JP2003124680A - Electromagnetic wave absorption material and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorption material which has a high absorption efficiency of an electromagnetic wave having the specific frequency of a higher frequency band, which exhibits good electromagnetic wave absorption characteristics, which can be reduced in thickness and which can sufficiently deal with requests for further increasing the density, the frequency and down sizing of a device, and to provide a method for manufacturing the same. SOLUTION: The electromagnetic wave absorption material comprises an insulating layer 11 having a predetermined thickness, and a laminate 1 obtained by alternatively stacking many flat magnetic materials 2 each having a predetermined planar shape and a predetermined thickness and disposed on the same planar surface so as not to be brought into contact with each other by orienting the materials 2 in the same direction and magnetic material distribution layers 12 of the structure in which the insulator 12a having the same thickness are filled between the materials 2. The method for manufacturing the electromagnetic wave absorption material comprises the steps of forming many vent holes arriving at a substrate corresponding to the planar shape of the magnetic material by a photolithography on a resist film, forming the magnetic material in which the magnetic materials are filled in the vent holes, and forming the magnetic material distribution layer by further polishing the magnetic materials and the resist film to a predetermined thickness.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electromagnetic wave absorbing material having a composite structure including a magnetic body and an insulator.

[0002]

2. Description of the Related Art In order to stabilize the functions of electronic devices, communication devices, etc., an electromagnetic wave absorbing material which absorbs an electromagnetic wave which becomes an obstacle is widely used. Particularly in mobile devices, in order to meet the demand for further reduction in size and weight, the electromagnetic wave absorbing material is also required to be in the form of an ultrathin sheet having a thickness of about several tens of μm. Ferrite materials have been mainly used as the electromagnetic wave absorbing material. The reason is that the magnetic field component, that is, the high-frequency magnetic field, is particularly problematic among electromagnetic waves, and the ferrite material having high soft magnetism and high electric resistance was excellent in absorption characteristics of the magnetic field component.

In the electromagnetic wave absorbing material, there are the complex permittivity and the complex magnetic permeability at a high frequency as material parameters involved in the electromagnetic wave absorbing characteristic, but the complex magnetic permeability μ = μ'-jμ "is required for absorbing the magnetic field component. The magnetic loss term μ ", which is an imaginary component, is strongly related. Further, it is the rotation of the magnetic moment in the electromagnetic wave absorbing material that influences the magnetic permeability with respect to a high frequency magnetic field such as a radio wave, and a high μ "is obtained near the resonance frequency with respect to the rotation of the magnetic moment.

However, with the recent development of electronic devices and communication devices, it has become difficult to say that ferrite-based materials have sufficient electromagnetic wave absorption characteristics. There are two reasons for this. First, ferrite-based materials have a characteristic limit called a snake limit for high-frequency magnetic fields, and the resonance frequency is as low as 0.2 GHz at most. In recent electronic devices and communication devices, electromagnetic waves of about 0.8 to 2 GHz often cause problems, and ferrite-based materials cannot cope with this.

Secondly, a ferrite material cannot be expected to have a high μ "because the number of magnetic moments that influence the magnetic loss term μ", that is, the saturation magnetization is small. In the future, it is expected that even higher absorptance will be required for electromagnetic wave absorbing materials, but the saturation magnetization of ferrite materials as described above is not sufficient at present.

Therefore, in order to obtain a high magnetic loss, an electromagnetic wave absorbing material made of a metallic soft magnetic material having a large number of magnetic moments causing the magnetic loss, that is, a large saturation magnetization has been studied. In an electromagnetic wave absorbing material using a metal soft magnetic material, it has been required to reduce eddy current loss in a higher frequency band to secure a high magnetic permeability. Developed along two technical directions: thinning the magnetic material and stacking multiple layers through a dielectric film, and pulverizing it to disperse it in an insulator such as resin. [The latest technology and application of new wave absorbers, electronic materials and technology series, supervised by Osamu Hashimoto, CMC Co., Ltd., published March 1, 1999].

