A PCB back-drill cover plate and its preparation method

Abstract

This invention relates to a PCB back-drill cover plate and its preparation method. The preparation method includes: (1) impregnating resin onto a backing paper A and baking it to obtain a resin semi-cured sheet; placing aluminum foil on a backing paper B and laminating it to obtain an aluminum foil backing paper; (2) stacking one side of the backing paper B with the resin semi-cured sheet and then hot-pressing it to obtain the PCB back-drill cover plate. This invention uses aluminum foil backing paper to replace traditional pure aluminum foil, which can reduce the thickness of the aluminum foil and enhance the processability by relying on the backing paper, solving the problems of easy wrinkling, stretching, and breakage in aluminum foil processing; at the same time, the preferred use of ultra-thin aluminum foil can also improve the back-drilling depth control accuracy, residual pile consistency, and hole concentricity, reduce the risk of overcutting and simplify the drilling process. By pre-laminating the aluminum foil backing paper and optimizing the paper weight and glue application amount, the support of the cover plate and the flatness of the board surface can be improved, and the separate glue application step on site can be eliminated, making the process simpler and the performance more stable.

Description

Technical Field

[0001] This invention relates to the field of PCB drilling technology, and in particular to a PCB back drill cover plate and its preparation method. Background Technology

[0002] The rapid development and large-scale commercialization of fifth-generation (5G) communication technology are driving the development of wireless communication, data centers, base station RF units, optical modules, and high-speed transmission equipment towards higher frequencies, higher speeds, larger bandwidths, and higher integration. With the continuous increase in signal rates, the densification of transmission links, and the continuous improvement of operating frequencies, the signal integrity (SI), impedance consistency, transmission reliability, and long-term operational stability of high-speed printed circuit boards (PCBs) have become key indicators determining the performance of the entire communication system. Against this backdrop, backdrilling, as a crucial process for improving the signal integrity of high-speed PCBs, selectively removes excess copper pillars (i.e., residual pillars / short tubes) in vias that are not involved in effective signal transmission. This significantly reduces signal reflection, crosstalk, delay, and resonant loss, effectively ensuring the stable transmission of high-frequency, high-speed signals. Therefore, backdrilling technology has become an indispensable core PCB manufacturing technology in 5G communication hardware systems.

[0003] However, in existing high-speed PCB back-drilling processes and control, the overall performance of the PCB is still constrained by multiple key factors, making it difficult to meet the stringent requirements of 5G high-frequency and high-speed scenarios in terms of signal integrity. To simultaneously meet the dual needs of high-speed signal transmission and efficient heat dissipation, single-sided aluminum-clad laminates (SCCLs) are gradually becoming the preferred substrate and back-drilling auxiliary / supporting material for 5G high-power and high-speed PCBs due to their advantages such as high thermal conductivity of the aluminum layer on one side, good structural rigidity, controllable cost, and superior adhesion and positioning compared to pure aluminum sheets. However, existing SCCLs used in back-drilling processes suffer from problems such as hole blockage caused by excessive aluminum foil thickness, poor aluminum surface adhesion, and difficulty in controlling depth accuracy. Therefore, it is necessary to reduce the aluminum foil thickness to improve drill sensitivity and achieve precise depth control. However, thinning the aluminum foil can lead to wrinkles, cutting difficulties, and other processing problems during production.

