JP2008016619A - Ferrite magnetic core and electronic component using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferrite magnetic core which has superior direct current superposition characteristics, proper magnetic characteristics with respect to stresses, and little variations in the magnetic permeability, in particular, and which is capable of obtaining stable inductance, and to provide an electronic component that uses this. <P>SOLUTION: There is provided a ferrite magnetic core that uses a compound magnetic substance comprising the first phase of ferrite containing Fe<SB>2</SB>O<SB>3</SB>, NiO (a part thereof may be substituted with CuO), and ZnO as major components and a second phase consisting of nonmagnetic ceramics. The core contains 2.5-25 wt.% of nonmagnetic ceramics, relative to the main components. In the core, an average ferrite crystal grain diameter is 0.3-2 μm, the linear expansion coefficient for nonmagnetic ceramics is smaller than the linear expansion coefficient for ferrite, and the linear expansion coefficient of the compound magnetic substance is 6-10 ppm/°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a ferrite magnetic core used as a chip inductor, in particular, a resin-molded inductor, a multilayer inductor having a metal conductor inside or outside, and a mounting electrode so that a semiconductor element can be mounted thereon. The present invention relates to an electronic component such as a module (composite component) mounted with a provided ferrite substrate, a semiconductor element, and another reactance element.

  Switching power supplies such as DCDC converters used in small electronic devices such as mobile phones, personal digital assistants (PDAs), notebook computers, and digital cameras are becoming increasingly smaller and lighter in recent years, and the operating frequency is also higher. Heading to. For this reason, there is an increasing demand for downsizing, weight reduction, and high performance of electronic components that constitute electric circuits. Ferrite cores used in such applications are required to exhibit non-linear characteristics with respect to the DC current value that flows superimposed on the windings. There is a demand for a stable inductance element and ferrite substrate having excellent DC superimposition characteristics.

  The ferrite composition used for such a ferrite core is desired to have a magnetic property that it is not easily saturated even in a high magnetic field by applying a large current, that is, has a high saturation magnetic flux density. As a ferrite composition having a high saturation magnetic flux density (Bs), MnZn-based ferrite is known. However, since electric resistance is low and direct winding cannot be performed, it is difficult to cope with downsizing and thinning. Therefore, although the absolute value of Bs is relatively lower than that of MnZn-based ferrite, NiZn-based ferrite and NiCuZn-based ferrite that have high electrical resistance and can be directly wound are often used.

  On the other hand, in order to improve the inductance value when DC is superimposed, a magnetic gap is arranged in the magnetic circuit of the ferrite core. For example, in the case of an open magnetic circuit type inductance element using a ferrite magnetic core as a drum magnetic core, or in the case of an EI magnetic core, the I-type magnetic core and the abutting surface side of the middle leg of the E-type magnetic core are more A magnetic gap is formed by forming a step and sandwiching a non-magnetic gap sheet such as paper or resin in a gap formed between the I-type magnetic core. In a multilayer inductor, a non-magnetic layer (for example, dielectric ceramics) is laminated between magnetic layers, or a gap is formed by eliminating carbon paste to form a magnetic gap. It is a magnetic path type inductance element.

  Thus, when providing a magnetic gap by devising the magnetic core shape or the like, a complicatedly shaped die is required, and it is also necessary to precisely process the magnetic core. However, in the present situation where the ferrite core itself is downsized, the processing becomes more difficult and there is a problem that the number of processes and facilities increases. In addition, in the case of a multilayer inductor, it is necessary to use two or more kinds of different materials in a stacked manner, and there is a problem that delamination (delamination) occurs between different material layers due to a decrease in adhesiveness. .

