Soft magnetic alloy powder and electronic device using the same

Abstract

The present invention provides a soft magnetic alloy powder capable of realizing use of electronic devices in a high-temperature environment. The present invention can obtain a soft magnetic alloy powder containing Si: 1.2 to 8% by weight, Cr: 0 to 9% by weight, and Al: 0.75 to 1.25% by weight, with the remainder being Fe and inevitable impurities, having a negative magnetic core loss temperature characteristic within 25°C to 150°C.

Description

Technical Field

[0001] This invention relates to soft magnetic alloy powder and electronic devices using the powder. Background Technology

[0002] Soft magnetic alloy powders are widely used in various electronic devices such as inductors. For example, in recent years, as power inductors used in power circuits, there has been a demand for soft magnetic materials that can operate at high currents and high frequencies, considering the requirements for miniaturization and low height. Previously, ferrite-based materials, as oxides, were used as the main materials for inductors, but their low saturation magnetization was detrimental to miniaturization. Therefore, in recent years, the use of metal inductors made from alloy materials with high saturation magnetization, which are beneficial for miniaturization and low height, has increased rapidly. As for metal inductors, it is known to use soft magnetic alloy powders with iron as the main material, and to produce pressed powder cores by mixing soft magnetic alloy powders with resin and then compressing them.

[0003] The growing concern for energy issues has spurred the electrification of automobiles and the energy efficiency of electronic devices, demanding further miniaturization and lower energy consumption of electronic components. For example, in automobiles, the so-called "mechatronics" approach—installing ECUs (Electronic Control Units) on actuators such as electric motors and solenoids to support improved control and thus achieve better environmental and driving performance—is constantly advancing. Consequently, the demand for installing ECUs in environments with higher temperatures, such as engine compartments, is increasing, requiring calendered magnetic cores suitable for ECUs that can operate in such high-temperature conditions.

[0004] In existing electronic devices such as pressed powder cores using soft magnetic alloy powder, it is known that core loss increases with rising temperature, and the core's own temperature rises due to heat generated by core loss during use. This temperature increase leads to increased core loss and heat generation, and repeated occurrences of this process may trigger thermal runaway. Therefore, research is underway to improve the temperature characteristics of core loss in the high-temperature range. For example, Patent Document 1 describes pressing Fe-Si-Al alloy powder with a specific composition to obtain a molded body, followed by heat treatment of the molded body; Reference 2 describes a soft magnetic alloy powder with an insulating film formed on the surface of Fe-Si-Al alloy powder with a specific composition. However, Fe-Si-Al alloy powder is difficult to form at high density due to its hardness and poor plasticity, and it is also difficult to obtain a high saturation magnetic flux density that is beneficial for the miniaturization of electronic devices.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2011 / 016207

[0008] Patent Document 2: Japanese Patent Application Publication No. 2012-9825 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] The purpose of this invention is to provide soft magnetic alloy powder that enables electronic devices to be used in high-temperature environments, and also to provide electronic devices.

[0011] Technical solutions adopted to solve technical problems

[0012] The inventors conducted various studies and discovered the composition of an iron-based soft magnetic alloy with negative core loss temperature characteristics, which ultimately led to the completion of this invention.

[0013] That is, the present invention is a soft magnetic alloy powder containing Si: 1.2-8 wt%, Cr: 0-9 wt% and Al: 0.75-1.25 wt%, with the remainder being Fe and unavoidable impurities, and has negative core loss temperature characteristics in the range of 25°C to 150°C.

[0014] According to one embodiment of the present invention, the above-mentioned soft magnetic alloy powder is provided, comprising Si: 1.5 to 7.5 wt%, Cr: 0 to 8.5 wt%, and Al: 0.8 to 1.2 wt%.

[0015] According to one embodiment of the present invention, the above-mentioned soft magnetic alloy powder is provided, having a particle size (D50) of 0.5 to 50 μm.

[0016] According to one embodiment of the present invention, the above-mentioned soft magnetic alloy powder is provided, which further comprises Ca: 0.001 to 0.02% by weight.

