A composite cover plate for PCB back drilling and a preparation method thereof

Abstract

The application discloses a composite cover plate for PCB back drilling and a preparation method thereof. The composite cover plate comprises an insulating layer, a spray film layer and a conductive layer which are stacked in sequence. The spray film layer comprises a porous matrix and a resin layer arranged on one side of the porous matrix. The resin layer is close to one side of the conductive layer. The resin layer is at least partially filled into the conductive layer. The porous matrix has communicating open pores. The resin layer is at least partially filled into the open pores of the porous matrix. The insulating layer is at least partially filled into the open pores of the porous matrix. The three layers of the composite cover plate for PCB back drilling form a mechanical interlocking structure, have excellent bonding strength, and can avoid problems such as layer separation and warping in the processing.

Description

Technical Field

[0001] This invention belongs to the field of back-drill cover plate technology, specifically relating to a composite cover plate for PCB back-drilling and its preparation method. Background Technology

[0002] During the mechanical drilling process of printed circuit boards (PCBs), a cover plate is usually placed on the surface of the board to be processed to adapt to the drilling process requirements. The core function of the cover plate is to protect the surface of the PCB board, effectively avoiding appearance defects such as scratches and marks on the board surface, while also suppressing the generation of burrs at the drill exit end, significantly improving the overall processing accuracy and finished product quality of PCB mechanical drilling.

[0003] PCB back-drilling processes are mostly completed using high-frequency electronic induction drilling machines. This equipment relies on high-frequency electronic conduction circuits to determine the drilling depth, using the contact between the drill tip and the cover plate conductor layer or PCB board surface as the depth calculation benchmark. Therefore, the conductivity accuracy, structural stability, high temperature resistance, and interlayer bonding performance of the cover plate directly determine the back-drilling depth accuracy and drilling yield.

[0004] Currently, mainstream back-drill cover plates consist of an insulating layer and a conductive layer. Adhesive is introduced between the insulating layer and the conductive layer for bonding. However, the current adhesive-based solution has disadvantages such as high cost, complex process, and long curing time. Therefore, an adhesive layer is introduced to replace the adhesive. It is bonded to the insulating layer and the conductive layer by hot-pressing and melting to achieve bonding between the insulating layer and the conductive layer.

[0005] Although the introduction of an adhesive layer can avoid the defects of adhesives, the adhesive layer still has some defects. For example, the bonding strength between the adhesive layer and the insulating or conductive layer is relatively low, and problems such as interlayer separation and lifting are prone to occur during application. At the same time, the overall flatness and processing accuracy of the cover plate including the adhesive layer are currently low, which can easily affect the PCB drilling quality. In addition, the high temperature resistance is poor, and it is prone to softening, deformation and breakage under the high temperature conditions of PCB back drilling, which cannot meet the requirements of high precision and high stability back drilling processing. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a composite cover plate for PCB back drilling and its preparation method.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a composite cover plate for PCB back-drilling, comprising an insulating layer, a coating layer, and a conductive layer stacked sequentially, wherein the coating layer comprises a porous substrate and a resin layer disposed on one side of the porous substrate, the resin layer being disposed near the conductive layer, wherein:

[0009] The resin layer is at least partially filled into the conductive layer, the porous substrate has interconnected open pores, the resin layer is at least partially filled into the open pores of the porous substrate, and the insulating layer is at least partially filled into the open pores of the porous substrate.

[0010] The composite cover plate provided by this invention has the following advantages:

[0011] i. By partially filling the resin layer into the conductive layer, a "first mechanical interlock" structure is formed between the resin layer and the conductive layer, thereby improving the bonding strength between the coating layer and the conductive layer;

[0012] ii. By partially filling the porous matrix with the resin layer, a "second mechanical interlock" structure is formed between the resin layer and the porous matrix, which improves the bonding strength between the resin layer and the porous matrix, thus improving the bonding performance of the coating layer itself.

[0013] iii. By partially filling the porous matrix with the insulating layer, a "third mechanical interlock" structure is formed between the insulating layer and the porous matrix, which improves the bonding strength between the insulating layer and the coating layer;

[0014] Therefore, the composite cover plate for PCB back drilling provided by the present invention forms a "mechanical interlocking" structure between the three layers, which has excellent bonding strength and can avoid problems such as interlayer separation and warping during processing.