Therefore, in recent years, methods have been studied that can improve DC superposition characteristics even in a closed magnetic circuit structure without a magnetic gap. For example, Patent Document 1 discloses that an inductance element is configured without adding a magnetic gap in a magnetic path by adding 0.1 wt% to 25 wt% of ZrO ₂ to Ni—Zn ferrite. ing.
Patent Document 2 discloses a ferrite powder mainly composed of Fe ₂ O ₃ , ZnO, CuO, and NiO, silicon (Si) powder, silica (SiO ₂ ) powder, alumina (Al ₂ O ₃ ) powder, and the like. Add and mix a small amount (several wt% or less), sinter, improve the direct current superposition characteristics of the material itself without damaging the original magnetic properties of the magnetic material, so that no magnetic gap is formed in the magnetic circuit A ferrite sintered body is disclosed.
Further, although there is no direct disclosure of the improvement of the DC superposition characteristics, Patent Document 3 discloses Fe ₂ O ₃ 40 to 52.5 mol%, ZnO 35 mol% or less, CuO 2 to 20 mol%, and the balance for the purpose of improving the mechanical strength. Is composed of NiO as a main component, and 0.01 to 3.0 wt% of zirconium oxide (ZrO ₂ ) or a salt containing a considerable amount of zirconium atoms is added thereto. In the comparative example, it is disclosed that when 10 wt% of zirconium oxide (ZrO ₂ ) is added, the initial permeability at 1 MHz is about ¼ compared with that without addition, and DC superposition characteristics can be improved. Has been suggested.
JP 2003-112968 A JP 2005-145781 A JP 07-133150 A

Generally, it is known that the magnetic permeability changes when a magnetic material is strained. This is a phenomenon called a magnetostrictive effect, and a change in magnetic permeability similarly occurs in the ferrite composition. Factors that cause distortion include, for example, the compressive stress generated when the resin shrinks when the ferrite core is molded with resin, and the difference in linear expansion coefficient between the ferrite core and the printed circuit board when soldered to the printed circuit board. There is a stress caused by.
The multilayer inductor was obtained by laminating and integrating a magnetic sheet or magnetic paste made of ferrite and a conductive paste for internal electrodes made of Ag or an Ag alloy by a thick film lamination technique, and then firing. The external electrode paste is printed or transferred to the surface of the fired body and then baked. The magnetic layer is subjected to stress due to a difference in linear expansion coefficient from the internal electrode. Further, when plating is performed, there is stress from a plating film or the like.
Thus, residual stress exists inside the ferrite core exposed to various stresses. As a result, the magnetic permeability of the ferrite is lowered by the magnetostrictive effect, and a desired inductance may not be obtained. .

According to the prior art in which the magnetic path is microscopically divided by a non-magnetic material such as ZrO ₂ , a higher magnetic permeability can be obtained even in a high magnetic field by applying a large current than when a non-magnetic material is not included. It can be said that this is an effective means for improving the DC superposition characteristics. However, no consideration was given to changes in magnetic properties with respect to stress.
SUMMARY OF THE INVENTION An object of the present invention is to provide a ferrite core that is excellent in direct current superposition characteristics, has little change in magnetic characteristics with respect to stress, particularly magnetic permeability, and can provide a stable inductance, and an electronic component using the same.

The present invention provides a composite magnetic material comprising a first phase of ferrite mainly composed of Fe ₂ O ₃ , NiO (partially substituted with CuO) and ZnO and a second phase composed of nonmagnetic ceramics. The ferrite core used includes 2.5 to 25 wt% of nonmagnetic ceramic with respect to the main component, the ferrite average crystal grain size is 0.3 to 2 μm, and the linear expansion coefficient of the nonmagnetic ceramic. Is a ferrite magnetic core that is smaller than the linear expansion coefficient of the ferrite, and that the composite magnetic body has a linear expansion coefficient of 6 to 10 ppm / ° C.
Ceramic nonmagnetic constituting the second phase, ZrSiO ₄ (zircon), ZrO _{2 (zirconia), Li 2 O · Al 2} O 3 · 4SiO 2 ( _{Supodeyumen), Li 2 O · Al 2} O 3 · 2SiO ₂ (eucryptite) is preferred.
Also, the ferrite constituting the first _{phase, Fe 2 O 3: 47~50.5mol%} , ZnO: 19~30mol% ( may be substituted following 15 mol% in CuO), the main component the remainder NiO Are preferred. Further, as subcomponents, Nb ₂ O ₅ , Ta ₂ O ₅ . V ₂ O ₅ , TiO ₂ , Bi ₂ O ₃ , Co ₃ O ₄ , SnO ₂ , CaO, and SiO ₂ may be contained in an amount of 1.5 wt% or less. These subcomponents precipitate at the crystal grain boundaries to promote sinterability, or dissolve at the crystal grain boundaries to improve the magnetocrystalline anisotropy.

  A second invention is an electronic component characterized in that in the ferrite magnetic core of the first invention, a line is formed therein to form an inductor. It is preferable to provide a terminal electrode connected to the line on the surface of the ferrite magnetic core. It is also preferable that a semiconductor element is mounted on the surface of the magnetic body and connected to the terminal electrode.

