CN115589673A - Machining method for realizing back drilling and shortening of stub - Google Patents

Abstract

The invention discloses a processing method for realizing the shortening of back drilling and stub, which forms a conducting loop between a back drilling machine and a through hole to be back drilled, thereby detecting and obtaining the resistance value on the loop by using a control system on the back drilling machine, when a drill bit continuously drills down to remove a hole wall copper layer and a bonding pad in the through hole, the resistance value on the loop is continuously changed, thereby judging whether the bonding pad of a certain layer is drilled away or not according to the comparison of the actual resistance value change value on the loop and a preset value, thus recording the total drilled away layers in the continuous drilling process, stopping the back drilling when the preset drilled away layers are reached, and then obtaining the length of the stub, namely the thickness of a medium between a non-drilled layer and the nearest drilled through layer in a back drilling hole, thereby realizing the high-precision control of the back drilling and the length of the stub, and controlling the size of the stub by controlling the thickness of the medium between the non-drilled layer and the nearest drilled through layer in the production board according to the mode.

Description

Machining method for realizing back drilling and shortening of stub

Technical Field

The invention relates to the technical field of printed circuit board manufacturing, in particular to a processing method for realizing back drilling and stub shortening.

Background

With the continuous improvement of the integration degree of electronic systems, the circuit boards are more and more integrated and functionalized, so that the design density of the PCB is also more and more necessary, and the high-speed interconnection is more and more applied, and the high-speed signal requirements on products are more and more high, such as 5G/6G communication, super computing, high-performance computing, cloud computing, big data and the like.

Since the application of high-frequency and high-speed products is greatly improved, new requirements on the integrity of high-speed digital signals are provided. The transmission line of the high-speed circuit puts a very high requirement on signal integrity under the condition of high frequency and high speed, the control and the realization of the signal integrity have strong correlation with the impedance and the insertion loss of the transmission line, and when the high-speed exceeds 25Gbps, the insertion loss has more and more great influence on the signal integrity. The length of the stub (stub) which is redundant at the high-speed via hole directly affects the size of the insertion loss, and in order to obtain better high-speed signal integrity, the length of the stub needs to be controlled as small as possible.

In order to reduce short piles, the prior art adopts a back drilling process to back drill a part of redundant short piles of a high-speed via hole, and because the thicknesses of media among layers on a plate have tolerance, the tolerance accumulated by the thicknesses of the media of a plurality of layers is larger; further, the large-sized circuit board has a large difference in board thickness in each area, and generally, the difference in board thickness is large and exceeds 0.2mm due to the difference in board thickness, which has a great influence on the accuracy of the back drilling of the whole board.

In order to improve the back drilling precision, the thickness of each layer of interlayer medium needs to be measured in a partitioning mode to be manually stacked, and the thickness of each interlayer medium is confirmed by a first piece during back drilling; in actual production, it is difficult to perform good plate thickness stacking, slicing is destructive, and slicing confirms that the plate thickness is limited to the first piece and is partial slicing, and therefore, the plate thickness cannot effectively distinguish the plate thickness difference of each region, and the influence of the plate thickness tolerance on the back drilling depth and the back drilling stub cannot be eliminated, and high-precision back drilling cannot be realized.

Disclosure of Invention

The invention provides a processing method for realizing the shortening of back drilling and stub, aiming at the defects of the prior art, and the method can accurately control the length of the stub to be the thickness of a medium layer between a back drilling layer and a non-drilling layer so as to realize the high-precision back drilling and the high-precision control of the length of the stub.

In order to solve the above technical problems, the present invention provides a method for making a back drill and a stub shorter, comprising the steps of:

s1, providing a production board with a plurality of inner-layer circuits, wherein both surfaces of the production board are copper surfaces, and a bonding pad with the same thickness and size is manufactured on each circuit layer at the position corresponding to a back drilling hole when the inner-layer circuits of the production board are manufactured;

s2, drilling a through hole on the production board and drilling a through hole with the aperture smaller than that of the bonding pad at the central position of the corresponding bonding pad;

s3, metallizing the holes through copper deposition and electroplating, and communicating the metallized through holes with the via holes through the board copper layer;

s4, fixing the production plate on the table board of the back drilling machine, leading out two signal wires which are respectively communicated with a control system of the back drilling machine on the back drilling machine, wherein the other end of one signal wire is communicated with a drill bit on the back drilling machine, the blade diameter of the drill bit is not less than the outer diameter of the bonding pad, and the other signal wire is communicated with the copper surface on the production plate;

s5, presetting the number of layers of the circuit layer to be drilled through during back drilling of the drill bit and a preset resistance value change value in a control system of the back drilling machine, wherein the resistance value change value is the resistance value change value during drilling and removing one layer of bonding pad in unit time, and the unit time is the time required for drilling and removing one layer of bonding pad; and controlling the drill bit to back drill the through hole, when the drill bit contacts the board surface, forming a loop between the production board and the drill bit through two signal lines, recording the layer number of the line as a first layer by the control system, monitoring the resistance value change of the drill bit during back drilling, recording the line drilled on a second layer by the control system when the drill bit continues to drill and monitors that the resistance value change value in unit time is not less than a preset value, and repeating the steps.

Further, in step S1, the bonding pad of each layer is not connected to the inner layer circuit in the corresponding layer.

Further, in step S1, one surface of the production board is a back drilling surface on which a back drilling hole needs to be drilled, the other surface is a non-back drilling surface, the inner layer circuit drilled during back drilling is a drilled-through layer, and the inner layer circuit not drilled is a non-drilled-through layer, so that a pad with the same size is manufactured at a position corresponding to the back drilling hole when each drilled-through layer of the production board is manufactured; in step S4, when the production plate is fixed on the table top of the back drilling machine, the back drilling surface of the production plate is positioned at the uppermost side.

Further, in step S4, a presser foot which can move up and down and is abutted against the plate surface of the production plate is provided on the back drilling machine, and the signal line is communicated with the plate surface copper layer of the production plate through the presser foot.

Further, in step S4, a clip capable of being clipped on the board surface of the production board is provided on the back drilling machine, and the signal line is communicated with the board surface copper layer of the production board through the clip.

