CN110253801B - Preparation method of dielectric gradient material and encapsulation method of electronic component - Google Patents

Preparation method of dielectric gradient material and encapsulation method of electronic component Download PDF

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CN110253801B
CN110253801B CN201910515375.4A CN201910515375A CN110253801B CN 110253801 B CN110253801 B CN 110253801B CN 201910515375 A CN201910515375 A CN 201910515375A CN 110253801 B CN110253801 B CN 110253801B
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inorganic particles
magnetic field
suspension
dielectric
magnetic
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CN110253801A (en
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申子魁
贾志东
王希林
张天枫
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Shenzhen Graduate School Tsinghua University
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Shenzhen Graduate School Tsinghua University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C39/00—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor
    • B29C39/02—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor for making articles of definite length, i.e. discrete articles
    • B29C39/10—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor for making articles of definite length, i.e. discrete articles incorporating preformed parts or layers, e.g. casting around inserts or for coating articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C39/00—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor
    • B29C39/22—Component parts, details or accessories; Auxiliary operations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C2791/00—Shaping characteristics in general
    • B29C2791/004—Shaping under special conditions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/06—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts
    • B29K2105/20—Inserts
    • B29K2105/203—Magnetic parts

Abstract

A preparation method of a dielectric gradient material comprises the following steps: mixing inorganic particles and liquid organic matters to obtain a suspension, wherein the inorganic particles at least comprise a magnetic material with a dielectric constant larger than 40; applying a magnetic field to the suspension, wherein under the action of the magnetic field, the magnetic field force applied to part of the inorganic particles is greater than the viscous resistance applied to the part of the inorganic particles in the suspension, so that the part of the inorganic particles are arranged in a chain shape along the direction of the magnetic field; and curing the suspension after the magnetic field is applied to cure the suspension to obtain the dielectric gradient material. The invention also provides a potting method of the electronic component. According to the preparation method provided by the invention, the magnetic field is applied to the suspension in situ, so that the inorganic particles in the suspension are arranged in a chain shape along the direction of the magnetic field, and the preparation method is simple and controllable and saves the cost.

Description

Preparation method of dielectric gradient material and encapsulation method of electronic component
Technical Field
The invention relates to the technical field of insulating material preparation, in particular to a preparation method of a dielectric gradient material and an encapsulating method of an electronic component.
Background
With the development of power systems towards ultra/extra-high voltage and high-capacity power transmission, and the development of high and new technical equipment such as pulse power, high-power microwave, high-power semiconductor devices and the like towards high voltage and miniaturization, the requirement on electrical insulation performance is increasingly strict, and the problems caused by insulation system, particularly solid insulation faults, in the operation process of equipment are increasingly prominent. It is considered that the high unevenness of the electric field (local electric field distortion) is a root cause of dielectric breakdown and creeping flashover. At interfaces of different media, such as three junctions of an electrode, insulation and gas, due to rapid change of dielectric parameters, electric field distribution is uneven, local electric field distortion is serious, primary electrons are easy to generate to cause local discharge, on one hand, aging of an insulation material is aggravated, and on the other hand, surface flashover is caused.
The insulation structure with the dielectric parameters distributed non-uniformly is constructed by utilizing the concept of Functional Gradient Materials (FGM), has obvious advantages in the aspects of homogenizing alternating current electric field and pulse electric field distribution, improving the electric resistance of an insulation system, simplifying the insulation structure and the like, and has great application potential. However, the operability, flexibility, efficiency and cost of the preparation method of the dielectric gradient material determine the application prospect of the dielectric gradient material.
At present, the existing preparation methods of the dielectric gradient material comprise a centrifugal casting method, a lamination method, an electrophoresis method and a magnetron sputtering method. The distribution of the material gradient structure prepared by the centrifugal casting method is limited by the physical law of the centrifugal process, the requirement of insulation design is difficult to meet, the flexibility and controllability are poor, and the material gradient structure is difficult to be applied in industry on a large scale. The dielectric constant of products prepared by the lamination method, such as disc type and pillar dielectric gradient insulators, changes monotonously or in a U shape along with the radius or height of the insulators, and the surface flashover strength under positive polarity lightning impulse voltage is improved by 10 to 25 percent; however, the lamination method cannot realize one-step integral molding, and easily has the defect of interlayer combination, and the dielectric characteristic jump between layers does not accord with the direction of the optimization design result. The electrophoresis technology is utilized to drive charged particles to move, gradient change of particulate matter concentration is achieved, and then the dielectric gradient material is constructed. All three techniques are to introduce particles with high dielectric constant and increase the local particle concentration of the composite material to increase the local dielectric constant. The highest dielectric constant which can be obtained when the particles are distributed in a disordered way is limited, if the volume fraction of the particles is small, the dielectric constant of the composite material is not changed greatly, and the effect of optimizing an electric field is weak; if the volume fraction added is too high, this will increase the viscosity of the mixture, which is detrimental to the cast molding process. In the existing preparation method, a magnetron sputtering method is utilized to sputter target materials (titanium dioxide, barium titanate and the like) onto the surface of the basin-type insulator, and gradient distribution of the dielectric constant of the 2D film is realized by controlling the sputtering time length of different areas. However, the technology realizes 2D dielectric distribution, has limited influence on the dielectric constant of the 3D insulator, and has limited application prospect.
