PCB (printed circuit board) back drilling stub length detection device and detection method

Abstract

The invention discloses a PCB (printed circuit board) back drilling stub length detection device and method, and belongs to the technical field of PCB detection, the PCB back drilling stub length detection device comprises a broadband light source, the output end of the broadband light source is connected with an optical fiber coupler, and one end, deviating from the broadband light source, of the optical fiber coupler is respectively connected with a first optical fiber collimator and a second optical fiber collimator; the first optical fiber collimator is provided with a lens and a reflector on an optical transmission path; the second optical fiber collimator is provided with a galvanometer on a light transmission path, and a scanning lens is arranged in the light emitting direction of the galvanometer; and the optical fiber coupler is also connected with a spectrograph. On the basis of the low-coherence light interference principle, the PCB back drilling stub length detection device is designed, the output power and the output bandwidth of a broadband light source are correspondingly adjusted, the insertion loss of an optical fiber coupler is controlled, the collection rate of a spectrograph is adjusted, finally, the axial resolution reaches 5 micrometers, the transverse resolution reaches 10 micrometers, and the requirements that the diameter is smaller than 0.1 mm, and the detection precision is larger than 0.1 mm can be met. And detecting the stub length of the deep micropore with the depth of less than 10mm.

Description

Technical Field

[0001] The invention belongs to the technical field of printed circuit board detection, and in particular relates to a PCB back-drilling stub length detection device and a detection method. Background Art

[0002] Printed circuit boards are the providers of electrical connections in electronic components. As digital signal transmission rates become faster and faster and frequencies become higher, signal integrity transmission becomes a key technology in the field of PCB board preparation. Among them, back drilling technology is a PCB board drilling technology that emerged to solve the electromagnetic interference problem caused by excess copper plating in copper-plated holes.

[0003] PCB boards usually involve multi-layer printed boards, and each printed board is metallized (copper-plated) in the through-hole to achieve signal transmission between layers; for layers that do not need to be connected or transmitted, the hole wall metal in the through-hole needs to be removed through the back drilling process. In the actual drilling process, if the drilling depth is too deep, the originally conductive circuit will be disconnected, and if the drilling depth is too shallow, it will cause signal crosstalk and other problems. Therefore, the actual drilling depth of the back drilling will seriously affect the performance of the PCB board. Therefore, it is also very important to detect the length of the stub at the drilled hole. When the length of the drilled stub is within the set standard range, the stable use of the PCB board can be ensured.

[0004] Existing detection of drilled stubs often has many problems. Traditional detection methods such as X-ray detection can penetrate circuit boards, but their resolution is limited. Especially for tiny back-drilled stubs, there will be problems of blurred imaging and reduced detection accuracy, which can easily lead to missed detections. Although ultrasonic detection technology can detect some internal defects, when faced with tiny cracks and delamination at the junction of the drilled stub and the substrate around the drilled hole, the detection sensitivity is often insufficient and the drill hole size cannot be effectively identified. Summary of the invention

[0005] In view of one or more of the above defects or improvement needs of the prior art, the present invention provides a PCB back-drilled stub length detection device and detection method, which are used to solve the problem that the existing drilled stub detection technology has insufficient detection accuracy and is prone to missed detection.

[0006] To achieve the above object, the present invention provides a method for detecting the length of a back-drilled hole stub of a PCB board, which comprises the following steps: S1. Select a broadband light source and use a fiber coupler to divide the broadband light source into sample light and reference light; S2, the reference light is transmitted along the set path and reflected back to the fiber coupler through the reflector; the sample light is transmitted to the back-drilled hole of the PCB board along the set path and returns to the fiber coupler after backscattering; S3, the reference light and the sample light interfere in the fiber coupler, and the coherent light after interference is transmitted to the spectrometer, which analyzes and obtains the one-dimensional data in the back-drilled hole of the PCB board; S4. Adjust the relative position of the sample light and the PCB board, use the fiber coupler to obtain the backscattered sample light, repeat step S3, obtain the three-dimensional data in the back drilling hole of the PCB board, and obtain the length of the back drilling stub of the PCB board.

