Blind hole alignment test module design and test method, system and application

Abstract

The invention belongs to the technical field of PCB product design, and discloses a blind hole alignment test module design and test method, system and application. The method comprises the following steps: designing an outer-layer measuring point, namely designing an END grounding measuring point welding pad, a measuring point welding pad, the center distance between adjacent welding pads and the total coupon width of a test area; designing inner layer measuring points, designing 1-N safe distance alignment measuring points of 2 layers (N + 1), and designing N + 2 blind-hole-free layer isolating rings; and carrying out alignment quantitative control, namely carrying out open circuit or short circuit measurement on a plurality of groups of set clear coupons with different safety distances, and quantitatively judging the maximum deviation condition and the alignment of the blind holes. The invention provides a universal blind hole alignment test module design and a test method, and the analysis efficiency and quantification accuracy of the blind hole alignment capability are improved.

Description

Technical Field

[0001] This invention belongs to the field of PCB product design technology, and in particular relates to the design, testing method, system and application of a blind via alignment test module. Background Technology

[0002] With the advent of the era of high-performance artificial intelligence and computing power, the complexity of PCB lightweighting, miniaturization, and integrated functions is increasing. To achieve arbitrary inter-layer interconnection and higher wiring density, the design requirement for HDI products to utilize high-order micro-blind vias instead of mechanical drilling is also gradually increasing. This brings the issue of blind via alignment reliability to a growing level. Currently, there is no simple, efficient, and quantifiable testing method for high-order HDI blind via alignment, specifically to determine the maximum offset of blind vias on any layer and the maximum offset of the overall blind via stack alignment.

[0003] Existing technology, slicing analysis: Traditional alignment analysis mainly relies on slicing. Due to the small size of blind vias, the selection of the slicing profile angle and the slicing grinding technique are highly demanding. For high-order HDI blind via stack vias, the maximum offset of a single layer is affected by the angle between the slicing profile direction and the actual maximum offset direction of the blind via, making it difficult to accurately quantify the maximum offset of each layer of blind vias and the overall maximum offset of the stack vias. Furthermore, the sampling position angle and slicing process are time-consuming and inefficient.

[0004] Existing X-ray analysis technology: X-ray can only identify and analyze the chromaticity difference between copper-free and copper-containing areas from the vertical direction. Due to the overlapping layers of high-order HDI blind via stacks, the shadows of the blind vias overlap, and X-ray cannot clearly identify the boundary of each layer of blind vias. Therefore, it is impossible to measure the maximum offset of each layer with precise quantization.

[0005] Existing electrical measurement technology: By using a specially designed alignment coupon to control the clearance between the bottom of the blind hole and the receiving pad, the maximum offset of a blind hole in any direction in any layer can be accurately measured. Currently, there is no universally applicable coupon design available. Summary of the Invention

[0006] To overcome the problems existing in related technologies, the present invention discloses an embodiment of a blind hole alignment test module design and test method, system and application, specifically involving a quantitative, efficient and universal HDI blind hole alignment test coupon design and test method.

[0007] The technical solution is as follows: Design and testing method of blind hole alignment test module, including the following steps:

[0008] S1, outer layer test point design, design END ground test point pad, test point pad, center spacing between adjacent pads, and total width of the test area coupon;

[0009] S2, inner layer measurement point design, design of first-order to Nth-order safety distance alignment measurement points for layers 2 to N+1, and design of isolation ring without blind holes for layer N+2;

[0010] S3, alignment quantitative control, measures open or short circuits of multiple sets of different safety distances, quantitatively judges the maximum deviation of blind holes and alignment;

[0011] In step S2, the design of the inner layer measurement points includes:

[0012] S201, first-order alignment measurement point safety distance design;

[0013] S202, design of overall alignment measurement points for safety distances from order 2 to order N;

[0014] S203 is for N+2 layer isolation ring design without blind holes.

