Sulfur-free CEM-3 copper-clad plate preparation method and CEM-3 copper-clad plate thereof

Abstract

The invention relates to the technical field of electronic information materials, and discloses a sulfur-free CEM-3 copper-clad plate preparation method and a CEM-3 copper-clad plate thereof. According to the preparation method of the sulfur-free CEM-3 copper-clad plate, the sulfur-free raw materials and the sulfur-free preparation technology are adopted in the whole process through the three steps of resin glue solution preparation, core material and surface material preparation and hot-pressing curing, especially the resin glue solution with a specific composition formula, and control over the specific temperature and time in the post-curing stage in hot-pressing curing are adopted, so that the sulfur-free CEM-3 copper-clad plate is obtained. The prepared CEM-3 copper-clad plate has the sulfur-free layering resistance, the copper foil peel strength is greater than or equal to 1.39 N / mm, the ion migration resistance is high, the dielectric loss Df is small, the dielectric constant Dk is stable, the relative tracking index CTI is remarkably improved, and the CTI value gt is remarkably increased; therefore, the stability and the reliability of the CEM-3 copper-clad plate in high-temperature welding and application environments are guaranteed.

Description

Technical Field

[0001] This application relates to the field of electronic information materials technology, and in particular to a method for preparing sulfur-free CEM-3 copper clad laminate and the CEM-3 copper clad laminate thereof. Background Technology

[0002] Copper clad laminate (CCL), as a fundamental material in the electronics and information industry, plays a crucial role in the manufacturing of electronic devices. With the continuous development of the electronics industry, the performance requirements for CCL are becoming increasingly stringent. CEM-3 CCL is a composite substrate CCL, with performance falling between paper-based CEM-1 and all-glass fiber cloth FR-4. It is a mid-range rigid CCL widely used in double-sided boards, LED displays, power modules, and low-to-mid-range consumer electronics, greatly promoting the development of related industries.

[0003] In the traditional preparation of CEM-3 copper clad laminates, the formulation system typically uses brominated epoxy resin as the resin matrix, combined with antimony / bromine synergistic flame retardants, such as antimony trioxide or brominated flame retardants, and uses silica powder as filler to achieve the UL94V-0 flame retardant rating. This formulation system, to a certain extent, ensures the flame retardancy and other basic properties of CEM-3 copper clad laminates, enabling their application in relevant electronic devices.

[0004] However, as the electronics industry moves towards higher density, higher frequency, and higher reliability, the sulfur impurities in traditional CEM-3 copper clad laminate materials are becoming increasingly prominent. Under high temperature, high humidity, and electric field conditions, sulfur ion migration can form conductive pathways, leading to deterioration of the board's insulation performance and a lower relative tracking index (CTI), thus affecting signal transmission. Simultaneously, the sulfur gas contained in the thermal decomposition products of traditional flame-retardant systems can cause cracks or interlayer delamination, affecting the mechanical integrity of the printed circuit board. Furthermore, polar impurities such as sulfur ions can increase dielectric loss (Df) and worsen the stability of the dielectric constant (Dk). These defects severely restrict the further development of CEM-3 copper clad laminates into high-end applications. Summary of the Invention

[0005] To at least overcome one of the problems existing in the prior art, one objective of this application is to provide a method for preparing sulfur-free CEM-3 copper clad laminates. This method involves three main steps: preparing a resin solution, preparing the core material and the surface material, and hot-pressing curing. The entire process uses sulfur-free raw materials and sulfur-free preparation processes, particularly the resin solution with a specific composition, and the control of specific temperature and time during the post-curing stage of hot-pressing curing. This results in a sulfur-free CEM-3 copper clad laminate with strong anti-delamination and anti-ion migration capabilities, low dielectric loss (Df), stable dielectric constant (Dk), and significantly improved relative tracking index (CTI), thereby ensuring the stability and reliability of the CEM-3 copper clad laminate in high-temperature soldering and application environments. A second objective of this application is to provide the CEM-3 copper clad laminate prepared by the aforementioned sulfur-free CEM-3 copper clad laminate preparation method.

[0006] Therefore, this application adopts the following technical solution: The first aspect of this application provides a method for preparing sulfur-free CEM-3 copper clad laminate, comprising the following steps: S1. Preparation of resin solution: Mix the raw material components of epoxy resin, isocyanate modified cyanate resin, halogen-free composite flame retardant, phenolic resin curing agent, latent curing accelerator, thermally conductive filler, and coupling agent according to a predetermined ratio to form a resin solution. S2. Preparation of core material and fabric: S2.1 Preparation of core material: Impregnate glass fiber paper with the resin solution obtained in step S1, and dry and pre-cur it into a semi-cured sheet to obtain the core material; S2.2 Preparation of fabric: Impregnate the split fiberglass cloth with the resin solution obtained in step S1, and dry and pre-cur it into a semi-cured sheet to obtain the fabric; S3. Hot pressing and curing: Stack 2 to 8 core materials, and attach one fabric layer to the upper and lower surfaces of the stacked core materials to form a composite substrate blank; cover the outer surface of at least one fabric layer with copper foil, and heat press and cure to obtain sulfur-free CEM-3 copper clad laminate. The hot-press curing process includes a post-curing stage where curing is carried out at 195~225℃ for more than 60 minutes.

[0007] In the method for preparing sulfur-free CEM-3 copper clad laminate of this application, the preparation method is divided into three major steps through a step-by-step design: resin preparation, core material and face material preparation, and hot-pressing curing. Step S1 involves preparing the resin solution by compounding sulfur-free raw material components such as epoxy resin and isocyanate-modified cyanate resin to form a resin solution with both adhesive and flame-retardant properties, facilitating subsequent impregnation and curing, thus laying the foundation for high-performance sulfur-free copper clad laminates. Step S2 involves preparing the core material and face material step-by-step. For the differentiated reinforcing substrates—using glass fiber paper for the core material and open-fiber glass fiber cloth for the face material—resin solution impregnation and pre-curing are performed. The fine texture of the glass fiber paper ensures the core material's... The smoothness and thorough impregnation of the resin adhesive, combined with the structural advantages of the split fiberglass cloth, enhance the mechanical strength and interlayer bonding of the fabric. After pre-curing, the core material and fabric of the semi-cured sheet are formed, providing a stable substrate for subsequent hot-pressing curing. In step S3, hot-pressing curing involves stacking 2 to 8 core materials, bonding one fabric layer on top and bottom, and covering the outer surface of at least one fabric layer with copper foil. After hot-pressing curing, the copper-clad laminate is shaped and its overall rigidity is improved. The post-curing process during hot-pressing curing promotes the full cross-linking and curing of the resin, thereby eliminating internal residual stress and improving the interfacial bonding between layers and between the copper foil and the substrate. Finally, a sulfur-free CEM-3 copper-clad laminate with excellent comprehensive performance is obtained.

