JPH07272919A - Oxide magnetic material and inductor using the same - Google Patents

Abstract

PURPOSE:To provide an oxide magnetic material, where the temperature coefficient of permeability is negative, and an inductor using it, where dispersion of inductance is small. CONSTITUTION:The composition rate of the main ingredients of oxide magnetic material is made a [Ni(1-x).CUx] O.bZnO.cFe2O3(but, x=0.1-0.8, a+b+c=100, b=0-35 (exclusive of 0), c=32-48.5), and Tc is made 100 deg.C or over. Moreover, in a mold-type inductor being gotten by compounding this oxide magnetic material and resin, the sectional area of the magnetic core of the oxide magnetic material is in the range of 100mm<2> or under, and crystal grains are 100 pieces or more in all, and the average crystal grain diameter is in the range of 0.4-20mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide magnetic material used in various electronic parts and an inductor using the same.

[0002]

2. Description of the Related Art At present, electronic parts such as inductors are being miniaturized and surface mounted. For example, an inductor having an element shape in which a magnetic core material and a copper wire are arranged and molded with a resin or the like to facilitate surface mounting has been industrialized.

Conventionally, this kind of magnetic core material has higher electric resistance and excellent frequency characteristics as compared with a metal material. Therefore, Mn-Zn ferrite, Ni-Zn ferrite, and Mn-Mg-Zn are used. Spinel type ferrite magnetic materials represented by the system ferrite have been used.
For these spinel-type ferrites, a material having higher magnetic permeability is useful, especially when there is no restriction by frequency. In addition, as an inductor formed by combining these ferrite magnetic materials and resin, an inductor whose inductance temperature change is zero or positive is used, so ferrite has a zero or positive temperature coefficient of magnetic permeability. Materials are used.

However, when ferrite having a positive temperature coefficient of magnetic permeability is used as the magnetic core material of the inductor, the stress generated in the ferrite due to the difference in thermal expansion coefficient between the composite resin and the ferrite causes However, there is a drawback that the variation of the inductance becomes extremely large.

At present, in order to reduce this variation, a method of reducing the variation in stress applied to the ferrite and reducing the variation range of the inductance of the element has been devised by a method in which the resin is multilayered. However, this method is not preferable as a manufacturing process because it requires many treatment steps. Therefore, from the above, industrially, a manufacturing method in which the ferrite magnetic material is directly compounded, for example, by directly molding a resin, and the change in the inductance of the inductor can be reduced is extremely useful.

By the way, the spinel type ferrite used for such an inductor has an easy magnetization direction with respect to a direction equivalent to [111] of the crystal axis. Further, it has a polycrystalline structure in which crystal grains having different directions are aggregated. Therefore, in an inductor using such spinel ferrite, the distribution of each crystal grain of ferrite in the easy magnetization direction has a great influence on the characteristics of the inductor.

That is, when the total number of crystal grains occupying the cross section of the magnetic core decreases, the overall variation in the easy magnetization direction of the crystal grains with respect to the magnetization direction of the magnetic core increases. Such an element has a large inductance variation, which is industrially disadvantageous. On the other hand, when the total number of crystal grains increases, the overall variation in the easy magnetization direction of the crystal grains with respect to the magnetization direction of the magnetic core decreases. As a result, the variation of the inductance is significantly reduced, which is very useful in industry.

When an inductor is manufactured in a manufacturing process in which a resin is directly molded into a ferrite magnetic material to form a composite, the minimum limit of the shape that can be manufactured is a cross-sectional area of about 0.4 m.
m ² . Therefore, when sintering such an extremely small ferrite, control of the crystal grain size becomes more important. This is because when the sintered body after sintering has a fine crystal grain size, usually, sintering is not progressing and a sufficient density is often not obtained. In such a state, one of the material properties is This is because the magnetic permeability is extremely low. Further, this is because such a sintered body has water absorbency and the characteristics (impedance, inductance) of the element may change depending on the use environment, which is industrially disadvantageous.

On the other hand, when the crystal grain size is large, the total number of crystal grains occupying the ferrite magnetic core cross section decreases,
The variation in the easy magnetization direction of the crystal grains with respect to the magnetization direction of the magnetic core increases, which causes a large variation in the inductance of the element, which is industrially disadvantageous.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides an inductor having a small temperature change and a small variation in the inductance when the inductor is formed by compounding a spinel type ferrite and a resin without performing a multilayer process. The purpose is.

