A method for manufacturing high-precision back-drilling and short pile

Abstract

The application discloses a kind of to realize high-precision back drilling and the manufacturing method of short pile, by making back drilling machine and the detection hole between the back drilling needed to form conducting loop, so that the resistance value on the loop can be detected and obtained using the control system on back drilling machine, when drill bit is continuously drilled and drills the connection between the copper layer of board surface and hole wall, instantaneous resistance value will be twice or more than one time than before drilling, recorded as the reference zero point of back drilling, when continue to drill and drill the connection between wire and hole copper, instantaneous resistance value will also be twice or more than one time than before drilling, recorded as the end point of back drilling, and the back drilling depth from reference zero point to end point can be obtained, by calculating, the average of back drilling depth of all detection holes is obtained, and the actual back drilling depth of production board back drilling hole is back drilled in the form of back drilling depth average obtained plus compensation value, which can greatly reduce the influence of factors such as board thickness tolerance when back drilling production board, so as to realize high-precision back drilling and meet the demand of short pile as small as possible.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing technology, specifically to a method for achieving high-precision back drilling and short pile manufacturing. Background Technology

[0002] As the integration of electronic systems continues to increase, circuit boards are becoming more integrated and functional. Therefore, it is inevitable that the design density of PCBs will also increase. In addition, the application of high-speed interconnects is becoming more and more common, which will place higher and higher demands on the high-speed signals of products, such as 5G / 6G communication, supercomputing, high-performance computing, cloud computing, big data, etc.

[0003] The significant increase in the application of high-frequency and high-speed products has placed new demands on the integrity of high-speed digital signals. High-speed circuit transmission lines, operating at high frequencies and speeds, face extremely high requirements for signal integrity. The control and implementation of signal integrity are strongly correlated with the impedance and insertion loss of the transmission line. When the speed exceeds 25Gbps, the impact of insertion loss on signal integrity becomes increasingly significant. The length of the excess stub at the high-speed via directly affects the insertion loss; to achieve better high-speed signal integrity, the length of the stub needs to be kept as small as possible.

[0004] To reduce the number of short pegs, the existing technology uses a back-drilling process to remove a portion of the excess short pegs in the high-speed through holes. However, since there are tolerances in the thickness of the dielectric material between different layers on the board, the cumulative tolerance of the dielectric material thickness of multiple layers becomes quite large. Moreover, the thickness of different areas of large-size circuit boards varies considerably, generally exceeding 0.2mm due to different board thicknesses. This has a significant impact on the back-drilling accuracy of the entire board.

[0005] To improve back drilling accuracy, it is necessary to manually stack the plates by measuring their thickness in different zones and to confirm the thickness of the medium between each layer during back drilling. However, in actual production, it is difficult to perform plate thickness stacking well. Slicing is destructive, and plate thickness confirmation by slicing is limited to the first piece and is only a local slice. Therefore, the plate thickness cannot effectively distinguish the differences in plate thickness in different areas, and it cannot eliminate the influence of plate thickness tolerance on back drilling depth and back drilling short piles, thus failing to achieve high-precision back drilling. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, this invention provides a method for achieving high-precision back drilling and the fabrication of short piles.

[0007] Firstly, in order to solve the above-mentioned technical problems, the present invention provides a method for manufacturing high-precision back drilling and short piles, comprising the following steps:

[0008] S1. A production board with several inner layer circuits is provided, both of which are copper surfaces. One surface of the production board is a back-drilled surface, and the other surface is a non-back-drilled surface. The bottom inner layer circuit that is drilled through during back drilling is called the drill-through layer, and the inner layer circuits adjacent to the drill-through layer that are not drilled through during back drilling are called non-drill-through layers. Several drill holes are provided on the edge of the drill-through layer and / or in the non-circuit area of ​​the production board, and a wire connecting the circuits in the board and the drill holes is also made on the drill-through layer. The drill holes are the positions where drilling is required in subsequent processing.

[0009] S2. Drill through holes on the production board and drill inspection holes at positions perpendicular to each drilled hole.

[0010] S3. Then, the holes are metallized by copper plating and electroplating. The metallized vias are connected to the circuitry in the drill-through layer, and the metallized test holes are connected to the conductors in the drill-through layer, so that the vias and test holes are connected.

[0011] S4. Then fix the production board on the table of the back drilling machine, with the back drilling surface facing upwards; lead out two signal lines from the back drilling machine and connect them to its control system, with the other end of one signal line connected to the drill bit on the back drilling machine. The cutting diameter of the drill bit is larger than the diameter of the detection hole, and the other signal line is connected to the copper surface on the production board.

[0012] S5. Control the drill bit to back-drill each detection hole. When the drill bit contacts the board surface, a circuit is formed between the production board and the drill bit through two signal lines. The resistance value change during back-drilling is monitored. When the drill bit continues to drill down and the resistance value is instantly doubled or more for the first time, it is recorded as the reference zero point of back-drilling. When the drill bit continues to drill down until the resistance value is instantly doubled or more for the second time, it is recorded as the end point of back-drilling. This process is repeated to obtain the back-drilling depth of each detection hole from the reference zero point to the end point, and the average back-drilling depth of all detection holes is calculated.

[0013] S6. The average back-drilling depth obtained in step S5 plus a compensation value is used as the actual back-drilling depth of the back-drilling hole in the production board. The compensation value is not greater than 50% of the design value of the medium thickness between the drilled layer and the non-drilled layer.

[0014] Furthermore, in step S1, a pad or copper ring with an outer diameter larger than the drilled hole is formed at the drilling location, and the wire is connected to the pad or copper ring; in step S2, the diameter of the detection hole is smaller than the outer diameter of the pad or equal to the inner diameter of the copper ring, so that the pad or copper ring is exposed on the hole wall of the detection hole.

[0015] Furthermore, in step S1, the production board is divided into multiple parts in an equal or unequal manner along the long side and / or short side, and several drilling positions are provided on the board edge and / or non-circuit area of ​​the drill-through layer in each part; in step S6, the actual back-drilling depth of the back-drilling hole in the board at that part is taken as the average back-drilling depth of all detection holes in each part plus a compensation value.

[0016] Furthermore, in step S1, 1-100 drill holes are provided at the edge of the drill-through layer and / or in the non-circuit area at each section.

[0017] Furthermore, in step S1, 2-9 drill holes are provided at the edge of the drill-through layer and / or in the non-circuit area at each section.

