JPH07106141A - Small size inductor and manufacture thereof - Google Patents

Abstract

PURPOSE:To lessen the deterioration in relative magnetic permeability characteristics by a method wherein a molded body, having a one-winding or multi-winding helical winding groove and a stepprovided terminal forming recessed part, is sintered and a metal conductor, having good electricity conducting characteristics, is filled in the winding groove and the terminal forming recessed part. CONSTITUTION:Square-shaped semiconductor windin grooves 2, consisting of the oxide magnetic material such as a manganese zinc ferrite, a nickel zinc ferrite and the like and having the high relative magnetic permeability characteristics, are provided. A stepping A is provided at the four corners of the square-shaped magnetic core on the winding groove formed part linking to the edge of the winding groove, and a terminal molded recessed part 5 is provided at the four corners of the magnetic core. Then, a sintered body is formed by sintering at a high temperature after conducting a degreasing process with which a binder is removed without changing the projection-molded configuration. Molten metal, having good electricity conducting characteristics, is filled in the winding groove 2 of the sintered bodsy and the terminal molded recessed part 5, the molten metal is cooled and a conductor, which becomes a winding, is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductor such as a choke coil or a transformer used in an electronic circuit, and in particular, it is formed into a square shape by injection molding using an oxide magnetic material having a high relative permeability characteristic and a high material resistivity value. The present invention relates to a small-sized inductor formed by winding a metal conductor on an annular magnetic core of a closed magnetic circuit obtained by molding and sintering, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Miniaturized inductors for choke coils, transformers, etc. have been required in a wide range with the recent miniaturization of electronic devices. Small inductors that are currently being put into practical use include a thin magnetic layer made of an oxide magnetic material having high relative magnetic permeability characteristics, a laminated inductor in which conductor layers forming windings are alternately laminated by printing, and a ring-shaped inductor. There are two types of wire-wound inductors in which a magnetic core of a closed magnetic circuit is wound. A laminated inductor has a structure in which a conductor forming a winding is continuously spirally embedded in a magnetic material, and a thin magnetic layer and a conductor of the winding are laminated by applying a printing technique. That is, a molded body obtained by alternately laminating a conductor and a magnetic layer formed into a paste by adding a binder to a powder of an oxide magnetic material so that some of the conductors forming the winding are connected to each other and are continuous. It is made by sintering at high temperature.

However, in the small inductor obtained by such a structure, since the metal element of the conductor is diffused into the magnetic body between the conductor and the magnetic body during the sintering process at high temperature, the space between the windings is reduced. It has a drawback that the electric breakdown voltage becomes low and that the winding is made of a printed conductor, so that the value of the allowable current of the winding is limited.

In an inductor in which a ring-shaped closed magnetic circuit core is provided with a winding, the magnetic core used in the conventional wound-type inductor is generally manufactured by a powder metallurgy method. That is, pressure is applied to a powder obtained by mixing a powder of an oxide magnetic material and a small amount of a binder, and compression molding is performed to obtain a molded product having a desired shape, and this is sintered in a gas atmosphere or in the air. Has been obtained by.

An inductor having a winding wound around a magnetic core obtained by applying a pressure to powder of an oxide magnetic material has an electric withstand voltage that is wound by using a resin case or a coil bobbin, or The allowable current value can be increased by increasing the wire diameter. However, with the miniaturization of inductors,
The ring-shaped closed magnetic circuit magnetic core formed by integral molding is difficult to automate the winding, and even if it is automated, it requires a complicated machine, and the winding takes time, which is a factor of increasing cost. On the other hand, in order to solve the above problems, the shape of the magnetic core has to be a closed magnetic circuit magnetic core by combining divided magnetic cores, and as an inductor due to the air gap formed in the magnetic circuit when miniaturized. There is a problem that the characteristics are deteriorated.

Further, since the magnetic core is formed by compression molding an oxide magnetic material under high pressure, a narrow winding groove for embedding a conductor forming a winding around the closed magnetic circuit magnetic core is formed. The provided one has a problem in that, during compression molding, the concavo-convex portion forming the winding groove is clogged with a magnetic material, which makes molding difficult.

[0007]

In order to solve the above problems, the present invention uses a molding raw material obtained by adding a binder to a fine powder of an oxide magnetic material having a high specific resistance in a soft magnetic material, and is conventionally subjected to injection molding. Compared to the magnetic core obtained from the powder compact of the above, the relative magnetic permeability characteristics are less deteriorated, and with a narrow winding groove that forms a winding with no void in the magnetic path in an annular closed magnetic circuit. After obtaining a ring-shaped annular shaped body, removing the binder, sintering at high temperature and filling the metal conductor into the winding groove and the terminal formation recess, it has high dimensional accuracy and excellent relative magnetic permeability characteristics. It is to provide a small inductor having the same and a manufacturing method thereof.