[0015] Preferably, the thickness of the resin layer filling the porous matrix is ​​5-20% of the thickness of the porous matrix, for example, 5%, 8%, 10%, 13%, 15%, 17%, 20% or any of the above values.

[0016] Preferably, the thickness of the insulating layer filling the porous matrix is ​​40-80% of the thickness of the porous matrix, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or any of the above values.

[0017] Preferably, the total thickness of the resin layer and the insulating layer filling the porous matrix is ​​more than 50% of the thickness of the porous matrix, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any of the above values.

[0018] The present invention further improves the bonding strength between the insulating layer and the coating layer by filling both the resin layer and the insulating layer into the porous matrix, preferably with a total filling depth of more than 50% of the thickness of the porous matrix. In the present invention, the total thickness of the resin layer and the insulating layer filling the porous matrix is ​​at most 100%.

[0019] In this invention, the method for testing the filling depth of the resin layer or insulating layer in the porous matrix includes: freezing and fracturing or ion cutting the composite cover plate to obtain a cleaned cross section, then performing SEM testing on the cross section to obtain a cross section SEM image, and performing EDS elemental analysis on the cross section SEM to distinguish the penetration thickness of the resin layer or insulating layer in the porous matrix.

[0020] Preferably, the average pore size of the porous matrix is ​​1-17 μm, for example, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 17 μm or any of the above values; the porosity is 30-60%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any of the above values; and the air permeability is ≥35 μm / (Pa·s), for example, 35 μm / (Pa·s), 36 μm / (Pa·s), 38 μm / (Pa·s), 40 μm / (Pa·s), 42 μm / (Pa·s), 45 μm / (Pa·s), 50 μm / (Pa·s), 55 μm / (Pa·s), 60 μm / (Pa·s), 65 μm / (Pa·s), 70 μm / (Pa·s) or any of the above values.

[0021] Meanwhile, by selecting a specific porous matrix, the present invention enables the resin slurry and insulating layer resin to flow and fill the pores of the porous matrix, forming a mechanically interlocking structure and improving the interlayer bonding effect.

[0022] Preferably, the basis weight of the porous matrix is ​​60-130 g / m³. 2 For example, 60 g / m 2 70 g / m 2 80 g / m 2 90g / m 2 100 g / m 2 110 g / m 2 120 g / m 2 130 g / m 2 Or any of the above values, with an ash content ≤0.5%, for example 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or any of the above values, and free of impurities with a diameter ≥50μm, and a metal impurity content ≤0.01%, for example 0.001%, 0.003%, 0.005%, 0.007%, 0.008%, 0.009%, 0.01% or any of the above values.

[0023] This invention avoids the impact of impurities on drilling by limiting the porous matrix to have low impurities.

[0024] Preferably, the surface roughness of the porous matrix is ​​4-10 μm, for example, 4 μm, 4.2 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any value between the above, and the water absorption is ≤100 g / m³. 2 For example, 8 g / m 2 20 g / m 2 30 g / m 2 40 g / m 2 50 g / m 2 80 g / m 2 100 g / m 2 Or any of the above values, preferably wet strength ≥10 N / cm, such as 10 N / cm, 12 N / cm, 15 N / cm, 18 N / cm, 20 N / cm, 25 N / cm, 30 N / cm or any of the above values.

[0025] This invention utilizes a porous matrix with a roughness of 4-10 μm and a porosity of 30-60%, which significantly increases the adhesion between the resin layer and the insulating layer, thereby improving the interlayer bonding effect.

[0026] In this invention, the testing standard for thickness is GB / T451.3, the testing standard for basis weight is GB / T451.2, the testing standard for air permeability is GB / T5453, the testing standard for Cobb water absorption 60s is GB / T1540, the testing standard for ash content is GB / T742, the testing standard for average pore size is the pore size bubble pressure method, and the testing standard for roughness Ra is GB / T10342.

[0027] Preferably, the roughness Ra of the conductive layer near the resin layer is 0.1-1.3 μm, for example, 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm or any of the above values, and the depth to which the resin layer fills the conductive layer is 0.1-1.3 μm, for example, 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm or any of the above values.

