Layer deviation detection system and method for multilayer printed circuit board

Abstract

The invention belongs to the technical field of circuit board manufacturing, and discloses a layer deviation detection system and method for a multilayer printed wiring board, and the method comprises the steps: obtaining real-time images and coordinate data of a detection hole and an inner-layer isolation ring through an automatic optical detection device, and carrying out the feature extraction of the real-time images of the detection hole and the inner-layer isolation ring; constructing an offset calculation model, determining the center offset, the offset direction angle and the dynamic offset trend by using the offset calculation model, and judging the layer offset tolerance; a compensation instruction is generated through a PID algorithm, and the compensation amount of the drilling machine table is adjusted; and recording offset data, updating parameters of the offset calculation model, and detecting the offset again. According to the invention, by designing the layer deviation detection module, poor layer deviation quality can be tested during normal electrical testing, no process is added, high-precision input of data is realized, and a reliable basis is provided for subsequent calculation; during normal electrical testing, the multi-layer board layer deviation can be effectively prevented from flowing to a next process or a client, the efficiency is improved, and the response is accelerated.

Description

Technical Field

[0001] The present invention belongs to the technical field of circuit board manufacturing, and in particular relates to a layer deviation detection system and method for a multi-layer printed circuit board. Background Art

[0002] A printed circuit board (PCB), also known as a printed circuit board, is an important electronic component that supports electronic components and acts as a carrier for their electrical connections. A multilayer PCB is a multilayer circuit board used in electrical products, utilizing more single-sided or double-sided wiring boards. PCBs with one double-sided inner layer and two single-sided outer layers, or two double-sided inner layers and two single-sided outer layers, are alternately joined together using a positioning system and insulating adhesive materials, with conductive patterns interconnected according to design requirements. These boards become high-layer printed circuit boards (PCBs) with four or six or more layers, also known as multilayer printed circuit boards.

[0003] Detecting layer misalignment between adjacent inner core boards is typically performed using X-ray inspection machines. This results in low measurement efficiency and limited testing of sampled boards. The data obtained cannot accurately support optimization of the preventive ratio of printed circuit boards on inner core boards. Furthermore, it is impossible to accurately identify and issue scrap warnings for products with excessive adjacent layer misalignment. Abnormal PCBs must be tested before defects are discovered, resulting in costly problems. The inability to accurately identify adjacent layer misalignment makes it impossible to meet the technical control requirements for layer misalignment in products with higher signal transmission requirements in the future.

[0004] Currently, overall layer misalignment detection relies on X-drill drones for identification, followed by manual sorting. This is not only inefficient but also prone to errors, resulting in scrapping of boards due to abnormal layer misalignment. Unqualified PCBs cannot be accurately and proactively scrapped, leading to unnecessary process costs.

[0005] Through the above analysis, the problems and defects of the existing technology are as follows:

[0006] (1) The layer deviation detection method for adjacent inner core boards has low measurement efficiency and can only detect random boards. The data obtained cannot accurately support the optimization of the prevention ratio of printed circuits on inner core boards.

[0007] (2) It is impossible to accurately identify products with excessive deviations in adjacent layers of online PCB boards and issue scrap warnings. Abnormal PCB boards must be tested to find defects, resulting in cost waste. Adjacent layer deviations cannot be accurately identified, and the technical control requirements for product layer deviations with higher signal transmission requirements in the future cannot be met.

[0008] (3) The overall layer deviation detection method is inefficient, and manual judgment often makes mistakes, resulting in abnormal layer deviation and scrapping of boards; unqualified PCB boards cannot be accurately scrapped in advance, resulting in cost waste. Summary of the Invention

[0009] To overcome the problems existing in the related art, the present invention discloses a system and method for detecting layer deviation of a multilayer printed circuit board. The technical solution is as follows:

[0010] The present invention is implemented as follows: a layer deviation detection system for a multilayer printed circuit board comprises:

[0011] A data acquisition module is used to obtain real-time images and coordinate data of the detection hole and the inner isolation ring through an automatic optical detection device. The coordinate data includes the drilling position and the coordinates of the inner layer pattern;

[0012] A feature extraction module is used to extract features from the real-time images of the detection hole and the inner isolation ring to obtain the coordinates of the detection hole center, the theoretical coordinates of the inner isolation ring center, and the measured isolation ring edge point set;

[0013] The layer deviation test module is used to build an offset calculation model, use the offset calculation model to determine the center offset and direction angle, and determine the layer deviation tolerance;

[0014] The dynamic adjustment module is used to generate compensation instructions using the PID algorithm to adjust the compensation amount of the drilling machine; record offset data, update the offset calculation model parameters, and re-detect the offset.

