Blind hole adhesive residue detection device and detection method

Abstract

The invention discloses a blind hole adhesive residue detection device and method, and belongs to the technical field of printed circuit board detection, and the method comprises the steps: selecting a broadband light source, and splitting the light emitted by the broadband light source into sample light and reference light through an optical fiber coupler; the reference light is transmitted according to a set path and is reflected back to the optical fiber coupler through the reflector; the sample light is transmitted into the blind hole of the PCB according to a set path, and returns to the optical fiber coupler after being subjected to backscattering; and the returned sample light and reference light interfere in the optical fiber coupler and form coherent light, a spectrometer is adopted to read coherent light parameters, and whether the residual glue exists at the irradiation point position or not is judged according to the light intensity of the coherent light. According to the blind hole adhesive residue detection device, the wavelength, the output power, the bandwidth and the like of the broadband light source are controlled, so that the detection device can detect the adhesive residue with the thickness of 0.007-10 mm, and the blind hole adhesive residue detection device has good penetrability, can detect the adhesive residue with the minimum thickness of 7 microns, and has high detection precision.

Description

Technical Field

[0001] The present invention belongs to the technical field of printed circuit board detection, and particularly relates to a blind via residual glue detection device and a detection method. Background Art

[0002] A printed circuit board is a provider of electrical connections in electronic components. With the increasing speed and frequency of digital signal transmission, the integrity transmission of signals is a key technology in the field of PCB board preparation. During the manufacturing process of a PCB board, the detection of blind vias on the PCB board can promptly discover whether the drilling parameters are appropriate and whether the electroplating process is normal. By feedback from the inspection of blind vias and adjusting and optimizing the production process, the production efficiency and quality of the PCB board can be improved.

[0003] During the inspection of blind vias on a PCB board, the detection of residual glue in the blind vias is also a very important link. When parameters such as the rotation speed and feed rate of the drill bit are inappropriate during drilling, it may cause local overheating of the board material, resulting in the melting of the resin and the formation of residual glue adhering to the hole wall. At the same time, when laminating the film, if the pressure is uneven or the temperature is inappropriate, there may be bubbles or poor adhesion between the dry film and the board material, uneven light reception in some areas during exposure, and it is also easy to leave residual dry film in the blind vias after development, forming residual glue.

[0004] For the residual glue in the blind vias of a PCB board, the current conventional detection methods include optical microscopes, scanning electron microscopes, and AOI automatic optical detection. Among them, the detection accuracy of optical microscopes and scanning electron microscopes is high, but the imaging depth is low and the detection speed is slow; while AOI automatic optical detection cannot detect deep micro vias. Therefore, the existing PCB board blind via detection technology cannot accurately distinguish the specific location and morphology of the residual glue. Summary of the Invention

[0005] In view of one or more of the above defects or improvement requirements in the prior art, the present invention provides a blind via residual glue detection method for detecting the location and morphology of residual glue in the blind vias of a PCB board.

[0006] To achieve the above object, the present invention provides a blind via residual glue detection method for detecting residual glue in the blind vias of a PCB board, which includes the following steps: S1. Select a broadband light source, and split the light emitted by the broadband light source into sample light and reference light through an optical fiber coupler; S2. The reference light is transmitted along a set path and reflected back to the optical fiber coupler through a mirror; the sample light is transmitted along a set path into the blind via of the PCB board and returns to the optical fiber coupler after backscattering; S3. The returned sample light and reference light interfere in the optical fiber coupler to form coherent light. A spectrometer is used to read the parameters of the coherent light, and it is judged whether there is residual glue at the irradiated position according to the light intensity of the coherent light.

[0007] As a further improvement of the present invention, the selection of the broadband light source in step S1 is determined according to the thickness of the residual glue to be detected in the blind hole of the PCB board.

[0008] As a further improvement of the present invention, the thickness of the residual glue to be detected in the blind hole of the PCB board is 0.007 mm to 10 mm, and the wavelength of the broadband light source is determined according to the maximum value of the thickness of the residual glue to be detected, so that the light emitted by the broadband light source can penetrate the residual glue and be received by the fiber coupler; the bandwidth of the broadband light source is determined according to the minimum value of the thickness of the residual glue to be detected, so that the residual glue can be detected and identified.

