Film-coated aluminum sheet for IC flexible substrate drilling and preparation method of film-coated aluminum sheet

Abstract

The invention belongs to the field of PCB processing, and discloses a film-coated aluminum sheet for IC flexible substrate drilling and a preparation method thereof.The film-coated aluminum sheet comprises an aluminum-based base material, the surface of the aluminum-based base material is sequentially provided with a pretreatment layer and a functional film-coated layer, and the functional film-coated layer is obtained by spraying and curing functional film-coated slurry; the functional coating slurry is prepared from the following raw materials: a modified acrylate copolymer, a hydroxyl-terminated polyurethane elastomer, 3-glycidyl ether oxypropyl trimethoxy silane, modified polytetrafluoroethylene micro powder, nano aluminum oxide, a cross-linking agent, a flatting agent, an antioxidant, an ultraviolet absorbent, deionized water and propylene glycol monomethyl ether; through composite modification of the functional coating layer of the coated aluminum sheet through the modified acrylate copolymer and the modified polytetrafluoroethylene micro powder, synergistic improvement of heat conduction, lubrication and water solubility is achieved, the coated aluminum sheet is excellent in drilling adaptability, and the high-precision drilling requirement for the ultra-fine aperture of the IC flexible substrate is met.

Description

Technical Field

[0001] This invention belongs to the field of PCB processing technology, specifically relating to a coated aluminum sheet for drilling holes in IC flexible substrates and its preparation method. Background Technology

[0002] With the development of integrated circuits (ICs) towards high density, miniaturization, and flexibility, flexible substrates such as polyimide (PI) and polyethylene terephthalate (PET) are widely used in high-end electronic fields such as flexible printed circuit boards (FPCs). Drilling is the core process in IC flexible substrate manufacturing, requiring the fabrication of precise vias ≤80μm (or even ≤50μm) on substrates tens of micrometers thick to achieve electrical connections. Due to the insufficient rigidity of the flexible substrate itself, deformation and tearing are prone to occur during drilling, leading to problems such as excessive hole diameter deviation and severe burrs on the hole walls. Therefore, the industry commonly uses coated aluminum sheets as drilling support materials. By bonding the coated aluminum sheet to the flexible substrate, the high rigidity of the aluminum sheet provides stable support, while the surface coating layer achieves functions such as positioning, anti-sticking, and substrate protection.

[0003] However, existing coated aluminum sheets have many technical defects: solvent-based coating systems are prone to volatile VOCs, which are harmful to health and do not comply with environmental protection policies. Solvent residues can penetrate the substrate and cause performance degradation. Some water-based system solutions have not solved the problem of balancing hydrophilicity, adhesion, and heat resistance, resulting in easy coating peeling, high residual adhesive rate, and impracticality. Existing coatings have low thermal conductivity and insufficient lubrication, and the heat accumulated during drilling cannot be conducted in time, leading to increased drill bit wear, aluminum sheet melting, large fluctuations in frictional resistance, high aluminum chip adhesion rate, and large hole diameter deviation, which cannot meet the requirements of ultra-fine hole diameter. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a coated aluminum sheet for drilling IC flexible substrates and its preparation method. The functional coating layer of the coated aluminum sheet of the present invention is obtained by spraying and curing a water-soluble functional coating slurry. Through composite modification of modified acrylate copolymer and modified polytetrafluoroethylene micro powder, the thermal conductivity, lubrication, and water solubility are synergistically improved, resulting in excellent drilling adaptability of the coated aluminum sheet, small hole diameter deviation, no aluminum shavings adhesion, no burrs, and reduced drill bit wear rate, thus meeting the high-precision drilling requirements of ultra-fine holes in IC flexible substrates.

[0005] The objective of this invention can be achieved through the following technical solutions: A coated aluminum sheet for drilling on a flexible IC substrate includes an aluminum substrate, which is an aluminum foil with a thickness of 50~100μm. A pretreatment layer and a functional coating layer are sequentially provided on the surface of the aluminum substrate. The pretreatment layer is obtained by spraying an aluminum substrate coating liquid and then curing it. The pretreatment layer enhances the interfacial adhesion between the aluminum substrate and the functional coating layer. The functional coating layer is obtained by spraying a functional coating slurry and then curing it. The functional coating slurry comprises the following raw materials in parts by weight: 50-55 parts modified acrylate copolymer, 12-14 parts hydroxyl-terminated polyurethane elastomer, 2-3 parts 3-glycidyl etheroxypropyltrimethoxysilane, 4-6 parts modified polytetrafluoroethylene micropowder, 1-2 parts nano-alumina, 5-8 parts crosslinking agent, 0.2-0.4 parts leveling agent, 0.2-0.4 parts antioxidant, 0.2-0.4 parts ultraviolet absorber, 20-22 parts deionized water, and 0.5-1 parts propylene glycol methyl ether. The modified acrylate copolymer is composed of acrylate grafted with hydrophilic sulfonic acid functional groups and thermally conductive phenylphosphonate functional groups. The modified polytetrafluoroethylene micropowder is composed of polytetrafluoroethylene microspheres with nano-zinc bridged on the surface by a silane coupling agent to form a polytetrafluoroethylene nano-zinc core-shell structure.

[0006] Preferably, the aluminum substrate coating solution is a 20-25 wt% epoxy-modified acrylic resin solution, and the solvent is a mixture of methyl ethyl ketone and toluene in a volume ratio of 1:1.

