Circuit board processing method and circuit board

Abstract

The invention provides a circuit board processing method and a circuit board, and the method comprises the steps: carrying out the first drilling of the circuit board, so as to form a plurality of through holes; acquiring horizontal position information of a target through hole in the plurality of through holes; according to the horizontal position information of the target through hole, the position of a target signal layer corresponding to the target through hole in the vertical direction is measured, the vertical position information of the target signal layer is obtained, and the target signal layer is exposed on the hole wall of the through hole; and according to the vertical position information of the target signal layer, performing second drilling at the target through hole position of the circuit board to form a back drilling hole, and enabling the stub length after the second drilling to be within a preset range. According to the method, the problems of line damage, excessive stub length and the like caused by position deviation can be effectively avoided, the stub length after back drilling can be strictly controlled within a preset range, and interference of the stub on high-frequency signals is remarkably reduced.

Description

Technical Field

[0001] The present application belongs to the technical field of circuit board back drilling processing, and in particular relates to a circuit board processing method and a circuit board. Background Art

[0002] With the rapid development of the electronic information industry, the manufacturing process precision of printed circuit boards (PCBs), as the core carrier of signal transmission and electrical connection of electronic products, has an increasingly significant impact on the performance of terminal devices.

[0003] A circuit board consists of multiple alternating dielectric and signal layers. The signal layers contain circuitry that electrically connects to the metal layers on the walls of through-holes in the target signal layer, thereby enabling signal transmission between different signal layers. Backdrilling is typically used to remove excess metal from the through-holes. The non-functional, dangling metal portions of the through-holes that are not completely drilled out, known as redundant conductive portions, form a stub (Studying the Unwanted Barrel, or stub). This stub is located between the bottom of the backdrilled hole and the target signal layer.

[0004] In the field of CNC, circuit boards, as the core carrier for device signal transmission and command execution, must rapidly transmit high-frequency signals. Their machining precision directly determines the device's response speed, operational stability, and anti-interference capabilities. The backdrilling process, a key step in optimizing high-frequency signal paths and reducing signal interference from residual piles, demands particularly stringent precision.

[0005] However, using current PCB processing methods, the backdrilling depth is difficult to control, which can easily lead to circuit damage or excessive residual length, making it difficult to meet the extremely high requirements for signal integrity in the CNC field. Summary of the Invention

[0006] The purpose of this application is to provide a circuit board processing method and a circuit board, aiming to solve the technical problem that the current relevant circuit board processing methods easily lead to circuit damage or excessive residual length.

[0007] To achieve the above objectives, the technical solutions adopted in this application are as follows: In a first aspect, a circuit board processing method is provided, comprising: Drilling the circuit board for the first time to form multiple through holes; Acquiring horizontal position information of a target through hole among the plurality of through holes; Measuring the vertical position of a target signal layer corresponding to the target through hole according to the horizontal position information of the target through hole, and obtaining the vertical position information of the target signal layer, wherein the target signal layer is exposed on the hole wall of the through hole; According to the vertical position information of the target signal layer, a second drilling is performed at the target through-hole position of the circuit board to form a back-drilled hole, and the length of the stub after the second drilling is within a preset range.

[0008] One possible scenario of the first aspect is that before drilling the circuit board for the first time, the method further includes: Acquiring horizontal position information of each signal layer in the circuit board; The position of the first drilling is determined according to the horizontal position information of each signal layer.

[0009] One possible scenario of the first aspect is that obtaining horizontal position information of each signal layer in the circuit board includes: identifying the signal layer by non-destructive measurement; Horizontal position information of each signal layer is measured.

[0010] One possible scenario of the first aspect is that before drilling the through hole position of the circuit board for the second time, the method further includes: Acquiring horizontal position information of the target signal layer in the horizontal direction; The target position of the second drilling is compensated and corrected according to the horizontal position information of the target signal layer.

[0011] One possible scenario of the first aspect is that after drilling the circuit board for the first time, the method further includes: Obtaining interlayer dielectric thickness information of the circuit board.

[0012] In one possible scenario of the first aspect, obtaining the interlayer dielectric thickness information of the circuit board includes: Applying an AC signal of a predetermined frequency to the drill bit in advance; A circuit is formed between the drilling platforms through the circuit board; Determining vertical position information of each signal layer by the amplitude of the electrical signal in the loop; determining the thickness of the interlayer dielectric according to the vertical position information of each of the signal layers; The depth of the backdrilled hole is determined according to the thickness of the interlayer dielectric.

[0013] One possible scenario of the first aspect is that acquiring vertical position information of the target signal layer in the vertical direction includes: The vertical position information of the target signal layer is obtained by optical measurement or non-destructive measurement.

[0014] One possible scenario of the first aspect is that obtaining the vertical position information of the target signal layer by an optical measurement method includes: Projecting an incident light onto the hole wall of the through hole and obtaining a projection angle of the incident light; Changing the projection angle of the incident light so that the projection position of the incident light on the hole wall of the through hole moves along the vertical direction, and the reflected light reflected by the hole wall of the through hole is emitted toward the light intensity meter; receiving, by a light intensity meter, reflected light from the hole wall of the through hole, and generating a light intensity signal according to the reflected light; The vertical position information of the target signal layer is acquired according to the change of the light intensity signal and the projection angle of the incident light.

[0015] One possible scenario of the first aspect is that obtaining the vertical position information of the target signal layer by an optical measurement method includes: Projecting the incident light obliquely toward the through hole, and allowing the incident light to pass through the dielectric layer of the circuit board and irradiate the target signal layer; receiving, by an interferometer, the reflected light reflected by the target signal layer, and obtaining interference information formed by the interference of the reflected light and the reference light; The vertical position information of the target signal layer is obtained according to the interference information and the inclination information of the incident light.

[0016] One possible scenario of the first aspect is that, after forming the back-drilled hole, the method further includes: Obtaining the depth value of the back-drilled hole, and / or, Obtaining the length of the residual pile in the back-drilled hole, and / or Obtain a deviation value between a central axis of the back-drilled hole and a central axis of the through hole.

[0017] One possible scenario of the first aspect is that, after forming the back-drilled hole, the method further includes: Aim the target through-hole with a CCD camera to obtain the center coordinates of the target through-hole; Aligning the CCD camera with the back-drilled hole to obtain the center coordinates of the back-drilled hole; A hole position deviation value of the back-drilled hole is determined according to the center coordinates of the target through hole and the center coordinates of the back-drilled hole.

[0018] One possible scenario of the first aspect is that, after forming the back-drilled hole, the method further includes: The multi-color light is sequentially split and focused and then emitted toward the back-drilled hole; Acquire first spectrum information of a first reflected light reflected by a bottom surface of the back-drilled hole and second spectrum information of a second reflected light reflected by the target signal layer; A depth value of the back-drilled hole is obtained according to the first spectral information; or a length value of a stump in the back-drilled hole is obtained according to the first spectral information and the second spectral information.

[0019] One possible scenario of the first aspect is that, after forming the back-drilled hole, the method further includes: projecting an incident light toward the back-drilled hole; Acquiring a first interference image formed by the incident light through an area scan camera; Determining a first distance value from the area scan camera to the board surface where the opening of the back-drilled hole is located based on the first interference image; Controlling the area scan camera to move a second distance value, and acquiring a second interference image formed by the incident light through the area scan camera; determining a third distance value from the area scan camera to the bottom surface of the back-drilled hole according to the second interference image; A depth value of the back-drilled hole is obtained according to the first distance value, the second distance value, and the third distance value.

[0020] One possible scenario of the first aspect is that, after drilling the circuit board for the first time, the method further includes: A metal layer is formed on the hole wall of the through hole.

[0021] One possible scenario of the first aspect is that, before drilling the circuit board for the first time, the method further includes: correcting drill tape data for the first drilling by reading first data in a first tag, wherein the first tag is generated on the circuit board, the first data including measurement data of the target signal layer before the first drilling and processing data of a previous process; After obtaining the vertical position information of the target signal layer, the method further includes: generating a second label on the circuit board, wherein the second label stores second data, and the second data includes measurement data of the through hole and the target signal layer after the first drilling; Before performing the second drilling, the method further includes: correcting the drill belt data of the second drilling by reading the second data in the second tag; After the second drilling is performed, the method further includes: generating a third label on the circuit board, wherein the third label stores third data, the third data including data related to residual piles and data related to residual copper in hole walls, and correcting the first data according to the third data.

[0022] In a second aspect, a circuit board is provided, which is manufactured by the circuit board processing method described in the above embodiments.

[0023] The technical effect of this application compared to the prior art is as follows: This circuit board processing method is designed to meet the stringent requirements for backdrilling accuracy in the field of numerical control for high-frequency signal transmission on circuit boards. By first forming multiple through holes and determining the horizontal position of the target through holes, the vertical position of the target signal layer exposed on the through hole wall is accurately measured based on this position, and then a second backdrill is performed based on this position, thereby achieving precise control of the backdrilling depth. This process effectively avoids problems such as line damage and excessive residual length caused by position deviation, and can strictly control the residual length after backdrilling within a preset range, significantly reducing the interference of the residual on the high-frequency signal, ensuring signal integrity, thereby improving the response speed, operating stability and anti-interference ability of the numerical control equipment, and meeting the extremely high requirements for circuit board processing accuracy in the field of numerical control. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0025] Figure 1 is a cross-sectional view of a circuit board provided in an embodiment of the present application; Figure 2 is a perspective view of a circuit board provided in an embodiment of the present application; Figure 3 is a flow chart of a circuit board processing method provided in an embodiment of the present application; Figures 4 to 8 It is a flowchart of different embodiments of obtaining vertical position information of a target signal layer in the vertical direction in the circuit board processing method provided by the present application; Figure 9 This is a flow chart of obtaining the deviation value between the central axis of the back-drilled hole and the central axis of the through hole in the circuit board processing method provided by the present application; Figure 10 This is a flow chart of obtaining the stump length value in the circuit board processing method provided by this application; Figure 11 This is a flow chart for obtaining back-drilling depth value and residual pile length value in the circuit board processing method provided by this application; Figure 12 This is a flow chart of obtaining the backdrilling depth value in the circuit board processing method provided by this application; Figure 13 yes Figure 12 Flowchart for projecting incident light toward the back-drilled hole; Figure 14 This is a flow chart of obtaining the backdrilling depth value in the circuit board processing method provided by this application; Figure 15 This is a flow chart of obtaining multiple backdrilling depth values ​​in the circuit board processing method provided by this application; Figure 16 This is a flow chart of full-process data management in the circuit board processing method provided in this application.

[0026] Description of reference numerals: 100, circuit board; 10a, first board surface; 10b, second board surface; 11, dielectric layer; 12, signal layer; 121, target signal layer; 101, target through hole; 102, metal through hole; 103, back drill hole; 1031, bottom surface; 13, metal layer. DETAILED DESCRIPTION

[0027] The following describes in detail embodiments of the present application, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application. In the description of this application, it should be understood that the terms "length", "width", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined. In this application, unless otherwise expressly specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components or interactions between two components. Those skilled in the art will understand the specific meanings of these terms in this application based on specific circumstances.

[0028] In order to make the purpose, technical solutions and advantages of this application more clear, this application is further described in detail below with reference to the accompanying drawings and embodiments.

[0029] With the rapid development of the electronic information industry, the manufacturing process precision of printed circuit boards (PCBs), as the core carrier of signal transmission and electrical connection of electronic products, has an increasingly significant impact on the performance of terminal equipment.

[0030] A circuit board consists of alternating dielectric and signal layers. The signal layers contain circuitry that electrically connects to the metal layers on the through-hole walls by surrounding the target signal layer, thereby enabling signal transmission between different signal layers. Backdrilling is typically used to remove excess metal from the through-holes. The non-functional, overhanging metal in the through-holes that is not completely drilled out, known as redundant conductive material, forms a stub (Studying the Unwanted Barrel, or stub). This stub is located between the bottom of the backdrilled hole and the target signal layer.

[0031] In the field of CNC, circuit boards, as the core carriers for device signal transmission and command execution, must rapidly transmit high-frequency signals. Their machining precision directly determines the device's response speed, operational stability, and anti-interference capabilities. The backdrilling process, a key step in optimizing high-frequency signal paths and reducing signal interference from stubs (residual metal segments within holes), demands particularly stringent precision. However, in current backdrilling processes, due to factors such as lamination errors in multi-layer circuit boards and offsets in previous drilling operations, the actual horizontal position of the target signal layer deviates from the designed coordinates. Furthermore, its vertical position between layers is susceptible to fluctuations due to uneven dielectric layer thickness.

