A multi-order HDI PCB laser drilling system and method based on real-time OCT detection

Abstract

The application discloses a multi-order HDI PCB laser drilling system and method based on real-time OCT detection, and the system comprises a laser processing unit, an OCT detection unit, a copper thickness-depth synchronous analysis unit, an energy closed-loop control unit and a motion and control unit; the copper thickness, drilling depth of the PCB drilling area and the relative height of the output end of the laser processing unit and the PCB to be processed are detected on line in the same axis, the reflection signals of the copper layer and the medium layer are collected, and the OCT detection unit is assisted in coaxial positioning correction through three-dimensional scanning or an additional CCD module; the reflection signals collected by the OCT detection unit are analyzed, the interlayer interface is recognized, the drilling depth and the relative height are calculated, the positioning signal is analyzed and positioning deviation data is generated; the relative height position of the output end of the laser processing unit and the PCB is adjusted according to the relative height information detected by the OCT detection unit, and the optimal processing distance is maintained; the method and the system can significantly improve the processing quality and the processing efficiency, and are better in adaptability and flexibility.

Description

Technical Field

[0001] This invention relates to the field of laser processing and intelligent manufacturing equipment technology, specifically to a multi-stage HDI PCB laser drilling system and method based on real-time detection of copper thickness and depth using OCT, particularly to PCB laser precision processing, multi-stage HDI blind / buried via manufacturing, online detection using optical coherence tomography (OCT), and closed-loop control of laser energy. Background Technology

[0002] In multi-layer HDI boards, the interlayer dielectric is thin, and copper and other dielectrics are alternately distributed. During laser drilling, the underlying copper foil is prone to overburning and breaking down (burning the bottom layer), which seriously affects the quality of PCB products. Traditional laser drilling uses offline inspection methods, which lag behind the processing and cannot correct the laser output energy in real time, resulting in low product yield and high scrap costs.

[0003] Current laser drilling technology lacks the ability to determine layers at the micron level online, and the processing relies on a preset process window, making it difficult to adapt to the processing requirements of complex structures such as multi-level HDI stacked vias and stepped vias. In the field of PCB laser drilling, ensuring the relative height between the laser processing head and the PCB to be processed and maintaining the optimal working distance for laser processing are crucial to ensuring processing accuracy. Currently, the industry widely uses off-axis laser displacement sensors to achieve this function, but during operation, the positions of the laser processing head and the laser displacement sensor need to be frequently switched to adjust the laser drilling working distance, which is cumbersome and inefficient.

[0004] The current positioning and correction of PCB laser drilling mainly relies on off-axis CCDs. Off-axis CCDs have problems such as positioning deviation (viewing angle deviation caused by non-coaxiality), additional equipment space required, and asynchronous operation with the processing laser. Furthermore, they cannot be integrated with depth detection and height monitoring functions, resulting in complex equipment structure and limited positioning accuracy, making it difficult to meet the high-precision positioning requirements of multi-level HDI micro-holes and stacked holes.

[0005] While existing technologies also use OCT technology, they are mostly applied to penetration depth monitoring in laser welding. They have not yet been applied to layer identification, energy closed-loop control, real-time monitoring of processing height, and coaxial positioning correction in PCB laser drilling, and there is a lack of corresponding technical means. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art by providing a multi-stage HDIPCB laser drilling system and method based on real-time OCT detection.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In the first aspect, a multi-stage HDI PCB laser drilling system based on real-time detection of copper thickness and depth using OCT is provided, including: a laser processing unit, an OCT detection unit, a copper thickness-depth synchronous analysis unit, an energy closed-loop control unit, and a motion and control unit; The laser processing unit is used for laser drilling of multi-stage HDI PCBs, and outputs an adjustable energy laser beam to the PCB set on the processing fixture. The OCT detection unit is used for coaxial online detection of the copper thickness, drilling depth, and relative height between the output end of the laser processing unit and the PCB to be processed in the PCB drilling area. It collects the reflection signals of the copper layer and the dielectric layer. At the same time, it assists the OCT detection unit in coaxial positioning and correction by three-dimensional scanning or by adding a CCD module. The copper thickness-depth synchronous analysis unit is used to analyze the reflection signal collected by the OCT detection unit, identify the interlayer interface, calculate the drilling depth and relative height, analyze the positioning signal and generate positioning deviation data; The energy closed-loop control unit adjusts the laser output energy of the laser processing unit in real time based on the analysis results; The motion and control unit adjusts the relative height position between the output end of the laser processing unit and the PCB based on the relative height information detected by the OCT detection unit to maintain the optimal processing distance, and adjusts the processing position according to the positioning deviation data to complete the positioning correction.

[0008] Furthermore, the laser processing unit includes a processing laser, a laser optical mirror group, a laser dichroic mirror, and a processing galvanometer. The processing galvanometer is located above the processing fixture. The laser beam of the processing laser is directed to the laser dichroic mirror via the laser optical mirror group, and then redirected by the laser dichroic mirror before being directed to the processing galvanometer.

