Magnetic fibers, methods of making and using the same

Abstract

The application provides a magnetic fiber, which comprises a ceramic matrix and magnetic particles dispersed in the ceramic matrix, the diameter of the magnetic fiber is 300-700 nm, the length is 3-15 mu m, and the length-diameter ratio is 10-50. The application also provides a preparation method of the magnetic fiber and an application of the magnetic fiber. The application directly and uniformly disperses the magnetic particles in the ceramic matrix, so that a high-dielectric magnetic nanofiber with uniform structure and excellent morphology is obtained, which is beneficial to obtaining a composite film for embedding, and the dielectric constant (Dk is up to 54) is significantly improved compared with the dielectric constant of traditional embedding materials.

Description

Technical Field

[0001] This application relates to a magnetic fiber, a method for preparing the magnetic fiber, a composite film using the magnetic fiber and a method for preparing the composite film, a circuit board using the composite film, and an electronic device using the circuit board. Background Technology

[0002] With the rapid development of electronic information technology, electronic products are becoming increasingly multifunctional, miniaturized, and highly integrated. The printed circuit boards (PCBs) used in these products also need to become more precise in their designs and thinner, multilayered. Therefore, it is becoming increasingly difficult to arrange and install a large number of electronic components on the PCB surface. To save PCB space, a large number of embeddable passive electronic components (capacitors and resistors, etc.) are typically embedded inside the PCB. Embedding capacitors is a technique that replaces the discrete capacitors on the PCB by embedding capacitor material (i.e., embedded capacitor material) inside the PCB. Embedding capacitors can shorten the wiring length between electronic components, increase the mounting density of electronic components on the PCB surface, and improve the utilization rate of the PCB. Furthermore, shortening the wiring between electronic components can improve electrical characteristics, reduce the number of solder joints on the PCB surface, reduce the introduced inductance, and thus reduce the impedance of packaged devices. In addition, reducing the number of solder joints on the PCB surface can improve the reliability of packaged devices.

[0003] Existing embedded capacitor materials face at least the following problems: the capacitance density (capacitance value / area) of embedded capacitor materials is very low, which can only be used for the production of low-end capacitors. They cannot meet the miniaturization of embedded capacitors, and thus cannot meet the current development needs of thin and multi-layer PCB boards. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above defects, it is necessary to propose a magnetic fiber with uniform structure, excellent morphology and high dielectric constant in the embodiments of this application.

[0005] Furthermore, embodiments of this application also propose a method for preparing the magnetic fiber, a composite film using the magnetic fiber and a method for preparing the composite film, a circuit board using the composite film, and an electronic device using the circuit board.

[0006] The first aspect of this application provides a magnetic fiber, the magnetic fiber comprising a ceramic matrix and magnetic particles dispersed in the ceramic matrix, the magnetic fiber having a diameter of 300 nm to 700 nm, a length of 3 μm to 15 μm, and an aspect ratio of 10 to 50.

[0007] By uniformly dispersing magnetic particles in a ceramic matrix, high-dielectric-activity fibers with uniform structure and excellent morphology are obtained. The ceramic matrix has a perfect crystal form and uniform structure, which can improve the dielectric constant of the magnetic fibers, resulting in a dielectric constant greater than or equal to 32. The magnetic particles are directly added to the ceramic matrix, which facilitates the adjustment of the size and amount of magnetic particles, thereby making it easy to achieve magnetic control of the magnetic fibers. The magnetic fibers can form a regular one-dimensional ordered structure under the action of a magnetic field, which is beneficial for obtaining composite films for embedded capacitors with high dielectric constants (Dk greater than or equal to 32, up to 54), which is significantly improved compared to the dielectric constant of traditional embedded capacitor materials (Dk of embedded capacitor materials for communication is about 10, and Dk of embedded capacitor materials for mobile phones is about 20).

[0008] In conjunction with the first aspect, in some embodiments, the ceramic matrix includes at least one of barium titanate crystals, barium strontium titanate crystals, calcium copper titanate crystals, and lead zirconate titanate crystals.

[0009] The above ceramic matrix has a high dielectric constant, which is beneficial to improving the dielectric constant of magnetic fibers.

[0010] In conjunction with the first aspect, in some embodiments, the ceramic matrix is ​​barium titanate crystal, and the average crystal size of the barium titanate phase is 50 nm to 200 nm.

[0011] Barium titanate has a high dielectric constant, which is beneficial for improving the dielectric constant of magnetic fibers. After the barium titanate fibers are oriented, the dielectric constant of the subsequently prepared composite can be further improved.

[0012] In conjunction with the first aspect, in some embodiments, the amount of magnetic particles added is 3wt% to 30wt%.

[0013] The magnetism of magnetic fibers can be easily controlled by adjusting the amount of magnetic particles added.

[0014] In conjunction with the first aspect, in some embodiments, the average particle size of the magnetic particles is 20 nm to 80 nm.

[0015] The magnetism of magnetic fibers can be easily controlled by adjusting the size of the magnetic particles.

[0016] In conjunction with the first aspect, in some embodiments, the magnetic particles include at least one of ferrite, cobalt ferrite, barium ferrite, and composite ferrite.

[0017] A second aspect of this application provides a method for preparing magnetic fibers, the method comprising the following steps:

[0018] Magnetic sol containing magnetic particles and ceramic matrix precursors is electrospinned and collected by rollers to obtain precursor fibers; and

[0019] The precursor fiber is calcined to obtain magnetic fiber. The magnetic fiber includes a ceramic matrix formed by the ceramic matrix precursor and magnetic particles dispersed in the ceramic matrix. The magnetic fiber has a diameter of 300 nm to 700 nm, a length of 3 μm to 15 μm, and an aspect ratio of 10 to 50.

[0020] Magnetic fibers are directly formed by electrospinning and roller receiving, which facilitates the uniform dispersion of magnetic fibers within the ceramic matrix. The resulting magnetic fibers are one-dimensional high-dielectric electromagnetic fibers with tunable magnetism, uniform structure, and excellent morphology. The method for preparing magnetic fibers in this application is simple, obtaining magnetic fibers in a single spinning step, greatly simplifying the complexity and difficulty of preparing magnetic fibers. The method for controlling the magnetism of the magnetic fibers is simple, easy to implement, and highly precise. No complex molding equipment is required, and molding conditions are easy to control, which is beneficial for large-scale industrial production.

[0021] In conjunction with the second aspect, in some embodiments, the ceramic matrix precursor includes at least one of barium titanate sol, barium strontium titanate sol, calcium copper titanate sol, and lead zirconate titanate sol.

[0022] In conjunction with the second aspect, in some embodiments, when the ceramic matrix precursor is barium titanate sol, the preparation method of the magnetic sol includes the following steps:

[0023] A solution of tetraisopropyl titanate was added to a barium acetate solution and stirred to obtain a barium titanate sol; and

[0024] The magnetic particles are dispersed in the barium titanate sol to obtain the magnetic sol.

[0025] Through the above steps, magnetic particles can be uniformly dispersed in barium titanate sol, which is beneficial for forming magnetic fibers with uniform structure and excellent morphology.

[0026] In conjunction with the second aspect, in some embodiments, the dispersion includes the following steps:

[0027] The magnetic particles and the barium titanate sol were magnetically stirred to obtain a preliminary mixed sol.

[0028] The pre-mixed sol is mixed in a homogenizer to obtain a pre-mixed sol. The homogenizer operates at a speed of 3500–4500 rpm / min, and the mixing time is 15–30 min.

[0029] The premixed sol is subjected to gradient ultrasonic dispersion, wherein the gradient ultrasonic dispersion includes: ultrasonicating the premixed sol at a power of 700-900W for 5-15 minutes, and then continuing to ultrasonicate at a power of 200-400W for 10-20 minutes.

[0030] Multi-step dispersion ensures that magnetic particles are uniformly dispersed in the ceramic matrix precursor sol and do not easily settle, thereby improving the quality of magnetic fibers and forming magnetic fibers with uniform structure and excellent morphology.

