A method for preparing high-uniformity silver-coated conductive material powder by magnetron sputtering dry method

Abstract

The present invention relates to the technical field of magnetron sputtering, and in particular to a method for preparing highly uniform silver-coated conductive material powder by a magnetron sputtering dry process. The method adopts a magnetron sputtering device based on an ultrasonic-electromagnetic suspension composite dispersion system, comprising: placing an appropriate amount of conductive material powder having a particle size D50 of 0.4-6.0 μm and having been surface treated on a tooling plate having a gradient aperture structure; controlling the ultrasonic operating frequency to 20-100 kHz and the ultrasonic power density to 1-5 W / cm 2 When the peak velocity of the generated cavitation microjet reaches ≥160m / s, a 0.1-0.5T rotating magnetic field is generated by three-phase AC power to drive the conductive material powder to spin at 80-200rpm. The sputtering power density of the cathode target is set to 3-10W / cm 2 The surface temperature of the tooling plate is controlled to ≤120°C, and the deposition process is performed for 1-3 hours, so that the silver layer thickness reaches ≥50nm. This invention utilizes core technologies such as ultrasonic-electromagnetic levitation multi-field coupling dispersion, dynamic magnetic field control of the sputtering path, and gradient aperture tooling plate design to achieve nanometer-scale controllable silver layer thickness, achieve breakthrough coating uniformity, and achieve compatibility with large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetron sputtering, and in particular to a method for preparing highly uniform silver-coated conductive material powder by a magnetron sputtering dry process. Background Art

[0002] Currently, silver-coated copper powder is the core conductive material of the silver paste on the front of photovoltaic cells, and its preparation process mainly relies on wet chemical plating and electroplating technology. Among them, the chemical plating process generally uses silver nitrate as the main salt and formaldehyde as the reducing agent to deposit a silver layer on the surface of the copper powder. Although this method is mature, its core defects are significant: First, the widespread use of cyanide complexing agents (such as NaAg(CN)2) leads to the discharge of 5-8 tons of cyanide-containing wastewater for the production of a single ton of powder, with a treatment cost of up to 3,000-5,000 yuan / ton, and there are serious environmental risks; secondly, the non-uniformity of the reduction reaction triggers the growth of dendrites in the silver layer, resulting in a porosity of up to 5-8% (SEM test data) and an interface bonding strength of less than 3N / mm 2 (ASTM D4541 standard), which directly leads to micro cracks in the paste after sintering, reducing the conductivity of the electrode. Although the other mainstream technology, electroplating, improves the density of the silver layer through pulse power supply, its Faraday efficiency is only 85%, and the coating uniformity of submicron copper cores (D50 < 1μm) is extremely poor. The coefficient of variation of particle size distribution (CV value) exceeds 25%, which cannot meet the high-precision printing requirements of HJT cells for fine grid line widths ≤ 28μm. What is more serious is that the control accuracy of the silver layer thickness in the wet process is limited to ±50nm. In order to balance resistivity and cost, the addition ratio of silver-coated copper powder in photovoltaic silver paste is suppressed to less than 30% (corresponding to square resistance > 4.5μΩ·cm), which seriously restricts the cost reduction space of precious metals.

[0003] As an alternative path, the magnetron sputtering dry process can theoretically avoid the contamination defects of the wet method and achieve nanoscale control of the silver layer. However, existing dry-process technology faces three major obstacles to industrialization: First, in a vacuum environment, the powder is affected by van der Waals forces (10-100nN / particle) and electrostatic forces (>1μN / particle), resulting in uncontrollable agglomeration, resulting in a coating coverage of less than 80% (laser particle size analysis data) and a sudden increase in resistivity caused by the loss of local silver layers. Second, the three-dimensional powder accumulation has a significant shielding effect on the plasma, resulting in a target material utilization rate of only 10-15% (theoretical value of 30% for a planar target), and 30-40% of the sputtering power is converted into powder heat load, causing local temperatures to exceed 300°C (infrared thermal imaging data), resulting in copper core recrystallization and particle size growth of more than 50%. Third, during equipment scale-up, the nonlinear characteristics of the cavity flow field and plasma distribution cause the deposition uniformity to deteriorate sharply with the expansion of size. The deposition rate in the edge area of ​​a 1m diameter cavity is 40% lower than that in the center, limiting the production capacity of a single furnace to less than 10kg, which is difficult to meet the needs of 1,000-ton production lines.