Further, in the step S3, a hole filling electroplating method is adopted for electroplating, only the thickness of the copper layer on the hole wall is increased, and the steps between the steps S3 and S4 further include the following steps:

s31, pasting a film on the production board, sequentially exposing and developing, forming a hole ring pattern arranged around the bonding pad on the back drilling surface of the production board corresponding to the periphery of the bonding pad, removing a copper layer on the hole ring pattern through etching, and finally removing the film to form the bonding pad with the same size as the bonding pad on the inner layer on the back drilling surface of the production board.

Further, in step S5, when the drill bit contacts the pad on the board surface, a loop is formed between the production board and the drill bit through two signal lines, and the resistance value change during back drilling of the drill bit is monitored, when the drill bit continues to drill down and the resistance value change value in unit time is monitored to be not less than a preset value, the control system records the line drilled through the first layer, and so on, and when the drill bit continues to drill down until the pad drilled through the preset number of layers is drilled, the control system receives a feedback signal of the corresponding number of layers drilled through and controls the drill bit to stop working, so as to complete back drilling of the through hole.

Further, in step S5, the preset resistance value R =4 ρ · T/(π D2 — π D2), where ρ is the resistivity, T is the thickness of the pad, D is the outer diameter of the pad, and D is the hole diameter of the non-metallized through hole or the hole diameter of the metallized through hole.

Further, in step S5, the unit time T = T/v, where T is the thickness of the pad and v is the drill-down speed of the drill.

In a second aspect, the present invention provides another processing method for realizing back drilling and stump shortening, comprising the following steps:

s10, providing a production plate with a plurality of inner-layer circuits, wherein the two surfaces of the production plate are copper surfaces, and a copper ring with the same thickness and size is manufactured on each circuit layer at the position corresponding to the back drilling hole when the inner-layer circuits of the production plate are manufactured;

s20, drilling a through hole on the production plate and drilling a through hole with the same diameter as the inner diameter of the copper ring at the position corresponding to the center of the copper ring so as to expose the inner circumferential surface of the copper ring on the inner wall of the through hole;

s30, metallizing the holes through copper deposition and full-board electroplating, and communicating the metallized through holes with the via holes through the board copper layer;

s40, fixing the production plate on a table board of a back drilling machine, leading out two signal wires which are respectively communicated with a control system of the back drilling machine from the back drilling machine, wherein the other end of one signal wire is communicated with a drill bit on the back drilling machine, the blade diameter of the drill bit is not less than the outer diameter of the bonding pad, and the other signal wire is communicated with a copper surface on the production plate;

s50, presetting the number of layers of line layers to be drilled through during back drilling of the drill bit and a preset resistance value change value in a control system of the back drilling machine, wherein the resistance value change value is the resistance value change value during each drilling and removing of one layer of copper ring in unit time, and the unit time is the time required for drilling and removing of one layer of copper ring; and controlling the drill bit to back drill the through hole, wherein when the drill bit contacts the board surface, a loop is formed between the production board and the drill bit through two signal lines, the control system records the number of layers of the circuit as a first layer and monitors the resistance value change of the drill bit during back drilling, when the drill bit continues to drill and monitors that the resistance value change value in unit time is not less than a preset value, the control system records that the circuit on a second layer is drilled, and so on, and when the drill bit continues to drill until a copper ring at the preset drilling layer number is drilled, the control system receives a feedback signal of the drilled corresponding number of layers and controls the drill bit to stop back drilling, thereby completing back drilling of the through hole.

Furthermore, the production board is a multilayer board formed by pressing an inner core board and an outer copper foil into a whole through a prepreg.

Compared with the prior art, the invention has the following beneficial effects:

in the method, a conducting loop is formed between a back drilling machine and a through hole needing back drilling, so that a resistance value on the loop can be detected and obtained by a control system on the back drilling machine, when a drill bit continuously drills and removes a hole wall copper layer and a bonding pad in the through hole, the resistance value on the loop is continuously changed, the resistance value of the bonding pad on each layer can be calculated (namely known) and used as a judged preset value, so that whether the bonding pad of a certain layer is drilled or not can be judged according to comparison between an actual resistance value change value on the loop and the preset value, in addition, in order to avoid the influence of the resistance value change caused by the hole wall copper layer, the time required for drilling and removing the bonding pad of the layer is used as a unit time, the resistance value change value in the unit time is compared with the preset value to be used as a basis for judging whether the bonding pad of the certain layer is drilled or not, the total number of layers drilled and removed can be recorded in the continuous drilling process, when the preset number of layers needing drilling and the preset layer is reached, the back drilling is stopped, the obtained stub length (stub) is the high-speed and high-speed control of the single-channel penetration of the single-board can be realized, and the high-speed transmission of the stub can be realized by the short-speed control of the single-layer.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

FIG. 1 is a schematic illustration of the plated plate of examples 1 and 3;

FIG. 2 is a schematic view of the production plate after being set in the back drilling machine in example 1;

FIG. 3 is a schematic representation of the production of backdrilling on boards in examples 1 and 3;

FIG. 4 is a schematic illustration of the plate after plating in example 2;

FIG. 5 is a schematic view of the production plate after being set in the back drilling machine in example 2;

FIG. 6 is a schematic illustration of backdrilling on production boards in examples 2 and 4;

FIG. 7 is a schematic view of example 3 after press-forming into a production sheet;

FIG. 8 is a schematic view of the production plate after being set in the back drilling machine in example 3;

fig. 9 is a schematic view of the production plate after being set in the back drilling machine in example 4.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

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

Example 1

The manufacturing method of the circuit board shown in this embodiment includes a manufacturing process of a back drilling hole, which can realize high-precision manufacturing of the back drilling hole and high-precision control of a stub, and by taking manufacturing of a ten-layer circuit board and drilling of the back drilling hole through seven layers of circuits as an example, the manufacturing method sequentially includes the following processing steps:

(1) Cutting: four core plates are cut according to the size of the jointed board of 520mm multiplied by 620mm, the thickness of each core plate is 0.5mm, and the thickness of copper layers on two surfaces of each core plate is 0.5oz.

(2) Inner layer circuit manufacturing (negative film process): transferring inner layer patterns, coating a photosensitive film on the core plates by using a vertical coating machine, controlling the film thickness of the photosensitive film to be 8 microns, completing inner layer line exposure by using 5-6 exposure rulers (21 exposure rulers) by using a full-automatic exposure machine, and forming inner layer line patterns after development, wherein the inner layer line patterns of the three core plates comprise pad patterns corresponding to the positions of back drilling holes, and the outer diameter of the pad patterns is less than or equal to the aperture of the back drilling holes; etching the inner layer, namely etching the exposed and developed core boards to form inner layer circuits and bonding pads, namely manufacturing bonding pads with the same size and thickness on two surfaces of three core boards, wherein the line width of the inner layer is 3mil; and (4) inner layer AOI, and then, detecting defects of an inner layer circuit, such as open short circuit, circuit notch, circuit pinhole and the like, and performing defect scrapping treatment, wherein a defect-free product is discharged to the next flow.