The effectiveness of using a dielectric gradient material to homogenize an electric field and improve the insulation performance has been verified by many research institutes, however, by means of a centrifugal casting method, a lamination method, an electrophoresis method, a magnetron sputtering method and the like, particles are locally disorderly aggregated, the dielectric constant obtained by the method is improved to a limited extent, and the large gradient dielectric distribution required by a very non-uniform electric field cannot be provided.
Disclosure of Invention
Accordingly, there is a need for a method for preparing a dielectric gradient material, which solves the above-mentioned problems of limited dielectric constant enhancement and failure to provide a large gradient dielectric distribution required by a highly non-uniform electric field.
In addition, it is also necessary to provide a method for encapsulating electronic components.
A preparation method of a dielectric gradient material comprises the following steps:
mixing inorganic particles and liquid organic matters to obtain a suspension, wherein the inorganic particles at least comprise a magnetic material with a dielectric constant larger than 40;
applying a magnetic field to the suspension, wherein under the action of the magnetic field, the magnetic field force applied to part of the inorganic particles is greater than the viscous resistance applied to the part of the inorganic particles in the suspension, so that the part of the inorganic particles are arranged in a chain shape along the direction of the magnetic field; and
and curing the suspension after the magnetic field is applied to cure the suspension to obtain the dielectric gradient material.
Further, the application mode of the magnetic field comprises that the magnetic field is generated by a permanent magnet or an external current coil.
Further, the magnetic field intensity formed by the magnetic field in the suspension can drive at least one type of the inorganic particles to move, and the magnetic field intensity in the suspension is less than or equal to 1T.
Further, the inorganic particles are of a core-shell structure and comprise a core and a shell covering the core, and the core and the shell at least comprise one magnetic material.
Further, the particle size of the inorganic particles is less than 100 μm; the liquid organic matter is a curable material; the volume fraction of the inorganic particles in the suspension is less than or equal to 50%; the viscosity of the suspension is less than or equal to 100Pa · s.
Further, before applying the magnetic field to the suspension, the method further comprises the step of pouring the suspension into a pouring mold or coating the suspension on the surface of an object.
Further, the applying of the magnetic field overlaps in time with the performing of the curing treatment, and the conditions of the curing treatment include at least one of standing, heating, light irradiation, and mechanical pressurization.
Further, the preparation method further comprises the step of carrying out coupling agent treatment on the inorganic particles, wherein the coupling agent treatment comprises the step of soaking the inorganic particles in a solution formed by ethanol and a coupling agent together, or the coupling agent is added into the suspension, and the mass of the coupling agent accounts for 0.5-2% of the total mass of the coupling agent and the inorganic particles.
An encapsulating method of an electronic component comprises the following steps:
providing at least two electronic components arranged in a packaging module of the electronic components;
adding inorganic particles and liquid organic matters into the packaging module to obtain a suspension, immersing the electronic component in the suspension, wherein the inorganic particles at least comprise a magnetic material with a dielectric constant larger than 40;
applying a magnetic field to the packaging module, wherein under the action of the magnetic field, the magnetic field force applied to part of the inorganic particles is greater than the viscous resistance applied to the part of the inorganic particles in the suspension, so that the part of the inorganic particles are arranged in a chain shape along the direction of the magnetic field; and
and curing the turbid liquid after the magnetic field is applied to cure the turbid liquid, so that the electronic components are encapsulated together.
Further, the application mode of the magnetic field comprises a magnetic field generated by a permanent magnet or an external current coil; the magnetic field intensity formed by the magnetic field in the suspension can drive at least one type of the inorganic particles to move, and the magnetic field intensity in the suspension is less than or equal to 1T.
According to the preparation method of the dielectric gradient material, a magnetic field is applied to a suspension in situ, inorganic particles in partial areas of the suspension are arranged in a chain shape along the direction of the magnetic field under the action of the magnetic field, and curing conditions are applied to obtain the composite material with the dielectric gradient. The preparation method can realize accurate control of the product to be prepared through the conditions of the magnitude of the magnetic field intensity, the gradient of the magnetic field intensity and the like, and is simple, controllable and cost-saving.
Drawings
Fig. 1 is a flowchart of a method for preparing a magnetic field induction-based dielectric gradient material according to an embodiment of the present invention.
FIG. 2 is a graph of the dielectric constant distribution of the dielectric gradient material according to different models.
FIG. 3 is a schematic diagram of a dielectric gradient material according to the present invention.
FIG. 4 is a schematic view of a disc-shaped mold for applying a magnetic field in an embodiment of the present invention.
FIG. 5A is a cross-sectional flux density vector field diagram of an applied magnetic field according to an embodiment of the present invention; FIG. 5B is a magnetic induction gradient vector field diagram in an embodiment; FIG. 5C is a graph of the results of finite element calculations of a three-dimensional magnetic induction cloud of the applied magnetic field of the example.
FIGS. 6A, 6B and 6C are optical microscope test charts of different magnifications in the region near the inner electrode for the dielectric gradient material prepared in the example; fig. 6D and 6E are optical microscopy test images of the dielectric gradient material at regions centered from and away from the inner electrode region, respectively.
