WO2003088281A1

WO2003088281A1 - Method of manufacturing soft magnetic powder and inductor using the same

Info

Publication number: WO2003088281A1
Application number: PCT/KR2003/000644
Authority: WO
Inventors: Kyu-Jin Kim; Jin-Young Park
Original assignee: HumanElecs Co Ltd
Current assignee: HumanElecs Co Ltd
Priority date: 2002-04-12
Filing date: 2003-03-31
Publication date: 2003-10-23
Anticipated expiration: 2004-10-12
Also published as: KR20030081738A; KR100478710B1; AU2003218817A1

Abstract

Disclosed herein is a method for manufacturing a shape-controlled soft magnetic powder which comprises adding a surfactant to a soft magnetic powder, and ball milling the mixture, wherein the shape-controlled soft magnetic powder has a thickness-to-diameter ratio of from 3 to 100. Further disclosed is a method for fabricating a wound-type inductor using the shape-controlled soft magnetic powder, comprising the steps of: coating a binder onto a shape-controlled soft magnetic powder; shaping the soft magnetic powder coated with the binder at room temperature; heat treating the shaped soft magnetic powder; and winding the heat-treated soft magnetic powder with a copper wire. Further disclosed is a method for fabricating a chip-type inductor using the shape-controlled soft magnetic powder.

Description

METHOD OF MANUFACTURING SOFT MAGNETIC POWDER AND INDUCTOR USING THE SAME

Technical Field

The present invention relates to a shape-controlled soft magnetic material used as a material of chip components such as chip inductors and chip beads, or radio-frequency shielding components such as wound-type inductors. The present invention also relates to a method for fabricating high frequency inductors.

Background Art

Recent developments in the field of electronic and communication equipments have led to the appearance of new industries, based on smaller and thinner electronic components and their improved packaging. The appearance of new industries, however, causes various social problems, e.g, environmental problems and communication interference, which were previously considered negligible. In particular, the commercialization of wireless communication devices and multi-environment exert a negative influence on electromagnetic environments around the world. Thus, many countries reinforce standards (FCC, CISPR, VDE,

MIL, etc) governing electromagnetic interference. There is a need to develop devices capable of managing radio-frequency interference (EMI/EMC). With increasing demand for the components of the devices, there have been many technological advances in terms of high complexity, high integration and high efficiency of the components. Soft magnetic materials, which are applied to magnetic devices such as electronic components for removing radio-frequency interference or for supplying power, are divided into various categories according to their different magnetic properties and frequency bands. Methods for manufacturing the soft magnetic materials move from conventional power metallurgy toward lamination of components. The method for manufacturing the soft magnetic materials using lamination of components is currently recognized as a manufacturing technique of small-sized chips in the field of ceramic electronic components.

In general, soft magnetic materials used in small-sized chip components used in chip inductors, chip beads, chip arrays, chip LC filters and chip transformers, etc., require high inductance. Examples of such soft magnetic materials include manganese-zinc (Mn-Zn) ferrites, nickel (Ni) ferrites, nickel-zinc (Ni-Zn) ferrites and nickel-copper-zinc (Ni-Cu-Zn) ferrites, etc. Among these ferrites, since the manganese-zinc (Mn-Zn) ferrites have advantages of high magnetic permeability and low power loss, they are commonly used as magnetic materials of power trans cores, filters for power lines, etc. The manganese-zinc (Mn-Zn) ferrites also have a disadvantage of low high-frequency characteristics. Accordingly, they cannot be used at a frequency band of 1 MHz or more. Magnetic materials currently used at high frequency bands are Ni ferrites, Ni-Zn ferrites and

Ni-Cu-Zn ferrites, etc.