[0008] Preferably, in the method for preparing sulfur-free CEM-3 copper clad laminate, in step S1, the resin solution comprises epoxy resin, isocyanate-modified cyanate resin, and halogen-free composite flame retardant in a weight ratio of (30~45):(20~30):(15~23).

[0009] Preferably, in the method for preparing sulfur-free CEM-3 copper clad laminate, in step S1, the resin solution comprises epoxy resin, isocyanate-modified cyanate resin, halogen-free composite flame retardant, and phenolic resin curing agent in a weight ratio of (30~45):(20~30):(15~23):(8~18).

[0010] Preferably, in the method for preparing the sulfur-free CEM-3 copper clad laminate, in step S1, the resin solution comprises epoxy resin, isocyanate-modified cyanate resin, halogen-free composite flame retardant, phenolic resin curing agent, and latent curing accelerator in a weight ratio of (30~45):(20~30):(15~23):(8~18):(0.02~0.1).

[0011] Preferably, in the method for preparing the sulfur-free CEM-3 copper clad laminate, in step S1, the resin solution comprises epoxy resin, isocyanate-modified cyanate resin, halogen-free composite flame retardant, phenolic resin curing agent, latent curing accelerator, and thermally conductive filler in a weight ratio of (30~45):(20~30):(15~23):(8~18):(0.02~0.1),(35~55).

[0012] Preferably, in the method for preparing the sulfur-free CEM-3 copper clad laminate, in step S1, the resin solution comprises epoxy resin, isocyanate-modified cyanate resin, halogen-free composite flame retardant, phenolic resin curing agent, latent curing accelerator, thermally conductive filler, and coupling agent in a weight ratio of (30~45):(20~30):(15~23):(8~18):(0.02~0.1),(35~55),(0.4~1).

[0013] In the aforementioned resin adhesive, epoxy resin itself possesses excellent adhesion and molding properties, while isocyanate-modified cyanate resin exhibits strong chemical resistance. Using 30-45 parts by weight of epoxy resin and 20-30 parts by weight of isocyanate-modified cyanate resin as the main curing agents, both are sulfur-free and their advantages are well-complemented, providing a solid foundation for dielectric stability. 15-23 parts by weight of halogen-free composite flame retardant enhances the flame retardant properties of the copper-clad laminate while avoiding excessive addition that could increase the resin adhesive's viscosity and reduce its impregnation. 8-18 parts by weight of phenolic resin curing agent fully cures and cross-links with the epoxy resin and isocyanate-modified cyanate resin, forming a dense cross-linked network. This helps improve the mechanical strength and resistance to ion migration of copper-clad laminates, avoiding incomplete curing due to insufficient curing agent or increased brittleness due to excessive curing agent; 0.02~0.1 parts by weight of latent curing accelerator shortens curing time and reduces curing energy consumption; 35~55 parts by weight of thermally conductive filler maximizes the thermal conductivity of copper-clad laminate while ensuring good impregnation properties, and dissipates the heat generated by electronic devices during operation in a timely manner; 0.4~1 parts by weight of coupling agent mainly improves the interfacial compatibility between inorganic and organic resin phases, reduces interfacial voids, and further enhances the mechanical strength and resistance to ion migration of copper-clad laminates.

[0014] Preferably, the epoxy resin is selected from at least one of bisphenol A type epoxy resin, biphenyl type epoxy resin, and bisphenol F type epoxy resin. More preferably, the epoxy resin is selected from at least one of bisphenol A type epoxy resin and biphenyl type epoxy resin.

[0015] Preferably, the isocyanate-modified cyanate resin is prepared by reacting cyanate monomers and diisocyanate compounds with a molar ratio of cyanate groups to isocyanate groups of (6~12):(1~1.5).

[0016] Preferably, the method for preparing the isocyanate-modified cyanate resin includes the following steps: Under inert gas protection, the cyanate monomers in a predetermined molar ratio are heated to 80-90°C and melted. The temperature is then raised to 90-110°C, and a diisocyanate compound is added dropwise. Then, an organometallic catalyst accounting for 0.01%-0.05% of the total feed mass is added, and the reaction is carried out at a constant temperature for 2-6 hours. The reaction endpoint is determined by monitoring the disappearance of the characteristic absorption peak of the isocyanate group in the system using Fourier transform infrared spectroscopy. After removing the solvent, washing, and drying, the isocyanate-modified cyanate resin is obtained.

[0017] Isocyanate-modified cyanate resin, obtained by reacting cyanate monomers and diisocyanate compounds in a specific molar ratio, ensures the introduction of an appropriate amount of isocyanate groups into the molecular chain of the cyanate monomer. This avoids excessive modification that could cause the cyanate monomer to lose its original high heat resistance and low dielectric loss properties. The introduction of isocyanate groups can react with functional groups such as hydroxyl groups in epoxy resins and phenolic resin curing agents, improving the compatibility of the modified cyanate resin with other resins. This allows the resin solution to form a uniform single-phase system, preventing phase separation of the resins after subsequent curing, which could lead to uneven performance or edge warping of the copper-clad laminate.

[0018] Preferably, the halogen-free composite flame retardant is composed of metal phosphinate and coated ammonium polyphosphate in a weight ratio of (1.5~4):(1~2).

[0019] Preferably, the metal phosphonate is selected from at least one of aluminum diethylphosphonate, aluminum diphenylphosphonate, and zinc phosphonate.