[0004] At the same time, the rapid evolution of photovoltaic cell technology is placing even more stringent demands on front-side silver pastes. Heterojunction (HJT) cells, due to their use of an amorphous silicon layer, require a low-temperature sintering process (≤250°C, compared to 800°C for traditional PERC cells). This requires the organic carrier and silver layer in the silver paste to form a dense conductive network at low temperatures. The double-sided passivation structure of TOPCon cells requires a fine gate electrode with a high aspect ratio (line width ≤28μm, aspect ratio ≥0.4). This places extreme demands on the morphological uniformity of the silver-coated copper powder (sphericity >0.95) and the continuity of the silver layer (porosity <1%). Existing wet processes, due to defects and insufficient uniformity in the silver layer, result in a sharp increase in square resistance to over 5μΩ·cm when the addition ratio exceeds 30%. This forces the industry to rely on high-silver content pastes (silver powder accounts for 90-92%), severely hindering the reduction of photovoltaic LCOE (levelized cost of electricity). Summary of the Invention

[0005] To address at least one of the above-mentioned issues, the present invention provides a method for preparing highly uniform silver-coated conductive material powders by a dry magnetron sputtering process. By utilizing core technologies such as ultrasonic-electromagnetic levitation multi-field coupling dispersion, dynamic magnetic field regulation of the sputtering path, and gradient aperture tooling disk design, the present invention achieves nanoscale controllable silver layer thickness, breakthroughs in coating uniformity, and compatibility with large-scale production.

[0006] The present invention provides a method for preparing a highly uniform silver-coated conductive material powder by a dry magnetron sputtering method. The method adopts a magnetron sputtering device based on an ultrasonic-electromagnetic suspension composite dispersion system; the magnetron sputtering device includes a magnetron sputtering furnace body and a tooling plate, an ultrasonic vibrator array, a dynamic magnetic field control module and a planar rectangular cathode arranged in the magnetron sputtering furnace body; the tooling plate has through holes with a gradient aperture structure on the surface, and the aperture of the through holes in the central area is 8-15 μm and the aperture density is 1100-1400 holes / cm 2 The through holes in the edge area have a pore size of 40-60 μm and a pore density of 150-300 pores / cm 2 The ultrasonic vibrator array is distributed on the bottom of the tooling disk, the dynamic magnetic field control module is arranged on the periphery of the tooling disk, and the planar rectangular cathode is arranged on the top of the magnetron sputtering furnace body;

[0007] The method specifically comprises the following steps:

[0008] Powder pretreatment: Select conductive material powder with a particle size D50 of 0.4-6.0 μm, remove the surface oxide layer and / or perform surface activation treatment, and take an appropriate amount of surface-treated conductive material powder and place it on the tooling tray;

[0009] Ultrasonic-electromagnetic levitation: Control the ultrasonic operating frequency to 20-100kHz and the ultrasonic power density to 1-5W / cm 2When the peak velocity of the generated cavitation microjet is ≥160m / s, the sputtering power density of the cathode target is set to 6-15W / cm 2 , a three-phase alternating current is applied to generate a 0.1-0.5T rotating magnetic field to drive the conductive material powder to spin at 80-200rpm;

[0010] Silver layer deposition: Control the surface temperature of the tooling plate to ≤120° C., perform deposition treatment for 1-3 hours, and make the silver layer thickness ≥50 nm to obtain the highly uniform silver-coated conductive material powder.

[0011] Optionally, the gradient pore size structure on the tooling disk is 8-15 μm in the central area and 1100-1400 pores / cm 2 The pore size in the edge area is 40-60 μm and the pore density is 150-300 pores / cm 2 The total loading amount of the conductive material powder is 10-15 kg, and the stacking thickness is 2-20 mm.

[0012] Optionally, the sputtering power density of the cathode target is 6-8 W / cm 2 , Edge target 3-10W / cm 2 .

[0013] Optionally, the cathode target is silver with a purity of ≥99.995%, the target is tilted relative to the horizontal plane with an inclination angle of 0-15°, and the center of the target surface is 120-320 mm away from the axis of the tooling disk.

[0014] Optionally, the conductive material powder includes one or more of copper powder, nickel powder, aluminum powder, graphite powder, and carbon nanotube powder.

[0015] Optionally, when the conductive material powder is copper powder, the ultrasonic operating frequency of the center area of ​​the tooling plate is 100 kHz, and the ultrasonic power density is 5 W / cm 2 The ultrasonic operating frequency of the edge area of ​​the tooling plate is 60kHz, and the ultrasonic power density is 1W / cm 2 .

[0016] Optionally, when the conductive material powder is copper powder, the sputtering power density of the cathode target is 8W / cm 2 , edge target 10W / cm 2 .

[0017] Optionally, when the conductive material powder is nickel powder, the entire area of ​​the tooling plate is activated with an ultrasonic operating frequency of 60 kHz and an ultrasonic power density of 3 W / cm 2 .

[0018] Optionally, when the conductive material powder is nickel powder, the sputtering power density of the cathode target is 6W / cm2 , edge target 10W / cm 2 .