Preferably, in order to facilitate the detection of the change of the resistance value in the later period, the bonding pad of each layer is not communicated with the inner layer circuit in the corresponding layer, so that the change of the resistance value is only caused by the bonding pad when the bonding pad is drilled away, and the influence of the resistance value of the inner layer circuit is avoided.

(3) And (3) laminating: the method comprises the steps of conducting brown oxidation at a brown oxidation speed according to the thickness of bottom copper, sequentially overlapping four core plates, a prepreg and outer copper foils according to requirements, wherein three core plates with bonding pads are adjacently arranged during pressing, the thickness of the outer copper foil is preferably 0.5oz, then pressing the laminated plate according to the sheet Tg under proper lamination conditions to form a ten-layer production plate, wherein two surfaces of the production plate are copper surfaces, eight layers of inner-layer circuits are arranged inside the production plate, the surface, close to the inner-layer bonding pad, of the production plate is a back drilling surface needing back drilling, the other surface of the production plate is a non-back drilling surface, the inner-layer circuits drilled during back drilling from the back drilling surface are drilling layers, the copper surfaces at the back drilling surface also belong to one layer of drilling layers, namely seven layers from the back drilling surface are drilling layers from the back drilling surface, the rest of the inner-layer circuits not drilled are non-drilling layers, and the copper surfaces at the non-back drilling surface also belong to one layer of non-drilling layers.

(4) Drilling: according to the existing drilling technology, drilling processing is carried out on a production plate according to design requirements, so that a through hole for conducting an upper plate surface and a lower plate surface is drilled, a through hole with the diameter smaller than that of a bonding pad is drilled at the central position of the corresponding bonding pad, and the bonding pad is formed into a hole ring.

(5) Copper deposition: and depositing a layer of thin copper on the plate surface and the hole wall by using a chemical copper plating method, and testing the thickness of the deposited copper in the hole to be 0.5 mu m by a backlight test grade 10.

(6) Electroplating the whole plate: the thickness of the via copper and the plate surface copper layer was increased by performing full-plate electroplating at a current density of 18ASF for 60min, as shown in FIG. 1.

(7) Back drilling: the method specifically comprises the following steps:

a. as shown in fig. 2, firstly fixing the production board 1 on the table top of the back drilling machine, wherein the back drilling surface is positioned at the uppermost side and is used as a first circuit layer, the non-back drilling surface is positioned at the lowermost side and is used as a tenth circuit layer, two signal wires 3 which are respectively communicated with a control system are led out from the back drilling machine, namely one ends of the two signal wires are connected with the control system 2, and the other end of one signal wire is communicated with a drill bit on the back drilling machine, namely, the signal wires are electrically connected, of course, the connection relation cannot influence the rotation of the drill bit, the blade diameter of the drill bit is matched with the designed aperture of the back drilling hole, namely, the blade diameter of the drill bit is larger than or equal to the outer diameter of the pad, so that the pad at the inner layer can be removed during back drilling, the other signal wire 3 is communicated with the copper surface on the production board 1, namely, the copper surface is communicated with the drill bit through the conduction of the control system, but a loop is not formed initially; the control system of the back drilling machine is a servo control system.

Preferably, the back drilling machine is provided with a presser foot 4 which can move up and down and is abutted with the plate surface of the production plate 1, the signal wire 3 is communicated with the plate surface copper layer of the production plate 1 through the presser foot 4, and the connection is convenient and the back drilling machine has universality by utilizing the manner of the presser foot.

In one embodiment, a back-drill is provided with a clamp (not shown) that can clamp the board surface of the production board, and the signal line is communicated with the board surface copper layer of the production board through the clamp.

b. The method comprises the steps of presetting the number of layers of a circuit layer needing to be drilled through during back drilling of a drill bit in a control system of the back drilling machine to be seven layers and presetting a resistance value, wherein the resistance value is the resistance value when one layer of bonding pad is drilled out in unit time, and the unit time is the time required for drilling out one layer of bonding pad.

Preferably, the resistance of the pad itself formed in the annular ring structure can be calculated by a formula R =4 ρ · T/(π D2 — π D2), where ρ is the resistivity, T is the thickness of the pad, D is the outer diameter of the pad, and D is the aperture of the unmetallized via, and the calculated value is used as a preset resistance variation value; of course, in a specific other embodiment, in order to improve the detection accuracy, d may also be a via hole diameter after metallization, and the thickness of the hole wall copper layer is calculated together, but the hole wall copper layer is relatively thin and has a small resistance value, so that it is generally negligible in calculation.

Preferably, in order to avoid an error between the calculated value and the actual value, the inputted preset value may be set to a tolerance value of 5%, that is, the preset value may be generally smaller than the value calculated by the formula R =4 ρ · T/(π D2 — π D2) by 5%.

Preferably, the unit time T = T/v, where T is the thickness of the pad and v is the drill-down speed of the drill bit.

c. As shown in fig. 3, the drill bit 5 is controlled to back drill the through hole, when the drill bit contacts the board surface, a loop is formed between the production board and the drill bit through two signal lines and a copper layer on the production board, so that the change of the resistance value of the drill bit during back drilling is monitored, the control system records that the number of the line layers is the first layer, namely, the drill bit contacts the first layer of the line layer, because the first layer on the board surface is the whole copper surface, even if the connection between the copper surface and the copper layer on the hole wall is cut off during down drilling, the change of the resistance value is slight, whether the first layer is drilled through or not is not identified, only the first layer is marked as the first layer drilled through when the loop is initially contacted and formed, the first layer is necessarily drilled through during the down drilling, and then whether the second layer is drilled through is directly monitored by detecting the change of the resistance value when the bonding pad 6 is drilled out; and when the drill bit continues to drill downwards and monitors that the resistance value change value in unit time is not less than the preset value, the control system records the line drilled through the second layer, and by analogy, when the drill bit continues to drill downwards, the drill bit can sequentially identify the drilling through of the third layer and the fourth layer until the welding pad at the seventh layer of the preset drilling through layer is drilled out, the control system receives the feedback signal of the corresponding layer drilled through layer and controls the drill bit to stop back drilling and quit, and the back drilling of the through hole is completed.

