A controllable preparation method for semiconductor-grade ultrafine spherical aluminum powder

Abstract

This invention relates to the manufacture of metal powders and discloses a controllable preparation method for semiconductor-grade ultrafine spherical aluminum powder, comprising: preparing a composite molten salt composed of a matrix salt and an interface pinning agent calcium fluoride and heating it to a dispersion temperature to form a homogeneous melt; shearing and dispersing liquid aluminum in the melt; performing temperature-controlled dissolution, controlling the cooling rate to allow calcium fluoride to precipitate in situ and adsorb before the aluminum droplets solidify, forming a physical pinning shell layer; and restricting solidification and removing the salt medium. This invention utilizes the temperature-dependent solubility characteristics to construct a microscopic physical barrier before the droplets solidify, effectively blocking droplet aggregation through steric hindrance, achieving high sphericity and extremely narrow particle size distribution of the aluminum powder; simultaneously, it utilizes calcium fluoride microcrystals to induce the formation of a dense fluorinated aluminum oxide composite passivation layer, improving the powder's resistance to electrochemical migration and insulation reliability.

Description

Technical Field

[0001] This invention relates to a controllable preparation method for semiconductor-grade ultrafine spherical aluminum powder, belonging to the field of metal powder manufacturing technology. Background Technology

[0002] Currently, semiconductor-grade ultrafine spherical aluminum powder is used as a core functional filler in photovoltaic conductive pastes, chip packaging materials, and conductive adhesives. The uniformity of particle size, sphericity, and surface purity determine the conductivity and rheological properties of electronic pastes. Existing industrial preparations of such metal powders mainly employ gas atomization, which utilizes high-speed airflow to impact and break up molten metal, relying on the surface tension of the droplets during the cooling process to naturally shrink into spheres. However, as semiconductor packaging technology develops towards finer pitch and higher density, the limitations of gas atomization become apparent. Obtaining ultrafine particle sizes requires applying high shear energy, inducing severe turbulence, causing the droplets to collide and adsorb fine droplets before solidification, forming satellite spherical structures. The extremely rapid cooling rate causes the droplets to freeze before completing sphericification and contraction, resulting in insufficient sphericity of the product. To avoid interference from gas phase turbulence, existing technologies attempt to use liquid phase dispersion, dispersing molten metal in a high-temperature molten salt or oil bath liquid phase medium to form an emulsion system. Although this approach provides a relatively mild fluid environment, there are fundamental thermodynamic constraints in the critical window period for the transition from the high-temperature dispersed state to the low-temperature solidified state.

[0003] In homogeneous liquid media, dispersed metal droplets are only subject to soft constraint by interfacial tension. As the system temperature drops to near the metal's freezing point, the thermal motion of the fine droplets becomes active. Due to the lack of rigid physical barriers at the droplet interfaces, collisions easily cause droplets to break through the liquid film's limitations and merge or undergo Oswald ripening. This aggregation behavior, stemming from the thermodynamically spontaneous tendency to reduce specific surface area, leads to an uncontrollable widening of the final product's particle size distribution, making it difficult to maintain a highly monodisperse state in the initial stage of dispersion. To compensate for the shortcomings of the physical fragmentation mechanism, existing technologies attempt to optimize the control of smelting, purification, and atomization parameters. For example, the authorization announcement number CN11... Chinese invention patent 7884621B discloses a high-purity ultrafine spherical aluminum powder for cold spraying and its preparation method. Although it introduces a specific refining agent system and degassing process to reduce the hydrogen content and inclusion level of aluminum powder and meet the purity requirements of cold spraying technology, the core powder preparation method still relies on inert gas atomization and an open forming path with high-speed gas as the dispersion medium. It lacks rigid physical constraints on micron-sized droplets and cannot block Brownian motion collisions and secondary fusion between droplets at the microscale. Even if the chemical purity is improved, this kind of technology cannot fundamentally eliminate satellite sphere adhesion and surface irregularities.

[0004] Therefore, constructing a dynamic physical isolation mechanism adapted to liquid-phase dispersion systems, locking the geometry of metal droplets in situ before solidification and blocking the thermodynamic coalescence path, is the technical problem to be solved by this invention. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A controllable preparation method for semiconductor-grade ultrafine spherical aluminum powder, comprising the following steps:

[0006] A thermosensitive dissolution molten salt medium was constructed, and a composite molten salt consisting of a matrix salt and an interface pinning agent was prepared. The interface pinning agent was selected as calcium fluoride, and the amount added was limited to 1.5 wt% to 3.0 wt% of the total mass of the matrix salt. The composite molten salt was heated to a dispersion temperature of 780°C to 800°C to form a homogeneous melt.

[0007] Shear dispersion is performed by adding metallic aluminum to a homogeneous melt under an inert atmosphere and at a dispersion temperature, and applying mechanical shear force to break the liquid aluminum into micron-sized droplets dispersed in the homogeneous melt.

[0008] Temperature-controlled dissolution and interfacial crystal pinning were performed, mechanical shear force was stopped, and the system temperature was controlled to decrease from the dispersion temperature to the anchoring temperature range of 670℃ to 685℃ at a rate of 5℃ / min to 10℃ / min. The characteristic that the solubility of calcium fluoride decreases with decreasing temperature was used to drive in-situ precipitation from the homogeneous melt. The precipitated calcium fluoride nanocrystals were induced to migrate directionally and adsorb onto the surface of micron-sized droplets. A solid particle shell layer covering the micron-sized droplets was constructed above the solidification temperature of aluminum. The steric hindrance effect generated by the solid particle shell layer was used to block the fusion path between micron-sized droplets.

