Printed circuit board and processing method for reducing signal loss of laser hole

Abstract

The invention belongs to the technical field of circuit boards, and discloses a printed circuit board and a processing method for reducing signal loss of a laser hole, and the method comprises the steps: S1, manufacturing an inner layer pattern, and not designing a blocking pad at a position where a high-speed line endpoint needs to be connected with the laser hole, so that the laser hole can be directly connected with an inner layer high-speed line; s2, a mechanical hole with the drilling diameter larger than 0.5 mm is found near the laser hole to serve as a reference hole, and pad blocking design is carried out in the reference hole of the target layer; s3, deep drilling rough machining is firstly adopted, then laser drilling fine machining is conducted, and therefore accurate machining of the reference hole depth is achieved; s4, machining conditions of the reference hole in the laser drilling fine machining process are obtained, and laser energy parameters of laser hole machining are determined according to the machining conditions; and S5, the target laser hole is machined according to the determined laser energy parameters for laser hole machining.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of circuit board, and relates to a printed circuit board and a processing method for reducing signal loss of a laser hole. BACKGROUND

[0002] With the continuous improvement of data transmission rate, high-frequency high-speed printed circuit boards (PCB) are increasingly widely used.

[0003] In the traditional PCB processing method, the connection between the laser hole and the inner layer high-speed line usually needs to be realized through a blocking pad (blocking pad). However, the existence of the blocking pad will cause the impedance on the signal transmission path to be discontinuous, thereby causing problems such as signal reflection and attenuation, which seriously affect the signal integrity.

[0004] In addition, the depth control precision of the laser hole in the traditional method is insufficient, which easily leads to unstable hole wall quality, further aggravating signal loss. SUMMARY

[0005] Objective: In order to overcome the deficiencies in the prior art, the present application provides a printed circuit board and a processing method for reducing signal loss of a laser hole, which effectively reduces signal loss, improves signal integrity, and realizes precise control of the depth of the laser hole.

[0006] Technical solution: The preferred technical solution adopted by the present application is: According to the first aspect of the present application, a processing method for reducing signal loss of a laser hole of a printed circuit board is provided, comprising: S1, inner layer pattern making, for the position where the high-speed line end point needs to be connected with the laser hole, no blocking pad is designed, so that the laser hole can be directly connected with the inner layer high-speed line; S2, a mechanical hole with a diameter of 0.5mm or more is found near the laser hole as a reference hole, and a blocking pad is designed in the reference hole of the target layer; S3, first, depth drilling rough machining is performed, and then laser drilling fine machining is performed, to realize precise machining of the depth of the reference hole; S4, the machining conditions in the laser drilling fine machining process of the reference hole are obtained, and the laser energy parameters for laser hole machining are determined according to the machining conditions; S5, the target laser hole is machined according to the determined laser energy parameters for laser hole machining.

[0007] In some embodiments, in S3, the depth drilling rough machining comprises: using a mechanical drill bit to rough machine the reference hole, drilling to a depth of 0.1mm from the target layer, and controlling the drilling depth error to be within ±0.05mm.

[0008] Further, during the deep drilling rough machining process, nitrogen is used as the auxiliary gas, and the pressure is set to 0.5 MPa to remove the debris generated during drilling.

[0009] In some embodiments, in S3, the laser drilling fine machining includes: using a laser drilling technology to fine machine the reference hole, and adjusting laser parameters to ensure that the depth accuracy of the reference hole reaches ±0.005 mm; the laser parameters include laser power, pulse width, and focal point position.

[0010] Further, the laser drilling fine machining uses a UV laser with a wavelength of 355 nm, a laser power of 8-15 W, and a pulse width of 20-50 ns, and the focal point position is located 10-20 μm below the surface of the plate.

[0011] In some embodiments, in S4, the machining conditions include laser energy, drilling speed, and hole wall temperature.