[0018] Furthermore, the steps between S3 and S4 include the following:

[0019] S31. A film is applied to the production board. After exposure and development, a hole ring pattern surrounding the detection hole is formed on the non-back-drilled surface of the production board. Then, the copper layer at the hole ring pattern is removed by etching. Finally, the film is removed so that the copper in the detection hole is disconnected from the copper surface of the non-back-drilled surface.

[0020] Furthermore, in step S4, the back drilling machine is equipped with pressure feet that can move up and down and abut against the surface of the production board, and the signal line is connected to the copper layer of the production board through the pressure feet.

[0021] Furthermore, in step S4, the back drilling machine is equipped with a clamp that can be held on the surface of the production board, and the signal line is connected to the copper layer of the production board through the clamp.

[0022] Furthermore, in step S5, the back-drilling depth s = v·t from the reference zero point to the end point, where v is the drilling speed of the drill bit and t is the back-drilling time from the reference zero point to the end point.

[0023] Secondly, the present invention also provides another method for manufacturing high-precision back drilling and short piles, comprising the following steps:

[0024] S11. A production board with several inner layer circuits is provided, both of which are copper surfaces. One surface of the production board is a back-drilled surface, and the other surface is a non-back-drilled surface. The bottom inner layer circuit that is drilled through during back drilling is called the drill-through layer, and the inner layer circuits adjacent to the drill-through layer that are not drilled through during back drilling are called non-drill-through layers. Several drill holes are provided on the edge of the drill-through layer and / or in the non-circuit area of ​​the production board, and a wire connecting the circuits in the board and the drill holes is also made on the drill-through layer. The drill holes are the positions where drilling is required in subsequent processing.

[0025] S12. Drill through holes on the production board and drill inspection holes at positions perpendicular to each drilled hole.

[0026] S13. Then, the holes are metallized by copper plating and electroplating. The metallized vias are connected to the circuitry in the drill-through layer, and the metallized test holes are connected to the conductors in the drill-through layer, so that the vias and test holes are connected.

[0027] S14. Then fix the production board on the table of the back drilling machine, with the back drilling surface facing upwards; lead out two signal lines from the back drilling machine and connect them to its control system, with the other end of one signal line connected to the drill bit on the back drilling machine, the cutting diameter of the drill bit being larger than the diameter of the detection hole, and the other signal line connected to the copper surface on the production board.

[0028] S15. Control the drill bit to back-drill the test holes one by one. When the drill bit contacts the board surface, a circuit is formed between the production board and the drill bit through two signal lines. This point is recorded as the reference zero point of back drilling. The resistance value change of the drill bit during back drilling is monitored. When the drill bit continues to drill down and the resistance value is monitored to increase by 100% or more twice, it is recorded as the end point of back drilling. By analogy, the back drilling depth of each test hole from the reference zero point to the end point can be obtained, and the average back drilling depth of all test holes can be calculated.

[0029] S16. The average back-drilling depth obtained in step S5 plus a compensation value is used as the actual back-drilling depth of the back-drilling hole in the production board. The compensation value is not greater than 50% of the design value of the medium thickness between the drilled layer and the non-drilled layer.

[0030] Thirdly, the present invention also provides another method for manufacturing high-precision back drilling and short piles, comprising the following steps:

[0031] S10. A production board with several inner layer circuits is provided, both surfaces of which are copper surfaces. One surface of the production board is a back-drilled surface, and the other surface is a non-back-drilled surface. The bottom inner layer circuit that is drilled through during back-drilling is the drill-through layer, and the inner layer circuits adjacent to the drill-through layer that are not drilled through during back-drilling are the non-drill-through layers. Several sets of detection modules are provided on the edge of the drill-through layer and / or in the non-circuit area of ​​the production board. Each set of detection modules includes two adjacent drill holes and a wire connecting the two drill holes. The drill holes are the positions where drilling is required in subsequent processing.

[0032] S20. Drill inspection holes at positions perpendicular to each drilled hole on the production board.

[0033] S30. Then, the holes are metallized by copper plating and electroplating, so that the two detection holes in each detection module are connected to the wires in the drill-through layer, thus connecting the two detection holes in each detection module.

[0034] S40. Then fix the production board on the table of the back drilling machine, with the back drilling surface facing upwards; lead out two signal lines from the back drilling machine and connect them to its control system, with the other end of one signal line connected to the drill bit on the back drilling machine, the cutting diameter of the drill bit being larger than the diameter of the detection hole, and the other signal line connected to the copper surface on the production board.

[0035] S50. Control the drill bit to back-drill one of the detection holes of each detection module in turn. When the drill bit contacts the board surface, a circuit is formed between the production board and the drill bit through two signal lines. The change in resistance value during back-drilling is monitored. When the drill bit continues to drill down and the resistance value is detected to increase by 100% or more for the first time, it is recorded as the reference zero point of back-drilling. When the drill bit continues to drill down until the resistance value is detected to increase by 100% or more for the second time, it is recorded as the end point of back-drilling. This process is repeated to obtain the back-drilling depth of each detection hole from the reference zero point to the end point, and the average back-drilling depth of all detection holes is calculated.

[0036] S60. The average back-drilling depth obtained in step S50 plus a compensation value is used as the actual back-drilling depth of the back-drilling hole in the production board. The compensation value is not greater than 50% of the design value of the medium thickness between the drilled layer and the non-drilled layer.

[0037] Furthermore, the production board is a multilayer board in which an inner core board and an outer copper foil are pressed together by a prepreg.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] In this invention, by forming a conductive circuit between the back-drilling machine and the detection hole to be back-drilled, the resistance value of this circuit can be detected and obtained by the control system on the back-drilling machine. When the drill bit continuously drills down and breaks the connection between the copper layer on the board surface and the copper layer on the hole wall, the instantaneous resistance value will be twice or more than twice that before the break. This instantaneous position can be recorded as the reference zero point of the back-drilling. Similarly, when drilling continues and breaks the connection between the wire in the drill-through layer and the copper of the detection hole, the instantaneous resistance value at the break will be twice or more than twice that before the break. This instantaneous position can be recorded as the end point of the back-drilling, and the distance from the reference zero point to the end point can be obtained. The back-drilling depth of the points is calculated by taking the average back-drilling depth of all test holes. Then, a compensation value of no more than 50% of the design value of the medium thickness between the drilled layer and the non-drilled layer is used as the back-drilling value. The average back-drilling depth plus the compensation value is used as the actual back-drilling depth of the back-drilling hole in the production board. This can greatly reduce the influence of factors such as board thickness tolerance during back-drilling of the production board, thereby achieving high-precision back-drilling. Moreover, the design of the compensation value can minimize the short pile length between the drilled layer and the non-drilled layer, meeting the requirement of minimizing the back-drilling short pile (stub value) under high-speed transmission rate exceeding 50Gbps.

