Capacitance film defect detection system and detection method thereof

Abstract

The invention relates to the technical field of capacitor film defect detection. The invention discloses a capacitance film defect detection system which comprises a hollow glass container, and a sealing interlayer between upper and lower layers of glass of the hollow glass container is filled with insulating liquid to form a uniform layer; the light source on one side emits light beams which penetrate through the liquid layer and the capacitance film, and the light source controller can adjust the output intensity; the image acquisition device on the other side acquires an optical signal; the angle adjusting device is connected with the light source and the image acquisition device to adjust irradiation and acquisition angles; the image processing unit analyzes the signals to identify flaws. Through the optical path difference amplification and double-beam interference technology of the insulating liquid, the nano-scale detection of the defects of the capacitor film is realized, and the bottleneck of traditional optical detection is broken through. A multi-dimensional verification mechanism can accurately distinguish different types of defects and is compatible with detection of capacitance films made of various materials. Defect detection, positioning and size measurement are achieved through full-process automatic design, quantitative quality data are provided for mass production, enterprises are assisted in reducing the rejection rate, and the packaging reliability of electronic components is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitor film defect detection, and in particular to a capacitor film defect detection system and a detection method thereof. Background Art

[0002] Polypropylene film, due to its high transparency, excellent barrier properties, and mechanical properties, has become a core material for the production of high-performance capacitors. With the rapid development of electronic information, new energy, and other fields, capacitors are evolving toward higher frequencies and miniaturization, placing higher demands on the quality of capacitor films. Minor defects on the surface or within the capacitor film can significantly affect the dielectric properties, withstand voltage, and service life of the capacitor, and may even cause device failure. According to industry statistics, the accuracy of capacitor film defect detection is directly related to the yield rate of the finished capacitor. Traditional detection technologies are no longer able to meet the needs of nano-level defect detection, and high-precision, non-contact detection solutions are urgently needed.

[0003] Existing capacitive film defect detection technology has the following main limitations: First, traditional optical detection methods are limited by the light scattering characteristics of transparent media, and have insufficient signal capture capabilities for nanoscale defects, especially when the defect size is smaller than the wavelength of light. The optical contrast is low, which can easily lead to missed detections; second, although contact detection can obtain surface contour information, it will cause mechanical damage to the ultra-thin capacitive film and cannot be adapted to high-speed mass production scenarios; third, although the detection technology based on white light interferometry has a certain degree of accuracy, due to the lack of an optical path difference amplification mechanism, its ability to identify interface defects of media with similar refractive indices is limited, and the detection efficiency is difficult to match the production line speed.

[0004] Furthermore, polypropylene capacitor films coated with a conductive layer exhibit complex defect characteristics, making it difficult to simultaneously identify anomalies in both the conductive and dielectric layers using a single traditional detection method. For example, pinhole defects in the metallization layer and thickness fluctuations in the dielectric layer can easily cause superimposed interference in the optical signal, leading to misjudgment of the defect type. Existing solutions improve detection by increasing the wavelength of the light source or optimizing image processing algorithms, but these solutions fail to address the physical mechanisms of optical path difference amplification and multi-dimensional defect verification, making it difficult to accurately locate and quantify defects. Summary of the Invention

[0005] In order to address the deficiencies of the prior art, the present invention discloses a capacitive film defect detection system and a detection method thereof that have high sensitivity, non-contact characteristics, and multi-dimensional verification capabilities.

[0006] The present invention discloses a capacitive film defect detection system, which includes:

[0007] Hollow glass container, the container is composed of two layers of glass and a sealed interlayer in the middle. The interlayer is filled with insulating liquid to form a uniform liquid layer;

[0008] The light source is located on one side of the hollow glass container and is used to emit a detection beam to penetrate the liquid layer and the capacitance film. The light source is equipped with a controller that can adjust the output intensity. The standard value is 100% of the rated output power of the light source.

[0009] An image acquisition device is provided on the other side of the capacitive film and is used to acquire light signals passing through the capacitive film;

[0010] An angle adjustment device, the angle adjustment device is connected to the light source and the image acquisition device respectively, and is used to adjust the illumination angle of the light source and the acquisition angle of the image acquisition device;

[0011] The image processing unit is connected to the image acquisition device and is used to analyze the light signal and identify defects in the capacitor film.

[0012] Furthermore, the interlayer thickness of the hollow glass container is 50-100 μm, the uniformity of the insulating liquid layer is controlled by a quartz gasket or a microfluidic structure, and a liquid injection port and a vacuum degassing interface are provided on the edge of the interlayer.

[0013] Furthermore, the absolute value of the difference between the refractive index of the insulating liquid and the refractive index of the capacitor film is 0.02-0.25, the insulating liquid is insulating silicone oil or fluorinated liquid, and the capacitor film is a polypropylene dielectric film coated with a conductive layer.

[0014] Furthermore, the light source is a laser or LED light source, and is combined with a narrow-band filter. The detection beam is divided into two coherent beams of light, one of which directly passes through the liquid layer and the capacitor film, and the other is obliquely incident on the capacitor film at an angle of 5°-15°. The two beams of light form an interference area on the target surface of the image acquisition device.

[0015] Furthermore, the angle adjustment device includes a rotating bracket driven by a servo motor, which is used to adjust the angle θ between the two beams of light so that the interference fringe spacing is 5-10 pixels, and the adjustment accuracy of the angle θ is ±0.5°.

[0016] Furthermore, the capacitive film defect detection system also includes an optical path adjustment component, which is connected to the light source and is arranged between the light source and the hollow glass container. The optical path adjustment component includes an aperture and a lens, and the aperture of the aperture is 90%-110% of the diameter of the detection beam.

[0017] Furthermore, the image processing unit pre-stores a standard defect feature library, and identifies conductive layer fractures, surface unevenness, and dielectric layer impurity defects of the capacitor film by comparing the offset, contrast, and bright spot distribution of the interference fringes.

