Low-flow FR-4 copper clad laminate and method of making the same

Abstract

This invention relates to a low-flow FR-4 copper-clad laminate and its preparation method, belonging to the field of copper-clad laminate manufacturing technology. The copper-clad laminate includes a reinforcing material layer, a resin composition layer, and a copper foil layer. The resin composition comprises an epoxy resin main system, bismaleimide resin, a latent curing agent system, a rheology control agent, a reactive diluent, fillers, and additives. This invention achieves precise control of resin flow during lamination by constructing a high-crosslink density skeleton using a high-rigidity resin and bismaleimide resin, forming a thixotropic network with nano-silica and organically modified montmorillonite, and using benzoxazine and carboxyl-terminated nitrile butadiene rubber to synergistically reduce internal stress. The preparation method includes resin solution preparation, step-by-step pre-curing to obtain a prepreg, and segmented pressurization and heating lamination molding. The product of this invention possesses excellent anti-flow properties, high bonding strength, and good heat resistance, making it suitable for the lamination manufacturing of multilayer printed circuit boards with multiple layers.

Description

Technical Field

[0001] This application relates to the fields of polymer composite materials and basic electronic circuit manufacturing, specifically to an FR-4 copper clad laminate suitable for multilayer printed circuit board lamination process and its preparation method, and more particularly to an FR-4 copper clad laminate with low resin flow characteristics during high temperature and high pressure lamination process. Background Technology

[0002] FR-4 copper-clad laminate, as a fundamental core material in the electronics industry, has been widely used in the field of multilayer printed circuit boards. In the lamination process of multilayer circuit boards, multiple pre-fabricated core boards and prepregs, which serve as interlayer adhesives, are typically laminated and cured into a single unit under high temperature and pressure. During this process, the resin contained in the prepreg melts, flows, and fills the interlayer gaps under the influence of temperature and pressure, ultimately curing to achieve reliable interlayer bonding.

[0003] However, the resin system of the prepreg used in traditional FR-4 copper clad laminates often faces the problem of resin overflow during the lamination process. Under the high temperature and pressure conditions of lamination, the resin has excessive fluidity and is prone to excessive flow, resulting in insufficient amount of resin actually used for bonding between layers, reducing the bonding strength between layers and thus affecting the mechanical properties of the circuit board. The overflowing resin will also contaminate the equipment and increase some unnecessary cleaning and maintenance costs.

[0004] To address the aforementioned issues, a new FR-4 copper clad laminate solution is needed to resolve the problem of excessive resin flow during the high-temperature, high-pressure lamination process, without compromising the overall performance of the copper clad laminate. Summary of the Invention

[0005] The purpose of this application is to provide a low-flow FR-4 copper clad laminate to solve the problem of excessive resin flow during high-temperature and high-pressure lamination.

[0006] In a first aspect, this application provides a low-flow FR-4 copper-clad laminate, which is formed by impregnating a reinforcing material with a resin composition and then curing it, wherein the resin composition comprises, by weight, the following: 40-70 parts epoxy resin, 15-35 parts high-performance resin, 2-10 parts latent curing agent; 3-8 parts rheology control agent, 5-20 parts toughening agent, 20-40 parts filler, 1-3 parts flame retardant, 0.5-1.5 parts silane coupling agent, and optional additives.

[0007] By adopting the above technical solutions, epoxy resin can be compounded with high-performance resin to form a rigid skeleton with high cross-linking density. Combined with the physical thixotropic network constructed by the rheology control agent and the interfacial toughening agent formed by the toughening agent and the low-shrinkage resin, effective control is achieved in the high-temperature and high-pressure pressing process, while maintaining the good bonding strength, heat resistance and dielectric properties of the copper clad laminate.

[0008] Optionally, the epoxy resin includes bisphenol A type epoxy resin and / or bisphenol F type epoxy resin, as well as naphthalene type epoxy resin.

[0009] Alternatively, the epoxy resin may be a bisphenol A type epoxy resin or a naphthalene type epoxy resin.

