JP2006294775A - Magnetic material and inductor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain high insulation and voltage resistance property along with high effective magnetic permeability property in an inductor. <P>SOLUTION: A magnetic material covers such a surface of magnetic metallic powder, hard Fe-Si system alloy magnetic powder, or ductile Fe-Ni system alloy magnetic powder with glass membrane, and covers the outside with thermosetting resin which serves both as an insulating material and a binding material. Further, an air core coil 1 is embedded into the powder consisting of the magnetic material, so that an inductor may be constituted by carrying out pressure molding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic material used for a choke coil, a power inductor, and the like, and an inductor configured using the magnetic material.

    In recent years, the processing speed of MPUs used in notebook personal computers and servers has been remarkably increased, and accordingly, the power supply power supply has been rapidly increased. There is also a demand for higher efficiency of circuits including power inductors from the viewpoint of energy saving. A powder magnetic core produced by compression molding metal magnetic powder has excellent DC superposition characteristics, and can realize a large current and a small size. As one using such a powder magnetic core, an integrally formed inductor as described in Patent Document 1 is known.

This is a structure as shown in FIG. 1, in which an air-core coil 1 is embedded in a composite magnetic powder in which metal magnetic powder and a binder are mixed and pressure-molded. The surface of the particles of the metal magnetic powder of the molded body 2 is insulated. Both ends of the coil 1 made of a flat wire are drawn out and bent to the electrode 3 as they are.
JP-A-9-120926 JP 2000-160204 A

  Conventionally, carbonyl iron powder, Fe—Si alloy, Fe—Ni alloy (permalloy), Fe—Si—Al alloy, iron-based amorphous alloy, and the like are used as metal magnetic powder. On the surface of the metal magnetic powder particles, an insulating coating is formed by means such as a chemical oxidation treatment with phosphate or the like, a self-oxidation method in which heat treatment is performed, or fine particles of an inorganic insulating material are adhered. An organic resin binder was mixed with the metal magnetic powder to form a mixed magnetic powder, and then pressure-molded to obtain an integrally molded inductor.

In order to increase the magnetic permeability of the dust core, the filling rate of the metal magnetic powder may be increased. for that purpose,
-Increase the pressing pressure to compress.
・ Reduce the amount of binder.
-Increase the particle size of the magnetic powder.
-Increase the mold temperature during compression molding.
Such means can be considered.

  However, any of these means has many problems in producing an integral-molded inductor in which an air-core coil is embedded and press-molded.

For example,
-When the press pressure is increased, the insulation coating of the embedded coil is damaged, and a short circuit failure between the conductors is likely to occur. The durability of the mold is also reduced.
・ If the amount of binder is reduced, the insulation and dielectric strength of the green compact will decrease.
・ When the particle size of the magnetic powder is increased, the high frequency characteristics are degraded.
-The method of raising the mold temperature leads to a decrease in workability and high equipment costs.
There are problems such as.

  For this reason, it is difficult to significantly improve the magnetic permeability, and the effective magnetic permeability of the mixed magnetic powder for the integral-type inductor remains at a low value of around 25.

  As described above, since the conventional integral-type inductor has a low effective magnetic permeability, the number of turns is increased to obtain the same inductance as that of an inductor using ferrite, resulting in a disadvantage that copper loss is increased. Further, when the effective magnetic permeability is increased by reducing the amount of the binder, the insulation and withstand voltage are low. An object of the present invention is to obtain high effective magnetic permeability as well as high insulation and voltage resistance characteristics in an inductor.

The magnetic material according to the present invention covers the surface of a magnetic metal powder such as hard Fe-Si alloy magnetic powder or ductile Fe-Ni alloy magnetic powder with a glass film, and further binds the outside to an insulating material. It is characterized by a structure coated with a thermosetting resin that also serves as a material.
Further, the present invention is characterized by the configuration of an inductor in which an air-core coil is embedded in a powder made of such a magnetic material and press-molded.