[0007] Preferably, the crosslinking agent is an aqueous isocyanate crosslinking agent, the leveling agent is a polyether-modified silicone leveling agent BYK-348, the antioxidant is antioxidant 1098, and the ultraviolet absorber is ultraviolet absorber UV-327.

[0008] Preferably, the method for preparing the modified acrylate copolymer includes the following steps: A. Add deionized water, propylene glycol methyl ether, and sodium dodecylbenzene sulfonate to a four-necked flask, stir and heat to 75°C, then add monomers methyl methacrylate, butyl acrylate, hydroxyethyl acrylate, styrenephosphonic acid, 2-acrylamide-2-methylpropanesulfonic acid, and dodecyl mercaptan in sequence, stir and emulsify for 20-40 minutes to obtain a stable monomer pre-emulsion with no layering or precipitation; B. Add 10wt% ammonium persulfate aqueous solution dropwise to the pre-emulsion, and stir at a constant temperature of 75℃ for 3-5 hours to obtain a semi-transparent emulsion; C. Cool the emulsion to 40°C and adjust the pH to 7.0~7.5 with 25wt% ammonia water to obtain the modified acrylate copolymer dispersion.

[0009] Preferably, the mass ratio of monomers methyl methacrylate, butyl acrylate, hydroxyethyl acrylate, styrenephosphonic acid, and 2-acrylamide-2-methylpropanesulfonate is 5:4:2:0.6:0.4. The amount of ammonium persulfate used is 2% to 4% of the total mass of the monomer.

[0010] Preferably, the preparation method of modified polytetrafluoroethylene micro powder includes the following steps: a. Add polytetrafluoroethylene micro powder, anhydrous ethanol and citric acid to a high-speed disperser and disperse for 15-25 min. Add mercaptopropyltrimethoxysilane, heat to 50°C, and stir to react for 0.5-1.5 h. b. Add hydrophilic nano zinc powder and deionized water to the system, disperse for 20-40 minutes, filter the micro powder suspension after reaction, vacuum dry it and sieve it through a 200-mesh filter to obtain modified polytetrafluoroethylene micro powder.

[0011] Preferably, the mass ratio of polytetrafluoroethylene micro powder, mercaptopropyltrimethoxysilane, and nano zinc powder is 20:1:2.

[0012] Preferably, the method for preparing the functional coating slurry includes the following steps: (1) Add modified acrylate copolymer aqueous dispersion and hydroxyl-terminated polyurethane elastomer to a high-speed dispersion kettle, stir and mix for 8-10 min until the system is uniform, add 3-glycidyl ether oxypropyltrimethoxysilane and crosslinking agent, stir and mix for 10-20 min to form a basic resin system; (2) Add modified polytetrafluoroethylene micro powder and nano alumina to the system, disperse for 20-40 min, then add antioxidant, ultraviolet absorber and leveling agent, stir for 5-15 min, and finally add deionized water and propylene glycol methyl ether to adjust the viscosity of the system to obtain functional coating slurry.

[0013] A method for preparing a coated aluminum sheet for drilling holes in an IC flexible substrate includes the following steps: S1. Immerse the aluminum foil in an alkaline degreasing agent at 50~60℃ and ultrasonically clean it for 4~6 minutes to remove surface oil. Use an electrochemical roughening method to form a uniform micro-rough structure on the surface of the aluminum foil with a roughness Ra=0.2~0.3μm. S2. Apply the primer treatment solution to the surface of the aluminum foil and dry it in an oven at 80°C for 1 to 2 minutes to form a primer coating with a dry film thickness of 0.5 to 1 μm; S3. Apply the coating slurry to the surface of the aluminum foil after the primer is applied, place it in an oven and use low-temperature stepwise cross-linking curing. After curing, the dry film thickness of the coating is 22~28μm. Cut the cured coated aluminum sheet into sizes that fit the IC flexible substrate to obtain the coated aluminum sheet for drilling the IC flexible substrate.

[0014] Preferably, the low-temperature stepwise crosslinking and curing process involves pre-drying and dehydrating at 75°C for 1.5–2.5 min, pre-crosslinking at 90°C for 1–2 min, and curing at 55°C for 18–24 h.

[0015] The beneficial effects of this invention are: The present invention relates to a coated aluminum sheet for drilling flexible IC substrates. The aluminum substrate has a pretreatment layer and a functional coating layer on its surface. The pretreatment layer enhances the interfacial adhesion between the aluminum substrate and the functional coating layer. The functional coating layer is obtained by spraying and curing a water-soluble functional coating slurry. The functional coating slurry is modified by the composite modification of modified acrylate copolymer and modified polytetrafluoroethylene micro powder, which achieves a synergistic improvement in thermal conductivity, lubrication and water solubility. This makes the coated aluminum sheet perform well in drilling adaptability, with small hole diameter deviation, no aluminum shavings adhesion, no burrs, and reduced drill wear rate, meeting the high-precision drilling requirements of ultra-fine holes in flexible IC substrates.

