CN115589674A

CN115589674A - Manufacturing method for realizing high-precision back drilling and short pile

Info

Publication number: CN115589674A
Application number: CN202211260312.7A
Authority: CN
Inventors: 袁为群; 姜雪飞; 邹金龙; 冯涛
Original assignee: Shenzhen Suntak Multilayer PCB Co Ltd
Current assignee: Shenzhen Suntak Multilayer PCB Co Ltd
Priority date: 2022-10-14
Filing date: 2022-10-14
Publication date: 2023-01-10

Abstract

The invention discloses a method for realizing high-precision back drilling and a short pile, which is characterized in that a conduction loop is formed between a back drilling machine and a detection hole to be back drilled, so that a control system on the back drilling machine can be used for detecting and obtaining a resistance value on the loop, when a drill bit continuously drills down to break the connection between a plate surface copper layer and a hole wall copper layer, the instantaneous resistance value is one time or more than one time larger than that before drilling, and is marked as a reference zero point of the back drilling, when the drill bit continuously drills down and breaks the connection between a lead and the hole copper, the instantaneous resistance value is also one time or more than that before drilling, and is marked as an end point of the back drilling, and the back drilling depth from the reference zero point to the end point can be obtained, the back drilling depth mean value of all detection holes is obtained through calculation, and the obtained back drilling depth mean value plus a compensation value is used as the actual back drilling depth of a back drilling hole in a production plate to carry out back drilling, so that the influence of factors such as plate thickness tolerance during back drilling can be greatly reduced, and the high-precision back drilling and the requirement that the short pile is as small as possible can be met.

Description

Manufacturing method for realizing high-precision back drilling and short pile

Technical Field

The invention relates to the technical field of printed circuit board manufacturing, in particular to a manufacturing method for realizing high-precision back drilling and short piles.

Background

With the continuous improvement of the integration level of electronic systems, the circuit boards are more and more integrated and functionalized, so that the design density of the PCB is higher and higher, and the application of high-speed interconnection is more and more, and the requirements on high-speed signals of products are higher and higher, 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 the plate thickness is confirmed by slicing only for the first piece and is partial, so that 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

Aiming at the defects of the prior art, the invention provides a method for realizing high-precision back drilling and manufacturing of a stub.

In order to solve the above technical problems, the present invention provides a method for implementing high-precision back drilling and short pile manufacturing, including the following steps:

s1, providing a production board with a plurality of inner layer circuits, wherein two surfaces of the production board are copper surfaces, one surface of the production board is a back drilling surface, the other surface of the production board is a non-back drilling surface, the bottommost inner layer circuit drilled during back drilling is a drilled-through layer, and the inner layer circuit which is adjacent to the drilled-through layer and is not drilled through during back drilling is a non-drilled-through layer; a plurality of drilling positions are arranged on the plate edge and/or the non-line area of the drilling layer of the production plate, and a lead for communicating the circuit in the plate with the drilling positions is also manufactured on the drilling layer, wherein the drilling positions are positions needing drilling in subsequent processing;

s2, drilling a through hole on the production plate and drilling a detection hole at a position vertical to each drilling position;

s3, metallizing the holes through copper deposition and electroplating, wherein the metallized via holes are communicated with in-board circuits in the drilled layer, and the metallized detection holes are communicated with wires in the drilled layer so as to communicate the via holes with the detection holes;

s4, fixing the production plate on a table board of a back drilling machine, wherein the back drilling surface is arranged upwards; two signal wires which are respectively communicated with a control system of the back drilling machine are led out from the back drilling machine, 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 larger than the aperture of the detection hole, and the other signal wire is communicated with a copper surface on the production plate;

s5, controlling the drill bit to back drill the detection holes one by one, forming a loop between the production board and the drill bit through two signal lines when the drill bit contacts the board surface, monitoring the resistance value change of the drill bit during back drilling, marking as a reference zero point of the back drilling when the drill bit continues to drill and the resistance value is instantly increased by one time or more for the first time, marking as an end point of the back drilling when the drill bit continues to drill until the resistance value is instantly increased by one time or more for the second time, and so on, obtaining the back drilling depth of each detection hole from the reference zero point to the end point, and calculating to obtain the back drilling depth mean value of all the detection holes;

and S6, back drilling is carried out by taking the mode of adding the compensation value to the mean value of the back drilling depth obtained in the step S5 as the actual back drilling depth of the back drilling hole in the production plate, wherein the compensation value is not more than 50% of the designed value of the thickness of the medium between the drilling-through layer and the non-drilling-through layer.