[0015] Furthermore, a total of 6 holes are designed in the layer deviation test module, the first hole is for grounding, and the outer layer is designed as a square PAD;

[0016] The 2nd to 6th holes are detection holes, designed as circular PADs;

[0017] The distance between the detection hole and the inner isolation ring is 5, 6, 7, 8, and 9 mil respectively;

[0018] The drilling diameter is 0.2mm, which is the smallest drill needle and hole ring design in the unit.

[0019] Furthermore, when there is a process edge design, the layer deviation test module is preferentially designed on the process edge;

[0020] When there is no process edge design, two groups are designed diagonally on the PNL edge, with the diagonals being the upper left corner and the lower right corner.

[0021] Another object of the present invention is to provide a method for detecting layer deviation of a multilayer printed circuit board, the method being used to control the layer deviation detection system of the multilayer printed circuit board, the method comprising:

[0022] S1, obtaining real-time images and coordinate data of the inspection hole and the inner isolation ring through an automatic optical inspection device, the coordinate data including the drilling position and the inner layer pattern coordinates;

[0023] S2, extracting features from the real-time images of the detection hole and the inner isolation ring to obtain the coordinates of the detection hole center, the theoretical coordinates of the inner isolation ring center, and the measured isolation ring edge point set;

[0024] S3, constructing an offset calculation model, using which the center offset, offset direction angle, and dynamic offset trend are determined, and layer deviation tolerance is determined;

[0025] S4, using the PID algorithm to generate compensation instructions, adjust the compensation amount of the drilling machine; record the offset data, update the offset calculation model parameters, and re-detect the offset.

[0026] In step S2, feature extraction of the real-time image of the detection hole and the inner isolation ring includes:

[0027] Use AOI equipment to capture the top or bottom image of the inspection hole;

[0028] After de-noising the top or bottom image of the detection hole using Gaussian filtering, perform Canny edge detection, binarize the detection results, and use Hough transform to determine the coordinates of the detection hole center as (x0, y0);

[0029] Obtain the theoretical position of the inner isolation ring in the PCB design file; align the design coordinates with the image coordinates through the PCB reference point, and determine the theoretical center coordinates of the inner isolation ring as (x i ,y i );

[0030] The theoretical position of the inner isolation ring (x i ,y i ) is used as the center to define the search area; use the Canny operator or adaptive threshold segmentation to extract all non-zero pixel coordinates as the measured isolation ring edge point set {(x k ,y k )}.

[0031] Furthermore, the search area is defined and the Canny operator is used to segment and extract all non-zero pixel coordinates including:

[0032] The theoretical center of the inner isolation ring (x i ,y i ) is used as the center to define the search area image and perform Gaussian blur;

[0033] Use the Sobel operator to calculate the gradient of the search area image in the x and y directions after Gaussian blur;

[0034] The pixel with the largest amplitude is retained along the gradient direction, the edge is refined, and a binary edge map is output.

[0035] In step S3, the offset calculation model is constructed by:

[0036] The actual center fitting of the isolation ring: The measured center coordinates of the inner isolation ring are (x c ,y c ), for the measured isolation ring edge point set {(x k ,y k )} perform least squares circle fitting;

[0037]

[0038] Where r is the measured radius of the inner isolation ring.

[0039] Composite offset calculation model construction: If the inner isolation ring is deformed, then:

[0040]

[0041] Among them, α is the weight coefficient, and ellipticity is the difference between the major axis and the minor axis.

[0042] In step S3, the center offset is determined using the offset calculation model as:

[0043]

[0044] Among them, Δd is the current center offset, x0 is the horizontal coordinate of the detection hole center, y0 is the vertical coordinate of the detection hole center, x i is the abscissa of the theoretical center of the inner isolation ring, y i It is the ordinate of the theoretical center of the inner isolation ring.

[0045] The offset direction angle is:

[0046]

[0047] Where θ is the offset direction angle.

[0048] The dynamic offset trend is:

[0049]

[0050] in, is the rate of change of the current circle center offset Δd over time, Δd t is the offset at the current time t, Δd t-1 is the offset from the previous moment t-1, and Δt is the time interval between two measurements.

