Circuit board and back drilling processing method

Abstract

The present application discloses a circuit board and a back-drilling processing method. The back-drilling processing method of the present application obtains a board to be back-drilled, including a target signal layer and at least two conductive reference layers; drills a through hole at a set position of the board to be back-drilled, and obtains the measured spacing between the two conductive reference layers based on the through hole; in response to the back-drilled hole to be back-drilled being of the first type, the target back-drilling depth is determined based on the measured spacing; the back-drilling drill bit is controlled to drill a back-drilling hole of the target back-drilling depth into the target signal layer; in response to the back-drilled hole to be back-drilled being of the second type, the target relative height of the back-drilling end point relative to the machine is determined based on the measured spacing; the back-drilling drill bit is controlled to drill a back-drilling hole of the target relative height into the target signal layer, thereby reducing the drilling error caused by uneven thickness at different positions of the circuit board, performing corresponding back-drilling methods for different types of holes to be back-drilled, improving the back-drilling accuracy of different types of holes to be drilled, and realizing high-precision control of the back-drilling stub length.

Description

Technical Field

[0001] The present application relates to the technical field of circuit boards, and in particular to a circuit board and a back drilling processing method. Background Art

[0002] With the continuous promotion of the information industry, the speed of digital signal transmission is getting faster and faster, the frequency is getting higher and higher, and it is becoming more and more critical to ensure the integrity of the signal. A section of useless copper in the metallized hole in the circuit board that is not used for signal transmission will increase the loss of signal transmission in the circuit board. And when the frequency of the circuit signal increases to a certain height, the excess copper plating in the useless copper hole is equivalent to an antenna, generating signal radiation that interferes with other surrounding signals, and in severe cases will destroy the integrity of signal transmission. Therefore, the back drilling processing method is usually used to drill out the excess copper plating as much as possible, thereby reducing its impact on the signal transmission of the metallized hole board.

[0003] At present, a preset back-drilling depth is usually set in advance, and then the metallized hole is back-drilled according to the preset back-drilling depth to remove the excess copper plating in the metallized hole. However, in actual production, due to various factors such as uneven board thickness and inner layer graphic design, the back-drilling accuracy of back-drilling to remove residual piles according to the preset back-drilling depth is insufficient, resulting in a large signal loss in the signal hole, which is difficult to meet the high-frequency and high-speed performance requirements of the product.

[0004] Therefore, how to improve back drilling accuracy is a major problem in circuit board processing. Summary of the invention

[0005] The present application provides a circuit board and a back drilling processing method to solve the problem of low back drilling accuracy in removing residual piles.

[0006] In order to solve the above technical problems, a technical solution adopted in the present application is: to provide a backdrilling processing method for a circuit board, comprising: obtaining a board to be backdrilled; wherein the board to be backdrilled comprises a target signal layer and at least two conductive reference layers; the target signal layer is a signal layer corresponding to a current backdrilling task; drilling a through hole at a set position of the board to be backdrilled, and obtaining a measured spacing between the two conductive reference layers of the board to be backdrilled based on the through hole; in response to the backdrilling hole to be backdrilled being of a first type, determining a target backdrilling depth based on the measured spacing; controlling a backdrilling drill bit to drill a backdrilling hole of the target backdrilling depth into the target signal layer, and the backdrilling does not drill through the target signal layer; in response to the backdrilling hole to be backdrilled being of a second type, determining a target relative height of a backdrilling end point relative to a machine platform based on the measured spacing; controlling the backdrilling drill bit to drill a backdrilling hole of the target relative height into the target signal layer, and the backdrilling does not drill through the target signal layer.

[0007] Optionally, the backdrilling processing method also includes: obtaining a preset backdrilling depth of the backdrilled hole on the board to be backdrilled; in response to the preset backdrilling depth being greater than or equal to a signal detection safety value, determining that the backdrilled hole is a first type; in response to the preset backdrilling depth being less than the signal detection safety value, determining that the backdrilled hole is a second type.

[0008] Optionally, the board to be back-drilled includes a first conductive reference layer, a second conductive reference layer and a third conductive reference layer, wherein the first conductive reference layer is a first surface conductive layer on a side of the board to be back-drilled, the second conductive reference layer is between the first surface conductive layer and the target signal layer, and the third conductive reference layer is a second surface conductive layer of the board to be back-drilled; the step of drilling a through hole at a set position of the board to be back-drilled and obtaining the measured spacing between the two conductive reference layers of the board to be back-drilled based on the through hole comprises: drilling a through hole from the second surface conductive layer at the set position of the board to be back-drilled, obtaining the measured spacing between the second surface conductive layer and the second conductive reference layer spacing; in response to the back-drilled hole to be back-drilled being of the second type, based on the measured spacing, determining the target relative height of the back-drilling endpoint relative to the machine; controlling the back-drill drill bit to drill the back-drilled hole to the target signal layer to the target relative height, and the back-drilling does not drill through the target signal layer, comprising: in response to the back-drilled hole to be back-drilled being of the second type, based on the measured spacing between the second surface conductive layer and the second conductive reference layer, determining the target relative height of the back-drilling endpoint relative to the machine; controlling the back-drill drill bit to drill from the first surface conductive layer side of the board to be back-drilled, back-drilling to the target signal layer, drilling to the target relative height, obtaining the back-drilled hole, and back-drilling does not drill through the target signal layer.

[0009] Optionally, in response to the back-drilled hole to be back-drilled being of the second type, based on the measured spacing between the second surface conductive layer and the second conductive reference layer, a target relative height of the back-drilling endpoint relative to the machine platform is determined, including: in response to the back-drilled hole to be back-drilled being of the second type, based on the measured spacing between the second surface conductive layer and the second conductive reference layer and a preset step-by-step depth control from the second conductive reference layer to the target signal layer, the target relative height of the back-drilling endpoint is determined relative to the machine platform.

[0010] Optionally, a pad is provided on one side of the second surface conductive layer of the board to be back-drilled; in response to the back-drilled hole to be back-drilled being of the second type, a target relative height of the back-drilling end point relative to the machine is determined based on the measured spacing between the second surface conductive layer and the second conductive reference layer, including: determining the target relative height of the back-drilling end point relative to the machine based on the measured spacing between the second surface conductive layer and the second conductive reference layer, a preset step-by-step depth control from the second conductive reference layer to the target signal layer, and the height of the pad relative to the machine.

