A circuit board insulating layer and a method for manufacturing the same

Abstract

The application relates to the technical field of insulating layer materials, in particular to a circuit board insulating layer and a preparation method thereof. The preparation method of the circuit board insulating layer comprises the following steps: immersing electronic-grade glass fiber cloth in an insulating layer resin material glue solution, carrying out semi-curing treatment on the electronic-grade glass fiber cloth after being impregnated with the glue, obtaining a semi-cured sheet, neatly stacking the semi-cured sheet and a copper foil, and carrying out hot-pressing forming to form the circuit board insulating layer; the raw materials of the insulating layer resin material glue solution comprise an epoxy resin, modified boron nitride, a synergistic composite filler, a curing agent and a curing agent accelerator. The modified boron nitride can reduce the stacking and agglomeration of boron nitride sheets, ensure effective heat conduction connectivity and improve the heat conduction performance of the insulating layer resin material; the addition and use of the synergistic composite filler are beneficial to optimizing the anti-breakdown performance and dielectric performance of the circuit board insulating layer.

Description

Technical Field

[0001] This invention relates to the field of insulating layer materials technology, and more specifically, to a circuit board insulating layer and its preparation method. Background Technology

[0002] With the rapid iteration of 5G high-frequency communication, high-power precision electronic equipment, smart terminals, and new energy power electronics technologies, circuit boards are rapidly developing towards higher frequencies, higher speeds, higher integration, and higher power, placing increasingly stringent performance requirements on the insulating substrate of circuit boards. Circuit board insulation layers not only need excellent electrical insulation and molding performance, but also need to simultaneously meet core indicators such as low dielectric constant, low dielectric loss, high thermal conductivity and heat dissipation, and high electrical breakdown strength to adapt to the needs of high-frequency signal transmission, high-density device heat dissipation, and long-term stable service. Epoxy resin, with its excellent insulation, good process adaptability, and low dielectric loss, is one of the most widely used basic resin materials in the field of circuit board insulation layers. However, due to the influence of internal defects and boundary scattering, most polymer materials generally have low intrinsic thermal conductivity. The thermal conductivity of conventional epoxy resin is typically between 0.1 and 0.5 W / (m·K), which is insufficient to meet the ever-increasing heat dissipation requirements of high-power electronic devices.

[0003] To improve the thermal conductivity of circuit board insulation layers, highly thermally conductive inorganic fillers are typically added to the resin matrix to construct thermal conductivity pathways. Among these, hexagonal boron nitride (BN) is a preferred thermally conductive filler for circuit board insulation layers due to its ultra-high thermal conductivity (up to 300 W / m·K), low dielectric loss, excellent electrical insulation, and chemical stability. Its lamellar structure can build basic thermal conductivity pathways in the resin matrix, effectively improving the overall thermal conductivity of the insulation layer. However, BN has a highly inert surface and a lack of active groups, making it prone to lamellar stacking and agglomeration in the resin system. It cannot be uniformly dispersed, which not only makes it difficult to construct a continuous and stable thermal conductivity network but also significantly increases the interfacial thermal resistance of the system, resulting in a significant reduction in the thermal conductivity modification effect.

[0004] Furthermore, wollastonite, as a natural silicate mineral filler, possesses characteristics such as low dielectric constant, low loss, high rigidity, low price, and excellent chemical stability. It can effectively improve the dielectric and mechanical properties of epoxy resin insulation layers and is a commonly used functional enhancement filler for high-frequency circuit board insulation layers, suppressing substrate polarization loss while ensuring insulation performance. However, wollastonite is rich in hydrophilic hydroxyl groups on its surface, exhibiting strong surface polarity. It disperses poorly in a hydrophobic epoxy resin matrix, easily agglomerating and settling, resulting in uneven composition of the insulation layer material. Moreover, it readily adsorbs moisture and impurities from the environment, significantly increasing interfacial polarization and ion migration rates, leading to increased dielectric constant and dielectric loss of the insulation layer, and a significant decrease in electrical breakdown performance. This fails to meet the core requirement of low-loss signal transmission in high-frequency, high-speed circuit boards. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a circuit board insulation layer and its preparation method.

[0006] A method for preparing a circuit board insulation layer includes the following steps: impregnating electronic-grade fiberglass cloth in an insulating resin material solution, placing the impregnated electronic-grade fiberglass cloth into a vertical gluing machine for semi-curing treatment to obtain a semi-cured sheet, neatly stacking the semi-cured sheet on at least one side of the copper foil along the thickness direction, and hot-pressing it through a vacuum hot press to form a circuit board insulation layer. The raw materials for the insulating resin material adhesive include: 100-140 parts by weight of epoxy resin, 9-17 parts by weight of modified boron nitride, 12-20 parts by weight of synergistic composite filler, 10-30 parts by weight of curing agent, and 1.3-5 parts by weight of curing accelerator. The modified boron nitride is boron nitride with chromium oxide grafted onto its surface; The enhanced composite filler is obtained by grafting heptaisobutyl monothiol POSS with vinyl cyclohexane molecules on the surface of modified wollastonite powder. The modified wollastonite powder is wollastonite grafted with vinyl cyclohexane molecules.