[0010] By adopting the above technical solutions, bisphenol A or F type epoxy resins provide the basic crosslinking structure and processability, while naphthalene type epoxy resins, due to their rigid naphthalene ring structure, can improve crosslinking density and heat resistance. The synergistic effect of the two helps to suppress resin flow at high temperatures and at the same time increase the glass transition temperature.

[0011] Optionally, the high-performance resin is selected from at least one of biphenyl-type epoxy resin, bismaleimide resin, benzoxazine resin, and cyanate ester resin.

[0012] Further optional, the high-performance resin is a bismaleimide resin or a benzoxazine resin.

[0013] By adopting the above technical solutions, bismaleimide resin has high heat resistance and high crosslinking density, which can further improve the thermal stability of the rigid skeleton; benzoxazine resin has low volume shrinkage during curing, which helps to improve the interfacial bonding strength and reduce internal stress. The synergy of the two can effectively improve the thermal shock resistance and dimensional stability of copper clad laminate.

[0014] Optionally, the latent curing agent is dicyandiamide and / or a phosphorus-containing phenolic resin curing agent; the rheology control agent is nano-sized silica and / or organically modified montmorillonite; and the toughening agent is carboxyl-terminated butadiene-acrylonitrile rubber and / or amino-terminated butadiene-acrylonitrile rubber.

[0015] Further optionally, the latent curing agent is dicyandiamide and phosphorus-containing phenolic resin curing agent; the rheology control agent is nano-sized silica and organically modified montmorillonite; and the toughening agent is carboxyl-terminated nitrile butadiene rubber.

[0016] By adopting the above technical solution, the curing reaction rate can be adjusted by combining dicyandiamide with phosphorus-containing phenolic resin curing agent, so that the resin system has a suitable flow window during the pressing process; nano-sized silica and organically modified montmorillonite synergistically construct a physical thixotropic network, in which the layered structure of organically modified montmorillonite can effectively hinder resin flow after high-speed dispersion and peeling; carboxyl-terminated nitrile rubber forms a rubber phase in the system, which improves toughness without affecting the integrity of the rigid skeleton.

[0017] Optionally, the filler comprises spherical silica and / or fused silica microparticles; the flame retardant comprises zinc borate and / or a combination of antimony trioxide and DOPO flame retardant; and the silane coupling agent is KH-560 type silane coupling agent.

[0018] Further optional, the filler comprises spherical silica and fused silica micropowder, the flame retardant comprises zinc borate and DOPO flame retardant; and the silane coupling agent is KH-560 type silane coupling agent.

[0019] Optionally, the adjuvant is selected from at least one of acetone, butanone, cyclohexanone, toluene, xylene, and ethylene glycol monomethyl ether.

[0020] Alternatively, the auxiliary agent may be acetone.

[0021] By adopting the above technical solutions, spherical silica can reduce the coefficient of thermal expansion of the resin system and improve its fluidity, while molten silica powder can further increase the filling density; zinc borate and DOPO flame retardant work synergistically to reduce the adverse effects on dielectric properties while ensuring flame retardant performance; KH-560 silane coupling agent can improve the interfacial bonding between inorganic fillers and resin matrix, and improve mechanical properties and moisture resistance.

[0022] Optionally, the resin composition comprises, by weight, 40-45 parts of bisphenol A type epoxy resin, 10-15 parts of naphthalene type epoxy resin, 10-15 parts of bismaleimide resin, 5-10 parts of benzoxazine resin, 2-5 parts of phosphorus-containing phenolic resin curing agent, 1-2 parts of dicyandiamide, 0.5-1 part of 2-methylimidazole, 2-5 parts of nano-sized silica, 1-3 parts of organically modified montmorillonite, 3-8 parts of carboxyl-terminated butadiene-acrylonitrile rubber, 20-30 parts of spherical silica, 3-6 parts of zinc borate, 1-3 parts of DOPO flame retardant, and 0.5-1.5 parts of KH-560 type silane coupling agent.

