Printed circuit quality monitoring device and detection method based on dual-wavelength synchronous transmission and reflection detection

Abstract

The invention provides a printed circuit quality monitoring device based on dual-wavelength synchronous transmission and reflection detection and a detection method. Real-time online monitoring of the conductivity, the size precision and the geometric deformation of a printed circuit is achieved. In the production process of a printed circuit, a metamaterial printing quality detection pattern with specific reflection and transmission performance is introduced, and key function parameters such as the conductivity, the thickness and the diffusion characteristic of printing ink are comprehensively evaluated by monitoring the transmission characteristic of the pattern to terahertz waves. According to the system, production deviation is detected in real time, production parameters are automatically adjusted, and production conditions are optimized, so that the output of unqualified products is remarkably reduced, the operation efficiency and economical efficiency of a production line are improved, resource waste is reduced, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of quality monitoring in a printed electronics production process, and in particular to a printed circuit quality monitoring device and a detection method based on dual-wavelength synchronous transflection detection. Background Art

[0002] Printed electronics is a cutting-edge technology that applies traditional printing processes to the manufacture of electronic components and devices. It can directly print electronic devices on various flexible substrates, thereby achieving low-cost and high-efficiency production of electronic products. This technology uses a variety of methods such as flexographic printing, inkjet printing, gravure printing and screen printing to print photonic devices and electronic products directly on a variety of substrates such as fabrics, paper, plastics, etc. This technology has been widely used in fields such as wearable devices, sports industry and flexible displays. Due to the fast production pace, there may be large differences in quality during the printing process.

[0003] The entire process of printed circuit manufacturing is generally divided into four main stages: (a) selecting ink and substrate, (b) implementing printing, (c) sintering treatment and (d) printing quality inspection. The first is to choose the right ink and substrate. Among the various available substrates, flexible substrates are particularly favored because of their unique bendability, stretchability and twistability while maintaining good electrical properties. A variety of conductive, semi-conductive and dielectric inks have been developed on the market to meet different printing needs, among which conductive inks are particularly concerned. It includes three categories: metal inks, carbon-based inks and composite inks. Among them, metal inks with metal particles such as gold, silver and copper as the conductive body have excellent conductive properties. They can improve signal transmission efficiency, reduce delays and reduce energy consumption in electronic circuits, so they have been widely used in commercial applications.

[0004] Once the substrate and ink are determined, the next step is printing. Printing technology is selected according to specific needs, including flexographic printing, gravure printing, screen printing and inkjet printing, which are widely used in the market. In the inkjet printing process, functional inks are prepared by uniformly dispersing functional materials (such as metal nanoparticles, conductive polymers or carbon nanotubes) in appropriate solvents to form a stable dispersion system, and the uniformity of the ink directly determines the quality and performance of the printed electronic circuits.

[0005] In addition, in the process of printed electronics manufacturing, the quality of ink directly determines the performance indicators of the final product, including power consumption, response speed and overall electrical performance. Therefore, the quality of ink must be strictly controlled during the manufacturing process to ensure the manufacturing of efficient and reliable electronic products.

[0006] Printing quality inspection is extremely critical throughout the production process, especially in a fast-production environment, where there may be large differences in quality during the printing process, which is also a major challenge facing the printed electronics field. Unlike the traditional graphic printing industry, where quality control mainly focuses on color, resolution, registration, and surface finish, printed electronics manufacturing must not only ensure the stability of the process itself, but also ensure the functionality of the device.

[0007] However, there are many challenges in achieving real-time, online process feedback in mass production, which is essential for industrial production. When the production process is out of control, manufacturers often face high costs. Problems are usually discovered only after the entire roll of products is produced. Evaluating the function of devices or materials on the substrate through off-line testing may cause a large amount of materials to be scrapped due to non-conformity, resulting in serious economic losses. To achieve the economic benefits of mass production, the scrap rate must be kept at a low level, which requires the implementation of real-time, non-destructive online quality control during the production process. In the production of printed circuits, both functional testing and appearance testing are indispensable. At present, machine vision-based inspection methods are mainly used to identify appearance defects. However, electrical performance testing, as one of the key indicators of printed circuits, has traditionally relied on contact methods such as multimeters or four-probe probes, which are not only difficult to be compatible with automated production, but sometimes also damage the device. In addition, the accuracy and repeatability of contact test methods are usually poor, so it is particularly important to find a non-contact, real-time measurement solution. Summary of the invention