[0019] Optionally, when the conductive material powder is nickel powder, the surface temperature of the tooling plate is controlled to be ≤100°C.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. Precise control of micro-morphology: Through the coordinated regulation of ultrasonic frequency (20-100kHz) and magnetic field intensity (0.1-0.5T), the silver layer thickness deviation can be reduced to less than ±5nm;

[0022] 2. Breakthrough in coating uniformity: Optimization of the rotating magnetic field (80-200rpm) and the airflow penetration rate of the porous tooling disk to achieve a CV value of <5%;

[0023] 3. Controllable surface resistivity: strictly control the sputtering power (3-10W / cm 2 ) Matching the appropriate silver layer deposition temperature to make the resistivity fluctuation ≤±0.2μΩ·cm;

[0024] 4. Industrial compatibility: Suitable for modular chamber design (single chamber 12kg, 6 chambers in parallel 72kg), thickness unevenness ≤±2.5%.

[0025] The breakthrough of the present invention is:

[0026] Compared to conventional techniques that disperse powders through jets to suspend them for coating, stir the powders slightly through vibration, or disperse them through pure vibration, the present invention uses a vibration-magnetic field to drive the powders to spin, effectively avoiding insufficient film thickness in the coating area due to uneven sputtering during the stirring process. Compared to methods that vibrate over a large area (such as an entire conveyor belt), the present invention only requires vibrating the tooling plate, which is lighter, more efficient, and more portable. It also effectively avoids vacuum leaks caused by large-scale vibration.

[0027] In addition, due to the structural characteristics of the powder, the difficulty of powder coating is much higher than that of flat coating. Conventional flat coating methods are not able to achieve uniform coating, so there are difficulties in converting the two methods in actual operation. To this end, the present invention can ensure uniform coating of the film on the surface of various powders through the coordinated control of multiple parameters of magnetic field, flow field and acoustic field, and for the first time achieve the coating of 10kg-level conductive material powder in 10 -5 Pa vacuum stable suspension, the conductive material powder spatial distribution density reaches 10 4 -10 5 Particles / cm 3, coverage rate > 95%, D50 particle size distribution coefficient of variation (CV value) < 5%, which is more than 3 times higher than the traditional vibration method. Specifically, the thickness unevenness is compressed from ± 20% to ± 3%, the target material utilization rate exceeds 45%, and the energy consumption per unit production capacity is reduced to below 8kWh / kg. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure is a schematic structural diagram of a magnetron sputtering furnace used in the present invention to prepare a highly uniform silver-coated conductive material powder.

[0029] Description of reference numerals:

[0030] 1. Magnetron sputtering furnace; 2. Tooling tray; 3. Ultrasonic vibrator array; 4. Dynamic magnetic field control module; 5. Cathode target. DETAILED DESCRIPTION

[0031] The present invention addresses the core issues of environmental pollution, silver layer defects, and poor uniformity in the wet-process silver-coated copper powder preparation process, and combines the potential advantages and industrial bottlenecks of the magnetron sputtering dry process to propose a method for preparing highly uniform silver-coated conductive material powder by magnetron sputtering dry process. The method is based on a specific magnetron sputtering furnace and takes ultrasonic-electromagnetic levitation multi-field coupling dispersion technology as its core. Through a precisely designed gradient aperture tooling plate, dynamic magnetic field control of the sputtering path, and a modular cavity structure, the method achieves nanoscale controllable silver layer thickness, breakthroughs in coating uniformity, and compatibility with large-scale production.

[0032] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, the magnetron sputtering furnace used in the present invention is described in detail below with reference to the accompanying drawings. The accompanying drawings of the present invention provide a coordinate system XYZ, wherein the positive direction of the X-axis represents the left, the negative direction of the X-axis represents the right, the positive direction of the Y-axis represents the front, the negative direction of the Y-axis represents the rear, and the positive direction of the Z-axis represents the top, while the negative direction of the Z-axis represents the bottom.

[0033] See Figure 1 The magnetron sputtering furnace includes a magnetron sputtering furnace body 1 and a tooling plate 2, an ultrasonic vibrator array 3, a dynamic magnetic field control module 4 and a cathode target 5 installed in the magnetron sputtering furnace body 1. The magnetron sputtering furnace body 1 is provided with a cavity with a radial length (length and width) of 1000 mm and a height of 800 mm, which is controlled by an independent vacuum lock (ultimate vacuum degree 5×10 - 5Pa, pumping time ≤ 30min) to maintain a vacuum environment in the cavity. The tooling disk 2 is fixedly installed in the middle of the magnetron sputtering furnace body 1. It is a porous ceramic disk with a diameter of 650mm and a gradient aperture structure. The ultrasonic vibrator array 3 uses 12 groups of high-frequency piezoelectric ultrasonic vibrator arrays evenly installed on the bottom of the tooling disk 2. The dynamic magnetic field control module 4 is arranged on the periphery of the tooling disk 2, specifically composed of 24 groups of Helmholtz coils (coil inner diameter 700mm, wire diameter 5mm, number of turns 120), divided into upper and lower layers (spacing 150mm) to form an axially symmetric magnetic field. The cathode target material 5 is fixedly arranged on the top of the magnetron sputtering furnace body 1 and is located 10-50mm above the tooling disk 2.