[0032] However, during the interlayer lamination step, the signal layer where the target signal layer is located may be affected by pressure and deviate from the original design position. During the through-hole processing process, the position of the through-hole may also deviate from the original design position due to reasons such as the vibration of the drill bit. In addition, both the interlayer lamination step and the through-hole processing step may cause the board surface of the circuit board at the through-hole to be uneven, causing the thickness of the circuit board to change, so that the position of the target signal layer in the vertical direction deviates from the original design position. Therefore, using the current relevant circuit board processing methods, it is difficult to control the position and depth of the back-drilled holes. Problems such as excessive back-drilling depth, insufficient back-drilling depth, or alignment deviation between the back-drilled hole and the target signal layer may occur. Excessive back-drilling depth will cause circuit damage, while insufficient back-drilling depth may easily lead to excessively long stumps. Back-drilling hole deviation will cause metal segments to remain in the through-hole. These two types of problems will cause impedance mutation, signal reflection, and crosstalk in high-frequency signal transmission, making it difficult to meet the extremely high requirements for signal integrity in the CNC field.

[0033] Based on this, an embodiment of the present application provides a circuit board processing method, which can accurately control the processing position and depth of the back drilling hole, avoid the problem of the back drilling hole depth being too large, too small or position offset, and improve the accuracy and reliability of circuit board processing.

[0034] Among them, see Figure 1 and Figure 2 The circuit board 100 includes a plurality of dielectric layers 11 and a plurality of signal layers 12, and the plurality of dielectric layers 11 and the plurality of signal layers 12 are alternately arranged in sequence, that is, a signal layer 12 is arranged between two adjacent dielectric layers 11, or a dielectric layer 11 is arranged between two adjacent signal layers 12. The signal layer 12 is made of a metal conductive material, while the dielectric layer 11 is made of an insulating material, such as glass fiber resin. In this embodiment of the application, the signal layer 12 includes at least one copper foil. Since there are multiple signal layers 12 in the circuit board 100, each signal layer 12 may have multiple copper foils. For the convenience of distinction, the copper foil to be processed can be named as the target copper foil. Correspondingly, the signal layer 12 formed after the target copper foil is punched through by the through hole is named as the target signal layer 121.

[0035] In the following embodiments, the circuit board 100 is defined as being placed horizontally, i.e., the plane on which the circuit board 100 is located is a horizontal plane, and the thickness direction of the circuit board 100 is vertical. The circuit board 100 has a first board surface 10a and a second board surface 10b that are opposite to each other in the vertical direction.

[0036] See also Figures 1 to 3 In this embodiment of the application, the processing method of the circuit board 100 includes: S1. Perform a first drilling on the circuit board 100 to form a plurality of through holes.

[0037] Based on the initial drill tape information, corresponding positions of the plurality of through holes in the drill tape information are determined. The corresponding positions of the plurality of through holes may be the corresponding positions of all through holes on the circuit board 100, or may be the corresponding positions of a portion of the through holes, without limitation. A drill is then used to perform a first drilling operation on the circuit board 100 in a vertical direction to form a plurality of through holes corresponding to the drill tape information, each through hole penetrating the first board surface 10a and the second board surface 10b.

[0038] S2. Acquire horizontal position information of a target through hole 101 among the plurality of through holes.

[0039] The target through hole 101 is the through hole that needs to be drilled for the second time among the multiple through holes. A three-dimensional coordinate system is established according to the position of the circuit board 100, wherein the two vertical directions on the horizontal plane where the circuit board 100 is located are defined as the X-axis direction and the Y-axis direction, and the vertical direction is defined as the Z-axis direction. The horizontal position information of the target through hole 101 includes the coordinate data of the through hole in the horizontal direction, such as the X-axis coordinate and the Y-axis coordinate of the center or the hole wall position of the through hole. Since the first drilling process may cause the shaking of the drill bit or the circuit board 100, the actual horizontal position of the target through hole 101 may deviate from the horizontal position in the drill belt information. Obtaining the horizontal position information of the target through hole 101 can provide an accurate horizontal positioning reference for the subsequent detection of the target signal layer 121. S3. According to the horizontal position information of the target through hole 101, the position of the target signal layer 121 corresponding to the target through hole 101 in the vertical direction is measured, and the vertical position information of the target signal layer 121 is obtained. The target signal layer 121 is exposed on the hole wall of the through hole.

[0040] The detection device can correct the position of the preset design detection area based on the measured horizontal position information of the target through-hole 101, obtaining the position information of the actual detection area that matches the actual horizontal coordinates of the target through-hole 101, ensuring that the detection direction of the detection device (e.g., the incident light and the detection light) can be accurately aligned with the detection area where the target through-hole 101 is located. Since the target through-hole 101 passes through the target signal layer 121, the target signal layer 121 can be exposed on the through-hole wall.

[0041] It should be noted that, considering that the second drilling may involve a station change or flipping of the circuit board 100, to prevent positional deviations caused by this movement or flipping from affecting detection accuracy, vertical position information must be acquired before the circuit board 100 is moved or flipped. This timing arrangement maximizes the accuracy of horizontal position calibration and reduces interference with detection alignment caused by mechanical operations.

[0042] The vertical position information of the target signal layer 121 includes the coordinate data of the target signal layer 121 in the vertical direction, such as the Z-axis coordinate of the midpoint position of the target signal layer 121 in the vertical direction in the three-dimensional space, the Z-axis coordinate of the inner annular surface of the target signal layer 121 or at least one surface in the vertical direction in the three-dimensional space, etc.

[0043] After forming the through-hole and measuring the vertical position of the target signal layer 121, the through-hole can be metallized. Specifically, a metal layer 13 is formed on the through-hole wall. This metal layer 13 forms a cylindrical structure and surrounds the metal through-hole 102. This metal layer 13 contacts the target signal layer 121 exposed on the through-hole wall, thereby achieving vertical conductivity of the target signal layer 121 in the circuit board 100.

[0044] S4. Drill the through hole position of the circuit board 100 for the second time according to the vertical position information of the target signal layer 121 to form the back-drilled hole 103 , and ensure that the length of the residual stub after the second drilling is within a preset range.

[0045] Based on the vertical position information of the target signal layer 121, the vertical movement distance of the drill bit or the Z-axis coordinate of the movement endpoint is obtained. Then, using a drill bit with an outer diameter larger than the diameter of the through-hole, a second drilling operation is performed on the through-hole location of the circuit board 100, moving vertically from the first surface 10a of the circuit board 100 toward the second surface 10b, thereby forming a back-drilled hole 103. The drill bit's final resting position does not reach the target signal layer 121, so that the back-drilled hole 103 is vertically spaced from the target signal layer 121. Prior to the second drilling operation, the circuit board 100 is drilled a second time, such that the opening of the back-drilled hole 103 is located on the first surface 10a. In other embodiments, the drill bit may also be moved from the second surface 10b of the circuit board 100 toward the first surface 10a to form the back-drilled hole 103, in which case the opening of the back-drilled hole 103 is located on the second surface 10b. This is not a limitation and the specific processing location can be selected based on processing requirements. The position of the drill bit before the first drilling and the position of the drill bit relative to the circuit board 100 before the second drilling may be the same or different, and there is no limitation here.

[0046] The diameter of the back-drilled hole 103 is larger than that of the through-hole. This allows the drill to remove a portion of the metal layer 13 during the second drilling process, reducing the vertical length of the stump. Upon completion of the second drilling process, a step structure is formed between the back-drilled hole 103 and the through-hole. The top of this step structure serves as the bottom surface 1031 of the back-drilled hole 103. The distance between the back-drilled hole 103 and the target signal layer 121 is the distance between the bottom surface 1031 of the back-drilled hole 103 and the surface of the target signal layer 121 facing the back-drilled hole 103, i.e., the length of the stump. The stump length is within a preset range, which can be selected from 50 μm to 250 μm.

[0047] After the second drilling, the back-drilled holes 103 and metal through-holes 102 are filled with insulating material, such as insulating resin, to eliminate the effects of air or potential conductive impurities in the holes on the performance of the circuit board 100. The insulating material protruding from the surface of the circuit board 100 is then removed, such as by grinding or scraping the first and second surfaces 10a, 10b flat. This eliminates uneven surface flatness caused by overflow or uneven shrinkage of the insulating material during the filling process, and prevents defects such as printed pattern deformation and poor pad contact caused by local protrusions or depressions. Of course, the insulating material can be filled only in the back-drilled holes 103 or only in the metal through-holes 102, or partially in the back-drilled holes 103 and / or partially in the metal through-holes 102, without limitation here.

[0048] This circuit board 100 processing method addresses the stringent requirements for backdrilling accuracy in the CNC field for high-frequency signal transmission of circuit boards 100. By first forming multiple through-holes and determining the horizontal position of the target through-hole 101, the spatial alignment accuracy of the target signal layer 121 during vertical position detection is ensured, providing a reliable data basis for subsequent backdrilling depth control based on vertical position information, thereby avoiding detection failures caused by horizontal deviations. The vertical position of the target signal layer 121 exposed on the through-hole wall is then measured, and a second backdrilling is performed based on this vertical position, achieving precise control of the depth of the backdrilled hole 103. This process effectively avoids problems such as line damage and excessive residual length caused by position deviations. It can strictly control the residual length after backdrilling within a preset range, significantly reducing the interference of the residual on the high-frequency signal, ensuring signal integrity, thereby improving the response speed, operating stability, and anti-interference capability of the CNC equipment, and meeting the extremely high requirements for circuit board 100 processing accuracy in the CNC field.

[0049] It is understandable that before the first drilling of the circuit board 100 is performed, the following steps are also included: S01 . Acquire horizontal position information of each signal layer 12 in the circuit board 100 .

[0050] The horizontal position information of each signal layer 12 includes coordinate data of each signal layer 12 in the horizontal direction, such as the X-axis coordinate and the Y-axis coordinate of the center of the designed perforation area of ​​the signal layer 12 or the boundary of the signal layer 12 .

[0051] S02 : Determine the position of the first drilling according to the horizontal position information of each signal layer 12 .

[0052] The first drilling position must be vertically within the boundaries of the target signal layer 121 to ensure that the target through hole 101 passes through the middle of the target signal layer 121 and is circumferentially closed around the target through hole 101. Before the first drilling, the drill tape information for the first drilling is corrected based on the position of the first drilling, and the horizontal position of the drill bit is adjusted accordingly to avoid deviation.

[0053] Before the first drilling, the horizontal position information of each signal layer 12 is obtained, and the position of the first drilling is determined accordingly. This can accurately compensate for the horizontal offset of the signal layer 12 position caused by interlayer pressing. By correcting the horizontal position of the drill bit, it is ensured that the target through hole 101 passes through the middle of the target signal layer 121, so that the formed signal layer 12 is circumferentially closed and accurately positioned, avoiding the target signal layer 121 from being broken or poorly connected due to the offset of the target through hole 101, laying the foundation for the precise positioning of the subsequent back drilling process, effectively improving the reliability and processing accuracy of the conductive connection of the circuit board 100, and reducing the scrap rate caused by position deviation.

[0054] The above-mentioned acquisition of the horizontal position information of each signal layer 12 in the circuit board 100 includes: S011, identifying each signal layer 12 through non-destructive measurement; S012 , measuring the horizontal position information of each signal layer 12 .

[0055] Non-destructive measurement methods include but are not limited to X-ray CT scanning, optical coherence tomography, ultrasonic microscopy, eddy current array testing, microwave testing, terahertz time-domain spectroscopy technology, etc., which are introduced below.

[0056] X-ray CT scans include: First, the circuit board 100 is fixed to the stage of the X-ray CT device. The CT device is then turned on to emit X-rays toward the circuit board 100. When the X-ray beam penetrates the multi-layer structure of the circuit board 100, the detector can capture the difference in attenuation signals in different areas due to the significant difference in the X-ray attenuation coefficients between the target copper foil (metal material) and the dielectric layer 11 (insulating material), forming a two-dimensional tomographic image containing the outlines of each signal layer 12.