FIG. 7 is a graph showing the results of the surface flashover voltage test of the dielectric gradient materials prepared in the examples of the present invention, comparative example 1 and comparative example 2.
Description of the main elements
Figure BDA0002094849490000041
Figure BDA0002094849490000051
The following detailed description will further illustrate the invention in conjunction with the above-described figures.
Detailed Description
So that the manner in which the above recited objects, features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. In addition, the embodiments and features of the embodiments of the present application may be combined with each other without conflict. In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention, and the described embodiments are merely a subset of the embodiments of the present invention, rather than a complete embodiment. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes all and any combination of one or more of the associated listed items.
In various embodiments of the present invention, for convenience in description and not in limitation, the term "coupled" as used in the specification and claims of the present application is not limited to physical or mechanical couplings, either direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships are changed accordingly.
Referring to fig. 1, a method for preparing a magnetic field-induced dielectric gradient material according to an embodiment of the present invention includes the following steps:
step S1: mixing inorganic particles and liquid organic matters to obtain a suspension, wherein the inorganic particles at least comprise a magnetic material with a dielectric constant larger than 40;
step S2: applying a magnetic field to the suspension, wherein under the action of the magnetic field, the magnetic field force applied to part of the inorganic particles is greater than the viscous resistance applied to the part of the inorganic particles in the suspension, so that the part of the inorganic particles are arranged in a chain shape along the direction of the magnetic field;
step S3: and curing the suspension after the magnetic field is applied to cure the suspension to obtain the dielectric gradient material.
The inorganic particles are dispersed in a liquid organic matter, and part of the inorganic particles move and/or turn or/and arrange under the action of a magnetic field, so that a particle distribution structure with similar electric field environment is achieved when the dielectric gradient material is applied; and obtaining the dielectric gradient material through a curing treatment. Wherein the inorganic particles are used as filler particles, and the liquid organic is used as a matrix material to form the dielectric gradient material.
In step S1, the inorganic particles are placed in a liquid organic material, and the inorganic particles are more uniformly dispersed in the liquid organic material by means of mechanical treatment such as ultrasonic treatment and/or mechanical stirring, thereby forming the suspension.
The magnetic material is a material that reacts in some way to a magnetic field. The inorganic particles include, but are not limited to, core-shell structure particles prepared from ceramic and/or non-metal compounds such as metal compounds and magnetic material particles, such as core-shell structure particles constructed from metal titanates, metal sulfates, metal oxides, non-metal oxides, metal fluorides, metal nitrides, metal carbides, and non-metal carbides with magnetic materials such as transition elements of iron, cobalt, nickel, and alloys thereof, and magnetic materials themselves, such as metal and alloy magnetic materials or ferrite magnetic materials.
Further, the inorganic particles are of a core-shell structure and comprise a core and a shell covering the core, the core and the shell at least comprise one magnetic material and one inorganic non-magnetic material, and the dielectric constant of the inorganic non-magnetic material is greater than or equal to 40. For example, the inorganic particles are titanium dioxide and ferroferric oxide (TiO)2@Fe3O4) Or barium titanate and ferroferric oxide (BaTiO)3@Fe3O4) In the core-shell structure formed in the embodiment, titanium dioxide and barium carbonate are respectively used as cores, ferroferric oxide is used as a shell to coat the cores, and the ferroferric oxide moves under the influence of a magnetic field in the magnetic field, so that the whole core-shell structure is driven to move. Inorganic particles with high dielectric constants such as titanium dioxide or barium titanate and the like are selected to construct core-shell structure particles together with magnetic materials to serve as the inorganic particles, so that the adding proportion of the filler particles can be reduced.
The inorganic particles have a particle size of less than 100 μm, for example 50 μm, 30 μm, 20 μm, 10 μm, 5 μm, 1 μm or nanometer size, the smaller particle size being advantageous for dispersing the inorganic particles in the liquid organic substance. The particle size of the inorganic particles may be determined by laser diffraction or equivalent methods, with at least 95% of the particles at or below the established particle size.
In one embodiment, the TiO particle size is 1 μm2@Fe3O4Mixed with an epoxy resin (type E51/MeHHPA) having a viscosity of 1Pa · s, and arranged in a chain shape for 20 minutes when induced with a neodymium-iron-boron permanent magnet.
Further, the suspension contains at least one inorganic particle with a particle size of less than 1 μm, which is advantageous for stabilizing the suspension. The inorganic particles having a particle size of less than 1 μm may be reduced by grinding the inorganic particles using one of ball milling, attrition milling, vibratory milling, and jet milling methods.
Further, the particles comprise zero-dimensional spheres, one-dimensional lines and two-dimensional sheets.
Further, the volume fraction of the inorganic particles in the suspension is less than or equal to 50%.
Preferably, the volume fraction of inorganic particles in the suspension is less than or equal to 5%.
In other embodiments, the method further comprises subjecting the inorganic particles to a coupling agent treatment step. The step of treating the coupling agent comprises the step of soaking the inorganic particles in a solution composed of ethanol and the coupling agent, or adding the coupling agent into the suspension. After the inorganic particles are treated by the coupling agent, the compatibility of the inorganic particles and the liquid organic matter can be improved, so that the bonding strength of the inorganic particles and the liquid organic matter is improved.