[0007] As a further improvement of the present invention, in step S4, the length of the back drilling stub of the PCB board is calculated as follows: The overall thickness a of the PCB board and the thickness d of the conductive layer are obtained, the back drilling depth c is obtained through the three-dimensional data in the back drilling hole of the PCB board, and the back drilling stub length b of the PCB board is obtained.

[0008] As a further improvement of the present invention, the output optical power of the broadband light source is greater than 15mW, and the bandwidth of the broadband light source is greater than 60nm; the insertion loss of the optical fiber coupler is less than 3dB; and the data acquisition speed of the spectrometer is greater than 200kHz.

[0009] As a further improvement of the present invention, in step S2, the transmission path of the reference light is: The fiber coupler splits the light transmitted from the broadband light source into sample light and reference light. The reference light is transmitted to the lens after passing through the first fiber collimator. The lens converges the reference light and transmits it to the reflector. The reflector reflects the reference light along the original transmission path, passes through the lens and the first fiber collimator, and finally reflects it to the fiber coupler.

[0010] As a further improvement of the present invention, in step S2, the transmission path of the sample light is: The sample light is collimated by the second fiber collimator and then transmitted to the galvanometer. The sample light emitted from the galvanometer is focused into the back-drilled hole of the PCB board through the scanning lens. The sample light is reflected back to the scanning lens on the surface of the back-drilled hole. Finally, the sample light is transmitted back to the fiber coupler along the original transmission path.

[0011] As a further improvement of the present invention, the acquisition of one-dimensional data in the back-drilled hole of the PCB board in step S3 includes: The spectrometer obtains the coherent light generated at the fiber coupler and uses Fourier transform to obtain the reflected or scattered light intensity distribution at different depths in the back-drilled hole of the PCB board; According to the intensity distribution of reflected or scattered light at different depths in the back-drilled hole of the PCB board, one-dimensional data along the back-drilled hole depth direction in the back-drilled hole of the PCB board at the detection position is obtained.

[0012] As a further improvement of the present invention, the acquisition of the three-dimensional data of the length of the back drilling stub of the PCB board in step S4 includes: S401, adjusting the relative position of the galvanometer and the PCB board along the first direction so that the sample light scans point by point in the PCB board, using a spectrometer to analyze the one-dimensional data of the back-drilled hole of the PCB board at the current position after adjustment along the depth direction, and collecting the data of multiple scanning points to construct a two-dimensional cross-sectional image data of the sample light in the back-drilled hole of the PCB board; S402, adjusting the relative position of the galvanometer and the PCB board along the second direction, repeating step S401, and obtaining two-dimensional cross-sectional image data of the sample light in the back-drilled hole of the PCB board under adjacent cross-sections; successively adjusting the relative position of the galvanometer and the PCB board along the second direction, obtaining a plurality of two-dimensional cross-sectional image data stacked along the second direction, and summarizing the plurality of two-dimensional cross-sectional image data in the back-drilled hole of the PCB board to obtain three-dimensional morphological data in the back-drilled hole of the PCB board.

[0013] As a further improvement of the present invention, after the three-dimensional data in the back drilled hole of the PCB board is obtained, it also includes: using image processing software to process and visualize the three-dimensional data in the back drilled hole of the PCB board to obtain a three-dimensional image of the PCB board.

[0014] As a further improvement of the present invention, the present invention further comprises step S5: The PCB back drilling stub length data is obtained, and the standard threshold of the PCB back drilling stub length is obtained according to the PCB preparation requirements. The PCB back drilling stub length data is compared with the standard threshold of the PCB back drilling stub length to determine whether the PCB back drilling stub length meets the standard.

