JP2001210510A - Soft magnetic powder and composite magnetic unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic interference suppressor, made of a soft magnetic powder that has a single composition and particle size distribution and a composite magnetic unit using it, capable of suppressing unwanted high-fre quency radiation extending over a broad band. SOLUTION: The specific surface area of the soft magnetic powder which is a fixed value or larger by generating two anisotropy magnetic fields of different magnitude, two kinds of magnetic resonances appear in the composite magnetic unit comprising this soft magnetic powder and a binder. Then electromagnetic interference suppression effect over a broad band in a high-frequency region is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic material having excellent magnetic loss characteristics in a high frequency range,
The present invention relates to a soft magnetic material excellent in complex magnetic permeability characteristics effective for suppressing unnecessary radiation which is a problem in high frequency electronic components or electronic devices, and a composite magnetic material using the same.

[0002]

2. Description of the Related Art In recent years, highly integrated semiconductor elements which operate at high speed have become remarkably widespread. As examples, random access memory (RAM), read only memory (RO)
M), a microprocessor (MPU), a central processing unit (CPU), and the like.

In these active elements, the operation speed and the signal processing speed are increasing at a rapid pace, and electric signals propagating through high-speed electronic circuits are accompanied by large fluctuations in voltage and current. Noise is easily generated, and is an unnecessary high-frequency radiation source.

[0004] On the other hand, the trend of lightening, thinning, and miniaturization of electronic parts and electronic devices has been progressing at a rapid pace, which is unaware that the flow will not stop. Accordingly, the degree of integration of semiconductor elements and the density of mounting electronic components on printed wiring boards have become extremely high.

[0005] Therefore, electronic elements and signal lines that are densely integrated or mounted are extremely close to each other,
High frequency noise in conjunction with the increase in the signal processing speed,
It is becoming more provoked. In addition, there is a high possibility that the occurrence and leakage of such high-frequency noise cause a malfunction due to mutual interference between elements.

In such electronic integrated devices or wiring boards in recent years, the problem of unnecessary radiation from power supply lines to active elements has been pointed out, and lumped components such as decoupling capacitors are inserted into power supply lines. And other measures have been taken.

[0007]

However, in a high-speed electronic integrated device or a wiring board, since a generated noise includes a harmonic component, a signal path behaves like a distributed constant. There has been a situation in which the noise countermeasures based on the lumped-constant circuit are not effective.

An object of the present invention is to provide a magnetic material which is effective for measures against unnecessary radiation in such semiconductor elements and electronic circuits operating at high speed. More specifically,
An object of the present invention is to provide a magnetic loss material that can easily and effectively deal with high-frequency unnecessary radiation over a wide frequency range.

[0009]

The present inventors have previously invented a composite magnetic material having a large magnetic loss at a high frequency, and arranged it near an unnecessary radiation source, thereby obtaining the above-described semiconductor element or electronic device. A method has been found for effectively suppressing unnecessary radiation generated from a circuit or the like.

The mechanism of the unnecessary radiation attenuation using the magnetic loss is based on recent research that an equivalent resistance component is added to an electronic circuit serving as an unnecessary radiation source. I know it. Here, the magnitude of the equivalent resistance component and the frequency region where its effect appears are as follows:
Each depends on the magnetic loss term μ ″ of the magnetic material and the range of its frequency dispersion.

Therefore, in order to obtain a larger attenuation of the unnecessary radiation, it is necessary to disperse a large μ ″ and μ ″ corresponding to the unnecessary radiation. In fact, the frequency distribution of the unwanted radiation generated in various electronic circuits is in most cases wide, so that the frequency dispersion of μ ″ of a normal magnetic loss material can be sufficiently covered. The present invention has been made in view of such circumstances.

In order to obtain a soft magnetic powder which gives a necessary magnitude of anisotropic magnetic field (Hk) in a wide frequency range in order to cope with unnecessary tail radiation in a wide frequency range, a plurality of soft magnetic powders having different sizes are required. Although there is a method of mixing a plurality of magnetic powders having an anisotropic magnetic field (Hk), the present inventors have made it simpler to use two different anisotropic magnetic fields of a powder having a single composition. A method for obtaining a magnetic powder having (Hk) has been found, and the present invention has been achieved.

According to the present invention, the composition has a single particle size distribution curve having a maximum value and no maximum value and no minimum value, and has two anisotropic magnetic fields having different magnitudes from each other. A characteristic soft magnetic powder is obtained.