Further, in the step S1, a bonding pad or a copper ring with the outer diameter larger than that of the drilling position is manufactured at the drilling position, and the wire is communicated with the bonding pad or the copper ring; in step S2, the aperture of the inspection hole is smaller than the outer diameter of the pad or equal to the inner diameter of the copper ring, so as to expose the pad or the copper ring on the hole wall of the inspection hole.

Further, in the step S1, the production plate is divided into a plurality of parts in a manner of equal division or unequal division in the direction of the long side and/or the short side, and a plurality of drilling positions are arranged on the plate edge and/or the non-line area of the drilling layer at each part; in step S6, the actual back drilling depth of the back drilling holes in the plate at each part is used for back drilling in a mode of adding the compensation value to the average value of the back drilling depths of all the detection holes at each part.

Further, in step S1, 1-100 drilling sites are provided at the board edge and/or non-wiring area of the drilled-through layer at each part.

Further, in step S1, 2-9 drilling sites are provided at the board edge and/or non-wiring area of the drilled-through layer at each portion.

Further, the following steps are also included between steps S3 and S4:

s31, pasting a film on the production board, forming a hole ring pattern arranged around the detection hole on the non-back drilling surface of the production board after exposure and development in sequence, removing a copper layer at the position of the hole ring pattern through etching, and finally removing the film to disconnect the hole copper in the detection hole from the copper surface of the non-back drilling surface.

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 step S5, the back drilling depth S = v · t from the reference zero point to the end point, where v is the drill bit down drilling speed and t is the back drilling time from the reference zero point to the end point.

In a second aspect, the present invention further provides another manufacturing method for realizing high-precision back drilling and short pile, including the following steps:

s11, providing a production board with a plurality of inner layer circuits, wherein two surfaces of the production board are copper surfaces, one surface of the production board is a back drilling surface, the other surface of the production board is a non-back drilling surface, the bottommost inner layer circuit drilled during back drilling is a drilled-through layer, and the inner layer circuit which is adjacent to the drilled-through layer and is not drilled through during back drilling is a non-drilled-through layer; a plurality of drilling positions are arranged on the plate edge and/or the non-line area of the drilling layer of the production plate, and a lead for communicating the line in the plate with the drilling positions is also manufactured on the drilling layer, wherein the drilling positions are positions needing drilling in subsequent processing;

s12, drilling a through hole on the production board and drilling a detection hole at a position vertical to each drilling position;

s13, metallizing the hole through copper deposition and electroplating, wherein the metallized via hole is communicated with an in-board circuit in the drilled layer, and the metallized detection hole is communicated with a lead in the drilled layer so as to communicate the via hole with the detection hole;

s14, fixing the production board on the table top of a back drilling machine, wherein the back drilling surface is arranged upwards; two signal wires which are respectively communicated with a control system of the back drilling machine are led out from the back drilling machine, 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 larger than the aperture of the detection hole, and the other signal wire is communicated with a copper surface on the production plate;

s15, controlling the drill bit to back drill the detection holes one by one, forming a loop between the production board and the drill bit through two signal lines when the drill bit contacts the board surface, marking the loop as a reference zero point of the back drill at the moment, monitoring the resistance value change of the drill bit during the back drilling, marking the loop as an end point of the back drill when the drill bit continues to drill and monitors that the resistance value is instantly doubled or doubled twice in a front-back mode, and so on, obtaining the back drilling depth of each detection hole from the reference zero point to the end point, and calculating the back drilling depth mean value of all the detection holes;

and S16, performing back drilling by taking the mode of adding the compensation value to the back drilling depth mean value obtained in the step S5 as the actual back drilling depth of the back drilling hole in the production plate, wherein the compensation value is not more than 50% of the designed thickness value of the medium between the drilling-through layer and the non-drilling-through layer.

In a third aspect, the present invention further provides another manufacturing method for realizing high-precision back drilling and short pile, including the following steps:

s10, providing a production board with a plurality of inner layer circuits, wherein two surfaces of the production board are copper surfaces, one surface of the production board is a back drilling surface, the other surface of the production board is a non-back drilling surface, the bottommost inner layer circuit drilled during back drilling is a drilled-through layer, and the inner layer circuit which is adjacent to the drilled-through layer and is not drilled through during back drilling is a non-drilled-through layer; the method comprises the following steps that a plurality of groups of detection modules are arranged on the plate edge and/or the non-line area of a drilling-through layer of a production plate, each group of detection modules comprises two adjacent drilling positions and a lead for communicating the two drilling positions, and the drilling positions are positions needing drilling in subsequent processing;

s20, drilling detection holes in positions, perpendicular to each drilling position, on the production board;

s30, metallizing the holes through copper deposition and electroplating, and enabling the two detection holes in each group of detection modules to be communicated with the lead in the drilled-through layer so as to communicate the two detection holes in each group of detection modules;

