JP7003046B2 - core - Google Patents

Description

The embodiment relates to a magnetic core.

Magnetic cores of conventional switching regulators and the like used in the high frequency region include crystalline materials such as permalloy and ferrite. However, since permalloy has a small resistivity, iron loss in a high frequency region is large. Ferrite has a small iron loss in a high frequency region, but has a low magnetic flux density, and is about 500 gauss (G). Therefore, when used at a large operating magnetic flux density, it approaches saturation and iron loss increases. On the other hand, iron-based soft magnetic alloys having a fine crystal structure having an average crystal grain size of 50 nm or less have been developed. The magnetic permeability μ of the iron-based soft magnetic alloy at a frequency of 1 kHz is about 100,000.

Parts such as power transformers, smoothing choke coils, and common mode choke coils used in switching regulators require miniaturization of the magnetic core. Similarly, parts such as noise filters and antennas also require miniaturization of the magnetic core.

A switching regulator is a type of switching power supply. Switching power supplies are widely used as power conversion devices for commercial power supplies. The switching power supply is a power supply device that stabilizes the output by controlling the on / off time ratio (duty ratio) of the semiconductor switching element by a feedback circuit. Switching power supplies are used in various devices such as medical devices, industrial devices, railways, and communication devices. The operating frequency is as high as 50 kHz or more as the performance of semiconductor switching elements increases. In a magnetic core having a magnetic permeability μ of 100,000 at a frequency of 1 kHz, the magnetic permeability μ at a frequency of 100 kHz is only about 20000. Therefore, it is difficult to reduce the size of the magnetic core in a high frequency region having a frequency of 50 kHz or higher.

Japanese Unexamined Patent Publication No. 10-008224

The problem to be solved by the present invention is to improve the magnetic permeability of the magnetic core.

The magnetic core of the embodiment is a plurality of iron-based soft magnetic alloy plates having a crystal structure having an average crystal grain size of 100 nm or less, and an insulating layer provided between one of the plurality of iron-based soft magnetic alloy plates and the other. And. The average thickness of each of the plurality of iron-based soft magnetic alloy plates is 30 μm or less. The thickness of the insulating layer is 0.1 μm or more and 10 μm or less. The insulating layer contains insulating fine particles having an average particle size of 0.001 μm or more and 0.1 μm or less. The insulating fine particles contain at least one oxide selected from the group consisting of silicon oxide, magnesium oxide, and aluminum oxide. The space factor of the plurality of iron-based soft magnetic alloy plates in the magnetic core is 65% or more, and the initial magnetic permeability at a frequency of 100 kHz is 25,000 or more.

It is sectional drawing which shows the structural example of the ticket circular magnetic core. It is sectional drawing which shows the structural example of a laminated magnetic core. It is sectional drawing which shows an example of the boundary between an iron-based soft magnetic alloy plate and an insulating layer.

Hereinafter, embodiments will be described with reference to the drawings. The drawings are schematic, for example, dimensions such as thickness and width of each component may differ from the dimensions of the actual component. Further, in the embodiment, substantially the same components may be designated by the same reference numerals and the description thereof may be omitted.

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

The magnetic core 1 shown in FIG. 1 is a circular magnetic core, in which one of a plurality of iron-based soft magnetic alloy plates 2 and the other one are laminated with an insulating layer 3 interposed therebetween, and the laminated body is wound around the laminated body. It is a wound body that is formed. The ticket-shaped magnetic core is also called a toroidal core. The magnetic core 1 shown in FIG. 1 has a hollow portion 4 at 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 one of a plurality of iron-based soft magnetic alloy plates 2 and the other one with an insulating layer 3 sandwiched between them.

A coil may be wound around the magnetic core 1 shown in FIGS. 1 and 2. The magnetic core 1 may be stored in a case if necessary. After storing the magnetic core 1 in the case, the coil may be wound.

The iron-based soft magnetic alloy plate 2 is composed of, for example, a soft magnetic alloy thin plate containing 50 atomic% or more of iron (Fe). The iron-based soft magnetic alloy plate 2 has a fine crystal structure having an average crystal grain size of 100 nm or less. If the average crystal grain size exceeds 100 nm, the soft magnetic properties deteriorate. Therefore, the average crystal grain size is preferably 100 nm or less, more preferably 50 nm or less. Further, the average crystal grain size is more preferably 10 nm or more and 30 nm or less, and more preferably 10 nm or more and less than 30 nm.

The average crystal grain size is obtained by the Scherrer equation from the half width of the diffraction peak obtained by X-ray diffraction (XRD) analysis. Scherrer's equation is expressed by D = (K · λ) / (βcosθ). Here, D is the average crystal grain size, K is the scherrer, λ is the wavelength of the X-ray, β is the full width at half maximum (FWHM), and θ is the Bragg angle. The shape factor K is 0.9. The Bragg angle is half of the diffraction angle 2θ. The XRD analysis is performed under the conditions of a Cu target, a tube voltage of 40 mV, a tube current of 40 mA, and a slit width (RS) of 0.20 mm.