  Since the magnetic material according to the present invention is coated with a hard glass film on the surface of the particles, the amount of resin binder required to ensure the same insulation and withstand voltage as conventional products can be reduced. Moreover, since the filling rate of the metal magnetic powder is increased by mixing the ductile Fe-Ni alloy, the effective permeability of the dust core can be increased without increasing the average particle size of the metal magnetic powder. The inductance value of the integrally molded inductor is also increased. On the other hand, when the inductance value is the same, the number of turns and the winding resistance are reduced, and the copper loss can be reduced.

  When a pressure-molded body was prototyped with the magnetic material according to the present invention, the effective magnetic permeability was 30 or more, which was about 1.4 times that of the conventional product of the same type. It was confirmed that the insulation heat deterioration characteristics and core loss were at the same level as the conventional dust core. Therefore, by using this magnetic material to form an integral-molded inductor, a highly reliable product with high efficiency and excellent insulation and molded body strength can be obtained.

[First embodiment]
A metal magnetic powder comprising an Fe—Si based alloy powder having an average particle size of 20 μm and a low melting point glass powder having a softening temperature of 500 ° C. or less are prepared. Add 78 wt% and mix. When this mixed powder is placed in a particle compounding device furnace and stirred for 30 minutes at the maximum rotation speed, a strong compressive and shearing force acts on the mixed powder, and a thin insulating film with a vitreous layer on the particle surface of the magnetic powder. Is formed. The atmosphere in the particle composite apparatus furnace is preferably in the atmosphere because the surface of the metal magnetic powder is oxidized and the wettability with the glass is increased.

  Next, 2.5 wt% of a thermosetting organic resin serving as both an insulating material and a binder is added to the stirring powder granulator for 100 wt% of the magnetic powder coated with the glass film, and stirred for about 20 minutes. By mixing and pre-drying, a powdery magnetic material in which the outside of the glass film was further coated with a thermosetting resin was produced. A powder magnetic core obtained by press-molding this double-insulated magnetic material was used as a sample no. Set to 1.

[Second Embodiment]
An Fe—Ni alloy powder having an average particle size of 10 μm and a low melting glass powder having a softening temperature of 500 ° C. or less are prepared, and 0.78 wt% of the low melting glass powder is added to 100 wt% of the Fe—Ni alloy powder. Mix. This mixed powder is put into a particle compounding device furnace and stirred for 30 minutes to obtain a magnetic powder coated with a glass film. Next, 2.5 wt% of the insulating and binding thermosetting organic resin for 100 wt% of the magnetic powder is put into a stirring granulator, mixed by stirring for about 20 minutes, and pre-dried. A powdery magnetic material was produced in which the outside of the glass film was further coated with a thermosetting resin. A powder magnetic core obtained by pressure-molding this magnetic material was designated as Sample No. 2.

[Comparative Examples 1 and 2]
Sample No. 1, no. Two magnetic materials were prepared by subjecting the above-described Fe—Si alloy powder and Fe—Ni alloy powder to an insulation coating treatment only with a thermosetting resin. A powder magnetic core obtained by pressure-molding each magnetic material was used as a sample No. 3, no. 4 Sample No. 1 and sample no. 3, Sample No. 2 and sample no. Sample No. 4 so that the magnetic permeability of each sample has the same value. 3, no. The amount of the thermosetting resin in No. 4 is 3.5 wt% with respect to 100 wt% of the alloy powder.

[Third embodiment]
Two kinds of metal magnetic powders of the glass-coated Fe—Si alloy powder and the glass-coated Fe—Ni alloy powder are 75 wt%: 25 wt%, 50 wt%: 50 wt%, and 25 wt%: 75% wt%, respectively. Three types of mixed magnetic powders mixed at a ratio of 2 wt% were prepared, and 2 wt% thermosetting organic resin was mixed with 100 wt% of these mixed magnetic powders to produce a powdered magnetic material. And each of the magnetic cores obtained by pressure-molding each magnetic material is sample No. 5, no. 6, no. 7 The average particle diameters of the Fe—Si based alloy powder and the Fe—Ni based alloy powder were 20 μm and 10 μm, respectively.