[0015] The present application also includes a PCB back-drilling stub length detection device, which includes: A broadband light source, wherein the output end of the broadband light source is connected to a fiber coupler, and the fiber coupler can split the light emitted by the broadband light source into reference light and sample light; One end of the optical fiber coupler away from the broadband light source is respectively connected to the first optical fiber collimator and the second optical fiber collimator; The first optical fiber collimator is provided with a lens and a reflector on the light transmission path, and the first optical fiber collimator is aligned with the lens and the reflector on the light path, so that the light reflected back by the reflector can be transmitted back to the first optical fiber collimator; The second optical fiber collimator is provided with a galvanometer on the light transmission path, a scanning lens is provided in the light emitting direction of the galvanometer, and the scanning lens is arranged toward the PCB board to be tested; The optical fiber coupler is also connected to a spectrometer, which is used to analyze the light returned to the optical fiber coupler to obtain the back drilling length of the PCB board to be tested; Among them, the output optical power of the broadband light source is greater than 15mW, and the bandwidth of the broadband light source is greater than 60nm; the insertion loss of the optical fiber coupler is below 3dB, and the acquisition rate of the spectrometer is greater than 200kHz.

[0016] The above-mentioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0017] In general, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects: (1) The PCB back-drilled hole stub length detection device of the present invention is based on the principle of low-coherence light interference. It measures the spectrum of the interference signal and performs Fourier inverse transformation to obtain the depth of the back-drilled hole of the PCB board to be tested, thereby achieving micron-level measurement, so as to greatly improve the accuracy of the PCB back-drilled hole stub length detection. At the same time, the present application designs a PCB back-drilled hole stub length detection device based on the principle of low-coherence light interference, and correspondingly adjusts the output power and output bandwidth of the broadband light source, controls the insertion loss of the optical fiber coupler, and adjusts the acquisition rate of the spectrometer, and finally achieves an axial resolution of 5μm and a lateral resolution of 10μm, which can meet the requirements of back-drilled holes with a diameter of less than 0.1mm and a depth of less than 10mm, and the accurate detection of deep micro-hole stub lengths of less than 0.2mm.

[0018] (2) The PCB back-drilled hole stub length detection device of the present invention uses a superluminescent diode with a central wavelength of 840nm and a bandwidth greater than 60nm as a light source, which greatly improves the circumferential resolution of light, so as to clearly distinguish the different hierarchical structures inside the PCB board and the tiny back-drilled hole stubs; at the same time, the present application uses low-loss optical fiber to reduce the reflection and scattering loss of light during the transmission process, improve the signal transmission quality, and further improve the accuracy of stub length detection.

[0019] (3) The PCB back-drilled hole stub length detection method of the present invention does not directly detect the back-drilled hole stub length, but is only used to obtain the three-dimensional morphology of the drilled hole, and at the same time uses the PCB board's own parameters to obtain the overall board thickness and conductive layer thickness of the PCB board, and then obtains the back-drilled hole depth through the PCB board back-drilled hole stub length detection device to calculate the back-drilled hole stub length. This method can avoid the problem of the difficulty in distinguishing the boundary between the back-drilled hole stub and the conductive layer through-hole in conventional detection technology, reduce the detection error, and improve the back-drilled hole stub length detection accuracy. At the same time, this application achieves high-precision measurement of the PCB back-drilled hole stub by optimizing the system light source and optical path design of the detection device, and adopts a high-precision scanning platform and a back-drilled hole depth calculation method, so that the axial resolution reaches 5μm and the lateral resolution reaches 10μm, and can achieve accurate detection of back-drilled holes with a diameter of less than 0.1mm and a depth of less than 10mm, and deep micro-hole stub lengths of less than 0.2mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the morphology of the back drilling stub of the PCB board in an embodiment of the present invention; Figure 2 1 is a schematic diagram of the overall structure of a device for detecting the length of a back-drilled hole stub of a PCB board according to an embodiment of the present invention; Figure 3 It is a flow chart of a method for detecting the length of a back-drilled hole stub of a PCB board in an embodiment of the present invention.

