JP2002141215A - Oxide magnetic material, its manufacturing method, and laminated chip inductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide oxide magnetic material which is superior in high-frequency performance, high in volume resistivity, can be burned at low temperatures, and restrains an inner conductor from disappearing due to diffusion of Ag, its manufacturing method, and to provide a laminated chip inductor formed of the material. SOLUTION: An oxide magnetic material includes 43.0 to 51.0 mol.% Fe2O3, 5.0 to 12.0 mol.% CuO, 8.0 to 39.0 mol.% NiO, and the residual mol.% ZnO as main components and 0.05 to 2.0 pts.mass Bi2O3, 0.2 to 2.0 pts.mass TiO2, and 0.1 to 1.0 pts.mass one or more elements from among MnO2, MoO2, RuO2, SnO2, TeO2, WO2 or IrO2 as auxiliary components with respect to 100 pts.mass main components. A laminated chip inductor has an inner conductor of Ag and a soft ferrite of the above oxide magnetic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft ferrite for a chip inductor, that is, a high-permeability oxide magnetic material used in a small electronic device or the like for measures against electromagnetic interference noise, a method for producing the same, and a method for manufacturing the same The present invention relates to a multilayer chip inductor using an oxide magnetic material.

[0002]

2. Description of the Related Art With the development of small OA equipment and mobile communication equipment typified by personal computers and mobile phones, electronic components mounted on these equipment have also been reduced in size, performance and price. Are strongly desired. One of those components is an EMI noise filter, and a multilayer chip inductor is used as an element for the EMI noise filter.

[0003] An inductor corresponds to a winding element having an air core or a soft magnetic material as a core material, and has a characteristic that the resistance value based on the inductance, that is, the impedance, increases as the frequency increases. Therefore, it has the function of a low-pass filter that allows necessary signals to pass, but blocks unnecessary signals and noise at a higher frequency than the signals, preventing electromagnetic interference between electronic devices and malfunctions due to external noise. Be utilized.

In recent years, personal computers, network devices, A
The frequency handled by electronic devices such as V devices is increasing, and digitalization is progressing, and the necessity of suppressing noise in higher frequency ranges is increasing. On the other hand, since these high-frequency signals are noise in other devices operating in a relatively low frequency range, it is necessary to prevent the intrusion of noise from the outside and prevent the signal from leaking to the outside. . Under such circumstances, there is a need for an inductor that operates effectively in a higher frequency range.

[0005] By reducing the size and performance of inductors,
What is applied to electronic circuit components is a multilayer chip inductor. FIG. 1 schematically shows an example of the internal structure. A winding line of a conductor 3 is formed inside a soft ferrite 1 having a rectangular parallelepiped shape. Has become. In this method, conductor paste lines are printed on a green sheet of soft ferrite, and this sheet is provided with through holes 5 in the figure and filled with conductor paste so that the conductor lines of each sheet are connected. It is manufactured by stacking and firing. The internal conductor is connected to the input / output end electrode 2 by a connection portion 4.

[0006] The performance of such an inductor is largely governed by the characteristics of the soft ferrite used, that is, a soft oxide magnetic material (hereinafter simply referred to as ferrite). Needless to say, the properties required for this soft ferrite are that it has a sufficiently high magnetic permeability in a high frequency band, but in addition, (1) a sufficient sintered density can be obtained at a low firing temperature, and ( 2) It is considered important to have a high volume resistivity.

[0007] Ferrite is generally composed of X-Fe ₂ O ₄ where X is Mn, Fe, Co, Ni, Cu,
It is a solid solution of a spinel oxide, which is a kind of Zn or a mixture of these elements. If the element size and the internal conductor shape of the laminated inductor are the same, the higher the magnetic permeability of the ferrite, the higher the inductance can be obtained. For example, a ferrite in which X is composed of Mn and Zn exhibits extremely high magnetic permeability. However, this MnZn ferrite does not have a high electric insulation resistance, and even if it is excellent in a low frequency range, its magnetic permeability decreases in a high frequency range. On the other hand, there are NiZn ferrite and CuNiZn ferrite as ferrites that can be used in a high frequency band.

