A method for preparing an antioxidant lead-free tin-based solder alloy for high temperature

Abstract

The application discloses a preparation method of an antioxidant lead-free tin-based solder alloy for high temperature, and belongs to the technical field of solder alloy production processes. When the solder alloy is prepared by the method, elements in raw materials include the following in percentage by mass: 88-95% of Sn, 1-4% of Ag, 0.5-3% of Bi, 0.1-1% of Y, 0.05-0.2% of Hf, and the balance is inevitable impurities. The preparation method of the solder alloy is as follows: after metal raw materials are pickled and dried, Sn is first smelted and kept warm under inert gas protection, then Ag and Bi are added, stirring and heating, Y and Hf are further added and ultrasonic smelting is conducted; after a deoxidizing agent is added and reacts, the solder alloy is placed and slag is removed; three-stage refining is conducted through plasma atomization, high-low frequency ultrasonic treatment and a pulse ultrasonic conversion system; finally, the solder alloy is cooled, sieved and annealed to obtain the solder alloy. The application combines plasma technology, gas atomization and ultrasonic technology, realizes preparation of a tin-based solder alloy with uniform composition, high oxidation resistance and excellent mechanical properties, and meets the needs of the electronic welding field under high temperature environment.

Description

Technical Field

[0001] This invention relates to a method for preparing an antioxidant high-temperature lead-free tin-based solder alloy, belonging to the field of solder alloy production technology. Background Technology

[0002] In today's booming electronics industry, lead-free tin-based solder has become the mainstream choice for soldering materials due to its environmental friendliness, low melting point, and excellent soldering performance. However, as electronic components move towards higher density, miniaturization, and higher reliability, more stringent requirements are placed on the comprehensive performance of solders, such as oxidation resistance, high-temperature stability, and microstructure uniformity. Traditional lead-free tin-based solders suffer from weak oxidation resistance, easily degraded mechanical properties, and uneven microstructure. Under high-temperature environments, the surface is prone to oxidation, and the oxide film reduces solder wettability, affecting solder joint quality and welding reliability. At the same time, the creep and fatigue properties of the solder deteriorate, and uneven distribution of alloying elements can also lead to brittle phases and stress concentration.

[0003] In high-temperature environments (such as above 250°C), the surface of traditional lead-free tin-based solders is highly susceptible to oxidation. The resulting oxide film reduces the solder's wettability, thus affecting solder joint quality and welding reliability. Simultaneously, high temperatures degrade the solder's creep and fatigue properties, leading to cracks or even failure of the solder joint during long-term use. Furthermore, uneven distribution of alloying elements can easily induce brittle phases or stress concentration, further weakening the solder's performance.

[0004] Atomization, ultrasonic vibration, and plasma technologies are commonly used in solder preparation. However, using only these three technologies, or even just a combination of two, to prepare solder alloys does not significantly improve the alloy's oxidation resistance, high-temperature stability, or microstructure uniformity. For example, melting solder under high-energy conditions may exacerbate the oxidation of metal elements. The combined use of ultrasonic vibration and plasma may not achieve grain refinement. Improper parameter adjustment in the combined use of atomization, ultrasonic vibration, and plasma technologies can easily lead to energy coupling imbalance, thereby disrupting the ultrasonic cavitation effect, or excessively high atomization rates may weaken the plasma surface modification effect. Furthermore, multi-physics coupling can induce complex material responses, resulting in poor solder alloy performance. Thanks to the unique process of this invention, the three technologies are combined and, through precise control of raw material ratios and process parameters, synergistically, the preparation of high-temperature oxidation-resistant lead-free solder is achieved. The prepared solder alloy possesses both fine particle size and oxidation resistance. The specific production process is as follows... Figure 2 As shown, by adjusting the gas pressure, nozzle design, and cooling rate, spherical powders with a particle size of 10-50 μm can be prepared, which are suitable for high-density packaging and high-precision welding applications. Summary of the Invention

[0005] One objective of this invention is to provide a method for preparing an anti-oxidation high-temperature lead-free tin-based solder alloy. The alloy raw material comprises, by mass percentage: 88-95% Sn, 1-4% Ag, 0.5-3% Bi, 0.1-1% Y, and 0.05-0.2% Hf, with the balance being unavoidable impurities. The preparation method specifically includes the following steps: (1) Pickling: Weigh the metal raw materials according to the proportion, pickle the metal raw materials, and then dry them.

[0006] (2) Melting process: Inert gas (preferably argon or nitrogen) is introduced into the melting device. Then, the pickled and dried Sn powder is melted and kept warm in the melting container. Then, the pickled and dried Ag and Bi particles are added to the melting container and stirred. Then, the temperature is raised. Then, the pickled and dried Y and Hf powders are added to the melting container and sonicated to complete the heating and melting. Then, a deoxidizer is added to carry out the deoxidation reaction. After the reaction is completed, the mixture is allowed to stand. Then, the surface is cleaned to obtain the melt.

[0007] (3) Atomization treatment: The melt continuously flowing out of the melting container is atomized by high pressure gas using an inert gas (preferably argon or nitrogen) to obtain the atomized melt.

[0008] (4) Refining process: An alternating electric field is generated by a high-frequency induction coil to ionize an inert gas (preferably argon or nitrogen) to form a plasma arc. After the plasma jet reaches the specified temperature, the plasma jet is brought into contact with the atomized melt to achieve the first refinement of the atomized melt. The melt after the first refinement is placed in an ultrasonic field and subjected to low-frequency ultrasonic and high-frequency ultrasonic treatment in sequence to achieve the second refinement. The melt is then refined for the third time through a pulsed ultrasonic conversion system. The melt after the three refinements is cooled, collected, and sieved to obtain metal particles.

[0009] (5) Annealing treatment: The metal particles are placed in an annealing device, then heated and kept at a constant temperature, while the metal particles are sonicated. After cooling, an anti-oxidation high-temperature lead-free tin-based solder alloy is obtained.

