CN110893629B

CN110893629B - Method for manufacturing circuit board and drilling machine

Info

Publication number: CN110893629B
Application number: CN201811066377.1A
Authority: CN
Inventors: 钟欢欢; 张涛
Original assignee: Tripod Wuxi Electronic Co Ltd
Current assignee: Tripod Wuxi Electronic Co Ltd
Priority date: 2018-09-13
Filing date: 2018-09-13
Publication date: 2022-05-20
Anticipated expiration: 2038-09-13
Also published as: CN110893629A

Abstract

The invention discloses a manufacturing method of a circuit board and a drilling machine, wherein the manufacturing method of the circuit board comprises the following steps: providing a drilling machine which comprises a workbench and a drill bit arranged above the workbench; arranging a circuit board on a workbench, wherein the circuit board is provided with a top surface and a bottom surface and comprises a plurality of board structures which are sequentially stacked from the top surface to the bottom surface, a preset back drilling hole area and a back drilling hole depth testing area are further defined on the circuit board, and one board structure of the plurality of board structures is provided with an inner layer detection metal pad in the back drilling hole depth testing area; contacting the top surface with a drill according to the back drilling depth test area to obtain first height information; contacting the inner detection metal pad with a drill according to the back drilling depth test area to obtain second height information; and calculating the actual back drilling depth value according to the first height information and the second height information.

Description

Method for manufacturing circuit board and drilling machine

Technical Field

The present invention relates to a method for manufacturing a circuit board and a drilling machine, and more particularly, to a method for manufacturing a circuit board and a drilling machine capable of improving the processing accuracy of a back drilling depth.

Background

In the conventional circuit board manufacturing method, when back drilling operation is carried out, depth values set by drilling are unified by taking the surface copper surface of the circuit board as a reference, and the influence of plate thickness difference or poor plate thickness uniformity between the circuit board and the circuit board on the processing precision of the back drilling depth (stub length) is not considered. Therefore, when the board thickness difference between the circuit boards is large or the board thickness uniformity is not good, the machining accuracy of the back drill depth becomes larger as the back drill depth becomes deeper, and the error range becomes larger. For example, when the depth of the back-drilled hole is greater than 90 mils, the machining accuracy of the back-drilled hole depth will have an error range of plus or minus 5 mils.

The present inventors have considered that the above-mentioned drawbacks can be improved, and have made intensive studies in cooperation with the application of scientific principles, and finally have proposed an invention that is reasonably designed and effectively improves the above-mentioned drawbacks.

Disclosure of Invention

The invention aims to provide a manufacturing method of a circuit board and a drilling machine, which can effectively overcome the defects of the existing circuit board and the manufacturing method thereof.

The invention discloses a manufacturing method of a circuit board, which comprises the following steps: providing a drilling machine; the drilling machine comprises a workbench, a drill bit and a control module, wherein the drill bit is arranged above the workbench at intervals; arranging a circuit board on the workbench of the drilling machine; the circuit board is provided with a top surface and a bottom surface, and comprises a plurality of board structures which are sequentially stacked from the top surface to the bottom surface; the circuit board is further defined with a preset back drilling hole area and a back drilling hole depth testing area adjacent to the preset back drilling hole area, and one of the board structures of the circuit board is provided with an inner layer detection metal pad at the back drilling hole depth testing area; performing a first inspection operation, comprising: contacting the top surface of the circuit board with the drill bit of the drilling machine according to the back drilling depth test area to obtain first height information of the top surface in the back drilling depth test area; performing a second inspection operation, comprising: drilling the circuit board by the drill bit of the drilling machine according to the back drilling depth test area until the drill bit contacts the inner layer detection metal pad of the circuit board to obtain second height information; calculating an actual back-drilled hole depth value by the control module of the drilling machine according to the first height information and the second height information; and performing a back drilling operation, comprising: and back drilling the circuit board at the preset back drilling area by the drill bit of the drilling machine according to the actual back drilling depth value so as to form a back drilling hole on the circuit board.