[0009] The process involves constrained solidification and separation, with the temperature further reduced below the melting point of metallic aluminum. This allows micron-sized droplets to undergo phase transformation solidification within the geometrically confined shell of solid particles, forming a mixture of solid aluminum powder and solid salt. Water-soluble salt components in the composite molten salt are then removed to obtain spherical aluminum powder.

[0010] Preferably, in the step of constructing the thermosensitive dissolution molten salt medium, the matrix salt is composed of potassium chloride, sodium chloride and aluminum fluoride, and the mass ratio of the three is limited to 40:45:15. This specific ratio ensures that the density of the composite molten salt at the dispersion temperature is less than the density of liquid aluminum, ensuring that the micron-sized droplets are in a suspended or slow settling state in the homogeneous melt, and providing a melt environment with a specific ionic strength for the dissolution and precipitation of calcium fluoride.

[0011] Preferably, in the shear dispersion step, the mechanical shear force is applied by setting the shear rate to 2800 rpm to 3500 rpm, and the shearing time is maintained at 15 to 20 minutes. This shear condition, combined with the interfacial tension of the composite molten salt, reduces the average particle size D of the micron-sized droplets. 50 The potential energy of calcium fluoride relative to the surface of micron-sized droplets was controlled between 2 and 5 micrometers, and the supersaturation potential energy of calcium fluoride in homogeneous melt was established.

[0012] Preferably, in the temperature-controlled dissolution and interface crystal pinning steps, the anchoring temperature range T is... anchorWith the melting point T of metallic aluminum m The following subcooling window relationship applies: 10℃≤T anchor -T m ≤25℃, where T anchor The control temperature for triggering the large-scale precipitation of calcium fluoride is T. m The standard melting point of aluminum is given; this relationship is defined within the thermodynamic time window for the construction of solid particle shells under the premise that micron-sized droplets remain in a liquid state.

[0013] Preferably, the interface pinning agent is calcium fluoride with an initial particle size D. 50 The raw material is specified to be less than or equal to 10 micrometers and with a purity greater than or equal to 99.5%. This specification ensures that calcium fluoride can be completely dissociated and dissolved in the matrix salt during the heating process to the dispersion temperature. This avoids undissolved coarse particles becoming non-uniform nucleation cores and interfering with the subsequent in-situ growth of calcium fluoride nanocrystals on the surface of micrometer-sized droplets.

[0014] Preferably, in the restricted curing and separation step, the operation of removing water-soluble salt components from the composite molten salt includes using deionized water to perform multi-stage countercurrent washing on the mixture of cured solid aluminum powder and solid salt. The washing process controls the water temperature to be between 40°C and 60°C. The trace amounts of calcium fluoride nanocrystals remaining on the surface of the spherical aluminum powder are used as in-situ precursors to induce the formation of a fluorinated aluminum oxide composite passivation layer with a thickness of 3 to 8 nanometers on the surface of the spherical aluminum powder in the water washing environment.

[0015] Preferably, the inert atmosphere is composed of high-purity nitrogen or argon, and the oxygen content is controlled at a level below 10 ppm. During the entire process of shear dispersion and temperature-controlled dissolution and interfacial crystal pinning, the gas pressure in the reaction system is maintained at a positive pressure of 0.1 MPa to 0.12 MPa to prevent external air from seeping in and causing premature oxidation of the surface of micron-sized droplets, which would hinder the adsorption of calcium fluoride nanocrystals.

[0016] Preferably, in the temperature-controlled dissolution and interface crystal pinning steps, the calcium fluoride nanocrystals precipitated in situ from the homogeneous melt have a particle size distribution between 50 nanometers and 200 nanometers. The adsorption coverage of these calcium fluoride nanocrystals on the surface of the micron-sized droplets is determined by the amount of interface pinning agent added and the rate of decrease in system temperature, so that the solid particle shell formed on the surface of the micron-sized droplets exhibits a discontinuous but sufficient Pickering emulsion structure to generate a steric hindrance effect.

[0017] Preferably, the method does not include any step of using airflow nozzles or high-pressure gas atomization. The spherical shaping of micron-sized droplets is entirely driven by the isotropic hydrostatic pressure field provided by the composite molten salt and the interfacial tension constraint of the solid particle shell. The sphericity of the prepared spherical aluminum powder is not less than 0.95.