[0023] By adopting the above technical solution, the ratio of each component within the preferred range is further defined. Under this ratio, the synergistic effect of each component is more significant, and better comprehensive performance can be obtained while achieving low adhesive flow, including higher peel strength, glass transition temperature, solderability resistance, and lower dielectric loss and coefficient of thermal expansion.

[0024] Secondly, this application provides a method for preparing a low-flow FR-4 copper-clad laminate as described in the first aspect, comprising the following steps: (1) Preparation of resin solution: Epoxy resin, high performance resin, toughening agent and latent curing agent are fused together and heated and stirred until uniform; after cooling, rheology control agent, filler and some flame retardant are added and dispersed at high speed; after cooling again, the remaining flame retardant, silane coupling agent and additives are added, stirred evenly, and the solution viscosity is adjusted. After filtration and standing, resin solution is obtained. (2) Preparation of semi-cured sheet: The reinforcing material is impregnated in the above-obtained resin solution, pre-cured by heating in a multi-stage oven, cooled and rolled up to obtain a semi-cured sheet; (3) Lamination of copper-clad laminate: Multiple prepreg sheets are stacked together, copper foil is applied on the top and bottom, and the copper-clad laminate is obtained by cooling and depressurizing after being pressed and heated in sections by a vacuum hot press.

[0025] Optionally, in step (1), the heating and stirring temperature is 70-90℃, the stirring time is 30-60 min, the high-speed dispersion speed is 1000-1500 rpm, the time is 60-90 min, and the viscosity is adjusted to 1500-2000 mPa·s at 25℃.

[0026] Optionally, in step (2), the temperatures of the multi-stage oven are 100-110℃, 130-140℃, 150-160℃, and 165-175℃ respectively, the total throughput time is 4-6 min, and the adhesive content is 40-45 wt%. In step (3), the segmented pressurization is a two-stage pressing process, with the pressure of the first stage being 5-8 kg / cm. 2 Heat to 170-180℃ and hold for 30-50 minutes; the pressure in the second stage is 15-20 kg / cm². 2 Heat to 190-200℃, hold for 90-110 minutes, and cool at a rate of 1.5-2.5℃ / min.

[0027] By adopting the above technical solutions and using a step-by-step mixing process, the components are fully dispersed and exert synergistic effects; gradient temperature pre-curing allows the solvent to fully evaporate and form a preliminary cross-linked structure; the two-stage pressing process initially fixes the thixotropic network in the low-temperature stage and fully cross-links the rigid skeleton in the high-temperature stage, which is conducive to forming a stable multi-level network interpenetrating structure, thereby obtaining FR-4 copper clad laminate with low adhesive flow and excellent comprehensive performance.

[0028] In summary, this application includes at least one of the following beneficial technical effects: 1. By compounding epoxy resin with high-performance resin to form a rigid skeleton with high cross-linking density, and combining it with a physical thixotropic network constructed by nano-sized silica and organic modified montmorillonite, excessive resin flow during high-temperature and high-pressure pressing is effectively suppressed, significantly improving the flow control capability of the prepreg and avoiding problems such as insufficient interlayer bonding and equipment contamination caused by excessive resin loss. 2. By combining the low shrinkage characteristics of benzoxazine resin with the toughening effect of carboxyl-terminated nitrile butadiene rubber, good interfacial bonding strength is maintained while achieving low resin flow, which improves the interlayer bonding reliability and thermal shock resistance of copper clad laminate, and achieves a comprehensive balance between resin flow control and mechanical properties and heat resistance. 3. Through the synergistic effect of spherical silica, zinc borate and DOPO flame retardant, copper clad laminate achieves excellent flame retardant performance and dimensional stability, while maintaining good dielectric properties. Its overall comprehensive performance is excellent and can meet the requirements for the preparation of high-performance multilayer printed circuit boards. Detailed Implementation

