WO2009057878A1

WO2009057878A1 - Low fired dielectric ceramic composition with high strength and high q-value

Info

Publication number: WO2009057878A1
Application number: PCT/KR2008/003695
Authority: WO
Inventors: Jeong Hyun Park; Jae Gwan Park; Kyoung Jin Choi; Dong-Wan Kim; Young Jin Choi; Hang-Won Lee
Original assignee: Korea Institute Of Science And Technology
Priority date: 2007-11-01
Filing date: 2008-06-26
Publication date: 2009-05-07
Also published as: KR100882922B1; JP2010531287A

Abstract

The present invention relates to a dielectric ceramic composition comprising a glass frit and a filler with a predetermined proportion, wherein the glass frit or the dielectric ceramic composition comprises a nucleating agent, thereby forming a specific crystal structure and providing low dielectric constant, low dielectric loss, high Q-value and high strength. As such, the low temperature fired dielectric ceramic composition having high strength and high Q-value according to the present invention can increase the size and improve the performance of a multilayered substrate for low temperature sintering and enable modulation of electronic parts with good impact resistance.

Description

[DESCRIPTION] [Invention Title]

LOW FIRED DIELECTRIC CERAMIC COMPOSITION WITH HIGH STRENGTH AND HIGH Q-VALUE

[Technical Field]

The present invention relates to a dielectric ceramic composition comprising a glass frit and a filler with a predetermined proportion. In particular, the present invention relates to a low temperature fired dielectric ceramic composition, wherein the glass frit or the dielectric ceramic composition comprises a nucleating agent and which forms a particular crystal structure when sintered at 850 to 950 ^°C, thereby providing high strength and high Q-value.

[Background Art] The development of telecommunication industry has been advanced toward a faster, multi-functional and wireless (mobile) one. In order to meet such needs, the necessity for better performance, more integrated telecommunication-related parts is on the increase. To ensure improved functionality, reliability and degree of integration with constant weight and volume, a thick-film lamination technique based on extreme material and molding techniques is necessary. An improved degree of integration and degree of complexity during thick-film lamination results in smaller product size, decreased cost, and improved reliability by reducing the number of parts and solder joints. Further, there are advantages of reducing parasitic components through decreasing the number of passive elements and, through this, improving electrical properties. As a technique of realizing a multifunctional module through such thick-film lamination, the low temperature co-fired ceramic (LTCC) technology is gaining attentions. Since LTCC technology can provide the integration of a substrate and the modulation of passive elements at the same time and is applicable to ultra-high-frequency applications, many researches have been conducted and various module products have been developed.

As a technology enabling a multifunctional module, LTCC technology provides the following advantages. First, LTCC technology enables lamination up to dozens of layers while maintaining the linewidth at about tens of micrometers. Accordingly, a higher degree of circuit integration is attainable compared with the PCB-based packaging, L, C or R passive elements with various values can be mounted, and a multifunctional module can be realized by mounting active elements in the module using, for example, the cavity method. Further, since the technology is applicable to ultra high frequency of 60 GHz or more, which is attributed to the high Q-value of ceramics, it will be particularly promising when the frequency bandwidth increases to millimeters. Until now, LTCC technology has been applied in Bluetooth modules, duplexer packages, front-end modules, RF power amplification modules, and the like. In the future, it is expected to be developed toward more complex, better-performance applications such as RF front-end all-in-one module, antenna integrated Bluetooth module, etc. Therefore, LTCC-based complex multifunctional electric device modules are sure to play a critical role in the mobile telecommunication industry.

The most basic of the LTCC is a low dielectric ceramic composition used to form a wiring substrate characterized by low dielectric constant, low loss and high Q-value. In general, such a composition comprises 50 to 90 weight % of a borosilicate-based glass composition and 10 to 50 weight % of a filler such as AIaOa_x SiO∑, etc.

