Adhesive sheet with ultra-low adhesive overflow amount, cover film, adhesive copper foil base material and cover plate

Abstract

The invention discloses an adhesive sheet with ultra-low glue overflow amount, a cover film, an adhesive copper foil base material and a cover plate, the adhesive sheet comprises an adhesive layer with ultra-low glue overflow amount, a polyimide film or a coating type polyimide layer, and the thickness of the adhesive layer with ultra-low glue overflow amount is 0.5-5 [mu] m. The method has excellent flatness, operability, insulativity and thermal stability, and can be used for compounding, thickness reduction and forming of materials due to the fact that the adhesive layer with the ultra-low adhesive overflow amount is extremely thin and the adhesive overflow amount is extremely low, and the method can adapt to the processing conditions of the circuit board technology.

Description

Technical Field

[0001] This invention belongs to the field of circuit board technology, and in particular relates to an adhesive sheet, cover film, adhesive copper foil substrate and cover plate with ultra-low adhesive overflow. Background Technology

[0002] In response to the demands for thinner and lighter products and improved form factors, a new type of equipment and application has emerged in the circuit board industry. This requires ensuring the integrity of the final appearance of adhesive sheets and copper foil substrates under specific high-density stamping processes. This necessitates metallization and liquid material filling of the stamped surfaces and interfaces to meet design requirements, and the addition of insulating and sealing films at the ports. While this type of application does not require the circuit filling functionality of traditional circuit board applications, it still demands reliable bonding interfaces to meet industry standards for circuit board specifications, representing a completely new material design requirement.

[0003] In the circuit board industry, polyimide is an excellent industrial plastic with superior thermal stability, chemical resistance, electrical properties, and mechanical properties, and is widely used. Specifically, for adhesive sheets, cover films, and copper foil substrates used in FPCs, polyimide films can meet these stringent requirements due to their properties. However, the resin systems commonly used for the adhesive layers, such as epoxy resin, acrylic resin, and polyolefin, still have shortcomings in terms of bonding strength, heat resistance, and extremely low pressure overflow. Summary of the Invention

[0004] The main technical problem solved by this invention is to provide an adhesive sheet, cover film, adhesive copper foil substrate and cover plate with ultra-low glue overflow, which has excellent flatness, operability, insulation and thermal stability. Because the ultra-low glue overflow adhesive layer is extremely thin and the glue overflow is extremely low, it can be used for material composite, thickness reduction and molding, and can be adapted to the process conditions of circuit board manufacturing.

[0005] To solve the above-mentioned technical problems, the present invention adopts a technical solution as follows: an adhesive sheet with ultra-low adhesive overflow, comprising, in sequence, a first release layer, an ultra-low adhesive overflow layer, a polyimide film, an ultra-low adhesive overflow layer and a second release layer, wherein the thickness of the ultra-low adhesive overflow layer is 0.5-5μm, preferably 0.5-2μm.

[0006] Typically, the first and second release layers of adhesive sheets are made of release film and release paper respectively for easy differentiation. However, depending on the needs and structural design, both release film or both release paper can be used, and markings can be made on their surfaces to distinguish between the light release surface and the heavy release surface.

[0007] An ultra-low adhesive overflow cover film comprises, in sequence, a polyimide film, an ultra-low adhesive overflow layer, and a release layer, wherein the thickness of the ultra-low adhesive overflow layer is 0.5-5 μm, preferably 0.5-2 μm.

[0008] An adhesive copper foil substrate with ultra-low adhesive overflow includes, in sequence, a copper foil layer, a coated polyimide layer, an ultra-low adhesive overflow layer, and a release layer. Its structure is a variant of a copper foil coating resin, consisting of a four-layer structure in which coated polyimide is formed on the copper foil, the adhesive is coated, and a release liner is bonded. The thickness of the ultra-low adhesive overflow layer is 0.5-5 μm, preferably 0.5-2 μm.

