CN220733071U

CN220733071U - Printing Circuit board

Info

Publication number: CN220733071U
Application number: CN202320471191.4U
Authority: CN
Inventors: 向铖
Original assignee: Zhuhai Founder Technology Multilayer PCB Co Ltd
Current assignee: Zhuhai Founder Technology Multilayer PCB Co Ltd
Priority date: 2023-03-10
Filing date: 2023-03-10
Publication date: 2024-04-05
Anticipated expiration: 2033-03-10

Abstract

The application provides a printed circuit board, including: a substrate, a first back drilling hole, a second back drilling hole and a through hole, the substrate comprises N copper layers which are arranged in a laminated manner and are not connected with each other, and an insulating layer is arranged between two adjacent copper layers; the first back drilling hole is positioned on the first side of the substrate and penetrates through the M1 copper layers; the first back drilling hole is a conical hole, and a first copper-clad layer is arranged on the wall of the first back drilling hole; the second back drilling hole is positioned on the second side of the substrate and penetrates through the M2 copper layers; second back drilling is a conical hole which is provided with a plurality of holes, a second copper-clad layer is arranged on the hole wall of the second back drilling hole; the through hole is communicated with the first back drilling hole and the second back drilling hole. According to the printed circuit board wiring structure, the electronic element can be buried in the first back drilling hole and the second back drilling hole, conduction with other circuit layers is achieved, the quantity of copper layers of the non-connectable circuit in the printed circuit board is reduced, the wiring space of the printed circuit board is improved, and the size of the printed circuit board is reduced.

Description

Printed circuit board

Technical Field

The present application relates to printed circuit board processing technology, and in particular, to a printed circuit board.

Background

Printed circuit boards (Printed circuit boards; PCBs), also known as printed circuit boards, are providers of electrical connections for electronic components, and are widely used in a variety of electronic products. As electronic technologies further permeate all industries, more and more electronic technologies tend to be fused, electronic products develop faster and more, and requirements on various aspects of printed circuit boards are higher and more; among them, the development of miniaturization and thinning of the printed circuit board is an important trend.

In order to pre-embed an electronic component on a printed circuit board and connect the electronic component with an internal copper layer, a printed circuit board is provided in the related art, a first side of the printed circuit board is provided with a conical back drilling hole, a second side is communicated with the back drilling hole through a through hole, a copper-clad layer is arranged on a hole wall of the back drilling hole, and the copper-clad layer is not arranged on a hole wall of the through hole. Through the structure, the electronic element can be buried in the conical back drilling hole, the electronic element is conducted with other circuit layers through the copper-clad layer on the wall of the back drilling hole, and the influence of the redundant copper-clad layer on the connecting signal wire can be reduced because the copper-clad layer is not arranged on the wall of the through hole.

However, the printed circuit board adopting the above scheme is large in size and small in wiring space.

Disclosure of Invention

In order to overcome the above-mentioned drawbacks of the related art, an object of the present application is to provide a printed circuit board, which is beneficial to improving the wiring space of the printed circuit board and reducing the volume of the printed circuit board.

The application provides a printed circuit board, including:

the substrate comprises N copper layers which are arranged in a stacked manner and are not connected with each other, and an insulating layer is arranged between two adjacent copper layers;

the first back drilling hole is positioned on the first side of the substrate, and penetrates through M1 copper layers along the thickness direction of the substrate; the first back drilling hole is a conical hole, and a first copper-clad layer is arranged on the hole wall of the first back drilling hole;

the second back drilling hole is positioned on the second side of the substrate and penetrates through M2 copper layers along the thickness direction of the substrate; the second back drilling hole is a conical hole, and a second copper-clad layer is arranged on the hole wall of the second back drilling hole;

the through hole is communicated with the first back drilling hole and the second back drilling hole;

wherein M1, M2 and N are all positive integers, and the sum of M1 and M2 is smaller than N.

The printed circuit board as described above may, optionally, the first back drilling hole, the second back drilling hole and the through hole are coaxially arranged.

The printed circuit board as described above, optionally, the aperture of the through hole is smaller than the apertures of the first back drilling hole and the second back drilling hole.