[0007] In some embodiments, the preparation of the insulating resin material adhesive includes the following steps: S1: Preparation of modified boron nitride: Boron nitride was pretreated with sodium hydroxide solution, and then the pretreated boron nitride was added to chromium trichloride solution. The mixture was stirred and reacted under alkaline and heating conditions. After cooling, centrifugation, washing and drying, modified boron nitride was obtained. S2: Preparation of modified wollastonite powder: Wollastonite powder is dispersed in anhydrous toluene to obtain a wollastonite suspension. Under a nitrogen atmosphere, the suspension is heated, and vinyl cyclohexane oxide and tetrabutyl titanate are added sequentially to the wollastonite suspension. The mixture is stirred and reacted. After cooling, filtration, washing and vacuum drying, the mixture is ground and sieved to obtain modified wollastonite powder. S3: Preparation of the enhanced composite filler: Through the mercapto-olefin click chemical reaction, under nitrogen atmosphere, the photoinitiator is excited by ultraviolet light to generate free radicals, which causes heptaisobutyl monothiol POSS to undergo directional free radical addition with the vinyl epoxy cyclohexane unsaturated double bond grafted on the modified wollastonite surface, anchoring the heptaisobutyl monothiol POSS on the modified wollastonite surface to obtain the enhanced composite filler; S4: Preparation of insulating layer resin material adhesive: 100-140 parts by weight of epoxy resin, 9-17 parts by weight of modified boron nitride, 12-20 parts by weight of synergistic composite filler, 10-30 parts by weight of curing agent, and 1.3-5 parts by weight of curing agent accelerator are mixed and processed to obtain an insulating layer resin material adhesive with fluidity and viscosity.

[0008] In some embodiments, the preparation of modified boron nitride in step S1 specifically includes the following steps: S1.1: Add boron nitride to a 0.5 mol / L sodium hydroxide solution with a solid-liquid mass ratio of 1:(15-20), stir at 40-50℃ for 1-2 h, then filter, wash until neutral, and dry to obtain pretreated boron nitride; S1.2: Add 6-10 parts by weight of chromium trichloride and 2-3.2 parts by weight of citric acid to 120-150 parts by weight of 50% ethylene glycol aqueous solution to obtain chromium trichloride solution. Add 12-16 parts by weight of pretreated boron nitride to chromium trichloride solution and sonicate for 20-30 min. Then slowly add ammonia water at a dropping rate of 1-2 mL / min to adjust the pH of chromium trichloride solution to 7.6-8.4. During the addition of ammonia water, slowly stir the chromium trichloride solution at a stirring speed of 80-120 rpm for 10-20 min to obtain mixed solution. S1.3: Heat the mixed solution to 110-140℃ and stir for 10-12 hours. After the reaction is completed and cooled to room temperature, centrifuge to separate the precipitate. The precipitate is washed and dried to obtain modified boron nitride.

[0009] In some embodiments, the boron nitride particle size is 5–10 μm.

[0010] In some embodiments, the preparation of the modified wollastonite powder in step S2 specifically includes the following steps: 18–22 parts by weight of wollastonite powder were added to 80–100 parts by weight of anhydrous toluene and ultrasonically dispersed for 20–40 min to obtain a wollastonite suspension. The wollastonite suspension was transferred to a three-necked flask equipped with a reflux condenser and heated to 90–100 °C under a nitrogen atmosphere. 2.5–3.5 parts by weight of vinylepoxycyclohexane were added and stirred for 10–20 min. Then, 0.5–1 parts by weight of tetrabutyl titanate was added and the mixture was stirred for 1–2 h. After the reaction was completed, the mixture was naturally cooled to room temperature. After filtration, washing, and vacuum drying, the mixture was ground and sieved to obtain modified wollastonite powder.

[0011] In some embodiments, the preparation of the synergistic composite filler in step S3 specifically includes the following steps: S3.1: Add modified wollastonite powder to anhydrous tetrahydrofuran at a solid-liquid mass ratio of 1:(8-10), and ultrasonically disperse for 10-20 min to obtain a modified wollastonite suspension. Add heptaisobutyl mercaptophosphate (POSS) to the modified wollastonite suspension at an amount of 6-10% of the mass of the modified wollastonite. Then add a photoinitiator at an amount of 2-4% of the mass of the heptaisobutyl mercaptophosphate (POSS). Stir to dissolve and obtain a reaction solution. S3.2: Under nitrogen protection, the reaction solution was irradiated with a 365nm ultraviolet light source with a light intensity of 20-30mW / cm². The mixture was stirred while irradiating for 40-60 minutes. After the reaction was completed, the powder was collected by vacuum filtration. The powder was washed with anhydrous tetrahydrofuran and anhydrous ethanol in sequence, vacuum dried, ground and sieved to obtain the enhanced composite filler, which was then vacuum sealed for later use.