[0008] The first object of the present invention is to provide a printed circuit quality monitoring device based on dual-wavelength synchronous transmissive reflection detection, comprising a computer, a terahertz receiver 1, a terahertz receiver 2, a terahertz transmitter 1, a terahertz transmitter 2, a quality detection pattern, a horn antenna, a coupling lens, a collimation, beam expansion and focusing module and a lock-in amplifier;

[0009] The terahertz emitter 1 and the terahertz emitter 2 are used to generate terahertz waves of two wavelengths;

[0010] The horn antenna is used to gradually expand the terahertz wave from the waveguide to the free space;

[0011] The coupling lens is used to adjust or focus the electromagnetic waves transmitted / received by the antenna;

[0012] The collimating, beam expanding and focusing module is composed of a Kepler type beam expander consisting of two lenses and a focusing lens.

[0013] Furthermore, the terahertz transmitter 1 and the terahertz transmitter 2 generate two terahertz waves of different wavelengths, which are uniformly propagated into space via the horn antenna, and the propagation direction and divergence angle of the beam are optimized through the coupling lens placed in front;

[0014] Then, after the two terahertz waves pass through a half-reflecting half-mirror, the propagation directions of the two terahertz waves are adjusted to the same direction, and then the diffusion and divergence angles of the beams are further reduced through the collimation, beam expansion and focusing modules, thereby improving the stability and directionality of the terahertz waves when transmitted in space, and focusing the two terahertz waves on the printed pattern sample to be tested;

[0015] Part of the beam is transmitted through the sample and named as beam 1, and the other part of the beam is reflected and named as beam 2. Both beam 1 and beam 2 adjust the beam propagation direction to the direction of the two terahertz receivers through reflectors, and then pass through focusing lenses to reach terahertz receiver 1 and terahertz receiver 2 respectively. Subsequently, the two terahertz receivers transmit the signal to the phase-locked amplifier to enhance the signal accuracy and signal-to-noise ratio. The amplified and processed signal is then transmitted to the computer for collection and processing. Finally, the final predicted conductivity data and the dimensional accuracy and geometric deformation data of the printed circuit are output after judgment by the pre-trained prediction model in the computer.

[0016] The second object of the present invention is to provide a printed circuit quality inspection method based on dual-wavelength synchronous transflection detection. By utilizing the dual-wavelength synchronous transflection measurement technology, the present invention effectively improves the accuracy and repeatability of printed circuit conductivity detection, while monitoring the dimensional accuracy and geometric deformation of the printed circuit, optimizing the printed electronic production quality monitoring method and reducing the output of defective products.

[0017] The manufacturing of printed circuits includes the following steps,

[0018] S1. Select ink and substrate;

[0019] S2, implement printing;

[0020] S3, sintering treatment;

[0021] S4. Printing quality inspection.

[0022] Specifically, in step S1, the ink is conductive ink, and the substrate is a flexible substrate.

[0023] Furthermore, the conductive ink is metal ink, carbon-based ink or composite ink.

[0024] Furthermore, the metal ink is a metal ink with gold, silver or copper metal particles as the conductive body.

[0025] Specifically, in step S2, the printing includes flexographic printing, gravure printing, screen printing and inkjet printing.

[0026] Specifically, in step S4, we propose a printed circuit quality inspection method based on dual-wavelength synchronous transflection inspection to achieve printing quality inspection.

[0027] Furthermore, in this detection method, by designing and optimizing the size parameters of the printed quality detection pattern (open ring metamaterial), two obvious resonance peaks are generated in the terahertz band, and the frequencies of the two resonance peaks are respectively adjusted to 200GHz and 300GHz by further optimizing the open ring structure parameters. Since the two resonance peaks respond to both the conductivity and the size of the metamaterial structure, the conductivity measurement error caused by the different incident positions of the electromagnetic wave on the quality control pattern and the differences in the quality control pattern during the printing process can be avoided by analyzing the difference or ratio between the two.

[0028] Furthermore, in step S4, through theoretical simulation or experimental calibration, a multi-dimensional data array of material conductivity-resonance peak position-resonance peak intensity-resonance peak Q factor is established as a calibration model for conductivity estimation, and after obtaining the characteristic spectrum of the open resonant ring array, the conductivity of the printed ink to be tested is estimated by searching for the best matching conductivity in the calibration data or model. At the same time, the same method can also be used to establish a calibration model for printed circuit dimensional accuracy and geometric deformation to estimate printed circuit dimensional accuracy and geometric deformation data.

