Flexible circuit printing system of cationic conductive ink

Abstract

The invention belongs to the technical field of electronic manufacturing, particularly relates to a flexible circuit printing system of cationic conductive ink, and aims to solve the problems of low printing precision of ink on a flexible substrate, inconsistent conductivity and low yield. The system comprises a substrate preprocessing and conveying module, a multi-physics field printing and curing head assembly and a dynamic process control and compensation module. The stability of a substrate is improved through plasma treatment and tension servo conveying, ink form fixing and selective body curing are achieved by combining piezoelectric ink jetting, in-situ metering, picosecond laser pinning and spatial modulation curing, and multivariable feed-forward compensation is conducted on the printing and curing process based on a physical information prediction model. According to the system, high-precision and high-consistency flexible circuit printing is realized, and the yield and the energy utilization efficiency are improved.

Description

Technical Field

[0001] This invention belongs to the field of electronic manufacturing technology, and specifically relates to a flexible circuit printing system using cationic conductive ink. Background Technology

[0002] Printed electronics, as an emerging electronic manufacturing technology, fabricates electronic devices and systems by directly printing functional materials onto substrates, demonstrating great potential in fields such as flexible displays, wearable devices, and smart sensors. The printing of conductive ink is a core step in achieving circuit interconnection, and its printing quality directly determines the performance and reliability of the final electronic product.

[0003] Flexible circuit printing technology, which uses conductive ink to create circuit patterns on flexible substrates, has attracted much attention due to its ability to adapt to complex shapes and endow electronic products with bendable and stretchable properties. This technology aims to efficiently construct high-precision conductive networks on the surface of non-rigid materials such as polymer films through precise additive manufacturing.

[0004] Existing flexible circuit printing systems are typically designed for general-purpose conductive inks, facing significant challenges when handling cationic conductive inks with unique curing mechanisms. Specifically, the curing units in existing systems often fail to provide energy conditions precisely matched to the kinetics of cationic polymerization, resulting in incomplete ink curing and severely impacting the circuit's conductivity and mechanical adhesion. Simultaneously, the lack of precise coordinated control between the printing module and the substrate transport mechanism makes it difficult to handle the minute deformations of the flexible substrate during transport, leading to uneven linewidth and positional shifts in the printed pattern. Furthermore, the system's insufficient adaptability to ink rheological properties prevents precise control of ink volume, further limiting the manufacturing precision and yield of complex, high-density flexible circuits. These issues collectively constitute a pressing technical challenge that needs to be addressed. Summary of the Invention

[0005] The purpose of this invention is to provide a flexible circuit printing system for cationic conductive ink, which aims to solve the technical problems of low printing accuracy, poor consistency of circuit conductivity, and low yield caused by the substrate's thermal sensitivity, difficulty in controlling ink rheology, and uneven curing process when printing cationic conductive ink on flexible substrates in the prior art.

[0006] To achieve the above objectives, this invention provides a flexible circuit printing system for cationic conductive ink, comprising: a substrate pretreatment and transport module, a multiphysics field printing and curing head assembly, and a dynamic process control and compensation module. The substrate pretreatment and transport module is used to perform surface energy modification treatment on the flexible substrate and achieve high-precision transport. The multiphysics field printing and curing head assembly works in conjunction with the substrate pretreatment and transport module to perform ink jetting, in-situ state metering, and staged energy delivery on the surface of the flexible substrate. The dynamic process control and compensation module interacts bidirectionally with both the substrate pretreatment and transport module and the multiphysics field printing and curing head assembly, and is used to predict process deviations based on real-time metering data using a preset physical information prediction model, and generate multivariate compensation control commands to perform closed-loop adaptive regulation of the printing and curing process.

[0007] In one embodiment of the present invention, the substrate pretreatment and conveying module includes a plasma surface treatment unit and a tension servo conveying unit. The plasma surface treatment unit is located before the flexible substrate enters the multiphysics printing and curing head assembly, and is used to emit an atmospheric pressure plasma jet to improve the wettability of the flexible substrate surface and achieve surface cleaning. The tension servo conveying unit includes an active drive roller, a driven tension roller, and a laser displacement sensor array disposed between them; the laser displacement sensor array monitors the flatness and tension state of the flexible substrate in real time and feeds back the monitoring data to the dynamic process control and compensation module, which dynamically adjusts the servo motor torque of the active drive roller and the driven tension roller accordingly to maintain constant tension and high-precision position of the flexible substrate in the printing area.

[0008] Furthermore, the multiphysics printing curing head assembly integrates a piezoelectric inkjet array, an in-situ metering subsystem, and a two-stage energy delivery subsystem. The piezoelectric inkjet array is used to spray cationic conductive ink droplets onto the surface of the flexible substrate according to the printing data instructions issued by the dynamic process control and compensation module.