[0017] According to one embodiment of the present invention, the above-mentioned soft magnetic alloy powder is provided, which contains Ca: 0.002 to 0.01% by weight.

[0018] According to one aspect of the present invention, an electronic device comprising the above-described soft magnetic alloy powder is provided.

[0019] According to one aspect of the present invention, the above-mentioned electronic device is provided as a pressed powder magnetic core, an electromagnetic wave absorbing shield, or an electromagnetic wave absorber.

[0020] According to one aspect of the present invention, a method for manufacturing an electronic device is provided, comprising pressing and forming the aforementioned soft magnetic alloy powder.

[0021] According to one aspect of the present invention, a method for manufacturing an electronic device is provided, comprising injection molding the aforementioned soft magnetic alloy powder.

[0022] Invention Effects

[0023] This invention provides soft magnetic alloy powder that enables electronic devices to be used in high-temperature environments. Detailed Implementation

[0024] The following is a detailed description of one embodiment of the present invention. The present invention is not limited to the following embodiment, and can be implemented with appropriate modifications without impairing the effects of the present invention. Furthermore, in the following description, "A to B" means "A or more and B or less".

[0025] The soft magnetic alloy powder of this embodiment contains 1.2 to 8 wt%, preferably 1.5 to 7.5 wt%, of Si, 0 to 9 wt%, preferably 0 to 8.5 wt%, of Cr, and 0.75 to 1.25 wt%, preferably 0.8 to 1.2 wt%, of Al, with the remainder being Fe and unavoidable impurities. By having a composition containing the above-mentioned amounts of Si, Cr, and Al, the soft magnetic alloy powder exhibits a negative core loss temperature characteristic within the range of 25°C to 150°C. Due to this characteristic, the soft magnetic alloy powder of this embodiment is suitable for use as a material in electronic devices used in high-temperature environments.

[0026] [Other elements]

[0027] In the soft magnetic alloy powder of this embodiment, elements such as N, S, and O can be included as unavoidable impurities within a range that does not affect the target properties.

[0028] [Negative core loss temperature characteristics]

[0029] A negative core loss temperature characteristic refers to the fact that the core loss of a soft magnetic alloy powder has a negative coefficient with respect to temperature, that is, the core loss of the soft magnetic alloy powder decreases as the temperature increases. The soft magnetic alloy powder of this embodiment, which exhibits a negative core loss temperature characteristic, can suppress the temperature rise of the core itself caused by heat generated from core loss during use because the core loss decreases with increasing temperature. As a result, it possesses characteristics suitable for use as a material in electronic devices that were previously difficult to operate in high-temperature environments. The reason why the soft magnetic alloy powder of this embodiment has a negative core loss temperature characteristic can be attributed to the positive value of the magnetostriction constant determined by its composition.

[0030] The preferred particle size (D50) of the soft magnetic alloy powder in this embodiment is 0.5 to 50 μm. "Particle size" refers to the median particle size D50, which can be determined by conventionally known methods, such as laser diffraction scattering. The effects related to the saturation magnetic flux density (Bs), permeability, and negative core loss temperature characteristics of the soft magnetic alloy powder described above can be obtained with soft magnetic alloy powders having a wide range of particle sizes, but particularly high effects can be obtained by setting the particle size (D50) to 0.5 to 50 μm, preferably 0.5 to 40 μm, more preferably 0.5 to 25 μm, and even more preferably 1.0 to 20 μm.

[0031] The soft magnetic alloy powder of this embodiment preferably contains Ca, comprising 0.001 to 0.02% by weight, preferably 0.002 to 0.01% by weight. By containing trace amounts of Ca, the permeability of the soft magnetic alloy powder is increased or the core loss is reduced. The presence of Ca within the above range results in a low specific surface area in the iron-based soft magnetic alloy powder, reducing the oxygen content in the powder. This is believed to be because Ca, with its high affinity for oxygen, alters the surface tension of the melt used to manufacture the alloy powder, thus changing the oxygen content of the melt. Furthermore, elements with the same high affinity for oxygen as Ca can achieve the same effect.

