Detection method, signal processing assembly and system for length of back drill stub

Abstract

The invention is suitable for the technical field of optical measurement, and provides a back drill stub length detection method, a signal processing assembly and a system. The method for detecting the length of the back drill stump comprises the steps that the optical path difference between first reflected light and second reflected light is obtained, the first reflected light is reflected light generated by reflecting an incident light beam of a back drill hole to be detected on the surface of a dielectric layer of the back drill hole to be detected, and the second reflected light is reflected light generated by reflecting the incident light beam of the back drill hole to be detected; the second reflected light is reflected light obtained by reflecting a light beam, passing through the dielectric layer, of the incident light beam by the signal layer of the back drilling hole to be detected; and according to the optical path difference and the refractive index of the dielectric layer, determining the stub length of the back drilling hole to be measured. According to the embodiment of the invention, the same incident light beam can be reflected by different layers of the back drilling hole to be detected, the stub length is determined based on the optical path difference between the two reflected light beams, and the detection efficiency is improved.

Description

Technical Field

[0001] The present application belongs to the field of optical measurement technology, and in particular relates to a method for detecting the length of a back-drilled residual pile, a signal processing component, and a system. Background Art

[0002] With the widespread use of printed circuit boards (PCBs) in communications and computing devices, the accuracy of the backdrilling process directly impacts signal transmission quality. Improper handling of the redundant conductive areas created by through-hole metallization in multilayer PCBs can cause signal reflections and interference. Controlling backdrill depth is crucial for controlling the length of the unwanted barrel (stub). Stub length refers to the non-functional, dangling conductor pillar (copper pillar) in the signal hole that remains after the backdrilling process is complete. Overdrilling can damage internal connections, while insufficient backdrilling depth can result in excessive stubs, compromising signal integrity.

[0003] Cross-section analysis is often used to determine stump length. This method requires vertically cutting the PCB at the back-drilled hole to be tested, which damages the sample and is extremely inefficient, making it unsuitable for production applications. Fiber optic penetration testing is prone to damage to the fiber, leading to increased testing costs and reduced efficiency. Summary of the Invention

[0004] The embodiments of the present application provide a method, signal processing component, and system for detecting the length of a back-drilled stump. The method can reflect the same incident light beam from different layers of a back-drilled hole to be measured, and determine the stump length based on the optical path difference between the two reflected light beams, thereby improving detection efficiency.

[0005] A first aspect of an embodiment of the present application provides a method for detecting the length of a back-drilled stump, comprising: obtaining an optical path difference between a first reflected light and a second reflected light, wherein the first reflected light is reflected by a surface of a dielectric layer of the back-drilled hole to be measured from an incident light beam of the back-drilled hole to be measured, and the second reflected light is reflected by a signal layer of the back-drilled hole to be measured from a light beam of the incident light beam passing through the dielectric layer; and determining the stump length of the back-drilled hole to be measured based on the optical path difference and the refractive index of the dielectric layer.

[0006] In some embodiments of the first aspect, the incident light beam of the back-drilled hole to be measured is obtained by splitting an outgoing light beam of a light source by a spectroscope, and the outgoing light beam of the light source is divided into a reference light beam and the incident light beam by the spectroscope; obtaining the optical path difference between the first reflected light and the second reflected light includes: during the process of the spectroscope moving along the depth direction of the back-drilled hole to be measured toward the back-drilled hole to be measured, obtaining a first interference signal between the first reflected light and the reference light beam and a second interference signal between the second reflected light and the reference light beam; and determining the optical path difference based on the first interference signal and the second interference signal.

[0007] In some embodiments of the first aspect, the optical path difference is determined based on the first interference signal and the second interference signal, including: determining the first position where the interference light intensity between the first reflected light and the reference beam is the strongest based on the first interference signal, and determining the first optical path of the first reflected light based on the first position; determining the first position where the interference light intensity between the first reflected light and the reference beam is greater than a first preset threshold based on the first interference signal, and determining the first optical path of the first reflected light based on the first position; determining the second position where the interference light intensity between the second reflected light and the reference beam is greater than a second preset threshold based on the second interference signal, and determining the second optical path of the second reflected light based on the second position; obtaining the optical path difference through the difference between the first optical path and the second optical path.

[0008] In some embodiments of the first aspect, determining the first position at which the intensity of the interference light between the first reflected light and the reference beam is greater than a first preset threshold based on the first interference signal includes: determining a first intensity change sequence of interference fringes between the first reflected light and the reference beam based on the first interference signal; converting the first intensity change sequence into a frequency domain signal using Fourier transform, and extracting the phase difference between the first reflected light and the reference beam from the frequency domain signal; calculating the optical path difference between the first reflected light and the reference beam based on the phase difference; and taking the position at which the optical path difference between the first reflected light and the reference beam is less than or equal to a difference threshold as the first position.

[0009] In some embodiments of the first aspect, determining the second position at which the intensity of the interference light between the second reflected light and the reference beam is greater than a second preset threshold based on the second interference signal includes: determining a second intensity change sequence of interference fringes between the second reflected light and the reference beam based on the second interference signal; converting the second intensity change sequence into a frequency domain signal using Fourier transform, and extracting the phase difference between the second reflected light and the reference beam from the frequency domain signal; calculating the optical path difference between the second reflected light and the reference beam based on the phase difference; and taking the position at which the optical path difference between the second reflected light and the reference beam is less than or equal to the difference threshold as the second position.

