Nondestructive testing method for cleanliness of bottom of blind hole in FPC (Flexible Printed Circuit) manufacturing process

Abstract

The invention relates to a nondestructive testing method for the cleanliness of the bottom of a blind hole in an FPC (Flexible Printed Circuit) manufacturing process. The method comprises the following steps: preparing an FPC (Flexible Printed Circuit) sample which is processed by a laser process and a Plasma process and is provided with a blind hole; positioning and amplifying the hole bottom area of the blind hole of the FPC sample by adopting a laser Raman spectrometer, and performing laser focusing on the surface of the hole bottom area of the blind hole; scanning the hole bottom area of the blind hole through a laser Raman spectrometer according to preset test parameters, and obtaining a Raman spectrogram of the hole bottom area of the blind hole; detecting whether Raman absorption peaks exist in the Raman spectrogram of the hole bottom area of the blind hole or not, if yes, judging that residues exist at the hole bottom of the blind hole, and if not, judging that no residues exist at the hole bottom of the blind hole. The method is simple in detection, efficient and accurate in detection and free of any damage to a detected sample, and residues can be qualitatively analyzed.

Description

Technical Field

[0001] This invention relates to the field of circuit board inspection technology, and in particular to a non-destructive testing method for the cleanliness of the bottom of blind vias in FPC manufacturing. Background Technology

[0002] Flexible printed circuit boards (FPCs) offer advantages such as bendability, foldability, light weight, and small size, leading to their widespread application in aerospace, mobile phones, computers, and digital cameras. In the manufacturing process of FPCs, after laser and plasma processing, inspecting the cleanliness of the bottom of blind vias is a crucial step. Since the bottom of these blind vias will subsequently undergo copper plating to establish electrical connections between different layers—such as connecting conductive paths in multilayer circuits and mounting components, and providing mounting locations for surface-mount components (like resistors and capacitors)—the presence of foreign matter or slag (residue) at the bottom of the blind vias after the laser and plasma processes can pose very serious risks. Residues may cause poor electrical conductivity or open circuits between the bottom of blind vias and the inner copper foil; or they may reduce the adhesion of the plating at the bottom of blind vias, resulting in poor plating quality; or the residues may volatilize or decompose at high temperatures, causing delamination of the plating at the bottom of blind vias, or produce chemical contamination that degrades circuit performance. All of these can lead to a decrease in product yield, an increase in rework rate, and consequently, an increase in manufacturing costs.

[0003] It is known that residues at the bottom of blind vias on circuit boards can severely affect the electrical performance, plating quality, reliability, and appearance of FPCs, increasing manufacturing costs. Therefore, during the production and processing of FPCs, the residues at the bottom of blind vias are typically detected and controlled. Traditionally, optical microscopes or scanning electron microscopes are used to detect these residues. However, both methods have limitations. For example, optical microscopes have low resolution, cannot provide clear observation, have low accuracy, and lack qualitative analysis capabilities to determine the source of the residues. Furthermore, scanning electron microscopes require destructive testing that damages the sample, making the process complex, the measurement results inaccurate, and requiring highly skilled personnel. Summary of the Invention

[0004] This invention provides a non-destructive testing method for the cleanliness of the bottom of blind holes in FPC manufacturing. The testing method is relatively simple, efficient and accurate, and does not damage the test sample. It can also perform qualitative analysis of residues.

[0005] To achieve the above objectives, the present invention provides a non-destructive testing method for the cleanliness of the bottom of blind vias in FPC manufacturing processes, the method comprising:

[0006] Prepare FPC samples with blind vias after laser and plasma processes.

[0007] Laser Raman spectroscopy was used to locate and magnify the bottom region of the blind hole in the FPC sample, and laser focusing was applied to the surface of the bottom region of the blind hole.

[0008] The bottom region of the blind hole was scanned using a laser Raman spectrometer with preset test parameters, and the Raman spectrum of the bottom region of the blind hole was obtained.