[0009] The copper foil layer of the adhesive copper foil substrate of the present invention can be rolled copper foil or electrolytic copper foil, with a thickness ranging from 2 to 35 μm.

[0010] The copper foil layer of the adhesive copper foil substrate of the present invention can be a carrier copper foil, which is composed of carrier copper, release agent and ultra-thin copper foil.

[0011] A cover plate with ultra-low glue overflow, wherein the cover plate is a two-layer cover plate or a four-layer cover plate; The two cover plates consist of a covering film, an adhesive sheet, and a covering film in sequence. The four-layer cover plate includes the following two structures: The first structure of the four-layer cover plate includes, in sequence, a cover film, an adhesive sheet, an adhesive copper foil substrate, a cover film, an adhesive sheet, and a cover film; The second structure of the four-layer cover plate includes, in sequence, a cover film, an adhesive sheet, an adhesive copper foil substrate, an adhesive sheet, an adhesive copper foil substrate, an adhesive sheet, and a cover film; The adhesive sheet comprises, in sequence, an ultra-low excess adhesive layer, a polyimide film, and an ultra-low excess adhesive layer; the cover film comprises, in sequence, a polyimide film and an ultra-low excess adhesive layer. The adhesive copper foil substrate comprises, in sequence, a copper foil layer, a coated polyimide layer, and an ultra-low adhesive layer; The thickness of the ultra-low overflow adhesive layer is 0.5-5 μm, preferably 0.5-2 μm.

[0012] The polyimide film of the cover film on the outer side of the cover plate is located on the outer side of the entire cover plate. That is, both the upper and lower cover films have polyimide layers facing outwards. There are no restrictions on the cover film and the adhesive copper foil substrate in the middle of the cover plate, as long as the cover film, the adhesive copper foil substrate, and the adhesive sheet can be bonded together by an ultra-low amount of adhesive layer.

[0013] Both the cover film and the adhesive copper foil substrate serve as cover plates, providing surface insulation and conductivity, respectively; while the adhesive sheet is suitable for shape cutting and bonding various interfaces as a material.

[0014] In the stack of adhesive sheet, cover film, adhesive copper foil substrate and cover plate, the adhesive in the ultra-low adhesive layer is selected from at least one of epoxy resin, acrylic resin, urethane resin, silicone rubber resin, poly(p-cycloxylene) resin and polyimide resin. The polyimide resin material is selected from at least one of bismaleimide resin, styrene-ethylene-butene-styrene block copolymer, polyimide resin and polyamide-imide, preferably at least one of polyimide resin and polyamide-imide; The epoxy resin is selected from at least two of the following: glycidylamine type epoxy resin, glycidyl ester type epoxy resin, epoxidized olefin compound, alicyclic epoxy resin, polyphenol type glycidyl ether epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic glycidyl ether epoxy resin, heterocyclic epoxy resin and mixed epoxy resin. The ultra-low overflow adhesive layer synthesized from the polyimide resin includes a polyimide resin material, an epoxy resin, and a curing agent. The curing agent is selected from at least one of amines (tertiary amines, quaternary ammonium salts, aliphatic amines, aromatic amines) and imidazole compounds (such as 2E4MZ). The ultra-low overflow adhesive layer comprises, by weight percentage, 70-95% polyimide resin, 1-25% epoxy resin, and 0-10% curing agent.

[0015] The ultra-low overflow adhesive layer synthesized from acrylic resin includes a main agent and a curing agent. The main agent is selected from at least one of methyl methacrylate (MMA) and nitrile rubber (NBR), and the curing agent includes at least one of methyl ethyl ketone peroxide (MEKP) and cobalt salt accelerator. The ultra-low overflow adhesive layer, by weight percentage, comprises 98.00-99.99% main agent with MMA not less than 60%, and 0.01%-2% curing agent.