[0018] The present invention discloses a method for detecting defects in a capacitor film, using a capacitor film defect detection system as described above, comprising:

[0019] S1: Pretreatment stage: Insulating liquid is filled into the interlayer of the hollow glass container. The thickness of the liquid layer is controlled to be 50-100 μm. The absolute value of the difference between the refractive index of the insulating liquid and the refractive index of the capacitor film is 0.02-0.25. The capacitor film is attached to the lower surface of the container. The bubbles in the liquid layer are removed by vacuum degassing process, and the film surface is treated with plasma to enhance wettability.

[0020] S2: Single-beam pre-detection stage: The light source is adjusted to single-beam mode with the intensity set to 30%-50% of the standard value. The light is directed through the liquid layer and the capacitive film to collect the transmitted light spot image. The edge detection algorithm is used to roughly locate surface protrusions or holes ≥5μm in size.

[0021] S3: Dual-beam interference amplification stage: switch the light source to dual-beam mode, adjust the beam angle to 5°-15°, scan within the pitch angle range of 10°-70°, collect interference images at different angles, lock the optimal detection angle based on the image clarity threshold, and use the refractive index difference between the insulating liquid and the capacitive film to amplify the optical path difference at the defect, causing the interference fringes to produce a recognizable offset;

[0022] S4: Quantitative analysis of optical path difference: fix the optimal detection angle, increase the light source intensity to 120%-150% of the standard value, and calculate the defect height by analyzing the interference phase difference and the refractive index difference between the insulating liquid and the capacitance film;

[0023] S5: Multi-dimensional verification stage, switch to an insulating liquid with a refractive index lower than the insulating liquid in S1, repeat steps S1-S4, and verify the authenticity of the defect through the consistency of the interference fringe offset under different insulating liquids.

[0024] Furthermore, the insulating liquid in S1 is methyl silicone oil or fluorinated liquid, which is filtered through a 0.1-0.3 μm filter membrane during filling, and a micro-flow groove is set at the edge of the interlayer to control the uniformity of the liquid layer, ensuring that the insulating liquid is tightly attached to the surface of the capacitor membrane without bubbles;

[0025] The capacitor film is a polypropylene dielectric film coated with a conductive layer.

[0026] Furthermore, the light source of the dual-beam interference in S3 is a 600-650nm laser. By adjusting the beam angle, the interference fringe spacing is made 5-10 pixels. When there are defects in the capacitor film, the optical path difference magnified by the liquid layer causes the fringe offset to be ≥1 pixel. The pixel is the physical pixel of the image acquisition device, and the pixel size is 5-10μm.

[0027] Beneficial effects of the present invention:

[0028] The capacitor film defect detection system and method provided by the present invention, through the synergy of insulating liquid optical path difference amplification and dual-beam interference technology, breaks through the bottleneck of traditional optical detection for the identification of nano-level defects and realizes high-precision quantitative analysis of capacitor film defects. The system uses the refractive index difference between the insulating liquid filled in the hollow glass container and the capacitor film to amplify the 0.1μm level defect optical path difference to a recognizable range, and cooperates with the dynamic fringe offset formed by dual-beam interference to improve the detection sensitivity of hidden defects such as pinholes in the conductive layer and fluctuations in the thickness of the dielectric layer to the nanometer level. Compared with traditional single-light source detection technology, this solution improves the defect detection accuracy from 5μm to below 0.1μm through the physical amplification mechanism of the liquid layer and the feature library comparison of the image processing unit, effectively solving the industry problem of weak defect signals and easy missed detection of transparent dielectric films, and providing reliable technical support for the quality control of raw materials for high-performance capacitors.

[0029] The multi-dimensional verification mechanism and compatible design give the detection solution a wide range of applicability and defect classification capabilities, effectively dealing with complex defect scenarios of capacitor films. By switching insulating liquids with different refractive indices for cross-validation, combined with the plasma surface treatment process in the pretreatment stage, the system can accurately distinguish different types of defects such as conductive layer fractures and dielectric layer impurities, and the classification accuracy is improved compared to traditional single-parameter detection. At the same time, by adjusting the light source wavelength and detection parameters, the solution is compatible with the detection needs of capacitor films of various materials such as PET and PI, without the need for additional hardware modification. The full-process automated design from physical environment preparation to optical signal analysis not only realizes the detection, positioning and size measurement of defects, but also provides quantitative quality data for the mass production of capacitor films, helping companies reduce scrap rates and significantly improve the reliability of electronic component packaging and production cost control capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of a method for detecting defects in a capacitor film in an embodiment of the present application. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the specific implementation manner of the present invention will be clearly and completely described below.

[0032] The present invention discloses a capacitor film defect detection system, which includes a hollow glass container, wherein the container is composed of two layers of glass, upper and lower, and a sealed interlayer in the middle, and the interlayer is filled with an insulating liquid to form a uniform liquid layer. A light source is provided on one side of the hollow glass container and is used to emit a detection light beam to penetrate the liquid layer and the capacitor film. The light source is provided with a controller with adjustable output intensity, and the standard value is 100% of the rated output power of the light source. An image acquisition device is provided on the other side of the capacitor film and is used to collect light signals passing through the capacitor film. An angle adjustment device is connected to the light source and the image acquisition device respectively, and is used to adjust the illumination angle of the light source and the acquisition angle of the image acquisition device. An image processing unit is connected to the image acquisition device and is used to analyze the light signal and identify defects in the capacitor film.