[0040] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0041] Figure 1 These are schematic diagrams showing the electroplating process on the board in Examples 1 and 2;

[0042] Figure 2 This is a schematic diagram of placing the production board behind the back drilling machine in Example 1;

[0043] Figure 3 This is a schematic diagram of back drilling at the inspection hole on the production board in Example 1;

[0044] Figure 4 This is a schematic diagram of the copper-free hole ring fabricated on the board in Example 2;

[0045] Figure 5 These are schematic diagrams of the electroplating process on the plate in Examples 3 and 4;

[0046] Figure 6 This is a schematic diagram of placing the production board behind the back drilling machine in Example 3;

[0047] Figure 7 This is a schematic diagram of back drilling at the inspection hole on the production board in Example 3;

[0048] Figure 8 This is a schematic diagram of the copper-free hole ring fabricated on the board in Example 4. Detailed Implementation

[0049] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0051] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0052] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0053] Example 1

[0054] This embodiment illustrates a method for manufacturing a circuit board, including a back-drilling process. This method enables high-precision back-drilling and high-precision control of short-pile drilling. Taking the manufacturing of a ten-layer circuit board with back-drilling through seven layers as an example, the process includes the following steps:

[0055] (1) Cutting: Cut four core boards according to the panel size of 520mm×620mm. The thickness of the core board is 0.5mm, and the copper layer thickness on both surfaces of the core board is 0.5oz. According to the design requirements, several positions for drilling after pressing are reserved on the edge of the core board and in the non-circuit area. These positions are called drilling positions.

[0056] (2) Inner Layer Circuit Fabrication (Negative Film Process): Inner layer pattern transfer: A photosensitive film is coated on the core board using a vertical coating machine. The film thickness is controlled at 8μm. A fully automatic exposure machine is used, with 5-6 exposure scales (or 21 exposure scales) to complete the inner layer circuit exposure. After development, the inner layer circuit pattern is formed, and the inner layer circuit pattern of one core board includes pad patterns or copper ring patterns with an outer diameter larger than the drill hole position. Inner layer etching: The inner layer circuit is etched out on the exposed and developed core board, and a pad or copper ring 30 is made on one surface of one core board at the position corresponding to all drill holes. In addition, the pad or copper ring is connected to the inner layer circuit through a conductor 40 made in the same layer (e.g., Figure 1 As shown), pads or copper rings are used to facilitate the connection between the copper layer on the hole wall and the inner layer circuit at the drilling position. The inner layer line width is measured to be 3mil. The inner layer is AOI, and then the inner layer circuit is checked for defects such as open circuits, short circuits, line gaps, and pinholes. Defective products are scrapped, and defect-free products are sent to the next process.

[0057] (3) Lamination: The browning speed is based on the thickness of the bottom copper layer. The four core boards, prepreg, and outer copper foil are laminated in sequence as required. During lamination, the circuit layer with pads or copper rings is placed on the seventh layer of the entire laminated structure. The thickness of the outer copper foil is preferably 0.5oz. Then, according to the Tg of the board material, appropriate lamination conditions are selected to laminate the laminated board to form a ten-layer production board. Both surfaces of the production board are copper surfaces, and there are eight inner layer circuits inside. The surface of the production board away from the inner layer pads or copper rings is the back-drilling surface that needs to be back-drilled, which is the first circuit layer. The other surface is the non-back-drilling surface, which is the tenth circuit layer. The bottommost circuit layer that is drilled through when back-drilling from the back-drilling surface is the drill-through layer, that is, the circuit layer with pads or copper rings is the drill-through layer. The inner layer circuits adjacent to the drill-through layer and not drilled through when back-drilling are the non-drill-through layers, that is, the eighth circuit layer of the production board is the non-drill-through layer.

[0058] In a specific implementation case, 1-100 drilling positions can generally be set on the edge of the drill-through layer and / or non-circuit area of ​​the production board, preferably 2-9. The drilling positions are generally evenly distributed in various positions of the core board to facilitate the back-drilling depth from the board surface to the drill-through layer at various positions on the board during the back-drilling test. By calculating the average back-drilling depth at each position, the thickness difference of the board in various areas can be eliminated as much as possible, and the influence of the board thickness tolerance on the back-drilling depth and back-drilling short piles can be reduced.

[0059] In a specific implementation case, to avoid the large differences in board thickness between different areas, which prevent the average back-drilling depth from being used to reduce the impact of back-drilling on the entire board, the production board can be first designed in sections. Then, detection holes are set in each section, and the average back-drilling depth of that section is calculated. This average back-drilling depth is used as the benchmark value for the back-drilling depth of that section. That is, when back-drilling is performed on the entire board, the back-drilling depth of each section may be the same or different, and will vary with the differences in board thickness between different sections. Specifically, the production board is divided into multiple parts in an equal or unequal manner along the long side and / or short side, and 1-100 drill holes are provided on the board edge and / or non-circuit area of ​​the drill-through layer in each section, preferably 2-9 holes.

[0060] (4) Drilling: Based on existing drilling technology, drilling is performed on the production board according to design requirements to drill through holes 10 that connect the inner and outer layers of the circuitry, and inspection holes 20 are drilled at positions perpendicular to each drilled hole. These through holes connect to the pads or copper rings via the seventh circuit layer and conductors. The diameter of the inspection hole is smaller than the outer diameter of the pad or the same as the inner diameter of the copper ring, so that the pad or copper ring 30 is exposed on the hole wall (e.g., ...). Figure 1 (As shown).

[0061] (5) Copper plating: A thin layer of copper is deposited on the board surface and hole walls using chemical copper plating. The backlight test is level 10. The copper plating thickness in the hole is 0.5μm. After metallization, the copper in the detection hole and the through hole not only forms a connection on the board surface, but also forms a connection at the seventh circuit layer, so as to form a parallel circuit between the inner and outer layers between the two holes.