[0029] Information on some of the raw materials used in Examples 1-16 is as follows: Bisphenol A type epoxy resin: purchased from Changchun Chemical (Jiangsu) Co., Ltd., EEW=185g / eq; Naphthalene-type epoxy resin: CAS No. 27610-48-6, viscosity ≤2000mPa·s, EEW=137-154g / eq; Bismaleimide resin (hereinafter referred to as BMI): CAS No. 13676-54-5; 2-Methylimidazole: CAS No. 693-98-1, purity ≥99%; Dicyandiamide: CAS No. 461-58-5, purity ≥99%; Phosphorus-containing phenolic resin curing agent: Product No. TPH890M60; Nanoscale silica (hydrophobic): specific surface area 200±25m² 2 / g; Spherical silica: average particle size 1 μm; Organically modified montmorillonite: CAS No. 1302-78-9, interlayer spacing 3-3.2 nm, specific gravity 1.8-2.0 g / cm³ 3 ; Benzoxazine resin: EEW = 210-230 g / eq; Carboxyl-terminated nitrile butadiene rubber (CTBN): CAS No. 25265-19-4, acrylonitrile content 26-40%; Zinc borate: CAS No. 1332-07-6, content ≥99%; DOPO flame retardant: CAS No. 35948-25-5, content ≥98.5%; KH-560 silane coupling agent: purchased from Anhui Boiling Point New Materials Co., Ltd., CAS No. 2530-85-0.

[0030] Example 1: A method for preparing a low-flow FR-4 copper-clad laminate, comprising the following components: 40 parts bisphenol A type epoxy resin, 15 parts naphthalene type epoxy resin, 15 parts bismaleimide resin, 8 parts benzoxazine resin, 5 parts CTBN, 3 parts phosphorus-containing phenolic resin curing agent, 3 parts nano-grade silica, 2 parts organically modified montmorillonite, 28 parts spherical silica, 5 parts zinc borate, 1.5 parts dicyandiamide, 0.8 parts 2-methylimidazole, 2 parts DOPO flame retardant, 1 part KH-560 silane coupling agent, and appropriate amount of acetone.

[0031] Preparation method: 1. Preparation of resin solution 1. Add bisphenol A type epoxy resin, naphthalene type epoxy resin, bismaleimide resin, benzoxazine resin, CTBN, and phosphorus-containing phenolic resin curing agent to a reaction vessel, heat to 80℃, and stir and mix at 400 rpm for 45 minutes until the system becomes a uniform and transparent solution. 2. After the temperature inside the reactor drops to 55°C, add nano-sized silica, organically modified montmorillonite, spherical silica and zinc borate, and increase the rotation speed to 1200 rpm for high-speed dispersion for 75 minutes. 3. After cooling the mixture to 40°C, add 2-methylimidazole, dicyandiamide, DOPO flame retardant and KH-560 silane coupling agent, stir at 400 rpm for 25 minutes to ensure uniform dispersion of each component, and finally add an appropriate amount of acetone solvent to adjust the viscosity of the resin solution at 25°C to 1800 mPa·s. 4. Filtration and settling: Filter the prepared adhesive solution through a 250-mesh filter to remove any possible particulate impurities, and then let it stand to defoam before use.

[0032] II: Preparation of Prepreg 1. Pass 1080 type electronic grade E glass fiber cloth through an impregnation tank under constant tension to fully impregnate it with the above-mentioned resin solution, and control the gap between the scraper rollers to ensure that the resin content reaches 42%; 2. The impregnated material is continuously passed through a multi-end oven for gradient temperature pre-curing. The oven temperature is set sequentially according to the conveying direction as follows: 105℃ for the first stage, 135℃ for the second stage, 155℃ for the third stage, and 170℃ for the fourth stage. The total passing time is controlled within 5 minutes. 3. Cool the pre-cured material to room temperature using a cooling roller, and then roll it up to obtain a semi-cured sheet.

