A soft and hard combined circuit board slotting process based on laser depth control technology

Abstract

The application discloses a soft and hard combined circuit board slotting process based on laser depth control technology, which comprises the following steps: pretreating the surface of the rigid layer of the soft and hard combined circuit board, and spraying a laser sensitive layer; adopting CNC depth control milling to form a slot rough structure on the surface of the pretreated rigid layer; using a positioning laser to scan and establish a three-dimensional model through collected reflection signals, then performing layered depth control ablation, sequentially adopting a second power laser for fine cutting and a third power laser for completing depth calibration to form a groove structure; cleaning the interface, scanning the groove bottom area and synchronously inputting low-temperature gas; then performing topography repair processing, adopting a short pulse laser to generate periodic micro-nano structures on the groove wall to form a stress concentration resistant surface; and depositing an insulating medium layer to form a continuous encapsulation protective layer on the groove wall and the bottom through a vacuum coating process; high-precision depth control slotting of the soft and hard combined circuit board is realized, and the soft and hard combined circuit board simultaneously has ultra-low thermal damage, fatigue resistant structure and long-term environmental stability.

Description

Technical Field

[0001] This invention relates to the field of circuit board technology, and in particular to a slotting process for a rigid-flex circuit board based on laser depth control technology. Background Technology

[0002] Rigid-flex circuit boards (PCBs) are key components for the miniaturization and functional integration of 3C electronic products, widely used in consumer electronics such as smartphones, foldable screen devices, and smartwatches. Taking a smart device's camera module as an example, its internal components need to integrate a rigid image sensor mounting area and a flexible circuit transmission channel within a circuit board with a thickness of ≤0.8mm. This requires high-precision slotting to achieve stress release and signal shielding in the rigid-flexible transition area. Traditional machining is prone to tearing of the flexible layer due to insufficient precision, while laser-controlled depth slotting technology has become the core process for achieving micron-level slot processing, directly impacting product thinness and reliability.

[0003] Currently, the 3C electronics field primarily uses a single laser for grooving rigid-flex PCBs, removing the rigid layer material layer by layer by fixing laser parameters. However, due to the significant differences in thermodynamic properties between the rigid and flexible layers in 3C products, two types of failure problems are easily caused by using a single laser energy parameter:

[0004] (1) In the high-energy mode, the heat generated during the ablation of the rigid layer is conducted to the flexible layer through the interface, resulting in the pyrolysis of carbon in the polyimide substrate and thermal damage to the flexible layer.

[0005] (2) In low-energy mode, the rigid layer is not cut completely, leaving unablated glass fibers, which causes delamination and cracking at the edge of the groove during the subsequent lamination process, seriously affecting the yield of the camera focusing module. This contradiction has become the core technical bottleneck restricting the high density and reliability improvement of 3C electronic products.

[0006] Therefore, it is necessary to improve the existing laser grooving technology for circuit boards to solve the technical problems of uncontrolled ablation depth, interface thermal damage, and insufficient lifespan of the groove structure caused by differences in material thermal response. Summary of the Invention

[0007] The purpose of this invention is to provide a slotting process for a rigid-flex PCB based on laser depth control technology, thereby solving the above-mentioned technical problems.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] A slotting process for a rigid-flex PCB based on laser depth control technology includes the following steps:

[0010] The rigid layer surface of the rigid-flex circuit board is pretreated. Specifically, the pretreatment involves first reducing the surface roughness by mechanical grinding, and then spraying a laser-sensitive layer onto the surface. The laser-sensitive layer contains optical materials for wavelength-selective absorption.

[0011] A slotted rough blank structure is formed on the surface of the pretreated rigid layer by CNC depth milling.

[0012] Laser scanning modeling is performed on the slotted blank structure, and a three-dimensional model including the density and thickness distribution of optical materials is established by collecting the reflection signals;

[0013] Laser finishing is performed based on the three-dimensional correction model. A second power laser is used for precision cutting, and a third power laser is used to complete the depth calibration, forming a stepped transition groove structure.

[0014] The interface of the processed tank is cleaned, and the bottom area of ​​the tank is scanned by ultraviolet laser while low-temperature gas is introduced simultaneously to remove residual adhesive and suppress the expansion of the heat-affected zone.

[0015] Optionally, the step of cleaning the interface of the processed tank, switching to ultraviolet laser scanning of the tank bottom area and simultaneously introducing low-temperature gas to remove residual adhesive and suppress the expansion of the heat-affected zone, further includes:

[0016] The surface of the cleaned tank is repaired by using a short-pulse laser to generate periodic micro-nano structures on the tank wall, forming a surface resistant to stress concentration.

[0017] An insulating dielectric layer is deposited on the surface of the repaired tank, and a continuous encapsulation protective layer is formed on the tank wall and bottom through a vacuum coating process.

[0018] Optionally, the laser-sensitive layer is specifically composed of:

[0019] 30%~45% wavelength selective absorber, 50%~65% thermally stable binder and 5%~8% dispersant;

[0020] The thickness of the laser-sensitive layer is 8~15μm, the absorption rate of 1064nm wavelength laser is ≥90%, and the reflectivity of 355nm wavelength laser is ≥85%.

[0021] Optionally, the wavelength-selective absorber is composed of carbon nanotubes and iron oxide composite nanoparticles, wherein the mass ratio of carbon nanotubes to iron oxide is 1:2 to 1:4; the thermally stable binder is selected as siloxane-modified epoxy resin; and the dispersing agent is selected as polyether-modified siloxane.

