An epoxy resin composition for copper clad laminates and its preparation method

Abstract

This invention relates to the field of resin technology, specifically to an epoxy resin composition for copper-clad laminates and its preparation method. The epoxy resin composition comprises, by weight, 500-700 parts of bisphenol A type epoxy resin, 50-70 parts of phenyl glycidyl ether, 30-50 parts of dodecyl glycidyl ether, 20-40 parts of dicyandiamide, 3-7 parts of 2-ethyl-4-methylimidazole, 800-1000 parts of modified spherical silica filler, and a solvent. The key lies in the partial end-capping of the silica surface, followed by the sequential construction of a bimodal siloxane brush layer, a reactive layer with epoxy functional groups, and a fluorinated brush layer. Then, an epoxy ring-opening anchoring aminopropyl isobutyl polysilsesquioxane cage and an aminopropyl-terminated polydimethylsiloxane are used, followed by final end-capping. This composition effectively solves the problems of poor filler dispersibility and high interfacial polarity under high filler conditions, significantly reduces dielectric loss, and improves electrical performance stability and lamination density under humid and hot environments.

Description

Technical Field

[0001] This invention relates to the field of resin technology, and in particular to an epoxy resin composition for copper clad laminates and its preparation method. Background Technology

[0002] With the rapid development of technologies such as 5G, the Internet of Things, artificial intelligence, and high-performance computing, signal transmission rates have entered the GHz and even higher frequency bands. This places unprecedented demands on copper-clad laminates (CCLs), the core basic material for electronic devices: not only do they need extremely low dielectric constants (Dk) and dielectric loss factors (Df) to ensure high-speed and integrity of signal transmission, but they also need to maintain the long-term stability of these properties in high-frequency, humid, and hot environments. Traditional epoxy resin systems for CCLs, although widely used due to their good adhesion, mechanical strength, and mature process foundation, have inherent polarity and polarization losses at high frequencies, making them difficult to meet the stringent requirements of current high-frequency, high-speed applications.

[0003] To reduce dielectric loss, a key strategy commonly adopted in the industry for material design is to fill the epoxy resin matrix with a large amount of inorganic fillers with low dielectric constants. Spherical fused silica is the preferred choice due to its excellent dielectric properties, low coefficient of thermal expansion, and good processability. Theoretically, increasing the filler content to dilute the volume percentage of the polar resin can effectively reduce the overall dielectric constant and loss of the composite material. However, this approach presents significant process and reliability challenges in practice. First, the high specific surface area of ​​silica particles is rich in silanol groups. These strongly polar groups not only cause filler particles to easily agglomerate through hydrogen bonding, forming difficult-to-disperse secondary aggregates, resulting in an actual dispersed particle size of the filler in the resin that is much larger than its original particle size, thus disrupting the system's uniformity; but also, filler agglomeration drastically increases the viscosity of the composite system during processing, severely deteriorating the wettability and flowability of the resin adhesive to reinforcing materials (such as fiberglass cloth), making prepreg preparation and lamination difficult.

[0004] More challengingly, these surface silanol groups and interfacial defects formed by filler agglomeration constitute potential water absorption and polarization centers. In humid environments, water molecules (with a Dk of approximately 80 and an extremely high Df) readily adsorb onto these polar sites, significantly exacerbating the interfacial polarization effect. This leads to a noticeable shift in the dielectric properties of the copper-clad laminate after water absorption, particularly the loss factor, which is extremely sensitive to humidity. This directly threatens the signal integrity and reliability of high-frequency circuits during long-term service. Furthermore, if the resin and filler rely solely on traditional silane coupling agents to form physical adsorption or limited chemical bonding, the interfacial bonding strength is often insufficient to withstand the thermal stress during lamination and the thermal cycling during device service. This easily leads to microcracks or lamination voids at the interface. These microscopic defects can also become obstacles to signal transmission and the starting point for performance degradation.

[0005] To address the aforementioned filler interface issues, existing technologies have explored various surface modification methods. For example, directly treating silica with long-chain alkyl silanes or polysiloxanes aims to reduce surface energy and improve dispersibility by introducing an organic layer. However, while such simple hydrophobic treatments may alleviate agglomeration to some extent, they often excessively passivate the filler surface, weakening the necessary chemical interactions between it and the epoxy resin matrix, leading to decreased interfacial adhesion and potentially impairing the heat resistance and mechanical properties of the laminate. Another approach is to introduce reactive silanes that can react with epoxy groups to enhance interfacial chemical bonding. However, improper treatment, such as excessively high local concentrations of reactive silanes or uneven distribution on the filler surface, can easily lead to self-condensation reactions, forming soft interfacial layers or ineffective siloxane bridges, failing to achieve the ideal balance between strong interfacial bonding and low polarity. Therefore, how to construct an interface structure on the surface of silica filler that can effectively shield polarity, inhibit agglomeration, reduce interfacial polarization, form a strong and stable chemical bond with epoxy resin, and ensure good processing fluidity even at high filler content has become a core technical challenge that urgently needs to be solved in the development of epoxy resin compositions for high-frequency and high-speed copper clad laminates. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide an epoxy resin composition for copper clad laminates and its preparation method, so as to solve the problems of existing epoxy resin compositions for copper clad laminates, which have poor filler dispersion, high interfacial polarity and weak bonding under high filler conditions, resulting in high dielectric loss, insufficient lamination density and significant decrease in electrical performance stability under humid and hot conditions.

[0007] To achieve the above objectives, the present invention provides an epoxy resin composition for copper clad laminates, comprising, by weight parts: 500-700 parts of bisphenol A type epoxy resin, 50-70 parts of phenyl glycidyl ether, 30-50 parts of dodecyl glycidyl ether, 20-40 parts of dicyandiamide, 3-7 parts of 2-ethyl-4-methylimidazole, 800-1000 parts of modified spherical silica filler, 600-800 parts of methyl ethyl ketone, and 300-500 parts of toluene.

[0008] The modified spherical silica filler consists of spherical molten silica micropowder with a surface partially end-capped with trimethylsilyl groups by hexamethyldisilazane. A bimodal siloxane brush layer is then constructed on the surface, formed by grafting short-chain hydroxyl-terminated polydimethylsiloxane and long-chain hydroxyl-terminated polydimethylsiloxane. A reaction layer with epoxy functional groups is introduced by γ-glycidoxypropyltrimethoxysilane, and a fluorinated brush layer is introduced by fluorosiloxane with trifluoropropyl side groups at the end-hydroxyl end. An epoxy ring-opening reaction occurs through the reaction layer with epoxy functional groups to anchor the aminopropyl isobutyl polysilsesquioxane cage and the aminopropyl-terminated polydimethylsiloxane. Finally, a final end-capping treatment with hexamethyldisilazane is performed to end-cap the remaining polar sites.