[0033] 3: Lamination of copper clad laminates 1. Take 8 prepreg sheets obtained in the previous step and stack them together, covering each with an electrolytic copper foil on the top and bottom, stacking them symmetrically according to the structure of "copper foil-prepreg-copper foil"; 2. Place the assembled unit into a vacuum hot press preheated to 90℃, and use a two-stage pressurization and heating process: The first stage involves applying 6 kg / cm². 2 The pressure was increased to 175°C at a rate of 2.5°C / min, and held at this temperature for 40 minutes; In the second stage, the pressure is increased to 18 kg / cm². 2 Heat the resin to 195°C and maintain this temperature and pressure for 100 minutes to ensure complete curing. 3. After the curing process is completed, the board is slowly cooled to below 50°C at a rate of 2°C / min under pressure, and the pressure is released to obtain the copper-clad laminate.

[0034] Example 2

[0035] The difference between this embodiment and Embodiment 1 is that the amount of bisphenol A type epoxy resin used is 45 parts.

[0036] Example 3

[0037] The difference between this embodiment and Embodiment 1 is that the amount of naphthalene-type epoxy resin used is 10 parts.

[0038] Example 4

[0039] The difference between this embodiment and Embodiment 1 is that the amount of dicyandiamide used is 2 parts.

[0040] Example 5

[0041] The difference between this embodiment and Embodiment 1 is that the amount of nano-sized silica used is 5 parts.

[0042] Example 6

[0043] The difference between this embodiment and Embodiment 1 is that the amount of zinc borate used is 6 parts.

[0044] Example 7

[0045] The difference between this embodiment and Embodiment 1 is that the bisphenol A epoxy resin is replaced with an equal amount of bisphenol F epoxy resin.

[0046] Example 8

[0047] The difference between this embodiment and Embodiment 1 is that the naphthalene epoxy resin is replaced with an equal amount of biphenyl epoxy resin.

[0048] Example 9

[0049] The difference between this embodiment and Embodiment 1 is that the bismaleimide resin is replaced with an equal amount of cyanate ester resin.

[0050] Example 10

[0051] The difference between this embodiment and Embodiment 1 is that the benzoxazine resin is replaced with an equal amount of cyanate ester resin.

[0052] Example 11

[0053] The difference between this embodiment and Embodiment 1 is that the carboxyl-terminated butadiene nitrile rubber (CTBN) is replaced with an equal amount of amino-terminated butadiene nitrile rubber (ATBN).

[0054] Example 12

[0055] The difference between this embodiment and Embodiment 1 is that the phosphorus-containing phenolic resin curing agent is replaced with an equal amount of phosphorus-containing epoxy resin curing agent.

[0056] Example 13

[0057] The difference between this embodiment and Embodiment 1 is that nano-sized silica is replaced with an equal amount of nano-alumina (which requires hydrophobic treatment).

[0058] Example 14

[0059] The difference between this embodiment and Embodiment 1 is that the organically modified montmorillonite is replaced with an equal amount of organically modified kaolinite.

[0060] Example 15

[0061] The difference between this embodiment and Embodiment 1 is that the spherical silica is replaced with an equal amount of molten silica powder.

[0062] Example 16

[0063] The difference between this embodiment and Embodiment 1 is that zinc borate is replaced with an equal amount of antimony trioxide.

[0064] Comparative Example 1 The difference between this comparative example and Example 1 is that no nano-sized silica and organically modified montmorillonite are added.

[0065] Comparative Example 2 The difference between this comparative example and Example 1 is that naphthalene-type epoxy resin and bismaleimide resin are not added, and their dosage is supplemented by bisphenol A-type epoxy resin.

[0066] Comparative Example 3 The difference between this comparative example and Example 1 is that benzoxazine resin and carboxyl-terminated nitrile butadiene rubber (CTBN) are not added.

[0067] Comparative Example 4 This comparative example uses the traditional FR-4 formulation, comprising: 70 parts bisphenol A epoxy resin, 2.5 parts dicyandiamide, 0.2 parts 2-methylimidazole, 20 parts spherical silica, and acetone and other additives as in Example 1. The preparation method employs a one-time mixing method, where all components are added at once, stirred at 40°C for 1 hour, and then the viscosity is adjusted to 1800 mPa·s with acetone before filtration.