[0062] (6) Full-board electroplating: Electroplating the entire board for 60 minutes at a current density of 18 ASF, increasing the thickness of the copper layer in the holes and on the board surface, such as... Figure 1 As shown.

[0063] (7) Back drilling: This includes the following steps:

[0064] a. such as Figure 2 As shown, production board 1 is first fixed on the table of the back drilling machine. The back drilling surface is located on the top side and serves as the first circuit layer, while the non-back drilling surface is located on the bottom side and serves as the tenth circuit layer. Two signal lines 3 are led out from the back drilling machine and connected to its control system. One end of each signal line is connected to the control system 2, and the other end of one of the signal lines is connected to the drill bit on the back drilling machine, thus forming an electrical connection. Of course, this connection should not affect the rotation of the drill bit. The cutting diameter of the drill bit is matched with the designed hole diameter of the back drilling hole, that is, the cutting diameter of the drill bit is larger than the outer diameter of the detection hole, so as to ensure the removal of the copper layer on the hole wall during back drilling. The other signal line 3 is connected to the copper surface on production board 1. That is, through the conduction of the control system, a conductive connection is formed between the copper surface and the drill bit, but a circuit is not formed at the beginning of back drilling. The control system of this back drilling machine is a servo control system.

[0065] Preferably, the back drilling machine is provided with a pressure foot 4 that can move up and down and abut against the surface of the production board 1. The signal line 3 is connected to the copper layer of the production board 1 through the pressure foot 4. The pressure foot method is convenient for connection and has universality.

[0066] In a specific implementation example, the back drilling machine is equipped with a clamp (not shown in the figure) that can be held on the surface of the production board, and the signal line is connected to the copper layer of the production board through the clamp.

[0067] b, such as Figure 3As shown, the control drill bit 5 performs back drilling on each detection hole. When the drill bit contacts the board surface, a circuit is formed between the production board and the drill bit through two signal lines and the copper layer on the production board. This circuit monitors the change in resistance value during back drilling. When the drill bit continues to drill down and detects for the first time that the resistance value increases by 100% or more, the control system records this as the reference zero point of back drilling. At this point, the connection between the copper layer on the board surface and the copper of the detection hole is broken. When the drill bit continues to drill down until the resistance value increases by 100% or more for the second time, the control system records this as the end point of back drilling and controls the drill bit to stop back drilling. At this point, the connection between the wire in the drill-through layer and the copper of the detection hole is broken. This process is repeated to obtain the back drilling depth of each detection hole from the reference zero point to the end point, and the average back drilling depth S1 of all detection holes on the board is calculated. Similarly, when the production board is partitioned, the average back drilling depth S2 of all detection holes in each part of the board can be calculated.

[0068] In the above process, when the drill bit continuously drills down and breaks the connection between the copper layer on the board surface and the copper layer on the hole wall, it is equivalent to forming an open circuit between the board surface and the copper of the detection hole drilled from the back. Its resistance is approximately at its maximum value. However, the circuit is still connected because the drill bit is in contact with the board surface and the copper of the hole. At this time, the resistance is not at its maximum value. Moreover, the resistivity of the drill bit is generally greater than the resistivity of copper. Therefore, the instantaneous resistance when the drill bit breaks the connection will be twice or more than twice that before the drill bit breaks the connection. Similarly, when the drill bit breaks the connection between the wire and the copper of the detection hole in the drilled layer, the instantaneous resistance will also be twice or more than twice that before the drill bit breaks the connection. The drill bit is preferably made of steel alloy.

[0069] Preferably, the back-drilling depth from the reference zero point to the end point is s = v·t, where v is the drilling speed of the drill bit and t is the back-drilling time from the reference zero point to the end point.

[0070] c. When the production board is not designed in sections, the average back-drilling depth S1 obtained in step b plus a compensation value is used as the actual back-drilling depth of the back-drilling holes in the production board. That is, the through holes that need to be back-drilled on the production board are back-drilled according to the obtained actual back-drilling depth. Similarly, when the production board is designed in sections, the average back-drilling depth S2 of each part is calculated and a compensation value is added to each part as the actual back-drilling depth of the back-drilling holes in each part. That is, the through holes that need to be back-drilled in each part are back-drilled according to the obtained actual back-drilling depth. Among them, the compensation value is not greater than 50% of the design value of the medium thickness between the drilled layer and the non-drilled layer. That is, when back-drilling, after drilling through the seventh layer of the circuit layer, the drilling should not continue for more than half the thickness of the lower layer medium, so as to remove as much residual pile length as possible between the drilled layer and the non-drilled layer.

[0071] Preferably, in addition to the percentage calculation method mentioned above, the compensation value can also be calculated based on the accuracy of the back drilling rig, the tolerance of the medium thickness between the drilled and non-drilled layers, and the minimum length of the stub based on the reliability of the line connection performance. For example, the design value of the medium thickness Ts between the drilled and non-drilled layers is 0.15mm, and its thickness tolerance is ±10%, i.e., Ts = 0.15 ± 0.015mm. The accuracy of the back drilling rig is ±0.025mm, and the length of the stub... The length should be ≥0.05mm. The compensation value is 0.15-0.015-0.025-0.05=0.06mm. Therefore, the actual back-drilling depth is the average back-drilling depth S1+0.06mm, or the actual back-drilling depth is the average back-drilling depth S2+0.06mm. This way, the length of the stub after back-drilling is controlled between 0.05-0.13mm, which can meet the requirement of the stub being as small as possible under high-speed transmission rates exceeding 50Gbps.

[0072] Preferably, since the back-drilling depth from the reference zero point to the end point is the depth value after drilling through the copper layer on the board surface, in order to avoid the influence of the copper thickness on the board surface during back-drilling, the actual back-drilling depth can also be increased by adding the thickness of the surface copper layer.

[0073] Of course, in a specific implementation case, the point when the drill bit just touches the board surface and forms a circuit can be taken as the reference zero point for back drilling. Then, when the resistance value is detected to increase by one or more times twice, it can be recorded as the end point of back drilling. In this way, the back drilling depth from the reference zero point to the end point will include the thickness of the copper layer on the board surface.

[0074] In the above, a Schmoll drilling machine can be selected as the back drilling machine. The control system on the back drilling machine provides a constant voltage U to the circuit formed by the drill bit during back drilling. During back drilling, the resistance in the circuit is constantly changing, so the current I in the circuit is also constantly changing. The Schmoll drilling machine can monitor the specific changes in the current in the circuit. Under the condition that the voltage is constant, it can calculate the real-time resistance R = voltage U / current I, and then determine whether a certain layer of the circuit has been drilled through by the change in resistance. Of course, the constant voltage U provided is generally 12-24V.