The mass of the coupling agent accounts for 0.5-2% of the total mass of the coupling agent and the inorganic particles.
In a specific embodiment, the coupling agent is gamma- (2, 3-glycidoxy) propyl trimethoxy silane (KH-560), and the addition amount of the coupling agent is 1.5% of the total mass of the inorganic particles and the coupling agent.
The liquid organic matter is a curable material, that is, the liquid organic matter is cured by certain curing conditions, and the organic matter comprises at least one of thermosetting plastics (such as epoxy resin or phenolic resin), thermoplastic plastics (such as polyethylene) and rubber (such as silicon rubber, nitrile rubber, ethylene propylene diene monomer rubber or vulcanized silicon rubber).
Further, the viscosity of the liquid organic substance is less than or equal to 10 pas. Preferably, the viscosity of the liquid organic substance is less than or equal to 1Pa · s or 100mPa · s.
Further, the viscosity of the suspension is less than or equal to 100Pa · s, and a smaller viscosity is advantageous for improving the magnetic field induction efficiency. The viscosity of the suspension can be reduced by reducing the filler fraction of the inorganic particles, reducing the particle size of the inorganic particles, heating, adding a defoamer, and the like.
Preferably, the viscosity of the suspension is 10Pa · s or less.
Further, the suspension liquid also comprises one or more of an accelerating agent and a curing agent. The accelerators serve to reduce the curing conditions and increase the curing speed, for example to reduce the temperature or time required for curing. The curing agent is used for curing the liquid organic matter.
In step S2, after the suspension is placed in the magnetic field, the inorganic particles in the suspension are magnetized under the action of the magnetic field, and at this time, the inorganic particles can be regarded as magnetic dipoles, and the magnetized inorganic particles are turned to be arranged in a chain shape due to the interaction, and at the same time, the directional movement of the magnetic particles (for example, the movement toward the N/S poles of the magnet) is caused by the magnetic field gradient, so that the magnetic particles are arranged in a gradient. Therefore, the inorganic particles have gradient chain-shaped arrangement under the action of the magnetic field.
Further, the inorganic particles are subjected to a magnetic field force of
Figure BDA0002094849490000081
When the inorganic particles move, the viscous resistance in the suspension is F ═ 6 pi η vr, and the movement speed of the inorganic particles is
Figure BDA0002094849490000082
Wherein V is the volume of the inorganic particles, r is the radius of the inorganic particles, μ0The magnetic permeability of the filler is shown, the specific susceptibility of the inorganic particles is shown, and the specific susceptibility of the liquid organic matter is shown in the matrix. The direction of the movement of the inorganic particles is related to the difference of magnetic susceptibilities of the inorganic particles and the liquid state organic matter and the distribution of the magnetic field. In particular, when Chi filler>When the X matrix is adopted, the inorganic particles move towards the direction of the magnetic field becoming stronger, and the volume fraction of the particles in the high-intensity magnetic field area is increased; "Danchi" filler<In the chi-type matrix, the inorganic particles move in the direction in which the magnetic field becomes weaker, and the volume fraction of the particles in the region of the weak magnetic field increases.
Specifically, the movement of inorganic particles in a suspension is subject to viscous resistance, so that the alignment of the particles in the matrix is a function of time and space when a magnetic field is applied. When χ filler > χ matrix, the motion toward high magnetic field strength region deposits and the magnetic particles are aligned in chains. In addition, the stronger the magnetic field is, the higher the volume fraction of the particles is, and the faster the particles are arranged; the weaker the magnetic field, the slower the alignment speed of the particles, and even when the magnetic field is small to a certain threshold, the magnetostatic force between the magnetized dipoles is smaller than the viscous resistance (such as surface tension) of the matrix, and the particles will be confined in the original position and cannot be aligned into chains.
By utilizing the characteristic, in the processing process of the insulating part, according to the structural shape of the insulating system, a magnetic field similar to the electric field distribution of the insulating system is applied, for example, the magnetic induction intensity in a region with a stronger electric field of the insulating system is higher, the directions are the same or similar, the proper action time is controlled, a relative dielectric constant which is several times or even dozens of times higher than that of other regions is accurately constructed in a local region with high electric field intensity, the size of a high dielectric constant and the size of a high dielectric constant region can be accurately controlled through the size of the magnetic field, the unevenness of the magnetic field and the application time, and the expected design can be achieved. According to the method, in the local part of high electric field intensity, the dielectric constant of the area along the electric field direction is improved by increasing the volume fraction of local particles and constructing chain-shaped arrangement. Meanwhile, the volume fraction of the filler in other areas is not high, so that the cost is saved, and the processing of the product is facilitated (the overall viscosity is low).