[0009] As a further improvement of the present invention, the wavelength of the broadband light source is calculated according to the Beer-Lambert law, and the wavelength of the broadband light source is derived from the absorption coefficient of the residual glue at a set wavelength.

[0010] As a further improvement of the present invention, the calculation method of the absorption coefficient of the residual glue at a set wavelength is as follows: (Formula 1) Wherein, α is the absorption coefficient of the residual glue at a set wavelength, d is the penetration depth, I is the light intensity at the laser penetration depth, and I 0 is the initial light intensity when the laser is incident on the resin surface; The residual glue is epoxy resin, and when the laser decays to 36.8% of the initial intensity, the resin can be penetrated, and the wavelength of the broadband light source is selected according to the absorption coefficient of the epoxy resin at different wavelengths.

[0011] As a further improvement of the present invention, the wavelength of the broadband light source is 840 nm.

[0012] As a further improvement of the present invention, the bandwidth of the broadband light source is calculated according to the Rayleigh length.

[0013] As a further improvement of the present invention, the calculation method of the bandwidth of the broadband light source is as follows: (Formula 2) Wherein, △λ is the bandwidth of the broadband light source; λ 0 is the central wavelength of the broadband light source; △z is the axial resolution.

[0014] As a further improvement of the present invention, the broadband light source is composed of a combination of two light sources with a bandwidth of 50 nm.

[0015] This application also includes a blind hole residual glue detection device, which includes: A broadband light source, the output end of the broadband light source is connected with a fiber coupler, and the fiber coupler can divide the light emitted by the broadband light source into reference light and sample light; One end of the fiber optic coupler facing away from the broadband light source is respectively connected to a first fiber optic collimator and a second fiber optic collimator; A lens and a reflector are arranged on the first fiber optic collimator in the optical transmission path. The first fiber optic collimator, the lens and the reflector are aligned in the optical path, so that the light reflected back by the reflector can be transmitted back to the first fiber optic collimator; A galvanometer is arranged on the second fiber optic collimator in the optical transmission path. A scanning lens is arranged in the light output direction of the galvanometer, and the scanning lens is arranged facing the blind hole of the PCB to be measured; The fiber optic coupler is also connected to a spectrometer, and the spectrometer is used to analyze the light returned to the fiber optic coupler to determine the light intensity of the coherent light; Wherein, the wavelength of the broadband light source is 840 nm, the output optical power of the broadband light source is greater than 20 mW, and the bandwidth of the broadband light source is greater than 100 nm; the insertion losses of the fiber optic coupler, the first fiber optic collimator and the second fiber optic collimator are less than 3 dB, and the acquisition speed of the spectrometer is greater than 250 kHz.

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

[0017] Generally speaking, compared with the prior art, the beneficial effects of the above technical solutions conceived by the present invention include: (1) The blind hole residual glue detection device of the present invention is based on the Michelson interferometer principle, uses the light emitted by a low-coherence broadband light source, and divides the light into reference light and sample light through a fiber optic coupler. Among them, the reference light is reflected by the reflector, and the sample light generates backscattered or reflected light after irradiating the copper plate or residual glue in the blind hole. When the optical path difference between the reference light and the sample light is within the coherence length of the light source, the two beams of light will interfere, and the spectrometer will then receive the interference signal. When the sample light hits the copper plate in the blind hole of the PCB, due to the extremely high reflectivity of the bottom copper layer, and there will be some backscattering when the light beam hits the blind hole residual glue, most of the light beam will continue to penetrate until the copper layer surface and backscatter, which makes the reflected light intensities of the sample light hitting the copper plate and the residual glue quite different; the tester can judge whether there is residual glue in the blind hole of the PCB according to the strength of the interference signal received by the spectrometer. At the same time, by controlling the wavelength, output power and bandwidth of the broadband light source, etc., the detection device can detect residual glue with a thickness of 0.007 mm to 10 mm, that is, the penetration thickness can reach 10 mm, and the minimum detection thickness can reach 7 μm. The blind hole residual glue detection device in this application has good penetration and can detect residual glue with a minimum thickness of 7 μm, with high detection accuracy.