[0022] Optionally, laser scanning modeling is performed on the slotted blank structure, and a three-dimensional model including the density and thickness distribution of optical materials is established by collecting the reflection signals, specifically including:

[0023] Plan the laser scanning path, generate the scanning trajectory based on the preset boundary coordinates of the slotted blank structure, set the line spacing of the scanning trajectory to 1 / 3 of the laser spot diameter, and preset a dynamic focusing compensation range of 0.05-0.2mm along the Z-axis direction;

[0024] Multispectral reflection signal acquisition was performed. A 532nm green laser was used to irradiate the surface of the rigid layer along the scanning trajectory with a pulse power of 8-12W. The 532nm fundamental frequency light intensity signal and the 1064nm second harmonic signal in the reflected light were received simultaneously to establish a material absorption characteristic distribution map.

[0025] Interferometric modeling is performed by introducing part of the reflected light into the interferometer through a beam splitter prism, calculating the surface height change based on the displacement of the interference fringes, and generating initial three-dimensional contour data.

[0026] A physical field model is established by integrating multimodal data. The material absorption characteristic distribution map and three-dimensional contour data are input into the finite element algorithm. Combined with the dielectric constant gradient parameter of the laser sensitive layer, the material density distribution inside the rigid layer and the thickness of the adhesive interface are calculated to establish a three-dimensional model.

[0027] The energy absorption threshold of the slotted region in the three-dimensional model is dynamically calibrated based on the density-thickness coupling relationship, and a digital processing map containing ablation priority markers is generated to optimize the three-dimensional model.

[0028] Optionally, the laser finishing process based on the three-dimensional correction model, which involves sequentially using a second-power laser for precision cutting and a third-power laser for depth calibration to form a stepped transition groove structure, specifically includes the following steps:

[0029] The ablation priority markers in the 3D model were analyzed, and the slotted area was divided into a core ablation zone and an edge transition zone. The core ablation zone was set as the first power laser action zone, and the edge transition zone was set as the second power laser action zone.

[0030] Perform first-power laser coarse cutting, using an infrared laser with a peak power of 30-50W to scan along the core area at a scanning speed of 400-600mm / s, to complete the first depth control of the grooving area, and simultaneously trigger the plasma spectral monitoring module to judge the residual glass fiber data in real time;

[0031] Adaptive energy gradient adjustment is implemented, and the parameters of the second power laser are dynamically adjusted according to the residual amount data. In the edge transition zone, 18-25W power is used to perform oblique scanning at a speed of 800-1000mm / s to form a groove structure with a groove wall cone angle of 5-15°.

[0032] A third-power laser with an annular spot is used to perform spiral precision depth calibration along the bottom contour of the groove at a speed of 1200-1500 mm / s. The depth deviation is fed back and compensated in real time by a confocal sensor.

[0033] Cross-layer thermal stress equalization treatment is performed. After each power cutting is completed, a preset delay period is inserted, and a high-frequency pulse is applied to the cutting surface to perform micro-impact, thereby eliminating the interlayer stress concentration of the groove structure.

[0034] Optionally, the annular light spot is set with an outer ring diameter of 80-120 μm and an inner ring diameter of 30-50 μm.

[0035] Optionally, the step of cleaning the interface of the processed tank, switching to ultraviolet laser scanning of the tank bottom area and simultaneously introducing low-temperature gas to remove residual adhesive and suppress the expansion of the heat-affected zone, specifically includes the following steps:

[0036] By setting low-temperature gas synergistic parameters and adjusting the nitrogen jet temperature and flow rate according to the depth gradient distribution of the tank, an axial temperature gradient field is formed at the bottom of the tank, causing the adhesive and polyimide layer to produce differential thermal strain.

[0037] Multi-mode laser cleaning is performed using a 355nm ultraviolet laser at a frequency of 20-30kHz and a power of 5-8W for spiral scanning. In the initial stage, a Gaussian spot is used to remove loose adhesives on the surface, and in the later stage, a flat-top spot is used to remove interface-bound residues.

[0038] Dynamic energy coupling regulation is implemented. Based on the feedback of real-time infrared thermal imaging data on the temperature field changes at the bottom of the tank, the laser duty cycle and gas flow rate are dynamically adjusted to ensure that the local temperature rise is always lower than the glass transition temperature of polyimide.

[0039] By detecting the characteristic peaks at the bottom of the tank online, the cleaning process is terminated when the signal intensity of the residual adhesive is less than a preset threshold. Simultaneously, the width data of the heat-affected zone is recorded for process iteration and optimization.

[0040] Optionally, the morphology repair treatment of the cleaned tank surface, which involves using a short-pulse laser to generate periodic micro / nano structures on the tank wall to form a stress-concentration-resistant surface, specifically includes the following steps:

[0041] Pre-treatment tank wall surface contaminants are pre-treated by laser full-area scanning to remove nanoscale oxide layers and activate surface chemical bonds.

[0042] A dual-beam interference processing field is constructed, and a short-pulse laser is split into two coherent beams to form interference fringes with adjustable spatial period on the surface of the groove wall. The phase difference is controlled by a piezoelectric ceramic displacement stage to induce plasmon-enhanced ablation on the surface.

[0043] Gradient energy etching is performed, and the laser flux is adjusted in three segments along the depth direction of the groove to generate a parallel groove structure in the groove opening area, a scale-like stacked structure in the middle section of the groove, and a radial ripple structure at the bottom of the groove, so as to generate a periodic micro-nano structure on the groove wall.

[0044] Dynamic stress compensation is performed by applying 40-60kHz ultrasonic vibration during laser processing, dynamically adjusting the laser repetition frequency and scanning speed to reduce the residual stress of the periodic micro-nano structure to a qualified threshold, thus forming a surface resistant to stress concentration.

