KR20160014936A - Composite magnetic powder and chip coil component using thereof - Google Patents

Abstract

The present invention relates to composite magnetic powder and a chip coil component. According to the present invention, the chip coil component comprises coil patterns laminated on a ceramic layer or coil patterns winded on a ceramic core. The ceramic layer or the ceramic core contains powder of a core-shell structure, the core in the core-shell structure powder consists of silica powder (SiO_2), and the shell consists of ferrite powder.

Description

TECHNICAL FIELD [0001] The present invention relates to a composite magnetic powder and a chip coil component using the composite magnetic powder,

The present invention relates to a composite magnetic powder and a chip coil component using the composite magnetic powder.

Inductors in chip coil components are one of the important passive components of electronic circuits together with resistors and capacitors. They are used as components to eliminate noise or to form LC resonance circuits.

The inductor may be manufactured by winding a coil on a ferrite core or printing, and forming electrodes on both ends of the ferrite core. Alternatively, the inductor may be manufactured by printing an internal electrode on a magnetic material or a dielectric and then laminating.

The inductors can be classified into a laminate type, a wire wound type, a thin film type, and the like depending on the structure. With the miniaturization and thinning of electric devices, the laminate type and the thin film type are becoming widespread among them.

The stacked inductor is fabricated by forming via holes in a plurality of ceramic sheets, forming conductive patterns according to the positions of the via holes, and stacking a plurality of ceramic sheets having conductive patterns formed thereon and firing the stacked inductors.

In recent years, due to high frequency hydration of passive products, there has been a problem that the performance of a product is deteriorated due to parasitic capacitance due to the dielectric constant of the ceramic powder constituting the sheet in a frequency band of several tens of GHz or more.

Accordingly, there is a demand for research on a magnetic body capable of minimizing the parasitic capacitance of a multilayer inductor suitable for a high frequency band of several tens of GHz or more.

Korean Patent Publication No. 2013-0014848

It is an object of the present invention to provide a ceramic sheet for a chip coil component or a composite magnetic powder for a ceramic core which can minimize parasitic capacitance and magnetic loss while maximizing inductance in a high frequency band of several tens GHz or more.

Another object of the present invention is to provide a chip coil component capable of improving the inductance due to the increase of the magnetic permeability at the same filling density in a high frequency band of several tens GHz or more by including the ceramic sheet or the ceramic core containing the compound magnetic powder .

The above object of the ceramic sheet for a chip coil component or the composite magnetic powder for a ceramic core according to the present invention,

To provide a ceramic dielectric ceramic powder for a ceramic sheet or a ceramic core capable of minimizing a parasitic capacitance due to the dielectric constant of the ceramic powder constituting the ceramic sheet or the ceramic core in a high frequency band of several tens GHz or more and maximizing the inductance.

In the case of only a low-permittivity core, the parasitic capacity is reduced while the permeability is lowered. When the ferrite core is composed of ferrite cores, the permeability is increased while the performance is deteriorated in the high-

The composite magnetic powder according to the present invention is formed of a core-shell structure in which a core is made of a low dielectric constant powder that is a nonmagnetic material and a shell surrounding the core is made of a ferrite powder that is a magnetic material having a high magnetic permeability, . ≪ / RTI >

Another object of the present invention is to provide a ceramic layer or a ceramic core containing a composite magnetic powder of a core-shell structure satisfying high permeability and low investment loss characteristics in a high frequency band of several tens GHz or more, Thereby improving the inductance value of the coil component.

The composite magnetic powder according to the present invention is formed into a core-shell structure that surrounds a low-permittivity core, which is a nonmagnetic material, with ferrite, which is a magnetic material, so that high permeability and low investment loss characteristics can be satisfied simultaneously in a high frequency band of several tens GHz or more.

In addition, according to the present invention, it is possible to manufacture a chip coil component that satisfies high efficiency characteristics by maximizing inductance in a high frequency band of several tens GHz or more by providing a ceramic sheet or a ceramic core containing the composite magnetic powder of the core- .

