A method for preparing a high-toughness, anti-bending integrated circuit board composite substrate

Abstract

The application discloses a kind of high toughness anti-bending integrated circuit board composite substrate preparation methods, comprising the following steps: step one, reinforcing fiber is carried out multistage surface treatment;Step two, prepare thermoplastic elastomer toughening resin matrix;Step three, adopt function gradient coating process to construct transition layer on the surface of reinforcing fiber, and the content of polyimide in transition layer changes along the thickness direction gradient;Step four, toughening resin system is impregnated with the reinforcing fiber after processing, and pre-preg is prepared by hot pressing molding;Step five, after curing treatment of pre-preg by stepwise heating, eliminate internal residual stress.The application significantly improves the fracture toughness and anti-bending fatigue performance of the composite substrate through the synergistic effect of function gradient transition layer and thermoplastic elastomer micro-phase separation toughening, while ensuring the heat resistance and dimensional stability of the substrate, suitable for the preparation of high-density interconnection printed circuit board.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit board material technology, specifically relating to a method for preparing a high-toughness, bending-resistant composite substrate for integrated circuit boards. Background Technology

[0002] Currently, most integrated circuit board substrates are made by combining epoxy resin or polyimide resin with glass fiber cloth.

[0003] When traditional materials are repeatedly bent or impacted, the resin matrix is ​​prone to developing microcracks, which can lead to the separation of fibers from the resin interface. Due to the curing shrinkage of the resin and the differences in the coefficients of thermal expansion of different materials, large internal stresses remain inside the board, making the circuit board highly susceptible to warping, deformation, or even cracking during processing, soldering, or subsequent use.

[0004] In addition, existing toughening methods often involve introducing rubber particles. While this method can slightly improve toughness, it leads to a significant decrease in the glass transition temperature and dimensional stability of the material, making it difficult to meet the stringent requirements of high-density interconnect circuits for the overall performance of the substrate. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate, in order to solve the technical problems that existing integrated circuit board substrates are prone to warping and even cracking, and that the materials have low glass transition temperature and dimensional stability, making it difficult to meet the comprehensive performance requirements of high-density interconnect circuits for the substrate.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate includes the following steps:

[0008] Step 1: Perform multi-stage surface treatment on the reinforcing fibers: First, activate the surface of the reinforcing fibers using plasma treatment equipment with a power of 50W to 300W and a treatment time of 30s to 300s, in an atmosphere of one or more of oxygen, nitrogen, or argon; then immerse the plasma-treated reinforcing fibers in a coupling agent solution for 5min to 60min, with a coupling agent concentration of 0.5wt% to 5wt%, and dry them at 60℃ to 120℃.

[0009] Step 2, Preparation of thermoplastic elastomer toughening resin matrix: The thermoplastic elastomer is heated to a molten state and mixed with epoxy resin at a mass ratio of 5wt% to 30wt%. The mixture is sheared and blended at 150℃ to 200℃ for 10min to 60min to form a uniformly dispersed toughening resin system. The thermoplastic elastomer is selected from one or more of styrene-ethylene-butene-styrene block copolymer, styrene-butadiene-styrene block copolymer, and polyurethane elastomer.

[0010] Step 3: Construct a transition layer on the surface of the reinforcing fiber using a functional gradient coating process: Apply a polyimide precursor solution to the surface of the reinforcing fiber in a multilayer coating manner, with each layer having a thickness of 0.5 μm to 5 μm and the number of coating layers ranging from 3 to 10. Adjacent layers are subjected to gradient drying at 80°C to 150°C, so that the polyimide content in the transition layer increases gradually along the thickness direction, with the gradient ranging from 5 wt% to 50 wt%.

[0011] Step 4: The toughening resin system and the treated reinforcing fiber are composite impregnated at an impregnation temperature of 80°C to 150°C, an impregnation time of 10 min to 120 min, and an impregnation pressure of 0.1 MPa to 1.0 MPa. The prepreg is then obtained by hot pressing at an temperature of 120°C to 200°C, a hot pressing pressure of 1 MPa to 10 MPa, and a holding time of 30 min to 180 min.