The composition of the iron-based soft magnetic alloy plate 2 is represented by, for example, the following general formula (composition formula).
General formula: Fe _a Cu _b M _{c M'd} M " _e Si _f B _g
(In the formula, 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 in the periodic table, and M'is from the group consisting of Mn, Al and platinum group elements. At least one element selected, 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 = 100 atomic%, and b is 0.01 ≦ b ≦. 8 is a number satisfying atomic%, c is a number satisfying 0.01 ≦ c ≦ 10 atomic%, d is a number satisfying 0 ≦ d ≦ 10, and e is a number satisfying 0 ≦ e ≦ 20 atoms. % Is a number satisfying, f is a number satisfying 10 ≦ f ≦ 25 atomic%, and g is a number satisfying 3 ≦ g ≦ 12 atomic%.)

Cu enhances corrosion resistance, prevents coarsening of crystal grains, and is effective in improving soft magnetic properties such as iron loss and magnetic permeability. The Cu content is preferably 0.01 atomic% or more and 8 atomic% or less (0.01 ≦ b ≦ 8). If the content is less than 0.01 atomic%, the effect of addition is small, and if it exceeds 8 atomic%, the magnetic properties deteriorate.

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 in the periodic table. Examples of Group 4 elements include Ti (titanium), Zr (zirconium), Hf (hafnium) and the like. Examples of Group 5 elements include V (vanadium), Nb (niobium), Ta (tantalum) and the like. Examples of Group 6 elements include Cr (chromium), Mo (molybdenum), W (tungsten) and the like. Examples of rare earth elements include Y (yttrium), lanthanoid elements, actinide elements and the like. The M element is effective for making the crystal grain size uniform and stabilizing the magnetic properties against temperature changes. The content of the M element is preferably 0.01 atomic% or more and 10 atomic% or less (0.01 ≦ c ≦ 10).

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

The M "element is at least one element selected from the group consisting of Co (cobalt) and Ni (nickel). The M" element is effective in improving soft magnetic properties such as saturation magnetic flux density. The content of the M "element is preferably 0 atomic% or more and 20 atomic% or less (0 ≦ e ≦ 20).

Si (silicon) and B (boron) aid in the amorphization of the alloy or the precipitation of microcrystals during production. Si and B are effective for improving the crystallization temperature and heat treatment for improving the magnetic properties. In particular, Si dissolves in Fe, which is the main component of fine crystal grains, and is effective in reducing magnetostriction and magnetic anisotropy. The Si content is preferably 10 atomic% or more and 25 atomic% or less (10 ≦ f ≦ 25). The content of B is preferably 3 atomic% or more and 12 atomic% or less (3 ≦ g ≦ 12).

When the above general formula is satisfied, a Fe ₃ Si phase is formed. A fine crystal having an average crystal grain size of 100 nm or less has at least one phase selected from the group consisting mainly of an α-Fe phase, a Fe ₃ Si phase, and a Fe ₂ B phase. Each crystal may contain a constituent element that satisfies the general formula.

It is preferable that tensile stress is generated in the direction parallel to the Fe ₃ Si crystal phase and compressive stress is generated in the vertical direction. The analysis of the presence or absence of tensile stress and compressive stress is performed using the residual stress analysis method of XRD. The parallel direction is the longitudinal direction of the iron-based soft magnetic alloy plate 2. That is, it is the longitudinal direction of the thin band produced by the roll quenching method. The vertical direction is the width direction of the thin band.

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

The largest peak that appears in the range where the diffraction angle (2θ) is 140 degrees or more and 180 degrees or less is used as a reference. The X-ray irradiation angle is measured while shifting it by 15 degrees to 45 degrees. When the position of this peak shifts to the right side, it becomes tensile stress, and when it shifts to the left side, it becomes compressive stress.

The generation of tensile stress and compressive stress on the Fe ₃ Si crystal phase indicates that the iron-based soft magnetic alloy plate has magnetic anisotropy. As described above, the iron-based soft magnetic alloy plate 2 containing Fe (iron), Si (silicon), and B (boron) as constituent elements is selected from the group consisting of α-Fe, Fe ₃ Si, and Fe ₂ B. Has at least one crystalline phase. Conventional magnetic materials having fine crystals can be imparted with soft magnetic properties by eliminating magnetic anisotropy. With this method, it is difficult to further improve the initial magnetic permeability.

The magnetic core of the embodiment can increase the initial magnetic permeability by imparting magnetic anisotropy to the Fe ₃ Si crystal phase. In particular, the initial magnetic permeability at a frequency of 100 kHz can be increased to 25,000 or more, and further to 30,000 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 plate 2 is preferably 30 μm or less. As the iron-based soft magnetic alloy plate 2 becomes thicker, the eddy current loss increases. The eddy current loss X is expressed by the equation: X = B ² f ² d ² / ρ. B represents the magnetic flux density of the magnetic core 1, f represents the frequency of the magnetic core 1, d represents the average thickness of the iron-based soft magnetic alloy plate 2, and ρ represents the electrical resistivity of the magnetic core 1. The average thickness of the iron-based soft magnetic alloy plate 2 is more preferably 20 μm or less, more preferably 18 μm or less. The average thickness is defined by the average value of the thicknesses of any five places when the cross section of the iron-based soft magnetic alloy plate 2 is observed using a scanning electron microscope (SEM).