[0045] Optionally, the step of depositing an insulating dielectric layer on the surface of the repaired tank and forming a continuous encapsulation protective layer on the tank wall and bottom through a vacuum coating process specifically includes the following steps:

[0046] An argon / oxygen mixture with a volume ratio of 4:1 is introduced into a vacuum chamber, and radio frequency power is applied to generate low-temperature plasma to etch and activate the surface of the micro-nano structure on the tank wall.

[0047] Gradient magnetron sputtering deposition was carried out, and a Cr transition layer of the first thickness and an alumina insulating layer of the second thickness were deposited successively. The full coverage deposition of the three-dimensional structure of the tank was achieved by adjusting the substrate rotation speed in real time.

[0048] After the encapsulation layer is completed, rapid thermal annealing is carried out under nitrogen protection at a rate of 10℃ / s to 350-400℃. Simultaneously, an axial magnetic field is applied to induce preferred grain orientation, so that the film density reaches the qualified density value.

[0049] Compared with existing technologies, this invention has the following advantages: First, the surface of the rigid layer of the rigid-flex circuit board is pre-treated by mechanical grinding to reduce roughness, and a laser-sensitive layer containing wavelength-selective absorption material is sprayed on. Then, CNC depth-controlled milling is used to form a slotted rough blank structure. A three-dimensional correction model containing the distribution of optical materials is established by scanning the reflected signal with a laser. Based on the model data, a second-power laser precision cutting and a third-power laser depth calibration are implemented in stages to form a stepped transition groove. Then, ultraviolet laser scanning combined with low-temperature gas purging is used to simultaneously remove the residue at the bottom of the groove and suppress the expansion of the heat-affected zone, completing the high-precision, low-damage slotting process. This process achieves high-precision depth-controlled slotting of the rigid-flex circuit board by integrating laser-sensitive layer control, three-dimensional modeling compensation, and stepped energy output, while also possessing ultra-low thermal damage, fatigue-resistant structure, and long-term environmental stability. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the 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.

[0051] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0052] Figure 1 This is one of the flowcharts illustrating the rigid-flex PCB slotting process based on laser depth control technology in this embodiment.

[0053] Figure 2 This is the second schematic diagram of the process for slotting a rigid-flex circuit board based on laser depth control technology in this embodiment.

[0054] Figure 3 This is a schematic diagram of the circuit board processing of the rigid-soft circuit board slotting process based on laser depth control technology in this embodiment. Detailed Implementation

[0055] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0056] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship 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. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0057] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0058] Combination Figures 1 to 3 As shown, this embodiment of the invention provides a slotting process for a rigid-flex circuit board based on laser depth control technology, including the following steps:

[0059] S1, the rigid layer surface of the rigid-flex circuit board 100 is pre-treated. Specifically, the surface roughness is reduced by mechanical grinding, and a laser-sensitive layer 101 is sprayed onto its surface. The laser-sensitive layer 101 contains optical materials for wavelength-selective absorption.

[0060] Mechanical grinding reduces the surface roughness of the rigid layer, eliminating the scattering interference of microscopic irregularities on the laser beam and providing a smooth substrate for the subsequent uniform coating of the laser-sensitive layer 101. The sprayed wavelength-selective absorption layer enhances the energy coupling efficiency for specific wavelength lasers, reduces ineffective heat diffusion, and ensures a clear energy threshold for the subsequent ablation process.

[0061] S2 employs CNC depth-controlled milling to form a slotted rough blank structure on the pre-treated rigid layer surface. This pre-formed slotted rough blank structure is then mechanically removed to remove large volumes of rigid layer material, avoiding prolonged heat exposure caused by direct laser processing. The milling depth is controlled within a preset range (50-100μm) from the bottom of the target slot, reducing subsequent laser processing while providing sufficient buffer space to prevent over-cutting and damage to the flexible layer.

[0062] S3, Laser scanning modeling of the slotted blank structure, and establishment of a three-dimensional model including the density and thickness distribution of optical materials by collecting the reflection signal;

[0063] Positioning laser scanning is used to acquire reflected signal intensity and phase information. Combined with differences in material optical properties, the density gradient of the rigid layer and the thickness distribution of the adhesive layer are deduced in reverse. The three-dimensional model can quantitatively characterize the differences in energy absorption characteristics of the processed area, providing physical field data support for the adaptive adjustment of layered ablation parameters and avoiding ablation depth deviations caused by material inhomogeneity.

[0064] S4, Laser finishing is performed based on the three-dimensional correction model. The second power laser is used for fine cutting and the third power laser is used to complete the depth calibration in sequence, forming a stepped transition groove structure 102.

[0065] Based on a 3D model, different power domains are defined, and a stepped energy progression strategy is used to remove material layer by layer: high-power coarse cutting for rapid depth control, medium-power fine finishing to adjust the groove wall morphology, and low-power annular spot calibration to ensure the preset depth is reached. The layered, multi-stage processing mode reduces single-pass heat input through dynamic energy distribution, alleviating thermal stress accumulation at the rigid / flexible interface.

[0066] S5, clean the interface of the processed tank, switch to ultraviolet laser to scan the bottom area of ​​the tank and simultaneously introduce low temperature gas to remove residual adhesive and suppress the expansion of the heat-affected zone;

[0067] The high photon energy of ultraviolet lasers can effectively break the molecular chains of adhesives, while the low-temperature nitrogen gas flow suppresses the expansion of the heat-affected zone and accelerates the vaporization and discharge of decomposition products. Through the synergistic effect of laser parameters and cooling medium, interfacial residues are thoroughly removed while maintaining the structural integrity of the polyimide insulating layer.

[0068] S6. The surface of the cleaned tank is repaired by using a short-pulse laser to generate a periodic tank structure 103 on the tank wall to form a stress-concentration resistant surface.

