Preparation method of lead-free tin-based solder alloy for oxidation resistance at high temperature

Abstract

The invention discloses a preparation method of a lead-free tin-based solder alloy for oxidation resistance at high temperature, and belongs to the technical field of solder alloy production processes. When the solder alloy is prepared through the method, raw materials comprise, 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 inevitable impurities. The preparation method of the solder alloy comprises the steps that after metal raw materials are subjected to acid pickling and drying, Sn is smelted and subjected to heat preservation under the protection of inert gas, then Ag and Bi are added, stirring and heating are conducted, and then Y and Hf are added for ultrasonic smelting; adding a deoxidizing agent, reacting, standing and removing slag; and carrying out three-stage refining through plasma atomization, high and low frequency ultrasonic treatment and a pulse ultrasonic conversion system, and finally cooling, screening and annealing to obtain the solder alloy. The plasma technology, the gas atomization method and the ultrasonic technology are cooperatively combined, preparation of the tin-based solder alloy which is uniform in component, high in oxidation resistance and excellent in mechanical property is achieved, and the requirements of the field of electronic welding in the high-temperature environment are met.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of an anti-oxidation high-temperature lead-free tin-based solder alloy and belongs to the technical field of solder alloy production processes. BACKGROUND

[0002] In the current booming electronic industry, lead-free tin-based solder has become the mainstream choice of welding materials due to its environmental protection, low melting point and excellent welding performance. However, as electronic components move towards high density, miniaturization and high reliability, more stringent requirements are placed on the comprehensive performance of solder, such as oxidation resistance, high-temperature stability and microstructure uniformity. Traditional lead-free tin-based solder has problems of weak oxidation resistance, easy mechanical property decline and uneven microstructure. In a high-temperature environment, the surface is easy to oxidize, the oxide film reduces the wettability of the solder, affects the quality of the solder joint and the welding reliability, and the creep and fatigue performance of the solder is poor. In addition, uneven distribution of alloying elements can also cause brittle phases and stress concentration.

[0003] In a high-temperature environment (such as above 250℃), the surface of traditional lead-free tin-based solder is prone to oxidation, and the generated oxide film can reduce the wettability of the solder, thereby affecting the quality of the solder joint and the welding reliability. At the same time, high temperature can make the creep and fatigue performance of the solder worse, leading to cracks or even failure of the solder joint during long-term use. In addition, uneven distribution of alloying elements can also cause brittle phases or stress concentration, further weakening the performance of the solder.

[0004] Atomization technology, ultrasonic vibration and plasma technology are commonly used in the preparation of solder. However, the use of atomization technology, ultrasonic vibration and plasma technology alone or the combination of two of them for the preparation of solder alloy does not significantly improve the oxidation resistance, high-temperature stability and microstructure uniformity of the alloy. For example, melting the solder under high-energy conditions can exacerbate the oxidation of metal elements; the combination of ultrasonic vibration and plasma may not achieve the purpose of refining the grain. The combined use of atomization technology, ultrasonic vibration and plasma technology can easily lead to energy coupling imbalance and destroy the ultrasonic cavitation effect if the parameters are not properly adjusted, or the surface modification effect of plasma can be weakened by too high an atomization rate. Moreover, the coupling of multiple physical fields can cause complex material responses, leading to poor performance of the solder alloy. Thanks to the special nature of the process of the present application, the three technologies are combined to prepare high-temperature oxidation-resistant lead-free solder through precise control of raw material ratio and process parameters. The prepared solder alloy has both grain refinement and oxidation resistance. The specific production process is shown in Figure 2 By adjusting the gas pressure, nozzle design and cooling rate, spherical powder with a particle size of 10-50μm can be prepared, which is suitable for high-density packaging and high-precision welding applications. SUMMARY

[0005] One of the purposes of the present application is to provide a preparation method of an anti-oxidation high-temperature lead-free tin-based solder alloy, which includes the following metal elements in the alloy raw material by mass percentage: 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 of inevitable impurities; the preparation method of the alloy specifically includes the following steps: (1) Pickling: the metal raw materials are weighed according to the proportion and subjected to pickling, and then dried.