As a result, in a laminated body of thin film magnetic materials, in order to prevent the magnetic permeability characteristic from being hindered by the displacement current generated due to the laminated structure, FIG.
As described in, a structure having a column-shaped laminated structure was considered. This structure is one of the most excellent electromagnetic wave absorbing materials for high frequencies at the present time. However, since this structure has a complicated structure and is difficult to manufacture inexpensively and easily, it has not been put to practical use.

[0008]

Therefore, it is assumed that the structure has a structure similar to that of the above-mentioned laminated body, and FIG.
An electromagnetic wave absorbing material having a dispersion structure in which a large number of flat magnetic powders made of a metal soft magnetic material are dispersed in an insulator such as a resin described in i. (JP-A-9-93034). In such a dispersion type electromagnetic wave absorbing material, the size and shape of individual magnetic powders are as uniform as possible, and
It is ideal that the magnetic powders are dispersed in the insulator independently without being in contact with each other, as uniformly spaced as possible, and oriented in the same direction as described above. .

However, in reality, it is difficult to obtain the above-mentioned ideal electromagnetic wave absorbing material because of the various problems described below. That is, the flat magnetic powder is
As described in the examples of the publication, spherical raw material powder obtained by a water atomizing method or the like is mechanically crushed using a ball mill or the like, mechanically crushed, stretched and torn to produce a flattened deformed product. To be done. However, even if the particle size of the spherical raw material powder, which is the raw material, is made almost constant,
Since the strength of pulverization, stretching and tearing applied to the raw material powder in the next step is different for each powder, the magnetic powder produced has a large variation in diameter and thickness between the powders.
The shape of each powder is irregular, and the diameter and thickness are not constant even within the same powder.

When a resin is used as an insulating material, the dispersion type electromagnetic wave absorbing material is formed by mixing magnetic powder, resin and solvent as described in the examples of the above publications. It is manufactured by coating the paste on a base material and drying it to remove the solvent. As another manufacturing method, there is also a method of melting and kneading the magnetic powder and the resin using an extruder and extrusion-molding. However, none of these methods can completely prevent magnetic powders from agglomerating in the resin and a plurality of powders coming into contact with each other. Further, even if they do not come into contact with each other, the dispersed state of the powder is inevitably non-uniform, and a high density portion and a low density portion of the magnetic substance powder are likely to occur in the resin.

Further, in the above-mentioned publication, in order to orient the magnetic powder in the same direction during film formation, the paste is applied in layers by applying stress by a doctor blade method or the like,
Although the film is further pressed to form a film, it is still impossible to orient all the magnetic powders in the same direction.
In the extrusion molding method, the magnetic powder is oriented in the same direction due to the stress during extrusion.
Not all magnetic powders can be oriented in the same direction.

Moreover, the stress when the magnetic powder is dispersed in the paste, the stress when the magnetic powder is oriented by applying and pressing the paste, or the magnetic powder is melted and kneaded with the resin and extruded. The magnetic powder is likely to be deformed or damaged due to stress at the time, and thus the variation in diameter and thickness may be further amplified. The frequency characteristics of the dispersion type electromagnetic wave absorbing material mainly depend on the diameter and thickness of the magnetic powder. Therefore, as described above, when the diameter and the thickness vary widely among the individual magnetic powders and within the powder, or when a plurality of powders come into contact with each other and the substantial diameter or thickness further varies,
The frequency characteristics will be averaged between the powders. That is, the electromagnetic wave absorbing material does not have a sharp peak for an electromagnetic wave of a specific frequency, but has a broad distribution over a wide frequency band. Therefore, the absorption efficiency for electromagnetic waves of a specific frequency is reduced.

Further, as described above, the magnetic powder has an irregular shape, particularly a planar shape, and has a variation in thickness and contains powder having a thickness of skin depth or more, and is easily aggregated. Therefore, the space factor in the resin, which is another factor that determines the electromagnetic wave absorption efficiency, cannot be increased so much. Moreover, all the magnetic powders cannot be oriented in the same direction, and magnetic powders that are directed in different directions and do not contribute to electromagnetic wave absorption are generated, so that the electromagnetic wave absorption efficiency is further reduced.

