A method for measuring the inner layer copper depth of a printed circuit board and an apparatus for implementing it.

Abstract

This invention relates to the field of printed circuit board (PCB) measurement technology, and discloses a method for measuring the inner layer copper depth of a PCB and an apparatus for implementing it. The method includes: using a confocal measuring lens to acquire the theoretical Z-coordinates zTop and zBtm of the upper and lower surfaces of the board at a preset position near the hole to be measured; inserting an optical probe into the hole and simultaneously acquiring data on the probe's depth and the wavelength of reflected light from the imaging module, generating a wavelength-to-position curve; using zTop, zBtm, and a preset burial depth k as references, identifying the actual coordinates rTop and rBtm of the upper and lower surfaces and the actual coordinates rDep of the inner layer copper from the curve; and calculating the actual burial depth of the inner layer copper based on rTop and rDep or rDep and rBtm. This invention uses theoretical coordinates to guide the search for reflected light peaks, solving the problem of difficulty in capturing signals from highly reflective surfaces, and possesses calibration and fault-tolerant measurement capabilities, resulting in high measurement accuracy and strong adaptability.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board measurement technology, and in particular to a method for measuring the inner copper depth of a printed circuit board and an apparatus for implementing it. Background Technology

[0002] In printed circuit board (PCB) manufacturing, accurate measurement of the inner copper layer embedment depth is crucial for controlling the processing precision of steps such as back drilling. Currently, the industry commonly uses in-hole optical inspection to measure the inner copper layer embedment depth: an optical probe is inserted into the hole to be inspected, and an imaging module collects the annular reflected light signal from the hole wall. The layer position is located based on the reflected light peaks corresponding to different copper layers, and then the embedment depth parameters of the inner copper layer are calculated. This type of inspection method requires the Z-axis coordinates of the upper and lower surfaces of the board as the reference value for depth calculation; the accuracy of the reference measurement directly determines the accuracy of the final inner copper layer embedment depth detection.

[0003] In existing technologies, the Z-axis coordinates of the upper and lower surfaces of a PCB board are typically obtained by pressing a contact displacement sensor down into the area around the hole. This contact measurement method has significant limitations: for thinner PCB boards, the pressure from the sensor causes slight bending deformation, resulting in a deviation between the measured surface coordinates and the true values, introducing systematic errors into the calculation of the inner copper layer depth; furthermore, when the copper layer on the PCB surface has high reflectivity, the strong surface reflection light and ambient stray light interfere with each other, making it difficult for the in-hole optical detection system to stably and accurately identify the reflected light peaks representing the upper and lower surfaces of the board. This significantly reduces the success rate of capturing the lower surface wave of highly reflective boards, and in extreme cases, it may even be impossible to complete the complete inner copper layer burial depth detection. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention is proposed.

[0005] Therefore, the technical problem that this invention aims to solve is how to provide a reliable reference coordinate for the in-hole optical inspection scheme in PCB inner layer copper buried depth detection, which is not affected by board thickness and surface reflectivity.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for measuring the depth of inner copper layers in a printed circuit board, comprising: using a confocal measuring lens at a preset position on the edge of the hole to be measured to measure and obtain the first theoretical Z-coordinate zTop of the upper surface and the second theoretical Z-coordinate zBtm of the lower surface of the board, which serve as the theoretical Z-coordinate references for the upper and lower surfaces of the board; aligning an optical probe with the hole to be measured and inserting it into the hole; a processing unit synchronously acquiring data on the depth of the optical probe and the wavelength of reflected light acquired by the imaging module in real time, generating a curve showing the relationship between the wavelength of reflected light and the Z-axis position of the optical probe; the processing unit using the theoretical Z-coordinate references zTop and zBtm and a preset theoretical burial depth k of the inner copper layer as references to identify the actual coordinate rTop representing the upper surface of the board, the actual coordinate rBtm representing the lower surface of the board, and the actual coordinate rDep representing the inner copper layer from the curve; the processing unit calculating the actual burial depth value of the inner copper layer based on rTop and rDep, or, when measuring the board by flipping it over, calculating the actual burial depth value of the inner copper layer based on rDep and rBtm.