[0006] (2) Melting treatment: inert gas (preferably argon or nitrogen as inert gas) is introduced into the melting device, and then Sn powder after pickling and drying is first melted in the melting container and kept warm, and then Ag and Bi particles after pickling and drying are added to the melting container and stirred, and then heated, and then Y and Hf powder after pickling and drying are added to the melting container and ultrasonic, and the heating and melting are completed; then a deoxidizer is added for deoxidation reaction, and after the reaction is completed, it is placed, and then the surface is treated to remove slag to obtain a melt.

[0007] (3) Atomization treatment: the continuously flowing melt in the melting container is subjected to high-pressure gas atomization by inert gas (preferably argon or nitrogen as inert gas) to obtain an atomized melt.

[0008] (4) Refining treatment: an alternating electric field is generated by a high-frequency induction coil to ionize inert gas (preferably argon or nitrogen as inert gas) to form a plasma arc, and after the plasma jet reaches a specified temperature, the plasma jet and the atomized melt are intersected to realize the first refinement of the atomized melt; the first refined melt is placed in an ultrasonic field and subjected to low-frequency ultrasonic wave and high-frequency ultrasonic wave treatment in turn to realize the second refinement; the third refinement of the melt is realized by a pulse ultrasonic conversion system, and the three times refined melt is cooled, collected and screened to obtain metal particles.

[0009] (5) Annealing treatment: the metal particles are placed in an annealing device, and then heated and kept warm, and at the same time, the metal particles are ultrasonic, and after cooling, an anti-oxidation high-temperature lead-free tin-based solder alloy is obtained.

[0010] Preferably, the pickling conditions in step (1) are as follows: ultrasonic pickling with 10% nitric acid aqueous solution for 5-10 min, and the pickling temperature is 40-50°C.

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

[0012] Preferably, in step (2), the deoxidizing agent is added to the metal sample after being heated and melted at a ratio of 0.05-0.2% of the deoxidizing agent to the mass percentage of the metal sample.

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

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

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

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

[0017] Preferably, in step (5), the ultrasonic treatment of the metal particles is performed under a vacuum degree of ≤10 -2 Pa; the ultrasonic conditions are as follows: the ultrasonic frequency is 30kHz; the metal particle heating conditions are as follows: the temperature is raised to 180-200℃; and the metal particle keeping conditions are as follows: the keeping time is 2h.

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

[0019] The device flow for preparing the lead-free tin-based solder alloy of the present application is shown in Figure 1 .

[0020] The mechanism of the present application is as follows: The application realizes the synergistic reinforcement between elements and preparation process by precisely regulating the proportion of Sn, Ag, Bi, Y and Hf (the metal elements include 88-95.5% of Sn, 1-4% of Ag, 0.5-3% of Bi, 0.1-1% of Y and 0.05-0.2% of Hf in terms of mass percentage) and combining the preparation process of the application, and lays a foundation for the solder performance.

[0021] The three-stage process of the application, i.e. "plasma high-temperature crushing-ultrasonic vibration secondary refinement-ultrasonic conversion deep homogenization", realizes the progressive reinforcement of "grain size refinement-component homogenization-oxidation-resistant film in-situ growth" through the synergistic effect of multiple energy fields, the "high-temperature activation" of plasma lays a foundation for ultrasonic refinement and element reaction, the "homogenization diffusion" of ultrasonic vibration creates conditions for the uniform growth of the subsequent oxidation-resistant film, and the "deep crushing + magnetic field guidance" of ultrasonic conversion finally realizes the synchronous achievement of ultra-fine particle size and dense oxidation film, and the three are indispensable and jointly break through the bottleneck of traditional process "difficulty in considering grain size refinement and oxidation resistance".

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

[0023] The application has the following beneficial effects: (1) The synergistic effect of high-temperature effect of plasma technology, ultrasonic vibration and high-speed cooling of gas atomization effectively inhibits the coarsening of intermetallic compounds, significantly refines the grain structure, and improves the strength and ductility of the alloy.

[0024] (2) The method is carried out under inert gas protection throughout the process, reducing the generation of oxides. The rare earth oxide coating coated on the surface further enhances the oxidation resistance, and compared with the traditional solder, the oxidation resistance in high-temperature environment is greatly improved.