Therefore, it is difficult to obtain an electromagnetic wave absorbing material capable of exhibiting expected electromagnetic wave absorbing characteristics in the dispersion type structure. In the future, it is clear that in electronic equipment, the density and frequency of devices will continue to increase, but with regard to the problem of crosstalk inside electronic equipment, existing electromagnetic wave absorbing materials as described above are sufficient. It is a situation that cannot be said. Further, it is expected that further measures against electromagnetic waves will be required due to the influence of leaked electromagnetic waves on the human body, as represented by, for example, mobile phones. Further, as downsizing is required, the electromagnetic wave absorbing material is also required to be as small (thin) as possible. However, it is difficult for existing electromagnetic wave absorbing materials to sufficiently meet such requirements.

The present invention has a high absorption efficiency for electromagnetic waves of a specific frequency in a higher frequency band, exhibits excellent electromagnetic wave absorption characteristics, and can be thinned, and the device can be made even higher in density and frequency. It is an object of the present invention to provide a novel electromagnetic wave absorbing material that can sufficiently meet requirements such as downsizing and an efficient manufacturing method thereof.

[0016]

[Means for Solving the Problems and Effects of the Invention] The invention according to claim 1 is (1) an insulating layer made of an insulating material and having a constant thickness, and (2) a predetermined planar shape and a constant thickness. A large number of flat fine magnetic substances having
Aligned in the same direction so as not to contact each other, and a magnetic material distribution layer having a structure in which each magnetic material is made of an insulating material and is filled with a continuous layered insulator having the same thickness as the magnetic material. An electromagnetic wave absorbing material comprising a laminated body in which a plurality of layers are alternately laminated.

The electromagnetic wave absorbing material of claim 1 can be manufactured by applying a technique for manufacturing a fine printed wiring board, such as a photolithography method. Therefore, a large number of magnetic bodies can be arranged in a flat shape having a predetermined planar shape and, in particular, a constant thickness equal to or less than the skin depth. In addition, a large number of magnetic materials in one magnetic material distribution layer,
They can also be arranged in high density so that they do not contact each other and the space factor can be maximized.

Further, a large number of magnetic bodies are arranged in the same magnetic plane in the same plane, oriented in the same direction, and the plurality of magnetic body distribution layers are insulated with a constant thickness. Since the layers are laminated via the layers, it is possible to orient all the magnetic bodies in all the magnetic body distribution layers constituting the electromagnetic wave absorbing material in the same direction. Therefore, the electromagnetic wave absorbing material has a sharp peak for an electromagnetic wave of a specific frequency.

Therefore, according to the structure of claim 1, the absorption efficiency for the electromagnetic wave of the specific frequency is higher than that of the prior art, the electromagnetic wave absorption characteristics are excellent, and the device can be made thin. It is possible to obtain an electromagnetic wave absorbing material that can sufficiently meet the demands for higher frequencies and downsizing. The invention according to claim 6 is the above-mentioned claim 1.
A method for producing the electromagnetic wave absorbing material as described above, comprising the step of forming an insulating layer containing an insulating material on the underlayer, and forming a resist film containing the insulating material from which the insulator is formed on the underlayer. After forming a large number of through holes in the resist film corresponding to the planar shape of the magnetic body to reach the underlying layer by the photolithography method, the through holes are filled with a magnetic material to form a magnetic body. A method of manufacturing an electromagnetic wave absorbing material, which comprises alternately performing a step of forming a magnetic material distribution layer by polishing a body and a resist film to a constant thickness to form a laminated body.

According to the sixth aspect of the present invention, the resist film for defining the shape of the magnetic substance is used as it is as an insulator constituting the magnetic substance distribution layer, and the so-called additive method is used in the method for manufacturing a printed wiring board. The electromagnetic wave absorbing material of the present invention can be manufactured by forming a laminate of the insulating layer and the magnetic material distribution layer. Therefore, according to the structure of claim 6, the electromagnetic wave absorbing material of the invention of claim 1 can be used more efficiently, cheaply and easily as compared with, for example, the conventional manufacturing of a structure having a column-shaped laminated structure. It becomes possible to manufacture.