[0011]

As a result of various studies, the present inventor has made negative the temperature coefficient of the spinel type Ni-based ferrite used as a magnetic core material, thereby making the temperature of the inductance of the resin mold type inductor smaller. It has been found that the changes can be significantly reduced.

At this time, in order to make the temperature coefficient of the above-mentioned spinel type Ni-based ferrite negative, the ratio of its main components is expressed by the formula a.
In _{[Ni (1-x) ·} Cu x] O · bZnO · cFe 2 O 3, x = 0.1~0.8, a + b + c = 100, b = 0
It was found that it is necessary to specify the composition as ˜35 and c = 32 to 48.5, and when the operating temperature of the inductor is taken into consideration, the Curie temperature Tc needs to be 100 ° C. or higher.

When an inductor is constructed using this spinel ferrite core, the crystal grain size occupying the magnetic core cross-section is 0.4 to 20 μm, and the total number of crystal grains is 100 or more, so that the inductance is reduced. It was found that it is possible to reduce the variation of the above and suppress the decrease.

[0014] That is, according to the present invention, the composition ratio of the main component has the formula _{a [Ni (1-x)} · Cu x] O · bZnO · cFe 2 O
₃ (However, x = 0.1 to 0.8, a + b + c = 100,
An oxide magnetic material represented by b = 0 to 35 (not including 0) and c = 32 to 48.5 and having Tc of 100 ° C. or higher is obtained.

Further, according to the present invention, in the mold type inductor formed by compounding the oxide magnetic material and the resin, the area of the magnetic core cross section of the oxide magnetic material is 10 or less.
In the range of 0 mm ² or less, the total number of crystal grains is 100 or more, and the average grain size is in the range of 0.4 to 20 μm.

Here, in the above composition formula, x = 0.
The reason for setting 1 to 0.8 is that the temperature coefficient of magnetic permeability of the ferrite magnetic material is negative in this range. Also, b = 0
.About.35 (not including 0) means that .mu. Improves with an increase in b, shows a maximum at 35, and above that, in addition to a decrease in .mu. This is because you cannot expect it. The reason for setting c = 32 to 48.5 is that the temperature coefficient of magnetic permeability is negative at 48.5 or less, and the loss coefficient tan δ becomes large at 32 or less. In addition, the reason why the Tc of the ferrite material is 100 ° C. or higher is that a significant decrease in μ occurs between a temperature 20 ° C. lower than Tc and Tc, so when designing a temperature rise of 80 ° C. This is because 100 ° C. or higher is required.

Further, the total number of crystal grains occupying the ferrite magnetic core cross-section is set to 100 or more. In this range, the variation in the easy magnetization direction of the crystal grains with respect to the magnetization direction of the magnetic core becomes large, and the variation of the inductance changes. This is because it becomes larger. Further, the crystal grain size occupying the ferrite magnetic core cross-section is set to 0.
The reason why it is set to 4 to 20 μm is that if it is less than 0.4 μm, a sufficient sintered body density cannot be obtained and the magnetic permeability decreases. On the other hand, if the crystal grain size exceeds 20 μm, the total number of crystal grains that occupy the magnetic core cross-section will be less than 100, and the inductance will fluctuate greatly. or,
The reason why the area of the magnetic core cross-section is 100 mm ² or less is that the variation and reduction of the inductance can be suppressed in this range.

[0018]

The composition of the main components is limited to obtain an oxide magnetic material which is a Ni-based ferrite in which the change in magnetic permeability with temperature is negative, and a resin is molded on the oxide magnetic material to obtain an inductor. This inductor has a small change in inductance with temperature. It is presumed that this is because the negative temperature change of the ferrite itself can reduce the change in the magnetic permeability related to the stress generated in the ferrite due to the difference in the coefficient of thermal expansion between the ferrite and the resin.

Further, in the above inductor, by increasing the total number of crystals in the ferrite magnetic core cross section and limiting the average crystal grain size, it is possible to reduce the overall variation in the easy magnetization direction of the crystal grains. It seems that the fluctuation of

[0020]

EXAMPLES The present invention will be described below with reference to examples.