[0009] Preferably, the bisphenol A type epoxy resin is Nan Ya Plastics NPEL-128.

[0010] Preferably, the short-chain hydroxyl-terminated polydimethylsiloxane is SiSiB OF0025, and the long-chain hydroxyl-terminated polydimethylsiloxane is SiSiB OF0156B.

[0011] Preferably, the fluorosiloxane with a hydroxyl-terminated end cap containing a trifluoropropyl side group is SiSiB OF9020.

[0012] Preferably, the aminopropyl isobutyl polysilsesquioxane cage is AM0265.

[0013] Preferably, the aminopropyl-terminated polydimethylsiloxane is SiSiB AF8250-120.

[0014] Preferably, the average particle size of the spherical fused silica micropowder is 2.5-3.5 μm.

[0015] Preferably, the mass ratio of the raw materials for preparing the modified spherical silica filler, including spherical molten silica micro powder, partially trimethylsilyl-terminated hexamethyldisilazane, short-chain hydroxyl-terminated polydimethylsiloxane, long-chain hydroxyl-terminated polydimethylsiloxane, γ-glycidyl etheroxypropyltrimethoxysilane, hydroxyl-terminated fluorosiloxane containing trifluoropropyl side groups, aminopropyl isobutyl polysilsesquioxane cage, aminopropyl-terminated polydimethylsiloxane, and hexamethyldisilazane for final end-capping is 1000:20-80:80-160:150-250:60-100:80-160:20-40:20-50:20-40.

[0016] Furthermore, the present invention also provides a method for preparing modified spherical silica filler, comprising the following steps:

[0017] (1) After dispersing spherical molten silica powder in anhydrous toluene, hexamethyldisilazane was added to carry out a capping reaction to obtain partially trimethylsilyl-capped spherical silica.

[0018] (2) The trimethylsilyl-terminated spherical silica obtained in step (1) is reacted with short-chain hydroxyl-terminated polydimethylsiloxane in anhydrous xylene and the byproducts are removed under reduced pressure to obtain polydimethylsiloxane-modified silica.

[0019] (3) The polydimethylsiloxane modified silica obtained in step (2) is reacted with long-chain hydroxyl-terminated polydimethylsiloxane in anhydrous xylene and the byproducts are removed under reduced pressure to obtain silica with a dual-mode siloxane brush layer.

[0020] (4) Disperse the silica obtained in step (3) in anhydrous toluene, add pre-hydrolyzed γ-glycidoxypropyltrimethoxysilane solution dropwise, react and reflux under reduced pressure to remove byproducts, and obtain brushed silica with epoxy functional groups.

[0021] (5) The epoxy-functionalized brushed silica obtained in step (4) is reacted with a fluorosiloxane with a hydroxyl-terminated trifluoropropyl side group in anhydrous xylene under reflux and the byproduct is removed under reduced pressure to obtain gradient brushed silica.

[0022] (6) The gradient brushed silica obtained in step (5) is reacted with aminopropyl isobutyl polysilsesquioxane cage and end-aminopropyl-terminated polydimethylsiloxane, so that the aminopropyl isobutyl polysilsesquioxane cage and the end-aminopropyl-terminated polydimethylsiloxane are anchored to the silica surface by epoxy ring opening, thus obtaining a double-anchored gradient brushed silica.

[0023] (7) The double-anchored gradient brushed silica obtained in step (6) is reacted with hexamethyldisilazane for final sealing treatment to obtain modified spherical silica filler.

[0024] Furthermore, the present invention also provides a method for preparing an epoxy resin composition for copper clad laminates, comprising the following steps: adding methyl ethyl ketone and toluene to a mixing vessel and adding bisphenol A type epoxy resin under stirring at 35-45°C for 20-40 min to dissolve; then adding phenyl glycidyl ether and dodecyl glycidyl ether and continuing stirring for 20-40 min; subsequently adding dicyandiamide and 2-ethyl-4-methylimidazole and stirring for 15-25 min to obtain a matrix resin varnish; then adding modified spherical silica filler in three portions, dispersing at 1200 rpm-1800 rpm for 15-25 min after each addition; after all the filler has been added, shearing and dispersing at 1800 rpm-2200 rpm for 20-40 min; and filtering through a 200-mesh filtration system to obtain the epoxy resin composition for copper clad laminates.

[0025] The beneficial effects of this invention are:

[0026] This invention significantly reduces the surface polarity of silica fillers and decreases silanol-driven hydrogen bond aggregation through partial trimethylsilyl end-capping and gradient siloxane brush layer construction, resulting in a narrower particle size distribution and better dispersion stability of the filler in the resin system. The sequential grafting of short-chain and long-chain polydimethylsiloxanes forms a bimodal brush layer structure; the dense inner layer inhibits re-agglomeration, while the flexible outer layer reduces interparticle friction, thereby maintaining good flowability and wettability of the composition under high filler loads.

[0027] By introducing epoxy functional groups onto the filler surface through a pre-hydrolysis dripping process, bridging phenomena caused by local self-condensation are effectively avoided, improving the uniformity of modification. During the curing process, the epoxy functional groups form chemical bonds with the resin network, enhancing the filler-resin interface bonding force, reducing lamination interface defects and microvoid formation, and improving the mechanical integrity of the board.

[0028] The outer fluorosiloxane brush layer containing trifluoropropyl side groups further reduces interfacial energy and polarity, suppressing water molecule adsorption and interfacial polarization effects, enabling the copper-clad laminate to maintain stable low-loss characteristics in humid and hot environments. The dual-anchoring structure of the rigid cage core and flexible siloxane forms spatial isolation and stress buffer at the interface, synergistically suppressing deformation caused by chain segment thermal motion and improving the thermal dimensional stability of the composite material.