The ratio Ks of the calculated value of the density to the measured value of the density of the iron-based soft magnetic alloy plate 2 is preferably a number satisfying 1.00 ≦ Ks ≦ 1.50. The calculated density value is a theoretical value obtained from the composition of the iron-based soft magnetic alloy plate 2. The calculated density when the composition of the iron-based soft magnetic alloy plate 2 is represented by the formula: Fe ₇₃ Cu ₁ Nb ₄ Si ₁₅ B ₇ is calculated as follows. The density of Fe is 7.87 g / cm ³ , the density of Cu is 8.96 g / cm ³ , the density of Nb is 8.56 g / cm ³ , the density of Si is 2.33 g / cm ³ , and the density of B is When the density is 2.37 g / cm ³ , the calculated density of the iron-based soft magnetic alloy plate 2 is 7.87 × 0.73 + 8.96 × 0.01 + 8.56 × 0.04 + 2.33 × 0. 15 + 2.37 × 0.07 = 6.6925 g / cm ³ (≈6.69 g / cm ³ ). The measured value of the density is calculated as follows. Cut out from the iron-based soft magnetic alloy plate 2 for an area of 1 cm and ² minutes, and measure the density. The measured density value is a value obtained by dividing the measured density by the average thickness of the iron-based soft magnetic alloy plate 2. The closer Ks is to 1.00, the closer the measured density value is to the theoretical value.

When Ks exceeds 1.50, it indicates that the surface of the iron-based soft magnetic alloy plate 2 has large irregularities or many convex portions. If the surface unevenness is 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 plate 2 and the insulating layer 3. It is more preferable that Ks is 1.00 or more and 1.30 or less.

If the information on the composition of the iron-based soft magnetic alloy plate 2 is available, Ks can be calculated by using the magnetic core 1 as it is. As will be described later, for example, when the insulating layer 3 having a thickness of 10 μm or less formed of an oxide is provided, the measured value of the density may be measured by using the magnetic core 1 as it is. In the case of the insulating layer 3 made of a thin oxide layer, Ks may 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 by using the magnetic core 1 as it is can be regarded as Ks obtained from the entire magnetic core 1. The Ks obtained from the entire magnetic core 1 is preferably 1.00 or more and 1.50 or less. It is more preferable that Ks is 1.1 or more and 1.3 or less.

When Ks ₁ is obtained from the entire magnetic core 1, the average thickness of the iron-based soft magnetic alloy plate 2 is 20 μm or less, and Ks ₁ satisfies 1.00 ≤ Ks ₁ ≤ 1.50. It is preferably a number. Further, Ks ₁ is a number satisfying 1.00 ≤ Ks ₁ ≤ 1.50, and the ratio Ks of the calculated value to the measured value of the density in each of the four divided pieces obtained by dividing the magnetic core 1 into four equal parts is calculated. When Ks ₂ is set, the difference between Ks ₂ and Ks ₁ is preferably within ± 0.2. Ks ₁ and Ks ₂ are calculated as follows. The magnetic core 1 is divided into four equal parts, and the measured densities obtained by measuring the densities of each of the four divided pieces are Ks ₂ . Further, Ks ₁ is defined by the average value of Ks ₂ in the four divided pieces. By calculating the above difference, it is possible to confirm the presence or absence of partial variation in the magnetic core 1. By reducing the partial variation 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 magnetic core 1 can be increased.

It is preferable that the magnetic core 1 has an insulating layer 3 and the space factor of the plurality of iron-based soft magnetic alloy plates 2 is 65% or more. When the insulating layer 3 is not provided, two structures are conceivable: (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 distance between the iron-based soft magnetic alloy plates 2 is large. When the iron-based soft magnetic alloy plates 2 come into direct contact with each other, the magnetic permeability decreases. 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, so that the magnetic permeability decreases. That is, in order to increase the magnetic permeability, it is necessary to insulate between the iron-based soft magnetic alloy plates 2 so that the iron-based soft magnetic alloy plates 2 do not come into direct contact with each other, and then increase the space factor. The space factor is more preferably 75% or more. The upper limit of the space factor is not particularly limited, but is preferably 95% or less. If the space factor exceeds 95%, interlayer insulation may be insufficient.

The method for measuring the space factor will be described below. First, an arbitrary cross section of the magnetic core 1 is observed by SEM to obtain the total area of the iron-based soft magnetic alloy plate 2 in the observation image. The space factor of five regions having a unit area of 500 μm × 500 μm is calculated by SEM observation of the cross section, and the average value is taken as the space factor of the magnetic 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, there may be a part where the interlayer insulation is insufficient. 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 or more and 10 μm or less, and more preferably 0.5 μm or more and 3 μm or less. The thickness of the insulating layer 3 is measured at any cross section of the magnetic core 1. This work is performed at any five places, and the average value is taken as the thickness of the insulating layer (average thickness).

The insulating layer 3 is preferably an insulating film formed by depositing insulating fine particles having an average particle size of 0.001 μm or more (1 nm or more). By depositing the insulating fine particles, it is possible to prevent stress from being applied to the iron-based soft magnetic alloy plate 2. Oxides are preferable as the insulating fine particles, and examples of the insulating fine particles include oxides such as silicon oxide (SiO ₂ ), magnesium oxide (MgO) and aluminum oxide (Al ₂ O ₃ ), and resin powder. It is particularly preferable to use silicon oxide (SiO ₂ ). Since the oxide does not shrink during drying, it is possible to suppress the generation of stress. In particular, since silicon oxide has good compatibility with the iron-based soft magnetic alloy plate 2, variation in magnetic permeability can be reduced. It is considered that this is because both silicon oxide and the iron-based soft magnetic alloy plate 2 contain silicon as an essential constituent element.

The average particle size of the insulating fine particles is preferably 0.001 μm or more and 0.1 μm or less. If the average particle size of the insulating fine particles exceeds 0.1 μm (100 nm), the gap between the insulating fine particles becomes wide, and it is difficult to improve the space factor. As described above, when the surface of the iron-based soft magnetic alloy plate 2 has minute irregularities, a gap is likely to be formed at the boundary between the iron-based soft magnetic alloy plate 2 and the insulating layer 3. When insulating fine particles are used, the insulating layer 3 can be formed by immersing the iron-based soft magnetic alloy plate 2 in a solution containing the insulating fine particles and drying the plate 2. In this method, no stress is applied to the iron-based soft magnetic alloy plate 2 because the insulating material is not shrunk. Therefore, the average particle size of the insulating fine particles is preferably 0.001 μm or more and 0.1 μm or less, and more preferably 0.005 μm or more and 0.05 μm or less (5 nm or more and 50 nm or less). Whether or not the insulating layer 3 contains the deposited insulating fine particles can be determined from an enlarged photograph obtained by, for example, SEM observation.

FIG. 3 is a schematic cross-sectional view showing an example of the boundary between the iron-based soft magnetic alloy plate 2 and the insulating layer 3. As will be described later, the iron-based soft magnetic alloy plate 2 is formed by using an amorphous iron-based alloy strip produced by a roll quenching method as a raw material. In the thin band produced by the roll quenching method, minute irregularities on the surface of the cooling roll affect the surface properties of the thin band surface. Therefore, when enlarged microscopically, minute irregularities are formed on the surface of the iron-based soft magnetic alloy plate 2. When the insulating fine particles are used, the insulating layer 3 can be provided so as to fill the minute irregularities of the magnetic thin band. On the other hand, in the case of the resin paste, since the resin layer is shrunk when solidified by heating, stress is generated in the iron-based soft magnetic alloy plate 2. When stress is generated in the iron-based soft magnetic alloy plate 2, the magnetic permeability is lowered.

At the boundary between the iron-based soft magnetic alloy plate 2 and the insulating layer 3, the total length P of the voids 5 per 100 μm unit length L is preferably 5 μm or less (including zero). By reducing the gap (gap) at the boundary between the iron-based soft magnetic alloy plate 2 and the insulating layer 3, the space factor can be improved by the thin insulating layer 3. As a result, the magnetic permeability can be improved. FIG. 3 shows an example in which the void 5 is one, but there may be a plurality of voids 5. If the total length is 5 μm or less, the space factor can be improved.

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

The magnetic core as described above has an initial magnetic permeability μ of 25,000 or more at a frequency of 100 kHz. Further, the initial magnetic permeability μ at a frequency of 100 kHz can be set to 30,000 or more. The method for measuring the initial magnetic permeability μ is room temperature, 1 turn, and 1 V with an impedance analyzer. The impedance analyzer is Hewlett-Packard Japan YHP4192A.

The magnetic core using the conventional iron-based soft magnetic alloy having a fine crystal structure has a limit in miniaturization in the region where the operating frequency is 50 kHz or more. It is considered that the cause of this is that the iron-based soft magnetic alloy plate having a fine crystal structure has a low magnetic permeability and a low space factor.

The magnetic core according to the embodiment has a high initial magnetic permeability μ of 25,000 or more at a frequency of 100 kHz, suppresses loss while increasing the space factor of the iron-based soft magnetic alloy plate to 65% or more. Thereby, the magnetic core 1 can be miniaturized.

In recent years, as the performance of semiconductor devices (semiconductor switching devices) has improved, the operating frequency has been as high as 50 kHz or more. The operating frequency of the semiconductor element is as high as 400 kHz. The magnetic core according to the embodiment has an initial magnetic permeability of 25,000 or more at a frequency of 100 kHz. Therefore, it exhibits excellent characteristics as a magnetic core mounted on an electronic device having a semiconductor element having an operating frequency of 50 kHz or more and 400 kHz or less.

Examples of electronic devices having semiconductor elements having an operating frequency of 50 kHz or more and 400 kHz include switching power supplies, antenna devices, inverters, and the like. Electronic devices include communication base stations, solar power plants, electric vehicles (EVs), hybrid-electric vehicles (HEVs), plug-in hybrid vehicles (Plug-in Hybrid Vehicles: PHVs), and the like. Used for automobiles, industrial equipment, etc. In addition to this, it can also be used for 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 relationship of the formula: AL value ∝μ × Ae / Le. μ represents the initial magnetic permeability, Ae represents the average magnetic path length, and Le represents the effective cross-sectional area. The AL value is an index showing the performance of the magnetic core 1. The higher the AL value, the higher the inductance value.

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

If the size of the magnetic core 1 is increased, the AL value will be increased. On the other hand, increasing the size of the magnetic core 1 causes a problem of arrangement space in the electronic device. The magnetic core according to the embodiment has a large initial magnetic permeability μ and a large space factor of the iron-based soft magnetic alloy plate. By improving the space factor, the volume of the magnetic core can be reduced if the amount of the iron-based soft magnetic alloy plate used is the same. As a result, the effective cross-sectional area Le of the magnetic core can be reduced. When the space factor is improved, when the size of the magnetic core is the same, the amount of the iron-based soft magnetic alloy plate 2 used increases, so that the average magnetic path length Ae can be lengthened. Since the magnetic core according to the embodiment has high both the initial magnetic permeability and the space factor, the AL value can be increased. The improvement of the AL value enables the miniaturization of the magnetic core. This makes it easier to reduce the weight of the magnetic core and secure a space for placement in electronic devices. Therefore, the degree of freedom in designing in the electronic device can be improved. For example, when comparing a magnetic core having an initial magnetic permeability μ of 17,000 and a magnetic core having an initial magnetic permeability of 30,000 at a frequency of 100 kHz, the diameter of the magnetic core having an initial magnetic permeability of 30,000 can be reduced by about 20%.

If the magnetic core 1 is made smaller, the number of materials constituting the magnetic core 1 can be reduced, so that the cost can be reduced. Even if the number of windings is reduced, the same characteristics can be obtained. Reducing the number of windings leads to cost reduction because the amount of windings used can be reduced. Further, by reducing the number of windings, the probability that the magnetic core is damaged during the winding process can be reduced. Therefore, the yield in the winding process can be improved. By reducing the number of windings, the amount of heat generated by the winding can be reduced.

The miniaturization of the magnetic core 1 also leads to weight reduction. That is, when the characteristics of the magnetic core 1 are equivalent to the characteristics of the conventional magnetic core, it is possible to reduce the size and weight. The miniaturization and weight reduction of the magnetic core 1 leads to the miniaturization and weight reduction of electronic devices such as switching power supplies, antenna devices, and inverters.

Next, a method for manufacturing the magnetic core 1 according to 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 configuration, but the following method can be mentioned as a method for obtaining a good yield.

First, an iron-based amorphous alloy strip is prepared. For the iron-based amorphous alloy, a raw material powder in which each component is mixed is prepared so as to satisfy the above-mentioned general formula (composition formula). Next, the raw material powder is melted to prepare a raw material molten metal. A long iron-based amorphous alloy strip is produced by a roll quenching method using a molten metal as a raw material. When the roll quenching method is performed, it is preferable that the surface roughness Ra of the cooling roll is 1 μm or less. By flattening the surface of the cooling roll, the unevenness on the surface of the obtained iron-based amorphous alloy strip can be reduced. Thereby, Ks can be set to 1.00 or more and 1.30 or less. In order to reduce the surface unevenness, it is also effective to perform it 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 by using, for example, insulating fine particles having an average particle size of 0.001 μm or more and 0.1 μm or less. The insulating fine particles are preferably formed using an oxide or a resin. In particular, it preferably contains at least one oxide selected from the group consisting of silicon oxide, magnesium oxide, and aluminum oxide. An alloy plate formed from an iron-based amorphous alloy strip is immersed in a solution containing insulating fine particles. After that, it is dried and the insulating layer 3 is provided on the alloy plate. If necessary, soaking and drying may be repeated alternately. The step of forming the insulating layer 3 may be performed after cutting the alloy plate to the size of the target magnetic core in advance, or may be performed with a long magnetic strip.

Next, the magnetic core 1 is manufactured. In the case of a winding type magnetic core, a long magnetic strip (iron-based soft magnetic alloy plate 2) provided with an insulating layer is wound. The outermost circumference of the ticket is spot welded and fixed with an adhesive. If the thickness of the insulating layer 3 is adjusted to 4 μm or less, the insulating layer is unlikely to be peeled off in the winding process.

In the case of a laminated magnetic core, a method of laminating a long magnetic strip (iron-based soft magnetic alloy plate 2) provided with an insulating layer 3 and then cutting the magnetic core into a required size can be mentioned. A long magnetic strip provided with the insulating layer 3 may be cut to a required size and then laminated. The sides of the laminate are fixed with an adhesive. It is preferable to coat the surface of the magnetic core with a resin. The resin coating can improve the strength of the magnetic core.

Next, the alloy plate is heat-treated to precipitate fine crystals to form the iron-based soft magnetic alloy plate 2. In the case of a winding type magnetic core, it is preferable to perform heat treatment after winding. In the case of the laminated magnetic core, the heat treatment may be performed after laminating, or the iron-based soft magnetic alloy plate 2 which has been heat-treated in advance may be laminated. Since the iron-based amorphous alloy plate becomes brittle by precipitating fine crystals, it is preferable to heat-treat after forming a magnetic core.

The heat treatment temperature is preferably a temperature near or higher than the crystallization temperature. A temperature higher than the crystallization temperature of −20 ° C. is preferable. In the case of the iron-based soft magnetic alloy plate 2 satisfying the above-mentioned general formula, the crystallization temperature is 500 ° C. or higher and 515 ° C. or lower. Therefore, the heat treatment temperature is preferably 480 ° C. or higher and 600 ° C. or lower. More preferably, it is 510 ° C. or higher and 560 ° C. or lower.

The heat treatment temperature is controlled so that the temperature of the magnetic core 1 is 480 ° C. or higher and 600 ° C. or lower. For example, in the case of an electric furnace, the temperature of the magnetic core can be controlled by adjusting the temperature of the electric heater. There is a difference in temperature between near and far from the electric heater. When a plurality of magnetic cores 1 are arranged and heat-treated, temperature variation 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. For example, a method of directly measuring the temperature of the magnetic core 1 using a thermocouple is effective.

The heat treatment temperature can be easily controlled by heat-treating a number of magnetic cores 1 that can suppress the temperature variation of the furnace. The heat treatment temperature may be controlled by providing a plurality of electric heaters in the furnace. By circulating the atmosphere in the furnace, it is possible to easily control the heat treatment temperature. The heat treatment temperature may be controlled by using a large heat treatment furnace. By surrounding the inside of the furnace with a material having high thermal conductivity and making the heat dissipation uniform, it is possible to easily control the heat treatment temperature.

The heat treatment time is preferably 30 hours or less. The heat treatment time is the time when the temperature of the magnetic core is 480 ° C. or higher and 600 ° C. or lower. If it exceeds 30 hours, the average particle size of the fine crystal grains may exceed 100 nm. The heat treatment time is more preferably 20 minutes or more and 20 hours or less. The heat treatment time is more preferably 1 hour or more and 10 hours or less. Within this range, it is easy to control the average crystal grain size to 50 nm or less.

The rate of temperature rise at the crystallization temperature is preferably 7 ° C./min or more and 30 ° C./min or less. Within this range, the above-mentioned tensile stress and compressive stress can be easily applied. If the rate of temperature rise exceeds 30 ° C./min, rapid grain growth may occur and the magnetic characteristics may deteriorate. The lower limit of the temperature rising rate is not particularly limited, but is preferably 1 ° C./min or more. If it is less than 1 ° C./min, the temperature rise time is too long and the mass productivity is lowered. Therefore, the rate of temperature rise at the crystallization temperature is preferably 7 ° C./min or more and 30 ° C./min or less, and more preferably 10 ° C./min or more and 20 ° C./min or less.

By performing the heat treatment as described above, the DC coercive force of the magnetic core 1 can be reduced to 2 A / m or more and 4 A / m or less. The conventional magnetic core has a DC coercive force of about 1 A / m after heat treatment. By setting the coercive force to 2 A / m or more and 4 A / m or less, the initial magnetic permeability can be increased. When the DC coercive force exceeds 4 A / m, the soft magnetic characteristics deteriorate.

Next, if necessary, further heat treatment in a magnetic field may be performed. In the heat treatment in a magnetic field, it is preferable to apply the magnetic field in the short side direction of the iron-based soft magnetic alloy plate 2. In the wound magnetic core, a magnetic field is applied in the width direction of the iron-based soft magnetic alloy plate 2. In the laminated magnetic core, a magnetic field is applied in the short side direction of the iron-based soft magnetic alloy plate 2. By performing the heat treatment while applying a magnetic field in the short side direction of the iron-based soft magnetic alloy plate 2, the magnetic wall of the iron-based soft magnetic alloy plate 2 can be eliminated. By reducing the domain wall, the loss is reduced and the magnetic permeability is improved. The applied magnetic field is preferably 80 kA / m or more, more preferably 100 kA / m or more. The heat treatment temperature is preferably 200 ° C. or higher and 700 ° C. or lower. The heat treatment time of the heat treatment in a magnetic field is preferably 20 minutes or more and 10 hours or less. The heat treatment in a magnetic field may be performed in one step with the heat treatment for fine crystal precipitation described above. If necessary, the magnetic core may be stored in the case. When it is mounted on various electronic devices, it may be wound if necessary.

With the above manufacturing method, the space factor can be improved and the initial magnetic permeability μ at a frequency of 100 kHz can be 25,000 or more, further 30,000 or more. By combining one or two or more of the space factor, the heat treatment for fine crystal precipitation, and the heat treatment in a magnetic field, the initial magnetic permeability μ at a frequency of 100 kHz can be increased to 25,000 or more, and further to 30,000 or more.

(Examples 1 to 8, Comparative Examples 1 to 2)
An iron-based amorphous alloy strip was prepared using the roll quenching method. The average thickness and Ks were changed by changing the conditions of the roll quenching method. By this work, iron-based amorphous alloy plates according to Samples 1 to 4 were prepared. Table 1 shows the average thickness and Ks of the iron-based amorphous alloy plate. The crystallization temperature of Samples 1 to 4 is 500 ° C. or higher and 515 ° C. or lower.

Next, an insulating layer was formed on the surface of the iron-based amorphous alloy plate. In Examples 1 to 8 and Comparative Example 1, as shown in Table 2, silicon oxide (SiO ₂ ), magnesium oxide (MgO), or aluminum oxide (Al ₂ O) is formed on the surface of any of the alloy plates of Samples 1 to 4. An insulating layer was formed by the above-mentioned method using the insulating fine particles of ₃ ). In Comparative Example 2, a resin paste was applied to the surface of the alloy plate of Sample 1 to form an insulating layer. Table 2 shows the material, average particle size, and thickness of the insulating layer of the insulating fine particles.

After forming the insulating layer, an alloy plate was wound to prepare a wound magnetic core. Then, a first heat treatment for precipitating fine crystals and a second heat treatment in a magnetic field were performed. As a result, the wound type magnetic cores according to Examples 1 to 8 and Comparative Examples 1 and 2 were produced. The size of the magnetic core according to the examples and comparative examples was unified to an outer diameter of 12 mm × an inner diameter of 10 mm × a width of 2 mm. The conditions of the first heat treatment and the second heat treatment are shown in Table 3. The coercive force of the magnetic core was measured after the first heat treatment. The results are shown in Table 3.

In the first heat treatment, the temperature of the magnetic core was measured with a thermocouple. In Examples 1 to 8, the heat treatment temperature was close to the crystallization temperature of the magnetic core. The heat treatment temperature was controlled by using a "furnace with a large electric capacity" so as to be within the range of Table 3. In the examples, the coercive force after the first heat treatment was 2 A / m or more and 4 A / m or less.

On the other hand, in Comparative Examples 1 and 2, the temperature rising rate was 50 ° C./min, which was out of the preferable range. For the wound cores of Examples and Comparative Examples, the average crystal grain size of the fine crystal structure and the stress of the Fe ₃ Si crystal phase were measured. The average crystal grain size of the fine crystal structure is obtained by Scherrer's formula from the half width of the diffraction peak obtained by XRD as described above. The stress of the Fe ₃ Si crystal phase was measured by the residual stress analysis method of XRD. Those in which both tensile stress and compressive stress were observed in the longitudinal component of the Fe ₃ Si crystal phase were designated as "○ (Good)", and those in which they were not observed were designated as "× (Bad)". The longitudinal direction is the longitudinal direction of the iron-based soft magnetic alloy plate, and the vertical direction is the width direction of the iron-based soft magnetic alloy plate. The results are shown in Table 4.

As can be seen from the table, the average crystal grain size of the magnetic core according to the examples was 50 nm or less. In the residual stress analysis by XRD analysis, it was confirmed that tensile stress was applied in the longitudinal direction and compressive stress was applied in the vertical direction. The average crystal grain size of the comparative example was 50 nm or less. However, it was not confirmed that both tensile stress and compressive stress were applied.

The space factor (%), the initial magnetic permeability μ, and the loss (kW / m ³ ) were measured for the wound cores of the examples and comparative examples. For the space factor, the area ratio of the iron-based soft magnetic alloy plate is measured at five locations with a unit area of 500 μm × 500 μm by observing an arbitrary cross section of the magnetic core by SEM, and the average value of the area ratio of the iron-based soft magnetic alloy plate is calculated. The area ratio (%) was used.

The method for measuring the initial magnetic permeability μ was performed with an impedance analyzer (YHP4192A, Hewlett-Packard Company, Japan) at room temperature, 1 turn, and 1 V. For the initial magnetic permeability μ, the initial magnetic permeability at a frequency of 10 kHz and the initial magnetic permeability at a frequency of 100 kHz were measured.

The loss was measured using a BH analyzer (SY-8216, Iwatsu Electric Co., Ltd.) at room temperature, 2 turns on the primary side, 2 turns on the secondary side, a frequency of 100 kHz, and 200 mT. The results are shown in Table 5.

As can be seen from the table, the initial magnetic permeability μ of the magnetic core according to the example at a frequency of 100 kHz was 25,000 or more, and further was 30,000 or more. It can be seen that the initial magnetic permeability μ at a frequency of 100 kHz can be increased by setting the space factor, the first heat treatment, and the second heat treatment as preferable conditions. On the other hand, in the magnetic core with a thick insulating material as in the comparative example, the space factor greatly decreased, and the magnetic permeability also decreased. The magnetic cores of the examples were all low in terms of loss. The initial magnetic permeability of the magnetic core in the comparative example at a frequency of 10 kHz was high, and was 90,000 or more and 95,000. However, the initial magnetic permeability at a frequency of 100 kHz decreased.

When the initial magnetic permeability μ of Example 1 and Comparative Example 1 at a frequency of 1 kHz was measured, there was no significant difference between Example 1 at 63000 and Comparative Example 1 at 100,000. Therefore, it can be seen that it is particularly effective when the operating frequency is as high as 50 kHz or more.

The cross section of the magnetic core was observed by SEM, and the abundance ratio of voids at the boundary between the iron-based soft magnetic alloy plate and the insulating layer was measured. The length of the void in a unit length of 100 μm in an arbitrary cross section was measured. The results are shown in Table 6. Ks ₁ obtained from the entire magnetic core and Ks ₂ obtained from a sample obtained by dividing the magnetic core into four equal parts (cut into 1/4 size) were measured. Table 6 shows Ks ₁ obtained from a sample obtained by dividing the magnetic core into four equal parts, and the minimum and maximum values among the four Ks ₂ .

As can be seen from the table, the magnetic core according to the embodiment had small voids (including zero) at the boundary between the iron-based soft magnetic alloy plate and the insulating layer. From this, it can be seen that the space factor can be improved by reducing the voids.

(Example 9, Comparative Example 3)
The same magnetic core as in Comparative Example 1 was produced as Comparative Example 3 except that the outer diameter was 37 mm, the inner diameter was 23 mm, and the width was 15 mm. Further, the same magnetic core as in Example 7 was produced as Example 9 except that the size was the same (outer diameter 37 mm × inner diameter 23 mm × width 15 mm). The initial magnetic permeability μ at a frequency of 100 kHz was 17,000 in Comparative Example 3 and 35,000 in Example 9.

The L value was 1.2 mH when the winding was wound around the magnetic core of Comparative Example 3 for 8 turns. On the other hand, the L value of the magnetic core obtained by winding the winding of Example 9 for 6 turns was 1.4 mH. When the magnetic core size was the same, the L value was larger in Example 9 having a frequency of 100 kHz and a large initial magnetic permeability μ, although the number of windings was smaller. Therefore, the number of windings can be reduced by increasing the initial magnetic permeability at a frequency of 100 kHz.

(Example 10, Comparative Example 4)
The magnetic core of Comparative Example 4 (outer diameter 37 mm × inner diameter 23 mm × width 15 mm, number of windings 8 turns, L value 1.2 mH) was prepared. The same magnetic core as in Example 9 is used except that the magnetic core size of Example 9 (initial magnetic permeability μ at a frequency of 100 kHz is 35000) is changed so that the L value of the magnetic core after winding is the same 1.2 mH. Made as. The magnetic core size of Example 10 could be reduced to an outer diameter of 29 mm, an inner diameter of 23 mm, and a width of 15 mm. The mass of the magnetic core of Comparative Example 4 was 57 g, whereas that of Example 10 was 21 g. It can be seen that when the initial magnetic permeability μ at a frequency of 100 kHz is increased in this way, miniaturization can be achieved if the same performance is required.

Although some embodiments of the present invention have been exemplified above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof. Each of the above embodiments can be implemented in combination with each other.

Claims (10)

A plurality of iron-based soft magnetic alloy plates having a crystal structure with an average crystal grain size of 100 nm or less,
A magnetic core comprising an insulating layer provided between one of the plurality of iron-based soft magnetic alloy plates and the other.
The average thickness of each of the plurality of iron-based soft magnetic alloy plates is 30 μm or less.
The thickness of the insulating layer is 0.1 μm or more and 10 μm or less.
The insulating layer contains insulating fine particles having an average particle size of 0.001 μm or more and 0.1 μm or less.
The insulating fine particles contain at least one oxide selected from the group consisting of silicon oxide, magnesium oxide, and aluminum oxide.
The space factor of the plurality of iron-based soft magnetic alloy plates in the magnetic core is 65% or more.
The initial magnetic permeability at a frequency of 100 kHz is 25,000 or more. The magnetic core according to claim 1, wherein the average crystal grain size is 50 nm or less. The composition of each of the plurality of iron-based soft magnetic alloy plates is
Formula: Fe _a Cu _b M _{c M'd} M " _e Si _f B _g
(In the formula, M represents at least one element selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, and rare earth elements in the periodic table, and M'consists of Mn, Al, and platinum group elements. Represents at least one element selected from the group, M "represents 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 = 100 atomic%, and b is 0.01 ≦. b is a number satisfying 8 atomic%, c is a number satisfying 0.01 ≦ c ≦ 10 atomic%, d is a number satisfying 0 ≦ d ≦ 10 atomic%, and e is a number satisfying 0 ≦ 0 ≦. 1 is a number that satisfies e ≦ 20, f is a number that satisfies 10 ≦ f ≦ 25 atomic%, and g is a number that satisfies 3 ≦ g ≦ 12 atomic%). Or the magnetic core according to claim 2 . The ratio of the calculated value of the density to the measured value of the density of the magnetic core Ks ₁ is a number satisfying 1.00 ≤ Ks ₁ ≤ 1.50, according to any one of claims 1 to 3. Magnetic core. When the magnetic core is divided into four equal parts, the difference between the ratio of the calculated value of the density to the measured value of the density of each of the four divided pieces, Ks ₂ and the value of Ks ₁ , is within ± 0.2. Item 4. The magnetic core according to item 4. The magnetic core according to any one of claims 1 to 5 , wherein the initial magnetic permeability is 30,000 or more. The invention according to any one of claims 1 to 6, wherein the total length of the voids per 100 μm unit length at the boundary between the iron-based soft magnetic alloy plate and the insulating layer is 0 μm or more and 5 μm or less. Magnetic core. The magnetic core according to any one of claims 1 to 7, wherein the operating frequency is 50 kHz or more. The magnetic core according to any one of claims 1 to 8 , wherein the insulating fine particles contain the silicon oxide. The magnetic core according to any one of claims 1 to 9, wherein the crystal structure has a Fe ₃ Si phase.

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