[0057] The CT device then rotates or translates the circuit board 100 through a precision mechanical transmission system, acquiring a series of continuous 2D slice images at different angles and positions. These 2D images are then fused and reconstructed into a 3D model of the circuit board 100 using a CT reconstruction algorithm (such as filtered back projection). Each signal layer 12 appears as a high-contrast metal density region in the model, clearly distinguishable from the surrounding dielectric layer 11.

[0058] Finally, the three-dimensional model is processed by image analysis software: in the horizontal plane, the edge contour of each signal layer 12 is identified, and its center coordinates, contour coordinates and other parameters are extracted to obtain the horizontal position information of each signal layer 12.

[0059] Ultrasonic microscopy uses high-frequency ultrasound (typically above 10 MHz) to scan the circuit board 100. By analyzing the acoustic impedance differences between different signal layers 12 (metal layer 13 and insulation layer), it generates a high-resolution image of the interlayer structure. This technique can accurately identify the vertical position and thickness of the signal layer 12, as well as its relationship to the through-hole. It is particularly suitable for inspecting the connection between the signal layer 12 and the hole wall.

[0060] Optical coherence tomography (OCT), based on the principle of light interference, provides micron-level resolution tomographic imaging of the internal structure of the circuit board 100. For surface and near-surface signal layers 12, it can clearly reveal their exposed edges within the through-hole walls. With its fast detection speed and zero radiation, OCT is suitable for precise position measurement of high-frequency signal layers 12.

[0061] Eddy current array testing uses a multi-channel eddy current probe to generate an alternating magnetic field around a through-hole. This induces eddy currents in the metal signal layer 12, whose changes are captured by the probe. By analyzing the phase and amplitude of the eddy current signal, the vertical position of the signal layer 12 on the hole wall and the distance between layers can be determined. This method is particularly suitable for detecting the boundaries of the conductive signal layer 12.

[0062] Microwave testing utilizes the reflection and transmission characteristics of microwaves in different media (the metal in signal layer 12 and the insulating substrate) to determine the spatial position of signal layer 12 by analyzing the echo signal. This technology has a certain ability to detect signal layers 12 buried deep within multilayer circuit boards 100, and the equipment is relatively low-cost, making it suitable for batch testing scenarios.

[0063] Terahertz time-domain spectroscopy (TDS) technology uses terahertz waves, which have strong penetration into non-metallic materials (such as the substrate of the circuit board 100) but produce strong reflections from the metallic signal layer 12. By analyzing the reflected signals from the terahertz pulses, the depth and boundaries of the signal layer 12 can be precisely located. This technique is particularly useful for detecting subtle positional deviations in the high-frequency signal layer 12.

[0064] The above-mentioned non-destructive measurement method is used to obtain the horizontal position information of each signal layer 12, which can penetrate the circuit board 100 in a non-contact manner. By virtue of the significant difference between the metal and dielectric layers 11, the contours of each signal layer 12 can be clearly identified, and the position parameters of each signal layer 12 can be accurately extracted. This method does not require destroying the structure of the circuit board 100, and can effectively avoid the damage that may be caused by traditional detection methods. At the same time, it breaks through the occlusion limitation of the multi-layer board structure of the circuit board 100 on the observation of the internal signal layer 12, greatly improving the measurement accuracy and reliability of the horizontal position information, and providing high-quality data support for the precise positioning of the subsequent first drilling process, which helps to reduce back-drilling defects caused by position deviation. It should be noted that the effects of the non-destructive measurement method used in the subsequent embodiments are the same as the effects of the non-destructive measurement method used in the detection of each signal layer 12, and will not be repeated in the subsequent embodiments.

[0065] It is understandable that after the first drilling of the circuit board 100, the following steps are also included: S11 . Obtaining interlayer dielectric thickness information of the circuit board 100 .

[0066] In the structure of a multilayer circuit board 100, the interlayer dielectric thickness refers to the distance between different signal layers 12 of the circuit board 100, that is, the thickness of the dielectric layer 11. This interlayer dielectric thickness determines the relative position of the signal layer 12 in the thickness direction (vertical direction) of the circuit board 100. During the production process of the circuit board 100, due to deviations during the lamination process of the circuit board 100, it is necessary to measure the actual interlayer dielectric thickness. This interlayer dielectric thickness information can be fed back to the lamination process to serve as a basis for adjusting the process parameters.

[0067] The step of obtaining the interlayer dielectric thickness information of the circuit board 100 includes: S111, identifying the signal layer 12 and / or the dielectric layer 11 by non-destructive measurement; S112 , measuring the thickness of the interlayer dielectric of each signal layer 12 to obtain interlayer dielectric thickness information.

[0068] The non-destructive measurement method, using X-ray CT scanning as an example, includes first constructing a three-dimensional model of the circuit board 100. The method of constructing the three-dimensional model of the circuit board 100 is similar to the method of constructing the three-dimensional model of the circuit board 100 when obtaining the horizontal position information of the target copper foil, and is not repeated here.

[0069] Then, the three-dimensional model is processed using image analysis software: in the vertical direction, the signal layer 12 is identified and the distance between two adjacent signal layers 12 is extracted, or two vertically opposite surfaces of the dielectric layer 11 are identified and the distance between the two surfaces is extracted, thereby obtaining the interlayer dielectric thickness information of the circuit board 100.

[0070] As an alternative embodiment, the interlayer dielectric thickness information of the circuit board 100 can be obtained by current measurement or capacitance measurement. Specifically, obtaining the interlayer dielectric thickness information of the circuit board 100 includes: S121 , applying an AC signal of a predetermined frequency to the drill bit in advance.

[0071] Both capacitive and amperometric measurements require applying an AC signal of a specific frequency to the drill bit used for drilling. This signal serves as a detection source, providing the basis for identifying the position of the signal layer 12 through subsequent changes in the electrical signal. In capacitive measurement, the AC signal is used to stimulate the charge and discharge process of the capacitor; in amperometric measurement, the AC signal provides the potential difference that generates the loop current.

[0072] S122 , forming a loop between the circuit board 100 and the drilling platform.

[0073] Capacitive measurement: The drilling platform of the circuit board 100 is grounded, and the upper and lower surfaces of the circuit board 100 are signal layers 12. A capacitor structure is formed between the drill bit and the drilling platform due to the signal layer 12 and the dielectric layer 11. The AC signal forms a capacitive circuit through the drill bit, circuit board 100, and drilling platform.

[0074] Current measurement: The ground terminal of the drilling machine control board is connected to each layer of signal layer 12. When the drill bit contacts a certain signal layer 12, a conductive loop is formed through the drill bit, signal layer 12, and the ground terminal of the control board, and the current signal can be transmitted along the loop.

[0075] S123 , determining the vertical position information of each signal layer 12 by the amplitude of the electrical signal in the loop.

[0076] Capacitive measurement: When the drill bit contacts the first signal layer 12, a capacitive charging circuit is formed. The receiving circuit detects a sudden change in the charging voltage amplitude (from zero to high). The drill bit feed depth at this time is recorded as the vertical position of the first signal layer 12. When the drill bit continues to feed and passes through the dielectric layer 11 to contact the next signal layer 12, the voltage amplitude suddenly changes again. The position of each signal layer 12 is determined by analogy.

[0077] Current measurement: When the drill bit contacts a certain signal layer 12, the circuit is connected, and the receiving circuit detects that the current signal amplitude increases from zero to something, and records the depth at this time as the position of the signal layer 12; after the drill bit drills through the signal layer 12, the circuit is disconnected and the current signal amplitude disappears, further verifying the boundary of the signal layer 12.

[0078] S124 , determining the thickness of the interlayer dielectric according to the vertical position information of each signal layer 12 .

[0079] Based on the vertical coordinates of two adjacent signal layers 12 (e.g., the first layer's depth is s1, and the second layer's is s2), the thickness of the dielectric layer 11 between the two signal layers 12 can be calculated by calculating the difference (s2-s1). This process directly correlates the position of the signal layer 12 with changes in the electrical signal, avoiding the indirect errors of traditional measurements.

[0080] S125 . Determine the depth of the backdrilled hole 103 according to the thickness of the interlayer dielectric.

[0081] The thickness of the interlayer dielectric reflects the spacing and distribution of the signal layer 12. Combined with the vertical position of the target signal layer 121 (such as the depth of the signal layer 12 that needs to be retained), the depth that the back-drilled hole 103 needs to reach (such as the preset distance from the surface to the top of the target signal layer 121) can be accurately calculated to ensure that the length of the residual pile after back-drilling is within the preset range.

[0082] Through capacitive or current electrical signal measurement methods, the vertical position of each signal layer 12 is directly identified by utilizing the electrical characteristics of the drill bit and the signal layer 12. The interlayer dielectric thickness can be acquired synchronously without the need for additional detection equipment, thereby simplifying the measurement process and reducing costs. The sudden change characteristics of the electrical signal amplitude ensure high-precision position identification of the signal layer 12 and reduce the error in calculating the interlayer thickness. The backdrilling depth is determined based on the measured interlayer thickness, which can be specifically adapted to the actual structure of the circuit board 100, effectively avoiding the problem of excessive residual length or drilling through the signal layer 12, and improving the reliability of the backdrilling process. It is particularly suitable for the strict requirements of high-frequency signal transmission on the precision of the circuit board 100 in the CNC field.

[0083] It should be noted that the interlayer dielectric thickness can also be used to obtain the vertical position information of the signal layer 12 in the vertical direction in subsequent steps. Specifically, during the production process of the circuit board 100, by measuring the interlayer dielectric thickness and combining it with the information of the layer where the signal layer 12 is located in the circuit board 100 design file, the depth range of the signal layer 12 in the vertical direction can be accurately calculated. For example, assuming that the circuit board 100 has three conductive layers, through measurement, it is known that the interlayer dielectric thickness between the first and second layers is h1, and the interlayer dielectric thickness between the second and third layers is h2. If the signal layer 12 is located in the second conductive layer, it can be preliminarily determined that the depth of the signal layer 12 from the top surface of the circuit board 100 is around h1.

[0084] The depth of backdrilled hole 103 is measured from the surface of PCB 100 to a specific location on signal layer 12 (typically, the starting point of the metal layer to be retained). Once the exact location of signal layer 12 is determined, the required depth of backdrilled hole 103 can be calculated based on information such as the thickness of the interlayer dielectric. For example, if the distance from the top surface of PCB 100 to the top of signal layer 12 is h1, to maintain a predetermined spacing d between the bottom of backdrilled hole 103 and the top of signal layer 12, the depth D of backdrilled hole 103 is calculated as h1 - d.

[0085] In this way, if the measured interlayer dielectric thickness deviates, causing the actual position of the signal layer 12 to be different from the expected position, the depth setting of the back drill hole 103 can be corrected in time to ensure the accuracy of the back drill processing, avoid the back drill hole 103 being too deep and damaging the target signal layer 121, or being too shallow and causing the residual pile to be too long, and ensure the electrical performance of the circuit board 100.

[0086] Furthermore, the thickness of the interlayer dielectric directly determines the process parameters such as dielectric hardness and thickness distribution that the drill must overcome. For example, if the dielectric thickness of a certain interlayer is abnormally large (exceeding the design value), it may indicate the presence of bubbles or uneven thickness in the dielectric layer 11 in that area. Drill speed and feed pressure must be adjusted to prevent interruptions. If the interlayer dielectric thickness is too small, the drilling depth must be controlled to prevent drilling through the underlying copper foil.

[0087] Wherein, obtaining the horizontal position information of the target signal layer 121 includes: S3011, identifying the target signal layer 121 through non-destructive measurement; S3012 , measuring the horizontal position information of the target signal layer 121 .

[0088] The non-destructive measurement method, using X-ray CT scanning as an example, includes first constructing a three-dimensional model of the circuit board 100. The method of constructing the three-dimensional model of the circuit board 100 is similar to the method of constructing the three-dimensional model of the circuit board 100 when obtaining the horizontal position information of the target copper foil, and is not repeated here.

[0089] Then, the three-dimensional model is processed by image analysis software: in the horizontal plane, the edge contour of the target signal layer 121 is identified, and its center coordinates, radius, inner annular surface coordinates, outer contour coordinates and other parameters are extracted to obtain the horizontal position information of the target signal layer 121.