[0004] Therefore, how to provide an aluminum foil back-drilling cover plate for PCB back-drilling process that can significantly reduce the thickness of aluminum foil, improve the back-drilling depth control accuracy and the consistency of residual piles, while solving the problems of easy wrinkling, difficult cutting, poor bonding and hole plugging in thin aluminum foil processing, and taking into account the flatness of the board surface, support rigidity and process simplicity, and meet the requirements of 5G high-frequency and high-speed PCB signal integrity and stable mass production, has become an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a PCB back-drill cover plate and its preparation method. It uses aluminum foil backing paper instead of traditional pure aluminum foil, which reduces the thickness of the aluminum foil and enhances processability through the backing paper, solving the problems of wrinkling, stretching, and breakage during aluminum foil processing. Simultaneously, the preferred use of ultra-thin aluminum foil improves the accuracy of back-drilling depth control, consistency of residual piles, and concentricity of hole positions, reducing the risk of over-cutting and simplifying the drilling process. By pre-compositing the aluminum foil backing paper and optimizing the paper weight and adhesive application amount, the cover plate's support and board surface flatness are improved, while eliminating the need for a separate on-site adhesive application step, resulting in a simpler process and more stable performance.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a PCB back-drill cover plate, the method comprising: (1) The resin is impregnated onto the backing paper A and baked to obtain a resin semi-cured sheet; Aluminum foil is placed on backing paper B, and after lamination, aluminum foil backing paper is obtained; (2) The PCB back drill cover plate is obtained by laminating one side of the aluminum foil backing paper B with the resin semi-cured sheet and then hot pressing it.

[0007] This invention provides a method for preparing a PCB back-drill cover plate, which uses aluminum foil backing paper instead of traditional pure aluminum foil. Compared with traditional pure aluminum foil, the aluminum foil, relying on the support of the backing paper, greatly improves the overall processability of the cover plate, effectively solving the problems of easy wrinkling, stretching, and local damage in aluminum foil processing, ensuring stable processing quality. Furthermore, through the pre-composite process of aluminum foil and backing paper, the support of the cover plate and the flatness of the board surface can be further improved by adjusting the weight of the backing paper and the amount of adhesive applied. It also eliminates the step of separately applying aluminum foil adhesive on site, making the process simpler, the performance more stable, and the batch consistency better.

[0008] Preferably, the resin comprises thermosetting phenolic resin and / or epoxy resin, and more preferably thermosetting phenolic resin.

[0009] The present invention preferably uses thermosetting phenolic resin, which has excellent high temperature resistance, chemical resistance and bonding strength, ensuring that the cover does not soften or deform during the high temperature processing of PCB back drilling, and forms a firm bond with the aluminum foil backing paper, ensuring the overall structural stability of the cover.

[0010] Preferably, the liner paper A comprises bleached wood pulp paper.

[0011] The liner paper A of this invention is preferably made of bleached wood pulp paper. Bleached wood pulp paper is a material rich in paper fibers. The fiber material can remove the residue after drilling, which can effectively reduce the axial force on the drill bit, protect the drill bit, and reduce the breakage rate.

[0012] Preferably, the basis weight of the liner paper A is 80-200 g / m². 2 For example, it could be 80 g / m 2 100 g / m 2 120 g / m 2 140 g / m 2 150 g / m 2 160 g / m 2 180 g / m 2 Or 200 g / m 2 wait.

[0013] Preferably, the basis weight of the resin semi-cured sheet is 120-340 g / m³. 2 For example, it could be 120 g / m 2 140 g / m 2 150 g / m 2 160 g / m 2 180 g / m 2 200 g / m 2 220 g / m 2 240 g / m 2 250 g / m 2 260 g / m 2 280g / m 2 300 g / m 2 320 g / m 2 Or 340 g / m 2 wait.

[0014] Preferably, the baking temperature is 150-170℃ (e.g., 150℃, 155℃, 160℃, 165℃ or 170℃, etc.), and the time is 80-120 s, e.g., 80 s, 90 s, 100 s, 110 s or 120 s, etc.

[0015] Preferably, the thickness of the aluminum foil is 4.5-50 μm, more preferably 4.5-7 μm, for example, it can be 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 10 μm, 20 μm, 30 μm, 40 μm or 50 μm, etc.

[0016] The present invention preferably uses ultra-thin aluminum foil (thickness of 4.5-7 μm), which can significantly improve the back drilling depth control accuracy and the consistency of the residual pile, optimize the hole position accuracy and concentricity, reduce the risk of off-center drilling and over-cutting, and reduce the number of step drilling processes to improve efficiency and reduce costs.

[0017] Preferably, the liner paper B includes any one of medical insurance paper, unbleached kraft paper, white kraft paper, white cardboard, bleached wood pulp paper, or coated paper.