[0009] Furthermore, the OCT detection unit includes an OCT system and an OCT two-dimensional galvanometer, wherein the OCT two-dimensional galvanometer is arranged coaxially with the processing galvanometer.

[0010] Furthermore, the CCD module includes a rangefinder CCD module and a coaxial CCD module. The rangefinder CCD module includes a rangefinder CCD and a rangefinder CCD lens barrel disposed on one side of the laser processing unit, with the rangefinder CCD lens barrel facing the PCB on the processing fixture. The coaxial CCD module includes a coaxial CCD and a coaxial CCD lens barrel, as well as a CCD dichroic mirror coaxially arranged with the laser processing unit and the OCT detection unit. The CCD dichroic mirror is disposed between the laser processing unit and the OCT detection unit. The coaxial CCD module serves as a supplement to the rangefinder CCD module and gradually replaces the rangefinder CCD module.

[0011] Furthermore, the processing laser is a CO2 laser, an ultraviolet laser, or an ultrafast laser, suitable for one or more processing scenarios including first-order to fourth-order HDI PCBs, arbitrary layer interconnect PCBs, stacked blind via PCBs, and microvias on IC substrates.

[0012] Secondly, a multi-stage HDI PCB laser drilling method based on real-time OCT copper thickness and depth detection is provided. This method employs the aforementioned multi-stage HDI PCB laser drilling system based on real-time OCT copper thickness and depth detection. The laser drilling method includes the following steps: Establish a multi-level HDI PCB OCT reflection signal library and a mapping table of drilling depth, relative height and laser output energy; calibrate the three-dimensional scanning positioning accuracy of the OCT detection unit or the image acquisition parameters of the CCD module, and establish a positioning deviation correction model; The multi-stage HDI PCB to be processed is fixed on the processing fixture, and coaxial positioning correction is completed based on the positioning deviation correction model; the position of the output end of the laser processing unit is adjusted so that the output end of the laser processing unit is at the optimal working distance from the PCB surface; The laser processing unit starts to output a laser beam to drill holes, and the OCT detection unit works coaxially with the processing laser beam to collect the hole bottom depth signal, reflection signals of different layers and positioning deviation signals in real time during the drilling process. Based on the collected reflection signals and the reflection signal library, high-reflection signals and low-reflection signals of different PCB layers are distinguished. The sudden change in the hole bottom depth signal is used to determine whether the target layer or the bottom copper foil has been reached, and the layer determination result is obtained. The collected processing height signal is used to determine whether there is a height deviation. The collected positioning deviation signal is used to determine whether there is a processing position offset. Based on the layer classification results, height deviation, and processing position offset, and in conjunction with the mapping table, the laser processing unit's laser output energy and processing position are adjusted online to form a closed-loop control.

[0013] Furthermore, the coaxial positioning correction steps include: scanning the PCB area to be processed using the three-dimensional scanning function of the OCT detection unit or in conjunction with the CCD module, acquiring the three-dimensional contour of the PCB surface and the coordinate information of the holes to be drilled, comparing it with the preset processing coordinates, generating positioning deviation data, and adjusting the position of the PCB or the output end of the laser processing unit by the motion and control unit to complete the coaxial positioning correction.

[0014] Furthermore, the closed-loop control process includes: maintaining the laser output energy required for the preset processing before the laser beam reaches the target layer; gradually reducing the laser output energy by using a stepped energy reduction method when approaching the target layer; immediately turning off the laser beam or maintaining it with micro-output energy when touching the bottom copper foil; simultaneously adjusting the position of the output end of the laser processing unit according to the height data monitored by the OCT detection unit; and adjusting the processing position in real time according to the positioning deviation signal.

[0015] Furthermore, to address issues such as uneven PCB thickness, laser energy attenuation, and positioning offset, the laser output energy and processing position are compensated in real time by combining the thickness, depth, height, and positioning information detected in real time by the OCT detection unit.

[0016] Furthermore, as the processing progresses, the frequency of use of the off-axis CCD module is gradually reduced. Through the synergistic effect of the three-dimensional scanning of the OCT detection unit and the coaxial CCD module, the off-axis CCD module is gradually replaced.