In conventional methods for manufacturing small-sized chip components using the soft magnetic materials, calcining is carried out at a temperature 1,000-1,200 ^°C for 1~5 hours. As an internal electrode used in chip inductors or chip bead filters and the like, a mercury (Hg) electrode is generally used. Since the calcining temperature exceeds the melting point of mercury (960 ^°C), the components to be fabricated are likely to be damaged when used at high frequency. Accordingly, a desired inductance cannot be readily achieved. In order to lower the calcining temperature of the soft magnetic materials, a conventional method is suggested which comprises finely grinding magnetic materials to a particle size of 0.01~0.5μm to lower the energy level of the particles of magnetic materials to ground state (quasi-level state), and increasing the movement of the particles during calcining, thereby improving the sinterability of the particles. However, the conventional method requires a large expenditure in additional equipments required for the fine grinding and complex manufacturing processes, and therefore increases the price of final products.

A method for calcining at low temperature is disclosed in Japanese Patent Laid-open No. 59-67119. According to the publication, the compound comprises zinc oxide (ZnO) and bismuth oxide (Bi₂O₃) as main ingredients. Methods capable of calcining at low temperature using boron oxide (B O₃)

(Japanese Patent Laid-open No. 64-45771), and using a flux of bismuth oxide (Bi₂O₃), vanadium pentooxide (N O₅) or lead oxide (PbO) as an additive to induce the interfacial diffusion of particles, are known and currently commercialized. However, since the addition of these low-melting point compounds impedes the behavior of cobalt (Co), which is a component improving high frequency characteristics, calcining effect is reduced. In addition, since the additive is present in the form of liquid at a temperature lower than the calcining temperature of the soft magnetic material as a perform, and is diffused into particles of the soft magnetic material, the additive is likely to be partially segregated. The partial segregation of the additive results in a decrease in inductance. Further, since there exists a danger that the additive reacts with an internal electrode (Hg electrode) or diffuses into the internal electrode, the electromagnetic properties (inductance, Q-factor) of chip inductors to be fabricated are deteriorated and thus the reliability of chip inductors is damaged.

Disclosure of the Invention

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a shape-controlled soft magnetic powder having excellent high frequency characteristics.

It is another object of the present invention to provide a method for fabricating a wound-type inductor comprising the steps of: (a) coating a binder onto a shape-controlled soft magnetic powder; (b) shaping the soft magnetic powder coated with the binder at room temperature; (c) heat treating the shaped soft magnetic powder; and (d) winding the heat-treated soft magnetic powder with a copper wire.

It is yet another object of the present invention to provide a method for fabricating a chip-type inductor comprising the steps of: (a) coating a binder onto a shape-controlled soft magnetic powder; (b) casting the coated soft magnetic powder into green sheets by a doctor blade process; (c) laminating the cast green sheets; (d) printing an internal electrode on the laminate of green sheets, and further laminating green sheets thereon; (e) calcining the laminate of (d) to obtain a sintered body; and (f) forming an external electrode on the sintered body. In accordance with the present invention, there is provided a shape- controlled soft magnetic material manufactured by adding a surfactant to a soft magnetic powder selected from pure iron (Fe) powder, cobalt (Co)-based powder, nanocrystalline (Finemet) powder, permalloy-based powder and amorphous powder, followed by ball milling the mixture, wherein the shape-controlled soft magnetic material has an aspect ratio (a thickness-to-diameter ratio) of from 3 to 100.

In accordance with one aspect of the present invention, there is provided a method for fabricating a wound-type inductor for low-temperature calcining comprising the steps of: (a) coating 0.2~3wt% of a binder onto a shape-controlled soft magnetic powder; (b) shaping the soft magnetic powder coated with the binder at room temperature; (c) heat treating the shaped soft magnetic powder at 50-700 ^°C ; and (d) winding the heat-treated soft magnetic powder with a copper wire.

In accordance with another aspect of the present invention, there is provided a method for fabricating a chip-type inductor comprising the steps of: (a) coating a binder onto a shape-controlled soft magnetic powder; (b) casting the coated soft magnetic powder into green sheets by a doctor blade process; (c) laminating the cast green sheets; (d) printing an internal electrode made of aluminum or a conductive polymer on the laminate of green sheets, and further laminating green sheets thereon; (e) calcining the laminate of (d) at 50-700 ^°C to obtain a sintered body; and (f) forming an external electrode on the sintered body.