[0018] The liner paper B of this invention is preferably any one of medical insurance paper, unbleached kraft paper, white kraft paper, white cardboard, bleached wood pulp paper, or coated paper. Each type of liner paper has its own advantages and is suitable for different needs: medical insurance paper (commonly used weight is 40-80 g / m²) 2 For example, it could be 40 g / m 2 50 g / m 2 60 g / m 2 70 g / m 2 Or 80 g / m 2 Highly breathable, low water permeability, and with high wet strength, this paper is soft and white, providing stable wet support while ensuring breathability; natural kraft paper (common weight 40-250 g / m²) 2 For example, it could be 40 g / m 2 60 g / m 2 80 g / m 2 100 g / m 2 150 g / m 2 200 g / m 2 Or 250 g / m 2 Highly tough, tear-resistant, and virtually waterproof, it is rough yet durable, suitable for applications where aesthetics are not critical; white kraft paper (common weight 40-300 g / m²) 2 For example, it could be 40 g / m 2 50 g / m 2 100 g / m 2 150 g / m 2 200 g / m 2 250 g / m 2 Or 300 g / m 2 (etc.) It combines high toughness and good stiffness; its white appearance makes it easier to observe the processing status; the fibers are coarse and provide good support; white cardboard (common basis weight is 210-300 g / m²) 2 For example, it could be 210 g / m 2 250 g / m 2 Or 300 g / m 2 (etc.) Extremely high stiffness, rigid texture, pure white, smooth and delicate, and almost waterproof, providing strong support for aluminum foil and ensuring the flatness of the board surface; bleached wood pulp paper (commonly weighing 50-120 g / m²) 2 For example, it could be 50 g / m 2 60 g / m 2 80 g / m 2 100 g / m2 Or 120 g / m 2 (e.g., white and delicate, with moderate air and water permeability, and a medium to soft texture, these papers are highly compatible with phenolic resin, facilitating uniform resin penetration. They also possess good temperature resistance, providing stable support for aluminum foil, and exhibit good compatibility with both aluminum foil and phenolic resin prepreg, ensuring structural stability after lamination.) Coated paper (commonly with a basis weight of 60-300 g / m²) 2 For example, it could be 60 g / m 2 100 g / m 2 150 g / m 2 200 g / m 2 250 g / m 2 Or 300 g / m 2 It has extremely low air permeability and is almost waterproof. It has a medium to high hardness and advantages such as high whiteness, high smoothness and fine printing. It can provide stable support for aluminum foil. Its excellent appearance characteristics make it easy to observe the status during the processing. It is suitable for scenarios with high requirements for the appearance and flatness of the cover plate. However, because its surface is a calcium carbonate or kaolin coating, the resin is difficult to penetrate into the paper fiber. The bonding mainly stays on the coating surface, which is prone to delamination and peeling.

[0019] Preferably, the basis weight of the backing paper B is 30-300 g / m². 2 For example, it could be 30 g / m 2 40 g / m 2 50 g / m 2 100 g / m 2 150 g / m 2 200 g / m 2 250 g / m 2 Or 300 g / m 2 wait.

[0020] Preferably, the thickness of the backing paper B is 0.05-0.3 mm. For example, it can be 0.05 mm, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm or 0.3 mm, etc.

[0021] Preferably, the thickness of the PCB back drill cover plate is 0.1-0.5 mm, for example, it can be 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm or 0.5 mm, etc.

[0022] The thickness of the PCB back drill cover plate provided by this invention is 0.1-0.5 mm. If the overall thickness of the cover plate is less than 0.1 mm, the cover plate is too thin, has poor rigidity, is easy to break, and will slightly dent after vacuum adsorption. The drill bit will trigger the zero point prematurely, resulting in insufficient actual drilling depth and an increase in residual piles. If the overall thickness of the cover plate is greater than 0.5 mm, the cutting load of the drill bit will increase, making it easy to break the bit. The thickness tolerance will increase, the length of the residual pile in the drilled hole will be higher, and the chip removal will be poor, leading to hole blockage and plugging.