[0015] In step S201, the design of the first-order alignment measurement point safety distance includes:

[0016] The END grounding point is a copper layer, D is the diameter of the blind via in the current layer, and the inner N+1 layer copper stripping design safety distance clearance = A / 2 isolation ring is located directly below the N-order test point. The copper is retained directly below the laser hole inside the isolation ring. Other test points in the N+1 layer are designed with blind via pads in the inner layer. The pads are circular pads, and the outer copper stripping design of the pads is an isolation ring to prevent the transition layer of other test points from being connected to the copper layer and affecting the judgment. If the deviation of the single-layer blind via in each order exceeds the clearance design, the outer ENG test point is connected to the circuit of each order test point, and it is determined that the alignment deviation of the single-layer blind via is greater than the current clearance.

[0017] In step S202, the design of the overall alignment measurement points for the 2nd to Nth order safety distances includes:

[0018] For N-order HDI, the safety distance clearance = A / 2 isolation ring is designed for copper removal from inner layers 2 to N+1 directly below the outer layer measuring point. Copper is retained directly below the laser via inside the isolation ring. The coupon pattern design is the same for symmetrical layers. If the blind via offset of any layer exceeds the safety distance clearance design, the outer layer ENG measuring point and the overall alignment measuring point circuit are connected, and it is determined that the overall alignment offset is greater than the current clearance.

[0019] In step S203, when designing the isolation ring for the N+2 layer without blind vias, the inner layer coupon is designed with a circular pad base, and the outer periphery of the pad is designed with copper holes to form an isolation ring; the total length of the coupon is consistent with that of the outer layer; the coupon graphic design for the symmetrical layer is the same.

[0020] In step S3, during the alignment quantification control, the maximum offset of a single-layer blind hole is required to be ≤D / 2. The coupon is located at the edge of the panel process and the edge of the graphic set process. According to the alignment control requirements, multiple sets of different safety distances clearance = A / 2 are set. The outer layer of the clearance coupon is marked with characters to distinguish the test areas of different safety distances. Based on the open circuit or short circuit of the clearance coupon in the test areas of different safety distances, the maximum deviation of the blind hole and the alignment are quantitatively judged.

[0021] Furthermore, based on the open or short circuit conditions of electrical tests in different safety distance test areas, the maximum deviation and alignment of blind holes are quantitatively determined, including:

[0022] Using X-ray imaging equipment, under open-circuit or short-circuit conditions in different safety distance test areas, determine whether the maximum offset distance of the isolation ring of different layers of blind holes is greater than the safety distance clearance = A / 2. Specifically, this includes:

[0023] In the X-ray image display equipment, the frequency domain direction of the safe distance image frame sequence extends from the first-order measurement point safe distance sub-image to the Nth measurement point safe distance sub-image. In the time domain direction, the isolation windows of different layers of blind holes are within the range of symbols from the second layer to the (N+1)th layer. The safe distance image frame sequence contains fixed complex frequency synchronization symbols, which will generate a peak at a fixed position on the signal spectrum. At the receiving end, the signal within the time domain of symbols 2-N+1 of the safe distance image frame sequence is extracted. A bandpass filter with a center frequency of 2×g Hz (where g is the bandwidth of the measurement point safe distance sub-image) and a bandwidth smaller than g is used to filter out redundant signal components. Then, the frequency offset value of the maximum offset distance signal of the isolation ring of different layers of blind holes is estimated based on the peak offset. This offset value is then compared with the safe distance clearance = A / 2.

[0024] The safe distance image frame sequence contains fixed complex symbols, generating a peak at a position of ±2×g Hz on the signal's spectrum. The specific method is as follows: after frame synchronization at the receiving end, the signal within the time domain of 2-N+1 symbols is extracted, and then convolved with a bandpass filter with a center frequency of 2×g Hz, an FFT point count of N_fft, a system sampling frequency of fs, and a bandwidth less than g to achieve filtering. Then, an N_fft-point FFT operation is performed on the signal, and the offset is calculated.