Usually, in order to obtain a dense ferrite having a high magnetic permeability, the oxide material is sufficiently mixed, and
The material calcined and synthesized at ℃ is pulverized into a raw material powder, a binder (a binder) is added, kneaded, compression-molded into a predetermined shape, and baked at a high temperature exceeding 1000 ° C. In the case of a laminated inductor, a conductor material serving as an internal conductor is printed on a green sheet before firing, and the sheet is laminated and formed, and then the ferrite and the conductor are simultaneously fired and integrated. For this reason, if the firing temperature is too high, the internal conductor flows out or diffuses into the ferrite, resulting in a reduction or disappearance of the conductor cross-sectional area.

On the other hand, an Ag-Pd alloy is often used as the internal conductor. When Pd is contained in Ag, the melting point increases, so that melting and diffusion can be suppressed, and further, there is an effect that the difference in heat shrinkage from ferrite after sintering can be reduced. However, when other metal elements such as Pd are added to Ag, the electrical resistance increases, and the internal resistance of the inductor increases. The increase in the internal resistance greatly increases the insertion loss of the inductor, that is, greatly reduces the Q value which is a quality index. Furthermore, in the case of a multilayer chip inductor for noise suppression, its use in a large current area is rapidly increasing, and heat generation during use becomes a problem.

[0010] The internal resistance of the laminated inductor is desirably as small as possible in view of the above point. As the internal conductor, it is best to use Ag in which other metal elements such as Pd are kept low, and if possible, Ag alone. However, the melting point of Ag is 961
In order to use Ag alone as the internal conductor, the firing temperature of the laminated inductor or ferrite should be suppressed to 900 ° C. or less, and a ferrite material that can be sufficiently sintered at such a low temperature is required.

For example, in Japanese Patent Publication No. 7-87149, A
The g as an internal conductor, as a main component CuNiZn ferrite, the invention of the laminated chip impedance is presented to which was added at least one _{Bi 2 O 3, V 2 O} 5 or lead silicate glass as the second component. However, although it is shown that the allowable current was increased by setting the firing temperature to 900 ° C. using the Ag conductor, various performances other than the composition range of each component and the allowable current were not shown.

In the multilayer inductor, the conductor is directly in contact with the ferrite and integrated. Therefore, when the electric resistance value of the ferrite is not sufficiently high, the leakage current increases, and the effect as an inductor is significantly reduced. In addition, an eddy current is generated in the ferrite due to the passage of a signal, which results in an increase in insertion loss. Therefore, the electric resistance of ferrite as an insulator must be as high as possible.

[0013] The electric resistance of this ferrite greatly depends on its composition. As described above, MnZn ferrite shows extremely high magnetic permeability, but does not have high electric insulation resistance. For high frequency, NiZn ferrite or CuNiZn ferrite which can be sintered at lower temperature is applied.

Japanese Patent Application Laid-Open No. 6-295811 discloses an example in which CuNiZn ferrite is used and the electric resistance is particularly high.
Patent Publication No. This invention was improved in permeability by adding a small amount of MoO _3, in particular Fe ₂ O ₃
Is limited to the range of 48 to 50 mol% to improve the volume resistivity (specific resistance). Further, the invention disclosed in Japanese Patent Application Laid-Open No. H11-219812 discloses that Mn is added to CuNiZn ferrite.
O in which was contained, 48 to the amount of Fe ₂ O ₃ Again
It seems that a high volume resistivity is realized by controlling to a narrow range of 49.5 mol%.

In these two inventions, those having a sufficiently high sintering density and a volume resistivity of 1 × 10 ¹⁰ Ω-cm or more are proposed, and it is considered that excellent ferrite is obtained.
However, in each case, firing is performed at a temperature of 950 to 1300 ° C. If sufficient characteristics are not exhibited unless firing at such a temperature, it is used for a multilayer inductor having Ag as an internal conductor. Can not do.

