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

Abstract

The invention relates to the technical field of magnetron sputtering, in particular to a method for preparing high-uniformity silver-coated conductive material powder through a magnetron sputtering dry method, and the high-uniformity silver-coated conductive material powder is prepared through a magnetron sputtering device based on an ultrasonic-electromagnetic suspension composite dispersion system. Comprising the following steps: taking a proper amount of conductive material powder which has the particle size D50 of 0.4-6.0 microns and is subjected to surface treatment, and placing the conductive material powder on a tool disc with a gradient aperture structure; the ultrasonic working frequency is controlled to be 20-100 kHz, the ultrasonic power density is controlled to be 1-5 W / cm < 2 > till the generated cavitation micro-jet velocity peak value is larger than or equal to 160 m / s, a three-phase alternating current is conducted to generate a 0.1-0.5 T rotating magnetic field so as to drive the conductive material powder to spin at the speed of 80-200 rpm, and the sputtering power density of the cathode target material is set to be 3-10 W / cm < 2 >; and the surface temperature of the tool disc is controlled to be smaller than or equal to 120 DEG C, deposition treatment is conducted for 1-3 h, and the thickness of a silver layer is larger than or equal to 50 nm. Through core technologies such as ultrasonic-electromagnetic suspension multi-field coupling dispersion, sputtering path regulation and control by a dynamic magnetic field and gradient aperture tool disc design, the nano-scale controllability of the thickness of the silver layer, coating uniformity breakthrough and large-scale production compatibility are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetron sputtering, and more particularly to a method for dry preparation of high-uniformity silver-coated conductive material powder by magnetron sputtering. Background Art

[0002] Currently, silver-coated copper powder, as the core conductive material for the front silver paste of photovoltaic cells, its preparation process mainly relies on wet chemical plating and electroplating technologies. 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 copper powder. Although this method has a mature process, its core defects are significant: First, the widespread use of cyanide complexing agents (such as NaAg(CN)2) results in the discharge of 5-8 tons of cyanide-containing wastewater per ton of powder production, with a treatment cost as high as 3000-5000 yuan / ton, and there are serious environmental risks; Second, the non-uniformity of the reduction reaction causes dendritic growth of the silver layer, resulting in a porosity as high as 5-8% (SEM test data), and the interfacial bonding strength is less than 3N / mm 2 (ASTM D4541 standard), directly leading to microcracks after the slurry is sintered, reducing the electrode conductivity. Another mainstream technology, the electroplating method, although improves the denseness of the silver layer through a pulsed power supply, its Faraday efficiency is only 85%, and the coating uniformity for sub-micron copper nuclei (D50 < 1μm) is extremely poor, and the coefficient of variation (CV value) of the particle size distribution exceeds 25%, which cannot meet the high-precision printing requirements of HJT cells for the fine grid line width ≤ 28μm. More severely, the thickness control accuracy of the silver layer in the wet process is limited to ±50nm. To balance the resistivity and cost, the addition ratio of silver-coated copper powder in photovoltaic silver paste is suppressed to less than 30% (corresponding sheet resistance > 4.5 μΩ·cm), severely restricting the cost reduction space of precious metals.

[0003] As an alternative path, the magnetron sputtering dry process can theoretically avoid the pollution defects of the wet process and achieve nanoscale silver layer control. However, the existing dry technologies face three major industrialization obstacles: First, under vacuum conditions, the powder is affected by van der Waals forces (10-100 nN / particle) and electrostatic forces (>1 μN / particle), resulting in uncontrollable agglomeration, leading to a coating coverage rate < 80% (laser particle size analysis data), and the sudden increase in resistivity caused by local silver layer loss; Second, the shielding effect of the three-dimensional powder packing on the plasma is significant, and the target utilization rate is only 10-15% (the theoretical value of the planar target is 30%), and 30-40% of the sputtering power is converted into the powder heat load, resulting in a local temperature exceeding 300°C (infrared thermal imaging data), leading to recrystallization of copper nuclei and a particle size increase > 50%; Third, during the equipment scaling-up process, the non-linear characteristics of the cavity flow field and plasma distribution cause the deposition uniformity to deteriorate rapidly with the increase in size. The deposition rate in the edge area of a 1m-diameter cavity decreases by 40% compared to the center, and the single-furnace production capacity is limited to less than 10kg, making it difficult to meet the demand of a thousand-ton production line.