The invention also discloses a drilling machine, comprising: a work table: wherein, the workbench can be provided with a circuit board arranged thereon; the drill bit is arranged above the workbench at intervals; the drill can move towards the direction of the workbench according to a back drilling depth test area of the circuit board in a first detection operation so as to contact with a top surface of the circuit board; the drill bit can move towards the direction of the workbench according to the back drilling depth test area of the circuit board in a second detection operation, and drill the circuit board until the drill bit contacts an inner layer detection metal pad arranged on one of a plurality of plate structures of the circuit board; the control module is electrically connected to the drill bit; wherein the control module is capable of sending a first current signal to the drill bit during the first detection operation, and when the drill bit contacts the top surface of the circuit board, the control module is capable of receiving a first feedback signal generated by the drill bit and the top surface and obtaining a first height information according to the first feedback signal; wherein the control module is capable of sending a second current signal to the drill bit during the second inspection operation, and when the drill bit contacts the inner inspection metal pad, the control module is capable of receiving a second feedback signal generated by the drill bit and the inner inspection metal pad and obtaining second height information according to the second feedback signal; the control module can calculate an actual back-drilled hole depth value according to the first height information and the second height information.

In summary, the method for manufacturing a circuit board and the drilling machine according to the embodiments of the invention can detect the top surface and the inner layer detection metal pad of the circuit board in the first and second detection operations respectively by the drill of the drilling machine to obtain the first and second height information respectively, and can calculate an actual back drilling depth value according to the first and second height information, so that the processing precision of the back drilling depth (stub length) is greatly improved.

For a better understanding of the nature and technical content of the present invention, reference should be made to the following detailed description of the invention and the accompanying drawings, which are provided for illustration purposes only and are not intended to limit the scope of the invention in any way.

Drawings

FIG. 1 is a schematic view of a drill rig according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of steps S101 and S102 of a method for manufacturing a circuit board according to an embodiment of the invention;

FIG. 3 is a first schematic view of step S103 of the method for manufacturing a circuit board according to the embodiment of the present invention;

FIG. 4 is a schematic view (II) of step S103 of the method for manufacturing a circuit board according to the embodiment of the present invention;

FIG. 5 is a diagram illustrating a step S104 of a method for manufacturing a circuit board according to an embodiment of the present invention;

FIG. 6 is a first schematic view of step S105 of the method for manufacturing a circuit board according to the embodiment of the present invention;

FIG. 7 is a diagram illustrating a step S105 of a method for manufacturing a circuit board according to an embodiment of the present invention;

FIG. 8 is a diagram illustrating a step S107 of a method for manufacturing a circuit board according to an embodiment of the present invention;

FIG. 9 is a schematic view of an inner detection metal pad electrically connected to a plurality of inner metal conductors according to an embodiment of the present invention;

FIG. 10 is a schematic view of a test borehole falling inside the profile of a window in accordance with an embodiment of the present invention.

Description of the symbols

100: drilling machine

110: working table

111: working table

120: drill bit

121: main shaft

122: first drill point

123: second drill point

124: third drill point

125: fourth drill point

130: control module

200: circuit board

201: the top surface

202: bottom surface

210: top conductive layer

220: bottom conductive layer

230: plate structure

231: inner layer detection metal pad

232: inner layer metal conductor

233: window opening

234: test drill hole

240: through hole

250: conductive layer

260: back drilling

DR: presetting back drilling area

TR: back-drilled hole depth test area

TR 1: a first test area

TR 2: second test area

H1: first height information

H2: second height information

SL: back drilling depth

P: projection plane

Detailed Description

Referring to fig. 1 to 10, it should be noted that, in the embodiment of the present invention, relevant numbers and shapes mentioned in the corresponding drawings are only used for describing the embodiments of the present invention in detail, so as to facilitate understanding of the content of the present invention, and are not used for limiting the scope of the present invention.