[0051] According to the design value of the spacing between the isolation rings, the maximum allowable offset is dynamically calculated as:

[0052] Δd max =r pad -rhole

[0053] Where Δd max is the maximum allowable offset, r pad is the radius of the detection hole, r hole is the drilling radius.

[0054] In step S4, if Δd>Δd max , then use the PID algorithm to generate compensation instructions and determine the fine-tuning coordinates of the drilling platform;

[0055] The compensation instruction generated by the PID algorithm is:

[0056]

[0057] Where u(t) is the total compensation output to the drilling machine; e(t) = Δd, which represents the current center offset; K p is the PID proportional gain coefficient, which indicates the response strength to the current error; K i is the PID integral gain coefficient, which represents the response to the historical error accumulation; K d is the PID differential gain coefficient, which represents the response to the error change trend; e(τ) represents the real-time offset error from time τ = 0 to the current time τ = t; Dτ is the time element, which represents the infinitesimal segmentation of the error in time.

[0058] After determining the fine-tuning coordinates of the drilling platform, record the offset data, update the offset calculation model parameters, and re-test the offset until Δd≤Δd is satisfied. max .

[0059] Furthermore, the calculation process of the drilling platform fine-tuning coordinates includes:

[0060] Decompose the total compensation amount u(t) of the drilling machine into X-axis and Y-axis components according to the offset direction θ;

[0061]

[0062] Read the current position coordinates (x drill ,y drill ).

[0063] The target coordinates after compensation (x new ,y new )for:

[0064]

[0065] Send instructions through PLC or motion control card.

[0066] In combination with all the above technical solutions, the beneficial effects of the present invention are as follows:

[0067] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving the problems, this paper closely combines the technical solutions to be protected by the present invention and the results and data during the research and development process, and analyzes in detail and in depth how the technical solutions of the present invention solve the technical problems, and some creative technical effects brought about by solving the problems, which are specifically described as follows:

[0068] 1. The present invention uses an automatic optical inspection device to obtain real-time images and coordinate data of the inspection hole and the inner isolation ring, achieving high-precision data input. The image resolution can reach 1μm / pixel, and the coordinate data error is less than ±0.5mil, providing a reliable basis for subsequent calculations. It is real-time, achieving millisecond-level data refresh to ensure dynamic response speed. It is fully automated, eliminating manual measurement errors and improving consistency.

[0069] 2. The present invention extracts features from real-time images of the detection hole and the inner isolation ring to obtain the theoretical center coordinates of the detection hole and the inner isolation ring and the measured edge point set of the isolation ring, thereby achieving precise positioning. The Hough transform has strong noise resistance and the center positioning error is <±0.2mil; the edge point set fitting can handle non-ideal circles, adapt to deformation, and improve robustness; ROI local processing reduces 90% of the calculation amount, improves efficiency, and accelerates response.

[0070] 3. The present invention constructs an offset calculation model, uses the offset calculation model to determine the center offset, offset direction angle and dynamic offset trend, and determines the layer deviation tolerance to achieve quantitative evaluation, clarify the offset and direction, and guide precise compensation; suppress overshoot in advance through differential terms, predict trends, and reduce oscillations; use dynamic tolerance judgment to support adaptive processes and achieve intelligent decision-making.

[0071] 4. The present invention uses a PID algorithm to generate compensation instructions, adjust the compensation amount of the drilling machine, and eliminate steady-state errors; record offset data, update the offset calculation model parameters, and re-test the offset. The model is updated online to adapt to long-term drift such as equipment aging and material changes. A real-time detection-compensation-verification cycle is implemented, and the final offset is ≤1 mil, which improves the efficiency and accuracy of measuring the offset data of adjacent layers and the overall layer offset of the PCB board.

[0072] Second, considering the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are described in detail as follows:

[0073] The present invention can test poor layer deviation quality during normal electrical testing by designing a layer deviation detection module without adding any process. During normal electrical testing, the present invention can effectively prevent the layer deviation of the multilayer board from flowing to the next process or the client.