[0010] In some embodiments of the first aspect, determining the stump length of the back-drilled hole to be measured based on the optical path difference and the refractive index of the dielectric layer includes: determining the thickness values ​​corresponding to each position on the surface of the dielectric layer based on the optical path difference and the refractive index of the dielectric layer; and determining the stump length of the back-drilled hole to be measured based on the thickness values ​​corresponding to each position on the surface of the dielectric layer.

[0011] In some embodiments of the first aspect, determining the stump length of the back-drilled hole to be measured based on the thickness values ​​corresponding to various positions on the surface of the dielectric layer includes: determining the thickness value from the dielectric layer on the stepped hole to the target layer based on the back-drilling process to form a stepped hole, and determining the minimum thickness value from the dielectric layer to the target layer as the stump length.

[0012] In some implementations of the first aspect, the method for detecting the backdrilling stump length further includes: determining a state classification result of the backdrilling process according to the stump lengths in the inner diameter direction of each plate surface of the stepped hole.

[0013] A second aspect of an embodiment of the present application provides a device for detecting the length of a back-drilled stump, comprising: an optical path difference acquisition unit, configured to acquire an optical path difference between a first reflected light and a second reflected light, wherein the first reflected light is reflected by a surface of a dielectric layer of a back-drilled hole to be measured from an incident light beam of the back-drilled hole to be measured, and the second reflected light is reflected by a signal layer of the back-drilled hole to be measured from a light beam of the incident light beam passing through the dielectric layer; and a stump length detection unit, configured to determine the stump length of the back-drilled hole to be measured based on the optical path difference and the refractive index of the dielectric layer.

[0014] A third aspect of an embodiment of the present application provides a signal processing component, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned method for detecting the length of a back-drilled residual pile when executing the computer program.

[0015] According to a fourth aspect of an embodiment of the present application, a back-drilled stump length detection system is provided, comprising: a light source; an optical device group, comprising a beam splitter and a reference mirror; the beam splitter is configured to split an outgoing light beam of the light source into a reference beam and an incident light beam of a back-drilled hole to be measured; the reference mirror is configured to reflect the reference light beam to the beam splitter; the incident light beam is reflected by a dielectric layer of the back-drilled hole to be measured to form a first reflected light, and the incident light beam is reflected by a signal layer of the back-drilled hole to be measured after passing through the dielectric layer to form a second reflected light; a photosensitive component is configured to collect an optical signal formed by interference, the optical signal formed by interference comprising an interference light signal formed by interference of the first reflected light with the reference beam via the beam splitter, and an interference light signal formed by interference of the second reflected light with the reference beam via the beam splitter; and a signal processing component is configured to obtain an optical path difference between the first reflected light and the second reflected light by using Fourier transform, and determine the stump length of the back-drilled hole to be measured based on the optical path difference and the refractive index of the dielectric layer.

[0016] In some embodiments of the fourth aspect, the output light beam of the light source is one of red light and infrared light.

[0017] According to a fifth aspect of the embodiments of the present application, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the above-mentioned method for detecting the length of a back-drilled residual pile are implemented.

[0018] A sixth aspect of the embodiments of the present application provides a computer program product, which enables the above-mentioned method for detecting the length of a back-drilled residual pile to be executed when the computer program is run.

[0019] In an embodiment of the present application, the surface of the dielectric layer of the back-drilled hole to be tested reflects an incident light beam from the back-drilled hole to be tested to form a first reflected light, and the signal layer of the back-drilled hole to be tested reflects the incident light beam passing through the dielectric layer to form a second reflected light. By obtaining the optical path difference between the first reflected light and the second reflected light, the stump length of the back-drilled hole to be tested is determined based on the optical path difference and the refractive index of the dielectric layer. On the one hand, the stump length can be obtained without damaging the PCB board and without the need for optical fiber insertion. On the other hand, the stump length can be determined based on two reflected light beams reflecting the same incident light beam from different layers of the back-drilled hole to be tested, eliminating the process of switching light sources or adjusting beam bands for different layers, thereby improving detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 1 is a structural diagram of a back-drilled residual pile length detection system provided in an embodiment of the present application; Figure 2 is a schematic diagram of back drilling provided in an embodiment of the present application; Figure 3 Schematic diagram of the specific structure of the back-drilled residual pile length detection system provided in an embodiment of the present application; Figure 4 This is a schematic diagram of the implementation process of a method for detecting the length of a back-drilled residual pile provided in an embodiment of the present application; Figure 5 Schematic diagram of the principle of the method for detecting the length of a back-drilled residual pile provided in an embodiment of the present application; Figure 6 is a schematic diagram of a first point cloud image provided in an embodiment of the present application; Figure 7 is a schematic diagram of a second point cloud image provided in an embodiment of the present application; Figure 8 is a schematic diagram of a stepped hole provided in an embodiment of the present application; Figure 9 Schematic diagram of the state classification result of back drilling processing provided by an embodiment of the present application; Figure 10 1 is a schematic structural diagram of a device for detecting the length of a back-drilled residual pile provided in an embodiment of the present application; Figure 11 It is a structural diagram of the signal processing component provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of this application more clear, the present application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without making any creative work are protected by this application.