[0012] In some embodiments, the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone.

[0013] In some embodiments, the epoxy resin is one or more of bisphenol A epoxy resin, phenolic epoxy resin, glycidyl ether epoxy resin, glycidyl ester epoxy resin, and glycidylamine epoxy resin.

[0014] In some embodiments, the curing agent is one or more of polyamine curing agents, phthalic anhydride curing agents, and ester curing agents.

[0015] In some embodiments, the curing accelerator is one or more of imidazole, 2-methylimidazolium, 2-ethylimidazolium, 2-phenylimidazolium, 2-ethyl-4-methylimidazolium, 1-cyanoethyl-2-ethyl-4-methylimidazolium, and 2-ethyl-4-phenylimidazolium.

[0016] Compared with the prior art, the present invention has at least the following advantages: 1. This invention pretreats boron nitride to generate boron hydroxyl groups at the surface edges and defect sites. The pretreated boron nitride is then added to a chromium trichloride solution. Citric acid in the chromium trichloride solution acts as a complexing agent, forming soluble complexed chromium ions with chromium ions in the system. Through electrostatic interaction and synergistic coordination of hydroxyl groups, the soluble complexed chromium ions can be uniformly adsorbed on the surface of the pretreated boron nitride. Subsequently, when the pH of the system changes to alkaline, the chromium ions are released and immediately react with hydroxide ions. Since the chromium ions are released within the complexes already adsorbed on the surface of the pretreated boron nitride, the chromium hydroxide generated in the reaction preferentially nucleates on the surface of the pretreated boron nitride. Then, after high-temperature hydrothermal treatment, the chromium hydroxide undergoes a dehydration phase transformation to generate chromium oxide grains. The boron hydroxyl groups on the surface of boron nitride undergo dehydration condensation with the Cr-OH groups on the surface of chromium oxide, forming stable covalent bonds. This allows chromium oxide to be firmly grafted and coated onto the surface of boron nitride, forming modified boron nitride. The chromium oxide graft layer on the surface of modified boron nitride can improve the surface roughness of boron nitride, separate adjacent modified boron nitride sheets through steric hindrance, promote the independent dispersion of modified boron nitride, form an effective sheet-to-sheet contact thermal conduction path, reduce the stacking and agglomeration of boron nitride sheets, ensure effective thermal conductivity, improve the thermal conductivity of the board insulation resin material, and thus improve the thermal conductivity of the circuit board insulation layer.

[0017] 2. In the preparation of modified wollastonite, tetrabutyl titanate undergoes a condensation reaction with the silanol groups on the surface of wollastonite to form stable covalent bonds, anchoring titanium atoms to the powder surface while retaining their Lewis acidity. Subsequently, the titanium atoms fixed on the wollastonite surface coordinate with the epoxy groups of vinylepoxycyclohexane, activating the epoxy groups. The remaining silanol groups on the wollastonite surface initiate epoxy ring opening and nucleophilic addition, allowing vinylepoxycyclohexane to be grafted onto the wollastonite powder surface. After grafting, the original hydrophilic sites of wollastonite can be covered, achieving hydrophobicity of the wollastonite powder surface and reducing interfacial polarization. While ensuring the low dielectric and low loss characteristics of wollastonite powder, it improves the dispersibility of modified wollastonite powder in insulating resin materials, inhibits water adsorption and ion migration, thereby improving the breakdown strength of insulating resin materials.

[0018] 3. This invention utilizes a mercapto-alkene click chemistry reaction. Under nitrogen atmosphere, a photoinitiator is excited by ultraviolet light to generate free radicals, inducing a directional free radical addition between the mercapto groups of heptaisobutyl monothiol POSS and the unsaturated double bonds of vinylepoxycyclohexane grafted onto the modified wollastonite surface. Stable thioether bonds uniformly anchor the heptaisobutyl monothiol POSS onto the modified wollastonite surface in a monomolecular suspension manner, resulting in a structurally stable synergistic composite filler. Applying this synergistic composite filler to insulating resin materials helps suppress dipole orientation polarization, reduces the charge trap density at the interface, thereby reducing ion migration and interfacial charge accumulation. This further reduces the dielectric constant and dielectric loss of the circuit board insulation layer and further enhances its breakdown strength. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0020] A method for preparing an insulating layer for a circuit board specifically includes the following steps: Electronic-grade fiberglass cloth is impregnated with insulating layer material adhesive. After impregnation, the electronic-grade fiberglass cloth is placed in a vertical gluing machine for semi-curing treatment at 100℃ for 1 hour to obtain a semi-cured sheet. Along the thickness direction of the copper foil, the semi-cured sheet is neatly stacked on one side of the copper foil and vacuum hot-pressed at 180℃ for 1 hour to obtain the circuit board insulation layer.

