CN109791831B

CN109791831B - Magnetic core

Info

Publication number: CN109791831B
Application number: CN201780060538.3A
Authority: CN
Inventors: 前田贵大; 齐藤忠雄; 土生悟; 山田胜彦; 日下隆夫; 井上哲夫
Original assignee: Toshiba Corp; Toshiba Materials Co Ltd
Current assignee: Toshiba Corp; Toshiba Materials Co Ltd
Priority date: 2016-09-29
Filing date: 2017-09-28
Publication date: 2021-10-12
Anticipated expiration: 2037-09-28
Also published as: KR20190062470A; JPWO2018062409A1; JP7003046B2; CN109791831A; KR102183923B1; WO2018062409A1

Abstract

A magnetic core is provided with: a plurality of iron-based soft magnetic alloy plates having a crystal structure with an average crystal grain size of 100nm or less, and an insulating layer provided between one and the other of the plurality of iron-based soft magnetic alloy plates. The plurality of iron-based magnetic alloy plates in the core have a space factor of 65% or more and an initial magnetic permeability at a frequency of 100kHz of 25000 or more.

Description

Magnetic core

Technical Field

Embodiments relate to magnetic cores.

Background

Magnetic cores of conventional switching regulators and the like used in a high-frequency range include crystalline materials such as permalloy and ferrite. However, since permalloy has a low specific resistance, it has a large iron loss in a high-frequency region. Ferrite has a low magnetic flux density of about 500 gauss (G), although it has a low iron loss in a high-frequency region. Therefore, when the magnetic flux is used at a high operating magnetic flux density, saturation is approached and the iron loss increases. In contrast, iron-based soft magnetic alloys having a fine crystal structure with an average crystal particle size of 50nm or less have been developed. The permeability μ of the iron-based soft magnetic alloy at a frequency of 1kHz is about 100000.

Components used in switching regulators, such as power transformers, smoothing chokes, and common mode chokes, require miniaturization of cores. Similarly, components such as noise filters and antennas are also required to be downsized.

A switching regulator is one type of switching power supply. Switching power supplies are widely used as power conversion devices for commercial power supplies. A switching power supply is a power supply device that stabilizes output power by controlling the on/off time ratio (duty ratio) of a semiconductor switching element using a feedback circuit. Switching power supplies are used in various devices such as medical equipment, industrial equipment, railways, and communication equipment. With the improvement of the performance of semiconductor switching elements, the operating frequency is as high as 50kHz or more. In the magnetic core having a magnetic permeability μ of 100000 at a frequency of 1kHz, the magnetic permeability μ of 100kHz is only about 20000. Therefore, it is difficult to miniaturize the magnetic core in a high frequency region of 50kHz or higher.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 10-008224

Disclosure of Invention

The invention aims to improve the magnetic permeability of a magnetic core.

The magnetic core of the embodiment is provided with: a plurality of iron-based soft magnetic alloy sheets having a crystal structure with an average crystal grain size of 100nm or less; and an insulating layer provided between one and the other of the plurality of iron-based soft magnetic alloy plates. The plurality of iron-based magnetic alloy plates in the core have a space factor of 65% or more and an initial magnetic permeability at a frequency of 100kHz of 25000 or more.

Drawings

Fig. 1 is a schematic cross-sectional view showing a structural example of a wound core.

Fig. 2 is a schematic cross-sectional view showing a structural example of the laminated core.

Fig. 3 is a cross-sectional view showing an example of the boundary between the iron-based soft magnetic alloy plate and the insulating layer.

Detailed Description

Hereinafter, embodiments will be described with reference to the drawings. The drawings are schematic, and dimensions such as thickness and width of each component may be different from actual dimensions of the component. In the embodiments, substantially the same constituent elements are denoted by the same reference numerals, and description thereof may be omitted.

Fig. 1 is a schematic cross-sectional view showing a structural example of a wound core. Fig. 2 is a schematic cross-sectional view showing an example of the structure of the laminated magnetic core. The magnetic core 1 shown in fig. 1 and 2 includes an iron-based soft magnetic alloy sheet 2 and an insulating layer 3.

The magnetic core 1 shown in fig. 1 is a wound core, and is a wound body formed by laminating one of a plurality of iron-based soft magnetic alloy plates 2 with an insulating layer 3 interposed therebetween and winding the laminated body. The winding type core is also called a toroidal core. The magnetic core 1 shown in fig. 1 has a hollow 4 in the center of the magnetic core 1.

The magnetic core shown in fig. 2 is a laminated magnetic core, and is a laminated body formed by laminating a plurality of iron-based soft magnetic alloy plates 2 with an insulating layer 3 interposed therebetween.

The coil may be wound around the core 1 shown in fig. 1 and 2. The magnetic core 1 may be housed in a case as needed. The coil may be wound after the core 1 is housed in the case.

The iron-based soft magnetic alloy sheet 2 is made of, for example, a soft magnetic alloy thin sheet containing 50 atomic% or more of iron (Fe). The iron-based soft magnetic alloy sheet 2 has a fine crystal structure with an average crystal grain size of 100nm or less. If the average crystal grain size exceeds 100nm, the soft magnetic characteristics are degraded. Therefore, the average crystal particle diameter is preferably 100nm or less, and more preferably 50nm or less. The average crystal particle diameter is more preferably 10nm to 30nm, and still more preferably 10nm or more and less than 30 nm.

