Magnetic material and method for producing the same

Abstract

To provide a high-performance magnetic material that can be used in a high-frequency band and a manufacturing method thereof.SOLUTION: A magnetic material includes magnetic powder containing Fe and Co in an amount of more than 0 mass% and 40 mass% or less, and has a relative magnetic permeability μ' of 20.0 or more at a frequency of 100 MHz. A manufacturing method of the magnetic material includes the steps of obtaining a magnetic slurry containing the magnetic powder and a resin, forming the magnetic slurry into a sheet, and performing heat treatment.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a magnetic material and a method for manufacturing the same.

Background Art

[0002] Conventionally, since the practical application range of soft magnetic materials was limited to about 10 MHz, various developments of magnetic materials that can be used in high-frequency bands of 100 MHz or higher have been carried out.

[0003] Patent Document 1 discloses a magnetic material that can be used in a high-frequency band and contains a specific amount of fine powder containing nickel.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In high-frequency bands of 100 MHz or higher, the effects of hysteresis loss, eddy current loss, and loss due to resonance phenomena become significant. Also, it is known that the magnetic properties (relative permeability μ') of magnetic materials tend to decrease as the frequency increases in high-frequency bands. Therefore, magnetic materials that can be used in high-frequency bands are required to have a high relative permeability and low losses.

[0006] In the magnetic material described in Patent Document 1, there are limitations in improving the relative permeability μ' in high-frequency bands of 100 MHz or higher and suppressing the above losses, and the development of a more excellent magnetic material has been demanded.

[0007] The present invention has been made in view of such problems, and an object thereof is to provide a high-performance magnetic material that can be used in a high-frequency band and a method for manufacturing the same.

Means for Solving the Problem

[0008] The magnetic material according to the present invention contains magnetic powder containing Fe and Co of more than 0 mass% and 40 mass% or less, and is characterized in that the relative permeability μ' at a frequency of 100 MHz is 20.0 or more.

[0009] In one embodiment of the magnetic material, the loss coefficient tanδ at a frequency of 100 MHz is 0.050 or less.

[0010] In one embodiment of the magnetic material, μ' / tanδ at a frequency of 50 MHz is 800 or more.

[0011] In one embodiment of the magnetic material, μ' / tanδ at a frequency of 100 MHz is 400 or more.

[0012] In one embodiment of the magnetic material, the powder thickness of the magnetic powder is 0.3 μm to 2.0 μm.

[0013] In one embodiment of the magnetic material, the aspect ratio of the magnetic powder is 10 to 50.

[0014] In one embodiment of the magnetic material, the content ratio of C in the magnetic powder is less than 0.20 mass%.

[0015] In one embodiment of the magnetic material, the magnetic powder contains 4 to 18 mass% in total of one or more of Cr, Si, Al and rare earth elements.

[0016] In one embodiment of the magnetic material, the surface of the magnetic powder has a SiO2 film.

[0017] In one embodiment of the magnetic material, it contains resin and the metal filling rate is 35 volume% or more.

[0018] In one embodiment of the magnetic material, it is in sheet form.

[0019] The manufacturing method of the magnetic material according to the present invention is characterized by having a step of obtaining a magnetic slurry containing magnetic powder and resin, a step of forming the magnetic slurry into a sheet shape, and a heat treatment step.

Effect of the Invention

[0020] According to the present invention, it is possible to provide a high-performance magnetic material that can be used in a high-frequency band and a method for manufacturing the same.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, the magnetic material according to the present invention will be described. Note that "~" indicating a numerical range includes the lower limit value and the upper limit value thereof unless otherwise specified.

[0022] <Magnetic Material> The magnetic material according to the present invention (hereinafter also referred to as the present magnetic material) contains magnetic powder (hereinafter also referred to as the first magnetic powder) containing Fe and Co of more than 0 mass% and 40 mass% or less, and the relative permeability μ' at a frequency of 100 MHz is 20.0 or more.

[0023] Since the relative permeability μ' of the present magnetic material at a frequency of 100 MHz is 20.0 or more, it can be stably used even in a high-frequency band. Further, μ' of the present magnetic material at a frequency of 100 MHz is preferably 30.0 or more, more preferably 40.0 or more. Further, from the viewpoint of ease of preparation, μ' at a frequency of 100 MHz is preferably 50.0 or less. Note that μ' can be measured by the method described later.

