Sulfur-free FR-4 copper-clad plate and preparation method thereof

Abstract

The invention discloses a sulfur-free FR-4 copper-clad plate and a preparation method thereof, and belongs to the technical field of copper-clad plates. The copper-clad plate is prepared from sulfur-free epoxy resin, a sulfur-free curing agent, a sulfur-free flame retardant, organic silicon hybrid macromolecules, tetrafunctional epoxy resin, linear phenolic resin, microencapsulated ammonium polyphosphate, melamine cyanurate, surface grafting modified boehmite nanorods and filler. Through the design of a sulfur-free system, the sulfur content of the product is lower than 50 ppm, and the problems of contact resistance increase, unstable signal transmission and the like caused by sulfide migration of a traditional FR-4 copper-clad plate in a high-temperature and high-humidity environment are thoroughly solved. Meanwhile, the organic silicon hybrid macromolecules and the high-functionality epoxy resin have a synergistic effect, so that the balance of high glass transition temperature and high toughness is realized. The copper-clad plate has excellent dielectric property, flame retardant property and long-term reliability, and meets the development requirements of high reliability and high performance of electronic products.

Description

A sulfur-free FR-4 copper clad laminate and its preparation method Technical Field

[0001] This application relates to the field of electronic circuit board materials technology, and in particular to a high-performance sulfur-free and environmentally friendly FR-4 copper clad laminate and its preparation method. Background Technology

[0002] Traditional FR-4 copper-clad laminates are widely used in printed circuit board manufacturing due to their excellent mechanical strength, electrical properties, heat resistance, and processability. These properties mainly rely on the synergistic effect of components such as epoxy resin, curing agent, flame retardant, and sulfur-containing curing accelerator. Furthermore, trace amounts of sulfur are inevitably introduced during the production and preparation of epoxy resin and curing agent.

[0003] Initially, halogen-free materials were a key research focus due to environmental concerns, and technological innovations have now effectively reduced the residue of halogens such as bromine and chlorine. However, sulfides pose a potential risk to halogen-free systems: on the one hand, sulfur-containing curing accelerators exhibit a significant synergistic flame-retardant effect with matrix materials such as epoxy resins; removing them necessitates reconstructing the balance between various material properties. On the other hand, using alternative materials to eliminate sulfur compounds often introduces new polar molecular structures, potentially affecting the dielectric properties of the material in an electric field, leading to increased dielectric loss and consequently negatively impacting the quality of high-frequency signal transmission. Therefore, maintaining the stability of the material's overall performance while eliminating sulfur remains a significant technical challenge.

[0004] Sulfur significantly impacts product reliability, primarily due to its reactive chemical properties. Under high temperature and humidity, sulfides in the substrate may decompose or migrate, reacting with silver in the chemical silver plating layer commonly used in circuit board surface treatment to form silver sulfide. This product increases contact resistance, leading to unstable signal transmission or even open-circuit failure. Similarly, sulfides can react with copper to form a passivation layer, further affecting the electrical connection performance and long-term reliability of the circuit board.

[0005] Therefore, developing sulfur-free FR-4 copper clad laminates is not only a key material technology challenge, but also an inevitable path to keep up with the trend of high reliability and high performance in electronic products. Summary of the Invention

[0006] To address the potential corrosion risks associated with traditional FR-4 copper clad laminates due to the use of sulfur-containing flame-retardant systems, and to improve their toughness, heat resistance, and reliability, this application provides a sulfur-free FR-4 copper clad laminate with excellent overall performance and environmental friendliness, as well as its preparation method.

[0007] In a first aspect, this application provides a sulfur-free FR-4 copper-clad laminate, comprising E-glass fiber cloth, copper foil, and sulfur-free resin adhesive, wherein the sulfur-free resin adhesive comprises the following components by weight: 60-80 parts epoxy resin, 20-40 parts curing agent, 15-35 parts organosilicon hybrid macromolecules, 5-25 parts modified boehmite nanorods, 20-35 parts flame retardant, and 80-120 parts solvent.