[0012] Step 5: Perform a stepped heating and curing treatment on the prepreg: In the first stage, heat the prepreg to 120°C to 160°C at a heating rate of 1°C / min to 5°C / min and hold for 1 to 3 hours; in the second stage, heat the prepreg to 180°C to 220°C at a heating rate of 0.5°C / min to 3°C / min and hold for 2 to 5 hours; after curing, cool the prepreg to room temperature at a rate of 5°C / min to 15°C / min.

[0013] The above technical solution introduces active functional groups on the fiber surface through plasma activation, significantly improving surface energy and wettability. Combined with the synergistic effect of the coupling agent solution, a strong interfacial bonding layer is formed on the fiber surface. The shear blending of thermoplastic elastomer and epoxy resin allows the elastomer to be uniformly distributed in the matrix in the form of discrete particles, forming a microphase separation structure. When cracks extend to the elastomer particles, deformation and interfacial debonding occur, thereby absorbing a large amount of fracture energy. The transition layer constructed by multi-layer gradient coating allows the polyimide content to change continuously along the thickness direction, establishing a smooth transition region of mechanical properties between the fiber and the matrix, effectively eliminating modulus abrupt changes and stress concentration at the interface. Stepped temperature curing allows the crosslinking reaction to proceed fully in stages, avoiding thermal stress concentration and microcrack initiation caused by one-time high temperature. Ultimately, the composite substrate achieves a comprehensive improvement in fracture toughness, bending fatigue life, and dimensional stability.

[0014] As a preferred embodiment of the present invention, in step one, the reinforcing fiber is selected from one or more of glass fiber, carbon fiber, and aramid fiber, with a fiber diameter of 5μm to 20μm and a single filament strength of not less than 2GPa. Glass fiber, carbon fiber, and aramid fiber each have their own characteristics. Glass fiber has low cost and excellent electrical insulation properties, carbon fiber has high specific strength and high modulus, and aramid fiber has both high toughness and impact resistance. Limiting the fiber diameter within a reasonable range ensures the fiber's own load-bearing capacity and flexibility, while avoiding excessive thickness of the substrate and decreased bending performance caused by excessively thick fibers. At the same time, it ensures that the single filament strength reaches a high level, allowing the reinforcing fiber to fully play its load-bearing role in the composite substrate, effectively improving the overall mechanical strength and bending resistance of the composite substrate.

[0015] As a preferred embodiment of the present invention, the coupling agent in step one is selected from one or more of silane coupling agents, titanate coupling agents, and aluminate coupling agents, preferably γ-methacryloyloxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane. Different types of coupling agents are suitable for different resin matrices and fiber surface chemical environments. Silane coupling agents have excellent coupling effects on silicon-containing fibers and polar resin systems, titanate coupling agents have good compatibility with inorganic fillers such as calcium carbonate, and aluminate coupling agents reduce system viscosity while improving filler dispersibility. Preferably, a silane coupling agent with a specific structure can form a dense organic modified layer on the fiber surface. One end of the silane coupling agent undergoes a condensation reaction with the hydroxyl groups on the fiber surface to form a covalent bond, while the organic functional groups carried at the other end chemically bond or physically entangle with the epoxy resin, thereby significantly improving the interfacial bonding strength and interfacial shear strength between the fiber and the resin.

[0016] In a preferred embodiment of the present invention, the number-average molecular weight of the thermoplastic elastomer in step two is 50,000 g / mol to 300,000 g / mol, forming a microphase separation structure with a particle size of 0.1 μm to 10 μm in the toughening resin system. The molecular weight of the thermoplastic elastomer directly affects its dispersion morphology and toughening efficiency in the epoxy resin matrix. If the molecular weight is too low, the elastomer will find it difficult to form a stable microphase separation structure, resulting in limited toughening effect. If the molecular weight is too high, the processing viscosity will increase sharply, making it difficult to achieve uniform dispersion. By controlling the size of the elastomer particles to the submicron to micron level, it can both act as a stress concentration point to induce energy dissipation mechanisms such as crazes and shear bands in the matrix, and avoid becoming a source of defects inside the material due to excessively large particles. This microphase separation structure plays a bridging role in the crack tip region, promoting fiber pull-out and crack deflection, significantly improving the fracture toughness of the material.