[0016]

SUMMARY OF THE INVENTION The present invention relates to an oxide magnetic material capable of obtaining high magnetic permeability and high volume resistivity in a high frequency range by sintering at a temperature within a range where Ag can be used for the internal conductor. And a method of manufacturing the same, and an object thereof is to obtain a high-performance chip inductor having low internal resistance and adaptable to a large current specification.

[0017]

The internal conductor of the multilayer chip inductor is printed on a ferrite green sheet in the form of a paste-like material, and after drying, the sheet is laminated and pressed to be integrally fired. The sintering is performed together with the ferrite.

For this internal conductor, the required firing temperature of the Ag paste was investigated first, with the aim of using a single body of Ag in order to minimize the electrical resistance. As a result, it was confirmed that the sintering of the Ag material on the green sheet sufficiently proceeded, and the firing temperature at which the resistance value of the conductor was minimized was 830 to 900 ° C. If the temperature rises above this range,
Ag conductors are prone to diffusion and reactions, resulting in a decrease in cross-sectional area and intrusion of other elements. When the conductors are low, sintering becomes insufficient, and in any case, the electrical resistance value as the conductor inside the inductor increases. Will come.

As a ferrite material, it is necessary that sintering proceed sufficiently and densely in the optimum sintering temperature range of the Ag conductor to obtain a high magnetic permeability, and further that a volume resistivity as high as possible can be obtained. is there. Various studies were made on the composition for obtaining ferrite having such performance. At that time, as for the performance of the ferrite after firing, the sintered density is
The target was 5.0 g / cm ³ or more, the magnetic permeability at 1 MHz was 300 or more, and the volume resistivity was 1000 MΩcm or more.

First, based on CuNiZn ferrite, the mixing ratio of Fe ₂ O ₃ , NiO, and ZnO that can sufficiently secure the magnetic permeability and the saturation magnetic flux density in a high frequency range was examined, and the effects of these components were confirmed. Then, an attempt was made to increase the CuO content in order to lower the sintering temperature. However, the inclusion of a large amount of CuO has a limit since the nonmagnetic wustite phase does not form a solid solution in ferrite and magnetic performance is significantly impaired. Therefore, as a result of studying the addition of a sintering aid, the CuO content was increased, and then Bi ₂ O ₃
It has been found that by adding a small amount of, ferrite dense sintering is possible at the sintering temperature of the Ag conductor. This was presumed to be because the melting point of Bi ₂ O ₃ was near the sintering temperature of the Ag conductor, and a slight liquid phase was generated to promote sintering at a low temperature.

Next, in order to increase the volume resistivity, Fe ₂
It was considered that the amount of O ₃ was about 49 mol%. However, when the sintering temperature is not high, the sintering density is not always sufficient, a high volume resistivity cannot be obtained stably, and the amount of Fe ₂ O ₃ is desired to be smaller from the viewpoint of the magnetic permeability and the sintering temperature. In some cases, the possibility of improving the volume resistivity by adding an auxiliary agent was examined. As a result, TiO ₂
It has been found that the addition of a small amount of an oxide having a tetravalent cation, such as or MnO ₂ , is effective.

Therefore, the effects of these oxide additions were investigated in more detail. As a result, TiO ₂ was added, and MnO ₂ , MoO ₂ , SnO ₂ , TeO ₂ , WO ₂ or IrO _2, etc. It has been found that adding oxides having tetravalent ions close to the radius of the ions is even more effective in increasing the volume resistivity.

From the above examination results, it has been found that the compositions which can almost achieve the target sintering density, magnetic permeability and volume resistivity are obtained.
In addition, the manufacturing conditions were clarified, and a multilayer inductor was manufactured to confirm the performance, thereby completing the invention. The gist of the present invention is as follows. _{(1) Fe 2 O 3:} 43.0~51.0 mol%, CuO: 5.0 to 12.0
Mol%, NiO: 8.0 to 39.0 mol% and ZnO: the remaining main component, and Bi ₂ O with respect to 100 parts by mass of the main component.
_3: 0.5 to 2.0 parts by weight, TiO _2: 0.2 to 2.0 parts by weight and M
An oxide magnetic material comprising at least one of nO ₂ , MoO ₂ , RuO ₂ , SnO ₂ , TeO ₂ , WO ₂ or IrO ₂ together with 0.1 to 1.0 parts by mass of a subcomponent. (2) Mixing the oxide raw materials, calcining and synthesizing, adding a binder etc. to the crushed and sized powder, kneading and shaping into a required shape, and firing at 830 to 900 ° C for 1 to 5 hours. The method for producing an oxide magnetic material according to the above (1). (3) A multilayer chip inductor comprising the Ag internal conductor and the oxide magnetic material of (1).