[0010] Preferably, the pickling conditions in step (1) are: ultrasonic pickling for 5-10 minutes using a 10% nitric acid aqueous solution, and the pickling temperature is 40-50℃.

[0011] Preferably, the conditions for melting Sn powder in the melting device in step (2) are: vacuum degree ≤ 10. -3Pa, the melting apparatus was heated to 250℃ at a heating rate of 5℃ / min, and then held at that temperature for 30min; after adding Ag and Bi particles, the melting conditions were: stirring was started at 200-300rpm, and then the temperature was raised to 350~380℃; after adding Y and Hf powder, the ultrasonic conditions were: ultrasonic frequency of 20kHz, ultrasonic power of 200W; and the temperature of the melt was 250-350℃.

[0012] Preferably, in step (2), the deoxidizer is added to the metal sample after heating and melting at a ratio of 0.05 to 0.2% of the mass of the deoxidizer and the metal sample.

[0013] Preferably, in step (3), the atomization process uses a high-pressure gas atomization device, and the nozzle gas pressure is controlled to be 0.6-1.2 MPa, and the gas flow rate is 2-5 times the flow rate of the molten metal.

[0014] Preferably, in step (4), the atomization process in the first refinement uses a high-pressure gas atomization device; the plasma power is 5-10kW; the plasma jet temperature is 7727-11727℃; and the first refinement time is 0.1-0.3s.

[0015] Preferably, in step (4), the frequency of the second refinement of the low-frequency ultrasonic processing is 30-50kHz; the high-frequency power is 500-800W; and the time of the second refinement is 0.2-0.5s.

[0016] Preferably, the conditions for using a pulsed ultrasonic conversion system in the third refinement of step (4) are: the duty cycle of the square wave pulse is 30-50%, the pulse frequency is 1-5MHz and superimposed with an axial magnetic field of 0.1-0.3T, the output power is 800-1500W, and the processing temperature is 80-120℃.

[0017] Preferably, in step (5), the metal particles are ultrasonically tested under a vacuum degree ≤10. -2 The procedure was performed under the following conditions: the ultrasonic frequency was 30 kHz; the metal particle heating conditions were: heating to 180~200℃; and the metal particle heat preservation conditions were: heat preservation for 2 hours.

[0018] Another object of the present invention is to provide an antioxidant high-temperature lead-free tin-based solder alloy obtained by the preparation method of the present invention.

[0019] The equipment process for preparing lead-free tin-based solder alloys according to this invention is as follows: Figure 1 As shown.

[0020] Mechanism of the invention: This invention achieves synergistic enhancement between elements and preparation process by precisely controlling the proportions of Sn, Ag, Bi, Y, and Hf (metallic elements include, by mass percentage: 88-95.5% Sn, 1-4% Ag, 0.5-3% Bi, 0.1-1% Y, and 0.05-0.2% Hf), and by combining this invention with the preparation process, thus laying the foundation for solder performance.

[0021] This invention features a unique three-stage process: "high-temperature plasma fragmentation - secondary ultrasonic vibration refinement - deep ultrasonic conversion homogenization." Through the synergistic effect of multiple energy fields, it achieves a progressive enhancement of "particle size refinement - composition homogenization - in-situ growth of the antioxidant film." The "high-temperature activation" of plasma lays the foundation for ultrasonic refinement and elemental reaction, while the "homogenization diffusion" of ultrasonic vibration creates conditions for the uniform growth of the subsequent antioxidant film. The "deep fragmentation + magnetic field guidance" of ultrasonic conversion ultimately achieves the simultaneous attainment of ultrafine particle size and dense oxide film. All three are indispensable and together break through the bottleneck of traditional processes where "particle size refinement and antioxidant properties are difficult to achieve simultaneously."

[0022] Under the synergistic effect of ultrasonic vibration and element diffusion, the synergistic effect between metallic elements significantly improves the mechanical strength and high-temperature oxidation resistance of the alloy (weight gain ≤ 0.02 mg / cm³ at 300℃). 3 ).

[0023] The beneficial effects of this invention are: (1) The high temperature effect of plasma technology, ultrasonic vibration and high-speed cooling of gas atomization work together to effectively suppress the coarsening of intermetallic compounds, significantly refine the grain structure and improve the strength and ductility of the alloy.

[0024] (2) This method is carried out under inert gas protection throughout, which reduces the formation of oxides. The rare earth oxide coating on the surface further enhances the oxidation resistance, and the oxidation resistance is greatly improved in high-temperature environments compared with traditional solders.

[0025] (3) The combined effect of ultrasound and plasma during the melting process, as well as the high-speed spray dispersion during atomization, avoids component segregation, ensures uniform alloy composition, makes the solder performance more stable, the product quality consistency better, and the product composition more uniform.

[0026] (4) By adjusting the gas pressure, nozzle design, and cooling rate, spherical powders with a diameter of 10-50 μm can be prepared. This precise particle size control makes the solder suitable for high-density packaging and high-precision soldering applications, meeting the needs of electronic components to develop towards high density and miniaturization, and expanding the application range of lead-free tin-based solder alloys.

[0027] (5) Multi-angle ultrasonic vibration improves the sphericity and uniformity of powder, and the buffer tank and flow equalization plate ensure stable and uniform gas, improve the consistency of powder quality, and comprehensively improve the performance of solder in all aspects, thus expanding the application range of lead-free tin-based solder alloy.

[0028] (6) The technology combined with this preparation method is suitable for large-scale industrial production, which can meet the market demand for lead-free tin-based solder alloys, and help reduce production costs and improve production efficiency.

[0029] (7) The addition of Hf element forms a denser and more stable oxide film on the alloy surface, which works synergistically with the rare earth oxide coating to greatly enhance the oxidation resistance of the solder in high-temperature environments. Under the same high-temperature test conditions, compared with the solder without Hf, the oxidation weight gain of the solder prepared by this invention is significantly reduced, thus extending its service life in high-temperature environments.