[0031] In conjunction with the second aspect, in some embodiments, after the step of dispersing the magnetic particles in the barium titanate sol, the method for preparing the magnetic sol further includes the step of:

[0032] A spinning aid is added to the barium titanate sol containing the magnetic particles.

[0033] The purpose of adding a spinning aid is to adjust the viscosity of the sol, so that the viscosity of the magnetic barium titanate sol is appropriate before curing and molding, so that the magnetic barium titanate sol can prevent the magnetic particles from settling while ensuring good spinnability, which is conducive to forming one-dimensional magnetic fibers with uniform structure and excellent morphology.

[0034] In conjunction with the second aspect, in some embodiments, the spinning aid includes at least one of polyvinylpyrrolidone, polyethylene oxide, polystyrene, and epoxy resin.

[0035] In conjunction with the second aspect, in some embodiments, the drum rotation speed of the drum collecting is 2000-3000 rpm / min.

[0036] The spinning quality can be improved by controlling the roller speed. The roller speed should not be lower than 2000 rpm / min. Below 2000 rpm / min, the fibers will overlap, resulting in a large number of overlapping fibers, making it difficult to form an ordered structure. When the roller speed is higher than 3000 rpm / min, fiber breakage will occur. Therefore, in this embodiment, the roller speed is controlled at 2000-3000 rpm / min, which can obtain one-dimensional ordered magnetic fibers with uniform structure and more uniform diameter.

[0037] In conjunction with the second aspect, in some embodiments, the viscosity of the magnetic sol is 2 to 12 Pa·s.

[0038] The viscosity of the sol containing magnetic particles and ceramic matrix precursors has a significant impact on the formation of magnetic fibers and the dispersion of magnetic particles after electrospinning. When the viscosity of the sol is too high, greater than 12 Pa·s, the spinnability of the sol is poor. At the same time, the high viscosity of the sol can also easily cause the magnetic particles to agglomerate and disperse unevenly. When the viscosity of the sol is too low, less than 2 Pa·s, the magnetic particles are prone to sedimentation in the dilute sol. In addition, the spinnability of the sol is poor and the precursor film is not easy to form.

[0039] In conjunction with the second aspect, in some embodiments, the calcination includes the following steps:

[0040] The precursor fiber was heated from room temperature to 340–360°C within 100 min, and held at 340–360°C for 50–70 min; then heated to 680–720°C within 100 min, and held at 680–720°C for 100–140 min.

[0041] Gradient heating calcination facilitates the full volatilization of organic impurities such as solvents within the intermediate alignment film, while also promoting the growth and crystal morphology improvement of barium titanate crystals, resulting in magnetic fibers with uniform structure and excellent morphology. The obtained magnetic fibers have diameters between 300 nm and 700 nm, and the barium titanate crystals within these fibers exhibit perfect crystal morphology and uniform structure, which is beneficial for improving the dielectric constant of the magnetic fibers.

[0042] A third aspect of this application provides a composite membrane comprising a polymer matrix and magnetic fibers dispersed in the polymer matrix, wherein the magnetic fibers are oriented along the thickness direction of the composite membrane, and the magnetic fibers are either the magnetic fibers described in the first aspect of this application or magnetic fibers prepared by the method described in the second aspect of this application.

[0043] By applying the magnetic fibers described in the first aspect of the embodiments of this application to the composite film, the dielectric constant of the composite film (Dk greater than or equal to 32, up to 54) can be significantly improved, thereby increasing the capacitance density of the composite film (capacitance density greater than or equal to 40 nF / in). 2 This composite film can be used as a high-dielectric embedded capacitor material in circuit boards.

[0044] In conjunction with the third aspect, in some embodiments, the amount of magnetic fiber added is 3wt% to 30wt%.

[0045] The magnetic properties of the composite film can be controlled by adjusting the amount of magnetic fibers added, thereby further improving the orientation of the magnetic fibers and thus further increasing the dielectric constant of the composite film.

[0046] In conjunction with the third aspect, in some embodiments, the thickness of the composite film is 10–50 μm.

[0047] In conjunction with the third aspect, in some embodiments, the polymer matrix includes at least one selected from polyimide, polyvinylidene fluoride, polypropylene, and silicone rubber.

[0048] In conjunction with the third aspect, in some embodiments, the dielectric constant of the composite film is greater than or equal to 32.

[0049] A fourth aspect of this application provides a method for preparing a composite membrane, the method comprising the following steps:

[0050] An intermediate film is formed by forming a mixed solution containing magnetic fibers, solvent and polymer precursor, wherein the magnetic fibers are the magnetic fibers described in the first aspect of the present application or the magnetic fibers prepared by the method described in the second aspect of the present application.

[0051] The intermediate film is placed in a magnetic field to orient the magnetic fibers along the thickness direction of the intermediate film, thereby obtaining an intermediate-oriented film; and

[0052] The intermediate orientation film is cured to solidify the polymer precursor to form a polymer matrix, thereby obtaining the composite film.

[0053] The embodiments of this application use a magnetic field to induce the orientation of magnetic fibers, resulting in a composite film with good orientation of magnetic fibers and a significant improvement in the dielectric constant of the composite film. The high dielectric constant composite film of the embodiments of this application has a simple and efficient process, the orientation of magnetic fibers can be adjusted, and conventional equipment can be used, which is conducive to realizing large-scale industrial applications.

[0054] In conjunction with the fourth aspect, in some embodiments, the mass ratio of the polymer precursor to the solvent in the mixed solution is (4:1) to (1:2).

[0055] The viscosity of the system with high magnetic fiber content can be adjusted by regulating the mass ratio of polymer precursor and solvent, thereby improving the orientation morphology of magnetic fibers and the uniformity of their dispersion in the composite film, and further increasing the dielectric constant of the formed composite film.

[0056] In conjunction with the fourth aspect, in some embodiments, the mass ratio of the polymer precursor to the solvent in the mixed solution is 3:1.

[0057] In conjunction with the fourth aspect, in some embodiments, the orientation temperature is 20–60°C and the time is 5–60 min.

[0058] Orientation temperature affects the rate of solvent evaporation. If the orientation temperature is too high, the solvent in the intermediate film will evaporate too quickly, and the magnetic fibers will not have enough time to be oriented. Orientation time affects the completion of magnetic fiber orientation. If the time is too short, the magnetic fibers cannot be fully oriented, and if the time is too long, it will affect production efficiency.

[0059] In conjunction with the fourth aspect, in some embodiments, prior to the step of curing the intermediate orientation film, the preparation method further includes the following steps:

[0060] The intermediate orientation film is sequentially placed in a forced-air drying oven and a vacuum drying oven for drying. The temperature in the forced-air drying oven is 60-100℃ and the drying time is 6-12 hours. The temperature in the vacuum drying oven is 60-100℃ and the drying time is 6-12 hours.

[0061] The two drying processes can effectively remove solvents from the surface and interior of the intermediate alignment film. In particular, drying in a vacuum oven is beneficial for the full evaporation of solvents inside the intermediate alignment film.

[0062] A fifth aspect of this application provides a circuit board, the circuit board including a base layer and a circuit layer located on at least one surface of the base layer, wherein the base layer is a composite film as described in the third aspect of this application or a composite film prepared by a method described in the fourth aspect of this application.

[0063] When the composite film described in the third aspect of the present application is used as a localized representative surface-mount capacitor, the composite film is embedded inside the circuit board. The composite film has a high dielectric constant and, when used as an embedded capacitor material, has a high capacitance density. This not only saves surface space of the circuit board, reduces the size of the circuit board, and reduces the weight and thickness of the circuit board, but also reduces the introduced inductance by eliminating solder joints on the surface of the circuit board, thereby reducing the impedance of the circuit board. In addition, eliminating solder joints can also improve the reliability of the circuit board.

[0064] A sixth aspect of this application provides an electronic device, the electronic device including a housing and a circuit board housed within the housing, the circuit board being the circuit board described in the fifth aspect of this application. Attached Figure Description

[0065] Figure 1 This is a schematic diagram of the preparation process of magnetic nanofibers according to an embodiment of this application.