[0024] In a high-frequency band of 100 MHz or more, in addition to hysteresis loss and eddy current loss, the influence of losses due to various resonance phenomena becomes large. The loss due to this resonance phenomenon can be evaluated by the ratio tanδ (= μ” / μ') of the relative permeability (real permeability) μ' and the imaginary permeability μ”. Here, from the perspective of stable use in the high-frequency band, the loss factor tanδ of this magnetic material at a frequency of 100 MHz is preferably 0.050 or less, and more preferably 0.040 or less. Note that tanδ can be measured by the method described later.

[0025] Also, from the perspective of stable use in the high-frequency band, the higher the performance factor represented by μ’ / tanδ of this magnetic material at a frequency of 50 MHz, the better. More specifically, the μ’ / tanδ is preferably 800 or more, more preferably 1000 or more, and even more preferably 1100 or more.

[0026] Furthermore, from the perspective of stable use in the high-frequency band, the higher the μ’ / tanδ of this magnetic material at a frequency of 100 MHz, the better. More specifically, it is preferably 400 or more, and more preferably 500 or more.

[0027] This magnetic material contains the first magnetic powder with a specific composition, and has a relative permeability μ’ of 20.0 or more at a frequency of 100 MHz, which is very high compared to conventional ones (many are less than 15). Therefore, it can be stably used in the high-frequency band. Note that this magnetic material can reduce the loss component μ” of the relative permeability.

[0028] The FeCo-based magnetic powder containing at least Fe and Co is an advantageous magnetic powder for increasing the relative permeability μ’ and reducing the loss factor tanδ in the high-frequency band.

[0029] The first magnetic powder containing Fe and Co in a specific composition has a large saturation magnetization, so it can increase the resonance frequency of the magnetic material. The first magnetic powder may contain elements other than Fe and Co, such as C, B, N, P, Mn, Ni, Cu, Al, Si, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, etc. Also, the first magnetic powder can contain inevitable impurities. As the first magnetic powder, for example, Fe-Co based alloy powders such as Fe-Co alloy powder and Fe-Co-V alloy powder can be used. However, from the viewpoint of maintaining high saturation magnetization, it is preferable to use Fe-Co alloy powder as the first magnetic powder.

[0030] In addition, this magnetic material can contain, as other magnetic powders in addition to the first magnetic powder, Fe-Ni alloy powder, Fe-Si-Cr alloy powder, Fe-Si-Al alloy powder, and Fe-based alloy powders such as Fe-Si, carbonyl iron, amorphous alloy, nanocrystalline alloy, etc., within the range where the effects of the present invention can be obtained. Here, from the viewpoint of maintaining a high μ' in the high-frequency band, the blending ratio of the first magnetic powder in all the magnetic powders is preferably 90 to 100% by mass. In particular, the magnetic powder used in the present invention is preferably composed of only the first magnetic powder.

[0031] The content ratio of the first magnetic powder in the magnetic material is preferably 90% by mass or more from the viewpoint of maintaining a high μ' in the high-frequency band, and preferably 96% by mass or less from the viewpoint of further improving the strength by adding resin.

[0032] The content ratio of Co in the first magnetic powder is more than 0% by mass and 40% by mass or less. By containing Co, the magnetocrystalline anisotropy becomes low, and the μ' of the magnetic material in the high-frequency band can be improved. Also, if the content ratio of Co is 40% by mass or less, it is possible to prevent the magnetostriction constant from increasing and causing strain when the magnetic powder is flattened, resulting in a decrease in μ'. From the viewpoint of improving μ' and the performance factor μ' / tanδ (= μ'Q), the content ratio of Co is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. Also, from the viewpoint of maintaining a high μ', the content ratio of Co is preferably 35% by mass or less, and more preferably 30% by mass or less.

[0033] The content ratio of Fe in the first magnetic powder can be, for example, the balance other than Co, and specifically, it is preferably 60 to 90% by mass. If the content ratio of Fe is 90% by mass or less, the crystal magnetic anisotropy becomes low, and μ' of the magnetic material in the high-frequency band can be further improved. Further, if the content ratio of Fe is 60% by mass or more, the magnetostriction constant increases, and when the magnetic powder is flattened, strain enters, and it is possible to easily prevent μ' from decreasing. From the viewpoint of improving μ' and improving the performance factor μ' / tanδ (= μ'Q), the content ratio of Fe is more preferably 85% by mass or less, and even more preferably 80% by mass or less. Further, from the viewpoint of maintaining a high μ', the content ratio of Fe is more preferably 65% by mass or more, and even more preferably 70% by mass or more.