[0011] Optionally, the board to be back-drilled includes a first conductive reference layer and a second conductive reference layer, wherein the first conductive reference layer is a first surface conductive layer on a side of the board to be back-drilled for back-drilling, and the second conductive reference layer is between the first surface conductive layer and the target signal layer; the step of drilling a through hole at a set position of the board to be back-drilled and obtaining the measured spacing between the two conductive reference layers of the board to be back-drilled based on the through hole comprises: drilling a through hole at a set position of the board to be back-drilled and obtaining the measured spacing between the first surface conductive layer and the second conductive reference layer of the board to be back-drilled based on the through hole. ; In response to the back-drilled hole to be back-drilled being of the first type, based on the measured spacing, determining a target back-drill depth; controlling the back-drill drill bit to drill a back-drill hole of the target back-drill depth toward the target signal layer without back-drilling through the target signal layer, the steps include: in response to the back-drilled hole to be back-drilled being of the first type, determining a target back-drill depth based on the measured spacing between the first surface conductive layer and the second conductive reference layer of the board to be back-drilled; controlling the back-drill drill bit to drill a back-drill hole of the target back-drill depth from the first surface conductive layer toward the target signal layer without back-drilling through the target signal layer.

[0012] Optionally, in response to the back-drilled hole to be back-drilled being of the first type, the step of determining a target back-drilling depth based on the actually measured spacing between the first surface conductive layer and the second conductive reference layer of the board to be back-drilled comprises: in response to the back-drilled hole to be back-drilled being of the first type, determining the target back-drilling depth based on the actually measured spacing between the first surface conductive layer and the second conductive reference layer and a preset stepped depth control from the second conductive reference layer to the target signal layer.

[0013] Optionally, the board to be back-drilled further includes a second surface conductive layer; the step of drilling a through hole at a set position of the board to be back-drilled and obtaining the measured spacing between the two conductive reference layers of the board to be back-drilled based on the through hole comprises: drilling a through hole at a set position of the board to be back-drilled and obtaining the measured spacing between the first surface conductive layer and the second conductive reference layer of the board to be back-drilled and the measured spacing between the first surface conductive layer and the second surface conductive layer of the board to be back-drilled based on the through hole; the step of determining a target back-drilling depth based on the measured spacing between the first surface conductive layer and the second surface conductive layer of the board to be back-drilled in response to the back-drilling hole to be back-drilled being of the first type comprises: obtaining a board thickness ratio value based on the measured spacing between the first surface conductive layer and the second surface conductive layer and a theoretical board thickness of the board to be back-drilled; in response to the back-drilling hole to be back-drilled being of the first type, determining the target back-drilling depth by the product of a preset step-controlled depth from the second conductive reference layer to the target signal layer and the board thickness ratio value and the sum of the measured spacing between the first surface conductive layer and the second conductive reference layer.

[0014] Optionally, the board to be back-drilled further includes a third conductive reference layer and a second surface conductive layer; wherein the third conductive reference layer is between the second surface conductive layer and the target signal layer; the step of drilling a through hole at a set position of the board to be back-drilled and obtaining the measured spacing between the two conductive reference layers of the board to be back-drilled based on the through hole comprises: drilling a through hole at a set position of the board to be back-drilled, and obtaining the measured spacing between the first surface conductive layer and the second conductive reference layer, the measured spacing between the second conductive reference layer and the third conductive reference layer, and the measured spacing between the second surface conductive layer and the third conductive reference layer based on the through hole; in response to the back-drilled hole to be back-drilled being of the first type, obtaining the measured spacing between the first surface conductive layer and the second conductive reference layer, the measured spacing between the second conductive reference layer and the third conductive reference layer, and the measured spacing between the second surface conductive layer and the third conductive reference layer based on the measured spacing between the first surface conductive layer and the second conductive reference layer, the measured spacing between the second conductive reference layer and the third conductive reference layer, and the measured spacing between the second surface conductive layer and the third conductive reference layer. The step of controlling the depth of the backdrill bit from the second conductive reference layer to the target signal layer to determine the target backdrill depth comprises: in response to the backdrill hole to be backdrilled being of the first type, obtaining an inter-layer ratio value based on the measured spacing and theoretical spacing between the second conductive reference layer and the third conductive reference layer; determining a first target backdrill depth by multiplying the product of the preset step-by-step depth control from the second conductive reference layer to the target signal layer and the inter-layer ratio value, and the sum of the measured spacing between the first surface conductive layer and the second conductive reference layer; the step of controlling the backdrill bit to drill a backdrill hole of the target backdrill depth toward the target signal layer without drilling through the target signal layer comprises: controlling the backdrill bit to drill a backdrill hole of the first target backdrill depth from the first surface conductive layer to the target signal layer, without drilling through the target signal layer.

[0015] Optionally, in response to the back-drilled hole to be back-drilled being of the first type, the step of determining the target back-drilling depth based on the measured spacing between the first surface conductive layer and the second conductive reference layer and the preset step-controlled depth from the second conductive reference layer to the target signal layer also includes: determining the second target back-drilling depth by multiplying the product of the preset step-controlled depth from the third conductive reference layer to the target signal layer and the inter-layer ratio value, and the sum of the measured spacing between the second surface conductive layer and the third conductive reference layer; the step of controlling the back-drilling drill bit to drill a back-drilling hole of the target back-drilling depth toward the target signal layer without back-drilling through the target signal layer includes: controlling the back-drilling drill bit to drill a back-drilling hole of the second target back-drilling depth from the second surface conductive layer to the target signal layer, without back-drilling through the target signal layer.

[0016] Optionally, the signal detection safety value is greater than or equal to 0.5 mm.

[0017] In order to solve the above technical problems, another technical solution adopted in the present application is: to provide a circuit board, which is manufactured by any of the back drilling processing methods described above.