[0016] The epoxy resin-synthesized ultra-low overflow adhesive layer includes epoxy resin, rubber, curing agent and solvent. The curing agent is selected from at least one of amines (tertiary amines, quaternary ammonium salts, aliphatic amines, aromatic amines) and imidazole compounds (such as 2E4MZ). The rubber is selected from at least one of nitrile rubber, cis-butadiene rubber, chloroprene rubber and natural rubber. The solvent is selected from methyl ethyl ketone. The ultra-low overflow adhesive layer comprises, by weight percentage, 30-75% epoxy resin, 10-35% rubber, 5-45% curing agent, and an appropriate amount of solvent.

[0017] The polyimide film is a commercially available polyimide film made by uniaxial stretching or biaxial stretching, with a thickness ranging from 3 μm to 75 μm.

[0018] This invention also provides a method for preparing an adhesive sheet with ultra-low adhesive overflow, comprising the following steps: Step 1: On a roll-to-roll coating machine, a polyimide film is coated with an ultra-low overflow adhesive layer. The film is then baked in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent, dry and cure, and then the first release layer is bonded on. Step 2: The semi-finished product obtained in Step 1 is rolled up and sent back to the other side to be coated with an ultra-low overflow adhesive layer. After baking in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent, the second release layer is attached to obtain the adhesive sheet.

[0019] The present invention also provides a method for preparing an ultra-low adhesive overflow cover film, comprising the following steps: feeding a polyimide film onto a roll-to-roll coating machine to coat an ultra-low adhesive overflow layer, baking it in a coating machine oven at 60-180℃ for 3-5 minutes to remove solvent and dry and cure it, and then attaching a release layer to obtain the cover film.

[0020] This invention also provides a method for preparing an adhesive-coated copper foil substrate with ultra-low adhesive overflow, comprising the following steps: Step 1: Feed copper foil onto a roll-to-roll coating machine and coat it with polyimide precursor varnish. Then, bake it in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent, dry and cure it, and roll it up for later use. Step 2: Send the semi-finished product obtained in Step 1 to a high-temperature continuous oxygen-free oven for roll-to-roll operation, dehydrate and close the ring of the precursor varnish to polymerize it into coated polyimide, and obtain the semi-finished product as a single-sided polyimide copper foil substrate. Step 3: Send the semi-finished product obtained in Step 2 onto a roll-to-roll coating machine, apply an ultra-low overflow adhesive layer to the polyimide surface, bake it in the coating machine oven at 60-180℃ for 3-5 minutes to remove solvent and dry and cure, and then attach the release layer to obtain the adhesive copper foil substrate.

[0021] The beneficial effects of the present invention include at least the following: The extremely thin adhesive layer of the present invention with extremely low adhesive overflow is applied to adhesive sheets, cover films and adhesive copper foil substrates, and has excellent bonding strength, operability, insulation and solder heat resistance. Due to its extremely low adhesive overflow, it can be used for material composite, thickness reduction and molding, and retains the designed irregular structure to the greatest extent after processing. It can be used as a multi-opening adhesive sheet and cover plate with interlayer interface and pore conduction but outer layer insulation. The adhesive sheet, cover film, and adhesive-coated copper foil substrate of the present invention have excellent flatness, operability, insulation, and thermal stability, and can meet the 288°C soldering conditions required for circuit board assembly in a short time. The adhesive layer of the present invention, through a formulation design without the addition of powder fillers and a precise coating design, can be coated on polyimide film and copper foil layer to generate corresponding adhesive sheets, cover films and copper foil substrates, and is suitable for the aforementioned die-cutting and cover plate applications, with excellent adhesion and low adhesive overflow. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the stacked structure of a covering film according to the present invention; Figure 2 This is a schematic diagram of the stacked structure of an adhesive sheet according to the present invention; Figure 3 This is a schematic diagram of the stacked structure of an adhesive copper foil substrate according to the present invention; Figure 4 This is a schematic diagram of the stacked structure of the two cover plates of the present invention; Figure 5 This is a schematic diagram of the first structure of the four-layer cover plate of the present invention. Figure 6 This is a schematic diagram of the stacked structure of the second type of four-layer cover plate of the present invention; The parts in the attached diagram are labeled as follows: 101. First release layer; 102. Ultra-low adhesive overflow layer; 103. Polyimide film; 104. Second release layer; 201. Release layer; 301, Copper foil layer; 302, Coated polyimide layer; 100. Adhesive sheet; 200. Covering film; 300. Copper foil substrate with adhesive. Detailed Implementation