[0023] Preferably, the step of placing the aluminum foil on the backing paper B includes directly bonding the aluminum foil to the backing paper B with an adhesive, or first applying an adhesive to one side of the backing paper B to obtain a coated paper, and then bonding it to the aluminum foil.

[0024] Preferably, the adhesive comprises any one or a combination of at least two of the following: non-hot melt polyurethane adhesives, acrylic emulsion adhesives, polyvinyl alcohol adhesives, EVA hot melt adhesives, polyolefin hot melt adhesives, polyester hot melt adhesives, polyamide hot melt adhesives, polyurethane hot melt adhesives, or SBC / SBS thermoplastic elastomer hot melt adhesives.

[0025] The adhesive used in this invention can be any adhesive commonly used in the field of PCB back-drill cover plates, without any special limitations or exclusive requirements. It can be flexibly selected according to actual production conditions, product performance requirements, raw material compatibility system and processing conditions.

[0026] Preferably, the adhesive comprises PE adhesive and / or PP adhesive.

[0027] Preferably, the application rate of the adhesive is 1.8-3.5 g / m³. 2 For example, it could be 1.8 g / m 2 2 g / m 2 2.2g / m 2 2.4 g / m 2 2.5 g / m 2 2.6 g / m 2 2.8 g / m 2 3 g / m 2 3.2 g / m 2 3.4 g / m 2 Or 3.5 g / m 2 wait.

[0028] Preferably, the compounding temperature is 40-80℃ (e.g., 40℃, 50℃, 60℃, 70℃, or 80℃), the compounding pressure is 0.3-0.6 MPa (e.g., 0.3 MPa, 0.4 MPa, 0.5 MPa, or 0.6 MPa), and the compounding time is 50-70 s (e.g., 50 s, 55 s, 60 s, 65 s, or 70 s).

[0029] Preferably, the hot pressing includes first hot pressing at 100-140℃ (e.g., 100℃, 110℃, 120℃, 130℃ or 140℃, etc.) and 4-6 MPa (e.g., 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa or 6 MPa, etc.) for 15-25 minutes (e.g., 15 min, 16 min, 18 min, 20 min, 22 min, 24 min or 25 min, etc.), then raising the temperature to 160-170℃ (e.g., 160℃, 162℃, 164℃, 165℃, 166℃, 168℃ or 170℃, etc.) and pressurizing to 8-10 MPa (e.g., 8 MPa, 8.5 MPa, 9 MPa, 9.5 MPa or 10 MPa, etc.) for 60-80 minutes (e.g., 60 min, 65 min, 70 min, 75 min or 80 min, etc.).

[0030] In a second aspect, the present invention provides a PCB back-drill cover plate, which is prepared by the preparation method described in the first aspect.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The present invention uses aluminum foil backing paper to replace traditional pure aluminum foil, which reduces the thickness of aluminum foil and improves the overall processability by relying on the backing paper support, effectively solving the defects of easy wrinkling, stretching and local damage in aluminum foil processing. At the same time, the preferred use of ultra-thin aluminum foil can significantly improve the back drilling depth control accuracy and the consistency of residual pile, optimize hole position accuracy and concentricity, reduce the risk of off-center drilling and over-cutting, and also reduce the number of step drilling processes.

[0032] (2) The present invention improves the support of the cover plate and the flatness of the plate by pre-composite process of aluminum foil and backing paper, and by adjusting the weight of the backing paper and the amount of adhesive applied. It can save the process of separately applying aluminum foil adhesive on site, making the process simpler and the performance more stable. Detailed Implementation