Generally, the inorganic particles are uniformly and randomly dispersed in the matrix material, and the dielectric constant of the dielectric gradient material can be calculated by some empirical formula, such as Maxwell-Garnett (Maxwell-Garnett) model, loyenga model, Bruggeman model, and other mixed models. The calculation formula listed is as follows:
Maxwell-Garnett formula:
Figure BDA0002094849490000091
bruggeman's formula:
Figure BDA0002094849490000092
the formula loyenga:
logεcompounding＝φlogεFiller material+(1-φ)logεBase body
Wherein
Figure BDA0002094849490000093
Is the volume fraction of the added inorganic particles, εCompoundingIs the dielectric constant, ε, of the dielectric gradient materialFiller materialIs the dielectric constant, ε, of the inorganic particlesBase bodyIs the dielectric constant of the liquid organic.
If the inorganic particles and the liquid organic material form a series structure or a parallel structure, the dielectric constant of the dielectric gradient material can be calculated by using a series model or a parallel model, and the formula is as follows:
series model:
Figure BDA0002094849490000101
parallel connection model:
εcompounding＝φεFiller material+(1-φ)εBase body
Among them, the parallel model can realize a dielectric constant much larger than other models in the case where the inorganic particles have a low filling volume fraction. The inorganic particles are arranged in a chain shape under the induction of the magnetic field, so that a parallel model is formed with the liquid organic matter, and a higher dielectric constant (relative to a mixed model) can be obtained under a low filling proportion.
Referring to fig. 2, taking barium titanate (relative dielectric constant 1250)/epoxy resin (relative dielectric constant 4.5) composite as an example, it can be seen that when the volume fraction of barium titanate is 10%, the relative dielectric constant of the dielectric gradient material of the parallel model is 20 times that of the mixed model; when the volume fraction of barium titanate is 20%, the relative dielectric constant of the parallel model is 30 times that of the mixed model. And at a low volume fraction (less than 30%), the relative dielectric constant of the dielectric gradient material of the mixed model is not effectively improved, for example, the addition volume fraction is 30%, the relative dielectric constant of the composite material calculated according to the Maxwell-Garnett formula is 10.3, and the relative dielectric constant is only improved by 2.28 times compared with that of epoxy resin. By using the parallel model, the dielectric constant of the composite material can be improved to 10.8 only by using 0.5 volume percent of barium titanate particles. It can be seen that the dielectric constant is improved by using the parallel model, and the raw material cost can be greatly saved. Meanwhile, the volume fraction of barium titanate is too high, which can cause the viscosity of suspension to increase and the fluidity to deteriorate, and is not beneficial to the pouring processing of products.
The magnetic field is applied in a manner that includes the magnetic field of the permanent magnet itself or the magnetic field generated by an external current coil.
The mass ratio of a portion of the inorganic particles to the total mass of the inorganic particles is related to the distribution of the magnetic field strength, for example, in one embodiment, 20% of the area of the inorganic particles is subjected to a magnetic field force greater than the viscous resistance, i.e., the mass ratio is 20%; in another embodiment, the inorganic particles in 70% of the area are subjected to a magnetic field force greater than the viscous resistance, i.e., the mass ratio is 70%.
Further, the magnetic field strength does not exceed a critical value that the dielectric gradient material or the dielectric gradient material can bear internally when used in an electronic component, for example, an internal precision structure in an electronic component is composed of a magnetic material (e.g., metallic iron), and the internal deformation may be caused by a strong magnetic field.
Further, the magnetic field strength can drive the at least one inorganic particle to move, turn or align in the suspension, for example, the magnetic field strength driving the at least one inorganic particle in the suspension can be less than 1T, less than 0.5T, less than 0.1T, less than 0.01T.
Further, the magnetic field induces movement, turning or alignment of the inorganic particles in the suspension, which may be distributed, for example, enriched in a certain region, depleted in a certain region, or arranged in a regular chain. The distribution of the inorganic particles can be determined by optical microscopy, scanning electron microscopy, light rate measurement or equivalent devices.
In one embodiment, the inorganic particles are observed to be arranged in a chain shape by an optical microscope after applying a magnetic field to the suspension for not more than 10 minutes. In other embodiments, the enrichment or depletion of the inorganic particles in a particular region is observed using an optical microscope after applying the magnetic field for no more than 20 minutes.
In another embodiment, before applying the voltage to the suspension, the method further comprises casting the suspension in a casting mold or coating the suspension on a surface of an object.
And pouring the suspension into a pouring mold, namely solidifying the suspension into the shape of a dielectric gradient material required by a user after solidification treatment in the pouring mold, wherein the dielectric gradient material comprises but is not limited to a basin insulator, a supporting insulator, a suspension insulator and a cable accessory.
Furthermore, the surface of the casting mold is coated with a release agent, so that the poured turbid liquid can be separated from the casting mold.
Further, the casting mold is made of a material with low magnetic permeability, such as metal except iron, cobalt, nickel, or polytetrafluoroethylene.
In step S3, the curing conditions include, but are not limited to, standing, heating, light (e.g., ultraviolet or visible light), mechanical pressure, and the like.
In one embodiment, the liquid organic is E51 epoxy resin and methyl hexahydrophthalic anhydride, and the curing conditions are that the epoxy resin is firstly cured for 2 hours at 100 ℃ and then cured for 2 hours at 120 ℃.
Further, the magnetic field induction and the curing conditions may overlap in time.