[0017] In a preferred embodiment of the present invention, the polyimide precursor solution in step three is a polyamic acid solution with a solid content of 10wt% to 35wt%, and the solvent is selected from one or more of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide. The solid content of polyamic acid, as a polyimide precursor, determines the thickness and density of each coating layer. If the solid content is too low, the single-layer film will be too thin, requiring too many coating passes to achieve the target thickness; if the solid content is too high, the solution viscosity will be too high, the coating uniformity will be poor, and cracks will easily occur during the drying process. Using an organic solvent of a specific polarity ensures both the complete dissolution and stable storage of the polyamic acid, and allows it to evaporate smoothly without residue during the subsequent imidization process, ultimately forming a dense, defect-free polyimide gradient transition layer. This transition layer possesses both high heat resistance and good adhesion to the fiber and resin matrix.

[0018] As a preferred embodiment of the present invention, the total thickness of the functionally graded transition layer in step three is 5 μm to 50 μm, and the interfacial shear strength between the transition layer and the reinforcing fiber is not less than 40 MPa. The total thickness of the transition layer determines the size of the stress buffer region. An excessively thin transition layer cannot effectively alleviate the modulus gradient change, while an excessively thick layer occupies too much volume fraction and reduces the fiber load-bearing efficiency. By gradually increasing the polyimide content along the thickness direction, the transition layer gradually transitions from high flexibility near the fiber side to high rigidity near the matrix side, forming a continuous mechanical property transition in the interfacial region, which significantly reduces the stress concentration factor at the interface. The improvement in interfacial shear strength means that the load transfer efficiency between the fiber and the matrix is ​​higher, and the fiber can more effectively bear external forces under bending and impact loads, thereby reducing the occurrence of interfacial debonding and delamination.

[0019] As a preferred embodiment of the present invention, the toughening resin system in step four further includes a curing agent, which is selected from one or more of diaminodiphenylmethane, diaminodiphenyl sulfone, and m-phenylenediamine. The equivalence ratio of the curing agent to the epoxy resin is 0.8:1 to 1.2:1. The choice of curing agent directly determines the structure and density of the epoxy resin crosslinking network. The crosslinking network formed by aromatic diamine curing agents has excellent heat resistance and chemical stability, making it suitable for high-performance circuit board substrates. By controlling the equivalence ratio of the curing agent to the epoxy resin within a range close to the stoichiometric ratio, it is possible to ensure sufficient crosslinking of the epoxy resin, obtain a high glass transition temperature and mechanical strength, and avoid system embrittlement or residual small molecules affecting the electrical insulation performance of the material due to excessive curing agent. Thus, the composite substrate obtains high toughness while maintaining the necessary rigidity and heat resistance.

[0020] As a preferred embodiment of the present invention, the toughening resin system in step four further includes inorganic nanofillers. The nanofillers are selected from one or more of nano-silica, nano-alumina, and nano-montmorillonite, with an addition amount of 1wt% to 10wt% and a particle size of 10nm to 200nm. Due to their extremely small particle size and large specific surface area, inorganic nanofillers can play multiple roles in the resin matrix. Nano-silica can improve the hardness and wear resistance of the matrix and induce crack deflection and bridging during crack propagation. Nano-alumina can improve the thermal conductivity and high-temperature resistance of the matrix. Nano-montmorillonite forms a nanoscale barrier in the matrix through the exfoliation and intercalation of its layered structure, hindering crack propagation and gas permeation. The addition of nanofillers can also produce a synergistic toughening effect with thermoplastic elastomer particles, forming a denser constraint layer around the elastomer particles, further improving fracture toughness.