[0025] (3) The combined effect of ultrasonic and plasma during smelting, and high-speed jet dispersion during atomization avoids composition 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, 10-50μm spherical powder can be prepared. This precise particle size control makes the solder suitable for high-density packaging and high-precision welding applications, meets the needs of electronic components for high-density and miniaturization, and expands the application range of lead-free tin-based solder alloys.

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

[0028] (6) The combined technology of the preparation method is suitable for industrial large-scale production, can meet the large demand of the market for the lead-free tin-based solder alloy, and is helpful to reduce the production cost and improve the production benefit.

[0029] (7) The addition of Hf element forms a more dense and stable oxide film on the surface of the alloy, which cooperates with the rare earth oxide coating, greatly enhances the oxidation resistance of the solder in a high temperature environment. Under the same high temperature test conditions, compared with the solder without adding Hf, the weight gain of the solder prepared by the present application is significantly reduced, and the service life in a high temperature environment is prolonged.

[0030] (8) The present application first proposes a three-stage process of "plasma high-temperature crushing-ultrasonic vibration secondary refinement-ultrasonic conversion deep homogenization", which realizes in-situ growth of the oxidation resistance film while refining the particle size through energy field synergistic regulation, solves the technical problem that the particle size refinement and oxidation resistance improvement are difficult to be considered in the traditional process. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The figure is a schematic diagram of the equipment process for preparing the lead-free tin-based solder alloy of the present application.

[0032] Figure 2 The figure is a schematic diagram of the production process for preparing the lead-free tin-based solder alloy of the present application. DETAILED DESCRIPTION

[0033] The technical solutions provided by the present application will be described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0034] The alloy elements of the examples and comparative examples of the present application are shown in Table 1.

[0035] Table 1 Example 1 A preparation method of an oxidation-resistant lead-free tin-based solder alloy for high temperature, specifically comprising the following steps: (1) The Sn, Ag, Bi, Y and Hf metal samples are weighed according to the proportions shown in Table 1, and then subjected to metal sample pickling with 10% nitric acid aqueous solution at 40 kHz frequency and 300 W power for 5 min at 40℃, and then vacuum dried at 100℃ under a vacuum degree of 10 Pa for 2 h, to ensure that the water content of the metal sample is ≤0.01%.

[0036] (2) The argon gas is introduced into the double-chamber vacuum induction melting furnace, and the temperature is raised to 250℃ at a rate of 5℃ / min under the condition of vacuum degree ≤10 -3 Pa, and the Sn powder after acid washing and drying is melted in the crucible. Then, the Ag and Bi particles after acid washing and drying are added into the crucible of the double-chamber vacuum induction melting furnace and are subjected to electromagnetic stirring at 200 rpm. Subsequently, the temperature is raised to 350℃, and then the Y and Hf powders after acid washing and drying are added into the crucible and are subjected to ultrasonic vibration at 20 kHz and 200 W for 10 min. The temperature is raised and the melting is completed (at this time, the temperature of the melt is 350℃). The deoxidizer is added into the metal sample after the temperature is raised and melted at a proportion of 0.05% of the mass percentage of the deoxidizer and the metal sample, and the deoxidation reaction is carried out. After the reaction is completed, the melt is obtained after being placed for 8 min and then being subjected to surface slag removal treatment.

[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 of 2 times the metal flow rate spray argon gas at a speed of 300 m / s, a pressure of 0.6 MPa, and a temperature of 11727℃. The argon gas flow impacts the metal flow to atomize it into small droplets. The small droplets are refined once at the nozzle, that is, plasma atomization. A 30 kHz high-frequency induction coil is used to generate high-temperature plasma in a 99.999% high-purity argon gas environment (the ionization rate of the plasma arc is ≥95%). The argon gas is ionized to form a plasma jet by applying a power of 5 kW. The jet impacts the small droplets at a spray angle of 30° under a gas pressure of 0.8 MPa, and the first refinement is realized within an action time of 0.1 s. Then, the second refinement is carried out: a 30 kHz, 600 W low-frequency transducer and a 2 MHz, 500 W high-frequency transducer are combined, an exponential amplitude horn with an amplification coefficient of 2.5 is used, and the second refinement of the melt is carried out under the conditions of an action distance of 10 mm, a vibration time of 0.2 s, and -20℃ nitrogen cooling (flow rate of 10 L / min). Then, a PZT-8 piezoelectric ceramic module is bonded to a titanium alloy substrate, and the third refinement of the melt is realized under the conditions of a pulse frequency of 1 MHz (duty cycle of 30%), a power of 800 W, an axial magnetic field of 0.1 T, a processing temperature of 80℃, an environmental oxygen content of ≤10 ppm, an action time of 0.8 s, and a processing temperature of 80℃. The refined melt powder enters the cooling and collection system with the gas flow, is separated and collected in a specific container, and is sieved using a vibrating screen to obtain metal particles.