[0007] As a preferred embodiment of the method for measuring the inner copper depth of a printed circuit board according to the present invention, wherein: the step of measuring zTop and zBtm at a preset position on the edge of the hole to be measured using a confocal measuring lens includes: measuring the Z coordinates of the upper surface and the lower surface at a distance s from the edge of the hole on both sides of the hole to be measured, respectively, to obtain two sets of upper surface values ​​zTop1, zTop2 and two sets of lower surface values ​​zBtm1, zBtm2; taking the maximum value of zTop1 and zTop2 as zTop, and taking the minimum value of zBtm1 and zBtm2 as zBtm.

[0008] As a preferred embodiment of the method for measuring the inner layer copper depth of a printed circuit board according to the present invention, the confocal measuring lens includes an upper confocal lens and a lower confocal lens. Before measuring and obtaining zTop and zBtm, a calibration step is also included: placing a standard block on the worktable, the standard block having known upper surface coordinates zCalibup and lower surface coordinates zCalibDown; obtaining the first calibration reading rawTop_calibration of the upper confocal lens on the upper surface of the standard block, and the second calibration reading rawBtm_calibration of the lower confocal lens on the lower surface of the standard block; determining the upper surface offset zoffsetup = zCalibup - rawTop_calibration, and the lower surface offset zoffsetDown = zCalibDown + rawBtm_calibration; when measuring the hole to be measured, zTop is obtained by adding the current upper confocal lens reading rawTop to zoffsetup, and zBtm is obtained by subtracting the current lower confocal lens reading rawBtm from zoffsetDown.

[0009] As a preferred embodiment of the method for measuring the inner copper depth of a printed circuit board according to the present invention, the processing unit identifies rTop, rBtm, and rDep from the relationship curve, including: setting a first search window ΔD1, a second search window ΔD2, and a third search window ΔD3; searching for the reflected light peak representing the upper surface within the range of (zTop-ΔD1, zTop+ΔD1) to obtain rTop; searching for the reflected light peak representing the lower surface within the range of (zBtm-ΔD3, zBtm+ΔD3) to obtain rBtm; searching for the reflected light peak representing the inner copper layer within the range of (rTop - k - ΔD2, rTop - k + ΔD2) to obtain rDep; wherein, if no peak meeting the requirements is found in the first search window, zTop is directly used as rTop; and / or, if no peak meeting the requirements is found in the third search window, zBtm is directly used as rBtm.

[0010] As a preferred embodiment of the method for measuring the inner copper depth of a printed circuit board according to the present invention, wherein: when multiple candidate peaks are identified in the search window, the processing unit performs a full permutation combination of all candidate upper surface peaks, inner copper peaks and lower surface peaks, calculates a thickness score and a depth score for each combination, and obtains a comprehensive score by weighted summation of the thickness score and depth score, and selects the peak position corresponding to the combination with the highest comprehensive score as rTop, rDep and rBtm.

[0011] In a preferred embodiment of the method for measuring the inner copper depth of a printed circuit board according to the present invention, when the board is flipped over for measurement, zTop corresponds to the lower surface of the board and zBtm corresponds to the upper surface of the board. The processing unit identifies rTop, rBtm, and rDep from the relationship curve with reference to this correspondence. The actual coordinate rDep, representing the inner copper layer, is obtained by searching within a search window centered on rBtm + k. Furthermore, the processing unit calculates the actual buried depth of the inner copper layer according to the formula Rst = rDep - rBtm.

[0012] In a preferred embodiment of the method for measuring the inner copper depth of a printed circuit board according to the present invention, the weighting coefficient of the depth component is greater than the weighting coefficient of the thickness component.

[0013] A second objective of this invention is to provide an apparatus for measuring the depth of inner-layer copper on a printed circuit board, comprising: a worktable for supporting the PCB board to be measured; a standard block disposed on the worktable, having known upper and lower Z-coordinates; an upper confocal lens and a lower confocal lens for measuring the Z-coordinates of the board surface from above and below, respectively; an optical probe having a light-guiding structure at its end, capable of extending into a hole to be measured on the PCB board and projecting light onto the hole wall; an imaging module for receiving light reflected from the hole wall and acquiring reflected light wavelength data; a driving mechanism for driving the worktable, upper confocal lens, lower confocal lens, and optical probe to move relative to each other in the X, Y, and Z axes; and a processing unit electrically connected to the upper confocal lens, lower confocal lens, imaging module, and optical probe.