[0028] The conductive layer has a higher roughness on the side near the resin layer, that is, the surface has a certain uneven structure. The resin layer fills into the uneven structure, which increases the contact area with the conductive layer and thus increases the peel strength between the resin layer and the conductive layer.

[0029] Preferably, the peel strength between the coating layer and the conductive layer is ≥0.6 N / mm, for example, 0.6 N / mm, 0.8 N / mm, 1.1 N / mm, 1.4 N / mm, 1.7 N / mm, 2.0 N / mm, 2.3 N / mm or any of the above values, and the peel failure mode is cohesive failure.

[0030] The test method for peel strength described in this invention is performed in accordance with GB / T2791-1995.

[0031] The coating layer and the conductive layer described in this invention also have excellent adhesion properties. When the two are peeled, the peeling failure mode is cohesive failure, that is, the interfacial bonding force between the two is greater than the strength of the coating layer itself, which can further avoid problems such as interlayer separation or lifting.

[0032] Preferably, the resin layer comprises a thermoplastic resin, more preferably modified polyethylene, more preferably maleic anhydride-grafted polyethylene resin, and even more preferably the maleic anhydride grafting rate is 0.5-3 wt%, for example 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.3 wt%, 2.5 wt%, 3 wt%, or any range of the above values.

[0033] Preferably, the melt index (190℃ / 2.16 kg) of the thermoplastic resin is 2-20 g / 10min, for example, 2 g / 10min, 5 g / 10min, 8 g / 10min, 12 g / 10min, 15 g / 10min, 18 g / 10min, 20 g / 10min or any of the above values, and the Vicat softening temperature is ≥80℃, for example, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃ or any of the above values.

[0034] This invention selects a thermoplastic resin with high fluidity, which, when processed and bonded with the conductive layer, can fully impregnate and fill the "uneven structure" on the surface of the conductive layer, forming a "mechanical interlocking" structure with the conductive layer.

[0035] Meanwhile, the present invention preferably uses a thermoplastic resin with high heat resistance, which has excellent deformation resistance and can avoid softening, deformation, and breakage under the high temperature conditions of PCB back drilling, so that the resulting composite cover plate for PCB back drilling can fully meet the requirements of high precision and high stability back drilling processing.

[0036] Preferably, the conductive layer and the resin layer are chemically bonded together.

[0037] In a second aspect, the present invention provides a method for preparing a composite cover plate for PCB back-drilling as described in the first aspect, the method comprising:

[0038] S1. An insulating layer, a coating layer, and a conductive layer are stacked sequentially, wherein the coating layer includes a porous substrate and a resin layer disposed on one side of the porous substrate, and the resin layer is close to the conductive layer.

[0039] S2. Hot pressing molding, so that the resin layer is at least partially filled into the conductive layer and the insulating layer is at least partially filled into the openings of the porous substrate, to obtain the composite cover plate for PCB back drilling.

[0040] Preferably, the preparation method of the coating layer includes: coating a resin slurry onto a porous substrate, and then pressing it together to obtain the coating layer.

[0041] Preferably, the pressure applied during the pressurization process is 0.3-0.5 MPa, for example, 0.3 MPa, 0.33 MPa, 0.35 MPa, 0.4 MPa, 0.44 MPa, 0.45 MPa, 0.5 MPa, or any value between the above, and the temperature is 120-150℃, for example, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, or any value between the above.

[0042] Preferably, the resin slurry is coated on the porous substrate at a basis weight of 5-30 g / m². 2 For example, 5 g / m 2 6g / m 2 8 g / m 2 10 g / m 2 12 g / m 2 15 g / m 2 18 g / m 2 20 g / m 2 22 g / m 2 25 g / m 2 28 g / m 2 30g / m 2 .

[0043] Preferably, the thickness of the coating layer is 25-140 μm, for example, 25 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm or any of the above values.

[0044] Preferably, the preparation method further includes: surface activation of the conductive layer by plasma treatment, and then bonding it with the coating layer.

[0045] This invention involves plasma treatment of the side of the conductive layer to be bonded to the coating layer, which not only forms a "rough and uneven structure" with a certain degree of roughness, but also gives the bonding surface of the conductive layer oxygen-containing functional groups, such as carboxyl groups and / or hydroxyl groups, which can react with maleic anhydride groups to form covalent bonds or have hydrogen bonding effects, thereby further improving the compatibility between the conductive layer and the resin layer.