[0025] Furthermore, the method for calculating the offset includes: first, transmitting the modulated signal, extracting the signal of 2-N+1 symbols in the time domain, filtering it through a filter with a center frequency of 2×g, performing an FFT operation on N_fft, and then saving it; after the received signal undergoes the FFT operation, performing a convolution operation with the saved data, the length of the signal after the N_fft FFT operation is N_fft, and the length of the result of the convolution operation is N_fft×2+1; the peak position of the convolution result is r1, if there is no offset, then r1=N_fft+1; if the offset is r1-N_fft-1, then the frequency offset estimate is: (r1-N_fft-1)×fs / N_fft(Hz);

[0026] The method for calculating the offset includes: after the received signal is processed by the FFT operation, the amplitude of the signal after the FFT is obtained. Only the amplitude within the frequency range of 1 to fs / 2 is taken. A peak value will appear. Let the position of the peak value be r2. Then the estimated value of the frequency offset is: (r2-1)×fs / N_fft–2×g.

[0027] The frequency synchronization method based on the TETRA II standard for signal frequency offset estimation includes: first, obtaining the estimated frequency offset value through an estimation algorithm, and then compensating for the frequency offset; the compensation is performed according to the Fourier transform formula. Where χ is the angular velocity, and χ=2π*g', g' is the frequency offset estimate, and g(t) is the signal with frequency offset at the receiving end.

[0028] Another object of the present invention is to provide a blind hole alignment test module design and test system, which is implemented using the aforementioned blind hole alignment test module design and test method. The system includes:

[0029] The outer layer test point design module is used to design the END grounding test point pad, test point pad, center spacing between adjacent pads, and total width of the test area coupon.

[0030] The inner layer measurement point design module is used for the design of first-order to N-order safety distance alignment measurement points for 2-N+1 layers, and the design of N+2 layers of isolation rings without blind holes.

[0031] The alignment quantification and control module is used to measure open or short circuits of multiple sets of different safety distances (clearance coupons) and to quantify the maximum deviation and alignment of blind holes.

[0032] Another objective of this invention is to provide an application of the aforementioned blind via alignment test module design and test method in the blind via alignment test of HDI boards.

[0033] Combining all the above technical solutions, the beneficial effects of this invention are as follows: This invention provides a universal blind via alignment test module design and test method, improving the analysis efficiency and quantitative accuracy of blind via alignment capability. The universal HDI blind via alignment coupon design and test method provided by this invention can efficiently and quickly determine the blind via alignment capability at each level and the overall stack-via blind via alignment capability of HDI boards of any order. Attached Figure Description

[0034] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure;

[0035] Figure 1 This is a diagram illustrating the design and testing method of the blind hole alignment test module provided in an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the outer measuring point design of the coupon provided in an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of the inner layer measuring point design of the coupon provided in an embodiment of the present invention. Detailed Implementation

[0038] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0039] Example 1, in the design and testing method of the blind via alignment test module, the test principle of the general test area coupon for blind via alignment is as follows: Utilizing the characteristic of a single-layer blind via connecting and conducting adjacent layers, a copper-free isolation ring of appropriate width is designed in each layer to shield the influence of blind via misalignment in other layers. A circuit is formed between the corresponding blind via test point and the END grounding test point using an electrical test pin. If the circuit is conductive, it indicates that the blind via misalignment of the layer corresponding to that test point exceeds the clearance of the copper-free isolation ring; if the circuit is not conductive, it indicates that the blind via misalignment of the layer corresponding to that test point does not exceed the clearance of the copper-free isolation ring. This coupon design of the present invention is small in size, saves space, and the alignment capability can be judged simply by checking whether the test point is open or short-circuited using an electrical test pin. It is simple, convenient, and highly practical.