[0033] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0034] The specific information of the materials used in the following specific embodiments of the present invention is as follows: Bleached wood pulp paper, basis weight 160 g / m² 2 ; Thermosetting phenolic resin, BF09-D, Shenzhen Yoshida Chemical Co., Ltd.; Medical insurance paper, with a basis weight of 40 g / m² 2The thickness is 0.04 mm; White kraft paper A, with a basis weight of 40 g / m² 2 The thickness is 0.04 mm; White kraft paper B, with a basis weight of 50 g / m² 2 The thickness is 0.05 mm; White kraft paper C, basis weight 30 g / m² 2 The thickness is 0.03 mm; White kraft paper D, with a basis weight of 300 g / m² 2 The thickness is 0.3 mm; White kraft paper E, with a basis weight of 200 g / m² 2 The thickness is 0.2 mm; White kraft paper F, with a basis weight of 28 g / m² 2 The thickness is 0.028 mm; White kraft paper G, with a basis weight of 320 g / m² 2 The thickness is 0.32 mm; Coated paper, 60 g / m² 2 The thickness is 0.06 mm; Laminated paper, 5210, purchased from Suzhou Yuxuan Paper Industry, basis weight 52 g / m². 2 The thickness is 0.052 mm; Adhesive, PE granules, purchased from Suzhou Yuxuan Paper Industry.

[0035] Example 1 This embodiment provides a PCB back-drill cover plate and its preparation method, the preparation method including: (1) Thermosetting phenolic resin is impregnated onto bleached wood pulp paper and baked at 160°C to obtain phenolic resin semi-cured sheets (basis weight of 266 g / m²). 2 ); Apply the adhesive at 2.5 g / m 2 The adhesive amount was applied to one side of the medical insurance paper and then bonded to the aluminum foil (7 μm). After bonding, the paper was cured at 60℃ and 0.5 MPa for 60 s to obtain an aluminum foil backing paper with a thickness tolerance of ±0.35 μm. (2) One side of the aluminum foil backing paper B is laminated with the phenolic resin semi-cured sheet, and then hot-pressed at 120°C and 5 MPa for 20 min, and then heated to 165°C and 9 MPa for 70 min. After cooling, the PCB back drill cover plate (thickness is 0.31 mm) is obtained.

[0036] Example 2 This embodiment provides a PCB back-drill cover plate and its preparation method, the preparation method including: (1) Thermosetting phenolic resin is impregnated onto bleached wood pulp paper and baked at 160°C to obtain phenolic resin semi-cured sheets (basis weight of 266 g / m²). 2 ); Apply the adhesive at 2.5 g / m 2 The amount of adhesive applied is coated on one side of white kraft paper A and then bonded to aluminum foil (6 μm). After bonding, the paper is cured at 60℃ and 0.5 MPa for 60 s to obtain aluminum foil backing paper with a thickness tolerance of ±0.3 μm. (2) One side of the aluminum foil backing paper B is laminated with the phenolic resin semi-cured sheet, and then hot-pressed at 120°C and 5 MPa for 20 min, and then heated to 165°C and 9 MPa for 70 min. After cooling, the PCB back drill cover plate (thickness is 0.31 mm) is obtained.

[0037] Example 3 This embodiment provides a PCB back-drill cover plate and its preparation method, the preparation method including: (1) Thermosetting phenolic resin is impregnated onto bleached wood pulp paper and baked at 160°C to obtain phenolic resin semi-cured sheets (basis weight of 266 g / m²). 2 ); Apply the adhesive at 2.5 g / m 2 The amount of adhesive applied is coated on one side of white kraft paper B and then bonded to aluminum foil (6 μm). After bonding, the paper is cured at 60℃ and 0.5 MPa for 60 s to obtain aluminum foil backing paper with a thickness tolerance of ±0.3 μm. (2) One side of the aluminum foil backing paper B is laminated with the phenolic resin semi-cured sheet, and then hot-pressed at 120°C and 5 MPa for 20 min, and then heated to 165°C and 9 MPa for 70 min. After cooling, the PCB back drill cover plate (thickness is 0.315 mm) is obtained.

[0038] Example 4 This embodiment provides a PCB back-drill cover plate and its preparation method, the preparation method including: (1) Thermosetting phenolic resin is impregnated onto bleached wood pulp paper and baked at 160°C to obtain phenolic resin semi-cured sheets (basis weight of 266 g / m²). 2 ); Apply the adhesive at 2.5 g / m 2 The amount of adhesive applied is coated on one side of the coated paper and then bonded to the aluminum foil (6 μm). After bonding, the paper is cured at 60℃ and 0.5 MPa for 60 s to obtain an aluminum foil backing paper with a thickness tolerance of ±0.3 μm. (2) One side of the aluminum foil backing paper B is laminated with the phenolic resin semi-cured sheet, and then hot-pressed at 120°C and 5 MPa for 20 min, and then heated to 165°C and 9 MPa for 70 min. After cooling, the PCB back drill cover plate (thickness is 0.32 mm) is obtained.