[0023] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0024] Example: An adhesive sheet with ultra-low adhesive overflow, such as Figure 2 As shown, it sequentially includes a first release layer 101, an ultra-low overflow adhesive layer 102, a polyimide film 103, an ultra-low overflow adhesive layer and a second release layer 104, wherein the thickness of the ultra-low overflow adhesive layer is 0.5-5μm, preferably 0.5-2μm.

[0025] Typically, the first and second release layers of adhesive sheets are made of release film and release paper respectively for easy differentiation. However, depending on the needs and structural design, both release film or both release paper can be used, and markings can be made on their surfaces to distinguish between the light release surface and the heavy release surface.

[0026] like Figure 1As shown, an ultra-low adhesive overflow cover film comprises, in sequence, a polyimide film, an ultra-low adhesive overflow layer, and a release layer 201, wherein the thickness of the ultra-low adhesive overflow layer is 0.5-5 μm, preferably 0.5-2 μm.

[0027] like Figure 3 As shown, an adhesive copper foil substrate with ultra-low adhesive overflow includes, in sequence, a copper foil layer 301, a coated polyimide layer (302), an ultra-low adhesive overflow layer, and a release layer. Its structure is a variant of a copper foil coating resin, which forms a four-layer structure in which a coated polyimide is generated on the copper foil, the adhesive is coated, and a release liner is attached. The thickness of the ultra-low adhesive overflow layer is 0.5-5 μm, preferably 0.5-2 μm.

[0028] The copper foil layer of the adhesive copper foil substrate of the present invention can be rolled copper foil or electrolytic copper foil, with a thickness ranging from 2 to 35 μm.

[0029] The copper foil layer of the adhesive copper foil substrate of the present invention can be a carrier copper foil, which is composed of carrier copper, release agent and ultra-thin copper foil.

[0030] A cover plate with ultra-low glue overflow, wherein the cover plate is a two-layer cover plate or a four-layer cover plate; like Figure 4 As shown, the two cover plates sequentially include a cover film 200, an adhesive sheet 100, and a cover film; The four-layer cover plate includes the following two structures: like Figure 5 As shown, the first structure of the four-layer cover plate includes, in sequence, a cover film, an adhesive sheet, a copper foil substrate 300 with adhesive, a cover film, an adhesive sheet, and a cover film; like Figure 6 As shown, the second structure of the four-layer cover plate includes, in sequence, a cover film, an adhesive sheet, an adhesive copper foil substrate, an adhesive sheet, an adhesive copper foil substrate, an adhesive sheet, and a cover film; The adhesive sheet comprises, in sequence, an ultra-low excess adhesive layer, a polyimide film, and an ultra-low excess adhesive layer; the cover film comprises, in sequence, a polyimide film and an ultra-low excess adhesive layer. The adhesive copper foil substrate comprises, in sequence, a copper foil layer, a coated polyimide layer, and an ultra-low adhesive layer; The thickness of the ultra-low overflow adhesive layer is 0.5-5 μm, preferably 0.5-2 μm.

[0031] The polyimide film of the cover film on the outer side of the cover plate is located on the outer side of the entire cover plate. That is, both the upper and lower cover films have polyimide layers facing outwards. There are no restrictions on the cover film and the adhesive copper foil substrate in the middle of the cover plate, as long as the cover film, the adhesive copper foil substrate, and the adhesive sheet can be bonded together by an ultra-low amount of adhesive layer.