[0009] The presence of Raman absorption peaks in the Raman spectrum of the bottom region of the blind hole is detected. If Raman absorption peaks are present, it is determined that there are residues at the bottom of the blind hole; otherwise, it is determined that there are no residues at the bottom of the blind hole.

[0010] Optionally, the step of detecting whether there is a Raman absorption peak in the Raman spectrum of the blind hole bottom region, and determining whether there is residue at the bottom of the blind hole if there is, and determining whether there is no residue at the bottom of the blind hole if there is no residue, includes:

[0011] Detect whether there are Raman absorption peaks in the Raman spectrum of the bottom region of the blind hole within a preset spectral range;

[0012] If a Raman absorption peak is present in the bottom region of the blind hole within the preset spectral range, it proves that there are residues at the bottom of the blind hole, and these residues should be treated.

[0013] If no Raman absorption peak is present in the bottom region of the blind hole within the preset spectral range, it proves that there is no residue at the bottom of the blind hole, and it flows directly into the next process.

[0014] Optionally, the step of scanning the bottom region of the blind hole with a laser Raman spectrometer using preset test parameters includes:

[0015] Random, individual scanning tests were performed on the bottom region of the blind hole using a laser Raman spectrometer with preset test parameters; or / and

[0016] The entire area at the bottom of the blind hole was scanned using a laser Raman spectrometer with preset test parameters.

[0017] Optionally, the preset test parameters include preset laser power, preset exposure time, preset pixel size, preset confocal aperture, preset integration time, preset number of scans, preset spectral range, and preset resolution.

[0018] Optionally, the preset laser power is 2-5mW, the preset exposure time is 0.18-0.22s, the preset pixel size is 1µm, the preset confocal aperture is 20-30µm, the preset integration time is 5-10s, the preset number of scans is 3-5, and the preset spectral range is 150-4000cm². -1 The preset resolution is 2-4cm. -1 .

[0019] Optionally, the step of locating and magnifying the blind hole bottom region of the FPC sample using a laser Raman spectrometer includes:

[0020] Turn on the laser Raman spectrometer and preheat it, then set its test laser wavelength;

[0021] Turn on the stage of the laser Raman spectrometer and place and position the FPC sample at the center of the stage;

[0022] Switch the laser Raman spectrometer to real-time image mode, and gradually adjust the laser Raman spectrometer according to the objective lens magnification from low to high, so as to magnify the bottom area of ​​the blind hole on the FPC sample to the preset magnification.

[0023] Optionally, the laser focusing of the surface of the bottom region of the blind hole includes:

[0024] The laser beam path of the laser Raman spectrometer is adjusted so that the laser is focused on the surface of the blind hole bottom region of the FPC sample, thereby achieving laser spot calibration.

[0025] Optionally, the preparation of the FPC sample with blind vias after laser and plasma processes includes:

[0026] Prepare one or more sets of FPC samples with blind vias; each set of FPC samples includes multiple FPC samples, and each FPC sample has been processed by Laser and Plasma processes.

[0027] Optionally, in one or more groups of FPC samples with blind holes, some of the FPC samples have blind holes without adhesive, while the other group of FPC samples have blind holes with adhesive.

[0028] Optionally, the diameter of the blind holes on the FPC sample is 50-100 μm.

[0029] The beneficial effects of the technical solution provided by this invention include:

[0030] Laser Raman spectroscopy is used to scan FPC samples with blind holes after laser and plasma processes. The scan is mainly performed on the bottom region of the blind holes to obtain the corresponding Raman spectrum. Then, the Raman spectrum obtained from the scan of the bottom region of the blind holes is analyzed to determine whether there are Raman absorption peaks. Based on this, it is determined whether there are residues in the bottom region of the blind holes, thus achieving non-destructive testing of the cleanliness of the bottom of the blind holes in the FPC samples.