[0040] like Figure 1 As shown, the design and testing method of the blind hole alignment test module include:

[0041] S1, outer layer test point design, design END ground test point pad, test point pad, center spacing between adjacent pads, and total width of the test area coupon;

[0042] The END grounding test point uses a 0.6mm square pad, and all test points use 0.6mm round pads with a 1mm center-to-center distance between adjacent pads. The total width of the test area coupon is 1mm, and the total length is adjusted according to the actual board order. The coupon graphic design is the same for symmetrical layers. A schematic diagram of the outer layer test point design of the coupon is shown below. Figure 2 As shown;

[0043] S2, inner layer measurement point design, design of first-order to Nth-order safety distance alignment measurement points for layers 2 to N+1, and design of isolation ring without blind holes for layer N+2;

[0044] S201, first-order alignment measurement point safety distance design;

[0045] The END grounding point is the copper foil, D is the diameter of the blind via in the current layer, and the inner layer N+1 is directly below the N-order test point (N=1, 2, 3...). A safety distance clearance = A / 2 isolation ring is designed, and the copper directly below the laser hole inside the isolation ring must be preserved. Other test points in layer N+1 are designed with blind via pads; the pads are 0.6mm circular pads, and a 0.8mm isolation ring is designed around the pads to ensure that the transition layer of other test points does not conduct with the copper foil, affecting the judgment. If the deviation of a single-layer blind via exceeds the clearance design, the outer layer ENG test point is connected to the circuit of each test point, indicating that the single-layer blind via alignment deviation is greater than the current clearance; conversely, the same applies.

[0046] S202, design of overall alignment measurement points for safety distances from order 2 to order N;

[0047] For N-order HDI, the copper removal design for inner layers 2 to N+1 directly below the outer layer measuring point should have a clearance of A / 2. Copper directly below the laser via inside the isolation ring must be retained. The coupon pattern design is the same for symmetrical layers. If any layer's blind via offset exceeds the clearance design, the outer layer ENG measuring point and the overall alignment measuring point loop will be connected, indicating that the overall alignment offset is greater than the current clearance; conversely, if the offset is less than the current clearance, the same applies.

[0048] For S203, when designing an N+2 layer without blind vias and an isolation ring, the inner layer coupon is designed as a 0.6mm circular pad, with a 0.8mm isolation ring created by copper-hole perforation around the pad (see N+2 layer illustration). The total width of the coupon is 1mm, and its total length is the same as the outer layer. The coupon graphic design is the same for symmetrical layers.

[0049] The inner layer measuring point design of the coupon is as follows: Figure 3 As shown;

[0050] S3, alignment quantitative control, measures open or short circuits of multiple sets of different safety distances, quantitatively judges the maximum deviation of blind holes and alignment;

[0051] Generally, the maximum offset requirement for a single-layer blind via is ≤D / 2. The above coupon can be set at appropriate locations on the panel process edge, graphic set process edge, or multiple pieces. Multiple sets of different safety distances clearance = A / 2 can be set according to the alignment control requirements (e.g., A = 25um, 40um, 50um, 60um, 70um, 80um, etc.). The outer label characters of the clearance coupon are distinguished by different safety distance test areas. Based on the open circuit or short circuit conditions of different clearance coupons, the maximum deviation of the blind via and the alignment capability can be quantitatively judged.

[0052] For example, in step S3, the maximum offset of a single-layer blind hole is required to be ≤D / 2. The coupon is located at the edge of the panel process and the edge of the graphic set process. According to the alignment control requirements, multiple sets of different safety distances clearance = A / 2 are set. The outer layer of the clearance coupon is marked with characters to distinguish the test areas of different safety distances. Based on the open circuit or short circuit of the clearance coupon in the test areas of different safety distances, the maximum deviation of the blind hole and the alignment are quantitatively judged.