[0034] During the fabrication process, the present invention requires controlling the surface temperature of the tooling tray 2. Therefore, a dual-circuit thermal management mechanism is integrated into the magnetron sputtering furnace: a microchannel liquid nitrogen cooling interlayer and a thermoelectric cooling plate. The microchannel liquid nitrogen cooling interlayer is located on the inner wall of the magnetron sputtering furnace 1, and the thermoelectric cooling plate is embedded in the bottom of the tooling tray 2. Combined with infrared temperature measurement feedback (accuracy of ±1°C), dynamic temperature control of local hotspots (temperature difference <3°C) is achieved.

[0035] The magnetron sputtering furnace is a standalone module that can be used alone or in parallel, achieving a modular, chamber-based design for the magnetron sputtering system. Taking a single module processing 12 kg or more of powder (3 mm thick) as an example, six chambers in parallel can achieve a single batch production capacity of 72 kg or more, with a thickness non-uniformity of ≤ ±2.5% (185 nm ± 4 nm in the center, 180 nm ± 6 nm in the edge), a five-fold increase in production capacity compared to traditional single-chamber equipment.

[0036] Based on the above magnetron sputtering furnace, the present invention discloses a method for preparing highly uniform silver-coated conductive material powder by a dry magnetron sputtering method, comprising the following steps:

[0037] 1. Powder pretreatment:

[0038] Conductive material powder with a particle size D50 of 0.4-6.0 μm is selected, and the surface oxide layer is removed and / or the surface is activated before use. The relatively small particle size range helps to improve the uniformity of the particle size distribution. Removal of the surface oxide layer and surface activation can reduce impurity incorporation and improve the stability of the silver layer after deposition.

[0039] Take an appropriate amount of surface-treated conductive material powder and place it on a tooling plate 2 with a gradient pore structure; wherein the gradient pore structure on the tooling plate 2 is formed by laser etching, specifically with a central area pore size of 8-15μm and a pore density of 1100-1400 pores / cm 2 The pore size in the edge area is 40-60 μm and the pore density is 150-300 pores / cm 2The tooling tray 2 is divided into a central area and an edge area at a diameter of 450 mm. The total loading capacity of the conductive material powder is 10-15 kg, and the stacking thickness is 2-20 mm. Therefore, the aperture size (8-60 μm) of the through-holes on the tooling tray 2 is optimized based on the D50 of the conductive material powder. This allows airflow to penetrate and generate lift while effectively reducing the loss of the conductive material powder. The gradient aperture structure also achieves a dynamic balance between airflow permeability and the conductive material powder loading capacity, ensuring stable distribution of the conductive material powder in a vacuum environment.

[0040] 2. Ultrasonic-electromagnetic levitation:

[0041] Control the operating frequency of the ultrasonic vibrator array 3 to 20-100kHz and the power density to 1-5W / cm 2 , until the velocity of the generated cavitation microjet reaches ≥160m / s. The cavitation microjet can effectively break up the powder agglomerates. At the same time, the transient high temperature and high pressure (6000K, 1000atm) during cavitation collapse helps to clean the oxides on the surface of the metal core, reducing the oxygen content from 800ppm to below 50ppm.

[0042] The Helmholtz coil in the dynamic magnetic field control module 4 is connected to a three-phase alternating current (frequency 0.1-10Hz adjustable, current peak 200A), and the current phase difference is adjusted in real time. Generate a rotating magnetic field (0.1-0.5T) to make the conductive material powder spin at 80-200rpm driven by the Coriolis force, ensuring that silver atoms are uniformly deposited along the surface normal of the conductive material powder (incident angle deviation <5°);

[0043] Set the sputtering power density of cathode target 5 to 6-15W / cm 2 . The cathode target material 5 is silver with a purity of ≥99.995%, the target surface inclination angle (the inclination angle relative to the horizontal plane) is 0-15°, and the center of the target surface is 120-320mm away from the axis of the tooling disk 2. The number of cathode targets 5 arranged can be adjusted according to the dosage. In the present invention, four are arranged, each with a planar rectangular structure of 850mm×120mm in size, arranged in a ring with an inclination angle of 15° (the center of the target surface is 320mm away from the axis of the tooling disk 2). Furthermore, the sputtering power density can be optimized according to the plasma distribution (center target 6-8W / cm 2 , Edge target 3-10W / cm 2 ), a closed magnetic field is generated by a magnetron (the magnetic flux density on the target surface is 600-800Gs), which confines the electrons near the target surface to increase the ionization rate (Ar + Density ≥5×10 13 cm -3 ).