[0038] (4) The metal particles are placed in a vacuum annealing furnace and heated to 180℃ under the condition of vacuum degree ≤10 -2 Pa and are kept for 2 h. An ultrasonic wave with a frequency of 30 kHz is applied during the annealing process. After cooling, the lead-free tin-based solder alloy for oxidation resistance at high temperature is obtained.

[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) Put the metal particles into a vacuum annealing furnace, heat to 182℃ under the condition of vacuum degree ≤10 -2 Pa and keep for 2h, and apply ultrasonic with frequency of 30kHz during the annealing process, and obtain the lead-free tin-based solder alloy for high temperature oxidation resistance after cooling.

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

[0046] The particle size distribution, oxidation resistance performance test, and Ag element segregation degree analysis test of the solder alloy prepared in Example 2 are carried out by using the same test method as in Example 1. The test result analysis shows that the alloy solder prepared in Example 2 has a relatively concentrated particle size distribution, excellent oxidation resistance performance and uniform metal element distribution. This is due to the synergistic effect of the three-stage process of "plasma high temperature crushing-ultrasonic vibration secondary refinement-ultrasonic conversion depth homogenization": the plasma high temperature makes the surface tension of the droplets uniformly distributed, the acoustic streaming effect of ultrasonic vibration eliminates the surface wrinkles of the droplets, and the pulse vibration of ultrasonic conversion further modifies the particle morphology. Finally, high-spherical particles are obtained under high-speed cooling, and the spherical degree deviation between different batches is extremely small.

[0047] Example 3 A preparation method of a lead-free tin-based solder alloy for high temperature oxidation resistance, specifically comprising the following steps: (1) The Sn, Ag, Bi, Y and Hf metal samples are weighed according to the proportions shown in Table 1, and acid pickling of the metal samples is carried out with 10% nitric acid aqueous solution at 45℃, 40kHz frequency and 300W power for 8min, and then vacuum drying at 100℃ for 2h under the condition of vacuum degree of 10Pa, to ensure that the water content of the metal sample is ≤0.01%.

[0048] (2) Argon is introduced into a double-chamber vacuum induction melting furnace, and the metal samples are melted under the condition of vacuum degree ≤10 -3The Sn powder after acid washing and drying is smelted in a crucible under the condition of 10

[0049] (3) The melt flows out through the small hole at the bottom of the crucible to form a continuous metal flow. A plurality of atomizing nozzles with a gas flow rate of 3 times the metal flow rate spray argon gas at a speed of 300 m / s, a pressure of 0.8 MPa, and a temperature of 9727°C. The argon gas stream impacts the metal flow to atomize it into small droplets. The small 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 in a 99.999% high-purity argon environment (the ionization rate of the plasma arc is ≥95%). By applying a power of 8 kW, the argon gas is ionized to form a plasma jet. Under the driving of a gas pressure of 1.0 MPa, the jet impacts the small droplets at an angle of 45° to achieve the first refinement in 0.2 s. Then, the second refinement is performed: a 40 kHz, 600 W low-frequency transducer and a 2 MHz, 700 W high-frequency transducer are combined to use an exponential amplitude horn with an amplification coefficient of 2.8 to perform the second refinement of the melt under the conditions of an action distance of 12 mm, a vibration time of 0.3 s, and -20°C nitrogen cooling (flow rate of 8 L / min). Then, a PZT-8 piezoelectric ceramic module is bonded to a titanium alloy substrate to achieve the third refinement of the melt under the conditions of a pulse frequency of 2 MHz (duty cycle of 40%), a power of 1000 W, an axial magnetic field of 0.2 T, a processing temperature of 100°C, an environmental oxygen content of ≤10 ppm, an action time of 0.8 s. The refined melt powder enters the cooling and collection system with the gas stream and is collected in a specific container after separation. The collected powder is sieved using a vibrating screen to obtain metal particles.