[0020] In halogen-free composite flame retardants, coated ammonium polyphosphate improves its dispersibility and water resistance in resin solutions, preventing uncoated ammonium polyphosphate from absorbing moisture. Simultaneously, it decomposes at high temperatures to produce phosphoric acid, promoting the carbonization of the resin matrix to form a dense char layer, thus enhancing its flame-retardant effect. The phosphorus-based free radicals generated from the decomposition of metal phosphinates can capture active free radicals during combustion, further improving the flame-retardant effect. Within the weight ratio range of this application, both contribute to achieving optimal flame-retardant performance, avoiding both the increased brittleness of copper-clad laminates caused by excessive metal phosphinate addition and the increased viscosity and decreased impregnation of the resin solution caused by excessive coated ammonium polyphosphate addition.

[0021] Preferably, the phenolic resin curing agent is a linear phenolic resin with a phenolic hydroxyl equivalent of 105-120 g / eq. More preferably, the phenolic resin curing agent is a linear phenolic resin with a phenolic hydroxyl equivalent of 110-120 g / eq.

[0022] Preferably, the latent curing accelerator is dicyandiamide modified with an organic acid. More preferably, the dicyandiamide modified with an organic acid is prepared by the following method: mixing dicyandiamide and an organic acid, reacting at 80-120°C for 1-3 hours, cooling, and pulverizing to obtain the dicyandiamide modified with an organic acid.

[0023] Preferably, the organic acid is selected from at least one of benzoic acid, maleic acid, lauric acid, and p-toluenesulfonic acid. More preferably, the organic acid is selected from at least one of benzoic acid, maleic acid, and lauric acid.

[0024] Linear phenolic resins with a phenolic hydroxyl equivalent of 105-120 g / eq have relatively large molecular weights. This not only helps them form a dense and uniform cross-linked network to improve mechanical strength when reacting with epoxy resins and isocyanate-modified cyanate resins, but more importantly, their high molecular weight reduces the source of migratable small molecule ions. The resulting low-polarity, high-density cured network helps reduce the material's water absorption rate and effectively blocks the penetration and diffusion of moisture and ions, thus improving the copper-clad laminate's resistance to ion migration and enhancing its CTI (Chemical Intensity Tolerance). Meanwhile, dicyandiamide latent curing accelerators modified with organic acids decompose at the curing temperature, releasing the active sites of dicyandiamide. This efficiently promotes the cross-linking and curing reaction of the resin system, thereby lowering the activation energy of the curing reaction and shortening the curing time.

[0025] Preferably, the thermally conductive filler comprises spherical alumina and silicon dioxide, wherein the particle size D50 of the spherical alumina is 2~10 μm, and the particle size D50 of the silicon dioxide is 0.5~3 μm. More preferably, the particle size D50 of the spherical alumina is 5~10 μm, and the particle size D50 of the silicon dioxide is 1~3 μm.

[0026] Spherical alumina with a particle size D50 of 2~10μm helps reduce filler agglomeration in the resin matrix, lowers the viscosity of the resin solution, and improves the impregnation properties of the solution. Silica with a particle size D50 of 1~3μm can fill the gaps between relatively large-particle-size spherical alumina to form a dense thermally conductive network, significantly improving the thermal conductivity of the copper-clad laminate. In addition, the thermally conductive fillers in the resin solution fully fill the pores of the glass fiber paper and the open-fiber glass fiber cloth, which helps to improve the interfacial bonding between the core material, the fabric material, and the copper foil, while maintaining the flatness of the copper-clad laminate surface.

[0027] Preferably, the coupling agent is selected from at least one of epoxy silane coupling agents, amino silane coupling agents, and methacryloxy silane coupling agents. More preferably, the coupling agent is selected from at least one of epoxy silane coupling agents and amino silane coupling agents.

[0028] Preferably, in step S1, before mixing the raw material components, the isocyanate-modified cyanate resin is further subjected to a dehydration treatment at a temperature of 80~110℃ and a vacuum degree of -0.095~-0.10MPa for 2~4 hours. More preferably, in step S1, before mixing the raw material components, the isocyanate-modified cyanate resin is further subjected to a dehydration treatment at a temperature of 85~110℃ and a vacuum degree of -0.095~-0.10MPa for 3~4 hours.

[0029] Preferably, before step S2, a solvent is added for reuse, wherein the solvent is selected from acetone, butanone, or methyl isobutyl ketone.

[0030] Preferably, in step S2, the impregnation time of the glass fiber paper is 30-90 seconds, the impregnation time of the split glass fiber cloth is 60-120 seconds, the drying temperature is 130-160°C, and the drying time is 5-15 minutes. More preferably, in step S2, the impregnation time of the glass fiber paper is 40-90 seconds, the impregnation time of the split glass fiber cloth is 70-120 seconds, the drying temperature is 140-160°C, and the drying time is 5-15 minutes.

[0031] Preferably, in step S3, the hot-press curing process specifically includes: a first stage: under a vacuum of -0.091 to -0.10 MPa, the temperature is increased to 110 to 130°C at a rate of 1.5 to 2.5°C / min, a pressure of 0.5 to 2.5 MPa is applied, and the temperature is maintained for 20 to 40 minutes; a second stage: the temperature is increased to 160 to 185°C at a rate of 1.0 to 2.0°C / min, the pressure is increased to 3 to 5 MPa, and the temperature is maintained for 50 to 90 minutes; a third stage: the temperature is increased to 195 to 225°C at a rate of 0.5 to 1.5°C / min, the pressure is maintained, and post-curing is carried out for 60 to 150 minutes.

[0032] More preferably, in step S3, the hot-press curing process specifically includes: a first stage: under a vacuum of -0.091 to -0.10 MPa, the temperature is increased to 115 to 130°C at a rate of 1.8 to 2.5°C / min, a pressure of 0.5 to 2.5 MPa is applied, and the temperature is maintained for 20 to 40 minutes; a second stage: the temperature is increased to 165 to 185°C at a rate of 1.5 to 2.0°C / min, the pressure is increased to 3 to 5 MPa, and the temperature is maintained for 50 to 90 minutes; a third stage: the temperature is increased to 205 to 225°C at a rate of 0.5 to 1.5°C / min, the pressure is maintained, and post-curing is carried out for 60 to 150 minutes.