[0023] With the widespread use of printed circuit boards in communications and computing devices, the accuracy of the backdrilling process has a direct impact on the quality of signal transmission. Improper handling of the redundant conductive portions formed by through-hole metallization in multi-layer circuit boards can cause signal reflections and interference. Controlling the depth of the backdrilling is key to controlling the length of the stubs. Stub length refers to the non-functional, suspended conductor posts in the signal hole that are not completely drilled out after the backdrilling process is completed, i.e., the redundant conductive portions. Overdrilling during backdrilling can damage internal connections, while insufficient backdrilling depth can result in excessive stubs that compromise signal integrity. In related technologies, stub length is often determined using a slicing analysis method. This method requires vertically cutting the PCB at the backdrilled hole location to be tested, which destroys the sample and is extremely inefficient, making it unsuitable for production applications. Fiber optic penetration testing can easily damage the optical fiber, leading to increased testing costs and reduced efficiency.

[0024] Based on this, the present application provides a method for detecting the length of back-drilled stumps, which can obtain the stump length without damaging the PCB board and without the need for optical fiber insertion, and can determine the stump length based on two reflected light beams that reflect the same incident light beam from different layers of the back-drilled hole to be tested, eliminating the process of switching light sources or adjusting beam bands for different layers, thereby improving detection efficiency.

[0025] In order to illustrate the technical solution of the present application, specific embodiments are provided below.

[0026] Please refer to Figure 1 , Figure 1 The present application provides a back-drilled pile length detection system. The back-drilled pile length detection system 1 may include: Light source 10; The optical device assembly 20 includes a beam splitter 201 and a reference mirror 202. The beam splitter 201 is used to split the outgoing light beam of the light source 10 into a reference beam and an incident light beam of the back-drilled hole to be measured. The reference mirror 202 is used to reflect the reference beam to the beam splitter 201. The incident light beam is reflected by the dielectric layer of the back-drilled hole to be measured to form a first reflected light. The incident light beam passes through the dielectric layer and is reflected by the signal layer of the back-drilled hole to be measured to form a second reflected light. The second reflected light is then collected by the photosensitive component. The photosensitive component 30 is used to collect the light signal formed by interference, wherein the light signal formed by interference includes the interference signal formed by the first reflected light and the reference beam through the beam splitter 201, and the interference signal formed by the second reflected light and the reference beam through the beam splitter 201; The signal processing component 40 is used to process the signal output by the photosensitive component 30, for example, to execute the steps of the back-drilled stump length detection method provided in the present application, so as to use Fourier transform to obtain the optical path difference between the first reflected light and the second reflected light, and determine the stump length of the back-drilled hole to be measured based on the optical path difference and the refractive index of the dielectric layer.

[0027] Figure 2 A schematic diagram of a backdrilled hole is shown. The dielectric and signal layers are arranged sequentially along the depth of the backdrilled hole. The signal layer houses the copper wires that transmit signals. The dielectric layer, also known as the insulating layer, is a layer of insulating material that separates and supports the copper wires in the signal layer. Stubs are non-functional, hanging copper pillars that were not completely drilled through the backdrilled hole.

[0028] To implement the detection method of the present application, the outgoing light beam from the light source 10 is partially absorbed by the insulating material of the dielectric layer and reflected by the material of the signal layer (typically copper). In some embodiments of the present application, the outgoing light beam from the light source 10 is one of red light and infrared light. The infrared light may specifically refer to near-infrared light. The specific wavelength of the outgoing light beam may be within the range of [750nm, 1750nm], and the wavelength value may be determined by the material of the dielectric layer.

[0029] In this way, when the incident light beam of the back-drilled hole to be tested is incident vertically onto the hole to be tested, the first reflection occurs when it contacts the surface of the dielectric layer for the first time. At the same time, part of the light passes through the dielectric layer and continues to irradiate downward to the signal layer, causing a second reflection. The two reflections form the first reflected light and the second reflected light respectively.

[0030] In some embodiments of this application, please refer to Figure 3 The optical device assembly 20 may include a beam splitter 201, a reference mirror 202, and an objective lens 203. The objective lens 203 may be used to shape the light beam emitted from the beam splitter 201 to the back-drilled hole to be measured, so that the incident light beam to the back-drilled hole to be measured is collimated light.

[0031] Furthermore, the objective lens 203 can be used to form a light spot of a preset size according to the focal length. The preset size may include but is not limited to 1mm×1mm, 4mm×4mm, 10mm×10mm, and the specific value can be set according to the detection accuracy and detection efficiency requirements.

[0032] In some embodiments of the present application, the optical device assembly 20 may further include one or more reflective mirrors for changing the optical path.

[0033] In some embodiments of the present application, the optical device group 20 may further include one or more lenses for light beam collimation.

[0034] In some embodiments of the present application, the photosensitive component 30 may include a pixel array and an integrated readout circuit. A reference beam is reflected by a reference mirror 202 back to the beam splitter 201, where it interferes with the two reflected beams from the back-drilled via to be measured (i.e., the first reflected light and the second reflected light). The pixel array is configured to receive the interference signal and perform photoelectric conversion. The integrated readout circuit is configured to process and transmit the converted electrical signal for signal processing by the signal processing component 40.

[0035] In some embodiments of the present application, the photosensitive component 30 and the signal processing component 40 may be integrated, for example, integrated on the same circuit board. In some embodiments of the present application, the photosensitive component 30 and the signal processing component 40 may be non-integrated, for example, the signal processing component 40 may be a processor on an intelligent electronic device (such as a computer or a smart phone), and the photosensitive component 30 may be a peripheral device of the intelligent electronic device.

