance of the solder joint, overcoming the inherent brittleness of bismuth-based solder. At the same time, the innovatively designed soldering paste uses a high-boiling point solvent compound system, combined with a high-temperature resistant network structure of modified resins such as polyisobutylene and rosin ester, so that the flux remains active in extreme environments above 255°C, avoiding premature carbonization and failure. The synergistic activation mechanism of the polybasic organic acid and amine components in the activator, supplemented by the inhibition of high-temperature oxidation by the antioxidant, significantly improves the wetting and spreading ability of the molten alloy on the metal surface, reduces cold solder joints, and forms dense solder joints. The thixotropic agent and fine grinding process give the solder paste excellent rheological stability, supporting continuous printing for more than 12 hours without viscosity decay, and leaving little residue and non-corrosive after high-temperature soldering. Ultimately, the solder melting point is raised to above 255°C, completely eliminating the risk of component displacement in high-temperature processes such as ICs and power devices, ensuring long-term product reliability while meeting lead-free environmental protection and industrial mass production requirements. DETAILED DESCRIPTION

[0037] The present application is further described in detail below with reference to preparation examples, embodiments and comparative examples.

[0038] Example

[0039] Example 1

[0040] A high-melting-point, high-temperature, lead-free, environmentally friendly solder paste is prepared by the following steps:

[0041] Step S1, weighing 34.9 g of hydrogenated rosin, 39 g of tripropylene glycol butyl ether, 13 g of hydrogenated castor oil, 7 g of sebacic acid, 3 g of malic acid, and 5.2 g of 2-ethylimidazole into a reactor, maintaining the reactor temperature at 80° C., starting stirring, and stirring for 2 hours to completely dissolve the components;

[0042] Step S2, the temperature in the reactor was steadily lowered to 65° C., and 10.4 g of polyamide-modified hydrogenated castor oil, 8 g of polyisobutylene 100, 6 g of polyisobutylene 300, and 4.5 g of C5 / C9 copolymer resin were added to the reactor, and the mixture was dispersed at a speed of 2000 rpm for 45 minutes to obtain a mixed paste;

[0043] Step S3: After the mixed paste is left to stand for 18 hours, the mixed paste is ground to a fineness of 12 μm using a three-roll grinder to obtain a soldering paste.

[0044] Step S4: Weigh 870 g of alloy powder, including 43.5 g of tin, 13.05 g of silver, 8.7 g of copper, 26.1 g of nickel, 1.74 g of antimony, and 776.91 g of bismuth, and weigh 130 g of the solder paste obtained in step S3; and mix them in a vacuum mixer for 15 minutes.

[0045] Step S5: evacuate to -0.095 MPa and continue stirring for 6 minutes;

[0046] Step S6: packaging in a nitrogen-filled environment to obtain a finished solder paste.

[0047] Examples 2-6

[0048] The difference between Examples 2-6 and Example 1 lies in the difference in the amount and type of raw materials used and the process, as shown in Table 1 below.

[0049] Table 1 Material types, material amounts and process conditions of Examples 1-6

[0050]

[0051] Comparative Example

[0052] Comparative Example 1

[0053] The difference between Comparative Example 1 and Example 1 is that the alloy powder of Comparative Example 1 uses 783g of bismuth and 87g of tin, and the flux is the same.

[0054] Comparative Example 2

[0055] The difference between Comparative Example 2 and Example 1 is that the alloy powder of Comparative Example 2 uses 839.9g of tin, 26.1g of silver, and 4.35g of copper, and the solder paste uses a rosin-glycol ether system with a boiling point of less than 200°C.

[0056] Comparative Example 3

[0057] The difference between Comparative Example 3 and Example 1 is that the alloy powder of Comparative Example 3 uses 43.5g of tin, 13.05g of silver, 8.7g of copper, and 804.75g of bismuth, and the flux is the same as that of Example 1.

[0058] Comparative Example 4

[0059] The difference between Comparative Example 4 and Example 1 is that the alloy powder used in Comparative Example 4 is the same as that in Example 1, and the soldering flux paste is replaced by an equal amount of a commercially available no-clean type containing diethylene glycol monobutyl ether.

[0060] Comparative Example 5

[0061] The difference between Comparative Example 5 and Example 2 is that the alloy powder used in Comparative Example 5 is the same as that in Example 2, and propyl gallate is omitted from the flux paste.

[0062] Comparative Example 6

[0063] The difference between Comparative Example 6 and Example 1 is that the alloy powder used in Comparative Example 6 is the same as that in Example 1, and the flux paste solvent is replaced by an equal amount of propylene glycol methyl ether, wherein the boiling point of propylene glycol methyl ether is 120°C.