[0030] (8) This invention proposes for the first time a three-stage process of “high-temperature plasma crushing - secondary ultrasonic vibration refining - deep ultrasonic conversion homogenization”. Through the coordinated regulation of the energy field, the in-situ growth of the antioxidant film is achieved while refining the particle size, thus solving the technical problem of “difficulty in achieving both particle size refinement and antioxidant capacity improvement” in traditional processes. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the equipment process for preparing lead-free tin-based solder alloys according to the present invention.

[0032] Figure 2 This is a schematic diagram of the production process for preparing lead-free tin-based solder alloys according to the present invention. Detailed Implementation

[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0034] The alloying elements of the embodiments and comparative examples of the present invention are shown in Table 1.

[0035] Table 1 Example 1 A method for preparing an antioxidant high-temperature lead-free tin-based solder alloy specifically includes the following steps: (1) Weigh Sn, Ag, Bi, Y and Hf metal samples according to the proportions shown in Table 1, and acid wash the metal samples with 10% nitric acid aqueous solution at 40℃ with a frequency of 40kHz and a power of 300W for 5 minutes. Then, vacuum dry the metal samples at 100℃ for 2 hours under a vacuum of 10Pa to ensure that the moisture content of the metal samples is ≤0.01%.

[0036] (2) Argon gas is introduced into the double-chamber vacuum induction furnace, and the vacuum degree is ≤10 -3 Under the condition of Pa, the temperature was raised to 250℃ in a double-chamber vacuum induction melting furnace at a heating rate of 5℃ / min and held for 30min. Then, the pickled and dried Sn powder was melted in the crucible. Pickled and dried Ag and Bi particles were added to the crucible of the double-chamber vacuum induction melting furnace and electromagnetically stirred at 200rpm. The temperature was then raised to 350℃. Pickled and dried Y and Hf powders were then added to the crucible and ultrasonically vibrated at 20kHz and 200W for 10min to complete the heating and melting (the temperature of the melt at this time is 350℃). Deoxidizer was added to the metal sample after heating and melting at a ratio of 0.05% of the mass of the deoxidizer and the metal sample to carry out the deoxidation reaction. After the reaction was completed, it was allowed to stand for 8min and then the surface was cleaned to obtain the melt.

[0037] (3) The melt flows out through the small hole at the bottom of the crucible to form a continuous metal flow. Multiple atomizing nozzles with a gas flow rate twice that of the metal flow rate spray argon gas at a speed of 300 m / s, with a pressure of 0.6 MPa and a temperature of 11727 °C, to impact the metal flow and atomize it into tiny droplets. The tiny droplets are refined once at the nozzle, i.e., plasma atomization: a 30 kHz high-frequency induction coil is used to generate high-temperature plasma (the ionization rate of the plasma arc is ≥95%) in a 99.999% high-purity argon environment. Argon gas is ionized by applying 5 kW power to form a plasma jet. Driven by a gas pressure of 0.8 MPa, the jet impacts the tiny droplets at a spray angle of 30° and achieves the first refinement within a time of 0.1 s. A second refinement process is then performed: combining a 30kHz, 600W low-frequency transducer and a 2MHz, 500W high-frequency transducer, using an exponential amplitude transformer with an amplification factor of 2.5, the melt is refined a second time under conditions of an action distance of 10mm, a vibration time of 0.2s, and nitrogen cooling at -20℃ (flow rate 10L / min). Next, a PZT-8 piezoelectric ceramic module is bonded to a titanium alloy substrate, and a third refinement of the melt is achieved under conditions of a pulse frequency of 1MHz (duty cycle 30%), a power of 800W, a 0.1T axial magnetic field, a processing temperature of 80℃, and an ambient oxygen content ≤10ppm, for 0.8s. The refined melt powder is then carried by the airflow into a cooling and collection system, separated and collected in a specific container, and sieved using a vibrating screen to obtain metal particles.

[0038] (4) Place the metal particles in a vacuum annealing furnace, with a vacuum degree ≤10 -2 Heating to 180℃ under Pa conditions and holding for 2 hours, followed by ultrasonic treatment at a frequency of 30kHz during annealing, and then cooling to obtain an antioxidant high-temperature lead-free tin-based solder alloy.

[0039] (5) The prepared antioxidant high-temperature lead-free tin-based solder alloy is vacuum-sealed in a dry argon environment with a dew point ≤ -40℃, with the addition of a desiccant (moisture absorption ≥ 10g) and an aluminum-plastic composite bag under a pressure ≤ 10Pa.

[0040] The anti-oxidation high-temperature lead-free tin-based solder alloy prepared in Example 1 was coated with Y2O3 using atomic layer deposition (ALD) to obtain a coating thickness of 2-3 mm. The particle size distribution was then tested using a high-precision Battlesize2000 laser particle size analyzer with an accuracy error of no more than 0.5%. Subsequently, the anti-oxidation performance of the solder alloy was tested and analyzed using an isothermal oxidation method. The method involved accurately weighing a portion of the powder material and then placing the sample into an isothermal furnace preheated to 350°C for 3 hours. After the set time is reached, the sample is removed, cooled to room temperature in a desiccator, and weighed accurately again. The specific surface area of ​​the powder is measured using a laser particle size analyzer (such as Battlesize2000). The oxidation weight gain of the sample is calculated by subtracting the sample mass before oxidation from the mass after oxidation and then dividing the result by the specific surface area of ​​the powder. This result is used to evaluate the antioxidant properties. An electron probe microanalyzer is used to test the Ag elemental segregation of the marked area for component analysis. Before the test, the electron probe microanalyzer is calibrated, and the sample stage is evacuated to a vacuum level <10. -4 To ensure the accuracy of the testing environment, an electron probe microanalyzer was used to detect Ag elements in a selected area, determining their form and approximate content range. Subsequently, a surface scan of the area was performed to obtain the distribution of Ag elements within that area. Particle size distribution, oxidation resistance testing, and Ag element segregation analysis revealed that the alloy solder prepared in Example 1 exhibits a relatively concentrated particle size distribution, excellent oxidation resistance, and uniform metal element distribution. This is attributed to the synergistic effect of the three-stage process: high-temperature plasma fragmentation, secondary ultrasonic vibration refinement, and deep ultrasonic conversion homogenization. High plasma temperature ensures uniform distribution of droplet surface tension, the acoustic flow effect of ultrasonic vibration eliminates surface wrinkles in the droplets, and the pulse vibration of ultrasonic conversion further corrects the particle morphology. Finally, high-speed cooling solidifies the particles into highly spherical particles with minimal sphericity deviation between different batches.