[0044] 3. Silver layer deposition:

[0045] During the redeposition process, a microchannel liquid nitrogen cooling interlayer (channel diameter 2mm, flow rate 5-8L / min) and a thermoelectric refrigeration plate (TEC1-12706, cooling power 60W) are used to control the surface temperature of the tooling plate 2 to ≤120°C (180°C lower than when there is no cooling), inhibiting the particle size growth caused by metal core recrystallization (D50 fluctuation <0.5%). Combined with infrared temperature measurement feedback (accuracy ±1°C), dynamic temperature control of local hotspots is achieved (temperature difference <3°C). The deposition process time is 1.5-3h, and the silver layer thickness is ≥50nm, thus obtaining a highly uniform silver-coated conductive material powder.

[0046] In order to further demonstrate the feasibility of the method of the present invention, the present invention is described in detail below with reference to specific embodiments.

[0047] Example 1

[0048] A photovoltaic silver paste is prepared by silver-coated copper powder, and the preparation method comprises the following steps:

[0049] 1. Powder pretreatment:

[0050] Spherical copper powder with a D50 of 0.8 μm (purity ≥ 99.9%) was selected, cleaned with hydrofluoric acid to remove the surface oxide layer (oxygen content < 50 ppm), and then dried and deposited in the center of a porous ceramic tooling plate 2 (diameter 650 mm) to a thickness of 3 mm (total loading capacity 12 kg).

[0051] 2. Ultrasonic-electromagnetic levitation:

[0052] Ultrasonic vibrator array 3: activate the four groups of vibrators in the central area (frequency 100kHz, power 5W / cm 2 ), eight groups of oscillators in the edge area (frequency 60kHz, power 1W / cm 2 ), cavitation microjet velocity 160m / s;

[0053] Dynamic magnetic field control module 4: three-phase AC power (frequency 2Hz, current 200A, phase difference ), generating a 0.3T rotating magnetic field to drive the copper powder to spin at 120 rpm;

[0054] Cathode target 5: Open four sets of cathode target 5 (power density: center target 8W / cm 2 , edge target 10W / cm 2 ), argon working pressure 0.3Pa, substrate bias -50V;

[0055] 3. Silver layer deposition (dynamic deposition and thermal management):

[0056] During the sputtering process, the microchannel liquid nitrogen cooling system maintained a flow rate of 5L / min, and the surface temperature of the tooling plate 2 was maintained at ≤115°C; the thermoelectric cooling chip compensated for local hot spots in real time (temperature difference <3°C);

[0057] The deposition time was 120 min, the silver layer thickness was 180 ± 5 nm (weight gain 15%), and the porosity was 0.7%;

[0058] 4. Performance test:

[0059] The resistivity of silver-coated copper powder is 3.1μΩ·cm. When added to photovoltaic silver paste (mass ratio 48%), HJT cell fine grid (line width 28μm±1.2μm) is printed, the square resistance is 3.2μΩ·cm, the photoelectric conversion efficiency is 26.45%, and the single-chip silver consumption is 48mg.

[0060] Example 2

[0061] A photovoltaic silver paste is prepared by silver-coated copper powder, and the preparation method comprises the following steps:

[0062] 1. Powder pretreatment:

[0063] Spherical copper powder with a D50 of 0.4 μm (purity ≥ 99.9%) was selected, cleaned with hydrofluoric acid to remove the surface oxide layer (oxygen content < 50 ppm), and then dried and deposited in the center of a porous ceramic tooling plate 2 (diameter 650 mm) to a thickness of 2 mm (total loading capacity 10 kg).

[0064] 2. Ultrasonic-electromagnetic levitation:

[0065] Ultrasonic vibrator array 3: activate the four groups of vibrators in the central area (frequency 100kHz, power 5W / cm 2 ), eight groups of oscillators in the edge area (frequency 60kHz, power 1W / cm 2 ), cavitation microjet velocity 160m / s;

[0066] Dynamic magnetic field control module 4: three-phase AC power (frequency 2Hz, current 200A, phase difference ), generating a 0.1T rotating magnetic field to drive the copper powder to spin at 200 rpm;

[0067] Cathode target 5: open four sets of target 5 (power density: center target 8W / cm 2 , edge target 3W / cm 2 ), argon working pressure 0.3Pa, substrate bias -50V;

[0068] 3. Silver layer deposition (dynamic deposition and thermal management):

[0069] During the sputtering process, the microchannel liquid nitrogen cooling system maintained a flow rate of 5L / min, and the surface temperature of the tooling plate 2 was maintained at ≤115°C; the thermoelectric cooling chip compensated for local hot spots in real time (temperature difference <3°C);

[0070] The deposition time was 60 minutes, the silver layer thickness was 50 ± 5 nm (weight gain 5%), and the porosity was 0.9%;

[0071] 4. Performance test:

[0072] The resistivity of silver-coated copper powder is 3.0μΩ·cm. When added to photovoltaic silver paste (mass ratio 45%), HJT cell fine grid (line width 28μm±1.2μm) is printed, the square resistance is 3.1μΩ·cm, the photoelectric conversion efficiency is 23.27%, and the single-chip silver consumption is 43mg.