Further, the chip coil component of the present invention includes the ceramic sheet or ceramic core containing the composite magnetic powder and can improve the inductance due to the increase of the magnetic permeability at the same filling density in the high frequency band of several tens of GHz or more. Thus, it is advantageous in actual mass production since there is no disadvantage such as an increase in resistance due to an increase in coil turn for improving inductance, an increase in process cost, and a reduction in yield.

1 is a cross-sectional view of a composite magnetic powder having a core-shell structure according to the present invention.
2 is a scanning electron microscope (SEM) photograph of SiO ₂ powder used in the composite magnetic powder of the present invention.
3 is a cross-sectional view of a multilayer inductor having a ceramic sheet containing a composite magnetic powder having a core-shell structure according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, it should be understood that the present invention is not limited to the embodiments disclosed herein but may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. It is intended that the scope of the invention be limited only by the terms of the claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a ceramic sheet for a chip coil component or a composite magnetic powder for a ceramic core according to the present invention and a chip coil component using the same will be described in detail with reference to FIG. 1 and FIG.

FIG. 1 is a cross-sectional view of a composite magnetic powder having a core-shell structure according to the present invention. FIG. 2 is a scanning electron microscope (SEM) of a SiO ₂ powder used in the composite magnetic powder of the present invention. ) It is a photograph.

Composite magnetic powder for ceramic sheet or ceramic core

The composite magnetic powder according to the present invention is used as a material of a ceramic sheet or a ceramic core in a chip inductor suitable for a high frequency band of several tens GHz or more, and is characterized by having a core-shell structure.

1, a composite magnetic powder 100 according to the present invention includes a core 110 and a core-shell 120 formed of a shell 120 coated on the surface of the core 110. The core- shell structure.

Preferably, the composite magnetic powder 100 has a core-shell structure composed of a non-magnetic substance and a magnetic substance, thereby maximizing inductance and minimizing magnetic loss in a high frequency band of several tens of GHz or more .

In chip inductors, the parasitic capacitance is proportional to the dielectric constant, epsilon, of the powder contained in the ceramic layer, and the inductance is inversely proportional to this parasitic capacitance.

The chip inductors used in the high frequencies of the existing tens of GHz range are mainly made of Al ₂ O ₃ powder as the ceramic layer because the material itself has a high strength and the dielectric loss value at high frequency is relatively low and stable. However, since the dielectric constant of Al ₂ O ₃ powder is as high as about 9 to 10, there is a problem of performance deterioration due to parasitic capacitance as the frequency of use continues to increase to the GHz range.

In addition, when a magnetic material powder such as ferrite is used as a core to improve the inductance, it is known that efficiency is reduced due to magnetic loss at a high frequency of several tens of GHz band.

In order to solve the above problems, it is preferable that the core 110 of the composite magnetic powder 100 at a high frequency in the GHz band region is formed of a non-magnetic material and a powder satisfying low dielectric constant characteristics.

In particular, in order to minimize the parasitic capacitance in the high frequency band of several tens GHz or more, it is more preferable that the core 110 is formed of a low dielectric constant powder having a dielectric constant epsilon of 5 or less.

For example, the core 110 may be made of silica (SiO ₂ , about ε = 3.8 to 5) powder, which is a non-magnetic material and widely known as a material having a low dielectric constant.

However, the dielectric constant of silica may vary depending on the particle size distribution, the degree of defects of the powder, and the impurity content.

2, it is preferable that the core 110 is formed of a uniform and dense sphere-shaped silica powder 112 so that the chip strength is given together with the low dielectric constant property.

This silica powder 112 is formed in a non-porous manner and is a densified powder having a density of 1.8 g / cm3 to 2.1 g / cm3.

If the density of the silica powder 112 is less than 1.8 g / cm 3, it may be difficult to impart the desired chip strength. On the other hand, if the density exceeds 2.1 g / cm 3, the increase of the parasitic capacity The inductance can be reduced below the threshold value.

Also, the silica powder 112 may be a nano-grade high-purity powder having an average particle size (particle size) of 400 nm to 500 nm. When the average particle size of the silica powder 112 is less than 400 nm, it is difficult to disperse in the batch process for producing the ceramic sheet, the yield for producing the powder is relatively low, and the manufacturing cost increases. On the other hand, when the average particle size of the silica powder 112 exceeds 500 nm, the dielectric constant may increase, and there may arise a problem in making the ceramic sheet thinner and miniaturizing the manufactured chip.