[0021] As a preferred embodiment of the present invention, the curing treatment after the stepwise heating in step five is carried out in a vacuum environment or under inert gas protection, with a vacuum degree not exceeding 100 Pa or an inert gas flow rate of 5 mL / min to 50 mL / min. Curing under vacuum or inert gas protection effectively eliminates dissolved oxygen and air bubbles in the curing system, preventing oxygen from inhibiting the curing reaction of epoxy resin and its adverse effects on the imidization process of polyimide. The vacuum environment also promotes the full removal of volatile components and small molecule byproducts from the resin matrix, reducing micropores and defects inside the cured material. The continuous flow of inert gas maintains the chemical inertness of the curing atmosphere, preventing oxidative degradation of the material surface at high temperatures, thereby ensuring that the composite substrate obtains a uniform, dense, and defect-free cross-linked structure, improving electrical insulation performance and long-term reliability.

[0022] As a preferred embodiment of the present invention, step six is ​​further included: after curing, the composite substrate is subjected to surface finishing treatment, including grinding and polishing until the surface roughness Ra does not exceed 0.5 μm, and then plasma cleaning is performed to remove surface organic contaminants. The grinding and polishing treatment removes the unevenness and burrs on the surface of the cured substrate, reducing the surface roughness to a low level, providing a flat base for the fine wiring of subsequent circuit patterns, and reducing the possibility of surface micro-defects acting as stress concentration sources; plasma cleaning further removes residual organic contaminants and weak interface layers on the surface, increases surface energy, and improves the bonding force between the metal and the substrate during subsequent copper foil lamination or circuit fabrication, thereby improving the overall interlayer bonding strength and reliability of the circuit board.

[0023] As a preferred embodiment of the present invention, the plasma treatment in step one employs atmospheric pressure plasma or low-temperature radio frequency plasma. The plasma treatment atmosphere may also contain carbon tetrafluoride, with a volume percentage of 0% to 20%. Atmospheric pressure plasma can achieve fiber surface treatment without vacuum equipment, making it suitable for continuous production processes. Low-temperature radio frequency plasma can perform gentle and uniform activation treatment on fibers at lower temperatures, avoiding damage to the intrinsic properties of fibers from high temperatures. Introducing fluorine-containing gas into the plasma atmosphere can introduce fluorine elements into the fiber surface, giving the fiber surface certain hydrophobicity and flame retardancy. At the same time, the introduction of fluorine elements can also adjust the interfacial polarity and adhesion strength between the fiber and the resin, providing an additional controllable dimension for interface optimization under different application scenarios, making the interfacial bonding between the fiber and the resin matrix more designable.

[0024] This invention also provides a high-toughness, high-bending-resistance integrated circuit board composite substrate prepared by the above-mentioned high-toughness, high-bending-resistance integrated circuit board composite substrate preparation method. The composite substrate has a fracture toughness (KIC) of not less than 1.5 MPa·m¹ / ², a three-point bending strength of not less than 500 MPa, a resistivity change rate of not more than 10% after 1000 180° bends, and a glass transition temperature of not less than 180°. Through the synergistic effect of the aforementioned preparation methods, the obtained composite substrate exhibits excellent fracture toughness, capable of withstanding large crack tip stress without catastrophic fracture; the three-point bending strength meets the mechanical load-bearing requirements of high-density interconnect circuit boards, and is not prone to bending damage during assembly and use; the resistivity change rate after repeated bending is extremely small, indicating that the internal conductive lines maintain a good bonding state with the substrate, without crack propagation or line breakage, and possesses excellent bending fatigue reliability; the glass transition temperature is maintained at a high level, ensuring that the circuit board does not soften or deform under high-temperature soldering processes and high-temperature operating environments, meeting the requirements of high-temperature processes such as lead-free soldering.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The composite substrate prepared using this method exhibits comprehensively optimized overall mechanical properties. The uniformly dispersed elastic microregions within the resin matrix demonstrate excellent energy absorption capacity under bending loads, effectively suppressing the initiation and propagation of microcracks, thus preventing brittle fracture under repeated bending conditions. The functionally graded transition layer breaks down the traditional clear physical boundaries between layers, greatly alleviating stress concentration caused by abrupt changes in material composition, significantly enhancing the stability of interlayer bonding, and preventing delamination under thermal cycling or mechanical impact. After special surface activation and chemical grafting treatment, the reinforcing fibers exhibit significantly improved interfacial wettability and mechanical interlocking strength with the resin matrix, ensuring efficient load transfer between the fibers and the matrix and fully leveraging the load-bearing capacity of the reinforcing fibers. Combined with a specific stepped heating and cooling heat treatment regime, the residual thermal stress within the material is fully released, which not only reduces the warping tendency of the substrate but also improves its dimensional stability under different ambient temperatures. Furthermore, this process does not rely solely on the large-scale addition of a single additive. Instead, through the synergistic cooperation of multiple mechanisms, it significantly improves toughness and bending resistance while maintaining the original electrical insulation and heat resistance properties of the substrate, thus extending the service life of the integrated circuit board under complex working conditions. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only examples of embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart of an embodiment of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0030] See Figure 1 The present invention provides the following embodiments and comparative examples.