The average crystal particle diameter is determined from the half-value width of the Diffraction peak determined by X-ray Diffraction (XRD) analysis by the Scherrer formula. The scherrer equation is expressed as D ═ K · λ)/(β cos θ). Where D is the average crystal grain size, K is the shape factor, λ is the wavelength of the X-ray, β is the peak full width at half maximum (FWHM), and θ is the bragg angle. The shape factor K is set to 0.9. The bragg angle is half the diffraction angle 2 θ. XRD analysis was carried out under conditions of a Cu target, a tube voltage of 40mV, a tube current of 40mA, and a slit width (RS) of 0.20 mm.

The composition of the iron-based soft magnetic alloy sheet 2 is represented by, for example, the following general formula (composition formula).

A compound of the general formula: fe_aCu_bM_cM’_dM”_eSi_fB_g

(wherein M is at least one element selected from the group consisting of group 4 elements, group 5 elements, group 6 elements and rare earth elements of the periodic table, M 'is at least one element selected from the group consisting of Mn, Al and platinum group elements, M' is at least one element selected from the group consisting of Co and Ni, a is a number satisfying a + b + c + d + e + f + g of 100 at%, b is a number satisfying 0.01. ltoreq. b.ltoreq.8 at%, c is a number satisfying 0.01. ltoreq. c.ltoreq.10 at%, d is a number satisfying 0. ltoreq. d.ltoreq.10, e is a number satisfying 0. ltoreq. e.ltoreq.20 at%, f is a number satisfying 10. ltoreq. f.25 at%, and g is a number satisfying 3. ltoreq. g.ltoreq.12 at%)

Cu is effective for improving the corrosion resistance and preventing coarsening of crystal grains, and is effective for improving soft magnetic characteristics such as iron loss and magnetic permeability. The content of Cu is preferably 0.01 atomic% to 8 atomic% (0.01. ltoreq. b. ltoreq.8). If the Cu content is less than 0.01 atomic%, the effect of addition is small, and if the Cu content exceeds 8 atomic%, the magnetic properties are degraded.

M is at least one element selected from the group consisting of group 4 elements, group 5 elements, group 6 elements and rare earth elements of the periodic table. Examples of the group 4 element include Ti (titanium), Zr (zirconium), Hf (hafnium), and the like. Examples of the group 5 element include V (vanadium), Nb (niobium), Ta (tantalum), and the like. Examples of the group 6 element include Cr (chromium), Mo (molybdenum), W (tungsten), and the like. Examples of the rare earth elements include Y (yttrium), lanthanides, and actinides. The M element is effective for uniformizing the crystal grain size and stabilizing the magnetic characteristics against temperature change. The content of the M element is preferably 0.01 atomic% to 10 atomic% (c is 0.01. ltoreq. c.ltoreq.10).

M' is at least one element selected from Mn (manganese), Al (aluminum) and platinum group elements. Examples of the platinum group element include Ru (ruthenium), Rh (rhodium), Pd (palladium), Os (osmium), Ir (iridium), Pt (platinum), and the like. The M' element is effective for improving soft magnetic characteristics such as saturation magnetic flux density. The content of M' element is preferably 0 atom% to 10 atom% (d is 0. ltoreq. d.ltoreq.10).

The M' element is at least one element selected from Co (cobalt) and Ni (nickel). The M' element is effective for improving soft magnetic characteristics such as saturation magnetic flux density. Preferably, the content of the M' element is 0 atom percent to 20 atom percent (e is more than or equal to 0 and less than or equal to 20).

Si (silicon) and B (boron) contribute to amorphization of the alloy or precipitation of microcrystals during production. Si and B are effective for heat treatment for improving the crystallization temperature and improving the magnetic properties. In particular, Si is dissolved in Fe, which is a main component of fine grains, in a solid solution, and is effective for reducing magnetostriction and magnetic anisotropy. The preferable Si content is 10 atom% to 25 atom% (f is 10. ltoreq. f.ltoreq.25). The content of B is preferably 3 atom% to 12 atom% (3. ltoreq. g. ltoreq.12).

When the above general formula is satisfied, Fe is formed₃A Si phase. Fine crystals having an average crystal particle diameter of 100nm or less mainly have a phase selected from the group consisting of alpha-Fe phase and Fe₃Si phase and Fe₂At least one of the B phases. Each crystal may also contain a constituent element satisfying the general formula.

Preferably with Fe₃Tensile stress is generated in a direction parallel to the Si crystal phase, and Fe is generated₃The Si crystal phase generates compressive stress in a vertical direction. The presence or absence of the tensile stress and the compressive stress is analyzed by a residual stress analysis method using XRD. The parallel direction is the longitudinal direction of the iron-based soft magnetic alloy sheet 2. That is, the parallel direction is the longitudinal direction of the ribbon produced by the chill roll extrusion method. The vertical direction refers to the width direction of the thin strip.

The residual stress analysis by XRD analysis was performed by the following method. XRD analysis was carried out under conditions of a Cu target, a tube voltage of 40mV, a tube current of 40mA, and a slit width (RS) of 0.20 mm.

The maximum peak appearing in the range of diffraction angle (2 θ) of 140 degrees to 180 degrees is taken as a reference. The measurement was performed while moving the irradiation angle of the X-ray to 45 degrees in units of 15 degrees. The peak is tensile stress if it is shifted to the right side, and compressive stress if it is shifted to the left side.

For Fe₃The generation of tensile stress and compressive stress in the Si crystal phase indicates that the iron-based soft magnetic alloy sheet has magnetic anisotropy. As described above, the iron-based soft magnetic alloy sheet 2 containing Fe (iron), Si (silicon), and B (boron) as constituent elements has a composition selected from the group consisting of α -Fe and Fe₃Si and Fe₂At least one crystalline phase of B. A magnetic material having conventional fine crystals can provide soft magnetic properties by eliminating magnetic anisotropy. This method is difficult to improve the initial permeability.