[0036] In some embodiments of the present application, the back-drilled stump length detection system 1 may further include a drive assembly for driving the beam splitter 201 in the optical device assembly 20 to move along the depth direction of the back-drilled hole to be measured. The objective lens 203 may move synchronously with the beam splitter 201.

[0037] In some embodiments of the present application, the movement speed and movement range of the above-mentioned drive assembly can be adjusted according to actual needs. The movement range of the drive assembly can refer to the focal depth, which can include but is not limited to 1.4mm, 0.7mm, and 0.35mm, so as to image the entire back-drilled hole to be tested.

[0038] The following combination Figure 4 The present application provides a method for detecting the length of a back-drilled stump. This method can be applied to a back-drilled stump length detection system 1 and executed by a signal processing component 40. Specifically, the method can include the following steps: S401 to S402.

[0039] Step S401: Acquire an optical path difference between a first reflected light and a second reflected light.

[0040] As mentioned above, the first reflected light is the reflected light from the dielectric layer surface of the back-drilled hole to be tested, and the second reflected light is the reflected light from the signal layer of the back-drilled hole to be tested, when the incident light beam passes through the dielectric layer.

[0041] In an embodiment of the present application, after the aforementioned photosensitive element receives the light signal and converts it into an electrical signal, the signal processing component 40 can obtain the optical path difference ΔL between the first reflected light and the second reflected light based on the electrical signal using Fourier transform.

[0042] Step S402 : determining the stump length of the back-drilled hole to be measured according to the optical path difference and the refractive index of the dielectric layer.

[0043] The refractive index n of the dielectric layer is related to the material of the dielectric layer and can be set according to the material of the dielectric layer. In the embodiment of the present application, the stump length of the back-drilled hole to be measured can be determined by the formula ΔL / n based on the optical path difference and the refractive index of the dielectric layer.

[0044] Figure 5 This schematic diagram illustrates the principle of the backdrilled stump length detection method provided by this application. An incident light beam from the backdrilled hole to be measured is reflected by the surface of the dielectric layer to form a first reflected light beam. The incident light beam then passes through the dielectric layer and is reflected by the surface of the signal layer to form a second reflected light beam. The optical path difference between the two beams is the product of the geometric path difference between the two reflected light beams and the refractive index of the dielectric layer. This geometric path difference between the two reflected light beams can be used to determine the stump length.

[0045] In an embodiment of the present application, the surface of the dielectric layer of the back-drilled hole to be tested reflects the incident light beam of the back-drilled hole to be tested to form a first reflected light, and the signal layer of the back-drilled hole to be tested reflects the incident light beam passing through the dielectric layer to form a second reflected light. By obtaining the optical path difference between the first reflected light and the second reflected light, the stump length of the back-drilled hole to be tested is determined according to the optical path difference and the refractive index of the dielectric layer. On the one hand, the stump length can be obtained without damaging the PCB board and without the need for optical fiber insertion. On the other hand, the stump length can be determined based on two reflected light beams reflecting the same incident light beam from different layers of the back-drilled hole to be tested, eliminating the process of switching the light source 10 or adjusting the beam band for different layers, thereby improving detection efficiency.

[0046] In addition, this application supports the detection of the back-drilled holes to be tested after the back-drilling process is completed. Compared with the method of calculating the residual length based on the parameters before the back-drilled holes are formed, the accuracy of the results will not be affected by the processes such as exposure and development of the outer layer circuit, etching of the outer layer circuit, removal of dry film, resin plugging, and board electrical measurement of signal on and off during the back-drilling process, which may easily lead to changes in the PCB board thickness and height deviation of the signal layer position. Therefore, the detection reliability can be improved.

[0047] In some embodiments of the present application, the incident light beam for the back-drilled hole to be measured is obtained by splitting the outgoing light beam from the light source 10 by the beam splitter 201. The outgoing light beam from the light source 10 is split by the beam splitter 201 into a reference beam and an incident light beam for the back-drilled hole to be measured. Obtaining the optical path difference between the first reflected light and the second reflected light may include: obtaining a first interference signal between the first reflected light and the reference beam, and a second interference signal between the second reflected light and the reference beam, as the beam splitter 201 moves toward the back-drilled hole to be measured along the depth direction of the back-drilled hole to be measured. Determining the optical path difference based on the first interference signal and the second interference signal.

[0048] The first interference signal and the second interference signal may refer to signals provided by the photosensitive component 30 to the signal processing component 40. Specifically, the drive component may drive the spectroscope 201 to move toward the back-drilled hole to be tested, along the depth direction of the back-drilled hole to be tested. As the spectroscope 201 moves toward the back-drilled hole to be tested, the first reflected light reflected from the surface of the dielectric layer of the back-drilled hole to be tested reaches the spectroscope 201, interferes with the reference beam, and forms interference light with annular interference fringes. The photosensitive element receives the interference light and performs photoelectric conversion, outputting the first interference signal to the signal processing component 40.

[0049] Similarly, the second reflected light from the back-drilled signal layer reaches the spectroscope 201 and interferes with the reference beam, forming interference light with annular interference fringes. The photosensitive element receives the interference light and performs photoelectric conversion, outputting a second interference signal to the signal processing component 40.

[0050] At this time, the first interference signal and the second interference signal carry light intensity information, and the light intensity information can be used to determine the optical path difference between the first reflected light and the second reflected light.