Here, the glass is softened at below 700 ^°C, forms a liquid at around 850 ^°C, and provides densification at 850 to 950 °C, where the LTCC is best sintered. And, the filler maintains the shape of the substrate during the sintering, and enhances mechanical strength of the sintered body. Specifically, a borosilicate-based glass including a small amount of alkali oxides is frequently used as the glass composition, because it is associated with low dielectric loss.

For example, U.S. Patent No. 5,902,758 discloses a composition for an LTCC wiring substrate. A glass composition comprising 75 to 85 weight %, Siθ2 and 15 to 25 weight % B2O3 as main components and 5 weight % or less alkali oxides is used, and alumina, mullite, etc., is used as a filler. The proportion of the filler to the glass composition is from 20 to 50 weight %. The alkali oxides included in the glass composition are Na2θ, K2O, etc. The resultant substrate is characterized by a dielectric constant of about 5.0 and dielectric loss of about 0.2 %. Similar wiring substrates with low dielectric constants are disclosed in U.S. Patent Nos. 6,835,682, 5,242,867, 5,825,632, 4,959,330 and 5,821,181.

Looking into the above-mentioned patents, dielectric ceramic compositions prepared from borosilicate glass composition mainly composed of silica and having high melting temperature, such as one manufactured by Finex Inc., have superior dielectric characteristics and chemical endurance, in general. However, because the quantity of glass frit in the composition is much greater than that of alumina or other filler, most of the compositions exhibit low strength of 200 MPa or lower (strength is an important factor with respect to modulation and widening of the substrate).

Recently, as the demand on high strength for low dielectric ceramic compositions for wiring substrates increases, Kyocera Corporation and other companies have developed high-strength LTCC substrate materials for modules, the strength of which is almost comparable to that of alumina. Since high-strength wiring substrates can be made to have a large size, a large number of electronic parts can be mounted thereon, and ultimately, they can be applied to multifunctional SIP (system in package). In general, crystallized glass compositions are used. Typical examples include U.S. Patent Nos. 6,953,756 and 6,897,172, and Japanese Patent Laid-Open Nos. 2003-165766, 2004-284937 and 2005-015239.

Such high-strength crystallized glass has the advantage that, because most of the glass frit is crystallized during sintering, fine crystals are deposited, which interfere with the propagation of the cracks caused by external impact, thereby greatly improving strength. Frequently used glass composition comprises a small amount of B2O3 and 20 weight % or more of SiCh, AI2O3 and alkali or alkaline earth oxides such as Li2U and MgO as main components, in order to facilitate crystallization. But, the alkali or alkaline earth oxides are associated with the problem that they may impair the chemical endurance of the resultant dielectric ceramic composition, compared with existing borosilicate glass compositions having a high melting point. Further, it is not easy to attain optimal densification at a sintering temperature of 900 ^°C or lower, because it is difficult to control the particle size of the deposited glass crystals arbitrarily.

[Disclosure] [Technical Problem]

An object of the present invention is to provide high Q-value and high strength to a low temperature fired dielectric ceramic composition with low dielectric constant and low dielectric loss. [Technical Solution]

In an aspect, the present invention provides a low temperature fired dielectric ceramic composition comprising 1) 35 to 60 weight % of at least one crystalline glass frit comprising SiC^₇ B2O3, AI2O3, ZnO, an alkaline earth metal oxide and an alkali metal oxide, and selected from wollastonite (CaSiC^), rankinite (Ca3Si2θ7), lamite (Ca2Siθ4), Ca₂SiOs, diopside (CaMgSi₂O₆), anorthite (CaAl₂Si₂O₈), cordierite (5SiO2-2Al₂O₃-2MgO), MgSiO₃, MgB₂O₄, SrSiO₃, SrAl₂Si₂O₈ and SrB₂O₄, and 2) 40 to 65 weight % of a filler, and further comprising 3) 0.3 to 3 mol % of a nucleating agent based on the glass frit or 0.5 to 15 weight % of a nucleating agent based on the dielectric ceramic composition.