[0021]

DETAILED DESCRIPTION OF THE INVENTION (Electromagnetic Wave Absorbing Material) FIG.
A cross-sectional view showing an example of an embodiment of an electromagnetic wave absorbing material of the present invention, and FIG. 1 (b) is a plan view showing a surface of a magnetic material distribution layer in the electromagnetic wave absorbing material of FIG. 1 (a). As shown in these figures, the electromagnetic wave absorbing material of this example includes the insulating layer 11 and
A magnetic body distribution layer 12 including a large number of magnetic bodies 2 and a laminated body 1 in which a plurality of layers are alternately laminated are provided.

The upper and lower outermost layers of the laminate 1 are insulating layers 11. This is because, when the magnetic body 2 is exposed at the outermost layer of the laminate 1, electromagnetic waves are reflected and the absorption efficiency is reduced. In the figure, the insulating layer 11 and the magnetic material distribution layer 12 are shown.
The electromagnetic wave absorbing material is formed by alternately stacking and 17 layers in total (9 layers of the insulating layer 11 and 8 layers of the magnetic material distribution layer 12), but the number of layers is not limited to the example of the figure. In order to improve the electromagnetic wave absorption characteristics, it is preferable to increase the number of layers as long as the space allows. For example, in an example described later, a total of 41 layers (21 insulating layers 11 and 20 magnetic material distribution layers 12) are alternately laminated. Moreover, since the total thickness of the laminated body 1 is still as small as 30.5 μm,
According to the configuration of the present invention, it can be seen that the electromagnetic wave absorbing material can be thinned.

The insulating layer 11 is made of an insulating material and has a constant thickness. The reason for this is as described above. The thickness of the insulating layer 11 is preferably as thin as possible. In an electromagnetic wave absorbing material having a composite structure including a magnetic substance and an insulator, the magnetic loss term μ ″ increases exponentially according to the space factor of the magnetic substance. Therefore, in order to obtain a high μ ″, It is necessary to make the space factor of the magnetic material as high as possible, and for that purpose, it is desirable to make the thickness of the insulating layer 11 thin.

The magnetic material distribution layer 12 includes a large number of flat, fine magnetic materials 2 having a predetermined planar shape and a constant thickness, which are oriented in the same plane (on the insulating layer 11) in the same direction. The magnetic members 2 are arranged so as not to come into contact with each other, and the magnetic members 2 are filled with a continuous layered insulating member 12a made of an insulating material and having the same thickness as the magnetic members 2. Of these, the magnetic body 2 is preferably disk-shaped as shown in the figure.

The magnitude of magnetic loss at high frequencies, particularly in the frequency band of several hundred MHz or more, depends on the behavior of the magnetic moment in the magnetic material. That is, it is known that a large magnetic loss is obtained when the rotation of the magnetic moment resonates with the frequency of the electromagnetic wave. The resonance frequency of the magnetic moment is determined by the anisotropic magnetic field inside the magnetic material. It is said that a state in which an anisotropic magnetic field is applied in the direction in which the magnetic moment is aligned in the plane is preferable. In order to uniformly receive the anisotropic magnetic field in such a direction by each magnetic moment, the shape of the magnetic body 2 is preferably a disk shape or a regular polygonal thin plate shape, and the disk shape is most preferable.

The thickness of the magnetic body 2 is preferably equal to or less than the skin depth which depends on the electric conductivity, magnetic permeability and frequency. A thickness greater than the skin depth is wasted in terms of space because it does not function effectively for electromagnetic wave absorption. Skin depth is σ / (μ · f) [where σ is conductivity, μ is magnetic permeability,
f is the frequency. ] Proportional to The aspect ratio (diameter / thickness) of the magnetic body 2 is preferably 10 to 200. When the aspect ratio is less than 10, the magnetic moments are not aligned in the same plane and the rotation becomes random, so that high magnetic loss may not be obtained. Also, the aspect ratio is 2
If it exceeds 00, the diameter of the magnetic body 2 becomes large, so that the property of the metal having a low electric resistance and easy reflection of electromagnetic waves becomes strong, and the electromagnetic wave absorption efficiency may decrease.