[0064] Performance testing experiment

[0065] The solder pastes prepared according to the methods of Examples 1-6 and Comparative Examples 1-6 were tested for melting point, spreading rate, shear strength, viscosity stability, and thermal fatigue life. Melting point was measured using differential scanning calorimetry (DSC) according to GB / T 8012-2013, with a heating rate of 2°C / min. Spreading rate was measured using GB / T 11364-2008, with the expansion diameter ratio calculated after nitrogen reflow at 260°C. Shear strength was measured using the solder joint shear test (GB / T 8749-2017), with a rate of 1 mm / min. Viscosity stability was measured using IPC-TM-650 2.4.44, with continuous printing at 25°C for 12 hours, and the viscosity change rate was recorded. Thermal fatigue life was measured using GB / T 15296-2022, with the resistance change rate after 1000 cycles from 55°C to 150°C. The results are shown in Table 2 below.

[0066] Table 2 Performance comparison experimental results

[0067]

[0068] Analysis of the experimental data and preparation methods above demonstrates that the inclusion of nickel in the alloy system design forms a high-melting-point Bi3Ni intermetallic compound with bismuth. This phase, acting as a rigid framework, significantly enhances the alloy's thermal stability, allowing the liquidus temperatures of Examples 1-6 to reach 255-270°C, significantly exceeding the melting point of conventional SAC305 alloy. The extreme-high-temperature formulation, represented by Example 5, exhibited only 0.01mm displacement during a 260°C hot-bed test, while the SAC305 alloy in Comparative Example 2 experienced 0.98mm component displacement due to secondary melting. This demonstrates that the high-melting-point design completely eliminates the risk of melt failure during high-temperature processes. At the same time, antimony element inhibits bismuth grain boundary segregation through solid solution strengthening, so that the bending strength of Example 2 is increased to 158 MPa, which is 70% higher than the 393 MPa of the comparative example lacking nickel and antimony. After 1000 thermal cycles from -55°C to 150°C, the resistance change rate is only 1.9%, which is much lower than the 12.7% of the comparative example 3, confirming the synergistic inhibitory effect of nickel and antimony on grain boundary cracks.

[0069] The flux system achieves breakthroughs in high-temperature stability through three key innovations. First, a high-boiling-point solvent blend, such as the 3:1 ratio of tripropylene glycol butyl ether to hydrogenated castor oil in Example 1, creates an intermolecular hydrogen-bonding network, reducing the solvent evaporation rate to 0.8 mg / min at 260°C—only 19% of that in Comparative Example 6, a low-boiling-point solvent. This ensures a viscosity change of less than 9% over 12 hours of continuous printing, compared to >19% viscosity fluctuation due to solvent evaporation in Comparative Example 4, a conventional formulation. Second, a three-dimensional, heat-resistant framework constructed from polyisobutylene 300 and rosin ester inhibits carbonization in the solder paste prepared in Example 2 above 255°C, reducing the flux residue ion contamination to 1.56 μg / cm² and maintaining a spreading rate above 84.2%. This represents an 18% improvement in spreading rate degradation due to carbonization compared to the flux paste prepared in Comparative Example 4. Furthermore, propyl gallate in the active agent system captures free radicals through phenolic hydroxyl groups, protecting organic acids such as sebacic acid from high-temperature oxidative inactivation, and extending the activity maintenance time at 260°C to more than 90 seconds. In contrast, the spreading rate of comparative example 5 decreased by 13% after the antioxidant was removed, revealing the key role of the antioxidant-activation synergistic mechanism.

[0070] Example 3 uses a synergistic activation method with a di-organic acid and 2-phenylimidazole to achieve an ultra-high spreading rate of 91.7%, meeting the requirements for precision component soldering. Example 4 reduces costs by 22% by reducing nickel / silver by 50%, while still maintaining an 86.4% spreading rate and 57.2 MPa shear strength, providing an economical solution for consumer electronics. Example 6 controls the grinding fineness to 8μm, increasing the contact area between the alloy powder and the flux by 35% and improving the fluidity index by 40%. Systematic failures in the comparative examples further validate the core technology barriers: the Bi-Sn binary alloy in Comparative Example 1 completely melts at 260°C due to the low-melting-point eutectic phase at 139°C. In Comparative Example 3, the lack of nickel causes the bismuth grains to coarsen to 120μm, leading to grain boundary stress concentration and a sharp drop in shear strength to 38.4 MPa. In Comparative Example 6, when using a 120°C boiling point solvent, boiling pores are generated at 220°C, causing the spreading rate to drop to 68.2%.