In the above, the back drilling machine may select a schmoll drilling machine, a constant voltage U is provided to a loop formed during back drilling of the drill bit by a control system on the back drilling machine, a resistance value on the loop is constantly changed during back drilling of the drill bit, so that a current I on the loop is also constantly changed, the schmoll drilling machine may monitor a specific change of the current on the loop, and under the condition that the voltage is not changed, a real-time resistance value R = voltage U/current I is calculated by the schmoll drilling machine, so that whether to drill through the pad of the inner layer may be determined according to a change value of the resistance value in unit time; of course, the constant voltage U is typically provided at 12-24V.

(8) Manufacturing an outer layer circuit (positive film process): transferring an outer layer pattern, completing outer layer line exposure by using a full-automatic exposure machine and a positive film line film with 5-7 exposure rulers (21 exposure rulers), and forming an outer layer line pattern on a production board through development; electroplating an outer layer pattern, then respectively plating copper and plating tin on the production plate, setting electroplating parameters according to the required finished copper thickness, wherein the copper plating is carried out for 60min in a full-plate electroplating way at the current density of 1.8ASD, and the plating tin is carried out for 10min at the current density of 1.2ASD, and the tin thickness is 3-5 mu m; then sequentially removing the film, etching and removing tin, and etching an outer layer circuit on the production board, wherein the copper thickness of the outer layer circuit is more than or equal to 70 mu m; and the outer layer AOI uses an automatic optical detection system to detect whether the outer layer circuit has the defects of open circuit, gap, incomplete etching, short circuit and the like by comparing with CAM data.

(9) Solder resist and silk screen characters: after the solder resist ink is printed on the surface of the production board in a silk-screen manner, the solder resist ink is cured into a solder resist layer through pre-curing, exposure, development and thermocuring treatment in sequence; specifically, solder resist ink is coated on the TOP surface, and UL marks are added to the TOP surface characters, so that a protective layer which prevents bridging between circuits during welding and provides a permanent electrical environment and chemical corrosion resistance is coated on the circuits and the base materials which do not need to be welded, and meanwhile, the effect of beautifying the appearance is achieved; the manufacturing process of the solder mask layer comprises the following steps:

(10) Surface treatment (nickel-gold deposition): the copper surface of the welding pad at the solder stop windowing position is communicated with a chemical principle, a nickel layer and a gold layer with certain required thickness are uniformly deposited, and the thickness of the nickel layer is as follows: 3-5 μm; the thickness of the gold layer is as follows: 0.05-0.1 μm.

(11) Electrical testing: the electric conduction performance of the finished board is tested, and the board use test method comprises the following steps: and (5) flying probe testing.

(12) Molding: according to the prior art and according to the design requirement, routing the shape, and obtaining the circuit board with the tolerance of +/-0.05 mm.

(13) FQC: according to the customer acceptance standard and the inspection standard of my department, the appearance of the circuit board is inspected, if a defect exists, the circuit board is repaired in time, and the excellent quality control is guaranteed to be provided for the customer.

(14) FQA: and (5) measuring whether the appearance, the hole copper thickness, the dielectric layer thickness, the green oil thickness, the inner layer copper thickness and the like of the circuit board meet the requirements of customers or not again.

(15) And (3) packaging: and hermetically packaging the circuit boards according to the packaging mode and the packaging quantity required by customers, putting a drying agent and a humidity card, and then delivering.

Example 2

The method for manufacturing a circuit board shown in this embodiment is substantially the same as that in embodiment 1, except that step (6) and step (7) and step (61) are added between steps (6) and (7), and the specific steps are as follows:

(6) Hole filling and electroplating: and electroplating by adopting a hole filling electroplating mode, wherein the thickness of the hole wall copper layer is only increased, namely after the film is pasted on the production board, the through hole is only exposed through exposure and development, and the board surface copper layer is covered and protected, so that the board surface copper thickness is basically consistent with the thickness of the inner layer of the bonding pad.

(61) Manufacturing an outer layer bonding pad: the method comprises the steps of pasting a film on a production board, sequentially carrying out exposure and development, forming a hole ring graph arranged around a bonding pad on the back drilling surface of the production board corresponding to the periphery of the bonding pad, wherein the back drilling surface is not fully exposed and is protected by the whole surface, removing a copper layer on the hole ring graph through etching, finally removing the film, forming a bonding pad with the same size as that of an inner bonding pad on the back drilling surface of the production board as an outer bonding pad, and isolating the bonding pad from a board surface copper layer, so that the first layer drilled through can be identified when the back drilling hole is removed in the later period, a drill bit is isolated from the copper surface on the back drilling surface, a communicated loop can be communicated with the back drilling surface copper layer only through the copper layer on a through hole and a through hole sequentially, and is communicated with a signal line to form a serial communication loop, namely the outer bonding pad and the inner bonding pad are sequentially connected in series on the loop, and the change of the resistance value can be conveniently calculated and monitored.

(7) Back drilling: the method specifically comprises the following steps:

a. as shown in fig. 5, firstly fixing the production board 1 on the table top of the back drilling machine, wherein the back drilling surface is located at the uppermost side and serves as a first circuit layer, the non-back drilling surface is located at the lowermost side and serves as a tenth circuit layer, two signal wires 3 which are respectively communicated with the control system 2 are led out from the back drilling machine, namely one ends of the two signal wires are connected with the control system 2, and the other end of one signal wire is communicated with the drill bit on the back drilling machine, namely, the signal wires are electrically connected, of course, the connection relation cannot influence the rotation of the drill bit, the blade diameter of the drill bit is matched with the designed aperture of the back drilling hole, namely, the blade diameter of the drill bit is larger than or equal to the outer diameter of the pad, so that the pad at the inner layer can be removed during back drilling, the other signal wire 3 is communicated with the copper surface on the production board 1, namely, the copper surface is communicated with the drill bit through the conduction of the control system, but a loop is not formed initially; the control system of the back drilling machine is a servo control system.

Preferably, the back drilling machine is provided with a presser foot 4 which can move up and down and is abutted with the plate surface of the production plate 1, the signal wire 3 is communicated with the plate surface copper layer of the production plate 1 through the presser foot 4, and the connection is convenient and the back drilling machine has universality by utilizing the manner of the presser foot.