[0029] The final sealing process passivates residual polar sites, blocking the penetration pathway of water molecules in humid and hot environments. This allows the low-polarity characteristics of the interface to be maintained even after multiple thermal histories, extending the service life of the copper-clad laminate under harsh operating conditions. The synergistic effect of this series of modification methods ultimately achieves a comprehensive improvement in dielectric properties, processing performance, and reliability. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0031] Figure 1 The infrared spectrum comparison diagram of polydimethylsiloxane modified silica obtained in Example 2 of the present invention, including bimodal siloxane brush layer modified silica, fluorinated brush layer silica, rigid cage core / flexible siloxane dual anchored brush layer silica, and modified spherical silica filler. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0033] Example 1:

[0034] Step S1: Add 1800g of anhydrous toluene to a reaction vessel equipped with mechanical stirring and reflux condenser, then add 1000g of spherical molten silica micropowder (average particle size 3.1μm), and stir at 500rpm for 20min at 25℃ to fully wet and disperse it; then add 20g of hexamethyldisilazane and purge with nitrogen for protection, heat the system to 110℃ and reflux for 3h, cool to 25℃ and filter, wash twice with anhydrous toluene and once with anhydrous xylene, and dry the obtained solid under vacuum at 120℃ for 5h to obtain partially trimethylsilyl-terminated spherical silica;

[0035] Step S2: Add 1800g of anhydrous xylene to the solid obtained in step S1, stir at 500rpm for 20min at 25℃, and then reflux at 135℃; under reflux, add 80g of hydroxyl-terminated polydimethylsiloxane (supplier: SiSiBSILICONES; model: SiSiB OF0025) and continue reflux for 2h, and maintain reduced pressure at 135℃ for 1h, then cool to 25℃ and filter, wash twice with anhydrous xylene and dry under vacuum at 120℃ for 5h to obtain polydimethylsiloxane modified silica;

[0036] Step S3: Add 1200g of anhydrous xylene to the solid obtained in step S2, stir at 500rpm for 15min at 25℃, and then reflux at 135℃; under reflux, add 150g of hydroxyl-terminated polydimethylsiloxane (supplier: SiSiB SILICONES; model: SiSiB OF0156B), continue reflux reaction for 2h, and maintain reduced pressure at 135℃ for 1h. After cooling and filtration, wash twice with anhydrous xylene, and dry under vacuum at 120℃ for 5h to obtain silica modified with a bimodal siloxane brush layer.

[0037] Step S4: Add 1200g of anhydrous toluene to the solid obtained in step S3, stir at 500rpm for 20min at 25℃, and then raise the temperature to 65℃ to obtain a silica dispersion system; in another container, add 150g of anhydrous isopropanol, 60g of γ-glycidyl etheroxypropyltrimethoxysilane, 5g of deionized water, and 1g of glacial acetic acid, mix and stir at 25℃ for 15min to complete pre-hydrolysis, and then add the pre-hydrolyzed solution to the above silica dispersion system dropwise at 65℃ for 45min. After the dropwise addition is completed, maintain the reaction at 65℃ for 1h, then raise the temperature to 105℃ and reflux for 1h while simultaneously removing volatile byproducts under reduced pressure. After cooling and filtration, wash twice with anhydrous toluene, and dry under vacuum at 120℃ for 5h to obtain a brushed silica with epoxy functional groups;

[0038] Step S5: Add 1200g of anhydrous xylene to the solid obtained in step S4, stir at 500rpm for 15min at 25℃, and then reflux at 130℃; under reflux, add 80g of fluorosiloxane with trifluoropropyl side groups (supplier: SiSiB SILICONES; model: SiSiB OF9020) with hydroxyl-terminated end groups, continue to reflux for 1h, and remove condensation byproducts under reduced pressure at 130℃ for 1h. After cooling and filtration, wash twice with anhydrous xylene, and dry under vacuum at 120℃ for 5h to obtain fluorinated brushed silica.

[0039] Step S6: Add 1000g of anhydrous toluene to the solid obtained in step S5, stir at 500rpm for 15min at 25℃, and then raise the temperature to 70℃; add 20g of aminopropyl isobutyl polysilsesquioxane cage (supplier: HybridPlastics; grade: AM0265) at 70℃ and react for 1h, then add 20g of terminally aminopropyl-terminated polydimethylsiloxane (supplier: SiSiB SILICONES; model: SiSiB AF8250-120) and continue to react for 1h, cool and filter, wash twice with anhydrous toluene, and vacuum dry at 120℃ for 5h to obtain a rigid cage core / flexible siloxane dual-anchored brushed silica layer;

[0040] Step S7: Add 800g of anhydrous toluene to the solid obtained in step S6, stir at 500rpm for 15min at 25℃, then heat to 100℃ and reflux; add 20g of hexamethyldisilazane under reflux conditions and react for 2h, cool and filter, wash twice with anhydrous toluene, and dry under vacuum at 120℃ for 6h to obtain modified spherical silica filler.

[0041] Step S8: Add 600g of methyl ethyl ketone and 300g of toluene to a mixing vessel with a stirring jacket. Add 500g of bisphenol A epoxy resin (supplier: Nan Ya Plastics; brand: NPEL-128) under stirring at 35°C and dissolve for 20 minutes. Then add 50g of phenyl glycidyl ether and 30g of dodecyl glycidyl ether as reactive diluents and continue stirring for 20 minutes. Subsequently, add 20g of dicyandiamide and 3g of 2-ethyl-4-methylimidazole and stir for 15 minutes to obtain a matrix resin varnish. Then add 800g of modified spherical silica filler in three portions, dispersing at 1200 rpm for 15 minutes after each addition. After all the filler has been added, shear and disperse at 1800 rpm for 20 minutes. Finally, filter through a 200-mesh filter to obtain an epoxy resin composition for copper clad laminates.

[0042] Step S9: Weigh 2000g of electronic grade alkali-free glass fiber cloth (model 7628) and impregnate it in the varnish obtained in step S8. After controlling the amount of adhesive by using a scraper, pre-bake at 70℃ for 4min and bake at 140℃ for 5min to obtain prepreg. Stack several sheets of prepreg with electrolytic copper foil, and complete the curing and lamination at 170℃ and 1MPa for 50min. Then, cure at 190℃ for 1h to obtain copper-clad laminate.

