Selective Mapping back drilling method

Abstract

The invention discloses a selective Mapping back drilling method. The method comprises the steps that whether the sum of plate thickness fluctuation of a core plate and the tolerance of back drilling equipment on the axis of a back drilling hole is smaller than the control range of a stub or not is judged; if yes, entering a direct back drilling mode; and otherwise, entering a Mapping back drilling mode. According to the method, through the mutual relation between the plate thickness processing capability tolerance of the core plate and the residual pile control range, under the condition that it is ensured that the back drilling mode is technically divided within the residual pile control range, and it is ensured that the sum of the plate thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is smaller than the residual pile control range, plate thickness detection is not carried out any more, and the detection efficiency is improved. In this way, the detection frequency in the back drilling process can be reduced, the detection time of back drilling is greatly shortened, the production efficiency is effectively improved, the back drilling output is improved, and the labor cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of back drilling method improvement, and particularly relates to a selective Mapping back drilling method. BACKGROUND

[0002] In order to solve the deficiency in precision of the traditional back drilling process, the existing back drilling process usually selects Mapping back drilling. The Mapping back drilling is to calculate the actual board thickness of each back drilling hole position more accurately through the detection of the height of the backing plate and the height of the board surface, and then to add a compensation value according to the actual board thickness variation, so as to effectively reduce the influence of the board thickness variation on the drilling depth and realize the accurate control of the drilling depth within the target range.

[0003] The Mapping back drilling needs to calculate the board thickness through the detection results of the height of the backing plate and the height of the board surface. With the development of the precision of PCB devices, the number of back drilling holes is increasing. Before each drilling, all the back drilling hole positions need to be fully detected, and then the drilling mode can be entered. This leads to a significant increase in the time of board thickness detection in the Mapping back drilling process, and the time of board surface detection accounts for more than 50% of the total production time, which seriously affects the production efficiency and output of the back drilling. SUMMARY

[0004] In view of this, the present application aims to at least partly solve the problems in the related art. One of the purposes of the present application is to provide a selective Mapping back drilling method. The relationship between the process capability tolerance of the board thickness of the core plate and the control range of the stub is determined. The back drilling mode is technically divided within the control range of the stub to ensure that the sum of the board thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the stub. In this case, the board thickness detection is no longer performed, and the back drilling is directly performed. In this way, the detection frequency in the back drilling process can be reduced, the detection time of the back drilling can be greatly reduced, the production efficiency can be effectively improved, the back drilling output can be improved, and the labor cost can be reduced.

[0005] A selective Mapping back drilling method, comprising: determining whether the sum of the board thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the stub; if yes, entering a direct back drilling mode; otherwise, entering a Mapping back drilling mode; the direct back drilling mode refers to directly performing back drilling according to the theoretical drilling depth without detecting the thickness of the core plate; the Mapping back drilling mode refers to detecting the thickness of the core plate first, and then calculating the theoretical drilling depth according to the thickness of the core plate.

[0006] Further, the specific formula for determining whether the sum of the board thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the stub is: (H - H-N) x k < ((Max stub - Min stub) - 2N) / 2; wherein, H refers to the ineffective drilling depth; Max stub refers to the upper limit of the stub, Min stub refers to the lower limit of the stub; N refers to the tolerance of the back drilling equipment on the back drilling hole axis, and k is a fluctuation parameter determined by the core plate parameters and the parameters of the back drilling equipment.

[0007] Further, during the back drilling process, a backing plate is placed below the core plate, and a cover plate is covered above the core plate.

[0008] Further, H refers to the sum of the thickness of the cover plate and the ineffective drill point depth, and the ineffective drill point depth is determined by the drill point angle of the drill bit and a drill hole diameter.

[0009] Further, the Mapping back drilling mode comprises: measuring the height h1 of the backing plate and the cover plate at the back drilling hole position, measuring the height h2 of the backing plate, core plate and cover plate at the back drilling hole position, calculating the thickness of the core plate according to the difference between h2 and h1, calculating the theoretical drilling depth according to the thickness of the core plate and the control range of the stub.

[0010] Further, the ineffective drill point depth = (a / 2) / tan(θ / 2) wherein θ represents the drill point angle of the drill bit, and a represents the radius of the drill hole.

[0011] Further, the value range of the fluctuation parameter k is less than or equal to 0.1.

[0012] Further, the difference between the upper limit of the stub and the lower limit of the stub is in the range of 6-10 mil.

[0013] Further, before the core plate is back drilled, it further comprises: calculating the theoretical drilling depth according to the upper limit of the stub, the lower limit of the stub, the drill hole diameter, and the drill point angle of the drill bit; and drawing a table containing the upper limit of the stub, the lower limit of the stub, the drill hole diameter, the drill point angle of the drill bit and the theoretical drilling depth; When the upper limit of the stub, the lower limit of the stub, the drill hole diameter, and the drill point angle of the drill bit are determined, it is determined whether the theoretical drilling depth of the back drilling hole is less than or equal to the corresponding theoretical drilling depth in the table. If it is less than or equal to the corresponding theoretical drilling depth in the table, it is determined that the sum of the thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the stub, and the direct back drilling mode is directly entered.

[0014] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art. The selective back drilling method provided by the present application judges whether the sum of the thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the residual stub; if yes, the direct back drilling mode is entered; otherwise, the Mapping back drilling mode is entered; the direct back drilling mode in the present application refers to that the thickness of the core plate is not detected, and the back drilling is directly performed according to the theoretical drilling depth; the Mapping back drilling mode refers to that the thickness of the core plate is detected first, and then the theoretical drilling depth is calculated according to the thickness of the core plate. The tolerance of the back drilling equipment on the back drilling hole axis is a fixed value, and the thickness fluctuation of the core plate is determined by the thickness process capability tolerance of the core plate. By the mutual relationship between the thickness process capability tolerance of the core plate and the control range of the residual stub, the back drilling mode is technically divided within the control range of the residual stub, so that the thickness detection is not performed again under the condition that the sum of the thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the residual stub, and the back drilling is directly performed. In this way, the detection times in the back drilling process can be reduced, the detection time of the back drilling can be greatly reduced, the production efficiency can be effectively improved, the back drilling output can be improved, and the labor cost can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without creative labor.

[0017] In the drawings: Figure 1 The accompanying drawings, which are incorporated into and form a part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0018] Reference signs: 11, cover plate; 12, core plate; 13, back drilling hole; 14, drilling hole. DETAILED DESCRIPTION

[0019] In order to make the technical features, objectives and effects of the present application clearer, the specific embodiments of the present application will be described in detail with reference to the drawings. In the following description, it should be understood that the directions or positional relationships indicated by "front", "back", "upper", "lower", "left", "right", "vertical", "horizontal", "vertical", "horizontal", "top", "bottom", "inner", "outer", "head", "tail" and the like are based on the directions or positional relationships shown in the drawings, constructed and operated in a particular direction, and are only for the convenience of describing the technical solutions, and cannot be understood as indicating that the indicated mechanisms or elements must have a particular direction, therefore, it cannot be understood as a limitation on the present application.

[0020] It should also be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing", "setting" and the like should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements or the interaction relationship between two elements. When an element is referred to as "on" or "below" another element, the element can be "directly" or "indirectly" above the other element, or there can be one or more intervening elements. The terms "first", "second", "third" and the like are only for the convenience of describing the technical solutions, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features, therefore, the features with "first", "second", "third" and the like can be explicitly or implicitly included one or more of the features. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0021] In the following description, specific details such as specific system structures, techniques, etc. are presented for the purpose of explanation, not for the purpose of limitation, so as to make the embodiments of the present application thoroughly understood. However, it should be clear to those skilled in the art that the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, mechanisms, circuits and methods are omitted to avoid unnecessary details that hinder the description of the present application.

[0022] Embodiment 1 The present application discloses a back drilling method of selective mapping, comprising: determining whether the sum of the thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the residual pile; If less, enter the direct back drilling mode; otherwise, enter the Mapping back drilling mode; the direct back drilling mode refers to directly back drilling according to the theoretical drilling depth without detecting the thickness of the core board; the Mapping back drilling mode refers to detecting the thickness of the core board first, and then calculating the theoretical drilling depth according to the thickness of the core board.

[0023] The reason why the Mapping back drilling needs to be performed in the prior art is to accurately control the depth of the stub to ensure the integrity of high-speed signal transmission. The stub is directly related to the thickness of the core board and is determined by the depth of the unconnected part of the via; too long or too short stubs will affect the performance of the device.

[0024] The reason why the thickness of the core board needs to be detected first is to map the fluctuation value of the medium thickness of the theoretical drilling depth part through the thickness of the core board, and then to confirm the accurate theoretical drilling depth while ensuring the length of the stub.

[0025] In the present application, the theoretical drilling depth refers to the drilling depth during actual drilling, and the target drilling depth refers to the drilling depth of the back drilling hole after actual drilling. In actual operation, (theoretical drilling depth-H-N) is the target drilling depth.

[0026] The principle of the present application is to confirm the medium thickness of the theoretical drilling depth, i.e., the fluctuation of the thickness of the core board, through the theoretical drilling depth and the parameters of the back drilling equipment. If the fluctuation value is small, it is considered that the stub will remain within the control range when the theoretical drilling depth is executed, and at this time, there is no need to detect the thickness of the core board. In this way, the core board thickness detection time can be greatly reduced, and the back drilling efficiency can be improved.

[0027] In the present application, the tolerance of the back drilling equipment on the back drilling hole axis is a fixed value, and the fluctuation of the thickness of the core board is determined by the process capability tolerance of the thickness of the core board. By analyzing the mutual relationship between the process capability tolerance of the thickness of the core board and the control range of the stub, the back drilling method is technically divided within the control range of the stub to ensure that the sum of the fluctuation of the thickness of the core board and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the stub. In this way, the detection frequency during back drilling can be reduced, the detection time of back drilling can be greatly reduced, the production efficiency can be effectively improved, the back drilling output can be improved, and the labor cost can be reduced.

[0028] Embodiment 2 The present application discloses a selective Mapping back drilling method, comprising: Determine whether the sum of the core plate thickness fluctuation and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the residual pile; if it is less, enter the direct back drilling mode; otherwise, enter the mapping back drilling mode; the direct back drilling mode refers to performing back drilling directly according to the theoretical drilling depth without detecting the thickness of the core plate; the mapping back drilling mode refers to first detecting the thickness of the core plate, and then calculating the theoretical drilling depth based on the thickness of the core plate.

[0029] During back drilling, a backing plate needs to be placed under the core board, and a cover plate needs to be placed on top of the core board. The cover plate is specifically a metal plate, such as an aluminum plate.

[0030] like Figure 1 As shown, when the core board 12 is back-drilled, its surface is covered by a cover plate 11. The back-drilled hole 13 in the core board 12 refers to drilling a hole on the back of a drill hole 14. During the back-drilling process, the layer above the cover plate 11 and the core board 12 is the layer that must be penetrated, and the layer below the drill hole 14 is the layer that cannot be penetrated.

[0031] This application uses the following formula to determine whether the sum of the core plate thickness fluctuation and the tolerance of the back drilling equipment on the axis of the back drilling hole is less than the control range of the residual pile: ((Theoretical drilling depth - HN))×k<((Max stub - Min stub)-2N) / 2; where H refers to the ineffective drilling depth; Max stub refers to the upper limit of the residual pile, Min stub refers to the lower limit of the residual pile; N refers to the tolerance of the back drilling equipment on the axis of the back drilling hole, and k is the fluctuation parameter, which is determined by the parameters of the core plate.

[0032] like Figure 1 As shown, H = cover plate thickness + λ, λ = a / tan(θ / 2), and the meanings of each letter are as follows: λ: Ineffective drill tip depth θ: The tip angle of the drill bit. D: The diameter of the first drill hole refers to the diameter of the existing drill hole before back drilling. In this application, back drilling refers to drilling a hole on the back side of an existing hole. The existing hole is the first drill hole. Back drilling is a second drilling on the back side of the first drill hole.

[0033] a: the radius of a drill hole; Min stub: Lower limit of residual stub, a preset value, usually 1mil to 2mil; Max stub: The upper limit of the residual pile, which is a preset value, and the difference between the upper limit of the residual pile and the lower limit of the residual pile is usually 6-10 mil; in this application, the control range of the residual pile refers to the difference between the upper limit of the residual pile and the lower limit of the residual pile.

[0034] For example, when D = 0.2 mm; θ = 90° λ = (0.2 / 2) / tan(45°) = 0.1 / 1 = 0.1mm.

[0035] In the above formula, H refers to the sum of the thickness of the cover plate and the ineffective drill tip depth, which together constitute the ineffective drilling depth.

[0036] The value range of the above fluctuation parameter k is less than or equal to 0.1. In actual operation, k can be taken as 0.1, that is, under the condition that the theoretical drilling depth fluctuates by 10% up and down, it is still within the control range of the residual pile, and at this time the thickness fluctuation of the core plate has little effect on the theoretical drilling depth, so the thickness detection can be omitted and the back drilling process can be directly executed. In actual operation, the fluctuation range of the theoretical drilling depth will not exceed 10%, therefore, the value of k can be selected as a value less than or equal to 0.1 according to the core plate parameters and the back drilling equipment parameters.

[0037] The back drilling hole needs to control both the drilling depth and the drilling depth in the present application. In order to ensure that both the drilling depth and the drilling depth are within the range required by the customer, the difference between the upper limit value of the residual pile and the lower limit value of the residual pile is divided by 2.

[0038] The Mapping back drilling mode in the present application can be any one of the prior art, specifically including: measuring the height h1 of the backing plate and the cover plate at the back drilling hole position, measuring the height h2 of the backing plate, core plate and cover plate at the back drilling hole position, calculating the thickness of the core plate according to the difference between h2 and h1, calculating the theoretical drilling depth according to the thickness of the core plate and the control range of the residual pile.

[0039] By analyzing the relationship between the thickness process capability tolerance of the core plate and the control range of the residual pile, the back drilling method is technically divided within the control range of the residual pile, and under the condition that the sum of the thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the residual pile, the thickness detection is no longer performed and the back drilling is directly performed. In this way, the detection frequency in the back drilling process can be reduced, the detection time of the back drilling can be greatly reduced, the production efficiency can be effectively improved, the back drilling output can be improved, and the labor cost can be reduced.

[0040] Example 3 The present application discloses a selective Mapping back drilling method, comprising: Determine whether the sum of the core plate thickness fluctuation and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the residual pile; if it is less, enter the direct back drilling mode; otherwise, enter the mapping back drilling mode; the direct back drilling mode refers to performing back drilling directly according to the theoretical drilling depth without detecting the thickness of the core plate; the mapping back drilling mode refers to first detecting the thickness of the core plate, and then calculating the theoretical drilling depth based on the thickness of the core plate.

[0041] During back drilling, a pad needs to be placed under the core board, and a cover plate needs to be placed on top of the core board. The cover plate is made of aluminum plate with a thickness of 0.13mm.

[0042] like Figure 1 As shown, when the core board 12 is back-drilled, its surface is covered by a cover plate 11. The back-drilled hole 13 in the core board 12 refers to drilling a hole on the back of a drill hole 14. During the back-drilling process, the layer above the cover plate 11 and the core board 12 is the layer that must be penetrated, and the layer below the drill hole 14 is the layer that cannot be penetrated.

[0043] This application uses the following formula to determine whether the sum of the core plate thickness fluctuation and the tolerance of the back drilling equipment on the axis of the back drilling hole is less than the control range of the residual pile: (Theoretical drilling depth - a / tan(θ / 2) - 0.0254mm - 0.13mm) × 10% < ((Max stub - Min stub) - 0.0508mm) / 2; where a represents the radius of a drill hole, θ represents the tip angle of the drill bit, 0.0254mm represents the tolerance of the back drilling equipment on the axis of the back drill hole, 0.13mm represents the thickness of the cover plate, Min stub represents the lower limit of the residual pile, which is a preset value, usually 1mil to 2mil; Max stub represents the upper limit of the residual pile, which is a preset value, and the difference between the upper limit of the residual pile and the lower limit of the residual pile is usually 6-10mil.

[0044] Before back drilling, the core board in this application also includes: The theoretical drilling depth is calculated based on the upper and lower limits of the residual pile, the borehole diameter, and the drill bit tip angle. A table is then created containing the upper and lower limits of the residual pile, the borehole diameter, the drill bit tip angle, and the theoretical drilling depth. Table 1 shows the theoretical drilling depth when the drill bit tip angle θ is 130°, the difference between the upper and lower limits of the residual pile is 6 mil, 7 mil, 8 mil, 9 mil, and 10 mil, and the borehole diameter is 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, and 0.8 mm, respectively.

[0045] As shown in Table 2, the drill bit angle θ of the drill bit is 150°, the difference range of the upper limit value and the lower limit value of the stub is 6mil, 7mil, 8mil, 9mil, 10mil, and the corresponding theoretical drilling depth when the drill hole diameter is 0.2mm, 0.25mm, 0.3mm, 0.35mm, 0.4mm, 0.45mm, 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm, 0.75mm, 0.8mm respectively.

[0046] As shown in Table 3, the drill bit angle θ of the drill bit is 165°, the difference range of the upper limit value and the lower limit value of the stub is 6mil, 7mil, 8mil, 9mil, 10mil, and the corresponding theoretical drilling depth when the drill hole diameter is 0.2mm, 0.25mm, 0.3mm, 0.35mm, 0.4mm, 0.45mm, 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm, 0.75mm, 0.8mm respectively.

[0047] Table 1 corresponding table when the drill bit angle θ of the drill bit is 130°

[0048] Table 2 corresponding table when the drill bit angle θ of the drill bit is 150°

[0049] Table 3 corresponding table when the drill bit angle θ of the drill bit is 165°

[0050] When the upper limit value of the stub, the lower limit value of the stub, the drill hole diameter, the drill bit angle of the drill bit are determined, whether the theoretical drilling depth of the back drilling hole is less than or equal to the corresponding theoretical drilling depth in the table is found out. If it is less than or equal to the corresponding theoretical drilling depth in the table, it is determined that the sum of the thickness fluctuation of the core plate and the tolerance of the back drilling equipment on the back drilling hole axis is less than the control range of the stub, and the direct back drilling mode is directly entered.

[0051] For example, in the case of a drill bit angle θ of 130°, a required stub control range of 6mil, an upper limit value of the stub of 0.1778mm, a lower limit value of the stub of 0.0254mm, and a drill hole diameter of 0.25mm, if the theoretical drilling depth is less than or equal to 0.7mm, it means that the theoretical drilling depth is still within the control range of the stub even if it fluctuates according to the maximum fluctuation range of 10%, and at this time, the direct drilling mode is entered for drilling, and the thickness detection is not required.

[0052] The present application can greatly reduce invalid time of panel detection by the interrelation between the theoretical drilling depth and the stub, can improve the mapping efficiency by 18%-40% under the condition of ensuring that the drilling depth meets the requirements, thereby effectively improving the production efficiency, improving the back drilling output, and reducing the labor cost.

[0053] It can be understood that the above embodiments only express the preferred embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the patent scope of the present application; it should be pointed out that for ordinary skilled in the art, the above technical features can be freely combined without departing from the concept of the present application, and several modifications and improvements can be made, which belong to the protection scope of the present application; therefore, any equivalent transformation and modification within the scope of the claims of the present application shall belong to the scope of the claims of the present application.

Claims

1. A selective mapping back-drilling method, characterized in that, include: Determine whether the sum of the core plate thickness fluctuation and the tolerance of the back drilling equipment on the axis of the back drilling hole is less than the control range of the residual pile; If the thickness is less than the required value, then proceed to the direct back-drilling mode; otherwise, proceed to the mapping back-drilling mode. The direct back-drilling mode refers to performing back-drilling directly according to the theoretical drilling depth without detecting the thickness of the core board. The Mapping back-drilling mode refers to first detecting the thickness of the core board, and then calculating the theoretical drilling depth based on the thickness of the core board.

2. The selective mapping back-drilling method according to claim 1, characterized in that, The specific formula for determining whether the sum of the core plate thickness fluctuation and the tolerance of the back drilling equipment on the axis of the back drilling hole is less than the control range of the residual pile is as follows: (Theoretical drilling depth - HN) × k < ((Max stub - Min stub) - 2N) / 2; where H refers to the ineffective drilling depth; Max stub refers to the upper limit of the residual pile, and Min stub refers to the lower limit of the residual pile; N refers to the tolerance of the back drilling equipment on the axis of the back drilling hole, and k is a fluctuation parameter, which is determined by the core plate parameters and the back drilling equipment parameters.

3. The selective mapping back-drilling method according to claim 2, characterized in that, During back drilling, a pad is placed below the core plate, and a cover plate is placed above the core plate.

4. The selective mapping back-drilling method according to claim 3, characterized in that, H refers to the sum of the thickness of the cover plate and the ineffective drill tip depth. The ineffective drill tip depth is determined by the drill bit tip angle and the first drill hole diameter, which refers to the diameter of the hole that existed before back drilling.

5. The selective mapping back-drilling method according to claim 3, characterized in that, The mapping back-drilling mode includes: Measure the height h1 of the pad and the cover plate at the location of the back drill hole. Measure the height h2 of the pad, core plate, and cover plate at the location of the back drill hole. The thickness of the core board is calculated based on the difference between h2 and h1. The theoretical drilling depth is calculated based on the thickness of the core plate and the control range of the residual pile.

6. The selective mapping back-drilling method according to claim 3, characterized in that, Ineffective drill tip depth = (a / 2) / tan(θ / 2) Where θ represents the drill bit tip angle, and a represents the radius of a drill hole.

7. The selective mapping back-drilling method according to claim 2, characterized in that, The value range of the fluctuation parameter k is less than or equal to 0.

1.

8. The selective mapping back-drilling method according to claim 2, characterized in that, The difference between the upper limit and the lower limit of the residual pile is 6-10 mil.

9. A selective mapping back-drilling method according to claim 2, characterized in that, Before back drilling, the core board also includes: The theoretical drilling depth is calculated based on the upper limit of the residual pile, the lower limit of the residual pile, the borehole diameter, and the drill bit tip angle; and a table containing the upper limit of the residual pile, the lower limit of the residual pile, the borehole diameter, the drill bit tip angle, and the theoretical drilling depth is drawn. When the upper limit value of the residual pile, the lower limit value of the residual pile, the borehole diameter, and the tip angle of the drill bit are determined, check whether the theoretical drilling depth of the hole to be back-drilled is less than or equal to the corresponding theoretical drilling depth in the table. If it is less than or equal to the corresponding theoretical drilling depth in the table, it is determined that the sum of the core plate thickness fluctuation and the tolerance of the back-drilling equipment on the axis of the back-drilling hole is less than the control range of the residual pile, and directly enter the direct back-drilling mode.

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