JPH11204360A - Manufacture of ferrite core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a ferrite core which is capable of improving the mechanical strength and thermal shock resistance and enables improvement in the yield and reliability. SOLUTION: The surface of a green compact of a drum-type core 1 is coated with a slurry of material powder having the same composition, and the slurry is filled in a defective portion on the surface of the compact, thus eliminating or reducing the defective portion. By doing so, the surface of the green compact after sintering is made smooth, preventing local concentration of a mechanical external force and stresses due to thermal shock. Thus, the mechanical strength and thermal shock resistance are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered ferrite core used for a magnetic core such as a coil.
More specifically, the present invention provides a method for producing a sintered ferrite core having excellent mechanical strength and thermal shock resistance.

[0002]

2. Description of the Related Art In recent years, with the drastic reduction in the number of components due to the progress of semiconductors, the promotion of digitalization has been remarkable along with the miniaturization of electronic devices, and the high functionality and reliability of electronic devices have been improved.

[0003] On the other hand, conduction noise and radiated noise generated from equipment, lightning surge and static electricity cause
This causes problems such as malfunctioning and functional failure of digital devices. This is extremely important,
In many cases, an inductance using a ferrite core or the like is frequently used.

[0004] In addition, a demand for a small size is strongly desired even for an inductance element which is difficult to replace with a semiconductor, and the improvement is progressing. In response to this request, the size of inductance components such as transformers and coils has been reduced, and in particular, the size of ferrite cores used in the magnetic core has been reduced.

For example, as a measure against noise, a drum-type ferrite core is used as a noise filter, and is used in a rectifying / smoothing circuit or the like of a power supply device of an electronic device to remove noise generated in a ripple voltage.

[0006] In general, in a communication line or an electronic circuit, a general coil is inserted in series with a circuit to block a signal in a specific frequency range, or inserted in parallel without impairing the impedance of the circuit. Is used for the purpose of superimposing.

As the transformer, a flat transformer using an ultra-thin E-shaped core, a transformer using an ultra-small pot core, and the like are used. These drum-type cores, E-type cores, and pot-type cores have been reduced in size, and at the same time, their usage has also changed, such as winding by automatic winding machines, the structure of attaching electrodes directly to the flange and the outer peripheral surface, etc. The use conditions are severe for ferrite cores.

[0008]

For example, in the case of a drum-type core used for noise suppression, the winding is applied by automation. There is a problem that cracks occur due to tension at the time and the yield is reduced.

As described above, in an inductor using a magnetic core such as a drum-type core, a thin E-type core, and a micro pot core, both ends of a wire after winding are drawn out to the end face of the core, and then the end face is drawn to the end face. By wrapping or temporarily fixing the lead wires placed in advance, and immersing these end surfaces in molten solder, the windings are fixed to the lead pins and the external connection electrodes, and used as external connection terminals. Have been done.

The above-described solder dip method is an extremely effective means for automating soldering and forming external electrodes. However, recently, 40%
High-temperature solder baths such as 0 ° C. have been used.

In such a method of use, the ferrite undergoes rapid thermal expansion locally and causes cracks, so that the defect rate is increased, which is a problem. In particular, a sintered high-frequency ferrite core containing nickel, for example, Ni-Z
In an n ferrite core, a Ni—Zn—Cu ferrite, etc., this thermal cracking is a major problem.

An object of the present invention is to provide a method of manufacturing a ferrite core which can improve mechanical strength and thermal shock resistance, and can improve yield and reliability.

[0013]

As a result of various investigations to solve the above-mentioned problems, the present invention provides a method for manufacturing a sintered ferrite core, which comprises the steps of: Is coated (applied) with a slurry (slurry) made from raw material powder of the same material, and then sintered to obtain a sintered ferrite core with excellent mechanical strength and thermal shock resistance. It is a thing.

The present invention is to improve the mechanical strength and thermal shock resistance of a sintered ferrite core containing nickel in particular.
An oxide sintered body represented by M.Fe ₂ O ₄ (M is a divalent metal such as Zn or Cu) is included.

[0015] These ferrite cores have wide applications in magnetic cores for high frequencies and the like. For example, Ni-Cu
-A Zn-based sintered ferrite core has an initial magnetic permeability of 100
It has the above characteristics and is widely used practically.

That is, the present invention relates to a method for producing a sintered ferrite core having a high mechanical strength and a high thermal shock resistance by a powder metallurgy method. This is a method for producing a ferrite core in which the surface of this green compact is coated with a slurry made of the same raw material powder and then sintered.

Further, the present invention is a method for producing a ferrite core using a ferrite powder containing nickel (Ni) in the composition of the raw material powder.

Further, the present invention is a method for producing a ferrite core in which a slurry is composed of a raw material powder, a binder, and either water or an organic solvent.

The present invention is also a method for producing a ferrite core using a slurry having a slurry concentration of 30% to 80%.

Further, the present invention is a method for producing a ferrite core for producing a drum core.

[0021]

Embodiments of the present invention will be described below.

The surface of the green compact has an infinite number of pores and scratches due to uneven filling when the raw material powder is supplied into the mold during molding and scratches on the mold surface. is there.
If sintering is performed in such a state, these defective portions remain in the sintered body. When a defect due to a mechanical external force or thermal shock is applied to such a defective portion, the stress tends to concentrate and a crack is generated as a starting point.

The larger the defect, the more the stress tends to be concentrated and the more likely it becomes the starting point. Therefore, it is necessary to eliminate as much as possible the larger the defect. When the size of the ferrite core is reduced, even a small defect tends to cause the defect portion relatively. Therefore, in improving the strength of the small core, the elimination of small defects is particularly effective.

