TWI674826B - Back drilling method of circuit board - Google Patents

Abstract

A method for back drilling a circuit board includes: providing a drilling machine comprising a workbench, a drill bit disposed above the workbench, and a control module electrically connected to the drill bit; and placing a first conductive sheet body on the workbench ; According to the preset back drilling area, the drill bit contacts the first conductive sheet body to obtain the first height information; the first conductive sheet body is removed; the circuit board is set on the workbench; the second conductive sheet body is set on the circuit On the board; according to the preset back drilling area, the drill bit contacts the second conductive sheet body to obtain the second height information; and the actual back drilling depth value is calculated according to the first height information and the second height information.

Description

Back drilling method for circuit board

The invention relates to a back drilling method of a circuit board, in particular to a back drilling method of a circuit board capable of improving the processing accuracy of the back drilling depth.

In the conventional back-drilling method of a circuit board, when performing a back-drilling operation, it uses the surface copper surface of the circuit board as a reference to uniformly drill down the set depth value, which does not take into account the distance between the circuit board and the circuit board. The influence of plate thickness difference or poor plate thickness uniformity on machining accuracy of back stub length. Therefore, when the thickness difference between the circuit board and the circuit board is large or the thickness uniformity is not good, the processing accuracy of the back drilling depth will be larger as the back drilling depth is deeper, and the error range will be larger. . For example, when the depth of the back drilling is greater than 90 mils, the error range of the machining accuracy of the back drilling depth will reach plus or minus 5 mils.

Therefore, the present inventor believes that the above-mentioned defects can be improved, and with special research and cooperation with the application of scientific principles, he finally proposes an invention with a reasonable design and effective improvement of the above-mentioned defects.

An embodiment of the present invention is to provide a back drilling method for a circuit board, which can effectively improve the defects existing in the existing back drilling method for a circuit board.

An embodiment of the present invention discloses a method for back drilling of a circuit board, which includes: providing a drilling machine; wherein the drilling machine includes a workbench and is disposed on the spaced interval; A drill bit above the workbench and a control module electrically connected to the drill bit; setting a first conductive sheet body on the workbench of the drilling machine; performing a first inspection operation, including: According to a preset back drilling area, the drill of the drilling machine contacts a detection surface of the first conductive sheet body to obtain the detection surface of the first conductive sheet body in the preset A first height information of the back drilling area; removing the first conductive sheet body; setting a circuit board on the working table of the drilling machine; setting a second conductive sheet body on the On the surface of the circuit board opposite to the workbench; performing a second inspection operation, including: contacting the drill bit of the drilling machine with the second conductive body according to the preset back drilling area A detection surface of the sheet body to obtain a second height information of the detection surface of the second conductive sheet body located in the preset back drilling area; according to the first height information and the second height The information uses the control module of the drilling machine to calculate an actual back drilling depth. And implementing a back drilling operation, comprising: drilling the circuit board with the drill bit of the drilling machine at the preset back drilling area according to the actual back drilling depth value, so that The circuit board is formed with a back hole.

Another embodiment of the present invention discloses a drilling machine, including: a worktable; wherein the worktable can provide a first conductive sheet body disposed thereon in a first inspection operation and can be used in a second inspection During operation, a circuit board and a second conductive sheet body located on the circuit board are provided thereon; a drill bit is disposed above the table at intervals; wherein the drill bit can be placed on the first During the inspection operation, a preset back drilling area is moved toward the table to contact a detection surface of the first conductive sheet body; wherein, the drill can be used according to the second inspection operation. The preset back drilling area is moved in the direction of the table to contact a detection surface of the second conductive sheet body; and a control module electrically connected to the drill bit; wherein the control mold The group can send a first current signal to the drill bit during the first detection operation, and when the drill bit contacts the detection surface of the first conductive sheet body, the control module can receive The drill bit and the first conductive sheet body A first feedback signal generated by the same, and according to the first feedback signal to obtain the first Height information; wherein the control module can send a second current signal to the drill during the second inspection operation, and when the drill contacts the detection surface of the second conductive sheet body , The control module can receive a second feedback signal generated by the drill bit and the second conductive sheet body, and obtain the second height information according to the second feedback signal; wherein, the The control module can calculate an actual back drilling depth value in a back drilling operation according to the first height information and the second height information.