In one embodiment, a back-drill is provided with a clamp (not shown) that can clamp the board surface of the production board, and the signal line is communicated with the board surface copper layer of the production board through the clamp.

b. The method comprises the steps of presetting the number of layers of a circuit layer needing to be drilled through during back drilling of a drill bit in a control system of the back drilling machine to be seven layers and presetting a resistance value, wherein the resistance value is the resistance value when one layer of bonding pad is drilled out in unit time, and the unit time is the time required for drilling out one layer of bonding pad.

Preferably, the resistance value of the pad formed in the annular-hole structure can be calculated by a formula R =4 ρ · T/(π D2 — π D2), where ρ is the resistivity, T is the thickness of the pad, D is the outer diameter of the pad in the inner layer, and D is the diameter of the unmetallized via hole, and the calculated value is used as a preset resistance value change value; of course, in a specific other embodiment, in order to improve the detection accuracy, d may also be a via hole diameter after metallization, and the thickness of the hole wall copper layer is calculated together, but the hole wall copper layer is relatively thin and has a small resistance value, so that it is generally negligible in calculation.

Preferably, in order to avoid an error between the calculated value and the actual value, the inputted preset value may be set to a tolerance value of 5%, that is, the preset value may be generally smaller than the value calculated by the formula R =4 ρ · T/(π D2 — π D2) by 5%.

Preferably, the unit time T = T/v, where T is the thickness of the pad and v is the drill-down speed of the drill.

c. As shown in fig. 6, the drill bit 5 is controlled to back drill the through hole, when the drill bit contacts the outer layer pad at the through hole, a loop is formed between the production board and the drill bit through two signal lines and the copper layer on the production board, so as to monitor the resistance value change during back drilling of the drill bit, when the drill bit continues to drill and monitors that the resistance value change value in unit time is larger than or equal to a preset value, the control system records the circuit drilled through the first layer, and so on, when the drill bit continues to drill downwards, the drill bit can sequentially identify the drilling through of the third layer and the fourth layer until the drill bit drills off the pad 6 at the seventh layer with the preset drilling layer number, the control system receives the feedback signal drilled through the preset corresponding layer number and controls the drill bit to stop back drilling and exit, and the back drilling of the through hole is completed.

Example 3

The manufacturing method of the circuit board shown in this embodiment includes a manufacturing process of back drilling, which can achieve high-precision manufacturing of back drilling holes and high-precision control of short piles, and includes the following processing steps in sequence, taking manufacturing of a ten-layer circuit board and drilling of back drilling holes through seven layers of circuits as an example:

(1) Cutting: four core plates are cut according to the size of the jointed board of 520mm multiplied by 620mm, the thickness of each core plate is 0.5mm, and the thickness of copper layers on two surfaces of each core plate is 0.5oz.

(2) Inner layer circuit manufacturing (negative film process): transferring inner layer patterns, coating photosensitive films on core plates by using a vertical coating machine, controlling the film thickness of the photosensitive films to be 8 mu m, completing inner layer circuit exposure by using 5-6 grids of exposure rulers (21 grids of exposure rulers) by using a full-automatic exposure machine, and forming inner layer circuit patterns after development, wherein the inner layer circuit patterns of three core plates comprise hole ring patterns corresponding to the positions of back drilling holes, the outer diameters of the hole ring patterns are less than or equal to the apertures of the back drilling holes, and the inner diameters of the hole ring patterns are equal to the apertures of small holes (namely through holes) in the back drilling holes; etching the inner layer, namely etching the exposed and developed core plates to form an inner layer circuit and a copper ring, namely manufacturing the copper rings with the same size and thickness on two surfaces of three core plates, wherein the line width of the inner layer is measured to be 3mil; and (4) inner layer AOI, and then, detecting defects of an inner layer circuit, such as open short circuit, circuit notch, circuit pinhole and the like, and performing defect scrapping treatment, wherein a defect-free product is discharged to the next flow.

Preferably, in order to facilitate the detection of the change of the resistance value in the later period, the copper ring of each layer is not communicated with the inner layer circuit in the corresponding layer, so that the change of the resistance value is only caused by the bonding pad when the bonding pad is drilled away, and the influence of the resistance value of the inner layer circuit is avoided.

(3) And (3) laminating: the browning speed is brown according to the thickness of bottom copper, four core plates, a prepreg and outer copper foils are sequentially laminated according to requirements, wherein three core plates with copper rings 7 are adjacently arranged during lamination, the thickness of the outer copper foil is preferably 0.5oz, then the laminated plate is laminated according to the sheet Tg under proper lamination conditions to form a ten-layer production plate (shown in figure 7), two surfaces of the production plate are copper surfaces, eight layers of inner layer circuits are arranged inside the production plate, the surface of the production plate close to the inner copper rings is a back drilling surface needing back drilling, the other surface of the production plate is a non-back drilling surface, the inner layer circuits drilled during back drilling from the back drilling surface are drilling layers, the copper surfaces at the back drilling surface also belong to one drilling layer, namely, from the design requirement of the back drilling seven layers, seven layers from the back drilling surface to the bottom are drilling layers, the rest of the inner layer circuits not drilled are non-drilling layers, and the copper surfaces at the non-back drilling surface also belong to one non-drilling layer.

(4) Drilling: according to the existing drilling technology, drilling machining is carried out on a production plate according to design requirements, so that a through hole for conducting an upper plate surface and a lower plate surface is drilled, and a through hole with the same diameter as the inner diameter of a copper ring is drilled at the position corresponding to the center of the copper ring.

(5) Copper deposition: and depositing a layer of thin copper on the plate surface and the hole wall by using a chemical copper plating method, testing the backlight to 10 grades, wherein the thickness of the deposited copper in the hole is 0.5 mu m, and the hole wall copper layer in the through hole is communicated with the copper ring.

(6) Electroplating the whole plate: the thickness of the hole copper and the plate surface copper layer is increased by performing full-plate electroplating for 60min at a current density of 18ASF, and the specific structure is also shown in FIG. 1.