[0034] The content ratio of elements other than Fe and Co in the first magnetic powder can be appropriately set within the range where the effects of the present invention can be obtained. However, from the viewpoint of maintaining a high saturation magnetization and maintaining a high μ' in a high-frequency band of 100 MHz or more, the lower the content ratio of other elements, the more preferable.

[0035] From such a viewpoint, specifically, the content ratio of C in the first magnetic powder is preferably less than 0.20% by mass, more preferably 0.15% by mass or less, and even more preferably 0.10% by mass or less.

[0036] The content ratio of B in the first magnetic powder is preferably 0.20% by mass or less, and more preferably 0.10% by mass or less, from the viewpoint of preventing the hardness of the alloy from increasing and the filling rate from not increasing sufficiently by high-pressure pressing or hot pressing.

[0037] For the same reason as B, the content ratio of N in the first magnetic powder is preferably 0.10% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less.

[0038] The content ratio of P in the first magnetic powder is preferably 0.10 mass% or less, more preferably 0.010 mass% or less, and even more preferably 0.005 mass% or less for the same reasons as B and N.

[0039] From the viewpoint of improving corrosion resistance and other properties, the first magnetic powder preferably contains other elements.

[0040] The first magnetic powder preferably contains a total of 4 to 18 mass% of one or more of Cr, Si, Al, and rare earth elements (for example, Sc, Y, Ce, etc.). For example, the first magnetic powder can be a magnetic powder composed of more than 0 mass% and 40 mass% or less of Co, 4 to 18 mass% of these other elements, and Fe (the balance: 42 to 96 mass%).

[0041] If the total content of these other elements is 4% by mass or more, the following excellent effects can be obtained. That is, when the magnetic material is molded into, for example, a composite magnetic sheet using a resin as a binder, these other elements form an oxide film on the surface of metal powder such as Fe or Co, so that the contact between the metal powder and the resin can be easily prevented. Here, when the metal powder is in contact with the resin, the resin may be catalytically decomposed, and this tendency may be particularly noticeable when Fe or Co is used as the metal powder. For this reason, by including the above-mentioned easily oxidizable elements such as Cr, Si, and Al in the first magnetic powder and actively forming an oxide film on the powder surface, the contact between the metal (Fe or Co) and the resin can be avoided, and the resin decomposition and the resulting gas generation (degassing) can be easily suppressed. As a result, when the magnetic material is embedded in a substrate and used, the occurrence of swelling, peeling, and warping of the substrate can be easily prevented during (lead-free) reflow processing such as soldering to a circuit substrate. From the same viewpoint, the total content of these other elements is more preferably 6% by mass or more. Furthermore, if the total content of these other elements is 18% by mass or less, it becomes easier to maintain a high μ' in the high frequency band. From the same viewpoint, the total content of these other elements is more preferably 15% by mass or less. The elemental composition of the magnetic powder can be identified by SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy).

[0042] The magnetic powder contained in the magnetic material is preferably a flat powder. By flattening the magnetic powder, the demagnetizing factor is reduced, and μ' in the high frequency band can be further increased. In addition, the magnetic powder may be heat-treated in advance to improve the characteristics.

[0043] The powder thickness of the magnetic powder (e.g., flattened powder) contained in this magnetic material is preferably 0.3 μm to 2.0 μm. By setting the powder thickness to 2.0 μm or less, eddy current loss can be further reduced, and high μ' (specifically, μ' ≥ 20) can be easily obtained in the high-frequency band. By setting the powder thickness to 0.3 μm or more, breakage of the magnetic powder can be easily suppressed in the process of flattening the magnetic powder, and a desired aspect ratio can be easily obtained. From the viewpoint of reducing eddy current loss, the powder thickness is more preferably 1.5 μm or less. Also, from the viewpoints of preventing breakage of the magnetic powder and easily obtaining a powder with a desired aspect ratio, the powder thickness is more preferably 0.4 μm or more. The powder thickness of the magnetic powder can be adjusted, for example, by adjusting the flattening time. Note that the powder thickness of the magnetic powder means the length in the short-axis direction of the magnetic powder. Specifically, a molded body (composite magnetic sheet) is produced, resin-embedded, and the cross-section obtained by polishing is observed with an SEM (scanning electron microscope), and the powder thickness is calculated from the length in the short-axis direction of the magnetic powder. This operation is performed on a plurality (e.g., 10 to 60) of powder particles, the powder thickness is calculated, and the average value is taken as the powder thickness of the magnetic powder.