[0033] The capacitor film defect detection system of the present invention achieves high-precision detection through modular design. The hollow glass container is composed of two layers of optical-grade glass, the upper and lower layers, and the middle sealed interlayer is filled with insulating liquid. The liquid layer thickness is controlled to 50-100μm by a quartz gasket or a microfluidic structure to ensure that the insulating liquid evenly covers the surface of the capacitor film. The light source is arranged on one side of the container, and its controller with adjustable output intensity can accurately control the beam energy. The standard value is defined as 100% of the rated output power of the light source. During detection, it can be switched to 30%-50% or 120%-150% of the rated power according to demand. After the detection light beam penetrates the liquid layer and the capacitor film, the light signal is received by the image acquisition device on the other side. The angle adjustment device synchronously controls the irradiation angle of the light source and the acquisition angle of the image acquisition device, so that the two beams of coherent light form an angle of 5°-15° on the surface of the capacitor film. Finally, the image processing unit analyzes the interference pattern and identifies defects.

[0034] The capacitor film defect detection system achieves defect detection through a three-level mechanism of liquid layer optical path difference amplification, dual-beam interference, and intelligent image analysis. The difference in refractive index between the insulating liquid and the capacitor film can amplify the optical path change at the defect. When there are defects such as protrusions and holes in the capacitor film, the difference in the path of light passing through the interface between the insulating liquid and the capacitor film is intensified by the liquid layer, forming a recognizable optical path difference. The angle adjustment device dynamically scans the pitch angle range of 10°-70°, locking the optimal detection angle so that the two beams of light form clear interference fringes on the target surface of the image acquisition device. The fringes in the defective area appear distorted, broken, or have brightness changes due to the offset of the optical path difference. The standard defect feature library pre-stored in the image processing unit can compare these abnormal signals in real time to accurately locate the position and type of the defect.

[0035] The significant advantage of the capacitive film defect detection system lies in its integrated multi-dimensional detection capabilities. Its liquid layer uniformity control and refractive index matching design address the weak signal of transparent capacitive film defects in traditional single-light source inspection, amplifying the optical path difference of 0.1μm defects to a recognizable range. Staged light intensity adjustment, combined with dual-beam interference, improves the contrast between light and dark at the defect edge by over 50%, making it particularly suitable for polypropylene capacitive film coated with a conductive layer. Automated angle scanning and intelligent image analysis enable full-process non-contact inspection, preventing damage to the capacitive film surface. Detection efficiency matches the pace of high-speed production lines, enabling real-time removal of defective capacitive film.

[0036] As an embodiment, the interlayer thickness of the hollow glass container is 50-100 μm, the uniformity of the insulating liquid layer is controlled by a quartz gasket or a microfluidic structure, and a liquid injection port and a vacuum degassing interface are provided on the edge of the interlayer.

[0037] The interlayer thickness of hollow glass containers is controlled through a collaborative process of precision mechanical structures and microfluidic technology. Quartz spacers, used as spacer elements, are optically polished to a precision tolerance of 50-100μm, with a parallelism error of ≤1μm, ensuring uniform spacing between the upper and lower glass layers. For scenarios requiring dynamic adjustment of the liquid layer thickness, a microfluidic structure can be employed. A network of micron-scale flow channels is etched along the edges of the glass interlayer. Air pressure is used to evenly distribute the insulating liquid within these channels, and a high-precision flow controller is used to achieve real-time calibration of the liquid layer thickness.

[0038] The insulating liquid injection port and vacuum degassing interface at the edge of the interlayer utilize an integrated sealing design. The injection port is connected to a micro-syringe pump, which injects the insulating liquid into the interlayer at a constant flow rate of 0.1 mL / min to prevent bubbles caused by turbulence. The degassing interface is connected to the vacuum chamber via a hose. During the injection of the insulating liquid, the pressure is simultaneously pumped down to a negative pressure of -0.1 MPa. This pressure difference allows the gas dissolved in the insulating liquid to escape, and ultrasonic vibrations are used to dissolve tiny bubbles. This mechanism controls the volume fraction of bubbles in the liquid layer to below 0.01%, ensuring that light is transmitted without scattering interference and maintaining the clarity of the interference fringes.

[0039] An optically uniform detection medium was constructed through the above design. The precise liquid layer thickness of 50-100μm makes the optical path difference amplification effect stable and controllable, avoiding phase noise caused by an excessively thick liquid layer. The combination of quartz gaskets and microfluidic structures not only meets the low-cost requirements of static detection, but also supports liquid layer optimization in dynamic scenarios. The vacuum degassing process completely eliminates the interference of bubbles on light propagation, which greatly improves the system's detection signal-to-noise ratio for 0.1μm-level defects. The vacuum degassing process uses a vacuum degree of -0.1MPa and a degassing time of 10min. This solution is particularly suitable for polypropylene capacitor films coated with a conductive layer. It can accurately identify hidden defects such as pinholes in the metallization layer and fluctuations in the thickness of the dielectric layer, providing a reliable hardware foundation for mass production quality control of capacitor films.

[0040] As an embodiment, the absolute value of the difference between the refractive index of the insulating liquid and the refractive index of the capacitor film is 0.02-0.25, the insulating liquid is insulating silicone oil or fluorinated liquid, and the capacitor film is a polypropylene dielectric film coated with a conductive layer.

[0041] The refractive index difference between the insulating liquid and the capacitor film is achieved through material screening and optical matching. First, the baseline refractive index of the polypropylene capacitor film coated with a conductive layer is measured, and then the medium whose absolute value of the difference between the refractive index and the baseline value is within the range of 0.02-0.25 is selected from the insulating liquid library. The refractive index of the polypropylene capacitor film is about 1.50, and the refractive index of the insulating silicone oil is about 1.47, which forms a difference of 0.03 with the polypropylene film. The refractive index of the fluorinated liquid is about 1.27, and the difference is 0.23, both of which meet the range requirements. During screening, the insulating performance and chemical stability of the insulating liquid are simultaneously verified to ensure that it does not swell the polypropylene film or corrode the conductive layer. Finally, the optical path difference response of the interface between the insulating liquid and the capacitor film is measured by optical interferometer to determine the best matching solution.