[0090] As an alternative embodiment, the step of obtaining the horizontal position information of the target signal layer 121 in the circuit board 100 includes: S3021 , collecting image information of the target through hole 101 , and measuring horizontal position information of the target through hole 101 according to the image information.

[0091] Using high-precision image acquisition equipment such as a CCD camera, the formed target through-hole 101 is photographed to obtain clear image information containing the target through-hole 101. Because the target through-hole 101 has undergone metallization, a conductive metal layer 13 is formed on its wall, resulting in the metal through-hole 102 being clearly distinguishable from the surrounding dielectric layer 11 in the image. By processing the captured image using image analysis technology, the horizontal position parameters of the target through-hole 101 can be accurately measured, including the X-axis and Y-axis coordinates of the center of the target through-hole 101 and the boundary coordinates of the metal through-hole 102 outline, thereby determining the horizontal position information of the target through-hole 101.

[0092] S3022 , obtaining horizontal position information of the target signal layer 121 according to the horizontal position information of the target through hole 101 .

[0093] During the design and processing of circuit board 100, target signal layer 121 and target via 101 are strictly coaxial, meaning their central axes coincide. Due to this structural characteristic, the horizontal position of target via 101 is consistent with that of target signal layer 121. Therefore, the horizontal position of target via 101 measured in S3021 can be directly equated with the horizontal position of target signal layer 121, eliminating the need for separate positioning of signal layer 121.

[0094] This method acquires the horizontal position information of the target through-hole 101 by capturing an image of the target through-hole 101, and utilizes the coaxial characteristics of the signal layer 12 and the target through-hole 101 to deduce the horizontal position of the signal layer 12. This method can achieve precise positioning without the need for complex internal detection equipment, thus simplifying the measurement process. With the help of image acquisition technologies such as CCD cameras, the metallization characteristics of the target through-hole 101 can be quickly captured, ensuring the measurement accuracy of the horizontal position parameters and effectively compensating for position deviations during the processing process. At the same time, this method directly derives based on the structural correlation between the two, avoiding direct detection of the signal layer 12, reducing operational difficulty and cost, providing reliable data support for the precise alignment of the subsequent drilling process, and improving the overall accuracy and efficiency of the circuit board 100 processing.

[0095] It is understandable that before drilling the target through hole 101 of the circuit board 100 for the second time, the following steps are also included: S401 : Acquire horizontal position information of the target signal layer 121 in the horizontal direction.

[0096] Because the processing position is changed or the circuit board 100 is flipped before the second drilling process, the position of the target through-hole 101 deviates from the drill tape information used in the second drilling process. Therefore, it is necessary to re-acquire the horizontal position information of the target signal layer 121 to accurately locate the second drilling position. The horizontal position information of the target signal layer 121 can be obtained by re-measurement or calculated based on a design deviation value or an empirical deviation value. This is not limited here, as long as the horizontal position information of the target signal layer 121 used in this step is within the allowable error range.

[0097] S402 , compensating and correcting the target position of the second drilling according to the horizontal position information of the target signal layer 121 .

[0098] The drill belt information may be modified according to the horizontal position information of the target signal layer 121 , and the drill bit may perform a second drilling according to the modified drill belt information, so that the formed back-drilled hole 103 is coaxial or nearly coaxial with the target through hole 101 .

[0099] Before the second drilling, the horizontal position information of the target signal layer 121 is obtained, and the target position of the second drilling is compensated and corrected accordingly. This can accurately offset the position deviation that may occur after the first drilling, ensure that the back-drilled hole 103 and the target signal layer 121 are accurately aligned in the vertical direction, and avoid the metal layer 13 in the target through-hole 101 remaining during back drilling due to horizontal misalignment, further improve the position accuracy of the back-drilling process, ensure the reliability of the via electrical connection and the high-frequency signal transmission performance, and reduce the risk of circuit failure caused by alignment deviation.

[0100] Among them, the above-mentioned method of obtaining the horizontal position information of the target signal layer 121 in the circuit board 100 is the same as the method of obtaining the horizontal position information of the target signal layer 121 before obtaining the vertical position information of the target signal layer 121 in the vertical direction. Both can be X-ray CT scanning or collecting image information of the target through hole 101, which will not be repeated here.

[0101] Please combine Figure 4 , obtaining vertical position information of the target signal layer 121 in the vertical direction, including: The vertical position information of the target signal layer 121 is obtained by optical measurement or non-destructive measurement.

[0102] Optical measurement or non-destructive measurement is used to obtain the vertical position information of the target signal layer 121. The depth coordinates of the target signal layer 121 can be accurately captured without damaging the structure of the circuit board 100. This avoids the risk of damage to the signal layer 12 caused by contact measurement, and can adapt to the detection needs of signal layers 12 with different materials and different burial depths. It provides reliable data support for the precise control of the subsequent back drilling depth 103, effectively ensures the compliance of the residual pile length, and improves the stability and processing yield of the high-frequency signal transmission of the circuit board 100.

[0103] Among them, in the non-destructive measurement method, X-ray CT scanning is taken as an example. The vertical position information of the target signal layer 121 is obtained by X-ray CT scanning, which includes: S311, identifying the target signal layer 121 through X-ray CT scanning; S312 : Measure vertical position information of the target signal layer 121 .

[0104] Specifically, a three-dimensional model of the circuit board 100 is first constructed. The method of constructing the three-dimensional model of the circuit board 100 is similar to the method of constructing the three-dimensional model of the circuit board 100 when obtaining the horizontal position information of the target copper foil, and is not repeated here.

[0105] Then, the three-dimensional model is processed using image analysis software: in the vertical direction, the starting and ending positions of the two surfaces of the target signal layer 121 in the Z-axis direction are determined through layer cutting analysis, the thickness of the target signal layer 121 is calculated, and combined with the three-dimensional coordinate system conversion, the vertical position information of the target signal layer 121 is finally obtained.

[0106] When both the vertical position information and the horizontal position information of the target signal layer 121 are acquired by X-ray CT scanning, the two pieces of information may be acquired simultaneously or in separate time periods, which is not limited here.

[0107] There are many ways to perform optical measurement, which are described below by way of example.

[0108] As a first implementation, please combine Figure 5 , obtaining vertical position information of the target signal layer 121 in the vertical direction by an optical measurement method includes: S321 , projecting the incident light onto the hole wall of the target through hole 101 , and obtaining the projection angle of the incident light.

[0109] A light source can be placed on one side of the first surface 10a of the circuit board 100, and the light source can be used to project incident light at an angle toward the first aperture so that the incident light can be projected onto the wall of the target through-hole 101. At the same time, the initial projection angle of the incident light, such as the angle between the incident light and the vertical direction, is recorded. The oblique incidence design ensures that the light can be effectively reflected from the hole wall, providing a basis for subsequent detection. The accurate recording of the projection angle is a key parameter for the subsequent calculation of the vertical position. The initial projection angle of the incident light must satisfy the requirement that the reflected light reflected from the wall of the target through-hole 101 can be at least partially emitted from the second aperture.

[0110] S322. Change the projection angle of the incident light so that the projection position of the incident light on the hole wall of the target through hole 101 moves in the vertical direction, and the reflected light reflected by the hole wall of the target through hole 101 is emitted toward the light intensity meter.

[0111] The light source is driven to rotate by a rotating assembly to change the projection direction of the incident light, causing the position where the incident light is projected on the wall of the target through-hole 101 to move vertically. Because the target signal layer 121 is made of metal and the rest of the wall is made of dielectric layer 11, the movement of the light projection position will cover areas of different materials. At the same time, the reflection of light by the wall of the target through-hole 101 must meet a specific path to ensure that the reflected light from the wall of the target through-hole 101 can be emitted from the second aperture and projected toward the light intensity meter. During this process, the rotation angle of the incident light can be synchronously recorded by an angular displacement sensor to generate angle information.

[0112] S323 , receiving the reflected light reflected by the hole wall of the target through hole 101 through a light intensity meter, and generating a light intensity signal according to the reflected light.

[0113] The light intensity meter receives the light reflected from the second aperture and converts the light signal into a quantifiable light intensity signal. When the light strikes dielectric layer 11, the reflected light intensity is relatively weak. However, when it strikes target signal layer 121 (metal), the light intensity signal is significantly enhanced due to the metal's high reflectivity. The angular displacement sensor measures the light's rotation angle in real time, providing data support for subsequent calculation of the vertical position of target signal layer 121 based on this angle.

[0114] S324 . Obtain vertical position information of the target signal layer 121 according to the change of the light intensity signal and the projection angle of the incident light.

[0115] When the light intensity signal increases from weak to strong and reaches a distinct peak, it indicates that the light has reached the target signal layer 121. By combining the light projection angle, the diameter of the target through-hole 101, and other parameters, and using geometric optics principles (such as trigonometric relationships), the position of the incident light's projection point on the wall of the target through-hole 101 in the depth direction of the target through-hole 101 can be calculated. This position, in other words, is the vertical distance of the target signal layer 121 relative to the board surface (or reference plane) of the circuit board 100. This allows the vertical position of the target signal layer 121 to be determined.

[0116] The first method realizes vertical scanning of the wall of the target through hole 101 by changing the projection angle of the incident light, and utilizes the reflectivity difference between the target signal layer 121 and the dielectric layer 11 to accurately locate the target signal layer 121 through the change of the light intensity signal, without contacting the wall of the target through hole 101, thus avoiding damage to the hole wall; the vertical position can be directly derived with the help of angle information and geometric calculations, and the operation process does not require complex mechanical moving components. The detection efficiency is high and the stability is strong, which can provide reliable data for the secondary drilling depth control, effectively reduce the processing defects caused by depth deviation, and is suitable for scenarios with high requirements for detection speed and non-contact.

[0117] As a second implementation, please combine Figure 6 , obtaining vertical position information of the target signal layer 121 in the vertical direction by an optical measurement method, including: S331 , moving the reflector vertically in the target through hole 101 , and obtaining the displacement of the reflector.

[0118] The reflector can be a reflecting prism having a reflective surface for reflecting light. When the reflector moves vertically within the target through-hole 101, the reflective surface tilts toward the light source. In this embodiment, the reflective surface can be at a 45° angle to the horizontal plane. The reflector displacement can be obtained via a position sensor or based on the drive amount of a drive mechanism that drives the reflector movement, which is not limited here. The reflector displacement can be obtained in real time or under set conditions, which is not limited here.

[0119] S332. Project the incident light toward the reflector.

[0120] The incident light generated by the light source is projected vertically toward the target through-hole 101. The incident light may first pass through a cylindrical objective lens to shape the point light into a line light before being projected into the target through-hole 101. In other embodiments, the incident light may also be at a certain angle to the vertical direction, as long as it can be projected onto the reflector.

[0121] S333 , the incident light is reflected to the hole wall of the target through hole 101 by the reflector, and the reflected light reflected back by the hole wall of the target through hole 101 is emitted toward the light intensity meter.

[0122] The reflector reflects the incident light onto the wall of the target through hole 101 through an inclined reflecting surface. The wall of the target through hole 101 reflects part of the incident light to form reflected light. The reflected light can be projected onto the reflecting surface and reflected by the reflecting surface to exit the target through hole 101 and head towards the light intensity meter.

[0123] S334. Receive the reflected light through a light intensity meter and generate a light intensity signal according to the reflected light.

[0124] Because target signal layer 121 is made of metal and dielectric layer 11 is insulating, the intensity of light reflected from target signal layer 121 is much higher than that from dielectric layer 11. Therefore, when the reflected light strikes target signal layer 121, the light intensity meter detects a distinct peak in intensity. However, when the reflected light strikes dielectric layer 11, the light intensity signal remains low and stable. This characteristic of the light intensity signal provides a direct basis for determining whether the reflected light has struck target signal layer 121.

[0125] S335 . Obtain vertical position information of the target signal layer 121 according to the change in the light intensity signal and the displacement of the reflector.

[0126] Since the light intensity signal measured by the light intensity meter reaches its maximum value when the reflector reflects the reflected light to the target signal layer 121, it can be determined that the projection position of the reflected light at this time is the location of the target signal layer 121. Since the incident light is incident in a vertical direction and the reflecting surface is 45° relative to the horizontal plane, the vertical position of the reflector when the light intensity signal measured by the light intensity meter reaches its maximum value is the vertical position of the target signal layer 121. The initial position of the reflector can be the first board surface 10a of the circuit board 100. The first board surface 10a of the circuit board 100 can be set as the reference plane. The reflector moves from the reference plane along the axis of the target through hole 101 toward the second board surface 10b. If the light intensity signal measured by the light intensity meter reaches its maximum value when the reflector moves a distance L in the target through hole 101, then the distance between the target signal layer 121 and the reference plane is also L.

