Electrowetting-assisted piezoelectric ink-jet printing circuit combination degree enhancing method

Abstract

The invention discloses an electrowetting-assisted piezoelectric ink-jet printing circuit combination degree enhancing method, which comprises the following steps of: integrating an interdigital electrode array on the back surface of a ceramic substrate, connecting interdigital electrodes in the interdigital electrode array with a controller through silver paste, and checking the pattern integrity of the interdigital electrodes by using an optical microscope; based on a dielectric wetting theory, establishing a quantitative regulation and control relationship between the electric field intensity and the contact angle, and setting electric field parameters; a single factor variable method and an orthogonal experiment method are combined, line width consistency and edge roughness serve as core evaluation indexes, and key printing parameters are optimized; a sintering procedure is determined based on a temperature-stress-conductivity coupling model, a printed sample is placed in a tubular sintering furnace, gradient sintering is carried out in a reducing atmosphere, and elimination of interface stress and strengthening of the binding degree are achieved through the following thermal field strategy of precise temperature control. The bonding strength of the piezoelectric ink-jet printing circuit and the surface of the ceramic substrate is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of piezoelectric inkjet printing, in particular to a method for enhancing the bonding degree of piezoelectric inkjet printing circuit assisted by electrowetting. BACKGROUND

[0002] Conformal circuit is a circuit manufacturing method that can be directly prepared on the surface of a complex structure by means of transfer printing, direct writing printing and thermal forming, etc., which reduces the size of the device and improves the space utilization of the device while retaining the electronic function. The integration of mechanical structure and electronic function improves the flexibility and reliability of the design, and realizes the replacement of traditional printed circuit boards and independent wires in the fields of communication devices, automotive electronics and medical devices, etc., and has a wide application prospect.

[0003] Piezoelectric inkjet printing technology has become an important means for preparing microelectronic circuits due to its high resolution and high forming quality printing characteristics. This technology produces pressure waves through the deformation of piezoelectric ceramics, and accurately deposits functional ink in the form of droplets on the surface of the substrate. However, the existing piezoelectric inkjet printing has insufficient ink deposition and substrate interface bonding force, especially prone to delamination or peeling of the circuit on the surface of the ceramic substrate. Among them, the surface energy of the ceramic (20-30 mN / m) is much lower than that of the metal ink (70-80 mN / m), resulting in a contact angle > 90°, and the actual peel strength is only 0.5-1.2 N / mm. In addition, in actual application, due to the coupling effect of manufacturing defects, load and environmental factors, the interface strength decreases or even fails, causing the electrical performance to decrease, affecting the reliability of the overall function, and it is difficult to meet the actual use requirements. Therefore, it is of important application value to develop a method that can effectively improve the bonding strength of piezoelectric inkjet printing circuit-ceramic substrate interface. SUMMARY

[0004] In order to solve the problems of insufficient interface bonding force, poor environmental reliability and limited process adaptability of the existing piezoelectric inkjet printing technology in the application of ceramic substrate, the present application provides a method for enhancing the bonding degree of piezoelectric inkjet printing circuit assisted by electrowetting, which effectively improves the bonding strength of piezoelectric inkjet printing circuit and ceramic substrate surface, and is particularly suitable for the preparation of high-precision and high-bonding electronic circuits.

[0005] The present application discloses a method for enhancing the bonding degree of piezoelectric inkjet printing circuit assisted by electrowetting, which comprises: Step 1: The ceramic substrate with a surface roughness less than a preset value is selected, and is sequentially subjected to stepwise ultrasonic cleaning with acetone, isopropyl alcohol and deionized water, and is dried with nitrogen; the cleaned ceramic substrate is placed in a plasma cleaning machine for oxygen plasma treatment to remove surface organic contaminants and improve the surface energy; Step 2: Electrode system integration: integrate the embedded transparent electrode array system, integrate the interdigital electrode array on the back of the ceramic substrate, the interdigital electrodes in the interdigital electrode array are connected to the controller through silver paste, use an optical microscope to check the integrity of the interdigital electrode pattern, and ensure that the interdigital electrodes have no short circuit or open circuit defects; Step 3: Electric field parameter setting: based on the theory of dielectric wetting, a quantitative regulation relationship between electric field strength and contact angle is established, and the electric field parameters are set; Step 4: Synchronous printing control: using the single factor variable method combined with the orthogonal experiment method, taking line width consistency and edge roughness as the core evaluation index, the key printing parameters are optimized; the key printing parameters include drop volume, nozzle temperature, and substrate temperature; Step 5: Gradient sintering treatment: based on the finite element analysis software, a multi-physical field digital simulation model is constructed, which is a temperature-stress-conductivity coupling model; based on the sintering program determined by the temperature-stress-conductivity coupling model, the printed sample is placed in a tube furnace for gradient sintering in a reducing atmosphere, and through the precise temperature control of the thermal field strategy, the interface stress is eliminated and the bonding degree is strengthened.

[0006] Further, the embedded transparent electrode array system includes a transparent electrode array, a multi-channel gating controller, a high-voltage alternating current signal source, and an FPGA master control unit; The transparent electrode array adopts indium tin oxide to prepare an interdigital electrode array on the back of the ceramic substrate through magnetron sputtering and photolithography process; each pair of interdigital electrodes of the interdigital electrode array is connected to the multi-channel gating controller; The multi-channel gating controller receives instructions from the FPGA master control unit to gate or turn off any pair of interdigital electrodes; High-voltage alternating current signal source and FPGA master control unit: the high-voltage alternating current signal source is controlled by the FPGA master control unit and is used to generate the required square wave signal; the FPGA master control unit receives the nozzle position coordinates from the motion platform.

[0007] Further, the working process and path matching process of the embedded transparent electrode array system are as follows: Coordinate mapping: before printing starts, the printing path planning file is preloaded into the controller, and a lookup table is established in the controller to map the nozzle two-dimensional plane coordinates (X, Y) to the electrode block area on the back of the substrate one by one; Real-time local regulation: during the printing process, the motion platform feeds back the precise position of the nozzle to the controller, and the controller calculates the specified electrode pair area covered directly below the nozzle according to the current nozzle coordinates through the lookup table; Precise empowerment: the controller sends instructions to the multiplexing controller, only enabling the electrode pair directly below the nozzle, while closing all other electrodes in the region; the square wave signal generated by the high-voltage signal source is precisely applied to the selected electrode pair; Dynamic following: as the nozzle moves, the controller refreshes the position data and switches the enabled electrode pairs, so that the generated strong electric field region always follows the print nozzle movement, achieving matching print path for local electric field regulation; the strong electric field region is the region where the electric field strength exceeds the preset value.