[0075] (8) Fabrication of outer layer circuitry (positive film process): The outer layer pattern is transferred using a fully automatic exposure machine and positive film circuitry film. The outer layer circuitry is exposed using an exposure ruler of 5 to 7 divisions (or 21 divisions). After development, the outer layer circuitry pattern is formed on the production board. The outer layer pattern is electroplated, and then copper and tin are plated on the production board respectively. The electroplating parameters are set according to the required copper thickness. Copper plating is performed at a current density of 1.8 ASD for 60 minutes, and tin plating is performed at a current density of 1.2 ASD for 10 minutes, with a tin thickness of 3 to 5 μm. Then, the film is removed, etched, and tin is removed in sequence to etch the outer layer circuitry on the production board. The copper thickness of the outer layer circuitry is greater than or equal to 70 μm. The outer layer AOI is performed using an automatic optical inspection system. By comparing with the CAM data, the outer layer circuitry is inspected for defects such as open circuits, gaps, incomplete etching, and short circuits.

[0076] (9) Solder resist and silkscreen printing: After silkscreen printing solder resist ink on the surface of the production board, it undergoes pre-curing, exposure, development, and heat curing processes to solidify the solder resist ink into a solder resist layer. Specifically, the solder resist ink on the TOP side and the TOP side characters are added with the "UL mark". This coats a layer on the lines and substrate that do not require soldering, preventing bridging between lines during soldering, providing a permanent electrical environment and resistance to chemical corrosion, while also enhancing the appearance. The solder resist layer manufacturing process includes the following steps:

[0077] (10) Surface treatment (immersion nickel and gold): The copper surface of the solder pads at the solder mask opening position is uniformly deposited with a nickel layer and a gold layer of a certain required thickness through chemical principle. The thickness of the nickel layer is 3-5μm; the thickness of the gold layer is 0.05-0.1μm.

[0078] (11) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0079] (12) Molding: Based on existing technology and design requirements, the circuit board is made with a shape tolerance of + / -0.05mm.

[0080] (13) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and our company's inspection standards. If there are any defects, repair them in time to ensure excellent quality control for customers.

[0081] (14) FQA: Re-test the appearance of the circuit board, the thickness of the copper in the holes, the thickness of the dielectric layer, the thickness of the solder mask, the thickness of the inner copper layer, etc. to see if they meet the customer's requirements.

[0082] (15) Packaging: The circuit boards are sealed according to the packaging method and quantity required by the customer, and desiccant and humidity card are placed in the packaging before shipment.

[0083] Example 2

[0084] The method for manufacturing a circuit board shown in this embodiment is basically the same as that in Embodiment 1, except that step (61) is added between steps (6) and (7), as follows:

[0085] (61) Fabrication of the outer ring: After exposure and development, a ring pattern surrounding the detection holes is formed on the non-back-drilled surface of the production board. Generally, the inner diameter of this ring pattern is larger than the diameter of the detection holes, so that the detection holes are covered by the film. Then, the copper layer at the ring pattern is removed by etching, and finally the film is removed to form a copper-free ring (e.g., Figure 4 As shown), this is to disconnect the copper in the test hole from the copper surface of the non-back-drilled surface.

[0086] Compared to Embodiment 1, this embodiment removes the parallel line connecting the detection hole and the through hole through the non-back-drilling surface in the conduction circuit. This makes the resistance change more obvious when back-drilling in the detection hole, thereby improving the sensitivity of the resistance monitoring signal.

[0087] Example 3

[0088] This embodiment illustrates a method for manufacturing a circuit board, including a back-drilling process. This method enables high-precision back-drilling and high-precision control of short-pile drilling. Taking the manufacturing of a ten-layer circuit board with back-drilling through seven layers as an example, the process includes the following steps:

[0089] (1) Cutting: Cut four core boards according to the panel size of 520mm×620mm. The thickness of the core board is 0.5mm and the copper layer thickness on both surfaces of the core board is 0.5oz. According to the design requirements, several sets of detection modules are reserved on the edge of the core board and in the non-circuit area. Each set of detection modules includes two adjacent drilling positions and a wire connecting the two drilling positions. The drilling positions are the positions where drilling is required after pressing.

[0090] (2) Inner Layer Circuit Fabrication (Negative Film Process): Inner layer pattern transfer: A photosensitive film is coated on the core board using a vertical coating machine. The film thickness is controlled at 8μm. A fully automatic exposure machine is used, with 5-6 exposure scales (or 21 exposure scales) to complete the inner layer circuit exposure. After development, the inner layer circuit pattern is formed, and the inner layer circuit pattern of one core board includes pad patterns or copper ring patterns with an outer diameter larger than the drill hole position. Inner layer etching: The inner layer circuit is etched out on the exposed and developed core board, and a pad or copper ring 30 is made on one surface of one core board at the position corresponding to all drill holes. In addition, the two pads or copper rings in each detection module are connected by a conductor 40 made in the same layer (e.g., Figure 5As shown), pads or copper rings are used to facilitate the connection of the copper layers of the hole walls at the two drilling positions of the same group of inspection modules. The inner layer line width is measured to be 3mil. The inner layer AOI is then used to check for defects such as open and short circuits, line gaps, and line pinholes in the inner layer circuit. Products with defects are scrapped, while products without defects are sent to the next process.

[0091] (3) Lamination: The browning speed is based on the thickness of the bottom copper layer. The four core boards, prepreg, and outer copper foil are laminated in sequence as required. During lamination, the circuit layer with pads or copper rings is placed on the seventh layer of the entire laminated structure. The thickness of the outer copper foil is preferably 0.5oz. Then, according to the Tg of the board material, appropriate lamination conditions are selected to laminate the laminated board to form a ten-layer production board. Both surfaces of the production board are copper surfaces, and there are eight inner layer circuits inside. The surface of the production board away from the inner layer pads or copper rings is the back-drilling surface that needs to be back-drilled, which is the first circuit layer. The other surface is the non-back-drilling surface, which is the tenth circuit layer. The bottommost circuit layer that is drilled through when back-drilling from the back-drilling surface is the drill-through layer, that is, the circuit layer with pads or copper rings is the drill-through layer. The inner layer circuits adjacent to the drill-through layer and not drilled through when back-drilling are the non-drill-through layers, that is, the eighth circuit layer of the production board is the non-drill-through layer.