[0018] The beneficial effects of the present application are as follows: Different from the prior art, the present application provides a backdrilling processing method for a circuit board, the processing method comprises obtaining a board to be backdrilled; wherein the board to be backdrilled comprises a target signal layer and at least two conductive reference layers; the target signal layer is a signal layer corresponding to a current backdrilling task; drilling a through hole at a set position of the board to be backdrilled, and obtaining a measured spacing between two conductive reference layers of the board to be backdrilled based on the through hole; in response to the backdrilling hole to be backdrilled being of the first type, determining a target backdrilling depth based on the measured spacing; controlling a backdrilling drill bit to drill a backdrilling hole of the target backdrilling depth into the target signal layer, and the backdrilling does not drill through the target signal layer; in response to the backdrilling hole to be backdrilled being of the second type, determining a target relative height of a backdrilling end point relative to a machine platform based on the measured spacing; controlling the backdrilling drill bit to drill a backdrilling hole of the target relative height into the target signal layer, and the backdrilling does not drill through the target signal layer. By obtaining the measured spacing between two conductive reference layers corresponding to the holes to be back-drilled when drilling a through hole, the target back-drilling depth or target relative height of different types of holes to be back-drilled is determined based on the measured spacing, thereby improving the accuracy of the target back-drilling depth or target relative height. Back-drilling is performed based on the target back-drilling depth or target relative height, thereby reducing the drilling error caused by uneven thickness at different positions of the circuit board, thereby improving the back-drilling accuracy of the circuit board. Corresponding back-drilling methods are performed for different types of holes to be back-drilled, thereby improving the back-drilling accuracy of different types of holes to be drilled, thereby achieving high-precision control of the back-drilling stub length Stub. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments and the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 It is a schematic flow chart of a first embodiment of a back drilling processing method for a circuit board provided by the present application;

[0021] Figure 2 It is a flow chart of a second embodiment of the back drilling processing method of a circuit board provided by the present application;

[0022] Figure 3 It is a structural schematic diagram of the first embodiment of the circuit board provided by the present application;

[0023] Figure 4 It is a flow chart of a second embodiment of the back drilling processing method of a circuit board provided by the present application;

[0024] Figure 5 is a structural schematic diagram of a second embodiment of a circuit board provided by the present application;

[0025] Figure 6 It is a flow chart of a third embodiment of the back drilling processing method of a circuit board provided by the present application;

[0026] Figure 7 It is a structural schematic diagram of the third embodiment of the circuit board provided in this application. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0028] The terms "first", "second", "third" in this application are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first", "second", "third" can expressly or implicitly include at least one of the features. In the description of this application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the embodiments of this application, all directional indications (such as up, down, left, right, front, back...) are only used to explain the relative position relationship, movement, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the steps or units listed, but optionally also includes steps or units that are not listed, or optionally also includes other steps or units inherent to these processes, methods, products or devices.

[0029] Reference to "embodiment" herein means that a particular feature, structure or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments in the absence of conflict. The following is a detailed description of each through specific embodiments.

[0030] The circuit board in the present application includes a printed circuit board, a PCB board, an FPC circuit board, etc., which can be a multilayer board. When the circuit board is a multilayer board, since the thickness of each layer of the multilayer board may be uneven, and in the process of making the multilayer board, the inner layer graphic design and processing and the lamination of the multilayer board will cause the thickness of the circuit board to be uneven, and will also cause the surface conductive layer used for the back drilling side to be unevenly spaced from the target signal layer corresponding to the current back drilling task. In this case, a conventional back drilling operation is performed according to a preset depth, which may cause the back drilling residual pile length Stub of the back drilling hole to be too long, or too short, or even the target signal layer may be drilled through, resulting in poor back drilling accuracy, large signal loss of the signal hole, and may even not be able to function normally as a signal hole. Based on this, the present application provides a circuit board and a back drilling processing method, for different back drilling holes on the circuit board, and its back drilling depth, etc., determine the corresponding target back drilling depth or target relative height, and perform back drilling based on the target back drilling depth or target relative height to improve the back drilling accuracy of back drilling to remove residual piles.

[0031] See also Figure 1 , Figure 1 This is a flow chart of a first embodiment of a back drilling method for a circuit board provided by the present application, which specifically includes:

[0032] S101: Acquire a board to be back-drilled; wherein the board to be back-drilled includes a target signal layer and at least two conductive reference layers; the target signal layer is a signal layer corresponding to the current back-drilling task.

[0033] The conductive reference layer in this embodiment may be additionally provided, or an existing metal conductive layer in the circuit board may be used, such as a surface conductive layer of the circuit board, a ground layer in the circuit board, a power layer or other signal layer.

[0034] It is understandable that a circuit board may have multiple signal layers, and this target signal layer is the signal layer corresponding to the current backdrilling task. Similarly, at least two conductive reference layers also correspond to the current backdrilling task, not to the circuit board to be backdrilled. Or it can be said that for a board to be backdrilled, the conductive reference layer in this step is not uniquely fixed, and the conductive reference layer in this step is relative to the backdrilling holes of the current backdrilling task. For the backdrilling holes of different backdrilling tasks, at least two conductive reference layers can be different conductive layers, and of course they can also be the same conductive layer.

[0035] In addition, there can be multiple signal layers on the circuit board, corresponding to multiple different back drill holes. The different back drill holes can be different types of back drill holes, such as single-sided back drill holes or double-sided back drill holes, or shallow back drill holes or deep back drill holes based on the preset back drill depth.

[0036] S102: drilling a through hole at a set position of the board to be back-drilled, and obtaining a measured spacing between two conductive reference layers of the board to be back-drilled based on the through hole.

[0037] In this step, a through hole is drilled at a set position corresponding to the hole to be back-drilled on the board to be back-drilled, and the measured spacing between two conductive reference layers of the board to be back-drilled is obtained based on the through hole. The measured spacing can be the measured spacing obtained when drilling the through hole, or it can be the measured spacing obtained based on relevant signals or data obtained when drilling the through hole.

[0038] Furthermore, a board to be back-drilled may include multiple holes to be back-drilled, and a through hole needs to be drilled at the set position of each hole to be back-drilled, and the measured spacing between the two conductive reference layers corresponding to each hole to be back-drilled is obtained based on the through hole. Since the at least two conductive reference layers corresponding to each hole to be back-drilled may be the same or different. Due to the different positions of the holes to be back-drilled on the board to be back-drilled and the different board thickness and dielectric thickness caused by operations such as conductive graphics during processing, even if the at least two conductive reference layers corresponding to different holes to be back-drilled are the same, the measured spacing between the two conductive reference layers may still be different. For each hole to be back-drilled, the measured spacing between the two conductive reference layers is obtained, which can reduce or even eliminate the influence of the board thickness and dielectric thickness.

[0039] Generally speaking, at the position where back drilling is required on the circuit board, a through hole needs to be drilled first, and then the through hole is metallized to obtain a metallized hole, and a back drilling operation is performed at the position of the metallized hole to obtain a back-drilled hole. After corresponding through holes are drilled at the set positions of all the holes to be back-drilled on the back-drilled board, and the measured spacing between two conductive reference layers corresponding to the holes to be back-drilled is obtained based on the through holes, the through holes are metallized to obtain metallized holes, and the operation of S103 is performed at the position of the metallized holes.