[0033] In step S3, the first stage involves low-temperature preheating at a vacuum of -0.091 to -0.10 MPa, which slowly removes air and low-molecular-weight volatiles from the composite substrate blank, preventing rapid escape of volatiles during subsequent high-temperature curing and the formation of pores inside the copper-clad laminate. The slow heating rate of 1.5 to 2.5 °C / min ensures uniform heating of each layer of the composite substrate blank, avoiding premature resin curing and poor interlayer bonding caused by excessively high local temperatures. Under a pressure of 0.5 to 2.5 MPa, the resin content of the core and surface materials becomes more uniform, resulting in tight adhesion between the layers of the stacked composite substrate blank.

[0034] In the second stage, the curing reaction proceeds smoothly at a heating rate of 1.0~2.0℃ / min. The main curing stage of the resin solution is reached when the temperature rises to 160~185℃. During this period, the functional groups of the resin react fully to form a cross-linked network. The pressure rises to 3~5MPa, which helps to promote the full wetting of the resin in the glass fiber paper and open-fiber glass fiber cloth, eliminate interlayer voids, improve the interfacial bonding force between the core material, the face material, and the copper foil, and at the same time make the thickness of the copper clad laminate more uniform. The holding time of 50~90min ensures that the main curing reaction is fully carried out and avoids the decrease in mechanical strength properties of the copper clad laminate caused by incomplete curing.

[0035] The third stage, with a slower heating rate of 0.5~1.5℃ / min, ensures uniform heating within the copper-clad laminate, avoiding residual stress caused by temperature gradients and helping to reduce warping and deformation. High-temperature post-curing at 195~225℃ promotes deep cross-linking and curing of the resin, further increasing cross-linking density, eliminating internal micropores, and improving the dimensional stability and ion migration resistance of the copper-clad laminate. Long-term post-curing under pressure (60~150min) results in tighter bonding between the copper foil and the fabric, and between the fabric and the core material, further enhancing the peel strength of the copper foil and preventing copper foil detachment during subsequent processing.

[0036] The second aspect of this application provides a CEM-3 copper clad laminate prepared according to the sulfur-free CEM-3 copper clad laminate preparation method described in the first aspect of this application.

[0037] The sulfur-free CEM-3 copper clad laminate described in this application has a sulfur content of <10ppm.

[0038] Preferably, the CEM-3 copper clad laminate comprises 2 to 8 core layers reinforced with glass fiber paper and fabric layers reinforced with open-fiber glass fiber cloth disposed on its upper and lower surfaces, and copper foil covering the outer surface of at least one of the fabric layers.

[0039] Compared with the prior art, this application has at least the following beneficial effects: 1) In the sulfur-free CEM-3 copper clad laminate preparation method of this application, the process involves preparing sulfur-free resin solution, preparing core material and face material in a differentiated manner, and hot-press curing, including the post-curing stage. The entire process uses sulfur-free raw materials and sulfur-free preparation process, which fundamentally eliminates sulfur impurities in the obtained CEM-3 copper clad laminate. Its relative tracking index (CTI) is significantly improved, and it has strong resistance to ion migration and delamination. At the same time, it has a high glass transition temperature (Tg) and thermal stability (Td), low dielectric loss (Df), and stable dielectric constant (Dk). This effectively ensures its long-term stability and signal integrity in high-temperature welding and harsh application scenarios, meeting the stringent performance requirements of copper clad laminates in high-end communication equipment, automotive electronics and other fields.

[0040] 2) In the sulfur-free CEM-3 copper clad laminate preparation method of this application, the specific composition and proportion of the resin adhesive formulation enable the resin system to possess excellent heat resistance, flame retardancy, and thermal conductivity. Simultaneously, the dehydration pretreatment of key resins and the three-stage hot-pressing curing process jointly ensure the resin adhesive fully impregnates the glass fiber paper and open-fiber glass fiber cloth, completely eliminates low-molecular-weight volatiles, and deeply cures the cross-linked network. This results in a dense internal structure of the substrate, strong interlayer bonding, and high copper foil peel strength, avoiding problems such as delamination, cracking, or poor performance caused by impurities, pores, or incomplete curing. Detailed Implementation

[0041] The following detailed description of the contents of this application is provided through specific embodiments, comparative examples, and tables, but is not limited to all the arguments and data.

[0042] The bisphenol A epoxy resin was sourced from Changchun Chemical (Jiangsu) Co., Ltd., with aluminum diethylphosphinate CAS number 225789-38-8; the coated ammonium polyphosphate was sourced from Shandong Changsheng Flame Retardant New Material Co., Ltd., model CS FRAPP 341; and the linear phenolic resin was sourced from Shandong Shengquan New Material Co., Ltd., with phenolic hydroxyl equivalents of 110 g / eq, 120 g / eq, and 130 g / eq, respectively.

[0043] Preparation Example 1: The preparation method of isocyanate-modified cyanate ester resin specifically includes the following steps: Nitrogen gas was introduced into a three-necked flask equipped with a stirrer, thermometer, condenser, and gas inlet tube. 1251 g (4.5 mol) of 2,2-bis(4-cyanooxyphenyl)propane was added, and the mixture was heated to 85°C to melt it. The temperature was then raised to 100°C, and 108.8 g (0.625 mol) of toluene diisocyanate was slowly added dropwise with stirring. After the addition was complete, 0.41 g of dibutyltin dilaurate (approximately 0.03% of the total feed mass) was added as a catalyst. The reaction was carried out at 100°C for 2–6 hours. During this time, the intensity of the characteristic absorption peak of the isocyanate group near 2270 cm⁻¹ was monitored using Fourier transform infrared spectroscopy. The reaction endpoint was determined when the peak essentially disappeared. After the reaction, the product was dissolved in acetone, precipitated with water, separated, washed, and dried to obtain isocyanate-modified cyanate resin.