[0021] In all the drawings, the same reference numerals represent the same technical features, specifically: 1. Broadband light source; 2. Fiber coupler; 3. First fiber collimator; 4. Lens; 5. Reflector; 6. Second fiber collimator; 7. Vibrating mirror; 8. Scanning lens; 9. PCB to be tested; 10. Spectrometer; 11. Control components. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] In the description of the present invention, it should be understood that, unless otherwise specified, terms such as “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention 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, and therefore cannot be understood as limiting the present invention.

[0024] In addition, unless otherwise specified, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0025] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0027] Example: See also Figures 1 to 3 The PCB back-drilling stub length detection device in the preferred embodiment of the present invention comprises a broadband light source 1, the output end of the broadband light source 1 is connected to a fiber coupler 2, and the fiber coupler 2 can split the light output by the broadband light source 1 into a reference light and a sample light; wherein a first fiber collimator 3 is provided on the transmission path of the reference light, and a lens 4 and a reflector 5 are provided in the transmission direction of the light emitted by the first fiber collimator 3, the reference light emitted by the first fiber collimator 3 is focused by the lens 4 and then emitted to the reflector 5, and is reflected by the reflector 5, and then passes through the lens 4 and the first fiber collimator 3, and finally transmitted to the fiber coupler 2; secondly, a second fiber collimator is provided on the transmission path of the sample light. A device 6 is provided, and a galvanometer 7 is provided in the light transmission direction emitted by the second optical fiber collimator 6. A scanning lens 8 is provided in the light emitting direction of the galvanometer 7, and the scanning lens 8 is provided toward the PCB board 9 to be tested; the sample light emitted by the second optical fiber collimator 6 can scan the back-drilled hole of the PCB board 9 to be tested after passing through the galvanometer 7 and the scanning lens 8. The light backscattered back after scanning is transmitted to the second optical fiber collimator 6 again, and finally returns to the optical fiber coupler 2. The sample light and the reference light are emitted and interfered in the optical fiber coupler 2, and finally received by the spectrometer 10 connected to the optical fiber coupler 2, and then the parameters of the spectrometer 10 are read and visualized by an external control device to realize the detection of the stub length of the back-drilled hole of the PCB board.

[0028] Further, as an optional embodiment of the present invention, the present application further includes a control component 11, which is communicatively connected with the spectrometer 10 and the galvanometer 7. The control component 11 can obtain the detection parameters of the spectrometer 10, and visualize the parameters obtained by the spectrometer 10, so as to facilitate the subsequent calculation of the length of the back-drilled stub of the PCB board; secondly, the control component 11 can adjust and control the parameters of the galvanometer 7, so that the PCB board back-drilled stub length detection device can detect PCB boards of different models, sizes or detection requirements.

[0029] Optionally, the broadband light source 1 in the present application refers to a laser that can emit laser. The fiber coupler 2 in the present application is a 2*2 fiber coupler 2, and its splitting ratio is 50 / 50. The first fiber collimator 3 and the second fiber collimator 6 in the present application are both used to collimate the laser emitted from the optical fiber, and to receive the laser returned to the fiber coupler 2. At the same time, the broadband light source 1 and the fiber coupler 2, the fiber coupler 2 and the first fiber collimator 3, the fiber coupler 2 and the second fiber collimator 6, and the fiber coupler 2 and the spectrometer 10 in the present application are connected and transmitted through optical fibers; the first fiber collimator 3 and the lens 4 and the reflector 5 are in the same light transmission direction.

[0030] Further, as an optional embodiment of the present invention, in conventional detection of drilled stub length, when the diameter of the back-drilled stub is below 0.1mm and the length is below 0.2mm, it is difficult for conventional detection methods to obtain clear imaging and accurate stub length. Based on this, the output optical power of the broadband light source 1 of the PCB back-drilled stub length detection device in the present application is greater than 15mW, the bandwidth of the broadband light source 1 is greater than 60nm, the insertion loss of each optical fiber coupler 2 is below 3dB, and the acquisition rate of the spectrometer 10 is greater than 200kHz. Under the above-mentioned setting conditions, the axial resolution of the PCB back-drilled stub length detection device in the present application can reach 5μm, and the lateral resolution can reach 10μm, which can meet the requirements of accurate detection of back-drilled holes with a diameter of less than 0.1mm and a depth of less than 10mm, and deep micro-hole stubs with a length of less than 0.2mm.