[0040] S103: In response to the back-drilled hole to be back-drilled being of the first type, a target back-drilling depth is determined based on the measured spacing; the back-drilling drill bit is controlled to drill a back-drilling hole of the target back-drilling depth into the target signal layer, and the back-drilling does not drill through the target signal layer; in response to the back-drilled hole to be back-drilled being of the second type, a target relative height of the back-drilling end point relative to the machine is determined based on the measured spacing; the back-drilling drill bit is controlled to drill a back-drilling hole of the target relative height into the target signal layer, and the back-drilling does not drill through the target signal layer.

[0041] In this step, depth control or relative height control is required according to different types of back-drilled holes, so as to perform depth-controlled back-drilling to obtain back-drilled holes, and control the length of the metal back-drilled stub of the back-drilled holes within a smaller range without drilling through the target signal layer, resulting in failure to realize the signal layer function.

[0042] In this embodiment, by obtaining the measured spacing between two conductive reference layers corresponding to the hole to be back-drilled when drilling a through hole, the target back-drilling depth or target relative height of different types of holes to be back-drilled is determined based on the measured spacing, thereby improving the accuracy of the target back-drilling depth or target relative height, and back-drilling is performed based on the target back-drilling depth or target relative height, thereby reducing the drilling error caused by uneven thickness at different positions of the circuit board, thereby improving the back-drilling accuracy of the circuit board, and performing corresponding back-drilling methods for different types of holes to be back-drilled, thereby improving the back-drilling accuracy of different types of holes to be drilled, and achieving high-precision control of the back-drilling stub length Stub.

[0043] Specifically, whether the back-drilled hole to be back-drilled is of the first type or the second type can be determined based on the preset back-drilling depth of the back-drilled hole, or can be determined based on the distance between the target signal layer and the surface of the side of the circuit board to be back-drilled. In the board to be back-drilled, the theoretical spacing between the target signal layer and the surface of the side to be back-drilled is known, and can be calculated based on the thickness of each layer of the sub-board and the dielectric layer in the board to be back-drilled. In order to prevent the back-drilling from drilling through the target signal layer, the preset back-drilling depth needs to be less than the theoretical spacing between the target signal layer and the surface of the side to be back-drilled, and the difference between the two corresponds to the theoretical back-drilling stub length Stub.

[0044] In a specific embodiment, the backdrilling method further includes obtaining a preset backdrilling depth of a backdrilled hole on a board to be backdrilled. In response to the preset backdrilling depth being greater than or equal to a signal detection safety value, the backdrilled hole is determined to be of the first type. In response to the preset backdrilling depth being less than the signal detection safety value, the backdrilled hole is determined to be of the second type.

[0045] Among them, the signal detection safety value is related to the drilling equipment. When drilling with the drilling equipment, if the distance between the two layers of the signal to be obtained is less than the signal detection safety value, the drilling equipment can only obtain the signal corresponding to the layer that the drill bit or drill needle contacts first, and the signal of the layer that contacts later is prone to abnormality, or is affected or interfered by the signal of the previous layer, resulting in the inability to obtain the actual measured distance between the two layers. In this embodiment, the signal detection safety value is greater than or equal to 0.5 mm. Specifically, according to different circuit board drilling equipment, the signal detection safety value can be 0.8mm, 1.0mm, 1.2mm, 1.4mm, etc.

[0046] In response to the preset backdrilling depth being greater than or equal to the signal detection safety value, the backdrilling hole is determined to be the first type, which can also be called a deep backdrilling hole. In response to the preset backdrilling depth being less than the signal detection safety value, the backdrilling hole is determined to be the second type, which can be called a shallow backdrilling hole.

[0047] In response to the preset back drilling depth being less than the signal detection safety value, when the back drilling hole is determined to be the second type, the back drilling processing method can be specifically referred to in Figure 2 and Figure 3 , Figure 2 is a flow chart of a second embodiment of a back drilling method for a circuit board provided by the present application, Figure 3 It is a structural schematic diagram of the first embodiment of the circuit board provided by this application.

[0048] S201: Acquire a board to be backdrilled; wherein the board to be backdrilled includes a target signal layer 31 and a first conductive reference layer, a second conductive reference layer and a third conductive reference layer; the target signal layer 31 is a signal layer corresponding to a current backdrilling task, the first conductive reference layer is a first surface conductive layer 32 on a drilling side of the board to be backdrilled, the second conductive reference layer 33 is between the first surface conductive layer 32 and the target signal layer 31, and the third conductive reference layer is a second surface conductive layer 34 of the board to be backdrilled.

[0049] For this step, please refer to the relevant description of S101, which will not be repeated here.

[0050] S202 : drilling a through hole 35 through the second surface conductive layer 34 at a set position of the board to be back-drilled, and obtaining a measured distance Z1 between the second surface conductive layer 34 and the second conductive reference layer 33 .

[0051] For this step, please refer to the relevant description of S102 and will not be repeated here.

[0052] S203 : In response to the back-drilled hole to be back-drilled being of the second type, determining a target relative height of the back-drilling end point relative to the machine platform based on the measured distance Z1 between the second surface conductive layer 34 and the second conductive reference layer 33 .

[0053] Specifically, based on the measured spacing Z1 between the second surface conductive layer 34 and the second conductive reference layer 33 and the preset step-controlled depth h1 from the second conductive reference layer 33 to the target signal layer 31 , the target relative height of the backdrilling end point relative to the machine is determined.

[0054] Furthermore, the back-drilled board can also be placed on a pad for drilling. At this time, the pad is arranged on one side of the second surface conductive layer 34 of the back-drilled board. The height of the pad relative to the machine can be obtained by the drilling equipment. Based on the measured spacing Z1 between the second surface conductive layer 34 and the second conductive reference layer 33, the preset step-controlled depth h1 from the second conductive reference layer 33 to the target signal layer 31, and the pad relative to the machine height, the target relative height of the back-drilling end point relative to the machine is determined.

[0055] Specifically, the target relative height of the back drilling end point relative to the machine is obtained by subtracting the preset step-controlled depth h1 from the second conductive reference layer 33 to the target signal layer 31 from the sum of the height of the pad relative to the machine, the measured spacing Z1 between the second surface conductive layer 34 and the second conductive reference layer 33, and the compensation value. The compensation value includes the relative height difference between the through hole and the back drilling drill tip and the machine.