[0018] (2) The blind via residual glue detection method of the present invention utilizes the principle of a Michelson interferometer. By the interference of the reference light and the sample light in the fiber coupler, and using a spectrometer to obtain the light intensity of the coherent light, the reflection or backscattering of the sample light in the blind via of the PCB board is obtained, and based on this, it is analyzed whether there is residual glue in the PCB board. At the same time, according to the requirements of residual glue detection, the wavelength and bandwidth of the broadband light source are obtained by using the Beer-Lambert law and the Rayleigh length calculation formula, so as to achieve the penetration detection of residual glue with a thickness of 10 mm and the resolution of residual glue with a minimum thickness of 7 μm, ensuring the accuracy of residual glue detection in the blind via. Moreover, in this application, two light sources with a bandwidth of 50 nm are combined to obtain light with a bandwidth of more than 100 nm, which doubles the axial resolution of the system, greatly improving the ability of the blind via residual glue detection method to distinguish residual glue, so that residual glue can be recognized even when it is very thin. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of light transmission at the blind via in the blind via residual glue detection device in the embodiment of the present invention; Figure 2 It is a schematic diagram of the overall structure of the blind via residual glue detection device in the embodiment of the present invention; Figure 3 It is a schematic diagram of the process of the blind via residual glue detection method in the embodiment of the present invention.

[0020] 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. Reflecting mirror; 6. Second fiber collimator; 7. Galvanometer; 8. Scanning lens; 9. PCB board to be measured; 10. Spectrometer; 11. Control component. Detailed Embodiments

[0021] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used 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.

[0022] In the description of the present invention, it should be understood that unless otherwise specified, the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0023] In addition, unless otherwise specified, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0024] In the present invention, unless otherwise clearly defined and limited, the terms "mounted", "connected", "connected to", "fixed", etc. shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] In the present invention, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0026] Embodiment: Please refer to Figures 1 to 3The blind hole residual glue 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 divide the light emitted by the broadband light source 1 into a reference light and a sample light; the end of the fiber coupler 2 away from the broadband light source 1 is respectively connected to a first fiber collimator 3 and a second fiber collimator 6; wherein, the first fiber collimator 3 is provided with a lens 4 and a reflector 5 on the light transmission path, and the first fiber collimator 3 is aligned with the lens 4 and the reflector 5 on the light path, so that the light reflected back by the reflector 5 can be transmitted back to the first fiber collimator 3; at the same time, the second fiber collimator 6 is provided with a galvanometer 7 on the light transmission path, and a scanning lens 8 is provided in the light output direction of the galvanometer 7, and the scanning lens 8 is arranged toward the blind hole of the PCB board 9 to be tested; at the same time, the fiber coupler 2 is also connected to a spectrometer 10, and the spectrometer 10 is used to analyze the light returned to the fiber coupler 2 to determine the light intensity of the coherent light.

[0027] At the same time, the wavelength of the broadband light source 1 of the blind hole residual glue detection device in the present application is 840nm, the output light power of the broadband light source 1 is greater than 20mW, and the bandwidth of the broadband light source 1 is greater than 100nm, and the insertion loss of the optical fiber coupler 2, the first optical fiber collimator 3 and the second optical fiber collimator 6 is less than 3dB, and the acquisition speed of the spectrometer is greater than 250kHz.

