Method for reducing tolerance of via hole stub processed by back drilling and circuit board

Abstract

The invention discloses a method for reducing the tolerance of a backdrill processing via hole stub and a circuit board wherein the method for reducing the tolerance of the backdrill processing via hole stub comprises the following steps: measuring the actual board thickness value of a preset backdrill area of the circuit board; after the thickness of the circuit board is measured, dividing the actual thickness into a first range and a second range, and dividing the actual thickness value by the theoretical thickness value of the circuit board to obtain a relative error; after the error is calculated, the relative error is multiplied by the theoretical drilling depth compensation to obtain actual drilling depth compensation; after the compensation value is calculated, the actual drilling depth compensation is added to the theoretical back drilling depth to obtain the actual back drilling depth; back-drilling processing: after calculating the back-drilling depth, performing back-drilling processing on a preset back-drilling area of the circuit board by taking the actual back-drilling depth as a processing parameter; the mode of measuring the preset back drilling area is more targeted, the accuracy of the back drilling depth is improved, higher back drilling machining precision is achieved, and more efficient signal transmission is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit board processing, and in particular to a method for reducing the tolerance of residual piles of back-drilled via holes, and a circuit board manufactured by using the method for reducing the tolerance of residual piles of back-drilled via holes Background Art With the rapid development of the communications industry, the requirements for high-speed and high-frequency signal transmission on circuit boards are getting higher and higher. Back drilling, as a key process for circuit boards, can remove excess copper in metallized holes above the signal layer, reducing signal loss during transmission. Via stubs refer to the part of the via that remains after back drilling and exceeds the actual needs of signal transmission. In an ideal back drilling operation, the back drilling depth is aimed at just removing the stub part of the via. The higher the back drilling processing accuracy, the faster and more accurate the signal transmission can be.

[0002] In the existing back drilling process, in order to ensure that a good back drilling effect can be achieved in different batches of production, it is necessary to determine a suitable drilling depth compensation and adjust the back drilling depth according to the actual production situation and quality inspection results. This drilling depth compensation is usually carried out by back drilling experiments on multiple test boards, measuring the difference between the actual drilling depth and the ideal depth, and then obtaining an average value or empirical value as the drilling depth compensation through statistical analysis, and then adjusting the back drilling depth according to the drilling depth compensation. However, due to the errors in the board surface processing, the thickness of the board at different positions of the same board is not the same, and there is a certain thickness tolerance. If the empirical value of statistical analysis, that is, drilling depth compensation, is used at different positions of the same board surface, the error value will be too large, exceeding the allowable range of the pre-set back drilling processing accuracy, thereby interfering with the signal transmission of the line and reducing the quality and reliability of signal transmission. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for reducing the tolerance of the residual pile of the back-drilled via hole, which can significantly improve the back-drilling accuracy, optimize signal transmission, enhance the electrical performance of the circuit board, and ensure product quality and reliability.

[0004] The present invention also proposes a circuit board manufactured by using the above method for reducing the tolerance of the residual pile of the back-drilled via hole.

[0005] The method for reducing the tolerance of the residual pile in back drilling processing according to the present invention comprises: Measure the thickness of the circuit board: measure the actual thickness of the preset back-drilling area of ​​the circuit board; Calculation error: After measuring the thickness of the circuit board, the actual thickness value is divided by the theoretical thickness value of the circuit board to obtain a relative error; Calculating the compensation value: after calculating the error, multiplying the relative error by the theoretical drilling depth compensation to obtain the actual drilling depth compensation; Calculating the back drilling depth: after calculating the compensation value, adding the actual drilling depth compensation to the theoretical back drilling depth to obtain the actual back drilling depth; Back drilling processing, after calculating the back drilling depth, taking the actual back drilling depth as a processing parameter, performing back drilling processing on the preset back drilling area of ​​the circuit board.