[0042] When the absolute difference between the refractive index of the insulating liquid and the refractive index of the capacitor film is 0.02-0.25, the optical path difference at the defect can be effectively amplified, improving detection sensitivity. When the capacitor film has a thickness fluctuation of 0.1μm, a refractive index difference of 0.03 can produce an optical path difference of 3nm, which is converted into a recognizable fringe offset after double-beam interference. If a fluorinated liquid is used, the optical path difference is amplified to 23nm, and the fringe offset is significantly increased, increasing the optical signal of nanoscale defects by 5-8 times. At the same time, the dielectric constant of the insulating liquid is close to that of the polypropylene film, avoiding capacitive interference with the conductive layer during the detection process and ensuring the compatibility of electrical performance and optical detection.

[0043] The matching scheme, with an absolute refractive index difference of 0.02-0.25, is specifically adapted for polypropylene capacitor films coated with a metallized layer. On the one hand, the low conductivity of the insulating liquid prevents short circuits in the conductive layer, ensuring safe online detection. On the other hand, the optical path difference amplification effect within the difference range can accurately identify complex defects such as conductive layer breaks and dielectric layer pinholes. For example, when a 0.5μm pinhole exists in the metallized layer, the refractive index difference at the interface between the insulating liquid and the capacitor film enhances light scattering at the pinhole edge. Combined with interference fringe distortion, this method can simultaneously locate conductive layer defects and dielectric layer anomalies. This significantly improves detection accuracy compared to traditional single-light source technology, providing a key quality control measure for high-precision mass production of capacitor films.

[0044] As an implementation method, the light source is a laser or LED light source, which is combined with a narrow-band filter. The detection beam is divided into two coherent beams of light. One beam directly passes through the liquid layer and the capacitor film, and the other beam is obliquely incident on the capacitor film at an angle of 5°-15°. The two beams of light form an interference area on the target surface of the image acquisition device.

[0045] The light source module achieves dual-beam interference through an optical beam-splitting assembly and an angle control mechanism. The light beam emitted by a laser or LED light source is filtered through a narrowband filter to a single wavelength and then split into two beams by a beam-splitting prism. The direct beam vertically penetrates the liquid layer and capacitor film of the hollow glass container, while the oblique beam is adjusted to an incident angle of 5°-15° by a reflector assembly. The two beams converge in the space behind the capacitor film and interfere with each other. The angle adjustment device uses a rotating bracket driven by a servo motor to precisely control the pitch and horizontal angles of the oblique beam, ensuring that the two beams form evenly spaced interference fringes on the target surface of the image acquisition device. The fringe density is fine-tuned to 5-10 per millimeter by the angle, facilitating subsequent image analysis.

[0046] The sensitivity of defect detection is significantly enhanced by comparing the optical path difference of the dual beam. When there are thickness fluctuations or surface defects in the capacitor film, the propagation paths of direct light and oblique light in the defect area are different. The refractive index difference between the liquid layer and the capacitor film further amplifies this difference, causing the interference fringes to shift, break, or change in brightness. For example, a 0.1μm change in the thickness of the capacitor film at an oblique angle of 10° can cause the interference fringes to shift by more than 0.5 pixels, and the narrowband filter ensures high contrast of monochromatic light interference, which increases the optical signal of nanometer-level defects by more than 3 times. Compared with single-beam detection, dual-beam interference can effectively distinguish between fabric texture and real defects, reducing the misjudgment rate.

[0047] The high coherence of the laser light source can penetrate the liquid layer and the metallized conductive layer, accurately capturing defects within the dielectric layer. The LED light source combined with a narrow-band filter can prevent strong light from interfering with the reflective reflection of the conductive layer, clearly presenting shallow surface defects. The dynamic fringes formed by the dual-beam interference can simultaneously reflect the fracture of the conductive layer and the abnormality of the dielectric layer. When there are pinholes in the metallized layer, the interference fringes show characteristic distortion at the edge of the pinhole. Combined with the standard defect library of the image processing unit, the position of the conductive layer defect and the fluctuation range of the dielectric layer thickness can be synchronously located. The detection efficiency is 50% higher than that of traditional single-light source technology, meeting the online quality monitoring needs of high-speed mass production of capacitor films.

[0048] As an embodiment, the angle adjustment device includes a rotating bracket driven by a servo motor, which is used to adjust the angle θ between the two beams of light so that the interference fringe spacing is 5-10 pixels, and the adjustment accuracy of the angle θ is ±0.5°.

[0049] The angle adjustment device achieves high-precision angle control through the collaboration of a servo motor and a precision mechanical structure. The servo motor uses a high-torque stepper motor and is paired with a harmonic reducer with a reduction ratio of 1:100 to ensure that the rotation accuracy of the rotating bracket reaches ±0.01°. The bracket adopts a dual-axis linkage design. The horizontal axis and vertical axis respectively control the pitch angle and horizontal angle of the light source and image acquisition device. The angle θ between the two beams of light is fed back to the controller in real time through the encoder, forming a closed-loop adjustment system. When the interference fringe spacing needs to be controlled within 5-10 pixels, the controller automatically calculates the optimal θ value based on the camera pixel size and the wavelength of the light source, and drives the motor to fine-tune with an accuracy of 0.1° / step until the fringe spacing reaches the preset range.

[0050] The ±0.5° adjustment accuracy and the 5-10 pixel fringe spacing design provide dual technical guarantees for defect detection. On the one hand, precise angle control can convert a 0.1μm change in capacitor film thickness into a recognizable fringe offset. When θ=10°, a 1-pixel fringe displacement corresponds to an optical path difference of approximately 10nm, which is sufficient to detect nanometer-level defects. On the other hand, the optimization of the fringe spacing enables the interference pattern to have both clarity and resolution. The 5-pixel spacing is suitable for capturing the overall outline of large-scale defects, while the 10-pixel spacing is convenient for identifying the edge features of subtle defects. This design breaks through the limitations of traditional fixed-angle detection and can dynamically match the optimal detection angle according to the capacitor film material and defect type, thereby increasing the contrast of the interference fringes to above 0.9.