[0041] Example 2 A method for preparing an antioxidant high-temperature lead-free tin-based solder alloy specifically includes the following steps: (1) Weigh Sn, Ag, Bi, Y and Hf metal samples according to the proportions shown in Table 1, and acid wash the metal samples with 10% nitric acid aqueous solution at 50℃ with a frequency of 40kHz and a power of 300W for 10min. Then, vacuum dry at 100℃ for 2h under a vacuum of 10Pa to ensure that the moisture content of the metal samples is ≤0.01%.

[0042] (2) Introduce nitrogen gas into the double-chamber vacuum induction furnace, and maintain a vacuum level ≤10. -3 Under the condition of Pa, the temperature was raised to 250℃ in a double-chamber vacuum induction melting furnace at a heating rate of 5℃ / min and held for 30min. Then, the pickled and dried Sn powder was melted in the crucible. Pickled and dried Ag and Bi particles were added to the crucible of the double-chamber vacuum induction melting furnace and electromagnetically stirred at 300rpm. The temperature was then raised to 370℃. Pickled and dried Y and Hf powders were then added to the crucible and ultrasonically vibrated at 20kHz and 200W for 10min to complete the heating and melting (the temperature of the melt at this time was 250℃). Deoxidizer was added to the metal sample after heating and melting at a ratio of 0.2% of the mass of the deoxidizer to the metal sample to carry out the deoxidation reaction. After the reaction was completed, it was allowed to stand for 8min and then the surface was cleaned to obtain the melt.

[0043] (3) The melt flows out through the small hole at the bottom of the crucible, forming a continuous metal flow. Multiple atomizing nozzles with a gas flow rate 5 times that of the metal flow rate spray nitrogen gas at a speed of 300 m / s, with a pressure of 1.2 MPa and a temperature of 7727 °C, impacting the metal flow and atomizing it into tiny droplets. The tiny droplets are refined once at the nozzle, i.e., plasma atomization: a 30 kHz high-frequency induction coil is used to generate high-temperature plasma (the ionization rate of the plasma arc is ≥95%) in a 99.999% high-purity argon environment. By applying 10 kW power, the nitrogen gas is ionized to form a plasma jet. Driven by a gas pressure of 1.2 MPa, the jet impacts the tiny droplets at a spray angle of 60°, achieving the first refinement within a time of 0.3 s. A second refinement process is then performed: combining a 50kHz, 600W low-frequency transducer and a 2MHz, 800W high-frequency transducer, using an exponential amplitude transformer with an amplification factor of 3.0, the melt is refined a second time under conditions of an action distance of 15mm, a vibration time of 0.5s, and nitrogen cooling at -20℃ (flow rate 5L / min). Next, a PZT-8 piezoelectric ceramic module is bonded to a titanium alloy substrate, and a third refinement of the melt is achieved under conditions of a pulse frequency of 5MHz (50% duty cycle), a power of 1500W, a 0.3T axial magnetic field, a processing temperature of 120℃, and an ambient oxygen content ≤10ppm, for 0.8s. The refined melt powder is then carried by the airflow into a cooling and collection system, separated and collected in a specific container, and sieved using a vibrating screen to obtain metal particles.

[0044] (4) Place the metal particles in a vacuum annealing furnace, with a vacuum degree ≤10 -2 Heating to 182℃ under Pa conditions and holding for 2 hours, followed by ultrasonic treatment at a frequency of 30kHz during annealing, and then cooling to obtain an antioxidant high-temperature lead-free tin-based solder alloy.

[0045] (5) The prepared antioxidant high-temperature lead-free tin-based solder alloy is vacuum-sealed in a dry argon environment with a dew point ≤ -40℃, with the addition of a desiccant (moisture absorption ≥ 10g) and an aluminum-plastic composite bag under a pressure ≤ 10Pa.

[0046] The solder alloy prepared in Example 2 was tested for particle size distribution, oxidation resistance, and Ag element segregation using the same testing methods as in Example 1. Analysis of the test results showed that the alloy solder prepared in Example 2 exhibited a relatively concentrated particle size distribution, excellent oxidation resistance, and uniform metal element distribution. This is attributed to the synergistic effect of the three-stage process: high-temperature plasma fragmentation, secondary ultrasonic vibration refinement, and deep homogenization via ultrasonic conversion. High-temperature plasma uniformly distributes the surface tension of the droplets, the acoustic flow effect of ultrasonic vibration eliminates surface wrinkles in the droplets, and the pulse vibration of ultrasonic conversion further corrects the particle morphology. Finally, it solidifies into highly spherical particles under high-speed cooling, with minimal sphericity deviation between different batches.

[0047] Example 3 A method for preparing an antioxidant high-temperature lead-free tin-based solder alloy specifically includes the following steps: (1) Weigh Sn, Ag, Bi, Y and Hf metal samples according to the proportions shown in Table 1, and acid wash the metal samples with 10% nitric acid aqueous solution at 45℃ with a frequency of 40kHz and a power of 300W for 8 minutes. Then, vacuum dry at 100℃ for 2 hours under a vacuum of 10Pa to ensure that the moisture content of the metal samples is ≤0.01%.