[0006] The method for reducing the tolerance of the residual pile of the back-drilling via according to the present invention has at least the following beneficial effects: measuring the actual plate thickness value of the preset back-drilling area, dividing the measured data by the theoretical plate thickness value to obtain the relative error, multiplying the relative error by the theoretical drilling depth compensation to obtain the actual drilling depth compensation, and performing back-drilling according to the actual drilling depth compensation. This method of measuring the preset back-drilling area is more targeted, and the actual drilling depth compensation is obtained by the precise actual plate thickness value, which improves the accuracy of the drilling depth compensation, thereby improving the accuracy of the back-drilling. Higher back-drilling processing accuracy is conducive to more efficient signal transmission, reduces signal transmission energy loss and reflection, and at the same time ensures that the via is completely connected to the inner layer circuit, thereby improving the reliability of the electrical connection.

[0007] According to the method for reducing the tolerance of the residual pile of the back-drilling via described in the present invention, when measuring the thickness of the circuit board, the circuit board is placed on the workbench of the back-drilling machine, and then the distance between the upper board surface of the circuit board and the end surface of the workbench is measured to obtain the actual board thickness value.

[0008] According to the method for reducing the tolerance of the residual pile of the back drilling processing through hole described in the present invention, a pad is also arranged between the circuit board and the workbench; it also includes the following steps: pad thickness measurement: in measuring the thickness of the circuit board, the thickness of the pad is measured to obtain the pad thickness value, the distance between the upper board surface of the circuit board and the end surface of the workbench is A, the pad thickness value is B, the actual board thickness value is C, C=AB.

[0009] According to the method for reducing the tolerance of the residual pile of the back drilling processing through hole described in the present invention, before calculating the error, the circuit board thickness is repeatedly measured multiple times to obtain a plurality of actual board thickness values; in calculating the error, the plurality of actual board thickness values ​​of the preset back drilling area are divided into a first range and a second range according to a preset interval, the relative error includes a first error and a second error, the median value of several actual board thickness values ​​within the first range is divided by the theoretical board thickness value of the circuit board to obtain a first relative error, and the median value of several actual board thickness values ​​within the second range is divided by the theoretical board thickness value of the circuit board to obtain a second relative error.

[0010] According to the method for reducing the tolerance of the residual pile of the back drilling hole described in the present invention, the preset interval is T, 20um≤T≤150um, the average of the multiple actual plate thickness values ​​is E, the first range is F, (ET / 2)≤F≤(E+T / 2).

[0011] According to the method for reducing the tolerance of residual piles of back-drilling through holes described in the present invention, the circuit board is provided with a plurality of points to be drilled, and the plurality of points to be drilled are respectively arranged in the preset back-drilling area, and the plurality of points to be drilled are respectively classified into the first range and the second range according to the actual board thickness value obtained from the preset back-drilling area; in the back-drilling process, the back-drilling machine first performs back-drilling processing on the points to be drilled in the first range, and then performs back-drilling processing on the points to be drilled in the second range.

[0012] The method for reducing the tolerance of via stumps in back drilling processing according to the present invention also includes the following steps: Optimization and adjustment: in the back drilling process, after processing several circuit boards of the same batch, the processing parameters of the actual back drilling depth are adjusted according to the depth of the via stumps at the processing site, so as to continue the back drilling process on the remaining circuit boards of the same batch.

[0013] According to the method for reducing the tolerance of via stumps in back drilling processing described in the present invention, during the optimization adjustment, the processed circuit board is sliced, the drilling depth and the via stump depth of the processed via stumps are measured, and the processing parameters of the actual back drilling depth are adjusted according to the drilling depth and the via stump depth.

[0014] According to the method for reducing the tolerance of the residual pile of the back drilling through hole of the present invention, the back drilling machine has a SMARTMAPPING function, and the SMART MAPPING function can measure the distance between the upper board surface of the circuit board and the end surface of the workbench.

[0015] The circuit board according to the present invention comprises the method for reducing the tolerance of the residual pile of the back drilling hole according to the present invention.

[0016] The circuit board according to the present invention has at least the following beneficial effects: the method of reducing the tolerance of the residual pile of the back drilling process is used to improve the accuracy of the back drilling process, and has the characteristics of high-quality and high-speed signal transmission, thereby improving the quality and reliability of the product.

[0017] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 A flow chart of a method for reducing the tolerance of a through-hole stump during back drilling according to an embodiment of the present invention; Figure 2 A schematic diagram of measuring the thickness of a backing plate in a method for reducing the tolerance of a residual pile in a back-drilling through-hole according to an embodiment of the present invention; Figure 3 A schematic diagram of measuring the thickness of a circuit board according to a method for reducing the tolerance of a back-drilled via stump in an embodiment of the present invention.