Best Mode for Carrying Out the Invention

Hereinafter, the present invention will be explained in more detail. Generally, the properties of magnetic materials are varied depending on the textures, compositions, shapes and frequency bands of the magnetic materials.

The shape-controlled magnetic powder (crystalline, nanocrystaline, amorphous, etc) usable in the present invention exhibits excellent electromagnetic properties at a high frequency of 10 kHz - several hundred MHz. As the shape- controlled magnetic powder exhibiting excellent high frequency characteristics, pure iron (Fe) powder, cobalt (Co)-based powder, permalloy-based powder, nanocrystalline powder (Finemet: Fe-Si-Nb-B-Cu-based powder, etc) or amorphous magnetic powder is available. Preferred soft magnetic powder includes Fe₈₀Ni ₀, Fe₅₀Ni₅₀, Fe (pure), Co (pure), Fe₈₄.1Si_10.1 l₅.₈- Fe ₉Co₄₉V₂, Fe_91.7Si_5.3B₃ (amorphous powder), Co_83.9Fe_5.34Si₈.₅₃B₂₄ (amorphous powder), Fe₈₃.₃₇Si₇.₇Nb_5.66B₁.₉₈Cu₁.₂

(nanocrystalline powder), etc.

In order to control the shape of the soft magnetic powder, a ball milling process is carried out using a chromium-coated ball or iron ball. The strength and weight of the ball are appropriately selected to prevent the aggregation of particles of the soft magnetic powder. The ball milling time is also determined to avoid the fracture of particles of the soft magnetic powder [J. D.James, B. Wilshire and D. Cleaver, Powder Metall. 33(3), 247(1990)]. In the present invention, the ball milling process is preferably carried out for 5 hours. In order to avoid the agglomeration between particles of the soft magnetic powder, a surfactant is added during the course of the ball milling. As the surfactant, stearic acid is most preferred.

The amount of the surfactant is preferably within the range of 0.1~2.0wt% based on the total weight of the soft magnetic powder and the surfactant. The weight of organic solvents used is excluded from the total weight. The shape- controlled soft magnetic powder manufactured in accordance with the present invention has an aspect ratio (a thickness-to-diameter ratio) of from 3 to 100.

If necessary, the shape-controlled soft magnetic powder thus manufactured is heat-treated at 200-400 ^°C to remove the surfactant. When the shape-controlled soft magnetic powder is mixed with an internal electrode (an aluminum electrode, a conductive polymer electrode, etc.) for low- temperature calcining to fabricate a device, the calcining temperature is lowered to 700 ^°C or less, which is advantageous in terms of processability. In contrast, in the case of the conventional methods using unshaped magnetic powder, the calcining is carried out at a temperature ranging from 850 to 1 ,350 ^°C .

As a binder used in the method for fabricating a wound-type inductor of the present invention, a polyimide-based or a phenol-based thermosetting resin is preferably used.

The binder, e.g., polyimide, is reacted with the soft magnetic powder to minimize the deterioration in the electromagnetic properties of a device to be fabricated. Particularly, since the electrical resistance in the magnetic layer of the device is increased by the binder, the device can be used even at high frequency. The binder added to the shape-controlled soft magnetic powder allows a chip to a have high quality factor (Q) and a low inductance at high frequency (~ a few GHz). Using these properties, chips having appropriate magnetic properties according to their uses can be fabricated.

The amount of the binder added is preferably within the range of 0.2-3.0wt% based on the total weight of the shape-controlled soft magnetic powder and the binder. When the amount of the binder is less than 0.2wt%, adhesive strength between the soft magnetic powder and the binder is low and thus it is difficult to obtain a bulky soft magnetic powder.

On the other hand, when an excess of binder is added, adhesive strength between the soft magnetic powder and the binder is high, but less soft magnetic powder is present in a shaped body, which results in deteriorated magnetic properties of a device to be fabricated. The weight of organic solvents used is excluded from the total weight.