[0031] Example 1:

[0032] Step 1: Multi-stage surface treatment of reinforcing fibers: E-type glass fiber roving with an average diameter of 10 μm was selected as the reinforcing fiber. The fiber surface was activated using an atmospheric pressure plasma treatment device. The treatment gas was a mixture of oxygen and argon (volume ratio 1:1), the treatment power was 150 W, and the treatment time was 120 s. The plasma-treated fiber was then immersed in a 2 wt% γ-methacryloyloxypropyltrimethoxysilane ethanol solution at room temperature for 30 min, and then dried in an 80℃ oven for 2 h.

[0033] Step 2, Preparation of the thermoplastic elastomer toughening resin matrix: Styrene-ethylene-butene-styrene block copolymer (SEBS) particles with a number average molecular weight of 150,000 g / mol were melted at 180°C. The SEBS melt was added to bisphenol A type epoxy resin (epoxy equivalent 185 g / eq) at a mass ratio of SEBS to epoxy resin of 15:85. The mixture was mechanically sheared and blended at 500 rpm for 30 minutes at 180°C to form a uniformly dispersed toughening resin system. Subsequently, diaminodiphenyl sulfone curing agent was added at a curing agent-to-epoxy resin equivalent ratio of 1:1. After thorough stirring, the mixture was degassed under vacuum.

[0034] Step 3, Construction of the functionally graded transition layer: A 20 wt% polyamic acid N-methylpyrrolidone solution was prepared as a polyimide precursor. Multiple layers were coated onto the surface-treated glass fiber using precision coating equipment. Specifically: the first layer had a polyamic acid concentration of 5 wt% and a coating thickness of 1 μm; the second layer had a concentration of 15 wt% and a coating thickness of 1.5 μm; and the third layer had a concentration of 30 wt% and a coating thickness of 2 μm. Each layer was dried at 120 °C for 15 min after coating, and finally imidized at 180 °C for 30 min to form a gradient transition layer with a total thickness of approximately 4.5 μm.

[0035] Step four, composite impregnation and hot pressing: The glass fibers coated with the transition layer are impregnated in the toughening resin system at an impregnation temperature of 120℃ for 60 minutes and an impregnation pressure of 0.5 MPa. After impregnation, the fiber bundles are neatly arranged and placed in a hot press, where they are held at 160℃ and 5 MPa for 90 minutes to obtain the prepreg board. The fiber volume fraction is controlled between 55% and 60%.

[0036] Step 5, Curing after stepped heating: Place the prepreg board in a programmable temperature-controlled oven. In the first stage, the temperature is increased from room temperature to 140°C at a rate of 2°C / min and held for 2 hours. In the second stage, the temperature is increased from 140°C to 200°C at a rate of 1°C / min and held for 3 hours. After curing, the board is naturally cooled to room temperature at a rate of 10°C / min to obtain the final composite substrate.

[0037] The composite substrate prepared in this embodiment has a fracture toughness (KIC) of 2.1 MPa·m¹ / ², a three-point bending strength of 612 MPa, a glass transition temperature of 198 °C, and a resistivity change rate of 4.3% after 1000 180° bends.