[0031] This method rapidly focuses the laser spot of a laser Raman spectrometer onto the bottom of the blind holes in an FPC sample. Organic matter or residual carbides (i.e., residues) at the bottom of these blind holes absorb Raman light very sensitively, while the copper surface at the bottom does not absorb it. Therefore, the presence of Raman peaks (i.e., Raman absorption peaks) in the Raman spectrum allows for a very rapid assessment of the cleanliness of the blind hole bottom. Thus, by testing the Raman spectrum of residues at the bottom of blind holes in an FPC using a laser Raman spectrometer, the cleanliness of the blind hole bottom can be quickly monitored. This method is simple, fast, efficient, and accurate, and it allows for qualitative analysis of the residues to determine their source, providing direction for failure analysis. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a simplified schematic diagram illustrating the steps of the non-destructive testing method for the cleanliness of the bottom of blind vias in the FPC process, as described in an embodiment of the present invention.

[0034] Figure 2 This is a simplified cross-sectional diagram of an FPC sample with adhesive-free blind holes, used in the non-destructive testing method for the cleanliness of the bottom of blind holes in the FPC process according to an embodiment of the present invention.

[0035] Figure 3 This is a simplified cross-sectional diagram of an FPC sample with adhesive blind holes, which is involved in the non-destructive testing method for the cleanliness of the bottom of blind holes in the FPC process described in this embodiment of the invention.

[0036] Figure 4 This is a simplified top view of the FPC sample with residue at the bottom of the blind hole, as described in the non-destructive testing method for the cleanliness of the bottom of the blind hole in the FPC process according to an embodiment of the present invention.

[0037] Figure 5The Raman absorption spectrum of the FPC sample when there are residues in the blind hole bottom region, as detected by the non-destructive testing method for the cleanliness of the blind hole bottom in the FPC process according to the embodiment of the present invention.

[0038] Figure 6 The Raman absorption spectrum of the FPC sample when there is no residue in the blind hole bottom region, as detected by the non-destructive testing method for the cleanliness of the blind hole bottom in the FPC process according to the embodiment of the present invention.

[0039] Figure 7 This is a comparison of Raman absorption spectra of the bottom region of blind holes in FPC samples with and without residue, as detected by the non-destructive testing method for the cleanliness of the bottom of blind holes in the FPC process described in this embodiment of the invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] In traditional techniques, optical microscopes or scanning electron microscopes are typically used to detect residues at the bottom of blind holes. However, both methods have limitations. For example, optical microscopes suffer from low resolution, unclear observation, low accuracy, and lack of qualitative analysis to determine the source of residues. Furthermore, scanning electron microscopes require destructive testing that damages the sample, making the process complex, the results inaccurate, and demanding on skilled personnel. To address these technical problems, this invention proposes a non-destructive testing method for the cleanliness of the bottom of blind holes in FPC processes.

[0042] Specifically, such as Figure 1 As shown, the non-destructive testing method for the cleanliness of the bottom of blind vias in the FPC process may include the following steps:

[0043] S100. Prepare FPC samples with blind vias after laser and Plasma processes.

[0044] S200. A laser Raman spectrometer is used to locate and magnify the bottom region of the blind hole in the FPC sample, and the surface of the bottom region of the blind hole is laser-focused.

[0045] S300. The bottom region of the blind hole is scanned using a laser Raman spectrometer with preset test parameters, and the Raman spectrum of the bottom region of the blind hole is obtained.

[0046] S400. Detect whether there is a Raman absorption peak in the Raman spectrum of the bottom region of the blind hole. If there is, it is determined that there is residue at the bottom of the blind hole; if not, it is determined that there is no residue at the bottom of the blind hole.

[0047] Laser Raman spectroscopy is a non-destructive analytical instrument that measures the molecular vibrational and rotational information of a sample through the interaction of a laser and the sample. Its principle is to irradiate the sample with a laser and measure the scattered spectrum produced. By measuring the intensity, frequency, and spectrum of the scattered light, information about the sample's molecular structure and chemical composition can be obtained. Laser Raman spectroscopy is used to scan FPC samples with blind holes after laser and plasma processing. The scan primarily focuses on the bottom region of the blind holes, acquiring the corresponding Raman spectrum. Then, the Raman spectrum obtained from the blind hole bottom region is analyzed to determine the presence of Raman absorption peaks. This analysis helps determine the presence of residues in the blind hole bottom region, thus achieving non-destructive testing of the cleanliness of the blind hole bottom of the FPC sample.