[0051] Specifically, determining the optical path difference based on the first interference signal and the second interference signal may include: determining a first position at which the intensity of interference light between the first reflected light and the reference beam is greater than a first preset threshold based on the first interference signal, and determining a first optical path of the first reflected light based on the first position. Determining a second position at which the intensity of interference light between the second reflected light and the reference beam is greater than a second preset threshold based on the second interference signal, and determining a second optical path of the second reflected light based on the second position. The optical path difference is obtained by taking the difference between the first optical path and the second optical path.

[0052] The first preset threshold and the second preset threshold can be set based on actual conditions and can be the same or different. The first preset threshold and the second preset threshold can be used to extract locations where the interference light intensity is stronger. The first location where the first preset threshold and the second location where the interference light intensity is greater than the second preset threshold can refer to locations on the surface of the dielectric layer and the location of the signal layer, respectively.

[0053] Specifically, determining the first position at which the intensity of the interference light between the first reflected light and the reference beam is greater than a first preset threshold based on the first interference signal may include: determining a first intensity change sequence of the interference fringes between the first reflected light and the reference beam based on the first interference signal; converting the first intensity change sequence into a frequency domain signal using Fourier transform, and extracting the phase difference between the first reflected light and the reference beam from the frequency domain signal; calculating the optical path difference between the first reflected light and the reference beam based on the phase difference; and taking the position at which the optical path difference between the first reflected light and the reference beam is less than or equal to the difference threshold as the first position.

[0054] The optical path difference between the first reflected light and the reference beam being less than or equal to the difference threshold can specifically refer to a position where the optical path difference is 0. Since the optical path difference between the first reflected light and the reference beam being 0 represents the first position where the interference fringe light intensity is strongest, the position where the optical path difference between the first reflected light and the reference beam is less than or equal to the difference threshold can be considered the first position. When the optical path difference is 0, the optical path of the reference beam is equivalent to the optical path of the first reflected light, and the optical path of the reference beam can be determined based on the structure. Therefore, based on the first position, the first optical path L1 of the first reflected light can be determined, i.e., the optical path of the first reflected light from the surface of the dielectric layer of the back-drilled via to be measured to the beam splitter 201.

[0055] Similarly, based on the second interference signal, determining the second position where the intensity of the interference light between the second reflected light and the reference beam is greater than a second preset threshold can include: determining a second intensity change sequence of the interference fringes between the second reflected light and the reference beam based on the second interference signal; using Fourier transform to convert the second intensity change sequence into a frequency domain signal, and extracting the phase difference between the second reflected light and the reference beam from the frequency domain signal; based on the phase difference, calculating the optical path difference between the second reflected light and the reference beam; and taking the position where the optical path difference between the second reflected light and the reference beam is less than or equal to the difference threshold as the second position.

[0056] The optical path difference between the second reflected light and the reference beam being less than or equal to the difference threshold can be specifically determined at a position where the optical path difference is 0. Since the optical path difference between the second reflected light and the reference beam being 0 represents the second position with the strongest interference fringe light intensity, the position where the optical path difference between the second reflected light and the reference beam is less than or equal to the difference threshold can be used as the second position. When the optical path difference is 0, the optical path of the reference beam is equivalent to the optical path of the second reflected light. Therefore, based on the second position, the second optical path L2 of the second reflected light can be obtained, i.e., the optical path of the second reflected light from the signal layer to the beam splitter 201.

[0057] At this point, the difference between the first optical path length L1 and the second optical path length L2 is calculated to obtain the optical path difference ΔL between the first reflected light and the second reflected light. Subsequently, the stump length of the backdrilled hole to be measured can be determined based on the optical path difference ΔL between the first reflected light and the second reflected light and the refractive index n of the dielectric layer.

[0058] In other embodiments of the present application, the above-mentioned acquisition of the optical path difference between the first reflected light and the second reflected light may further include: determining a first point cloud image of the surface of the dielectric layer based on the first interference signal, wherein the pixel value of each pixel in the first point cloud image represents the optical path of the first reflected light reflected at the corresponding position on the surface of the dielectric layer. Determining a second point cloud image of the signal layer based on the second interference signal, wherein the pixel value of each pixel in the second point cloud image represents the optical path of the second reflected light reflected at each position on the signal layer. Determining the optical path difference between the first reflected light and the second reflected light based on the lowest pixel value in the first cloud image and the lowest pixel value in the second cloud image, and using the optical path difference as the stump length.

[0059] Example type, Figure 6 and Figure 7 The first point cloud image and the second point cloud image are shown respectively. Assuming that the lowest pixel value in the first point cloud image is -152 and the lowest pixel value in the second point cloud image is -496, the optical path difference ΔL can be calculated as -152-(-496). At this time, the optical path difference ΔL / n is the length of the residual pile.

[0060] In some embodiments of the present application, determining the stump length of the back-drilled hole to be measured based on the optical path difference and the refractive index of the dielectric layer may include: determining the thickness values ​​corresponding to various positions on the surface of the dielectric layer based on the optical path difference and the refractive index of the dielectric layer; and determining the stump length of the back-drilled hole to be measured based on the thickness values ​​corresponding to various positions on the surface of the dielectric layer.

[0061] In some embodiments of the present application, determining the residual length of the back-drilled hole to be measured based on the thickness values ​​corresponding to various positions on the surface of the dielectric layer may include: forming a stepped hole based on back drilling processing, determining the thickness value from the dielectric layer on the stepped hole to the target layer, and determining the minimum value of the thickness from the dielectric layer to the target layer as the residual length.