[0044] In Preparation Example 1, the molar ratio of cyanate groups to isocyanate groups was 9:1.25.

[0045] Preparation Example 2: The preparation method of isocyanate-modified cyanate ester resin specifically includes the following steps: Nitrogen gas was introduced into a three-necked flask equipped with a stirrer, thermometer, condenser, and gas inlet tube. 834 g (3.0 mol) of 2,2-bis(4-cyanooxyphenyl)propane was added, and the mixture was heated to 85°C to melt it. The temperature was then raised to 100°C, and 87 g (0.5 mol) of toluene diisocyanate was slowly added dropwise with stirring. After the addition was complete, 0.28 g of dibutyltin dilaurate (approximately 0.03% of the total feed mass) was added as a catalyst. The reaction was carried out at 100°C for 2–6 hours. During this time, the intensity of the characteristic absorption peak of the isocyanate group near 2270 cm⁻¹ was monitored using Fourier transform infrared spectroscopy. The reaction endpoint was determined when the peak essentially disappeared. After the reaction, the product was dissolved in acetone, precipitated with water, separated, washed, and dried to obtain isocyanate-modified cyanate resin.

[0046] In Preparation Example 2, the molar ratio of cyanate groups to isocyanate groups was 6:1.

[0047] Preparation Example 3: The preparation method of isocyanate-modified cyanate ester resin specifically includes the following steps: Nitrogen gas was introduced into a three-necked flask equipped with a stirrer, thermometer, condenser, and gas inlet tube. 1668 g (3.0 mol) of 2,2-bis(4-cyanooxyphenyl)propane was added, and the mixture was heated to 85°C to melt it. The temperature was then raised to 100°C, and 87 g (0.5 mol) of toluene diisocyanate was slowly added dropwise with stirring. After the addition was complete, 0.53 g of dibutyltin dilaurate (approximately 0.03% of the total feed mass) was added as a catalyst. The reaction was carried out at 100°C for 2–6 hours. During this time, the intensity of the characteristic absorption peak of the isocyanate group near 2270 cm⁻¹ was monitored using Fourier transform infrared spectroscopy. The reaction endpoint was determined when the peak essentially disappeared. After the reaction, the product was dissolved in acetone, precipitated with water, separated, washed, and dried to obtain isocyanate-modified cyanate resin.

[0048] In Preparation Example 3, the molar ratio of cyanate groups to isocyanate groups was 12:1.

[0049] Preparation Example 4: The preparation method of lauric acid-modified dicyandiamide specifically includes the following steps: In a 250mL three-necked flask equipped with a mechanical stirrer, thermometer, and air condenser, 100g of dicyandiamide and 95.2g of lauric acid were added. The flask was placed in a heating mantle, and stirring was started to initially mix the solid powder. The mixture was heated to 110℃ and stirred at a constant temperature for 2.5h. Then, the heating was stopped, and the molten product was poured into a clean stainless steel tray while still hot. It was allowed to cool and solidify naturally at room temperature to obtain a waxy solid block. This block was crushed with a pulverizer and passed through a 100-mesh sieve to obtain a fine powder product, which is the lauric acid-modified dicyandiamide.

[0050] It is particularly important to emphasize that, unless otherwise specified, the raw materials, reagents or devices used in this application can be obtained from conventional commercial sources.

[0051] The method for preparing sulfur-free CEM-3 copper clad laminate of this application specifically includes the following steps: S1. Preparation of resin solution: Place the raw material components of 30~45g epoxy resin, 20~30g isocyanate modified cyanate resin, 15~23g halogen-free composite flame retardant, 8~18g phenolic resin curing agent, 0.02~0.1g latent curing accelerator, 35~55g thermally conductive filler, and 0.4~1g coupling agent in a high-speed disperser and stir at 40~60℃ until all components are mixed evenly. Then add 50~120g solvent and stir evenly again to form resin solution. S2. Preparation of core material and fabric: S2.1 Preparation of core material: Impregnate glass fiber paper with the above resin solution obtained in step S1 for 30~90s, take it out, and dry and pre-cur it at 130~160℃ for 5~15min to form a semi-cured sheet, thus obtaining the core material; S2.2 Preparation of fabric: Impregnate the split fiberglass cloth with the resin solution obtained in step S1 for 60~120s, and dry and pre-cur it at 130~160℃ for 5~15min to form a semi-cured sheet to obtain the fabric. S3. Hot-press curing: Stack 2-8 core materials, and attach a fabric sheet to the upper and lower surfaces of the stacked core materials to form a composite substrate blank; cover the outer surface of at least one fabric sheet with copper foil, and place it in a vacuum hot press to perform the following three-stage hot-press curing process to form the final product: First stage: Evacuate to -0.091~-0.10MPa. Slowly heat to 110~130℃ at a heating rate of 1.5~2.5℃ / min, then apply a pressure of 0.5~2.5MPa and maintain for 20~40min; Second stage: Continue to increase the temperature to 160~185℃ at a rate of 1.0~2.0℃ / min, increase the pressure to 3~5MPa, and maintain for 50~90min; The third stage involves heating the temperature to 195-225℃ at a rate of 0.5-1.5℃ / min, maintaining the pressure, and performing post-curing for 60-150 minutes to obtain the sulfur-free CEM-3 copper-clad laminate.