s40, fixing the production board on a table top of a back drilling machine, wherein the back drilling surface is arranged upwards; two signal wires which are respectively communicated with a control system of the back drilling machine are led out from the back drilling machine, 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 larger than the aperture of the detection hole, and the other signal wire is communicated with a copper surface on the production plate;

s50, controlling the drill bit to back drill one of the detection holes of each group of detection modules one by one, when the drill bit contacts the plate surface, forming a loop between the production plate and the drill bit through two signal lines, monitoring the resistance value change during back drilling of the drill bit, marking as a reference zero point of the back drill when the drill bit continues to drill and the resistance value is instantly increased by one time or more for the first time, marking as an end point of the back drill when the drill bit continues to drill until the resistance value is instantly increased by one time or more for the second time, and so on, obtaining the back drilling depth of each detection hole from the reference zero point to the end point, and calculating to obtain the back drilling depth mean value of all the detection holes;

and S60, performing back drilling by taking the back drilling depth mean value obtained in the step S50 plus a compensation value as the actual back drilling depth of the back drilling hole in the production plate, wherein the compensation value is not more than 50% of the designed thickness value of the medium between the drilling-through layer and the non-drilling-through layer.

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 detection hole needing back drilling, so that a resistance value on the loop can be detected and obtained by using a control system on the back drilling machine, when a drill bit continuously drills down and breaks the connection between a copper layer on the surface of a board and a copper layer on a hole wall, the instantaneous resistance value is one time or more than one time larger than that before drilling, so that the instantaneous position can be marked as a reference zero point of back drilling, when the drill bit continuously drills down and breaks the connection between a lead in a drilling layer and the copper in the detection hole, the instantaneous resistance value during drilling likewise is one time or more than one time larger than that before drilling, so that the instantaneous position can be marked as an end point of back drilling, the back drilling depth from the reference zero point to the end point can be obtained, the back drilling depth mean value of all detection holes is obtained through calculation, the compensation value is used as the compensation value when the back drilling depth is not more than 50% of the designed thickness value of a medium between the drilling layer and the non-drilling layer as much as the back drilling depth, the compensation value is used as the actual thickness of a back drilling layer, and the back drilling depth of the back drilling depth is reduced as much as possible, and the high-drilling depth of a high-speed drilled pile is reduced as much as possible.

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 2;

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 view of the back drilling at the inspection hole on the production board in example 1;

FIG. 4 is a schematic illustration of example 2 after a copper-free orifice ring has been formed on the plate;

FIG. 5 is a schematic illustration of the plated plate of examples 3 and 4;

FIG. 6 is a schematic view of example 3 after the production board was set in a back drilling machine;

FIG. 7 is a schematic view of the back-drilling at the inspection hole on the production board in example 3;

fig. 8 is a schematic illustration of example 4 after a copper free ring was formed on the plate.

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 derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within 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 of the invention. 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 any and all possible combinations of one or more of the associated listed items and includes such combinations.

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: cutting four core plates according to the size of the jointed board of 520mm multiplied by 620mm, wherein 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; according to the design requirement, a plurality of positions for drilling after pressing are reserved on the plate edge and the non-circuit area of the core plate, and the positions are called drilling positions.

(2) Inner layer circuit manufacturing (negative film process): transferring inner layer patterns, coating a photosensitive film on a core plate by using a vertical coating machine, controlling the film thickness of the photosensitive film to be 8 microns, completing inner layer circuit exposure by using a 5-6-grid exposure ruler (21-grid exposure ruler) by using a full-automatic exposure machine, and forming inner layer circuit patterns after development, wherein the inner layer circuit patterns of one core plate comprise a pad pattern or a copper ring pattern with the outer diameter larger than that of a drilling position; etching the inner layer, etching the exposed and developed core boards to form an inner layer circuit, manufacturing a bonding pad or a copper ring 30 on one surface of one core board at a position corresponding to all drilling positions, communicating the bonding pad or the copper ring with the inner layer circuit through a lead 40 manufactured on the same layer (as shown in figure 1), facilitating the communication of a hole wall copper layer at the drilling position at the later stage with the bonding pad or the copper ring, and measuring the line width of the inner layer 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.