[0032] Both the cover film and the adhesive copper foil substrate serve as cover plates, providing surface insulation and conductivity, respectively; while the adhesive sheet is suitable for shape cutting and bonding various interfaces as a material.

[0033] In the stack of adhesive sheet, cover film, adhesive copper foil substrate and cover plate, the adhesive in the ultra-low adhesive layer is selected from at least one of epoxy resin, acrylic resin, urethane resin, silicone rubber resin, poly(p-cycloxylene) resin and polyimide resin. The polyimide resin material is selected from at least one of bismaleimide resin, styrene-ethylene-butene-styrene block copolymer, polyimide resin and polyamide-imide, preferably at least one of polyimide resin and polyamide-imide; The epoxy resin is selected from at least two of the following: glycidylamine type epoxy resin, glycidyl ester type epoxy resin, epoxidized olefin compound, alicyclic epoxy resin, polyphenol type glycidyl ether epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic glycidyl ether epoxy resin, heterocyclic epoxy resin and mixed epoxy resin. The ultra-low overflow adhesive layer synthesized from the polyimide resin includes a polyimide resin material, an epoxy resin, and a curing agent. The curing agent is selected from at least one of amines (tertiary amines, quaternary ammonium salts, aliphatic amines, aromatic amines) and imidazole compounds (such as 2E4MZ). The ultra-low overflow adhesive layer comprises, by weight percentage, 70-95% polyimide resin, 1-25% epoxy resin, and 0-10% curing agent.

[0034] The ultra-low overflow adhesive layer synthesized from acrylic resin includes a main agent and a curing agent. The main agent is selected from at least one of methyl methacrylate (MMA) and nitrile rubber (NBR), and the curing agent includes at least one of methyl ethyl ketone peroxide (MEKP) and cobalt salt accelerator. The ultra-low overflow adhesive layer, by weight percentage, comprises 98.00-99.99% main agent with MMA not less than 60%, and 0.01%-2% curing agent.

[0035] The epoxy resin-synthesized ultra-low overflow adhesive layer includes epoxy resin, rubber, curing agent and solvent. The curing agent is selected from at least one of amines (tertiary amines, quaternary ammonium salts, aliphatic amines, aromatic amines) and imidazole compounds (such as 2E4MZ). The rubber is selected from at least one of nitrile rubber, cis-butadiene rubber, chloroprene rubber and natural rubber. The solvent is selected from methyl ethyl ketone. The ultra-low overflow adhesive layer comprises, by weight percentage, 30-75% epoxy resin, 10-35% rubber, 5-45% curing agent, and an appropriate amount of solvent.

[0036] The polyimide film is a commercially available polyimide film made by uniaxial stretching or biaxial stretching, with a thickness ranging from 3 μm to 75 μm.

[0037] Regarding the ultra-low adhesive layer of this application, several synthesis schemes are briefly described, but it should be noted that the specific implementation methods and the scope of protection are not limited thereto. This invention also provides a method for preparing an adhesive sheet with ultra-low adhesive overflow, comprising the following steps: Step 1: On a roll-to-roll coating machine, a polyimide film is coated with an ultra-low overflow adhesive layer. The film is then baked in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent, dry and cure, and then the first release layer is bonded on. Step 2: The semi-finished product obtained in Step 1 is rolled up and sent back to the other side to be coated with an ultra-low overflow adhesive layer. After baking in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent, the second release layer is attached to obtain the adhesive sheet.

[0038] The present invention also provides a method for preparing an ultra-low adhesive overflow cover film, comprising the following steps: feeding a polyimide film onto a roll-to-roll coating machine to coat an ultra-low adhesive overflow layer, baking it in a coating machine oven at 60-180℃ for 3-5 minutes to remove solvent and dry and cure it, and then attaching a release layer to obtain the cover film.