[0068] Comparative Example 5 The difference between this comparative example and Example 1 is that it uses a commercially available low-flow adhesive FR-4 formulation, with the following specific components: The preparation process is the same as in Example 1, consisting of 50 parts of bisphenol A type epoxy resin, 15 parts of phenolic epoxy resin, 2 parts of dicyandiamide, 0.2 parts of 2-methylimidazole, 5 parts of nano-sized silica, 30 parts of spherical silica, and acetone solvent and other additives.

[0069] Performance testing: The samples prepared in Examples 1-16 and Comparative Examples 1-5 were subjected to performance testing. The specific testing methods are as follows: Adhesive flow during lamination: The resin flow distance of the prepreg during the lamination process was measured according to IPC-TM-650 2.3.17 method; Peel strength: The peel strength between the copper foil and the substrate was determined according to IPC-TM-650 2.4.8 method; Glass transition temperature: Tested according to IPC TM-650 2.4.24.1 (TMA method); Solderability resistance: Tested according to IPC TM-650 2.4.13 test method; Dielectric loss Df and dielectric constant Dk: Tested according to IPC TM-650 2.5.5.13 test method; Flame retardancy: Tested according to UL94 test method; Z-axis coefficient of thermal expansion (CTE): The average coefficient of thermal expansion in the range of 50-260℃ was determined using a thermomechanical analyzer (TMA) according to method IPC-TM-650 2.4.24.

[0070] The test results are shown in Table 1.

[0071] System performance tests were conducted on the copper-clad laminates prepared in Examples 1-16 and Comparative Examples 1-5. The test items included adhesive flow rate, peel strength, glass transition temperature, thermal decomposition temperature, solderability, dielectric properties, flame retardancy rating, and Z-axis coefficient of thermal expansion.

[0072] Example 1 serves as the baseline formulation, exhibiting excellent overall performance. It controls the adhesive flow rate at a low level, resulting in high peel strength, high glass transition temperature, long solder immersion time, excellent dielectric properties, the highest level of flame retardancy, and a low coefficient of thermal expansion, thus meeting the requirements for high-performance copper-clad laminates.

[0073] Examples 2-6 changed the dosage of the main components. In Example 2, the dosage of bisphenol A epoxy resin was increased, and the performance was basically the same as in Example 1. In Example 3, the dosage of naphthalene epoxy resin was reduced, the amount of resin flow increased, the glass transition temperature decreased, and the peel strength decreased slightly. It can be seen that naphthalene epoxy resin plays an important role in improving crosslinking density, inhibiting resin flow, and improving heat resistance. In Example 4, the dosage of dicyandiamide was increased, the amount of resin flow was further reduced, the glass transition temperature was increased, but the peel strength decreased. Appropriately increasing the curing agent can improve the degree of crosslinking, but may have a slight impact on toughness. In Example 5, the dosage of nano-silica was increased, the amount of resin flow was significantly reduced, and the peel strength remained good. It can be seen that nano-silica has a strengthening effect on the thixotropic network. In Example 6, the dosage of zinc borate was increased, the coefficient of thermal expansion decreased, and the flame retardant performance remained good. Zinc borate also has a significant effect on the entire system.