[0066] Figure 2 This is a schematic diagram of the structure of the composite membrane provided in the embodiments of this application.

[0067] Figure 3a and Figure 3b These are schematic diagrams of the magnetic nanofibers in the embodiments of this application before and after orientation in a magnetic field.

[0068] Figure 4 This is a schematic diagram of the preparation process of the composite membrane in the embodiments of this application.

[0069] Figure 5 This is a schematic diagram of a circuit board according to an embodiment of this application.

[0070] Figure 6 This is a schematic diagram of an electronic device according to an embodiment of this application.

[0071] Figure 7 This is a morphology image of the ordered magnetic nanofibers prepared in Example 1.

[0072] Figure 8 The image shows the morphology of the disordered magnetic nanofibers prepared in Comparative Example 1.

[0073] Figure 9a and Figure 9b The figures show a comparison of the dielectric properties of the 9mBT (30wt%) / PI composite films before and after magnetic nanofiber orientation in Example 1 and Comparative Example 1, respectively.

[0074] Figure 10a and Figure 10b These are viscosity graphs of the 9mBT (40wt%) / PI system with different solvent ratios.

[0075] Figures 11a to 11c These are magnetic nanofiber orientation morphology images of 9mBT (40wt%) / PI composite films with different solvent ratios.

[0076] Figure 12a and Figure 12b The figures show the dielectric constants of the 9mBT (40wt%) / PI composite film with different solvent ratios.

[0077] Explanation of main component symbols

[0078] Composite membrane 100

[0079] Polymer matrix 10

[0080] Magnetic nanofibers 20

[0081] Polymer precursor 30

[0082] Intermediate membrane 40

[0083] Intermediate orientation film 50

[0084] Circuit board 200

[0085] 210 at the grassroots level

[0086] Line layer 220

[0087] Electronic device 300

[0088] Casing 310

[0089] Thickness direction a Detailed Implementation

[0090] The embodiments of this application are described below with reference to the accompanying drawings. Unless otherwise specified, the data range values ​​described in this application shall include the end values.

[0091] Because traditional embedded capacitor materials have low capacitance density, researchers need to increase the capacitance density of embedded capacitors to miniaturize them. A key method to increase the capacitance density of embedded capacitor materials is to increase their capacitance value. Furthermore, according to the formula... It is known that the capacitance value of embedded capacitors is directly proportional to their dielectric constant. Therefore, preparing embedded capacitors with high dielectric constants is the key to improving their capacitance density.

[0092] To address the above issues, this application provides a composite film with a high dielectric constant. This composite film can be used as an embedded capacitor material in circuit boards, including but not limited to printed circuit boards (PCBs) or flexible printed circuit boards (FPCs). This composite film is formed by uniformly dispersing and orienting magnetic fibers with uniform structure, excellent morphology, and high dielectric constant in a polymer matrix. The magnetic fibers are optimized to ensure that the dielectric constant (Dk) of the high-dielectric composite film is greater than or equal to 32, and the capacitance density used as an embedded capacitor material is greater than or equal to 40 nF / in. 2 This effectively improves the utilization rate of the circuit board surface, reduces the size of the circuit board, reduces the weight and thickness of the circuit board, and improves the reliability of the circuit board.

[0093] The magnetic fibers provided in this application include a ceramic matrix and magnetic particles dispersed in the precursor solution. The magnetic fibers have a diameter of 300 nm to 700 nm, a length of 3 μm to 15 μm, and an aspect ratio of 10 to 50. In some embodiments, the magnetic fibers in this application have a diameter at the nanometer scale, thus they are magnetic nanofibers with a one-dimensional structure and are magnetic, used to orient themselves in a magnetic field to form an ordered structure. The ceramic matrix is ​​formed by crystallization of a dielectric ceramic precursor solution. In some embodiments, when the magnetic fibers are magnetic nanofibers, the added magnetic particles are also nanoscale particles. It is understood that the diameter of the magnetic fibers can also be other sizes. The preparation method of magnetic fibers of other sizes is the same as that of magnetic nanofibers, except that the diameter of the magnetic fibers needs to be controlled within different size ranges. For example, micrometer-sized magnetic fibers can be applied to applications with thicker composite films to meet different application scenarios.

[0094] Currently, commonly used embedded capacitor materials are typically composite materials formed by adding fillers with high dielectric constants to a polymer matrix. Based on theoretical model predictions combined with computer simulations, compared to zero-dimensional (i.e., granular) fillers, one-dimensional (with a large aspect ratio, i.e., fibrous) fillers, when vertically oriented, exhibit strong interactions between continuously arranged fillers in a vertical direction under an electric field, forming a continuous high-polarizability phase along the electric field direction. This maximizes the polarization of the entire composite material, significantly improving the dielectric constant of the embedded capacitor material. Furthermore, according to percolation theory, compared to granular fillers, fibrous fillers have a significantly lower percolation threshold because they are more easily interconnected to form current paths, thus achieving a higher dielectric constant. Therefore, in this embodiment, magnetic nanoparticles are directly added to a ceramic matrix to form nanometer-sized fibers, resulting in magnetic nanofibers with a large aspect ratio. These magnetic nanofibers possess a high dielectric constant and can form a one-dimensional ordered structure in a magnetic field, further improving the dielectric constant of the composite film using these magnetic nanofibers, thereby increasing the capacitance density of the composite film.

[0095] In some embodiments, the ceramic matrix may be, but is not limited to, at least one of barium titanate crystal, barium strontium titanate crystal, calcium copper titanate crystal, and lead zirconate titanate crystal. The above ceramic matrices have high dielectric constants, which is beneficial for improving the dielectric constant of magnetic fibers.

[0096] Barium titanate has a high dielectric constant, and barium titanate crystals are used as the ceramic matrix in this application embodiment. Compared to zero-dimensional barium titanate nanoparticles, one-dimensional barium titanate nanofibers have a larger aspect ratio and a lower specific surface area. Therefore, with the same filler content, barium titanate nanofibers are easier to disperse uniformly in the polymer matrix, enabling the embedded capacitor composite film to obtain a higher dielectric constant. Furthermore, one-dimensional barium titanate nanofibers are more likely to interconnect and form current pathways, exhibiting a smaller percolation threshold, thereby further improving the dielectric constant of the embedded capacitor composite film. Therefore, by orienting the embedded capacitor material containing barium titanate fibers, aligning the barium titanate nanofibers vertically, and thus preparing a high-dielectric composite film, the capacitance density of the embedded capacitor composite film can be significantly improved. This application embodiment adds magnetic nanoparticles to barium titanate to prepare one-dimensional magnetic nanofibers with uniform structure and excellent morphology. While retaining the original high dielectric properties of barium titanate, it also endows the barium titanate nanofibers with adjustable magnetism, so that the magnetic nanofibers can be oriented under the action of a magnetic field, thereby further improving the dielectric constant of the composite film prepared by the magnetic nanofibers and increasing the capacitance density of the composite film.

[0097] In some embodiments, the average crystal size of barium titanate crystals is 50 nm to 200 nm, and more specifically 100 to 150 nm.

[0098] In some embodiments, the average particle size of the magnetic nanoparticles is 20 nm to 80 nm, more specifically 35 nm to 60 nm. The average particle size is typically, but not limited to, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, or 80 nm. If the particle size of the magnetic nanoparticles is too large, the gravitational force on individual particles increases, making them prone to sedimentation in the solution. If the particle size is too small, the large specific surface area leads to particle aggregation, making dispersion difficult. Therefore, only magnetic nanoparticles within a suitable particle size range can be uniformly dispersed in barium titanate crystals to obtain magnetic nanofibers with a uniform structure. Understandably, "uniform structure" means that, firstly, the crystal units that make up barium titanate nanofibers—barium titanate crystals—have perfect crystal forms, and the crystal structure is not affected by magnetic particles, with uniform average crystal size; secondly, in magnetic barium titanate nanofibers, magnetic nanoparticles are uniformly dispersed, and the structure of magnetic barium titanate nanofibers is consistent from the outside to the inside, without any layered structure between the surface and the core.