The diameter here means the diameter of a circle as it is in the case of a disk-shaped magnetic substance powder. In the case of magnetic powder having a planar shape other than a disk shape such as a regular polygonal thin plate shape, the diameter of a circle having an area matching the area obtained from the planar shape is indicated. As a material for forming the magnetic body 2, a metallic soft magnetic material having a large saturation magnetization as described above is preferable. As the metal soft magnetic material, for example,
Examples thereof include (a) one metal selected from Ni, Fe, and Co, or (b) an alloy of two or more metals containing at least one of the above metals. Further, as the alloy of (b), an alloy consisting of only two or three metals among Ni, Fe or Co, and an alloy of one to three metals among Ni, Fe or Co and other metals. Can be given.

In the one magnetic substance distribution layer 12, it is preferable to arrange the magnetic substances 2 so that the distances between the adjacent magnetic substances 2 are equal to each other in order to obtain uniform electromagnetic wave absorption characteristics. Also, it is preferable for improving the space factor of the magnetic material described above. For example, in the case of a disc-shaped magnetic body 2, if the centers of three adjacent magnetic bodies 2 are located at the vertices of an equilateral triangle indicated by the chain double-dashed line in the figure as shown in FIG. The distance between the matching magnetic bodies 2 becomes equal in all directions. Therefore, the electromagnetic wave absorption characteristics of the magnetic material distribution layer 12 can be made uniform. Further, since no extra gap is generated, the shortest distance D1 between the adjacent magnetic bodies 2 is reduced, so that the density of the magnetic bodies in the magnetic body distribution layer 12 is improved and the space occupied by the magnetic bodies 2 in the electromagnetic wave absorbing material is increased. The product ratio can be improved.

The magnetic bodies 2 in the upper and lower magnetic body distribution layers 12 sandwiching one insulating layer 11 are preferably arranged so as to be offset from each other in the plane direction. In particular, it is preferable to arrange the magnetic body 2 of the other magnetic body distribution layer 12 so as to fill the gap between the magnetic bodies 2 of the one magnetic body distribution layer 12. For example, in the example of FIG. 1 (b), one magnetic material in the lower magnetic material distribution layer 12 shown by a broken line in the drawing is arranged so that one magnetic material is located at the center of the above-mentioned equilateral triangle. The magnetic bodies 2 in the layer 12 are arranged offset from each other.

With such an arrangement, the gap between the magnetic bodies 2 which functions as a "hole" through which electromagnetic waves can pass can be made as small as possible, and the electromagnetic wave absorption efficiency can be further improved.
Further, it is also possible to eliminate the uneven distribution of the magnetic material 2 between the upper and lower magnetic material distribution layers 12 and make the electromagnetic wave absorption characteristics uniform. As the insulating material forming the insulator 12a of the insulating layer 11 and the magnetic material distribution layer 12, various insulating materials having film-forming properties can be used, and resin is particularly preferable.

In the electromagnetic wave absorbing material of the present invention, as described above, the resonance frequency, that is, the absorption frequency can be determined by selecting the shape and size of the magnetic body 2 and the metal soft magnetic material forming the magnetic body 2. It can be designed analytically. Further, by selecting the arrangement of the magnetic body 2, the thickness of the insulating layer 11, the number of laminated layers of the insulating layer 11 and the magnetic body distribution layer 12, and the like, optimum electromagnetic wave absorption characteristics can be obtained.

(Manufacturing Method of Electromagnetic Wave Absorbing Material) The electromagnetic wave absorbing material of the present invention can be manufactured by applying various conventionally known techniques when manufacturing a fine printed wiring board as described above. it can. Above all, the manufacturing method of the present invention is particularly preferably used because the electromagnetic wave absorbing material can be manufactured efficiently, inexpensively and easily. Below, Figure 1 (a)
The production method of the present invention will be described by taking the case of producing the electromagnetic wave absorbing material of the example (b) as an example.