[0048] (2) Argon gas is introduced into the double-chamber vacuum induction furnace, and the vacuum degree is ≤10 -3Under the condition of Pa, the temperature was raised to 250℃ in a double-chamber vacuum induction melting furnace at a heating rate of 5℃ / min and held for 30min. Then, the pickled and dried Sn powder was melted in the crucible. Pickled and dried Ag and Bi particles were added to the crucible of the double-chamber vacuum induction melting furnace and electromagnetically stirred at 250rpm. The temperature was then raised to 380℃. Pickled and dried Y and Hf powders were then added to the crucible and ultrasonically vibrated at 20kHz and 200W for 10min to complete the heating and melting (the temperature of the melt at this time was 300℃). Deoxidizer was added to the metal sample after heating and melting at a ratio of 0.1% of the deoxidizer to the metal sample mass to carry out the deoxidation reaction. After the reaction was completed, it was allowed to stand for 8min and then the surface was cleaned to obtain the melt.

[0049] (3) The melt flows out through the small hole at the bottom of the crucible to form a continuous metal flow. Multiple atomizing nozzles with a gas flow rate three times that of the metal flow rate spray argon gas at a speed of 300 m / s with a pressure of 0.8 MPa and a temperature of 9727 °C, which impacts the metal flow and atomizes it into tiny droplets. The tiny droplets are refined once at the nozzle, i.e., plasma atomization: a 30 kHz high-frequency induction coil is used to generate high-temperature plasma (the ionization rate of the plasma arc is ≥95%) in a 99.999% high-purity argon environment. By applying 8 kW power, the argon gas is ionized to form a plasma jet. Driven by a gas pressure of 1.0 MPa, the jet impacts the tiny droplets at a spray angle of 45°, and the first refinement is achieved within 0.2 s. A second refinement process followed: combining a 40kHz, 600W low-frequency transducer and a 2MHz, 700W high-frequency transducer, and employing an exponential amplitude transformer with an amplification factor of 2.8, the melt underwent a second refinement under conditions of an operating distance of 12mm, a vibration time of 0.3s, and nitrogen cooling at -20℃ (flow rate 8L / min). Then, a PZT-8 piezoelectric ceramic module was bonded to a titanium alloy substrate, and a third refinement of the melt was achieved under conditions of a pulse frequency of 2MHz (duty cycle 40%), a power of 1000W, a 0.2T axial magnetic field, a processing temperature of 100℃, and an ambient oxygen content ≤10ppm, for 0.8s. The refined melt powder was then carried by the airflow into a cooling and collection system, separated and collected in a specific container, and sieved using a vibrating screen to obtain metal particles.

[0050] (4) Place the metal particles in a vacuum annealing furnace, with a vacuum degree ≤10 -2 Heating to 200℃ under Pa conditions and holding for 2 hours, followed by ultrasonic treatment at a frequency of 30kHz during annealing, and then cooling to obtain an antioxidant high-temperature lead-free tin-based solder alloy.

[0051] (5) The prepared antioxidant high-temperature lead-free tin-based solder alloy is vacuum-sealed in a dry argon environment with a dew point ≤ -40℃, with the addition of a desiccant (moisture absorption ≥ 10g) and an aluminum-plastic composite bag under a pressure ≤ 10Pa.

[0052] The solder alloy prepared in Example 3 was subjected to particle size distribution, oxidation resistance, and Ag elemental segregation analysis using the same testing methods as in Example 1. Analysis of the test results showed that the D50 particle size of the solder alloy prepared in Example 3 was 12 μm, with 95% of the particles being 10-50 μm in diameter. The sphericity of the solder alloy was ≥90%, and the fine powder ratio (D<10 μm) was 30-40%, indicating good sphericity and uniform particle size distribution. The oxidation resistance test results showed that the oxidation weight gain of the solder alloy prepared in Example 3 was only 0.015 mg / cm³. 3 It exhibits excellent oxidation resistance; the Ag element segregation degree is ≤2%, proving that the element distribution in the solder alloy is uniform. This is due to the synergistic effect of the three-stage process of "high-temperature plasma crushing - secondary ultrasonic vibration refinement - deep homogenization by ultrasonic conversion": the high temperature of plasma makes the surface tension of the droplets uniformly distributed, the acoustic flow effect of ultrasonic vibration eliminates the wrinkles on the surface of the droplets, and the pulse vibration of ultrasonic conversion further corrects the particle morphology. Finally, it is solidified into high sphericity particles under high-speed cooling (≥-170℃ / s), and the sphericity deviation between different batches is ≤5%.

[0053] Comparative Example 1 A method for preparing an antioxidant high-temperature lead-free tin-based solder alloy specifically includes the following steps: (1) Weigh Sn, Ag, Bi, Y and Hf metal samples according to the proportions shown in Table 1, and acid wash the metal samples with 10% nitric acid aqueous solution at 45℃ with a frequency of 40kHz and a power of 300W for 8 minutes. Then, vacuum dry at 100℃ for 2 hours under a vacuum of 10Pa to ensure that the moisture content of the metal samples is ≤0.01%.

[0054] (2) Argon gas is introduced into the double-chamber vacuum induction furnace, and the vacuum degree is ≤10 -3Under the condition of Pa, the temperature was raised to 250℃ in a double-chamber vacuum induction melting furnace at a heating rate of 5℃ / min and held for 30min. Then, the pickled and dried Sn powder was melted in the crucible. Pickled and dried Ag and Bi particles were added to the crucible of the double-chamber vacuum induction melting furnace and electromagnetically stirred at 250rpm. The temperature was then raised to 380℃. Pickled and dried Y and Hf powders were then added to the crucible and ultrasonically vibrated at 20kHz and 200W for 10min to complete the heating and melting. Deoxidizer was added to the metal sample after heating and melting at a ratio of 0.1% of the deoxidizer to the metal sample mass to carry out the deoxidation reaction. After the reaction was completed, the sample was allowed to stand for 8min and then surface slag removal treatment was performed to obtain the melt.

[0055] (3) The melt flows out through the small hole at the bottom of the crucible to form a continuous metal flow. Multiple atomizing nozzles with a gas flow rate three times that of the metal flow rate spray argon gas at a speed of 300 m / s with a pressure of 0.8 MPa and a temperature of 9727 °C, impacting the metal flow and atomizing it into tiny powders. The atomized powders enter the cooling and collection system with the gas flow and are separated and collected in a specific container. The collected powders are sieved using a vibrating screen to obtain metal particles.