(3) And (3) laminating: the method comprises the steps of conducting brown oxidation at a bottom copper thickness, sequentially overlapping four core plates, a prepreg and an outer copper foil according to requirements, laminating a circuit layer with a bonding pad or a copper ring on a seventh layer of the whole laminated structure during lamination, wherein the thickness of the outer copper foil is preferably 0.5oz, then laminating the laminated plate under proper lamination conditions according to the Tg of a plate material to form a ten-layer production plate, wherein both surfaces of the production plate are copper surfaces, eight layers of inner circuits are arranged inside the production plate, the surface of the production plate, far away from the inner bonding pad or the copper ring, is a back drilling surface needing back drilling, namely a first layer of circuit layer, the other surface of the production plate is a non-back drilling surface, namely a tenth layer of circuit layer, the bottom layer drilled during back drilling from the back drilling surface is a drilling-through layer, namely the circuit layer with the bonding pad or the copper ring is a drilling-through layer, the inner circuit layer, which is adjacent to the drilling-through layer and is not drilled through during back drilling is a non-drilling layer, and the eighth layer of the production plate is a non-drilling-through layer.

In a specific embodiment, 1-100 drilling positions, preferably 2-9 drilling positions, are generally uniformly distributed at each position of a core plate, so that the back drilling depth from the plate surface to the drilled layer at each position on the plate can be obtained during back drilling detection at a later stage, and then the plate thickness difference of each region on the plate can be eliminated as much as possible and the influence of the plate thickness tolerance on the back drilling depth and the back drilling short pile can be reduced.

In a specific embodiment, in order to avoid that the influence of the back drilling on the whole plate cannot be reduced by calculating the back drilling depth mean value because the plate thickness difference between the regions is large, the production plate can be designed in regions, then each region is provided with a detection hole and the back drilling depth mean value of the region is calculated, and the detection hole is used as the reference value of the back drilling depth of the region, namely the back drilling depths of the regions can be the same or different when the back drilling is carried out on the whole plate, and can change along with the plate thickness difference between the regions; the method comprises the following specific steps: the production plate is divided into a plurality of parts in the long side and/or short side direction in an equal or unequal manner, and the plate edge and/or non-line area of the drilled-through layer at each part is provided with 1-100 drilling sites, preferably 2-9.

(4) Drilling: according to the conventional drilling technology, a via hole 10 for conducting the inner and outer layers of wiring is drilled on the production board according to the design requirement, and a detection hole 20 is drilled at a position perpendicular to each drilling position, the via hole is communicated with the pad or the copper ring through the seventh wiring layer and the conductive wire, and 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 the copper ring 30 is exposed on the wall of the detection hole (as shown in fig. 1).

(5) Copper deposition: depositing a layer of thin copper on the board surface and the hole wall by using a chemical copper plating method, testing the thickness of the deposited copper in the hole to be 10 grades in a backlight test, and after metallization, enabling the hole copper of the detection hole and the via hole to be communicated on the board surface and the seventh layer of circuit layer so as to form an inner-outer layer parallel circuit between the two holes.

(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 the outer diameter of a detection hole, so that a copper layer on the hole wall can be removed during back drilling, the other signal wire 3 is communicated with the copper surface on the production board 1, namely, the conduction between the copper surface and the drill bit is formed through the conduction of the control system, but no loop is formed at the beginning of back drilling; 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 clip (not shown) is provided on the back drill to clamp the face of the production board, and the signal lines are connected to the face copper layer of the production board through the clip.

b. As shown in fig. 3, the drill bit 5 is controlled to back-drill the detection holes one by one, 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 as to monitor the resistance value change when the drill bit backs up, when the drill bit continues to drill and monitors the resistance value instantly becoming one time or more than one time for the first time, the control system records the reference zero point of the back drilling at the moment, the connection between the copper layer on the board surface and the detection hole copper is just drilled off, when the drill bit continues to drill until the resistance value is monitored instantly becoming one time or more than one time for the second time, the control system records the end point of the back drilling at the moment and controls the drill bit to stop back drilling, at the moment, the connection between the conducting wire in the drilling layer and the detection hole copper is just drilled off, and so on, the back drilling depth of each detection hole from the reference zero point to the end point can be obtained, and the back drilling depth of each detection hole on the board can be calculated to obtain the average value S of the back drilling depth of all the detection holes on the board ₁ (ii) a Similarly, when the production board is designed in a partition mode, the back drilling depth mean value S of all detection holes in each part of the board can be calculated ₂ 。

In the above, when the drill bit is used for continuously drilling and breaking the connection between the copper layer of the panel surface and the copper layer of the hole wall, which is equivalent to that an open circuit is formed between the panel surface and the copper layer of the detection hole drilled on the back, the resistance of the open circuit is approximate to a maximum value, but the loop is still communicated because the drill bit is in contact with the panel surface and the copper layer of the hole, the resistance is not the maximum value at this moment, and the resistivity of the drill bit is generally larger than that of the copper, so that the instantaneous resistance value during drilling and breaking is one time or more than one time larger than that before drilling and breaking, and similarly, the instantaneous resistance value during drilling and breaking the connection between the lead in the drilling layer and the copper layer of the detection hole is also one time or more than that before drilling and breaking; the drill bit is preferably made of a steel alloy.