[0004] Meanwhile, the rapid iteration of photovoltaic cell technology poses more stringent requirements for front silver pastes: Heterojunction (HJT) cells use amorphous silicon layers and need to be adapted to low-temperature sintering processes (≤250°C, while traditional PERC cells are at 800°C), requiring 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 that the fine grid electrodes have a high aspect ratio (line width ≤ 28μm, aspect ratio ≥ 0.4), which poses extreme requirements for the morphology uniformity (sphericity > 0.95) of silver-coated copper powder and the silver layer continuity (porosity < 1%). Existing wet processes have sharp increases in sheet resistance to above 5 μΩ·cm when the addition ratio exceeds 30% due to silver layer defects and insufficient uniformity, forcing the industry to still rely on high-silver-content pastes (silver powder accounts for 90 - 92%), severely restricting the decline of the levelized cost of electricity (LCOE) for photovoltaics. Summary of the Invention

[0005] To solve at least one of the above problems, the present invention provides a method for magnetron sputtering dry preparation of high-uniformity silver-coated conductive material powder. Through core technologies such as ultrasonic-electromagnetic suspension multi-field coupling dispersion, dynamic magnetic field regulation of the sputtering path, and gradient aperture tooling plate design, it realizes nanoscale controllability of the silver layer thickness, breakthrough in coating uniformity, and compatibility with large-scale production.

[0006] A method for magnetron sputtering dry preparation of high-uniformity silver-coated conductive material powder provided by the present invention is prepared using 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 oscillator array, a dynamic magnetic field regulation module, and a planar rectangular cathode arranged in the magnetron sputtering furnace body; the surface of the tooling plate has through holes with a gradient aperture structure, the aperture of the through holes in the central region is 8 - 15μm, and the hole density is 1100 - 1400 holes / cm 2 , and the aperture of the through holes in the edge region is 40 - 60μm, and the hole density is 150 - 300 holes / cm 2 ; the ultrasonic oscillator array is distributed at the bottom of the tooling plate, the dynamic magnetic field regulation module is arranged on the periphery of the tooling plate, and the planar rectangular cathode is arranged at the top of the magnetron sputtering furnace body;

[0007] The method specifically includes the following steps:

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

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

[0010] Silver layer deposition: controlling the surface temperature of the tooling plate ≤ 120 °C, depositing for 1-3 h, so that the silver layer thickness reaches ≥ 50 nm, thus obtaining the high-uniformity silver-coated conductive material powder.

[0011] Optionally, the gradient aperture structure on the tooling plate has an aperture of 8-15 μm in the central region and a pore density of 1100-1400 pores / cm 2 , an aperture of 40-60 μm in the edge region and a pore density of 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 for the central target 2 and 3-10 W / cm for the edge target 2 .

[0013] Optionally, the cathode target is silver with a purity ≥ 99.995%, the target is inclined 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 plate.

[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 working frequency in the central area of the tooling plate is 100 kHz, and the ultrasonic power density is 5 W / cm 2 ; the ultrasonic working frequency in the edge area of the tooling plate is 60 kHz, and the ultrasonic power density is 1 W / cm 2 .

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

[0017] Optionally, when the conductive material powder is nickel powder, the ultrasonic working frequency of 60 kHz is enabled in the entire area of the tooling plate, and the ultrasonic power density is 3 W / cm 2 .

[0018] Optionally, when the conductive material powder is nickel powder, the sputtering power density of the cathode target is 6 W / cm for the central target2 , edge target 10 W / cm 2 .