After shaping, heat treatment is carried out at a temperature of 50-700 ^°C for 0.1-1 hour to impart mechanical strength to the shaped body. The temperature is preferably elevated at a rate of 10 ^°C or less per minute.

In accordance with the method of the present invention, wound-type inductors which have excellent magnetic properties, a quality factor of at least 100, a peak band of about 10 MHz or more, and an inductance of at least 1.7, can be fabricated at a relatively low temperature, compared to conventional wound-type inductors.

The binder used in the method for fabricating a chip-type inductor of the present invention is preferably at least one organic polymer selected from polyvinylbutyl (PNB), methylene chloride (MC), oleic acid, polyethylene glycol (PEG), toluene, mannitol and polyimide. The mixing ratio (wt%) of the soft magnetic powder to the binder is preferably within the range of 1 : 1 to 1 : 1.4.

The internal electrode is preferably made of at least one material selected from aluminum, mercury, polypyrrole, polyacetylene and polyphenylene. The calcining is preferably carried out at 50-700 ^°C . In accordance with the method of the present invention, the chip-type inductor can be fabricated at a temperature 700 ^°C) lower than the calcining temperature of the conventional chip-type inductors. In particular, the chip-type inductor using a conductive polymer as an internal electrode can be fabricated at a calcining temperature of 300 ^°C or less. Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these examples are given for the purpose of illustration and are not to be construed as limiting the scope of the invention. <Example 1> Manufacture of shape-controlled soft magnetic powders 0.5wt% of stearic acid was added to Fe₈₀Ni₂₀ as a soft magnetic powder, and then a ball milling process was carried out for 5 hours to control the shape of the soft magnetic powder. The aspect ratio (a thickness-to-diameter ratio) of the shape- controlled soft magnetic powder was adjusted to 5. The shape-controlled powder was heat-treated at about 300 ^°C to remove the stearic acid (Example 1-A).

Shape-controlled powders of Example 1-B to Example 1-1 were manufactured in the same manner as in Example 1-A under conditions stated in Table 1.

[Table 1]

^ shape-controlled soft magnetic powder [Aspect ratio (a thickness-to- diameter ratio) = 3—100]

<Example 2> Fabrication of wound-type inductors using shape-controlled powders

0.5wt% of polyimide as a binder was added to the shape-controlled soft magnetic powder (FesoNi₂o) manufactured in accordance with Example 1-A, dried, shaped into a toroidal core (outer diameter: 9.65mm, inner diameter: 4.78mm, height: 3.68mm), and heat-treated to impart magnetic properties to the toroidal core. The temperature for the heat-treatment was raised to about 700 ^°C at a rate of 10^°C per minute. The temperature was maintained to be constant for about 1 hour, and then cooled to room temperature at a rate of 10 ^°C per minute. The heat-treated soft magnetic powder was wound with 20 turns of an enamel copper wire (diameter 0.55mm) (Example 2-A).

Wound-type inductors of Example 2-B to Example 2-1 were fabricated in the same manner as in Example 2-A under conditions stated in Table 2.

[Table 2]

<Comparative Example 1> Fabrication of wound-type inductors using conventional soft magnetic powders

A wound-type inductor was fabricated in the same manner as in Example 2- C, except that commercially available spherical pure iron powder was used without ball milling (that is, unshaped) (Comparative Example 1-A).

A wound-type inductor was fabricated in the same manner as in Example 2- A, except that commercially available spherical Fe₈₀Ni₂o powder was used without ball milling (that is, unshaped) (Comparative Example 1-B).

Inductances of the wound-type inductors fabricated in accordance with Example 2 and Comparative Example 1 were measured at a frequency band of 10 kHz - several hundred MHz using an impedance analyzer (HP 4194A).

The results are shown in Table 3 below. [Table 3]

As can be seen from Table 3, the sintered body calcined in Example 2 had an inductance of 1.7μH or more, and no changes in the inductance at a frequency band of 10 kHz~l MHz. Particularly, the sintered bodies calcined in Examples 2-H and 2-1 had an inductance of 3μH or more. It is determined that the high inductances result from amorphous and nanocrystalline phase of the sintered bodies.