[0008] Further, the step 3 comprises: Output adjustable AC square wave signal through the controller, and apply the adjustable AC square wave signal to the electric field for regulating the wetting behavior of the ink; set the electric field parameters, including the working voltage, frequency, and duty cycle; the electric field parameters are set based on the Young-Lippmann equation; Specifically, the Young-Lippmann equation is:

[0009] Wherein, is the dynamic contact angle after applying the electric field strength E, is the intrinsic contact angle without the electric field, is the vacuum permittivity, is the relative permittivity of the functional ink dielectric layer, and γ is the gas-liquid surface tension of the ink; the Young-Lippmann equation theoretically quantitatively describes that the cosine value of the contact angle is linearly proportional to the square of the applied electric field strength E; According to the Young-Lippmann equation and considering the characteristics of the selected nano-silver ink, the optimal electric field strength control value is determined; an adjustable AC square wave signal is output through the controller, and the value of the applied voltage V is controlled to make the calculated electric field strength E stable at the specified value.

[0010] Further, the electric field strength E is determined by the voltage V applied to the interdigital electrode and the electrode geometry structure, and the electric field strength between the adjacent two interdigital electrodes is calculated, and the calculation formula is:

[0011] Wherein, V is the peak voltage applied to the interdigital electrode pair, and d is the spacing of the interdigital electrode.

[0012] Further, the step 4 comprises: Inject the nano-silver conductive ink into the piezoelectric inkjet printer cartridge, set the nozzle temperature and ink droplet volume; under the synchronous assistance of the electric field, establish a flow field that optimizes the ink droplet deposition morphology: The electric field force increases the electrical stress at the solid-liquid-gas three-phase contact point, thereby increasing the contact linear velocity, optimizing the flow field, and effectively suppressing the rebound effect of ink droplets; Electric field modulation induces convection exceeding the preset intensity, the internal flow field optimizes particle transport, effectively eliminates the coffee ring effect, and makes the deposited film layer more uniform. The combined effect of an electric field and an optimized flow field ensures that the outline of the ink droplet after shaping is clear and the edges are smooth. A motion platform is used to achieve spatial synchronization between the print head and the electric field, and encoder feedback ensures that the lag time is less than the preset time; during the printing process, the substrate temperature and ambient humidity are controlled to meet the printing requirements.

[0013] Furthermore, optimizing the droplet volume includes: the droplet volume directly determines the size and resolution of the deposited ink dots; under the condition of determining the ink material properties, testing the change in droplet volume to determine the droplet volume that meets the requirements, so as to ensure the consistency of linewidth from the source; the ink material properties include particle size, viscosity and composition; Optimizing the printhead temperature includes: printhead temperature directly affects the viscosity and surface tension of the ink; monitoring the viscosity change of the ink at different temperatures to determine the optimal value of the printhead temperature to ensure that the shape and volume of each ink droplet are highly consistent; The substrate temperature mainly controls the evaporation rate and spreading of ink droplets after they impact the ceramic substrate; under the assistance of an electric field, the effect of different substrate temperatures on the edge morphology of printed lines is tested; the required substrate temperature is determined by the heat flow induced by the temperature difference between the substrate temperature and the printhead temperature.

[0014] Furthermore, the precise temperature control thermal field strategy for eliminating interfacial stress and strengthening adhesion includes: Interface diffusion layer optimization: Heat to a specified temperature at a preset rate and hold for a period of time to promote the formation of an interface transition layer and promote the interdiffusion between metal nanoparticles and ceramic surface atoms to form a transition layer. Internal defect elimination: Based on the specified temperature, the temperature is increased and maintained to achieve full sintering of conductive particles. The thermal field causes the conductive particles to aggregate and grow, increasing the sintering density and eliminating related defects, including internal pores. Residual stress relief: Cool the interface transition layer to room temperature at a specified rate to eliminate thermal stress.

[0015] Furthermore, the temperature-stress-conductivity coupling model is established, including: Geometric modeling and material property definition: A three-dimensional structure including a ceramic substrate, a metal circuit pattern, and an interface layer is established in the simulation software, and temperature-related material parameters are input for each component; the relevant material parameters include the coefficient of thermal expansion, elastic modulus, Poisson's ratio of the ceramic substrate and ink, the conductivity of the metal circuit, and the activation energy of the interface layer; Physics Field Setup and Coupling: A solid heat transfer module is introduced to simulate the transfer of the temperature field to the sample and the temperature distribution inside the sample; a solid mechanics module is introduced, with the thermal field as input; the thermal stress caused by the mismatch between the ceramic substrate and the circuit material is calculated by solving the thermoelastic constitutive equation; a current module is introduced, with the sintering temperature field as input; the Arrhenius equation is used to simulate the effect of temperature on the conductivity of the metallic circuit; the temperature field is used as the independent variable, simultaneously driving the stress field and conductivity changes, to achieve coupled simulation.

[0016] Furthermore, after step 5, the method further includes: optimizing the electric field parameters and sintering curves based on the test results, and establishing a process-performance correspondence database; the test results are the results of peeling tests performed using a micro-force tester; the process-performance correspondence database includes process input parameters and their corresponding performance output indicators; the process input parameters include electrowetting parameters, printing parameters, and sintering parameters; the performance output indicators include interface performance, electrical performance, morphological performance, and environmental reliability. After establishing the process-performance correspondence database, the process also includes quality inspection and packaging. The quality inspection and packaging include: An automated optical inspection system is used to check circuit integrity, measuring the linewidth consistency and edge roughness after flow field optimization; products that meet the requirements are subjected to anti-oxidation encapsulation treatment, and a protective layer is formed by vacuum phase deposition; products undergo full inspection to ensure no interface defects.

[0017] Due to the adoption of the above technical solution, this application has the following advantages: This application innovatively introduces electrowetting to form a three-field synergistic control mechanism of "electric field-flow field-thermal field", which significantly improves the bonding strength, environmental stability and process compatibility of the circuit-substrate interface, and has the following significant effects and advantages: (1) The interfacial bonding strength is significantly improved. The dynamic electrowetting stage in this application reduces the contact angle of the functional ink on the ceramic substrate surface from >90° to below 35° by precisely controlling the electric field parameters (2kV / mm, 5kHz), resulting in a 300% improvement in interface energy. Combined with the optimized interface diffusion layer in the gradient sintering stage, an ultra-high peel strength of 3.8N / mm is ultimately achieved, which is 217% higher than that of the traditional plasma treatment process (1.2N / mm), meeting the reliability requirements of microelectronic circuits under complex operating conditions.

[0018] (2) Environmental stability has been greatly enhanced Based on the electric field-induced chemical bonding mechanism and the stress relief effect of gradient sintering, the fabricated circuits exhibit excellent performance under harsh conditions: after 1000 thermal cycles at -40~150℃, the bonding strength retention rate is >95%; after aging at 85℃ / 85%RH for 1000h, the interface resistance change rate is <3%; and the mechanical bending resistance is improved to 5000 bends (radius 5mm) without cracking.

[0019] (3) Improved printing accuracy and consistency The electrowetting effect effectively suppresses the coffee ring phenomenon. Combined with optimized piezoelectric jetting parameters (4pL droplets, 35℃ printhead temperature), it achieves: minimum linewidth of 20μm (CV<5%); edge roughness of <0.5μm (reduced by 70%); and interlayer alignment accuracy of ±1.5μm.