[0069] The short pulse width of the laser suppresses the conduction of heat effects. By precisely controlling the interaction between the laser and the material, a periodic groove structure 103 is induced on the surface of the groove wall. This type of structure can change the stress distribution pattern, dispersing concentrated stress to multiple microstructural units, thereby improving the fatigue resistance of the flexible layer under dynamic bending conditions.

[0070] S7. An insulating dielectric layer 104 is deposited on the surface of the repaired tank, and a continuous encapsulation protective layer is formed on the tank wall and bottom through a vacuum coating process.

[0071] Vacuum deposition technology deposits a dense insulating layer in a low-pollution environment. Its stepped deposition parameters ensure a continuous, covering encapsulation layer on the three-dimensional surface of the tank. This protective layer not only provides electrical insulation but also prevents the penetration of environmental moisture and contaminants, ensuring the long-term reliability of the rigid-flexible transition area under complex operating conditions.

[0072] The working principle of this invention is as follows: First, the rigid layer surface of the rigid-flex circuit board 100 is pre-treated by mechanical grinding to reduce roughness and spraying a laser-sensitive layer 101 with wavelength selective absorption characteristics. Then, a positioning laser is used to scan the slotted area, and a three-dimensional model containing material density and thickness distribution is constructed based on the reflected signal. According to the model data, a stepped groove structure 102 is formed by layered controlled-depth ablation with high, medium, and low power lasers. The bottom of the groove is scanned with an ultraviolet laser and a low-temperature gas is introduced to remove residual adhesive and suppress the expansion of the heat-affected zone. A periodic groove structure 103 is generated on the groove wall using a short-pulse laser to optimize stress distribution. Finally, an insulating dielectric layer 104 is deposited on the surface of the groove, and a continuous encapsulation protective layer is formed by vacuum deposition to achieve full coverage. Processing flow; This process achieves precise control of the ablation depth of the rigid layer through the synergistic effect of wavelength-selective laser sensitive layer 101 and 3D modeling, avoiding damage to the flexible layer; Layered controlled-depth ablation combined with a stepped structural design significantly reduces the risk of thermal stress accumulation and material delamination; The synergistic effect of ultraviolet laser cleaning and cryogenic gas reduces the width of the heat-affected zone and eliminates interface residues; The tank wall structure 103 improves the bending fatigue life of the flexible layer; The vacuum encapsulation layer effectively isolates environmental erosion, enabling the tank structure 102 to maintain stable electrical performance in high-temperature and high-humidity environments. Through multi-modal laser collaborative processing and dynamic closed-loop control, high-precision controlled-depth slotting of the rigid-flex circuit board 100 is achieved, while also possessing ultra-low thermal damage, fatigue-resistant structure, and long-term environmental stability.

[0073] In this embodiment, the laser-sensitive layer 101 is specifically composed of:

[0074] 30%~45% wavelength selective absorber, 50%~65% thermally stable binder and 5%~8% dispersant;

[0075] A 30%-45% absorber concentration range ensures efficient absorption of 1064nm laser (≥90%) while avoiding coating embrittlement caused by excessive addition; a 50%-65% binder ratio ensures adhesion between the coating and the rigid substrate and dimensional stability at high temperatures; and a 5%-8% dispersant ratio effectively inhibits nanoparticle agglomeration and ensures coating uniformity.

[0076] The thickness of the laser-sensitive layer 101 is 8~15μm, the absorption rate of 1064nm wavelength laser is ≥90%, and the reflectivity of 355nm wavelength laser is ≥85%.

[0077] The thickness range of 8-15μm matches the penetration depth requirements of laser ablation. Too thin a thickness can lead to insufficient energy absorption, while too thick a thickness increases the process cost. The ≥90% 1064nm absorption rate ensures efficient utilization of laser energy during processing, and the ≥85% 355nm reflectance provides optical isolation protection for subsequent UV cleaning processes.

[0078] In this embodiment, it is further explained that the wavelength selective absorber is composed of carbon nanotubes and iron oxide composite nanoparticles, wherein the mass ratio of carbon nanotubes to iron oxide is 1:2 to 1:4; the thermally stable binder is selected as siloxane-modified epoxy resin; and the dispersing agent is selected as polyether-modified siloxane.

[0079] It should be noted that carbon nanotubes provide broadband absorption characteristics and conductive and thermally conductive pathways, while iron oxide nanoparticles enhance the local surface plasmon resonance effect for near-infrared light. A mass ratio of 1:2 to 1:4 forms the optimal synergistic absorption ratio between the two, which avoids the enhanced laser scattering caused by excessive carbon nanotubes and prevents the decrease in thermal stability caused by an excessive proportion of iron oxide.

[0080] In this embodiment, step S2 specifically includes:

[0081] S21, plan the laser scanning path, generate the scanning trajectory according to the preset boundary coordinates of the slotted blank structure, set the line spacing of the scanning trajectory to 1 / 3 of the laser spot diameter, and preset a dynamic focusing compensation range of 0.05-0.2mm along the Z-axis direction.

[0082] By setting the scan line spacing to 1 / 3 of the laser spot diameter, appropriate overlap between adjacent scan trajectories is ensured, avoiding local data loss due to excessive gaps, while suppressing the heat accumulation effect caused by excessive overlap. The preset dynamic focus compensation range (0.05-0.2mm) allows the laser focus to adaptively adjust with surface undulations, ensuring real-time matching between the focal plane and the material surface during scanning, and establishing stable optical conditions for subsequent signal acquisition.