[0016] This invention modifies the acrylate copolymer by grafting sulfonic acid hydrophilic functional groups and thermally conductive phenylphosphonate functional groups onto the acrylate copolymer. 2-Acrylamido-2-methylpropanesulfonic acid is grafted onto the molecular chain of the acrylate copolymer. The sulfonic acid groups of 2-acrylamido-2-methylpropanesulfonic acid are strong hydrophilic groups, which ionize in water to form a negative charge, creating electrostatic repulsion between the resin molecular chains. This allows the resin to be stably dispersed in water in emulsion form, achieving water dispersibility and completely replacing organic solvents. After the phenylphosphonate groups of styrene phosphonic acid are grafted onto the resin molecular chain, the large π-conjugated structure of the benzene ring forms a continuous thermally conductive pathway. The P=O double bonds of the phosphonate form hydrogen bonds with the hydroxyl groups of adjacent molecular chains, constructing an intermolecular thermally conductive network and increasing the thermal conductivity of the resin. This thermal conductivity is intrinsic, unlike the physical thermal conductivity achieved by adding thermally conductive fillers. It exhibits no agglomeration or performance degradation, and can quickly conduct frictional heat during drilling, preventing heat buildup in the drill bit and melting of aluminum chips. The modification process retains the hydroxyl groups on the resin molecular chain. These hydroxyl groups can undergo nucleophilic addition reactions with the water-based isocyanate crosslinking agent to form a dense three-dimensional network crosslinking structure, which not only ensures the adhesion between the coating and the aluminum base but also improves the thermal stability of the resin.

[0017] This invention relates to modified polytetrafluoroethylene (PTFE) micropowder, in which nano-zinc is bridged to the surface of PTFE microspheres via a silane coupling agent, forming a PTFE nano-zinc core-shell structure. Pure PTFE micropowder has extremely low surface energy and poor compatibility with acrylate resins, making it prone to agglomeration. By using a mercaptosilane coupling agent, the siloxane group at one end undergoes hydrolysis and condenses with the hydroxyl groups on the PTFE surface activated by citric acid etching to form a covalent bond. The mercapto group at the other end undergoes an addition reaction with the double bonds of the modified acrylate resin and simultaneously forms a coordination bond with the metal hydroxyl groups of the nano-zinc powder, achieving chemical bonding between the PTFE micropowder and the aluminum-based substrate. This completely solves the PTFE compatibility problem, resulting in uniform dispersion of the micropowder in the resin without agglomeration or precipitation. The high thermal conductivity of nano zinc powder, when uniformly coated on the surface of polytetrafluoroethylene micro powder, forms core-shell structured thermally conductive microspheres. These microspheres form thermally conductive nodes in the resin matrix and are interconnected with the phenylphosphonate thermally conductive pathways of the modified resin, constructing a continuous dual thermally conductive network. This improves the overall thermal conductivity of the coating, achieving synergistic thermal conductivity enhancement and rapid conduction of drilling friction heat. Polytetrafluoroethylene (PTFE) is a super-lubricating material. The sheet-like structure of nano-zinc provides a rolling lubrication effect. After being coated on the PTFE surface, the friction mode between the drill bit and the coating changes from sliding friction to sliding plus rolling friction, further reducing the coefficient of friction. Simultaneously, the silane coupling agent coating further reduces the surface energy of PTFE, decreasing the physical adsorption of aluminum shavings and micropowder, achieving zero aluminum shavings adhesion. The uniform dispersion of modified PTFE micropowder ensures a uniform hardness distribution on the coating surface, evenly distributing the cutting force of the drill bit during drilling. The low coefficient of friction also reduces wear between the drill bit and the coating. The metallic hardness of nano-zinc enhances the wear resistance of the coating, preventing excessive wear on the drill bit edge and reducing the drill bit wear rate.

[0018] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 A modified acrylate copolymer, wherein the modified acrylate copolymer is composed of acrylate grafted with sulfonic acid hydrophilic functional groups and thermally conductive phenylphosphonate functional groups, and its preparation method includes the following steps: A. Add 80 mL of deionized water, 5 mL of propylene glycol methyl ether, and 0.8 g of sodium dodecylbenzene sulfonate to a four-necked flask, stir and heat to 75 °C, then add 25 g of methyl methacrylate, 20 g of butyl acrylate, 10 g of hydroxyethyl acrylate, 3 g of styrenephosphonic acid, 2 g of 2-acrylamido-2-methylpropanesulfonic acid, and 0.3 g of dodecyl mercaptan in sequence, stir and emulsify for 30 min to obtain a monomer pre-emulsion; B. Add 3 mL of 10% ammonium persulfate aqueous solution to the pre-emulsion, stir at 75°C for 4 h to obtain a translucent emulsion; C. Cool the emulsion to 40°C and adjust the pH to 7.0~7.5 with 25% ammonia water to obtain the modified acrylate copolymer dispersion.

[0021] Example 2 A modified polytetrafluoroethylene (PTFE) micropowder, wherein the modified PTFE micropowder is formed by bridging zinc nanoparticles on the surface of PTFE microspheres with a silane coupling agent to form a PTFE nano-zinc core-shell structure, and its preparation method includes the following steps: a. Add 100g of polytetrafluoroethylene micro powder, 200mL of anhydrous ethanol and 0.5g of citric acid to a high-speed disperser and disperse for 20min. Add 5g of mercaptopropyltrimethoxysilane, heat to 50℃ and stir to react for 1h. b. Add 8g of nano zinc powder and 50mL of deionized water to the system, disperse for 30min, filter the micro powder suspension after reaction, vacuum dry it and sieve it through a 200-mesh filter to obtain modified polytetrafluoroethylene micro powder.

