Method for detecting PCB (Printed Circuit Board) back drilling hole residual copper defect and distribution

Abstract

The invention provides a PCB back drilling hole residual copper defect and distribution detection method, and relates to the technical field of PCBs. The invention discloses a method for detecting PCB back drilling hole residual copper defects and distribution. The specific detection method comprises the following steps that S1, an X-ray imaging device with the resolution ratio being 6-30 microns is selected; a ray source in the X-ray imaging device can move bidirectionally; s2, the numerical value of the scanning process is 20 microns; s3, setting scanning coordinates of X rays; s4, the maximum threshold value A and the minimum threshold value B of the residual copper length are set; s5, acquiring a top view image of the back drilling hole to be detected by adopting X rays; s6, X-ray scanning is carried out, and scanning process numerical values N1 of the residual copper tip and N2 of the residual copper bottom are generated; and S7, judging whether the residual copper length L value is within (A, B) or not. According to the method, the residual copper defect and the distribution condition of the back drilling hole of the whole PCB can be accurately and quickly detected and judged.

Description

Technical Field

[0001] The present invention relates to the technical field of PCB boards, and in particular to a method for detecting residual copper defects and their distribution in back-drilled holes of PCB boards. Background Art

[0002] PCB (printed circuit board) backdrilling is a process used to remove excess drill cuttings from the bottom of blind vias in multilayer boards and improve signal integrity. Its quality directly impacts the electrical performance and reliability of the board. Nondestructive testing (NDT) is a technique that verifies key parameters such as backdrilled hole size, location, and hole wall condition without damaging the PCB. It is a crucial quality control step in the PCB production process.

[0003] Nondestructive testing of backdrilled via quality is a core quality control measure in PCB manufacturing. The appropriate testing technology should be selected based on the product type (e.g., consumer electronics, industrial control) and quality requirements. Optical and X-ray inspections are suitable for mass production screening.

[0004] For example, the invention patent with patent application number "202311549514.8" and titled "A Method for Nondestructive Testing and Defect Judgment of PCB Back Drilling Holes" adopts X-ray detection. The specific detection method includes: Step 1: Using X-rays to obtain a cross-sectional image of the back-drilled hole to be tested; Step 2: Using the surface layer where the drilling surface of the back-drilled hole is located as the reference layer on the cross-sectional image, the theoretical depth of the target layer is calculated based on the layer of the target layer and the theoretical thickness of each layer between the target layer and the reference layer, thereby preliminarily locating the target layer; Step 3: Using the theoretical depth of the target layer as the reference, search for the layer with a sudden grayscale value mutation based on the actual deviation range of the target layer, and determine it as the actual target layer; Step 4: Identify the tip CN 117274254B end Ltip of the stump tip on the cross-sectional image, and measure the distance between the tip Ltip of the stump tip and the target layer to obtain the stump length Ltip. This method for nondestructive testing and defect judgment of PCB back-drilling hole quality can effectively judge the depth and defects.

[0005] In X-ray inspection, resolution is a key technical indicator that directly impacts the accuracy and reliability of test results. Different application scenarios, inspection objects, and standards have different requirements for resolution. The aforementioned patent document describes a method for nondestructive testing and defect determination of PCB back-drilled holes. This method comprehensively detects back-drilled hole depth, residual piles, and drill deviation. This method places very high demands on resolution. The higher the resolution, the slower the calculation speed, making it impossible to quickly detect and determine residual copper defects in back-drilled holes across the entire PCB. Summary of the Invention

[0006] Based on this, it is necessary to provide a method for detecting residual copper defects and their distribution in PCB back-drilled holes to address the existing technical problems, which can quickly and accurately detect and judge the residual copper defects in the back-drilled holes of the entire PCB board.

[0007] In order to solve the problems of the prior art, the present invention adopts the following technical solutions:

[0008] A method for detecting residual copper defects and their distribution in back-drilled holes on PCB boards. The specific detection method is as follows:

[0009] S1: Select an X-ray imaging device with a resolution of 6 to 30 μm. The resolution is adjustable and is set appropriately according to the thickness and size of the PCB to be inspected. The ray source in the X-ray imaging device can move in both directions.

[0010] S2: Set the scanning process of the X-ray imaging device according to the thickness of the PCB to be inspected, with the specific scanning process value being 20 μm;

[0011] S3: There are through holes and back-drilled holes on the PCB to be inspected. According to the position coordinates of the back-drilled holes on the PCB to be inspected, the X-ray scanning coordinates are set and accurate scanning is performed according to the preset scanning coordinates;

[0012] S4: According to the processing requirements of the PCB board to be tested, the maximum threshold value A and the minimum threshold value B of the residual copper length are set;

[0013] S5: Using X-rays to obtain a top view image of the back-drilled hole to be tested. The specific scanning method is as follows: starting from the PCB surface, the X-rays scan inward layer by layer from the PCB surface, and generate specific scanning progress values;

[0014] S6: When the X-ray first scans the tip of the residual copper on the back of the PCB board, the top view image is an incomplete circular image. At this time, the scanning node N1 is recorded and the scanning process value N1 corresponding to N1 is generated. 残铜尖端 When scanning to the bottom of the residual copper, the top view image presented is a complete circular image. At this time, the scanning node N2 is recorded and the scanning process value N2 corresponding to N is generated. 残铜底部 , the distance from the tip of the residual copper to the bottom of the residual copper is the length L of the residual copper;

[0015] S7: The calculation formula for the remaining copper length L is: Remaining copper length L = N2 残铜尖端 -N1 残铜底部 , determine whether the residual copper length L is within (A, B);

[0016] S8:

[0017] If the residual copper length L value in S7 is within (A, B), it is judged to be qualified;

[0018] If the residual copper length L value in S7 is not within (A, B), it is judged as unqualified.

[0019] The beneficial effects of the present invention are as follows: the present invention provides a method for detecting residual copper defects and their distribution in back-drilled holes of a PCB board, which can quickly and accurately detect and judge the residual copper defects and their distribution in the back-drilled holes of an entire PCB board, thereby improving the detection efficiency and accuracy, and having a very positive effect on the quality assurance of the PCB board back-drilling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a schematic top view of the front side of the PCB board of the present invention;

[0021] Figure 2 This is a schematic diagram of the PCB back drilling standard;

[0022] Figure 3 This is a top view of a PCB back-drilled hole with residual copper.

[0023] Figure 4 This is a cross-sectional diagram of a PCB back-drilled hole with residual copper;

[0024] Figure 5 This is a schematic diagram of the residual copper in the PCB back drilling; Figure 6 Scan the top view of the PCB surface; Figure 7 This is a top view of the layer when scanning to the tip of the residual copper drilled on the back of the PCB board; Figure 8 This is a top view of the layer when scanning to the bottom of the residual copper drilled on the back of the PCB board. DETAILED DESCRIPTION

[0025] In order to further understand the features, technical means, specific objectives and functions achieved by the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] A method for detecting residual copper defects in back-drilled holes on PCB boards. The specific detection method is as follows:

[0028] S1: Select an X-ray imaging device with a resolution of 6 to 30 μm. The resolution is adjustable and is set appropriately according to the thickness and size of the PCB to be inspected. The radiation source in the X-ray imaging device can move in both longitudinal and transverse directions.

[0029] In the field of X-rays, resolution usually refers to the smallest structure size that can be distinguished during imaging, that is, spatial resolution. So the 6-30μm here means that the size of details that the X-ray imaging system can distinguish is within this range;

[0030] Higher-resolution X-ray imaging may require more complex equipment, such as synchrotron radiation sources or special detectors, while resolutions of 6-30 microns may be more easily achieved with laboratory-grade equipment, at a lower cost and suitable for widespread application;

[0031] X-rays with a resolution of 6 to 30 μm (usually classified as microfocus X-rays or micro X-rays) have unique advantages in imaging and detection, and are particularly suitable for scenarios that require a balance between detail resolution and penetration.

[0032] The resolution of 6 to 30 μm can directly observe the back-drilled hole cross-section, clearly distinguish the copper foil (signal layer), substrate (such as FR4) and residual copper boundaries, and achieve quantitative measurement of residual copper length (error ≤ 5 μm).

[0033] S2: Setting the scanning process value of the X-ray imaging device according to the thickness of the PCB board to be inspected;

[0034] The "scanning process value" refers to the real-time depth coordinate value when the X-ray starts from the PCB surface (starting point) and penetrates the circuit board layer by layer, usually in microns (μm).

[0035] For example, if the depth of the PCB surface is 0 μm, each time a layer (such as substrate or copper layer) is scanned downward, the process value increases, such as 20 μm / layer, until the entire back drilling area is penetrated.

[0036] The purpose of setting the scan process value is:

[0037] It is used to accurately record the physical depth of the current X-ray scan, corresponding to the axial position of the back-drilled hole, so as to match it with the image data and realize quantitative analysis of the residual copper length.

[0038] The smaller the scanning process value (such as 5μm), the longer the total scanning time, but the higher the spatial resolution of the reconstructed image; conversely, a scanning process value of 20μm can shorten the scanning time.

[0039] Scan process value comparison table:

[0040] Process Value Spatial resolution Single sample scanning time Error margin 5μm ≤10μm 20-50 minutes ±5~10μm 20μm 15~25μm 5-10 minutes ±20~30μm

[0041] The 20μm speed is suitable for rapid sampling inspections on mass production lines. It can complete the initial screening of back-drilling depths of multiple PCB boards within 10 minutes, making it suitable for rapid batch inspection of PCB back-drilling holes.

[0042] S3: There are through holes and back-drilled holes on the PCB to be inspected. According to the position coordinates of the back-drilled holes on the PCB to be inspected, the X-ray scanning coordinates are set and accurate scanning is performed according to the preset scanning coordinates;

[0043] In PCB (printed circuit board) inspection, for boards containing both through holes and back drill holes, precise X-ray scanning based on the back drill hole location coordinates is a key technology to improve inspection efficiency and accuracy.

[0044] S3.1 Acquisition of back-drilling hole position coordinates

[0045] Data source: Extract backdrill hole coordinate information (X / Y axis position, unit: mm or mil) from PCB design files (such as Gerber files);

[0046] Format conversion: Convert the coordinate data into a format supported by the X-ray equipment software (such as CSV, DXF), ensuring that the coordinate origin (usually the lower left corner or center of the PCB board) is consistent with the equipment coordinate system.

[0047] S3.2 Setting of X-ray Scanning Coordinates

[0048] Software interface operation: Import the coordinate file into the X-ray detection software and use the "ROI (Region of Interest) tool" to select the scanning range of a single or batch back-drilled hole;

[0049] Supports manual fine-tuning: For back-drilled holes with individual position deviations, you can drag the ROI box in the 3D preview image to adjust the coordinates.

[0050] Coordinate calibration: By placing a calibration plate of known size (such as an aluminum template with standard holes), verify the consistency of the device coordinate system with the actual physical coordinates. The error must be controlled within ±50μm.

[0051] Precision X-ray scanning based on backdrilled hole coordinates is a data-driven, intelligent inspection solution. Through a comprehensive process encompassing "coordinate acquisition - precise positioning - automated scanning - and data closure," it enables efficient and high-precision inspection of through-holes and backdrilled holes on PCBs. Its core advantages lie in reducing ineffective scanning areas, improving defect location efficiency, and supporting process traceability and optimization. It is particularly well-suited for mass production of complex PCBs, such as high-density interconnect (HDI) boards and multi-layer, high-speed boards.

[0052] S4: According to the processing requirements of the PCB board to be tested, the maximum threshold value A and the minimum threshold value B of the residual copper length are set;

[0053] In PCB backdrill inspection, residual copper length refers to the length of the copper pillar or substrate left after backdrilling, which directly affects signal integrity (especially high-frequency signals) and reliability. Setting the maximum and minimum residual copper length thresholds (A and B) is a core part of quality control. Accurate threshold setting is crucial for ensuring signal performance, especially in high-frequency and high-speed PCB production.

[0054] S5: Using X-rays to obtain a top view image of the back-drilled hole to be tested. The specific scanning method is as follows: starting from the PCB surface, the X-rays scan inward layer by layer from the PCB surface, and generate specific scanning progress values;

[0055] With the PCB surface as depth zero, X-rays are scanned downward layer by layer (in the Z-axis direction) at a preset speed (e.g., 20μm / layer). Each scan generates a top-down image at the corresponding depth. The scanning range must cover the entire axial depth of the backdrilled hole (from hole opening to hole bottom).

[0056] S6: Image acquisition. In the top view image of each layer scan, the back-drilled hole appears as a circle, and the residual copper (copper not removed by back drilling) appears as edge residue.

[0057] When X-ray scanning the tip of the residual copper on the back of the PCB board is displayed as edge residue, the scanning node is recorded and the corresponding depth coordinate value N1 is generated. 残铜尖端 When scanning to the bottom of the residual copper, the top view image presented is a circle. At this time, the scanning node is recorded and the corresponding depth coordinate value N2 is generated. 残铜底部 , the distance from the tip of the residual copper to the bottom of the residual copper is the length L of the residual copper;

[0058] See attached for details Figure 6-8 , which is an X-ray scanning top view imaging diagram of the PCB surface layer - residual copper tip - residual copper bottom.

[0059] S7: The calculation formula for the remaining copper length L is: Remaining copper length L = N2 残铜底部 -N1 残铜尖端 , determine whether the residual copper length L is within (A, B);

[0060] S8: If the residual copper length L value in S7 is within (A, B), it is judged to be qualified;

[0061] If the residual copper length L value in S7 is not within (A, B), it is judged as unqualified.

[0062] Example 2

[0063] Based on Example 1, this example discloses a method for determining the distribution of residual copper at different depths, which is as follows:

[0064] Steps S1-S5 are the same as those in Example 1;

[0065] S6: Image acquisition. In the top view image of each layer scan, the back-drilled hole appears as a circle, and the residual copper (copper not removed by back drilling) appears as edge residue.

[0066] When X-ray scanning is performed on the tip of the residual copper at the back of the PCB board, it is displayed as an edge residue. At this time, the scanning node is recorded and the corresponding depth coordinate value N1 is generated. 残铜尖端 When scanning to the bottom of the residual copper, the top view image is a circle. At this time, the scanning node is recorded and the corresponding depth coordinate value N2 is generated. 残铜底部 ;

[0067] S7: Determine the target layer where the residual copper is located

[0068] The interlayer spacing G of each layer from LI to L7 of the PCB board 板层高度 It is known that, for example, the interlayer spacing is 20μm. Of course, the spacing between PCB layers varies. Here, we use 20μm as an example. Then the depth of L1-L2 is 20μm, the depth of L2-L3 is 40μm, and so on.

[0069] If N1 残铜尖端 If the value is 15, it means the tip of the residual copper is between the board layers L1 and L2.

[0070] If N2 残铜底部 If the value is 18, it is determined that the bottom of the residual copper is between the board layers L1 and L2;

[0071] Then determine whether the residual copper is distributed in the board layer L1-L2.

[0072] Each scan layer corresponds to a process value (such as depth 20μm, 40μm...), which is used to mark the position in the image to facilitate subsequent analysis of the distribution of residual copper at different depths.

[0073] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for detecting residual copper defects and their distribution in back-drilled holes on PCB boards. The specific detection method is as follows: S1: Select an X-ray imaging device with a resolution of 6 to 30 μm. The resolution is adjustable and is set appropriately according to the thickness and size of the PCB to be inspected. The ray source in the X-ray imaging device can move in both directions. S2: Set the scanning process of the X-ray imaging device according to the thickness of the PCB to be inspected, with the specific scanning process value being 20 μm; S3: There are through holes and back-drilled holes on the PCB to be inspected. According to the position coordinates of the back-drilled holes on the PCB to be inspected, the X-ray scanning coordinates are set and accurate scanning is performed according to the preset scanning coordinates; S4: According to the processing requirements of the PCB board to be tested, the maximum threshold value A and the minimum threshold value B of the residual copper length are set; S5: Using X-rays to obtain a top view image of the back-drilled hole to be tested. The specific scanning method is as follows: starting from the PCB surface, the X-rays scan inward layer by layer from the PCB surface, and generate specific scanning progress values; S6: When the X-ray scans the tip of the residual copper on the back of the PCB board, the top view image is an incomplete circular image. At this time, the scanning node N1 is recorded and the scanning process value N1 corresponding to N1 is generated. 残铜尖端 When scanning to the bottom of the residual copper, the top view image presented is a complete circular image. At this time, the scanning node N2 is recorded and the scanning process value N2 corresponding to N is generated. 残铜底部 , the distance from the tip of the residual copper to the bottom of the residual copper is the length L of the residual copper; S7: The calculation formula for the remaining copper length L is: Remaining copper length L = N2 残铜尖端 -N1 残铜底部 , determine whether the residual copper length L is within (A, B); S8: If the residual copper length L value in S7 is within (A, B), it is judged to be qualified; If the residual copper length L value in S7 is not within (A, B), it is judged as unqualified.

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