[0038] Example 2:

[0039] The difference from Example 1 is as follows: in step one, the plasma treatment power is 200W and the treatment time is 180s; in step two, the thermoplastic elastomer is replaced with a polyurethane elastomer (number average molecular weight 120,000 g / mol) at an addition ratio of 20wt%; in step three, the transition layer is replaced with a 5-layer coating with a concentration gradient of 5wt%, 12wt%, 20wt%, 30wt%, and 40wt%, with each layer having a thickness of 1μm to 2μm and a total thickness of approximately 7.5μm. All other process parameters are the same as in Example 1.

[0040] The composite substrate prepared in this embodiment has a fracture toughness (KIC) of 2.3 MPa·m¹ / ², a three-point bending strength of 635 MPa, a glass transition temperature of 195 °C, and a resistivity change rate of 3.7% after 1000 180° bends.

[0041] Example 3:

[0042] The difference from Example 1 is as follows: In step one, the reinforcing fiber is replaced with T300 grade carbon fiber (7μm in diameter), the plasma treatment atmosphere is nitrogen, the treatment power is 250W, and the treatment time is 90s; in step two, SEBS (10wt%) and nano-silica (3wt%, particle size 50nm) are added simultaneously; in step three, the transition layer is a 4-layer coating with polyimide content gradients of 8wt%, 18wt%, 28wt%, and 40wt%; in step five, the heating rate in the first stage is 3℃ / min, and the heating rate in the second stage is 1.5℃ / min. All other process parameters are the same as in Example 1.

[0043] The composite substrate prepared in this embodiment has a fracture toughness (KIC) of 2.5 MPa·m¹ / ², a three-point bending strength of 721 MPa, a glass transition temperature of 205 °C, and a resistivity change rate of 2.8% after 1000 180° bends.

[0044] Comparative Example 1:

[0045] The traditional epoxy resin / glass fiber composite material preparation process was adopted. The reinforcing fibers were only impregnated with a 2wt% silane coupling agent ethanol solution for 30 minutes, without plasma treatment, without constructing a functionally graded transition layer, and without adding thermoplastic elastomer toughening agents. The curing process involved a one-time heating to 180℃ and holding for 4 hours.

[0046] Tests showed that the fracture toughness (KIC) of this comparative composite substrate was 0.9 MPa·m¹ / ², the three-point bending strength was 480 MPa, and the electrical resistance change rate after 1000 180° bends was 28.5%, with obvious delamination and microcracks appearing in the material.

[0047] Comparative Example 2:

[0048] The difference from Example 1 is that step three, the construction of the functional gradient transition layer, is omitted; only steps one, two, four, and five are performed. That is, after the reinforcing fibers are treated with plasma and a coupling agent, they are directly composited and cured with SEBS toughened epoxy resin.

[0049] Tests showed that the fracture toughness (KIC) of the comparative example composite substrate was 1.4 MPa·m¹ / ², the three-point bending strength was 540 MPa, and the resistivity change rate after 1000 180° bends was 12.6%. The performance was better than Comparative Example 1, but significantly lower than Example 1, indicating that the functionally graded transition layer plays a crucial role in improving interfacial toughness.

[0050] Comparative Example 3:

[0051] The difference from Example 1 is that step two, the thermoplastic elastomer toughening, is omitted; only pure epoxy resin is used in combination with fully treated reinforcing fibers. Specifically, plasma treatment, coupling agent treatment, and gradient transition layer construction are performed, but SEBS is not added to the resin matrix.

[0052] Tests showed that the fracture toughness (KIC) of the comparative example composite substrate was 1.3 MPa·m¹ / ², the three-point bending strength was 560 MPa, and the resistivity change rate after 1000 180° bends was 14.2%. These performance characteristics are superior to Comparative Example 1 but inferior to Example 1, demonstrating that the toughening effect of thermoplastic elastomers on the matrix toughness is indispensable.

[0053] Performance Comparison Summary Table:

[0054] Example 1 2.1 612 198 4.3 none Example 2 2.3 635 195 3.7 none Example 3 2.5 721 205 2.8 none Comparative Example 1 0.9 480 175 28.5 obvious Comparative Example 2 1.4 540 190 12.6 slight Comparative Example 3 1.3 560 188 14.2 slight

[0055] As can be seen from the above comparative data, the overall performance of Examples 1 to 3 of the present invention is significantly better than that of the traditional process (Comparative Example 1), and the effect produced by the synergistic effect of the functional gradient transition layer and the thermoplastic elastomer toughening (Example 1) far exceeds the simple superposition of a single modification scheme (the sum of the performance increments of Comparative Example 2 and Comparative Example 3 is still less than the increment of Example 1).