[0008] By adopting the above technical solution, a main reaction system is composed of epoxy resin and curing agent in a specific ratio. Organosilicon hybrid macromolecules and surface-modified boehmite nanorods are used as key modifying components, and synergistic effects are achieved with microencapsulated flame retardants. This results in a balanced improvement in the overall performance of copper-clad laminates without introducing any sulfur-containing accelerators. This system not only eliminates the introduction of sulfur at the source, completely eliminating the risk of silver or copper surface corrosion caused by sulfide migration, but also significantly improves the long-term reliability of electronic products in high-temperature and high-humidity environments. Simultaneously, the organosilicon hybrid macromolecules, through their flexible siloxane segments and active epoxy groups, effectively enhance the toughness, heat resistance, and dielectric properties of the resin system. The modified boehmite nanorods, through their nano-effects and surface-grafted phosphorus functional groups, further strengthen the interfacial bonding, flame retardant synergy, and resistance to sulfur corrosion. The above components work together to ensure that the copper-clad laminate has a high glass transition temperature, excellent dielectric stability, good flame retardancy and strong peel strength even under sulfur-free conditions, thus meeting the stringent requirements of high-performance and high-reliability electronic circuits for substrate materials.

[0009] Optionally, the epoxy resin is composed of bisphenol A type epoxy resin and tetrafunctional epoxy resin.

[0010] Optionally, the mass ratio of bisphenol A epoxy resin to tetrafunctional epoxy resin is 1:1 to 1:3.

[0011] Optionally, the curing agent consists of linear phenolic resin and microencapsulated latent curing agent.

[0012] Optionally, the amount of linear phenolic resin is 20-40 parts, and the amount of microencapsulated latent curing agent is 0.3-0.8 parts.

[0013] Optionally, the flame retardant is composed of microencapsulated ammonium polyphosphate and melamine cyanurate; wherein the mass ratio of microencapsulated ammonium polyphosphate to melamine cyanurate is 3:1 to 5:1.

[0014] Optionally, the solvent is methyl isobutyl ketone.

[0015] By adopting the above technical solutions, the composition and proportion of key components have been further refined. The bisphenol A type and tetrafunctional epoxy resin are compounded in a ratio of 1:1 to 1:3, achieving an optimal balance between processability and high heat resistance. The linear phenolic resin dosage of 20-40 parts ensures sufficient curing, cross-linking, and toughening effects; the microencapsulated latent curing agent dosage of 0.3-0.8 parts is sufficient to initiate the curing reaction and maintain adhesive stability. The flame retardant is a high-ratio compound of microencapsulated ammonium polyphosphate and melamine cyanurate (3:1 to 5:1), which not only exhibits excellent synergistic effects in intumescent flame retardancy, but the microencapsulation treatment also significantly improves the hydrolysis resistance of ammonium polyphosphate and its compatibility with the resin, enhancing the long-term reliability of the board. Methyl isobutyl ketone is selected as the solvent, possessing good solubility and a suitable evaporation rate, which is beneficial for controlling the impregnation process.

[0016] Optionally, the preparation method of the organosilicon hybrid macromolecule includes the following steps: mixing terminal hydrogen polydimethylsiloxane with allyl glycidyl ether, adding toluene and Karstedt catalyst, and reacting at 85°C to obtain intermediate A; adding the terminal hydrogen polydimethylsiloxane and toluene again to the reaction system of intermediate A, and heating to 95°C to continue the reaction to obtain reaction solution B; slowly adding the allyl glycidyl ether to reaction solution B, removing the toluene by rotary evaporation after the reaction is completed, removing the Karstedt catalyst by filtration, and vacuum drying to obtain the organosilicon hybrid macromolecule.

[0017] By adopting the above technical solution, the epoxy groups can be chemically bonded to the main resin and firmly embedded in the curing network. At the same time, the long-chain polysiloxane segments can form flexible micro-regions in the epoxy network, thereby achieving efficient toughening without easy migration and precipitation, and significantly improving the impact resistance, damp heat cycling resistance and delamination resistance of copper clad laminates.

[0018] Optionally, the modified boehmite nanorods are obtained by surface grafting modification of boehmite nanorods after activation with a silane coupling agent and then with 2-methacryloyloxyethylphosphorylcholine through a polymerization reaction.