[0009] In one embodiment of the present invention, the in-situ metrology subsystem is coaxially positioned adjacent to the nozzle exit of the piezoelectric inkjet array and synchronized with the ink jetting process at the microsecond level. This in-situ metrology subsystem includes a stroboscopic imaging sensor, a confocal dispersion sensor, and a micro-Raman spectrometer. The stroboscopic imaging sensor captures and analyzes the volume, velocity, and spreading morphology of ink droplets during flight and upon impact with the substrate using a short-pulse light source synchronized with the driving pulse of the piezoelectric inkjet array. The confocal dispersion sensor is used for non-contact, real-time measurement of the three-dimensional morphology of ink lines deposited on the substrate, acquiring their width, height, and cross-sectional profile data. The micro-Raman spectrometer, through an integrated fiber optic probe, acquires the Raman scattering spectrum of the deposited ink and calculates the conversion rate of the cationic polymerization reaction in the ink, i.e., the degree of curing, in real time by analyzing changes in specific chemical bond vibration peaks.

[0010] Furthermore, the dual-stage energy delivery subsystem is sequentially arranged after the piezoelectric inkjet array along the substrate delivery direction, and includes a picosecond laser pinning unit and a spatial modulation curing unit. The picosecond laser pinning unit emits an ultrashort pulse laser with a picosecond-level pulse width. This laser beam is focused on the location where the ink droplets are deposited on the substrate, triggering a polymerization reaction in the extremely shallow region of the ink droplet surface through instantaneous high peak power, causing a sharp increase in viscosity, thereby fixing the geometric shape of the ink droplets on the substrate and inhibiting their further flow and wetting expansion. The spatial modulation curing unit includes a digital micromirror device and an ultraviolet light-emitting diode array light source. The ultraviolet light-emitting diode array light source provides the energy required for curing, and the digital micromirror device generates a dynamic photomask that is completely consistent with the target circuit pattern according to the circuit design layout data, precisely and graphically projecting ultraviolet light energy onto the ink line area for selective bulk curing, while avoiding thermal radiation effects on the surrounding flexible substrate area.

[0011] In one embodiment of the present invention, the dynamic process control and compensation module is functionally divided into a data acquisition and fusion unit, a physical information prediction model unit, and a multivariable drive control unit. The data acquisition and fusion unit is used to receive and synchronously process all sensor data from the in-situ metering subsystem, the laser displacement sensor data from the tension servo conveying unit, and the data from the external environmental temperature and humidity sensor, forming a high-dimensional state vector with a unified timestamp.

[0012] Furthermore, the physical information prediction model unit incorporates a pre-trained numerical model based on the principles of ink rheology, photochemical reaction kinetics, and heat transfer. This model receives a high-dimensional state vector output from the data acquisition and fusion unit as input, and calculates and predicts in real time the process deviations that will occur in the subsequent printing area under the current operating conditions. These process deviations include line width deviations, incomplete curing, or over-curing.

[0013] Furthermore, the multivariable drive control unit executes a multi-objective optimization compensation algorithm based on the prediction deviation output by the physical information prediction model unit. This algorithm calculates a set of optimal compensation control parameters in real time and generates corresponding drive commands, which are then sent to the various actuators of the system. The drive commands include: fine-tuning the drive waveform of a specific printhead in the piezoelectric inkjet array to change the volume and initial velocity of the ejected ink droplets; adjusting the laser pulse energy and frequency of the picosecond laser pinning unit to change the pinning effect of the ink droplets; performing pixel-level correction on the dynamic photomask pattern generated by the digital micromirror device in the spatial modulation curing unit, and adjusting the local light intensity and irradiation duration of the ultraviolet light-emitting diode array light source to achieve refined redistribution of curing energy; and fine-tuning the conveying speed of the tension servo conveying unit. Through this multivariable, feedforward-based collaborative compensation, the system can eliminate deviations before they actually occur, thereby achieving highly consistent control over the geometric accuracy and electrical performance of the final circuit product.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are as follows: 1. This invention decouples the ink morphology fixation from the bulk curing process by setting up a two-stage energy delivery subsystem. The picosecond laser pinning unit instantaneously locks the ink droplet geometry in a non-thermal manner, fundamentally suppressing the wetting and diffusion of ink on the flexible substrate and capillary effects. This greatly improves the edge sharpness of circuit patterns and the minimum linewidth control capability, making it possible to print high-density circuits on flexible substrates with high surface energy or uneven surfaces.

[0015] 2. This invention constructs an in-situ, multimodal metrology subsystem, integrating stroboscopic imaging, confocal sensing, and Raman spectroscopy into the printhead. For the first time, it achieves synchronous, real-time, and non-contact monitoring of ink geometry, three-dimensional contours, and chemical curing levels during the printing process. This online, end-to-end quality monitoring capability replaces traditional offline, sample-based inspection methods, providing essential, highly timely feedback data for achieving closed-loop process control.