[0044] The aspect ratio of the magnetic powder (e.g., flattened powder) contained in this magnetic material is preferably 10 to 50. By setting the aspect ratio of the magnetic powder to 10 or more, when the magnetic material is formed into a sheet shape, the obtained magnetic sheet becomes less likely to crack, and high μ' can be easily obtained in the high-frequency band. From the same viewpoint, the aspect ratio of the magnetic powder is more preferably 20 or more, and even more preferably 25 or more. Also, by setting the aspect ratio of the magnetic powder to 50 or less, for example, the dispersibility of the magnetic powder in a slurry can be further improved, the amount of solvent when forming the slurry can be set to an appropriate amount, and the coatability can be further improved. Further, when a magnetic sheet is formed, it is possible to easily suppress the formation of severe irregularities on the sheet surface. From the same viewpoint, the aspect ratio of the magnetic powder is more preferably 45 or less. The aspect ratio of the magnetic powder means the length in the major axis direction of the magnetic powder / the length in the minor axis direction. Specifically, a molded body (composite magnetic sheet) is produced, resin-embedded, and the cross-section obtained by polishing is observed with an SEM (scanning electron microscope), and the aspect ratio is calculated from the lengths in the major axis direction and the minor axis direction of the magnetic powder. This operation is performed on a plurality (for example, 10 to 60) of powder particles, the aspect ratio is calculated, and the average value is taken as the aspect ratio of the magnetic powder.

[0045] A coating film may be formed on the surface of the magnetic powder. By forming a coating film, contact between the metal part and the resin can be prevented, and outgassing due to resin decomposition can be easily suppressed. As a result, in the reflow operation after incorporating the magnetic material into the substrate, swelling, peeling, and warping of the substrate can be easily prevented. As the coating film, various materials can be appropriately used, but from the viewpoint of suppressing outgassing due to resin decomposition, it is preferable to use a SiO2 film. Note that the film ratio by the coating film on the powder surface can be appropriately set within the range in which the effects of the present invention can be obtained, and is not particularly limited.

[0046] In addition to the magnetic powder described above, this magnetic material can be a composite material containing a binder (e.g., resin) capable of binding the magnetic powder and an additive (e.g., thickener). As the binder and the additive, it is preferable to use resins having different thermo-gravimetric characteristics (TG characteristics). The resin used as the additive is preferably one that decomposes at a lower temperature than the resin used as the binder and reduces in weight. More specifically, as the binder, it is preferable to use a binder in which the weight loss of the solid component that can bind the magnetic powder and at least partially decomposes upon heating to generate gas is 4.0 wt% (mass%) or less at 220°C. For example, an epoxy resin can be used. In addition, other resins (e.g., phenolic resin) can be used in combination as the binder. As the thickener, it is preferable to use a thickener in which the weight loss of the solid component is 5.0 wt% (mass%) or more at 220°C. For example, a polyacrylate ester can be used. The above thickener can be incompatible with the above binder. If both resins are incompatible, when mixed, the two resins are partially mixed while being partially segregated, and a segregation part due to the thickener is formed.

[0047] The blending ratios of the binder and the additive can be appropriately set within the range in which the effects of the present invention can be obtained. For example, the blending ratio of the binder resin with respect to the (first) magnetic powder is preferably 2 to 15 mass%. If the blending ratio of the binder resin is 2 mass% or more, the desired strength can be easily imparted to the magnetic material. If it is 15 mass% or less, the filling rate of the magnetic powder can be easily adjusted to an appropriate range, and the desired magnetic permeability can be easily obtained.

[0048] In addition, the blending ratio of the thickener with respect to the binder resin is preferably, for example, 20 to 150% by mass. If the blending ratio of the thickener is 20% by mass or more, the desired viscosity can be easily obtained when made into a slurry, and uniform coating can be easily achieved. Further, if the blending ratio of the thickener is 150% by mass or less, the adhesive force by the binder resin can be easily adjusted within an appropriate range, and the desired strength can be easily imparted. Furthermore, the filling rate of the magnetic powder can be easily adjusted within an appropriate range, and the desired magnetic permeability can be easily obtained.