In the printed circuit board as described above, optionally, in a direction perpendicular to the substrate, a cross-sectional area of the first back drilling hole is gradually increased in a direction away from the through hole, and a cross-sectional area of the second back drilling hole is gradually increased in a direction away from the through hole.

Optionally, the through hole is a laser perforation, and the first back drilling hole and the second back drilling hole are mechanical drilling holes.

The printed circuit board as described above, optionally, the aperture of the through hole is 1mm or more.

In the printed circuit board described above, the thickness of the first copper-clad layer may be 25 μm or more, and the thickness of the second copper-clad layer may be 25 μm or more.

The printed circuit board as described above, optionally, the first copper-clad layer and the second copper-clad layer are both prepared by chemical deposition and electroplating.

The printed circuit board is characterized in that the first copper-clad layer and the second copper-clad layer are prepared by blind-through co-plating.

The printed circuit board as described above, optionally, the M1 and M2 are equal or unequal.

The application provides a printed circuit board, including: the substrate comprises N copper layers which are arranged in a laminated mode and are not connected with each other, and an insulating layer is arranged between two adjacent copper layers; the first back drilling hole is positioned on the first side of the substrate, and penetrates through the M1 copper layers along the thickness direction of the substrate; the first back drilling hole is a conical hole, and a first copper-clad layer is arranged on the wall of the first back drilling hole; the second back drilling hole is positioned on the second side of the substrate, and penetrates through the M2 copper layers along the thickness direction of the substrate; the second back drilling hole is a conical hole, and a second copper-clad layer is arranged on the wall of the second back drilling hole; the through hole is communicated with the first back drilling hole and the second back drilling hole; wherein M1, M2 and N are all positive integers, and the sum of M1 and M2 is smaller than N. The application processes the first back drilling hole, the second back drilling hole and the through hole in the substrate, the first back drilling hole and the second back drilling hole are conical holes, the wall of the first back drilling hole is provided with a first copper coating layer, the wall of the second back drilling hole is provided with a second copper coating layer, therefore, the electronic element can be buried in the first back drilling hole and the second back drilling hole, so that the electronic element can be communicated with other circuit layers, a copper-clad layer is not arranged on the wall of the through hole, the signal transmission capacity can be improved, and the heat dissipation efficiency is improved; compared with the scheme in the related art, the copper layer quantity of the unconnectable circuit in the printed circuit board is reduced, so that the wiring space of the printed circuit board is increased, and the size of the printed circuit board is reduced.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the following description will make a brief description of the drawings used in the embodiments or the related art description, and it is apparent, the drawings in the following description are illustrative of certain embodiments of the present application and other drawings may be made from these drawings by those of ordinary skill in the art without undue burden.

FIG. 1 is a flow chart of a method of manufacturing a printed circuit board according to the related art;

fig. 2 (a) -2 (e) are schematic diagrams corresponding to each step in the manufacturing process of the printed circuit board shown in fig. 1;

FIG. 3 is a schematic diagram of a printed circuit board according to an embodiment of the present application;

fig. 4 is a flowchart of a method for manufacturing a printed circuit board according to an embodiment of the present disclosure;

fig. 5 (a) -5 (d) are schematic diagrams of the printed circuit board shown in fig. 4, which correspond to the steps in the manufacturing process.

Reference numerals:

100-a substrate; 110-copper layer; 120-an insulating layer; 130-process holes; 131-a copper layer of the process hole; 140-back drilling; 141-back drilling a copper-clad layer; 150-through holes;

200-a first back drilling; 210-a first copper-clad layer;

300-second back drilling; 310-a second copper-clad layer;

400-through holes.

Detailed Description

For the purposes of making the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments.

All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure. The following embodiments and features of the embodiments may be combined with each other without conflict.

As described in the background art, in order to pre-embed an electronic component on a printed circuit board and connect the electronic component with an internal copper layer, there is provided a printed circuit board in the related art, in which a first side of the printed circuit board is provided with a tapered back drilling hole, a second side is communicated with the back drilling hole through a through hole, and a copper-clad layer is provided on a wall of the back drilling hole, and no copper-clad layer is provided on a wall of the through hole. Through the structure, the electronic element can be buried in the conical back drilling hole, the electronic element is conducted with other circuit layers through the copper-clad layer on the wall of the back drilling hole, and the influence of the redundant copper-clad layer on the connecting signal wire can be reduced because the copper-clad layer is not arranged on the wall of the through hole.