Magnetic core of the embodiment passes through Fe₃The Si crystal phase imparts magnetic anisotropy, and can increase initial magnetic permeability. In particular, the initial permeability at a frequency of 100kHz can be increased to 25000 or more, and further to 30000 or more. By imparting magnetic anisotropy, the dc coercive force of the magnetic core after heat treatment can be increased.

The average thickness of the iron-based soft magnetic alloy sheet 2 is preferably 30 μm or less. If the iron-based soft magnetic alloy sheet 2 becomes thick, the eddy current loss becomes large. The eddy current loss X is represented by the formula X ═ B²f²d²And/p. B represents the magnetic flux density of the core 1, f represents the frequency of the core 1, d represents the average thickness of the iron-based soft magnetic alloy sheet 2, and ρ represents the resistivity of the core 1. The average thickness of the iron-based soft magnetic alloy sheet 2 is more preferably 20 μm or less, and still more preferably 18 μm or less. When the cross section of the iron-based soft magnetic alloy sheet 2 was observed using a Scanning Electron Microscope (SEM), the average thickness was defined by the average value of the thicknesses at 5 arbitrary positions.

The ratio of the calculated value of the density of the iron-based soft magnetic alloy sheet 2 to the measured value of the densityKs is preferably a number satisfying 1.00. ltoreq. Ks.ltoreq.1.50. The calculated value of the density is a theoretical value determined from the composition of the iron-based soft magnetic alloy sheet 2. The composition of the iron-based soft magnetic alloy sheet 2 is represented by the formula Fe₇₃Cu₁Nb₄Si₁₅B₇The calculated value of the density at the time of the expression is calculated as follows. The density of Fe was set to 7.87g/cm³The density of Cu was set to 8.96g/cm³The density of Nb was set to 8.56g/cm³The density of Si was set to 2.33g/cm³The density of B was set to 2.37g/cm³The calculated density of the iron-based soft magnetic alloy sheet 2 was 7.87 × 0.73+8.96 × 0.01+8.56 × 0.04+2.33 × 0.15+2.37 × 0.07 ═ 6.6925g/cm³(≈6.69g/cm³). The measured value of the density is calculated as follows. Only 1cm of the alloy was cut out of the iron-based soft magnetic alloy sheet 2²The density was measured. The measured value of the density is a value obtained by dividing the measured density by the average thickness of the iron-based soft magnetic alloy sheet 2. The closer Ks is to 1.00, the closer the measured value of density is to the theoretical value.

Ks exceeding 1.50 indicates that the surface of the iron-based soft magnetic alloy sheet 2 has large irregularities or a large number of projections. If the surface irregularities are too large, it becomes difficult to increase the space factor of the plurality of iron-based soft magnetic alloy plates 2 in the magnetic core 1. As will be described later, it is also difficult to reduce the gap between the iron-based soft magnetic alloy sheet 2 and the insulating layer 3. More preferably, the Ks is 1.00 to 1.30.

When the composition of the iron-based soft magnetic alloy sheet 2 is obtained, Ks can be calculated by directly using the core 1. As described later, for example, when the insulating layer 3 made of an oxide having a thickness of 10 μm or less is provided, the actual measurement value of the density can be measured by using the magnetic core 1 as it is. In the case of the insulating layer 3 formed of a thin oxide layer, Ks can be calculated without considering the mass of the insulating layer 3 because the ratio of the mass of the insulating layer 3 to the mass of the magnetic core 1 is 3% or less. Ks measured directly using the core 1 can be regarded as Ks determined from the entire core 1. Preferably, Ks obtained from the entire magnetic core 1 is 1.00 to 1.50. The Ks is more preferably 1.1 to 1.3.

Preferably, Ks obtained from the entire core 1 is defined asKs₁The average thickness of the iron-based soft magnetic alloy sheet 2 is 20 μm or less, Ks₁To satisfy Ks of 1.00 ≦ Ks₁The number is less than or equal to 1.50. In addition, at Ks₁To satisfy Ks of 1.00 ≦ Ks₁The ratio Ks of the calculated density of each of the four divided pieces obtained by dividing the magnetic core 1 into four equal parts is set to be less than or equal to 1.50₂When it is, Ks₂And Ks₁The difference is preferably within. + -. 0.2. Ks₁、Ks₂Calculated as follows. The magnetic core 1 was divided into four parts, and the actual measured value of the density obtained by measuring the density of each of the four divided pieces was designated as Ks₂. In addition, Ks₁Ks composed of four divided pieces₂Is defined as the average value of. By calculating the difference, the presence or absence of local unevenness of the core 1 can be confirmed. By reducing the local unevenness of Ks, the thin insulating layer 3 can be provided, and the space factor of the plurality of iron-based soft magnetic alloy plates 2 in the core 1 can be increased.

The magnetic core 1 preferably has the insulating layer 3, and the space factor of the plurality of iron-based soft magnetic alloy sheets 2 is 65% or more. In the case where the insulating layer 3 is not provided, the following two structures are considered: (1) a structure in which the iron-based soft magnetic alloy plates 2 are in contact with each other, and (2) a structure in which the iron-based soft magnetic alloy plates 2 are spaced apart from each other by a large distance. If the iron-based soft magnetic alloy plates 2 are in direct contact with each other, the magnetic permeability is lowered. If the distance between the iron-based soft magnetic alloy plates 2 is large, the space factor of the iron-based soft magnetic alloy plates 2 decreases, and therefore the magnetic permeability decreases. That is, in order to increase the magnetic permeability, it is necessary to insulate the iron-based soft magnetic alloy plates 2 from each other and increase the space factor so that the iron-based soft magnetic alloy plates 2 do not directly contact each other. The duty factor is more preferably 75% or more. The upper limit of the duty ratio is not particularly limited, but is preferably 95% or less. If the space factor exceeds 95%, there is a possibility that the interlayer insulation becomes insufficient.