[0014] In a preferred embodiment of the printed circuit board inner layer copper depth measuring device of the present invention, the processing unit uses the standard block for calibration in the following ways: storing the known upper surface coordinates zCalibup and lower surface coordinates zCalibDown of the standard block; during calibration, acquiring the first calibration reading rawTop_calibration of the upper confocal lens on the upper surface of the standard block, and the second calibration reading rawBtm_calibration of the lower confocal lens on the lower surface of the standard block; calculating the upper surface offset zoffsetup = zCalibup - rawTop_calibration and the lower surface offset zoffsetDown = zCalibDown + rawBtm_calibration; during measurement, calculating the theoretical Z coordinates according to the current upper confocal lens reading rawTop and lower confocal lens reading rawBtm, using zTop = rawTop + zoffsetup and zBtm = zoffsetDown - rawBtm.

[0015] As a preferred embodiment of the printed circuit board inner layer copper depth measurement device of the present invention, the processing unit identifies rTop, rBtm and rDep by: searching for reflected light peaks in each search window centered on zTop, a second search window centered on zBtm and a third search window centered on zTop-k or zBtm+k; if no peak meeting the requirements is found in the first search window or the second search window, then zTop or zBtm is directly used as the corresponding actual coordinates rTop or rBtm.

[0016] The beneficial effects of this invention are as follows: This invention uses a confocal measuring lens to non-contactly acquire the theoretical Z-coordinate reference of the upper and lower surfaces of the board at a preset position at the hole edge, replacing the pressure measurement method of contact displacement sensors. This fundamentally eliminates the reference coordinate deviation caused by bending deformation of thin boards due to downward pressure. Simultaneously, it transforms the real-time trigger positioning mechanism into a theoretical reference-guided reflected light peak search mechanism. When dealing with high-reflectivity boards, even if the surface reflected light peaks are difficult to capture due to strong reflection and stray light interference, the theoretical coordinates can still be directly used as the actual surface position to continue searching for and calculating the depth of the inner copper peaks, achieving fault-tolerant measurement under extreme conditions. The strategy of sampling the maximum and minimum values ​​of the upper and lower surfaces on both sides can accommodate local unevenness at the hole edge, ensuring that the search window does not miss real surface signals. The multi-peak scoring mechanism further improves the measurement robustness under complex conditions. This invention provides a stable and reliable depth calculation reference for in-hole optical inspection schemes, significantly improving the adaptability and accuracy of inner copper burial depth measurement under complex conditions such as thin boards and high reflectivity. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the overall structure of the device for measuring the inner copper depth of a printed circuit board.

[0019] Figure 2 This is a partial schematic diagram of a device for measuring the depth of inner copper layers on a printed circuit board.

[0020] Figure 3 This is a schematic diagram of the standard block calibration of the present invention.

[0021] Figure 4 This is a schematic diagram of the dual-side sampling value acquisition rules of the present invention.

[0022] Figure 5 This is a schematic diagram of the relationship between the wavelength of the reflected light and the Z-axis position of the optical probe in this invention.

[0023] Figure 6 This is a schematic diagram showing the unidentified reflection peaks on the surface of the plate in this invention.

[0024] Figure 7 This is a schematic diagram illustrating the principle of the multi-peak scoring mechanism of the present invention.

[0025] Figure 8 This is a flowchart of the overall measurement method of the present invention. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0028] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it an embodiment that is mutually exclusive, either alone or selectively, with other embodiments.

[0029] Example 1, referring to Figures 1-8 This is the first embodiment of the present invention, which provides a device for measuring the depth of inner copper layers on a printed circuit board. The device includes a worktable 1, a standard block 2, an upper confocal lens 3, a lower confocal lens 4, an optical probe 5, an imaging module 6, a driving mechanism, and a processing unit.

[0030] A worktable 1 is mounted on a base 8 to support the PCB board under test. A standard block 2 is mounted on the worktable 1 and has precisely known upper surface Z-coordinates zCalibup and lower surface Z-coordinates zCalibDown, serving as a reference for calibrating the upper confocal lens 3 and the lower confocal lens 4. The drive mechanism includes a moving component 7 and slide assemblies along each axis, used to drive the worktable 1, the upper confocal lens 3, the lower confocal lens 4, and the optical probe 5 to move relative to each other in the X, Y, and Z axes. Specifically, the moving component 7 preferably uses a linear motor, including a mover mounted on the worktable 1, the first slide 81, and the second slide 82, and a stator mounted on the base 8, used to drive the relative movement of the worktable 1 along the Y direction and the first slide 81 and the second slide 82 along the X direction, achieving precise positioning of the hole under test.