Also, in a chip inductor, the inductance is proportional to the permeability of the material. Therefore, it is preferable that the shell 120 is formed of a high-resistance magnetic material having a magnetic permeability of 1 or more.

For example, the shell 120 is made of ferrite powder to which magnetism is imparted. Since the ferrite powder should be used at a high frequency of several to several tens of GHz, a hexagonal ferrite material is preferably used .

In general, the hexaferrite powder has an easy magnetization direction in a plane perpendicular to the c-axis of the crystal, and therefore has a magnetic anisotropy characteristic. Therefore, the frequency range of the spinel ferrite exceeds the frequency limit of the spinel ferrite And is known to maintain a predetermined permeability. Therefore, the hexaferrite powder can be used in a high frequency band of several to several tens of GHz band.

The hexaferrite powder may be represented by the following formula (1).

[Chemical Formula 1]

Ba _1-x Sr _x Co _1-y [Me] _y Fe _m O _n

X, y <1, 12 <m <36 and 19 <n <60), where [Me]

The hexaferrite powder has a crystal structure classified into M type, U type, W type, X type, Y type, Z type and the like. Of these, the M type is preferably applied to the shell 120.

This is because the M type hexaferrite powder exhibits a high magnetic anisotropy and a high resonance frequency in a high frequency band and thus can be effective in reducing magnetic loss in a frequency band of several tens of GHz.

The M-type hexaferrite powder can be represented by the following formula (2).

(2)

Ba _1-x Sr _x Zn _y Mn _z Fe ₁₂ O ₁₉

(Where 0? X? 1, 0? Y? 1, and 0? Z? 1)

In the above, the shell 120 is preferably formed to a thickness of 10 nm to 50 nm. If the thickness of the shell 120 is less than 10 nm, a desired permeability can not be obtained. On the other hand, when the thickness exceeds 50 nm, the filling rate in manufacturing a ceramic sheet, a ceramic core or the like may be lowered, and an increase in investment loss The risk also increases.

The composite magnetic powder 100 may be prepared by subjecting a material constituting the core to a reduction, filtration, washing and drying process using a liquid phase method, and then adding a shell forming material to coat the shell on the surface of the core. But is not limited thereto.

As described above, the composite magnetic powder 100 of the present embodiment is formed by coating the surface of the low dielectric constant core 110 with the shell 120 and the ferrite having high magnetic permeability, The permittivity and the investment rate can be adjusted to lower the investment loss and increase the investment rate.

As a result, the composite magnetic powder 100 can minimize the parasitic capacitance and the magnetic loss while maximizing the inductance in a high frequency band of several tens GHz or more. The magnetic powder 100 has a permeability (mu) of 1.5 or more and a dielectric constant (epsilon) in a frequency band of 1 to 10 GHz. 5 or less and an investment loss (tan delta) of 0.03 or less.

The composite magnetic powder 100 preferably has a permeability of 1.5 to 2, a dielectric constant of 3.5 to 5.0, and an investment loss of 0.01 to 0.03 in a frequency band of 1 to 10 GHz.

Due to this characteristic, the composite magnetic powder 100 has an effect of improving the inductance value after application of an external current when applied to a ceramic layer of a chip inductor.

On the other hand, in the chip inductor, the inductance is proportional not only to the magnetic permeability of the coil material but also to the number of turns of the coil. At this time, an increase in the number of turns of the coils causes an increase in resistance.

However, the composite magnetic powder 100 of the present embodiment does not need to increase the number of coil turns in order to increase the inductance as compared with the inductor of the dielectric alone, by increasing the inductance through the increase of the magnetic permeability. As a result, the composite magnetic powder 100 has advantages such as an increase in resistance due to an increase in the number of coil turns, an increase in process cost, and a reduction in yield, which is advantageous in actual mass production.