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

c. When the production board is not designed in a partition mode, the back drilling depth mean value S obtained in the step b is used ₁ Adding a compensation value as the actual back drilling depth of the back drilling hole in the production board for back drilling, namely back drilling the via hole needing back drilling on the production board according to the obtained actual back drilling depth; similarly, when the production board is designed in a partition mode, the back drilling depth mean value S of each part is calculated ₂ The compensation values are added in a one-to-one correspondence mode to be used as the actual back drilling depth of the back drilling holes in each part of the board for back drilling, namely back drilling is carried out on the through holes needing back drilling in each part according to the obtained actual back drilling depth; and the compensation value is not more than 50% of the design value of the thickness of the medium between the drilled layer and the non-drilled layer, namely, during back drilling, after the seventh line layer is drilled through, the drilling is continued to be not more than half of the thickness of the medium of the lower layer, so that the length of the residual pile between the drilled layer and the non-drilled layer is removed as much as possible.

Preferably, the compensation value can be calculated according to the precision of a back drilling machine, the tolerance of the thickness of a medium between a drilling layer and a non-drilling layer and the minimum length value of a stub (stub) based on the reliability of the line connection performance, besides the percentage calculation mode; for example, the design value of the thickness Ts of the medium between the drilled layer and the non-drilled layer is 0.15mm, the thickness tolerance is +/-10%, namely Ts =0.15 +/-0.015 mm, the precision of the back drilling machine is +/-0.025 mm, the length of the short pile is more than or equal to 0.05mm, the compensation value =0.15-0.015-0.025-0.05=0.06mm, therefore, the actual back drilling depth = the average value S of the back drilling depth ₁ +0.06mm, or actual backdrilling depth = backdrilling depth mean S ₂ +0.06mm, so that the length of the stub (stub) after back drilling is controlled between 0.05-0.13mm, and the requirement that the stub of back drilling is as small as possible under the condition that the high-speed transmission rate exceeds 50Gbps can be met.

Preferably, the back drilling depth from the reference zero point to the end point is a depth value after drilling through the board surface copper layer, and the actual back drilling depth may be added with the thickness of the surface copper layer in order to avoid the influence of the board surface copper thickness during back drilling.

Of course, in a specific embodiment, the drill bit may be used as a reference zero point of the back drill when it just contacts the board surface and forms a loop, and then the back drill is marked as an end point of the back drill when the resistance value is instantly increased by one time or more than two times before and after the monitoring, so that the back drill depth from the reference zero point to the end point includes the thickness of the board surface copper layer.

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 the schmoll drilling machine, so as to determine whether a certain line layer is drilled or not according to a 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 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 tin on the production plate, setting electroplating parameters according to the required finished copper thickness, wherein the copper plating is carried out for 60min at the current density of 1.8ASD, and the tin plating 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 through comparison 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 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: testing the electrical conduction performance of the finished board, wherein the board use testing 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 external 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.

Example 2

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

(61) Manufacturing an outer-layer hole ring: after exposure and development, an annular ring pattern arranged around the detection hole is formed on the non-back drilling surface of the production board, generally, the inner diameter of the annular ring pattern is larger than the aperture of the detection hole, so that the detection hole is covered by the film, then, a copper layer at the annular ring pattern is removed by etching, and finally, the film is removed, so that a copper-free annular ring (as shown in fig. 4) is formed, so that the copper in the hole is disconnected from the copper surface of the non-back drilling surface.

Compared with embodiment 1, the embodiment eliminates one parallel line in which the detection hole and the via hole are communicated through the non-back drilling surface in the conducting loop, so that the resistance value change in the back drilling process in the detection hole is more obvious, and the sensitivity of the resistance value monitoring signal can be improved.

Example 3

(1) Cutting: cutting four core plates according to the size of the jointed board of 520mm multiplied by 620mm, wherein 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; according to design requirements, a plurality of groups of detection modules are reserved on the board edge and the non-circuit area of the core board, each group of detection modules comprises two adjacent drilling positions and a lead for communicating the two drilling positions, and the drilling positions are positions needing drilling after pressing.