[0016] 3. This invention uniquely introduces a dynamic process control and compensation module based on a physical information prediction model. This module does not rely on simple error feedback adjustment, but rather, through a deep understanding of the multi-physics coupling process, it proactively predicts impending process deviations and implements multi-variable collaborative compensation. This feedforward control mechanism elevates the system from a passive "error correction" system to an active "error prevention" system, effectively addressing random disturbances such as material batch differences and environmental fluctuations. This ensures high uniformity, consistency, and reliability of printed circuits under continuous production conditions, significantly improving the overall product yield.

[0017] 4. This invention employs a spatial modulation curing unit, which precisely delivers curing energy to the ink area via digital micromirror devices, avoiding ineffective heating of the heat-sensitive flexible substrate. This "digital lithography" curing method completely solves the problems of low energy utilization and substrate thermal damage faced by traditional oven or floodlight curing, ensuring the mechanical flexibility and dimensional stability of the flexible circuit, while significantly reducing system energy consumption. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall technical architecture of the flexible circuit printing system using cationic conductive ink proposed in this invention. Detailed Implementation Example 1, please refer to Figure 1 To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0019] This invention provides a flexible circuit printing system using cationic conductive ink. This system aims to address a series of technical challenges encountered in manufacturing high-precision circuits using cationic polymeric conductive inks on thermosensitive flexible substrates such as polyimide and polyethylene terephthalate. These challenges primarily stem from the ease with which flexible substrates undergo thermal and mechanical deformation during processing, the complex rheological properties of cationic inks themselves, their sensitivity to curing conditions, and the difficulty of achieving precise control over the physical and chemical processes at the microscale using traditional printing and curing processes. This invention constructs a closed-loop control system integrating online metering and feedforward compensation. Through the synergistic effect of multiple physical fields, it achieves precise control over the entire process of ink application, from spraying, deposition, pinning to final curing. This significantly improves the geometric accuracy, conductivity consistency, and final product yield of the printed circuit while ensuring the integrity of the flexible substrate.

[0020] The flexible circuit printing system for cationic conductive ink provided by this invention comprises three core components: a substrate pretreatment and transport module, a multiphysics field printing and curing head assembly, and a dynamic process control and compensation module. The substrate pretreatment and transport module, as the system's physical input, is responsible for the crucial surface energy regulation of the roll-shaped or sheet-shaped flexible substrate, transporting it to the core processing area with extremely high stability and positional accuracy. The multiphysics field printing and curing head assembly is the system's core actuator. With the precise cooperation of the substrate pretreatment and transport module, it performs precise ink jetting at designated locations on the flexible substrate, in-situ real-time metering of the ink's state after jetting and deposition, and staged, regional energy delivery to complete the forming and curing of the circuit pattern. The dynamic process control and compensation module, as the system's intelligent hub, interacts bidirectionally and in real-time with both the substrate pretreatment and transport module and the multiphysics field printing and curing head assembly via a high-speed data link. It continuously receives real-time measurement data from each sensing unit, uses a built-in, physics-based prediction model to predict upcoming process deviations, and generates a set of multivariable, collaborative compensation control commands based on the prediction results. These commands are then sent to each execution unit, thereby implementing closed-loop, adaptive dynamic control of the entire printing and curing process.

[0021] In a specific application scenario, the system is deployed in a temperature- and humidity-controlled cleanroom for the continuous production of flexible printed circuit boards. Flexible substrates are fed into the system in roll form from the unwinding device, first undergoing pre-treatment and conveying by the substrate pretreatment and conveying module, then passing under the multi-physics field printing and curing head assembly to complete the printing and curing of the circuit patterns, and finally collected by the rewinding device. The entire process operates fully automatically under the unified scheduling and monitoring of the dynamic process control and compensation module.

[0022] The core function of the substrate pretreatment and transport module is to create ideal substrate conditions for subsequent precision printing processes. Physically, this module comprises a plasma surface treatment unit and a tension servo transport unit. The plasma surface treatment unit is strategically positioned along the path of the flexible substrate before it enters the printing area. Its main purpose is to address the poor wettability of cationic conductive inks on flexible substrates, especially those with low surface energy. This unit employs a dielectric barrier discharge structure. Under the excitation of a high-frequency, high-voltage power supply, a mixture of inert gas, such as argon or nitrogen, and trace amounts of active gas, such as oxygen or air, is ionized to generate a low-temperature, highly active atmospheric pressure plasma jet. When the flexible substrate passes through this jet region, the high-energy particles in the plasma, including ions, electrons, and free radicals, undergo a series of physical and chemical interactions with the polymer molecular chains on the substrate surface. The physical interactions manifest as micro-etching of the surface, removing adsorbed organic contaminants and microparticles, achieving nanoscale surface cleaning. The chemical reaction involves introducing oxygen-containing polar functional groups, such as hydroxyl, carboxyl, and carbonyl groups, onto the polymer surface. The introduction of these functional groups significantly increases the surface free energy of the substrate, thereby greatly improving the spreading and adhesion properties of subsequent ink droplets on the substrate, laying the foundation for the formation of uniform and continuous conductive lines.