Example 1 Iron oxide (α-Fe ₂ O ₃ ), nickel oxide (NiO), cupric oxide (CuO) and zinc oxide (ZnO) were used as raw materials, and the chemical composition ratio was 23 [Ni
Represented by _{(1-x) · Cu x} ] O · 30ZnO · 47Fe 2 O 3, x is 0,0.1,0.2,0.3,0.4,0.
The amounts were changed to 5, 0.6, 0.7, 0.8, 0.9 and 1.0, weighed so that the respective compositions were obtained, and wet mixed in a ball mill for 20 hours. Next, these raw material powders are calcined in the air at 800 ° C. for 2 hours, and then 2
It was wet-milled for 0 hours.

Next, 1 wt% of PVA was added to this pulverized powder and wet-mixed to obtain a molding powder. This powder is pressed at a pressure of 2t
A mold was used to perform compression molding so as to obtain a ring-shaped molded body having an outer diameter of about 18 mm, an inner diameter of about 12 mm, and a height of about 7 mm at on / cm ² . The obtained molded body was held at 1000 ° C. for 4 hours in the air with slow heating and furnace cooling, and sintered.

Next, an insulation-coated copper wire having a diameter of 0.26 mm was wound 10 times on this sintered body, and then 100 k in the range of 0 ° C. to 60 ° C. using an impedance analyzer made by YHP.
The magnetic permeability μ was measured by applying a current of Hz and 1 mA. or,
The temperature change rate Δμ _T of μ was determined. Note that Δμ _T is 0 to 6
Μ of temperature change of ferrite magnetic material at 0 ℃
It is standardized at (20 ° C.), and the rate of change with respect to 1 ° C. is obtained, which is expressed by Equation 1.

[0024]

[Equation 1]

Here, μ (60 ° C.) is 1 at 60 ° C.
The magnetic permeability μ (0 ° C.) at 00 kHz is 10 at 0 ° C.
It represents the magnetic permeability at 0 kHz. Therefore, in equation 1,
When μ _T is negative, it is understood that μ is a ferrite material exhibiting negative temperature characteristics.

FIG. 1 shows the relationship between the magnetic permeability μ (20 ° C.) and Δμ _T of the sintered body at 20 ° C. with respect to the composition value x of CuO. It can be seen that Δμ _T is negative when x is in the range of 0.1 to 0.8.

Example 2 A sintered body was produced in the same procedure as in Example 1 except for the chemical composition ratio. The chemical composition ratio is (5
3-b) (Ni _0.7・ Cu _0.3 ) O ・ bZnO ・ 47Fe
₂ O ₃ and b is 0, 5, 10, 15, 20, 25, ₃
It was changed to 0, 35, 40. After obtaining a ring-shaped ferrite sintered body by the same procedure as in Example 1, the magnetic permeability was measured at 100 kHz and 1 mA over the range of 0 to 60 ° C., and μ (20 ° C.) and Δμ _T were obtained. It was A differential scanning calorimeter was used for a sintered body having b of 25 or less, and Tc was determined by measuring a temperature change of μ by heating in a constant temperature bath for b of 30 or more.

The results are shown in FIG. Δμ _T is negative over the entire range of this example. Tc is Zn
It decreases linearly as the O composition value b increases. μ
(20 ° C.) improves with an increase in b, and shows a maximum at 35. Therefore, the range of b of 0 to 35 is industrially useful.

Example 3 A sintered body was produced in the same procedure as in Example 1 except for the chemical composition ratio. The chemical composition ratio is (7
0-c) (Ni _0.7 · Cu _0.3 ) O · 30 ZnO · CFe
₂ O ₃ and c is 30, 35, 40, 45, 46, 47,
It was changed to 48, 49. After obtaining a ring-shaped ferrite sintered body by the same procedure as in Example 1, the magnetic permeability was measured at 100 kHz and 1 mA over the range of 0 ° C to 60 ° C, and µ (20 ° C) and Δμ _T were measured. I asked. At this time, the loss coefficient tan δ was also determined at the same time.

The results are shown in FIG. The composition value c of Fe ₂ O ₃ is 48.5 or less, and Δμ _T is negative. On the other hand, tan δ becomes significantly higher when c is 48.5 or more,
Further, even if it is 32 or less, it clearly shows a high value. μ (20
C) increases with the increase of c. Therefore, c is in the range of 32 to 48.5 that is useful as the magnetic core characteristics.