[0049] The metal filling rate in the magnetic material can be appropriately set within the range in which the effects of the present invention can be obtained. However, from the viewpoint of maintaining high μ' and a high performance factor (μ' / tanδ) in a high-frequency band of 100 MHz or more, 35% by volume or more is preferable, 40% by volume or more is more preferable, and 45% by volume or more is even more preferable. On the other hand, from the viewpoint of suppressing an increase in the loss factor tanδ in a high-frequency band of 100 MHz or more and maintaining high μ' and a high performance factor (μ' / tanδ) in a high-frequency band of 100 MHz or more, the metal filling rate is preferably 60% by volume or less, and more preferably 55% by volume or less.

[0050] The filling rate (% by volume) of the metal component in the magnetic material can be specified, for example, by the following method using the magnetic material (formed body) after molding. In addition, a conventionally well-known measuring device can be used suitably for density measurement. (1) From the density of each component (for example, magnetic powder and resin) contained in the magnetic material and the blending ratio (% by weight) of each component, the volume ratio (% by volume) of each component is calculated. (2) Among all the components used in the magnetic material, the change amount of the components that cause a weight change by a heat treatment process (for example, hot pressing) is measured respectively. For example, the weight change amount by a heat treatment process of the binder (for example, epoxy resin) or the additive (for example, polyacrylate) alone, for example, the heat treatment at 300°C for 1 hour (hot pressing condition) is measured. (3) Among the volume ratios obtained in the above (1), assuming a weight loss measured in the above (2), calculate the theoretical density of the magnetic material. At this time, the reduction (disappearance) is regarded as voids. (4) Measure the density (actual measured density) of the measurement sample (for example, a composite magnetic sheet). (5) Assuming that the difference between the actual measured density and the theoretical density is due to the void volume, calculate the void volume in the magnetic material from the actual measured density and calculate the metal filling rate (volume %).

[0051] Note that the shape of this magnetic material is not particularly limited, but as a sheet shape, it is preferably used as a composite magnetic sheet. The composite magnetic sheet can be used, for example, by being incorporated in a circuit board of a digitizer.

[0052] Whether the composite magnetic sheet is suitable for being incorporated into a circuit board can be determined, for example, by performing a reflow test described later on the composite magnetic sheet. From the viewpoint of obtaining a composite magnetic sheet suitable for being incorporated into a circuit board, it is preferable that the weight reduction by the above reflow test is 0.25% or less.

[0053] <Method for manufacturing magnetic material> The method for manufacturing the magnetic material (more specifically, a composite magnetic sheet) according to the present invention (hereinafter sometimes referred to as this manufacturing method) has the following steps. By using this manufacturing method, a high-performance magnetic material that can be used in a high-frequency band of 100 MHz or more can be easily manufactured. · Step of obtaining a magnetic slurry containing magnetic powder and resin (slurry step). · Step of forming the magnetic slurry into a sheet shape (forming step). · Step of heat treatment (heat treatment step).

[0054] This manufacturing method can also have the following steps. · Step of preparing magnetic powder (powder preparation step). · Step of coating the magnetic slurry (coating step). Further, the above powder preparation step can also have a step of flattening the magnetic powder (flattening step). Each process will be described in detail below.

[0055] (Magnetic powder preparation process) First, magnetic powder is prepared. The magnetic powder contains Fe and Co in an amount greater than 0 mass% and less than or equal to 40 mass%, and the above-described first magnetic powder can be used. This magnetic powder is flattened using a device such as a ball mill or a pearl mill (flattening process). The flattening conditions can be appropriately set within the range where the effects of the present invention can be obtained, but it is preferable to perform the process under conditions that satisfy the preferable ranges of the powder thickness and aspect ratio described above.

[0056] (Slurry process) Subsequently, the flattened magnetic powder is mixed with a binder liquid containing a resin, an additive, a solvent, etc. to produce a magnetic slurry. The solvent can be appropriately selected according to the desired viscosity of the slurry and is not particularly limited, but it is preferable to use a solvent that easily volatilizes at a relatively low temperature of about 60°C. As the solvent, for example, a solvent such as methyl ethyl ketone, toluene, ethanol (EtOH), or a glycol such as methylpropylene diglycol (MPDG) can be used alone or in combination of multiple types. The mixing ratio of the solvents is not particularly limited and can be appropriately set. The addition amount of the solvent is appropriately changed according to the viscosity (fluidity and viscosity) of the slurry. The slurry is preferably set to a viscosity such that a uniform film thickness can be obtained and dripping or the like does not occur when coated. Also, regarding the resin and the additive, those described above can be appropriately used.