[0048] This method rapidly focuses the laser spot of a laser Raman spectrometer onto the bottom of the blind holes in an FPC sample. Organic matter or residual carbides (i.e., residues) at the bottom of these blind holes absorb Raman light very sensitively, while the copper surface at the bottom does not absorb it. Therefore, the presence of Raman peaks (i.e., Raman absorption peaks) in the Raman spectrum allows for a very rapid assessment of the cleanliness of the blind hole bottom. Thus, by testing the Raman spectrum of residues at the bottom of blind holes in an FPC using a laser Raman spectrometer, the cleanliness of the blind hole bottom can be quickly monitored. This method is simple, fast, efficient, and accurate, and it allows for qualitative analysis of the residues to determine their source, providing direction for failure analysis.

[0049] Furthermore, in step S100, preparing the FPC sample with blind vias after laser and plasma processes may further include the following steps:

[0050] Prepare one or more sets of FPC samples with blind vias; each set of FPC samples includes multiple FPC samples, and each FPC sample has been processed by Laser and Plasma processes.

[0051] like Figure 4As shown, since foreign matter or coke (which can be called residue) is more likely to appear at the bottom of the blind vias of FPCs processed by Laser and Plasma processes, FPCs with blind vias processed by Laser and Plasma processes can be used as FPC samples for testing. Furthermore, at least one set of FPC samples can be prepared, and each set can include multiple FPC samples. This allows for the separate testing of multiple FPC samples; the more samples tested, the more accurate and reliable the test results.

[0052] Furthermore, such as Figures 2 to 4 As shown, in one or more groups of FPC samples with blind holes, some FPC samples have adhesive-free blind holes, while others have adhesive-containing blind holes. For different types of blind holes, the types, morphological characteristics, and causes of residue at the bottom of the blind hole vary, leading to different risks and requiring different remedial measures. This allows for the detection of the bottom of blind holes with different residues, facilitating the analysis of their specific types and causes, and enabling the adoption of corresponding remedial measures. Furthermore, this method allows for the coverage of various types of FPC samples, broadening the applicability of the detection.

[0053] Specifically, such as Figure 2 and Figure 4 As shown, in FPC samples, for FPC samples with adhesive-free blind vias, there is typically a first copper layer, other structural layers located at the bottom of the first copper layer, and a first PI layer, an adhesive layer, a second PI layer, and a second copper layer sequentially located on top of the first copper layer. The blind via penetrates from the second copper layer to the top surface of the first copper layer, forming the bottom of the blind via on the top surface of the first copper layer. Residue usually forms on the top surface of the first copper layer (i.e., the bottom of the blind via). The residue at the bottom of the blind via in adhesive-free blind vias is usually copper debris, carbides, glass fiber debris, and metal oxides. Its morphological characteristics are usually uneven distribution and sharp burrs. The risks include poor electrical connection, insufficient mechanical strength, and high-frequency loss. These can be improved through laser parameter optimization, copper removal, and micro-etching processes.

[0054] In addition, such as Figure 3 and Figure 4As shown, for FPC samples with adhesive-bonded blind vias, the structure typically includes a first copper layer, other structural layers at the bottom of the first copper layer, and an adhesive layer, a PI layer, and a second copper layer sequentially disposed on top of the first copper layer. The blind via extends from the second copper layer to the top surface of the first copper layer, forming the bottom of the blind via on the top surface of the first copper layer. Residue usually forms on the top surface of the first copper layer (i.e., the bottom of the blind via). The residue at the bottom of the blind via with adhesive-bonded blind vias is typically uncured resin, carbides, and filler particles. Its morphological characteristics usually exhibit central agglomeration and tight interfacial adhesion. The risks include insulation failure, thermal expansion cracking, and ion migration, which can be improved through resin curing control, plasma cleaning, and other methods.