[0043] Example 2:

[0044] Step S1: Add 2000g of anhydrous toluene to a reaction vessel equipped with mechanical stirring and reflux condenser, then add 1000g of spherical molten silica micropowder (average particle size 3.1μm), and stir at 600rpm for 30min at 25℃ to fully wet and disperse it; then add 40g of hexamethyldisilazane and purge with nitrogen for protection, heat the system to 110℃ and reflux for 4h, cool to 25℃ and filter, wash twice with anhydrous toluene and once with anhydrous xylene, and dry the obtained solid under vacuum at 120℃ for 6h to obtain partially trimethylsilyl-terminated spherical silica;

[0045] Step S2: Add 2000g of anhydrous xylene to the solid obtained in step S1, stir at 600rpm for 30min at 25℃, and then reflux at 135℃; add 120g of hydroxyl-terminated polydimethylsiloxane (supplier: SiSiBSILICONES; model: SiSiB OF0025) under reflux and continue reflux reaction for 3h, and maintain reduced pressure at 135℃ for 1h, then cool to 25℃ and filter, wash twice with anhydrous xylene and dry under vacuum at 120℃ for 6h to obtain polydimethylsiloxane modified silica;

[0046] Step S3: Add 1500g of anhydrous xylene to the solid obtained in step S2, stir at 600rpm for 20min at 25℃, and then reflux at 135℃; under reflux, add 200g of hydroxyl-terminated polydimethylsiloxane (supplier: SiSiB SILICONES; model: SiSiB OF0156B), continue reflux reaction for 3h, and maintain reduced pressure at 135℃ for 1h. After cooling and filtration, wash twice with anhydrous xylene, and dry under vacuum at 120℃ for 6h to obtain silica modified with a bimodal siloxane brush layer.

[0047] Step S4: Add 1500g of anhydrous toluene to the solid obtained in step S3, stir at 600rpm for 30min at 25℃, and then raise the temperature to 70℃ to obtain a silica dispersion system; in another container, add 200g of anhydrous isopropanol, 80g of γ-glycidyl etheroxypropyltrimethoxysilane, 6g of deionized water, and 2g of glacial acetic acid, mix and stir at 25℃ for 20min to complete pre-hydrolysis, and then add the pre-hydrolyzed solution to the above silica dispersion system dropwise at 70℃ for 60min. After the dropwise addition is completed, maintain the reaction at 70℃ for 2h, then raise the temperature to 110℃ and reflux for 1h while simultaneously removing volatile byproducts under reduced pressure. After cooling and filtration, wash twice with anhydrous toluene, and dry under vacuum at 120℃ for 6h to obtain a brushed silica with epoxy functional groups;

[0048] Step S5: Add 1500g of anhydrous xylene to the solid obtained in step S4, stir at 600rpm for 20min at 25℃, and then reflux at 135℃; under reflux, add 120g of fluorosiloxane with trifluoropropyl side groups (supplier: SiSiB SILICONES; model: SiSiB OF9020) with hydroxyl-terminated end groups, continue to reflux for 2h, and remove condensation byproducts under reduced pressure at 135℃ for 1h. After cooling and filtration, wash twice with anhydrous xylene, and dry under vacuum at 120℃ for 6h to obtain fluorinated brushed silica.

[0049] Step S6: Add 1200g of anhydrous toluene to the solid obtained in step S5, stir at 600rpm for 20min at 25℃, and then raise the temperature to 80℃; add 30g of aminopropyl isobutyl polysilsesquioxane cage (supplier: HybridPlastics; grade: AM0265) at 80℃ and react for 1h, then add 30g of terminally aminopropyl-terminated polydimethylsiloxane (supplier: SiSiB SILICONES; model: SiSiB AF8250-120) and continue to react for 1h. After cooling and filtration, wash twice with anhydrous toluene and vacuum dry at 120℃ for 6h to obtain a rigid cage core / flexible siloxane dual-anchored brushed silica layer.

[0050] Step S7: Add 1000g of anhydrous toluene to the solid obtained in step S6, stir at 600rpm for 20min at 25℃, then reflux at 110℃; add 30g of hexamethyldisilazane under reflux conditions and react for 2h, cool and filter, wash twice with anhydrous toluene, and dry under vacuum at 120℃ for 8h to obtain modified spherical silica filler.

[0051] Step S8: Add 700g of methyl ethyl ketone and 400g of toluene to a mixing vessel with a stirring jacket. Add 600g of bisphenol A epoxy resin (supplier: Nan Ya Plastics; brand: NPEL-128) under stirring at 40°C and dissolve for 30 minutes. Then add 60g of phenyl glycidyl ether and 40g of dodecyl glycidyl ether as reactive diluents and continue stirring for 30 minutes. Subsequently, add 30g of dicyandiamide and 5g of 2-ethyl-4-methylimidazole and stir for 20 minutes to obtain a matrix resin varnish. Then add 900g of modified spherical silica filler in three portions, dispersing at 1500rpm for 20 minutes after each addition. After all the filler has been added, shear and disperse at 2000rpm for 30 minutes. Finally, filter through a 200-mesh filter to obtain an epoxy resin composition for copper clad laminates.

[0052] Step S9: Weigh 2000g of electronic grade alkali-free glass fiber cloth (model 7628) and impregnate it in the varnish obtained in step S8. After controlling the amount of adhesive by using a scraper, pre-bake at 80℃ for 5min and bake at 150℃ for 6min to obtain prepreg. Stack several sheets of prepreg with electrolytic copper foil, and complete the curing and lamination at 180℃ and 2MPa for 60min. Then, cure at 200℃ for 2h to obtain copper-clad laminate.

[0053] Example 3:

[0054] Step S1: Add 2200g of anhydrous toluene to a reaction vessel equipped with mechanical stirring and reflux condenser, then add 1000g of spherical molten silica micropowder (average particle size 3.1μm), and stir at 700rpm for 40min at 25℃ to fully wet and disperse it; then add 80g of hexamethyldisilazane and purge with nitrogen for protection, heat the system to 110℃ and reflux for 5h, cool to 25℃ and filter, wash twice with anhydrous toluene and once with anhydrous xylene, and dry the obtained solid under vacuum at 120℃ for 7h to obtain partially trimethylsilyl-terminated spherical silica;

[0055] Step S2: Add 2200g of anhydrous xylene to the solid obtained in step S1, stir at 700rpm for 40min at 25℃, and then reflux at 135℃; add 160g of hydroxyl-terminated polydimethylsiloxane (supplier: SiSiBSILICONES; model: SiSiB OF0025) under reflux and continue reflux reaction for 4h, and maintain reduced pressure at 135℃ for 2h, then cool to 25℃ and filter, wash twice with anhydrous xylene and dry under vacuum at 120℃ for 7h to obtain polydimethylsiloxane modified silica;

[0056] Step S3: Add 1800g of anhydrous xylene to the solid obtained in step S2, stir at 700rpm for 25min at 25℃, and then reflux at 135℃; under reflux, add 250g of hydroxyl-terminated polydimethylsiloxane (supplier: SiSiB SILICONES; model: SiSiB OF0156B), continue reflux reaction for 4h, and maintain reduced pressure at 135℃ for 2h. After cooling and filtration, wash twice with anhydrous xylene, and dry under vacuum at 120℃ for 7h to obtain silica modified with a bimodal siloxane brush layer.