[0017] Compared with existing technologies, the beneficial effects of this invention are as follows: 1. This multi-stage HDI PCB laser drilling system based on real-time OCT copper thickness and depth detection integrates multiple detection functions through the above-mentioned unit settings. It can simultaneously complete copper layer thickness measurement, drilling depth monitoring, processing height measurement, and coaxial positioning correction. Moreover, the detection laser, positioning laser, and processing laser are coaxial, eliminating the need for frequent switching of component positions. This solves the pain point of cumbersome operation of off-axis displacement sensors in the industry, as well as the problems of positioning deviation and complex equipment structure of off-axis CCDs. 2. This laser drilling method uses the OCT detection unit to detect the difference in reflection signals between the copper layer and the dielectric layer in real time, achieving accurate layer judgment. Combined with closed-loop adjustment of laser energy, it completely eliminates core defects such as burn-in and over-etching. The drilling yield is improved by more than 15% compared with traditional technologies, the hole position deviation is controlled within ±2μm, the drilling depth detection accuracy is ≤±5μm, the hole shape is regular, and the hole wall is burr-free, fully meeting the requirements of multi-stage HDI. The processing quality requirements for high-end products such as PCBs and IC substrates have been significantly improved; 3. By utilizing the integrated height monitoring and coaxial positioning functions of the OCT system, the frequent switching of the laser processing head and the position of the off-axis displacement sensor and off-axis CCD is eliminated, simplifying the operation process and improving processing efficiency by more than 10%; at the same time, the OCT detection response time is ≤1ms and the laser energy adjustment response time is ≤1ms, achieving millisecond-level closed-loop control, avoiding efficiency losses caused by processing lag, adapting to the needs of large-volume, high-precision PCB processing, and significantly optimizing processing efficiency; 4. This laser drilling method is based on the difference in reflection signals between the copper layer / dielectric layer detected by the OCT detection unit and the drilling... Dual-signal depth detection enables precise machining of multi-level HDI stacked holes and blind holes, adapting to stepped layer structures; it allows for flexible selection of OCT-only positioning or OCT+coaxial CCD collaborative positioning modes based on machining accuracy requirements, adapting to different machining needs such as conventional, medium-high, and ultra-high precision; 5. Through multi-functional OCT integration, it replaces the height monitoring function of the off-axis laser displacement sensor, and can gradually replace the positioning function of the off-axis CCD, reducing the number of equipment parts, simplifying the equipment structure, and lowering equipment procurement and maintenance costs (maintenance costs reduced by more than 8%); it eliminates the need for additional offline testing equipment, reducing testing steps and scrap costs, and improving production economic efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a multi-stage HDI PCB laser drilling system based on real-time OCT detection according to the present invention; Figure 2 This is a flowchart illustrating a multi-stage HDI PCB laser drilling method based on real-time OCT detection according to the present invention. In the diagram: 1. OCT system; 2. OCT 2D galvanometer; 3. CCD dichroic mirror; 4. Coaxial CCD lens barrel; 5. Coaxial CCD; 6. Processed laser; 7. Laser optical lens group; 8. Laser dichroic mirror; 9. Processed galvanometer; 10. Off-axis CCD; 11. Off-axis CCD lens barrel; 12. PCB; 13. Processing fixture. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and 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.

[0020] In the description of this invention, it should be noted that the terms "middle", "upper", "lower", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this 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. Therefore, they should not be construed as limitations on this invention.

[0021] Example 1: A multi-stage HDI PCB laser drilling system based on real-time OCT copper thickness and depth detection is provided, including: a laser processing unit, an OCT detection unit, a copper thickness-depth synchronous analysis unit, an energy closed-loop control unit, and a motion and control unit; The laser processing unit is used for laser drilling of multi-stage HDI PCBs, and outputs an adjustable energy laser beam to the PCB set on the processing fixture. The OCT detection unit is used for coaxial online detection of the copper thickness, drilling depth, and relative height between the output end of the laser processing unit and the PCB to be processed in the PCB drilling area. It collects the reflection signals of the copper layer and the dielectric layer. At the same time, it assists the OCT detection unit in coaxial positioning and correction by three-dimensional scanning or by adding a CCD module. The copper thickness-depth synchronous analysis unit is used to analyze the reflection signal collected by the OCT detection unit, identify the interlayer interface, calculate the drilling depth and relative height, analyze the positioning signal and generate positioning deviation data; The energy closed-loop control unit adjusts the laser output energy of the laser processing unit in real time based on the analysis results; The motion and control unit adjusts the relative height position between the output end of the laser processing unit and the PCB based on the relative height information detected by the OCT detection unit to maintain the optimal processing distance, and adjusts the processing position according to the positioning deviation data to complete the positioning correction.

[0022] This multi-stage HDI PCB laser drilling system, based on real-time OCT copper thickness and depth detection, integrates multiple detection functions through the above-mentioned unit settings. It can simultaneously complete copper layer thickness measurement, drilling depth monitoring, processing height measurement, and coaxial positioning correction. Moreover, the detection laser, positioning laser, and processing laser are coaxial, eliminating the need for frequent switching of component positions. This solves the pain point of cumbersome operation of off-axis displacement sensors in the industry, as well as the problems of positioning deviation and complex equipment structure of off-axis CCDs.

[0023] Furthermore, in combination Figure 1 As shown, the laser processing unit includes a processing laser 6, a laser optical lens group 7, a laser dichroic mirror 8, and a processing galvanometer 9. The processing galvanometer 9 is located above the processing fixture 13. The laser beam of the processing laser 6 is directed to the laser dichroic mirror 8 via the laser optical lens group 7, and after being redirected by the laser dichroic mirror 8, it is directed to the processing galvanometer 9. The laser beam is then directed from the processing galvanometer 9 to the PCB 12 on the processing fixture 13.