[0057] (Coating process) The obtained slurry is coated using a conventionally known coater or the like. For example, the magnetic slurry may be coated on a substrate such as a PET (polyethylene terephthalate) film using the die slot method. In the coating process, the solvent in the magnetic slurry is volatilized by heating at a temperature at which the solvent in the magnetic slurry volatilizes, for example, about 60 to 100°C, to obtain a coating film.

[0058] (Forming process) The coating film is punched into a predetermined shape using a device such as a die-cut roll, and one or more of them are laminated to form the magnetic slurry into a sheet shape. The number of coating films to be laminated can be set according to the use of the produced magnetic material and is not particularly limited. The obtained sheet may be subjected to a compression treatment at a pressure of about 2 MPa, for example.

[0059] (Heat treatment process) Next, the laminate obtained by forming into a sheet shape is heat-treated. The heat treatment is usually carried out at about 200 °C, but by carrying it out at a high temperature (for example, 300 °C), the thickener added to the magnetic material can be sufficiently decomposed, and the expansion of the magnetic material due to the gas generated by the decomposition of the thickener during the reflow treatment, which is usually carried out at a relatively high temperature of 220 °C or higher, can be easily prevented. When the magnetic material expands, for example, a phenomenon such as the magnetic sheet peeling off from the circuit board may occur, so it is very preferable to suppress such expansion.

[0060] The heating temperature during the heat treatment is preferably equal to or higher than the reflow treatment temperature, specifically 220 °C or higher, more preferably 260 °C or higher, and even more preferably 300 °C or higher. By setting the heating temperature of the heat treatment to 220 °C or higher, the expansion of the magnetic material can be prevented, and a high metal filling rate and a high relative permeability μ' can be easily obtained. Specifically, before curing, the binder forms a fluid phase, and the additive decomposes in the fluid phase to generate gas. At this time, the part of the additive mixed with the binder decomposes, and the segregated part of the additive decomposes to form pores in the laminate. The pores are connected to each other and form a discharge path extending from the deep layer to the surface layer of the laminate. The gas generated by the decomposition of the additive is confined in the pores by heating to a high temperature of 220 °C or higher and is discharged to the outside of the laminate through the discharge path together with the air confined in the pores. Thus, by performing the heat treatment at a temperature equal to or higher than the reflow treatment temperature, the gas and air can be discharged from the laminate, and the expansion of the magnetic material during the reflow treatment can be easily suppressed. As a result, a high metal filling rate and a high relative permeability μ' can be easily obtained.

[0061] Furthermore, from the viewpoint of preventing decomposition of the binder resin or the like, the heating temperature of the heat treatment is preferably 400 °C or lower, and more preferably 350 °C or lower.

[0062] The heat treatment step may be carried out in air or in vacuum.

[0063] From the viewpoint of obtaining a high metal filling rate and a high relative permeability μ', high-pressure pressing (for example, at a relatively low temperature of room temperature (for example, 25 °C) to 200 °C or lower) or hot pressing (for example, at the heat treatment temperature) may be carried out during or before the heat treatment. For example, in the heat treatment step, high-pressure pressing under room temperature conditions and hot pressing under heating conditions may be continuously carried out for press molding. By performing high-pressure pressing or hot pressing in the heat treatment step, the air and gas trapped in the pores are more easily discharged to the outside due to the pressure applied to the laminate, and it becomes easier to obtain a high metal filling rate and a high relative permeability μ'.

[0064] The pressure (pressing pressure) during high-pressure pressing can be set as appropriate. For example, it is preferably set to 0.05 to 6 tons / cm 2 Further, the hot pressing can be carried out, for example, by raising the temperature from room temperature to 300 °C over about 30 minutes, then holding at 300 °C for 1 hour, and then cooling in the furnace. At that time, the pressing pressure can also be set as appropriate. For example, it can be 0.05 tons / cm 2 constantly.