[0055] Furthermore, the pore size of the blind holes on the FPC samples is 50-100 μm. That is, the pore size of the blind holes can be 50 μm, 100 μm, or any value between 50 and 100 μm, which can cover blind holes of different sizes. Moreover, if needed, the pore size of the blind holes can also be less than 50 μm.

[0056] Furthermore, in step S200, the blind hole bottom region of the FPC sample is located and magnified using a laser Raman spectrometer, which may further include the following steps:

[0057] S210. Turn on the laser Raman spectrometer and preheat it, then set its test laser wavelength.

[0058] After preparing the FPC sample to be tested, and then using a laser Raman spectrometer...

[0059] Before testing FPC samples, they should be preheated to a stable operating state. This ensures the accuracy, repeatability, and reliability of subsequent test results. Temperature control eliminates the impact of temperature fluctuations on the instrument's core components (laser, optical system, detector, and electronic components). After preheating, the laser wavelength for testing can be set. In this embodiment, the test laser wavelength can be set to 532nm. However, other wavelengths can be used as needed.

[0060] S220. Open the stage of the laser Raman spectrometer and place and position the FPC sample at the center of the stage.

[0061] After preheating the laser Raman spectrometer, the FPC sample to be tested can be placed on the stage. First, open the stage and place the FPC sample at the center of the stage to ensure alignment with the laser emitted by the spectrometer. Furthermore, after placing the FPC sample on the stage, it can be positioned and fixed using sample clips or magnetic sheets to ensure stability and flatness, facilitating subsequent stable detection.

[0062] S230. Switch the image mode of the laser Raman spectrometer to the real-time image mode, and gradually adjust the laser Raman spectrometer according to the objective lens magnification from low to high, so as to magnify the bottom area of ​​the blind hole on the FPC sample to be tested to the preset magnification.

[0063] In image mode, laser Raman spectrometers can correlate Raman spectral information of micrometer-scale micro-regions with spatial location information to generate two-dimensional or three-dimensional distribution maps in grayscale / color format using Raman characteristic parameters (such as peak intensity, peak position, and peak width). Furthermore, by adjusting the instrument's image mode to real-time image mode, real-time image acquisition can be achieved during the observation of FPC samples, allowing for real-time acquisition of detection results.

[0064] By gradually adjusting the objective magnification of the laser Raman spectrometer from low to high, rapid macroscopic navigation can be achieved at low magnification, efficiently locating the analytical region of the FPC sample (i.e., the bottom region of the blind hole). Furthermore, by progressively increasing the objective magnification, precise focusing on the bottom region of the blind hole in the FPC sample is ensured, preventing collisions between the FPC sample and the objective. This objective magnification adjustment method also helps match laser focusing and optimize signal collection. In summary, this adjustment method improves operational efficiency, protects the sample and instrument, and ensures analytical accuracy. In this embodiment, the objective magnification can be gradually adjusted from low to high, up to 500X (i.e., 500x), allowing the laser Raman spectrometer to clearly locate and magnify the bottom region of the blind hole.

[0065] Furthermore, in step S200, laser focusing on the surface of the bottom region of the blind hole may further include the following steps:

[0066] S240. Adjust the laser path of the laser Raman spectrometer so that the laser is focused on the surface of the blind hole bottom area of ​​the FPC sample to achieve laser spot calibration.

[0067] By adjusting the laser beam path of the laser Raman spectrometer, the laser is focused onto the surface of the bottom of the blind hole in the FPC sample, resulting in a minimum and bright spot. The main purpose of laser spot calibration is to ensure that the laser focusing position and size are consistent with the settings, providing a precise micro-area analysis basis for subsequent Raman detection and directly determining the accuracy and repeatability of the data.

[0068] Laser spot calibration typically involves calibrating the spot position to ensure the laser is aligned with the field of view. The goal is to ensure that the center of the laser spot completely coincides with the "crosshairs" or markers in the microscope's field of view. Then, the spot size also needs to be calibrated to ensure that the actual size of the spot matches the setting. The purpose is to verify whether the set spot size (e.g., 1 μm) matches the actual spot size irradiated on the FPC sample. The spot diameter can be calculated through signal spatial scanning.