[0056] In this embodiment, the relative height relative to the machine platform may be a vertical coordinate relative to the machine platform coordinate system.

[0057] S204: Control the backdrill drill bit to drill from the first surface conductive layer 32 of the backdrilled board to the target signal layer 31 to the target relative height to obtain a backdrill hole 36 without drilling through the target signal layer.

[0058] Prior to this step, the through hole 35 is metallized to obtain a metallized through hole. In this step, based on the opening of the metallized through hole, the back drilling bit is controlled to drill from the first surface conductive layer 32 of the board to be back drilled, and the back drilling is performed until the target relative height is reached, which is the end point of the back drilling.

[0059] In this embodiment, the second conductive reference layer 33 is arranged between the first surface conductive layer 32 on the back drilling side and the target signal layer 31. The distance between the second conductive reference layer 33 and the first surface conductive layer 32 on the back drilling side and the distance between the second conductive reference layer 33 and the target signal layer 31 can be set accordingly according to specific circumstances. For example, the second conductive reference layer 33 can be arranged at a position closer to the target signal layer 31, that is, the distance between the second conductive reference layer 33 and the first surface conductive layer 32 on the back drilling side is greater than the distance between the first surface conductive layer 32 and the target signal layer 31. In this case, since the through hole is actually being drilled, the measured spacing Z1 between the second surface conductive layer 34 and the second conductive reference layer 33 is obtained through the through hole, which is more accurate. The smaller the preset step-by-step control depth h1 from the second conductive reference layer 33 to the target signal layer 31, the less the back drilling is affected by the plate thickness error, and the more accurate the depth control of the back drilling is.

[0060] In this embodiment, the backdrilling hole is of the second type, that is, the preset backdrilling depth is less than the signal detection safety value. The sum of the preset backdrilling depth and the preset step-controlled depth h1 from the second conductive reference layer 33 to the target signal layer 31 is the distance between the first surface conductive layer 32 and the target signal layer 31 on the backdrilling side. Among them, the preset step-controlled depth h1 is generally very small, so the distance between the first surface conductive layer 32 and the second conductive reference layer 33 on the backdrilling side is also less than the signal detection safety value. Therefore, whether drilling from the first surface conductive layer 32 side or drilling from the second surface conductive layer 34 side to drill a through hole, the measured distance between the first surface conductive layer 32 and the second conductive reference layer 33 cannot be obtained. Therefore, it is impossible to perform backdrilling by using the measured distance between the first surface conductive layer 32 and the second conductive reference layer 33 and the preset step-controlled depth h1 from the second conductive reference layer 33 to the target signal layer 31 as the depth control depth. Instead, in the present embodiment, a through hole is drilled from one side of the second surface conductive layer 34 to obtain the measured distance between the second surface conductive layer 34 and the second conductive reference layer 33, and then depth-controlled back-drilling is performed based on the target relative height of the back-drilling end point relative to the machine, so as to achieve more accurate back-drilling depth control, so that the back-drilling residual stub length Stub is smaller without drilling through the target signal layer.

[0061] In other embodiments, the back-drilled board not only has the back-drilled holes of this embodiment, but also has the back-drilled holes in the opposite direction to the back-drilled holes of this embodiment. The back-drilled holes in the opposite direction can also be drilled in the relevant steps of the back-drilling method of this embodiment, by drilling through holes in the opposite direction of the back-drilling drilling direction, and obtaining the measured spacing between the surface conductive layer on the drilling side of the through-hole and the middle conductive reference layer, wherein the middle conductive reference layer is between the surface conductive layer on the drilling side of the back-drilling drilling and the target signal layer. Based on the measured spacing, the target relative height of the back-drilling end point relative to the machine is obtained, and depth-controlled back-drilling is performed according to the target relative height, thereby also achieving more accurate depth-controlled back-drilling.

[0062] In response to the preset back drilling depth being greater than or equal to the signal detection safety value, when the back drilling hole is determined to be the first type, the back drilling processing method can be specifically referred to in Figure 4 and Figure 5 , Figure 4 is a flow chart of a second embodiment of a back drilling method for a circuit board provided by the present application, Figure 5 It is a structural schematic diagram of the second embodiment of the circuit board provided in this application.

[0063] S401: Acquire the board to be backdrilled; wherein the board to be backdrilled includes a target signal layer 51 and a first conductive reference layer and a second conductive reference layer 53; the target signal layer 51 is a signal layer corresponding to the current backdrilling task, the first conductive reference layer is a first surface conductive layer 52 on the drilling side of the board to be backdrilled, and the second conductive reference layer 53 is between the first surface conductive layer 52 and the target signal layer 51.

[0064] For this step, please refer to the relevant description of S101, which will not be repeated here.

[0065] S402: drilling a through hole at a set position of the board to be back-drilled, and obtaining a measured distance Z2 between the first surface conductive layer 52 and the second conductive reference layer 53 of the board to be back-drilled based on the through hole.

[0066] S403 : In response to the back-drilled hole being of the first type, determining a target back-drilling depth H based on a measured distance Z2 between the first surface conductive layer 52 and the second conductive reference layer 53 of the board to be back-drilled.

[0067] Specifically, in response to the back-drilled hole to be back-drilled being of the first type, a target back-drilling depth H is determined based on the measured spacing Z2 between the first surface conductive layer 52 and the second conductive reference layer 53 of the board to be back-drilled and the preset step-controlled depth h2 from the second conductive reference layer 53 to the target signal layer 51. Further, the target back-drilling depth H is the sum of the measured spacing Z2 and the preset step-controlled depth h2, that is, the formula is satisfied: target back-drilling depth H = measured spacing Z2 + preset step-controlled depth h2.

[0068] In a specific embodiment, the board to be back-drilled further includes a second surface conductive layer 54. In S402, the measured spacing between the first surface conductive layer 52 and the second surface conductive layer 54 is obtained based on the through hole. And based on the measured spacing between the first surface conductive layer 52 and the second surface conductive layer 54 and the theoretical board thickness of the board to be back-drilled, the board thickness ratio value x is obtained. Specifically, the board thickness ratio value x is the ratio of the measured spacing between the first surface conductive layer 52 and the second surface conductive layer 54 to the theoretical board thickness of the board to be back-drilled. In this S403, based on the measured spacing Z2 between the first surface conductive layer 52 and the second conductive reference layer 53 of the board to be back-drilled, the preset step-controlled depth h2 from the second conductive reference layer 53 to the target signal layer 51, and the board thickness ratio value x, the target back-drilling depth H is determined. Specifically, the target backdrilling depth H is the sum of a preset step-controlled depth h2 from the second conductive reference layer 53 to the target signal layer 51 and a board thickness ratio x, and a measured spacing Z2 between the first surface conductive layer 52 and the second conductive reference layer 53 .