  In addition, in order to improve the lubricity between particles, 0.1 to 0.5 wt% of a lubricant such as stearate may be added to the mixed magnetic powder. The average particle size of the metal magnetic powder is preferably about 10 μm to 30 μm. When the particle size is larger than this, the core loss is increased. When the particle size is smaller than this, it is difficult to obtain a high magnetic permeability and at the same time, it is difficult to form a glass film. The average particle size of the glass powder is preferably selected from the range of 1/5 to 1/10 of the average particle size of the magnetic powder to be coated.

  Sample No. mentioned above. 1-No. The result of measuring the electrical and magnetic characteristics of each dust core of No. 7 is as shown in FIG. Sample No. using the magnetic material of the present invention. 1, no. 2 has a magnetic permeability of a comparative sample No. 3, no. Although it is almost the same as 4, it can be seen that the insulation resistance and the withstand voltage show high values. The insulation resistance and withstand voltage characteristics are 3, no. If the level is equal to 4, the sample No. 1, no. It is possible to further reduce the organic resin amount 2.5 wt% used in No. 2 and to easily increase the permeability to 29, 27 or more. However, sample no. The core loss is slightly increased only with the Fe—Si based alloy powder such as No. 1; The material cost becomes expensive only with the Fe—Ni alloy powder such as 2. These problems can be solved by mixing Fe—Ni-based alloy powder and Fe—Ni-based alloy powder smaller than the average particle diameter of Fe—Si-based alloy powder.

In the measurement of the characteristics shown in FIG. 2, 1 g of powdered magnetic material was put into a mold and press-molded at a pressure of 5 ton / cm ² , the outer diameter was 14.4 mm, the inner diameter was 10.3, and the thickness was about A 2 mm ring-shaped dust core was used as a sample for measuring permeability and core loss. Then, using an AC B-H curve measuring device, the AC relative permeability (μa) and the core loss when the applied magnetic flux density was 40 mT at a measurement frequency of 300 KHz were measured.

In addition, a sample for measuring insulation resistance and withstand voltage is a circle having an outer diameter of 7.2 mmφ and a thickness of about 2 mm by placing 0.45 g of a powdered magnetic material in a mold and press-molding at a pressure of 5 ton / cm ^2. A columnar dust core was formed. And the electrode of 5 mm x 5 mm was attached to the upper and lower surfaces, and the inter-surface resistance and withstand voltage between electrodes were measured with the insulation resistance measuring device and the pressure | voltage resistant tester.

  Sample No. of dust core according to the present invention. 1, no. 2 and Comparative Sample No. 3, no. FIG. 3 shows the thermal deterioration characteristics of the insulation resistance No. 4. Sample No. 3, no. Compared to 4, it is clear that the dust core of the present invention is less deteriorated in insulation resistance even when exposed to a high temperature for a long time. By using a dust core with excellent insulation resistance and thermal degradation characteristics, a highly reliable power inductor can be manufactured.

  Insulation resistance / thermal degradation characteristics were measured by placing a dust core for measuring insulation resistance in a thermostat at 150 ° C. and measuring the value of insulation resistance over time. It has been experimentally confirmed that the rate at which the insulation resistance of the dust core progresses decreases with an approximate expression close to the Arrhenius reaction formula that “the reaction rate doubles every time the temperature rises by 10 ° C.” . Therefore, the insulation resistance value after 150 ° C.-3000 hours is equivalent to 100 ° C.-96000 hours, and is an index for determining the life and warranty period of the product.