[0056] (4) Place the metal particles in a vacuum annealing furnace, with a vacuum degree ≤10 -2 Heating to 200℃ under Pa conditions and holding for 2 hours, followed by ultrasonic treatment at a frequency of 30kHz during annealing, and then cooling to obtain an antioxidant high-temperature lead-free tin-based solder alloy.

[0057] (5) The prepared antioxidant high-temperature lead-free tin-based solder alloy is vacuum-sealed in a dry argon environment with a dew point ≤ -40℃, with the addition of a desiccant (moisture absorption ≥ 10g) and an aluminum-plastic composite bag under a pressure ≤ 10Pa.

[0058] The lead-free tin-based solder alloy for high-temperature oxidation resistance prepared in Comparative Example 1 was subjected to the same particle size distribution, oxidation resistance, and Ag elemental segregation analysis as in Example 1. The tests showed that the D50 particle size of the solder alloy prepared in Comparative Example 1 was 120 μm, with only 35% being 10-50 μm, and a sphericity of 30%. The solder alloy exhibited poor sphericity and a relatively dispersed particle size distribution. The oxidation weight gain was 0.18 mg / cm³. 3 The solder alloy exhibits poor oxidation resistance; the Ag element segregation degree is 25%, indicating uneven element distribution in the solder alloy. This is because the solder alloy was only subjected to one high-pressure gas atomization treatment during preparation, resulting in incomplete particle refinement and thus failing to exhibit excellent particle size characteristics, oxidation resistance, and uniform element distribution.

[0059] Comparative Example 2 A method for preparing an antioxidant high-temperature lead-free tin-based solder alloy specifically includes the following steps: (1) Weigh Sn, Ag, Bi, Y and Hf metal samples according to the proportions shown in Table 1, and acid wash the metal samples with 10% nitric acid aqueous solution at 45℃ with a frequency of 40kHz and a power of 300W for 8 minutes. Then, vacuum dry at 100℃ for 2 hours under a vacuum of 10Pa to ensure that the moisture content of the metal samples is ≤0.01%.

[0060] (2) Argon gas is introduced into the double-chamber vacuum induction furnace, and the vacuum degree is ≤10 -3 Under the condition of Pa, the temperature was raised to 250℃ in a double-chamber vacuum induction melting furnace at a heating rate of 5℃ / min and held for 30min. Then, the pickled and dried Sn powder was melted in the crucible. Pickled and dried Ag and Bi particles were added to the crucible of the double-chamber vacuum induction melting furnace and electromagnetically stirred at 250rpm. The temperature was then raised to 380℃. Pickled and dried Y and Hf powders were then added to the crucible and ultrasonically vibrated at 20kHz and 200W for 10min to complete the heating and melting. Deoxidizer was added to the metal sample after heating and melting at a ratio of 0.1% of the deoxidizer to the metal sample mass to carry out the deoxidation reaction. After the reaction was completed, the sample was allowed to stand for 8min and then surface slag removal treatment was performed to obtain the melt.

[0061] (3) The melt flows out through the small hole at the bottom of the crucible to form a continuous metal flow. Multiple atomizing nozzles with a gas flow rate three times that of the metal flow rate spray argon gas at a speed of 300 m / s with a pressure of 0.8 MPa and a temperature of 9727 °C, which impacts the metal flow and atomizes it into tiny droplets. The tiny droplets are refined once at the nozzle, i.e., plasma atomization: a 30 kHz high-frequency induction coil is used to generate high-temperature plasma (the ionization rate of the plasma arc is ≥95%) in a 99.999% high-purity argon environment. By applying 8 kW power, the argon gas is ionized to form a plasma jet. Driven by a gas pressure of 1.0 MPa, the jet impacts the tiny droplets at a spray angle of 45° and refines them into powder within a time of 0.2 s. The refined powder enters the cooling and collection system with the gas flow and is separated and collected in a specific container. The collected powder is sieved using a vibrating screen to obtain metal particles.

[0062] (4) Place the metal particles in a vacuum annealing furnace, with a vacuum degree ≤10 -2 Heating to 200℃ under Pa conditions and holding for 2 hours, followed by ultrasonic treatment at a frequency of 30kHz during annealing, and then cooling to obtain an antioxidant high-temperature lead-free tin-based solder alloy.

[0063] (5) The prepared antioxidant high-temperature lead-free tin-based solder alloy is vacuum-sealed in a dry argon environment with a dew point ≤ -40℃, with the addition of a desiccant (moisture absorption ≥ 10g) and an aluminum-plastic composite bag under a pressure ≤ 10Pa.

[0064] The lead-free tin-based solder alloy for high-temperature oxidation resistance prepared in Comparative Example 2 was subjected to the same particle size distribution, oxidation resistance, and Ag elemental segregation analysis as in Example 1. The tests showed that the D50 particle size of the solder alloy prepared in Comparative Example 2 was 65 μm, with 60% being 10-50 μm, and a sphericity of 40%. The solder alloy exhibited poor sphericity and a relatively dispersed particle size distribution. The oxidation weight gain was 0.08 mg / cm³. 3 The solder alloy exhibits poor oxidation resistance; the Ag element segregation degree is 15%, indicating uneven element distribution in the solder alloy. This is because only one plasma atomization refining treatment was performed during the solder alloy preparation process, resulting in incomplete particle refinement and thus failing to exhibit excellent particle size characteristics, oxidation resistance, and uniform element distribution.

[0065] Comparative Example 3 A method for preparing an antioxidant high-temperature lead-free tin-based solder alloy specifically includes the following steps: (1) Weigh Sn, Ag, Bi, Y and Hf metal samples according to the proportions shown in Table 1, and acid wash the metal samples with 10% nitric acid aqueous solution at 40℃ with a frequency of 40kHz and a power of 300W for 8 minutes. Then, vacuum dry at 100℃ for 2 hours under a vacuum of 10Pa to ensure that the moisture content of the metal samples is ≤0.01%.