[0069] In this specific embodiment, the plate thickness ratio value x is used to reduce or even eliminate the error between the dielectric thickness and the plate thickness of the preset step-by-step depth control h2 part, thereby making the target back drilling depth H more accurate and achieving more precise depth-controlled back drilling.

[0070] S404: Control the back drilling drill bit to drill a back drilling hole of a target back drilling depth from the first surface conductive layer 52 to the target signal layer 51 , and the back drilling does not penetrate the target signal layer.

[0071] In this embodiment, the back-drilled hole is of the first type, that is, the preset back-drilling depth is greater than or equal to the signal detection safety value. And the theoretical spacing between the first surface conductive layer 52 and the second conductive reference layer 53 needs to be greater than the signal detection safety value, otherwise according to the back-drilling method of the previous embodiment, the back-drilled hole can also be classified as the second type.

[0072] In this embodiment, based on the measured spacing Z2 between the first surface conductive layer 52 and the second conductive reference layer 53 obtained through the through hole, and together with the preset step-controlled depth h2 from the second conductive reference layer 53 to the target signal layer 51, the target back-drilling depth H is determined, thereby improving the accuracy and precision of the target back-drilling depth H, reducing the drilling error caused by the plate thickness, and improving the back-drilling accuracy to achieve the back-drilling accuracy of this back-drilling task, so that the length of the back-drilling residual pile can be better controlled within a suitable range without drilling through the target signal layer. Furthermore, by obtaining the plate thickness ratio value x, the error between the dielectric thickness and the plate thickness of the preset step-controlled depth h2 is reduced or even eliminated, thereby making the target back-drilling depth H more accurate, and achieving more precise depth-controlled back-drilling.

[0073] See also Figure 6 and Figure 7 , Figure 6 is a flow chart of a third embodiment of a back drilling method for a circuit board provided in the present application. Figure 7 Schematic diagram of the structure of the third embodiment of the circuit board provided by the present application. The back drilling method of this embodiment includes:

[0074] S601: Acquire the board to be backdrilled; wherein the board to be backdrilled includes a target signal layer 71, a first conductive reference layer 72, a second conductive reference layer 73, a second surface conductive layer 74, and a third conductive reference layer 75; the target signal layer 71 is a signal layer corresponding to the current backdrilling task, the first conductive reference layer 72 is the first surface conductive layer 72 on the drilling side of the board to be backdrilled, the second conductive reference layer 73 is between the first surface conductive layer 72 and the target signal layer 71, and the third conductive reference layer 75 is between the second surface conductive layer 74 and the target signal layer 71.

[0075] S602: Drill a through hole at a set position of the board to be back-drilled, and based on the through hole, obtain the measured spacing Z3 between the first surface conductive layer 72 and the second conductive reference layer 73, the measured spacing Z4 between the second conductive reference layer 73 and the third conductive reference layer 75, and the measured spacing Z5 between the second surface conductive layer 74 and the third conductive reference layer 75.

[0076] S603 : In response to the back-drilled hole to be back-drilled being of the first type, obtaining an inter-layer ratio value y based on a measured spacing Z4 and a theoretical spacing between the second conductive reference layer 73 and the third conductive reference layer 75 .

[0077] Specifically, the interlayer ratio value y is obtained by calculating the ratio of the measured spacing Z4 between the second conductive reference layer 73 and the third conductive reference layer 75 to the theoretical spacing between the second conductive reference layer 73 and the third conductive reference layer 75. The theoretical spacing between the second conductive reference layer 73 and the third conductive reference layer 75 can be determined according to the theoretical plate thickness and the dielectric layer thickness.

[0078] S604 : Determine a first target backdrilling depth H1 by multiplying a preset step-controlled depth h3 from the second conductive reference layer 73 to the target signal layer 71 by the interlayer ratio value and the measured distance Z3 between the first surface conductive layer 72 and the second conductive reference layer 73 .

[0079] Furthermore, the first target backdrilling depth H1 can be determined by the product of the preset step-controlled depth h3 from the second conductive reference layer 73 to the target signal layer 71 and the inter-layer ratio value, the measured spacing Z3 between the first surface conductive layer 72 and the second conductive reference layer 73, and the sum of the compensation value. Specifically, the compensation value can include the electroplated copper thickness, the relative height difference between the through hole and the backdrilling drill tip, etc.

[0080] S605: Control the back drilling drill bit to drill a back drilling hole with a first target back drilling depth H1 from the first surface conductive layer 72 to the target signal layer 71, and the back drilling does not penetrate the target signal layer.

[0081] Furthermore, the back drilling method of this embodiment also includes: determining the second target back drilling depth H2 by multiplying the preset step-controlled depth h4 from the third conductive reference layer 75 to the target signal layer 71 by the interlayer ratio value y, and the sum of the measured spacing Z5 between the second surface conductive layer 74 and the third conductive reference layer 75. Controlling the back drilling drill to drill a back drilling hole of the second target back drilling depth H2 from the second surface conductive layer 74 to the target signal layer 71, and the back drilling does not penetrate the target signal layer. The interlayer ratio value y here is the interlayer ratio value y obtained in S603.

[0082] By backdrilling from the first surface conductive layer 72 and the second surface conductive layer 74 to the target signal layer 71 , a double-sided back-drilled hole is obtained.

[0083] In this embodiment, the back-drilling holes on both sides are of the first type, that is, the preset back-drilling depth of the back-drilling on both sides is greater than or equal to the signal detection safety value, and the theoretical spacing between the first surface conductive layer 72 and the second conductive reference layer 73 needs to be greater than the signal detection safety value, and the theoretical spacing between the second surface conductive layer 74 and the third conductive reference layer 75 needs to be greater than the signal detection safety value. If the back-drilling on any side does not meet the requirements, the back-drilling on the corresponding side is performed according to the relevant back-drilling method of the second type.