[0046] Preferably, the hot pressing temperature is 140-160℃, for example, 140℃, 145℃, 148℃, 150℃, 155℃, 158℃, 160℃ or any range between the above values, and the pressure is 5-7 MPa, for example, 5 MPa, 5.2 MPa, 5.5 MPa, 6 MPa, 6.5 MPa, 6.8 MPa, 7 MPa or any range between the above values.

[0047] Preferably, the conductive layer comprises an aluminum foil layer or an aluminum alloy layer, and preferably has a thickness of 5-50 μm, such as 5 μm, 12 μm, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm or any of the above values.

[0048] Preferably, the insulating layer comprises a phenolic resin semi-cured layer, and preferably has a thickness of 0.05-1 mm, such as 0.05 mm, 0.2 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.9 mm, 1 mm or any of the above values.

[0049] In this invention, the thicknesses of the conductive layer, the coating layer, and the insulating layer are all the thicknesses before hot pressing.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) The composite cover plate for PCB back drilling provided by the present invention has excellent interlayer bonding force, which can avoid problems such as interlayer separation and warping during the processing;

[0052] (2) The composite cover plate for PCB back drilling provided by the present invention has high overall flatness and processing precision, and its application can improve the quality of PCB drilling.

[0053] (3) The composite cover plate for PCB back drilling provided by the present invention has good heat resistance and can avoid the defects such as softening and deformation under the high temperature working conditions of PCB back drilling. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0055] Unless otherwise specified, the raw materials involved in the following specific embodiments of the present invention are all conventional materials in the art, and can be purchased from commercially available products. Some raw material information is as follows:

[0056] Aluminum foil: thicknesses of 10 μm and 50 μm, both purchased from Zhongji Aluminum Coil;

[0057] Porous Matrix-1: Average pore size is 9 μm, porosity is 40%, air permeability is 210 μm / (Pa•s), and basis weight is 62 g / m³. 2 The ash content is 0.4%, the surface roughness is 5 μm, and the water absorption is 58 g / m². 2 The thickness is 80 μm, purchased from Minfeng Special Paper Co., Ltd., grade PCB-M80;

[0058] Porous Matrix-2: Average pore size is 12 μm, porosity is 45%, air permeability is 120 μm / (Pa•s), and basis weight is 92 g / m³. 2 It has an ash content of 0.5%, a surface roughness of 6 μm, and a water absorption of 75 g / m³. 2 The thickness is 120 μm, purchased from Minfeng Special Paper Co., Ltd., grade PCB-M120;

[0059] Porous Matrix-3: Average pore size 250 nm, porosity 60%, air permeability 35 μm / (Pa•s), basis weight 98 g / m³ 2 The ash content is 0.02%, the surface roughness is 3 μm, and the water absorption is 5 g / m². 2 The thickness is 130 μm, purchased from Yantai Minshida Special Paper Co., Ltd., brand name Metastar YT812-130 meta-aramid paper for honeycomb;

[0060] Thermoplastic resin-1: maleic anhydride-grafted LDPE, with a grafting rate of 1.2%, a melt index (190℃ / 2.16 kg) of 2.5 g / 10min, and a Vicat softening temperature of 92℃, was purchased from Shanghai Jiuju Polymer, with the grade HZEA203.

[0061] Thermoplastic resin-2: maleic anhydride-grafted HDPE, with a grafting rate of 1.4%, a melt index (190℃ / 2.16 kg) of 2 g / 10 min, and a Vicat softening temperature of 126℃, was purchased from Shanghai Jiuju Polymer, with the grade HZEA305.

[0062] Thermoplastic resin-3: LDPE, melt index (190℃ / 2.16 kg) of 7.3 g / 10min, Vicat softening temperature of 82℃, purchased from LG Chem, grade LB7000;

[0063] Insulation layer-1: Impregnated with cashew phenol-modified thermosetting phenolic resin (Jinan Shengquan, brand name PF9402-2) at a density of 140g / m². 2 Bleached wood pulp paper (Shandong Chenming Paper Industry (Shouguang)), baked at 150℃ for 100 seconds, with an sizing rate of 40%;

[0064] Insulation layer-2: Impregnated with 200 g / m² thermosetting phenolic resin (Shandong Dongrun New Material Co., Ltd., brand name DR-TH08). 2 Bleached wood pulp paper (Shandong Chenming Paper Industry (Shouguang)), baked at 150℃ for 110 seconds, with 50% sizing.