[0024] Furthermore, the OCT detection unit includes an OCT system 1 (containing a broadband light source, a spectrometer, and necessary optical components) and an OCT two-dimensional galvanometer 2, wherein the OCT two-dimensional galvanometer 2 is coaxially arranged with the processing galvanometer 9.

[0025] Furthermore, the CCD module includes a rangefinder CCD module and a coaxial CCD module. The rangefinder CCD module includes a rangefinder CCD 10 and a rangefinder CCD lens barrel 11 disposed on one side of the laser processing unit, with the rangefinder CCD lens barrel 11 facing the PCB on the processing fixture 13. The coaxial CCD module includes a coaxial CCD 5 and a coaxial CCD lens barrel 4, as well as a CCD dichroic mirror 3 coaxially arranged with the laser processing unit and the OCT detection unit. The CCD dichroic mirror 3 is disposed between the laser processing unit and the OCT detection unit. The coaxial CCD module serves as a supplement to the rangefinder CCD module and gradually replaces the rangefinder CCD module.

[0026] By configuring the above structure, it can be ensured that the OCT two-dimensional galvanometer 2, the CCD dichroic mirror 3, the laser dichroic mirror 8, and the processing galvanometer 9 are arranged coaxially. The laser beam can act on the PCB to be processed after passing through the laser dichroic mirror 8 and the processing galvanometer 9. The optical signal of the OCT detection unit can be coaxially oriented towards the PCB through its OCT two-dimensional galvanometer 2, the CCD dichroic mirror 3, the laser dichroic mirror 8, and the processing galvanometer 9. The optical signal of the coaxial CCD module can also be coaxial with it after passing through the CCD dichroic mirror 3. This configuration simplifies the structure of the entire system, facilitates real-time signal feedback, and allows for targeted adjustment of the processing position and output energy based on the feedback signal, thereby improving processing quality and efficiency.

[0027] By integrating multiple OCT functions, the height monitoring function of the off-axis laser displacement sensor can be replaced, and the positioning function of the off-axis CCD can be gradually replaced. This reduces the number of equipment parts, simplifies the equipment structure, and lowers the equipment procurement and maintenance costs (maintenance costs are reduced by more than 8%). There is no need to add additional offline testing equipment, reducing testing steps and scrap costs, and improving production efficiency.

[0028] This system innovatively applies OCT technology to the field of PCB laser drilling, which can expand the functional boundaries of OCT, optimize the adaptation to PCB material characteristics, and realize the four-in-one closed-loop processing of "depth-energy-height-positioning", breaking through the bottleneck of traditional processing technology and forming a means that is different from existing technologies.

[0029] Furthermore, the processing laser can be a CO2 laser, an ultraviolet laser, or an ultrafast laser, suitable for one or more processing scenarios including first- to fourth-order HDI PCBs, arbitrary-layer interconnect PCBs, stacked blind via PCBs, and microvias on IC substrates. It can also be adapted to PCB products with different copper layer thicknesses and different dielectric materials; depending on the processing accuracy requirements, it can flexibly select OCT-only positioning or OCT+coaxial CCD collaborative positioning modes to adapt to different processing needs such as conventional accuracy, medium-high accuracy, and ultra-high accuracy.

[0030] Example 2: A multi-stage HDI PCB laser drilling method based on real-time detection of copper thickness and depth using OCT is provided, which adopts the multi-stage HDI PCB laser drilling system based on real-time detection of copper thickness and depth using OCT as described in Example 1.

[0031] Combination Figure 2 As shown, the laser drilling method includes the following steps: (1) System calibration: Establish a multi-level HDI PCB OCT reflection signal library and a mapping table of drilling depth, relative height and laser output energy; calibrate the three-dimensional scanning positioning accuracy of the OCT detection unit or the image acquisition parameters of the CCD module, and establish a positioning deviation correction model; Specifically, an OCT reflection signal library for commonly used HDI PCB materials such as copper foil, FR-4, and resin is established to clarify the characteristic differences of reflection signals from different materials; a mapping table of drilling depth, relative height, and laser output energy is established; at the same time, the positioning accuracy of OCT three-dimensional scanning and the image acquisition parameters of the coaxial CCD module (if applicable) are calibrated, and a positioning deviation correction model is established to provide a basis for subsequent closed-loop control and positioning correction.