[0028] The blind hole residual glue detection device in the present application is based on the principle of Michelson interferometer, using the light emitted by a low-coherence broadband light source 1, and dividing the light into reference light and sample light through a fiber coupler 2. Among them, the reference light is reflected by a reflector 5, and the sample light is irradiated on the copper plate or residual glue in the blind hole to generate backscattering or reflected light. When the optical path difference between the reference light and the sample light is within the coherence length of the light source, the two beams of light will interfere, and the spectrometer 10 will then receive the interference signal. When the sample light hits the copper plate in the blind hole of the PCB board, due to the extremely high reflectivity of the bottom copper layer, the light beam will be partially backscattered when hitting the residual glue in the blind hole, and most of the light beam will continue to penetrate until the surface of the copper layer, and backscattering will occur, which makes the sample light hit the copper plate and the residual glue on the reflected light intensity have a large difference; the detection personnel can judge whether there is residual glue in the blind hole of the PCB board according to the strength of the interference signal received by the spectrometer 10. At the same time, by controlling the wavelength, output power and bandwidth of the broadband light source 1, the present application enables the detection device to detect residual adhesive with a thickness of 0.007mm~10mm, that is, the penetration thickness can reach 10mm, and the minimum detection thickness can reach 7um. The blind hole residual adhesive detection device in the present application has good penetration, and can detect residual adhesive with a minimum thickness of 7um, with high detection accuracy.

[0029] Further, as an alternative embodiment of the present invention, the broadband light source 1 in the present application is composed of a combination of two light sources with a bandwidth of 50 nm. The combination of two light sources with a bandwidth of 50 nm results in a bandwidth of more than 100 nm, which doubles the axial resolution of the system and greatly improves the ability to distinguish residual glue, enabling the residual glue to be recognized even when it is very thin.

[0030] Further, as an alternative embodiment of the present invention, the present application further includes a control component 11, which is communicatively connected to the spectrometer 10 and the galvanometer 7. The control component 11 can obtain the detection parameters of the spectrometer 10 and calculate the light intensity of the coherent light accordingly. After calculating the light intensity of the coherent light, by identifying the strength of the coherent light intensity and comparing it with the coherent light intensity when the sample light hits the copper plate under standard conditions, it is confirmed whether there is residual glue in the blind hole of the PCB board.

[0031] Optionally, the broadband light source 1 in the present application refers to a laser that can emit laser light. The fiber coupler 2 in the present application is a 2*2 fiber coupler 2 with a splitting ratio of 50 / 50. The first fiber collimator 3 and the second fiber collimator 6 in the present application are both used to collimate the laser light emitted from the fiber and to receive the laser light 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 are all connected and transmitted through optical fibers; the first fiber collimator 3, the lens 4, and the mirror 5 are in the same optical transmission direction.

[0032] Further, for the blind hole residual glue detection device in the present application, the present application further includes a blind hole residual glue detection method, which is used for detecting the residual glue in the blind hole of the PCB board, and specifically includes the following steps: S1. Select the broadband light source 1, and split the light emitted by the broadband light source 1 into sample light and reference light through the fiber coupler 2; S2. The reference light is transmitted along a set path and reflected back to the fiber coupler 2 through the mirror 5; the sample light is transmitted along a set path to the blind hole of the PCB board and returns to the fiber coupler 2 after backscattering; S3. The returned sample light and reference light interfere in the fiber coupler 2 to form coherent light. The spectrometer 10 is used to read the parameters of the coherent light, and it is judged whether there is residual glue at the irradiated position according to the light intensity of the coherent light.

[0033] Further, as an alternative embodiment of the present invention, the selection of the broadband light source 1 in step S1 is determined according to the thickness of the residual glue to be inspected in the blind hole of the PCB board. Specifically, the wavelength and bandwidth of the broadband light source 1 determine the penetration rate and resolution of the laser for the residual glue. By corresponding requirements, the parameters of the broadband light source 1 are adjusted to achieve high penetration rate and high resolution of the laser for the residual glue.

[0034] Further, as an alternative embodiment of the present invention, the thickness of the residual glue to be inspected in the blind hole of the PCB board in this application is 0.007 mm to 10 mm. Among them, the wavelength of the broadband light source 1 is determined according to the maximum value of the thickness of the residual glue to be inspected, so that the light emitted by the broadband light source 1 can penetrate the residual glue and be received by the fiber optic coupler 2; the bandwidth of the broadband light source 1 is determined according to the minimum value of the thickness of the residual glue to be inspected, so that the residual glue can be detected and identified.