[0031] As an optional embodiment of the present invention, the broadband light source 1 in the present application uses a superluminescent diode with a central wavelength of 840nm and a bandwidth greater than 60nm as a light source to improve the axial resolution of the light, so as to clearly distinguish the different hierarchical structures inside the PCB board and the tiny back-drilled stubs. In addition, the present application uses low-loss optical fiber to reduce the reflection and scattering losses of light to improve the transmission quality of the signal.

[0032] The PCB back-drilled hole stub length detection method in the present application is based on the principle of low-coherence light interference, and obtains the depth information inside the sample by measuring the spectrum of the interference signal and performing an inverse Fourier transform, so that its detection accuracy can reach the micron level, meeting the requirements of accurate detection of back-drilled holes with a diameter of less than 0.1 mm and a depth of less than 10 mm, and deep micro-hole stub lengths of less than 0.2 mm.

[0033] Further, with respect to the PCB back drilling stub length detection device in the present application, the present application also includes a PCB back drilling stub length detection method, which includes the following steps: S1, select a broadband light source 1, and use a fiber coupler 2 to divide the broadband light source 1 into a sample light and a reference light; S2, the reference light is transmitted along the set path and reflected back to the fiber coupler 2 through the reflector 5; the sample light is transmitted to the back-drilled hole of the PCB along the set path and returns to the fiber coupler 2 after backscattering; S3, the reference light and the sample light interfere with each other in the optical fiber coupler 2, and the coherent light after interference is transmitted to the spectrometer 10, and the spectrometer 10 analyzes and obtains the one-dimensional data of the length of the back-drilled hole stub of the PCB board; S4, adjust the relative position of the sample light and the PCB board, use the fiber coupler 2 to obtain the backscattered sample light, repeat step S3, obtain the three-dimensional data in the back drilling hole of the PCB board, and obtain the length of the back drilling stub of the PCB board.

[0034] Further, as an optional embodiment of the present invention, in step S4, the length of the back drilling stub of the PCB board is calculated as follows: The overall thickness a of the PCB board and the thickness d of the conductive layer are obtained, and the depth c of the back-drilled hole is obtained through the three-dimensional data in the back-drilled hole of the PCB board, and the length b of the back-drilled hole stub of the PCB board is obtained. In the conventional back-drilled hole stub length detection process, since the back-drilled hole stub is connected to the through hole on the conductive layer, it is difficult for conventional detection equipment to distinguish between the back-drilled hole stub and the conductive layer through hole. The back-drilled hole stub length obtained by the detection equipment often has deviations, and the cumulative error of the detection of the detection equipment itself is easy to cause the problem of error in the final back-drilled hole stub length detection. Compared with conventional detection methods, the present application does not directly detect the length of the back-drilled hole stub, but is only used to obtain the three-dimensional morphology inside the back-drilled hole. Since the overall size of the back-drilled hole is slightly larger than the diameter of the through hole on the conductive layer, the depth of the back-drilled hole can be clearly identified by obtaining the internal morphology of the back-drilled hole. When the overall thickness of the PCB board and the thickness of the conductive layer are known (the overall thickness of the PCB board and the thickness of the conductive layer can be obtained by querying the generated manufacturing parameters, without the need to use the detection equipment for detection again), the length of the back-drilled hole stub can be calculated. Specifically, the calculation method of the back-drilled hole stub length in the present application is: b=adc; wherein a is the overall board thickness of the PCB board, d is the thickness of the conductive layer, and c is the drilled hole depth.

[0035] Optionally, the thickness of the PCB board and the conductive layer in the present application may also be obtained by using other detection technologies, thereby calculating the length of the back-drilled hole stub.