[0029] Due to the adoption of the above technical solution, compared with the prior art, the advantages of the present invention are:

[0030] (1) Using a non-contact detection method, compared with existing methods on the market that rely on contact methods such as multimeters or four-probes to monitor the quality of printed circuits, our method avoids sample damage or test interference that may be caused by physical contact, and is particularly suitable for flexible electronic production with high precision and high sensitivity requirements. In addition, real-time monitoring technology ensures that any quality deviation can be immediately discovered and handled, greatly reducing the production of unqualified products and improving the economic benefits of the production process;

[0031] (2) Compared with the traditional single-wavelength measurement, the present invention uses a dual-wavelength transmission and reflection synchronous measurement method for the production process of roll-to-roll printed circuits. This method optimizes the traditional single-wavelength measurement and effectively analyzes the electrical properties and physical structure changes of the material by simultaneously monitoring the reflection and transmission spectra at two specific frequencies (wavelengths). This technology can significantly improve the accuracy of detection and achieve strong suppression of environmental fluctuations and mechanical errors during the detection process;

[0032] (3) The data processing system of the present invention can analyze the detection data (such as the resonance peak position and resonance peak intensity and Q factor) in real time and automatically adjust the production parameters according to the data feedback. This real-time feedback and adjustment mechanism is significantly better than the usually delayed feedback in the prior art, and improves production efficiency and product quality;

[0033] (4) The present invention establishes a database containing multiple test indicators (such as resonance peak position, intensity, Q factor, etc.) and a comparison method based on the database and formula calculation to achieve accurate estimation of the conductivity, dimensional accuracy and geometric deformation data of the printed circuit. Compared with the traditional direct measurement method, it not only improves the accuracy and efficiency of the measurement, but also can realize dynamic regulation and optimization of the production process. By instantly comparing the actual measurement data with the theoretical or previous experimental data, this method can quickly identify and correct any deviations in production, greatly reducing the output of defective products and improving economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of the synchronous transflective system in Example 1;

[0035] Figure 2 is a schematic diagram of the double reflection system in Example 1;

[0036] Figure 3 is a schematic diagram of the dual transmission system in Example 1;

[0037] Figure 4 is a flow chart of quality detection of synchronous transflective system in Example 1;

[0038] Figure 5 is a schematic diagram of the THz wave incident on the open ring array in Example 2;

[0039] Figure 6 is a schematic diagram of the open ring resonant metamaterial in Example 2;

[0040] Figure 7 is a schematic diagram of the double resonance peak in Example 2;

[0041] Figure 8 is a schematic diagram of conductivity change in Example 2;

[0042] Fig. 9 It is a schematic diagram of the change of geometric dimensions (line width t) in Example 2. DETAILED DESCRIPTION

[0043] Example 1

[0044] like Figures 1 to 4As shown in the figure below, a printed circuit quality monitoring device based on dual-wavelength synchronous transflection detection, the present invention provides a printing quality monitoring device based on dual-wavelength (dual-frequency) transflection synchronous measurement, as shown in the figure below, we have designed three sets of measurement systems for printed circuit quality detection: synchronous transflection system, dual reflection system, dual transmission system,

[0045] Since the incident position of the terahertz spot on the quality control pattern may drift during the online inspection of roll-to-roll printed circuits due to a series of mechanical rotations or translations, the signal error may be caused by the different incident positions of the terahertz wave during the inspection process, thus affecting the accuracy of the inspection results. This error will be reflected in its reflection or transmission spectrum, which may affect the position and intensity of the resonance peak. In order to avoid problems such as reduced detection repeatability caused by the terahertz incident position, we propose a method based on synchronous transmission and reflection measurement to improve detection accuracy and optimize repeatability.

[0046] Components in the transflective system: 901 is a computer, 902 is a terahertz receiver 1, 903 is a terahertz receiver 2, 904 is a terahertz transmitter 1, 905 is a terahertz transmitter 2 (904 and 905 are used to generate terahertz waves of two wavelengths (frequencies)), 906 is a quality detection pattern, 907 is a horn antenna (used to gradually expand the terahertz wave from the waveguide to the free space), 908 is a coupling lens (used to adjust or focus the electromagnetic waves transmitted / received by the antenna), 909 is a collimation, beam expansion and focusing module, which is composed of a Kepler-type beam expander composed of two lenses and a focusing lens, and 910 is a phase-locked amplifier.

[0047] The overall workflow is explained by taking the synchronous transmission and reflection measurement system as an example: the terahertz transmitters 904 and 905 generate two terahertz waves of different wavelengths, which are evenly propagated into space via the horn antenna, and the propagation direction and divergence angle of the beams are optimized by the coupling lens placed in front. Then, after the two terahertz waves pass through a half-reflecting half-mirror, the propagation directions of the two terahertz waves are adjusted to the same direction, and then the collimation, beam expansion and focusing module 909 is used to further reduce the diffusion and divergence angle of the beams, improve the stability and directionality of the terahertz waves when they are transmitted in space, and focus the two terahertz waves on the printed pattern sample to be tested. A part of the beam is transmitted through the sample and named as beam 1, and the other part of the beam is reflected and named as beam 2. Both beam 1 and beam 2 adjust the beam propagation direction to the direction of the two terahertz receivers through the reflector, and then reach the terahertz receivers 902 and 903 respectively through the focusing lens. Then the two terahertz receivers transmit the signal to the phase-locked amplifier 910 to enhance the signal accuracy and signal-to-noise ratio, and then transmit the amplified and processed signal to the computer 901 for collection and processing. Finally, the final predicted conductivity data and the dimensional accuracy and geometric deformation data of the printed circuit are output after judgment by the pre-trained prediction model in the computer.

[0048] The synchronous measurement technology based on reflection and transmission adopted by the present invention is helpful to effectively screen abnormal conditions in the process of printed circuit quality inspection. The synchronous transflection measurement system ensures that the relationship between the two signals remains consistent by simultaneously measuring the reflection and transmission spectra of the open ring metamaterial. If this correspondence fails to meet or the deviation exceeds the predetermined range in the actual detection, the test result is deemed abnormal and will not be regarded as a valid printed circuit conductivity test. In addition, the system automatically stores these abnormal data to facilitate the staff to subsequently troubleshoot and solve problems that arise in the production process. In addition, the synchronous transflection measurement technology is based on dual-wavelength synchronous measurement. The system can comprehensively analyze the electrical properties and physical structure of the material, avoiding the accuracy errors that may be caused by using a single wavelength measurement, and further improving the accuracy and sensitivity of the measurement. At the same time, the dual-wavelength transflection synchronous measurement technology effectively eliminates the influence of environmental fluctuations and mechanical errors, ensuring the stability of the test results. Due to the synchronization of the dual signals, any errors caused by different incident positions or external interference can be effectively suppressed, significantly improving the repeatability and accuracy of the detection.

[0049] In addition, the dual-wavelength transmission and reflection synchronous measurement system can provide real-time feedback on any deviations in the production process. When a problem is detected, the system will automatically adjust production parameters (such as ink flow rate, sintering temperature, etc.) to further optimize the production process, improve production efficiency and reduce scrap rate. The entire measurement system is compatible with automated production and can provide real-time, high-precision quality inspection solutions during the production of printed circuits, thereby ensuring efficient and accurate production processes and consistent product quality.

[0050] Example 2

[0051] Printed electronics is a cutting-edge technology that applies traditional printing processes to the manufacture of electronic components and devices. It can directly print electronic devices on various flexible substrates, thereby achieving low-cost and high-efficiency production of electronic products. This technology uses a variety of methods such as flexographic printing, inkjet printing, gravure printing and screen printing to print photonic devices and electronic products directly on a variety of substrates such as fabrics, paper, plastics, etc. This technology has been widely used in fields such as wearable devices, sports industry and flexible displays. Due to the fast production pace, there may be large differences in quality during the printing process.

[0052] The process of printed electronics manufacturing is generally divided into four main stages: (a) selecting ink and substrate, (b) implementing printing, (c) sintering treatment and (d) printing quality inspection. The first is to choose the right ink and substrate. Among the various available substrates, flexible substrates are particularly favored because of their unique bendability, stretchability and twistability while maintaining good electrical properties. A variety of conductive, semi-conductive and dielectric inks have been developed on the market to meet different printing needs, among which conductive inks are particularly concerned. It includes three categories: metal inks, carbon-based inks and composite inks. Among them, metal inks with metal particles such as gold, silver and copper as the conductive body have excellent conductive properties. They can improve signal transmission efficiency, reduce latency and reduce energy consumption in electronic circuits, so they have been widely used in commercial applications.

[0053] Once the substrate and ink are determined, the next step is printing. Printing technology is selected according to specific needs, including flexographic printing, gravure printing, screen printing and inkjet printing, which are widely used in the market. In the inkjet printing process, functional inks are prepared by uniformly dispersing functional materials (such as metal nanoparticles, conductive polymers or carbon nanotubes) in appropriate solvents to form a stable dispersion system, and the uniformity of the ink directly determines the quality and performance of the printed electronic circuits.

[0054] In addition, in the process of printed electronics manufacturing, the quality of ink directly determines the performance indicators of the final product, including power consumption, response speed and overall electrical performance. Therefore, the quality of ink must be strictly controlled during the manufacturing process to ensure the manufacturing of efficient and reliable electronic products.

[0055] Printing quality inspection is extremely critical throughout the production process, especially in a fast-production environment, where there may be large differences in quality during the printing process, which is also a major challenge facing the printed electronics field. Unlike the traditional graphic printing industry, where quality control mainly focuses on color, resolution, registration, and surface finish, printed electronics manufacturing must not only ensure the stability of the process itself, but also ensure the functionality of the device.

[0056] However, there are many challenges in achieving real-time, online process feedback in mass production, which is essential for industrial production. When the production process is out of control, manufacturers often face high costs. Problems are usually discovered only after the entire roll of products is produced. Evaluating the function of devices or materials on the substrate through off-line testing may cause a large amount of materials to be scrapped due to non-conformity, resulting in serious economic losses. To achieve the economic benefits of mass production, the scrap rate must be kept at a low level, which requires the implementation of real-time, non-destructive online quality control during the production process. In the production of printed circuits, both functional testing and appearance testing are indispensable. At present, machine vision-based inspection methods are mainly used to identify appearance defects. However, electrical performance testing, as one of the key indicators of printed circuits, has traditionally relied on contact methods such as multimeters or four-probe probes, which are not only difficult to be compatible with automated production, but sometimes also damage the device. In addition, the accuracy and repeatability of contact test methods are usually poor, so it is particularly important to find a non-contact, real-time measurement solution.

[0057] The present invention aims to overcome the shortcomings of the prior art and provide a non-contact detection method, structure and device for printed circuit quality. The method is mainly used to detect the conductivity, diffusion characteristics and dimensional accuracy of conductive ink in the printing process, so as to improve the product qualification rate in the roll-to-roll printing process. This detection method not only speeds up the quality control process, but also avoids physical damage to the printed circuit through its non-contact characteristics, ensuring the integrity and functionality of the circuit.

[0058] The present invention proposes an innovative method, which introduces a metamaterial-based quality control pattern in the production process of printed circuits, such as Figure 5 and Figure 6 As shown, considering that the conductive materials commonly used in the field of printed electronics have a unique modulation effect on terahertz waves, the present invention uses this property to achieve non-contact online measurement of the conductivity of printed circuits and the dimensional accuracy and deformation of printed circuits. Specifically, we designed metamaterial control patterns with specific reflection and transmission properties, which can comprehensively evaluate key functional parameters such as conductivity, thickness and diffusion characteristics of printed inks through their transmission characteristics (such as resonant frequency, intensity and Q factor).

[0059] By deeply studying the resonant properties of open resonant ring array metamaterials, especially the effect of material conductivity on these properties, we found that when the conductivity of the material changes, the intensity at its resonant frequency shows a significant change. Specifically, the higher the conductivity, the greater the resonance intensity, and the higher the corresponding characteristic peak Q factor. This finding means that by real-time analysis of the intensity of the resonance peak and the characteristic peak Q factor, the conductivity of the printed ink can be monitored in real time. Therefore, this phenomenon provides a very valuable physical basis for non-contact detection of printed circuit conductivity, which helps to monitor the electrical properties of printed circuits in real time and ensure product quality. In addition, the application potential of this method is not limited to printed circuits, but may also be extended to other fields involving the performance evaluation of conductive materials.

[0060] In order to achieve the purpose of real-time monitoring of the conductivity of printed ink in the present invention, one method is to use a spectral scanning method based on a time-domain terahertz system. The advantage of this method is that it can achieve comprehensive detection of the characteristic peaks of the metamaterial and the overall reflection and transmission spectra. However, its biggest limitation is that this method has certain disadvantages in terms of real-time performance because it requires mechanical scanning to sample the time domain delay of the terahertz pulse, which undoubtedly limits its requirements for online real-time detection in automated production lines. For example, in the current roll-to-roll printed circuit process, the printing speed often reaches 50m / min, and the scanning speed of the conventional time-domain terahertz system is difficult to meet the above requirements.

[0061] In view of the above difficulties, the present invention proposes a printed circuit detection method based on dual-frequency excitation and detection. Taking the open-ring metamaterial based on conductive silver paste as an example, we design and optimize the size parameters of the open ring to produce two obvious resonance peaks in the terahertz band. Since the two resonance peaks respond to both conductivity and the size of the metamaterial structure, the conductivity measurement error caused by the different incident positions of the electromagnetic wave in the quality control pattern and the difference in the quality control pattern during the printing process can be avoided by analyzing the difference or ratio between the two, thereby greatly improving the measurement accuracy of the conductivity. Therefore, compared with single-frequency measurement, our dual-frequency method has higher measurement accuracy and sensitivity. At the same time, in order to further improve the accuracy and robustness of the detection, we further optimized the design of the open ring structure, and gradually adjusted the frequencies of the two resonance peaks to 200 GHz (0.2 THz) and 300 GHz (0.3 THz) respectively by precisely adjusting the key size parameters of the open ring. Figure 7As shown. The selection of these two frequencies is mainly based on the following considerations: the current commercial single-frequency source has a high radiation power at these two frequencies, and the related detection technology is very mature and complete, capable of providing high-precision signal measurement and real-time monitoring, which enables experiments and detections at these two frequency ranges to obtain stronger signal quality and lower noise levels. This optimized design not only enhances the sensitivity of the detection signal, but also makes the system more compatible with existing commercial terahertz detection equipment, thereby improving the overall practicality and operability.

[0062] Figure 8 The changes of the resonance peaks at different conductivity are shown. When the conductivity changes from 6000S / m to 60000S / m, the resonance peak transmittance at 200GHz changes from 0.325 to 0.062, and the resonance peak transmittance at 300GHz changes from 0.556 to 0.289. The resonance intensity of the two resonance peaks increases. Therefore, the matching relationship or mapping matrix between the resonance peak characteristics (resonance peak intensity 1, resonance peak intensity 2) of the open ring metamaterial and the material conductivity can be established through theoretical simulation or test calibration methods. It is also possible to associate the resonance peak input characteristics with the conductivity output by establishing a deep learning model. This method can improve the accuracy and efficiency of prediction, thereby providing strong technical support for the quality control and performance optimization of printed circuits.

[0063] In the example implementation, the present invention proposes a conductivity estimation method based on optimal matching. First, through theoretical simulation or experimental calibration, a multidimensional data array of material conductivity-resonance peak position-resonance peak intensity-resonance peak Q factor is established as a calibration model for conductivity estimation. In the actual test process, after we obtain the characteristic spectrum of the open resonant ring array, we estimate the conductivity of the printed ink to be tested by searching for the best matching conductivity in the calibration data or model. In order to establish the relationship between the intensity of resonance peak 1 and resonance peak 2 and conductivity, in the example we intend to use a quadratic regression model to fit the data. Assuming that the intensity of resonance peak 1 is x1, the intensity of resonance peak 2 is x2, and the conductivity is the dependent variable y, we construct a regression model containing linear terms, quadratic terms, and cross terms of the independent variables:

[0064]

[0065] The residual sum of squares (RSS) is the sum of the residual squares of all sample points, which represents the total amount of error in model fitting. The formula is:

[0066]

[0067] The core goal of the least squares method is to minimize the residual sum of squares by adjusting the regression coefficients β0, β1, ..., β5. Specifically, the core principle of the least squares method is to find the best fitting curve by minimizing the residual sum of squares of all data points, where the residual refers to the difference between the actual observed value and the model predicted value. Through this process, we can get a set of regression coefficients that make the model fit the data best. On this basis, we can predict the conductivity of the material through the regression model, and further analyze the effect of the resonance peak intensity on the conductivity, revealing the linear and nonlinear relationship between the two. This regression analysis provides an effective mathematical tool for in-depth understanding of the conductive properties of materials, and also provides a theoretical basis for subsequent material design and performance optimization. In the actual application process, we will judge the pros and cons of the fitting model by testing the mean square error of the model and the adjusted coefficient of determination, while avoiding the problem of overfitting.

[0068] The training data (calibration spectrum) of the above regression model can be measured in the laboratory and saved in the database. The parameters in the database can be directly read when the model parameters are actually trained. At the same time, the operating data in the production line can also be added to the database after processing to adjust the test accuracy of the model and improve the model performance.

[0069] In another embodiment, we use calibration data to train a support vector regression (SVR)-based model to predict the conductivity of printing ink. The input variables of the model include the intensity of resonance peak 1 and resonance peak 2, and the output is the conductivity of the printing ink. By fine-tuning the hyperparameters of the model, we are able to optimize the model performance, thereby significantly improving the estimation accuracy of the conductivity of the printing ink. In addition, on the actual production line, we regularly integrate newly collected data into the training set, which not only helps the model adapt to changes in the production environment, but also further improves the accuracy of the prediction and the generalization ability of the model. This continuous data update and model iteration is a key strategy to ensure long-term stability and improve prediction performance.

[0070] In addition, since the modulation characteristics of the quality control pattern on the terahertz wave not only depend on the conductivity, but also on another important quality indicator of the printed pattern (size line width and geometric deformation). In order to avoid the influence of the size error or deformation of the quality control pattern during the printing process on the conductivity detection accuracy, and to realize the real-time monitoring of the size accuracy and deformation of the printed circuit, we proposed two auxiliary detection schemes to optimize the accuracy and reliability of the detection process: 1. The first scheme is based on the resonance design. By utilizing the dependence of its resonant frequency on parameters such as the size and line width of the resonant ring and monitoring its resonant position, the detection of the printing ink size can be effectively realized. For example, our research found that when the line width t of the resonant ring changes from 40μm to 80μm, the center position of the resonant frequency of one of the resonance peaks moves from 186GHz to 199GHz, and the other resonance peak moves from 283GHz to 297GHz. Fig. 9 As shown. Therefore, by monitoring the position of its resonant frequency, the detection of the line width accuracy and diffusion function of the printed pattern can be effectively achieved. 2. The second is a method based on machine vision, which detects through image processing algorithms to obtain the dimensional accuracy and deformation characteristics of the printed pattern. The conductivity detection accuracy is improved by updating the parameters of the geometric line width in the conductivity estimation model of the printing ink in real time. When the system detects that the conductivity or dimensional accuracy of the printing ink exceeds a reasonable range, it will automatically adjust the ink flow rate, thickness, concentration or proportion of conductive particles, sintering temperature and other parameters to optimize the production process and improve the yield rate of roll-to-roll printing. These measures ensure the continuity of the production process and the consistency of product quality.

[0071] In addition, the present invention provides two methods for eliminating environmental interference based on dual-frequency analysis. The first method is to optimize the metamaterial structure so that the change in the conductivity of the printed material only affects a specific frequency range, and has almost no effect on other frequency bands. The response ratio of the characteristic frequency band and the reference frequency band cleverly provides information on the transmission characteristics of the studied parameters on the structure. Since the two are measured synchronously, the normalization effect can be achieved through the ratio, and the interference from environmental fluctuations or other uncertain factors can be effectively suppressed. Alternatively, the second method can be used. By optimizing the structure of the open resonant ring or metamaterial, two or even more resonance peaks can be obtained in a broadband range, and the resonance peaks respond to changes in conductivity and size structure. By analyzing the difference or ratio between the two, factors such as environmental fluctuations can also be effectively suppressed, thereby avoiding conductivity measurement errors caused by different positions of THz waves incident on the quality control pattern, differences in quality control patterns during printing, etc., and optimizing the measurement accuracy of conductivity. This is also the reason why we previously optimized the open ring structure to produce two characteristic resonance peaks.

[0072] Through the above methods, we can detect the electrical properties (such as conductivity) and appearance indicators (such as dimensional accuracy and geometric deformation) of printed circuits online. This is especially critical for roll-to-roll printing production. These technologies not only help prevent the production process from getting out of control and generating a large amount of waste, thereby avoiding waste and loss, but are also extremely beneficial for the development of new products or processes, and can significantly shorten the development cycle of new equipment testing and new process debugging. In short, the non-destructive, non-contact, online detection method based on metamaterials proposed in the present invention provides an effective new way of printing quality control in the field of printed electronics, and is expected to be widely used in quality inspection and quality control of printed electronics.

[0073] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A printed circuit quality monitoring device based on dual-wavelength synchronous transmissive and reflective detection, characterized in that: It includes a computer, a terahertz receiver 1, a terahertz receiver 2, a terahertz transmitter 1, a terahertz transmitter 2, a quality detection pattern, a horn antenna, a coupling lens, a collimation, beam expansion and focusing module and a phase-locked amplifier; The terahertz emitter 1 and the terahertz emitter 2 are used to generate terahertz waves of two wavelengths; The horn antenna is used to gradually expand the terahertz wave from the waveguide to the free space; The coupling lens is used to adjust or focus the electromagnetic waves transmitted / received by the antenna; The collimating, beam expanding and focusing module is composed of a Kepler type beam expander consisting of two lenses and a focusing lens.

2. A printed circuit quality monitoring device based on dual-wavelength synchronous transmissive and reflective detection according to claim 1, characterized in that: Terahertz transmitter 1 and terahertz transmitter 2 generate two terahertz waves of different wavelengths. The terahertz waves are evenly propagated into space via the horn antenna, and the propagation direction and divergence angle of the beams are optimized through the coupling lens placed in front. Then, after the two terahertz waves pass through a half-reflecting half-mirror, the propagation directions of the two terahertz waves are adjusted to the same direction, and then the diffusion and divergence angles of the beams are further reduced through the collimation, beam expansion and focusing modules, thereby improving the stability and directionality of the terahertz waves when transmitted in space, and focusing the two terahertz waves on the printed pattern sample to be tested; Part of the beam is transmitted through the sample and named as beam 1, and the other part of the beam is reflected and named as beam 2. Both beam 1 and beam 2 adjust the beam propagation direction to the direction of the two terahertz receivers through reflectors, and then pass through focusing lenses to reach terahertz receiver 1 and terahertz receiver 2 respectively. Subsequently, the two terahertz receivers transmit the signal to the phase-locked amplifier to enhance the signal accuracy and signal-to-noise ratio. The amplified and processed signal is then transmitted to the computer for collection and processing. Finally, the final predicted conductivity data and the dimensional accuracy and geometric deformation data of the printed circuit are output after judgment by the pre-trained prediction model in the computer.

3. A printed circuit quality inspection method based on dual-wavelength synchronous transmissive and reflective inspection according to claim 1, characterized in that: The manufacturing of printed circuits includes the following steps, S1. Select ink and substrate; S2, implement printing; S3, sintering treatment; S4. Printing quality inspection.

4. A printed circuit quality inspection method based on dual-wavelength synchronous transmissive and reflective inspection according to claim 3, characterized in that: In step S1 , the ink is conductive ink, and the substrate is a flexible substrate.

5. A printed circuit quality inspection method based on dual-wavelength synchronous transmissive and reflective inspection according to claim 4, characterized in that: The conductive ink is metal ink, carbon-based ink or composite ink.

6. A printed circuit quality inspection method based on dual-wavelength synchronous transmissive and reflective inspection according to claim 5, characterized in that: The metal ink is a metal ink with gold, silver or copper metal particles as the conductive body.

7. A printed circuit quality inspection method based on dual-wavelength synchronous transmissive and reflective inspection according to claim 3, characterized in that: In step S2, the printing includes flexographic printing, gravure printing, screen printing and inkjet printing.

8. A printed circuit quality inspection method based on dual-wavelength synchronous transmissive and reflective inspection according to claim 3, characterized in that: In step S4, by designing and optimizing the size parameters of the printed quality inspection pattern, two obvious resonance peaks are generated in the terahertz band, and the frequencies of the two resonance peaks are respectively adjusted to 200 GHz and 300 GHz by optimizing the open ring structure parameters. Since the two resonance peaks respond to both the conductivity and the size of the metamaterial structure, the conductivity measurement error caused by the different incident positions of the electromagnetic wave on the quality control pattern and the difference in the quality control pattern during the printing process can be avoided by analyzing the difference or ratio between the two.

9. A printed circuit quality inspection method based on dual-wavelength synchronous transmissive and reflective inspection according to claim 8, characterized in that: In step S4, through theoretical simulation or experimental calibration, a multidimensional data array of material conductivity-resonance peak position-resonance peak intensity-resonance peak Q factor is established as a calibration model for conductivity estimation. After obtaining the characteristic spectrum of the open resonant ring array, the conductivity of the printed ink to be tested is estimated by searching for the best matching conductivity in the calibration data or model; at the same time, the same method is used to establish a calibration model for the dimensional accuracy and geometric deformation of the printed circuit to estimate the dimensional accuracy and geometric deformation data of the printed circuit.

Images