[0008]

The present invention has a particle size of 10 μm.
The average particle size is about 1.2 with a particle size distribution of about 0.1 μm.
An oxide magnetic material such as nickel (Ni) zinc (Zn) ferrite having a high specific resistance of μm and a high relative magnetic permeability characteristic is used, and a melt florate of 3.0 g / 10 is used as a binder added to the oxide magnetic material. Density 0.93 g / c in minutes
40% to 45% by weight of m ³ low density polyethylene
%, Paraffin wax having an average molecular weight of 400, in a weight ratio of 40% to 45%, and dioctyl phthalate in a ratio of 10% to 20% in a total amount of 100% in a total of 100%, respectively, and a binder is used as an oxide magnetic material. 7.5 wt% to 22 wt% in a weight ratio to, and kneaded at 80 ° C to 130 ° C and crushed to form a raw material for molding, and the outer periphery is formed into a linear shape by injection molding at a molding temperature of 130 ° C to 160 ° C. A square-shaped injection molded body having a closed magnetic circuit having thin winding grooves that circulate around and a terminal forming recess at four corners is obtained. In order to remove the binder, the injection-molded body is heated at about 50 ° C. for about 1 hour and kept at 350 ° C. to 500 ° C. to remove the binder, then sintered at 1200 ° C. for about 2 hours in the air and wound around the outer periphery. A sintered body having a groove and a recess for forming a terminal is obtained. Next, an electroless nickel plating film is formed on the winding groove and the terminal formation recess,
After forming a copper film on the nickel film, solder is coated to form a small inductor.

That is, the present invention is as follows. It was formed on the outer circumference of the magnetic core of the closed magnetic circuit in a square shape obtained by injection molding by adding an organic binder to an oxide magnetic material having a soft magnetic property and a high specific resistance value.
Sintering a molded body having a spiral winding groove of a winding or a plurality of windings, and a terminal forming concave portion provided with a step on the winding groove forming portion connected to the substrate conductor at both ends of the winding groove, A small inductor, characterized in that the winding groove and the terminal forming recess of the obtained sintered body are filled with a metal conductor having good electric conductivity.

2. Soft magnetic and high specific resistance oxide magnetic material powder having a particle size distribution of 0.1 μm to 10 μm, low density polyethylene in a weight ratio of 40% to 45%, and paraffin wax in a weight ratio of 40% to 40%. Four
5%, dioctyl phthalate 10% to 2 by weight
A binder mixed so that the total amount becomes 0% to 100% is added to the oxide magnetic material powder in a weight ratio of 7.5% to 22.0%, and the mixture is kneaded and crushed at 80 ° C to 130 ° C. After that, at a molding temperature of 130 ° C to 160 ° C, injection molding is performed into a square-shaped molded body provided with a winding groove and a terminal forming recess, and then the temperature is raised at a rate of about 50 ° C per hour to 350 ° C to 500 ° C. The degreased body from which the binder was removed by holding for 1 hour at 1100 ° C to 1
A sintered body is obtained by sintering at 250 ° C. for 30 minutes to 2 hours, and the winding groove and the terminal forming recess formed at the time of injection molding of the sintered body are filled with a metal conductor of an electrically conductive material to form a winding and a terminal. Is a method for manufacturing a small-sized inductor.

[0011]

The present inventor, when forming a magnetic core using fine powder of an oxide magnetic material, has an advantage of improving the winding density of the winding core formed on the surface of the magnetic core and the magnetic core. As a result of diligent studies on whether a groove can be formed, the groove width can be determined by the injection molding method by selecting the particle size distribution of the fine powder of the oxide magnetic material, the type of binder added to the fine powder, and the weight ratio to be added. Was 0.1 mmR and the interval between the winding grooves was 0.1 mm, and a small inductor having winding grooves was obtained by injection molding, and the relative magnetic permeability of the closed magnetic circuit annular magnetic core obtained by injection molding was high. The value of magnetic susceptibility is several% compared with the magnetic core obtained by the conventional sintering method, even with the material having the relative magnetic permeability of 2000.
This is due to the fact that the small inductor of the present invention is expected to be obtained because the deterioration is moderate and the characteristic value is sufficiently practical.