[0020] (4) The process window has been significantly widened. This method exhibits excellent process adaptability: it is compatible with various functional inks (including nano silver, conductive polymers, etc.) with a viscosity range of 1-50 cP; it is suitable for various ceramic substrates such as Al2O3, AlN, and ZrO2 (surface energy 20-45 mN / m); and its operating temperature range is extended to -40~250℃.

[0021] (5) Prominent industrialization advantages High equipment compatibility: The embedded electrode module can be directly integrated into commercial piezoelectric inkjet systems such as Dimatix and Ricoh; Optimized production costs: Reduces equipment investment by 40% and energy consumption by 35% compared to laser activation process; High production efficiency: Online processing speed reaches 20cm² / min, suitable for roll-to-roll manufacturing.

[0022] (6) No damage to the material system The electric field treatment process is free of electric arc discharge, avoiding breakdown damage to the substrate surface; the low-temperature sintering process (≤250℃) maintains the mechanical properties of the substrate; and the reducing atmosphere protection prevents oxidation of metal nanoparticles. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings.

[0024] Figure 1 This is a schematic diagram of an embodiment of the electrowetting-assisted method for enhancing interfacial adhesion in this application; Figure 2This is a schematic diagram illustrating the principle of enhanced bonding between the piezoelectric inkjet printing circuit and the ceramic substrate in an embodiment of this application. Figure 3 This is a schematic diagram illustrating the principle of the gradient sintering method according to an embodiment of this application; Figure description: 1-Curved substrate; 2-Embedded transparent electrode; 3-High voltage AC signal source; 4-Circuit array. Detailed Implementation

[0025] The present application will be further described in conjunction with the accompanying drawings and embodiments. The described embodiments are only some, not all, of the embodiments of the present application. All other embodiments obtained by those skilled in the art should fall within the protection scope of the embodiments of the present application.

[0026] See Figure 2 This application provides an embodiment of a method for enhancing the bonding strength of piezoelectric inkjet printing circuits with electrowetting assistance, comprising: Step 1: Pretreatment of curved substrate. A ceramic substrate is selected and ultrasonically cleaned in sequence with acetone, isopropanol and deionized water, and then dried with nitrogen. The cleaned substrate is placed in a plasma cleaner for oxygen plasma treatment to remove surface organic contaminants and improve surface energy. The ceramic substrate can be an AlN ceramic substrate with a surface roughness Ra < 0.1 μm. The nitrogen concentration exceeds the preset concentration value. Step 2: Electrode System Integration: Integrate an embedded transparent electrode array system. Integrate the finger electrode array on the back of the ceramic substrate. The electrodes are connected to the controller via silver paste. Use an optical microscope to check the integrity of the interdigitated electrode pattern to ensure that the interdigitated electrodes are free from short circuits or open circuits. The controller can be an FPGA controller. The finger electrode array can be a transparent indium tin oxide interdigitated electrode array. Step 3: Electric field parameter setting: Based on the dielectric wetting theory, establish a quantitative control relationship between electric field strength and contact angle, and set the electric field parameters; Step 4: Synchronous Printing Control: A combination of single-factor variable method and orthogonal experimental method is used to optimize key printing parameters, with line width consistency and edge roughness as the core evaluation indicators. Key printing parameters include droplet volume, printhead temperature, and substrate temperature. Step 5: Gradient sintering treatment: A multiphysics digital simulation model is constructed based on finite element analysis software. The multiphysics digital simulation model is a temperature-stress-conductivity coupled model. Based on the sintering program determined by the temperature-stress-conductivity coupled model, the printed sample is placed in a tube sintering furnace and gradient sintering is carried out in a reducing atmosphere. Through a precise temperature control thermal field strategy, the interface stress is eliminated and the bonding is strengthened.

[0027] Optionally, the embedded transparent electrode array system includes a transparent electrode array, a multiplexer controller, a high-voltage AC signal source, and an FPGA main control unit; The transparent electrode array is fabricated on the back of a ceramic substrate using magnetron sputtering and photolithography with indium tin oxide. Each pair of interdigitated electrodes in the interdigitated electrode array is connected to a multiplexer controller. The multiplexing controller receives instructions from the FPGA main control unit to enable or disable any pair of interdigital electrodes; High-voltage AC signal source and FPGA main control unit: The high-voltage AC signal source is controlled by the FPGA main control unit to generate the required square wave signal; the FPGA main control unit receives the nozzle position coordinates from the motion platform.

[0028] Optionally, the working process and path matching process of the embedded transparent electrode array system are as follows: Coordinate mapping: Before printing begins, the print path planning file is preloaded into the controller, and the controller internally establishes a lookup table that maps the two-dimensional plane coordinates (X,Y) of the nozzle to the electrode blocks on the back of the substrate. Real-time local control: During the printing process, the motion platform feeds back the precise position of the printhead to the controller. The controller calculates the designated electrode pair area directly below the printhead by using a lookup table based on the current printhead coordinates. Precise Enabling: The controller sends a command to the multi-channel selection controller to enable only the electrode pair directly below the nozzle, while shutting down the electrodes in all other areas; the square wave signal generated by the high-voltage signal source is precisely applied to the selected electrode pair. Dynamic tracking: As the printhead moves, the controller refreshes the position data and switches the enabled electrode pairs, so that the generated strong electric field area always closely follows the movement of the printhead, achieving local electric field control by matching the printing path; the strong electric field area is the region where the electric field strength exceeds the preset value.

[0029] Optionally, step 3 includes: An adjustable AC square wave signal is output by the controller, and an electric field is applied to the adjustable AC square wave signal to regulate the ink wetting behavior; the electric field parameters are set, including the operating voltage, frequency, and duty cycle; the electric field parameters are set based on the Young-Lippmann equation; Specifically, the Young-Lippmann equation:

[0030] in, The dynamic contact angle after applying an electric field intensity E. The intrinsic contact angle when no electric field is applied. The vacuum permittivity, γ represents the relative permittivity of the functional ink dielectric layer, and γ represents the gas-liquid surface tension of the ink. The Young-Lippmann equation theoretically and quantitatively describes the cosine value of the contact angle. It is linearly proportional to the square of the applied electric field intensity E; Based on the Young-Lippmann equation and considering the characteristics of the selected nano-silver ink, the optimal electric field strength control value is determined; by outputting an adjustable AC square wave signal through the controller and controlling the value of the applied voltage V, the calculated electric field strength E is stabilized at the specified value.

[0031] Optionally, the electric field strength E is determined by the voltage V applied to the interdigital electrodes and the electrode geometry. The electric field strength between two adjacent interdigital electrodes is calculated using the following formula:

[0032] Where V is the peak voltage applied to the interdigital electrode pair, and d is the spacing between the interdigital electrodes.