[0083] S22, perform multispectral reflection signal acquisition, use 532nm green laser with 8-12W pulse power to irradiate the surface of rigid layer along the scanning trajectory, and simultaneously receive the 532nm fundamental frequency light intensity signal and 1064nm second harmonic signal in the reflected light to establish the material absorption characteristic distribution map;

[0084] A 532nm green laser was used to excite the surface response within a power range of 8-12W. Its wavelength characteristics allow it to penetrate the laser-sensitive layer 101 without damaging the substrate. Simultaneous acquisition of the fundamental frequency intensity signal and the second harmonic signal reflects the macroscopic absorption characteristics of the surface, while the second harmonic signal enhances the sensitivity to the chemical bond state of the material through nonlinear optical effects. Fusion of the dual-spectral data provides a more comprehensive characterization of the material's photo-thermal response properties, offering multidimensional physical field information for modeling.

[0085] S23, implement interferometric modeling, guide part of the reflected light into the interferometer through a beam splitter, calculate the surface height change based on the displacement of the interference fringes, and generate initial three-dimensional contour data;

[0086] The reflected light is guided into the interferometer using a beam splitter prism, and the surface height change is calculated by the displacement of the interference fringes. Compared with traditional confocal measurements, interferometry has higher longitudinal resolution and can accurately capture the microscopic undulations of rigid layer surfaces.

[0087] S24. A physical field model is established by integrating multimodal data. The material absorption characteristic distribution map and three-dimensional contour data are input into the finite element algorithm. Combined with the dielectric constant gradient parameter of the laser sensitive layer 101, the material density distribution inside the rigid layer and the thickness of the adhesive interface are calculated in reverse to establish a three-dimensional model.

[0088] By inputting the absorption characteristic distribution and three-dimensional contour data into the finite element algorithm, and combining the dielectric constant gradient parameter of the laser-sensitive layer 101, the inversion calculation of material density and adhesive thickness is achieved. This multimodal fusion method overcomes the limitations of a single data source, reveals the internal structural characteristics of the material through the physical field coupling relationship, and significantly improves the model's adaptability to actual processing scenarios.

[0089] S25. Based on the density-thickness coupling relationship, the energy absorption threshold of the slotted area in the three-dimensional model is dynamically calibrated to generate a digital processing map containing ablation priority markers in order to optimize the three-dimensional model.

[0090] The energy absorption threshold is dynamically calibrated based on the density-thickness coupling relationship, transforming the theoretical model into an executable processing strategy. The introduction of ablation priority marking enables differentiated energy allocation, prioritizing high-density / thick binder regions to avoid over- or under-burning issues caused by uniform energy input, thereby improving processing efficiency and consistency.

[0091] In this embodiment, step S3 specifically includes the following steps:

[0092] S31, analyze the ablation priority marker in the 3D model, divide the slotted area into a core ablation zone and an edge transition zone, where the core ablation zone is set as the first power laser action zone and the edge transition zone is set as the second power laser action zone.

[0093] By analyzing the ablation priority markers of the 3D model, the grooving area is divided into a core area and an edge transition area. The core area uses a high-power laser to rapidly remove the main material, while the edge area is finely trimmed using a low-power laser. This strategy achieves precise energy allocation based on differences in material density distribution, avoiding insufficient cutting in high-density areas or over-burning in low-density areas caused by uniform power input. It also allows for machining allowances for subsequent cone angle control.

[0094] S32 performs first-power laser coarse cutting, using an infrared laser with a peak power of 30-50W and a pulse width of 200-400ns to scan along the core area at a scanning speed of 400-600mm / s, completing the first depth control of the grooving area, and simultaneously triggering the plasma spectral monitoring module to judge the residual amount of glass fiber in real time.

[0095] An infrared laser with a peak power of 30-50W and a pulse width of 200-400ns is used to achieve efficient removal of the rigid layer substrate material at a scanning speed of 400-600mm / s. Simultaneously triggered plasma spectral monitoring allows for real-time determination of the residual material by analyzing the intensity changes of characteristic spectral lines of the glass fiber (such as Si-O bond vibration peaks). This combined design ensures processing efficiency while providing quantitative data for subsequent process adjustments.

[0096] S33, implement adaptive energy gradient adjustment, dynamically adjust the second power laser parameters according to residual data, and use 18-25W power and 100-150ns pulse width in the edge transition zone to perform oblique scanning at a speed of 800-1000mm / s to form a groove structure 102 with a groove wall cone angle of 5-15°.

[0097] S34 uses a third-power laser with an annular spot to perform spiral precision depth calibration along the bottom contour of the groove at a speed of 1200-1500 mm / s. The depth deviation is fed back and compensated in real time by a confocal sensor. Specifically, the annular spot is set with an outer ring diameter of 80-120 μm and an inner ring diameter of 30-50 μm.

[0098] A spiral finishing process is achieved using a ring-shaped light spot with an outer diameter of 80-120 μm and an inner diameter of 30-50 μm. Its hollow beam characteristics homogenize the energy distribution at the bottom of the groove. A high scanning speed of 1200-1500 mm / s, matched with the real-time feedback frequency of the confocal sensor, ensures precise depth control. This design effectively eliminates the groove bottom bulge defect caused by excessively high energy at the center of traditional Gaussian light spots.

[0099] S35, cross-layer thermal stress equalization treatment is performed. After each power cutting is completed, a 50-100μs delay period is inserted, and a 10-20kHz high-frequency pulse is applied to the cutting surface to perform micro-impact, thereby eliminating interlayer stress concentration in the groove structure 102.

[0100] A 50-100μs delay period is inserted after each layer is processed to allow the material thermal relaxation process to complete. Combined with the mechanical micro-shock wave generated by the 10-20kHz high-frequency pulse, it promotes the recombination of lattice dislocations and releases residual stress.