In contrast, the wound-type inductor fabricated using unshaped powders in Comparative Example 1 showed higher inductance at low frequency (10 kHz), but showed sharply decreased inductance with increasing frequency and finally showed the lowest inductance at 1 MHz. Accordingly, it can be seen that the wound-type inductors fabricated using shape-controlled powders has improved high frequency characteristics due to their magnetic anisotropy.

<Example 3> Fabrication of chip-type inductors using the shape-controlled soft magnetic powders (1) The shape-controlled soft magnetic powder (Fe₈₀Ni₂o) manufactured in

Example 1-A was dried, and then polyvinylbutyl (PVB) as a binder was added thereto at a rate of 1:1-1:1.4 (soft magnetic powder: binder, wt%). The mixture was cast into green sheets having a thickness of lOOμm by a doctor blade process.

The cast green sheets were laminated with five layers, and then an internal electrode made of polypyrrole, a conductive polymer, was printed on the laminate of the green sheets. Again, green sheets were laminated thereon, and then calcined at

650 ^°C for 2 hours to obtain a sintered body. An external electrode was formed on the sintered body to fabricate a chip-type inductor (Example3-A).

Chip-type inductors of Example 3-B to Example 3-1 were fabricated in the same manner as in Example 3- A under conditions stated in Table 4.

[Table 4]

<Comparative Example 2> Fabrication of chip-type inductors using conventional soft magnetic powders

A chip inductor was fabricated in the same manner as in Example 3-C, except that commercially available spherical pure iron powder was used without ball milling (that is, unshaped) (Comparative Example 2-A). A chip inductor was fabricated in the same manner as in Example 3 -A, except that commercially available spherical Fe₈₀Ni₂₀ powder was used without ball milling (that is, unshaped) (Comparative Example 2-B).

Electromagnetic properties of the chip inductors fabricated in accordance with Example 3 and Comparative Example 2 were measured using an impedance analyzer (HP 4194A). The results are shown in Table 5 below.

[Table 5]

As shown in Tables 4 and 5, the chip-type inductors of Example 3 were fabricated at a relatively low calcining temperature, compared to conventional chip- type inductors (400-800 ^°C). In particular, in the case of the chip-type inductor using polypyrrole as an internal electrode, the calcining temperature was 300 ^°C or less. The chip-type inductors fabricated in Example 3 exhibited excellent electromagnetic properties, e.g., an inductance of 140 nH or more, and a quality factor (Q) of about 39 even at high frequency, similar to conventional chip-type inductors. <Example 4> Fabrication of chip-type inductors using the shape-controlled soft magnetic powders (2)

A chip inductor was fabricated in the same manner as in Example 3 -A, except that the shape-controlled powder (Fe₈₀Ni ₀) manufactured in Example 1-A exhibiting excellent high frequency characteristics as shown in Table 3 was used and an aluminum (Al) electrode was used as an internal electrode (Example 4- A).

Chip inductors of Example 4-B to Example 4-F were fabricated in the same manner as in Example 4-A under conditions stated in Table 6, except that the shape- controlled powder [Fe₈₃.₃₇Si₇. Nb₅.₆₆Bι_.98Cuι. ₉ (nanocrystalline powder)] manufactured in Example l-I exhibiting excellent high frequency characteristics as shown in Table 3 was used.

[Table 6]

<Comparative Example 3> Fabrication of chip inductors using conventional soft magnetic powder [(Fe₂O₃)₄₉.₅(NiO)ι₀.ι-(ZnO)₃ι.₃₅(CuO)₈.₈₅]

A chip inductor was fabricated in the same manner as in Example 3 -A, except that (Fe₂O₃)₄₉.₅(NiO)₁o.₁-(ZnO)_31.35(CuO)_8.85, a conventional ferrite material, was used without ball milling (that is, unshaped), a mercury electrode was used as an internal electrode, and the calcining was carried out at 1000^°C .

Electromagnetic properties of the chip inductors fabricated in accordance with Example 4 and Comparative Example 3 were measured using an impedance analyzer (HP 4194A). The results are shown in Table 7 below.