[ method for producing Circuit Board ]

The embodiment discloses a manufacturing method of a circuit board. The manufacturing method of the circuit board comprises a step S101, a step S102, a step S103, a step S104, a step S105, a step S106 and a step S107. It should be noted that the order of the steps and the actual operation manner carried out in the embodiment can be adjusted according to the requirement, and are not limited to the embodiment.

Referring to fig. 1 and 2, step S101 is to provide a drilling machine 100. The drilling machine 100 includes a table 110, a drill 120, and a control module 130. Wherein the working platform 110 has a working platform 111. The drill 120 includes a main shaft 121, and the main shaft 121 can be replaced and provided with different drill points (e.g., a first drill point 122, a second drill point 123, a third drill point 124, and a fourth drill point 125) according to different manufacturing process requirements. Further, the drill 120 is disposed above the working platform 111 of the working platform 110 at an interval and can move toward the working platform 111 to perform a detection operation (a first detection operation and a second detection operation as described below) or a drilling operation (a 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), and the control module 130 is electrically connected to the drill 120. The operation and functions of the drill 120 and the control module 130 are described in detail in the following steps.

Referring to fig. 2, in step S102, a circuit board 200 is disposed on the working platform 111 of the working platform 110. In more detail, the circuit board 200 has a top surface 201 and a bottom surface 202, and the circuit board 200 includes a top conductive layer 210, a bottom conductive layer 220, and a plurality of board structures 230 located between the top conductive layer 210 and the bottom conductive layer 220. Wherein a surface of the top conductive layer 210 opposite to the plurality of plate structures 230 is defined as the top surface 201, and a surface of the bottom conductive layer 220 opposite to the plurality of plate structures 230 is defined as the bottom surface 202. That is, a plurality of the plate structures 230 are sequentially stacked from the top surface 201 to the bottom surface 202. Further, in the present embodiment, the circuit board 200 has a through hole 240 penetrating through the top surface 201 and the bottom surface 202, and a conductive layer 250 plated on a wall of the through hole 240, and the conductive layer 250 is electrically connected to the top conductive layer 210 and the bottom conductive layer 220.

It should be noted that, in order to facilitate the subsequent manufacturing steps, the circuit board 200 of the present embodiment further defines a predetermined back-drilling region DR and a back-drilling depth testing region TR adjacent to the predetermined back-drilling region DR. One board structure 230 of the plurality of board structures 230 of the circuit board 200 is provided with an inner detection metal pad 231 at the back drilling depth test region TR to facilitate the subsequent detection (such as the second detection described below), and the through hole 240 and the conductive layer 250 of the circuit board 200 are both located within the predetermined back drilling region DR to facilitate the subsequent drilling (such as the back drilling described below).

In more detail, the back-drilling depth test area TR of the circuit board 200 of the present embodiment is further divided into a first test area TR1 and a second test area TR2 adjacent to the first test area TR1, and the inner-layer detection metal pads 231 are located in the second test area TR 2. Further, in an embodiment of the present invention, the circuit board 200 has a board thickness of not more than 4 millimeters (mm), a board length of not more than 480 mm, and a board width of not more than 400 mm, but the present invention is not limited thereto.

Referring to FIG. 3, step S103 is to perform a windowing operation. The windowing operation comprises: a portion of the top conductive layer 210 in the back drill depth test region TR is removed to form a window 233. The position of the window 233 corresponds to the position of the inner detection metal pad 231.

In more detail, with reference to fig. 3, in the present embodiment, the window 233 is formed by disposing a first drill pin 122 (e.g., a drill pin with a diameter of 1 mm) on the main shaft 121 of the drill 120 and drilling a portion of the top conductive layer 210 located in a second test region TR2 of the back-drilled hole depth test region TR by using the first drill pin 122, so that a portion of the top conductive layer 210 and a portion of the plurality of plate structures 230 are removed, thereby forming the window 233; in this case, the window 233 has an inverted conical shape in a shape that fits the shape of the first drill 122, but the present invention is not limited thereto. For example, as shown in fig. 4, in another embodiment of the present invention, the window 233 may also be formed by, for example, performing an etching process on a portion of the top conductive layer 210 located in the second test region TR2 of the back drill depth test region TR to form the window 233; in this case, the etching process only removes a portion of the top conductive layer 210 and does not react to the plate structure 230.