[Advantageous Effects]

When sintered at a temperature range of 850 to 950 °C, the low temperature fired dielectric ceramic composition according to the present invention has a dielectric constant of 6 to 9 (1 MHz), a dielectric loss of 0.05 to 0.1 %, a Q-value of 1,000 to 2,000 and a strength of 250 to 400 MPa. As such, the low temperature fired dielectric ceramic composition having high strength and high Q-value according to the present invention can increase the size and improve the performance of a multilayered substrate for low temperature sintering and enable modulation of electronic parts with good impact resistance.

[Description of Drawings]

FIG. 1 shows the shrinkage (@ 875 "C) of the low dielectric ceramic composition of Example 3 depending on alumina particle size.

FIG. 2 shows the degree of densification (@ 875 "C) of the low dielectric ceramic composition of Example 3 depending on alumina particle size, observed by FESEM. FIG. 3 shows the XRD (X-ray diffraction) crystallization pattern of the glass frit of Preparation Example 16 at room temperature and upon heat treatment at 950 ^°C for 5 hours.

FIG. 4 shows the TEM images showing that localized crystallization has occurred in nano scale in the liquefied glass frit by the nucleating agent TiO₂ included in the glass composition of Example 23.

[Best Mode]

The present invention relates to a low temperature fired dielectric ceramic composition comprising a glass frit and a filler with a predetermined proportion, wherein the glass frit or the dielectric ceramic composition includes a nucleating agent to form crystals, so as to attain improved dielectric constant, dielectric loss, Q-value and strength by sintering at low temperature of 850 to 950 °C .

Hereunder is given a more detailed description of the present invention.

In the present invention, 35 to 60 weight % of a glass frit comprising SiO₂, B2O3, AI2O3, ZnO, an alkaline earth metal oxide and an alkali metal oxide is used. Preferably, the glass frit may comprise 45 to 70 mol % of SiO₂, 15 to 30 mol % of B₂O₃, 0.5 to 5 mol % of Al₂O₃, 0.5 to 2 mol % of ZnO, 4 to 20 mol % of an alkaline earth metal oxide and 0.1 to 13 mol % of an alkali metal oxide. When the content of SiO₂ is below 45 mol %, mechanical, chemical and physical stabilities may be insufficient. When it exceeds 70 mol %, glassification may not occur even at 1600 °C or higher temperature. When the content of B₂O₃ is below 15 mol %, glassification may not occur. When it exceeds 30 mol %, chemical and physical stabilities may not be sufficient. When the content of Al₂O₃ is below 0.5 mol %, it is difficult to obtain improved chemical endurance. When it exceeds 5 mol %, glassification temperature increases, and crystallization of glass may occur excessively. When the content of ZnO is below 0.5 mol %, glassification may not occur. And, when it exceeds 2 mol %, electrical properties of glass may be deteriorated.

The alkaline earth metal oxide may be one commonly used in the related art and is not particularly limited. For example, at least one oxide selected from BaO, MgO, CaO and SrO may be used. The alkaline earth metal oxide is used to induce crystallization of glass at around 900 °C at which the sintering of the LTCC composition is carried out. When the content of the alkaline earth metal oxide is below 4 mol %, the formation of embryos for crystal growth may be insufficient. And, when it exceeds 20 mol %, problems may occur with regard to crystallization or melting of glass, because of devitrification and increased viscosity. Further, dielectric characteristics may be deteriorated. And, the alkali metal oxide may be one commonly used in the related art and is not particularly limited. For example, at least one oxide selected from Li₂O and Na₂O may be used. The alkali metal oxide is used to reduce melting temperature during glass making while minimizing the deterioration of physical properties of glass. When the content of the alkali metal oxide is below 0.1 mol %, the effect becomes insufficient. And, when it exceeds 13 mol %, hydration may occur and physical/ chemical properties of glass may change drastically, including increase of thermal shock resistance. The aforesaid contents of the components were determined to minimize dielectric loss while retaining the characteristics of liquefied sintered material during the mixing of the glass frit with the filler and sintering, and to ensure glassification at around 1600 ^°C while retaining strength. It is preferable to maintain the aforesaid relative molar ratio. Glass transition temperature (T_g), softening temperature (Ts) and electrical properties are measured from the inflection points determined by dilatometry.