[0071] The conclusion shows that this application, through the reconstruction of bismuth-based high-entropy alloy and the innovation of high-temperature resistant chemical system of flux, has for the first time achieved the triangular balance of melting point > 255°C, shear strength > 54MPa, and 12-hour printing viscosity fluctuation < 9% in lead-free solder.

[0072] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A high melting point, high temperature, lead-free, environmentally friendly solder paste, characterized in that: Comprising alloy powder and solder paste, wherein, by mass percentage, the alloy powder accounts for 85-89% and the solder paste accounts for 11-15%; The alloy powder contains the following elements in percentage by mass: 0.5-7.0% tin 0.2-3.0% silver 0.2-1.5% copper 0.5-5.0% nickel 0.02-0.8% antimony Balance % of bismuth; The soldering solder paste contains the following components in percentage by mass: 30-50% solvent 10-25% modified resin 8-20% active agent 4-10% thixotropic agent Balance % rosin.

2. The high melting point, high temperature, lead-free, environmentally friendly solder paste according to claim 1, characterized in that: The solvent includes one or a combination of high-boiling-point ethers, alcohols, and vegetable oils; the high-boiling-point ether includes at least one of tripropylene glycol butyl ether, diethylene glycol dibutyl ether, diethylene glycol hexyl ether, and anisole; the alcohol includes at least one of decanol, dodecanol, and benzyl alcohol; and the vegetable oil includes one or a combination of two of hydrogenated castor oil and palm oil derivatives.

3. The high melting point, high temperature, lead-free, environmentally friendly solder paste according to claim 1, characterized in that: The modified resin includes at least two of polyisobutylene, hydrocarbon resin, rosin ester, and tackifying resin, the polyisobutylene is a combination of polyisobutylene 100 and polyisobutylene 300, the hydrocarbon resin is formed by copolymerization of C5 resin and C9 resin, the rosin ester includes one of rosin pentaerythritol ester and rosin glycerol ester, and the tackifying resin is P-105 type tackifying resin.

4. The high melting point, high temperature, lead-free, environmentally friendly solder paste according to claim 1, characterized in that: The active agent includes one or more of an organic acid component, an amine component, and a halogen substitute, wherein the organic acid component includes at least two of sebacic acid, decyltetradecanoic acid, adipic acid, succinic acid, glutaric acid, and malic acid; the amine component includes at least one of 2-ethylimidazole, 2-phenylimidazole, triethanolamine, triisopropanolamine, and an ethylenediamine derivative; and the halogen substitute is an organic halide or diphenyl phosphate.

5. The high melting point, high temperature, lead-free, environmentally friendly solder paste according to claim 1, characterized in that: The thixotropic agent includes at least one of polyamide-modified hydrogenated castor oil, ethylene bisstearamide, microcrystalline wax, organic bentonite, and fumed silica.

6. The high melting point, high temperature, lead-free, environmentally friendly solder paste according to claim 1, characterized in that: The rosin includes at least one of hydrogenated rosin, polymerized rosin, disproportionated rosin and maleic rosin.

7. The high melting point, high temperature, lead-free, environmentally friendly solder paste according to claim 2, characterized in that: The solvent comprises a composition with a boiling point greater than 250° C., specifically a mixture of tripropylene glycol butyl ether and hydrogenated castor oil in a ratio of 3:1, or a mixture of diethylene glycol dibutyl ether and benzyl alcohol in a ratio of 3:

1.

8. The high melting point, high temperature, lead-free, environmentally friendly solder paste according to claim 4, characterized in that: The active agent further comprises 0.5-5% of an antioxidant component, wherein the antioxidant component comprises at least one of propyl gallate, butylated hydroxyanisole, and tocopherol.

9. The method for preparing a high melting point, high temperature, lead-free, environmentally friendly solder paste according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step S1: Add rosin, solvent and active agent into a reaction kettle and stir at 75-85°C for 1-2 hours until they are completely dissolved; Step S2: cooling to 60-70° C., adding a thixotropic agent and a modified resin, and dispersing at a high speed of 1000-3000 rpm for 30-60 minutes to obtain a mixed paste; Step S3, after the mixed paste is allowed to stand for 12-24 hours, it is ground 2-3 times with a three-roll grinder until the fineness is ≤15 μm to obtain a soldering paste; Step S4: weigh the alloy powder and solder paste in proportion, and mix them in a vacuum mixer for 10-20 minutes; Step S5: evacuate to -0.095 ~ -0.085 MPa and continue stirring for 3-8 minutes; Step S6: packaging the finished solder paste in a nitrogen-filled environment.

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