[0084] The back drilling method of this embodiment is to respectively set the second surface conductive layer 74 and the third conductive reference layer 75 between the first surface conductive layer 72 of the back-drilled board and the target signal layer 71, and between the second surface conductive layer 74 and the target signal layer 71, and drill through holes to obtain the measured spacing Z3 between the first surface conductive layer 72 and the second conductive reference layer 73, the measured spacing Z4 between the second conductive reference layer 73 and the third conductive reference layer 75, and the measured spacing Z5 between the second surface conductive layer 74 and the third conductive reference layer 75 based on the through holes, and obtain the inter-layer ratio value y from the ratio of the measured spacing Z4 between the second conductive reference layer 73 and the third conductive reference layer 75 to the theoretical spacing, and respectively obtain the first target back drilling depth H1 and the second target back drilling depth H2 based on the above data more accurately. Then, back drilling is started from the first surface conductive layer 72 and the second surface conductive layer 74 to the target signal layer 71, and depth-controlled back drilling is performed according to the first target back drilling depth H1 and the second target back drilling depth H2, respectively, to obtain a double-sided back drilling hole. The measured spacing Z3 and the measured spacing Z5 obtained through actual measurement, as well as the interlayer ratio value y, reduce or even eliminate the errors in the dielectric thickness and the plate thickness of the preset step-controlled depth h3 and the preset step-controlled depth h4, thereby making the target back-drilling depth H more accurate and achieving more precise depth-controlled back-drilling.

[0085] In the above embodiment, the spacing between the target signal layer and the conductive reference layer of its inner layer can be called the back drilling safety distance W, and its value needs to be greater than or equal to the sum of the back drilling stub length Stub and the voltage safety design value, for example, greater than or equal to 0.45mm. Among them, the voltage design safety value, which can also be called the voltage safety distance, is related to the voltage, temperature, humidity and other conditions when the circuit board product is used. The setting of the voltage safety design value is to prevent the circuit board product from having a too short distance between the target signal layer and the conductive reference layer of the inner layer under specific voltage, temperature and humidity conditions, or the distance between the back drilling stub of the target signal layer and the conductive reference layer of the inner layer is too short, which is easy to cause voltage breakdown, and electrons migrate between the target signal layer and the conductive reference layer of the inner layer to form a channel, causing a short circuit. The voltage design safety value can be 0.1mm, 0.3mm, 0.5mm, etc., and can be set according to the actual circuit board product, and is not limited here.

[0086] For double-sided back drilling, the distances between the target signal layer and the inner conductive reference layers on both sides are the safe back drilling distance W2 and the safe back drilling distance W3, both of which need to meet the back drilling safety distance. And for double-sided back drilling, in order to obtain the measured distance between the two inner conductive reference layers, the distance between the two inner conductive reference layers needs to be greater than or equal to the signal detection safety value K, or in other words, double-sided back drilling needs to meet the back drilling safety distance W2 ≥ K / 2 and the back drilling safety distance W3 ≥ K / 2, where K is the signal detection safety value, and the sum of the back drilling safety distance W2 and the back drilling safety distance W3 is approximately the distance between the two inner conductive reference layers. Under the limited conditions, the smaller the distance between the target signal layer and the inner conductive reference layer and the safety distance W, the greater the control accuracy of the back drilling.

[0087] It can be understood that when the circuit board to be back-drilled includes the above-mentioned multiple types of holes to be back-drilled, corresponding back-drilling operations can be performed according to the corresponding back-drilling processing methods, so as to calculate the controlled depth or relative height according to each hole to be back-drilled and different types of holes to be back-drilled, so as to achieve precise back-drilling.

[0088] The present application also provides a circuit board, which is manufactured by the back drilling processing method provided by the present application. The back drilling processing method provided by the present application obtains the measured spacing between two conductive reference layers corresponding to the hole to be back drilled when drilling a through hole, determines the target back drilling depth or target relative height of different types of holes to be back drilled based on the measured spacing, improves the accuracy of the target back drilling depth or target relative height, performs back drilling based on the target back drilling depth or target relative height, reduces the drilling error caused by uneven thickness at different positions of the circuit board, improves the back drilling accuracy of the circuit board, performs corresponding back drilling methods for different types of holes to be back drilled, improves the back drilling accuracy of different types of holes to be drilled, realizes high-precision control of the back drilling stump length Stub, and simultaneously obtains a circuit board including a high-precision back drilling stump length Stub.

[0089] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A back drilling method for a circuit board, characterized in that: The back drilling method comprises: A board to be backdrilled is obtained; wherein the board to be backdrilled comprises a target signal layer, a first conductive reference layer, a second conductive reference layer, a third conductive reference layer and a second surface conductive layer, wherein the first conductive reference layer is the first surface conductive layer on the drilling side of the board to be backdrilled, the second conductive reference layer is between the first surface conductive layer and the target signal layer; the third conductive reference layer is between the second surface conductive layer and the target signal layer; the target signal layer is a signal layer corresponding to the current backdrilling task; Drilling a through hole at a set position of the board to be back-drilled, and obtaining the measured spacing between the two conductive reference layers of the board to be back-drilled based on the through hole; wherein, drilling a through hole at a set position of the board to be back-drilled, and obtaining the measured spacing between the first surface conductive layer and the second conductive reference layer, the measured spacing between the second conductive reference layer and the third conductive reference layer, and the measured spacing between the second surface conductive layer and the third conductive reference layer based on the through hole; In response to the back-drilled hole to be back-drilled being of the first type, a target back-drilling depth is determined based on the measured spacing; wherein an inter-layer ratio value is obtained based on the measured spacing and theoretical spacing between the second conductive reference layer and the third conductive reference layer; a first target back-drilling depth is determined by the product of a preset step-by-step controlled depth from the second conductive reference layer to the target signal layer and the inter-layer ratio value, and the sum of the measured spacing between the first surface conductive layer and the second conductive reference layer; Controlling a backdrill bit to drill a backdrill hole of the target backdrill depth toward the target signal layer without drilling through the target signal layer; in response to the backdrill hole to be backdrilled being of the second type, determining a target relative height of a backdrilling end point relative to a machine platform based on the measured spacing; controlling the backdrill bit to drill a backdrill hole of the target relative height toward the target signal layer without drilling through the target signal layer, wherein the backdrill bit is controlled to drill a backdrill hole of the first target backdrill depth from the first surface conductive layer toward the target signal layer without drilling through the target signal layer.