[0065] As described above, a high-performance magnetic material (composite magnetic sheet) that can be used in a high-frequency band can be obtained. The obtained magnetic material can have pores inside. However, the pores may be impregnated (blocked) with resin. The magnetic material produced using this manufacturing method can suppress expansion during the reflow process and prevent the magnetic material from peeling off from the circuit board.

Examples

[0066] Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. Note that the present invention is not limited by these descriptions.

[0067] [Example 1] Fe-Co alloy powder (Co content: 25% by mass, Fe content: the balance) (hereinafter sometimes referred to as Fe-25Co) was flattened using a pearl mill.

[0068] To 100 parts by mass of the flattened Fe-Co alloy powder, 4 parts by mass of an epoxy resin as a binder, 2 parts by mass of a polyacrylate ester as a thickener, and 295 parts by mass of a solvent were mixed to prepare a slurry. As the solvent, a mixed solvent of EtOH:MPDG = 20:80 (mass% ratio) was used. The addition amount of the solvent was adjusted so that when the slurry was scooped up with a spatula, the slurry flowed moderately, and when the slurry was spread with an applicator or the like to form a film, the film thickness was visually uniform and no dripping occurred when the film was tilted.

[0069] The obtained slurry was applied onto a PET film by the die slot method and dried at 80°C for 1 hour to remove the solvent. Thereafter, the PET film was peeled off to obtain a coated film.

[0070] The obtained coated film was punched into a 65 mm square using a die cut roll, and a plurality of them were laminated to obtain a laminate. Thereafter, the laminate was heat-treated and press-molded. Specifically, the obtained laminate was subjected to press at room temperature (room temperature press) and press under heating conditions (hot press) in this order to obtain a molded body. More specifically, first, the obtained laminate was placed in a mold, and using a hydraulic press, under room temperature (25°C) conditions, 2 pressurization (room temperature press) was performed at a press pressure of 2 tons / cm for 5 seconds to obtain a pressed body. Next, the obtained pressed body and a shim spacer were sandwiched between iron plates and hot press was performed using a hot press machine. At that time, the press pressure of the hot press was 0.05 tons / cm throughout. 2It was set to this value, heated from room temperature (25 °C) to 300 °C over 30 minutes, then held at 300 °C for 1 hour, and thereafter furnace-cooled. Note that a Shim's spacer with a thickness of 0.5 mm was used so that the thickness of the resulting product (composite magnetic sheet) would be 0.5 mm.

[0071] The obtained molded body was machined for evaluation. Specifically, for measuring the magnetic permeability, it was processed into a toroidal shape using a punching die to produce a ring sample (φ10.5 - 3 mm). Then, using a material analyzer, the relative magnetic permeability μ' and μ'' at a frequency of 100 MHz were measured, and tanδ (μ' / μ'') and μ' / tanδ were calculated. Furthermore, the thickness and aspect ratio of the used (after flattening) magnetic powder, and the metal filling rate of the molded body were measured. Also, a reflow test described later was conducted to measure the weight change of the molded body. The measurement methods of these parameters are explained below. Note that since the measurement method of the metal filling rate has been described above, the description is omitted. The evaluation results are shown in Table 1 described later. Note that the content ratio of C element in the magnetic powder used in Example 1 was 0.10 mass% or less.

[0072] (μ', μ'' and tanδ) μ', μ'' and tanδ were measured under the following conditions. · Equipment used: Product name: E4991A RF Impedance / Material Analyzer (manufactured by KEYSIGHT) · Measurement sample: Ring sample (φ (diameter) 10.5 - 3 mm)

[0073] (Powder thickness, aspect ratio) The produced molded body (composite magnetic sheet) was resin-embedded, and the cross-section obtained by polishing was observed with an SEM, and the powder thickness and aspect ratio were calculated from the lengths of the magnetic powder in the vertical and horizontal (short-axis direction and long-axis direction). This was carried out for 50 powder particles, and the average value was calculated and used as the powder thickness and aspect ratio of the magnetic powder.

[0074] (Reflow test) The fabricated molded body (composite magnetic sheet) was subjected to a single reflow treatment at a temperature of 260°C, and the weight change (%) due to the reflow treatment was measured. Specifically, the molded body was heated and the temperature was continuously raised until it reached 260°C. During this heating process, the molded body was held at a temperature of 220°C or higher for 60 seconds and then held at a temperature of 240 to 250°C for 10 seconds or less.