[0033] Optionally, step 4 includes: Nano-silver conductive ink is injected into a piezoelectric inkjet printer cartridge, and the printhead temperature and droplet volume are set. With the synchronous assistance of an electric field, a flow field that optimizes the droplet deposition morphology is established. The electric field force increases the electrical stress at the solid-liquid-gas three-phase contact point, thereby increasing the contact linear velocity, optimizing the flow field, and effectively suppressing the rebound effect of ink droplets; Electric field modulation induces convection exceeding the preset intensity, the internal flow field optimizes particle transport, effectively eliminates the coffee ring effect, and makes the deposited film layer more uniform. The combined effect of an electric field and an optimized flow field ensures that the outline of the ink droplet after shaping is clear and the edges are smooth. A motion platform is used to achieve spatial synchronization between the print head and the electric field, and encoder feedback ensures that the lag time is less than the preset time; during the printing process, the substrate temperature and ambient humidity are controlled to meet the printing requirements.

[0034] Optionally, optimizing the droplet volume includes: the droplet volume directly determines the size and resolution of the deposited ink dots; under the condition of determining the ink material properties, testing the change in droplet volume to determine the droplet volume that meets the requirements, so as to ensure the consistency of linewidth from the source; the ink material properties include particle size, viscosity and composition; Optimizing the printhead temperature includes: printhead temperature directly affects the viscosity and surface tension of the ink; monitoring the viscosity change of the ink at different temperatures to determine the optimal value of the printhead temperature to ensure that the shape and volume of each ink droplet are highly consistent; The substrate temperature mainly controls the evaporation rate and spreading of ink droplets after they impact the ceramic substrate; under the assistance of an electric field, the effect of different substrate temperatures on the edge morphology of printed lines is tested; the required substrate temperature is determined by the heat flow induced by the temperature difference between the substrate temperature and the printhead temperature.

[0035] Optionally, the thermal field strategy of precisely controlling temperature to eliminate interfacial stress and enhance bonding includes: Interface diffusion layer optimization: Heat to a specified temperature at a preset rate and hold for a period of time to promote the formation of an interface transition layer and promote the interdiffusion between metal nanoparticles and ceramic surface atoms to form a transition layer. Internal defect elimination: Based on the specified temperature, the temperature is increased and maintained to achieve full sintering of conductive particles. The thermal field causes the conductive particles to aggregate and grow, increasing the sintering density and eliminating related defects, including internal pores. Residual stress relief: Cool the interface transition layer to room temperature at a specified rate to eliminate thermal stress.

[0036] Optionally, the temperature-stress-conductivity coupling model is established, including: Geometric modeling and material property definition: A three-dimensional structure including a ceramic substrate, a metal circuit pattern, and an interface layer is established in the simulation software, and temperature-related material parameters are input for each component; the relevant material parameters include the coefficient of thermal expansion, elastic modulus, Poisson's ratio of the ceramic substrate and ink, the conductivity of the metal circuit, and the activation energy of the interface layer; Physics Field Setup and Coupling: A solid heat transfer module is introduced to simulate the transfer of the temperature field to the sample and the temperature distribution inside the sample; a solid mechanics module is introduced, with the thermal field as input; the thermal stress caused by the mismatch between the ceramic substrate and the circuit material is calculated by solving the thermoelastic constitutive equation; a current module is introduced, with the sintering temperature field as input; the Arrhenius equation is used to simulate the effect of temperature on the conductivity of the metallic circuit; the temperature field is used as the independent variable, simultaneously driving the stress field and conductivity changes, to achieve coupled simulation.

[0037] Optionally, after step 5, the method further includes: optimizing the electric field parameters and sintering curve based on the test results, and establishing a process-performance correspondence database; the test results are the results of peeling tests performed using a micro-force tester; the process-performance correspondence database includes process input parameters and their corresponding performance output indicators; the process input parameters include electrowetting parameters, printing parameters, and sintering parameters; the performance output indicators include interface performance, electrical performance, morphological performance, and environmental reliability; After establishing the process-performance correspondence database, the process also includes quality inspection and packaging. The quality inspection and packaging include: An automated optical inspection system is used to check circuit integrity, measuring the linewidth consistency and edge roughness after flow field optimization. Products that meet the requirements are subjected to anti-oxidation encapsulation treatment, which can be achieved by vacuum phase deposition of parylene to form a protective layer. All products are subjected to full inspection to ensure that there are no interface defects.

[0038] For ease of understanding, this application also provides a more specific embodiment: The interface bonding of the circuitry on the surface of the ceramic curved substrate 1 was enhanced. The entire process, through the synergistic interaction of an electric field, a flow field, and a thermal field, achieved a breakthrough improvement in interface bonding strength: the electric field modulates ink wetting behavior, the flow field optimizes ink droplet deposition morphology, and the thermal field eliminates interfacial stress. (See also...) Figure 1 A schematic diagram of the electrowetting-assisted method for enhancing interfacial bonding includes a ceramic curved substrate 1, an electrostatic generator 2, a high-voltage AC signal source 3, and a circuit array 4. Before formal printing, it is necessary to establish and optimize the matching relationship between the specific functional ink and the electric field parameters. In this embodiment, nano silver ink (DGP-40LT) is used as an example, and the specific optimization matching process is as follows. (1) Determination of key characteristic parameters of ink: The intrinsic contact angle of the ink on the ceramic substrate without electric field is measured using a contact angle measuring instrument. The measured value is ; Use a surface tension meter to measure the gas-liquid surface tension of the ink. The measured value is The relative permittivity of the ink was measured using an impedance analyzer. The measured value is 5.2; (2) Calculation of theoretical electric field strength: According to the Yang-Lippmann equation of dielectric wetting theory, the target contact angle is set. for (Right now ); the parameters measured above ( , , Substituting into the equation, the required theoretical electric field strength is obtained. This value is the initial optimization target; (3) Frequency and waveform optimization experiment: fix the electric field strength as ,exist The frequency of the AC electric field was scanned within the range; the optimization goal was to find a frequency point that could maintain stable wetting behavior without electrolysis or charge accumulation; the experimental results showed that when the frequency was below 1 kHz, ink electrolysis was observed; when the frequency was above 10 kHz, the uniformity of the electric field decreased due to the skin effect. Finally, 5 kHz was selected as the optimal frequency, at which the contact angle was stable and the repeatability was good; (4) Experimental verification and fine-tuning: in , Actual printing tests were conducted under the specified parameters, and the measured contact angle was 38°, slightly higher than the theoretical value. The reason for this was that the theoretical model did not fully account for factors such as interface slip and ink viscosity. Therefore, fine-tuning was performed: the electric field strength was gradually increased to 2.0 kV / mm; under these parameters (2 kV / mm, 5 kHz), the measured contact angle stabilized at [value missing]. Furthermore, the ink droplet spreading shape is optimal, with no backsplattering or coffee ring phenomenon. This set of parameters was determined to be the optimal matching parameters for this ink; (5) Database establishment: Repeat the above process to test various different inks (such as conductive polymer PEDOT:PSS, viscosity 15cP, Each ink type is paired with an ink model, and a database of their corresponding "ink characteristics - optimal electric field parameters" is established and entered into the system. During subsequent printing, the system will automatically retrieve the preset optimal electric field parameters simply by selecting the ink type from the database.