[0031] The upper confocal lens 3 and the lower confocal lens 4 are preferably spectral confocal lenses, used for non-contact measurement of the Z-coordinate of the plate surface from above and below, respectively. The upper confocal lens 3 is mounted on the first slide base 81, arranged parallel to the optical probe 5 and sharing the same Z-axis slide for overall lifting. The lower confocal lens 4 is mounted on the second slide base 82, arranged parallel to the imaging module 6 and sharing another independent Z-axis slide for overall focusing. The upper confocal lens 3 and the lower confocal lens 4 maintain a defined relative positional relationship with the optical probe 5 and the imaging module 6 in the X and Y axes, respectively. This positional relationship is recorded by the processing unit after calibration and used for subsequent coordinate transformation.

[0032] An optical probe 5 is mounted on a first slide base 81, and its end has a light-guiding structure that guides incident light rays to the aperture wall. An imaging module 6 is mounted on a second slide base 82 and is used to receive light rays reflected from the aperture wall and acquire the wavelength data of the reflected light. The specific optical path structure between the optical probe 5 and the imaging module 6 can be referred to the semi-transparent lens group and light source layout disclosed in the applicant's prior patent CN 120558117B. The core of this method is to reflect the light from the light source to the end of the optical probe 5, and then reflect it back to the imaging module 6 from the aperture wall. This will not be elaborated further here.

[0033] The processing unit is electrically connected to the Z-axis grating ruler of the upper confocal lens 3, the lower confocal lens 4, the imaging module 6, the optical probe 5, and each driving component, and is configured to perform the steps of the following measurement method.

[0034] The following describes in detail the specific process of measuring the inner copper depth using the above-mentioned device.

[0035] Calibration steps:

[0036] Reference Figure 3 Before conducting batch measurements, the device needs to be calibrated. Move the first slide 81 and the second slide 82 so that the upper confocal lens 3 is directly above the upper surface of the standard block 2 and the lower confocal lens 4 is directly below the lower surface of the standard block 2, and ensure that the distance between the two and the surface of the standard block 2 is consistent with the subsequent PCB measurement. The processing unit records the reading rawTop_calibration of the upper confocal lens 3 on the upper surface of the standard block 2 and the reading rawBtm_calibration of the lower confocal lens 4 on the lower surface of the standard block 2. The absolute Z coordinates of the upper and lower surfaces of the standard block 2 in the machine coordinate system are known values, and are denoted as zCalibup and zCalibDown, respectively. The processing unit calculates the upper surface offset zoffsetup and the lower surface offset zoffsetDown according to equations (1) and (2):

[0037] zoffsetup = zCalibup - rawTop_calibration(1)

[0038] zoffsetDown = zCalibDown + rawBtm_calibration(2)

[0039] These two offsets are stored in the processing unit. Their physical meaning is as follows: adding zoffsetup to the reading of the upper confocal lens 3 yields the actual Z-coordinate of that point; subtracting zoffsetDown from the reading of the lower confocal lens 4 yields the actual Z-coordinate of that point. This calibration process establishes a mapping relationship between sensor readings and absolute physical coordinates, and can effectively eliminate system errors introduced by sensor zero drift and differences in installation height.

[0040] S1: Reference Measurement Procedure:

[0041] Reference Figure 4 The PCB board to be tested is mounted on the workbench 1 and fixed. The first hole to be tested is selected according to the preset program. The workbench 1 and the first slide base 81 and the second slide base 82 are moved so that the upper confocal lens 3 and the lower confocal lens 4 are respectively aligned with the upper and lower surface positions at a preset distance s from the edge of the hole. The distance s is preset according to process experience. In this embodiment, s = 0.1 mm is taken. In order to accommodate the local unevenness of the hole edge, sampling is performed at symmetrical positions on both sides of the hole. For the upper surface, two sets of readings rawTop1 and rawTop2 are obtained, which are converted into two sets of Z coordinate values ​​zTop1 and zTop2 according to formula (3); for the lower surface, two sets of readings rawBtm1 and rawBtm2 are obtained, which are converted into two sets of Z coordinate values ​​zBtm1 and zBtm2 according to formula (4):