  According to the present invention, it is possible to provide a ferrite core that is excellent in direct current superposition characteristics, has little change in magnetic characteristics with respect to stress, in particular, magnetic permeability, and can provide a stable inductance, and an electronic component using the same.

The best mode for carrying out the invention will be described below.
In the present invention, a ferrite calcined body mainly composed of Fe ₂ O ₃ , ZnO, NiO (a part of which may be replaced with CuO) is classified by adjusting the grinding conditions or by classifying the ground powder. A ferrite powder having a BET specific surface area of 5 to ²⁰ m ² / g obtained by spray roasting an aqueous solution of each of chlorides of Fe, Ni and Zn and nonmagnetic ceramics are mixed into a predetermined shape. The formed molded body is fired at a temperature of 1000 ° C. or less, and a first phase of ferrite mainly composed of Fe ₂ O ₃ , ZnO, NiO (a part of which may be replaced by CuO), and non- A ferrite core in which the second phase composed of magnetic ceramics coexists in the structure is obtained.

In the present invention, the ferrite composition constituting the first phase is mainly composed of Fe ₂ O ₃ , ZnO, NiO (part of which may be replaced with CuO), and further, Nb as a subcomponent. , Ta, V, Ti, Bi, Co, Sn, Ca, Si may be included. The ferrite constituting the first phase is mainly composed of Fe ₂ O ₃ : 47 to 50.5 mol%, ZnO: 19 to 30 mol%, and the balance NiO (15 mol% or less may be replaced with CuO). preferable.

In the ferrite composition according to the present invention, the reason why Fe is contained in an amount of 47 to 50.5 mol% in terms of Fe ₂ O ₃ is to obtain a high saturation magnetic flux density Bs without reducing the magnetic permeability. If it is less than 47 mol%, the desired magnetic permeability and saturation magnetic flux density cannot be obtained, and if it exceeds 50.5 mol%, there is a problem that the resistance value decreases due to an increase in Fe ²⁺ .
The reason why Zn is contained in an amount of 19 to 30 mol% in terms of ZnO is to obtain a high saturation magnetic flux density. If it is less than 19 mol%, the desired magnetic flux density cannot be obtained, and if it exceeds 30 mol%, the Curie temperature is lowered, resulting in a problem that it falls below the practical temperature range. For the purpose of low-temperature sintering, a part of Ni may be replaced with Cu by 15 mol% or less (CuO conversion). Ni is the remainder obtained by subtracting the Fe ₂ O ₃ amount and the ZnO amount from the main component composition. In order to obtain a high saturation magnetic flux density while obtaining a desired magnetic permeability, the NiO / CuO molar ratio is preferably set to 0.3 to 5.8.

In the ferrite composition according to the present invention, Nb, Ta, V, Ti, Bi, Co, Sn, Ca, and Si oxides are further added as subcomponents to Nb ₂ O ₅ , Ta ₂ O ₅ , and V ₂ , respectively. In terms of O ₅ , TiO ₂ , Bi ₂ O ₃ , Co ₃ O ₄ , SnO ₂ , CaO, SiO ₂ , Nb ₂ O ₅ : 0.01 to 1.0 wt%, Ta ₂ O ₅ : 0.1 to 1 _{.5wt%, V 2 O 5:} 0.1~1.5wt%, TiO 2: 0.1~1.5wt%, Bi 2 O 3: 0.1~1.5wt%, Co 3 O 4: 0 _{.1~1.5wt%, SnO 2: 0.1~1.5wt%} , CaO: 0.1~1.5wt%, SiO 2: may contain 0.1~1.5wt%.
If Nb is contained as an auxiliary component in an amount of 0.01 to 1.0 wt% in terms of Nb ₂ O ₅ , the effect of controlling the crystal grain size is obtained. The Ta by containing 0.01 to 1.0% by _Ta 2 _{O 5} in terms, it is possible to improve the resistivity. The resistivity can be improved by containing 0.01 to 2.0 wt% of Ti in terms of TiO. The reason why V is contained in an amount of 0.1 to 1.5 wt% in terms of V ₂ O ₅ is to promote low-temperature sintering. The reason why Bi is contained in an amount of 0.1 to 1.5 wt% in terms of Bi ₂ O ₃ is to promote low temperature sintering and improve resistivity. The reason why Co is contained in an amount of 0.1 to 1.5 wt% in terms of Co ₃ O ₄ is to reduce high-frequency loss. The reason for containing 0.1 to 1.5 wt% of Sn in terms of SnO ₂ is to reduce hysteresis loss. The reason why Ca is contained in an amount of 0.1 to 1.5 wt% in terms of CaO is to suppress grain growth. The reason why Si is contained in an amount of 0.1 to 1.5 wt% in terms of SiO ₂ is to suppress grain growth.