[0036] Further, as an optional embodiment of the present invention, in the above step S2, the transmission path of the reference light is: the optical fiber coupler 2 splits the light transmitted from the broadband light source 1 into sample light and reference light, the reference light is transmitted to the lens 4 after passing through the first optical fiber collimator 3, the lens 4 converges the reference light and transmits it to the reflector 5, the reflector 5 reflects the reference light according to the original transmission path, passes through the lens 4 and the first optical fiber collimator 3, and finally reflects to the optical fiber coupler 2.

[0037] Further, as an optional embodiment of the present invention, in the above step S2, the transmission path of the sample light is: the optical fiber coupler 2 divides the light transmitted from the broadband light source 1 into sample light and reference light, the sample light is collimated by the second optical fiber collimator 6 and then transmitted to the galvanometer 7, the sample light emitted from the galvanometer 7 is focused into the back-drilled hole of the PCB board through the scanning lens 8, the sample light is reflected back to the scanning lens 8 on the surface of the back-drilled hole, and finally the sample light is transmitted back to the optical fiber coupler 2 along the original transmission path.

[0038] It is worth noting that the transmission path of the reference light is known, while the transmission path of the sample light varies at different positions of the back-drilled hole; the reference light and the sample light interfere with each other in the fiber coupler 2, and finally the interference light is transmitted to the spectrometer 10, and analyzed by the spectrometer 10 to obtain the irradiation position of the sample light in the back-drilled hole.

[0039] Further, as an optional embodiment of the present invention, in step S3 of the present application, the acquisition of one-dimensional data in the back-drilled hole of the PCB board includes: The spectrometer 10 acquires the coherent light generated at the fiber coupler 2, and uses Fourier transform to obtain the intensity distribution of the reflected or scattered light at different depths in the back-drilled hole of the PCB board; based on the intensity distribution of the reflected or scattered light at different depths in the back-drilled hole of the PCB board, one-dimensional data along the back-drilled hole depth direction in the back-drilled hole of the PCB board at the detection position is obtained.

[0040] Specifically, the generation of one-dimensional data in the back-drilled hole of the PCB board mainly includes the generation of interference signals, the acquisition of spectral data, and the use of Fourier transform calculation. In the interference signal generation stage: the light emitted by the broadband light source 1 is divided into reference light and sample light, the reference light is reflected by the reflector 5, the sample light is focused to different depths inside the sample and backscattered or reflected, and finally the reference light and the sample light converge at the fiber coupler 2 to generate an interference signal.

[0041] In the spectral data acquisition stage: the generated interference signal is decomposed into different wavelengths by the spectrometer 10 and recorded by the linear array CCD to form a series of interference spectrum data that varies with the wavelength; by repeating the detection process at different lateral positions of the sample, the interference light information at multiple lateral positions can be obtained; In the Fourier transform calculation stage: the collected interference spectrum data at each lateral position is fast Fourier transformed. According to the principle of optical coherence, after the interference spectrum signal is Fourier transformed, its frequency domain information corresponds to the intensity distribution of reflected or scattered light at different depths in the sample, thereby obtaining the one-dimensional structural information of the sample at the lateral position along the depth direction, that is, the one-dimensional data along the back-drilled hole depth direction in the back-drilled hole of the PCB board.

[0042] Further, as an optional embodiment of the present invention, in step S4 of the present application, the acquisition of three-dimensional data in the back-drilled hole of the PCB board includes: S401, adjusting the relative position of the galvanometer 7 and the PCB board along the first direction so that the sample light scans point by point in the back-drilled hole of the PCB board, and using the spectrometer 10 to analyze the one-dimensional data of the back-drilled hole of the PCB board at the current position after adjustment along the depth direction; the data of multiple scanning points are collected to construct a two-dimensional cross-sectional image data of the sample light in the back-drilled hole of the PCB board; S402, adjusting the relative position of the galvanometer 7 and the PCB board along the second direction, repeating step S401, obtaining the two-dimensional section image data of the sample light in the back-drilled hole of the PCB board under the adjacent section; successively adjusting the relative position of the galvanometer 7 and the PCB board along the second direction, obtaining multiple two-dimensional section image data stacked along the second direction, summarizing the multiple two-dimensional section image data in the back-drilled hole of the PCB board, and obtaining the three-dimensional morphology data in the back-drilled hole of the PCB board. Preferably, the first direction and the second direction here are directions perpendicular to each other in the horizontal plane.