[0019] Description of Figure Numbers: Measuring the thickness of the circuit board S100; calculating the error S200; calculating the compensation value S300; calculating the back drilling depth S400; back drilling processing S500; Workbench 100; pad 200; circuit board 300; auxiliary contact component 400; drill bit 500; electronic circuit 600; composite cover plate for back drilling 700. DETAILED DESCRIPTION

[0020] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0021] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0022] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0023] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0024] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0025] Back drilling is a key process for circuit boards. The higher the back drilling accuracy, the faster and more accurate the signal transmission can be. A drilling depth compensation value is usually set in the back drilling process to improve the processing accuracy. The drilling depth compensation is usually an empirical value obtained based on statistical analysis. However, due to a certain thickness tolerance in board processing, if the empirical drilling depth compensation based on statistical analysis is used at different positions on the same board, the error value will be too large, exceeding the allowable range of the pre-set back drilling accuracy, thereby interfering with the signal transmission of the line and reducing the quality and reliability of signal transmission.

[0026] To this end, this embodiment discloses a method for manufacturing a circuit board. The method for manufacturing a circuit board includes measuring the thickness of the circuit board S100, calculating the error S200, calculating the compensation value S300, calculating the back drilling depth S400, and back drilling S500. It must be noted that the order of the steps described in this embodiment and the actual operation method can be adjusted according to needs and are not limited to those described in this embodiment.

[0027] During the processing of the circuit board 300, the thickness of the incoming circuit boards 300 is usually roughly distinguished, and the circuit boards 300 with different thicknesses are classified, and then the back drilling processing is performed on the circuit boards 300 with the same thickness range. Specifically, Figure 1As shown, the method for reducing the tolerance of the residual pile of the back-drilling processing through hole proposed by the present invention includes the following steps: measuring the thickness of the circuit board S100: measuring the actual thickness value of the preset back-drilling area of ​​the circuit board 300, in the back-drilling processing process, it is determined in the design stage which areas where the holes are located need to be back-drilled, and the specific area where the back-drilling operation is to be performed is pre-set, and the range where the determined holes are located is the preset back-drilling area; calculating the error S200: the circuit board 300 is set with a theoretical thickness value according to the actual use scenario. After measuring the thickness of the circuit board 300, the actual thickness value is divided by the theoretical thickness value of the circuit board 300 to obtain the relative error. The relative error can more intuitively reflect the degree of deviation of the theoretical thickness value from the actual thickness value; calculating the compensation value S300: after calculating the error, the relative error is multiplied by the theoretical drilling depth compensation to obtain the actual drilling depth compensation; the relative error is the deviation ratio, which can more objectively and accurately reflect the degree of change of the board thickness, so that the drilling depth compensation is more scientific. Calculating the back drilling depth S400: After calculating the compensation value, the actual drilling depth compensation is added to the theoretical back drilling depth to obtain the actual back drilling depth; Back drilling processing S500: After calculating the back drilling depth, the actual back drilling depth is used as a processing parameter to perform back drilling processing on the preset back drilling area of ​​the circuit board 300. Performing back drilling processing according to the actual drilling depth compensation is more targeted. The actual drilling depth compensation is obtained through the accurate actual board thickness value, which improves the accuracy of drilling depth compensation and the precision of back drilling.

[0028] In some embodiments of the present invention, Figure 3 As shown, in measuring the thickness of the circuit board 300, the circuit board 300 is placed on the workbench 100 of the back drilling machine, and the end face of the workbench 100 of the back drilling machine is used as a reference base for measurement, which provides a uniform and stable reference surface for measuring the thickness of the circuit board 300. With the help of the auxiliary contact component 400 of the workbench 100, the circuit board 300 is pressed and placed on the workbench 100, and then the distance between the upper board surface of the circuit board 300 and the end face of the workbench 100 is measured to obtain the actual board thickness value.