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

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

[0021] 1. Precise control of microtopography: Through the synergistic regulation of ultrasonic frequency (20 - 100 kHz) and magnetic field strength (0.1 - 0.5 T), the thickness deviation of the silver layer is achieved < ±5 nm;

[0022] 2. Breakthrough in coating uniformity: By optimizing the rotating magnetic field (80 - 200 rpm) and the gas flow penetration rate of the porous tooling plate, the CV value < 5%;

[0023] 3. Controllable surface resistivity: By strictly controlling the sputtering power (3 - 10 W / cm 2 ) and matching with a suitable silver layer deposition temperature, the resistivity fluctuation ≤ ±0.2 μΩ·cm;

[0024] 4. Industrial compatibility: Suitable for modular split - cavity design (12 kg per single cavity, 72 kg in parallel for 6 cavities), the thickness non - uniformity ≤ ±2.5%.

[0025] The breakthrough of the present invention lies in:

[0026] Compared with the conventional technology of suspending powder for film coating by jet dispersion, slightly turning over the powder by vibration, and dispersing by pure vibration, the present invention drives the powder to spin by vibration - magnetic field, which can effectively avoid insufficient film thickness caused by uneven sputtering in the coating area during the turning - over process; compared with the method of large - range vibration (such as the entire conveyor belt), the method of only vibrating the tooling plate in the present invention has the characteristics of being lighter, more effective, and portable, and can also effectively avoid vacuum leakage caused by large - range vibration;

[0027] In addition, due to the structural characteristics of the powder, the difficulty of powder coating is much higher than that of planar coating. When using the conventional planar coating method for powder coating, it does not have the ability to uniformize the coating. Therefore, there are difficulties in conversion between the two in actual operation. For this reason, the present invention can ensure uniform coating of the film layer on the surface of various powders through the multi - parameter synergistic regulation of magnetic field - flow field - sound field, and for the first time realizes the stable suspension of 10 kg - level conductive material powder at a vacuum degree of 10 -5 Pa, and the spatial distribution density of the conductive material powder reaches 10 4 -10 5 particles / cm 3, the coverage rate > 95%, the coefficient of variation (CV value) of the D50 particle size distribution < 5%, which is more than 3 times higher than that of the traditional vibration method. Specifically, the thickness non-uniformity is compressed from ±20% to ±3%, the target utilization rate breaks through 45%, and the energy consumption per unit production capacity is reduced to less than 8 kWh / kg. Description of the Drawings

[0028] Figure 1 It is a schematic structural diagram of a magnetron sputtering furnace used in the present invention for preparing high-uniformity silver-coated conductive material powder.

[0029] Description of the reference numerals:

[0030] 1. Magnetron sputtering furnace body; 2. Tooling plate; 3. Ultrasonic oscillator array; 4. Dynamic magnetic field regulation module; 5. Cathode target. Detailed Description of the Invention

[0031] Aiming at the core problems such as environmental pollution, silver layer defects and poor uniformity in the wet process for preparing silver-coated copper powder, the present invention combines the potential advantages and industrialization bottlenecks of the magnetron sputtering dry process, and proposes a method for preparing high-uniformity silver-coated conductive material powder by magnetron sputtering dry process. Based on a specific magnetron sputtering furnace, with the ultrasonic-electromagnetic suspension multi-field coupling dispersion technology as the core, through a precisely designed gradient aperture tooling plate, dynamic magnetic field regulation of the sputtering path and a modularized cavity structure, it realizes nano-level controllability of the silver layer thickness, breakthrough of the coating uniformity and compatibility with large-scale production.

[0032] To make the above objects, features and advantages of the present invention more obvious and understandable, the magnetron sputtering furnace used in the present invention will be described in detail below with reference to the drawings. A coordinate system XYZ is set in the drawings of the present invention, where 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 back, the positive direction of the Z-axis represents the top, and the negative direction of the Z-axis represents the bottom.