[0053] Based on the open or short circuit conditions of electrical tests in different safety distance test areas, the maximum deviation and alignment of blind holes are quantitatively determined, including:

[0054] Using X-ray imaging equipment, under open-circuit or short-circuit conditions in different safety distance test areas, determine whether the maximum offset distance of the isolation ring of different layers of blind holes is greater than the safety distance clearance = A / 2. Specifically, this includes:

[0055] In the X-ray image display equipment, the frequency domain direction of the safe distance image frame sequence extends from the first-order measurement point safe distance sub-image to the Nth measurement point safe distance sub-image. In the time domain direction, the isolation windows of different layers of blind holes are within the range of symbols from the second layer to the (N+1)th layer. The safe distance image frame sequence contains fixed complex frequency synchronization symbols, which will generate a peak at a fixed position on the signal spectrum. At the receiving end, the signal within the time domain of symbols 2-N+1 of the safe distance image frame sequence is extracted. A bandpass filter with a center frequency of 2×g Hz (where g is the bandwidth of the measurement point safe distance sub-image) and a bandwidth smaller than g is used to filter out redundant signal components. Then, the frequency offset value of the maximum offset distance signal of the isolation ring of different layers of blind holes is estimated based on the peak offset. This offset value is then compared with the safe distance clearance = A / 2.

[0056] The safe distance image frame sequence contains fixed complex symbols, generating a peak at a position of ±2×g Hz on the signal's spectrum. The specific method is as follows: after frame synchronization at the receiving end, the signal within the time domain of 2-N+1 symbols is extracted, and then convolved with a bandpass filter with a center frequency of 2×g Hz, an FFT point count of N_fft, a system sampling frequency of fs, and a bandwidth less than g to achieve filtering. Then, an N_fft-point FFT operation is performed on the signal, and the offset is calculated.

[0057] The method for calculating the offset includes: first, transmitting the modulated signal, extracting the signal of 2-N+1 symbols in the time domain, filtering it through a filter with a center frequency of 2×g, performing an FFT operation on N_fft, and then saving it; after the received signal undergoes an FFT operation, performing a convolution operation with the saved data, the length of the signal after the N_fft FFT operation is N_fft, and the length of the result of the convolution operation is N_fft×2+1; the peak position of the convolution result is r1, if there is no offset, then r1=N_fft+1; if the offset is r1-N_fft-1, then the frequency offset estimate is: (r1-N_fft-1)×fs / N_fft(Hz);

[0058] The method for calculating the offset includes: after the received signal undergoes an FFT operation, the amplitude of the signal after the FFT is obtained. Only the amplitude within the frequency range of 1 to fs / 2 is taken, which will result in a peak value. Let the position of the peak value be r2, then the estimated value of the frequency offset is:

[0059] (r²-1)×fs / N_fft–2×g

[0060] The frequency synchronization method based on the TETRA II standard for signal frequency offset estimation includes: first, obtaining the estimated frequency offset value through an estimation algorithm, and then compensating for the frequency offset; the compensation is performed according to the Fourier transform formula. Where χ is the angular velocity, and χ=2π*g', g' is the frequency offset estimate, and g(t) is the signal with frequency offset at the receiving end.

[0061] For example, when an HDI symmetrical layer has blind holes on one side and no blind holes on the other side, the coupon can be designed on the blind hole side, and electrical testing can be performed on a single side with a needle.

[0062] Example 2: The blind hole alignment test module design and test system include:

[0063] The outer layer test point design module is used to design the END grounding test point pad, test point pad, center spacing between adjacent pads, and total width of the test area coupon.

[0064] The inner layer measurement point design module is used for the design of first-order to N-order safety distance alignment measurement points for 2-N+1 layers, and the design of N+2 layers of isolation rings without blind holes.

[0065] The alignment quantification and control module is used to measure open or short circuits of multiple sets of different safety distances (clearance coupons) and to quantify the maximum deviation and alignment of blind holes.