[0074] The design of the present invention can ensure the process control of its PCB production quality and reduce defects. Even if the layer deviation is scrapped, it can be intercepted in the factory through electrical testing and will not flow to the client to cause PCBA scrap losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure;

[0076] Figure 1 This is a flow chart of a method for detecting layer deviation of a multilayer printed circuit board provided by an embodiment of the present invention;

[0077] Figure 2 It is a schematic diagram of the design of a layer deviation test module provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0078] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0079] Example 1, as Figure 1 As shown, the layer deviation detection method of the multilayer printed circuit board provided by the embodiment of the present invention specifically includes the following steps:

[0080] S1, obtaining real-time images and coordinate data of the inspection hole and the inner isolation ring through an automatic optical inspection device, the coordinate data including the drilling position and the inner layer pattern coordinates;

[0081] S2, extracting features from the real-time images of the detection hole and the inner isolation ring to obtain the coordinates of the detection hole center, the theoretical coordinates of the inner isolation ring center, and the measured isolation ring edge point set;

[0082] S3, constructing an offset calculation model, using which the center offset, offset direction angle, and dynamic offset trend are determined, and layer deviation tolerance is determined;

[0083] S4, using the PID algorithm to generate compensation instructions, adjust the compensation amount of the drilling machine; record the offset data, update the offset calculation model parameters, and re-detect the offset.

[0084] The present invention performs feature extraction on the real-time image of the detection hole and the inner isolation ring, including:

[0085] Use AOI equipment to capture the top or bottom image of the inspection hole;

[0086] After de-noising the top or bottom image of the detection hole using Gaussian filtering, perform Canny edge detection, binarize the detection results, and use Hough transform to determine the coordinates of the detection hole center as (x0, y0);

[0087] Obtain the theoretical position of the inner isolation ring in the PCB design file; align the design coordinates with the image coordinates through the PCB reference point, and determine the theoretical center coordinates of the inner isolation ring as (x i ,y i );

[0088] The theoretical position of the inner isolation ring (x i ,y i ) is used as the center to define the search area; use the Canny operator or adaptive threshold segmentation to extract all non-zero pixel coordinates as the measured isolation ring edge point set {(x k ,y k )}.

[0089] The present invention defines the search area and uses the Canny operator to segment and extract all non-zero pixel coordinates including:

[0090] The theoretical center of the inner isolation ring (x i ,y i ) is used as the center to define the search area image and perform Gaussian blur;

[0091] Use the Sobel operator to calculate the gradient of the search area image in the x and y directions after Gaussian blur;

[0092] The pixel with the largest amplitude is retained along the gradient direction, the edge is refined, and a binary edge map is output.

[0093] The process of constructing the offset calculation model provided by the embodiment of the present invention includes:

[0094] The actual center fitting of the isolation ring: The measured center coordinates of the inner isolation ring are (x c ,y c ), for the measured isolation ring edge point set {(x k ,y k )} perform least squares circle fitting;

[0095]

[0096] Where r is the measured radius of the inner isolation ring.

[0097] Composite offset calculation model construction: If the inner isolation ring is deformed, then:

[0098]

[0099] Among them, α is the weight coefficient, and ellipticity is the difference between the major axis and the minor axis.

[0100] The present invention uses an offset calculation model to determine the center offset as:

[0101]

[0102] Among them, Δd is the current center offset, x0 is the horizontal coordinate of the detection hole center, y0 is the vertical coordinate of the detection hole center, x i is the abscissa of the theoretical center of the inner isolation ring, y i It is the ordinate of the theoretical center of the inner isolation ring.

[0103] The offset direction angle is:

[0104]

[0105] Where θ is the offset direction angle.

[0106] The dynamic offset trend is:

[0107]

[0108] in, is the rate of change of the current circle center offset Δd over time, Δd t is the offset at the current time t, Δd t-1 is the offset from the previous moment t-1, and Δt is the time interval between two measurements.

[0109] According to the design value of the spacing between the isolation rings, the maximum allowable offset is dynamically calculated as:

[0110] Δd max =r pad -r hole

[0111] Where Δd max is the maximum allowable offset, r pad is the radius of the detection hole, r hole is the drilling radius.

[0112] If Δd>Δd max , then use the PID algorithm to generate compensation instructions and determine the fine-tuning coordinates of the drilling platform;

[0113] The compensation instruction generated by the PID algorithm is:

[0114]

[0115] Where u(t) is the total compensation output to the drilling machine; e(t) = Δd, which represents the current center offset; K pis the PID proportional gain coefficient, which indicates the response strength to the current error; K i is the PID integral gain coefficient, which represents the response to the historical error accumulation; K d is the PID differential gain coefficient, which represents the response to the error change trend; e(τ) represents the real-time offset error from time τ = 0 to the current time τ = t; Dτ is the time element, which represents the infinitesimal segmentation of the error in time.