[0069] Furthermore, in step S300, scanning the bottom region of the blind hole using a laser Raman spectrometer with preset test parameters may further include the following steps:

[0070] S310. Randomly scan and test the bottom region of the blind hole using a laser Raman spectrometer with preset test parameters.

[0071] After completing the preparation work for the scanning test, a random individual scanning test is performed on the bottom area of ​​the blind hole. Under the premise of stable preset parameters, the bottom of the hole can be accurately located, test points can be randomly selected and spectra can be collected individually, avoiding the spatial limitations (such as narrowness or tilt) and contamination interference of the bottom of the hole, thus ensuring the objectivity and validity of the data.

[0072] Furthermore, the random individual scanning test mainly includes the following steps: first, generating and selecting random test points, which can be done automatically by software or manually; after the selection of the test points is completed, individual scanning can begin for each test point, and the spectrum can be viewed immediately after the scanning of each point is completed.

[0073] Or / and, S320, perform a surface scan test on the entire bottom region of the blind hole using a laser Raman spectrometer with preset test parameters.

[0074] By performing a full-surface scanning test on the bottom region of a blind hole, a two-dimensional distribution image of the Raman signal can be obtained by completely covering the bottom region of the blind hole and continuously sampling the space, based on the stability of preset parameters. This can solve the spatial limitations (such as hole depth and diameter) and scanning integrity problems of blind holes, and enable the visualization analysis of the material composition / structure of the residue at the bottom of the hole.

[0075] Furthermore, the surface scanning test of the entire bottom area of ​​the blind hole mainly includes the following steps: First, the scanning area is delineated to ensure that the scan can completely cover the bottom of the blind hole. Usually, the entire bottom area of ​​the blind hole is delineated as the scanning area (which can be automatically delineated by software or manually delineated by manual means). After the scanning area is delineated, surface scanning and real-time monitoring can be started to complete the scanning of the entire bottom area of ​​the blind hole.

[0076] Furthermore, during the scanning process, the preset test parameters may include preset laser power, preset exposure time, preset pixel size, preset confocal aperture, preset integration time, preset number of scans, preset spectral range, and preset resolution. Moreover, in this embodiment, the preset laser power can be 2-5mW, the preset exposure time can be 0.18-0.22s, the preset pixel size can be 1µm, the preset confocal aperture can be 20-30µm, the preset integration time can be 5-10s, the preset number of scans can be 3-5, and the preset spectral range can be 150-4000cm². -1 The preset resolution is 2-4cm. -1 .

[0077] Specifically, for the preset laser power, the initial power can be set to 2mW during testing, and then gradually increased until the signal is clear (to avoid ablation), generally not exceeding 5mW; for the preset exposure time, it is generally about 0.2S, and can fluctuate around this value; for the preset pixel size, it can generally be set to 1µm to achieve greater clarity; for the preset confocal aperture, its aperture can be 25µm, and can also fluctuate around this value; for the preset integration time, the spectral quality can be observed after a rapid scan with a short integration time (e.g., 5S). If the spectral quality is poor, the integration time can be increased to 10S; for the preset number of scans, it is generally 3-5 scans averaged to improve the signal-to-noise ratio; for the preset spectral range, it is generally set to 150-4000cm⁻¹; for the preset resolution, it is usually 4cm by default. -1 High precision adjustable up to 2cm -1 .