[0056] Summary table of key process parameter ranges:

[0057] Plasma processing power 50W~300W plasma processing time 30s~300s Coupling agent solution concentration 0.5wt%~5wt% thermoplastic elastomer addition amount 5wt%~30wt% Thermoplastic elastomer molecular weight 50,000~300,000 g / mol Elastomer microparticle size 0.1μm~10μm Transition layer single layer thickness 0.5μm~5μm Total thickness of transition layer 5μm~50μm PI content gradient range 5wt%~50wt% Immersion temperature 80℃～150℃ Hot pressing temperature 120℃～200℃ First stage curing temperature 120℃～160℃ Second stage curing temperature 180℃～220℃ fracture toughness KIC ≥1.5MPa·m¹ / ² Three-point bending strength ≥500MPa Rate of change of resistance after 1000 bends ≤10% Glass transition temperature Tg ≥180℃

[0058] In summary, the preparation method of this invention solves the above problems by constructing a multi-scale synergistic enhancement system.

[0059] First, the reinforcing fiber undergoes multi-stage activation treatment. Plasma etching is used to increase the surface roughness of the fiber and introduce active functional groups. Then, with the help of the molecular bridging effect of the coupling agent, the interfacial bonding force between the fiber and the resin matrix is ​​significantly improved, so that stress can be effectively transferred from the matrix to the high-strength fiber.

[0060] Secondly, thermoplastic elastomers are introduced into the resin system, utilizing their unique microphase separation structure to form dispersed elastic microregions within the continuous resin phase. When the material is subjected to external bending forces, these microregions can absorb impact energy by generating deformation and force the crack propagation path to deflect, thereby hindering the direct penetration of cracks.

[0061] Most importantly, the functionally graded transition layer has a resin content that varies continuously along the thickness direction, eliminating abrupt changes in physical properties at a single interface and allowing stress to transition smoothly between layers, significantly reducing interlayer shear stress. Combined with a stepped heating and cooling curing process, this further releases the residual thermal stress generated during molding, ultimately achieving a simultaneous improvement in the overall toughness and reliability of the board.

[0062] During use, thermoplastic elastomers and functional additives are added to the resin precursor according to the specified ratio, and a uniform modified adhesive solution is obtained by mechanical stirring or ultrasonic dispersion. Reinforcing fibers treated with plasma and coupling agents are then immersed in the adhesive solution, and the pulling speed is controlled to obtain the preset resin content.

[0063] In the lamination process, a prepared gradient transition layer slurry is coated between two layers of fiber prepreg. The solid content of this slurry needs to be precisely controlled to achieve a gradient distribution. The laminated board is then fed into a hot press, where a stepped heating program is implemented. First, the solvent evaporates and preliminary gelation occurs at a lower temperature, then the temperature is increased to complete deep cross-linking and curing. Finally, the board is cooled to room temperature at a controlled, slow rate. After the cured board has cooled and set, surface finishing is performed to remove burrs and irregular edges. Finally, it is cut into integrated circuit board substrates of the required specifications, ready for subsequent circuit fabrication processes.