[0116] After determining the fine-tuning coordinates of the drilling platform, record the offset data, update the offset calculation model parameters, and re-test the offset until Δd≤Δd is satisfied. max .

[0117] The calculation process of the drilling platform fine-tuning coordinates provided in the embodiment of the present invention includes:

[0118] Decompose the total compensation amount u(t) of the drilling machine into X-axis and Y-axis components according to the offset direction θ;

[0119]

[0120] Read the current position coordinates (x drill ,y drill ).

[0121] The target coordinates after compensation (x new ,y new )for:

[0122]

[0123] Send instructions through PLC or motion control card.

[0124] In embodiment 2, a layer deviation detection system for a multilayer printed circuit board provided by an embodiment of the present invention includes:

[0125] A data acquisition module is used to obtain real-time images and coordinate data of the detection hole and the inner isolation ring through an automatic optical detection device. The coordinate data includes the drilling position and the coordinates of the inner layer pattern;

[0126] A feature extraction module is used to extract features from the real-time images of the detection hole and the inner isolation ring to obtain the coordinates of the detection hole center, the theoretical coordinates of the inner isolation ring center, and the measured isolation ring edge point set;

[0127] The layer deviation test module is used to build an offset calculation model, use the offset calculation model to determine the center offset and direction angle, and determine the layer deviation tolerance;

[0128] The dynamic adjustment module is used to generate compensation instructions using the PID algorithm to adjust the compensation amount of the drilling machine; record offset data, update the offset calculation model parameters, and re-detect the offset.

[0129] like Figure 2 As shown, the layer deviation test module provided by the embodiment of the present invention is designed with 6 holes in total, the first hole is for grounding, and the outer layer is designed as a square PAD;

[0130] The 2nd to 6th holes are detection holes, designed as circular PADs;

[0131] The distance between the detection hole and the inner isolation ring is 5, 6, 7, 8, and 9 mil respectively;

[0132] The drilling diameter is 0.2mm, which is the smallest drill needle and hole ring design within the unit.

[0133] When process edge design exists, the layer deviation test module is preferentially designed on the process edge;

[0134] When there is no process edge design, two groups are designed diagonally on the PNL edge, the diagonals being the upper left corner and the lower right corner.

[0135] The above description is only a preferred specific implementation method of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A layer deviation detection system for a multi-layer printed circuit board, characterized in that: The floor deviation detection system includes: A data acquisition module is used to obtain real-time images and coordinate data of the detection hole and the inner isolation ring through an automatic optical detection device. The coordinate data includes the drilling position and the coordinates of the inner layer pattern; A feature extraction module is used to extract features from the real-time images of the detection hole and the inner isolation ring to obtain the coordinates of the detection hole center, the theoretical coordinates of the inner isolation ring center, and the measured isolation ring edge point set; The layer deviation test module is used to build an offset calculation model, use the offset calculation model to determine the center offset and direction angle, and determine the layer deviation tolerance; The dynamic adjustment module is used to generate compensation instructions using the PID algorithm to adjust the compensation amount of the drilling machine; record offset data, update the offset calculation model parameters, and re-detect the offset.

2. The layer deviation detection system for a multilayer printed circuit board according to claim 1, characterized in that: The layer deviation test module is designed with 6 holes in total. The first hole is for grounding and the outer layer is designed as a square PAD. The 2nd to 6th holes are detection holes, designed as circular PADs; The distance between the detection hole and the inner isolation ring is 5, 6, 7, 8, and 9 mil respectively; The drilling diameter is 0.2mm, which is the smallest drill needle and hole ring design in the unit.

3. The layer deviation detection system for a multilayer printed circuit board according to claim 1, characterized in that: When process edge design exists, the layer deviation test module is preferentially designed on the process edge; When there is no process edge design, two groups are designed diagonally on the PNL edge, with the diagonals being the upper left corner and the lower right corner.

4. A method for detecting layer deviation of a multilayer printed circuit board, characterized in that: The method is used to control the layer deviation detection system of the multilayer printed circuit board according to any one of claims 1 to 3, and the method comprises: S1, obtaining real-time images and coordinate data of the inspection hole and the inner isolation ring through an automatic optical inspection device, the coordinate data including the drilling position and the inner layer pattern coordinates; S2, extracting features from the real-time images of the detection hole and the inner isolation ring to obtain the coordinates of the detection hole center, the theoretical coordinates of the inner isolation ring center, and the measured isolation ring edge point set; S3, constructing an offset calculation model, using which the center offset, offset direction angle, and dynamic offset trend are determined, and layer deviation tolerance is determined; S4, using the PID algorithm to generate compensation instructions, adjust the compensation amount of the drilling machine; record the offset data, update the offset calculation model parameters, and re-detect the offset.