[0039] The above-described optimization matching process demonstrates that the "establishment of optimized matching" in this application is a closed-loop process based on theoretical guidance and precise calibration through experimental verification and feedback, ensuring that the method has good adaptability and repeatability for different inks.

[0040] The specific implementation steps are as follows: Step 1: Pre-treatment of curved substrates, selecting surface roughness The AlN ceramic substrate was subjected to a stepwise ultrasonic cleaning process using acetone, isopropanol, and deionized water (5 minutes each), followed by drying with high-purity nitrogen. The cleaned substrate was then placed in a plasma cleaner and treated with oxygen plasma at 100W for 3 minutes to remove surface organic contaminants and increase surface energy.

[0041] Step 2: Electrode System Integration The aim is to integrate an embedded transparent electrode array system and explain how it provides the hardware foundation for achieving precise electrowetting assistance. Step two corresponds to "electric field" modulation, integrating a transparent indium tin oxide (ITO) interdigitated electrode array on the back of the substrate. The electrode linewidth is designed to be 80±5μm, the spacing is 150±10μm, and the sheet resistance is controlled at 15-20Ω / The electrodes are connected to the FPGA controller via silver paste to ensure signal transmission stability. An optical microscope is used to inspect the integrity of the interdigital electrode pattern to ensure there are no short circuits or open circuits.

[0042] The embedded transparent electrode array system mainly consists of three parts: (1) Transparent circuit array: The circuit array (e.g., indium tin oxide (ITO) is used to fabricate the circuit array on the back of the AlN ceramic substrate by magnetron sputtering and photolithography. Figure 3(As shown). The circuit linewidth is 80±5μm, the spacing is 150±10μm, and the sheet resistance is controlled at 15-20Ω / □. This design makes the electrode array optically highly transparent (>85%), and there is almost no obstruction when observing the printing process from the front, which meets the premise of "not affecting the printing observation"; (2) Multiplexer controller: Each pair of interdigitated electrodes of the electrode array is connected to the multiplexer controller (MUX) through a micro-wire. The controller receives instructions from the main control FPGA and can independently and quickly (switching time <1μs) select or close any pair of interdigitated electrodes; (3) High voltage AC signal source 3 and FPGA main control unit: The precision high voltage AC signal source 3 controlled by the FPGA program is used to generate the required square wave signal (2kV / mm, 5kHz, 50% duty cycle). The FPGA main control unit is the "brain" of the whole system, and receives the nozzle position coordinates from the motion platform in real time. The working principle and path matching process of the system are as follows: (1) Coordinate mapping: Before printing begins, the printing path planning file (such as G code) is preloaded into the FPGA. The FPGA establishes a lookup table that maps the two-dimensional plane coordinates (X,Y) of the nozzle to the electrode blocks (Zone) on the back of the substrate; (2) Real-time local control: During printing, the high-precision motion platform feeds back the precise position of the nozzle to the FPGA in real time. The FPGA calculates the specific electrode pair area covered directly below the nozzle based on the current nozzle coordinates through the lookup table; (3) Precise empowerment: Subsequently, the FPGA sends an instruction to the multi-channel selection controller to enable only 1-2 pairs of electrodes directly below the nozzle, while turning off the electrodes in all other areas. The square wave signal generated by the high-voltage signal source is precisely applied to this set of selected electrode pairs; (4) Dynamic following: As the nozzle moves, the FPGA continuously refreshes the position data and dynamically and quickly switches the enabled electrode pairs, so that the generated strong electric field area always follows the movement of the printing nozzle, realizing "real-time matching of printing path for local electric field control". The advantages of this design are: (1) It greatly saves energy consumption and avoids the entire substrate being in a high voltage electric field at all times; (2) It achieves precise local control, with the electric field acting only on the small area that needs to be printed immediately, avoiding premature activation or interference with the surrounding printed areas; (3) Through the combination of hardware integration and software algorithms, it achieves precise synchronization of electrowetting assistance and printing process in time and space.

[0043] Step 3: Setting electric field parameters aims to establish a quantitative control relationship between electric field strength and contact angle based on dielectric wetting theory, and to set precise electric field parameters accordingly.

[0044] In this application, "electric field strength" (E) specifically refers to the electric field strength between two adjacent interdigital electrodes, determined by the voltage (V) applied to the interdigital electrodes and the electrode geometry. The calculation formula is as follows: Where V is the peak voltage applied to the interdigital electrode pair, and d is the spacing between the interdigital electrodes in this embodiment (150 μm). The electric field strength under this definition is an independent variable that can be precisely controlled directly through electrical parameters (V) and structural parameters (d). (Clarifying the specific means of "electric field control") An adjustable AC square wave signal is output through the FPGA controller, and this adjustable AC square wave signal is applied to the electric field used to control the ink wetting behavior. The operating voltage is set to 2 kV / mm (the actual voltage value is automatically calculated based on the substrate thickness), the frequency is 5 kHz, and the duty cycle is 50%. (Explaining the effect of "controlling wetting behavior") This electric field parameter is optimized based on dielectric wetting theory. Specifically, it is based on the Young-Lippmann equation: ,in: The dynamic contact angle after applying an electric field intensity E. The intrinsic contact angle without an applied electric field ( ), The vacuum permittivity, The relative permittivity of the functional ink dielectric layer, Let $\frac{ ... ) and the applied electric field strength ( The square of is linearly proportional to .

[0045] The application of this electric field can create a non-uniform electric field distribution on the surface of the ceramic curved substrate, effectively reducing the contact angle of the functional ink (from...). Down to This achieves interface activation. An oscilloscope is used to monitor the electrode output waveform in real time, ensuring the waveform distortion rate is less than 3%. The system has a built-in impedance matching module that automatically optimizes output parameters based on the substrate's dielectric constant. In this embodiment, to achieve the contact angle from... Down to The goal is to achieve the objectives described in the above equations, taking into account the characteristics of the selected nano-silver ink. , Through calculation and experimental verification, the optimal electric field strength control value was determined. Therefore, by outputting an adjustable AC square wave signal through the FPGA controller and controlling the applied voltage V, the calculated electric field strength E is stabilized at 2kV / mm (frequency 5kHz, duty cycle 50%). The system has a built-in impedance matching module that can automatically fine-tune the output according to the substrate dielectric constant to maintain the stability of the electric field strength. In actual process debugging, the contact angle values ​​under different electric field strengths were recorded using a high-speed contact angle measuring instrument. The experimental data showed a high degree of agreement with the theoretical curve. This further verified the reliability of the quantitative control relationship, and based on this, the final process parameters were precisely optimized.