[0039] This invention also provides a method for preparing an adhesive-coated copper foil substrate with ultra-low adhesive overflow, comprising the following steps: Step 1: Feed copper foil onto a roll-to-roll coating machine and coat it with polyimide precursor varnish. Then, bake it in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent, dry and cure it, and roll it up for later use. Step 2: Send the semi-finished product obtained in Step 1 to a high-temperature continuous oxygen-free oven for roll-to-roll operation, dehydrate and close the ring of the precursor varnish to polymerize it into coated polyimide, and obtain the semi-finished product as a single-sided polyimide copper foil substrate. Step 3: Send the semi-finished product obtained in Step 2 onto a roll-to-roll coating machine, apply an ultra-low overflow adhesive layer to the polyimide surface, bake it in the coating machine oven at 60-180℃ for 3-5 minutes to remove solvent and dry and cure, and then attach the release layer to obtain the adhesive copper foil substrate.

[0040] Figure 1 , Figure 2 , Figure 3The following tests were performed on the structure: insulation resistance (IPC-TM-650 2.4.17), adhesion strength (IPC-TM-650 2.4.9 D), solder heat resistance (IPC-TM-650 2.4.13 F), thermal stress (IPC-TM-650 2.6.8.1(9 / 91)), and excess adhesive (IPC-TM-650 2.3.17.1), and the results are shown in Table 1.

[0041] The insulating layer in Examples 1 and 2 was a commercially available polyimide film, specifically GF100 from PIAM Corporation. The insulating layer in Example 3 is a coated polyimide.

[0042] An ultra-low overflow adhesive layer, an acrylic adhesive (synthesis method: 67g of methyl methacrylate (MMA) and 33g of nitrile rubber, heated to 90°C and stirred for 4 hours, then mixed with 1g of methyl ethyl ketone peroxide (MEKP), with a coating thickness of 2μm. The release layer and the second release layer in this embodiment are Lintec's EX-16. The first release layer used in Example 2 is CA-9057 from Kunshan Yasen Electronics Co., Ltd. The copper foil layer is VF-12 of South Asia Copper Foil (selected in Example 3) and MT-18FL of Mitsui Copper Foil (selected in Example 4).

[0043] The actual preparation method follows the steps described in the preceding paragraphs. Example 1 is as follows: Figure 1 The covering membrane of the structure, Example 2 is Figure 2 The adhesive sheet of the structure, Example 3 is Figure 3 The structure of the adhesive-coated copper foil substrate, Example 4 is Figure 3 The adhesive copper foil substrate of the structure was stripped of the carrier copper. Comparative Example 1 used commercially available cover film material (Yasen Electronics Materials, AHICX020X2SYN). Release material / release layer was removed during the test comparison.

[0044] Table 1: The adhesive sheets, cover films, and adhesive copper foil substrates with ultra-low adhesive overflow obtained by this invention have excellent insulation, heat resistance, and peel strength. At the same time, as cover plates, they have excellent thickness control and extremely low adhesive overflow, which is conducive to the molding of irregular structures in applications.

[0045] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An adhesive sheet with ultra-low adhesive overflow, characterized in that: It sequentially includes a first release layer (101), an ultra-low overflow adhesive layer (102), a polyimide film (103), an ultra-low overflow adhesive layer and a second release layer (104), wherein the thickness of the ultra-low overflow adhesive layer is 0.5-5μm.

2. The adhesive sheet with ultra-low adhesive overflow according to claim 1, characterized in that: The adhesive in the ultra-low overflow adhesive layer is selected from at least one of epoxy resin, acrylic resin, urethane resin, silicone rubber resin, poly(p-cycloxylene) resin, and polyimide resin.

3. A cover film with ultra-low adhesive overflow, characterized in that: It comprises, in sequence, a polyimide film, an ultra-low overflow adhesive layer, and a release layer (201), wherein the thickness of the ultra-low overflow adhesive layer is 0.5-5 μm.