[0018] Preferably, the method is used to prepare conductive fillers for use in semiconductor chip encapsulation adhesives. After the spherical aluminum powder is prepared, it further includes a heat treatment step in a vacuum at 300°C to 350°C. This step is used to remove the water of crystallization in the fluorine oxyaluminum composite passivation layer and further densify the solid particle shell, thereby improving the anti-electrochemical migration performance of the spherical aluminum powder under high temperature and high humidity conditions.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. This invention utilizes the characteristic that the solubility of interfacial pinning agents in molten salt media decreases sharply with cooling, solving the problem of metal droplet agglomeration due to thermal motion collisions before solidification in liquid-phase dispersion methods. During the cooling process, the interfacial pinning agent, in a supersaturated state, precipitates from the continuous phase and migrates directionally to the surface of the aluminum droplets driven by the difference in wetting angle. Before the droplets solidify, a sterically hindered solid microcrystalline shell is formed. The microcrystalline shell establishes a rigid physical isolation wall at the microscale, blocking the thermodynamic path of adsorption and fusion between droplets via van der Waals forces. This allows the metal droplets to maintain an independent geometric shape during the phase transition window from liquid to solid, avoiding the coarse particle tailing and satellite sphere adhesion phenomena commonly seen in traditional molten salt or gas atomization methods. As a result, the final aluminum powder has an extremely narrow particle size distribution and high monodispersity.

[0021] 2. Based on the dual shaping mechanism of isotropic hydrostatic pressure and interfacial energy modification, a near-equilibrium state with high density sphericity is obtained. Through the synergistic effect of the hydrostatic pressure field of the liquid medium and the interfacial tension gradient, the thermodynamic equilibrium state shaping of metal droplets is achieved. Unlike the dynamic deformation of droplets caused by high-speed turbulent shearing during gas atomization, aluminum droplets are in an isotropic liquid pressure environment. The adsorbed surface solid microcrystals tend to preferentially occupy the region with higher surface energy curvature abrupt change, thus smoothing out surface energy fluctuations. The dual constraint mechanism forces the droplets to shrink to the minimum surface area reference geometric sphere before solidification, suppressing surface collapse or dendrite growth caused by uneven cooling rate. The resulting aluminum powder exhibits extremely high sphericity and surface density, improving the filling fluidity and packing density of semiconductor packaging pastes.

[0022] 3. Through time-series reconstruction and media participation, excellent insulation and withstand voltage properties are imparted to the powder surface in situ. By adopting a molten salt encapsulation and curing path, the oxidation and passivation process of the aluminum powder surface is decoupled from the high-temperature forming stage and postponed to the subsequent mild cleaning process. The residual fluorine-containing microcrystalline shell on the particle surface during the curing process serves as an in-situ precursor in the subsequent salt removal process to participate in the interfacial reaction, inducing the formation of a dense and uniformly thick fluorinated alumina composite passivation film on the aluminum powder surface. Compared with the amorphous alumina layer formed by natural oxidation, the composite interfacial layer has a higher electronic band gap and breakdown voltage. It grows in a liquid phase environment, avoiding micropore defects and impurity inclusions caused by high-temperature gas phase oxidation, thereby improving the electrochemical migration resistance and insulation reliability of aluminum powder conductive adhesives or electronic packaging materials. Attached Figure Description

[0023] Figure 1 This is a flow chart of the controllable preparation process of semiconductor-grade ultrafine spherical aluminum powder according to the present invention.

[0024] Figure 2 This is a trend diagram showing the effect of the amount of interface pinning agent added in this invention on the key physical properties of aluminum powder;

[0025] Figure 3 This is a schematic diagram of the structure of the shear dispersion reaction device and the in-situ interface pinning mechanism of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be described in detail below with reference to specific implementation methods and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the scope of protection of the present invention. Non-essential modifications or adjustments made by those skilled in the art based on the content disclosed in the present invention shall fall within the scope of protection of the present invention.

[0027] This invention discloses a controllable preparation method for semiconductor-grade ultrafine spherical aluminum powder, comprising four core stages: construction of a thermosensitive dissolution molten salt medium, liquid shear emulsification dispersion, temperature-controlled interface crystal pinning and shaping, and confined phase change solidification and separation. This method utilizes the characteristic that the solubility of the solute in the liquid medium changes with temperature to transform the thermodynamic state change of the continuous phase into physical boundary constraints on the surface of the dispersed phase droplets, achieving geometric locking and coalescence blocking within the critical window period before the solidification of the metal droplets.

[0028] In the process of preparing semiconductor packaging fillers, to solve the problem of molding runaway caused by turbulence in the gas phase environment, this invention uses molten salt as a liquid-phase continuous medium. The medium construction procedure is as follows: A matrix salt is prepared, composed of potassium chloride (KCl), sodium chloride (NaCl), and aluminum fluoride (AlF3), with a mass ratio of 40:45:15. This ratio is used to ensure that the density of the molten salt is slightly lower than the density of liquid aluminum at the working temperature, approximately 2.35 g / cm³, so that aluminum droplets remain suspended or slowly settle in the medium. An interface pinning agent is introduced into the matrix salt. This interface pinning agent is calcium fluoride (CaF2) with a purity greater than or equal to 99.5%, and the initial raw material particle size D... 50 For samples with a diameter of 10 micrometers or less, the amount of calcium fluoride added is limited to 1.5 wt% to 3.0 wt% of the total mass of the matrix salt. This amount is determined based on the solubility characteristics of calcium fluoride in chloride molten salts: at a dispersion temperature of 780°C to 800°C, this amount is below the solubility limit and is used to form a homogeneous transparent melt; in the temperature range close to the solidification point of aluminum, i.e., 670°C to 685°C, this amount is in a supersaturated state and is used to trigger the subsequent precipitation pinning mechanism. After mixing the above components, they are loaded into a reactor and heated to 780°C to 800°C under an inert atmosphere. The temperature is maintained and stirred until the system becomes clear, forming a homogeneous melt.