[0012] In some embodiments, in S5, the laser hole machining uses a step power control, the initial power is used to remove the copper foil, and then the power is reduced to fine machine the resin layer.

[0013] In some embodiments, in S2, the diameter of the blocking pad is designed to be about 0.3 mm; the annular ring width between the blocking pad and the edge of the reference hole is not less than 0.1 mm.

[0014] In some embodiments, after the target laser hole machining is completed, S6, subsequent processing is further included: the reference hole is drilled in the mechanical hole machining process.

[0015] According to a second aspect of the present application, a printed circuit board is provided, which is made by the method.

[0016] Advantages: The present application provides a processing method for reducing signal loss of laser holes of a printed circuit board, which has the following advantages: 1. Signal integrity improvement: By canceling the blocking pad design of the high-speed line end point, the laser hole is directly connected with the inner layer high-speed line, effectively reducing signal reflection and attenuation, and improving signal integrity.

[0017] 2. High depth control accuracy: The scheme of deep drilling rough machining combined with laser fine machining is adopted, the depth accuracy of the reference hole reaches ±0.01 mm, which provides accurate parameter basis for laser hole machining, and ensures that the depth of all laser holes meets the requirements.

[0018] 3. Improved processing efficiency: The existing mechanical hole is used as the reference hole, without the need for additional design of the target, simplifying the process flow and reducing production cost.

[0019] 4. Strong compatibility: This method is applicable to a variety of PCB materials (such as FR-4, polyimide, etc.) and is compatible with existing PCB manufacturing equipment. Attached Figure Description

[0020] Figure 1 A schematic flowchart illustrating a method for processing a printed circuit board according to an embodiment of the present invention; Figure 2 This is a side view of the printed circuit board product prepared according to an embodiment of the present invention; Figure 3 This is a top view schematic diagram of the printed circuit board product prepared according to an embodiment of the present invention; In the diagram, the laser passes through layer 1, high-speed line 2, and laser aperture ring 3. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] For the purposes of this specification and the appended claims, unless otherwise stated, all expressions, percentages, or proportions, and other numerical values ​​used in this specification and the appended claims, are to be understood to be modified by the term "about" in all cases. Furthermore, all scopes disclosed herein include their endpoints and can be combined independently.

[0024] This invention provides a method for reducing laser aperture signal loss in printed circuit boards. This method is applicable to the fabrication of the printed circuit boards provided in this invention. Figure 1 A flowchart illustrating a method for manufacturing a printed circuit board according to an embodiment of the present invention is shown below. Figure 1 As shown, a processing method for reducing laser aperture signal loss in a printed circuit board includes: S1. Inner layer pattern creation: When creating the inner layer pattern, no pads are designed for the high-speed line endpoints that need to be connected to the laser holes, so that the laser holes can be directly connected to the inner layer high-speed lines.

[0025] It should be noted that in this step S1, the blocking solder pad is not designed to enable the laser hole to be directly connected to the inner layer high-speed line, and this technical solution avoids the influence of the blocking solder pad on the signal, thereby reducing signal reflection and attenuation and improving signal integrity.

[0026] S2, reference hole selection and blocking solder pad design: find a mechanical hole with a diameter of 0.5 mm or more near the laser hole as a reference hole, and design a blocking solder pad in the reference hole of the target layer.

[0027] Further, the diameter of the blocking solder pad is designed to be about 0.3 mm; the annular ring width of the blocking solder pad and the edge of the reference hole is not less than 0.1 mm.

[0028] It should be noted that the diameter of the blocking solder pad is designed to be about 0.3 mm to ensure accurate positioning reference for laser hole processing without affecting subsequent processing of the mechanical hole.

[0029] In addition, ensuring that the annular ring width of the blocking solder pad and the edge of the reference hole is not less than 0.1 mm is to meet the requirements of the IPC-2222 standard.

[0030] S3, first rough machining by deep drilling, and then fine machining by laser drilling to achieve accurate machining of the depth of the reference hole.