Specifically, fig. 1 is a flowchart of a method for manufacturing a printed circuit board in the related art; fig. 2 (a) -2 (e) are schematic diagrams of the printed circuit board shown in fig. 1, corresponding to each step in the manufacturing process. Referring to fig. 1, 2 (a) -2 (e), a related art printed circuit board may be manufactured by the following steps:

step S110, providing a substrate, wherein the substrate comprises N copper layers which are arranged in a stacked mode and are not connected with each other, and an insulating layer is arranged between two adjacent copper layers.

As illustrated in fig. 2 (a), the substrate 100 may include a plurality of copper layers 110 and a plurality of insulating layers 120 stacked, and the number N of the copper layers 110 in the substrate 100 may be determined as needed, where N is a positive integer, preferably N is a positive integer greater than or equal to 5. The insulating layer 120 is disposed between two adjacent copper layers 110, and the number of insulating layers 120 may be N-1.

Step S120, a process hole is drilled on the substrate, and the process hole penetrates through the substrate.

Illustratively, as shown in fig. 2 (b), a process hole 130 is provided in the substrate 100 therethrough. The process holes 130 may be machined, for example, by mechanical drilling. Alternatively, the aperture of the process hole 130 is smaller than the aperture of the final through hole (e.g., may be 0.3mm smaller).

Step S130, drilling back holes on the first side of the process holes, wherein the back holes are conical holes, and the back holes penetrate through the M copper layers along the thickness direction of the substrate.

As shown in fig. 2 (c), the back-drilled holes 140 are formed on the first side of the process holes 130, and the back-drilled holes 140 penetrate through the M copper layers 110, where M is a positive integer and M is less than N. That is, the back-drilled holes 140 do not penetrate the substrate 100.

And S140, preparing a back drilling copper-clad layer on the wall of the back drilling hole, and preparing a process hole copper-clad layer on the wall of the process hole.

Illustratively, as shown in fig. 2 (d), a back-drilled copper-clad layer 141 is deposited in the back-drilled hole 140, and a process-hole copper-clad layer 131 is deposited in the process hole 130. In depositing the copper-clad layer, a method of chemical deposition followed by electroplating may be employed.

And S150, secondarily drilling, widening the process hole, and simultaneously removing the copper-clad layer of the process hole to obtain a through hole communicated with the back drilling.

For example, as shown in fig. 2 (e), during secondary drilling, a drill bit with a drill bit size larger than the diameter of the process hole may be selected, and during drilling, the drill bit is preferably aligned with the axis of the process hole to drill, thereby widening the process hole uniformly and obtaining the through hole 150.

However, only one electronic component can be connected in one hole by adopting the scheme, the size of the printed circuit board is large, and the wiring space is small. And the operation of twice drilling the through holes is needed, the same-hole positioning capability of the mechanical drill is poor, the drill is easy to deviate during the secondary drilling, and the copper-clad layer of the process hole is possibly not cleaned.

In view of this, the embodiment of the present application aims to provide a printed circuit board, by processing a first back drilling hole, a second back drilling hole and a through hole in a substrate, where the first back drilling hole and the second back drilling hole are tapered holes, a first copper-clad layer is disposed on a hole wall of the first back drilling hole, and a second copper-clad layer is disposed on a hole wall of the second back drilling hole, so that an electronic component can be buried in the first back drilling hole and the second back drilling hole, conduction with other circuit layers is achieved, no copper-clad layer is disposed on a hole wall of the through hole, signal transmission capability can be improved, and heat dissipation efficiency is improved; compared with the scheme in the related art, the copper layer quantity of the unconnectable circuit in the printed circuit board is reduced, so that the wiring space of the printed circuit board is increased, and the size of the printed circuit board is reduced.

The following detailed description of embodiments of the present application will be presented in conjunction with the accompanying drawings to enable one skilled in the art to more fully understand the present application.