[0042] zTop_i = rawTop_i + zoffsetup (i=1,2) (3)

[0043] zBtm_j = zoffsetDown - rawBtm_j (j=1,2) (4)

[0044] zTop = max(zTop_1, zTop_2)

[0045] zBtm = min(zBtm_1, zBtm_2)

[0046] The maximum value among the two sets of measurements on the upper surface is taken as the final theoretical Z-coordinate zTop of the upper surface, and the minimum value among the two sets of measurements on the lower surface is taken as the final theoretical Z-coordinate zBtm of the lower surface. This value selection logic is based on the following physical considerations: the maximum value represents the highest point of the upper surface in this region, and the minimum value represents the lowest point of the lower surface. Using this as a theoretical benchmark can ensure that the subsequent search window for reflected light peaks will not miss the real surface signal due to local depressions or bulges.

[0047] S2: Steps for obtaining the spectral curve:

[0048] After completing the baseline measurement, the first slide base 81 and the second slide base 82 are moved back to directly above and below the hole to be measured, aligning the optical probe 5 with the center of the hole. The light source is activated, and the light, after being reflected by the semi-transparent mirror group, illuminates the conical reflective film at the end of the optical probe 5, reflecting off the hole wall. Driven by the Z-axis slide, the optical probe 5 slowly extends into the hole. During this process, the processing unit synchronously records the Z-axis depth of the optical probe 5 (provided in real time by the grating ruler) and the characteristic wavelength data of the reflected light from the hole wall received by the imaging module 6 at a fixed sampling frequency, generating a curve with the Z-axis position of the optical probe 5 as the horizontal axis and the characteristic wavelength of the reflected light as the vertical axis. This curve fully records the spectral response characteristics of each layer of the hole wall to the incident light when the optical probe 5 passes through different depths within the hole.

[0049] S3: Peak Search and Extraction Steps:

[0050] Reference Figures 5-7 The processing unit first sets three search window radii: the upper surface wave search distance ΔD1, the inner layer search distance ΔD2, and the lower surface wave search distance ΔD3. Then, guided by the theoretical Z-coordinate references zTop and zBtm, it defines search intervals on the relationship curve.

[0051] Within the first search interval (zTop-ΔD1, zTop+ΔD1), find the peak of reflected light representing the upper surface of the plate.

[0052] Within the third search interval (zBtm-ΔD3, zBtm+ΔD3), search for the peak of reflected light representing the lower surface of the plate.

[0053] Based on the search results, the processing unit handles them according to the following situations:

[0054] Firstly, if a suitable peak is found in both the upper and lower surface waves, their corresponding Z-coordinates are directly recorded as the actual coordinates rTop and rBtm. Specifically, if the copper layer on the PCB surface has excessively high reflectivity or other factors cause a surface wave to fail to find a suitable peak, a fault-tolerant mechanism is activated, directly assigning the corresponding theoretical coordinate values ​​to the actual coordinates, i.e., setting rTop = zTop and / or rBtm = zBtm. This ensures that even if surface wave capture fails under extreme conditions, the system can still reliably enter the inner copper peak search phase without interrupting the measurement process. Subsequently, with rTop - k (without flipping) or rBtm + k (flipped) as the center, the system searches for inner copper peaks within a search interval with a radius of ΔD2. If a unique inner copper peak is found, it is directly identified as rDep; if multiple peaks are found, these candidate inner copper peaks are scored and the best one is selected as rDep.

[0055] Secondly, if multiple candidate peaks exist in the upper or lower surface wave (e.g., due to multi-layer structure, rough hole walls, etc.), all candidate upper and lower surface peaks are recorded. For the case where the surface is not flipped, the corresponding inner copper peak is searched within a ΔD2 window centered on rTopPeak_i - k, using each candidate upper surface peak rTopPeak_i as a reference. For the case where the surface is flipped, the corresponding inner copper peak is searched within a ΔD2 window centered on rBtmPeak_j + k, using each candidate lower surface peak rBtmPeak_j as a reference. Subsequently, all candidate upper, lower, and inner copper peaks are permuted to form several candidate combinations (rTopPeak, rDepPeak, rBtmPeak). For each combination, the thickness and depth components are calculated.