[0127] The second method uses the synergy of the vertical movement of the reflector and the reflection of light, and utilizes the reflectivity difference between the metal target signal layer 121 and the dielectric layer 11 to accurately locate the vertical position of the target signal layer 121 through the peak value of the light intensity signal. It has the advantage of non-contact measurement and can avoid damage to the wall of the target through-hole 101. At the same time, the direct correlation between the reflector displacement and the light intensity signal can quickly convert the detection results into the Z-axis coordinates of the target signal layer 121. It is easy to operate and responds quickly. The use of line light also improves the detection stability in complex hole wall environments, providing high-precision vertical position data for the drilling depth control of the second drilling, and effectively reducing the line damage or excessive length of the residual pile caused by depth deviation.

[0128] In other embodiments, if the incident light is not incident in a vertical direction, or the reflecting surface is not inclined at a 45° angle, the projection position information of the reflected light on the wall of the target through hole 101 can be obtained based on the incident angle of the incident light, the inclination angle of the reflecting surface and the displacement of the reflector. The projection position is the specific position of the target signal layer 121 in the vertical direction.

[0129] As a third implementation method, please combine Figure 7 , obtaining vertical position information of the target signal layer 121 in the vertical direction by an optical measurement method, including: S341 , attaching the probe assembly to the hole wall of the target through hole 101 , and moving it in the vertical direction, and obtaining the displacement of the probe assembly.

[0130] The probe assembly is electrically connected to a power source to form a circuit with the power source, providing a basis for subsequent electrical signal detection. The displacement of the probe assembly can be measured by a displacement measuring device, which can be a grating ruler, encoder, etc. The displacement measuring device can record the distance moved by the probe assembly in real time. This displacement will serve as a key parameter for calculating the vertical position of the target signal layer 121. Its measurement accuracy directly affects the accuracy of the final position information.

[0131] S342. Obtain the electrical signal of the probe assembly during the movement through the electrical signal measurement assembly.

[0132] The electrical signal measurement assembly monitors changes in the electrical signal on the probe assembly. These signals include at least one of inductance, current, voltage, capacitance, and resistance. Because target signal layer 121 is metallic (conductive), while the rest of the target via 101 wall is dielectric layer 11 (insulating or with poor conductivity), the difference in conductivity between dielectric layer 11 and target signal layer 121 can lead to significant changes in the electrical signal when the probe moves from dielectric layer 11 to target signal layer 121. These changes, such as an increase in inductance or a sudden drop in resistance, are accurately captured by the electrical signal measurement assembly.

[0133] S343 , determining the vertical position information of the target signal layer 121 through the change of the electrical signal and the displacement of the probe assembly.

[0134] Using the first surface 10a of the circuit board 100 as a reference (i.e., the starting point of displacement), the controller synchronously receives the displacement of the probe assembly and the signal data from the electrical signal measurement component. When the electrical signal experiences a sudden change (such as a sudden increase in inductance or a sudden decrease in resistance), it indicates that the probe assembly has contacted the conductive target signal layer 121. The movement distance recorded by the displacement measurement component is the vertical distance of the target signal layer 121 relative to the reference plane. This correspondence allows the specific position of the target signal layer 121 within the thickness direction of the circuit board 100 to be directly determined.

[0135] This third method uses the difference in conductive properties between the metal and dielectric layers 11 through direct electrical contact between the probe assembly and the target signal layer 121 to keenly capture sudden changes in the electrical signal to locate the target signal layer 121, and has the characteristics of rapid response and accurate identification; combined with the real-time recording of the moving distance by the displacement measuring component, the electrical signal change can be directly associated with the vertical position without the need for complex signal conversion algorithms. It is easy to operate and has strong anti-interference ability, and can provide reliable vertical position data for secondary drilling depth control, effectively avoiding line damage or excessive length of residual piles due to depth deviation, and is particularly suitable for mass production scenarios with high requirements for detection efficiency and stability.

[0136] As a fourth implementation method, please combine Figure 8 , obtaining vertical position information of the target signal layer 121 in the vertical direction by an optical measurement method, including: S351 , projecting the incident light obliquely toward the target through-hole 101 , and allowing the incident light to pass through the dielectric layer 11 and irradiate the target signal layer 121 ; An incident light beam is projected at a certain angle toward the target through-hole 101. Because the dielectric layer 11 is permeable to the incident light beam, the light beam is able to pass through the dielectric layer 11 and reach the target signal layer 121. The target signal layer 121 has a first surface vertically parallel to the first surface 10a of the circuit board 100 and an opposing second surface. The incident light beam is projected from the first surface 10a of the circuit board 100 onto the first surface of the target signal layer 121. Because the target signal layer 121 is made of metal and has a high reflectivity, it reflects the incident light beam, forming reflected light. This reflected light beam then exits the circuit board 100, providing a signal source for subsequent interference detection.

[0137] S352 , receiving the reflected light reflected by the target signal layer 121 through an interferometer, and obtaining interference information formed by the interference of the reflected light and the reference light.

[0138] The interferometer is equipped with a reference beam (e.g., a beam of light from the same source that has traveled a fixed optical path). After receiving the reflected light from the target signal layer 121, the reflected light and the reference beam interfere with each other within the interferometer, forming alternating light and dark interference fringes. The interferometer collects these interference fringes to obtain interference information. This interference information can include the distribution characteristics of the interference fringes, the displacement of the interference fringes, the contrast of the interference fringes, and the position of the zero-order fringes.

[0139] S353 , obtaining vertical position information of the target signal layer 121 according to the interference information and the inclination information of the incident light.

[0140] Based on the interference information, the optical path of the reflected light can be derived, that is, the total distance of the incident light from the light source to the first surface of the target signal layer 121 and then back to the interferometer. Combined with the inclination information of the incident light and the vertical direction, using trigonometric function relationships (such as the relationship between the projection of the optical path in the vertical direction and the cosine of the inclination angle), the vertical distance of the first surface of the target signal layer 121 relative to the reference plane of the circuit board 100 (such as the first board surface 10a) can be calculated, and the vertical position information of the target signal layer 121 can be determined.

[0141] The fourth method uses the interference principle of light to accurately obtain the optical path of the reflected light through interference information, and calculates the vertical position of the target signal layer 121 in combination with the incident inclination angle. It has extremely high measurement accuracy and can meet the strict requirements of the high-density circuit board 100 for positioning the target signal layer 121; the incident light penetrates the dielectric layer 11 and directly acts on the target signal layer 121 without contacting or scanning the hole wall, avoiding mechanical interference and damage to the hole wall, and the detection process is stable and reliable; at the same time, the interference technology is highly sensitive to changes in the optical path, and even slight differences in the vertical position of the target signal layer 121 can be captured, providing ultra-precision data support for the second drilling depth control, effectively reducing processing defects caused by depth errors, and is suitable for the precision manufacturing scenarios of high-end high-frequency circuit boards 100.

[0142] Please refer again Figures 1 to 3 After forming the back-drilled hole 103, the process further includes step S5, which includes: Obtaining the depth value of the back-drilled hole 103, and / or, Obtain the length of the stump in the back-drilled hole 103, and / or The deviation value between the central axis of the back-drilled hole 103 and the central axis of the target through hole 101 is obtained.

[0143] That is, after the back-drilled hole 103 is formed, at least one of the depth value, the stump length value, and the center axis deviation value of the back-drilled hole 103 is obtained.

[0144] Among them, obtaining the depth value of the back-drilled hole 103 can verify whether the actual drilling depth meets the design requirements, and avoid damaging the target signal layer 121 due to insufficient depth causing the residual pile to be too long or too deep; measuring the residual pile length value can directly determine whether it is within the preset range, ensuring that high-frequency signal transmission is not interfered with by the residual pile and guaranteeing signal integrity; the deviation value of the central axis of the back-drilled hole 103 and the through hole is used to evaluate the position alignment accuracy of the two drillings, prevent metal residue on the hole wall or damage to the line due to horizontal offset, and avoid affecting the reliability of the electrical connection.

[0145] These parameters are not only an important basis for judging whether the circuit board 100 is qualified, but also provide data support for subsequent process optimization. By analyzing the causes of deviations (such as equipment accuracy, positioning errors, etc.), drilling parameters or equipment calibration can be adjusted in a targeted manner, and the stability of the backdrilling process can be continuously improved, ultimately meeting the strict requirements of the CNC field for the high-frequency signal transmission performance and structural reliability of the circuit board 100.

[0146] It should be noted that the depth value, the residual pile length value and the center axis deviation value of the back-drilled hole 103 are obtained in any order. In some embodiments, only one or two of the values ​​may be obtained, which is not limited here.

[0147] There are many methods for obtaining the depth value of the back-drilled hole 103 and the length value of the residual pile, which are described below with examples.

[0148] As one of the implementation methods for obtaining the deviation value between the central axis of the back-drilled hole 103 and the central axis of the target through hole 101, please combine Figure 9 , after forming the back drill hole 103, further comprising: S511 , aligning the target through-hole 101 with the CCD camera to obtain the center coordinates of the target through-hole 101 .

[0149] Leveraging the high-precision imaging capabilities of a CCD camera, the camera is focused on the target through-hole 101 formed by the initial drilling process to capture a clear image of the target through-hole 101. Image recognition algorithms (such as edge detection and circle center fitting) analyze the contour features of the target through-hole 101 wall and accurately calculate the horizontal center coordinates of the target through-hole 101 (typically expressed as the left side of the X-axis and the Y-axis coordinates) as a positional reference.

[0150] S512, aligning the back-drilled hole 103 with a CCD camera to obtain the center coordinates of the back-drilled hole 103; The same CCD camera is used, with the lens adjusted to focus on the back-drilled hole 103 formed by the second drilling, to capture an image of the back-drilled hole 103. Image analysis techniques are also used to extract edge information from the back-drilled hole 103 wall, and the center coordinates of the back-drilled hole 103 are calculated using fitting techniques as parameters for the actual machining position.

[0151] S513 , determining a hole position deviation value of the back-drilled hole 103 according to the center coordinates of the target through hole 101 and the center coordinates of the back-drilled hole 103 .

[0152] The center coordinates of the target through hole 101 are compared with the center coordinates of the back-drilled hole 103. The horizontal deviation between the two (including the X-axis deviation, the Y-axis deviation, and the comprehensive offset distance) is obtained by calculating the coordinate difference (such as the Euclidean distance formula). This deviation is the hole position deviation value of the back-drilled hole 103.

[0153] This solution uses a CCD camera to precisely capture the center coordinates of the target through-hole 101 and the back-drilled hole 103 and calculate the hole position deviation. This can intuitively quantify the horizontal alignment accuracy of the two drill holes, providing objective data for evaluating the back-drilling process quality. The deviation value can be used as a basis for process optimization, helping to trace the cause of position deviation (such as equipment accuracy, positioning error, etc.), and then adjust drilling parameters to reduce subsequent processing deviation. At the same time, the non-contact optical measurement method avoids damage to the circuit board 100, ensuring the safety and accuracy of the inspection process, ultimately improving the stability of the circuit board 100 back-drilling process and guaranteeing the reliability of high-frequency signal transmission.

[0154] One of the ways to get the length of the stump is to combine Figure 10 , after forming the back drill hole 103, further comprising: S521, projecting the incident light toward the back-drilled hole 103; Incident light enters the back-drilled hole 103 vertically and undergoes a first reflection upon contacting the bottom surface 1031 of the back-drilled hole 103, forming a first reflected light. Simultaneously, due to the permeability of the dielectric layer 11, some light can pass through the dielectric layer 11 and continue onto the target signal layer 121, where it undergoes a second reflection, forming a second reflected light. Both the first and second reflected lights are emitted toward the photosensitive element.

[0155] S522 : Obtain an optical path difference between a first reflected light reflected by the bottom surface 1031 of the back-drilled hole 103 and a second reflected light reflected by the target signal layer 121 .

[0156] The photosensitive element may convert the optical signal into an electrical signal after receiving the first reflected light and the second reflected light, and may obtain the optical path difference between the first reflected light and the second reflected light based on the electrical signal.