(Embodiment 4) By the same procedure as in Embodiment 2,
Chemical composition ratio (53-b) (Ni _0.7 · Cu _0.3 ) O · bZ
In nO · 47Fe ₂ O ₃ , b was changed to obtain a Ni—Cu—Zn based ferrite sintered body having Δμ _T of 0.05, 0, −0.05, −0.12, −0.25. Outer diameter 1m
m, and processed into a rod shape having a length of 3 mm.

Next, an insulation-coated copper wire having a diameter of 30 μm was wound 150 times on these processed bodies and injection-molded at 150 ° C. using a polyester-based resin and an epoxy-based resin. A rectangular parallelepiped molded inductor having a width of 1.5 mm and a length of 3.5 mm was manufactured.

Further, a current of 0.1 mA was applied at 500 kHz, and the inductance of these obtained inductors in the range of -20 ° C to 80 ° C was measured using an impedance analyzer made by YHP. Also, -20 ℃
The temperature change of the inductance at -80 ° C was standardized by the inductance at 20 ° C to obtain the inductance change rate ΔL (%). It should be noted that ΔL was calculated by the equation (2).

[0034]

[Equation 2]

Here, L (-20 ° C) is the inductance at -20 ° C, L (20 ° C) is the inductance at 20 ° C, and L (80 ° C) is the inductance at 80 ° C.

FIG. 4 shows the relationship between the temperature change rate ΔL of these mold type inductors and the temperature change rate Δμ _T of the ferrite material. It can be seen that the temperature change of the molded inductor is significantly small in the region where the temperature change Δμ _T of the ferrite material is negative.

(Embodiment 5) By the same procedure as in Embodiment 1, the chemical composition ratio is 23 (Ni _0.8 .Cu _0.2 ) O.30 ZnO.
A compression molded body of 47Fe ₂ O ₃ was obtained and sintered at a temperature of 1100 ° C. to prepare a sintered body having an average crystal grain size of 20 μm.

Next, the obtained sintered body has the same dimensions in the vertical and horizontal directions and is 0.15, 0.18, 0.20 and 0.2, respectively.
Six types of rectangular parallelepipeds having a length of 5, 0.30, 0.40 mm and a length of 2 mm were processed, and 10 samples were obtained for each type.

Further, when the total number of crystal grains occupying the cross section of the sintered body was observed for each type of sample using an optical microscope, 65, 80, 100, 160, 230, respectively.
It was 400 pieces.

Furthermore, after insulating-coated copper wire having a diameter of 30 μm was wound 50 times on these samples, injection molding was performed with an epoxy resin at 150 ° C., and the shape was 1.2 mm × 1.2 mm ×.
A 3.5 mm rectangular parallelepiped molded inductor was produced.

Then, a current of 0.1 mA was passed at 500 kHz, and the inductance at 20 ° C. was measured using an impedance analyzer made by YHP.

The results are shown in FIG. The results are shown by the relationship between the total number of crystal grains in the cross section of the ferrite core and the ratio of the variation (σ _n-1 ) to the average value (L _a ) of the inductance. When the total number of crystal grains occupying the ferrite magnetic core cross section is 100 or more, the variation in inductance is remarkably reduced. Therefore, by limiting the total number of crystal grains in the cross section of the magnetic core, the quality of the inductor is improved, which is very useful industrially.

Example 6 A sample was prepared in the same procedure as in Example 5. That is, the chemical composition ratio is 23 (Ni _0.8 · Cu
_0.2 ) O.30ZnO.47Fe ₂ O ₃ was subjected to a predetermined procedure to obtain a compression molded body, and this compression molded body was sintered, and the average crystal grain size was 0.2, 0.3, 0.4, 0. .5, 0.
6,0.7,15.0,20.0,25.0,30.0
A sintered body having a thickness of μm was produced. Further, these sintered bodies were processed to prepare 10 samples each having a shape of 0.2 mm × 0.2 mm × 2 mm. Diameter 3 for these samples
After winding a 0 μm insulating coated copper wire 50 times, it was injection molded with an epoxy resin at 150 ° C., and the shape was 1.2 mm × 1.
A 2 mm x 3.5 mm rectangular parallelepiped mold type micro inductor was produced.