[0062] The target layer can refer to the backdrill stop layer, which is the signal layer where the drill bit is scheduled to stop during backdrilling. Figure 8 , because after back drilling, the back drilled hole to be tested forms a stepped hole, and the surface of the dielectric layer of the stepped hole is inclined. The depth at each position along the inner diameter direction of the board surface of the back drilled hole to be tested (perpendicular to the depth direction) is different. Among them, the inner diameter direction of the board surface refers to the direction of the ray radiating along the PCB board surface with the center of the back drilled hole to be tested as the origin. The optical path difference and the corresponding thickness value corresponding to the first reflected light reflected at different positions on the dielectric layer surface may be different. In order to accurately determine the residual length of the back drilled hole to be tested, the thickness value from the dielectric layer to the target layer on the stepped hole can be determined, and the minimum value of the thickness from the dielectric layer to the target layer is determined as the residual length to obtain the accurate residual length.

[0063] More specifically, for each location on the surface of each dielectric layer, the thickness of the dielectric layer along the depth direction at that location can be determined using the formula ΔL / n based on the optical path difference corresponding to the first reflected light at that location and the refractive index of the dielectric layer. This is the thickness value corresponding to that location. The lowest thickness value corresponding to all locations is then used as the stump length of the backdrilled hole to be measured.

[0064] Taking into account that the back-drilled hole is a hole-like structure, in some embodiments of the present application, determining the residual length of the back-drilled hole to be measured based on the thickness values ​​corresponding to each position on the surface of the dielectric layer may include: determining the minimum thickness value in the inner diameter direction of each board surface based on the thickness values ​​corresponding to each position in the inner diameter direction of multiple board surfaces; and using the minimum thickness value in the inner diameter direction of each board surface as the residual length in the inner diameter direction of the corresponding board surface.

[0065] for example, Figure 8 The two inner diameter directions A and B shown in the figure can each determine the corresponding minimum thickness value and obtain the stump length in each inner diameter direction. This allows stump length calculation to be performed for different orientations of the back-drilled hole to be measured. The aforementioned multiple inner diameter directions can be set as needed. For example, every 10° in a horizontal plane perpendicular to the depth direction can be used as a single inner diameter direction.

[0066] In some embodiments of the present application, the method for detecting backdrill stump length may further include determining a backdrilling status classification result based on the stump lengths of each stepped hole in the inner diameter direction of the board surface. The backdrilling status classification result indicates the accuracy of the backdrilling depth and position during backdrilling of the backdrilled hole to be tested. The status classification result may be specifically determined based on the stump lengths of each stepped hole in the inner diameter direction of the board surface.

[0067] For details, please refer to Figure 9 If the length of the residual stubs in the inner diameter direction of each board surface is greater than the first length threshold, the state classification result of the backdrilling process is that the residual stubs are too long, indicating that the backdrilling depth is insufficient. If the length of the residual stubs in the inner diameter direction of each board surface is less than the second length threshold, for example, the residual stub length is 0, the state classification result of the backdrilling process is a damaged line, indicating that the backdrilling depth is too deep. If the difference in the length of the residual stubs between the inner diameter directions of different board surfaces is greater than the difference threshold, the state classification result of the backdrilling process is hole copper residue, indicating that part of the hole copper remains due to reasons such as center offset during backdrilling. If the length of the residual stubs in the inner diameter direction of each board surface is less than or equal to the first length threshold, and greater than or equal to the second length threshold, the state classification result of the backdrilling process is determined to be correct backdrilling.

[0068] The specific values ​​of the first length threshold, the second length threshold and the difference threshold can be set according to actual conditions.

[0069] It should be noted that, for the sake of simplicity of description, the aforementioned method embodiments are all expressed as a series of action combinations. However, those skilled in the art should be aware that this application is not limited to the described order of actions, because according to this application, certain steps can be performed in other orders.

[0070] like Figure 10 FIG2 is a schematic structural diagram of a back-drilled stump length detection device 1000 provided in an embodiment of the present application. The back-drilled stump length detection device 1000 is configured on the signal processing component 40 .

[0071] Specifically, the device 1000 for detecting the length of a back-drilled residual pile may include: An optical path difference acquisition unit 1001 is configured to acquire an optical path difference between a first reflected light and a second reflected light, wherein the first reflected light is a reflected light from a dielectric layer surface of a back-drilled hole to be measured that reflects an incident light beam from the back-drilled hole to be measured, and the second reflected light is a reflected light from a signal layer of the back-drilled hole to be measured that reflects the incident light beam passing through the dielectric layer; The stump length detection unit 1002 is configured to determine the stump length of the back-drilled hole to be measured according to the optical path difference and the refractive index of the dielectric layer.

[0072] In some embodiments of the present application, the incident light beam of the back-drilled hole to be measured is obtained by splitting the outgoing light beam of the light source 10 by the spectrometer 201, and the outgoing light beam of the light source 10 is divided into the reference light beam and the incident light beam by the spectrometer 201; the optical path difference acquisition unit 1001 is specifically used to: when the spectrometer 201 moves toward the back-drilled hole to be measured along the depth direction of the back-drilled hole to be measured, obtain a first interference signal between the first reflected light and the reference light beam and a second interference signal between the second reflected light and the reference light beam; and determine the optical path difference based on the first interference signal and the second interference signal.