[0032] [Manufacturing method of soft magnetic alloy powder]

[0033] The soft magnetic alloy powder of this embodiment can be manufactured by conventionally known methods, as exemplified below as a method for manufacturing metal powder. However, as long as it has the composition of this embodiment, it can have the above-mentioned magnetic properties, so there is no particular limitation on the manufacturing method.

[0034] • Atomization methods: water atomization, gas atomization, centrifugal atomization, etc.

[0035] Mechanical processing methods: crushing, mechanical alloying, etc.

[0036] Melt spinning

[0037] • Rotary electrolysis (REP) method: Plasma REP method, etc.

[0038] • Chemical treatment methods: oxide reduction, chloride reduction, hydrometallurgical techniques, carbonyl reaction methods, etc.

[0039] Among the manufacturing methods exemplified above, the atomization method, in particular, can mass-produce small-diameter, spherical soft magnetic alloy powders under atmospheric pressure. Furthermore, the water atomization method allows for low-cost manufacturing.

[0040] In the case of manufacturing soft magnetic alloy powder using water atomization, high-pressure water with set parameters is sprayed onto the molten material, which is melted to achieve the desired composition, to achieve the required cooling conditions and particle size. This causes the molten material to disperse and solidify, resulting in powder. The obtained powder is then dried, graded, and surface-treated as needed to obtain the target soft magnetic alloy powder.

[0041] When adding Ca, it is done by adding metallic Ca to the molten metal. There is no restriction on the order of addition. However, because Ca is prone to turning into oxides, a certain degree of excess Ca needs to be added relative to the target alloy composition.

[0042] The electronic device of this embodiment comprises the aforementioned soft magnetic alloy powder. This electronic device is not only commonly used in electronic devices such as motors, reactors, and transformers, but also in a wide range of industrial fields, such as solenoid valves, solenoids, and sensors used in transportation equipment like automobiles. Furthermore, the electronic device of this embodiment is an electromagnetic wave absorbing shield or electromagnetic wave absorber used for the purpose of absorbing electromagnetic waves of a specific frequency.

[0043] The electronic device in this embodiment is a pressed powder magnetic core, an electromagnetic wave absorbing shield, or an electromagnetic wave absorber.

[0044] The pressed powder magnetic core, electromagnetic wave absorbing shield, or electromagnetic wave absorber of this embodiment comprises the aforementioned soft magnetic alloy powder. Preferably, the pressed powder magnetic core of this embodiment comprises soft magnetic alloy powder in a granulated form, mixed with a resin or the like that imparts insulation and processability. Preferably, at least a portion of the electromagnetic wave absorbing shield of this embodiment is coated with a paste prepared by mixing and preparing a soft magnetic alloy powder, resin, and ink. Preferably, at least a portion of the electromagnetic wave absorber of this embodiment is adhered with a sheet material prepared by mixing and molding a soft magnetic alloy powder, resin, and rubber to a desired thickness.

[0045] The powder-pressed magnetic core of this embodiment comprises, for example,

[0046] The process of forming a film on the surface of soft magnetic alloy powder to obtain granulated powder;

[0047] The process of pressing granulated powder to obtain a shaped body;

[0048] The process of heat treating the molded body

[0049] It is manufactured using this method.

[0050] In the process of obtaining granulated powder, a coating is formed using conventionally known resins such as epoxy resin, silicone resin, and acrylic resin in order to impart insulation, corrosion resistance, etc. to the target.

[0051] The temperature during the heat treatment process is 550°C to 950°C, preferably 600°C to 900°C. Furthermore, the heating time is preferably about 30 minutes to 2 hours. For the soft magnetic alloy powder constituting the formed body before heat treatment, strain is introduced by pressure forming. This strain is a major cause of increased hysteresis loss, which is one of the main reasons for decreased magnetic permeability and core loss. Therefore, by heat treating the formed body under the above conditions, the strain can be effectively removed. The heat treatment is preferably carried out in an inert gas atmosphere such as nitrogen, or in a reduced pressure atmosphere.

[0052] The method for manufacturing the electronic device according to this embodiment includes injection molding the aforementioned soft magnetic alloy powder. Injection molding allows for the formation of complex shapes with higher precision. After molding, degreasing, heat treatment, etc., are performed as needed to obtain an electronic device with the desired shape and properties.