[0051] When pinholes exist in the metallization layer of the capacitor film, adjusting θ to 15° can enhance the light scattering interference effect at the pinhole edge, doubling the degree of fringe distortion. For fluctuations in dielectric layer thickness, a small angle of 5° can highlight subtle changes in optical path difference, increasing the thickness detection resolution to 50nm. In addition, the servo motor's high-speed response can match the high-speed operation rhythm of the capacitor film production line, achieving online detection of more than 50 meters per minute, and simultaneously completing automatic adaptation of detection parameters for different batches and different materials of capacitor films, significantly reducing manual debugging costs and missed detection rates.

[0052] As an embodiment, the capacitive film defect detection system also includes an optical path adjustment component, which is connected to the light source and is arranged between the light source and the hollow glass container. The optical path adjustment component includes an aperture and a lens, and the aperture of the aperture is 90%-110% of the diameter of the detection beam.

[0053] The optical path adjustment assembly coordinates precision mechanical structures and optical elements to control beam quality. The iris utilizes an adjustable metal blade structure, driven by a stepper motor to open and close the blades. The aperture range is precisely controlled to 90%-110% of the detection beam diameter. When the beam diameter is 10mm, the iris aperture is dynamically adjusted to 9-11mm. A plano-convex lens is mounted on a two-dimensional adjustment bracket in front of the iris. A threaded knob fine-tunes the distance between the lens and the light source so that the divergent beam is collimated by the lens and incident perpendicularly to the center of the iris. This ensures that the beam edge and the iris aperture are closely aligned to avoid light leakage or energy loss.

[0054] The aperture range of 90%-110% achieves a balance between beam energy and detection accuracy. If the aperture is less than 90%, excessive obstruction of the beam edge will cause energy attenuation, affecting the brightness of the interference fringes; if the aperture is greater than 110%, the excess beam will illuminate the non-detection area of ​​the capacitor film, generating stray light interference. This range allows the beam to just cover the area to be detected, and combined with the optical path difference amplification effect of the liquid layer, the contrast of light intensity changes at the defect can be increased by more than 40%. For example, when there is a 0.1μm protrusion on the capacitor film, the beam after aperture limitation can accurately capture the optical path difference change at the edge of the protrusion, preventing the light in the non-detection area from masking the defect signal.

[0055] The combined design of the lens and the aperture significantly improves the optical performance of the light beam. The lens converts the divergent light source into a collimated beam, ensuring that the light beam penetrates the liquid layer and the capacitor film vertically, reducing the optical path difference error caused by oblique incidence. The aperture further trims the edge of the light beam to regularize the shape of the light spot and form a uniform interference background on the target surface of the image acquisition device. This synergistic effect is particularly important for polypropylene capacitor films coated with a conductive layer. The collimated light beam can penetrate the metallized conductive layer, avoiding uneven reflection of the conductive layer caused by beam divergence, and the light beam range limited by the aperture can accurately locate the conductive layer break or dielectric layer defect, so that the detection system's detection rate for pinhole defects below 0.5μm is increased to more than 95%.

[0056] As an embodiment, the image processing unit pre-stores a standard defect feature library, and identifies conductive layer fractures, surface unevenness, and dielectric layer impurity defects of the capacitor film by comparing the offset, contrast, and bright spot distribution of the interference fringes.

[0057] The standard defect feature library of the image processing unit is constructed through multi-dimensional sample collection and feature extraction. First, different types of capacitor film defect samples are collected, including typical defects such as conductive layer fractures, surface bumps, and dielectric layer impurities. The interference images of each defect are collected under standard working conditions using the detection system. Through edge detection, frequency domain analysis and other algorithms, the offset distribution, contrast threshold and bright spot morphological characteristics of the interference fringes are extracted from the image to establish a parameterized defect feature template. For example, for a surface protrusion of 0.1μm, the fringe offset amplitude, the degree of contrast attenuation of adjacent fringes and the bright spot shape parameters caused by it are recorded, and finally a standard library containing hundreds of sets of feature data is formed.

[0058] During real-time inspection, the image processing unit preprocesses the captured interference image, removing noise through Fourier filtering, and then extracts the fringe offset, contrast distribution, and bright spot location of the current image. The system then matches these real-time parameters with templates in a standard feature library for similarity, calculating the parameter deviation using a dynamic time warping algorithm. When the deviation exceeds a preset threshold, the defect recognition logic is automatically triggered. For example, if the fringe offset exceeds 0.5 pixels and the contrast attenuation exceeds 30%, the characteristic template of a conductive layer fracture is matched, and the defect is then located and classified. This comparison process is completed within 50ms, meeting the real-time inspection requirements of high-speed production lines.

[0059] The standard feature library covers complex defect scenarios for capacitor films and can simultaneously detect anomalies in both the conductive and dielectric layers. For example, pinholes in the metallization layer can cause localized breakage of stripes, while impurities in the dielectric layer can cause stripe disorder. Feature library comparison allows for precise differentiation between these two types of defects, avoiding misjudgments associated with traditional single-parameter testing. Furthermore, the feature library supports self-learning, continuously incorporating new types of defect data to continuously improve the system's detection rate for new defects. In actual applications, the positioning accuracy of impurities in the dielectric layer reaches 10μm, significantly reducing the missed detection rate and manual re-inspection costs of capacitor films, and providing quality assurance for high-reliability packaging of electronic components.

[0060] The present invention discloses a method for detecting defects in a capacitor film, using a capacitor film defect detection system as described above, comprising:

[0061] S1: Pretreatment stage: Insulating liquid is filled into the interlayer of the hollow glass container. The thickness of the liquid layer is controlled to be 50-100 μm. The absolute value of the difference between the refractive index of the insulating liquid and the refractive index of the capacitor film is 0.02-0.25. The capacitor film is attached to the lower surface of the container. The bubbles in the liquid layer are removed by vacuum degassing process. The surface of the capacitor film is treated with plasma to enhance wettability.