[0066] Example 3: Application of the blind via alignment test module design and test method of the present invention in the blind via alignment test of HDI board.

[0067] Application example: The project designs coupons according to the principles shown in the diagram. The number of measuring points and the length are designed according to the maximum grade of the actual product. The clearance value A is adjusted according to actual needs. Multiple sets of different clearance coupons can be set at the same time.

[0068] Electrical testing is performed on the coupon test points. The maximum deviation of single-layer blind holes and overall alignment is determined by the open or short circuit between the END pad and each test point.

[0069] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A design and testing method for a blind hole alignment test module, characterized in that, The method includes the following steps: S1, outer layer test point design, design END ground test point pad, test point pad, center spacing between adjacent pads, and total width of the test area coupon; S2, inner layer measurement point design, design of first-order to Nth-order safety distance alignment measurement points for layers 2 to N+1, and design of isolation ring without blind holes for layer N+2; S3, alignment quantitative control, measures open or short circuits of multiple sets of different safety distance clearance coupons, and quantitatively judges the maximum deviation and alignment of blind holes.

2. The blind hole alignment test module design and test method according to claim 1, characterized in that, In step S2, the design of the inner layer measurement points includes: S201, first-order alignment measurement point safety distance design; S202, design of overall alignment measurement points for safety distances from order 2 to order N; S203 is for N+2 layer isolation ring design without blind holes.

3. The blind hole alignment test module design and test method according to claim 2, characterized in that, In step S201, the design of the first-order alignment measurement point safety distance includes: The END grounding point is a copper layer, D is the diameter of the blind via in the current layer, and the inner N+1 layer copper stripping design safety distance clearance = A / 2 isolation ring is located directly below the N-order test point. The copper is retained directly below the laser hole inside the isolation ring. Other test points in the N+1 layer are designed with blind via pads in the inner layer. The pads are circular pads, and the outer copper stripping design of the pads is an isolation ring to prevent the transition layer of other test points from being connected to the copper layer and affecting the judgment. If the deviation of the single-layer blind via in each order exceeds the clearance design, the outer ENG test point is connected to the circuit of each order test point, and it is determined that the alignment deviation of the single-layer blind via is greater than the current clearance.

4. The design and testing method of the blind hole alignment test module according to claim 2, characterized in that, In step S202, the design of the overall alignment measurement points for the 2nd to Nth order safety distances includes: For N-order HDI, the safety distance clearance = A / 2 isolation ring is designed for copper removal from inner layers 2 to N+1 directly below the outer layer measuring point. Copper is retained directly below the laser via inside the isolation ring. The coupon pattern design is the same for symmetrical layers. If the blind via offset of any layer exceeds the safety distance clearance design, the outer layer ENG measuring point and the overall alignment measuring point circuit are connected, and it is determined that the overall alignment offset is greater than the current clearance.

5. The design and testing method of the blind hole alignment test module according to claim 2, characterized in that, In step S203, when designing the isolation ring for the N+2 layer without blind vias, the inner layer coupon is designed with a circular pad base, and the outer periphery of the pad is designed with copper holes to form an isolation ring; the total length of the coupon is consistent with that of the outer layer; the coupon graphic design for the symmetrical layer is the same.

6. The design and testing method of the blind hole alignment test module according to claim 1, characterized in that, In step S3, during the alignment quantification control, the maximum offset of a single-layer blind hole is required to be ≤D / 2. The coupon is located at the edge of the panel process and the edge of the graphic set process. According to the alignment control requirements, multiple sets of different safety distances clearance = A / 2 are set. The outer label characters of the clearance coupon are distinguished in different safety distance test areas. Based on the open circuit or short circuit status of the clearance coupon in different safety distance test areas, the maximum deviation of the blind hole and the alignment are quantitatively judged.