[0073] In some embodiments of the present application, the optical path difference acquisition unit 1001 is specifically used to: determine, based on the first interference signal, a first position where the intensity of the interference light between the first reflected light and the reference beam is greater than a first preset threshold, and determine the first optical path of the first reflected light based on the first position; determine, based on the second interference signal, a second position where the intensity of the interference light between the second reflected light and the reference beam is greater than a second preset threshold, and determine the second optical path of the second reflected light based on the second position; and obtain the optical path difference by the difference between the first optical path and the second optical path.

[0074] In some embodiments of the present application, the optical path difference acquisition unit 1001 is specifically used to: determine a first intensity change sequence of interference fringes between the first reflected light and the reference beam based on the first interference signal; use Fourier transform to convert the first intensity change sequence into a frequency domain signal, and extract the phase difference between the first reflected light and the reference beam from the frequency domain signal; calculate the optical path difference between the first reflected light and the reference beam based on the phase difference; and take the position where the optical path difference between the first reflected light and the reference beam is less than or equal to a difference threshold as the first position.

[0075] In some embodiments of the present application, the optical path difference acquisition unit 1001 is specifically used to: determine a second intensity change sequence of interference fringes between the second reflected light and the reference beam based on the second interference signal; use Fourier transform to convert the second intensity change sequence into a frequency domain signal, and extract the phase difference between the second reflected light and the reference beam from the frequency domain signal; calculate the optical path difference between the second reflected light and the reference beam based on the phase difference; and take the position where the optical path difference between the second reflected light and the reference beam is less than or equal to a difference threshold as the second position.

[0076] In some embodiments of the present application, the stump length detection unit 1002 is specifically used to: determine the thickness value corresponding to each position on the surface of the dielectric layer according to the optical path difference and the refractive index of the dielectric layer; and determine the stump length of the back-drilled hole to be measured based on the thickness value corresponding to each position on the surface of the dielectric layer.

[0077] In some embodiments of the present application, the stump length detection unit 1002 is specifically configured to: form a stepped hole based on back drilling, determine the thickness value from the dielectric layer on the stepped hole to the target layer, and determine the minimum thickness value from the dielectric layer to the target layer as the stump length.

[0078] In some embodiments of the present application, the backdrilling stump length detection device 1000 further includes a classification unit, specifically configured to determine a status classification result of the backdrilling process according to the stump lengths in the inner diameter direction of each plate surface of the stepped hole.

[0079] It should be noted that, for the convenience and simplicity of description, the specific working process of the above-mentioned back-drilled residual pile length detection device 1000 can be referred to Figures 4 to 9 The corresponding process of the method will not be described in detail here.

[0080] like Figure 11FIG. 4 is a schematic diagram of a signal processing component 40 provided in an embodiment of the present application. Specifically, the signal processing component 40 may include: a processor 400, a memory 401, and a computer program 402 stored in the memory 401 and executable on the processor 400, such as a back-drilled stump length detection program. When the processor 400 executes the computer program 402, the steps of the above-mentioned back-drilled stump length detection method embodiments are implemented, such as Figure 4 Alternatively, when the processor 400 executes the computer program 402, the functions of the modules / units in the above-mentioned device embodiments are realized, for example, Figure 10 The functions of the optical path difference acquisition unit 1001 and the stump length detection unit 1002 are shown.

[0081] The computer program may be divided into one or more modules / units, which are stored in the memory 401 and executed by the processor 400 to complete the present application. The one or more modules / units may be a series of computer program instruction segments capable of performing specific functions, and the instruction segments are used to describe the execution process of the computer program in the signal processing component 40.

[0082] For example, the computer program can be divided into an optical path difference acquisition unit and a stump length detection unit. The specific functions of each unit are as follows: the optical path difference acquisition unit is configured to acquire the optical path difference between a first reflected light and a second reflected light, where the first reflected light is the light reflected from the dielectric layer surface of the back-drilled via to be measured from an incident light beam of the back-drilled via to be measured, and the second reflected light is the light reflected from the signal layer of the back-drilled via to be measured from the incident light beam passing through the dielectric layer; the stump length detection unit is configured to determine the stump length of the back-drilled via to be measured based on the optical path difference and the refractive index of the dielectric layer.

[0083] The signal processing component 40 may include, but is not limited to, a processor 400 and a memory 401. Those skilled in the art will understand that Figure 11 This is merely an example of the signal processing component 40 and does not constitute a limitation of the signal processing component 40. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the signal processing component 40 may also include input and output devices, network access devices, buses, etc.

[0084] The processor 400 may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), off-the-shelf programmable gate arrays or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor.

[0085] The memory 401 can be an internal storage unit of the signal processing component 40, such as a hard drive or memory of the signal processing component 40. The memory 401 can also be an external storage device of the signal processing component 40, such as a plug-in hard drive, a Smart Media Card (SMC), a Secure Digital (SD) card, a flash memory card, etc. equipped on the signal processing component 40. Furthermore, the memory 401 can include both the internal storage unit of the signal processing component 40 and an external storage device. The memory 401 is used to store the computer program and other programs and data required by the signal processing component 40. The memory 401 can also be used to temporarily store data that has been output or is about to be output.

[0086] It should be noted that, for the convenience and brevity of description, the structure of the above-mentioned signal processing component 40 can also refer to the specific description of the structure in the method embodiment, and will not be repeated here.