[0039] Example 5 This embodiment provides a PCB back-drill cover plate and its preparation method, which differs from Embodiment 3 in that the thickness of the aluminum foil is adjusted to 5 μm.

[0040] Example 6 This embodiment provides a PCB back-drill cover plate and its preparation method, which differs from Embodiment 3 in that the thickness of the aluminum foil is adjusted to 4.5 μm.

[0041] Example 7 This embodiment provides a PCB back-drill cover plate and its preparation method, which differs from Embodiment 3 in that the thickness of the aluminum foil is adjusted to 14 μm.

[0042] Example 8 This embodiment provides a PCB back-drill cover plate and its preparation method, which differs from Embodiment 3 in that the thickness of the aluminum foil is adjusted to 50 μm.

[0043] Example 9 This embodiment provides a PCB back-drill cover plate and its preparation method, the preparation method including: (1) Thermosetting phenolic resin is impregnated onto bleached wood pulp paper and baked at 160°C to obtain phenolic resin semi-cured sheets (basis weight of 266 g / m²). 2 ); The adhesive-coated side of the coated paper is bonded to the aluminum foil (18 μm). After bonding, it is cured at 120℃ and 2MPa for 60s to obtain an aluminum foil backing paper with a thickness tolerance of ±0.35μm. (2) One side of the aluminum foil backing paper B is laminated with the phenolic resin semi-cured sheet, and then hot-pressed at 120°C and 5 MPa for 20 min, and then heated to 165°C and 9 MPa for 70 min. After cooling, the PCB back drill cover plate (thickness is 0.32 mm) is obtained.

[0044] Example 10 This embodiment provides a PCB back-drill cover plate and its preparation method. The difference from Embodiment 3 is that white kraft paper B is replaced with white kraft paper C, and the thickness of the PCB back-drill cover plate is 0.3 mm.

[0045] Example 11 This embodiment provides a PCB back-drill cover plate and its preparation method. The difference from Embodiment 3 is that white kraft paper B is replaced with white kraft paper D, and the thickness of the PCB back-drill cover plate is 0.48 mm.

[0046] Example 12 This embodiment provides a PCB back-drill cover plate and its preparation method. The difference from Embodiment 3 is that white kraft paper B is replaced with white kraft paper E, and the thickness of the PCB back-drill cover plate is 0.42 mm.

[0047] Example 13 This embodiment provides a PCB back-drill cover plate and its preparation method. The difference from Embodiment 3 is that white kraft paper B is replaced with white kraft paper F, and the thickness of the PCB back-drill cover plate is 0.28 mm.

[0048] Example 14 This embodiment provides a PCB back-drill cover plate and its preparation method. The difference from Embodiment 3 is that white kraft paper B is replaced with white kraft paper G, and the thickness of the PCB back-drill cover plate is 0.5 mm.

[0049] Comparative Example 1 This comparative example provides a PCB back-drill cover plate and its preparation method, the preparation method including: (1) Thermosetting phenolic resin is impregnated onto bleached wood pulp paper and baked at 160°C to obtain phenolic resin semi-cured sheets (basis weight of 266 g / m²). 2 ); The adhesive is impregnated on one side of the medical insurance paper and baked at 120°C to obtain an adhesive semi-cured sheet; (2) Adhesive prepreg and phenolic resin prepreg are stacked on the upper surface of aluminum foil in sequence. After pressing, PCB back drill cover plate is obtained. First, it is hot-pressed at 120℃ and 5 MPa for 20 min, then heated to 165℃ and 9 MPa for 70 min. After cooling, the PCB back drill cover plate (thickness is 0.32 mm) is obtained.