[0022] Example 3 A coated aluminum sheet for drilling on a flexible IC substrate includes an aluminum substrate, which is an aluminum foil with a thickness of 50 μm. A pretreatment layer and a functional coating layer are sequentially disposed on the surface of the aluminum substrate. The pretreatment layer is obtained by spraying an aluminum substrate coating treatment liquid and then curing it. The pretreatment layer enhances the interfacial adhesion between the aluminum substrate and the functional coating layer. The functional coating layer is obtained by spraying a functional coating slurry and then curing it. The aluminum substrate coating solution is a 25wt% epoxy-modified acrylic resin solution, and the solvent is a mixture of methyl ethyl ketone and toluene in a volume ratio of 1:1. The functional coating slurry comprises the following raw materials in parts by weight: 50 parts modified acrylate copolymer, 14 parts hydroxyl-terminated polyurethane elastomer, 2 parts 3-glycidyl etheroxypropyltrimethoxysilane, 6 parts modified polytetrafluoroethylene micropowder, 1 part nano-alumina, 8 parts waterborne isocyanate crosslinking agent, 0.2 parts leveling agent BYK-348, 0.4 parts antioxidant 1098, 0.2 parts ultraviolet absorber UV-327, 22 parts deionized water, and 0.5 parts propylene glycol methyl ether. The modified acrylate copolymer was prepared in Example 1, and the modified polytetrafluoroethylene micropowder was prepared in Example 2.

[0023] The preparation method of functional coating slurry includes the following steps: (1) Add modified acrylate copolymer aqueous dispersion and hydroxyl-terminated polyurethane elastomer to the high-speed dispersion kettle, stir and mix for 10 min until the system is uniform, add 3-glycidyl ether oxypropyltrimethoxysilane and waterborne isocyanate crosslinking agent, stir and mix for 10 min to form the basic resin system; (2) Add modified polytetrafluoroethylene micro powder and nano alumina to the system, disperse for 40 min, then add antioxidant 1098, ultraviolet absorber UV-327 and leveling agent BYK-348, stir for 5 min, and finally add deionized water and propylene glycol methyl ether to adjust the viscosity of the system to obtain functional coating slurry.

[0024] The method for preparing coated aluminum sheets for drilling holes in IC flexible substrates includes the following steps: S1. Immerse the aluminum foil in an alkaline degreasing agent at 60℃ and ultrasonically clean for 4 minutes to remove surface oil. Use an electrochemical roughening method to form a uniform micro-rough structure on the surface of the aluminum foil with a roughness Ra=0.3μm. S2. Apply the primer treatment solution to the surface of the aluminum foil and dry it in an oven at 80°C for 1 minute to form a primer coating with a dry film thickness of 1μm; S3. Apply the coating slurry to the surface of the aluminum foil after the primer, place it in an oven, and use low-temperature stepwise cross-linking curing: pre-drying and dehydration at 75℃ for 1.5 min, pre-cross-linking at 90℃ for 2 min, and low-temperature curing at 55℃ for 18 h. The dry film thickness after curing is 28 μm. Cut the cured coated aluminum sheet into sizes that fit the IC flexible substrate to obtain coated aluminum sheets for drilling holes in the IC flexible substrate.

[0025] Example 4 A coated aluminum sheet for drilling on a flexible IC substrate includes an aluminum substrate, which is an aluminum foil with a thickness of 100μm. A pretreatment layer and a functional coating layer are sequentially provided on the surface of the aluminum substrate. The pretreatment layer is obtained by spraying an aluminum substrate coating liquid and then curing it. The pretreatment layer enhances the interfacial adhesion between the aluminum substrate and the functional coating layer. The functional coating layer is obtained by spraying a functional coating slurry and then curing it. The aluminum substrate coating solution is a 20wt% epoxy-modified acrylic resin solution, and the solvent is a mixture of methyl ethyl ketone and toluene in a volume ratio of 1:1. The functional coating slurry comprises the following raw materials in parts by weight: 55 parts modified acrylate copolymer, 12 parts hydroxyl-terminated polyurethane elastomer, 3 parts 3-glycidyl etheroxypropyltrimethoxysilane, 4 parts modified polytetrafluoroethylene micropowder, 2 parts nano-alumina, 5 parts waterborne isocyanate crosslinking agent, 0.4 parts leveling agent BYK-348, 0.2 parts antioxidant 1098, 0.4 parts ultraviolet absorber UV-327, 20 parts deionized water, and 1 part propylene glycol methyl ether. The modified acrylate copolymer was prepared in Example 1, and the modified polytetrafluoroethylene micropowder was prepared in Example 2.

[0026] The preparation method of functional coating slurry includes the following steps: (1) Add modified acrylate copolymer aqueous dispersion and hydroxyl-terminated polyurethane elastomer to the high-speed dispersion kettle, stir and mix for 8 min until the system is uniform, add 3-glycidyl ether oxypropyltrimethoxysilane and waterborne isocyanate crosslinking agent, stir and mix for 20 min to form the basic resin system; (2) Add modified polytetrafluoroethylene micro powder and nano alumina to the system, disperse for 20 min, then add antioxidant 1098, ultraviolet absorber UV-327 and leveling agent BYK-348, stir for 15 min, and finally add deionized water and propylene glycol methyl ether to adjust the viscosity of the system to obtain functional coating slurry.

[0027] The method for preparing coated aluminum sheets for drilling holes in IC flexible substrates includes the following steps: S1. Immerse the aluminum foil in an alkaline degreasing agent at 50°C and ultrasonically clean for 6 minutes to remove surface oil. Use an electrochemical roughening method to form a uniform micro-rough structure on the surface of the aluminum foil with a roughness Ra=0.2μm. S2. Apply the primer treatment solution to the surface of the aluminum foil and dry it in an oven at 80°C for 2 minutes to form a primer coating with a dry film thickness of 0.5μm; S3. Apply the coating slurry to the surface of the aluminum foil after the primer is applied, place it in an oven, and use low-temperature stepwise cross-linking and curing. Pre-dry and dehydrate at 75℃ for 2.5 min, pre-cross-link at 90℃ for 1 min, and cure at 55℃ for 24 h. The dry film thickness after curing is 22 μm. Cut the cured coated aluminum sheet into sizes that fit the IC flexible substrate to obtain coated aluminum sheets for drilling holes in the IC flexible substrate.