The following describes a method of measuring the duty factor. First, SEM observation was performed on an arbitrary cross section of the core 1, and the total area of the iron-based soft magnetic alloy plates 2 in the observation image was obtained. The space factor of 5 regions having a unit area of 500. mu. m.times.500. mu.m was calculated by SEM observation of the cross section, and the average value thereof was defined as the space factor (%) of the core.

The thickness of the insulating layer 3 is preferably 0.1 μm or more. If the thickness of the insulating layer 3 is less than 0.1 μm, a portion where interlayer insulation is insufficient may be locally generated. The thickness of the insulating layer 3 is preferably 10 μm or less. If the thickness of the insulating layer 3 exceeds 10 μm, it is difficult to increase the space factor. That is, the thickness of the insulating layer 3 is preferably 0.1 μm to 10 μm, and more preferably 0.5 μm to 3 μm. The thickness of the insulating layer 3 is measured in an arbitrary cross section of the magnetic core 1. This operation was performed at any 5 points, and the average value thereof was taken as the thickness of the insulating layer (average thickness).

The insulating layer 3 is preferably an insulating film formed by stacking insulating fine particles having an average particle diameter of 0.001 μm or more (1nm or more). By depositing the insulating fine particles, stress can be not applied to the iron-based soft magnetic alloy sheet 2. The insulating fine particles are preferably oxides, and examples of the insulating fine particles include silicon oxide (SiO)₂) Magnesium oxide (MgO), aluminum oxide (Al)₂O₃) And oxides, resin powders. Particular preference is given to using silicon oxide (SiO)₂). Since the oxide does not shrink during drying, the generation of stress can be suppressed. In particular, since the silicon oxide has good compatibility with the iron-based soft magnetic alloy sheet 2, variation in magnetic permeability can be reduced. This is believed to be due to: both silicon oxide and the iron-based soft magnetic alloy sheet 2 contain silicon as an essential constituent element.

The average particle diameter of the insulating fine particles is preferably 0.001 to 0.1. mu.m. If the average particle diameter of the insulating fine particles exceeds 0.1 μm (100nm), the gap between the insulating fine particles becomes wider, and it is difficult to increase the space factor. As described above, when the surface of the iron-based soft magnetic alloy sheet 2 has minute irregularities, a gap is easily formed at the boundary between the iron-based soft magnetic alloy sheet 2 and the insulating layer 3. When insulating fine particles are used, insulating layer 3 can be formed by a method of immersing iron-based soft magnetic alloy sheet 2 in a solution containing the insulating fine particles and drying the immersed iron-based soft magnetic alloy sheet. This method does not involve shrinkage of the insulating material, and therefore stress is not applied to the iron-based soft magnetic alloy sheet 2. Therefore, the average particle diameter of the insulating fine particles is preferably 0.001 to 0.1. mu.m, and more preferably 0.005 to 0.05. mu.m (5 to 50 nm). Whether or not the insulating layer 3 contains the deposited insulating fine particles can be determined by, for example, an enlarged photograph obtained by SEM observation or the like.

Fig. 3 is a schematic cross-sectional view showing an example of the boundary between the iron-based soft magnetic alloy sheet 2 and the insulating layer 3. As described later, the iron-based soft magnetic alloy sheet 2 is formed using, as a raw material, an amorphous iron-based alloy ribbon produced by a chill roll extrusion method. In the ribbon produced by the chill roll extrusion method, minute irregularities on the surface of the chill roll affect the surface properties of the ribbon surface. Therefore, if microscopic enlargement is performed, fine irregularities are formed on the surface of the iron-based soft magnetic alloy sheet 2. If insulating fine particles are used, the insulating layer 3 can be provided so as to fill the fine irregularities of the magnetic thin band. On the other hand, in the case of the resin paste, since shrinkage of the resin layer is accompanied when the resin paste is cured by heating, stress is generated in the iron-based soft magnetic alloy sheet 2. If stress is generated in the iron-based soft magnetic alloy sheet 2, the magnetic permeability is lowered.

The total length P of the voids 5 per 100 μm unit length L at the boundary between the iron-based soft magnetic alloy sheet 2 and the insulating layer 3 is preferably 5 μm or less (including zero). By reducing the gap (clearance) at the boundary between the iron-based soft magnetic alloy sheet 2 and the insulating layer 3, the space factor can be increased with a thin insulating layer 3. As a result, the magnetic permeability can be improved. Fig. 3 shows an example in which the number of the gaps 5 is 1, but a plurality of gaps may be provided. If the total length is 5 μm or less, the duty factor can be increased.

The ratio of voids (area ratio) at the boundary between the iron-based soft magnetic alloy sheet 2 and the insulating layer 3 was measured by a cross-sectional photograph obtained by SEM observation. In the SEM observation image, the contrast of the voids 5 is different from that of the iron-based soft magnetic alloy sheet 2 and the insulating layer 3. The proportion of the voids is, for example, preferably 5% or less, and more preferably 2% or less.

The initial permeability μ of the core as described above at a frequency of 100kHz is 25000 or more. The initial permeability μ at a frequency of 100kHz can be set to 30000 or more. The method for measuring the initial permeability μ was set by using an impedance analyzer to: room temperature, 1 turn, 1V. The impedance analyzer was set to Hewlett-Packard Japan, Ltd. system YHP 4192A.