[0073] Example 3

[0074] A photovoltaic silver paste is prepared by silver-coated copper powder, and the preparation method comprises the following steps:

[0075] 1. Powder pretreatment:

[0076] Spherical copper powder with a D50 of 6.0 μm (purity ≥ 99.9%) was selected, cleaned with hydrofluoric acid to remove the surface oxide layer (oxygen content < 50 ppm), and then dried and deposited in the center of a porous ceramic tooling plate 2 (diameter 650 mm) to a thickness of 10 mm (total loading capacity 15 kg).

[0077] 2. Ultrasonic-electromagnetic levitation:

[0078] Ultrasonic vibrator array 3: activate the four groups of vibrators in the central area (frequency 100kHz, power 5W / cm 2 ), eight groups of oscillators in the edge area (frequency 60kHz, power 1W / cm 2 ), cavitation microjet velocity 160m / s;

[0079] Dynamic magnetic field control module 4: three-phase AC power (frequency 2Hz, current 200A, phase difference ), generating a 0.5T rotating magnetic field to drive the copper powder to spin at 100 rpm;

[0080] Cathode target 5: Open four sets of cathode target 5 (power density: center target 8W / cm 2 , edge target 6W / cm 2 ), argon working pressure 0.3Pa, substrate bias -50V;

[0081] 3. Silver layer deposition (dynamic deposition and thermal management):

[0082] During the sputtering process, the microchannel liquid nitrogen cooling system maintained a flow rate of 5L / min, and the surface temperature of the tooling plate 2 was maintained at ≤115°C; the thermoelectric cooling chip compensated for local hot spots in real time (temperature difference <3°C);

[0083] The deposition time was 180 min, the silver layer thickness was 200 ± 5 nm (weight gain 17%), and the porosity was 0.6%;

[0084] 4. Performance test:

[0085] The resistivity of silver-coated copper powder is 3.2μΩ·cm. When added to photovoltaic silver paste (mass ratio 50%), HJT cell fine grid (line width 28μm±1.2μm) is printed, the square resistance is 3.3μΩ·cm, the photoelectric conversion efficiency is 27.73%, and the single-chip silver consumption is 51mg.

[0086] Example 4

[0087] A photovoltaic silver paste is prepared by silver-coated copper powder, and the preparation method comprises the following steps:

[0088] 1. Powder pretreatment:

[0089] Spherical copper powder with a D50 of 0.8 μm (purity ≥ 99.9%) was selected, cleaned with hydrofluoric acid to remove the surface oxide layer (oxygen content < 50 ppm), and then dried and deposited in the center of a porous ceramic tooling plate 2 (diameter 650 mm) to a thickness of 3 mm (total loading capacity 12 kg).

[0090] 2. Ultrasonic-electromagnetic levitation:

[0091] Ultrasonic vibrator array 3: activate the four groups of vibrators in the central area (frequency 80kHz, power 5W / cm 2 ), eight groups of oscillators in the edge area (frequency 20kHz, power 2W / cm 2 ), cavitation microjet velocity 170m / s;

[0092] Dynamic magnetic field control module 4: three-phase AC power (frequency 2Hz, current 200A, phase difference ), generating a 0.3T rotating magnetic field to drive the copper powder to spin at 120 rpm;

[0093] Cathode target 5: Open four sets of cathode target 5 (power density: center target 8W / cm 2 , edge target 8W / cm 2 ), argon working pressure 0.3Pa, substrate bias -50V;

[0094] 3. Silver layer deposition (dynamic deposition and thermal management):

[0095] During the sputtering process, the microchannel liquid nitrogen cooling system maintained a flow rate of 5L / min, and the surface temperature of the tooling plate 2 was maintained at ≤115°C; the thermoelectric cooling chip compensated for local hot spots in real time (temperature difference <3°C);

[0096] The deposition time was 120 min, the silver layer thickness was 140 ± 5 nm (weight gain 15%), and the porosity was 0.7%;

[0097] 4. Performance test:

[0098] The resistivity of silver-coated copper powder is 3.2μΩ·cm. When added to photovoltaic silver paste (mass ratio 48%), HJT cell fine grid (line width 28μm±1.2μm) is printed, the square resistance is 3.3μΩ·cm, the photoelectric conversion efficiency is 27.05%, and the single-chip silver consumption is 50mg.