[0101] In this embodiment, step S4 specifically includes the following steps:

[0102] S41, set low temperature gas synergistic parameters, adjust the nitrogen jet temperature (-50℃ to -30℃) and flow rate (5-15L / min) according to the depth gradient distribution of the tank, form an axial temperature gradient field at the bottom of the tank, and cause the adhesive and polyimide layer to produce differential thermal strain.

[0103] By controlling the nitrogen jet temperature (-50℃ to -30℃) and flow rate (5-15L / min), an axial temperature gradient field is constructed at the bottom of the tank. Utilizing the difference in thermal expansion coefficients between the adhesive (CTE≈150ppm / ℃) and polyimide (CTE≈40ppm / ℃), directional thermal strain is induced at the interface. This design weakens the bond strength between the adhesive and the substrate through a thermo-mechanical coupling effect, providing pre-peeling conditions for subsequent laser cleaning. Simultaneously, the low-temperature environment suppresses thermal diffusion caused by laser action.

[0104] S42 performs multi-mode laser cleaning, using a 355nm ultraviolet laser at a frequency of 20-30kHz and a power of 5-8W for spiral scanning. In the initial stage, a Gaussian spot is used to remove loose adhesives on the surface, and in the later stage, a flat-top spot is used to remove interface-bound residues.

[0105] In the initial stage, a Gaussian spot (energy density gradient distribution) is used to efficiently remove loose adhesives from the surface. In the later stage, a flat-top spot (uniform energy distribution) is used to remove chemically bonded residues at the interface. The high photon energy (3.5 eV) of the 355 nm ultraviolet laser can selectively break the adhesive molecular chains (CC bond energy ≈ 3.6 eV), and the 20-30 kHz frequency matches the material's thermal relaxation period (10-50 μs), achieving a balance between removal efficiency and thermal damage control.

[0106] S43 implements dynamic energy coupling regulation, and dynamically adjusts the laser duty cycle and gas flow rate based on the real-time infrared thermal imaging data feedback of the temperature field change at the bottom of the tank, so that the local temperature rise is always lower than the glass transition temperature of polyimide.

[0107] Based on real-time feedback of the temperature field distribution at the bottom of the tank using infrared thermal imaging data, the laser duty cycle (10-40%) and gas flow rate (5-15 L / min) are dynamically adjusted to form a negative feedback control loop. This mechanism avoids the pyrolysis and carbonization of the flexible layer by limiting local temperature rise (<280℃, glass transition point of polyimide), while ensuring the effective discharge of thermal decomposition products of the adhesive.

[0108] S44, by detecting the characteristic peaks at the bottom of the tank online, terminates the cleaning process when the residual adhesive signal intensity is less than a preset threshold, and simultaneously records the width data of the heat-affected zone for process iteration and optimization.

[0109] The intensity of the adhesive's characteristic peak signals was monitored online using Raman spectroscopy. Cleaning was terminated when the residual amount was less than the 3% threshold to avoid overtreatment and damage to the polyimide substrate.

[0110] In this embodiment, step S5 specifically includes the following steps:

[0111] S51, pretreatment of contaminants on the tank wall surface using laser (wavelength 515nm, pulse width 400-600fs) at 0.5-1.5J / cm². 2 Energy density is used for full-domain scanning to remove nanoscale oxide layers and activate surface chemical bonds.

[0112] Using a 515nm laser at a speed of 0.5-1.5J / cm 2 The energy density is scanned across the entire domain, and its ultrashort pulse width suppresses thermal diffusion effects. Nanoscale oxide layers are removed through photoexfoliation, while laser-induced surface electron excitation exposes active chemical bond sites. This pretreatment provides a clean and highly reactive interface for subsequent processing of the tank structure 103, improving the energy coupling efficiency between the laser and the material.

[0113] S52, construct a dual-beam interference processing field, split the short-pulse laser into two coherent beams, form spatially periodically adjustable interference fringes on the surface of the groove wall, control the phase difference through a piezoelectric ceramic displacement stage, and induce plasmon-enhanced ablation on the surface.

[0114] A short-pulse laser is split into two coherent beams, and the optical path difference is adjusted using a piezoelectric ceramic displacement stage to form spatially periodic interference fringes on the surface of the groove wall. The plasmon resonance enhancement effect localizes the laser energy to the antinodes of the interference field, achieving subwavelength precision selective ablation. This technique overcomes the diffraction limit, generating high-precision periodic structures while avoiding thermal damage.

[0115] S53, gradient energy etching is performed, and the laser flux is adjusted in three segments along the depth direction of the groove to generate a parallel groove structure in the groove opening area, a scale-like stacked structure in the middle section of the groove, and a radial ripple structure at the bottom of the groove, so as to generate a periodic groove structure 103 on the groove wall.

[0116] The laser flux (0.8-1.2 J / cm²) is adjusted in three segments along the depth of the tank. 2 The parallel grooves in the groove opening area enhance bending resistance through directional stress dispersion; the scale-like layered structure in the middle section of the groove utilizes biomimetic geometry to strengthen the interlayer bonding strength; the radial corrugations at the bottom of the groove (wavelength 150-250nm) suppress crack propagation through multi-directional stress transfer. The gradient design matches the groove structure 103 with the actual stress distribution, maximizing the effect against stress concentration.

[0117] S54 performs dynamic stress compensation by applying 40-60kHz ultrasonic vibration during laser processing, dynamically adjusting the laser repetition frequency and scanning speed to reduce the residual stress of the periodic groove structure 103 to the qualified threshold, forming a stress-concentration resistant surface.

[0118] In this embodiment, step S6 specifically includes the following steps:

[0119] S61, an argon / oxygen mixed gas with a volume ratio of 4:1 is introduced into the vacuum chamber, and radio frequency power is applied to generate low temperature plasma to etch and activate the surface of the tank wall structure 103, thereby activating the surface.