(7) Back drilling: the method specifically comprises the following steps:

a. as shown in fig. 8, firstly fixing the production board 1 on the table top of the back drilling machine, wherein the back drilling surface is located at the uppermost side and serves as a first circuit layer, the non-back drilling surface is located at the lowermost side and serves as a tenth circuit layer, two signal wires 3 which are respectively communicated with the control system are led out from the back drilling machine, namely, one ends of the two signal wires are connected with the control system 2, and the other end of one signal wire is communicated with the drill bit on the back drilling machine, namely, the signal wires are electrically connected, of course, the connection relation cannot influence the rotation of the drill bit, the blade diameter of the drill bit is matched with the designed aperture of the back drilling hole, namely, the blade diameter of the drill bit is larger than or equal to the outer diameter of the copper ring, so that the inner copper ring can be removed during back drilling, the other signal wire 3 is communicated with the copper surface on the production board 1, namely, the communication between the copper surface and the drill bit is formed through the conduction of the control system, but a loop is not formed initially; the control system of the back drilling machine is a servo control system.

Preferably, the back drilling machine is provided with a presser foot 4 which can move up and down and is abutted with the plate surface of the production plate 1, the signal wire 3 is communicated with the plate surface copper layer of the production plate 1 through the presser foot 4, and the connection is convenient and the back drilling machine has universality by utilizing the manner of the presser foot.

In one embodiment, a back-drill is provided with a clamp (not shown) that can clamp the board surface of the production board, and the signal line is communicated with the board surface copper layer of the production board through the clamp.

b. The method comprises the steps of presetting the number of layers of a circuit layer needing to be drilled through during back drilling of a drill bit in a control system of a back drilling machine to be seven layers and presetting a resistance value, wherein the resistance value is the resistance value when a layer of copper ring is drilled out in unit time, and the unit time is the time required for drilling out a layer of copper ring.

Preferably, the resistance value of the copper ring itself can be calculated by a formula R =4 ρ · T/(π D2 — π D2), where ρ is the resistivity, T is the thickness of the copper ring, D is the outer diameter of the copper ring, D is the aperture of the non-metallized through hole, and the calculated value is used as the preset resistance value change value; of course, in a specific other embodiment, in order to improve the detection accuracy, d may also be a via hole diameter after metallization, and the thickness of the hole wall copper layer is calculated together, but the hole wall copper layer is relatively thin and has a small resistance value, so that it is generally negligible in calculation.

Preferably, in order to avoid an error between the calculated value and the actual value, the inputted preset value may be set to a tolerance value of 5%, that is, the preset value may be generally smaller than the value calculated by the formula R =4 ρ · T/(π D2 — π D2) by 5%.

Preferably, the unit time T = T/v, where T is the thickness of the copper ring and v is the drill-down speed of the drill bit.

c. As shown in fig. 3, the drill bit 5 is controlled to back drill the through hole, when the drill bit contacts the board surface, a loop is formed between the production board and the drill bit through two signal lines and the copper layer on the production board, so that the resistance value change during back drilling of the drill bit is monitored, the control system records the number of the circuit layers as a first layer, namely, the drill bit contacts the first circuit layer, because the first layer on the board surface is a whole copper surface, even if the connection between the copper surface and the copper layer on the hole wall is cut off during down drilling, the resistance value change is very small, so that whether the first layer is drilled through or not is not identified, only the first layer is marked as drilled through when the loop is initially contacted and formed, the first layer is drilled through inevitably during down drilling, and then whether the second layer is drilled through or not is directly monitored by detecting the resistance value change during drilling of removing the copper ring 7; and when the drill bit continues to drill downwards and monitors that the resistance value change value in unit time is not less than the preset value, the control system records the line drilled through the second layer, and by analogy, when the drill bit continues to drill downwards, the drill bit can sequentially identify the drilling through of the third layer and the fourth layer until the copper ring at the seventh layer of the preset drilling through layer is drilled out, the control system receives the feedback signal of the corresponding layer of the drilled through layer and controls the drill bit to stop back drilling and quit, and the back drilling of the through hole is completed.

In the above, the back drilling machine may select a schmoll drilling machine, a constant voltage U is provided to a loop formed during back drilling of the drill bit by a control system on the back drilling machine, when the drill bit is back drilling, a resistance value on the loop is constantly changed, so that a current I on the loop is also constantly changed, the schmoll drilling machine may monitor a specific change of the current on the loop, and under the condition that the voltage is not changed, a real-time resistance value R = voltage U/current I is calculated by using the constant voltage, a resistance value change value in a unit time can be obtained, and further, whether a certain layer of circuit layer is drilled is determined by the change value of the resistance value; of course, the constant voltage U is typically provided at 12-24V.

(8) Manufacturing an outer layer circuit (positive film process): transferring an outer layer pattern, completing the exposure of the outer layer pattern by using a full-automatic exposure machine and a positive film line film with 5-7 grids of exposure rulers (21 grids of exposure rulers), and forming an outer layer pattern on a production board through development; electroplating an outer layer pattern, then respectively plating copper and plating tin on the production plate, setting electroplating parameters according to the required finished copper thickness, wherein the copper plating is carried out for 60min in a full-plate electroplating way at the current density of 1.8ASD, and the plating tin is carried out for 10min at the current density of 1.2ASD, and the tin thickness is 3-5 mu m; then sequentially removing the film, etching and removing tin, and etching an outer layer circuit on the production board, wherein the copper thickness of the outer layer circuit is more than or equal to 70 mu m; and the outer layer AOI uses an automatic optical detection system to detect whether the outer layer circuit has the defects of open circuit, gap, incomplete etching, short circuit and the like by comparing with CAM data.

(9) Solder resist and silk screen printing of characters: after the solder resist ink is printed on the surface of the production board in a silk-screen manner, the solder resist ink is cured into a solder resist layer through pre-curing, exposure, development and thermocuring treatment in sequence; specifically, solder resist ink is coated on the TOP surface, and UL marks are added to the TOP surface characters, so that a protective layer which prevents bridging between circuits during welding and provides a permanent electrical environment and chemical corrosion resistance is coated on the circuits and the base materials which do not need to be welded, and meanwhile, the effect of beautifying the appearance is achieved; the manufacturing process of the solder mask layer comprises the following steps:

(10) Surface treatment (nickel-gold deposition): the chemical principle is applied to a copper surface of a welding pad of a welding-resistant window opening position, a nickel layer and a gold layer with certain required thickness are uniformly deposited, and the thickness of the nickel layer is as follows: 3-5 μm; the thickness of the gold layer is as follows: 0.05-0.1 μm.

(11) Electrical testing: the electric conduction performance of the finished board is tested, and the board use test method comprises the following steps: and (5) flying probe testing.