Fig. 3 is a schematic diagram of a printed circuit board according to an embodiment of the present application.

Referring to fig. 3, the present embodiment provides a printed circuit board, including:

the substrate 100, the substrate 100 includes N copper layers 110 that are not connected to each other and are stacked, and an insulating layer 120 is provided between two adjacent copper layers 110. In this embodiment, the number N of the copper layers 110 in the substrate 100 may be determined according to need, where N is a positive integer, and preferably N is a positive integer greater than or equal to 5. The insulating layer 120 is disposed between two adjacent copper layers 110, and the number of insulating layers 120 may be N-1.

The first back drilling 200, the first back drilling 200 is located at a first side of the substrate 100, and the first back drilling 200 penetrates through the M1 copper layers 110 along the thickness direction of the substrate 100; the first back drilling hole 200 is a conical hole, and a first copper-clad layer 210 is arranged on the hole wall of the first back drilling hole 200. Alternatively, the first back drilling 200 may be machined by mechanical drilling or laser machining, and a taper drill may be used to drill the taper hole. The first back via 200 penetrates the M1 copper layers 110, wherein M1 is a positive integer, and M1 is smaller than N.

The second back drilling 300, the second back drilling 300 is located at the second side of the substrate 100, and the second back drilling 300 penetrates through the M2 copper layers 110 along the thickness direction of the substrate 100; the second back drilling hole 300 is a conical hole, and a second copper-clad layer 310 is arranged on the hole wall of the second back drilling hole 300. Alternatively, the second back drilling 300 may be machined by mechanical drilling or laser machining, and a taper drill may be used to drill the taper hole. The second back via 300 penetrates the M2 copper layers 110, where M2 is a positive integer, M1 and M2 may be equal or different, and the sum of M1 and M2 is smaller than N. That is, the first back drilling 200 and the second back drilling 300 do not penetrate the substrate 100.

The through hole 400, the through hole 400 communicates with the first back drilling 200 and the second back drilling 300. Alternatively, the through hole 400 may be machined by mechanical drilling or laser, and may be specifically selected according to needs.

In this embodiment, the electronic components may be buried in the first back drilling hole 200 and the second back drilling hole 300, so as to realize conduction with other circuit layers, which is beneficial to reducing the number of copper layers of the unconnectable circuit in the printed circuit board, thereby improving the wiring space of the printed circuit board.

In one possible implementation, the first back drilling 200, the second back drilling 300, and the through hole 400 of the present embodiment are coaxially disposed. The aperture of the through hole 400 is smaller than the apertures of the first back drilling 200 and the second back drilling 300.

Specifically, as shown in fig. 3, the cross-sectional area of the first back drilling 200 gradually increases in a direction away from the through-hole 400 in a direction perpendicular to the substrate 100, and the cross-sectional area of the second back drilling 300 gradually increases in a direction away from the through-hole 400.

Alternatively, the aperture of the through hole 400 is 1mm or more.

In one possible implementation, the first copper-clad layer 210 and the second copper-clad layer 310 of this embodiment are both prepared by chemical deposition and electroplating. The thickness of the first copper-clad layer 210 is 25 μm or more, and the thickness of the second copper-clad layer 310 is 25 μm or more, thereby satisfying the connection requirements of electronic components on the surface of the printed circuit board.

The first copper-clad layer 210 and the second copper-clad layer 310 can also be prepared by adopting a blind-passing co-plating process, so that copper plating can be realized together with other through holes or blind holes on the printed circuit board, thereby being beneficial to reducing the copper plating times of the printed circuit board.

Fig. 4 is a flowchart of a method for manufacturing a printed circuit board according to an embodiment of the present disclosure; fig. 5 (a) -5 (d) are schematic diagrams of the printed circuit board shown in fig. 4, which correspond to the steps in the manufacturing process.

Referring to fig. 4, 5 (a) -5 (d), the present embodiment provides a method for manufacturing a printed circuit board, which includes:

step S210, providing a substrate, wherein the substrate comprises N copper layers which are arranged in a stacked mode and are not connected with each other, and an insulating layer is arranged between two adjacent copper layers.