[0075] [Examples 2 to 8] A composite magnetic sheet was produced in the same manner as in Example 1, except that the manufacturing conditions of the molded body were changed as shown in Table 1, and the measurement of each parameter was performed in the same manner. More specifically, in Examples 2 to 4, the pressing pressure in the high-pressure pressing was changed with respect to Example 1. In Example 5, the heating temperature in the hot pressing was changed with respect to Example 1. Furthermore, in Examples 6 to 8, the composition of the magnetic powder used was changed with respect to Example 1. Specifically, in Examples 6 to 8, Fe-Co alloy powders with Co content ratios of 10, 30, and 40 mass% (the remainder being Fe) were used (sometimes referred to as Fe-10Co, Fe-30Co, and Fe-40Co, respectively).

[0076] [Comparative Example 1] The magnetic powder was changed to an Fe-Si alloy powder (Si: 1 mass%, Co: 0 mass%, Fe: the remainder) (hereinafter sometimes referred to as Fe-1Si), and the blending amount of the solvent was changed. Otherwise, a composite magnetic sheet was produced in the same manner as in Example 1, and the measurement of each parameter was performed in the same manner.

[0077] [Comparative Example 2] The magnetic powder was changed to an Fe-Co-V alloy powder (Co: 49 mass%, V: 2 mass%, Fe: the remainder) (hereinafter sometimes referred to as Fe-49Co), and the blending amount of the solvent was changed. Otherwise, a composite magnetic sheet was produced in the same manner as in Example 1, and the measurement of each parameter was performed in the same manner.

[0078] [Comparative Example 3] A composite magnetic sheet was produced in the same manner as in Example 1, except that the magnetic powder was changed to Fe-Si-Al alloy powder and the blending amount of the solvent was changed. The measurement of each parameter was also performed in the same manner.

[0079] [Comparative Examples 4 to 6] A composite magnetic sheet was produced in the same manner as in Example 1, except that the hot press temperature was changed to 200°C and the press pressure of the high-pressure press was changed as shown in Table 1. The measurement of each parameter was also performed in the same manner. The evaluation results of each example and comparative example are shown in Table 1.

[0080]

Table 1

[0081] Referring to Table 1, it can be seen that for the magnetic materials obtained in Comparative Examples 1 to 6, the magnetic materials obtained in Examples 1 to 8 can achieve both high relative permeability and low loss. In addition, the magnetic materials obtained in Examples 1 to 8 had an appropriate range of metal filling ratios. Thus, the invention according to this embodiment was able to provide a high-performance magnetic material that can be stably used in the high-frequency band.

[0082] Note that the present invention is not limited to the above embodiment and can be appropriately changed without departing from the gist thereof.

Claims

1. containing a magnetic powder comprising Fe and 10% by mass or more and 40% by mass or less of Co, the relative permeability μ' at a frequency of 100 MHz is 20.0 or more, the powder thickness of the magnetic powder is 0.3 μm to 2.0 μm, the aspect ratio of the magnetic powder is 10 to 50, a magnetic material characterized by this.

2. the magnetic material according to Claim 1, wherein the loss factor tanδ at a frequency of 100 MHz is 0.050 or less.

3. the magnetic material according to Claim 1 or 2, wherein μ' / tanδ at a frequency of 50 MHz is 800 or more.

4. the magnetic material according to any one of Claims 1 to 3, wherein μ' / tanδ at a frequency of 100 MHz is 400 or more.

5. the magnetic material according to any one of Claims 1 to 4, wherein the content ratio of C in the magnetic powder is less than 0.20% by mass.

6. the magnetic material according to any one of Claims 1 to 5, wherein the magnetic powder contains 4 to 18% by mass in total of one or more of Cr, Si, Al, and rare earth elements.

7. The surface of the magnetic powder has SiO ２ coating, and the magnetic material according to any one of claims 1 to 6.

8. the magnetic material according to any one of Claims 1 to 7, containing a resin and having a metal filling rate of 35% by volume or more.

9. the magnetic material according to any one of Claims 1 to 8, which is in sheet form.

10. a method for manufacturing the magnetic material according to any one of Claims 1 to 9, a step of obtaining a magnetic slurry containing the magnetic powder and a resin, a step of forming the magnetic slurry into a sheet shape, a step of heat treatment, a method for manufacturing a magnetic material, characterized by having these steps.

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