[0028] Example 5 A coated aluminum sheet for drilling on a flexible IC substrate includes an aluminum substrate, which is an aluminum foil with a thickness of 75μm. A pretreatment layer and a functional coating layer are sequentially disposed on the surface of the aluminum substrate. The pretreatment layer is obtained by spraying an aluminum substrate coating liquid and then curing it. The pretreatment layer enhances the interfacial adhesion between the aluminum substrate and the functional coating layer. The functional coating layer is obtained by spraying a functional coating slurry and then curing it. The aluminum substrate coating solution is a 22wt% epoxy-modified acrylic resin solution, and the solvent is a mixture of methyl ethyl ketone and toluene in a volume ratio of 1:1. The functional coating slurry comprises the following raw materials in parts by weight: 52.5 parts modified acrylate copolymer, 13 parts hydroxyl-terminated polyurethane elastomer, 2.5 parts 3-glycidyl etheroxypropyltrimethoxysilane, 5 parts modified polytetrafluoroethylene micropowder, 1.5 parts nano alumina, 6.5 parts waterborne isocyanate crosslinking agent, 0.3 parts leveling agent BYK-348, 0.3 parts antioxidant 1098, 0.3 parts ultraviolet absorber UV-327, 21 parts deionized water, and 0.8 parts propylene glycol methyl ether. The modified acrylate copolymer was prepared in Example 1, and the modified polytetrafluoroethylene micropowder was prepared in Example 2.

[0029] The preparation method of functional coating slurry includes the following steps: (1) Add modified acrylate copolymer aqueous dispersion and hydroxyl-terminated polyurethane elastomer to the high-speed dispersion kettle, stir and mix for 10 min until the system is uniform, add 3-glycidyl ether oxypropyltrimethoxysilane and waterborne isocyanate crosslinking agent, stir and mix for 15 min to form the basic resin system; (2) Add modified polytetrafluoroethylene micro powder and nano alumina to the system, disperse for 30 min, then add antioxidant 1098, ultraviolet absorber UV-327 and leveling agent BYK-348, stir for 10 min, and finally add deionized water and propylene glycol methyl ether to adjust the viscosity of the system to obtain functional coating slurry.

[0030] The method for preparing coated aluminum sheets for drilling holes in IC flexible substrates includes the following steps: S1. Immerse the aluminum foil in an alkaline degreasing agent at 55°C and ultrasonically clean for 5 minutes to remove surface oil. Use an electrochemical roughening method to form a uniform micro-rough structure on the surface of the aluminum foil with a roughness Ra=0.25μm. S2. Apply the primer treatment solution to the surface of the aluminum foil and dry it in an oven at 80°C for 1.5 min to form a primer coating with a dry film thickness of 0.8 μm; S3. Apply the coating slurry to the surface of the aluminum foil after the primer, place it in an oven, and use low-temperature stepwise cross-linking curing: pre-dry and dehydrate at 75℃ for 25 min, pre-cross-link at 90℃ for 1.5 min, and cure at 55℃ for 20 h. The dry film thickness after curing is 25 μm. Cut the cured coated aluminum sheet into sizes that fit the IC flexible substrate to obtain coated aluminum sheets for drilling holes in the IC flexible substrate.

[0031] Comparative Example 1 A coated aluminum sheet for drilling on a flexible IC substrate includes an aluminum substrate, which is an aluminum foil with a thickness of 75μm. A pretreatment layer and a functional coating layer are sequentially disposed on the surface of the aluminum substrate. The pretreatment layer is obtained by spraying an aluminum substrate coating liquid and then curing it. The pretreatment layer enhances the interfacial adhesion between the aluminum substrate and the functional coating layer. The functional coating layer is obtained by spraying a functional coating slurry and then curing it. The aluminum substrate coating solution is a 22wt% epoxy-modified acrylic resin solution, and the solvent is a mixture of methyl ethyl ketone and toluene in a volume ratio of 1:1. The functional coating slurry comprises the following raw materials in parts by weight: 52.5 parts of acrylate copolymer, 13 parts of hydroxyl-terminated polyurethane elastomer, 2.5 parts of 3-glycidyl etheroxypropyltrimethoxysilane, 5 parts of modified polytetrafluoroethylene micropowder, 1.5 parts of nano-alumina, 6.5 parts of isocyanate crosslinking agent, 0.3 parts of antioxidant 1010, 0.3 parts of ultraviolet absorber UV-531, 14-18 parts of ethyl acetate, and 6-8 parts of ethanol. The acrylate copolymer is composed of ungrafted sulfonic acid hydrophilic functional groups and thermally conductive phenylphosphonate functional groups. The modified polytetrafluoroethylene micropowder is prepared in Example 2.