When these subcomponents are more than a predetermined amount, there are problems that the low temperature sinterability is hindered, the sintered density is lowered, and the mechanical strength (bending strength) is lowered. In addition, when the amount is small, a clear effect due to the addition cannot be obtained. The subcomponents may be added alone or in combination of two or more. In the case of complex addition, the total amount is preferably 5 wt% or less. Even when the total amount exceeds 5 wt%, the sinterability may be hindered.
Inevitable impurities such as Na, S, Cl, P, W, and B that are inevitably contained in the raw material are preferably reduced as much as possible. Inclusion is allowed and is preferably 0.05 wt% or less.

  The content of the main component and subcomponent in the ferrite composition is measured using X-ray fluorescence analysis and ICP emission spectroscopic analysis. The elements contained are qualitatively determined by fluorescent X-ray analysis in advance, and the elements contained are quantified by a calibration curve method based on comparison with a standard sample prepared in advance.

The ferrite composition is provided in a powder state, and the BET specific surface area is preferably 5 to ²⁰ m ² / g. The larger the BET specific surface area, the higher the activity for the reaction. Therefore, the densification is promoted from a low temperature in firing, and the ferrite can be densified even at a low firing temperature of 1000 ° C. or less. The particle size is small and uniform.
Further, if the BET specific surface area of the ferrite powder is less than 5 m ² / g, the average crystal grain size of ferrite (first phase) in the sintered body may exceed 2 μm, and the BET specific surface area exceeds 20 m ² / g. If it is, it will become easy to aggregate and it will become easy to adsorb | suck a water | moisture content on the powder surface, Therefore Uniform mixing with a nonmagnetic ceramic powder becomes difficult.

In the present invention, the nonmagnetic ceramic constituting the second phase is a ceramic that is poorly reactive with Fe ₂ O ₃ , NiO, ZnO, etc. at the firing temperature, and is ZrSiO ₄ (zircon), ZrO ₂ (zirconia), Li _{2 O · Al 2 O 3 ·} 4SiO 2 ( _{Supodeyumen),} such as _{Li 2 O · Al 2 O 3} · 2SiO 2 ( eucryptite) are exemplified. As the non-magnetic ceramic, it is preferable to use a powder having a BET specific surface area of 5 to ²⁰ m ² / g similarly to the ferrite powder. More preferably, both the ferrite powder and the non-magnetic ceramic powder have a BET specific surface area of 10 m. ² / g or less powder.

When the BET specific surface area of the nonmagnetic ceramic powder is less than 5 m ² / g, the effect of suppressing the grain growth of ferrite is hardly exhibited, and coarse ferrite crystal grains are easily generated. Non-magnetic ceramics do not substantially grow during firing and exist as the second phase, serving as a nucleus that suppresses the grain growth of ferrite constituting the first phase. As a result, ferrite (first phase) is formed in the sintered body. Has an average crystal grain size of 0.3 to 2 μm, and has a structure having no coarse crystal grains of 10 μm or more.
When the nonmagnetic ceramic powder has a BET specific surface area of more than 20 m ² / g, it is easy to agglomerate and moisture is easily adsorbed on the surface of the powder. It becomes difficult to mix uniformly.

  The average crystal grain size of ferrite (first phase) affects the change in initial permeability μi due to internal and external stress. That is, when the average crystal grain size is increased, the domain wall is easily moved, and it is easily affected by stress, and it is difficult to obtain stable characteristics. On the other hand, if the average crystal grain size is too small, the initial permeability μi, the saturation magnetic flux density Bs are lowered, and the coercive force Hc is significantly increased. Therefore, in the present invention, the average crystal grain size is in the range of 0.3 to 2 μm.

  In the first place, the initial permeability (μi) of ferrite is defined by the following formula, but since NiZn ferrite and NiCuZn ferrite have negative magnetostriction constants, the initial permeability μi increases when compressive stress is applied, Maximum under certain stress. And when the compressive stress is further applied, the behavior decreases.