[0032] (2) Processing preparation: Fix the multi-stage HDI PCB to be processed on the processing fixture, and complete the coaxial positioning correction based on the positioning deviation correction model; adjust the position of the output end (laser processing head) of the laser processing unit so that the output end of the laser processing unit is at the optimal working distance from the PCB surface; Specifically, the 3D scanning function of the OCT detection unit or in conjunction with the CCD module scans the PCB area to be processed, collects the 3D contour of the PCB surface and the coordinate information of the holes to be drilled, compares it with the preset processing coordinates, generates positioning deviation data, and the motion and control unit adjusts the position of the PCB or the output end of the laser processing unit to complete coaxial positioning correction; at the same time, the OCT detection unit collects the height information of the PCB surface and adjusts the position of the output end of the laser processing unit to make the output end of the laser processing unit at the optimal working distance from the PCB surface and maintain this distance stably.

[0033] (3) Processing start: The laser processing unit starts to output a laser beam to drill holes. The OCT detection unit works coaxially with the processing laser beam and collects the hole bottom depth signal, reflection signal of different layers and positioning deviation signal in real time during the drilling process (if there is a deviation, it will be fed back in real time).

[0034] (4) Layer, height and positioning judgment: Based on the collected reflection signals and the reflection signal library, distinguish between high reflection signals (copper layer / bottom copper foil) and low reflection signals (dielectric layer) of different PCB layers. Determine whether the target layer or bottom copper foil has been reached by the sudden change of the hole bottom depth signal, and obtain the layer judgment result; determine whether there is a height deviation based on the collected processing height signal. If there is a height deviation, the motion and control unit will adjust it in time; determine whether there is a processing position offset based on the collected positioning deviation signal. If there is a processing position offset, immediately provide feedback and complete the positioning correction to ensure the drilling position is accurate.

[0035] (5) Closed-loop control: Based on the layer judgment results, height deviation and processing position offset, combined with the mapping table, the laser output energy and processing position of the laser processing unit are adjusted online to form closed-loop control.

[0036] Specifically, before the laser beam reaches the target layer, it maintains the laser output energy required for the preset processing; as it approaches the target layer, it gradually reduces the laser output energy using a stepped energy reduction method; when it touches the bottom copper foil, it immediately shuts off the laser beam or maintains it with micro-output energy to completely avoid problems such as burning the bottom and over-etching; at the same time, based on the height data monitored by the OCT detection unit, the position of the output end of the laser processing unit is adjusted synchronously to ensure processing accuracy; based on the positioning deviation signal, the processing position is adjusted in real time to ensure accurate hole positioning.

[0037] (6) Quality compensation: In response to problems such as uneven PCB thickness, laser energy attenuation and positioning offset, the thickness, depth, height and positioning information detected in real time by the OCT detection unit are combined to compensate the laser output energy and processing position in real time, so as to ensure the stability of hole shape and hole position quality.

[0038] (7) Positioning replacement optimization: As the processing progresses, the frequency of use of the off-axis CCD module is gradually reduced. Through the three-dimensional scanning of the OCT detection unit and the synergistic effect of the coaxial CCD module, the off-axis CCD module is gradually replaced, simplifying the operation process and reducing equipment maintenance costs.

[0039] This laser drilling method uses an OCT detection unit to detect the difference in reflected signals between the copper layer and the dielectric layer in real time, achieving accurate layer identification. Combined with closed-loop adjustment of laser energy, it completely eliminates core defects such as burn-in and over-etching. The drilling yield is improved by more than 15% compared with traditional technology, the hole position deviation is controlled within ±2μm, the drilling depth detection accuracy is ≤±5μm, the hole shape is regular, and the hole wall is burr-free, which fully meets the processing quality requirements of high-end products such as multi-level HDI PCBs and IC substrates.

[0040] Furthermore, by integrating height monitoring and coaxial positioning functions into the OCT system, there is no need to frequently switch the position of the laser processing head and the off-axis displacement sensor and off-axis CCD, simplifying the operation process and improving processing efficiency by more than 10%. At the same time, the OCT detection response time is ≤1ms and the laser energy adjustment response time is ≤1ms, achieving millisecond-level closed-loop control, avoiding efficiency loss caused by processing lag, and adapting to the needs of high-volume, high-precision PCB processing.

[0041] This laser drilling method is based on the dual signal layer determination of the difference between the reflection signal of the copper layer / dielectric layer and the drilling depth detected by the OCT detection unit, which enables the precise processing of multi-level HDI stacked vias and blind vias, and is suitable for stepped layer structures.

[0042] Example 3: This example uses the processing of stacked blind holes on a second-order HDI mobile phone motherboard (conventional precision scenario) as an example to further illustrate this laser drilling method.

[0043] Processing target: Second-order HDI mobile phone motherboard, substrate is FR-4, surface copper thickness is 18μm, inner copper thickness is 35μm, interlayer dielectric thickness is 50μm, requires processing of stacked blind vias with a diameter of 0.1mm, the via position deviation is required to be ≤±2μm, no burn-in or over-etching defects, adapt to the high-density interconnection requirements of mobile phone motherboard, used for interlayer conduction of core circuit of smartphone.