When the surface of the green compact is coated with a slurry of the raw material powder having the same composition, the defective portion on the surface of the green compact is filled with the slurry and disappears or shrinks. Smooth, mechanical external force,
Also, stress due to thermal shock does not concentrate locally, and mechanical strength and thermal shock resistance are significantly improved.

The slurry to be coated is desirably composed of a raw material powder, an organic binder, an organic solvent and the like, but the same effect can be obtained by simply mixing the raw material powder and water.

If the concentration of the slurry is extremely low, the defective portion will not be sufficiently smooth. Therefore, it is desirable that the concentration be as high as possible within the range where coating is possible.
0% is appropriate. However, it is not limited to this. Depending on the particle size and distribution of the ferrite raw material powder,
The concentration of the slurry is also selected.

The thickness of the layer to be coated may be such that the surface of the green compact becomes smooth, and may be at most a range not exceeding the dimensional specification after sintering.

The coating method may be any method such as spraying, other application or dipping, but it is preferable that the layer is coated so as not to cause local unevenness in thickness. In particular, the method of the present invention comprises:
Effective for small cores.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to a drum type ferrite core shown in FIG.

In this embodiment, a Ni--Zn--Cu sintered ferrite is used. The ferrite of this system is Fe _{2
O 3: 47.0~50.0mol%, NiO:} 15~ 35
mol%, CuO: 10 mol% or less (excluding 0),
Many sintered bodies composed of ZnO: 10 to 33 mol% have been put to practical use. Here, as a representative example, the main component composition is Fe ₂ O ₃ : 47.5 mol%, NiO: 15 mo
1%, CuO: 5.5 mol%, ZnO: 32 mol%
And

Example 1 A green compact of a drum core having the shape shown in FIG. 1 was compacted by dry pressing.

The slurry was prepared by using the ferrite raw material powder used for preparing the above-mentioned drum core,
7 parts by weight of polyvinyl butyral, 60 parts by weight of ethyl cellosolve, and 1.5 parts by weight of butyl butylphthalylglycolate were added to 00 parts by weight, and the mixture was stirred with a stirrer to prepare a mixture.

This slurry was sprayed onto the surface of the compact of the drum-shaped core by spraying to apply a coating. After drying, this was sintered at 1200 ° C. for 2 hours to obtain a sintered body of a drum type core.

Using an automatic winding machine, a copper wire having a wire diameter of 3 mm was wound around the drum core 50 times. As a result, 1
No cracking occurred in 00 pieces. The core after winding is placed in a solder bath with a surface temperature of 400 ° C., and the surface of the core flange is placed on the solder bath.
Dipped for seconds. Also in this case, 100 pieces were tested, and no crack was generated.

Example 2 A powder compact of a drum-type core similar to that of Example 1 was produced. As a slurry to be applied, a raw material powder and pure water were dispersed by a stirrer to obtain a 50% aqueous solution.

The slurry was sprayed onto the surface of the compact of the drum core by spraying to apply a coating. After drying, this was sintered at 1200 ° C. for 2 hours to obtain a sintered body of a drum type core.

Using an automatic winding machine, a copper wire having a diameter of 3 mm was wound around the drum core 50 times. As a result, 1
No cracking occurred in 00 pieces. The core after winding was dipped in a solder bath having a surface temperature of 400 ° C. for 3 seconds on the surface of the flange of the core. Also in this case, 100 pieces were tested, and no crack was generated.

(Comparative Example) As a comparative example, a green compact was manufactured under the same conditions as the drum-type core manufactured in Example 1, and sintering was performed under the same conditions without coating the slurry. Produced. Winding was performed under the same conditions as in the example. As a result, 8 out of 100 cracks occurred.
When the solder bath was dipped under the same conditions as in Example 1, cracks occurred in 53 out of 100 cores.

(Embodiment 3) Next, a length of 50 mm and a width of 15 m
m, a rectangular compact having a height of 6 mm was prepared, and a sintered body was prepared with or without slurry coating.

Using the sintered body, a three-point bending strength test was performed. As a result, the bending strength of the coated sintered body was 310 MPa for the average of 30 test pieces, and the bending strength of the sintered body without the coating was 152 MPa for the average of 30 test pieces. . From this, it was found that the bending strength was remarkably improved by the production method according to the present invention.

In the above, the sintered ferrite core using the Ni-containing ferrite powder has been described.
Similar effects were obtained with ferrite cores of other compositions such as Mn-based and Li-based.

[0042]

As described above, according to the manufacturing method of the present invention, the mechanical strength and the thermal shock resistance are remarkably improved, and an excellent sintered ferrite which can be applied to high-temperature soldering and mechanical handling. A core is provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a drum type ferrite core used in Examples and Comparative Examples, FIG. 1 (a) is a front view, and FIG. 1 (b) is a plan view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drum-type core 2 Flange 3 Body 4 Lead lead groove

Claims (5)

[Claims] In a ferrite core manufacturing method for manufacturing a sintered ferrite core having a high mechanical strength and a high thermal shock resistance by a powder metallurgy method, after a raw material powder is compacted, a surface of the compacted body is formed. A method for producing a ferrite core, comprising coating a slurry prepared from the same raw material powder and then sintering the slurry. 2. The method for producing a ferrite core according to claim 1, wherein a ferrite powder containing nickel (Ni) is used in the composition of the raw material powder. 3. The method for producing a ferrite core according to claim 1, wherein the slurry comprises a raw material powder, a binder, and either water or an organic solvent. 4. The method for producing a ferrite core according to claim 1, wherein the concentration of the slurry ranges from 30% to 80%. 5. The method for producing a ferrite core according to claim 1, wherein a drum-type core is produced.