Conventional magnetic cores using iron-based soft magnetic alloys having a fine crystal structure have had a limit to miniaturization in the region where the operating frequency is 50kHz or more. The reason is considered to be: the iron-based soft magnetic alloy sheet having a fine crystal structure has a low magnetic permeability and a low space factor.

The core according to the embodiment is a core in which loss is suppressed while increasing the space factor of the iron-based soft magnetic alloy sheet to 65% or more, and the initial magnetic permeability μ at a frequency of 100kHz is high and 25000 or more. This enables the core 1 to be reduced in size.

In recent years, with the increase in performance of semiconductor devices (semiconductor switching devices), the operating frequency has been increased to 50kHz or more. The operating frequency of the semiconductor element becomes as high as 400 kHz. The core of the embodiment has an initial permeability at a frequency of 100kHz set to 25000 or more. Therefore, the magnetic core exhibits excellent characteristics as a magnetic core mounted in an electronic device having a semiconductor element with an operating frequency of 50kHz to 400 kHz.

Examples of electronic devices having a semiconductor element with an operating frequency of 50kHz to 400kHz include switching power supplies, antenna devices, and inverters. Electronic devices are used in communication base stations, solar power plants, Electric Vehicles (EV), Hybrid-Electric vehicles (HEV), Plug-in Hybrid vehicles (PHV), and industrial equipment. In addition, the present invention can be used in Office Automation (OA) equipment such as personal computers and servers.

The magnetic core of the embodiment can increase the AL value. The AL value satisfies the expression "AL value ^ μ × Ae/Le". μ denotes initial permeability, Ae denotes average magnetic path length, and Le denotes effective cross-sectional area. The AL value is an index indicating the performance of the magnetic core 1. Higher values of AL indicate higher inductance values.

When the size (Ae/Le) of the magnetic core is the same, the larger the initial permeability μ is, the higher the AL value becomes. By decreasing the effective cross-sectional area Le or increasing the average magnetic path length Ae, the AL value becomes large. By increasing the average magnetic path length Ae, the AL value becomes large. By reducing the effective cross-sectional area Le, the AL value becomes large.

If the size of the core 1 is increased, the AL value becomes large. On the other hand, the increase in size of the core 1 causes a problem of an arrangement space in the electronic device. The magnetic core of the embodiment increases the initial permeability μ and increases the space factor of the iron-based soft magnetic alloy sheet. If the space factor is increased, the volume of the magnetic core can be reduced if the amount of the iron-based soft magnetic alloy sheet used is the same. Thereby, the effective cross-sectional area Le of the magnetic core can be reduced. If the space factor is increased, the amount of the iron-based soft magnetic alloy sheet 2 used increases when the size of the magnetic core is the same, and therefore the average magnetic path length Ae can be increased. In the core according to the embodiment, both the initial permeability and the space factor are high, and therefore the AL value can be increased. The increase in AL value enables miniaturization of the magnetic core. This makes it easy to reduce the weight of the magnetic core and to secure an arrangement space in the electronic device. Therefore, the degree of freedom in design in the electronic apparatus can be improved. For example, when comparing a core having an initial permeability μ of 17000 at a frequency of 100kHz with a core having an initial permeability of 30000, the diameter of the core having an initial permeability of 30000 can be reduced to about 20%.

If the core 1 is made smaller, the material constituting the core 1 is small, and therefore, the cost can be reduced. Even if the number of windings is reduced, the same characteristics can be obtained. The reduction in the number of windings can reduce the amount of windings used, which leads to a reduction in cost. Further, by reducing the number of windings, the probability of breakage of the magnetic core in the winding process can be reduced. Therefore, the yield in the winding process can be improved. If the number of windings is reduced, the amount of heat generated by the windings can be reduced.

The miniaturization of the magnetic core 1 also leads to a reduction in weight. That is, when the characteristics of the core 1 are equivalent to those of a conventional core, the size and weight can be reduced. The reduction in size and weight of the magnetic core 1 leads to reduction in size and weight of electronic devices such as switching power supplies, antenna devices, and inverters.

Next, a method for manufacturing the magnetic core 1 of the embodiment will be described. The method for manufacturing the magnetic core 1 is not particularly limited as long as the magnetic core 1 has the above-described configuration, but the following method can be cited as a method for manufacturing the magnetic core 1 with a good yield.

First, an iron-based amorphous alloy ribbon is produced. A raw material powder in which the respective constituent components are mixed is prepared so that the iron-based amorphous alloy satisfies the above general formula (composition formula). Then, the raw material powder is melted to produce a raw material melt. A long strip of an iron-based amorphous alloy is produced by a chill roll extrusion method using a raw material melt. In the case of the chill roll extrusion method, the surface roughness Ra of the chill roll is preferably 1 μm or less. By flattening the surface of the cooling roll, the irregularities on the surface of the obtained iron-based amorphous alloy ribbon can be reduced. Therefore, Ks can be set to be 1.00-1.30. In order to reduce surface irregularities, it is also effective to perform the treatment in an inert atmosphere. Argon is preferred as the inert atmosphere. The average thickness can be controlled by controlling the rotation speed of the cooling roll, the temperature of the atmosphere, and the like.

Next, the insulating layer 3 is formed. The insulating layer 3 is formed using, for example, insulating fine particles having an average particle diameter of 0.001 to 0.1 μm. The insulating fine particles are preferably formed using an oxide or a resin. Particularly preferably contains at least one oxide selected from the group consisting of silicon oxide, magnesium oxide and aluminum oxide. An alloy sheet formed of an iron-based amorphous alloy ribbon is immersed in a solution containing insulating fine particles. After that, it is dried to provide the insulating layer 3 on the alloy plate. The impregnation and drying may be alternately repeated as necessary. The step of forming the insulating layer 3 may be performed after cutting the alloy sheet in advance to a size of a target magnetic core, or may be performed in a state of a long magnetic thin strip.