[0065] Examples 1-7

[0066] This embodiment provides a method for preparing a composite cover plate for PCB back drilling, as follows:

[0067] S1. The conductive layer is surface activated by argon-oxygen plasma treatment to give the surface of the conductive layer oxygen-containing functional groups. The parameters of the argon-oxygen plasma treatment include: using a mixture of O2 and Ar (3:7), power of 220-350 W, and pressure of 10-22 Pa. By adjusting the power and pressure, the surface roughness of the conductive layer is made different. The specific parameters of the roughness are shown in Table 1.

[0068] S2. Apply the resin slurry onto the porous substrate, using a coating density of (10 g / m²). 2 After pressing, a coating layer is obtained;

[0069] S3. The insulating layer, the coating layer and the conductive layer are stacked sequentially, wherein the resin layer is close to the conductive layer.

[0070] S4. Hot pressing molding, so that the resin layer is at least partially filled into the conductive layer and the insulating layer is at least partially filled into the openings of the porous substrate, to obtain a composite cover plate for PCB back drilling.

[0071] Some parameters involved in the embodiments are shown in Table 1:

[0072] Table 1

[0073]

[0074] Note:

[0075] The resin layer filling thickness / μm refers to the actual thickness of the resin layer filling the conductive layer.

[0076] The resin layer filling thickness / % refers to the percentage of the porous matrix whose thickness is equal to the thickness of the porous matrix.

[0077] The insulation layer filling thickness / % refers to the percentage of the thickness of the porous matrix that the insulation layer fills.

[0078] Comparative Example 1

[0079] This comparative example provides a method for preparing a composite cover plate for PCB back drilling.

[0080] The difference from Example 6 is that, in this comparative example, thermoplastic resin-1 is replaced with thermoplastic resin-3.

[0081] Comparative Example 2

[0082] This comparative example provides a method for preparing a composite cover plate for PCB back drilling.

[0083] The difference from Example 6 is that, in this comparative example, porous matrix-1 is replaced with porous matrix-3.

[0084] Comparative Example 3

[0085] This comparative example provides a method for preparing a composite cover plate for PCB back drilling.

[0086] The difference from Example 6 is that in this comparative example, the pressure for pressing in step S2 is 0.1 MPa.

[0087] Comparative Example 4

[0088] This comparative example provides a method for preparing a composite cover plate for PCB back drilling.

[0089] The difference from Example 6 is that in this comparative example, the pressure for hot pressing in step S4 is 4 MPa.

[0090] Performance testing

[0091] The performance of the samples provided in the examples and comparative examples was tested using the following methods:

[0092] (1) Interlayer peel strength; The test method refers to GB / T2791-1995, and the peel strength between the conductive layer and the coating layer is tested;

[0093] (2) Drilling quality: PCB board (0.8 mm Shengyi S-1000, 3PNL), cover plate is sample, pad is wood fiberboard, through hole drilling test is performed using Jinzhou 0.45 mm drill bit to check for CPK, wire wrapping and other phenomena;

[0094] (3) Heat resistance: The sample was subjected to gradient heating test, and baked at 90℃ / 100℃ / 120℃ for 5-30 minutes. If there was no change after baking for 30 minutes, the temperature was increased and the conductive layer was observed to see if it bulged. The treatment temperature of the conductive layer bulging was recorded as the evaluation standard of heat resistance.

[0095] (4) Warp performance: The test method refers to GB / T15102-2017, and the diagonal height warp ratio after hot pressing and deburring is calculated;

[0096] (5) Water absorption rate: The test method is in accordance with GB / T1303.6-2009;

[0097] (6) Electrical insulation performance: Volume resistivity is tested, and the test method refers to GB / T1410-2006;

[0098] The test results are as follows:

[0099] Table 2

[0100]

[0101] As can be seen from the embodiments and performance tests, the composite cover plate for PCB back drilling provided by the present invention has excellent interlayer bonding force, which can avoid problems such as interlayer separation and warping during processing. It has high overall flatness and processing accuracy. Its application can improve the quality of PCB drilling and has good heat resistance. It can avoid the defects such as softening and deformation under the high temperature conditions of PCB back drilling.