(12) Molding: according to the prior art and according to the design requirement, routing the shape, and obtaining the circuit board with the tolerance of +/-0.05 mm.

(13) FQC: according to the customer acceptance standard and the inspection standard of my department, the appearance of the circuit board is inspected, if a defect exists, the circuit board is repaired in time, and the excellent quality control is guaranteed to be provided for the customer.

(14) FQA: and (5) measuring whether the appearance, the hole copper thickness, the dielectric layer thickness, the green oil thickness, the inner layer copper thickness and the like of the circuit board meet the requirements of customers or not.

(15) Packaging: and hermetically packaging the circuit boards according to the packaging mode and the packaging quantity required by customers, putting a drying agent and a humidity card, and then delivering.

Compared with the embodiments 1 and 2, the copper ring is directly formed on the inner layer, so that the difficulty of later-stage through hole drilling can be reduced, and the loss of the drill bit during through hole drilling is reduced.

Example 4

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

(6) Hole filling and electroplating: and electroplating by adopting a hole filling electroplating mode, wherein the thickness of the hole wall copper layer is only increased, namely after the film is pasted on the production board, the through hole is only exposed through exposure and development, and the board surface copper layer is covered and protected, so that the thickness of the board surface copper layer is basically consistent with that of the inner-layer bonding pad.

(61) Manufacturing an outer-layer copper ring: the method comprises the steps of pasting a film on a production board, sequentially exposing and developing, forming a hole ring graph arranged around a welding pad on the back drilling surface of the production board corresponding to the periphery of the welding pad, fully exposing the non-back drilling surface and protecting the whole surface, removing a copper layer at the position of the hole ring graph by etching, finally removing the film, forming a copper ring (the specific structure can be shown in figure 4) with the same outer diameter as that of the copper ring of an inner layer on the back drilling surface of the production board to serve as an outer copper ring, and forming isolation between the copper ring and a copper layer of a board surface, so that a first drilled hole can be identified when the back drilling hole is drilled later, a drill bit is isolated from the copper surface on the back drilling surface, and a communicated loop can be communicated with the copper layer of the back drilling surface sequentially through a through hole and the copper layer on a through hole and is further communicated with a signal wire to form a serially connected communicated loop, namely the outer copper ring and the inner copper ring are sequentially connected in series on the loop, and the change of the resistance value can be conveniently calculated and monitored.

(7) Back drilling: the method specifically comprises the following steps:

a. as shown in fig. 9, firstly fixing the production board 1 on the table top of the back drilling machine, wherein the back drilling surface is located at the uppermost side and serves as a first circuit layer, the non-back drilling surface is located at the lowermost side and serves as a tenth circuit layer, two signal wires 3 which are respectively communicated with a control system are led out from the back drilling machine, namely one ends of the two signal wires are connected with the control system 2, and the other end of one signal wire is communicated with a drill bit on the back drilling machine, namely, the signal wires are electrically connected, of course, the connection relation cannot influence the rotation of the drill bit, the blade diameter of the drill bit is matched with the designed aperture of the back drilling hole, namely, the blade diameter of the drill bit is larger than or equal to the outer diameter of the copper ring, so that the inner copper ring can be removed during back drilling, and the other signal wire 3 is communicated with the copper surface on the production board 1, namely, through the conduction of the control system, the conduction between the copper surface and the drill bit is formed without a loop initially; the control system of the back drilling machine is a servo control system.

Preferably, the back drilling machine is provided with a presser foot 4 which can move up and down and is abutted with the plate surface of the production plate 1, the signal wire 3 is communicated with the plate surface copper layer of the production plate 1 through the presser foot 4, and the connection is convenient and the back drilling machine has universality by utilizing the manner of the presser foot.

In one embodiment, a back-drill is provided with a clamp (not shown) that can clamp the board surface of the production board, and the signal line is communicated with the board surface copper layer of the production board through the clamp.

b. The method comprises the steps of presetting the number of layers of a circuit layer needing to be drilled through during back drilling of a drill bit in a control system of a back drilling machine to be seven layers and presetting a resistance value, wherein the resistance value is the resistance value when a layer of copper ring is drilled out in unit time, and the unit time is the time required for drilling out a layer of copper ring.

Preferably, the resistance of the copper ring formed into the ring-hole structure can be calculated by the formula R =4 ρ · T/(pi D2-pi D2), where ρ is the resistivity, T is the thickness of the copper ring, D is the outer diameter of the copper ring in the inner layer, and D is the diameter of the unmetallized through hole, and the calculated value is used as the preset resistance change value; of course, in a specific other embodiment, in order to improve the detection accuracy, d may also be a via hole diameter after metallization, and the thickness of the hole wall copper layer is calculated together, but the hole wall copper layer is relatively thin and has a small resistance value, so that it is generally negligible in calculation.

Preferably, in order to avoid an error between the calculated value and the actual value, the inputted preset value may be set to a tolerance value of 5%, that is, the preset value may be generally smaller than the value calculated by the formula R =4 ρ · T/(π D2 — π D2) by 5%.

Preferably, the unit time T = T/v, where T is the thickness of the copper ring and v is the drill-down speed of the drill bit.

c. As shown in fig. 6, the drill bit 5 is controlled to back drill the through hole, when the drill bit contacts the outer copper ring at the through hole, a loop is formed between the production board and the drill bit through two signal lines and the copper layer on the production board, so as to monitor the resistance value change during back drilling of the drill bit, when the drill bit continues to drill and monitors that the resistance value change value in unit time is larger than or equal to a preset value, the control system records the circuit drilled through the first layer, and so on, when the drill bit continues to drill downwards, the drill bit can sequentially identify the drilling through of the third layer and the fourth layer until the copper ring at the seventh layer of the preset drilling through layer is drilled, the control system receives the feedback signal of the corresponding layer number drilled through and controls the drill bit to stop back drilling and exit, and the back drilling of the through hole is completed.

In fig. 1 to 9, the thick lines on the circuit board are copper layers.

The technical solutions provided by the embodiments of the present invention are described in detail above, and the principles and embodiments of the present invention are explained herein by using specific examples, and the descriptions of the embodiments are only used to help understanding the principles of the embodiments of the present invention; meanwhile, for a person skilled in the art, according to the embodiments of the present invention, the specific implementation manners and the application ranges may be changed, and in conclusion, the content of the present specification should not be construed as limiting the invention.