(Equation 1)
μi∝Bs ² / (aK1 + bλsσ)
(Bs = saturation magnetic flux density, K1 = magnetic anisotropy constant, λs = magnetostriction constant, σ = stress, a and b are constants)

According to the above equation, it can be seen that by relaxing the stress on the spinel crystal of ferrite, the stress term σ in the above equation can be reduced, and the reduction of the initial permeability μi can be suppressed. In the present invention, the linear expansion coefficient of the nonmagnetic ceramic is set to be smaller than the linear expansion coefficient of ferrite. For this reason, as the amount of nonmagnetic ceramic added increases, a large tensile stress acts on the ferrite (first phase). The stress on the spinel crystal is relaxed by the action of such tensile stress, and the change in the initial permeability μi with respect to the stress is made slow.
In addition, by relaxing the lattice strain, the magnetic anisotropy constant K1 and the saturation magnetostriction constant λs are reduced. As a result, the deterioration of the initial permeability μi with respect to stress is reduced, and a stable inductance can be obtained.

By the way, the coercive force Hc, which is one of the magnetic characteristics, is determined by the ease of movement of the domain wall by the external magnetic field, such as the size of the crystal grains of the magnetic material, residual strain, grain boundary products, and vacancies in the crystal grains. It is well known that it varies with the amount of structural defects. When the crystal grains are fine or there is residual strain, the frequency of domain wall pinning for magnetization reversal increases, and the coercive force Hc increases. Further, when the crystal grains decrease, the frequency of domain wall pinning increases in the same manner, so that the coercive force Hc increases. In general, the coercive force Hc is known to increase monotonously regardless of the tension and compression of the uniaxial stress. In the present invention, the average crystal grain size of ferrite is made fine. This increases the coercive force Hc. However, the present inventors have found that when the linear expansion coefficient of the nonmagnetic ceramic (second phase) is smaller than the linear expansion coefficient of the ferrite (first phase), the addition amount of the ceramic powder whose coercive force Hc is nonmagnetic It was newly found that it does not increase monotonously but shows a maximum value.
Such a behavior is caused by the fact that the residual strain in the ferrite crystal is reduced by the tensile stress based on the tensile stress, and the lattice constant is changed by relaxing the strain and stress of the ionic arrangement forming the ferrite spinel crystal. it is conceivable that. Although the coercive force Hc is related to the hysteresis loss, the increase in the hysteresis loss can be suppressed. Therefore, the coercive force Hc is effective in preventing a significant increase in the core loss of the ferrite core.

(Example 1)
(Preparation of mixed powder of ferrite and non-magnetic ceramics)
First, constituting the ferrite Fe2 O3, NiO, CuO and the main component of ZnO, and _Co 3 _{O 4,} BiO _2, after SnO 2, and a sub-component of SiO ₂ and dried after wet mixing for 2 hours at 850 ° C. It was calcined. Next, the calcined powder was pulverized with a ball mill for 18 hours until the BET specific surface area became 7.1 m ² / g, and then a predetermined amount of nonmagnetic ceramic having a predetermined BET specific surface area shown in Table 1 was added for 2 hours. Mixing was performed to prepare a calcined mixed powder.
Furthermore, after adding polyvinyl alcohol as a binder to the calcined mixed powder and granulating it with a spray dryer, it is molded into a predetermined shape, and is baked at 950 ° C. for 2 hours in the atmosphere, with an outer diameter of φ14 mm, an inner diameter of φ7 mm, A toroidal magnetic core and a square magnetic core having a thickness of 5 mm were obtained. The obtained samples were evaluated for crystal grain size, initial magnetic permeability μi, magnetic properties such as saturation magnetic flux density Bs, anti-stress properties, and direct current superposition properties. Table 1 shows the evaluation results together with the composition of each sample. In addition, the crystal phase of the sample was identified by X-ray diffraction measurement using Cu-Kα rays. In the table, the sample number attached with * is a comparative example, and the others are examples.
Incidentally, the ferrite _{composition, Fe 2 O 3: 47.5mol%} , NiO: 19.7mol%, CuO: 8.8mol%, ZnO: a 24.0Mol% as a main component, Bi ₂ to this main component O ₃ : 1 wt%, Co ₃ O ₄ : 0.08 wt%, SnO ₂ : 0.5 wt%, SiO ₂ : 0.5 wt% were added and contained as subcomponents (Sample No. 1 in Table 1) .

  In Table 1, the specific gravity and linear expansion coefficient of nonmagnetic ceramics are literature values from physics and chemistry dictionaries. Conversion of volume% (vol%) and mass% (wt%) in the amount of nonmagnetic ceramic added is performed based on the specific gravity.