[0023] The tension servo conveying unit is responsible for precisely controlling the mechanical state of the flexible substrate throughout the entire processing and printing process. The unit's mechanical structure consists of an active drive roller and a driven tension roller, between which the flexible substrate is tensioned and conveyed. The active drive roller is driven by an AC servo motor with a high-resolution encoder, providing the main conveying power. The driven tension roller is controlled by another AC servo motor operating in torque mode to apply precise tension. In the critical area between the two rollers, directly below the multiphysics printing and curing head assembly, a one-dimensional or two-dimensional array of multiple laser displacement sensors is deployed. These sensors utilize the principle of laser triangulation, non-contactly monitoring the three-dimensional contour of the flexible substrate within the printing area in real time with sub-micron resolution and kilohertz sampling frequency, thereby obtaining precise data on its flatness and minute sag changes caused by tension fluctuations. This sensor data is transmitted in real time to the dynamic process control and compensation module. The module's internal control algorithms, such as proportional-integral-derivative controllers or more complex fuzzy logic controllers, dynamically and collaboratively adjust the speed of the active drive roller servo motor and the output torque of the driven tension roller servo motor based on the real-time position deviation fed back by the laser displacement sensor array and the preset target flatness. This closed-loop feedback control mechanism effectively suppresses tension fluctuations caused by uneven substrate roll thickness, ambient temperature changes, or dynamic disturbances during the start-up and shutdown process of the conveyor, ensuring that the flexible substrate maintains constant tension and high-precision spatial position during microsecond-level printing, providing a stable mechanical platform for achieving high-fidelity circuit pattern transfer.

[0024] The multiphysics printing curing head assembly is the most core and complex integrated component in the technical solution of this invention. It highly integrates ink jetting, process metering, and energy delivery functions into a compact head unit, achieving seamless connection of the process flow in space and time. This assembly specifically comprises three main parts: a piezoelectric inkjet array, an in-situ metering subsystem, and a two-stage energy delivery subsystem.

[0025] Piezoelectric inkjet arrays are direct actuators that realize circuit patterning. They consist of hundreds or even thousands of individual nozzles manufactured using microelectromechanical systems (MEMS) technology, arranged linearly or in two dimensions. Behind each nozzle is a piezoelectric ceramic actuator. A dynamic process control and compensation module converts the circuit layout data, processed by a raster image processor, into a series of precise voltage drive waveform commands for each nozzle. These commands are transmitted to the printhead drive circuitry via a high-speed data interface. The voltage waveform applied by the drive circuitry, such as an optimized double trapezoidal pulse, causes precise micro-deformation of the piezoelectric ceramic, squeezing the cationic conductive ink in the ink chamber, thereby ejecting ink droplets of uniform size (pixel-level) from the corresponding nozzle. By fine-tuning the drive waveform parameters, such as the pulse amplitude, width, and rise / fall slope, the volume, initial velocity, and flight attitude of the ejected ink droplets can be precisely controlled; this is one of the important means of subsequent compensation control.

[0026] The in-situ metrology subsystem is the data acquisition foundation for achieving closed-loop process control. Its design philosophy is to perform non-contact, undisturbed, real-time measurement of key physical and chemical quantities at the same location and moment during the printing process. This system is located adjacent to the nozzle exit of the piezoelectric inkjet array, coaxial with the printhead or set in parallel with a fixed offset, ensuring that its measurement area accurately covers the entire ink process from ejection to deposition. In terms of timing, the triggering of its internal sensors is synchronized with the ejection pulses of the piezoelectric inkjet array at the microsecond level. Specifically, this system integrates three different sensing technologies: a stroboscopic imaging sensor, a confocal dispersion sensor, and a micro-Raman spectrometer.

[0027] The stroboscopic imaging sensor focuses on capturing the dynamic behavior of ink droplets during their flight and impact on a substrate. It consists of a short-pulse LED light source with a pulse width in the nanosecond range and a high-speed camera equipped with a microscope objective. The flash of the light source is precisely triggered by a drive signal from a piezoelectric inkjet array and can be adjusted in microseconds via a programmable delay generator. By setting different delay times, images of the ink droplet at any position along its flight path can be "frozen," or its morphology at the instant it impacts the substrate and begins to spread can be captured. Image processing software performs real-time analysis on the acquired sequence of images, calculating the volume and sphericity of the ink droplet during flight using edge detection and pixel integration algorithms, and determining its flight velocity by analyzing the displacement of the droplet's centroid in two consecutive frames. For images at the moment of impact, the droplet's spreading diameter and contact angle are analyzed; these parameters directly affect the width and edge quality of the final line.