[0050] (4) The metal particles are placed in a vacuum annealing furnace and heated to 200°C under the condition of a vacuum degree ≤10 -2 Pa and annealed for 2 h. An ultrasonic wave with a frequency of 30 kHz is applied during the annealing process. After cooling, an oxidation-resistant high-temperature lead-free solder alloy is obtained.

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

[0052] The solder alloy prepared in Example 3 was tested for particle size distribution, oxidation resistance, and Ag element segregation degree analysis using the same test method as in Example 1. The test results showed that the solder alloy prepared in Example 3 had a D50 particle size of 12μm, with a particle size of 10-50μm accounting for 95%, a solder alloy sphericity of ≥90%, and a fine powder rate (D<10μm) of 30-40%. The solder alloy had a good sphericity and uniform particle size distribution. The oxidation resistance test results showed that the solder alloy prepared in Example 3 had an oxidation weight gain of only 0.015mg / cm 3 , with excellent oxidation resistance; the Ag element segregation degree was ≤2%, proving that the elements in the solder alloy were uniformly distributed. This was due to the synergistic effect of the three-stage process of "plasma high-temperature crushing-ultrasonic vibration secondary refinement-ultrasonic conversion depth homogenization": the plasma high temperature made the liquid drop surface tension uniformly distributed, the acoustic streaming effect of ultrasonic vibration eliminated the liquid drop surface wrinkles, and the ultrasonic conversion pulse vibration further corrected the particle morphology, finally solidified into high-sphericity particles under high-speed cooling (≥-170℃ / s), with a sphericity deviation of ≤5% between different batches.

[0053] Comparative Example 1 A method for preparing an antioxidant high-temperature lead-free tin-based solder alloy, specifically comprising the following steps: (1) The Sn, Ag, Bi, Y, and Hf metal samples were weighed according to the proportions shown in Table 1, and then acid washed with a 10% nitric acid aqueous solution at 45℃, a frequency of 40kHz, and a power of 300W for 8min. After that, the metal samples were vacuum dried at 100℃ for 2h under a vacuum degree of 10Pa to ensure that the water content of the metal samples was ≤0.01%.

[0054] (2) Argon was introduced into a double-chamber vacuum induction melting furnace, and the vacuum degree was controlled to be ≤10 -3The Sn powder after acid washing and drying is smelted in a crucible under the condition of 10 Pa in a double-chamber vacuum induction smelting furnace at a temperature rising rate of 5 ℃ / min to 250 ℃, and is kept for 30 min. Then, the Ag and Bi particles after acid washing and drying are added into the crucible of the double-chamber vacuum induction smelting furnace and are electromagnetically stirred at 250 rpm. Subsequently, the temperature is raised to 380 ℃. Then, the Y and Hf powders after acid washing and drying are added into the crucible and are ultrasonically vibrated at 20 kHz and 200 W for 10 min, and the smelting and temperature rising are completed. The deoxidizer is added into the metal sample after smelting and temperature rising at a proportion of 0.1% of the mass percentage of the deoxidizer and the metal sample, and a deoxidation reaction is performed. After the reaction is completed, the sample is kept for 8 min, and then surface slag removal treatment is performed, so as to obtain a melt.

[0055] (3) The melt flows out through the small holes at the bottom of the crucible to form a continuous metal flow. A plurality of atomizing nozzles with a gas flow rate of 3 times the metal flow rate are used to spray argon gas at a speed of 300 m / s, a pressure of 0.8 MPa, and a temperature of 9727 ℃, so as to impact the metal flow and atomize it into fine powders. The atomized powders enter a cooling and collecting system along with the gas flow, and are collected in a specific container after being separated. The collected powders are sieved by using a vibrating screen, so as to obtain metal particles.

[0056] (4) The metal particles are placed in a vacuum annealing furnace, heated to 200 ℃ under the condition of 10 Pa, and kept for 2 h. An ultrasonic wave with a frequency of 30 kHz is applied during the annealing process. After cooling, a lead-free tin-based solder alloy for oxidation resistance at high temperature is obtained. -2

[0057] (5) The lead-free tin-based solder alloy for oxidation resistance at high temperature prepared is vacuum packaged in an aluminum-plastic composite bag under the condition of 10 Pa in a dry argon gas environment with a dew point of ≤-40 ℃, by adding a drying agent (moisture absorption capacity ≥10 g).