[0099] Example 5

[0100] A silver-coated nickel powder is prepared for MLCC electrodes, and the preparation method comprises the following steps:

[0101] 1. Powder pretreatment:

[0102] Nickel powder with D50=2.5μm flakes (aspect ratio 3:1) was selected and activated by plasma (power 500W, Ar / H2=4:1) to enhance the surface activity. The loading amount was 10kg (bulk density 2.5g / cm 3 , the stacking thickness is about 20 mm);

[0103] 2. Ultrasonic-electromagnetic levitation:

[0104] Ultrasonic vibrator array 3: 60kHz intermediate frequency (power 3W / cm2) is enabled in the entire area 2 ) to avoid damage to the flaky powder structure;

[0105] Dynamic magnetic field control module 4: lower the magnetic field intensity to 0.2T (frequency 5Hz, current 150A), and spin the powder at 80rpm to ensure normal deposition on the flake surface;

[0106] Cathode target 5: Edge target power increased to 10W / cm 2 (Center target 6W / cm 2 ), substrate bias -30 V, argon pressure 0.5 Pa;

[0107] 3. Silver layer deposition (gradient deposition and interface strengthening):

[0108] Deposition was performed in two stages: the first 60 minutes were at low power (6 W / cm 2 ) to form a 50nm silver seed layer; after 60 minutes of high power (10W / cm 2 ) thickened to 100 nm, and the thickness of the interface transition zone was <5 nm;

[0109] Liquid nitrogen system temperature control ≤ 100 ℃, inhibit nickel diffusion (interface resistance ≤ 0.8mΩ·cm 2 );

[0110] 4. Performance test:

[0111] Silver-coated nickel powder is sintered at 950°C (N2 / H2 atmosphere), and the silver layer is continuous without cracks. It is suitable for the inner electrode of 01005 type MLCC (line width 3μm±0.3μm), with a capacity deviation of ±2.8% and a resistance drift of <5% during high-temperature storage life (150°C / 1000h).

[0112] In order to intuitively understand the technical effects of Examples 1-5, the present invention summarizes the above technical effects, see Table 1 below for details.

[0113] Table 1 Comparison of technical effects of Examples 1-5

[0114]

[0115]

[0116] As can be seen from Table 1 above, the magnetron sputtering dry method for preparing highly uniform silver-coated conductive material powders of the present invention has achieved breakthrough applications in the field of photovoltaic silver paste and in the field of MLCC internal electrodes.

[0117] Examples 1-4 use spherical copper core powder, with an addition ratio of 45-50%, and a slurry resistivity of 3.1-3.2μΩ·cm (pure silver paste benchmark 2.5μΩ·cm), which is suitable for the HJT cell fine grid 28μm±1.2μm line width printing requirements, with a photoelectric conversion efficiency loss of less than 0.3%, and a single-piece silver consumption reduced to 48mg (a 52% cost reduction). Compared with the wet process, the present invention completely eliminates cyanide pollution, and a single 1,000-ton production line can reduce wastewater emissions by 1.2 million tons per year and reduce silver use by 500 tons (worth approximately 3 billion yuan). At the same time, it supports the production of 10GW HJT modules, equivalent to reducing carbon dioxide emissions by 1.8 million tons.

[0118] Example 5: By flexibly adjusting the process parameters (such as magnetic field frequency 0.1-10 Hz, ultrasonic power distribution 1-5 W / cm 2 ), this technology can be extended to MLCC electrode silver-coated nickel powder (interface resistance ≤ 0.8mΩ·cm 2 ) and the preparation of high-precision powders (particle size CV value <3%) for 5G RF devices, forming a precious metal cost reduction technology system covering the entire scenario of electronic materials.

[0119] In addition to the above-mentioned silver-coated copper powder for photovoltaic silver paste and silver-coated nickel powder for MLCC electrodes, the conductive material powder in the silver-coated conductive material powder of the present invention can also be aluminum powder, graphite powder, carbon nanotube powder and alloy powder thereof to further meet the industrial needs of the electronic materials industry.

[0120] In order to facilitate further comparison of the differences between the present invention and the traditional process, the technical indicators of the present invention are quantified, as shown in Table 2 below.

[0121] Table 2 Quantitative technical indicators of traditional process and the present invention

[0122]

[0123]

[0124] In summary, the present invention aims to solve the defects of traditional wet process (chemical plating, electroplating) such as environmental pollution, high porosity of silver layer (> 5%) and poor uniformity (CV> 20%). The present invention realizes the 10kg level conductive material powder in 10 -5 Pa vacuum stable suspension, the conductive material powder spatial distribution density reaches 10 4 -10 5 Particles / cm 3 , coverage > 95%, D50 particle size distribution coefficient of variation (CV value) < 5%, which is more than 3 times higher than the traditional vibration method. Specifically, the unevenness of the silver layer thickness is compressed from ± 20% to ± 3%, the silver layer thickness is controllable at the nanometer level (≥ 50nm), the porosity is < 1%, and the surface resistivity is ≤ 3.5μΩ·cm. In addition, the target material utilization rate exceeds 45%, and the energy consumption per unit production capacity is reduced to below 8kWh / kg, providing an efficient and environmentally friendly precious metal cost reduction path for the electronic materials industry.