[0056] Thickness score: The score is based on the deviation between the Z-axis distance between the upper and lower surface peaks and the theoretical thickness of the board, as well as the intensity of the two peaks. The smaller the deviation and the higher the peak intensity, the higher the thickness score.

[0057] Depth score: Based on (rTopPeak, rDepPeak) when the surface is not flipped, and based on (rBtmPeak, rDepPeak) when the surface is flipped, the deviation between the distance between the two peaks in the combination and the theoretical burial depth k, as well as the intensity of the two peaks, are evaluated. The smaller the deviation and the higher the intensity, the higher the depth score.

[0058] Next, the thickness and depth scores are weighted and summed to obtain the overall score of the combination. Preferably, the depth score weighting coefficient is set to 75%, and the thickness score weighting coefficient is set to 25%. Experimental verification shows that this weighting ratio can minimize the overall measurement error of the final selected peak combination under actual working conditions. The processing unit finally selects the combination with the highest overall score and uses its corresponding peak position as the final rTop, rDep, and rBtm.

[0059] S4: Depth calculation steps:

[0060] For a standard measurement orientation (optical probe 5 extends from the front of the plate), the actual burial depth of the inner copper layer is calculated according to formula (5):

[0061] Rst = rTop - rDep (5)

[0062] For the special case where the board is thick and the inner copper layer to be measured is very close to the top surface, if the optical probe 5 still enters from the front, the distance between the lower imaging module 6 and the end of the optical probe 5 is too far, and the received reflected light signal is greatly attenuated, which may not be able to reliably capture the peak. At this time, the PCB board needs to be flipped over and all the above measurement steps need to be performed. After flipping, the original upper surface of the board is facing down and the original lower surface is facing up. At this time, the upper confocal lens 3 measures the original lower surface (now facing up), and the lower confocal lens 4 measures the original upper surface (now facing down). Therefore, zTop corresponds to the lower surface of the board and zBtm corresponds to the upper surface of the board. The processing unit adjusts the search benchmark of the inner copper peak accordingly: the actual coordinate rDep of the inner copper is changed to be searched within the search interval with rBtm + k as the center and a radius of ΔD2. The final buried depth value is calculated according to formula (6):

[0063] Rst = rDep - rBtm (6)

[0064] Equation (6) is mathematically equivalent to Equation (5), both reflecting the vertical distance of the inner copper layer relative to its nearest surface.

[0065] Example 2, refer to Figure 8 This is the second embodiment of the present invention, which illustrates the above process by combining a set of simulation calibration and measurement data.

[0066] Suppose the values ​​obtained during the calibration process at a certain workstation are as follows:

[0067] zCalibup = 2.000mm, zCalibDown = -1.000mm;

[0068] During calibration, the reading of the upper confocal lens 3 (rawTop_calibration) is 15.500mm, and the reading of the lower confocal lens 4 (rawBtm_calibration) is 15.300mm.

[0069] According to equations (1) and (2), we can calculate:

[0070] zoffsetup = 2.000 - 15.500 = -13.500mm,

[0071] zoffsetDown = -1.000 + 15.300 = 14.300mm.

[0072] Subsequently, a hole to be tested on a mass-produced PCB board was measured. The confocal lens was moved to a sampling point s=0.1mm from the hole edge, and the current readings rawTop = 15.480mm and rawBtm = 15.320mm were obtained. Substituting into equations (3) and (4), we get:

[0073] zTop = 15.480 + (-13.500) = 1.980mm,

[0074] zBtm = 14.300 - 15.320 = -1.020mm.

[0075] It can be known that the thickness of the plate is 1.980 - (-1.020) = 3.000mm. After sampling from both sides and taking the maximum value, we assume that zTop = 1.980mm and zBtm = -1.020mm.

[0076] Next, a peak search is performed. ΔD1 = ΔD3 = 0.020mm, ΔD2 = 0.015mm, and the theoretical burial depth k = 0.500mm. In the relationship curve, the upper surface reflection peak is successfully captured within the window (1.960, 2.000), corresponding to the position rTop = 1.982mm; the lower surface reflection peak rBtm = -1.018mm is captured within the window (-1.040, -1.000). Furthermore, the inner copper peak rDep = 1.485mm is found within the interval (1.982 - 0.500 - 0.015, 1.982 - 0.500 + 0.015), i.e., (1.467, 1.497). Therefore, the inner copper burial depth Rst = 1.982 - 1.485 = 0.497mm. If no effective peak is detected in the upper surface window due to high reflectivity, then directly set rTop = zTop = 1.980mm, and continue to search for rDep based on this. The burial depth is calculated to be 1.980 - 1.485 = 0.495mm, which can still effectively complete the measurement.