[0057] Step S4: Add 1800g of anhydrous toluene to the solid obtained in step S3, stir at 700rpm for 40min at 25℃, and then raise the temperature to 75℃ to obtain a silica dispersion system; in another container, add 250g of anhydrous isopropanol, 100g of γ-glycidyl etheroxypropyltrimethoxysilane, 7g of deionized water, and 3g of glacial acetic acid, mix and stir at 25℃ for 25min to complete pre-hydrolysis, and then add the pre-hydrolyzed solution to the above silica dispersion system dropwise at 75℃ for 75min. After the dropwise addition is completed, maintain the reaction at 75℃ for 3h, then raise the temperature to 115℃ and reflux for 2h while simultaneously removing volatile byproducts under reduced pressure. After cooling and filtration, wash twice with anhydrous toluene, and dry under vacuum at 120℃ for 7h to obtain a brushed silica with epoxy functional groups;

[0058] Step S5: Add 1800g of anhydrous xylene to the solid obtained in step S4, stir at 700rpm for 25min at 25℃, and then reflux at 140℃; under reflux, add 160g of fluorosiloxane with trifluoropropyl side groups (supplier: SiSiB SILICONES; model: SiSiB OF9020) with hydroxyl-terminated end groups, continue to reflux for 3h, and remove condensation byproducts under reduced pressure at 140℃ for 2h. After cooling and filtration, wash twice with anhydrous xylene, and dry under vacuum at 120℃ for 7h to obtain fluorinated brushed silica.

[0059] Step S6: Add 1400g of anhydrous toluene to the solid obtained in step S5, stir at 700rpm for 25min at 25℃, and then raise the temperature to 90℃; add 40g of aminopropyl isobutyl polysilsesquioxane cage (supplier: HybridPlastics; grade: AM0265) at 90℃ and react for 2h, then add 40g of terminally aminopropyl-terminated polydimethylsiloxane (supplier: SiSiB SILICONES; model: SiSiB AF8250-120) and continue to react for 2h. After cooling and filtration, wash twice with anhydrous toluene and dry under vacuum at 120℃ for 7h to obtain a rigid cage core / flexible siloxane dual-anchored brushed silica layer.

[0060] Step S7: Add 1200g of anhydrous toluene to the solid obtained in step S6, stir at 700rpm for 25min at 25℃, then heat to 120℃ and reflux; add 40g of hexamethyldisilazane under reflux conditions and react for 3h, cool and filter, wash twice with anhydrous toluene, and dry under vacuum at 120℃ for 10h to obtain modified spherical silica filler.

[0061] Step S8: Add 800g of methyl ethyl ketone and 500g of toluene to a mixing vessel with a stirring jacket. Add 700g of bisphenol A epoxy resin (supplier: Nan Ya Plastics; brand: NPEL-128) under stirring at 45°C and dissolve for 40min. Then add 70g of phenyl glycidyl ether and 50g of dodecyl glycidyl ether as reactive diluents and continue stirring for 40min. Subsequently, add 40g of dicyandiamide and 7g of 2-ethyl-4-methylimidazole and stir for 25min to obtain a matrix resin varnish. Then add 1000g of modified spherical silica filler in three portions, dispersing at 1800rpm for 25min after each addition. After all the filler has been added, shear and disperse at 2200rpm for 40min. Finally, filter through a 200-mesh filter to obtain an epoxy resin composition for copper clad laminates.

[0062] Step S9: Weigh 2000g of electronic grade alkali-free glass fiber cloth (model 7628) and impregnate it in the varnish obtained in step S8. After controlling the amount of adhesive by using a scraper, pre-bake at 90℃ for 6min and bake at 160℃ for 7min to obtain prepreg. Stack several sheets of prepreg with electrolytic copper foil, and complete the curing and lamination at 190℃ and 3MPa for 70min. Then, cure at 210℃ for 3h to obtain copper-clad laminate.

[0063] Comparative Example 1:

[0064] The difference between Comparative Example 1 and Example 2 is that: hexamethyldisilazane is not added in step S1, the spherical molten silica micropowder is not partially end-capped with trimethylsilyl, and spherical molten silica micropowder that has not been partially end-capped with trimethylsilyl is used as silica raw material in subsequent reactions from step S2 to step S9; the other conditions are the same as in Example 2.

[0065] Comparative Example 2:

[0066] The difference between Comparative Example 2 and Example 2 is that the amount of hexamethyldisilazane used in step S1 was adjusted from 40g to 120g; the other conditions were the same as in Example 2.

[0067] Comparative Example 3:

[0068] The difference between Comparative Example 3 and Example 2 is that in step S3, 200g of hydroxyl-terminated polydimethylsiloxane (supplier: SiSiB, model: SiSiB OF0025) was used instead of 200g of hydroxyl-terminated polydimethylsiloxane (supplier: SiSiB, model: SiSiB OF0156B) for reflux reaction; the other conditions were the same as in Example 2.

[0069] Comparative Example 4:

[0070] The difference between Comparative Example 4 and Example 2 is that in step S5, 80g of hydroxyl-terminated polydimethylsiloxane (supplier: SiSiB, model: SiSiB OF0156B) was used instead of 80g of hydroxyl-terminated fluorosiloxane containing trifluoropropyl side groups (supplier: SiSiB, model: OF9020) for reflux reaction; the other conditions were the same as in Example 2.

[0071] Comparative Example 5:

[0072] The difference between Comparative Example 5 and Example 2 is that in step S6, 25g of aminopropyl isobutyl polysilsesquioxane cage (supplier: SiSiB, model: AM0265) is not added, but only 50g of terminally aminopropyl-terminated polydimethylsiloxane (supplier: SiSiB, model: AF8250-120) is added for the reaction; the other conditions are the same as in Example 2.

[0073] Comparative Example 6:

[0074] The difference between Comparative Example 6 and Example 2 is that hexamethyldisilazane is not added for final sealing in step S7, and the solid obtained in step S6 is directly used as modified spherical silica filler in steps S8 and S9 after being cooled, filtered, washed and vacuum dried; the other conditions are the same as in Example 2.