Hereinafter, the evaluation method for each evaluation item will be briefly described.
(Average grain size of ferrite)
The surface of the ferrite core is photographed with a plurality of samples at a magnification of 5000 using an electron microscope and a plurality of fields of view, and a line of a certain length is drawn on the photograph in an arbitrary direction. Is measured to obtain a value obtained by dividing the length by the number of particles, and the average value is taken as the average crystal grain size. In addition, composition analysis by EPMA or EDX was performed in the same field of view as photography, and non-magnetic ceramics and ferrite crystals were distinguished.

(Initial permeability μi)
A copper wire was wound around the toroidal ferrite core for 7 turns, the inductance was measured using an LCR meter at a measurement frequency of 100 KHz and a measurement current of 1 mA, and the initial permeability μi was calculated using the following equation.
Initial permeability μi = (le × L) / (μ0 × Ae × N ² )
le: Magnetic path length L: Sample inductance, μ0: Vacuum permeability = 4π × 10 ⁻⁷ (H / m)
Ae: cross-sectional area of sample, N: number of turns of coil

(Linear expansion coefficient)
Using the cylindrical sample after sintering, the thermal expansion coefficient was measured from room temperature to 900 ° C., and the average linear thermal expansion coefficient from room temperature to 890 ° C. was calculated.

(Resistivity)
The toroidal ferrite core was cut in half, and the conductive paste was applied to the entire two cut surfaces, dried, and the resistance was measured using an insulation resistance meter between the two surfaces coated with the conductive paste. .
Thereafter, the resistivity was calculated from the measured resistance value and the area and length of the sample.

(Saturation magnetic flux density, residual magnetic flux density, coercivity)
The strength of the magnetic field was set to 4000 A / m, the measurement frequency was set to 10 kHz, and the residual magnetic flux density Br and the coercive force Hc were measured with a BH analyzer.

(Anti-stress characteristics)
After winding a copper wire 12 times on a square magnetic core of 8 mm x 4 mm x 2 mm, this was placed in a pressure jig equipped with a tension meter, and a compressive force was applied from one axial direction, and the inductance value at this time was The measurement was continuously performed, and the inductance change rate was calculated from the obtained measurement value. The inductance change rate was obtained by the following equation.
(L1-L0) / L0 × 100 (%)
L1: Inductance value when uniaxial compressive force is applied
L0: Inductance value without application of uniaxial compressive force

(DC superposition characteristics)
The measurement conditions are in accordance with the measurement conditions of DC superimposing inductance of JISC2514. Under the conditions that the set voltage is 0.1 V and the frequency is 10 kHz, a copper wire is wound around the obtained toroidal core, and then a direct current is applied to the toroidal core. The amount of change in inductance was measured while increasing the amount of current.

As shown in Table 1, among the non-magnetic ceramics, MgO · SiO _{2 (enstatite), CaO · Al 2 O 3} · 2SiO 2 ( _{anorthite), BaO · Al 2 O 3} · 2SiO 2 a (celsian) When used, it reacts with Fe, Zn, Cu, etc., and other crystal phases are precipitated, resulting in problems such as low density, increased coercive force, and increased core loss. In addition, Zr ₂ (WO ₄ ) (PO ₄ ) ₂ (zirconium tungstate phosphate) was decomposed to precipitate tungsten, which caused a significant decrease in specific resistance.
On the other hand, the ZrSiO ₄ (zircon), ZrO _{2 (zirconia), Li 2 O · Al 2} O 3 · 4SiO 2 ( _{Supodeyumen), Li 2 O · Al 2} O 3 · 2SiO 2 ( eucryptite), decomposition, reaction The new crystal phase produced by was not seen.