Referring to FIG. 5, step S104 is to perform a first detection operation. The first detection operation comprises: the drill 120 of the drilling machine 100 contacts the top surface 201 of the circuit board 200 according to the back drill depth test region TR to obtain a first height information H1 that the top surface 201 is located in the back drill depth test region TR.

More specifically, in the present embodiment, the first detection operation is performed by disposing a second drill point 123 (e.g., a drill point with a diameter of 0.4 mm) on the main shaft 121 of the drill 120 and using the second drill point 123 of the drill 120 to contact a portion of the top surface 201 of the top conductive layer 210 located in the first test region TR1 of the back-drilling depth test region TR to obtain the first height information H1.

Further, when the first detection operation is performed, the capacitive sensing unit (e.g., CBD capacitive sensor) of the control module 130 of the drilling machine 100 can send a first current signal to the second drill point 123 of the drill 120, and when the second drill point 123 of the drill 120 contacts the top surface 201 of the top conductive layer 210 and is electrically connected to the top surface 201 of the top conductive layer 210, the signal processing unit of the control module 130 of the drilling machine 100 can receive a first feedback signal generated by the second drill point 123 of the drill 120 and the top surface 201 of the top conductive layer 210, and perform signal processing according to the first feedback signal to obtain the first height information H1.

It should be noted that in an embodiment of the present invention, the area of the top surface 201 of the top conductive layer 210 must be large enough to enable the detection operation to be successfully started when the second drill tip 123 of the drill 120 contacts the top surface 201 of the top conductive layer 210 (e.g., the area of the top surface 201 of the top conductive layer 210 must be larger than the surface area of the main shaft 121 of the drill 120 to form a sufficient capacitance and to enable the capacitance value to be larger than a standard value).

Referring to fig. 6 and 7, step S105 is to perform a second detection operation. The second detection operation comprises: the circuit board 200 is drilled by the drill 120 of the drilling machine 100 according to the back drilling depth test region TR until the drill 120 contacts the inner detection metal pad 231 of the circuit board 200, so as to obtain a second height information H2.

More specifically, in the present embodiment, the second inspection operation is performed by providing a third drill 124 (e.g., a drill with a diameter of 0.4 mm) on the main shaft 121 of the drill 120, and drilling the circuit board 200 through the window 233 by using the third drill 124 of the drill 120 until the third drill 124 of the drill 120 contacts the inner-layer inspection metal pad 231 of the second test region TR2 located in the back-drilling depth test region TR, so as to obtain the second height information H2 (see fig. 6), and forming a test drill 234 (see fig. 7) spatially connecting the window 233 and the inner-layer inspection metal pad 231 on the circuit board 200. The aperture of the window 233 is preferably larger than that of the test drilling hole 234, and referring to fig. 10, when the circuit board 200 is projected on a projection plane P along the normal direction, the test drilling hole 234 falls inside the outline of the window 233.

Further, when the second detection operation is performed, the capacitive sensing unit of the control module 130 of the drilling machine 100 can send a second current signal to the third drill point 124 of the drill 120, and when the third drill point 124 of the drill 120 contacts the inner detection metal pad 231 and is electrically connected to the inner detection metal pad 231, the signal processing unit of the control module 130 of the drilling machine 100 can receive a second feedback signal generated by the third drill point 124 of the drill 120 and the inner detection metal pad 231 together and perform signal processing according to the second feedback signal to obtain the second height information H2.