[0052] Regarding step S1, in some specific embodiments, the epoxy resin may be selected from at least one of bisphenol A type epoxy resin, biphenyl type epoxy resin, and bisphenol F type epoxy resin. The isocyanate-modified cyanate resin is prepared by reacting cyanate monomers and diisocyanate compounds with a molar ratio of cyanate groups to isocyanate groups of 6:1, 6:1.5, 9:1.25, 10:1.5, or 12:1. The halogen-free composite flame retardant is composed of metal phosphinate and coated ammonium polyphosphate in a weight ratio of 1.5:1, 1.5:2, 3:1, 3:2, or 4:1, wherein the metal phosphinate may be selected from at least one of diethylaluminum phosphinate, diphenylaluminum phosphinate, and zinc phosphinate. The phenolic resin curing agent is a linear phenolic resin with a phenolic hydroxyl equivalent of 105 g / eq, 110 g / eq, or 120 g / eq. The latent curing accelerator is dicyandiamide modified with an organic acid, wherein the organic acid can be selected from at least one of benzoic acid, maleic acid, lauric acid, and p-toluenesulfonic acid. The thermally conductive filler includes spherical alumina and silica, wherein the particle size D50 of the spherical alumina is 2 μm, 5 μm, or 10 μm; and the particle size D50 of the silica is 0.5 μm, 1 μm, 2 μm, or 3 μm. The coupling agent can be selected from at least one of epoxysilane coupling agents, aminosilane coupling agents, and methacryloxysilane coupling agents. The amount of epoxy resin can be 30g, 35g, 40g or 45g; the amount of isocyanate-modified cyanate resin can be 20g, 23g, 26g or 30g; the amount of halogen-free composite flame retardant can be 15g, 18g, 20g or 23g; the amount of phenolic resin curing agent can be 8g, 10g, 12g, 14g or 18g; the amount of latent curing accelerator can be 0.02g, 0.05g, 0.09g or 0.1g; the amount of thermally conductive filler can be 35g, 40g, 43g, 48g or 55g; the amount of coupling agent can be 0.4g, 0.6g, 0.8g or 1g; and the amount of solvent can be 50g, 60g, 70g, 90g or 120g. Before mixing the raw material components, the isocyanate-modified cyanate resin is dehydrated for 3 hours, 3.5 hours, or 4 hours at temperatures of 85°C, 90°C, or 110°C and vacuum conditions of -0.095 MPa or -0.10 MPa. The stirring temperature can be 40°C, 50°C, or 60°C.

[0053] Regarding step S2, in some specific implementations, in S2.1, during the preparation of the core material, the impregnation time of the glass fiber paper can be 30s, 50s, 60s, 80s, or 90s, the drying temperature can be 130℃, 140℃, 145℃, or 160℃, and the drying time can be 5min, 10min, or 15min. In S2.2, during the preparation of the fabric, the impregnation time of the split glass fiber cloth can be 60s, 80s, 100s, or 120s, the drying temperature can be 130℃, 140℃, 145℃, or 160℃, and the drying time can be 5min, 10min, or 15min.

[0054] Regarding step S3, in some specific implementations, the number of core materials stacked can be 2, 3, 5, 7, or 8 sheets. In the three-stage hot-pressing curing, the vacuum degree in the first stage can be -0.091MPa, -0.095MPa, or -0.10MPa, the heating rate can be 1.5℃ / min, 2℃ / min, or 2.5℃ / min, heated to 110℃, 120℃, 125℃, or 130℃, the applied pressure can be 0.5MPa, 1.0MPa, 1.5MPa, or 2.5MPa, and the holding time can be 20min, 30min, or 40min; in the second stage, the heating rate can be... The heating rate is 1.0℃ / min, 1.5℃ / min, or 2.0℃ / min, raising the temperature to 160℃, 170℃, 175℃, or 185℃, and the pressure is raised to 3MPa, 4MPa, 4.5MPa, or 5MPa, with a holding time of 50min, 60min, 80min, or 90min; the third stage: the heating rate can be 0.5℃ / min, 1.0℃ / min, or 1.5℃ / min, raising the temperature to 195℃, 200℃, 210℃, or 225℃, maintaining the pressure, and performing post-curing for 60min, 80min, 120min, or 150min to obtain the sulfur-free CEM-3 copper-clad laminate.

[0055] Based on the method for preparing sulfur-free CEM-3 copper clad laminate of this application, the following examples and comparative examples are provided: Example 1

[0056] A method for preparing sulfur-free CEM-3 copper clad laminate specifically includes the following steps: S1. Preparation of resin solution: 35g of bisphenol A type epoxy resin, 25g of isocyanate modified cyanate resin of Preparation Example 1, 20g of aluminum diethylphosphinate and coated ammonium polyphosphate in a weight ratio of 2:1, 13g of linear phenolic resin with a phenolic hydroxyl equivalent of 110g / eq, 0.05g of dicyandiamide modified with lauric acid in Preparation Example 4, 40g of spherical alumina with a particle size D50 of 5~8μm and silica with a particle size D50 of 1~2μm in a weight ratio of 3:1, and 2.5g of KH-550 type aminosilane coupling agent are placed in a high-speed disperser and stirred at 50°C until all components are mixed evenly. Then, 80g of solvent is added and stirred evenly again to form a resin solution. S2. Preparation of core material and fabric: S2.1 Preparation of core material: Impregnate glass fiber paper with a standard weight of 100~110g / m2 with the above resin solution obtained in step S1 for 60s, take it out, and dry and pre-cur it at 150℃ for 10min to form a semi-cured sheet to obtain the core material; S2.2 Preparation of fabric: Impregnate 2116 type open-fiber glass fiber cloth with the resin solution obtained in step S1 for 80s, and dry and pre-cur it at 150℃ for 10min to form a semi-cured sheet to obtain the fabric. S3. Hot-press curing: Six core materials are stacked, and a fabric sheet is attached to the upper and lower surfaces of the stacked core materials to form a composite substrate blank; copper foil is covered on the outer surface of one fabric sheet, and the substrate is placed in a vacuum hot press for the following three stages of hot-press curing to form the final product: First stage: Evacuate to -0.09 MPa. Slowly heat to 120°C at a heating rate of 2.0°C / min, then apply a pressure of 2.0 MPa and maintain for 40 min; Second stage: Continue to increase the temperature to 175℃ at a rate of 1.5℃ / min, increase the pressure to 4MPa, and maintain for 70min; The third stage: the temperature is increased to 210℃ at a rate of 1.0℃ / min, the pressure is maintained, and post-curing is carried out for 90 minutes to obtain the sulfur-free CEM-3 copper clad laminate. Example 2

[0057] A method for preparing sulfur-free CEM-3 copper clad laminate is the same as in Example 1, except that in step S1 of Example 2, the isocyanate-modified cyanate resin of Preparation Example 1 is replaced by an equal amount of isocyanate-modified cyanate resin of Preparation Example 2. Example 3

[0058] A method for preparing sulfur-free CEM-3 copper clad laminate is the same as in Example 1, except that in step S1 of Example 3, the isocyanate-modified cyanate resin of Preparation Example 1 is replaced by an equal amount of isocyanate-modified cyanate resin of Preparation Example 3. Example 4

[0059] A method for preparing sulfur-free CEM-3 copper clad laminate is the same as in Example 1, except that in step S1 of Example 4, the linear phenolic resin with a phenolic hydroxyl equivalent of 110 g / eq is replaced by an equal amount of linear phenolic resin with a phenolic hydroxyl equivalent of 120 g / eq. Example 5

[0060] A method for preparing sulfur-free CEM-3 copper clad laminate is the same as in Example 1, except that the third stage in step S3 of Example 5 is: heating to 195°C at a rate of 1.0°C / min, maintaining pressure, and performing post-curing for 90 minutes to obtain the sulfur-free CEM-3 copper clad laminate.