[0044] The implementation process of the laser drilling method is as follows: (1) OCT height setting: After the PCB to be processed is fixed, the OCT detection unit emits low coherence light and is coaxially coupled with the laser beam of the laser processing unit to irradiate the PCB surface. By detecting the reflected optical path difference, the relative height between the output end of the laser processing unit and the PCB surface is obtained in real time. The processing head position is automatically adjusted to control the height error within ±3μm, maintain the optimal working distance for laser processing, and avoid the problem of uneven aperture caused by height deviation.

[0045] (2) CCD positioning: The coaxial CCD module added to the OCT system is used to acquire the pad image of the PCB to be processed area. Combined with the OCT three-dimensional scanning signal for collaborative analysis, the preset processing coordinates of the blind hole are identified and compared with the actual processing position to generate positioning deviation data. The position is adjusted by the motion and control unit to complete the positioning correction. The positioning accuracy reaches ±2μm, solving the problem of the off-axis CCD viewing angle deviation.

[0046] (3) Laser drilling: Start the ultraviolet laser processing unit, output the appropriate laser energy according to the preset process parameters, and perform blind hole processing on the PCB. The laser output energy real-time adjustment unit is in standby mode and adjusts the energy at any time according to the depth measurement results.

[0047] (4) Real-time measurement of drilling depth: During the drilling process, the OCT detection unit works synchronously with the processing laser to collect drilling depth signals and reflection signals of copper layer and dielectric layer in real time. By analyzing the difference in reflection signals, the interlayer interface is accurately identified and the drilling depth is monitored in real time. When the drilling depth is detected to be close to the inner copper foil (5μm away from the inner copper foil), the signal is fed back to the laser energy adjustment unit to reduce the laser energy in a stepwise manner. When the laser energy is detected to reach the surface of the inner copper foil, it is immediately turned off to avoid burning the bottom.

[0048] In this embodiment, a total of 10,000 blind holes were processed, with hole position deviations controlled within ±2μm. There were no defects such as burn-in or over-etching, the hole shape was regular, the drilling yield reached 99.8%, and the processing efficiency was improved by 10% compared with traditional technology, meeting the high-density and high-precision processing requirements of mobile phone motherboards.

[0049] Example 4: This example uses the processing of stepped holes in a three-stage HDI automotive electronic PCB (medium-to-high precision scenario) to further illustrate this laser drilling method.

[0050] Processing target: Three-layer HDI automotive electronic PCB, substrate is high heat resistant resin, surface copper thickness 35μm, middle copper thickness 50μm, bottom copper thickness 70μm, interlayer dielectric thickness 40μm, requires processing of stepped holes with a diameter of 0.08mm, used for automotive electronic control modules, requires drilling depth accuracy ≤±5μm, hole wall roughness meets the standard, no burrs or over-etching, suitable for the high temperature and high reliability working environment of automotive electronics.

[0051] The implementation process of the laser drilling method is as follows: (1) OCT height setting: Considering the slight unevenness of the thickness of the automotive electronic PCB substrate (maximum deviation 4μm), the OCT detection unit performs a full-area scan of the PCB to be processed, monitors the relative height of different processing positions in real time, and dynamically adjusts the output end position of the laser processing unit to ensure that the height error of each processing point is controlled within ±3μm, ensuring consistent laser energy efficiency and avoiding hole depth deviation caused by uneven substrate thickness.

[0052] (2) CCD positioning: The “OCT three-dimensional scanning + coaxial CCD” collaborative positioning mode is adopted. OCT three-dimensional scanning obtains the three-dimensional contour of the PCB surface, and coaxial CCD acquires the images of the preset positions of each step of the stepped hole. Through algorithm fusion and analysis, the processing coordinates of each step of the hole are accurately located, and the positioning deviation is corrected to within ±1.5μm. This meets the high precision requirements of multi-step positioning of stepped holes and solves the step offset problem caused by the positioning deviation of traditional off-axis CCD.

[0053] (3) Laser drilling: The ultrafast laser processing unit is used to output laser energy in stages. First, the first-order hole is processed, then the second-order hole is processed, and finally the third-order hole is processed. Before each drilling, the height is recalibrated by OCT to ensure processing accuracy.

[0054] (4) Real-time measurement of drilling depth: During each drilling process, the OCT detection unit collects drilling depth signals in real time. By analyzing the difference in reflection signals between the copper layer and the dielectric layer, it accurately determines whether the target layer of that stage has been reached. When the depth is detected to reach the preset value (40μm for first-stage hole, 80μm for second-stage hole, and 120μm for third-stage hole), the signal is fed back to the laser energy adjustment unit to reduce the laser energy to the end threshold and complete the drilling of that stage, avoiding over-etching or incomplete drilling. At the same time, the uniformity of hole depth is monitored in real time, and the laser energy is compensated in a timely manner for depth deviation.