It should be noted that, if only the inner detection metal pad 231 is used as a conductor for starting the second detection operation, there may be a problem that the capacitance is insufficient and the detection operation cannot be performed smoothly. Referring to fig. 9, in an embodiment of the invention, in order to increase the conductive area to facilitate the increase of the capacitance and to smoothly start the detection operation, among the plurality of board structures 230 of the circuit board 200, the board structure 230 having the inner detection metal pad 231 is further provided with a plurality of additional inner metal conductors 232 (e.g., additional metal pads), and the inner detection metal pad 231 is electrically connected to the plurality of inner metal conductors 232, thereby increasing the conductive area to increase the capacitance and smoothly start the detection operation, but the invention is not limited thereto. For example, in another embodiment of the present invention (not shown), the inner detection metal pad 231 can also be electrically connected to the conductive layer 250 plated on the wall of the through hole 240 and to other additional electrical conductors (such as the top conductive layer 210 or the bottom conductive layer 220) through the conductive layer 250, for example, so as to increase the conductive area.

It should be noted that, in the present embodiment, the portion of the circuit board 200 between the inner detection metal pad 231 and the window 233 preferably only includes an insulating material and does not include any other metal conductor (as shown in fig. 3 and 4). Thus, when the second inspection operation is performed, the third drill tip 124 of the drill 120 does not contact any other metal conductor after the circuit board 200 is drilled through the window 233 and before it contacts the inner inspection metal pad 231 of the circuit board 200 (see fig. 6).

It should be noted that, in the present embodiment, the diameter of the first drill 122 is larger than that of the third drill 124, so that the diameter of the window 233 is larger than that of the test borehole 234 (see fig. 7). Furthermore, since the second drill point 123 and the third drill point 124 are used for performing the inspection operation, it is preferable to use drill points having the same diameter; alternatively, in an embodiment of the present invention, the second drill point 123 and the third drill point 124 may also use the same drill point to perform the first detection operation and the second detection operation, and the present invention is not limited thereto.

In step S106, an actual back-drilling depth value is calculated by the arithmetic logic unit of the control module 130 of the drilling machine 100 according to the first height information H1 and the second height information H2, so as to facilitate the subsequent drilling operation (step S107).

More specifically, in an embodiment of the present invention, the calculating method of the actual back-drilled hole depth value includes: the first height information H1 and second height information H2 are subtracted and the absolute value is taken to obtain the actual back-drilled hole depth value, but the present invention is not limited thereto.

Referring to fig. 8, step S107 is to perform a back drilling operation. The back drilling operation comprises: the circuit board 200 is back-drilled at the predetermined back-drilled hole area DR by the drill 120 of the drilling machine 100 according to the actual back-drilled hole depth value, so that the circuit board 200 is formed with a back-drilled hole 260.

More specifically, in the present embodiment, the back drilling operation is performed by providing a fourth drill point 125 on the main shaft 121 of the drill 120 and drilling a hole through the through hole 240 and the conductive layer 250 at the predetermined back drilling area DR by using the fourth drill point 125 of the drill 120 to form the back drilling hole 260. The down-drilling depth of the circuit board 200 drilled by the fourth drill point 125 of the drill 120 is the back-drilling depth.

Further, since the fourth drill tip 125 of the drill 120 drills the through hole 240 and the conductive layer 250 at the predetermined back drilling region DR, the back drilling hole 260 of the circuit board 200 overlaps at least a portion of the through hole 240 after the back drilling operation is performed, so that at least a portion of the conductive layer 250 is removed and the wall of the back drilling hole 260 does not have any conductive layer 250. The diameter of the fourth drill point 125 of the drill 120 is preferably larger than that of the through hole 240, so that the diameter of the back drilling hole 260 is larger than that of the through hole 240, but the invention is not limited thereto.

In summary, in the method for manufacturing a circuit board according to the embodiment of the invention, the drill 120 of the drilling machine 100 can respectively perform the first and second inspection operations on the top surface 201 and the inner layer inspection metal pad 231 of the circuit board 200 to respectively obtain the first and second height information H1, H2, and can calculate an actual back drilling depth value according to the first and second height information H1, H2, so that the processing precision of the back drilling depth sl (stub length) is greatly improved.