In addition to the aforesaid components, 0.3 to 8 mol % of a nucleating agent may be further included. The nucleating agent may be one commonly used in the related art and is not particularly limited. For example, at least one selected from TiCh, ZrO₂, P2O5, V2O5, Pt, Au, La₂O₃ and Ceθ2 may be used. When the nucleating agent is used in an amount smaller than 0.3 mol % based on the total glass frit composition, the nucleating agent may not sufficiently act as foreign particles to induce formation and growth of crystals. And, when it is used in an amount exceeding 8 mol %, glassification may not occur even at 1600 ^°C . Further, the dielectric constant of the resultant glass increases as the content of the nucleating agent increases. Hence, the aforesaid range is preferred.

The glass frit according to the present invention may be prepared by a method commonly used in the related art and is not particularly limited. For example, the following method may be employed. The aforesaid components of the glass frit are weighed and mixed in dry state, put in a platinum crucible and melted at 1400 to 1600 ^°C to obtain a melt solution. The melt solution is quenched, crudely ground in an agate mortar, finely ground in a polyethylene bowl along with zirconia balls using ethanol as a solvent, and then ground again by attrition, in order to obtain a glass frit.

The resultant glass frit is a borosilicate glass frit with high melting point characterized by, as shown in FIG. 3, a typical amorphous XRD pattern upon heat treatment along with crystallinity of one or more of wollastonite (CaSiOs), rankinite (CaSSi₂Oz), lamite (Ca₂SiO₄), Ca₂SiO₅, diopside (CaMgSi₂O₆), anorthite (CaAl₂Si₂O₈), cordierite (5SiO₂-2Al₂O₃- 2MgO), MgSiO₃, MgB₂O₄, SrSiO₃, SrAl₂Si₂O₈, and SrB₂O₄.

Conventionally, a borosilicate glass frits with no crystallinity or a recrystallized aluminosilicate-based or other glass frit, which includes a large quantity of alumina or magnesium oxide and includes no or a minimal quantity of boron (B₂O₃) and crystallization occurs in 70 volume % or more upon heat treatment, have been reported. The glass frit with no crystallinity, which exhibits a typical amorphous XRD pattern, provides good dielectric characteristics when mixed with a filler such as alumina and sintered, but it has a low strength of 200 MPa or below. As for the recrystallized glass frit, sinterability is poor because it is mostly crystallized and converted to ceramics during the sintering process, and densif ication does not occur sufficiently at around 900 ^°C . For this reason, the recrystallized glass frit exhibits increased dielectric constant and dielectric loss, and decreased Q-value, in general. Further, strength changes little or even decreases in spite of the presence of nano- sized crystals, because densification does not occur sufficiently at around 900 ^°C .

In contrast, the present invention attains low dielectric constant, low dielectric loss, high Q-value and high strength using the nano-sized crystalline glass frit comprising a borosilicate glass with a high melting point.

The glass frit is comprised in an amount of 35 to 60 weight % based on the total dielectric ceramic composition. When the content of the glass frit is below 35 weight %, densification may not occur sufficiently during the sintering. And, when it exceeds 60 weight %, isolated pores may grow inside the sintered body, resulting in deterioration of dielectric characteristics and strength. Hence, the aforesaid range is preferred.

In the present invention, a filler known to have high strength is used. For example, at least one selected from AI2O3, MgAl₂C^, cordierite (Cordierite), mullite, quartz(Quartz), ZrSiC>4, Mg2SiC>4, MgTiCb and ZnAbC^ is used as a filler in order to improve strength, dielectric constant, dielectric loss, Q-value, and the like while enabling sintering at low temperature of 850 to 950 ^°C as compared with the conventional sintering temperature of 1200 ^°C or higher. Conventionally, a single compound such as Siθ2 has been used as a filler. In contrast, the filler according to the present invention has high strength, low dielectric constant and low dielectric loss, and provides significantly improved strength, dielectric constant, dielectric loss and Q-value when a wiring substrate is prepared from the dielectric ceramic composition comprising the same.