[0032] The preparation method of acrylate copolymers includes the following steps: A. Add 25 mL of ethyl acetate and 10 mL of ethanol to a four-necked flask, add 0.05 g of hydroquinone and stir until completely dissolved. Heat to 70 °C and stir for 10 min. Then add 30 g of methyl methacrylate, 22 g of butyl acrylate, 8 g of hydroxyethyl acrylate, 2 g of methacrylic acid, and 0.3 g of dodecyl mercaptan in sequence. Stir magnetically for 5 min until well mixed to obtain a monomer premix. B. Add 0.6g of azobisisobutyronitrile to the monomer premix and stir until completely dissolved. Add the prepared monomer premix to a constant pressure dropping funnel and add it dropwise to the reaction vessel at a constant temperature of 70℃ and a stirring speed of 250rpm. The dropping rate is controlled at 1mL / min and the total dropping time is 4h. C. After the monomer premixed liquid is added dropwise, keep the reactor temperature at 70℃ and the stirring speed at 250rpm, and keep the reaction at a constant temperature for 2 hours. Then, let it cool naturally to room temperature and continue stirring for 10 minutes to allow the resin system to stabilize fully. Filter the resin solution through a 200-mesh nylon filter to obtain the acrylate copolymer.

[0033] The preparation method of the functional coating slurry includes the following steps: adding acrylate copolymer, hydroxyl-terminated polyurethane elastomer, ethyl acetate and ethanol to a high-speed disperser and dispersing at 1000 rpm for 15 min; then adding 3-glycidyl etheroxypropyltrimethoxysilane and modified polytetrafluoroethylene micro powder, increasing the speed to 3000 rpm and dispersing for 30 min; finally adding nano-alumina, isocyanate crosslinking agent, antioxidant 1010 and ultraviolet absorber UV-531, and stirring at low speed for 10 min until the system is homogeneous.

[0034] The preparation method of the coated aluminum sheet for drilling IC flexible substrates is the same as in Example 5.

[0035] Comparative Example 2 A coated aluminum sheet for drilling on a flexible IC substrate includes an aluminum substrate, which is an aluminum foil with a thickness of 75μm. A pretreatment layer and a functional coating layer are sequentially disposed on the surface of the aluminum substrate. The pretreatment layer is obtained by spraying an aluminum substrate coating liquid and then curing it. The pretreatment layer enhances the interfacial adhesion between the aluminum substrate and the functional coating layer. The functional coating layer is obtained by spraying a functional coating slurry and then curing it. The aluminum substrate coating solution is a 22wt% epoxy-modified acrylic resin solution, and the solvent is a mixture of methyl ethyl ketone and toluene in a volume ratio of 1:1. The functional coating slurry comprises the following raw materials in parts by weight: 52.5 parts of acrylate copolymer, 13 parts of hydroxyl-terminated polyurethane elastomer, 2.5 parts of 3-glycidyl etheroxypropyltrimethoxysilane, 5 parts of polytetrafluoroethylene micro powder, 1.5 parts of nano-alumina, 6.5 parts of waterborne isocyanate crosslinking agent, 0.3 parts of leveling agent BYK-348, 0.3 parts of antioxidant 1098, 0.3 parts of ultraviolet absorber UV-327, 21 parts of deionized water, and 0.8 parts of propylene glycol methyl ether. The modified acrylate copolymer is prepared in Example 1.

[0036] The preparation method of the functional coating slurry is the same as that in Example 5, except that in step (2), the modified polytetrafluoroethylene micro powder is replaced with an equal amount of unmodified polytetrafluoroethylene micro powder, and the preparation method of the coated aluminum sheet for drilling IC flexible substrate is the same as that in Example 5.

[0037] Performance testing The performance of the coated aluminum sheets for drilling IC flexible substrates prepared in Example 5, Comparative Example 1, and Comparative Example 2 was tested. In Example 5, the functional coating layer of the coated aluminum sheet contained hydrophilic and thermally conductive modified acrylate copolymers and modified polytetrafluoroethylene micropowder. In Comparative Example 1, the hydrophilic and thermally conductive modified acrylate copolymers in the functional coating layer of the coated aluminum sheet were replaced with ordinary solvent-based acrylate copolymers. In Comparative Example 2, the modified polytetrafluoroethylene micropowder in the functional coating layer of the coated aluminum sheet was replaced with unmodified polytetrafluoroethylene micropowder.

[0038] I. Functional Coating Performance Test (1) Water solubility test: Take 10g of functional coating slurry (uncoated) of each sample, add 90g of deionized water, stir magnetically for 5min at room temperature (300rpm), let stand for 24h, and observe the state of the system; at the same time, test the VOC residue (organic solvent content) of the coated product according to GB / T23986-2009. (2) Thermal conductivity test: Laser thermal conductivity meter (steady-state method) was used. Dry film of the coating layer of each sample (after peeling off the aluminum base) was taken and a Φ20mm sample was cut. The thermal conductivity of the coating was tested at room temperature (25℃). Five parallel samples were tested for each group of samples and the average value was taken. (3) Lubrication performance test: In accordance with GB / T3960-2016, a friction and wear tester was used under dry friction conditions. The grinding part was a carbide drill bit (for drilling IC substrates), with a load of 5N and a sliding speed of 100mm / min. The dynamic friction coefficient of the coated surface was tested. Each group was tested 5 times and the average value was taken.

[0039] The obtained data is shown in Table 1 below.