As shown in fig. 5 (a), the substrate 100 of the present embodiment includes a plurality of copper layers 110 and a plurality of insulating layers 120 stacked, where the number N of the copper layers 110 in the substrate 100 may be determined according to need, N is a positive integer, and preferably N is a positive integer greater than or equal to 5. The insulating layer 120 is disposed between two adjacent copper layers 110, and the number of insulating layers 120 may be N-1.

Step S220, drilling a first back drilling hole on the first side of the substrate, wherein the first back drilling hole penetrates through M1 copper layers along the thickness direction of the substrate; drilling a second back drilling hole on the second side of the substrate, wherein the second back drilling hole penetrates through M2 copper layers along the thickness direction of the substrate, and the first back drilling hole and the second back drilling hole are coaxially arranged; the first back drilling hole and the second back drilling hole are conical holes.

Illustratively, as shown in fig. 5 (b), a first side of the substrate 100 is provided with a first back-drilled hole 200, the first back-drilled hole 200 penetrating M1 copper layers 110. A second back-drilled hole 300 is provided on the second side of the substrate 100, the second back-drilled hole 300 penetrating the M2 copper layers 110. Wherein M1 and M2 are positive integers, and the sum of M1 and M2 is smaller than N. That is, the first back drilling 200 and the second back drilling 300 do not penetrate the substrate 100.

In one possible embodiment, step S120 may be manufactured by the following method:

firstly, processing a first center point on a first side of a substrate; and aiming the conical drill bit at the first center point to control the depth of the back drilling to obtain a first back drilling hole.

Then, turning over the substrate, and processing a second center point on the second side of the substrate, wherein the first center point corresponds to the second center point along the thickness direction of the substrate; and aiming the conical drill bit at a second center point to control the depth of the back drilling to obtain a second back drilling hole.

Step S230, preparing a first copper-clad layer on the hole wall of the first back drilling hole; and preparing a second copper-clad layer on the hole wall of the second back drilling hole.

Illustratively, as shown in fig. 5 (c), a first copper-clad layer 210 is deposited in the first back-drilled hole 200, and a second copper-clad layer 310 is deposited in the second back-drilled hole 300.

In one possible embodiment, step S130 may be manufactured by the following method:

firstly, depositing a first sub-copper-clad layer on the hole wall of a first back drilling hole by adopting a chemical deposition method, and simultaneously depositing a second sub-copper-clad layer on the hole wall of a second back drilling hole, wherein the thickness of the first sub-copper-clad layer is less than or equal to 1 mu m; the thickness of the second sub-copper-clad layer is less than or equal to 1 mu m.

Then, copper is electroplated on the surface of the first sub-copper-clad layer to obtain a first copper-clad layer 210, copper is electroplated on the surface of the second sub-copper-clad layer to obtain a second copper-clad layer 310, and the thickness of the first copper-clad layer 210 is greater than or equal to 25 μm in this embodiment, and the thickness of the second copper-clad layer 310 is greater than or equal to 25 μm.

Optionally, electroplating copper on the surface of the first sub-copper-clad layer by adopting a blind-passing co-plating process to obtain a first copper-clad layer; and electroplating copper on the surface of the second sub-copper-clad layer by adopting a blind-passing co-plating process to obtain the second copper-clad layer so as to reduce the copper electroplating times on the printed circuit board.

Step S240, drilling a through hole in the bottom wall of the first back drilling hole or the bottom wall of the second back drilling hole, wherein the through hole is communicated with the first back drilling hole and the second back drilling hole.

Illustratively, as shown in fig. 5 (d), the first back drilling 200 and the second back drilling 300 are communicated with each other through a through hole 400. Alternatively, the aperture of the through hole 400 may be smaller than that of the first back drilling 200.

In one possible embodiment, step S240 may be manufactured by the following method:

first, a third center point is processed on the bottom wall of the first back drilling hole or the bottom wall of the second back drilling hole, and the third center point is positioned on the axes of the first back drilling hole and the second back drilling hole along the thickness direction of the substrate.

And then drilling by taking the third center point as the center in a laser or mechanical drilling mode to obtain the through hole.