The invention also provides an encapsulating method of the electronic component, which comprises the following steps:
step S101: providing at least two electronic components arranged in a packaging module of the electronic components;
step S102: adding the inorganic particles and the liquid organic matter into the packaging module to obtain a suspension, immersing the electronic component in the suspension, wherein the inorganic particles at least comprise a magnetic material with a dielectric constant larger than 40;
step S103: applying a magnetic field to the packaging module, wherein under the action of the magnetic field, the magnetic field force applied to part of the inorganic particles is greater than the viscous resistance applied to the part of the inorganic particles in the suspension, so that the part of the inorganic particles are arranged in a chain shape along the direction of the magnetic field;
step S104: and curing the turbid liquid after the magnetic field is applied to cure the turbid liquid, so that the electronic components are encapsulated together.
In step S101, the electronic component includes, but is not limited to, an Insulated Gate Bipolar Transistor (IGBT), a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), and the like.
In step S103, the strength of the applied magnetic field does not exceed a critical value that the dielectric gradient material or the electronic component can withstand internally.
Furthermore, in the process of applying the magnetic field, the electronic component can be electrified, so that suspension filled and sealed in the electronic component can adapt to the working conditions of the subsequent electronic component during operation after being solidified.
The invention also provides a dielectric gradient material, which is prepared by the preparation method of the dielectric gradient material based on magnetic field induction. The dielectric gradient material is used in various fields, for example, for internal insulation of electronic components, external insulation of electric equipment, and electrical insulation within electric equipment.
Specifically, the internal insulation of the electronic component includes potting adhesive, such as insulating potting adhesive used in an Insulated Gate Bipolar Transistor (IGBT) module, a cable accessory, and the like; the external insulation of the electronic component comprises a printed circuit board; the internal insulation of the electric equipment comprises dry composite sleeves, power cables, internal insulation of motors and the like; the external insulation of the electric equipment comprises various insulators, such as a composite suspension insulator, a composite hollow insulator, a composite post insulator, a basin insulator, a supporting insulator and the like.
In a specific embodiment, the dielectric gradient material is used for connecting at least two electronic components, and the electronic components are connected through the dielectric gradient material but are insulated from each other. The electronic component includes, but is not limited to, an insulated gate bipolar Transistor, a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), and the like.
In another embodiment, the dielectric gradient material is used in basin insulators for circuit breakers and Gas Insulated metal enclosed Switchgear (GIS) applications.
The invention also provides a dielectric gradient material, which is prepared by the preparation method of the dielectric gradient material based on magnetic field induction. The dielectric gradient material is suitable for various electronic components, such as a basin insulator applied to a circuit breaker and Gas Insulated metal enclosed Switchgear (GIS), an insulating potting adhesive applied to an Insulated Gate Bipolar Transistor (IGBT) module and a cable accessory.
In addition, the dielectric gradient material is also used as a potting material for connecting at least two electronic components which are connected by the dielectric gradient material but are insulated from each other. The electronic component includes, but is not limited to, an insulated gate bipolar Transistor, a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), and the like.
Further, the dielectric gradient material is also applied to the electric equipment and the electronic component as an insulating coating.
The dielectric gradient material comprises a matrix material and filler particles, wherein the filler particles are dispersed in the matrix material, the filler particles are granular, and the filler particles at least comprise a magnetic material with a dielectric constant larger than 40. The filler particles are the inorganic particles, and the matrix material is the liquid organic matter and is formed by solidification.
The filler particles have a dielectric constant greater than or equal to 40, the filler particles having a dielectric constant that is 1-50 times the dielectric constant of the matrix material.
The dielectric gradient material comprises a first region S1A second area S2And is located in the first area S1And a second area S2Third region S in between3Said third region S3As a first region S1And a second area S2A transition region of (a); the filler particles are in the first region S1Towards the second area S2In a chain-like arrangement, the filler particles being in the second region S2Disordered distribution of the filler particles in the third region S3Transition from ordered to disordered, i.e. close to said first region S1Are arranged approximately in a chain shape and are close to the second area S2The positions of (a) are approximately randomly distributed.
In one embodiment, the first region S1And a second area S2The inner electrode and the outer electrode are divided according to the positions of the inner electrode and the outer electrode which generate the magnetic field in the process of preparing the dielectric gradient material, the outer electrode is arranged around the inner electrode, the magnetic field intensity of the area which is closer to the inner electrode is larger, and the magnetic field intensity of the area which is farther from the inner electrode is smaller. Referring to FIG. 3, the inner electrode is disposed at the origin A, the outer electrode is a ring B, and the first region S1The more the region is close to the origin A (i.e. the region is farther from the circular ring B), the more the filler particles are arranged in a chain shape, and the dielectric gradient material is arranged in the first region S close to the origin A1The larger the dielectric constant of (a); the farther away from the origin A (i.e., the closer to the ring B), the more disordered the arrangement of the filler particles is, and the farther away from the origin A, the second region S of the dielectric gradient material is2The smaller the dielectric constant of (a). Therefore, the dielectric constant of the dielectric gradient material is distributed in a gradient manner.
In other embodiments, the dielectric gradient material is not limited to the circular shape shown in fig. 3, and the actual shape may be changed as needed, for example, the shape may also be square, oval, and other irregular shapes.