[0029] To suppress secondary oxidation during the liquid metal crushing process, the system performs shear dispersion under inert gas protection. The inert atmosphere consists of high-purity nitrogen or argon with an oxygen content below 10 ppm. The gas pressure within the reaction system is maintained at a positive pressure of 0.1 MPa to 0.12 MPa. The replacement and maintenance of the inert atmosphere within the reaction system adopts a closed-loop control procedure based on the oxygen partial pressure feedback at the outlet end. Before the heating program starts, the reactor undergoes pulsed gas replacement until the oxygen content measured by the online oxygen analyzer on the reactor exhaust pipeline is consistently below 5 ppm for 10 consecutive minutes, at which point the system atmosphere is deemed to meet the standard. During the shear dispersion and temperature-controlled dissolution stages, the system adjusts the opening of the inlet flow valve to dynamically compensate for minor leakage at the agitator shaft seal, maintaining the exhaust end monitoring pressure at 0. A positive pressure setting range of 0.1 MPa to 0.12 MPa is used. Under this environment, aluminum ingots with a purity of ≥99.99% are added to a homogeneous melt at the dispersion temperature. After the aluminum ingots are completely melted, a high-shear dispersion device is activated. The mechanical shear force application parameters are: shear rate 2800 rpm to 3500 rpm, shear time 15 to 20 minutes. This shearing process utilizes the shear stress generated by high-speed rotation to overcome the surface tension and viscosity of the aluminum melt, breaking the continuous aluminum melt flow into discrete micron-sized droplets. At this time, the temperature is maintained at 780℃ to 800℃, and calcium fluoride is completely dissolved in the molten salt. The system presents an emulsion state in which aluminum droplets are dispersed in a homogeneous molten salt. This step reduces the average particle size D of the micron-sized droplets. 50 The micrometers should be controlled between 2 and 5 micrometers.

[0030] To address the issue of droplet aggregation due to Brownian motion collisions during cooling, this invention employs a temperature-controlled dissolution and interfacial crystal pinning procedure; it stops applying mechanical shear force and controls the system temperature to decrease from the dispersion temperature to the anchoring temperature range at a rate of 5°C / min to 10°C / min. This anchoring temperature range is T... anchor With the melting point T of metallic aluminum m Satisfying the supercooling window relationship: 10℃≤T anchor -T m ≤25℃; During this cooling process, the solubility product of calcium fluoride in the matrix salt reaches saturation and decreases rapidly. The supersaturated calcium fluoride precipitates in situ from the continuous phase. Due to the difference in the three-phase wetting angle between the calcium fluoride microcrystals and the liquid aluminum and chloride salt medium, the precipitated calcium fluoride microcrystals with a particle size of 50 nm to 200 nm spontaneously migrate to the surface of the aluminum droplet and are adsorbed. Before the aluminum droplet solidifies, this process constructs a discontinuous and dense solid particle shell. This shell utilizes the steric hindrance generated by the Pickering emulsion effect to lock the spherical geometry of the aluminum droplet and block the fusion path between droplets.

[0031] After interface pinning is completed, the temperature is further reduced to below the melting point of metallic aluminum, allowing the micron-sized droplets encased in the microcrystalline shell to undergo phase transformation and solidification within the geometric confinement of the solid particle shell. After the system cools to room temperature, the mixture of solid aluminum powder and solid salt is removed and crushed. The mixture is then subjected to multi-stage countercurrent washing with deionized water at a temperature controlled between 40°C and 60°C. This step dissolves and removes water-soluble matrix salts, leaving trace amounts of calcium fluoride microcrystals on the surface of the spherical aluminum powder. In an aqueous environment, a fluorinated aluminum oxide composite passivation layer with a thickness of 3 to 8 nanometers is induced on the surface of the aluminum powder. After solid-liquid separation and drying, semiconductor-grade ultrafine spherical aluminum powder is obtained.

[0032] Example 1: In a typical industrial application scenario for conductive adhesive fillers used in 5G high-frequency communication chip packaging, the conductive phase material faces a difficult physical contradiction between ultrafine particle size and absolute morphological purity. The gas-phase turbulence mechanism in traditional gas atomization processes inevitably generates micron- or even nano-sized satellite sphere defects. These micro-droplets adsorbed on the surface of the main particles become the core cause of electrochemical migration short circuits and breakdown failures under the influence of a high-frequency electric field. To address this macroscopic reliability bottleneck caused by microstructural defects, this example utilizes a thermosensitive molten salt medium system with a density-matched carrier constructed from potassium chloride, sodium chloride, and aluminum fluoride, combined with 1.5wt% to 3.0wt% calcium fluoride as an interface pinning agent, to reconstruct the forming kinetics of aluminum droplets in a liquid phase environment. As the reaction system temperature precisely decreases from the dispersed state of 790℃ to the anchoring range of 680℃, the originally completely dissolved calcium fluoride undergoes a thermodynamic solubility product K... sp Driven by a sharp drop in temperature, nanocrystals precipitate in situ from the continuous phase and migrate directionally to the surface of aluminum droplets. This creates a discontinuous but strongly sterically hindered solid particle shell within a critical window period when the aluminum droplet temperature is still above its 660°C freezing point and it possesses high surface activity. This in-situ generated Pickering shell not only uses isotropic hydrostatic pressure to forcibly correct the droplet's geometric sphericity but also constructs a rigid physical barrier at the microscale, blocking the aggregation behavior caused by Brownian collisions between droplets and the adsorption pathway of the microdroplets to its nucleation. This results in the aluminum powder, after final solidification and separation, exhibiting a D-shape. 50 It exhibits monodisperse characteristics with a particle size of 3.2 micrometers and a span of 0.85. This interface engineering strategy based on phase equilibrium thermodynamic control completely eliminates the presence of satellite spheres and irregularly shaped particles, resulting in a 40% increase in the breakdown voltage of the prepared conductive adhesive layer compared to similar products using gas-atomized aluminum powder.