[0021] The raw materials for the insulating resin material adhesive include: 120 parts by weight of bisphenol A epoxy resin, 13 parts by weight of modified boron nitride, 16 parts by weight of synergistic composite filler, 16 parts by weight of diethylenetriamine, and 3.1 parts by weight of 2-methylimidazole.

[0022] S1: Preparation of modified boron nitride, S1.1: Add boron nitride with a particle size of 5-10 μm to a sodium hydroxide solution with a concentration of 0.5 mol / L, with a solid-liquid mass ratio of 1:17, stir at 45℃ for 1.5 h, then filter, wash until neutral, and dry to obtain pretreated boron nitride; S1.2: Add 8 parts by weight of chromium trichloride and 2.6 parts by weight of citric acid to 135 parts by weight of 50% ethylene glycol aqueous solution to obtain chromium trichloride solution. Add 14 parts by weight of pretreated boron nitride to chromium trichloride solution and sonicate for 25 min. Then slowly add ammonia water at a dropping rate of 1.5 mL / min to adjust the pH of chromium trichloride solution to 8. During the addition of ammonia water, slowly stir the chromium trichloride solution at a stirring speed of 100 rpm for 15 min to obtain a mixed solution. S1.3: Add the mixed solution to a hydrothermal reactor, heat to 125°C and stir for 11 hours. After the reaction is completed and cooled to room temperature, centrifuge to separate the precipitate. The precipitate is washed and dried to obtain modified boron nitride. S2: Preparation of modified wollastonite powder 20 parts by weight of wollastonite powder were added to 90 parts by weight of anhydrous toluene and ultrasonically dispersed for 30 min to obtain a wollastonite suspension. The wollastonite suspension was transferred to a three-necked flask equipped with a reflux condenser and heated to 95°C under a nitrogen atmosphere. 3 parts by weight of vinylepoxycyclohexane were added and stirred for 15 min. Then 0.75 parts by weight of tetrabutyl titanate were added and stirred for 1.5 h. After the reaction was completed, the mixture was naturally cooled to room temperature. After filtration, washing and vacuum drying, the mixture was ground and sieved to obtain modified wollastonite powder. S3: Preparation of synergistic composite fillers S3.1: Modified wollastonite powder was added to anhydrous tetrahydrofuran at a solid-liquid mass ratio of 1:9 and ultrasonically dispersed for 15 minutes to obtain a modified wollastonite suspension. Heptaisobutyl mercaptophosphate (POSS) was added to the modified wollastonite suspension at an amount equal to 8% of the mass of the modified wollastonite. Then, 2,2-dimethoxy-2-phenylacetophenone was added at an amount equal to 3% of the mass of the heptaisobutyl mercaptophosphate (POSS). The mixture was stirred to dissolve the POSS and a reaction solution was obtained. S3.2: Under nitrogen protection, the reaction solution was irradiated with a 365nm ultraviolet light source with a light intensity of 25mW / cm². The mixture was stirred while irradiating for 50min. After the reaction was completed, the powder was collected by vacuum filtration. The powder was washed three times each with anhydrous tetrahydrofuran and anhydrous ethanol, dried under vacuum at 50℃ for 24h, ground and sieved to obtain the enhanced composite filler, which was then vacuum sealed for later use. S4: Preparation of insulating layer resin material adhesive solution, 120 parts by weight of bisphenol A epoxy resin, 13 parts by weight of modified boron nitride, 16 parts by weight of synergistic composite filler, 20 parts by weight of diethylenetriamine, and 3.1 parts by weight of 2-methylimidazole are mixed and processed to obtain an insulating resin material liquid with flowability and viscosity. Example

[0023] A method for preparing an insulating layer for a circuit board specifically includes the following steps: Electronic-grade fiberglass cloth is impregnated with insulating layer material adhesive. After impregnation, the electronic-grade fiberglass cloth is placed in a vertical gluing machine for semi-curing treatment at 100℃ for 1 hour to obtain a semi-cured sheet. Along the thickness direction of the copper foil, the semi-cured sheet is neatly stacked on one side of the copper foil and vacuum hot-pressed at 180℃ for 1 hour to obtain the circuit board insulation layer.

[0024] The raw materials for the insulating resin material adhesive include: 140 parts by weight of bisphenol A epoxy resin, 17 parts by weight of modified boron nitride, 20 parts by weight of synergistic composite filler, 30 parts by weight of diethylenetriamine, and 5 parts by weight of 2-methylimidazole.

[0025] S1: Preparation of modified boron nitride, S1.1: Add boron nitride with a particle size of 5-10 μm to a sodium hydroxide solution with a concentration of 0.5 mol / L, with a solid-liquid mass ratio of 1:20, stir at 50℃ for 2 h, then filter, wash until neutral, and dry to obtain pretreated boron nitride; S1.2: Add 10 parts by weight of chromium trichloride and 3.2 parts by weight of citric acid to 150 parts by weight of 50% ethylene glycol aqueous solution to obtain chromium trichloride solution. Add 16 parts by weight of pretreated boron nitride to chromium trichloride solution and sonicate for 30 min. Then slowly add ammonia water at a dropping rate of 2 mL / min to adjust the pH of chromium trichloride solution to 8.4. During the addition of ammonia water, slowly stir the chromium trichloride solution at a stirring speed of 120 rpm for 20 min to obtain a mixed solution. S1.3: Add the mixed solution to a hydrothermal reactor, heat to 140℃ and stir for 12 hours. After the reaction is completed and cooled to room temperature, centrifuge to separate the precipitate. The precipitate is washed and dried to obtain modified boron nitride. S2: Preparation of modified wollastonite powder 22 parts by weight of wollastonite powder were added to 100 parts by weight of anhydrous toluene and ultrasonically dispersed for 40 min to obtain a wollastonite suspension. The wollastonite suspension was transferred to a three-necked flask equipped with a reflux condenser and heated to 100°C under a nitrogen atmosphere. 3.5 parts by weight of vinylepoxycyclohexane were added and stirred for 20 min. Then 1 part by weight of tetrabutyl titanate was added and stirred for 2 h. After the reaction was completed, the mixture was naturally cooled to room temperature, filtered, washed and vacuum dried, ground and sieved to obtain modified wollastonite powder. S3: Preparation of synergistic composite fillers S3.1: Modified wollastonite powder was added to anhydrous tetrahydrofuran at a solid-liquid mass ratio of 1:10 and ultrasonically dispersed for 20 min to obtain a modified wollastonite suspension; heptaisobutyl mercaptophosphate (POSS) was added to the modified wollastonite suspension at an amount of 10% of the mass of modified wollastonite, and then 2,2-dimethoxy-2-phenylacetophenone was added at an amount of 4% of the mass of heptaisobutyl mercaptophosphate (POSS). The mixture was stirred and dissolved to obtain a reaction solution. S3.2: Under nitrogen protection, the reaction solution was irradiated with a 365nm ultraviolet light source with a light intensity of 30mW / cm². The mixture was stirred while irradiating for 60min. After the reaction was completed, the powder was collected by vacuum filtration. The powder was washed three times each with anhydrous tetrahydrofuran and anhydrous ethanol, dried under vacuum at 50℃ for 24h, ground and sieved to obtain the enhanced composite filler, which was then vacuum sealed for later use. S4: Preparation of insulating layer resin material adhesive solution, 140 parts by weight of bisphenol A epoxy resin, 17 parts by weight of modified boron nitride, 20 parts by weight of synergistic composite filler, 30 parts by weight of diethylenetriamine, and 5 parts by weight of 2-methylimidazole are mixed and processed to obtain an insulating resin material liquid with flowability and viscosity. Example

[0026] A method for preparing an insulating layer for a circuit board specifically includes the following steps: Electronic-grade fiberglass cloth is impregnated with insulating layer material adhesive. After impregnation, the electronic-grade fiberglass cloth is placed in a vertical gluing machine for semi-curing treatment at 100℃ for 1 hour to obtain a semi-cured sheet. Along the thickness direction of the copper foil, the semi-cured sheet is neatly stacked on one side of the copper foil and vacuum hot-pressed at 180℃ for 1 hour to obtain the circuit board insulation layer.

[0027] The raw materials for the insulating resin material adhesive include: 100 parts by weight of bisphenol A epoxy resin, 9 parts by weight of modified boron nitride, 12 parts by weight of synergistic composite filler, 5 parts by weight of diethylenetriamine, and 1.3 parts by weight of 2-methylimidazole.

[0028] S1: Preparation of modified boron nitride, S1.1: Add boron nitride with a particle size of 5-10 μm to a sodium hydroxide solution with a concentration of 0.5 mol / L, with a solid-liquid mass ratio of 1:15, stir at 40℃ for 1 h, then filter, wash until neutral, and dry to obtain pretreated boron nitride; S1.2: Add 6 parts by weight of chromium trichloride and 2 parts by weight of citric acid to 120 parts by weight of 50% ethylene glycol aqueous solution to obtain chromium trichloride solution. Add 12 parts by weight of pretreated boron nitride to chromium trichloride solution and sonicate for 20 min. Then slowly add ammonia water at a dropping rate of 1 mL / min to adjust the pH of chromium trichloride solution to 7.6. During the addition of ammonia water, slowly stir the chromium trichloride solution at a stirring speed of 80 rpm for 10 min to obtain a mixed solution. S1.3: Add the mixed solution to a hydrothermal reactor, heat to 110°C and stir for 10 hours. After the reaction is completed and cooled to room temperature, centrifuge to separate the precipitate. The precipitate is washed and dried to obtain modified boron nitride. S2: Preparation of modified wollastonite powder 18 parts by weight of wollastonite powder were added to 80 parts by weight of anhydrous toluene and ultrasonically dispersed for 20 min to obtain a wollastonite suspension. The wollastonite suspension was transferred to a three-necked flask equipped with a reflux condenser and heated to 90°C under a nitrogen atmosphere. 2.5 parts by weight of vinylepoxycyclohexane were added and stirred for 10 min. Then 0.5 parts by weight of tetrabutyl titanate were added and stirred for 1 h. After the reaction was completed, the mixture was naturally cooled to room temperature. After filtration, washing and vacuum drying, the mixture was ground and sieved to obtain modified wollastonite powder. S3: Preparation of synergistic composite fillers S3.1: Modified wollastonite powder was added to anhydrous tetrahydrofuran at a solid-liquid mass ratio of 1:8 and ultrasonically dispersed for 10 min to obtain a modified wollastonite suspension. Heptaisobutyl mercaptophosphate (POSS) was added to the modified wollastonite suspension at a mass of 6% of the modified wollastonite mass. Then, 2,2-dimethoxy-2-phenylacetophenone was added at a mass of 2% of the heptaisobutyl mercaptophosphate (POSS). The mixture was stirred to dissolve the POSS and a reaction solution was obtained. S3.2: Under nitrogen protection, the reaction solution was irradiated with a 365nm ultraviolet light source with a light intensity of 20mW / cm². The mixture was stirred while irradiating for 40min. After the reaction was completed, the powder was collected by vacuum filtration. The powder was washed three times each with anhydrous tetrahydrofuran and anhydrous ethanol, dried under vacuum at 50℃ for 24h, ground and sieved to obtain the enhanced composite filler, which was then vacuum sealed for later use. S4: Preparation of insulating layer resin material adhesive solution, 100 parts by weight of bisphenol A epoxy resin, 9 parts by weight of modified boron nitride, 12 parts by weight of synergistic composite filler, 10 parts by weight of diethylenetriamine, and 1.3 parts by weight of 2-methylimidazole are mixed and processed to obtain an insulating resin material liquid with flowability and viscosity.

[0029] Comparative Example 1 Compared with Example 1, the difference of Comparative Example 1 is that the modified boron nitride in step S4 is replaced with an equal part by weight of boron nitride, while the other steps remain unchanged, and an insulating layer resin material solution is prepared, which is referred to as Comparative Example 1.

[0030] Comparative Example 2 Compared with Example 1, Comparative Example 2 differs in that steps S1.2-S1.3 are removed. 8 parts by weight of chromium trichloride and 2.6 parts by weight of citric acid are added to 135 parts by weight of a 50% (v / v) ethylene glycol aqueous solution to obtain a chromium trichloride solution. The pH of the chromium trichloride solution is adjusted to 8 using ammonia. During the dropwise addition of ammonia, the chromium trichloride solution is slowly stirred at 100 rpm for 15 minutes to obtain a reaction solution. The reaction solution is added to a hydrothermal reactor, heated to 125°C, and stirred for 11 hours. After the reaction is completed and cooled to room temperature, the mixture is centrifuged, and the precipitate is collected. The precipitate is washed and dried to obtain chromium oxide. The obtained chromium oxide is physically mixed with 14 parts by weight of pretreated boron nitride to obtain a mixed filler. The modified boron nitride in step S4 is replaced with an equal part by weight of the mixed filler, while the other steps remain unchanged. An insulating resin material solution is prepared and designated as Comparative Example 2.

[0031] The insulating resin materials prepared in Examples 1-3 and Comparative Examples 1-2 were cured to form insulating resin materials with a diameter of 50 mm and a thickness of 5 mm. Five insulating resin materials from each of Examples 1-3 and Comparative Examples 1-2 were randomly selected as test objects. Using the ISO22007-2 standard, the thermal conductivity of each group of test objects was measured using a thermal conductivity meter at 23±2℃ and 50±5%RH. The measured thermal conductivity results for each group of test objects were statistically analyzed, and the average value was taken as the final result. The results are shown in Table 1.

[0032] Table 1:

[0033] As shown in Table 1, the thermal conductivity of the insulating resin materials in Examples 1-3 is ≥1.95 W / (m•K), which is significantly better than that of the insulating resin materials in Comparative Examples 1-2. This indicates that, compared with Comparative Example 1, which directly uses unmodified boron nitride, and Comparative Example 2, which simply mixes pretreated boron nitride with chromium oxide, the modified boron nitride prepared in Examples 1-3 can construct an efficient thermal conductivity pathway in the insulating resin material, improve the thermal conductivity of the insulating resin material, and thus help improve the thermal conductivity of the circuit board insulation layer.

[0034] Comparative Example 3 Compared with Example 1, the difference of Comparative Example 3 is that step S3 is removed, and the synergistic composite filler in step S4 is replaced with an equal part by weight of modified wollastonite powder. The remaining steps remain unchanged, and an insulating layer resin material solution is prepared. This is referred to as Comparative Example 3.

[0035] Comparative Example 4 Compared with Example 1, the difference of Comparative Example 4 is that steps S2-S3 are removed, and the synergistic composite filler in step S4 is replaced with an equal part by weight of wollastonite powder. The remaining steps remain unchanged, and an insulating layer resin material solution is prepared. This is referred to as Comparative Example 4.

[0036] The insulating resin materials prepared in Examples 1-3 and Comparative Examples 3-4 were cured and processed to form insulating resin materials with dimensions of 50mm×50mm×1mm.

[0037] According to GB / T1409-2006 standard, five insulating resin materials were randomly selected from the insulating resin materials of Examples 1-3 and Comparative Examples 3-4 as test objects, and their dielectric properties were tested at 23±2℃ and 50±5%RH environment, with a test frequency of 1MHz. According to GB / T1408.1-2016 standard, five insulating resin materials were randomly selected from the test objects of Examples 1-3 and Comparative Examples 3-4 as test objects. The breakdown strength test was carried out in an air environment of 23±2℃ and 50±5%RH, using continuous uniform voltage increase at a rate of 500V / s. The test results of dielectric constant, dielectric loss and breakdown strength of each group of test objects were statistically analyzed, and the average value was taken as the final result. The results are shown in Table 2.

[0038] Table 2:

[0039] As shown in Table 2, the insulating resin materials of Examples 1-3 have a dielectric constant ≤2.89, a dielectric loss ≤0.0030, and a breakdown strength of 15.5-16.4 kV / mm. Compared with Comparative Example 3, which uses only vinyl cyclohexane grafted modified wollastonite powder, and Comparative Example 4, which uses pure wollastonite powder directly, the insulating resin materials of Examples 1-3 have lower dielectric constants and dielectric losses, and significantly improved breakdown strength, exhibiting excellent low dielectric constant, low dielectric loss, and breakdown resistance. This indicates that the synergistic modification operation of vinyl cyclohexane grafting modification and heptaisobutyl monothiol POSS grafting reinforcement can effectively improve the dielectric properties and breakdown resistance of the insulating resin materials, thus facilitating the preparation of circuit board insulating layers with low dielectric constant, low loss, and high breakdown strength.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an insulating layer on a circuit board, characterized in that, The process includes the following steps: impregnating electronic-grade fiberglass cloth in an insulating resin material solution, placing the impregnated electronic-grade fiberglass cloth into a vertical gluing machine for semi-curing treatment to obtain a semi-cured sheet, neatly stacking the semi-cured sheet on at least one side of the copper foil along the thickness direction, and hot-pressing it through a vacuum hot press to form the circuit board insulation layer. The raw materials for the insulating resin material adhesive include: 100-140 parts by weight of epoxy resin, 9-17 parts by weight of modified boron nitride, 12-20 parts by weight of synergistic composite filler, 10-30 parts by weight of curing agent, and 1.3-5 parts by weight of curing accelerator. The modified boron nitride is boron nitride with chromium oxide grafted onto its surface; The enhanced composite filler is obtained by grafting heptaisobutyl monothiol POSS with vinyl cyclohexane molecules on the surface of modified wollastonite powder. The modified wollastonite powder is wollastonite grafted with vinyl cyclohexane molecules.

2. The preparation method according to claim 1, characterized in that, The preparation of the insulating resin material solution includes the following steps: S1: Preparation of modified boron nitride: Boron nitride was pretreated with sodium hydroxide solution, and then the pretreated boron nitride was added to chromium trichloride solution. The mixture was stirred and reacted under alkaline and heating conditions. After cooling, centrifugation, washing and drying, modified boron nitride was obtained. S2: Preparation of modified wollastonite powder: Wollastonite powder is dispersed in anhydrous toluene to obtain a wollastonite suspension. Under a nitrogen atmosphere, the suspension is heated, and vinyl cyclohexane oxide and tetrabutyl titanate are added sequentially to the wollastonite suspension. The mixture is stirred and reacted. After cooling, filtration, washing and vacuum drying, the mixture is ground and sieved to obtain modified wollastonite powder. S3: Preparation of the enhanced composite filler: Through the mercapto-olefin click chemical reaction, under nitrogen atmosphere, the photoinitiator is excited by ultraviolet light to generate free radicals, which causes heptaisobutyl monothiol POSS to undergo directional free radical addition with the vinyl epoxy cyclohexane unsaturated double bond grafted on the modified wollastonite surface, anchoring the heptaisobutyl monothiol POSS on the modified wollastonite surface to obtain the enhanced composite filler; S4: Preparation of insulating layer resin material adhesive: 100-140 parts by weight of epoxy resin, 9-17 parts by weight of modified boron nitride, 12-20 parts by weight of synergistic composite filler, 10-30 parts by weight of curing agent and 1.3-5 parts by weight of curing accelerator are mixed and processed to obtain an insulating layer resin material adhesive with fluidity and viscosity.