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the ferrite composition is limited as described above for the following reasons.

Fe ₂ O ₃ is a main component of ferrite, and the main component of the ferrite is X-Fe ₂ O ₄ (X is C
u, Ni, Zn, etc.), it must constitute 43.0 to 51.0 mol% of the solid solution having an inverse spinel structure. If it is less than 43.0 mol%, sufficient magnetic permeability cannot be obtained, and the impedance when incorporated in a multilayer chip inductor will be insufficient. On the other hand, if the content exceeds 51.0 mol%, sufficient sintering density cannot be obtained, the volume resistivity becomes low, and furthermore, the mechanical strength of the multilayer chip inductor becomes insufficient, and furthermore, the performance degradation due to long-term use may occur. Resistance,
That is, the weather resistance may be deteriorated.

CuO is one of the main components of ferrite.
0 to 12.0 mol%. This is C
This is because uO greatly contributes to lowering the sintering temperature by coexisting with Bi ₂ O ₃ described later. But 5.
If the amount is less than 0 mol%, the sintering density becomes insufficient when firing is carried out in the low temperature range which is the object of the present invention, which causes insufficient mechanical strength and poor weather resistance. On the other hand, if it exceeds 12.0 mol%, a glassy mixed phase is formed on the surface during firing, and it becomes easy to weld to the holding table, so that productivity is reduced and the volume resistivity is also reduced.

NiO is contained to ensure the magnetic permeability of the ferrite in the high frequency range. The amount is 8.0 mol%
If it is less than 39.0 mol% because it is too large, on the other hand, the magnetic permeability in the high frequency range is reduced. Therefore, the content of ferrite in the main component is limited to 8.0 to 39.0 mol%.

ZnO is an important element for improving the magnetic permeability of ferrite.
_The remaining portion except for ₂ O ₃ , CuO and NiO is to be constituted. However, if the content ratio is less than 6.0 mol%, problems such as insufficient magnetic properties and insufficient sintering density of the obtained ferrite occur, and conversely, if it exceeds 36.0 mol%, the magnetic properties deteriorate, so it is desirable. Is in the range of 6.0 to 36.0 mol%.

An auxiliary component having the following composition is added to the main component constituting the ferrite as an auxiliary. The required amount of each sub-component and its action are as follows. In this case, when the total amount of the main components of the ferrite is 100 parts by mass, the amounts of the respective subcomponents are indicated by parts by mass.

Bi ₂ O ₃ is contained in an amount of 0.5 to 2.0 parts by mass to promote sintering of ferrite at a low temperature. Bi ₂ O ₃
If the amount is less than 0.5 parts by mass, sintering becomes insufficient at the target temperature, and a sufficient sintered density and magnetic permeability of the ferrite after firing cannot be obtained. On the other hand, if it exceeds 2.0 parts by mass, the cross-sectional area of the Ag internal conductor is significantly reduced during firing, and the internal resistance may be increased.

TiO ₂ is added in an amount of 0.2 to 2.0 parts by mass to increase the volume resistivity of ferrite. If TiO ₂ is less than 0.2 parts by mass, the increase in volume resistivity is insufficient, and if it exceeds 2.0 parts by mass, the magnetic permeability decreases.
MnO ₂ , MoO ₂ , RuO ₂ , SnO ₂ , TeO ₂ , WO ₂
Alternatively, at least one of IrO ₂ is contained in a total amount of 0.1 to 1.0 part by mass. This can further increase the volume resistivity by being contained together with the above TiO ₂ . If the total content of these oxides is less than 0.1 part by mass, a sufficient effect cannot be obtained, and if the total content exceeds 1.0 part by mass, sinterability may be deteriorated.