Next, a current of 0.1 mA was passed at 500 kHz, and the inductance at 20 ° C. was measured using an impedance analyzer made by YHP.

The results are shown in FIG. The results show that the average crystal grain size of the ferrite magnetic core cross-section and the variation in the inductance and the average value (L _a ) of the inductance (σ
_n-1 ). When the average crystal grain size of the ferrite magnetic core cross-section is less than 0.4 μm, a reduction in inductance is confirmed. Further, when the thickness is 20.0 μm or less, the variation in the inductance is remarkably reduced. Therefore, it is understood that the average crystal grain size of 0.4 to 20 μm is effective.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments.
Various changes are possible.

For example, the main components are NiO, CuO, Zn
If it is composed of O, Fe ₂ O ₃ , Co, Mn, C
It is within the scope of the present invention whether it contains additives such as a, Cr, Al or Ti, or contains impurities contained in the raw material.

Further, in the manufacturing method, although the powder is calcined and the molded body is sintered in the air in this embodiment, if the sintered body after sintering is a spinel type ferrite, it is calcined. Even if the none method, coprecipitation method, hydrothermal synthesis method, spray roasting method, etc. are applied, they are within the scope of the present invention. Also, the method for molding the molded body is not particularly limited.

In this embodiment, a rectangular parallelepiped inductor having a ferrite magnetic core cross-sectional area of 0.4 mm ² has been described, but even if the element has a shape other than this, the total number of crystal grains is 100 or more. If the average crystal grain size is in the range of 0.4 to 20 μm, the same effect can be obtained.

[0050]

As it can be seen from the above embodiments according to the present invention, the present invention, the composition ratio of main component, wherein _{a [Ni (1-x)} · Cu x]
Indicated by _{O · bZnO · cFe 2 O 3} , x = 0.1~0.
8, a + b + c = 100, b = 0 to 35 (not including 0), and c = 32 to 48.5.
It is possible to obtain an oxide magnetic material having a negative μ _T and a small loss. Further, by using an oxide magnetic material having a negative temperature change rate Δμ _{T of} magnetic permeability, the temperature change of the mold type inductor can be remarkably reduced.

Further, by setting the total number of crystal grains occupying the ferrite magnetic core cross section of these inductors to 100 or more and setting the crystal grain size to 0.4 to 20 μm, it is possible to reduce the variation and reduction of the inductance. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between μ (20 ° C.) and Δμ _T of a ferrite sintered body with respect to a composition value x of CuO in Example 1.

FIG. 2 is a diagram showing a relationship between μ (20 ° C.), Tc and Δμ _T of a ferrite sintered body with respect to a composition value b of ZnO in Example 2.

[Figure 3] mu (20 ° C.) of the ferrite sintered body with respect to the composition value c of FeO ₃ in Example 3, tan [delta and △ mu _T
FIG.

FIG. 4 is a ΔL of the molded inductor according to the fourth embodiment.
FIG. 5 is a diagram showing the relationship between Δμ _T and the ferrite magnetic material.

FIG. 5 is a diagram showing the relationship between the total number of crystal grains in the ferrite magnetic core cross section of the inductor of Example 5 and the ratio of variation (σ _n−1 ) to the average value (L _a ) of inductance.

FIG. 6 is a diagram showing the relationship between the average crystal grain size of the ferrite magnetic core cross-section of the inductor of Example 6 and the ratio of the inductance and the variation (σ _n−1 ) to the average value (L _a ) of the inductance.

[Explanation of symbols]

 1 Polyester resin 2 Epoxy resin

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01F 17/04 F 8123-5E 27/32 A C04B 35/30 Z

Claims (2)

[Claims] 1. The composition ratio of the main components is expressed by the formula a [Ni _(1-x) .C.
u _x ] O.bZnO.cFe ₂ O ₃ [where x = 0.1
0.8, a + b + c = 100, b = 0 to 35 (not including 0), c = 32 to 48.5], and the Curie temperature is 100 ° C. or higher. Magnetic material. 2. A mold-type inductor formed by combining the oxide magnetic material according to claim 1 and a resin,
The area of the magnetic core cross section of the oxide magnetic material is 100 mm ^2.
In the following range, the total number of crystal grains is 100 or more, and the average crystal grain size is in the range of 0.4 to 20 μm.