[0092] In a specific implementation case, 1-100 sets of detection modules, preferably 2-9 sets, can be set on the edge of the drill-through layer and / or non-circuit area of ​​the production board. The detection modules are generally evenly distributed in various positions of the core board to facilitate the back-drilling depth from the board surface to the drill-through layer at various positions on the board during the back-drilling test. By calculating the average back-drilling depth at each position, the thickness difference of the board in various areas can be eliminated as much as possible, and the influence of the board thickness tolerance on the back-drilling depth and back-drilling short piles can be reduced.

[0093] In a specific implementation case, to avoid the large differences in board thickness between different areas, which prevent the average back-drilling depth from being used to reduce the impact of back-drilling on the entire board, the production board can be first designed in sections. Then, detection holes are set in each section, and the average back-drilling depth of that section is calculated. This average back-drilling depth is used as the benchmark value for the back-drilling depth of that section. That is, when back-drilling is performed on the entire board, the back-drilling depth of each section may be the same or different, and will vary with the differences in board thickness between different sections. Specifically, the production board is divided into multiple parts in an equal or unequal manner along the long side and / or short side, and 1-100 sets of detection modules are provided on the board edge and / or non-circuit area of ​​the drill-through layer in each section, preferably 2-9 sets.

[0094] (4) Drilling: Based on existing drilling technology, drilling is performed on the production board according to design requirements to drill through holes for connecting inner and outer layer circuits, and inspection holes 20 are drilled at positions perpendicular to each drilled hole (e.g., Figure 5As shown), the diameter of the detection hole is smaller than the outer diameter of the pad or the same as the inner diameter of the copper ring, so that the pad or copper ring is exposed on the hole wall of the detection hole. One detection hole in the same group of detection modules is used as a hole for back drilling detection in the later stage, and the other is used as a through hole for the circuit.

[0095] (5) Copper plating: A thin layer of copper is deposited on the board surface and hole walls using chemical copper plating. The backlight test is level 10. The copper plating thickness in the hole is 0.5μm. In addition to forming a connection on the board surface, the two detection holes in the same detection module also form a connection at the seventh circuit layer to form a parallel circuit between the inner and outer layers between the two holes.

[0096] (6) Full-board electroplating: Electroplating the entire board for 60 minutes at a current density of 18 ASF, increasing the thickness of the copper layer in the holes and on the board surface, such as... Figure 5 As shown.

[0097] (7) Back drilling: This includes the following steps:

[0098] a. such as Figure 6 As shown, production board 1 is first fixed on the table of the back drilling machine. The back drilling surface is located on the top side and serves as the first circuit layer, while the non-back drilling surface is located on the bottom side and serves as the tenth circuit layer. Two signal lines 3 are led out from the back drilling machine and connected to its control system. One end of each signal line is connected to the control system 2, and the other end of one of the signal lines is connected to the drill bit on the back drilling machine, thus forming an electrical connection. Of course, this connection should not affect the rotation of the drill bit. The cutting diameter of the drill bit is matched with the designed hole diameter of the back drilling hole, that is, the cutting diameter of the drill bit is larger than the outer diameter of the detection hole, so as to ensure the removal of the copper layer on the hole wall during back drilling. The other signal line 3 is connected to the copper surface on production board 1. That is, through the conduction of the control system, a conductive connection is formed between the copper surface and the drill bit, but a circuit is not formed at the beginning of back drilling. The control system of this back drilling machine is a servo control system.

[0099] Preferably, the back drilling machine is provided with a pressure foot 4 that can move up and down and abut against the surface of the production board 1. The signal line 3 is connected to the copper layer of the production board 1 through the pressure foot 4. The pressure foot method is convenient for connection and has universality.

[0100] In a specific implementation example, the back drilling machine is equipped with a clamp (not shown in the figure) that can be held on the surface of the production board, and the signal line is connected to the copper layer of the production board through the clamp.

[0101] b, such as Figure 7As shown, the control drill bit 5 performs back drilling on one of the detection holes in each group of detection modules. When the drill bit contacts the board surface, a circuit is formed between the production board and the drill bit through two signal lines and the copper layer on the production board. This circuit monitors the change in resistance value during back drilling. When the drill bit continues to drill down and detects for the first time that the resistance value increases by 100% or more, the control system records this as the reference zero point of back drilling. At this point, the connection between the copper layer on the board surface and the copper of the detection hole is broken. When the drill bit continues to drill down until the resistance value increases by 100% or more for the second time, the control system records this as the end point of back drilling and controls the drill bit to stop back drilling. At this point, the connection between the wire in the drill-through layer and the copper of the detection hole is broken. This process is repeated to obtain the back drilling depth of each detection hole from the reference zero point to the end point, and the average back drilling depth S1 of all detection holes on the board is calculated. Similarly, when the production board is partitioned, the average back drilling depth S2 of all detection holes in each part of the board can be calculated.

[0102] Preferably, the back-drilling depth from the reference zero point to the end point is s = v·t, where v is the drilling speed of the drill bit and t is the back-drilling time from the reference zero point to the end point.

[0103] c. When the production board is not partitioned, the average back-drilling depth S1 obtained in step b plus a compensation value is used as the actual back-drilling depth of the back-drilling holes in the production board. That is, the copper holes that need to be back-drilled on the production board are back-drilled according to the obtained actual back-drilling depth. Similarly, when the production board is partitioned, the average back-drilling depth S2 of each part is calculated and a compensation value is added to each part as the actual back-drilling depth of the back-drilling holes in each part. That is, the through holes that need to be back-drilled in each part are back-drilled according to the obtained actual back-drilling depth. The compensation value is not greater than 50% of the design value of the medium thickness between the drilled layer and the non-drilled layer. That is, when back-drilling, after drilling through the seventh circuit layer, the drilling should not exceed half the thickness of the lower medium layer, so as to remove as much residual pile length between the drilled layer and the non-drilled layer as possible.