Further, is located in the second area S2The dielectric constant of the dielectric gradient material is 1-5 times of that of the substrate, and is positioned in the first region S1The dielectric constant of the dielectric gradient material is in the second region S2Is 1-50 times of the dielectric constant of the dielectric gradient material, is positioned in the third region S3The dielectric gradient material has a dielectric constant between that of the first region S1The dielectric constant of the dielectric gradient material is in the second region S2Of said dielectric gradient material. The dielectric gradient material is positioned in the first region S in practical application1The dielectric gradient material is preferentially arranged in a region with relatively high electric field intensity and is positioned in a second region S2Is placed in a region of relatively low electric field strength.
Further, at least one of the filler particles has a dielectric constant greater than or equal to 40 times the dielectric constant of the matrix material.
Further, the density of the filler particles is distributed in the matrix material in a gradient manner and is positioned in the first area S1Has a density greater than or equal to that of the filler particles in the second region S2The density of the filler particles of (a).
The matrix material also comprises one or more of an accelerator, a curing agent, a defoaming agent and a coupling agent.
The present invention will be specifically described below with reference to specific examples.
Examples
Adding photosensitive bisphenol A epoxy acrylate resin and a defoaming agent TL-X60 into a mixing tank according to the mass ratio of 100:0.4 to obtain a mixed solution, stirring for 0.5h at the speed of 600r/min in an ultrasonic environment, and degassing for 0.5h in a vacuum environment at the temperature of 50 ℃.
Adding the mixture, barium titanate @ ferroferric oxide core-shell structure particles with the particle size of 1 mu m and KH-560 silane coupling agent into a mixing tank according to the mass ratio of 100:2.5:0.0375, stirring for 0.5 hour at the speed of 600 rpm in an ultrasonic environment, and degassing for 0.5 hour in a vacuum environment at the temperature of 50 ℃ to obtain a suspension, wherein the barium titanate @ ferroferric oxide accounts for 0.5 percent of the total volume of the suspension in terms of volume fraction.
Referring to fig. 4, the suspension is placed in a disc-shaped mold, the disc-shaped mold is made of polytetrafluoroethylene, a Plumbum 909A release agent is coated on the surface of the disc-shaped mold, a tubular brass electrode with a radius of 5mm coaxially penetrates through the center of the disc-shaped mold and serves as an inner electrode, magnets and a middle cushion block are placed in the brass electrode according to the sequence of neodymium iron boron magnet (N-S) -polytetrafluoroethylene-neodymium iron boron magnet (S-N), the magnets and the cushion block are cylinders with a radius of 4.5mm, the heights of the two magnets are both 6mm, the height of the cushion block is 3mm, the cushion block is flush with the upper surface and the lower surface of the disc-shaped mold, and; and applying a magnetic field to the disc-shaped mold by using the neodymium iron boron magnet, wherein the remanence of the magnet is 0.9T, and the central surface magnetism calculation value of a single magnet is about 0.3T.
And pouring the suspension subjected to the magnetic field into a horizontally placed mold, standing for 30min, placing the mold into an ultraviolet lamp box for irradiating for 2h, and curing to obtain the dielectric gradient material based on the magnetic field induction.
Comparative example 1
In contrast to the examples: and directly curing the mixture to obtain the insulating part without adding barium titanate @ ferroferric oxide core-shell structure particles and KH-560 silane coupling agent or applying magnetic field induction.
The rest is the same as the embodiment and is not described in detail herein.
Comparative example 2
In contrast to the examples: and (4) directly curing the suspension without applying magnetic field induction to obtain the insulating part.
The rest is the same as the embodiment and is not described in detail herein.
Referring to fig. 5A, 5B and 5C, fig. 5A is a cross-sectional magnetic induction vector field diagram of an applied magnetic field in an embodiment, fig. 5B is a magnetic induction gradient vector field diagram in an embodiment, and fig. 5C is a finite element calculation result diagram of a three-dimensional magnetic induction cloud diagram of an applied magnetic field in an embodiment. As can be seen from fig. 5A, the magnetic field intensity near the inner electrode in the epoxy resin is distributed substantially radially, which is similar to the electric field distribution of the dielectric gradient material in actual working conditions, and the magnetic particles are arranged in a chain shape along the magnetic field direction; as can be seen in fig. 5B, the gradient in the epoxy resin near the inner electrode increases and is directed substantially radially inward, which results in the deposition of magnetic particles moving toward the surface of the inner electrode.
Referring to fig. 6A, 6B, 6C, 6D and 6E, fig. 6A, 6B and 6C are optical microscope test charts of different magnifications of the dielectric gradient material near the inner electrode region prepared in the embodiment, wherein the magnifications are increased sequentially from fig. 6A, 6B to 6C; fig. 6D and 6E are optical microscope test images at the same magnification and in different areas as fig. 6C, wherein fig. 6C is the area closest to the inner electrode, fig. 6E is the area farthest from the inner electrode, and fig. 6D is the area centered on the inner electrode.
As can be seen from fig. 6A, 6B and 6C, the filler particles are distributed in radial chains and in the matrix, the chains are continuous without interruption, and near the surface of the inner electrode, there is a deposition layer of about 1mm, and the annular (0.5mm) profile of the inner electrode can be seen in fig. 6B. From fig. 6D and 6E, as compared with fig. 6C, the inorganic particles in fig. 6D still exhibit a certain orientation, but the chain length is shorter and more dispersed, and a continuous chain distribution is not formed, and the inorganic particle orientation in fig. 6E is further decreased, and the chain is shorter and more dispersed.