[0062] S2: Single-beam pre-detection stage: The light source is adjusted to single-beam mode with the intensity set to 30%-50% of the standard value. The light is directed through the liquid layer and the capacitive film to collect the transmitted light spot image. The edge detection algorithm is used to roughly locate surface protrusions or holes ≥5μm in size.

[0063] S3: Dual-beam interference amplification stage: switch the light source to dual-beam mode, adjust the beam angle to 5°-15°, scan within the pitch angle range of 10°-70°, collect interference images at different angles, lock the optimal detection angle based on the image clarity threshold, and use the refractive index difference between the insulating liquid and the capacitive film to amplify the optical path difference at the defect, causing the interference fringes to produce a recognizable offset;

[0064] S4: Quantitative analysis of optical path difference: fix the optimal detection angle, increase the light source intensity to 120%-150% of the standard value, and calculate the defect height by analyzing the interference phase difference and the refractive index difference between the insulating liquid and the capacitance film;

[0065] S5: Multi-dimensional verification stage, switch to an insulating liquid with a refractive index lower than the insulating liquid in S1, repeat steps S1-S4, and verify the authenticity of the defect through the consistency of the interference fringe offset under different insulating liquids.

[0066] In S1, high-precision quartz spacers are placed between the upper and lower glass layers of the hollow glass container, or the thickness of the interlayer is controlled through a micron-scale flow channel network on a microfluidic chip to ensure uniform distribution of the liquid layer. Insulating liquid is injected through a liquid inlet at the edge of the interlayer at a constant flow rate of 0.1 mL / min. Simultaneously, a negative pressure of -0.1 MPa is applied through a vacuum degassing port and maintained for 10 minutes. Combined with 40 kHz ultrasonic vibration, the volume fraction of bubbles in the insulating liquid is controlled to below 0.01%. During capacitive film bonding, a plasma treatment device is used to treat the capacitive film surface for 30 seconds to increase its surface affinity and ensure a tight bond between the insulating liquid and the capacitive film surface, eliminating micron-sized bubbles. The precise liquid layer thickness of 50-100 μm and the bubble-free environment prevent interference from light scattering and refraction, providing a stable physical foundation for subsequent optical detection. The plasma treatment reduces the contact angle between the insulating liquid and the capacitive film surface from 80° to below 30°, eliminating interfacial gaps and ensuring that optical path difference is solely due to defects in the capacitive film itself.

[0067] During the single-beam pre-detection stage in S2, the light source is switched to single-beam mode, with the intensity set to 30%-50% of the rated power to prevent image saturation caused by strong light and reduce energy consumption. The light beam vertically penetrates the insulating liquid layer and the capacitive film, and the image acquisition device captures the transmitted light spot image at a rate of 200fps. An edge detection algorithm is used to extract areas with sudden grayscale value changes in the image. Combined with morphological filtering, surface protrusions, holes, or impurities with a size of ≥5μm are coarsely located to generate defect ROI coordinates. Single-image analysis can be completed within 20ms, quickly eliminating defect-free areas and narrowing the detection range of dual-beam interference to the pre-positioned ROI, improving overall detection efficiency by more than 30%. The combination of a low-intensity light source and edge detection effectively distinguishes real defects from artifacts caused by slight unevenness in the liquid layer, reducing the amount of subsequent processing calculations. The edge detection algorithm can be, for example, Canny edge detection.

[0068] The dual-beam interference amplification stage in the S3 uses a beamsplitter prism to split the light source into two coherent beams. One beam is incident vertically, while the other is adjusted by a servo motor-driven rotating bracket to an angle of 5°-15°, with an angle adjustment accuracy of ±0.5°, ensuring that the two beams form interference fringes with a spacing of 5-10 pixels on the target image surface. The system scans in 1° steps over the pitch angle range of 10°-70°, calculating the contrast of the captured image in real time. When the contrast is ≥0.7, the current angle is locked as the optimal detection angle. At this point, the optical path difference at the defect causes the interference fringes to shift by ≥1 pixel. By utilizing the refractive index difference between the insulating liquid and the capacitor film, a 0.1μm change in the capacitor film thickness is converted into a detectable optical path difference, resulting in an interference fringing offset of more than 0.5 pixels for nanoscale defects, significantly improving detection sensitivity compared to a single-beam system. Angle scanning automatically matches the optimal detection angle for different defect types, avoiding missed detections at fixed angles.

[0069] In the optical path difference quantification analysis phase of S4, the light source intensity is increased to 120%-150% of the rated power. Ten frames of images are collected and average filtered. The filtered image is Fourier transformed to extract the phase information of the interference fringes. A phase shift algorithm is used to calculate the phase difference between the defective area and the standard area. Combined with the refractive index data of the insulating liquid and the capacitor film recorded during the preprocessing phase, the defect height is inferred. For example, when the refractive index of the insulating liquid is 1.47 and the refractive index of the capacitor film is 1.50, a thickness change of 0.1μm corresponds to an optical path difference of 0.03μm. The fringe offset can be used to calculate the actual defect size with an accuracy of less than 100nm. This upgrade from defect presence determination to defect size measurement can accurately distinguish thickness fluctuations of 0.1μm and 0.2μm, providing data support for quality grading. Intense light illumination increases the signal-to-noise ratio of the interference fringes from 5:1 to 15:1, enabling accurate identification of even impurities within transparent dielectric layers through fringe distortion. The defect height can also be calculated by comparing the interference fringe phase difference between the standard film and the film to be tested, combined with a preset correspondence table between the refractive index difference and the fringe offset. The specific correspondence table between the refractive index difference and the fringe offset is obtained by integrating historical data.