First, as shown in FIG. 2A, a substrate S for laminating and forming the laminated body 1 thereon is prepared, and a resin layer which is a base of the first insulating layer 11 is provided on the surface of the substrate S. R1 is formed. As the substrate S, various substrates having a smooth surface are
Any of them can be used, but a substrate S which can easily peel off the formed laminated body 1 is particularly preferable. As the substrate S, for example, a substrate made of a low melting point alloy that melts at a temperature lower than the heat resistant temperature of the resin (thermal decomposition temperature, softening temperature, glass transition temperature, melting temperature, etc.) is preferably used. After the laminated body 1 is formed, the substrate S made of the low melting point alloy is melted by immersing the whole body in hot water set to a temperature equal to or higher than the melting point of the low melting point alloy, so that the laminated body 1 can be easily peeled off.

Further, the resin layer R1 is formed of the same resin composition as the resist film forming the insulator 12a of the magnetic substance distribution layer 12 described below, that is, the resist is used to enhance the binding property between the two layers. In addition, it is preferable to form the more integrated laminate 1 by making the expansion and contraction rates of both layers uniform. When the resin layer (resist film) R1 is formed of, for example, a negative type ultraviolet curable resist as in the example described later, after applying the resist to form the resist film R1,
As shown in the figure, when the whole is irradiated with ultraviolet rays UV and cured, a strong insulating layer 11 is formed [FIG. 2 (b)].

Next, the insulator 1 is formed on the insulating layer 11.
2a is applied to form a resist film R2 [FIG. 2 (c)], and a mask pattern M corresponding to the planar shape and arrangement of the magnetic material is further laid on the resist film R2 and ultraviolet UV
(Fig. 2 (d)). As described above, when the negative type UV curable resist is used as the resist, as the mask pattern M, as shown in the figure, the portion corresponding to the magnetic material does not pass the UV light and the other portion does not pass the UV light. A light-transmitting portion M2 that allows light to pass therethrough is used.

Then, when ultraviolet rays are irradiated, the resist film R
Of the two, only the portion corresponding to the light transmitting portion M2 is selectively ultraviolet-cured. After that, when the resist film R2 is developed using a resist-dedicated developer, the uncured portion of the resist film R2 corresponding to the non-light-transmitting portion M1 is selectively removed. Then, the magnetic film 2 is formed on the resist film R2.
A large number of through holes H1 reaching the insulating layer 11 which is the underlayer corresponding to the plane shape of the above are formed [FIG. 2 (e)].

When a positive type UV curable resist is used as the resist, on the contrary, a mask corresponding to the magnetic substance is a transparent portion which transmits ultraviolet rays, and the other portion is a transparent portion which does not transmit ultraviolet rays. Use a pattern. Then, when the resist film R2 is irradiated with ultraviolet rays, only the portion corresponding to the light-transmitting portion can be selectively removed with a dedicated developer. Therefore, when the resist film R2 is developed with this developer, as shown in FIG. It becomes the state shown in.

Next, by depositing a magnetic material which is a base of the magnetic body 2 on the entire surface of the resist film R2,
The inside of the through hole H1 is filled with the film F1 of the magnetic material [FIG. 3 (a)]. As a method for depositing the magnetic material, a conventionally known film forming method such as a vapor deposition method such as a vacuum vapor deposition method, a sputtering method, an ion plating method or a CVD method, or a wet plating method can be employed.

Then, by polishing the surface to remove the film F2 on the resist film R2, the film F1 having a predetermined thickness is obtained.
A large number of magnetic bodies 2 each having the same size, shape and distribution as defined by the mask pattern M are arranged on the surface of the insulating layer 11 as the underlying layer on the same plane, and the gap between them is hardened. Resist film R2
A magnetic material distribution layer 12 having a structure filled with a continuous layered insulator 12a is formed [FIG. 3 (b)]
The insulating layer 11 is formed again on the magnetic material distribution layer 12. For example, in the case of using a negative type ultraviolet curable resist, first, a resist is applied on the magnetic material distribution layer 12 to form a resist layer R3, and then the whole is irradiated with ultraviolet UV to be cured, whereby a strong insulating layer is obtained. 11 is formed [FIG. 3 (c)-(d)].

Thereafter, the operations of FIGS. 2 (c) to 3 (d) are repeated to laminate the insulating layer 11 and the magnetic material distribution layer 12 by a predetermined number of layers, and the substrate S is further processed as described above. When removed by melting or the like, the laminate 1 as an electromagnetic wave absorbing material is obtained.

[0041]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples. Example 1 (Step 1) Negative ultraviolet liquid UV in a yellow room on a substrate S made of a low melting point alloy (melting point 70 ° C.) whose surface is finished to have a center line average roughness Ra = 0.02 μm or less. The cured resist is applied with a spin coater to a thickness of 0.5.
After coating so as to have a thickness of μm, the entire resist film R1 was irradiated with ultraviolet rays UV to be cured [FIG. 2 (a)]. As a result, as shown in FIG. 2B, the insulating layer 11 having a thickness of 0.5 μm is formed.
Was formed.

(Step 2) The same negative type UV curable resist was applied on the insulating layer 11 in a yellow room by using a spin coater so as to have a thickness of 1.0 μm [FIG. 2 (c)]. . Then, a mask pattern M corresponding to the planar shape and arrangement of the magnetic body 2 was superposed on the resist film R2 and irradiated with ultraviolet rays UV [FIG. 2 (d)].

The mask pattern M is made of an ultraviolet-transparent film, and a large number of non-transparent portions M1 corresponding to the planar shape of the magnetic body 2 are arranged on the film, and the film portion around it is transparent. The light part M2 was used. As a result, of the resist film R2, only the portion irradiated with the ultraviolet rays through the light transmitting portion M2 was selectively cured.
Next, the resist film R2 is formed by using a resist developer.
Is developed to selectively remove the uncured portion corresponding to the non-light-transmitting portion M1, so that the resist film R2 corresponds to the planar shape of the magnetic body 2 as shown in FIG. 2 (e). A large number of through holes H1 reaching the insulating layer 11, which is the base layer, were formed.

Next, the entire surface of the resist film R2 is coated with Fe by sputtering to a thickness of about 1.0 μm.
The sputtering film F on the resist film R2 is polished by filling the through hole H1 with the sputtering film F1 of Fe [FIG.
By removing 2 the magnetic substance distribution layer 1 with a thickness of 1.0 μm
2 was formed [Fig. 3 (b)]. Magnetic substance distribution film 1 formed
2 is a disk-shaped magnetic body 2 made of a sputtering film F1
Are arranged on the surface of the insulating layer 11 as the underlying layer on the same plane so as to be oriented in the plane direction of the insulating layer 11 so as not to contact each other, and the hardened resist is provided between the magnetic bodies 2. The structure was filled with a continuous layered insulator 12a made of the film R2.

The size, shape and distribution of the magnetic material 2 in the magnetic material distribution layer 12 are the same as described above for the resist film R2.
And the pattern on the mask pattern M. That is, the thickness of both the insulator 12a and the magnetic body 2 was 1.0 μm. This thickness is
It was determined from the skin depth for an electromagnetic wave with a frequency of 2 GHz in Fe. Further, the planar shape of the magnetic body 2 has a diameter of 20.
It has a circular shape with a diameter of 20 μm and a thickness of 1 μm.
It became a disk shape of m.

Each magnetic body 2 is, as shown in FIG.
The centers of three adjacent magnetic bodies 2 are arranged so as to be respectively located at the vertices of an equilateral triangle indicated by the chain double-dashed line in the figure, and the shortest distance between adjacent magnetic bodies 2 (D1 in FIG. 1 (b)) )
Became 1 μm. (Step 3) The same liquid type negative UV curable resist was applied again on the magnetic material distribution layer 12 in a yellow room by using a spin coater so as to have a thickness of 0.5 μm, and then the whole was coated. Ultraviolet rays UV were irradiated to cure the entire resist film R3 [FIG. 3 (c)]. As a result,
As shown in (d), an insulating layer 11 having a thickness of 0.5 μm was formed.

The above steps 2 and 3 were then alternately repeated 20 times each. When forming the magnetic substance distribution layer 12, the mask pattern M was shifted and ultraviolet rays were irradiated each time. As a result, one magnetic material in the lower magnetic material distribution layer 12 shown by the broken line in FIG. 1 (b) is positioned above and below the magnetic material distribution layer 12 such that one magnetic material is located at the center of the equilateral triangle. The magnetic bodies 2 therein were arranged so as to be offset from each other.

The entire laminated body is immersed in hot water at 70 ° C. to dissolve and remove the substrate S, so that the insulating layers 11 and the magnetic material distribution layers 12 are alternately laminated as shown in FIG. And the outermost layers above and below the insulating layer 11 are made up of a 41-layer laminated body with a total thickness of 40.5 μm.
Was manufactured. The space factor of the magnetic material was 55% by volume. The electromagnetic wave absorbing material obtained in Example 1 above,
It was pasted on an IC that generates noise of 0 to 3 GHz, and the noise reduction effect before and after that was measured. The results are shown in Fig. 4 (a). In addition, as Comparative Example 1, a commercially available electromagnetic wave absorption sheet having a thickness of 50 μm was attached on the same IC,
The noise reduction effect before and after that was measured. The results are shown in Fig. 4 (b). These figures show values obtained by subtracting the noise intensity before attachment from the noise intensity after attachment.

As is apparent from the figure, the first embodiment has 0 to 3
It was confirmed to have a noise reduction effect of 3 to 6 dB over the entire frequency range of GHz. On the other hand, Comparative Example 1
Was found to have a noise reducing effect in the frequency band of 1 GHz, but it was found that most noise could not be reduced in the band of about 1 to 2 GHz.

[Brief description of drawings]

FIG. 1 (a) is a cross-sectional view showing an example of an embodiment of an electromagnetic wave absorbing material of the present invention, and FIG. 1 (b) is a sectional view of a magnetic material distribution layer of the electromagnetic wave absorbing material of FIG. It is a top view showing the surface.

2 (a) to 2 (e) are cross-sectional views showing respective steps of the method for producing an electromagnetic wave absorbing material of the present invention.

FIG. 3A to FIG. 3D are cross-sectional views showing subsequent steps of the manufacturing method.

FIG. 4 (a) is a graph showing a noise reducing effect for each frequency in the electromagnetic wave absorbing material of Example 1 of the present invention, and FIG. 4 (b) is a commercially available electromagnetic wave absorbing sheet as a comparative example, It is a graph which shows the noise reduction effect for every frequency.

[Explanation of symbols]

1 stack 11 insulating layer 12 Magnetic material distribution layer 12a insulator 2 magnetic material

Claims (6)

[Claims] 1. An (1) insulating layer made of an insulating material and having a constant thickness, and (2) a large number of flat, fine magnetic bodies having a predetermined planar shape and a constant thickness, on the same plane. A magnetic substance distribution layer having a structure in which the magnetic substances are oriented in the same direction so as not to contact each other, and each magnetic substance is filled with a continuous layered insulator made of an insulating material and having the same thickness as the magnetic substance. And an electromagnetic wave absorbing material comprising a laminated body in which a plurality of layers are alternately laminated. 2. The electromagnetic wave absorbing material according to claim 1, wherein the outermost layer of the laminate is an insulating layer. 3. The electromagnetic wave absorbing material according to claim 1, wherein the magnetic material is disk-shaped. 4. The electromagnetic wave absorbing material according to claim 1, wherein the thickness of each magnetic substance distribution layer is not more than skin depth. 5. The electromagnetic wave absorbing material according to claim 1, wherein the magnetic bodies in the upper and lower magnetic body distribution layers sandwiching one insulating layer are arranged so as to be offset from each other in the plane direction. 6. The method for producing an electromagnetic wave absorbing material according to claim 1, wherein the step of forming an insulating layer containing an insulating material on the underlayer, and the insulating material which is the basis of the insulator on the underlayer. A resist film containing a material is formed, and a large number of through holes reaching the underlayer corresponding to the planar shape of the magnetic body are formed in the resist film by a photolithography method, and then the through holes are filled with a magnetic material. A step of forming a magnetic material, and further polishing the magnetic material and the resist film to a certain thickness to form a magnetic material distribution layer,
The method for producing an electromagnetic wave absorbing material, wherein the steps are alternately performed to form a laminate.