[0120] An argon / oxygen mixture (volume ratio 4:1) is introduced and 200-400W of radio frequency power is applied. Argon physically cleans the surface through ion bombardment, while oxygen participates in a chemical reaction to remove organic contaminants and introduce active groups such as hydroxyl groups. Low-temperature plasma (electron temperature 3-5eV) improves the surface roughness of the tank structure 103 (Ra=0.1→0.4μm) through etching while avoiding thermal damage. At the same time, the activated surface energy (60-72mN / m) significantly enhances the adhesion of the film.

[0121] S62, gradient magnetron sputtering is implemented to deposit a Cr transition layer of the first thickness and an alumina insulating layer of the second thickness in sequence. The full coverage deposition of the three-dimensional structure of the tank is achieved by adjusting the substrate rotation speed in real time.

[0122] First, a Cr transition layer of initial thickness (800-1200W power, -150V bias) is deposited. Its high ductility alleviates the thermal expansion mismatch stress between the substrate and the insulating layer. Then, a second aluminum oxide insulating layer of initial thickness (1500-2000W power, -300V bias) is deposited. Its amorphous structure provides stable dielectric properties. By adjusting the substrate rotation speed in real time, centrifugal force is used to improve the film thickness uniformity on the sidewalls and bottom of the tank.

[0123] S63, after completing the encapsulation layer post-processing, rapid thermal annealing is carried out under nitrogen protection at a rate of 10℃ / s to 350-400℃, and an axial magnetic field is applied simultaneously to induce preferred grain orientation so that the film density reaches the qualified density value.

[0124] Under nitrogen protection, rapid thermal annealing at a rate of 10℃ / s to 350-400℃ induces the transformation of amorphous alumina into the γ phase, eliminating porosity within the film. Simultaneously, an axial magnetic field of 0.5-1.2T is applied, utilizing Lorentz force to induce preferential grain orientation along the plane, forming a dense columnar crystal structure. This composite treatment increases the film density and significantly enhances moisture resistance and mechanical strength.

[0125] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A rigid-flex PCB slotting process based on laser depth control technology, characterized in that, Includes the following steps: The rigid layer surface of the rigid-flex circuit board is pretreated. Specifically, the pretreatment involves first reducing the surface roughness by mechanical grinding, and then spraying a laser-sensitive layer onto the surface. The laser-sensitive layer contains optical materials for wavelength-selective absorption. A slotted rough blank structure is formed on the surface of the pretreated rigid layer by CNC depth milling. Laser scanning modeling is performed on the slotted blank structure, and a three-dimensional model including the density and thickness distribution of optical materials is established by collecting the reflection signals; Laser finishing is performed based on the three-dimensional model. A second power laser is used for precision cutting, and a third power laser is used to complete the depth calibration, forming a stepped transition groove structure. The interface of the processed tank is cleaned, and the bottom area of ​​the tank is scanned by ultraviolet laser while low-temperature gas is introduced simultaneously to remove residual adhesive and suppress the expansion of the heat-affected zone. Laser scanning modeling is performed on the slotted blank structure. A three-dimensional model containing the density and thickness distribution of optical materials is established using the acquired reflection signals. Specifically, this includes: Plan the laser scanning path, generate the scanning trajectory based on the preset boundary coordinates of the slotted blank structure, set the line spacing of the scanning trajectory to 1 / 3 of the laser spot diameter, and preset a dynamic focusing compensation range of 0.05-0.2mm along the Z-axis direction; Multispectral reflection signal acquisition was performed. A 532nm green laser was used to irradiate the surface of the rigid layer along the scanning trajectory with a pulse power of 8-12W. The 532nm fundamental frequency light intensity signal and the 1064nm second harmonic signal in the reflected light were received simultaneously to establish a material absorption characteristic distribution map. Interferometric modeling is performed by introducing part of the reflected light into the interferometer through a beam splitter prism, calculating the surface height change based on the displacement of the interference fringes, and generating initial three-dimensional contour data. A physical field model is established by integrating multimodal data. The material absorption characteristic distribution map and three-dimensional contour data are input into the finite element algorithm. Combined with the dielectric constant gradient parameter of the laser sensitive layer, the material density distribution inside the rigid layer and the thickness of the adhesive interface are calculated to establish a three-dimensional model. The energy absorption threshold of the slotted region in the three-dimensional model is dynamically calibrated based on the density-thickness coupling relationship, and a digital processing map containing ablation priority markers is generated to optimize the three-dimensional model.

2. The slotting process for a rigid-flex circuit board based on laser depth control technology according to claim 1, characterized in that, The process involves cleaning the interface of the processed tank, switching to ultraviolet laser scanning of the tank bottom area while simultaneously introducing low-temperature gas to remove residual adhesive and suppress the expansion of the heat-affected zone. This is followed by: The surface of the cleaned tank is repaired by using a short-pulse laser to generate periodic micro-nano structures on the tank wall, forming a surface resistant to stress concentration. An insulating dielectric layer is deposited on the surface of the repaired tank, and a continuous encapsulation protective layer is formed on the tank wall and bottom through a vacuum coating process.

3. The rigid-flex PCB slotting process based on laser depth control technology according to claim 1, characterized in that, The laser-sensitive layer is specifically composed of: 30%~45% wavelength selective absorber, 50%~65% thermally stable binder and 5%~8% dispersant; The thickness of the laser-sensitive layer is 8~15μm, the absorption rate of 1064nm wavelength laser is ≥90%, and the reflectivity of 355nm wavelength laser is ≥85%.