The filler is included in an amount of 40 to 65 weight % based on the total dielectric ceramic composition. When the content of the filler is below 40 weight %, the glass may be exposed on the surface of the sintered body. And, when it exceeds 65 weight %, sintering temperature has to be elevated. Hence, the aforesaid range is preferred.

The low temperature fired dielectric ceramic composition according to the present invention may be prepared by a method commonly used in the related art and is not particularly limited. For example, the following method may be employed. 35 to 60 weight % of the aforesaid glass frit and 40 to 65 weight % of the aforesaid filler are weighed and mixed to obtain a dielectric mixture. Then, such prepared dielectric mixture is sintered at 850 to 950 ^°C .

Alternatively, the low temperature fired dielectric ceramic composition may be prepared by a preparation method comprising the steps of 1) weighing 45 to 70 mol % of SiO₂, 15 to 30 mol % of B₂O₃, 0.5 to 5 mol % of Al₂O₃, 0.5 to 2 mol % of ZnO, 4 to 20 mol % of an alkaline earth metal oxide and 0.1 to 13 mol % of an alkali metal oxide, mixing the same, and melting the same at 1400 to 1600 ^°C to obtain a melt solution, 2) quenching the melt solution, and grinding the same to obtain at least one crystalline glass frit selected from wollastonite (CaSiO₃), rankinite (Ca₃Si₂Oy), lamite (Ca₂SiO₄), Ca₃SiOs, diopside (CaMgSi₂Oo), anorthite (CaAl₂Si₂O₈), cordierite (5SiO₂-2Al₂O₃-2MgO), MgSiO₃, MgB₂O₄, SrSiO₃, SrAl₂Si₂O₈ and SrB₂O₄, 3) weighing 35 to 60 weight % of the glass frit, 40 to 65 weight % of a filler and

0.5 to 15 weight % of a nucleating agent, and mixing the same to obtain a dielectric mixture, and 4) sintering the dielectric mixture at 850 to 950 ^°C .

The nucleating agent is included in an amount from 0.5 to 15 weight % based on the total low temperature fired dielectric ceramic composition. When the content of the nucleating agent is below 0.5 weight %, it may be difficult to form embryos for crystal growth. And, when it exceeds 15 weight %, strength of the dielectric ceramic composition may decrease. Hence, the aforesaid range is preferred. The low temperature fired dielectric ceramic composition according to the present invention necessarily comprises the nucleating agent. But, the nucleating agent may be included in either the glass frit composition or the dielectric ceramic composition.

To conclude, in the present invention, a borosilicate-based glass frit is used as base material in order to provide low dielectric loss and high Q-value, a filler known to have good strength is used to provide high strength, and a nucleating agent is added to further improve strength through localized crystallization in the dimension of 10 to 300 nm during heat treatment. The conventional glass frit exhibiting low dielectric loss and high Q-value is associated with the problem of poor strength because of the typical amorphous pattern of glass. And, the conventional diopside (CaMgSi₂Oo)- or anorthite (CaAkSiaC^-based high strength crystallized glass frit is associated with the problem that it is difficult to control the sintering temperature and dielectric characteristics because 70 volume % or more of glass is crystallized during heat treatment. In contrast, the present invention provides improved a low temperature fired dielectric ceramic composition with improved dielectric loss and Q- value by adequately controlling the contents of alkali metal oxide or alkaline earth metal oxide in the glass frit and with improved strength by employing a nucleating agent so as to facilitate nano-sized crystallization of the glass frit.

The low temperature fired dielectric ceramic composition according to the present invention, which comprises a specific glass frit, a filler and a nucleating agent, has a dielectric constant of 6 to 9 (1 MHz), a dielectric loss of 0.05 to 0.1 %, a Q-value of 1,000 to 2,000, a strength of 250 to 400 MPa and a sintering temperature of 850 to 950 ^°C, and can be effectively applied in resonators or parts of filters, antennas, etc., to form multilayered ceramic packages. Further, it may be effectively applied in constructing composite modules of electronic parts.