A binder made of a resin, a plasticizer or the like is added and kneaded, and then injection molding is carried out to obtain a molded product, which is then heated at a low temperature rising rate of about 50 ° C. for 1 hour from room temperature to obtain an injection molded shape. The binder can be removed without deformation and a degreasing step is performed to obtain a degreased body, which is then sintered at high temperature to obtain a sintered body of an oxide magnetic material having a required shape. This is because it is possible to obtain a product with a complicated shape, which is difficult to obtain with a compacted product obtained by adding a small amount of a binder to a conventionally used oxide magnetic material and compression-molding, with high dimensional accuracy and mass productivity. It shows that there is an advantage. By using the powder injection molding method, it is possible to form a thin winding groove for a conductor that forms a winding, which is difficult to obtain by ordinary powder metallurgy, on the outer circumference of a small square-shaped magnetic core. A small inductor made of an oxide magnetic material having a closed magnetic circuit with no voids in the magnetic circuit can be easily obtained.

The inductor is obtained by filling the winding groove portion of the magnetic core of the oxide magnetic material obtained by the above method with the molten metal and cooling it to form the conductor to be the winding. In this case, the upper and lower surfaces and the inner and outer peripheral surfaces of the winding groove forming portion may be polished as needed. In addition, as a method of forming the conductor, a method of forming a conductor by filling the melting groove portion with metal powder and melting it, or forming a nickel film by electroless nickel plating on the winding groove portion, and forming a copper film on it The film may be formed by plating or the like and then solder-plated. Since the inductor according to the present invention can be made extremely small and has a closed magnetic circuit with no air gap in the magnetic path, it has a large inductance with the same volume of magnetic core as compared with a laminated inductor having an open magnetic circuit in the surface direction. Therefore, an inductor having the same inductance can be downsized. Further, the shape of the magnetic core can be molded into any shape by using a metal mold for injection molding such as a square shape, the flexibility of determining the shape of the magnetic core is large, and the shape can be appropriately changed depending on the purpose of use.

When the oxide magnetic material is produced, the amount of the binder containing an organic polymer compound as a main component, which is added to the powder of the oxide magnetic material, is not more than 7.5% by weight. The fluidity for filling the mold during injection molding is insufficient, and it becomes difficult to form a thin winding groove on the surface of the magnetic core. If the added amount is 22% by weight or more, the molded body can be smoothly removed during degreasing. It becomes difficult to remove the binder, and the degreased body becomes cracked or chipped. Therefore, the amount of the binder added to the oxide magnetic powder is in the range of 7.5% by weight to 22% by weight, and the preferable amount of addition for forming a fine groove of 0.1 mmR is 9% by weight. % To 18% by weight is suitable.

The particle size of the oxide magnetic material powder is 0.
If the ratio is less than 1 μm, the flow becomes poor when the same amount of binder is added, and the surface of the winding groove becomes rough with powder having a particle size of 10 μm or more, and the kneading temperature with the binder is 1
When the temperature is 30 ° C. or higher, the binder flow becomes large and it becomes difficult to knead, and when the temperature is 80 ° C. or lower, the binder is hard to adapt to the oxide magnetic material powder, and it is most suitable to knead at around 100 ° C. If the injection molding temperature is 160 ° C. or higher, the mold is likely to be seized, and if the injection molding temperature is 130 ° C. or lower, the flow is poor and it becomes difficult to accurately form the shape of the thin winding groove. The slower the temperature rise rate when forming the defatted body, the better, but in practice it is 1
About 50 ° C. per hour is preferable, and if the temperature rising rate is increased, chipping may occur in the thin portion of the degreased body, which is not preferable. If the holding temperature for removing the binder is 350 ° C. or less, the binder is not completely decomposed, and if the holding temperature is 500 ° C. or more, sintering starts in a part of the powder, and the shape of the degreased body is not uniform, so that the part is chipped. It is not desirable because it occurs.

[0016]

EXAMPLE A small inductor and a method of manufacturing the same according to the present invention will be described with reference to examples. (Embodiment 1) FIG. 1 is a small inductor of the present invention having a single-layer winding, and a closed magnetic circuit is formed in a square shape having a winding groove 2 into which a metal conductor 4 forming the winding is inserted. FIG. 3 is a perspective view of a small inductor including a magnetic core made of a ring-shaped oxide magnetic material. The magnetic core 1 is a manganese zinc ferrite (Mn-Z
n ferrite) or nickel zinc ferrite (Ni-
(Zn ferrite) or other oxide magnetic material having high relative permeability characteristics, and a winding groove 2 having a semicircular cross section with a radius of 0.1 mm for forming a conductor is provided in a square-shaped magnetic path. , To connect to a lead wire (not shown) that connects to an external conductor, connect to the end of the winding groove for forming the winding, and form steps A at the four corners of the square-shaped magnetic core with respect to the winding groove forming portion. Thus, the terminal molding recesses 5 are provided at the four corners of the magnetic core.