[0077] The original readings of the confocal lens are mapped to the absolute physical coordinate system through calibration using standard block 2, eliminating long-term sensor drift and installation deviations, and providing a reliable coordinate origin for all subsequent measurements. Non-contact measurements are performed on both sides of the hole edge, and the maximum value on the upper surface and the minimum value on the lower surface are taken as the theoretical Z-reference. This avoids bending deformation of the thin plate caused by contact sensors and provides a reliable local containment reference for peak search. When the optical probe 5 extends into the hole, the wavelength-position relationship curve of the reflected light throughout the entire path is recorded simultaneously, changing "real-time point triggering" to "post-curve analysis," so that the longitudinal information within the entire hole is completely preserved. Guiding the search window with the theoretical reference can significantly reduce the risk of missed surface peaks due to factors such as high reflectivity; the fault-tolerance mechanism and intelligent multi-peak scoring mechanism further ensure that the true position of each layer can still be accurately extracted under extreme or complex working conditions. Finally, the true buried depth of the inner copper relative to the nearest surface is obtained directly by the difference between rTop and rDep or rDep and rBtm. This value can be directly used for depth compensation in precision machining processes such as back drilling, thus realizing a complete closed loop from benchmark establishment to accurate output.

[0078] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for measuring the inner layer copper depth of a printed circuit board, characterized in that, include: Using a confocal measuring lens at a preset position on the edge of the hole to be measured, the first theoretical Z coordinate zTop of the upper surface of the board and the second theoretical Z coordinate zBtm of the lower surface are measured and obtained, which serve as the theoretical Z coordinate references for the upper and lower surfaces of the board. The optical probe is aligned with the hole to be tested and inserted into the hole. The processing unit collects the depth of the optical probe and the wavelength data of the reflected light obtained by the imaging module in real time and synchronously, and generates a curve showing the relationship between the wavelength of the reflected light and the position of the optical probe along the Z-axis. The processing unit uses the theoretical Z-coordinate references zTop and zBtm and a preset theoretical burial depth k of the inner copper layer as a reference to identify the actual coordinates rTop representing the upper surface of the plate, rBtm representing the lower surface of the plate, and rDep representing the inner copper layer from the relationship curve. The processing unit calculates the actual burial depth of the inner copper layer based on rTop and rDep, or, when measuring the plate surface, calculates the actual burial depth of the inner copper layer based on rDep and rBtm. The processing unit identifies rTop, rBtm, and rDep from the relationship curve, including: Set the first search window ΔD1, the second search window ΔD2, and the third search window ΔD3; Search for the reflected light peak representing the upper surface within the range of (zTop-ΔD1, zTop+ΔD1) to obtain rTop; Search for the reflected light peak representing the lower surface within the range of (zBtm-ΔD3, zBtm+ΔD3) to obtain rBtm; Search for the reflected light peak representing the inner copper layer within the range of (rTop - k - ΔD2, rTop - k + ΔD2) to obtain rDep; Specifically, if no peak meeting the requirements is found in the first search window, zTop is directly used as rTop; and / or, if no peak meeting the requirements is found in the third search window, zBtm is directly used as rBtm.

2. The method for measuring the inner layer copper depth of a printed circuit board according to claim 1, characterized in that, The method of measuring zTop and zBtm at a preset position on the edge of the hole to be measured using a confocal measuring lens includes: Measure the Z coordinates of the upper and lower surfaces at distances s from the edge of the hole on both sides of the hole to be tested, and obtain two sets of upper surface values ​​zTop1, zTop2 and two sets of lower surface values ​​zBtm1, zBtm2. The maximum value between zTop1 and zTop2 is taken as zTop, and the minimum value between zBtm1 and zBtm2 is taken as zBtm.