Claims (10)

1. A processing method for realizing back drilling and stub shortening is characterized by comprising the following steps:

s1, providing a production board with a plurality of inner-layer circuits, wherein both surfaces of the production board are copper surfaces, and a bonding pad with the same thickness and size is manufactured on each circuit layer at the position corresponding to a back drilling hole when the inner-layer circuits of the production board are manufactured;

s2, drilling a via hole on the production board and drilling a through hole with the aperture smaller than that of the bonding pad at the central position of the corresponding bonding pad;

s3, metallizing the holes through copper deposition and electroplating, and communicating the metallized through holes with the via holes through the board copper layer;

s4, fixing the production plate on the table board of the back drilling machine, leading out two signal wires which are respectively communicated with a control system of the back drilling machine on the back drilling machine, wherein the other end of one signal wire is communicated with a drill bit on the back drilling machine, the blade diameter of the drill bit is not less than the outer diameter of the bonding pad, and the other signal wire is communicated with the copper surface on the production plate;

s5, presetting the number of layers of the line layer to be drilled through during back drilling of the drill bit and a preset resistance value change value in a control system of the back drilling machine, wherein the resistance value change value is the resistance value change value of each layer of bonding pad drilled and removed in unit time, and the unit time is the time required for drilling and removing one layer of bonding pad; and controlling the drill bit to back drill the through hole, wherein when the drill bit contacts the board surface, a loop is formed between the production board and the drill bit through two signal lines, the control system records the number of layers of the circuit as a first layer and monitors the resistance value change of the drill bit during back drilling, when the drill bit continues to drill and monitors that the resistance value change value in unit time is not less than a preset value, the control system records that the circuit of a second layer is drilled, and so on, and when the drill bit continues to drill until the welding pads at the preset drilling layer number are drilled, the control system receives a feedback signal of the drilled corresponding number of layers and controls the drill bit to stop back drilling, thereby completing the back drilling of the through hole.

2. The processing method of claim 1, wherein in step S1, the bonding pads of each layer are not connected to the inner layer circuit of the corresponding layer.

3. The processing method of claim 1, wherein in step S1, one surface of the production board is a back drilling surface on which a back drilling hole is to be drilled, the other surface is a non-back drilling surface, the inner layer circuit drilled during back drilling is a drilled-through layer, and the inner layer circuit not drilled through is a non-drilled-through layer, so as to fabricate each drilled-through layer of the production board by fabricating a pad with the same size at a position corresponding to the back drilling hole; and S4, when the production plate is fixed on the table board of the back drilling machine, the back drilling surface of the production plate is positioned at the uppermost side.

4. The processing method of claim 1, wherein in step S4, a press foot is provided on the back drill to be movable up and down and to be brought into contact with the surface of the production board, and the signal line is connected to the surface copper layer of the production board through the press foot.

5. The processing method of claim 1, wherein in step S4, a clip capable of being clipped on the surface of the production board is provided on the back drilling machine, and the signal line is connected to the copper layer on the surface of the production board through the clip.

6. The processing method of claim 1, wherein the step S3 is performed by hole-filling electroplating, only the thickness of the copper layer on the hole wall is increased, and the steps between S3 and S4 further comprise the following steps:

s31, pasting a film on the production board, sequentially exposing and developing, forming a hole ring pattern arranged around the bonding pad on the back drilling surface of the production board corresponding to the periphery of the bonding pad, removing a copper layer on the hole ring pattern through etching, and finally removing the film to form the bonding pad with the same size as the bonding pad on the inner layer on the back drilling surface of the production board.

7. The processing method for realizing back drilling and stub shortening as claimed in claim 6, wherein in step S5, when the drill bit contacts the pad on the board surface, a loop is formed between the production board and the drill bit through two signal lines, and the resistance change during back drilling of the drill bit is monitored, when the drill bit continues to drill down and the resistance change value per unit time is monitored to be greater than or equal to a preset value, the control system records the line drilled through the first layer, and so on, and when the drill bit continues to drill down until the pad drilled through the preset number of layers is drilled, the control system receives the feedback signal of the number of layers drilled through and controls the drill bit to stop working, thereby completing the back drilling of the through hole.

8. The method as claimed in claim 1, wherein in step S5, the predetermined resistance value R =4 ρ · T/(π D2 — π D2), where ρ is the resistivity, T is the thickness of the bonding pad, D is the outer diameter of the bonding pad, and D is the hole diameter of the non-metallized through hole or the hole diameter of the metallized through hole.

9. The method as claimed in claim 1, wherein in step S5, the unit time T = T/v, where T is the thickness of the bonding pad and v is the drilling speed of the drill.

10. A processing method for realizing back drilling and stub shortening is characterized by comprising the following steps:

s10, providing a production plate with a plurality of inner-layer circuits, wherein the two surfaces of the production plate are copper surfaces, and a copper ring with the same thickness and size is manufactured on each circuit layer at the position corresponding to the back drilling hole when the inner-layer circuits of the production plate are manufactured;

s20, drilling a through hole on the production plate and drilling a through hole with the same diameter as the inner diameter of the copper ring at the position corresponding to the center of the copper ring so as to expose the inner circumferential surface of the copper ring on the inner wall of the through hole;

s30, metallizing the holes through copper deposition and full-board electroplating, and communicating the metallized through holes with the via holes through a board copper layer;

s40, fixing the production plate on the table board of a back drilling machine, leading out two signal wires which are respectively communicated to a control system of the back drilling machine on the back drilling machine, wherein the other end of one signal wire is communicated with a drill bit on the back drilling machine, the blade diameter of the drill bit is not less than the outer diameter of a bonding pad, and the other signal wire is communicated with a copper surface on the production plate;

s50, presetting the number of layers of line layers to be drilled through during back drilling of the drill bit and a preset resistance value change value in a control system of the back drilling machine, wherein the resistance value change value is the resistance value change value during each drilling and removing of one layer of copper ring in unit time, and the unit time is the time required for drilling and removing of one layer of copper ring; and controlling the drill bit to back drill the through hole, when the drill bit contacts the board surface, forming a loop between the production board and the drill bit through two signal lines, recording the layer number of the line as a first layer by the control system, monitoring the resistance value change of the drill bit during back drilling, recording the line drilled on a second layer by the control system when the drill bit continues to drill and monitors that the resistance value change value in unit time is not less than a preset value, and repeating the steps.

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