[0043] Optionally, in the above step S401, when the relative position between the galvanometer 7 and the PCB board is adjusted, the galvanometer 7 or the PCB board may be moved to adjust the relative position between the two.

[0044] After obtaining the three-dimensional data of the PCB board, the back drilling depth of the PCB board can be intuitively calculated, and then the back drilling stub length of the PCB board can be obtained.

[0045] Further, as an optional embodiment of the present invention, the present application also includes step S4: three-dimensional visualization processing, using image processing software to process and visualize the three-dimensional data in the back drilling of the PCB board to form a three-dimensional image of the PCB board. After obtaining the three-dimensional data in the back drilling of the PCB board, its visualization degree is not high, resulting in the inability of relevant inspection personnel to intuitively obtain the length of the back drilling stub of the PCB board. In order to facilitate subsequent inspection personnel to judge whether the length of the back drilling stub of the PCB board is qualified, the present application also uses surface rendering and volume rendering to present the three-dimensional morphology of the PCB board in the form of intuitive images or videos to speed up the inspection efficiency of the inspection personnel.

[0046] Further, as an optional embodiment of the present invention, after obtaining the PCB board back drilling stub length data in the present application, it also includes a judgment on whether the PCB board back drilling stub length meets the standard: obtaining the PCB board back drilling stub length data, and obtaining the PCB board back drilling stub length standard threshold according to the PCB board preparation requirements; when the detected PCB board back drilling stub length is within the PCB board back drilling stub length standard threshold, the PCB board back drilling stub length meets the standard; when the detected PCB board back drilling stub length is greater than or less than the PCB board back drilling stub length standard threshold, the PCB board back drilling stub length does not meet the standard.

[0047] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting the length of a PCB back-drilled hole stub, characterized in that: The steps include: S1. Select a broadband light source and use a fiber coupler to divide the broadband light source into sample light and reference light; S2, the reference light is transmitted along the set path and reflected back to the fiber coupler through the reflector; the sample light is transmitted to the back-drilled hole of the PCB board along the set path and returns to the fiber coupler after backscattering; S3, the reference light and the sample light interfere in the fiber coupler, and the coherent light after interference is transmitted to the spectrometer, which analyzes and obtains the one-dimensional data in the back-drilled hole of the PCB board; S4. Adjust the relative position of the sample light and the PCB board, use the fiber coupler to obtain the backscattered sample light, repeat step S3, obtain the three-dimensional data in the back drilling hole of the PCB board, and obtain the length of the back drilling stub of the PCB board.

2. The method for detecting the length of a PCB back-drilled hole stub according to claim 1, characterized in that: In step S4, the length of the back drilling stub of the PCB board is calculated as follows: The overall thickness a of the PCB board and the thickness d of the conductive layer are obtained, the back drilling depth c is obtained through the three-dimensional data in the back drilling hole of the PCB board, and the back drilling stub length b of the PCB board is obtained.

3. The method for detecting the length of a PCB back-drilled hole stub according to claim 1, characterized in that: The output optical power of the broadband light source is greater than 15mW, and the bandwidth of the broadband light source is greater than 60nm; the insertion loss of the optical fiber coupler is less than 3dB; and the data acquisition speed of the spectrometer is greater than 200kHz.

4. The method for detecting the length of a PCB back-drilled hole stub according to claim 1, characterized in that: In step S2, the transmission path of the reference light is: The fiber coupler splits the light transmitted from the broadband light source into sample light and reference light. The reference light is transmitted to the lens after passing through the first fiber collimator. The lens converges the reference light and transmits it to the reflector. The reflector reflects the reference light along the original transmission path, passes through the lens and the first fiber collimator, and finally reflects it to the fiber coupler.