Further, according to the present invention, there is obtained a soft magnetic powder having a specific surface area of at least 0.3 m ² / g.

According to the present invention, there is provided a soft magnetic powder characterized in that the composition has a magnetostriction constant other than 0 at least near the surface of the soft magnetic powder.

According to the present invention, there is provided a soft magnetic powder characterized in that the soft magnetic powder has a flat shape.

Further, according to the present invention, there is obtained a composite magnetic material comprising the above-described soft magnetic powder and a binder and exhibiting two magnetic resonances in mutually different frequency ranges.

Further, according to the present invention, there can be obtained a composite magnetic body characterized in that the soft magnetic powder is oriented and arranged in the composite magnetic body.

[0019]

According to the present invention, there is provided a powder magnetic material obtained by processing a raw material magnetic material having a single kind of composition so that the specific surface area thereof is equal to or greater than a certain value.
Based on the discovery of For more information about this phenomenon, see S.
Yoshida et al .: J. Appl. Phys., Vol. 85, No. 8, 4636-4638
(1999). In the following, when the raw material magnetic material of a single species has a specific non-surface area or more,
The reason why two different magnitudes of anisotropic magnetic field (Hk) are shown will be described.

Among the magnetic factors of the soft magnetic powder, the magnitude of the demagnetizing field and the magnitude of the eddy current flowing in the particles depend on the shape of the powder. For example, in an isotropic magnetic powder produced by an atomizing method or the like, since a demagnetizing field derived from the powder shape exists isotropically, and a loss due to eddy current appears from a relatively low frequency region,
It is difficult to obtain excellent magnetic characteristics in a high frequency range.

However, when the powder having an isotropic shape is mechanically ground, the shape of the powder is flattened as the powder progresses, and the magnetic permeability characteristics are greatly improved. This is because the flattening of the powder significantly reduces the demagnetizing field in the flat plane direction, and the length in the direction perpendicular to the flat plane, that is, the thickness of the powder, is reduced. Losses are also brought about by the synergistic effect of being greatly reduced.

When the mechanical grinding is further continued, cracks are generated in the flat surface, and the flat powder changes to a finer flat powder. The flattening of the powder by mechanical grinding proceeds in such a process, but the specific surface area of the powder is proportional to the grinding time. That is,
By changing the grinding time, flat magnetic powders having different specific surface areas can be obtained. Further, by changing the particle diameter or the specific surface area of the starting raw material powder, flat powders having different specific surface areas can be obtained.

The present inventors have proposed Fe-Si-Al and Ni-
With respect to typical soft magnetic metal powders such as Fe, various flat powders with different specific surface areas were prototyped, and their magnetic properties were examined. It has been found that magnetic resonance appears. That is, in addition to the conventional magnetic resonance that appears at a frequency depending on the composition, shape, and residual stress, a magnetic resonance based on a larger magnetic anisotropy appears. This phenomenon is slightly different in ease of expression depending on the magnitude of the magnetostriction constant derived from the composition of the magnetic material, but the composition of typical soft magnetic metals such as Fe-Si-Al and Ni-Fe In the case of the flat powder, it can be recognized when the approximate specific surface area is about 0.3 m ² / g or more.

This phenomenon is obtained, for example, because the shape factor such as the particle shape, particle diameter, or aspect ratio of the flat magnetic powder has a binomial distribution for some reason. This is a phenomenon essentially different from the case where two kinds of powders having different Hk) are mixed, and the volume occupied by the portion near the surface of the powder becomes nonnegligible with respect to the powder volume. This is considered to be a phenomenon caused by the development of magnetic anisotropy. Therefore, it is needless to say that this is completely different from the case where two kinds of powders having different anisotropies are mixed and used.

Regarding the appearance of two magnetic resonances considered to be caused by the surface magnetic anisotropy, the surface area per unit weight of the powder, that is, the specific surface area is a dominant factor. The surface area where the two resonances appear differs depending on the other factors that occur, for example, the magnitude of the magnetoelastic effect, that is, the magnitude of the magnetostriction constant, and the magnitude of the strain remaining in the powder. It is difficult.

However, it has been recognized that the larger the powder has anisotropy due to the magnetoelastic effect, the smaller the surface area where two magnetic resonances appear. Therefore, in mechanically milled and flattened powders, the residual stress due to milling is considered to be quite large, so that two resonances are often observed with a relatively small surface area.