[0033] Specifically refer to Figure 1 , the magnetron sputtering furnace includes a magnetron sputtering furnace body 1 and a tooling plate 2, an ultrasonic oscillator array 3, a dynamic magnetic field regulation module 4 and a cathode target 5 installed in the magnetron sputtering furnace body 1. Among them, a cavity with a radial length (both length and width) of 1000 mm and a height of 800 mm is provided in the magnetron sputtering furnace body 1, and it is connected through an independent vacuum lock (ultimate vacuum degree 5×10 - 5Pa, with a pumping time ≤ 30 min) to maintain a vacuum environment inside the cavity. The tooling plate 2 is fixedly installed in the middle of the magnetron sputtering furnace body 1 and is a porous ceramic plate with a diameter of 650 mm and a gradient aperture structure. The ultrasonic oscillator array 3 is uniformly installed at the bottom of the tooling plate 2 with 12 groups of high-frequency piezoelectric ultrasonic oscillator arrays. The dynamic magnetic field regulation module 4 is arranged on the periphery of the tooling plate 2 and is specifically composed of 24 groups of Helmholtz coils (coil inner diameter 700 mm, wire diameter 5 mm, number of turns 120), forming an axisymmetric magnetic field in two upper and lower layers (spacing 150 mm). The cathode target 5 is fixedly arranged at the top of the magnetron sputtering furnace body 1 and is located 10 - 50 mm above the tooling plate 2.

[0034] During the preparation process, since the present invention needs to control the surface temperature of the tooling plate 2, a dual-cycle thermal management mechanism is also integrated in the magnetron sputtering furnace: namely, a microchannel liquid nitrogen cooling sandwich and a thermoelectric cooler. The microchannel liquid nitrogen cooling sandwich is arranged on the inner wall of the magnetron sputtering furnace body 1, and the thermoelectric cooler is embedded at the bottom of the tooling plate 2. Combining with infrared temperature measurement feedback (accuracy ±1 °C), dynamic temperature control of local hot spots (temperature difference < 3 °C) is achieved.

[0035] The above magnetron sputtering furnace is an independent module, which can be used alone or in parallel with multiple units to achieve a split-chamber modular design of the magnetron sputtering device. Taking a single module processing powder volume ≥ 12 kg (stacking thickness 3 mm) as an example, a single-batch production capacity of ≥ 72 kg is achieved through 6-chamber parallel connection, with a thickness non-uniformity ≤ ±2.5% (central area 185 nm ± 4 nm, edge area 180 nm ± 6 nm), and the production capacity is increased by 5 times compared with traditional single-chamber equipment.

[0036] Based on the above magnetron sputtering furnace, a method for magnetron sputtering dry preparation of high-uniformity silver-coated conductive material powder includes the following steps:

[0037] I. Powder pretreatment:

[0038] 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 set aside; the relatively small range of the above particle size helps to improve the uniformity of the particle size distribution, and removing the surface oxide layer and surface activation can reduce impurity incorporation and improve the stability after silver layer deposition;

[0039] Take an appropriate amount of surface-treated conductive material powder and place it on the tooling plate 2 with a gradient aperture structure; among them, the gradient aperture structure on the tooling plate 2 is formed by laser etching, specifically with a central area aperture of 8 - 15 μm and a pore density of 1100 - 1400 pores / cm 2 , and an edge area aperture of 40 - 60 μm and a pore density of 150 - 300 pores / cm 2, and the tooling plate 2 distinguishes the central area and the edge area with the position of a diameter of 450 mm as the boundary; the total loading amount of the conductive material powder is 10 - 15 kg, and the stacking thickness is 2 - 20 mm. Thus, the aperture size (8 - 60 μm) of the through holes on the tooling plate 2 is optimized according to the D50 of the conductive material powder, which not only allows the air flow to penetrate and generate lift, but also can effectively reduce the leakage of the conductive material powder. Moreover, the air flow penetration rate of the gradient aperture structure and the loading capacity of the conductive material powder can achieve a dynamic balance to ensure the stable distribution of the conductive material powder in a vacuum environment.