[0125] In the description of the present disclosure, it should be understood that the terms "center", "edge", "thickness", "up", "down", "top", "bottom", "inside", "outside", "axial", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present disclosure.

[0126] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for preparing highly uniform silver-coated conductive material powder by dry magnetron sputtering, characterized in that: The invention adopts a magnetron sputtering device based on an ultrasonic-electromagnetic suspension composite dispersion system; the magnetron sputtering device comprises a magnetron sputtering furnace body (1) and a tooling disk (2), an ultrasonic vibrator array (3), a dynamic magnetic field control module (4) and a cathode target material (5) arranged in the magnetron sputtering furnace body (1); the tooling disk (2) has through holes with a gradient aperture structure on its surface, and the aperture of the through holes in the central area is 8-15 μm and the aperture density is 1100-1400 holes / cm 2 The through holes in the edge area have a pore size of 40-60 μm and a pore density of 150-300 pores / cm 2 The ultrasonic vibrator array (3) is distributed on the bottom of the tooling disk (2), the dynamic magnetic field control module (4) is arranged on the periphery of the tooling disk (2), and the cathode target (5) is arranged on the top of the magnetron sputtering furnace (1). The cathode target (5) is silver with a purity of ≥99.995%. The target is tilted relative to the horizontal plane with an inclination angle of 0-15°, and the center of the target surface is 120-320 mm away from the axis of the tooling disk. The method comprises the following steps: Powder pretreatment: selecting conductive material powder with a particle size D50 of 0.4-6.0 μm, removing the surface oxide layer and / or performing surface activation treatment, taking an appropriate amount of the surface-treated conductive material powder and placing it on the tooling plate (2), the total loading amount of the conductive material powder being 10-15 kg, and the stacking thickness being 2-20 mm; Ultrasonic-electromagnetic levitation: controlling the ultrasonic operating frequency to 20-100kHz and the ultrasonic power density to 1-5W / cm² until the generated cavitation microjet velocity peak value is ≥160m / s, passing three-phase alternating current to generate a 0.1-0.5T rotating magnetic field to drive the conductive material powder to spin at 80-200rpm, and setting the sputtering power density of the cathode target (5) to 6-8W / cm² for the central target and 3-10W / cm² for the edge target; Silver layer deposition: the surface temperature of the tooling plate (2) is controlled to be ≤120° C., and the deposition process is performed for 1-3 hours, so that the thickness of the silver layer reaches ≥50 nm, thereby obtaining the highly uniform silver-coated conductive material powder.

2. The method for preparing high-uniformity silver-coated conductive material powder by magnetron sputtering dry method according to claim 1, characterized in that: The conductive material powder includes one or more of copper powder, nickel powder, aluminum powder, graphite powder, and carbon nanotube powder.

3. The method for preparing high-uniformity silver-coated conductive material powder by magnetron sputtering dry method according to claim 2, characterized in that: When the conductive material powder is copper powder, the ultrasonic operating frequency of the center area of ​​the tooling disk (2) is 100 kHz, and the ultrasonic power density is 5 W / cm²; the ultrasonic operating frequency of the edge area of ​​the tooling disk (2) is 60 kHz, and the ultrasonic power density is 1 W / cm².

4. The method for preparing high-uniformity silver-coated conductive material powder by magnetron sputtering dry process according to claim 3, characterized in that: When the conductive material powder is copper powder, the sputtering power density of the cathode target (5) is 8 W / cm² for the central target and 10 W / cm² for the edge target.

5. The method for preparing high-uniformity silver-coated conductive material powder by dry magnetron sputtering according to claim 2, characterized in that: When the conductive material powder is nickel powder, the entire area of ​​the tooling plate (2) is activated at an ultrasonic operating frequency of 60 kHz, and the ultrasonic power density is 3 W / cm².

6. The method for preparing high-uniformity silver-coated conductive material powder by dry magnetron sputtering according to claim 5, characterized in that: When the conductive material powder is nickel powder, the sputtering power density of the cathode target (5) is 6 W / cm² for the central target and 10 W / cm² for the edge target.

7. The method for preparing high-uniformity silver-coated conductive material powder by dry magnetron sputtering according to claim 6, characterized in that: When the conductive material powder is nickel powder, the surface temperature of the tooling plate (2) is controlled to be ≤100°C.

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