Next, the magnetic core 1 is manufactured. In the case of a wound core, a long magnetic thin strip (iron-based soft magnetic alloy sheet 2) provided with an insulating layer is wound. The outermost periphery of the winding is fixed by spot welding or an adhesive. If the thickness of the insulating layer 3 is adjusted to 4 μm or less, the insulating layer is less likely to peel off in the winding step.

In the case of a laminated core, the following methods may be mentioned: a long magnetic thin strip (iron-based soft magnetic alloy sheet 2) provided with an insulating layer 3 is laminated and then cut into a desired size. The long magnetic tape provided with the insulating layer 3 may be cut into a desired size and then laminated. The side surface of the laminate is fixed with an adhesive. The surface of the magnetic core is preferably coated with a resin. The strength of the magnetic core can be improved by resin coating.

Next, the alloy sheet is heat-treated to precipitate fine crystals, thereby forming an iron-based soft magnetic alloy sheet 2. In the case of a wound core, it is preferable to perform heat treatment after winding. In the case of a laminated core, the lamination may be followed by heat treatment, or an iron-based soft magnetic alloy sheet 2 that has been heat-treated in advance may be laminated. The iron-based amorphous alloy sheet is preferably subjected to heat treatment after the production of the magnetic core, because it becomes brittle by precipitation of fine crystals.

The heat treatment temperature is preferably a temperature near the crystallization temperature or a temperature higher than the crystallization temperature. Preferably above the crystallization temperature-20 ℃. In the case of the iron-based soft magnetic alloy sheet 2 satisfying the above general formula, the crystallization temperature is 500 to 515 ℃. Therefore, the heat treatment temperature is preferably 480 to 600 ℃. Further preferably 510 to 560 ℃.

The heat treatment temperature is controlled so that the temperature of the magnetic core 1 becomes 480 to 600 ℃. For example, in the case of an electric furnace, the temperature of the core can be controlled by adjusting the temperature of the electric heater. A difference in temperature may occur between a place near the electric heater and a place far from the electric heater. If a plurality of cores 1 are arranged and heat-treated, temperature unevenness in the furnace occurs. In order to control the heat treatment temperature of the magnetic core 1, it is preferable to measure the temperature of the magnetic core 1 during the heat treatment using a temperature sensor. A method of directly measuring the temperature of the magnetic core 1 using a thermocouple, for example, is effective.

By performing heat treatment on the number of magnetic cores 1 capable of suppressing the temperature variation of the furnace, the heat treatment temperature can be easily controlled. The heat treatment temperature may be controlled by providing electric heaters in the furnace at a plurality of positions. By circulating the atmosphere in the furnace, the heat treatment temperature can be easily controlled. The heat treatment temperature can also be controlled by using a large heat treatment furnace. By surrounding the furnace with a material having high thermal conductivity, heat dissipation properties can be made uniform, and the heat treatment temperature can be easily controlled.

The heat treatment time is preferably 30 hours or less. The heat treatment time is a time when the temperature of the magnetic core is 480 to 600 ℃. If it exceeds 30 hours, the average particle diameter of the fine crystal grains may exceed 100 nm. The heat treatment time is more preferably 20 minutes to 20 hours. The heat treatment time is more preferably 1 hour to 10 hours. When the average crystal grain size is within this range, the average crystal grain size can be easily controlled to 50nm or less.

The temperature rise rate at the time of crystallization temperature is preferably 7 ℃/min to 30 ℃/min. If the amount is within this range, the tensile stress and the compressive stress are easily applied. If the temperature increase rate exceeds 30 ℃/min, rapid grain growth may occur, and the magnetic properties may be degraded. The lower limit of the temperature increase rate is not particularly limited, but is preferably 1 ℃/min or more. If the temperature is less than 1 ℃/minute, the temperature rise time becomes too long, and the mass productivity is lowered. Therefore, the temperature increase rate at the crystallization temperature time is preferably 7 ℃/min to 30 ℃/min, and more preferably 10 ℃/min to 20 ℃/min.

By performing the heat treatment as described above, the DC coercive force of the core 1 can be set to 2A/m to 4A/m. The DC coercive force of the conventional magnetic core after heat treatment is about 1A/m. The initial permeability can be increased by setting the coercive force to 2A/m to 4A/m. If the DC coercive force exceeds 4A/m, the soft magnetic properties are degraded.

Next, if necessary, heat treatment in a magnetic field may be further performed. In the heat treatment in the magnetic field, the magnetic field is preferably applied in the short side direction of the iron-based soft magnetic alloy sheet 2. In the wound core, a magnetic field is applied in the width direction of the iron-based soft magnetic alloy sheet 2. In the laminated core, a magnetic field is applied in the direction of the short sides of the iron-based soft magnetic alloy sheet 2. By applying a magnetic field in the short side direction of iron-based soft magnetic alloy plate 2 and performing heat treatment, the magnetic domain wall of iron-based soft magnetic alloy plate 2 can be eliminated. By lowering the domain wall the losses are reduced and thus the permeability is increased. The applied magnetic field is preferably 80kA/m or more, and more preferably 100kA/m or more. The heat treatment temperature is preferably 200 ℃ to 700 ℃. The heat treatment time of the heat treatment in the magnetic field is preferably 20 minutes to 10 hours. The heat treatment in the magnetic field may be performed in one step together with the above-described heat treatment for precipitating fine crystals. The magnetic core may be housed in the case as needed. When mounted on various electronic devices, the winding process may be performed as necessary.