3. The preparation method according to claim 2, characterized in that, Step S1, the preparation of modified boron nitride, specifically includes the following steps: S1.1: Add boron nitride to a 0.5 mol / L sodium hydroxide solution with a solid-liquid mass ratio of 1:(15-20), stir at 40-50℃ for 1-2 h, then filter, wash until neutral, and dry to obtain pretreated boron nitride; S1.2: Add 6-10 parts by weight of chromium trichloride and 2-3.2 parts by weight of citric acid to 120-150 parts by weight of 50% ethylene glycol aqueous solution to obtain chromium trichloride solution. Add 12-16 parts by weight of pretreated boron nitride to chromium trichloride solution and sonicate for 20-30 min. Then slowly add ammonia water at a dropping rate of 1-2 mL / min to adjust the pH of chromium trichloride solution to 7.6-8.

4. During the addition of ammonia water, slowly stir the chromium trichloride solution at a stirring speed of 80-120 rpm for 10-20 min to obtain mixed solution. S1.3: Heat the mixed solution to 110-140℃ and stir for 10-12 hours. After the reaction is completed and cooled to room temperature, centrifuge to separate the precipitate. The precipitate is washed and dried to obtain modified boron nitride.

4. The preparation method according to claim 3, characterized in that, The particle size of boron nitride is 5–10 μm.

5. The preparation method according to claim 2, characterized in that, Step S2, the preparation of modified wollastonite powder, specifically includes the following steps: 18–22 parts by weight of wollastonite powder were added to 80–100 parts by weight of anhydrous toluene and ultrasonically dispersed for 20–40 min to obtain a wollastonite suspension. The wollastonite suspension was transferred to a three-necked flask equipped with a reflux condenser and heated to 90–100 °C under a nitrogen atmosphere. 2.5–3.5 parts by weight of vinylepoxycyclohexane were added and stirred for 10–20 min. Then, 0.5–1 parts by weight of tetrabutyl titanate was added and the mixture was stirred for 1–2 h. After the reaction was completed, the mixture was naturally cooled to room temperature. After filtration, washing, and vacuum drying, the mixture was ground and sieved to obtain modified wollastonite powder.

6. The preparation method according to claim 2, characterized in that, Step S3, the preparation of the synergistic composite filler, specifically includes the following steps: S3.1: Add modified wollastonite powder to anhydrous tetrahydrofuran at a solid-liquid mass ratio of 1:(8-10), and ultrasonically disperse for 10-20 min to obtain a modified wollastonite suspension. Add heptaisobutyl mercaptophosphate (POSS) to the modified wollastonite suspension at an amount of 6-10% of the mass of the modified wollastonite. Then add a photoinitiator at an amount of 2-4% of the mass of the heptaisobutyl mercaptophosphate (POSS). Stir to dissolve and obtain a reaction solution. S3.2: Under nitrogen protection, the reaction solution was irradiated with a 365nm ultraviolet light source with a light intensity of 20-30mW / cm². The mixture was stirred while irradiating for 40-60 minutes. After the reaction was completed, the powder was collected by vacuum filtration. The powder was washed with anhydrous tetrahydrofuran and anhydrous ethanol in sequence, vacuum dried, ground and sieved to obtain the enhanced composite filler, which was then vacuum sealed for later use.

7. The preparation method according to claim 6, characterized in that, The photoinitiator is 2,2-dimethoxy-2-phenylacetophenone.

8. The preparation method according to claim 2, characterized in that, The epoxy resin is one or more of the following: bisphenol A epoxy resin, phenolic epoxy resin, glycidyl ether epoxy resin, glycidyl ester epoxy resin, and glycidylamine epoxy resin.

9. The preparation method according to claim 8, characterized in that, The curing agent is one or more of the following: polyamine curing agents, phthalic anhydride curing agents, and ester curing agents.

10. The preparation method according to claim 9, characterized in that, The curing accelerator is one or more of imidazole, 2-methylimidazolium, 2-ethylimidazolium, 2-phenylimidazolium, 2-ethyl-4-methylimidazolium, 1-cyanoethyl-2-ethyl-4-methylimidazolium, and 2-ethyl-4-phenylimidazolium.

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