[0099] In some embodiments, the magnetic nanoparticles include at least one of ferrite (Fe3O4), cobalt ferrite, barium ferrite, and composite ferrite, wherein the composite ferrite is a ferrite formed by combining two or more single-component ferrites, or a ferrite formed by iron oxide and two or more metal oxides.

[0100] In some embodiments, the content of magnetic nanoparticles is 3 wt% to 30 wt%, more preferably 8 to 25 wt%, and even preferably 10 to 20 wt%. Typical, but not limited, content of magnetic nanoparticles is 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, or 30 wt%. On the one hand, since ceramic matrices such as barium titanate crystals are not magnetic, it is necessary to add magnetic nanoparticles to give them good magnetic responsiveness to achieve good magnetic field orientation. Therefore, the amount of magnetic nanoparticles added should not be too low; otherwise, the magnetic nanofibers will have too low a magnetic field and cannot achieve magnetic field orientation. On the other hand, since magnetic nanoparticles are usually magnetic metals and their oxides, their density is relatively high. If the amount of magnetic nanoparticles added is too high, the magnetic nanoparticles will have excessive gravity in the solution and will not be able to suspend well in the solution, causing them to settle to the bottom of the solution, which is not conducive to subsequent electrospinning and also to subsequent magnetic field orientation. Therefore, in this application, the amount of magnetic nanoparticles added must be in the range of 3wt% to 30wt% to achieve a balance between magnetism and dispersibility.

[0101] In some embodiments, the diameter of the magnetic nanofibers is further 300–500 nm, further 400–500 nm, typically but not limited to 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, or 700 nm. The length of the magnetic nanofibers is further 5–10 μm, further 5–8 μm, typically but not limited to 3 μm, 4 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm. The aspect ratio of the magnetic nanofibers is controlled between 10 and 50, as the aspect ratio directly affects the internal orientation structure and quality of the formed composite film. If the aspect ratio is too small, the anisotropy of the magnetic nanofibers is not prominent enough, which is not conducive to the formation of an ordered structure after the magnetic nanofibers are oriented in a magnetic field. If the aspect ratio is too large, it will lead to an increase in steric hindrance during the orientation process of the magnetic nanofibers and an increase in the orientation time of the magnetic nanofibers. Furthermore, an excessively large aspect ratio will lead to an increase in the thickness of the final composite film, which cannot meet the requirements of thinning and miniaturization of products using this composite film.

[0102] This application embodiment obtains high dielectric magnetic nanofibers with uniform structure and excellent morphology by uniformly dispersing magnetic nanoparticles in a ceramic matrix. The ceramic matrix has a perfect crystal form and uniform structure, which can improve the dielectric constant of the magnetic nanofibers, resulting in a dielectric constant of the obtained magnetic nanofibers greater than or equal to 32, and as high as 54. The magnetic nanoparticles are directly added to the ceramic matrix, which facilitates the adjustment of the size and amount of magnetic nanoparticles, and thus makes it easy to achieve magnetic control of the magnetic nanofibers. The magnetic nanofibers can form a regular one-dimensional spatial structure under the action of a magnetic field, which is beneficial to obtaining composite films for embedded capacitors with high dielectric constants (Dk greater than or equal to 32, and as high as 54), which is significantly improved compared with the dielectric constant of traditional embedded capacitor materials (Dk of embedded capacitor materials for communication is about 10, and Dk of embedded capacitor materials for mobile phones is about 20).

[0103] In this embodiment, the aforementioned one-dimensional high dielectric electromagnetic nanofibers with uniform structure and excellent morphology are obtained by electrospinning.

[0104] Electrospinning is one of the most studied methods for preparing micro and nanofibers, and the aggregation morphology of the fibers can be controlled by designing a receiving device. Traditional flat-plate receiving devices, however, only collect two-dimensional fiber membranes with disordered fiber stacking during electrospinning, which have limitations in terms of morphology oriented by a magnetic field. Therefore, this application, based on traditional electrospinning, utilizes a roller-type oriented collection device to achieve macroscopic oriented arrangement of the fibers, satisfying the special structural design requirements of magnetic nanofibers and enabling more precise control of the material structure, thereby producing magnetic nanofibers with superior performance.

[0105] See also Figure 1 The method for preparing the magnetic nanofibers includes the following steps:

[0106] Step S11: The magnetic sol containing magnetic nanoparticles and ceramic matrix precursors is electrospun and collected by roller to obtain precursor fibers.

[0107] Step S12: The precursor fiber is calcined to obtain the aforementioned magnetic nanofiber. The magnetic nanofiber includes a ceramic matrix formed by the ceramic matrix precursor and magnetic nanoparticles dispersed in the ceramic matrix. For the specific parameters of the magnetic nanofiber, please refer to the foregoing. They will not be elaborated here.

[0108] In step S11, the ceramic matrix precursor can be at least one of barium titanate sol, barium strontium titanate sol, calcium copper titanate sol, and lead zirconate titanate sol. When the ceramic matrix precursor is barium titanate sol, the specific preparation method of the magnetic sol (i.e., magnetic barium titanate sol) includes the following steps:

[0109] The first step is to dissolve a certain amount of barium acetate in acetic acid until it is fully dissolved to obtain the first solution.

[0110] The second step involves adding tetraisopropyl titanate to a mixture of acetylacetone and ethanol, mixing thoroughly to obtain a second solution.

[0111] The third step involves adding the second solution dropwise to the first solution while stirring. After stirring for a certain period, once the solution turns pale yellow, deionized water is added dropwise until a transparent and homogeneous barium titanate sol is obtained. Adding the second solution dropwise to the first solution ensures that tetraisopropyl titanate and barium acetate react completely to form barium titanate.

[0112] The fourth step involves adding magnetic nanoparticles to the barium titanate sol and achieving good dispersion of the magnetic nanoparticles through stepwise dispersion. First, the magnetic nanoparticles and barium titanate sol are initially mixed uniformly by magnetic stirring for approximately 1.5–2.5 hours (approximately 2 hours). Second, the mixture is further thoroughly mixed using a high-speed mixer in Mixing mode, ensuring the magnetic nanoparticles and barium titanate sol are fully and uniformly mixed under high-speed rotation, resulting in a sol with a uniform appearance and color. The mixing speed is 3500–4500 rpm / min (approximately 4000 rpm / min), and the mixing time is 15–30 minutes (approximately 20 minutes). Finally, the uniformly mixed sol is placed in a water bath ultrasonic machine for multiple ultrasonic dispersions to obtain a uniformly dispersed magnetic barium titanate sol. The power and time of the multiple ultrasonic dispersions vary gradually, initially using a higher power of 700–900 W for 5–15 minutes to disperse any potentially agglomerated magnetic particles. Since prolonged high-power ultrasound can cause the sol to heat up, leading to solvent evaporation and affecting electrospinning, the power was reduced to 200-400W in the later stages, and ultrasound was continued for 10-20 minutes to further disperse the magnetic nanoparticles in the barium titanate sol, ultimately resulting in a uniformly dispersed magnetic barium titanate sol.

[0113] In some embodiments, the type, particle size, and amount of magnetic nanoparticles are described above.

[0114] Fifth step: Add a small amount of spinning aid to the magnetic barium titanate sol, and stir thoroughly to obtain a sol with good spinnability.