[0055] The processing results of this embodiment are as follows: 8,000 stepped holes were processed, with the depth deviation of each step ≤ ±5μm. There were no burrs or over-etching on the hole walls, the burn-in defect rate was 0, the drilling yield reached 99.7%, and the processing efficiency was improved by 12% compared with traditional technology, meeting the high reliability and high precision processing requirements of automotive electronic PCBs.

[0056] Example 5: This example uses the micro-hole processing of IC substrates (high-precision scenario) as an example to further illustrate this laser drilling method.

[0057] Processing target: IC substrate (suitable for high-end chip packaging), substrate is BT resin, copper thickness is 12μm, dielectric layer thickness is 30μm, micro-holes with a diameter of 0.05mm need to be processed for interconnection between chip and substrate. The hole position deviation is required to be ≤±1μm, the drilling depth accuracy is required to be ≤±3μm, and there should be no burn-in or hole shape distortion. It is suitable for the high-density and ultra-high precision processing requirements of IC substrate micro-holes, which fits the natural advantages of laser drilling in the field of micro-holes.

[0058] The implementation process of the laser drilling method is as follows: (1) OCT Height Fixation: The flatness of the IC substrate surface is required to be extremely high. The OCT detection unit adopts a high-precision scanning mode to monitor the relative height between the output end of the laser processing unit and the substrate surface in real time, strictly controlling the height error within ±2μm. At the same time, it compensates for the slight warping of the substrate itself (warping amount ≤3μm) to ensure that the laser focus is accurately applied to the processing surface and avoid micro-hole diameter deviation.

[0059] (2) CCD positioning: A high-precision coaxial CCD module is used, combined with OCT three-dimensional scanning signal, to accurately position the micro-holes to be processed on the IC substrate. The positioning resolution is improved by sub-pixel interpolation technology, and the positioning deviation is corrected to within ±1μm, which fully meets the ultra-high precision positioning requirements of the micro-holes on the IC substrate and solves the pain point of insufficient positioning accuracy of traditional off-axis CCD.

[0060] (3) Laser drilling: The ultraviolet laser processing unit outputs low-energy, high-frequency lasers to avoid hole distortion caused by overheating of the substrate, while ensuring micro-hole processing efficiency and adapting to the high-density micro-hole processing requirements of IC substrates.

[0061] (4) Real-time measurement of drilling depth: During the drilling process, the OCT detection unit collects drilling depth signals and reflection signals in milliseconds, accurately identifies the interface between the copper layer and the dielectric layer, and monitors the micro-hole depth in real time. When the depth is detected to reach 30μm (dielectric layer thickness) and close to the bottom copper foil, the laser energy is immediately reduced to the micro-energy threshold. The laser is turned off after drilling to the target depth to completely prevent burning the bottom. At the same time, the depth data is fed back in real time to compensate the laser energy online and ensure that the depth of all micro-holes is consistent.

[0062] The processing results of this embodiment are as follows: 15,000 micro-holes were processed with hole position deviation ≤ ±1μm and hole depth deviation ≤ ±3μm. There was no burn-in or hole shape distortion. The micro-hole yield reached 99.9%. The processing efficiency was improved by 15% compared with traditional technology. It is fully adapted to the processing requirements of high-end IC substrates and provides reliable interconnection guarantee for chip packaging.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A multi-stage HDI PCB laser drilling system based on real-time OCT copper thickness and depth detection, characterized in that, include: Laser processing unit, OCT detection unit, copper thickness-depth synchronous analysis unit, energy closed-loop control unit, and motion and control unit; The laser processing unit is used for laser drilling of multi-stage HDI PCBs, and outputs an adjustable energy laser beam to the PCB set on the processing fixture. The OCT detection unit is used for coaxial online detection of the copper thickness, drilling depth, and relative height between the output end of the laser processing unit and the PCB to be processed in the PCB drilling area. It collects the reflection signals of the copper layer and the dielectric layer. At the same time, it assists the OCT detection unit in coaxial positioning and correction by three-dimensional scanning or by adding a CCD module. The copper thickness-depth synchronous analysis unit is used to analyze the reflection signal collected by the OCT detection unit, identify the interlayer interface, calculate the drilling depth and relative height, analyze the positioning signal and generate positioning deviation data; The energy closed-loop control unit adjusts the laser output energy of the laser processing unit in real time based on the analysis results; The motion and control unit adjusts the relative height position between the output end of the laser processing unit and the PCB based on the relative height information detected by the OCT detection unit to maintain the optimal processing distance, and adjusts the processing position according to the positioning deviation data to complete the positioning correction.

2. The multi-stage HDI PCB laser drilling system based on real-time OCT copper thickness and depth detection according to claim 1, characterized in that, The laser processing unit includes a processing laser, a laser optical mirror group, a laser dichroic mirror, and a processing galvanometer. The processing galvanometer is located above the processing fixture. The laser beam of the processing laser is directed to the laser dichroic mirror via the laser optical mirror group, and then redirected by the laser dichroic mirror before being directed to the processing galvanometer.