[Table 7]

As shown in Table 7, the chip-type inductors fabricated using various conductive polymer electrodes, an aluminum electrode, etc., as internal electrodes in accordance with the method of the present invention had electromagnetic properties similar to the ferrite chip inductor (Comparative Example 3) using a mercury electrode as an internal electrode. Accordingly, aluminum and conductive polymers are preferred as novel electrode materials of an internal electrode for low- temperature calcining. Particularly, when polypyrrole was used as an internal electrode material, the most excellent high frequency characteristics were obtained.

Industrial Applicability As apparent from the above description, the present invention provides a method for manufacturing a soft magnetic material having high frequency characteristics even at low temperatures. The method of the present invention does not require additional costly manufacturing equipments and has no difficulties in management of the method. In accordance with the method of the present invention, soft magnetic materials for fabricating chip inductors can be provided at low cost due to simplified process manner and reduced process temperature.

In addition, the shape-controlled soft magnetic material of the present invention can be calcined even at low temperature and has few changes in electromagnetic properties by an externally applied stress. Furthermore, the shape- controlled soft magnetic material of the present invention has excellent high frequency characteristics. The present invention further provides inductors fabricated using the shape-controlled soft magnetic material.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

Claims:

1. A method for manufacturing a shape-controlled soft magnetic powder which comprises adding a surfactant to a soft magnetic powder, and ball milling the mixture, wherein the shape-controlled soft magnetic powder has a thickness-to- diameter ratio of from 3 to 100.

2. The method according to claim 1, further comprising heat treating the shape-controlled soft magnetic powder at 200-400 ^°C to remove the surfactant.

3. The method according to claim 1, wherein the soft magnetic powder is at least one powder selected from the group consisting of pure iron (Fe) powder, cobalt (Co)-based powder, permalloy-based powder and amorphous magnetic powder.

4. The method according to claim 1 , wherein the surfactant is stearic acid.

5. The method according to claim 1, wherein the surfactant is added in an amount of 0.1~2.0wt% based on the total weight of the soft magnetic powder and the surfactant.

6. A method for fabricating a wound-type inductor comprising the steps of:

(a) coating a binder onto the shape-controlled soft magnetic powder manufactured in accordance with the method of claim 1 ;

(b) shaping the soft magnetic powder coated with the binder at room temperature;

(c) heat treating the shaped soft magnetic powder; and

(d) winding the heat-treated soft magnetic powder with a copper wire.

7. The method according to claim 6, wherein the binder is at least one compound selected from polyimide and phenol.

8. The method according to claim 6, wherein the amount of the binder is within the range of 0.2~3wt% based on the total weight of the shape-controlled soft magnetic powder and the binder.

9. The method according to claim 6, wherein the heat treatment is ca ried out at a temperature of 50-700 ^°C, and the temperature is elevated at a rate of 10°C or less per minute.

10. A method for fabricating a chip-type inductor comprising the steps of:

(a) coating a binder onto the shape-controlled soft magnetic powder manufactured in accordance with the method of claim 1;

(b) casting the coated soft magnetic powder into green sheets by a doctor blade process;

(c) laminating the cast green sheets;

(d) printing an internal electrode on the laminate of green sheets, and further laminating green sheets thereon;

(e) calcining the laminate of (d) to obtain a sintered body; and (f) forming an external electrode on the sintered body.

11. The method according to claim 10, wherein the binder is at least one organic polymer selected from polyvinylbutyl, mannitol, methylene chloride, oleic acid, polyethylene glycol, toluene and polyimide.

12. The method according to claim 10, wherein the binder is added to the soft magnetic powder at a ratio of 1 : 1 to 1 : 1.4 (binder: soft magnetic powder (wt%)).

13. The method according to claim 10, wherein the internal electrode is made of at least one material selected from aluminum, mercury, polypyrrole, polyacetylene and polyphenylene.

14. The method according to claim 10, wherein the calcining is carried out at 50-700 ^°C .