2. The back drilling method according to claim 1, characterized in that: The back drilling method further comprises: Obtaining a preset back-drilling depth of the back-drilled hole on the board to be back-drilled; In response to the preset back-drilling depth being greater than or equal to the signal detection safety value, determining that the back-drilled hole is of the first type; In response to the preset back-drilling depth being less than the signal detection safety value, determining that the back-drilling hole is a second type.

3. The back drilling method according to claim 2, characterized in that: The board to be back-drilled comprises a first conductive reference layer, a second conductive reference layer and a third conductive reference layer, wherein the first conductive reference layer is a first surface conductive layer on a side of the board to be back-drilled, the second conductive reference layer is between the first surface conductive layer and the target signal layer, and the third conductive reference layer is a second surface conductive layer of the board to be back-drilled; The step of drilling a through hole at a set position of the board to be back-drilled and obtaining a measured spacing between two conductive reference layers of the board to be back-drilled based on the through hole comprises: At a set position of the board to be back-drilled, drilling a through hole through the second surface conductive layer to obtain the measured distance between the second surface conductive layer and the second conductive reference layer; The step of determining, in response to the back-drilled hole to be back-drilled being of the second type, a target relative height of a back-drilling end point relative to a machine platform based on the measured spacing; and controlling a back-drilling drill bit to drill a back-drilled hole at the target relative height toward the target signal layer without back-drilling through the target signal layer comprises: In response to the back-drilled hole to be back-drilled being of the second type, determining a target relative height of a back-drilling endpoint relative to a platform based on the measured spacing between the second surface conductive layer and the second conductive reference layer; The backdrilling drill bit is controlled to drill from the first surface conductive layer side of the backdrilled board to the target signal layer, drill to the target relative height, obtain the backdrill hole, and the backdrilling does not penetrate the target signal layer.

4. The back drilling method according to claim 3, characterized in that: In response to the back-drilled hole to be back-drilled being of the second type, determining a target relative height of a back-drilling endpoint relative to a platform based on the measured spacing between the second surface conductive layer and the second conductive reference layer, comprises: In response to the back-drilled hole to be back-drilled being of the second type, a target relative height of a back-drilling end point relative to the machine is determined based on the measured spacing between the second surface conductive layer and the second conductive reference layer and a preset stepped depth control from the second conductive reference layer to the target signal layer.

5. The back drilling method according to claim 4, characterized in that: A pad is provided on one side of the second surface conductive layer of the board to be back-drilled; In response to the back-drilled hole to be back-drilled being of the second type, determining a target relative height of a back-drilling endpoint relative to a platform based on the measured spacing between the second surface conductive layer and the second conductive reference layer, comprises: Based on the measured spacing between the second surface conductive layer and the second conductive reference layer, the preset step-by-step depth control from the second conductive reference layer to the target signal layer, and the height of the pad relative to the machine, the target relative height of the back drilling end point relative to the machine is determined.

6. The back drilling method according to claim 2, characterized in that: The step of drilling a through hole at a set position of the board to be back-drilled and obtaining a measured spacing between two conductive reference layers of the board to be back-drilled based on the through hole comprises: Drilling a through hole at a set position of the board to be back-drilled, and obtaining a measured distance between the first surface conductive layer and the second conductive reference layer of the board to be back-drilled based on the through hole; The step of determining a target backdrilling depth based on the measured spacing in response to the backdrilling hole to be backdrilled being of the first type; and controlling the backdrill drill bit to drill a backdrilling hole of the target backdrilling depth into the target signal layer without drilling through the target signal layer comprises: In response to the backdrilled hole to be backdrilled being of the first type, determining a target backdrilling depth based on the measured spacing between the first surface conductive layer and the second conductive reference layer of the board to be backdrilled; The back drilling drill bit is controlled to drill a back drilling hole of the target back drilling depth from the first surface conductive layer to the target signal layer, and the back drilling does not penetrate the target signal layer.

7. The back drilling method according to claim 6, characterized in that: The step of determining a target backdrilling depth based on the measured spacing between the first surface conductive layer and the second conductive reference layer of the board to be backdrilled in response to the backdrilled hole being of the first type comprises: In response to the backdrilled hole being of the first type, the target backdrilling depth is determined based on the measured spacing between the first surface conductive layer and the second conductive reference layer and a preset stepped depth control from the second conductive reference layer to the target signal layer.

8. The back drilling method according to claim 7, characterized in that: The board to be back-drilled further comprises a second surface conductive layer; The step of drilling a through hole at a set position of the board to be back-drilled and obtaining a measured spacing between two conductive reference layers of the board to be back-drilled based on the through hole comprises: Drilling a through hole at a set position of the board to be back-drilled, and obtaining a measured distance between the first surface conductive layer and the second conductive reference layer, and a measured distance between the first surface conductive layer and the second surface conductive layer of the board to be back-drilled based on the through hole; The step of determining a target backdrilling depth based on the measured spacing between the first surface conductive layer and the second conductive reference layer of the board to be backdrilled in response to the backdrilled hole being of the first type comprises: Obtaining a board thickness ratio value based on the measured distance between the first surface conductive layer and the second surface conductive layer and the theoretical board thickness of the board to be back-drilled; In response to the back-drilled hole to be back-drilled being of the first type, the target back-drilling depth is determined by the product of a preset step-controlled depth from the second conductive reference layer to the target signal layer and a board thickness ratio value, and the sum of the measured spacing between the first surface conductive layer and the second conductive reference layer.

9. The back drilling method according to claim 1, characterized in that: The step of determining the target backdrilling depth based on the measured spacing between the first surface conductive layer and the second conductive reference layer and the preset step-by-step depth control from the second conductive reference layer to the target signal layer in response to the backdrilled hole to be backdrilled being of the first type, further includes: Determine a second target backdrilling depth by multiplying the preset step-by-step controlled depth from the third conductive reference layer to the target signal layer by the inter-layer ratio value and the sum of the measured distance between the second surface conductive layer and the third conductive reference layer; The step of controlling the back drilling drill bit to drill a back drilling hole of the target back drilling depth into the target signal layer without drilling through the target signal layer includes: The back drilling drill bit is controlled to drill a back drilling hole of the second target back drilling depth from the second surface conductive layer to the target signal layer, and the back drilling does not penetrate the target signal layer.

10. The back drilling method according to any one of claims 2 to 9, characterized in that: The signal detection safety value is greater than or equal to 0.5 mm.

11. A circuit board, characterized in that: It is manufactured by the back drilling method described in any one of claims 1-10.

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