[0075] Performance testing:

[0076] Sample preparation: Each group of compositions was prepared according to the steps described in the examples and comparative examples respectively; then, copper-clad laminate samples were prepared according to step S9 of Example 2: Electronic grade alkali-free glass fiber cloth (model 7628) was impregnated with varnish, and the resin content of the prepreg was controlled to be 42% by using a scraper. It was pre-baked at 80℃ for 5 min and pre-baked at 160℃ for 3 min to reduce the volatile content of the prepreg to 0.50%. Then, 8 sheets of prepreg were stacked with an electrolytic copper foil with a thickness of 18 μm. The curing and lamination were completed by hot pressing at 180℃ and 2MPa for 60 min, and then cured at 200℃ for 2 h to obtain the copper-clad laminate.

[0077] Infrared spectral characterization of modified spherical silica fillers: 0.50 g each of the polydimethylsiloxane-modified silica obtained in Example 2, the bimodal siloxane brush-layer modified silica, the fluorinated brush-layer silica, the rigid cage core / flexible siloxane dual-anchored brush-layer silica, and the modified spherical silica filler were dried under vacuum at 120℃ for 2 h and then equilibrated at 23℃ and 50% relative humidity for 30 min. Infrared spectroscopy was used for testing, with the wavenumber range set to 4000-400 cm⁻¹. -1 The resolution is 4cm. -1 .

[0078] Particle size distribution of modified spherical silica filler: According to GB / T 19077-2024, 0.50 g of each of the modified spherical silica filler obtained in the examples and comparative examples were weighed and added to 100 mL of anhydrous isopropanol. After ultrasonic dispersion at 300 W for 5 min, the particles were immediately transferred to the wet circulation tank of a laser particle size analyzer. The circulation flow rate was set to 30%, and the stirring speed was set to 1500 rpm. Background correction was performed with anhydrous isopropanol before the test. The volume distributions D10, D50, and D90 were output according to the standard. D90 was used to sensitively characterize the agglomerates.

[0079] Viscosity determination of epoxy resin composition for copper clad laminate: The compositions corresponding to the examples and comparative examples were placed in a constant temperature oven at 25℃ for 2 hours to eliminate the influence of temperature gradient and air bubbles. 50 mL of each composition was placed in a 250 mL standard viscosity cup. A single-cylinder rotational viscometer was used with rotor No. 3 selected, rotation speed 30 r / min, and test temperature 25℃. After the rotor was immersed, the viscosity was placed for 60 s and then the viscosity reading was taken. The readings were taken 5 times and the arithmetic mean was taken. Three samples were prepared in parallel for each group and the average of the three samples was taken as the result of the group.

[0080] Observation of delamination and voids in copper-clad laminate cross sections: The microscopic observation methods described in GB / T 4722-2017 were followed. Sample blocks of 10mm × 10mm were cut from the copper-clad laminates of the examples and comparative examples. After being cold-mounted with epoxy resin and cured at room temperature for 24 hours, the samples were ground with graded sandpaper (P400, P800, P1200, P2000) and polished with diamond to 0.5μm. Subsequently, at least 10 fields of view were continuously photographed along the thickness direction using a metallographic microscope at 100x magnification. The void area fraction was calculated using grayscale threshold segmentation method using image analysis software, and the presence or absence of delamination interfaces was recorded.

[0081] Relative permittivity and loss tangent of copper-clad laminate in microwave band: According to GB / T 43801-2024, the copper foil on both sides of the copper-clad laminate samples of the examples and comparative examples were etched away with ferric chloride aqueous solution, rinsed with deionized water until neutral, wiped with anhydrous isopropanol and dried at 60°C for 1 hour; the copper-removed substrate was cut into 50mm×35mm rectangular pieces, and two pieces of the same group were stacked to achieve a total thickness of 0.80mm to reduce the error of thin samples; the test environment was set at 23°C and 50% relative humidity. The samples were tested after equilibration in this environment for 24 hours. A vector network analyzer was connected to the discrete dielectric resonator fixture, and the nominal test frequency was set to 10GHz. The relative permittivity Dk and loss tangent Df were measured respectively. Five samples were tested in each group and the arithmetic mean was taken.

[0082] Water absorption and dielectric loss drift before and after water absorption of copper-clad laminate: Water absorption was tested according to GB / T 1034-2008. Dielectric drift was performed on the same batch of samples in conjunction with the test of relative permittivity and loss tangent of copper-clad laminate in the microwave band: The copper-removed substrates of the examples and comparative examples were cut into 50mm×50mm sheets and vacuum dried at 50℃ for 24h. After cooling to 23℃, the dry mass m0 was weighed. The sample was completely immersed in deionized water at 23℃ for 24h and then removed. The surface was wiped 10 times in one direction with lint-free paper to remove the surface water film. The wet mass m1 was weighed within 60s after removal. The water absorption rate W was calculated as (m1-m0) / m0×100%. Then, the relative permittivity and loss tangent of copper-clad laminate in the microwave band was immediately retested at 10GHz and the loss tangent drift ΔDf before and after water absorption was calculated as Df (after water absorption) - Df (dry state).

[0083] The linear thermal expansion coefficient of the cured resin was determined according to GB / T 36800.2-2018. Each group of cured resin sheets was cut into 6mm×6mm×1mm cubes with the stress surface flat. The thermomechanical analyzer was used in compression mode with a quartz probe diameter of 3mm, a static load of 0.05N, a nitrogen atmosphere of 50mL / min, and a temperature program set from 30℃ to 260℃ with a heating rate of 5℃ / min. The sample length change ΔL was recorded, and the linear thermal expansion coefficient α1 in the 30℃-150℃ range and the linear thermal expansion coefficient α2 in the 200℃~250℃ range were calculated.

[0084] The test results are shown in Table 1.