[0115] In some embodiments, the viscosity of the sol containing magnetic nanoparticles and a ceramic matrix precursor has a significant impact on the formation of magnetic nanofibers and the dispersion of magnetic nanoparticles after electrospinning. When the viscosity of the sol is too high, greater than 12 Pa·s, the spinnability of the sol is poor, and the high viscosity also easily causes the magnetic nanoparticles to agglomerate and disperse unevenly. When the viscosity of the sol is too low, less than 2 Pa·s, the magnetic nanoparticles are prone to sedimentation in the dilute sol. In addition, the spinnability of the sol is poor, and the precursor fibers are not easy to form. Therefore, in the embodiments of this application, the viscosity of the sol is 2 to 12 Pa·s, more specifically 5 to 8 Pa·s. The viscosity of the sol is typically, but not limited to, 2 Pa·s, 3 Pa·s, 4 Pa·s, 5 Pa·s, 6 Pa·s, 7 Pa·s, 8 Pa·s, 9 Pa·s, 10 Pa·s, 11 Pa·s, or 8 Pa·s. In this embodiment, the purpose of adding a spinning aid to the magnetic barium titanate sol is to adjust the viscosity of the sol so that the viscosity of the magnetic barium titanate sol is appropriate during electrospinning, so that the magnetic barium titanate sol can prevent the magnetic particles from settling while ensuring good spinnability.

[0116] In some embodiments, the spinning aid includes at least one of polyvinylpyrrolidone, polyethylene oxide, polystyrene, and epoxy resin. Specifically, it may be polyvinylpyrrolidone.

[0117] In some embodiments, the amount of the spinning aid added is 25–50 wt%, more specifically 35–40 wt%. By adjusting the amount of the spinning aid added, the viscosity of the aforementioned electrospinning sol can be adjusted within a suitable range to improve spinnability and simultaneously facilitate the uniform dispersion of magnetic nanoparticles.

[0118] In some embodiments, the dispersion is carried out in a multi-step manner, and the total time should be greater than or equal to 3 hours, so as to fully mix the magnetic barium titanate sol and disperse the magnetic nanoparticles more evenly in the barium titanate sol, thereby obtaining a uniform sol.

[0119] In step S11, the specific process of magnetic barium titanate sol electrospinning is as follows:

[0120] The first step involves adding magnetic barium titanate sol to a syringe with a volume of 5–20 ml, an inner diameter of 8–15.5 mm, and an inner diameter of 0.10–0.21 mm for the needle tip. The syringe volume plays a crucial role in the sedimentation of the magnetic nanoparticles. A larger syringe volume results in a larger volume of sol for electrospinning, requiring a longer spinning time, and potentially causing the magnetic nanoparticles to settle later, hindering uniform dispersion within the sol. Conversely, a syringe volume that is too small affects spinning efficiency. Therefore, in this embodiment, the syringe volume is 5–20 ml, specifically 10 ml, which ensures uniform dispersion of the magnetic nanoparticles while improving spinning efficiency. The inner diameter of the needle tip affects the fiber diameter and can be adjusted according to the actual diameter requirements of the magnetic nanofibers.

[0121] The second step involves using a high-speed directional roller collector to receive precursor fibers, which are then collected as a precursor fiber membrane formed by a large number of orderly arranged precursor fibers.

[0122] In some embodiments, the roller speed is controlled at 2000–3000 rpm / min, and more specifically 2400–2800 rpm / min. The roller speed should not be lower than 2000 rpm / min; below this speed, fibers will overlap, resulting in a large number of overlapping fibers, making it difficult to form an ordered structure. When the roller speed exceeds 3000 rpm / min, the excessively fast winding speed can cause fiber breakage. Therefore, in this embodiment, controlling the roller speed to 2000–3000 rpm / min yields one-dimensional ordered magnetic nanofibers with a uniform structure and more uniform diameter.

[0123] In some embodiments, the spinning temperature is 25–35°C, and the relative humidity should be less than or equal to 80%. If the spinning temperature is too high, the solvent in the precursor fiber evaporates too quickly, easily leading to excessive viscosity of the sizing solution and poor spinnability. If the temperature is too low, the solvent evaporates too slowly, causing the precursor fiber to flow too easily on the roller, resulting in poor final fiber quality. Furthermore, the flow of the precursor fiber can easily cause uneven dispersion of the magnetic nanoparticles. Therefore, this embodiment employs a segmented temperature setting method, setting the temperature at the filament exit point at a slightly lower range (25–30°C) and the temperature at the roller rewinder at a slightly higher range (30–35°C) to ensure the quality of the magnetic nanofibers.

[0124] In some embodiments, the spinning voltage is 15–25 kV and the feeding rate is 1.0–2.0 ml / h.

[0125] In some embodiments, the needle oscillation width is 100-150 mm and the needle oscillation speed is 10-20 mm / sec.

[0126] In some embodiments, the spinning time is 3 to 5 hours.

[0127] In step S12, during the calcination process, the precursor fiber needs to be placed between two quartz plates to prevent the precursor fiber from bending and deforming during calcination, thereby improving the quality of the magnetic nanofiber.

[0128] In step S12, the precursor fibers are calcined using a gradient heating method, specifically including the following steps:

[0129] The temperature is raised from room temperature to 340–360°C within approximately 100 minutes, and then held at 340–360°C for 50–70 minutes, specifically at approximately 350°C for 60 minutes, to fully remove organic impurities from the precursor film.

[0130] The temperature was raised to 680–720℃ within approximately 100 minutes, and then held at 680–720℃ for 100–140 minutes, specifically at approximately 700℃ for 120 minutes. This gradient heating calcination method facilitates the complete evaporation of solvents and the removal of organic impurities within the precursor fibers. It also promotes the growth and crystal formation of barium titanate crystals, resulting in magnetic nanofibers with uniform structure and excellent morphology. The obtained magnetic nanofibers have diameters between 300–700 nm, lengths between 3–15 μm, and aspect ratios between 10–50. The barium titanate crystals in the magnetic nanofibers are well-formed and uniform in structure, which is beneficial for improving the dielectric constant of the magnetic nanofibers. Furthermore, the magnetic properties of the magnetic nanofibers can be adjusted according to the size and amount of magnetic nanoparticles added. After electrospinning, directional roller collection, and speed matching control, an in-plane ordered barium titanate nanofiber film can be obtained. Here, "ordered" refers to the directional arrangement of a large number of barium titanate nanofibers in the film, without overlapping.

[0131] In this embodiment, barium titanate sol was obtained by in-situ growth of barium acetate and tetraisopropyl titanate. Magnetic nanoparticles were then added to the barium titanate sol and uniformly dispersed. Magnetic nanofibers were fabricated by electrospinning and collected by roller winding to obtain an ordered magnetic barium titanate nanofiber precursor film. Finally, after high-temperature calcination, magnetic barium titanate nanofibers with an oriented structure were obtained. First, magnetic nanofibers with uniformly dispersed magnetic nanoparticles within a ceramic matrix were directly formed by electrospinning and roller winding. The resulting magnetic nanofibers are one-dimensional high-dielectric electromagnetic nanofibers with tunable magnetism, uniform structure, and excellent morphology. Secondly, by multi-step dispersion and adjusting the viscosity of the magnetic barium titanate sol, the magnetic nanoparticles are uniformly dispersed in the barium titanate sol and are less prone to sedimentation, thereby improving the quality of the magnetic nanofibers. Furthermore, by controlling the roller speed and spinning temperature, the spinning quality can be improved, resulting in one-dimensional magnetic nanofibers with uniform diameter, uniform structure, and excellent morphology. Even further, by using stepwise calcination, organic impurities inside the precursor fibers can be fully removed, which is beneficial for the growth and crystal form perfection of barium titanate crystals, thus obtaining magnetic nanofibers with uniform structure and excellent morphology. The method for preparing magnetic nanofibers in this application is simple, with magnetic nanofibers obtained in a single spinning process, greatly simplifying the complexity and difficulty of preparing magnetic nanofibers. The method for controlling the magnetism of the magnetic nanofibers is simple, easy to implement, and has high control precision. No complex molding equipment is required, and the molding conditions are easy to control, which is conducive to large-scale industrial production.

[0132] Please see Figure 2 Based on the same inventive concept, this application also provides a composite membrane 100, which includes a polymer matrix 10 and magnetic nanofibers 20 dispersed in the polymer matrix 10. The magnetic nanofibers 20 are oriented along the thickness direction a of the composite membrane 100, and the magnetic nanofibers 20 are the aforementioned magnetic nanofibers.