[Mode for Invention]

The following examples illustrate the present invention in further detail and are not intended to limit the same.

Preparation Examples 1 to 19 and Comparative Preparation Examples 1 to 5

Glass frit components in powder form presented in the following Tables 1 and 2 were weighed, mixed in dry status, put in a platinum crucible, and kept at 1400 to 1600 °C for 2 hours. The resultant melt solution was quenched in a cooling water bath. The prepared glass was crudely ground in an agate mortar, finely ground for 24 hours in a polyethylene bowl along with zirconia balls using ethanol as a solvent, and then ground again for 5 hours by attrition, in order to obtain a borosilicate glass frit. [Table 1]

Glass Mt composition mole?.] Thermal Glass Glass Dielectric transition softening constant

Classification Nucleating agent Density expansion

Crystal tvpe coefficient temperature temperature (W

[g/cm³] [ 10^'Bppm/

SiO₂ AI₂O₃ CaO MgO SrO Li₂O ZnO TiID₂ ZrO₂ ^•c] (T₅) [^"CI (Ts) [ t] [SlMHz]

Preparation 70.0 21.0 3.0 4.0 - 1.5 0.5 - - CaSIOs 2.24 4.16 572 635 4.3

Preparation Example 2 65.8 24.2 1.9 6.0 - 1.2 0.9 - - CaS i Os 2.23 4.57 542 598 4.4

Preparation Example 3 62.3 22.9 2.9 10.5 - 0.5 0.9 - - CaS iOj 2.30 4.45 658 715 4.7

Preparation Example 4 55.3 24.9 4.3 12.0 - 2.0 1.5 - - CaSiOs 2.38 6.08 648 696 5.3

Preparation 62.0 Example 5 24.6 3.0 - 9.0 0.3 1.1 - - MgSiO₃ 2.29 3.S6 658 714 4.4

Preparation Example 6 60.0 23.7 4.1 5.2 5.8 0.7 0.5 - - Diopsiαe 2.34 4.63 675 726 4.8

Preparation Example 7 57.8 21.0 1.9 7.3 1.0 9.2 1.8 - - CaSiθ3,Ca3Siθ5 2.41 5.91 630 669 5.3

Preparation Example 8 57.9 20. B 5.0 9.0 5 .0 2.0 0.6 - - Anorthlte 2.50 5.63 661 711 5.6

Preparation Example 9 54.9 23.1 2.0 7.0 S .0 6.0 1.0 - - SrAIjSi₂Os 2.49 5.65 639 682 5.5

Preparation Example 10 46.8 26.4 1.5 - - 16.2 7.1 2.0 - - SrA I zSi Λ 2.79 7.46 683 700 6.3

Preparation Example 11 65.7 20.7 1.8 9.7 - 0.3 0.9 0.9 - CaSiO₃ 2.32 4.25 664 719 4.9

Preparation Example 12 61.7 21.0 1.5 12.0 - 1.0 1.3 1.5 CaSiOs 2.39 4.55 655 703 5.3

Preparation Example 13 56.9 22.1 J.δ 8.8 - 1.5 1.1 8.0 - CaSiOs 2.33 4.27 658 704 6.0

Preparation Example 14 64.3 19.0 4.0 9.5 - 1 1 0.3 0.8 - 1.0 Anorthlte 2.42 4.46 673 726 5.0

Preparation Example 15 66.0 19.0 2.0 10.0 - 0.5 2.0 - 0.5 CasSiOs 2.36 4.33 663 719 4.8

Preparation Example 16 55.9 22.7 2.4 15.5 - 1.2 2.0 - 0.3 CasSiOδ 2.47 5.13 657 702 5.4

Preparation 4 Anorthite, Example 17 56. 24.3 6.0 9.5 - 1 0 1.0 0.5 1.0 0.3 2.41 4.82 662 711 5.2 CajSiOs

Preparation Example 18 55.1 15.5 3.3 8.5 - 2 1 13.0 0.7 1.5 0.3 CasS i Os 2.54 7.38 Θ47 681 6.2