[0031] The deep drilling rough machining includes rough machining of the reference hole by a mechanical drill bit of a numerical control drilling machine to a depth of 0.1 mm from the target layer, with a drilling depth error controlled within ±0.05 mm.

[0032] Further, during the deep drilling rough machining, nitrogen is used as an auxiliary gas with a pressure of 0.5 MPa to remove debris generated during drilling, thereby improving the quality of the hole wall.

[0033] The laser drilling fine machining includes fine machining of the reference hole by laser drilling technology to ensure that the depth accuracy of the reference hole reaches ±0.005 mm by adjusting laser parameters; the laser parameters include laser power, pulse width, and focal point position.

[0034] In some embodiments, the laser drilling fine machining uses UV laser with a wavelength of 355 nm, a laser power of 8-15 W, a pulse width of 20-50 ns, and a focal point position located 10-20 μm below the surface of the plate.

[0035] More specifically, in some embodiments, the laser drilling fine machining includes: fixing the rough-machined PCB board onto the worktable of the laser drilling equipment, and using the through holes drilled by the X-ray target machine as coarse positioning coordinates. A UV laser (wavelength 355nm) is used to fine-machine the reference holes, with the laser power set to 10W, pulse width 30ns, and the focal point located 10μm below the surface of the board. A spiral scanning mode is used, with a scanning speed of 500mm / s, repeated 3 times to ensure hole wall smoothness and depth accuracy.

[0036] S4. Processing Condition Acquisition and Parameter Adjustment: Acquire the processing conditions during the laser drilling fine machining process of the reference hole, and determine the laser energy parameters for laser hole machining based on the processing conditions; wherein the processing conditions include laser energy, drilling speed and hole wall temperature; During the fine machining of a reference hole using laser drilling technology, machining conditions, including laser energy, drilling speed, and hole wall temperature, are acquired in real time. Based on these acquired conditions, the laser parameters are automatically adjusted by a closed-loop control system. S5. Laser Hole Machining: Machin the target laser holes according to the determined laser energy parameters for laser hole machining, ensuring that the machining depth of all laser holes meets the requirements.

[0037] Furthermore, the laser hole processing employs graded power control. The initial power is used to remove the copper foil, and then the power is reduced to finely process the resin layer. More specifically, the initial power of 15W is used to remove the copper foil, and then the power is reduced to 8W to finely process the resin layer, ensuring the consistency of the laser hole depth and diameter.

[0038] It should be noted that the correlation model between the laser energy parameter E and the penetration depth D of the dielectric layer is as follows: E=k・(D・ρ・C p ) / (α・(1-R)) Where E represents the laser energy parameter, k represents the material heat loss correction factor, D represents the penetration depth of the dielectric layer, ρ represents the dielectric density, and C... p Let α represent the specific heat capacity, α represent the absorption coefficient, and R represent the surface reflectivity.

[0039] In practical applications, after laser hole processing is completed, a plasma cleaning process is performed to remove carbon residue on the hole wall and improve the quality of subsequent metallization.

[0040] Then, following the standard procedures, processes such as outer layer circuit fabrication, electroplating, and solder masking are carried out to finally produce a PCB circuit board that meets the requirements.

[0041] In some embodiments, after the target laser hole is processed, the process further includes S6, post-processing: drilling a reference hole in the mechanical hole processing step.

[0042] Note that the reference hole is used for positioning and reference during processing, and will be drilled in subsequent mechanical hole processing.

[0043] Application Example:

[0044] Objective: Process a blind hole with a depth of 80 μm on a 6-layer FR-4 PCB without a lower copper barrier.

[0045] Parameters: Ultraviolet laser (wavelength 355 nm), initial pulse energy 3 mJ, frequency 20 kHz, spot diameter 30 μm.