7. The design and testing method of the blind hole alignment test module according to claim 6, characterized in that, Based on the open or short circuit conditions of electrical tests in different safety distance test areas, the maximum deviation and alignment of blind holes are quantitatively determined, including: Using X-ray imaging equipment, under open-circuit or short-circuit conditions in different safety distance test areas, determine whether the maximum offset distance of the isolation ring of different layers of blind holes is greater than the safety distance clearance = A / 2. Specifically, this includes: In the X-ray image display equipment, the frequency domain direction of the safe distance image frame sequence extends from the first-order measurement point safe distance sub-image to the Nth measurement point safe distance sub-image. In the time domain direction, the isolation windows of different layers of blind holes are within the range of symbols from the second layer to the (N+1)th layer. The safe distance image frame sequence contains fixed complex frequency synchronization symbols, which will generate a peak at a fixed position on the signal spectrum. At the receiving end, the signal within the time domain of symbols 2-N+1 of the safe distance image frame sequence is extracted. A bandpass filter with a center frequency of 2×g Hz (where g is the bandwidth of the measurement point safe distance sub-image) and a bandwidth smaller than g is used to filter out redundant signal components. Then, the frequency offset value of the maximum offset distance signal of the isolation ring of different layers of blind holes is estimated based on the peak offset. This offset value is then compared with the safe distance clearance = A / 2. The safe distance image frame sequence contains fixed complex symbols, generating a peak at a position of ±2×g Hz on the signal's spectrum. The specific method is as follows: after frame synchronization at the receiving end, the signal within the time domain of 2-N+1 symbols is extracted, and then convolved with a bandpass filter with a center frequency of 2×g Hz, an FFT point count of N_fft, a system sampling frequency of fs, and a bandwidth less than g to achieve filtering. Then, an N_fft-point FFT operation is performed on the signal, and the offset is calculated.

8. The design and testing method of the blind hole alignment test module according to claim 7, characterized in that, The method for calculating the offset includes: first, transmitting the modulated signal, extracting the signal of 2-N+1 symbols in the time domain, filtering it through a filter with a center frequency of 2×g, performing an FFT operation on N_fft, and then saving it; after the received signal undergoes an FFT operation, performing a convolution operation with the saved data, the length of the signal after the N_fft FFT operation is N_fft, and the length of the result of the convolution operation is N_fft×2+1; the peak position of the convolution result is r1, if there is no offset, then r1=N_fft+1; if the offset is r1-N_fft-1, then the frequency offset estimate is: (r1-N_fft-1)×fs / N_fft(Hz); The method for calculating the offset includes: after the received signal is processed by the FFT operation, the amplitude of the signal after the FFT is obtained. Only the amplitude within the frequency range of 1 to fs / 2 is taken. A peak value will appear. Let the position of the peak value be r2. Then the estimated value of the frequency offset is: (r2-1)×fs / N_fft–2×g. The frequency synchronization method based on the TETRA II standard for signal frequency offset estimation includes: first, obtaining the estimated frequency offset value through an estimation algorithm, and then compensating for the frequency offset; the compensation is performed according to the Fourier transform formula. Where χ is the angular velocity, and χ=2π*g', g' is the frequency offset estimate, and g(t) is the signal with frequency offset at the receiving end.

9. A blind hole alignment test module design and test system, characterized in that, This system is implemented using the blind hole alignment test module design and test method described in any one of claims 1-8. The system includes: The outer layer test point design module is used to design the END grounding test point pad, test point pad, center spacing between adjacent pads, and total width of the test area coupon. The inner layer measurement point design module is used for the design of first-order to N-order safety distance alignment measurement points for 2-N+1 layers, and the design of N+2 layers of isolation rings without blind holes. The alignment quantification and control module is used to measure open or short circuits of multiple sets of different safety distances (clearance coupons) and to quantify the maximum deviation and alignment of blind holes.

10. The application of a blind via alignment test module design and test method as described in any one of claims 1-8 in the blind via alignment test of HDI boards.

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