[0066] (2) Argon gas is introduced into the double-chamber vacuum induction furnace, and the vacuum degree is ≤10 -3 Under the condition of Pa, the temperature was raised to 250℃ in a double-chamber vacuum induction melting furnace at a heating rate of 5℃ / min and held for 30min. Then, the pickled and dried Sn powder was melted in the crucible. Pickled and dried Ag and Bi particles were added to the crucible of the double-chamber vacuum induction melting furnace and electromagnetically stirred at 250rpm. The temperature was then raised to 380℃. Pickled and dried Y and Hf powders were then added to the crucible and ultrasonically vibrated at 20kHz and 200W for 10min to complete the heating and melting. Deoxidizer was added to the metal sample after heating and melting at a ratio of 0.1% of the deoxidizer to the metal sample mass to carry out the deoxidation reaction. After the reaction was completed, the sample was allowed to stand for 8min and then surface slag removal treatment was performed to obtain the melt.

[0067] (3) The melt flows out through the small hole at the bottom of the crucible, forming a continuous metal flow. Multiple atomizing nozzles with a gas flow rate three times that of the metal flow rate spray argon gas at a speed of 300 m / s, with a pressure of 0.8 MPa and a temperature of 9727 °C, impacting the metal flow and atomizing it into tiny droplets. The tiny droplets are refined once at the nozzle, i.e., plasma atomization: a 30 kHz high-frequency induction coil is used to generate high-temperature plasma (the ionization rate of the plasma arc is ≥95%) in a 99.999% high-purity argon environment. By applying 8 kW power, the argon gas is ionized to form a plasma jet. Driven by a gas pressure of 1.0 MPa, the jet impacts the tiny droplets at a spray angle of 45°, achieving the first refinement within a time of 0.2 s. A second refinement process is then performed: combining a 40kHz, 600W low-frequency transducer and a 2MHz, 700W high-frequency transducer, using an exponential amplitude transformer with an amplification factor of 2.8, the melt is refined a second time under the conditions of an action distance of 12mm, a vibration time of 0.3s, and nitrogen cooling at -20℃ (flow rate of 8L / min), resulting in refined powder. This powder enters the cooling and collection system with the airflow and is then separated and collected in a specific container. The collected powder is then sieved using a vibrating screen to obtain metal particles.

[0068] (4) Place the metal particles in a vacuum annealing furnace, with a vacuum degree ≤10 -2 Heating to 200℃ under Pa conditions and holding for 2 hours, followed by ultrasonic treatment at a frequency of 30kHz during annealing, and then cooling to obtain an antioxidant high-temperature lead-free tin-based solder alloy.

[0069] (5) The prepared antioxidant high-temperature lead-free tin-based solder alloy is vacuum-sealed in a dry argon environment with a dew point ≤ -40℃, with the addition of a desiccant (moisture absorption ≥ 10g) and an aluminum-plastic composite bag under a pressure ≤ 10Pa.

[0070] The lead-free tin-based solder alloy for high-temperature oxidation resistance prepared in Comparative Example 3 was subjected to the same particle size distribution, oxidation resistance, and Ag elemental segregation analysis as in Example 1. The tests showed that the D50 particle size of the solder alloy prepared in Comparative Example 3 was 30 μm, with 85% being 10-50 μm, and a sphericity of 70%. The solder alloy exhibited poor sphericity and a relatively dispersed particle size distribution. The oxidation weight gain was 0.04 mg / cm³. 3 The solder alloy exhibits poor oxidation resistance; the Ag element segregation degree is 5%, indicating uneven element distribution in the solder alloy. This is because the solder alloy was only subjected to one plasma atomization refinement treatment, one high-pressure gas atomization treatment, and one ultrasonic vibration refinement treatment during preparation, resulting in incomplete refinement of the alloy particles, and thus failing to exhibit excellent particle size characteristics, oxidation resistance, and uniform element distribution.

[0071] Comparative Example 4 The preparation of lead-free tin-based solder alloys using traditional processes includes the following steps: Using single-gas atomization as the core, the molten metal flow is broken up solely by the shear force of a high-speed gas flow, without subsequent ultrasonic or plasma refinement steps. The specific steps are as follows: (1) Raw material pretreatment: The oxide film on the surface of Sn, Ag and Cu raw materials is removed by conventional pickling (10% dilute sulfuric acid aqueous solution by mass percentage), rinsed with water and air-dried naturally; weigh the metal powder and prepare the solder alloy. The alloy element composition by mass percentage includes: 96.5% Sn, 3% Ag and 0.5% Cu.

[0072] (2) Smelting: A conventional induction melting furnace (vacuum degree ≥10) is used. -1 The mixture is heated to above the Sn melting point (232°C) in air or a weakly inert atmosphere. After melting, the components are mixed by mechanical stirring (100 rpm) without ultrasonic assistance; natural degassing is achieved through the smelting process.

[0073] (3) Atomization treatment: A low-pressure gas atomization device with a single nozzle is used, with nitrogen as the atomization medium (purity ≤99.9%); gas pressure 0.6MPa, flow rate 200m / s, the nozzle and melt flow angle is fixed at 45°, and there is no temperature control; the molten metal forms a liquid flow through the bottom nozzle (5mm in diameter), is impacted and broken into droplets by the high-speed airflow, and is naturally cooled and solidified in the air (cooling rate ≤-171℃ / s).

[0074] (4) Subsequent processing: The atomized powder is directly sieved to remove oversized particles; there is no vacuum annealing or surface coating step, and it is packaged after natural drying.