[0033] Example 2: To verify the actual effectiveness of the temperature-controlled dissolution and interfacial crystal pinning mechanism of the present invention in a liquid-phase dispersion system, and to confirm the rationality of the numerical range of the interfacial pinning agent dosage in the technical solution of the present invention, this example designed a set of comparative experiments including gradient variables. Under simulated thermodynamic fluctuations in a continuous industrial production environment, the effects of different calcium fluoride addition amounts on the final aluminum powder microstructure, particle size distribution, and surface integrity were quantitatively analyzed to reveal the intrinsic correlation between the technical effect and key process parameters. The experiment was conducted with a precision programmable temperature control system (temperature control accuracy ±...). The experiment was conducted in a 5L Hastelloy reactor with online torque monitoring function (0.5℃). The matrix salt system strictly followed the mass ratio of KCl:NaCl:AlF3=40:45:15 to ensure the consistency of melt density and surface tension. The process parameters for the shearing and dispersion stage were uniformly set as follows: temperature 790℃, shearing rate 3200rpm, shearing time 18 minutes. The cooling rate for the cooling stage was uniformly controlled at 8℃ / min, and the anchoring temperature was set at 680℃. High-frequency electromagnetic interference was introduced to simulate the complex electromagnetic environment of the industrial site.

[0034] To construct a multidimensional control system, the experiment was set up with four parallel sample groups, and the only variable was the interface pinning agent (calcium fluoride, purity ≥99.5%, D). 50 The addition ratio (wt%) of ≤10μm particles relative to the total mass of the matrix salt: Control group A (blank group): 0wt% addition, used to simulate the baseline state of the traditional molten salt dispersion method; Experimental group B (lower limit of the scope of this invention): 1.5wt% addition; Experimental group C (median of the scope of this invention): 2.5wt% addition; Control group D (upper limit of the scope): 5.0wt% addition; All samples were tested using the same characterization method after solidification, washing and drying: particle size distribution (D) was determined using a laser particle size analyzer. 50 The sphericity of particles and the proportion of satellite spheres were statistically analyzed using scanning electron microscopy (SEM). The key experimental data are recorded in Table 1.

[0035] Table 1: Data on the Influence of Interface Pinning Agent Addition Amount on Key Performance Indicators of Aluminum Powder

[0036]

[0037] Data from control group A ( =8.4μm, Span=1.92) clearly reveals the physical consequences of soft constraint failure: in the absence of interfacial pinning agents, even with sufficient initial shear dispersion, droplets cannot resist the thermodynamic spontaneous aggregation tendency during cooling, leading to coarsening of particle size and widening of distribution; in contrast, the data from experimental groups B and C show drastically different trends. When the calcium fluoride addition is within the range of 1.5wt% to 2.5wt% as defined in this invention, D 50 The particle size decreased to 3.5 μm and 2.8 μm, and the Span value narrowed to below 0.9, with the sphericity approaching 1.0. This result strongly proves that the precipitated calcium fluoride microcrystals successfully constructed a Pickering shell. The steric hindrance effect generated by this shell not only locked the spherical geometry of the droplets, but also physically blocked the fusion path between droplets, achieving a particle size locking effect obtained by shearing. However, the data of control group D shows that the technical effect does not increase linearly and infinitely with the amount added. When the amount added reaches 5.0 wt%, although the particle size is still maintained at a fine level (3.1 μm), the excessively high supersaturation causes the calcium fluoride crystals to agglomerate. These coarse crystal clusters are mechanically trapped on the surface of aluminum powder, which not only destroys the surface smoothness of the particles (sphericity decreases to 0.91), but also becomes a potential source of impurities.

[0038] To further confirm the microscopic chemical structure of the aluminum fluoride-oxygenate composite passivation layer and its quantitative contribution to insulation performance, surface energy dispersive spectroscopy (EDS) and electrochemical characterization were performed on aluminum powder samples (group C, with 2.5 wt% calcium fluoride addition). X-ray photoelectron spectroscopy analysis showed that, in the depth range of 0 nm to 5 nm on the aluminum powder surface, in addition to the 72.6 eV aluminum peak and the 74.4 eV alumina peak, an independent characteristic peak was resolved at 75.8 eV in the Al2p core energy level spectrum. This binding energy strictly corresponds to the Al-OF bonding structure, confirming that the residual calcium fluoride microcrystals underwent in-situ hydrolysis and surface doping reactions during water washing. Further electrochemical impedance spectroscopy tests showed that the polarization resistance of the composite passivation layer was stable at 1.5 × 10⁻⁶. 6 Ω·cm 2 Up to 1.8×10 6 Ω·cm 2 The improvement in the fluorine-free natural alumina layer in the control group A is approximately 450%, thus providing irrefutable microstructural evidence and quantitative performance indicators to support the superior anti-electrochemical migration performance claimed in the technical solution of this invention. The above gradient experimental data constitute a complete chain of evidence, objectively confirming that the calcium fluoride addition of 1.5wt% to 3.0wt% is an exact process window that has been optimized through engineering. Within this range, the dissolution mechanism and interfacial adsorption kinetics reach the optimal balance, enabling the stable and reproducible preparation of semiconductor-grade ultrafine aluminum powder with high sphericity, narrow distribution, and no satellite sphere defects, thus solving the agglomeration and satellite sphere problems mentioned in the background art.