4. The rigid-flex PCB slotting process based on laser depth control technology according to claim 3, characterized in that, The wavelength-selective absorber is composed of carbon nanotubes and iron oxide composite nanoparticles, wherein the mass ratio of carbon nanotubes to iron oxide is 1:2 to 1:4; the thermally stable binder is selected as siloxane-modified epoxy resin. The dispersant was selected as polyether-modified siloxane.

5. The rigid-flex PCB slotting process based on laser depth control technology according to claim 1, characterized in that, The laser finishing process based on the three-dimensional model, which involves sequentially using a second-power laser for precision cutting and a third-power laser for depth calibration to form a stepped transition groove structure, specifically includes the following steps: The ablation priority markers in the 3D model were analyzed, and the slotted area was divided into a core ablation zone and an edge transition zone. The core ablation zone was set as the first power laser action zone, and the edge transition zone was set as the second power laser action zone. Perform first-power laser coarse cutting, using an infrared laser with a peak power of 30-50W to scan along the core area at a scanning speed of 400-600mm / s, to complete the first depth control of the grooving area, and simultaneously trigger the plasma spectral monitoring module to judge the residual glass fiber data in real time; Adaptive energy gradient adjustment is implemented, and the parameters of the second power laser are dynamically adjusted according to the residual amount data. In the edge transition zone, 18-25W power is used to perform oblique scanning at a speed of 800-1000mm / s to form a groove structure with a groove wall cone angle of 5-15°. A third-power laser with an annular spot is used to perform spiral precision depth calibration along the bottom contour of the groove at a speed of 1200-1500 mm / s. The depth deviation is fed back and compensated in real time by a confocal sensor. Cross-layer thermal stress equalization treatment is performed. After each power cutting is completed, a preset delay period is inserted, and a high-frequency pulse is applied to the cutting surface to perform micro-impact, thereby eliminating the interlayer stress concentration of the groove structure.

6. The rigid-flex PCB slotting process based on laser depth control technology according to claim 5, characterized in that, The annular light spot is set with an outer ring diameter of 80-120 μm and an inner ring diameter of 30-50 μm.

7. The rigid-flex PCB slotting process based on laser depth control technology according to claim 1, characterized in that, The process of cleaning the interface of the processed tank, switching to ultraviolet laser scanning of the tank bottom area and simultaneously introducing low-temperature gas to remove residual adhesive and inhibit the expansion of the heat-affected zone, specifically includes the following steps: By setting low-temperature gas synergistic parameters and adjusting the nitrogen jet temperature and flow rate according to the depth gradient distribution of the tank, an axial temperature gradient field is formed at the bottom of the tank, causing the adhesive and polyimide layer to produce differential thermal strain. Multi-mode laser cleaning is performed using a 355nm ultraviolet laser at a frequency of 20-30kHz and a power of 5-8W for spiral scanning. In the initial stage, a Gaussian spot is used to remove loose adhesives on the surface, and in the later stage, a flat-top spot is used to remove interface-bound residues. Dynamic energy coupling regulation is implemented. Based on the real-time infrared thermal imaging data, the temperature field changes at the bottom of the tank are fed back, and the laser duty cycle and gas flow rate are dynamically adjusted to ensure that the local temperature rise is always lower than the glass transition temperature of polyimide. By detecting the characteristic peaks at the bottom of the tank online, the cleaning process is terminated when the signal intensity of the residual adhesive is less than a preset threshold. Simultaneously, the width data of the heat-affected zone is recorded for process iteration and optimization.

8. The slotting process for a rigid-flex circuit board based on laser depth control technology according to claim 2, characterized in that, The surface of the cleaned tank is repaired by using a short-pulse laser to generate periodic micro-nano structures on the tank wall, forming a surface resistant to stress concentration. This process includes the following steps: Pre-treatment tank wall surface contaminants are pre-treated by laser full-area scanning to remove nanoscale oxide layers and activate surface chemical bonds. A dual-beam interference processing field is constructed, and a short-pulse laser is split into two coherent beams to form interference fringes with adjustable spatial period on the surface of the groove wall. The phase difference is controlled by a piezoelectric ceramic displacement stage to induce plasmon-enhanced ablation on the surface. Gradient energy etching is performed, and the laser flux is adjusted in three segments along the depth direction of the groove to generate a parallel groove structure in the groove opening area, a scale-like stacked structure in the middle section of the groove, and a radial ripple structure at the bottom of the groove, so as to generate a periodic micro-nano structure on the groove wall. Dynamic stress compensation is performed by applying 40-60kHz ultrasonic vibration during laser processing, dynamically adjusting the laser repetition frequency and scanning speed to reduce the residual stress of the periodic micro-nano structure to a qualified threshold, thus forming a surface resistant to stress concentration.

9. The rigid-flex PCB slotting process based on laser depth control technology according to claim 2, characterized in that, The process of depositing an insulating dielectric layer on the surface of the repaired tank and forming a continuous encapsulation protective layer on the tank wall and bottom using a vacuum coating process specifically includes the following steps: An argon / oxygen mixture with a volume ratio of 4:1 is introduced into a vacuum chamber, and radio frequency power is applied to generate low-temperature plasma to etch and activate the surface of the micro-nano structure on the tank wall. Gradient magnetron sputtering deposition was carried out, and a Cr transition layer of the first thickness and an alumina insulating layer of the second thickness were deposited successively. The full coverage deposition of the three-dimensional structure of the tank was achieved by adjusting the substrate rotation speed in real time. After the encapsulation layer is completed, rapid thermal annealing is carried out under nitrogen protection at a rate of 10℃ / s to 350-400℃. Simultaneously, an axial magnetic field is applied to induce preferred grain orientation, so that the film density reaches the qualified density value.

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