[0035] Further, as an alternative embodiment of the present invention, the wavelength of the broadband light source 1 in this application is calculated according to the Beer-Lambert law, and the wavelength of the broadband light source 1 is derived from the absorption coefficient of the residual glue at a set wavelength.

[0036] Further, as an alternative embodiment of the present invention, the calculation method of the absorption coefficient of the residual glue at a set wavelength in this application is: (Formula 1) Where α is the absorption coefficient of the residual glue at a set wavelength, d is the penetration depth, I is the light intensity at the penetration depth of the laser, and I 0 is the initial light intensity when the laser is incident on the resin surface.

[0037] Specifically, when a beam of parallel monochromatic light perpendicularly passes through a certain uniform non-scattering light-absorbing substance, its absorbance is proportional to the concentration of the light-absorbing substance and the thickness of the absorption layer. When the type of the residual glue is confirmed, according to the maximum thickness of the residual glue to be detected and the absorbance of the light in the residual glue, the wavelength of the light can be reversely derived.

[0038] Specifically, the Beer-Lambert law formula is as follows: (Formula 3) Formula 3 is transformed to solve for the absorption coefficient of the residual glue at a set wavelength, and Formula 1 is obtained.

[0039] At the same time, the residual glue in this application is epoxy resin. When the laser decays to 36.8% of the initial intensity, it is set as the absorption degree when the resin is penetrated. In this way, the absorption coefficient of the epoxy resin residual glue at a set wavelength can be obtained, and then by reversely looking up the absorption coefficient reference table of epoxy resin at different wavelengths, the wavelength of the light emitted by this broadband light source is selected.

[0040] Optionally, the wavelength of the light emitted by the broadband light source 1 in this application is 840 nm, and the penetration depth calculated therefrom is: (Formula 4) At this time, the penetration depth is greater than 20 mm, that is, when the thickness of the epoxy resin residual glue is within 10 mm, the light emitted by the broadband light source 1 can be reflected after entering the residual glue and can be received by the fiber coupler 2.

[0041] Furthermore, as an optional embodiment of the present invention, the bandwidth of the broadband light source 1 in this application is calculated according to the Rayleigh length. The axial resolution (resolution in the direction of the residual glue thickness) of the light emitted by the broadband light source 1 is mainly determined by the bandwidth of the light emitted by the broadband light source 1. When the minimum resolvable thickness of the residual glue is limited, the bandwidth of the broadband light source 1 can be reversely calculated according to the Rayleigh length formula.

[0042] Specifically, the calculation method of the bandwidth of the broadband light source 1 is: (Formula 2) where Δλ is the bandwidth of the broadband light source 1; λ 0 is the central wavelength of the broadband light source 1; Δz is the axial resolution.

[0043] In this application, Δz is limited to 7 μm, and the calculated bandwidth of the broadband light source 1 is 100 nm.

[0044] When the blind hole residual glue detection method in this application detects the thickness of the residual glue, the wavelength, bandwidth, etc. of the broadband light source 1 are all determined, and the epoxy resin is selected as the residual glue. At this time, the intensity of the relevant light received by the spectrometer 10 is positively correlated with the thickness of the residual glue. Therefore, in addition to detecting whether there is residual glue in the blind hole of the PCB board through the blind hole residual glue detection method, this application can also determine the thickness of the residual glue in the blind hole according to the comparison table of the blind hole residual glue thickness and the coherent light intensity.

[0045] Specifically, the blind hole residual glue detection method in this application further includes the following steps: Establish a comparison table of the blind hole residual glue thickness and the coherent light intensity. The spectrometer 10 obtains the coherent light in the fiber coupler 2, obtains the intensity of the coherent light, and obtains the blind hole residual glue thickness according to the comparison table of the blind hole residual glue thickness and the coherent light intensity.

[0046] Specifically, the comparison table of the blind hole residual glue thickness and the coherent light intensity can be obtained by pre-inserting residual glue with a set thickness into the blind hole and then detecting it through the blind hole residual glue detection device.