(2) Inner layer circuit manufacturing (negative film process): transferring inner layer patterns, coating a photosensitive film on a core plate by using a vertical coating machine, controlling the film thickness of the photosensitive film to be 8 microns, completing inner layer circuit exposure by using a 5-6-grid exposure ruler (21-grid exposure ruler) by using a full-automatic exposure machine, and forming inner layer circuit patterns after development, wherein the inner layer circuit patterns of one core plate comprise a pad pattern or a copper ring pattern with the outer diameter larger than that of a drilling position; etching an inner layer, etching the exposed and developed core board to form an inner layer circuit, manufacturing a bonding pad or a copper ring 30 on one surface of one core board at a position corresponding to all drilling positions, communicating two bonding pads or copper rings in each group of detection modules through a lead 40 manufactured in the same layer (as shown in figure 5), facilitating the communication of hole wall copper layers at two drilling positions of the same group of detection modules in the later period by utilizing the bonding pads or the copper rings, and measuring the line width of the inner layer 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.

(3) And (3) laminating: the brown oxidation speed is brown oxidation according to the thickness of bottom copper, four core plates, prepregs and outer copper foils are sequentially overlapped according to requirements, circuits with bonding pads or copper rings are manufactured during pressing and are arranged on a seventh layer of the whole overlapped structure in a laminating mode, the thickness of the outer copper foil is preferably 0.5oz, then the laminated plate is pressed according to a proper laminating condition selected according to the Tg of a plate material to form a ten-layer production plate, the two surfaces of the production plate are copper surfaces, eight layers of inner layer circuits are arranged inside the production plate, the surface, far away from the inner bonding pads or the copper rings, of the production plate is a back drilling surface needing back drilling, namely a first layer circuit layer, the other surface is a non-back drilling surface, namely a tenth layer circuit layer, the bottommost layer drilled during back drilling from the back drilling surface is a drilling-through layer, namely the circuit layer with the bonding pads or the copper rings is a drilling-through layer, the inner layer circuits which are adjacent to the drilling-through layer and are not drilled during back drilling are a non-through layer, and the eighth layer of the production plate is a non-through layer.

In a specific embodiment, 1-100 groups of detection modules, preferably 2-9 groups, can be generally and uniformly arranged at the edge and/or non-line area of the drilled layer of the production board, and the detection modules are generally and uniformly distributed at each position of the core board, so that the back drilling depth from the board surface to the drilled layer at each position on the board can be obtained in the later back drilling detection, and then the average value of the back drilling depth at each position is calculated, so that the board thickness difference of each area on the board can be eliminated as much as possible, and the influence of the board thickness tolerance on the back drilling depth and the back drilling short pile can be reduced.

In a specific embodiment, in order to avoid that the plate thickness difference between each region is large and the influence of the whole plate on back drilling cannot be reduced through the calculated back drilling depth mean value, the production plate can be designed in different regions, then each region is provided with a detection hole and the back drilling depth mean value of the region is calculated, and the detection hole is used as a reference value of the back drilling depth of the region, namely the back drilling depth of each region can be the same or different when back drilling is carried out on the whole plate, and can change along with the plate thickness difference between the regions; the method specifically comprises the following steps: the production board is divided into a plurality of parts in an equal or unequal manner in the long side and/or short side direction, and the board edge and/or the non-line area of the drilling-through layer at each part is provided with 1-100 groups of detection modules, preferably 2-9 groups.

(4) Drilling: according to the existing drilling technology, drilling processing is carried out on a production board according to design requirements, through holes for conducting inner and outer layer circuits in the board are drilled, and detection holes 20 (shown in fig. 5) are drilled at positions perpendicular to each drilling position, the hole diameter of each detection hole is smaller than the outer diameter of a bonding pad or is the same as the inner diameter of a copper ring, so that the bonding pad or the copper ring is exposed on the hole wall of each detection hole, one detection hole in the same group of detection modules is used as a hole for back drilling detection in the later period, and the other detection hole is used as a through hole of a loop.

(5) Copper deposition: a layer of thin copper is deposited on the plate surface and the hole wall by using a chemical copper plating method, the backlight test is carried out for 10 grades, the thickness of the deposited copper in the hole is 0.5 mu m, and besides the communication between the detection holes after metallization is formed on the plate surface, the two detection holes in the same group of detection modules are also communicated at the seventh layer of circuit layer, so that an inner-layer parallel circuit and an outer-layer parallel circuit are formed between the two holes.

(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. 5.