[0053] Example

[0054] The following are embodiments of the present invention. The content of the present invention is not limited to these embodiments.

[0055] Manufacturing of soft magnetic alloy powder

[0056] The materials, adjusted to the compositions shown in Tables 1 and 2, were melted in a high-frequency induction furnace, and soft magnetic alloy powder was obtained using a water atomization method. The conditions for the water atomization method are as follows.

[0057] <Water atomization conditions>

[0058] Water pressure: 100MPa

[0059] • Water flow rate: 100L / minute

[0060] Water temperature: 20℃

[0061] • Orifice diameter: φ4mm

[0062] Melt temperature: 1800℃

[0063] The soft magnetic alloy powder obtained by drying using a vibration vacuum dryer (VU-60: manufactured by Chuo Kagaki Co., Ltd.). The drying conditions are as follows.

[0064] <Drying conditions>

[0065] Temperature: 100℃

[0066] • Pressure: Below 10 kPa

[0067] • Time: 60 minutes

[0068] The composition of the dried soft magnetic alloy powder was quantitatively analyzed using an ICP-based luminescence analyzer [SPS3500DD: manufactured by Hitachi High Technology Co., Ltd.].

[0069] The dried soft magnetic alloy powder was classified using an air classifier (TURBO-CLASSIFIER: manufactured by Nisshin Engineering Co., Ltd.) to obtain the target soft magnetic alloy powder. The particle size (D50) of the obtained soft magnetic alloy powder was determined using a wet particle size analyzer (MT3300EXⅡ: manufactured by Microtrail Bell).

[0070] [Sample Preparation]

[0071] The soft magnetic alloy powders prepared above were mixed with epoxy resin to produce granulated powder. The weight ratio of the soft magnetic alloy powder to epoxy resin was 97:3.

[0072] Each granulated powder is pressed into a ring shape (forming pressure: 500MPa) to make a pressed powder magnetic core (outer diameter: 15mm, inner diameter: 9mm, thickness: 3mm).

[0073] The following evaluations were made on each powder-pressed magnetic core.

[0074] A toroidal core was fabricated by winding 0.3 mm diameter copper wire onto a powder-pressed magnetic core using a double-wire winding method, and this core served as an evaluation sample. The core loss was measured using a BH analyzer (SY8258: manufactured by Iwatsu Measurement Co., Ltd.) at a measurement frequency of 1 MHz and a maximum magnetic flux density of 25 mT, within a temperature range of 25–150 °C. Next, the permeability was measured at a measurement frequency of 1 MHz, a maximum magnetic flux density of 10 mT, and a temperature of 150 °C.

[0075] [Evaluation Results]

[0076] The evaluation results are shown in Tables 1 and 2.

[0077] The symbols 〇, △, and × in "Temperature Characteristics" in Tables 1 and 2 represent the following meanings: × indicates that the core loss increases with increasing temperature; △ indicates a negative core loss temperature characteristic in the temperature range of 25℃ to 120℃, but the core loss increases in the temperature range above 120℃; ○ indicates a negative core loss temperature characteristic in the temperature range of 120℃ to 150℃, and no increase in core loss.

[0078] The symbols ◎, 〇, △, and × in "Magnetic Properties" in Tables 1 and 2 represent the results of comparing the magnetic permeability and core loss at 150°C with those of comparative examples having the same D50 and the same composition except for Al and Ca. [For example, Examples 1-(1) to 1-(11) are compared with Comparative Example 1, Examples 2-(1) to 2-(11) are compared with Comparative Example 2, and Examples 5 to 12 are compared with Comparative Examples 5 to 12 respectively.] The evaluation criteria are as follows.

[0079] ×...The case where neither magnetic permeability nor core loss is improved.

[0080] △···The case where only one of the magnetic permeability or core loss increases.

[0081] 〇··· Case where both permeability and core loss are increased

[0082] ◎···When both permeability and core loss are increased by more than 20%

[0083] Here, an increase in permeability refers to an increase in the measured value of permeability, while an increase in core loss refers to a decrease in core loss.