[0029] In some embodiments of the present invention, Figure 2 and Figure 3As shown, if the circuit board 300 is placed directly on the workbench 100 during the back drilling process, the bottom surface of the circuit board 300 is in contact with the workbench 100. During the drilling process, due to factors such as the high-speed rotation of the drill bit 500 and possible tiny defects on the surface of the workbench 100, the bottom surface of the circuit board 300 can easily be scratched or worn. Therefore, a pad 200 is also arranged between the circuit board 300 and the workbench 100. The pad 200 is used to protect the bottom surface of the circuit board 300 and assist in back drilling processing, and also includes the following steps: Pad 200 thickness measurement: In measuring the thickness of the circuit board 300, firstly place the pad 200 on the workbench 100 and use the auxiliary contact component 400 to press the pad 200, measure the thickness of the pad 200, measure the distance between the upper surface of the pad 200 in the preset back drilling area and the end face of the workbench 100, so as to obtain the pad 200 thickness value, and then, the pad 200 and the circuit board 300 are stacked on the workbench in sequence. At this time, according to the distance between the upper board surface of the circuit board 300 and the end face of the workbench 100 is A, and the pad 200 thickness value is B, the actual board thickness value can be obtained as C, C=AB. The pad 200 can serve as a buffer layer between the bottom surface of the circuit board 300 and the workbench 100 , and can reasonably disperse the pressure applied by the drill bit 500 on the circuit board 300 during back drilling.

[0030] In other embodiments of the present invention, Figure 2 and Figure 3 During the back drilling operation, the drill bit 500 rotates at high speed and contacts the circuit board 300 to drill holes. During the process, the vibration and deviation of the drill bit 500 may cause physical damage such as wear to the surface of the circuit board 300. Therefore, the back drilling machine is provided with a composite cover plate 700 for back drilling. The composite cover plate 700 for back drilling covers the surface of the circuit board 300 and can serve as a protective barrier to block the impact caused by the drill bit 500. The composite cover plate 700 for back drilling has a certain elasticity and buffering capacity. It can evenly disperse the pressure transmitted by the drill bit 500, reduce the local pressure on the surface of the circuit board 300, and thus reduce the deformation and indentation of the circuit board 300 caused by the concentrated pressure. In other embodiments, the surface of the composite cover plate 700 for back drilling will have some pre-set positioning marks, such as cross lines, circular marks, etc., which correspond to the positions of the holes that need to be back-drilled on the circuit board 300. During the back drilling process, the operator can align the drill bit 500 with the target hole points on the circuit board 300 by observing the positioning marks on the composite cover plate 700 for back drilling, thereby improving the accuracy of drilling positioning and ensuring the quality of the back drilling process.

[0031] In some embodiments of the present invention, before calculating the error, the thickness of the circuit board 300 is repeatedly measured multiple times to obtain multiple actual thickness values. The actual thickness value of each preset back-drilling area is measured in a full coverage manner to comprehensively obtain the thickness information of each part in the preset back-drilling area, providing a more reliable and detailed data basis for subsequent accurate error calculation and back-drilling processing and other operations. In calculating the error, the multiple actual thickness values ​​of the preset back-drilling area are divided into a first range and a second range according to a preset interval. The relative error includes the first error and the second error. The median of several actual thickness values ​​in the first range is divided by the theoretical thickness value of the circuit board 300 to obtain the first relative error. The median of several actual thickness values ​​in the second range is divided by the theoretical thickness value of the circuit board 300 to obtain the second relative error. It should be noted that by selecting the median value for calculation, the excessive influence of individual extreme values ​​that are too large or too small on the relative error calculation result can be avoided, and the calculated relative error can better represent the general deviation of the actual thickness value within the range relative to the theoretical thickness value. Secondly, by dividing the difference range and calculating the relative error, the overall operation process can comprehensively and carefully evaluate the deviation between the plate thickness value and the theoretical plate thickness value in the preset back-drilling area from the perspective of different thickness ranges.

[0032] In some embodiments of the present invention, the preset interval is T, 20um≤T≤150um, this range can adapt to various circuit board 300 thicknesses, the average of multiple actual board thickness values ​​is E, the first range is F, (ET / 2)≤F≤(E+T / 2).

[0033] Specifically, in some embodiments of the present invention, the circuit board 300 is provided with a plurality of points to be drilled, and it is determined in the design stage that the area where the points to be drilled are located needs to be back-drilled, and the plurality of hole points are respectively arranged in the preset back-drilling area, and the plurality of hole points are set with corresponding serial numbers for identification and positioning by the back-drilling machine, and the plurality of hole points to be drilled are respectively classified into the first range and the second range according to the actual board thickness value obtained from the preset back-drilling area. It should be noted that in the back-drilling process, the back-drilling machine first back-drills the points to be drilled in the first range, and then back-drills the points to be drilled in the second range. By classifying the points to be drilled, it is possible to carry out targeted classification in combination with the actual board thickness of the circuit board 300 in the back-drilling area, and to carry out accurate drilling depth compensation according to the board thickness corresponding to the points to be drilled, thereby improving the accuracy of the back-drilling process.

[0034] Furthermore, in some embodiments of the present invention, multiple actual board thickness values ​​of a preset back-drilling area are divided into multiple ranges according to preset intervals. To avoid excessive interval distribution, resulting in complex rules and affecting production operations, the interval is set to 100um, and the board is divided into 5 thickness ranges in total. Then, the 5 thickness ranges are calculated, as shown in the following table.

[0035]

[0036] In some embodiments of the present invention, the following steps are also included: Optimization and adjustment: In the back drilling process, after processing several circuit boards 300 of the same batch, due to a slight error between the equipment setting parameters and the actual processing value, it is necessary to measure the depth of the via stumps at the processing location, and adjust the processing parameters of the actual back drilling depth according to the depth of the via stumps at the processing location, so as to continue the back drilling process for the remaining circuit boards 300 of the same batch. Timely optimization and adjustment can check the processing quality of this part. If a problem is found, it can be quickly located and the processing parameters can be adjusted to avoid the continuation of the problem and ensure the quality stability of the entire back drilling process. In some application scenarios, after processing several points to be drilled within the first range, the depth of the via stumps of the processed drilling points is measured, and the processing parameters of the actual back drilling depth are adjusted according to the measured depth. After adjustment, all the points to be drilled within the first range are processed, and when processing the points to be drilled within the second range, the measurement and adjustment operations are repeated. Refer to the processing of the points to be drilled within the first range, and no further details will be given here.

[0037] In a further embodiment of the present invention, during the optimization adjustment, the processed circuit board 300 is sliced, and the drilling depth and the via stump depth of the processed via stump are measured. The slice measurement can directly observe the via stump situation inside the processed area, and accurately measure its drilling depth and the via stump depth, understand the deviation of the current back drilling process, and adjust the actual back drilling depth processing parameters according to the drilling depth and the via stump depth. This optimization adjustment method based on feedback of the actual processing effect can make the back drilling processing parameters more in line with the actual situation and processing requirements of the circuit board 300, effectively avoid the accumulation of processing errors that may be caused by fixed parameter settings, and continuously improve the accuracy of the back drilling process.

[0038] In a further embodiment of the present invention, referring to Figure 2 and Figure 3 The back drill is provided with an electronic circuit 600, and the back drill has a SMART MAPPING function. The SMART MAPPING function can quickly and accurately identify the points to be drilled on the circuit board 300, and digitally map and mark the information of these points to be drilled. Through the circuit induction of the electronic circuit 600 and the "SMART MAPPING" function of the drill, the board height of the pre-drilling area is measured. The SMART MAPPING function can measure the distance between the upper board surface of the circuit board 300 and the end surface of the workbench 100.

[0039] The circuit board according to the embodiment of the present invention is manufactured by using the above-mentioned method for reducing the tolerance of the residual pile of the back drilling via hole.

[0040] According to the circuit board of the embodiment of the present invention, by using the method of reducing the tolerance of the residual pile of the back drilling via of the embodiment of the present invention, the actual drilling depth compensation is obtained through the precise actual board thickness value during the back drilling process, thereby improving the accuracy of the drilling depth compensation, thereby improving the precision of the back drilling. Higher back drilling processing accuracy is conducive to more efficient signal transmission, reducing signal transmission energy loss and reflection, while ensuring the integrity of the connection between the via and the inner layer circuit, thereby improving the reliability of the electrical connection.