[0104] Preferably, in addition to the percentage calculation method mentioned above, the compensation value can also be calculated based on the accuracy of the back drilling rig, the tolerance of the medium thickness between the drilled and non-drilled layers, and the minimum length of the stub based on the reliability of the line connection performance. For example, the design value of the medium thickness Ts between the drilled and non-drilled layers is 0.15mm, and its thickness tolerance is ±10%, i.e., Ts = 0.15 ± 0.015mm. The accuracy of the back drilling rig is ±0.025mm, and the length of the stub... The length should be ≥0.05mm. The compensation value is 0.15-0.015-0.025-0.05=0.06mm. Therefore, the actual back-drilling depth is the average back-drilling depth S1+0.06mm, or the actual back-drilling depth is the average back-drilling depth S2+0.06mm. This way, the length of the stub after back-drilling is controlled between 0.05-0.13mm, which can meet the requirement of the stub being as small as possible under high-speed transmission rates exceeding 50Gbps.

[0105] (8) Fabrication of outer layer circuitry (positive film process): The outer layer pattern is transferred using a fully automatic exposure machine and positive film circuitry film. The outer layer circuitry is exposed using an exposure ruler of 5 to 7 divisions (or 21 divisions). After development, the outer layer circuitry pattern is formed on the production board. The outer layer pattern is electroplated, and then copper and tin are plated on the production board respectively. The electroplating parameters are set according to the required copper thickness. Copper plating is performed at a current density of 1.8 ASD for 60 minutes, and tin plating is performed at a current density of 1.2 ASD for 10 minutes, with a tin thickness of 3 to 5 μm. Then, the film is removed, etched, and tin is removed in sequence to etch the outer layer circuitry on the production board. The copper thickness of the outer layer circuitry is greater than or equal to 70 μm. The outer layer AOI is performed using an automatic optical inspection system. By comparing with the CAM data, the outer layer circuitry is inspected for defects such as open circuits, gaps, incomplete etching, and short circuits.

[0106] (9) Solder resist and silkscreen printing: After silkscreen printing solder resist ink on the surface of the production board, it undergoes pre-curing, exposure, development, and heat curing processes to solidify the solder resist ink into a solder resist layer. Specifically, the solder resist ink on the TOP side and the TOP side characters are added with the "UL mark". This coats a layer on the lines and substrate that do not require soldering, preventing bridging between lines during soldering, providing a permanent electrical environment and resistance to chemical corrosion, while also enhancing the appearance. The solder resist layer manufacturing process includes the following steps:

[0107] (10) Surface treatment (immersion nickel and gold): The copper surface of the solder pads at the solder mask opening position is uniformly deposited with a nickel layer and a gold layer of a certain required thickness through chemical principle. The thickness of the nickel layer is 3-5μm; the thickness of the gold layer is 0.05-0.1μm.

[0108] (11) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0109] (12) Molding: Based on existing technology and design requirements, the circuit board is made with a shape tolerance of + / -0.05mm.

[0110] (13) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and our company's inspection standards. If there are any defects, repair them in time to ensure excellent quality control for customers.

[0111] (14) FQA: Re-test the appearance of the circuit board, the thickness of the copper in the holes, the thickness of the dielectric layer, the thickness of the solder mask, the thickness of the inner copper layer, etc. to see if they meet the customer's requirements.

[0112] (15) Packaging: The circuit boards are sealed according to the packaging method and quantity required by the customer, and desiccant and humidity card are placed in the packaging before shipment.

[0113] Example 4

[0114] The method for manufacturing a circuit board shown in this embodiment is basically the same as that in embodiment 3, except that step (61) is added between steps (6) and (7), as follows:

[0115] (61) Fabrication of the outer ring: After exposure and development, a ring pattern surrounding the detection holes is formed on the non-back-drilled surface of the production board. Specifically, the ring pattern is formed only at one detection hole in each detection module, and generally, the inner diameter of the ring pattern is larger than the diameter of the detection hole, thus covering the detection hole with the film. The copper layer at the ring pattern is then removed by etching, and finally, the film is removed to form a copper-free ring (e.g., ...). Figure 8 As shown), this is to disconnect the copper in the test hole from the copper surface of the non-back-drilled surface.

[0116] Compared to Embodiment 3, this embodiment removes the parallel line connecting the two detection holes of each group of detection modules in the conduction circuit through the non-back-drilling surface. This makes the resistance change more obvious when back-drilling in the detection hole, thereby improving the sensitivity of the resistance monitoring signal.

[0117] The above Figures 1 to 8 In the circuit board, the thickened lines are the copper layers.

[0118] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for manufacturing high-precision back-drilling and short stubs, characterized in that, Includes the following steps: S1. A production board with several inner layer circuits is provided, both of which are copper surfaces. One surface of the production board is a back-drilled surface, and the other surface is a non-back-drilled surface. The bottom inner layer circuit that is drilled through during back drilling is called the drill-through layer, and the inner layer circuits adjacent to the drill-through layer that are not drilled through during back drilling are called non-drill-through layers. Several drill holes are provided on the edge of the drill-through layer and / or in the non-circuit area of ​​the production board, and a wire connecting the circuits in the board and the drill holes is also made on the drill-through layer. The drill holes are the positions where drilling is required in subsequent processing. S2. Drill through holes on the production board and drill inspection holes at positions perpendicular to each drilled hole. S3. Then, the holes are metallized by copper plating and electroplating. The metallized vias are connected to the circuitry in the drill-through layer, and the metallized test holes are connected to the conductors in the drill-through layer, so that the vias and test holes are connected. S4. Then fix the production board on the table of the back drilling machine, with the back drilling surface facing upwards; lead out two signal lines from the back drilling machine and connect them to its control system, with the other end of one signal line connected to the drill bit on the back drilling machine. The cutting diameter of the drill bit is larger than the diameter of the detection hole, and the other signal line is connected to the copper surface on the production board. S5. Control the drill bit to back-drill each detection hole. When the drill bit contacts the board surface, a circuit is formed between the production board and the drill bit through two signal lines. The resistance value change during back-drilling is monitored. When the drill bit continues to drill down and the resistance value is instantly doubled or more for the first time, it is recorded as the reference zero point of back-drilling. When the drill bit continues to drill down until the resistance value is instantly doubled or more for the second time, it is recorded as the end point of back-drilling. This process is repeated to obtain the back-drilling depth of each detection hole from the reference zero point to the end point, and the average back-drilling depth of all detection holes is calculated. S6. The average back-drilling depth obtained in step S5 plus a compensation value is used as the actual back-drilling depth of the back-drilling hole in the production board. The compensation value is not greater than 50% of the design value of the medium thickness between the drilled layer and the non-drilled layer.