[0046] Step 4: Synchronous Printing Control Using a strategy combining single-factor variable method and orthogonal experimental method, and taking line width consistency (coefficient of variation CV) and edge roughness (Ra) as the core evaluation indicators, the following three key printing parameters were optimized: (1) ink droplet volume ( Optimization of droplet volume: Droplet volume directly determines the size and resolution of deposited ink dots; excessively large volume can lead to droplet fusion and uneven linewidth; excessively small volume requires higher printing precision and is prone to line breaks. Under constant conditions, the droplet volume variation from 2 pL to 6 pL was tested. The results show that a 4 pL droplet exhibits the best flight stability while ensuring sufficient resolution (achieving a minimum linewidth of 20 μm), and its coefficient of variation is [missing information]. This ensures the consistency of line width from the source; (2) nozzle temperature ( Optimization of the printhead: Printhead temperature directly affects the viscosity and surface tension of the ink. Too low a temperature results in high viscosity, easily causing nozzle clogging and unstable jetting; too high a temperature results in low surface tension, easily leading to droplet tailing and star-shaped droplets. Monitoring the viscosity changes of the ink at different temperatures revealed that when the printhead temperature is within a certain range... At that time, the viscosity of the selected nano-silver ink remained stable at Within the optimal ejection window. At this viscosity, the pressure wave energy generated by the piezoelectric actuator is most effectively converted into the kinetic energy of the droplets, ensuring that the shape and volume of each droplet are highly consistent, significantly reducing linewidth fluctuations. (3) The substrate temperature mainly controls the evaporation rate and spreading kinetics of ink droplets after they hit the substrate. If the temperature is too low, evaporation is slow, and adjacent ink droplets are prone to merging, resulting in coffee rings; if the temperature is too high, evaporation is too fast, which can easily lead to edge pinning and increased roughness. Under the assistance of an electric field, the effect of different substrate temperatures on the edge morphology of printed lines was tested. When the substrate temperature is set to At that time, it is related to the nozzle temperature ( The tiny temperature difference formed () This induces a moderate thermal Marangoni flow (flowing from the high-temperature region to the low-temperature region). This internal flow field effectively counteracts the capillary flow caused by solvent evaporation, which leads to the coffee ring effect, thereby greatly homogenizing the deposition distribution of nanoparticles and optimizing edge roughness to a minimum. .

[0047] Step four corresponds to "flow field" control: inject nano-silver conductive ink (such as DGP-40LT) into the piezoelectric inkjet printer cartridge, and set the printhead temperature to... The volume of the ink droplet is (Clarify the specific means and effects of “flow field optimization”) With the synchronous assistance of the electric field, the flow field for optimizing the deposition morphology of ink droplets can be established. Specifically, it is manifested as follows: (1) Initial impact period (0-50μs): The electric field force increases the electrical stress at the contact point of the solid-liquid-gas three phases, which increases the contact linear velocity by about 40%, optimizes the flow field, and effectively suppresses the rebound effect of ink droplets; (2) Stable spreading period (50-200μs): The electric field regulation induces Marangoni convection exceeding the preset intensity. This internal flow field optimizes particle transport, effectively eliminates the coffee ring effect, and makes the deposited film layer more uniform; (3) Equilibrium shaping period (200-500μs): Under the combined action of the electric field and the optimized flow field, the outline of the ink droplet after shaping is clear and the edge is smooth.

[0048] A high-precision motion platform (positioning accuracy ±1μm) is employed to achieve spatial synchronization between the printhead and the electric field, with encoder feedback ensuring a lag time of less than 1ms. This spatial-temporal synchronization guarantees the precise instantaneous coupling of "electric field control" and "flow field formation," which is crucial for optimizing the deposition morphology. During the printing process, the substrate temperature is maintained at... Environmental humidity is controlled at .

[0049] Step 5: Gradient sintering treatment The temperature-stress-conductivity coupling model is a multiphysics digital simulation model built based on finite element analysis software. The establishment process is as follows: (1) Geometric modeling and material property definition: A three-dimensional structure containing ceramic substrate, metal circuit pattern and interface layer is established in the simulation software. Temperature-related material parameters are input for each component: thermal expansion coefficient (CTE), elastic modulus, Poisson's ratio (for calculating stress) of substrate and ink; electrical conductivity of metal circuit (for evaluating performance); and activation energy of interface layer (for simulating diffusion); (2) Physical field setting and coupling: The "solid heat transfer" module is introduced to simulate the transfer of temperature field to sample and temperature distribution inside sample; the "solid mechanics" module is introduced and the thermal field is used as input. The thermal stress caused by the mismatch between substrate and circuit material is calculated by solving the thermoelastic constitutive equation; the "current" module is introduced and the sintering temperature field is used as input. The influence of temperature on the electrical conductivity of metal circuit is simulated using the Arrhenius equation. Thus, the temperature field, as the independent variable, drives the changes of the two dependent variables, stress field and conductivity, realizing the coupling simulation of the three.

[0050] The application and optimization process of the temperature-stress-conductivity coupling model is as follows: (1) Preliminary simulation and problem identification: Input the traditional sintering curve (such as rapid heating to 300℃ and holding). The simulation results show that during the rapid heating stage, there is a huge transient thermal stress at the interface (exceeding the tensile strength of the ceramic), which is predicted to cause microcracks; at the same time, the excessively fast sintering rate is predicted to form a porous structure, resulting in low electrical conductivity; (2) Iterative optimization and parameter determination: Based on the model's predictions, multiple rounds of simulation iterations were performed. To eliminate interface stress, the model simulated the stress evolution at different heating rates, demonstrating that controlling the heating rate within a certain range... At that time, the peak thermal stress can be reduced by 70% to below the safe range; to optimize the interface diffusion layer, the model simulated different low-temperature insulation stages ( The effect of this on the interatomic interdiffusion thickness at the interface. Simulation results show that, Holding at a lower temperature for 10 minutes promotes the formation of an optimized transition layer of approximately 2-5 nm without inducing excessive stress. To achieve sufficient densification, the model uses a conductivity module to inversely optimize the maximum sintering temperature. Simulations show that... By maintaining the temperature for 5 minutes, the conductivity of the circuit can reach more than 98% of the fully dense state, thus avoiding thermal damage to the substrate from higher temperatures. (3) Model verification: The final optimized sintering curve of the model ( The cooling process was applied to actual production, and the interfacial bonding strength (3.8 N / mm) and conductivity were measured. The measured data showed a high degree of agreement with the model predictions, verifying the accuracy and reliability of the coupling model, which was then formalized as the standard sintering procedure of this application.