[0046] Process: 1. First layer processing (0-30 μm): energy 4 mJ, fast removal of surface copper layer; 2. Middle layer (30-70 μm): energy linearly reduced to 2 mJ to avoid overburning; 3. Bottom layer trimming (70-80 μm): energy 1 mJ + pulse number control, accuracy ± 2 μm.

[0047] Results: Hole bottom is flat, lower layer medium is undamaged, no need for a barrier layer.

[0048] The processing method for reducing signal loss of a printed circuit board in the present application has the following advantages: 1. Signal integrity improvement: By canceling the solder pad design at the end of the high-speed line, the laser hole is directly connected to the inner layer high-speed line, effectively reducing signal reflection and attenuation, and improving signal integrity.

[0049] 2. High depth control accuracy: The scheme of depth drilling rough machining combined with laser fine machining is adopted, the reference hole depth accuracy reaches ±0.01 mm, which provides accurate parameter basis for laser hole processing, and ensures that the depth of all laser holes meets the requirements.

[0050] 3. Improved processing efficiency: Use the existing mechanical hole as a reference hole, no need for additional target design, simplify the process flow, and reduce production cost.

[0051] 4. Strong compatibility: The method is suitable for various PCB materials (such as FR-4, polyimide, etc.), and is compatible with existing PCB manufacturing equipment.

[0052] Based on the same inventive concept, the embodiments of the present application also provide a printed circuit board, as shown in Figure 2 , Figure 3 The printed circuit board is made by the method provided by any of the embodiments of the present application, has the same beneficial effects as the above method, and can refer to the above description, which will not be repeated here.

[0053] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A processing method for reducing laser aperture signal loss in printed circuit boards, characterized in that, include: S1. Inner layer pattern creation: For the high-speed line endpoints that need to be connected to the laser holes, no pads are designed so that the laser holes can be directly connected to the inner layer high-speed lines. S2. Find a mechanical hole with a drilling diameter of 0.5mm or more near the laser hole as a reference hole, and design a pad block in the reference hole of the target layer. S3. First, use deep drilling for rough machining, and then use laser drilling for fine machining to achieve precise machining of the reference hole depth; S4. Obtain the processing conditions during the laser drilling fine machining process of the reference hole, and determine the laser energy parameters for laser hole machining based on the processing conditions; S5. Process the target laser hole according to the determined laser energy parameters for laser hole processing.

2. The method according to claim 1, characterized in that, In S3, the deep drilling roughing process includes: using a mechanical drill bit to rough-machine the reference hole to a depth of 0.1 mm from the target layer, and controlling the drilling depth error within ±0.05 mm.

3. The method according to claim 2, characterized in that, During the deep drilling roughing process, nitrogen is used as an auxiliary gas at a pressure of 0.5 MPa to remove debris generated during drilling.

4. The method according to claim 1, characterized in that, In S3, the laser drilling fine processing includes: using laser drilling technology to fine process the reference hole, and adjusting the laser parameters to ensure that the depth accuracy of the reference hole reaches ±0.005mm; the laser parameters include laser power, pulse width, and focal position.

5. The method according to claim 4, characterized in that, The laser drilling and fine machining process uses a UV laser with a wavelength of 355nm, a laser power of 8-15W, a pulse width of 20-50ns, and a focal position located 10-20μm below the surface of the board.

6. The method according to claim 1, characterized in that, In S4, the processing conditions include laser energy, drilling speed, and hole wall temperature.

7. The method according to claim 1, characterized in that, In S5, the laser hole processing employs graded power control, with initial power used to remove copper foil, followed by power reduction to finely process the resin layer.

8. The method according to claim 1, characterized in that, In S2, the diameter of the baffle pad is designed to be about 0.3mm; the annular width between the baffle pad and the edge of the reference hole is not less than 0.1mm.

9. The method according to claim 1, characterized in that, After the target laser hole is processed, the process also includes S6, post-processing: in the mechanical hole processing step, the reference hole is drilled.

10. A printed circuit board, characterized in that, It is prepared by the method described in any one of claims 1-9.

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