[0019] By employing the above-mentioned technical solution to perform dual surface modification on boehmite nanorods, their interfacial bonding with organic resins is improved, enhancing hydrophilicity and biocompatibility. Overall, this improves the dispersibility of nanoparticles in the resin matrix, prevents agglomeration, and may promote the formation of a dense char layer during combustion, synergistically enhancing flame retardant effects. Moreover, the good dispersibility maximizes the reinforcing, toughening, and heat-resistant properties of the resin matrix.

[0020] Secondly, this application provides a sulfur-free FR-4 copper-clad laminate as described in the first aspect, which is prepared by the following method: the epoxy resin, the curing agent, the organosilicon hybrid macromolecule, the modified boehmite nanorods, and the flame retardant are mixed and dispersed uniformly under vacuum conditions, and then the solvent is added to adjust the viscosity to obtain a sulfur-free resin solution; the E-glass fiber cloth is impregnated with the sulfur-free resin solution and pre-cured to obtain a prepreg; multiple layers of the prepreg are stacked and covered with copper foil on the upper and lower surfaces, and then cured by heating and pressurizing to obtain the sulfur-free FR-4 copper-clad laminate.

[0021] By adopting the above technical solution, air bubbles introduced in the raw materials and during the mixing process can be effectively eliminated, ensuring the uniformity and stability of the adhesive solution. This is a prerequisite for obtaining high-performance, defect-free boards. Through impregnation and pre-curing treatments, the degree of resin wetting of the fiberglass cloth and the resin flowability and volatile content of the prepreg are precisely controlled, laying a good foundation for subsequent multilayer lamination. The final heating and pressurizing curing process allows the resin to fully flow, wet, and completely cross-link and cure, forming a dense and robust three-dimensional network structure. This ensures that the final copper-clad laminate product has excellent interlayer bonding, low dielectric constant, low loss, high heat resistance, high flame retardancy, and excellent mechanical strength.

[0022] In summary, this application includes at least one of the following beneficial technical effects: 1. By adopting a sulfur-free epoxy resin, curing agent, and flame retardant system, the introduction of sulfur is eliminated at the source. The sulfur content of the product is less than 50 ppm, fundamentally solving the problem that traditional FR-4 copper-clad laminates react with metals such as silver and copper due to sulfide migration under high temperature and high humidity environments, leading to increased contact resistance, unstable signal transmission, or even open circuit failure, significantly improving the long-term reliability of the product; 2. By introducing organosilicon hybrid macromolecules, their flexible polysiloxane segments can effectively disperse stress and inhibit crack propagation, significantly improving the brittleness of epoxy resin; at the same time, the high-functionality tetrafunctional epoxy resin and linear phenolic resin are synergistically cured, constructing a three-dimensional network structure with high cross-linking density. The synergistic effect of these two factors enables the copper-clad laminate to maintain a high glass transition temperature while also possessing excellent impact resistance and delamination resistance. Furthermore, by employing a flame-retardant system composed of microencapsulated ammonium polyphosphate and melamine cyanurate, along with surface-grafted boehmite nanorods, a synergistic effect of gas-phase and condensed-phase flame retardancy is achieved, ensuring the high flame retardancy of the board. Simultaneously, this sulfur-free system avoids dielectric property degradation caused by the introduction of polar molecules, resulting in a lower dielectric constant and dielectric loss factor for the copper-clad laminate at 10 GHz, meeting the requirements of high-frequency signal transmission. Detailed Implementation

[0023] The present application will be further described in detail below with reference to preparation examples and embodiments.