FIG. 1 shows non-magnetic ceramics: Li ₂ O · Al ₂ O ₃ · 4SiO ₂ (spodumene): sample number 3, Li ₂ O · Al ₂ O ₃ · 2SiO ₂ (eucryptite): sample number 7, ZrO ₂ (zirconia): Sample No. 11, ZrSiO ₄ (Zircon): DC superposition characteristics diagram of sample added with sample No. 15 (Example) and sample not containing nonmagnetic ceramics (Sample No. 1: comparative example) It is.
It can be seen that the direct current superimposition characteristics are improved in all the samples of the examples as compared with the comparative example. Moreover, although there is a difference in the initial value of the inductance value of each sample (applied magnetic field 0 A / m), Li ₂ O.Al ₂ O ₃ .4SiO ₂ (spodumene), ZrO ₂ (zirconia), ZrSiO ₄ (zircon) Shows a relationship with the coefficient of linear expansion of non-magnetic ceramics. The smaller the difference in coefficient of linear expansion from ferrite, the smaller the tensile stress acting on the ferrite, so the lowering of the permeability is suppressed, and it is relatively large. Indicates the inductance value. Li ₂ O.Al ₂ O ₃ .2SiO ₂ (eucryptite) having a negative linear expansion coefficient behaves differently from the above description from other nonmagnetic ceramics. The reason for this is not clear, but it is also assumed that a compressive stress is applied to the ferrite, and it is considered that the compressive stress and the tensile stress are offset and a relatively high inductance value is exhibited.

  FIG. 2 is a diagram showing the anti-stress characteristic of the inductance. Compared with the sample of the comparative example, it can be seen that the sample of the example has a low rate of change in inductance and is excellent in anti-stress characteristics. Moreover, when the behavior of the change rate of the inductance with respect to a compressive stress is seen, it turns out that the big tensile stress is acting on the ferrite in the sample of an Example compared with the sample of a comparative example.

  FIG. 3 is a coercivity characteristic diagram with respect to the addition amount of nonmagnetic ceramics. It can be seen that the coercive force Hc does not increase monotonously with the addition amount of the nonmagnetic ceramic powder, but shows a maximum value. When the ferrite constituting the first phase is in the composition range described above, the coercive force is 1300 A / m at the maximum, and the ferrite core of the present invention is exclusively used in a closed magnetic circuit. ) Has a coercive force larger than that of only the above structure, but there is no practical problem.

(Example 2)
Next, a multilayer electronic component constructed using the ferrite magnetic core according to the present invention will be described.
The multilayer electronic component of the present invention is formed by multilayerly laminating a magnetic ferrite layer and internal electrodes, and the magnetic ferrite layer is mainly composed of Fe ₂ O ₃ , NiO (a part of which may be replaced with CuO), and ZnO. The composite magnetic material includes a first phase of ferrite as a component and a second phase composed of nonmagnetic ceramics.
FIG. 4 is an internally transparent perspective view showing an example of a multilayer chip inductor which is an embodiment of the multilayer electronic component of the present invention. The multilayer chip inductor 1 has a multilayer structure in which magnetic ferrite layers 2 and internal electrodes 3 are alternately laminated and integrated, and external electrodes 5 and 5 electrically connected to the internal electrode 3 are provided at the ends thereof. Is provided.
The magnetic ferrite layer 2 constituting the multilayer chip inductor is composed of the ferrite composition disclosed in Example 1 and nonmagnetic ceramics. As the ferrite composition, Fe ₂ O ₃ : 47.5 mol%, NiO: 19.7 mol%, CuO: 8.8 mol%, ZnO: 24.0 mol% as main components, Bi ₂ O ₃ : 1 wt%, Co ₃ O ₄ : 0.08 wt%, SnO _{2: 0.5wt%,} SiO _2: a 0.5 wt% and a subcomponent, a further non-magnetic ceramics, ZrSiO ₄ (zircon), ZrO _{2 (zirconia), Li 2 O · Al 2} O 3 · 4SiO ₂ including _{(Supodeyumen), Li 2 O · Al 2} O 3 · 2SiO 2 ( eucryptite).
This mixed powder is kneaded in a ball mill with a binder mainly composed of polyvinyl butyral and a solvent such as ethanol, toluene and xylene to prepare a slurry, and after adjusting the viscosity, a doctor blade method is applied on a resin film such as a polyester film. The magnetic ferrite layer sheet is obtained by coating with, for example, and drying. An internal electrode paste is printed on the magnetic ferrite layer sheet, dried, laminated, and then fired.
Alternatively, a magnetic ferrite layer paste may be prepared by kneading together with a binder such as ethyl cellulose and a solvent such as terpineol or butyl carbitol, and this paste may be printed and laminated alternately with the internal electrode paste, followed by firing. good.

  The internal electrode 3 constituting the multilayer chip inductor 1 is preferably formed using a conductive material mainly composed of Ag having a low resistivity and a small loss when the inductor is used. Further, Ag is also preferable because firing can be performed in the air. The internal electrode 3 is connected by a via hole or the like in a coil shape or a spiral shape so that the number of turns is about 1.5 to 20.5 turns, and the pattern is circular, oval, rectangular, It becomes a shape such as a square. The internal electrode 3 constitutes a closed magnetic circuit coil, and both ends thereof extend to the outer surface and are connected to the external electrodes 5 and 5.