In summary, the method for back-drilling a circuit board according to an embodiment of the present invention can detect the first and second conductive sheet bodies in the first and second inspection operations by the drill bit of the drilling machine, respectively. The first and second height information is obtained, and an actual back drilling depth value can be calculated according to the first and second height information, so that the processing accuracy of the back drilling depth (stub length) is greatly improved.

In order to further understand the features and technical contents of the present invention, please refer to the following detailed description and drawings of the present invention, but these descriptions and drawings are only used to illustrate the present invention, and not to make any limitation to the scope of the present invention limit.

100‧‧‧ Drilling Machine

110‧‧‧Workbench

111‧‧‧worktop

120‧‧‧drill

121‧‧‧ Spindle

122‧‧‧ Drill Pin

130‧‧‧control module

200‧‧‧ the first conductive sheet body

210‧‧‧ detection surface

220‧‧‧testing points

300‧‧‧Circuit Board

310‧‧‧through hole

320‧‧‧ conductive layer

330‧‧‧Back drilling

400‧‧‧Second conductive sheet body

410‧‧‧test surface

420‧‧‧testing points

DR‧‧‧ preset back drilling area

D1, D2‧‧‧thickness

H1‧‧‧ First Height Information

H2‧‧‧Second Height Information

SL‧‧‧Back drilling depth

P‧‧‧ projection plane

R‧‧‧ closed area

FIG. 1 is a schematic diagram of a drilling machine according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of step S101 of a back drilling method for a circuit board according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of step S102 of a back drilling method for a circuit board according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of step S103 of a back drilling method for a circuit board according to an embodiment of the present invention.

FIG. 5 is a schematic diagram of step S1O4 of a back drilling method for a circuit board according to an embodiment of the present invention.

FIG. 6 is a schematic diagram of step S105 of a back drilling method for a circuit board according to an embodiment of the present invention.

FIG. 7 is a schematic diagram of step S107 of a back drilling method for a circuit board according to an embodiment of the present invention.

FIG. 8 is a schematic diagram of a detection point of the second conductive sheet body falling within a closed area formed by the three detection points of the first conductive sheet body according to the embodiment of the present invention.

FIG. 9 is a schematic diagram of one detection point of the second conductive sheet body falling within a closed area formed by the four detection points of the first conductive sheet body according to the embodiment of the present invention.

Please refer to FIGS. 1 to 9, which are embodiments of the present invention. It should be noted that this embodiment corresponds to the related quantities and appearances mentioned in the drawings, and is only used to specifically describe the embodiments of the present invention, so that In order to understand the content of the present invention, it is not intended to limit the protection scope of the present invention.

[Back drilling method of circuit board]

This embodiment discloses a back drilling method for a circuit board. The back drilling method of a circuit board includes steps S101, S102, S103, S104, S105, S106, and S107. It must be noted that the order of the steps and the actual operation mode in this embodiment can be adjusted according to requirements, and are not limited to those in this embodiment.

As shown in FIGS. 1 and 2, step S101 is to provide a drilling machine 100. The drilling machine 100 includes a work table 110, a drill bit 120, and a control module 130. The workbench 110 has a worktable surface 111. The drill bit 120 includes a main shaft 121 and a drill pin 122 disposed on the main shaft 121. Preferably, the main shaft 121 is sandwiched between the drill pins 122. Further, the drill bit 120 is disposed above the work surface 111 of the work table 110 at intervals, and can be moved in the direction of the work surface 111 to perform a detection operation (as described in Inspection operation and second inspection operation) or a drilling operation (back drilling operation as described below). The control module 130 includes a capacitive sensing unit (not shown), a signal processing unit (not shown), and an arithmetic logic unit (not shown). The control module 130 is Electrically connected to the drill bit 120. The operation modes and functions that can be performed of the drill bit 120 and the control module 130 will be described in due course in the following steps.

As shown in FIG. 3, step S102 is to set a first conductive sheet body 200 on the work surface 111 of the work platform 110. In this embodiment, the first conductive sheet body 200 is preferably The ground is a metal conductive sheet body having a sheet shape and a uniform thickness, and the first conductive sheet body 200 is more preferably an aluminum sheet cover, but the present invention is not limited thereto. In more detail, a surface of the first conductive sheet body 200 opposite to the work surface 111 is defined as a detection surface 210, and the detection surface 210 can be used to provide contact with the drill pin 122 of the drill bit 120. To perform a first detection job as described below.

As shown in FIG. 4, step S103 is to perform a first detection operation. The first detection operation includes: contacting the drill pin 122 of the drill 120 with the detection surface 210 of the first conductive sheet body 200 according to a preset back drilling area DR to obtain the detection of the first conductive sheet body 200 The surface 210 is located at a first height information H1 of the preset back drilling area DR.

More specifically, during the first detection operation, the capacitive sensing unit (such as a CBD capacitive sensor) of the control module 130 of the drilling machine 100 can send a first current signal to the drill 120. A drill pin 122, and when the drill pin 122 of the drill bit 120 contacts the detection surface 210 of the first conductive sheet body 200 and is electrically connected to the detection surface 210, the signal processing unit of the control module 130 of the above-mentioned drilling machine 100 The first feedback signal generated by the drill pin 122 of the drill bit 120 and the first conductive sheet body 200 can be received, and signal processing is performed according to the first feedback signal to obtain the first height information H1.

It is worth mentioning that, in an embodiment of the present invention, the area of the detection surface 210 of the first conductive sheet body 200 must be sufficiently large so that when the drill pin 122 of the drill bit 120 contacts the first conductive When the detection surface 210 of the sheet 200 is used, the detection operation can be started smoothly (for example, the area of the detection surface 210 must be larger than the surface area of the main shaft 121 of the drill 120 to facilitate the formation of sufficient capacitance and the capacitance value to be greater than a standard value).

Next, after the first detection operation is performed and the first height information H1 is obtained, the drill pin 122 of the drill 120 will move away from the work surface 111, and the first conductive sheet body 200 will be Removal (such as: using a robotic arm or manual handling) to facilitate subsequent manufacturing steps.

As shown in FIG. 5, step S104 is to set a circuit board 300 on the work surface 111 of the work table 110, and set a second conductive sheet body 400 on a side of the circuit board 300 opposite to the work surface 111 of the work table 110. on the surface.

In more detail, the circuit board 300 has two surfaces (not shown in the figure) located on opposite sides, and includes a plurality of board structures (not shown in the figure) disposed between the two surfaces. In addition, the circuit board 300 further has a through hole 310 penetrating the two surfaces and includes a conductive layer 320 plated on the hole wall of the through hole 310. Wherein, when the circuit board 300 is disposed on the work surface 111 of the workbench 110, the through holes 310 and the conductive layer 320 of the circuit board 300 are both located within the range of the preset back drilling region DR. Wherein, in an embodiment of the present invention, the circuit board 300 has a board thickness of not more than 4 millimeters (mm), a board length of not more than 480 millimeters, and a board width of not more than 400 millimeters. Limited to this.

In this embodiment, the second conductive sheet body 400 is similar to the first conductive sheet body 200 and is a thin metal sheet with a uniform thickness, and the second conductive sheet body 400 is more preferably a Aluminum sheet cover, but the present invention is not limited to this. In more detail, a surface of the second conductive sheet body 400 opposite to the circuit board 300 is defined as a detection surface 410, and the detection surface 410 can be used to provide contact with the drill pin 122 of the drill bit 120, To perform a second detection job as described below.

As shown in FIG. 6, step S105 is to perform a second detection operation. The second detection operation includes: contacting the detection surface 410 of the second conductive sheet body 400 with the drill pin 122 of the drill bit 120 according to the preset back drilling area DR to obtain the second conductive sheet body 400. The detection surface 410 is located at a second height information H2 of the preset back drilling area DR.

More specifically, when the second detection operation is performed, the capacitive sensing unit (such as a CBD capacitive sensor) of the control module 130 of the drilling machine 100 can send a second current signal to the drill 120. A drill pin 122, and when the drill pin 122 of the drill bit 120 contacts the detection surface 410 of the second conductive sheet body 400 and is electrically connected to the detection surface 410, the signal processing unit of the control module 130 of the drilling machine 100 described above Capable of receiving both the drill pin 122 of the drill bit 120 and the second conductive sheet body 400 The second feedback signal is processed according to the second feedback signal to obtain the second height information H2.

It is worth mentioning that, in an embodiment of the present invention, an area of the detection surface 410 of the second conductive sheet body 400 is preferably larger than an area of a surface (such as an upper surface) of the circuit board 300. Thereby, the conductive area on the surface of the circuit board 300 can be improved (capacitance can be improved), and when the drill pin 122 of the drill bit 120 contacts the detection surface 410 of the second conductive sheet body 400, Start the inspection job smoothly.

It is also worth mentioning that, in an embodiment of the present invention, the thickness D1 (as shown in FIG. 4) of the first conductive sheet body 200 at the preset back drilling region DR is preferably substantially equal to the first The thickness D2 of the two conductive sheet bodies 400 at the preset back drilling region DR (see FIG. 6). Therefore, in the subsequent step of calculating the actual plate thickness value, the above-mentioned structural features can improve the calculation accuracy of the actual plate thickness value (to avoid calculation errors caused by thickness differences).

Further, when the detection surface 210 of the first conductive sheet body 200 is contacted by the drill pin 122 of the drill bit 120 during the first detection operation, micro-dent marks are generated. Therefore, if the second detection operation is performed with the same conductive sheet body, the calculation accuracy of the actual plate thickness value may be reduced (because micro-dent marks have been generated at the same detection point, which will affect the measurement of height information). In order to avoid the above defects, in an embodiment of the present invention, the first conductive sheet body 200 is discarded after the first inspection operation is performed, and when the second inspection operation is performed, the second conductive sheet body 400 The conductive sheet is the same as the first conductive sheet 200 (eg, the same size, thickness, and material), but the second conductive sheet 400 is an unused conductive sheet. It should be noted that the present invention is not limited to the above embodiments. For example, in another embodiment of the present invention, the second conductive sheet body 400 may be the same as the first conductive sheet. The body 200 uses the same conductive sheet body, that is, the first conductive sheet body 200 can be reused after being used, and is used as the second conductive sheet body 400.

Step S106 is to calculate an actual back drilling depth value based on the first height information H1 and the second height information H2 by using the arithmetic logic unit of the control module 130 of the drilling machine 100, to facilitate the subsequent drilling operation. (Step S107).

In more detail, in an embodiment of the present invention, the calculation method of the actual back drilling depth value includes: subtracting the second height information H2 from the first height information H1 and taking an absolute value to Obtaining an actual plate thickness value; dividing the actual plate thickness value with a theoretical plate thickness value stored in the control module (storage unit) to obtain a correction ratio value; and dividing the correction ratio value Multiplying with a back drilling depth setting value stored in the control module 130 (storage unit) to obtain the actual back drilling depth value, but the present invention is not limited thereto.

As shown in FIG. 7, step S107 is to perform a back drilling operation. The back drilling operation includes: drilling the circuit board 300 with the drill pin 122 of the drill bit 120 at a preset back drilling area DR according to the actual back drilling depth value, so that the circuit board 300 is formed. There is a back hole 330. Wherein, the drilling depth of the drill pin 122 of the drill bit 120 for drilling the circuit board 300 is the back drilling depth value.

In more detail, in the present embodiment, since the drill pin 122 of the drill bit 120 is drilled toward the through hole 310 and the conductive layer 320 at the preset back drilling area DR, the back drilling is implemented. After the hole operation, the back-drilled hole 330 of the circuit board 300 overlaps at least a part of the through-hole 310 so that at least a part of the conductive layer 320 is removed, and the back-drilled hole 330 is a hole The wall does not have any conductive layer 320. The diameter of the back-drilled hole 330 is larger than the diameter of the through-hole 310, but the present invention is not limited thereto.

In summary, the method for back drilling of a circuit board according to the embodiment of the present invention can pass through the drill bit 120 of the drilling machine 100 to the first and second conductive sheet bodies 200 and 400 in the first and second inspection operations, respectively. Perform detection to obtain first and second height information H1, H2, respectively, and calculate an actual back drilling depth value according to the first and second height information H1, H2, so that the back drilling depth SL (stub length) The machining accuracy has been greatly improved.

In more detail, when the conventional back-drilling method of a circuit board performs a back-drilling operation, it uses the surface copper surface of the circuit board as a reference to uniformly drill down the set depth value, which does not take into account the The influence of the difference in board thickness or the poor uniformity of the board thickness on the processing accuracy of the back stub length. Therefore, when the thickness difference between the circuit board and the circuit board is large or the thickness uniformity is not good, the processing accuracy of the back drilling depth will increase with the depth of the back drilling, and the error range will increase . For example, when the depth of the back drilling is greater than 90 mils, the error range of the machining accuracy of the back drilling depth will reach plus or minus 5 mils.

Compared with the above-mentioned deficiency, the method for back drilling of the circuit board according to the embodiment of the present invention can greatly improve the processing accuracy of the back drilling depth SL (see FIG. 7) of the manufactured circuit board 300. For example, when the back drilling depth SL is less than 90mil, the processing accuracy of the back drilling depth SL is within plus or minus 2mil, and when the back drilling depth SL is less than 90mil, the back drilling depth SL The processing accuracy of SL is within 3mil.

It is also worth mentioning that, since the area for testing the first and second height information H1, H2 in the embodiment of the present invention is the same as the area where the back drilling is performed (both are the preset back drilling area DR), the present invention is implemented The back drilling method of the example circuit board can further calculate a more reasonable actual back drilling depth by evaluating the actual board thickness value of the circuit board 300 located in the preset back drilling area DR, thereby greatly increasing the back drilling depth. Machining accuracy of SL.

As shown in FIG. 8 and FIG. 9, further, in another embodiment of the present invention, in order to improve the accuracy of the actual plate thickness value, the first conductive sheet 200 The detection surface 210 defines at least three detection points 220 (eg, the three detection points 220 in FIG. 8 or the four detection points 220 in FIG. 9) at a preset back drilling area DR. The drill bit 122 of the drill bit 120 Can respectively contact at least three of the detection points 220 of the first conductive sheet body 200 to obtain the The height information of the three detection points 220 is less, and the first detection operation further includes: using the control module 130 according to the height information of the at least three detection points 220 of the first conductive sheet body 200. (Arithmetic logic unit) calculates the first height information H1. More specifically, the calculation method of the first height information H1 is to calculate the height information of at least three of the detection points 220 in a least square method to obtain a table height function, and then according to the The table height function calculates the first height information H1 of the surface compensation, but the present invention is not limited to this. For example, the calculation method of the first height information H1 may also be performed by using an arithmetic mean or a geometric mean, for example.

In addition, when the second inspection operation is performed, the detection surface 410 of the second conductive sheet body 400 defines a detection point 420 at a preset back drilling area DR, and the drill pin 122 of the drill 120 can One of the detection points 420 of the second conductive sheet body 400 is contacted to obtain the second height information H2.

Please continue with FIGS. 8 and 9, at least three of the detection points 220 of the first conductive sheet body 200 are not in line with each other; wherein, when the first conductive sheet body 200 and the second conductive sheet body 400 are along When its normal direction is projected onto a projection plane P, one of the detection points 420 of the second conductive sheet body 400 is formed by at least three of the detection points 220 of the first conductive sheet body 200. Within a range of a closed area R (such as the triangular closed area R in FIG. 8 or the square closed area R in FIG. 9).

[driller]

The above is the description of the back drilling method of the circuit board according to the embodiment of the present invention, and the following describes the drilling machine 100 that can be used for the back drilling method of the circuit board. It must be noted that although the drilling machine 100 of this embodiment can be used for the above-mentioned method of back drilling a circuit board, the present invention is not limited thereto. That is, the drilling machine 100 of this embodiment can also be used for other kinds of circuit board drilling methods.

As shown in FIG. 1 and FIG. 2, this embodiment further discloses a drilling machine 100. The drilling machine 100 includes a worktable 110 and a drill bit spaced above the worktable 110. 120, and a control module 130 electrically connected to the drill bit 120.

As shown in FIG. 3 and FIG. 5, the table 110 can provide a first conductive sheet body 200 on a first inspection operation (see FIG. 3), and can provide a circuit during a second inspection operation. The board 300 and a second conductive sheet body 400 on the circuit board 300 are disposed thereon (see FIG. 5).

As shown in FIG. 4 and FIG. 6, the drill bit 120 can be moved in the direction of the worktable 110 according to a preset back drilling area DR during the first inspection operation to contact a detection surface 210 of the first conductive sheet body 200. (As shown in FIG. 4), and the drill bit 120 can be moved in the direction of the worktable 110 according to the preset back drilling area DR in a second inspection operation to contact a detection surface of the second conductive sheet body 400. 410 (see Figure 6).

The control module 130 can send a first current signal to the drill bit 120 during a first inspection operation, and when the drill bit 120 contacts the detection surface 210 of the first conductive sheet body 200, the control module 130 130 can receive a first feedback signal generated by the drill 120 and the first conductive sheet body 200, and obtain the first height information H1 according to the first feedback signal. Furthermore, the control module 130 can send a second current signal to the drill bit 120 during the second detection operation, and when the drill bit 120 contacts the detection surface 410 of the second conductive sheet body 400, the control module 130 The control module 130 can receive a second feedback signal generated by the drill 120 and the second conductive sheet body 400 and obtain the second height information H2 according to the second feedback signal. The control module 130 can calculate an actual back drilling depth value in a back drilling operation according to the first height information H1 and the second height information H2.

[Technical effect of the embodiment of the present invention]

In summary, the method for back drilling and the drilling machine of the circuit board according to the embodiment of the present invention can pass through the drill bit 120 of the drilling machine 100 to the first and second conductive sheet bodies in the first and second inspection operations, respectively. 200 and 400 are performed to obtain the first and second height information H1 and H2 respectively, and an actual back drilling depth value can be calculated according to the first and second height information H1 and H2, so that the back Drilling depth length) processing accuracy has been greatly improved.

The above are only the preferred and feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Any equal changes and modifications made in accordance with the scope of patent application of the present invention shall fall within the protection scope of the claims of the present invention .

Claims (9)

A method for back drilling a circuit board includes: providing a drilling machine; wherein the drilling machine includes a workbench, a drill bit spaced above the workbench, and an electrical connection to the drill bit. A control module; setting a first conductive sheet body on the working table of the drilling machine; carrying out a first inspection operation, including: The drill bit contacts a detection surface of the first conductive sheet body to obtain a first height information that the detection surface of the first conductive sheet body is located in the preset back drilling area; removing the A first conductive sheet body; a circuit board is disposed on the workbench of the drilling machine; a second conductive sheet body is disposed on a surface of the circuit board opposite to the side of the workbench Performing a second inspection operation, including: contacting the drill of the drilling machine with a detection surface of the second conductive sheet body to obtain the second conductive sheet according to the preset back drilling area The detection surface of the body is located at a second height of the preset back drilling area Information; calculating an actual back drilling depth value using the control module of the drilling machine based on the first height information and the second height information; and implementing a back drilling operation, including: The actual back drilling depth value is used to drill the circuit board with the drill bit of the drilling machine at the preset back drilling area, so that the circuit board is formed with a back drill. The back drilling method for a circuit board according to claim 1, wherein a thickness of the first conductive sheet body at the preset back drilling area is equal to a thickness of the second conductive sheet body at the preset back Thickness at the drilled area. The back drilling method for a circuit board according to claim 1, wherein an area of the detection surface of the second conductive sheet body is larger than an area of the surface of the circuit board. The back drilling method for a circuit board according to claim 1, wherein the circuit board has a through hole and includes a conductive layer plated on a hole wall of the through hole; wherein when the circuit When the board is set on the working table of the drilling machine, the through-holes and the conductive layers of the circuit board are both within the range of the preset back drilling area; After the back-drilling operation, the back-drilled holes of the circuit board overlap at least part of the through holes, so that at least part of the conductive layer is removed, and the back-drilled holes are made. The wall does not have any conductive layers. The back drilling method for a circuit board according to claim 1, wherein, when the first inspection operation is performed, the control module of the drilling machine can send a first current signal to the drill bit, And when the drill bit contacts the detection surface of the first conductive sheet body, the control module can receive a first feedback signal generated by the drill bit and the first conductive sheet body together, and Obtaining the first height information according to the first feedback signal; wherein, when the second inspection operation is performed, the control module of the drilling machine can send a second current signal to the drill bit, And when the drill bit contacts the detection surface of the second conductive sheet body, the control module can receive a second feedback signal generated by the drill bit and the second conductive sheet body together, and Obtaining the second height information according to the second feedback signal. The back drilling method of a circuit board according to claim 5, wherein before the back drilling operation is performed, the control module of the drilling machine can be based on the first height information and the first Two height information calculates the actual back drilling depth value; wherein the calculation method of the actual back drilling depth value includes: subtracting the second height information from the first height information to obtain an actual Plate thickness value; dividing the actual plate thickness value with a theoretical plate thickness value stored in the control module to obtain a corrected ratio value; and Multiplying the correction ratio value with a back drilling depth setting value stored in the control module to obtain the actual back drilling depth value. The back drilling method for a circuit board according to claim 1, wherein, when the first inspection operation is performed, the detection surface of the first conductive sheet body is defined at the preset back drilling region There are at least three detection points, and the drill bit of the drilling machine can respectively contact at least three of the detection points of the first conductive sheet body to obtain at least three positions of the first conductive sheet body respectively. The height information of the detection point, and the first detection operation further comprises: calculating the first height information by the control module according to the height information of at least three of the detection points of the first conductive sheet body ; Wherein, when the second inspection operation is performed, a detection point is defined on the detection surface of the second conductive sheet body at the preset back drilling area, and the The drill can contact one of the detection points of the second conductive sheet body to obtain the second height information. The back drilling method for a circuit board according to claim 7, wherein at least three of the detection points of the first conductive sheet body are not collinear with each other; wherein when the first conductive sheet body and the When the second conductive sheet body is projected onto a projection plane along its normal direction, one of the detection points of the second conductive sheet body falls on at least three of the detection points of the first conductive sheet body. Within the bounds of a closed area. The back drilling method for a circuit board according to any one of claims 1 to 8, wherein when the depth of the back drill (stub length) is less than 90 mil, the machining accuracy of the back drill depth is positive or negative Within 2 mils; wherein, when the back stub length is greater than 90 mils, the processing accuracy of the back boring depth is within plus or minus 3 mils.