[0040] II. Ultrasonic - electromagnetic suspension:

[0041] Control the working frequency of the ultrasonic oscillator array 3 to be 20 - 100 kHz and the power density to be 1 - 5 W / cm 2 , so that the velocity of the cavitation micro - jet generated is ≥160 m / s. The cavitation micro - jet can effectively break up the powder agglomerates. At the same time, the transient high temperature and high pressure (6000 K, 1000 atm) during the collapse of the air bubbles helps to clean the oxide on the surface of the metal core, reducing the oxygen content from 800 ppm to below 50 ppm;

[0042] The Helmholtz coil in the dynamic magnetic field regulation module 4 is passed through by three - phase alternating current (the frequency is adjustable from 0.1 - 10 Hz, and the current peak value is 200 A). By adjusting the current phase difference in real - time a rotating magnetic field (0.1 - 0.5 T) is generated, so that the conductive material powder spins at 80 - 200 rpm under the drive of the Coriolis force, ensuring that silver atoms are uniformly deposited along the normal direction of the surface of the conductive material powder (the incident angle deviation <5°);

[0043] Set the sputtering power density of the cathode target 5 to be 6 - 15 W / cm 2 . The cathode target 5 is silver with a purity ≥99.995%, the target surface inclination angle (the inclination angle relative to the horizontal plane) is 0 - 15°, and the distance from the center of the target surface to the axis of the tooling plate 2 is 120 - 320 mm. The arrangement quantity of the cathode target 5 can be adjusted according to the usage amount. In the present invention, four are arranged, each with a planar rectangular structure of 850 mm × 120 mm, and are arranged in an annular shape with an inclination angle of 15° (the distance from the center of the target surface to the axis of the tooling plate 2 is 320 mm). Further, the sputtering power density can be optimized according to the plasma distribution (the central target is 6 - 8 W / cm 2 , the edge target is 3 - 10 W / cm 2 ), a closed magnetic field (the magnetic flux density on the target surface is 600 - 800 Gs) is generated through the magnetron, and the electrons are confined near the target surface to increase the ionization rate (Ar + density ≥5×10 13 cm -3 ).

[0044] III. Silver layer deposition:

[0045] During the redeposition process, the surface temperature of the tooling plate 2 is controlled ≤ 120 °C (reduced by 180 °C compared to without cooling) by using a microchannel liquid nitrogen cooling sandwich (channel diameter 2 mm, flow rate 5 - 8 L / min) and a thermoelectric cooler (TEC1-12706 type, refrigeration power 60 W), suppressing the particle size growth caused by the recrystallization of metal nuclei (D50 fluctuation < 0.5%), and combined with infrared temperature measurement feedback (accuracy ±1 °C), realizing dynamic temperature control of local hot spots (temperature difference < 3 °C); the deposition treatment time is 1.5 - 3 h, so that the silver layer thickness ≥ 50 nm, and a silver-coated conductive material powder with high uniformity is obtained.

[0046] To further prove the feasibility of the method of the present invention, the present invention will be described in detail below in conjunction with specific embodiments.

[0047] Example 1

[0048] Preparation of silver-coated copper powder for photovoltaic silver paste, and its preparation method includes the following steps:

[0049] I. Powder pretreatment:

[0050] Select spherical copper powder with D50 = 0.8 μm (purity ≥ 99.9%), remove the surface oxide layer (oxygen content < 50 ppm) by hydrofluoric acid cleaning, and after drying, stack it in the central area of the porous ceramic tooling plate 2 (diameter 650 mm), with a stacking thickness of 3 mm (total loading 12 kg);

[0051] II. Ultrasonic - electromagnetic suspension:

[0052] Ultrasonic oscillator array 3: Activate four groups of oscillators in the central area (frequency 100 kHz, power 5 W / cm 2 ), and eight groups of oscillators in the edge area (frequency 60 kHz, power 1 W / cm 2 ), and the cavitation micro - jet velocity is 160 m / s;

[0053] Dynamic magnetic field regulation module 4: Pass in three - phase alternating current (frequency 2 Hz, current 200 A, phase difference ), generate a 0.3 T rotating magnetic field, and drive the copper powder to spin at 120 rpm;

[0054] Cathode target 5: Turn on four sets of cathode targets 5 (power density: central target 8 W / cm 2 , edge target 10 W / cm 2 ), the working pressure of argon is 0.3 Pa, and the substrate bias voltage is - 50 V;

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

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

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

[0058] IV. Performance testing:

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

[0060] Example 2

[0061] The preparation of silver-coated copper powder for photovoltaic silver paste, and its preparation method includes the following steps:

[0062] I. Powder pretreatment:

[0063] Select spherical copper powder with D50 = 0.4 μm (purity ≥ 99.9%). After being cleaned with hydrofluoric acid to remove the surface oxide layer (oxygen content < 50 ppm), it is dried and piled up in the central area of the porous ceramic tooling plate 2 (diameter 650 mm), with a stacking thickness of 2 mm (total loading amount 10 kg);

[0064] II. Ultrasonic - electromagnetic suspension:

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

[0066] Dynamic magnetic field regulation module 4: Pass in three-phase alternating current (frequency 2 Hz, current 200 A, phase difference ), generate a 0.1 T rotating magnetic field, and drive the copper powder to spin at 200 rpm;

[0067] Cathode target 5: Turn on four sets of targets 5 (power density: central target 8 W / cm 2 , edge target 3 W / cm 2 ), the working pressure of argon is 0.3 Pa, and the substrate bias voltage is -50 V;

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

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

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

[0071] IV. Performance testing:

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

[0073] Example 3

[0074] Preparation of silver-coated copper powder for photovoltaic silver paste, and its preparation method includes the following steps:

[0075] I. Powder pretreatment:

[0076] Select spherical copper powder with D50 = 6.0 μm (purity ≥99.9%), remove the surface oxide layer by hydrofluoric acid cleaning (oxygen content <50 ppm), and after drying, stack it in the central area of the porous ceramic tooling plate 2 (diameter 650 mm), with a stacking thickness of 10 mm (total loading amount 15 kg);

[0077] II. Ultrasonic-electromagnetic suspension:

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

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

[0080] Cathode target 5: Turn on four sets of cathode targets 5 (power density: central target 8 W / cm 2 , edge target 6 W / cm 2 ), the working pressure of argon is 0.3 Pa, and the substrate bias voltage is -50 V;

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

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

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

[0084] IV. Performance testing:

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

[0086] Example 4

[0087] The preparation of silver-coated copper powder for photovoltaic silver paste includes the following steps:

[0088] I. Powder pretreatment:

[0089] Spherical copper powder with D50 = 0.8 μm (purity ≥99.9%) is selected. After being cleaned with hydrofluoric acid to remove the surface oxide layer (oxygen content <50 ppm), it is dried and piled up in the central area of the porous ceramic tooling plate 2 (diameter 650 mm), with a stacking thickness of 3 mm (total loading 12 kg);

[0090] II. Ultrasonic-electromagnetic suspension:

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

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

[0093] Cathode target 5: Turn on four sets of cathode targets 5 (power density: central target 8 W / cm 2 , edge target 8 W / cm 2 ), the working pressure of argon is 0.3 Pa, and the substrate bias voltage is -50 V;

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

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

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

[0097] IV. Performance testing:

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

[0099] Example 5

[0100] Preparation of silver-coated nickel powder for MLCC electrodes, and its preparation method includes the following steps:

[0101] I. Powder pretreatment:

[0102] Select flaky nickel powder with D50 = 2.5 μm (aspect ratio 3:1), and improve the surface activity through plasma activation (power 500 W, Ar / H2 = 4:1). The loading amount is 10 kg (bulk density 2.5 g / cm 3 , and the stacking thickness is about 20 mm);

[0103] II. Ultrasonic-electromagnetic suspension:

[0104] Ultrasonic oscillator array 3: The 60 kHz intermediate frequency is enabled in the whole region (power 3 W / cm 2 ), to avoid damage to the flaky powder structure;

[0105] Dynamic magnetic field regulation module 4: Lower the magnetic field strength to 0.2 T (frequency 5 Hz, current 150 A), and the powder spins at 80 rpm to ensure normal deposition on the flaky surface;

[0106] Cathode target 5: The power of the edge target is increased to 10 W / cm 2 (the power of the central target is 6 W / cm 2 ), the substrate bias voltage is -30 V, and the argon gas pressure is 0.5 Pa;

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

[0108] Deposit in two stages: In the first 60 minutes, a low power (6 W / cm 2 ) is used to form a 50 nm silver seed layer; in the next 60 minutes, a high power (10 W / cm 2 ) is used to thicken it to 100 nm, and the thickness of the interface transition zone <5 nm;

[0109] The temperature of the liquid nitrogen system is controlled at ≤100 °C to inhibit nickel diffusion (interface resistance ≤0.8 mΩ·cm 2 );

[0110] IV. Performance Test:

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

[0112] To intuitively understand the technical effects of Examples 1-5, the present invention summarizes the above technical effects, as specifically shown in Table 1 below.

[0113] Table 1 Comparison Table of Technical Effects of Examples 1-5

[0114]

[0115]

[0116] As can be seen from the above Table 1, the method for dry preparation of high-uniformity silver-coated conductive material powder by magnetron sputtering of the present invention has achieved breakthrough applications in both the field of photovoltaic silver paste and the field of MLCC inner electrodes.

[0117] In Examples 1-4, spherical copper core powder is used, and the addition ratio reaches 45-50%. The resistivity of the slurry is 3.1-3.2 μΩ·cm (the benchmark of pure silver paste is 2.5 μΩ·cm), which meets the printing requirements of the fine grid of HJT batteries with a line width of 28 μm ± 1.2 μm. The loss of photoelectric conversion efficiency is <0.3%, and the silver consumption per single piece is reduced to 48 mg (cost reduction of 52%). Compared with the wet process, the present invention completely eliminates cyanide pollution, reduces the annual wastewater discharge of a single thousand-ton production line by 1.2 million tons, reduces the use of silver by 500 tons (worth about 3 billion yuan), and at the same time supports the production of 10 GW HJT modules, equivalently reducing carbon dioxide emissions by 1.8 million tons.

[0118] In Example 5, through flexible regulation of 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 the preparation of silver-coated nickel powder for MLCC electrodes (interface resistance ≤0.8 mΩ·cm 2 ) and high-precision powder for 5G radio frequency devices (CV value of particle size <3%), forming a precious metal cost reduction technology system covering the entire scenario of electronic materials.

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

[0120] To facilitate further comparison of the differences between the present invention and traditional processes, the technical indicators of the present invention are now quantified, as shown in Table II below.

[0121] Table II Quantified Technical Indicator Table of Traditional Processes and the Present Invention

[0122]

[0123]