In one possible implementation, before the bottom wall of the first back drilling or the bottom wall of the second back drilling drills a through hole, the method of the present embodiment further includes:

preparing a first tin plating layer on the surface of the first copper-clad layer; and preparing a second tin plating layer on the surface of the second copper-clad layer. The first tin plating layer can protect the first copper-clad layer from subsequent processes, and the second tin plating layer can protect the second copper-clad layer from subsequent processes.

Further, preparing a first tin plating layer on the surface of the first copper-clad layer; after preparing the second tin-plated layer on the surface of the second copper-clad layer, the method of the present embodiment further includes:

and etching the copper layer on the first side of the substrate and the copper layer on the second side of the substrate to obtain an outer layer circuit.

Further, after drilling a through hole in the bottom wall of the first back drilling or the bottom wall of the second back drilling, the through hole being in communication with the first back drilling and the second back drilling, the method of the present embodiment further comprises:

get rid of first tin-plating layer and second tin-plating layer, can get rid of burr between first back drilling and the through-hole, the burr between second back drilling and the through-hole in the lump when getting rid of first tin-plating layer and second tin-plating layer to be favorable to improving the quality of printed circuit board.

According to the embodiment, the first back drilling hole, the second back drilling hole and the through hole are machined in the substrate, the first back drilling hole and the second back drilling hole are conical holes, the first copper-clad layer is arranged on the hole wall of the first back drilling hole, and the second copper-clad layer is arranged on the hole wall of the second back drilling hole, so that the electronic element can be buried in the first back drilling hole and the second back drilling hole, the connection with other circuit layers is realized, the copper-clad layer is not arranged on the hole wall of the through hole, the signal transmission capacity can be improved, and the heat dissipation efficiency is improved; compared with the scheme in the related art, the copper layer quantity of the unconnectable circuit in the printed circuit board is reduced, so that the wiring space of the printed circuit board is increased, and the size of the printed circuit board is reduced.

The embodiment only needs one through hole drilling process, is beneficial to reducing process steps and improving productivity, and has no copper-clad layer in the wall of the through hole, thereby solving the problem of residual copper-clad layer in the through hole in the related technology.

In the description of the present application, it should be understood that the terms "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," etc. indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, are merely for convenience in describing the present application and simplifying the description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be configured and operated in a particular orientation, and therefore should not be construed as limiting the present application.

In this application, unless specifically stated and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art as the case may be.

It should be noted that in the description of the present application, the terms "first," "second," and the like are merely used for convenience in describing the various components and are not to be construed as indicating or implying a sequential relationship, relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature.

In this application, each embodiment or implementation is described in a progressive manner, and each embodiment focuses on a difference from other embodiments, and identical and similar parts between the embodiments are only needed to see each other.

In the description of the present application, descriptions of the terms "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. In this application, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A printed circuit board, comprising:

wherein M1, M2 and N are all positive integers, and the sum of M1 and M2 is smaller than N;

the cross-sectional area of the first back drilling hole gradually increases in a direction away from the through hole along a direction perpendicular to the substrate, and the cross-sectional area of the second back drilling hole gradually increases in a direction away from the through hole;

the first copper-clad layer and the second copper-clad layer are prepared by adopting a blind-through co-plating process;

a first tin plating layer is prepared on the surface of the first copper-clad layer; and a second tin plating layer is prepared on the surface of the second copper-clad layer.

2. The printed circuit board of claim 1, wherein the first back-drilled hole, the second back-drilled hole, and the through-hole are coaxially disposed.

3. The printed circuit board of claim 2, wherein the aperture of the through hole is smaller than the apertures of the first back drilling and the second back drilling.

4. The printed circuit board of claim 1, wherein the through hole is a laser radium hole and the first back drilling and the second back drilling are mechanical drilling.

5. The printed circuit board of claim 4, wherein the aperture of the through hole is 1mm or more.

6. The printed circuit board of claim 1, wherein the first copper-clad layer has a thickness of 25 μm or more and the second copper-clad layer has a thickness of 25 μm or more.

7. The printed circuit board of claim 6, wherein the first copper-clad layer and the second copper-clad layer are both prepared by electroless deposition and electroplating.

8. The printed circuit board of claim 1, wherein M1 and M2 are equal or unequal.