[0028] A confocal dispersion sensor is used to accurately measure the three-dimensional morphology of ink that has been deposited on a substrate to form wet film lines. This sensor utilizes a white light source and a specially designed lens group with strong dispersion characteristics. When white light is focused onto the surface of the object being measured, different wavelengths of light focus at different vertical heights. The sensor analyzes the spectrum of the reflected light using a built-in spectrometer, and accurately derives the height information of the measurement point based on which wavelength has the greatest intensity. Through two-dimensional scanning or in conjunction with substrate transport motion, three-dimensional point cloud data of the deposited ink lines can be quickly acquired, allowing for real-time calculation of key geometric parameters such as precise width, height, cross-sectional area, and edge steepness.

[0029] The micro-Raman spectrometer provides the system with in-depth online monitoring capabilities at the chemical reaction level. It uses a fiber optic probe integrating laser excitation and signal collection to focus a low-power monochromatic laser beam onto the deposited ink lines. Molecules in the ink undergo Raman scattering under laser irradiation, and the scattered light contains characteristic information about molecular vibrations and rotations. The collected scattered light is transmitted back to the spectrometer via fiber optic cable for analysis, yielding the Raman spectrum of the ink. For cationic polymer inks, the monomers typically contain specific functional groups, such as epoxy groups or vinyl ethers, which correspond to specific, sharp vibrational peaks in the Raman spectrum. As the polymerization reaction proceeds, the intensity of these monomer characteristic peaks gradually decreases, while new characteristic peaks representing the polymer backbone are gradually generated or enhanced. By calculating the intensity ratio of a specific monomer characteristic peak to an internal standard peak or polymer characteristic peak in real time and comparing it with a pre-established calibration curve, the conversion rate of the cationic polymerization reaction in the ink, i.e., the degree of curing, can be calculated quantitatively and in real time. This is the first time that direct online monitoring of chemical curing kinetics has been achieved in the printed electronics manufacturing process.

[0030] The dual-stage energy delivery subsystem is an innovative design proposed in this invention to address the core contradiction between ink rheology control and efficient curing on flexible substrates. It abandons the traditional single heating or UV curing method, decomposing the curing process into two independent stages: "pinning" and "bulk curing," which are sequentially positioned after the piezoelectric inkjet array along the substrate transport direction. Specifically, this subsystem includes a picosecond laser pinning unit and a spatial modulation curing unit.

[0031] The picosecond laser pinning unit rapidly "freezes" the geometry of ink droplets within an extremely short time after deposition on the substrate surface. This prevents uncontrolled flow, spreading, or satellite droplet coalescence caused by the interaction of surface tension, gravity, or substrate surface energy—phenomena that are the main causes of irregular line edges, out-of-tolerance linewidth, and short-circuit defects. This unit employs an ultrashort pulse laser with a pulse width in the range of 10 to 100 picoseconds. Such a short pulse width allows the laser energy to be highly concentrated on the ink material before heat diffuses to the surrounding substrate. By selecting an appropriate laser wavelength, it can be efficiently absorbed by the photoinitiator in the ink through multiphoton or two-photon absorption processes. This generates extremely high instantaneous peak power, sufficient to trigger a localized, rapid polymerization reaction in a very shallow region of the ink droplet surface, typically at a depth of micrometers or submicrometers. This reaction causes a gel or solid shell to rapidly form on the ink droplet surface, with a sharp increase in viscosity, effectively fixing the entire macroscopic geometry of the ink droplet onto the substrate. Because the action time is extremely short and the total energy input is very low, almost no heat is transferred to the heat-sensitive flexible substrate. Therefore, this is a "cold" processing process with no thermal effect or only a slight thermal effect.