Ceramic Sheet for Chip Inductors

The ceramic sheet according to the present invention is a sheet containing a compound magnetic powder 100 (see FIG. 1) having a core 110-shell 120 structure described above as a filler. The composite magnetic powder 100 is a And thus redundant description thereof will be omitted.

The ceramic sheet of the present invention is characterized by having a density within a range of 1.5 g / m 3 to 2.0 g / m 3.

In the case of a ceramic sheet for a multilayered inductor, since the process firing temperature for chip firing due to the low melting point (960 DEG C) of the metal Ag electrode should not exceed 920 DEG C, generally, a glass is added in addition to the above- Adjust the temperature. Therefore, the density has a certain range according to the amount of glass added.

Further, the ceramic sheet of the present invention satisfies the characteristics of a permeability (mu) of 1.5 or more, a dielectric constant (epsilon) of 5 or less, and an investment loss (tan delta) of 0.03 or less in a frequency band of 1 to 10 GHz.

Preferably, the ceramic sheet of the present invention satisfies the characteristics of a permeability of 1.5 to 2, a dielectric constant of 3.5 to 5.0, and an investment loss of 0.01 to 0.03 in a frequency band of 1 to 10 GHz.

The ceramic sheet is applied in a plate state by a screen printing method, a dot blade method, or the like in a paste state in which the above-described composite magnetic powder 100 (see Fig. 1) of a core-shell structure is mixed with a glass for sintering auxiliary composition, a binder, And a sintered ceramic sheet sintered through a sintering process of temperature and time.

An example of a manufacturing process of a ceramic sheet for a multilayer inductor using the composite magnetic powder 100 having a core-shell structure according to the present invention is as follows.

First, calcined powders were prepared at a composition ratio of 93 to 95 wt% with respect to the composite magnetic powder (100) having the core-shell structure shown in Fig. 1 while varying the glass content ratio from 7: 3 to 5: 5, The paste is prepared by mixing.

The binder may be an organic binder that imparts liquid characteristics to the paste, and may further include an organic solvent. The organic binder and the organic solvent may be an organic vehicle. The binder, the organic solvent, and the like may be any of conventionally known materials without any particular limitation.

Thereafter, the paste is applied on a workpiece by screen printing or the like, and then baked at about 900 to 920 DEG C to complete a sintered ceramic sheet.

At this time, the content ratio of the core-shell composite magnetic powder contained in the ceramic sheet may vary depending on the frequency-dependent inductance and the Q characteristic of the chip, and is preferably 50% to 70%. If the content of the core-shell composite magnetic powder is less than 50%, it may be difficult to ensure the inductance. On the other hand, if the content exceeds 70%, it is difficult to set the firing temperature to 920 캜 or less.

The ceramic sheet prepared by containing the composite magnetic powder 100 (see FIG. 1) of the core-shell structure is a ceramic layer of a chip inductor suitable for a high frequency band of several tens of GHz or more due to the properties such as permeability, permittivity, It is suitable for use.

Chip inductor

The chip inductor of the chip coil component may include a ceramic sheet containing the composite magnetic powder 100 (see Fig. 1) of the core-shell structure described above.

Hereinafter, a multilayered inductor of a chip inductor will be described. Since the composite magnetic powder 100 (see FIG. 1) and the ceramic sheet having the core-shell structure are the same as those described above, a duplicate description thereof will be omitted.

3 is a cross-sectional view of a multilayer inductor having a ceramic sheet containing a composite magnetic powder having a core-shell structure according to the present invention.

3, the multilayer inductor 300 according to the present embodiment is formed of a laminate in which a plurality of ceramic layers 310 are laminated, and a coil pattern 320 is interposed between the plurality of ceramic layers 310 .

The plurality of ceramic layers 310 may be formed into a plate-shaped ceramic sheet using the composite magnetic powder 100 (see FIG. 1) of the core-shell structure.

Each of the ceramic layers 310 composed of a ceramic sheet is coated in a plate state by a dot blade method or the like in a paste state in which a composite magnetic powder 100 (see Fig. 1) having a core-shell structure and a glass for sintering auxiliary composition are mixed with a binder, And a sintered ceramic sheet sintered at a predetermined temperature and time. A plurality of sintered ceramic sheets manufactured in this way are stacked to form the ceramic layer 310.