[0064] The above description illustrates the basic principles of the present invention. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The above embodiments and descriptions in the specification are only for illustrating the principles of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and scope of the present invention without departing from the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate, characterized in that... Includes the following steps: Step 1: Perform multi-stage surface treatment on the reinforcing fibers: First, activate the surface of the reinforcing fibers using plasma treatment equipment with a power of 50W to 300W and a treatment time of 30s to 300s, in an atmosphere of one or more of oxygen, nitrogen, or argon; then immerse the plasma-treated reinforcing fibers in a coupling agent solution for 5min to 60min, with a coupling agent concentration of 0.5wt% to 5wt%, and dry them at 60℃ to 120℃. Step 2, Preparation of thermoplastic elastomer toughening resin matrix: The thermoplastic elastomer is heated to a molten state and mixed with epoxy resin at a mass ratio of 5wt% to 30wt%. The mixture is sheared and blended at 150℃ to 200℃ for 10min to 60min to form a uniformly dispersed toughening resin system. The thermoplastic elastomer is selected from one or more of styrene-ethylene-butene-styrene block copolymer, styrene-butadiene-styrene block copolymer, and polyurethane elastomer. Step 3: Construct a transition layer on the surface of the reinforcing fiber using a functional gradient coating process: Apply a polyimide precursor solution to the surface of the reinforcing fiber in a multilayer coating manner, with each layer having a thickness of 0.5 μm to 5 μm and the number of coating layers ranging from 3 to 10. Adjacent layers are subjected to gradient drying at 80°C to 150°C, so that the polyimide content in the transition layer increases gradually along the thickness direction, with the gradient ranging from 5 wt% to 50 wt%. Step 4: The toughening resin system and the treated reinforcing fiber are composite impregnated at an impregnation temperature of 80°C to 150°C, an impregnation time of 10 min to 120 min, and an impregnation pressure of 0.1 MPa to 1.0 MPa. The prepreg is then obtained by hot pressing at an temperature of 120°C to 200°C, a hot pressing pressure of 1 MPa to 10 MPa, and a holding time of 30 min to 180 min. Step 5: Perform a stepped heating and curing treatment on the prepreg: In the first stage, heat the prepreg to 120°C to 160°C at a heating rate of 1°C / min to 5°C / min and hold for 1 to 3 hours; in the second stage, heat the prepreg to 180°C to 220°C at a heating rate of 0.5°C / min to 3°C / min and hold for 2 to 5 hours; after curing, cool the prepreg to room temperature at a rate of 5°C / min to 15°C / min.

2. The method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate according to claim 1, characterized in that: The reinforcing fiber mentioned in step one is selected from one or more of glass fiber, carbon fiber, and aramid fiber, with a fiber diameter of 5μm to 20μm and a single filament strength of not less than 2GPa.

3. The method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate according to claim 1, characterized in that: The coupling agent mentioned in step one is selected from one or more of silane coupling agents, titanate coupling agents, and aluminate coupling agents, preferably γ-methacryloyloxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane.

4. The method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate according to claim 1, characterized in that: The thermoplastic elastomer described in step two has a number-average molecular weight of 50,000 g / mol to 300,000 g / mol, forming a microphase separation structure with a particle size of 0.1 μm to 10 μm in the toughening resin system.

5. The method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate according to claim 1, characterized in that: The polyimide precursor solution mentioned in step three is a polyamic acid solution with a solid content of 10wt% to 35wt%, and the solvent is selected from one or more of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

6. The method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate according to claim 1, characterized in that: The total thickness of the functionally graded transition layer in step three is 5 μm to 50 μm, and the interfacial shear strength between the transition layer and the reinforcing fiber is not less than 40 MPa.

7. The method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate according to claim 1, characterized in that: The toughening resin system described in step four also includes a curing agent, which is selected from one or more of diaminodiphenylmethane, diaminodiphenyl sulfone, and m-phenylenediamine. The equivalent ratio of the curing agent to the epoxy resin is 0.8:1 to 1.2:

1.

8. The method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate according to claim 1, characterized in that: The toughening resin system described in step four also includes inorganic nanofillers, which are selected from one or more of nano silica, nano alumina, and nano montmorillonite, with an addition amount of 1 wt% to 10 wt% and a particle size of 10 nm to 200 nm.

9. The method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate according to claim 1, characterized in that: The step-by-step heating and curing process described in step five is carried out in a vacuum environment or under inert gas protection, with a vacuum degree not exceeding 100 Pa or an inert gas flow rate of 5 mL / min to 50 mL / min.

10. The method for preparing a high-toughness, bend-resistant integrated circuit board composite substrate according to claim 1, characterized in that: It also includes step six: after curing, the composite substrate is surface finished, including grinding and polishing until the surface roughness Ra does not exceed 0.5μm, and then plasma cleaning is performed to remove surface organic contaminants.

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