[0133] By applying the aforementioned magnetic nanofibers of this application to the composite film 100, the dielectric constant of the composite film 100 can be significantly increased (Dk is greater than or equal to 32, up to 54), thereby increasing the capacitance density of the composite film 100 (capacitance density is greater than or equal to 40 nF / in). 2 This composite film can be used as a high-dielectric embedded capacitor material in circuit boards.

[0134] In some embodiments, the polymer matrix includes at least one of polyimide, polyvinylidene fluoride, polypropylene, and silicone rubber. Because polyimide possesses excellent heat resistance, mechanical properties, dielectric properties, and flexibility, this application embodiment selects polyimide as the polymer matrix.

[0135] In some embodiments, the amount of magnetic nanofibers 20 added is 3 wt% to 30 wt%, more preferably 8 to 25 wt%, more preferably 10 to 20 wt%, and the amount of magnetic nanofibers 20 added is typically, but not limited to, 3 wt%, 5 wt%, 8 wt%, 9 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, or 30 wt%. The dielectric constant of the composite film 100 can be further improved by adjusting the content of magnetic nanofibers 20.

[0136] In some embodiments, the thickness of the composite film 100 is 10–50 μm, more particularly 20–40 μm. The thickness of the composite film 100 is typically, but not limited to, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm. When the thickness of the composite film 100 is too large, it does not meet the application requirements of ultra-thin and ultra-small products. When the thickness of the composite film 100 is too small, the magnetic nanofibers 20 cannot achieve orientation, and the purpose of improving the dielectric constant of the composite film 100 cannot be achieved.

[0137] Please refer to the following: Figure 4 Combined with reference Figure 2 The method for preparing the composite membrane 100 includes the following steps:

[0138] Step S21: The mixed solution containing the aforementioned magnetic nanofibers 20 and polymer precursor 30 is used to form an intermediate film 40.

[0139] Step S22: The intermediate membrane 40 is placed in a magnetic field so that the magnetic nanofibers 20 are oriented along the thickness direction a of the intermediate membrane 40, thereby obtaining the intermediate oriented membrane 50.

[0140] Step S23: Curing intermediate orientation film 50 to cure polymer precursor 30 to form polymer matrix 10, thereby obtaining composite film 100.

[0141] In step S21, the method for preparing the mixed solution is as follows:

[0142] The first step is to add magnetic nanofibers 20 to the solvent and mix them thoroughly to obtain a magnetic nanofiber dispersion.

[0143] In some embodiments, the solvent may be at least one of dimethylacetamide (DMAC) or N-methylpyrrolidone (NMP). Specifically, DMAC is selected as the solvent.

[0144] In some embodiments, the size and amount of magnetic nanofibers 20 are as described above.

[0145] In the second step, the polymer precursor 30 is added to the magnetic nanofiber dispersion from the first step and mixed thoroughly to obtain the mixed solution.

[0146] In some embodiments, the polymer precursor 30 is the polymer before the aforementioned polymer matrix is ​​cross-linked and cured. Specifically, the polymer precursor 30 may be polyamic acid (PAA).

[0147] In some embodiments, the mass ratio of polymer precursor 30 to solvent is (4:1) to (1:2), typically but not limited to 4:1, 3:1, 2:1, 1:1, 1:1.5, or 1:2. Specifically, in this application embodiment, the mass ratio is polyamic acid to DMAC. Typically, polymer precursor 30 (e.g., PAA) has a high viscosity and is too viscous, making it difficult for magnetic nanofibers 20 to disperse well in the polymer precursor 30 solution. Therefore, solvent dilution is required to adjust the viscosity of the polymer precursor 30, thereby allowing the magnetic nanofibers 20 to disperse and oriented better. As the solvent content increases, the solvent ratio increases, and the viscosity of the system decreases, which is beneficial for the orientation of magnetic nanofibers 20 in the polymer precursor 30 and for improving the dielectric constant of the composite film 100. However, if the viscosity is too low, the magnetic nanofibers 20 are prone to sedimentation, which is detrimental to the uniformity of dispersion of the magnetic nanofibers 20 in the polymer precursor 30. Therefore, in this embodiment, the viscosity of the system with high magnetic nanofiber content is adjusted by controlling the mass ratio of polymer precursor and solvent, thereby improving the orientation morphology of magnetic nanofibers and the uniformity of dispersion in the composite film, and thus increasing the dielectric constant of the formed composite film.

[0148] In step S21, an intermediate film 40 is formed by a doctor blade coating method. The thickness of the doctor blade determines the thickness of the final composite film 100. The doctor blade thickness is 50 to 300 μm, and more specifically 100 to 200 μm. The doctor blade thickness is typically, but not limited to, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, or 300 μm.

[0149] In step S22, the magnetic field type is a static magnetic field provided by a permanent magnet, the magnetic field direction is perpendicular to the intermediate film 40 (i.e., the thickness direction a of the intermediate film 40), and the effective space is 50×30×140mm. 3The magnetic field uniformity is >99%, and the magnetic field strength is 0.4T. The orientation temperature is 20–60℃, further 30–50℃, typically but not limited to 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, or 60℃; the orientation time is 5–60 min, further 10–50 min, further 20–40 min, typically but not limited to 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min. The orientation temperature affects the rate of solvent evaporation. If the orientation temperature is too high, the solvent in the intermediate film 40 evaporates too quickly, and the magnetic nanofibers do not have enough time to align. The orientation time affects the completion of the magnetic nanofiber orientation; if the time is too short, the magnetic nanofibers cannot be completely oriented, and if the time is too long, it affects production efficiency. Figure 3a As shown, before orientation, the magnetic nanofibers are dispersed randomly in the polymer precursor; as Figure 3b As shown, after orientation, the magnetic nanofibers are uniformly and regularly arranged in the polymer precursor.

[0150] In step S23, before curing the intermediate alignment film 50, it is necessary to dry the intermediate alignment film 50, specifically using a step-by-step drying method to thoroughly remove residual solvents inside the intermediate alignment film 50. The intermediate alignment film is sequentially placed in a forced-air oven and a vacuum oven for drying. The temperature in the forced-air oven is 60–100°C, and the drying time is 6–12 hours. The temperature in the vacuum oven is also 60–100°C, and the drying time is 6–12 hours. This two-stage drying process effectively removes solvents from both the surface and interior of the intermediate alignment film 50. Drying in the vacuum oven, in particular, facilitates the complete evaporation of solvents from the interior of the intermediate alignment film 50.

[0151] In step S23, when the polymer precursor 30 is polyamic acid, the curing in this step is an imidization reaction of the polyamic acid. The entire reaction is carried out under an argon atmosphere. The specific steps are as follows:

[0152] The first step is to raise the temperature from room temperature to approximately 100°C at a rate of approximately 2°C / min, and then hold the temperature at 100°C for approximately 1 hour.

[0153] The second step is to raise the temperature from 100°C to approximately 150°C at a heating rate of approximately 2°C / min, and then hold the temperature for approximately 1 hour.

[0154] The third step is to raise the temperature from 150°C to approximately 200°C at a heating rate of approximately 2°C / min, and then hold the temperature for approximately 1 hour.

[0155] The fourth step involves heating the temperature from 200°C to approximately 300°C at a rate of approximately 2°C / min, maintaining this temperature for approximately 1 hour, and then ending the heating process to obtain the composite membrane 100.

[0156] This application employs a 0.4T uniform static magnetic field to induce the orientation of magnetic nanofibers, resulting in a composite film with excellent orientation and a significantly improved dielectric constant. The viscosity of the system (especially with high magnetic nanofiber content) is adjusted by regulating the mass ratio of the polymer precursor to the solvent, thereby improving the orientation morphology of the magnetic nanofibers and the uniformity of their dispersion in the composite film, further enhancing the dielectric constant of the formed composite film. This application utilizes a magnetic field to induce the orientation of magnetic nanofibers in a polymer precursor, fixes the orientation by evaporating the solvent, and then undergoes a curing reaction to obtain a composite film for embedded capacitors that combines excellent orientation and a high dielectric constant. This process is simple and efficient, the orientation of the magnetic nanofibers is adjustable, and conventional equipment is available, facilitating large-scale industrial applications.