[0040] Table 1. Test results of functional coating performance

[0041] As can be seen from the data in Table 1, Example 5 is an aqueous dispersion system with no stratification and a VOC of only 0.02%, while Comparative Example 1 is a solvent-based resin, which is completely incompatible with the aqueous dispersion medium. The slurry agglomerates and stratifies, and the VOC is as high as 2.8%. The reason is that the modified resin is grafted with a strong hydrophilic functional group of 2-acrylamide-2-methylpropanesulfonic acid. The sulfonic acid groups / carboxyl groups on the molecular chain ionize in water to form hydrophilic groups, achieving aqueous dispersion, completely replacing organic solvents, and is environmentally friendly and free from substrate pollution. Example 5 shows a thermal conductivity 4.5 times that of Example 1, a significant improvement in thermal conductivity. This is because the modified resin was grafted with phenylphosphonate thermally conductive functional groups, and the conjugated structure of the benzene ring forms a continuous thermally conductive pathway, endowing the resin with intrinsic thermal conductivity. In contrast, the original resin has no thermally conductive functional groups and relies solely on the thermal conduction of the resin molecular chains, resulting in extremely poor thermal conductivity. Example 5 shows a thermal conductivity twice that of Example 2, a significant improvement in thermal conductivity. This is because nano-zinc has extremely high thermal conductivity, and after being coated on the surface of polytetrafluoroethylene, it forms thermally conductive nodes, which synergize with the thermally conductive pathways of the modified resin to construct a dual thermally conductive network of resin micropowder. In contrast, pure polytetrafluoroethylene has low thermal conductivity and no thermal conductivity enhancement effect. The coefficient of friction in Example 5 was comparable to that in Comparative Example 1, but much lower than that in Comparative Example 2, indicating improved lubricity. This is because the sheet-like structure of the modified polytetrafluoroethylene micropowder and zinc nanoparticles further reduced the surface friction resistance. At the same time, the bridging effect of the silane coupling agent allowed the polytetrafluoroethylene micropowder to be uniformly dispersed in the resin, resulting in a continuous lubrication layer. In contrast, pure polytetrafluoroethylene micropowder tends to agglomerate, leading to uneven lubricity.

[0042] II. Drilling Performance Testing (1) Drilling compatibility test: A mechanical drilling machine for IC flexible substrates was selected. The drill bit was a carbide micro drill (80μm / 50μm, two types of hole diameters). The drilling object was a PI flexible substrate (drilled after bonding with a coated aluminum sheet). The drilling parameters were: rotation speed 80000r / min, feed rate 0.01mm / r, and 10000 holes for each type. After drilling, the following were observed using a metallographic microscope (200x): ① Hole diameter deviation (actual hole diameter - theoretical hole diameter); ② Whether there are aluminum chips, coating residue, or hole burrs on the surface of the PI substrate; ③ Wear condition of the drill bit edge. (2) Aluminum chip adhesion rate test: collect aluminum chips / resin chips generated during the drilling process, observe the adhesion state between aluminum chips and coating using an electron microscope, and count the proportion of adhered aluminum chips. (3) Drill bit wear rate detection: The morphology of the drill bit cutting edge before and after drilling was observed using a scanning electron microscope (SEM), and the wear amount (change in cutting edge thickness) of the drill bit cutting edge was measured. Drill bit wear rate = (cutting edge thickness after wear - original cutting edge thickness) / original cutting edge thickness × 100%; The obtained data is shown in Table 2 below.

[0043] Table 2 Drilling performance test results of coated aluminum sheets

[0044] As shown in Table 2, the aperture deviation in Comparative Example 1 was 5.2 μm, and the aluminum chip adhesion rate reached 8.5%. The core reason was poor thermal conductivity; the frictional heat between the drill bit and the coating could not be quickly conducted during drilling, leading to heat accumulation in the drill bit, melting of the aluminum foil, and adhesion of aluminum chips. Simultaneously, the aperture deviation occurred due to thermal expansion and contraction. In Example 5, the aluminum chip adhesion rate was 0%, and the drill wear rate was only 3.8%. Comparative Example 2 had 3.2% aluminum chip adhesion and a drill wear rate of 7.6%. This was because the modified polytetrafluoroethylene (PTFE) micropowder had a lower surface energy, and the nano-zinc coating reduced the physical adsorption between the PTFE micropowder and aluminum chips, improving lubricity and reducing frictional resistance and wear. In contrast, pure PTFE micropowder had poor compatibility with resin, easily agglomerating into particles, leading to increased drill wear and aluminum chip adhesion. Example 5 showed no burrs, while Comparative Example 2 showed slight burrs. The reason is that the uniform dispersion of the modified polytetrafluoroethylene micro powder resulted in a smoother coating surface and more uniform cutting force of the drill bit during drilling. In contrast, the agglomerated particles of pure polytetrafluoroethylene micro powder caused uneven force during drill bit cutting, resulting in burrs in the hole diameter.

[0045] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A coated aluminum sheet for drilling holes in a flexible IC substrate, characterized in that, The invention includes an aluminum-based substrate, wherein the aluminum-based substrate is an aluminum foil with a thickness of 50~100μm, and a pretreatment layer and a functional coating layer are sequentially provided on the surface of the aluminum-based substrate. The pretreatment layer is obtained by spraying an aluminum base coating treatment liquid and then curing it. The pretreatment layer enhances the interfacial adhesion between the aluminum-based substrate and the functional coating layer. The functional coating layer is obtained by spraying a functional coating slurry and then curing it. The functional coating slurry comprises the following raw materials in parts by weight: 50-55 parts modified acrylate copolymer, 12-14 parts hydroxyl-terminated polyurethane elastomer, 2-3 parts 3-glycidyl etheroxypropyltrimethoxysilane, 4-6 parts modified polytetrafluoroethylene micropowder, 1-2 parts nano-alumina, 5-8 parts crosslinking agent, 0.2-0.4 parts leveling agent, 0.2-0.4 parts antioxidant, 0.2-0.4 parts ultraviolet absorber, 20-22 parts deionized water, and 0.5-1 parts propylene glycol methyl ether. The modified acrylate copolymer is an acrylate copolymer grafted with sulfonic acid hydrophilic functional groups and thermally conductive phenylphosphonate functional groups. The modified polytetrafluoroethylene micropowder is polytetrafluoroethylene microspheres with nano-zinc bridged on the surface by a silane coupling agent to form a polytetrafluoroethylene nano-zinc core-shell structure.