[0058] The lead-free tin-based solder alloy for oxidation resistance at high temperature prepared in Comparative Example 1 is subjected to the same particle size distribution detection, oxidation resistance detection, and Ag element segregation degree analysis as in Example 1. It is tested that the D50 particle size of the solder alloy prepared in Comparative Example 1 is 120 μm, the proportion of 10-50 μm is only 35%, the sphericity is 30%, the sphericity of the solder alloy is poor, and the particle size distribution is relatively dispersed. The oxidation weight gain test result is 0.18 mg / cm 3 , and the oxidation resistance of the solder alloy is poor. The Ag element segregation degree is 25%, indicating that the element distribution in the solder alloy is uneven. This is because the solder alloy is only subjected to one high-pressure gas atomization treatment during the preparation process, resulting in incomplete refinement of the alloy particles, and thus the excellent particle size characteristics, oxidation resistance, and element uniform distribution characteristics are not exhibited.

[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 packaged in an aluminum plastic composite bag under the condition of a dry argon environment with a dew point of less than or equal to -40°C, adding a desiccant (moisture absorption capacity of greater than or equal to 10 g) and a pressure of less than or equal to 10 Pa.

[0064] The antioxidant high-temperature lead-free tin-based solder alloy prepared in Comparative Example 2 is subjected to the same particle size distribution test, oxidation resistance test, and Ag element segregation analysis as in Example 1. The test results show that the D50 particle size of the solder alloy prepared in Comparative Example 2 is 65 μm, the proportion of 10-50 μm is 60%, the sphericity is 40%, the sphericity of the solder alloy is poor and the particle size distribution is relatively dispersed; the oxidation weight gain test result is 0.08 mg / cm 3 , the oxidation resistance of the solder alloy is poor; the Ag element segregation degree is 15%, indicating that the element distribution in the solder alloy is uneven. This is because the solder alloy is only subjected to one plasma atomization and refinement treatment during preparation, resulting in incomplete refinement of the alloy particles, and thus not exhibiting excellent particle size characteristics, oxidation resistance, and element uniform distribution characteristics.

[0065] Comparative Example 3 A preparation method of an antioxidant high-temperature lead-free tin-based solder alloy, specifically comprising the following steps: (1) The Sn, Ag, Bi, Y, and Hf metal samples are weighed according to the proportions shown in Table 1, and then subjected to acid pickling at 40°C with a 10% nitric acid aqueous solution at a frequency of 40 kHz and a power of 300 W for 8 min. After that, the metal samples are vacuum dried at 100°C for 2 h under a vacuum degree of 10 Pa to ensure that the water content of the metal samples is less than or equal to 0.01%.

[0066] (2) Argon is introduced into a double-chamber vacuum induction melting furnace, and the temperature is raised to 250°C at a rate of 5°C / min under a vacuum degree of less than or equal to 10 -3 Pa. The acid-washed and dried Sn powder is then melted in the crucible. The acid-washed and dried Ag and Bi particles are then added to the crucible of the double-chamber vacuum induction melting furnace and subjected to electromagnetic stirring at 250 rpm. The temperature is then raised to 380°C, and the acid-washed and dried Y and Hf powders are then added to the crucible and subjected to ultrasonic vibration at 20 kHz and 200 W for 10 min to complete the temperature rising and melting. The deoxidizer is then added to the metal samples after temperature rising and melting at a proportion of 0.1% of the mass percentage of the deoxidizer and the metal samples, and a deoxidation reaction is carried out. After the reaction is completed, the mixture is allowed to stand for 8 min, and then surface slag removal treatment is carried out to obtain a melt.