[0039] Example 3: This example combines Figures 1 to 3 A controllable preparation method for semiconductor-grade ultrafine spherical aluminum powder is described, such as... Figure 1 As shown, the preparation process involves a composite molten salt medium construction step, preparing a matrix salt composed of potassium chloride, sodium chloride, and aluminum fluoride, and adding 1.5wt% to 3.0wt% of the interface pinning agent CaF2. The mixture is heated to a dispersion temperature of 780°C to 800°C to form a homogeneous transparent melt, and then metallic aluminum is added. Liquid-liquid shear emulsification and dispersion are completed under an inert atmosphere and with mechanical shear applied, forming D... 50 For micron-sized droplets ranging from 2μm to 5μm, a temperature-controlled dissolution and interface crystal pinning step is then performed. By cooling to the anchoring range, CaF2 is precipitated in situ, and the droplets are locked using the Pickering effect. In this stage, a real-time supersaturation feedback module is used to dynamically adjust the cooling rate by monitoring the conductivity inflection point to correct parameters. Under the geometric confinement of the solid shell and the mechanism of blocking droplet aggregation, a confined phase transformation solidification is completed. Finally, the salt medium is removed by countercurrent washing and in-situ passivation, and a fluorinated aluminum oxide composite passivation layer is generated. The final product is a semiconductor-grade ultrafine spherical aluminum powder with a sphericity greater than 0.95 and with reliable electrochemical migration resistance and insulation performance.

[0040] like Figure 2 As shown in the figure, the graph displays the physical properties of aluminum powder prepared under different CaF2 addition levels (0.0 to 5.0 on the horizontal axis). The solid line represents the average particle size D. 50 μm shows that this value rapidly decreases from 8.4 μm to around 3 μm and remains stable as the amount added increases. The dashed line represents the particle size distribution span, showing a non-monotonic change of first decreasing and then increasing. The dotted line with a triangle represents the mean sphericity, which initially increases to near 1.0 and then slowly decreases as the amount added increases. Figure 3 As shown, the main body of the preparation device includes a temperature control jacket to perform cooling and dissolution operations. The interior contains molten salt medium and aluminum droplets and is equipped with a stirring component that generates a mechanical shear force field. A high-purity inert atmosphere composed of N2 / Ar is continuously introduced from the top to maintain a positive pressure environment. The enlarged microscopic schematic diagram on the right clearly shows the core forming mechanism, that is, the micron-sized aluminum droplets in the liquid state are tightly surrounded by CaF2 nanocrystals precipitated in situ. These microcrystals are adsorbed on the surface of the droplets to form an interfacial pinning layer, which forms a stable physical barrier before the droplets solidify by utilizing the Pickering effect.

[0041] Example 4: In industrial mass production scenarios requiring precise control of the aluminum powder preparation process to ensure product consistency, setting a static anchoring temperature is often insufficient to address the inherent thermal hysteresis and localized supercooling fluctuations in large-scale molten salt systems. Therefore, this example establishes a dynamic control procedure based on real-time supersaturation feedback for the core steps of temperature-controlled dissolution and interface crystal pinning. This procedure defines the initial state of the molten salt system as follows: the matrix salt composition is KCl:NaCl:AlF3 = 40:45:15, the amount of calcium fluoride added as the interface pinning agent is 2.5 wt%, the total mass of the system is 500 kg, and the dispersion temperature is stabilized at 790℃. Under these conditions, the system monitors the changes in the conductivity of the molten salt in real time using an immersion conductivity probe. As a key process parameter indirectly characterizing the dissolution state and precipitation trend of calcium fluoride, the control system executes a cooling operation according to a preset cooling rate (8℃ / min) upon initiation of the cooling program. During this process, the system continuously collects the conductivity data of the molten salt and calculates its real-time rate of change (dκ / dt). When the temperature approaches the preset anchoring range (around 680℃), calcium fluoride begins to precipitate from the melt, causing a small but measurable abrupt change in the concentration of free ions in the molten salt, manifested as an inflection point on the conductivity rate of change curve. The inflection point determination logic uses a sliding time window algorithm to process the second-order difference of the real-time conductivity data. The inflection point is defined as the second derivative of conductivity with temperature change dκ / dt within three consecutive sampling periods of no more than 500 milliseconds. 2 κ / dT 2 The absolute value consistently exceeds 0.05 μS / (cm·℃) 2 At this point, the mathematical criterion eliminates the noise from mechanical stirring and liquid surface fluctuations. The system only responds to the sudden change signal of calcium fluoride phase transition ion concentration, triggering the isothermal anchoring procedure.