[0024] The raw materials used in the preparation examples and embodiments were all commercially available products, and the specific information is as follows: Hydrogen-terminated polydimethylsiloxane: average molecular weight Mn = 1000 g / mol (corresponding to the number of repeating units n≈14), hydrogen content (as Si-H) 1.0 wt%, CAS No. 70900-21-9, purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.; Allyl glycidyl ether: purity ≥99%, CAS No. 106-92-3, purchased from Shanghai Kangtuo Chemical Co., Ltd.; Karstedt catalyst (platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex): analytical grade, CAS No. 81032-58-8, purchased from Guangdong Keton Chemical Co., Ltd.; Toluene: analytical grade, CAS No. 108-88-2, purchased from Nanjing Chemical Reagent Co., Ltd.; Boehmite nanorods: particle size 50 nm. Purity >99.5%, CAS No. 1318-23-6, provided by Wuhan Kemike Biomedical Technology Co., Ltd.; Silane coupling agent KH-560 (γ-methacryloyloxypropyltrimethoxysilane): CAS No. 2530-85-0, provided by Anhui Boiling Point New Materials Co., Ltd.; 2-Methacryloxyethylphosphorylcholine: Purity ≥97%, CAS No. 67881-98-5, purchased from Shandong Borun Biotechnology Co., Ltd.; Azobisisobutyronitrile: Purity ≥99.9%, purchased from Shandong Hairui New Materials Co., Ltd.; Bisphenol A type epoxy resin: Epoxy equivalent EEW=185 g / eq, sulfur content <3 ppm, purchased from Changchun Chemical (Jiangsu) Co., Ltd.; tetrafunctional epoxy resin: epoxy equivalent EEW=110-130 g / eq, CAS No. 28768-32-3, purchased from Shexian Yatai Chemical Co., Ltd.; linear phenolic resin: hydroxyl equivalent = 105 g / eq, CAS No. 9003-35-4, purchased from Puyang Enying Polymer Materials Co., Ltd.; microencapsulated liquid latent curing agent: item number HX3941, purchased from Guangzhou Yihuisheng Chemical Co., Ltd.; microencapsulated ammonium polyphosphate: phosphorus content ≥30%, decomposition temperature ≥280℃, purchased from Shenzhen Zhongherun Technology Co., Ltd.; melamine cyanurate: content ≥99.5%, CAS No. 37640-57-6, purchased from Wuxi Haotuo Electronic Materials Co., Ltd.; methyl isobutyl ketone: purity ≥99.5%, CAS No. 108-10-1, purchased from Nanjing Chemical Reagent Co., Ltd.

[0025] Preparation Example 1: Preparation of Organosilicon Hybrid Macromolecules. In a dry three-necked flask, 21.6 g of hydrogen-terminated polydimethylsiloxane and 0.68 g of allyl glycidyl ether were added, with a molar ratio controlled at Si-H = 1:0.8. A suitable amount of toluene was added as a solvent. Nitrogen gas was introduced for protection, and the temperature was raised to 85 °C. Under stirring, 20 μL of Karstedt catalyst was added dropwise, and the reaction was carried out at 90-100 °C for 6-8 h until a value of 2160 cm⁻¹ was detected. -1The characteristic Si-H absorption peak intensity at the site essentially disappeared, indicating the completion of the surface hydrosilylation reaction, yielding intermediate A. In the reaction system of intermediate A, 20.0 g of hydrogen-terminated polydimethylsiloxane and 150 mL of dry toluene were added, the temperature was raised to 85 °C, and the mixture was stirred thoroughly under nitrogen protection. Then, 50 μL of Karstedt catalyst was added, the temperature was raised to 95 °C, and stirring was continued for approximately 7 hours until a peak value of 2160 cm⁻¹ was observed. -1 The intensity of the Si-H characteristic absorption peak decreased to less than 5% of the initial value. 0.63 g of allyl glycidyl ether was slowly added, and the reaction continued at 95°C for 6 hours after the addition was complete, until the concentration reached 2160 cm⁻¹. -1 The Si-H characteristic absorption peaks completely disappeared, indicating the end of the reaction. The reaction system was cooled to room temperature to obtain a reaction solution. Most of the toluene was removed by rotary evaporation of the above reaction solution at 60℃ and -0.095MPa. The remaining liquid was dissolved in 50mL of tetrahydrofuran and filtered through a glass frit funnel with neutral alumina to remove the Karstedt catalyst. The filtrate was then removed by rotary evaporation at 40℃ and -0.095MPa. The resulting primary product was vacuum dried at 80℃ for 24 hours to obtain an organosilicon hybrid macromolecule.

[0026] Preparation Example 2: Preparation of Modified Boehmite Nanorods. 50 g of boehmite nanorods were added to 300 mL of anhydrous ethanol and ultrasonically dispersed for 30 minutes to obtain a uniform suspension. 6 g of KH-560 silane coupling agent was mixed with 100 mL of anhydrous ethanol and 2 mL of deionized water and stirred at 40°C for 30 minutes to obtain a clear hydrolysate. The hydrolysate was slowly added dropwise to the boehmite suspension, and the mixture was stirred and refluxed at 60°C for 6 hours. After the reaction, the solid was separated by centrifugation, washed three times with anhydrous ethanol, and vacuum dried at 80°C for 6 hours to obtain an activated boehmite intermediate with carbon-carbon double bonds on its surface.

[0027] All the activated boehmite intermediates, 40 parts of 2-methacryloyloxyethyl phosphorylcholine monomer, and approximately 100 parts of anhydrous ethanol were mixed in a reactor and stirred under nitrogen protection, then heated to 80°C to disperse the mixture evenly. 1.6 parts of the initiator benzoyl peroxide were dissolved in a small amount of warm anhydrous ethanol and slowly added dropwise to the reaction system. The mixture was then stirred and refluxed at 85°C under a nitrogen atmosphere for 8-10 hours.

[0028] After the reaction solution was cooled, the solid product was obtained by centrifugation. The solid product was washed repeatedly with a large amount of anhydrous ethanol at least five times until the washing liquid was colorless and transparent. The product was placed in a vacuum dryer at 80°C for 12 hours and then sieved to obtain white powdered modified boehmite nanorods.

[0029] Example 1

[0030] Raw material ratio: 20 parts bisphenol A epoxy resin, 40 parts tetrafunctional epoxy resin, 35 parts linear phenolic resin, 0.5 parts microencapsulated liquid latent curing agent, 25 parts organosilicon hybrid macromolecule (obtained in Preparation Example 1), 15 parts modified boehmite nanorods (obtained in Preparation Example 2), 20 parts microencapsulated ammonium polyphosphate, 5 parts melamine cyanurate, and 100 parts methyl isobutyl ketone. Preparation method: 1. Preparation of sulfur-free resin liquid: By weight, place 20 parts bisphenol A epoxy resin, 40 parts tetrafunctional epoxy resin, 35 parts linear phenolic resin, and 0.5 parts microencapsulated latent curing agent in a mixing container. Heat the mixture to 60°C and stir at 300-500 rpm. Add 25 parts organosilicon hybrid macromolecule and continue stirring for 30-45 minutes until the system is homogeneous. Subsequently, 20 parts of microencapsulated ammonium polyphosphate, 5 parts of melamine cyanurate, and 15 parts of surface-modified boehmite nanorods were added sequentially. The stirring speed was increased to 800-1000 rpm, and the mixture was degassed for 60 minutes under a vacuum of not less than -0.095 MPa to ensure uniform dispersion of the filler. Finally, approximately 100 parts of methyl isobutyl ketone solvent were added to adjust the viscosity of the adhesive to 25±3 cP, thus obtaining the sulfur-free resin adhesive.

[0031] 2. The prepreg was prepared by impregnating E-glass fiber cloth with the sulfur-free resin solution obtained in step 1. The amount of resin applied was controlled at 42±2% by adjusting the gap between the extrusion rollers. The impregnated glass fiber cloth was then conveyed through a drying tunnel with three independent temperature zones for pre-curing. The temperatures of the three zones were set at 110°C, 140°C, and 160°C, respectively. The total material throughput time was 8 minutes. This process yielded a sulfur-free prepreg with a resin flowability of approximately 22%.

[0032] 3. Lamination and Curing: Take eight of the above-mentioned sulfur-free prepreg sheets and stack them together. Apply an electrolytic copper foil to each of the upper and lower surfaces of the stack to form a blank. Place the blank in a hot press for programmed temperature and pressure curing. The specific program is as follows: First stage: heat to 120°C at a rate of 2-3°C / min, simultaneously apply a pressure of 5 MPa, and maintain this temperature and pressure for 30 minutes; Second stage: continue heating to 200°C at a rate of 1-2°C / min, maintain a pressure of 5 MPa, and cure under these conditions for 90 minutes; Third stage: while maintaining pressure, allow the laminate to cool naturally to below 60°C, then release the pressure and remove it to obtain the sulfur-free FR-4 copper-clad laminate.

[0033] Example 2

[0034] The difference between this embodiment and Embodiment 1 is that the amount of organosilicon hybrid macromolecules in step 1 is 15 parts.

[0035] Example 3

[0036] The difference between this embodiment and Embodiment 1 is that the amount of organosilicon hybrid macromolecules in step 1 is 35 parts.

[0037] Example 4

[0038] The difference between this embodiment and Embodiment 1 is that, in step 1, the amount of microencapsulated ammonium polyphosphate is 12 parts and the amount of melamine cyanurate is 3 parts.

[0039] Example 5

[0040] The difference between this embodiment and Embodiment 1 is that, in step 1, the amount of microencapsulated ammonium polyphosphate is 28 parts and the amount of melamine cyanurate is 7 parts.

[0041] Example 6

[0042] The difference between this embodiment and Embodiment 1 is that, in step 1, the amount of microencapsulated ammonium polyphosphate is 15 parts and the amount of melamine cyanurate is 10 parts.

[0043] Example 7

[0044] The difference between this embodiment and Embodiment 1 is that the modified boehmite nanorods in step 1 are 5 parts.

[0045] Example 8

[0046] The difference between this embodiment and Embodiment 1 is that the modified boehmite nanorods in step 1 are 25 parts.

[0047] Comparative Example 1 differs from Example 1 in that no organosilicon hybrid macromolecules are added in step 1.

[0048] The difference between Comparative Example 2 and Example 1 is that 0.3 parts of 2-methylimidazole were used instead of the microencapsulation latent curing agent.

[0049] The difference between Comparative Example 3 and Example 1 is that an equal amount of ordinary boehmite powder was used instead of the modified boehmite nanorods.

[0050] Sulfur content testing in copper clad laminates: Inductively coupled plasma mass spectrometry; Sulfur corrosion resistance test method according to GB / T 2423.51 "Environmental testing of electrical and electronic components - Part 2: Test methods Ke: Corrosion test of flowing mixed gases" Method 1, the test duration is 96 hours. After the test, the mold area of ​​the copper clad laminate is directly calculated. Specifically, after the test, each copper clad laminate is placed at 21-25℃ for 4-8 hours, then the copper clad laminate is photographed, and the blackened area of ​​the copper clad laminate photograph is calculated. The calculation method adopts grid method or software method. (The grid method divides the metal foil area in the image into sufficiently small square grids, and calculates the proportion of the blackened grid to the total grid to obtain the blackened area of ​​the metal foil. The software method uses software such as Image-ProPlus or Photoshop to intelligently calculate the blackening ratio of the metal foil by distinguishing the colors of the blackened and unblackened areas.) Dk / Df test method: IPC-TM-650 2.5.5.5 standard method, frequency 10GHz; Glass transition temperature (Tg) test: Differential scanning calorimetry instrument, heating rate 20℃ / min, nitrogen atmosphere; Peel strength is tested according to IPC-TM-650-2.4.8C method; Test results are shown in Table 1.

[0051] Table 1

[0052] As shown in Table 1, through reasonable design and adjustment of each component of the formulation, the sulfur content of the copper-clad laminates prepared in all examples was controlled at an extremely low level (<50ppm), eliminating the risk of sulfide migration corrosion at its source. While maintaining sulfur-free characteristics, each example still exhibited excellent overall performance, demonstrating the synergistic optimization effect among key components.

[0053] Example 1 serves as the base formulation, exhibiting balanced overall performance. This formulation utilizes 25 parts of organosilicon hybrid macromolecules and 15 parts of modified boehmite nanorods as key functional components. The organosilicon hybrid macromolecules introduce epoxy groups through hydrosilylation, enhancing compatibility and reactivity with epoxy resins. This not only increases the crosslinking density and glass transition temperature of the system but also improves the material's toughness and thermal stability by introducing siloxane segments. The phosphorylcholine structure grafted onto the surface of the modified boehmite nanorods combines polarity and flame retardancy, effectively improving its dispersibility and interfacial adhesion strength in the resin. It also forms a synergistic flame retardant system with microencapsulated ammonium polyphosphate and melamine cyanurate. This combined effect enables the board to maintain high resistance to sulfur corrosion, good dielectric properties, and peel strength even under completely sulfur-free conditions.

[0054] In Example 2, the amount of organosilicon hybrid macromolecule was adjusted to 15 parts. Compared to Example 1, this reduced component ratio resulted in a relatively weaker crosslinking density and contribution from the flexible siloxane segments. Consequently, the glass transition temperature and peel strength decreased slightly, and the resistance to sulfur corrosion was also slightly affected, though still maintained at a high level. This indicates that an appropriate amount of organosilicon structure plays a beneficial role in maintaining the material's high-temperature performance and interfacial stability.

[0055] Example 3 increased the amount of organosilicon hybrid macromolecule to 35 parts. Increasing the content of this component further enhanced the system's flexibility and thermal stability, increased the glass transition temperature, and optimized the dielectric constant and loss factor due to the increased number of siloxane segments. The resistance to sulfide corrosion remained good, demonstrating the role of this component in improving the overall reliability of the material.

[0056] In Example 4, the amount of microencapsulated ammonium polyphosphate in the flame retardant system was adjusted to 12 parts, and melamine cyanurate was adjusted to 3 parts. This ratio reduced the total flame retardant content, which may affect the synergistic efficiency of flame retardancy between the gas phase and condensed phase. However, the system still maintained a good balance between flame retardancy and corrosion resistance through the surface phosphorus structure of the modified boehmite nanorods and the thermal stabilization effect of organosilicon macromolecules, and no significant decrease in various properties was observed.

[0057] In Example 5, the amount of microencapsulated ammonium polyphosphate was increased to 28 parts, and melamine cyanurate was adjusted to 7 parts. Increasing the flame retardant content enhanced the flame retardant performance of the system. At the same time, due to the design of the microencapsulation structure, it was well dispersed in the resin without causing significant negative impact on the dielectric properties. The corrosion resistance and thermal properties remained excellent, indicating that the flame retardant system has good compatibility with the sulfur-free resin matrix.

[0058] Example 6 further adjusted the flame retardant ratio to 15 parts microencapsulated ammonium polyphosphate and 10 parts melamine cyanurate. The higher proportion of melamine cyanurate in this formulation may have increased the system polarity to some extent, leading to a slight increase in dielectric constant and loss factor, and a slight decrease in glass transition temperature and peel strength. However, it is still superior to the comparative example, indicating that the type and ratio of flame retardant need to be synergistically optimized to balance electrical and mechanical properties.

[0059] In Example 7, the amount of modified boehmite nanorods was reduced to 5 parts. The reduction in the content of nanofillers weakened their role in improving interfacial bonding, inhibiting sulfide corrosion, and assisting in flame retardancy. As a result, the corrosion resistance, glass transition temperature, and peel strength all decreased to some extent, demonstrating the important function of this component in enhancing overall performance.

[0060] Example 8 increased the amount of modified boehmite nanorods to 25 parts. Increasing the nanofiller content further enhanced the interfacial reinforcement and corrosion inhibition capabilities, achieving optimal resistance to sulfide corrosion. Simultaneously, due to the synergistic effect of uniform nanoparticle dispersion and the surface modification layer, both dielectric and thermal properties were further improved, indicating that appropriately increasing this component helps to construct a more stable sulfur-free composite material system.

[0061] Comparative Example 1, without the addition of organosilicon hybrid macromolecules, resulted in a decrease in the system's flexibility and thermal stability, a significant reduction in glass transition temperature and peel strength, and a substantial weakening of its resistance to sulfur corrosion, highlighting the crucial role of this component in regulating the balance between material structure and performance.

[0062] Comparative Example 2 used a sulfur-containing accelerator, 2-methylimidazole, which introduced a significant sulfur content, resulting in a sharp decline in resistance to sulfur corrosion. Furthermore, the presence of sulfur affected the crosslinking structure and interfacial stability, and all performance characteristics were inferior to those of the sulfur-free example. This, in turn, confirms the necessity of the sulfur-free system for improving long-term reliability.

[0063] Compared to Example 3, unmodified boehmite powder was used instead of modified boehmite nanorods. Due to the lack of surface functionalization, the dispersibility of the filler and its bonding with the resin interface were poor, resulting in inferior mechanical properties, heat resistance, and corrosion resistance compared to the corresponding examples. This indicates that surface modification plays a crucial role in achieving the functionalization of nanofillers and improving the overall performance of composite materials.

[0064] In summary, this application, through the synergistic combination of key components such as organosilicon hybrid macromolecules, surface-modified boehmite nanorods, and microencapsulated flame retardants, enables copper-clad laminates to possess excellent sulfur corrosion resistance, high glass transition temperature, stable dielectric properties, and good bonding strength while completely eliminating the introduction of sulfur elements. It achieves a balance between sulfur-free and high performance, and has significant practical value and promotion prospects.

[0065] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this application.

Claims

1. A sulfur-free FR-4 copper-clad laminate, comprising E-glass fiber cloth, copper foil, and sulfur-free resin adhesive, characterized in that, The sulfur-free resin adhesive comprises the following raw materials in parts by weight: 60-80 parts epoxy resin, 20-40 parts curing agent, 15-35 parts organosilicon hybrid macromolecule, 5-25 parts modified boehmite nanorods, 20-35 parts flame retardant, and 80-120 parts solvent.

2. The sulfur-free FR-4 copper-clad laminate according to claim 1, characterized in that, The epoxy resin is composed of bisphenol A type epoxy resin and tetrafunctional epoxy resin.

3. The sulfur-free FR-4 copper-clad laminate according to claim 2, characterized in that, The mass ratio of the bisphenol A type epoxy resin to the tetrafunctional epoxy resin is 1:1 to 1:

3.

4. The sulfur-free FR-4 copper-clad laminate according to claim 1, characterized in that, The curing agent consists of linear phenolic resin and microencapsulated latent curing agent.

5. The sulfur-free FR-4 copper-clad laminate according to claim 4, characterized in that, The amount of the linear phenolic resin is 20-40 parts, and the amount of the microencapsulated latent curing agent is 0.3-0.8 parts.

6. The sulfur-free FR-4 copper-clad laminate according to claim 1, characterized in that, The flame retardant is composed of microencapsulated ammonium polyphosphate and melamine cyanurate; wherein the mass ratio of microencapsulated ammonium polyphosphate to melamine cyanurate is 3:1 to 5:

1.

7. The sulfur-free FR-4 copper-clad laminate according to claim 1, characterized in that, The solvent is methyl isobutyl ketone.

8. The sulfur-free FR-4 copper-clad laminate according to claim 1, characterized in that, The method for preparing the organosilicon hybrid macromolecule includes the following steps: mixing terminal hydrogen polydimethylsiloxane with allyl glycidyl ether, adding toluene and Karstedt catalyst, and reacting at 85°C to obtain intermediate A; adding the terminal hydrogen polydimethylsiloxane and toluene again to the reaction system of intermediate A, and heating to 95°C to continue the reaction to obtain reaction solution B; slowly adding the allyl glycidyl ether to reaction solution B, removing the toluene by rotary evaporation after the reaction is completed, removing the Karstedt catalyst by filtration, and vacuum drying to obtain the organosilicon hybrid macromolecule.

9. A sulfur-free FR-4 copper-clad laminate according to claim 1, characterized in that, The modified boehmite nanorods are obtained by surface grafting modification of boehmite nanorods with 2-methacryloyloxyethylphosphorylcholine through a polymerization reaction after activation with a silane coupling agent.

10. A method for preparing a sulfur-free FR-4 copper-clad laminate as described in any one of claims 1-9, characterized in that, The process includes the following steps: mixing and dispersing the epoxy resin, curing agent, organosilicon hybrid macromolecule, modified boehmite nanorods, and flame retardant uniformly under vacuum conditions, then adding the solvent to adjust the viscosity to obtain a sulfur-free resin solution; impregnating the E-glass fiber cloth with the sulfur-free resin solution, and pre-curing it to obtain a prepreg; stacking multiple layers of the prepreg and covering the upper and lower surfaces with the copper foil, and then curing it under heat and pressure to obtain the sulfur-free FR-4 copper-clad laminate.

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