[0051] Step five corresponds to "thermal field" control. The printed sample is placed in a tubular sintering furnace. Gradient sintering is performed under a reducing atmosphere. The following precise temperature control thermal field strategy is used to eliminate interfacial stress and strengthen the bonding, such as... Figure 3 As shown: (1) Interface diffusion layer optimization: Firstly, with The rate of heating up to And maintain for 10 minutes to promote the formation of the interface transition layer, promote the interdiffusion between metal nanoparticles and ceramic surface atoms, and form a 2-5nm transition layer, laying the foundation for high-strength bonding, while avoiding thermal stress caused by excessive heating; (2) Elimination of internal defects: continue heating to Hold for 5 minutes to achieve full sintering of the conductive particles. The thermal field at this stage allows the conductive particles to fully aggregate and grow, achieving a sintering density of over 98%, eliminating defects such as internal pores; (3) Residual stress release: Finally, The temperature is slowly reduced to room temperature to eliminate thermal stress, and temperature fluctuations are monitored in real time using an infrared thermometer throughout the process. The entire gradient sintering thermal field, combined with a reducing atmosphere, not only prevented metal oxidation but also promoted interfacial chemical reactions, ultimately achieving a high interfacial bonding strength. .

[0052] Step Six: Performance Testing and Optimization Using a micro-force tester (Instron 5944) Peeling tests were conducted at a loading rate of 0.5 mm / min to verify the ultra-high interfacial bonding strength (3.8 N / mm) obtained after the above three-field synergistic process. Sheet resistance was measured using a four-probe tester, and the interface morphology was observed using a scanning electron microscope (SEM). Based on the test results, the electric field parameters and sintering curves were optimized, and a process-performance correspondence database was established, as shown in Table 1.

[0053] Table 1. Example of a process-performance correspondence database

[0054] Step 7: Quality Inspection and Packaging Using an automated optical inspection (AOI) system for circuit integrity checks can measure the linewidth consistency after flow field optimization. ) and edge roughness ( Products that meet the requirements undergo anti-oxidation encapsulation treatment. Parylene C is used for vacuum phase deposition to form a protective layer 5-10 μm thick. Finally, the products are fully inspected under a 100x microscope to ensure that there are no interface defects.

[0055] This application achieves a breakthrough improvement in interfacial bonding strength by controlling ink wetting behavior with an electric field, optimizing ink droplet deposition morphology with a flow field, and eliminating interfacial stress with a thermal field. The embedded transparent electrode array system of this application can perform local electric field control in real time to match the printing path, achieving precise electrowetting assistance without affecting printing observation.

[0056] Dynamic electrowetting stage (interface activation): A quantitative control relationship between electric field strength and contact angle is established based on dielectric wetting theory. An AC electric field of a specific frequency (1-10kHz) is applied through an ITO transparent electrode array, forming a non-uniform electric field distribution on the ceramic substrate surface. According to the Young-Lippmann equation, the electric field-induced change in interfacial energy causes the ink contact angle to change from the initial... Down to The following innovative square wave modulation technology (duty cycle 30-70%) avoids the charge accumulation effect of DC electric fields and overcomes the skin effect of high-frequency AC electric fields. The electrode design employs an interdigitated structure (linewidth 80±5μm, spacing 150±10μm), achieving over 85% light transmittance while ensuring electric field uniformity (±5%). The key to this stage lies in establishing an optimized match between electric field parameters (voltage 2kV / mm, frequency 5kHz) and ink properties (dielectric constant, surface tension) to provide ideal wetting conditions for subsequent printing.

[0057] Precision Printing Stage (Circuit Printing): This stage innovatively couples the electrowetting effect with piezoelectric inkjet dynamics. Under the assistance of an electric field, the spreading process of ink droplets after impacting the substrate can be divided into three stages: ① Initial Impact Period (0-50μs): The electric field force increases the contact linear velocity by 40%, suppressing the rebound effect; ② Stable Spreading Period (50-200μs): Electric field-controlled Marangoni convection effectively eliminates the coffee ring effect; ③ Equilibrium and Shaping Period (200-500μs): Electric field-induced interfacial chemical bonding begins to form. This is achieved by optimizing printing parameters (printer temperature). Droplet volume 4±0.5 pL, substrate temperature To achieve consistent line width ( Significant improvement in edge roughness (<0.5μm).

[0058] Gradient sintering stage (bonding enhancement): This stage employs a multi-temperature zone precise temperature control strategy. By establishing a coupled model of temperature-stress-conductivity, it achieves: ① Interface diffusion layer optimization: ① The n-segment promotes the formation of a 2-5nm transition layer at the metal-ceramic interface; ② Internal defect elimination: the 250℃ / 5min sintering process achieves a conductive particle density of over 98%; ③ Residual stress release: the heating rate is controlled. This reduces thermal mismatch stress by 70%. A reducing atmosphere is innovatively introduced (…). This process not only prevents metal oxidation but also promotes interfacial chemical reactions, resulting in an interfacial bonding strength of 3.8 N / mm, which is 300% higher than that of traditional processes.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of this application. Any modifications or equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of the claims of this application.

Claims

1. An electro-wetting assisted piezoelectric inkjet printing circuitry bond enhancement method, characterized by, Comprise: Step 1: curved substrate pretreatment Select ceramic substrate with surface roughness less than a predetermined value, sequentially use acetone, isopropanol and deionized water for stepwise ultrasonic cleaning, dry with nitrogen; Put the cleaned ceramic substrate in the plasma cleaning machine and perform oxygen plasma treatment to remove surface organic contaminants and improve surface energy; Step 2: electrode system integration: integrate the embedded transparent electrode array system, integrate the interdigital electrode array on the back of the ceramic substrate, the interdigital electrodes in the interdigital electrode array are connected to the controller through silver paste, use an optical microscope to check the integrity of the interdigital electrode pattern, ensure that the interdigital electrodes have no short circuit or open circuit defects; Step 3: electric field parameter setting: based on the theory of dielectric wetting, establish a quantitative control relationship between electric field strength and contact angle, and set the electric field parameters; Step 4: synchronous printing control: combine single factor variable method with orthogonal experiment method, take line width consistency and edge roughness as core evaluation indexes, optimize key printing parameters; Key printing parameters include ink drop volume, nozzle temperature, substrate temperature; Step 5: gradient sintering treatment: based on finite element analysis software, construct a multi-physical field digital simulation model, which is a temperature-stress-conductivity coupled model; based on the sintering program determined by the temperature-stress-conductivity coupled model, place the printed sample in a tube furnace and perform gradient sintering in a reducing atmosphere; through the precise temperature control of the thermal field strategy, the interface stress is eliminated and the bonding degree is strengthened.

2. The method of claim 1, wherein, The embedded transparent electrode array system comprises a transparent electrode array, a multiplexing controller, a high-voltage alternating current signal source and an FPGA master control unit; The transparent electrode array adopts indium tin oxide to prepare the interdigital electrode array on the back of the ceramic substrate through magnetron sputtering and photolithography process; each pair of interdigital electrodes of the interdigital electrode array is connected to the multiplexing controller; The multiplexing controller receives instructions from the FPGA master control unit and selects or turns off any pair of interdigital electrodes; The high-voltage alternating current signal source and the FPGA master control unit: the high-voltage alternating current signal source is controlled by the FPGA master control unit and is used to generate the required square wave signal; the FPGA master control unit receives the nozzle position coordinates from the motion platform.