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

a. as shown in fig. 6, 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 hole diameter of the back drilling hole, namely, the blade diameter of the drill bit is larger than the outer diameter of a detection hole, so that a copper layer on the hole wall can be removed during back drilling, the other signal wire 3 is communicated with the copper surface on the production board 1, namely, the conduction between the copper surface and the drill bit is formed through the conduction of the control system, but no loop is formed at the beginning of back drilling; the control system of the back drilling machine is a servo control system.

b. As shown in fig. 7, the drill bit 5 is controlled to back-drill one of the detection holes of each group of detection modules, 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 as to monitor the change of the resistance value when the drill bit backs up, when the drill bit continues to drill down and the resistance value is instantly increased by one time or more than one time for the first time, the control system records the reference zero point of the back drilling at the moment, the connection between the copper layer on the board surface and the copper of the detection hole is just drilled off, when the drill bit continues to drill down until the resistance value is instantly increased by one time or more than one time for the second time, the control system records the end point of the back drilling at the moment and controls the drill bit to stop the back drilling, at the moment, the connection between the lead in the drilling layer and the copper of the detection hole is just drilled off, and so on, the back drilling depth of each detection hole from the reference zero point to the end point can be obtained, and the back drilling depth S-average value S of all the detection holes on the board can be calculated ₁ (ii) a Similarly, when the production board is designed in a partition mode, the back drilling depth mean value S of all detection holes in each part of the board can be calculated ₂ 。

c. When the production board is not designed in a partition mode, the back drilling depth mean value S obtained in the step b is used ₁ Adding a compensation value as the actual back drilling depth of the back drilling hole in the production plate for back drilling, namely back drilling the copper hole needing back drilling on the production plate according to the obtained actual back drilling depth; similarly, when the production board is designed in a partition mode, the back drilling depth mean value S of each part is calculated ₂ With compensation values added in one-to-one correspondence as back-drilled holes in each part of the boardBack drilling is carried out according to the actual back drilling depth, namely, back drilling is carried out on through holes needing back drilling in each part according to the obtained actual back drilling depth; and the compensation value is not more than 50% of the design value of the thickness of the medium between the drilled layer and the non-drilled layer, namely, during back drilling, after the seventh line layer is drilled, the drilling is continued to be not more than half of the thickness of the medium of the lower layer, so that the length of the residual pile between the drilled layer and the non-drilled layer is removed as much as possible.

Preferably, the compensation value can be calculated according to the precision of a back drilling machine, the tolerance of the thickness of a medium between a drilling layer and a non-drilling layer and the minimum length value of a short pile (stub) based on the connection performance reliability of the line in addition to the percentage calculation mode; for example, the design value of the thickness Ts of the medium between the drilled layer and the non-drilled layer is 0.15mm, the thickness tolerance is +/-10%, namely Ts =0.15 +/-0.015 mm, the precision of the back drilling machine is +/-0.025 mm, the length of the short pile is more than or equal to 0.05mm, the compensation value =0.15-0.015-0.025-0.05=0.06mm, therefore, the actual back drilling depth = the average value S of the back drilling depth ₁ +0.06mm, or actual backdrilling depth = backdrilling depth mean S ₂ +0.06mm, so that the length of the stub (stub) after back drilling is controlled between 0.05-0.13mm, and the requirement that the stub of back drilling is as small as possible under the condition that the high-speed transmission rate exceeds 50Gbps can be met.

(8) Manufacturing an outer layer circuit (positive 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 tin on the production plate, setting electroplating parameters according to the required finished copper thickness, wherein the copper plating is carried out for 60min at the current density of 1.8ASD, and the tin plating 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 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.

(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.

(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.

Example 4

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

(61) Manufacturing an outer-layer hole ring: after exposure and development, a hole ring pattern arranged around the detection holes is formed on the non-back drilling surface of the production board, of course, a hole ring pattern surrounding the detection holes is formed only at one detection hole in each group of detection modules, and generally, the inner diameter of the hole ring pattern is larger than the hole diameter of the detection hole, so that the detection hole is covered by the film, then, the copper layer at the hole ring pattern is removed by etching, and finally, the film is removed to form a copper-free hole ring (as shown in fig. 8), so that the hole copper in the detection hole is disconnected from the copper surface of the non-back drilling surface.

Compared with embodiment 3, the embodiment eliminates one parallel line of the two detection holes of each group of detection modules in the conduction loop, which are communicated through the non-back drilling surface, so that the resistance value change in the detection holes during back drilling is more obvious, and the sensitivity of the resistance value monitoring signal can be improved.

In fig. 1 to 8, 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, there may be variations in the specific implementation manners and application ranges, and in summary, the content of the present description should not be construed as a limitation to the present invention.