With the above manufacturing method, the initial permeability μ at a frequency of 100kHz can be set to 25000 or more, and further to 30000 or more while increasing the space factor. By combining 1 or 2 or more of the space factor, the heat treatment for fine crystal precipitation, and the heat treatment in the magnetic field, the initial magnetic permeability μ at the frequency of 100kHz can be increased to 25000 or more, and further to 30000 or more.

Examples

(examples 1 to 8, comparative examples 1 to 2)

An iron-based amorphous alloy ribbon was produced by a chill roll extrusion method. By varying the chill roll extrusion process conditions, the average thickness and Ks were varied. By this operation, iron-based amorphous alloy sheets of samples 1 to 4 were prepared. The average thickness, Ks, of the iron-based amorphous alloy sheet is shown in table 1. The crystallization temperature of samples 1 to 4 was 500 ℃ to 515 ℃.

[ Table 1]

Next, an insulating layer was formed on the surface of the iron-based amorphous alloy sheet. In examples 1 to 8 and comparative example 1, silicon oxide (SiO) was used as shown in Table 2 on the surface of any of the alloy sheets of samples 1 to 4₂) Magnesium oxide (MgO) or aluminum oxide (Al)₂O₃) The insulating fine particles of (3) and the insulating layer is formed by the above-mentioned method. In comparative example 2, a resin paste was applied to the surface of the alloy plate of sample 1 to form an insulating layer. Insulation property ofThe material, average particle diameter, and thickness of the insulating layer of the fine particles are shown in table 2.

[ Table 2]

After the insulating layer is formed, the alloy sheet is wound to produce a wound core. Thereafter, the 1 st heat treatment for precipitating fine crystals and the 2 nd heat treatment in a magnetic field were performed. Thus, the wound cores of examples 1 to 8 and comparative examples 1 to 2 were produced. The dimensions of the magnetic cores of the examples and comparative examples were set to 12mm in outer diameter, 10mm in inner diameter, and 2mm in width. The conditions of the 1 st heat treatment and the 2 nd heat treatment are shown in table 3. The coercive force of the magnetic core was measured after the 1 st heat treatment. The results are shown in table 3.

[ Table 3]

In the 1 st heat treatment, the temperature of the core was measured by a thermocouple. In examples 1 to 8, the heat treatment temperature was around the crystallization temperature of the magnetic core. The heat treatment temperature was controlled using a "furnace having a large electric capacity" so as to fall within the range shown in table 3. In example 1, the coercivity after the heat treatment was 2A/m to 4A/m.

On the other hand, in comparative examples 1 and 2, the temperature increase rate was 50 ℃/min, which was out of the preferable range. Regarding the wound cores of examples and comparative examples, the average crystal grain size and Fe for the fine crystal structure₃The stress of the Si crystal phase was measured. The average crystal particle diameter of the fine crystal structure is determined from the half-value width of the diffraction peak determined by XRD by the scherrer equation, as described above. Fe₃The stress of the Si crystal phase is determined by residual stress analysis by XRD. Will be at Fe₃A core in which tensile stress is observed in the longitudinal direction component of the Si crystal phase and compressive stress is observed in the perpendicular direction component is set to "o (good)", and a core other than this is set to "x (poor)". Length direction of the filmThe length direction of the iron-based soft magnetic alloy sheet is referred to, and the vertical direction is referred to the width direction of the iron-based soft magnetic alloy sheet. The results are shown in table 4.

[ Table 4]

As can be seen from the table, the average crystal grain size of the magnetic cores of the examples was 50nm or less. It was also confirmed that tensile stress was applied in the longitudinal direction and compressive stress was applied in the vertical direction in the residual stress analysis by XRD analysis. The average crystal grain size of the comparative examples was 50nm or less. However, the application of both tensile stress and compressive stress was not confirmed.

The space factor (%), initial permeability μ, and loss (kW/m) were measured for the wound cores of examples and comparative examples³). The space factor is obtained by SEM observation of an arbitrary cross section of the core, and the area ratio of the iron-based soft magnetic alloy sheet is measured for a unit area of 500 μm × 500 μm at 5 positions, and the average value of the area ratios of the iron-based soft magnetic alloy sheets is set as the space factor (%).

The initial permeability μ was measured at room temperature with 1-turn and 1V by using an impedance analyzer (Hewlett-Packard Japan, Ltd., YHP 4192A). The initial permeability μ was measured at 10kHz and 100 kHz.

The loss was measured using a BH analyzer (Kawasaki communications SY-8216) at room temperature, 2 turns on the 1 st side, 2 turns on the 2 nd side, a frequency of 100kHz, and a frequency of 200 mT. The results are shown in table 5.

[ Table 5]

As can be seen from the table, the initial permeability μ at a frequency of 100kHz of the magnetic core of the example was 25000 or more, and further 30000 or more. Therefore, the following steps are carried out: by setting the space factor, the 1 st heat treatment, and the 2 nd heat treatment to the preferable conditions, the initial magnetic permeability μ at the frequency of 100kHz can be increased. In contrast, in the case of the core having a thick insulating material as in the comparative example, the space factor is greatly reduced and the magnetic permeability is also reduced. The magnetic cores of the examples were also all low values with respect to loss. The core of the comparative example had a high initial permeability at a frequency of 10kHz, of 90000 or more and 95000. However, the initial permeability at the frequency of 100kHz is lowered.

As a result of measuring the initial magnetic permeability μ at a frequency of 1kHz in example 1 and comparative example 1, there was no significant difference between 63000 in example 1 and 100000 in comparative example 1. Therefore, it can be seen that: this is particularly effective when the operating frequency is increased to 50kHz or more.