[0157] S533 , obtaining the length of the stub in the back-drilled hole 103 according to the optical path difference and the refractive index of the dielectric layer 11 in the circuit board 100 .

[0158] The refractive index n of the dielectric layer 11 is related to the material of the dielectric layer 11 and can be set according to the material of the dielectric layer 11. In the embodiment of the present application, the stump length of the back-drilled hole 103 to be measured can be determined according to the formula ΔL / n based on the optical path difference and the refractive index of the dielectric layer 11.

[0159] Determining the stump length of the back-drilled hole 103 to be measured based on the optical path difference and the refractive index of the dielectric layer 11 may include: determining thickness values ​​corresponding to various positions on the surface of the dielectric layer 11 based on the optical path difference and the refractive index of the dielectric layer 11; and determining the stump length of the back-drilled hole 103 to be measured based on the thickness values ​​corresponding to various positions on the surface of the dielectric layer 11.

[0160] In an embodiment of the present application, incident light from the back-drilled hole 103 to be tested is reflected by the surface of the dielectric layer 11 of the back-drilled hole 103 to be tested to form a first reflected light, and the incident light passing through the dielectric layer 11 is reflected by the signal layer 12 of the back-drilled hole 103 to be tested to form a second reflected light. By obtaining the optical path difference between the first reflected light and the second reflected light, the stub length of the back-drilled hole 103 to be tested is determined based on the optical path difference and the refractive index of the dielectric layer 11. On the one hand, the stub length can be obtained without damaging the circuit board 100 or requiring optical fiber insertion. On the other hand, the stub length can be determined based on two beams of reflected light reflected from different layers of the back-drilled hole 103 to be tested from the same incident light, eliminating the process of switching light sources or adjusting light wavelengths for different layers, thereby improving detection efficiency.

[0161] In addition, the present application supports the inspection of the back-drilled hole 103 to be tested after the back-drilling process is completed. Compared with the method of calculating the residual length based on the parameters before the back-drilled hole 103 is formed, the accuracy of the result will not be affected by the processes such as exposure and development of the outer layer circuit, etching of the outer layer circuit, removal of dry film, resin plugging, and board electrical signal measurement during the back-drilling process, which may easily lead to changes in the thickness of the circuit board 100 and height deviation of the signal layer 12. Therefore, the reliability of the inspection can be improved.

[0162] S525 , obtaining the length values ​​of the residual pile at various positions around the back-drilled hole 103 , and determining the classification result of the back-drilled hole 103 .

[0163] After backdrilling, the surface of the dielectric layer 11 of the back-drilled hole 103 to be tested becomes inclined. The depth varies at different locations along the horizontal direction (perpendicular to the depth direction) of the back-drilled hole 103 to be tested. The aforementioned first reflected light is light reflected from the surface of the dielectric layer 11. The optical path difference and corresponding thickness values ​​corresponding to the first reflected light reflected from different locations on the surface of the dielectric layer 11 may vary. To accurately determine the stump length of the back-drilled hole 103 to be tested, an analysis is required based on the thickness values ​​corresponding to each location on the surface of the dielectric layer 11. For each location on the surface of the dielectric layer 11, the thickness value of the dielectric layer 11 along the depth direction at that location, i.e., the thickness value corresponding to that location, can be determined using the formula ΔL / n based on the optical path difference corresponding to the first reflected light reflected at that location and the refractive index of the dielectric layer 11. In some embodiments, the lowest thickness value corresponding to all locations can be used as the stump length of the back-drilled hole 103 to be tested.

[0164] Taking the center of the back-drilled hole 103 as the center of the circle, the thickness values ​​corresponding to each position in multiple central angle directions are used to determine the lowest thickness value in each central angle direction; the lowest thickness value in each central angle direction is used as the residual pile length in the corresponding central angle direction.

[0165] In some embodiments of the present application, after obtaining the stump lengths in each central angle direction, the stump length detection method may further include: determining a classification result of the back-drilled hole 103 to be tested according to the stump lengths in each central angle direction.

[0166] Specifically, if the length of the residual stub in each central angle direction is greater than the first length threshold, the classification result of the back-drilled hole 103 to be tested is a back-drilled hole 103 with excessive residual stub, indicating that the back-drilling depth is insufficient. If the length of the residual stub in each central angle direction is less than the second length threshold, the classification result of the back-drilled hole 103 to be tested is a damaged line back-drilled hole 103, indicating that the back-drilling depth is too deep. If the residual stub length difference between the different central angle directions is greater than the difference threshold, the classification result of the back-drilled hole 103 to be tested is a back-drilled hole 103 with residual copper in the hole, indicating that some copper in the hole remains due to reasons such as center offset during backdrilling. If the length of the residual stub in each central angle direction is less than or equal to the first length threshold and greater than or equal to the second length threshold, the classification result of the back-drilled hole 103 to be tested is determined to be a correct back-drilled hole 103.

[0167] As one of the implementation methods for obtaining the depth value of the back-drilled hole 103 and the length value of the residual pile, please combine Figure 11 , after forming the back drill hole 103, further comprising: S531 , the multi-color light is sequentially split and focused and then emitted toward the back-drilled hole 103 .

[0168] In the embodiment of the present application, the polychromatic light source can be turned on to generate polychromatic light containing multiple wavelength components according to preset parameters (such as light intensity, spectral range, etc.).

[0169] In the embodiment of the present application, the distance between the optical lens module and the circuit board 100 can be precisely adjusted by a corresponding drive assembly. The purpose of the adjustment is to enable the optical lens module to accurately capture the light signal reflected from the back-drilled hole 103, ensuring that the light propagation path and focusing effect are optimal, thereby improving the accuracy of detection.

[0170] S532, obtaining first spectrum information of the first reflected light reflected by the bottom surface 1031 of the back-drilled hole 103 and second spectrum information of the second reflected light reflected by the target signal layer 121; After being split by the beam splitter in the optical lens module, the complex light forms a first reflected light and a second reflected light. The first reflected light is the reflected light of the dielectric layer 11 in the back-drilled hole 103 , and the second reflected light is the reflected light of the target signal layer 121 in the back-drilled hole 103 .

[0171] In the embodiment of the present application, during optical measurement, when light enters the back-drilled via 103, it is reflected by the dielectric layer 11 and the signal layer 12. The first reflected light and the second reflected light correspond to reflected light at different locations (the dielectric layer 11 and the signal layer 12), respectively. Since the propagation speed of light in a medium is related to the medium's refractive index, and the length of the stump results in different optical paths for the two reflected light beams, analyzing their spectral information allows the optical path difference to be calculated, thereby deriving the stump length. A spectrometer can detect the spectral information of the first and second reflected lights, which includes parameters such as wavelength and intensity. Light of different wavelengths exhibits different propagation characteristics in an optical system.

[0172] S533. Obtain a depth value of the back-drilled hole 103 based on the first spectral information; or, obtain a length value of the stump in the back-drilled hole 103 based on the first spectral information and the second spectral information; or, control the radial movement of the polychromatic light along the back-drilled hole 103 to obtain the stump length values ​​at different circumferential positions of the target through hole 101 based on the first spectral information and the second spectral information at each position.

[0173] Spectral analysis techniques, such as Fourier transform, can be used to extract information related to the optical path from the spectral information. Specific wavelengths can correspond to different depths. After obtaining the first spectral information, the depth of the back-drilled hole 103 can be calculated based on the wavelength.

[0174] Because the two reflected light beams have different optical path lengths, their spectra exhibit phase differences. By analyzing this phase difference at different wavelengths, the optical path difference (OPD) can be calculated. For example, for light of a specific wavelength, there is a definite relationship between its phase change and the OPD. By measuring the phase change at multiple wavelengths, the OPD can be accurately calculated. The formula for calculating the OPD is OPD = 2 × n × L (where n is the refractive index of dielectric layer 11, and L is the stump length. The multiplication by 2 accounts for the round-trip propagation of light). After calculating the OPD, combined with the known refractive index n of dielectric layer 11, the stump length of the backdrilled via 103 can be calculated.

[0175] The measuring device for the circuit board 100 provided in the embodiment of the present application does not need to directly contact the back-drilled hole 103, thereby avoiding damage to the back-drilled hole 103 that may be caused by contact. It is also suitable for some difficult-to-contact or precise circuit board 100 detection scenarios.

[0176] In the step of obtaining the stump length values ​​at different positions around the target through hole 101, the optical lens module can be moved, or the circuit board 100 can be moved to achieve relative movement of the two along the surface of the circuit board 100. During the movement process, the step size and direction of the movement need to be precisely controlled to ensure that all back-drilled holes 103 positions that need to be detected on the circuit board 100 can be covered. At each detection position, according to the previous method, that is, using a polychromatic light source to generate polychromatic light, after processing by the optical lens module, the stump lengths of each detection position around the back-drilled hole 103 are determined based on the first spectral information and the second spectral information after spectral separation. According to the distribution of the stump length values, it can be seen whether the stump length values ​​are uniform around the back-drilled hole 103. If the difference between the maximum length value and the minimum length value exceeds the design error, it indicates that the horizontal position of the back-drilled hole 103 has a large offset.

[0177] As one of the implementation methods for obtaining the depth value of the back-drilled hole 103, please combine Figure 12 , after forming the back drill hole 103, further comprising: S541 , projecting the incident light toward the back-drilled hole 103 .

[0178] When the user needs to detect the depth of the back-drilled hole 103 of the printed circuit board 100, the position of the area scan camera is first recorded as the initial acquisition position, and the light source emits an incident light with a preset light output angle to the first board surface 10a of the circuit board 100 where the hole of the back-drilled hole 103 is located.

[0179] S542 . Acquire a first interference image formed by the incident light through an area scan camera.

[0180] An interference image formed by the reflected light reflected by the first plate surface 10a is collected to obtain a first interference image, and the first interference image is sent to a processing device, which receives first interference information returned by the area scan camera.

[0181] S543 : Determine a first distance value from the area scan camera to the board surface where the opening of the back-drilled hole 103 is located based on the first interference image.

[0182] After the processing device acquires the first interference image of the back-drilled hole 103 through the area scan camera, it can determine a first distance from the area scan camera to the top surface of the back-drilled hole 103 according to the first interference image.

[0183] The processing device may calculate the corresponding fringe height according to the parallel fringes of the first interference image, and determine the fringe height as the first distance.

[0184] S544 , controlling the area scan camera to move a second distance value, and acquiring a second interference image formed by the incident light through the area scan camera.

[0185] After determining a first distance value from the area scan camera to the top surface of the back-drilled hole 103 based on the first interference image, the processing device can send a movement command containing a second distance value to the area scan camera. The area scan camera receives and responds to the movement command, moving the second distance value from its initial acquisition position toward the circuit board 100. The processing device records the area scan camera's position after the movement as the current acquisition position. Incident light at a preset emission angle is emitted toward the back-drilled hole 103, and an interference image formed by the reflected light of the high-incident light is captured to obtain a second interference image. This second interference image is then sent to the processing device, which receives the second interference image returned by the area scan camera. Since the current acquisition position is closer to the bottom surface 1031 of the back-drilled hole 103 than the initial acquisition position, the incident light emitted from the current acquisition position is more likely to impinge on the bottom surface 1031 of the back-drilled hole 103. Based on the current acquisition position, the captured second interference image is closer to the actual interference image formed by the bottom surface 1031 of the back-drilled hole 103. Therefore, the second interference image is the interference image formed by the bottom surface 1031 of the back-drilled hole 103.

[0186] S545 : Determine a third distance value from the area scan camera to the bottom surface 1031 of the back-drilled hole 103 according to the second interference image.

[0187] In an embodiment of the present application, after the processing device controls the area scan camera to move a second distance value to obtain a second interference image of the back-drilled hole 103, a third distance value from the area scan camera to the bottom surface 1031 of the back-drilled hole 103 can be determined based on the second interference image.

[0188] Specifically, after the processing device controls the area scan camera to move the second distance value to acquire a second interference image of the back-drilled hole 103, a first pixel position corresponding to the current acquisition position of the area scan camera and a second pixel position corresponding to the bottom surface 1031 can be determined in the second interference image, and a third distance value can be calculated based on the first pixel position and the second pixel position. Calculating the third distance value based on the current acquisition position and the pixel position corresponding to the bottom surface 1031 in the second interference image facilitates improving the accuracy of calculating the third distance value.