[0070] During the multi-dimensional verification phase in S5, the current insulating liquid is drained through a microfluidic valve and a second insulating liquid with a refractive index 0.1-0.2 lower than the original insulating liquid is injected. The dual-beam interferometry detection process is repeated, keeping other parameters unchanged. The direction and amplitude of the fringe offset at the same location in the two tests are compared. If the offset difference is less than 20% and the direction is consistent, it is determined to be a real defect. If the difference is greater than 30%, it is determined to be an artifact caused by an uneven liquid layer or residual bubbles and is eliminated. The traditional single-liquid detection error rate is approximately 5%, but after verification with multiple insulating liquids, it is reduced to less than 0.3%. In particular, it can eliminate false defect signals caused by impurities in the insulating liquid itself or slight contamination on the surface of the capacitor film. The refractive index difference between different insulating liquids will change the optical path difference magnification. For example, silicone oil and water will have different fringe offsets for the same defect. Combined with the feature library, it can further distinguish between conductive layer fractures and dielectric layer wrinkles, improving the classification accuracy to a high level.

[0071] A capacitor film defect detection method of the present invention can identify 0.1μm-level dielectric layer thickness fluctuations and 0.5μm conductive layer pinholes, with a detection accuracy of nanometers, far exceeding the industry's conventional 5μm detection standard. The detection time for a single capacitor film is less than 1 second, and it is suitable for 60m / min high-speed production lines; by changing the insulating liquid and light source parameters, it is compatible with capacitor films of different materials such as PET and PI. The combination of multi-dimensional verification and quantitative analysis realizes the automation of the entire process of defect detection, positioning, classification and size measurement, helping enterprises to reduce the scrap rate of capacitor films and reduce production costs. There is no need to contact the surface of the capacitor film throughout the process, avoiding damage to the capacitor film caused by traditional mechanical scanning, and it is particularly suitable for the detection of ultra-thin capacitor films. Through the above steps, this capacitor film defect detection method constructs a complete technical chain from physical environment preparation to optical signal enhancement, and then to intelligent analysis and verification, providing a systematic solution for high-precision detection of capacitor films.

[0072] As an embodiment, the insulating liquid in S1 is methyl silicone oil or fluorinated liquid. During filling, it is filtered through a 0.1-0.3μm filter membrane. Microfluidics are set at the edge of the interlayer to control the uniformity of the liquid layer, ensuring that the insulating liquid adheres tightly to the surface of the capacitor film without bubbles. The capacitor film is a polypropylene dielectric film coated with a conductive layer.

[0073] In step S1, the insulating liquid is selected from methyl silicone oil or fluorinated liquid, based on its stable insulating properties and specific refractive index design. The refractive index of methyl silicone oil is 1.47, which is 0.03 lower than that of polypropylene film, which is 1.50. The refractive index of fluorinated liquid is 1.27, with a difference of 0.23, both meeting the range requirement of 0.02-0.25. Before filling the insulating liquid, it is filtered through a polytetrafluoroethylene filter membrane with a pore size of 0.1-0.3μm to intercept dust particles or colloidal impurities that may exist in the insulating liquid, ensuring that the cleanliness of the insulating liquid injected into the interlayer reaches ISO4406 standard 16 / 14 level. The micro-flow grooves at the edge of the interlayer are etched on the glass substrate using a photolithography process, with a groove width of 50-100μm and a depth of 30-50μm. When the insulating liquid is injected, it is evenly diffused to the entire interlayer through the capillary action of the micro-flow grooves. In conjunction with the vacuum degassing interface, the gap between the insulating liquid and the surface of the capacitor film is controlled to be less than 10nm, and no bubbles are visible to the naked eye.

[0074] 0.1-0.3μm membrane filtration and microfluidic design work together to improve the quality of the liquid layer. The membrane filter effectively removes impurities that may interfere with light propagation and avoids scattering noise caused by particles larger than 5μm. The microfluidic channel guides the insulating liquid to spread evenly, controlling the difference in liquid layer thickness in different areas of the interlayer to within ±2μm, ensuring the consistency of the optical path difference amplification effect. The high chemical inertness of methyl silicone oil and the low surface tension characteristics of fluorinated liquid prevent it from swelling the polypropylene substrate and corroding the surface conductive layer, ensuring the stability of the electrical properties of the capacitor film during the detection process. The combination of vacuum degassing and microfluidic channels increases the light transmittance uniformity of the liquid layer to more than 98%. Compared with the traditional gravity filling method, the bubble residue rate is reduced from 1% to 0.005%, significantly reducing the interference of background noise on the interference fringes.

[0075] As an implementation method, the light source of the dual-beam interference in S3 is a 600-650nm laser. By adjusting the beam angle, the interference fringe spacing is made 5-10 pixels. When there are defects in the capacitor film, the optical path difference amplified by the liquid layer causes the fringe offset to be ≥1 pixel. The pixel is the physical pixel of the image acquisition device, and the pixel size is 5-10μm.

[0076] The S3 step uses a laser with a wavelength of 600-650nm as the light source. The absorption rate of light in this wavelength band is low in insulating liquids and polypropylene films, and it can effectively penetrate the conductive layer and stimulate a significant interference effect. The laser is divided into two beams by a beam splitter prism, one beam is incident vertically, and the other beam is driven by a servo motor to rotate the bracket. The angle is adjusted with an accuracy of ±0.5° so that the two beams of light form interference fringes with a spacing of 5-10 pixels on the target surface of the image acquisition device. When there are defects in the capacitor film, the refractive index difference between the liquid layer and the capacitor film amplifies the optical path difference at the defect, causing the interference fringes to produce an offset of ≥1 pixel. The system collects fringe images in real time and captures the offset through a sub-pixel edge detection algorithm to ensure that the optical signal of nanoscale defects can be quantified.