SEM observation of the cross section of the core revealed that the percentage of voids present at the boundary between the iron-based soft magnetic alloy sheet and the insulating layer was measured. The length of the voids per unit length of 100 μm in any cross section was measured. The results are shown in table 6. Measuring Ks determined from the whole core₁Ks obtained from a sample obtained by quartering (cutting into 1/4 size) the magnetic core₂. Ks obtained from a sample obtained by quartering a magnetic core₁And four Ks₂The minimum and maximum values in (a) are shown in table 6.

[ Table 6]

As can be seen from the table, with the magnetic cores of the examples, the voids located at the boundary between the iron-based soft magnetic alloy plate and the insulating layer were small (including zero). Thus, it can be seen that: by reducing the void, the space factor can be increased.

(example 9, comparative example 3)

A magnetic core was produced as comparative example 3, and the magnetic core was the same as comparative example 1 except that the outer diameter was 37mm × the inner diameter was 23mm × the width was 15 mm. A magnetic core was produced as in example 9, and the same as in example 7 except that the magnetic core was set to the same dimensions (outer diameter 37mm × inner diameter 23mm × width 15 mm). The initial permeability μ at a frequency of 100kHz was 17000 for comparative example 3 and 35000 for example 9.

The L value of the core in which 8 windings were wound around the core of comparative example 3 was 1.2 mH. In contrast, the L value of the magnetic core of example 9 in which the 6-turn winding was wound was 1.4 mH. In example 9 in which the initial permeability μ of the 100kHz frequency is large, the L value is large although the number of windings is small, when the core size is the same. Therefore, the number of windings can be reduced by increasing the initial permeability at a frequency of 100 kHz.

(example 10, comparative example 4)

A magnetic core (outer diameter 37 mm. times. inner diameter 23 mm. times. width 15mm, number of windings 8, L value 1.2mH) of comparative example 4 was prepared. A core was produced as example 10, and the same as example 9 except that the core size of example 9 (initial permeability μ at 100kHz frequency of 35000) was changed so that the L value of the core after winding became the same 1.2 mH. The magnetic core of example 10 has dimensions of 29mm in outer diameter, 23mm in inner diameter, and 15mm in width, and is reduced in size. The mass of the magnetic core of comparative example 4 was 57g, while that of example 10 was 21 g. Therefore, the following steps are carried out: when the initial permeability μ of the frequency of 100kHz is increased in this manner, the size can be reduced if the same performance is required.

While several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be implemented in other various forms, and various omissions, substitutions, and changes may be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof. The above embodiments may be combined with each other.

Claims

1. A magnetic core is provided with: a plurality of iron-based soft magnetic alloy sheets having a crystal structure with an average crystal grain size of 100nm or less; and an insulating layer provided between one and the other of the plurality of iron-based soft magnetic alloy plates,

wherein the plurality of iron-based soft magnetic alloy plates each have an average thickness of 30 [ mu ] m or less,

the thickness of the insulating layer is 0.1-10 μm,

the insulating layer contains insulating fine particles having an average particle diameter of 0.001 to 0.1 [ mu ] m,

the insulating fine particles contain at least one oxide selected from the group consisting of silicon oxide, magnesium oxide, and aluminum oxide,

the plurality of iron-based soft magnetic alloy plates in the core have a space factor of 65% or more and an initial magnetic permeability at a frequency of 100kHz of 25000 or more.

2. The magnetic core according to claim 1, wherein the average crystal particle diameter is 50nm or less.

3. The magnetic core according to claim 1, wherein the composition of each of the plurality of iron-based soft magnetic alloy plates is represented by the following formula,

formula (II): fe_aCu_bM_cM’_dM”_eSi_fB_g

Wherein M represents at least one element selected from group 4 elements, group 5 elements, group 6 elements and rare earth elements of the periodic table, the group 4 element contains titanium, zirconium or hafnium, the group 5 element contains vanadium, niobium or tantalum, the group 6 element contains chromium, molybdenum or tungsten, M 'represents at least one element selected from Mn, Al and platinum group elements, M' represents at least one element selected from Co and Ni, a is a number satisfying a + b + c + d + e + f + g as 100 atomic%, b is a number satisfying 0.01. ltoreq. b.ltoreq.8 atomic%, c is a number satisfying 0.01. ltoreq. c.ltoreq.10 atomic%, d is a number satisfying 0. ltoreq. d.ltoreq.10 atomic%, e is a number satisfying 0. ltoreq. e.ltoreq.20 atomic%, f is a number satisfying 10. ltoreq. f.ltoreq.25atomic%, and g is a number satisfying 3. ltoreq. g.ltoreq.12 atomic%.

4. The core according to claim 1, wherein a ratio Ks of a calculated value of the density of the core to an actual measured value of the density₁To satisfy Ks of 1.00 ≦ Ks₁The number is less than or equal to 1.50.

5. The magnetic core according to claim 4, wherein, when the magnetic core is divided into four parts, a ratio Ks of a calculated value of density of each of the four divided pieces to an actually measured value of the density₂And said Ks₁The difference of the values of (A) is within. + -. 0.2.

6. The magnetic core according to claim 1, wherein the initial permeability is 30000 or more.

7. The magnetic core according to claim 1, wherein the total length of voids per 100 μm unit length at the boundary where the iron-based soft magnetic alloy sheet and the insulating layer are in contact is 0 μm to 5 μm.

8. The magnetic core according to claim 1, wherein the operating frequency is 50kHz or higher.

9. The magnetic core according to claim 1, wherein the insulating fine particles contain the silicon oxide.

10. The magnetic core of claim 1, wherein the crystal structure has Fe₃A Si phase.