[0078] Furthermore, in step S400, such as Figures 5 to 7 As shown, the Raman spectrum of the blind hole bottom region is checked for Raman absorption peaks. If a peak is present, it indicates the presence of residue at the bottom of the blind hole; otherwise, it indicates the absence of residue. This process may further include the following steps:

[0079] S410. Detect whether there are Raman absorption peaks in the Raman spectrum of the bottom region of the blind hole within the preset spectral range;

[0080] Because the various materials used in the FPC industry, including organic, inorganic, and elemental carbon, all absorb Raman light generated by laser Raman spectrometers, especially elemental carbon formed from carbonized coke residue after laser and plasma processes, which has a very sensitive absorption of Raman light, by capturing the Raman light reflected by this material, the material will have characteristic Raman peak spectra. Elemental metals such as copper, however, do not absorb Raman light, and the laser spot of the Raman spectrometer can be as small as 1µm. For very small blind holes, the laser spot can be focused very quickly on the bottom of the hole. Therefore, residual organic matter or carbonized adhesives after laser and plasma processes can quickly absorb Raman light, and characteristic Raman absorption peak spectra of the residue will appear on the spectrum within seconds. The copper surface at the bottom of the blind hole does not absorb Raman light, so the presence of residue at the bottom of the hole can be quickly determined through the spectrum. Furthermore, spectral library comparison can be performed based on the characteristic peaks in the spectrum to qualitatively determine the source of the residue.

[0081] S420. If a Raman absorption peak is present in the bottom region of the blind hole within the preset spectral range, it proves that there are residues at the bottom of the blind hole, and these residues should be treated.

[0082] Specifically, such as Figure 5 As shown, if the bottom area of ​​the blind hole is between 150-4000 cm... -1 The presence of Raman absorption peaks within the spectral range indicates the presence of residue at the bottom of the blind via, posing a risk to subsequent processes and requiring treatment; it cannot be directly transferred to the next process.

[0083] S430. If there is no Raman absorption peak in the bottom region of the blind hole within the preset spectral range, it proves that there is no residue at the bottom of the blind hole and it flows directly into the next process.

[0084] Specifically, such as Figure 6 As shown, if the bottom area of ​​the blind hole is between 150-4000 cm... -1 If no Raman absorption peaks are present in the spectral range, it means that the bottom of the blind hole is very clean and there are no residues, and it can be directly flowed into the next process for testing.

[0085] The detection method proposed in this invention can be used to perform detection simply and efficiently with a laser Raman spectrometer. It can accurately detect whether there are residues at the bottom of the blind hole of the FPC in just a few seconds. It can quickly, efficiently and non-destructively detect the quality of the bottom of the blind hole, and can monitor and qualitatively analyze the cleanliness of the bottom of the blind hole in a small range (even a few micrometers).

[0086] When using a laser Raman spectrometer for detection, the laser spot size of this device's test light source is as small as 1µm, enabling the detection of very small areas. Since the residues after laser and plasma processes are mostly residual carbonized coke residue, and Raman spectroscopy is highly sensitive to carbon materials, which exhibit very standard G and D peaks, it's possible to quickly determine whether there is residual carbon at the bottom of the pores. Because organic matter, inorganic matter, and elemental carbon powder all exhibit Raman absorption, any residue will show characteristic peaks in the Raman spectrum, allowing for rapid identification. This method detects whether there are residues at the bottom of blind holes. It is a non-destructive testing method, requiring no sample pretreatment. The testing speed is extremely fast; simply place the sample on the platform, quickly position it, and a Raman spectrum is generated in just a few seconds. Spectral analysis is simple; the presence of spectral peaks indicates the presence of residues at the bottom of the blind hole. This method allows for qualitative analysis of residues, using spectral library comparison to identify the material and trace its origin. The operation is simple and requires no personnel qualifications or experience. Therefore, this method is a simple, rapid, efficient, and accurate qualitative measurement method, applicable to very small sample sizes, and suitable for monitoring the cleanliness of blind hole bottoms.

[0087] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0088] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0089] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A non-destructive testing method for the cleanliness of the bottom of blind vias in FPC manufacturing, characterized in that, The method includes: Prepare FPC samples with blind vias after laser and plasma processes. Laser Raman spectroscopy was used to locate and magnify the bottom region of the blind hole in the FPC sample, and laser focusing was applied to the surface of the bottom region of the blind hole. The bottom region of the blind hole was scanned using a laser Raman spectrometer with preset test parameters, and the Raman spectrum of the bottom region of the blind hole was obtained. The presence of Raman absorption peaks in the Raman spectrum of the bottom region of the blind hole is detected. If Raman absorption peaks are present, it is determined that there are residues at the bottom of the blind hole; otherwise, it is determined that there are no residues at the bottom of the blind hole.