[0041] Other structures and operations of the circuit board according to the embodiment of the present invention are known to those skilled in the art and will not be described in detail here.

[0042] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A method for reducing the tolerance of a back-drilled through-hole stump, characterized in that: The following steps are involved: Measure the thickness of the circuit board: measure the actual thickness of the preset back-drilling area of ​​the circuit board; Calculation error: After measuring the thickness of the circuit board, the actual thickness value is divided by the theoretical thickness value of the circuit board to obtain a relative error; Calculating the compensation value: after calculating the error, multiplying the relative error by the theoretical drilling depth compensation to obtain the actual drilling depth compensation; Calculating the back drilling depth: after calculating the compensation value, adding the actual drilling depth compensation to the theoretical back drilling depth to obtain the actual back drilling depth; Back drilling processing, after calculating the back drilling depth, taking the actual back drilling depth as a processing parameter, performing back drilling processing on the preset back drilling area of ​​the circuit board.

2. The method for reducing the tolerance of the residual pile in the back drilling process according to claim 1 is characterized in that: In measuring the thickness of the circuit board, the circuit board is placed on a workbench of a back drilling machine, and then the distance between the upper surface of the circuit board and the end surface of the workbench is measured to obtain the actual thickness value.

3. The method for reducing the tolerance of the residual pile in the back drilling process according to claim 2, characterized in that: A pad is also provided between the circuit board and the workbench; The following steps are also included: Pad thickness measurement: When measuring the thickness of a circuit board, the thickness of the pad is measured to obtain the pad thickness value. The distance between the upper surface of the circuit board and the end surface of the workbench is A, the pad thickness value is B, and the actual board thickness value is C, where C=AB.

4. The method for reducing the tolerance of the residual pile in the back drilling process according to claim 1, characterized in that: Before calculating the error, repeatedly measuring the thickness of the circuit board for multiple times to obtain multiple actual thickness values; In calculating the error, the multiple actual board thickness values ​​of the preset back-drilling area are divided into a first range and a second range according to a preset interval, the relative error includes a first error and a second error, the median value of several actual board thickness values ​​within the first range is divided by the theoretical board thickness value of the circuit board to obtain a first relative error, and the median value of several actual board thickness values ​​within the second range is divided by the theoretical board thickness value of the circuit board to obtain a second relative error.

5. The method for reducing the tolerance of the residual pile in the back drilling process according to claim 4 is characterized in that: The preset interval is T, 20um≤T≤150um, the average of the plurality of actual plate thickness values ​​is E, the first range is F, (ET / 2)≤F≤(E+T / 2).

6. The method for reducing the tolerance of the residual pile in the back drilling process according to claim 4, characterized in that: The circuit board is provided with a plurality of points to be drilled, and the plurality of points to be drilled are respectively arranged in the preset back drilling area, and the plurality of points to be drilled are respectively classified into the first range and the second range according to the actual board thickness value obtained from the preset back drilling area; In the back drilling process, the back drilling machine first performs back drilling processing on the points to be drilled in the first range, and then performs back drilling processing on the points to be drilled in the second range.

7. The method for reducing the tolerance of the residual pile in the back drilling process according to claim 1 is characterized in that : Also includes the following steps: Optimization and adjustment: In the back drilling process, after processing several circuit boards of the same batch, the processing parameters of the actual back drilling depth are adjusted according to the depth of the via stumps at the processing location, so as to continue the back drilling process for the remaining circuit boards of the same batch.

8. The method for reducing the tolerance of the residual pile in the back drilling process according to claim 7, characterized in that: In the optimization adjustment, the processed circuit board is sliced, the drilling depth and the via stump depth of the processed via stump are measured, and the processing parameters of the actual back drilling depth are adjusted according to the drilling depth and the via stump depth.

9. The method for reducing the tolerance of the residual pile in the back drilling process according to claim 2, characterized in that: The back drilling machine has a SMART MAPPING function, and the SMART MAPPING function can measure the distance between the upper board surface of the circuit board and the end surface of the workbench.

10. A circuit board, characterized in that: The method for reducing the tolerance of the residual pile in the back drilling process is used as claimed in any one of claims 1 to 9.

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