[0042] Once this inflection point signal is detected, and the corresponding real-time temperature T real With the melting point T of metallic aluminum m Satisfying 10℃≤T real -T m Under a supercooling window condition of ≤25℃, the control system immediately triggers the constant temperature anchoring mode, automatically adjusting the heating power to maintain the current temperature constant until the conductivity reading stabilizes again, indicating that the precipitation and interfacial adsorption processes of calcium fluoride have reached thermodynamic equilibrium. Only then does the system continue to execute the subsequent cooling and curing procedures. This dynamic control strategy based on real-time feedback of process parameters effectively eliminates process deviations caused by batch-to-batch raw material differences or ambient temperature fluctuations, ensuring that the sphericity and particle size distribution of each batch of aluminum powder products can stably fall within the optimal index range.

[0043] Example 5: In complex industrial application networks involving multiple raw material supply locations and cross-regional deployment, ensuring the robustness and consistency of technical solutions under different environmental boundary conditions is a core threshold for moving from the laboratory to large-scale commercial use. Therefore, this example constructs a standardized pre-deployment procedure for the critical engineering link of initial state calibration and environmental adaptive calibration. The core of this procedure lies in establishing a traceable baseline database. Before formally starting production or deployment, the system executes a fingerprinting procedure for raw material characteristics. For different batches of aluminum ingot raw materials, the content of trace impurity elements is determined using inductively coupled plasma mass spectrometry (ICP-MS), and the actual melting point deviation is determined by differential scanning calorimetry (DSC). These basic physicochemical parameters are input to the system's central control unit, and processed through internal... The system employs a compensation algorithm to automatically fine-tune the proportioning coefficient and dispersion temperature setpoint of the subsequent molten salt system to offset the thermodynamic potential energy differences caused by raw material fluctuations. The system then enters an environmental adaptive calibration phase. Considering that differences in altitude, air pressure, and ambient temperature at different deployment locations may have a nonlinear impact on the heat dissipation rate of the molten salt system, the procedure requires a thermal balance test under no-load conditions in the reactor. By recording the heating curve and natural cooling rate under specific heating power, the system calculates the heat loss coefficient under the current environment and corrects the PID parameters of the temperature control program accordingly. This pre-calibration step ensures that, under actual load operation, both the cooling rate from the dispersed state to the anchored state and the temperature stability during the isothermal anchoring phase are strictly locked within the preset process window, guaranteeing the accurate triggering and execution of the temperature control dissolution mechanism under any operating condition.

[0044] Example 6: In the system deployment for automotive power battery electrode slurry applications, due to the slight fluctuations in matrix salt composition between production batches and the drift in heat conduction efficiency caused by equipment aging, standard process parameters often cannot directly guarantee the consistency of aluminum powder particle size distribution. This example constructs a standardized offline calibration and adaptive parameter generation procedure to establish the optimal shear energy input parameters under different working conditions. This procedure defines the shear energy density index (SEI) as the core control variable, and the calculation formula is SEI=(τ·t) / V, where τ is the torque value output by the shearing device, t is the shearing time, and V is the total volume of the molten salt system. The physical quantity quantification unit in the shear energy density index (SEI) calculation model is defined as: shear torque τ is Newton-meter (N·m), shearing time is... The value is in minutes (min), and the total volume of the molten salt system is in liters (L). This index is used as a normalized dimensionless process control parameter. The value corresponds to the shear work equivalent borne by a unit volume of melt per unit time. It eliminates the difference in flow field magnification due to the geometric size of the reactor. The control system calculates the cumulative energy density by trapezoidal integral method based on the real-time collected torque data stream. When the deviation between the calculated value and the preset target particle size model value is less than 0.5%, it is considered that the shear dispersion step is completed.

[0045] Before formal production, a set of orthogonal experiments were conducted to establish the relationship between SEI and aluminum powder particle size D. 50 The characteristic correlation curves between them were determined. In the experiment, gradient shear rate and time combinations were set, torque data were collected in real time and the corresponding SEI values ​​were calculated. Simultaneously, laser particle size analysis was performed on each group of products. Based on the above experimental data, the system constructed a D-value using a linear regression algorithm. 50 The predictive model of f(SEI) is used to perform a single benchmark test after raw material replacement or equipment maintenance to measure the torque response under the current operating conditions. Based on this model, the system reverse-calculates the corrected shear rate and time parameters required to achieve the target particle size. This procedure transforms complex fluid dynamics variables into a single quantifiable control index, ensuring that the particle size control accuracy of the aluminum powder preparation process is always maintained within the tolerance range of ±0.2 micrometers even in non-ideal industrial environments, thus solving the problem of batch-to-batch quality fluctuations caused by equipment differences.