[0050] Comparative Example 2 This comparative example provides a PCB back-drill cover plate and its preparation method, the preparation method including: Thermosetting phenolic resin was impregnated onto bleached wood pulp paper and baked at 160°C to obtain a phenolic resin semi-cured sheet (basis weight 266 g / m²). 2 ); Adhesive is applied to one side of the aluminum foil and bonded to the phenolic resin prepreg. The foil is first hot-pressed at 120°C and 5 MPa for 20 minutes, and then hot-pressed at 165°C and 9 MPa for 70 minutes. After cooling, the PCB back-drill cover plate (thickness 0.32 mm) is obtained.

[0051] Comparative Example 3 This comparative example provides a PCB back-drill cover plate and its preparation method, which differs from Example 3 in that the thickness of the aluminum foil is adjusted to 54 μm.

[0052] Test methods The following performance tests were performed on the PCB back-drill cover plates provided in the embodiments and comparative examples: (1) Hole position accuracy (Cpk): Using a Vega drilling machine and a Jinzhou USF 0.45 mm × 7.0 mm drill bit, the drilling parameters are S100.F1.0R20N2000. The PCB back drill cover sample was tested for drilling on Panasonic M7 board material. Hole position accuracy is characterized by Cpk. (2) Depth control accuracy (residual pile length mil): The length of the residual pile is tested by metallographic sectioning method.

[0053] The test results are shown in Table 1 below: Table 1 The test results show that: (1) As can be seen from Examples 1-14, the present invention uses aluminum foil backing paper to replace traditional pure aluminum foil, which can reduce the thickness of aluminum foil and improve the overall processability by relying on backing paper, solving the problems of easy wrinkling, stretching and breakage of aluminum foil processing; it can also effectively improve the hole position accuracy of PCB back drilling, reduce the risk of off-center drilling and overcutting, and simplify the drilling step-by-step process, thereby improving the overall production efficiency.

[0054] (2) As can be seen from Examples 3, 5-8 and Comparative Example 3, the present invention preferably uses 4.5-7 μm ultra-thin aluminum foil to achieve the best hole position accuracy and depth control effect, while relying on the backing paper to avoid the processing defects of thin aluminum foil; however, when the aluminum foil thickness is less than 4.5 μm, the mechanical strength of the aluminum foil body is insufficient. Even with the support of backing paper, local deformation is still likely to occur during the drilling process. Although the residual pile length is slightly reduced and the depth control accuracy is slightly improved, the overall plate stability deteriorates, the batch processing defect rate increases, and it is not suitable for large-scale production; when the aluminum foil thickness is greater than 7 μm, the aluminum foil rigidity is too large, the drill bit response sensitivity is reduced, the depth control accuracy deteriorates, the residual pile length increases, and it is easy to cause problems such as hole blockage and off-center drilling. Although the processing performance is not good, it can still meet the basic usage requirements (through hole position accuracy >2, residual pile length <5 mil); however, when the aluminum foil thickness is further greater than 50 μm, it does not meet the usage conditions and cannot be processed normally.

[0055] (3) As can be seen from Examples 2-3 and 10-14, the present invention can precisely control the overall thickness, stiffness, and support performance of the aluminum foil backing paper by further limiting the basis weight of the backing paper B: In Example 13, due to the low basis weight of the backing paper B, the overall stiffness and support are insufficient, and the flatness of the board surface is poor; the paper absorbs too much glue during resin impregnation, which easily causes the aluminum foil to break under stress, and the stability of the finished PCB back drill cover plate decreases. In Example 14, due to the high basis weight of the backing paper B and its dense fibers, the resin cannot fully penetrate the paper layer, the bonding force between the aluminum foil backing paper and the prepreg is insufficient, and the finished product is prone to delamination defects. By selecting a backing paper B with a suitable basis weight within the range, the best balance can be achieved between support, flatness, and drilling accuracy.