  Sample No. of the dust core of the present invention. 5, no. 6, no. FIG. 4 shows the thermal deterioration characteristics of the insulation resistance No.7. Sample No. of these dust core comparison products 3, no. It can be seen that it is equal to or greater than 4. As is clear from FIG. 2, high magnetic permeability and high insulation are obtained. No. with a high blending ratio of Fe-Si alloy magnetic powder. No. 5 has a core loss increased, and No. 5 having a high blending ratio of the Fe—Ni alloy magnetic powder. 7 has a reduced withstand voltage. This blending ratio may be appropriately selected depending on which of core loss and withstand voltage characteristics is important. Overall, the most excellent magnetic properties are obtained when the blending ratio of the Fe—Si alloy magnetic powder and the Fe—Ni alloy magnetic powder is within the range of 70 wt%: 30 wt% to 30 wt%: 70 wt%. It was.

  Next, an example of manufacturing an integrally molded inductor using the magnetic material of the present invention will be described. Sample No. with the greatest effect was obtained. A prototype was made using the magnetic material used in No. 5. This magnetic material is a mixture of a Fe—Si based alloy powder and a Fe—Ni based alloy powder in which the particle surface is covered with a glass film and a thermosetting resin.

  First, a 2.5-turn air-core coil is prepared by edgewise winding two layers with an inner diameter of 5 mmφ using a rectangular wire that is an insulation-coated copper wire having a cross-sectional dimension of 0.8 mm in length × 2 mm in width. The air core coil was set in a molding die, and the magnetic material was filled in a 3.3 g die so that the air core coil was embedded.

Then, it was pressure-molded at a pressure of 5 tons / cm ² , and the molded product taken out from the mold was preheated at 85 ° C. for 2 hours and at 150 ° C. for 30 minutes to cure the thermosetting resin as a binder. Thereafter, the end of the coil was bent to form an integrally molded inductor as shown in FIG. 1 having a length of 12.5 mm × width of 12.2 mm × height of 4.7 mm.

  For comparison of characteristics, a conventional magnetic material not coated with glass and a rectangular wire (2.5 mm, edgewise wound on two layers with an inner diameter of 5 mmφ, which is an insulation-coated copper wire having a cross-sectional dimension of 0.6 mm × width 2 mm) Turn) air-core coil was prepared, and an integrally molded inductor having the same shape was produced. Table 1 shows the inductance value and the coil resistance value of the inductor according to the conventional manufacturing method and the inductor according to the manufacturing method of the present invention described above.

  As is apparent from Table 1, the inductor manufactured using the magnetic material of the present invention is an air-core coil having a resistance value reduced by about 20%, but has a higher inductance than the conventional product.

Perspective view showing a configuration example of an inductor Powder core sample No. 1-No. 7 Measurement data of electrical and magnetic characteristics Powder core sample No. 1-No. 4 Insulation resistance / thermal deterioration characteristics Powder core sample No. 3-No. 7 Insulation resistance / thermal degradation characteristics

Explanation of symbols

1 Coil 2 Molded body 3 Electrode

Claims (6)

A magnetic material characterized in that the surface of metal magnetic powder particles is covered with a glass film, and the outside thereof is covered with a thermosetting resin. The magnetic material according to claim 1, wherein the metal magnetic powder is an Fe-Si alloy. The magnetic material according to claim 1, wherein the metal magnetic powder is an Fe-Ni alloy. The metal magnetic powder is composed of a first magnetic powder made of an Fe-Si alloy and a second magnetic powder made of an Fe-Ni alloy, and the first magnetic powder and the second magnetic powder are mixed. Item 1. A magnetic material according to item 1. The magnetic material according to claim 4, wherein a blending ratio of the first magnetic powder and the second magnetic powder is 30 to 70 wt%: 70 to 30 wt%. An inductor, wherein an air-core coil is embedded in a powder made of the magnetic material according to any one of claims 1 to 5 and pressure-molded.

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