[0046] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A controllable preparation method for semiconductor-grade ultrafine spherical aluminum powder, characterized in that, Includes the following steps: A thermosensitive dissolution molten salt medium was constructed, and a composite molten salt consisting of a matrix salt and an interface pinning agent was prepared. The interface pinning agent was selected as calcium fluoride, and the amount added was limited to 1.5 wt% to 3.0 wt% of the total mass of the matrix salt. The composite molten salt was heated to a dispersion temperature of 780°C to 800°C to form a homogeneous melt. Shear dispersion is performed by adding metallic aluminum to a homogeneous melt under an inert atmosphere and at a dispersion temperature, and applying mechanical shear force to break the liquid aluminum into micron-sized droplets dispersed in the homogeneous melt. Temperature-controlled dissolution and interfacial crystal pinning were performed, mechanical shear force was stopped, and the system temperature was controlled to decrease from the dispersion temperature to the anchoring temperature range of 670℃ to 685℃ at a rate of 5℃ / min to 10℃ / min. The characteristic that the solubility of calcium fluoride decreases with decreasing temperature was used to drive in-situ precipitation from the homogeneous melt. The precipitated calcium fluoride nanocrystals were induced to migrate directionally and adsorb onto the surface of micron-sized droplets. A solid particle shell layer covering the micron-sized droplets was constructed above the solidification temperature of aluminum. The steric hindrance effect generated by the solid particle shell layer was used to block the fusion path between micron-sized droplets. By performing confined solidification and separation, the temperature is further reduced to below the melting point of metallic aluminum, allowing micron-sized droplets to complete phase transformation solidification within the geometric confinement of the solid particle shell, forming a mixture of solid aluminum powder and solid salt. The water-soluble salt components in the composite molten salt are then removed to obtain spherical aluminum powder. Furthermore, in the step of constructing the thermosensitive dissolution molten salt medium, the matrix salt is composed of potassium chloride, sodium chloride and aluminum fluoride, and the mass ratio of the three is limited to 40:45:

15. This specific ratio ensures that the density of the composite molten salt at the dispersion temperature is less than that of liquid aluminum, ensuring that the micron-sized droplets are in a suspended or slow settling state in the homogeneous melt, and providing a melt environment with specific ionic strength for the dissolution and precipitation of calcium fluoride. In the shear dispersion step, mechanical shear force is applied by setting the shear rate to 2800 rpm to 3500 rpm and the shear time is maintained at 15 minutes to 20 minutes. This shear condition, combined with the interfacial tension of the composite molten salt, controls the average particle size D50 of the micron-sized droplets to between 2 microns and 5 microns, and establishes the supersaturated potential energy of calcium fluoride relative to the surface of the micron-sized droplets in the homogeneous melt. During the temperature-controlled dissolution and interface crystal pinning steps, the anchoring temperature range T is... anchor With the melting point T of metallic aluminum m The following subcooling window relationship applies: 10℃≤T anchor -T m ≤25℃, where T anchor The control temperature for triggering the large-scale precipitation of calcium fluoride is T. m This is the standard melting point of metallic aluminum; this relationship is limited to the thermodynamic time window for the construction of solid particle shells under the premise that micron-sized droplets remain in a liquid state. The calcium fluoride used as the interface pinning agent has an initial particle size D50 of less than or equal to 10 micrometers and a purity of greater than or equal to 99.5%. This raw material specification ensures that the calcium fluoride can be completely dissociated and dissolved in the matrix salt during the heating to the dispersion temperature, avoiding undissolved coarse particles from becoming non-uniform nucleation cores and interfering with the subsequent in-situ growth of calcium fluoride nanocrystals on the surface of micron-sized droplets. In the temperature-controlled melting and interfacial crystal pinning steps, calcium fluoride nanocrystals precipitated in situ from the homogeneous melt have a particle size distribution between 50 nanometers and 200 nanometers. The adsorption coverage of these calcium fluoride nanocrystals on the surface of micron-sized droplets is determined by the amount of interfacial pinning agent added and the rate of decrease in system temperature. This results in a discontinuous but sufficient Pickering emulsion structure in the solid particle shell formed on the surface of the micron-sized droplets to generate a steric hindrance effect.

2. The controllable preparation method of semiconductor-grade ultrafine spherical aluminum powder according to claim 1, characterized in that, In the restricted curing and separation process, the operation of removing water-soluble salt components from the composite molten salt includes multi-stage countercurrent washing of the cured solid aluminum powder and solid salt mixture with deionized water. The washing process controls the water temperature at 40°C to 60°C. The trace amounts of calcium fluoride nanocrystals remaining on the surface of the spherical aluminum powder are used as in-situ precursors to induce the formation of a fluorinated aluminum oxide composite passivation layer with a thickness of 3 to 8 nanometers on the surface of the spherical aluminum powder in the water washing environment.

3. The controllable preparation method of semiconductor-grade ultrafine spherical aluminum powder according to claim 1, characterized in that, The inert atmosphere consists of high-purity nitrogen or argon, with the oxygen content controlled at less than 10 ppm. Throughout the shear dispersion, temperature-controlled dissolution, and interfacial crystal pinning processes, the gas pressure within the reaction system is maintained at a positive pressure of 0.1 MPa to 0.12 MPa to prevent external air from seeping in and causing premature oxidation of the surface of the micron-sized droplets, which would hinder the adsorption of calcium fluoride nanocrystals.

4. The controllable preparation method of semiconductor-grade ultrafine spherical aluminum powder according to claim 1, characterized in that, The method does not include any steps of using airflow nozzles or high-pressure gas atomization. The spherical shaping of micron-sized droplets is entirely driven by the isotropic hydrostatic pressure field provided by the composite molten salt and the interfacial tension constraint of the solid particle shell. The sphericity of the prepared spherical aluminum powder is not less than 0.95.

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