The coil pattern 320 may be formed on a ceramic sheet constituting the ceramic layer 310 by a screen printing technique or the like. The coil pattern 320 may be formed by winding one or more turns on one ceramic sheet.

The coil patterns 320 of each layer are electrically connected through the vias 330 formed in the ceramic layer 310 and the coil patterns 320 formed at the uppermost layer and the lowermost layer are electrically connected to the external electrodes 340 .

The vias 330 are formed by filling a conductive material into via holes (not shown) formed in a plurality of ceramic sheets.

The coil pattern 320, the via 330, and the external electrode 340 are not particularly limited as long as they are made of a conductive material. For example, silver (Ag), nickel (Ni), copper (Cu) Pt, Pt, Pd, Al, Fe, Ti, and Cr, or an alloy thereof.

The stacked inductor 300 may further include a gap layer 350 in the ceramic layer 310 to improve DC bias characteristics. The gap layer 350 is inserted into the ceramic layer 310 to cut off the magnetic flux to reduce the variation of the inductance due to the application of the current.

As the gap layer 350, a nonmagnetic ferrite having a paramagnetic property (usually, ZnCu ferrite) may be used.

As described above, the multilayer inductor 300 of the present embodiment includes the ceramic layer 310 made of the ceramic sheet containing the above-described core-shell composite magnetic powder 100 (see FIG. 1), thereby maximizing the inductance, The magnetic loss can be minimized and the inductance value after the external current is applied in the high frequency band of several tens GHz or more can be improved. That is, the stacked inductor 300 has the advantage of improving the inductance against the increase of the permeability at the same filling density.

As a result, the multilayer inductor 300 of the present embodiment satisfies the characteristics of a permeability (mu) of 1.5 or more, a dielectric constant (epsilon) of 5 or less, and an investment loss (tan delta) of 0.03 or less in a frequency band of 1 to 10 GHz.

Preferably, the ceramic sheet of the present invention satisfies the characteristics of a permeability of 1.5 to 2, a dielectric constant of 3.5 to 5.0, and an investment loss of 0.01 to 0.03 in a frequency band of 1 to 10 GHz.

For the sake of convenience of explanation, the present invention is limited to the laminated type inductor among the chip coil parts, but is not limited thereto.

The composite magnetic powder 100 (see FIG. 1) of the core-shell structure of the present invention is formed of a thin film or a core and is applicable to a thin film type inductor and a wound type inductor, and the same effect as in the case of a stacked type inductor can be exhibited.

The thin film type inductor may include an external electrode in which a plurality of coil patterns and ceramic layers are alternately formed on an insulating substrate and a plurality of coil patterns are connected through via holes and are electrically connected to the coil pattern on both sides of the chip inductor, Its structure is very similar to stacked inductors.

Here, the insulating substrate may be at least one of an insulating ceramic substrate, an insulating polymer substrate, and a composite substrate in which ceramic and polymer are mixed. The coil pattern of the thin film type inductor can be formed using an additive process method or the like.

A wound-type inductor has an air-core structure in which a coil pattern is wound on a ceramic core.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Preparation of specimens

Example 1

3 g of a SiO ₂ -BaFe ₁₂ O ₁₉ composite magnetic powder having a core-shell structure having an average particle size of 500 nm was mixed with 0.3 g of an epoxy binder to prepare a standard toroidal shape for a network analyzer measurement And then dried in an oven maintained at 150 ° C. to prepare test specimens.

The SiO ₂ -BaFe ₁₂ O ₁₉ composite magnetic powder was prepared by a conventional liquid phase method and BaFe ₁₂ O ₁₉ ferrite powder having an average particle size of 10 nm coated on the surface of SiO ₂ powder to a thickness of 50 nm was used.

Example 2

The remainder is the same as in Example 1, except that the average particle size is 400 nm.

Example 3

Except that the thickness of the ferrite coating was changed to 10 nm.

Comparative Example 1

3 g of a core-shell Ba ₂ Co ₂ Fe ₁₂ O ₂₂ -BaFe ₁₂ O ₁₉ composite magnetic powder having an average particle size of 500 nm was mixed with 0.3 g of an epoxy binder to prepare a standard toroidal powder for network analyzer measurement. And then dried in an oven maintained at 150 ° C. to prepare test specimens.