More specifically, in the conventional circuit board manufacturing method, the depth value set for the back drilling is set to be uniform with reference to the surface copper surface of the circuit board when the back drilling operation is performed, and the influence of the difference in board thickness or the poor uniformity of board thickness between the circuit board and the circuit board on the processing accuracy of the back drilling depth (stub length) is not considered. Therefore, when the board thickness difference between the circuit boards is large or the board thickness uniformity is not good, the machining accuracy of the back drill depth becomes larger as the back drill depth becomes deeper, and the error range becomes larger. For example, when the depth of the back-drilled hole is greater than 90 mils, the machining accuracy of the back-drilled hole depth will have an error range of plus or minus 5 mils.

In contrast to the above-mentioned disadvantages, the method for manufacturing a circuit board according to the embodiment of the present invention can greatly improve the processing accuracy of the back drilling depth SL (see fig. 8) of the manufactured circuit board 200. For example, when the back-drilling depth SL is less than 90mil, the machining precision of the back-drilling depth SL is within plus or minus 1.5mil, and when the back-drilling depth SL is less than 90mil, the machining precision of the back-drilling depth SL is within plus or minus 2 mil.

[ drilling machines ]

The above is a description of the method of manufacturing a circuit board according to the embodiment of the present invention, and the following is a description of the drill 100 that can be used for the above-described method of manufacturing a circuit board. It should be noted that although the drill 100 of the present embodiment can be used for the above-described method for manufacturing a circuit board, the present invention is not limited thereto. That is, the drill 100 of the present embodiment may be used in other types of circuit board manufacturing methods.

Referring to fig. 1 and 2, the present embodiment further discloses a drilling machine 100. The drilling machine 100 includes a worktable 110, a drill 120 spaced above the worktable 110, and a control module 130 electrically connected to the drill 120.

Referring to fig. 2, the table 110 can provide a circuit board 200 disposed thereon. As shown in fig. 5 and 6, the drill 120 can move toward the worktable 110 according to a back drilling depth test region TR of the circuit board 200 in a first inspection operation to contact a top surface 201 (as shown in fig. 5) of the circuit board 200. In a second inspection operation, the drill 120 can move toward the worktable 110 according to the back drilling depth test region TR of the circuit board 200 and drill the circuit board 200 until the drill 120 contacts the inner inspection metal pad 231 (see fig. 6) disposed on one of the board structures 230 of the circuit board 200.

The control module 130 can send a first current signal to the drill 120 in the first detection operation, and when the drill 120 contacts the top surface 201 of the pcb 200, the control module 130 can receive a first feedback signal generated by the drill 120 and the top surface 201 and obtain a first height information H1 according to the first feedback signal. Furthermore, the control module 130 can send a second current signal to the drill 120 during the second detection operation, and when the drill 120 contacts the inner detection metal pad 231, the control module 130 can receive a second feedback signal generated by the drill 120 and the inner detection metal pad 231 and obtain the second height information H2 according to the second feedback signal. The control module 130 can calculate an actual back-drilled hole depth value according to the first height information H1 and the second height information H2.

[ technical effects of the embodiments of the present invention ]

In summary, the method for manufacturing a circuit board and the drilling machine 100 according to the embodiments of the invention can respectively perform the first and second inspection operations on the top surface 201 and the inner layer inspection metal pad 231 of the circuit board 200 by the drill 120 of the drilling machine 100 to respectively obtain the first and second height information H1, H2, and can calculate an actual back drilling depth value according to the first and second height information H1, H2, so that the processing precision of the back drilling depth sl (stub length) is greatly improved.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the scope of the present invention, which is defined by the appended claims.

Claims

1. A method of manufacturing a circuit board, comprising:

providing a drilling machine; the drilling machine comprises a workbench, drill bits arranged above the workbench at intervals and a control module electrically connected with the drill bits;

arranging a circuit board on the workbench of the drilling machine; the circuit board is provided with a top surface and a bottom surface, and comprises a plurality of board structures which are sequentially stacked from the top surface to the bottom surface; the circuit board is further defined with a preset back drilling hole area and a back drilling hole depth testing area adjacent to the preset back drilling hole area, and one of the board structures of the circuit board is provided with an inner layer detection metal pad at the back drilling hole depth testing area;