[0102] The present invention has been illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite cover plate for PCB back drilling, characterized in that, The structure comprises an insulating layer, a coating layer, and a conductive layer stacked sequentially. The coating layer includes a porous substrate and a resin layer disposed on one side of the porous substrate, with the resin layer adjacent to the conductive layer. The resin layer is at least partially filled into the conductive layer, the porous substrate has interconnected open pores, the resin layer is at least partially filled into the open pores of the porous substrate, and the insulating layer is at least partially filled into the open pores of the porous substrate.

2. The composite cover plate for PCB back drilling according to claim 1, characterized in that, The thickness of the resin layer filling the porous matrix is ​​5-20% of the thickness of the porous matrix; And / or, the thickness of the insulating layer filling the porous matrix is ​​40-80% of the thickness of the porous matrix.

3. The composite cover plate for PCB back drilling according to claim 1 or 2, characterized in that, The total thickness of the resin layer and the insulating layer filling the porous matrix is ​​more than 50% of the thickness of the porous matrix.

4. The composite cover plate for PCB back drilling according to any one of claims 1-3, characterized in that, The average pore size of the open pores in the porous matrix is ​​1-17 μm, the porosity is 30-60%, and the air permeability is ≥35 μm / (Pa·s); And / or, the basis weight of the porous matrix is ​​60-130 g / m³. 2 The ash content is ≤0.5%, and there are no impurities with a diameter ≥50 μm, and the metal impurity content is ≤0.01%; And / or, the surface roughness of the porous matrix is ​​4-10 μm, and the water absorption is ≤100 g / m³. 2 .

5. The composite cover plate for PCB back drilling according to any one of claims 1-4, characterized in that, The surface roughness Ra of the conductive layer near the resin layer is 0.1-1.3 μm, and the depth to which the resin layer fills the conductive layer is 0.1-1.3 μm.

6. The composite cover plate for PCB back drilling according to any one of claims 1-5, characterized in that, The peel strength between the coating layer and the conductive layer is ≥0.6 N / mm, and the peel failure mode is cohesive failure.

7. The composite cover plate for PCB back drilling according to any one of claims 1-6, characterized in that, The resin layer comprises a thermoplastic resin, preferably modified polyethylene, more preferably maleic anhydride-grafted polyethylene resin, and even more preferably, the maleic anhydride grafting rate is 0.5-3 wt%. Preferably, the thermoplastic resin has a melt index of 2-20 g / 10min and a Vicat softening temperature of ≥80℃; Preferably, the conductive layer and the resin layer are chemically bonded together.

8. A method for preparing a composite cover plate for PCB back drilling as described in any one of claims 1-7, characterized in that, The preparation method includes: S1. An insulating layer, a coating layer, and a conductive layer are stacked sequentially, wherein the coating layer includes a porous substrate and a resin layer disposed on one side of the porous substrate, and the resin layer is close to the conductive layer. S2. Hot pressing molding, so that the resin layer is at least partially filled into the conductive layer and the insulating layer is at least partially filled into the openings of the porous substrate, to obtain the composite cover plate for PCB back drilling.

9. The preparation method according to claim 8, characterized in that, The method for preparing the coating layer includes: coating a resin slurry onto a porous substrate, and then pressing it together under pressure to obtain the coating layer. Preferably, the pressure applied during the pressurization process is 0.3-0.5 MPa, and the temperature is 120-150℃. Preferably, the resin slurry is coated on the porous substrate at a basis weight of 5-30 g / m². 2 ; Preferably, the thickness of the coating layer is 25-140 μm.

10. The preparation method according to claim 8 or 9, characterized in that, The preparation method further includes: surface activation of the conductive layer by plasma treatment, and then bonding it with the coating layer; And / or, the hot pressing temperature is 140-160℃ and the pressure is 5-7 MPa; And / or, the conductive layer comprises an aluminum foil layer or an aluminum alloy layer, preferably with a thickness of 5-50 μm; And / or, the insulating layer comprises a phenolic resin semi-cured layer, preferably with a thickness of 0.05-1 mm.

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