That is, according to the present invention, in a soft magnetic powder having a single composition and particle size distribution, two specific anisotropic magnetic fields (Hk) having mutually different magnitudes are expressed by specifying a specific surface area, This is to obtain a broadband μ ″ dispersion characteristic.

Here, the raw materials used in the present invention will be described. As the soft magnetic powder used in the present invention,
Pulverizing, softening, stretching, and tearing metal soft magnetic materials such as Fe-Al-Si alloys (Sendust), Fe-Ni alloys (Permalloy), and amorphous alloys with high high-frequency permeability What was done is mentioned as a representative.

Further, powders of oxide soft magnetic materials such as spinel type ferrite, planar type ferrite, hematite, magnetite, and maghetite can also be used.

On the other hand, the binder used as an auxiliary material for obtaining the composite magnetic material of the present invention is chlorinated, which can provide excellent flexibility and flame retardancy in consideration of use near an electronic circuit. Polyethylene is preferred, but other organic binders that can be used include polyester resins, polyethylene resins, polyvinyl chloride resins, polyvinyl butyral resins, polyurethane resins, cellulose resins, ABS resins, ethylene-acetic acid. Thermoplastic resins such as vinyl copolymer, acrylonitrile-butadiene rubber, styrene-butadiene rubber, silicone rubber, and thermoplastic elastomers, thermosetting resins such as epoxy resin, phenol resin, amide resin, and imide resin, etc. Is mentioned.

In addition, it is a matter of course that any other thermoplastic resin or thermosetting resin having moderate adhesiveness and flexibility can be used as the binder of the present invention. The means for kneading and dispersing the above-described constituents of the present invention to obtain a composite magnetic material is not particularly limited, and a preferred method may be selected based on the properties of the binder used and the ease of the process.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to specific examples. Here, as the flat soft magnetic powder, 9.8% by weight of Si, Al
Is 5.9% by weight, and the balance is Fe.
Si alloy powder, Fe-Ni alloy powder having a composition of 80% by weight of Ni and 20% by weight of Fe was used. In order to make these alloys into flat powders, a method of drawing and pulverizing using an attritor and a pin mill was used. Magnetite powder was used as the soft magnetic powder having an irregular shape.

To make the above soft magnetic powder into a composite magnetic material, 90 parts by weight of the soft magnetic material powder, 10 parts by weight of chlorinated polyethylene resin as a binder, and 50 parts by weight of toluene as a solvent are used. Weigh and mix the paste,
A method of forming a film by a doctor blade method, applying a hot press, and then curing at 85 ° C. for 24 hours was used.

[0034]

Example 1 Example 1
Three types of e-Al-Si alloy powder were prepared. Their specific surface areas measured by the BET method are 0.67 m ² /
g, is a 1.33m ² /g,0.17m ² / g. FIG.
FIG. 2 is a view showing the particle size distribution of an Fe—Al—Si alloy powder having a specific surface area of 0.67 m ² / g. This particle size distribution curve has a maximum value and no maximum value or minimum value, and indicates that the alloy powder has a single particle size distribution. The same applies to the particle size distribution of other alloy powders. As a result of surface analysis of these alloy powders,
It was presumed that the surface of the alloy powder had an excess composition of iron compared to the starting composition.

These alloy powders were used as composite magnetic sheets by the above-mentioned method to prepare samples for evaluating the characteristics. For convenience, those having a specific surface area of a composite magnetic body using the alloy powder of 0.67 m ² / g was used as a sample 1, and so 1.33 m ² / g sample things 2,0.17M ² / G
This is designated as Sample 3.

When these samples were analyzed using a vibrating magnetometer and a scanning electron microscope, the easy axis of magnetization and the direction of particle orientation were in the in-plane directions of the samples. Also,
In order to verify the performance of these composite magnetic material samples, the permeability-frequency (μ-f) characteristics and the electromagnetic interference suppressing effect of these samples were examined. Here, in the measurement of the μ-f characteristic, a composite magnetic material sample processed into a toroidal shape was inserted into a test fixture forming a one-turn coil, and the impedance was measured to obtain μ ′ and μ of the complex magnetic permeability. ″.