[0061] Comparative Example 1: A method for preparing sulfur-free CEM-3 copper clad laminate is the same as in Example 1, except that the amount of isocyanate-modified cyanate resin used in step S1 of Comparative Example 1 is changed to 15g.

[0062] Comparative Example 2: A method for preparing sulfur-free CEM-3 copper clad laminate is the same as in Example 1, except that in step S1 of Comparative Example 2, the isocyanate-modified cyanate resin of Preparation Example 1 is replaced by an equal amount of unmodified 2,2-bis(4-cyanooxyphenyl)propane.

[0063] Comparative Example 3: A method for preparing sulfur-free CEM-3 copper clad laminate is the same as in Example 1, except that in step S1 of Comparative Example 3, the linear phenolic resin with a phenolic hydroxyl equivalent of 110 g / eq is replaced by an equal amount of linear phenolic resin with a phenolic hydroxyl equivalent of 130 g / eq.

[0064] Comparative Example 4: A method for preparing sulfur-free CEM-3 copper clad laminate is the same as in Example 1, except that the third stage in step S3 of Comparative Example 4 is as follows: the temperature is increased to 180°C at a rate of 1.0°C / min, the pressure is maintained, and post-curing is performed for 110 min to obtain the sulfur-free CEM-3 copper clad laminate.

[0065] Material performance testing: The CEM-3 copper-clad laminates obtained in Examples 1-5 and Comparative Examples 1-4 were subjected to various performance tests, and the test methods are as follows: 1. Sulfur content: Tested according to IPC TM-650 2.3.17 test method.

[0066] 2. Relative Tracking Index (CTI): Tested according to IEC 60112 test method.

[0067] 3. Dielectric loss Df and dielectric constant Dk: Tested according to IPC TM-650 2.5.5.13 test method.

[0068] 4. Glass transition temperature Tg: Tested according to IPC TM-650 2.4.24.1 (TMA method).

[0069] 5. Thermal stability Td: Tested according to IPC-TM-650 2.3.41 (TGA thermogravimetric analysis).

[0070] 6. Flame retardancy: Tested according to UL94 test method.

[0071] 7. Copper foil peel strength: Tested according to IPC TM-650 2.4.8 test method.

[0072] 8. Solderability resistance: Tested according to IPC TM-650 2.4.13 test method.

[0073] The test performance of CEM-3 copper clad laminates in Examples 1-5 and Comparative Examples 1-4 is shown in Table 1 below:

[0074] The sulfur-free CEM-3 copper clad laminate preparation method in Examples 1-5 involves three main steps: preparing the resin solution, preparing the core and face materials, and hot-pressing curing. In particular, the specific ratio of isocyanate-modified cyanate resin and phenolic resin curing agent in the resin solution, the modification process parameters, and the temperature limitation during the curing stage after hot-pressing curing fundamentally eliminate sulfur impurities in the resulting CEM-3 copper clad laminate. This significantly improves its relative tracking index (CTI), enhances its resistance to ion migration and delamination, and ensures that its sulfur content is <10ppm, CTI value >600V, dielectric loss Df is in the range of 7.7~8.2×10⁻³, Tg ≥152℃, Td ≥358℃, copper foil peel strength ≥1.39N / mm, solderability at 288℃ ≥290s, and UL94 flame retardancy reaches V-0 level. This method also considers both environmental friendliness and the comprehensive performance required for high-end applications.

[0075] Compared with Example 1, the difference in Comparative Example 1 is that the amount of isocyanate-modified cyanate resin used was changed to 15g, which is not within the range limited by this application. The results showed that the CTI of the CEM-3 copper clad laminate of Comparative Example 1 decreased to 575V, Df increased to 8.9×10-3, Tg was only 143℃, the copper foil peel strength decreased to 1.32N / mm, and the solderability at 288℃ also decreased. This may be because the amount of isocyanate-modified cyanate resin was insufficient, resulting in a relatively high proportion of epoxy resin in the resin system, which reduced the density of the cross-linked network, weakened the adhesion between the resin and the copper foil and glass fiber substrate, and failed to fully utilize the advantages of low dielectric loss and high heat resistance of the isocyanate-modified cyanate resin. At the same time, the increase in migratable small molecules led to insufficient resistance to ion migration.

[0076] Compared with Example 1, Comparative Example 2 used unmodified 2,2-bis(4-cyanooxyphenyl)propane instead of the isocyanate-modified cyanate resin specified in this application. The results showed that the dielectric properties of the CEM-3 copper-clad laminate in Comparative Example 2 decreased significantly, with Dk increasing to 4.25, Df reaching 9.4 × 10⁻³, CTI only 550V, copper foil peel strength decreasing to 1.24 N / mm, and solderability at 288°C only 180 s. This may be due to the insufficient compatibility of the unmodified cyanate resin with epoxy and phenolic resin curing agents, leading to phase separation in the system and the inability to form a uniform and dense cross-linked network. The presence of numerous micropores within the substrate not only reduces its resistance to ion migration and dielectric stability but also weakens the interfacial bonding between the copper foil and the substrate, resulting in a decrease in copper foil peel strength.