Referring to fig. 7, in order to test the results of the surface flashover voltage test on the materials prepared in examples (with 0.5% of inorganic particles added and magnetic field induced), comparative examples 1 (without inorganic particles added) and comparative examples 2 (with 0.5% of inorganic particles added and magnetic field induced), it can be seen that the flashover voltage of the material prepared in examples is 23.1kV with a probability of 63.2%; while the flashover voltage of the material prepared in comparative example 1 with a probability of 63.2% is 19.3kV, the flashover voltage of the example is increased by 19.7% compared with that of comparative example 1; the flashover voltage of the dielectric gradient material of comparative example 2 with a probability of 63.2% was 20.4kV, which was a 14.2% increase in the flashover voltage of the example over comparative example 2.
According to the preparation method of the dielectric gradient material, a magnetic field is applied to a suspension in situ, inorganic particles in partial areas of the suspension are arranged in a chain shape along the direction of the magnetic field under the action of the magnetic field, and curing conditions are applied to obtain the composite material with the dielectric gradient. The preparation method can realize accurate control of the product to be prepared through the conditions of the magnitude of the magnetic field intensity, the gradient of the magnetic field intensity and the like, and is simple, controllable and cost-saving.
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention.

Claims (9)

1. The preparation method of the dielectric gradient material is characterized by comprising the following steps of:
mixing inorganic particles and liquid organic matters to obtain a suspension, wherein the inorganic particles at least comprise a magnetic material with a dielectric constant larger than 40; the inorganic particles are of a core-shell structure, the inorganic particles comprise a core and a shell for coating the core, the core and the shell at least comprise one magnetic material and one inorganic non-magnetic material, and the dielectric constant of the inorganic non-magnetic material is greater than or equal to 40; the suspension liquid at least contains inorganic particles with the particle size of less than 1 mu m; the inorganic particles are treated by a coupling agent; the viscosity of the suspension is less than or equal to 100 Pa.s;
applying a magnetic field to the suspension, wherein under the action of the magnetic field, the magnetic field force applied to part of the inorganic particles is greater than the viscous resistance applied to the part of the inorganic particles in the suspension, so that the part of the inorganic particles are arranged in a chain shape along the direction of the magnetic field; and
and curing the suspension after the magnetic field is applied to cure the suspension to obtain the dielectric gradient material.
2. The method of claim 1, wherein the magnetic field is applied by a permanent magnet itself or by an external current coil.
3. The method of claim 1, wherein the magnetic field in the suspension is of a strength to drive at least one of the inorganic particles to move, and the strength of the magnetic field in the suspension is less than or equal to 1T.
4. The method of claim 1, wherein the inorganic particles have a particle size of less than 100 μm; the liquid organic matter is a curable material; the volume fraction of the inorganic particles in the suspension is less than or equal to 50%.
5. The method of claim 1, further comprising the step of casting the suspension in a casting mold or coating the suspension on a surface of an object before applying the magnetic field to the suspension.
6. The method of claim 1, wherein the applying the magnetic field overlaps in time with the performing a curing process, the curing process including at least one of standing, heating, light irradiation, and mechanical pressing.
7. The method of claim 1, wherein the coupling agent treatment comprises immersing the inorganic particles in a solution of ethanol and a coupling agent, or adding the coupling agent to the suspension, wherein the coupling agent accounts for 0.5-2% of the total mass of the coupling agent and the inorganic particles.
8. The encapsulating method of the electronic component is characterized by comprising the following steps:
providing at least two electronic components arranged in a packaging module of the electronic components;
adding inorganic particles and liquid organic matters into the packaging module to obtain a suspension, immersing the electronic component in the suspension, wherein the inorganic particles at least comprise a magnetic material with a dielectric constant larger than 40; the inorganic particles are of a core-shell structure, the inorganic particles comprise a core and a shell for coating the core, the core and the shell at least comprise one magnetic material and one inorganic non-magnetic material, and the dielectric constant of the inorganic non-magnetic material is greater than or equal to 40; the suspension liquid at least contains inorganic particles with the particle size of less than 1 mu m; the inorganic particles are treated by a coupling agent; the viscosity of the suspension is less than or equal to 100 Pa.s;
applying a magnetic field to the packaging module, wherein under the action of the magnetic field, the magnetic field force applied to part of the inorganic particles is greater than the viscous resistance applied to the part of the inorganic particles in the suspension, so that the part of the inorganic particles are arranged in a chain shape along the direction of the magnetic field; and
and curing the turbid liquid after the magnetic field is applied to cure the turbid liquid, so that the electronic components are encapsulated together.
9. A method for potting an electronic component as claimed in claim 8, wherein the magnetic field is applied in a manner including a magnetic field generated by a permanent magnet itself or an external current coil; the magnetic field intensity formed by the magnetic field in the suspension can drive at least one type of the inorganic particles to move, and the magnetic field intensity in the suspension is less than or equal to 1T.
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