FIG. 2 shows an outline of an evaluation apparatus for verifying the effect of suppressing the electromagnetic interference of the composite magnetic body. Here, a copper sheet 22 was lined with a square composite magnetic material sheet 21 having a thickness of 2 mm and a side of 200 mm, which was used as an evaluation sample 23. To evaluate the effect of suppressing electromagnetic interference, micro-loop antennas 25 and 26 for transmitting and receiving electromagnetic fields having a loop diameter of 1.5 mm were used as wave source elements and receiving elements using the electromagnetic wave source oscillator 24. A network analyzer (electromagnetic field intensity measuring device) 27 was used for measuring the coupling level.

FIGS. 3, 4 and 5 show the μ-f characteristics of Sample 1, Sample 2 and Sample 3, respectively. FIG.
4, it can be seen that the value of μ ″ in the high-frequency region is large due to the appearance of two magnetic resonances, and that the value extends over a wide band. In contrast, in FIG.
μ ″ does not spread over a wide band, and shows μ-f characteristics generally found in a composite magnetic material.

From these results, only one magnetic resonance is observed in the composite magnetic material using the alloy powder having a relatively small specific surface area, but in the composite magnetic material using the alloy powder having a large specific surface area, In spite of a single particle size distribution, two magnetic resonances are clearly observed, and as a result, the magnetic loss term μ ″ also shows two dispersions over a wide band. The larger the specific surface area of the alloy powder becomes, the more remarkable, that is, Sample 1 and Sample 2 using alloy powder having a specific surface area of 0.3 m ² / g or more.
It can be seen that has a wide band magnetic loss characteristic in a high frequency region.

Next, the μ ″ distribution and the effect of suppressing electromagnetic interference of each sample will be described. Here, the value of the effect of suppressing electromagnetic interference is the signal attenuation when the copper plate is used as a reference (0 dB). Shows these results.

[0041]

[Table 1]

From Table 1, the following effects are apparent. That is, Sample 1 and Sample 2 show a good electromagnetic interference suppression effect in both the 800 MHz band and 1.9 GHz band, whereas Sample 3 shows
The effect of suppressing electromagnetic interference in the 1.9 GHz band is considerably inferior. Therefore, it can be understood that the effect of expanding the μ ″ distribution according to the present invention is extremely effective in suppressing unnecessary radiation over a wide frequency range.

Example 2 Next, as a soft magnetic material powder,
An example using Fe—Ni alloy powder will be described. Again, the specific surface areas are 0.13 m ^{2 /} g and 0.47 m, respectively.
^A composite magnetic body was produced in the same manner as in Example 1 by using a flat alloy powder of ² / g and 0.61 m ² / g. Also,
It has been confirmed that the particle size distribution of each powder shows a single dispersion.

Here, for convenience, the specific surface area is 0.13 m.
^{2 /g,0.47m 2 /g,0.61m 2} / g of the alloy powder composed of a composite magnetic body using the characterization samples each sample 4 for sample 5, and sample 6. 6, 7, and 8
9 is a diagram showing evaluation results of the magnetic permeability characteristics of Sample 4, Sample 5, and Sample 6, respectively.

From these results, only one magnetic resonance was observed in sample 4 using the alloy powder having a relatively small specific surface area, but in sample 5 and sample 6 using the alloy powder having a large specific surface area. Shows that two magnetic resonances are observed in spite of a single particle size distribution, and that the phenomenon is clearer when the specific surface area is larger. As a result, the magnetic loss term μ ″ also has two dispersions, and thus covers a wide band.

(Embodiment 3) Embodiments 1 and 2 are directed to the case where a flat magnetic powder is used. As described above, the phenomenon that two magnetic resonances occur is caused by the surface magnetic difference. Since it is considered to be due to anisotropy, the same phenomenon is exhibited even if the powder shape is not a flat shape. An example is shown below. As a magnetic powder, it has an irregular shape,
Magnetite (Fe ₃ O ₄ ) whose particle size distribution shows monodispersion
Powder was prepared. Also in this case, the specific surface area is 0.20 m ² /
g and 1.3 m ² / g of magnetic powder, and the samples made of the composite magnetic material prepared in the same manner as in Example 1 are referred to as Sample 7 and Sample 8, respectively.

FIGS. 9 and 10 show samples 7 and 8, respectively.
5 shows the results of evaluation of the magnetic permeability characteristics of the sample. From these results, only one magnetic resonance is observed in the sample using the magnetic powder having a relatively small specific surface area, but in the sample using the magnetic powder having a large specific surface area, a single particle size distribution is obtained. Nevertheless, two magnetic resonances have developed.