3. The method for measuring the inner layer copper depth of a printed circuit board according to claim 1 or 2, characterized in that, The confocal measurement lens includes an upper confocal lens and a lower confocal lens. Before measuring and obtaining zTop and zBtm, a calibration step is also included: A standard block is placed on the worktable. The standard block has known upper surface coordinates zCalibup and lower surface coordinates zCalibDown. Obtain the first calibration reading rawTop_calibration of the upper confocal lens on the upper surface of the standard block, and the second calibration reading rawBtm_calibration of the lower confocal lens on the lower surface of the standard block; Determine the upper surface offset zoffsetup = zCalibup - rawTop_calibration, and the lower surface offset zoffsetDown = zCalibDown + rawBtm_calibration; When measuring the aperture to be measured, zTop is obtained by adding the current upper confocal lens reading rawTop to zoffsetup, and zBtm is obtained by subtracting the current lower confocal lens reading rawBtm from zoffsetDown.

4. The method for measuring the inner layer copper depth of a printed circuit board according to claim 1, characterized in that, When multiple candidate peaks are identified within the search window, the processing unit performs a full permutation of all candidate upper surface peaks, inner copper peaks, and lower surface peaks, calculates thickness and depth scores for each combination, and performs a weighted summation of the thickness and depth scores to obtain a comprehensive score. The peak position corresponding to the combination with the highest comprehensive score is selected as rTop, rDep, and rBtm.

5. The method for measuring the inner layer copper depth of a printed circuit board according to claim 1, characterized in that, When the board is flipped over for measurement, zTop corresponds to the lower surface of the board and zBtm corresponds to the upper surface of the board. The processing unit uses this correspondence as a reference to identify rTop, rBtm and rDep from the relationship curve. The actual coordinate rDep, which represents the inner copper layer, is obtained by searching within a search window centered on rBtm+k. Furthermore, the processing unit calculates the actual burial depth of the inner copper layer according to the formula Rst = rDep - rBtm.

6. The method for measuring the inner layer copper depth of a printed circuit board according to claim 4, characterized in that, The weighting coefficient of the depth component is greater than the weighting coefficient of the thickness component.

7. A device for measuring the inner layer copper depth of a printed circuit board, used to implement the method for measuring the inner layer copper depth of a printed circuit board as described in any one of claims 1 to 6, characterized in that, include: The workbench is used to support the PCB board to be tested. A standard block, set on the worktable, has known upper surface Z-coordinates and lower surface Z-coordinates; The upper confocal lens and the lower confocal lens are used to measure the Z coordinate of the plate surface from above and below, respectively; An optical probe with a light-guiding structure at its end can extend into the hole to be tested on a PCB board and project light onto the hole wall. An imaging module is used to receive light reflected from the aperture wall and acquire the wavelength data of the reflected light; A drive mechanism is used to drive the worktable, upper confocal lens, lower confocal lens and optical probe to move relative to each other in the X, Y and Z axis directions; The processing unit is electrically connected to the upper confocal lens, the lower confocal lens, the imaging module, and the optical probe, and is configured to perform the steps of the method as described in any one of claims 1 to 6.

8. The printed circuit board inner layer copper depth measuring device according to claim 7, characterized in that, The specific method by which the processing unit performs calibration using the standard block is as follows: Store the known upper surface coordinates zCalibup and lower surface coordinates zCalibDown of the standard block; During calibration, the first calibration reading rawTop_calibration of the upper confocal lens on the upper surface of the standard block and the second calibration reading rawBtm_calibration of the lower confocal lens on the lower surface of the standard block are obtained. Calculate the upper surface offset zoffsetup = zCalibup - rawTop_calibration and the lower surface offset zoffsetDown = zCalibDown + rawBtm_calibration; During measurement, the theoretical Z coordinates are calculated based on the current upper confocal lens reading rawTop and the lower confocal lens reading rawBtm, according to zTop = rawTop + zoffsetup and zBtm = zoffsetDown - rawBtm.

9. The printed circuit board inner layer copper depth measuring device according to claim 7, characterized in that, The processing unit identifies rTop, rBtm, and rDep in the following ways: The reflected light peaks are searched within the first search window centered on zTop, the second search window centered on zBtm, and the third search window centered on zTop-k or zBtm+k, respectively. If no matching peak is found in the first or second search window, zTop or zBtm is directly used as the corresponding actual coordinates rTop or rBtm.

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