[0032] Following the picosecond laser pinning unit, the spatial modulation curing unit is tasked with fully and deeply curing the pinned ink lines to achieve the desired mechanical strength and conductivity. At the heart of this unit is a digital, programmable ultraviolet (UV) light delivery system. This system includes a high-power array of UV-emitting diodes (LEDs) to provide the photon energy required for curing. The UV light emitted by the source is uniformly illuminated by a homogenizing system onto the surface of a digital micromirror device. This device is a semiconductor light modulator with millions of micron-sized mirrors integrated on its surface that can switch rapidly between two angles. A dynamic process control and compensation module calculates the area requiring illumination for each frame in real time based on the circuit layout data and converts this information into control signals for the digital micromirror device. Each micromirror deflects according to instructions, reflecting the UV light of its corresponding pixel into the projection lens or deflecting it into a light absorption trap. Finally, the projection lens precisely images the pattern formed by all the activated micromirrors onto the ink line area of ​​the moving flexible substrate below. This creates a dynamic, maskless virtual photomask, allowing curing energy to be precisely and graphically projected onto the areas requiring curing, while the surrounding substrate area remains completely untouched by ultraviolet light. This selective curing method not only significantly improves energy efficiency but, more importantly, completely avoids the ineffective heat radiation and thermal damage to the flexible substrate caused by traditional floodlight curing or oven heating, thus ensuring the mechanical flexibility and dimensional stability of the final flexible circuit.

[0033] The dynamic process control and compensation module, as the intelligent decision-making core of the entire system, is further divided into a data acquisition and fusion unit, a physical information prediction model unit, and a multivariable drive control unit.

[0034] The data acquisition and fusion unit serves as the module's sensing entry point. It receives data streams from sensors throughout the system in parallel via high-speed, synchronous hardware interfaces, such as field-programmable gate arrays (FPGAs) or dedicated data acquisition cards. This includes ink droplet dynamic parameters from the stroboscopic imaging sensor within the in-situ metrology subsystem, 3D morphology data from the confocal dispersion sensor, curing degree data from the micro-Raman spectrometer, and substrate flatness and tension state data from the laser displacement sensor array in the tension servo conveying unit. Simultaneously, it also acquires data from external environmental sensors deployed at key locations on the equipment, such as temperature and humidity. The core task of this unit is to assign a unified, high-precision timestamp to these heterogeneous data streams from different sources and with varying sampling rates, achieving precise temporal alignment. Subsequently, it integrates this synchronized data into a high-dimensional state vector, which comprehensively describes the physical, geometric, and chemical state of the current printing process at every moment.

[0035] The Physical Information Prediction Model (PIM) unit is crucial for achieving feedforward control. This unit embeds a core numerical model, which is not a simple black-box model based on data, but rather a "grey-box" model deeply integrating physical mechanisms from multiple fields. During the development phase, researchers constructed a complex multi-physics coupled finite element or finite volume simulation model based on the rheological constitutive equation of cationic conductive ink, the photochemical reaction kinetics model, and the heat transfer model under laser and ultraviolet light. Through extensive simulation calculations and experimental data calibration, this complex model was trained and dimensionality reduced to form a computationally efficient surrogate model or response surface model, which was ultimately deployed in the PIM unit. During system operation, the model receives high-dimensional state vectors output in real time by the data acquisition and fusion unit as input. Based on these current, realistic operating parameters, the model can predict, through high-speed calculations, the downstream region along the substrate transport direction under the current state, and predict potential process deviations in the downstream printing and curing areas under the current operating conditions. The predicted deviation is multi-dimensional and can be quantified as the amount by which the line width will exceed the tolerance range, the percentage by which the conversion rate will be lower than the target value after curing, or the risk index of material embrittlement that may result from over-curing.

[0036] The core prediction function of the physical information prediction model unit can be characterized by the following state transition equation:

[0037] in, It is a vector of process results predicted at the next time step or spatial location, which includes key quality indicators such as line width and curing degree. This represents a pre-trained physical information prediction model that can run in real time. It is a high-dimensional state vector provided by the data acquisition and fusion unit at the current moment, capturing the complete state of the system at the current moment. It is the vector of control parameters currently applied to the system, including piezoelectric nozzle drive waveform parameters, laser energy, etc. This is the measured environmental disturbance vector, such as changes in temperature and humidity. The significance of this equation lies in the fact that, based on a comprehensive understanding of the current system state, control inputs, and environmental disturbances, it proactively calculates potential deviations in future process results through a model that incorporates physical laws.

[0038] The multivariable drive control unit is the center for generating and executing compensation commands. This unit receives the prediction deviation vector output from the physical information prediction model unit and immediately initiates a multi-objective optimization compensation algorithm. The goal of this algorithm is to find a set of optimal control parameter adjustments so that the adjusted system behavior can eliminate the predicted deviation in its early stages. This process can be described as solving an optimization problem whose objective function aims to minimize the weighted sum of the prediction deviation and the control adjustment cost.

[0039] The goal of this optimization process is to find the optimal control adjustment. To minimize a certain cost function J:

[0040] in, This is the desired process objective vector. The first term... It is composed of the weight matrix The second norm of the weighted prediction error represents the required process accuracy. (Second term) It is composed of the weight matrix The quadratic norm of the weighted control adjustment represents a constraint on control costs or actuator adjustment range, aiming to ensure the smoothness and stability of the control process. Algorithms, such as model predictive control or sequential quadratic programming, calculate this optimal control adjustment in real time. .