[0189] Among them, the processing device can draw a ray in any direction with the center of the concentric ring-shaped interference fringes corresponding to the second interference image as the endpoint. The intersection of the ray and the outer circle is the first pixel position, and the intersection of the ray and the inner circle is the second pixel position.

[0190] In some embodiments, the first pixel position may include a preset number of first sub-pixel positions, and the second pixel position may include a preset number of second sub-pixel positions.

[0191] The processing device can divide the second interference image into a preset number of sector images, and determine a first sub-pixel position corresponding to the current acquisition position and a second sub-pixel position corresponding to the bottom surface 1031 in each sector image, to obtain a preset number of first sub-pixel positions and a preset number of second sub-pixel positions, and calculate a corresponding sub-distance value based on a first sub-pixel position and a second sub-pixel position corresponding to each sector image to obtain a preset number of sub-distance values, and determine the average value of the preset number of sub-distance values ​​as the third distance value. Determining the third distance value based on the average value of the distance values ​​calculated based on multiple pixel positions is conducive to further improving the accuracy of the third distance value.

[0192] S546 : Obtain a depth value of the back-drilled hole 103 according to the first distance value, the second distance value, and the third distance value.

[0193] After the processing device determines the third distance value from the area scan camera to the bottom surface 1031 of the back-drilled hole 103 based on the second interference image, it can determine the back-drilled hole 103 depth of the back-drilled hole 103 based on the first distance value, the second distance value and the third distance value, thereby realizing the detection of the depth of the back-drilled hole 103 based on the interference image of the back-drilled hole 103 captured by the area scan camera, which can avoid damage to the printed circuit board 100 caused by metallographic sectioning of the printed circuit board 100 having the back-drilled hole 103, and is conducive to improving the detection efficiency of the depth of the back-drilled hole 103.

[0194] Specifically, after the processing device determines the third distance value from the area scan camera to the bottom surface 1031 of the back-drilled hole 103 based on the second interference image, it can calculate the sum of the second distance value and the third distance value to obtain the sum of the distance values, and calculate the difference between the sum of the distance values ​​and the first distance value, and the difference is the depth value of the back-drilled hole 103.

[0195] The solution provided in this embodiment uses an area scan camera to capture a first interference image of the back-drilled hole 103. Based on the first interference image, a first distance from the area scan camera to the top surface of the back-drilled hole 103 is determined. The area scan camera is then controlled to move a second distance to capture a second interference image of the back-drilled hole 103. Based on the second interference image, a third distance from the area scan camera to the bottom surface 1031 of the back-drilled hole 103 is determined. Furthermore, the depth of the back-drilled hole 103 is determined based on the first, second, and third distances. This allows for depth detection of the back-drilled hole 103 based on the interference image of the back-drilled hole 103 captured by the area scan camera. The use of non-contact detection can avoid damage to the printed circuit board 100 that would otherwise occur during metallographic sectioning of the printed circuit board 100 having the back-drilled hole 103. By utilizing the fringe features of the interference image, multi-position acquisition, and multi-pixel averaging, the accuracy of distance measurement is improved, thereby enhancing the accuracy of depth detection of the back-drilled hole 103. At the same time, it does not require complex mechanical structures, has an efficient operating process, and can quickly provide feedback on whether the backdrilling depth meets the standards, providing a timely basis for process adjustments, effectively ensuring the quality of backdrilling, and is suitable for efficient quality inspection scenarios in mass production.

[0196] As an alternative implementation, please combine Figure 13 , projecting the incident light toward the back-drilled hole 103 further includes: S5411 , determining the hole position angle of the back-drilled hole 103 .

[0197] In this embodiment, when the user needs to detect the depth of the back-drilled hole 103 of the printed circuit board 100, a detection instruction can be sent to the processing device. The processing device receives and responds to the detection instruction and can determine the hole angle of the back-drilled hole 103.

[0198] The hole angle of the back-drilled hole 103 may be used to represent the ratio of the hole radius of the back-drilled hole 103 to the depth of the back-drilled hole 103 .

[0199] The processing device can obtain the thickness of the printed circuit board 100 having the back-drilled hole 103, and determine the hole angle according to the hole radius of the back-drilled hole 103 and the thickness of the circuit board 100. The hole angle is calculated based on the thickness of the circuit board 100 and the hole radius of the back-drilled hole 103, which is conducive to improving the calculation accuracy of the hole angle of the back-drilled hole 103.

[0200] The processing device may generate upload prompt information and receive the thickness of the circuit board 100 and the hole radius of the back-drilled hole 103 uploaded by the user according to the upload prompt information.

[0201] The upload prompt information can be used to prompt the user to upload the thickness and hole radius of the circuit board 100 to the processing equipment. The upload prompt information can be at least any one of text prompt information, sound prompt information or light prompt information, etc., which is not limited here.

[0202] In one application scenario, the thickness of the printed circuit board 100 may be D, and the hole radius of the back-drilled hole 103 of the printed circuit board 100 may be r. The hole angle θ may be calculated according to the thickness D of the circuit board 100 and the hole radius r using the following formula: θ=arctan(r / D).

[0203] S5412. Configure the preset light angle for the surface scanning camera according to the hole position angle.

[0204] In this embodiment, after the processing device determines the hole position angle of the back-drilled hole 103, a preset light-emitting angle can be configured for the surface scanning camera according to the hole position angle. When the emission angle of the surface scanning camera is too large, the emitted light cannot illuminate the bottom surface 1031 of the back-drilled hole 103. Therefore, a smaller light-emitting angle can be configured for the surface scanning camera according to the hole position angle to improve the success rate of the emitted light irradiating the bottom surface 1031 of the back-drilled hole 103, which is beneficial to improving the acquisition accuracy of the second interference image.

[0205] The maximum light-emitting angle can be calculated according to the hole position angle, and it is determined that the preset light-emitting angle is smaller than the maximum light-emitting angle.

[0206] In an application scenario, the preset light-emitting angle of the area scan camera may be θ0, and the maximum light-emitting angle θ1 of the area scan camera may be calculated according to the hole angle θ as follows.

[0207] θ1=2θ=2arctan(r / D).

[0208] The preset light-emitting angle θ0 of the area scan camera may be configured to be an angle smaller than the maximum light-emitting angle θ1.

[0209] As one of the implementation methods for obtaining the depth value of the back-drilled hole 103, please combine Figure 14 , after forming the back drill hole 103, further comprising: S551 , projecting the incident light toward the back-drilled hole 103 .

[0210] The light emitted by the light source is split into a reference light and an incident light by a spectroscope. The incident light is projected toward the back-drilled hole 103. The incident light can be reflected at the bottom surface 1031 of the back-drilled hole 103 to form a third reflected light, and can also be reflected on the surface of the circuit board 100 to form a fourth reflected light.

[0211] S552 : Acquire third interference information of the third reflected light reflected by the bottom surface 1031 of the back-drilled hole 103 and fourth interference information of the fourth reflected light reflected by the target signal layer 121 .

[0212] The third and fourth reflected lights can return to the optical device assembly and interfere with the reference light obtained by the spectroscopic analysis. The photosensitive component can collect signals from the interference light to obtain third interference information between the third reflected light and the reference light, and fourth interference information between the fourth reflected light and the reference light.

[0213] S553 : Obtain a depth value of the back-drilled hole 103 according to the third interference information and the fourth interference information.

[0214] Based on the third interference information, the vertical position information of the bottom surface 1031 of the back-drilled hole 103 can be obtained. Based on the fourth interference information, the vertical position information of the board surface of the circuit board 100 can be obtained. Based on the vertical position information of the bottom surface 1031 of the back-drilled hole 103 and the vertical position information of the board surface of the circuit board 100, the depth difference between the bottom surface 1031 of the back-drilled hole 103 and the board surface of the circuit board 100 can be obtained. This depth difference is the hole depth of the back-drilled hole 103.

[0215] This method splits incident light into a reference beam and an incident light beam. It then uses the third reflected light reflected from the bottom surface 1031 of the back-drilled hole 103 and the fourth reflected light reflected from the surface of the circuit board 100 to interfere with the reference beam. The third and fourth interference signals are then used to accurately determine the vertical positions of the three reflected lights, thereby calculating the depth of the back-drilled hole 103. This non-contact measurement method, based on the principle of optical interference, avoids damage to the hole structure caused by mechanical contact. The high sensitivity of the interference signal to positional variations enables micron-level measurement accuracy, ensuring the accuracy of back-drilled hole 103 depth detection. This provides reliable data for determining whether the backdrilling is too deep or too shallow, helping to optimize backdrilling process parameters and improve the processing quality of the circuit board 100.

[0216] A plurality of back-drilled holes 103 are formed on the circuit board 100. The processing method of the circuit board 100 further includes obtaining depth values ​​of the plurality of back-drilled holes 103. As one embodiment of obtaining the depth values ​​of the plurality of back-drilled holes 103, please refer to Figure 15 , after forming the back drill hole 103, further comprising: S561: Obtain the focal depth of the measuring instrument.

[0217] The measuring instrument transmits light into the circuit board 100 and back-drilled hole 103 and receives reflected light to determine the actual hole depth of the back-drilled hole 103. The measuring instrument has a defined depth of focus, also known as focal depth. This refers to the distance the focal point (focal plane) can move along the lens' optical axis while maintaining a clear image. In other words, once the focal position is determined, a clear image can be obtained within the focal depth range.

[0218] S562: Divide the depth measurement intervals into multiple intervals according to the focal depth.

[0219] Specifically, multiple depth measurement intervals are divided according to the focal depth, such that the interval distance of each depth measurement interval is less than or equal to the focal depth. This ensures that when the focus of the measuring instrument is within the depth measurement interval, the back-drilled hole 103 within the depth measurement interval can be accurately measured. The theoretical hole depth of each back-drilled hole 103 is divided into each depth measurement interval.

[0220] By dividing the circuit board 100 into measurement areas, the measuring instrument not only avoids repeated depth measurements of the back-drilled holes 103, but also improves the efficiency of measuring the depth of the back-drilled holes 103. Furthermore, the measuring instrument can sequentially measure the depth of the back-drilled holes 103 in each measurement area of ​​the circuit board 100, ensuring that each back-drilled hole 103 can be detected.

[0221] S563: Adjust the height of the measuring instrument so that the focus of the measuring instrument is located in different depth measurement intervals.

[0222] When the focus of the measuring instrument moves to any depth measurement interval, each measurement area in the circuit board 100 needs to be moved sequentially in the vertical direction of the measuring instrument to ensure that the depth of all back-drilled holes 103 in the entire circuit board 100 whose theoretical hole depth is within the depth measurement interval can be measured, and the depth measurement accuracy of each back-drilled hole 103 can be guaranteed. At the same time, the number of vertical movements of the measuring instrument is equal to the number of depth measurement intervals. This greatly reduces the number of vertical movements of the measuring instrument and reduces the shaking of the measuring instrument caused by movement, thereby protecting the optical components in the measuring instrument and improving the testing stability and long-term service life of the measuring instrument. In addition, when the focus corresponding to the initial position of the measuring instrument is in the first depth measurement interval, the number of vertical movements of the measuring instrument is one less than the number of depth measurement intervals, further reducing the number of vertical movements of the measuring instrument.

[0223] S564 , measuring the depths of the back-drilled holes 103 of different depths in the circuit board 100 using a measuring instrument.

[0224] Specifically, a first distance D1 between the first surface 10a of the circuit board 100 is measured by a measuring instrument, and then a second distance D2 between the bottom surface 1031 of the back-drilled hole 103 is measured by a measuring instrument. Then, the depth value of the back-drilled hole 103 is obtained by the difference between the first distance D1 and the second distance D2.

[0225] The depth detection method in this embodiment divides the depth measurement intervals according to the focal depth of the measuring instrument and sequentially adjusts the height of the measuring instrument so that the focus of the measuring instrument is sequentially located in different depth measurement intervals. This allows the actual hole depths of the back-drilled holes 103 in the different depth measurement intervals to be accurately measured sequentially. This allows not only the actual hole depths of each back-drilled hole 103 in the circuit board 100 to be measured using the same measuring instrument, but also ensures that each back-drilled hole 103 is measured within the focal depth range of the measuring instrument, thereby ensuring the depth measurement accuracy of each back-drilled hole 103.