3. The multi-stage HDI PCB laser drilling system based on real-time OCT copper thickness and depth detection according to claim 2, characterized in that, The OCT detection unit includes an OCT system and an OCT two-dimensional galvanometer, wherein the OCT two-dimensional galvanometer is arranged coaxially with the processing galvanometer.

4. The multi-stage HDI PCB laser drilling system based on real-time OCT copper thickness and depth detection according to claim 1, characterized in that, The CCD module includes a rangefinder CCD module and a coaxial CCD module. The rangefinder CCD module includes a rangefinder CCD and a rangefinder CCD lens barrel disposed on one side of the laser processing unit, with the rangefinder CCD lens barrel facing the PCB on the processing fixture. The coaxial CCD module includes a coaxial CCD and a coaxial CCD lens barrel, as well as a CCD dichroic mirror coaxially arranged with the laser processing unit and the OCT detection unit. The CCD dichroic mirror is disposed between the laser processing unit and the OCT detection unit. The coaxial CCD module serves as a supplement to the rangefinder CCD module and will gradually replace the rangefinder CCD module.

5. The multi-stage HDI PCB laser drilling system based on real-time OCT copper thickness and depth detection according to claim 2, characterized in that, The processing laser is a CO2 laser, an ultraviolet laser, or an ultrafast laser, and is suitable for one or more processing scenarios, including first-order to fourth-order HDI PCBs, arbitrary-layer interconnect PCBs, stacked blind via PCBs, and microvias on IC substrates.

6. A multi-stage HDI PCB laser drilling method based on real-time OCT copper thickness and depth detection, characterized in that, The multi-stage HDI PCB laser drilling system based on real-time OCT copper thickness and depth detection, as described in any one of claims 1 to 5, is employed. The laser drilling method includes the following steps: Establish a multi-level HDI PCB OCT reflection signal library and a mapping table of drilling depth, relative height and laser output energy; calibrate the three-dimensional scanning positioning accuracy of the OCT detection unit or the image acquisition parameters of the CCD module, and establish a positioning deviation correction model; The multi-stage HDI PCB to be processed is fixed on the processing fixture, and coaxial positioning correction is completed based on the positioning deviation correction model; the position of the output end of the laser processing unit is adjusted so that the output end of the laser processing unit is at the optimal working distance from the PCB surface; The laser processing unit starts to output a laser beam to drill holes, and the OCT detection unit works coaxially with the processing laser beam to collect the hole bottom depth signal, reflection signals of different layers and positioning deviation signals in real time during the drilling process. Based on the collected reflection signals and the reflection signal library, high-reflection signals and low-reflection signals of different PCB layers are distinguished. The sudden change in the hole bottom depth signal is used to determine whether the target layer or the bottom copper foil has been reached, and the layer determination result is obtained. The collected processing height signal is used to determine whether there is a height deviation. The collected positioning deviation signal is used to determine whether there is a processing position offset. Based on the layer classification results, height deviation, and processing position offset, and in conjunction with the mapping table, the laser processing unit's laser output energy and processing position are adjusted online to form a closed-loop control.

7. The multi-stage HDI PCB laser drilling method based on real-time OCT copper thickness and depth detection according to claim 6, characterized in that, The steps of coaxial positioning correction include: scanning the PCB area to be processed using the three-dimensional scanning function of the OCT detection unit or in conjunction with the CCD module, collecting the three-dimensional contour of the PCB surface and the coordinate information of the holes to be drilled, comparing it with the preset processing coordinates, generating positioning deviation data, and adjusting the position of the PCB or the output end of the laser processing unit by the motion and control unit to complete the coaxial positioning correction.

8. The multi-stage HDI PCB laser drilling method based on real-time OCT copper thickness and depth detection according to claim 6, characterized in that, The closed-loop control process includes: maintaining the laser output energy required for the preset processing before the laser beam reaches the target layer; gradually reducing the laser output energy by using a stepped energy reduction method when approaching the target layer; immediately turning off the laser beam or maintaining it with micro-output energy when touching the bottom copper foil; simultaneously adjusting the position of the output end of the laser processing unit according to the height data monitored by the OCT detection unit; and adjusting the processing position in real time according to the positioning deviation signal.

9. The multi-stage HDI PCB laser drilling method based on real-time OCT copper thickness and depth detection according to claim 6, characterized in that, To address issues such as uneven PCB thickness, laser energy attenuation, and positioning offset, the laser output energy and processing position are compensated in real time by combining the thickness, depth, height, and positioning information detected in real time by the OCT detection unit.

10. The multi-stage HDI PCB laser drilling method based on real-time OCT copper thickness and depth detection according to claim 6, characterized in that, As the processing progresses, the frequency of use of the off-axis CCD module is gradually reduced. Through the synergistic effect of the three-dimensional scanning of the OCT detection unit and the coaxial CCD module, the off-axis CCD module is gradually replaced.

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