2. The non-destructive testing method for the cleanliness of the bottom of blind vias in FPC manufacturing according to claim 1, characterized in that, The detection method involves checking whether a Raman absorption peak is present in the Raman spectrum of the blind hole bottom region. If a peak is present, it indicates the presence of residue at the bottom of the blind hole; otherwise, it indicates the absence of residue at the bottom of the blind hole. This includes: Detect whether there are Raman absorption peaks in the Raman spectrum of the bottom region of the blind hole within a preset spectral range; If a Raman absorption peak is present in the bottom region of the blind hole within the preset spectral range, it proves that there are residues at the bottom of the blind hole, and these residues should be treated. If no Raman absorption peak is present in the bottom region of the blind hole within the preset spectral range, it proves that there is no residue at the bottom of the blind hole, and it flows directly into the next process.

3. The non-destructive testing method for the cleanliness of the bottom of blind vias in FPC manufacturing according to claim 1, characterized in that, The step of scanning the bottom region of the blind hole using a laser Raman spectrometer with preset test parameters includes: Random, individual scanning tests were performed on the bottom region of the blind hole using a laser Raman spectrometer with preset test parameters; or / and The entire area at the bottom of the blind hole was scanned using a laser Raman spectrometer with preset test parameters.

4. The non-destructive testing method for the cleanliness of the bottom of blind vias in FPC manufacturing according to claim 3, characterized in that, The preset test parameters include preset laser power, preset exposure time, preset pixel size, preset confocal aperture, preset integration time, preset number of scans, preset spectral range, and preset resolution.

5. The non-destructive testing method for the cleanliness of the bottom of blind vias in FPC manufacturing according to claim 4, characterized in that, The preset laser power is 2-5mW, the preset exposure time is 0.18-0.22s, the preset pixel size is 1µm, the preset confocal aperture is 20-30µm, the preset integration time is 5-10s, the preset number of scans is 3-5, and the preset spectral range is 150-4000cm². -1 The preset resolution is 2-4cm. -1 .

6. The non-destructive testing method for the cleanliness of the bottom of blind vias in FPC manufacturing according to claim 1, characterized in that, The method of locating and magnifying the blind hole bottom region of the FPC sample using a laser Raman spectrometer includes: Turn on the laser Raman spectrometer and preheat it, then set its test laser wavelength; Turn on the stage of the laser Raman spectrometer and place and position the FPC sample at the center of the stage; Switch the laser Raman spectrometer to real-time image mode, and gradually adjust the laser Raman spectrometer according to the objective lens magnification from low to high, so as to magnify the bottom area of ​​the blind hole on the FPC sample to the preset magnification.

7. The non-destructive testing method for the cleanliness of the bottom of blind vias in FPC processes according to claim 6, characterized in that, The laser focusing of the surface of the bottom region of the blind hole includes: The laser beam path of the laser Raman spectrometer is adjusted so that the laser is focused on the surface of the blind hole bottom region of the FPC sample, thereby achieving laser spot calibration.

8. The non-destructive testing method for the cleanliness of the bottom of blind vias in FPC manufacturing according to claim 1, characterized in that, The preparation of the FPC sample with blind vias after laser and plasma processes includes: Prepare one or more sets of FPC samples with blind vias; each set of FPC samples includes multiple FPC samples, and each FPC sample has been processed by Laser and Plasma processes.

9. The non-destructive testing method for the cleanliness of the bottom of blind vias in FPC processes according to claim 8, characterized in that, In one or more groups of FPC samples with blind holes, some FPC samples have blind holes without adhesive, while others have blind holes with adhesive.

10. The non-destructive testing method for the cleanliness of the bottom of blind vias in FPC processes according to claim 8, characterized in that, The diameter of the blind holes on the FPC sample is 50-100 μm.

Images