[0041] Once the optimal compensation control parameters are calculated, the multivariable drive control unit immediately translates them into specific hardware drive instructions and sends them to various distributed actuators in the system via a high-speed control bus. These instructions are coordinated and precise. For example, they may make minute voltage or time adjustments to the printhead drive waveform in a specific area of ​​the piezoelectric inkjet array to change the volume or initial velocity of subsequent ejected ink droplets, thereby compensating for linewidth variations that may be caused by local fluctuations in substrate surface energy; dynamically adjust the pulse energy or repetition frequency of the picosecond laser pinning unit to change the pinning effect of ink droplets and adapt to the slight differences in the rheological properties of different batches of ink; finely adjust the dynamic photomask pattern generated by the digital micromirror device in the spatial modulation curing unit at the pixel level, or finely redistribute the light intensity and irradiation time of a specific area of ​​the ultraviolet light-emitting diode array light source to compensate for differences in curing energy absorption caused by uneven ink line height; and even accelerate or decelerate the conveying speed of the tension servo conveying unit at the microsecond level to adjust the residence time of ink in the curing area. Through this multivariate input and multivariate output, model-based feedforward collaborative compensation, the system can proactively and predictively completely offset process deviations before they actually form and solidify. This achieves extremely high consistency control over the geometric accuracy and electrical performance of the final circuit product, and can maintain robust production quality even when faced with uncertainties such as raw material batch fluctuations, environmental disturbances, and drift caused by long-term equipment operation.

[0042] The core advantage of this invention lies in its systematic and innovative design, which fundamentally reconstructs the printing and manufacturing paradigm of flexible circuits. Firstly, by introducing a two-stage energy delivery subsystem, particularly picosecond laser pinning technology, it successfully decouples the two physical processes of ink morphology fixation and chemical solidification. This strategy of instantaneously locking the geometry of ink droplets without thermal effects suppresses ink wetting and diffusion on the flexible substrate at its source, significantly improving the edge sharpness of circuit patterns and the control over minimum feature sizes.

[0043] Secondly, the in-situ, multimodal metering subsystem constructed in this invention integrates various advanced sensing technologies into the printhead, achieving for the first time synchronous, real-time, and non-contact monitoring of ink geometry, three-dimensional contours, and chemical curing degree during the printing process. This end-to-end online quality monitoring capability provides unprecedentedly timely and high-dimensional feedback data for achieving closed-loop process control.

[0044] Most importantly, this invention uniquely introduces a dynamic process control and compensation module based on a physical information prediction model. This module's operating mechanism surpasses traditional error feedback regulation. Through a deep understanding of the multi-physics coupling process, it proactively predicts impending process deviations and implements multi-variable collaborative compensation. This feedforward control mechanism elevates the system from a passive "error correction" system to an active "error prevention" system, effectively responding to various random disturbances and ensuring high uniformity, consistency, and reliability of printed circuits under continuous production conditions, thereby significantly improving the overall product yield and production efficiency.

[0045] Finally, the use of spatial modulation curing units precisely delivers curing energy to the ink area via digital micromirror devices, avoiding ineffective heating of the heat-sensitive flexible substrate. This "digital lithography" curing method completely solves the problems of low energy utilization and substrate thermal damage faced by traditional curing processes, ensuring the mechanical properties and dimensional stability of flexible circuits, while achieving significant energy-saving effects.