[0085] Table 1 Test Results

[0086] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Particle size D50 (μm) 3.32 3.25 3.38 3.8 3.40 3.55 3.32 3.45 3.72 Particle size D90 (μm) 6.45 6.05 6.70 11.20 7.80 8.92 6.31 7.35 9.61 Viscosity (mPa·s) 11800 10200 11000 18500 12500 16000 9900 13200 17000 Void area fraction (%) 0.4 0.2 0.3 1.8 0.9 1.3 0.3 0.8 1.1 Relative permittivity Dk 3.16 3.12 3.14 3.22 3.09 3.18 3.17 3.19 3.23 Loss tangent Df 0.003 0.002 0.003 0.007 0.003 0.005 0.004 0.004 0.006 Water absorption rate (%) 0.2 0.1 0.2 0.3 0.1 0.2 0.2 0.2 0.3 Water absorption loss drift ΔDf 0.002 0.001 0.002 0.004 0.002 0.003 0.003 0.003 0.004 <![CDATA[α1(×10 -6 / ℃)]]> 34.5 31.8 33.2 38.0 36.2 36.8 33.5 35.6 37.5 <![CDATA[α2(×10 -6 / ℃)]]> 112.1 104.2 109.0 128.8 123.2 126.5 118.0 124.1 130.2

[0087] Data Analysis:

[0088] As can be seen from the data in Examples 1-3 in Table 1, the present invention partially end-capsulates silica particles with hexamethyldisilazane and sequentially grafts hydroxyl-terminated polydimethylsiloxane, γ-glycidyl etheroxypropyltrimethoxysilane, and hydroxyl-terminated fluorosiloxane containing trifluoropropyl side groups onto the particle surface, constructing a low surface energy gradient siloxane brush layer, making the filler particle size distribution more concentrated. The composition maintains processability and fluidity while inhibiting the formation of voids in the board cross-section. At the same time, the reaction combination of epoxy functional groups and epoxy resin curing network, as well as the dual anchoring effect of aminopropyl isobutyl polysilsesquioxane cage and aminopropyl-terminated polydimethylsiloxane, reduce interfacial polarity and interfacial polarization, thereby obtaining a lower relative permittivity and loss tangent in high-frequency and high-speed applications, and maintaining stable electrical performance after water absorption. In addition, the synergistic constraint of the filler-resin interface reduces the linear thermal expansion of the curing system, which is beneficial to improving the signal integrity and reliability of copper-clad laminates.

[0089] As can be seen from the data in Table 1 for Example 2 and Comparative Examples 1 and 6, when partial or final end-capping with hexamethyldisilazane is lacking, the silanol groups remaining on the surface of the silica particles are more prone to hydrogen bonding and condensation, leading to a wider particle size distribution, increased viscosity of the composition, and the formation of more difficult-to-remove microvoids during lamination. These polar sites also increase water absorption sensitivity, inducing stronger interfacial polarization at the interface, resulting in increased loss tangent and loss drift after water absorption. Therefore, the synergistic effect of double end-capping and subsequent brush layer grafting can simultaneously achieve dispersion, density, and stable high-frequency electrical properties.

[0090] As can be seen from the data in Table 1 for Example 2 and Comparative Example 2, when the amount of hexamethyldisilazane is too high, although the increased hydrophobicity of the particle surface makes the decrease in water absorption rate and relative permittivity more obvious, excessive passivation weakens the number of reaction sites introduced by γ-glycidoxypropyltrimethoxysilane, resulting in insufficient chemical bonding between the brush layer and the epoxy resin network, limited interfacial wetting and stress transfer, thus making the board density and electrical property stability after water absorption inferior to Example 2. This result indicates that partial end-capping and epoxy functionalization must achieve a balance between reactivity and low polarity to obtain unpredictable overall performance.

[0091] As can be seen from the data in Example 2 and Comparative Example 3 in Table 1, replacing the hydroxyl-terminated polydimethylsiloxane with a short-chain type reduced the thickness of the flexible brush layer on the particle surface and the chain segment entanglement ability, making it difficult to form an effective steric shield, leading to an increased tendency for aggregation, which in turn caused an increase in the viscosity of the composition and an increase in lamination voids. Aggregation and voids amplify interfacial polarization and dielectric loss, causing an increase in the loss tangent under high-frequency conditions and the loss drift after water absorption. Therefore, it is evident that the long-chain siloxane brush layer makes a crucial contribution to dispersion stability and low loss at high frequencies.

[0092] As can be seen from the data in Table 1 for Example 2 and Comparative Example 4, when a hydroxyl-terminated polydimethylsiloxane is used instead of a fluorosiloxane with trifluoropropyl side groups for the outer layer, the wettability and spreadability of the composition are maintained well, and the cross-sectional voids are not significantly worsened. However, due to the lack of further regulation of surface energy and interfacial polarity by the trifluoropropyl side groups in the outer layer, the polarization loss and water absorption-induced loss drift at the interface are more difficult to suppress, resulting in a higher loss tangent and its drift than in Example 2. This result indicates that there is a synergistic effect of polarization reduction and bonding preservation between the fluorosiloxane outer layer and the epoxy-functionalized inner layer.

[0093] As can be seen from the data in Table 1 for Example 2 and Comparative Example 5, when only aminopropyl-terminated polydimethylsiloxane is used for ring-opening grafting without the aminopropyl isobutyl polysilsesquioxane cage, although the interface has a certain degree of flexibility, the rigid cage core's constraint on chain segment movement and thermally induced deformation is weakened, resulting in an increase in the linear thermal expansion coefficient of the cured resin sheet and a decrease in electrical property stability after water absorption. In Example 2, the dual anchoring of the aminopropyl isobutyl polysilsesquioxane cage and the aminopropyl-terminated polydimethylsiloxane can simultaneously provide rigid support and flexible buffering, exhibiting an interface regulation effect greater than 2 (1+1>2).

[0094] from Figure 1 It can be seen that all five modified silica samples are at approximately 1100 cm⁻¹ -1 and 800cm -1The presence of characteristic absorption peaks of the Si-O-Si framework indicates that the main silica structure was not destroyed during each stage of modification. Following the sequential grafting of polydimethylsiloxane, a bimodal siloxane brush layer, fluorinated siloxane, and a rigid core / flexible siloxane dual-anchoring structure from steps S2 to S7 in Example 2, the peak at 2960 cm⁻¹... -1 and 2900cm -1 The nearby CH stretching vibration peak and 1260 cm⁻¹ -1 The deformation vibration peaks of nearby Si-CH3 gradually increase, while the peak at 3740 cm⁻¹... -1 and 3400cm -1 The absorption of Si-OH in the vicinity is significantly reduced; in the fluorine-brushed silica sample, the absorption at 1240-1150 cm⁻¹ is significantly reduced. -1 Strong and broad CF-related absorption was observed in the interval, accompanied by 910 cm⁻¹. -1 The epoxy group characteristic peak is visible nearby, while in the modified spherical silica filler with rigid core / flexible siloxane dual anchoring and final sealing, the epoxy peak shows a significant attenuation, reaching 3300 cm⁻¹. -1 and 1550cm -1 The presence of NH stretching and bending vibration peaks nearby, along with the further enhancement of the Si-CH3 related peaks, indicates that the epoxy functional groups have undergone ring-opening anchoring with the aminopropyl polysilsesquioxane cage and the aminopropyl-terminated polydimethylsiloxane, and have been finally capped by hexamethyldisilazane. This significantly reduces the number of polar sites on the particle surface, and the interface is gradually modulated towards lower polarity and lower surface energy.