[0047] Furthermore, as an optional embodiment of the present invention, it is assumed that the blind hole residual glue in the PCB board of this application is all in the shape of droplets. According to the volume calculation formula of the droplets on the plane: (Formula 5) When the thickness h of the residual glue is already known, the radius r of the spherical cap formed by the droplet on the plane can be calculated, and finally the volume of the residual glue can be calculated. This application can also judge the influence of the residual glue on the subsequent PCB board processing according to the detected volume of the spherical cap. Generally, when the theoretical thickness of the residual glue is less than 7 μm and the overall shape is spherical cap-shaped, even if there is residual glue inside the blind hole, a stable conduction can still be formed when the external structure contacts the bottom of the blind hole. Therefore, this application can further determine whether there is residual glue in the blind hole and whether the amount of residual glue will substantially affect the conduction of the PCB board according to the thickness and morphology of the residual glue.

[0048] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting residual glue in blind holes of PCB boards, characterized in that: The steps include: S1. Select a broadband light source, and split the light emitted by the broadband light source into sample light and reference light through a fiber coupler; 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 blind hole of the PCB board along the set path and returns to the fiber coupler after backscattering; S3. The returned sample light and reference light interfere with each other in the fiber coupler to form coherent light. The coherent light parameters are read by a spectrometer, and the presence of residual glue at the irradiation point is determined based on the intensity of the coherent light.

2. The blind hole adhesive residue detection method according to claim 1, characterized in that: The selection of the broadband light source in step S1 is determined according to the thickness of the residual glue to be tested in the blind hole of the PCB board.

3. The blind hole adhesive residue detection method according to claim 2, characterized in that: The thickness of the residual glue to be inspected in the blind hole of the PCB board is 0.007mm~10mm, and the wavelength of the broadband light source is determined according to the maximum value of the thickness of the residual glue to be inspected, so that the light emitted by the broadband light source can penetrate the residual glue and be received by the optical fiber coupler; the bandwidth of the broadband light source is determined according to the minimum value of the thickness of the residual glue to be inspected, so that the residual glue can be detected and identified.

4. The blind hole adhesive residue detection method according to claim 3, characterized in that: The wavelength of the broadband light source is calculated according to the Beer-Lambert law, and the wavelength of the broadband light source is derived according to the absorption coefficient of the residual glue at a set wavelength.

5. The blind hole adhesive residue detection method according to claim 4, characterized in that: The absorption coefficient of the residual glue at the set wavelength is calculated as follows: (Formula 1) Among them, α is the absorption coefficient of residual glue at the set wavelength, d is the penetration depth, I is the light intensity at the laser penetration depth, and I0 is the initial light intensity when the laser is incident on the resin surface; The residual glue is epoxy resin. The laser can penetrate the resin when it is attenuated to 36.8% of the initial intensity. The wavelength of the broadband light source is selected according to the absorption coefficient of the epoxy resin at different wavelengths.

6. The method for detecting residual adhesive in blind holes according to claim 5, characterized in that: The wavelength of the broadband light source is 840 nm.

7. The blind hole adhesive residue detection method according to claim 6, characterized in that: The bandwidth of the broadband light source is calculated according to the Rayleigh length.

8. The method for detecting residual adhesive in blind holes according to claim 7, characterized in that: The bandwidth of the broadband light source is calculated as follows: (Formula 2) Among them, △λ is the bandwidth of the broadband light source; λ0 is the central wavelength of the broadband light source; △z is the axial resolution.

9. The method for detecting residual adhesive in blind holes according to claim 8, characterized in that: The broadband light source is formed by combining two light sources with a bandwidth of 50 nm.

10. A blind hole adhesive residue 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 separate the light emitted by the broadband light source into reference light and sample light; One end of the fiber coupler away from the broadband light source is respectively connected to the first fiber collimator and the second 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 blind hole of 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 determine the intensity of the coherent light; Among them, the wavelength of the broadband light source is 840nm, the output optical power of the broadband light source is greater than 20mW, and the bandwidth of the broadband light source is greater than 100nm; the insertion loss of the optical fiber coupler, the first optical fiber collimator and the second optical fiber collimator is less than 3dB, and the acquisition speed of the spectrometer is greater than 250kHz.

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