[0074] Examples 7-16 verify the functional roles of each component by replacing key components. In Example 7, replacing bisphenol A epoxy resin with bisphenol F epoxy resin resulted in only minor differences in performance. In Example 8, replacing naphthalene epoxy resin with biphenyl epoxy resin increased the glass transition temperature, decreased the amount of adhesive flow, and slightly decreased the dielectric constant, indicating that biphenyl epoxy resin can also be considered as an alternative material. In Example 9, replacing BMI with cyanate ester significantly reduced the dielectric constant and dielectric loss, and slightly decreased the peel strength, showing that cyanate ester is beneficial for high-frequency performance, but lacks toughness. In Example 10, replacing benzoxazine with cyanate ester significantly reduced the peel strength and shortened the solder dip time, demonstrating that the low shrinkage characteristics of benzoxazine are crucial for interfacial bonding and thermal shock reliability, and it is difficult to completely replace it with cyanate ester. In Example 11, replacing CTBN with ATBN did not significantly change the performance, indicating that ATBN can be used as an equivalent replacement for the toughening agent. Example 12: Replacing the phosphorus-containing phenolic curing agent with a phosphorus-containing epoxy curing agent yielded the same performance, indicating that phosphorus-containing curing agents provide equivalent performance when replacing phosphorus-containing phenolic curing agents. Example 13: Replacing nano-alumina with nano-silica resulted in a slight increase in adhesive flow and a slight decrease in peel strength, indicating that nano-silica has a superior thixotropic effect. Example 14: Replacing organo-modified kaolin with organo-montmorillonite resulted in an increase in adhesive flow, indicating that the layered structure of montmorillonite is more effective for the thixotropic network. Example 15: Replacing spherical silica with fused silica powder resulted in a slight increase in the coefficient of thermal expansion, indicating that spherical silica is better at reducing the coefficient of thermal expansion. Example 16: Replacing zinc borate with antimony trioxide maintained the highest flame retardant performance, but zinc borate has better environmental performance than antimony trioxide.

[0075] Comparative Examples 1-5 further validated the key components. Comparative Example 1, lacking nano-silica and organically modified montmorillonite, resulted in a sharp increase in adhesive flow, a decrease in peel strength, and a deterioration in dielectric properties, demonstrating that the thixotropic network constructed in the formulation system of these examples is the core of controlling adhesive flow. Comparative Example 2, lacking naphthalene-type epoxy resin and BMI, saw a significant increase in adhesive flow, a marked decrease in glass transition temperature, a shortened solder dip time, and a significant decrease in peel strength, indicating the decisive role of the high-heat-resistant resin skeleton in heat resistance and anti-flow properties. Comparative Example 3, lacking benzoxazine and CTBN, showed a significant decrease in peel strength and a shortened solder dip time, but the adhesive flow remained at a low level, indicating that anti-flow properties mainly depend on the thixotropic network and modified heat-resistant resin, while bond strength and thermal shock reliability depend on the synergy of benzoxazine and CTBN. Comparative Example 4 used the traditional FR-4 formulation, resulting in high adhesive flow, low peel strength, low glass transition temperature, short solder dip time, and poor overall performance. Comparative Example 5 used commercially available low-flow adhesive tablets, which had a better flow rate than traditional products, but the flow control, bond strength, and coefficient of thermal expansion differed from the products obtained in the examples.

[0076] In summary, the construction of a physical thixotropic network using nano-silica and organically modified montmorillonite, combined with a high-crosslinking density skeleton formed by naphthalene-type epoxy resin and bismaleimide resin, effectively suppressed excessive resin flow during the pressing process. The low shrinkage characteristics of benzoxazine resin, combined with the toughening effect of carboxyl-terminated nitrile rubber, improved interlayer bond strength and thermal shock resistance. The synergistic effect of spherical silica, zinc borate, and DOPO flame retardant achieved excellent flame retardant performance and dimensional stability. The synergistic effect of these components resulted in a comprehensive balance in terms of resin flow control, bond strength, heat resistance, coefficient of thermal expansion, and dielectric properties for the copper-clad laminate.

[0077] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-flow FR-4 copper-clad laminate, characterized in that, The copper-clad laminate is formed by impregnating a reinforcing material with a resin composition and then curing it. The resin composition comprises, by weight, the following components: 40-70 parts epoxy resin, 15-35 parts high-performance resin, 2-10 parts latent curing agent; 3-8 parts rheology control agent, 5-20 parts toughening agent, 20-40 parts filler, 1-3 parts flame retardant, 0.5-1.5 parts silane coupling agent, and optional additives.