The particle size of the oxide magnetic material powder is 0.1 μm.
The average particle size is approximately 1.
Prepare a Ni-Zn ferrite pre-calcined powder of 2 μm
-The mixing ratio of the three kinds of organic materials forming the binder to the Zn ferrite pre-calcined powder is ³ , low-density polyethylene having a melt flow rate of 3.0 g / 10 min and a density of 0.93 g / cm ^{3 in} a weight ratio of 3, the average. Paraffin wax having a molecular weight of 400 was added in a weight ratio of 3, dioctyl phthalate was added in a weight ratio of 1, and the addition amount was 7.0% by weight, 7.5% by weight, 9.0% by weight with respect to the ferrite pre-calcined powder. 11.
0% by weight, 18.0% by weight, 22.0% by weight, 24.0
Seven types of raw materials having different addition amounts of 7% by weight were made, kneaded at 100 ° C. and crushed to obtain a raw material for molding. Using this forming raw material, the conductor forming diameter shown in FIG.
In order to obtain a molded body of an oxide magnetic material having winding grooves of 2 mmR and 0.3 mmR, injection molding was performed at 130 ° C. in a mold for injection molding, and molded bodies having respective binder mixing ratios were prepared under each condition 1
I got 00 each.

Then, the molded body is heated to 500 ° C. at a heating rate of 50 ° C./hour and held until degreasing is completed,
Degreasing was performed. Table 1 shows the degree of completion of the groove of the molded body at the time of injection molding, and the value of the non-defective product rate without cracking and chipping occurring in the degreased body after degreasing while keeping the groove at 500 degrees. The obtained degreased body was subjected to high temperature sintering in the air at 1200 ° C. for 2 hours to obtain a magnetic core 1 of an oxide magnetic material having a winding groove for forming a conductor shown in FIG. Using this, molten solder was poured into the winding groove 2 for forming a conductor and cooled to obtain an annular inductor.

[0019]

[Table 1]

Example 2 In Example 2, an oxide magnetic material powder of the same raw material and material as used in Example 1 and a binder added to the oxide magnetic material powder were used, but the binder was low in weight ratio. Density polyethylene was mixed at a ratio of 4.5, paraffin wax at a ratio of 4.5, and dioctyl phthalate at a ratio of 1. The binder raw materials blended in the above values are 7.0% by weight, 7.5% by weight, 9.0% by weight, 11% by weight, 18% by weight, 22% by weight, and 24% by weight with respect to the oxide magnetic material powder. %, And kneaded and crushed at 100 ° C. to obtain a raw material for molding. Using this molding raw material, the molded body shown in FIG. 1 was obtained in the same procedure as in Example 1. Table 2 shows the results of the completion of the winding grooves of the injection-molded body after injection molding in Example 2 determined by the relationship between the occurrence of cracking and chipping of the degreased body after degreasing at 500 ° C. and the binder addition amount.

[0021]

[Table 2]

Example 3 In Example 3, the same raw materials and materials were used as the oxide magnetic material powder used in Example 1 and the binder added to the oxide magnetic material powder, except that the binder was low in weight ratio. Binder raw material having density polyethylene 4, paraffin wax 4 and dioctyl phthalate 2 was 7.0% by weight, 7.5% by weight, 9.0% by weight, 11% by weight with respect to the oxide magnetic material powder. %, 22% and 24% by weight were added, and the mixture was kneaded and crushed at 100 ° C. to obtain a raw material for molding. Using this molding raw material, the molded body shown in FIG. 1 was obtained in the same procedure as in Example 1.
The degree of completion of the winding groove of the molded body of the injection molded body in Example 3 was determined by determining the binder addition amount of the degreased body after degreasing at 500 ° C. and the occurrence of cracks and chips in the degreased body, and The relationship is shown in Table 3.