[0067] (3) The melt flows out through the small hole at the bottom of the crucible to form a continuous metal stream, and multiple atomizing nozzles with a gas flow rate 3 times that of the metal flow rate are sprayed at a speed of 300 m / s, a pressure of 0.8 MPa, and a temperature of 9727°C argon gas flow, impacting the metal stream to 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, and the argon gas is ionized to form a plasma jet by applying a power of 8 kW; under the driving of a gas pressure of 1.0 MPa, the jet impacts the tiny droplets at an angle of 45°, and the first refinement is achieved within an action time of 0.2 s. Then, the second refinement is performed: a 40 kHz, 600 W low-frequency transducer and a 2 MHz, 700 W high-frequency transducer are combined, an exponential amplitude transformer with an amplification coefficient of 2.8 is used, and the second refinement of the melt is performed under the conditions of an action distance of 12 mm, a vibration time of 0.3 s, and -20°C nitrogen cooling (flow rate of 8 L / min) to obtain refined powder. The powder enters the cooling and collecting system with the gas flow and is collected in a specific container after separation. The collected powder is sieved using a vibrating screen to obtain metal particles.

[0068] (4) The metal particles are placed in a vacuum annealing furnace and heated to 200°C under a vacuum degree of ≤10 -2 Pa for 2 h. An ultrasonic wave with a frequency of 30 kHz is applied during the annealing process, and an anti-oxidation high-temperature lead-free tin-based solder alloy is obtained after cooling.

[0069] (5) The anti-oxidation high-temperature lead-free tin-based solder alloy prepared is vacuum packaged in an aluminum-plastic composite bag under the conditions of a dry argon gas environment with a dew point of ≤-40°C, the addition of a drying agent (moisture absorption capacity ≥10 g), and a pressure of ≤10 Pa.

[0070] The anti-oxidation high-temperature lead-free tin-based solder alloy prepared in Comparative Example 3 is subjected to the same particle size distribution detection, anti-oxidation performance detection, and Ag element segregation analysis as in Example 1. The test results show that the D50 particle size of the solder alloy prepared in Comparative Example 3 is 30 μm, the proportion of 10-50 μm is 85%, the sphericity is 70%, the sphericity of the solder alloy is poor, and the particle size distribution is relatively dispersed; the oxidation weight gain test result is 0.04 mg / cm 3 , the anti-oxidation performance of the solder alloy is poor; the Ag element segregation degree is 5%, indicating that the element distribution in the solder alloy is uneven. This is because the solder alloy is only subjected to one plasma atomization refinement treatment, one high-pressure gas atomization treatment, and one ultrasonic vibration refinement treatment during the preparation process, resulting in incomplete refinement of the alloy particles, and thus the alloy does not exhibit excellent particle size characteristics, anti-oxidation performance, and element uniform distribution characteristics.

[0071] Comparative Example 4 The lead-free tin-based solder alloy is prepared by a traditional process, specifically including the following steps: Taking single gas atomization as the core, only the high-speed airflow shear force is used to break the molten metal stream, without subsequent ultrasonic or plasma refining steps, and the specific steps are as follows: (1) Raw material pretreatment: The conventional pickling (10% mass fraction of dilute sulfuric acid aqueous solution) is used to remove the oxide film on the surface of Sn, Ag and Cu raw materials, and then the water is washed and naturally dried. The metal powder is weighed and the solder alloy is prepared. The alloy element composition includes 96.5% Sn, 3% Ag and 0.5% Cu by mass fraction.

[0072] (2) Melting: The ordinary induction melting furnace (vacuum degree ≥10 -1 Pa) is used to heat to above the Sn melting point (232℃) in air or weak inert atmosphere. After melting, the components are mixed by mechanical stirring (speed 100 rpm) without ultrasonic assistance; rely on natural degassing during the melting process.

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

[0074] (4) Subsequent treatment: The atomized powder is directly screened to remove oversized particles; there is no vacuum annealing or surface coating step, only natural drying before packaging.

[0075] The traditional lead-free tin-based solder alloy prepared in Comparative Example 4 is subjected to the same particle size distribution test as Example 1, and the test results show that the solder alloy D50 prepared in Comparative Example 4 is 50-80 μm, the sphericity is 40-60%, the fine powder rate (D<10 μm) is 5-10%, the solder alloy particle morphology is mostly irregular block or polyhedron, and there are obvious wrinkles and edges on the surface. The alloy powder particle size is large, and it is difficult to achieve ultra-fine particle size and high sphericity. This is because the traditional process only relies on the airflow shear force of single gas atomization, the droplet cooling speed is slow (≤-171℃ / s), and there is no auxiliary shaping means, so that the droplet is difficult to form a symmetrical spherical structure during the solidification process, resulting in low and poor consistency of sphericity.