2. The coated aluminum sheet for drilling IC flexible substrates according to claim 1, characterized in that, The aluminum substrate coating solution is a 20-25 wt% epoxy-modified acrylic resin solution, and the solvent is a mixture of butanone and toluene in a volume ratio of 1:

1.

3. The coated aluminum sheet for drilling IC flexible substrates according to claim 1, characterized in that, The crosslinking agent is an aqueous isocyanate crosslinking agent, the leveling agent is a polyether-modified silicone leveling agent BYK-348, the antioxidant is antioxidant 1098, and the ultraviolet absorber is ultraviolet absorber UV-327.

4. The coated aluminum sheet for drilling IC flexible substrates according to claim 1, characterized in that, The preparation method of the modified acrylate copolymer includes the following steps: A. Add deionized water, propylene glycol methyl ether and sodium dodecylbenzene sulfonate to a four-necked flask, stir and heat to 75°C, then add monomers methyl methacrylate, butyl acrylate, hydroxyethyl acrylate, styrene phosphonic acid, 2-acrylamide-2-methylpropanesulfonic acid and dodecyl mercaptan in sequence, stir and emulsify for 20-40 min to obtain monomer pre-emulsion. B. Add 10wt% ammonium persulfate aqueous solution dropwise to the pre-emulsion, stir at 75℃ for 3-5 hours to obtain a semi-transparent emulsion; C. Cool the emulsion to 40°C and adjust the pH to 7.0~7.5 with 25wt% ammonia water to obtain a dispersion of the modified acrylate copolymer.

5. The coated aluminum sheet for drilling IC flexible substrates according to claim 4, characterized in that, The mass ratio of the monomers methyl methacrylate, butyl acrylate, hydroxyethyl acrylate, styrenephosphonic acid, and 2-acrylamide-2-methylpropanesulfonate is 5:4:2:0.6:0.

4. The amount of ammonium persulfate used is 2% to 4% of the total mass of the monomer.

6. The coated aluminum sheet for drilling IC flexible substrates according to claim 1, characterized in that, The preparation method of the modified polytetrafluoroethylene micro powder includes the following steps: a. Add polytetrafluoroethylene micro powder, anhydrous ethanol and citric acid to a high-speed disperser and disperse for 15-25 min. Add mercaptopropyltrimethoxysilane, heat to 50°C, and stir to react for 0.5-1.5 h. b. Add hydrophilic nano zinc powder and deionized water to the system, disperse for 20-40 minutes, filter the micro powder suspension after reaction, vacuum dry it and sieve it through a 200-mesh filter to obtain modified polytetrafluoroethylene micro powder.

7. The coated aluminum sheet for drilling IC flexible substrates according to claim 6, characterized in that, The mass ratio of the polytetrafluoroethylene micro powder, mercaptopropyltrimethoxysilane, and nano zinc powder is 20:1:

2.

8. The coated aluminum sheet for drilling IC flexible substrates according to claim 1, characterized in that, The preparation method of the functional coating slurry includes the following steps: (1) Add modified acrylate copolymer aqueous dispersion and hydroxyl-terminated polyurethane elastomer to a high-speed dispersion kettle, stir and mix for 8-10 min until the system is uniform, add 3-glycidyl ether oxypropyltrimethoxysilane and crosslinking agent, stir and mix for 10-20 min to form a basic resin system; (2) Add modified polytetrafluoroethylene micro powder and nano alumina to the system, disperse for 20-40 min, then add antioxidant, ultraviolet absorber and water-based leveling agent, stir for 5-15 min, and finally add deionized water and propylene glycol methyl ether to adjust the viscosity of the system to obtain functional coating slurry.

9. A method for preparing a coated aluminum sheet for drilling holes in an IC flexible substrate as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Immerse the aluminum foil in an alkaline degreasing agent at 50~60℃ and ultrasonically clean it for 4~6 minutes to remove surface oil. Use an electrochemical roughening method to form a uniform micro-rough structure on the surface of the aluminum foil with a roughness Ra=0.2~0.3μm. S2. Apply the primer treatment solution to the surface of the aluminum foil and dry it in an oven at 80°C for 1 to 2 minutes to form a primer coating with a dry film thickness of 0.5 to 1 μm; S3. Apply the coating slurry to the surface of the aluminum foil after the primer is applied, place it in an oven and use low-temperature stepwise cross-linking curing. After curing, the dry film thickness of the coating is 22~28μm. Cut the cured coated aluminum sheet into sizes that fit the IC flexible substrate to obtain the coated aluminum sheet for drilling the IC flexible substrate.

10. The method for preparing the coated aluminum sheet for drilling IC flexible substrates according to claim 9, characterized in that, The low-temperature stepwise crosslinking and curing process involves pre-drying and dehydrating at 75°C for 1.5–2.5 min, pre-crosslinking at 90°C for 1–2 min, and curing at 55°C for 18–24 h.

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