2. The low-flow FR-4 copper-clad laminate according to claim 1, characterized in that, The epoxy resin includes bisphenol A type epoxy resin and / or bisphenol F type epoxy resin, as well as naphthalene type epoxy resin.

3. The low-flow FR-4 copper-clad laminate according to claim 1, characterized in that, The high-performance resin is selected from at least one of biphenyl-type epoxy resin, bismaleimide resin, benzoxazine resin, and cyanate ester resin.

4. The low-flow FR-4 copper-clad laminate according to claim 1, characterized in that, The latent curing agent is dicyandiamide and / or a phosphorus-containing phenolic resin curing agent; the rheology control agent is nano-sized silica and / or organically modified montmorillonite; the toughening agent is carboxyl-terminated butadiene-acrylonitrile rubber and / or amino-terminated butadiene-acrylonitrile rubber.

5. The low-flow FR-4 copper-clad laminate according to claim 1, characterized in that, The filler comprises spherical silica and / or molten silica powder; the flame retardant comprises zinc borate and / or a combination of antimony trioxide and DOPO flame retardant; the silane coupling agent is KH-560 type silane coupling agent.

6. The low-flow FR-4 copper-clad laminate according to claim 1, characterized in that, The additive is selected from at least one of acetone, butanone, cyclohexanone, toluene, xylene, and ethylene glycol monomethyl ether.

7. The low-flow FR-4 copper-clad laminate according to claim 2, characterized in that, The resin composition comprises, by weight, the following: 40-45 parts of bisphenol A type epoxy resin, 10-15 parts of naphthalene type epoxy resin, 10-15 parts of bismaleimide resin, 5-10 parts of benzoxazine resin, 2-5 parts of phosphorus-containing phenolic resin curing agent, 1-2 parts of dicyandiamide, 0.5-1 part of 2-methylimidazole, 2-5 parts of nano-sized silica, 1-3 parts of organically modified montmorillonite, 3-8 parts of carboxyl-terminated butadiene-acrylonitrile rubber, 20-30 parts of spherical silica, 3-6 parts of zinc borate, 1-3 parts of DOPO flame retardant, and 0.5-1.5 parts of KH-560 type silane coupling agent.

8. A method for preparing a low-flow FR-4 copper-clad laminate as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) Preparation of resin solution: Epoxy resin, high performance resin, toughening agent and latent curing agent are mixed and heated and stirred until uniform; after cooling, rheology control agent, filler and some flame retardant are added and dispersed at high speed; After cooling down again, add the remaining flame retardant, silane coupling agent and additives, stir evenly, adjust the solution viscosity, filter and let stand to obtain resin solution; (2) Preparation of semi-cured sheet: The reinforcing material is impregnated in the above-obtained resin solution, pre-cured by heating in a multi-stage oven, cooled and rolled up to obtain a semi-cured sheet; (3) Lamination of copper-clad laminate: Multiple prepreg sheets are stacked together, copper foil is applied on the top and bottom, and the copper-clad laminate is obtained by cooling and depressurizing after being pressed and heated in sections by a vacuum hot press.

9. The method for preparing the low-flow FR-4 copper-clad laminate according to claim 8, characterized in that, In step (1), the heating and stirring temperature is 70-90℃, the stirring time is 30-60 min, the high-speed dispersion speed is 1000-1500 rpm, the time is 60-90 min, and the viscosity adjustment is 1500-2000 mPa·s at 25℃.

10. The method for preparing FR-4 copper-clad laminate according to claim 8, characterized in that, In step (2), the temperatures of the multi-stage oven are 100-110℃, 130-140℃, 150-160℃, and 165-175℃ respectively, with a total throughput of 4-6 minutes and a glue content of 40-45 wt%. In step (3), the segmented pressurization is a two-stage pressing process, with the first stage pressure being 5-8 kg / cm². 2 Heat to 170-180℃ and hold for 30-50 minutes; the pressure in the second stage is 15-20 kg / cm². 2 Heat to 190-200℃, hold for 90-110 minutes, and cool at a rate of 1.5-2.5℃ / min.

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