Further, when one or both of Ag ₂ O and Rh ₂ O ₃ are contained, diffusion of Ag at the time of firing is suppressed, and a decrease in the cross-sectional area of the Ag internal conductor can be reduced. Therefore, it is desirable to contain these oxides as necessary. In that case, the content is 0.01 to 0.07 parts by mass for Ag ₂ O and 0.2 to 1.5 parts by mass for Rh ₂ O ₃ , and other components are mixed. It is preferable to add the calcined synthetic powder after calcining and calcinate.

In addition to these compositions, some inevitable impurities can be mixed as long as they do not significantly affect the properties of ferrite.

The production of the oxide magnetic material having the above composition may be carried out in accordance with a general method. The production of a laminated inductor will be described as follows. First,
The main component and the subcomponent are mixed and calcined in the atmosphere at a temperature of about 800 ° C., and the calcined powder is pulverized and sized. A binder is added to the sized powder, the mixture is sufficiently kneaded, and formed into a green sheet by a doctor blade method or the like.

The conductor paste is printed on the green sheet, the sheets are laminated, cut into a predetermined shape, and baked at 830 to 900 ° C. for 1 to 5 hours. If the firing temperature is lower than 830 ° C, the sintering will be insufficient and the magnetic properties and mechanical strength will be inferior.If the firing temperature is higher than 900 ° C, the inner conductor will be thinned or disappear, and a good chip inductor will be produced. No longer available. If the sintering time is less than 1 hour, sintering will be insufficient, but if heating is continued more than necessary, almost no improvement in performance will be recognized, and heating time and energy will be wasted, so at most 5 hours Up to. After firing, the input / output end electrodes are attached to the conductors connected to the internal conductors, to form chip inductors.

[0036]

EXAMPLES Example 1 Raw materials having the composition ratios shown in Table 1 were weighed to a total amount of 250 g each, and the resulting mixture was passed through a ball mill using zirconia grinding balls together with 1 liter of pure water. After mixing for 24 hours, the raw material powder is separated and dried,
It was transferred to a zirconia crucible and calcined at 800 ° C. After calcination, it was confirmed by X-ray diffraction that the required compound was obtained.

The calcined synthetic powder is wet-pulverized by a ball mill,
The mixture was separated and dried, and sized with a mesh sieve so that the particle size became 0.8 to 1.0 μm. 10% by mass of P as a binder
After adding the VA solution and granulating with a raikai machine, pressing and molding the granulated powder in a mold, calcination is performed in the air at 850 ° C. for 2.0 hours, and an outer diameter of 10 mm and a thickness of 3 mm And a toroidal test piece having an outer diameter of 16 mm, an inner diameter of 8 mm, and a thickness of 3 mm were prepared.

Further, a green sheet having a thickness of 70 μm was prepared from the calcined synthetic powder by a doctor blade method, and a paste having a single composition of Ag as an internal conductor was formed on the sheet surface to a line width of 150 μm and a thickness of 20 μm. Print in a pattern equivalent to the internal conductor, put a green sheet on it, cut it into chips after crimping, and at 850 ° C
The firing was performed for 2.0 hours. After firing, the cross section of the test piece was polished, and the conductor shape was observed with a scanning electron microscope.

After measuring the density of the obtained cylindrical test piece by the liquid immersion weighing method, an In-Ga alloy was applied to the upper and lower surfaces to provide electrodes, and a DC constant voltage power supply (HP4140B manufactured by Hewlett-Packard Japan) was provided. ), The insulation resistance was measured at a DC value of 50 V for one minute, and the volume resistivity was calculated from the electrode area and the distance between the electrodes. The magnetic permeability at 1 MHz of the toroidal test piece was determined using an impedance measuring device (HP4291A) and a magnetic permeability measuring device (HP16454A) manufactured by Hewlett-Packard Japan.