At this time, the Ba ₂ Co ₂ Fe ₁₂ O ₂₂ -BaFe ₁₂ O ₁₉ composite magnetic powder was prepared by a conventional liquid phase method, and a BaFe ₁₂ O ₁₉ ferrite having an average particle size of 10 nm on the surface of Ba ₂ Co ₂ Fe ₁₂ O ₂₂ powder A powder coated to a thickness of 50 nm was used.

Comparative Example 2

Except that BaFe ₁₂ O ₁₉ was coated to a thickness of 100 nm on the surface of the SiO ₂ powder.

2. Property evaluation

The permeability, permittivity and investment loss of the specimens according to Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated according to the frequency, and the results are shown in Table 1 together with the specimen conditions.

Each item was made using Agilient's E5071C ENA measuring equipment, and the sample was made in toroidal form having an outer diameter of 7 mm and an inner diameter of 3.04 mm.

The measurement was carried out by measuring the s-parameters of the toroidal sample using the coaxial airline method and converting it into a conversion equation to calculate the permeability and permittivity. The measurement frequency was changed from 500 MHz to 8 GHz, and the permeability, permittivity and investment loss shown in Table 1 are values at 1 GHz.

 [Table 1]

Referring to Table 1, Examples 1 to 3 satisfying the conditions of the present invention show low dielectric characteristics and low investment loss characteristics as compared with Comparative Examples 1 and 2 which do not satisfy the conditions of the present invention. It can be expected that the inductance increase and the Q characteristic improvement effect due to the parasitic capacitance decrease when manufacturing with the chip.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, and that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention. However, it should be understood that such substitutions, changes, and the like fall within the scope of the following claims.

100: composite magnetic powder 110: core
120: shell 300: stacked inductor
310: ceramic layer 320: coil pattern
330: via 340: external electrode
350: gap layer

Claims (13)

Having a core-shell structure,
Wherein the core is made of silica (SiO ₂ ) powder, and the shell is made of a ferrite powder.
The method according to claim 1,
Wherein the ferrite powder is a hexagonal ferrite powder.
3. The method of claim 2,
The hexaferrite powder is represented by the following formula (1).
[Chemical Formula 1]
Ba _1-x Sr _x Co _1-y [Me] _y Fe _m O _n
X, y <1, 12 <m <36 and 19 <n <60), where [Me]
3. The method of claim 2,
Wherein the hexaferrite powder is M type.
5. The method of claim 4,
The M type hexaferrite powder is represented by the following formula (2).
The M-type hexaferrite powder can be represented by the following formula (2).
(2)
Ba _1-x Sr _x Zn _y Mn _z Fe ₁₂ O ₁₉
(Where 0? X? 1, 0? Y? 1, and 0? Z? 1)
The method according to claim 1,
Wherein the average particle size of the silica powder is 400 nm to 500 nm.
The method according to claim 1,
Wherein the silica powder has a density of 1.8 g / cm3 to 2.1 g / cm3.
The method according to claim 1,
Wherein the thickness of the shell is 10 nm to 50 nm.
The method according to claim 1,
Wherein the composite magnetic powder has a permeability of 1.5 to 2, a dielectric constant of 3.5 to 5.0 and an investment loss of 0.01 to 0.03 in a frequency band of 1 to 10 GHz.
1. A chip coil component comprising a coil pattern laminated on a ceramic layer or a coil pattern wound on a ceramic core,
Wherein the ceramic layer or the ceramic core contains a powder of a core-shell structure,
Wherein the core of the core-shell structure powder is made of silica (SiO ₂ ) powder, and the shell is made of ferrite powder.
11. The method of claim 10,
Wherein the ferrite powder is a hexagonal ferrite powder.
12. The method of claim 11,
Wherein the hexaferrite powder is an M type chip coil component.
11. The method of claim 10,
Wherein the content of the core-shell composite magnetic powder in the ceramic sheet or the ceramic core is 50% to 70%.

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