3. The method of claim 2, wherein, The working process and path matching process of the embedded transparent electrode array system are as follows: Coordinate mapping: before printing starts, the printing path planning file is preloaded into the controller, and a lookup table is established in the controller to map the nozzle two-dimensional plane coordinates (X, Y) and the electrode block area on the back of the substrate one by one; Real-time local regulation: during the printing process, the motion platform feeds back the accurate position of the nozzle to the controller, and the controller calculates the specified electrode pair area covered directly below the nozzle according to the current nozzle coordinates through the lookup table; Precise energization: the controller sends instructions to the multiplexing controller to enable only the electrode pair directly below the nozzle, while turning off the electrodes in all other regions; the square wave signal generated by the high-voltage signal source is accurately applied to the selected electrode pair. Dynamic following: as the nozzle moves, the controller refreshes the position data and switches the enabled electrode pairs, so that the generated strong electric field area always follows the printing nozzle movement, realizes the matching printing path for local electric field regulation; the strong electric field area is the area where the electric field intensity exceeds the preset value.

4. The method of claim 1, wherein, The step 3 comprises: An adjustable AC square wave signal is output by the controller, and the adjustable AC square wave signal is applied to an electric field for regulating the wetting behavior of the ink; the electric field parameters are set, and the electric field parameters include working voltage, frequency, and duty cycle; the electric field parameters are set based on the Young-Lippmann equation; Specifically, the Young-Lippmann equation is: wherein, is the dynamic contact angle after applying the electric field intensity E, is the intrinsic contact angle without the electric field, is the vacuum permittivity, is the relative permittivity of the functional ink dielectric layer, and γ is the air-liquid surface tension of the ink; the Young-Lippmann equation quantitatively describes the contact angle cosine value is linearly proportional to the square of the applied electric field intensity E. According to the Young-Lippmann equation and considering the characteristics of the selected nano-silver ink, the optimal electric field intensity control value is determined; an adjustable AC square wave signal is output by the controller, and the value of the applied voltage V is controlled so that the calculated electric field intensity E is stabilized at a specified value.

5. The method of claim 4, wherein, The electric field intensity E is determined by the voltage V applied to the interdigital electrode and the electrode geometry, and the electric field intensity between the two adjacent interdigital electrodes is calculated, and the calculation formula is: Wherein, V is the peak voltage applied to the interdigital electrode pair, and d is the spacing of the interdigital electrode.

6. The method of claim 1, wherein, The step 4 comprises: The nano-silver conductive ink is injected into the piezoelectric inkjet printer cartridge, and the nozzle temperature and ink drop volume are set; under the synchronous assistance of the electric field, a flow field for optimizing the deposition morphology of the ink drop is established: The electric field force increases the electric stress at the solid-liquid-gas three-phase contact to improve the contact line speed, optimize the flow field, and effectively suppress the rebound effect of the ink drop; The electric field regulation induces convection exceeding the preset intensity, the internal flow field optimizes the particle transport, effectively eliminates the coffee ring effect, and makes the deposited film layer more uniform; Through the joint action of the electric field and the optimized flow field, the profile of the ink drop after shaping is clear and the edge is smooth; A motion platform is used to realize the spatial synchronization of the printing nozzle and the electric field, and an encoder is used to feedback to ensure that the lag time is less than the preset time; the substrate temperature and the environmental humidity are controlled during printing to meet the printing requirements.

7. The method according to claim 1 or 6, characterized in that, Optimizing the ink drop volume includes: the ink drop volume directly determines the size and resolution of the deposited ink dot; under the condition of determining the ink material properties, the change of the ink drop volume is tested, and the volume of the ink drop meeting the requirements is determined to ensure the consistency of the line width from the source; the ink material properties include particle size, viscosity and composition; Optimizing the nozzle temperature includes: the nozzle temperature directly affects the viscosity and surface tension of the ink; the viscosity change of the ink at different temperatures is monitored to determine the optimal value of the nozzle temperature, so as to ensure that the shape and volume of each ink drop are highly consistent; The substrate temperature mainly controls the evaporation rate and spreading of the ink drop after impacting the ceramic substrate; under the assistance of the electric field, the influence of different substrate temperatures on the edge morphology of the printed line is tested; the heat flow induced by the temperature difference between the substrate temperature and the nozzle temperature is determined to meet the requirements of the substrate temperature.

8. The method of claim 1, wherein, The thermal field strategy through precise temperature control realizes the elimination of interfacial stress and the strengthening of bonding degree, which comprises: Interface diffusion layer optimization: warming up to a specified temperature at a preset rate and keeping for a period of time, promoting the formation of the interface transition layer, promoting the interdiffusion between the metal nanoparticles and the ceramic surface atoms, forming the transition layer; Internal defect elimination: on the basis of the specified temperature, continue to warm up and keep, realize the full sintering of the conductive particles, the thermal field makes the conductive particles gather and grow, improves the sintering density, eliminates the related defects; the related defects include internal porosity; Residual stress release: cooling the interface transition layer to room temperature at a specified rate to eliminate thermal stress.

9. The method of claim 1, wherein, The temperature-stress-conductivity coupling model is established, including: Geometric modeling and material property definition: a three-dimensional structure containing ceramic substrate, metal circuit pattern and interface layer is established in the simulation software, and temperature-related material parameters are input for each component; the related material parameters include the thermal expansion coefficient, elastic modulus, Poisson's ratio of the ceramic substrate and ink, the conductivity of the metal circuit, and the activation energy of the interface layer; Physical field setting and coupling: introduce the solid heat transfer module to simulate the temperature field transfer to the sample and the temperature distribution inside the sample; introduce the solid mechanics module and take the thermal field as the input; solve the thermoelastic constitutive equation to calculate the thermal stress generated by the mismatch between the ceramic substrate and the circuit material; introduce the current module and take the sintering temperature field as the input; use the Arrhenius equation to simulate the effect of temperature on the conductivity of the metal circuit; the temperature field as the independent variable, while driving the stress field and the conductivity change, realizing the coupled simulation.

10. The method of claim 1, wherein, After step 5, it further includes: feeding back the optimization of the electric field parameters and the sintering curve according to the test results, establishing a process-performance correspondence database; the test results are the results of the peeling test using a micro-force tester; the process-performance correspondence database includes process input parameters and corresponding performance output indicators; the process input parameters include electrowetting parameters, printing parameters and sintering parameters; the performance output indicators include interface performance, electrical performance, morphology performance and environmental reliability; After establishing the process-performance correspondence database, it further includes quality detection and packaging; The quality detection and packaging includes: Using an automatic optical detection system to perform circuit integrity inspection, measuring the line width consistency and edge roughness after flow field optimization; packaging the products that meet the requirements to prevent oxidation, forming a protective layer by vacuum vapor deposition; performing full inspection on the products to ensure no interface defects.

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