[0056] (4) As can be seen from Example 3 and Comparative Examples 1-2, the present invention adopts the core process of pre-composite aluminum foil and backing paper to prepare aluminum foil backing paper, which eliminates the process of separate on-site glue application and step-by-step stacking. This not only simplifies the production process and reduces labor and material costs, but also ensures uniform glue layer and tight composite structure, ultimately achieving higher hole position accuracy and depth control consistency. In contrast, the comparative examples adopt the traditional process of on-site step-by-step glue application and direct aluminum foil glue application and stacking. The glue layer thickness is uneven, the aluminum foil is not supported by backing paper, the adhesion is poor during processing, and it is easy to deform. Ultimately, the hole position accuracy and depth control accuracy are greatly deteriorated, and the residual length exceeds the standard, which cannot meet the requirements of high-end PCB back drilling.

[0057] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a PCB back-drill cover plate, characterized in that, The preparation method includes: (1) The resin is impregnated onto the backing paper A and baked to obtain a resin semi-cured sheet; Aluminum foil is placed on backing paper B, and after lamination, aluminum foil backing paper is obtained; (2) The PCB back drill cover plate is obtained by laminating one side of the aluminum foil backing paper B with the resin semi-cured sheet and then hot pressing it.

2. The method for preparing a PCB back-drill cover plate according to claim 1, characterized in that, The resin includes thermosetting phenolic resin and / or epoxy resin, preferably thermosetting phenolic resin.

3. The method for preparing a PCB back-drill cover plate according to claim 1 or 2, characterized in that, The liner paper A includes medical insurance paper, unbleached kraft paper, white kraft paper, white cardboard, bleached wood pulp paper, or coated paper; Preferably, the basis weight of the liner paper A is 80-200 g / m². 2 ; Preferably, the basis weight of the resin semi-cured sheet is 120-340 g / m³. 2 .

4. The method for preparing a PCB back-drill cover plate according to any one of claims 1-3, characterized in that, The baking process is carried out at a temperature of 150-170℃ for 80-120 seconds.

5. The method for preparing a PCB back-drill cover plate according to any one of claims 1-4, characterized in that, The thickness of the aluminum foil is 4.5-50 μm, more preferably 4.5-7 μm.

6. The method for preparing a PCB back-drill cover plate according to any one of claims 1-5, characterized in that, The liner paper B includes any one of medical insurance paper, unbleached kraft paper, white kraft paper, white cardboard, bleached wood pulp paper, or coated paper; Preferably, the basis weight of the backing paper B is 30-300 g / m². 2 Further preferred is 40-200 g / m 2 ; Preferably, the thickness of the liner paper B is 0.03-0.3 mm; Preferably, the thickness of the PCB back drill cover is 0.1-0.5 mm.

7. The method for preparing a PCB back-drill cover plate according to any one of claims 1-6, characterized in that, The method of placing aluminum foil on backing paper B includes directly bonding aluminum foil to backing paper B with an adhesive or first applying an adhesive to one side of backing paper B to obtain coated paper and then bonding it to aluminum foil. Preferably, the adhesive comprises any one or a combination of at least two of the following: non-hot melt polyurethane adhesive, acrylic emulsion adhesive, polyvinyl alcohol adhesive, EVA hot melt adhesive, polyolefin hot melt adhesive, polyester hot melt adhesive, polyamide hot melt adhesive, polyurethane hot melt adhesive, or SBC / SBS thermoplastic elastomer hot melt adhesive. Preferably, the adhesive comprises PE adhesive and / or PP adhesive; Preferably, the application rate of the adhesive is 1.8-3.5 g / m³. 2 .

8. The method for preparing a PCB back-drill cover plate according to any one of claims 1-7, characterized in that, The composite temperature is 40-80℃, the composite pressure is 0.3-0.6 MPa, and the composite time is 50-70 s.

9. The method for preparing a PCB back-drill cover plate according to any one of claims 1-8, characterized in that, The hot pressing includes first hot pressing at 100-140℃ and 4-6 MPa for 15-25 min, and then hot pressing at 160-170℃ and 8-10 MPa for 60-80 min.

10. A PCB back-drill cover plate, wherein the PCB back-drill cover plate is prepared by the preparation method according to any one of claims 1-9.

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