[0023]

[Table 3]

1 obtained according to Examples 1 to 3
To the winding groove of the magnetic core after sintering at 200 ° C, paste-like solder is directly applied and baked, or a conductor is formed by conductive paint to form a small inductor, or electroless nickel plating is performed on it. The winding may be formed by forming a copper film and applying solder plating. FIG. 2 shows an example in which a common choke coil having the same number of turns in the same direction is formed on two magnetic legs of a square-shaped magnetic core 1 according to the method of the present invention. In addition,
1 and 2, the surface of the portion forming the terminal 3 is provided with a step A with respect to the surface of the winding portion, and the conductor surface formed in the winding groove to be the winding should be coated with a resin coating film. Thus, the surface mount type can be easily obtained. In addition, the outer diameter of a small inductor manufactured by injection molding is 5 mm to 3 m on one side of the square shape.
Molding is possible even with a length of about m. Further, in the examples of the present invention, an example using Ni-Zn ferrite having a high material resistivity and high relative magnetic permeability characteristics was shown, but another oxide magnetic material having a high material resistivity and high relative magnetic permeability characteristics was used. Even if it is used, it is obvious that a small inductor similar to the present invention can be obtained.

In the embodiment of the present invention, a Ni-Zn ferrite powder having a relative magnetic permeability of 2000 is used, and the outer diameter is 3.4 mm, the height is 1.5 mm, and the width of the magnetic core is 0.7 mm. In the small inductor in which the winding groove of 0.1 mmR was formed at 0.1 mm intervals and the winding groove of 28 turns was formed all around the magnetic leg, and the conductor was formed in the winding groove, the inductance value was 170 μH.

Further, in the embodiment of the present invention, the example in which the magnetic core has one winding or two windings is described, but by applying the present invention, a plurality of windings can be provided in one magnetic core. It goes without saying that a wound transformer or the like can also be configured.

[0027]

EFFECTS OF THE INVENTION A degreased body obtained by adding a proper amount of a binder combining a plurality of organic materials according to the present invention to a fine powder of an oxide magnetic material to obtain a molded body by injection molding and firing at low temperature to remove the binder. The sintered body obtained by sintering at a high temperature can provide a small inductor at a low cost with a step formed in the thin winding groove and the terminal forming recess. The small-sized inductor and the manufacturing method thereof by injection molding according to the present invention have a structure in which the groove width of the winding groove can be easily increased and heat dissipation is good as compared with the conventional method, so that the small-sized inductor having a relatively large current capacity can be obtained. It also has an industrially useful effect that the inductor can be provided at low cost.

[Brief description of drawings]

FIG. 1 is an external perspective view showing an example of a single-layer winding of a small inductor according to the present invention.

FIG. 2 is an external perspective view of a small inductor according to the present invention, showing an example in which two windings are wound in the same phase to form a common choke coil.

[Explanation of symbols]

 1 magnetic core 2 winding groove 3 terminal 4 metal conductor 5 terminal forming recess A step

Claims (2)

[Claims] 1. A single- or multi-turn winding formed on the outer periphery of a closed magnetic circuit magnetic core in a square shape obtained by injection-molding an oxide magnetic material having soft magnetic properties and a high specific resistance value. A molded body having a spiral winding groove and terminal-formed recessed portions provided at both ends of the winding groove with step differences with respect to the winding groove forming portion connected to the substrate conductor is sintered to obtain a sintered body. A small inductor characterized in that the winding groove and the terminal forming recess are filled with a metal conductor having a good electrical conductivity characteristic. 2. An oxide magnetic material powder having a particle size distribution of 0.1 μm to 10 μm and having a soft magnetic property and a high specific resistance value, and low-density polyethylene in a weight ratio of 40% to 4%.
5%, paraffin wax 40% to 45% by weight
%, Dioctyl phthalate in a weight ratio of 10% to 20
% Of the binder mixed in a total of 100% to the oxide magnetic material powder in a weight ratio of 7.5% to 22.0%, and the mixture is kneaded at 80 ° C. to 130 ° C. and crushed. After injection molding at a molding temperature of 130 ° C to 160 ° C into a square-shaped molded body provided with winding grooves and terminal forming recesses, the temperature is raised at a rate of about 50 ° C per hour at 350 ° C to 500 ° C. The degreased body from which the binder has been removed is kept at a temperature of 1100 ° C to 1 for 1 hour.
A sintered body is obtained by sintering at 250 ° C. for 30 minutes to 2 hours, and the winding groove and the terminal forming recess formed at the time of injection molding of the sintered body are filled with a metal conductor of an electrically conductive material to form a winding and a terminal. A method for manufacturing a small inductor, comprising: