JP3926447B2 - Method for producing composite magnetic material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a composite magnetic body used for suppressing electromagnetic interference caused by interference of unwanted electromagnetic waves in a high frequency region, and more particularly, a complex magnetic permeability effective for suppressing electromagnetic interference which is a problem in high frequency electronic circuits / devices. The present invention relates to a method for producing a composite magnetic body having excellent characteristics.
[0002]
[Prior art]
Conventionally, electronic components and printed wiring that are densely mounted have been improved in signal processing speed. Therefore, there is an increase in line-to-line coupling due to electrostatic and electromagnetic coupling and interference due to radiation noise. There are not a few situations that hinder the normal operation of equipment.
[0003]
For such so-called electromagnetic interference, conventionally, a low-pass filter or the like is connected to each output terminal of the circuit to suppress unnecessary high-frequency current or take measures to keep the problematic circuit away. The causative electromagnetic coupling, unwanted radiation and conduction noise were suppressed.
[0004]
As specific measures to realize further miniaturization and weight reduction of these high-frequency electronic devices, for example, different circuits are mixed in one printed wiring board (for example, a power circuit and a small signal circuit), or each circuit is made smaller. In many cases, measures such as mounting them in a superimposed manner are taken.
[0005]
However, especially when multiple wiring boards are stacked and mounted, the possibility of electromagnetic interference due to electromagnetic interference between components and wiring boards is extremely high, and some countermeasures are indispensable. . As a countermeasure against interference between these wiring boards, generally, a conductive shield material (copper, aluminum, etc.) is inserted between the wiring boards. In the wiring board described above, since the component mounting density is high, the high frequency magnetic field wave has a low impedance with respect to the noise source.
[0006]
However, although the wiring board described above can be expected to have a shielding effect against the other wiring board that faces one wiring board that is a noise source, reflection of unnecessary radiation occurs on the same board surface. Secondary electromagnetic coupling in the same wiring board on the noise source side is promoted.
[0007]
Therefore, electromagnetic interference using a composite magnetic material that has the same shielding effect as the conductive shield material for transmission of electromagnetic waves, and at least does not promote electromagnetic coupling by reflection, for reflection of electromagnetic waves. A suppressor is proposed in Japanese Patent Laid-Open No. 7-212079. This type of electromagnetic interference suppressor is mainly composed of a composite magnetic material in which soft magnetic powder is mixed in an organic binder, and by absorbing the electromagnetic wave that arrives at the composite magnetic material, unwanted electromagnetic waves can be generated. Suppress interference. That is, it is used for suppressing electromagnetic interference caused by interference of unnecessary electromagnetic waves.
[0008]
Hereinafter, an example of the electromagnetic interference suppression body using the conventional composite magnetic body disclosed by Unexamined-Japanese-Patent No. 7-212079 is demonstrated. The composite magnetic body constituting the electromagnetic interference suppressing body includes a flat (or needle-like) soft magnetic powder and an organic binder.
[0009]
Examples of the organic binding solvent constituting the composite magnetic material include thermoplastic resins such as polyester resins, polyvinyl chloride resins, polyvinyl butyral resins, polyurethane resins, cellulose resins, nitrile-butadiene rubbers, and styrene-butadiene rubbers. These copolymers, thermosetting resins such as epoxy resins, phenol resins, amide resins, imide resins and the like are employed.
[0010]
Examples of soft magnetic powders include iron-aluminum-silicon alloys (Sendust) and iron-nickel alloys (Permalloy) with high high-frequency magnetic permeability, and the aspect ratio of the powder is sufficiently large (approximately 10: 1 or more). Is desirable.
[0011]
The present inventors have determined the high-frequency transmission of the soft magnetic material with respect to an effective parameter for quantitatively grasping the degree of orientation of the flat soft magnetic powder in the in-plane direction of the composite magnetic material, that is, the arrangement of the soft magnetic powder. We focused on the fact that the magnetic susceptibility strongly depends on the magnitude of the demagnetizing field. By obtaining a ratio H _dd / H _de between the demagnetizing field H _{dd in the} hard axis direction and the demagnetizing field H _{de in the} easy axis direction as a parameter that can quantitatively grasp the magnitude of the demagnetizing field, a composite magnetic body Even when the filling rate of the magnetic powder in the sample and the demagnetizing factor of the powder itself change, the effective demagnetizing field size can be grasped, and the ratio is 4 when the sample shape is a cube. It has been found that excellent permeability characteristics can be obtained by the above. Further, the ratio H _dd / H _de can be controlled by the method for producing a composite magnetic material as described above.
[0012]
Here, the “demagnetizing field” Hd will be described with reference to FIG. The composite magnetic material sample is marked so as to know the orientation direction of the magnetic particles, and processed into a cubic shape. Using this VSM (vibration magnetometer), the MH curve (magnetization curve) of each of the orientation direction (magnetization easy axis direction) and the direction perpendicular to the orientation direction (hard magnetization axis direction) of this cubic sample Ask for. The MH curve is shown in FIG. A straight line (shown by a dotted line in FIG. 5) passing through the origin in parallel with the linear region portion of the obtained MH curve is drawn, and the magnetic field corresponding to the intersection of this straight line and the Ms line (saturated magnetization line) is expressed as “reverse”. Magnetic field “Hd”. The demagnetizing field in the “easy axis direction” is represented by H _de and the demagnetizing field in the “magnetization axis direction” is represented by H _dd .
[0013]
[Problems to be solved by the invention]
A method by injection molding is well known for producing the above-described composite magnetic body. In the injection molding, if only injection molding is performed, the orientation of the flat magnetic powder is limited by the injection speed and the flow of raw materials, and a desired degree of orientation cannot be obtained.
[0014]
In addition, for example, personal computers and the like that are adjacent to low-frequency noise and high-frequency noise can be dealt with by using corresponding composite magnetic bodies in their adjacent portions, but the number of parts increases for management purposes. As a result, there arises a problem that costs are increased.
[0015]
Therefore, the problem of the present invention is to solve the above-mentioned problems, obtain a desired degree of orientation with a simple structure, and to provide a composite magnetic body that can cope with low frequency noise and adjacent high frequency noise at low cost. It is to provide a manufacturing method.
[0016]
[Means for Solving the Problems]
According to the present invention, in a method for producing a composite magnetic body comprising at least a flat soft magnetic powder and an organic binder by injection molding, the flat soft magnetic powder and organic bond in the mold used for the injection molding are provided. Rutotomoni a slit immediately after the inlet of the injection materials containing agent, to place the electromagnet adjacent the slit, an injection material with passing into the slit, the flat soft magnetic powder that passes through the slit by applying a magnetic field orientation, method of manufacturing a composite magnetic body characterized by orienting, arranged flat soft magnetic powder definitive in the composite magnetic body is obtained.
[0018]
Further, according to the present invention, the to the composite magnetic body is shaped to have a low frequency corresponding portion and a high frequency corresponding portion, as the inlet of the mold, flat soft magnetic powder for low-frequency noise And a second inlet for the injection material containing the flat soft magnetic powder for high-frequency noise is provided .
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a view showing a composite magnetic body obtained by the production method of the present invention. 1A is a plan view, FIG. 1D is a perspective view of FIG. 1A, and FIGS. 1B and 1C are enlarged perspective views of portions for a high frequency band and a low frequency band, respectively. As shown in FIG. 1, the composite magnetic body 1 is divided into a low frequency part 2 for a low frequency band and a high frequency part 3 for a high frequency band. Accordingly, it is possible to deal with low frequency noise and adjacent high frequency noise in one product.
[0022]
Then, when the slit is not in a mold used in injection molding, the ratio of the orientation is dependent only by the flow of the raw material, the demagnetizing field H _de easy axis direction and the demagnetizing field H _dd hard axis magnetic H _dd / H _de (hereinafter referred to as “orientation degree”) is less than 2.9 and is not so obtained. Therefore, as shown in FIG. 2, the degree of orientation is improved to around 3.6 by providing a slit 14 in a mold 11 used for injection molding.
[0023]
Here, in order to manufacture the composite magnetic body 1 shown in FIG. 1, the metal mold | die 11 as shown to Fig.3 (a) is used. Actually, after covering a lid (not shown) from above the mold 11 shown in FIG. 3A, the material constituting the composite magnetic material is poured from the nozzle 21 into the groove of the mold 11. The arrows in the figure indicate the range of flow when pouring. FIG. 3B is a sectional view taken along line AA ′ in FIG. As shown in FIG. 4, an electromagnet 12 and an electromagnet 13 for applying a magnetic field orientation are arranged around the low frequency part 2 and the high frequency part 3 below the mold 11. Specifically, as shown in FIG. 3B, the electromagnet 12 and the electromagnet 13 have grooves that are shaped so that the electromagnet can be embedded in the periphery of the low frequency portion 2 on the lower side of the mold 11 and the periphery of the high frequency portion 3. Is formed. Further, slits 31 as shown in FIG. 3C are formed in the grooves for forming the low frequency part 2 and the high frequency part 3 below the mold 11. When this magnetic field orientation is used, a high orientation degree of about 3.9 is obtained.
[0024]
In addition, as shown in FIG. 1, in the case of manufacturing a molded body partially divided into two characteristics for the high frequency band and the low frequency band, if the injection is performed so that the raw materials can be separately injected, the required molded body is obtained. Can do. In addition, the orientation can be obtained by the above-described slit injection method or magnetic field orientation using an electromagnet, and can be molded as an integral part having partially different functions.
[0025]
【The invention's effect】
According to the present invention, the orientation of the magnetic powder can be obtained by providing a slit in the mold and allowing the slit to pass therethrough.
[0026]
Further, according to the present invention, when partial orientation is required, the orientation by the magnetic field can be limitedly performed by arranging the electromagnet in advance in a predetermined part of the mold corresponding to the part. .
[0027]
Further, according to the present invention, even when low-frequency and high-frequency noise sources are adjacent to each other, it is possible to cope with a single composite magnetic body by performing partial molding.
[Brief description of the drawings]
FIG. 1A is a top view showing an embodiment of a composite magnetic body obtained by the manufacturing method of the present invention, FIG. 1B is a perspective view of FIG. 1A, and FIG. It is an expansion perspective view of a low frequency part, (d) is an expansion perspective view of a high frequency part.
FIG. 2A is a view showing a part of a mold provided with a slit, and FIG. 2B is a side view of a slit portion after molding.
3A is a view showing a structure of a mold for manufacturing the composite magnetic body of FIG. 1, and FIG. 3B is a sectional view taken along line AA ′ of FIG. ) Is a sectional view taken along line BB ′ in FIG.
4A is a view showing a state in which an electromagnet for applying magnetic field orientation is incorporated in a mold, FIG. 4B is a view showing an embodiment of an electromagnet, and FIG. FIG. 5 is a diagram showing another embodiment of an electromagnet.
FIG. 5 is a diagram for explaining a “demagnetizing field” used in the description of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Composite magnetic body 2 Low frequency part 3 High frequency part 11 Mold 12, 13 Electromagnet 14, 31 Slit 21 Nozzle

Claims (2)

In a method for producing a composite magnetic body comprising at least a flat soft magnetic powder and an organic binder by injection molding,
The injection molding is used comprising a flat soft magnetic powder and an organic binder in a mold provided with a slit immediately after the inlet of the injection material Rutotomoni, to place the electromagnet adjacent the slit, the injection material together are passed through a slit, by applying a magnetic field oriented in a flat soft magnetic powder that passes through the slit, the composite magnetic body characterized by orienting, arranged flat soft magnetic powder definitive in the composite magnetic body Manufacturing method. Wherein in order to composite magnetic body is shaped to have a low frequency corresponding portion and a high frequency corresponding portion, as the inlet of the mold, a first injection material comprising flat soft magnetic powder for low-frequency noise 2. The method of manufacturing a composite magnetic body according to claim 1 , further comprising an inlet and a second inlet of an injection material containing a flat soft magnetic powder for high-frequency noise .

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