[0087] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0088] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0089] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0090] In the embodiments provided in the present application, it should be understood that the disclosed device / signal processing component 40 and method can be implemented in other ways. For example, the device / signal processing component 40 embodiment described above is merely schematic. For example, the division of the modules or units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0091] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0092] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0093] If the integrated module / unit is implemented as a software functional unit and sold or used as a standalone product, it can be stored in a computer-readable storage medium. Based on this understanding, the present application can implement all or part of the process steps in the above-mentioned method embodiments by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When executed by a processor, the computer program can implement the steps of each of the above-mentioned method embodiments. The computer program includes computer program code, which can be in source code form, object code form, executable file, or some intermediate form. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal, and software distribution medium. It should be noted that the content of the computer-readable medium can be appropriately increased or decreased based on the requirements of legislation and patent practice in a jurisdiction. For example, in some jurisdictions, based on legislation and patent practice, computer-readable media does not include electric carrier signals and telecommunication signals.

[0094] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for detecting the length of a back-drilled residual pile, characterized in that: include: Obtaining an optical path difference between a first reflected light and a second reflected light, where the first reflected light is reflected by a surface of a dielectric layer of the back-drilled hole to be measured from an incident light beam of the back-drilled hole to be measured, and the second reflected light is reflected by a signal layer of the back-drilled hole to be measured from a light beam of the incident light beam passing through the dielectric layer; The length of the residual pile of the back-drilled hole to be measured is determined according to the optical path difference and the refractive index of the dielectric layer.

2. The method for detecting the length of a back-drilled residual pile according to claim 1, wherein: The incident light beam is obtained by splitting the outgoing light beam of the light source by a spectroscope, and the outgoing light beam of the light source is split into a reference light beam and the incident light beam by the spectroscope; The obtaining of the optical path difference between the first reflected light and the second reflected light includes: Acquire a first interference signal between the first reflected light and the reference beam and a second interference signal between the second reflected light and the reference beam during a process in which the beam splitter moves toward the back-drilled hole to be measured along a depth direction of the back-drilled hole to be measured; The optical path difference is determined based on the first interference signal and the second interference signal.

3. The method for detecting the length of a back-drilled residual pile according to claim 2, wherein: The determining the optical path difference based on the first interference signal and the second interference signal includes: determining, based on the first interference signal, a first position at which the intensity of interference light between the first reflected light and the reference beam is greater than a first preset threshold, and determining, based on the first position, a first optical path length of the first reflected light; determining, based on the second interference signal, a second position at which the intensity of interference light between the second reflected light and the reference beam is greater than a second preset threshold, and determining a second optical path length of the second reflected light based on the second position; The optical path difference is obtained by the difference between the first optical path and the second optical path.

4. The method for detecting the length of a back-drilled residual pile according to claim 3, wherein: The determining, based on the first interference signal, a first position at which the intensity of interference light between the first reflected light and the reference beam is greater than a first preset threshold comprises: determining a first intensity variation sequence of interference fringes between the first reflected light and the reference beam based on the first interference signal; Converting the first intensity variation sequence into a frequency domain signal by Fourier transform, and extracting a phase difference between the first reflected light and the reference beam from the frequency domain signal; calculating an optical path difference between the first reflected light and the reference beam based on the phase difference; A position where the optical path difference between the first reflected light and the reference beam is less than or equal to a difference threshold is used as the first position.

5. The method for detecting the length of a back-drilled residual pile according to any one of claims 1 to 4, characterized in that: The determining, based on the optical path difference and the refractive index of the dielectric layer, the residual pile length of the back-drilled hole to be measured comprises: determining thickness values ​​corresponding to various positions on the surface of the dielectric layer according to the optical path difference and the refractive index of the dielectric layer; The length of the residual pile of the back-drilled hole to be measured is determined based on the thickness values ​​corresponding to various positions on the surface of the dielectric layer.

6. The method for detecting the length of a back-drilled residual pile according to claim 5, wherein: The determining the residual pile length of the back-drilled hole to be measured based on the thickness values ​​corresponding to various positions on the surface of the dielectric layer includes: A stepped hole is formed based on back drilling, a thickness value from a dielectric layer on the stepped hole to a target layer is determined, and a minimum thickness value from the dielectric layer to the target layer is determined as the stump length.

7. The method for detecting the length of a back-drilled residual pile according to claim 6, wherein: The method for detecting the length of the back-drilled residual pile further comprises: The state classification result of the back drilling process is determined according to the length of the residual pile in the inner diameter direction of each plate surface of the stepped hole.

8. A signal processing component comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method for detecting the length of a back-drilled stump according to any one of claims 1 to 7 are implemented.

9. A system for detecting the length of a back-drilled residual pile, characterized in that: include: light source; An optical device group, comprising a beam splitter and a reference mirror; the beam splitter is used to split the outgoing light beam of the light source into a reference beam and an incident light beam of the back-drilled hole to be measured; The reference mirror is used to reflect the reference beam to the beam splitter; the incident beam is reflected by the dielectric layer of the back-drilled hole to be measured to form a first reflected light, and the incident beam passes through the dielectric layer and is reflected by the signal layer of the back-drilled hole to be measured to form a second reflected light; a photosensitive component for collecting light signals formed by interference, wherein the light signals formed by interference include an interference light signal formed by the interference of the first reflected light and the reference beam via the beam splitter, and an interference light signal formed by the interference of the second reflected light and the reference beam via the beam splitter; The signal processing component is used to obtain the optical path difference between the first reflected light and the second reflected light by Fourier transform, and determine the residual length of the back-drilled hole to be measured according to the optical path difference and the refractive index of the dielectric layer.

10. The back-drilled stump length detection system according to claim 9, characterized in that: The output light beam of the light source is one of red light and infrared light.

Images