2. The method for achieving high-precision back drilling and short pile fabrication according to claim 1, characterized in that, In step S1, a pad or copper ring with an outer diameter larger than the drilled hole is formed at the drilling location, and the wire is connected to the pad or copper ring; in step S2, the diameter of the detection hole is smaller than the outer diameter of the pad or equal to the inner diameter of the copper ring, so that the pad or copper ring is exposed on the hole wall of the detection hole.

3. The method for achieving high-precision back drilling and short pile fabrication according to claim 1, characterized in that, In step S1, the production board is divided into multiple parts in an equal or unequal manner along the long side and / or short side, and several drilling positions are provided on the board edge and / or non-circuit area of ​​the drill-through layer in each part; in step S6, the back drilling is performed by taking the average back drilling depth of all detection holes in each part plus a compensation value as the actual back drilling depth of the back drilling hole in that part.

4. The method for achieving high-precision back drilling and short pile fabrication according to claim 3, characterized in that, In step S1, 1-100 drill holes are provided at the edge of the drill-through layer and / or in the non-circuit area at each section.

5. The method for achieving high-precision back drilling and short pile fabrication according to claim 4, characterized in that, In step S1, 2-9 drill holes are provided at the edge of the board and / or the non-circuit area of ​​the drill-through layer in each section.

6. The method for achieving high-precision back drilling and short pile fabrication according to claim 1, characterized in that, The steps between steps S3 and S4 also include the following: S31. A film is applied to the production board. After exposure and development, a hole ring pattern surrounding the detection hole is formed on the non-back-drilled surface of the production board. Then, the copper layer at the hole ring pattern is removed by etching. Finally, the film is removed so that the copper in the detection hole is disconnected from the copper surface of the non-back-drilled surface.

7. The method for achieving high-precision back drilling and short pile fabrication according to claim 1, characterized in that, In step S4, the back drilling machine is equipped with pressure feet that can move up and down and abut against the surface of the production board. The signal line is connected to the copper layer of the production board through the pressure feet.

8. The method for achieving high-precision back drilling and short pile fabrication according to claim 1, characterized in that, In step S5, the back-drilling depth from the reference zero point to the end point is s = v·t, where v is the drilling speed of the drill bit and t is the back-drilling time from the reference zero point to the end point.

9. A method for manufacturing high-precision back drilling and short piles, characterized in that, Includes the following steps: S11. A production board with several inner layer circuits is provided, both of which are copper surfaces. One surface of the production board is a back-drilled surface, and the other surface is a non-back-drilled surface. The bottom inner layer circuit that is drilled through during back drilling is called the drill-through layer, and the inner layer circuits adjacent to the drill-through layer that are not drilled through during back drilling are called non-drill-through layers. Several drill holes are provided on the edge of the drill-through layer and / or in the non-circuit area of ​​the production board, and a wire connecting the circuits in the board and the drill holes is also made on the drill-through layer. The drill holes are the positions where drilling is required in subsequent processing. S12. Drill through holes on the production board and drill inspection holes at positions perpendicular to each drilled hole. S13. Then, the holes are metallized by copper plating and electroplating. The metallized vias are connected to the circuitry in the drill-through layer, and the metallized test holes are connected to the conductors in the drill-through layer, so that the vias and test holes are connected. S14. Then fix the production board on the table of the back drilling machine, with the back drilling surface facing upwards; lead out two signal lines from the back drilling machine and connect them to its control system, with the other end of one signal line connected to the drill bit on the back drilling machine, the cutting diameter of the drill bit being larger than the diameter of the detection hole, and the other signal line connected to the copper surface on the production board. S15. Control the drill bit to back-drill the test holes one by one. When the drill bit contacts the board surface, a circuit is formed between the production board and the drill bit through two signal lines. This point is recorded as the reference zero point of back drilling. The resistance value change of the drill bit during back drilling is monitored. When the drill bit continues to drill down and the resistance value is monitored to increase by 100% or more twice, it is recorded as the end point of back drilling. By analogy, the back drilling depth of each test hole from the reference zero point to the end point can be obtained, and the average back drilling depth of all test holes can be calculated. S16. The average back-drilling depth obtained in step S5 plus a compensation value is used as the actual back-drilling depth of the back-drilling hole in the production board. The compensation value is not greater than 50% of the design value of the medium thickness between the drilled layer and the non-drilled layer.

10. A method for manufacturing high-precision back drilling and short piles, characterized in that, Includes the following steps: S10. A production board with several inner layer circuits is provided, both surfaces of which are copper surfaces. One surface of the production board is a back-drilled surface, and the other surface is a non-back-drilled surface. The bottom inner layer circuit that is drilled through during back-drilling is the drill-through layer, and the inner layer circuits adjacent to the drill-through layer that are not drilled through during back-drilling are the non-drill-through layers. Several sets of detection modules are provided on the edge of the drill-through layer and / or in the non-circuit area of ​​the production board. Each set of detection modules includes two adjacent drill holes and a wire connecting the two drill holes. The drill holes are the positions where drilling is required in subsequent processing. S20. Drill inspection holes at positions perpendicular to each drilled hole on the production board. S30. Then, the holes are metallized by copper plating and electroplating, so that the two detection holes in each detection module are connected to the wires in the drill-through layer, thus connecting the two detection holes in each detection module. S40. Then fix the production board on the table of the back drilling machine, with the back drilling surface facing upwards; lead out two signal lines from the back drilling machine and connect them to its control system, with the other end of one signal line connected to the drill bit on the back drilling machine, the cutting diameter of the drill bit being larger than the diameter of the detection hole, and the other signal line connected to the copper surface on the production board. S50. Control the drill bit to back-drill one of the detection holes of each detection module in turn. When the drill bit contacts the board surface, a circuit is formed between the production board and the drill bit through two signal lines. The change in resistance value during back-drilling is monitored. When the drill bit continues to drill down and the resistance value is detected to increase by 100% or more for the first time, it is recorded as the reference zero point of back-drilling. When the drill bit continues to drill down until the resistance value is detected to increase by 100% or more for the second time, it is recorded as the end point of back-drilling. This process is repeated to obtain the back-drilling depth of each detection hole from the reference zero point to the end point, and the average back-drilling depth of all detection holes is calculated. S60. The average back-drilling depth obtained in step S50 plus a compensation value is used as the actual back-drilling depth of the back-drilling hole in the production board. The compensation value is not greater than 50% of the design value of the medium thickness between the drilled layer and the non-drilled layer.

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