[0076] The lead-free tin-based solder alloy prepared in Comparative Examples 1, 2, 3 and Example 3 is subjected to particle size distribution test, oxidation resistance test and element distribution uniformity test. The test results are shown in Table 2.

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

[0078] Table 3 Embodiments of the application have been described above, with the understanding that these descriptions are exemplary only, and are not intended to be exhaustive or to limit the embodiments disclosed to the precise forms disclosed. Many modifications and variations are possible in light of the above teachings. The selected terms are used in the description solely to provide a clear understanding of the principles, actual applications, or improvements on which the various embodiments are based, or to make apparent to others of ordinary skill in the art the teachings that are more or less closely related to the various embodiments disclosed herein.

Claims

1. A method of producing an antioxidant lead-free tin-based solder alloy for high temperature use, characterized by, The metal elements in the alloy raw material include, by mass percentage: 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 of inevitable impurities; the preparation method of the alloy specifically includes the following steps: (1) pickling: the metal raw material is weighed according to the proportion, and the metal raw material is pickled, and then dried; (2) smelting treatment: inert gas is introduced into the smelting device, then Sn powder after pickling and drying is smelted in the smelting container and kept warm, then Ag and Bi particles after pickling and drying are added to the smelting container and stirred, then heated, then Y and Hf powder after pickling and drying are added to the smelting container and ultrasonic, complete the heating and smelting; then add deoxidizer and ultrasonic, carry out deoxidation reaction, after the reaction is completed, stand, then carry out surface slag removal treatment, obtain the melt; (3) atomization treatment: the continuously flowing melt in the smelting container is subjected to high-pressure gas atomization by inert gas, and the atomized melt is obtained; (4) refining treatment: an alternating electric field is generated by a high-frequency induction coil to ionize inert gas to form a plasma arc, after the plasma jet reaches a specified temperature, the plasma jet and the atomized melt are intersected to realize the first refinement of the atomized melt; the once-refined melt is placed in an ultrasonic field and sequentially subjected to low-frequency ultrasonic wave and high-frequency ultrasonic wave treatment to realize the second refinement; the third refinement of the melt is realized through a pulse ultrasonic conversion system, and the thrice-refined melt 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 warm, and at the same time, the metal particles are ultrasonic, and after cooling, the anti-oxidation high-temperature lead-free solder alloy is obtained.

2. The preparation method of 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: 10% nitric acid aqueous solution is used for ultrasonic pickling for 5-10 min, and the pickling temperature is 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 Sn powder in the step (2) is smelted in a smelting device under the condition that the vacuum degree is less than or equal to 10 -3 Pa, and the smelting device is heated to 250 DEG C at a heating rate of 5 DEG C / min, and then is kept for 30 min; the smelting condition after the Ag and Bi particles are added is that the stirring is started at 200-300 rpm, and then the temperature is increased to 350-380 DEG C; the ultrasonic condition after the Y and Hf powders are added is that the ultrasonic frequency is 20 kHz, and the ultrasonic power is 200 W; and the temperature of the melt is 250-350 DEG C.

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), the deoxidizer is added to the metal sample after heating and melting at a proportion of 0.05-0.2% of the mass percentage 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 treatment uses a high-pressure gas atomization device, and the nozzle gas pressure is controlled at 0.6-1.2 MPa, and the gas flow is 2-5 times the metal melt flow.

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 high-pressure gas atomization device is used for the first refinement; the power of the plasma is 5-10 kW; the temperature of the plasma jet is 7727-11727℃; and the time for the first refinement 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 the second refinement in step (4), the frequency of the low-frequency ultrasonic wave treatment is 30-50 kHz; the high-frequency power is 500-800 W; and the time for 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, In the third refinement in step (4), the pulse ultrasonic conversion system is used under the following conditions: the duty cycle of the square wave pulse is 30-50%, the pulse frequency is 1-5 MHz, an axial magnetic field of 0.1-0.3T is superimposed, the output power is 800-1500 W, and the treatment 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, The ultrasonic treatment of the metal particles in the step (5) is carried out under a vacuum degree of ≤10 -2 Pa; the ultrasonic treatment is carried out at an ultrasonic frequency of 30 kHz; the metal particles are heated to 180-200 °C; and the metal particles are kept for 2 h.

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

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