Claims

1. A manufacturing method for realizing high-precision back drilling and short piles is characterized by comprising the following steps:

s1, providing a production board with a plurality of inner layer circuits, wherein two surfaces of the production board are copper surfaces, one surface of the production board is a back drilling surface, the other surface of the production board is a non-back drilling surface, the bottommost inner layer circuit drilled during back drilling is a drilled-through layer, and the inner layer circuit which is adjacent to the drilled-through layer and is not drilled through during back drilling is a non-drilled-through layer; a plurality of drilling positions are arranged on the plate edge and/or the non-line area of the drilling layer of the production plate, and a lead for communicating the line in the plate with the drilling positions is also manufactured on the drilling layer, wherein the drilling positions are positions needing drilling in subsequent processing;

s3, metallizing the hole through copper deposition and electroplating, wherein the metallized via hole is communicated with an in-board circuit in the drilled layer, and the metallized detection hole is communicated with a lead in the drilled layer so as to communicate the via hole with the detection hole;

s4, fixing the production board on a table top of a back drilling machine, wherein the back drilling surface is arranged upwards; two signal wires which are respectively communicated with a control system of the back drilling machine are led out from the back drilling machine, 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 larger than the aperture of the detection hole, and the other signal wire is communicated with a copper surface on the production plate;

s5, controlling the drill bit to back drill the detection holes one by one, forming a loop between the production board and the drill bit through two signal lines when the drill bit is in contact with the board surface, monitoring the resistance value change of the drill bit during back drilling, recording the reference zero point of the back drill when the drill bit continues to drill and the resistance value is instantly increased by one time or more for the first time, recording the end point of the back drill when the drill bit continues to drill until the resistance value is instantly increased by one time or more for the second time, and so on to obtain the back drilling depth of each detection hole from the reference zero point to the end point, and calculating the back drilling depth mean value of all the detection holes;

and S6, performing back drilling by taking the mode of adding the compensation value to the mean value of the back drilling depth obtained in the step S5 as the actual back drilling depth of the back drilling hole in the production plate, wherein the compensation value is not more than 50% of the designed value of the thickness of the medium between the drilling-through layer and the non-drilling-through layer.

2. The method for manufacturing high-precision back drill and stub as claimed in claim 1, wherein in step S1, a bonding pad or a copper ring with an outer diameter larger than that of the drilling site is manufactured at the drilling site, and the wire is connected to the bonding pad or the copper ring; in step S2, the aperture of the inspection hole is smaller than the outer diameter of the pad or equal to the inner diameter of the copper ring, so as to expose the pad or the copper ring on the hole wall of the inspection hole.

3. The manufacturing method for realizing high-precision back drilling and short piles according to claim 1, wherein in the step S1, the production plate is divided into a plurality of parts in an equally or unequally divided manner in the direction of the long side and/or the short side, and a plurality of drilling positions are arranged on the plate edge and/or the non-line area of the drilling-through layer at each part; in step S6, back drilling is performed by taking the mean value of the back drilling depths of all the detection holes at each part plus the compensation value as the actual back drilling depth of the back drilling holes in the board at the part.

4. The method for realizing high-precision back drilling and short pile manufacturing according to claim 3, wherein in step S1, 1-100 drilling positions are provided at the plate edge and/or non-line area of the drilling-through layer at each part.

5. The method for realizing high-precision back drilling and short pile manufacturing according to claim 4, wherein in step S1, 2-9 drilling positions are provided at each part of the plate edge and/or non-line area of the drilled layer.

6. The manufacturing method for realizing high-precision back drilling and short piles according to claim 1, wherein the following steps are further included between the steps S3 and S4:

7. The method of claim 1, wherein in step S4, the back drill is provided with a press foot which is vertically movable and abuts against 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.

8. The method of claim 1, wherein in step S5, the back drilling depth from the reference zero point to the end point is S = v.t, where v is the drill bit down-drilling speed and t is the back drilling time from the reference zero point to the end point.

9. A manufacturing method for realizing high-precision back drilling and short piles is characterized by comprising the following steps:

s11, providing a production board with a plurality of layers of inner-layer circuits, wherein both surfaces of the production board are copper surfaces, one surface of the production board is a back drilling surface, the other surface of the production board is a non-back drilling surface, the bottommost inner-layer circuit drilled through during back drilling is a drilled-through layer, and the inner-layer circuit which is adjacent to the drilled-through layer and is not drilled through during back drilling is a non-drilled-through layer; a plurality of drilling positions are arranged on the plate edge and/or the non-line area of the drilling layer of the production plate, and a lead for communicating the line in the plate with the drilling positions is also manufactured on the drilling layer, wherein the drilling positions are positions needing drilling in subsequent processing;

and S16, back drilling is carried out by taking the mode of adding the compensation value to the mean value of the back drilling depth obtained in the step S5 as the actual back drilling depth of the back drilling hole in the production plate, wherein the compensation value is not more than 50% of the designed value of the thickness of the medium between the drilling-through layer and the non-drilling-through layer.

10. A manufacturing method for realizing high-precision back drilling and short piles is characterized by comprising the following steps:

s30, metallizing the holes through copper deposition and electroplating, and communicating the two detection holes in each group of detection modules with the lead in the drilled layer so as to communicate the two detection holes in each group of detection modules;