[0084] [Table 1]

[0085]

[0086] [Table 2]

[0087]

[0088] As shown in Tables 1 and 2, the powder-pressed magnetic core using the soft magnetic alloy powder of the embodiments surprisingly exhibits negative core loss temperature characteristics not only in the temperature range of 25°C to 120°C, but also in a very high temperature range of 120°C to 150°C. Furthermore, compared to powder-pressed magnetic cores using the soft magnetic alloy powders of the comparative examples (existing Fe-Si alloy powders and Fe-Si-Cr alloys), the powder-pressed magnetic core using the soft magnetic alloy powder of the embodiments surprisingly shows at least one improvement in permeability and core loss at a very high temperature of 150°C. In other words, the soft magnetic alloy powder of the present invention possesses excellent properties, particularly suitable as a material for powder-pressed magnetic cores, enabling applications in electronic devices, especially those used in high-temperature environments.

[0089] Furthermore, surprisingly, the permeability and core loss of the powder-pressed core using soft magnetic alloy powder with added Ca were further improved compared to those using soft magnetic alloy powder without added Ca.

[0090] As shown in Tables 1 and 2, it can be seen that the present invention can achieve the above-mentioned effects regardless of the particle size (D50) of the powder.

[0091] As described above, the soft magnetic alloy powder of the present invention has excellent properties that enable electronic devices to be used in high-temperature environments.

[0092] (Modified Example)

[0093] In the above embodiments, an example of an electronic device using the soft magnetic alloy powder of one embodiment was a pressed powder core manufactured by pressure forming. However, the embodiment is not limited to this example. For example, an electronic device manufactured by injection molding could be used. The results from the above embodiments also show that electronic devices using the soft magnetic alloy powder of the present invention, which has negative core loss temperature characteristics, are suitable for use in high-temperature environments.

[0094] Other examples of electronic devices as one embodiment include electromagnetic wave absorbing shields or electromagnetic wave absorbers. Electromagnetic wave absorbing shields are used to block electromagnetic waves of a specific frequency, and can be used, for example, in the casing of mobile devices such as mobile phones. Electromagnetic wave absorbing shields are obtained by preparing and mixing magnetic powder, resin, and ink to form a paste under conditions that achieve the desired characteristics, and then applying the paste to appropriate areas. Furthermore, vacuum degassing can be performed during paste preparation to promote the dispersion of the magnetic powder.

[0095] Electromagnetic wave absorbers are used to block electromagnetic waves of specific frequencies, such as in anechoic chambers used at ETC (Electronic Toll Collection) system entrances and exits or in EMC testing. Electromagnetic wave absorbers are obtained by modulating, mixing, and molding magnetic powder, resin, and rubber into a sheet to achieve the desired characteristics, and then attaching the sheet to the appropriate location.

Claims

1. Soft magnetic alloy powder, containing Si: 1.2–8% by weight Cr: 0–9% by weight, and Al: greater than 1.0 and less than 1.25% by weight. Ca: 0.001–0.02% by weight The remainder consists of Fe and unavoidable impurities. It exhibits negative core loss temperature characteristics within the range of 25℃ to 150℃.

2. The soft magnetic alloy powder as described in claim 1, comprising... Si: 1.5–7.5% by weight Cr: 0–8.5% by weight, and Al: greater than 1.0 and less than 1.2% by weight. Ca: 0.001–0.02% by weight.

3. The soft magnetic alloy powder as described in claim 1 or 2, wherein the particle size D50 is 0.5 to 50 μm.

4. The soft magnetic alloy powder as described in claim 1, wherein it contains 0.002 to 0.01% by weight of Ca.

5. An electronic device comprising the soft magnetic alloy powder according to any one of claims 1 to 4.

6. The electronic device as described in claim 5 is a pressed powder magnetic core, an electromagnetic wave absorbing shield, or an electromagnetic wave absorber.

7. A method for manufacturing an electronic device, comprising pressing and forming the soft magnetic alloy powder according to any one of claims 1 to 4.

8. A method for manufacturing an electronic device, comprising injection molding the soft magnetic alloy powder according to any one of claims 1 to 4.

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