performing a first inspection operation comprising: contacting the top surface of the circuit board with the drill bit of the drilling machine according to the back drilling depth test area to obtain first height information of the top surface in the back drilling depth test area;

performing a second inspection operation comprising: drilling the circuit board by the drill bit of the drilling machine according to the back drilling depth test area until the drill bit contacts the inner layer detection metal pad of the circuit board to obtain second height information;

calculating an actual back-drilled hole depth value by the control module of the drilling machine according to the first height information and the second height information; and

performing a back drilling operation comprising: backdrilling the circuit board at the preset backdrilling area with the drill bit of the drilling machine according to the actual backdrilling depth value to form a backdrilling hole in the circuit board,

the circuit board further comprises a top conducting layer and a bottom conducting layer, the plurality of plate structures are positioned between the top conducting layer and the bottom conducting layer, and the side surface of the top conducting layer opposite to the plurality of plate structures is the top surface; before the second detection operation is performed, the method for manufacturing a circuit board further includes performing a windowing operation, and the windowing operation includes: removing a portion of the top conductive layer located in the back-drilled hole depth test area to form a window corresponding in position to the inner detection metal pad.

2. The method for manufacturing a circuit board according to claim 1, wherein the circuit board has a through hole penetrating the top surface and the bottom surface, and a conductive layer plated on a wall of the through hole; wherein the through hole and the conductive layer of the circuit board are both located within the range of the preset back drilling hole area; wherein, after performing the backdrilling operation, the backdrilled hole of the circuit board is overlapped with at least a part of the through-hole such that at least a part of the conductive layer is removed and a hole wall of the backdrilled hole is free of any conductive layer.

3. The method of claim 1, wherein the control module of the drilling machine is capable of sending a first current signal to the drill bit while performing the first inspection operation, and the control module is capable of receiving a first feedback signal generated by the drill bit and the top surface when the drill bit contacts the top surface of the circuit board and obtaining the first height information according to the first feedback signal; wherein, when the second detection 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 inner detection metal pad, the control module can receive a second feedback signal generated by the drill bit and the inner detection metal pad and obtain the second height information according to the second feedback signal.

4. The method of manufacturing a circuit board according to claim 1, wherein the drill of the drill is capable of drilling the circuit board through the window while performing the second inspection work, so that the circuit board is formed with a test drill communicating the window and the inner-layer inspection metal pad.

5. The manufacturing method of a circuit board according to claim 4, wherein an aperture of the window is larger than an aperture of the test drill, and the test drill falls inside a contour of the window when the circuit board is projected onto a projection plane in a normal direction thereof.

6. The method of claim 4, wherein after the windowing operation is performed, a portion of the circuit board between the inner detection metal pad and the window comprises only an insulating material and does not comprise any metal conductor, such that the drill head of the drilling machine does not contact any metal conductor after drilling the circuit board through the window and before contacting the inner detection metal pad of the circuit board.

7. The method of manufacturing a circuit board according to claim 1, wherein, among a plurality of the board structures of the circuit board, the board structure provided with the inner detection metal pad is further provided with a plurality of inner metal conductors, and the inner detection metal pad is electrically connected to the plurality of inner metal conductors.

8. The method of manufacturing a circuit board according to claim 1, wherein the back-drilled hole depth test area of the circuit board is further divided into a first test area and a second test area adjacent to the first test area, and the inner layer detection metal pad is located in the second test area; wherein the first height information is obtained by the drill head of the drilling machine contacting a portion of the top surface located at the first test area when the first detection work is performed; wherein the second height information is obtained by the drill of the drilling machine contacting the inner detection metal pad located at the second test area when the second detection work is performed.

9. The method for manufacturing a circuit board according to any one of claims 1 to 8, wherein when the depth (stub length) of the back-drilled hole is less than 90 mils, the processing accuracy of the depth of the back-drilled hole is within plus or minus 1.5 mils; wherein, when the depth (stub length) of the back-drilled hole is greater than 90mil, the processing precision of the back-drilled hole depth is within plus-minus 2 mil.