[0157] Please see Figure 5 Based on the same inventive concept, this application also provides a circuit board 200 using the aforementioned high-dielectric composite film 100. The circuit board 200 includes a base layer 210 and a circuit layer 220 located on at least one surface of the base layer 210, wherein the base layer 210 is the aforementioned composite film 100. In this embodiment, a circuit layer 220 is provided on both opposite surfaces of the base layer 210, and the composite film 100 can be used as a capacitor in the circuit board 200. The circuit board 200 can be a PCB or an FPC, but is not limited thereto; the capacitor can be, but is not limited to, a filter capacitor.

[0158] In this embodiment of the application, when the composite film 100 is used as a localized representative surface-mount capacitor, the composite film 100 is embedded inside the circuit board 200. This not only saves valuable surface space of the circuit board 200, reduces the size of the circuit board 200, and reduces the weight and thickness of the circuit board 200, but also reduces the introduced inductance by eliminating solder joints on the surface of the circuit board 200, thereby reducing the impedance of the circuit board 200. In addition, eliminating solder joints can also improve the reliability of the circuit board 200.

[0159] Please see Figure 6 Based on the same inventive concept, this application also provides an electronic device 300 that uses the aforementioned circuit board 200. The electronic device 300 includes a housing 310 and a circuit board 200 located within the housing 310.

[0160] It is understood that the electronic device 300 can be various electronic devices, including but not limited to mobile phones, computers, and cameras.

[0161] The technical solutions of the embodiments of this application will be further described below through specific examples.

[0162] Preparation Example 1

[0163] 1) Dissolve 2.55g of barium acetate in 9.5g of acetic acid until fully dissolved and label as solution A. Add 2.88g of tetraisopropyl titanate to a mixture of acetylacetone and ethanol and mix thoroughly, labeling as solution B. Add solution B dropwise to solution A while stirring. After stirring for 10 minutes, when the solution turns pale yellow, add deionized water until a transparent and homogeneous barium titanate sol is obtained. Then add 0.432g of iron(III) oxide nanoparticles to the barium titanate sol and disperse it by multiple ultrasonic processes and mix it with a high-speed mixer to obtain a uniformly dispersed magnetic barium titanate sol. Finally, add 1.7g of polyvinylpyrrolidone as a spinning aid to obtain a magnetic barium titanate solution with good spinnability.

[0164] 2) Add the obtained magnetic barium titanate solution into a syringe with a volume of 10 ml, an inner diameter of 15.5 mm, and an inner diameter of 0.21 mm. Use a high-speed directional roller collector to collect the fibers and form a precursor film. Control the roller speed to be 2000-3000 rpm / min, the temperature to be 25℃, the relative humidity to be less than or equal to 80%, the spinning voltage to be 25 kV, the feeding rate to be 2.0 ml / h, the needle oscillation width to be 100 mm, and the needle oscillation speed to be 20 mm / sec.

[0165] 3) Place the precursor film between two quartz plates to prevent it from bending and deforming during calcination. Then, calcinate it using a gradient heating method, raising the temperature from room temperature to about 350°C in about 100 minutes, and holding it at 350°C for about 60 minutes to remove organic impurities. Then, raise the temperature to about 700°C in about 100 minutes and hold it at 700°C for about 120 minutes. This temperature is conducive to the growth and improvement of barium titanate crystals, thereby obtaining magnetic nanofibers (denoted as 9mBT).

[0166] The morphology of 9mBT fiber is as follows Figure 7 As shown, the diameter of the 9mBT fiber is between 300 and 700 nm. The magnetic nanofiber structure is uniform, the fiber morphology is regular, and there is no overlap.

[0167] Comparative Preparation Example 1

[0168] A randomly arranged barium titanate nanofiber filler, differing from Example 1 in that a flat receiving device is used to receive the fibers during electrospinning, and the fiber morphology is as follows. Figure 8 As shown, the fibers exhibit a disordered network structure.

[0169] Example 1

[0170] 1) Accurately weigh 500 mg of the 9 mBT fiber prepared in Preparation Example 1 and disperse it in 1.6 g of DMAC. Mix it evenly and then add 5 g of PAA and mix it again (where PAA:DMAC is 3:1) to obtain a 30 wt% 9 mBT / PAA solution.

[0171] 2) Take 3 mL of the above 9 mBT / PAA solution, adjust the doctor blade scale to 200 μm to obtain an intermediate film, place the intermediate film in a magnetic field, and align it at room temperature for 30 min to obtain an intermediate oriented film. First, dry the intermediate oriented film in a 60℃ forced-air oven for 12 h, and then put it in a vacuum drying oven at 80℃ for 12 h before taking out the film;

[0172] 3) The dried intermediate orientation film is placed in a tube furnace and subjected to an imidization reaction under argon conditions. The specific steps are as follows:

[0173] (1) Heat from room temperature to 100℃ at a heating rate of 2℃ / min and hold at 100℃ for 1 hour;

[0174] (2) Increase the temperature from 100℃ to 150℃ at a heating rate of 2℃ / min and hold the temperature for 1 hour;

[0175] (3) Increase the temperature from 150℃ to 200℃ at a heating rate of 2℃ / min and hold the temperature for 1 hour;

[0176] (4) The temperature was increased from 200℃ to 300℃ at a heating rate of 2℃ / min and held at the temperature for 1 hour. After heating was stopped and the temperature was cooled, a 9mBT / PI composite membrane with magnetic field orientation and 9mBT addition of 30wt% was obtained, which is represented as 9mBT(30wt%) / PI composite membrane.

[0177] Example 2

[0178] A magnetically oriented high-dielectric thin film differs from Example 1 in that the amount of ordered 9mBT fibers added is 800 mg, corresponding to a 9mBT content of 40 wt% in the solution, resulting in a magnetically oriented 9mBT / PI composite film, denoted as 9mBT(40 wt%) / PI composite film.

[0179] Example 3

[0180] A magnetic field-oriented high-dielectric thin film differs from Example 1 in that the amount of solvent DMAC added is 2.5g, corresponding to a solvent ratio of PAA:DMAC of 2:1.

[0181] Example 4

[0182] A magnetic field-oriented high-dielectric thin film differs from Example 1 in that the amount of solvent DMAC added is 3.3g, corresponding to a solvent ratio of PAA:DMAC of 1.5:1.

[0183] Example 5

[0184] A magnetic field-oriented high-dielectric thin film differs from Example 1 in that the amount of solvent DMAC added is 5g, corresponding to a solvent ratio of PAA:DMAC of 1:1.

[0185] Example 6

[0186] A magnetic field-oriented high-dielectric thin film differs from Example 2 in that the amount of solvent DMAC added is 7.5g, corresponding to a solvent ratio of PAA:DMAC of 1:1.5.

[0187] Comparative Example 1

[0188] A magnetic field-oriented high-dielectric thin film, which differs from Example 1 in that the 9mBT fibers used are the disordered magnetic nanofibers of Comparative Preparation Example 1.

[0189] The dielectric test results of Example 1 and Comparative Example 1 are as follows: Figure 9a and 9b As shown, the results indicate that, compared to the dielectric constant of the composite film with randomly arranged fibers oriented by a magnetic field collected by a plate in Comparative Example 1, the dielectric constant of the composite film with ordered fibers oriented by a magnetic field collected by a roller in Example 1 is significantly improved.

[0190] The viscosity test results of Examples 1-5 are as follows: Figure 10a and Figure 10b As shown in the figure. The results indicate that with the increase of solvent content and solvent ratio, especially when PAA:DMAC is 1:1 and 1:1.5, the viscosity of the system decreases significantly, which is more conducive to the orientation of magnetic nanofibers under the action of a magnetic field.