[0095] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. An epoxy resin composition for copper-clad laminates, characterized in that, By weight, it includes the following components: 500-700 parts bisphenol A type epoxy resin, 50-70 parts phenyl glycidyl ether, 30-50 parts dodecyl glycidyl ether, 20-40 parts dicyandiamide, 3-7 parts 2-ethyl-4-methylimidazole, 800-1000 parts modified spherical silica filler, 600-800 parts methyl ethyl ketone, and 300-500 parts toluene; The modified spherical silica filler consists of spherical molten silica micropowder with a surface partially end-capped with trimethylsilyl groups by hexamethyldisilazane. A bimodal siloxane brush layer is then constructed on the surface, formed by grafting short-chain hydroxyl-terminated polydimethylsiloxane and long-chain hydroxyl-terminated polydimethylsiloxane. A reaction layer with epoxy functional groups is introduced by γ-glycidoxypropyltrimethoxysilane, and a fluorinated brush layer is introduced by fluorosiloxane with trifluoropropyl side groups at the end-hydroxyl end. An epoxy ring-opening reaction occurs through the reaction layer with epoxy functional groups to anchor the aminopropyl isobutyl polysilsesquioxane cage and the aminopropyl-terminated polydimethylsiloxane. Finally, a final end-capping treatment with hexamethyldisilazane is performed to end-cap the remaining polar sites.

2. The epoxy resin composition for copper-clad laminates according to claim 1, characterized in that, The bisphenol A type epoxy resin is Nan Ya Plastics NPEL-128.

3. The epoxy resin composition for copper-clad laminates according to claim 1, characterized in that, The short-chain hydroxyl-terminated polydimethylsiloxane is SiSiB OF0025, and the long-chain hydroxyl-terminated polydimethylsiloxane is SiSiB OF0156B.

4. The epoxy resin composition for copper-clad laminates according to claim 1, characterized in that, The fluorosiloxane with hydroxyl-terminated trifluoropropyl side groups is SiSiB OF9020.

5. The epoxy resin composition for copper-clad laminates according to claim 1, characterized in that, The aminopropyl isobutyl polysilsesquioxane cage is AM0265, and the aminopropyl-terminated polydimethylsiloxane is SiSiB AF8250-120.

6. The epoxy resin composition for copper-clad laminates according to claim 1, characterized in that, The average particle size of the spherical fused silica micropowder is 2.5-3.5 μm.

7. The epoxy resin composition for copper-clad laminates according to claim 1, characterized in that, The raw materials for preparing the modified spherical silica filler include spherical molten silica micro powder, partially trimethylsilyl-terminated hexamethyldisilazane, short-chain hydroxyl-terminated polydimethylsiloxane, long-chain hydroxyl-terminated polydimethylsiloxane, γ-glycidyl etheroxypropyltrimethoxysilane, hydroxyl-terminated fluorosiloxane containing trifluoropropyl side groups, aminopropyl isobutyl polysilsesquioxane cage, aminopropyl-terminated polydimethylsiloxane, and hexamethyldisilazane for final end-capping treatment in a mass ratio of 1000:20-80:80-160:150-250:60-100:80-160:20-40:20-50:20-40.

8. The epoxy resin composition for copper-clad laminates according to claim 1, characterized in that, The preparation method of the modified spherical silica filler includes the following steps: (1) After dispersing spherical molten silica powder in anhydrous toluene, hexamethyldisilazane was added to carry out a capping reaction to obtain partially trimethylsilyl-capped spherical silica. (2) The trimethylsilyl-terminated spherical silica obtained in step (1) is reacted with short-chain hydroxyl-terminated polydimethylsiloxane in anhydrous xylene and the byproducts are removed under reduced pressure to obtain polydimethylsiloxane-modified silica. (3) The polydimethylsiloxane modified silica obtained in step (2) is reacted with long-chain hydroxyl-terminated polydimethylsiloxane in anhydrous xylene and the byproducts are removed under reduced pressure to obtain silica with a dual-mode siloxane brush layer. (4) Disperse the silica obtained in step (3) in anhydrous toluene, add pre-hydrolyzed γ-glycidoxypropyltrimethoxysilane solution dropwise, react and reflux under reduced pressure to remove byproducts, and obtain brushed silica with epoxy functional groups. (5) The epoxy-functionalized brushed silica obtained in step (4) is reacted with a fluorosiloxane with a hydroxyl-terminated trifluoropropyl side group in anhydrous xylene under reflux and the byproduct is removed under reduced pressure to obtain gradient brushed silica. (6) The gradient brushed silica obtained in step (5) is reacted with aminopropyl isobutyl polysilsesquioxane cage and end-aminopropyl-terminated polydimethylsiloxane, so that the aminopropyl isobutyl polysilsesquioxane cage and the end-aminopropyl-terminated polydimethylsiloxane are anchored to the silica surface by epoxy ring opening, thus obtaining a double-anchored gradient brushed silica. (7) The double-anchored gradient brushed silica obtained in step (6) is reacted with hexamethyldisilazane for final sealing treatment to obtain modified spherical silica filler.

9. A method for preparing an epoxy resin composition for copper-clad laminates according to any one of claims 1-8, characterized in that, Includes the following steps: Methyl ethyl ketone and toluene were added to a mixing vessel, and bisphenol A epoxy resin was added and dissolved for 20-40 minutes under stirring at 35-45°C. Then, phenyl glycidyl ether and dodecyl glycidyl ether were added and stirring was continued for 20-40 minutes. Subsequently, dicyandiamide and 2-ethyl-4-methylimidazole were added and stirred for 15-25 minutes to obtain a matrix resin varnish. Modified spherical silica filler was then added in three batches, and after each addition, it was dispersed at 1200-1800 rpm for 15-25 minutes. After all the filler was added, it was sheared and dispersed at 1800-2200 rpm for 20-40 minutes, and then filtered through a 200-mesh filter to obtain the epoxy resin composition for copper clad laminate.

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