[0226] Please combine Figure 16 During the processing of the circuit board 100, a full-process data management can be established, including the following steps: P1. Before drilling the circuit board 100 for the first time, it also includes: correcting the drill tape data for the first drilling by reading the first data in the first tag. A first tag is generated on the circuit board 100. The first data includes the measurement data of the target signal layer 121 before the first drilling and the processing data of the previous process.

[0227] After the lamination process, the circuit board 100 generates a first label containing first data (which can be encoded in the form of a Quick Response Matrix (QR) code). This first data includes measurement data of the target signal layer 121 before the first drilling (such as interlayer alignment data obtained through X-ray inspection technology) and processing data from previous processes (such as the lamination process). Before the first drilling, the first label is scanned and the first data is uploaded to the cloud. This data is used to compensate the Gerber file, generate appropriate drill tape data for the first drilling, and correct the drill bit path and parameters to ensure that the first drilling is precisely aligned with the target signal layer 121, reducing positioning errors caused by lamination deviations.

[0228] P2. After obtaining the vertical position information of the target signal layer 121, the method further includes: generating a second label on the circuit board 100, wherein the second label stores second data, and the second data includes measurement data of the target through hole 101 and the target signal layer 121 after the first drilling.

[0229] After the first drilling process forms a through-hole, the horizontal position of the target through-hole 101, the vertical position of the target signal layer 121, and the thickness of the interlayer dielectric are measured and acquired. These data together constitute the second data. A new QR code is generated on the circuit board 100 as a second label, storing the second data therein, uniquely binding this critical data to the circuit board 100. Simultaneously, the second data is uploaded to the cloud, providing an accurate basis for generating the drill tape for the subsequent second drilling process and laying the foundation for data traceability and process integration.

[0230] P3. Before performing the second drilling, the method further includes: correcting the drill belt data for the second drilling by reading the second data in the second tag.

[0231] Before the second drilling, the QR code is scanned to read the second data from the second tag. The cloud then compensates the Gerber file based on this data to generate drill strip data for the second drilling. This drill strip data allows for targeted adjustments to the backdrilling depth and position, ensuring precise control of the stump length during backdrilling 103, avoiding damage to the target signal layer 121, and achieving high-precision machining for the second drilling.

[0232] P4. After the second drilling is performed, the method further includes: generating a third tag on the circuit board 100, wherein the third tag stores third data, the third data including data related to residual piles and data related to residual copper in the hole wall, and correcting the first data according to the third data.

[0233] After the second drilling process forms back-drilled hole 103, back-drilled hole 103 undergoes quality inspection to collect data related to the stump, such as its length and shape, as well as data related to the residual copper in the hole wall, such as its area and distribution. This data constitutes the third data. A new QR code is then generated on circuit board 100 as a third tag, and the third data is stored therein, uniquely associated with the circuit board 100 and uploaded to the cloud. Based on a comparison and analysis of the third data with the first data, if problems such as excessive stump length or excessive residual copper in the hole wall are detected, the source of the deviation is traced back to the measurement data of the target signal layer 121 before the first drilling and the processing data from the previous process. The source of the deviation is then corrected in the first data. For example, if the excessive stump length is due to errors in interlayer alignment data, the interlayer alignment data in the first data is corrected, providing a more accurate initial data basis for the subsequent processing of circuit boards 100 of the same batch or similar type.

[0234] Furthermore, this third-level data can be fed back into the Laser Direct Imaging (LDI) process, allowing issues like residual copper distribution on the via wall and residual stub position deviation to be traced back to the exposure accuracy of the circuit pattern during the LDI process (e.g., line width deviation and pattern alignment error). By analyzing the correlation between this third-level data and LDI process parameters, adjustments can be made to the LDI laser exposure focal length, path, or pattern compensation values ​​to optimize the edge alignment between the signal layer 12 circuit and the via ring. This reduces residual copper or residual stub anomalies caused by pattern deviation, further improving the accuracy of pattern transfer on the PCB 100 and strengthening the collaborative optimization capabilities of the entire process.

[0235] This full-process data management solution uses QR codes to achieve precise binding of processing and measurement data and full-process traceability, and uses cloud-based data compensation to generate drill tapes to ensure that the parameters of the two drillings dynamically match the actual state of the circuit board 100, significantly improving processing accuracy. Key data is fed back to the pressing and LDI processes to form a closed-loop control, which can continuously optimize process parameters and reduce systematic errors. At the same time, the quality inspection data after backdrilling (residual piles, residual copper in the hole wall, etc.) is linked with the full-process data to provide a basis for quality analysis and process improvement, effectively improving the processing yield and performance stability of the circuit board 100, and meeting the stringent requirements of the CNC field for high-frequency signal transmission.

[0236] The embodiment of the present application further provides a circuit board 100 , which can be manufactured by the above processing method. The circuit board 100 has multiple performance advantages: First, relying on the precise positioning and compensation mechanism of the two drillings (such as measuring the vertical position of the target signal layer 121 based on the horizontal position of the target through-hole 101 and correcting the backdrilling parameters), the back-drilled hole 103 and the through-hole are aligned with extremely high accuracy, and the residual pile length is strictly controlled within a preset range, effectively reducing interference and loss in high-frequency signal transmission and ensuring signal integrity. Second, by combining non-destructive measurement and optical inspection to accurately control the position of the signal layer 12, the thickness of the interlayer dielectric, and the backdrilling quality, the interlayer structural stability and electrical connection reliability of the circuit board 100 are significantly improved, and the risks of defects such as line damage and residual copper in the hole wall are reduced. Third, full-process data management (labeled traceability and data reverse correction) ensures that the parameters of each process are dynamically matched to the actual status, resulting in strong process consistency and high product yield. Fourth, it adapts to the strict requirements of the CNC field on equipment response speed and anti-interference capability, demonstrates excellent operational stability in scenarios with rapid high-frequency signal transmission, and has broad industrial application value.

[0237] The above descriptions are merely some specific embodiments of the present application and specifically describe the technical principles of the present application. These descriptions are intended only to explain the principles of the present application and should not be construed in any way as limiting the scope of protection of the present application. Based on the explanations herein, any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present application, as well as other specific implementations of the present application that can be conceived by those skilled in the art without inventive effort, shall be included within the scope of protection of the present application.

Claims

1. A circuit board processing method, characterized in that: include: Drilling the circuit board for the first time to form multiple through holes; Acquiring horizontal position information of a target through hole among the plurality of through holes; Measuring the vertical position of a target signal layer corresponding to the target through hole according to the horizontal position information of the target through hole, and obtaining the vertical position information of the target signal layer, wherein the target signal layer is exposed on the hole wall of the through hole; According to the vertical position information of the target signal layer, a second drilling is performed at the target through-hole position of the circuit board to form a back-drilled hole, and the length of the stub after the second drilling is within a preset range.

2. The circuit board processing method according to claim 1, wherein: Before drilling the circuit board for the first time, the method further includes: Acquiring horizontal position information of each signal layer in the circuit board; The position of the first drilling is determined according to the horizontal position information of each signal layer.

3. The circuit board processing method according to claim 2, wherein: The acquiring of horizontal position information of each signal layer in the circuit board includes: identifying the signal layer by non-destructive measurement; Horizontal position information of each signal layer is measured.

4. The circuit board processing method according to claim 1, wherein: Before drilling the through hole position of the circuit board for the second time, the method further includes: Acquiring horizontal position information of the target signal layer in the horizontal direction; The target position of the second drilling is compensated and corrected according to the horizontal position information of the target signal layer.

5. The circuit board processing method according to claim 1, wherein: After the first drilling of the circuit board, the method further includes: Obtaining interlayer dielectric thickness information of the circuit board.

6. The circuit board processing method according to claim 5, wherein: Obtaining the interlayer dielectric thickness information of the circuit board includes: Applying an AC signal of a predetermined frequency to the drill bit in advance; A circuit is formed between the drilling platforms through the circuit board; Determining vertical position information of each signal layer by the amplitude of the electrical signal in the loop; determining the thickness of the interlayer dielectric according to the vertical position information of each of the signal layers; The depth of the backdrilled hole is determined according to the thickness of the interlayer dielectric.

7. The circuit board processing method according to claim 1, wherein: The acquiring vertical position information of the target signal layer in the vertical direction includes: The vertical position information of the target signal layer is obtained by optical measurement or non-destructive measurement.

8. The circuit board processing method according to claim 7, wherein: The obtaining of vertical position information of the target signal layer by an optical measurement method includes: Projecting an incident light onto the hole wall of the through hole and obtaining a projection angle of the incident light; Changing the projection angle of the incident light so that the projection position of the incident light on the hole wall of the through hole moves along the vertical direction, and the reflected light reflected by the hole wall of the through hole is emitted toward the light intensity meter; receiving, by a light intensity meter, reflected light from the hole wall of the through hole, and generating a light intensity signal according to the reflected light; The vertical position information of the target signal layer is acquired according to the change of the light intensity signal and the projection angle of the incident light.

9. The circuit board processing method according to claim 7, wherein: The obtaining of vertical position information of the target signal layer by an optical measurement method includes: Projecting the incident light obliquely toward the through hole, and allowing the incident light to pass through the dielectric layer of the circuit board and irradiate the target signal layer; receiving, by an interferometer, the reflected light reflected by the target signal layer, and obtaining interference information formed by the interference of the reflected light and the reference light; The vertical position information of the target signal layer is obtained according to the interference information and the inclination information of the incident light.

10. The circuit board processing method according to claim 1, wherein: After forming the back drilling hole, the method further includes: Obtaining the depth value of the back-drilled hole, and / or, Obtaining the length of the residual pile in the back-drilled hole, and / or Obtain a deviation value between a central axis of the back-drilled hole and a central axis of the through hole.

11. The circuit board processing method according to claim 1, wherein: After forming the back drilling hole, the method further includes: Aim the target through-hole with a CCD camera to obtain the center coordinates of the target through-hole; Aligning the CCD camera with the back-drilled hole to obtain the center coordinates of the back-drilled hole; A hole position deviation value of the back-drilled hole is determined according to the center coordinates of the target through hole and the center coordinates of the back-drilled hole.

12. The circuit board processing method according to claim 1, wherein: After forming the back drilling hole, the method further includes: The multi-color light is sequentially split and focused and then emitted toward the back-drilled hole; Acquire first spectrum information of a first reflected light reflected by a bottom surface of the back-drilled hole and second spectrum information of a second reflected light reflected by the target signal layer; A depth value of the back-drilled hole is obtained according to the first spectral information; or a length value of a stump in the back-drilled hole is obtained according to the first spectral information and the second spectral information.

13. The circuit board processing method according to claim 1, wherein: After forming the back drilling hole, the method further includes: projecting an incident light toward the back-drilled hole; Acquiring a first interference image formed by the incident light through an area scan camera; Determining a first distance value from the area scan camera to the board surface where the opening of the back-drilled hole is located based on the first interference image; Controlling the area scan camera to move a second distance value, and acquiring a second interference image formed by the incident light through the area scan camera; determining a third distance value from the area scan camera to the bottom surface of the back-drilled hole according to the second interference image; A depth value of the back-drilled hole is obtained according to the first distance value, the second distance value, and the third distance value.

14. The circuit board processing method according to claim 1, wherein: After drilling the circuit board for the first time, the method further includes: A metal layer is formed on the hole wall of the through hole.

15. The circuit board processing method according to claim 1, wherein: Before drilling the circuit board for the first time, the method further includes: correcting drill tape data for the first drilling by reading first data in a first tag, wherein the first tag is generated on the circuit board, and the first data includes measurement data of the target signal layer before the first drilling and processing data of a previous process; After obtaining the vertical position information of the target signal layer, the method further includes: generating a second label on the circuit board, wherein the second label stores second data, and the second data includes measurement data of the through hole and the target signal layer after the first drilling; Before performing the second drilling, the method further includes: correcting the drill belt data of the second drilling by reading the second data in the second tag; After the second drilling, the method further includes: generating a third label on the circuit board, wherein the third label stores third data, the third data including data related to residual piles and data related to residual copper in hole walls, and correcting the first data according to the third data.

16. A circuit board, characterized in that: The circuit board is manufactured by the circuit board processing method according to any one of claims 1 to 15.

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