5. The method for detecting layer deviation of a multilayer printed circuit board according to claim 4, wherein: In step S2, feature extraction of the real-time image of the detection hole and the inner isolation ring includes: Use AOI equipment to capture the top or bottom image of the inspection hole; After de-noising the top or bottom image of the detection hole using Gaussian filtering, perform Canny edge detection, binarize the detection results, and use Hough transform to determine the coordinates of the detection hole center as (x0, y0); Obtain the theoretical position of the inner isolation ring in the PCB design file; align the design coordinates with the image coordinates through the PCB reference point, and determine the theoretical center coordinates of the inner isolation ring as (x i ,y i ); The theoretical position of the inner isolation ring (x i ,y i ) is used as the center to define the search area; use the Canny operator or adaptive threshold segmentation to extract all non-zero pixel coordinates as the measured isolation ring edge point set {(x k ,y k )}.

6. The method for detecting layer deviation of a multilayer printed circuit board according to claim 5, wherein: Define the search area and use the Canny operator to extract all non-zero pixel coordinates including: The theoretical center of the inner isolation ring (x i ,y i ) is used as the center to define the search area image and perform Gaussian blur; Use the Sobel operator to calculate the gradient of the search area image in the x and y directions after Gaussian blur; The pixel with the largest amplitude is retained along the gradient direction, the edge is refined, and a binary edge map is output.

7. The method for detecting layer deviation of a multilayer printed circuit board according to claim 4, wherein: In step S3, the offset calculation model is constructed by: The actual center fitting of the isolation ring: The measured center coordinates of the inner isolation ring are (x c ,y c ), for the measured isolation ring edge point set {(x k ,y k )} perform least squares circle fitting; Where r is the measured radius of the inner isolation ring; Composite offset calculation model construction: If the inner isolation ring is deformed, then: Among them, α is the weight coefficient, and ellipticity is the difference between the major axis and the minor axis.

8. The method for detecting layer deviation of a multilayer printed circuit board according to claim 4, wherein: In step S3, the center offset is determined using the offset calculation model as: Among them, Δd is the current center offset, x0 is the horizontal coordinate of the detection hole center, y0 is the vertical coordinate of the detection hole center, x i is the abscissa of the theoretical center of the inner isolation ring, y i is the theoretical ordinate of the center of the inner isolation ring; The offset direction angle is: Where θ is the offset direction angle; The dynamic offset trend is: in, is the rate of change of the current circle center offset Δd over time, Δd t is the offset at the current time t, Δd t-1 is the offset of the previous moment t-1, and Δt is the time interval between two measurements; According to the design value of the spacing between the isolation rings, the maximum allowable offset is dynamically calculated as: Δd max =r pad -r hole Where Δd max is the maximum allowable offset, r pad is the radius of the detection hole, r hole is the drilling radius.

9. The method for detecting layer deviation of a multilayer printed circuit board according to claim 4, wherein: In step S4, if Δd>Δd max , then use the PID algorithm to generate compensation instructions and determine the fine-tuning coordinates of the drilling platform; The compensation instruction generated by PID algorithm is: Where u(t) is the total compensation output to the drilling machine; e(t) = Δd, which represents the current center offset; K p is the PID proportional gain coefficient, which indicates the response strength to the current error; K i is the PID integral gain coefficient, which represents the response to the historical error accumulation; K d is the PID differential gain coefficient, which represents the response to the error change trend; e(τ) represents the real-time offset error from time τ = 0 to the current time τ = t; Dτ is the time element, which represents the infinitesimal segmentation of the error in time; After determining the fine-tuning coordinates of the drilling platform, record the offset data, update the offset calculation model parameters, and re-test the offset until Δd≤Δd is satisfied. max .

10. The method for detecting layer deviation of a multilayer printed circuit board according to claim 9, wherein: The calculation process of the drilling platform fine-tuning coordinates includes: Decompose the total compensation amount u(t) of the drilling machine into X-axis and Y-axis components according to the offset direction θ; Read the current position coordinates (x drill ,y drill ); The target coordinates after compensation (x new ,y new )for: Send instructions through PLC or motion control card.

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