[0124] In summary, aiming at the defects of traditional wet processes (electroless plating, electroplating) such as environmental pollution, high silver layer porosity (>5%) and poor uniformity (CV>20%), the present invention realizes the stable suspension of 10 kg-level conductive material powder under a vacuum of 10 -5 Pa through core technologies such as ultrasonic-electromagnetic suspension multi-field coupling dispersion, dynamic magnetic field regulation of sputtering path, and gradient aperture tooling plate design. The spatial distribution density of the conductive material powder reaches 10 4 -10 5 particles / cm 3 , the coverage rate > 95%, the coefficient of variation (CV value) of the D50 particle size distribution < 5%, which is more than 3 times higher than that of the traditional vibration method. Specifically, the non-uniformity of the silver layer thickness is compressed from ±20% to ±3%, the silver layer thickness is controllable at the nanoscale (≥50 nm), the porosity < 1%, and the surface resistivity ≤ 3.5 μΩ·cm. In addition, the target utilization rate breaks through 45%, and the unit production energy consumption is reduced to less than 8 kWh / kg, providing an efficient and environmentally friendly path for reducing the cost of precious metals in the electronic materials industry.

[0125] In the description of the present disclosure, it should be understood that the orientation or positional relationship indicated by the terms "center", "edge", "thickness", "upper", "lower", "top", "bottom", "inner", "outer", "axial", etc. is based on the orientation or positional relationship shown in the drawings, and is 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 construed as a limitation to 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 can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A method for preparing high-uniformity silver-coated conductive material powder by magnetron sputtering dry method, 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 plate (2) arranged in the magnetron sputtering furnace body (1), an ultrasonic vibrator array (3), a dynamic magnetic field control module (4) and a planar rectangular cathode (5); the tooling plate (2) 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 (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 planar rectangular cathode (5) is arranged on the top of the magnetron sputtering furnace body (1); 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, and placing an appropriate amount of the conductive material powder after surface treatment on the tooling plate (2); Ultrasonic-electromagnetic suspension: Control the ultrasonic working frequency to 20-100kHz and the ultrasonic power density to 1-5W / cm 2 When the peak velocity of the generated cavitation microjet reaches ≥160 m / s, a three-phase alternating current is applied to generate a 0.1-0.5 T rotating magnetic field to drive the conductive material powder to spin at 80-200 rpm, and the sputtering power density of the cathode target (5) is set to 3-10 W / cm 2 ; Silver layer deposition: the surface temperature of the tooling plate (2) is controlled to be ≤120°C, and the deposition treatment is performed for 1-3 hours, so that the thickness of the silver layer reaches ≥50nm, thereby obtaining the highly uniform silver-coated conductive material powder.

2. The method for preparing high-uniformity silver-coated conductive material powder by dry magnetron sputtering according to claim 1, characterized in that: The total loading amount of the conductive material powder is 10-15 kg, and the stacking thickness is 2-20 mm.

3. The method for preparing high uniformity silver-coated conductive material powder by magnetron sputtering dry method according to claim 1, characterized in that: The sputtering power density of the cathode target (5) is 6-8 W / cm for the central target. 2 , Edge target 3-10W / cm 2 .

4. The method for preparing high uniformity silver-coated conductive material powder by dry magnetron sputtering according to claim 3, characterized in that: The cathode target material (5) is silver with a purity of ≥99.995%, the target material 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.

5. The method for preparing high uniformity silver-coated conductive material powder by dry magnetron sputtering according to any one of claims 1 to 4, characterized in that: The conductive material powder includes one or more of copper powder, nickel powder, aluminum powder, graphite powder and carbon nanotube powder.

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 copper powder, the ultrasonic working frequency of the central area of ​​the tooling plate (2) 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 (2) is 60kHz, and the ultrasonic power density is 1W / cm 2 .

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 copper powder, the sputtering power density of the cathode target (5) is 8W / cm 2 , Edge target 10W / cm 2 .

8. 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 whole area of ​​the tooling plate (2) is activated with an ultrasonic working frequency of 60 kHz, and the ultrasonic power density is 3 W / cm 2 .

9. The method for preparing high-uniformity silver-coated conductive material powder by dry magnetron sputtering according to claim 8, characterized in that: When the conductive material powder is nickel powder, the sputtering power density of the cathode target (5) is 6 W / cm 2 , Edge target 10W / cm 2 .

10. The method for preparing high-uniformity silver-coated conductive material powder by dry magnetron sputtering according to claim 9, 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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