Preparation Example 19 63.1 18.7 5.0 - - 9 9 1.2 0.5 1.1 0.5 SrAUSIjOe 2.57 4.99 674 725 5.4

[Table 2]

Examples 1 to 32 and Comparative Examples 1 to 14

The glass frits prepared in Preparation Examples were mixed with the fillers and the nucleating agents presented in the following Table 3, and sintered at 850 to 950 °C to obtain dielectric ceramic compositions. [Table 3]

FIG. 1 shows the shrinkage (@ 875 ^"C) of the low dielectric ceramic composition of Example 3 depending on alumina particle size, and FIG. 2 shows the degree of densification (@ 875 "C) of the low dielectric ceramic composition of Example 3 depending on alumina particle size, observed by FESEM. From the figures, it can be seen that the strength depends not only on the addition amount of the nucleating agent but also on the particle size of the filler alumina. It is because the degree of densification of the dielectric ceramic composition is dependent upon the alumina particle size. In particular, it was ascertained that an optimized densification can be obtained when the alumina particle size ranges from 1 to 1.5 μm. As can be seen from Table 3, at least one crystalline glass frit selected from wollastonite (CaSiOs), rankinite (Ca₃Si₂Oy), lamite (Ca2SiC>4), Ca₃SiOs, diopside (CaMgSi2C>6), anorthite (CaAl₂Si₂O₈), cordierite (5SiO₂-2Al₂O₃-2MgO), MgSiO₃, MgB₂O₄, SrSiO₃, SrAl₂Si₂O₈ and SrB₂O₄ could be attained by sintering at low temperature. As a result, dielectric ceramic compositions having a low dielectric constant of 6 to 9 (1 MHz), a low dielectric loss of 0.05 to 0.1 %, a high Q-value of 1,000 to 2,000, and a high strength of 250 to 400 MPa could be prepared. When compared with the conventional dielectric ceramic composition (Comparative Example 13), all of the dielectric constant, dielectric loss, Q-value and strength were improved.

The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

[CLAIMS] [Claim 1]

A low temperature fired dielectric ceramic composition comprising:

1) 35 to 60 weight % of at least one crystalline glass frit comprising SiCh, B₂O₃, AI₂O3, ZnO, an alkaline earth metal oxide and an alkali metal oxide, and selected from wollastonite

(CaSiCb), rankinite (Ca₃Si2θ7), lamite (Ca2SiC>4), Ca₂SiOs, diopside (CaMgSi₂Oe), anorthite (CaAl₂Si₂O₈), cordierite (5SiO₂-2Al₂O₃-2MgO), MgSiO₃, MgB₂O₄, SrSiO₃, SrAl₂Si₂O₈ and SrB₂O₄; and

2) 40 to 65 weight % of a filler, and further comprising:

3) 0.3 to 3 mol % of a nucleating agent based on the glass frit or 0.5 to 15 weight % of a nucleating agent based on the dielectric ceramic composition.

[Claim 2] The low temperature fired dielectric ceramic composition according to claim 1, wherein the glass frit comprises 45 to 70 mol % of SiO₂, 15 to 30 mol % of B₂O₃, 0.5 to 5 mol % of Al₂O₃, 0.5 to 2 mol % of ZnO, 4 to 20 mol % of an alkaline earth metal oxide and 0.1 to 13 mol % of an alkali metal oxide.

[Claim 3]

The low temperature fired dielectric ceramic composition according to claim 1, wherein the alkaline earth metal oxide is at least one selected from BaO, MgO, CaO and SrO.

[Claim 4] The low temperature fired dielectric ceramic composition according to claim 1, wherein the alkali metal oxide is at least one selected from Li₂O and Na2θ.

[Claim 5] The low temperature fired dielectric ceramic composition according to claim 1, wherein the filler is at least one selected from AkOs, MgAl2θ4, cordierite, mullite, quartz, ZrSiO₄, Mg₂SiO₄, MgTiO₃ and ZnAl₂O₄.