[0075] The traditional lead-free tin-based solder alloy prepared in Comparative Example 4 was subjected to the same particle size distribution test as in Example 1. The test results showed that the solder alloy prepared in Comparative Example 4 had a D50 of 50-80 μm, a sphericity of 40-60%, and a fine powder ratio (D<10 μm) of 5-10%. The solder alloy particles were mostly irregular blocks or polyhedra with obvious wrinkles and sharp edges on the surface. Moreover, the alloy powder particles were relatively large, making it difficult to achieve ultra-fine particle size and high sphericity. This is because the traditional process relies solely on the shear force of the gas flow from a single gas atomization, resulting in a slow droplet cooling rate (≤-171℃ / s) and no auxiliary shaping methods. Consequently, the droplets are unable to form a symmetrical spherical structure during solidification, resulting in low sphericity and poor consistency.

[0076] The anti-oxidation high-temperature lead-free tin-based solder alloys prepared in Comparative Examples 1, 2, 3 and Example 3 were subjected to particle size distribution testing, anti-oxidation performance testing, and elemental distribution uniformity testing. The test results are shown in Table 2.

[0077] Table 2 The particle size analysis was performed on the solder alloys prepared in Comparative Example 4 and Example 3, and the test results are shown in Table 3.

[0078] Table 3 The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing an antioxidant high-temperature lead-free tin-based solder alloy, characterized in that, The metallic elements in this alloy raw material, by mass percentage, include: 88-95% Sn, 1-4% Ag, 0.5-3% Bi, 0.1-1% Y, and 0.05-0.2% Hf, with the balance being unavoidable impurities. The preparation method of this alloy specifically includes the following steps: (1) Pickling: Weigh the metal raw materials according to the proportion, pickle the metal raw materials, and then dry them; (2) Smelting process: Inert gas is introduced into the smelting device, and then the pickled and dried Sn powder is smelted and kept at a constant temperature in the molten container. Then, the pickled and dried Ag and Bi particles are added to the molten container and stirred. Then, the temperature is raised, and then the pickled and dried Y and Hf powders are added to the molten container and sonicated to complete the heating and smelting. Then, a deoxidizer is added and sonicated to carry out the deoxidation reaction. After the reaction is completed, the mixture is allowed to stand, and then the surface is cleaned to obtain the melt. (3) Atomization treatment: The melt continuously flowing out of the melting container is atomized by high-pressure gas using inert gas to obtain atomized melt; (4) Refining process: An alternating electric field is generated by a high-frequency induction coil to ionize the inert gas and form a plasma arc. After the plasma jet reaches the specified temperature, the plasma jet is combined with the atomized melt to achieve the first refinement of the atomized melt. The melt after the first refinement is placed in an ultrasonic field and subjected to low-frequency ultrasonic and high-frequency ultrasonic treatment in sequence to achieve the second refinement. The melt is refined for the third time through a pulsed ultrasonic conversion system. The melt after the three refinements is cooled, collected, and screened to obtain metal particles. (5) Annealing treatment: The metal particles are placed in an annealing device, then heated and kept at a constant temperature, while the metal particles are sonicated. After cooling, an anti-oxidation high-temperature lead-free tin-based solder alloy is obtained.

2. The method for preparing the antioxidant high-temperature lead-free tin-based solder alloy according to claim 1, characterized in that, The pickling conditions in step (1) are as follows: ultrasonic pickling is performed for 5-10 minutes using a 10% nitric acid aqueous solution at a pickling temperature of 40-50℃.

3. The method for preparing the antioxidant high-temperature lead-free tin-based solder alloy according to claim 1, characterized in that, The conditions for melting Sn powder in the melting device in step (2) are: vacuum degree ≤ 10 -3 Pa, the melting apparatus was heated to 250℃ at a heating rate of 5℃ / min, and then held at that temperature for 30min; after adding Ag and Bi particles, the melting conditions were: stirring was started at 200-300rpm, and then the temperature was raised to 350~380℃; after adding Y and Hf powder, the ultrasonic conditions were: ultrasonic frequency of 20kHz, ultrasonic power of 200W; and the temperature of the melt was 250-350℃.

4. The method for preparing the antioxidant high-temperature lead-free tin-based solder alloy according to claim 1, characterized in that, In step (2), deoxidizer is added to the metal sample after heating and melting at a ratio of 0.05~0.2% of the mass of the deoxidizer and the metal sample.

5. The method for preparing the antioxidant high-temperature lead-free tin-based solder alloy according to claim 1, characterized in that, In step (3), the atomization process uses a high-pressure gas atomization device, and the nozzle gas pressure is controlled to be 0.6-1.2 MPa, and the gas flow rate is 2-5 times the flow rate of the molten metal.

6. The method for preparing the antioxidant high-temperature lead-free tin-based solder alloy according to claim 1, characterized in that, In step (4), the atomization process in the first refinement stage uses a high-pressure gas atomization device; the plasma power is 5-10kW; the plasma jet temperature is 7727-11727℃; and the time for the first refinement stage is 0.1-0.3s.

7. The method for preparing the antioxidant high-temperature lead-free tin-based solder alloy according to claim 1, characterized in that, In step (4), the frequency of the second refinement of the low-frequency ultrasonic processing is 30-50kHz; the high-frequency power is 500-800W; and the time of the second refinement is 0.2-0.5s.

8. The method for preparing the antioxidant high-temperature lead-free tin-based solder alloy according to claim 1, characterized in that, The conditions for using a pulsed ultrasonic conversion system in the third refinement of step (4) are: the duty cycle of the square wave pulse is 30-50%, the pulse frequency is 1-5MHz and superimposed with an axial magnetic field of 0.1-0.3T, the output power is 800-1500W, and the processing temperature is 80-120℃.

9. The method for preparing the antioxidant high-temperature lead-free tin-based solder alloy according to claim 1, characterized in that, In step (5), the ultrasonication of the metal particles is performed under a vacuum degree ≤10. -2 The procedure was performed under the following conditions: the ultrasonic frequency was 30 kHz; the metal particle heating conditions were: heating to 180~200℃; and the metal particle heat preservation conditions were: heat preservation for 2 hours.

10. The antioxidant high-temperature lead-free tin-based solder alloy prepared by the method according to any one of claims 1 to 9.

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