Table 1 also shows the measurement results of the sintered density, volume resistivity and magnetic permeability. As is evident from these results, those in which the composition ratio of the main component and the amount of the subcomponent are within the range specified in the present invention have a high density and magnetic permeability, and a ferrite with a high volume resistivity has been obtained. . That is, the ferrite has an initial target sintering density of 5.0 g / cm ³ or more, a magnetic permeability at 1 MHz of 300 or more, and a volume resistivity of 1000 MΩcm or more.

[0041]

[Table 1]

For the Ag conductor inside the ferrite, B
Except for Test No. 14, which contains a large amount of i ₂ O _3, no decrease or diffusion was observed in any case. This is an effect of reducing the firing temperature.

Example 2 Using a ferrite having the composition of Sample No. 5 shown in Table 1, a thickness of 70% was obtained by a doctor blade method.
A μm green sheet was prepared, and a paste pattern of a single Ag composition serving as an internal conductor was screen-printed on the sheet surface. A laminated chip is formed as an internal conductor pattern having the internal conductor structure schematically shown in FIG. In this case, the chip is 2125 size (2.0mm long, 1.2mm wide)
5mm, thickness 0.5mm), the printed line width of the paste is 150μm, the thickness is 20μm, the number of internal conductor turns is 8, and the connection between the conductors of the laminated sheet uses through holes, which are filled with conductive paste did.

After laminating and pressing the sheet, it was cut into the above chip size, and fired at 850 ° C. for 2.0 hours in the air.
The magnetic permeability of the ferrite in this case was 350 (1 MHz).

Input and output electrodes were attached to both ends of the fired chip, and the impedance and inductance were measured using an impedance measuring device (HP4291A type) manufactured by Hewlett-Packard Company. For the allowable current value, the maximum current value at which the increase in the surface temperature was within + 3 ° C. was obtained by changing various currents. The results are as follows. Impedance | Z |: 1200 Ω (100 MHz) Inductance Ls: 450 nH (100 MHz) Maximum allowable current Ip: 3.0 A As described above, the multilayer chip inductor according to the present invention is:
Both the impedance and the inductance show high values, and the allowable current value is sufficiently large.

[0046]

The oxide magnetic material of the present invention, that is, soft ferrite, has a sufficiently high magnetic permeability even in a high frequency range, has a high volume resistivity, and is sintered by firing at a lower temperature than conventional ones. And the disappearance of the internal conductor due to the diffusion of Ag can be suppressed. This ferrite multilayer chip inductor can use Ag with low electric resistance for the inner conductor, so it is especially suitable for large current specifications.
Since it has excellent high-frequency characteristics and low internal resistance, it can be effectively used for improving the performance of electronic devices.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating the structure of an internal conductor of a multilayer chip inductor.

[Explanation of symbols]

 1. Ferrite laminated sintered body part End electrode for input / output 3. Internal conductor 4. Conductive part connected to input / output electrode 5. Through hole for connection between internal conductors

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4G002 AA06 AA07 AB01 AE02 4G018 AA01 AA02 AA15 AA21 AA23 AA24 AA25 AA33 AA37 AA38 AC16 5E041 AB14 AB19 BD01 CA01 HB00 HB01 HB03 HB05 NN02 NN17 NB13 CB

Claims (3)

[Claims] (1) Fe ₂ O ₃ : 43.0 to 51.0 mol%, CuO: 5.
0-12.0 mol%, NiO: 8.0-39.0 mol% and Zn
O: a main component the balance, Bi ₂ O ₃ with respect to the main component of 100 parts by: 0.5 to 2.0 parts by weight, TiO _2: 0.2 to 2.0 parts by weight, and _{MnO 2, MoO 2, RuO 2} , SnO 2 , Te
One or more of O ₂ , WO _{2 and} IrO ₂ are combined with 0.1 to
An oxide magnetic material comprising 1.0 parts by mass of a subcomponent. 2. Mixing the oxide raw materials, calcining and synthesizing, adding a binder or the like to the pulverized and sized powder, kneading the mixture, shaping it into a required shape, and firing at 830 to 900 ° C. for 1 to 5 hours. The method for producing an oxide magnetic material according to claim 1, wherein: 3. A multilayer chip inductor comprising an Ag internal conductor and the oxide magnetic material according to claim 1.