[0048]

As described above, a specific example has been described.
When the specific surface area of the magnetic powder reaches a certain level, magnetic resonance newly appears on the high frequency side even with a single composition and a single particle size distribution. That is, in addition to the conventional magnetic resonance that appears at a frequency depending on the composition, shape, and residual stress, a magnetic resonance based on a larger magnetic anisotropy appears.

Also in the embodiment of the present invention, the shape and the particle size distribution of the powder used are single. Further, in this embodiment, many examples of the soft magnetic metal fine particles having a flat shape are given. However, the appearance of two magnetic resonances in the single fine particles of the present invention is caused by a magnetic powder having an irregular shape whose magnetostriction constant is not zero. For example, in a magnetite or the like, this phenomenon occurs when the surface area of the powder reaches a certain size.

As described above, the soft magnetic material powder of the present invention and the composite magnetic material using the same have a single composition and particle size distribution, but two magnetic resonances appear in different frequency regions from each other. The imaginary part magnetic permeability μ ″ is a magnetic loss term necessary for absorbing electromagnetic waves, and has a large value of μ ″ and excellent noise suppression due to its wide band. The effect appears.

Thus, it is possible to provide a thin composite magnetic material that is effective for suppressing noise inside high-frequency electronic devices such as mobile communication devices. Further, the soft magnetic material powder of the present invention and the composite magnetic material using the same can easily impart flexibility due to the features of the constituent elements, and can cope with complicated shapes and have severe vibration resistance. It is possible to meet the demand for impact resistance.

As described above, the soft magnetic material powder and the composite magnetic material using the same according to the present invention are effective materials for suppressing the radiation of unnecessary electromagnetic waves, and are used for electronic parts, especially active elements which operate at high speed. It is very effective for preventing noise in printed wiring boards and high-density mounting.

[Brief description of the drawings]

FIG. 1 is a diagram showing a particle size distribution of a magnetic powder used in the present invention.

FIG. 2 is a view schematically showing an apparatus for evaluating the electromagnetic interference suppressing effect of the composite magnetic body of the present invention.

FIG. 3 is a graph showing μ-f characteristics of Sample 1 in an example of the present invention.

FIG. 4 is a graph showing μ-f characteristics of Sample 2 in an example of the present invention.

FIG. 5 is a diagram showing μ-f characteristics of Sample 3 in an example of the present invention.

FIG. 6 is a graph showing μ-f characteristics of Sample 4 in an example of the present invention.

FIG. 7 is a graph showing μ-f characteristics of Sample 5 in an example of the present invention.

FIG. 8 is a diagram showing μ-f characteristics of Sample 6 in an example of the present invention.

FIG. 9 is a graph showing μ-f characteristics of Sample 7 in the example of the present invention.

FIG. 10 is a graph showing μ-f characteristics of Sample 8 in an example of the present invention.

DESCRIPTION OF SYMBOLS 21 Composite magnetic body 22 Copper plate 23 Evaluation sample 24 Oscillator for electromagnetic field wave source 31 Magnetic resonance 1 32 Magnetic resonance 2 33 Peak corresponding to magnetic resonance 1 34 Peak corresponding to magnetic resonance 2

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G002 AA03 AB02 AD04 AE02 4K018 AA26 BA16 BB01 BB04 BD05 5E041 AA04 AA07 AB14 CA06 HB17 NN06 NN15 5E321 AA32 BB32 BB44 BB53 BB55 GG05 GG07

Claims (6)

[Claims] A soft material having a single composition, a particle size distribution curve having a maximum value and no maximum value and no minimum value, and having two anisotropic magnetic fields having mutually different magnitudes. Magnetic powder. 2. The soft magnetic powder according to claim 1, wherein the specific surface area is 0.3 m ² / g or more. 3. The soft magnetic powder according to claim 1, wherein a magnetostriction constant of the composition at least near the surface is not zero. 4. The soft magnetic powder according to claim 1, which has a flat shape. 5. A composite magnetic body comprising the soft magnetic powder according to claim 1 and a binder, and exhibiting two magnetic resonances in mutually different frequency regions. 6. The composite magnetic body according to claim 5, wherein the soft magnetic powders are oriented and arranged.