5. The method for detecting the length of a PCB back-drilled hole stub according to claim 4, characterized in that: In step S2, the transmission path of the sample light is: The sample light is collimated by the second fiber collimator and then transmitted to the galvanometer. The sample light emitted from the galvanometer is focused into the back-drilled hole of the PCB board through the scanning lens. The sample light is reflected back to the scanning lens on the surface of the back-drilled hole. Finally, the sample light is transmitted back to the fiber coupler along the original transmission path.

6. The method for detecting the length of a PCB back-drilled hole stub according to claim 1, characterized in that: The acquisition of one-dimensional data in the back-drilled hole of the PCB board in step S3 includes: The spectrometer obtains the coherent light generated at the fiber coupler and uses Fourier transform to obtain the reflected or scattered light intensity distribution at different depths in the back-drilled hole of the PCB board; According to the intensity distribution of reflected or scattered light at different depths in the back-drilled hole of the PCB board, one-dimensional data along the back-drilled hole depth direction in the back-drilled hole of the PCB board at the detection position is obtained.

7. The method for detecting the length of a PCB back-drilled hole stub according to claim 6, characterized in that: The acquisition of the three-dimensional data of the length of the back drilling stub of the PCB board in step S4 includes: S401, adjusting the relative position of the galvanometer and the PCB board along the first direction so that the sample light scans point by point in the PCB board, using a spectrometer to analyze the one-dimensional data of the back-drilled hole of the PCB board at the current position after adjustment along the depth direction, and collecting the data of multiple scanning points to construct a two-dimensional cross-sectional image data of the sample light in the back-drilled hole of the PCB board; S402, adjusting the relative position of the galvanometer and the PCB board along the second direction, repeating step S401, and obtaining two-dimensional cross-sectional image data of the sample light in the back-drilled hole of the PCB board under adjacent cross-sections; successively adjusting the relative position of the galvanometer and the PCB board along the second direction, obtaining a plurality of two-dimensional cross-sectional image data stacked along the second direction, and summarizing the plurality of two-dimensional cross-sectional image data in the back-drilled hole of the PCB board to obtain three-dimensional morphological data in the back-drilled hole of the PCB board.

8. The method for detecting the length of a PCB back-drilled hole stub according to claim 1, characterized in that: After the three-dimensional data in the back drilling hole of the PCB board is obtained, the method further includes: using image processing software to process and visualize the three-dimensional data in the back drilling hole of the PCB board to obtain a three-dimensional image of the PCB board.

9. The method for detecting the length of a PCB back-drilled hole stub according to claim 1, characterized in that: The step S5 is also included: The PCB back drilling stub length data is obtained, and the standard threshold of the PCB back drilling stub length is obtained according to the PCB preparation requirements. The PCB back drilling stub length data is compared with the standard threshold of the PCB back drilling stub length to determine whether the PCB back drilling stub length meets the standard.

10. A PCB back-drilling stub length detection device, characterized in that: include: A broadband light source, wherein the output end of the broadband light source is connected to a fiber coupler, and the fiber coupler can split the light emitted by the broadband light source into reference light and sample light; One end of the optical fiber coupler away from the broadband light source is respectively connected to the first optical fiber collimator and the second optical fiber collimator; The first optical fiber collimator is provided with a lens and a reflector on the light transmission path, and the first optical fiber collimator is aligned with the lens and the reflector on the light path, so that the light reflected back by the reflector can be transmitted back to the first optical fiber collimator; The second optical fiber collimator is provided with a galvanometer on the light transmission path, a scanning lens is provided in the light emitting direction of the galvanometer, and the scanning lens is arranged toward the PCB board to be tested; The optical fiber coupler is also connected to a spectrometer, which is used to analyze the light returned to the optical fiber coupler to obtain the back drilling length of the PCB board to be tested; Among them, the output optical power of the broadband light source is greater than 15mW, and the bandwidth of the broadband light source is greater than 60nm; the insertion loss of the optical fiber coupler is below 3dB, and the acquisition rate of the spectrometer is greater than 200kHz.

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