  There are no particular restrictions on the external dimensions of the multilayer chip inductor 1. It can set suitably according to a use. If a general shape is illustrated, the dimension will be a substantially rectangular parallelepiped shape of about 0.4 to 4.5 mm × 0.2 to 3.2 mm × 0.15 to 1.9 mm.

  When using Ag as the internal electrode 3, the temperature during firing is preferably 800 to 930 ° C, and more preferably 850 to 900 ° C. If the firing temperature is less than 800 ° C., the firing is insufficient. On the other hand, if it exceeds 930 ° C., Ag diffuses and the resistivity and electromagnetic characteristics may be significantly lowered. In the case where the firing temperature is kept low, the sintering can be prevented from being insufficient if the firing time held at 800 to 930 ° C. is lengthened. Preferably, the firing time is 1 to 5 hours.

  The multilayer chip inductor thus obtained was evaluated for direct current superposition characteristics and anti-stress characteristics. As with the results disclosed in Example 1, excellent characteristics were obtained.

(Example 3)
A module shown in FIG. 5 was manufactured by the same manufacturing process as in Example 2. This module incorporates an inductor Lout (not shown) in a multilayer substrate 1a and mounts a semiconductor integrated circuit IC including a switching element and a capacitor C on a mounting electrode formed on the main surface. The step-down DC-DC converter shown in FIG. 6 is configured. Terminal electrodes for mounting on the printed circuit board are also formed on the back surface. The obtained multilayer substrate 1a was evaluated for direct current superposition characteristics and anti-stress characteristics. As with the results disclosed in Example 1, excellent characteristics were obtained. Moreover, when the DC-DC converter was operated, it was confirmed that excellent conversion efficiency could be obtained.

  According to the present invention, it is possible to provide a ferrite core that is excellent in direct current superposition characteristics, has little change in magnetic characteristics with respect to stress, in particular, magnetic permeability, and has a stable inductance, and an electronic component using the same.

It is a direct current superimposition characteristic figure of the sample concerning one example of the present invention, and the sample concerning a comparative example. It is an anti-stress characteristic figure of the sample concerning one example of the present invention, and the sample concerning a comparative example. It is a characteristic view which shows the relationship between a nonmagnetic ceramic addition amount and a coercive force. 1 is an external perspective view of an electronic component according to an embodiment of the present invention. It is an external appearance perspective view of the electronic component which concerns on the other Example of this invention. It is the equivalent circuit schematic of the electronic component which concerns on the other Example of this invention.

Explanation of symbols

1 multilayer chip inductor 2 magnetic ferrite layer 3 internal electrode 5 external electrode

Claims (6)

Ferrite core using a composite magnetic material including a first phase of ferrite mainly composed of Fe ₂ O ₃ , NiO (a part of which may be replaced with CuO), and a second phase composed of nonmagnetic ceramics. Because
Nonmagnetic ceramic is contained in an amount of 2.5 to 25 wt% with respect to the main component, the ferrite average crystal grain size is 0.3 to 2 μm, and the linear expansion coefficient of the nonmagnetic ceramic is the linear expansion coefficient of the ferrite. A ferrite magnetic core having a linear expansion coefficient of 6 to 10 ppm / ° C. Ceramic nonmagnetic constituting the second phase, ZrSiO ₄ (zircon), ZrO _{2 (zirconia), Li 2 O · Al 2} O 3 · 4SiO 2 ( _{Supodeyumen), Li 2 O · Al 2} O 3 · 2SiO _2. The ferrite magnetic core according to claim 1, wherein the ferrite magnetic core is any one of ₂ (eucryptite). The main components are Fe ₂ O ₃ : 47 to 50.5 mol%, ZnO: 19 to 30 mol%, and the balance NiO (15 mol% or less may be replaced with CuO). The ferrite core described in 1.   4. An electronic component according to claim 1, wherein a line is formed inside the ferrite magnetic core to form an inductor.   The electronic component according to claim 4, wherein a terminal electrode connected to the line is provided on a surface of the ferrite magnetic core.   The electronic component according to claim 5, wherein a semiconductor element is mounted on the surface of the magnetic body and connected to the terminal electrode.

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