[0077] The 600-650nm laser wavelength is optimally matched to a pixel size of 5-10μm. This wavelength corresponds to a low Rayleigh scattering coefficient in insulating liquids, reducing background noise. The 5-10 pixel fringe spacing ensures the interference pattern is neither too dense nor too sparse. Combined with the image acquisition device's 12-bit grayscale resolution, it can detect fringe deviations as small as 0.1 pixel, corresponding to a change in optical path difference of approximately 10nm. This parameter combination increases the system's sensitivity for detecting dielectric layer thickness fluctuations as small as 0.1μm to three times that of traditional white-light interferometry, while also improving the detection rate of pinholes in conductive layers.

[0078] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A capacitive film defect detection system, characterized in that: include: Hollow glass container, the container is composed of two layers of glass and a sealed interlayer in the middle. The interlayer is filled with insulating liquid to form a uniform liquid layer; The light source is located on one side of the hollow glass container and is used to emit a detection beam to penetrate the liquid layer and the capacitance film. The light source is equipped with a controller that can adjust the output intensity. The standard value is 100% of the rated output power of the light source. An image acquisition device is provided on the other side of the capacitive film and is used to acquire light signals passing through the capacitive film; An angle adjustment device, the angle adjustment device is connected to the light source and the image acquisition device respectively, and is used to adjust the illumination angle of the light source and the acquisition angle of the image acquisition device; The image processing unit is connected to the image acquisition device and is used to analyze the light signal and identify defects in the capacitor film.

2. The capacitive film defect detection system according to claim 1, characterized in that: The interlayer thickness of the hollow glass container is 50-100 μm. The uniformity of the insulating liquid layer is controlled by a quartz gasket or a microfluidic structure, and a liquid injection port and a vacuum degassing interface are provided on the edge of the interlayer.

3. The capacitive film defect detection system according to claim 2, characterized in that: The absolute value of the difference between the refractive index of the insulating liquid and the refractive index of the capacitor film is 0.02-0.

25. The insulating liquid is insulating silicone oil or fluorinated liquid, and the capacitor film is a polypropylene dielectric film coated with a conductive layer.

4. The capacitive film defect detection system according to claim 1, characterized in that: The light source is a laser or LED light source, which is matched with a narrow-band filter. The detection beam is divided into two coherent beams. One beam directly passes through the liquid layer and the capacitor film, and the other beam is incident on the capacitor film at an angle of 5°-15°. The two beams of light form an interference area on the target surface of the image acquisition device.

5. The capacitive film defect detection system according to claim 1, characterized in that: The angle adjustment device includes a rotating bracket driven by a servo motor, which is used to adjust the angle θ between the two beams of light so that the interference fringe spacing is 5-10 pixels. The adjustment accuracy of the angle θ is ±0.5°.

6. The capacitive film defect detection system according to claim 1, characterized in that: The capacitive film defect detection system also includes an optical path adjustment component, which is connected to the light source and is arranged between the light source and the hollow glass container. The optical path adjustment component includes an aperture and a lens. The aperture of the aperture is 90%-110% of the diameter of the detection beam.

7. The capacitive film defect detection system according to claim 1, characterized in that: The image processing unit pre-stores a standard defect feature library, and identifies conductive layer fractures, surface unevenness, and dielectric layer impurity defects of the capacitor film by comparing the offset, contrast, and bright spot distribution of the interference fringes.

8. A capacitive film defect detection method, using a capacitive film defect detection system according to any one of claims 1 to 7, characterized in that: include: S1: Pretreatment stage: Insulating liquid is filled into the interlayer of the hollow glass container. The thickness of the liquid layer is controlled to be 50-100 μm. The absolute value of the difference between the refractive index of the insulating liquid and the refractive index of the capacitor film is 0.02-0.

25. The capacitor film is attached to the lower surface of the container. The bubbles in the liquid layer are removed by vacuum degassing process, and the film surface is treated with plasma to enhance wettability. S2: Single-beam pre-detection stage: The light source is adjusted to single-beam mode with the intensity set to 30%-50% of the standard value. The light is directed through the liquid layer and the capacitive film to collect the transmitted light spot image. The edge detection algorithm is used to roughly locate surface protrusions or holes ≥5μm in size. S3: Dual-beam interference amplification stage: switch the light source to dual-beam mode, adjust the beam angle to 5°-15°, scan within the pitch angle range of 10°-70°, collect interference images at different angles, lock the optimal detection angle based on the image clarity threshold, and use the refractive index difference between the insulating liquid and the capacitive film to amplify the optical path difference at the defect, causing the interference fringes to produce a recognizable offset; S4: Quantitative analysis of optical path difference: fix the optimal detection angle, increase the light source intensity to 120%-150% of the standard value, and calculate the defect height by analyzing the interference phase difference and the refractive index difference between the insulating liquid and the capacitance film; S5: Multi-dimensional verification stage, switch to an insulating liquid with a refractive index lower than the insulating liquid in S1, repeat steps S1-S4, and verify the authenticity of the defect through the consistency of the interference fringe offset under different insulating liquids.

9. The method for detecting capacitive film defects according to claim 8, wherein: include: The insulating liquid in S1 is methyl silicone oil or fluorinated liquid. It is filtered through a 0.1-0.3μm filter membrane during filling, and a micro-flow groove is set at the edge of the interlayer to control the uniformity of the liquid layer, ensuring that the insulating liquid is tightly attached to the surface of the capacitor membrane without bubbles. The capacitor film is a polypropylene dielectric film coated with a conductive layer.

10. The method for detecting capacitive film defects according to claim 8, wherein: include: The light source for dual-beam interference in S3 is a 600-650nm laser. By adjusting the beam angle, the interference fringe spacing is adjusted to 5-10 pixels. When there are defects in the capacitive film, the optical path difference amplified by the liquid layer causes the fringe offset to be ≥1 pixel. The pixel is the physical pixel of the image acquisition device, and the pixel size is 5-10μm.

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