[Claim 6] The low temperature fired dielectric ceramic composition according to claim 1, wherein the nucleating agent is at least one selected from TiO₂, ZrO₂, P₂Os, V₂Os, Pt, Au, La₂O₃ and CeO₂.

[Claim 7] The low temperature fired dielectric ceramic composition according to any of claims

1 to 6, which has a dielectric constant of 6 to 9 (1 MHz), a dielectric loss of 0.05 to 0.1 %, a Q- value of 1,000 to 2,000, a strength of 250 to 400 MPa and a sintering temperature of 850 to 950 °C .

[Claim 8]

A preparation method of a low temperature fired dielectric ceramic composition comprising the steps of:

1) weighing 45 to 70 mol % of SiO₂, 15 to 30 mol % of B₂O₃, 0.5 to 5 mol % of Al₂O₃,

0.5 to 2 mol % of ZnO, 4 to 20 mol % of an alkaline earth metal oxide, 0.1 to 13 mol % of an alkali metal oxide and 0.3 to 3 mol % of a nucleating agent, mixing the same, and melting the same at 1400 to 1600 ^°C to obtain a melt solution;

2) quenching the melt solution, and grinding the same to obtain at least one crystalline glass frit selected from wollastonite (CaSiOa), rankinite (Ca₃Si₂Oz), lamite (Ca₂SiO₄), Ca₃SiO₅, diopside (CaMgSi₂O₆), anorthite (CaAl₂Si₂O₈), cordierite (5SiO₂-2Al₂O₃- 2MgO), MgSiO₃, MgB₂O₄, SrSiO₃, SrAl₂Si₂O₈ and SrB₂O₄;

3) weighing 35 to 60 weight % of the glass frit and 40 to 65 weight % of a filler and mixing them to obtain a dielectric mixture; and

4) sintering the dielectric mixture at 850 to 950 ^°C .

[Claim 9]

1) weighing 45 to 70 mol % of SiO₂, 15 to 30 mol % of B₂O₃, 0.5 to 5 mol % of Al₂O₃, 0.5 to 2 mol % of ZnO, 4 to 20 mol % of an alkaline earth metal oxide and 0.1 to 13 mol % of an alkali metal oxide, mixing the same, and melting the same at 1400 to 1600 "C to obtain a melt solution;

2) quenching the melt solution, and grinding the same to obtain at least one crystalline glass frit selected from wollastonite (CaSiO₃), rankinite (Ca₃Si₂Oz), lamite (Ca₂SiO₄), Ca₃SiO₅, diopside (CaMgSi₂O₆), anorthite (CaAl₂Si₂O₈), cordierite (5SiO₂-2Al₂O₃- 2MgO), MgSiO₃, MgB₂O₄, SrSiO₃, SrAl₂Si₂O₈ and SrB₂O₄;

3) weighing 35 to 60 weight % of the glass frit, 40 to 65 weight % of a filler and 0.5 to 15 weight % of a nucleating agent, and mixing the same to obtain a dielectric mixture; and

4) sintering the dielectric mixture at 850 to 950 "C .

[Claim 10]

The preparation method of a low temperature fired dielectric ceramic composition according to claim 8 or 9, wherein the alkaline earth metal oxide is at least one selected from BaO, MgO, CaO and SrO.

[Claim 11]

The preparation method of a low temperature fired dielectric ceramic composition according to claim 8 or 9, wherein the alkali metal oxide is at least one selected from Li₂O and Na₂O.

[Claim 12]

The preparation method of a low temperature fired dielectric ceramic composition according to claim 8 or 9, wherein the filler is at least one selected from Al₂Os, MgAl₂θ4, cordieiϊte, mullite, quartz, ZrSiθ4, Mg₂Siθ4, MgTiθ3 and ZnAl₂θ4.

[Claim 13]

The preparation method of a low temperature fired dielectric ceramic composition according to claim 8 or 9, wherein the nucleating agent is at least one selected from TiO₂, ZrO₂, P₂O₅, V₂O₅, Pt, Au, La₂O₃ and CeO₂.