[0191] The morphological results of the magnetic nanofibers inside the composite films of Examples 3, 5, and 6 in the magnetic field under orientation are as follows: Figures 11a to 11c As shown in the figure, direction B represents the magnetic field direction. The results indicate that increasing the solvent ratio reduces viscosity, which is more conducive to the orientation of magnetic nanofibers, resulting in an ordered arrangement of magnetic nanofibers along the thickness direction of the composite film, forming an oriented structure.

[0192] The dielectric property test results of Examples 3, 5, and 6 are as follows: Figure 12a and Figure 12b As shown in the figure. The results indicate that increasing the solvent ratio significantly improves the dielectric constant of the back-oriented composite film.

[0193] In the current system, using a magnetic field strength of 0.4T, a high-dielectric film with a dielectric constant of 32 can be obtained in the 9mBT (30wt%) / PI composite film system with a solvent ratio of PAA:DMAC of 3:1; and a high-dielectric film with a dielectric constant as high as 54 can be obtained in the 9mBT (40wt%) / PI composite film system with a solvent ratio of PAA:DMAC of 1:1.5. Compared with the dielectric constant of commonly used capacitor films on the market, the dielectric constant of the current high-dielectric composite film with 40wt% barium titanate content reaches the dielectric constant of capacitor films with approximately 80wt% barium titanate content on the market. Furthermore, the dielectric constant of the composite film can be further improved by increasing the content of magnetic nanofibers, adjusting the magnetism of the magnetic nanofibers, and increasing the magnetic field strength to enhance the orientation of the magnetic nanofibers.

[0194] It should be noted that the above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Where there is no conflict, the embodiments and features described in the embodiments of this application can be combined with each other. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A composite membrane, characterized in that, The composite film comprises a polymer matrix and magnetic fibers dispersed in the polymer matrix, the magnetic fibers being oriented along the thickness direction of the composite film. The magnetic fibers are obtained by electrospinning and roller collection of a magnetic sol containing magnetic particles and a ceramic matrix precursor, followed by calcination. The magnetic fibers comprise a ceramic matrix formed from the ceramic matrix precursor and the magnetic particles dispersed in the ceramic matrix. The diameter of the magnetic fibers is 300 nm to 700 nm, the length is 3 μm to 15 μm, the aspect ratio of the magnetic fibers is 10 to 50, and the dielectric constant of the composite film is greater than or equal to 32.

2. The composite membrane according to claim 1, characterized in that, The amount of magnetic fiber added is 3 wt% to 30 wt%.

3. The composite membrane according to claim 1 or 2, characterized in that, The thickness of the composite membrane is 10 μm to 50 μm.

4. The composite membrane according to claim 1, characterized in that, The polymer matrix includes at least one of polyimide, polyvinylidene fluoride, polypropylene, and silicone rubber.

5. The composite membrane according to claim 1, characterized in that, The ceramic matrix includes at least one of barium titanate crystals, barium strontium titanate crystals, calcium copper titanate crystals, and lead zirconate titanate crystals.

6. The composite membrane according to claim 5, characterized in that, When the ceramic matrix includes the barium titanate crystal, the average crystal size of the barium titanate crystal is 50 nm to 200 nm.

7. The composite membrane according to claim 1, characterized in that, The amount of magnetic particles added is 3 wt% to 30 wt%.

8. The composite membrane according to claim 1, characterized in that, The average particle size of the magnetic particles is 20 nm to 80 nm.

9. The composite membrane according to claim 1, characterized in that, The magnetic particles include at least one of ferrite, cobalt ferrite, barium ferrite, and composite ferrite.

10. A method for preparing a composite membrane, characterized in that, Includes the following steps: An intermediate membrane is formed by forming a mixed solution containing magnetic fibers, solvent and polymer precursor, wherein the magnetic fibers are obtained by electrospinning and roller collection of a magnetic sol containing magnetic particles and ceramic matrix precursor, and calcination. The magnetic fibers include a ceramic matrix formed by the ceramic matrix precursor and magnetic particles dispersed in the ceramic matrix. The magnetic fibers have a diameter of 300 nm to 700 nm, a length of 3 μm to 15 μm, and an aspect ratio of 10 to 50. The intermediate film is placed in a magnetic field so that the magnetic fibers are oriented along the thickness direction of the intermediate film to obtain an intermediate oriented film. as well as The intermediate orientation film is cured to solidify the polymer precursor to form a polymer matrix, thereby obtaining the composite film, wherein the dielectric constant of the composite film is greater than or equal to 32.

11. The method for preparing the composite membrane according to claim 10, characterized in that, The mass ratio of the polymer precursor to the solvent in the mixed solution is (4:1) to (1:2).

12. The method for preparing the composite membrane according to claim 11, characterized in that, The mass ratio of the polymer precursor to the solvent in the mixed solution is 3:

1.

13. The method for preparing the composite membrane according to claim 10, characterized in that, The orientation temperature is 20~60℃, and the time is 5~60 min.

14. The method for preparing the composite membrane according to any one of claims 10 to 13, characterized in that, Prior to the step of curing the intermediate orientation film, the preparation method further includes the following steps: The intermediate orientation film was sequentially dried in a forced-air oven and a vacuum oven, wherein the temperature in the forced-air oven was 60~100 ℃ and the drying time was 6~12 h, and the temperature in the vacuum oven was 60~100 ℃ and the drying time was 6~12 h.

15. The method for preparing the composite membrane according to claim 10, characterized in that, The ceramic matrix precursor includes at least one of barium titanate sol, barium strontium titanate sol, calcium copper titanate sol, and lead zirconate titanate sol.

16. The method for preparing the composite membrane according to claim 15, characterized in that, When the ceramic matrix precursor is barium titanate sol, the preparation method of the magnetic sol includes the following steps: A solution of tetraisopropyl titanate was added to a barium acetate solution and stirred to obtain a barium titanate sol; and The magnetic particles are dispersed in the barium titanate sol to obtain the magnetic sol.

17. The method for preparing the composite membrane according to claim 16, characterized in that, The dispersion includes the following steps: The magnetic particles and the barium titanate sol were magnetically stirred to obtain a preliminary mixed sol. The pre-mixed sol is mixed in a homogenizer to obtain a pre-mixed sol. The homogenizer operates at a speed of 3500-4500 rpm / min, and the mixing time is 15-30 min. The premixed sol is subjected to gradient ultrasonic dispersion, wherein the gradient ultrasonic dispersion includes: ultrasonicating the premixed sol at a power of 700~900 W for 5~15 min, and then continuing to ultrasonicate at a power of 200~400 W for 10~20 min.

18. The method for preparing the composite membrane according to claim 16 or 17, characterized in that, Following the step of dispersing the magnetic particles in the barium titanate sol, the method for preparing the magnetic sol further includes the following step: A spinning aid is added to the barium titanate sol containing the magnetic particles.

19. The method for preparing the composite membrane according to claim 18, characterized in that, The spinning aid includes at least one of polyvinylpyrrolidone, polyethylene oxide, polystyrene, and epoxy resin.

20. The method for preparing the composite membrane according to claim 10, characterized in that, The drum for collecting the water droplets rotates at a speed of 2000~3000 rpm / min.

21. The method for preparing the composite membrane according to claim 10, characterized in that, The viscosity of the magnetic sol is 2~12 Pa·s.

22. The method for preparing the composite membrane according to claim 10, characterized in that, The calcination includes the following steps: The precursor fiber was heated from room temperature to 340-360 °C within 100 min and held at 340-360 °C for 50-70 min; then heated to 680-720 °C within 100 min and held at 680-720 °C for 100-140 min.

23. A circuit board, characterized in that, It includes a base layer and a circuit layer located on at least one surface of the base layer, wherein the base layer is a composite film as described in any one of claims 1 to 9 or a composite film prepared by a method described in any one of claims 10 to 22.

24. An electronic device, characterized in that, It includes a housing and a circuit board housed within the housing, the circuit board being the circuit board as described in claim 23.

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