Claims

1. A flexible circuit printing system for cationic conductive inks, characterized in that, The application relates to a flexible circuit printing and curing system. The application comprises: a substrate pretreatment and conveying module for surface energy modification and high-precision position conveying of a flexible substrate; a multi-physical-field printing and curing head assembly cooperatively arranged with the substrate pretreatment and conveying module, which integrally comprises: a piezoelectric inkjet array for spraying cation conductive ink droplets on the surface of the flexible substrate according to printing data instructions; an in-situ metrology subsystem coaxially arranged with the piezoelectric inkjet array for non-contact real-time metrology of multi-dimensional state parameters of the ink droplets from spraying to deposition, and generation of real-time metrology data; and a two-stage energy delivery subsystem arranged behind the piezoelectric inkjet array along the substrate conveying direction for performing morphology pinning and selective bulk curing of the deposited ink; 2. The flexible circuit printing system of cationic conductive ink according to claim 1, characterized in that, a dynamic process control and compensation module bidirectionally communicated with the substrate pretreatment and conveying module and the multi-physical-field printing and curing head assembly, which is used for receiving the real-time metrology data generated by the in-situ metrology subsystem, prospectively predicting process deviations of subsequent printing and curing processes through a built-in physical information prediction model, and calculating and generating a set of multivariable compensation control instructions according to the predicted process deviations, and issuing the multivariable compensation control instructions to the substrate pretreatment and conveying module, the piezoelectric inkjet array and the two-stage energy delivery subsystem to perform closed-loop adaptive regulation and control on the printing and curing processes. The in-situ metrology subsystem comprises: a stroboscopic imaging sensor for capturing and analyzing the volume and speed of the ink droplets in the flight process and the spreading morphology at the substrate impact moment through a short-pulse light source synchronized with the driving pulse of the piezoelectric inkjet array; a confocal dispersion sensor for real-time measurement of the three-dimensional morphology of the ink line deposited on the substrate to obtain the width, height and cross-section profile data thereof; 3. The flexible circuit printing system of cationic conductive ink according to claim 2, characterized in that, a micro-Raman spectrometer for real-time calculation of the conversion rate of the cation polymerization reaction in the ink by collecting the Raman scattering spectrum of the deposited ink and analyzing the change of the vibration peak of a specific chemical bond. The two-stage energy delivery subsystem comprises: a picosecond laser pinning unit arranged behind the piezoelectric inkjet array for emitting ultrashort pulse laser with a picosecond pulse width, which is focused on the position of the ink droplet just deposited on the substrate to initiate the polymerization reaction of the surface layer region of the droplet through instantaneous high peak power to fix the geometric morphology of the ink droplet; 4. The flexible circuit printing system of cationic conductive ink according to claim 3, characterized in that, a spatial modulation curing unit arranged behind the picosecond laser pinning unit for selectively bulk curing the ink line which has been pinned.

5. The flexible circuit printing system of cationic conductive ink according to claim 4, characterized in that, The spatial modulation curing unit comprises an ultraviolet light-emitting diode surface array light source and a digital micro-mirror device; the ultraviolet light-emitting diode surface array light source provides the energy required for curing, and the digital micro-mirror device generates a dynamic mask consistent with the target circuit pattern according to the circuit design layout data, and the energy is graphically projected to the ink line area. The substrate pretreatment and conveying module comprises: a plasma surface treatment unit arranged at a position before the flexible substrate enters the multi-physical-field printing and curing head assembly for emitting an atmospheric pressure plasma jet to improve the wettability of the surface of the flexible substrate. A tension servo feed unit for maintaining constant tension and high precision position of a flexible substrate in a printing area.

6. The flexible circuit printing system of cationic conductive ink according to claim 5, characterized in that, The tension servo feed unit comprises a driving roller, a driven tension roller and a laser displacement sensor array disposed between the two rollers; the laser displacement sensor array monitors the flatness and tension state of the flexible substrate in real time and feeds back the monitoring data to a dynamic process control and compensation module, which dynamically adjusts the servo motor torque of the driving roller and the driven tension roller accordingly.

7. The flexible circuit printing system of cationic conductive ink according to claim 6, characterized in that, The dynamic process control and compensation module comprises: a data acquisition and fusion unit for receiving and synchronously processing sensor data from the in-situ metrology subsystem and the substrate pretreatment and feed module, as well as external environmental temperature and humidity data, to form a high-dimensional state vector with a unified timestamp; a physical information prediction model unit for receiving the high-dimensional state vector as input and predicting process deviations; a multivariable drive control unit for generating the multivariable compensation control instruction based on the predicted process deviations.

8. The flexible circuit printing system of cationic conductive ink according to claim 7, characterized in that, The physical information prediction model unit has a numerical model pre-trained based on the principles of ink rheology, photochemical reaction kinetics and heat transfer; the prediction function of the model is characterized by: based on the high-dimensional state vector representing the current complete state of the system, the current applied control parameter vector and the measured environmental disturbance vector, the numerical model is used to prospectively calculate the process result vector including line width and solidification degree to be generated at the next time step or spatial position.

9. The flexible circuit printing system of cationic conductive ink according to claim 8, characterized in that, The multivariable drive control unit executes a multi-objective optimization compensation algorithm, the solution process of which is characterized by: solving a set of optimal control parameter adjustment amounts that make a cost function reach a minimum value, the cost function being composed of the weighted sum of the quadratic norm of the predicted error representing the process accuracy requirement and the quadratic norm of the control adjustment amount representing the control cost.

10. The flexible circuit printing system of cationic conductive ink according to claim 9, characterized in that, The multivariable compensation control instruction includes at least one of the following: adjusting the drive waveform of a specific nozzle in the piezoelectric inkjet array to change the volume and initial velocity of the ejected ink droplets; adjusting the laser pulse energy and frequency of the picosecond laser pinning unit; correcting the dynamic mask pattern generated by the digital micro-mirror device in the spatial modulation curing unit and adjusting the local light intensity and irradiation time of the ultraviolet light-emitting diode surface array light source; adjusting the feed speed of the tension servo feed unit.

Images