4. The cover film with ultra-low adhesive overflow according to claim 3, characterized in that: The adhesive in the ultra-low overflow adhesive layer is selected from at least one of epoxy resin, acrylic resin, urethane resin, silicone rubber resin, poly(p-cycloxylene) resin, and polyimide resin.

5. A copper foil substrate with ultra-low adhesive overflow, characterized in that: It comprises, in sequence, a copper foil layer (301), a coated polyimide layer (302), an ultra-low adhesive layer and a release layer, wherein the thickness of the ultra-low adhesive layer is 0.5-5 μm.

6. The adhesive-coated copper foil substrate with ultra-low adhesive overflow according to claim 5, characterized in that: The adhesive in the ultra-low overflow adhesive layer is selected from at least one of epoxy resin, acrylic resin, urethane resin, silicone rubber resin, poly(p-cycloxylene) resin, and polyimide resin.

7. A cover plate with ultra-low glue overflow, characterized in that: The cover plate is a two-layer cover plate or a four-layer cover plate; The two cover plates sequentially include a cover film (200), an adhesive sheet (100), and a cover film; The four-layer cover plate includes the following two structures: The first structure of the four-layer cover plate includes, in sequence, a cover film, an adhesive sheet, a copper foil substrate with adhesive (300), a cover film, an adhesive sheet, and a cover film; The second structure of the four-layer cover plate includes, in sequence, a cover film, an adhesive sheet, an adhesive copper foil substrate, an adhesive sheet, an adhesive copper foil substrate, an adhesive sheet, and a cover film; The adhesive sheet comprises, in sequence, an ultra-low excess adhesive layer, a polyimide film, and an ultra-low excess adhesive layer; the cover film comprises, in sequence, a polyimide film and an ultra-low excess adhesive layer. The adhesive copper foil substrate comprises, in sequence, a copper foil layer, a coated polyimide layer, and an ultra-low adhesive layer; The thickness of the ultra-low overflow adhesive layer is 0.5-5 μm; The polyimide film of the cover film on the outer side of the cover plate is located on the entire outer side of the cover plate.

8. A method for preparing an adhesive sheet with ultra-low adhesive overflow as described in any one of claims 1-2, characterized in that: Includes the following steps: Step 1: On a roll-to-roll coating machine, a polyimide film is coated with an ultra-low overflow adhesive layer. The film is then baked in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent, dry and cure, and then the first release layer is bonded on. Step 2: The semi-finished product obtained in Step 1 is rolled up and sent back to the other side to be coated with an ultra-low overflow adhesive layer. After baking in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent, the second release layer is attached to obtain the adhesive sheet.

9. A method for preparing a cover film with ultra-low adhesive overflow as described in any one of claims 3-4, characterized in that: Includes the following steps: The polyimide film is coated with an ultra-low overflow adhesive layer on a roll-to-roll coating machine. After being baked in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent and dry and cure, a release layer is attached to obtain the cover film.

10. A method for preparing an ultra-low adhesive-coated copper foil substrate as described in any one of claims 5-6, characterized in that: Includes the following steps: Step 1: Feed copper foil onto a roll-to-roll coating machine and coat it with polyimide precursor varnish. Then, bake it in the coating machine oven at 60-180℃ for 3-5 minutes to remove the solvent, dry and cure it, and roll it up for later use. Step 2: Send the semi-finished product obtained in Step 1 to a high-temperature continuous oxygen-free oven for roll-to-roll operation, dehydrate and close the ring of the precursor varnish to polymerize it into coated polyimide, and obtain the semi-finished product as a single-sided polyimide copper foil substrate. Step 3: Send the semi-finished product obtained in Step 2 onto a roll-to-roll coating machine, apply an ultra-low overflow adhesive layer to the polyimide surface, bake it in the coating machine oven at 60-180℃ for 3-5 minutes to remove solvent and dry and cure, and then attach the release layer to obtain the adhesive copper foil substrate.

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