[0077] Compared with Example 1, Comparative Example 3 used a linear phenolic resin with a phenolic hydroxyl equivalent of 130 g / eq instead of the linear phenolic resin in Example 1. The results showed that the CTI of the CEM-3 copper-clad laminate in Comparative Example 3 decreased to 525 V, Tg was only 140 °C, Td was 343 °C, the solder resistance at 288 °C was only 100 s, and Df increased to 9.2 × 10⁻³. This may be because the high phenolic hydroxyl equivalent phenolic resin has a large molecular weight, resulting in a significant decrease in reactivity. This leads to insufficient crosslinking reaction with isocyanate-modified cyanate ester resin and epoxy resin, resulting in a loose crosslinking network with a large number of migratable small molecules.

[0078] Compared to Example 1, Comparative Example 4 differs in that the post-curing temperature in step S3 of Comparative Example 4 was changed to 180°C. The results showed that the CTI of the CEM-3 copper-clad laminate in Comparative Example 4 was 575V, the Tg was 148°C, the copper foil peel strength was 1.31 N / mm, the solder resistance at 288°C was only 120 s, and the Df increased to 8.7 × 10⁻³. This may be due to insufficient post-curing temperature, resulting in insufficient overall cross-linking of the resin and the inability to fully release the residual stress generated internally. This weakens the bonding force between the copper foil and the substrate, as well as between layers, to some extent, leading to a decline in related performance.

[0079] Obviously, the above embodiments of this application are merely examples for clearly illustrating this application, and are not intended to limit the implementation of this application. For those skilled in the art, other variations or modifications can be made based on the above description. Any obvious variations or modifications derived from the technical solutions of this application are still within the protection scope of this application.

Claims

1. A method for preparing sulfur-free CEM-3 copper clad laminate, characterized in that, Includes the following steps: S1. Preparation of resin solution: Mix the raw material components of epoxy resin, isocyanate modified cyanate resin, halogen-free composite flame retardant, phenolic resin curing agent, latent curing accelerator, thermally conductive filler, and coupling agent according to a predetermined ratio to form a resin solution. S2. Preparation of core material and fabric: S2.1 Preparation of core material: Impregnate glass fiber paper with the resin solution obtained in step S1, and dry and pre-cur it into a semi-cured sheet to obtain the core material; S2.2 Preparation of fabric: Impregnate the split fiberglass cloth with the resin solution obtained in step S1, and dry and pre-cur it into a semi-cured sheet to obtain the fabric; S3. Hot pressing and curing: Stack 2 to 8 core materials, and attach one fabric layer to the upper and lower surfaces of the stacked core materials to form a composite substrate blank; cover the outer surface of at least one fabric layer with copper foil, and heat press and cure to obtain sulfur-free CEM-3 copper clad laminate. The hot-press curing process includes a post-curing stage where curing is carried out at 195~225℃ for more than 60 minutes.

2. The method for preparing sulfur-free CEM-3 copper clad laminate according to claim 1, characterized in that, In step S1, the resin solution comprises the following raw material components in parts by weight: 30-45 parts epoxy resin; 20-30 parts of isocyanate-modified cyanate resin; 15-23 parts of halogen-free composite flame retardant; 8-18 parts of phenolic resin curing agent; 0.02~0.1 parts of latent curing accelerator; 35-55 parts of thermally conductive filler; 0.4 to 1 part of coupling agent.

3. The method for preparing sulfur-free CEM-3 copper clad laminate according to claim 1, characterized in that, The isocyanate-modified cyanate resin is prepared by reacting cyanate monomers and diisocyanate compounds with a molar ratio of cyanate groups to isocyanate groups of (6~12):(1~1.5).

4. The method for preparing sulfur-free CEM-3 copper clad laminate according to claim 1, characterized in that, The halogen-free composite flame retardant is composed of metal phosphinate and coated ammonium polyphosphate in a weight ratio of (1.5~4):(1~2).

5. The method for preparing sulfur-free CEM-3 copper clad laminate according to claim 4, characterized in that, The metal phosphonate is selected from at least one of aluminum diethylphosphonate, aluminum diphenylphosphonate, and zinc phosphonate.

6. The method for preparing sulfur-free CEM-3 copper clad laminate according to claim 1, characterized in that, The phenolic resin curing agent is a linear phenolic resin with a phenolic hydroxyl equivalent of 105~120g / eq; The latent curing accelerator is dicyandiamide modified with organic acid.

7. The method for preparing sulfur-free CEM-3 copper clad laminate according to claim 1, characterized in that, The thermally conductive filler comprises spherical alumina and silicon dioxide, wherein the particle size D50 of the spherical alumina is 2~10μm and the particle size D50 of the silicon dioxide is 0.5~3μm.

8. The method for preparing sulfur-free CEM-3 copper clad laminate according to claim 1, characterized in that, In step S1, before mixing the raw material components, the isocyanate-modified cyanate resin is further subjected to dehydration treatment for 2-4 hours at a temperature of 80-110℃ and a vacuum degree of -0.095--0.10MPa.

9. The method for preparing sulfur-free CEM-3 copper clad laminate according to claim 1, characterized in that, In step S3, the hot-press curing process specifically includes: First stage: Under a vacuum of -0.091 to -0.10 MPa, the temperature is increased to 110 to 130℃ at a rate of 1.5 to 2.5℃ / min, and a pressure of 0.5 to 2.5 MPa is applied and maintained for 20 to 40 minutes; Second stage: Increase the temperature to 160~185℃ at a rate of 1.0~2.0℃ / min, increase the pressure to 3~5MPa, and maintain for 50~90min; Third stage: Increase the temperature to 195~225℃ at a rate of 0.5~1.5℃ / min, maintain the pressure, and perform post-curing for 60~150min.

10. A CEM-3 copper clad laminate, characterized in that, The CEM-3 copper clad laminate is prepared by the method of any one of claims 1 to 9, wherein the CEM-3 copper clad laminate comprises 2 to 8 core layers reinforced with glass fiber paper and fabric layers reinforced with open-fiber glass fiber cloth disposed on its upper and lower surfaces, and copper foil covering the outer surface of at least one of the fabric layers; the sulfur content of the copper clad laminate is <10ppm.

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